JP3746501B2 - ELECTRODE MATERIAL FOR LITHIUM SECONDARY BATTERY, LITHIUM SECONDARY BATTERY, AND METHOD FOR PRODUCING ELECTRODE MATERIAL FOR LITHIUM SECONDARY BATTERY - Google Patents

Description

  The present invention relates to an electrode material for a lithium secondary battery, a method for producing the same, and a lithium secondary battery.

As an electrode material for a lithium secondary battery that can be alloyed with Li and exhibits a high charge / discharge capacity, an alloy material containing Si, Sn, or the like has been studied. These alloy materials are said to be superior in cycle characteristics in an amorphous structure or a fine crystalline structure rather than a crystalline structure. For example, in order to obtain an alloy material containing Si and having an amorphous structure or a fine crystalline structure, generally, other elements such as Al are added to Si to form a molten alloy, which is rapidly cooled to obtain a quenched alloy. Means to do this have been proposed.
JP 2002-216746 A

  However, in the case of producing a quenched alloy containing Si, in order to make the quenched alloy microstructure amorphous or fine crystalline, it is necessary to prevent the precipitation of a relatively large Si single phase. The content of Si must be at least 50% or less. When the Si content is 50% or less, there is a problem that the amount of the negative electrode active material is substantially reduced and the charge / discharge capacity is lowered.

  In addition, as a means for obtaining 100% Si and an amorphous or fine crystallized structure, there is a means for forming a Si film by a CVD method using silane gas or the like. There is a problem that a sufficient amount of electrode material cannot be obtained.

  The present invention has been made in view of the above circumstances, and provides an electrode material for a lithium secondary battery that has a fine crystalline structure and contains Si as a main component, and a lithium secondary battery including the electrode material. The purpose is to do. Moreover, an object of this invention is to provide the manufacturing method of the said electrode material for lithium secondary batteries.

In order to achieve the above object, the present invention employs the following configuration.
The electrode material for a lithium secondary battery of the present invention contains Si as a main component, and the interplanar spacing of the (111) plane of Si by X-ray diffraction is in the range of 3.15 mm to 3.20 mm. Features.
The electrode material for a lithium secondary battery of the present invention contains Si and one or more elements Y selected from Ag, Cu, and Au, and contains Si (111 by X-ray diffraction). ) The surface spacing is in the range of 3.15 mm to 3.20 mm.

According to the above configuration, since the surface spacing of the Si (111) plane by X-ray diffraction is in the above range and has a microcrystalline structure, the volume change of the electrode material itself accompanying charge / discharge is reduced. , Cycle characteristics can be improved.
Further, by including the element Y, the specific resistance of the electrode material itself can be reduced. Thereby, the alloying of lithium with respect to the electrode material at the time of charge becomes easy, and the charge / discharge capacity of the electrode material can be increased.

An electrode material for a lithium secondary battery according to the present invention is the electrode material for a lithium secondary battery described above, and contains Si and an element X that can be alloyed with Si, and the content of Si is SiX. It is formed by removing the element X by chemical treatment from a quenched alloy that is equal to or lower than the eutectic point of the alloy. However, the element X is Al, B, P, Ge, Sn, Pb, Ni, Co, Mn, Mo, Cr, V, Cu, Fe, Ni, W, Ti, Zn, alkali metal, alkaline earth metal Is at least one element.
The electrode material for a lithium secondary battery according to the present invention is the electrode material for a lithium secondary battery described above, and contains the element X which can be alloyed with Si and Si and the element Y, and the Si material. It is formed by removing the element X by chemical treatment from a quenched alloy having a content equal to or lower than the eutectic point of the SiX alloy. However, the element X is Al, B, P, Ge, Sn, Pb, Ni, Co, Mn, Mo, Cr, V, Cu, Fe, Ni, W, Ti, Zn, alkali metal, alkaline earth metal Is at least one element. However, Cu is not selected at the same time in the element X and the element Y.

  According to the above configuration, since the quenched alloy is formed from Si and the element X, and further, the element X is removed from the quenched alloy, the Si content in the electrode material can be increased, and the charge / discharge capacity can be increased. Can be improved.

  In the electrode material for a lithium secondary battery of the present invention, the Si content is preferably in the range of 70% by mass to less than 100% by mass. With this configuration, the Si content in the electrode material can be increased, and the charge / discharge capacity can be improved.

In the lithium secondary battery electrode material of the present invention, it preferably has a specific surface area in the range of less 2m 2 ^{/ g} or more 30 m 2 / ^g. With this configuration, the contact area between Si and lithium ions can be increased, and alloying of Si and lithium can be facilitated to improve cycle characteristics.

  Moreover, in the electrode material for lithium secondary batteries of this invention, it is preferable that a particle size is the range of 0.2 micrometer or more and 50 micrometers or less. With this configuration, alloying with lithium proceeds to the inside of the particles constituting the electrode material, and the charge / discharge capacity can be improved.

  The electrode material for a lithium secondary battery of the present invention is characterized in that the electrode material for a lithium secondary battery described above is combined with graphite. According to this configuration, graphite functions as a negative electrode active material by inserting and desorbing lithium during charge and discharge, and also functions as a conductive material of an electrode material containing Si, thereby facilitating the charge and discharge reaction of Si. Can do.

  Next, the lithium secondary battery of the present invention is characterized by comprising the electrode material for a lithium secondary battery as described above. With this configuration, a lithium secondary battery having excellent cycle characteristics and high charge / discharge capacity can be provided.

  Next, a method for producing an electrode material for a lithium secondary battery according to the present invention includes an alloy containing Si and Si and an element X that can be alloyed, and the Si content is equal to or less than the eutectic point of the SiX alloy. The molten metal is quenched to form a quenched alloy, and the element X is removed by impregnating the quenched alloy in a solution in which the element X can be dissolved.

  Further, the method for producing an electrode material for a lithium secondary battery of the present invention contains an element X that can be alloyed with Si and Si and one or more elements Y selected from Ag, Cu, and Au. And quenching the molten alloy having a Si content equal to or lower than the eutectic point of the SiX alloy to form a quenched alloy, and impregnating the quenched alloy in a solution in which the element X can be dissolved to remove the element X. It is characterized by.

According to the above configuration, a quenched alloy having a microcrystalline structure can be obtained by quenching a molten alloy containing Si and the element X and having a Si content equal to or lower than the eutectic point of the SiX alloy. And the content rate of Si can be relatively raised by removing the element X from this quenching alloy.
Since the electrode material thus obtained has a high Si content and a microcrystalline structure, the charge / discharge capacity can be increased and the cycle characteristics can be improved.
Further, since the Si content is equal to or lower than the eutectic point, a relatively large Si single phase is not generated in the structure of the rapidly cooled alloy powder, and the entire structure can be made into a microcrystalline structure.

  As described above, according to the electrode material for a lithium secondary battery of the present invention, since the Si content is high and it has a microcrystalline structure, the charge / discharge capacity can be increased and the cycle characteristics can be increased. Can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The electrode material for a lithium secondary battery according to the present invention is made of a powder containing Si as a main component, and the interplanar spacing of the Si (111) plane by X-ray diffraction is in the range of 3.15 to 3.20. It is characterized by.
The electrode material for a lithium secondary battery of the present invention comprises an alloy powder containing Si and any one or more elements Y selected from Ag, Cu, and Au, and is made of Si by X-ray diffraction. The (111) plane spacing is in the range of 3.15 mm to 3.20 mm.

  The above-mentioned electrode material for a lithium secondary battery contains Si, Si and an element X that can be alloyed, and further, from a quenched alloy powder to which the element Y is further added as necessary, by chemical treatment. It is formed by removing the element X. As the element X, for example, Al, B, P, Ge, Sn, Pb, Ni, Co, Mn, Mo, Cr, V, Cu, Fe, Ni, W, Ti, Zn, alkali metal, alkaline earth At least one element among the similar metals can be used. However, Cu is not selected at the same time in the element X and the element Y.

  The above-mentioned electrode material for a lithium secondary battery is obtained by forming a quenched alloy powder from Si and the element X and further removing the element X from the quenched alloy powder, so that the Si content in the electrode material is increased. And charge / discharge capacity can be improved. In addition, the quenched alloy powder composed of Si and the element X has a microcrystalline structure, and this microcrystalline structure is maintained even after the element X is removed, so that Si composed of the microcrystalline structure can be easily obtained.

Si forms an Li _x Si _y phase by alloying with lithium at the time of charging, and releases lithium at the time of discharging to return to Si alone. This Si functions as a substantial negative electrode active material of the lithium secondary battery. Moreover, this Si is comprised from the microcrystalline structure | tissue which contains many fine crystal grains. For this reason, there is little volume change at the time of charging / discharging, pulverization of electrode material itself is prevented, and cycling characteristics improve.

  Moreover, the specific resistance of the electrode material itself can be reduced by adding at least one element Y selected from Ag, Cu, and Au. Thereby, the alloying of lithium with respect to the electrode material at the time of charge becomes easy, and the charge / discharge capacity of the electrode material is improved.

Among the electrode materials for lithium secondary batteries described above, in an electrode material containing Si as a main component, the Si content is preferably 70% by mass or more, and Si is particularly preferably 100% by mass. .
Of the electrode materials for lithium secondary batteries, the electrode material containing Si and the element Y preferably has a Si content in the range of 70% by mass to less than 100% by mass.
If the Si content is less than 70% by mass, the amount of Si in the electrode material decreases, and the charge / discharge capacity decreases, which is not preferable.
The reason why the upper limit of Si in the electrode material containing Si and the element Y is set to less than 100% by mass is that the element Y is necessarily included in addition to Si. The content of element Y in the electrode material is
About 0.1-30 mass% is preferable. With the above configuration, the Si content in the electrode material can be increased, and the charge / discharge capacity can be improved.

  Si having a microcrystalline structure preferably has a (111) plane spacing in the range of 3.15 to 3.20. Those having a (111) plane spacing of less than 3.15 mm are preferred because the crystal grains are coarsened and cannot be called a microcrystalline structure, and the volume change during charge / discharge increases and cycle characteristics deteriorate. Absent. A (111) plane spacing of 3.20 mm or more is not preferable because it cannot be said to be a Si single phase structure.

The electrode for a lithium secondary battery material of the present invention preferably has a BET specific surface area by nitrogen adsorption method is in the range of less 2m 2 ^{/ g} or more 30 m 2 / ^g. When the BET specific surface area is in the above range, the contact area between Si and lithium ions can be increased, and the alloying of Si and lithium can be facilitated to improve cycle characteristics.

  In the electrode material for a lithium secondary battery of the present invention, it is preferable that the particle size of the particles constituting the powder is 0.2 μm or more and 50 μm or less. By including fine particles having a particle size of 0.2 to 50 μm, alloying with lithium proceeds to the inside of the particles, and charge / discharge capacity can be improved.

  Further, in the present invention, a powder obtained by fixing the above-mentioned electrode material powder on the surface of the graphite particles may be used. This composite electrode material functions as a negative electrode active material by inserting and detaching lithium during charging and discharging, and graphite functions as a conductive material for electrode materials mainly composed of Si. The charge / discharge reaction can proceed smoothly. Further, the above electrode material may be simply mixed with graphite without being compounded.

Next, the manufacturing method of the electrode material for lithium secondary batteries of this invention is demonstrated.
This method for producing an electrode material includes a step of obtaining a quenched alloy powder and a step of removing the element X from the quenched alloy powder.

In the step of obtaining a rapidly cooled alloy powder, first, a mixture of Si and element X or a mixture of Si and element X previously melted into an ingot is further heated and melted to obtain a molten alloy. Is rapidly cooled to obtain a rapidly cooled alloy powder. Alloy melts are Si, Al, B, P, Ge, Sn, Pb, Ni, Co, Mn, Mo, Cr, V, Cu, Fe, Ni, W, Ti, Zn, alkali metals, alkaline earth metals And at least one element X. The Si content in the molten alloy is preferably equal to or lower than the eutectic point of the SiX alloy. Since the eutectic point varies depending on the type of the element X, the Si content may be determined according to the element X. For example, when the element X is Al, the eutectic composition of the SiAl alloy is 12.1% by mass for Si and 87.9% by mass for Al, so the Si content should be 12.1% by mass or less. Is preferred.
If the Si content exceeds the eutectic point composition, the Si single phase precipitates in the structure of the rapidly cooled alloy powder, and the entire structure cannot be made into a microcrystalline structure, such being undesirable.

  Further, one or more elements Y selected from Ag, Cu, and Au may be added to the molten alloy. In this case, the Si content in the molten alloy is preferably equal to or lower than the eutectic point of the SiX alloy regardless of the amount of element Y added. The amount of element Y added is preferably in the range of 0.1 to 30% by mass with respect to Si.

  As a method for rapidly cooling the molten alloy, for example, a gas atomizing method, a water atomizing method, a roll quenching method, or the like can be used. In the gas atomization method and the water atomization method, a powdery quenching alloy is obtained, and in the roll quenching method, a ribbon-like quenching alloy is obtained. The ribbon-like quenched alloy is further pulverized into a powder. The average particle size of the quenched alloy powder thus obtained becomes the average particle size of the electrode material powder to be finally obtained. Therefore, when obtaining a rapidly cooled alloy powder, it is necessary to adjust the average particle size in the range of 0.2 μm to 50 μm.

The rapidly cooled alloy powder obtained from the molten alloy becomes a rapidly cooled alloy having a part of the amorphous phase and the rest having a microcrystalline structure, or a structure having a microcrystalline structure as a whole.
The quenched alloy powder always contains a SiX phase, and when the element X is excessive, an element X single phase is also included. When element Y is further added, element Y single phase or SiY phase is precipitated.

  In addition, it is preferable that the rapid cooling rate at the time of rapid cooling is 100 K / second or more. If the quenching rate is less than 100 K / sec, the SiX phase, the X phase, the Y phase, or the SiY phase may not be uniformly precipitated in the alloy structure, and the crystal size of each phase becomes too large. It is not preferable because it is difficult to obtain a sufficient expansion suppressing effect and conductivity imparting effect.

Next, in the step of removing the element X from the quenched alloy powder, the element X contained in the quenched alloy powder is eluted and removed. In order to elute and remove the element X, it is preferable to impregnate the quenched alloy powder in a solution in which only the element X is dissolved but Si and the element Y are not dissolved.
For example, when the element X is Al, it is preferable to use hydrochloric acid as the impregnation solution.
Specifically, the quenched alloy powder is impregnated with an aqueous hydrochloric acid solution, and then washed and dried. The impregnation condition is preferably a condition that is slowly stirred at room temperature for about 30 minutes to 5 hours. The concentration of the aqueous hydrochloric acid solution is preferably in the range of 1 to 5N.

  The impregnation conditions described here are only a guideline, and the impregnation conditions can be determined by confirming that the element X does not actually remain in the quenched alloy powder. If the impregnation condition is insufficient, the element X remains as a SiX alloy, and Si contained in the SiX alloy does not contribute to the charge / discharge reaction with lithium, and as a result, the charge / discharge capacity is reduced, which is preferable. Absent.

The specific surface area of the quenched alloy powder after removal of the element X becomes much more ^{30 m} 2 / g or less ^2m 2 / g. This is about 100 times the specific surface area of the original quenched alloy powder. The reason why the specific surface area increases in this way is that the portion from which the element X is removed becomes a void when the element X is removed.

  Finally, the rapidly cooled alloy powder after removal of the element X is washed and dried to obtain the electrode material for a lithium secondary battery of the present invention.

Next, the lithium secondary battery of the present invention will be described.
The lithium secondary battery of the present invention comprises at least a negative electrode provided with the above-mentioned electrode material for a lithium secondary battery as a negative electrode active material, a positive electrode, and an electrolyte.

Examples of the negative electrode of the lithium secondary battery include a material obtained by solidifying and molding the above-mentioned electrode material for a lithium secondary battery into a sheet with a binder.
Moreover, it is not restricted to what was solidified and formed in said sheet form, The pellet solidified and formed in the column shape, the disk shape, the plate shape, or the column shape may be sufficient.

The binder may be either organic or inorganic, but any binder may be used as long as it is dispersed or dissolved in a solvent together with the electrode material, and further the electrode material is bound by removing the solvent. Further, the electrode materials may be bonded together by mixing together with the electrode material and performing solidification molding such as pressure molding. As such a binder, for example, vinyl resin, cellulose resin, phenol resin, thermoplastic resin, thermosetting resin and the like can be used, such as polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, styrene butadiene rubber, etc. Resins can be exemplified.
In addition, in the negative electrode according to the present invention, carbon black, graphite, or the like may be added as a conductive additive in addition to the electrode material and the binder.

Next, as the positive electrode, for example, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , TiS, MoS, etc., and positive electrode capable of inserting and extracting lithium such as organic disulfide compounds and organic polysulfide compounds The thing containing an active material can be illustrated.
In addition to the positive electrode active material, a binder such as polyvinylidene fluoride or a conductive additive such as carbon black may be added to the positive electrode.
As a specific example of the positive electrode, a material obtained by applying the positive electrode to a current collector made of a metal foil or a metal net and forming it into a sheet shape can be exemplified.

Further, examples of the electrolyte include an organic electrolytic solution in which a lithium salt is dissolved in an aprotic solvent.
As aprotic solvents, propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl Sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl butyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate , Diethylene glycol, dimethyl An aprotic solvent such as ether or a mixed solvent in which two or more of these solvents are mixed can be exemplified, and in particular, any one of propylene carbonate, ethylene carbonate (EC) and butylene carbonate must be included and dimethyl carbonate It is preferable to always include any one of (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC).

As the lithium _{salt, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiClO 4, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, LiSbF 6, LiAlO 4, _{LiAlCl 4, LiN (C x F} 2x + 1 SO 2) (C y F 2y _tens 1 _SO 2) (provided that x, y is a natural number), LiCl, by mixing one or more lithium salts of such LiI In particular, those containing any one of LiPF ₆ and LiBF ₄ are preferable.
In addition to this, a conventionally known organic electrolyte for a lithium secondary battery may be used.

As another example of the electrolyte, a so-called polymer electrolyte such as a polymer obtained by mixing any of the above lithium salts with a polymer such as PEO or PVA, or a polymer having a high swellability impregnated with an organic electrolytic solution is used. It may be used.
Furthermore, the lithium secondary battery of the present invention is not limited to the positive electrode, the negative electrode, and the electrolyte, and may include other members as necessary. For example, the lithium secondary battery may include a separator that separates the positive electrode and the negative electrode. .

As described above, according to the electrode material for a lithium secondary battery of the present invention, the interplanar spacing of the Si (111) plane by X-ray diffraction is in the above range, and has a microcrystalline structure. By using the electrode material for the negative electrode of the lithium secondary battery, the cycle characteristics can be improved.
Further, by including the element Y, the specific resistance of the electrode material itself can be reduced. Thereby, the alloying of lithium with respect to the electrode material at the time of charge becomes easy, and the charge / discharge capacity of the electrode material can be increased.

In addition, according to the above-described method for producing an electrode material for a lithium secondary battery, a microcrystalline material is obtained by quenching a molten alloy containing Si and the element X and having a Si content equal to or lower than the eutectic point of the SiX alloy. A quenched alloy powder having a texture is obtained. And the content rate of Si can be relatively raised by removing the element X from this quenching alloy powder.
Since the electrode material thus obtained has a high Si content and a microcrystalline structure, the charge / discharge capacity can be increased and the cycle characteristics can be improved.
Further, since the Si content is equal to or lower than the eutectic point, no Si single phase is generated in the structure of the quenched alloy powder, and the entire structure can be made into a microcrystalline structure.

Example 1
11 parts by weight of granular Si and 89 parts by weight of Al powder were prepared, mixed, and then melted by a high-frequency heating method in an argon atmosphere to obtain a molten alloy. The molten alloy is rapidly cooled by a roll quenching method using a rotating roll made of Cu to form a quenched ribbon, and the quenched ribbon is further pulverized to obtain a quenched alloy powder having a BET specific surface area of 0.1 m ² / g. Obtained.
Next, 10 g of the obtained rapidly cooled alloy powder was placed in a 2N hydrochloric acid aqueous solution and impregnated for 4 hours with slow stirring at 30 ° C. Then, after thoroughly washing with pure water and drying at 100 ° C. for 2 hours, the particle size was adjusted to an average particle size of 15 μm. Thus, the electrode material for lithium secondary batteries of Example 1 was produced.

(Example 2)
11 parts by weight of granular Si, 88 parts by weight of Al powder, and 1 part by weight of Ag powder were prepared, mixed, and then melted by a high-frequency heating method in an argon atmosphere to obtain a molten alloy. A lithium secondary battery electrode material of Example 2 was produced in the same manner as Example 1 except for the above.
The BET specific surface area of the quenched alloy powder immediately after pulverization was 0.1 m ² / g.

(Comparative Example 1)
Si powder having an average particle size of 15 μm was used as the electrode material of Comparative Example 1.

(Comparative Example 2)
92 parts by weight of granular Si and 8 parts by weight of Ag powder were prepared, mixed, and then melted by a high-frequency heating method in an argon atmosphere to obtain a molten alloy. This molten alloy was rapidly cooled by a roll quenching method using a rotating roll made of Cu to form a quenched ribbon, and the quenched ribbon was pulverized to obtain a quenched alloy powder having an average particle size of 15 μm. This quenched alloy powder was used as the electrode material of Comparative Example 2.

With respect to the electrode materials of Examples 1 and 2 and Comparative Examples 1 and 2, the BET specific surface area was measured by a nitrogen adsorption method. The results are shown in Table 1.
Further, for each electrode material, X-ray diffraction measurement was performed, a qualitative analysis of the structure contained in the electrode material was performed, and the spacing of the (111) plane of Si was measured. Table 1 also shows the measurement results of the surface spacing.

  As shown in Table 1, it can be seen that the specific surface areas of the electrode materials of Examples 1 and 2 increased 110 times in Example 1 and 100 times in Example 2 before and after the impregnation treatment, respectively. This is because voids were generated in the particles of the electrode material by removing Al. Thus, the reaction area between Si and lithium can be increased by increasing the specific surface area.

  Also, as shown in Table 1, it can be seen that the surface spacing of the (111) planes of Examples 1 and 2 is significantly greater than that of Comparative Example 2 made of Si powder. This indicates that the electrode materials of Examples 1 and 2 have a fine crystalline structure with low crystallinity.

Further, only the Si phase is detected for Example 1, the Si phase and the Ag phase are detected for Example 2, only the Si phase is detected for Comparative Example 1, and the Si phase and Ag phase are detected for Comparative Example 2. Was detected. Therefore, for Examples 1 and 2, it was found that Al added during the production of the quenched alloy powder was completely removed by the impregnation treatment.
In addition, when the composition ratio of Si and Ag was analyzed about the electrode material of Example 2, 8 mass% Ag was added with respect to Si. This is almost the same as the composition of the electrode material of Comparative Example 2.

Next, lithium secondary batteries were manufactured using the electrode materials of Examples 1 and 2 and Comparative Examples 1 and 2. 70 parts by weight of each electrode material, 20 parts by weight of graphite powder having an average particle diameter of 3 μm as a conductive material, and 10 parts by weight of polyvinylidene fluoride were mixed, and N-methylpyrrolidone was added thereto, followed by stirring to prepare a slurry. Next, this slurry was applied onto a copper foil having a thickness of 14 μm, dried, and rolled to prepare a negative electrode having a thickness of 40 μm. The prepared negative electrode was punched into a circle having a diameter of 13 mm, and a metallic polypropylene was stacked on the negative electrode with a porous polypropylene separator interposed therebetween. Further, LiPF ₆ was added to a mixed solvent having a volume ratio of EC: DEC = 3: 7. A coin-type lithium secondary battery was manufactured by injecting an electrolytic solution added at a concentration of 1.3 mol / L.

  The obtained lithium secondary battery was repeatedly charged and discharged with a current density of 0.2 C for 10 cycles in the battery voltage range of 0V to 1.5V. At this time, the discharge capacity at the first cycle and the discharge capacity at the 10th cycle were determined. The results are shown in Table 2. The discharge capacity was the capacity per electrode material weight.

The electrode materials of Example 1 and Comparative Example 1 both contain only Si, and as shown in Table 2, the discharge capacity at the first cycle is almost the same, but after 10 cycles, the example 1 is higher.
Similarly, the electrode materials of Example 2 and Comparative Example 2 both contain 8% by mass of Ag with respect to Si, and as shown in Table 2, the discharge capacity at the first cycle is approximately the same. However, Example 2 is higher after 10 cycles.

As described above, the electrode materials of Examples 1 and 2 obtained by the treatment for removing Al from the rapidly quenched alloy powder containing Al are more cycle characteristics than those of Comparative Examples 1 and 2 that are not treated for Al removal. It turns out that it is excellent in.
As can be seen from the value of the (111) plane spacing shown in Table 1, in Examples 1 and 2, the volume change during charge / discharge was alleviated due to the decrease in Si crystallinity. It is thought to be due to.
In addition, it is considered that the increase in the specific surface area increases the contact area between lithium ions and Si, and the smooth alloying of lithium with Si is considered to have an influence.

Furthermore, the discharge capacity for each cycle of Example 2 is higher than that of Example 1 because the specific resistance of the electrode material itself is lowered by Ag added to Example 2 and the utilization rate of Si is increased. This is thought to be due to the fact that the alloying of lithium and Si was performed more smoothly while improving.

Claims (11)

  An electrode material for a lithium secondary battery, wherein Si is contained as a main component, and an interplanar spacing of Si (111) by X-ray diffraction is in a range of 3.15 to 3.20.   Si and at least one element Y selected from Ag, Cu, and Au are contained, and the plane spacing of the (111) plane of Si by X-ray diffraction is 3.15 to 3.20. An electrode material for a lithium secondary battery, characterized by being in the following range. It was formed by removing the element X by chemical treatment from a quenched alloy containing Si and an element X that can be alloyed with Si and having a Si content equal to or lower than the eutectic point of the SiX alloy. The electrode material for a lithium secondary battery according to claim 1, wherein the electrode material is a material.
However, the element X is Al, B, P, Ge, Sn, Pb, Ni, Co, Mn, Mo, Cr, V, Cu, Fe, Ni, W, Ti, Zn, alkali metal, alkaline earth metal Is at least one element. The element X is removed by chemical treatment from a quenched alloy containing the element X that can be alloyed with Si and Si and the element Y, and the Si content is equal to or lower than the eutectic point of the SiX alloy. The electrode material for a lithium secondary battery according to claim 2, wherein the electrode material is formed by:
However, the element X is Al, B, P, Ge, Sn, Pb, Ni, Co, Mn, Mo, Cr, V, Cu, Fe, Ni, W, Ti, Zn, alkali metal, alkaline earth metal Is at least one element. However, Cu is not selected at the same time in the element X and the element Y.   3. The electrode material for a lithium secondary battery according to claim 2, wherein the Si content is in a range of 70% by mass or more and less than 100% by mass. Lithium secondary battery electrode material according to any of claims 1 to 5, wherein the specific surface area in the range of less 2m 2 ^{/ g} or more 30 m 2 / ^g.   The electrode material for a lithium secondary battery according to any one of claims 1 to 6, wherein a particle diameter is in a range of 0.2 µm to 50 µm.   An electrode material for a lithium secondary battery according to any one of claims 1 to 7, wherein the electrode material for a lithium secondary battery is combined with graphite.   A lithium secondary battery comprising the electrode material for a lithium secondary battery according to any one of claims 1 to 8.   A solution that contains Si and Si and an element X that can be alloyed and that has a Si content equal to or lower than the eutectic point of the SiX alloy to rapidly cool the molten alloy, thereby dissolving the element X A method for producing an electrode material for a lithium secondary battery, comprising impregnating the quenched alloy to remove the element X. Contains element X which can be alloyed with Si and Si, and one or more elements Y selected from Ag, Cu and Au, and the Si content is equal to or lower than the eutectic point of the SiX alloy. A method for producing an electrode material for a lithium secondary battery, wherein a molten alloy is quenched to form a quenched alloy, and the quenched alloy is impregnated in a solution capable of dissolving the element X to remove the element X.