JP2005071938A - Negative electrode activator for secondary battery, negative electrode and secondary battery using the same, and manufacturing method of negative electrode activator for secondary battery and negative electrode for secondary battery using the activator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a sufficient cycle property when using an Li storing substance which forms an alloy with lithium on a negative electrode. <P>SOLUTION: The secondary battery uses complex grains 30 including Li storing materials 34 in a carbonaceous material 32. The complex grain satisfies at least one condition out of following conditions (i) to (iii). (i) The center of gravity of a Li storing substance grain is located inside the complex grain. (ii) The center of gravity of all Li storing material grains contained in one complex grain is located on an inscribed circle of the complex grain with the center of gravity as a center, having a maximum area out of cross sectional planes of the complex grain. (iii) The coefficient of variation obtained by multiplying 100 on a value calculated by dividing the standard deviation of distances between center of gravity of the respective Li absorbing material grains contained in one complex grain and the center of gravity of the complex grain by a mean value of the distances, is not less than 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a negative electrode active material for a secondary battery, a negative electrode for a secondary battery and a secondary battery using the same, a negative electrode active material for a secondary battery and a method for producing a negative electrode for a secondary battery using the same.

  With the widespread use of mobile terminals such as mobile phones and portable notebook personal computers, the role of secondary batteries, which serve as the power source, is regarded as important. These secondary batteries are required to have a small size, a light weight, and a high capacity, and a performance that hardly deteriorates even after repeated charging and discharging.

  As the negative electrode of such a secondary battery, metallic lithium may be used from the viewpoint of high energy density and light weight. In this case, acicular crystals (dendrites) are formed on the lithium surface during charging as the charging / discharging cycle proceeds. In some cases, the crystals pass through the separator, causing an internal short circuit and shortening the battery life.

  On the other hand, when a carbon material such as graphite or hard carbon capable of occluding and releasing lithium ions is used as the negative electrode, the charge / discharge cycle can be favorably repeated. However, graphite materials have smaller capacities than metallic lithium and lithium alloys, and hard carbon has a large irreversible capacity at the first charge / discharge and low charge / discharge efficiency, so these materials have a lower energy density than metal lithium. .

Thus, as a material for increasing the energy density, the use of a Li storage material that forms an alloy with lithium represented by the composition formula Li _X A (A is made of a metal such as Al) as the negative electrode active material has been studied. . This negative electrode has a large amount of occlusion and release of lithium ions per unit volume, and has a high capacity. Recently, it has been disclosed that a metal oxide containing Sn or the like is used as a negative electrode material (Patent Document 1). It is said that a high capacity negative electrode can be obtained by using such a negative electrode material.

  However, the negative electrode using this type of Li storage material has a large amount of storage and release of lithium ions per unit volume, and has a high capacity. However, when lithium ions are stored and released, the lithium storage material is an electrode active material. Since it expanded and contracted itself, pulverization proceeded, the irreversible capacity in the first charge / discharge was large, and the charge / discharge cycle life was short.

Therefore, as a method for improving the cycle life of the negative electrode using the Li storage material, a method of covering the Li storage material that forms an alloy with an alkali metal with a carbonaceous material has been proposed (Patent Document 2). However, in these carbon coating materials, the Li storage material may expand during the charge / discharge process, and the carbonaceous material may be destroyed. When the carbonaceous material is destroyed, the conductivity is lowered, and the charge / discharge cycle characteristics may be significantly lowered.
JP 11-45712 A JP-A-6-279112

  As described above, when a Li storage material that forms an alloy with lithium is used for the negative electrode, sufficient cycle characteristics cannot be obtained with the conventional technology. The present inventor examined the cause of this, and it was considered that the current collection characteristics deteriorated due to expansion and contraction of the Li storage material of the negative electrode during charge and discharge.

  This invention is made | formed in view of the said situation, The objective is to provide the technique which improves the cycling characteristics of a secondary battery.

According to the present invention, the carbon material particles include composite particles in which at least part of the lithium storage material particles capable of storing and releasing lithium is embedded, and the center of gravity of each of the lithium storage material particles is in the composite particles. located in the negative electrode active material for a secondary battery, wherein the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman of the carbonaceous material particles is 10 or less is provided.

  In the present invention, lithium occlusion includes, for example, an aspect in which an intercalation compound is formed with lithium, an aspect in which lithium and a crystal interstitial compound are formed, an aspect in which lithium ions are inserted between crystals, and an aspect in which an alloy is formed with lithium. It is. The Li storage material particles are preferably particles capable of storing more lithium ions than the theoretical capacity of lithium storage of the carbon material.

  In the negative electrode active material for a secondary battery of the present invention, the center of gravity of each Li storage material particle is located in the composite particle. For this reason, the Li storage material particles can be reliably embedded in the composite particles. For this reason, electrical contact between the carbon material and the Li storage material can be ensured. Therefore, the current collecting property of the negative electrode can be improved. Therefore, the cycle characteristics of the secondary battery can be improved.

In addition, the structure of the carbon material constituting the composite particle is destroyed at the site where the Li storage material particles are embedded, and the adhesion between the carbon material and the Li storage material particles is increased. However, if all the carbon material is destroyed, the irreversible capacity increases and the charge / discharge characteristics deteriorate. For this reason, it is preferable that the presence of the crystalline carbon region is ensured. In order to obtain composite particles having both the adhesion and charge-discharge characteristics, the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman and 10 or less. As described above, the adhesion between the carbon material and the Li storage material particles can be maintained, and the cycle characteristics of the carbon material itself can be improved.

According to the present invention, the carbon material particles include composite particles in which at least a part of Li storage material particles capable of occluding and releasing lithium are embedded, and the carbon material particles are 1360 cm to 1580 cm ⁻¹ by argon laser Raman. ^{-1 is} a peak intensity ratio of 10 or less, and in one section of the composite particle, the position of the center of gravity of each of the Li storage material particles existing in one composite particle is determined based on the cross-sectional area. When the center of gravity of all the Li storage material particles present in one composite particle is calculated by multiplying the position of the center of gravity by the weight of the cross-sectional area and calculating the center of gravity of the composite particle. A negative electrode active material for a secondary battery is provided, wherein the center of gravity of the entire Li storage particle is located in an inscribed circle of the composite particle having a maximum area.

  In the negative electrode active material for a secondary battery of the present invention, in one cross section of the composite particle, the composite particle includes an inscribed circle having a maximum area centered on the center of gravity of the composite particle. The center of gravity of the entire Li storage particle is positioned. For this reason, it can be set as the state which Li occlusion material particle | grains disperse | distributed in the composite particle | grains without bias. Therefore, even if Li occlusion particles repeat volume expansion and contraction due to charge and discharge, the composite particles are not destroyed, and electrical contact between the carbon material and the Li occlusion material can be ensured. Therefore, the current collecting property of the negative electrode can be improved. For this reason, the cycling characteristics of a secondary battery can be improved.

  In the present invention, the specific gravity of each Li storage material particle is substantially equal, and each Li storage material particle has a shape close to a spherical shape. For this reason, when calculating the center of gravity, the specific gravity of each particle can be replaced with the volume. And about the cross section of a composite particle, the concept of a weight can be approximated using the area of each particle | grain. Further, in the present invention, when calculating the above-mentioned center of gravity, an arbitrary cross section of the composite particles may be evaluated.

According to the present invention, the carbon material particles include composite particles in which at least a part of Li storage material particles capable of occluding and releasing lithium are embedded, and the carbon material particles are 1360 cm to 1580 cm ⁻¹ by argon laser Raman. ^{-1 is} a peak intensity ratio of 10 or less, and the standard deviation of the distances between the centroids of all the Li storage material particles contained in one composite particle and the respective centroids of the composite particles is the average of the distances A negative electrode active material for a secondary battery is provided, wherein a variation coefficient obtained by multiplying a value divided by 100 by 100 is 10 or more.

  The negative electrode active material for a secondary battery of the present invention is obtained by calculating the standard deviation of the distance between the center of gravity of all the Li storage material particles contained in one composite particle and the center of gravity of the composite particle by the average value of the distances. Composite particles having a variation coefficient of 10 or more obtained by multiplying the divided value by 100 are included. For this reason, the Li storage material particles can be uniformly dispersed in the composite particles. By increasing the dispersibility of the Li storage material particles, it is possible to suppress the destruction of the carbon material due to the volume change when the Li storage material particles store and release lithium. For this reason, electrical contact between the Li storage material particles and the carbon material particles can be ensured, and the current collecting property can be improved. Therefore, the cycle characteristics of the battery can be improved.

  In the negative electrode active material for a secondary battery of the present invention, the Li storage material particles include at least one metal selected from the group consisting of Si, Ge, In, Sn, Ag, Al, or Pb or an oxide thereof. Can do. In the negative electrode active material for a secondary battery of the present invention, when a material having a large charge / discharge capacity such as Si particles or Ge particles is used as the Li storage material particles, the carbon material is also used when the Li storage material particles are pulverized. Good electrical contact with the particles can be maintained. For this reason, the cycle characteristics of the battery can be improved.

  In the negative electrode active material for a secondary battery of the present invention, the Li storage material particles include at least one metal selected from the group consisting of Si, Ge, In, Sn, Ag, Al, or Pb, or an oxide thereof, and Fe. , Co, Ni, Cu, Ti, Mo, Ta, Mg, Cr, Nb, Mn, V, W, and an alloy or mixture with at least one metal selected from the group consisting of Zr. By doing so, a negative electrode active material having more excellent current collecting characteristics can be obtained.

  In the negative electrode active material for a secondary battery of the present invention, the Li storage material particles may have an amorphous structure. By doing so, the current collection characteristics of the composite particles can be improved more reliably.

  In the negative electrode active material for a secondary battery of the present invention, an average particle diameter of the Li storage material particles in the composite particles may be 5 μm or less. By carrying out like this, the surface area per volume of Li occlusion material particle | grains can be kept large. Therefore, in the composite particles, it is possible to maintain good electrical contact between the Li storage material and the carbon material.

  According to this invention, the negative electrode for secondary batteries characterized by including the layer which has the said negative electrode active material for secondary batteries, and a negative electrode electrical power collector is provided. Since the negative electrode for a secondary battery according to the present invention has a negative electrode active material excellent in current collection characteristics, the cycle characteristics of the secondary battery can be improved.

  In the negative electrode for secondary battery of the present invention, the volume filling factor of the negative electrode active material in the layer having the negative electrode active material may be 45% or more and 75% or less. By setting the volume filling ratio of the negative electrode active material for secondary batteries to 45% or more, the battery capacity can be sufficiently increased. In addition, by setting the volume filling rate of the negative electrode active material for the secondary battery to 75% or less, it is possible to maintain sufficient current collecting ability even when the Li storage material particles are pulverized and to improve cycle characteristics. Can do.

  According to the present invention, a secondary battery including at least a positive electrode and a negative electrode, the secondary battery including the negative electrode for a secondary battery is provided. Since the secondary battery according to the present invention has a negative electrode active material excellent in current collecting characteristics, high cycle characteristics can be stably exhibited.

According to the present invention, a step of mechanically mixing carbon material particles and Li storage material particles capable of occluding and releasing lithium to produce composite particles, and a step of sampling and inspecting the obtained composite particles The negative electrode active material, wherein the mixing operation is terminated when the sampled composite particles satisfy any of the following conditions (i) to (iii) as a result of the inspection: A manufacturing method is provided.
(I) The center of gravity of the Li storage material particle is located in the composite particle. (Ii) In one cross section of the composite particle, the cross sectional area of all the Li storage material particles present in one composite particle. When calculating the center of gravity of all the Li storage material particles existing in one of the composite particles by calculating the position of each center of gravity based on the above, multiplying the position of the center of gravity by the weight of the cross-sectional area, In addition, the center of gravity of the entire Li-occlusion particle is located in the inscribed circle of the composite particle centering on the center of gravity of the composite particle and having the largest area (iii) included in one composite particle The variation coefficient obtained by multiplying the value obtained by dividing the standard deviation of the distance between the center of gravity of each of the Li storage material particles and the center of the composite particles by the average value of the distances by 100 is 10 or more.

  In the production method according to the present invention, the mixing operation is terminated when the sampled composite particles satisfy any of the following conditions (i) to (iii). For this reason, the composite particle which satisfy | fills any one of said (i) thru | or (iii) can be manufactured reliably. Therefore, composite particles having excellent adhesion between the Li storage material particles and the carbon material particles can be obtained. Alternatively, since the dispersibility of the Li storage material particles in the composite particles can be improved, the destruction of the composite particles due to the expansion and contraction of the Li storage material particles during charge / discharge can be suppressed.

  Therefore, a negative electrode active material having excellent current collecting characteristics can be reliably produced. In the present invention, it is more preferable that the composite particles satisfy two or more of the conditions (i) to (iii), and it is even more preferable that all the conditions are satisfied.

  According to the present invention, a step of obtaining a negative electrode active material by the method for producing a negative electrode active material, a step of preparing a paste by dissolving or dispersing the negative electrode active material and a binder in a solvent, and the paste A method for producing a negative electrode for a secondary battery comprising: a step of applying a current collector and then drying it.

  According to the production method of the present invention, a negative electrode having excellent current collecting characteristics can be produced easily and reliably.

  In the present invention, the current collecting property of the negative electrode can be improved by making most of the composite particles satisfy any one of the above conditions (i) to (iii). Specifically, the majority of the composite particles are preferably a majority, more preferably 70% or more of the composite particles. For all composite particles, it is preferable that all Li storage material particles in the composite particles satisfy the conditions (i) to (iii).

  According to the present invention, the cycle characteristics of the secondary battery can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1A and FIG. 1B are schematic views showing the configuration of the lithium ion secondary battery in the embodiment of the present invention. The lithium ion secondary battery 10 includes a negative electrode 16 composed of a layer 12 having a negative electrode active material and a negative electrode current collector 14, a positive electrode 22 composed of a layer 18 having a positive electrode active material and a positive electrode current collector 20, Electrolytic solution 24 and separator 26 are included. As shown in FIG. 1 (a), the negative electrode 16 and the positive electrode 22 include a layer 12 having a negative electrode active material and a layer 18 having a positive electrode active material on only one side of the negative electrode current collector 14 and the positive electrode current collector 20, respectively. A formed structure may also be used. Further, as shown in FIG. 1B, the negative electrode current collector 14 and the positive electrode current collector 20 have a structure in which a layer 12 having a negative electrode active material and a layer 18 having a positive electrode active material are formed on both surfaces, respectively. You can also.

(First embodiment)
The lithium ion secondary battery of the present embodiment has composite particles including carbon particles and a Li storage material as a negative electrode active material.
FIG. 2 is a cross-sectional view schematically showing composite particles 30 that are negative electrode active materials in the layer 12 having a negative electrode active material of the lithium ion secondary battery shown in FIGS. 1 (a) and 1 (b). is there.

  As shown in FIG. 2, the composite particle 30 includes a carbon material 32 and a Li storage material particle 34. The average particle size of the composite particles 30 is, for example, not less than 500 nm and not more than 60 μm.

  The material of the carbon material 32 can be carbon capable of occluding Li. For example, graphite, fullerene, carbon nanotube, DLC (diamond-like carbon), amorphous carbon, hard carbon, or a mixture thereof can be used. The carbon material 32 is preferably graphite. By doing so, the cycle characteristics of the battery can be reliably improved.

  The material of the Li storage material particles 34 may be a metal microcrystal or an amorphous metal containing an element that forms an alloy with Li. Of these, an amorphous structure is desirable. Specifically, it contains at least one element selected from Si, Sn, Ag, Ge, Pb, In, or Al, and includes a metal, an alloy, a metal oxide, an amorphous metal, or the metal or alloy containing the element. , Metal oxide, and amorphous metal. Further, the Li storage material particle 34 is an alloy of the above-described element that stores Li and Fe, Co, Ni, Cu, Ti, Mo, Ta, Mg, Cr, Nb, Mn, V, W, or Zr. You may contain a mixture. Specifically, a composite material of SiO or SnO and the above metal such as Fe, Co, or Ni can be used as such a material. By doing so, the current collection efficiency can be further improved. Further, the Li storage material particles 34 may be doped with B, P, As, or Sb to lower the resistivity.

  The average particle diameter of the Li storage material particles 34 can be, for example, 20 μm or less. The average particle diameter of the Li storage material particles 34 is preferably 5 μm or less, and more preferably 1 μm or less. By doing so, the cycle life of the lithium secondary battery can be kept long. Moreover, although there is no restriction | limiting in particular in the minimum of the average particle diameter of Li occlusion material particle 34, For example, it can be 10 nm or more.

  Moreover, it is preferable to reduce the average particle diameter of the Li storage material particles 34 with respect to the average radius of the composite particles 30. By doing so, the surface area per volume of the Li storage material particles 34 can be kept large, and in the composite particles 30, the electrical contact between the Li storage material particles 34 and the carbon material 32 containing them can be kept good. it can.

  At least a part of the Li storage material particle 34 is embedded in the carbon material 32, and there are a particle whose surface is completely covered with the carbon material 32 and a particle whose part is exposed to the outside of the carbonaceous material. . Although it is preferable that the surface of the composite particle 30 is completely covered with the carbon material 32, a part of the surface may be exposed to the outside of the carbon material 32. Further, one composite particle 30 includes one or a plurality of Li storage material particles 34 embedded in the carbon material 32. In particular, even if a large number of Li storage material particles 34 are present, there is no problem in terms of characteristics if they are embedded in the carbon material 32. It is preferable that the carbon material 32 is in contact with the Li storage material particles 34. By having such a structure, charge / discharge characteristics are improved.

Here, the composite particle 30 satisfies the following condition (i).
(I) The center of gravity of each of the Li storage material particles 34 present in the composite particle 30 is located inside the composite particle 30.

  When the composite particle 30 satisfies the above (i), the current collecting property of the composite particle 30 is improved. For this reason, when it uses as a negative electrode active material of a secondary battery, the cycling characteristics of a battery can be improved.

  Next, the determination method of (i) will be described with reference to FIGS. 3 (a) and 3 (b). First, a cross-sectional photograph of the composite particle 30 included in the layer 12 having the negative electrode active material is taken with a scanning electron microscope (SEM).

  The cross section of the composite particle 30 can be observed by embedding the composite particle 30 with a resin and observing the sliced slice with an SEM. Here, it is desirable to take a cross-sectional photograph including 5 to 10 composite particles 30 by SEM.

  The cross section may be any one cross section for the composite particle 30. At this time, five or more composite particles 30 are included (FIG. 3A). Moreover, it is desirable that the composite particles 30 included in the cross-sectional photograph of the layer 12 having the negative electrode active material be 10 or less. FIG. 3A illustrates a case where five composite particles 30 are included.

  For any five composite particles 30 present in the obtained cross-sectional photograph, the cross-sectional area and position of each of the Li storage material particles 34 present in the composite particle 30 are calculated, and the geometric center of gravity g1 is calculated. . However, the geometric centroid means the centroid of the two-dimensional figure in the particle cross section. And it is determined whether each geometric gravity center g1 is located in the composite particle 30. FIG.

  For most of the composite particles 30, the geometric centroid g 1 of all the Li storage material particles 34 included in one composite particle 30 is present in the carbon material 32, thereby collecting the current of the composite particles 30. Can be improved. Here, the majority of the composite particles 30 are specifically preferably a majority, more preferably 70% or more of the composite particles 30. Moreover, it is preferable that the geometric center of gravity g1 of all the Li storage material particles 34 in the composite particle 30 exist in the carbon material 32 for all the composite particles 30.

The specific surface area of the composite particle 30 is preferably 10 m ² / g or less. By carrying out like this, the irreversible capacity | capacitance resulting from the irreversible site of the composite particle 30 surface can be reduced.

  Next, a method for producing the composite particle 30 will be described. The composite particle 30 is obtained by mechanically mixing the carbon material 32 and the Li storage material particle 34. In mixing, the carbon material 32 and the Li storage material particles 34 are mechanically pressed to form the Li storage material particles 34 embedded in the carbon material 32.

  Specifically, a jet mill, which is a method in which the raw material powder is placed on a moving gas and collides with each other, hybridization that strikes the powder against a strong wall, and through a narrow space with great force, shear force is applied to the powder. A method using a given mechanofusion is given. Alternatively, a method using a ball mill, a vibrating ball mill, a planetary ball mill, or a rolling ball mill that gives a moving body that does not react with the raw material powder and gives vibration, rotation, or a combination of these to the moving body can be used. The composite particles can also be obtained by a method in which the Li storage material particles 34 are embedded in the carbon material 32 by mechanical pulverization and pressure contact, and then carbonized by mixing with a carbon precursor, or by carbon coating by CVD. 30 can be manufactured.

  Here, particles satisfying the above (i) can be obtained by devising conditions for applying pressure mechanically between the particles. For example, when a planetary ball mill is used, the mixing ratio of the carbon material 32 and the Li storage material particles 34, the particle size, the shape of the particles, the amount of balls used for milling, the particle size of the balls, the number of rotations, and milling are performed. Particles satisfying the above (i) can be obtained by optimizing the size of the container and the volume of the material occupying the container.

  FIG. 6 is a diagram showing a procedure for producing the composite particle 30. First, in order to embed the Li storage material particles 34 in the carbon material 32, the carbon material 32 and the composite particles 30 are mechanically mixed by the above-described method (S11). After mixing for a predetermined time, a part of the composite particles 30, for example, 5 to 10 composite particles 30 are sampled (S12). And it is confirmed whether said (i) is materialized about all the sampled composite particles 30 with the method mentioned above using FIG.

  If the above (i) is established for all the sampled composite particles 30 (YES in S13), mixing is terminated at that time, and composite particles 30 are obtained. If the above (i) is not satisfied for all the sampled composite particles 30 (NO in S13), a cycle composed of mixing and sampling steps is repeated. In this way, most of the composite particles 30 can satisfy the above (i).

In the process of mechanical pulverization and pressure contact, Li storage material particles 34 are embedded in the carbon material 32, and the structure of the carbon material 32 is destroyed at the site where the Li storage material particles 34 are embedded. it is desirable to retain the crystalline carbon region, the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman carbon material 32 is preferably 10 or less.

  Returning to FIG. 1, the negative electrode current collector 14 is an electrode that takes out current to the outside of the battery during charging / discharging or takes in current into the battery from the outside. The negative electrode current collector 14 may be made of any material as long as it is a conductive metal foil. The negative electrode current collector 14 is made of, for example, aluminum, copper, stainless steel, gold, tungsten, or molybdenum. Preferably, the negative electrode current collector 14 is composed of a rolled copper foil or an electrolytic copper foil. The negative electrode current collector 14 has a thickness of about 5 μm to 25 μm, for example.

  The layer 12 having the negative electrode active material can be manufactured, for example, as follows. First, the composite particles 30, a conductive material such as carbon black, and a binder such as polyvinylidene fluoride (PVDF) are dispersed and kneaded with a solvent such as N-methyl-2-pyrrolidone (NMP) to obtain a coating solution. Next, this coating solution is applied onto the negative electrode current collector 14. As a coating method, a doctor blade method, spray coating, or the like can be used. Thereby, the negative electrode 16 having the configuration shown in FIG. Also, as shown in FIG. 4, the negative electrode 16 having the configuration shown in FIG. 1B is manufactured by applying a coating solution on both surfaces of the negative electrode current collector 14.

  Here, the volume filling rate of the negative electrode active material in the layer 12 having the negative electrode active material containing the composite particles 30 is preferably 45% or more and 75% or less. By doing so, the current collecting property is maintained, and the breakage of the composite particles 30 is suppressed, and the charge / discharge cycle characteristics are improved.

  Like the negative electrode current collector 14, the positive electrode current collector 20 is an electrode that takes out current from the outside of the battery during charging and discharging, and takes in current from the outside into the battery. The positive electrode current collector 20 can be made of the same material as the negative electrode current collector 14, or can be made of other materials exemplified as the material of the negative electrode current collector 14.

In the positive electrode 22, examples of the positive electrode active material included in the layer 18 having the positive electrode active material include LiCoO ₂ , Li _x Co _{1 -y My} O ₂ , Li ₂ NiO ₂ , Li _x MnO ₂ , and Li _x MnF _{2. , Li x MnS 2, Li x} Mn 1-y M y O 2, Li x Mn 1-y M y O 2, Li x Mn 1-y M y O 2-z F z, Li x Mn 1-y MyO _{2-z S z, Li x} Mn 2 O 4, Li x Mn 2 F 4, Li x Mn 2 S 4, Li x Mn 2-y M y O 4, Li x Mn 2-y M y O 4-z F _z or Li _x Mn _2-y MyO _4-z S _z (0 <x ≦ 1.5, 0 <y <1.0, Z ≦ 1.0, M represents at least one or more transition metals ) And the like. The layer 18 having the positive electrode active material has a thickness of 10 μm or more and 500 μm or less, for example.

  Like the negative electrode current collector 14, the positive electrode current collector 20 is an electrode that takes out current from the outside of the battery during charging and discharging, and takes in current from the outside into the battery. The positive electrode current collector 20 can be made of the same material as the negative electrode current collector 14, or can be made of other materials exemplified as the material of the negative electrode current collector 14.

  The positive electrode 22 can be manufactured, for example, as follows. First, a positive electrode active material, a conductive material such as carbon black, and a binder such as polyvinylidene fluoride (PVDF) are dispersed and kneaded with a solvent such as N-methyl-2-pyrrolidone (NMP) to obtain a coating solution. . Next, this coating solution is applied onto the positive electrode current collector 20. Here too, a doctor blade method, spray coating, or the like can be used as the coating method. Thereby, the positive electrode 22 having the configuration shown in FIG. Moreover, the positive electrode 22 of the structure shown in FIG.1 (b) is manufactured by apply | coating a coating liquid on both surfaces of the positive electrode electrical power collector 20. FIG.

  Examples of the electrolytic solution 24 include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. (EMC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-ethoxy Chain ethers such as ethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylphenol Lumamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- Aprotic organic solvents such as oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, and N-methylpyrrolidone can be used singly or in combination.

The electrolyte solution 24 can also be used by dissolving a lithium salt that dissolves in these organic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ). ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, and the like can be used. Further, a polymer electrolyte can be used instead of the above-described electrolytic solution.

  As the separator 26, for example, a material having a porous film such as a polyolefin such as polypropylene or polyethylene, or a fluororesin can be used.

  The lithium ion secondary battery 10 may be composed of a negative electrode 16, a separator 26, and a positive electrode 22 that are laminated or wound, and then housed in a battery can or made of a laminate of a synthetic resin and a metal foil. It can be manufactured by sealing with a flexible film or the like.

  The shape of the container that can be used in the lithium secondary battery of the present invention can be, for example, a bottomed cylindrical shape, a bottomed rectangular tube shape, or a bag shape. These containers can be formed from a film material, a metal plate, etc., for example. A container (metal can) made from a metal plate can be formed from aluminum, iron, stainless steel, nickel, or the like. Examples of the film material constituting the container include a metal film, a resin film such as a thermoplastic resin, a composite film including a metal layer and a resin layer, for example, one or both sides of a flexible metal layer like a thermoplastic resin. For example, a laminate film having a structure coated with a resin layer may be used.

  Among these, a laminate film is desirable because it is lightweight, has high strength, and can prevent moisture from entering from the outside. The metal film can be formed from, for example, aluminum, iron, stainless steel, nickel, or the like. The resin layer which comprises the said composite film can be formed from a thermoplastic resin, for example. Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene. The resin layer can be formed from one kind of resin or two or more kinds of resins. The metal layer of the composite film can be formed from, for example, aluminum, iron, stainless steel, nickel, or the like. The metal layer can be formed of one kind of metal or two or more kinds of metals. Among these, it is desirable to form from aluminum that can prevent water from entering the battery.

  The container manufactured using the composite film is sealed by, for example, heat sealing. For this reason, it is desirable to arrange a thermoplastic resin on the inner surface of the container. The melting point of the thermoplastic resin is preferably 120 ° C or higher, more preferably 140 ° C to 250 ° C. Examples of the thermoplastic resin include polyolefins such as polyethylene and polypropylene. In particular, it is desirable to use polypropylene having a melting point of 150 ° C. or higher because the sealing strength of the heat seal portion is increased.

  The thickness of the film material and the metal plate is desirably 0.5 mm or less. When the thickness of the film material and the metal plate exceeds 0.5 mm, improvement of the volume energy density and weight energy density of the lithium ion secondary battery is hindered. The thickness of the film material and the metal plate is more preferably 0.05 mm or more and 0.5 mm or less. By making the thickness of the film material and the metal plate within the above-mentioned range, the strength of the container can be ensured and the volume energy density and the weight energy density of the lithium ion secondary battery can be improved. . A particularly desirable thickness range is 0.05 mm or more and 0.5 mm or less. Thereby, thinning and weight reduction of a battery are realizable, ensuring the intensity | strength of a container.

  Next, the operation of the negative electrode 16 of the battery of FIG. 1 will be described in detail. During charging, the negative electrode 16 receives lithium ions from the positive electrode 22 side through the electrolytic solution 24. Next, the lithium ions are occluded in the carbon material 32 and the Li occlusion material particle 34 in the composite particle 30 included in the layer 12 having the negative electrode active material. Conversely, during discharge, lithium ions occluded during charging are released from the carbon material 32 and the Li occlusion material particles 34. At the time of charging, since the Li storage material particles 34 have a large storage amount, the volume expansion coefficient becomes larger than that of the carbon material. Therefore, the composite particles 30 containing the Li storage material particles 34 also expand in volume. On the other hand, at the time of discharge, Li is released from the Li storage material particles 34, so that the Li storage material particles 34 contract to return to the original volume.

  When the occlusion and release of lithium ions are repeated, the Li storage material particles 34 are gradually pulverized due to the stress due to volume expansion / contraction. However, in the present embodiment, since the average radius of the Li storage material particles 34 with respect to the average radius of the composite particles 30 is small, and the center of gravity of the Li storage material particles 34 exists in the carbon material 32, The electrical contact between the Li storage material particles 34 and the carbon material 32 containing them can be kept good. Thereby, deterioration of the current collecting property of the negative electrode 16 can be suppressed.

(Second embodiment)
In the lithium ion secondary battery described in the first embodiment, the composite particles 30 used as the negative electrode active material can be configured as follows.

In the present embodiment, the Li storage material particles 34 are preferably uniformly distributed in the composite particles 30 and satisfy the following (ii).
(Ii) With respect to all the Li storage material particles 34 existing in one composite particle 30 in one cross section of the composite particle 30, the position of each center of gravity is calculated based on the cross-sectional area, and the position of the center of gravity is calculated. A composite particle having a maximum area centered on the center of gravity of the composite particle 30 when the center of gravity of all the Li storage material particles 34 existing in the composite particle 30 is calculated by weighting the cross-sectional area. The center of gravity of the entire Li storage material particle 34 is located in 30 inscribed circles.

  Since the composite particles 30 satisfy the above (ii), the Li storage material particles 34 are stably embedded in the composite particles 30. For this reason, the current collection property of the carbon material 32 and the Li storage material particle 34 is suitably ensured. Therefore, the cycle characteristics of the battery can be improved when used as a negative electrode active material.

  Next, the authorization method (ii) will be described with reference to FIGS. 4 (a) to 4 (c). First, as in the first embodiment, a photograph of an arbitrary cross section of the composite particle 30 including five or more composite particles 30 is taken with a scanning electron microscope (SEM). The composite particles 30 included in the cross-sectional photograph are desirably 5 or more and 10 or less.

  For any five composite particles 30 present in the obtained image, the area and position of each Li storage material particle 34 present in the composite particle 30 are calculated, and the position of the geometric gravity center g1 is obtained.

  Further, with all the Li storage material particles 34 present in one composite particle 30 as one system, the position of the center of gravity of the Li storage material particles 34 and the cross-sectional area of each of the Li storage material particles 34, the Li storage material particles The entire center of gravity g2 is calculated (FIG. 4B).

  Further, the center of gravity g3 of the entire composite particle is obtained. For each composite particle 30, an inscribed circle having a maximum area around the center of gravity g3 of the composite particle is drawn, and it is determined whether the center of gravity g2 of the entire Li storage material particle is located in the inscribed circle.

  Since the composite particle 30 according to the present embodiment satisfies the condition (ii), the dispersibility of the Li storage material particles 34 in the carbon material 32 is ensured satisfactorily. For this reason, it can use suitably as a negative electrode active material of the lithium ion secondary battery excellent in the current collection characteristic.

In this embodiment, the specific gravity of each Li storage material particle 34 is substantially equal, and each Li storage material particle 34 has a shape close to a sphere. For this reason, the concept of weight can be approximated using the area of each particle. Thus, the specific gravity of each particle can be replaced with the volume. And weighting according to the cross-sectional area of each particle | grain can calculate the gravity center g2 of the whole Li storage material particle reflecting the specific gravity of each particle | grain.

  The composite particle 30 according to the present embodiment can be obtained by devising conditions for applying pressure mechanically between particles. For example, when a planetary ball mill is used, the mixing ratio of the carbon material 32 and the Li storage material particles 34, the particle size, the shape of the particles, the amount of balls used for milling, the particle size of the balls, the number of rotations, and milling are performed. Particles satisfying the condition (ii) can be obtained by optimizing the size of the container and the volume of the material occupying the container.

  For the production of the composite particle 30, the procedure shown in FIG. 6 described in the first embodiment can be used. First, in order to embed the Li storage material particles 34 in the carbon material 32, the carbon material 32 and the composite particles 30 are mechanically mixed by the above-described method (S11). After mixing for a predetermined time, a part of the composite particles 30, for example, 5 to 10 composite particles 30 are sampled (S12). Then, by the method described above with reference to FIG. 4, it is confirmed whether or not the condition (ii) is satisfied for all sampled composite particles 30.

  By satisfying the above condition (ii) for most of the composite particles 30, the current collecting property of the composite particles 30 can be improved. Here, the majority of the composite particles 30 are specifically preferably a majority, more preferably 70% or more of the composite particles 30. Moreover, it is preferable that all the composite particles 30 satisfy the condition (ii).

(Third embodiment)
In the lithium ion secondary battery described in the first embodiment, the composite particles 30 used as the negative electrode active material can be configured as follows.

In the present embodiment, it is preferable that the Li-occlusion material particles 34 are uniformly distributed in the composite particle 30 and satisfies the following (iii).
(Iii) A value obtained by multiplying the value obtained by dividing the standard deviation of the distance between the center of gravity of all the Li storage material particles 34 included in one composite particle 30 and the center of gravity of the composite particle 30 by the average value by 100. That is, the variation coefficient is 10 or more.

  Next, the authorization method (iii) will be described with reference to FIGS. 5 (a) and 5 (b). Whether or not the composite particle 30 satisfies the above (iii) is identified by observing an arbitrary cross section of the composite particle 30 with a scanning electron microscope (SEM) in the same manner as in the first and second embodiments. .

  That is, the cross section of the composite particle 30 can be observed by embedding the composite particle 30 with a resin and observing a slice obtained by slicing the composite particle 30 with an SEM. Here, it is desirable to take a cross-sectional photograph including 5 to 10 composite particles 30 by SEM.

  For any five composite particles 30 present in the obtained image, the area and position of each of the composite particles 30 and the Li storage material particles 34 present in the composite particles 30 are calculated, and the same as in the first embodiment. Thus, the position of the geometric gravity center g1 is obtained. Further, the position of the center of gravity g3 of the entire composite particle 30 is obtained in the same manner as in the second embodiment (FIG. 5A).

  For all the Li storage material particles 34 present in one composite particle 30, the distance L between the center of gravity g1 of the Li storage material particle 34 and the center of gravity g3 of the composite particle 30 is calculated (FIG. 5B).

  For all the Li storage material particles 34 present in one composite particle 30, the standard deviation and average value of the distance L are calculated, and the variation coefficient, which is a value obtained by multiplying the standard deviation by the average value, is 100. calculate. If the variation coefficient is 10 or more, it can be determined that the condition (iii) of the present embodiment is satisfied.

  Since the composite particle 30 according to the present embodiment satisfies the above (iii), the dispersibility of the Li storage material particles 34 in the carbon material 32 is ensured satisfactorily. Therefore, when the distribution of the Li storage material particles 34 in the composite particles 30 satisfies the above (iii), a uniform force is applied to the composite particles 30 even when the Li storage material particles 34 expand and contract during charging and discharging. In addition, the destruction of the composite particles 30 is suppressed, and the current collection characteristics are improved. Therefore, it can be suitably used as a negative electrode active material for a lithium ion secondary battery.

  The composite particles 30 according to the present embodiment can obtain particles satisfying the above (iii) by devising conditions for applying mechanical pressure to the particles. For example, when a planetary ball mill is used, the mixing ratio of the carbon material 32 and the Li storage material particles 34, the particle size, the shape of the particles, the amount of balls used for milling, the particle size of the balls, the number of rotations, and milling are performed. Particles satisfying the above (iii) can be obtained by optimizing the size of the container and the volume of the material occupying the container.

  For the production of the composite particle 30, the procedure shown in FIG. 6 described in the first and second embodiments can be used. First, in order to embed the Li storage material particles 34 in the carbon material 32, the carbon material 32 and the composite particles 30 are mechanically mixed by the above-described method (S11). After mixing for a predetermined time, a part of the composite particles 30, for example, 5 to 10 composite particles 30 are sampled (S12). And it is confirmed whether said (iii) is materialized about all the sampled composite particles 30 by the method mentioned above using FIG.

  By satisfying the above (iii) for most of the composite particles 30, the current collecting property of the composite particles 30 can be improved. Here, the majority of the composite particles 30 are specifically preferably a majority, more preferably 70% or more of the composite particles 30. Moreover, it is preferable that all the composite particles 30 satisfy the above (iii).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to these.

(Example)
(Example 1)
As the Li storage material particles 34, amorphous Si particles having an average particle diameter of 5 μm were used, and as the carbon material 32, artificial graphite particles having an average particle diameter of 30 μm were used. A ball mill in which the amorphous Si particles and the artificial graphite particles are blended at a weight ratio of 3: 7, and this is repeated with a planetary ball mill apparatus with a stop time of 10 minutes every 20 minutes to repeat mechanical pressure welding. Treatment was applied for 20 hours. The ball mill container and the ball having a diameter of 10 mm were made of zirconia, and the powder adjustment and the ball mill were performed in an Ar atmosphere. The N-methylpyrrolidone solution of PVDF and the Si-graphite composite powder were kneaded so that the weight ratio of Si-graphite composite powder: PVDF = 85: 15 was applied to a Cu foil having a thickness of 20 μm. This was dried at 120 ° C. for 10 minutes and then dried at 90 ° C. for 24 hours. Then, it pressure-molded until the volume filling rate of the electrode application part became 60% with the roller press, and was finally punched out to a diameter of 20 mm, and it was set as the negative electrode.

As the positive electrode active material, LiCoO ₂ powder having an average particle diameter of 10 μm was used. The mixture was mixed so that the weight ratio of LiCoO ₂ powder: graphite: PVDF = 90: 6: 4 was formed to form a slurry. At this time, an N-methylpyrrolidone solution was used as in the negative electrode. This slurry was sufficiently kneaded and then applied to an Al foil having a thickness of 20 μm. After drying this at 120 ° C. for 1 hour, the electrode was pressure-molded by a roller press and finally punched out to a diameter of 20 mm to obtain a positive electrode. Here, since the capacity of the negative electrode was large, the weight ratio of the positive electrode mixture to the negative electrode mixture was set to 7.

The above-described negative electrode and positive electrode constitute a coin-type battery, and their characteristics were evaluated. As the electrolytic solution, a solution obtained by dissolving 1 mol / liter of LiPF ₆ in a 3: 7 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used.

  A charge / discharge cycle test was performed in which the battery was charged at a charge current of 1 mA and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 mA and a discharge end voltage of 2.7 V.

(Example 2)
Polycrystalline Si particles having an average particle diameter of 5 μm were used as the Li storage material particles 34. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 3)
As the Li storage material particles 34, amorphous Sn particles having an average particle diameter of 5 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 4)
As the Li storage material particles 34, amorphous SiO particles having an average particle diameter of 5 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 5)
As the Li storage material particles 34, amorphous SnO particles having an average particle diameter of 1 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 6)
As the Li storage material particles 34, amorphous FeSi particles having an average particle diameter of 5 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 7)
As the Li storage material particles 34, amorphous NiSi particles having an average particle diameter of 5 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 8)
As the Li storage material particles 34, amorphous TiSi particles having an average particle diameter of 5 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 9)
As the Li storage material particles 34, amorphous Ge particles having an average particle diameter of 5 μm were used. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 10)
As the Li storage material particles 34, SiO particles and Ni particles were mixed at a weight ratio of 1: 4, pressed by ball mill treatment, fired, and then composite particles having an average particle size of 5 μm by pulverization treatment were used. . Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 11)
As the Li storage material particles 34, SiO particles and Fe particles were mixed at a weight ratio of 1: 4, pressed by ball mill treatment, fired, and then composite particles having an average particle size of 5 μm by pulverization treatment were used. . Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 12)
The negative electrode was manufactured by performing the mechanical pressure-contact process by the ball mill performed in Example 1 for 1 hour. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

  In addition, the negative electrode active material of Examples 1-12 shall satisfy | fill the conditions of (ii) mentioned above.

(Example 13)
A negative electrode was produced without performing the mechanical pressure contact treatment by the ball mill performed in Example 1. Other than this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 14)
The negative electrode was manufactured by performing the mechanical pressure-contact process by the ball mill performed in Example 1 for 15 minutes. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 15)
An artificial graphite particle having an average particle diameter of 30 μm was used as the carbon material 32, and a negative electrode not including the Li storage material particles 34 was produced without performing the mechanical pressure contact treatment by the ball mill performed in Example 1. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Evaluation 1)
The peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 in an argon laser Raman analysis of the carbonaceous portion of the composite particle 30 used in Examples 1 to 15 shown in Table 1. In addition, Table 1 shows capacity retention rates after 100 cycles of Examples 1 to 15. The capacity retention rate after 100 cycles was calculated using the following formula (1).
(Discharge capacity in each cycle) / (Discharge capacity in the fifth cycle) (1)

Example 1 Example 12, the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 in an argon laser Raman analysis of the carbonaceous portion of the composite particle 30 took the value of 1 to 10. On the other hand, in Examples 13 to 15, the peak intensity ratio was 12 to 10,000. Further, in Examples 1 to 12, the energy density of the negative electrode was 1.2 as compared with Example 15 in which the active material was only carbon. In addition, the capacity retention rate after 100 cycles of Examples 1 to 12 increased by 24% or more compared to Examples 13 and 14 where the peak intensity ratio of Raman analysis was in the range exceeding 10.

Example 13 peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 in an argon laser Raman analysis is more than 10, Example 14, is poor adhesion of the Li storage material particles 34 and the carbon material 32, current collecting property is deteriorated In contrast, cycle deterioration occurs, but in Examples 1 to 12, it is considered that the above characteristics were obtained because the adhesion between the Li storage material particles 34 and the carbon material 32 was good.

  As described above, Examples 1 to 12 proved that a battery having good cycle characteristics using the Li storage material as a part of the negative electrode active material can be provided.

(Example 16)
As the Li storage material particles 34, metal Sn particles having an average particle diameter of 5 μm were used. The negative electrode volume filling rate after preparation of the negative electrode was 45%. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 17)
Polycrystalline Sn particles having an average particle diameter of 5 μm were used as the Li storage material particles 34. The negative electrode volume filling rate after preparation of the negative electrode was 75%. Except for this, a coin-type battery was produced by the same electrode design and production method as in Example 1.

(Example 18)
The negative electrode volume filling rate after preparation of the negative electrode was set to 35%. Other than this, a coin-type battery was manufactured by the same electrode design and manufacturing method as in Example 16.

(Example 19)
The negative electrode volume filling rate after preparation of the negative electrode was 80%. Other than this, a coin-type battery was manufactured by the same electrode design and manufacturing method as in Example 16.

(Example 20)
Polycrystalline Sn particles having an average particle diameter of 20 μm were used as the Li storage material particles 34. Other than this, a coin-type battery was manufactured by the same electrode design and manufacturing method as in Example 12.

(Evaluation 2)
Table peak intensity of 1360 cm ^-1 ratio 1580 cm ^-1 in an argon laser Raman analysis of the carbonaceous portion of the composite particles 30, the packing density of the negative electrode coating portion, the capacity maintenance rate after 100 cycles was used in Example 16 to Example 19 It is shown in 2. The capacity retention rate after 100 cycles was calculated by the equation (1).

  From Table 2, Example 16 and Example 17 in which the volume filling rate of the negative electrode application part is in the range of 45% to 75% are Example 18, and the volume filling rate of the negative electrode application part is 35%. Compared with Example 19 in which 80%, the capacity retention after 100 cycles increased by 30% or more. In Example 18 in which the volume filling rate of the negative electrode application part is 35%, the current collection between the particles is poor, and thus cycle deterioration occurs. In Example 16 and Example 17, the current collection between the particles is good. It is considered that the above characteristics were obtained.

  Further, in Example 19 in which the volume filling rate of the negative electrode application part is 80%, since there are few voids in the negative electrode application part, the influence of expansion and contraction of the Li storage material during charge / discharge is unavoidable, and cycle deterioration occurs. On the other hand, in Example 16 and Example 17, since the influence of the Li storage material can be alleviated by the voids present in the negative electrode coating portion, it is considered that the above characteristics were obtained. Thus, Example 16 and Example 17 proved that a battery having good cycle characteristics using the Li storage material can be provided.

Further, the peak intensity of 1360 cm ^-1 ratio 1580 cm ^-1 in an argon laser Raman analysis of the carbonaceous portion of the composite particle 30 used in Example 16 and Example 20, the capacity maintenance after particle size 100 cycles of Li storage material particles 34 The rates are shown in Table 3. The capacity retention rate after 100 cycles was calculated by the equation (1).

  In Example 16 in which the particle size of the Li storage material particles 34 was 5 μm, the capacity retention rate after 100 cycles increased by 30% or more compared to Example 20 in which the particle size of the Li storage material particles 34 was 20 μm. In Example 20 in which the particle size of the Li storage material particles 34 is 20 μm, cycle deterioration occurs due to pulverization due to expansion and contraction of the Li storage material during charging and discharging, whereas in Example 16, pulverization due to expansion and contraction of the Li storage material. Since the degree is small, it is considered that the above characteristics were obtained. Thus, according to Example 16, it was found that a battery having good cycle characteristics using the Li storage material can be provided.

(Example 21)
Sn Li alloy particles having an average particle diameter of 5 μm were used as the Li storage material particles 34, and scaly natural graphite particles having an average particle diameter of 40 μm were used as the carbon material 32. The above-mentioned SnSi alloy particles and the above-mentioned natural graphite particles were blended at a weight ratio of 1: 4, and subjected to mechanofusion treatment in which mechanical press contact was repeated. The treated composite particles 30 were taken out as appropriate, and cross-sectional SEM observation of the particles was performed. An image containing five or more composite particles 30 is selected, and the center of gravity g1 of the Li storage material particles 34 is calculated from the obtained image according to the calculation method described above with reference to FIG. It was determined whether or not the center of gravity g1 of 34 is located, and the mechanofusion process was repeated until the condition (i) was satisfied.

  Further, heat treatment was performed at 1000 ° C. for 2 hours in an Ar atmosphere. An N-methylpyrrolidone solution of PVDF and an SnSi alloy-graphite composite powder were kneaded so as to have a weight ratio of SnSi alloy-graphite composite powder: PVDF = 90: 10 and applied to a Cu foil having a thickness of 20 μm. After drying this at 120 degreeC for 1 hour, the electrode was pressure-molded with the roller press, and it was set as the negative electrode, after cut | disconnecting to 7 cm width.

As the positive electrode active material, LiCoO ₂ powder having an average particle diameter of 10 μm was used. The mixture was mixed so that the weight ratio of LiCoO ₂ powder: graphite: PVDF = 90: 6: 4 was formed to form a slurry. At this time, an N-methylpyrrolidone solution was used as in the negative electrode. This slurry was sufficiently kneaded and then applied to an Al foil having a thickness of 20 μm. After drying this at 120 degreeC for 1 hour, the electrode was pressure-molded with the roller press and it was set as the positive electrode.

The obtained negative electrode and positive electrode constituted a cylindrical battery, and the characteristics were evaluated. As the electrolytic solution, a solution obtained by dissolving 1 mol / L of LiPF ₆ in a 3: 7 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used.

  A charge / discharge cycle test was performed in which the battery was charged at a charge current of 1 A and a charge end voltage of 4.2 V, and discharged at a discharge current of 1 A and a discharge end voltage of 2.7 V.

(Example 22)
The composite particles 30 obtained in the middle of the mechanofusion treatment of Example 21 that do not satisfy the condition (i) were used. Except for this, a cylindrical battery was produced by the same SEM observation, electrode design and production method as in Example 21.

(Evaluation 3)
Examples 21 and peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 in an argon laser Raman analysis of the carbonaceous portion of the composite particle 30 used in Example 22, the minimum distance between the composite particles 30 of each Li storage material particles 34 Table 4 shows the value (μm) and the capacity retention after 100 cycles. The capacity retention rate after 100 cycles was calculated by the equation (1).

  In Example 21 in which the center of gravity g1 of all the Li storage material particles 34 is located in the composite particle 30 as compared with Example 22 including the Li storage material particle 34 in which the center of gravity g1 of the Li storage material particle 34 is not located in the composite particle 30. The cycle characteristics were improved by 30%. In Example 22 including the Li storage material particles 34 in which the center of gravity g1 of the Li storage material particles 34 particles is not located in the composite particles 30, the Li storage material particles 34 are easily detached from the composite particles 30 during charge and discharge, and thus the current collection characteristics are high. In contrast, in Example 21, the Li storage material particles 34 are unlikely to be detached from the composite particles 30, so it is considered that the above characteristics were obtained. Thus, it was found that by using the composite particles 30 that satisfy the above condition (i), it is possible to provide a battery having good cycle characteristics using a Li storage material.

(Example 23)
Si Li alloy particles having an average particle diameter of 5 μm were used as the Li storage material particles 34, and scaly natural graphite particles having an average particle diameter of 50 μm were used as the carbon material 32. The SiGe alloy particles and the natural graphite particles were blended at a weight ratio of 1: 4, and subjected to mechanofusion treatment in which mechanical press contact was repeated.

  The treated composite particles 30 were taken out as appropriate, and cross-sectional SEM observation of the particles was performed. An image containing five or more composite particles 30 is selected, and the center of gravity g2 of the entire m system and the inscribed circle of the composite particle 30 are calculated from the obtained image according to the calculation method described above with reference to FIG. It was determined whether or not the center of gravity g2 is located in the inscribed circle of the composite particle 30, and the mechanofusion process was repeated until the above condition (ii) was satisfied.

  An N-methylpyrrolidone solution of PVDF and a SiGe-graphite composite powder were kneaded so as to have a weight ratio of SiGe alloy-graphite composite powder: PVDF = 90: 10, and applied to a Cu foil having a thickness of 20 μm. After drying this at 120 degreeC for 1 hour, the electrode was pressure-molded with the roller press and cut into 7 cm width, and it was set as the negative electrode. Except for this, a cylindrical battery was fabricated by the same electrode design and fabrication method as in Example 21.

(Example 24)
The composite particles 30 obtained in the middle of the mechanofusion process of Example 23 were used that did not satisfy the conditions of the calculation method (ii). Except for this, a cylindrical battery was fabricated by the same electrode design and fabrication method as in Example 21.

(Evaluation 4)
Example 23 and Example 24 in the peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 in an argon laser Raman analysis of the carbonaceous portion of the composite particles 30 used, the entire system of the center of gravity g2 and inscribed circle of the composite particle 30, 100 cycles The subsequent capacity retention rate is shown in Table 5. The capacity retention rate after 100 cycles was calculated using the above formula (1).

  In Example 23 in which the center of gravity g2 of the entire system is located in the inscribed circle of the composite particle 30 as compared with Example 24 including the composite particle 30 in which the center of gravity g2 of the entire system is not located in the inscribed circle of the composite particle 30, The characteristic was improved by 32%. In Example 24 including the composite particles 30 in which the center of gravity g2 of the entire system is not located in the inscribed circle of the composite particles 30, the position distribution in the composite particles 30 of the Li storage material particles 34 is biased. The composite particles 30 are easily broken due to the expansion and contraction of the material particles 34, whereas in Example 23, the Li storage material particles 34 are not easily detached from the composite particles 30, so it is considered that the above characteristics were obtained. Thus, it was found that by using the composite particles 30 satisfying the above condition (ii), a battery having good cycle characteristics using a Li storage material can be provided.

(Example 25)
As the Li storage material particles 34, metal Al particles having an average particle diameter of 5 μm were used, and as the carbon material 32, spherical artificial graphite having an average particle diameter of 50 μm was used. The metal Al particles and the spherical artificial graphite particles were blended at a weight ratio of 1: 4, and subjected to ball mill treatment in which mechanical press contact was repeated with a vibration type ball mill apparatus. The treated composite particles 30 were taken out as appropriate, and cross-sectional SEM observation of the particles was performed. An image containing five or more composite particles 30 was selected, and a variation coefficient was calculated from the obtained image according to the calculation method described above, and the ball mill process was repeated until the above condition (iii) was satisfied.

  The ball mill container and the ball having a diameter of 10 mm were made of zirconia, and the powder adjustment and the ball mill were performed in an Ar atmosphere. Furthermore, heat treatment was performed at 1200 ° C. for 2 hours in an Ar atmosphere. An N-methylpyrrolidone solution of PVDF and an Al-graphite composite powder were kneaded so that the weight ratio of Al-graphite composite powder: PVDF = 90: 10 was applied to a Cu foil having a thickness of 20 μm. After drying this at 120 degreeC for 1 hour, the electrode was pressure-molded with the roller press and cut into 7 cm width, and it was set as the negative electrode. Except for this, a cylindrical battery was fabricated by the same electrode design and fabrication method as in Example 21.

(Example 26)
The composite particles 30 obtained in the course of the ball mill treatment of Example 25 were used that did not satisfy the conditions of the calculation method (iii) described above. Except for this, a cylindrical battery was fabricated by the same electrode design and fabrication method as in Example 21.

(Evaluation 5)
Table 6 shows the results of the laser Raman measurement and the cycle characteristic test of Example 25 and Example 26. Compared with Example 26 in which the variation coefficient was 9, Example 25 in which the variation coefficient was 30 improved the cycle characteristics by 25%. In Example 26 in which the variation coefficient is 9, since the distance from the center of the composite particle 30 of the Li storage material particle 34 is small, a specific content in the composite particle 30 is caused by expansion and contraction of the Li storage material particle 34 during charge and discharge. Since the load is applied to the part and the composite particles 30 are easily broken, the current collecting characteristics are deteriorated.

  On the other hand, in Example 25, since the Li storage material particles 34 are uniformly dispersed in the composite particles 30, the composite particles 30 are not easily broken even during charge and discharge, and it is considered that the above characteristics were obtained. Thus, it was found that by using the composite particles 30 satisfying the above condition (iii) as the negative electrode active material, a battery having good cycle characteristics using the Li storage material can be provided.

It is the schematic which shows the structure of the lithium ion secondary battery in embodiment. It is sectional drawing which shows the structure of the negative electrode active material in embodiment. It is sectional drawing which shows the structure of the negative electrode active material in embodiment. It is sectional drawing which shows the structure of the negative electrode active material in embodiment. It is sectional drawing which shows the structure of the negative electrode active material in embodiment. It is a figure which shows the preparation procedures of the composite particle in embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 12 Negative electrode active material 14 Negative electrode collector 16 Negative electrode 18 Positive electrode active material 20 Positive electrode collector 22 Positive electrode 24 Electrolyte 26 Separator 30 Composite particle 32 Carbon material 34 Li storage material particle

Claims (12)

In the carbon material particles, including composite particles in which at least a part of Li storage material particles capable of occluding and releasing lithium are embedded,
The center of gravity of each of the Li storage material particles is located in the composite particle,
Negative electrode active material for a secondary battery peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman of the carbon material particles characterized in that 10 or less. In the carbon material particles, including composite particles in which at least a part of Li storage material particles capable of occluding and releasing lithium are embedded,
Peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman of the carbonaceous material particles is 10 or less,
In one cross section of the composite particle,
For all the Li storage material particles present in one composite particle, calculate the position of each center of gravity based on the cross-sectional area,
When the center of gravity of all the Li storage material particles present in one of the composite particles is calculated by multiplying the position of the center of gravity by the weight of the cross-sectional area,
A negative electrode active material for a secondary battery, characterized in that the center of gravity of the entire Li storage particle is located in an inscribed circle of the composite particle having a maximum area centered on the center of gravity of the composite particle. In the carbon material particles, including composite particles in which at least a part of Li storage material particles capable of occluding and releasing lithium are embedded,
Peak intensity ratio of 1360 cm ^-1 relative to 1580 cm ^-1 with an argon laser Raman of the carbonaceous material particles is 10 or less,
A variation coefficient obtained by multiplying a value obtained by dividing the standard deviation of the distance between the center of gravity of each of the Li storage material particles contained in one composite particle and the center of gravity of the composite particle by the average value of the distances by 100 Is a negative electrode active material for a secondary battery, wherein   4. The negative electrode active material for a secondary battery according to claim 1, wherein the Li storage material particles are at least one metal selected from the group consisting of Si, Ge, In, Sn, Ag, Al, or Pb. 5. Or the negative electrode active material for secondary batteries characterized by including the oxide.   4. The negative electrode active material for a secondary battery according to claim 1, wherein the Li storage material particles are at least one metal selected from the group consisting of Si, Ge, In, Sn, Ag, Al, or Pb. 5. Or an alloy or a mixture of the oxide and at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Ti, Mo, Ta, Mg, Cr, Nb, Mn, V, W, and Zr. A negative electrode active material for a secondary battery, comprising:   6. The negative electrode active material for a secondary battery according to claim 1, wherein the Li storage material particles have an amorphous structure.   The negative electrode active material for a secondary battery according to any one of claims 1 to 6, wherein an average particle size of the Li storage material particles in the composite particles is 5 µm or less. .   A negative electrode for a secondary battery comprising a layer having a negative electrode active material for a secondary battery according to claim 1 and a negative electrode current collector.   9. The negative electrode for a secondary battery according to claim 8, wherein a volume filling rate of the negative electrode active material in the layer having the negative electrode active material is 45% or more and 75% or less.   A secondary battery comprising at least a positive electrode and a negative electrode, comprising the negative electrode for a secondary battery according to claim 8 or 9. A step of mechanically mixing carbon material particles and lithium storage material particles capable of occluding and releasing lithium to produce composite particles;
Sampling and inspecting the obtained composite particles;
In order,
As a result of the inspection, when the sampled composite particles satisfy any of the following conditions (i) to (iii), the mixing operation is terminated.
(I) The center of gravity of the Li storage material particles is located in the composite particles. (Ii) In one cross section of the composite particles,
For all the Li storage material particles present in one composite particle, calculate the position of each center of gravity based on the cross-sectional area,
When the center of gravity of all the Li storage material particles present in one of the composite particles is calculated by multiplying the position of the center of gravity by the weight of the cross-sectional area,
The center of gravity of the Li-occlusion particle is located in the inscribed circle of the composite particle having the maximum area centered on the center of gravity of the composite particle. (Iii) All contained in one composite particle The variation coefficient obtained by multiplying the standard deviation of the distance between the center of gravity of each of the Li storage material particles and the center of gravity of the composite particles by the average value of the distances by 100 is 10 or more. A step of obtaining a negative electrode active material by the method for producing a negative electrode active material according to claim 11;
A step of preparing a paste by dissolving or dispersing the negative electrode active material and a binder in a solvent;
Applying the paste onto the current collector and then drying the paste;
The manufacturing method of the negative electrode for secondary batteries characterized by including.

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