JP6992578B2 - Electrodes for lithium-ion secondary batteries and lithium-ion secondary batteries using them - Google Patents

Description

The present invention relates to an electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.

Conventionally, as a positive electrode material (positive electrode active material) of a lithium ion secondary battery, a layered compound such as LiCoO ₂ or LiNi _1/3 Mn _1/3 Co _1/3 O ₂ or a spinel compound such as LiMn ₂ O ₄ has been used. There is. In recent years, compounds having a structure containing a phosphoric acid skeleton represented by LiFePO ₄ , compounds having a structure of silicic acid and boric acid, and sulfide compounds have been attracting attention as positive electrode materials.

Since these electrode materials have low electron conductivity, it is generally practiced to add a conductive auxiliary agent for imparting electron conductivity to prepare an electrode. Attempts have been made to develop high capacity by adding a conductive auxiliary agent to increase electron conductivity, and to improve cycle characteristics by adjusting the ratio of carbon as a conductive auxiliary agent (Patent Document 1). ..

Amorphous carbon such as carbon black is used as the conductive auxiliary agent, and graphite, carbon nanotubes, graphene and the like are used.

Although the conductivity can be enhanced by using these carbonaceous materials, the use of these carbonaceous materials is not sufficient to improve the cycle characteristics.

JP-A-2014-72062

However, various characteristics are not yet satisfied by the method of the prior art, and improvement of the cycle characteristics is particularly required.

The present invention has been made in view of the above-mentioned problems of cycle characteristics of the prior art, and provides an electrode for a lithium ion secondary battery capable of improving cycle characteristics and a lithium ion secondary battery using the same. The purpose is.

The electrode for a lithium ion secondary battery according to the present invention includes a current collector and an active material layer provided on the current collector, and the active material layer is an active material particle that stores and releases lithium ions. And a binder and a conductive auxiliary agent, the conductive auxiliary agent is composed of carbon containing carbon stable isotope 13C at a carbon stable isotope ratio δ13C of −35 to −20 ‰, and is at least a part of the conductive auxiliary agent. Is attached to the surface of the active material particles.

The cycle characteristics are improved by using the electrode for the lithium ion secondary battery according to the present invention.

The lithium ion secondary battery according to the present invention includes the above-mentioned electrode and a counter electrode facing the electrode via a separator, and the separator holds an electrolyte.

With such a configuration, it is possible to provide a lithium ion secondary battery having excellent cycle characteristics.

By using the electrode for a lithium ion secondary battery according to the present invention and the lithium ion secondary battery using the electrode, it is possible to improve the cycle characteristics.

It is a schematic cross-sectional view of the lithium ion secondary battery using the electrode which concerns on this embodiment.

Hereinafter, preferred embodiments of the active material of the present invention will be described in detail with reference to the drawings. However, the electrode of the present invention is not limited to the following embodiments. Further, the dimensional ratios in the drawings are not limited to the ratios shown in the drawings.

FIG. 1 is a schematic cross-sectional view of an electrode according to the present embodiment and a lithium ion secondary battery 100 using the electrode.
The lithium ion secondary battery 100 mainly includes a laminate 30, a case 50 that houses the laminate 30 in a sealed state, and a pair of leads 60, 62 connected to the laminate 30.

In the laminated body 30, a pair of positive electrodes 10 and a negative electrode 20 are arranged so as to face each other with the separator 18 interposed therebetween. The positive electrode 10 has a positive electrode active material layer 14 provided on a plate-shaped (film-shaped) positive electrode current collector 12. The negative electrode 20 is a plate-shaped (film-shaped) negative electrode current collector 22 provided with a negative electrode active material layer 24. The positive electrode active material layer 14 and the negative electrode active material layer 24 are in contact with both sides of the separator 18, respectively. Leads 62 and 60 are connected to the ends of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the ends of the leads 60 and 62 extend to the outside of the case 50.

Hereinafter, the positive electrode 10 and the negative electrode 20 are collectively referred to as electrodes 10 and 20, and the positive electrode current collector 12 and the negative electrode current collector 22 are collectively referred to as current collectors 12 and 22, and the positive electrode active material layer 14 and the negative electrode are used. The active material layers 24 are collectively referred to as active material layers 14 and 24.

The electrodes 10 and 20 according to the present embodiment include current collectors 12 and 22, and active material layers 14 and 24 containing an active material and provided on the current collector. The active material layers 14 and 24 are active material particles that absorb and release lithium ions (hereinafter, may be referred to as a positive electrode active material or a negative electrode active material. Further, the positive electrode active material and the negative electrode active material are collectively referred to as an active material. ), A binder, and a conductive additive composed of carbon bound to the surface of the particles by the binder, the conductive auxiliary agent having a stable carbon isotope ¹³ C and a stable carbon isotope ratio δ ¹³ C. It contains -35 to -20 ‰.

Hereinafter, the electrodes 10 and 20 according to this embodiment will be specifically described.
(Positive electrode 10)
The positive electrode current collector 12 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used. The positive electrode active material layer 14 contains a positive electrode active material, a conductive auxiliary agent, and a binder. The binder binds the positive electrode active materials to each other, the conductive auxiliary agents to each other, and the positive electrode active material to the conductive auxiliary agent, and binds these to the positive electrode current collector 12.

The positive electrode active material is not particularly limited as long as it is a material that can occlude and release lithium ions, and a known positive electrode active material for a battery can be used. Examples of the positive electrode active material include those containing at least one kind consisting of a transition metal-containing oxide, a phosphoric acid compound, a silicic acid compound, a boric acid compound, and a sulfide. Specifically, the transition metal-containing oxide is a group consisting of a lithium element and Mn, Co, Ni, Al, Ba, Ca, Cu, Fe, Mg, Ti, V, Zn, W, Mo, Nb, and Zr. It is an oxide containing at least one element selected from, specifically, LiCoO ₂ , LiNi _0.85 Co _0.1 Al _0.05 , LiNi _1/3 Mn _1/3 Co _1/3 . , Li _1.2 Mn _0.55 Ni _0.3 Co _0.15 O ₂ , LiCo _0.95 Mg _0.05 O ₂ , and the like. Examples of the phosphoric acid compound include LiFePO ₄ , LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ and the like. Examples of the silicic acid compound include Li ₂ FeSiO ₄ , Li ₂ VOSiO ₄ , LiMnSiO ₄ , and Li (FeMn) SiO ₄ . Examples of the boric acid compound include LiFeBO ₃ , LiMnBO ₃ , and LiVOBO ₃ . Examples of the sulfide include FeS ₂ and the like.

The conductive auxiliary agent is composed of carbon, and examples thereof include carbon black such as oil furnace, ketjen black, acetylene black, carbon nanotubes, graphene, graphite, hard carbon, and soft carbon.

In the present invention, the stable carbon isotope ratio is measured by an isotope mass analyzer, and the numerical value is a value calculated by the following formula (1).
δ ¹³ C = {( ¹³ C / ¹² C molar ratio of sample) / ( ¹³ C / ¹² C molar ratio of standard sample ) -1} × 1000 ... (1)

In the measurement using the isotope mass analyzer according to the present embodiment, a standard sample of Yaishi with ¹² C of 98.894% and ¹³ C of 1.106% can be used.

When the conductive auxiliary agent contains the carbon stable isotope ¹³ C at a carbon stable isotope ratio δ ¹³ C of −35 to −20 ‰, the electrode has the following effects.

The stable carbon isotope ¹³ C is considered to have a higher electron density than ¹² C, and it is considered that the presence of ¹³ C with respect to ¹² C causes polarization in the conductive auxiliary agent composed of carbon. Be done. In the particles that occlude and release lithium ions, it is considered that the portion destabilized by lattice defects or the like is polarized. When the conductive auxiliary agent bound on the surface of the particles that occlude and release lithium ions contains carbon stable isotope ¹³ C at a carbon stable isotope ratio δ ¹³ C of -35 ‰ or more and -20 ‰ or less, it becomes polarized. Since the conductive auxiliary agent can stabilize the surface of the particles that occlude and release lithium ions, the cycle characteristics are improved.

On the other hand, when the carbon stable isotope ¹³ C has a carbon stable isotope ratio δ ¹³ C and is more than -20 ‰, the proportion of ¹³ C in the carbon constituting the conductive auxiliary agent is large, so that the degree of polarization of the conductive auxiliary agent is high. Is weakened, the surface of the particles that occlude and release lithium ions cannot be stabilized, and the cycle characteristics deteriorate. On the other hand, if it is less than -35 ‰, the proportion of ¹³ C in the carbon constituting the conductive film becomes small, so that the polarization of the conductive film becomes small, and the surface of the particles that occlude and release lithium ions cannot be stabilized, resulting in a cycle. The characteristics are reduced.

From the viewpoint of further suppressing the deterioration of cycle characteristics, the conductive auxiliary agent preferably contains the carbon stable isotope ¹³ C at a carbon stable isotope ratio of δ ¹³ C, preferably −33 ‰ or more and -22 ‰ or less, and preferably -30 ‰ or more. It is more preferable to contain -24 ‰ or less.

The carbon stable isotope ¹³ C is preferably unevenly distributed on the interface side with the active material particles in the conductive auxiliary agent. ¹³ C is unevenly distributed at the interface between the conductive auxiliary agent and the particles that occlude and release lithium ions, so that the conductive auxiliary agent with a large polarization directly acts on the particles that occlude and release lithium ions. can. As a result, the surface of the particles that occlude and release lithium ions is more stabilized, and the cycle characteristics are further improved.

The material of the binder may be any material as long as the above-mentioned bonds are possible, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene. -Perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride ( Fluororesin such as PVF) can be mentioned.

In addition to the above, examples of the binder include vinylidenefluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber) and vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based). Fluororubber), vinylidenefluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidenefluo Vinylidene fluoride-based fluorine such as ride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluorine rubber (VDF-PFMVE-TFE-based fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene-based fluorine rubber (VDF-CTFE-based fluorine rubber) Rubber may be used.

In addition to the above, for example, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, polyamideimide, cellulose, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber and the like may be used as the binder. In addition, thermoplastic elastomeric polymers such as styrene / butadiene / styrene block copolymers, their hydrogenated products, styrene / ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers, and their hydrogenated products. May be used. Further, using syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (2 to 12 carbon atoms) copolymer, polyacrylic acid, lithium polyacrylate, carboxymethyl cellulose and the like. May be good.

As the binder, an electronically conductive conductive polymer or an ionic conductive polymer may be used. Examples of the electron-conducting conductive polymer include polyacetylene and the like. In this case, since the binder also exerts the function of the conductive material, it is not necessary to add the conductive material.

As the ionic conductive polymer, for example, one having ionic conductivity such as lithium ion can be used, and for example, a polymer compound (polyether-based polymer compound such as polyethylene oxide and polypropylene oxide) can be used. , Polyether compound cross-linked polymer, polyepicrolhydrin, polyphosphazene, polysiloxane, polyvinylpyrrolidone, polyvinylidene carbonate, polyacrylonitrile, etc.) and LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, LiBr, Examples thereof include a compound of a lithium salt such as Li (CF ₃ SO ₂ ) ₂ N and LiN (C ₂ F ₅ SO ₂ ) ₂ or an alkali metal salt mainly composed of lithium. Examples of the polymerization initiator used for the composite include a photopolymerization initiator or a thermal polymerization initiator compatible with the above-mentioned monomers.

The content of the binder contained in the positive electrode active material layer 14 is preferably 0.5 to 6% by mass based on the mass of the active material layer. When the content of the binder is less than 0.5% by mass, the amount of the binder is too small and the tendency that it becomes difficult to form a strong active material layer increases. Further, when the content of the binder exceeds 6% by mass, the amount of the binder that does not contribute to the electric capacity increases, and it tends to be difficult to obtain a sufficient volume energy density. Further, in this case, especially when the electron conductivity of the binder is low, the electric resistance of the active material layer increases, and the tendency that a sufficient electric capacity cannot be obtained increases.

(Negative electrode 20)
The negative electrode current collector 22 may be a conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

The negative electrode active material is not particularly limited, and a known negative electrode active material for a battery can be used. Examples of the negative electrode active material include graphite capable of occluding / releasing (intercalating / deintercalating, or doping / dedoping) lithium ions, graphitized carbon, easily graphitized carbon, and low-temperature fired carbon. A carbon material, a metal that can be combined with lithium such as aluminum, silicon, and tin, an amorphous compound mainly composed of oxides such as SiO, SiO ₂ , and SnO ₂ , lithium titanate (Li ₄ Ti ₅ O ₁₂ ). ), Fe ₂ O ₃ and the like. As the binder and the conductive auxiliary agent, the same ones as those for the positive electrode can be used.

Next, an example of the manufacturing method of the electrodes 10 and 20 according to the present embodiment will be described.
(Manufacturing method of electrodes 10 and 20)
The method for manufacturing the electrodes 10 and 20 according to the present embodiment includes a step of applying a paint which is a raw material of the electrode active material layers 14 and 24 onto the aggregate (hereinafter, may be referred to as a “coating step”). The present invention comprises a step of removing the solvent in the paint applied on the electric body (hereinafter, may be referred to as a “solvent removing step”).

(Applying process)
The coating process of applying the paint to the current collectors 12 and 22 will be described. The coating material contains the positive electrode active material or the negative electrode active material, the binder, the conductive auxiliary agent, and the solvent. In addition to these components, the paint may contain, for example, a conductive material for further increasing the conductivity of the active material. As the solvent, for example, N-methyl-2-pyrrolidone, N, N-dimethylformamide and the like can be used.

The method of mixing the components constituting the coating material such as the active material, the binder, the conductive auxiliary agent, and the solvent is not particularly limited, and the mixing order is also not particularly limited. For example, first, the active material, the conductive auxiliary agent and the binder are mixed, and N-methyl-2-pyrrolidone is added to the obtained mixture and mixed to prepare a paint.

The above paint is applied to the current collectors 12 and 22. The coating method is not particularly limited, and a method usually adopted when manufacturing an electrode can be used. For example, the slit die coat method and the doctor blade method can be mentioned.

(Solvent removal step)
Subsequently, the solvent in the paint applied on the current collectors 12 and 22 is removed. The removal method is not particularly limited, and the current collectors 12 and 22 coated with the paint may be dried in an atmosphere of, for example, 80 ° C to 150 ° C.

Then, the electrodes on which the active material layers 14 and 24 are formed in this way may be subsequently pressed, if necessary, by, for example, a roll press device or the like. The linear pressure of the roll press can be, for example, 10 to 50 kgf / cm.

Through the above steps, the electrode according to the present embodiment can be manufactured.

By using the electrode according to this embodiment for at least one of the positive electrode and the negative electrode, the cycle characteristics are improved.

Here, other components of the lithium ion secondary battery 100 using the electrodes manufactured as described above will be described.

The electrolyte is contained inside the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte is not particularly limited, and for example, in the present embodiment, an electrolyte solution containing a lithium salt (an aqueous electrolyte solution, an electrolyte solution using an organic solvent) can be used. However, the aqueous electrolyte solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the withstand voltage during charging is limited to be low due to the electrochemically low decomposition voltage. As the electrolyte solution, a solution in which a lithium salt is dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN. Salts such as (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB, LiFSI can be used. In addition, these salts may be used individually by 1 type and may use 2 or more types together.

Further, as the organic solvent, for example, propylene carbonate, ethylene carbonate, diethyl carbonate and the like, or fluoropropylene carbonate, fluoroethylene carbonate, fluorodiethyl carbonate and the like in which these hydrogen atoms are replaced with fluorine atoms are preferably mentioned. .. These may be used alone, or two or more kinds may be mixed and used at an arbitrary ratio.

In the present embodiment, the electrolyte may be a gel-like electrolyte obtained by adding a gelling agent in addition to the liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

The separator 18 is an electrically insulating porous body, and is, for example, a single layer of a film made of polyethylene, polypropylene, polyolefin, polyamide, polyimide, or polyamide-imide, a stretched film of a laminate or a mixture of the above resins, or cellulose. Examples thereof include a fibrous non-woven fabric made of at least one constituent material selected from the group consisting of polyester and polypropylene.

The case 50 seals the laminate 30 and the electrolyte solution inside the case 50. The case 50 is not particularly limited as long as it can suppress leakage of the electrolytic solution to the outside and invasion of water or the like into the electrochemical device 100 from the outside. For example, as the case 50, as shown in FIG. 1, a metal laminating film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. As the metal foil 52, for example, an aluminum foil can be used, and as the polymer film 54, a film such as polypropylene can be used. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). preferable.

The leads 60 and 62 are made of a conductive material such as aluminum.

Then, the leads 60 and 62 are welded to the positive electrode current collector 12 and the negative electrode current collector 22, respectively by a known method, and a separator is provided between the positive electrode active material layer 14 of the positive electrode 10 and the negative electrode active material layer 24 of the negative electrode 20. With the 18 sandwiched, it may be inserted into the case 50 together with the electrolytic solution to seal the entrance of the case 50.

Although the electrodes of the present invention, the lithium ion secondary battery provided with the electrodes, and a preferred embodiment of the method for manufacturing the electrodes have been described in detail above, the present invention is not limited to the above embodiments. In the present embodiment, the active material, the binder, and the conductive auxiliary agent are mixed in the solvent and applied to the current collector. For example, the active material, the binder, and the conductive auxiliary agent are mechanically actuated by mechanical milling or the like. May bind the conductive additive onto the surface of the active material.

For example, the electrode of the present invention can also be used for an electrochemical element other than a lithium ion secondary battery. Electrochemical elements include secondary batteries other than lithium ion secondary batteries such as metallic lithium secondary batteries (using the electrode of the present invention as the cathode and metallic lithium as the anode), and electrochemical such as lithium capacitors. Examples include capacitors. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

(Example 1)
<Manufacturing of conductive auxiliary agent>
A mixed gas of ^{13 C methane gas with a purity of 13 C} of 99% and ¹² C methane gas with a purity of ¹² C of 99.9% ( ¹² C / ¹³ ) with the annular furnace decompressed to 1 Pa and heated to 700 ° C. By flowing C mixed methane gas), carbon particles as a conductive auxiliary agent were obtained.

<Manufacturing of positive electrode>
LiCoO ₂ was used as the active material particles, polyvinylidene fluoride (PVdF) was used as the binder, and the carbon particles prepared by the above method were used as the conductive auxiliary agent. The active material, the binder and the carbon particles are mixed at 96.5% by mass, 1.5% by mass and 2% by mass, respectively, and N-methylpyrrolidone (MNP) is added to form a slurry-like paint, which is applied to an aluminum foil, dried and rolled. By doing so, an electrode (positive electrode) was produced.

<Manufacturing of negative electrode>
A mixture of silicon monoxide and graphite as active material particles with a mass ratio of 1: 9 and a mixture of polyamide-imide (PAI) as a binder and acetylene black as a solvent are used as a solvent, N-methyl-2-pyrrolidone (NMP). ) To prepare a slurry. The slurry was prepared so that the mass ratio of the active substance, acetylene black, and PAI was 90: 2: 8. This slurry was applied onto a copper foil as a current collector, dried, and then rolled to obtain an electrode (negative electrode) on which an active material layer was formed.

<Manufacturing of lithium-ion secondary battery>
The prepared positive electrode, negative electrode and separator were punched into a predetermined mold. As the separator, a membrane having a two-layer structure of a polyethylene porous membrane and a polyamide-imide porous layer was used. The negative electrode, the separator, the positive electrode, the separator, and the negative electrode were laminated in this order, and the combination of any one of the positive electrode and the negative electrode and one separator was made into one layer, and six of these were laminated to prepare a six-layer laminate. As the electrolytic solution, a solvent obtained by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a mass ratio of 3: 7 and dissolving LiPF ₆ at a mass ratio of 1 M was used as the electrolytic solution. The laminate was placed in an aluminum laminate pack, the electrolytic solution was injected into the aluminum laminate pack, and then vacuum-sealed to prepare an evaluation cell of Example 1.

(Examples 2 to 9)
Carbon particles having an adjusted ¹² C / ¹³ C mixing ratio were prepared by changing the mixing ratio of the mixed gas with ¹² C methane gas having a purity of ¹² C of 99.9%, and used as a conductive auxiliary agent. Other than that, the evaluation cells of Examples 2 to 9 were prepared in the same manner as in Example 1.

(Example 10)
An evaluation cell of Example 6 was prepared in the same manner as in Example 2 except that LiFePO ₄ was used as the active material particles.

(Example 11)
An evaluation cell of Example 7 was prepared in the same manner as in Example 2 except that LiVOPO ₄ was used as the active material particles.

(Example 12)
An evaluation cell of Example 8 was prepared in the same manner as in Example 2 except that LiNi _0.85 Co _0.1 Al _0.05 O ₂ was used as the active material particles.

(Example 13)
An evaluation cell of Example 9 was prepared in the same manner as in Example 2 except that LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the active material particles.

(Comparative Examples 1 and 2)
Carbon particles having an adjusted ¹² C / ¹³ C mixing ratio were prepared by changing the mixing ratio of the mixed gas with ¹² C methane gas having a purity of ¹² C of 99.9%, and used as a conductive auxiliary agent. Other than that, the evaluation cells of Comparative Examples 1 and 2 were prepared in the same manner as in Example 1.

<Measurement of cycle characteristics>
Using the manufactured lithium-ion secondary battery, the battery is charged at a charging rate of 0.5C (current value that ends discharge in 2 hours when constant current discharge is performed at 25 ° C), and the cycle of discharging at 1C is repeated. , The capacity after the first cycle and the capacity after 300 cycles were compared, and the capacity retention rate was obtained.

10 ... Positive electrode, 20 ... Negative electrode, 12 ... Positive electrode current collector, 14 ... Positive electrode active material layer, 18 ... Separator, 22 ... Negative electrode current collector, 24 ... Negative electrode Active material layer, 30 ... power generation element, 50 ... case, 60, 62 ... lead, 100 ... lithium ion secondary battery.

Claims (3)

With the current collector,
The active material layer provided on the current collector is provided.
The active material layer contains active material particles that occlude and release lithium ions, a binder, and a conductive auxiliary agent.
The conductive auxiliary agent is composed of carbon containing carbon stable isotope ¹³ C at a carbon stable isotope ratio δ ¹³ C of -30 to −26 ‰ .
At least a part of the conductive auxiliary agent is an electrode for a lithium ion secondary battery, which is attached to the surface of the active material particles. The carbon stable isotope ¹³ The electrode for a lithium ion secondary battery according to claim 1, wherein C is unevenly distributed on the interface side with the active material particles in the conductive auxiliary agent. Lithium, which comprises the lithium ion secondary battery electrode according to any one of claims 1 or 2, a separator, a counter electrode facing the lithium ion secondary battery electrode via the separator, and an electrolyte. Ion secondary battery.

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