JP2011100625A - Positive electrode active material for lithium secondary battery, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel and inexpensive positive electrode active material for a lithium secondary battery, having a large discharge capacity, and to provide a method of manufacturing the same. <P>SOLUTION: A lithium vanadium metasilicate compound having a monoclinic pyroxene structure expressed by composition formula Li<SB>1-y</SB>A<SB>y</SB>V<SB>1-x</SB>M<SB>x</SB>Si<SB>2</SB>O<SB>6-α</SB>F<SB>α</SB>(A is at least one kind of alkali metal selected from a group consisting of Na, K, Rb, Cs and Fr; M is at least one kind of element selected from a group consisting of Al, Sc, Ti, Cr, Mn, Fe and In; and x, y and α are respectively in the range of 0≤x≤0.3, 0≤y≤0.3, 0≤α≤0.1) is used as an active constituent of the positive electrode active material for the lithium secondary battery. The method of manufacturing the lithium vanadium metasilicate compound includes: a first complexing step of performing a heat treatment after performing a mechanical milling process on a raw material mixture including an oxygen-containing lithium compound and an oxygen-containing silicon compound; and a second complexing step of performing the heat treatment after performing the mechanical milling process on a raw material mixture including a product in the first complexing step and an oxygen-containing vanadium compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  In recent years, with the widespread use of portable electronic devices such as notebook computers, mobile phones, and PDAs, the size of secondary batteries used as a power source has been reduced in order to reduce the weight of these devices and enable them to be used for a long time. In addition, high energy density is required. Conventionally, nickel-cadmium batteries, nickel-hydrogen batteries, etc. have been mainstream as secondary batteries, but the use of lithium secondary batteries tends to increase due to the demands for downsizing and higher energy density. .

Currently, lithium secondary batteries generally use lithium cobaltate (LiCoO ₂ ) as a positive electrode, a carbon electrode as a negative electrode, and a nonaqueous electrolytic solution in which lithium ions are dissolved in an organic solvent such as propylene carbonate as an electrolyte. .

As other positive electrodes, transition metal oxides containing lithium ions such as lithium nickelate (LiNiO ₂ ) and spinel type lithium manganate (LiMn ₂ O ₄ ) are known. In LiCoO ₂ is used.

As a general method for producing LiCoO ₂ , a method of firing at a high temperature using lithium carbonate (Li ₂ CO ₃ ) and cobalt hydroxide (Co (OH) ₂ ) as starting materials is widely known. However, since the recoverable reserves of cobalt are extremely small at 8.4 million tons, considering the possibility that the price of cobalt will rise in the future, and in order to meet the demand for lowering the cost of batteries, it is an alternative to LiCoO ₂ There is a need for materials.

For example, spinel lithium manganate (LiMn ₂ O ₄ ) has been actively researched and developed as a next-generation low-cost positive electrode material. However, the discharge capacity of spinel type lithium manganate is 100 mAh / g, which is smaller than the discharge capacity of LiCoO ₂ , and in addition, trivalent manganese is eluted into the electrolyte during charge and discharge at high temperature, Since the manganese eluted in the deposits, the charge / discharge characteristics are significantly deteriorated.

Further, LiCoO ₂ and LiMn ₂ O ₄ having a discharge plateau at a specific potential are excellent for discharging at a constant potential, but it is difficult to determine the remaining capacity from the battery potential. For this reason, it is the mainstream to check the remaining battery level mainly in three stages: high / medium / low, but the potential drops rapidly after the discharge plateau at a specific potential, so it is moderately low. There is a problem that the decrease after it becomes fast.

  An active material in a battery material system often does not exhibit good battery characteristics simply by showing a new combination of existing materials, and is not predictable. For this reason, it is necessary to evaluate a battery material system even if it is an existing substance, as a battery, and prove its usefulness from the results. In other words, even if the substance itself is existing, if it has not been evaluated as a battery, it can be said that it is an unknown substance in the battery material system. Furthermore, since a battery is meaningless unless it operates as a system, even if it is a useful active material, it is necessary to fully consider compatibility with binders, conductive assistants, current collectors, and the like. .

Therefore, the present inventors are less stable than LiCoO ₂ , have a larger discharge capacity than LiMn ₂ O ₄ , and are stable in view of compatibility with conventional binders, conductive assistants, current collectors, and the like. We continued to search for a positive electrode material having a crystal structure, and paid attention to lithium vanadium metasilicate (LiVSi ₂ O ₆ ) having a monoclinic pyroxene structure, which was not evaluated at all as a positive electrode active material for a lithium secondary battery.

As a method for obtaining LiVSi ₂ O ₆ , for example, in the following Non-Patent Document 1, (1) a step of mixing Li ₂ CO and SiO ₂ and heat-treating this mixture at 725 ° C. for 50 hours, (2) obtaining The obtained material is pulverized again and subjected to heat treatment at 730 ° C. for 20 hours to obtain LiSi ₂ O _x . (3) A pellet in which the LiSi ₂ O _x and V ₂ O ₃ are mixed is prepared. A method comprising sintering at 990 ° C. for 40 hours is described.

In Non-Patent Document 2 below, Li ₂ SiO ₃ , SiO ₂ , V ₂ O ₅ , and V ₂ O ₃ are weighed and stirred so as to have a target composition, heat-treated at 1100 ° C. for 96 hours, and then gradually cooled. Thus, a method for obtaining LiVSi ₂ O ₆ is described.

However, in these synthesis methods, the mixing is insufficient, the reaction is uneven, the raw materials such as Li ₂ CO ₃ , SiO ₂ , V ₂ O ₃ , unreacted materials, V ₂ O ₅ , by-products such as Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ and LiSiO ₄ may be contained as impurities. For example, in the method described in Non-Patent Document 1, the purity of LiVSi ₂ O ₆ is about 95%, and the remaining 5% is SiO ₂ .

Such impurities do not contribute to the charge / discharge reaction, resulting in a decrease in battery capacity. In particular, depending on the combination with the electrolytic solution, they are decomposed, gas is emitted inside the battery, and the active material itself is deactivated. There are problems. Further, the stability of LiVSi ₂ O ₆ and the safety when configuring the battery are not sufficient, and furthermore, in mass production, when the amount of impurities contained in LiVSi ₂ O ₆ varies from production lot to production lot, There is also a problem in that the capacity of the battery manufactured using this varies.

For this reason, it is necessary to remove impurities as much as possible to produce LiVSi ₂ O ₆ with high purity. In addition, the methods described in Non-Patent Documents 1 and 2 need to maintain a high temperature for a very long time, which is a major factor that increases the manufacturing cost.

The European Physical Journal B, 55, 219-228, 2007 Acta Cryst. C53, 1727-1728, 1997

The present invention has been made in view of the current state of the prior art described above, and its main object is that it is cheaper than LiCoO ₂ , has a larger discharge capacity than LiMn ₂ O ₄ , and has a conventional binder, conductive assistant, It is to provide a novel positive electrode active material that also has good compatibility with electrical conductors, etc., and to provide a novel manufacturing method that can effectively demonstrate the performance of such a novel positive electrode active material. .

  As a result of intensive studies to achieve the above-mentioned object, the present inventor has heretofore been disclosed that lithium vanadium metasilicate having a monoclinic pyroxene structure that has not been evaluated at all as a positive electrode active material for lithium secondary batteries. The compound has excellent performance as a positive electrode active material for a lithium secondary battery, and in particular, when a specific manufacturing method combining a two-stage composite treatment is adopted, it is also a relatively simple manufacturing method. Regardless, the reaction of the raw material can proceed uniformly to obtain a nanoparticulate high-purity lithium vanadium metasilicate compound with a small amount of impurities, which is particularly excellent as a positive electrode active material for lithium secondary batteries. As a result, the present invention has been completed.

That is, this invention provides the following positive electrode active material for lithium secondary batteries, and its manufacturing method.
1. Composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α
(In the formula, A represents at least one alkali metal element selected from the group consisting of Na, K, Rb, Cs, and Fr, and M represents Al, Sc, Ti, Cr, Mn, Fe, Ga, and In. And at least one element selected from the group consisting of: x, y, and α are numerical values in the ranges of 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.3, and 0 ≦ α ≦ 0.1, respectively. And a positive electrode active material for a lithium secondary battery comprising a lithium vanadium metasilicate compound having a monoclinic pyroxene structure represented by
2. In the composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α , the value of y is in the range of 0.01 ≦ y ≦ 0.3. Positive electrode active material for lithium secondary battery.
3. In the above formula 1 or 2, wherein in the composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α , the value of x is in the range of 0.01 ≦ x ≦ 0.3. The positive electrode active material for lithium secondary batteries as described.
4). Composition _formula: in _{Li 1-y A y V 1} -x M x Si 2 O 6-α F α, the value of alpha is the term 1-3 in the range of 0.01 ≦ α ≦ 0.1 The positive electrode active material for lithium secondary batteries in any one.
5. Item 5. The positive electrode active material for a lithium secondary battery according to any one of Items 1 to 4, wherein the primary particle size is nanoparticles in the range of 200 to 800 nm.
6). Item 6. The positive electrode active material for a lithium secondary battery according to any one of Items 1 to 5, which has a coating with carbon or a conductive metal.
7). Compositional formula including the following steps: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α
(In the formula, A represents at least one alkali metal element selected from the group consisting of Na, K, Rb, Cs and Fr, and M consists of Al, Sc, Ti, Cr, Mn, Fe and In. And at least one element selected from the group, wherein x, y, and α are numerical values in the ranges of 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.3, and 0 ≦ α ≦ 0.1, respectively. Method for producing a lithium vanadium metasilicate compound having a monoclinic pyroxene structure represented by:
(1) A first compounding step in which a heat treatment is performed after mechanical milling is performed on the raw material mixture for the first compounding step including the oxygen-containing lithium compound and the oxygen-containing silicon compound.
(2) A second compounding step in which heat treatment is performed after subjecting the raw material mixture for the second compounding step containing the product of the first compounding step and the oxygen-containing vanadium compound to mechanical milling.
8). Either or both of the raw material mixture for the first composite process and the raw material mixture for the second composite process are further selected from the group consisting of an oxygen-containing alkali metal compound, a compound containing element M and an oxygen atom, and a metal fluoride. Item 8. The method for producing a lithium vanadium metasilicate compound according to Item 7, comprising at least one selected component.
9. The above-mentioned raw material mixture for the second compounding step contains an oxidizing agent or a reducing agent of an oxidation equivalent or more or a reduction equivalent or more necessary for making the vanadium element in the oxygen-containing vanadium compound contained in the mixture trivalent vanadium. Item 9. A method for producing a lithium vanadium metasilicate compound according to Item 7 or 8.
10. 10. The lithium metal vanadium metasilicate compound according to any one of Items 7 to 9, wherein the mechanical milling treatment of the first compounding step and the second compounding step is performed at a gravitational acceleration of 50 to 200 G using a planetary mill. Production method.
11. Item 11. The production of a lithium vanadium metasilicate compound according to any one of Items 7 to 10, wherein the heat treatment temperature in the first compounding step is 500 to 800 ° C, and the heat treatment temperature in the second compounding step is 700 to 1300 ° C. Method.
12 Carbon, wherein the positive electrode active material for lithium secondary battery according to any one of the above items 1 to 5 and a carbon precursor are mixed and heated at 400 to 900 ° C. in a non-oxidizing atmosphere. A method for producing a coated positive electrode active material for a lithium secondary battery.
13. Item 13. The carbon-coated lithium secondary battery according to item 12, wherein the carbon precursor is at least one component selected from the group consisting of adhesive hydrocarbon-based organic matter, coal-based pitch, and petroleum-based pitch. A method for producing a positive electrode active material.
14 The lithium secondary battery which contains the positive electrode containing the positive electrode active material as described in any one of said items 1-5 as a component.

  Hereinafter, the lithium vanadium metasilicate compound which is an active ingredient of the positive electrode active material for a lithium secondary battery of the present invention and a method for producing the compound will be described in detail.

(1) Lithium vanadium metasilicate compound Lithium vanadium metasilicate compound, which is an active ingredient of the positive electrode active material for lithium secondary batteries of the present invention,
Composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α
(In the formula, A represents at least one alkali metal element selected from the group consisting of Na, K, Rb, Cs and Fr, and M consists of Al, Sc, Ti, Cr, Mn, Fe and In. And at least one element selected from the group, wherein x, y, and α are numerical values in the ranges of 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.3, and 0 ≦ α ≦ 0.1, respectively. A monoclinic pyroxene structure represented by

In the above composition formula, M is at least one element selected from the group consisting of Al, Sc, Ti, Cr, Mn, Fe, Ga, and In. These elements M are present in the V site mainly by substituting a part of the element V in the crystal of lithium vanadium metasilicate having a monoclinic pyroxene structure represented by LiVSi ₂ O _6. is there. For this reason, the element of the ion size close | similar to V ion size is preferable, and, specifically, Al, Mn, and Fe are preferable.

The lithium vanadium metasilicate compound in which the element M is substituted at the V site is superior in charge / discharge capacity and high rate charge / discharge characteristics as compared with LiVSi ₂ O ₆ . However, if the substitution amount of the element M increases, the charge / discharge capacity decreases, and it becomes difficult to maintain a stable monoclinic pyroxene structure, and the charge / discharge cycle characteristics become poor.

  For this reason, the substitution amount x of the element M may be in the range of about 0 ≦ x ≦ 0.3. However, in order to exert the substitution effect of the element M, 0.01 ≦ x ≦ 0.3 The range is preferably within a range of about 0.01 ≦ x ≦ 0.1.

In the composition formula, A is at least one alkali metal element selected from the group consisting of Na, K, Rb, Cs, and Fr. Alkali metal element A replaces a part of Li present in the crystal of LiVSi ₂ O ₆ and is present at the Li site. From the safety of handling and good substitution to the Li site, Na and K is preferred. The lithium vanadium metasilicate compound substituted with the alkali metal element A has a slightly reduced charge / discharge capacity, but can suppress volume expansion / contraction when lithium is occluded / released. However, when the substitution amount of the alkali metal element A increases, the amount of Li in the lithium vanadium metasilicate compound decreases, and the positive electrode capacity decreases.

  For this reason, the substitution amount y of the alkali metal element A may be in the range of about 0 ≦ y ≦ 0.3. In particular, in order to sufficiently exhibit the substitution effect of the alkali metal element A, 0 It is preferable to set about .01 ≦ y ≦ 0.3, and it is more preferable to set about 0.01 ≦ y ≦ 0.2.

In the above compositional formula, the fluorine element F is present at the O site by substituting part of O present in the LiVSi ₂ O ₆ crystal, and the lithium vanadium metasilicate compound substituted by the fluorine element F is Although the initial charge / discharge capacity is slightly reduced, the charge / discharge cycle characteristics are improved by about 10 to 20%, and at the same time, the discharge voltage is increased by about 0.05 to 0.2V. However, as the substitution amount of the fluorine element F increases, the Li amount decreases and the positive electrode capacity decreases.

  The substitution amount α of the fluorine element F may be in the range of 0 ≦ α ≦ 0.1. However, in order to sufficiently exert the substitution effect of the fluorine element F, 0.01 ≦ α ≦ 0.1 The range is preferable, and the range of 0.02 ≦ α ≦ 0.05 is more preferable.

(2) manufacturing method above-mentioned composition formula of metasilicate lithium vanadium compound _Production Method of _{Li 1-y A y V 1} -x M x Si 2 O 6-α F metasilicate lithium vanadium compound represented by _alpha Is not particularly limited, and can be obtained by, for example, the methods described in Non-Patent Document 1 and Non-Patent Document 2 described above. In particular, a raw material mixture containing an oxygen-containing lithium compound and an oxygen-containing silicon compound is mechanically used. A first compounding step of forming a composite containing lithium and silicon (lithium silicon composite metal oxide) by firing after milling, and adding an oxygen-containing vanadium compound to the lithium silicon composite metal oxide to mechanically It is preferable to manufacture by the method including the 2nd compounding process of baking after giving a milling process. According to this method, by producing a target vanadium lithium metasilicate compound through a two-stage compounding process, the reaction proceeds uniformly and the amount of impurities is very high. Series compounds can be obtained. The resulting lithium vanadium metasilicate compound is composed of high purity, fine nanoparticles, large capacity, stable performance with little variation, and safety in battery construction. It becomes a positive electrode active material for lithium secondary batteries having high and excellent performance.

  Hereinafter, this manufacturing method will be specifically described.

(I) First composite process:
In the first compounding step, an oxygen-containing lithium compound and an oxygen-containing silicon compound are used as raw materials.

As the oxygen-containing lithium compound, any compound containing Li and oxygen can be used without particular limitation. Specific examples include LiNO ₃ , LiNO ₂ , LiOH, LiOH · H ₂ O, CH ₃ OOLi, Li ₂ O, Examples include Li ₂ O ₂ , Li ₂ SO ₄ , dicarboxylic acid Li, citric acid Li, and fatty acid Li. Among these oxygen-containing lithium compounds, lithium compounds that do not contain nitrogen atoms and sulfur atoms are particularly preferable in that no harmful substances such as SO _x and NO _x are generated during the firing treatment. In particular, Li ₂ CO ₃ is preferable because it is easy to handle and relatively inexpensive. These lithium compounds may be used individually by 1 type, and may use 2 or more types together.

The oxygen-containing silicon compound may be a compound containing silicon and oxygen. For example, SiO, SiO ₂ , Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ Si ₃ O ₇ , Li ₈ SiO ₆ , Li ₆ Si ₂ O ₇ , Li ₂ Si ₂ O ₅ , Li ₂ Si ₃ O ₅ , Si ₂ N ₂ O, SiP ₂ O ₇ , Si ₃ (PO ₄ ) ₄ , H ₂ Si ₂ O ₅ , H ₂ Si ₆ O ₁₃ H ₄ SiO ₃ , H ₄ Si ₃ O ₈ , H ₆ Si ₄ O ₁₁ , and the like can be used. Among these oxygen-containing silicon compounds, silicon compounds that do not contain nitrogen atoms and sulfur atoms are particularly preferable in that no harmful substances such as SO _x and NO _x are generated during the firing treatment. Considering these points, SiO ₂ , SiO ₂ , Li ₂ SiO ₃ , Li ₄ SiO ₄ , Li ₂ Si ₃ O ₇ , Li ₈ SiO ₆ , Li ₆ Si ₂ O ₇ , Li ₂ Si ₂ O ₅ , Li ₂ Si ₃ O ₅ or the like is preferable, and SiO ₂ is particularly preferable because it is easy to handle and relatively inexpensive. These silicon compounds may be used individually by 1 type, and may use 2 or more types together.

Furthermore, when the target vanadium lithium metasilicate compound represented by the composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α contains an alkali metal element A, that is, y Is larger than 0, an oxygen-containing alkali metal compound is used as a raw material for one or both of the first composite step and the second composite step described later. In addition, when the lithium vanadium metasilicate compound represented by the above composition formula contains the element M, that is, when x is larger than 0, either the first compounding step or the second compounding step described later is selected. A compound containing element M and oxygen is used as a raw material for one or both steps. Further, when the lithium vanadium metasilicate compound represented by the above composition formula contains a fluorine atom, that is, when α is larger than 0, either the first composite step or the second composite step described later Metal fluoride is used as a raw material for one or both steps.

Among the above-described raw materials, the oxygen-containing alkali metal compound can be used without particular limitation as long as it is a compound containing an alkali metal other than lithium and oxygen. Specific examples thereof include NaNO ₃ , NaNO ₂ , NaOH, NaOH · H ₂ O, CH ₃ IONa, Na ₂ O, Na ₂ O ₂ , Na ₂ SO ₄ , dicarboxylic acid Na, citric acid Na, fatty acid Na, and KNO. ₃ , KNO ₂ , KOH, KOH · H ₂ O, CH ₃ OOK, K ₂ O, K ₂ O ₂ , K ₂ SO ₄ , dicarboxylic acid K, citric acid K, fatty acid K, RbNO ₃ , RbNO ₂ , RbOH, RbOH · H ₂ O, CH ₃ OORb, Rb ₂ O, Rb ₂ O ₂ , Rb ₂ SO ₄ , dicarboxylic acid Rb, citric acid Rb, fatty acid Rb, CsNO ₃ , CsNO ₂ , CsOH, CsOH · H ₂ O, CH ₃ OOCs, Cs ₂ O, Cs ₂ O ₂ , Cs ₂ SO ₄ , dicarboxylic acid Cs, citric acid Cs, fatty acid Cs and the like. Among the oxygen-containing alkali metal compounds, alkali metal compounds that do not contain nitrogen atoms or sulfur atoms are preferable in that no harmful substances such as SO _x and NO _x are generated during the firing treatment. Of these, Na ₂ CO ₃ and K ₂ CO ₃ are particularly preferable because they are easy to handle and relatively inexpensive. These oxygen-containing alkali metal compounds may be used alone or in combination of two or more.

As the metal fluoride, for example, LiF, MgF ₂ or the like can be used.

As the compound containing the element M and the oxygen atom, any compound containing the element M and the oxygen atom can be used without particular limitation. For example, M (OH) ₃ , M ₂ O ₃ , M ₂ (SO ₄ ) _{3 and the} like can be used. Can be used. Specific examples of such compounds include Al (OH) ₃ , Sc (OH) ₃ , Ti (OH) ₃ , Cr (OH) ₃ , Mn (OH) ₃ , Fe (OH) ₃ , and Ga (OH). ₃ , In (OH) ₃ , Al ₂ O ₃ , Sc ₂ O ₃ , Ti ₂ O ₃ , Cr ₂ O ₃ , Mn ₂ O ₃ , Fe ₂ O ₃ , Ga ₂ O ₃ , In ₂ O ₃ , Al ₂ (SO ₄ ) ₃ , Sc ₂ (SO ₄ ) ₃ , Ti ₂ (SO ₄ ) ₃ , Cr ₂ (SO ₄ ) ₃ , Mn ₂ (SO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₃ , Ga ₂ (SO ₄ ) ₃ , In ₂ (SO ₄ ) _{3 and the} like.

  In the first compounding step in the production method of the present invention, an oxygen-containing lithium compound and an oxygen-containing silicon compound are used as raw materials, and in the first compounding step, any or all of elements A, M and F are used. In the case of compounding, raw materials containing these elements are also added to obtain a raw material mixture. About the mixing ratio of each raw material, what is necessary is just to make it become the same element ratio as the ratio of the metal element and fluorine in the target lithium vanadium metasilicate compound. In addition, as mentioned above, since the raw material containing each element of A, M and F can be used as a raw material for either one or both of the first compounding step and the second compounding step, This total amount should just be the same element ratio as the element ratio in the target lithium vanadium metasilicate compound.

  Next, the raw material mixture is subjected to mechanical milling using a ball mill apparatus. There are mainly two types of ball mill devices used for performing mechanical milling: a planetary ball mill and a vibration type ball mill. In the present invention, any ball mill device may be used. For example, a rolling mill, a vibration mill, a planetary mill, a rocking mill, a horizontal mill, an attritor mill, and the like can be used. The raw material mixture can be pulverized to a sufficiently fine state by mechanical milling using these ball mill apparatuses.

  In the present invention, it is particularly preferable to use a planetary mill because it can be efficiently pulverized to a sufficiently fine state. In the mechanical milling process using a planetary mill, the raw material mixture is put into a mill container together with balls, and the raw material mixture is mixed and pulverized by mechanical energy generated by rotation and revolution. At this time, by increasing the rotation speed, the gravitational acceleration generated in the mill container increases, and the mechanical energy increases. If the gravitational acceleration at this time is less than 50 G, the pulverization force is insufficient, so that the composite treatment is not uniformly performed, and the particle size of the obtained positive electrode active material powder is large, so that the output characteristics are deteriorated. This is not preferable. Further, when the gravitational acceleration exceeds 200 G, the time required for the compounding process can be shortened, but this is not preferable because not only the necessary apparatus becomes large but also the material of the mill container itself is mixed. For this reason, when using a planetary mill, it is preferable to make gravity acceleration into about 50-200G, and it is more preferable to set it as about 70-150G. Although it depends on the acceleration of gravity, the grinding time is usually about 0.1 to 12 hours, preferably about 0.5 to 10 hours. In this case, if the pulverization time is too short, the composite is not sufficiently performed. On the other hand, if the pulverization time is too long, a remarkable effect cannot be obtained.

  There is no particular limitation on the atmosphere in the mill container at the time of mechanical milling, and it may be handled in the air.

  Next, after the mechanical milling process is finished, heat treatment is performed. Thereby, each component of the raw material mixture described above sufficiently reacts, and the first stage of compounding is performed. The heat treatment temperature is preferably about 500 to 800 ° C, and more preferably about 600 to 700 ° C. The heat treatment time is preferably about 1 to 48 hours, and more preferably about 8 to 24 hours.

  The atmosphere during the heat treatment is not particularly limited, and may be any atmosphere such as an oxidizing atmosphere such as an air atmosphere, a reducing atmosphere such as a hydrogen gas atmosphere, and an inert gas atmosphere such as an Ar gas atmosphere.

  By the above-described method, each component in the raw material mixture containing the oxygen-containing lithium compound and the oxygen-containing silicon compound reacts to obtain a composite oxide containing the metal component in the used raw material. Hereinafter, the obtained composite oxide may be referred to as a lithium silicon composite metal oxide.

(Ii) Second compounding step In the second compounding step, the lithium silicon compound metal oxide obtained by compounding the raw material containing the oxygen-containing lithium compound and the oxygen-containing silicon compound in the first compounding step is further combined with oxygen. A compounding treatment is performed by adding the vanadium compound.

The target composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α is a lithium metal vanadium compound represented by alkali metal element A, element M, and fluorine. In the case of containing at least one element selected from the group consisting of atoms, when the raw material containing these elements is not added in the first compounding step, or the addition amount of the raw material containing these elements is the target In the case where the element ratio is insufficient, a necessary component among the components including the oxygen-containing alkali metal compound, the compound containing the element M and the oxygen atom, and the metal fluoride is further used as a raw material for the second compounding step. Use.

In the second compounding step, as the oxygen-containing vanadium compound, any compound containing vanadium and oxygen can be used without particular limitation. Specific examples thereof include VO, VO ₂ , V ₂ O ₃ , V ₂ O ₄ , V ₂ O ₅ , VOSO ₄ , NH ₄ VO _{3 and the} like.

Among these vanadium compounds, compounds that do not contain nitrogen atoms or sulfur atoms are preferable in that they do not generate harmful substances such as SO _x and NO _x and moisture during firing, and in particular, VO, VO ₂ , V ₂ O ₃ , V ₂ O ₄ , V ₂ O _{5 and the} like are preferable. These vanadium compounds can be used singly or in combination of two or more.

In addition, when the vanadium element contained in the vanadium compound used as a raw material has a valence other than trivalent, an oxidizing agent or a reducing agent is added to the raw material in the second compounding step in order to make vanadium into a trivalent state. Added. For this reason, V ₂ O ₃ is particularly preferable in that an oxidizing agent and a reducing agent are not required.

  The blending amount of the oxidizing agent or the reducing agent may be determined by estimating an oxidation equivalent or a reduction equivalent necessary for making the vanadium compound a trivalent vanadium compound according to the type and amount of the vanadium compound to be used.

For example, in order to produce a trivalent vanadium oxide from V _δ O _ε , when V _δ O _ε is 1 equivalent, an oxidizing agent having a 3-β oxidation equivalent or more may be used. However, when the value of 3-β is a negative real number, a reducing agent having a β-3 reducing equivalent may be used. In V _δ O _ε , a relationship of δ × β = ε × 2 is established among the number of atoms δ of vanadium V, the number of atoms ε of oxygen O, and the valence β of vanadium V. The number of atoms of each element is defined so as to conform to each valence.

  Specific examples of the amount of the oxidizing agent or reducing agent used in the case of assuming an ideal reaction will be given below.

For example, when 1 equivalent of VO (V valence β is 2+) is used as a raw material, trivalent vanadium oxide V ₂ O ₃ can be obtained by adding an oxidizing agent of 1 oxidation equivalent or more. When 1 equivalent of VO ₂ (V valence β is 4+) is used as a raw material, trivalent vanadium oxide V ₂ O ₃ can be obtained by adding a reducing agent of 1 reducing equivalent or more. When one equivalent of V ₂ O ₄ (V valence β is 2+) is used as a raw material, a trivalent vanadium oxide V ₂ O ₃ can be obtained by adding an oxidizing agent of one oxidation equivalent or more. . When 1 equivalent of V ₂ O ₅ (V valence β is 5+) is used as a raw material, a trivalent vanadium oxide V ₂ O ₃ can be obtained by adding a reducing agent of 2 reduction equivalents or more. When 1 equivalent of VOSO ₄ (V valence β is 4+) is used as a raw material, trivalent vanadium oxide V ₂ O ₃ can be obtained by adding a reducing agent of 1 reducing equivalent or more. When 1 equivalent of NH ₄ VO ₃ (V valence β is 5+) is used as a raw material, a trivalent vanadium oxide V ₂ O ₃ can be obtained by adding a reducing agent of 2 reduction equivalents or more. .

  However, since an ideal reaction is difficult in practice, it is preferable to use about 1 to 6 times the amount of oxidizing agent or reducing agent, more preferably about 1 to 3 times the amount equivalent to the theoretical equivalent.

  The oxidizing agent can be used without particular limitation as long as it has oxidizing power, and specific examples include oxygen, chlorine, bromine, chlorate, hypochlorite, aqueous hydrogen peroxide, In particular, oxygen, hydrogen peroxide water and the like are preferable.

  As the reducing agent, it can be used without any limitation as long as it has a reducing power. For example, hydrogen, formaldehyde, sodium isoascorbate, sodium ascorbate and the like can be used, and in particular, hydrogen, isoascorbic acid. Sodium and the like are preferable.

  The oxidizing agent or reducing agent may be a suitable gas. That is, the vanadium compound used as a raw material can be made into a trivalent vanadium compound by performing a mechanical milling process which will be described later in an oxidizing or reducing gas atmosphere.

As the gaseous oxidant, for example, air diluted with an inert gas, oxidizing gas (O ₂ , O ₃ , N ₂ O, etc.) and the like can be used in addition to air. As the gaseous reducing agent, a reducing gas such as H ₂ , H ₂ S, SO ₂ , and HCHO can be used. In addition, when the second compounding step is performed in the air, oxidation of the vanadium compound proceeds. Therefore, when a trivalent vanadium compound is used as a raw material, it is in an inert gas atmosphere such as nitrogen, helium, neon, or argon. It is preferable to perform mechanical milling.

  As described above, in the second composite step, the lithium silicon composite metal oxide and the oxygen-containing vanadium compound obtained in the first composite step are further added to an oxygen-containing alkali metal compound, element M, and oxygen atom as necessary. And / or a metal fluoride is added to form a raw material mixture. About the mixing ratio of each raw material, what is necessary is just to make it become the same element ratio as the ratio of the metal element and fluorine in the target lithium vanadium metasilicate compound. In addition, as mentioned above, since the raw material containing each element of A, M and F can be used as a raw material for either one or both of the first compounding step and the second compounding step, This total amount should just be the same element ratio as the element ratio in the target lithium vanadium metasilicate compound.

  In the second compounding step, first, mechanical milling is performed on the above-described raw material mixture. The conditions for the mechanical milling process may be the same as in the first compounding step.

  Next, heat treatment is performed after the mechanical milling process. As a result, the reaction of each component contained in the raw material mixture sufficiently proceeds and the second-stage complexation is performed. The heat treatment temperature is preferably about 700 to 1300 ° C, more preferably about 800 to 1000 ° C. The heat treatment time is preferably about 1 to 48 hours, and more preferably about 8 to 24 hours.

  In order to prevent oxidation, the atmosphere during the heat treatment is preferably a reducing atmosphere such as a hydrogen gas atmosphere, an inert atmosphere such as an argon atmosphere, or a mixed gas atmosphere of a reducing gas and an inert gas. In particular, it is preferable to perform the heat treatment in an Ar gas atmosphere in which about 1 to 5 vol% of hydrogen is mixed.

According to the method described above, the composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α
A lithium vanadium metasilicate compound having a monoclinic pyroxene structure represented by the formula (wherein A, Mx, y, and α are the same as described above) can be obtained.

  According to this method, the reaction of the raw material material occurs uniformly, and a nanoparticulate high-purity lithium vanadium metasilicate compound having a small amount of impurities is obtained. The resulting vanadium metasilicate compound is a fine nanoparticle having a primary particle system of about 200 to 800 nm with good uniformity.

  Note that when this crystalline material is finely pulverized by mechanical milling or the like to give a fine crystal of 10 nm or less, the X-ray diffraction pattern becomes broad and appears to be amorphous. In this case, although the initial capacity is somewhat reduced, the output characteristics can be improved.

(3) Conductive coating treatment The lithium vanadium metasilicate compound obtained by the above-described method can further improve conductivity by forming a conductive coating with a conductive metal, carbon or the like. Thereby, it has a more favorable battery characteristic as a positive electrode active material for lithium batteries.

  As a method for forming a conductive coating such as a conductive metal or carbon on the lithium vanadium metasilicate compound, known techniques such as sputtering, vapor deposition, MA method, and electroless plating can be used.

  In this case, as the material used for the conductive coating, in addition to carbon, for example, a material having corrosion resistance up to about 4.5 V is preferable. Specific examples include Al, Ti, V, Cr, Zr, Nb, Mo , Pt, Au, and a conductive metal such as stainless steel (SUS) can be used. Among these, carbon, Al, Cr, Zr, SUS and the like are preferable from the viewpoint of cost.

  When the coating amount of the conductive coating is too small, the effect of improving the conductivity is not sufficient. On the other hand, when the coating amount is too large, the surface of the lithium vanadium metasilicate compound is almost covered and it is difficult to insert and desorb lithium ions. This is not preferable. For this reason, the coating amount of the conductive coating is preferably about 0.1 to 30 parts by weight, more preferably about 1 to 30 parts by weight with respect to 100 parts by weight of the lithium vanadium metasilicate compound. More preferably, it is about 1 to 10 parts by weight.

  In particular, according to the method of mixing a lithium vanadium metasilicate compound and a carbon precursor, and heating in a non-oxidizing atmosphere to form a coating with carbon, a simple apparatus can be used without using a large-scale apparatus. The method is advantageous in that a coating with carbon having excellent uniformity can be formed.

  The carbon precursor used in this method may be an organic material that is carbonized by heating. For example, a sticky hydrocarbon-based organic material, coal-based pitch, petroleum-based pitch, or the like can be used. Among these, examples of the sticky hydrocarbon organic substance include phenol resin, furan resin, citric acid, urushiol, and the like. These carbon precursors can be used singly or in combination of two or more.

  The heating temperature should just be the temperature which a carbon precursor carbonizes, for example, it is preferable to set it as about 300-900 degreeC, and it is more preferable to set it as about 500-800 degreeC. In this case, if the heating temperature is too low, the carbon precursor is not easily carbonized. On the other hand, if the heating temperature is too high, there is a risk that the coated carbon may be reduced, and the apparatus becomes large and expensive. Therefore, it is not preferable.

  The heat treatment time may be a time during which the carbon precursor is carbonized, and is usually about 1 to 24 hours. When the heating time is too short, the carbon precursor is not sufficiently carbonized, which is not preferable because it becomes a negative electrode with poor electron conductivity. On the other hand, if the heating time is too long, the heat treatment is useless, which is not economically preferable.

The atmosphere during the carbonization treatment may be a non-oxidizing atmosphere such as an inert atmosphere or a reducing atmosphere. Specifically, the atmosphere may be He (helium), Ne (neon), Ar (argon), N ₂ (nitrogen), H ₂ (hydrogen), or the like. In addition, since the commercially available inert gas contains a small amount of oxygen, even when the heat treatment is performed in an inert gas atmosphere, if the heating temperature is too high, or if the heating time is too long, carbonization proceeds too much. Care must be taken because the conductivity cannot be sufficiently improved.

(4) Positive electrode active material for lithium secondary battery Any of the lithium vanadium metasilicate compounds described above and a compound having a conductive coating formed thereon can be effectively used as the positive electrode active material for lithium secondary batteries. A positive electrode using this positive electrode active material can have the same structure as a normal positive electrode for a lithium secondary battery.

  For example, acetylene black (AB), ketjen black (KB), vapor-grown carbon fiber to the above-described lithium vanadium metasilicate compound or a compound having a conductive coating such as a conductive metal or carbon formed thereon. (Vapor Grown Carbon Fiber: VGCF) and other conductive aids, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR) binders, N-methyl- A positive electrode can be produced by adding a solvent such as 2-pyrrolidone (NMP) to form a paste and applying it to a current collector. The amount of the conductive auxiliary agent used is not particularly limited, but can be, for example, about 20 to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material. Further, the amount of the binder used is not particularly limited, but can be, for example, about 10 to 20 parts by weight with respect to 100 parts by weight of the positive electrode active material.

  The current collector is not particularly limited, and materials conventionally used as positive electrodes for lithium secondary batteries, such as aluminum foil, aluminum mesh, and stainless steel mesh, can be used.

A lithium secondary battery using the positive electrode for a lithium secondary battery described above can be manufactured by a known method. For example, as the negative electrode material, a known negative electrode material, for example, a carbon-based negative electrode material such as graphite; an alloy-based negative electrode material such as Cu ₆ Sn ₅ ; an oxide-based negative electrode material such as SnO or SiO; and a nitride-based material such as LiN A negative electrode material or the like can be used.

  Moreover, since the lithium secondary battery using the positive electrode of this invention needs to contain lithium ion, lithium salt is preferable as electrolyte salt. The lithium salt is not particularly limited, and specific examples include lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium trifluoromethanesulfonate. . These lithium salts can be used singly or in combination of two or more. Since the above lithium salt has high electronegativity and is easily ionized, it has excellent charge / discharge cycle characteristics and can improve the charge / discharge capacity of the secondary battery.

  Examples of the solvent for the electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and γ-butyrolactone, and these solvents can be used alone or in combination of two or more. In particular, propylene carbonate alone, a mixture of ethylene carbonate and diethyl carbonate, or γ-butyrolactone alone is suitable. In addition, the mixing ratio of the mixture of ethylene carbonate and diethyl carbonate can be arbitrarily adjusted in a range where one component is 10% by volume or more and 90% by volume or less.

  The lithium secondary battery having the above-described structure can exhibit excellent performance as a secondary battery having a high capacity and a good cycle life.

The lithium vanadium metasilicate compound, which is an active ingredient of the positive electrode active material for lithium secondary batteries of the present invention, is a material that has not been known to be effective as a positive electrode active material for lithium secondary batteries. Compared to LiCoO ₂ which is a positive electrode active material mainly used in secondary batteries, it is a cheaper material and has a higher charge / discharge capacity than LiMn ₂ O ₄ . Further, the operating voltage is in a wide range of 4.5 to 1.5 V, and can be used for various applications.

  In particular, the lithium vanadium metasilicate compound obtained through the two-stage compounding process according to the production method of the present invention is a nanoparticle having high purity and good uniformity, and thus has particularly excellent performance as a positive electrode active material. Can demonstrate. Moreover, according to the production method of the present invention, the target lithium vanadium metasilicate compound can be obtained in a short production time by a relatively simple production method.

  Furthermore, the performance as the positive electrode active material can be further improved by applying a conductive coating such as a conductive metal or carbon to the lithium vanadium metasilicate compound of the present invention.

Therefore, according to the present invention, a novel positive electrode active material for a lithium secondary battery is provided that is cheaper than LiCoO ₂ , has a larger discharge capacity than LiMn ₂ O ₄ , and has excellent performance.

The synchrotron radiation X-ray-diffraction figure of the lithium vanadium metasilicate compound obtained in Example 1. FIG. 1 is a schematic diagram showing a crystal structure of a lithium vanadium metasilicate compound obtained in Example 1. FIG. 3 is an SEM image of the lithium vanadium metasilicate compound obtained in Example 2. FIG. The graph which shows the discharge curve in each cycle of the bipolar evaluation cell which uses the lithium vanadium metasilicate compound obtained in Example 2 as a positive electrode active material. The initial discharge curve in each discharge current (25 degreeC) of the bipolar evaluation cell which uses the lithium vanadium metasilicate compound obtained in Example 2 as a positive electrode active material. The initial discharge curve (60 degreeC) in each discharge current of the bipolar evaluation cell which uses the lithium vanadium metasilicate compound obtained in Example 2 as a positive electrode active material.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

Examples 1 to 13 and Comparative Example 1
(1) First compounding step In a glove box substituted with Ar gas, a total of about 2 g of the raw materials shown in Table 1 below were weighed and sealed together with 100 zirconia balls (φ8 mm) in a 100 mL zirconia milling container. . The inside of the milling container was evacuated at a vacuum degree of 6 × 10 ⁻⁵ Pa for 1 hour or more, and then the container was filled with Ar gas at 1 MPa. Then, the mechanical milling process was performed by the planetary ball mill apparatus on condition of gravitational acceleration 50G and 2 hours.

  Next, the sample after milling was subjected to heat treatment at a temperature of 730 ° C. for 2 hours in an air atmosphere to obtain a composite (lithium silicon composite metal oxide) containing lithium and silicon as intermediate products 1 to 7. It was.

(2) Second compounding step In a glove box substituted with Ar gas, a total of about 2 g of the materials shown in Table 2 below was weighed and sealed together with 100 zirconia balls (φ8 mm) in a 100 mL zirconia milling container. . The inside of the milling container was evacuated at a vacuum degree of 6 × 10 ⁻⁵ Pa for 1 hour or more, and then the container was filled with Ar gas at 1 MPa. Then, the mechanical milling process was performed with the planetary ball mill apparatus. In Example 11, the milling vessel was filled with 2 reduction equivalents of hydrogen gas relative to V ₂ O ₅ , and in Example 12, the milling vessel was filled with 1 reduction equivalent of hydrogen gas relative to VO ₂ . In Example 13, the milling treatment was performed by filling the milling vessel with an oxygen equivalent of one oxidation equivalent to V ₂ O ₄ .

Then, the sample after milling completion, a mixed gas atmosphere of hydrogen and argon _{(H 2: Ar = 10vol%} : 90vol%) subjected to a heat treatment of 3 hours at a temperature 950 ° C. Under the compositional formula: _{Li 1-} Lithium vanadium metasilicate having a monoclinic pyroxene structure represented by _y A _y V _1-x M _x Si ₂ O _6-α F _α (where A, Mx, y, and α are the same as above) A system compound was obtained. Table 2 shows the conditions of milling (gravity acceleration and processing time) and heating (heating temperature and heating time) using a planetary ball mill.

  In each sample obtained in Examples 2 to 13, 10 parts by weight of citric acid was mixed with 100 parts by weight of the sample obtained by milling and heating, and the temperature was 600 ° C. in a hydrogen gas atmosphere. Then, a heat treatment was performed for 3 hours to form 3 parts by weight of a carbon coating with respect to 100 parts by weight of the lithium vanadium metasilicate compound.

(3) Results of Structural Analysis FIG. 1 shows a synchrotron radiation X-ray diffraction pattern of the lithium vanadium metasilicate compound obtained in Example 1. Rietveld analysis revealed that LiVSi ₂ O ₆ had a high purity of 97.13%. The other phases were found to be Li ₂ Si ₂ O ₅ and V ₂ O ₃ . The LiVSi ₂ O ₆ phase had an a-axis length of 9.627 mm, a b-axis length of 8.608 mm, a c-axis length of 5.297 mm, and a lattice volume of 413.61 mm ³ .

Further, when precision crystal structure analysis was performed, it was found that the crystal structure of LiVSi ₂ O _{6 was} the monoclinic pyroxene structure shown in FIG. 2 and had the atomic coordinates shown in Table 3 (n is the coordination number) , G are occupancy rates, and x, y, and z are respective vectors). Lithium ions were present along the b-axis of the bc plane, and the distance between the lithium ions was 5.635 Å and 4.493 Å.

(4) SEM Observation An SEM photograph of the lithium vanadium metasilicate compound obtained in Example 2 is shown in FIG. The primary particle diameter in the state covered with carbon is about 0.5 μm, and it can be confirmed that the particles have a uniform shape.

(5) Using each sample of Battery Test Examples 1 to 13 and Comparative Example 1 as the positive electrode active material, a test electrode was prepared using the positive electrode active material (composition of the positive electrode active material: active material 70 wt.%, Conductive aid) (Ketjen Black (KB)) 20 wt.%, Binder (PTFE) 10 wt.%).

A metallic lithium foil is used as a counter electrode, and a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 1: 1 is used as an electrolytic solution. A bipolar evaluation cell (coin 2032 type cell) was prepared and a charge / discharge test was performed at 25 ° C. The test was controlled by a cut-off voltage (4.5-1.5 V), and the charge / discharge current corresponding to 0.2 C was performed.

  About the battery which used each sample of Examples 1-13 and Comparative Example 1 as the positive electrode active material, the initial discharge capacity after performing the activation cycle until the electrode capacity in the initial cycle reaches the maximum value and the 300th cycle Each discharge capacity retention rate is shown in Table 4 below. Table 4 shows the potential at the time of half of the discharge capacity at the 300th cycle as the intermediate discharge voltage.

The following results can be seen from Table 4 above.
(1) The sample of Comparative Example 1 subjected to the mechanical milling process with a gravitational acceleration of 30 G is greatly inferior to the sample of the Example 1 subjected to the mechanical milling process with a gravitational acceleration of 60 G. It was. This is considered to be due to the fact that the sample of Comparative Example 1 has insufficient milling treatment, so that there are a large amount of unreacted substances and by-products, and the amount of the positive electrode active material as a whole is small.
(2) The discharge capacity of the sample of Example 2 in which a carbon coating was formed on the lithium vanadium metasilicate compound obtained under the same conditions as in Example 1 was significantly improved compared to the sample of Example 1. did. In addition, the sample of Example 3 which performed the milling process by the gravitational acceleration of 100 G showed no improvement in the discharge capacity as compared with the sample of Example 2.
(3) samples of LiVSi ₂ Example 4 Example of Na or K is substituted into Li site O ₆ 5, as compared with the samples of Examples 1 to 3 that the LiVSi ₂ O ₆ as a main component, the charge and discharge Although the capacity decreased slightly, the discharge capacity retention rate after 300 cycles was high, and the cycle life characteristics were improved.
(4) The samples of Examples 6 to 9 in which the V site of LiVSi ₂ O ₆ is substituted with Al, Mn, or Fe are larger than the samples of Examples 1 to 3 whose main component is LiVSi ₂ O _6. Discharge capacity improved.
(5) each sample LiVSi ₂ Examples 10-13 in which element F is substituted with O site O _6, as compared with the samples of Examples 1 to 3 that the LiVSi ₂ O ₆ as a main component, the initial discharge capacity Although it slightly decreased, the cycle life characteristics were improved, and at the same time, the discharge voltage increased by about 0.1 to 0.2V.

  As an example, a charge / discharge curve in each cycle is shown in FIG. 4 for a bipolar evaluation cell (coin 2032 type cell) using the sample of Example 2 as a positive electrode active material. The active material capacity per weight after 40 cycles was about 95 mAh / g, corresponding to about 75% of the theoretical capacity.

  Moreover, about the bipolar evaluation cell which used the sample of Example 2 as a positive electrode active material, the discharge curve in each discharge current is shown in FIG. As can be seen from FIGS. 4 and 5, the battery using the sample of Example 2 as the positive electrode active material draws a charge / discharge curve with almost no charge / discharge plateau, and this is the characteristic of the positive electrode active material of the present invention. It is one of. For this reason, it is estimated that there is about 90% remaining capacity at 4V discharge, about 70% at 3.5V, about 60% at 3V, about 50% at 2.5V, and 30% at 2V. Can do.

  Next, for the bipolar evaluation cell using the sample of Example 2 as the positive electrode active material, a charge / discharge test was conducted at 60 ° C. in the same manner instead of the charge / discharge test at 25 ° C. described above. The discharge curve at each discharge current is shown in FIG. From this result, it was confirmed that the charge / discharge test at 60 ° C. showed a higher discharge capacity than the charge / discharge test at 25 ° C., and the battery characteristics at high temperature were good.

Claims (14)

Composition formula: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α
(In the formula, A represents at least one alkali metal element selected from the group consisting of Na, K, Rb, Cs and Fr, and M represents Al, Sc, Ti, Cr, Mn, Fe, Ga and In. And at least one element selected from the group consisting of x, y, and α, each having a numerical value in the range of 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.3, and 0 ≦ α ≦ 0.1. A positive electrode active material for a lithium secondary battery, comprising as an active ingredient a lithium vanadium metasilicate compound having a monoclinic pyroxene structure represented by Composition _formula: in _{Li 1-y A y V 1} -x M x Si 2 O 6-α F α, the value of y is, according to claim 1 which is in the range of 0.01 ≦ y ≦ 0.3 Positive electrode active material for lithium secondary battery. Composition _formula: in _{Li 1-y A y V 1} -x M x Si 2 O 6-α F α, the value of x, to claim 1 or 2 in the range of 0.01 ≦ x ≦ 0.3 The positive electrode active material for lithium secondary batteries as described. Composition _formula: in _{Li 1-y A y V 1} -x M x Si 2 O 6-α F α, the value of alpha is, of claims 1 to 3 in the range of 0.01 ≦ α ≦ 0.1 The positive electrode active material for lithium secondary batteries in any one. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein the primary particle diameter is nanoparticles in the range of 200 to 800 nm. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5, which has a coating with carbon or a conductive metal. Compositional formula including the following steps: Li _1-y A _y V _1-x M _x Si ₂ O _6-α F _α
(In the formula, A represents at least one alkali metal element selected from the group consisting of Na, K, Rb, Cs and Fr, and M consists of Al, Sc, Ti, Cr, Mn, Fe and In. And at least one element selected from the group, wherein x, y, and α are numerical values in the ranges of 0 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.3, and 0 ≦ α ≦ 0.1, respectively. Method for producing a lithium vanadium metasilicate compound having a monoclinic pyroxene structure represented by:
(1) A first compounding step in which a heat treatment is performed after mechanical milling is performed on the raw material mixture for the first compounding step including the oxygen-containing lithium compound and the oxygen-containing silicon compound.
(2) A second compounding step in which heat treatment is performed after subjecting the raw material mixture for the second compounding step containing the product of the first compounding step and the oxygen-containing vanadium compound to mechanical milling. Either or both of the raw material mixture for the first composite process and the raw material mixture for the second composite process are further selected from the group consisting of an oxygen-containing alkali metal compound, a compound containing element M and an oxygen atom, and a metal fluoride. The method for producing a lithium vanadium metasilicate compound according to claim 7, comprising at least one selected component. The raw material mixture for the second complexing step contains an oxidizing agent or a reducing agent of an oxidation equivalent or more or a reduction equivalent or more necessary for making the vanadium element in the oxygen-containing vanadium compound contained in the mixture into trivalent vanadium. Item 9. A method for producing a lithium vanadium metasilicate compound according to Item 7 or 8. The mechanical milling process of a 1st compounding process and a 2nd compounding process is performed by the gravitational acceleration of 50-200G using a planetary mill, The vanadium lithium metasilicate type compound of any one of Claims 7-9 Production method. The heat treatment temperature in the first composite step is 500 to 800 ° C, and the heat treatment temperature in the second composite step is 700 to 1300 ° C. Production of lithium vanadium metasilicate compound according to any one of claims 7 to 10 Method. Carbon, wherein the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 5 and a carbon precursor are mixed and heated at 400 to 900 ° C in a non-oxidizing atmosphere. A method for producing a coated positive electrode active material for a lithium secondary battery. 13. The carbon-coated lithium secondary battery according to claim 12, wherein the carbon precursor is at least one component selected from the group consisting of adhesive hydrocarbon-based organic matter, coal-based pitch, and petroleum-based pitch. A method for producing a positive electrode active material. The lithium secondary battery which contains the positive electrode containing the positive electrode active material as described in any one of Claims 1-5 as a component.

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