JP2007128659A - Anode for lithium secondary battery, and lithium secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain breakdown of activator caused by compression force between activator particles generated at swelling due to absorption of lithium ions, especially to restrain breakdown of neighboring area of an interface between a current collector and the activator layer that is liable to be influenced by the expansion and contraction accompanied by charging and discharging, and the activator located at neighborhood of the surface thereof, where a space for expansion is less and is liable to generate breakdown of particles, by using the activator of high capacity. <P>SOLUTION: An anode 20 includes a current collector 1 and a current collector layer 2 and the current collector layer 2 held on the current collector 1. The activator layer 2 contains a compound, containing silicon and oxygen or a compound containing tin or oxygen, and particles 21 grown in an oblique direction of arc-shape so that current collector 1 side becomes convex with respect to the direction of the normal line direction of the current collector 1. The angle formed by the growth direction of the particle and the normal line direction of the current collector is not smaller than 20° and not larger than 90°. The density of oxygen at a first region 2a on the current collector side of the particle and that at a third region 2c on the surface side of the activator layer are higher than that at a second region located in between the first region and the third region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery using the same, and more particularly to a negative electrode for a lithium secondary battery containing, as an active material, a compound containing silicon and oxygen or a compound containing tin and oxygen. .

  In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as power sources has increased. A battery used for the above applications is required to have a high energy density and excellent cycle characteristics.

  In response to this requirement, high-capacity active materials have been newly developed for each of the positive electrode and the negative electrode, and a solution can be achieved by using an alloy or oxide containing silicon or tin that can provide a high capacity in the negative electrode active material. I am trying to do. At that time, the problem is deformation of the negative electrode. When lithium ions are inserted and desorbed during charge and discharge, the active material is greatly expanded and contracted, so that the negative electrode is greatly distorted and undulated. For this reason, there is a concern that a space is generated between the negative electrode and the separator, the charge / discharge reaction becomes non-uniform, and the charge / discharge cycle characteristics deteriorate.

In order to solve this problem, an active material in the form of a thin film using silicon or tin as a single substance, an oxide or an alloy as an active material is separated into a columnar shape, and an uneven valley on the surface of the current collector in the thickness direction of the thin film It has been proposed to suppress the deformation of the current collector by forming a gap that becomes wider as it goes to (see, for example, Patent Document 1).
JP 2002-313319 A

  However, since the space for absorbing expansion during charging is formed in the conventional negative electrode configuration, it is effective against deformation during initial charging / discharging, but this configuration also expands when repeated charging / discharging cycles. The resulting issues are not yet fully resolved.

  In addition, mass production of lithium secondary batteries is required, and a simple manufacturing process is indispensable. Therefore, a can roll method is generally used in which a thin film including an active material layer is continuously formed on a current collector while moving the current collector using a thin film process such as an evaporation method, a sputtering method, or a CVD method.

  However, in the can roll method, the columnar particles constituting the active material have a shape that gradually grows in the film surface direction as the particles grow in the film thickness direction. For this reason, the phenomenon that the head of the columnar particles becomes thicker toward the active material layer surface side occurs. As a result, the columnar particles approach the adjacent columnar particles near the surface. For this reason, when the expansion of the columnar particles is large, there is a problem that the particles constituting the active material are cracked due to the mutual compressive force between the adjacent columnar particles.

  The present invention solves the above-described conventional problems, and has a negative electrode for a lithium secondary battery (hereinafter also referred to as a negative electrode) having excellent charge / discharge cycle characteristics, and a lithium secondary battery (hereinafter also referred to as a battery) using the same. The purpose is to provide.

In order to solve the above conventional problems, the negative electrode of the present invention is
A negative electrode comprising a current collector and an active material layer carried on the current collector,
The active material layer includes a compound containing silicon and oxygen, or a compound containing tin and oxygen,
The active material layer includes particles grown in an arch shape in an oblique direction so that the current collector side is convex with respect to the normal direction of the current collector,
The angle θ1 formed by the growth direction of the particles and the normal direction of the current collector is 20 ° or more and less than 90 °,
The first oxygen concentration in the first region on the current collector side of the particles grown in an arc shape and the third oxygen concentration in the third region on the surface side of the active material layer are the first between the first region and the third region. It is characterized by being higher than the second oxygen concentration in the two regions.

  Since the negative electrode having this configuration can reduce the compressive force between the active material particles generated during expansion due to occlusion of lithium ions, the charge / discharge cycle characteristics can be improved.

The battery of the present invention is
A positive electrode capable of inserting and extracting lithium ions;
A negative electrode of the present invention;
A separator disposed between the positive electrode and the negative electrode;
And an electrolyte having lithium ion conductivity.

  Since the battery of this structure has the negative electrode of the present invention, it can be a battery with high capacity and excellent charge / discharge cycle characteristics.

  According to the negative electrode of the present invention and a battery using the negative electrode, the high capacity active material is used, and the active material expands due to the insertion of lithium ions. It is possible to suppress the breakage of the active material layer in the vicinity of the interface between the current collector and the active material layer, which is easily affected, and in the vicinity of the active material layer surface where the expansion space is small and particle breakage easily occurs. Further, by making the active material layer an aggregate of bow-shaped active material particles, it is possible to suppress the breakage of the active material layer constituting particles due to the compressive force generated in the normal direction of the separator surface. With these effects, a battery having excellent cycle characteristics can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a cross-section of the negative electrode according to Embodiment 1 of the present invention. In FIG. 1, the negative electrode 20 includes an active material layer 2 supported on a current collector 1. The active material layer 2 includes a compound containing silicon and oxygen, or a compound containing tin and oxygen. Further, as shown in FIG. 1, the active material layer 2 includes a plurality of active material particles grown in a bow shape in an oblique direction so that the current collector 1 side is convex with respect to the normal direction D of the current collector 1. 21 (hereinafter also referred to as particle 21). The active material layer 2 including the particles 21 grown in an oblique shape in such an oblique direction uses the current collector 1 having irregularities on the surface, and when the active material layer 2 is formed by a can roll method, Details such as the ratio of gaps formed between the two 21 are different, but can be obtained. A method for forming the active material layer 2 by the can roll method will be described later.

  Further, the oxygen concentration in the active material layer 2 and the volume expansion coefficient of the active material layer 2 are closely related. For example, when the active material layer 2 is a silicon oxide and contains almost no oxygen, the particles 21 undergo a volume expansion of 400% by charging. When the amount of oxygen atoms relative to silicon atoms in active material layer 2 is 30%, volume expansion of 350% occurs, and when the amount of oxygen atoms is 60%, volume expansion of 280% occurs. When the amount is 100%, a volume expansion of 200% occurs.

  Such volume expansion is closely related to the volume ratio of the particles 21 in the film (hereinafter referred to as film density) when the active material layer 2 is viewed as one film. When the film density is low, the particles 21 are generated isotropically. However, when the density of the particles 21 in the in-plane direction becomes dense, a space for isotropic expansion cannot be secured in the in-plane direction. Is mainly expanded in the film thickness direction and reaches the above-described volume expansion coefficient. Therefore, when the composition of the active material particles 21 is uniform, the expansion of the particles 21 on the current collector 1 where no substantial expansion occurs near the interface between the current collector 1 and the active material layer 2. Therefore, the current collector 1 and the particles 21 are easily destroyed. Further, in the vicinity of the surface of the active material layer 2 where the gaps between the particles 21 tend to be reduced, the isotropic expansion in the in-plane direction of the active material layer 2 is hindered, so that expansion in the film thickness direction occurs. In that case, it can be easily guessed that an extremely large stress is generated in the in-plane direction of the active material layer 2.

  In order to avoid such a situation, in the present invention, the active material particles 21 in the active material layer 2 are divided into first to third regions having different oxygen ratios. Among these regions, the first oxygen concentration in the first region 2a on the current collector 1 side and the third oxygen concentration in the third region 2c on the surface side of the active material layer 2 are the second region between them. Higher than the second oxygen concentration in 2b.

  By providing the first region 2 a having a high oxygen concentration in the vicinity of the interface between the current collector 1 and the active material layer 2, the difference in expansion coefficient between the current collector 1 and the active material layer 2 is reduced, and the vicinity of the current collector 1. The expansion of the particles 21 can be suppressed. As a result, even if charge / discharge cycles are repeated, the detachment and pulverization of the particles 21 near the interface between the current collector 1 and the active material layer 2 are less likely to occur. Further, the third region 2c having a high oxygen concentration is also provided on the surface side of the active material layer 2 where the compressive force between the adjacent particles 21 becomes strong. Thereby, the rate of expansion and contraction of the particles 21 is reduced, and the breakage of the particles 21 can be suppressed even in the vicinity of the surface of the active material layer 2 having a small expansion space. On the other hand, the second region 2b located between the first region 2a and the third region 2c having a high oxygen concentration lowers the oxygen concentration. Thereby, the occlusion ability of lithium ions is increased, so that the negative electrode 20 having a high energy density can be obtained.

  In the first region 2a, the second region 2b, and the third region 2c described above, the first region 2a has a chemical composition represented by the following general formula (1), and the second region 2b has the following general formula ( 2), and the third region 2c preferably has a chemical composition represented by the following general formula (3).

MOx ₁ (1)
MOx ₂ (2)
MOx ₃ (3)
(In the formula, M is one of Si and Sn, and x ₁ , x ₂ and x ₃ are 0.1 ≦ x ₁ ≦ 2.0, 0 ≦ x ₂ ≦ 1.0, 0.1 ≦ x ₃ ≦ 2.0, x ₁ > x ₂ , x ₃ > x ₂ are satisfied.)
The second region 2b with less oxygen may be a simple substance of Si or Sn, but from the viewpoint of reducing the difference in expansion coefficient at the interface between the first region 2a and the third region 2c generated by expansion and contraction. The region 2b is more preferably an oxide layer.

  In addition, each of the first region 2a to the third region 2c may be formed separately and separately. However, since the difference in expansion coefficient at the interface continuously changes when the regions are continuously formed, each region It is desirable because it can reduce stress during In particular, the oxygen concentration of the first region 2a is 20% to 100%, the oxygen concentration of the second region 2b is 0% to 80%, the oxygen concentration of the third region 2c is 20% to 100%, and In order to achieve the object of the present invention, it is more desirable that the oxygen concentration in the first region 2a and the third region 2c is higher than that in the second region 2b.

  Various methods can be used to measure the oxygen concentration in each region, and for example, XMA (X-ray microanalyzer) can be used. In order to perform the oxygen concentration measurement of the second region 2b, which is a portion having a lower oxygen concentration, in addition to narrowing the irradiation range, an active material layer for measurement having an oxygen concentration equivalent to that of the portion to be measured on the surface layer, It is also effective to form it separately.

  The thicknesses of the first region 2a and the third region 2c having a high oxygen concentration are 1% to 30% and 5%, respectively, of the total thickness of the active material layer 2 from the viewpoints of conductivity, energy density, and expansion coefficient. It is preferably ˜80%, more preferably 3% to 20% and 10% to 60%, respectively. If the thickness of the first region 2a and the third region 2c where the oxygen concentration is high is too thin, the effect of suppressing the expansion of the present invention cannot be obtained sufficiently. Conversely, if the thickness is too thick, sufficient battery energy can be obtained. Absent.

  The total thickness of the active material layer 2 is not particularly limited, but is preferably 0.5 μm to 100 μm, more preferably 1 μm to 60 μm, from the viewpoint of battery energy density, high rate characteristics, productivity, and the like. If the active material layer 2 is too thin, sufficient battery energy cannot be obtained, and if the active material layer 2 is too thick, cracks may occur during film formation.

  FIG. 2 is a schematic diagram for explaining the inclination of the particles 21 constituting the active material layer 2. The particles 21 grow in a bow shape in an oblique direction so that the current collector 1 side is convex with respect to the normal direction D of the current collector 1. The growth direction D1 of the particles 21 has an angle θ1 with respect to the normal direction D. The growth direction D1 of the particle 21 is a direction in which the particle 21 grows at a point where the particle 21 and the current collector 1 are in contact with each other. The growth direction D1 can be observed by cutting the negative electrode 20 in a direction in which the angle θ1 is maximum. The growth direction D1 is an imaginary line A− parallel to the current collector 1 where the particle 21 and the current collector 1 are in contact with each other and the cross section of the particle 21 is ½ the height of the particle 21. It can be defined as the direction connecting the midpoint of the width of the particle 21 when cut at A ′. Here, the angle θ1 is not less than 20 ° and less than 90 °. Note that the angle θ2 formed by the growth direction D2 on the surface side of the particle 21 along the line AA ′ and the normal direction D of the current collector 1 is bowed in an oblique direction so that the current collector 1 side is convex. Since it is growing, it satisfies θ1> θ2. Further, the angle θ2 is preferably 10 ° or more and 70 ° or less.

  At this time, the space ratio in the active material layer 2 (hereinafter referred to as a gap ratio) increases as the angle θ1 increases. Depending on the size of the irregularities on the surface of the current collector 1, for example, when the average roughness Ra of the surface of the current collector 1 is 1.5 μm to 2.5 μm and the angle θ1 is 10 °, the gap ratio is 5%. It will be about. Similarly, when the angle θ1 is 20 °, the gap ratio is about 10%, when the angle θ1 is 30 °, the gap ratio is about 20%, and when the angle θ1 is 60 °, the gap ratio is about 50% and the angle θ1 is 80. When the angle is °, the gap ratio is about 70%. Since the growth direction of the particles 21 changes in the film thickness direction of the active material layer 2, the gap ratio in the active material layer 2 as a whole depends on the gap ratio described above according to the growth direction of the particles 21. The integrated average value is obtained at.

  The preferable structure of the active material particles 21 in the first embodiment is that the particles 21 grow at an angle of 20 ° or more and less than 90 ° from the normal direction D of the current collector 1, and the thickness of the active material particles is from 1 μm. At 30 μm, the gap ratio is 10% to 70%.

  The gap ratio is obtained as follows. First, sample 1 in which a thin film of an active material is uniformly formed on the entire surface of a copper foil as a base material, sample 2 in which a gap is formed by adjusting the growth direction of the active material particles, and when samples 1 and 2 are produced The copper foil used as the base material is cut into the same size, and the respective masses are measured. At this time, the thicknesses of the two samples 1 and 2 are set to the same condition. Next, the mass of the copper foil is subtracted from the mass of Sample 1 to calculate the active material mass. Similarly, for sample 2, the mass of the copper foil is similarly subtracted, and the active material mass of each sample is calculated. Finally, the ratio of the active material is calculated from the ratio of the mass of the active material particles to the mass of the active material formed on the entire surface of the copper foil, and the difference between 100% and the active material ratio is defined as the gap ratio.

  As described above, the thicknesses of the first region 2a and the third region 2c having a high oxygen concentration are 1% to 30% and 5% to 80% of the total thickness of the active material layer, respectively. Is appropriately determined from the shape of the gap formed by the growth direction of the active material particles 21 and the amount of active material estimated from the required amount of Li storage. Thus, it is considered that the problem relating to the expansion stress is solved by controlling the growth direction, the film thickness, the gap, and the oxygen concentration in the thickness direction of the active material particles.

  Next, an example of a method for manufacturing the negative electrode 20 shown in FIG. 1 will be described. FIG. 3 is a schematic diagram showing an example of a method for manufacturing the negative electrode 20 of the first embodiment. In FIG. 3, the inside of the vacuum chamber 3 is exhausted by an exhaust pump 13. In the vacuum chamber 3, the current collector 1, which is a thin film base material, is sent from the unwinding roll 10 through the transport roller 11 and travels along the can roll 5. In the meantime, an active material vapor made of silicon or tin is supplied from the evaporation source 4 in an atmosphere containing oxygen, and an active material vapor that has passed through the opening of the mask 6 and has an active material particle 21 that includes a plurality of active material particles 21 on the surface of the current collector 1. A material layer 2 is formed. The electrode plate thus obtained is wound up on a winding roll 12.

  The growth direction of the particles 21 is strongly controlled by the incident direction of the active material vapor at the time of film formation. For example, when the angle formed between the incident direction and the normal direction D of the current collector (hereinafter referred to as the incident angle) is 30 °, the angle θ1 formed between the growth direction D1 of the particles 21 and the normal direction D is about 16 °. When the incident angle is 50 °, the angle θ1 is about 30 °, and when the incident angle is 80 °, the angle θ1 is about 60 °. The relationship between the incident angle and the angle θ1 can be estimated from a generally known tangent law.

  For the evaporation source 4, a crucible or the like in which silicon or tin as an active material is held is used. The higher the purity of silicon or tin, the better. As a method of heating the evaporation source 4, a resistance heating method or a heating method by electron beam irradiation can be used.

  In order to produce the negative electrode 20 having the first region 2 a to the third region 2 c, oxygen gas is introduced from the second oxygen nozzle 8 and the third oxygen nozzle 9 simultaneously with introduction of oxygen gas from the first oxygen nozzle 7. The 1st oxygen nozzle 7 is installed so that oxygen may spread over the whole active material vapor | steam. The second oxygen nozzle 8 is installed in the vicinity of the opening of the mask 6 so that oxygen can be supplied when particles start to form on the current collector 1. The third oxygen nozzle 9 is installed near the opening of the mask 6 so that oxygen can be supplied to the particles 21 being formed on the current collector 1.

With the above configuration, the oxygen concentration can be increased at the initial stage of formation of the active material 2 (first region 2a) and at the end of formation of the active material layer 2 (third region 2c), so that the negative electrode 20 shown in FIG. Is done. The amount of oxygen in each region includes the amount of oxygen introduced from each oxygen nozzle, the shape of the vacuum chamber 3, the exhaust capacity of the exhaust pump 13, the evaporation rate of the active material (silicon or tin), and the activity on the current collector 1. The film formation width of the material layer 2 and other manufacturing conditions can be changed as appropriate. As an example, the volume of the vacuum tank is 0.4 m ³ , the vacuum diffusion is performed by an oil diffusion pump with an exhaust speed of 2.2 m ³ / s, and the amount of gas introduced into the first to third oxygen nozzles is generally at the exchange 25 ° C. 1 atm may be set to 0.0005m ³ /s~0.005m ³ / s.

  The method for forming the active material layer 2 is not particularly limited as long as the negative electrode 20 of the present invention can be obtained, but it is preferable to use a dry process such as a vapor deposition method, a sputtering method, or a CVD method. In particular, the vapor deposition method is a highly productive method, and is suitable as a method for forming the active material layer 2 continuously and in large quantities on the moving current collector 1.

  The current collector 1 can be made of a foil such as copper or nickel. From the viewpoints of strength, volumetric efficiency as a battery, and ease of handling, the thickness of the foil is preferably 4 to 30 μm, more preferably 5 to 10 μm. Although the surface of the foil may be smooth, it is preferable to use a concavo-convex foil having an arithmetic average roughness Ra of about 0.1 to 4 μm in order to increase the adhesion strength with the active material layer. The arithmetic average roughness Ra is defined in Japanese Industrial Standard (JISB 0601-1994), and can be measured by, for example, a surface roughness meter. The unevenness of the foil also has the effect of forming voids between the particles 21 constituting the active material layer 2. From the point of adhesion, Ra = 0.4 to 2.5.

The negative electrode 20 obtained by such a technique includes a positive electrode plate containing a commonly used positive electrode active material such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , a separator made of a microporous film, and hexafluoride. A lithium secondary battery can be produced by using lithium phosphate or the like together with an electrolyte having lithium ion conductivity having a generally known composition in which cyclic carbonates such as ethylene carbonate and propylene carbonate are dissolved.

  The negative electrode of the present invention can be applied to lithium secondary batteries having various shapes such as a cylindrical shape, a flat shape, a coin shape, and a square shape, and the shape and sealing form of the battery are not particularly limited. A case of applying to a laminated lithium secondary battery will be described with reference to the drawings.

  FIG. 4 is a schematic cross-sectional view of the laminated lithium secondary battery of the present invention. In FIG. 4, a laminated cell case 19 includes a negative electrode 20 of the present invention, a positive electrode 31 including a positive electrode current collector 16 and a positive electrode active material 17 capable of absorbing and releasing lithium ions formed thereon, and a negative electrode A separator 18 disposed between 20 and the positive electrode 31 and an electrolyte (not shown) having lithium ion conductivity are disposed and hermetically sealed. A negative electrode lead (not shown) for current collection is connected to the negative electrode 20, and a positive electrode lead (not shown) for current collection is connected to the positive electrode 31, and each is led out of the laminate cell case 19. The laminate cell case 19 can be produced by, for example, thermally welding a laminate film having a structure in which both surfaces of an aluminum foil are sandwiched between PET and polyolefin resin.

  The case where the negative electrode of the present invention is applied to a wound lithium secondary battery will be described with reference to the drawings.

  FIG. 5 is a schematic cross-sectional view of a wound lithium secondary battery of the present invention. In FIG. 5, the strip-shaped positive electrode 31 and the strip-shaped negative electrode 20 of the present invention are wound together with a strip-shaped separator that is disposed between them and wider than both plates to form a plate group 32. . A positive electrode lead 34 made of aluminum or the like is connected to the positive electrode 31, and one end thereof is connected to a sealing plate 39 in which an insulating packing 40 made of polypropylene or the like is arranged on the periphery. A negative electrode lead 35 made of copper or the like is connected to the negative electrode 20, and one end thereof is connected to a battery can 38 that houses the electrode plate group 32. An upper insulating ring 36 and a lower insulating ring 37 are arranged above and below the electrode plate group 32, respectively. The electrode plate group 32 is impregnated with the above-described electrolyte (not shown) having lithium ion conductivity. The opening of the battery can 38 is closed with a sealing plate 39. As the negative electrode 20, a negative electrode having the active material layer 2 only on one side of the current collector 1 as shown in FIG. 1 and a negative electrode having the active material layer 2 on both sides of the current collector 1 can be applied. The same applies to the corresponding positive electrode.

  The negative electrode according to the present invention, and a battery using the negative electrode, use a high-capacity active material, and breakage due to compressive force between active material particles during expansion of the active material due to occlusion of lithium ions, particularly expansion / contraction due to charge / discharge Since the active material layer in the vicinity of the interface between the current collector and the active material layer, which is susceptible to the influence of the active material layer, and the active material layer near the surface of the active material layer where there is little expansion space and particle breakage can be suppressed, the negative electrode, and It is useful as a battery using

Schematic diagram showing a cross section of the negative electrode according to Embodiment 1 of the present invention. Schematic diagram for explaining the inclination of particles in Embodiment 1 of the present invention The schematic diagram which shows an example of the method for manufacturing the negative electrode of this Embodiment 1. Schematic cross-sectional view of laminated battery in the first embodiment Schematic cross-sectional view of a wound battery according to the first embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current collector 2 Active material layer 2a 1st area | region 2b 2nd area | region 2c 3rd area | region 3 Vacuum tank 4 Evaporation source 5 Can roll 6 Mask 7 1st oxygen nozzle 8 2nd oxygen nozzle 9 3rd oxygen nozzle 10 Unwinding roll DESCRIPTION OF SYMBOLS 11 Conveyance roller 12 Winding roll 13 Exhaust pump 16 Positive electrode collector 17 Positive electrode active material 18, 33 Separator 19 Laminate cell case 20 Negative electrode 21 Active material particle 31 Positive electrode 32 Electrode plate group 34 Positive electrode lead 35 Negative electrode lead 36 Upper insulating ring 37 Lower insulation ring 38 Battery can 39 Sealing plate 40 Insulation packing

Claims (4)

A negative electrode for a lithium secondary battery, comprising: a current collector; and an active material layer carried on the current collector,
The active material layer includes a compound containing silicon and oxygen, or a compound containing tin and oxygen,
The active material layer includes particles grown in an arcuate shape in an oblique direction so that the current collector side is convex with respect to the normal direction of the current collector,
An angle θ1 formed by the growth direction of the particles and the normal direction of the current collector is 20 ° or more and less than 90 °,
The first oxygen concentration in the first region on the current collector side of the particles grown in an arc shape and the third oxygen concentration in the third region on the surface side of the active material layer are the first region and the third oxygen concentration. Higher than the second oxygen concentration in the second region between the regions,
A negative electrode for a lithium secondary battery. The first region has a chemical composition represented by the following general formula (1):
The second region has a chemical composition represented by the following general formula (2):
The third region has a chemical composition represented by the following general formula (3).
The negative electrode for a lithium secondary battery according to claim 1.
MOx ₁ (1)
MOx ₂ (2)
MOx ₃ (3)
(In the formula, M is one of Si and Sn, and x ₁ , x ₂ and x ₃ are 0.1 ≦ x ₁ ≦ 2.0, 0 ≦ x ₂ ≦ 1.0, 0.1 ≦ x ₃ ≦ 2.0, x ₁ > x ₂ , x ₃ > x ₂ are satisfied.) The film density of the second region is sparser than the film density of the third region;
The negative electrode for a lithium secondary battery according to claim 1. A positive electrode capable of inserting and extracting lithium ions;
A negative electrode for a lithium secondary battery according to any one of claims 1 to 3,
A separator disposed between the positive electrode and the negative electrode for a lithium secondary battery;
An electrolyte having lithium ion conductivity;
Including lithium secondary battery.