JP2023027874A - Negative electrode and lithium ion secondary battery - Google Patents

Abstract

[Problem] To provide a negative electrode and the like capable of improving charge/discharge cycle characteristics. [Solution] A negative electrode 30C includes a current collector layer 32 and a lithium metal foil 34 disposed on the current collector layer 32. The current collector layer 32 is porous, and at least the inner and outer surfaces of the current collector layer are conductive. [Selected Figure] Figure 1

Description

The present invention relates to a negative electrode and a lithium ion secondary battery.

Since lithium-ion secondary batteries can achieve higher capacity than conventional nickel-metal hydride batteries and lead-acid batteries, they are attracting attention and being introduced as power sources for mobile phones, notebook computers, large-scale power storage, and power sources for automobiles. is progressing. However, due to the increasing sophistication of various electronic devices and the increasing demand for power sources, it is expected that the capacity of lithium ion secondary batteries will be further increased. Lithium metal as a negative electrode active material has a capacity several times to ten times that of graphite, and is therefore highly expected (see Patent Documents 1 and 2).

JP-A-11-214008 JP-A-2000-133314

A problem that occurs when lithium metal is used as the negative electrode active material is that non-uniform nucleation and growth of lithium metal occur on the surface of the negative electrode during charging, greatly deteriorating the charge-discharge cycle characteristics of the battery.

Specifically, since the tip of the deposited lithium metal can come into contact with the electrolytic solution, the deposition of lithium becomes easier than at other locations. Therefore, as the charge-discharge cycle progresses, charging in the negative electrode progresses in such a manner that the tip of the deposited lithium metal is further extended. As a result, elongated lithium metal is deposited, causing an internal short circuit between the positive electrode and the negative electrode, resulting in failure of the battery to function properly.

In addition, when the lithium metal dissolves during discharge, the elongated lithium metal peels off from the negative electrode, creating a portion that cannot contribute to discharge (dead lithium), which reduces the discharge capacity and shortens the battery life.

Furthermore, there is also the problem that the thickness of the negative electrode increases due to elongated lithium metal and by-products after charge-discharge cycles.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a negative electrode and the like capable of improving charge-discharge cycle characteristics.

A negative electrode according to one aspect of the present invention includes a current collector layer and a lithium metal foil disposed on the current collector layer. The current collector layer is porous, and at least the inner and outer surfaces of the current collector layer are electrically conductive.

The negative electrode may include a pair of current collector layers, and the lithium metal foil may be disposed between the pair of current collector layers.

The current collector layer may have a body portion and a tab portion, and the lithium metal foil may be arranged from between the body portion of the current collector to between the tab portions of the current collector. .

One surface of the lithium metal foil can be in contact with one of the current collector layers, and the other surface of the lithium metal foil can be in contact with the other of the current collector layers.

The negative electrode may include a pair of lithium metal foils between the pair of current collector layers, and a metal foil other than lithium may be arranged between the pair of lithium metal foils.

The current collector layer can have a porous electrically insulating substrate and conductive layers provided on the inner and outer surfaces of the electrically insulating substrate.

The conductive layer may be a metal or alloy layer containing at least one selected from the group consisting of copper, nickel, tin, aluminum, zinc, iron, magnesium, manganese, cobalt, and titanium.

The current collector layer may have a porosity of 50 to 95%.

A lithium-ion secondary battery according to one aspect of the present invention includes any of the negative electrodes described above and a positive electrode.

ADVANTAGE OF THE INVENTION According to this invention, the negative electrode etc. which can improve charge-discharge cycling characteristics are provided.

FIG. 1 is a cross-sectional view of a negative electrode 30C according to one embodiment. FIG. 2 is an enlarged cross-sectional view of part of the current collector 32 in the negative electrode 30C of FIG. 3A is an exploded perspective view of the negative electrode 30C of FIG. 1, and FIG. 3B is a top view of the negative electrode 30C of FIG. FIG. 4(a) is a cross-sectional view of a negative electrode 30A according to another embodiment, and FIG. 4(b) is a cross-sectional view of a negative electrode 30B according to another embodiment. FIG. 5 is a schematic cross-sectional view of a lithium ion secondary battery according to one embodiment.

Preferred embodiments of the present invention will be described with reference to the drawings.

(Negative electrode 30C)
A negative electrode 30C according to one embodiment of the present invention is shown in FIG. A negative electrode 30</b>C according to this embodiment includes a pair of current collector layers 32 and a lithium metal foil 34 arranged between the pair of current collector layers 32 .

As shown in FIG. 2, the current collector layer 32 has pores 32b that communicate the inside and outside of the current collector layer 32 with each other. The pores 32b communicate between the opposing outer surfaces of the current collector layer 32 . Specifically, the current collector layer 32 includes a porous electrically insulating substrate 32a, a conductive layer 32c provided on the inner surface of the pores 32b of the electrically insulating substrate 32a, and the electrically insulating substrate 32a. and a conductive layer 32d provided on the outer surface of the. The surface of conductive layer 32 c forms the conductive inner surface of current collector layer 32 , and the surface of conductive layer 32 d forms the conductive outer surface of current collector layer 32 .

The material of the electrically insulating substrate 32a may be any electrically insulating material (non-metallic material). An example of an electrically insulating substrate is a microporous film of resin. Examples of resins are polyimide resins, polyolefin resins such as polyethylene and polypropylene. The resin may be a homopolymer, a copolymer, or a mixture of polymers. A resin microporous film can be produced by stretching a resin film (dry method) or removing a pore-forming agent from the resin film (wet method).

Another example of the electrically insulating base material 32a is a non-woven fabric (paper) of various fibers. Examples of fibers are fibers of the above resins, cellulose fibers, polyester fibers, polyamide fibers, polyacrylonitrile fibers, and glass fibers.

The electrically insulating substrate 32a may be a single layer of the above materials, or may be a laminate of any two or more of the above materials.

The material of the conductive layers 32c and 32d may be any material that has a higher conductivity than the electrically insulating base material 32a, but is preferably a metal or an alloy.

The material of the conductive layers 32c and 32d is a metal or alloy containing at least one selected from the group consisting of copper, nickel, tin, aluminum, zinc, iron, magnesium, manganese, cobalt, and titanium. can.

Above all, from the viewpoint of obtaining the effect of increasing the activity of lithium by alloying it with lithium and facilitating and smoothing the deposition of lithium metal from the alloy, the materials of the conductive layers 32c and 32d are tin and aluminum. , zinc and magnesium are preferred.

The thickness of the conductive layers 32c and 32d is not particularly limited, but may be 0.1 to 2 μm, may be 1.5 μm or less, or may be 1.0 μm or less.

Such a current collector layer 32 can be obtained by electroless plating a porous electrically insulating substrate 32a.

The porosity of the electrically insulating base material 32a before plating is preferably 40 to 98%.

The porosity of the current collector layer 32 after plating may be 30% or more, may be 40% or more, and is preferably 50 to 95%. The porosity can be measured by the Archimedes method, the gas adsorption method, the mercury intrusion method, or the like, in which the pores are replaced with a liquid.

The average pore diameter of the current collector layer 32 after plating can be, for example, 0.1 to 3 μm. The average pore diameter of the current collector is measured in the direction parallel to the thickness direction (vertical) and in the direction perpendicular to the thickness direction (horizontal) in a scanning electron micrograph of a cross section parallel to the thickness direction of the current collector (or negative electrode). The number of cells (the number of pores) per inch length is measured, the average value is calculated, and the reciprocal of the average value can be obtained as the average pore diameter.

The thickness of the current collector layer 32 is not limited, but may be 5 μm or more, and may be 10 μm or more. The thickness can be 40 μm or less.

The thickness of the lithium metal foil 34 is not particularly limited, but may be 2 μm or more and 50 μm or less.

The overall thickness of the negative electrode 30C can be 1-150 μm.

As shown in FIGS. 3A and 3B, the current collector layer 32 has a body portion 32m and a tab portion 32t protruding from the body portion 32m. The lithium metal foil 34 has a body portion 34m and a tab portion 34t protruding from the body portion 34m.

A projection length D1 of the tab portion 34t of the lithium metal foil 34 from the main body portion 34m is set shorter than a projection length D2 of the tab portion 32t of the current collector layer 32 from the main body portion 32m.

As shown in FIG. 3B, the portion between the pair of tab portions 34t where the lithium metal foil 34 is not sandwiched has a weld portion 32t' where the tab portions 34t are welded together. can be

The negative electrode 30C having such a configuration can be easily manufactured by punching out a laminate having a structure of current collector layer/lithium metal foil/current collector layer with a die corresponding to the shape of the main body portion and the tab portion. be able to. The lithium metal foil 34 has the tab portion 34t, that is, the end surface L2 of the lithium metal foil of the laminate before punching is aligned with the predetermined position of the end surface L1 of the body portion 32m of the current collector layer 32 and the end surface of the tab portion 32t. By punching this laminate while it is arranged between the predetermined position of L3, the area of the main body portion 34m of the lithium metal foil 34 becomes smaller than the area of the main body portion 32m of the current collector layer 32. It can be prevented and is preferable. In addition, it is preferable to have a welding portion 32t' between the tab portions 32t of the current collector layer 32 because the electric resistance of the battery can be reduced.

(Mechanism of action)
According to the present embodiment, the current collector layer 32 is porous and has conductive inner and outer surfaces, so that the current collector layer 32 can retain liquid. A redox reaction (charging and discharging) of lithium metal can be caused by using the surface.

The specific surface area of the current collector layer 32 is large due to its porosity, so that the current density during charging is smoothed, and lithium metal can be deposited in the pores 32b of the current collector layer 32. As a result, deposition of elongated lithium metal is suppressed. Therefore, generation of dead lithium and short circuit due to dendrites can be suppressed, and cycle characteristics can be improved.

In addition, since lithium metal deposited during charging and various decomposition products generated in accordance with the progress of cycles can be deposited in the pores 32b of the current collector layer 32, the thickness of the negative electrode 30C increases with the progress of cycles. The increase can also be suppressed. Since the thickness of the decomposition product layer formed on the current collector layer 32 is reduced due to the increase in the specific surface area of the current collector layer 32, it is possible to suppress the increase in electrical resistance with the lapse of cycles.

Furthermore, since the lithium metal foil 34 is disposed between the pair of current collector layers 32, the negative electrode 30C can be handled during battery assembly or the like without contacting the lithium metal foil 34 with other members. be. This eliminates the need to apply a coating or other surface treatment to the surface of the lithium metal foil 34 in order to reduce reactivity, thereby inhibiting the deposition and dissolution rate of lithium metal and reducing redox reactivity. can be suppressed. When the lithium metal foil is brought into contact with other members such as devices, problems tend to occur due to the stickiness of the lithium metal.

Furthermore, since both sides of the lithium metal foil 34 are in contact with the current collector layers 32, the gaps between the current collector layers 32 can be effectively used to dispose a large amount of lithium metal, thereby increasing the volumetric energy density. improvement is possible.

In addition, since the current collector layer 32 has a porous electrically insulating substrate 32a and conductive layers 32c and 32d provided on the inner and outer surfaces of the electrically insulating substrate 32a, the current collector Compared to the case where the layer 32 is a pure metal porous body, the weight of the current collector layer 32 can be reduced, and the mass energy density can be improved. Furthermore, flexibility is imparted to the current collector layer 32, which facilitates handling.

(Negative electrode 30A)
Next, a negative electrode 30A according to another embodiment will be described with reference to FIG. 4(a). The negative electrode 30A shown in FIG. 4A differs from the negative electrode 30C shown in FIG. is that a metal foil 36 other than lithium is provided.

Metal foil 36 other than lithium may be other than lithium metal foil, but specifically, it is selected from the group consisting of copper, nickel, tin, aluminum, zinc, iron, magnesium, manganese, cobalt, and titanium. It can be a metal or alloy foil containing at least one of

The thickness of the lithium metal foil 34 in this embodiment can be 1 to 50 μm. The thickness of the collector layer 32 can be the same as that of the negative electrode 30C.

Also, the thickness of the metal foil 36 other than lithium can be 6 μm.

The total thickness of the negative electrode 30A can be 2-100 μm.

Such a negative electrode 30A can be obtained by arranging current collector layers 32 on both sides of a laminate foil (cladding material) in which lithium metal foils 34 are attached to both sides of a metal foil 36, respectively. Affixing can be performed by rolling or the like.

If the metal foil 36 other than lithium, such as Cu, is attached between the lithium metal foils 34 as in the present embodiment, wrinkling and breakage of the foil are prevented, and the electric field is easily made uniform.

(Negative electrode 30B)
Next, a negative electrode 30B according to another embodiment will be described with reference to FIG. 4(b). The negative electrode 30B shown in FIG. 4B differs from the negative electrode 30C shown in FIG. 1 in that the collector layer 32 is provided only on one side in the thickness direction. Such a negative electrode 30B is suitable for use as the outermost negative electrode of the battery. This negative electrode 30B is preferably laminated in the battery such that the current collector layer 32 is arranged outside the lithium metal foil 34 .

(Another embodiment of the negative electrode)
In the above embodiment, the current collector layer 32 has a porous electrically insulating substrate 32a and conductive layers 32c and 32d provided on the inner and outer surfaces of the electrically insulating substrate 32a. The current collector layer 32 may be a porous body that does not have the electrically insulating substrate 32a and is made only of a conductive material.

For example, as the current collector layer 32, the porous electrically insulating substrate 32a made of resin and conductive layers 32c and 32d provided on the inner surface and the outer surface of the electrically insulating substrate 32a are provided. A conductive porous body obtained by removing the electrically insulating base material 32a from the current collector layer 32 may be used. Heating or the like in an oxidizing atmosphere or a non-oxidizing atmosphere can be employed for removing the base material.

Porous metal foil such as mesh metal foil may be used as the current collector layer 32 . Examples of metals can be similar to the conductive materials described above.

Further, the planar shape of the current collector layer and the lithium metal foil can take various shapes according to the shape of the final battery. For example, the current collector layer may have a tab portion and the lithium metal foil may not have a tab portion, and a shape in which both the current collector layer and the lithium metal foil do not have a tab portion is not excluded. Also, the shape of the main body may be circular.

(lithium ion secondary battery)
Next, a lithium ion secondary battery 100 using the negative electrode described above will be described with reference to FIG.

A lithium ion secondary battery 100 according to this embodiment includes a power generation element 90 and a case 80 . The power generation element 90 is a laminate having a large number of negative electrodes 30C, positive electrodes 10, and separators 20. As shown in FIG. In the power generation element 90, the negative electrodes 30C and the positive electrodes 10 are alternately arranged, and the separator 20 is arranged between the negative electrodes 30C and the positive electrodes 10. As shown in FIG. Each layer of the power generation element 90 is impregnated with a non-aqueous electrolyte.

In this embodiment, both outermost layers of the power generating element 90 are the negative electrodes 30C, but the present invention is not limited to this. For example, both outermost layers of the power generating element 90 may be positive electrodes.

The number of layers of the positive electrode (or negative electrode) is not particularly limited.

The positive electrode 10 has a positive electrode current collector 12 and positive electrode active material layers 14 provided on both sides of the positive electrode current collector 12 .

The positive electrode current collector 12 may be any conductive plate material, and may be, for example, a foil of a metal such as aluminum, copper, or nickel.

The positive electrode active material layer 14 contains a positive electrode active material, a conductive aid, and a binder.

The positive electrode active material is an active material that can reversibly absorb and release lithium ions, desorb and insert (intercalate) lithium ions, or dope and dedope lithium ions and counter anions. include.

The positive electrode active material is, for example, a composite metal oxide. Examples of composite _metal oxides include lithium cobaltate ( _LiCoO2 ), lithium nickelate ( _LiNiO2 ), lithium manganate ( _LiMnO2 ), lithium manganese spinel ( _LiMn2O4 ), and general formula: _{LiNixCo yMn z} M _a O ₂ compound (in the general formula, x + y + z + a = 1, 0 ≤ x < 1, 0 ≤ y < 1, 0 ≤ z < 1, 0 ≤ a < 1, M is Al, Mg, Nb, one or more elements selected from Ti, Cu, Zn, and Cr), lithium vanadium compound (LiV ₂ O ₅ ), olivine-type LiMPO ₄ (where M is Co, Ni, Mn, Fe, Mg, Nb, Ti , Al, and one or more elements selected from Zr or VO), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), LiNi _x Co _y Al _z O ₂ (0.9<x+y+z<1.1) be. The positive electrode active material may be organic. For example, examples of organic cathode active materials are polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene.

A conductive aid enhances the electronic conductivity between the positive electrode active materials. Examples of conductive aids include carbon powders such as carbon black, acetylene black, and ketjen black; carbon nanotubes; carbon materials; metal fine powders such as copper, nickel, stainless steel and iron; mixtures of carbon materials and metal fine powders; It is a conductive oxide. Carbon materials such as carbon black, acetylene black, and ketjen black are preferable as the conductive aid.

The binder binds the active materials together. A known binder can be used as the binder. Examples of binders are fluororesins. Examples of fluororesins include 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 (PVF) and the like.

Other examples of binders include vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluororubber) and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubber (VDF-HFP-TFE fluororubber). , vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-per Vinylidene fluoride-based fluororubbers such as fluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber) and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber). . Still other examples of binders include cellulose, styrene/butadiene rubber, ethylene/propylene rubber, polyimide resin, polyamideimide resin, and acrylic resin.

Separator 20 has an electrically insulating and porous structure. An example of the separator 20 is a resin microporous film. Examples of resins are polyimide resins; polyolefin resins such as polyethylene and polypropylene. The resin may be a homopolymer, a copolymer, or a mixture of polymers. A resin microporous film can be produced by stretching a resin film (dry method) or removing a pore-forming agent from the resin film (wet method).

Another example of the separator 20 is a non-woven fabric (paper) of various fibers. Examples of fibers are fibers of the above resins, cellulose fibers, polyester fibers, polyamide fibers, polyacrylonitrile fibers, and glass fibers.

Yet another example of separator 20 is a solid electrolyte. Examples of solid electrolytes are polymer solid electrolytes, oxide solid electrolytes, and sulfide solid electrolytes.

The separator 20 may be a single layer of the above materials, or may be a laminate of any two or more of the above materials.

(Non-aqueous electrolyte)
The non-aqueous electrolyte is enclosed in the exterior body 50 and impregnates the power generating element 90 . The non-aqueous electrolyte has, for example, a non-aqueous solvent and an electrolyte. The electrolyte is dissolved in a non-aqueous solvent.

Non-aqueous solvents include, for example, cyclic carbonates and chain carbonates. Cyclic carbonates solvate electrolytes. Cyclic carbonates are, for example, ethylene carbonate, propylene carbonate and butylene carbonate. The cyclic carbonate preferably contains at least propylene carbonate. Chain carbonates reduce the viscosity of cyclic carbonates. Chain carbonates are, for example, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate. Non-aqueous solvents may also include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like. .

The electrolyte is, for example, a lithium salt. The electrolyte is, for example, _LiPF6 , _LiClO4 , _{LiBF4, LiCF3SO3 , LiCF3CF2SO3} , LiC _{( CF3SO2} ) ₃ , LiN( _{FSO2 ) 2 ,} LiN _{( CF3SO2 ) 2} , LiN( _{CF3CF2SO2 ) 2 ,} LiN( _{CF3SO2 )} ( _{C4F9SO2 ) ,} LiN( _CF3CF2CO ) ₂ , LiBOB, _and the like. Lithium salt may be used individually by 1 type, and may use 2 or more types together.

(Exterior body)
The exterior body 50 seals the power generation element 90 and the non-aqueous electrolyte inside. The exterior body 50 prevents the leakage of the non-aqueous electrolyte to the outside and the intrusion of moisture into the inside of the lithium ion secondary battery 100 from the outside.

Although not shown, the exterior body 50 can have a metal foil and resin layers laminated on both sides of the metal foil.

For example, aluminum foil can be used as the metal foil. A polymer film such as polypropylene can be used for the resin layer. The material forming the resin layer may be different between the inner side and the outer side. For example, a polymer with a high melting point such as polyethylene terephthalate (PET) or polyamide (PA) is used as the outer material, and polyethylene (PE) or polypropylene (PP) is used as the inner polymer film material. be able to.

Although not shown, leads respectively connected to the tab portions of the positive electrode and the negative electrode generally communicate the inside and outside of the exterior body. The leads may be formed from a conductive material such as aluminum, nickel, or nickel-plated metal plate on copper. In particular, it is preferable to use an aluminum metal plate for the lead connected to the positive electrode 10 side, and to use a nickel metal plate or a nickel-plated metal plate for the lead connected to the negative electrode 30C side.

(Other lamination structure of power generation element)
The lithium-ion secondary battery of the present invention is not limited to a lamination form as long as it employs the negative electrode described above.
For example, in the power generation element 90, the negative electrode 30A may be employed instead of the negative electrode 30C. Also, the negative electrode 30B may be employed instead of the outermost negative electrode 30C or the negative electrode 30A in the power generation element 90 .

(Example 1)
Production of Current Collector Layer and Negative Electrode 30C A polyimide resin having a thickness of 20 μm and a porosity of 80% was prepared as an electrically insulating substrate. This base material was brought into contact with an electroless plating solution to form a Cu layer having a thickness of 0.5 μm on the inner and outer surfaces of the electrically insulating base material, thereby obtaining a current collector layer having a porosity of 60%.
Lithium metal foil having a thickness of 20 μm was placed on both sides of the current collector layer, and then cut into a predetermined shape to obtain the negative electrode 30C having the shape shown in FIGS. 1 and 2 and having a main body and a tab. The structure of the negative electrode 30C has a structure of porous current collector layer/lithium metal foil/porous current collector layer.

Manufacture of Positive Electrode A positive electrode slurry was applied to one surface of an aluminum foil having a thickness of 15 μm and cut into a predetermined shape having a main body portion and a tab portion similar to those of the negative electrode. A positive electrode slurry was prepared by mixing a positive electrode active material, a conductive aid, a binder, and a solvent.

_{LiNixCoyMnzMaO2} (x ₌ 0.83, y = 0.09 _{, z} = 0.07 _, a = 0.01, M = Al) was used. Carbon black was used as a conductive aid. Polyvinylidene fluoride (PVDF) was used as a binder. The mass ratio of the positive electrode active material, conductive aid, and binder was 95:2:3. The amount of the positive electrode active material supported in the dried positive electrode active material layer was 20 mg/cm ² . A positive electrode was produced by removing the solvent from the positive electrode slurry in a drying furnace.

(Production of lithium ion secondary battery for evaluation)
The produced negative electrode 30C and positive electrode were alternately laminated via a polypropylene separator having a thickness of 10 μm, and a laminate was produced by laminating 11 sheets of the negative electrode 30C and 10 sheets of the positive electrode. Both outermost electrodes were negative electrodes 30C. Further, a negative electrode lead made of nickel was attached to the tab portion of the negative electrode of the laminate, and a positive electrode lead made of aluminum was attached to the tab portion of the positive electrode of the laminate by an ultrasonic welding machine.

Then, this laminate was inserted into a case and heat-sealed except for one peripheral portion to form a closed portion. After that, a non-aqueous electrolyte was injected into the case. The non-aqueous electrolyte was prepared by adding 4M (mol/L) LiN(FSO ₂ ) ₂ as a lithium salt to a 1,2-dimethoxyethane solvent. Then, the remaining one portion was heat-sealed while being decompressed by a vacuum sealer to fabricate a lithium ion secondary battery (full cell).

Next, using a secondary battery charge/discharge tester (manufactured by Hokuto Denko Co., Ltd.), the required current capacity retention rate of the lithium-ion secondary battery after the lapse of cycles was measured. In an environment of 25 ° C., constant current and constant voltage charge to 4.3 V at 0.2 C and constant current discharge to 3.0 V at 1 C are set as one charge and discharge cycle, and 80% of the initial capacity. The number of cycles required to drop below was measured.

In addition, after 100 cycles, the lithium ion secondary battery was disassembled to measure changes in the thickness of the negative electrode. The thickness change rate was determined by (“thickness of negative electrode after 100 cycles”−“thickness of negative electrode before first charge”)/(“thickness of negative electrode before first charge”)×100.

Furthermore, the mass energy density was calculated by multiplying the initial capacity by the nominal voltage of 3.7 V/the mass of the battery.

Examples 2-8
Example 1 was repeated except that the conductive layer electrolessly plated on the porous substrate was changed from copper to nickel, tin, aluminum, zinc, iron, magnesium and titanium.

Example 9
The same procedure as in Example 1 was carried out except that the electrically insulating substrate had a thickness of 20 μm and a porosity of 47%, and the porosity of the current collector layer was 21%.

Example 10
The same procedure as in Example 1 was carried out except that the electrically insulating substrate had a thickness of 20 μm and a porosity of 50%, and the porosity of the current collector layer was 28%.

Example 11
The same procedure as in Example 1 was carried out except that the electrically insulating substrate had a thickness of 20 μm and a porosity of 62%, and the porosity of the current collector layer was 40%.

Example 12
The same procedure as in Example 1 was carried out except that the electrically insulating substrate had a thickness of 20 μm and a porosity of 75%, and the porosity of the current collector layer was 54%.

Example 13
The same procedure as in Example 1 was carried out except that the electrically insulating substrate had a thickness of 20 μm and a porosity of 95%, and the porosity of the current collector layer was 78%.

Example 14
The same procedure as in Example 1 was carried out except that the electrically insulating substrate had a thickness of 20 μm and a porosity of 97%, and the porosity of the current collector layer was 82%.

Example 15
The same procedure as in Example 1 was carried out except that the thickness of the Cu layer formed on the inner and outer surfaces of the electrically insulating substrate was set to 0.1 μm, and the porosity of the current collector layer was set to 75%.

Example 16
Example 1 was the same as in Example 1, except that the thickness of the Cu layer formed on the inner and outer surfaces of the electrically insulating substrate was 1.0 μm, and the porosity of the current collector layer was 43%.

Example 17
The same procedure as in Example 1 was carried out except that the thickness of the Cu layer formed on the inner and outer surfaces of the electrically insulating substrate was set to 1.7 μm, and the porosity of the current collector layer was set to 21%.

Example 18
The same procedure as in Example 1 was performed except that the negative electrode 30A in FIG. 4(a) was used instead of the negative electrode 30C. The negative electrode 30A has a structure of porous current collector layer/Li metal foil/Cu foil/Li metal foil/porous current collector layer.

Example 19
The procedure was the same as in Example 1, except that 10 negative electrodes 30C and 11 positive electrodes were used, and both of the outermost electrodes were positive electrodes.

Example 20
The same procedure as in Example 1 was performed except that the negative electrode 30C was replaced with the negative electrode 30B in both outermost electrodes. The negative electrode 30B has a porous collector layer/Li metal foil structure in order from the outside.

Comparative example 1
The procedure was the same as in Example 1, except that a non-porous copper foil (thickness: 6 μm) was used instead of the porous current collector. That is, the negative electrode of Comparative Example 1 has a structure of lithium metal foil (thickness 20 μm)/non-perforated copper foil/lithium metal foil (thickness 20 μm).

Table 1 shows the results.

It was confirmed that the negative electrodes according to the examples had improved cycle characteristics.

DESCRIPTION OF SYMBOLS 10... Positive electrode, 20... Separator, 30A, 30B, 30C... Negative electrode, 32... Collector layer, 32a... Electrically insulating substrate, 32c, 32d... Conductive layer, 32t... Tab portion of collector layer, 32m... Body portion of collector layer 34 Lithium metal foil 34t Lithium metal foil tab portion 34m Lithium metal foil body 36 Metal foil other than lithium 100 Lithium ion secondary battery.

Claims (9)

comprising a current collector layer and a lithium metal foil disposed on the current collector layer;
The negative electrode, wherein the collector layer is porous, and at least the inner and outer surfaces of the collector layer are conductive. 2. The negative electrode according to claim 1, comprising a pair of said current collector layers, wherein said lithium metal foil is disposed between said pair of current collector layers. The current collector layer has a body portion and a tab portion,
3. The negative electrode according to claim 2, wherein the lithium metal foil is arranged from between the body portion of the current collector to between the tab portions of the current collector. 4. The method according to claim 2 or 3, wherein one surface of said lithium metal foil is in contact with one of said current collector layers, and the other surface of said lithium metal foil is in contact with said other of said current collector layers. negative electrode. 4. The negative electrode according to claim 2, wherein a pair of said lithium metal foils is provided between said pair of current collector layers, and a metal foil other than lithium is arranged between said pair of lithium metal foils. 6. The collector layer according to any one of claims 1 to 5, wherein the current collector layer has a porous electrically insulating substrate and conductive layers provided on the inner and outer surfaces of the electrically insulating substrate. The negative electrode described in . 6. The conductive layer is a metal or alloy layer containing at least one selected from the group consisting of copper, nickel, tin, aluminum, zinc, iron, magnesium, manganese, cobalt, and titanium. The negative electrode described in . The negative electrode according to any one of claims 1 to 7, wherein the current collector layer has a porosity of 50 to 95%. A lithium ion secondary battery comprising the negative electrode according to any one of claims 1 to 8 and a positive electrode.

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