WO2023162040A1 - Method for preparing lithium metal phosphate, lithium metal phosphate, positive electrode material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

The purpose of the present invention is to provide a method for preparing a lithium metal phosphate having a stable crystal structure and excellent electric capacity and electric conductivity.　The present invention pertains to a method for preparing a lithium metal phosphate having an olivine-type crystal structure, the method comprising: a mixing step for obtaining a mixture of a solute raw material and a flux, the solute raw material containing a compound containing element Li, a compound containing metal element M (M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn), at least one among a compound containing element B and a compound containing element Si, and a pyrophosphate ion-containing compound containing element P; a melting step for obtaining a melt of the mixture; and a cooling step for cooling the melt to obtain precipitates. A tetraborate ion-containing compound containing element B may be used instead of or in addition to the pyrophosphate ion-containing compound containing element P.

Description

Method for producing lithium metal phosphate, lithium metal phosphate, positive electrode material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery

The present invention relates to a method for producing a lithium metal phosphate, a lithium metal phosphate, a positive electrode material for lithium ion secondary batteries, a positive electrode for lithium ion secondary batteries, and a lithium ion secondary battery.

LiCoO ₂ (LCO) is known as a positive electrode material for lithium ion secondary batteries. LCO has a high energy density (electromotive voltage x electric capacity), but has problems in stability and life. An olivine-type lithium metal phosphate represented by the general formula LiFePO ₄ has been put to practical use as a more stable material to replace LCO. On the other hand, Li ₂ FeSiO ₄ , which is similar to lithium metal phosphate, is expected to double the electric capacity because it has two Li in the molecule, but it cannot be used as a positive electrode material because it is an insulator. .

By the way, as a transition metal element (hereinafter referred to as "M" or "M element") that has a valence of +2 in the stoichiometric composition and can change its valence to +3 in order to maintain charge neutrality with the desorption of Li, , Fe, Co, Ni, and Mn are known (eg, Patent Document 1). However, as described in Patent Document 1, the electrical conductivity of olivine-type lithium metal phosphate is generally low. Therefore, olivine-type lithium metal phosphates other than LiFePO ₄ (for example, LiCoPO ₄ and LiMnPO ₄ ) are not widely used (Patent Document 2).

Therefore, attempts have been made to improve the electrical conductivity of this material by substituting part of the pentavalent element P with a trivalent element such as B or Al and compensating for the charge by adding Li or oxygen defects. is done. However, when the ratio of B to P is increased, spinel (M ₃ O ₄ ), fondenite (M ₃ BO ₅ ), metal borate {M ₃ (BO ₃ ) ₂ }, lithium metal borate, lysicone Li A different phase such as _3-2αMα (P,B)O ₄ (a Li in the Li ₃ PO _{4 structure} in which part of Li is substituted with a divalent metal element) is formed, and the electrical conductivity deteriorates. Also, in powder sintering of Li _1+x Fe(P _1-x , B _x )O ₄ , heterogeneous phases are mixed into the olivine phase and the electrical conductivity is deteriorated (Patent Document 3). This phenomenon also occurs in powder sintering of Li _1+x M(P _1-x , B _x )O ₄ , and the amount of B substitution is significantly limited (Patent Document 4). In addition, in the composition formula, M represents a transition metal.

Some of the undesirable side reactions from the viewpoint of lowering the purity of crystals in the production of olivine-type lithium metal phosphate are shown below in terms of increasing electrical conductivity and electrical capacity. In each composition formula, M represents a transition metal.
3Li ₂ O+3MCl ₂ +O→M ₃ O ₄ +6LiCl (formation of spinel)
3/2Li ₂ O+3MCl ₂ +Li ₃ BO ₃ +1/2(O)→M ₃ BO ₅ +6LiCl (formation of fondenite)
Li ₃ PO ₄ +xMCl ₂ →Li _3-2x MxPO _{4 +2x} LiCl (formation of LISICON)
Li ₃ BO ₃ +MCl ₂ →LiMBO ₃ +2LiCl (formation of metal lithium borate salt)
2Li ₃ BO ₃ +3MCl ₂ →M ₃ (BO ₃ ) ₂ +6LiCl (formation of metal borate)

JP 2008-184346 A JP 2008-130525 A JP 2004-178835 A JP 2010-123339 A

In general, a substance having a high ratio of Li in its composition can be expected to have a high electric capacity. Further, by substituting a portion of P with another doping element, an improvement in electrical conductivity can be expected. Therefore, based on the findings of Patent Documents 3 and 4, P ⁵⁺ is replaced with B ³⁺ or Si ⁴⁺ with a smaller ionic radius in order to increase the ratio of Li that contributes to the electric capacity in the olivine-type lithium metal phosphate. We considered how to increase the substitution rate by using However, the inventors have found that the olivine structure tends to become unstable when the substitution rate is increased.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a lithium metal phosphate that has a stable crystal structure and excellent electrical capacity and electrical conductivity. The present invention also provides a lithium metal phosphate having a stable crystal structure and excellent electrical capacity and electrical conductivity, a positive electrode material for a lithium ion secondary battery using the lithium metal phosphate, and a lithium ion secondary battery. An object of the present invention is to provide a positive electrode and a lithium ion secondary battery.

As a result of intensive studies by the inventors in order to solve the above problems, the adoption of a high-temperature flux method (flux method), doping of boron or silicon to partially replace phosphorus, and phosphate used as a raw material By at least part of the pyrophosphate, or at least part of the boron-doped material is tetraborate, an olivine type with a stable crystal structure while maintaining excellent electrical capacity and electrical conductivity The inventors have found that the structure can be obtained, and have completed the present invention.

That is, the present invention provides a compound containing Li element; a compound containing metal element M (M is at least one selected from the group consisting of Fe, Co, Ni, and Mn); a compound containing B element and Si element. at least one of the compounds containing; and a solute raw material containing a compound containing a P element containing pyrophosphate ions, a mixing step of obtaining a mixture of a flux and a mixing step of obtaining a mixture, a melting step of obtaining a melt of the mixture, and cooling the melt and a cooling step of obtaining a precipitate by means of cooling.

In this case, the compound containing element B may contain tetraborate ions.

Further, the present invention provides a compound containing Li element; a compound containing metal element M (M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn); B element containing tetraborate ion and a compound containing a P element containing a phosphate ion, a mixing step of obtaining a mixture of a solute raw material and a flux, a melting step of obtaining a melt of the mixture, and a precipitate by cooling the melt and a cooling step of obtaining

In this case, the solute raw material may further contain a compound containing Si element.

In one aspect, the melting temperature in the melting step is preferably 600°C or higher.

In one aspect, the ratio of B element to P element in the mixture is preferably 1/99 to 99/1.

In one aspect, the ratio of Si element to P element in the mixture is preferably 1/99 to 99/1.

The present invention provides a lithium metal phosphate having an olivine-type crystal structure represented by the general formula LiM(P,Q)O ₄ and an electrical conductivity of 10 ⁻⁸ S/cm or higher.
(In the formula, M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn. (P, Q) indicates that part of P is replaced with Q. , Q is at least one of B and Si.)

The present invention also provides a lithium metal phosphate having an olivine-type crystal structure represented by the general formula Li _1+α M(P _1-xy B _x Si _y )O ₄ .
(Wherein, M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn. In addition, x is 0 to 0.6, y is 0 to 0.6, x + y = more than 0.2 0.8 or less, α is 0.4 to 1.2.)

In this case, the electrical conductivity may be 10 ⁻⁸ S/cm or more.

The present invention provides a positive electrode material for a lithium ion secondary battery, containing the lithium metal phosphate described above.

The present invention provides a positive electrode for a lithium-ion secondary battery containing the positive electrode material described above.

The present invention provides a lithium ion secondary battery comprising the positive electrode described above.

According to the present invention, it is possible to provide a method for producing a lithium metal phosphate that has a stable crystal structure and excellent electrical capacity and electrical conductivity. According to the present invention, a lithium metal phosphate having a stable crystal structure and excellent electrical capacity and electrical conductivity, a positive electrode material for a lithium ion secondary battery using the lithium metal phosphate, and a lithium ion secondary battery can provide a positive electrode and a lithium ion secondary battery.

Since the lithium metal phosphate according to the present invention can have a crystal structure with a high Li ratio, excellent electric capacity can be expected, and because it has a stable olivine-type crystal structure (also referred to as an olivine structure). Long life of the positive electrode can be expected.

1 is a powder X-ray diffraction chart in Example 1. FIG. 4 is a powder X-ray diffraction chart in Example 2. FIG. 4 is a powder X-ray diffraction chart in Example 3. FIG. 4 is a powder X-ray diffraction chart in Example 4. FIG. 2 is a powder X-ray diffraction chart in Example 5. FIG. 2 is a powder X-ray diffraction chart in Example 6. FIG. 2 is a powder X-ray diffraction chart in Example 7. FIG. 2 is a powder X-ray diffraction chart in Example 8. FIG. 4 is a powder X-ray diffraction chart in Comparative Example 1. FIG. 4 is a powder X-ray diffraction chart in Comparative Example 2. FIG. 4 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 1. FIG. 4 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 2. FIG. 10 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 3. FIG. 10 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 4. FIG. 10 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 5. FIG. 10 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 6. FIG. FIG. 10 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 7. FIG. 10 is a graph showing the electrical conductivity evaluation results of lithium metal phosphate in Example 8. FIG. 4 is a graph showing electrical conductivity evaluation results of lithium metal phosphate in Comparative Example 1. FIG.

Several embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

<Method for Producing Lithium Metal Phosphate>
A method for producing a lithium metal phosphate includes a mixing step of obtaining a mixture of a raw material compound and a flux, a melting step of obtaining a melt of the mixture, a cooling step of cooling the melt to obtain a precipitate, Prepare.

The above production method employs a high-temperature flux method (flux method), dopes boron or silicon to partially replace phosphorus, and replaces at least a portion of the compound containing the P element with a compound containing pyrophosphate ions. Or, it is essential that at least part of the compound containing the B element for boron doping is a compound containing tetraborate ions, thereby maintaining excellent capacitance and electrical conductivity, An olivine structure with a stable crystal structure can be obtained.

(Mixing process)
From the viewpoint of suppressing the formation of metal oxides as impurities due to side reactions and improving the yield of lithium metal phosphate having an olivine structure, the following two steps can be adopted as the mixing step.

That is, in the mixing step, a compound containing Li element; a compound containing metal element M (M is at least one selected from the group consisting of Fe, Co, Ni, and Mn); a compound containing B element and Si element. and at least one of the compounds containing P, pyrophosphate ions, and a flux. In this case, the solute raw material contains a compound containing B element when the compound containing Li element does not contain B element (borate ion), and when the compound containing Li element does not contain Si element (silicate ion) contains a compound containing Si element, and can contain a compound containing P element when the compound containing Li element does not contain P element (pyrophosphate ion). Note that the compound containing element B may contain tetraborate ions.

In addition, the mixing step includes a compound containing Li element; a compound containing metal element M (M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn); B element containing tetraborate ion and a compound containing P element containing phosphate ions, and a mixing step of obtaining a mixture of a flux and a solute raw material. In this case, the solute raw material contains a compound containing B element containing tetraborate ions when the compound containing Li element does not contain tetraborate ions, and when the compound containing Li element does not contain phosphate ions Compounds containing the P element containing phosphate ions can be included. The solute raw material may further contain a compound containing Si element, and in this case, when the compound containing Li element does not contain Si element (silicate ion), it may further contain a compound containing Si element.

The compound containing Li element is not particularly limited, and includes lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium phosphate, lithium pyrophosphate, lithium dihydrogen phosphate, lithium borate, lithium tetraborate, silicic acid. Examples include lithium, lithium metasilicate, anhydrides or hydrates thereof, and the like. In particular, lithium pyrophosphate and lithium tetraborate are preferable from the viewpoint of suppressing the formation of metal oxides as impurities due to side reactions and improving the yield of olivine.

The compound containing the metal element M is not particularly limited, and iron oxalate, iron chloride, iron sulfate, iron nitrate, iron oxide, iron hydroxide, anhydrides or hydrates of these compounds containing Fe element (compound The valence of Fe in may be divalent or trivalent); compounds containing Co elements such as cobalt carbonate, cobalt oxalate, cobalt chloride, anhydrides or hydrates thereof; nickel carbonate, nickel oxalate , nickel chloride, their anhydrides or hydrates; and manganese carbonate, manganese oxalate, manganese chloride, and their anhydrides or hydrates.

The compound containing the B element is not particularly limited, and includes boron oxide; boric acid, boric anhydride, compounds containing borate ions such as lithium borate; compounds containing tetraborate ions such as lithium tetraborate, and the like. mentioned. In particular, from the viewpoint of suppressing the formation of metal oxides as impurities due to side reactions and improving the yield of olivine, at least part of the compound containing element B is preferably a compound containing tetraborate ions, and the compound Lithium tetraborate is preferred.

The compound containing Si element is not particularly limited, and silicon oxide, silica gel, lithium silicate, lithium metasilicate, etc. can be used. Of these, lithium silicate is preferred from the viewpoint of purity and reactivity.

Compounds containing the P element include compounds containing phosphate ions (PO ₄ ³⁻ ) and compounds containing pyrophosphate ions (P ₂ O ₇ ⁴⁻ ). Compounds containing phosphate ions are not particularly limited, and ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate, phosphoric acid, diphosphorus pentoxide, and these Anhydrides or hydrates are mentioned. Compounds containing pyrophosphate ions include pyrophosphate, lithium pyrophosphate, anhydrides and hydrates thereof. In particular, from the viewpoint of suppressing the formation of metal oxides as impurities due to side reactions and improving the yield of olivine, it is preferable that at least part of the compound containing the P element is a compound containing pyrophosphate ions, and the compound is preferably lithium pyrophosphate.

Using a compound containing two or more of Li element, M element, B element, Si element and P element facilitates the mixing process. For example, lithium borate can be used as a compound containing Li and B elements. Lithium phosphate and lithium dihydrogen phosphate can also be used as compounds containing Li elements and phosphate ions. In this way, a compound containing the Li element, a compound containing the metal element M, a compound containing the B element, a compound containing the Si element, and a compound containing the P element may be prepared and used. In addition, a compound containing the P element, a compound containing the metal element M, a compound containing the B element, and a compound containing the Si element may be prepared.

Advantages of converting part or all of the phosphate ions to pyrophosphate ions in a compound containing the P element will be described. For example, when pyrophosphoric acid is used as the compound containing the element P, reaction between pyrophosphoric acid (H ₄ P ₂ O ₇ ) and an equivalent amount of Li ₂ O produces Li ₄ P ₂ O ₇ and water. However, if Li is added in excess of what would produce such a pure phosphate, pyrophosphate (H ₄ P ₂ O ₇ ) reacts with excess Li ₂ O to form 2Li ₃ PO ₄ . At this time, the chemical reaction of Li ₃ PO ₄ in the active state, the divalent transition metal salt, and excess lithium is accelerated due to the decrease in activation energy, and Li _1+αM (P,Q)O ₄ is produced. As a result, the production of spinel, fondenite, and lysicone, which are metal oxides as impurities due to side reactions, can be suppressed, and the yield of olivine can be improved.

In the compound containing element B, the advantages of using tetraborate ions for some or all of the borate ions are the same as the advantages of using pyrophosphate ions for some or all of the phosphate ions. That is, for example, when lithium tetraborate is used as the compound containing element B, lithium tetraborate Li ₂ B ₄ O ₇ reacts with excess Li ₂ O to produce 4LiBO ₂ . LiBO ₂ in this active state suppresses the formation of metal oxides as impurities due to side reactions and improves the yield of olivine.

From the viewpoint of more easily suppressing the formation of metal oxides as impurities due to side reactions, some or all of the phosphate ions are replaced with pyrophosphate ions, and some or all of the borate ions are replaced with tetraborate ions. may be used together.

The element ratio (molar ratio) of the M element, the P element, the B element and the Si element in the raw material weighing of each compound described above can be 0.8 to 1.2:1. From the viewpoint of the theoretical ratio of lithium metal phosphate having an olivine-type crystal structure, the ratio may be 1:1.

The element ratio of the B element to the P element (B element/P element) can be 1/99 to 99/1 or 10/90 to 99/1. However, from the viewpoint of obtaining the desired crystal structure and exhibiting better electrical conductivity and capacitance, the ratio can be 15/85 to 50/50, and 10/90 to 30/70. good too.
The element ratio of Si element to P element (Si element/P element) can be 1/99 to 99/1 or 10/90 to 99/1. However, from the viewpoint of obtaining the desired crystal structure and exhibiting better electrical conductivity and capacitance, the ratio can be 15/85 to 50/50, and 10/90 to 30/70. good too.

The amount of each element of P element, B element and Si element is adjusted so that Li element is large. From the stoichiometric ratio of the lithium metal phosphate represented by LiFePO ₄ , the element ratio of Li and P is 1:1, but by adjusting the respective element amounts of P element, B element and Si element, , the element ratio of Li and (P+B+Si) can be increased to about 2:1 in the subsequent melting and cooling steps. Further, the reason why the Li element is adjusted to be large is that there is evaporation loss of Li and that pyrophosphate ions are completely decomposed into phosphate ions. Excess lithium promotes the formation of olivine and has the effect of suppressing the generation of heterophases. Excess lithium is removed during the washing process that separates the single crystal. For example, when lithium pyrophosphate is used, the reaction formula is as follows. Since pyrophosphate becomes active phosphoric acid, the reaction to produce olivine is dominant.
_{Li4P2O7 + Li2O → 2Li3PO4 _}
1 _{/ 2Li3PO4 +} 1/ _2Li3BO3 + _MCl2 +1/ _2Li2O → _Li2M ( _P0.5 , _B0.5 ) _O4 +2LiCl

Regarding the use of excess lithium, specifically, when mixing a compound containing the Li element, a compound containing the metal element M, a compound containing the B element, a compound containing the Si element, and a compound containing the P element, The element ratio of the Li element to the B element, Si element and P element (Li element/(B element + Si element + P element)) is 1.4 to 1.4 from the viewpoint of maintaining electrical neutrality and easily obtaining a stable olivine structure. It is preferably 2.2, more preferably 1.5 to 2.0.

Flux is a compound used in the high-temperature flux method (flux method), a type of crystal production method, and is an inorganic compound that acts as a solvent to dissolve the desired crystal. The high-temperature flux method utilizes the property that the solubility of crystals, which are solutes, in a solvent changes with temperature. If a flux is used that has a high solubility at high temperatures and a low solubility at low temperatures, the solubility in the flux exceeds with cooling, and the target substance in a supersaturated state precipitates as crystals. As the flux, a compound that melts at a temperature lower than that of the target crystal may be selected. Fluxes include lithium chloride, lithium carbonate, lithium fluoride, lithium vanadate, sodium dihydrogen phosphate, lead fluoride, lead oxide, bismuth oxide, molybdate, tungstate, etc., and these are one type. It can be used alone or in combination of two or more. When there are multiple solute components, a specific solute component is increased and the component ratio is intentionally deviated from the desired component ratio (stoichiometric ratio) so that the solute component also functions as a flux. A self-flux method can also be used. That is, the compound containing Li element used in excess is also used as a self-flux.

In the mixing process, each compound that becomes the solute is mixed with the flux to obtain a mixture. Each compound is appropriately weighed so as to obtain the desired composition of lithium metal phosphate. The mixing ratio of each compound and flux is preferably 1:0.1 to 1:1, more preferably 1:0.2 to 1:0.5, from the viewpoint of the melting temperature and solubility of the raw materials. more preferred. The mixing method may be either a dry mixing method or a wet mixing method. Specifically, a method of mechanically mixing each raw material using a mortar, a ball mill, etc., a coprecipitation method in which each raw material is dissolved in water and then precipitated and mixed, and a sol in which each raw material is dissolved is gelled. A sol-gel method, etc., in which the components are mixed together can be used.

(melting process)
In the melting step, the mixture obtained in the mixing step is melted. The mixture is placed in a predetermined container such as a platinum crucible as required, put into a firing furnace, and melted in an inert atmosphere or an inert atmosphere containing a small amount of oxygen. Examples of the inert atmosphere include an atmosphere substituted with argon gas, nitrogen gas, helium gas, or the like. These inert gases may contain less than 100 ppm of oxygen. The melt in the melting step means that the flux added as a solvent is completely melted, and most of the solute is (a compound containing the Li element, a compound containing the metal element M, a compound containing the B element, a compound containing the Si element, compounds, and compounds containing P elements including phosphate ions and pyrophosphate ions) are in a state of being melted in the flux. The melt may contain unmelted solutes.

The melting temperature in the melting process can be set to a temperature at which most or all of the solute melts in the molten flux. For example, a high temperature of 1000° C. or more is required to melt a mixture containing SiO ₂ without using a flux, but the use of a flux enables melting at a lower temperature. Although it depends on the composition of the mixture and is not necessarily limited, the melting temperature can be at least 600°C or higher since the melting point of lithium chloride, which is the main flux component, is 605°C, and may be 650°C or higher, or 700°C or higher. may be The upper limit of the melting temperature can be 1000° C. or lower from the viewpoint of suppressing the decomposition and evaporation of the raw material and the lithium compound, and may be 900° C. or lower. The holding time at the melting temperature can be set to a time for a certain amount of solute to melt, for example, it can be at least 3 hours or more, may be 4.5 hours or more, or 6 hours or more. may be The upper limit of the holding time can be 24 hours or less from the viewpoint of suppressing decomposition and evaporation of the raw material and the lithium compound, and may be 12 hours or less.

If the flux is not completely melted during the melting process, or if most of the solute is not dissolved in the flux, the resulting lithium metal phosphate having an orthorhombic olivine-type crystal structure will not contain There is a possibility that impurities such as reaction raw materials and flux components may be mixed in and compounded. These impurities are compounds that are produced when the mixture is simply sintered, and are factors that reduce the electrical conductivity of lithium metal phosphate having an olivine-type crystal structure. The sintering referred to here is a method that does not use flux, and heats the raw materials at a high temperature that does not completely melt the raw materials to cause the raw materials to react with each other, thereby obtaining a sintered product having a composition according to the raw materials. be. Since the solid-phase diffusion during firing facilitates the progress of the reaction, unreacted portions may remain, and the distribution of elements in the product tends to become non-uniform. Also, since calcination is based on a solid state reaction, it is practically impossible to produce crystals large enough to be separated. Therefore, when sintering without using flux, it is necessary to repeat sintering, pulverization, and re-mixing many times in order to produce a homogeneous material with a complicated structure and a variety of elements.

From the viewpoint of suppressing the generation of impurities such as unreacted raw materials and flux components, a calcination process may be performed prior to the melting process. In the calcination step, the mixture can be calcined at about 400 to 600° C. to obtain a calcined product. The calcined product can be subjected to a melting step.

(Cooling process)
The resulting melt is cooled to room temperature by this step. The cooling rate is preferably 5° C./hour or less until solidification at the fastest. If the cooling rate is too fast, defects may occur in the crystal.

The recovered product (cooled product) obtained after the cooling step contains the deposit of the lithium metal phosphate having the desired olivine type crystal structure, as well as other components such as flux components, unreacted substances, and side reaction products. obtain. For example, by washing the collected material with warm water (pure water at 60° C., etc.) and filtering only the hardly soluble crystals, the remaining collected material can be visually observed to have the desired olivine-type crystal structure. Only lithium metal phosphate can be selected. From this point of view, the manufacturing method of the present embodiment may include a washing step of washing the recovered material obtained in the cooling step. It can be confirmed by X-ray diffraction method or the like that the obtained crystal is a lithium metal phosphate having an olivine type crystal structure.

<Lithium metal phosphate>
The lithium metal phosphate of the present embodiment is a part of P in a compound represented by the general formula Li ₂ MPO ₄ (wherein M is at least one selected from the group consisting of Fe, Co, Ni and Mn) is substituted with B, Si, or B and Si. Lithium metal phosphate has an olivine structure.

In general, the olivine structure has a hexagonal close-packed oxygen skeleton, with P ions at the tetracoordinated tetrahedral sites and Li ions and transition metal ions M at the hexacoordinated octahedral sites. In the lithium metal phosphate of this embodiment, some of the pentavalent P ions are replaced with trivalent B ions and tetravalent Si ions. The valence of M is +2 in the stoichiometric composition, and can change from +2 to +4 in order to keep the charge neutral with the elimination of Li.

Such lithium metal phosphates can be referred to as boron silicon-doped lithium metal phosphates or boron phosphorus-doped lithium metal silicates _Li2M (P,B,Si) _O4 .

The lithium metal phosphate of the present embodiment has an olivine-type crystal structure represented by the general formula Li _1+α M(P _1-xy B _x Si _y )O ₄ .
In the above formula, M represents at least one selected from the group consisting of Fe, Co, Ni and Mn. Further, x is 0 to 0.6, y is 0 to 0.6, x+y is more than 0.2 and 0.8 or less, and α is 0.4 to 1.2.

Although x may be 0, when x is more than 0, excellent electric capacity and electric conductivity can be exhibited. From this point of view, x is preferably 0.3 or more, more preferably 0.4 or more.
When x is 0.6 or less, heterogeneous phases are less likely to occur and the yield is improved. From this point of view, x is preferably 0.5 or less.

Although y may be 0, when y is more than 0, excellent electric capacity and electric conductivity can be exhibited. From this point of view, y is preferably 0.2 or more, more preferably 0.3 or more.
Electric conductivity improves because y is 0.6 or less. From this point of view, y is preferably 0.5 or less.
In addition, it is preferable that x<y from the viewpoint of easily suppressing the generation of a different phase.

When x+y is more than 0.2, excellent electric capacity and electric conductivity can be exhibited. From this point of view, x+y is preferably 0.3 or more, more preferably 0.4 or more.
When x+y is 0.8 or less, heterogeneous phases are less likely to occur and the yield is improved. From this point of view, x+y is preferably 0.7 or less.

When α is 0.4 or more, excellent electric capacity and electric conductivity can be exhibited. From this point of view, α is preferably 0.5 or more.
When α is 1.2 or less, heterogeneous phases are less likely to occur and the yield is improved. From this point of view, α is preferably 1 or less.

Since the above lithium metal phosphate has excellent electrical conductivity, it has an olivine-type crystal structure represented by the general formula LiM(P,Q)O ₄ and has an electrical conductivity of 10 ⁻⁸ S/cm or more. It can also be called lithium metal phosphate. Here, the electric conductivity is a value measured based on the fact that the electric conductivity of LiFePO ₄ is 10 ⁻⁸ /cm.
In the formula, M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn. (P, Q) indicates that part of P is replaced with Q, and Q is B or B and Si.

The reason why the electrical conductivity is improved in the boron- or silicon-doped lithium metal phosphate having an olivine-type crystal structure is not clear, but the inventor speculates as follows.

First, the transition metal is in a state of equilibrium with oxygen in the atmosphere in a high-temperature molten state, and in the presence of a small amount of oxygen, divalent and trivalent transition metal ions are in a state of coexistence. In the crystal structure, the crystal radius of the 4-coordination site is Si ⁴⁺ >P ⁵⁺ >B ³⁺ , and 0.40 of Si is the largest, and the crystal radius of the transition metal of the 6-coordination site is 0.75 to 0.83. , B and Si are usually not considered to enter the six-coordinated sites occupied by transition metals. In the crystal structure, Si and B are substituted and solid-soluted at the position of P, which is 4-coordinate, so if the atmosphere is reducing and Li is excessive, Li ions further increase at the 6-coordinate position for charge compensation. . Or, if somewhat oxidizing, a trivalent transition metal will enter. If there are trivalent transition metal ions in the crystal, it is considered that electron transfer occurs between the divalent and trivalent transition metal ions, thereby developing electron conductivity.

It is also known that Li ₂ FeSiO ₄ in which all four coordination sites are Si has very poor electrical conductivity. It is presumed that the reason for this is that Si is strongly and tightly bound to the surrounding oxygen and has no flexibility in the crystal structure, making it difficult for Li ⁺ ions to move. The melting point of a solid solution is generally lower than that of a pure one because the crystal lattice is distorted, weakening the binding force between the constituent cations and oxygen ions. A solid solution in which an element other than Si is mixed in the 4-coordination site has a weaker bonding force with oxygen than pure silicate, and it is considered that Li ions corresponding to the valence change of the transition metal tend to move. It is believed that this is the same for the lithium metal phosphate, and that the electron mobility is therefore increased. It is speculated that ionic conduction and electronic conduction complementarily contribute to the improvement of electrical conductivity.

When part of Si in Li ₂ SiO ₄ , which is _an insulator, is replaced with P, electrical conductivity appears. When part of P in LiFePO ₄ is replaced with B, the electrical conductivity is further increased, but the crystal structure becomes unstable and it becomes difficult to maintain the olivine structure. When replacing P in _LiFePO4 with Si, the crystal structure is not as distorted as in the case of B, and when part of the P is replaced with Si and B, the solid solution region of B increases, so the electrical conductivity increases despite being olivine. . That is, it is considered that when the types of elements at the 4-coordination sites are mixed and solid-dissolved, the bond with oxygen is weakened and the Li ^{2 +} ions are more likely to move.

The olivine structure is derived from the olivine X ₂ SiO ₄ structure, a natural silicate mineral (wherein X contains the divalent metals Mg and Fe in a ratio of about 9:1). In X ₂ SiO ₄ , oxygen is nearly hexagonally densely packed, and there are 8 gaps per 4 oxygen atoms surrounded by 4 oxygen atoms, and Si occupies ⅛ of these gaps. There are also 4 gaps surrounded by 6 oxygen atoms per 6 oxygen atoms, and X occupies 1/2 of them. On the other hand, in Li ₂ MSiO ₄ (M=Fe, Co, Ni, Mn) to which P and B are added, P and B are included in part of Si, and two Li and M are included in X. When equivalent amounts of P and B are substituted for Li ₂ MSiO ₄ , the ratio of Li in the molecule does not change due to the substitution of pentavalent P and trivalent B for tetravalent Si.

<Lithium ion secondary battery>
A lithium-ion secondary battery includes a positive electrode that includes a positive electrode material comprising the lithium metal phosphate described above. More specifically, a lithium ion secondary battery includes the positive electrode, negative electrode, electrolyte, and the like.

(positive electrode)
The positive electrode can contain, in addition to the above positive electrode material, a conductive aid, a binder, and the like.

The conductivity aid is not particularly limited, and includes acetylene black, carbon black, graphite, carbon fiber, metal fiber, aluminum powder, fluorocarbon, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. These can be used individually by 1 type or in combination of 2 or more types.

The binder is not particularly limited and includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer and the like. These can be used individually by 1 type or in combination of 2 or more types.

(negative electrode)
The negative electrode may consist of the negative electrode active material itself, or may contain the negative electrode active material and a binder. That is, the negative electrode may consist of metallic lithium, a lithium-aluminum alloy, a lithium-tin alloy, or may contain graphite, carbon fiber, coke, mesocarbon microbeads (MCMB), etc., and a binder.

(Electrolytes)
The electrolyte may be liquid or solid.

When the electrolyte is liquid (that is, an electrolytic solution is used), it is possible to use an organic solvent in which the supporting electrolyte is dissolved. Examples of organic solvents include, but are not limited to, carbonates, halogenated carbohydrates, ethers, ketones, nitriles, lactones, oxolane compounds, and the like. These can be used individually by 1 type or in combination of 2 or more types.

The supporting electrolyte is not particularly limited, and inorganic salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , LiSO ₃ CF ₃ , LiC(SO ₃ CF ₃ ) ₂ , LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ), and derivatives thereof.

When using an electrolytic solution, a porous synthetic resin film (especially a porous film of polyolefin molecules) may be used as a separator.

When the electrolytic solution is solid (that is, when a solid electrolyte is used), compounds such as oxides and sulfides can be used. _The oxide compounds include _{La0.51Li0.34TiO2.94} , NASICON _{- type Li1.3Al0.3Ti1.7} ( _PO4 ), and _garnet - _{type LI7La3Zr2 .} Examples of sulfide-based compounds include two-component systems such as Li ₂ S—SiS ₂ systems, and three-component systems in which LiI, LI ₃ PO _{4 ,} etc. are added thereto. be done.

A lithium-ion secondary battery is manufactured, for example, as follows.

A coating liquid is prepared by dispersing the negative electrode active material and binder in a solvent. The obtained coating liquid is uniformly applied on the negative electrode current collector and dried to obtain a laminate composed of the negative electrode current collector and the negative electrode active material layer. This laminate is housed in a negative electrode member so that the negative electrode current collector and the inner surface of the negative electrode member are in contact with each other to obtain a negative electrode. In addition, when metallic lithium foil or the like is used, the itself may be used as the negative electrode.

Next, a coating liquid is prepared by dispersing the positive electrode active material, conductive aid, and binder in a solvent. The obtained coating liquid is uniformly applied on the positive electrode current collector and dried to obtain a laminate composed of the positive electrode current collector and the positive electrode active material layer. A positive electrode is obtained by housing this laminate in a positive electrode member so that the positive electrode current collector and the inner surface of the positive electrode member are in contact with each other.

When using an electrolytic solution, the negative electrode and the positive electrode manufactured as described above are superimposed so that a separator is interposed between the negative electrode active material layer and the positive electrode active material layer, the electrolyte is filled, and the battery is sealed with a sealing material. A lithium ion secondary battery is completed by sealing the inside.

On the other hand, when a solid electrolyte is used, for example, a negative electrode raw material powder is deposited to a uniform thickness to form a negative electrode powder layer, and a solid charge layer containing a solid electrolyte powder is formed on the negative electrode powder layer. The raw material powder is deposited to a uniform thickness to form a solid electrolyte powder layer, and the positive electrode raw material powder is deposited to a uniform thickness on the solid electrolyte layer powder layer to form a positive electrode powder layer. After that, these three layers are compression-molded to obtain a powder laminate. A lithium ion battery can be obtained using the obtained powder laminate. A solid electrolyte, a negative electrode, and a positive electrode can also be formed separately and laminated to obtain a lithium ion secondary battery.

The shape of the lithium-ion secondary battery is not particularly limited, and may be cylindrical, rectangular, coin-shaped, button-shaped, or the like.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

(Example 1: Preparation of _Li2 (Fe0.5 _{, Mn0.5} )(P0.33 _, B0.33 _{, Si0.33} ) _O4 )
As a compound containing Li element and P element, lithium pyrophosphate Li ₄ P ₂ O ₇ obtained by reacting commercially available pyrophosphoric acid with lithium carbonate Li ₂ CO ₃ in excess of the equivalent amount (however, the excess lithium carbonate Li ₂ CO ₃ ), iron chloride FeCl ₂ and manganese chloride MnCl 2 as compounds containing metal element M, lithium borate Li ₄ B ₂ O _{5 as} compounds containing B element, and Li ₂ SiO ₃ as compounds containing Si element, Prepared as a solute powder. These were weighed so that the elemental ratio (molar ratio) of Li:Fe:Mn:P:B:Si=40:9:9:6:6:6. Lithium carbonate and lithium chloride were prepared as fluxes. The mixing ratio of the solute powder and the flux was adjusted to a mass ratio of 5:1. The weighed solute powder and flux were thoroughly mixed using a mortar and pestle to obtain a mixed powder.

The mixed powder was placed in a platinum crucible and placed in an atmosphere-controlled electric furnace. Then, the temperature was raised to 890° C. while general nitrogen was circulated in the electric furnace, and the temperature was maintained for 3 hours. Thus, the mixed powder was melted to obtain a melt. The oxygen concentration at the outlet of the furnace was several tens of ppm. The melt was then slowly cooled at 1°C/hr.

After cooling the melt to room temperature, the platinum crucible was taken out. The content of the platinum crucible was washed with hot water to remove flux and the like, and the hardly soluble crystals were filtered to separate and collect only granular black-brown crystals with facets of 1 mm or more. This allowed pure isolation of the desired substance only.

(Example 2: Preparation of _Li2 (Fe0.5 _{, Co0.5} )(P0.33 _{, B0.33, Si0.33} ) _O4 )
As compounds containing metal element M, iron chloride _FeCl2 and cobalt chloride _CoCl2 were prepared. Then, each compound was weighed so that the element ratio was Li:Fe:Co:P:B:Si=40:9:9:6:6:6. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Example 3: Preparation of _Li2 (Fe0.33 _, Mn0.33 _{, Co0.33} )(P0.33 _, B0.33 _{, Si0.33} ) _O4 )
As compounds containing metal element M, iron chloride FeCl ₂ , manganese chloride MnCl ₂ and cobalt chloride CoCl ₂ were prepared. Then, each compound was weighed so that the element ratio was Li:Fe:Co:Mn:P:B:Si=40:6:6:6:6:6:6. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Example 4: Preparation of _Li2Co (P0.5 _{, B0.5} ) _O4 )
Cobalt chloride _CoCl2 was prepared as a compound containing metal element M. Also, Li ₂ SiO ₃ was not used as a compound containing Si element. Then, each compound was weighed so that the element ratio was Li:Co:P:B=27:10:5:5. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Example 5: Preparation of _Li2 (Fe0.5 _, Mn0.5 ₎ (P0.5 _{, B0.5} ) _O4 )
As compounds containing metal element M, iron chloride _FeCl2 and manganese chloride _MnCl2 were prepared. Also, Li ₂ SiO ₃ was not used as a compound containing Si element. Then, each compound was weighed so that the element ratio was Li:Fe:Mn:P:B=27:5:5:5:5. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Example 6: Preparation of _Li2 (Fe0.5 _{, Mn0.5} )(P0.5 _{, B0.5} ) _O4 )
Lithium phosphate Li ₃ PO ₄ as a compound containing Li element and P element, iron chloride FeCl ₂ and manganese chloride MnCl ₂ as a compound containing metal element M, and lithium tetraborate Li ₂ B ₄ O ₇ as a compound containing B element. was prepared as a solute powder. These were weighed so that the elemental ratio of the crystal was Li:Fe:Mn:P:B=24:5:5:5:5. Lithium chloride LiCl was prepared as a flux. The mixing ratio of the solute powder and the flux was adjusted to a mass ratio of 5:1. The weighed solute powder and flux were well mixed using a mortar and pestle to obtain a mixed powder. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Example 7: Preparation of _Li1.5Co (P0.5 _{, Si0.5} ) _O4 )
Lithium pyrophosphate Li ₄ P ₂ O ₇ as a compound containing Li element and P element, cobalt chloride CoCl ₂ as a compound containing metal element M, and SiO ₂ as a compound containing Si element were prepared as solute powders. These were weighed so as to obtain a crystal element ratio of Li:Co:P:Si=22:10:5:5. Lithium chloride LiCl was prepared as a flux. A mixing ratio of the solute powder and the flux was adjusted to a weight ratio of 5:1. The weighed solute powder and flux were well mixed using a mortar and pestle to obtain a mixed powder. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Example 8: Preparation of _Li1.5Mn (P0.75 _{, B0.25} ) _O4 )
Lithium pyrophosphate Li ₄ P ₂ O ₅ as a compound containing Li element and P element, manganese chloride MnCl ₂ as a compound containing metal element M, and boron oxide B ₂ O ₃ as a compound containing B element were prepared as solute powders. . These were weighed so that the elemental ratio of the crystal was Li:Mn:P:B=10:4:3:1. Also, lithium carbonate Li ₂ CO ₃ and lithium chloride LiCl were prepared as fluxes. The mixing ratio of the solute powder and the flux was adjusted to a mass ratio of 5:1. The weighed solute powder and flux were thoroughly mixed using a mortar and pestle to obtain a mixed powder. Except for this, the experiment was carried out in the same manner as in Example 1, and black sparingly soluble granular crystals were recovered.

(Comparative Example 1: Preparation of _LiFePO4 )
Lithium phosphate Li ₃ PO ₄ as a compound containing Li element and phosphate ions, and iron chloride FeCl ₂ as a compound containing metal element M were prepared as solute powders. These were weighed so as to obtain a crystal element ratio of Li:Fe:P=1:1:1. Also, lithium carbonate Li ₂ CO ₃ and lithium chloride LiCl were prepared as fluxes. The mixing ratio of the solute powder and the flux was adjusted to a mass ratio of 5:1. The weighed solute powder and flux were thoroughly mixed using a mortar and pestle to obtain a mixed powder. Except for this, the experiment was carried out in the same manner as in Example 1 to obtain sparingly soluble granular crystals.

(Comparative example 2)
Lithium phosphate was prepared instead of lithium pyrophosphate. Then, each compound was weighed so that the element ratio was Li:Co:B:P=27:10:5:5. Except for this, the experiment was carried out in the same manner as in Example 1, and bluish-black insoluble granular crystals were recovered.

(Powder X-ray diffraction analysis)
When the crystal structure of the precipitates collected in Examples 1 to 8 was confirmed by X-ray diffraction method (characteristic X-ray: CuKα), the precipitates (granular crystals) were identified as single crystals with an olivine structure.
When the crystal structure of the precipitate collected in Comparative Example 1 was confirmed by X-ray diffraction, the precipitate was identified as a single crystal of LiFePO ₄ .
When the crystal structure of the precipitate recovered in Comparative Example 2 was confirmed by X-ray diffraction, the precipitate was identified as a mixture of cobalt borate and olivine. Since no compound containing pyrophosphate ions or compounds containing tetraborate ions was used, the olivine structure became unstable as the ratio of B increased, and it is believed that a heterophase other than olivine was produced.

1 to 10 are powder X-ray diffraction charts in Examples 1 to 8 and Comparative Examples 1 and 2, respectively.

(Evaluation of electrical conductivity)
The electrical conductivity on the two opposing surfaces of the crystal (0.5-2 mm thick) obtained in each example was measured using a DC voltage generator (1 V-2.5 KV), a current measuring instrument (1-110 μA) and a control A system with a PC was used to evaluate at room temperature. As terminals for measurement, a platinum wire with a diameter of 0.5 mm was used for the anode, and an aluminum foil was used for the cathode. The results are shown in the figure. 11 to 19 are graphs showing the electrical conductivity evaluation results of the lithium metal phosphates of Examples 1 to 8 and Comparative Example 1, respectively. In the figure, the dashed line indicates the applied electric field (left vertical axis: V/mm), and the solid line indicates the detected current (right vertical axis: μA). The horizontal axis of the graph indicates elapsed time (×0.1 sec).

In Examples 1 to 8, M in the lithium metal phosphate is at least one of Fe, Mn and Co, and B and Si are dissolved in P. As a result, electrical conductivity comparable to or higher than that of the LiFePO ₄ single crystal of Comparative Example 1 was obtained while having an olivine structure.
Comparing the minimum electric field intensity at which a current of 1 μA or more flows after 5 minutes, it is 600 V/mm in Comparative Example 1 and ranges from 300 to 1200 V/mm in Examples. According to Non-Patent Document 1, the electrical conductivity of LiFePO ₄ is on the order of 10 ⁻⁸ S/cm. Therefore, when the minimum electric field strength at which a current of 1 μA or more flows after 5 minutes is within the above range, LiFePO ₄ It can be judged that an electric conductivity of the order of 10 ⁻⁸ S/cm equivalent to that of 10 −8 S/cm is developed.

Table 1 summarizes the compositions of Examples 1 to 8 and Comparative Example 1, the applied electric field (electric field strength), and the values of the detected current.

With LiCoPO ₄ and LiMnPO ₄ without B or Si substitution, no current could be detected even at the upper limit of 2500 V applied to the DC voltage generator. On the other hand, the lithium metal phosphate of the above example, whose current was detected at a voltage as low as or lower than that of LFePO ₄ , is considered to have an electrical conductivity equivalent to that of LiFePO ₄ and on the order of 10 ⁻⁸ S/cm. , LiFePO ₄ , can be suitably used as a positive electrode material for lithium ion secondary batteries.
Moreover, since the lithium metal phosphate of the above example has a large content of B and Si, it contains more Li than LiMPO ₄ . This is expected to increase the electric capacity (when the same amount of P and B is added, the Li content is twice that of LiFePO ₄ ).
Furthermore, the lithium metal phosphates of the above examples contain Co and Mn instead of Fe as metal elements, and even in this case the electrical conductivity is equivalent to that of LiFePO ₄ . As a result, the output voltage increases, and overall the energy density (output voltage per gram×electrical capacity) greatly exceeds that of LiFePO ₄ , and may even surpass LCO.
In addition, since the lithium metal phosphates of the above Examples can have an olivine structure, the crystal structure is less likely to break even after repeated charging and discharging, and the life and stability are considered to be superior to those of LCO.

According to the present invention, a lithium metal phosphate having an olivine-type crystal structure with excellent electrical conductivity can be obtained. Since the lithium metal phosphate of the present invention has a stable olivine structure, it has a long life, and since P in the crystal is replaced with Si or B, the ratio of Li is high, compared to _LiFePO4. Larger electrical capacity can be expected for

Further, according to the production method of the present invention, a lithium metal phosphate having an olivine-type crystal structure can be produced. Furthermore, the lithium metal phosphate having an olivine-type crystal structure according to the present invention can be used as a positive electrode material for lithium-ion secondary batteries, has higher energy density and electrical capacity than LCO, and similar to LFP. It is possible to provide a lithium-ion secondary battery with safety and long life.

Claims (13)

1. A compound containing Li element; a compound containing metal element M (M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn); at least one of a compound containing B element and a compound containing Si element and a mixing step of obtaining a mixture of a solute raw material containing a compound containing a P element containing pyrophosphate ions and a flux,
   a melting step of obtaining a melt of the mixture;
   a cooling step of cooling the melt to obtain a precipitate;
   A method for producing a lithium metal phosphate having an olivine-type crystal structure, comprising:
2. compound containing Li element; compound containing metal element M (M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn); compound containing B element containing tetraborate ion; and phosphorus a mixing step of obtaining a mixture of a solute raw material containing a compound containing P element containing acid ions and a flux;
   a melting step of obtaining a melt of the mixture;
   a cooling step of cooling the melt to obtain a precipitate;
   A method for producing a lithium metal phosphate having an olivine-type crystal structure, comprising:
3. The production method according to claim 1, wherein the compound containing element B contains a tetraborate ion.
4. The production method according to claim 2, wherein the solute raw material further contains a compound containing Si element.
5. The production method according to any one of claims 1 to 4, wherein the melting temperature in the melting step is 600°C or higher.
6. The production method according to any one of claims 1 to 5, wherein the ratio of B element to P element in the mixture is 1/99 to 99/1.
7. The production method according to claim 1 or 4, wherein the ratio of Si element to P element in the mixture is 1/99 to 99/1.
8. A lithium metal phosphate having an olivine-type crystal structure represented by the general formula LiM(P,Q)O ₄ and having an electrical conductivity of 10 ⁻⁸ S/cm or more.
   (In the formula, M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn. (P, Q) indicates that part of P is replaced with Q. , Q is at least one of B and Si.)
9. A lithium metal phosphate having an olivine-type crystal structure represented by the general formula Li _1+α M(P _1-xy B _x Si _y )O ₄ .
   (Wherein, M represents at least one selected from the group consisting of Fe, Co, Ni, and Mn. In addition, x is 0 to 0.6, y is 0 to 0.6, x + y = more than 0.2 0.8 or less, α is 0.4 to 1.2.)
10. 10. The lithium metal phosphate of claim 9, having an electrical conductivity of ^10-8 S/cm or higher.
11. A positive electrode material for a lithium ion secondary battery, comprising the lithium metal phosphate according to any one of claims 8 to 10.
12. A positive electrode for a lithium ion secondary battery, comprising the positive electrode material according to claim 11.
13. A lithium ion secondary battery comprising the positive electrode according to claim 12.

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