JP2019160613A - Negative electrode active material for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery using the same - Google Patents

Abstract

To provide a negative electrode active material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery that have small gas generation and volume expansion of a cell and are excellent in charge and discharge cycle characteristics.SOLUTION: A negative electrode for a lithium ion secondary battery according to the present invention includes a negative electrode mixture layer on at least one main surface of a negative electrode current collector, and the negative electrode mixture layer includes a negative electrode active material capable of absorbing and releasing lithium ions, and a protein modified with a functional group containing fluorine is provided on at least a part of the surface of the negative electrode active material.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a negative electrode active material for a lithium ion secondary battery, 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 not only for portable electronic devices but also for 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, smartphones, and tablet 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 or a lithium secondary battery in response to the above-mentioned demand, a metal negative electrode or a metal oxide negative electrode showing a high theoretical capacity has attracted attention, for example, silicon (Si) or silicon oxide (SiOx). And an alloy-based negative electrode active material containing silicon. Since these alloy-based negative electrode active materials exhibit a theoretical capacity far higher than the theoretical capacity of 372 mAh · g ^{−1 of} graphite currently in practical use, they are the most promising materials for increasing the energy density of batteries. A group.

  However, in the case of a negative electrode using silicon as the negative electrode active material, the negative electrode active material has a large volume expansion due to charge and discharge, so that the negative electrode active material is cracked and gradually pulverized. Moreover, the negative electrode active material peeled or dropped from the current collector due to a decrease in binder binding due to pulverization, and there was a problem in that capacity was reduced, that is, charge / discharge cycle characteristics were reduced.

  In order to solve such a problem, a technique of coating the surface of silicon particles with a thermoplastic resin has been disclosed (Patent Document 1). In addition, a technique using an electrolytic solution containing 4-fluoro-1,3-dioxolan-2-one (also referred to as fluoroethylene carbonate) is disclosed (Patent Document 2).

JP 2003-000000 A JP 2006-134719 A

  As a result of intensive studies by the present inventors, when the technique of Patent Document 1 was used for silicon, there was a problem that excellent charge / discharge cycle characteristics could not be obtained. Furthermore, a decrease in the initial charge / discharge capacity was also confirmed. On the other hand, when the electrolytic solution of Patent Document 2 was used, the initial charge / discharge cycle characteristics were improved, but the charge / discharge cycle characteristics were deteriorated early and sufficient charge / discharge cycle characteristics were not obtained. In addition, there is a problem that the swelling of the battery becomes large.

  Although the detailed reason for the problem is unclear, when the technique of Patent Document 1 is used, the silicon-coated thermoplastic resin inhibits lithium ion insertion / desorption, resulting in a decrease in capacity. Conceivable. Furthermore, since the thermoplastic resin cannot follow the volume expansion of silicon, it is considered that the volume expansion of silicon could not be sufficiently suppressed. This seems to cause cracks in the silicon, exposing the new surface, and causing the new surface to react with the electrolyte, resulting in blistering due to gas generation. And it is thought that sufficient charge / discharge cycle characteristics could not be obtained by this gas generation.

  When the method of Patent Document 2 is used, it is suitable for charge / discharge reaction on the silicon surface by electrolysis of 4-fluoro-1,3-dioxolan-2-one (hereinafter sometimes referred to as fluoroethylene carbonate or FEC). As the solid electrolyte membrane (SEI) is generated, the initial charge / discharge cycle characteristics are improved. However, since the volume expansion of silicon cannot be sufficiently suppressed only by the SEI, the silicon has cracks as in Patent Document 1. It appears that the new surface is exposed, and the new surface reacts with the electrolyte, causing swelling due to gas generation and insufficient charge / discharge cycle characteristics.

  An object of the present invention has been made in view of the above circumstances, and by suppressing gas generation, the cell volume expansion is small, and the negative electrode active material for a lithium ion secondary battery excellent in charge / discharge cycle characteristics, lithium ion It is providing the negative electrode for secondary batteries, and a lithium ion secondary battery.

  A negative electrode active material for a lithium ion secondary battery according to the present invention is a negative electrode active material capable of occluding and releasing lithium ions, and at least a part of the surface of the negative electrode active material is modified with a functional group containing fluorine It is characterized by having the protein made.

  The protein preferably has at least one of a carboxy group and a hydroxyl group, and at least one of the carboxy group and the hydroxyl group is preferably modified with a functional group containing fluorine.

The functional group containing fluorine is a monofluoromethyl group (—CH ₂ F), a difluoromethyl group (—CF ₂ H), a trifluoromethyl group (—CF ₃ ), a 2,2,2, -trifluoroethyl group. It contains at least one of (—CH ₂ CF ₃ ), difluoromethylene group (—CH═CF ₂ ), trifluoromethylsulfonyl group (—SO ₂ CF ₃ ), and trifluoroacetyl group (—CO—CF ₃ ). Is preferred.

  The protein preferably contains casein, albumin, lysozyme, globulin, and at least one of these alkali metal salts, alkaline earth metal salts, and magnesium salts.

In the infrared absorption spectrum, the protein has a wavelength near 1640 ± 10 cm ⁻¹ (C═O stretching vibration, also referred to as amide I band), 1520 ± 10 cm ⁻¹ (also referred to as N—H bending vibration, amide II band), Those exhibiting a spectrum attributed to the vicinity of 1225 ± 10 cm ⁻¹ (also referred to as CN stretching vibration, amide III band) 1270 ± 10 cm ^{−1 and the} vicinity of 1160 ± 10 cm ⁻¹ (CF stretching vibration) are preferable.

  The protein coating amount is preferably 0.02 to 10% by weight based on the weight of the negative electrode active material.

  The negative electrode for lithium ion secondary batteries which concerns on this invention is a negative electrode for lithium ion secondary batteries which has the negative electrode active material for lithium ion secondary batteries in any one of the said.

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

  According to the negative electrode active material of the present invention, since at least a part of the surface of the negative electrode active material has a protein modified with a functional group containing fluorine, gas generation and cell volume expansion are small, and excellent charge / discharge A lithium ion secondary battery exhibiting cycle characteristics can be provided.

It is sectional drawing showing the structure of the lithium ion secondary battery which concerns on one Embodiment of this invention. FT-IR spectra of sodium caseinate modified with a functional group containing fluorine according to Example 2 and sodium caseinate according to Comparative Example 2

  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 type shown in FIG. 1, and may be any of a cylindrical shape, a square shape, a coin shape, and the like. In this embodiment, a laminate film is used as the outer package 50, and in the example, a laminate type battery is manufactured 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. Contains possible negative electrode active materials.

[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 having a high capacity, that is, the volume expansion is more effective in achieving the effect of the present invention.

  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 contain silicon microcrystals and an amorphous phase of silicon dioxide, in which case the atomic ratio of silicon to oxygen is such that the silicon microcrystals and the silicon dioxide amorphous phase. The ratio is included. That is, the silicon oxide includes a structure in which silicon microcrystals are dispersed in an amorphous silicon dioxide matrix, and the amorphous silicon dioxide and the silicon dispersed therein. It is sufficient that the atomic ratio x satisfies the following condition: 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 silicon alloy includes, 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. The particle size of the negative electrode active material is not particularly limited and can be appropriately used. For example, a particle diameter of 0.01 to 10 μm can be used.

  Furthermore, in addition to the 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.

  Furthermore, the negative electrode active material according to the present embodiment preferably has a protein modified with a functional group containing fluorine on at least a part of the surface of the negative electrode active material.

  In the protein, at least one of a carboxy group and a hydroxyl group is preferably modified with a functional group containing fluorine.

  The functional group containing fluorine is at least a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2, -trifluoroethyl group, a difluoromethylene group, a trifluoromethylsulfonyl group, or a trifluoroacetyl group. It is preferable that 1 type is included.

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

  Thus, a negative electrode active material having a protein in which at least one of a carboxy group and a hydroxyl group is modified with a functional group containing fluorine on a part of the surface is excellent by using this for a negative electrode for a lithium ion secondary battery. It is possible to provide a lithium ion secondary battery that exhibits high charge / discharge cycle characteristics.

  The reason is considered as follows. A protein in which at least one of a carboxy group and a hydroxyl group is modified with a functional group containing fluorine is chemically stable and is hardly decomposed by oxidation-reduction associated with a charge / discharge reaction. Therefore, since the protein modified with the functional group containing fluorine can be present on the surface of the negative electrode active material without being decomposed, it is difficult to expose the new surface even when a crack occurs in the negative electrode active material. Thereby, since the gas generation by charging / discharging reaction is suppressed, the swelling of a battery can be made small.

  Further, the protein is denatured by an oxidation-reduction reaction that accompanies a charge / discharge reaction, thereby causing expansion and contraction of the molecular structure. Therefore, since the protein can follow the volume expansion of the negative electrode active material, it is difficult to peel off the surface of the negative electrode active material. Thereby, the outstanding charge / discharge cycle can be expressed.

  Further, the coating amount of the protein is preferably 0.02 to 10% by mass with respect to the mass of the negative electrode active material. This is because when the coating amount is within this range, more excellent charge / discharge cycle characteristics can be obtained.

  The protein coating may contain particles. The surface of the negative electrode active material is coated with particles, and the protein coating is coated on the surface of the negative electrode active material, so that the protein enters the gap between the particles, and the protein coating easily adheres to the surface of the negative electrode active material. Further, since the particles can disperse the stress of expansion and contraction that accompanies charge / discharge, the protein film is difficult to peel from the negative electrode active material.

  The particles are preferably smaller than the particles of the negative electrode active material, and particles of 500 nm or less are particularly 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.

  The material of the particles may be an inorganic material or an organic material. For example, amorphous carbon, titanium oxide, aluminum oxide, zirconium oxide, zinc oxide, silicon oxide, silicon carbide, polyacrylic acid, polymethyl methacrylate, polyurethane , Polystyrene, styrene butadiene rubber (SBR), and the like.

[Method for producing negative electrode active material]
The negative electrode active material according to the present embodiment has a protein modified with a functional group containing fluorine on at least a part of the surface of the negative electrode active material. Examples of the method for coating the protein on the surface of the negative electrode active material include a dip coating method and a solidification drying method. These methods may be used alone, or two or more methods may be used in combination. For example, in the dip coating method, a negative electrode active material is put into a glass beaker containing an aqueous protein solution, and a slurry is prepared by stirring with a stirrer. The slurry is transferred to a filter paper, and the excess protein aqueous solution is removed by suction filtration, and then dried. Then, by crushing the dried product, a protein film can be formed on the surface of the negative electrode active material.

  In the solidification drying method, a negative electrode active material is placed in a plastic ointment container, an aqueous protein solution is added thereto, and kneaded using a rotating and rotating stirrer (trade name: hybrid mixer) to prepare a slurry. Next, the obtained slurry is dried, and the dried product is crushed, so that the protein can be uniformly coated on the surface of the negative electrode active material. The protein aqueous solution may be added in the form of protein powder. The slurry temperature rises by kneading, and protein powder is dissolved in ion-exchanged water, so that the surface of the negative electrode active material is coated in the slurry. The slurry is preferably kneaded in a relatively high viscosity state. By kneading in a high-viscosity state, the negative electrode active material is crushed and the dispersibility is increased due to collision between the negative electrode active materials, so that the protein can be uniformly coated. The protein coating amount and coating thickness can be easily controlled by variously adjusting the number of coating treatments, the amount of protein added, the solid content concentration and viscosity of the slurry, and the like.

[Modification of functional group containing fluorine to protein]
In the protein coated on the surface of the negative electrode active material, the carboxy group and / or the carboxy group in the protein can be modified with a functional group containing fluorine. Examples of the functional group containing fluorine that can be modified to a carboxy group include a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a difluoromethylene group, and trifluoromethyl. A sulfonyl group etc. are mentioned. As a method for modifying the carboxy group, a protein is added to a solvent such as monofluoromethyl alcohol, difluoromethyl alcohol, trifluoromethyl alcohol, 2,2,2-trifluoroethyl alcohol, difluoromethylene alcohol, and trifluoromethanesulfonic acid. The functional group can be modified by immersing the coated negative electrode active material. In particular, trifluoroethanol is preferred as a solvent, and N, N′-diisopropylcarbodiimide or di-t-butylcarbodiimide is preferably added as a dehydration catalyst.

  Furthermore, examples of the functional group containing fluorine that can be modified to a hydroxyl group of a protein include a trifluoroacetyl group. As a modification method, a negative electrode active in which a protein is coated in a solvent such as trifluoroacetic anhydride. The functional group containing fluorine can be modified by immersing the substance.

  In addition, what is necessary is just to immerse in the mixed solvent of the solvent mentioned above when modifying the functional group containing a fluorine in both a carboxy group and a hydroxyl group. Or you may immerse in each solvent sequentially.

  Although it does not specifically limit as said process conditions, It is preferable to immerse in the temperature of 20-80 degreeC where a solvent does not volatilize easily. There is no particular limitation on the immersion time, and it can be confirmed whether or not the functional group containing fluorine has been substituted into the molecular structure of the protein by appropriately measuring the protein after immersion by FT-IR analysis or the like. .

  The manufacturing method of the said negative electrode active material can be changed suitably. For example, a protein solution modified with a functional group containing fluorine in advance is prepared by treating protein with the solvent, and the negative electrode active material according to the present embodiment is similarly applied to the negative electrode active material. Can be produced.

[Identification of protein coating]
The identification of the protein coated on the surface of the negative electrode active material according to the present embodiment includes, for example, a field emission scanning electron microscope (FE-SEM), a scanning transmission electron microscope-energy dispersive X-ray analysis (STEM-EDS), Fourier Conversion infrared spectroscopy (FT-IR) can be performed by attenuated total reflection (ATR method), X-ray photoelectron spectroscopy (XPS), pyrolysis gas chromatograph mass spectrometry, or the like.

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

In FT-IR analysis, each protein powder desired to be coated is measured alone, the absorption spectrum position of each protein is confirmed, and then the absorption spectrum position of the negative electrode active material coated with each protein is measured and compared. By doing so, the presence or absence of a protein coating on the surface of the negative electrode active material can be confirmed. In the analysis of proteins by FT-IR analysis, collect the absorption spectrum in the range of 4000 to 400 ^-1, 1640 ± 10 cm near ^-1 (C = O stretching vibration, also referred to as amide I band), 1520 ± 10 cm ^-1 Near (N—H bending vibration, also called Ami II band), around 1225 ± 10 cm ⁻¹ (also called C—N stretching vibration, amide III band), around 3260 ± 10 cm ⁻¹ (N—H stretching vibration), The vicinity of 1400 ± 20 cm ⁻¹ (COO ^— stretching vibration) can be analyzed as an absorption spectrum.

Further, the functional group containing fluorine modified to the carboxy group and / or hydroxy group of the protein absorbs around 1270 ± 10 cm ⁻¹ (CF stretching vibration) and 1160 ± 10 cm ⁻¹ (CF stretching vibration). It can be analyzed as a spectrum.

[Amount of protein coating]
The coating amount of the protein modified with the functional group containing fluorine according to the present embodiment can be performed by, for example, thermal mass differential thermal (TG-DTA) analysis. By heating the negative electrode active material coated with the protein to a temperature at which the protein is thermally decomposed, it is possible to confirm a weight loss attributable to the protein. The amount of protein coating can be calculated from the weight reduction.

[Calculation of protein coating thickness]
The coating thickness of the protein modified with the functional group containing fluorine according to the present embodiment can be calculated, for example, by image processing of a mapping image of STEM-EDS analysis. In the STEM-EDS mapping image of the negative electrode active material coated with protein, the coating thickness can be estimated from the thickness of elemental mapping of carbon attributed to protein. In the silicon element mapping region belonging to the negative electrode active material and the carbon element mapping region belonging to the coated protein, the carbon mapping region that does not overlap the silicon element mapping region can be estimated as the protein coating thickness. it can.

[Negative Conductive Aid]
The negative electrode mixture layer 14 according to the present embodiment may contain 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 and thermal black, carbon fiber such as vapor grown carbon fiber (VGCF) and carbon nanotube (CNT), and carbon such as graphene and graphite The material is mentioned, These 1 type (s) or 2 or more types can be used.

[Negative electrode binder]
The negative electrode mixture layer 14 according to this embodiment may include 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 this embodiment may be an organic solvent binder or an aqueous binder. For example, polyamideimide, polyimide, polyamide, polyacrylic acid, polyacrylate, alginate, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyurethane and the like may be used, and one of these may be used. Two or more kinds can be used in combination. In particular, when a silicon-based negative electrode active material having a large volume expansion due to charge / discharge is used, polyamideimide, polyimide, polyamide, and polyacrylic acid having relatively high binder strength 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, copper, stainless steel, nickel, titanium, or these alloy foils and clad foils are used. Can be used. 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 the present embodiment is preferably a lithium-containing compound such as lithium metal oxide, lithium metal sulfide, or an intercalation compound containing lithium, and a mixture of two or more of these may be used. Good. 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 ; LMO) having a spinel crystal structure, lithium iron phosphate having an olivine crystal structure (LiFePO ₄ ; LFP), and the like can also obtain a high energy density. Therefore, it is preferable.

Examples of the lithium composite oxide include lithium cobalt oxide (LiCoO ₂ ; LCO), nickel-cobalt aluminum (Li (Ni _x Co _y Al _z ) O ₂ (0.9 <x + y + z <1.1); NCA), Nickel / manganese / cobalt (Li (Ni _x Mn _y Co _z ) O ₂ (0.9 <x + y + z <1.1); NMC), lithium nickelate (LiNiO ₂ ), LiNi _x Co _y Mn _z MaO 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 ), LiMPO ₄ which is a polyanion containing phosphorus (where M is Co, Ni, Mn, Fe, Mg, Nb, T) and one or more elements selected from i, Al, and Zr, or VO), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), 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.

[Binder for positive electrode]
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, LiPF6 can be preferably used because it can obtain high ion 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]
The negative electrode 10 according to the present embodiment includes a negative electrode active material in which at least a part of the surface of the negative electrode active material is coated with a protein modified with a functional group containing fluorine, a negative electrode conductive additive, a negative electrode binder, and a solvent. A paste-like negative electrode slurry is prepared by mixing and dispersing. 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 or both surfaces of the negative electrode current collector 12 such as a copper foil using a comma roll coater, for example, and a negative electrode mixture layer 14 having a predetermined thickness is applied, and the solvent is removed in a drying furnace. dry. 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.

[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 this 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. Hereinafter, the charge / discharge current is expressed in C (sea) rate. nC (mA) is a current that can charge and discharge the nominal capacity (mAh) at 1 / n (h). For example, in the case of a battery with a nominal capacity of 70 mAh, the current of 0.05 C is 3.5 mA (calculation formula 70 × 0.05 = 3.5). Similarly, a 0.2 C current is 14 mA, and a 2 C current is 140 mA. 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. In addition, the charging / discharging cycle characteristic in this embodiment is defined by the following calculation formulas.
Discharge capacity maintenance ratio after predetermined cycle (%) = (discharge capacity after predetermined cycle ÷ discharge capacity after first cycle) × 100

[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.
Expansion rate (%) at a predetermined cycle time = (thickness of laminate cell after predetermined cycle [mm] −thickness of laminate cell before charge / discharge [mm]) ÷ thickness of laminate cell before charge / discharge [mm] × 100

  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.

Example 1
A slurry was prepared by kneading 20 g of silicon as a negative electrode active material and 10 g of an aqueous solution in which 0.2 g of sodium caseinate was dissolved as a protein using a hybrid mixer. The slurry was dried and crushed at 80 ° C. to produce silicon coated with 1.0% by mass of sodium caseinate.

  As a result of calculating the coating amount of the casein sodium by TG-DTA analysis, the coating amount was 1.0% by mass with respect to silicon. In addition, the coating amount of casein sodium was calculated from the weight loss rate in the range of 150 to 800 ° C. obtained from the TG-DTA analysis.

  Next, 10 g of silicon coated with 1.0% by mass of sodium caseinate was transferred to a reaction vessel, sealed by adding 75 ml of trifluoroacetic anhydride, and immersed for 24 hours at a constant temperature of 25 ° C. This was subjected to suction filtration, and dried at 60 ° C. to produce silicon according to Example 1.

  The silicon according to Example 1 was confirmed by FE-SEM and STEM-EDS analysis that casein sodium covered a part of the silicon surface. Further, it was confirmed by XPS and FT-IR analysis that the hydroxy group of sodium caseinate was modified with a trifluoroacetyl group. The same analysis was performed in the following examples and comparative examples.

(Example 2)
The negative electrode active material according to Example 2 was produced by the following procedure. 10 g of silicon coated with 1.0% by mass of sodium caseinate was transferred to a reaction vessel, 75 ml of 2,2,2, -trifluoroethanol and 25 ml of N, N′-diisopropylcarbodiimide were added and sealed, and a constant temperature of 60 ° C. The immersion treatment was performed for 24 hours. This was subjected to suction filtration, and dried at 60 ° C. to produce silicon according to Example 2.

  The silicon according to Example 2 was confirmed to be modified with a 2,2,2, -trifluoroethyl group on the carboxy group of sodium caseinate.

(Example 3)
The negative electrode active material according to Example 3 was produced by the following procedure. 10 g of silicon coated with 1.0% by mass of sodium caseinate was transferred to a reaction vessel, sealed with 3 ml of trifluoroacetic anhydride, and immersed for 24 hours at a constant temperature of 25 ° C. After removing trifluoroacetic anhydride by suction filtration, 3 ml of 2,2,2, -trifluoroethanol and 1 ml of N, N′-diisopropylcarbodiimide were added and sealed, and the mixture was kept at a constant temperature of 60 ° C. for 24 hours. Immersion treatment. After the immersion, suction filtration was performed, and after drying at 60 ° C., silicon according to Example 3 was produced.

  The silicon according to Example 3 was confirmed to be modified with a trifluoroacetyl group on the hydroxy group of casein sodium and a 2,2,2, -trifluoroethyl group on the carboxy group.

(Examples 4 to 6)
The negative electrode active materials according to Examples 4 to 6 were prepared by coating silicon with 1.0% by mass of albumin, lysozyme, and globulin, respectively, and performing the same treatment as in Example 2, whereby albumin, lysozyme, Silicon in which 2,2,2, -trifluoroethyl group was modified on each carboxy group of globulin was prepared.

(Comparative Example 1)
The negative electrode active material according to Comparative Example 1 was silicon.

(Comparative Example 2)
The negative electrode active material according to Comparative Example 2 was silicon coated with 1.0% by mass of sodium caseinate.

(Comparative Example 3)
The negative electrode active material according to Comparative Example 3 was produced by preparing silicon coated with 1.0% by mass of carboxymethylcellulose (CMC), and performing the same treatment as in Example 2 to add 2 to the carboxy group of CMC. Silicon modified with 2,2, -trifluoroethyl group was prepared.

(Comparative Example 4)
As the negative electrode active material according to Comparative Example 4, silicon coated with 1.0% by mass of polyvinylidene fluoride (PVdF) was produced.

(Examples 7 to 14)
The negative electrode active materials according to Examples 7 to 14 were prepared by making various adjustments to the amount of sodium caseinate so that silicon coated with 0.02 to 15% by mass of sodium caseinate was prepared. By performing the above, silicon in which 2,2,2, -trifluoroethyl group was modified on the carboxy group of the casein sodium was produced.

(Examples 15 to 22)
The negative electrode active materials according to Examples 15 to 22 were produced by changing the negative electrode active material to silicon oxide and preparing silicon oxides coated with 0.02 to 15% by mass of sodium caseinate. By performing the same treatment as in Example 2 on the silicon oxide, silicon oxide in which 2,2,2, -trifluoroethyl group was modified on the carboxy group of sodium caseinate was produced.

(Comparative Example 5)
The negative electrode active material according to Comparative Example 5 was silicon oxide.

(Comparative Example 6)
The negative electrode active material according to Comparative Example 6 was a silicon oxide coated with 1.0% by mass of sodium caseinate.

(Preparation of negative electrode for lithium ion secondary battery)
As the negative electrode active material, 80% by mass of the negative electrode active materials for lithium ion secondary batteries of Examples and Comparative Examples prepared above, 5% by mass of acetylene black as a conductive additive, and 15% by mass of polyamideimide as a binder % And N-methyl-2-pyrrolidone as a solvent were mixed and dispersed with a hybrid mixer to prepare a paste-like negative electrode slurry. Using a comma roll coater, a negative electrode mixture layer was applied to the surface of the rolled copper foil (thickness 10 μm) with a predetermined thickness using this negative electrode slurry. 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 applied to the back side of the rolled copper foil in the same procedure. And the negative electrode layer in which the said negative mix layer was formed was crimped | bonded to both surfaces of the rolled copper foil with the roll press machine, and the negative electrode which has a predetermined density was produced.

The weight (weight per unit area) of the negative electrode active material for a lithium ion secondary battery contained in the negative electrode mixture layer was appropriately changed according to the negative electrode active material. When silicon was used as the negative electrode active material, it was 1.4 mg · cm ⁻² , and when silicon oxide was used, it was 3.3 mg · cm ⁻² .

The negative electrode was punched into a 19 mm × 23 mm size electrode with a mold, and then heated to 150 ° C. at a temperature increase rate of 30 ° C. · min ^{−1 in} a heat treatment furnace for 6 hours for the purpose of drying and removing the residual solvent. The negative electrodes for lithium ion secondary batteries according to the examples and the comparative examples were obtained by rapidly cooling to room temperature after being held. The heat treatment was performed in a vacuum under reduced pressure.

(Preparation of positive electrode for lithium ion secondary battery)
96% by mass of lithium nickel cobaltate (NCA) as a positive electrode active material for a lithium ion secondary battery, 2% by mass of ketjen black as a conductive additive, 2% by mass of PVdF as a binder, N-methyl-2 -A pyrrolidone solvent was mixed and dispersed to prepare a paste-like positive electrode slurry. Then, using a comma roll coater, this positive electrode slurry was applied to the surface of an aluminum foil (thickness 20 μm) with a positive electrode mixture layer having a predetermined thickness. 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 positive electrode mixture layer was applied to the back side of the aluminum foil in the same procedure. And the positive electrode layer in which the said positive mix layer was formed was crimped | bonded to both surfaces of the aluminum foil with the roll press machine, and the positive electrode which has a predetermined density was produced.

The weight (weight per unit area) of the positive electrode active material for a lithium ion secondary battery contained in the positive electrode mixture layer was 24 mg · cm ⁻² .

  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 lithium ion secondary batteries according to the examples and comparative examples were prepared by using the negative electrode for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a polyethylene separator having a thickness of 16 μm and a size of 22 mm × 23 mm. Thus, an electrode laminate was produced. 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 exterior body. From this opening, 1 mol of LiPF ₆ is used as a lithium salt in a solvent containing FEC: DEC in a volume ratio of 3: 7. ^-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. The lithium ion secondary battery was manufactured in a dry room.

  The lithium ion secondary batteries according to Examples and Comparative Examples prepared above are constant current and constant voltage charging (CC-CV) until a battery voltage of 4.2 V is obtained at a constant current of 0.2 C rate in an environment of 25 ° C. The battery was discharged until a battery voltage of 2.5 V was reached at a constant current of 0.5 C rate. The charge and discharge described above were regarded as one cycle, and the discharge capacity retention rate after repeating this for 100 cycles was evaluated as charge / discharge cycle characteristics.

Further, the gas generation amount of the lithium ion secondary battery according to the example and the comparative example is calculated by calculating the volume of the lithium ion secondary battery cell before and after charging and discharging by the following calculation formula of the Archimedes method, respectively. The difference in volume between the front and rear cells was taken as the gas generation amount.
Volume of lithium ion secondary battery cell (cm ³ ) = (cell weight in air (g) −weight in water before charge / discharge (g)) ÷ density of water (g · cm ⁻³ )

Furthermore, the expansion coefficient of the cell of the lithium ion secondary battery which concerns on an Example and a comparative example measured the thickness of the cell before charging / discharging and 100 cycles after, and computed it from the following formula | equation.
Expansion rate (%) = (cell thickness after 100 cycles−cell thickness before charge / discharge) ÷ cell thickness before charge / discharge × 100

(result)
As representative examples, FT-IR spectra of sodium caseinate according to Example 2 (solid line) and Comparative Example 2 (broken line) are shown in FIG. The sodium caseinate according to the second embodiment, respectively ^{1640 cm -1,} 1520 cm -1, amide attributable to the protein in the vicinity of 1225 cm ^-1 I, amide II, in addition to the absorption spectrum of the amide ^III, 1160 cm -1, the 1270 cm ^-1 A peak attributed to CF stretching vibration in CF ₃ was confirmed. On the other hand, in casein sodium according to Comparative Example 2, although absorption spectra of the amide I, amide II, and amide III can be confirmed, an absorption spectrum attributed to the CF stretching vibration was not confirmed. From the above results, it was confirmed that in casein sodium according to Example 2, the functional group containing fluorine, that is, 2,2,2, -trifluoroethyl group, was modified.

  Furthermore, the result of the battery characteristic of the lithium ion secondary battery which concerns on Examples 1-6 and Comparative Examples 1-4 is shown in Table 1. In addition, about the gas generation amount, the expansion rate of a laminate cell, and the charge / discharge cycle characteristics, the measurement results of Comparative Example 1 are each set to 100%, and the relative ratios to the results of Comparative Example 1 are Examples 1 to 6 and Comparative Example 2. Results of ~ 4 are shown.

  In the lithium ion secondary batteries of Examples 1-3 in which the surface of silicon was coated with sodium caseinate modified with 2,2,2, -trifluoroethyl group and / or trifluoroacetyl group, Comparative Examples 1-2 As a result, the gas generation amount was suppressed and the expansion rate was also suppressed. In addition, the charge / discharge cycle characteristics were more excellent. Furthermore, the same effect was confirmed also in Examples 4 to 6 in which albumin, lysozyme, and globulin modified with 2,2,2, -trifluoroethyl groups were coated. In the lithium ion secondary battery of Comparative Example 3 coated with carboxymethyl cellulose modified with 2,2,2, -trifluoroethyl group, the gas generation amount was slightly reduced, but the charge / discharge cycle characteristics were Comparative Example 1. It was equivalent. Moreover, the comparative example 4 which coat | covered the polyvinylidene fluoride which has a fluoro group also had much gas generation amount, and became a result inferior to the Examples 1-6 in the expansion coefficient and charging / discharging cycling characteristics of a cell.

  Table 2 shows the battery characteristics of the lithium ion secondary batteries according to Examples 7 to 14 and Comparative Example 1. In addition, about the amount of gas generation, the expansion coefficient of a laminate cell, and the charge / discharge cycle characteristics, the measurement results of Comparative Example 1 are each 100%, and the results of Examples 7 to 14 are shown as relative ratios to the results of Comparative Example 1. . In the lithium ion secondary batteries of Examples 7 to 14 in which sodium caseinate whose carboxy group was modified with 2,2,2, -trifluoroethyl group was coated on the surface of silicon at various coating amounts, the lithium ion secondary batteries of Examples 7 to 14 Gas generation amount and expansion rate were suppressed, and charge / discharge cycle characteristics were also excellent. In particular, when the amount of sodium caseinate was 0.1 to 10% by mass, both the suppression of the expansion rate and the charge / discharge cycle characteristics were more excellent.

  Table 3 shows the battery characteristics of the lithium ion secondary batteries according to Examples 15 to 22 and Comparative Example 5. In addition, about the gas generation amount, the expansion coefficient of the laminate cell, and the charge / discharge cycle characteristics, the measurement results of Comparative Example 5 were set to 100%, respectively, and Examples 15 to 22 and Comparative Example 6 were used as relative ratios to the results of Comparative Example 5. The results are shown. Even when the negative electrode active material was changed to silicon oxide, in the lithium ion secondary batteries of Examples 15 to 22 coated with sodium caseinate having a carboxyl group modified with a trifluoroethyl group, gas was generated from Comparative Examples 5 to 6. It became the result which was more excellent in each of quantity, an expansion coefficient, and charging / discharging cycling characteristics.

  From the above results, according to the technology disclosed herein, a negative electrode active material for a lithium ion secondary battery in which at least a part of the surface of silicon or silicon oxide is coated with a protein modified with a functional group containing fluorine, In addition, the negative electrode and the lithium ion secondary battery using the negative electrode active material for the lithium ion secondary battery are further improved in charge and discharge because the gas generation amount and the cell volume expansion accompanying the charge and discharge of the lithium ion secondary battery are suppressed. 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 body, 50 ... exterior body

Claims (8)

  A negative electrode active material capable of occluding and releasing lithium ions, wherein the negative electrode active material has a protein modified with a functional group containing fluorine on at least a part of a surface thereof, and the negative electrode active material is silicon, or A negative electrode active material for a lithium ion secondary battery, which is a silicon oxide.   2. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein at least one of a carboxyl group and a hydroxy group of the protein is modified with a functional group containing fluorine.   The functional group containing fluorine is at least one selected from a monofluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a trifluoroethyl group, a difluoromethylene group, a trifluorometasulfonic acid group, and a trifluoroacetyl group. The negative electrode active material for lithium ion secondary batteries according to claim 1 or 2, further comprising:   The lithium protein according to any one of claims 1 to 3, wherein the protein includes casein, albumin, lysozyme, globulin, and at least one of an alkali metal salt, an alkaline earth metal salt, and a magnesium salt thereof. Negative electrode active material for secondary battery. The protein, in the infrared absorption spectrum, C = O stretching vibration in the vicinity of 1640 ± 10cm ^-1, N-H deformation vibration near 1520 ± 10cm ^-1, C-N stretching vibration in the vicinity of 1225 ± 10 cm ^-1, 5. The negative electrode active material for a lithium ion secondary battery according to claim 1, which exhibits C—F stretching vibration at 1270 ± 10 cm ⁻¹ and 1160 ± 10 cm ⁻¹ .   The negative electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the protein content is 0.02 to 10% by weight based on the weight of the negative electrode active material.   The negative electrode for lithium ion secondary batteries which has the negative electrode active material for lithium ion secondary batteries as described in any one of Claims 1-6.   A lithium ion secondary battery comprising the lithium ion secondary battery negative electrode according to claim 7, a positive electrode, a separator interposed between the lithium ion secondary battery negative electrode and the positive electrode, and an electrolyte.

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