JP2020105053A - Method for producing lithium metal phosphate, lithium metal phosphate, positive electrode material for lithium ion secondary battery, lithium ion secondary battery - Google Patents

Abstract

To provide a method for producing a lithium metal phosphate excellent in electric conductivity.SOLUTION: A method for producing a lithium metal phosphate comprises a mixing step of obtaining a mixture of a compound containing a Li element, a compound containing a metal element M (M is at least one selected from the group consisting of Fe, Co, Ni and Mn), a compound containing a B element, and a phosphate ion, and a flux, a melting step of obtaining a melt of the mixture, and a cooling step of cooling the melt to obtain a precipitate.SELECTED DRAWING: Figure 1

Description

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

LiCoO ₂ (LCO) is known as a positive electrode material for lithium-ion secondary batteries. An olivine-type lithium metal phosphate represented by the general formula LiMPO ₄ is being developed as a more reliable material to replace the LCO. Note that M is a transition metal element having a +2 valence in the stoichiometric composition and capable of changing its valence to a +3 valence in order to maintain charge neutrality with the elimination of Li, such as Fe, Co, Ni and Mn. Is known (for example, Patent Document 1).

JP, 2008-184346, A

By the way, as described in Patent Document 1, the electrical conductivity of olivine-type lithium metal phosphate is generally low. Because of being used as a positive electrode material for secondary batteries, lithium metal phosphate is required to have higher electric conductivity in addition to reliability.

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 having excellent electrical conductivity. Another object of the present invention is to provide a lithium metal phosphate obtained by the manufacturing method, a positive electrode material for a lithium ion secondary battery, and a lithium ion secondary battery.

As a result of intensive studies by the inventor to solve the above problems, the use of the high temperature flux method (flux method) and the doping with boron are effective in producing a lithium metal phosphate having excellent electrical conductivity. It was found to be important, and the present invention was completed. That is, the present invention includes a compound containing a Li element, a compound containing a metal element M (M is at least one selected from the group consisting of Fe, Co, Ni and Mn), a compound containing a B element, and a phosphate ion. Provided is a method for producing a lithium metal phosphate, comprising: a mixing step of obtaining a mixture of a compound and a flux; a melting step of obtaining a melt of the mixture; and a cooling step of cooling the melt to obtain a precipitate. To do.

In the manufacturing method of the present invention, the melting temperature in the melting step may be 600°C or higher.

In the manufacturing method of the present invention, the element ratio of the B element to the P element in the mixture may be 1/99 to 99/1.

The present invention also comprises a compound represented by the general formula LiMPO ₄ (wherein M is at least one selected from the group consisting of Fe, Co, Ni and Mn), and a part of P is substituted with B. Providing lithium metal phosphate.

The lithium metal phosphate of the present invention has a general formula Li _1+α M(B _x P _1-x )O ₄ (wherein x is 0.01 to 0.99 and α is more than 0 and 2x or less). May have.

The lithium metal phosphate of the present invention may be used as a positive electrode material of a lithium ion secondary battery.

The present invention also provides a positive electrode material for a lithium ion secondary battery, which is composed of the above lithium metal phosphate.

Further, the present invention provides a lithium ion secondary battery including a positive electrode containing the above positive electrode material.

According to the present invention, it is possible to provide a method for producing a lithium metal phosphate having excellent electrical conductivity. Moreover, according to this invention, the lithium metal phosphate obtained by the said manufacturing method, the positive electrode material of a lithium ion secondary battery, and a lithium ion secondary battery can be provided.

It is a graph which shows the electric conductivity evaluation result of the lithium metal phosphate which concerns on an Example. It is a graph which shows the electric conductivity evaluation result of the lithium metal phosphate which concerns on an Example. It is a graph which shows the electric conductivity evaluation result of the lithium metal phosphate which concerns on an Example. It is a graph which shows the electric conductivity evaluation result of the lithium metal phosphate which concerns on an Example. It is a graph which shows the electric conductivity evaluation result of the lithium metal phosphate which concerns on a comparative example.

Hereinafter, some embodiments of the present invention will be described in detail. 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 compound containing a Li element, a compound containing a metal element M (M is at least one selected from the group consisting of Fe, Co, Ni and Mn), a compound containing an B element, and The method includes a mixing step of obtaining a mixture of a compound containing phosphate ions (PO ₄ ³⁻ ) and a flux, a melting step of obtaining a melt of the mixture, and a cooling step of cooling the melt to obtain a precipitate. .. According to the production method of the present embodiment, a part of P in the compound represented by the general formula LiMPO ₄ (wherein M is at least one selected from the group consisting of Fe, Co, Ni and Mn) is substituted with B. A lithium metal phosphate can be obtained.

(Mixing process)
The compound containing the Li element is not particularly limited, and includes lithium carbonate, lithium acetate, lithium nitrate, lithium hydroxide, lithium chloride, lithium phosphate, lithium dihydrogen phosphate, lithium borate, their anhydrides or hydrates. Things etc. are mentioned.

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

Among these compounds, a compound containing a divalent transition metal element can be adopted as the compound containing the metal element M from the viewpoint of exhibiting excellent electrical conductivity. Although the reason why the electrical conductivity is particularly improved by using a compound containing a divalent transition metal element in the boron-doped lithium metal phosphate is not clear, the inventor speculates as follows. That is, the transition metal is in a state of equilibrium with oxygen in the atmosphere in a molten state at high temperature, and in the presence of a trace amount of oxygen, it is in a coexisting state of divalent and trivalent. The substitution and solid solution of B at the 4-coordinate P position in the crystal structure further increases Li ions or hexavalent transition metal at the 6-coordinate position for charge compensation. It is considered that the ratio of trivalent in the crystal is increased and the crystal is blackened, electrons are transferred between the divalent and trivalent transition metals, and electrical conductivity is exhibited. Further, it is considered that the Li ion corresponding to the change in valence of the transition metal when the electron moves is easily moved as compared with the silicate, and therefore the electron mobility is considered to be increased. It is speculated that ionic conduction and electronic conduction complementarily contribute to the improvement of electrical conductivity.

The compound containing the element B is not particularly limited, and boron oxide, boric acid, boric anhydride, lithium borate, or the like can be used.

The compound containing a phosphate ion is not particularly limited, and ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate, phosphoric acid, diphosphorus pentoxide, these An anhydride, a hydrate, etc. are mentioned.

The use of a compound containing two or more of Li element, M element, B element and phosphate ion facilitates the mixing step. For example, lithium borate can be used as a compound containing a Li element and a B element. Further, lithium phosphate and lithium dihydrogen phosphate can be used as a compound containing a Li element and a phosphate ion. As described above, a compound containing a Li element, a compound containing a metal element M, a compound containing a B element, and a compound containing a phosphate ion may be prepared and used, and for example, a lithium element is contained and a phosphate ion is contained. A compound containing, a compound containing the metal element M, and a compound containing the B element may be prepared and used.

The elemental ratio of the M element to the P element and the B element in the raw material weighing of each of the above compounds can be 0.8 to 1.2:1. It may be 1:1 from the viewpoint of the stoichiometric ratio of the lithium metal phosphate. On the other hand, the element ratio of the B element to the P element can be 1/99 to 99/1. However, the element ratio may be 5/95 to 50/50, and may be 10/90 to 30/70, from the viewpoint of obtaining a desired crystal structure and exhibiting superior electrical conductivity. The element ratio of the Li element to the P element and the B element must be adjusted so that the Li element becomes large. From the stoichiometric ratio of the lithium metal phosphate, the element ratio is 1:1 because the evaporation loss of Li occurs during the melting process and the cooling process.

Flux is a compound used in a high-temperature fluxing method (flux method), which is a type of crystal production method, and is an inorganic compound that acts as a solvent for dissolving a target crystal. The high temperature flux method utilizes the property that the solubility of crystals, which are solutes, in a solvent changes depending on the temperature. When a flux having a high solubility at a high temperature and a low solubility at a low temperature is used, the solubility in the flux is increased with cooling, and the target substance in a supersaturated state is precipitated as crystals. A compound that melts at a temperature lower than that of the target crystal may be selected as the flux. Examples of the flux include lithium chloride, lithium fluoride, lithium vanadate, sodium dihydrogen phosphate, lead fluoride, lead oxide, bismuth oxide, molybdate, tungstate, and the like. Alternatively, two or more kinds can be used in combination. When there are multiple solute components, the specific solute component is increased and the component ratio is intentionally deviated from the desired component ratio (stoichiometric ratio), and the solute component also functions as a flux. The self-flux method can also be used.

In the mixing step, a flux is mixed with each compound weighing raw material to be a solute to obtain a mixture. The mixing method may be either a dry mixing method or a wet mixing method. Specifically, a method in which each raw material is mechanically mixed using a mortar, a ball mill, or the like, 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 of mixing by mixing can be used.

(Melting process)
In the melting step, the mixture obtained in the mixing step is melted. The mixture is put in a predetermined container as needed, 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. Oxygen of less than 1000 ppm may be contained in these inert gases. The melt in the melting step means that the flux added as a solvent is completely melted and most of the solutes (compounds containing Li element, compounds containing metal element M, compounds containing B element, and phosphate ion) (Including compounds) refers to the state of being dissolved in the flux. The solute may contain unmelted solute.

The melting temperature in the melting step can be set to a temperature at which most of the solute is melted in the melted flux or all the solutes are melted. The melting temperature may be at least 600° C. or higher, may be 650° C. or higher, and may be 700° C. or higher, though it depends on the composition of the mixture. The upper limit of the melting temperature can be 1000° C. or lower, and may be 900° C. or lower, from the viewpoint of suppressing decomposition and evaporation of the raw material and the lithium compound. The holding time at the melting temperature can be set to a time for melting a certain amount of solute, for example, at least 3 hours or more, and may be 4.5 hours or more, and 6 hours or more. May be The upper limit of the holding time can be 24 hours or less, and may be 12 hours or less, from the viewpoint of suppressing decomposition and evaporation of the raw material and the lithium compound.

If the flux is not completely melted during the melting process, or if most of the solutes are not dissolved in the flux, impurities such as unreacted flux components are mixed in the lithium metal phosphate obtained after cooling, There is a risk of being compounded. These impurities are compounds that are generated when the mixture is simply fired, and become a factor that reduces the electrical conductivity of the lithium metal phosphate. It should be noted that the term "firing" as used herein refers to a method that does not use a flux, and is a method of obtaining a fired product having a composition according to the raw materials by heating the raw materials at a high temperature that does not completely melt the raw materials. is there. During firing, the reaction proceeds due to solid-phase diffusion of elements, so unreacted portions may remain, and the element distribution in the product tends to be non-uniform. Further, since firing is based on a solid-phase reaction, it is practically impossible to produce crystals having a size that can be separated. Therefore, it is necessary to repeat firing and disintegration/remixing many times in order to produce a homogeneous substance having a complicated structure and various elements.

From the viewpoint of suppressing the generation of impurities, the calcination step may be performed before the melting step. In the calcination step, the mixture can be calcinated at about 400 to 600° C. to obtain a calcination product. The calcinated product can be subjected to a melting step.

(Cooling process)
The obtained melt is cooled to room temperature by this step. Cooling is preferably performed at a rate of 5° C./hour or less 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 may contain other components such as a flux component, an unreacted product, and a side reaction product, in addition to a desired lithium metal phosphate precipitate. For example, only the desired lithium metal phosphate can be obtained from the recovered product by, for example, washing the recovered product with warm water (60° C. pure water or the like) and filtering out only the hardly soluble crystals. 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. In addition, it can be confirmed by an X-ray diffraction method that the obtained crystal is a lithium metal phosphate.

<Lithium metal phosphate>
In the lithium metal phosphate of the present embodiment, a part of P in the compound represented by the general formula LiMPO ₄ (wherein M is at least one selected from the group consisting of Fe, Co, Ni and Mn) is B. It is replaced with. Lithium metal phosphate has an olivine structure. Generally, the olivine structure has a hexagonal close-packed oxygen skeleton, and P ions are present at the tetracoordinate tetrahedral site, and Li ions and transition metal ions M are present at the hexacoordinate octahedral site. In the lithium metal phosphate of the present embodiment, part of pentavalent P ions is replaced with trivalent B ions. The valence of M is +2 in the stoichiometric composition, and the valence may change to +3 in order to maintain the charge neutrality with the elimination of Li. Such a lithium metal phosphate can be referred to as boron-doped lithium metal phosphate (LiM(B,P)O ₄ ), and can be represented by, for example, the following general formula (X).

Li _1+α M(B _x P _1-x )O ₄ (X)
In the formula, x is 0.01 to 0.99, and α is more than 0 and 2x or less. Note that if x is too small, electric conductivity tends to be insufficient, and if x is too large, a different phase occurs and the yield tends to decrease. From the viewpoint of efficiently obtaining a desired crystal structure and exhibiting more excellent electrical conductivity, x can be 0.05 to 0.5, and may be 0.1 to 0.3.

The reason why the lithium metal phosphate of the present embodiment has excellent electric conductivity is not always clear, but the inventors speculate as follows. Generally, in a lithium metal phosphate having an olivine structure, the charge/discharge process of Li is represented by Li _1-y (M ²⁺ _1-y , M ³⁺ _y )PO ₄ . At the same time as Li enters the crystal by y by the discharge, an equivalent amount of electrons flows into the transition metal M, which was 3+, and the valence of y changes to 2+M. On the other hand, in the case of lithium metal phosphate doped with B, when α=2x, the charge/discharge process of Li is Li _1+2x−y (M ₂ ⁺ _{1 −y} , M ³⁺ _y )( presumably _{B x P 1-x) O} 4 ( range x 0.01 to 0.99, the range of y is 0.01 or more and 1 or less). First, at the same time as Li enters the crystal by y by the discharge, an equivalent amount of electrons flows into the transition metal M which was 3+, and the valence changes to 2+M by y. Next, when α=2x due to charging, one Li ion may escape to become 3+M and further charging may cause another 2x Li ions to escape to become 4+ or 5+M. It is considered that electric conductivity is improved by hopping conduction of electrons due to valence mixture of transition metals. This is considered to be because the solid solution of P and B loosens the oxygen lattice and facilitates the movement of Li ions, so that charge compensation is performed quickly. Thus, the B-doped lithium metal phosphate is considered to have excellent electrical conductivity. It is surprising that the olivine type lithium metal phosphate, which has a more robust structure than the layered rock salt type LiCoO ₂ , can obtain such excellent electrical conductivity as well as reliability, The boron-doped lithium metal phosphate according to the present embodiment is extremely suitable as a positive electrode material (positive electrode active material) of a lithium ion secondary battery.

It is believed that the lithium metal phosphate crystal of the present embodiment deviates from the conventional definition of the olivine structure to be precise. The olivine structure is a crystal having the same crystal structure as olivine X ₂ SiO ₄ which is a natural silicate mineral (in the formula, X contains divalent metals Mg and Fe in a ratio of about 9:1). In X ₂ SiO ₄ , oxygen is packed in a hexagonal closest packing, and there are 8 gaps surrounded by 4 oxygens per 4 oxygens, and 1/8 of that is occupied by Si. There are four spaces for four oxygens surrounded by six oxygens, and X occupies one half of them. On the other hand, in LiMPO ₄ (M=Fe, Co, Ni, Mn) to which B is not added, P replaces Si and Li and M enter X. The ultimate content of excess Li is Li ₃ PO ₄ that does not contain M at all, but this crystal has a structure of γ-Li ₃ PO ₄ type, which is different from olivine. In γ-Li ₃ PO ₄ as well, oxygen forms a skeleton that is nearly hexagonally close-packed, and Li occupies 1/2 of the gap surrounded by 6 oxygens and is surrounded by 4 oxygens. It enters the gap and occupies 1/8 of it. It is speculated that when B is added to LiMPO ₄ , B partially replaces P, and the shortage of positive charge due to the replacement of pentavalent P with trivalent B is compensated by the excess of Li. To be done. From this, it is presumed that the lithium metal phosphate crystal of the present embodiment may have a novel crystal structure intermediate between the olivine type and the γ-Li ₃ PO ₄ type.

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

(Positive electrode)
The positive electrode may contain a conductive auxiliary agent, a binder and the like in addition to the above positive electrode material.

The conductive aid is not particularly limited, and examples thereof include acetylene black, carbon black, graphite, carbon fiber, metal fiber, aluminum powder, fluorocarbon, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative. These may be used alone or in combination of two or more.

The binder is not particularly limited, and examples thereof include polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, and the like. These may be used alone or in combination of two or more.

(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 be made of metallic lithium, a lithium-aluminum alloy, a lithium-tin alloy, or the like, and contains graphite, carbon fiber, coke, mesocarbon microbeads (MCMB), and a binder. It may be.

(Electrolytes)
The electrolyte may be liquid or solid.

When the electrolyte is liquid (that is, the electrolytic solution is used), a solution obtained by dissolving a supporting electrolyte in an organic solvent can be used. The organic solvent is not particularly limited, and examples thereof include carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like. These may be used alone or in combination of two or more.

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 ₃ CF ₃ ) ₂ , LiN( Examples thereof include organic salts such as SO ₂ C ₂ F ₅ ) ₂ and LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ), and derivatives of these salts.

When an electrolytic solution is used, a porous synthetic resin film (particularly a polyolefin polymer porous film) may be used as the separator.

When the electrolyte is in a solid state (that is, a solid electrolyte is used), an oxide-based compound, a sulfide-based compound, or the like can be used. Examples of the oxide-based compound include La _0.51 Li _0.34 TiO _2.94 , NASICON-type Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , and garnet-type Li ₇ La ₃ Zr. include materials such as ₂ O ₁₂ is, compounds of the _sulfide, Li 2 S-SiS two-component ₂ system or the like and, there LiI, the material of the ternary plus _Li 3 PO ₄ etc. Can be mentioned.

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

A negative electrode active material and a binder are dispersed in a solvent to prepare a coating liquid. The obtained coating liquid is uniformly applied onto the negative electrode current collector and dried to obtain a laminate including the negative electrode current collector and the negative electrode active material layer. The laminated body is housed in the 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 the negative electrode. When a metallic lithium foil or the like is used, it may be used as the negative electrode itself.

Next, the positive electrode active material, the conductive additive and the binder are dispersed in a solvent to prepare a coating liquid. The obtained coating liquid is uniformly applied onto the positive electrode current collector and dried to obtain a laminate including the positive electrode current collector and the positive electrode active material layer. The laminated body is housed in the 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 to obtain the positive electrode.

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

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

The shape of the lithium ion secondary battery is not particularly limited, and examples thereof include a cylindrical type, a square type, a coin type, a button type and 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)
As the solute powder, lithium phosphate Li ₃ PO ₄ as a compound containing Li element and phosphate ion, cobalt chloride CoCl ₂ as a compound containing Co element (metal element M), and boron oxide B ₂ as a compound containing B element. O ₃ was prepared. These were weighed so that the element ratio was Li:Co:B:P=24:10:2:8. As the flux, lithium carbonate Li ₂ CO ₃ and lithium chloride LiCl were prepared. The mixing ratio of the solute powder and the flux was adjusted so that the weight ratio was 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 put in a platinum crucible and left standing in an atmosphere-controlled electric furnace. Then, the temperature was raised to 890° C. while circulating general nitrogen in the electric furnace, and the temperature was maintained for 3 hours. Thereby, the mixed powder was melted to obtain a melt. The oxygen concentration at the furnace outlet was several tens of ppm. Then, the melt was gradually cooled at 1° C./hr.

After cooling the melt to room temperature, the platinum crucible was removed. The platinum crucible contents were washed with warm water to remove flux and the like, and only the hardly soluble precipitate was collected by filtration.

When the crystal structure of the recovered precipitate was confirmed by X-ray diffractometry, the precipitate was identified as single crystal Li _{1+ α} Co(B _x P _1-x )O ₄ .

(Example 2)
An experiment was conducted in the same manner as in Example 1 except that manganese chloride MnCl ₂ was used as a compound containing an Mn element instead of cobalt chloride, and a hardly soluble precipitate was recovered.

When the crystal structure of the recovered precipitate was confirmed by X-ray diffractometry, the precipitate was identified as single crystal Li _1+α Mn(B _x P _1-x )O ₄ .

(Example 3)
An experiment was conducted in the same manner as in Example 1 except that iron chloride FeCl ₂ was used as the compound containing Fe element instead of cobalt chloride, and a hardly soluble precipitate was recovered.

When the crystal structure of the recovered precipitate was confirmed by X-ray diffractometry, the precipitate was identified as single crystal Li _1+α Fe(B _x P _1-x )O ₄ .

(Example 4)
An experiment was conducted in the same manner as in Example 1 except that nickel chloride NiCl ₂ was used as a compound containing Ni element instead of cobalt chloride, and a hardly soluble precipitate was recovered.

When the crystal structure of the recovered precipitate was confirmed by X-ray diffractometry, the precipitate was identified to be single crystal Li _1+α Ni(B _x P _1-x )O ₄ .

(Comparative Example 1)
As the solute powder, lithium phosphate Li ₃ PO ₄ was prepared as a compound containing Li element and phosphate ions, and cobalt chloride CoCl ₂ was prepared as a compound containing Co element. These were weighed so that the element ratio was Li:Co:P=3:1:1. As the flux, lithium carbonate Li ₂ CO ₃ and lithium chloride LiCl were prepared. The mixing ratio of the solute powder and the flux was adjusted so that the weight ratio was 5:1. The weighed solute powder and flux were thoroughly mixed using a mortar and pestle to obtain a mixed powder.

An experiment was conducted in the same manner as in Example 1 except that the mixed powder thus prepared was used, and a hardly soluble precipitate was recovered.

When the crystal structure of the recovered precipitate was confirmed by X-ray diffractometry, the precipitate was identified as single crystal LiCoPO ₄ .

(Electrical conductivity evaluation)
The electric conductivity on the two opposite surfaces of the single crystal (thickness 0.5 to 2 mm) obtained in each example was controlled by a direct current voltage generator (1 V to 2.5 kV), a current measuring device (1-110 μA) and control. Evaluation was performed at room temperature using a system equipped with a personal computer. As a terminal for measurement, a platinum wire was used for the anode and an aluminum foil was used for the cathode. The results are shown in the figure. 1 to 4 are graphs showing the electric conductivity evaluation results of the lithium metal phosphates according to Examples 1 to 4, respectively, and FIG. 5 is an electric conductivity evaluation of the lithium metal phosphate according to Comparative Example 1. It is a graph which shows a result. In the figure, the broken line shows the applied voltage (V) and the solid line shows the detection current (μA).

As shown in the figure, a constant current was observed in the examples, whereas no current was observed in the comparative examples. The electrical conductivity of the example was overwhelmingly superior to that of the comparative example.

Incidentally, considering from the figure, the current due to ionic conduction seems to appear at the time of boosting and rapidly decay (FIG. 2). On the other hand, in the case of electron conduction, it changes according to the voltage according to Ohm's law (Fig. 3). Immediately after the application, ionic conduction and electronic conduction coexist, but it is considered that the current becomes constant only in about 3 minutes after the application of electricity, and only the electric conduction is measured. When the electronic conductivity is higher than the ionic conductivity, ionic conduction does not occur and it is considered that Ohm's law is obeyed from the beginning. It is considered that when heat is generated by electron conduction and the temperature of the crystal rises, the electric resistance decreases and the current value rises contrary to metal (FIG. 1).

Claims (8)

A compound containing a Li element, a compound containing a metal element M (M is at least one selected from the group consisting of Fe, Co, Ni and Mn), a compound containing a B element, and a compound containing a phosphate ion, and a flux. A mixing step to obtain a mixture of
A melting step to obtain a melt of the mixture,
A cooling step of cooling the melt to obtain a precipitate,
A method for producing a lithium metal phosphate, comprising: The manufacturing method according to claim 1, wherein the melting temperature in the melting step is 600° C. or higher. The manufacturing method according to claim 1, wherein the element ratio of the B element to the P element in the mixture is 1/99 to 99/1. A lithium metal phosphate in which a part of P in the compound represented by the general formula LiMPO ₄ (wherein M is at least one selected from the group consisting of Fe, Co, Ni and Mn) is substituted with B. .. The lithium according to claim 4, having the general formula Li _1+α M(B _x P _1-x )O ₄ (wherein x is 0.01 to 0.99 and α is more than 0 and 2x or less). Metal phosphate. The lithium metal phosphate according to claim 4 or 5, which is a positive electrode material for a lithium ion secondary battery. A positive electrode material for a lithium ion secondary battery, comprising the lithium metal phosphate according to claim 6. A lithium ion secondary battery comprising a positive electrode including the positive electrode material according to claim 7.