WO2013161733A1

WO2013161733A1 - Negative electrode active material for a lithium secondary battery and method for manufacturing same

Info

Publication number: WO2013161733A1
Application number: PCT/JP2013/061726
Authority: WO
Inventors: 晃二久幸
Original assignee: 昭和電工株式会社
Priority date: 2012-04-24
Filing date: 2013-04-22
Publication date: 2013-10-31
Also published as: CN104054197A; JP2013229111A

Abstract

This negative electrode material for a lithium secondary battery is formed from a powder formed by carrying out in order a step for creating an etched foil by etching both surfaces of a foil that has a Fe content of 0.05% by mass or less and Al as a main component and a step for cutting that etched foil. This powder includes particles (1) that have holes (2) that are opened in the surface of the particles and have a hole diameter of 0.5 µm or greater. The total of the opening surface area for all of the holes (2) in the surface of a particle (1) in the particles (1) having the holes (2) is 10% or greater of the surface area of the particle having the holes (2). With the use of this negative electrode material (1) for a lithium secondary battery, increased life for cycle life of the lithium secondary battery can be achieved.

Description

Negative electrode active material for lithium secondary battery and method for producing the same

The present invention relates to a negative electrode active material for a lithium secondary battery and a method for producing the same, and more specifically, a negative electrode active material for a non-aqueous electrolyte secondary battery capable of reversibly occluding and releasing Li ions in large quantities and the production thereof. Regarding the method. Here, the nonaqueous electrolyte secondary battery includes a secondary battery using a nonaqueous electrolyte obtained by dissolving an electrolyte in an organic solvent, and a secondary battery using a nonaqueous electrolyte such as a polymer electrolyte or a gel electrolyte. .

Lithium secondary batteries such as lithium ion batteries and lithium polymer batteries have a high energy density and are not only used as main power sources for mobile communication devices and portable electronic devices, but also for large-scale power storage. It is also attracting attention as a power source and an on-vehicle power source.

As a negative electrode of such a lithium secondary battery, conventionally, those formed from various carbon materials such as graphite and carbon having a low crystallinity have been widely used. However, a negative electrode made of a carbon material has a low usable current density and an insufficient theoretical capacity. For example, graphite, which is one of the carbon materials, has a theoretical capacity of only 372 mAh / g, and therefore a higher capacity is desired.

On the other hand, when a negative electrode formed from metallic Li is used for a lithium secondary battery, it is known that a high theoretical capacity can be obtained. However, during charging, metallic Li precipitates on the negative electrode in a dendrite-like manner, and is charged. There is a major drawback in that the growth continues by repeating the discharge and reaches the positive electrode side to cause an internal short circuit. In addition, the deposited dendritic metal Li has a high specific activity, and thus has a high reaction activity, and an interfacial film made of a decomposition product of a solvent having no electron conductivity is formed on the surface, thereby forming an internal resistance of the battery. As a result, the charge / discharge efficiency decreases. For these reasons, lithium secondary batteries using a negative electrode formed from metal Li have the disadvantages of low reliability and short cycle life, and have not yet reached the stage of wide practical use.

From such a background, a negative electrode active material made of a material other than metal Li, which is a substance having a discharge capacity larger than that of a general-purpose carbon material, is desired. For example, elements such as Sn, Si and Ag, nitrides, oxides and the like of these can occlude Li ions to form an alloy with Li ions, and the occlusion amount is much larger than various carbon materials. It is known to show a value.

However, when a negative electrode formed from an element such as Sn, Si, or Ag, or a nitride or oxide thereof is used for a lithium secondary battery, the Li-ion occlusion / Along with the release, the negative electrode is greatly expanded / contracted, and the negative electrode is cracked or pulverized due to the expansion / contraction. Therefore, a lithium secondary battery using a negative electrode formed from the above-described substances such as Sn, Si, Ag, etc., and their nitrides and oxides cannot be used as a practical battery because its cycle life is reduced. .

As a countermeasure, a negative electrode active material is an alloy of two or more phases composed of a metal that easily stores and releases Li ions and a metal that does not store and release, and the metal that does not store and release does not store and release Li ions. A negative electrode active material intended to suppress the expansion / contraction of the negative electrode during discharge and the cracking or pulverization of the negative electrode due to expansion / contraction has been proposed.

For example, Patent Document 1 discloses a raw material melt consisting of a Li ion storage phase α and a phase β made of an intermetallic compound or a solid solution of an element constituting the Li ion storage phase α and another element and having a selected composition. , An anode active material having a structure rapidly quenched and solidified by an atomizing method, a roll quenching method, or the like is described. Patent Document 2 discloses Ag, Al, Au, Ca, Cu, Fe, In, Mg, Pd, Pt, Y Zn, Ti, V, Cr, Mn, Co, Ni, Y, Zr, Nb, Mo, Hf, Ta, W and an A component that is at least one element selected from the group consisting of rare earth elements, and Ga, A negative electrode made of a composite powder formed by mixing a raw material consisting of a B component, which is at least one element selected from the group consisting of Ge, Sb, Si and Sn, and performing mechanical alloying treatment Substances have been described.

However, in the negative electrode formed from the negative electrode active material described in

Patent Documents

1 and 2, a large initial discharge capacity is obtained, but the negative electrode is caused by expansion / contraction of the negative electrode and the expansion / contraction caused by repeated charge / discharge. Cracking and pulverization cannot be effectively suppressed, and the cycle life has not been extended.

JP 2001-297757 A JP 2005-78999 A

The object of the present invention is to solve the above-described problems, and to increase the amount of occlusion / release of Li ions, thus increasing the charge / discharge capacity and reducing the capacity decrease due to repeated charge / discharge. An object of the present invention is to provide a negative electrode active material for a lithium secondary battery and a method for producing the same, which can achieve a longer cycle life.

The present invention comprises the following aspects in order to achieve the above object.

1) Formed by performing in this order the steps of etching the both sides of a foil containing Fe as a main component with an Fe content of 0.05% by mass or less and cutting the etching foil. A negative electrode active material for a lithium secondary battery comprising the prepared powder.

2) The negative electrode active material for lithium secondary batteries according to 1) above, wherein the Al purity of the foil mainly composed of Al is 90% by mass or more.

3) The powder formed by cutting the etching foil contains particles having a plurality of holes that are open on the surface and have a hole diameter of 0.5 μm or more. The negative electrode active material for a lithium secondary battery according to the above 1) or 2), wherein the total opening area to the surface is 10% or more of the surface area of each particle having the pores.

4) The particle size of all particles is 5 to 150 μm, the pore size of the particles having pores is 0.5 to 15 μm, and the ratio of the pore size to the particle size (pore size / particle size) of the particles having pores is 0. The negative electrode active material for lithium secondary batteries according to 3) above, which is less than 1.

5) The negative electrode active material for a lithium secondary battery according to any one of 1) to 4) above, wherein at least some of the etching holes formed in the etching foil are through holes.

6) Cutting an etching foil having a Fe content of 0.05% by mass or less and etching both surfaces of a foil containing Al as a main component and having a porous layer on both surfaces into a powder. A method for producing a negative electrode active material for a lithium secondary battery.

7) The method for producing a negative electrode active material for a lithium secondary battery according to 6) above, wherein the Al purity of the foil mainly composed of Al is 90% by mass or more.

8) The etching foil has a thickness of 200 μm or less, the hole diameter of the etching holes in both porous layers is 0.5 to 15 μm, and the total opening area of all the etching holes in both porous layers is the surface area of both surfaces of the etching foil. The method for producing a negative electrode active material for a lithium secondary battery as described in 6) or 7) above, wherein at least some of the etching holes are through-holes.

9) The method for producing a negative electrode active material for a lithium secondary battery according to 8) above, wherein an etching foil having a thickness of 50 to 150 μm is used.

10) A negative electrode for a lithium secondary battery in which a mixed material containing a negative electrode active material, a conductive additive and a binder described in any one of 1) to 5) above is attached on a current collector.

11) A lithium secondary battery comprising the negative electrode described in 10) above, a separator, and a positive electrode for a lithium secondary battery.

According to the negative electrode active material for lithium secondary batteries of 1) to 5) above, a process for producing an etching foil by etching both surfaces of a foil having an Fe content of 0.05% by mass or less and containing Al as a main component And the powder formed by cutting the etching foil in this order, the powder formed by cutting the etching foil includes particles having a plurality of holes opened on the surface. . Accordingly, the volume change of the negative electrode active material during charging / discharging is reduced, and the volume change of the negative electrode active material during charging / discharging is increased. Separation of substances from conductive aids and binders can be effectively suppressed, and capacity reduction due to repeated charging and discharging is reduced, and the cycle life of lithium secondary batteries is extended. Will be possible. The reason is estimated as follows. That is, in the lithium secondary battery including the negative electrode formed from the negative electrode active materials 1) to 5) above, Li ions enter the pores of the particles during charging, and a compound containing Li ions is formed in the pores. In addition, a compound containing Li ions is formed in the gap formed between the particles of the powder of the negative electrode active material, and the expansion of the negative electrode active material during charging can be suppressed. Further, the shrinkage of the negative electrode active material when Li ions exit from the negative electrode active material during discharge is reduced. As a result, it is estimated that the volume change of the negative electrode active material during charging / discharging is reduced.

Moreover, since the Fe content of the etching foil is 0.05% by mass or less, it is possible to prevent a short circuit when Li preferentially precipitates on Fe during charge and discharge.

In addition, the lithium secondary battery including the negative electrode formed from the negative electrode active materials 1) to 5) described above is compared with the lithium secondary battery including the negative electrode formed from the negative electrode active material formed of various carbon materials. In addition, a large amount of Li ions can be occluded / released, and the charge / discharge capacity is increased.

According to the negative electrode active material for lithium secondary batteries of 2) to 5) above, the volume change at the time of charging / discharging of the lithium secondary battery using the negative electrode formed from the negative electrode active material is further effectively reduced. be able to.

According to the above method 6), an etching foil having an Fe content of 0.05% by mass or less and made by etching both surfaces of a foil mainly composed of Al and having a porous layer on both surfaces is cut. Therefore, the negative electrode active material for a lithium secondary battery can be easily manufactured.

According to the methods 7) to 9), the negative electrode active materials 2) to 4) can be easily produced.

According to the negative electrode of 10) and the lithium secondary battery of 11), there are remarkable effects as described in the negative electrode active materials of 1) to 5).

It is an expansion perspective view which shows the particle | grains of the negative electrode active material for lithium secondary batteries by this invention. It is a figure explaining the hole diameter of the particle | grains of the negative electrode active material for lithium secondary batteries of FIG. It is a general | schematic vertical sectional view which shows the apparatus which cut | disconnects etching foil and forms the powder used as the negative electrode active material for lithium secondary batteries. It is a partially cutaway front view which shows the lithium secondary battery which has a negative electrode formed using the negative electrode active material for lithium secondary batteries of FIG.

(1): Particle
(2): Hole
(10): Lithium secondary battery
(12): Negative electrode
(13): Positive electrode
(14): Separator

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows particles constituting the negative electrode active material for a lithium secondary battery according to the present invention, and FIG. 2 shows pores formed in the particles of the negative electrode active material for the lithium secondary battery of FIG. 3 shows an apparatus for cutting the etching foil to form a powder that becomes the negative electrode active material for the lithium secondary battery of FIG. 1, and FIG. 4 is formed using the negative electrode active material for the lithium secondary battery of FIG. 1 shows an example of a lithium secondary battery having a negative electrode formed.

A negative electrode active material for a lithium secondary battery is a step of etching an both sides of a foil having an Fe content of 0.05% by mass or less and having Al as a main component to form an etching foil, and a step of cutting the etching foil Are formed in this order. Here, “foil” means that the thickness is 0.006 to 0.2 mm as defined in JIS. “Powder” means an aggregate of particles having a maximum dimension of 1 mm or less, as defined in JIS Z2500.

The powder constituting the negative electrode active material for a lithium secondary battery includes particles having various shapes. As shown in FIG. 1, a plurality of pores (2) that are open on the surface and have a pore diameter of 0.5 μm or more. It is preferable that particles (1) having) are contained. This is because if the pore diameter is less than 0.5 μm, Li ions cannot penetrate into the inside of the pores (2), and the occlusion amount of Li ions may be reduced. The upper limit of the pore diameter of the pores (2) of the particles (1) is preferably 15 μm. In order to make the hole diameter of the hole (2) exceed 15 μm, it is necessary to make the particle diameter of the particle (1) larger than 150 μm. In this case, the conductive auxiliary agent and the binder This is because, when mixed, the paste does not become an appropriate paste and it may be difficult to coat the current collector. The total opening area of all the pores (2) to the surface of the particles (1) in each particle (1) having the pores (2) is 10% or more of the surface area of each particle (1) having the pores (2). It is preferable that When the total area of the openings of all the pores (2) to the surface of the particles (1) is less than 10% of the surface area of each particle (1) having the pores (2), they enter the pores (2). This is because the amount of occlusion of Li ions may be reduced. In particles having a plurality of holes (2), at least some of the holes (2A) may be through-holes.

Further, the particle diameter of all the particles (1) is preferably 5 to 150 μm. When the particle diameter exceeds 150 μm, when mixed with a conductive additive and a binder in producing a negative electrode, it does not form an appropriate paste, and coating on the current collector may be difficult. In the case of the particles (1) having the pores (2), if the particle size of the particles (1) is less than 5 μm, the pores (2) having a pore size of 0.5 μm or more cannot be formed. In the case of particles (1) having pores (2), the ratio of pore diameter to particle diameter (pore diameter / particle diameter) is preferably less than 0.1.

Here, since the opening of the hole (2) to the particle (1) surface is often not circular, the term “hole diameter” means the area of the hole (2) as shown in FIG. It shall mean the equivalent circle diameter represented by the diameter (D) of a circle (C) equal to the area. In addition, depending on the particle, a plurality of holes (2) may be bonded. In this case, as shown in FIGS. 2 (b) and (c), the area of each bonded hole (2) is reduced. The equivalent circle diameter represented by the diameter (D) of the circle (C) equal to this area is referred to as the hole diameter.

In addition, the powder which comprises the negative electrode active material for lithium secondary batteries may contain the particle | grains which do not have a hole.

The charge / discharge was limited to the etching foil used to form the negative electrode active material, which had an Fe content of 0.05% by mass or less and was etched on both sides of the foil containing Al as a main component. This is because sometimes it is possible to prevent a short circuit when Li is preferentially deposited on Fe, and to increase the amount of occlusion / release of Li ions to the negative electrode made of the formed negative electrode active material. In particular, the purity of the foil whose Fe content is 0.05% by mass or less and whose main component is Al is preferably 90% by mass or more. In this case, the initial charge / discharge capacity of the lithium secondary battery using the negative electrode formed of the negative electrode active material can be increased, and a decrease in capacity due to repeated charge / discharge can be reduced.

In addition, since the etching foil used to form the negative electrode active material is etched on both sides, a porous layer is formed on both sides, but the etching foil is formed on the porous layer of the etching foil. The hole diameter of the etching holes is preferably 0.5 to 15 μm, and more preferably 0.5 to 5 μm. Here, since the opening of the etching hole to the etching foil surface is often not circular, as in the case of the particle (1) described above, the term “hole diameter” means that the area of the etching hole is equal to this area. The equivalent circle diameter represented by the diameter of. In the porous layer of the etching foil, a plurality of etching holes may be bonded. In this case, the area of each bonded etching hole is equivalent to a circle represented by the diameter of a circle equal to this area. The diameter is referred to as the hole diameter. Moreover, the depth of the etching hole of etching foil is not specifically limited, It is preferable that at least one part etching hole of all the etching holes is a through-hole which penetrated etching foil. Moreover, it is preferable that the sum total of the opening area to the etching foil surface of all the etching holes is 10% or more of the surface area of both surfaces of the etching foil on both surfaces of the etching foil. When the etching foil satisfies these conditions, the powder particles formed by cutting the etching foil satisfy the above-described conditions. Furthermore, the thickness of the etching foil is preferably 200 μm or less. When the thickness of the etching foil exceeds 200 μm, cutting becomes difficult. The thickness of the etching foil is more preferably 50 to 150 μm. In this case, the production efficiency of the particles (1) having the above-mentioned particle diameter is excellent.

Conditions such as the hole diameter of the etching hole of the etching foil and the ratio of the total opening area of all the etching holes to the surface area of the etching foil depend on the condition of the Li ions into the pores of the powder particles formed by cutting the etching foil. It is determined from the viewpoint of absorbing the occlusion amount, the expansion of the negative electrode during charging of the lithium secondary battery including the negative electrode made of the negative electrode active material, and the contraction of the negative electrode during discharge.

As such an etching foil, for example, a material satisfying the above-mentioned conditions can be used from those commercially available as an electrode foil for an aluminum electrolytic capacitor. In other words, an etching foil for an aluminum electrolytic capacitor is formed with an anodized film corresponding to the operating voltage, but the hole diameter is determined so that the hole is not crushed by this anodized film. The etching foil for use does not satisfy the conditions such as the hole diameter of the etching foil forming the negative electrode active material of the present invention having different purposes of use and the opening area of the etching hole. However, in the etching foil for aluminum electrolytic capacitors, the same conditions as the etching foil for forming the powder that is the negative electrode active material of the present invention, that is, the thickness, the hole diameter of the etching hole, and the etching foil surface of all the etching holes There are those having a ratio of the total opening area to the surface area of the etching foil.

The etching foil used to form the negative electrode active material is, for example, an Al foil having a purity of 90% by mass or more, preferably an Al foil having a purity of 99.9% by mass or more, and an Fe content of 0.05% by mass. 2% or less of hydrochloric acid on both surfaces of an Al foil in which 70% or more, preferably 90% or more, and desirably 95% or more of the crystal grains having (100) faces out of all the crystal grains are present. A first etching treatment step of performing direct current etching in an aqueous solution containing 0.01% by mass to 5% by mass of at least one acid selected from the group consisting of sulfuric acid, oxalic acid, and phosphoric acid, NH 4 ⁺ or Na ⁺ electrochemically or chemically one or more intermediate processing steps of forming a surface oxide film in an aqueous solution containing sodium chloride, ammonium chloride, Cl of potassium chloride ^- at least one kind of neutral salts comprising And a second etching treatment step in which direct etching is performed in an aqueous solution containing 0.1 to 10% by weight of a neutral salt, the hole diameter of the etching holes and the opening area of all the etching holes on the etching foil surface. It may be produced so as to satisfy the conditions such as the ratio of the total etching foil to the surface area.

When the purity of the Al foil used for producing the etching foil is low and the Fe content exceeds 0.05 mass%, the foil surface is dissolved during etching, and it becomes difficult to form a desired etching hole. As described above, the higher the purity of the Al foil used, the better. Similarly, when the ratio of the crystal grains having the (100) face is low in the total crystal grains of the Al foil used to produce the etching foil, the foil surface dissolves during etching and desired etching holes are formed. Therefore, as described above, it is desirable that the ratio of the crystal grains having the (100) plane is higher among all the crystal grains of the Al foil.

In the above, the purity of the Al foil represents the balance obtained by subtracting the total amount of Fe, Si and Cu from 100% by mass, as defined in JIS H4170.

Further, as long as a predetermined etching hole is formed, the etching is not limited to direct current etching, and may be alternating current etching or chemical etching, or at least two of these three types of etching are appropriately performed. You may carry out combining in order.

In addition, as an etching foil used for forming the negative electrode active material, it is preferable to use an unformed foil whose surface is not subjected to a chemical conversion treatment.

As the cutting method of cutting the etching foil into powder, a method of cutting finely with a blade is preferable, and the method of tearing or knocking may cause the opening to the particle surface of the formed powder to be crushed Therefore, it is not preferable. As a method of finely cutting using a blade, there is a method of using an apparatus including a movable blade and a fixed blade, rotating the movable blade at a high speed, and cutting with the fixed blade. In this case, a screen having a large number of sieves is arranged below the movable blade and the fixed blade, and by adjusting the size of the sieve appropriately, among the particles of the powder formed by cutting the etching foil, The size of the particles that have passed through the sieve can be 5 to 150 μm.

FIG. 3 schematically shows a specific example of an apparatus for cutting an etching foil.

The housing (21) of the cutting device (20) is provided with a cutting chamber (22) and a powder recovery chamber (23) located below the cutting chamber (22). The housing (21) is provided with an etching foil inlet (24) facing the cutting chamber (22) and a powder recovery port (25) facing the powder recovery chamber (23). It can be freely opened and closed by means of lids (26) and (27) which are detachably attached to.

In the cutting chamber (22) of the housing (21) of the cutting device (20), a plurality of rotations attached to the rotating body (28) at intervals in the rotating direction of the rotating body (28) and the rotating body (28) A rotary cutting machine (30) having a blade (29) is installed. In addition, a plurality of fixed blades (31) are attached to the housing (21) so that the front end portion is desired in the cutting chamber (22). Then, when the rotating body (28) is rotated, the etching foil is cut by the rotating blade (29) and the fixed blade (31).

A screen (32) having a plurality of sieves is arranged between the cutting chamber (22) and the powder recovery chamber (23) in the housing (21) of the cutting device (20). The opening of the screen (32) is adjusted so that only particles having a particle size of 150 μm or less can pass through.

In such a cutting apparatus, when the etching foil is introduced from the inlet (24) and then the inlet (24) is closed by the lid (26) and the rotating body (28) is rotated, the rotary blade (29) and the fixed blade (31), the etching foil is cut until it becomes a particle having a size passing through the sieve of the screen (32), and particles having a particle size of 150 μm or less pass through the sieve of the screen (32), and the powder recovery chamber (23 ) Thereafter, the lid (27) is opened, and the powder composed of particles having a particle size of 150 μm or less is taken out from the powder collection chamber (23). In this way, a negative electrode active material is obtained.

The negative electrode active material is used for, for example, a coin-type lithium secondary battery (10) as shown in FIG. The coin-type lithium secondary battery (10) is sandwiched between a negative electrode (12), a positive electrode (13) facing the negative electrode (12), and a negative electrode (12) and a positive electrode (13) in a case (11). The separator (14) and a non-aqueous electrolyte (not shown) are enclosed.

The negative electrode (12) is obtained by adhering a mixture (16) containing a negative electrode active material, a conductive additive and a binder on a current collector (15). As the current collector (15), for example, a rolled copper foil or a copper foil such as an electrolytic copper foil is used. As the conductive auxiliary agent, ketjen black or acetylene black is used, but it is not limited to this. As the binder, polyvinylidene fluoride is used, but is not limited thereto.

As the positive electrode (13), for example, a material made of LiCoO ₂ is used as an active material, and a mixture of the active material, a conductive additive and a binder is attached on a current collector made of aluminum foil. However, the present invention is not limited to this.

In the above-described lithium secondary battery (10), during charging, Li ions enter the pores (2) of the particles (1) of the negative electrode active material contained in the negative electrode (12), and Li ions are contained in the pores (2). In addition to the formation of the compound containing the negative electrode active material particles (1), into the gap formed between the negative electrode active material particles (1) to form a compound containing Li ions in the gap, Expansion of 1) can be suppressed. Further, since the expansion during charging is suppressed, the shrinkage of the particles (1) when Li ions exit from the particles (1) of the negative electrode active material during discharging is also reduced. As a result, the volume change of the negative electrode active material particles (1) during charge / discharge is reduced, and the volume change of the negative electrode active material particles (1) during charge / discharge is increased (1 ) Cracking and pulverization, and separation of the negative electrode active material particles (1) from the conductive assistant and binder, and capacity reduction due to repeated charging and discharging are reduced. Thus, it becomes possible to prolong the cycle life of the lithium secondary battery (10).

Also, the initial charge / discharge capacity of the lithium secondary battery (10) is increased, and the capacity reduction due to repeated charge / discharge is reduced.

In the above embodiment, the negative electrode active material according to the present invention is used in a coin-type lithium secondary battery. However, the present invention is not limited to this, and known lithium secondary batteries such as a square type, a cylindrical type, and a laminate type are used. Used for secondary batteries.

Hereinafter, specific examples of the present invention will be described together with comparative examples.
Example After double-sided etching for commercially available medium and high voltage (anode for electrolytic capacitor of 170 V or higher) and Fe content of 0.01% by mass was shredded by a shredder device, The negative electrode active material which consists of powder was grind | pulverized with the grinder. The particle diameter of the particles in the obtained negative electrode active material was in the range of 1 to 50 μm. Moreover, when the particles of the negative electrode active material were observed with an electron microscope, the pores confirmed at the foil stage remained.

Then, negative electrode active material: 85 parts by weight, binder made of polyvinylidene fluoride: 8 parts by weight, and conductive auxiliary agent made of acetylene black: 7 parts by weight are mixed, and the mixture is made from a 10 μm thick copper foil. It was applied on a current collector. Next, the current collector coated with the mixture was punched with a 1 cm ² circular punch, and this was used as the negative electrode. Then, a separator made of polyethylene having a micropore structure with a porosity of 40 vol% is sandwiched between the positive electrode and the negative electrode, and a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC + DMC = 1). 1 (volume ratio)) was dissolved in 1 mol / liter LiPF ₆ as an electrolyte, and a coin-type model battery (CR2032 type) was produced in a dry box having an atmosphere with a dew point of −50 ° C. or lower.
Comparative Example A high-purity annealed Al foil having a purity of 99.99% by mass was shredded by a shredder apparatus and then pulverized by a pulverizer to produce a negative electrode active material made of powder. The particle diameter of the particles in the obtained negative electrode active material was in the range of 1 to 50 μm.

Then, negative electrode active material: 85 parts by weight, binder made of polyvinylidene fluoride: 8 parts by weight, and conductive auxiliary agent made of acetylene black: 7 parts by weight are mixed, and the mixture is made from a 10 μm thick copper foil. It was applied on a current collector. Next, the current collector coated with the mixture was punched with a 1 cm ² circular punch, and this was used as the negative electrode. Then, a separator made of polyethylene having a micropore structure with a porosity of 40 vol% is sandwiched between the positive electrode and the negative electrode, and a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC + DMC = 1). 1 (volume ratio)) was dissolved in 1 mol / liter LiPF ₆ as an electrolyte, and a coin-type model battery (CR2032 type) was produced in a dry box having an atmosphere with a dew point of −50 ° C. or lower.
Evaluation test About the model battery produced in the Example and the comparative example, the negative electrode was evaluated by the following method.

First, the model battery was charged at a constant current of 0.2 mA / cm ² until reaching 1 V, rested for 10 minutes, and then discharged at a constant current of 0.2 mA / cm ² until it reached 0 V. This was defined as one cycle, and charging / discharging was repeated to examine the discharge capacity.

Table 1 shows the number of cycles and the discharge capacity of the model batteries produced in the examples and comparative examples.

As is apparent from Table 1, the model battery produced in the example has a higher initial discharge capacity than the model battery produced in the comparative example, and the discharge capacity after 100 cycles has decreased sufficiently. It can be seen that this value is maintained. Therefore, in the model battery manufactured in the example, the cycle life is extended as compared with the model battery manufactured in the comparative example.

The negative electrode active material for a lithium secondary battery according to the present invention is suitably used for a negative electrode of a lithium secondary battery, and it is possible to achieve a long cycle life of the lithium secondary battery.

Claims

It was formed by performing an etching foil forming step by etching both surfaces of a foil containing Fe as a main component with an Fe content of 0.05% by mass or less and cutting the etching foil in this order. A negative electrode active material for a lithium secondary battery comprising powder.
The negative electrode active material for a lithium secondary battery according to claim 1, wherein the Al purity of the foil containing Al as a main component is 90% by mass or more.
The powder formed by cutting the etching foil contains particles having a plurality of holes that are open on the surface and have a hole diameter of 0.5 μm or more. 3. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the total opening area is 10% or more of the surface area of each particle having the pores.
The diameter of all particles is 5 to 150 μm, the diameter of the pore-containing particles is 0.5 to 15 μm, and the ratio of the pore diameter to the diameter of the pore-containing particles (pore diameter / particle diameter) is less than 0.1 The negative electrode active material for a lithium secondary battery according to claim 3.
2. The negative electrode active material for a lithium secondary battery according to claim 1, wherein at least some of the etching holes formed in the etching foil are through holes.
Etching foil having a Fe content of 0.05% by mass or less and having a porous layer on both sides, which is made by etching both sides of a foil containing Al as a main component, is cut into powder. A method for producing a negative electrode active material for a lithium secondary battery.
The manufacturing method of the negative electrode active material for lithium secondary batteries of Claim 6 whose Al purity of the foil which has Al as a main component is 90 mass% or more.
The etching foil has a thickness of 200 μm or less, the hole diameters of the etching holes in both porous layers are 0.5 to 15 μm, and the total opening area of all the etching holes in both porous layers is 10% of the surface area of both surfaces of the etching foil. The method for producing a negative electrode active material for a lithium secondary battery according to claim 6 or 7, wherein at least some of the etching holes are through-holes.
9. The method for producing a negative electrode active material for a lithium secondary battery according to claim 8, wherein an etching foil having a thickness of 50 to 150 μm is used.
A negative electrode for a lithium secondary battery, wherein a mixed material containing the negative electrode active material according to claim 1, a conductive additive and a binder is attached on a current collector.
A lithium secondary battery comprising the negative electrode according to claim 10, a separator, and a positive electrode for a lithium secondary battery.