CN117337497A

CN117337497A - Coated positive electrode active material, positive electrode material, and battery

Info

Publication number: CN117337497A
Application number: CN202280034726.XA
Authority: CN
Inventors: 佐佐木出
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2021-05-20
Filing date: 2022-03-18
Publication date: 2024-01-02

Abstract

The coated positive electrode active material (103) in one embodiment of the present disclosure is provided with a positive electrode active material (101) and a coating layer (102) that coats at least a part of the surface of the positive electrode active material (101). The positive electrode material (1000) in one embodiment of the present disclosure contains a coated positive electrode active material (103) and a 1 st solid electrolyte (104). A battery (2000) according to one embodiment of the present disclosure is provided with a positive electrode (201) containing a positive electrode material (1000), a negative electrode (203), and an electrolyte layer (202) provided between the positive electrode (201) and the negative electrode (203).

Description

Coated positive electrode active material, positive electrode material, and battery

Technical Field

The present disclosure relates to a coated positive electrode active material, a positive electrode material, and a battery.

Background

Patent document 1 discloses a battery including a positive electrode containing a sulfide solid electrolyte.

Patent document 2 discloses a battery including a positive electrode containing a halide solid electrolyte.

Prior art literature

Patent literature

Patent document 1: international publication No. 2007/004590

Patent document 2: international publication No. 2018/025582

Disclosure of Invention

Problems to be solved by the invention

In the prior art, it is desired to achieve both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode.

Means for solving the problems

One aspect of the present disclosure relates to a coated positive electrode active material, comprising:

positive electrode active material

A coating layer that covers at least a part of the surface of the positive electrode active material;

the coating layer contains a sulfide solid electrolyte and a halide solid electrolyte.

Effects of the invention

According to the present disclosure, the thermal stability of the positive electrode and the low interface resistance in the positive electrode can be compatible.

Drawings

Fig. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material in embodiment 1.

Fig. 2 is a cross-sectional view showing a schematic configuration of the battery according to embodiment 2.

Fig. 3 is a graph showing the results of measuring the resistance of the batteries of examples 1 to 3 and comparative example 1.

Fig. 4 is a graph showing the measurement results of the heat generation start temperatures of the batteries of examples 1 to 3 and comparative example 1.

Fig. 5 is a graph showing the results of measuring the resistance of the batteries of examples 4 to 6 and comparative example 2.

Fig. 6 is a graph showing the measurement results of the heat generation start temperatures of the batteries of examples 4 to 6 and comparative example 2.

Detailed Description

(insight underlying the present disclosure)

Patent document 1 discloses an all-solid lithium battery including a positive electrode containing a sulfide solid electrolyte. The sulfide solid electrolyte has a low young's modulus, i.e., is excellent in deformability. Therefore, if a sulfide solid electrolyte is used, an interface having a low interface resistance is easily formed. On the other hand, sulfide solid electrolytes have low thermal stability.

Patent document 2 discloses a lithium ion battery including a lithium ion battery containing Li ₃ YCl ₆ 、Li ₃ YBr ₆ An all-solid lithium battery of a positive electrode of a halide solid electrolyte. The halide solid electrolyte has high thermal stability. On the other hand, the halide solid electrolyte has a high young's modulus, i.e., lacks deformability. Therefore, if a halide solid electrolyte is used, it is difficult to form an interface having a low interface resistance.

The thermal stability of a positive electrode containing a solid electrolyte is greatly affected by the reactivity of the solid electrolyte with oxygen released from the positive electrode, in addition to the thermal stability of the solid electrolyte itself. When the positive electrode active material contains oxygen, the structure of the positive electrode active material may be unstable due to charging, and oxygen may be released from the positive electrode active material. In particular, if an excessive current flows in the battery due to a short circuit or the like, and the battery generates heat, the positive electrode active material is heated, and oxygen is more easily released from the positive electrode active material. If heat is generated by the reaction of the solid electrolyte contained in the positive electrode with oxygen, the positive electrode active material is further heated by using the heat of reaction as a heat source, and the oxidation reaction of the solid electrolyte is accelerated. In order to improve the thermal stability of the positive electrode, it is required that the amount of heat generated by the oxidation reaction between oxygen and the solid electrolyte is small in addition to the high thermal stability of the solid electrolyte itself. The halide solid electrolyte has excellent thermal stability as compared with the sulfide solid electrolyte, and has low reactivity with oxygen. That is, the amount of heat of the oxidation reaction of the halide solid electrolyte is small. Therefore, in the positive electrode containing the halide solid electrolyte, high thermal stability can be achieved.

In the positive electrode containing a solid electrolyte, in order to achieve low interface resistance, the positive electrode active material needs to be in close contact with the solid electrolyte. Generally, an all-solid battery is manufactured by applying a load to a positive electrode and bringing a positive electrode active material into contact with a solid electrolyte. At this time, the higher the deformability of the solid electrolyte, the closer the positive electrode is in contact with the solid electrolyte even when the same load is applied. The sulfide solid electrolyte generally has a lower young's modulus and excellent deformability than the halide solid electrolyte. That is, by the sulfide solid electrolyte, the positive electrode active material and the solid electrolyte are easily brought into closer contact. Therefore, in the positive electrode containing the sulfide solid electrolyte, low interface resistance can be achieved.

The present inventors have conducted intensive studies to achieve both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode. As a result, a coated positive electrode active material was found that was provided with a positive electrode active material and a coating layer that covers at least a part of the surface of the positive electrode active material, the coating layer containing a sulfide solid electrolyte and a halide solid electrolyte. When such a coated positive electrode active material is used, a low interfacial resistance can be achieved by the sulfide solid electrolyte contained in the coating layer, and a high thermal stability can be achieved by the halide solid electrolyte contained in the coating layer in the positive electrode.

(summary of one aspect of the disclosure)

The 1 st aspect of the present disclosure relates to a coated positive electrode active material, comprising:

positive electrode active material

According to the above configuration, in the positive electrode, the sulfide solid electrolyte contained in the coating layer can realize low interface resistance, and the halide solid electrolyte contained in the coating layer can realize high thermal stability. That is, the thermal stability of the positive electrode and the low interface resistance in the positive electrode can be both achieved.

In the 2 nd aspect of the present disclosure, for example, the coated positive electrode active material according to the 1 st aspect, the ratio of the volume of the halide solid electrolyte to the volume of the coating layer may also be 60% or less. With the above configuration, both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode can be achieved.

In the 3 rd aspect of the present disclosure, for example, the coated positive electrode active material according to the 1 st or 2 nd aspect, the ratio of the volume of the halide solid electrolyte to the volume of the coating layer may also be 40% or less. With the above configuration, both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode can be achieved.

In the 4 th aspect of the present disclosure, for example, the coated positive electrode active material according to any one of the 1 st to 3 rd aspects, the halide solid electrolyte may also be represented by the following composition formula (1).

Li _α M _β X _γ (1)

Wherein, alpha, beta and gamma are respectively independent and are values larger than 0. M contains at least 1 element selected from metal elements other than Li and semi-metal elements. X comprises at least 1 selected from F, cl, br and I. With the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

In the 5 th aspect of the present disclosure, for example, the coated positive electrode active material according to the 4 th aspect, the composition formula (1) may also satisfy 2.5.ltoreq.α.ltoreq.3, 1.ltoreq.β.ltoreq.1.1, and γ=6. With the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

In the 6 th aspect of the present disclosure, for example, the coated positive electrode active material according to the 4 th or 5 th aspect, in the composition formula (1), M may also contain yttrium. With the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

In the 7 th aspect of the present disclosure, for example, the coated positive electrode active material according to any one of the 1 st to 6 th aspects, the coating layer may be a single layer. With the above configuration, the desired effect can be easily obtained while suppressing an increase in the manufacturing cost of the coated positive electrode active material.

In the 8 th aspect of the present disclosure, for example, the coated positive electrode active material according to any one of the 1 st to 7 th aspects, the coating layer may contain a mixture of the sulfide solid electrolyte and the halide solid electrolyte. With the above configuration, a desired effect can be obtained in the entire coating layer.

A 9 th aspect of the present disclosure relates to a positive electrode material containing:

the coated positive electrode active material according to any one of aspects 1 to 8; and

1 st solid electrolyte.

With the above configuration, both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode can be achieved.

In the 10 th aspect of the present disclosure, for example, the positive electrode material according to the 9 th aspect, the 1 st solid electrolyte may also contain at least 1 selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. With the above configuration, the heat stability of the positive electrode can be improved. In addition, the interface resistance in the positive electrode can be reduced.

An 11 th aspect of the present disclosure relates to a battery, which includes:

a positive electrode containing the positive electrode material of the 9 th or 10 th aspect;

a negative electrode; and

an electrolyte layer disposed between the positive electrode and the negative electrode.

Embodiments of the present disclosure will be described below with reference to the drawings.

(embodiment 1)

Fig. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 in embodiment 1. The positive electrode material 1000 in embodiment 1 contains the coated positive electrode active material 103. The coated positive electrode active material 103 in embodiment 1 will be described with reference to fig. 1.

[ coated cathode active Material ]

The coated positive electrode active material 103 in embodiment 1 includes a positive electrode active material 101 and a coating layer 102. The coating layer 102 coats at least a part of the surface of the positive electrode active material 101.

The coating layer 102 is in direct contact with the positive electrode active material 101.

Hereinafter, the material constituting the coating layer 102 is referred to as "coating material". The coated positive electrode active material 103 in embodiment 1 contains the positive electrode active material 101 and a coating material. The coating material forms the coating layer 102 by being present on at least a part of the surface of the positive electrode active material 101.

The coating layer 102 may uniformly coat the positive electrode active material 101. According to the above configuration, the positive electrode active material 101 and the coating layer 102 are in close contact, and therefore both the thermal stability of the positive electrode and the low interface resistance in the positive electrode can be achieved.

The coating layer 102 may cover only a part of the surface of the positive electrode active material 101. The particles of the positive electrode active material 101 are brought into direct contact with each other via the portion not covered with the covering layer 111, and the electron conductivity between the particles of the positive electrode active material 101 is improved. As a result, the battery can operate with high output power.

The coating of the positive electrode active material 101 by the coating layer 102 can suppress formation of an oxide film caused by oxidative decomposition of other solid electrolytes in battery charging. As a result, the charge/discharge efficiency of the battery is improved. The other solid electrolyte is, for example, the 1 st solid electrolyte 104 described later.

(coating layer)

The coating layer 102 contains a sulfide solid electrolyte and a halide solid electrolyte.

With the above configuration, in the positive electrode, the sulfide solid electrolyte contained in the coating layer 102 can realize low interface resistance, and the halide solid electrolyte contained in the coating layer 102 can realize high thermal stability. Furthermore, the inventors found that: regardless of the thermal stability and interfacial resistance of the positive electrode, the structure near the interface where the positive electrode active material 101 and other solid electrolytes are in contact is greatly affected. According to the above constitution, the heat stability can be improved significantly and the interface resistance can be reduced as compared with a constitution in which the sulfide solid electrolyte and the halide solid electrolyte are contained singly in other solid electrolytes.

In this embodiment, the coating layer 102 is a single layer. With the above configuration, the desired effect can be easily obtained while suppressing an increase in the manufacturing cost of the coated positive electrode active material 103.

The coating layer 102 may be formed of a plurality of layers. In this case, at least 1 layer of the plurality of coating layers 102 may contain a sulfide solid electrolyte and a halide solid electrolyte. The plurality of coating layers 102 may contain sulfide solid electrolytes and halide solid electrolytes, respectively.

In the present embodiment, the coating layer 102 contains a mixture of sulfide solid electrolyte and halide solid electrolyte. With the above configuration, a desired effect can be obtained in the entire coating layer 102.

In this embodiment, the coating layer 102 has a substantially uniform composition. That is, the sulfide solid electrolyte and the halide solid electrolyte are uniformly mixed in the coating layer 102. With the above configuration, a desired effect can be obtained in the entire coating layer 102.

The halide solid electrolyte may also be sulfur-free. With the above configuration, generation of hydrogen sulfide gas can be suppressed. Therefore, a battery with improved safety can be realized.

The halide solid electrolyte can be represented by the following composition formula (1), for example.

Li _α M _β X _γ (1)

Wherein, alpha, beta and gamma are respectively independent and are values larger than 0. M contains at least 1 element selected from metal elements other than Li and semi-metal elements. X comprises at least 1 selected from F, cl, br and I.

In the present disclosure, the "half metal element" is B, si, ge, as, sb and Te. The term "metal element" refers to all elements contained in groups 1 to 12 of the periodic table excluding hydrogen and all elements contained in groups 13 to 16 of the periodic table excluding B, si, ge, as, sb, te, C, N, P, O, S and Se. That is, the "semi-metallic element" or "metallic element" is an element group that can become a cation when forming an inorganic compound with a halogen element.

The halide solid electrolyte represented by the composition formula (1) has higher ion conductivity than a halide solid electrolyte such as LiI composed of Li and a halogen element. Therefore, according to the halide solid electrolyte represented by the composition formula (1), the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

In the composition formula (1), M may be at least 1 element selected from metal elements other than Li and semi-metal elements.

In the composition formula (1), X may be at least 1 selected from F, cl, br and I.

The composition formula (1) can also satisfy that alpha is more than or equal to 2.5 and less than or equal to 3, beta is more than or equal to 1 and less than or equal to 1.1 and gamma=6. With the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

In the composition formula (1), M may contain Y (=yttrium). That is, the halide solid electrolyte may contain Y as a metal element. With the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

The halide solid electrolyte containing Y may be, for example, li _a Me _b Y _c X ₆ A compound represented by the formula (I). Wherein a+mb+3c=6 and c > 0 are satisfied. Me is at least 1 element selected from the group consisting of metal elements and semi-metal elements other than Li and Y. m is the valence of the element Me. X is at least 1 selected from F, cl, br and I.

Me may be, for example, at least 1 selected from Mg, ca, sr, ba, zn, sc, al, ga, bi, zr, hf, ti, sn, ta and Nb.

With the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved.

As the halide solid electrolyte, for example, the following materials can be used. According to the following configuration, the ionic conductivity of the halide solid electrolyte can be further improved, and the interface resistance in the positive electrode can be further reduced.

The halide solid electrolyte may be a material represented by the following composition formula (A1).

Li _6-3d Y _d X ₆ (A1)

In the composition formula (A1), X is at least 1 selected from F, cl, br and I. Furthermore, 0 < d < 2 is satisfied.

The halide solid electrolyte may be a material represented by the following composition formula (A2).

Li ₃ YX ₆ (A2)

In the composition formula (A2), X is at least 1 selected from F, cl, br and I.

The halide solid electrolyte may be a material represented by the following composition formula (A3).

Li _3-3δ Y _1+δ Cl ₆ (A3)

In the composition formula (A3), 0 < delta is satisfied.

The halide solid electrolyte may be a material represented by the following composition formula (A4).

Li _3-3δ Y _1+δ Br ₆ (A4)

In the composition formula (A4), 0 < delta is satisfied to be less than or equal to 0.25.

The halide solid electrolyte may be a material represented by the following composition formula (A5).

Li _3-3δ+a Y _1+δ-a Me _a Cl _6-x-y Br _x I _y (A5)

In the composition formula (A5), me includes at least 1 selected from Mg, ca, sr, ba and Zn. Me may be at least 1 selected from Mg, ca, sr, ba and Zn.

In the composition formula (A5), delta is more than-1 and less than 2, a is more than 0 and less than 3, 0 is less than (3-3 delta+a), 0 is less than (1+delta-a), x is more than or equal to 0 and less than or equal to 6, y is more than or equal to 0 and less than or equal to 6, and (x+y) is more than or equal to 6.

The halide solid electrolyte may be a material represented by the following composition formula (A6).

Li _3-3δ Y _1+δ-a Me _a Cl _6-x-y Br _x I _y (A6)

In the composition formula (A6), me includes at least 1 selected from Al, sc, ga, and Bi. Me may be at least 1 selected from Al, sc, ga and Bi.

In the composition formula (A6), delta is more than-1 and less than 1, a is more than 0 and less than 2, 0 is less than (1+delta-a), x is more than or equal to 0 and less than or equal to 6, y is more than or equal to 0 and less than or equal to 6, and (x+y) is more than or equal to 6.

The halide solid electrolyte may be a material represented by the following composition formula (A7).

Li _3-3δ-a Y _1+δ-a Me _a Cl _6-x-y Br _x I _y (A7)

In the composition formula (A7), me includes at least 1 selected from Zr, hf, and Ti. Me may be at least 1 selected from Zr, hf and Ti.

In the composition formula (A7), delta is more than-1 and less than 1, a is more than 0 and less than 1.5, 0 is less than (3-3 delta-a), 0 is less than (1+delta-a), x is more than or equal to 0 and less than or equal to 6, y is more than or equal to 0 and less than or equal to 6, and x+y is more than or equal to 6.

The halide solid electrolyte may be a material represented by the following composition formula (A8).

Li _3-3δ-2a Y _1+δ-a Me _a Cl _6-x-y Br _x I _y (A8)

In the composition formula (A8), me includes at least 1 selected from Ta and Nb. Me may be at least 1 selected from Ta and Nb.

In the composition formula (A8), delta is more than-1 and less than 1, a is more than 0 and less than 1.2, 0 is less than (3-3 delta-2 a), 0 is less than (1+delta-a), x is more than or equal to 0 and less than or equal to 6, y is more than or equal to 0 and less than or equal to 6, and x+y is more than or equal to 6.

As the halide solid electrolyte, more specifically, li, for example, can be used ₃ YX ₆ 、Li ₂ MgX ₄ 、Li ₂ FeX ₄ 、Li(Al、Ga、In)X ₄ 、Li ₃ (Al、Ga、In)X ₆ Etc. Wherein X is at least 1 selected from F, cl, br and I.

In the present disclosure, the expression "(A, B, C)" means "at least 1 kind selected from A, B and C". For example, "(Al, ga, in)" is synonymous with "at least 1 kind selected from Al, ga and In". The same applies to other elements.

The halide solid electrolyte may be a compound containing Li, M2, X2, and O (oxygen), respectively. Wherein M2 comprises at least 1 selected from Nb and Ta, for example. In addition, X2 is at least 1 selected from F, cl, br and I.

The compound containing Li, M2, X2 and O (oxygen) can be represented by the following composition formula (2), for example.

Li _x M2O _y X2 _5+x-2y (2)

Wherein x may also satisfy 0.1 < x < 7.0.y may also satisfy 0.4 < y < 1.9. According to the above constitution, the halide solid electrolyte has high ionic conductivity. According to the halide solid electrolyte, the battery can exhibit excellent charge-discharge efficiency.

As the sulfide solid electrolyte, li ₂ S-P ₂ S ₅ 、Li ₂ S-SiS ₂ 、Li ₂ S-B ₂ S ₃ 、Li ₂ S-GeS ₂ 、Li _3.25 Ge _0.25 P _0.75 S ₄ 、Li ₁₀ GeP ₂ S ₁₂ Etc. In addition, li is also used ₆ PS ₅ Cl、Li ₆ PS ₅ Br、Li ₆ PS ₅ Sulfide solid electrolyte of sulfur silver germanium ore (argyrodite) structure represented by I, etc. LiX and Li may be added to these sulfide solid electrolytes ₂ O、MO _q 、Li _p MO _q Etc. Wherein X is at least 1 selected from F, cl, br and I. M is at least 1 selected from P, si, ge, B, al, ga, in, fe and Zn. p and q are natural numbers, respectively. Sulfide solid electrolytes selected from 1 or two or more of the above materials may be used.

With the above configuration, the ionic conductivity of the sulfide solid electrolyte can be further improved. This can further improve the charge/discharge efficiency of the battery.

In the coated positive electrode active material 103 according to embodiment 1, the ratio of the volume of the halide solid electrolyte to the volume of the coating layer 102 may be 60% or less. The ratio of the volume of the halide solid electrolyte to the volume of the coating layer 102 may be 40% or less. With the above configuration, both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode can be achieved.

In the coated positive electrode active material 103 according to embodiment 1, the ratio of the volume of the halide solid electrolyte to the volume of the coating layer 102 may be 5% or more. If the ratio of the volume of the halide solid electrolyte to the volume of the coating layer 102 is 5% or more, the contact ratio of the positive electrode active material 101 and the sulfide solid electrolyte contained in the coating layer 102 decreases, and therefore high thermal stability can be maintained.

The ratio of the volume of the halide solid electrolyte to the volume of the coating layer 102 can be calculated, for example, in the following manner. The coated positive electrode active material 103 is dissolved with an acid or the like to obtain a solution. Alternatively, only the coating layer 102 coating the positive electrode active material 103 is dissolved by using a highly polar organic solvent or the like, thereby obtaining a solution. The element ratio of the coating layer 102 can be specified by analyzing the obtained solution by ICP emission spectrometry or ion chromatography. The ratio of the volume of the halide solid electrolyte to the volume of the coating layer 102 can be calculated from the specified element ratio.

The thickness of the coating layer 102 may be, for example, 1nm to 500 nm.

By setting the thickness of the coating layer 102 to 1nm or more, the positive electrode active material 101 and the coating layer 102 are satisfactorily adhered, and therefore, both the thermal stability of the positive electrode and the low interface resistance in the positive electrode can be achieved.

Further, by setting the thickness of the coating layer 102 to 500nm or less, the internal resistance of the battery due to the thickness of the coating layer 102 can be sufficiently reduced. Therefore, the energy density of the battery can be improved.

The method for measuring the thickness of the coating layer 102 is not particularly limited. For example, the thickness of the coating layer 102 can be obtained by direct observation using a transmission electron microscope or the like. Further, by measuring XPS while removing the coating layer 102 by Ar sputtering, the thickness of the coating layer 102 can be obtained from the change in the spectrum derived from the active material.

(cathode active material)

The positive electrode active material 101 contains a material having a property of intercalating and deintercalating metal ions (for example, lithium ions). As the positive electrode active material 101, for example, a lithium-containing transition metal oxide, a transition metal fluoride, a polyanion material, a fluorinated polyanion material, a transition metal sulfide, a transition metal oxysulfide, and a transition metal oxynitride can be used. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material 101, the manufacturing cost can be reduced and the average discharge voltage can be increased. Examples of the lithium-containing transition metal oxide include Li (Ni, co, mn) O ₂ 、Li(Ni、Co、Al)O ₂ 、Li(NiCoMn)O ₂ 、Li(NiCoAl)O ₂ 、LiCoO ₂ Etc.

The positive electrode active material 101 may contain Ni, co, and Mn. The positive electrode active material 101 may contain lithium nickel cobalt manganese oxide (i.e., NMC). The positive electrode active material 101 may be NMC. For example, the positive electrode active material 101 may be Li (NiCoMn) O ₂ . With the above configuration, the energy density and the charge/discharge efficiency of the battery can be further improved.

The positive electrode active material 101 may contain Ni, co, and Al. The positive electrode active material 101 may contain nickel cobalt lithium aluminate (i.e., NCA). The positive electrode active material 101 may be NCA. For example, the positive electrode active material 101 may be Li (NiCoAl) O ₂ . With the above configuration, it is possible to furtherThe energy density and the charge and discharge efficiency of the battery are improved.

The shape of the positive electrode active material 101 in embodiment 1 is not particularly limited. The positive electrode active material 101 may have a needle shape, a spherical shape, an elliptic spherical shape, or the like, for example. For example, the positive electrode active material 101 may be in the form of particles.

The mass ratio of the coating layer 102 to the positive electrode active material 101 may be 0.01% or more and 30% or less. If the mass ratio of the coating layer 102 to the positive electrode active material 101 is 0.01% or more, the positive electrode active material 101 and the coating layer 102 adhere well, and therefore the interface resistance decreases. If the mass ratio of the coating layer 102 to the positive electrode active material 101 is 30% or less, the coating layer 102 is excessively thickened, so that the internal resistance of the battery can be sufficiently reduced. Therefore, the energy density of the battery can be improved.

The coating layer 102 may cover 30% or more of the surface of the positive electrode active material 101, 60% or more, or 90% or more. The coating layer 102 may cover substantially the entire surface of the positive electrode active material 101.

The positive electrode active material 101 may have at least a part of its surface covered with a coating material different from the coating material constituting the coating layer 102. Examples of such a coating material include sulfide solid electrolyte, oxide solid electrolyte, and halide solid electrolyte. As the sulfide solid electrolyte and the halide solid electrolyte used for such a coating material, those exemplified as the coating material constituting the coating layer 102 can also be used. Examples of the oxide solid electrolyte used for such a coating material include LiNbO ₃ Equal Li-Nb-O compound, liBO ₂ 、Li ₃ BO ₃ Equal Li-B-O compound, liAlO ₂ Equal Li-Al-O compound, li ₄ SiO ₄ Equal Li-Si-O compound, li ₂ SO ₄ 、Li ₄ Ti ₅ O ₁₂ Equal Li-Ti-O compound, li ₂ ZrO ₃ Equal Li-Zr-O compound, li ₂ MoO ₃ Equal Li-Mo-O compound, liV ₂ O ₅ Equal Li-V-O compound, li ₂ WO ₄ Equal Li-W-O compound, li ₃ PO ₄ And Li-P-O compounds. With the above configuration, the oxidation resistance of the positive electrode material 1000 can be further improved. This can suppress an increase in internal resistance of the battery during charging.

Method for producing sulfide solid electrolyte

The sulfide solid electrolyte contained in the coating layer 102 can be produced, for example, by the following method.

Raw material powders of sulfide are prepared in such a manner that the compounding ratio of the target composition is reached, and mixed. For example, in the production of Li ₂ S-P ₂ S ₅ In the case of (2), a raw material powder Li of sulfide was prepared in a molar ratio of 75:25 ₂ S and P ₂ S ₅ 。

After the raw material powder is fully mixed, the raw material powder is mutually mixed, crushed and reacted by adopting a mechanochemical grinding method. Alternatively, the raw material powder may be sufficiently mixed and then sintered in vacuum.

Thus, li in the form of glass ceramic, which is a sulfide solid electrolyte, can be obtained ₂ S-P ₂ S ₅ 。

Method for producing halide solid electrolyte

The halide solid electrolyte contained in the coating layer 102 can be produced, for example, by the following method.

Raw material powders of binary halides are prepared so as to achieve a blending ratio of a target composition, and mixed. For example, in the production of Li ₃ YCl ₆ In the case of (2), raw material powders LiCl and YCl of binary halide were prepared in a molar ratio of 3:1 ₃ 。

In this case, the type of the raw material powder is selected, so that "M", "Me" and "X" in the above-described composition formula can be determined. The values "α", "β", "γ", "d", "δ", "a", "x" and "y" in the above-described composition formulas can be adjusted by adjusting the types, the mixing ratios, and the synthesis processes of the raw material powders.

Thus, li, which is a halide solid electrolyte, can be obtained ₃ YCl ₆ 。

By adjusting the reaction method and reaction conditions of the raw material powders with each other, the structure (i.e., crystal structure) of the crystal phase in the halide solid electrolyte can be determined.

Method for producing coated positive electrode active material

The coated positive electrode active material 103 can be produced, for example, by the following method.

As the coating material, a sulfide solid electrolyte powder and a halide solid electrolyte powder were prepared. The powder of the positive electrode active material 101 and the powder of the coating material are mixed in a proper ratio to obtain a mixture. The mixture is subjected to a milling treatment, whereby mechanical energy is imparted to the mixture. As the grinding treatment, a mixing device such as a ball mill can be used. In order to suppress oxidation of the material, the polishing treatment may be performed in a dry atmosphere and an inert atmosphere.

The coated positive electrode active material 103 may be produced by a dry particle recombination method. The treatment by the dry particle recombination method includes imparting mechanical energy to the positive electrode active material 101 and the coating material of at least 1 selected from the group consisting of impact, compression, and shearing. The positive electrode active material 101 and the coating material may be mixed in an appropriate ratio.

The device used in the method for producing the coated positive electrode active material 103 is not particularly limited, and may be a device capable of imparting mechanical energy such as impact, compression, and shearing to the mixture of the positive electrode active material 101 and the coating material. Examples of the device capable of imparting mechanical energy include a ball mill, "MECHANO FUSION" (manufactured by Hosokawa Micron corporation), and a compression shear processing device (particle compounding device) such as "NOBILTA" (manufactured by Hosokawa Micron corporation).

"MECHANO FUSION" is a particle compounding device that employs a dry mechanical compounding technique that applies intense mechanical energy to a plurality of different feedstock particles. In MECHANO FUSION, the powder raw material fed between a rotating container and a press head (press head) is subjected to mechanical energy such as compression, shearing and friction to produce particle recombination.

"NOBILTA" is a particle compounding apparatus that adopts a dry mechanical compounding technology developed from a particle compounding technology for compounding nanoparticles as a raw material. The NOBILTA produces composite particles by imparting mechanical energy such as impact, compression, and shearing to a plurality of raw material powders.

"NOBILTA" is a process in which a rotor disposed in a horizontal cylindrical mixing vessel with a predetermined gap between the rotor and the inner wall of the mixing vessel is rotated at a high speed, and raw material powder is forced to pass through the gap repeatedly a plurality of times. By applying such forces as impact, compression, and shearing to the mixture, composite particles of the positive electrode active material 101 and the coating material can be produced. The rotating speed of the rotor, the processing time, the feeding amount and other conditions can be properly adjusted.

[ Positive electrode Material ]

The positive electrode material 1000 in embodiment 1 contains a 1 st solid electrolyte 104 in addition to the coating positive electrode active material 103. The 1 st solid electrolyte 104 is, for example, in the form of particles. According to the 1 st solid electrolyte 104, the cathode material 1000 can achieve high ion conductivity.

The positive electrode active material 101 is separated from the 1 st solid electrolyte 104 by the coating layer 102. The positive electrode active material 101 may not be in direct contact with the 1 st solid electrolyte 104. With the above configuration, the oxidation resistance of the positive electrode material 1000 is further improved. This can suppress an increase in internal resistance of the battery during charging.

(1 st solid electrolyte)

The 1 st solid electrolyte 104 is a bulk solid electrolyte. The 1 st solid electrolyte 104 contains at least 1 selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. With the above configuration, the thermal stability of the positive electrode can be further improved. In addition, the interface resistance in the positive electrode can be reduced. The halide solid electrolyte has high ionic conductivity and high thermal stability. Therefore, when the 1 st solid electrolyte 104 contains a halide solid electrolyte, the thermal stability of the positive electrode can be further improved. The sulfide solid electrolyte has high ionic conductivity, low Young's modulus, and excellent deformability. Therefore, in the case where the 1 st solid electrolyte 104 contains a sulfide solid electrolyte, the coated positive electrode active material 103 and the 1 st solid electrolyte 104 are easily in closer contact. This can further reduce the interface resistance in the positive electrode. In addition, if two solid electrolytes of widely different structures are in contact, a large resistance can be generated in the interface thereof. Therefore, when both the coating layer 102 and the 1 st solid electrolyte 104 contain a halide solid electrolyte or a sulfide solid electrolyte, lithium ions are easily transferred to and from the interface between the coating layer 102 and the 1 st solid electrolyte 104. This can reduce the interface resistance in the positive electrode.

As the halide solid electrolyte, the halide solid electrolyte described with respect to the coating layer 102 can be used. As the sulfide solid electrolyte, the sulfide solid electrolyte described with respect to the coating layer 102 can be used.

As the oxide solid electrolyte, for example, liTi can be used ₂ (PO ₄ ) ₃ NASICON type solid electrolyte represented by element substitution body thereof, (LaLi) TiO ₃ Perovskite-based solid electrolyte comprising Li ₁₄ ZnGe ₄ O ₁₆ 、Li ₄ SiO ₄ 、LiGeO ₄ Lisicon type solid electrolyte represented by element substitution body thereof, and lithium ion secondary battery ₇ La ₃ Zr ₂ O ₁₂ Garnet-type solid electrolyte represented by its element substitution body, and Li ₃ PO ₄ And N-substituted body thereof, and LiBO ₂ 、Li ₃ BO ₃ Based on an equal Li-B-O compound and adding Li ₂ SO ₄ 、Li ₂ CO ₃ Glass or glass ceramic, etc. An oxide solid electrolyte selected from 1 or two or more of the above materials may be used.

In the present disclosure, a gel is contained in the "solid" of the "polymer solid electrolyte".

As the polymer solid electrolyte, for example, a polymer compound and a compound of lithium salt can be used. The polymer compound may have an ethylene oxide structure. The polymer compound having an ethylene oxide structure can contain a large amount of lithium salt. Thus, ion conductivity can be further improved. As lithium salt, liPF can be used ₆ 、LiBF ₄ 、LiSbF ₆ 、LiAsF ₆ 、LiSO ₃ CF ₃ 、LiN(SO ₂ CF ₃ ) ₂ 、LiN(SO ₂ C ₂ F ₅ ) ₂ 、LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ) LiC (SO) ₂ CF ₃ ) ₃ Etc. The lithium salt may be used in an amount of 1 or two or more selected from the above lithium salts. The polymer solid electrolyte that the 1 st solid electrolyte 104 may contain may be gelled by containing an organic solvent.

As the complex hydride solid electrolyte, liBH, for example, can be used ₄ -LiI、LiBH ₄ -P ₂ S ₅ Etc.

The 1 st solid electrolyte 104 may be a mixture of two or more kinds selected from the group consisting of a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. For example, the 1 st solid electrolyte 104 may be a mixture of a halide solid electrolyte and an oxide solid electrolyte. The 1 st solid electrolyte 104 may be a mixture of a sulfide solid electrolyte and an oxide solid electrolyte.

The shape of the 1 st solid electrolyte 104 in embodiment 1 is not particularly limited. The 1 st solid electrolyte 104 may have a needle shape, a sphere shape, an elliptic sphere shape, or the like, for example. For example, the 1 st solid electrolyte 104 may be in the form of particles.

For example, when the 1 st solid electrolyte 104 has a particle shape (e.g., spherical shape), the 1 st solid electrolyte 104 may have a median particle diameter of 100 μm or less. When the median particle diameter of the 1 st solid electrolyte 104 is 100 μm or less, the coating of the positive electrode active material 103 and the 1 st solid electrolyte 104 in the positive electrode material 1000 can form a good dispersion state. This improves the charge/discharge characteristics of the battery.

The 1 st solid electrolyte 104 may have a median particle diameter of 10 μm or less or 1 μm or less. With the above configuration, the positive electrode material 1000 can be coated with the positive electrode active material 103 and the 1 st solid electrolyte 104 in a well-dispersed state.

The median particle diameter of the 1 st solid electrolyte 104 may be smaller than the median particle diameter of the coated positive electrode active material 103. With the above configuration, the 1 st solid electrolyte 104 and the coated positive electrode active material 103 can be formed in a more dispersed state in the positive electrode material 1000.

The median particle diameter of the coated positive electrode active material 103 may be 0.1 μm or more and 100 μm or less. When the median particle diameter of the coated cathode active material 103 is 0.1 μm or more, the coated cathode active material 103 and the 1 st solid electrolyte 104 can form a good dispersion state in the cathode material 1000. This improves the charge/discharge characteristics of the battery. When the median particle diameter of the coated positive electrode active material 103 is 100 μm or less, the lithium diffusion rate in the coated positive electrode active material 103 can be sufficiently ensured. Thus, the battery can operate with high output power.

The median particle diameter of the coated positive electrode active material 103 may be larger than that of the 1 st solid electrolyte 104. Thus, the coated positive electrode active material 103 and the 1 st solid electrolyte 104 can be in a good dispersion state.

In the present disclosure, the median particle diameter refers to a particle diameter (d 50) at which the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution can be measured by, for example, a laser diffraction type measuring device or an image analyzing device.

In the positive electrode material 1000 according to embodiment 1, the 1 st solid electrolyte 104 and the coated positive electrode active material 103 may be in contact with each other. At this time, the coating layer 102 and the positive electrode active material 101 are in contact with each other.

The positive electrode material 1000 in embodiment 1 may contain a plurality of particles of the 1 st solid electrolyte 104 and a plurality of particles of the coated positive electrode active material 103.

In the positive electrode material 1000 according to embodiment 1, the content of the 1 st solid electrolyte 104 and the content of the coated positive electrode active material 103 may be the same as each other or may be different from each other.

Method for producing positive electrode material

The cathode material 1000 is obtained by mixing the coated cathode active material 103 and the 1 st solid electrolyte 104. The method of mixing the coated positive electrode active material 103 and the 1 st solid electrolyte 104 is not particularly limited. For example, the coated positive electrode active material 103 and the 1 st solid electrolyte 104 may be mixed by a device such as a mortar, or the coated positive electrode active material 103 and the 1 st solid electrolyte 104 may be mixed by a mixing device such as a ball mill. The mixing ratio of the coated positive electrode active material 103 and the 1 st solid electrolyte 104 is not particularly limited.

(embodiment 2)

Embodiment 2 will be described below. The description repeated with embodiment mode 1 will be omitted as appropriate.

Fig. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 in embodiment 2.

The battery 2000 in embodiment 2 includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203. The positive electrode 201 contains the positive electrode material 1000 in embodiment 1. The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203.

The volume ratio "v1:100-v1" of the coated positive electrode active material 103 and the 1 st solid electrolyte 104 contained in the positive electrode 201 may satisfy 30.ltoreq.v1.ltoreq.95. Where v1 represents the volume ratio of the coated positive electrode active material 103 when the total volume of the coated positive electrode active material 103 and the 1 st solid electrolyte 104 contained in the positive electrode 201 is set to 100. When 30.ltoreq.v1 is satisfied, sufficient energy density of the battery 2000 can be ensured. When v1 is satisfied to be 95 or less, the battery 2000 can operate with high output power.

The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 is 10 μm or more, a sufficient energy density of the battery 2000 can be ensured. When the thickness of the positive electrode 201 is 500 μm or less, the battery 2000 can operate with high output.

The electrolyte layer 202 is a layer containing an electrolyte. The electrolyte is, for example, a solid electrolyte. The solid electrolyte contained in the electrolyte layer 202 is defined as the 2 nd solid electrolyte. That is, the electrolyte layer 202 may contain a 2 nd solid electrolyte layer.

As the 2 nd solid electrolyte, the solid electrolyte described in embodiment mode 1 can also be used. That is, as the 2 nd solid electrolyte, a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte may be used. With the above configuration, the output density and the charge/discharge characteristics of the battery 2000 can be further improved.

The electrolyte layer 202 may contain a 2 nd solid electrolyte as a main component. That is, the electrolyte layer 202 may contain, for example, 50% or more (i.e., 50% or more by mass) of the 2 nd solid electrolyte relative to the mass ratio of the entire electrolyte layer 202. With the above configuration, the charge/discharge efficiency of the battery 2000 can be further improved.

The electrolyte layer 202 may contain 70% or more (i.e., 70% or more by mass) of the 2 nd solid electrolyte with respect to the mass ratio of the entire electrolyte layer 202. With the above configuration, the charge/discharge efficiency of the battery 2000 can be further improved.

The electrolyte layer 202 contains the 2 nd solid electrolyte as a main component, but may further contain unavoidable impurities, starting materials used in synthesizing the 2 nd solid electrolyte, byproducts, decomposition products, and the like.

The electrolyte layer 202 may contain, for example, the 2 nd solid electrolyte in a mass ratio of 100% (i.e., 100 mass%) to the entire electrolyte layer 202, in addition to the unavoidable impurities. With the above configuration, the charge/discharge efficiency of the battery 2000 can be further improved.

Thus, the electrolyte layer 202 may be composed of only the 2 nd solid electrolyte.

The electrolyte layer 202 may contain two or more materials listed as the 2 nd solid electrolyte. For example, the electrolyte layer 202 may also contain a halide solid electrolyte and a sulfide solid electrolyte.

The electrolyte layer 202 may be formed by stacking the 1 st electrolyte layer and the 2 nd electrolyte layer. The composition of the 2 nd solid electrolyte contained in the 1 st electrolyte layer and the composition of the 2 nd solid electrolyte contained in the 2 nd electrolyte layer may be different. For example, the 2 nd solid electrolyte contained in the 1 st electrolyte layer is a halide solid electrolyte, and the 2 nd solid electrolyte contained in the 2 nd electrolyte layer may be a sulfide solid electrolyte. In this case, the 1 st electrolyte layer may be disposed on the side contacting the positive electrode 201, and the 2 nd electrolyte layer may be disposed on the side contacting the negative electrode 203. With the above configuration, the thermal stability, the output characteristics, and the energy density of the battery 2000 can be improved.

The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 are less likely to be short-circuited. When the thickness of the electrolyte layer 202 is 300 μm or less, the battery 2000 can operate with high output.

The negative electrode 203 contains a material having such a property that metal ions (for example, lithium ions) can be intercalated and deintercalated. The negative electrode 203 contains, for example, a negative electrode active material.

As the negative electrode active material, a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like can be used. The metal material may be a simple metal or an alloy. Examples of the metal material include lithium metal and lithium alloy. Examples of the carbon material include natural graphite, coke, graphitizable carbon, carbon fibers, spherical carbon, artificial graphite, amorphous carbon, and the like. The capacity density can be increased by using silicon (Si), tin (Sn), silicon compounds, tin compounds, and the like.

The negative electrode 203 may contain a solid electrolyte. As the solid electrolyte, the solid electrolyte described in embodiment mode 1 can also be used. With the above configuration, the lithium ion conductivity in the negative electrode 203 is improved, and the battery 2000 can operate with high output.

The shape of the anode active material in embodiment 2 is not particularly limited. The shape of the negative electrode active material may be needle-like, spherical, elliptic spherical, or the like, for example. For example, the negative electrode active material may be in the form of particles.

The shape of the solid electrolyte contained in the anode 203 in embodiment 2 is not particularly limited. The solid electrolyte contained in the negative electrode 203 may have a needle shape, a sphere shape, an elliptic sphere shape, or the like, for example. For example, the solid electrolyte contained in the negative electrode 203 may be in the form of particles.

When the solid electrolyte contained in the negative electrode 203 has a particle shape (for example, spherical shape), the solid electrolyte may have a median particle diameter of 100 μm or less. When the median particle diameter of the solid electrolyte is 100 μm or less, a good dispersion state can be formed of the anode active material and the solid electrolyte in the anode 203. This improves the charge/discharge characteristics of the battery 2000.

The median particle diameter of the solid electrolyte contained in the negative electrode 203 may be 10 μm or less or 1 μm or less. With the above configuration, the anode active material and the solid electrolyte can be well dispersed in the anode 203.

The solid electrolyte contained in the negative electrode 203 may have a median particle diameter smaller than that of the negative electrode active material. With the above configuration, the negative electrode active material and the solid electrolyte can be more dispersed in the negative electrode 203.

The median particle diameter of the negative electrode active material may be 0.1 μm or more and 100 μm or less. When the median particle diameter of the anode active material is 0.1 μm or more, the anode active material and the solid electrolyte in the anode 203 can be formed in a good dispersion state. This improves the charge/discharge characteristics of the battery 2000. When the median particle diameter of the negative electrode active material is 100 μm or less, the lithium diffusion rate in the negative electrode active material can be sufficiently ensured. Therefore, the battery 2000 can operate with high output power.

The median particle diameter of the anode active material may also be larger than the median particle diameter of the solid electrolyte contained in the anode 203. Thus, the negative electrode active material and the solid electrolyte can be well dispersed.

The volume ratio "v 2:100-v 2" of the anode active material and the solid electrolyte contained in the anode 203 may satisfy 30.ltoreq.v2.ltoreq.95. Where v2 represents the volume ratio of the anode active material when the total volume of the anode active material and the solid electrolyte contained in the anode 203 is set to 100. When 30.ltoreq.v2 is satisfied, sufficient energy density of the battery 2000 can be ensured. When v2 is satisfied to be 95 or less, the battery 2000 can operate with high output power.

The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, a sufficient energy density of the battery 2000 can be ensured. When the thickness of the negative electrode 203 is 500 μm or less, the battery 2000 can operate with high output.

At least 1 selected from the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder for the purpose of improving the adhesion between particles. The binder is used to improve the adhesion of the materials constituting the electrode. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, ethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, polyhexafluoropropylene, styrene-butadiene rubber, and carboxymethyl cellulose. As the binder, a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropene, fluoromethyl vinyl ether, acrylic acid, and hexadiene can be used. Further, as the binder, a mixture of two or more kinds selected from the above materials may be used.

At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive for the purpose of improving electron conductivity. Examples of the conductive auxiliary agent include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black and ketjen black, conductive fibers such as carbon fibers and metal fibers, metal powder such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxide such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole and polythiophene. When the carbon conductive additive is used, the cost can be reduced.

The shape of the battery 2000 in embodiment 2 includes, for example, coin type, cylinder type, square type, sheet type, button type, flat type, and laminated type.

Examples

Hereinafter, details of the present disclosure will be described with reference to examples and comparative examples.

[ production of sulfide solid electrolyte ]

In an argon glove box with a dew point below-60 ℃ to reach Li ₂ S∶P ₂ S ₅ Raw material powder, li, was weighed in a molar ratio of =75:25 ₂ S and P ₂ S ₅ . The raw material powders were pulverized with a mortar and mixed. Then, the obtained mixture was subjected to a grinding treatment using a planetary ball mill (model P-7, manufactured by the company Fritsch) under conditions of 10 hours and 510 rpm. Thus, a glassy solid electrolyte was obtained. The obtained glassy solid electrolyte was subjected to heat treatment at 270 degrees for 2 hours in an inert atmosphere. Thereby, li in the form of glass ceramic, which is a sulfide solid electrolyte, is obtained ₂ S-P ₂ S ₅ 。

[ production of halide solid electrolyte ]

In an argon glove box with the dew point below-60 ℃ to reach LiBr:YBa ₃ ∶LiCl∶YCl ₃ Raw material powders, i.e., liBr, YBr were weighed in a molar ratio of =1:1:5:1 ₃ LiCl and YCl ₃ . Then, a planetary ball mill (manufactured by Fritsch Co., ltd., type P-7) was used, and grinding treatment was performed at 600rpm for 25 hours. Thereby, li, which is a halide solid electrolyte, is obtained ₃ YBr ₂ Cl ₄ Is a powder of (a).

Example 1

[ production of coated cathode active Material ]

Li (NiCoAl) O was used as the positive electrode active material ₂ (hereinafterRecorded as NCA). As the coating material, the sulfide solid electrolyte produced and the halide solid electrolyte produced were used. In an argon glove box, NCA, sulfide solid electrolyte, and halide solid electrolyte were weighed in a volume ratio of 90:8:2. These materials were put into a dry particle compounding apparatus (NOBILTA, manufactured by Hosokawa Micron Co.) and subjected to compounding treatment at 6500rpm for 30 minutes. Thus, a coating layer composed of a mixture of a sulfide solid electrolyte and a halide solid electrolyte is formed on the surface of the NCA particles. By this method, the coated positive electrode active material of example 1 was obtained.

[ production of Positive electrode Material ]

The produced coated positive electrode active material and the produced halide solid electrolyte were weighed so that the volume ratio reached 100:20. That is, in example 1, a halide solid electrolyte was used as the 1 st solid electrolyte. The positive electrode material of example 1 was produced by mixing them with an agate mortar.

[ production of Battery ]

The conductive auxiliary agent was weighed so that the mass ratio thereof was 100:1.5 with respect to the positive electrode active material contained in the positive electrode material. The binder was weighed so that the mass ratio of the binder to the positive electrode active material contained in the positive electrode material was 100:0.5. Tetrahydronaphthalene (tetralin) was added as a solvent, and mixed by an ultrasonic disperser, thereby obtaining a slurry containing a positive electrode material. The slurry was applied to an aluminum positive electrode current collector and dried to produce a positive electrode of example 1.

Li is used as the negative electrode active material ₄ Ti ₅ O ₁₂ . The anode active material and the sulfide solid electrolyte were weighed in such a manner that the volume ratio reached 65:25. The negative electrode material of example 1 was produced by mixing them with an agate mortar. Using the negative electrode material thus produced, a negative electrode of example 1 was produced in the same manner as the positive electrode.

The electrolyte layer was disposed between the fabricated positive electrode and negative electrode, and the resulting positive electrode and negative electrode were press-molded. After the collector leads are mounted on the laminate of the positive electrode, the electrolyte layer, and the negative electrode, the laminate is put into a laminate package, and the package is sealed. Thus, the battery of example 1 was obtained.

Example 2

In the step of producing the coated positive electrode active material, NCA, sulfide solid electrolyte and halide solid electrolyte were weighed so that the volume ratio became 90:6:4. The procedure was the same as in example 1, except that the battery of example 2 was obtained.

Example 3

In the step of producing the coated positive electrode active material, NCA, sulfide solid electrolyte and halide solid electrolyte were weighed so that the volume ratio became 90:4:6. The procedure was the same as in example 1, except that the battery of example 3 was obtained.

Comparative example 1

In the step of producing the coated positive electrode active material, NCA, sulfide solid electrolyte and halide solid electrolyte are weighed so that the volume ratio reaches 90:10:0. That is, the coating material of comparative example 1 does not contain a halide solid electrolyte. The procedure was the same as in example 1, except that the battery of comparative example 1 was obtained.

Example 4

In the production of the positive electrode material, the produced coated positive electrode active material and the produced sulfide solid electrolyte were weighed so that the volume ratio became 100:20. That is, in example 4, a sulfide solid electrolyte was used as the 1 st solid electrolyte. The procedure was the same as in example 1, except that the battery of example 4 was obtained.

Example 5

In the step of producing the coated positive electrode active material, NCA, sulfide solid electrolyte and halide solid electrolyte were weighed so that the volume ratio became 90:6:4. The procedure was the same as in example 4, except that the battery of example 5 was obtained.

Example 6

In the step of producing the coated positive electrode active material, NCA, sulfide solid electrolyte and halide solid electrolyte were weighed so that the volume ratio became 90:4:6. The procedure was the same as in example 4, except that the battery of example 6 was obtained.

Comparative example 2

In the step of producing the coated positive electrode active material, NCA, sulfide solid electrolyte and halide solid electrolyte are weighed so that the volume ratio reaches 90:10:0. That is, the coating material of comparative example 2 does not contain a halide solid electrolyte. The procedure was the same as in example 4, except that the battery of comparative example 2 was obtained.

(measurement of cell resistance)

The interface resistance ratio of the battery was calculated using the fabricated battery as follows.

The fabricated battery was placed in a constant temperature bath at 25 ℃. The charge was ended by constant-current charging to a voltage of up to 2.7V at a current value of 0.2mA at a rate of 0.1C (10 hour rate) with respect to the theoretical capacity of the battery, and then constant-voltage charging was performed at a voltage of 2.7V, to a current value of 0.02mA at a rate of 0.01C. Then, at a current value of 0.667mA to a 1/3C rate (3.3 hour rate), the constant current was discharged to a voltage of up to 1.5V, and then at a voltage of 1.5V, the constant voltage was discharged to a rate of up to 0.01C.

Then, the charging was performed again under the same conditions, constant current was discharged at a rate of 1/3C to a voltage of up to 2.15V, and then constant voltage was discharged at a voltage of 2.15V to a rate of up to 0.01C. After the stop, constant current discharge was performed for 10 seconds at a current value of 8mA. The dc resistance of the battery calculated by the following equation (3) is described as DCR (Direct Current Resistance).

DCR＝(Vo-V)×S/I (3)

Where Vo is the voltage before discharge for 10 seconds. V is the voltage after 10 seconds of discharge. S is the contact area of the positive electrode and the electrolyte layer. I is a current value of 8mA.

The batteries of examples 1 to 3 and comparative example 1 show the DCR ratio based on the DCR calculated by the above formula (3) together with the volume ratio (%) of the halide solid electrolyte to the coating layer in table 1. The batteries of examples 4 to 6 and comparative example 2 show the DCR ratio based on the DCR calculated by the above formula (3) together with the volume ratio (%) of the halide solid electrolyte to the coating layer in table 2. The DCR ratio in table 1 is a value normalized by taking the DCR of the battery of comparative example 1 as 100. The DCR ratio in table 2 is a value normalized by taking the DCR of the battery of comparative example 2 as 100. Further, DCR represents the internal resistance of the battery. Since the interfacial resistance occupies most of the internal resistance of the battery, the DCR ratio essentially represents the interfacial resistance ratio.

(measurement of fever)

The amount of heat generated by the charged positive electrode was measured by using the positive electrode produced in the battery production step as follows.

First, 80mg of Li was charged as a sulfide solid electrolyte into an insulating outer tube ₂ S-P ₂ S ₅ . The material was subjected to compression molding at a pressure of 360MPa, whereby an electrolyte layer was obtained. Subsequently, metal Li is charged. The negative electrode made of metallic Li was produced by press molding the material at a pressure of 80 MPa. Next, a positive electrode is put into the electrolyte layer on the side opposite to the side in contact with the metal Li. Thus, a laminate including a positive electrode, an electrolyte layer, and a negative electrode in this order is obtained. Current collectors made of stainless steel are disposed on the upper and lower sides of the obtained laminate, and current collecting leads are provided on the current collectors. Finally, the inside of the insulative outer can was isolated from the external atmosphere by using an insulative collar, and sealed, thereby manufacturing a battery.

The fabricated battery was placed in a constant temperature bath at 25 ℃. After charging to 4.2V by constant current charging, the constant voltage is charged to a current value lower than 0.01C. And decomposing the charged battery and taking out the positive electrode. The positive electrode thus extracted was sealed in a SUS-made sealing bag (sealed pan), and the heat generation amount was measured by a differential scanning calorimeter (DSC-6200, manufactured by Seiko Instruments Co.). The heating speed is 10 ℃/min, and the scanning temperature range is normal temperature to 500 ℃. The temperature exceeding the predetermined heat generation amount was measured as the heat generation start temperature (. Degree. C.). The predetermined amount of heat generation is not uniquely determined because it varies depending on the weight of the sample, the type of differential scanning calorimeter used, the volume of the sealing package, the temperature rise rate, and the like. An example of the predetermined amount of heat generation is an amount of heat generation confirmed at a temperature of 100 ℃ or higher, which is clearly larger than the amount of heat generation of the background, and which is an amount of heat generation until the initial heat generation peak is reached. Within this range, the effect of improving heat resistance of the battery of the present disclosure can be sufficiently confirmed.

The measurement results of the heat generation start temperatures (. Degree. C.) are shown in Table 1 for the batteries of examples 1 to 3 and comparative example 1. The measurement results of the heat generation start temperatures (. Degree. C.) of the batteries of examples 4 to 6 and comparative example 2 are shown in Table 2.

Fig. 3 and 4 are diagrams for plotting the results of table 1. Fig. 5 and 6 are diagrams for plotting the results of table 2. Fig. 3 is a graph showing the results of measuring the resistance of the batteries of examples 1 to 3 and comparative example 1. Fig. 5 is a graph showing the results of measuring the resistance of the batteries of examples 4 to 6 and comparative example 2. In fig. 3 and 5, the vertical axis represents the interfacial resistance ratio, and the horizontal axis represents the volume ratio of the halide solid electrolyte to the coating layer. Fig. 4 is a graph showing the measurement results of the heat generation start temperatures of the batteries of examples 1 to 3 and comparative example 1. Fig. 6 is a graph showing the measurement results of the heat generation start temperatures of the batteries of examples 4 to 6 and comparative example 2. In fig. 4 and 6, the vertical axis represents the heat generation start temperature, and the horizontal axis represents the volume ratio of the halide solid electrolyte to the coating layer.

TABLE 1

TABLE 2

Investigation (investigation)

In the coated positive electrode active material, the heating start temperature tends to increase as the volume ratio of the halide solid electrolyte to the coating layer increases.

When the positive electrode active material contained in the positive electrode has oxygen, the structure of the positive electrode active material is not stabilized by charging, and oxygen is easily released from the positive electrode active material. Compared with sulfide solid electrolyte, halide solid electrolyte has excellent thermal stability, low reactivity to oxygen released from the positive electrode active material, and small heat of oxidation reaction. Therefore, when the positive electrode contains a sulfide solid electrolyte and a halide solid electrolyte, the greater the volume ratio of the halide solid electrolyte, the more the thermal stability of the positive electrode is improved. In particular, it is important to suppress reactivity with a solid electrolyte in the vicinity of the positive electrode active material. In the coated positive electrode active material, it is considered that the heat generation start temperature significantly increases with an increase in the volume ratio of the halide solid electrolyte to the coating layer.

On the other hand, in the coated positive electrode active material, the interfacial resistance ratio increases with an increase in the volume ratio of the halide solid electrolyte to the coating layer.

Generally, sulfide solid electrolytes have a smaller young's modulus and higher deformability than halide solid electrolytes. Therefore, when the positive electrode contains a sulfide solid electrolyte, by bringing the positive electrode active material and the sulfide solid electrolyte into close contact, low interface resistance can be achieved. When the positive electrode contains a sulfide solid electrolyte and a halide solid electrolyte, it is considered that the larger the volume ratio of the sulfide solid electrolyte, that is, the smaller the volume ratio of the halide solid electrolyte, the lower the interface resistance can be realized. By increasing the volume ratio of the halide solid electrolyte to the coating layer, the thermal stability of the positive electrode can be improved.

From the above examination, it was found that the use of the coated positive electrode active materials of examples 1 to 6 can achieve both the thermal stability of the positive electrode and the low interfacial resistance in the positive electrode.

As shown in examples 1 to 6, when the volume ratio of the halide solid electrolyte to the coating layer in the coated positive electrode active material is 60% or less, both the thermal stability of the positive electrode and the low interface resistance in the positive electrode can be achieved.

As shown in examples 1 and 2, when a halide solid electrolyte is used as the 1 st solid electrolyte, the interface resistance in the positive electrode can be further reduced while maintaining high thermal stability when the volume ratio of the halide solid electrolyte to the coating layer in the coated positive electrode active material is 40% or less. As shown in examples 4 and 5, when a sulfide solid electrolyte is used as the 1 st solid electrolyte, the interface resistance in the positive electrode can be further reduced while maintaining high thermal stability when the volume ratio of the halide solid electrolyte to the coating layer in the coated positive electrode active material is 40% or less.

As shown in example 1, when the halide solid electrolyte was used as the 1 st solid electrolyte, the heat generation start temperature was 10 ℃ or higher than that of comparative example 1 in which the coating layer did not contain the halide solid electrolyte, even if the volume ratio of the halide solid electrolyte to the coating layer was 20% in the coated positive electrode active material. As shown in example 4, when a sulfide solid electrolyte was used as the 1 st solid electrolyte, even if the volume ratio of the halide solid electrolyte to the coating layer was 20% in the coated positive electrode active material, a heat generation start temperature higher than 25 ℃ was able to be achieved as compared with comparative example 2 in which the coating layer did not contain the halide solid electrolyte.

Industrial applicability

The battery of the present disclosure may be used, for example, as an all-solid lithium secondary battery or the like.

Symbol description:

1000. positive electrode material

101. Positive electrode active material

102. Coating layer

103. Coated positive electrode active material

104. No. 1 solid electrolyte

2000. Battery cell

201. Positive electrode

202. Electrolyte layer

203. Negative electrode

Claims

1. A coated positive electrode active material is provided with:

positive electrode active material

wherein the coating layer contains a sulfide solid electrolyte and a halide solid electrolyte.

2. The coated positive electrode active material according to claim 1, wherein a ratio of a volume of the halide solid electrolyte to a volume of the coating layer is 60% or less.

3. The coated positive electrode active material according to claim 1 or 2, wherein a ratio of a volume of the halide solid electrolyte to a volume of the coating layer is 40% or less.

4. The coated positive electrode active material according to any one of claims 1 to 3, wherein the halide solid electrolyte is represented by the following composition formula (1),

Li _α M _β X _γ (1)

Wherein, alpha, beta and gamma are respectively independent and are values larger than 0,

M contains at least 1 element selected from metal elements other than Li and semi-metal elements,

x contains at least 1 selected from F, cl, br and I.

5. The coated positive electrode active material according to claim 4, wherein the composition formula (1) satisfies 2.5.ltoreq.α.ltoreq.3, 1.ltoreq.β.ltoreq.1.1, and γ=6.

6. The coated positive electrode active material according to claim 4 or 5, wherein M in the composition formula (1) contains yttrium.

7. The coated positive electrode active material according to any one of claims 1 to 6, wherein the coating layer is a single layer.

8. The coated positive electrode active material according to any one of claims 1 to 7, wherein the coating layer contains a mixture of the sulfide solid electrolyte and the halide solid electrolyte.

9. A positive electrode material, comprising:

the coated positive electrode active material according to any one of claims 1 to 8; and

1 st solid electrolyte.

10. The positive electrode material according to claim 9, wherein the 1 st solid electrolyte contains at least 1 selected from a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

11. A battery is provided with:

a positive electrode comprising the positive electrode material according to claim 9 or 10;

a negative electrode; and