JP2017162693A - Negative electrode for lithium ion secondary battery and lithium ion secondary battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium ion secondary battery, excellent in charge/discharge cycle characteristics, and a lithium ion secondary battery.SOLUTION: In a negative electrode for a lithium ion secondary battery, a negative electrode mixture layer is provided on at least one main surface of a negative electrode collector. The negative electrode mixture layer contains a negative electrode active material capable of absorbing and desorbing lithium ions, and has a coat of protein on at least a part of a surface thereof. The protein preferably contains at least one of an alkaline metal salt of casein, a magnesium salt of casein, an alkaline earth metal salt of casein, an ammonium salt of casein, albumin, lysozyme, and globulin.SELECTED DRAWING: Figure 2

Description

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

In recent years, lithium ion secondary batteries have been widely used as power sources for portable electronic devices, automobiles, and power storage. The lithium ion secondary battery is mainly composed of a positive electrode, a negative electrode, a separator that insulates the positive electrode from the negative electrode, and an electrolyte that enables ions to move between the positive electrode and the negative electrode. Since lithium ion secondary batteries have high energy density, they have been put into practical use as power sources for portable electronic devices such as mobile phones and notebook computers, and are widely used. In recent years, with the remarkable development of portable electronic devices, communication devices, and the like, there is a strong demand for lithium ion secondary batteries with higher energy density from the viewpoints of downsizing and weight reduction of devices. Further, there is a strong demand for extending the life of automobile batteries. As a negative electrode for a lithium ion secondary battery in response to the above demand, a metal negative electrode and a metal oxide negative electrode showing high theoretical capacity are attracting attention, and include, for example, silicon such as silicon (Si) and silicon oxide (SiO _x ). The negative electrode active material is a material most expected in increasing the energy density of the battery because it exhibits a theoretical capacity much higher than the theoretical capacity of 372 mAh · g ^{−1 of} graphite currently in practical use.

  However, in a negative electrode using a negative electrode active material containing silicon, the behavior of expansion and contraction of the negative electrode due to insertion and extraction of lithium ions by charging and discharging is enormously larger than that of a negative electrode using graphite as a negative electrode active material. Therefore, in the lithium ion secondary battery using the negative electrode, cracking occurred in the negative electrode mixture layer or fine powdering of the negative electrode active material occurred due to repeated charging and discharging. That is, in the case of a negative electrode containing silicon, the surface area of the negative electrode mixture layer and the negative electrode active material due to expansion increases, the decomposition reaction of the electrolyte increases, and as a result, the electrolytic mass decreases and the electrolyte sufficient for the positive and negative electrodes and the separator, That is, there is a problem that lithium ions are not supplied and excellent charge / discharge cycle characteristics cannot be obtained.

  In order to solve such a problem, Prior Art Document 1 discloses a technique of covering a negative electrode mixture layer with a cross-linked film formed from a low cross-linkable monomer and a polymer support.

  However, when the method described in Prior Art Document 1 was used, excellent charge / discharge cycle characteristics could not be obtained in our study.

JP-A-2005-197258

  The objective of this invention is made | formed in view of the said situation, and is providing the negative electrode for lithium ion secondary batteries excellent in charging / discharging cycling characteristics, and a lithium ion secondary battery using the same.

  The negative electrode for a lithium ion secondary battery according to the present invention is provided with a negative electrode mixture layer on at least one main surface of a negative electrode current collector, and the negative electrode mixture layer is capable of absorbing and releasing lithium ions. It contains a substance and has a protein film on at least a part of the surface of the negative electrode mixture layer.

  Furthermore, the protein preferably contains at least one of alkali metal salt of casein, magnesium salt of casein, alkaline earth metal salt of casein, ammonium caseinate, albumin, lysozyme, and globulin.

  The protein is an alkali metal salt of casein, and the alkali metal salt of casein preferably contains at least one of sodium caseinate, lithium caseinate, and potassium caseinate.

  The protein is at least one of a magnesium salt of casein and an alkaline earth metal salt of casein, and the magnesium salt of casein is casein magnesium, and the alkaline earth metal salt includes casein calcium, casein strontium, It is preferable to include at least one casein barium.

  Furthermore, it is preferable that the loading amount of the film containing protein is 0.5 to 50% by weight with respect to the weight of the negative electrode active material.

  A lithium ion secondary battery according to the present invention includes a positive electrode that occludes and releases lithium ions, a negative electrode for the lithium ion secondary battery, a separator interposed between the positive electrode and the negative electrode for the lithium ion secondary battery, and A lithium ion secondary battery including an electrolyte is provided.

  According to the negative electrode of the present invention, by having a protein film on at least a part of the surface of the negative electrode mixture layer, excellent charge / discharge cycle characteristics can be obtained by suppressing expansion associated with charge / discharge.

It is sectional drawing showing the structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. 4 is a surface view of a negative electrode mixture layer of a negative electrode for a lithium ion secondary battery according to Example 4. (FE-SEM photo) It is a surface form of the negative mix layer of the negative electrode for lithium ion secondary batteries which concerns on the comparative example 1. FIG. (FE-SEM photo) It is a FT-IR spectrum of the negative mix layer of the negative electrode for lithium ion secondary batteries which concerns on Example 4 and Comparative Example 1. It is the surface form of the negative mix layer of the negative electrode for lithium ion secondary batteries which concerns on Example 4 after 300 cycles. (FE-SEM photo) It is the surface form of the negative mix layer of the negative electrode for lithium ion secondary batteries which concerns on the comparative example 1 after 300 cycles. (FE-SEM photo)

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
FIG. 1 shows a structural cross-sectional view of a lithium ion secondary battery 100 according to this embodiment. The lithium ion secondary battery 100 includes a negative electrode 10 for a lithium ion secondary battery and a positive electrode 20 for a lithium ion secondary battery, and a separator interposed between the negative electrode for a lithium ion secondary battery and the positive electrode for a lithium ion secondary battery. 18 and the electrolyte, and the separator 18 prevents physical contact between the positive electrode and the negative electrode, and the positive electrode, the negative electrode, and the separator are impregnated with the electrolyte.

  The shape of the lithium ion secondary battery is not limited to the laminate film type of FIG. 1, and may be any of a cylindrical type, a square type, a coin type, and the like. In this embodiment, a laminate film is used as the outer package 50, and in the example, a laminate film type battery is produced and evaluated. As said laminated film, what is comprised as a 3 layer structure by which a polypropylene, aluminum, and polyamide are laminated | stacked in this order, for example can be used.

(Anode for lithium ion secondary battery)
In the negative electrode 10 for a lithium ion secondary battery according to this embodiment, a negative electrode mixture layer 14 is provided on at least one main surface of a negative electrode current collector, and the negative electrode mixture layer 14 occludes and releases lithium ions. The negative electrode mixture layer 14 includes a negative electrode active material containing silicon, and has a protein film on at least a part of its surface.

  In particular, the protein preferably contains at least one of alkali metal salt of casein, magnesium salt of casein, alkaline earth metal salt of casein, ammonium caseinate, albumin, lysozyme, and globulin.

  Among them, the protein according to the present embodiment is more preferably at least one of an alkali metal salt of casein, a magnesium salt of casein, and an alkaline earth metal salt of casein.

  Further, the alkali metal salt of casein contains at least one of sodium caseinate, lithium casein, and potassium casein, the magnesium salt of casein is magnesium casein, and the alkaline earth metal salt of casein is casein calcium, casein strontium It is preferable that at least one casein barium is included.

  Thus, when the negative electrode having the protein coating on at least a part of the surface of the negative electrode mixture layer 14 was used as a negative electrode for a lithium ion secondary battery, the expansion of the negative electrode accompanying charge / discharge was suppressed, which was excellent. A lithium ion secondary battery exhibiting charge / discharge cycle characteristics is obtained.

  The above action is considered to be achieved by the following effects. The protein coated on at least a part of the surface of the negative electrode mixture layer is affected by the oxidation-reduction reaction of the charge / discharge reaction, and the three-dimensional structure of the protein expands and contracts to expand and contract the negative electrode mixture layer. It can suppress suitably. Therefore, since the crack to the negative electrode mixture layer is suppressed, side reaction with the electrolytic solution, that is, decomposition of the electrolytic solution can be suppressed. Due to the above effects, a lithium ion secondary battery having excellent charge / discharge cycle characteristics can be obtained.

  Furthermore, the amount of the protein coating supported is preferably 0.5 to 50% by weight based on the weight of the negative electrode active material. This is because when the amount is within this range, more excellent charge / discharge cycle characteristics can be obtained.

  The protein coating may contain particles. The particles are preferably smaller than the particle size of the negative electrode active material, and in particular, nano-sized particles of 500 nm or less are preferable. The shape of the particles is not particularly limited, but may be appropriately used such as a true sphere, a substantially spherical shape, a polygonal shape, a scale shape, and a plate shape. By having the particles on the surface of the negative electrode mixture layer, it becomes easier for proteins to be carried in the voids between the particles, so that a protein film is easily formed uniformly on the surface of the negative electrode mixture layer.

  The material of the particles may be an inorganic material or an organic material, and examples thereof include amorphous carbon, titanium oxide, aluminum oxide, zinc oxide, silicon oxide, polymethyl methacrylate, and polystyrene.

[Negative electrode active material]
The negative electrode active material according to the present embodiment is preferably, for example, silicon (Si), tin, germanium, iron, or a compound or alloy thereof that electrochemically occludes and releases lithium ions, and particularly silicon having a high capacity is preferable. . This is because the negative electrode active material in which cracks in the negative electrode mixture layer due to expansion and fine pulverization of the negative electrode active material are remarkable exerts the effects of the present invention more suitably.

  Silicon may be used alone, a silicon compound or a silicon alloy may be used, and two or more of these may be used in combination.

Examples of the silicon compound include silicon oxide, which is expressed as SiO _x (provided that the atomic ratio x of oxygen to silicon satisfies 0 <x ≦ 2).

  The silicon oxide may include silicon microcrystals and an amorphous phase of silicon dioxide, in which case the atomic ratio of silicon to oxygen includes the silicon microcrystals and the silicon dioxide amorphous phase. Ratio. That is, silicon oxide includes a structure in which silicon microcrystals are dispersed in a matrix of amorphous silicon dioxide, and the amorphous silicon dioxide and the silicon dispersed therein are included. In combination with the microcrystal, the atomic ratio x may satisfy 0 <x ≦ 2. For example, in the case of a compound in which silicon is dispersed in an amorphous silicon dioxide matrix and the molar ratio of silicon dioxide to silicon is 1: 1, x = 1, so that the structural formula is expressed as SiO. Is done. The amorphous silicon dioxide matrix may contain amorphous silicon monoxide.

  Further, the above-described silicon alloy is composed of, for example, tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as the second constituent element other than silicon. The thing containing at least 1 sort (s) of a group is mentioned.

  The negative electrode active material according to this embodiment may be coated with carbon on the surface. This is because good electron conductivity can be obtained by coating the surface of the negative electrode active material with carbon.

  Furthermore, the shape of the negative electrode active material can be appropriately used without particular limitation, such as an indefinite shape, a spherical shape, a granular shape, a polygonal shape, a scale shape, a plate shape, and a fiber shape. In particular, in the case of a polygonal shape, the number of contacts between the conductive auxiliary agent and the current collector in the negative electrode mixture layer and the adjacent negative electrode active materials tends to increase, which is preferable in terms of electronic conductivity.

  Further, in addition to the above-described negative electrode active material, a carbon-based negative electrode active material may be used in combination. For example, crystalline carbon, amorphous carbon, or a combination thereof may be used. Examples of the crystalline carbon include natural graphite such as amorphous, spherical, granular, polygonal, scaly, plate-like, and fibrous, or artificial graphite. As the amorphous carbon, For example, soft carbon, hard carbon, mesophase pitch carbide, fired coke and the like can be mentioned.

  Further, the negative electrode active material according to the present embodiment is not limited to the above-described materials, and any other material that can electrochemically occlude and release lithium ions is not particularly limited.

[Negative Conductive Aid]
The negative electrode mixture layer 14 according to the present embodiment may add a conductive additive for the purpose of improving conductivity. The conductive auxiliary agent used in the present embodiment is not particularly limited, and a known material can be used. For example, carbon black such as acetylene black, ketjen black, furnace black, channel black, thermal black, carbon fiber such as vapor grown carbon fiber (VGCF), carbon nanotube (CNT), graphene, and carbon materials such as graphite 1 type or 2 types or more can be used.

[Negative electrode binder]
The negative electrode mixture layer 14 according to this embodiment may use a binder for the purpose of improving the binding properties of the negative electrode active material, the negative electrode conductive additive, and the negative electrode current collector 12. The negative electrode binder used in the negative electrode mixture layer of the present embodiment may be an organic solvent binder or an aqueous binder. For example, polyamideimide, polyimide, polyamide, polyacrylic acid, polyacrylate, alginate, styrene-butadiene copolymer (SBR), carboxymethylcellulose (CMC), polyurethane and the like can be mentioned. It is also possible to use multiple types in combination. In particular, when a silicon-based negative electrode active material having a large expansion due to charge / discharge is used, polyamideimide, polyimide, polyamide, and polyacrylic acid can be preferably used. In addition, it is not limited to these enumerated binders.

[Negative electrode current collector]
The negative electrode current collector 12 according to this embodiment is made of a conductive material, and the negative electrode mixture layer 14 is disposed on one main surface or both surfaces thereof. Although the material which comprises the said negative electrode collector 12 is not specifically limited, As the negative electrode collector 12 used for the negative electrode 10, using copper, stainless steel, nickel, titanium, or these alloy foils. it can. In particular, copper, a copper alloy, and stainless steel are preferable. From the viewpoint of cost, an electrolytic copper foil and a rolled copper foil can be suitably used. From the viewpoint of strength, a rolled foil of stainless steel or copper alloy can be suitably used.

(Positive electrode for lithium ion secondary battery)
In the positive electrode 20 for a lithium ion secondary battery according to this embodiment, a positive electrode mixture layer 24 is provided on at least one main surface of a positive electrode current collector 22, and the positive electrode mixture layer 24 occludes at least lithium ions. It contains a positive electrode active material to be released.

[Positive electrode active material]
The positive electrode active material according to this embodiment is preferably a lithium-containing compound such as lithium oxide, lithium sulfide, or an intercalation compound containing lithium, and a mixture of two or more of these may be used. In particular, in order to increase the energy density, a lithium composite oxide represented by the general formula Li _x MO ₂ or an intercalation compound containing lithium is preferable. M is preferably one or more transition metals, specifically, at least one of Co, Ni, Mn, Fe, Al, V, and Ti is preferable. x varies depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. In addition, manganese spinel (LiMn ₂ O ₄ ) having a spinel crystal structure, lithium iron phosphate (LiFePO ₄ ) having an olivine crystal structure, and the like are preferable because they can provide a high energy density.

Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), LiNi _x Co _y Mn _z M _a O ₂ (x + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and 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) , and the like. Further, the material is not limited to these materials, and any other positive electrode active material that electrochemically occludes and releases lithium ions is not particularly limited.

[Positive electrode conductive aid]
In the positive electrode mixture layer 24 according to the present embodiment, a conductive additive may be added for the purpose of improving conductivity. The conductive auxiliary agent used in the present embodiment is not particularly limited, and a known material similar to the conductive auxiliary agent used in the negative electrode mixture layer can be used.

[Positive electrode binder]
The positive electrode mixture layer 24 according to this embodiment may use a binder for the purpose of improving the binding properties of the positive electrode active material, the positive electrode conductive additive, and the positive electrode current collector 22. The positive electrode binder used for the positive electrode mixture layer 24 of the present embodiment may be an organic solvent binder or an aqueous binder. For example, polyvinylidene fluoride (PVdF), polyimide, polyamideimide, polyamide, polyurethane, polyethylene vinyl alcohol, polyacrylate, styrene-butadiene copolymer (SBR), carboxymethylcellulose (CMC), polyurethane, and the like can be mentioned. Species may be used, and multiple types may be used in combination. In addition, it is not limited to these enumerated binders.

[Positive electrode current collector]
The positive electrode current collector 22 according to the present embodiment is made of a conductive material, and the positive electrode mixture layer 24 is disposed on one main surface or both surfaces thereof. Although the material which comprises the said positive electrode collector 22 is not specifically limited, As the positive electrode collector 22 used for the positive electrode 20, using aluminum, stainless steel, nickel, titanium, or these alloy foils. In particular, aluminum foil is preferable.

(separator)
The separator 18 according to the present embodiment is interposed between the negative electrode 10 and the positive electrode 20, prevents a short circuit due to contact between the two electrodes, and is impregnated with an electrolyte, thereby allowing lithium ions to pass therethrough. The separator 18 includes, for example, a porous film having a large number of minute pores. Specific materials of the separator 18 include polyolefin-based porous films such as polyethylene and polypropylene, polyimide, and polyamideimide. Examples thereof include a highly heat-resistant porous film, a composite film of the polyolefin-based porous film and the highly heat-resistant porous film, and a nonwoven fabric such as aromatic polyamide, polyimide, and polyamideimide. The separator 18 preferably has, for example, a thickness in the range of 5 μm to 50 μm, and a porosity representing a void volume ratio in the total volume of 20% to 60%.

(Electrolytes)
The electrolyte according to this embodiment is impregnated in the separator 18 and includes, for example, a solvent and an electrolyte salt dissolved in the solvent, and may include an additive as necessary. Examples of the electrolyte solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Esters, chain carboxylic acid esters such as methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), or γ-butyrolactone (GBL), γ-valerolactone (GVL) ) And the like. Any one of these may be used as a solvent by mixing two or more. Moreover, it is not limited to the enumerated solvent as long as it does not impair the characteristics when the electrolyte salt is dissolved to form the lithium ion secondary battery 100.

  Examples of the solvent include cyclic carbonates having an unsaturated bond such as vinylene carbonate (VC), fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), and 1,3-propane. A flame-retardant liquid such as a sulfur-containing compound such as sultone (PS) or a phosphazene compound can be mixed and used as a solvent.

(Electrolyte salt)
Examples of the electrolyte salt according to the present embodiment include a lithium salt, which dissociates in the electrolyte and supplies lithium ions. As the lithium salt, is not particularly limited, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5) 4, LiCH 3 SO 3, LiC (SO 2 CF 3) ₃ , LiN (CF ₃ SO ₂ ) ₂ (also referred to as LiTFSI), LiN (C ₂ F ₅ SO ₂ ) ₂ (also referred to as LiBETI), LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN (CF ₃ SO ₂ ) (C ₃ F ₇ SO ₂ ), LiN (CF ₃ SO _{2) (C 4 F 9 SO} 2), LiN (SO 2 F) 2 ( also known sometimes referred to as _{LiFSI), LiAlCl 4, LiSiF 6} , LiCl, LiC BO ₈ (aka, sometimes referred to as LiBOB), or the like can be mentioned LiBr, can be used those selected from any combination of one, or two or more thereof. In particular, LiPF ₆ can be suitably used because it can obtain high ionic conductivity.

(Method for producing lithium ion secondary battery)
The lithium ion secondary battery 100 according to the present embodiment can be manufactured as follows, for example.

[Production method of negative electrode]
In the negative electrode 10 according to the present embodiment, a negative electrode active material, a negative electrode conductive additive, a negative electrode binder, and a solvent are mixed and dispersed to prepare a paste-like negative electrode slurry. As the solvent, it is desirable to use a good solvent for the binder added to the negative electrode slurry. For example, in the case of an organic solvent-based binder, N-methyl-2-pyrrolidone (NMP), N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, methyl ethyl ketone, acetonitrile and the like can be mentioned, and if it is an aqueous binder, ion-exchanged water, distilled water and the like can be mentioned.

  Next, the negative electrode slurry is applied to one surface or both surfaces of the negative electrode current collector 12 such as a copper foil by using a comma roll coater, for example, and the solvent is dried in a drying furnace. Let In addition, when apply | coating the negative mix layer 14 on both surfaces of the said negative electrode collector 12, it is desirable that it is a negative mix layer which becomes the same film thickness on both surfaces.

  Subsequently, the negative electrode on which the negative electrode mixture layer 14 is formed is adjusted to have a predetermined thickness and density by a roll press or the like, and at the same time, the negative electrode mixture layer 14 is pressure-bonded to one side or both sides of the negative electrode current collector 12. The adhesion between the negative electrode mixture layer 14 and the negative electrode current collector 12 is increased.

  The negative electrode is punched into a predetermined electrode size with a mold to obtain a negative electrode 10 for a lithium ion secondary battery. The area of the negative electrode 10 is preferably equal to or larger than the area of the positive electrode 20. This is to prevent the occurrence of an internal short circuit due to lithium deposition by making the area of the negative electrode 10 equal to or larger than the area of the opposing positive electrode 20.

  The negative electrode 10 is heat-treated in vacuum or in an inert gas atmosphere at a temperature not higher than the temperature at which the binder is thermally decomposed, whereby the interface between the negative electrode mixture layer 14 and the negative electrode current collector 12 is obtained by polymerization and / or crosslinking of the binder. , And the adhesion between the negative electrode active materials can be further increased. Further, if the surface of the negative electrode current collector 12 has a certain surface roughness, an anchor effect acts between the binder and the negative electrode current collector 12 by allowing the binder to enter the uneven portions of the surface, Adhesion is improved. Therefore, even when the negative electrode active material undergoes volume expansion due to insertion and extraction of lithium ions, peeling of the negative electrode mixture layer 14 from the negative electrode current collector 12 can be suppressed.

  The negative electrode 10 according to the present embodiment has a protein film on at least a part of the surface of the negative electrode mixture layer 14. Examples of the method for forming a protein film include a liquid phase method such as a coating method, a dipping method, or a dip coating method. These methods may be used alone, or two or more methods may be used in combination. For example, in the immersion method, the negative electrode 10 is impregnated in a protein-containing solution for several seconds to several minutes, and then the negative electrode 10 is pulled up and dried. Alternatively, in the coating method, a protein film is formed by applying a solution containing the protein onto the surface of the negative electrode mixture layer 14 of the negative electrode 10 and drying the solution. In the coating method, devices such as a comma roll coater, a doctor blade, and a spin coater can be used. Furthermore, the amount of the protein film supported can be easily controlled by adjusting the concentration of the protein-containing solution, the number of impregnations, the number of times of application, and the like.

[Identification of protein coating]
The identification of the protein film formed on the surface of the negative electrode mixture layer of the negative electrode according to the present embodiment is performed by, for example, a field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDX), Fourier It can be performed by total reflection attenuation method (ATR method) of conversion infrared spectroscopic analysis (FT-IR), laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), pyrolysis gas chromatograph mass spectrometry, or the like.

  In the observation by FE-SEM, the presence or absence of the coating can be easily confirmed by observing the surface of the negative electrode mixture layer before and after forming the protein coating.

  In FT-IR analysis, each protein to be coated is measured as a single powder, the absorption spectrum position of each protein is confirmed, and then the absorption spectrum position of the negative electrode on which each protein film is formed is measured. The presence or absence of a protein coating on the surface of the mixture layer can be confirmed.

In the analysis of proteins by FT-IR analysis in the present embodiment collects the absorption spectrum in the range of 4000 to 400 ^-1, peptide bond absorption spectrum around 1630cm ^-1 (C = O stretching vibration), 1510 cm Absorption spectrum in the vicinity of ⁻¹ is a peptide bond (N—H bending vibration and CN stretching vibration), and absorption spectrum in the vicinity of 1225 cm ⁻¹ is a peptide bond (CN stretching vibration and N—H bending vibration), 3260 cm. The absorption spectrum in the vicinity of ^{−1 was} the amino group (NH stretching vibration) of the side chain of the protein, and the absorption spectrum in the vicinity of 1400 cm ⁻¹ was taken as the absorption spectrum belonging to the side chain carboxyl group of the protein.

  Furthermore, casein sodium, casein lithium, casein potassium, casein magnesium, casein calcium, caseinstrontium, casein barium, and casein ammonium are analyzed by analyzing metal elements contained in casein by LA-ICP-MS analysis or EDX analysis. Each casein can be identified.

[Production method of positive electrode]
In the positive electrode 20 according to the present embodiment, a positive electrode active material, a positive electrode conductive additive, a positive electrode binder, and a solvent are mixed and dispersed to produce a paste-like positive electrode slurry. Next, the positive electrode slurry is applied to one surface or both surfaces of the positive electrode current collector 22 such as an aluminum foil by using a comma roll coater, for example, and the solvent is dried in a drying furnace. Let In addition, when apply | coating the positive mix layer 24 on both surfaces of the said positive electrode collector 22, it is desirable that it is a positive mix layer which becomes the same film thickness on both surfaces.

  Next, the positive electrode on which the positive electrode mixture layer 24 is formed is adjusted to have a predetermined thickness and density by a roll press or the like, and at the same time, the positive electrode mixture layer 24 is pressure-bonded to one side or both sides of the positive electrode current collector 22. The adhesion between the positive electrode mixture layer 24 and the positive electrode current collector 22 is improved.

  The positive electrode is punched into a predetermined electrode size with a mold to obtain a positive electrode 20 for a lithium ion secondary battery of this embodiment. As described above, the area of the positive electrode 20 is preferably equal to or smaller than the area of the negative electrode 10. This is to prevent the occurrence of an internal short circuit due to lithium deposition by making the area of the positive electrode 20 equal to or smaller than the area of the opposing negative electrode 10.

  Also, the positive electrode 20 may be appropriately heat-treated depending on the binder used, as with the negative electrode 10.

[Production of electrode laminate]
The electrode laminate 30 is produced by laminating the negative electrode 10 and the positive electrode 20 via the separator 18. The electrode laminate 30 can be configured by any number of layers. In addition, in order to prevent the negative electrode 10 and the positive electrode 20 from contacting directly, the separator 18 can use the thing larger than a negative electrode and a positive electrode suitably.

  Next, in the negative electrode 10 of the electrode laminate 30, a negative electrode lead 60 made of nickel is attached to the protruding end portion of the negative electrode current collector that is not provided with the negative electrode mixture layer 14, while the positive electrode 20 of the electrode laminate 30 is provided. , The positive electrode lead 62 made of aluminum is attached to the protruding end portion of the positive electrode current collector not provided with the positive electrode mixture layer 24 by an ultrasonic welding machine. Then, the electrode laminate 30 is inserted into an aluminum laminate film outer package 50 and heat-sealed except for one peripheral portion to form a closed portion, and a predetermined amount of electrolyte is formed in the outer package 50. After the injection, the remaining one portion is sealed by heat-sealing while reducing the pressure, and the lithium ion secondary battery 100 (hereinafter sometimes referred to as a laminate cell) can be manufactured.

  In the lithium ion secondary battery 100, when charged, for example, lithium ions are released from the positive electrode mixture layer 24 and inserted into the negative electrode mixture layer 14 through the electrolytic solution. Further, when discharging is performed, for example, lithium ions are released from the negative electrode mixture layer 14 and are occluded in the positive electrode mixture layer 24 through the electrolytic solution.

(Battery evaluation)
The lithium ion secondary battery produced in the present embodiment can be evaluated for the following battery characteristics.

[Charge / discharge cycle test]
The lithium ion secondary battery according to the present embodiment can evaluate charge / discharge cycle characteristics, for example, according to the following charge / discharge conditions. The charge / discharge cycle test conditions were as follows: constant current and constant voltage charge (CC-CV charge) until a battery voltage of 4.2 V was reached at a constant current of 0.5 C in an environment of 25 ° C., and then 1.0 C Discharge until the battery voltage reaches 2.5 V at a constant current (CC discharge). The above charge and discharge were set as one cycle, and the discharge capacity retention rate after repeating this to a predetermined number of cycles was evaluated as charge / discharge cycle characteristics. The 1C rate is a current value for charging or discharging the lithium ion secondary battery in one hour. For example, at a 1 C rate in a lithium ion secondary battery with a nominal capacity of 1 Ah, the current value is 1 A. In addition, the charging / discharging cycle characteristic in this embodiment is defined by the following calculation formulas.

  For example, when a silicon-based negative electrode active material is used in a lithium ion secondary battery, the discharge capacity maintenance rate can be evaluated by, for example, the discharge capacity maintenance rate at 300 cycles. On the other hand, when a negative electrode active material containing graphite is used for a lithium ion secondary battery, the discharge capacity retention rate is relatively high, and therefore, it can be evaluated by, for example, the discharge capacity retention rate at 600 cycles.

[Thickness expansion test of laminate cell]
The lithium ion secondary battery (laminate cell) according to the present embodiment evaluates the expansion coefficient of the laminate cell thickness by measuring the thickness of the laminate cell before charging / discharging and when the predetermined charging / discharging is repeated. Can do. In addition, the expansion coefficient in this embodiment is defined by the following calculation formula.

[Observation of deterioration state of negative electrode]
The deterioration state of the negative electrode active material accompanying charging / discharging can be easily performed by observing the particle form of the negative electrode active material in the negative electrode mixture layer. For example, lithium ion secondary batteries before and after charging / discharging are prepared, these are decomposed in a dry room, and negative electrodes are collected respectively. Next, the collected negative electrode was washed with dimethyl carbonate (DMC), dried in a dry room, and then observed for deterioration from the particle form of the negative electrode active material using a field emission scanning electron microscope (FE-SEM). can do.

  As mentioned above, although embodiment concerning this invention was described in detail, it is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, the laminated film type lithium ion secondary battery has been described. However, the present invention can be similarly applied to a lithium ion secondary battery having a structure in which a positive electrode, a negative electrode, and a separator are wound or folded. it can. Furthermore, it can apply suitably also about lithium ion secondary batteries, such as a cylindrical shape, a square shape, and a coin type, as a battery shape.

  Hereinafter, based on the above-described embodiment, the present invention will be described in more detail using examples and comparative examples.

(Preparation of negative electrode for lithium ion secondary battery)
As a paint composition ratio, 83% by weight of silicon as a negative electrode active material, 2% by weight of acetylene black as a conductive auxiliary agent, and 15% by weight of polyamideimide as a binder were weighed, and a stirrer (product name: The mixture was dispersed using a hybrid mixer, and finally N-methyl-2-pyrrolidone was added as a solvent to prepare a paste-like negative electrode slurry adjusted to a predetermined viscosity. And using the comma roll coater, this negative electrode slurry apply | coated the negative mix layer by predetermined thickness on the copper foil (thickness 10 micrometers) surface. The weight of the negative electrode active material contained in the negative electrode mixture layer was 2.0 mg · cm ⁻² per unit area of the negative electrode mixture layer. After the N-methyl-2-pyrrolidone solvent in the negative electrode mixture layer was dried and removed in a drying furnace at 100 ° C., the negative electrode mixture layer was formed on the back side of the other copper foil by the same procedure. Applied. In addition, the negative electrode active material weight contained in the negative electrode mixture layer on the back side was also 2.0 mg · cm ⁻² per unit area of the negative electrode mixture layer.

  The negative electrode on which the negative electrode mixture layer was formed was pressure-bonded to both surfaces of the negative electrode current collector by a roll press to obtain a negative electrode having a predetermined density.

The negative electrode is punched into a 19 mm × 23 mm size electrode with a die, and then crosslinked at a polyamide imide serving as a binder and dried to remove residual solvent at a heating rate of 30 ° C. · min ^{−1 in} a heat treatment furnace. The temperature was raised to 350 ° C., held for 1 hour, and then rapidly cooled to room temperature to obtain a negative electrode for a lithium ion secondary battery. The heat treatment was performed in a vacuum under reduced pressure.

(Examples 1-8)
In the negative electrodes for lithium ion secondary batteries according to Examples 1 to 8, the negative electrode was impregnated with 0.2 wt% sodium caseinate aqueous solution for 1 minute, and then the negative electrode was pulled up and dried in a dryer at 60 ° C. The sodium caseinate film was supported on the surface of the negative electrode mixture layer. The sodium caseinate aqueous solution was prepared by dissolving 0.2% by weight of sodium caseinate powder in ion-exchanged water. The coating amount of sodium caseinate was adjusted to the loading amount shown in Table 1 by adjusting the number of impregnations. In addition, the coating amount of sodium caseinate was calculated from a change in the weight of the negative electrode before and after the impregnation, and expressed as a weight percent with respect to the weight of the negative electrode active material.

(Comparative Example 1)
The negative electrode for a lithium ion secondary battery according to Comparative Example 1 did not carry a sodium caseinate coating.

(Examples 9 to 16)
In the negative electrodes for lithium ion secondary batteries according to Examples 9 to 16, the negative electrode active material is changed to silicon oxide, and the weight of the negative electrode active material contained in the negative electrode mixture layer is set to 3 per unit area of the negative electrode mixture layer. A negative electrode for a lithium ion secondary battery was produced in the same procedure as in Example 1 except that the concentration was 3 mg · cm ⁻² . The coating amount of sodium caseinate was adjusted to the loading amount shown in Table 2 by adjusting the number of impregnations.

(Comparative Example 2)
In the negative electrode for a lithium ion secondary battery according to Comparative Example 2, the negative electrode active material of Comparative Example 1 was changed to silicon oxide, and the weight of the negative electrode active material contained in the negative electrode mixture layer was determined per unit area of the negative electrode mixture layer. It was set to 3.3 mg · cm ⁻² . As in Comparative Example 1, a sodium caseinate coating was not supported.

(Examples 17 to 22)
The negative electrodes for lithium ion secondary batteries according to Example 17, Example 19, and Example 20 were prepared by using the negative electrode of Example 4 in which a 5% by weight sodium casein coating was supported, a 1% by weight lithium hydroxide aqueous solution, A weight percent calcium chloride aqueous solution and a 1 weight percent magnesium chloride aqueous solution were impregnated, respectively, and the negative electrode was pulled up and dried in a dryer at 60 ° C. By replacing the sodium ions in the sodium caseinate molecule, which is a coating, with each metal ion in the aqueous solution, a coating of casein lithium, casein calcium, and casein magnesium was supported on the surface of the negative electrode mixture layer. As a result of LA-ICP-MS analysis and EDX analysis of the negative electrode mixture layer according to each example, each metal ion was detected, and it was confirmed that casein lithium, casein calcium, and casein magnesium were generated. .

  In the negative electrode for a lithium ion secondary battery according to Example 18, the negative electrode of Comparative Example 1 was impregnated with 0.2 wt% potassium casein aqueous solution for 1 minute, and then the negative electrode was pulled up and dried in a dryer at 60 ° C. Thus, a potassium casein film was supported on the surface of the negative electrode mixture layer. The casein potassium aqueous solution was prepared by dissolving 0.2% by weight of potassium casein powder in ion-exchanged water. The amount of potassium casein was adjusted to the amount shown in Table 3 by adjusting the number of impregnations.

  In the negative electrode for a lithium ion secondary battery according to Example 21, the negative electrode of Comparative Example 1 was impregnated with a 0.2% weight aqueous casein ammonium solution for 1 minute, and then the negative electrode was pulled up and dried in a dryer at 60 ° C. Thus, a casein ammonium film was supported on the surface of the negative electrode mixture layer. The casein ammonium aqueous solution was prepared by dissolving 0.2% by weight of casein powder in 0.05% by mass of ammonia water. The amount of casein ammonium supported was adjusted to the amount shown in Table 3 by adjusting the number of impregnations.

  The negative electrode for a lithium ion secondary battery according to Example 22 was prepared by impregnating the negative electrode of Example 21 supporting casein ammonium with 0.05% hydrochloric acid for 1 minute, and then lifting the negative electrode in a dryer at 60 ° C. The casein film was supported on the surface of the negative electrode mixture layer. Since casein did not dissolve in ion-exchanged water, it was converted to casein by substituting ammonium ion of casein ammonium in Example 21 with hydrogen ion of hydrochloric acid.

(Examples 23 to 30)
In the negative electrodes for lithium ion secondary batteries according to Examples 23 to 30, the negative electrode of Comparative Example 1 was impregnated with 0.2% by weight albumin aqueous solution for 1 minute, and then the negative electrode was pulled up and dried in a dryer at 60 ° C. By doing so, the albumin coating was supported on the surface of the negative electrode mixture layer. The albumin aqueous solution was prepared by dissolving 0.2% by weight of albumin powder in ion-exchanged water. The supported amount of albumin was adjusted to the supported amount shown in Table 4 by adjusting the number of impregnations.

(Examples 31-37)
In the negative electrodes for lithium ion secondary batteries according to Examples 31 to 37, the negative electrode of Comparative Example 1 was impregnated with 0.2% by weight lysozyme aqueous solution for 1 minute, and then the negative electrode was pulled up and dried in a dryer at 60 ° C. As a result, a lysozyme film was supported on the surface of the negative electrode mixture layer. The lysozyme aqueous solution was prepared by dissolving 0.2% by weight of lysozyme powder in ion-exchanged water. The supported amount of lysozyme was adjusted to the supported amount shown in Table 5 by adjusting the number of impregnations.

(Examples 38 to 44)
In the negative electrodes for lithium ion secondary batteries according to Examples 38 to 44, the negative electrode of Comparative Example 1 was impregnated with a 0.2 wt% globulin aqueous solution for 1 minute, and then the negative electrode was pulled up and dried in a dryer at 60 ° C. As a result, a globulin film was supported on the surface of the negative electrode mixture layer. The globulin aqueous solution was prepared by dissolving 0.2% by weight of globulin powder in ion exchange water. The supported amount of globulin was adjusted to the supported amount shown in Table 6 by adjusting the number of impregnations.

(Comparative Example 3)
In the negative electrode for a lithium ion secondary battery according to Comparative Example 3, the negative electrode active material of Comparative Example 1 was changed to graphite, and the weight of the negative electrode active material contained in the negative electrode mixture layer was set to 14 per unit area of the negative electrode mixture layer. A negative electrode for a lithium ion secondary battery was produced in the same procedure as in Comparative Example 1 except that the concentration was 0.0 mg · cm ⁻² .

(Example 45)
The negative electrode for a lithium ion secondary battery according to Example 45 was obtained by supporting 5% by weight of sodium caseinate on the surface of the negative electrode mixture layer of Comparative Example 3 as a negative electrode for a lithium ion secondary battery of Comparative Example 4.

(Comparative Example 4)
In the negative electrode for a lithium ion secondary battery according to Comparative Example 4, the negative electrode active material is changed to a mixed negative electrode active material (50% by weight: 50% by weight) of silicon and graphite, and the negative electrode active material contained in the negative electrode mixture layer A negative electrode for a lithium ion secondary battery was produced in the same procedure as Comparative Example 1 except that the weight of was 2.7 mg · cm ⁻² per unit area of the negative electrode mixture layer.

(Example 46)
The negative electrode for a lithium ion secondary battery according to Example 46 was obtained by supporting 5% by weight of sodium caseinate on the surface of the negative electrode mixture layer of Comparative Example 4 as the negative electrode for a lithium ion secondary battery of Example 46.

(Comparative Example 5)
In the negative electrode for a lithium ion secondary battery according to Comparative Example 5, the negative electrode active material was changed to a mixed negative electrode active material of silicon oxide and graphite (50 wt%: 50 wt%), and the negative electrode active material contained in the negative electrode mixture layer A negative electrode for a lithium ion secondary battery was produced in the same procedure as Comparative Example 1 except that the weight of the substance was 5.0 mg · cm ⁻² per unit area of the negative electrode mixture layer.

(Example 47)
The negative electrode for a lithium ion secondary battery according to Example 47 was obtained by supporting 5% by weight of sodium caseinate on the surface of the negative electrode mixture layer of Comparative Example 5 as the negative electrode for a lithium ion secondary battery of Example 47.

(Preparation of positive electrode for lithium ion secondary battery)
96 wt% of nickel cobalt lithium aluminate (NCA) as a positive electrode active material, 2 wt% of ketjen black as a conductive additive, 2 wt% of PVdF as a binder, a solvent of N-methyl-2-pyrrolidone, Were mixed and dispersed to prepare a paste-like positive electrode slurry.
Then, using a comma roll coater, the positive electrode mixture layer was uniformly applied on both surfaces of the aluminum foil having a thickness of 20 μm so as to have a predetermined thickness. The weight of the positive electrode active material contained in the positive electrode mixture layer was 22 mg · cm ⁻² per unit area of the positive electrode mixture layer. Next, N-methyl-2-pyrrolidone in the positive electrode mixture layer was dried and removed in a drying furnace in an air atmosphere at 110 ° C. In addition, the thickness of the coating film of the positive mix layer apply | coated to both surfaces of the said aluminum foil was adjusted to the substantially same film thickness. The positive electrode on which the positive electrode active material was formed was pressure-bonded to both surfaces of the positive electrode current collector by a roll press to obtain a positive electrode having a predetermined density.

  The positive electrode was punched into an electrode size of 18 mm × 22 mm using a mold to produce a positive electrode for a lithium ion secondary battery.

(Production of lithium ion secondary battery)
The negative electrode for a lithium ion secondary battery according to the above-described Examples and Comparative Examples was laminated with the positive electrode for a lithium ion secondary battery via a polyethylene separator having a thickness of 16 μm and a size of 22 mm × 23 mm, An electrode laminate was prepared. This was used as one electrode body, and an electrode laminate composed of four layers was produced by the same production method. In addition, since the said negative electrode and a positive electrode are equipped with each mixture layer on both surfaces, they are comprised by 3 negative electrodes, 2 positive electrodes, and 4 separators. Furthermore, in the negative electrode of the electrode laminate, a negative electrode lead made of nickel is attached to the protruding end of the copper foil not provided with the negative electrode mixture layer, while the positive electrode mixture layer is provided in the positive electrode of the electrode laminate. The positive electrode lead made of aluminum was attached to the protruding end portion of the aluminum foil that was not formed by an ultrasonic fusion machine. Then, this electrode laminate was fused to an aluminum laminate film for an exterior body, and the laminate film was folded to insert the electrode body into the exterior body. A closed portion is formed by heat-sealing except for one side around the outer casing, and 1 mol of LiPF ₆ is used as a lithium salt in a solvent in which FEC / DEC is mixed at a volume ratio of 3: 7 from the opening. ^-The electrolyte solution added so that it might become L- ¹ was inject | poured. And the opening part of the said exterior body was sealed by heat sealing, reducing pressure with a vacuum sealing machine, and the laminate type lithium ion secondary battery which concerns on an Example and a comparative example was produced, respectively.

(result)
As representative examples, FE-SEM photographs of negative electrodes for lithium ion secondary batteries according to Example 4 and Comparative Example 1 are shown in FIGS. In the negative electrode for a lithium ion secondary battery according to Example 4 (FIG. 2), the presence of a coating that was considered to be sodium caseinate was observed on the surface of the negative electrode mixture layer. On the other hand, in the negative electrode for a lithium ion secondary battery according to Comparative Example 1 (FIG. 3), the presence of a coating on the surface of the negative electrode mixture layer was not observed.

The result of the FT-IR analysis of the negative electrode for lithium ion secondary batteries according to Example 4 and Comparative Example 1 is shown in FIG. In the negative electrode for a lithium ion secondary battery according to Example 4, 3260Cm near 1630 cm ^-1 an absorption spectrum attributable to the peptide bond sodium caseinate, 1510 cm around ^-1, the absorption spectrum attributable to the amino groups of the side chains of sodium caseinate ^-1 was confirmed in the vicinity. On the other hand, in the negative electrode for lithium ion secondary batteries according to Comparative Example 1, the absorption spectrum was not confirmed. Furthermore, sodium element was detected from the surface of the negative electrode mixture layer according to Example 4 from the results of EDX analysis (or LA-ICP-MS analysis). From the above analysis results, it was confirmed that the coating (FIG. 3) carried on the surface of the negative electrode mixture layer according to Example 4 was sodium caseinate.

  Also in the negative electrode for lithium ion secondary batteries according to the other examples, it was confirmed that the protein coating was supported on the surface of the negative electrode mixture layer using the same analysis method as in Example 4.

Table 1 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Examples 1 to 8 and Comparative Example 1. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 1 is set to 100%, and the relative ratio to the measurement result of Comparative Example 1 is shown. In the lithium ion secondary battery according to the example in which the sodium caseinate film is supported on the negative electrode mixture layer containing silicon, the thickness expansion of the laminate cell is larger than that of the lithium ion secondary battery according to Comparative Example 1 in which the film is not supported. The rate was suppressed, and the charge / discharge cycle characteristics were also excellent. In particular, when the amount of sodium caseinate coating was 0.5 to 50% by weight, the charge / discharge cycle characteristics were more excellent. When the coating amount of sodium caseinate was 60% by weight, the charge / discharge cycle characteristics tended to deteriorate. This is presumably because when the amount of the coating film is excessive, the coating film becomes a resistance component, which inhibits occlusion and release of lithium ions.

Table 2 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Examples 9 to 16 and Comparative Example 2. In addition, about the charging / discharging cycle characteristic and the thickness expansion coefficient of a laminate cell, the measurement result of the comparative example 2 is set as 100%, and it shows as a relative ratio with respect to the measurement result of the comparative example 2. Even in the case of using silicon oxide as the negative electrode active material, in the lithium ion secondary battery according to the example in which the negative electrode mixture layer is supported with the sodium casein film, the lithium ion according to Comparative Example 2 that does not carry the film. The thickness expansion coefficient of the laminate cell was suppressed as compared with the secondary battery, and the charge / discharge cycle characteristics were also excellent. In particular, when the amount of sodium caseinate coating was 0.5 to 50% by weight, the charge / discharge cycle characteristics were more excellent.

Table 3 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Examples 17 to 22. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 1 is set to 100%, and the relative ratio to the measurement result of Comparative Example 1 is shown. In the lithium ion secondary batteries according to Examples 17 to 22 in which the negative electrode mixture layer is loaded with a casein lithium, casein potassium, casein calcium, casein magnesium, casein ammonium, and casein film, Comparative Example 1 in which no film is supported The thickness expansion coefficient of the laminate cell was suppressed and the charge / discharge cycle characteristics were superior to those of the lithium ion secondary battery according to the present invention. In particular, in the examples in which a coating of casein alkali metal salt, casein alkaline earth metal salt, and casein magnesium was supported, the effect of improving the thickness expansion coefficient and charge / discharge cycle characteristics was great.

Table 4 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Examples 23 to 30. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 1 is set to 100%, and the relative ratio to the measurement result of Comparative Example 1 is shown. In the lithium ion secondary batteries according to Examples 23 to 30 in which the negative electrode mixture layer was supported with the albumin coating, the thickness expansion coefficient of the laminate cell was higher than that of the lithium ion secondary battery according to Comparative Example 1 that was not supporting the coating. The charge / discharge cycle characteristics were excellent. In particular, when the amount of the albumin film supported was 0.5 to 50% by weight, the charge / discharge cycle characteristics were more excellent.

Table 5 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Examples 31 to 37. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 1 is set to 100%, and the relative ratio to the measurement result of Comparative Example 1 is shown. In the lithium ion secondary batteries according to Examples 31 to 37 in which the negative electrode mixture layer was supported with the lysozyme film, the expansion of the laminate cell was suppressed as compared with the lithium ion secondary battery according to Comparative Example 1 that was not supported with the film. Furthermore, the charge / discharge cycle characteristics were excellent. In particular, when the coating amount of lysozyme was 0.5 to 50% by weight, the charge / discharge cycle characteristics were more excellent.

Table 6 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Examples 38 to 44. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 1 is set to 100%, and the relative ratio to the measurement result of Comparative Example 1 is shown. In the lithium ion secondary batteries according to Examples 38 to 44 in which the globulin film was supported on the negative electrode mixture layer, the thickness expansion coefficient of the laminate cell was higher than that of the lithium ion secondary battery of Comparative Example 1 that did not support the film. In addition, the charge / discharge cycle characteristics were excellent. In particular, when the globulin film carrying amount was 0.5 to 50% by weight, the charge / discharge cycle characteristics were more excellent.

Table 7 shows the results of the battery characteristics (after 600 cycles) of the lithium ion secondary batteries according to Example 45 and Comparative Example 3. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 3 is set to 100%, and the relative ratio to the measurement result of Comparative Example 3 is shown. In the lithium ion secondary battery according to Example 45 using graphite as the negative electrode active material, the thickness expansion coefficient and charge / discharge cycle characteristics of the laminate cell were significantly improved even when the sodium caseinate film was supported on the negative electrode mixture layer. The effect could not be confirmed.

Table 8 shows the results of the battery characteristics (after 300 cycles) of the lithium ion secondary batteries according to Example 46 and Comparative Example 4. In addition, about the charge / discharge cycle characteristic and the thickness expansion coefficient of the laminate cell, the measurement result of Comparative Example 4 is set to 100%, and the relative ratio to the measurement result of Comparative Example 4 is shown. In the lithium ion secondary battery according to Example 46 in which silicon and graphite were mixed as the negative electrode active material, the negative electrode mixture layer was supported with the sodium caseinate coating, which was more than the comparative example 4 that did not support the coating. The thickness expansion coefficient of the laminate cell was suppressed, and the charge / discharge cycle characteristics were excellent.

Table 9 shows the results of the battery characteristics (after 600 cycles) of the lithium ion secondary batteries according to Example 47 and Comparative Example 5. In addition, about the charging / discharging cycle characteristic and the thickness expansion coefficient of a laminate cell, the measurement result of the comparative example 5 is set as 100%, and it shows as a relative ratio with respect to the measurement result of the comparative example 5. In the lithium ion secondary battery according to Example 47 in which silicon oxide and graphite were mixed as the negative electrode active material, the negative electrode mixture layer was supported with a sodium caseinate coating, which was compared with Comparative Example 5 where no coating was supported. Also, the thickness expansion coefficient of the laminate cell was suppressed, and the charge / discharge cycle characteristics were excellent.

  Next, FIG. 5 shows a FE-SEM photograph of the negative electrode after 300 cycles of the lithium ion secondary battery according to Example 4 carrying a sodium caseinate coating as a representative. In the negative electrode, even after 300 cycles, the surface of the negative electrode mixture layer was covered with a sodium caseinate coating, and cracks in the negative electrode mixture layer were suppressed. Furthermore, the negative electrode active material present on the surface of the negative electrode mixture layer maintained its form, and no significant pulverization was observed.

  On the other hand, FIG. 6 shows an FE-SEM photograph of the negative electrode after 300 cycles of the lithium ion secondary battery according to Comparative Example 1 that does not carry a sodium caseinate coating. In the negative electrode, many cracks were observed in the negative electrode mixture layer after 300 cycles. In particular, the negative electrode active material present on the surface of the negative electrode mixture layer was pulverized in a coral shape due to expansion and contraction associated with charge and discharge. Therefore, in the negative electrode according to Comparative Example 1, the formation of a new surface becomes remarkable, and the side reaction with the electrolyte, that is, the decomposition reaction of the electrolyte becomes excessive. As a result, it seems that excellent charge / discharge cycle characteristics cannot be obtained. .

  From the above results, according to the technology disclosed herein, by using a negative electrode having a protein coating on the surface of the negative electrode mixture layer, the thickness expansion of the lithium ion secondary battery due to the charge / discharge reaction is suppressed. And a lithium ion secondary battery having excellent charge / discharge cycle characteristics can be realized.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

DESCRIPTION OF SYMBOLS 100 ... Lithium ion secondary battery, 10 ... Positive electrode (synonymous: Positive electrode for lithium ion secondary batteries), 12 ... Positive electrode collector, 14 ... Positive electrode mixture layer, 60 ... Positive electrode Lead,
20 ... Negative electrode (synonymous: negative electrode for lithium ion secondary battery), 22 ... Negative electrode current collector, 24 ... Negative electrode mixture layer, 62 ... Negative electrode lead, 18 ... Separator, 30. ..Electrode laminated body, 50 ... exterior body

Claims (6)

  A negative electrode mixture layer is provided on at least one main surface of the negative electrode current collector, the negative electrode mixture layer includes a negative electrode active material capable of occluding and releasing lithium ions, and at least a surface of the negative electrode mixture layer A negative electrode for a lithium ion secondary battery partially having a protein film.   2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the protein includes at least one of alkali metal salt of casein, magnesium salt of casein, alkaline earth metal salt of casein, ammonium caseinate, albumin, lysozyme, and globulin. .   3. The lithium ion according to claim 1, wherein the protein is an alkali metal salt of casein, and the alkali metal salt of casein includes at least one of sodium caseinate, lithium caseinate, and potassium caseinate. 4. Negative electrode for secondary battery.   The protein is a magnesium salt of casein or an alkaline earth metal salt of casein, and the magnesium salt of casein is casein magnesium, and the alkaline earth metal salt is at least calcium caseinate, casein strontium, or casein barium. The negative electrode for lithium ion secondary batteries as described in any one of Claim 1 or 2 containing 1 type.   The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein a loading amount of the protein-containing film is 0.5 to 50% by weight based on the weight of the negative electrode active material.   A positive electrode for a lithium ion secondary battery that occludes and releases lithium ions, a negative electrode for a lithium ion secondary battery according to any one of claims 1 to 5, and a separator interposed between the positive electrode and the negative electrode And a lithium ion secondary battery comprising an electrolyte.

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