JP5601157B2 - Positive electrode active material, positive electrode active material layer, all-solid battery, and method for producing positive electrode active material - Google Patents

Description

  The present invention relates to a positive electrode active material capable of reducing initial interface resistance with a solid electrolyte material.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

  The lithium batteries that are currently on the market use an electrolyte that uses a flammable organic solvent as a solvent. Improvement is needed. In contrast, a lithium battery in which the electrolyte is changed to a solid electrolyte layer to make the battery completely solid does not use a flammable organic solvent in the battery, so the safety device can be simplified, and the manufacturing cost and productivity It is considered excellent.

In the field of such all solid state batteries, there have been attempts to improve the performance of all solid state batteries by focusing attention on the interface between the positive electrode active material and the solid electrolyte material. For example, it is known to reduce the interface between the positive electrode active material and the solid electrolyte material by coating the surface of the positive electrode active material with LiNbO ₃ . However, when the surface of the positive electrode active material is coated with LiNbO ₃ , the interface resistance between the positive electrode active material and the solid electrolyte material can be reduced in the initial stage, but the interface resistance increases over time. there were. On the other hand, for example, Patent Document 1 discloses an all solid state battery using a positive electrode active material whose surface is covered with a reaction suppressing portion made of a polyanion structure-containing compound. This is because the surface of the positive electrode active material is coated with a compound having a highly electrochemically stable polyanion structure, thereby suppressing an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time. High durability is achieved. On the other hand, Non-Patent Document 1 discloses a polymer battery using LiCoO ₂ (positive electrode active material) whose surface is coated with Li ₃ PO ₄ . This is because the surface of LiCoO ₂ is coated with Li ₃ PO ₄ to suppress the oxidative decomposition of the polymer solid electrolyte that occurs at the interface between LiCoO ₂ and the polymer solid electrolyte, thereby increasing the output and capacity of the battery. It is intended.

JP 2010-135090 A

Yo Kobayashi et al., “Development of high-voltage and high-capacity all-solid-state lithium secondary batteries”, Journal of Power Sources 146 (2005) 719-722

As described in the example of Patent Document 1, by forming a reaction suppression portion made of Li ₃ PO ₄ —Li ₄ SiO _{4 on} the surface of LiCoO ₂ , the interface resistance of the positive electrode active material and the solid electrolyte material can be reduced. Although the increase over time can be suppressed, there is a problem that the initial interface resistance is high. The present invention has been made in view of the above problems, and a main object of the present invention is to provide a positive electrode active material capable of reducing initial interface resistance with a solid electrolyte material.

  In order to solve the above-described problems, the present invention includes a positive electrode active material exhibiting strong basicity and a coat layer that is formed so as to cover the surface of the positive electrode active material and includes a polyanion structure that exhibits acidity. A positive electrode active material is provided.

  According to the present invention, the coating layer having an acidic polyanion structure portion is formed so as to cover the surface of the strongly basic positive electrode active material. Since the basicity is different, the affinity at the interface between the two is improved, and the interface resistance can be lowered. Thereby, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced. Moreover, since the coat layer provided with the polyanion structure part with high electrochemical stability is formed so as to cover the positive electrode active material, the reaction between the coat layer, the positive electrode active material, and the solid electrolyte material can be suppressed. It is possible to suppress an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time.

  In the said invention, it is preferable that the said positive electrode active material is an oxide positive electrode active material. This is because a positive electrode active material with high energy density can be obtained.

In the above invention, the positive electrode active material is composed mainly of a compound represented by the general formula LiNi _x Co _y Mn _z O ₂ (x + y + z = 1, y ≠ 1, and z ≠ 1). It is preferable to do.

In the above invention, the polyanion structure is preferably _PO ^{4 3-} or _BO ³ is ^3. This is because the initial interface resistance between the positive electrode active material and the solid electrolyte material can be effectively reduced.

  The present invention also provides a positive electrode active material layer comprising the above-described positive electrode active material and a high resistance layer-forming solid electrolyte material that reacts with the positive electrode active material to form a high resistance layer. To do.

  According to the present invention, by using the positive electrode active material described above, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced, and a positive electrode active material layer having excellent output characteristics can be obtained. . Moreover, the increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time can be suppressed, and a positive electrode active material layer having excellent durability can be obtained.

  Further, in the present invention, an all-solid battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, An all-solid-state battery is provided in which the positive electrode active material layer is the positive electrode active material layer described above.

  According to the present invention, by using the positive electrode active material layer described above, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced, and an all-solid battery excellent in output characteristics can be obtained. In addition, an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time can be suppressed, and an all-solid battery excellent in durability can be obtained.

  In the present invention, a positive electrode active material having a strong basicity and a coat layer formed so as to cover the surface of the positive electrode active material and having a polyanion structure portion exhibiting acidity are produced. A method for preparing a coating layer forming coating solution containing a compound having a polyanion structure part exhibiting acidity, and coating the surface of the positive electrode active material with the coating layer forming coating solution A method for producing a positive electrode active material comprising: a coating step; and a heat treatment step of heat-treating the positive electrode active material whose surface is coated with the coating layer forming coating solution to form the coat layer. provide.

  According to the present invention, the polarity (acid-basic) of the positive electrode active material and the coat layer is formed by forming the coat layer including the polyanion structure portion showing acidity so as to cover the surface of the positive electrode active material showing strong basicity. ), The wettability is improved, the interface resistance between the cathode active material and the coating layer can be reduced, and the initial interface resistance between the cathode active material and the solid electrolyte material can be reduced. Can be obtained. Moreover, since the surface of the positive electrode active material is coated with a coating layer having a polyanion structure portion having high electrochemical stability, it is possible to suppress an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time.

  In this invention, there exists an effect that the positive electrode active material material which can reduce initial stage interface resistance with a solid electrolyte material can be obtained.

It is a schematic sectional drawing which shows an example of the positive electrode active material material of this invention. It is a schematic diagram which shows an example of the positive electrode active material layer of this invention. It is a schematic sectional drawing which shows an example of the electric power generation element of the all-solid-state battery of this invention. It is a flowchart which shows an example of the manufacturing method of the positive electrode active material of this invention. It is a graph which shows the result of the composition analysis by XPS measurement of the surface of the positive electrode active material material obtained in Example 1, 2 and Comparative Example 1, 2. It is a graph which shows the result of the initial stage interface resistance measurement of the all-solid-state battery obtained in Example 1, 2, Comparative Example 1, 2 and Reference Example 1,2.

  Hereinafter, the positive electrode active material, the positive electrode active material layer, the all-solid battery, and the method for producing the positive electrode active material of the present invention will be described in detail.

A. First, the positive electrode active material of the present invention will be described. The positive electrode active material of the present invention is characterized by having a positive basic active material exhibiting strong basicity and a coating layer formed so as to cover the surface of the positive active material and having a polyanion structure portion exhibiting acidity. To do.

  FIG. 1 is a schematic cross-sectional view showing an example of the positive electrode active material of the present invention. A positive electrode active material 1 shown in FIG. 1 has a positive electrode active material 2 and a coat layer 3 formed so as to cover the surface of the positive electrode active material 2. In FIG. 1, the positive electrode active material 2 exhibits strong basicity, and the coat layer 3 includes a polyanion structure portion exhibiting acidity.

According to the present invention, the coating layer having an acidic polyanion structure portion is formed so as to cover the surface of the strongly basic positive electrode active material. Since the basicity is different, the affinity at the interface between the two is improved, and the interface resistance can be lowered. Thereby, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced. Moreover, since the coat layer provided with the polyanion structure part with high electrochemical stability is formed so as to cover the positive electrode active material, the reaction between the coat layer, the positive electrode active material, and the solid electrolyte material can be suppressed. It is possible to suppress an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time.
Note that the affinity at the interface between the positive electrode active material and the coating layer is improved. Specifically, the acidic structure portion and the basic structure portion are neutralized and bonded, thereby reducing the surface energy. Is estimated.
Hereinafter, the positive electrode active material of the present invention will be described for each configuration.

1. First, the positive electrode active material in the present invention will be described. The positive electrode active material in the present invention exhibits strong basicity, and differs depending on the type of conductive ions of the intended all solid state battery. For example, when the positive electrode active material of the present invention is used for an all-solid lithium secondary battery, the positive electrode active material occludes and releases Li ions. Moreover, the positive electrode active material in the present invention usually reacts with a solid electrolyte material (high resistance layer forming solid electrolyte material) described later to form a high resistance layer. Formation of the high resistance layer can be confirmed by a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDX).

The positive electrode active material in the present invention is greatly characterized by showing strong basicity. In the present invention, “strongly basic” means that the pH value of the positive electrode active material-containing aqueous solution when the positive electrode active material-containing aqueous solution obtained by adding 2 mol of the positive electrode active material to 100 ml of water and reaching equilibrium is reached. Is 10 or more. When the pH value is 10 or more, it is possible to obtain an initial interface resistance with a solid electrolyte material equivalent to a positive electrode active material whose surface is coated with a conventional niobium oxide (for example, LiNbO ₃ ). In addition, although the stirring time until it reaches | attains equilibrium changes with positive electrode active materials, it is about 5 to 15 minutes, for example. Moreover, as a measuring method of pH, a pH meter, a litmus paper, etc. can be used.

Here, in Patent Document 1 described above, the positive electrode active material layer made of _{LiCoO 2, Li 3 PO 4 -Li} 4 reaction suppressing portion made of SiO _4, i.e. the total solids comprising the positive electrode coating layer is formed A battery is disclosed (Example 1 of Patent Document 1). LiCoO ₂ (positive electrode active material) used in this example has a pH value of 9 and does not exhibit strong basicity. Therefore, it is considered that the wettability with PO ₄ ⁴⁻ which is a polyanion structure part exhibiting acidity is not so good and the interface resistance between the positive electrode active material and the coating layer is increased, and as a result, as shown in Comparative Example 1 described later. In addition, the initial interface resistance between the positive electrode active material layer and the solid electrolyte layer is increased. On the other hand, since the positive electrode active material in the present invention has a pH value of 10 or more and exhibits strong basicity, the wettability is improved and the interface resistance between the positive electrode active material and the coating layer is improved. It is thought that it can be lowered. Therefore, as shown in Example 1 described later, the initial interface resistance between the positive electrode active material layer and the solid electrolyte layer can be reduced.

The positive electrode active material in the present invention is not particularly limited as long as it exhibits strong basicity and reacts with the high-resistance layer-forming solid electrolyte material to form a high-resistance layer. Substances are preferred. This is because a positive electrode active material with high energy density can be obtained by using an oxide positive electrode active material. When the positive electrode active material of the present invention is used in an all-solid lithium battery, examples of the oxide positive electrode active material used include, for example, the general formula LiNi _x Co _y Mn _z O ₂ (x + y + z = 1, y ≠ 1 Yes, z ≠ 1)), and a positive electrode active material whose main component is a compound represented by: The range of x is 0 ≦ x = 1, the range of y is 0 ≦ y <1, and the range of z is 0 ≦ z <1. Specific examples of such a compound include LiNiO ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .
The oxide positive electrode active material other than the general formula LiNi _x Co _y Mn _z O ₂ is a general formula LiNi _1-x M _x O ₂ (M is at least one selected from metal elements other than Ni, 0.5 <x <1)), and a positive electrode active material whose main component is a compound represented by: Examples of M include Co, Al, and Fe. Specific examples of such a compound include LiNi _0.8 Co _0.2 O ₂ and LiNi _0.85 Co _0.10 Al _0.05 O ₂ .
Further, as the oxide positive electrode active material, the general formula X (Li (Li _1/3 M _2/3 ) O ₂ ) · Y (LiM′O ₂ ) (M is at least one selected from tetravalent metal elements. M ′ is at least one selected from transition metal elements, 0 <X <1, 0 <Y <1, and X + Y = 1.) A positive electrode active material may be used. Examples of M include Mn. Examples of M ′ include Ni, Mn, Co, and Fe. Specific examples of such a composition include Li _1.2 Mn _0.5 Ni _0.15 Co _0.15 O _{2 and the} like.
In the present invention, “mainly comprising” means that the positive electrode active material contains a compound or composition represented by the above general formula to such an extent that the effects of the present invention can be exhibited. Specifically, the proportion of the compound or composition represented by the above general formula with respect to all the materials constituting the positive electrode active material is 50 mol% or more. Among these, in the present invention, the ratio is preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and particularly preferably 90 mol% or more. Moreover, in this invention, a positive electrode active material may consist only of a compound or composition represented by the said general formula.

  Examples of the shape of the positive electrode active material include a particle shape, and among them, a true spherical shape or an elliptical spherical shape is preferable. Moreover, when a positive electrode active material is a particle shape, it is preferable that the average particle diameter exists in the range of 0.1 micrometer-50 micrometers, for example.

2. Next, the coat layer in the present invention will be described. The coating layer in this invention is formed so that the surface of the said positive electrode active material may be coat | covered, and is provided with the polyanion structure part which shows the acidity. The coat layer has a function of suppressing the reaction between the positive electrode active material and the high-resistance layer-forming solid electrolyte material that occurs when the battery is used. In the present invention, since the coating layer has an acidic polyanion structure, wettability is improved with respect to the positive active material having strong basicity described above, and the interface resistance between the positive active material and the coating layer is reduced. As a result, the initial interface resistance with the solid electrolyte material can be reduced.

The coating layer according to the present invention is characterized by having a polyanion structure portion showing acidity. In the present invention, “acidic” refers to a property capable of exhibiting affinity at the interface with the above-described positive active material exhibiting strong basicity to such an extent that the effects of the present invention can be obtained. Specifically, it means that the acid dissociation constant (pKa) at the first stage is 10 or less when the polyanion structure becomes a hydride. The hydrides such, _PO ^{4 3-} _{If, H 3 PO 4 (pKa =} 2.12), BO 3 3- _If, is that of _{H 3 BO 3 (pKa = 9.24} ). Examples of the method for measuring the acid dissociation constant include neutralization titration, preparing a titration curve, and obtaining the acid dissociation constant from the pH value based on the titration curve.

Moreover, the polyanion structure part with which the said coating layer is provided is normally comprised from the central element covalently bonded with the some oxygen element. Since the central element and the oxygen element are covalently bonded, the electrochemical stability can be increased. In the present invention, the difference between the electronegativity of the central element and the electronegativity of the oxygen element is preferably 1.7 or less. This is because a stable covalent bond can be formed. Here, in the Pauling electronegativity, the electronegativity of the oxygen element is preferably 3.44, considering that the electronegativity of the oxygen element is 3.44. Furthermore, in the present invention, the electronegativity of the central element is preferably 1.8 or more, and more preferably 1.9 or more. This is because a more stable covalent bond can be formed. For reference, Table 1 shows electronegativity of elements belonging to Groups 12 to 16 in Pauling electronegativity. Although not shown in Table 1 below, the electronegativity of Nb used in a conventional niobium oxide (for example, LiNbO ₃ ) is 1.60.

The polyanion structure in the present invention is not particularly limited as long as it is acidic and is composed of a central element covalently bonded to a plurality of oxygen elements. For example, PO ₄ ³⁻ , BO ₃ ^{3 −} , SO ₄ ²⁻ , CO ₃ ²⁻ , NO ₃ ^{− and the} like can be mentioned, among which PO ₄ ³⁻ and BO ₃ ³⁻ are preferable. This is because the initial interface resistance between the positive electrode active material and the solid electrolyte material can be effectively reduced.

The coat layer in the present invention may include a plurality of the polyanion structure parts described above, or may further include SiO ₄ ^4- in addition to the polyanion structure parts described above. By having SiO ₄ ⁴⁻ , ion conductivity can be improved. Since SiO ₄ ⁴⁻ is a neutral polyanion structure, it is considered that the polarity (acid basicity) of the coating layer is not significantly affected. Such a coating layer is prepared, for example, by preparing a precursor solution containing a compound having a polyanion structure portion exhibiting acidity and a compound having SiO ₄ ⁴⁻ and a liquid phase method (for example, sol-gel) using the precursor solution. Method). Further, a vapor phase method such as a CVD method or a PVD method may be used.

Moreover, the coating layer in this invention is equipped with the cation part normally comprised from the metal element used as a conduction ion other than the polyanion structure part which shows the acidity mentioned above. That is, the coat layer is usually composed of a polyanion structure-containing compound having the polyanion structure part and the cation part. The metal element in the cation portion differs depending on the type of the all-solid battery in which the positive electrode active material of the present invention is used. For example, alkali metal elements such as Li and Na, and Mg and Ca are used. An alkaline earth metal element etc. can be mentioned, Among these, an alkali metal element is preferable and especially Li is preferable. That is, in the present invention, the cation part is preferably Li ⁺ . This is because all-solid lithium batteries useful for various applications can be obtained.

  Moreover, it is preferable that the coat layer in this invention consists of an amorphous polyanion structure containing compound. This is because by using an amorphous polyanion structure-containing compound, a thin and uniform coat layer can be formed, and by increasing the coverage, the effects of the present invention can be sufficiently exerted. In addition, since the amorphous polyanion structure-containing compound has high ion conductivity, the output of the battery can be increased by using the positive electrode active material of the present invention for an all-solid battery. The amorphous polyanion structure-containing compound can be confirmed by X-ray diffraction (XRD) measurement.

The thickness of the coating layer formed so as to cover the surface of the positive electrode active material is such that when the positive electrode active material of the present invention is used for an all-solid battery, the positive electrode active material and the solid electrolyte material react with each other. The thickness is preferably such that it does not occur. For example, the thickness is preferably in the range of 1 nm to 500 nm, and more preferably in the range of 2 nm to 100 nm. This is because if the thickness of the coat layer is too small, the positive electrode active material and the solid electrolyte material may react, and if the thickness of the coat layer is too large, the ion conductivity may be reduced. It is. In addition, the average value measured based on the image analysis using a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. can be used for the thickness of the said coating layer, for example.
The coat layer preferably covers a larger area of the positive electrode active material, and more preferably covers the entire surface of the positive electrode active material. It is because the effect of the present invention can be exhibited more. Specifically, the coverage of the coating layer formed so as to cover the surface of the positive electrode active material is, for example, preferably 20% or more, and more preferably 50% or more. In addition, as a measuring method of the coating rate of the said coating layer, TEM, XPS etc. can be mentioned, for example.

  Examples of the method for forming a coat layer in the present invention include a rolling fluid coating method (sol-gel method), a CVD method, and a PVD method.

3. Cathode active material The method for producing the cathode active material of the present invention is not particularly limited as long as it is a method capable of obtaining the above-described cathode active material. For example, “D. Examples include the method described in “Material Production Method”.
Moreover, it is preferable that the positive electrode active material of this invention is used as a positive electrode active material of an all-solid-state battery, for example. This is because the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced, and an increase in the interface resistance between the positive electrode active material and the solid electrolyte material over time can be suppressed. Thereby, an all-solid-state battery excellent in output characteristics and durability can be obtained.

B. Next, the positive electrode active material layer of the present invention will be described. The positive electrode active material layer of the present invention is characterized by containing the positive electrode active material described above and a high resistance layer forming solid electrolyte material that reacts with the positive electrode active material to form a high resistance layer.

  FIG. 2 is an explanatory diagram showing an example of the positive electrode active material layer of the present invention. The positive electrode active material layer 11 shown in FIG. 2 contains a positive electrode active material 1 and a high resistance layer-forming solid electrolyte material 4 that reacts with the positive electrode active material 2 to form a high resistance layer (not shown). It is. The positive electrode active material 1 has a positive electrode active material 2 and a coat layer 3 formed so as to cover the surface of the positive electrode active material 2. The present invention is characterized in that the positive electrode active material 1 is the positive electrode active material described in “A. Positive electrode active material”.

According to the present invention, by using the positive electrode active material described above, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced, and a positive electrode active material layer having excellent output characteristics can be obtained. . Moreover, the increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time can be suppressed, and a positive electrode active material layer having excellent durability can be obtained.
Hereinafter, the positive electrode active material layer of the present invention will be described for each configuration.

1. Positive electrode active material The positive electrode active material in the present invention is the same as the content described in the above-mentioned “A. Positive electrode active material”, and therefore description thereof is omitted here. The content of the positive electrode active material in the positive electrode active material layer is, for example, preferably in the range of 10% by volume to 99% by volume, and more preferably in the range of 20% by volume to 99% by volume.

2. Next, the high resistance layer-forming solid electrolyte material in the present invention will be described. The high-resistance layer-forming solid electrolyte material in the present invention reacts with the positive electrode active material to form a high-resistance layer. Formation of the high resistance layer can be confirmed by a transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDX). The positive electrode active material layer of the present invention can improve ion conductivity by containing a high resistance layer-forming solid electrolyte material.

In the present invention, the high resistance layer-forming solid electrolyte material preferably has a crosslinked chalcogen. This is because the ion conductivity of the positive electrode active material layer can be further improved. On the other hand, a solid electrolyte material having a crosslinked chalcogen (crosslinked chalcogen-containing solid electrolyte material) reacts with a conventional coating layer (for example, a coating layer made of LiNbO ₃ ) because the electrochemical stability of the crosslinked chalcogen is relatively low. Therefore, it is easy to form a high resistance layer, and it is considered that the increase in interfacial resistance with time is remarkable. On the other hand, since the coating layer of the positive electrode active material in the present invention has high electrochemical stability, the coating layer hardly reacts with the cross-linked chalcogen-containing solid electrolyte material and suppresses the formation of a high resistance layer. Can do. Thereby, it is considered that an increase in interfacial resistance with time can be suppressed while improving ion conductivity.

In the present invention, the crosslinked chalcogen is preferably crosslinked sulfur (—S—) or crosslinked oxygen (—O—), and more preferably crosslinked sulfur. It is because it can be set as the solid electrolyte material excellent in ion conductivity. The solid electrolyte material having a crosslinked sulfur, for _example, a _{Li 7 P 3 S 11, 60Li} 2 S-40SiS 2, 60Li 2 S-40GeS 2 or the like. Here, the above _Li 7 _P 3 _{S 11 has} a S ₃ PS-PS 3 structure, a solid electrolyte material having a PS _{4 structure,} S ₃ PS-PS 3 structure has a bridging sulfur . Thus, in the present invention, the high resistance layer-forming solid electrolyte material preferably has an S ₃ P—S—PS ₃ structure. On the other hand, as a solid electrolyte material having bridging oxygen, for example, 95 (0.6Li ₂ S-0.4SiS ₂ ) -5Li ₄ SiO ₄ , 95 (0.67Li ₂ S-0.33P ₂ S ₅ ) -5Li ₃ PO _4, may be mentioned _{95 (0.6Li 2 S-0.4GeS 2} ) -5Li 3 PO 4 and the like.

Moreover, when the high-resistance layer-forming solid electrolyte material is a material that does not have a crosslinked chalcogen, specific examples thereof include 75Li ₂ S-25P ₂ S ₅ , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _1.3 Al _0.3 Ge _1.7 (PO ₄ ) ₃ , Li _3.25 Ge _0.25 P _0.75 S _{4 and the} like. In the present invention, a sulfide solid electrolyte material or an oxide solid electrolyte material can be used as the high resistance layer forming solid electrolyte material.

  Further, examples of the shape of the high-resistance layer-forming solid electrolyte material include a particle shape, and among them, a true spherical shape or an elliptical spherical shape is preferable. Moreover, when the high-resistance layer-forming solid electrolyte material has a particle shape, the average particle diameter is preferably in the range of 0.1 μm to 50 μm, for example. The content of the high-resistance layer-forming solid electrolyte material in the positive electrode active material layer is, for example, in the range of 0.1% by volume to 80% by volume, especially in the range of 1% by volume to 60% by volume, in particular, 10% by volume. It is preferable to be within the range of ˜50% by volume.

  In the present invention, the coating layer described above may be formed so as to cover the surface of the high-resistance layer-forming solid electrolyte material.

3. Positive electrode active material layer The positive electrode active material layer of the present invention may further contain at least one of a conductive material and a binder in addition to the positive electrode active material and the high-resistance layer-forming solid electrolyte material. Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. Moreover, it is preferable that the thickness of the said positive electrode active material layer exists in the range of 0.1 micrometer-1000 micrometers, for example. Moreover, as a formation method of a positive electrode active material layer, the method etc. which compression-mold the material which comprises a positive electrode active material layer can be mentioned, for example. Moreover, the said positive electrode active material layer is normally used for a battery, and it is preferable that it is especially used for an all-solid-state battery.

C. Next, the all solid state battery of the present invention will be described. The all solid state battery of the present invention is an all solid state battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, The positive electrode active material layer is the positive electrode active material layer described above.

  FIG. 3 is an explanatory diagram showing an example of the power generation element of the all solid state battery of the present invention. The power generation element 20 of the all-solid battery shown in FIG. 3 includes a positive electrode active material layer 11, a negative electrode active material layer 12, a solid electrolyte layer 13 formed between the positive electrode active material layer 11 and the negative electrode active material layer 12, Have The present invention is greatly characterized in that the positive electrode active material layer 11 is the positive electrode active material layer described in the above “B. Positive electrode active material layer”.

According to the present invention, by using the positive electrode active material layer described above, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced, and an all-solid battery excellent in output characteristics can be obtained. In addition, an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time can be suppressed, and an all-solid battery excellent in durability can be obtained.
Hereinafter, the all solid state battery of the present invention will be described for each configuration.

1. Positive Electrode Active Material Layer The positive electrode active material layer in the present invention is the same as the content described in the above “B. Positive electrode active material layer”, and therefore description thereof is omitted here.

2. Next, the solid electrolyte layer in the present invention will be described. The solid electrolyte layer in the present invention is a layer formed between the positive electrode active material layer and the negative electrode active material layer, and is a layer composed of a solid electrolyte material. The solid electrolyte material contained in the solid electrolyte layer is not particularly limited as long as it has ion conductivity.

  In the present invention, the solid electrolyte material contained in the solid electrolyte layer is preferably a high resistance layer forming solid electrolyte material. This is because the effects of the present invention can be sufficiently exhibited. The content of the high-resistance layer-forming solid electrolyte material in the solid electrolyte layer is not particularly limited as long as a desired insulating property is obtained. For example, the content is in the range of 10% by volume to 100% by volume. , Preferably in the range of 50% to 100% by volume. In particular, in the present invention, it is preferable that the solid electrolyte layer is composed only of a high resistance layer-forming solid electrolyte material.

  Note that the high-resistance layer-forming solid electrolyte material is the same as that described in “B. Positive electrode active material layer”. Moreover, about solid electrolyte materials other than high resistance layer forming solid electrolyte material, the same material as the solid electrolyte material used for a general all-solid-state battery can be used.

  In the present invention, when the solid electrolyte layer contains a high-resistance layer-forming solid electrolyte material, the positive-electrode active material material of the positive-electrode active material layer comes into contact with the high-resistance layer-forming solid electrolyte material of the solid electrolyte layer. . At that time, the above-described coat layer may be formed so as to cover the surface of the high-resistance layer-forming solid electrolyte material, or the above-described coat layer may not be formed.

  The solid electrolyte layer may contain a binder. This is because a solid electrolyte layer having flexibility can be obtained by containing a binder. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. The thickness of the solid electrolyte layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

3. Next, the negative electrode active material layer in the present invention will be described. The negative electrode active material layer in the present invention is a layer containing at least a negative electrode active material, and may contain at least one of a solid electrolyte material, a conductive material and a binder as necessary.

  As a negative electrode active material, although it changes with kinds of the conductive ion of the target all-solid-state battery, a metal active material and a carbon active material can be mentioned, for example. Examples of the metal active material include In, Al, Si, and Sn. On the other hand, examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Further, the content of the negative electrode active material in the negative electrode active material layer is, for example, preferably in the range of 10% by volume to 99% by volume, and more preferably in the range of 20% by volume to 99% by volume.

  The solid electrolyte material is preferably the high resistance layer-forming solid electrolyte material described in “B. Positive electrode active material layer” above. The content of the high-resistance layer-forming solid electrolyte material in the negative electrode active material layer is, for example, in the range of 0.1% by volume to 80% by volume, especially in the range of 1% by volume to 60% by volume, in particular, 10% by volume. It is preferable to be within the range of ˜50% by volume.

  Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. Moreover, it is preferable that the thickness of a negative electrode active material layer exists in the range of 0.1 micrometer-1000 micrometers, for example.

4). Other Configurations The all solid state battery of the present invention has at least the positive electrode active material layer, the solid electrolyte layer, and the negative electrode active material layer described above. Furthermore, it usually has a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Among them, SUS is preferable. On the other hand, examples of the material for the negative electrode current collector include SUS, copper, nickel, and carbon. Among them, SUS is preferable. In addition, the thickness and shape of the positive electrode current collector and the negative electrode current collector are preferably appropriately selected according to the use of the all solid state battery. Moreover, the battery case of a general all-solid-state battery can be used for the battery case used for this invention. Examples of the battery case include a SUS battery case.

5. All-solid battery In the present invention, by using the positive electrode active material layer described above, the initial interface resistance between the positive electrode active material and the solid electrolyte material can be reduced, and the interface between the positive electrode active material and the solid electrolyte material can be reduced. Since the increase in resistance over time can be suppressed, the type of conductive ions is not particularly limited. Examples of the all-solid battery of the present invention include an all-solid lithium battery, an all-solid sodium battery, an all-solid magnesium battery, and an all-solid calcium battery. Of these, an all-solid lithium battery and an all-solid sodium battery are preferred. In particular, an all solid lithium battery is preferable. Further, the all solid state battery of the present invention may be a primary battery or a secondary battery, but among them, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as a vehicle-mounted battery. Examples of the shape of the all solid state battery of the present invention include a coin type, a laminate type, a cylindrical type, and a square type.

  Moreover, the manufacturing method of the all-solid-state battery of this invention will not be specifically limited if it is a method which can obtain the all-solid-state battery mentioned above, The method similar to the manufacturing method of a general all-solid-state battery is used. be able to. As an example of a method for producing an all-solid-state battery, a power generation element is manufactured by sequentially pressing a material constituting the positive electrode active material layer, a material constituting the solid electrolyte layer, and a material constituting the negative electrode active material layer, A method of storing the power generation element in the battery case and caulking the battery case can be exemplified.

D. Next, a method for producing the positive electrode active material of the present invention will be described. A method for producing a positive electrode active material according to the present invention includes a positive electrode active material exhibiting strong basicity and a coat layer formed so as to cover the surface of the positive electrode active material and having a polyanion structure portion exhibiting acidity. A method for producing an active material, comprising: a preparation step of preparing a coating layer forming coating solution containing a compound having a polyanion structure part exhibiting the acidity; and a surface of the positive electrode active material is coated with the coating layer forming coating. A coating step of coating with a coating solution; and a heat treatment step of heat-treating the positive electrode active material whose surface is coated with the coating layer-forming coating solution to form the coating layer. .

  According to the present invention, the polarity (acid-basic) of the positive electrode active material and the coat layer is formed by forming the coat layer including the polyanion structure portion showing acidity so as to cover the surface of the positive electrode active material showing strong basicity. ), The wettability is improved, the interface resistance between the cathode active material and the coating layer can be reduced, and the initial interface resistance between the cathode active material and the solid electrolyte material can be reduced. Can be obtained. Moreover, since the surface of the positive electrode active material is coated with a coating layer having a polyanion structure portion having high electrochemical stability, it is possible to suppress an increase in the interfacial resistance between the positive electrode active material and the solid electrolyte material over time.

FIG. 4 is a flowchart for explaining an example of the method for producing the positive electrode active material of the present invention. In FIG. 4, first, as starting materials, H ₃ PO ₄ (a compound having a polyanion structure portion showing acidity), LiOH (a metal compound having a cation portion composed of a metal element that becomes a conductive ion), ethanol, (Solvent) is prepared, and these are mixed at a predetermined ratio to prepare a coating solution for forming a coat layer (preparation step). Next, the surface of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (positive electrode active material exhibiting strong basicity) is coated with a coating layer forming coating solution (coating step). Subsequently, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ whose surface is coated with a coating layer forming coating solution is heat-treated to form a coat layer having a polyanion structure portion exhibiting acidity (heat treatment step) ). Thereby, the positive electrode active material which has the positive electrode active material which shows strong basicity, and the coating layer which is formed so that the surface of the said positive electrode active material may be covered, and is equipped with the polyanion structure part which shows acidity can be obtained.
Hereafter, the manufacturing method of the positive electrode active material of this invention is demonstrated for every process.

1. Preparation Step First, the preparation step in the present invention will be described. The preparation step in the present invention is a step of preparing a coating layer forming coating solution containing a compound having a polyanion structure portion showing acidity. The polyanion structure is the same as that described in “A. Cathode active material”, and the description is omitted here.

The compound having the polyanion structure part used in this step is not particularly limited as long as it has an acid polyanion structure part, and varies depending on the target positive electrode active material. In the case where the polyanion structure is PO ₄ ³⁻ , examples of the compound having the polyanion structure include lithium phosphate. In addition, when the polyanion structure is BO ₃ ³⁻ , examples of the compound having the polyanion structure include lithium borate.
The concentration of the compound having a polyanion structure part contained in the coating layer forming coating solution is appropriately selected according to the target positive electrode active material.

The coating layer-forming coating solution used in this step contains a metal compound having a cation moiety usually composed of a metal element that becomes a conductive ion, in addition to the compound having the polyanion structure. The metal compound having a cation moiety is not particularly limited as long as it is a metal compound having a cation moiety composed of a metal element serving as a conduction ion, and may vary depending on the target positive electrode active material. is there. Examples of the metal compound having a cation moiety include metal hydroxide, metal acetate, and metal alkoxide. Specifically, for example, when the cation moiety is Li ⁺ , lithium hydroxide, lithium acetate, lithium ethoxide, and the like can be given.
Moreover, the density | concentration of the metal compound which has the said cation part contained in the coating layer formation coating liquid is suitably selected according to the target positive electrode active material material.

  In this step, a coating layer-forming coating solution is usually prepared by dissolving or dispersing the compound having the polyanion structure portion and the metal compound having the cation portion in a solvent. The solvent used in this step is not particularly limited as long as it can dissolve or disperse the compound having the polyanion structure part and the metal compound having the cation part. For example, ethanol, propanol And methanol.

  In this step, an optional additive may be added to the coating layer forming coating solution as necessary.

2. Coating process Next, the coating process in the present invention will be described. The coating step in the present invention is a step of coating the surface of the positive electrode active material exhibiting strong basicity with the coating layer forming coating solution. Note that the positive electrode active material exhibiting strong basicity is the same as the content described in “A. Positive electrode active material” above, and thus the description thereof is omitted here.

In this step, the film thickness of the coating layer forming coating solution that covers the surface of the positive electrode active material is appropriately selected according to the thickness of the target coating layer, and is, for example, in the range of 0.1 nm to 500 nm. Is preferably within the range of 1 nm to 100 nm. In addition, as a measuring method of the film thickness of the said coating layer forming coating liquid, TEM etc. can be mentioned, for example.
Further, in this step, the surface of the positive electrode active material is coated with a coating layer forming coating solution, but it is preferable that a larger area of the positive electrode active material is coated, and the entire surface of the positive electrode active material is covered. It is more preferable to coat. It is because the effect of the present invention can be exhibited more. Specifically, the coating rate of the coating layer forming coating solution that covers the surface of the positive electrode active material is, for example, preferably 20% or more, and more preferably 50% or more. Examples of the method for measuring the coverage of the coating layer forming coating solution include TEM and XPS.

  In this step, the positive electrode active material may be dried with warm air after the surface of the positive electrode active material is coated with the coating layer forming coating solution. By removing the solvent by such drying, a coating layer covering the surface of the positive electrode active material can be efficiently formed in the heat treatment step described later.

3. Next, the heat treatment process in the present invention will be described. In the heat treatment step of the present invention, the positive electrode active material whose surface is coated with the coating layer forming coating solution is heat-treated to form a polyanion structure portion that is formed so as to cover the surface of the positive electrode active material and exhibits acidity. It is a step of forming a coat layer provided. In this step, the surface of the positive electrode active material is coated by removing the solvent remaining in the coating layer forming coating solution coated in the coating step and promoting densification by performing a heat treatment. A thin film (coat layer) is produced.

The heat treatment temperature in this step is preferably in the range of 200 ° C to 500 ° C, and more preferably in the range of 300 ° C to 400 ° C.
In addition, the heat treatment time in this step is preferably in the range of 0.5 hours to 20 hours, and more preferably in the range of 0.5 hours to 10 hours.

  The heat treatment atmosphere in this step is not particularly limited as long as the target coat layer can be formed and the cathode active material material is not deteriorated. For example, air atmosphere; nitrogen atmosphere and argon atmosphere Inert gas atmosphere such as ammonia atmosphere, hydrogen atmosphere and reducing atmosphere such as carbon monoxide atmosphere; vacuum and the like. Examples of the heat treatment method for the positive electrode active material include a method using a firing furnace.

4). Others In the present invention, a positive electrode active material formed so that the coat layer covers the surface of the positive electrode active material by a liquid phase method can be obtained through the above-described steps. By using the liquid phase method, it is possible to improve the wettability of the coating layer including the polyanion structure portion exhibiting acidity with respect to the positive electrode active material exhibiting strong basicity. In addition, since the liquid phase method is a method using a solution-based precursor, a coat layer can be easily formed so as to cover a larger area on the surface of the positive electrode active material. Examples of the liquid phase method include a sol-gel method. Since the sol-gel method is a chemical coating method, it is formed so as to cover the surface of the positive electrode active material because the bond between the positive electrode active material and the coating layer is stronger than the method of coating by mechanical physical force. Thus, a positive electrode active material material in which the coated layer is difficult to peel off can be obtained.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. Are included in the technical scope.

  The present invention will be described more specifically with reference to the following examples.

[Example 1]
(Preparation of positive electrode active material)
First, in ethanol, lithium hydroxide (LiOH), phosphoric acid aqueous solution (H ₃ PO ₄ , 85%) and tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) in a molar ratio of Li: P: Si = The mixture was mixed to 7: 1: 1 to prepare a coating layer forming coating solution. Next, the coating liquid for coating layer formation is applied onto the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) in a coating apparatus using a rolling fluidized bed, and warm air And dried. Subsequently, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder coated with the coating layer forming coating solution is heat-treated in the atmosphere at 300 ° C. for 5 hours, so that the thickness becomes 20 nm. A coat layer made of Li ₃ PO ₄ —Li ₄ SiO ₄ was formed. As a result, a positive electrode active material made of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ whose surface was coated with the coating layer was obtained.

(Synthesis of high resistance layer forming solid electrolyte material)
First, lithium sulfide (Li ₂ S) and phosphorus pentasulfide (P ₂ S ₅ ) were used as starting materials. These powders were weighed in a glove box under an Ar atmosphere (dew point −70 ° C.) so as to have a molar ratio of Li ₂ S: P ₂ S ₅ = 75: 25, mixed in an agate mortar, and a raw material composition Got. Next, 1 g of the obtained raw material composition was put into a 45 ml zirconia pot, and zirconia balls (Φ10 mm, 10 pieces) were further put in, and the pot was completely sealed (Ar atmosphere). This pot was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed at a base plate rotation speed of 370 rpm for 40 hours to obtain 75Li ₂ S-25P ₂ S ₅ .

(Production of all-solid battery)
First, Li ₇ P ₃ S ₁₁ was obtained by the same method as that described in JP-A-2005-228570. Next, the power generation element 20 of the all-solid-state battery as shown in FIG. 3 was manufactured using a press machine. As a material constituting the positive electrode active material layer 11, a positive electrode mixture in which the above positive electrode active material and 75Li ₂ S-25P ₂ S ₅ are mixed so as to have a weight ratio of 7: 3 is used, and a negative electrode active material layer In foil was used as a material for forming 12, and Li ₇ P ₃ S ₁₁ was used as a material for forming the solid electrolyte layer 13. An all solid state battery was obtained using this power generation element.

[Example 2]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, in ethanol, lithium acetate (CH ₃ COOLi), boric acid (H ₃ BO ₃ ), and tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) in a molar ratio of Li: B: Si = 7: 1 Was mixed so that the coating layer forming coating solution was prepared. Next, the coating liquid for coating layer formation is applied onto the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) in a coating apparatus using a rolling fluidized bed, and warm air And dried. Subsequently, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder coated with the coating layer forming coating solution is heat-treated in the atmosphere at 400 ° C. for 1 hour, so that the thickness becomes 4 nm. A coat layer made of Li ₃ BO ₃ —Li ₄ SiO ₄ was formed. As a result, a positive electrode active material made of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ whose surface was coated with the coating layer was obtained.

[Comparative Example 1]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, in ethanol, lithium hydroxide (LiOH), phosphoric acid aqueous solution (H ₃ PO ₄ , 85%) and tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) in a molar ratio of Li: P: Si = The mixture was mixed to 7: 1: 1 to prepare a coating layer forming coating solution. Next, the coating liquid for forming a coating layer was applied onto the positive electrode active material (LiCoO ₂ ) with a coating apparatus using a rolling fluidized bed and dried with warm air. Subsequently, the LiCoO ₂ powder coated with the coating layer forming coating solution is heat-treated in the atmosphere at 300 ° C. for 5 hours, thereby forming Li ₃ PO ₄ —Li ₄ SiO ₄ having a thickness of 50 nm. A coat layer was formed. This gave a positive electrode active material composed of LiCoO ₂ having a surface coated with a said coating layer.

[Comparative Example 2]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, in ethanol, lithium acetate (CH ₃ COOLi), boric acid (H ₃ BO ₃ ), and tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) in a molar ratio of Li: B: Si = 7: 1 Was mixed so that the coating layer forming coating solution was prepared. Next, the coating liquid for forming a coating layer was applied onto the positive electrode active material (LiCoO ₂ ) with a coating apparatus using a rolling fluidized bed and dried with warm air. Subsequently, the LiCoO ₂ powder coated with the coating layer forming coating solution is heat-treated at 400 ° C. for 1 hour in the air, thereby forming Li ₃ BO ₃ —Li ₄ SiO ₄ having a thickness of 20 nm. A coat layer was formed. This gave a positive electrode active material composed of LiCoO ₂ having a surface coated with a said coating layer.

[Reference Example 1]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, ethoxylithium (LiOC ₂ H ₅ ) and pentaethoxyniobium (Nb (OC ₂ H ₅ ) ₅ ) are mixed in ethanol so that the molar ratio is Li: Nb = 1: 1, thereby forming a coating layer. A coating solution was prepared. Next, the coating liquid for forming a coating layer was applied onto the positive electrode active material (LiCoO ₂ ) with a coating apparatus using a rolling fluidized bed and dried with warm air. Subsequently, the LiCoO ₂ powder coated with the coating layer forming coating solution is heat-treated in the atmosphere at 350 ° C. for 5 hours, thereby forming LiNbO ₃ having a thickness of 10 nm and a coverage of 80%. A coat layer was formed. This gave a positive electrode active material composed of LiCoO ₂ having a surface coated with a said coating layer.

[Reference Example 2]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, ethoxylithium (LiOC ₂ H ₅ ) and pentaethoxyniobium (Nb (OC ₂ H ₅ ) ₅ ) are mixed in ethanol so that the molar ratio is Li: Nb = 1: 1, thereby forming a coating layer. A coating solution was prepared. Next, the coating liquid for coating layer formation is applied onto the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) in a coating apparatus using a rolling fluidized bed, and warm air And dried. Subsequently, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder coated with the coating layer forming coating solution is heat-treated in the atmosphere at 350 ° C. for 5 hours to obtain a thickness of 10 nm. Then, a coating layer made of LiNbO ₃ having a coverage of 80% was formed. As a result, a positive electrode active material made of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ whose surface was coated with the coating layer was obtained.

[Evaluation]
(Composition analysis by X-ray photoelectron spectroscopy)
Composition analysis by X-ray photoelectron spectroscopy (XPS) measurement was performed on the surfaces of the positive electrode active material materials obtained in Examples 1 and 2 and Comparative Examples 1 and 2, and P element or B per Si in the coating layer. The concentration ratio of elements (P / Si or B / Si) was determined. The result is shown in FIG. Table 2 summarizes the combinations of the positive electrode active material and the coating layer of the positive electrode active material obtained in Examples 1 and 2, Comparative Examples 1 and 2, and Reference Examples 1 and 2.
As shown in FIG. 5, in Examples 1 and 2, it was confirmed that P / Si or B / Si significantly exceeded 1. This is because P / Si or B / Si is usually 1 as in Comparative Example 2, but in Examples 1 and 2, the positive electrode active material is strongly basic LiNi _1/3 Co _1/3 Mn _{1. / 3} O ₂ , and the coat layer has acidic PO ₄ ³⁻ or BO ₃ ³⁻ , so that the wettability of the coat layer with respect to the positive electrode active material is improved, so that the P element or the B element in the coat layer is improved. The concentration is considered to have increased. In Comparative Example 1, P / Si was significantly smaller than 1. This is thought to be because P has precipitated.

(Initial interface resistance measurement)
The initial interface resistance was measured for all solid state batteries obtained in Examples 1 and 2, Comparative Examples 1 and 2 and Reference Examples 1 and 2. The initial interface resistance was measured as follows. First, the all solid state battery was charged. Charging was performed at a constant voltage of 3.34 V for 12 hours. After charging, the interface resistance between the positive electrode active material layer and the solid electrolyte layer was determined by impedance measurement. The impedance measurement conditions were a voltage amplitude of 10 mV, a measurement frequency of 1 MHz to 0.1 Hz, and 25 ° C. The result is shown in FIG.
As shown in FIG. 6, it was confirmed that the initial interface resistance in Example 1 is significantly lower than that in Comparative Example 1. In addition, it was confirmed that the initial interface resistance of Example 2 is significantly lower than that of Comparative Example 2. In particular, Example 2 showed an initial interface resistance equivalent to Reference Examples 1 and 2. Thereby, it was suggested that the positive electrode active material of the present invention can exhibit the same initial battery characteristics as those of the positive electrode active material whose surface is coated with a conventional coating layer made of LiNbO ₃ . Note that Reference Example 2 had a slight initial interface resistance higher than that of Reference Example 1, but the effect of the present invention (reduction in initial interface resistance) was that LiNi _1/3 Co _{1 /} It is considered that it is not due to the use of ₃ Mn _1/3 O ₂ but to a combination of the positive electrode active material and the coating layer.

[Example 3]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, lithium hydroxide (LiOH) and an aqueous phosphoric acid solution (H ₃ PO ₄ , 85%) are mixed in ethanol so that the molar ratio is Li: P = 3: 1, and coating for forming a coat layer is performed. A liquid was prepared. Next, the coating liquid for coating layer formation is applied onto the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) in a coating apparatus using a rolling fluidized bed, and warm air And dried. Subsequently, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder coated with the coating layer forming coating solution is heat-treated in the atmosphere at 300 ° C. for 5 hours, so that the thickness becomes 20 nm. A coat layer made of Li ₃ PO ₄ was formed. As a result, a positive electrode active material made of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ whose surface was coated with the coating layer was obtained.

[Example 4]
An all-solid battery was obtained in the same manner as in Example 1 except that the positive electrode active material was produced as follows.

(Preparation of positive electrode active material)
First, in ethanol, lithium acetate (CH ₃ COOLi) and boric acid (H ₃ BO ₃ ) are mixed so that the molar ratio is Li: B = 3: 1 to prepare a coating layer forming coating solution. did. Next, the coating liquid for coating layer formation is applied onto the positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) in a coating apparatus using a rolling fluidized bed, and warm air And dried. Subsequently, the LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder coated with the coating layer forming coating solution is heat-treated at 400 ° C. for 1 hour in the air, so that the thickness becomes 10 nm. A coat layer made of Li ₃ BO ₃ was formed. As a result, a positive electrode active material made of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ whose surface was coated with the coating layer was obtained.

When the initial interface resistance was measured in the same manner as described above for the all solid state batteries obtained in Examples 3 and 4, the interface resistance was lower than when LiCoO ₂ was used as the positive electrode active material. Was confirmed.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material 2 ... Positive electrode active material 3 ... Coat layer 4 ... High resistance layer formation solid electrolyte material 11 ... Positive electrode active material layer 12 ... Negative electrode active material layer 13 ... Solid electrolyte layer 20 ... Electric power generation element of all-solid-state battery

Claims (7)

a positive electrode active material having a pH value of 10 or more and exhibiting strong basicity;
A coating layer having a polyanion structure part formed so as to cover the surface of the positive electrode active material and exhibiting acidity;
The pH value is the pH value of the positive electrode active material-containing aqueous solution when the positive electrode active material-containing aqueous solution obtained by adding 2 mol of the positive electrode active material to 100 ml of water and reaching equilibrium,
Wherein said polyanion structure is at least _{^{PO 4 3-, BO 3 3-,}} SO 4 2- or NO ₃ ^- Ri der either,
A positive electrode active material for an all-solid battery , wherein the positive electrode active material is an oxide positive electrode active material. The positive electrode active material is mainly composed of a compound represented by the general formula LiNi _x Co _y Mn _z O ₂ (x + y + z = 1, y ≠ 1 and z ≠ 1). The positive electrode active material for an all-solid battery according to claim 1 . Wherein said polyanion structure is at least _BO ³ 3-, _SO ^{4 2-} or NO ₃ ^- positive electrode active material for all-solid-state cell according to claim 1 or claim 2, characterized in that either. Wherein said polyanion structure section, the positive electrode active material for all-solid-state cell according to any one of claims of claims 1 to 3, characterized in that further comprises SiO ₄ ^4-a. A positive electrode active material for an all solid state battery according to any one of claims 1 to 4 ,
A positive electrode active material layer comprising: a high resistance layer-forming solid electrolyte material that reacts with the positive electrode active material to form a high resistance layer. An all-solid battery having a positive electrode active material layer, a negative electrode active material layer, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer,
The all-solid-state battery, wherein the positive electrode active material layer is the positive electrode active material layer according to claim 5 . A method for producing a positive electrode active material for an all-solid battery according to any one of claims 1 to 4 ,
A preparation step of preparing a coating layer-forming coating solution containing a compound having a polyanion structure part exhibiting acidity;
A coating step of coating the surface of the positive electrode active material with the coating layer forming coating solution;
And a heat treatment step of heat-treating the positive electrode active material whose surface is coated with the coating layer forming coating solution to form the coat layer.

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