Method for manufacturing lithium-ion battery positive electrode material

Abstract

The present invention pertains to a method for manufacturing a lithium-ion battery positive electrode material containing a lithium compound (A) represented by LiMn2-xSixO4 (0.25≤x≤1), the method comprising a process (I) which is a step for synthesizing a lithium compound (B) represented by formula: LiMn2-xSixO4 (0.25≤x≤1) by sintering a mixture of a lithium precursor, a manganese precursor, and a silicon precursor at a temperature of 350-850°C in an oxidative atmosphere, and a process (II) which is a step for obtaining the lithium compound (A) by heating the lithium compound (B) obtained in said process (I) at a temperature of 300-550°C in a non-oxidative atmosphere.

Description

Method for manufacturing positive electrode materials for lithium-ion batteries

[0001] The present invention relates to a method for producing a positive electrode material for a lithium ion battery.

[0002] As a positive electrode material for lithium-ion batteries, Li ２ MnO ４ and LiMn ２ O ４ These compounds are made of inexpensive, abundantly available elements, which means they have a low environmental impact and a high operating voltage, making them attractive candidates for the positive electrode of lithium-ion batteries.

[0003] The rapid development of the electric vehicle industry has created a demand for lithium batteries with high energy density. However, because the gram capacity of lithium manganese oxide is approximately 140 to 150 mAh / g, it is difficult to obtain lithium ion batteries with the required energy density. Therefore, there is a demand for lithium ion batteries with even higher energy density.

[0004] In relation to the present invention, Patent Document 1 discloses a new positive electrode material for lithium ion batteries, which has a spinel structure and the formula: LiMnSiO ４ This document also describes a lithium manganese silicate material represented by the formula: LiMnSiO ４ It is also described that Mn is capable of transferring two electrons and that the theoretical capacity is about 330 mAh / g.

[0005] Chinese Patent Application Publication No. 107464928

[0006] LiMnSiO described in Patent Document 1 ４ has been considered to be a preferable cathode material for lithium ion batteries due to its high theoretical capacity, improved reversibility, and low cost. However, according to the investigations of the present inventors, LiMnSiO produced by the method described in Patent Document 1 ４The actual energy density of lithium ion batteries is lower than the theoretical amount. Therefore, an object of the present invention is to provide a method for producing a positive electrode material for lithium ion batteries having a high energy density.

[0007] In order to achieve the above object, the present invention provides a method for producing a positive electrode material for a lithium battery, comprising: ２－ｘ Si ｘ O ４ A method for producing a positive electrode material for a lithium ion battery, comprising: (A) a lithium compound represented by the formula: LiMn ２－ｘ Si ｘ O ４ (x≦1) (step (II): synthesizing a lithium compound (B) represented by the formula (0.25≦x≦1); and step (II): heating the lithium compound (B) obtained in step (I) to a temperature of 300° C. or higher and 550° C. or lower in a non-oxidizing atmosphere to obtain a lithium compound (A).

[0008] According to the present invention, a method for producing a positive electrode material for a lithium ion battery having a high energy density can be provided.

[0009] 1 is a flowchart showing an outline of a method for producing a positive electrode material for a lithium battery according to the present invention; 2 is an X-ray diffraction diagram of a lithium compound (A) obtained in Example 5; 3 is an X-ray diffraction diagram of a lithium compound (B) obtained at firing temperatures of 300°C, 350°C, 450°C, 550°C, 600°C, and 700°C;

[0010] The following describes embodiments of the present invention. In this specification, "α to β" means "α or more and β or less."

[0011] 1) Method for producing a positive electrode material for a lithium ion battery The method for producing a positive electrode material for a lithium ion battery according to an embodiment of the present invention is to produce a material having the formula: LiMn ２－ｘ Si ｘ O ４The method for producing a positive electrode material for a lithium ion battery, which contains a lithium compound (A) represented by the formula (0.25≦x≦1), includes steps (I) and (II).

[0012] An outline of the method for producing a positive electrode material for a lithium ion battery of the present invention is shown in Figure 1. As shown in Figure 1, the production method of the present invention includes a step (I) of calcining a mixture (precursor mixture) of a lithium precursor, a manganese precursor, and a silicon precursor at a predetermined temperature in an oxidizing atmosphere to obtain a lithium compound (B) (synthesis of lithium compound (B)), and a step (II) of subjecting the obtained lithium compound (B) to a heat treatment (thermal reduction treatment) at a predetermined temperature in a reducing atmosphere to obtain a lithium compound (A).

[0013] (1) Step (I) In step (I), a mixture of a lithium precursor, a manganese precursor, and a silicon precursor is fired at a temperature of 350°C or higher and 850°C or lower in an oxidizing atmosphere to obtain a compound of the formula: LiMn ２－ｘ Si ｘ O ４ This is a step of synthesizing a lithium compound (B) represented by (0.25≦x≦1).

[0014] <Precursor> The lithium precursor, manganese precursor, and silicon precursor used in the present invention are not particularly limited. Examples include simple substances, oxides, nitrides, hydroxides, halides such as chlorides and fluorides, inorganic salts such as carbonates, sulfates, nitrates, and phosphates, organic acid salts such as acetates and citrates, alkoxides, oxoacids, and oxoacid salts of each element. Alternatively, compounds containing two or more of the above elements may be used. Each compound may also be a hydrate.

[0015] Specific examples of the lithium precursor used in the present invention include lithium carbonate, lithium hydroxide, lithium acetate, lithium citrate, lithium nitrate, lithium chloride, and hydrates of these compounds. From the viewpoint of easily obtaining a lithium compound (B) with few impurities, lithium acetate, lithium nitrate, lithium hydroxide, lithium citrate, and hydrates of these compounds are preferred.

[0016] The manganese precursor is preferably a Mn(II) compound. Examples include manganese(II) oxide, manganese(II) nitrate, manganese(II) acetate, manganese(II) citrate, and hydrates of these compounds. From the viewpoint of easily obtaining a lithium compound (B) with few impurities, manganese(II) acetate, manganese(II) citrate, or hydrates of these compounds are preferred.

[0017] Examples of the silicon precursor include silicon tetraacetate, orthosilicic acid, tetraalkylorthosilicate such as tetraethoxysilane, and silicon dioxide. From the viewpoint of easily obtaining a lithium compound (B) with few impurities, orthosilicic acid, tetraalkylorthosilicate, or silicon dioxide is preferred.

[0018] The blending ratio of the lithium precursor, manganese precursor, and silicon precursor used in the present invention is expressed by the formula: LiMn ２－ｘ Si ｘ O ４ The mixing ratio of these precursors to a total of 100 parts by mass of the lithium precursor, manganese precursor, and silicon precursor varies depending on the preparation method of the precursors, although it also depends on the value of x in the formula. ２ O 17 to 25 parts, MnO as a manganese precursor 40 to 75 parts, SiO as a silicon precursor ２ In the case of the sol-gel method, the lithium precursor is lithium acetate, and the manganese precursor is manganese (II) acetate, and the silicon precursor is tetraethyl orthosilicate, and ... silicon precursor is tetraethyl orthosilicate, and the manganese precursor is manganese (II) acetate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the manganese precursor is manganese (II) acetate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, and the silicon precursor is tetraethyl orthosilicate, ４ and LiMn １．７５ Si ０．２５ O ４ It was decided by.

[0019] <Preparation of Precursor Mixture> In step (I), first, a mixture of a lithium precursor, a manganese precursor, and a silicon precursor (hereinafter, sometimes referred to as a "precursor mixture") is prepared. Examples of methods for preparing the precursor mixture include a method in which predetermined amounts of a lithium precursor, a manganese precursor, and a silicon precursor are mixed in a solid state, and a sol-gel method in which deionized water, an alcohol having 1 to 3 carbon atoms, or a mixed solvent consisting of deionized water and an alcohol having 1 to 3 carbon atoms (hereinafter, sometimes referred to as "deionized water, etc.") is added to predetermined amounts of a lithium precursor, a manganese precursor, and a silicon precursor, and the entire mixture is stirred to obtain a slurry. Among these, the sol-gel method is preferred because it is a simple method that makes it easy to obtain a precursor mixture with a uniform composition.

[0020] An example of the former method is a method in which predetermined amounts of lithium carbonate, manganese(II) oxide, and silicon dioxide are mixed in a solid state. An example of the latter method is a method in which predetermined amounts of lithium acetate, manganese(II) acetate, and tetraethoxyorthosilicate are mixed, and then a predetermined amount of deionized water or the like is added, and the entire mixture is stirred to form a slurry. In the latter sol-gel method, the amount of deionized water or the like added is typically 300 to 1,000 parts, preferably 500 to 1,000 parts, per 100 parts by mass of the total amount of the lithium precursor, manganese precursor, and silicon precursor.

[0021] Furthermore, in the case of the sol-gel method, a preferred method is to mix a lithium precursor, a manganese precursor, and a silicon precursor using a high-energy milling process to obtain a lithium manganese silicate precursor (precursor mixture). For example, the slurry (a) obtained by the sol-gel method is placed in a ball mill and uniformly milled to obtain a slurry (b) having a particle size of 200 to 300 nm, and the resulting slurry (b) is then spray-dried to obtain a spherical lithium manganese silicate precursor having a particle size of 3 to 6 μm. This method makes it possible to obtain a lithium manganese silicate precursor (precursor mixture) having a uniform composition more simply and efficiently.

[0022] <Caking of Precursor Mixture> Next, the obtained precursor mixture is calcined in an oxidizing atmosphere at a temperature of 350° C. or higher and 850° C. or lower to obtain a lithium compound (B).

[0023] In the present invention, the precursor mixture is calcined in an oxidizing atmosphere. If the precursor mixture is not calcined in an oxidizing atmosphere, it becomes difficult to obtain the desired lithium compound (B) having a spinel structure.

[0024] In the present invention, "under an oxidizing atmosphere" means an atmosphere of an oxidizing gas, preferably an atmosphere of air or oxygen.

[0025] The oxidizing atmosphere in step (I) is preferably oxygen, air, or a mixed gas containing oxygen or air and an inert gas. Examples of the inert gas include Ar, N ２ , He, Ne, Kr, Xe, etc. When a mixed gas atmosphere containing oxygen or air and an inert gas is used as the oxidizing atmosphere, the mixed gas preferably contains 5.0% (v / v) or more of oxygen.

[0026] The temperature at which the precursor mixture is fired is 350° C. or higher and 850° C. or lower, preferably 500° C. or higher and 850° C. or lower, and more preferably 650° C. or higher and 850° C. or lower. When the firing temperature (firing temperature) is lower than 350° C., the precursor mixture is converted into a compound of the formula: LiMn ２－ｘ Si ｘ O ４ On the other hand, if the calcination temperature exceeds 850°C, the produced lithium compound (B) may be thermally decomposed.

[0027] In this way, the compound of the formula: LiMn ２－ｘ Si ｘ O ４ In the formula, x is a positive number of 0.25 or more and 1 or less, preferably a positive number of 0.5 or more and 1 or less, and more preferably a positive number of 0.7 or more and 1 or less.

[0028] (2) Step (II) Step (II) is a step of heating the lithium compound (B) obtained in step (I) to a temperature of 300° C. or higher and 550° C. or lower in a non-oxidizing atmosphere to obtain the lithium compound (A).

[0029] Formula: LiMn ２－ｘ Si ｘ O ４ When a lithium compound represented by (0.25≦x≦1) is used as a positive electrode material for a lithium ion battery, it is ideal that all of the Mn is Mn(III) from the viewpoint of electrochemical properties.

[0030] However, according to the investigations of the present inventors, the LiMnSiO produced by the method described in Patent Document 1 ４ The actual energy density of the lithium compound (B) was lower than the theoretical amount. The inventors conducted extensive research into the cause of this finding and found that the lithium compound (B) obtained by calcining the precursor mixture contained, in addition to Mn(III), Mn(IV), which was thought to be produced by overoxidation of Mn(II). The presence of Mn(IV) was considered to be the cause of the deterioration of the electrochemical performance of the lithium compound (B) as a positive electrode material for lithium-ion batteries. Therefore, the inventors devised a method of reducing the Mn(IV) contained in the lithium compound (B) to Mn(III) by subjecting the calcined lithium compound (B) to a treatment (thermal reduction treatment) in which the lithium compound (B) obtained by calcination was heated at a predetermined temperature in a non-oxidizing atmosphere.

[0031] Although it is not clear what form or amount of Mn(IV) contained in lithium compound (B) is present, the results of differential thermal analysis (DTA) have shown that when lithium compound (B) is heated to a temperature of 300°C or higher and 550°C or lower in a non-oxidizing atmosphere, oxygen is released from the crystals of lithium compound (B), and the weight of lithium compound (B) decreases. On the other hand, the results of X-ray diffraction measurements of lithium compound (B) and lithium compound (A) show no change in the peak positions of the X-ray diffraction patterns of lithium compound (B) and lithium compound (A). Therefore, it is believed that lithium compound (B) contains a mixture of Mn(III) and Mn(IV), and that by heating to a temperature of 300°C or higher and 550°C or lower in a non-oxidizing atmosphere, Mn(IV) is reduced (thermally reduced) to Mn(III) while maintaining the crystalline structure, thereby obtaining lithium compound (A).

[0032] This is also supported by the fact that, as shown in the Examples, the electrochemical properties of the lithium compound (A), such as discharge voltage, discharge capacity, and energy density, are improved compared to those of the lithium compound (B). That is, from the viewpoint of electrochemical properties, the lithium compound (A) has the formula: LiMn ２－ｘ Si ｘ O ４ Ideally, all of the Mn in the lithium compound represented by (0.25≦x≦1) is Mn(III). Regardless of the firing temperature (350° C. or higher and 850° C. or lower) in step (I), the electrochemical properties of the lithium compound (A) obtained through step (II) are improved compared to the lithium compound (B) before step (II).

[0033] The non-oxidizing atmosphere in step (II) is preferably a non-oxidizing gas atmosphere. Examples of the non-oxidizing gas include Ar, N ２ , He, Ne, Kr, Xe, or a mixed gas of two or more of these gases. Ar gas is preferred because it is easier to obtain the excellent effects of the present invention.

[0034] The higher the purity of the non-oxidizing gas, the more preferable. The purity of the non-oxidizing gas is preferably 99% or more, more preferably 99.9% or more, and particularly preferably 99.99% or more. If the purity of the non-oxidizing gas used is low, undesirable side reactions may occur in the thermal reduction treatment, and the electrochemical performance of the resulting lithium compound (A) as a positive electrode material for lithium ion batteries may be reduced.

[0035] The heating temperature in step (II) is 300°C or higher, preferably 350°C or higher, more preferably 400°C or higher, and even more preferably 450°C or higher. The heating temperature in step (II) is 550°C or lower, preferably 530°C or lower, more preferably 520°C or lower, and even more preferably 500°C or lower. If the heating temperature in step (II) is too low, lithium compound (B) may not be obtained. On the other hand, if the heating temperature is too high, lithium compound (A) may be thermally decomposed.

[0036] The heating time in step (II) is not particularly limited, but is preferably between 30 minutes and 4 hours, and more preferably between 30 minutes and 3 hours. If the heating time is too short, the reaction of reducing Mn(IV) present in the lithium compound (B) to Mn(III) may not proceed sufficiently, and a lithium compound (A) having excellent electrochemical properties may not be obtained. On the other hand, if the heating time is too long, the resulting lithium compound (A) may be thermally decomposed.

[0037] The method of the thermal reduction treatment in the step (II) is not particularly limited as long as it involves heating the lithium compound (B) in a non-oxidizing atmosphere at a predetermined temperature for a predetermined time. From the viewpoint of the efficiency of the thermal reduction treatment, however, a method in which the lithium compound (B) is placed in a tubular furnace, and the inside of the tubular furnace is heated to a predetermined temperature while a non-oxidizing gas is flowed through the tubular furnace is preferred.

[0038] The flow rate of the non-oxidizing gas flowing through the tubular furnace is preferably less than 50 mL / min, more preferably less than 30 mL / min, and even more preferably less than 20 mL / min. If the flow rate of the non-oxidizing gas flowing through the tubular furnace is 50 mL / min or more, the lithium compound may decompose. The lower limit of the flow rate of the non-oxidizing gas flowing through the tubular furnace is not particularly limited, but is usually 3 mL / min or more.

[0039] In this manner, the lithium compound (A) can be obtained. Formula: LiMn ２－ｘ Si ｘ O ４ In order to obtain a lithium battery with a high energy density, the value of x is 0.25 or more and 1 or less, preferably 0.5 or more and 1 or less, more preferably 0.7 or more and 1 or less, and particularly preferably 1.

[0040] The crystals of the lithium compound (A) have a cubic spinel structure, the space group is Fd-3m, and have a stable crystal structure, so that a lithium ion battery using the lithium compound (A) as a positive electrode material exhibits stable battery performance.

[0041] The positive electrode material for lithium ion batteries obtained by the production method of the present invention has excellent electrochemical properties. As shown in the examples, the energy density of a lithium battery having a positive electrode using the positive electrode material of the present invention is higher than that of a lithium ion battery using lithium compound (B), regardless of the firing temperature (350 to 800°C) at which lithium compound (B) is obtained.

[0042] According to the production method of the present invention, a positive electrode material for a lithium ion battery having excellent electrochemical properties can be produced efficiently by a simple method using raw materials that are inexpensive, abundant in resources, and have a low environmental impact.

[0043] 2) Positive electrode of lithium ion battery A positive electrode of a lithium ion battery according to another embodiment of the present invention contains a positive electrode material for lithium ion batteries (hereinafter, sometimes referred to as the "positive electrode material of the present invention") obtained by the manufacturing method of the present invention. The positive electrode of the present invention has excellent electrochemical properties because it contains the positive electrode material of the present invention.

[0044] The positive electrode of the lithium ion battery of the present invention can be formed from a positive electrode composition for lithium ion batteries containing the positive electrode material of the present invention, a binder resin, a conductive additive, and a dispersant. For example, the positive electrode can be produced by applying a paste of the positive electrode composition for lithium ion batteries to a current collector and drying it.

[0045] Examples of binder resins contained in the positive electrode composition for lithium ion batteries include starch, polyvinylidene fluoride, polyvinyl alcohol, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, carboxymethyl cellulose, polyethylene, and polypropylene.

[0046] Examples of the conductive additive include metals such as aluminum, stainless steel, silver, gold, copper, and titanium; graphite, acetylene black, ketjen black, furnace black, channel black, and thermal lamp black; carbon nanofibers, carbon nanotubes, graphene, and mixtures thereof.

[0047] Examples of dispersants include polymethyl methacrylate, polyethylene glycol, polyvinylpyrrolidone, linear alkylbenzene sodium sulfonate, alkyl polyoxyethylene ether, sodium lauryl sulfate, and alkyl sulfonic acid.

[0048] The positive electrode composition for a lithium ion battery may further contain a solvent or an adhesive, if desired.

[0049] The content of each component in the positive electrode composition for lithium ion batteries is not particularly limited, but the content of the positive electrode material of the present invention is about 50% by mass to 75% by mass, the content of the binder resin is about 1 to 20% by mass, the content of the dispersant is about 0.05% by mass to 0.1% by mass, and the content of the conductive agent is about 0.9% by mass to 1.5% by mass, relative to the entire positive electrode composition for lithium ion batteries.

[0050] The current collector has a function of mediating the movement of electrons from the positive electrode and the negative electrode. There are no particular limitations on the material constituting the current collector. For example, metals and conductive resins can be used as the material constituting the current collector.

[0051] Examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper.

[0052] The positive electrode of the lithium ion battery of the present invention contains a positive electrode material for lithium ion batteries having excellent electrochemical properties, and therefore has excellent electrochemical properties.

[0053] 3) Lithium-ion battery A lithium-ion battery according to yet another embodiment of the present invention includes the positive electrode of the lithium-ion battery of the present invention. The lithium-ion battery of the present invention includes the positive electrode of the present invention, which has excellent electrochemical properties, and therefore exhibits excellent battery characteristics.

[0054] The lithium ion battery of the present invention may be a lithium ion battery in which the electrolyte is liquid, a semi-solid battery in which the electrolyte is semi-solid (gel), or an all-solid battery in which the electrolyte is solid.

[0055] The lithium ion battery according to the embodiment of the present invention includes, as a positive electrode, the positive electrode of the lithium ion battery of the present invention, and, as a negative electrode, a negative electrode formed by applying a slurry of a negative electrode active material and a binder resin in a solvent and drying the slurry.

[0056] Examples of the negative electrode active material include metallic lithium, carbon materials such as graphite, silicon materials such as silicon thin films, alloy materials such as copper-tin and cobalt-tin, and oxide materials such as lithium titanate. Examples of the binder resin include the resins listed above as being usable in the positive electrode composition for lithium ion batteries.

[0057] The lithium ion battery of the present invention can have the structure of any of various conventionally known lithium ion batteries, except that it has the positive electrode of the present invention as the positive electrode. Furthermore, the lithium ion battery of the present invention can be manufactured by any of various conventionally known methods for manufacturing lithium ion batteries.

[0058] <Lithium-ion battery with liquid electrolyte> A lithium-ion battery with liquid electrolyte contains at least a positive electrode, a negative electrode, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are inserted and removed back and forth between the positive and negative electrodes. The electrolyte serves to conduct the ions between the positive and negative electrodes.

[0059] The separator is placed between the positive and negative electrodes and serves mainly to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through.

[0060] The separator is a microporous polymer film, and examples of polymers that make up the polymer film include nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene.

[0061] The electrolyte used is one containing lithium, for example, LiClO ４ , LiAsF ６ , LiPF ６ , LiBF ４ , LiB(C ６ H ５ ) ４ , LiCl, LiBr, CH ３ SO ３ Li, CF ３ SO ３ An example of the electrolyte is an electrolytic solution in which Li or the like is dissolved in an organic solvent.

[0062] Examples of the organic solvent include carbonates, ethers, ketones, thioethers, nitriles, halogenated hydrocarbons, amides, and phosphate esters.

[0063] <Semi-solid Battery> The semi-solid battery includes a battery that includes at least a positive electrode, a negative electrode, and a gel electrolyte, and has the positive electrode of the present invention as the positive electrode.

[0064] The gel electrolyte may be one having a structure in which a liquid electrolyte is injected into a matrix polymer having lithium ion conductivity.

[0065] Examples of the matrix polymer include polymers having polyethylene oxide in the main chain or side chain, polyacrylonitrile, polymethacrylic acid ester, polyvinylidene fluoride, and copolymers of polyvinylidene fluoride and hexafluoropropylene.

[0066] As the liquid electrolyte, those listed above as the electrolyte for the lithium ion battery can be used.

[0067] <All-Solid-State Battery> The all-solid-state battery includes at least a positive electrode, a negative electrode, and a solid electrolyte, and has the positive electrode of the present invention as the positive electrode.

[0068] As the solid electrolyte, a polymer solid electrolyte, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or the like can be used.

[0069] The polymer solid electrolyte may be one that has a structure in which a lithium salt is dissolved in a matrix polymer and does not contain an organic solvent, such as a polymer having polyethylene oxide in the main chain or side chain, polyacrylonitrile, polymethacrylic acid ester, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0070] The sulfide-based solid electrolyte is Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P２ S ５ , LiI-Li ２ O-Li ２ S-P ２ S ５ , LiI-Li ２ S-P ２ O ５ , LiI-Li ３ P.O. ４ -P ２ S ５ , Li ２ S-P ２ S ５ , Li ３ P.S. ４ etc.

[0071] Examples of oxide-based solid electrolytes include LLTO-based compounds, LIPON-based compounds, NASICON-based compounds, and garnet-based compounds.

[0072] The content of the solid electrolyte is not particularly limited, and is preferably 1% by mass or more and 40% by mass or less, more preferably 2% by mass or more and 30% by mass or less, and even more preferably 3% by mass or more and 20% by mass or less, relative to 100% by mass of the positive electrode material of the present invention.

[0073] The method for preparing the electrolyte solution is not particularly limited, and any method can be used as long as it can mix the above-mentioned compound, solvent, and lithium salt, as well as any optional components added as needed, and uniformly dissolve or disperse each component.

[0074] As described above, the resulting lithium ion battery has excellent battery characteristics because it is provided with a positive electrode having excellent electrochemical properties. Furthermore, the lithium ion battery of the present invention exhibits stable and excellent battery performance.

[0075] The present invention will be described in more detail below with reference to examples. The following examples illustrate one embodiment of the present invention, and the present invention is not limited thereto. In the following, "parts" are based on mass.

[0076] (Example 1) Lithium Compound (A) (Thermal Reduction Treated LiMnSiO ４ ) Production of (1) LiMnSiO ４Synthesis of [Lithium Compound (B)]: 12.7 parts of lithium acetate, 47.2 parts of manganese (II) acetate tetrahydrate, and 74 parts of citric acid were placed in a container equipped with a stirrer, and 1,500 parts of deionized water was added thereto. The entire mixture was stirred to obtain solution (1). Separately, 40.1 parts of tetraethyl orthosilicate were dissolved in 400 parts of isopropanol to obtain solution (2). Solution (1) and solution (2) were combined and stirred to obtain a dispersion solution. The obtained dispersion solution was heated under vacuum at 80°C for 2 hours to evaporate the solution, obtaining a gel. The obtained gel was further dried under vacuum at 80°C for 24 hours to obtain a lithium manganese silicate precursor powder. The obtained precursor powder was placed in a tubular furnace and pre-calcined for 1 hour while flowing oxygen gas into the tubular furnace at a flow rate of 100 ml / min, and then heated to 700°C and calcined for 4 hours. The obtained LiMnSiO ４ The lithium compound (B) was taken out of the tubular furnace and crushed in a mortar to obtain a powder of lithium compound (B).

[0077] (2) LiMnSiO ４ Thermal Reduction Treatment of [Lithium Compound (B)] The lithium compound (B) obtained above was placed in a tubular furnace, and while Ar gas (purity 99.99%) was flowed into the tubular furnace at a flow rate of 10 ml / min, the inside of the tubular furnace was heated to 500°C and maintained at the same temperature for 30 minutes, thereby obtaining lithium compound (A) of Example 1.

[0078] (Examples 2 to 10, Comparative Examples 1 to 12) Lithium compounds (B) and lithium compounds (A) of Examples 2 to 10 and Comparative Examples 1 to 12 were obtained in the same manner as in Example 1, except that the firing temperature, the heating temperature and the heating conditions of the thermal reduction treatment were changed to those shown in the following Table 1. In Table 1, "none" means that no heat treatment was performed.

[0079]

[0080] The X-ray diffraction pattern of the lithium compound (lithium compound (A)) obtained in Example 5 is shown in Figure 2. In Figure 2, the horizontal axis represents the diffraction angle (2θ) and the vertical axis represents the peak intensity (au).

[0081] The X-ray diffraction pattern of the lithium compound (B), which is a production intermediate, is shown in Figure 3. In Figure 3, the horizontal axis represents the diffraction angle (2θ) and the vertical axis represents the peak intensity (a.u.). In Figure 2, "300°C" represents the X-ray diffraction pattern of the lithium compound (B) obtained at a firing temperature of 300°C. The same applies to "350°C," "450°C," "550°C," "600°C," and "700°C."

[0082] Comparing the X-ray diffraction pattern in Figure 2 with the X-ray diffraction pattern at "600°C" in Figure 3, the peak positions of both are the same, which indicates that there is no change in the crystal structure of the lithium compound before and after the thermal reduction treatment.

[0083] <Evaluation of Electrochemical Performance of Positive Electrode Materials for Lithium-Ion Batteries> Positive electrodes were fabricated using the positive electrode materials for lithium-ion batteries obtained in Examples 1 to 10 and Comparative Examples 1 to 12. Furthermore, button batteries having the fabricated positive electrodes were fabricated, and evaluation tests of their electrochemical performance (discharge voltage, initial discharge capacity, energy density, and durability) were carried out.

[0084] (1) Preparation of Positive Electrode The lithium compound (A) obtained in Example 1, conductive carbon powder, and polyvinylidene fluoride (PVDF) were uniformly mixed in a mass ratio of 8:1:1, and an appropriate amount of solvent (N-methylpyrrolidone) was added. The resulting mixture was thoroughly stirred to form a viscous slurry, which was then uniformly coated on the surface of aluminum foil and air-dried. The resulting coated aluminum foil was placed in a vacuum drying oven at 120°C for 8 hours and rolled multiple times to obtain a positive electrode sheet. The resulting positive electrode sheet was punched into a disk with a diameter of 12 mm to obtain a positive electrode for a lithium-ion battery. After accurately measuring the mass of this product, the LiMnSiO contained in the pole piece based on the blending composition was measured. ４ The mass was calculated.

[0085] Positive electrode sheets were obtained in the same manner as above using the lithium compounds obtained in Examples 2 to 10 and Comparative Examples 1 to 12. After accurately measuring the mass of these positive electrodes, the LiMnSiO contained in the pole piece was calculated based on the blended composition. ４ The mass was calculated.

[0086] (2) Preparation of Lithium-ion Battery Next, the positive electrode for the lithium-ion battery obtained in (1) above, a microporous polypropylene membrane with a diameter of 19 mm, and a negative electrode lithium sheet with a diameter of 15 mm were used to prepare a lithium-ion battery. The separator was a Celgard polypropylene (PP) film, and the concentration of LiPF was 1 mol / L. ６ A button-type lithium ion battery (button battery) was assembled in a glove box filled with argon gas using a solution of carbonate (volume ratio of diethyl carbonate (DEC) / ethylene carbonate (EC) = 1:1) as an electrolyte.

[0087] (3) Electrochemical Performance Evaluation Test (Part 1) (i) Measurement of Discharge Voltage Each of the button batteries obtained in (2) above was charged and discharged at a rate of 0.2 C between 2.2 and 4.5 V to measure the discharge voltage. The measurement results are summarized in Table 2 below.

[0088] (ii) Measurement of Discharge Voltage 8 Each of the button batteries obtained in (2) above was charged and discharged at a rate of 0.2 C between 2.2 and 4.5 V, and the discharge voltage was measured.

[0089] (iii) Measurement of Initial Discharge Capacity Each of the button batteries obtained in (2) above was discharged at a rate of 0.2 C between 2.2 and 4.5 V to measure the initial discharge capacity.

[0090] (iii) Calculation of Energy Density From the measurement results obtained in (i) and (ii) above, the energy density of each of the button batteries obtained in (2) above was calculated according to the formula: (energy density (Wh / kg)) = (first discharge voltage (V) × initial discharge capacity (mAh / g)).

[0091] (iv) Evaluation of durability The durability of each of the button batteries obtained in (2) above was evaluated. As a result of the durability evaluation test, cases where "durability was present" were evaluated as "Fair," and cases where "durability was not present" were evaluated as "Poor."

[0092] The results are summarized in Table 2. In Table 2, "x" indicates that the lithium compound (A) could not be produced and therefore various evaluation tests could not be carried out.

[0093]

[0094] Tables 1 and 2 show that when the calcination temperature was 300°C, the desired lithium compound (A) was not obtained, either without or with thermal reduction treatment (Comparative Examples 1 to 6). When the calcination temperature was 350°C and thermal reduction treatment was not performed, or when the thermal reduction treatment temperature was 250°C, the desired lithium compound (A) was obtained, but the lithium ion batteries using the resulting lithium compound (A) had poor electrochemical performance (Comparative Examples 7 and 8). When the calcination temperature was 350°C or higher and 800°C or lower, and the thermal reduction treatment temperature was 500°C, the desired lithium compound (A) was obtained. Furthermore, the lithium ion batteries using the resulting lithium compound (A) had excellent electrochemical properties (Examples 1 to 10). Furthermore, the lithium ion batteries using the lithium compound (A) obtained at a firing temperature of 700°C or 800°C without thermal reduction treatment, or the lithium compound (A) obtained at a firing temperature of 700°C or 800°C and a thermal reduction temperature of 250°C, were inferior in electrochemical properties to the lithium ion batteries using the lithium compound (A) obtained in Examples 1 to 10 (Comparative Examples 9 to 12).

[0095] (4) Electrochemical Performance Evaluation Test (Part 2) Button-type lithium-ion batteries were fabricated in the same manner as described above using the lithium compounds obtained by the thermal reduction treatment and the corresponding lithium compounds before the thermal reduction treatment. For each of the fabricated button-type lithium-ion batteries, the discharge voltage and initial discharge capacity were measured and the energy density was calculated in the same manner as described above.

[0096] From Table 2, it can be seen that the lithium batteries having positive electrodes prepared using the lithium compound (A) obtained by thermal reduction treatment all exhibit higher discharge voltages than the corresponding lithium batteries having positive electrodes prepared using the lithium compound (B) before thermal reduction treatment, regardless of the firing temperature.

[0097] (ii) Measurement of Initial Discharge Capacity Table 2 shows that the lithium battery having a positive electrode prepared using the lithium compound (A) exhibits a higher initial discharge capacity value than the lithium battery having a positive electrode prepared using the lithium compound (B), regardless of the firing temperature.

[0098] (iii) Measurement of Energy Density Table 2 shows that a lithium battery having a positive electrode prepared using the lithium compound (A) obtained by thermally reducing the lithium compound (B) exhibits a higher energy density and is superior in battery performance, regardless of the firing temperature, compared to a lithium battery having a positive electrode prepared using the corresponding lithium compound (B) before the thermal reduction treatment.

[0099] As described above, by using the lithium compound (A) obtained by thermal reduction of the lithium compound (B) at a specific temperature (300°C or higher and 550°C or lower) as a positive electrode material for a lithium ion battery, a positive electrode for a lithium battery with excellent electrochemical properties can be produced. A lithium ion battery having this positive electrode exhibits a higher energy density and excellent battery performance, regardless of the firing temperature (350°C or higher and 850°C or lower), compared to a lithium battery having a positive electrode prepared using the corresponding lithium compound (B) before thermal reduction treatment. This was demonstrated by the fact that the lithium ion batteries using the lithium compound (A) obtained in Examples 1 to 10 exhibited excellent battery performance.

[0100] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of the present invention.

Claims

1. Formula: LiMn ２－ｘ Si ｘ O ４ A method for producing a positive electrode material for a lithium ion battery, comprising: (A) a lithium compound represented by the formula: LiMn ２－ｘ Si ｘ O ４ (x≦1) (Step (II): Heating the lithium compound (B) obtained in Step (I) at a temperature of 300° C. or higher and 550° C. or lower in a non-oxidizing atmosphere to obtain a lithium compound (A).

2. The non-oxidizing atmosphere in step (II) is a non-oxidizing gas atmosphere, and the non-oxidizing gas is Ar, N ２ 2. The method for producing a positive electrode material for a lithium ion battery according to claim 1, wherein the gas is selected from the group consisting of He, Ne, Kr, Xe, and a mixed gas of two or more of these gases.

3. The method for producing a positive electrode material for a lithium ion battery according to claim 2, wherein the heating temperature in step (II) is 450°C or higher and 520°C or lower.

4. The method for producing a positive electrode material for a lithium ion battery according to claim 1, wherein the heating time of the lithium compound (B) in step (II) is 30 minutes or more and 4 hours or less.

5. The method for producing a positive electrode material for a lithium ion battery according to claim 2, wherein the heat treatment of the lithium compound (B) in step (II) is carried out in a tubular furnace while a non-oxidizing gas is circulated through the furnace at a flow rate of less than 50 mL / min.

6. The method for producing a positive electrode material for a lithium ion battery according to claim 2, wherein the non-oxidizing atmosphere in step (II) is an Ar gas atmosphere having a purity of 99% or more.

7. The method for producing a positive electrode material for a lithium ion battery according to claim 1, wherein the oxidizing atmosphere in step (I) is an oxidizing gas atmosphere, and the oxidizing gas is oxygen, air, or a mixed gas containing oxygen or air and an inert gas.

8. Formula: LiMn ２－ｘ Si ｘ O ４ The method for producing a positive electrode material for a lithium ion battery according to claim 1, wherein the value of x in (0.25≦x≦1) is 1.

9. The method for producing a positive electrode material for a lithium ion battery according to claim 1, comprising mixing a lithium precursor, a manganese precursor, and a silicon precursor using a sol-gel method in step (I).

10. The method for producing a positive electrode material for a lithium ion battery according to claim 9, wherein the lithium precursor is lithium acetate, lithium nitrate, lithium hydroxide, or lithium citrate; the manganese precursor is manganese (II) acetate, manganese (II) nitrate, or manganese (II) citrate; and the silicon precursor is orthosilicic acid, tetraalkyl orthosilicic acid, or silicon dioxide.

11. The method for producing a positive electrode material for a lithium ion battery according to claim 1, wherein the mixture of the lithium precursor, the manganese precursor, and the silicon precursor in step (I) is calcined at 650°C to 850°C.

12. The method for producing a positive electrode material for a lithium-ion battery according to claim 1, wherein the synthesis reaction of lithium compound (B) in step (I) is carried out by mixing and pulverizing a mixture of a lithium precursor, a manganese precursor, and a silicon precursor using a ball mill, and then firing the resulting mixture at a temperature in the range of 500°C to 850°C.

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