JP2007200686A - Negative electrode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance charge discharge cycle characteristics by sufficiently bonding a negative mix layer with a negative current collector in a lithium secondary battery using a negative electrode in which the negative mix layer containing negative active material particles containing silicon and/or silicon alloy and a binder are formed on the surface of the negative current collector. <P>SOLUTION: In the lithium secondary battery equipped with a positive electrode 1, a negative electrode 2 and a nonaqueous electrolyte, the negative mix layer containing the negative active material particles containing silicon and/or silicon alloy and the binder is formed on the surface of the negative current collector by baking, and the ratio of the binder in the vicinity of the negative current collector is made 2.5 times or more that in the position far from the negative current collector. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery and a negative electrode for a lithium secondary battery used for a negative electrode of the lithium secondary battery, and in particular, a negative electrode mixture containing negative electrode active material particles containing silicon and / or a silicon alloy and a binder. In a lithium secondary battery using a negative electrode for a lithium secondary battery having a layer formed on the surface of the negative electrode current collector, the negative electrode for the lithium secondary battery is improved to improve the charge / discharge cycle characteristics of the lithium secondary battery. It has the characteristic in the made point.

  In recent years, lithium secondary batteries that use non-aqueous electrolyte and charge and discharge by moving lithium ions between positive and negative electrodes have been used as new secondary batteries with high output and high energy density. It became so.

  Here, in such a lithium secondary battery, as one of the negative electrodes, a material that is alloyed with lithium is used as the negative electrode active material, and the negative electrode mixture layer including the negative electrode active material particles and the binder is used as the negative electrode collector. What is formed on the surface of the electric body is used.

  However, when a lithium secondary battery using a material that is alloyed with lithium as the negative electrode active material is charged and discharged in this way, the volume of the negative electrode active material particles expands and contracts when lithium is absorbed and released. Thus, the negative electrode active material particles are pulverized, or the negative electrode active material is peeled off from the current collector, so that the current collecting property in the negative electrode is lowered and the charge / discharge cycle characteristics of the lithium secondary battery are deteriorated. there were. In particular, in order to increase the capacity of the lithium secondary battery, when silicon and / or silicon alloy having a large ability to occlude and release lithium is used as a material to be alloyed with lithium, the volume of the negative electrode active material particles is expanded. -There was a problem that shrinkage was increased and charge / discharge cycle characteristics were greatly deteriorated.

  In recent years, as a negative electrode for a lithium secondary battery, silicon and / or on the surface of a negative electrode current collector made of a roughened conductive metal foil having a surface roughness Ra of 0.2 μm or more. Using a negative electrode active material particle containing a silicon alloy and a negative electrode mixture layer containing a binder sintered in a non-oxidizing atmosphere, and improving the adhesion between the negative electrode mixture layer and the negative electrode current collector There has been proposed a battery that improves charge / discharge cycle characteristics in a lithium secondary battery (see, for example, Patent Document 1).

However, even when the negative electrode for a lithium secondary battery as described above is used, the adhesion between the negative electrode mixture layer and the negative electrode current collector is not necessarily sufficient. When the negative electrode active material particles are brought into direct contact with the negative electrode current collector to reduce the resistance between the negative electrode active material particles and the negative electrode current collector, There is a problem that stress due to the volume change of the substance particles directly acts on the negative electrode current collector, and the negative electrode mixture layer is easily separated from the negative electrode current collector.
Japanese Patent Laid-Open No. 2002-260637

  The present invention relates to a lithium secondary battery using a negative electrode for a lithium secondary battery in which a negative electrode mixture layer containing negative electrode active material particles containing silicon and / or a silicon alloy and a binder is formed on the surface of a negative electrode current collector. It is an object to solve the above problems.

  That is, the present invention further improves the adhesion between the negative electrode mixture layer using the negative electrode active material particles containing silicon and / or silicon alloy and the negative electrode current collector in the lithium secondary battery as described above. Even when the particle size of the active material particles is increased, the negative electrode mixture layer is sufficiently adhered to the negative electrode current collector to improve the charge / discharge cycle characteristics of the lithium secondary battery. Is.

  In the negative electrode for a lithium secondary battery according to the present invention, in order to solve the above problems, a negative electrode mixture layer containing negative electrode active material particles containing silicon and / or a silicon alloy and a binder is provided on the surface of the negative electrode current collector. In the negative electrode for a lithium secondary battery formed by firing, the binder ratio in the vicinity of the negative electrode current collector was set to be 2.5 times or more of the binder ratio in a position away from the negative electrode current collector. .

  Here, in manufacturing the negative electrode for a lithium secondary battery as described above, a negative electrode mixture slurry containing negative electrode active material particles containing silicon and / or a silicon alloy and a binder is applied to the surface of the negative electrode current collector. Thus, a negative electrode mixture layer is formed, which is rolled and sintered. When the negative electrode mixture layer is sintered on the surface of the negative electrode current collector as described above, sintering is performed in a non-oxidizing atmosphere so that the binder and the negative electrode current collector in the negative electrode mixture layer are not oxidized. It is preferable.

  Here, when the ratio of the binder in the vicinity of the negative electrode current collector is 2.5 times or more of the ratio of the binder in the position away from the negative electrode current collector as described above, the above negative electrode mixture slurry In order to make the negative electrode active material particles and the binder, the proportion of the solvent added to the negative electrode mixture is increased, and the viscosity of the negative electrode mixture slurry is lowered to be applied to the surface of the negative electrode current collector. it can. In this way, immediately after the negative electrode mixture slurry is applied to the surface of the negative electrode current collector, the solution containing the binder flows and is dried in the vicinity of the negative electrode current collector. The ratio is higher than the position away from the negative electrode current collector. The viscosity of the negative electrode mixture slurry varies depending on the type of the binder and is not particularly limited, but is generally preferably 100 mPa · S or less, more preferably 25 mPa · S or less at 25 ° C.

  In addition, in order to make the ratio of the binder in the vicinity of the negative electrode current collector larger than the position away from the negative electrode current collector, a negative electrode mixture slurry having a high binder concentration is applied to the surface of the negative electrode current collector. It is also possible to apply a negative electrode mixture slurry having a binder concentration lower than that from above, or to coat the surface of the negative electrode current collector in advance with only a binder, and then the negative electrode containing negative electrode active material particles and a binder It is also possible to apply a mixture slurry.

  Here, as said negative electrode collector used in this invention, it is preferable to use that whose surface roughness Ra is 0.2 micrometer or more. Thus, when the negative electrode current collector having a surface roughness Ra of 0.2 μm or more is used and the negative electrode mixture layer is formed on the negative electrode current collector, the anchor effect by the binder in the negative electrode mixture layer is greatly obtained. The adhesion between the negative electrode current collector and the negative electrode mixture layer is greatly improved.

  Then, when obtaining the negative electrode current collector having a surface roughness Ra of 0.2 μm or more as described above, the surface of the negative electrode current collector is roughened.

  Here, as a method for roughening the surface of the negative electrode current collector in this way, for example, a plating method, a vapor phase growth method, an etching method, a polishing method, or the like can be used.

  As a plating method, an electrolytic plating method or an electroless plating method can be used. Further, as the vapor phase growth method, a sputtering method, a CVD method, an evaporation method, or the like can be used. As an etching method, a physical etching method or a chemical etching method can be used. In addition, as a polishing method, polishing by sandpaper, polishing by a blast method, or the like can be performed.

  Moreover, as a material of the negative electrode current collector, for example, a metal such as copper, nickel, iron, titanium, cobalt, or an alloy thereof can be used, and in particular, a metal foil containing a copper element is preferably used. More preferably, a copper foil or a copper alloy foil is used. Moreover, as said metal foil containing a copper element, the layer containing a copper element may be formed in the surface of the metal foil which consists of metal elements other than copper.

  In addition, the thickness of the negative electrode current collector is not particularly limited, but usually a thickness in the range of 10 μm to 100 μm is used.

  Further, the upper limit of the surface roughness Ra of the negative electrode current collector is not particularly limited, but the thickness of the negative electrode current collector is preferably in the range of 10 μm to 100 μm. The upper limit of Ra is 10 μm or less.

  Moreover, as said negative electrode collector, it is preferable that the surface roughness Ra and the average space | interval S of a local peak have the relationship of 100Ra> = S. Here, the surface roughness Ra and the average distance S between the local peaks are defined by Japanese Industrial Standards (JIS B 0601-1994), and can be measured by, for example, a surface roughness meter.

  In addition, the negative electrode active material particles used in the present invention only need to contain silicon and / or a silicon alloy as described above, and contain a material that is alloyed with lithium in addition to silicon and / or a silicon alloy. There may be. Here, as a material to be alloyed with lithium, for example, germanium, tin, lead, zinc, magnesium, sodium, aluminum, gallium, indium, and alloys thereof can be used. However, in order to increase the capacity of the negative electrode, it is preferable to use only the above silicon and / or silicon alloy as the negative electrode active material particles, and it is particularly preferable to use silicon.

  Here, examples of the silicon alloy include a solid solution of silicon and one or more other elements, an intermetallic compound of silicon and one or more other elements, and a eutectic of silicon and one or more other elements. An alloy or the like can be used. As a method for producing such an alloy, an arc melting method, a liquid quenching method, a mechanical alloying method, a sputtering method, a chemical vapor deposition method, a firing method, or the like can be used.

  Further, the average particle diameter of the negative electrode active material particles is not particularly limited, but as the particle diameter increases, the resistance between the negative electrode active material particles and the negative electrode current collector is reduced, while the negative electrode during charge and discharge is reduced. Since the stress due to the volume change of the active material particles directly acts on the negative electrode current collector, and the negative electrode mixture layer easily peels from the negative electrode current collector, the average particle size of the negative electrode active material particles may be 20 μm or less. preferable. On the other hand, when the particle size of the negative electrode active material particles becomes too small, the surface area of the negative electrode active material particles per unit weight increases, the area in contact with the non-aqueous electrolyte increases, the irreversible reaction increases, and the capacity decreases. Therefore, the average particle diameter of the negative electrode active material particles is preferably 0.3 μm or more.

  In order to improve the adhesion of the negative electrode mixture layer to the negative electrode current collector, a thermoplastic resin is preferably used as the binder used in the negative electrode mixture layer, and more preferably polyimide is used. .

  Moreover, in order to improve the electroconductivity in this negative mix layer and to improve the current collection property in a negative electrode, electroconductive powder can be added in this negative mix layer.

  Here, as the conductive powder, it is preferable to use the same material as the negative electrode current collector, specifically, metals such as copper, nickel, iron, titanium, cobalt, An alloy or a mixture thereof can be used. The average particle size of the conductive powder added to the negative electrode mixture layer is not particularly limited, but generally it is preferably 100 μm or less, more preferably 50 μm or less, and most preferably 10 μm or less. Like that.

  In sintering the negative electrode mixture layer as described above, the binder in the negative electrode mixture layer is thermally fused to the negative electrode current collector to obtain a sufficient anchor effect. Sintering is preferably performed at a temperature 20 ° C. or more higher than the glass transition temperature. However, if the sintering temperature becomes too high and the binder is decomposed, the adhesion between the negative electrode active material in the negative electrode mixture layer and the adhesion between the negative electrode mixture layer and the negative electrode current collector are reduced. Therefore, it is preferable to sinter at a temperature at which the above binder does not decompose. For example, when polyimide is used as the binder, it is preferable to sinter at 600 ° C. or less at which the polyimide does not completely decompose.

  In addition, in the case of using a copper foil as the negative electrode current collector, if the sintering temperature is too high, the strength of the negative electrode current collector is greatly reduced due to a change in crystallinity of copper, etc. Is sintered at 500 ° C. or lower, more preferably 450 ° C. or lower.

  Further, as described above, in order to improve the adhesion between the negative electrode mixture layer and the negative electrode current collector, it is preferable to sinter at a temperature 20 ° C. higher than the glass transition temperature of the binder. When copper foil is used, it is preferable to use a binder having a glass transition temperature of 450 ° C. or lower.

  In the lithium secondary battery of the present invention, in the lithium secondary battery including the positive electrode, the negative electrode, and the nonaqueous electrolyte, the above-described negative electrode for a lithium secondary battery is used as the negative electrode.

Here, the nonaqueous electrolyte used in the lithium secondary battery of the present invention is not particularly limited, and any commonly used one can be used. For example, a nonaqueous electrolyte obtained by dissolving a solute in a nonaqueous solvent, Further, a gel polymer electrolyte obtained by impregnating the above-mentioned non-aqueous electrolyte into a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

  Further, the above non-aqueous solvent is not particularly limited, and those commonly used can be used. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl A mixed solvent of a chain carbonate such as carbonate or a mixed solvent of a cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane or 1,2-diethoxyethane can be used.

Further, the solute is not particularly limited, and those commonly used can be used. For example, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C _{2 F 5 SO 2) 2, LiN} (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, LiAsF 6, LiClO 4, Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , a mixture thereof, or the like can be used.

Further, there is no particular limitation on the positive electrode active material used in the positive electrode, in general there can be used those which are used, for _{example, LiCoO 2, LiNiO 2, LiMn} 2 O 4, LiMnO 2, LiCo 0.5 Ni 0.5 O 2 , LiNi _0.7 Co _0.2 Mn _0.1 O _{2 and} other lithium-containing transition metal oxides, MnO ₂ and other metal oxides not containing lithium, and the like can be used.

  In the negative electrode for a lithium secondary battery according to the present invention, as described above, the negative electrode mixture layer containing negative electrode active material particles containing silicon and / or a silicon alloy and a binder is formed on the surface of the negative electrode current collector by firing. The adhesion ratio of the negative electrode mixture layer to the negative electrode current collector is improved because the binder ratio in the vicinity of the negative electrode current collector is more than 2.5 times the binder ratio at a position away from the negative electrode current collector. However, even when negative electrode active material particles having a large average particle diameter are used, the negative electrode mixture layer is sufficiently suppressed from peeling from the negative electrode current collector.

  Further, in the lithium secondary battery according to the present invention, since the negative electrode for a lithium secondary battery as described above is used, the negative electrode mixture layer is also used as a negative electrode current collector even when the lithium secondary battery is charged and discharged. Separation from the body was sufficiently prevented, and the cycle life of the lithium secondary battery was improved.

  Hereinafter, the negative electrode for a lithium secondary battery according to the present invention and the lithium secondary battery using the negative electrode for a lithium secondary battery will be specifically described with reference to examples, and in the lithium secondary battery according to the examples, Shows that the cycle life is improved by giving a comparative example. In addition, the negative electrode for lithium secondary batteries and the lithium secondary battery according to the present invention are not limited to those shown in the following examples, and can be implemented with appropriate modifications without departing from the scope of the invention. .

Example 1
In Example 1, a negative electrode, a positive electrode, and a nonaqueous electrolytic solution prepared as described below were used.

[Production of negative electrode]
Silicon powder (purity 99.9%) having an average particle diameter of 15 μm is used as the negative electrode active material particles, polyimide is used as the binder, and the above-mentioned negative electrode active material particles, the binder, and the solvent N-methyl-2-pyrrolidone are 9: A negative electrode mixture slurry was prepared by mixing at a weight ratio of 1: 9.2. Here, the negative electrode mixture slurry thus prepared had a viscosity at 25 ° C. of 12.3 mPa · S.

Further, as the negative electrode current collector, both surfaces of a rolled copper alloy foil having a thickness of 18 μm and a tensile strength of 900 N / mm ² were roughened by electrolytic treatment with copper, the thickness was 21 μm, and the surface roughness Ra was 0. .2 μm was used.

  Then, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector, and dried to form a negative electrode mixture layer on both surfaces of the negative electrode current collector, which is cut into a 380 mm × 52 mm rectangular shape. After being rolled by a rolling roller, this was sintered at 400 ° C. for 1 hour in an argon atmosphere to produce a negative electrode.

  And the cross section of the negative electrode produced as mentioned above was observed with the scanning electron microscope (SEM), and while showing the result in FIG. 1, based on this FIG. 1, the range of 6.0 micrometers from a negative electrode electrical power collector is shown. In the vicinity of the negative electrode current collector and the position away from the negative electrode current collector in the range of 6.0 μm from the surface of the negative electrode mixture layer, the negative electrode active material particle portion and the binder portion each having an area of 60 μm width Was determined from the contrast, and the ratio of the binder to the total of the negative electrode active material particles and the binder was determined.

  As a result, the binder ratio A in the vicinity of the negative electrode current collector was 31.5%, the binder ratio B in the position away from the negative electrode current collector was 4.6%, and the binder in the position away from the negative electrode current collector. The ratio (A / B) of the binder ratio A in the vicinity of the negative electrode current collector to the ratio B of 6.8 was 6.8 times.

[Production of positive electrode]
In producing the positive electrode active material, Li ₂ Co ₃ and CoCo ₃ were used and weighed so that the atomic ratio of Li: Co was 1: 1, and these were mixed in a mortar. after by press pressure molding in a mold, which in air, and calcined at a temperature of 800 ° C. 24 hours to produce a sintered body of LiCoO _2, a sintered body of this LiCoO ₂ was pulverized in a mortar, LiCoO ₂ powder having an average particle size of 20 μm was obtained.

Then, 5 parts by weight of N-methyl-containing 3 parts by weight of an artificial graphite powder as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder with respect to 94 parts by weight of the positive electrode active material particles made of this LiCoO ₂ powder. A 2-pyrrolidone solution was mixed to prepare a positive electrode mixture slurry.

  Next, this positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector made of aluminum foil, dried and rolled, and then cut into a size of 402 mm × 50 mm, and the positive electrode current collector was cut on both surfaces of the positive electrode current collector. A positive electrode on which an agent layer was formed was produced.

[Preparation of non-aqueous electrolyte]
In preparing the non-aqueous electrolyte, LiPF ₆ was dissolved in a mixed solvent in which ethylene carbonate and diethylene carbonate were mixed at a volume ratio of 3: 7 to a concentration of 1 mol / liter, and further 25 ° C. Then, carbon dioxide was blown in for 10 minutes, and carbon dioxide was dissolved until the saturation amount was reached to prepare a non-aqueous electrolyte.

  And in producing a lithium secondary battery, as shown to FIG. 2 (A), (B), while attaching the positive electrode current collection tab 1a which consists of aluminum to said positive electrode 1, from said nickel to said negative electrode 2 A negative electrode current collecting tab 2a was attached, and the positive electrode 1 and the negative electrode 2 were wound so as to face each other with a separator 3 made of a polyethylene porous body, to produce an electrode body 10.

  Next, as shown in FIG. 3, the electrode body 10 is inserted into the exterior body 20 made of an aluminum laminate film, and the nonaqueous electrolyte is added to the exterior body 20. The opening of the outer package 20 was sealed so that the positive electrode current collecting tab 1a and the negative electrode current collecting tab 2a were taken out.

(Comparative Example 1)
In Comparative Example 1, in preparing the negative electrode in Example 1 above, the negative electrode active material particles, the binder, and the solvent N-methyl-2-pyrrolidone were 9: 1 in preparing the negative electrode mixture slurry: A lithium secondary battery was fabricated in the same manner as in Example 1 except that the weight ratio was 5.6. The negative electrode mixture slurry prepared as described above had a viscosity at 25 ° C. of 30.0 mPa · S.

  And the cross section of the negative electrode produced in this comparative example 1 was observed with the scanning electron microscope (SEM), and while showing the result in FIG. 4, based on this FIG. 4, similarly to said Example 1, a negative electrode In the vicinity of the negative electrode current collector in the range of 6.0 μm from the current collector and the position away from the negative electrode current collector in the range of 6.0 μm from the surface of the negative electrode mixture layer, the negative electrode actives each having an area of 60 μm in width. The material particle portion and the binder portion were identified from the contrast, and the ratio of the binder to the total of the negative electrode active material particles and the binder was determined.

  As a result, the binder ratio A in the vicinity of the negative electrode current collector was 12.4%, the binder ratio B in the position away from the negative electrode current collector was 5.3%, and the binder in the position away from the negative electrode current collector. The ratio (A / B) of the binder ratio A in the vicinity of the negative electrode current collector with respect to the ratio B of 2.3 was 2.3 times.

  Next, the lithium secondary batteries of Example 1 and Comparative Example 1 manufactured as described above were charged to 4.2 V at a current value of 1000 mA in an atmosphere at 25 ° C., and then 2 at a current value of 1000 mA. The battery was discharged up to .75 V and charged and discharged repeatedly as one cycle, and the number of cycles until the discharge capacity reached 80% of the discharge capacity at the first cycle was determined as the cycle life. The results are shown in Table 1 below with an index with the cycle life of the lithium secondary battery of Example 1 as 100.

  As a result, the lithium secondary battery of Example 1 using the negative electrode in which the ratio of the binder ratio A in the vicinity of the negative electrode current collector to the binder ratio B at a position away from the negative electrode current collector was larger than 2.5 times. The secondary battery was a lithium of Comparative Example 1 using a negative electrode in which the ratio of the binder ratio A in the vicinity of the negative electrode current collector to the negative electrode current collector B at a position away from the negative electrode current collector was smaller than 2.5 times. The cycle life was greatly improved compared to the secondary battery.

  This is because the binder in the vicinity of the negative electrode current collector is not less than 2.5 times the ratio of the binder in the position away from the negative electrode current collector as described above. As a result of increasing the amount, it is considered that the adhesion between the negative electrode mixture layer and the negative electrode current collector greatly increased.

(Example 2)
In Example 2, in the production of the negative electrode in Example 1 above, silicon powder (purity 99.9%) having an average particle size of 25 μm was used as the negative electrode active material particles, and otherwise, the negative electrode active material particles of Example 1 above were used. A lithium secondary battery was produced in the same manner as in the case.

(Example 3)
In Example 3, in the production of the negative electrode in Example 1 above, silicon powder (purity 99.9%) having an average particle size of 0.1 μm was used as the negative electrode active material particles, and otherwise, the above Example In the same manner as in the case of No. 1, a lithium secondary battery was produced.

  And also about the negative electrode produced in said Example 2 and Example 3, similarly to said Example 1, the ratio A of the binder in the negative electrode collector vicinity, and the binder in the position away from the negative electrode collector. The ratio (A / B) of the ratio A of the binder in the vicinity of the negative electrode current collector to the ratio B of the binder at a position away from the negative electrode current collector was calculated, and the result is shown in Table 2 below. It was shown to.

  In addition, each of the lithium secondary batteries of Examples 2 and 3 manufactured as described above was repeatedly charged and discharged in the same manner as the lithium secondary battery of Example 1, and the discharge capacity was 1 cycle. The number of cycles to reach 80% of the discharge capacity of the eye was measured, and the cycle life of each lithium secondary battery was shown in the following Table 2 as an index with the cycle life of the lithium secondary battery of Example 1 as 100. It was shown to.

  As a result, the lithium secondary battery of Example 2 using silicon powder having an average particle size of 25 μm as negative electrode active material particles and Example 3 using silicon powder having an average particle size of 0.1 μm as negative electrode active material particles. The cycle life of the lithium secondary battery was lower than that of the lithium secondary battery of Example 1 using silicon powder having an average particle size of 15 μm as the negative electrode active material particles.

  This is because, as described above, when negative electrode active material particles having a large average particle diameter exceeding 20 μm are used, stress due to volume change of the negative electrode active material particles during charge / discharge directly acts on the negative electrode current collector, This is because the negative electrode mixture layer is easily peeled off from the negative electrode current collector, and when negative electrode active material particles having an average particle size of less than 0.3 μm are used, the area in contact with the non-aqueous electrolyte increases. However, this is considered to be because the irreversible reaction increased and the capacity was reduced.

It is the figure which showed the state of the negative electrode produced in Example 1 of this invention. It is the schematic plan view and partial cross-section explanatory drawing of the electrode body produced in Example 1 and Comparative Example 1 of this invention. It is a schematic plan view of the lithium secondary battery produced in Example 1 and Comparative Example 1 of the present invention. 6 is a view showing a state of a negative electrode produced in Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode current collection tab 2 Negative electrode 2a Negative electrode current collection tab 3 Separator 10 Electrode body 20 Exterior body

Claims (7)

  In the negative electrode for a lithium secondary battery in which a negative electrode mixture layer containing negative electrode active material particles containing silicon and / or a silicon alloy and a binder is formed on the surface of the negative electrode current collector by firing, in the vicinity of the negative electrode current collector A negative electrode for a lithium secondary battery, wherein the binder ratio in the battery is at least 2.5 times the binder ratio at a position away from the negative electrode current collector.   2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode mixture layer is formed by sintering in a non-oxidizing atmosphere on a surface of a negative electrode current collector made of a metal foil. A negative electrode for a lithium secondary battery.   The negative electrode for a lithium secondary battery according to claim 1 or 2, wherein the binder in the negative electrode mixture layer is a polyimide.   The negative electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the average particle diameter of the negative electrode active material particles is in the range of 0.3 µm to 20 µm. Negative electrode for secondary battery.   The negative electrode for a lithium secondary battery according to any one of claims 1 to 4, wherein the negative electrode current collector is a copper or copper alloy foil, and a copper or copper alloy layer is formed on the surface. A negative electrode for a lithium secondary battery, which is one type selected from metal foils.   6. The negative electrode for a lithium secondary battery according to claim 5, wherein the negative electrode current collector comprises an electrolytic copper foil, an electrolytic copper alloy foil, a metal foil provided with electrolytic copper on the surface, and an electrolytic copper alloy provided on the surface. A negative electrode for a lithium secondary battery, wherein the negative electrode is one selected from metal foils.   A lithium secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode for a lithium secondary battery according to any one of claims 1 to 6 is used as the negative electrode. Next battery.