JP2010123494A - Negative electrode for lithium secondary battery, lithium secondary battery, and method of manufacturing negative electrode for lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of charge and discharge capacity in the charge and discharge cycle of a lithium secondary battery. <P>SOLUTION: This lithium secondary battery 20 is equipped with a negative electrode 23 including a negative electrode active material 11 containing a group 6 element oxide, a negative electrode collector 12 in which the surface roughness Rzjis(μm) satisfies d≤Rzjis≤4d, where the particle diameter of the negative electrode active material is set as d(μm), and a negative electrode binder 13 formed on the negative electrode collector 12 together with the negative electrode active material. Since the negative electrode collector has proper roughness, influence of deactivation and a volume change due to the crystal structure change of the negative electrode active material 11 caused by charge and discharge is eased. Further, the negative electrode active material 11 is formed on the negative electrode collector 12 together with the negative electrode binder 13, and thereby, peeling of the negative electrode active material 11 is suppressed. The negative electrode 23 for the lithium secondary battery is preferably heat-treated at a prescribed temperature, a temperature of not less than the melting point of the negative electrode binder for instance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing a negative electrode for a lithium secondary battery.

Conventionally, a lithium secondary battery has an active material containing tungsten dioxide doped with a metal dopant that improves charge / discharge capacity per unit weight of an active material such as aluminum or manganese, and a polymer binder such as polyvinylidene fluoride. An electrode composition having an electrode composition has been proposed (for example, see Patent Document 1). In the lithium secondary battery of Patent Document 1, the charge / discharge capacity per unit weight of the active material is improved by the metal dopant. Moreover, as a lithium secondary battery, the thing which suppresses the side reaction in the first charge by using fluorinated tungsten oxide for a negative electrode active material, and is excellent in the first charge / discharge efficiency is proposed ( For example, see Patent Document 2).
Japanese translation of PCT publication No. 2003-509829 JP 2006-172991 A

  Tungsten oxide is a material that is thermally stable and exhibits a high theoretical capacity density, but lithium intercalation may occur in multiple stages. This tungsten oxide is less susceptible to capacity degradation when the insertion amount of lithium is small, but there is a problem that the capacity is greatly degraded during repeated charging and discharging when the insertion amount of lithium is increased. In the lithium secondary batteries described in Patent Documents 1 and 2, although the charge / discharge characteristics are improved by adding a metal dopant or performing a fluorination treatment, it is still not sufficient, and the lithium insertion amount is further increased. There was a problem that the capacity deteriorated when it was increased.

  The present invention has been made in view of such a problem, and a lithium secondary battery capable of suppressing capacity deterioration associated with charge / discharge even when the amount of lithium inserted into the negative electrode active material is increased in the charge / discharge cycle. The main object is to provide a negative electrode for a battery, a lithium secondary battery, and a method for producing a negative electrode for a lithium secondary battery.

  In order to achieve the above-described object, the present inventors use a Group 6 element oxide as the negative electrode active material, and optimize the relationship between the surface roughness of the negative electrode current collector and the particle diameter of the negative electrode active material. I examined that. As a result, it has been found that a reduction in charge / discharge capacity can be suppressed even in a charge / discharge cycle in which the amount of lithium inserted into the negative electrode active material is large, and the present invention has been completed.

That is, the negative electrode for a lithium secondary battery of the present invention is
A negative electrode active material containing a Group 6 element oxide;
When the particle diameter of the negative electrode active material is d (μm), the negative electrode current collector satisfying d ≦ Rzjis ≦ 4d with a surface roughness Rzjis (μm);
And a negative electrode binder formed on the negative electrode current collector together with the negative electrode active material.

The lithium secondary battery of the present invention is
A positive electrode including a positive electrode active material;
A negative electrode for a lithium secondary battery as described above;
An ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions.

Furthermore, the method for producing a negative electrode for a lithium secondary battery according to the present invention includes:
When the negative electrode active material containing a Group 6 element oxide is d (μm) and the particle size of the negative electrode active material is d (μm), the surface roughness Rzjis (μm) is on the negative electrode current collector satisfying d ≦ Rzjis ≦ 4d together with the negative electrode binder An electrode forming step to be formed.

  In the negative electrode obtained by this negative electrode for lithium secondary battery, lithium secondary battery, and negative electrode for lithium secondary battery, even if the amount of lithium inserted into the negative electrode active material is increased in the charge / discharge cycle, it accompanies charge / discharge. Capacity degradation can be suppressed. The reason why such an effect can be obtained is not clear, but the negative electrode current collector has an appropriate roughness, so that the effects of deactivation and volume change due to the change in the crystal structure of the negative electrode active material accompanying charge / discharge are alleviated. This is presumed to be because of this. In addition, by forming a negative electrode active material together with a negative electrode binder on such a negative electrode current collector, the negative electrode active material forms a good contact interface on the negative electrode current collector, thereby suppressing peeling of the negative electrode active material. It is guessed that it is to be done.

  A negative electrode for a lithium secondary battery of the present invention includes a negative electrode active material containing a Group 6 element oxide, a negative electrode current collector having a surface roughness appropriate for the particle diameter of the negative electrode active material, and a negative electrode active material And a negative electrode binder formed on the surface of the negative electrode current collector. This negative electrode for lithium secondary batteries can be used as a negative electrode for lithium secondary batteries such as lithium ion secondary batteries and lithium air batteries. Among these, it is preferable to utilize for the negative electrode of a lithium ion secondary battery.

In the negative electrode for a lithium secondary battery of the present invention, the negative electrode active material contains a Group 6 element oxide. As the Group 6 element oxide, for example, at least one of tungsten oxide (for example, WO ₂ ), molybdenum oxide (for example, MoO ₂ ), chromium oxide (for example, CrO ₂ ), and the like can be used. The Group 6 element oxide is not particularly limited, but preferably has a rutile structure. In these oxides, lithium can be inserted into and extracted from a tunnel-like site surrounded by a rutile chain, thereby functioning as an electrode of a lithium secondary battery. Of these, tungsten oxide is preferable. Tungsten oxide undergoes lithium insertion / extraction at a lower potential than molybdenum oxide or chromium oxide. For this reason, when tungsten oxide is used as the negative electrode, the battery voltage determined by the potential difference between the positive electrode and the negative electrode can be increased. Further, it is thermally stable and exhibits a high theoretical capacity density. The particle diameter of the negative electrode active material is preferably 0.07 μm or more and 7 μm or less, and more preferably 2 μm or more and 7 μm or less. This is because particles are easily handled in such a range. The particles may be primary particles or secondary particles, or may include both. Here, the particle diameter of the negative electrode active material is a value calculated by measuring with a laser diffraction particle size distribution measuring apparatus using ethanol as a solvent and calculating as a median diameter.

In the negative electrode for a lithium secondary battery of the present invention, the negative electrode active material preferably has 0.5 mol or more of lithium inserted into 1 mol of the Group 6 element oxide at the end of charging. In this way, high battery performance can be obtained. The reason is presumed as follows. For example, in Li _x WO ₂ that is a group 6 element oxide, lithium intercalation may generally occur in multiple stages. In this Li _x WO ₂ , when lithium is inserted and desorbed up to a range of 0.5 ≦ x ≦ 1, a high theoretical capacity is shown, but Li _x WO ₂ becomes electrically inactive with repeated charge and discharge. For example, capacity degradation may increase. On the other hand, when lithium is inserted and desorbed when x is less than 0.5, capacity deterioration due to repeated charge and discharge is further suppressed, but the capacity may be inferior. In contrast, the negative electrode for a lithium secondary battery of the present invention has a negative electrode binder, and the surface of the negative electrode current collector has an appropriate surface roughness with respect to the particle size of the negative electrode active material. For example, in Li _x WO ₂ , lithium can be inserted and desorbed to a range of 0.5 ≦ x ≦ 1. Therefore, it can be close to the theoretical capacity, and higher battery performance can be obtained.

  In the negative electrode for a lithium secondary battery of the present invention, the negative electrode current collector has an appropriate surface roughness Rzjis. The negative electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil formed of a metal such as copper, stainless steel, or nickel-plated steel can be used. The surface roughness Rzjis of the negative electrode current collector is such that the surface roughness Rzjis (μm) satisfies d ≦ Rzjis ≦ 4d, where the particle diameter of the negative electrode active material is d (μm). If d ≦ Rzjis, the effect of roughening is obtained, and if Rzjis ≦ 4d, the particle diameter is not too rough. Furthermore, the surface roughness Rzjis is preferably larger than 0.25 μm and not larger than 7 μm. If the surface roughness Rzjis is larger than 0.25 μm, it is possible to ensure adhesion when forming the negative electrode active material on the negative electrode current collector, and to suppress capacity deterioration due to repeated charge and discharge. In addition, in order to form irregularities on the current collector surface, the thickness of the negative electrode current collector corresponding to the unevenness is required, but when the surface roughness Rzjis is 7 μm or less, the thickness of the negative electrode current collector is suppressed to about 30 μm. be able to. Here, the surface roughness Rzjis is also referred to as ten-point average roughness, and refers to the surface roughness determined based on JIS-B0601: 2001 Annex 1 (reference).

  In the negative electrode for a lithium secondary battery of the present invention, the negative electrode binder is formed on the surface of the negative electrode current collector together with the negative electrode active material. The negative electrode binder plays a role of connecting the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), a fluorine-containing resin such as fluorine rubber, or polypropylene, Thermoplastic resins such as polyethylene and polyimide, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Among these, a thermoplastic resin is preferable. This is because an increase in the effect of connecting the active material particles and the conductive material particles by heat treatment can be expected. The binder amount is preferably 5% or more and 20% or less with respect to the negative electrode active material. If the amount of the binder is 5% or more, the effect of adding the binder can be easily obtained, and if the amount of the binder is 20% or less, a decrease in the electrode energy density can be suppressed.

  In the negative electrode for a lithium secondary battery of the present invention, the negative electrode active material and the negative electrode binder formed on the negative electrode current collector are preferably heat-treated at a predetermined temperature. When the negative electrode binder of the present invention is heat-treated at a temperature higher than the melting point, the binding force increases, and the capacity deterioration due to repeated charge / discharge can be further suppressed. Further, it is considered that the negative electrode binder is diffused into the negative electrode active material by the heat treatment, and an effect of increasing the binding force or suppressing the change of the crystal structure can be obtained. For example, polyimide is preferably heat treated at 300 ° C. to 500 ° C., and preferably heat treated at 500 ° C. or lower in order to avoid thermal decomposition. Polyvinylidene fluoride is preferably heat-treated at 160 ° C. or higher, but is preferably heat-treated at 350 ° C. or lower because it is thermally decomposed at 350 ° C. or higher. The melting point of polytetrafluoroethylene is preferably 327 ° C. and heat-treated at a temperature higher than this temperature. Especially, it is more preferable that the main component of a negative electrode binder is polyvinylidene fluoride and the temperature of the said heat processing is 200 degreeC or more and 300 degrees C or less. For heat treatment, in addition to heating in an electric furnace, a discharge plasma sintering method or a hot press method may be used. The atmosphere during the heat treatment is preferably performed in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as a vacuum, a nitrogen atmosphere, an argon atmosphere, or a reducing atmosphere such as a hydrogen atmosphere. Good.

  The negative electrode for a lithium secondary battery according to the present invention is prepared by, for example, mixing a negative electrode active material, a negative electrode binder, and a conductive material, adding an appropriate solvent to form a paste-like negative electrode material, and drying the coating on the surface of the current collector And it is good also as what was compressed and formed in order to raise the electrode density as needed. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. Examples of the solvent for dispersing the negative electrode active material, the negative electrode binder, and the negative electrode conductive material include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape.

  A lithium secondary battery of the present invention includes a positive electrode including a positive electrode active material, a negative electrode for a lithium secondary battery described above, and an ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions. It is.

The positive electrode of the lithium secondary battery of the present invention is, for example, a mixture of a positive electrode active material and a conductive material and a binder, and an appropriate solvent is added to form a paste-like positive electrode mixture on the surface of the positive electrode current collector. And it can compress and form so that an electrode density may be raised as needed. As the positive electrode active material, an oxide containing lithium and a transition metal element or a polyanionic compound can be used. Specifically, for example, lithium cobalt composite oxide (such as Li _(1-x) CoO ₂ (0 <x <1, the same applies hereinafter)), lithium nickel composite oxide (such as Li _(1-x) NiO ₂ ), Lithium manganese composite oxide (Li _(1-x) MnO ₂ , Li _(1-x) Mn ₂ O ₄ etc.), lithium iron composite phosphorous oxide (LiFePO ₄ etc.), lithium vanadium composite oxide (LiV ₂ O ₃₎ Etc.). The positive electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil or mesh formed of a metal such as aluminum, copper, stainless steel, or nickel-plated steel may be used. it can. The binder plays a role of connecting the active material particles and the conductive material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene is used. be able to. The conductive material is for ensuring the electrical conductivity of the positive electrode. For example, one or more of carbon powder materials such as carbon black, acetylene black, natural graphite, artificial graphite, and cokes are mixed. Things can be used. As the solvent for dispersing the positive electrode active material, the conductive material, and the binder, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

In the lithium secondary battery of the present invention, as the ion conductive medium, a nonaqueous electrolytic solution, an ionic liquid, a gel electrolyte, a solid electrolyte, or the like in which a supporting salt is dissolved in an organic solvent can be used. Of these, a non-aqueous electrolyte is preferable. Examples of the supporting salt include known LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₃ ), LiN (C ₂ F ₅ SO ₂ ), and the like. Supporting salts can be used. The concentration of the supporting salt is preferably 0.1 to 2.0M, and more preferably 0.8 to 1.2M. As an organic solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), diethyl carbonate (DEC), dimethyl carbonate (DMC) and the like are used for conventional secondary batteries and capacitors. An organic solvent is mentioned. These may be used alone or in combination. Further, the ionic liquid is not particularly limited, but 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide, 1-ethyl-3-butylimidazolium tetrafluoroborate, or the like is used. Can do. The gel electrolyte is not particularly limited. For example, a polymer such as polyvinylidene fluoride, polyethylene glycol, or polyacrylonitrile, or a saccharide such as an amino acid derivative or sorbitol derivative is added with an electrolyte containing a supporting salt. And a gel electrolyte. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes. Well-known inorganic solid electrolytes include, for example, Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li 2 S-SiS 2, sulfide Examples thereof include phosphorus compounds. These may be used alone or in combination. Examples of the organic solid electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyvinylidene fluoride, polyphosphazene, polyethylene sulfide, polyhexafluoropropylene, and derivatives thereof. These may be used alone or in combination.

  The lithium secondary battery of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it has a composition that can withstand the use range of the secondary battery. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a microporous film of an olefin resin such as polyethylene or polypropylene Is mentioned. These may be used alone or in combination.

  The shape of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc. An example of this lithium secondary battery is shown in FIG. FIG. 1 is a cross-sectional view schematically showing the configuration of the coin-type battery 20. The coin-type battery 20 includes a cup-shaped battery case 21, a positive electrode 22 provided inside the battery case 21, a negative electrode 23 provided at a position facing the positive electrode 22 via a separator 24, A non-aqueous electrolyte solution 27 containing a supporting salt, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed in the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. Yes. The negative electrode 23 includes a negative electrode active material 11 containing a Group 6 element oxide, and a negative electrode current collector having a surface roughness Rzjis (μm) satisfying d ≦ Rzjis ≦ 4d, where d (μm) is the particle diameter of the negative electrode active material 11. And a negative electrode binder 13 formed on the negative electrode current collector 12 together with the negative electrode active material 11.

  The lithium secondary battery of the present invention is preferably charged until 0.5 mol or more of lithium is inserted with respect to 1 mol of the group 6 element oxide of the negative electrode active material. The lithium secondary battery of the present invention can suppress capacity deterioration even in repeated charging and discharging in which charging is performed until 0.5 mol or more of lithium is inserted. And since 0.5 mol or more of lithium can be inserted, the battery capacity can be brought close to the theoretical capacity, and higher battery performance can be obtained. The lithium secondary battery of the present invention may be charged until 1 mole of lithium is inserted per 1 mole of the Group 6 element oxide of the negative electrode active material.

  Next, the manufacturing method of the negative electrode for lithium secondary batteries is demonstrated. The method for producing a negative electrode for a lithium secondary battery of the present invention comprises (1) a roughening step for roughening the surface of the negative electrode current collector, and (2) a negative electrode current collector having a roughened surface. An electrode forming step of forming the negative electrode active material together with the negative electrode binder, and (3) a heat treatment step of performing a heat treatment at a temperature equal to or higher than the melting point of the negative electrode binder after the electrode forming step may be included.

(1) Roughening step The negative electrode current collector having a roughened surface used in the method for producing a negative electrode for a lithium secondary battery may be produced by a roughening step. The material of the negative electrode current collector is not particularly limited as long as it is formed of a conductive material. For example, a foil formed of a metal such as copper, stainless steel, or nickel-plated steel can be used. The roughening step is not particularly limited as long as the surface of the negative electrode current collector is roughened. For example, the surface of the negative electrode current collector may be precipitated by an electrolytic method or the like, and the surface thereof may be roughened. Thereby, the surface roughness Rzjis can be controlled. The surface roughness Rzjis of the negative electrode current collector may be such that the surface roughness Rzjis (μm) satisfies d ≦ Rzjis ≦ 4d, where d (μm) is the particle diameter of the negative electrode active material described later. If d ≦ Rzjis, the effect of roughening is obtained, and if Rzjis ≦ 4d, the particle diameter is not too rough. Furthermore, the surface roughness Rzjis is more preferably set to be larger than 0.25 μm and not larger than 7 μm. When the surface roughness Rzjis is larger than 0.25 μm, it is possible to ensure adhesion when forming the negative electrode active material on the negative electrode current collector, and to suppress capacity deterioration due to repeated charge and discharge. In addition, in order to form irregularities on the current collector surface, the thickness of the negative electrode current collector corresponding to the unevenness is required, but if the surface roughness Rzjis is 7 μm or less, the thickness of the negative electrode current collector is about 30 μm. Can be suppressed.

(2) Electrode formation process Next, the negative electrode active material containing a group 6 element oxide is formed with a negative electrode binder on the negative electrode collector by which the surface was roughened as mentioned above. At this time, the conductive material may be formed together with the negative electrode active material and the negative electrode binder. The formation method is not particularly limited, but for example, a negative electrode active material, a negative electrode binder, and a conductive material are mixed, and an appropriate solvent is added to form a paste-like negative electrode material, which is applied to the surface of the current collector and dried. You may compress and form so that an electrode density may be raised as needed. As the negative electrode active material, a material containing a Group 6 element oxide is used. For example, tungsten oxide (WO ₂ ), molybdenum oxide (MoO ₂ ), chromium oxide (CrO ₂ ), or the like can be used as the Group 6 element. The Group 6 element oxide is not particularly limited, but preferably has a rutile structure. In these oxides, lithium can be inserted into and desorbed from a tunnel-like site surrounded by a rutile chain, and thus can function as an electrode of a lithium secondary battery. Of these, tungsten oxide is preferable. The negative electrode active material preferably has a particle size of 0.07 μm or more and 7 μm or less, and more preferably 2 μm or more and 7 μm or less. The particles may be primary particles or secondary particles, or may include both. The negative electrode binder plays a role of connecting the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing resin such as fluororubber, polypropylene, polyethylene, etc. , Thermoplastic resins such as polyimide, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Among these, a thermoplastic resin is preferable. This is because an increase in the effect of connecting the active material particles and the conductive material particles can be expected by the heat treatment. The binder amount is preferably 5% or more and 20% or less with respect to the negative electrode active material. If the amount of the binder is 5% or more, the effect of adding the binder can be obtained, and if the amount of the binder is 20% or less, a decrease in the electrode energy density can be suppressed. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. Examples of the solvent for dispersing the negative electrode active material, the negative electrode binder, and the negative electrode conductive material include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropyl. Organic solvents such as amine, ethylene oxide, and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape.

(3) Heat treatment step Next, the negative electrode active material and the negative electrode binder formed on the negative electrode current collector are heat-treated. This heat treatment may be performed at a temperature lower than the melting point of the negative electrode binder, but is preferably performed at a temperature higher than the melting point of the negative electrode binder. When the negative electrode binder of the present invention is heat-treated at a temperature higher than the melting point, the binding force increases, and the capacity deterioration accompanying repeated charge / discharge can be further suppressed. For example, polyimide is preferably heat treated at 300 ° C. to 500 ° C., and is preferably heat treated at 500 ° C. or lower in order to avoid thermal decomposition. Polyvinylidene fluoride is preferably heat-treated at 160 ° C. or higher, but is preferably heat-treated at 350 ° C. or lower because it is thermally decomposed at 350 ° C. or higher. Polytetrafluoroethylene has a melting point of 327 ° C. and is preferably heat-treated at a temperature higher than this temperature. It is particularly preferable to use a binder mainly composed of polyvinylidene fluoride as the negative electrode binder, and to perform the heat treatment at a temperature of 200 ° C. or higher and 300 ° C. or lower in the heat treatment step. The atmosphere during the heat treatment is preferably performed in a non-oxidizing atmosphere. For example, the heat treatment can be performed in an inert gas atmosphere such as a vacuum, a nitrogen atmosphere, or an argon atmosphere, or a reducing atmosphere such as a hydrogen atmosphere.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the manufacturing method includes the roughening step, but this step may be omitted by using a roughened negative electrode current collector. In the embodiment described above, the manufacturing method includes a heat treatment step, but this step may be omitted.

[Experimental Example 1]
The negative electrode was produced as follows. 85 by weight ratio of WO ₂ (made by high-purity chemical) having a rutile structure as a negative electrode active material having a particle diameter of 7 μm and carbon black (# TB-5500, produced by Tokai Carbon Co., Ltd.) as a conductive material. : Weighed to 10 and mixed in a mortar to obtain a mixed powder. An N-methylpyrrolidone (NMP) solution in which 12% polyvinylidene fluoride (PVdF) as a negative electrode binder was dissolved was weighed so that the weight ratio of the mixed powder to PVdF was 95: 5, and then mixed powder. In addition, a negative electrode slurry was prepared. This negative electrode slurry was coated on the negative electrode current collector by the doctor blade method. As the negative electrode current collector, an electrolytic foil having a thickness of, for example, 30 μm made of roughened copper having a surface roughness Rzjis of 7 μm on which copper was deposited on the surface by an electrolytic method was prepared. The coated electrode was dried at 120 ° C. under reduced pressure for 6 hours or more. This electrode was pressed using a roll press so that the packing density of the active material was 2.0 g / cm ³ . In addition, the particle diameter of the WO ₂ negative electrode active material was measured using a laser diffraction particle size distribution analyzer (SALD-2200 manufactured by Shimadzu Corporation) using ethanol as a solvent, and was calculated as a median diameter.

Next, the obtained coated negative electrode was heat-treated in a non-oxidizing atmosphere. The negative electrode was placed in an annular furnace made of alumina (manufactured by Fulltech Co., Ltd.) and replaced with Ar gas twice to obtain a complete non-oxidizing atmosphere. While introducing 30 cc / min Ar, the temperature was set to 300 ° C. at a rate of 2 ° C./min, followed by heat treatment for 12 hours. The temperature was similarly lowered at 2 ° C./min, and then the electrode was taken out and it was confirmed that the copper foil was not oxidized. The electrode thus obtained was punched out to 2.035 cm ² and used as the negative electrode (working electrode) of Experimental Example 1.

[Experiment 2]
A negative electrode of Experimental Example 2 was produced in the same manner as Experimental Example 1 except that a WO ₂ negative electrode active material having a rutile structure with a particle size of 2 μm was used.

[Experiment 3]
A negative electrode of Experimental Example 3 was produced in the same manner as Experimental Example 2 except that a negative electrode current collector having a surface roughness Rzjis of 4.5 μm was used.

[Experimental Examples 4 to 10]
The negative electrode of Experimental Example 4 was produced in the same manner as Experimental Example 1 except that the heat treatment temperature was 250 ° C. Further, the negative electrode of Experimental Example 5 was produced in the same manner as Experimental Example 1 except that the heat treatment temperature was 200 ° C. Further, the negative electrode of Experimental Example 6 was produced in the same manner as Experimental Example 1 except that the heat treatment temperature was 150 ° C. Further, the negative electrode of Experimental Example 7 was produced in the same manner as Experimental Example 1 except that the heat treatment temperature was 100 ° C. Further, the negative electrode of Experimental Example 8 was produced in the same manner as Experimental Example 1 except that no heat treatment was performed. Further, the negative electrode of Experimental Example 9 was produced in the same manner as Experimental Example 1 except that the heat treatment temperature was 350 ° C. Further, the negative electrode of Experimental Example 10 was produced in the same manner as Experimental Example 1 except that the heat treatment temperature was 400 ° C.

[Experimental Examples 11 and 12]
The negative electrode of Experimental Example 11 was produced in the same manner as Experimental Example 1 except that a negative electrode current collector having a surface roughness Rzjis of 4.5 μm was used. Further, the negative electrode of Experimental Example 12 was produced in the same manner as Experimental Example 1 except that a negative electrode current collector having a surface roughness Rzjis of 0.25 μm was used.

[Experimental Example 13]
A negative electrode of Experimental Example 13 was produced in the same manner as Experimental Example 2 except that a negative electrode current collector having a surface roughness Rzjis of 0.25 μm was used.

[Production of bipolar cell]
Using the negative electrode thus produced, a bipolar cell was produced as follows. A non-aqueous electrolyte was prepared by adding lithium hexafluorophosphate to a non-aqueous solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 30:70 so as to be 1 mol / L. The negative electrode is used as a working electrode, a Li foil (thickness: 300 μm) is used as a counter electrode, and a bipolar cell is prepared by filling the non-aqueous electrolyte with a separator (manufactured by Tonen Tapils) between the working electrode and the counter electrode. did.

[Electrochemical measurement]
Using the bipolar cell thus produced, the initial charge capacity was measured by reducing (charging) to 0.4 V at 0.4 mA. At this time, it is considered that 1 mol of Li is inserted into 1 mol of WO ₂ in the negative electrode active material. Thereafter, oxidation (discharge) was performed at 0.4 mA to 1.5 V, and an initial discharge capacity was measured. Subsequently, the charge / discharge test was performed 20 cycles under the same conditions, and the 20th cycle charge capacity and the 20th cycle discharge capacity were measured. A charge capacity maintenance rate (%) represented by (20th cycle charge capacity / initial charge capacity) × 100 and a discharge capacity maintenance rate represented by (20th cycle discharge capacity / initial discharge capacity) × 100 ( %). The charge / discharge test was conducted in a constant temperature bath at 20 ° C.

[Experimental result]
The test results of Experimental Examples 1 to 13 are shown in Table 1. Table 1 shows active material particle diameter d (μm), current collector roughness Rzjis (μm), electrode heat treatment temperature t (° C.), initial charge capacity (mAh), initial discharge capacity (mAh), 20th cycle The charge capacity (mAh), the discharge capacity (mAh) at the 20th cycle, the charge capacity retention rate (%), and the discharge capacity retention rate (%) are shown. According to the results of Experimental Examples 1 to 13, in Experiment Examples 1 to 10 where the WO ₂ negative electrode active material particle diameter d (μm) and the current collector surface roughness Rzjis satisfy d ≦ Rzjis ≦ 4d, the discharge capacity retention rate is 60. It became more than%. From this, it was found that a decrease in charge / discharge capacity when charging / discharging was repeated could be suppressed. Furthermore, with respect to Experimental Examples 1 to 5 in which the electrode heat treatment temperature is in the range of 200 ° C. to 300 ° C., since the discharge capacity retention rate was 80% or more, the suppression effect on the decrease in charge / discharge capacity was particularly high. all right. In addition, in this experiment, when it is reduced (charged) to 0.4 V, it is considered that 1 mol of Li is inserted with respect to 1 mol of WO ₂ . It turns out that it is possible.

2 is a cross-sectional view illustrating an outline of a configuration illustrating an example of a coin-type battery 20. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Negative electrode active material, 12 Negative electrode collector, 13 Negative electrode binder, 20 Coin type battery, 21 Battery case, 22 Positive electrode, 23 Negative electrode, 24 Separator, 25 Gasket, 26 Sealing plate, 27 Nonaqueous electrolyte.

Claims (6)

A negative electrode active material containing a Group 6 element oxide;
When the particle diameter of the negative electrode active material is d (μm), the negative electrode current collector satisfying d ≦ Rzjis ≦ 4d with a surface roughness Rzjis (μm);
A negative electrode binder formed on the negative electrode current collector together with the negative electrode active material;
A negative electrode for a lithium secondary battery comprising:   2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode for a lithium secondary battery is such that the negative electrode active material formed on the negative electrode current collector and the negative electrode binder are heat-treated at a predetermined temperature. .   3. The lithium according to claim 1, wherein the negative electrode for a lithium secondary battery has the negative electrode active material inserted with 0.5 mol or more of lithium with respect to 1 mol of the Group 6 element oxide at the end of charging. Negative electrode for secondary battery. A positive electrode including a positive electrode active material;
The negative electrode for a lithium secondary battery according to any one of claims 1 to 3,
An ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts lithium ions;
Rechargeable lithium battery. A method for producing a negative electrode for a lithium secondary battery, comprising:
When the negative electrode active material containing a Group 6 element oxide is d (μm) and the particle size of the negative electrode active material is d (μm), the surface roughness Rzjis (μm) is on the negative electrode current collector satisfying d ≦ Rzjis ≦ 4d together with the negative electrode binder An electrode forming step to be formed;
The manufacturing method of the negative electrode for lithium secondary batteries containing. A method for producing a negative electrode for a lithium secondary battery according to claim 5,
The manufacturing method of the negative electrode for lithium secondary batteries including the heat processing process which heat-processes the said negative electrode active material and the said negative electrode binder which were formed on the said negative electrode collector after the said electrode formation process.

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