JP5299971B2 - Electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Description

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

  Currently, lithium ion secondary batteries are attracting attention as power sources for portable devices such as mobile phones and notebook computers, and as power sources for next-generation electric vehicles, and higher performance is desired. In particular, when used as these power sources, it is required that the operation time per charge is long, and high energy density of the battery is a top priority issue.

In the current general lithium ion secondary battery, LiCoO ₂ is used as the positive electrode active material, and graphite is used as the negative electrode active material. The effective capacity of these active materials is 134 mAh / g for LiCoO _{2 and} 342 mAh / g for graphite, and it is necessary to develop an electrode material with a larger charge / discharge capacity.

Sulfur has a high theoretical capacity of about 1670 mAh / g and a large amount of resource reserves, making it a promising candidate for an inexpensive high-capacity electrode material. When sulfur and lithium are reacted by heat treatment, lithium sulfide is formed. However, lithium sulfide has low electronic conductivity, and there is a problem that battery systems using current non-aqueous electrolytes elute into the electrolyte (non-patent literature). 1).

For this reason, attempts have been made to synthesize new lithium-containing metal sulfides by combining lithium sulfide with other elements. Lithium-containing metal sulfide has conductivity higher than semiconductivity, relatively little elution into the electrolyte, and is expected to have a capacity of about 1000 mAh / g, which is higher than current oxide materials. Capacity can be expected.

  As a method for producing a lithium-containing metal sulfide, for example, a heat treatment method in which lithium sulfide and metal sulfide are placed in an alumina container, further covered with a graphite container, and the whole is placed in a quartz tube and heated in an electric furnace. Is known (Non-Patent Document 2). As another method, there is also known a mechanical milling method in which lithium sulfide and metal sulfide are filled together with zirconia balls in a stainless steel container and milled by a planetary ball mill (Non-patent Document 3). However, both methods require a long time to produce the desired lithium-containing metal sulfide, and the constituent elements of the container are mixed as impurities during the reaction, and the purity of the produced lithium-containing metal sulfide is significantly reduced. There is a problem of making it.

R.D.Rauh, K.M.Abraham, G.F.Pearson, J.K.Suprenant, S.B.Brummer, J. Electrochem.Soc., Vol.126, pp. 523-527 (1979). E.E.Hellstrom, R.A.Huggins, Mat.Res.Bull., Vo. 14, pp.881-889 (1979). A. Hayashi, T. Fukuda, H. Morimoto, T. Minaimi. M. Tatsumisago, J. Mat. Sci., Vol. 39, pp. 5125-5127 (2004).

The present invention has been made in view of the above-described conventional state of the art, and its main purpose is to provide a material having a higher capacity than a conventional active material as an electrode active material for a lithium ion secondary battery. Furthermore, it is to provide a method capable of producing the active material efficiently and in a short time.

  The present inventor has intensively studied to achieve the above-described object. As a result, a lithium-containing metal sulfide represented by a specific general formula that has never been used as an electrode active material for a lithium ion secondary battery has a high capacity as an electrode active material for a lithium ion secondary battery. It was found that it has. According to the method of using specific sulfides as a raw material in combination, filling them in a conductive container, and applying a DC pulse current in a non-oxidizing atmosphere to cause a heat reaction, the target lithium-containing metal It has been found that sulfides can be easily produced in a short time, and the present invention has been completed here.

That is, this invention provides the following electrode active material for lithium ion secondary batteries, and its manufacturing method.
1. Composition formula; Li _x MS _{2 (where,} M is B, Ga or a Tl, x is 0 <a number in the range of x ≦ 1.) Lithium of lithium-containing metal sulfide represented by Negative electrode active material for ion secondary battery.
2. Item _{2. The} negative electrode active material for a lithium ion secondary battery according to Item 1, wherein the lithium-containing metal sulfide is Li _x GaS ₂ .
3. The lithium ion secondary battery containing the negative electrode active material for lithium ion secondary batteries of said claim | item 1 or 2 .
4). Li _x MS ₂ (wherein, M is B, Al, Ga, In, or Tl, and x is a numerical value in the range of 0 <x ≦ 1). A positive electrode active material for a lithium ion secondary battery.
5. Item 5. The positive electrode active material for a lithium ion secondary battery according to Item 4, wherein the lithium-containing metal sulfide is Li _x AlS ₂ or Li _x GaS ₂ .
6). The lithium ion secondary battery containing the positive electrode active material for lithium ion secondary batteries of said claim | item 4 or 5.
7). Chemical material: Lithium sulfide represented by Li ₂ S and M ₂ S ₃ (wherein M is B, Al, Ga, In, or Tl), a raw material containing metal sulfide has conductivity. Li _x MS ₂ (in the formula, M is the same as above, 0 <x ≦ 1 is a numerical value in the range of 1.).
8). Item 8. The method according to Item 7, wherein the reaction is performed at 400 to 1200 ° C under a pressure of 10 MPa or more.

  Hereinafter, the electrode active material for a lithium ion secondary battery of the present invention will be specifically described.

Electrode active material for lithium ion secondary battery The electrode active material for lithium ion secondary battery of the present invention is a lithium-containing metal sulfide represented by a composition formula; Li _x MS ₂ . In this composition formula, M is B, Al, Ga, In or Tl, and x is
It is a numerical value in the range of 0 <x ≦ 1. In particular, when x is in the range of about 0.2 ≦ x ≦ 1, the stability of the crystal structure is preferable, and the range of about 0.5 ≦ x ≦ 1 is more preferable.

Specific examples of the compound represented by the composition formula include Li _x AlS ₂ and Li _x GaS ₂ .

These materials act as electrode active materials for lithium ion secondary batteries according to the following reaction formula.For example, LiAlS ₂ has a very high theoretical capacity of 1435 mAh / g and LiGaS ₂ has a very high theoretical capacity of 952 mAh / g. Material.

_{^{LiAlS 2 + 5.25Li + + 5.25e -}} = 0.25 (Li 9 Al 4) + 2Li 2 S
_{^{LiGaS 2 + 5Li + + 5e -}} = Li 2 Ga + 3Li 2 S
The lithium-containing metal sulfide represented by the above composition formula: Li _x MS ₂ can be used as a positive electrode active material or a negative electrode active material of a lithium ion secondary battery. In particular, when used as a negative electrode active material, a lithium ion secondary battery having a high energy density and a negative electrode having the same potential as a negative electrode of a conventional lithium ion secondary battery and having a high capacity can be obtained. A battery can be obtained.

A lithium ion secondary battery using the above-described lithium-containing metal sulfide as a positive electrode active material or a negative electrode active material can be produced by a known method.

For example, when the lithium-containing metal sulfide is used as a positive electrode active material, as a negative electrode active material, a metal lithium that is a known material, a carbon-based material doped with lithium (activated carbon, graphite), or the like is used. For example, ethylene carbonate: EC, dimethyl carbonate:
Using a known electrolyte solution in which a lithium salt such as lithium perchlorate: LiClO ₄ and lithium hexafluorophosphate: LiPF ₆ is dissolved in a solvent such as DMC, and other known battery components What is necessary is just to assemble a lithium ion secondary battery according to a conventional method. Further, when the lithium-containing metal sulfide is used as the negative electrode active material, as the positive electrode material, known materials such as LiCoO ₂ and lithium nickelate: LiNiO ₂ are used, and the others are the same as described above. Then, a lithium ion secondary battery may be assembled according to a conventional method.

  According to the lithium ion secondary battery having such a configuration, a high energy density lithium ion secondary battery can be obtained by utilizing the high capacity of the lithium-containing metal sulfide used as the electrode active material.

Method for Producing Lithium-Containing Metal Sulfide The above-described composition formula; lithium-containing metal sulfide represented by Li _x MS ₂ is a known substance, for example, produced by mechanical milling using Li ₂ S and M ₂ S ₃ as raw materials. how can be produced by a known method such as a method of firing a mixture of Li ₂ S and M ₂ S _3, in particular, using a Li ₂ S and M ₂ S ₃ as raw materials, electrically conductive raw material It is preferable to manufacture by a method in which a mold having s is filled and a direct current pulse current is passed in a non-oxidizing atmosphere to cause a heating reaction. According to this method, since the reaction is performed in a non-oxidizing atmosphere in a conductive container, it is possible to suppress sulfur oxidation and dissipation, and to heat the raw material uniformly in a short time by pulse energization. Therefore, the target lithium-containing metal sulfide can be easily obtained. Hereinafter, this manufacturing method will be described more specifically.

First, lithium sulfide represented by a composition formula: Li ₂ S and a metal sulfide represented by a composition formula: M ₂ S ₃ are used as raw materials.

  Among these, the shape of lithium sulfide is not particularly limited, but it is usually preferable to use a powder having an average particle size of about 1 to 50 μm.

Further, in the metal sulfide represented by the composition formula: M ₂ S ₃ , M is B, Al, Ga, In, or Tl. For specific types of M, the target composition formula: Li _x MS It may be determined according to the lithium-containing metal sulfide represented by ₂ . The shape of the metal sulfide is not particularly limited, but usually a powdery raw material having an average particle size of about 1 to 50 μm may be used.

Regarding the mixing ratio of lithium sulfide and metal sulfide described above, the atomic ratio should be the same as the atomic ratio of Li and M in the target lithium-containing metal sulfide. If the amount of sulfur is insufficient In this case, sulfur powder may be added separately. Although there is no particular limitation on the shape of sulfur as a raw material, it is usually preferable to use a powdery one having an average particle diameter of about 1 to 300 μm.

  In the method for producing a lithium-containing metal sulfide of the present invention, first, lithium sulfide and a metal sulfide as raw materials are further mixed with sulfur if necessary, and then filled into a conductive mold. Then, in a non-oxidizing atmosphere, the raw material mixture is sintered by an electric current sintering method in which a direct current pulse current is passed, which is called a discharge plasma sintering method, a pulse electric current sintering method, a plasma activated sintering method or the like. As a result, the reaction between lithium sulfide and metal sulfide proceeds in a short time, and the target lithium-containing metal sulfide can be obtained.

  Specifically, in a non-oxidizing atmosphere, a conductive mold having a predetermined shape is filled with a mixture containing lithium sulfide and metal sulfide as raw materials, and pulsed ON-OFF is performed in a non-oxidizing atmosphere. By applying a direct current, current sintering can be performed.

  The material of the conductive container is not particularly limited, but has sufficient conductivity and heat resistance against the heating temperature when a DC pulse current is passed, and consists of components that do not react with sulfur to produce a compound, And what is necessary is just to have sufficient intensity | strength. For example, carbon (graphite etc.), tungsten carbide, etc. can be used conveniently.

The reaction between lithium sulfide and metal sulfide is carried out in a non-oxidizing atmosphere, for example, in an inert gas atmosphere such as Ar or N _2, or in a reducing atmosphere such as H ₂ . Thereby, oxidation, such as a sulfur content, can be suppressed.

  In the case of using a container that can ensure a sufficiently sealed state as the conductive container, the inside of the conductive container may be a non-oxidizing atmosphere.

  Further, the conductive container may not be in a completely sealed state, and a gas such as an inert gas may permeate to some extent as long as a closed state capable of preventing the transpiration of sulfur can be secured. When such an incompletely sealed conductive container is used, the conductive container is accommodated in a reaction chamber, and the reaction chamber is placed in a non-oxidizing atmosphere such as an inert gas atmosphere or a reducing atmosphere. That's fine. Thereby, the reaction between lithium sulfide and metal sulfide can be performed in a non-oxidizing atmosphere. In this case, for example, if the reaction chamber has an inert gas atmosphere or a reducing gas atmosphere of about 0.1 MPa or more, the transpiration of sulfur from the conductive container can be effectively suppressed.

  As an apparatus for conducting an energization process, a current sufficient to cause discharge can be energized, and a container filled with the raw material can be adjusted to a predetermined atmosphere. It is only necessary to pressurize lithium sulfide and metal sulfide to a predetermined pressure. For example, a commercially available current sintering apparatus (discharge plasma sintering apparatus) can be used. Such an electric current sintering apparatus and its operating principle are described in, for example, Japanese Patent Application Laid-Open No. 10-251070.

  Hereinafter, with reference to FIG. 1 which shows the schematic diagram of an example of a discharge plasma sintering apparatus, the manufacturing method of a lithium containing metal sulfide is demonstrated.

  A discharge plasma sintering apparatus 1 shown in FIG. 1 has a conductive die (die) 3 loaded with a raw material mixture 2 and a pair of upper and lower punches 4 and 5. The punches 4 and 5 are respectively supported by punch electrodes 6 and 7, and a pulse current is supplied to the raw material 2 loaded in the conductive die (die) 3 through the punch electrodes 6 and 7. Can do. The punch electrode can also be used to pressurize the raw material.

  Examples of the material of the conductive die used for filling the raw material include materials that have electronic conductivity and do not easily react with lithium sulfide and metal sulfide, for example, carbide such as carbon and tungsten carbide. An alloy, a mixture thereof, a mixture obtained by adding a reinforcing material such as silicon nitride to these, and the like can be used in appropriate combination.

The heating reaction between lithium sulfide and metal sulfide needs to be performed in a non-oxidizing atmosphere. As the non-oxidizing atmosphere, a reduced pressure state with a sufficiently low oxygen concentration may be used, but an inert gas atmosphere such as Ar or N ₂ , a reducing atmosphere such as H _2, or the like is preferable, and an Ar atmosphere is particularly preferable.

  In the apparatus shown in FIG. 1, the current-carrying portion including the conductive mold 3, the current-carrying punches 4 and 5, and the punch electrodes 6 and 7 is housed in a water-cooled vacuum chamber 8. It can be adjusted to a predetermined atmosphere by the mechanism 15. Therefore, the atmosphere control mechanism 15 may be used to adjust the inside of the chamber to a non-oxidizing atmosphere.

  The control device 12 drives and controls the pressurization mechanism 13, the pulse power source 11, the atmosphere control mechanism 15, the water cooling mechanisms 16 and 10, and the temperature measurement device 17. The control device 12 is configured to drive the pressurizing mechanism 13 so that the punch electrodes 6 and 7 pressurize the raw material mixture at a predetermined pressure.

When conducting the energization treatment, it is not necessary to apply pressure to the raw material mixture of lithium sulfide and metal sulfide, but in order to promote the reaction between lithium sulfide and metal sulfide, the pressure is about 30 MPa or more. Is preferably added. The upper limit of the pressure is not particularly limited, but is usually about 500 MPa, preferably about 450 MPa.

  The heating temperature during the energization treatment is usually about 400 to 1200 ° C, and preferably about 800 to 1000 ° C. By heating in the above-mentioned temperature range by the electric current sintering method, the reaction between lithium sulfide and metal sulfide proceeds in a short time, and the target lithium-containing metal sulfide can be obtained.

As the pulse current to be energized for heating, for example, a pulsed ON-OFF direct current having a pulse width of about 2 to 3 milliseconds and a period of about 3 Hz to 300 Hz can be used. Since the current value varies depending on the type and size of the mold material, the rate of temperature increase, etc., the current value may be controlled so as to reach a predetermined temperature by increasing or decreasing the current value while monitoring the temperature of the mold material. For example, when the temperature is raised at 10 ° C./min using a graphite mold having an inner diameter of about 15 mm, the current value is preferably about 100 to 600 A, and when the temperature is raised at 200 ° C./min, 100 to It is preferable to have a current value of about 1000A,
Further, when the temperature is raised at 10 ° C./min using a mold material having an inner diameter of about 100 mm, a current value of about 1000 to 8000 A is preferable.

  The sintering time by electric current sintering varies depending on the amount of raw materials used, the sintering temperature, etc., and thus cannot be specified in general, but it is usually sufficient to heat until reaching the heating temperature range described above, and the temperature range described above. If it reaches | attains, you may cool immediately, or you may hold | maintain in this temperature range, for example to about 2 hours.

  By applying a DC pulse current by the above method and conducting current sintering under pressure, using the discharge phenomenon that occurs in the particle gap between the filled lithium sulfide and metal sulfide, discharge plasma, discharge impact pressure, etc. The action of purification of the particle surface by the electric field, the electric field diffusion effect caused by the electric field, the thermal diffusion effect due to Joule heat, the plastic deformation pressure due to pressurization, etc. serve as the driving force for the joining, and the reaction between lithium sulfide and metal sulfide proceeds. Thus, the target lithium-containing metal sulfide can be obtained in a short time.

  The obtained lithium-containing metal sulfide can be recovered as a lithium-containing metal sulfide powder by removing from the mold after cooling and, for example, lightly pulverizing with a mortar or the like.

  When a large amount of energization processing is performed, the above process may be scaled up using a large mold material.

The composition formula which is an active ingredient of the electrode active material for lithium ion secondary battery of the present invention; the lithium-containing metal sulfide represented by Li _x MS ₂ has been conventionally used as an active material for lithium ion secondary battery It is a novel material with no capacity and an active material having a high capacity. Therefore, a lithium ion secondary battery having a high energy density can be obtained by using the lithium-containing metal sulfide as an electrode active material of a lithium ion secondary battery.

  Further, by adopting a discharge plasma sintering method as a method for producing the lithium-containing metal sulfide, it becomes possible to produce the lithium-containing metal sulfide efficiently in a short time. Industrial use as an electrode active material of a lithium ion secondary battery becomes easy.

It is the schematic of an example of a discharge plasma sintering apparatus. 2 is an X-ray diffraction pattern of a sample obtained in Example 1. FIG. 3 is an X-ray diffraction pattern of a sample obtained in Example 2. FIG. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which measured in Example 3 and uses the sample obtained in Example 1 as a positive electrode active material. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which measured in Example 4 and uses the sample obtained in Example 2 as a positive electrode active material. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which measured in Example 5 and uses the sample obtained in Example 1 as a negative electrode active material. It is a graph which shows the charging / discharging characteristic of the lithium ion secondary battery which measured in Example 6 and uses the sample obtained in Example 2 as a negative electrode active material.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 :
Lithium sulfide (Li ₂ S) (purity 99.9%) and aluminum sulfide (Al ₂ S ₃ ) (purity 98%
) Was weighed at a molar ratio of 1: 1, and a total amount of 0.5 g was mixed with a planetary ball mill for about 30 minutes.

  Next, the obtained mixture was filled in a graphite mold having an inner diameter of 15 mm and accommodated in an electric current sintering apparatus having a structure shown in FIG. The current-carrying part including the graphite mold and electrode part is housed in a vacuum chamber, and the chamber is filled with high-purity argon gas (oxygen concentration: about 0.2 ppm) to atmospheric pressure after vacuum (about 20 Pa) deaeration. did.

After that, pressurize the raw material filled in the graphite mold at about 30MPa while applying a pulse current of about 900A (
A pulse width of 2.5 milliseconds and a period of 28.6 Hz) was applied. The vicinity of the graphite mold was heated at a temperature increase rate of about 200 ° C./min, and reached 900 ° C. 4 minutes and 30 seconds after the start of pulse current application. Immediately thereafter, the current application and pressurization were stopped and the mixture was allowed to cool naturally.

The X-ray diffraction pattern of the generated object is shown in FIG. Figure 2 shows literature values (EE Hellstrom, RA
Huggins, Mat. Res. Bull., Vo. 14, pp.881-889 (1979).) X-ray diffraction peak values for LiAlS ₂ are also shown. From this result, it was confirmed that the lithium-containing metal sulfide represented by LiAlS ₂ was obtained by the method described above.

Example 2
Lithium-containing metal sulfide was obtained by the discharge plasma sintering method in the same manner as in Example 1 except that gallium sulfide (Ga ₂ S ₃ ) (purity 99.9%) was used instead of aluminum sulfide (Al ₂ S ₃ ). A product was made.

The X-ray diffraction pattern of the generated object is shown in FIG. Figure 3 shows the literature values (R. Hoppe, Bull
Soc. Chim. France, Vol. 32, pp. 1115-1121 (1965).) X-ray diffraction peak values for LiGaS ₂ are also shown. From this result, it was confirmed that the lithium-containing metal sulfide represented by LiGaS ₂ was obtained by the method described above.

Example 3
Using the lithium-containing metal sulfide obtained in Example 1 as a positive electrode active material of a lithium ion secondary battery, charge / discharge characteristics were measured by the following method.

First, 3.5 mg of the lithium-containing metal sulfide represented by LiAlS ₂ obtained in Example 1 was mixed, 1.0 mg of acetylene black as a conductive material and 0.5 mg of PTFE as a binder were mixed, and Cu
A positive electrode was produced by pressure bonding to a mesh (diameter 12 mm). Using this as the positive electrode material, Li metal as the negative electrode material, and 1M LiPF ₆ / (EC + DMC) as the electrolyte, respectively, the experimental cell was configured, and the current value was set to 100 mA / g per sulfide weight The charge / discharge test was conducted at 30 ° C. The results are shown in FIG.

As is clear from FIG. 4, the lithium-containing metal sulfide represented by LiAlS ₂ exhibits a high initial discharge capacity of about 900 mAh / g as the positive electrode active material, and the charge / discharge capacity at the second cycle is 450 mAh. It was confirmed that the material was chargeable / dischargeable at the third cycle or more at about / g.

Example 4
An experimental cell was prepared in the same manner as in Example 3 except that the lithium-containing metal sulfide represented by LiGaS ₂ obtained in Example 2 was used instead of the positive electrode active material used in Example 3. The charge / discharge test was conducted under the same conditions as in Example 3. The results are shown in FIG.

As is clear from FIG. 5, the lithium-containing metal sulfide represented by LiGaS ₂ has a high initial discharge capacity of about 950 mAh / g as the positive electrode active material, and the charge / discharge capacity at the second cycle is 430 mAh / g. It was confirmed that charging and discharging were possible in the same manner in the third cycle or more at about g.

Example 5
Using the lithium-containing metal sulfide obtained in Example 1 as a negative electrode active material of a lithium ion secondary battery, charge / discharge characteristics were measured by the following method.

First, 3.5 mg of the lithium-containing metal sulfide represented by LiAlS ₂ obtained in Example 1 was mixed, 1.0 mg of acetylene black as a conductive material and 0.5 mg of PTFE as a binder were mixed, and Cu
A negative electrode was produced by pressure bonding to a mesh (diameter 12 mm). This was used as a negative electrode material. As a positive electrode material, a mixture of LiCoO ₂ : acetylene black: PTFE in a ratio of 7: 2: 1 and pelleted to a total weight of 100 mg was used. As an electrolyte, 1M LiPF ₆ / ( A test cell was constructed using EC + DMC), and a charge / discharge test was conducted at 30 ° C. with a current value of 100 mA / g per weight of sulfide. The results are shown in FIG.

As is clear from FIG. 6, the lithium-containing metal sulfide represented by LiAlS ₂ has a high initial charge capacity of about 1000 mAh / g as a negative electrode active material, and an initial discharge capacity of about 260 mAh / g. Further, it was confirmed that charge and discharge were possible in the second and subsequent cycles.

Example 6
A test cell was prepared in the same manner as in Example 5 except that the lithium-containing metal sulfide represented by LiGaS ₂ obtained in Example 2 was used instead of the negative electrode active material used in Example 5. The charge / discharge test was performed under the same conditions as in Example 5. The results are shown in FIG.

As is clear from FIG. 7, the lithium-containing metal sulfide represented by LiGaS ₂ has a high initial charge capacity of about 870 mAh / g as a negative electrode active material, and an initial discharge capacity of about 320 mAh / g. Further, it was confirmed that charge and discharge were possible in the second and subsequent cycles.

1 Electric current sintering equipment 2 Sample 3 Die (conductive container)
4, 5 Punch 6, 7 Punch electrode 8 Water-cooled vacuum chamber 9 Cooling water channel 10, 16 Water cooling mechanism 11 Power source for sintering 12 Controller 13 Pressurizing mechanism 14 Position measuring mechanism 15 Atmosphere controlling mechanism 17 Temperature measuring apparatus

Claims (8)

Composition formula; Li _x MS _{2 (where,} M is B, Ga or a Tl, x is 0 <a number in the range of x ≦ 1.) Lithium of lithium-containing metal sulfide represented by Negative electrode active material for ion secondary battery. The negative electrode active material for a lithium ion secondary battery according to claim 1, wherein the lithium-containing metal sulfide is Li _x GaS ₂ . The lithium ion secondary battery containing the negative electrode active material for lithium ion secondary batteries of Claim 1 or 2 . Composition formula; Li _x MS ₂ (Wherein M is B, Al, Ga, In, or Tl, and x is a numerical value in a range of 0 <x ≦ 1). Positive electrode active material. Lithium-containing metal sulfide _x AlS ₂ Or Li _x GaS ₂ The positive electrode active material for a lithium ion secondary battery according to claim 4. The lithium ion secondary battery containing the positive electrode active material for lithium ion secondary batteries of Claim 4 or 5. Chemical formula: Li ₂ Lithium sulfide represented by S and M ₂ S _Three (In the formula, M is B, Al, Ga, In or Tl.) A raw material containing a metal sulfide represented by the formula is filled in a conductive mold, and a DC pulse current is applied in a non-oxidizing atmosphere. A composition formula characterized by heating and reaction; Li _x MS ₂ (Wherein M is the same as above, and is a numerical value in the range of 0 <x ≦ 1). The method according to claim 7, wherein the reaction is performed at 400 to 1200 ° C. under a pressure of 10 MPa or more.

Images