JP7126028B2 - lithium ion secondary battery - Google Patents

Description

The present invention relates to lithium ion secondary batteries.

Lithium ion secondary batteries are widely used in various devices that require charging. Many existing lithium-ion secondary batteries employ a powder-dispersed positive electrode (so-called coated electrode), which is prepared by coating and drying a positive electrode mixture containing a positive electrode active material, a conductive aid, a binder, and the like. ing.

In general, a powder-dispersed positive electrode contains a relatively large amount (for example, about 10% by weight) of components (binders and conductive aids) that do not contribute to capacity. Low packing density. Therefore, the powder-dispersed positive electrode has much room for improvement in terms of capacity and charge/discharge efficiency. Accordingly, attempts have been made to improve the capacity and charge/discharge efficiency by forming the positive electrode or positive electrode active material layer from a sintered plate of lithium composite oxide. In this case, since the positive electrode or the positive electrode active material layer does not contain a binder or a conductive aid (for example, conductive carbon), the packing density of the lithium composite oxide increases, resulting in high capacity and good charge-discharge efficiency. expected to be obtained. For example, Patent Document 1 (Japanese Patent No. 5587052) describes a lithium ion secondary battery comprising a positive electrode current collector and a positive electrode active material layer bonded to the positive electrode current collector via a conductive bonding layer. is disclosed. This positive electrode active material layer is said to be made of a lithium composite oxide sintered plate having a thickness of 30 μm or more, a porosity of 3 to 30%, and an open pore ratio of 70% or more. Further, Patent Document 2 (Japanese Patent No. 6374634) discloses a lithium composite oxide sintered plate such as lithium cobalt oxide LiCoO ₂ (hereinafter referred to as LCO), which is used for the positive electrode of a lithium ion secondary battery. ing. This lithium composite oxide sintered plate has a structure in which a plurality of primary particles having a layered rock salt structure are bonded, has a porosity of 3 to 40%, and has an average pore diameter of 15 μm or less. , the open pore ratio is 70% or more, the thickness is 15 to 200 μm, and the primary particle diameter, which is the average particle diameter of a plurality of primary particles, is 20 μm or less. In addition, in this lithium composite oxide sintered plate, the average value of the angles formed by the (003) planes of the plurality of primary particles and the plate surface of the lithium composite oxide sintered plate, that is, the average inclination angle is 0 °. and 30° or less.

On the other hand, it has also been proposed to use a titanium-containing sintered plate as the negative electrode. For example, Patent Document 3 (Japanese Patent Application Laid-Open No. 2015-185337) discloses a lithium ion secondary battery using a lithium titanate (Li ₄ Ti ₅ O ₁₂ ) sintered body as a positive electrode or a negative electrode. Patent Document 4 (Japanese Patent No. 6392493) discloses a sintered body plate of lithium titanate Li ₄ Ti ₅ O ₁₂ (hereinafter referred to as LTO) used for the negative electrode of a lithium ion secondary battery. This LTO sintered plate has a structure in which a plurality of primary particles are bonded, has a thickness of 10 to 290 μm, and has a primary particle diameter of 1.2 μm, which is the average particle diameter of the plurality of primary particles. below, the porosity is 21 to 45%, and the open pore ratio is 60% or more.

Japanese Patent No. 5587052 Japanese Patent No. 6374634 JP 2015-185337 A Japanese Patent No. 6392493

In recent years, there has been a demand for lithium-ion secondary batteries that are compact and thin, yet have high capacity and high output. Therefore, in anticipation of high capacity and good charge-discharge efficiency, a lithium composite oxide sintered plate (for example, LCO sintered plate) containing no conductive carbon is used for the positive electrode and does not contain conductive carbon. It has been proposed to use a titanium-containing sintered plate (for example, an LTO sintered plate) for the negative electrode (for example, Patent Document 4). However, when a lithium ion secondary battery was actually produced using these sintered plates, that is, a ceramic positive electrode plate and a ceramic negative electrode plate, it was found that the expected capacity could not be obtained.

The present inventors have recently developed a lithium ion secondary battery comprising a positive electrode plate that is a lithium composite oxide sintered plate and a negative electrode plate that is a titanium-containing sintered plate. is bonded through the positive electrode side conductive bonding layer Sp, and the area Sn where the negative electrode current collector and the negative electrode plate are bonded through the negative electrode side conductive bonding layer is 1.0 ≤ Sn / Sp ≤ It was found that both capacity and cycle characteristics can be improved by satisfying the relationship of 5.0.

Accordingly, an object of the present invention is to improve both capacity and cycle characteristics while having a configuration including a positive electrode plate that is a lithium composite oxide sintered plate and a negative electrode plate that is a titanium-containing sintered plate. Another object of the present invention is to provide a lithium ion secondary battery.

According to one aspect of the invention,
a positive electrode plate that is a lithium composite oxide sintered plate containing no conductive carbon;
a negative electrode plate that is a titanium-containing sintered plate containing no conductive carbon;
a separator interposed between the positive electrode plate and the negative electrode plate;
a positive electrode current collector provided on a surface of the positive electrode plate away from the separator;
a negative electrode current collector provided on a surface of the negative electrode plate remote from the separator;
an electrolytic solution impregnated in the positive electrode plate, the negative electrode plate, and the separator;
A lithium ion secondary battery comprising
At least part of the surface of the positive electrode plate facing the positive electrode current collector is bonded to the positive electrode current collector via a positive electrode side conductive bonding layer,
at least part of the surface of the negative electrode plate facing the negative electrode current collector is bonded to the negative electrode current collector via a negative electrode-side conductive bonding layer;
An area Sp where the positive electrode current collector and the positive electrode plate are bonded via the positive electrode side conductive bonding layer, and the negative electrode current collector and the negative electrode plate are bonded via the negative electrode side conductive bonding layer. Provided is a lithium ion secondary battery in which the area Sn satisfies the relationship of 1.0≦Sn/Sp≦5.0.

1 is a schematic cross-sectional view of an example of a lithium ion secondary battery of the present invention; FIG. It is a SEM image which shows an example of the cross section perpendicular|vertical to the board surface of an oriented positive electrode plate. 3 is an EBSD image of a cross section of the oriented positive plate shown in FIG. 2; 4 is a histogram showing the distribution of orientation angles of primary particles in the EBSD image of FIG. 3 on an area basis;

FIG. 1 schematically shows an example of the lithium ion secondary battery of the present invention. A lithium-ion secondary battery 10 shown in FIG. The positive electrode plate 12 is a sintered lithium composite oxide plate containing no conductive carbon. The negative electrode plate 14 is a titanium-containing sintered plate containing no conductive carbon. A separator 16 is interposed between the positive plate 12 and the negative plate 14 . The positive electrode current collector 18 is provided on the surface of the positive electrode plate 12 away from the separator 16 . The negative electrode current collector 20 is provided on the surface of the negative electrode plate 14 away from the separator 16 . The electrolyte solution 22 impregnates the positive electrode plate 12 , the negative electrode plate 14 and the separator 16 . At least part of the surface of the positive electrode plate 12 facing the positive electrode current collector 18 is bonded to the positive electrode current collector 18 via the positive electrode side conductive bonding layer 24 . At least part of the surface of the negative electrode plate 14 facing the negative electrode current collector 20 is bonded to the negative electrode current collector 20 via the negative electrode side conductive bonding layer 26 .

Then, an area Sp where the positive electrode current collector 18 and the positive electrode plate 12 are bonded via the positive electrode side conductive bonding layer 24, and the negative electrode current collector 20 and the negative electrode plate 14 are bonded via the negative electrode side conductive bonding layer 26 and the area Sn satisfies the relationship of 1.0≦Sn/Sp≦5.0. The area Sp where the positive electrode current collector 18 and the positive electrode plate 12 are bonded via the positive electrode side conductive bonding layer 24 is the positive electrode contributing to the bonding between the positive electrode current collector 18 and the positive electrode plate 12 . It means the area occupied by the side conductive bonding layer 24, and does not include the area of the region where the positive electrode current collector 18 and the positive electrode plate 12 contact or face each other without the positive electrode side conductive bonding layer 24 intervening. . Similarly, the area Sn where the negative electrode current collector 20 and the negative electrode plate 14 are bonded via the negative electrode side conductive bonding layer 26 contributes to the bonding between the negative electrode current collector 20 and the negative electrode plate 14. It means the area occupied by the negative electrode side conductive bonding layer 26, and does not include the area of the region where the negative electrode current collector 20 and the negative electrode plate 14 contact or face each other without the negative electrode side conductive bonding layer 26 interposed. do. In the lithium ion secondary battery 10 including the positive electrode plate 12 which is a lithium composite oxide sintered plate and the negative electrode plate 14 which is a titanium-containing sintered plate, the positive electrode current collector 18 and the positive electrode plate 12 is bonded through the positive electrode side conductive bonding layer 24, and the area Sn where the negative electrode current collector 20 and the negative electrode plate 14 are bonded via the negative electrode side conductive bonding layer 26 is 1.0≦ By satisfying the relationship of Sn/Sp≦5.0, both capacity and cycle characteristics can be improved.

As described above, a lithium composite oxide sintered plate that does not contain conductive carbon (for example, LCO sintered plate) is used for the positive electrode, and a titanium-containing sintered plate that does not contain conductive carbon (for example, LTO sintered It was found that when a lithium-ion secondary battery was actually produced using the body plate) as the negative electrode, the expected capacity could not be obtained. This is presumably because when the function of electron conduction in the direction of the negative electrode surface is to be ensured by the titanium-containing sintered plate, the lack of electron conductivity in the direction of the negative electrode surface prevents sufficient extraction of capacity. By arranging the positive electrode side conductive bonding layer 24 and the negative electrode side conductive bonding layer 26 so as to satisfy the relationship of 1.0≦Sn/Sp≦5.0, the above problem can be conveniently solved. At the same time, cycle characteristics can also be improved.

This is considered as follows. That is, Sn/Sp being 1.0 or more means that the area Sn where the negative electrode current collector 20 and the negative electrode plate 14 are bonded via the negative electrode side conductive bonding layer 26 is equal to that of the positive electrode current collector 18 and the positive electrode. It means that the plate 12 is equal to or larger than the area Sp where the plate 12 is bonded via the positive electrode side conductive bonding layer 24 . That is, by increasing the bonding area Sn between the negative electrode current collector 20 and the negative electrode plate 14 to a size equal to or greater than the area Sp, the negative electrode current collector 20 and the negative electrode-side conductive bonding layer 26 can conduct electrons in the direction of the negative electrode surface. It is thought that it will be possible to supplement the function and take out a sufficient capacity. In addition, when Sn/Sp is 1.0 to 5.0, the junction area Sp between the positive electrode current collector 18 and the positive electrode plate 12 is reduced to a size equal to or smaller than the area Sn, but it is excessively small. By adjusting the junction area Sp between the positive electrode current collector 18 and the positive electrode plate 12 so as to fall within such a selective range, it is possible to improve cycle characteristics. In this regard, when the joint area Sp between the positive electrode current collector 18 and the positive electrode plate 12 is made larger than the area Sn (that is, Sn/Sp is less than 1.0), the negative electrode plate 14 (that is, the negative electrode active material) faces the The part of the positive electrode plate 12 (positive electrode active material) that is joined to the positive electrode current collector 18 that is not connected to the positive electrode current collector 18 also contributes greatly to charging and discharging, and a potential distribution occurs in the positive electrode plate 12 that contributes to charging and discharging, and the electrolytic solution etc. It is considered that the non-uniform growth of the film due to oxidative decomposition deteriorates the cycle characteristics. In addition, when the joint area Sp between the positive electrode current collector 18 and the positive electrode plate 12 is too small to less than one-fifth of the area Sn (that is, Sn/Sp exceeds 5.0), the positive electrode plate 12 Since the expansion and contraction of the lithium composite oxide (e.g., LCO) due to lithium absorption/desorption is larger than that of the titanium-containing sintered body (e.g., LTO) that constitutes the negative electrode plate 14, the expansion and contraction of the positive electrode plate 12 due to charging and discharging It is considered that the separation between the positive electrode plate 12 and the positive electrode current collector 18 progresses and the cycle characteristics deteriorate. From the above viewpoint, the Sn/Sp ratio is 1.0 to 5.0, preferably 1.1 to 5.0, more preferably 1.5 to 5.0, still more preferably 2.5 to 5.0. is 0.

As described above, at least part of the surface of the negative electrode plate 14 facing the negative electrode current collector 20 is bonded to the negative electrode current collector 20 via the negative electrode-side conductive bonding layer 26, and preferably the negative electrode of the negative electrode plate 14 At least 70%, more preferably at least 80%, still more preferably 90%, and most preferably all (100%) of the surface on the side of the current collector 20 is through the negative electrode current collector 20 and the negative electrode side conductive bonding layer 26. are joined together. By increasing the bonding area ratio of the negative electrode-side conductive bonding layer 26 in this manner, the negative electrode current collector 20 and the negative electrode-side conductive bonding layer 26 can more effectively supplement the electron conduction function in the negative electrode surface direction. , more capacity can be extracted.

The positive electrode plate 12 is a sintered lithium composite oxide plate containing no conductive carbon. That the positive electrode plate 12 is a sintered plate means that the positive electrode plate 12 does not contain a binder or a conductive aid. This is because even if the green sheet contains a binder, the binder disappears or is burned off during firing. In addition, since the positive electrode plate 12 does not contain a binder, there is an advantage that deterioration of the positive electrode due to the electrolytic solution 22 can be avoided. The lithium composite oxide forming the sintered plate is particularly preferably lithium cobaltate (typically LiCoO ₂ (hereinafter sometimes abbreviated as LCO)). Various lithium composite oxide sintered plates or LCO sintered plates are known, for example, those disclosed in Patent Document 1 (Patent No. 5587052) and Patent Document 2 (Patent No. 6374634). can be used.

According to a preferred embodiment of the present invention, the positive electrode plate 12, that is, the lithium composite oxide sintered plate, contains a plurality of primary particles composed of a lithium composite oxide, and the plurality of primary particles are formed on the plate surface of the positive electrode plate. It is an oriented positive electrode plate oriented at an average orientation angle of more than 0° and 30° or less. 2 shows an example of a cross-sectional SEM image perpendicular to the plate surface of the oriented positive electrode plate 12, while FIG. 3 is an electron backscatter diffraction (EBSD) image in a cross section perpendicular to the plate surface of the oriented positive electrode plate 12. indicates FIG. 4 shows a histogram showing the distribution of orientation angles of the primary particles 11 in the EBSD image of FIG. 3 on an area basis. A discontinuity in crystal orientation can be observed in the EBSD image shown in FIG. In FIG. 3, the orientation angle of each primary particle 11 is indicated by the shade of color, and the darker the color, the smaller the orientation angle. The orientation angle is the inclination angle formed by the (003) plane of each primary particle 11 with respect to the plate surface direction. In addition, in FIGS. 2 and 3 , the portions shown in black inside the oriented positive electrode plate 12 are pores.

The oriented positive electrode plate 12 is an oriented sintered body composed of a plurality of primary particles 11 bonded together. Each primary particle 11 is mainly plate-shaped, but may include rectangular parallelepiped, cubic, and spherical primary particles. The cross-sectional shape of each primary particle 11 is not particularly limited, and may be rectangular, polygonal other than rectangular, circular, elliptical, or any other complex shape.

Each primary particle 11 is composed of a lithium composite oxide. Lithium composite oxide means Li _x MO ₂ (0.05<x<1.10, M is at least one transition metal, and M is typically one or more of Co, Ni and Mn including). A lithium composite oxide has a layered rock salt structure. The layered rock salt structure is a crystal structure in which a lithium layer and a transition metal layer other than lithium are alternately laminated with an oxygen layer sandwiched therebetween, that is, a transition metal ion layer and a lithium single layer are alternately formed via oxide ions. It refers to a laminated crystal structure (typically, an α-NaFeO ₂ type structure, ie, a structure in which transition metals and lithium are regularly arranged in the [111] axis direction of a cubic rocksalt structure). Examples of lithium composite oxides include Li _x CoO ₂ (lithium cobalt oxide), Li _x NiO ₂ (lithium nickel oxide), Li _x MnO ₂ (lithium manganate), and Li _x NiMnO ₂ (lithium nickel-manganese oxide). _{. _ _ _ _ _ _ _} (lithium cobaltate, typically LiCoO ₂ ). Lithium composite oxides include Mg, Al, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ag, Sn, Sb, Te, Ba , Bi, and W may be included.

As shown in FIGS. 3 and 4, the average value of the orientation angles of the primary particles 11, that is, the average orientation angle is more than 0° and 30° or less. This provides various advantages: First, since each primary particle 11 lies in a state inclined with respect to the thickness direction, the adhesion between the primary particles can be improved. As a result, it is possible to improve the lithium ion conductivity between a certain primary particle 11 and other primary particles 11 adjacent to both sides in the longitudinal direction of the primary particle 11, thereby improving the rate characteristics. Second, rate characteristics can be further improved. As described above, when lithium ions enter and leave the oriented positive plate 12, the expansion and contraction in the thickness direction is more dominant than in the plate surface direction. This is because the input and output of lithium ions become smoother.

The average orientation angle of primary particles 11 is obtained by the following method. First, in an EBSD image of a rectangular region of 95 μm×125 μm observed at a magnification of 1000 as shown in FIG. and draw three vertical lines that divide the Next, the average orientation angle of the primary particles 11 is obtained by arithmetically averaging the orientation angles of all the primary particles 11 intersecting at least one of the three horizontal lines and the three vertical lines. The average orientation angle of the primary particles 11 is preferably 30° or less, more preferably 25° or less, from the viewpoint of further improving rate characteristics. From the viewpoint of further improving the rate characteristics, the average orientation angle of the primary particles 11 is preferably 2° or more, more preferably 5° or more.

As shown in FIG. 4, the orientation angle of each primary particle 11 may be widely distributed from 0° to 90°, but most of them are distributed in the region of more than 0° and 30° or less. is preferred. That is, when the cross section of the oriented sintered body constituting the oriented positive electrode plate 12 is analyzed by EBSD, the orientation angle of the primary particles 11 included in the analyzed cross section with respect to the plate surface of the oriented positive electrode plate 12 is 0°. The total area of the primary particles 11 (hereinafter referred to as low-angle primary particles) that is more than 30 ° or less is included in the cross section of the primary particles 11 (specifically, 30 primary particles 11 used to calculate the average orientation angle) It is preferably 70% or more, more preferably 80% or more, of the total area of . As a result, the ratio of the primary particles 11 having high mutual adhesion can be increased, so that the rate characteristics can be further improved. Further, the total area of the low-angle primary particles having an orientation angle of 20° or less is more preferably 50% or more of the total area of the 30 primary particles 11 used to calculate the average orientation angle. . Furthermore, the total area of the low-angle primary particles having an orientation angle of 10° or less is more preferably 15% or more of the total area of the 30 primary particles 11 used to calculate the average orientation angle. .

It is preferable that the average particle size of the plurality of primary particles constituting the oriented sintered body is 5 μm or more. Specifically, the average particle size of the 30 primary particles 11 used to calculate the average orientation angle is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 12 μm or more. As a result, the number of grain boundaries between the primary particles 11 in the direction in which lithium ions are conducted is reduced, and the lithium ion conductivity as a whole is improved, so that the rate characteristics can be further improved. The average particle diameter of the primary particles 11 is a value obtained by arithmetically averaging the equivalent circle diameters of the primary particles 11 . The equivalent circle diameter is the diameter of a circle having the same area as each primary particle 11 on the EBSD image.

The positive plate 12 preferably contains pores. Since the sintered body contains pores, particularly open pores, when it is incorporated into a battery as a positive electrode plate, the electrolyte can permeate the inside of the sintered body, and as a result, the lithium ion conductivity is improved. be able to. This is because there are two types of lithium ion conduction in the sintered body: conduction through the constituent particles of the sintered body and conduction through the electrolyte in the pores. This is because it is overwhelmingly fast.

The positive electrode plate 12, that is, the lithium composite oxide sintered plate, preferably has a porosity of 20 to 60%, more preferably 25 to 55%, still more preferably 30 to 50%, and particularly preferably 30 to 45%. is. A stress releasing effect and a high capacity can be expected by the pores, and the mutual adhesion between the primary particles 11 can be further improved, so that the rate characteristics can be further improved. The porosity of the sintered body is calculated by binarizing the obtained SEM image after polishing the cross section of the positive electrode plate by CP (cross section polisher), observing it with an SEM at a magnification of 1000. The average circle equivalent diameter of each pore formed inside the oriented sintered body is not particularly limited, but is preferably 8 μm or less. The smaller the average equivalent circle diameter of each pore, the more the mutual adhesion between the primary particles 11 can be improved, and as a result, the rate characteristics can be further improved. The average equivalent circle diameter of pores is a value obtained by arithmetically averaging the equivalent circle diameters of 10 pores on the EBSD image. The equivalent circle diameter is the diameter of a circle having the same area as each pore on the EBSD image. Each pore formed inside the oriented sintered body is preferably an open pore leading to the outside of the positive electrode plate 12 .

The average pore size of the positive electrode plate 12, that is, the sintered lithium composite oxide plate is preferably 0.1 to 10.0 μm, more preferably 0.2 to 5.0 μm, and still more preferably 0.3 to 3.0 μm. .0 μm. Within the above range, stress concentration in large pores is suppressed, and the stress in the sintered body is easily released uniformly.

The thickness of the positive electrode plate 12 is preferably 60-450 μm, more preferably 70-350 μm, still more preferably 90-300 μm. Within such a range, the energy density of the lithium ion secondary battery 10 is improved by increasing the active material capacity per unit area, and the battery characteristics deteriorate due to repeated charging and discharging (especially an increase in resistance value). can be suppressed.

The negative electrode plate 14 is a titanium-containing sintered plate containing no conductive carbon. The titanium-containing sintered plate preferably contains lithium titanate Li ₄ Ti ₅ O ₁₂ (hereinafter referred to as LTO) or niobium titanium composite oxide Nb ₂ TiO ₇ , more preferably LTO. Although LTO is typically known to have a spinel structure, other structures can be adopted during charging and discharging. For example, in LTO, the reaction proceeds in the two-phase coexistence of Li ₄ Ti ₅ O ₁₂ (spinel structure) and Li ₇ Ti ₅ O ₁₂ (rock salt structure) during charging and discharging. Therefore, LTO is not limited to spinel structures.

That the negative electrode plate 14 is a sintered plate means that the negative electrode plate 14 does not contain a binder or a conductive aid. This is because even if the green sheet contains a binder, the binder disappears or is burned off during firing. Since the negative electrode plate does not contain a binder, the filling density of the negative electrode active material (for example, LTO or Nb ₂ TiO ₇ ) is increased, thereby achieving high capacity and good charge/discharge efficiency. The LTO sintered plate can be produced according to the methods described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2015-185337) and Patent Document 4 (Japanese Patent No. 6392493).

The negative electrode plate 14, that is, the titanium-containing sintered body plate has a structure in which a plurality of (that is, many) primary particles are bonded together. Therefore, it is preferred that these primary particles consist of LTO or Nb ₂ TiO ₇ .

The thickness of the negative electrode plate 14 is preferably 70-500 μm, preferably 85-400 μm, more preferably 95-350 μm. The thicker the LTO sintered plate, the easier it is to achieve a battery with high capacity and high energy density. The thickness of the negative electrode plate 14 can be obtained, for example, by measuring the distance between plate surfaces observed substantially parallel when the cross section of the negative electrode plate 14 is observed with a SEM (scanning electron microscope).

The primary particle diameter, which is the average particle diameter of the plurality of primary particles constituting the negative electrode plate 14, is preferably 1.2 μm or less, more preferably 0.02 to 1.2 μm, and still more preferably 0.05 to 0.7 μm. . Within such a range, it is easy to achieve both lithium ion conductivity and electronic conductivity, which contributes to the improvement of rate performance.

The negative plate 14 preferably contains pores. Since the sintered body plate contains pores, particularly open pores, the electrolytic solution can permeate the inside of the sintered body plate when it is incorporated in a battery as a negative electrode plate, and as a result, the lithium ion conductivity is improved. can be improved. This is because there are two types of lithium ion conduction in the sintered body: conduction through the constituent particles of the sintered body and conduction through the electrolyte in the pores. This is because it is overwhelmingly fast.

The porosity of the negative electrode plate 14 is preferably 20-60%, more preferably 30-55%, still more preferably 35-50%. Within such a range, it is easy to achieve both lithium ion conductivity and electronic conductivity, which contributes to the improvement of rate performance.

The average pore size of the negative plate 14 is 0.08-5.0 μm, preferably 0.1-3.0 μm, more preferably 0.12-1.5 μm. Within such a range, it is easy to achieve both lithium ion conductivity and electronic conductivity, which contributes to the improvement of rate performance.

Separator 16 is preferably a cellulose, polyolefin, polyimide, polyester (eg, polyethylene terephthalate (PET)), or ceramic separator. Cellulose separators are advantageous in that they are inexpensive and have excellent heat resistance. Polyimide, polyester (e.g., polyethylene terephthalate (PET)) or cellulose separators not only have excellent heat resistance, unlike the widely used polyolefin separators, which have poor heat resistance. It also has excellent wettability with electrolyte components. Therefore, the electrolytic solution can be sufficiently permeated into the separator (without being repelled). On the other hand, the separator made of ceramic has the advantage that it is excellent in heat resistance and can be manufactured together with the positive electrode plate 12 and the negative electrode plate 14 as one integrated sintered body as a whole. In the case of a ceramic separator, the ceramic constituting the separator is preferably at least one selected from MgO, Al ₂ O ₃ , ZrO ₂ , SiC, Si ₃ N ₄ , AlN, and cordierite, more preferably At least one selected from MgO, Al ₂ O ₃ and ZrO ₂ .

The electrolytic solution 22 is not particularly limited, and a commercially available electrolytic solution for lithium batteries, such as a solution in which a lithium salt is dissolved in a non-aqueous solvent such as an organic solvent, may be used. Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), vinylethylene carbonate (VEC), cyclic carbonates such as fluoroethylene carbonate (FEC), and dimethyl carbonate (DMC). , diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and other chain carbonates, cyclic ethers such as tetrahydrofuran (THF), chain ethers such as dimethoxyethane (DME), lactones such as γ-butyrolactone (GBL) , nitriles such as acetonitrile (AN), cyclic sulfones such as sulfolane (SL), and cyclic sulfonate esters such as propanesultone (PS). Such non-aqueous solvents may be used alone or as a mixture of two or more. Examples of lithium salts include lithium perchlorate (LiClO4), lithium hexafluorophosphate ( _LiPF6 ), lithium _{tetrafluoroborate} ( _LiBF4 ), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisfluorosulfonylimide (LiFSI), lithium bis(oxalate)borate (LiBOB), and the like. Such lithium salts may be used alone or as a mixture of two or more. The lithium salt concentration in the electrolytic solution 22 is preferably 0.5 to 2 mol/L, more preferably 0.6 to 1.9 mol/L, still more preferably 0.7 to 1.7 mol/L, particularly preferably 0.8 to 1.5 mol/L.

Preferably, the lithium-ion secondary battery 10 further includes a pair of exterior films 28, the outer peripheries of the exterior films 28 are sealed together to form an internal space, and the positive electrode current collector 18 and the positive electrode side are placed in the internal space. It accommodates the conductive bonding layer 24, the positive electrode plate 12, the separator 16, the negative electrode plate 14, the negative electrode side conductive bonding layer 26, the negative current collector 20, and the electrolyte 22 (hereinafter collectively referred to as battery elements). That is, as shown in FIG. 1, the battery element, which is the content of the lithium ion secondary battery 10, is wrapped and sealed with a pair of exterior films 28, and as a result, the lithium ion secondary battery 10 is It is in the form of a so-called film-clad battery. The outer edge of the lithium ion secondary battery 10 is preferably sealed by heat-sealing the exterior films 28 to each other. Sealing by heat sealing is preferably performed using a heat bar (also referred to as a heating bar) commonly used in heat sealing applications. Typically, the lithium ion secondary battery 10 has a quadrilateral shape, and it is preferable that the outer peripheral edges of the pair of exterior films 28 are sealed over all four sides of the outer periphery.

A commercially available exterior film may be used for the exterior film 28 . The thickness of each outer film 28 is preferably 50-80 μm, more preferably 55-70 μm, still more preferably 55-65 μm. A preferable exterior film 28 is a laminate film containing a resin film and a metal foil, and more preferably an aluminum laminate film containing a resin film and an aluminum foil. It is preferable that the laminated film has a resin film on both sides of a metal foil such as an aluminum foil. In this case, the resin film on one side of the metal foil (hereinafter referred to as the surface protective film) is made of a material with excellent reinforcing properties such as nylon, polyamide, polyethylene terephthalate, polyimide, polytetrafluoroethylene, polychlorotrifluoroethylene, etc. It is preferable that the resin film on the other side of the metal foil is made of a heat-sealing material such as polypropylene.

The positive electrode current collector 18 is provided on the surface of the positive electrode plate 12 away from the separator 16 , while the negative electrode current collector 20 is provided on the surface of the negative electrode plate 14 away from the separator 16 . Accordingly, the positive electrode current collector 15 is interposed between the positive electrode plate 12 and the packaging film 28 , while the negative electrode current collector 20 is interposed between the negative electrode plate 14 and the packaging film 28 . Preferably, one of the positive electrode current collector 15 and the exterior film 28 is adhered, and the other of the negative electrode current collector 20 and the exterior film 28 is adhered. Although the positive electrode current collector 15 and the negative electrode current collector 20 are not particularly limited, they are preferably metal foils such as copper foil and aluminum foil.

The positive electrode tab terminal 19 is connected to the positive electrode current collector 18 and extends outward from the sealed portion of the pair of exterior films 28 , while the negative electrode tab terminal (not shown) is connected to the negative electrode current collector 20 . , and extends outward from the sealing portion of the pair of exterior films 28 . Note that the negative electrode tab terminal is hidden behind the positive electrode tab terminal 19 in FIG. 1 and is therefore not depicted. More specifically, the positive electrode tab terminal 19 and the negative electrode tab terminal extend from different positions or different sides of a common side of the sealed portion of the exterior film 28 . Although the positive electrode tab terminal 19 and the negative electrode tab terminal are not particularly limited, they can be made of the same or different materials as the positive electrode current collector 15 and the negative electrode current collector 20, respectively, and are preferably metal foil such as copper foil or aluminum foil. . The connection between the positive electrode tab terminal 19 and the positive electrode current collector 15 and the connection between the negative electrode tab terminal and the negative electrode current collector 20 may be performed by known connection methods such as welding and adhesives, and are not particularly limited. Alternatively, the positive tab terminal 19 and the positive current collector 15 or the negative tab terminal and the negative current collector 20 may be a single piece made of the same material.

At least part of the surface of the positive electrode plate 12 facing the positive electrode current collector 18 is bonded to the positive electrode current collector 18 via the positive electrode side conductive bonding layer 24 . At least part of the surface of the negative electrode plate 14 facing the negative electrode current collector 20 is bonded to the negative electrode current collector 20 via the negative electrode side conductive bonding layer 26 . Both the positive electrode-side conductive bonding layer 24 and the negative electrode-side conductive bonding layer 26 are not particularly limited as long as they use a known or commercially available conductive adhesive. Examples include those containing agents in a predetermined blending ratio. Examples of conductive materials include conductive carbon materials such as carbon black, acetylene black, graphite, carbon fibers, and carbon nanotubes. Examples of binders include acrylic binders and styrene-butadiene rubber binders. Examples of thickeners include carboxymethylcellulose and the like.

Manufacturing method of the positive electrode plate The positive electrode plate 12, that is, the lithium composite oxide sintered plate may be manufactured by any method, but preferably (a) preparation of a lithium composite oxide-containing green sheet, ( b) preparation of an excess lithium source-containing green sheet, and (c) lamination and firing of the green sheets.

(a) Preparation of Lithium Composite Oxide-Containing Green Sheet First, a raw material powder composed of a lithium composite oxide is prepared. Preferably, the powder comprises as _- synthesized platelets (eg, LiCoO2 platelets) of composition LiMO ₂ , where M is as previously described. The volume-based D50 particle size of the raw material powder is preferably 0.3 to 30 μm. For example, a method of making LiCoO ₂ tabular particles can be carried out as follows. First, Co ₃ O ₄ raw powder and Li ₂ CO ₃ raw powder are mixed and fired (500 to 900° C., 1 to 20 hours) to synthesize LiCoO ₂ powder. By pulverizing the obtained LiCoO ₂ powder with a pot mill to a volume-based D50 particle size of 0.2 μm to 10 μm, plate-like LiCoO ₂ particles capable of conducting lithium ions parallel to the plate surface are obtained. Such LiCoO2 particles can be produced in a plate _- like form by a method of grain _- growing a green sheet using a LiCoO2 powder slurry and then pulverizing it, or by a flux method, hydrothermal synthesis, single crystal growth using a melt, or a sol-gel method. It can also be obtained by a method of synthesizing crystals. The obtained LiCoO ₂ particles are in a state where they are easily cleaved along the cleavage plane. LiCoO ₂ plate-like particles can be made by cleaving the LiCoO ₂ particles by crushing.

The plate-like particles may be used alone as the raw material powder, or a mixed powder of the plate-like powder and other raw material powders (for example, Co ₃ O ₄ particles) may be used as the raw material powder. In the latter case, it is preferable to have the plate-like powder function as template particles for imparting orientation, and other raw material powders (eg, Co ₃ O ₄ particles) to function as matrix particles capable of growing along the template particles. In this case, it is preferable to use a powder obtained by mixing template particles and matrix particles at a ratio of 100:0 to 3:97 as the raw material powder. When the Co ₃ O ₄ raw material powder is used as matrix particles, the volume _- based D50 particle size of the Co ₃ O ₄ raw material powder is not particularly limited, and can be, for example, 0.1 to 1.0 μm. is preferably smaller than the volume-based D50 particle size of This matrix particle can also be obtained by heat-treating a Co(OH) ₂ raw material at 500° C. to 800° C. for 1 to 10 hours. In addition to Co ₃ O ₄ , Co(OH) ₂ particles or LiCoO ₂ particles may be used as the matrix particles.

When the raw material powder is composed of 100% LiCoO2 template particles, or when LiCoO2 particles _are used as matrix particles, a large _- sized (e.g., 90 mm x 90 mm _square ) and flat LiCoO2 sintered body plate is obtained by firing. can be done. Although the mechanism is not clear, it is expected that the volume change during firing or the local unevenness is unlikely to occur because LiCoO ₂ is not synthesized during the firing process.

A raw material powder is mixed with a dispersion medium and various additives (a binder, a plasticizer, a dispersant, etc.) to form a slurry. A lithium compound other than LiMO ₂ (for example, lithium carbonate) may be added to the slurry in excess of about 0.5 to 30 mol % for the purpose of promoting grain growth or compensating for volatile matter during the firing step described later. It is desirable not to add pore formers to the slurry. The slurry is preferably stirred under reduced pressure to remove air bubbles and adjusted to have a viscosity of 4,000 to 10,000 cP. The resulting slurry is formed into a sheet to obtain a lithium composite oxide-containing green sheet. The green sheet thus obtained is an independent sheet-like compact. An independent sheet (sometimes referred to as a "self-supporting film") refers to a sheet that can be handled independently from other supports (including flakes with an aspect ratio of 5 or more). That is, the independent sheet does not include a sheet fixed to another support (substrate or the like) and integrated with the support (it cannot be separated or becomes difficult to separate). Sheet forming is preferably carried out using a forming technique capable of applying a shearing force to plate-like particles (for example, template particles) in the raw material powder. By doing so, the average tilt angle of the primary particles can be set to more than 0° and not more than 30° with respect to the plate surface. A doctor blade method is suitable as a molding method capable of applying a shearing force to the plate-like particles. The thickness of the lithium composite oxide-containing green sheet may be appropriately set so as to achieve the desired thickness as described above after firing.

(b) Preparation of excess lithium source-containing green sheet (optional step)
If desired, a green sheet containing an excess lithium source is produced separately from the green sheet containing the lithium composite oxide. This excess lithium source is preferably a lithium compound other than LiMO ₂ in which the components other than Li disappear upon firing. A preferred example of such a lithium compound (excess lithium source) is lithium carbonate. The excess lithium source is preferably in powder form, and the volume-based D50 particle size of the excess lithium source powder is preferably 0.1-20 μm, more preferably 0.3-10 μm. Then, the lithium source powder is mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. It is preferable to stir the obtained slurry under reduced pressure to remove air bubbles and to adjust the viscosity to 1000 to 20000 cP. The resulting slurry is formed into a sheet to obtain an excess lithium source-containing green sheet. The green sheet thus obtained is also an independent sheet-like compact. Sheet molding can be performed by various known methods, but is preferably performed by a doctor blade method. Regarding the thickness of the excess lithium source-containing green sheet, the molar ratio (Li/Co ratio) of the Li content in the excess lithium source-containing green sheet to the Co content in the lithium composite oxide-containing green sheet is preferably 0.1 or more. , more preferably 0.1 to 1.1.

(c) Lamination and Firing of Green Sheets Lithium composite oxide-containing green sheets (e.g. LiCoO2 green sheets) and, if desired, excess lithium source-containing green sheets ₍ e.g. _Li2CO3 green sheets) are placed in order _on the lower setter. and place the upper setter on it. The upper and lower setters are made of ceramics, preferably zirconia or magnesia. Pores tend to be smaller when the setter is made of magnesia. The upper setter may have a porous structure, a honeycomb structure, or a dense structure. If the upper setter is dense, the pores in the sintered plate tend to be small and the number of pores tends to be large. If necessary, the excess lithium source-containing green sheet preferably has a molar ratio (Li/Co ratio) of the Li content in the excess lithium source-containing green sheet to the Co content in the lithium composite oxide-containing green sheet. It is preferably used by being cut into a size of 1 or more, more preferably 0.1 to 1.1.

At the stage where the lithium composite oxide-containing green sheet (eg LiCoO ₂ green sheet) is placed on the lower setter, the green sheet may optionally be degreased and then calcined at 600 to 850° C. for 1 to 10 hours. . In this case, an excess lithium source-containing green sheet (for example, a _Li2CO3 green sheet) and an upper setter may be sequentially placed _on the obtained calcined plate.

Then, with the green sheet and/or calcined plate sandwiched between setters, if desired, after degreasing, heat treatment (firing) at a firing temperature in a medium temperature range (for example, 700 to 1000 ° C.) is performed to obtain a lithium composite oxide. A sintered plate is obtained. This firing step may be performed in two steps or in one step. When baking in two steps, the first baking temperature is preferably lower than the second baking temperature. The sintered plate thus obtained is also an independent sheet.

Manufacturing Method of Negative Electrode Plate The negative electrode plate 14, that is, the titanium-containing sintered body plate may be manufactured by any method. For example, the LTO sintered plate is preferably produced through (a) preparation of an LTO-containing green sheet and (b) firing of the LTO-containing green sheet.

(a) Preparation of LTO-Containing Green Sheet First, a raw material powder (LTO powder) composed of lithium titanate Li ₄ Ti ₅ O ₁₂ is prepared. A commercially available LTO powder may be used as the raw material powder, or a new one may be synthesized. For example, a powder obtained by hydrolyzing a mixture of titanium tetraisopropoxyalcohol and isopropoxylithium may be used, or a mixture containing lithium carbonate, titania, etc. may be fired. The volume-based D50 particle size of the raw material powder is preferably 0.05 to 5.0 μm, more preferably 0.1 to 2.0 μm. If the particle size of the raw material powder is large, the pores tend to be large. In addition, when the raw material particle size is large, pulverization treatment (for example, pot mill pulverization, bead mill pulverization, jet mill pulverization, etc.) may be performed so as to obtain a desired particle size. Then, the raw material powder is mixed with a dispersion medium and various additives (binder, plasticizer, dispersant, etc.) to form a slurry. A lithium compound other than LiMO ₂ (for example, lithium carbonate) may be added to the slurry in excess of about 0.5 to 30 mol % for the purpose of promoting grain growth or compensating for volatile matter during the firing step described later. It is desirable not to add pore formers to the slurry. The slurry is preferably stirred under reduced pressure to remove air bubbles and adjusted to have a viscosity of 4,000 to 10,000 cP. The resulting slurry is formed into a sheet to obtain an LTO-containing green sheet. The green sheet thus obtained is an independent sheet-like compact. An independent sheet (sometimes referred to as a "self-supporting film") refers to a sheet that can be handled independently from other supports (including flakes with an aspect ratio of 5 or more). That is, the independent sheet does not include a sheet fixed to another support (substrate or the like) and integrated with the support (it cannot be separated or becomes difficult to separate). Sheet molding can be performed by various known methods, but is preferably performed by a doctor blade method. The thickness of the LTO-containing green sheet may be appropriately set so as to have the desired thickness as described above after firing.

(b) Firing of LTO-containing green sheet An LTO-containing green sheet is placed on a setter. The setter is made of ceramics, preferably zirconia or magnesia. The setter is preferably embossed. The green sheet thus placed on the setter is put into a sheath. The sheath is also made of ceramics, preferably alumina. Then, in this state, the LTO sintered body plate is obtained by sintering after degreasing if desired. This firing is preferably carried out at 600-900° C. for 1-50 hours, more preferably at 700-800° C. for 3-20 hours. The sintered plate thus obtained is also an independent sheet. The heating rate during firing is preferably 100 to 1000° C./h, more preferably 100 to 600° C./h. In particular, this rate of temperature increase is preferably employed in the process of increasing temperature from 300°C to 800°C, more preferably in the process of increasing temperature from 400°C to 800°C.

(c) Summary An LTO sintered plate can be preferably produced as described above. In this preferred production method, it is effective to 1) adjust the particle size distribution of the LTO powder and/or 2) change the rate of temperature increase during firing, and these are effective in realizing various characteristics of the LTO sintered plate. It is thought that it contributes to

The invention is further illustrated by the following examples. _In the following examples, LiCoO2 is abbreviated as " _LCO ", and _Li4Ti5O12 is abbreviated as " _LTO ".

Example 1
(1) Fabrication of positive electrode plate (1a) Fabrication of LCO green sheet , a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) 10 parts by weight, a plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurogane Kasei Co., Ltd.) 2 parts by weight, and a dispersant (Product name: Rheodol SP-O30, manufactured by Kao Corporation) was mixed with 4.5 parts by weight. A slurry was prepared by stirring the resulting mixture under reduced pressure to remove air bubbles and adjusting the viscosity to 4000 cP. Viscosity was measured with a Brookfield LVT viscometer. A green sheet was formed by forming the slurry thus prepared into a sheet on a PET film by a doctor blade method. The thickness of the LCO green sheet after drying was 110 μm.

(1b) Preparation of LCO sintered plate A 35 mm square LCO green sheet peeled from the PET film was cut with a cutter and placed in the center of a magnesia setter (dimension 90 mm square, height 1 mm) as a lower setter. As an upper setter, a setter made of porous alumina (dimensions: 40 mm square, height: 3 mm) was placed in the center on the green sheet. The green sheet on the setter was fired at 900° C. for 15 hours to obtain an LCO sintered plate. Thus, an LCO sintered plate was obtained as a positive electrode plate. The obtained positive electrode plate was laser-processed into a 32 mm×32 mm square shape.

(2) Fabrication of negative electrode plate (2a) Fabrication of LTO green sheet 10 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.), a plasticizer (DOP: Di (2-ethylhexyl) phthalate, manufactured by Kurogane Kasei Co., Ltd.) 2 parts by weight, and a dispersant ( Product name: Rheodol SP-O30, manufactured by Kao Corporation) was mixed with 1 part by weight. An LTO slurry was prepared by stirring the obtained negative electrode raw material mixture under reduced pressure to remove air bubbles and adjusting the viscosity to 4000 cP. Viscosity was measured with a Brookfield LVT viscometer. The slurry thus prepared was formed into a sheet on a PET film by a doctor blade method to form an LTO green sheet. The thickness of the LTO green sheet after drying was 110 μm.

(2b) Production of LTO sintered plate The obtained green sheet was cut into 35 mm squares with a cutter knife and placed on a magnesia setter (dimensions: 90 mm square, height: 1 mm). As an upper setter, a setter made of porous alumina (dimensions: 40 mm square, height: 3 mm) was placed in the center on the green sheet. The green sheet on the setter was fired at 760° C. for 5 hours to obtain an LTO sintered plate. Thus, an LTO sintered plate was obtained as a negative electrode plate. The obtained negative electrode plate was laser-processed into a 30 mm×30 mm square shape.

(3) Production of Current Collector A 20 μm aluminum foil was cut into a size of 35 mm×45 mm. A tab lead was arranged so as to protrude from the end of the cut aluminum foil on the short side, and the aluminum foil and the tab lead were ultrasonically bonded to obtain a current collector.

(4) Preparation of conductive adhesive 30 parts by weight of a conductive material (acetylene black), 60 parts by weight of a binder (acrylic binder), and 10 parts by weight of a thickener (carboxymethyl cellulose) are mixed, and pure water is added. A conductive adhesive was produced.

(5) Fabrication of Positive Electrode A conductive adhesive was applied to an aluminum foil constituting a current collector in an area of 810 mm ² , and a positive electrode plate was adhered so as to cover the entire area coated with the conductive adhesive. The positive electrode was obtained by drying this at 100 degreeC for 12 hours.

(6) Preparation of negative electrode A conductive adhesive was applied in an area of 810 mm ² to an aluminum foil constituting another current collector, and the negative electrode plate was adhered so as to cover the entire area coated with the conductive adhesive. . The negative electrode was obtained by drying this at 100 degreeC for 12 hours.

(7) Fabrication of Electrode Group The positive electrode and the negative electrode thus obtained were opposed to each other with a separator interposed therebetween, and fixed by winding a tape around the periphery. At this time, the tab lead of the positive electrode and the tab lead of the negative electrode were arranged so as to extend in opposite directions from different sides facing each other. In addition, the entire negative electrode plate constituting the negative electrode was arranged to face the positive electrode plate constituting the positive electrode.

(8) Production of Pre-Injection Battery Two laminate films were prepared and placed on the outer surfaces of the positive and negative electrodes of the electrode group. Next, the laminate film arranged on the positive electrode side and the laminate film arranged on the negative electrode side were heat-sealed at three peripheral edges of the electrode group. At this time, the positions of the two sides where the tab leads are arranged were adjusted so that the overlapping portions of the insulating film provided on the tab leads and the laminate were heat-sealed so that a part of the tab leads protruded from the laminate film. . This projecting tab lead was used as a terminal to be connected to the device during charging and discharging. The other side on which the tab lead was not arranged was heat-sealed so as to be perpendicular to the two sealing sides on which the tab lead was arranged.

(9) Injection of Non-Aqueous Electrolyte A non-aqueous electrolyte (electrolytic solution) was injected from the side that was not thermally welded. A 1:1 mixture of ethylene carbonate and ethyl methyl carbonate was used as the non-aqueous solvent for the non-aqueous electrolyte, and 1 mol/l lithium hexafluorophosphate was used as the electrolyte.

(10) Fabrication of Battery After the non-aqueous electrolyte was injected, the remaining one side was heat-sealed to obtain a battery for charge-discharge cycle test.

(11) Evaluation of 0.2C Discharge Capacity Before Cycle Using the obtained battery, the battery capacity was confirmed under an environment of 25°C. The charging was constant-current and constant-voltage charging. Specifically, constant-current charging was performed at 0.2C until the voltage reached 2.7V, and then constant-voltage charging was performed at 2.7V until the current value reached 0.02C. . Discharge was performed at a constant current of 0.2C until the voltage reached 1.5V. The discharge capacity thus obtained was divided by the weight of the negative electrode plate measured in advance to obtain the 0.2C discharge capacity before the cycle.

(12) Cycle test Next, a charge-discharge cycle test was carried out. The charge/discharge cycle test was performed by repeating charge/discharge 1000 times in an environment of 25°C. The battery was charged at a constant voltage of 2.7V until the current reached 0.2C. Discharge was performed by constant current discharge at 1C until the voltage reached 1.5V.

(13) Evaluation of Capacity Retention Rate after 1000 Cycles The battery capacity was confirmed in an environment of 25° C. for the battery that had been repeatedly charged and discharged for 1000 cycles. The charging was constant-current and constant-voltage charging. Specifically, constant-current charging was performed at 0.2C until the voltage reached 2.7V, and then constant-voltage charging was performed at 2.7V until the current value reached 0.02C. . Discharge was performed at a constant current of 0.2C until the voltage reached 1.5V. The discharge capacity obtained in this way was divided by the weight of the negative electrode plate measured in advance, and the 0.2C discharge capacity after 1000 cycles was obtained. Also, this value was divided by the 0.2C discharge capacity before the cycle and multiplied by 100 to obtain the capacity retention rate (%) after 1000 cycles.

Example 2
A battery was fabricated and evaluated in the same manner as in Example 1, except that in (5) above, the conductive adhesive for the positive electrode was applied in an area of 162 mm ² .

Example 3
Same as Example 1 except that the positive electrode conductive adhesive was applied with an area of 630 mm ² in (5) above, and the negative electrode conductive adhesive was applied with an area of 630 mm ² in (6) above. A battery was fabricated and evaluated.

Example 4
In the same manner as in Example 1, except that the positive electrode conductive adhesive was applied in an area of 126 mm ² in (5) above, and the negative electrode conductive adhesive was applied in an area of 630 mm ² in (6) above. A battery was produced and evaluated.

example 5
Same as Example 1 except that the positive electrode conductive adhesive was applied in an area of 900 mm ² in (5) above, and the negative electrode conductive adhesive was applied in an area of 900 mm ² in (6) above. A battery was fabricated and evaluated.

Example 6
Same as Example 1 except that the positive electrode conductive adhesive was applied with an area of 818 mm ² in (5) above, and the negative electrode conductive adhesive was applied with an area of 900 mm ² in (6) above. A battery was fabricated and evaluated.

Example 7
Same as Example 1 except that the positive electrode conductive adhesive was applied in an area of 360 mm ² in (5) above, and the negative electrode conductive adhesive was applied in an area of 900 mm ² in (6) above. A battery was fabricated and evaluated.

Example 8
Same as Example 1 except that the positive electrode conductive adhesive was applied in an area of 180 mm ² in (5) above, and the negative electrode conductive adhesive was applied in an area of 900 mm ² in (6) above. A battery was fabricated and evaluated.

Example 9 (Comparison)
Same as Example 1 except that the positive electrode conductive adhesive was applied with an area of 1000 mm ² in (5) above, and the negative electrode conductive adhesive was applied with an area of 900 mm ² in (6) above. A battery was fabricated and evaluated.

Example 10 (comparative)
Example 1 except that the positive electrode conductive adhesive was applied in an area of 176.5 mm ² in (5) above, and the negative electrode conductive adhesive was applied in an area of 900 mm ² in (6) above. Batteries were produced and evaluated in the same manner.

Example 11 (Comparison)
Same as Example 1 except that the positive electrode conductive adhesive was applied with an area of 700 mm ² in (5) above, and the negative electrode conductive adhesive was applied with an area of 630 mm ² in (6) above. A battery was fabricated and evaluated.

Results Table 1 shows the evaluation results of the batteries produced in Examples 1-11. In Table 1, Sn/Sp is the area Sp where the positive electrode current collector and the positive electrode plate are bonded via the conductive adhesive (positive electrode side conductive bonding layer). It means the ratio of the area Sn bonded via a conductive adhesive (negative electrode side conductive bonding layer).

As is clear from Table 1, in Examples 1 to 8 that satisfy the relationship of 1.0 ≤ Sn / Sp ≤ 5.0, compared to Examples 9 to 11 that do not satisfy the above relationship, after 1000 cycles A capacity retention rate was realized.

Claims (7)

a positive electrode plate that is a lithium composite oxide sintered plate containing no conductive carbon;
a negative electrode plate that is a titanium-containing sintered plate containing no conductive carbon;
a separator interposed between the positive electrode plate and the negative electrode plate;
a positive electrode current collector provided on a surface of the positive electrode plate away from the separator;
a negative electrode current collector provided on a surface of the negative electrode plate remote from the separator;
an electrolytic solution impregnated in the positive electrode plate, the negative electrode plate, and the separator;
A lithium ion secondary battery comprising
At least part of the surface of the positive electrode plate facing the positive electrode current collector is bonded to the positive electrode current collector via a positive electrode side conductive bonding layer,
at least part of the surface of the negative electrode plate facing the negative electrode current collector is bonded to the negative electrode current collector via a negative electrode-side conductive bonding layer;
An area Sp where the positive electrode current collector and the positive electrode plate are bonded via the positive electrode side conductive bonding layer, and the negative electrode current collector and the negative electrode plate are bonded via the negative electrode side conductive bonding layer. A lithium ion secondary battery in which an area Sn satisfies a relationship of 1.0≦Sn/Sp≦5.0. 2. The lithium ion secondary battery in accordance with claim 1, wherein at least 70% of the surface of said negative electrode plate facing said negative electrode current collector is bonded to said negative electrode current collector via said negative electrode side conductive bonding layer. 2. The lithium ion secondary battery in accordance with claim 1, wherein the entire surface of said negative electrode plate facing said negative electrode current collector is bonded to said negative electrode current collector via said negative electrode side conductive bonding layer. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the positive electrode plate has a thickness of 60 to 450 µm. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the lithium composite oxide is lithium cobaltate. The lithium ion secondary battery according to any one of claims 1 to 5, wherein the negative electrode plate has a thickness of 70 to 500 µm. The lithium ion secondary battery according to any one of claims 1 to 6, wherein the titanium-containing sintered body contains lithium titanate or niobium titanium composite oxide.

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