Positive electrode active material, lithium secondary battery, and method for producing positive electrode active material

Abstract

This positive electrode active material contains LixMnyO2 (where 1.012≥x≥0.683 and 0.91≤y≤1.0).

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material, a lithium secondary battery, and a method for producing a positive electrode active material. [Background technology]

[0002] Manganese dioxide, which has a tunnel or layer structure, is known as one of the positive electrode active materials for lithium secondary batteries. Manganese dioxide comes in various crystal structures, such as α-MnO2, β-MnO2, and γ-MnO2. Manganese dioxide is expressed as "MnO2" in chemical formula, but is actually a non-stoichiometric compound.

[0003] Since manganese dioxide does not contain Li, lithium secondary batteries using manganese dioxide as the positive electrode active material must be in a charged state when assembled. This means that it is difficult to use graphite as the negative electrode active material, and it is necessary to use Li metal or LiAl alloy as the negative electrode active material.

[0004] As is well known to those skilled in the art, lithium secondary batteries using Li metal as the negative electrode active material have poor reversibility. When Li alloys, such as LiAl alloys, are used instead of Li metal, the cycle characteristics are good at shallow depths. However, repeated charging and discharging at deep depths results in the battery reaching the end of its life after a small number of charge-discharge cycles. Therefore, lithium secondary batteries using manganese dioxide as the positive electrode active material are only used in applications requiring repeated charging and discharging at shallow depths, such as memory backup applications.

[0005] Patent Document 1 discloses the use of a product obtained by mixing and firing LiOH and MnO2 as a positive electrode active material. At first glance, the product appears to contain LiMnO2, but in reality, the valence of Mn remains almost unchanged from tetravalent, and Li is hardly doped into MnO2. In other words, even if the raw material powders are mixed and fired, LiMnO2 is not produced, or if it is produced, it is produced in very small amounts. Therefore, in the examples of Patent Document 1, a LiPb alloy is used as a negative electrode active material, and after battery assembly, discharge is the first step.

[0006] Non-Patent Document 1 reveals that the product obtained by mixing and firing LiOH and MnO2 is a composite of Li2MnO3 and MnO2. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 3-43968 [Non-patent literature]

[0008] [Non-Patent Document 1] N. Furukawa, T. Noma, K. Terashi, I. Nakane, Y. Yamamoto, and T. Saito, "Lithium-containing manganese dioxide as a positive electrode active material for lithium secondary batteries," Electrochemistry and Industrial Physical Chemistry, 57, No. 6, pp. 533-538 (1989) Summary of the Invention

[0009] In view of the above, the present disclosure provides LiMnO2 preloaded with lithium.

[0010] The present disclosure provides: Li x Mn y O2(1.012≧x≧0.683 and 0.91≦y≦1.0, A positive electrode active material is provided.

[0011] According to the present disclosure, the positive electrode active material contains lithium in advance. x Mn y Because it contains O2, it is possible to construct lithium secondary batteries using a variety of negative electrode active materials. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a lithium secondary battery according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a process diagram showing a method for producing a positive electrode active material. [Figure 3A] FIG. 3A shows the charge / discharge curves for the first cycle of the lithium secondary battery of Example 1. [Figure 3B] FIG. 3B shows the charge-discharge curves for the second cycle of the lithium secondary battery of Example 1. [Figure 3C] FIG. 3C is a graph showing the relationship between the discharge capacity density and the number of discharge cycles of the lithium secondary battery of Example 1. [Figure 4A] FIG. 4A shows the charge / discharge curves for the first cycle of the lithium secondary battery of Example 2. [Figure 4B] FIG. 4B shows the charge-discharge curves for the second cycle of the lithium secondary battery of Example 2. [Figure 4C] FIG. 4C is a graph showing the relationship between the discharge capacity density and the number of discharge cycles of the lithium secondary battery of Example 2. [Figure 5A] FIG. 5A shows the charge-discharge curves for the first cycle of the lithium secondary battery of Example 3. [Figure 5B] FIG. 5B shows the charge / discharge curves for the second cycle of the lithium secondary battery of Example 3. [Figure 5C] FIG. 5C is a graph showing the relationship between the discharge capacity density and the number of discharge cycles of the lithium secondary battery of Example 3. [Figure 6A] FIG. 6A shows the charge / discharge curves for the first cycle of the lithium secondary battery of Example 4. [Figure 6B] FIG. 6B shows the charge-discharge curves for the second cycle of the lithium secondary battery of Example 4. [Figure 6C] FIG. 6C is a graph showing the relationship between the discharge capacity density and the number of discharge cycles of the lithium secondary battery of Example 4. [Figure 7A] FIG. 7A shows the discharge curve of the lithium secondary battery of Reference Example 1 in the first cycle. [Figure 7B] FIG. 7B shows the charging curve for the first cycle of the lithium secondary battery of Reference Example 1. [Figure 8] FIG. 8 is a diagram showing powder X-ray diffraction patterns of the positive electrode active materials of Example 2 and Reference Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Findings that formed the basis of this disclosure) Typically, secondary batteries are required to be able to withstand deep charge / discharge cycles. One example is to use MnO2 as the positive electrode and LiC6, which has Li pre-absorbed, as the negative electrode. However, the preparation of LiC6 is complicated, making it impractical to use LiC6 as the negative electrode. Therefore, to achieve good cycle performance at deep charge / discharge cycles using highly reversible graphite as the negative electrode, it is necessary to incorporate a sufficient amount of Li into MnO2 as the positive electrode active material and change the valence of Mn to approximately trivalent.

[0014] Even if an attempt is made to prepare LiMnO2 using a conventional method such as that described in Patent Document 1, Mn is hardly reduced and remains almost tetravalent. Because the valence of Mn is close to tetravalent, it is virtually impossible to extract Li from a compound such as Li2MnO3, even if it contains Li.

[0015] Therefore, there is a demand for LiMnO2 that already contains lithium and can be charged.

[0016] (Summary of one aspect of the present disclosure) The positive electrode active material according to the first embodiment of the present disclosure comprises Li x Mn y O2 (1.012≧x≧0.683 and 0.91≦y≦1.0). The positive electrode active material contains lithium in advance.x Mn y Because it contains O2, various negative electrode active materials can be used. x Mn y A lithium secondary battery using O2 as the positive electrode active material can start with charging.

[0017] In the second embodiment of the present disclosure, for example, the positive electrode active material according to the first embodiment may satisfy the relationship 1.012≧x≧0.864, which further increases the capacity density of the lithium secondary battery.

[0018] In the third aspect of the present disclosure, for example, the valence of Mn in the positive electrode active material according to the first or second aspect may be 2.987 or more and 3.316 or less. By changing the valence of Mn between trivalent and tetravalent, charging and discharging of the lithium secondary battery is performed smoothly.

[0019] In the fourth aspect of the present disclosure, for example, in the positive electrode active material according to any one of the first to third aspects, the valence of Mn may be 2.987 or more and 3.136 or less.

[0020] A method for producing a positive electrode active material according to a fifth embodiment of the present disclosure includes contacting MnO2 with a lithium solution in which lithium metal is dissolved in an organic solvent.

[0021] The disclosed method utilizes the strong reducing power of organic solvents containing dissolved Li metal. The reducing power of the lithium solution reduces the valence of Mn in MnO2 to trivalent, and Li ions are doped into MnO2 in the form of charge compensation. MnO2 is reduced to trivalent by electrochemical reduction (discharge). One electron of Li is incorporated into MnO2.

[0022] In a sixth aspect of the present disclosure, for example, in the method for producing a positive electrode active material according to the fifth aspect, MnO may contain at least one selected from the group consisting of γ-β-MnO, ramsdellite, and β-MnO. Ramsdellite, γ-β-MnO that can be produced from electrolytic manganese dioxide, and β-MnO that can also be produced from electrolytic manganese dioxide all have a tunnel structure, are inexpensive, and are easily available.

[0023] In a seventh aspect of the present disclosure, for example, in the method for producing a positive electrode active material according to the fifth or sixth aspect, the organic solvent may contain at least one selected from the group consisting of glyme and chain carbonate.

[0024] In an eighth aspect of the present disclosure, for example, in the method for producing a positive electrode active material according to the fifth or sixth aspect, the organic solvent may contain at least one selected from the group consisting of triglyme, dimethoxyethane, and methyl ethyl carbonate.

[0025] In a ninth aspect of the present disclosure, for example, in the method for producing a cathode active material according to the fifth or sixth aspect, the organic solvent may contain a mixture of triglyme and methyl ethyl carbonate. Use of the mixture of triglyme and methyl ethyl carbonate allows the preparation of a lithium solution with strong reducing power, thereby enabling the doping of lithium into MnO to proceed rapidly.

[0026] In a tenth aspect of the present disclosure, for example, in the method for producing a positive electrode active material according to the fifth or sixth aspect, the organic solvent may contain a mixture of dimethoxyethane and methyl ethyl carbonate. Use of the mixture of dimethoxyethane and methyl ethyl carbonate allows the preparation of a lithium solution with strong reducing power, thereby enabling the doping of lithium into MnO to proceed rapidly.

[0027] In an eleventh aspect of the present disclosure, for example, in the method for producing a positive electrode active material according to any one of the fifth to tenth aspects, the lithium solution may further contain an aromatic compound. A solution containing an aromatic compound has the property of releasing solvated electrons of lithium and dissolving lithium as cations.

[0028] In a twelfth aspect of the present disclosure, for example, in the method for producing a positive electrode active material according to the eleventh aspect, the aromatic compound may contain benzophenone.

[0029] A lithium secondary battery according to a thirteenth aspect of the present disclosure includes a positive electrode containing the positive electrode active material according to any one of the first to fourth aspects. x Mn y Because it contains O2, it is possible to use a variety of negative electrode active materials.

[0030] In a fourteenth aspect of the present disclosure, for example, in the lithium battery according to the thirteenth aspect, the positive electrode may include an aluminum positive electrode current collector. Aluminum and its alloys are suitable materials for the positive electrode current collector because they are inexpensive and easy to form into a thin film.

[0031] In a fifteenth aspect of the present disclosure, for example, the lithium battery according to the thirteenth or fourteenth aspect may be in a discharged state upon completion of assembly, or may be capable of starting charging. With this configuration, a material with excellent cycle characteristics, such as graphite, can be used as the negative electrode active material.

[0032] In a sixteenth aspect of the present disclosure, for example, the lithium battery according to any one of the thirteenth to fifteenth aspects may further include a negative electrode containing graphite, which is particularly recommended because graphite is resistant to deterioration even when repeatedly charged and discharged at a deep depth.

[0033] In a seventeenth aspect of the present disclosure, for example, in the lithium battery according to the sixteenth aspect, the negative electrode may not contain lithium upon completion of assembly. With this configuration, a material with excellent cycle characteristics, such as graphite, can be used as the negative electrode active material.

[0034] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0035] FIG. 1 is a cross-sectional view of a lithium secondary battery according to one embodiment of the present disclosure. The lithium secondary battery 10 of this embodiment includes a negative electrode 13, a positive electrode 16, a non-aqueous electrolyte 19, a separator 17, and an outer casing 18. The negative electrode 13 includes a negative electrode current collector 11 and a negative electrode active material layer 12. The negative electrode active material layer 12 is disposed on the negative electrode current collector 11. The positive electrode 16 includes a positive electrode current collector 14 and a positive electrode active material layer 15. The positive electrode active material layer 15 is disposed on the positive electrode current collector 14. A separator 17 is disposed between the negative electrode 13 and the positive electrode 16. The negative electrode 13 and the positive electrode 16 face each other with the separator 17 interposed therebetween. The negative electrode 13, the positive electrode 16, the separator 17, and the non-aqueous electrolyte 19 are housed in an outer casing 18.

[0036] The negative electrode active material layer 12 may contain a negative electrode active material capable of absorbing and releasing lithium ions. Examples of negative electrode active materials capable of absorbing and releasing lithium ions include graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. One or more of these negative electrode active materials may be used alone or in combination.

[0037] The negative electrode active material layer 12 may contain graphite as the negative electrode active material. Graphite alone may be used as the negative electrode active material. Graphite is particularly recommended because it is resistant to deterioration even when repeatedly charged and discharged at a deep depth. Graphite alone may be contained as the negative electrode active material in the negative electrode active material layer 12. Carbon materials other than graphite may be used as the negative electrode active material.

[0038] The negative electrode 13 may not contain lithium when the assembly of the lithium secondary battery 10 is completed. In this embodiment, the lithium secondary battery 10 is in a discharged state when the assembly is completed, and charging can be started. In other words, a material with excellent cycle characteristics, such as graphite, can be used as the negative electrode active material. "When the assembly is completed" refers to any point in time during the period from when the manufacturing of the lithium secondary battery 10 is completed to when the lithium secondary battery 10 is connected to an external power source and a charge / discharge process is performed.

[0039] The negative electrode active material layer 12 may contain a conductive additive, an ion conductor, a binder, and the like.

[0040] The conductive additive and ion conductor are used to reduce the resistance of the negative electrode 13. Examples of the conductive additive include carbon materials (carbon conductive additives) such as carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Examples of the ion conductor include gel electrolytes such as polymethyl methacrylate and polymethyl methacrylate, organic solid electrolytes such as polyethylene oxide, and Li7La3Zr2O. 12 Inorganic solid electrolytes such as may be used.

[0041] The binder is used to improve the binding property of the material that constitutes the negative electrode 13. As the binder, polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide can be used.

[0042] The negative electrode current collector 11 may be a sheet or film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material such as carbon may be applied to the surface of the negative electrode current collector 11 as a conductive auxiliary material.

[0043] The positive electrode active material layer 15 contains Li as the positive electrode active material. x Mn y O2 (1.012≧x≧0.683 and 0.91≦y≦1.0). In particular, when the lithium secondary battery 10 is assembled, the positive electrode active material is Li x Mn y O2 (1.012≧x≧0.683 and 0.91≦y≦1.0. The positive electrode active material has lithium in advance. x Mn y Because it contains O2, various negative electrode active materials can be used. x Mn y When O2 is used as the positive electrode active material and graphite is used as the negative electrode active material, the lithium secondary battery 10 is in a discharged state when assembly is completed. Therefore, the lithium secondary battery 10 can be started from charging after assembly. The positive electrode active material layer 15 is made of Li x Mn y The positive electrode active material may contain other positive electrode active materials than O2, and Li x Mn y It may contain only O2.

[0044] In addition, manganese dioxide MnO z In this case, the value of z can be 1.92≦z≦2.0 (see, for example, Toyo Soda Research Report, Vol. 20, No. 2, p. 133, Table 1). y When converted to O2, the value of y is 1.82 / 2.0≦y≦2.0 / 2.0, that is, 0.91≦y≦1.0. x Mn y In O2, y satisfies 0.91≦y≦1.0. The value of y may be, for example, y=1.

[0045] Li x Mn y In O2, the relationship 1.012≧x≧0.864 may be satisfied, in which case the capacity density of the lithium secondary battery 10 is further increased.

[0046] Li x Mn y In O2, the valence of Mn is, for example, 2.987 or more and 3.316 or less. The valence of Mn changes between trivalent and tetravalent, allowing smooth charging and discharging of the lithium secondary battery 10. The valence of Mn may be 2.987 or more and 3.136 or less.

[0047] The positive electrode active material layer 15 may contain a conductive additive, an ion conductor, a binder, etc. The same materials that can be used for the negative electrode active material layer 12 can be used for the positive electrode active material layer 15 as the conductive additive, ion conductor, and binder.

[0048] The positive electrode current collector 14 can be a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. Aluminum and its alloys are suitable materials for the positive electrode current collector 14 because they are inexpensive and easy to form into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, or the like may be used as the sheet or film. A carbon material such as carbon may be applied to the surface of the positive electrode current collector 14 as a conductive auxiliary material.

[0049] The non-aqueous electrolyte 19 is, for example, an electrolytic solution impregnated into the negative electrode 13, the positive electrode 16, and the separator 17. The non-aqueous electrolyte 19 may fill the internal space of the exterior casing 18. The non-aqueous electrolyte 19 functions to allow lithium ions to travel between the negative electrode 13 and the positive electrode 16.

[0050] The non-aqueous electrolyte 19 contains a non-aqueous solvent and a lithium salt.

[0051] The non-aqueous solvent may be a cyclic carbonate, a chain carbonate, an ester, a cyclic ether, a chain ether, a nitrile, an amide, etc. One selected from these solvents may be used, or two or more may be used in combination.

[0052] Examples of lithium salts that can be used include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One or more of these electrolyte salts may be used alone or in combination.

[0053] The separator 17 has lithium ion conductivity. There are no particular limitations on the material of the separator 17 as long as it allows the passage of lithium ions. The material of the separator 17 can be at least one selected from the group consisting of solid electrolytes, gel electrolytes, ion exchange resin membranes such as lithium cation exchange resins, semipermeable membranes, and porous membranes. If the separator 17 is made of these materials, the safety of the lithium secondary battery 10 can be sufficiently ensured. Examples of solid electrolytes include sulfide solid electrolytes such as Li2S-P2S5, Li7La3Zr2O 12 Examples of the electrolyte membrane include oxide solid electrolytes such as LLZ. Examples of the gel electrolyte include gel electrolytes containing fluororesins such as PVdF. Examples of the ion exchange resin membrane include cation exchange membranes and anion exchange membranes. Examples of the porous membrane include porous membranes made of polyolefin resin and porous membranes made of glass paper obtained by weaving glass fibers into nonwoven fabric.

[0054] The exterior 18 is made of a material obtained by laminating a metal foil such as an aluminum foil with a resin film such as a PET film, etc. The exterior 18 may also be a container made of resin or metal.

[0055] There are no particular limitations on the shape of the lithium secondary battery 10. The lithium secondary battery 10 may be in a variety of shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type.

[0056] The lithium secondary battery 10 may be an all-solid-state battery.

[0057] Next, a method for producing a positive electrode active material will be described. Figure 2 is a process chart showing the method for producing a positive electrode active material.

[0058] In step S1, lithium metal is dissolved in an organic solvent to prepare a lithium solution. The lithium solution exhibits strong reducing power. At least one organic solvent selected from the group consisting of glymes and chain carbonates can be used. These solvents can dissolve aromatic compounds such as benzophenone. When lithium metal is added to a solution prepared from these solvents and aromatic compounds such as benzophenone, the lithium metal transfers its outermost electron to the solution and becomes an ion. The solution that has received the electrons is in a solvated state with the electrons, and the lithium metal is dissolved in the solution. Its potential is close to that of lithium metal, but the value varies depending on the combination of aromatic compound and solvent.

[0059] The glyme may be at least one selected from the group consisting of dimethoxyethane, diglyme, triglyme, tetraglyme, and polyethylene glycol dimethyl ether.The linear carbonate may be at least one selected from the group consisting of methyl ethyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0060] Typically, the organic solvent comprises at least one selected from the group consisting of triglyme, dimethoxyethane, and methyl ethyl carbonate.

[0061] The lithium solution may further contain an aromatic compound. A solution containing an aromatic compound has the property of releasing solvated electrons of lithium and dissolving lithium as cations. In other words, the aromatic compound has the property of accepting the electrons released when lithium dissolves in an organic solvent as solvated electrons and dissolving in the solvent of the lithium solution. An amount of lithium equal to the amount of the aromatic compound can be dissolved in the organic solvent. For example, when the concentration of the aromatic compound in the lithium solution is 1 mol / liter, the concentration of lithium in the lithium solution is also approximately 1 mol / liter.

[0062] The aromatic compound may be at least one selected from the group consisting of benzophenone, biphenyl, phenanthrene, naphthalene, anthracene, o-terphenyl, triphenylene, trans-stilbene, 2,2'-bipyridine, 4,4'-bipyridine, 3,3'-bipyridine, 2,3'-bipyridine, 2,4'-bipyridine, 3,4'-bipyridine, 1,10-phenanthroline, cis-stilbene, and fluorene. The aromatic compound may typically be benzophenone. The immersion time of MnO2 in the lithium solution is adjusted depending on the type and concentration of the aromatic compound.

[0063] The organic solvent may contain a mixture of triglyme and methyl ethyl carbonate. Using a mixture of triglyme and methyl ethyl carbonate allows the preparation of a lithium solution with strong reducing power, thereby enabling the doping of lithium into MnO2 to proceed rapidly. The mixing ratio of triglyme and methyl ethyl carbonate is not particularly limited and can be adjusted within a range satisfying 0.1≦(triglyme / methyl ethyl carbonate)≦0.9 in volume ratio. The organic solvent may contain only triglyme and methyl ethyl carbonate as the solvent.

[0064] The organic solvent may contain a mixture of dimethoxyethane and methyl ethyl carbonate. Using a mixture of dimethoxyethane and methyl ethyl carbonate allows the preparation of a lithium solution with strong reducing power, thereby enabling the doping of lithium into MnO2 to proceed rapidly. The mixing ratio of dimethoxyethane and methyl ethyl carbonate is not particularly limited and can be adjusted within a range satisfying 0.1≦(dimethoxyethane / methyl ethyl carbonate)≦0.9 in volume ratio. The organic solvent may contain only dimethoxyethane and methyl ethyl carbonate as the solvent.

[0065] In step S2, MnO2 is brought into contact with a lithium solution. Typically, MnO2 is immersed in the lithium solution. This allows lithium to be doped into MnO2, which has a layered structure or a tunnel structure, and Li x Mn y O2 is produced. Mn is reduced from tetravalent to trivalent. MnO2 may be formed into the shape of an electrode. That is, an electrode containing MnO2 as the active material may be immersed in a lithium solution. The lithium solution may be heated above room temperature to speed up the reaction.

[0066] The crystal structure of MnO2 is not particularly limited. Various crystal structures of MnO2 are available, including α-MnO2, β-MnO2, γ-MnO2, ε-MnO2, λ-MnO2, δ-MnO2, γ-β-MnO2, and R-MnO2 (ramsdellite-type manganese dioxide). MnO2 may contain multiple crystalline phases or may be a mixed crystal. MnO2 may contain at least one selected from the group consisting of γ-β-MnO2, ramsdellite, and β-MnO2. Ramsdellite, γ-β-MnO2, which can be prepared from electrolytic manganese dioxide, and β-MnO2, which can also be prepared from electrolytic manganese dioxide, all have a tunnel structure and are inexpensive and readily available. In particular, γ-β-MnO2 exhibits the highest discharge capacity density when used as an active material in primary batteries. In other words, Mn is easily reduced. Note that γ-β-MnO2 represents a mixed crystal of γ-MnO2 and β-MnO2.

[0067] After immersing the MnO2 in the lithium solution, in step S3, a predetermined time is allowed to elapse. x Mn y This is the time required for lithium to be doped into MnO2 until the condition x is satisfied (1.012 ≥ x ≥ 0.683 or 0.864). The reduction rate of Mn varies depending on conditions such as the reducing strength of the lithium solution, the lithium concentration in the lithium solution, the temperature of the lithium solution, and the form of MnO2 (powder or compact). Therefore, the optimal predetermined time is experimentally determined in advance.

[0068] After a predetermined time has elapsed, in step S4, Li x Mn y Separating O2 from the lithium solution. Li x Mn y The O2 is washed and dried. This allows Li to be used as the positive electrode active material. x Mn y O2 (1.012≧x≧0.683 and 0.91≦y≦1.0) is obtained. x Mn y The lithium secondary battery 10 described with reference to FIG. 1 can be manufactured using O2 as the positive electrode active material. x Mn y Using O2 (1.012≧x≧0.683 and 0.91≦y≦1.0) and graphite as the negative electrode active material, a lithium secondary battery 10 can be manufactured. The lithium secondary battery 10 is in a discharged state when assembly is complete, and charging can be started. [Example]

[0069] Example 1 A slurry was prepared by mixing PVdF as a binder, γ-β-MnO powder, and a solvent. The slurry was applied to an Al current collector to form a coating film. The coating film was dried and rolled to obtain an electrode measuring 2 cm x 2 cm.

[0070] A mixed solution was prepared by mixing benzophenone and methyl ethyl carbonate. The benzophenone concentration in the mixed solution was 1 mol / L. Li metal was dissolved in this mixed solution until it reached a saturated concentration, preparing a lithium solution. The lithium concentration in the lithium solution was 1 mol / L.

[0071] The electrode was immersed in the lithium solution for 137.9 days. After 137.9 days, the electrode was removed from the lithium solution, washed with methyl ethyl carbonate, and dried in a vacuum to obtain the positive electrode of Example 1.

[0072] A lithium secondary battery of Example 1 was fabricated using the Li metal as the positive electrode and negative electrode and the electrolyte of Example 1. The electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L in an organic solvent containing ethylene carbonate and methyl ethyl carbonate in a 1:1 volume ratio. A charge / discharge test was conducted on the resulting lithium secondary battery. The test began with charging. The charge / discharge current was 0.05 mA, the end-of-charge voltage was 4.3 V, and the end-of-discharge voltage was 1.5 V. The results are shown in Figures 3A, 3B, and 3C.

[0073] Fig. 3A shows the charge-discharge curve for the first cycle of the lithium secondary battery of Example 1. Fig. 3B shows the charge-discharge curve for the second cycle of the lithium secondary battery of Example 1. Fig. 3C is a graph showing the relationship between the discharge capacity density and the number of discharge cycles of the lithium secondary battery of Example 1. The horizontal axis of Figs. 3A and 3B represents the capacity density (mAh / g) of the lithium secondary battery, and the vertical axis represents the voltage (V). The horizontal axis of Fig. 3C represents the number of discharges (number of cycles), and the vertical axis represents the discharge capacity density (mAh / g).

[0074] As shown in Fig. 3A, the lithium secondary battery of Example 1 was in a discharged state immediately after assembly and was chargeable from the first cycle, indicating that a sufficient amount of lithium was doped into MnO2 to form LiMnO2.

[0075] 3A and 3B, the discharge capacity density at the first cycle was roughly equal to that at the second cycle. As shown in Fig. 3C, the discharge capacity density hardly changed even after 10 charge-discharge cycles.

[0076] The amount of Li doped into MnO2 during the reduction process and the valence of Mn were calculated from the charge capacity density (309.5 mAh / g) at the first cycle. The amount of Li doped was 1.012 moles per mole of MnO2. The valence of Mn after the reduction process was 2.987.

[0077] Example 2 A mixed solution was prepared by adding benzophenone at a concentration of 1 mol / L to a mixed solvent containing triglyme and methyl ethyl carbonate in a 1:1 volume ratio. Li metal was dissolved in this mixed solution to prepare a lithium solution. The lithium concentration in the lithium solution was 1 mol / L.

[0078] The same electrode as in Example 1 was immersed in the lithium solution for 1.8 days. Thereafter, a lithium secondary battery of Example 2 was fabricated in the same manner as in Example 1, and a charge-discharge test was carried out. The results are shown in Figures 4A, 4B, and 4C. Figures 4A, 4B, and 4C are graphs showing the test results for the same items as in Figures 3A, 3B, and 3C, respectively.

[0079] As shown in Fig. 4A, the lithium secondary battery of Example 2 was in a discharged state immediately after assembly and was chargeable from the first cycle. As shown in Fig. 4C, the discharge capacity density hardly changed even after 10 charge-discharge cycles.

[0080] The amount of Li doped into MnO2 during the reduction treatment and the valence of Mn were calculated from the charge capacity density (276 mAh / g) at the first cycle. As a result, the amount of Li doped was 0.905 moles per mole of MnO2. The valence of Mn after the reduction treatment was 3.094. The reduction treatment time in Example 2 was 1.8 days, which was significantly shorter than the reduction treatment time in Example 1.

[0081] Example 3 A lithium secondary battery of Example 3 was fabricated in the same manner as in Example 2, except that the immersion time of the electrodes in the lithium solution was changed to 2.8 days, and a charge-discharge test was carried out. The results are shown in Figures 5A, 5B, and 5C. Figures 5A, 5B, and 5C are graphs showing the test results for the same items as Figures 3A, 3B, and 3C, respectively.

[0082] As shown in Fig. 5A, the lithium secondary battery of Example 3 was in a discharged state immediately after assembly and was chargeable from the first cycle. As shown in Fig. 5C, the discharge capacity density hardly changed even after 10 charge-discharge cycles.

[0083] The amount of Li doped into MnO2 during the reduction treatment and the valence of Mn were calculated from the charge capacity density (276 mAh / g) at the first cycle. As a result, the amount of Li doped was 0.864 moles per mole of MnO2. The valence of Mn after the reduction treatment was 3.136. The reduction treatment time in Example 3 was 2.8 days, which was significantly shorter than the reduction treatment time in Example 1.

[0084] Example 4 A treatment solution was prepared by adding benzophenone at a concentration of 1 mol / L to a mixed solvent containing dimethoxyethane and methyl ethyl carbonate in a 1:1 volume ratio. Li metal was dissolved in this treatment solution to prepare a lithium solution. The lithium concentration in the lithium solution was 1 mol / L.

[0085] The same electrode as in Example 1 was immersed in the lithium solution for 1.8 days. Thereafter, a lithium secondary battery of Example 4 was fabricated in the same manner as in Example 1, and a charge-discharge test was carried out. The results are shown in Figures 6A, 6B, and 6C. Figures 6A, 6B, and 6C are graphs showing the test results for the same items as in Figures 3A, 3B, and 3C, respectively.

[0086] As shown in Fig. 6A, the lithium secondary battery of Example 4 was in a discharged state immediately after assembly and was chargeable from the first cycle. As shown in Fig. 6C, the discharge capacity density hardly changed even after 10 charge-discharge cycles.

[0087] The amount of Li doped into MnO2 during the reduction treatment and the valence of Mn were calculated from the charge capacity density (210.54 mAh / g) at the first cycle. As a result, the amount of Li doped was 0.683 moles per mole of MnO2. The valence of Mn after the reduction treatment was 3.316. The reduction treatment time in Example 4 was 1.8 days, which was significantly shorter than the reduction treatment time in Example 1.

[0088] (Reference example 1) A slurry was prepared by mixing PVdF as a binder, γ-β-MnO powder, and a solvent. The slurry was applied to an Al current collector to form a coating film. The coating film was dried and rolled to obtain an electrode measuring 2 cm × 2 cm. A lithium secondary battery of Reference Example 1 was fabricated in the same manner as in Example 1, except that this electrode was used as the positive electrode, and a charge-discharge test was performed. However, the test began with discharge. The results are shown in Figures 7A and 7B.

[0089] FIG. 7A shows the discharge curve for the first cycle of the lithium secondary battery of Reference Example 1. FIG. 7B shows the charge curve for the first cycle of the lithium secondary battery of Reference Example 1. The amount of Li and the valence of Mn doped into the positive electrode during the first cycle discharge were calculated from the discharge capacity density for the first cycle. As a result, the amount of Li doped was 0.929 moles per mole of MnO2. The valence of Mn was 3.071.

[0090] (Powder X-ray diffraction measurement) Powder X-ray diffraction measurements were carried out on the positive electrode active material of Example 2 and the positive electrode active material of Reference Example 1. The results are shown in Fig. 8. The relationship between the results shown in Fig. 8 and the samples is as follows.

[0091] DIS: After the first discharge of Reference Example 1 DIS-CHA…After the first charge of Reference Example 1 DIS-CHA-DIS: After the second discharge cycle of Reference Example 1 LiDope: After charge and discharge in Example 2 (after Li doping) Blank: polyethylene bag used during measurement

[0092] The results shown in Figure 8 show that the "DIS," "DIS-CHA-DIS," and "LiDope" samples have the same structure. [Industrial Applicability]

[0093] The technology of the present disclosure can be applied to lithium secondary batteries. [Explanation of symbols]

[0094] 10. Lithium secondary battery 11 Negative electrode current collector 12 Negative electrode active material layer 13 Negative electrode 14 Positive electrode current collector 15 Cathode active material layer 16 positive electrode 17 Separator 18 Exterior 19 Non-aqueous electrolytes

Claims

1. MnO 2 contacting the The organic solvent comprises a glyme and a chain carbonate. A method for producing a positive electrode active material.

2. A method for producing a lithium-ion battery comprising contacting MnO 2 with a lithium solution in which lithium metal is dissolved in an organic solvent, the lithium solution further comprises an aromatic compound; A method for producing a positive electrode active material.

3. MnO 2 is γ-β-MnO 2 , ramsdellite and β-MnO 2 At least one selected from the group consisting of: The method for producing a positive electrode active material according to claim 1 or 2.

4. The glyme comprises at least one selected from the group consisting of triglyme and dimethoxyethane. The method for producing the positive electrode active material according to claim 1 .

5. The chain carbonate comprises methyl ethyl carbonate. The method for producing the positive electrode active material according to claim 1 .

6. The organic solvent contains a mixture of triglyme as the glyme and methyl ethyl carbonate as the chain carbonate. The method for producing the positive electrode active material according to claim 1 .

7. The organic solvent contains a mixture of dimethoxyethane as the glyme and methyl ethyl carbonate as the chain carbonate. The method for producing the positive electrode active material according to claim 1 .

8. the lithium solution further comprises an aromatic compound; The method for producing the positive electrode active material according to claim 1 .

9. The aromatic compound comprises benzophenone. The method for producing a positive electrode active material according to claim 2 or 8.

10. The organic solvent comprises at least one selected from the group consisting of glyme and chain carbonate. The method for producing a positive electrode active material according to claim 2 .

11. The method according to claim 1, wherein the organic solvent comprises at least one selected from the group consisting of triglyme, dimethoxyethane, and methyl ethyl carbonate. The method for producing a positive electrode active material according to claim 2 .

12. The method of claim 1, wherein the organic solvent comprises a mixture of triglyme and methyl ethyl carbonate. The method for producing a positive electrode active material according to claim 2 .

13. The method of claim 1, wherein the organic solvent comprises a mixture of dimethoxyethane and methyl ethyl carbonate. The method for producing a positive electrode active material according to claim 2 .

Images