JP7021466B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery.

Generally, a lithium ion secondary battery includes a positive electrode, a negative electrode and an electrolytic solution as main components. Then, an appropriate electrolyte is added to the electrolytic solution in an appropriate concentration range. For example, lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, and (CF ₃ SO ₂ ) ₂ NLi are added to the electrolyte of a lithium ion secondary battery as an electrolyte. Here, the concentration of the lithium salt in the electrolytic solution is generally set to about 1 mol / L.

Further, as the organic solvent used in the electrolytic solution, an organic solvent having a high relative permittivity such as ethylene carbonate or propylene carbonate and a high dipole moment is mixed at about 30% by volume or more in order to suitably dissolve the electrolyte. Is common.

Further, as reported in many documents, it is common to use a metal foil made of aluminum for the current collector in the positive electrode of the lithium ion secondary battery.

Actually, in Patent Document 1, a mixed organic solvent containing 33% by volume of ethylene carbonate, an electrolytic solution containing LiPF ₆ at a concentration of 1 mol / L, and a positive electrode using a positive electrode current collector foil made of aluminum are used. A lithium ion secondary battery comprising the above is disclosed.

Recently, Patent Document 2 reports an electrolytic solution containing a metal salt as an electrolyte at a high concentration and a lithium ion secondary battery provided with the electrolytic solution, and the electrolytic solution is compared with a low-concentration electrolytic solution. It has also been reported that corrosion of aluminum can be suitably suppressed (see Example A, Comparative Example A, Evaluation Example A, etc.).

Further, the lithium ion secondary battery is provided on a positive electrode plate provided with a positive electrode current collector foil and a positive electrode active material layer formed on the surface of the positive electrode current collector foil, and on the surfaces of the negative electrode current collector foil and the negative electrode current collector foil. A negative electrode plate provided with the formed negative electrode active material layer and a separator are provided, and the positive electrode plate and the negative electrode plate are generally facing each other with the separator interposed therebetween, and further, the positive electrode current collector foil. In general, the uncoated portion of the positive electrode on which the positive electrode active material layer is not formed and the end portion of the negative electrode active material layer face each other.
Lithium ions tend to concentrate at the ends of the negative electrode active material layer, and although there is a concern that metallic lithium may precipitate due to the concentration of lithium ions, the uncoated part of the positive electrode that does not have lithium ions that can be released. By setting the end of the negative electrode active material layer to face each other, it is possible to suppress the concentration of lithium ions on the end of the negative electrode active material layer and suppress the precipitation of metallic lithium. be.

Japanese Unexamined Patent Publication No. 2013-149477 International Publication No. 2016/063468

The present inventor has actually manufactured a lithium ion secondary battery including a positive electrode provided with a positive electrode current collector foil made of aluminum and an electrolytic solution containing (FSO ₂ ) ₂ NLi at a concentration of 2.4 mol / L. As a result of a charge / discharge test, aluminum was eluted from the positive electrode current collector foil of the lithium ion secondary battery and the negative electrode was subjected to charging / discharging at a potential at which it was assumed that aluminum corrosion would not occur. The phenomenon of depositing on top was confirmed. Therefore, the present inventor recognized that there is room for improvement in the point of aluminum elution from the aluminum positive electrode current collector foil.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a lithium ion secondary battery in which aluminum elution from a positive electrode current collector foil made of aluminum is reduced.

When the present inventor closely observed the positive electrode current collector foil of the lithium ion secondary battery after the charge / discharge test described above, the aluminum in the positive electrode uncoated portion facing the end of the negative electrode active material layer was corroded. I found out that. Based on this finding, under charge and discharge conditions, the aluminum in the uncoated portion of the positive electrode that was facing the end of the negative electrode active material layer was dissolved in the electrolytic solution as aluminum ions, and the aluminum ions were reduced on the negative electrode. It is thought to be deposited as aluminum or an aluminum compound. Therefore, the present inventor solves the above-mentioned problems by suppressing the contact between the uncoated portion of the positive electrode and the electrolytic solution in the aluminum positive electrode current collecting foil and suppressing the elution of aluminum into the electrolytic solution. I remembered that.

The lithium ion secondary battery of the present invention is
A positive electrode plate provided with a positive electrode current collector foil made of aluminum and a positive electrode active material layer formed on the surface of the positive electrode current collector foil, and a negative electrode active material formed on the surface of the negative electrode current collector foil and the negative electrode current collector foil. A negative electrode plate including a layer, a separator, and an electrolytic solution containing a lithium salt selected from the following general formulas (1) and (2) are provided.
On the surface of the positive electrode current collector foil, there is a positive electrode uncoated portion on which the positive electrode active material layer is not formed.
A lithium ion secondary battery in which the positive electrode plate and the negative electrode plate face each other with the separator interposed therebetween, and the uncoated portion of the positive electrode and the end portion of the negative electrode active material layer face each other.
It is characterized in that a positive electrode current collector foil protective layer is provided on the surface of the positive electrode current collector foil in the positive electrode uncoated portion facing the end portion of the negative electrode active material layer.

(R ¹ X ¹ ) (R ² SO ₂ ) NLi general formula (1)
(R ¹ 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, a substituent or a substituent. An unsaturated cycloalkyl group optionally substituted with, an aromatic group optionally substituted with a substituent, a heterocyclic group optionally substituted with a substituent, an alkoxy group optionally substituted with a substituent. , An unsaturated thioalkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN. Will be done.
^R2 is a hydrogen, a 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 that may be substituted, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, an alkoxy group that may be substituted with a substituent, Selected from an unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, OCN. To.
Further, R ¹ and R ² may be combined 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 may be independently substituted with hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, or a non-substituted group. Saturated alkyl group, unsaturated cycloalkyl group optionally substituted with substituent, aromatic group optionally substituted with substituent, heterocyclic group optionally substituted with substituent, substituted with substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH. , SH, CN, SCN, OCN.
Further, R ^a and R ^b may be combined with R ¹ or R ² to form a ring. )
R ³ SO ₃ Li General formula (2)
(R ³ is selected from an alkyl group or a halogen-substituted alkyl group.)

In the lithium ion secondary battery of the present invention, the protective layer of the positive electrode current collector foil suppresses contact between the uncoated portion of the positive electrode and the electrolytic solution in the positive electrode current collector foil made of aluminum, so that aluminum is eluted from the positive electrode collector foil. Can be reduced.

It is a schematic diagram of the lithium ion secondary battery of Example 1. FIG. It is a perspective view of the positive electrode plate of the lithium ion secondary battery of Example 2. FIG.

Hereinafter, embodiments for carrying out the present invention will be described. Unless otherwise specified, the numerical range "a to b" described in the present specification includes the lower limit a and the upper limit b in the range. Then, a numerical range can be configured by arbitrarily combining these upper limit values and lower limit values, as well as the numerical values listed in the examples. Further, a numerical value arbitrarily selected from these numerical values can be used as a new upper limit or lower limit numerical value.

The lithium ion secondary battery of the present invention is
A positive electrode plate provided with a positive electrode current collector foil made of aluminum and a positive electrode active material layer formed on the surface of the positive electrode current collector foil, and a negative electrode active material formed on the surface of the negative electrode current collector foil and the negative electrode current collector foil. A negative electrode plate including a layer, a separator, and an electrolytic solution containing a lithium salt selected from the above general formulas (1) and (2) are provided.
On the surface of the positive electrode current collector foil, there is a positive electrode uncoated portion on which the positive electrode active material layer is not formed.
A lithium ion secondary battery in which the positive electrode plate and the negative electrode plate face each other with the separator interposed therebetween, and the uncoated portion of the positive electrode and the end portion of the negative electrode active material layer face each other.
A positive electrode current collector foil protective layer is provided on the surface of the positive electrode current collector foil in the positive electrode uncoated portion facing the end portion of the negative electrode active material layer (hereinafter, may be simply referred to as “end portion”). It is characterized by having.

The positive electrode plate used in the lithium ion secondary battery of the present invention is formed on the surface of the positive electrode current collector foil made of aluminum, the positive electrode active material layer formed on the surface of the positive electrode current collector foil, and the surface of the positive electrode current collector foil. It is provided with a positive electrode current collecting foil protective layer.

The positive electrode current collector foil made of aluminum is made of aluminum or an aluminum alloy. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or higher is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is called 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.

Further, as aluminum or an aluminum alloy, specifically, for example, A1000 series alloys such as JIS A1085 and A1N30 (pure aluminum series), A3000 series alloys such as JIS A3003 and A3004 (Al—Mn series), JIS A8079, A8021 and the like. A8000 series alloy (Al—Fe series) can be mentioned.

The thickness of the positive electrode current collector foil is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 50 μm, and even more preferably in the range of 10 μm to 30 μm. As the positive electrode current collector foil, the surface thereof may be treated by a known method and adopted.

The positive electrode active material layer contains a positive electrode active material and, if necessary, a binder and / or a conductive auxiliary agent. The thickness of the positive electrode active material layer is preferably in the range of 1 μm to 500 μm, more preferably in the range of 5 μm to 200 μm, and even more preferably in the range of 10 μm to 100 μm.

As the positive electrode active material, the general formula of the layered rock salt structure: Li _a Ni _b Co _c Mn _{d De Of} (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ _e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, Li ₂ MnO, a lithium composite metal oxide represented by 1.7 ≦ f ≦ 3), which is at least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V. ₃ can be mentioned. Further, as the positive electrode active material, a metal oxide having a spinel structure such as LiMn ₂ O ₄ , a solid solution composed of a mixture of the metal oxide having a spinel structure and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (in the formula). M is selected from at least one of Co, Ni, Mn, and Fe) and the like. Further, examples of the positive electrode active material include a tabolite compound represented by LiMPO ₄ F (M is a transition metal) such as LiFePO ₄ F, and a borate compound represented by LiMBO ₃ (M is a transition metal) such as LiFeBO ₃ . be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as the basic composition, and those in which the metal element contained in the basic composition is replaced with another metal element can also be used. Further, as the positive electrode active material, a substance that does not contain a charge carrier (for example, lithium ions that contribute to charge / discharge) may be used. For example, sulfur alone, compounds that combine sulfur and carbon, metal sulfides such as TiS ₂ , oxides such as _V2O5 and _MnO2 , polyaniline and anthraquinone, and compounds containing these aromatics in their chemical structures, conjugated _two . Conjugated materials such as acetic acid-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronylnitroxide, galbinoxyl, phenoxyl and the like may be adopted as the positive electrode active material.
When a positive electrode active material that does not contain a charge carrier such as lithium is used, it is necessary to add a 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 may be added in a nonionic state such as a metal. For example, when the charge carrier is lithium, a lithium foil may be attached to the positive electrode and / or the negative electrode to integrate them.

From the viewpoint of high capacity and excellent durability, as a positive electrode active material, a general formula of a layered rock salt structure: Li _a Ni _b Co _c Mn _{d De Of} (0.2 ≦ a ≦ 2, b + c + d + _e = 1, 0 ≦) e <1, D are W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, It is represented by at least one element selected from Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P and V, 1.7 ≦ f ≦ 3). It is preferable to use a lithium composite metal oxide.

In the above general formula, the values of b, c, and d are not particularly limited as long as they satisfy the above conditions, but those having 0 <b <1, 0 <c <1, 0 <d <1 are used. Good, and at least one of b, c, and d is in the range of 10/100 <b <90/100, 10/100 <c <90/100, 5/100 <d <70/100. More preferably, the range is 20/100 <b <80/100, 12/100 <c <70/100, 10/100 <d <60/100, and 30/100 <b <70/100, It is more preferably in the range of 15/100 <c <50/100 and 12/100 <d <50/100.

As for a, e, and f, any numerical value within the range specified by the above general formula may be used, and preferably 0.5 ≦ a ≦ 1.5, 0 ≦ e <0.2, 1.8 ≦ f ≦ 2. 5.5, more preferably 0.8 ≦ a ≦ 1.3, 0 ≦ e <0.1, 1.9 ≦ f ≦ 2.1 can be exemplified respectively.

As a specific positive electrode active material, at least one selected from Li _x A _y Mn _2-y O ₄ (A is Ca, Mg, S, Si, Na, K, Al, P, Ga, Ge) having a spinel structure. Examples thereof include at least one metal element selected from elements and 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 examples of the positive electrode active material 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. As another specific positive electrode active material, Li ₂ MnO ₃ -LiCoO ₂ can be exemplified.

One type of positive electrode active material may be used, or a plurality of types may be used in combination. As an example of combined use of the positive electrode active material, the general formula of the layered rock salt structure: Li _a Ni _b Co _c Mn _{d De Of} (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ _e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, At least one element selected from Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V, and a lithium composite metal oxide represented by 1.7 ≦ f ≦ 3). Examples thereof include combined use with a polyanionic compound represented by LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (M in the formula is selected from at least one of Co, Ni, Mn and Fe). In the combined use of the lithium composite metal oxide and the polyanionic compound, the mass ratio thereof is preferably in the range of lithium composite metal oxide: polyanionic compound = 90:10 to 50:50, and 80:20 to 60:40. The range of is more preferable. Further, the positive electrode active material may be coated with carbon.

The mass% of the positive electrode active material in the positive electrode active material layer is preferably 60 to 100% by mass, more preferably 80 to 99% by mass, still more preferably 85 to 96% by mass.

As the binder and the conductive auxiliary agent, those described in the negative electrode active material layer may be adopted as necessary. The mass% of the binder in the positive electrode active material layer is preferably 0.1 to 10% by mass, more preferably 0.5 to 7% by mass, still more preferably 1 to 5% by mass. This is because if the amount of the binder is too small, the moldability is lowered, while if the amount of the binder is too large, the energy density is lowered. The mass% of the conductive auxiliary agent in the positive electrode active material layer is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, still more preferably 1 to 10% by mass. This is because if the amount of the conductive auxiliary agent is too small, an efficient conductive path may not be formed, while if the amount of the conductive auxiliary agent is too large, the moldability is deteriorated and the energy density of the electrode is lowered.

In order to form the positive electrode active material layer on the surface of the positive electrode current collector foil, 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, or a curtain coating method is used. The positive electrode active material may be applied to the surface of the positive electrode current collector foil. Specifically, the positive electrode active material, the solvent, and if necessary, the binder and the conductive auxiliary agent are mixed to form a slurry, and then the slurry is applied to the surface of the positive electrode current collector foil and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried one may be compressed.

The positive electrode current collector foil protective layer suppresses direct contact between the positive electrode current collector foil and the electrolytic solution. Due to the presence of the positive electrode current collector foil protective layer, it is possible to suppress the aluminum of the positive electrode current collector foil from moving to the negative electrode plate via the electrolytic solution. The positive electrode current collector foil protective layer is arranged in the positive electrode uncoated portion facing the end of the negative electrode active material layer at the distance from the negative electrode active material layer in the positive electrode uncoated portion. Is the closest, and aluminum is considered to be the most corroded place.
Further, since the positive electrode active material is present at the portion of the positive electrode current collector foil on which the positive electrode active material layer is formed (hereinafter, may be referred to as a positive electrode coating portion), the electrons extracted from the positive electrode during charging emit Li ions. It is preferentially brought about by the oxidation reaction of the positive electrode active material accompanied by. On the other hand, since the positive electrode active material does not exist in the positive electrode uncoated portion, if there are electrons extracted from the positive electrode uncoated portion facing the end of the negative electrode active material layer during charging, aluminum ion emission is emitted. It is thought to be caused by the accompanying oxidation of aluminum. Therefore, it is considered that the uncoated portion of the positive electrode facing the end of the negative electrode active material layer is the portion where aluminum is most easily corroded.

As the material of the positive electrode current collector foil protective layer, a material that does not allow the electrolytic solution to permeate and is physically and chemically stable under the conditions of use of the lithium ion secondary battery of the present invention is preferable. Examples of such materials include polymers such as synthetic resins and adhesives, and various carbon materials such as various ceramics and graphite.

As polymers such as synthetic resins and adhesives, polyolefins typified by polyethylene and polypropylene, polyesters typified by polyethylene terephthalate and polybutylene terephthalate, polyimides, polyamide resins typified by polyamideimide, and polyvinylidene fluoride. And a fluororesin typified by polytetrafluoroethylene, and a silicone resin can be exemplified.

The silicone resin is R _y SiO _{(4-y) × 0.5} (R is a monovalent or divalent hydrocarbon group having 1 to 20 carbon atoms which may be substituted independently, and y is It is a polymer having a plurality of unit structures represented by (0 to 3) and having a skeleton due to a siloxane bond. The carbon number of the monovalent or divalent hydrocarbon group represented by R may be in the range of 1 to 14, 1 to 12. Examples of the hydrocarbon group include at least one selected from an alkyl group, an alkenyl group, an aryl group, an aralkyl group or an alkylene group. 2 or more of R may be an alkenyl group. Specific examples of the alkyl group include a methyl group. Specific examples of the alkenyl group include at least one selected from a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group or a heptenyl group. Specific examples of the aryl group include a phenyl group. y is preferably 2.

Ceramics include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , MgO, SiC, AlN, BN, CaCO ₃ , MgCO ₃ , BaCO ₃ , talc, mica, kaolinite, CaSO ₄ , Л ₄ , BaSO ₄ , CaO, ZnO, and zeolite can be exemplified.

The positive electrode current collector foil protective layer may be formed on the surface of the uncoated portion of the positive electrode by using or using the above-mentioned materials alone or in combination. As a method of forming the positive electrode current collecting foil protective layer on the surface of the positive electrode uncoated portion, a method of crimping the above-mentioned material on the surface of the positive electrode uncoated portion and a method of heating the above-mentioned material on the surface of the positive electrode uncoated portion. A method of fusing, a method of adhering the above-mentioned material to the surface of the uncoated portion of the positive electrode using an adhesive, the above-mentioned material or a monomer and a solvent which are precursors of the material are contained in the surface of the uncoated portion of the positive electrode. Examples of the method of applying the paste to be dried or polymerized, or the method of depositing the above-mentioned material on the surface of the uncoated portion of the positive electrode can be exemplified.

The size of the positive electrode current collector foil protective layer is not particularly limited. However, it is preferable that the positive electrode current collector foil protective layer is present in the entire portion of the uncoated portion where the positive electrode is not coated and which faces the negative electrode active material layer. Further, the positive electrode current collector foil protective layer may also be present in a portion of the uncoated portion of the positive electrode that does not face the negative electrode active material layer. In this case, it is possible to more preferably reduce the elution of aluminum from the positive electrode current collector foil.

Further, the positive electrode current collector foil in the positive electrode uncoated portion is composed of a positive electrode current collector foil surplus portion extending from the positive electrode coated portion and a tab portion extending from the positive electrode current collector foil surplus portion and connected to the outside. It may be. In this case, the positive electrode current collector foil protective layer may be present on the surfaces of both the positive electrode current collector foil surplus portion and the tab portion. In this case, it is possible to more preferably reduce the elution of aluminum from the positive electrode current collector foil, and it is possible to suppress direct contact between the tab portion and another member (for example, the tab portion of the negative electrode plate). It is also effective in preventing short circuits. As the shape of the tab portion, it can be said that a shape extending from the positive electrode current collector foil surplus portion to a shorter width than the positive electrode current collector foil surplus portion is preferable from the viewpoint of workability.

As suitable shapes of the positive electrode current collector foil surplus portion and the tab portion, a T-shape or an L-shape can be exemplified. As the distance of the positive electrode current collector foil surplus portion from the end of the positive electrode current collector foil on which the positive electrode active material layer is formed to the tab portion, 1 to 50 mm, 2 to 30 mm, 3 to 10 mm, and 4 to 8 mm can be exemplified. ..

It is more preferable that the positive electrode current collector foil protective layer is arranged in the uncoated portion of the positive electrode with its end in contact with the end of the positive electrode active material layer. When the positive electrode current collector foil protective layer is arranged so as to be laminated on the upper surface of the positive electrode active material layer, the movement of lithium ions between the positive electrode active material layer and the negative electrode active material layer may be suppressed.

The thickness of the positive electrode current collector foil protective layer is preferably in the range of 1 μm to 500 μm, more preferably in the range of 5 μm to 200 μm, and further preferably in the range of 10 μm to 100 μm. The thickness of the positive electrode current collector foil protective layer is preferably about the same as the thickness of the positive electrode active material layer or thinner than the thickness of the positive electrode active material layer. The thickness of the positive electrode current collector foil protective layer with respect to the thickness of the positive electrode active material layer is preferably 0.1 ≦ (thickness of the positive electrode current collector foil protective layer) / (thickness of the positive electrode active material layer) ≦ 10, and 0.2 ≦ ( The thickness of the positive electrode current collector foil protective layer) / (thickness of the positive electrode active material layer) ≦ 5 is more preferable.
When the thickness of the positive electrode current collector foil protective layer is significantly thicker than the thickness of the positive electrode active material layer, it becomes difficult to keep the surface of the positive electrode active material layer parallel to the surface of the negative electrode active material layer. It is assumed that the distance between the surface of the material layer and the surface of the negative electrode active material layer differs depending on the location, or the surface pressure applied to the positive electrode active material layer and the negative electrode active material layer becomes non-uniform depending on the location. Therefore, there is a possibility that the charge / discharge reaction may be uneven.

The negative electrode plate used in the lithium ion secondary battery of the present invention includes a negative electrode current collector foil and a negative electrode active material layer formed on the surface of the negative electrode current collector foil.

Negative negative current collector foils include 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. Metallic materials can be exemplified. The negative electrode current collector foil may be coated with a known protective layer. A material obtained by treating the surface of the negative electrode current collector foil by a known method may be used as the negative electrode current collector foil.

The thickness of the negative electrode current collector foil is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 50 μm, and even more preferably in the range of 8 μm to 30 μm.

The negative electrode active material layer contains a negative electrode active material and, if necessary, a binder and / or a conductive auxiliary agent. The thickness of the negative electrode active material layer is preferably in the range of 5 μm to 500 μm, more preferably in the range of 10 μm to 200 μm, and even more preferably in the range of 20 μm to 100 μm.

As the negative electrode active material, a material capable of occluding and releasing lithium ions can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy or compound capable of occluding and releasing lithium ions. For example, Li, Group 14 elements such as carbon, silicon, germanium, and tin, Group 13 elements such as aluminum and indium, Group 12 elements such as zinc and cadmium, Group 15 elements such as antimony and bismuth, and magnesium as negative electrode active materials. , Alkaline earth metals such as calcium, and Group 11 elements such as silver and gold may be used alone. When silicon or the like is used as the negative electrode active material, one atom of silicon reacts with a plurality of lithiums, resulting in a high-capacity active material. However, there is a problem that volume expansion and contraction due to occlusion and release of lithium become remarkable. Therefore, in order to reduce the risk, it is also preferable to use an alloy or compound in which a simple substance such as silicon is combined with another element such as a transition metal as a negative electrode active material. Specific examples of alloys or compounds include tin-based materials such as Ag—Sn alloys, Cu—Sn alloys, and Co—Sn alloys, carbon-based materials such as various graphites, elemental silicon, and SiO _x that disproportionates to elemental silicon and silicon dioxide. Examples thereof include a silicon-based material such as 0.3 ≦ x ≦ 1.6), a simple substance of silicon, or a composite of a silicon-based material and a carbon-based material. Further, as the negative electrode active material, oxides 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 =). A nitride represented by Co, Ni, Cu) may be adopted. One or more of these can be used as the negative electrode active material.

As a more specific negative electrode active material, a material containing graphite or silicon can be exemplified. The material containing silicon may be any material containing Si and functioning as a negative electrode active material. Specific examples of the Si-containing negative electrode active material include elemental silicon, SiOx (0.3≤x≤1.6), alloys of Si with other metals, and the silicon material described in International Publication No. 2014/08608. can. The Si-containing negative electrode active material may be coated with carbon. The carbon-coated Si-containing negative electrode active material has excellent conductivity.

The silicon material described in International Publication No. 2014/08608 (hereinafter, may be simply referred to as “silicon material”) will be described in detail. The silicon material is, for example, subjected to a step of reacting CaSi ₂ with an acid to synthesize a layered silicon compound containing polysilane as a main component, and a step of heating the layered silicon compound at 300 ° C. or higher to release hydrogen. It is manufactured.

The method for producing a silicon material described in International Publication No. 2014/08608 is shown below by an ideal reaction formula when hydrogen chloride is used as an acid.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂
Si 6H ₆ → 6Si _{+ 3H 2 ↑}

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is usually used as a reaction solvent from the viewpoint of removing by-products and impurities. Since Si ₆ H ₆ can react with water, the layered silicon compound is rarely produced as containing only Si ₆ H ₆ in the step of synthesizing the layered silicon compound including the reaction in the upper stage, and is layered. Silicon compounds are represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an acid anion, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as a compound. In the above chemical formula, unavoidable impurities such as Ca that may remain are not considered. The silicon material obtained by heating the layered silicon compound also contains an element derived from an anion of oxygen or acid.

The silicon material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. In order for a charge carrier such as lithium ion to efficiently occlude and release, the plate-shaped silicon body preferably has a thickness in the range of 10 nm to 100 nm, and more preferably in the range of 20 nm to 50 nm. The length of the plate-shaped silicon body in the longitudinal direction is preferably in the range of 0.1 μm to 50 μm. Further, the plate-shaped silicon body preferably has (length in the longitudinal direction) / (thickness) in the range of 2 to 1000. The laminated structure of the plate-shaped silicon body can be confirmed by observation with a scanning electron microscope or the like. Further, this laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

The silicon material preferably contains amorphous silicon and / or silicon crystallites. In particular, in the plate-shaped silicon body, it is preferable that amorphous silicon is used as a matrix and silicon crystallites are scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, further preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from Scherrer's equation using the half width of the diffraction peak on the Si (111) plane of the obtained X-ray diffraction chart by performing X-ray diffraction measurement on the silicon material. ..

The abundance and size of the plate-shaped silicon body, amorphous silicon and silicon crystallites contained in the silicon material mainly depend on the heating temperature and the heating time. The heating temperature is preferably in the range of 350 ° C to 950 ° C, more preferably in the range of 400 ° C to 900 ° C.

In a lithium ion secondary battery provided with a negative electrode plate provided with a graphite or Si-containing negative electrode active material, it is assumed that the positive electrode current collector foil is exposed to a high voltage during charging. Therefore, in the lithium ion secondary battery of the present invention provided with the negative electrode plate provided with the graphite or Si-containing negative electrode active material, it can be said that the aluminum elution reduction effect of the positive electrode current collector foil protective layer is suitably exhibited.

The mass% of the negative electrode active material in the negative electrode active material layer is preferably 60 to 100% by mass, more preferably 80 to 99% by mass, still more preferably 85 to 98% by mass.

The binder plays a role of binding the active material, the conductive auxiliary agent, etc. to the surface of the current collector foil.

Examples of the binder include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins and styrene butadiene. A known material such as rubber may be used.

Further, a polymer having a hydrophilic group may be adopted as the binder. The lithium ion secondary battery of the present invention provided with a polymer having a hydrophilic group as a binder can more preferably maintain the capacity. Examples of the hydrophilic group of the polymer having a hydrophilic group include a carboxyl group, a sulfo group, a silanol group, an amino group, a hydroxyl group, a phosphoric acid group and the like, and the like. Of these, polymers containing a carboxyl group in molecules such as polyacrylic acid, carboxymethyl cellulose, and polymethacrylic acid, or polymers containing a sulfo group such as poly (p-styrene sulfonic acid) are preferable.

Polymers rich in carboxyl groups and / or sulfo groups, such as polyacrylic acid or polymers of acrylic acid and vinyl sulfonic acid, are water soluble. The polymer having a hydrophilic group is preferably a water-soluble polymer, and in terms of chemical structure, a polymer containing a plurality of carboxyl groups and / or sulfo groups in one molecule is preferable.

The polymer containing a carboxyl group in the molecule can be produced, for example, by a method of polymerizing an acid monomer, a method of imparting a carboxyl group to the polymer, or the like. Acid monomers include acrylic acid, methacrylic acid, vinyl benzoic acid, crotonic acid, pentenic acid, angelic acid, tigric acid and other acid monomers having one carboxyl group in the molecule, itaconic acid, mesaconic acid, citraconic acid and fumaric acid. , Maleic acid, 2-pentenedioic acid, methylene succinic acid, allylmalonic acid, isopropyridene succinic acid, 2,4-hexadienyldioic acid, acetylenedicarboxylic acid and other acid monomers having two or more carboxyl groups in the molecule. Will be done.

A copolymerized polymer obtained by polymerizing two or more kinds of acid monomers selected from the above acid monomers may be used as a binder.

Further, for example, a polymer containing an acid anhydride group formed by condensing the carboxyl groups of a copolymer of acrylic acid and itaconic acid, as described in JP2013-0654993, in the molecule. Is also preferably used as a binder. When the binder has a structure derived from a highly acidic monomer having two or more carboxyl groups in one molecule, it becomes easier for the binder to trap lithium ions and the like before the electrolyte decomposition reaction occurs during charging. It is considered. Further, the polymer has more carboxyl groups per monomer than polyacrylic acid or polymethacrylic acid, so that the acidity is increased, but a predetermined amount of carboxyl groups are changed to acid anhydride groups, so that the acidity is high. Does not rise too much. Therefore, the secondary battery having a negative electrode using the polymer as a binder improves the initial efficiency and the input / output characteristics.

Further, a crosslinked polymer in which a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid disclosed in International Publication No. 2016/06382 is crosslinked with a diamine may be used as a binder.

Examples of the diamine used in the crosslinked polymer include alkylene diamines such as ethylenediamine, propylenediamine and hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophoronediamine and bis (4-aminocyclohexyl) methane. Saturated carbocyclic diamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, bis (4-aminophenyl) sulfone, benzidine, o-tridine, 2,4- Examples thereof include aromatic diamines such as tolylene diamine, 2,6-tolylene diamine, xylylene diamine and naphthalenediamine.

Further, a mixture or reaction product of a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid and polyamide-imide may be used as a binder.

Polyamide-imide means a compound having two or more amide bonds and two or more imide bonds in the molecule. Polyamideimide is produced by reacting an acid component that becomes a carbonyl moiety in an amide bond and an imide bond with a diamine component or a diisocyanate component that becomes a nitrogen moiety in an amide bond and an imide bond. In order to obtain a polyamide-imide, it may be produced by the method, or a commercially available polyamide-imide may be purchased.

The acid components used in the production of polyamideimide include trimellitic acid, pyromellitic acid, biphenyltetracarboxylic acid, diphenylsulfonetetracarboxylic acid, benzophenonetetracarboxylic acid, diphenylethertetracarboxylic acid, oxalic acid, adipic acid, and malonic acid. Sebatic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), cyclohexane-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, Examples of dicyclohexylmethane-4,4'-dicarboxylic acid, terephthalic acid, isophthalic acid, bis (carboxyphenyl) sulfone, bis (carboxyphenyl) ether, naphthalenedicarboxylic acid, and anhydrides, acid halides and derivatives thereof. Can be done. As the acid component, the above compounds may be used alone or in combination of two or more. However, from the viewpoint of forming an imide bond, the acid component in which the carboxyl group is present in the adjacent carbon of the carbon to which the carboxyl group is bonded or The equivalent is essential. As the acid component, trimellitic acid anhydride is preferable from the viewpoint of reactivity, heat resistance and the like. In addition to trimellitic acid anhydride, pyromellitic acid anhydride, benzophenone tetracarboxylic acid anhydride, and biphenyltetra as part of the acid component, in terms of tensile strength, tensile elasticity, and electrolyte resistance of polyamideimide. It is preferable to use carboxylic acid anhydride.

As the diamine component used for producing the polyamide-imide, the diamine used for the above-mentioned crosslinked polymer may be adopted. From the viewpoint of heat resistance and solubility, 4,4'-diaminodiphenylmethane, 2,4-tolylenediamine, o-trizine, naphthalenediamine, and isophoronediamine are preferable. From the viewpoint of tensile strength and tensile elastic modulus of polyamide-imide, o-tolidine and naphthalenediamine are preferable.

Examples of the diisocyanate component used for producing the polyamide-imide include those in which the amine of the diamine component is replaced with isocyanate.

The mass% of the binder in the negative electrode active material layer is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, still more preferably 1 to 10% by mass. This is because if the amount of the binder is too small, the moldability is lowered, while if the amount of the binder is too large, the energy density is lowered.

Conductive aids are added to increase the conductivity of the electrodes. Therefore, the conductive auxiliary agent 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 auxiliary agent may be a chemically inert electron high conductor, and examples thereof include carbon black, which are carbonaceous fine particles, graphite, Vapor Grown Carbon Fiber, and various metal particles. To. Examples of carbon black include acetylene black, Ketjen black (registered trademark), furnace black, and channel black. These conductive auxiliary agents can be added to the active material layer alone or in combination of two or more.

The mass% of the conductive auxiliary agent in the negative electrode active material layer is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, still more preferably 1 to 10% by mass. This is because if the amount of the conductive auxiliary agent is too small, an efficient conductive path may not be formed, while if the amount of the conductive auxiliary agent is too large, the moldability is deteriorated and the energy density of the electrode is lowered.

In order to form the negative electrode active material layer on the surface of the negative electrode current collector foil, 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, or a curtain coating method is used. The negative electrode active material may be applied to the surface of the negative electrode current collector foil. Specifically, the negative electrode active material, the solvent, and if necessary, the binder and the conductive auxiliary agent are mixed to form a slurry, and then the slurry is applied to the surface of the negative electrode current collector foil and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried one may be compressed.

A separator is used in the lithium ion secondary battery of the present invention. The separator separates the positive electrode plate and the negative electrode plate, and allows lithium ions to pass through while preventing a short circuit due to contact between the two electrodes. As the separator, a known one may be adopted, 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, and sverin, porous bodies using one or more electrically insulating materials such as ceramics, non-woven fabrics, and woven fabrics. Further, the separator may have a multi-layer structure.

The separator is located between the positive electrode plate and the negative electrode plate so as to prevent contact between the positive electrode plate and the negative electrode plate. The separator preferably has a larger surface than the surfaces of the positive electrode active material layer and the negative electrode active material layer facing each other. From the viewpoint of preventing short circuit and preventing metal lithium precipitation, the surface size is preferably in the order of separator> negative electrode active material layer> positive electrode active material layer. As for the facing state of the separator, the positive electrode active material layer, and the negative electrode active material layer, the negative electrode active material layer faces the positive electrode active material layer in a manner of covering the entire surface of the positive electrode active material layer, and the positive electrode active material layer and the negative electrode active material layer are faced to each other. It is preferable that the separator faces the positive electrode active material layer and the negative electrode active material layer so as to cover the entire surface of the material layer.

The lithium ion secondary battery of the present invention comprises an electrolytic solution containing a lithium salt selected from the following general formulas (1) and (2).

(R ¹ X ¹ ) (R ² SO ₂ ) NLi general formula (1)
(R ¹ 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, a substituent or a substituent. An unsaturated cycloalkyl group optionally substituted with, an aromatic group optionally substituted with a substituent, a heterocyclic group optionally substituted with a substituent, an alkoxy group optionally substituted with a substituent. , An unsaturated thioalkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN. Will be done.
^R2 is a hydrogen, a 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 that may be substituted, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, an alkoxy group that may be substituted with a substituent, Selected from an unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, OCN. To.
Further, R ¹ and R ² may be combined 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 may be independently substituted with hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, or a non-substituted group. Saturated alkyl group, unsaturated cycloalkyl group optionally substituted with substituent, aromatic group optionally substituted with substituent, heterocyclic group optionally substituted with substituent, substituted with substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH. , SH, CN, SCN, OCN.
Further, R ^a and R ^b may be combined with R ¹ or R ² to form a ring. )

R ³ SO ₃ Li General formula (2)
(R ³ is selected from an alkyl group or a halogen-substituted alkyl group.)

The phrase "may be substituted with a substituent" in the chemical structure represented by the general formula (1) will be described. For example, "an alkyl group that may be substituted with a substituent" means an alkyl group in which one or more of hydrogens of the alkyl group is substituted with a substituent, or an alkyl group having no substituent. do.

The substituents 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, a halogen and an 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, phosphate amide group, sulfo group, carboxyl group, Examples thereof include a hydroxamic acid group, a sulfino group, a hydradino group, an imino group, a silyl group and the like. These substituents may be further substituted with substituents. When there are two or more substituents, the substituents may be the same or different.

The lithium salt is preferably represented by the following general formula (1-1).

(R ²³ X ² ) (R ²⁴ SO ₂ ) NLi general formula (1-1)
(R ²³ and R ²⁴ are _{C nHa F b Cl c Br d I e (} CN) _f (SCN) _g (OCN) _h , respectively.
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.
Further, R ²³ and R ²⁴ may be coupled to each other to form a ring, in which case 2n = a + b + c + d + e + f + g + h is satisfied.
X ² is selected from SO ₂ , C = O, C = S, R ^c P = O, R ^d P = S, S = O, and Si = O.
R ^c and R ^d may be independently substituted with hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, or a non-substituted group. Saturated alkyl group, unsaturated cycloalkyl group optionally substituted with substituent, aromatic group optionally substituted with substituent, heterocyclic group optionally substituted with substituent, substituted with substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH. , SH, CN, SCN, OCN.
Further, R ^c and R ^d may be combined with R ²³ or R ²⁴ to form a ring. )

In the chemical structure represented by the general formula (1-1), the meaning of the phrase "may be substituted with a substituent" is synonymous with that described in the general formula (1).

In the chemical structure represented by the general formula (1-1), 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. When R ²³ and R ²⁴ of the chemical structure represented by the above general formula (1-1) are bonded to form a ring, n is preferably an integer of 1 to 8 and 1 to 7. An integer of 1 to 3 is more preferable, and an integer of 1 to 3 is particularly preferable.

The lithium salt is more preferably represented by the following general formula (1-2).

(R ²⁵ SO ₂ ) (R ²⁶ SO ₂ ) NLi general formula (1-2)
(R ²⁵ and R ²⁶ are C _{n Ha F b Cl c} Br _d I _e , respectively, independently of each other.
n, a, b, c, d, and e are independently integers of 0 or more, and satisfy 2n + 1 = a + b + c + d + e.
Further, R ²⁵ and R ²⁶ may be combined with each other to form a ring, in which case 2n = a + b + c + d + e is satisfied. )

In the chemical structure represented by the general formula (1-2), 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. When R ²⁵ and R ²⁶ of the chemical structure represented by the above general formula (1-2) are bonded to form a ring, n is preferably an integer of 1 to 8 and 1 to 7. An integer of 1 to 3 is more preferable, and an integer of 1 to 3 is particularly preferable.

Further, in the chemical structure represented by the general formula (1-2), those in which a, c, d and e are 0 are preferable.

In the general formula (2), the carbon number of R ³ is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 2. Fluorine is preferable as the halogen of the halogen-substituted alkyl group.

Lithium salts are (CF ₃ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, (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 The one selected from is particularly preferable.

In the electrolytic solution, one kind of the lithium salt selected from the general formula (1) and the general formula (2) may be adopted, or a plurality of kinds may be used in combination. Further, the electrolytic solution may contain an electrolyte other than the lithium salt selected from the general formula (1) and the general formula (2). The ratio of the lithium salt selected from the general formula (1) and the general formula (2) to the entire electrolyte in the electrolytic solution is preferably 30 to 100 mol%, more preferably 50 to 95 mol%, and 70 to 90 mol%. Is more preferable. The concentrations of the electrolyte containing the lithium salt selected from the general formula (1) and the general formula (2) in the electrolytic solution are 1.5 to 3 mol / L and 1.6 to 2.8 mol / L, 1.8. Examples thereof include ~ 2.6 mol / L and 2 to 2.5 mol / L.

Specific examples of the electrolyte other than the lithium salt selected from the general formula (1) and the general formula (2) include LiPF ₆ , LiPF ₂ (OCOCOO) ₂ , LiBF ₄ , LiAsF ₆ and Li ₂ SiF ₆ . All of these electrolytes have an F that can be desorbed as F ⁻ . Then, F ^- can react with aluminum to form a stable Al-F bond. Therefore, even if there is a part of the uncoated portion of the positive electrode that is not protected by the positive electrode current collector foil protective layer, it can be expected that the surface thereof is protected by a passivation film containing an Al—F bond.

The electrolytic solution contains an organic solvent for dissolving an electrolyte containing a lithium salt selected from the general formula (1) and the general formula (2). As the organic solvent, an organic solvent that can be used for a non-aqueous secondary battery may be used, and it is particularly preferable to use a low-polarity organic solvent that does not easily dissolve aluminum.

As a low-polarity organic solvent, a chain carbonate represented by the following general formula (3) can be mentioned.

R ¹⁰ OCOOR ¹¹ General formula (3)
(R ¹⁰ and R ¹¹ are independently chain alkyls, C _{nH a F b C Br d I e, or C m H f F g Cl h Br i I ,} which contains a cyclic alkyl in the chemical structure. It is selected from any of _j . N is an integer of 1 or more, m is an integer of 3 or more, and a, b, c, d, e, f, g, h, i, and j are independently integers of 0 or more. 2n + 1 = a + b + c + d + e, 2m-1 = 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. For m, an integer of 3 to 8 is preferable, an integer of 4 to 7 is more preferable, and an integer of 5 to 6 is particularly preferable.

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

R ¹² OCOOR ¹³ General formula (3-1)
(R ¹² and R ¹³ are independently selected from either C _{nH a F b, which is a chain alkyl, or C m H f F g ,} which contains a cyclic alkyl in the chemical structure. N is 1 The above integer, m is an integer of 3 or more, and a, b, f, and g are independently integers of 0 or more, satisfying 2n + 1 = a + b, 2m-1 = 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. For m, an integer of 3 to 8 is preferable, an integer of 4 to 7 is more preferable, and an integer of 5 to 6 is particularly preferable.

Among the chain carbonates represented by the above general formula (3-1), dimethyl carbonate (hereinafter, may be referred to as "DMC"), diethyl carbonate (hereinafter, may be referred to as "DEC"), ethylmethyl. Carbonate (hereinafter sometimes referred to as "EMC"), fluoromethylmethyl carbonate, difluoromethylmethyl carbonate, trifluoromethylmethylcarbonate, bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) Particularly preferred are carbonate, fluoromethyldifluoromethyl carbonate, 2,2,2-trifluoroethylmethyl carbonate, pentafluoroethylmethyl carbonate, ethyltrifluoromethylcarbonate and bis (2,2,2-trifluoroethyl) carbonate.

One type of chain carbonate may be used as the electrolytic solution, or a plurality of types may be used in combination. By using a plurality of chain carbonates in combination, it is possible to suitably secure the low temperature fluidity of the electrolytic solution and the lithium ion transportability at low temperature. Examples of the combined use of the chain carbonate include two or three kinds selected from DMC, DEC and EMC. In the combined use of DMC with DEC or EMC, these molar ratios are preferably in the range of DMC: DEC or EMC = 60: 40 to 95: 5, more preferably in the range of 70:30 to 95: 5. The range of 80:20 to 95: 5 is more preferable.

In the electrolytic solution, in addition to the above-mentioned chain carbonate, another organic solvent that can be used for the electrolytic solution such as a lithium ion secondary battery (hereinafter, may be simply referred to as “another organic solvent”) is contained. You may.

The electrolytic solution preferably contains the above-mentioned chain carbonate in an amount of 70% by volume, 70% by mass or more, or 70 mol% or more, and 80% by volume, 80% by mass or more, based on the total organic solvent contained in the electrolytic solution. Alternatively, it is more preferably contained in an amount of 80 mol% or more, further preferably contained in an amount of 90% by volume, 90% by mass or more, or 90 mol% or more, and further preferably contained in an amount of 95% by volume, 95% by mass or more or 95 mol% or more. Is particularly preferable. All the organic solvents contained in the electrolytic solution may be the above-mentioned chain carbonate.

Specific examples of other organic solvents include nitriles such as acetonitrile, propionitrile, acrylonitrile, and malononitrile, 1,2-dimethoxyethane, 1,2-diethoxyethane, isocyanate, 1,2-dioxane, 1, Ethers such as 3-dioxane, 1,4-dioxane, 2,2-dimethyl-1,3-dioxolane, 2-methyltetrahydropyran, 2-methyltetrahydrogen, crown ether, fluoroethylene carbonate, 4- (trifluoromethyl) )-1,3-Dioxolan-2-one and other fluorine-containing cyclic carbonates, ethylene carbonate, propylene carbonate and other fluorine-free cyclic carbonates, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N. -Amids such as methylpyrrolidone, isocyanates such as isopropylisocyanate, n-propylisocyanate, chloromethylisocyanate, methyl acetate, ethyl acetate, butyl acetate, propyl acetate, methyl propionate, methyl isomerate, ethyl isomerate, vinyl acetate, methyl Esters such as acrylates and methylmethacrylates, glycidylmethyl ethers, epoxybutanes, epoxies such as 2-ethyloxylan, oxazoles such as oxazole, 2-ethyloxazole, oxazoline and 2-methyl-2-oxazoline, acetone, methylethylketone, Ketones such as methylisobutylketone, acid anhydrides such as acetic acid anhydride and propionic acid anhydride, sulfonates such as dimethylsulfone and sulfolane, sulfoxides such as dimethylsulfoxide, nitros such as 1-nitropropane and 2-nitropropane, Francs such as furan and furfural, cyclic esters such as γ-butyrolactone, γ-valerolactone and δ-valerolactone, aromatic heterocycles such as thiophene and pyridine, tetrahydro-4-pyrone, 1-methylpyrrolidin, N. -Heterocyclics such as methylmorpholine and phosphate esters such as trimethyl phosphate and triethyl phosphate can be mentioned.

Known additives may be added to the electrolytic solution without departing from the spirit of the present invention. As an example of known additives, cyclic carbonates having unsaturated bonds typified by vinylene carbonate (VC), vinylethylene carbonate (VEC), methylvinylene carbonate (MVC), ethylvinylene carbonate (EVC); phenylethylene carbonate and Carbonate compounds typified by erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic acid anhydride, cyclopentanetetracarboxylic acid. Bianhydride, carboxylic acid anhydride represented by phenylsuccinic anhydride; γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, lactone represented by ε-caprolactone; 1 , Cyclic ether typified by 4-dioxane; represented by ethylene sulphite, 1,3-propane sulton, 1,4-butane sulton, methyl methanesulfonate, bushalphane, sulforane, sulfolene, dimethyl sulfone, tetramethylthium monosulfide. Sulfur-containing compounds; including 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide. Nitrogen compounds; Phosphates typified by monofluorophosphates and difluorophosphates; Saturated hydrocarbon compounds typified by heptane, octane and cycloheptane; Partial hydrogenation of biphenyl, alkylbiphenyl, terphenyl and turphenyl Examples thereof include unsaturated hydrocarbon compounds typified by the body, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran.

In the lithium ion secondary battery of the present invention, the laminated body in which the positive electrode plate, the separator and the negative electrode plate are laminated may be a wound type in which the laminated body is wound, or the positive electrode plate, the separator and the negative electrode plate are in a flat state. It may be a laminated type as it is laminated in. The laminated type is preferable from the viewpoint of controlling the face-to-face relationship between the uncoated portion of the positive electrode and the end portion of the negative electrode active material layer and the face-to-face relationship between the end portion of the negative electrode active material layer and the positive electrode current collector foil protective layer.

As the material of the battery container of the lithium ion secondary battery of the present invention, a laminate obtained by laminating a metal such as aluminum, stainless steel, resin, or aluminum and a resin can be exemplified. The shape of the battery container of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical type, a square type, a coin type, and a laminated type can be adopted.

Since the lithium ion secondary battery of the present invention can reduce aluminum elution from the positive electrode current collector foil due to the presence of the positive electrode current collector foil protective layer, it can be used under high voltage conditions. Specifically, as the high voltage condition, the condition that the potential with respect to the lithium to which the positive electrode is exposed is 4 V or more, 4 to 5.5 V, 4.1 to 5 V, and 4.3 to 4.8 V can be exemplified. The lithium ion secondary battery of the present invention can also be recognized as a lithium ion secondary battery for high voltage.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, it is advisable to connect a plurality of lithium ion secondary batteries in series to form an assembled battery. In addition to vehicles, devices equipped with lithium-ion secondary batteries include various battery-powered home appliances such as personal computers and portable communication devices, office equipment, and industrial equipment. Further, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydraulic power generation and other power storage devices and power smoothing devices, power sources for ships and / or auxiliary equipment, aircraft, and aircraft. Power and / or auxiliary power sources for spacecraft, etc., auxiliary power sources for vehicles that do not use electricity as power sources, power sources for mobile home robots, power sources for system backup, power sources for non-disruptive power sources, It may be used as a power storage device that temporarily stores the electric power required for charging in a charging station for an electric vehicle or the like.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. As long as it does not deviate from the gist of the present invention, it can be carried out in various forms with modifications, improvements, etc. that can be made by those skilled in the art. In the present specification, as an embodiment of the present invention, a lithium ion secondary battery in which the charge carrier is lithium is specifically described, but the technical matter disclosed in the present specification is that the charge carrier is sodium. It is also applicable to a sodium ion secondary battery, a potassium ion secondary battery in which the charge carrier is potassium, a magnesium ion secondary battery in which the charge carrier is magnesium, and the like. When the technical matters disclosed in the present specification are applied to a sodium ion secondary battery or a potassium ion secondary battery, the description of "lithium" and "Li" in the present specification is referred to as "sodium" and "Li", respectively. It may be read as "Na" or "potassium" and "K". When the technical matters disclosed in the present specification are applied to a magnesium ion secondary battery, the descriptions of "lithium" and "Li" in the present specification are appropriately matched in valence as necessary. Above, it may be read as "magnesium" and "Mg".

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to these examples.

(Example 1)
FIG. 1 shows a schematic diagram of the lithium ion secondary battery of Example 1 when observed from the thickness side of the positive electrode plate, the separator, and the negative electrode plate. In the following description, the vertical means the vertical direction in FIG. 1, and the horizontal means the front side-back side direction of the paper surface in FIG. 1.

The lithium ion secondary battery 1 of the first embodiment is
On the surface of the positive electrode plate 2 provided with the positive electrode current collector foil 20 made of aluminum and the positive electrode active material layer 21 formed on the surface of the positive electrode current collector foil 20, the negative electrode current collector foil 30 and the negative electrode current collector foil 30. A negative electrode plate 3 including the formed negative electrode active material layer 31, a separator 4, and an electrolytic solution 5 containing (FSO ₂ ) ₂ NLi as a lithium salt are provided.
On the surface of the positive electrode current collector foil 20, there is a positive electrode uncoated portion 22 on which the positive electrode active material layer 21 is not formed.
A lithium ion secondary battery in which the positive electrode plate 2 and the negative electrode plate 3 face each other with the separator 4 interposed therebetween, and the positive electrode uncoated portion 22 and the end portion 32 of the negative electrode active material layer 31 face each other. 1 and
The positive electrode current collector foil protective layer 23 is provided on the surface of the positive electrode current collector foil 20 in the positive electrode uncoated portion 22 facing the end portion 32 of the negative electrode active material layer 31.

The positive electrode current collector foil 20 is JIS A1000 series pure aluminum, and is a foil having a thickness of 15 μm, a length of 40 mm, and a width of 30 mm. On one surface of the positive electrode current collector foil 20, the positive electrode active material layer 21 is formed with a width of 30 mm and a thickness of 22 μm, starting from the lower end in the vertical direction of the positive electrode current collector foil 20 and extending 25 mm toward the upper end. In the positive electrode active material layer 21, 90 parts by mass of LiNi _50/100 Co _35/100 Mn _15/100 O ₂ which is a positive electrode active material, 5 parts by mass of acetylene black which is a conductive auxiliary agent, and graphite which is a conductive auxiliary agent. Is contained in 3 parts by mass, and polyvinylidene fluoride, which is a binder, is contained in 2 parts by mass.

Further, on the surface of the positive electrode current collector foil 20, the positive electrode uncoated portion 22 on which the positive electrode active material layer 21 is not formed is formed from the portion where the positive electrode active material layer 21 is formed, that is, from the end of the positive electrode coated portion. , Exists over the upper end of the positive electrode current collector foil 20. The positive electrode uncoated portion 22 is in a facing relationship with the end portion 32 of the negative electrode active material layer 31 via the separator 4. A positive electrode current collector foil protective layer 23 having a thickness of 55 μm is arranged on the positive electrode uncoated portion 22 facing the end portion 32. The lower end of the positive electrode current collector foil protective layer 23 is in contact with the upper end of the positive electrode active material layer 21. The positive electrode current collector foil protective layer 23 is composed of a polyimide film and a silicone resin coated on one surface of the polyimide film, and the silicone resin functions as an adhesive for adhering the polyimide film and the positive electrode uncoated portion 22.

Since the positive electrode current collector foil protective layer 23 suppresses contact between the positive electrode uncoated portion 22 and the electrolytic solution 5, the elution of aluminum from the positive electrode uncoated portion 22 facing the end portion 32 is suppressed. ..
The upper end of the positive electrode current collector foil 20 is connected to the external power source 15 via the positive electrode conducting wire 24.

The negative electrode current collector foil 30 is a copper foil having a thickness of 10 μm, a length of 40 mm, and a width of 32 mm. On one surface of the negative electrode current collector foil 30, the negative electrode active material layer 31 is formed with a width of 32 mm and a thickness of 40 μm over 30 mm in the lower end direction starting from the upper end in the vertical direction of the negative electrode current collector foil 30. The negative electrode active material layer 31 contains 98 parts by mass of graphite as a negative electrode active material, 1 part by mass of carboxymethyl cellulose as a binder, and 1 part by mass of styrene-butadiene rubber as a binder.
The lower end of the negative electrode current collector foil 30 is connected to the external power supply 15 via the negative electrode lead wire 34.

The separator 4 is a polyethylene porous membrane having a thickness of 16 μm. The separator 4 has a larger surface than the surface of the positive electrode active material layer 21 and the negative electrode active material layer 31 facing the separator 4. The separator 4 is located between the positive electrode plate 2 and the negative electrode plate 3 so as to prevent contact between the positive electrode plate 2 and the negative electrode plate 3.

The positive electrode plate 2, the negative electrode plate 3, and the separator 4 are sealed inside the battery container 10 in a laminated state while maintaining a flat surface. The battery container 10 is made of an aluminum laminated film. The electrolytic solution 5 is injected into the inside of the battery container 10. The electrolytic solution 5 contains (FSO ₂ ) ₂ NLi as a lithium salt and contains a mixed solvent as an organic solvent in which dimethyl carbonate and ethyl methyl carbonate are mixed at a molar ratio of 9: 1. The concentration of (FSO ₂ ) ₂ NLi in the electrolytic solution 5 is 2.4 mol / L.

(Comparative Example 1)
The lithium ion secondary battery of Comparative Example 1 has the same configuration as the lithium ion secondary battery of Example 1 except that it does not have a positive electrode current collector foil protective layer.

(Evaluation example 1)
The lithium ion secondary battery of Example 1 was charged to 4.1 V at a constant current of 5 C rate under the condition of 25 ° C., and then charged to maintain the same voltage for 2 hours. Then, under the condition of 60 ° C., the charge / discharge cycle of discharging to 3.3 V at a constant current of 2 C rate and charging to 4.1 V was repeated 30 times. Further, under the condition of 25 ° C., the battery was discharged to 3.0 V at a constant current of 1 C rate, and then the same voltage was maintained for 2 hours.
The lithium ion secondary battery of Example 1 that has been charged and discharged as described above is disassembled, and the negative electrode plate is allowed to stand in a dimethyl carbonate solution for 10 minutes, which is repeated three times while changing the solution, so that the remaining electrolysis occurs. The liquid components were washed and then the negative electrode plate was subjected to analysis. The amount of aluminum adhering to the negative electrode plate was measured by ICP emission analysis. The same evaluation was performed for the lithium ion secondary battery of Comparative Example 1. The results are shown in Table 1.

From the results in Table 1, it can be seen that the presence of the positive electrode current collector foil protective layer significantly suppresses the precipitation of aluminum on the negative electrode plate. It can be said that the positive electrode current collector foil protective layer suppresses the contact between the uncoated portion of the positive electrode and the electrolytic solution in the positive electrode current collector foil made of aluminum, and suppresses the elution of aluminum into the electrolytic solution.

(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 shapes of the positive electrode plate and the positive electrode current collector foil protective layer are different. Hereinafter, the positive electrode plate in the lithium ion secondary battery of Example 2 will be described with respect to the difference from the positive electrode plate in the lithium ion secondary battery of Example 1.

FIG. 2 shows a perspective view of a positive electrode plate in the lithium ion secondary battery of Example 2.

The positive electrode plate 2 in the lithium ion secondary battery of Example 2 includes a positive electrode current collector foil 20 made of aluminum and a positive electrode active material layer 21 formed on the surface of the positive electrode current collector foil 20. On the surface of the positive electrode current collector foil 20, there is a positive electrode uncoated portion 22 on which the positive electrode active material layer 21 is not formed. The positive electrode current collector foil 20 in the positive electrode uncoated portion 22 has a positive electrode current collector foil surplus portion 22a extending upward from a portion where the positive electrode active material layer 21 is formed, that is, a positive electrode coated portion, and a positive electrode current collector foil surplus. It is composed of a tab portion 22b that extends upward from the portion 22a with a shorter width than the positive electrode current collector foil surplus portion 22a and is connected to the outside.

In the positive electrode plate 2 of the lithium ion secondary battery of Example 2, the positive electrode current collector foil protective layer 23 is present on the surfaces of both the positive electrode current collector foil surplus portion 22a and the tab portion 22b along the shapes of the positive electrode collector foil surplus portion 22a and the tab portion 22b. By the presence of the positive electrode current collector foil protective layer 23 on a part of the surface of the tab portion 22b, it is possible to suitably reduce the elution of aluminum from the positive electrode uncoated portion 22, and the tab portion 22b and other members. It is effective in preventing short circuits because it can partially suppress the direct contact of the aluminum.

1 Lithium ion secondary battery 2 Positive electrode plate 3 Negative electrode plate 4 Separator 5 Electrolyte 10 Battery container 15 External power supply 20 Positive electrode current collector foil 21 Positive electrode active material layer 22 Positive electrode uncoated part 22a Positive electrode current collector foil surplus part 22b Tab part 23 Positive electrode collector foil protective layer 24 Positive electrode wire 30 Negative electrode current collector foil 31 Negative electrode active material layer 32 End 34 Negative electrode wire

Claims (6)

A positive electrode plate provided with a positive electrode current collector foil made of aluminum and a positive electrode active material layer formed on the surface of the positive electrode current collector foil, and a negative electrode active material formed on the surface of the negative electrode current collector foil and the negative electrode current collector foil. A negative electrode plate including a layer, a separator, and an electrolytic solution containing a lithium salt selected from the following general formulas (1) and (2) are provided.
On the surface of the positive electrode current collector foil, there is a positive electrode uncoated portion on which the positive electrode active material layer is not formed.
A lithium ion secondary battery in which the positive electrode plate and the negative electrode plate face each other with the separator interposed therebetween, and the uncoated portion of the positive electrode and the end portion of the negative electrode active material layer face each other.
A positive electrode current collector foil protective layer is provided on the surface of the positive electrode current collector foil in the positive electrode uncoated portion facing the end portion of the negative electrode active material layer.
The material of the positive electrode current collector foil protective layer includes a polymer, ceramics, or carbon material selected from synthetic resins or adhesives.
The positive electrode current collector foil protective layer is a lithium ion secondary battery characterized by suppressing direct contact between the positive electrode current collector foil and the electrolytic solution .
(R ¹ X ¹ ) (R ² SO ₂ ) NLi general formula (1)
(R ¹ 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, a substituent or a substituent. An unsaturated cycloalkyl group optionally substituted with, an aromatic group optionally substituted with a substituent, a heterocyclic group optionally substituted with a substituent, an alkoxy group optionally substituted with a substituent. , An unsaturated thioalkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, CN, SCN, OCN. Will be done.
^R2 is a hydrogen, a 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 that may be substituted, an aromatic group that may be substituted with a substituent, a heterocyclic group that may be substituted with a substituent, an alkoxy group that may be substituted with a substituent, Selected from an unsaturated alkoxy group that may be substituted with a substituent, a thioalkoxy group that may be substituted with a substituent, an unsaturated thioalkoxy group that may be substituted with a substituent, CN, SCN, OCN. To.
Further, R ¹ and R ² may be combined 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 may be independently substituted with hydrogen, halogen, an alkyl group which may be substituted with a substituent, a cycloalkyl group which may be substituted with a substituent, or a non-substituted group. Saturated alkyl group, unsaturated cycloalkyl group optionally substituted with substituent, aromatic group optionally substituted with substituent, heterocyclic group optionally substituted with substituent, substituted with substituent An alkoxy group which may be substituted, an unsaturated alkoxy group which may be substituted with a substituent, a thioalkoxy group which may be substituted with a substituent, an unsaturated thioalkoxy group which may be substituted with a substituent, OH. , SH, CN, SCN, OCN.
Further, R ^a and R ^b may be combined with R ¹ or R ² to form a ring. )
R ³ SO ₃ Li General formula (2)
(R ³ is selected from an alkyl group or a halogen-substituted alkyl group.) The lithium ion secondary battery according to claim 1, wherein the concentration of the electrolyte containing the lithium salt in the electrolytic solution is 1.5 to 3 mol / L. The positive electrode current collector foil in the positive electrode uncoated portion includes a positive electrode current collector foil surplus portion extending from the positive electrode current collector foil on which the positive electrode active material layer is formed, and the positive electrode current collector from the positive electrode current collector foil surplus portion. It consists of a tab part that extends shorter than the foil surplus part and is connected to the outside.
The lithium ion secondary battery according to claim 1 or 2, wherein the positive electrode current collector foil protective layer is provided on the surfaces of both the positive electrode current collector foil surplus portion and the tab portion. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the positive electrode plate, the negative electrode plate, and the separator are laminated in a flat state. The lithium according to any one of claims 1 to 4, wherein the positive electrode current collecting foil protective layer is arranged in a positive electrode uncoated portion with its end in contact with the end of the positive electrode active material layer. Ion secondary battery. The lithium ion secondary battery according to any one of claims 1 to 5, wherein the thickness of the positive electrode current collector foil protective layer is in the range of 1 μm to 500 μm.

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