JP7822892B2 - Secondary battery, battery pack and vehicle - Google Patents

Description

Embodiments relate to secondary batteries, battery packs, and vehicles.

The use of electrodes containing niobium titanium oxide as the negative electrode active material in secondary batteries is being considered. However, these secondary batteries have issues with their lifespan performance. The reasons for this include gas generation and increased resistance.

Japanese Patent Application Laid-Open No. 2021-144819 International Publication No. 2013/137418 International Publication No. 2013/145109

The Roles of Sulfur-Containing Additives and Their Working Mechanism on the Temperature-Dependent by Zeli Wu et al. Performances of Li-Ion Batteries, Journal of The Electrochemical Society, 165 (11) A2792-A2800 (2018)

The present embodiments aim to provide a secondary battery that can suppress gas generation and resistance increases, a battery pack including the secondary battery, and a vehicle including the battery pack.

According to an embodiment, a secondary battery is provided that includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the positive electrode active material-containing layer. The non-aqueous electrolyte includes a sulfur-containing compound consisting of at least one of a sulfur- containing imide compound and a sultone compound. The negative electrode includes a negative _electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the negative electrode active material-containing layer. The _{negative electrode active material-containing layer includes at least one selected from the group consisting of niobium titanium composite oxides represented by the general formula LixTi1} - _yM1yNb2 - zM2zO7 _{+ δ} and _{niobium titanium composite} oxides represented by the general formula LixTi1 _-yM3y + zNb2 _{- zO7-δ} . The M1 is at least one selected from the group consisting of Zr, Si, and Sn, the M2 is at least one selected from the group consisting of V, Ta, and Bi, and the M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The x satisfies 0≦x≦5, the y satisfies 0≦y<1, the z satisfies 0≦z<2, and the δ satisfies −0.3≦δ≦0.3. The secondary battery also satisfies the following formulas (1) and (2) :

1×10 ⁻⁶ ≦E/A≦9×10 ⁻⁴ (1)
In formula (1), A is the mass (g/ ^m3 ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode as determined by inductively coupled plasma atomic emission spectrometry , and is in the range of greater than 0 (g / ^m3 ) and less than or equal to 3500 (g/m3 ⁾ , and E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte as determined by inductively coupled plasma atomic emission spectrometry .
2×10 ⁻⁶ ≦E/D≦3×10 ⁻⁴ (2)
In equation (2), D is the mass of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode (g/m3) determined by inductively coupled plasma atomic emission spectroscopy ^, and E is the concentration of the sulfur-containing compound in the non-aqueous electrolyte (mol/L) determined by inductively coupled plasma atomic emission spectroscopy .

According to another embodiment, a battery pack including the secondary battery of the embodiment is provided.

According to another embodiment, a vehicle is provided that includes a battery pack of the embodiment.

2 is a cross-sectional view of the secondary battery according to the embodiment, taken along a direction perpendicular to the terminal extending direction. FIG. FIG. 2 is an enlarged cross-sectional view of part A in FIG. 1 . FIG. 2 is a partially cutaway cross-sectional view of the secondary battery according to the embodiment. FIG. 4 is a side view of the battery of FIG. 3 . 5A to 5C are schematic plan views showing an example of a method for manufacturing a secondary battery according to an embodiment. FIG. 2 is an exploded perspective view of the battery pack according to the embodiment. FIG. 7 is a block diagram showing the electrical circuitry of the battery pack of FIG. 6 . 1 is a schematic diagram showing an example of a vehicle equipped with a secondary battery according to an embodiment; FIG. 10 is a diagram schematically illustrating another example of a vehicle according to an embodiment. FIG. 10 shows a total ion chromatogram (TIC) of the nonaqueous electrolyte of Example 28. 11 is an enlarged view of the vicinity of peak _P1 in the TIC of FIG. 10 . 11 is an enlarged view of the vicinity of 7 to 9 Time/min in the TIC of FIG. 10.

(First embodiment)
According to a first embodiment, a secondary battery is provided that includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the positive electrode active material-containing layer. The non-aqueous electrolyte includes at least one of a sulfur-containing imide compound and a sultone compound, or a sulfur-containing compound including at least one of a sulfur-containing imide compound, a sultone compound, and a propane sulfonate ester. The secondary battery also satisfies the following formula (1):

1×10 ⁻⁶ ≦E/A≦9×10 ⁻⁴ (1)
In formula (1), A is the mass of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode (g/m ³ ), and E is the concentration of the sulfur-containing compound in the non-aqueous electrolyte (mol/L).
As a result of extensive research, the present inventors have found that the presence of a sulfur-containing compound (hereinafter referred to as "sulfur-containing compound") in a non-aqueous electrolyte, which is composed of at least one of a sulfur-containing imide compound and a sultone compound, or at least one of a sulfur-containing imide compound, a sultone compound, and a propanesulfonic acid ester, improves the life performance of a secondary battery. The mechanism behind this is presumed to be as follows. At high temperatures, particularly under high SOC (state of charge) conditions, a reaction between the non-aqueous electrolyte and the positive electrode proceeds, resulting in oxidative decomposition of the non-aqueous electrolyte and the generation of gas. The presence of a sulfur-containing compound in the non-aqueous electrolyte causes the sulfur-containing compound to react with the positive electrode and decompose, thereby suppressing the reaction between the positive electrode and components other than the sulfur-containing compound (e.g., non-aqueous solvent) in the non-aqueous electrolyte. Furthermore, the presence of a sulfur-containing layer in at least a portion of the positive electrode active material-containing layer can suppress the reaction between the positive electrode and the non-aqueous electrolyte. E/A represents the balance between the amount of sulfur-containing compound in the non-aqueous electrolyte and the amount of sulfur-containing layer in the positive electrode active material-containing layer. For example, when E is small or A is large, E/A becomes small. Furthermore, when E is large or A is small, E/A becomes large. In each case, the reaction between the positive electrode and components other than the sulfur-containing compound in the non-aqueous electrolyte proceeds more rapidly than the reaction between the sulfur-containing compound in the non-aqueous electrolyte and the positive electrode, resulting in gas generation or an increase in resistance. When E/A satisfies the range of formula (1), the reaction between the sulfur-containing compound in the non-aqueous electrolyte and the positive electrode proceeds under high temperature and high SOC conditions, thereby suppressing the reaction between the positive electrode and components other than the sulfur-containing compound in the non-aqueous electrolyte under high temperature and high SOC conditions, and enhancing the protective function of the positive electrode by the sulfur-containing layer. Therefore, gas generation under high temperature and high SOC conditions can be suppressed, and an increase in battery resistance can be suppressed. This can improve the life performance of the secondary battery.

Furthermore, in the secondary battery of the embodiment, the negative electrode may include a negative electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the negative electrode active material-containing layer. It is desirable that this secondary battery satisfy the following formula (2):

2×10 ⁻⁶ ≦E/D≦3×10 ⁻⁴ (2)
In formula (2), D is the mass of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode (g/m ³ ), and E is the concentration of the sulfur-containing compound in the non-aqueous electrolyte (mol/L).

Satisfying formula (2) can further improve the life performance of secondary batteries. The mechanism behind this is presumed to be as follows: In high-temperature environments, in addition to reactions between the positive electrode and non-aqueous electrolyte, reactions can also occur between the negative electrode and non-aqueous electrolyte. Satisfying formula (2) can promote the reaction between the sulfur-containing compound in the non-aqueous electrolyte and the negative electrode, thereby suppressing reactions between components other than the sulfur-containing compound in the non-aqueous electrolyte and the negative electrode under high-temperature conditions. Furthermore, the sulfur-containing layer's protective function for the negative electrode can be enhanced, thereby suppressing gas generation under high-temperature conditions and suppressing increases in battery resistance. This can improve the life performance of secondary batteries.

The positive electrode, negative electrode, sulfur-containing layer, and nonaqueous electrolyte will be described below. The secondary battery of the embodiment may further include a separator and an exterior member in addition to these components. The configurations of these components will also be described below.
1) Positive Electrode The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may include a positive electrode active material and, optionally, a conductive agent and a binder.

For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one type of compound alone as the positive electrode active material, or may contain a combination of two or more types of compounds. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

Examples of such compounds include manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxides (e.g., Li _x Mn ₂ O ₄ or Li _x MnO ₂ ; 0<x≦1), lithium nickel composite oxides (e.g., Li _x NiO ₂ ; 0<x≦1), lithium cobalt composite oxides (e.g., Li _x CoO ₂ ; 0<x≦1), lithium nickel cobalt composite oxides (e.g., Li _x Ni _1-y Co _y O ₂ ; 0<x≦1, 0<y<1), lithium manganese cobalt composite oxides (e.g., Li _x Mn _y Co _1-y O ₂ ; 0<x≦1, 0<y<1), and lithium manganese nickel composite oxides having a spinel structure (e.g., Li _x Mn _2-y Ni _y O _{4 ;} 0<x≦1, 0<y<2), lithium phosphate oxides having an olivine _structure (e.g., _LixFePO4 ; 0<x≦1, _{LixFe1 - yMnyPO4} ; 0<x≦1, 0<y≦ ₁ , _LixCoPO4 ; 0<x≦1), iron sulfate ( _Fe2 ( _SO4 ) ₃ ), vanadium oxides (e.g. _{, V2O5} ), _LiNixCoyMzO2 (x+ _y + _z = ₁ , x≧0.8, M consists of Mn and Al), and lithium nickel cobalt _manganese composite oxides ( _{LixNi1 -yzCoyMnzO2 ;} 0<x≦1 _, 0<y<1, 0<z<1, y+z<1).

Among the above, examples of more preferred compounds as the positive electrode active material include _lithium manganese composite oxides having a spinel structure (e.g., _LixMn2O4 ; 0<x≦ ₁ ), lithium manganese nickel composite oxides having a spinel structure ( _{LixMn2 - yNiyO4} ; 0<x≦1, ₀ <y< ₂ ), lithium nickel cobalt manganese composite oxides ( _{LixNi1 -yzCoyMnzO2 ;} 0<x≦1 _, 0<y<1, 0<z<1, y+z<1), and lithium phosphate _oxides having an olivine structure (e.g., _LixFePO4 ; 0<x≦ ₁ , _{LixFe1 - yMnyPO4} ; 0<x≦1, 0<y≦ ₁ , _LixCoPO4 ; 0<x≦1). The use of these compounds as the positive electrode active material can increase battery voltage. In the lithium nickel cobalt manganese composite oxide represented _{by LixNi1 - yzCoyMnzO2} , when y and z are in the _range of 0<y+z≦0.2, a high energy density can be realized.

The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. Positive electrode active materials with a primary particle size of 100 nm or more are easy to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or less allow lithium ions to diffuse smoothly within the solid.

The specific surface area of the positive electrode active material is preferably 0.1 ^m /g or more and 10 ^m /g or less. A positive electrode active material having a specific surface area of 0.1 ^m /g or more can ensure sufficient sites for occlusion and desorption of Li ions. A positive electrode active material having a specific surface area of ^{10 m} /g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

The binder is blended to fill the gaps between the dispersed positive electrode active material and to bind the positive electrode active material to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as binders.

Conductive agents are added to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination. The conductive agent may also be omitted.

In the positive electrode active material-containing layer, the positive electrode active material and binder are preferably blended in proportions of 80% by mass or more and 98% by mass or less, and 2% by mass or more and 20% by mass or less, respectively.

By using a binder amount of 2% by mass or more, sufficient electrode strength can be achieved. The binder can also function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably blended in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent that comes into contact with the electrolyte can be reduced. This low proportion can reduce electrolyte decomposition during high-temperature storage.

The positive electrode current collector is preferably aluminum foil or aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

The positive electrode current collector may also include a portion on its surface where the positive electrode active material-containing layer is not formed. This portion can function as a positive electrode current collecting tab.

For example, a positive electrode is prepared by suspending a positive electrode active material, a conductive agent, and a binder in a solvent to prepare a slurry. This slurry is then applied to one or both sides of a current collector. The applied slurry is then dried to obtain a laminate of an active material-containing layer and a current collector. This laminate is then pressed. In this manner, a positive electrode is produced. Alternatively, the positive electrode may be produced by the following method. First, the active material, the conductive agent, and the binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Next, these pellets are placed on a current collector to obtain a positive electrode.
2) Negative Electrode The negative electrode may include a current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one or both sides of the current collector. The negative electrode active material-containing layer may include a negative electrode active material, and optionally a conductive agent and a binder.

The negative electrode active material is not particularly limited as long as it can absorb and release lithium or lithium ions. The type of negative electrode active material used can be one or more types. Examples of negative electrode active materials include titanium-containing oxides and carbon materials. Examples of titanium-containing oxides include lithium titanate having a ramsdellite structure (e.g., Li _2+y Ti ₃ O ₇ , 0≦y≦3), lithium titanate having a spinel structure (e.g., Li _4+x Ti ₅ O ₁₂ , 0≦x≦3), monoclinic titanium dioxide (TiO ₂ ), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, orthorhombic titanium composite oxide, and niobium titanium composite oxide. The lithium ion absorption and desorption potential of the titanium-containing oxide is 0.4 V (vs. Li/Li ⁺ ) or higher.

An example of the orthorhombic titanium-containing composite oxide is a compound represented by Li2 _+aM (I) _2- bTi6 _-cM (II) _{dO14 +σ} . Here, M(I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M(II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2 _, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. A specific example of the orthorhombic titanium-containing composite oxide is Li2 _{+ aNa2Ti6O14} (0≦a≦ ₆ ).

An example of the niobium titanium composite oxide is a monoclinic niobium titanium composite oxide. An example of the monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M1 _y Nb _2-z M2 _z O _7+δ . Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3. A specific example of the monoclinic niobium titanium composite oxide is Li _x Nb ₂ TiO ₇ (0≦x≦5).

Another example of a monoclinic niobium titanium composite oxide is a compound represented by Li _x Ti _1-y M3 _y+z Nb _2-z O _7-δ , where M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

Examples of carbon materials include graphite and hard carbon. When a carbon material is used for the negative electrode, copper foil is used for the negative electrode current collector.

Among negative electrode active materials, monoclinic niobium titanium composite oxide has a lithium ion absorption/desorption potential of approximately 1.0 V (vs. Li/Li ⁺ ), which allows for a moderate decomposition reaction with the sulfur-containing compound. Note that the lithium ion absorption/desorption potential of lithium titanate is approximately 1.4 V (vs. Li/ ^{Li +} ), and the lithium ion absorption/desorption potential of carbon materials is approximately 0 V (vs. Li/Li ⁺ ).

Conductive agents are added to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon nanotubes, carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with carbon or an electronically conductive inorganic material.

Binders are added to fill the gaps between the dispersed active material and to bind the active material and current collector together. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. These may be used alone or in combination.

As an example, the active material, conductive agent, and binder in the active material-containing layer preferably have a negative electrode active material, conductive agent, and binder content of 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By using a conductive agent content of 2% by mass or more, the current collection performance of the active material-containing layer can be improved. Furthermore, by using a binder content of 2% by mass or more, sufficient adhesion between the active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to use a conductive agent and binder content of 30% by mass or less each in order to achieve high capacity.

The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted and extracted from the active material. When a negative electrode active material having a lithium ion insertion/extraction potential of 0.4 V (vs. Li/Li ⁺ ) or higher is used, examples of the current collector include copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

The current collector may also include a portion on its surface where the negative electrode active material-containing layer is not formed. This portion can function as a negative electrode current collecting tab.

The negative electrode can be produced, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of an active material-containing layer and a current collector. Then, this laminate is pressed. In this manner, the negative electrode is produced. Alternatively, the negative electrode may be produced by the following method. First, the active material, the conductive agent, and the binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Next, these pellets are placed on a current collector to obtain a negative electrode.
3) Sulfur-Containing Layer The sulfur-containing layer is present on at least a portion of the surface of the positive electrode active material-containing layer. The sulfur-containing layer may be present on at least a portion of the surface of the negative electrode active material-containing layer.

The sulfur-containing layer is formed by decomposing a sulfur-containing compound, which is composed of at least one of a sulfur-containing imide compound and a sultone compound, or at least one of a sulfur-containing imide compound, a sultone compound, and a propanesulfonic acid ester, in the positive electrode active material-containing layer or the negative electrode active material-containing layer.

Examples of sulfur-containing imide compounds include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(fluoromethanesulfonyl)amide (LiFSA), and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA). The sulfur-containing compound may contain one compound selected from the group consisting of these compounds, or may contain a mixture of two or more compounds.

Examples of sultone compounds include 1,3-propane sultone (PS), 1,4-butane sultone, 1,3-propene sultone, and 2,4-butane sultone. The sulfur-containing compound may contain one compound selected from the group consisting of these compounds, or may contain a mixture of two or more compounds.

Among sulfur-containing compounds, sultone compounds are preferred. Sulfur-containing compounds undergo decomposition reactions before the electrolyte decomposes, suppressing gas generation, and the decomposition potential of sultone compounds is appropriate.

The sulfur-containing layer may contain other types of atoms in addition to sulfur atoms (S). Examples of other types of atoms include oxygen atoms (O) and carbon atoms (C).

When the sulfur-containing layer is formed on at least a portion of the positive electrode active material-containing layer, the mass (g/m ³ ) A of sulfur atoms per unit volume of the sulfur-containing layer can be set to a range of more than 0 (g/m ³ ) and not more than 3500 (g/m ³ ). By setting A in the above range, the sulfur-containing layer does not inhibit the absorption and release of lithium ions by the positive electrode, and an increase in positive electrode resistance can be suppressed. The preferred upper limit of A is 3260 (g/m ³ ). In order to ensure sufficient protection of the positive electrode by the sulfur-containing layer, the lower limit of A is desirably 430 (g/m ³ ).

When the sulfur-containing layer is formed on at least a portion of the negative electrode active material-containing layer, the mass (g/m ³ ) D of sulfur atoms per unit volume of the sulfur-containing layer can be set to a range of more than 0 (g/m ³ ) and not more than 6600 (g/m ³ ). By setting D in the above range, the sulfur-containing layer does not inhibit the absorption and release of lithium ions by the negative electrode, and an increase in negative electrode resistance can be suppressed. The preferred upper limit of D is 4720 (g/m ³ ). In order to ensure sufficient protection of the negative electrode by the sulfur-containing layer, the lower limit of D is desirably 700 (g/m ³ ).
4) Nonaqueous Electrolyte The nonaqueous electrolyte contains a sulfur-containing compound consisting of at least one of a sulfur-containing imide compound and a sultone compound, or at least one of a sulfur-containing imide compound, a sultone compound, and a propanesulfonic acid ester.

The nonaqueous electrolyte may be, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte. The liquid nonaqueous electrolyte contains an electrolyte salt, an organic solvent capable of dissolving the electrolyte salt, and a sulfur-containing compound. The concentration of the electrolyte salt is preferably 0.5 mol/L or more and 2.5 mol/L or less. The sulfur-containing compound may also serve as the electrolyte salt or the organic solvent.

The sulfur-containing imide compound and sultone compound may or may not function as an electrolyte salt or an organic solvent. Examples of sulfur-containing imide compounds and sultone compounds are as described in the sulfur-containing layer.

The concentration (mol/L) E of the sulfur-containing compound in the nonaqueous electrolyte can be set to a range greater than 0 (mol/L) and not greater than 4.5×10 ⁻¹ (mol/L). By setting E in this range, the ionic conductivity of the nonaqueous electrolyte can be kept within an appropriate range. A preferred upper limit value for E is 1.6×10 ⁻¹ (mol/L). In order to enhance the effect of suppressing gas generation and resistance increase, it is desirable to set the lower limit value for E to 8.2×10 ⁻² (mol/L).

Examples of electrolyte salts include lithium salts such as lithium perchlorate ( _LiClO4 ), lithium hexafluorophosphate ( _LiPF6 ), lithium tetrafluoroborate ( _LiBF4 ), lithium hexafluoride ( _LiAsF6 ), lithium trifluoromethanesulfonate ( _LiCF3SO3 ), LiTFSI, and LiFSI, and mixtures thereof. The electrolyte salt is preferably one that _is difficult to oxidize even at high potentials, and _LiPF6 is most preferred.

Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and propione methyl carbonate (PMC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); dimethoxyethane (DME), and diethoxyethane (diethoxyethane); These organic solvents include chain ethers such as diethyl ether (DEE), gamma-butyrolactone (GBL), acetonitrile (AN), sulfolane (SL), and ethyl propionate (EP). These organic solvents can be used alone or in combination.

Gel-type non-aqueous electrolytes are prepared by combining a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room-temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, etc. may also be used as nonaqueous electrolytes.

The nonaqueous electrolyte contained in the secondary battery of the embodiment may further contain a propanesulfonic acid ester. This can enhance the effect of suppressing gas generation during high-temperature storage, especially under conditions of high temperature and high SOC, thereby further suppressing increases in battery resistance. As a result, the life performance of the secondary battery can be further improved. Examples of propanesulfonic acid esters include at least one selected from the group consisting of methyl propanesulfonate, ethyl propanesulfonate, and propyl propanesulfonate.

The non-aqueous electrolyte may contain a sultone compound and a propanesulfonate ester as sulfur-containing compounds. In a total ion chromatogram obtained by gas chromatography-mass spectrometry (GC-MS) of the non-aqueous electrolyte, when the peak area value A of the sultone compound is set to 10, the peak area value B of the propanesulfonate ester is preferably 0.01 to 40. By setting the peak area value B to 0.01 to 40, the resistance value of the secondary battery can be kept low while suppressing the amount of gas generation when the secondary battery is used at high temperatures and under conditions of high temperature and high SOC. A more preferable range for the peak area value B is 0.2 to 20. The method of gas chromatography-gravimetric analysis is described below.

5) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and are capable of interrupting current.

An electrolyte layer containing an inorganic solid electrolyte may be used as the separator. Examples of the lithium ion conductive inorganic solid electrolyte include a lithium ion conductive oxide-based solid electrolyte and a lithium ion conductive sulfide-based solid electrolyte. Examples of the lithium ion conductive oxide-based _solid electrolyte include a lithium phosphate solid electrolyte with a NASICON structure, _amorphous LIPON ( _{Li2.9PO3.3N0.46 )} , or LLZ _{( Li7La3Zr2O12} ) with a _garnet structure.
6) Exterior Member As the exterior member, for example, a container made of a laminate film or a metal container can be used.

The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

The laminate film used is a multilayer film containing multiple resin layers and metal layers sandwiched between these resin layers. The resin layers contain polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it with heat.

The wall thickness of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content thereof is preferably 100 ppm by mass or less.

The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be selected appropriately depending on the battery dimensions and intended use.

The method for measuring the mass of sulfur atoms per unit volume (g/m ³ ) of the sulfur-containing layer and the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte will be described below.
The exterior packaging of a secondary battery with a state of charge (SOC) of 50% is opened and the electrode group is removed. The jig (such as tape) holding the electrode group together is removed, and if the outermost layer is a separator, the separator is peeled back to remove the first layer of electrode (e.g., negative electrode). The separator is then peeled back to remove the first layer of electrode (e.g., positive electrode). The process of peeling back the separator and removing the electrodes is repeated until all positive and negative electrodes constituting the electrode group are removed. The removed electrodes and separator are centrifuged to extract the non-aqueous electrolyte. The concentration of sulfur-containing compounds in the non-aqueous electrolyte is measured by ICP (Inductively Coupled Plasma) optical emission spectrometry.
On the other hand, when measuring the sulfur atomic mass per unit volume of the sulfur-containing layer, the positive and negative electrodes placed in the centrifuge are washed with methyl ethyl carbonate (MEC) and vacuum dried. Each electrode is punched out to a fixed area (2 × 2 cm ² ), a fixed amount of pure water (10 cc) is added, and ultrasonic irradiation is performed for 30 minutes or more. The extracted solution is analyzed by ICP to measure the amount of sulfur in the extracted solution, thereby obtaining the sulfur atomic mass per unit volume of the sulfur-containing layer of each electrode.

This article explains gas chromatography-mass spectrometry (GC-MS) of non-aqueous electrolytes.

The non-aqueous electrolyte extracted using the method described above is diluted with acetonitrile to a volume of 20 times to prepare the measurement sample. GCMS measurement is performed on the measurement sample under the conditions shown in Table 1A below.

The components contained in a measured sample can be identified from its mass spectrum. For example, peaks appearing at m/z 122.65 and 58 in the mass spectrum are due to propane sultone. Furthermore, peaks appearing at m/z 124, 111, and 83 in the mass spectrum are due to ethyl propanesulfonate.

Based on the mass spectrum results, the peak area value A of a sultone compound such as propane sultone and the peak area value B of a propanesulfonate ester such as ethyl propanesulfonate are determined in the total ion chromatogram (TIC) of the measurement sample. The peak area value B is calculated when the peak area value A is set to 10.

An example of a secondary battery according to an embodiment will be described with reference to Figures 1 to 4.

Figures 1 and 2 show an example of a secondary battery using an exterior member made of laminate film.

As shown in Figures 1 and 2, the flat wound electrode group 1 is housed in a bag-shaped exterior member 12 made of a laminate film with a metal layer sandwiched between two resin films. The flat wound electrode group 1 is formed by spirally winding a laminate consisting of, from the outside, a negative electrode 4, a separator 5, a positive electrode 3, and a separator 5, in that order, around an axis parallel to the short side direction, and then press-molding the laminate. The outermost negative electrode 4, as shown in Figure 2, has a negative electrode layer (negative electrode active material-containing layer) 4b containing a negative electrode active material formed on one side of the inner surface of the negative electrode current collector 4a. The other negative electrodes 4 have negative electrode layers 4b formed on both sides of the negative electrode current collector 4a. The positive electrode 3 has a positive electrode layer (positive electrode active material-containing layer) 3b formed on both sides of the positive electrode current collector 3a.

Near the outer periphery of the wound electrode group 1, the negative electrode terminal 13 is connected to the negative electrode current collector 4a of the outermost negative electrode 4, and the positive electrode terminal 14 is connected to the positive electrode current collector 3a of the innermost positive electrode 3. These negative electrode terminals 13 and positive electrode terminals 14 extend outward from the opening of the bag-shaped exterior member 12. The opening of the bag-shaped exterior member 12 is heat-sealed to hermetically seal the wound electrode group 1. When heat-sealing, the negative electrode terminal 13 and positive electrode terminal 14 are sandwiched between the bag-shaped exterior member 12 at this opening. The sulfur-containing layer 15 is formed on part of the surface of the positive electrode active material-containing layer 3b and is in contact with the separator 5.

Figures 3 and 4 show an example of a secondary battery using a metal container.

The electrode group 1 is housed in a rectangular cylindrical metal container 2. The electrode group 1 is formed, for example, by winding a positive electrode 3 and a negative electrode 4, with a separator 5 interposed between them, into a flat spiral around an axis parallel to the short side direction. Although not shown, the sulfur-containing layer is formed on a portion of the surface of the positive electrode active material-containing layer 3b and is in contact with the separator 5. As shown in Figure 4, strip-shaped positive electrode leads 6 are electrically connected to multiple locations on the end of the positive electrode 3 located on the end face of the electrode group 1 that intersects the electrode stacking direction. Similarly, strip-shaped negative electrode leads 7 are electrically connected to multiple locations on the end of the negative electrode 4 located on this end face. These multiple positive electrode leads 6 are bundled together and electrically connected to a positive electrode current collector tab 8. The positive electrode leads 6 and the positive electrode current collector tab 8 form a positive electrode terminal. Similarly, the negative electrode leads 7 are bundled together and connected to a negative electrode current collector tab 9. The negative electrode terminal is composed of the negative electrode lead 7 and the negative electrode current collector tab 9. A metal sealing plate 10 is fixed to the opening of the metal container 2 by welding or the like. The positive electrode current collector tab 8 and the negative electrode current collector tab 9 are each pulled out to the outside through an extraction hole provided in the sealing plate 10. The inner surface of each extraction hole in the sealing plate 10 is covered with an insulating member 11 to prevent short circuits due to contact with the positive electrode current collector tab 8 and the negative electrode current collector tab 9. A method for manufacturing a secondary battery according to this embodiment will be described with reference to Figure 5. Figure 5 is a schematic diagram showing an outline of a method for manufacturing a secondary battery using a bag-shaped exterior member made of laminate film.

First, a separator 5 is placed between a positive electrode 3 without a sulfur-containing layer and a negative electrode 4 without a sulfur-containing layer to prepare an electrode group 1. A positive electrode terminal 14 is electrically connected to the positive electrode 3 of the electrode group 1, and a negative electrode terminal 13 is electrically connected to the negative electrode 4 of the electrode group 1.

An electrode group 1 having positive and negative electrode terminals 13, 14 is housed in a bag-shaped exterior member 12 made of laminate film, and then the other end 21b, excluding the first end 21a, is sealed by heat fusion. Next, a nonaqueous electrolyte is injected into the bag-shaped exterior member 12 through the first end 21a, and the first end 21a is sealed by heat fusion under reduced pressure. This results in a secondary battery 30 with a primary seal.

Next, the secondary battery 30 after the first sealing is subjected to an initial charge/discharge at room temperature (e.g., 25°C), and then aging is performed at a temperature equal to or higher than room temperature. The aging temperature can be, for example, in the range of 30°C to 80°C. Through the initial charge/discharge and aging, a sulfur-containing layer 15 is formed on at least a portion of the surface of the positive electrode active material-containing layer 3b. At this time, by adjusting the state of charge (SOC) of the battery, the negative electrode potential, the aging temperature and time, etc., a sulfur-containing layer can be formed on at least a portion of the surface of the negative electrode active material-containing layer 4b.
After aging, the temperature of the secondary battery 30 is returned to room temperature, and then in an argon atmosphere, the bag-shaped exterior member 12 is cut along the unsealed cutting line 22 inside the first end 21a and opened to release the gas inside the bag-shaped exterior member 12 to the outside. The portion cut from the bag-shaped exterior member 12 along the cutting line 22 is indicated by the reference numeral 23.

Next, a sulfur-containing compound or a nonaqueous electrolyte containing a sulfur-containing compound is supplied into the bag-shaped exterior member 12, and a second sealing is performed by sealing the edge 24 along the cutting line 22 under reduced pressure (e.g., -90 kPa). The sulfur-containing compound in the nonaqueous electrolyte is consumed by the formation of the sulfur-containing layer, but the concentration of the sulfur-containing compound in the nonaqueous electrolyte can be set to the desired range by subsequently replenishing the sulfur-containing compound or the nonaqueous electrolyte containing the sulfur-containing compound. Therefore, by adjusting manufacturing conditions such as temperature, time, or SOC during the initial charge/discharge process or the aging process, and the amount of sulfur-containing compound replenished, the E/A ratio can be set to the desired range. This results in the secondary battery 31 of this embodiment.

When a propanesulfonic acid ester is contained in the non-aqueous electrolyte of the secondary battery of this embodiment, the aging temperature in the above-described method is preferably set to a range greater than 95°C and less than 120°C. This promotes the reaction between a sultone compound, such as propane sultone, and an organic solvent, facilitating the production of the propanesulfonic acid ester. Ethyl propanesulfonate can be obtained, for example, by using a sultone compound and an organic solvent containing DEC and/or EP. Methyl propanesulfonate can be obtained, for example, by using a sultone compound and an organic solvent containing MEC. Meanwhile, propyl propanesulfonate can be obtained, for example, by using a sultone compound and an organic solvent containing PC. Furthermore, by replenishing the sultone compound or a non-aqueous electrolyte containing a sultone compound to replenish the sultone compound consumed during the aging process, the concentration of the sulfur-containing compound in the non-aqueous electrolyte can be set within the desired range.

Instead of the above method, the propanesulfonic acid ester may be incorporated into the non-aqueous electrolyte by the following method. That is, by incorporating the propanesulfonic acid ester into the non-aqueous electrolyte that is initially injected before the first sealing in the above method, the propanesulfonic acid ester can be incorporated into the non-aqueous electrolyte. In this case, it is possible to omit the need to replenish the sultone compound after gas release.

According to the secondary battery of the first embodiment described above, the following formula (1) (1×10 ⁻⁶ ≦E/A≦9×10 ⁻⁴ ) is satisfied: Since these satisfy the above requirements, it is possible to suppress the amount of gas generated and the increase in resistance at high temperatures, and it is possible to achieve excellent life performance even at high temperatures.
Second Embodiment
The battery pack according to the second embodiment may include one or more secondary batteries (single cells) according to the embodiment. The secondary batteries may be electrically connected in series, in parallel, or in a combination of series and parallel to form a battery assembly. The battery pack according to the embodiment may include a plurality of battery assemblies.

The battery pack according to the embodiment may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobiles, etc.) may also be used as the protection circuit for the battery pack.

The battery pack according to the embodiment may further include external terminals for current flow. The external terminals for current flow are for outputting current from the secondary battery to the outside and inputting current to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. Furthermore, when the battery pack is charged, charging current (including regenerative energy from the power of a vehicle such as an automobile) is supplied to the battery pack through the external terminals for current flow.

Figures 6 and 7 show an example of a battery pack 50. This battery pack 50 includes multiple flat batteries having the structure shown in Figure 6. Figure 6 is an exploded perspective view of the battery pack 50, and Figure 7 is a block diagram showing the electrical circuit of the battery pack 50 shown in Figure 6.

Multiple cells 51 are stacked so that the negative and positive terminals 13 and 14 extending outward are aligned in the same direction, and are fastened together with adhesive tape 52 to form a battery pack 53. These cells 51 are electrically connected in series as shown in Figure 7.

The printed wiring board 54 is positioned opposite the side of the battery cell 51 from which the negative terminal 13 and positive terminal 14 extend. As shown in Figure 7, the printed wiring board 54 is equipped with a thermistor 55, a protective circuit 56, and an external terminal 57 for supplying power to an external device. An insulating plate (not shown) is attached to the surface of the printed wiring board 54 facing the battery pack 53 to prevent unnecessary connection with the wiring of the battery pack 53.

The positive electrode lead 58 is connected to the positive electrode terminal 14 located on the bottom layer of the battery pack 53, and its tip is inserted into and electrically connected to the positive electrode connector 59 on the printed wiring board 54. The negative electrode lead 60 is connected to the negative electrode terminal 13 located on the top layer of the battery pack 53, and its tip is inserted into and electrically connected to the negative electrode connector 61 on the printed wiring board 54. These connectors 59, 61 are connected to the protection circuit 56 through wiring 62, 63 formed on the printed wiring board 54.

The thermistor 55 detects the temperature of the cell 51 and sends the detection signal to the protection circuit 56. Under certain conditions, the protection circuit 56 can interrupt the positive wiring 64a and negative wiring 64b between the protection circuit 56 and the external terminal 57 for supplying current to an external device. The predetermined condition is, for example, when the temperature detected by the thermistor 55 exceeds a predetermined temperature. Another predetermined condition is when an overcharge, overdischarge, overcurrent, or other condition is detected in the cell 51. This overcharge detection is performed for each cell 51 or for all cells 51. When detecting an individual cell 51, the battery voltage or the positive or negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 51. In the cases shown in Figures 6 and 7, voltage detection wiring 65 is connected to each cell 51, and a detection signal is sent to the protection circuit 56 via these wirings 65.

Protective sheets 66 made of rubber or resin are placed on each of the three sides of the battery pack 53, excluding the sides from which the positive and negative terminals 14 and 13 protrude.

The battery pack 53 is housed in a storage container 67 together with the protective sheets 66 and printed wiring board 54. That is, protective sheets 66 are placed on both long-side and short-side inner surfaces of the storage container 67, and the printed wiring board 54 is placed on the inner surface opposite the short side. The battery pack 53 is located in the space surrounded by the protective sheets 66 and printed wiring board 54. A lid 68 is attached to the top of the storage container 67.

In addition, heat-shrink tape may be used instead of adhesive tape 52 to secure the battery pack 53. In this case, protective sheets are placed on both sides of the battery pack, heat-shrink tape is wrapped around it, and then the heat-shrink tape is thermally shrunk to bind the battery pack.

Figures 6 and 7 show the cells 51 connected in series, but they may also be connected in parallel to increase battery capacity. Alternatively, a combination of series and parallel connections may be used. The assembled battery pack can also be further connected in series or parallel.

Furthermore, while the battery packs shown in Figures 6 and 7 include one battery assembly, the battery packs according to the embodiments may include multiple battery assembly connections. The multiple battery assembly connections are electrically connected in series, in parallel, or in a combination of series and parallel connections.

The battery pack configuration can be modified as appropriate depending on the application. The battery pack according to the embodiment is suitable for use in applications that require excellent cycle performance when drawing a large current. Specifically, it can be used as a power source for digital cameras, or as a vehicle battery for, for example, two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, or railway vehicles (e.g., electric trains), or as a stationary battery. In particular, it is suitable for use as an on-board battery installed in a vehicle.

The battery pack of the second embodiment described above includes the secondary battery of the embodiment, and therefore can suppress gas generation and an increase in battery resistance at high temperatures, thereby achieving excellent life performance even at high temperatures.
(Third embodiment)
The vehicle of the third embodiment includes one or more secondary batteries of the embodiment, or includes a battery pack of the embodiment.

In a vehicle such as an automobile equipped with a battery pack according to the third embodiment, the battery pack may, for example, recover regenerative energy from the vehicle's power. The vehicle may also include a mechanism for converting the vehicle's kinetic energy into regenerative energy.

Figure 8 shows an example of a vehicle equipped with an example battery pack according to an embodiment.

The automobile 71 shown in Figure 8 is equipped with an example battery pack 72 according to an embodiment in the engine compartment at the front of the vehicle. The location of the battery pack in an automobile is not limited to the engine compartment. For example, the battery pack can also be equipped at the rear of the automobile or under the seat.

Figure 9 is a diagram showing a schematic configuration of an example vehicle according to an embodiment. The vehicle 300 shown in Figure 9 is an electric vehicle.

The vehicle 300 shown in Figure 9 includes a vehicle power supply 301, a vehicle ECU (Electric Control Unit) 380 which is the host control means for the vehicle power supply 301, an external terminal 370, an inverter 340, and a drive motor 345.

The vehicle 300 is equipped with a vehicle power supply 301, for example, in the engine compartment, at the rear of the vehicle body, or under a seat. However, Figure 9 only shows the location of the secondary battery installed in the vehicle 300 in a simplified manner.

The vehicle power supply 301 includes multiple (e.g., three) battery packs 312a, 312b, and 312c, a battery management unit (BMU) 311, and a communication bus 310.

The three battery packs 312a, 312b, and 312c are electrically connected in series. Battery pack 312a includes a battery pack 314a and a battery pack monitoring device (VTM: Voltage Temperature Monitoring) 313a. Battery pack 312b includes a battery pack 314b and a battery pack monitoring device 313b. Battery pack 312c includes a battery pack 314c and a battery pack monitoring device 313c. Battery packs 312a, 312b, and 312c can each be removed independently and replaced with a different battery pack.

Each of the battery packs 314a to 314c includes multiple secondary batteries connected in series. Each secondary battery is a secondary battery according to the embodiment. Each of the battery packs 314a to 314c is charged and discharged via a positive terminal 316 and a negative terminal 317.

To collect information related to the maintenance of the vehicle power supply 301, the battery management device 311 communicates with the battery pack monitoring devices 313a-313c to collect information such as the voltage and temperature of the secondary batteries of the battery packs 314a-314c included in the vehicle power supply 301.

A communication bus 310 is connected between the battery management unit 311 and the assembled battery monitoring units 313a to 313c. The communication bus 310 is configured so that a set of communication lines is shared by multiple nodes (a battery management unit and one or more assembled battery monitoring units). The communication bus 310 is configured, for example, based on the CAN (Control Area Network) standard.

The battery pack monitoring devices 313a-313c measure the voltage and temperature of each secondary battery that makes up the battery packs 314a-314c based on commands received via communication from the battery management device 311. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all secondary batteries.

The vehicle power supply 301 may also have an electromagnetic contactor (for example, the switch device 333 shown in Figure 9) for connecting and disconnecting the positive and negative terminals. The switch device 333 includes a pre-charge switch (not shown) that turns on when the assembled batteries 314a-314c are being charged, and a main switch (not shown) that turns on when battery output is supplied to a load. The pre-charge switch and main switch are equipped with relay circuits (not shown) that are turned on and off by signals supplied to coils located near the switch elements.

The inverter 340 converts the input DC voltage into a three-phase AC high voltage for driving the motor. The output voltage of the inverter 340 is controlled based on control signals from the battery management unit 311 (described below) or the vehicle ECU 380, which controls the overall operation of the vehicle. The three-phase output terminals of the inverter 340 are connected to the three-phase input terminals of the drive motor 345.

The drive motor 345 rotates using power supplied from the inverter 340, and transmits the rotation to the axles and drive wheels W, for example, via a differential gear unit.

In addition, although not shown, the vehicle 300 is equipped with a regenerative braking mechanism that rotates the drive motor 345 when the vehicle 300 is braked, converting kinetic energy into regenerative energy in the form of electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 340 and converted into direct current. The direct current is input to the vehicle power supply 301.

One terminal of connection line L1 is connected to the negative terminal 317 of the vehicle power supply 301 via a current detection unit (not shown) in the battery management device 311. The other terminal of connection line L1 is connected to the negative input terminal of the inverter 340.

One terminal of the connection line L2 is connected to the positive terminal 316 of the vehicle power supply 301 via a switch device 333. The other terminal of the connection line L2 is connected to the positive input terminal of the inverter 340.

The external terminal 370 is connected to the battery management device 311, which will be described later. The external terminal 370 can be connected to, for example, an external power source.

The vehicle ECU 380 manages the entire vehicle by controlling the battery management unit 311 in cooperation with other devices in response to operational inputs from the driver and other personnel. Data related to the maintenance of the vehicle power supply 301, such as the remaining capacity of the vehicle power supply 301, is transferred via a communication line between the battery management unit 311 and the vehicle ECU 380.

The vehicle of the embodiment includes a battery pack including the secondary battery of the embodiment, and the battery pack (e.g., battery packs 312a, 312b, and 312c) has excellent life performance, resulting in a vehicle with excellent charge/discharge performance and high reliability. Furthermore, each battery pack is inexpensive and highly safe, thereby reducing vehicle costs and improving safety.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the embodiments listed below.
Example 1
A secondary battery was fabricated in the following manner.

<Preparation of Positive Electrode>
_A lithium nickel composite oxide ( _{LiNi0.8Co0.1Mn0.1O2 )} powder was prepared as the positive electrode active material. Acetylene black was prepared as the conductive agent. Polyvinylidene fluoride (PVdF) was prepared as the binder. Next, the positive _electrode active material, conductive agent, and binder were added to N-methylpyrrolidone (NMP) in a ratio of 90 parts by weight:10 parts by weight:10 parts by weight and mixed to prepare a positive electrode slurry. This positive electrode slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm. Next, the coating was dried in a thermostatic oven at 120°C to form a positive electrode active material-containing layer, and the positive electrode active material-containing layer was pressed to obtain a positive electrode.
<Preparation of negative electrode>
Niobium titanium composite oxide (Nb ₂ TiO ₇ ) powder was prepared as the negative electrode active material. The average secondary particle diameter of the niobium titanium composite oxide was 7.5 μm. The specific surface area of the niobium titanium composite oxide was 4.0 m ² /g. Acetylene black was prepared as a conductive agent, and polyvinylidene fluoride (PVdF) was prepared as a binder. Next, the negative electrode active material, conductive agent, and binder were added to N-methylpyrrolidone (NMP) in a ratio of 90 parts by weight:10 parts by weight:10 parts by weight to prepare a negative electrode slurry. This negative electrode slurry was applied to both sides of a current collector made of aluminum foil with a thickness of 15 μm. Next, the coating was dried in a thermostatic oven at 120°C to form a negative electrode active material-containing layer, and the negative electrode active material-containing layer was pressed to obtain a negative electrode.
<Preparation of electrode group>
Two 25 μm thick polyethylene nonwoven fabrics were prepared as separators. Next, a positive electrode, a separator, a negative electrode, and a separator were stacked in this order to obtain a laminate. This laminate was then spirally wound. This was then hot-pressed at 80°C to produce a flat electrode assembly. A positive electrode terminal was electrically connected to the positive electrode of the electrode assembly. A negative electrode terminal was also electrically connected to the negative electrode of the electrode assembly.
<Storage of electrode group>
A container was prepared, which was made of a 0.1 mm thick laminate film having a three-layer structure of nylon, aluminum, and polyethylene. The electrode assembly prepared above was placed in this container. Next, with a portion of the periphery of the container open, the inside of the container was dried in a vacuum at 80°C for 16 hours.
<Preparation of Liquid Non-Aqueous Electrolyte>
_LiPF6 was dissolved as an electrolyte at a concentration of 1 mol/L in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2). Furthermore, 1,3-propane sultone (PS) was dissolved as a sulfur-containing compound so that its concentration in the non-aqueous electrolyte was 0.5 wt %. Thus, a liquid non-aqueous electrolyte (non-aqueous electrolyte solution) was obtained. The preparation of the non-aqueous electrolyte was carried out in an argon box. The composition of the liquid non-aqueous electrolyte at this stage is the final composition after secondary battery production.
<Battery construction>
A nonaqueous electrolyte was poured into the container containing the electrode group. The open peripheral edges of the container were then heat-sealed to hermetically seal the container. This resulted in a battery with external dimensions of 11 cm × 8 cm × 0.3 cm, excluding the positive and negative electrode terminals (also referred to as positive and negative electrode tabs), and internal dimensions (dimensions of the sealed portion) of 9 cm × 7 cm × 0.25 cm. This battery is referred to as the first sealed battery.
<First charge>
The first sealed battery was subjected to initial charging in an environment of 25° C. in the following manner. First, the first sealed battery was charged at a constant current (CC) of 0.2 C until a voltage of 3 V was reached. Next, the first sealed battery was charged at a constant voltage (CV) of 3 V. The constant voltage charging was terminated when the total time of the constant current charging and constant voltage charging reached 10 hours.
<First discharge>
Next, the first sealed battery was discharged at a constant current (CC) of 0.2 C in an environment of 25° C. until the voltage reached 1.5 V.
<Post-processing>
Next, the first sealed battery was charged at a constant current (CC) of 0.2 C in an environment of 25°C until a voltage of 3 V was reached. The first sealed battery was then charged at a constant voltage (CV) of 3 V until the current value reached 1/20 C. That is, the first sealed battery was subjected to constant current/constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). The first sealed battery was placed in a thermostatic chamber at 80°C and aged for 24 hours. The first sealed battery was then placed in an argon box, and one location on the sealed portion of the exterior member was cut using the method described with reference to FIG. 5 to release the gas inside the exterior member. Liquid nonaqueous electrolyte was added to the battery to achieve the same concentration as before the initial charge/discharge, and the end opened by the cut was heat-sealed. In this manner, a secondary battery according to Example 1 was fabricated. The composition of the liquid nonaqueous electrolyte added in the post-treatment is shown in Table 5.
(Examples 2, 3, 6-20, 22-24, 26, and 27)
Secondary batteries were fabricated in the same manner as in Example 1, except that the composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the nonaqueous electrolyte, E/A, E/ ^D , the mass A (g/ ^m3 ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m3) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/ _L ) of the sulfur-containing compound in the nonaqueous electrolyte, and the composition of the nonaqueous electrolyte added in post-treatment were set as shown in Tables 1 to 6 below. The positive electrode active material _LiMn2O4 used in these examples has a spinel-type crystal structure. On the other hand, _LiFePO4 has an olivine-type crystal structure.
Example 4
The composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the non-aqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte, and the composition of the non-aqueous electrolyte added in post-treatment were set as shown in Tables 1, 3, and 5 below, and secondary batteries were fabricated in the same manner as in Example 1, except that the aging conditions were changed.
The aging conditions for Example 4 were as follows: the first sealed battery was charged at a constant voltage (CV) of 3.3 V until the current value reached 1/20 C. The first sealed battery was placed in a thermostatic chamber at 80° C. and held there for 24 hours to perform aging.
Example 5
A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the non-aqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte, and the composition of the non-aqueous electrolyte added in post-treatment were set as shown in Tables 1, 3, and 5 below, and aging was not performed.
(Example 21)
A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the non-aqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte, and the composition of the non-aqueous electrolyte added in post-treatment were set as shown in Tables 2, 4, and 6 below, and the charge-discharge conditions from initial charging to post-treatment were set as shown below.
The positive electrode active material Li(Ni _0.5 Mn _1.5 )O ₄ used in Example 21 is a 5V positive electrode active material having a spinel-type crystal structure.

The secondary battery of Example 21 uses Li(Ni _0.5 Mn _1.5 )O ₄ as the positive electrode active material, and therefore the charge/discharge conditions from the initial charge to the post-treatment were as follows.

<First charge>
The first sealed battery was subjected to initial charging in an environment of 25° C. in the following manner. First, the first sealed battery was charged at a constant current (CC) of 0.2 C until a voltage of 3.7 V was reached. Next, the first sealed battery was charged at a constant voltage (CV) of 3.7 V. The constant voltage charging was terminated when the total time of the constant current charging and constant voltage charging reached 10 hours.
<First discharge>
Next, the first sealed battery was discharged at a constant current (CC) of 0.2 C in an environment of 25° C. until the voltage reached 2.5 V.
<Post-processing>
Next, the first sealed battery was charged at a constant current (CC) of 0.2 C in an environment of 25°C until a voltage of 3.7 V was reached. The first sealed battery was then charged at a constant voltage (CV) of 3.7 V until the current value reached 1/20 C. That is, the first sealed battery was subjected to constant current constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). This first sealed battery was placed in a thermostatic chamber at 80°C and held for 24 hours for aging. The subsequent steps were the same as in Example 1, and a secondary battery according to Example 21 was fabricated.
Example 25
A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the non-aqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte, and the composition of the non-aqueous electrolyte added in post-treatment were set as shown in Tables 2, 4, and 6 below, and the charge-discharge conditions from initial charging to post-treatment were set as shown below.

The graphite-containing negative electrode of Example 25 was prepared by the following method. Graphite powder and polyvinylidene fluoride (PVdF) were mixed in a weight ratio of 90:10, and the resulting mixture was kneaded in the presence of an organic solvent (N-methylpyrrolidone) to prepare a slurry. The resulting slurry was applied to a copper foil with a thickness of 15 μm, dried, and pressed to obtain a negative electrode. When using a graphite-containing negative electrode, a secondary battery was prepared by carrying out the steps from initial charging to post-treatment as follows.
<First charge>
The first sealed battery was subjected to initial charging in an environment of 25° C. in the following manner. First, the first sealed battery was charged at a constant current (CC) of 0.2 C until a voltage of 4.15 V was reached. Next, the first sealed battery was charged at a constant voltage (CV) of 4.15 V. The constant voltage charging was terminated when the total time of the constant current charging and constant voltage charging reached 10 hours.
<First discharge>
Next, the first sealed battery was discharged at a constant current (CC) of 0.2 C in an environment of 25° C. until the voltage reached 2 V.
<Post-processing>
Next, the first sealed battery was charged at a constant current (CC) of 0.2 C in an environment of 25°C until a voltage of 4.15 V was reached. The first sealed battery was then charged at a constant voltage (CV) of 4.15 V until the current value reached 1/20 C. That is, the first sealed battery was subjected to constant current/constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). The first sealed battery was placed in a thermostatic chamber at 80°C and aged for 24 hours. The first sealed battery was then placed in an argon box, and one location on the sealed portion of the exterior member was cut using the method described with reference to FIG. 5 to release the gas inside the exterior member. Liquid nonaqueous electrolyte was added to the battery to achieve the same concentration as before the initial charge/discharge, and the end opened by the cut was heat-sealed. In this way, a secondary battery according to Example 25 was fabricated.
(Comparative Example 1)
The composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the non-aqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, and the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte were set as shown in Tables 2 and 4 below, and secondary batteries were fabricated in the same manner as in Example 1, except that no liquid non-aqueous electrolyte was added after the degassing post-treatment and the ends opened by cutting were sealed with heat sealing.
(Comparative Example 2-3)
A secondary battery was fabricated in the same manner as in Example 1, except that the composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the non-aqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte, and the composition of the non-aqueous electrolyte added in post-treatment were set as shown in Tables 2, 4, and 6 below.
<Storage test>
A storage test was carried out on each secondary battery as follows.

All batteries except those in Examples 21 and 25 were charged at a constant current (CC) of 0.2 C until a voltage of 3 V was reached. The batteries were then charged at a constant voltage (CV) of 3 V until the current reached 1/20 C. In other words, the batteries were subjected to constant-current, constant-voltage (CCCV) charging until their SOC reached 100%. The charged batteries were then placed in a 55°C thermostatic chamber. Every 10 days, the batteries were removed from the 55°C thermostatic chamber, cooled to 25°C, and then subjected to CCCV charging at 3 V again before being placed in the 55°C thermostatic chamber. This process was repeated until the batteries were cooled to 25°C and stored in the thermostatic chamber for 90 days. The volume was then measured, and the difference from the volume before and after the test was taken as the gas generation volume [ml]. The result for Example 1 was 14 mL after 90 days. The gas generation volume is an indicator of life characteristics in a high-temperature environment.

The battery of Example 21 was charged at a constant current (CC) of 0.2 C until a voltage of 3.7 V was reached. The battery was then charged at a constant voltage (CV) of 3.7 V until the current value reached 1/20 C. In other words, the battery was subjected to constant current/constant voltage (CCCV) charging until its SOC reached 100%. The battery in this charged state was placed in a thermostatic chamber at 55°C. Every 10 days, the battery was removed from the 55°C thermostatic chamber, cooled to 25°C, and then subjected to CCCV charging at 3.7 V again before being placed in the 55°C thermostatic chamber. This process was repeated until the battery had been stored in the thermostatic chamber for 90 days. After cooling to 25°C, the volume was measured, and the difference from the volume before the test was taken as the amount of gas generated [ml].

The battery of Example 25 was charged at a constant current (CC) of 0.2 C until a voltage of 4.15 V was reached. The battery was then charged at a constant voltage (CV) of 4.15 V until the current value reached 1/20 C. That is, the battery was subjected to constant current/constant voltage (CCCV) charging to bring its SOC to 100%. The battery in this charged state was placed in a thermostatic chamber at 55°C. Every 10 days, the battery was removed from the thermostatic chamber at 55°C, cooled to 25°C, and then subjected to CCCV charging at 4.15 V again and placed in the thermostatic chamber at 55°C. This process was repeated, and the battery was stored in the thermostatic chamber for 90 days. After cooling to 25°C, the volume was measured, and the difference from the volume before the test was defined as the amount of gas generated [ml].
<Direct Current (DC) resistance measurement>
For each secondary battery except for Examples 21 and 25, DC resistance measurements were performed as follows before the storage test. The battery was discharged at a constant current (CC) of 0.2 C until the voltage reached 1.5 V. The battery was then charged at a constant current (CC) of 0.2 C until the voltage reached 2.25 V. The battery was then charged at a constant voltage (CV) of 2.25 V until the current value reached 1/20 C, thereby bringing the battery to a state of charge of 50% SOC. The battery adjusted to 50% SOC was discharged at a constant current (CC) of 10 C for 10 ms, and the DC resistance [mΩ] was calculated from the difference between the voltage and current values at this time. In the case of Example 1, the resistance increase rate was 1.5 after 90 days.

Prior to conducting a storage test, DC resistance measurements were performed on the secondary battery of Example 21 as follows. The battery was discharged at a constant current (CC) of 0.2 C until the voltage reached 2.5 V. The battery was then charged at a constant current (CC) of 0.2 C until the voltage reached 3.1 V. The battery was then charged at a constant voltage (CV) of 3.1 V until the current value reached 1/20 C, bringing the battery's state of charge to 50% SOC. The battery adjusted to 50% SOC was discharged at a constant current (CC) of 10 C for 10 ms, and the DC resistance [mΩ] was calculated from the difference between the voltage and current values at this time.

Prior to conducting a storage test, DC resistance measurements were performed on the secondary battery of Example 25 as follows. The battery was discharged at a constant current (CC) of 0.2 C until the voltage reached 2.0 V. The battery was then charged at a constant current (CC) of 0.2 C until the voltage reached 3.8 V. The battery was then charged at a constant voltage (CV) of 3.8 V until the current value reached 1/20 C, bringing the battery's state of charge to 50% SOC. The battery adjusted to 50% SOC was discharged at a constant current (CC) of 10 C for 10 ms, and the DC resistance [mΩ] was calculated from the difference between the voltage and current values at this time.

Tables 1 to 6 show the composition of the positive electrode active material, the composition of the negative electrode active material, the composition of the nonaqueous electrolyte, E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, the concentration E (mol/L) of the sulfur-containing compound in the nonaqueous electrolyte, the amount of gas generated after 90 days [mL], the rate of resistance increase, and the composition of the nonaqueous electrolyte added in post-treatment for each secondary battery. The values of E/A, E/D, A, D, and E were determined by the method described above. Tables 3 and 4 show the results of calculating the concentration E (mol/L) of the sulfur-containing compound in the nonaqueous electrolyte using 6.25*10 ⁻³ L of nonaqueous electrolyte instead of 6.25 mL, as well as the E/A and E/D obtained based on these calculation results.

As is clear from Tables 1 to 6, Examples 1-27 showed a lower amount of gas generated and a lower rate of increase in resistance after 90 days of storage compared to Comparative Examples 1-3. Comparative Examples 1 to 3 are examples in which the nonaqueous electrolyte did not contain either a sulfur-containing imide compound or a sultone compound.

Comparing Examples 1 to 14, which have the same composition of positive and negative electrode active materials, it can be seen that Examples 1-8, 13, and 14, which contain a sultone compound in the non-aqueous electrolyte, tend to be more effective at suppressing gas generation and resistance increase than Examples 9-12, which contain a sulfur-containing imide compound in the non-aqueous electrolyte.

Furthermore, as shown in Examples 15-27, the effect of suppressing gas generation and resistance increase can be achieved even when the positive electrode active material or negative electrode active material is different from that used in Example 1. For example, the positive electrode active material is changed to a lithium manganese composite oxide having a spinel structure, a lithium phosphate oxide having an olivine structure, a lithium cobalt composite oxide, etc., or the negative electrode active material is changed to lithium titanate having a spinel structure, a carbon material, an orthorhombic titanium composite oxide, a monoclinic titanium dioxide, etc.

According to at least one of these embodiments or examples of the secondary battery, the following formula (1) (1×10 ⁻⁶ ≦E/A≦9×10 ⁻⁴ ) is satisfied: Since these satisfy the above requirements, it is possible to suppress the amount of gas generated and the increase in resistance at high temperatures, and it is possible to achieve excellent life performance even at high temperatures.
(Example 28)
<Preparation of electrode group>
An electrode group was prepared in the same manner as described in Example 1.
<Storage of electrode group>
The procedure was the same as that described in Example 1.
<Preparation of Liquid Non-Aqueous Electrolyte>
_LiPF6 was dissolved as an electrolyte at a concentration of 1 mol/L in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2). 1,3-propane sultone (PS) and ethyl propanesulfonate were prepared as sulfur-containing compounds. These were dissolved in the nonaqueous electrolyte to a concentration of 1.5 wt %. Thus, a liquid nonaqueous electrolyte (nonaqueous electrolyte solution) was obtained. The nonaqueous electrolyte was prepared in an argon box.
<Battery construction>
The procedure was the same as that described in Example 1.
<First charge>
The procedure was the same as that described in Example 1.
<First discharge>
The procedure was the same as that described in Example 1.
<Post-processing>
Next, the first sealed battery was charged at a constant current (CC) of 0.2 C in an environment of 25°C until a voltage of 3 V was reached. The first sealed battery was then charged at a constant voltage (CV) of 3 V until the current value reached 1/20 C. That is, the first sealed battery was subjected to constant current/constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). This first sealed battery was placed in a thermostatic chamber at 80°C and aged for 24 hours. Thereafter, the first sealed battery was placed in an argon box, and one location of the sealed portion of the exterior member was cut using the method described with reference to FIG. 5 to release the gas inside the exterior member. Next, the end opened by the cut was sealed with a heat seal to perform a second sealing. In this manner, a secondary battery according to Example 28 was fabricated.
(Example 29)
A secondary battery was fabricated in the same manner as in Example 28, except for using a liquid nonaqueous electrolyte described below. _LiPF6 was dissolved as the electrolyte at a concentration of 1 mol/L in a mixed solvent of propylene carbonate (PC) and methyl ethyl carbonate (MEC) (volume ratio 1:2). 1,3-propane sultone (PS) and methyl propanesulfonate were prepared as sulfur-containing compounds. These were each dissolved in the nonaqueous electrolyte to a concentration of 1.5 wt %. Thus, a liquid nonaqueous electrolyte (nonaqueous electrolyte solution) was obtained.
(Example 30)
A secondary battery was fabricated in the same manner as in Example 28, except for using a liquid nonaqueous electrolyte described below. _LiPF6 was dissolved as the electrolyte at a concentration of 1 mol/L in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2). 1,3-propane sultone (PS) and propyl propanesulfonate were prepared as sulfur-containing compounds. These were each dissolved in the nonaqueous electrolyte to a concentration of 1.5 wt %. Thus, a liquid nonaqueous electrolyte (nonaqueous electrolyte solution) was obtained.
(Examples 31 to 33)
Secondary batteries were manufactured in the same manner as in Example 1, with the following exceptions: The composition of the liquid nonaqueous electrolyte injected the first time was changed as shown in Table 9; the aging conditions in the post-treatment were changed to a temperature of 120°C for 24 hours; and the composition of the liquid nonaqueous electrolyte added in the post-treatment was changed as shown in Table 11.
(Example 34)
A secondary battery was produced in the same manner as in Example 28, except that the same type of positive electrode active material as used in Example 15 was used as the positive electrode active material.
(Example 35)
A secondary battery was produced in the same manner as in Example 28, with the following exceptions: The same type of positive electrode active material as used in Example 16 was used as the positive electrode active material, and the composition of the liquid nonaqueous electrolyte was changed as shown in Table 10.
(Example 36)
A secondary battery was produced in the same manner as in Example 28, except that the same type of positive electrode active material as used in Example 18 was used as the positive electrode active material.
(Example 37)
A secondary battery was produced in the same manner as in Example 28, except that the same type of positive electrode active material as used in Example 19 was used as the positive electrode active material.
(Example 38)
A secondary battery was produced in the same manner as in Example 28, except that the same type of positive electrode active material as used in Example 20 was used as the positive electrode active material.
(Example 39)
<Preparation of electrode group>
An electrode group was prepared in the same manner as described in Example 21.
<Storage of electrode group>
The procedure was the same as that described in Example 21.
<Preparation of Liquid Non-Aqueous Electrolyte>
_LiPF6 was dissolved as an electrolyte at a concentration of 1 mol/L in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2). 1,3-propane sultone (PS) and ethyl propanesulfonate were prepared as sulfur-containing compounds. These were dissolved in the nonaqueous electrolyte to a concentration of 1.5 wt %. Thus, a liquid nonaqueous electrolyte (nonaqueous electrolyte solution) was obtained. The nonaqueous electrolyte was prepared in an argon box.
<Battery construction>
The procedure was the same as that described in Example 21.

<First charge>
The procedure was the same as that described in Example 21.
<First discharge>
The procedure was the same as that described in Example 21.
<Post-processing>
Next, the first sealed battery was charged at a constant current (CC) of 0.2 C in an environment of 25°C until a voltage of 3.7 V was reached. The first sealed battery was then charged at a constant voltage (CV) of 3.7 V until the current value reached 1/20 C. That is, the first sealed battery was subjected to constant current/constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). This first sealed battery was placed in a thermostatic chamber at 80°C and aged for 24 hours. The first sealed battery was then placed in an argon box, and one location on the sealed portion of the exterior member was cut using the method described with reference to Figure 5 to release the gas inside the exterior member. Next, the end opened by the cut was secondarily sealed with heat sealing. In this manner, a secondary battery according to Example 39 was fabricated.
(Example 40)
A secondary battery was produced in the same manner as in Example 28, except that the same type of positive electrode active material as used in Example 22 was used as the positive electrode active material.
(Example 41)
A secondary battery was produced in the same manner as in Example 28, except that the same type of positive electrode active material as used in Example 23 was used as the positive electrode active material.
(Example 42)
A secondary battery was produced in the same manner as in Example 28, except that the same type of negative electrode active material as used in Example 24 was used as the negative electrode active material.
(Example 43)
<Preparation of electrode group>
An electrode group was prepared in the same manner as described in Example 25.
<Storage of electrode group>
The procedure was the same as that described in Example 25.
<Preparation of Liquid Non-Aqueous Electrolyte>
_LiPF6 was dissolved as an electrolyte at a concentration of 1 mol/L in a mixed solvent of propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio 1:2). 1,3-propane sultone (PS) and ethyl propanesulfonate were prepared as sulfur-containing compounds. These were dissolved in the nonaqueous electrolyte to a concentration of 1.5 wt %. Thus, a liquid nonaqueous electrolyte (nonaqueous electrolyte solution) was obtained. The nonaqueous electrolyte was prepared in an argon box.
<Battery construction>
The procedure was the same as that described in Example 25.

<First charge>
The procedure was the same as that described in Example 25.
<First discharge>
The procedure was the same as that described in Example 25.
<Post-processing>
Next, the first sealed battery was charged at a constant current (CC) of 0.2 C in an environment of 25°C until a voltage of 4.15 V was reached. The first sealed battery was then charged at a constant voltage (CV) of 4.15 V until the current value reached 1/20 C. That is, the first sealed battery was subjected to constant current/constant voltage (CCCV) charging. As a result, the SOC of the first sealed battery was (100%). This first sealed battery was placed in a thermostatic chamber at 80°C and aged for 24 hours. The first sealed battery was then placed in an argon box, and one location on the sealed portion of the exterior member was cut using the method described with reference to Figure 5 to release the gas inside the exterior member. Next, the end opened by the cut was secondarily sealed with heat sealing. In this manner, the secondary battery of Example 43 was fabricated.
(Example 44)
A secondary battery was produced in the same manner as in Example 28, except that the same type of negative electrode active material as used in Example 26 was used as the negative electrode active material.
(Example 45)
A secondary battery was produced in the same manner as in Example 28, except that the same type of negative electrode active material as used in Example 27 was used as the negative electrode active material.

Table 11 shows the E/A, E/D, the mass A (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, the mass D (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, and the concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte for Examples 28 to 45. The concentration E (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte was calculated using 6.25*10 ⁻³ L as the amount of non-aqueous electrolyte.
<Storage test and DC (Direct Current) resistance measurement>
For the secondary battery of Example 39, these measurements were performed under the same conditions as those described in Example 21. For the secondary battery of Example 43, these measurements were performed under the same conditions as those described in Example 25.

For Examples 28 to 38, 40 to 42, 44, and 45, excluding Examples 39 and 43, these measurements were carried out under the same conditions as those carried out for the subjects other than Examples 21 and 25. These results are shown in Table 12.
<Measurement of gas generation amount after 150 days>
For Examples 1 to 45, a storage test was carried out under the same conditions as described above, except that the storage period in the thermostatic chamber was extended from 90 days to 150 days. The results are shown in Tables 7, 8, and 12.
<Measurement of area value B>
The nonaqueous electrolytes of the secondary batteries of Examples 28 to 45 were subjected to GCMS measurement under the conditions described above, and the peak area value B was determined when the peak area value A was set to 10. The peak area value B is shown in Table 12. The total ion chromatogram (TIC) of the nonaqueous electrolyte of Example 28 is shown in FIG. 10. FIG. 11 shows an enlarged view of the vicinity of peak _P1 in the TIC of FIG. 10. Furthermore, FIG. 12 shows an enlarged view of the vicinity of 7 to 9 Time/min in the TIC of FIG. 10.

In the TIC shown in Figure 10, the vertical axis is Intensity/au (arbitrary unit of peak intensity) and the horizontal axis is Time/min (retention time). Peak _P1 is derived from propane sultone. Peak _P2 , which appears around 7 to 9 Time/min in Figure 12, is derived from ethyl propanesulfonate. Peak _P3 , which appears between 5 and 7 Time/min in Figure 10, is derived from propylene carbonate. Peak _P4 , which appears in the range less than 5 Time/min in Figure 10, is derived from diethyl carbonate. The results of GCMS measurements of the nonaqueous electrolytes of Examples 31-33 confirmed the following: Example 31 contained ethyl propanesulfonate; Example 32 contained methyl propanesulfonate; and Example 33 contained propyl propanesulfonate. As for Examples other than Examples 31 to 33, it was confirmed by GCMS measurement that the types of propanesulfonate esters listed in Tables 9 and 10 were contained.

The results in Tables 7 to 12 reveal the following: The secondary batteries of Examples 28-45 generated less gas after 90 days of storage and after 150 days of storage, and had a low rate of increase in resistance. Comparing the amount of gas generated after 150 days of storage in Examples 28-45 and in Examples 1-27, the amount of gas generated after 150 days of storage in Examples 28-45 was lower. This is because Examples 28-45 contain a propanesulfonic acid ester in the non-aqueous electrolyte.

Furthermore, as shown in Examples 34-45, the effect of suppressing gas generation and resistance increase can be achieved even when the positive electrode active material or negative electrode active material is different from that of Example 28. For example, the positive electrode active material is changed to a lithium manganese composite oxide having a spinel structure, a lithium phosphate oxide having an olivine structure, a lithium cobalt composite oxide, etc., or the negative electrode active material is changed to lithium titanate having a spinel structure, a carbon material, an orthorhombic titanium composite oxide, a monoclinic titanium dioxide, etc.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

The original embodiment of the invention as filed is appended below.
[1]
a positive electrode, a negative electrode, and a non-aqueous electrolyte;
the positive electrode includes a positive electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the positive electrode active material-containing layer,
the non-aqueous electrolyte contains a sulfur-containing compound consisting of at least one of a sulfur-containing imide compound and a sultone compound;
A secondary battery that satisfies the following formula (1):

1×10 ⁻⁹ ≦E/A≦9×10 ⁻⁷ (1)
In formula (1), A is the mass (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode, and E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte.
[2]
The secondary battery according to [1], wherein A is in the range of more than 0 (g/m ³ ) and not more than 3500 (g/m ³ ).
[3]
The secondary battery according to [1] or [2], wherein E is in the range of more than 0 (mol/L) and not more than 4.5×10 ⁻⁴ (mol/L).
[4]
the negative electrode includes a negative electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the negative electrode active material-containing layer,
The secondary battery according to any one of [1] to [3], which satisfies the following formula (2):

2× ¹⁰ ≦E/D≦3× ¹⁰ (2)
In formula (2), D is the mass (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode, and E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte.
[5]
The secondary battery according to [4], wherein D is in the range of more than 0 (g/m ³ ) and not more than 6600 (g/m ³ ).
[6]
the negative electrode active material-containing layer contains at least one selected from the group consisting of niobium titanium composite oxides represented by the general formula Li _x Ti 1 _{- y} M1 _y Nb _2-z M2 _z O _7+δ and niobium titanium composite oxides represented by the general formula Li _x Ti 1-y M3 _y+z Nb _2-z O _7-δ ;
The secondary battery according to any one of [4] to [5], wherein M1 is at least one selected from the group consisting of Zr, Si, and Sn, M2 is at least one selected from the group consisting of V, Ta, and Bi, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, x satisfies 0≦x≦5, y satisfies 0≦y<1, z satisfies 0≦z<2, and δ satisfies −0.3≦δ≦0.3.
[7]
A battery pack including one or more secondary batteries according to any one of [1] to [6].
[8]
An external terminal for applying current;
The battery pack according to [7], further comprising a protection circuit.
[9]
The battery pack according to [7] or [8], which includes two or more of the secondary batteries, and the two or more secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. [10]
A vehicle equipped with the battery pack according to any one of [7] to [9].
[11]
The vehicle according to [10], further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.
<1>
a positive electrode, a negative electrode, and a non-aqueous electrolyte;
the positive electrode includes a positive electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the positive electrode active material-containing layer,
the non-aqueous electrolyte contains a sulfur-containing compound consisting of at least one of a sulfur-containing imide compound and a sultone compound, or at least one of a sulfur-containing imide compound, a sultone compound, and a propanesulfonic acid ester;
A secondary battery that satisfies the following formula (1):
1×10 ⁻⁶ ≦E/A≦9×10 ⁻⁴ (1)
In formula (1), A is the mass (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode , and E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte.
<2>
The secondary battery according to <1>, wherein A is in the range of more than 0 (g/m ³ ) and not more than 3500 (g/m ³ ).
<3>
The secondary battery according to <1> or <2>, wherein E is in the range of more than 0 (mol/L) and not more than 4.5×10 ⁻¹ (mol/L).
＜4＞
the negative electrode includes a negative electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the negative electrode active material-containing layer,
The secondary battery according to <1> or <2>, which satisfies the following formula (2):
2×10 ⁻⁶ ≦E/D≦3×10 ⁻⁴ (2)
In formula (2), D is the mass (g/m ³ ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode , and E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte.
<5>
The secondary battery according to <4>, wherein D is in the range of more than 0 (g/m ³ ) and not more than 6600 (g/m ³ ).
<6>
the negative electrode active material-containing layer contains at least one selected from the group consisting of niobium titanium composite oxides represented by the general formula Li x Ti ₁ - _{y M1} y _Nb 2 _-z M2 _z O _7+δ and niobium titanium composite oxides represented by the general formula Li _x Ti 1-y M3 _y+z Nb _2-z O _7-δ ;
The secondary battery according to <4>, wherein M1 is at least one selected from the group consisting of Zr, Si, and Sn, M2 is at least one selected from the group consisting of V, Ta, and Bi, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, x satisfies 0≦x≦5, y satisfies 0≦y<1, z satisfies 0≦z<2, and δ satisfies −0.3≦δ≦0.3.
＜７＞
The secondary battery according to <1> or <2>, wherein the sulfur-containing compound of the non-aqueous electrolyte contains the propanesulfonic acid ester and the sultone compound.
＜8＞
The secondary battery according to <1> or <2>, wherein the propanesulfonate ester is at least one selected from the group consisting of methyl propanesulfonate, ethyl propanesulfonate, and propyl propanesulfonate.
＜９＞
<7> The secondary battery according to <7>, wherein, in a total ion chromatogram obtained by gas chromatography-gravimetric analysis of the nonaqueous electrolyte, when a peak area value A of the sultone compound is set to 10, a peak area value B of the propanesulfonate ester is 0.01 or more and 40 or less.
<10>
A battery pack including one or more secondary batteries according to <1> or <2>.
<11>
An external terminal for applying current;
The battery pack according to <10>, further comprising a protection circuit.
<12>
The battery pack according to <10>, comprising two or more of the secondary batteries, the two or more secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel.
<13>
A vehicle equipped with the battery pack described in <10>.
<14>
The vehicle according to <13>, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

DESCRIPTION OF SYMBOLS 1...electrode group, 2...container (exterior member), 3...positive electrode, 3a...positive electrode current collector, 3b...positive electrode active material-containing layer, 4...negative electrode, 4a...negative electrode current collector, 4b...negative electrode active material-containing layer, 5...separator, 6...positive electrode lead, 7...negative electrode lead, 8...positive electrode current collector tab, 9...negative electrode current collector tab, 10...sealing plate, 11...insulating member, 12...exterior member, 13...negative electrode terminal, 14...positive electrode terminal, 30...secondary battery with first sealing, 31...secondary battery, 50...battery pack, 51...unit cell, 53...battery assembly, 54...plate Lint wiring board, 55... thermistor, 56... protection circuit, 57... external terminal for current supply, 71... automobile, 72... battery pack, 300... vehicle, 301... vehicle power supply, 310... communication bus, 311... battery management device, 312a-c... battery packs, 313a-c... assembled battery monitoring device, 314a-c... assembled battery, 316... positive terminal, 317 negative terminal, 340... inverter, 345... drive motor, 370... external terminal, 380... vehicle ECU, L1, L2... connection line, W... drive wheel.

Claims (11)

a positive electrode, a negative electrode, and a non-aqueous electrolyte;
the positive electrode includes a positive electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the positive electrode active material-containing layer,
the non-aqueous electrolyte contains a sulfur-containing compound consisting of at least one of a sulfur- containing imide compound and a sultone compound;
the negative electrode includes a negative electrode active material-containing layer and a sulfur-containing layer formed on at least a portion of the negative electrode active material-containing layer,
the negative electrode active material-containing layer contains at least one selected from the group consisting of niobium titanium composite oxides represented by the general formula Li x Ti ₁ - _{y M1} y _Nb 2 _-z M2 _z O _7+δ and niobium titanium composite oxides represented by the general formula Li _x Ti 1-y M3 _y+z Nb _2-z O _7-δ ;
M1 is at least one selected from the group consisting of Zr, Si, and Sn, M2 is at least one selected from the group consisting of V, Ta, and Bi, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo, x satisfies 0≦x≦5, y satisfies 0≦y<1, z satisfies 0≦z<2, and δ satisfies −0.3≦δ≦0.3,
A secondary battery that satisfies the following formulas (1) and (2) :
1×10 ⁻⁶ ≦E/A≦9×10 ⁻⁴ (1)
In formula (1), A is the mass (g/ ^m3 ) of sulfur atoms per unit volume of the sulfur-containing layer of the positive electrode as determined by inductively coupled plasma atomic emission spectrometry, and is in the range of greater than 0 (g / ^m3 ) and not more than 3500 (g/m3 ⁾ , E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte as determined by inductively coupled plasma atomic emission spectrometry ,
2×10 ⁻⁶ ≦E/D≦3×10 ⁻⁴ (2)
In formula (2), D is the mass (g/ ^m3 ) of sulfur atoms per unit volume of the sulfur-containing layer of the negative electrode as determined by inductively coupled plasma atomic emission spectroscopy , and E is the concentration (mol/L) of the sulfur-containing compound in the non-aqueous electrolyte as determined by inductively coupled plasma atomic emission spectroscopy . 2. The secondary battery according to claim 1 , wherein E is in the range of greater than 0 (mol/L) and not more than 4.5×10 ⁻¹ (mol/L). 2. The secondary battery according to claim 1 , wherein D is in the range of more than 0 (g/m ^<3> ) and not more than 6600 (g/m ^<3> ). 3. The secondary battery according to claim 1, wherein the sulfur-containing compound of the non-aqueous electrolyte contains a propanesulfonate ester and a sultone compound different from the propanesulfonate ester . 5. The secondary battery according to claim 4 , wherein the propanesulfonate ester is at least one selected from the group consisting of methyl propanesulfonate, ethyl propanesulfonate, and propyl propanesulfonate. 5. The secondary battery according to claim 4, wherein, in a total ion chromatogram obtained by gas chromatography-gravimetric analysis of the non-aqueous electrolyte, when a peak area value A of the sultone compound is set to 10, a peak area value B of the propanesulfonate ester is 0.01 or more and 40 or less. A battery pack containing one or more secondary batteries according to claim 1 or 2. An external terminal for applying current;
The battery pack according to claim 7 , further comprising a protection circuit. The battery pack according to claim 7 , comprising two or more secondary batteries, the two or more secondary batteries being electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with the battery pack according to claim 7 . The vehicle of claim 10 , further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.