JP6661934B2 - Positive electrode for power storage device and power storage device - Google Patents

Description

  The present invention relates to a power storage device represented by a lithium ion secondary battery, a lithium ion capacitor, and the like, and a positive electrode used for the power storage device.

  BACKGROUND ART As a general power storage device represented by a lithium ion secondary battery, a device including a negative electrode, a positive electrode, and an electrolyte is known. Of these, the electrolytic solution is generally formed by dissolving a lithium salt as a metal salt (that is, an electrolyte salt) in an organic solvent.

Various efforts have been made to improve the performance of power storage devices. As one of them, it has been proposed to directly add the above-mentioned lithium salt to the negative electrode active material layer and / or the positive electrode active material layer (for example, see Patent Documents 1 and 2). Hereinafter, as occasion demands, the positive electrode active material layer and the negative electrode active material layer may be collectively referred to as an electrode active material layer. Also, the positive electrode and the negative electrode may be collectively referred to as electrodes.
Patent Literature 1 uses lithium bisfluorosulfonylimide as a lithium salt, and Patent Literature 2 uses LiPF ₆ and / or LiBF ₄ as a lithium salt.

  It is considered that the lithium salt can be decomposed by charge and discharge and become a material of a film formed on the surface of the electrode active material layer. It is considered that the lithium salt directly added to the electrode active material layer is supplied to the vicinity of the surface of the electrode active material layer, for example, by gradually dissolving into the electrolytic solution in a power storage device such as a lithium ion secondary battery. For this reason, it is considered that by directly adding a lithium salt to the electrode active material layer, there is an advantage that the material of the coating can be positively and continuously supplied to the surface of the electrode active material layer. Alternatively, the lithium salt eluted into the electrolyte and not used as the material of the coating may be a metal salt of the electrolyte.

  By the way, each of the lithium salts used in Patent Documents 1 and 2 has a fluoro group directly bonded to S, P or B. These lithium salts easily absorb moisture contained in the air, and may further react with water molecules to generate hydrogen fluoride. Hydrogen fluoride generated during the production of the electrode not only deteriorates the production equipment, but also degrades the electrode material and may cause a reduction in the capacity of the power storage device. To address this problem, for example, Patent Literature 2 proposes manufacturing an electrode in an environment having a dew point of −20 ° C. or lower, and preferably a dew point of −40 ° C. or lower, as a manufacturing method for reducing moisture adsorption.

However, in order to ensure quality, it is necessary to monitor that hydrogen fluoride is not generated in the manufacturing process, which complicates the manufacturing process and increases costs.
Therefore, a technology that can further improve the performance of the power storage device while suppressing generation of hydrogen fluoride during manufacturing is desired.

JP 2014-086354 A JP 2011-192561 A

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a technology capable of further improving the performance of a power storage device.

The positive electrode for a power storage device of the present invention that solves the above problems,
A positive electrode having a positive electrode active material layer containing a metal salt represented by the following general formula (1).
(R ¹ SO ₂ ) (R ² SO ₂ ) NLi General formula (1)
(R ¹ and R ² are each independently a fluoroalkyl group or an alkyl group.
Further, R ¹ and R ² may combine with each other to form a ring. )

  The positive electrode for a power storage device of the present invention has improved battery performance.

  Hereinafter, embodiments for implementing the present invention will be described. Unless otherwise specified, the numerical range “ab” described in this specification includes the lower limit a and the upper limit b. A numerical range can be formed by arbitrarily combining these upper and lower limits and the numerical values listed in the examples. Further, numerical values arbitrarily selected from within the numerical value range can be set as upper and lower limit numerical values.

Power storage device positive electrode of the present invention,
A positive electrode having a positive electrode active material layer containing a metal salt represented by the following general formula (1).
(R ¹ SO ₂ ) (R ² SO ₂ ) NLi General formula (1)
(R ¹ and R ² are each independently a fluoroalkyl group or an alkyl group.
Further, R ¹ and R ² may combine with each other to form a ring. )

  Further, the power storage device of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and the positive electrode active material layer included in the positive electrode includes the metal salt represented by the general formula (1).

(Metal salts for electrodes)
The positive electrode for a power storage device and the power storage device of the present invention include a metal salt having a lithium element in a positive electrode active material layer, which is an electrode active material layer, separately from the electrolytic solution. Hereinafter, the metal salt mixed in the positive electrode active material layer as necessary is referred to as “metal salt for electrode” and is distinguished from the metal salt contained in the electrolytic solution, that is, the supporting salt.
In the positive electrode for a power storage device and the power storage device according to the present invention, various effects derived from previously mixing the metal salt for an electrode into the positive electrode active material layer can be expected as in the above-described conventional technology.

Further, in the metal salt represented by the general formula (1), R ¹ and R ² directly bonded to S are not a fluoro group but a fluoroalkyl group or an alkyl group, so that when the metal salt is decomposed, However, it is difficult to release fluorine immediately. Therefore, it is considered that the positive electrode for a power storage device and the power storage device of the present invention can suppress generation of hydrogen fluoride at least during manufacturing.
Therefore, the positive electrode for a power storage device of the present invention can impart excellent battery characteristics to the power storage device while suppressing generation of hydrogen fluoride during manufacturing. In addition, the power storage device of the present invention is one in which generation of hydrogen fluoride during production is suppressed and battery characteristics are excellent. Hereinafter, the positive electrode for a power storage device and the power storage device of the present invention may be collectively referred to as a power storage device of the present invention.

  The metal salt for an electrode is an imide salt containing lithium as a cation, and lithium contained in the metal salt for an electrode can function as at least a part of a charge carrier of a power storage device represented by a lithium ion secondary battery or the like. That is, the metal salt for an electrode can function as a Li conductor at the interface between the electrolytic solution and the electrode active material, and as a supporting salt in the power storage device of the present invention. Such a metal salt for an electrode may be the same as or different from the metal salt contained in the electrolytic solution.

R ¹ and R ² in the general formula (1) may be a fluoroalkyl group and / or an alkyl group, and the number of carbon atoms and the chain length are not particularly limited. R ¹ and R ² may each be linear or branched. Further, R ¹ and R ² may combine with each other to form a ring.

R ^{1, R 2} are each _{independently, C n H a F b (} n is an integer of 1 or more, a, b is an integer of 0 or more, satisfying the 2n + 1 = a + b. ) A is preferably. n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. b is preferably an integer of 1 or more, and a is preferably 0.

When R ¹ and R ² are bonded to each other to form a ring, C _n H _a F _b (n is an integer of 1 or more, a and b are integers of 0 or more, and satisfy 2n = a + b .). n is preferably an integer of 1 to 5, more preferably an integer of 2 to 4, and particularly preferably an integer of 2 to 3. b is preferably an integer of 1 or more, and a is preferably 0.

Preferably, R ¹ and R ² are both fluoroalkyl groups. Further, the number of fluorine contained in the fluoroalkyl group is preferably large. As described later, a special SEI film, that is, a film containing S and O may be formed on the electrode surface, but it is presumed that F may also be a component of the special SEI film. Therefore, when both R ¹ and R ² are fluoroalkyl groups or when the number of fluorines contained in the fluoroalkyl group is large, it is considered that the special SEI coating is easily formed on the electrode surface, It is considered that the effect derived from the coating increases.

Specifically, the metal salt for an electrode is (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ It is preferable to use one of CF ₂ SO ₂ ) NLi, (C ₂ H ₅ SO ₂ ) ₂ NLi, and (CH ₃ SO ₂ ) ₂ NLi alone or in combination of two or more.

More preferably, the metal salt for an electrode is (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, and (SO ₂ CF ₂ CF) ₂ CF ₂ SO ₂ ) NLi.

  The metal salt for an electrode may be blended in the positive electrode active material layer, and its method is not particularly limited. As an example, a metal salt for an electrode may be directly mixed into a positive electrode mixture as a material of the positive electrode active material layer when the positive electrode active material layer is manufactured. Alternatively, for example, the negative electrode active material layer may be composed of a plurality of layers, and a metal salt for an electrode may be directly mixed into one of the layers.

In the power storage device of the present invention, the distribution of the metal salt for an electrode in the positive electrode active material layer is not particularly limited, but at least the surface of the positive electrode active material layer, that is, the interface with the electrolytic solution in the positive electrode active material layer. It is preferable that the metal salt for an electrode is distributed in the portion.
That is, the metal salt for an electrode may be distributed over the entire positive electrode active material layer, or may be distributed on the surface of the positive electrode active material layer. However, in any case, the metal salt for an electrode is preferably present on the surface of the positive electrode active material layer at least before the positive electrode active material layer comes into contact with the electrolytic solution. This makes it easier for the metal salt for an electrode to come into contact with the electrolytic solution and to be easily eluted into the electrolytic solution. Therefore, the effect of blending the electrode metal salt in the positive electrode active material layer, such as the effect as a Li conductor at the interface between the electrolyte and the positive electrode active material as described above, and the effect as a part of the SEI film, are obtained. It is thought that it will be easier to demonstrate. It is more preferable that the metal salt for an electrode is distributed near the surface of the positive electrode active material on the surface. Since the above-mentioned SEI film is formed on the surface of the positive electrode active material, the metal salt for an electrode is distributed in this manner, so that the metal salt for an electrode and its decomposition product are easily supplied to the SEI film. Similarly, regarding the effect as the Li conductor described above, at least in the stage before contact with the electrolytic solution, the metal salt for an electrode is distributed near the surface of the positive electrode active material, and the effect is easily exerted. Conceivable.

  Before the positive electrode active material layer comes into contact with the electrolytic solution, the metal salt for an electrode preferably covers the surface of the positive electrode active material uniformly or substantially uniformly. This is because various effects of the above-described metal salt for electrodes are sufficiently exhibited. In addition, it is more preferable that at least a part of the metal salt for an electrode remains on the surface of the positive electrode active material even after the positive electrode active material layer comes into contact with the electrolytic solution.

Note that the metal salt for an electrode mixed in the positive electrode active material layer may not only constitute a part of the SEI coating as described above, but also take other forms. For example, it is conceivable that a part of the metal salt for the electrode does not elute in the electrolyte solution but remains on the surface of the positive electrode active material as it is, and another part of the metal salt for the electrode elutes in the electrolyte solution. It is also conceivable to function as a supporting salt. It is presumed that the metal salt for an electrode which is not eluted in the electrolytic solution and exists on the surface of the positive electrode active material also has a function as a Li conductor and a function as an electronic insulator like the SEI coating.

  The positive electrode and the power storage device of the present invention may include the metal salt for an electrode in the positive electrode active material layer, and even if the amount of the metal salt for the electrode contained in the positive electrode active material layer is small, the effect is exhibited. Therefore, in the present invention, the amount of the metal salt for an electrode is not particularly limited, but the concentration of the metal salt for an electrode in the positive electrode active material layer is preferably more than 0% by mass and 15% by mass or less, and 0.1% by mass or less. The content is more preferably from 10% by mass to 10% by mass, more preferably from 0.3% by mass to 8% by mass, and still more preferably from 0.5% by mass to 5% by mass.

(Positive electrode for power storage device)
The positive electrode for a power storage device of the present invention has a positive electrode active material layer. The positive electrode active material layer includes the positive electrode active material and is provided on the current collector.

As the positive electrode active material, those capable of inserting and extracting charge carriers can be used. For example, if the charge carrier in the power storage device of the present invention is lithium ions, the positive electrode active material only needs to be able to occlude and release lithium ions.
The positive electrode active material layer contains a positive electrode active material and, if necessary, a binder and / or a conductive auxiliary.

As the positive electrode active material, a layered compound _{Li a Ni b Co c Mn d} D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, Cr, At least one element selected from Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W and La, 1.7 ≦ f ≦ 2.1), and Li ₂ MnO ₃ . As the positive electrode active material, a metal oxide having a spinel structure such as LiMn ₂ O ₄ or a solid solution composed of a mixture of a metal oxide having a spinel structure and a layered compound, LiMPO ₄ , LiMVO _4, or Li ₂ MSiO ₄ (formula Wherein M is selected from at least one of Co, Ni, Mn, and Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any of the metal oxides used as the positive electrode active material may have the above composition formula as the basic composition, and those obtained by replacing the metal element contained in the basic composition with another metal element can also be used. In addition, as the positive electrode active material, a material that does not include a charge carrier (for example, lithium ions that contribute to charge and discharge) may be used. For example, elemental sulfur (S), a compound obtained by combining sulfur and carbon, metal sulfides such as TiS ₂ , oxides such as V ₂ O ₅ and MnO ₂ , polyaniline and anthraquinone, and compounds containing these aromatics in the chemical structure Conjugated materials such as conjugated diacetate-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, and phenoxyl may be employed as the positive electrode active material. When a positive electrode active material containing no charge carrier such as lithium is used, it is necessary to add the charge carrier to the positive electrode and / or the negative electrode in advance by a known method. The charge carrier may be added in an ionic state or in a non-ionic state such as a metal. For example, when the charge carrier is lithium, the lithium foil may be integrated by attaching a lithium foil to the positive electrode and / or the negative electrode.

Specific examples of the positive electrode active material include LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , and LiNi _1/3 Co ₁ having a layered rock salt structure. _{3 Mn 1/3 O 2, LiNi 0.5} Mn 0.5 O 2, LiNi 0.75 Co 0.1 Mn 0.15 O 2, LiMnO 2, LiNiO 2, and LiCoO ₂ can be exemplified. As another specific positive electrode active material _can be exemplified by Li ₂ MnO 3 -LiCoO _2.

Specific positive electrode active _{material, Li x A y Mn 2-} y O 4 (A spinel structure, Ca, Mg, S, Si , Na, K, Al, P, Ga, at least one selected from Ge Element and at least one metal element selected from transition metal elements, 0 <x ≦ 2.2, 0 ≦ y ≦ 1). More specifically, LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ can be exemplified.

Specific other positive electrode active materials include LiFePO ₄ , Li ₂ FeSiO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F.

  In particular, a positive electrode active material that can be used in a so-called 3V class, 4V class, and 5V class, which can be used at an upper limit potential of 3 V or more and less than 6 V, is obtained by combining a positive electrode active material layer containing a metal salt for an electrode and a selective electrolytic solution described later. In this case, it can be particularly preferably used. Here, “upper limit electric potential of 3 V or more and less than 6 V” means that lithium ions are inserted and desorbed at a potential of 3 V or more and less than 6 V with respect to the lithium electric potential. It is considered that the power storage device of the present invention is preferable to be combined with a positive electrode active material having an upper potential of 4 V, which is regarded as a high potential, in the middle to 5 V class.

As the positive electrode active materials of 3V class to 5V class, specifically, LiNi _0.5 Co _0.3 Mn _0.2 O ₂ and LiNi _0.5 Co _0.2 listed as the positive electrode active materials of the layered rock salt structure Mn _0.3 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.75 Co _0.1 Mn _0.15 O ₂ , LiMnO ₂ , LiNiO ₂ , LiCoO ₂ and Li ₂ MnO ₃ —LiCoO ₂ , LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ listed as positive electrode active materials having a spinel structure, and LiFePO ₄ listed as other positive electrode active materials And Li ₂ MnSiO ₄ . As the high-potential positive electrode active material, those having the above-described spinel structure are preferably used, and in particular, LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ are mentioned.

The following reason is presumed as the reason that the power storage device of the present invention can be used even at a high potential.
It is considered that by adding the metal salt for the electrode to the positive electrode active material layer, the salt concentration near the positive electrode active material increases or SEI is formed on the positive electrode. In these cases, it is considered that the oxidation resistance of the positive electrode is improved and, consequently, the life of the positive electrode is improved. Therefore, the positive electrode of the present invention in which the metal salt for an electrode is added to the positive electrode active material layer has the above-described high potential positive electrode active property. It is considered to withstand use as a high potential positive electrode containing a substance.

  Note that the SEI coating prevents Li from entering and exiting the positive electrode active material, and may be a factor of reaction resistance. However, it is presumed that when the components derived from the metal salt for electrodes typified by S and O are included in the SEI coating, the above-described reaction resistance derived from the SEI coating is reduced and the input / output characteristics of the power storage device are improved. You.

  As described above, the positive electrode active material layer contains a binder and / or a conductive additive as necessary, in addition to the positive electrode active material.

  The binder serves to anchor the positive electrode active material and, if necessary, the conductive auxiliary agent to the surface of a current collector described later.

  Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, fluororesins such as fluororubber, thermoplastic resins such as polypropylene and polyethylene, aqueous binders such as carboxymethylcellulose and polyacrylic acid, polyimide, polyamideimide and the like. Any known resin such as an imide-based resin, an alkoxysilyl group-containing resin, and styrene-butadiene rubber may be used.

  The compounding ratio of the binder in the positive electrode active material layer is preferably from 1: 0.005 to 1: 0.3 by mass ratio, that is, positive electrode active material: binder. If the amount of the binder is too small, the moldability of the electrode is reduced, and if the amount of the binder is too large, the energy density of the electrode is reduced.

  The conductive additive is added to increase the conductivity of the electrode. Therefore, the conductive assistant may be arbitrarily added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive assistant may be any chemically inert electronic high conductor, and may be carbon fine particles such as carbon black, graphite, acetylene black, Ketjen Black (registered trademark), and vapor grown carbon fiber (Vapor Carbon Carbon). Fiber: VGCF) and various metal particles. These conductive assistants can be used alone or in combination of two or more. It is preferable that the mixing ratio of the conductive auxiliary in the positive electrode active material layer is positive electrode active material: conductive auxiliary = 1: 0.01 to 1: 0.5 by mass ratio. If the amount of the conductive auxiliary agent is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary agent is too large, the moldability of the positive electrode active material layer deteriorates and the energy density of the electrode decreases.

The positive electrode active material layer is provided on the current collector.
The current collector refers to a chemically inert high-electron conductor for continuously supplying current to the electrodes while the power storage device is discharging or charging. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel A metal material can be exemplified. The current collector may be covered with a known protective layer. A current collector whose surface is treated by a known method may be used as the current collector.

  In particular, when the positive electrode is used at a high potential, for example, when the potential of the positive electrode is set to 4 V or more on the basis of lithium, it is preferable to use aluminum capable of withstanding the high potential as the current collector.

  Specifically, it is preferable to use a collector made of aluminum or an aluminum alloy as the positive electrode current collector. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is referred to as an aluminum alloy. Examples of the aluminum alloy include Al-Cu, Al-Mn, Al-Fe, Al-Si, Al-Mg, AL-Mg-Si, and Al-Zn-Mg.

  Specific examples of the aluminum or aluminum alloy include, for example, A1000-based alloys (pure aluminum-based) such as JIS A1085 and A1N30, A3000-based alloys (Al-Mn-based) such as JIS A3003 and A3004, and JIS A8079, A8021 and the like. A8000-based alloy (Al-Fe-based).

  The current collector may be covered with a known protective layer. A current collector whose surface is treated by a known method may be used as the current collector.

  The current collector may be in the form of a foil, a sheet, a film, a line, a bar, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of a foil, sheet, or film, the thickness is preferably in the range of 1 μm to 100 μm.

  In order to form an active material layer on the surface of the current collector, current collection is performed by using a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method. The active material may be applied to the surface of the body. Specifically, a composition for forming an active material layer containing an active material and, if necessary, a binder and a conductive auxiliary is prepared, and an appropriate solvent is added to the composition to form a paste, and then the composition is collected. After coating on the surface of the conductor, it is dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried product may be compressed to increase the electrode density.

(Negative electrode)
The power storage device of the present invention includes a negative electrode in addition to the above-described positive electrode. The negative electrode has a negative electrode active material layer. The negative electrode active material layer contains the negative electrode active material and is provided on the current collector similarly to the positive electrode active material layer.

As the negative electrode active material, a material capable of occluding and releasing charge carriers such as lithium ions can be used, and there is no particular limitation as long as it is a simple substance, an alloy or a compound capable of occluding and releasing charge carriers.
For example, if the charge carrier is lithium ion, as the negative electrode active material, Li, carbon, silicon, germanium, a group 14 element such as tin, aluminum, a group 13 element such as indium, zinc, a group 12 element such as cadmium, antimony, Group 15 elements such as bismuth, alkaline earth metals such as magnesium and calcium, and group 11 elements such as silver and gold may be used alone. When silicon or the like is used for the negative electrode active material, one atom of silicon reacts with a plurality of lithium atoms, resulting in a high-capacity active material. However, there is a problem that the expansion and contraction of the volume accompanying the occlusion and release of lithium become remarkable. In order to reduce such a risk, it is also preferable to employ an alloy or compound in which a simple substance such as silicon is combined with another element such as a transition metal as the negative electrode active material. Examples of alloys or compounds, Ag-Sn alloy, Cu-Sn alloy, Co-Sn tin based materials such as alloys, carbon-based materials such as various graphite, _SiO x to disproportionation to silicon simple substance and silicon dioxide ( 0.3.ltoreq.x.ltoreq.1.6), a simple substance of silicon, or a composite of a combination of a silicon-based material and a carbon-based material. As the negative electrode active material, an oxide such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = Co , Ni, Cu) may be used. One or more of these materials can be used as the negative electrode active material. Among them, silicon-based materials and / or carbon-based materials are particularly preferably used.

Specific examples of the silicon-based material include SiO _x (0.3 ≦ x ≦ 1.6) disproportionated into two phases of a Si phase and a silicon oxide phase. The Si phase in SiO _x can occlude and release lithium ions, and changes in volume as the secondary battery is charged and discharged. The silicon oxide phase has a smaller volume change due to charge and discharge than the Si phase. That is, SiO _x as the negative electrode active material realizes a high capacity by the Si phase, and suppresses a volume change of the whole negative electrode active material by having the silicon oxide phase. If x is less than the lower limit, the ratio of Si becomes excessively large, so that the volume change during charging and discharging becomes too large, and the cycle characteristics of the secondary battery deteriorate. On the other hand, if x exceeds the upper limit, the Si ratio becomes too small and the energy density decreases. The range of x is more preferably 0.5 ≦ x ≦ 1.5, and even more preferably 0.7 ≦ x ≦ 1.2.
In the above-described SiO _x , it is considered that an alloying reaction occurs between lithium and silicon in the Si phase during charging and discharging of the lithium ion secondary battery. And it is thought that this alloying reaction contributes to the charge and discharge of the lithium ion secondary battery.

  The above-mentioned silicon-based material is preferably combined with a carbon-based material to form a negative electrode active material. Due to the composite, the structure of the silicon-based material is particularly stabilized, and the durability of the negative electrode is improved. The compounding may be performed by a known method. As the carbon-based material used for the composite, graphite, hard carbon, soft carbon, or the like may be used. The graphite may be natural graphite or artificial graphite. These carbon-based materials can also be used as a negative electrode active material.

  Among the carbon-based materials, graphite is preferably used as the negative electrode active material in the power storage device of the present invention. Specific examples of graphite as a negative electrode active material include graphite having a major axis / minor axis value of 1 to 5, preferably 1 to 3. Here, the major axis means the length of the longest part of the graphite particles. The minor axis means the length of the longest part in the direction orthogonal to the major axis. Spheroidal graphite and mesocarbon microbeads correspond to the graphite. Spheroidal graphite is a carbon material such as artificial graphite, natural graphite, easily graphitizable carbon, and non-graphitizable carbon, and has a spherical or almost spherical shape.

  Spheroidal graphite is obtained by pulverizing graphite with an impact-type pulverizer having relatively small crushing power to form flakes, and compressing and spheroidizing the flakes. Examples of the impact mill include a hammer mill and a pin mill. It is preferable that the above operation is performed by setting the outer peripheral linear velocity of the hammer or the pin of the mill to about 50 to 200 m / sec. It is preferable that the supply and discharge of graphite to and from the mill be performed in association with an air current such as air.

The graphite preferably has a BET specific surface area of 0.5 to 15 m ² / g. If the BET specific surface area is too large, a side reaction between graphite and the electrolyte may be accelerated, and if the BET specific surface area is too small, the reaction resistance of the graphite may increase.

  Among the various negative electrode active materials described above, a silicon-based material and a carbon-based material can be used at a relatively low potential, and thus are preferable as a negative electrode active material for a power storage device, particularly, a secondary battery. Among them, a carbon-based material is particularly preferable, and among them, graphite can be used at a low potential of 1 V or less in average potential, and thus is particularly preferable as a negative electrode active material for a power storage device of the present invention. Here, “the average potential is 1 V or less” means that lithium ions are occluded and released by the negative electrode at a potential of 1.0 V or less on average with respect to the lithium potential.

As the binder and the conductive additive for the negative electrode, those described for the positive electrode for a power storage device may be employed in the same mixing ratio.
The current collector of the negative electrode is not particularly limited as long as it is a metal capable of withstanding a voltage suitable for the active material to be used, and the same current collector as the positive electrode of the power storage device can be used.

  The current collector for the negative electrode can take various forms, such as a sheet, similarly to the current collector of the positive electrode for a power storage device. The preferred form and thickness of the current collector for the negative electrode are also the same as those of the current collector of the positive electrode for a power storage device described above.

(Electrolyte)
As the electrolytic solution, a solution containing an organic solvent and a metal salt dissolved in the organic solvent may be used. The metal salt in the electrolytic solution is also called a supporting salt or a supporting electrolyte, and as described above, may be the same as or different from the electrode metal salt.

  Organic solvents are also called non-aqueous solvents. As the organic solvent for the electrolytic solution, cyclic esters, chain esters, ethers and the like can be used. Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, vinylene carbonate, 2-methyl-gamma-butyrolactone, acetyl-gamma-butyrolactone, and gamma-valerolactone. Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, alkyl propionate, dialkyl malonate, and alkyl acetate. Examples of the ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of the hydrogen in the specific chemical structure of the solvent is substituted with fluorine may be used.

When the power storage device of the present invention is, for example, a lithium ion secondary battery, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ is used as the metal salt. Can be illustrated.
As the electrolytic solution, a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate, and a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO _{3 in a} proportion of 0.5 mol / L to 1.7 mol. / L can be exemplified.

By the way, an appropriate electrolyte is added to an electrolyte solution for a power storage device in an appropriate concentration range. For example, as described above, the electrolyte of the lithium ion secondary battery includes a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, or the like. , And the concentration of the lithium salt in the electrolyte is generally about 1 mol / L.

  The organic solvent used for the electrolyte is mixed with an organic solvent having a high relative dielectric constant and a high dipole moment such as ethylene carbonate or propylene carbonate at about 30% by volume or more in order to dissolve the electrolyte suitably. It is common.

Actually, JP-A-2013-149777 discloses a lithium ion secondary battery using a mixed organic solvent containing 33% by volume of ethylene carbonate and using an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L. Have been. In JP 2013-134922 A, a mixed organic solvent containing 66 vol% of ethylene carbonate and propylene carbonate is used, and an electrolytic solution containing (CF ₃ SO ₂ ) ₂ NLi at a concentration of 1 mol / L is used. Lithium ion secondary batteries have been disclosed.

  In addition, for the purpose of improving the performance of the secondary battery, studies on adding various additives to an electrolyte solution containing a lithium salt have been actively conducted.

For example, JP-A-2013-145724 discloses a method in which a mixed organic solvent containing 30% by volume of ethylene carbonate is used, and a specific additive is added in a small amount to an electrolyte solution containing LiPF ₆ at a concentration of 1 mol / L. An electrolyte is described, and a lithium ion secondary battery using the electrolyte is disclosed. JP 2013-137873 A also discloses an electrolysis in which a mixed organic solvent containing 30% by volume of ethylene carbonate is used, and a small amount of phenylglycidyl ether is added to an electrolyte containing LiPF ₆ at a concentration of 1 mol / L. And a lithium ion secondary battery using this electrolyte.
As described in JP-A-2013-149777, JP-A-2013-134922, JP-A-2013-145724, JP-A-2013-137873, etc., conventionally used in lithium ion secondary batteries. In the electrolytic solution, a mixed organic solvent containing at least about 30% by volume of an organic solvent having a high relative dielectric constant and a high dipole moment such as ethylene carbonate and propylene carbonate, and a lithium salt in a concentration of about 1 mol / L are used. Inclusion was a common technical knowledge. And, as described in these documents, it is general that attention is paid to an additive that is separate from the lithium salt in the study of improvement of the electrolytic solution.
In the power storage device of the present invention, a metal salt composed of a specific electrolyte and a hetero element-containing organic solvent including an organic solvent having a low relative dielectric constant and / or a low dipole moment may be used in combination as an electrolytic solution. it can. Further, focusing on the molar ratio between the organic solvent and the metal salt, the molar ratio can be set to a specific range. Such an electrolytic solution is a novel electrolytic solution that has never existed before, and when such a novel electrolytic solution is used in combination with the power storage device of the present invention, further improvement in the performance of the power storage device may be expected. Hereinafter, if necessary, a new electrolytic solution combining the above-mentioned "metal salt composed of a specific electrolyte and a hetero element-containing organic solvent containing only an organic solvent having a low dielectric constant and / or a low dipole moment" is used. It is called "selective electrolyte" to distinguish it from general electrolytes.

As the selective electrolyte, for example,
A specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5 D or less, or a hetero element-containing organic solvent containing the specific organic solvent,
A metal salt containing an alkali metal, an alkaline earth metal or aluminum as a cation and an anion having a chemical structure represented by the following general formula (2) can be selected.
(R ³ X ¹ ) (R ⁴ SO ₂ ) N: General formula (2)
(R ³ is hydrogen, halogen, an alkyl group optionally substituted with a substituent, a cycloalkyl group optionally substituted with a substituent, an unsaturated alkyl group optionally substituted with a substituent, An unsaturated cycloalkyl group which may be substituted with a substituent, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, and an alkoxy group which may be substituted with a substituent Selected from an unsaturated alkoxy group optionally substituted with a substituent, a thioalkoxy group optionally substituted with a substituent, an unsaturated thioalkoxy group optionally substituted with a substituent, CN, SCN, and OCN. Is done.
R ⁴ is hydrogen, halogen, an alkyl group optionally substituted with a substituent, a cycloalkyl group optionally substituted with a substituent, an unsaturated alkyl group optionally substituted with a substituent, or a substituent. An unsaturated cycloalkyl group which may be substituted, an aromatic group which may be substituted with a substituent, a heterocyclic group which may be substituted with a substituent, an alkoxy group which may be substituted with a substituent, Selected from an unsaturated alkoxy group optionally substituted with a substituent, a thioalkoxy group optionally substituted with a substituent, an unsaturated thioalkoxy group optionally substituted with a substituent, CN, SCN, and OCN. You.
Further, R ³ and R ⁴ may combine with each other to form a ring.
X ¹ is selected from SO ₂ , C = O, C = S, R ^a P = O, R ^b P = S, S = O, and Si = O.
R ^a and R ^b are each independently hydrogen, halogen, an alkyl group optionally substituted with a substituent, a cycloalkyl group optionally substituted with a substituent, or a non-alkyl group optionally substituted with a substituent. Saturated alkyl group, unsaturated cycloalkyl group optionally substituted with a substituent, aromatic group optionally substituted with a substituent, heterocyclic group optionally substituted with a substituent, substituted with a substituent An optionally substituted alkoxy group, an unsaturated alkoxy group optionally substituted with a substituent, a thioalkoxy group optionally substituted with a substituent, an unsaturated thioalkoxy group optionally substituted with a substituent, OH , SH, CN, SCN, OCN.
In addition, R ^a and R ^b may combine with R ³ or R ⁴ to form a ring. )

  Examples of the cation of the metal salt include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, calcium, strontium, and barium; and aluminum. The cation of the metal salt is preferably the same metal ion as the charge carrier of the battery using the electrolyte. By the way, in the power storage device of the present invention, the electrode active material layer contains a metal salt for an electrode. Lithium derived from the metal salt for an electrode can function as a charge carrier. Therefore, it is preferable to select lithium as the cation of the metal salt of the electrolytic solution.

  The wording "may be substituted with a substituent" in the chemical structure represented by the general formula (2) will be described. For example, if "an alkyl group optionally substituted with a substituent", an alkyl group in which one or more of the hydrogens of the alkyl group is substituted with a substituent, or an alkyl group having no particular substituent Means

  Examples of the substituent in the phrase "may be substituted with a substituent" include an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, halogen, OH , SH, CN, SCN, OCN, nitro group, alkoxy group, unsaturated alkoxy group, amino group, alkylamino group, dialkylamino group, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, Acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonylamino group, sulfamoyl group, carbamoyl group, alkylthio group, arylthio group, sulfonyl group, sulfinyl group, ureido group, phosphoric amide group, sulfo group, carboxyl group, Hydroxamic acid group, Rufino group, a hydrazino group, an imino group, and a silyl group. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different.

  The chemical structure of the anion of the metal salt is preferably a chemical structure represented by the following general formula (2-1).

(R ³¹ X ² ) (R ⁴¹ SO ₂ ) N General formula (2-1)
^{(R 31, R 41} are each _{independently C n H a F b Cl c} Br d I e (CN) f (SCN) g (OCN) h.
n, a, b, c, d, e, f, g, and h are each independently an integer of 0 or more and satisfy 2n + 1 = a + b + c + d + e + f + g + h.
R ³¹ and R ⁴¹ may be bonded to each other to form a ring, and in this case, 2n = a + b + c + d + e + f + g + h is satisfied.
X ^{2 _{is, SO 2, C = O,}} C = S, R c P = O, R d P = S, S = O, is selected from Si = O.
R ^c and R ^d each independently represent hydrogen, halogen, an alkyl group optionally substituted with a substituent, a cycloalkyl group optionally substituted with a substituent, or a cycloalkyl group optionally substituted with a substituent. Saturated alkyl group, unsaturated cycloalkyl group optionally substituted with a substituent, aromatic group optionally substituted with a substituent, heterocyclic group optionally substituted with a substituent, substituted with a substituent An optionally substituted alkoxy group, an unsaturated alkoxy group optionally substituted with a substituent, a thioalkoxy group optionally substituted with a substituent, an unsaturated thioalkoxy group optionally substituted with a substituent, OH , SH, CN, SCN, OCN.
R ^c and R ^d may combine with R ³¹ or R ⁴¹ to form a ring. )

  In the chemical structure represented by the general formula (2-1), the meaning of the phrase “may be substituted with a substituent” has the same meaning as that described in the general formula (2).

In the chemical structure represented by the general formula (2-1), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. In the case where R ³¹ and R ^{41 in the} chemical structure represented by the general formula (2-1) form a ring by bonding, n is preferably an integer of 1 to 8, and 1 to 7 Is more preferable, and an integer of 1 to 3 is particularly preferable.

  The chemical structure of the metal salt anion is more preferably represented by the following general formula (2-2).

_{^{(R 32 SO 2) (R}} 42 SO 2) N ......... formula (2-2)
^{(R 32, R 42} are each _{independently C n H a F b Cl c} Br d I e.
n, a, b, c, d, and e are each independently an integer of 0 or more, and satisfy 2n + 1 = a + b + c + d + e.
R ³² and R ⁴² may be bonded to each other to form a ring, and in this case, 2n = a + b + c + d + e is satisfied. )

In the chemical structure represented by the general formula (2-2), n is preferably an integer of 0 to 6, more preferably an integer of 0 to 4, and particularly preferably an integer of 0 to 2. Incidentally, the chemical structure represented by the general formula ^{(2-2), when R 32} and ^{R 42} combine together to form a ring, n is preferably an integer of 1 to 8, 1 to 7 Is more preferable, and an integer of 1 to 3 is particularly preferable.

  In the chemical structure represented by the general formula (2-2), those in which a, c, d, and e are 0 are preferable.

The metal salts include (CF ₃ SO ₂ ) ₂ NLi (hereinafter sometimes referred to as “LiTFSA”), (FSO ₂ ) ₂ NLi (hereinafter sometimes referred to as “LiFSA”), and (C ₂ F ₅ SO). ₂ ) ₂ NLi, FSO ₂ (CF ₃ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi, FSO ₂ (CH ₃ SO ₂ ) NLi _{, FSO 2 (C 2 F 5} SO 2) NLi, or _{FSO 2 (C 2 H 5 SO} 2) NLi are particularly preferred.

  As the metal salt in the selective electrolytic solution, a combination of an appropriate number of the cations and anions described above may be used. One type of metal salt in the selective electrolyte may be used, or a plurality of types may be used in combination.

  In addition to the above-mentioned metal salts, other electrolytes that can be used for the electrolyte of the power storage device may be included in the selective electrolyte. The selective electrolytic solution preferably contains the metal salt in an amount of 50% by mass or more, more preferably 70% by mass or more, and preferably 90% by mass or more, based on the total electrolyte contained in the selective electrolytic solution. More preferably, it is performed.

  The selective electrolyte includes a hetero element-containing organic solvent, and the hetero element-containing organic solvent includes a specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5 D or less. The organic solvent containing a hetero element may be any organic solvent that can be used for an electrolyte of a power storage device as long as it contains a hetero element. The specific organic solvent may be a hetero element-containing organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5 D or less.

  Since the hetero element-containing organic solvent or the specific organic solvent has a hetero element, the metal salt can be suitably dissolved at a certain concentration. On the other hand, an organic solvent composed of a hydrocarbon having no hetero element cannot dissolve the metal salt suitably.

As the hetero element-containing organic solvent or the specific organic solvent, an organic solvent in which the hetero element is at least one selected from nitrogen, oxygen, sulfur, and halogen is preferable, and an organic solvent in which the hetero element is oxygen is more preferable. In addition, as the hetero element-containing organic solvent or the specific organic solvent, an aprotic solvent having no proton donating group such as an NH group, an NH ₂ group, an OH group, and an SH group is preferable.

  Specific examples of the hetero element-containing organic solvent include nitriles such as acetonitrile, propionitrile, acrylonitrile, malononitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 1,3-dioxane, 1,4-dioxane, 2,2-dimethyl-1,3-dioxolan, 2-methyltetrahydropyran, 2-methyltetrahydrofuran, ethers such as crown ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, Carbonates such as diethyl carbonate and ethyl methyl carbonate; amides such as formamide, N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone; isopropyl isocyanate; Isocyanates such as pyrisocyanate and chloromethyl isocyanate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl formate, ethyl formate, vinyl acetate, esters such as methyl acrylate and methyl methacrylate, glycidyl methyl ether, epoxy butane, Epoxys such as 2-ethyloxirane, oxazoles such as oxazole, 2-ethyloxazole, oxazoline and 2-methyl-2-oxazoline; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; acetic anhydride and propionic anhydride; Acid anhydrides, sulfones such as dimethyl sulfone and sulfolane, sulfoxides such as dimethyl sulfoxide, nitros such as 1-nitropropane and 2-nitropropane, and furans such as furan and furfural. , Cyclic esters such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, aromatic heterocycles such as thiophene and pyridine, tetrahydro-4-pyrone, 1-methylpyrrolidine, N-methylmorpholine and the like And phosphoric esters such as trimethyl phosphate and triethyl phosphate.

  The specific organic solvent is compared with a hetero element-containing organic solvent having a relative dielectric constant of more than 10 and / or a dipole moment of more than 5D (hereinafter, may be referred to as “other hetero organic solvent”) other than the specific organic solvent. And the polarity is low. Therefore, it is considered that the affinity between the specific organic solvent and the metal ion is inferior to the affinity between the other hetero organic solvent and the metal ion. Then, when the selective electrolyte is used as the electrolyte of the secondary battery, it can be said that it is difficult to dissolve the aluminum and the transition metal constituting the electrode of the secondary battery as ions in the selective electrolyte.

  Here, in a secondary battery using a general electrolytic solution, aluminum and a transition metal constituting the positive electrode are in a highly oxidized state particularly under a high-voltage charging environment, and are dissolved in the electrolytic solution as metal ions as cations. The metal ions eluted into the electrolyte are attracted to the electron-rich negative electrode due to electrostatic attraction, and are reduced by being combined with electrons on the negative electrode, and may be precipitated as a metal. It is known. It is known that when such a reaction occurs, the capacity of the positive electrode may decrease, the decomposition of the electrolyte on the negative electrode may occur, and the battery performance may decrease. However, since the selective electrolyte has the features described in the preceding paragraph, the use of the selective electrolyte in the power storage device of the present invention can suppress the elution of metal ions from the positive electrode and the deposition of metal on the negative electrode. That is, according to the power storage device of the present invention using the selective electrolyte, the battery characteristics are further improved.

  The relative dielectric constant of the specific organic solvent is preferably 10 or less, more preferably 7 or less, and still more preferably 5 or less. Although the lower limit of the relative dielectric constant of the specific organic solvent is not particularly limited, dare to say, one or more, two or more, and 2.5 or more can be exemplified.

  Further, the dipole moment of the specific organic solvent is preferably 5D or less, more preferably 2.5D or less, further preferably 1D or less. The lower limit of the dipole moment of the specific organic solvent is not particularly limited, but if it dares to be described, it can be 0.05 D or more, 0.1 D or more, 0.2 D or more.

  The specific organic solvent preferably contains carbonate in its chemical structure. More preferred specific organic solvents include chain carbonates represented by the following general formula (3).

R ⁵ OCOOR ⁶ General formula (3)
^(R 5, ^{R 6} are each independently a linear alkyl _{C n H a F b Cl c} Br d I e, _{or, C m H f F g Cl} h Br i contains a cyclic alkyl in the chemical structure _j is selected from any of the following: n is an integer of 1 or more, m is an integer of 3 or more, a, b, c, d, e, f, g, h, i, and j are each independently an integer of 0 or more. 2n + 1 = a + b + c + d + e, and 2m = f + g + h + i + j.)

  In the chain carbonate represented by the general formula (3), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

  Among the chain carbonates represented by the general formula (3), those represented by the following general formula (3-1) are particularly preferable.

R ⁵¹ OCOOR ⁶¹ General formula (3-1)
^{(R 51, R 61} are each independently a linear alkyl _C n _H a _{F b,} or, .n are selected from any of _C m _H f _{F g} including cyclic alkyl chemical structure 1 The above integer, m is an integer of 3 or more, a, b, f, and g are each independently an integer of 0 or more, satisfying 2n + 1 = a + b and 2m = f + g.)

  In the chain carbonate represented by the general formula (3-1), n is preferably an integer of 1 to 6, more preferably an integer of 1 to 4, and particularly preferably an integer of 1 to 2. m is preferably an integer of 3 to 8, more preferably an integer of 4 to 7, and particularly preferably an integer of 5 to 6.

  Among the chain carbonates represented by the general formula (3-1), dimethyl carbonate (hereinafter may be referred to as “DMC”), diethyl carbonate (hereinafter may be referred to as “DEC”), and ethyl methyl. Carbonate (hereinafter may be referred to as "EMC"), fluoromethylmethyl carbonate, difluoromethylmethyl carbonate, trifluoromethylmethyl carbonate, bis (fluoromethyl) carbonate, bis (difluoro) methylcarbonate, bis (trifluoromethyl) Carbonate, fluoromethyldifluoromethylcarbonate, 2,2,2-trifluoroethylmethylcarbonate, pentafluoroethylmethylcarbonate, ethyltrifluoromethylcarbonate, bis (2,2,2-trifluoroethyl ) Carbonate is particularly preferred.

  Further, from the disclosure of the present specification, the hetero element-containing organic solvent containing a chain carbonate represented by the above general formula (3) can be obtained by using an alkali metal, an alkaline earth metal or aluminum as a cation, The selective electrolyte contained in the molar ratio of 3 to 5 with respect to the metal salt having the chemical structure represented by the formula as an anion can be grasped.

  In a selective electrolytic solution using a suitable specific organic solvent, the concentration of a metal salt exhibiting suitable ionic conductivity becomes relatively high. Furthermore, in the selective electrolytic solution using the chain carbonate represented by the above general formula (3) as the specific organic solvent, the ionic conductivity has little change with respect to a slight change in the metal salt concentration. It has the advantage of being excellent. Moreover, the chain carbonate represented by the general formula (3) has excellent stability against oxidation and reduction. In addition, the chain carbonate represented by the general formula (3) has many free rotatable bonds and a flexible chemical structure. Therefore, the selective electrolyte using the chain carbonate has a high concentration. Even when a metal salt is included, a remarkable increase in the viscosity is suppressed, and high ionic conductivity can be obtained.

  The specific organic solvent described above may be used alone for the electrolytic solution, or a plurality of them may be used in combination.

  For reference, Table 1 lists the relative dielectric constants and dipole moments of various organic solvents.

The ratio between the hetero element-containing organic solvent or the specific organic solvent and the metal salt in the selective electrolytic solution is not particularly limited. However, as described below, the molar ratio of the hetero element-containing organic solvent or the specific organic solvent is relative to the metal salt. It is preferably included in 1 to 8.
In addition, in this specification, it may be expressed as "a selective electrolytic solution contains a hetero element-containing organic solvent and the metal salt in a molar ratio of 1 to 8". The molar ratio referred to in the present specification is a value obtained by dividing the former by the latter, that is, (moles of the hetero element-containing organic solvent contained in the selective electrolytic solution) / (moles of the metal salt contained in the selective electrolytic solution) ). In a secondary battery using a selective electrolyte, the SEI film formed at the electrode / electrolyte interface is not mainly composed of a conventional organic solvent-derived component but contains a large amount of a metal salt-derived component having a low-resistance S = O structure. In addition, the reaction resistance is relatively small because of the high concentration of Li ions in the coating and the like. The meaning of the range of the above molar ratio 1 to 8 is a range in which the reaction resistance of the secondary battery is relatively small and a range in which the ionic conductivity of the electrolytic solution is suitable. If the molar ratio is 3 to 6, it can be said that the range is more preferable in consideration of the balance between the reaction resistance of the secondary battery, the ionic conductivity of the electrolytic solution, and the temperature characteristics thereof. In the electrolytic solution of the present invention, the molar ratio between the hetero element-containing organic solvent and the metal salt is preferably in the range of 1 to 8 as described above, and more preferably in the range of 2 to 6. , And more preferably in the range of 3 to 5.5. Further, it is more preferably in the range of 3.2 to 5.2, and most preferably in the range of 3.5 to 5. In the conventional electrolytic solution, the molar ratio between the hetero element-containing organic solvent and the electrolyte or metal salt is approximately about 10.

  In the selective electrolyte, it is presumed that the metal salt and the hetero element-containing organic solvent have an interaction. Microscopically, the selective electrolyte contains a stable cluster composed of a metal salt and a hetero element-containing organic solvent, formed by coordination bonding between the metal salt and the hetero element of the hetero element-containing organic solvent. It is estimated that

  It can be said that the selective electrolyte has a higher proportion of the metal salt than the conventional electrolyte. Then, it can be said that the selective electrolyte has a different environment in which the metal salt and the organic solvent exist as compared with the conventional electrolyte. Therefore, in a power storage device using a selective electrolyte, the improvement of the metal ion transport rate in the electrolyte, the improvement of the reaction rate at the interface between the electrode and the electrolyte, and the metal salt of the electrolyte occurring during high-rate charging and discharging of the secondary battery It can be expected that the uneven distribution of the concentration is reduced, the liquid retention of the electrolyte at the electrode interface is improved, and the so-called liquid withdrawal state where the electrolyte is insufficient at the electrode interface is suppressed. Furthermore, in the selective electrolyte, the vapor pressure of the organic solvent contained in the electrolyte decreases. As a result, volatilization of the organic solvent from the selective electrolyte can be reduced.

The density d (g / cm ³ ) of the selective electrolyte will be described. In addition, in this specification, density means the density at 20 degreeC. The density d (g / cm ³ ) of the selective electrolyte is preferably 1.0 ≦ d, more preferably 1.1 ≦ d.

For reference, Table 2 lists the densities (g / cm ³ ) of typical hetero element-containing organic solvents.

  Describing the viscosity η (mPa · s) of the selective electrolyte, the range of 3 <η <50 is preferable, the range of 4 <η <40 is more preferable, and the range of 5 <η <30 is more preferable.

  In addition, the higher the ion conductivity σ (mS / cm) of the electrolytic solution, the more easily ions move in the electrolytic solution. Therefore, such an electrolyte can be an excellent electrolyte for a battery. In terms of the ionic conductivity σ (mS / cm) of the selective electrolyte, it is preferable that 1 ≦ σ. If the ionic conductivity σ (mS / cm) of the selective electrolyte is arbitrarily set to a suitable range including the upper limit, a range of 2 ≦ σ <100 is preferable, a range of 3 ≦ σ <50 is more preferable, and a range of 4 ≦ σ <50 is more preferable. It is more preferable that ≦ σ <30.

  By the way, the selective electrolyte contains a metal salt cation at a high concentration. For this reason, the distance between adjacent cations in the selective electrolyte is extremely short. When cations such as lithium ions move between the positive electrode and the negative electrode during charge and discharge of the power storage device, cations closest to the destination electrode are first supplied to the electrode. Then, another cation adjacent to the cation moves to the place where the supplied cation was present. That is, in the selective electrolyte solution, it is expected that a domino-destroying phenomenon occurs in which adjacent cations change positions one by one toward the electrode to be supplied in order. Therefore, it is considered that the movement distance of the cation during charging and discharging is short, and the movement speed of the cation is correspondingly high. Then, due to this, the reaction speed of the power storage device including the selective electrolyte is considered to be high.

  The selective electrolytic solution may contain, besides the specific organic solvent, an organic solvent composed of a hydrocarbon having no other hetero organic solvent or hetero element as described above. The selective electrolytic solution preferably contains the specific organic solvent in an amount of 80% by volume or more, more preferably 90% by volume or more, and more preferably 95% by volume or more, based on the total solvent contained in the selective electrolytic solution. More preferably, it is performed. In addition, the selective electrolytic solution preferably contains the specific organic solvent in an amount of 80 mol% or more, more preferably 90 mol% or more, and more preferably 95 mol% or more based on the total solvent contained in the selective electrolyte solution. More preferably, it is included.

  As one embodiment of the selective electrolyte, the specific organic solvent having a relative dielectric constant of 10 or less and / or a dipole moment of 5 D or less is represented by the above general formula (2) using alkali metal, alkaline earth metal or aluminum as a cation. An electrolytic solution contained in a molar ratio of 3 to 5 with respect to a metal salt having a chemical structure as an anion.

  In addition, the selective electrolytic solution containing another hetero organic solvent in addition to the specific organic solvent, when compared with the selective electrolytic solution not containing other hetero organic solvent, when the viscosity increases or when the ionic conductivity decreases. is there. Further, a secondary battery using a selective electrolyte containing another hetero organic solvent in addition to the specific organic solvent may have an increased reaction resistance.

  In addition, a selective electrolytic solution containing an organic solvent composed of the above-mentioned hydrocarbons in addition to the specific organic solvent can be expected to have an effect of lowering the viscosity.

  Specific examples of the organic solvent comprising the hydrocarbon include benzene, toluene, ethylbenzene, o-xylene, m-xylene, p-xylene, 1-methylnaphthalene, hexane, heptane, and cyclohexane.

  Further, a flame-retardant solvent can be added to the selective electrolyte. By adding a flame-retardant solvent to the selective electrolyte, the safety of the selective electrolyte can be further increased. Examples of the flame-retardant solvent include halogen solvents such as carbon tetrachloride, tetrachloroethane and hydrofluoroether, and phosphoric acid derivatives such as trimethyl phosphate and triethyl phosphate.

  When the electrolyte is mixed with a polymer or an inorganic filler to form a mixture, the mixture encapsulates the electrolyte and becomes a quasi-solid electrolyte. By using the quasi-solid electrolyte as the electrolyte of the power storage device of the present invention, leakage of the electrolyte in the battery can be suppressed. In this case, the electrolytic solution may be the above-described selective electrolytic solution or another electrolytic solution.

  Further, known additives may be added to the electrolytic solution in the power storage device of the present invention without departing from the spirit of the present invention. Examples of known additives include cyclic carbonates having an unsaturated bond represented by vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC) and ethyl vinylene carbonate (EVC), fluoroethylene carbonate, Carbonate compounds such as trifluoropropylene carbonate, phenylethylene carbonate and erythritan carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid Acid anhydride, carboxylic acid anhydride represented by cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride, γ-butyrolactone, γ-valerolactone, γ- Prolactone, δ-valerolactone, lactone represented by δ-caprolactone and ε-caprolactone, cyclic ether represented by 1,4-dioxane, ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, Sulfur-containing compounds typified by methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone and tetramethylthiuram monosulfide, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone , 1,3-dimethyl-2-imidazolidinone and nitrogen-containing compounds represented by N-methylsuccinimide, phosphates represented by monofluorophosphate and difluorophosphate, heptane, octane and cycloheptane Typical saturated charcoal Hydrogen compounds, and unsaturated hydrocarbon compounds represented by biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran, and the like. .

  The selective electrolyte described above exhibits excellent ionic conductivity and is therefore suitably used as an electrolyte for a power storage device. In particular, it is preferably used as an electrolyte for a lithium ion secondary battery.

  Incidentally, it is generally known that a film is formed on the surfaces of a positive electrode and a negative electrode in a power storage device. The coating is also called SEI (Solid Electrolyte Interphase), and is made of a reduced decomposition product of an electrolytic solution or the like. For example, JP-A-2007-19027 describes an SEI coating.

  The SEI coating on the positive electrode surface and the negative electrode surface allows passage of charge carriers such as lithium ions. Further, for example, it is considered that the SEI coating on the negative electrode surface exists between the negative electrode surface and the electrolytic solution, and suppresses further reductive decomposition of the electrolytic solution. In particular, it is considered that the presence of an SEI film is essential for a low-potential negative electrode using graphite or a Si-based negative electrode active material.

  It is considered that if continuous decomposition of the electrolytic solution is suppressed by the presence of the SEI coating, the discharge characteristics of the power storage device after the lapse of the charge / discharge cycle can be improved. However, on the other hand, in conventional secondary batteries, the SEI coatings on the positive electrode surface and the negative electrode surface did not necessarily contribute to the improvement of battery characteristics.

In the power storage device of the present invention, the chemical structure of the general formula (1) representing the metal salt for an electrode contains SO ₂ . Further, also in the selective electrolyte solution, SO ₂ is contained in the chemical structure of the general formula (2) of the metal salt. When charging and discharging the power storage device of the present invention, at least a part of the metal salt for an electrode included in the electrode or a part of the metal salt included in the selective electrolyte is decomposed to form a positive electrode and / or a negative electrode. It is presumed that a special SEI film containing S and O is formed on the surface. The coating is presumed to have an S = O structure. Since the electrode is covered with the coating, deterioration of the electrode and the electrolytic solution is suppressed, and as a result, it is considered that the durability of the power storage device is improved. Furthermore, in the present invention, it is presumed that the presence of the metal salt for an electrode that can be a material of the coating in the positive electrode active material layer itself on which the coating is formed further increases the S and O concentrations of the coating. . As a result, it is presumed that the battery performance is further improved as compared with the case where the selective electrolyte is simply used.

  In addition, in the selective electrolyte, cations and anions are present closer to each other than in the conventional electrolyte, and the anions are reduced and decomposed compared to the conventional electrolyte by being strongly affected by the cations electrostatically. It will be easier. In a conventional power storage device using a conventional electrolytic solution, an SEI film is formed by a decomposition product generated by reductive decomposition of a cyclic carbonate such as ethylene carbonate contained in the electrolytic solution. However, as described above, in the selective electrolyte, the anion is easily reduced and decomposed, and the concentration of the anion in the electrolyte is high because the metal salt is contained at a higher concentration than the conventional electrolyte. For this reason, it is considered that the SEI coating formed on the electrode of the power storage device when the selective electrolyte is used, that is, the coating containing S and O described above contains a large amount derived from anions. In the power storage device of the present invention using the selective electrolyte, the SEI film can be formed without using a cyclic carbonate such as ethylene carbonate. Hereinafter, as necessary, the SEI film formed on the electrode of the power storage device when the selective electrolyte is used, that is, the film containing S and O described above may be referred to as “S and O-containing film”. .

By the way, in the power storage device of the present invention, the metal salt for an electrode is mixed in the electrode active material layer. As described above, this metal salt for an electrode contains SO ₂ , similarly to the metal salt blended in the selective electrolytic solution, and the surface of the positive electrode active material layer has the above-mentioned coating derived from the metal salt for an electrode. Can be formed. That is, the power storage device of the present invention can be said to have excellent durability even when the above-described selective electrolyte is not used.

  It is known that the SEI film in the negative electrode can be formed using a carbon-based active material containing graphite and a silicon-based active material containing simple silicon or a silicon-based material as the negative electrode active material. Therefore, in order to form the SEI coating derived from the above-described electrode metal salt on the negative electrode of the power storage device of the present invention and to impart the effect derived from the coating to the negative electrode of the power storage device of the present invention, the negative electrode active material It is considered preferable to use a carbon-based active material and / or a silicon-based active material.

In addition, cations of the metal salt for an electrode contained in the positive electrode active material layer can be eluted in the electrolytic solution in the power storage device of the present invention. Then, when the cation of the metal salt for an electrode is eluted, it is considered that the electrolyte in the vicinity of the positive electrode active material layer contains the cation at a higher concentration than the electrolyte in other regions. That is, in the electrolyte solution near the positive electrode active material layer, it is supposed that the movement speed of the cation is increased as in the above-described selective electrolyte solution. It is presumed that the reaction speed of the power storage device is improved due to this.
Further, it is considered that the cation can move into the inside of the negative electrode active material, and the cation transferred to the negative electrode active material contributes to the charge / discharge reaction similarly to the cation of the supporting salt transferred to the negative electrode active material by charge / discharge. It is presumed that it can be done. For example, if the power storage device is a lithium ion secondary battery, an increase in battery capacity can be expected. In addition, in the case of a lithium ion capacitor, it is estimated that the cation transferred to the negative electrode active material produces an effect as if the negative electrode active material was pre-doped, and as a result, a reduction in the potential of the negative electrode active material can be expected. That is, it is presumed that the addition of the metal salt for an electrode to the positive electrode active material layer imparts these various excellent battery characteristics to the power storage device of the present invention.

  The power storage device of the present invention includes the positive electrode, the negative electrode, and the electrolytic solution described above, and may have a separator interposed between the positive electrode and the negative electrode as necessary to form an electrode body.

  The separator separates the positive electrode and the negative electrode, and prevents lithium ions from passing therethrough while preventing current short circuit due to contact between the two electrodes. Known separators may be used as the separator, and synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, and polyacrylonitrile; polysaccharides such as cellulose and amylose; and fibroin. , Natural polymers such as keratin, lignin, suberin, and the like, porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as ceramics. Further, the separator may have a multilayer structure.

  The electrode body may be any of a stacked type in which a positive electrode, a separator, and a negative electrode are stacked, or a wound type in which a positive electrode, a separator, and a negative electrode are wound. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal communicating with the outside using a current collecting lead or the like, it is preferable to add an electrolytic solution to the electrode body to form a power storage device. . Further, the power storage device of the present invention only needs to perform charge and discharge in a voltage range suitable for the type of active material included in the electrode.

  The shape of the power storage device of the present invention is not particularly limited, and various shapes such as a cylindrical type, a square type, a coin type, and a laminate type can be adopted.

  The power storage device of the present invention may be mounted on a vehicle. As the power storage device of the present invention mounted on a vehicle, a lithium ion secondary battery is particularly preferable. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or a part of its power source, such as an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of the device on which the power storage device is mounted include various home appliances, office devices, and industrial devices driven by a battery, such as a personal computer and a portable communication device, in addition to the vehicle. Further, the power storage device of the present invention is a power storage device and a power smoothing device for wind power generation, solar power generation, hydroelectric power generation and other power systems, power supply sources for motive power of ships and the like and / or auxiliary equipment, aircraft, spacecraft, and the like. Power supply for motive power and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, power supply for electric vehicles It may be used for a power storage device that temporarily stores power required for charging at a charging station or the like.

  Although the embodiment of the power storage device of the present invention has been described above, the present invention is not limited to the above embodiment. The present invention can be implemented in various forms with modifications, improvements, and the like that can be made by those skilled in the art without departing from the gist of the present invention.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Note that the present invention is not limited by these examples. In the following, “parts” means parts by mass, and “%” means mass% unless otherwise specified.

(Example 1)
The lithium ion secondary battery of Example 1 was manufactured as follows.

90 parts by mass of a lithium-containing metal oxide having a layered rock salt structure represented by LiNi _5/10 Co _3/10 Mn _2/10 O _{2 as} a positive electrode active material, 8 parts by mass of acetylene black as a conductive additive, and binding 2 parts by mass of polyvinylidene fluoride as an agent were mixed. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a primary slurry. To this primary slurry, 3.09 parts by mass of (CF ₃ SO ₂ ) ₂ NLi as a metal salt for an electrode was added and mixed again to obtain a secondary slurry.
An aluminum foil having a thickness of 15 μm was prepared as a positive electrode current collector. The secondary slurry was applied to the surface of the aluminum foil using a doctor blade so as to form a film. The aluminum foil to which the secondary slurry was applied was dried at 80 ° C. for 20 minutes, and then pressed to obtain a bonded product. The obtained joint was dried by heating at 120 ° C. for 6 hours using a vacuum drier to obtain an aluminum foil on which a positive electrode active material layer was formed. This was used as the positive electrode of Example 1.
The positive electrode active material layer in the positive electrode of Example 1 is an electrode metal salt when the sum of the masses of the positive electrode active material, the conductive auxiliary agent, the binder, and the electrode metal salt is 100% by mass (CF ₃ SO ₂ ) ₂ NLi in an amount of 3% by mass.

  98 parts by mass of spherical graphite as a negative electrode active material, 1 part by mass of styrene butadiene rubber (SBR) as a binder and 1 part by mass of carboxymethyl cellulose (CMC) were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. A 10-μm-thick copper foil was prepared as a negative electrode current collector. The slurry was applied to the surface of the copper foil in the form of a film using a doctor blade. The copper foil to which the slurry was applied was dried to remove water, and then the copper foil was pressed to obtain a joined product. The obtained joint was dried by heating at 100 ° C. for 6 hours using a vacuum dryer to obtain a copper foil on which a negative electrode active material layer was formed. This was used as a negative electrode.

(FSO ₂ ) ₂ NLi as a supporting salt was dissolved in an organic solvent in which dimethyl carbonate, which is a specific organic solvent, and ethyl methyl carbonate, which is also a specific organic solvent, were added at a molar ratio of 9: 1. ₂ ) An electrolytic solution having a concentration of ₂ NLi of 2.6 mol / L was produced. This electrolytic solution is one type of a selective electrolytic solution, and the electrolytic solution contains 1 mol of a supporting salt with respect to 3.6 mol of an organic solvent.

A 20 μm-thick cellulose nonwoven fabric was prepared as a separator.
A separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. This electrode plate group was covered with a pair of laminated films, and after sealing three sides, the above-mentioned electrolyte solution was injected into the bag-shaped laminated film. Thereafter, by sealing the remaining one side, the four sides were hermetically sealed to obtain a lithium ion secondary battery in which the electrode group and the electrolyte were sealed. This battery was used as the lithium ion secondary battery of Example 1.

  The amount of the metal salt for an electrode and the composition of the electrolytic solution in the lithium ion secondary battery of Example 1 are shown in Table 3 described later. The same applies to Examples 2 to 4 and Comparative Examples 1 and 2 described later.

(Example 2)
The lithium ion secondary battery of Example 2 is the same as the lithium ion secondary battery of Example 1 except that the positive electrode active material layer contains 1% by mass of (CF ₃ SO ₂ ) ₂ NLi which is a metal salt for an electrode. Things.

(Example 3)
The lithium ion secondary battery of Example 3 is the same as the lithium ion secondary battery of Example 1 except for the electrolytic solution. The electrolyte used in the lithium ion secondary battery of Example 3 was manufactured as follows.
LiPF ₆ as a supporting salt was dissolved in an organic solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were added at a volume ratio of 3: 3: 4, and the concentration of LiPF ₆ was 1.0 mol / L. An electrolyte was produced. This electrolyte contains about 1 mol of the supporting salt per 10 mol of the organic solvent. Note that dimethyl carbonate and ethyl methyl carbonate used in Example 3 are specific organic solvents, and ethylene carbonate is another hetero organic solvent. The electrolyte used in Example 3 was not a selective electrolyte.

(Example 4)
The lithium ion secondary battery of Example 4 is the same as the lithium ion secondary battery of Example 3 except that the positive electrode active material layer contains 1% by mass of (CF ₃ SO ₂ ) ₂ NLi which is a metal salt for an electrode. Things.

(Comparative Example 1)
The lithium ion secondary battery of Comparative Example 1 is the same as the lithium ion secondary battery of Example 1, except that the negative electrode active material layer does not include a metal salt for an electrode.

(Comparative Example 2)
The lithium ion secondary battery of Comparative Example 2 is the same as the lithium ion secondary battery of Example 3 except that the negative electrode active material layer does not contain a metal salt for an electrode.

The meanings of the abbreviations in the following table are as follows.
LiFSA: (FSO ₂ ) ₂ NLi
LiTFSA: (CF ₃ SO ₂ ) ₂ NLi
DMC: dimethyl carbonate EMC: ethyl methyl carbonate EC: ethylene carbonate DMC: dimethyl carbonate

(Battery activation)
The lithium ion secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were first charged to 4.1 V (vs. Li reference) at 25 ° C. at a constant current of 0.1 C rate. The battery was discharged to 0 V (vs. Li reference).
After the first charge / discharge described above, charge / discharge was repeated 50 times at a constant current of 25 ° C. and a rate of 1 C in a range of 3.0 V to 4.1 V.

(Resistance evaluation test)
After the activation of the above-mentioned batteries, each lithium ion secondary battery was charged at 25 ° C. so that the SOC (state of charge) became 60%. The current capacity during charging of the lithium ion secondary battery from 3 V to 4.1 V was defined as SOC 100%. Thereafter, the AC impedance of each lithium ion secondary battery was measured at -10C. The arc-shaped component drawn by the plot corresponding to the frequency of 0.1 to 1000 Hz in the complex plane plot was measured as the reaction resistance. Table 4 shows the reaction resistance of the positive electrodes of Example 2 and Comparative Example 1.

  As shown in Table 4, the lithium ion secondary battery of Example 2 including the metal salt for the electrode in the positive electrode had a positive electrode reaction compared to the lithium ion secondary battery of Comparative Example 1 including no metal salt for the electrode in the positive electrode. The resistance has dropped. From this result, it is found that the positive electrode active material layer contains the metal salt for an electrode, so that the positive electrode reaction resistance of the power storage device is reduced, and that even if the amount of the metal salt for an electrode mixed in the positive electrode is 1% by mass, It shows that it is effective. That is, from the resistance evaluation test shown in Table 4, it can be seen that the cathode reaction resistance is reduced when the electrode metal salt is added to the cathode active material layer even in a trace amount. That is, from the viewpoint of reducing the positive electrode reaction resistance, the amount of the metal salt for an electrode in the positive electrode active material layer may be more than 0% by mass. The amount of the metal salt for an electrode is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 1% by mass or more as in Examples 1 and 4. It is preferable.

(Cycle characteristic evaluation test)
After the activation of the above-described batteries, the lithium ion secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were charged and discharged between 3.0 V and 4.2 V at a constant current of 25 ° C. and 1 C rate. Was repeated for 200 cycles. Then, based on the discharge capacity at the first cycle and the discharge capacity at the 200th cycle, the capacity retention ratio of each lithium ion secondary battery was calculated. Specifically, the capacity retention ratio (%) was calculated by (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100. Table 4 shows the results of the cycle characteristic evaluation test.

As shown in Table 4, when the positive electrode active material layer contains the metal salt for an electrode, regardless of the type and concentration of the electrolytic solution and the charge carrier, the improvement of the capacity retention rate of the lithium ion secondary battery, It can be seen that the cycle durability of the ion secondary battery is improved.
In addition, the results show that the higher the content of the metal salt for the electrode in the positive electrode active material layer, the higher the capacity retention ratio of the lithium ion secondary battery and the cycle durability regardless of the type of the electrolyte and the charge carrier and their concentrations. You can see that it is excellent.
Further, when comparing Examples 1 and 2 with Examples 3 and 4, the lithium ion secondary batteries of Examples 1 and 2 using the selective electrolyte are the same as those of Examples 3 and 4 using no selective electrolyte. The capacity retention rate was higher than that of the lithium ion secondary battery. From these results, it can be said that the power storage device of the present invention using the positive electrode of the present invention and the selective electrolyte solution together has a higher capacity retention ratio and excellent cycle durability.

  In consideration of the results shown in Table 4, the concentration of the metal salt for an electrode in the positive electrode active material layer exceeds 0% by mass to achieve both a reduction in the positive electrode reaction resistance and an improvement in cycle durability. % By mass or less, more preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 8% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. It is considered that it is more preferable that the content is not more than mass%.

(Dissolution evaluation test)
With respect to the lithium ion secondary batteries of Example 2 and Example 4 after the above-described cycle characteristic evaluation test, the concentration of the metal salt for an electrode eluted in the electrolytic solution was measured.
First, after the cycle characteristic evaluation test, that is, after 200 cycles, the lithium ion secondary batteries of Examples 2 and 4 were disassembled, and the electrolyte of each lithium ion secondary battery was recovered.

Difluorobenzene was used as an internal standard, and propylene carbonate was used as a diluting solvent. Propylene carbonate was added to 60 μl of difluorobenzene to obtain a 5 ml internal standard mixture. Next, the internal standard mixture was added to and mixed with 40 μl of the above-mentioned electrolytic solution to obtain a 300 μl analysis sample.
This analysis sample was subjected to NMR analysis to obtain a fluorine signal. The concentration of LiTFSA eluted in the electrolytic solution was calculated from the intensity ratio of the signal derived from LiTFSA as a metal salt for an electrode and the signal derived from difluorobenzene as an internal standard. Table 5 shows the results.

The amount of LiTFSA in the positive electrode of the lithium ion secondary battery of Example 2 was the same as the amount of LiTFSA in the positive electrode of the lithium ion secondary battery of Example 4. However, as shown in Table 5, the LiTFSA concentration of the electrolyte was lower in the lithium ion secondary battery of Example 2 than in the lithium ion secondary battery of Example 4. That is, in the lithium ion secondary battery of Example 2, elution of LiTFSA into the electrolytic solution was suppressed more than in the lithium ion secondary battery of Example 4.
The difference between the lithium ion secondary battery of Example 2 and the lithium ion secondary battery of Example 4 is only the electrolytic solution, and the above result is considered to be due to the difference in the electrolytic solution. That is, the electrolytic solution used in the lithium ion secondary battery of Example 2 is a selective electrolytic solution, which contains an organic solvent having a low relative dielectric constant as a main component and has a high concentration of a supporting salt. It is considered that the use of such a selective electrolytic solution suppressed the elution of LiTFSA into the electrolytic solution. That is, according to the power storage device of the present invention in which the selective electrolytic solution and the positive electrode of the present invention are combined, elution of the metal salt for an electrode such as LiTFSA into the electrolytic solution is suppressed, the reaction resistance of the positive electrode is reduced, and the durability of the power storage device is deteriorated. It is considered that the effect of the present invention such as suppression can be more suitably obtained.

Claims (3)

(CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (SO ₂ CF ₂ CF ₂ SO ₂ ) NLi, and (SO ₂ CF ₂ CF ₂ CF ₂ SO ₂ ) NLi A positive electrode for a lithium ion secondary battery having a positive electrode active material layer containing at least one metal salt , a negative electrode, and an electrolytic solution,
The electrolyte solution ,
90% by mass or more of (FSO ₂ ) ₂ NLi with respect to the total electrolyte contained in the electrolytic solution ;
A hetero element-containing organic solvent containing a specific organic solvent containing a hetero element and having a relative dielectric constant of 10 or less and / or containing a hetero element and having a dipole moment of 5 D or less, at 80% by volume or more or 80 mol% or more; Containing
A lithium ion secondary battery including the specific organic solvent or the hetero element-containing organic solvent in a molar ratio of 3 to 6 with respect to the (FSO ₂ ) ₂ NLi . The lithium ion secondary battery according to claim 1 , wherein the specific organic solvent is at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. 3. The lithium ion secondary battery according to claim 1 , wherein the positive electrode active material layer includes a positive electrode active material having an upper limit potential of 3 V or more and less than 6 V. 4.