JP2013182845A - Negative electrode active material for lithium secondary battery, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for a lithium secondary battery, capable of achieving prolonged cycle life of a lithium secondary battery.SOLUTION: A negative electrode material for a lithium secondary battery comprises powder of an aggregate of particles formed by cutting an aluminum foil with a thickness of 0.15 mm or less. Each of the particles has a size that allows each particle to pass through a sieve with an aperture of 0.1 mm (in accordance with JIS Z8801-3), and the powder has a specific surface area as determined by a BET method of 0.3 m/g or more.

Description

  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, 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 which is a substance having a discharge capacity larger than that of a general-purpose carbon material and made of a material other than metal Li 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 includes a raw material melt composed 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. , A negative electrode active material having a structure rapidly quenched and solidified by an atomizing method, a roll rapid cooling 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 active material comprising a composite powder formed by mixing a raw material comprising a B component, which is at least one element selected from the group consisting of Ge, Sb, Si and Sn, and subjecting it to mechanical alloying treatment The quality is listed.

  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.

  In order to achieve the above object, the present invention comprises the following aspects.

1) Made of powder that is an aggregate of particles formed by cutting an aluminum foil having a thickness of 0.15 mm or less, and each particle passes through a sieve (based on JIS Z8801-1) having an aperture of 0.1 mm. A negative electrode active material for a lithium secondary battery that has a size that can be measured and that has a specific surface area of 0.3 m ² / g or more by the BET method of the powder.

  2) The negative electrode active material for a lithium secondary battery according to 1), wherein each of the particles has a size capable of passing through a sieve having an opening of 0.045 mm (based on JIS Z8801-1).

  3) The negative electrode active material for a lithium secondary battery according to 1) above, wherein the projected equivalent circle diameter of each particle is 0.010 mm or less.

  4) The negative electrode active material for a lithium secondary battery according to 1) above, wherein the projected equivalent circle diameter of each particle is 0.005 mm or less.

5) The negative electrode active material for a lithium secondary battery according to any one of 1) to 4) above, wherein the powder has a specific surface area of 0.5 m ² / g or more by the BET method.

  6) The negative electrode active material for a lithium secondary battery according to any one of 1) to 5), wherein the aluminum foil is made of Al having a purity of 99% by mass or more.

  7) The negative electrode active material for a lithium secondary battery according to any one of 1) to 5), wherein the aluminum foil is made of Al having a purity of 99.9% by mass or more.

  8) The lithium secondary battery according to any one of 1) to 7) above, wherein the particles are formed by cutting an aluminum foil having a thickness of 0.15 mm or less and pulverizing by a method in which a compressive stress is applied. Negative electrode active material for secondary battery.

  9) The negative electrode active material for a lithium secondary battery according to any one of 1) to 8), wherein the particles are chemically dissolved using an acid or an alkali.

10) Powder is made by cutting aluminum foil with a thickness of 0.15 mm or less to form particles, and each particle constituting the powder is passed through a sieve having a mesh opening of 0.1 mm (based on JIS Z8801-1). A method for producing a negative electrode active material for a lithium secondary battery, characterized in that the specific surface area of the powder according to the BET method is 0.3 m ² / g or more.

  11) The method for producing a negative electrode active material for a lithium secondary battery as described in 10) above, wherein each particle is sized so as to pass through a sieve having an aperture of 0.045 mm (based on JIS Z8801-1).

  12) The method for producing a negative electrode active material for a lithium secondary battery as described in 10) above, wherein the projected circumference equivalent circle diameter of each particle is 0.010 mm or less.

  13) The method for producing a negative electrode active material for a lithium secondary battery as described in 10) above, wherein the projected equivalent circle length of each particle is 0.005 mm or less.

  14) The method for producing a negative electrode active material for a lithium secondary battery according to any one of 10) to 13), wherein the aluminum foil is made of Al having a purity of 99% by mass or more.

  15) The method for producing a negative electrode active material for a lithium secondary battery according to any one of 10) to 13), wherein the aluminum foil is made of Al having a purity of 99.9% by mass or more.

  16) The lithium secondary battery according to any one of 10) to 15) above, wherein an aluminum foil having a thickness of 0.15 mm or less is cut and then subjected to chemical dissolution treatment with an acid or an alkali to form particles. For producing a negative electrode active material.

  17) The negative electrode active for lithium secondary batteries according to any one of 10) to 15) above, wherein the aluminum foil having a thickness of 0.15 mm or less is cut and pulverized by a method to which compressive stress is applied to form particles. A method for producing a substance.

  18) Among the above 10) to 15) in which an aluminum foil having a thickness of 0.15 mm or less is cut, pulverized by a method in which compressive stress is applied, and further subjected to chemical dissolution treatment using an acid or alkali to form particles. The manufacturing method of the negative electrode active material for lithium secondary batteries in any one of these.

  19) A negative electrode for a lithium secondary battery, wherein a mixed material containing a negative electrode active material, a conductive additive and a binder described in any one of 1) to 9) above is attached on a current collector.

  20) A lithium secondary battery comprising the negative electrode described in 19) above, a separator, and a positive electrode for a lithium secondary battery.

  The present invention also includes the following aspects.

  a) The negative electrode active material for a lithium secondary battery according to 1) above, wherein each of the particles has a size capable of passing through a sieve having an aperture of 0.010 mm (based on JIS Z8801-1).

  b) The negative electrode active material for a lithium secondary battery according to 1) above, wherein each of the particles has a size capable of passing through a sieve having an aperture of 0.005 mm (based on JIS Z8801-1).

  c) The method for producing a negative electrode active material for a lithium secondary battery according to 10) above, wherein each particle is sized so as to pass through a sieve having an aperture of 0.010 mm (based on JIS Z8801-1).

  d) The method for producing a negative electrode active material for a lithium secondary battery as described in 10) above, wherein each particle is sized so as to pass through a sieve having an aperture of 0.005 mm (based on JIS Z8801-1).

According to the negative electrode active material for lithium secondary batteries of 1) to 9) above, the negative active material for lithium secondary battery comprises a powder that is an aggregate of particles formed by cutting an aluminum foil having a thickness of 0.15 mm or less. The size is such that it can pass through a sieve with a mesh size of 0.1 mm (based on JIS Z8801-1), and the specific surface area of the powder by the BET method is 0.3 m ² / g or more. Thus, the specific surface area of the powder formed is increased. 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, when Li ions are alloyed with Al, a compound containing Li ions is formed on the surface of the particles by preferential reaction from the surface of the particles, but the specific surface area of the powder by the BET method is 0. If it is 3 m < ² > / g or more, the compound containing many Li ions will be formed in the surface of particle | grains, and it can suppress the expansion | swelling of the negative electrode active material at the time of charge. 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, in the lithium secondary battery provided with the negative electrode formed from the negative electrode active material of the above 1) to 9), compared with the lithium secondary battery provided with the negative electrode formed from the negative electrode active material made 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 the above 2) to 9), 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 10), a powder is prepared by cutting an aluminum foil having a thickness of 0.15 mm or less to form particles, and each particle constituting the powder is sieved with a sieve having a mesh size of 0.1 mm (JIS Z8801). 1), and the specific surface area of the powder by the BET method is only 0.3 m ² / g or more, so that a negative electrode active material for a lithium secondary battery can be easily produced. can do.

  According to the methods 11) to 18), the negative electrode active materials 2) to 9) can be easily produced.

  According to the negative electrode of 19) and the lithium secondary battery of 20), there are remarkable effects as described in the negative electrode active materials of 1) to 9).

It is a partial cross-section enlarged perspective view showing particles of a negative electrode active material for a lithium secondary battery according to the present invention. 1 is a schematic vertical sectional view showing an apparatus for cutting an aluminum foil to form a powder that becomes a negative electrode active material for a lithium secondary battery according to the present invention. 1 is a partially cutaway front view showing a lithium secondary battery having a negative electrode formed using a negative electrode active material for a lithium secondary battery according to the present invention.

  Embodiments of the present invention will be described below 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 an apparatus for cutting an aluminum foil to form a powder that becomes a negative electrode active material for a lithium secondary battery according to the present invention. FIG. 3 shows an example of a lithium secondary battery having a negative electrode formed using the negative electrode active material for a lithium secondary battery according to the present invention.

A negative electrode active material for a lithium secondary battery is made of powder which is an aggregate of particles formed by cutting an aluminum foil having a thickness of 0.15 mm or less, and each particle has a sieve having an opening of 0.1 mm (JIS The specific surface area of the powder by the BET method is 0.3 m ² / g or more.

  Here, the “foil” means one having a thickness of 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 reason why the thickness of the aluminum foil to be used is limited to 0.15 mm is that when the thickness of the aluminum foil exceeds 0.15 mm, cutting becomes difficult and the production efficiency decreases. The aluminum foil to be used is preferably made of Al having a purity of 99% by mass or more, and is preferably made of Al having a purity of 99.9% by mass or more. This is for increasing the amount of insertion / extraction of Li ions to / from the negative electrode made of the formed negative electrode active material. In particular, when composed of Al having a purity of 99.9% by mass or more, 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 the capacity by repeating charge / discharge can be increased. Reduction can be reduced. In addition, the purity of aluminum foil represents the remainder which reduced the total amount of Fe, Si, and Cu from 100 mass%, as prescribed | regulated to JIS H4170.

  The powder, which is an aggregate of particles formed by cutting the aluminum foil, includes particles of various shapes, but when the aluminum foil having a thickness of 0.15 mm or less is cut, the foil is divided. As a result, a new surface is formed and a stretched portion is formed by bending, resulting in an increase in specific surface area. For example, the particle (1) has a shape as shown in FIG.

  The particles constituting the powder serving as the negative electrode active material for a lithium secondary battery may be formed by cutting the aluminum foil and pulverizing it by a method in which a compressive stress is applied. The particles may be formed by cutting the aluminum foil and subjecting it to chemical dissolution treatment using acid or alkali. Further, the particles may be formed by cutting the aluminum foil, pulverizing it by a method in which a compressive stress is applied, and then performing a chemical dissolution treatment using an acid or an alkali.

  In addition, the size of the particles is limited to a size that can pass through a sieve having a mesh size of 0.1 mm (based on JIS Z8801-1). This is because when mixed with the binder, the paste does not form an appropriate paste, and coating on the current collector becomes difficult. The size of each particle is preferably a size that can pass through a sieve having an aperture of 0.045 mm (based on JIS Z8801-1), and the projected circumferential ellipse equivalent diameter is 0.010 mm or less. More preferably, it is desirable that the projected circumference circle equivalent diameter is 0.005 mm or less. Further, the size of each particle is preferably a size that can pass through a sieve having an opening of 0.045 mm (based on JIS Z8801-1), and a sieve having an opening of 0.010 mm (based on JIS Z8801-1). ) Is more preferable, and it is desirable that the size be able to pass through a sieve having an aperture of 0.005 mm (based on JIS Z8801-1).

Furthermore, the specific surface area by the BET method of the powder that is an aggregate of the particles is limited to 0.3 m ² / g or more because the amount of insertion / extraction of Li ions to the negative electrode made of the formed negative electrode active material is increased. It is to do. The specific surface area is preferably 0.5 ² / g or more.

  Here, the specific surface area by BET method is calculated | required as follows by a well-known method. That is, the solid substance and the gas present around it attract each other by van der Waals force when rapidly cooled, so measure the amount of adsorbed gas and calculate the surface area of the solid by substituting it into the BET equation. can do. In the above, the specific surface area of the powder is determined by the BET method using nitrogen gas as the adsorption gas, helium as the carrier gas, and liquid nitrogen as the coolant. Note that helium, which is a carrier gas, is a diluted gas and is used as a mixed gas mixed with nitrogen gas. Here, the nitrogen gas concentration in the mixed gas is 29.8%.

  Conditions such as the thickness of the aluminum foil, the size of the particles, and the specific surface area of the powder by the BET method include the amount of Li ions occluded on the surface of the powder particles formed by cutting the aluminum foil, and the negative electrode active material. It is determined from the viewpoint of absorbing the expansion of the negative electrode during charging of the lithium secondary battery including the negative electrode and the contraction of the negative electrode during discharging.

  As a cutting method of cutting aluminum 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, it is possible to adjust the size of the particles by arranging a screen having a large number of sieves below the movable blade and the fixed blade and appropriately adjusting the size of the sieves.

  FIG. 2 schematically shows a specific example of an apparatus for cutting an aluminum 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 a foil inlet (24) facing the cutting chamber (22) and a powder recovery port (25) facing the powder recovery chamber (23). The lids (26) and (27) can be opened and closed freely.

  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, by rotating the rotating body (28), the aluminum foil is cut by the rotating blade (29) and the fixed blade (31).

  A screen (32) having a plurality of sieves is disposed between the cutting chamber (22) and the powder recovery chamber (23) in the housing (21) of the cutting device (20). The screen (32) comprises a sieve (based on JIS Z8801-1) having an aperture of 0.1 mm, preferably 0.045 mm, more preferably 0.010 mm, and desirably 0.005 mm.

  In such a cutting device, after the aluminum foil is introduced from the foil inlet (24), the foil inlet (24) is closed by the lid (26), and the rotating body (28) is rotated. With the fixed blade (31), the aluminum foil is cut until the size of the particles passes through the screen (32), and the particles passing through the screen (32) are put into the powder recovery chamber (23). enter. Thereafter, the lid (27) is opened and the powder is taken out from the powder collection chamber (23). In this way, a negative electrode active material is obtained.

  As shown in FIG. 3, the negative electrode active material is used, for example, in a coin-type lithium secondary battery (10). 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 assistant, ketjen black or acetylene black is used, but is not limited thereto. 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 material in which a mixture of the active material, a conductive additive and a binder is attached on a current collector made of aluminum foil is used. However, the present invention is not limited to this.

  In the above-described lithium secondary battery (10), during charging, a compound containing Li ions is formed on the surface of the negative electrode active material particles (1) in which Li ions are contained in the negative electrode (12). Expansion of the negative electrode active material particles (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, as well as separation of the negative electrode active material particles (1) from the conductive additive and the binder, and a decrease in capacity due to repeated charging and discharging are small. Thus, the cycle life of the lithium secondary battery (10) can be extended.

  Further, 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 1
A commercially available aluminum foil made of Al with a purity of 99.9% by mass having a thickness of 0.12 mm was shredded by a shredder apparatus, and then a screen made of a sieve (based on JIS Z8801-1) having an opening of 0.045 mm ( The negative electrode active material made of powder was pulverized by a pulverizer shown in FIG. The particles in the obtained negative electrode active material have a size that can pass through a sieve having an aperture of 0.045 mm (based on JIS Z8801-1), and the specific surface area of the powder by the BET method is 0.6 m ² / g. It was.

Then, 90 parts by weight of the negative electrode active material, 5 parts by weight of a binder made of polyvinylidene fluoride, and 5 parts by weight of a conductive auxiliary agent made of acetylene black were mixed, and the mixture was made from a copper foil having a thickness of 10 μm. It was applied on a current collector. Next, the current collector coated with the above mixture was punched with a 1 cm ² circular punch, and this was used as a 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.

Example 2
A commercially available aluminum foil made of Al with a purity of 99.9% by mass having a thickness of 0.12 mm was shredded by a shredder apparatus, and then a screen made of a sieve (based on JIS Z8801-1) having an aperture of 0.045 mm ( The powder was pulverized by the pulverizer shown in FIG. The particles in the obtained powder have a size that can pass through a sieve having an opening of 0.045 mm (based on JIS Z8801-1).

Next, the powder particles obtained as described above were subjected to a chemical dissolution treatment in 5N HCl at a liquid temperature of 60 ° C. for 40 minutes to produce a negative electrode active material. The specific surface area by the BET method of the powder which comprises the obtained negative electrode active material was 1.1 m < ² > / g.

Then, 90 parts by weight of the negative electrode active material, 5 parts by weight of a binder made of polyvinylidene fluoride, and 5 parts by weight of a conductive auxiliary agent made of acetylene black were mixed, and the mixture was made from a copper foil having a thickness of 10 μm. It was applied on a current collector. Next, the current collector coated with the above mixture was punched with a 1 cm ² circular punch, and this was used as a 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 commercially available aluminum foil made of Al having a purity of 99.9% by mass and having a thickness of 0.12 mm was shredded by a shredder apparatus, and then pulverized by a ball mill, and made of a powder that is an aggregate of flat particles. A negative electrode active material was made. The particles in the obtained negative electrode active material have a size that can pass through a sieve having an aperture of 0.050 mm (based on JIS Z8801-1), and the specific surface area of the powder by the BET method is 0.07 m ² / g. It was.

Then, 90 parts by weight of the negative electrode active material, 5 parts by weight of a binder made of polyvinylidene fluoride, and 5 parts by weight of a conductive auxiliary agent made of acetylene black were mixed, and the mixture was made from a copper foil having a thickness of 10 μm. It was applied on a current collector. Next, the current collector coated with the above mixture was punched with a 1 cm ² circular punch, and this was used as a 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 Examples 1-2 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, and rested for 10 minutes, and then discharged at a constant current of 0.2 mA / cm ² until reaching 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 in the model batteries produced in Examples 1 and 2 and the comparative example.

  As is clear from Table 1, in the model batteries produced in Examples 1 to 1, the initial discharge capacity was higher than that of the model battery produced in the comparative example, and the discharge capacity decreased after 100 cycles. It can be seen that a small and sufficient 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.

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

Claims (20)

It consists of powder which is an aggregate of particles formed by cutting an aluminum foil having a thickness of 0.15 mm or less, and each particle can pass through a sieve (based on JIS Z8801-1) having an aperture of 0.1 mm. A negative electrode active material for a lithium secondary battery that is large in size and has a powder specific surface area of 0.3 m ² / g or more by the BET method. 2. The negative electrode active material for a lithium secondary battery according to claim 1, wherein each of the particles has a size capable of passing through a sieve having an aperture of 0.045 mm (based on JIS Z8801-1). 2. The negative electrode active material for a lithium secondary battery according to claim 1, wherein each particle has a projected circumference equivalent circle equivalent diameter of 0.010 mm or less. 2. The negative electrode active material for a lithium secondary battery according to claim 1, wherein each particle has a projected circumference equivalent circle equivalent diameter of 0.005 mm or less. The negative electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein a specific surface area of the powder by a BET method is 0.5 m ² / g or more. The negative electrode active material for a lithium secondary battery according to any one of claims 1 to 5, wherein the aluminum foil is made of Al having a purity of 99 mass% or more. The negative electrode active material for a lithium secondary battery according to any one of claims 1 to 5, wherein the aluminum foil is made of Al having a purity of 99.9% by mass or more. 8. The lithium secondary battery according to claim 1, wherein the particles are formed by cutting an aluminum foil having a thickness of 0.15 mm or less and pulverizing by a method in which a compressive stress is applied. Negative electrode active material. The negative electrode active material for a lithium secondary battery according to any one of claims 1 to 8, wherein the particles are chemically dissolved using an acid or an alkali. A powder is formed by cutting an aluminum foil having a thickness of 0.15 mm or less to form particles, and each particle constituting the powder can pass through a sieve having a mesh size of 0.1 mm (based on JIS Z8801-1). A method for producing a negative electrode active material for a lithium secondary battery, characterized in that the specific surface area of the powder according to the BET method is 0.3 m ² / g or more. The manufacturing method of the negative electrode active material for lithium secondary batteries of Claim 10 which makes the said each particle | grain the magnitude | size which can pass the sieve (based on JISZ8801-1) of 0.045mm of opening. The method for producing a negative electrode active material for a lithium secondary battery according to claim 10, wherein a projected circumference equivalent circle diameter of each particle is set to 0.010 mm or less. The method for producing a negative electrode active material for a lithium secondary battery according to claim 10, wherein a projected circumference equivalent circle diameter of each particle is 0.005 mm or less. The method for producing a negative electrode active material for a lithium secondary battery according to any one of claims 10 to 13, wherein the aluminum foil is made of Al having a purity of 99 mass% or more. The method for producing a negative electrode active material for a lithium secondary battery according to any one of claims 10 to 13, wherein the aluminum foil is made of Al having a purity of 99.9 mass% or more. The negative electrode active for a lithium secondary battery according to any one of claims 10 to 15, wherein a particle is formed by cutting an aluminum foil having a thickness of 0.15 mm or less and then performing chemical dissolution treatment using an acid or an alkali. A method for producing a substance. The production of a negative electrode active material for a lithium secondary battery according to any one of claims 10 to 15, wherein an aluminum foil having a thickness of 0.15 mm or less is cut and pulverized by a method in which a compressive stress is applied to form particles. Method. The aluminum foil having a thickness of 0.15 mm or less is cut, pulverized by a method in which compressive stress is applied, and further subjected to chemical dissolution treatment using an acid or alkali to form particles. The manufacturing method of the negative electrode active material for lithium secondary batteries as described in any one of. A negative electrode for a lithium secondary battery, wherein a mixed material containing the negative electrode active material according to any one of claims 1 to 9, a conductive additive, and a binder is attached on a current collector. A lithium secondary battery comprising the negative electrode according to claim 19, a separator, and a positive electrode for a lithium secondary battery.

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