JP2024026930A - Positive electrode mixture material and lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode mixture material which can increase rate characteristics of a lithium ion battery.

SOLUTION: A positive mixture material includes: a sulfide solid electrolyte; a material A having electronic conductivity with an average small hole diameter of 10 nm or smaller than 10 nm; a material B as conductive carbon for which a ratio (G/D) of an area of a G-band and an area of a D-band in Laman measurement is at least 0.6; and at least one of elemental sulfur and a discharge product of the elemental sulfur in at least a part of the small holes of the material A. A ratio [S/(A+B)] of total mass (S) of the sulfur of the elemental sulfur and the discharge product of the elemental sulfur to total mass (A+B) of the materials A and B is at least 2.5.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a positive electrode composite material and a lithium ion battery.

Regarding the electric capacity of all-solid-state lithium ion batteries, since the theoretical capacity is large, methods of using sulfur in the positive electrode are being considered. However, since sulfur has low electronic conductivity and low lithium ion conductivity, there is a problem that the discharge capacity at high current density is small (rate characteristic).

To address the above-mentioned problem, a sulfur positive electrode composite material in which activated carbon is impregnated with sulfur and then composited with a solid electrolyte has been studied (see, for example, Patent Documents 1 and 2). Further, a positive electrode composite material in which a fibrous conductive additive such as vapor grown carbon fiber (VGCF) and a sulfur-containing compound are mixed is disclosed (for example, see Patent Document 3). However, there is a need for further improvement in the rate characteristics of lithium ion batteries.

Patent No. 6243103 JP2020-161288A JP2021-26838A

An object of the present invention is to provide a positive electrode mixture that can improve the rate characteristics of lithium ion batteries.

According to the present invention, the following positive electrode composite materials and the like are provided.
1. sulfide solid electrolyte,
An electronically conductive material A having an average pore radius of 10 nm or less;
Material B is conductive carbon with a ratio of G band area to D band area (G/D) in Raman measurement of 0.6 or more;
At least one of elemental sulfur and discharge products of elemental sulfur present in at least a portion of the pores of the material A,
A positive electrode, wherein the ratio [S/(A+B)] of the total mass (S) of the elemental sulfur and the sulfur of the discharge product of elemental sulfur to the total mass (A+B) of the materials A and B is 2.5 or more. Composite material.
2. The ratio of the total mass of the material A, the material B, the elemental sulfur and the sulfur of the discharge product of the elemental sulfur (A:B:S) is 5 to 15:1 to 10:30 to 50. The positive electrode composite material described in 1.
3. 3. The positive electrode composite material according to 1 or 2, wherein the material A has an average pore radius of less than 5 nm.
4. 4. The positive electrode composite material according to any one of 1 to 3, wherein the material A is a porous carbon material.
5. 5. The positive electrode composite material according to any one of 1 to 4, wherein the material B has a micropore amount of 0.1 cc/g or less.
6. 6. The positive electrode composite material according to any one of 1 to 5, wherein the material B is carbon fiber.
7. 7. The positive electrode composite material according to any one of 1 to 6, wherein the ratio of the area of the G band to the area of the D band (G/D) in Raman measurement of the material A is less than 0.6.
8. 8. The positive electrode composite material according to any one of 1 to 7, wherein the total pore volume of the material A and the material B is 1.0 cc/g or more.
9. The positive electrode composite material according to any one of 1 to 8, wherein the total sulfur content of the elemental sulfur and the discharge product of the elemental sulfur is 1.0 cc or more per 1 g of the total mass of the material A and the material B. .
10. 10. The positive electrode composite material according to any one of 1 to 9, wherein the total sulfur content of the elemental sulfur and the discharge product of the elemental sulfur is 70% or more of the total pore volume of the material A and the material B.
11. A positive electrode for a lithium ion battery, comprising the positive electrode composite material according to any one of items 1 to 10.
A lithium ion battery comprising the positive electrode for a lithium ion battery according to 12.11.
13. A step of heating material A having electronic conductivity with an average pore radius of 10 nm or less and elemental sulfur at a temperature equal to or higher than the melting point of the elemental sulfur to form a material A-elementary sulfur composite powder;
The material A - elemental sulfur composite powder, the material B which is conductive carbon with a G band area/D band area of 0.6 or more in Raman measurement, and a sulfide solid electrolyte are mixed, and a positive electrode is formed. A method for producing a positive electrode composite material, including a step of making it into a material.

According to the present invention, it is possible to provide a positive electrode composite material that can improve the rate characteristics of a lithium ion battery.

1 is an SEM image of a cross section of the positive electrode composite material produced in Example 1.

1. Positive electrode composite material A positive electrode composite material according to an embodiment of the present invention includes a sulfide solid electrolyte, a material A having electron conductivity with an average pore radius of 10 nm or less, and the area of the G band and the D band in Raman measurement. Material B is conductive carbon having an area ratio (G/D) of 0.6 or more. and at least one of elemental sulfur and discharge products of elemental sulfur present in at least a part of the pores of material A, and elemental sulfur and at least one of the discharge products of elemental sulfur, and The ratio (S/A+B) of the total mass (S) of the discharge products of elemental sulfur in terms of sulfur is 2.5 or more.

In this embodiment, it is presumed that material A has the function of holding elemental sulfur and discharge products of elemental sulfur and smoothly supplying electrons and ions by keeping the particle sizes of these elements small. On the other hand, material B facilitates electron conductivity to the entire positive electrode due to its high electron conductivity due to its high degree of graphitization, and is therefore presumed to contribute to improving the rate characteristics.

In addition, in this embodiment, elemental sulfur or a discharge product of elemental sulfur existing in a part of the pores of material A is included, and elemental sulfur and elemental sulfur are The ratio (S/A+B) of the total mass (S) of the sulfur discharge products in terms of sulfur is 2.5 or more. This requirement means that the amount of elemental sulfur contained in the positive electrode mixture is large, and a battery with high energy density can be obtained.

In one embodiment, the aspect ratio of material B is 5 or more. By using two types of materials A and B with different shapes, even if a small amount of materials A and B are added to sulfur, which does not have electronic conductivity or ionic conductivity, electronic conductivity can be imparted uniformly. be able to. Furthermore, since sulfur can be maintained in a finely divided state where lithium ions are easily supplied, the rate characteristics of the battery can be improved while increasing the sulfur content in the positive electrode mixture.

Since material A has pores, it is presumed that elemental sulfur can be highly dispersed. On the other hand, since elemental sulfur is insulating, a large content inhibits electron movement within the positive electrode. When the aspect ratio of material B is large, electron transfer over a longer distance can be achieved compared to material A even if the content of elemental sulfur is large. From the above effects, it is estimated that a lithium ion battery using the positive electrode mixture of this embodiment as a positive electrode has improved rate characteristics.
The constituent members of this embodiment will be explained below.

[Material A]
Material A is not particularly limited as long as it has electron conductivity and has pores with an average pore radius of 10 nm or less.
In one embodiment, the average pore radius of the pores that material A has is preferably 7 nm or less, more preferably less than 5 nm, and even more preferably 4 nm or less. The smaller the average pore radius, the greater the rate characteristic improvement effect. Although the lower limit of the average pore radius of the pores of material A is not particularly limited, it is usually 0.1 nm or more.

In one embodiment, material A is preferably a porous carbon material.
Preferred examples of the porous carbon material include carbon black such as Ketjenblack (registered trademark), activated carbon, Knobel (registered trademark), and the like. Among these, activated carbon is preferred. These may be used alone or in combination of two or more.

In one embodiment, the pore volume of material A is preferably 1.0 cc (mL)/g or more. This increases the amount of sulfur that can be retained, leading to an increase in the energy density of the battery. The pore volume of material A is more preferably 1.5 cc/g or more, further preferably 2.0 cc/g or more. The pore volume of the electronically conductive material A is usually 10 cc/g or less.

In the present invention, the average pore radius and pore volume can be measured by the Brennauer-Emmet-Telle (BET) method or the BJH method (Barrett-Joyner-Halenda method).
Specifically, it can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas to the electron conductive material A under liquid nitrogen temperature.
As a measuring device, for example, a specific surface area/pore distribution measuring device (Autosorb-3) manufactured by Quantacrome can be used.

[Elementary sulfur]
Although there is no particular limitation on the elemental sulfur (sulfur), the purity is preferably 95% by mass or more, more preferably 96% by mass or more, and particularly preferably 97% by mass or more.
Examples of crystal systems of elemental sulfur include α sulfur (orthorhombic system), β sulfur (monoclinic system), γ sulfur (monoclinic system), amorphous sulfur, and the like. These may be used alone or in combination of two or more. Elemental sulfur becomes a melt when heated.

Part or all of elemental sulfur is converted into a discharge product during a battery reaction. Therefore, in the positive electrode mixture (positive electrode) of one embodiment, a discharge product of elemental sulfur is present. When discharge products are present, the sulfur contained in the positive electrode mixture is the total amount of elemental sulfur and sulfur contained in the discharge products.
Examples of discharge products of elemental sulfur include Li ₂ S in a fully discharged state and polysulfide lithium in an intermediate stage such as Li ₂ S ₂ , Li ₂ S ₄ , Li ₂ S ₆ , and Li ₂ S ₈ .

In the positive electrode composite material, part or all of the elemental sulfur is impregnated into the pores of material A. Elemental sulfur that is not impregnated into the pores is present so as to cover part or all of materials A and B. To determine whether the pores of material A are impregnated with sulfur, analyze the particle cross section of material A using an analysis method that allows elemental mapping such as SEM-DES or TEM-EDX, and check the elements and sulfur derived from material A. This can be confirmed by evaluating the overlap of elements.
In one embodiment, since the content of elemental sulfur in the positive electrode composite material is large, elemental sulfur also exists outside the pores of material A. In this case, the composite of elemental sulfur and material A becomes a pellet-like lump, but it can be turned into powder by mechanically crushing it.

[Material B]
Material B is conductive carbon, and the ratio of the area of G band to the area of D band (G/D) in Raman measurement, which indicates the degree of graphitization of the carbon material, is 0.6 or more.
The area of the G band is the area of the peak between 1800 cm ⁻¹ and 1475 cm ⁻¹ , and the area of the D band is the area of the peak between 1475 cm ⁻¹ and 700 cm ⁻¹ . The area of the D band indicates the amount of defects in the carbon material. A carbon material having the ratio (G/D) of 0.6 or more is graphitized, and therefore can be expected to have high electrical conductivity. The ratio (G/D) is more preferably 0.7 or more, more preferably 1.0 or more, 1.5 or more, and even more preferably 2.0 or more. In addition, the ratio (G/D) is infinite since there is no D band in completely defect-free graphite, but it is usually 100 or less, and preferably 10 or less.
The area of G band and the area of D band in Raman measurement are measured by the method described in Examples.

In one embodiment, the ratio (G/D) in Raman measurements of material A is less than 0.6, preferably less than 0.55. Being less than 0.6 means that material A has a moderate defect structure, and Li ion conduction within the material through the defects can be expected. It can also be expected that sulfur will be more likely to be impregnated from defective parts and the like.
For example, in a carbon material such as diamond that does not have a graphite structure, the G band does not appear, so the ratio (G/D) is 0, but as a conductive material, the ratio (G/D) is preferably 0.1 or more, and 0.2 or more. More preferred. When it is 0.1 or more, material A contains an appropriately developed graphite structure, and suitable electronic conductivity can be obtained.

In one embodiment, the aspect ratio of material B is 5 or more, preferably 10 or more, and more preferably 15 or more. The higher the aspect ratio, the more electronic conductivity can be imparted to the entire electrode with a smaller amount of material. The aspect ratio of material B is preferably 5,000 or less, more preferably 3,000 or less, and even more preferably 2,000 or less. If the aspect ratio is too high, it will lead to a decrease in the bulk density of the powder, which will increase transportation costs and also lead to a decrease in mixability.

The aspect ratio of material B is calculated by the following formula.
Aspect ratio of material B=average fiber length of material B/average fiber diameter of material B The aspect ratio is evaluated by an appropriate method depending on the size of the material. For example, a scanning electron microscope (SEM) can be used.

As material B, carbon fiber is preferable. Examples of carbon fibers include carbon nanotubes, vapor grown carbon fibers (VGCF), and the like. In addition, acetylene black, Denka Black (registered trademark), thermal black, channel black, etc., which have a structured structure and function as a conductive additive with a substantially high aspect ratio, and graphene, which is an electron conductor on a flat plate, Reduced graphene, flaky graphite, etc. can also be used as material B.
These may be used alone or in combination of two or more.

The average fiber length of material B is preferably 3 μm or more, more preferably 5 μm or more. Further, the average fiber length of material B is preferably 500 μm or less, more preferably 100 μm or less. By adjusting the average fiber length in this manner, electronic conductivity can be imparted to the entire electrode with a small amount of material.

The average fiber diameter of material B is preferably 2 nm or more, more preferably 5 nm or more. Further, the average fiber diameter of material B is preferably 1000 nm or less, more preferably 300 nm or less. By adjusting the average fiber diameter in this way, electron conductivity can be imparted to the entire electrode even with a small mixing amount while maintaining sufficient electron conduction.

In one embodiment, material B has a micropore content of 0.1 cc/g or less. Here, micropores generally mean pores with a pore diameter of 2 nm or less. When the amount of micropores is 0.1 cc/g, it is assumed that material B has substantially no micropores. The amount of micropores in material B is more preferably 0.05 cc/g or less. Since material B has no internal pores, it has high electronic conductivity, so it can impart electronic conductivity to the entire positive electrode with a small amount added.
The amount of micropores can be analyzed from the nitrogen adsorption isotherm of material B using t-plot. In addition, the absence of sulfur-containing micropores can also be determined by evaluating the presence or absence of non-overlapping particles of C and S using analysis methods that allow elemental mapping such as SEM-EDS and TEM-EDX. can.

[Sulfide solid electrolyte]
The sulfide solid electrolyte is a solid electrolyte that contains at least a sulfur atom and exhibits ionic conductivity due to the metal atoms contained.In addition to the sulfur atom, it preferably contains a lithium atom and a phosphorus atom, and more preferably a lithium atom. It is a solid electrolyte that contains lithium atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to lithium atoms.
The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte.

(Amorphous sulfide solid electrolyte)
As the amorphous sulfide solid electrolyte, any material that contains at least a sulfur atom and exhibits ionic conductivity due to the metal atoms contained can be used without any particular restriction, and representative examples include, for example: , Li ₂ SP ₂ S ₅ - Solid electrolyte containing sulfur atoms, lithium atoms, and phosphorus atoms, composed of lithium sulfide and phosphorus sulfide; Li ₂ SP ₂ S ₅ -LiI, Li ₂ S- A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -LiBr, Li ₂ S-P ₂ S ₅ -LiI-LiBr; Further, solid electrolytes containing other elements such as oxygen element and silicon element, such as Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, are preferable. Can be mentioned. From the viewpoint of obtaining higher ionic conductivity, Li ₂ S-P ₂ S ₅ -LiI, Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -LiBr, Li ₂ S-P ₂ S A solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as ₅ -LiI-LiBr, is preferred.
The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed using, for example, an ICP emission spectrometer.

When the amorphous sulfide solid electrolyte has at least Li ₂ S-P ₂ S ₅ , the molar ratio of Li ₂ S and P ₂ S ₅ has high chemical stability and higher ionic conductivity. From the viewpoint of obtaining a high degree of strength, the ratio is preferably 30 to 85:15 to 70, more preferably 40 to 80:20 to 60, and even more preferably 45 to 78:22 to 55.
When the amorphous sulfide solid electrolyte is, for example, Li ₂ SP ₂ S ₅ -LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 30 to 95 mol%, and 35 It is more preferably 90 mol%, and even more preferably 40 to 85 mol%. Further, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and even more preferably 50 to 70 mol%. % is particularly preferred.

When the amorphous sulfide solid electrolyte contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, the blending ratio (molar ratio) of these atoms is 1.0 to 1.8:1.0 to 2. 0:0.1~0.8:0.01~0.6 is preferable, 1.1~1.7:1.2~1.8:0.2~0.6:0.05~0. 5 is more preferred, and 1.2-1.6: 1.3-1.7: 0.25-0.5: 0.08-0.4 is even more preferred.
In addition, when bromine and iodine are used together as halogen atoms, the blending ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine atoms, and iodine atoms is 1.0-1.8:1.0- 2.0:0.1~0.8:0.01~0.3:0.01~0.3 is preferable, 1.1~1.7:1.2~1.8:0.2~ 0.6:0.02~0.25:0.02~0.25 is more preferable, 1.2~1.6:1.3~1.7:0.25~0.5:0.03 ~0.2:0.03~0.2 is more preferable, 1.35~1.45:1.4~1.7:0.3~0.45:0.04~0.18:0. 04 to 0.18 is more preferable. By setting the blending ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, a solid electrolyte with higher ionic conductivity having a thiolithicone region II type crystal structure described below can be obtained. It becomes easier.

Further, the shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D ₅₀ ) of the particulate amorphous sulfide solid electrolyte can be, for example, within the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.
In this specification, the average particle diameter (D ₅₀ ) is the particle diameter that reaches 50% of the total when a particle diameter distribution integration curve is drawn, and is accumulated sequentially from the smallest particle diameter, and the volume distribution is , for example, is an average particle size that can be measured using a laser diffraction/scattering particle size distribution measuring device.

(Crystalline sulfide solid electrolyte)
The crystalline sulfide solid electrolyte may be, for example, a so-called glass ceramic obtained by heating the above-mentioned amorphous sulfide solid electrolyte above the crystallization temperature, and a sulfide solid electrolyte having the following crystal structure: can be adopted.
Examples of crystal structures that the crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, and phosphorus atoms may have include Li ₃ PS ₄ crystal structure, Li ₄ P ₂ S ₆ crystal structure, Li ₇ PS ₆ crystal structure, and Li ₇ Examples include a P ₃ S ₁₁ crystal structure, a crystal structure having peaks near 2θ=20.2° and near 23.6° (for example, Japanese Patent Application Publication No. 2013-16423).

In addition, as a crystal structure that a crystalline sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms can have, Li _4-x Ge _1-x P _x S _4- based thio-silicone region II (thio- LISICON Region II) type crystal structure (see Kanno et al., Journal of The Electrochemical Society, 148(7) A742-746 (2001)), Li _4-x Ge _{1 -x P} hio- LISICON Region II) type (see Solid State Ionics, 177 (2006), 2721-2725), and the like. Here, "thio-LISICON Region II type crystal structure" refers to Li _4-x Ge _1-x P _x S ₄ -based thio-LISICON Region II (thio-LISICON Region II) type crystal structure, Li _4-x Ge _1-x Indicates that it has a crystal structure similar to P _x S ₄ -based thio-LISICON Region II (thio-LISICON Region II) type.

In X-ray diffraction measurement using CuKα rays, the diffraction peaks of the Li ₃ PS ₄ crystal structure are, for example, around 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. The diffraction peaks of the Li ₄ P ₂ S ₆ crystal structure appear, for example, around 2θ=16.9°, 27.1°, and 32.5°, and the diffraction peaks of the Li ₇ PS ₆ crystal structure appear, for example, around 2θ = 15.3°, 25.2°, 29.6°, 31.0°, and the diffraction peaks of the Li ₇ P ₃ S ₁₁ crystal structure are, for example, 2θ = 17.8°, 18.5°, It appears around 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li _4-x Ge _1-x P _x S _4- based thiolysicone region II The diffraction peaks of the (thio-LISICON Region _II ) type crystal structure appear, for example, around 2θ ₌ 20.1°, _23.9 °, and _29.5 °. Diffraction peaks of a crystal structure similar to thio-LISICON Region II type appear, for example, around 2θ=20.2° and 23.6°. Note that these peak positions may be different within a range of ±0.5°.

Furthermore, the crystal structure of the crystalline sulfide solid electrolyte includes an argyrodite crystal structure. Examples of the argyrodite crystal structure include Li ₇ PS ₆ crystal structure; compositional formulas Li _{7 -x} P _{1 -y} Si _y S ₆ and Li _7+x P _1-y Si _y S _{6 having a structural skeleton of Li 7 PS 6} ; (x is -0.6 to 0.6, y is 0.1 to 0.6); Li _7-x-2y PS _6-x-y Cl _x (0.8≦x≦1 .7, 0<y≦-0.25x+0.5); Li _7-x PS _6-x Ha _x (Ha is Cl or Br, x is preferably 0.2 to 1.8); The crystal structure shown is mentioned.

Among the above crystal structures, preferred crystal structures of the crystalline sulfide solid electrolyte include Li ₃ PS ₄ crystal structure, thiolisicone region II type crystal structure, and argyrodite type crystal structure.

The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle size (D ₅₀ ) of the particulate crystalline sulfide solid electrolyte is similar to the average particle size (D ₅₀ ) of the amorphous sulfide solid electrolyte described above, for example, from 0.01 μm to 500 μm, 0. An example is a range of .1 to 200 μm.

[Mixing ratio]
In the positive electrode composite material of this embodiment, the content of material B is preferably 20 to 200 parts by mass, more preferably 30 to 100 parts by mass, when material A is 100 parts by mass. By satisfying the above range, the conductivity within the positive electrode mixture can be maintained high and the rate characteristics can be easily improved.

Further, the ratio [S/(A+B)] of the total mass (S) of elemental sulfur and discharge products of elemental sulfur in terms of sulfur to the total mass (A+B) of materials A and B is 2.5 or more. The ratio [S/(A+B)] is preferably 3 or more. The higher the ratio of elemental sulfur in the positive electrode mixture, the higher the energy density of the battery can be expected as long as the utilization rate of sulfur is the same. On the other hand, since it becomes difficult to provide sufficient electron conduction within the positive electrode, the ratio [S/(A+B)] is preferably 10 or less, more preferably 5 or less.

The mass ratio (A:B:S) of material A, material B, and the total mass (S) in terms of sulfur of elemental sulfur and discharge products of elemental sulfur is 5 to 15:1 to 10:30 to 50. The ratio is preferably 5 to 10:2 to 8:35 to 45, particularly preferably 7 to 10:3 to 8:35 to 45. This provides a good balance between the effect of improving the efficiency of ionic conduction and electron conduction by filling the pores of material A with sulfur and retaining it as small particles, and the effect of material B imparting electronic conductivity to the entire electrode. It functions well and provides good battery characteristics.

The content of the sulfide solid electrolyte is preferably 5 to 200 parts by mass, more preferably 10 to 120 parts by mass, when the total of material A, material B, and elemental sulfur is 100 parts by mass. . If the solid electrolyte content is less than 5 parts by mass, it will be difficult to obtain sufficient ionic conduction, and if the solid electrolyte content is 200 parts by mass or more, the active material content will decrease, making it difficult to improve energy density. .

In one embodiment, the total content in terms of sulfur of elemental sulfur and discharge products of elemental sulfur in the positive electrode mixture is preferably 1.0 cc or more, more preferably 1.5 cc or more per 1 g of materials A and B in total. , more preferably 2.0 cc or more. Further, the total content of elemental sulfur and discharge products of elemental sulfur in terms of sulfur is preferably 10 cc or less, more preferably 5.0 cc or less, and even more preferably 4.0 cc or less per 1 g of the above materials A and B in total. . By setting it within the above range, the content of elemental sulfur becomes sufficient, and the rate characteristics tend to improve.
In addition, when converting, the density of elemental sulfur is assumed to be 2 g/cc.

In one embodiment, the total content in terms of sulfur of elemental sulfur and discharge products of elemental sulfur in the positive electrode composite material is preferably 70% or more of the total pore volume of material A and material B, and more preferably 100% or more. Preferably, 120% or more is more preferable. As a result, the content of elemental sulfur is sufficient, and high energy density can be obtained. The total content of elemental sulfur and the discharge product of elemental sulfur in terms of sulfur is preferably 300% or less, more preferably 200% or less, and even more preferably 170% or less of the total pore volume of material A and material B.
The total pore volume of material A and material B can be calculated from the charged amounts (g) of materials A and B and the pore volume (cc/g) described above.

In one embodiment, the positive electrode mixture may or may not contain components other than the sulfur-based active material, solid electrolyte, and conductive aid. Other components are not particularly limited, and include, for example, a binder, a solvent, and a dispersant.
The positive electrode composite material of this embodiment can be manufactured, for example, by the manufacturing method of the invention described below.

2. Method for manufacturing positive electrode composite material A method for manufacturing a positive electrode composite material according to an embodiment of the present invention includes the following steps (1) and (2).
Step (1): Material A having electron conductivity with an average pore radius of 10 nm or less and elemental sulfur are heated at a temperature equal to or higher than the melting point of the elemental sulfur to form material A-elementary sulfur composite powder. Process Process (2): Mix material A - elemental sulfur composite powder, material B which is conductive carbon with a G band area/D band area of 0.6 or more in Raman measurement, and a sulfide solid electrolyte. The process of making a positive electrode composite material

[Step (1)]
In step (1), for example, material A and elemental sulfur are mixed and sealed, and then the mixture is heated to melt the elemental sulfur and impregnate the pores with elemental sulfur, thereby forming the material A-elementary sulfur composite. Manufacture powder.

In step (1), the mixing ratio of material A and elemental sulfur can be adjusted as appropriate depending on the materials used.
In one embodiment, as described above, the content of elemental sulfur is preferably 1.0 cc or more per 1 g of material A. Further, it is preferable that the content of elemental sulfur is 10 cc or less per 1 g of material A.
In one embodiment, the content of elemental sulfur is preferably 70% or more of the total pore volume of material A. Moreover, it is preferable to set it to 300% or less of the total pore volume.

A mixture of material A and elemental sulfur is heated at a temperature higher than the melting point of elemental sulfur (approximately 115°C). The heating temperature is adjusted depending on the material A and the elemental sulfur, but is preferably 130°C or higher, more preferably 150°C or higher. The upper limit of the heating temperature is a temperature below the boiling point of elemental sulfur (about 445°C). The heating time is preferably 0.1 to 24 hours.
By cooling after heating, material A-elementary sulfur composite powder is obtained. If necessary, a pulverization step may be performed after cooling.

[Step (2)]
In step (2), material A - elemental sulfur composite powder, material B which is conductive carbon with a G band area/D band area of 0.6 or more in Raman measurement, and a sulfide solid electrolyte are mixed. Then, prepare a positive electrode composite material.
For example, after the above step (1), material A-element sulfur composite powder and material B are mixed while applying mechanical stress to form a positive electrode composite material. Here, "applying mechanical stress" means mechanically applying shearing force, impact force, etc. Examples of means for applying mechanical stress include pulverizers such as planetary ball mills, vibration mills, and rolling mills, and kneaders.
A part of materials A and B may be crushed by this step.

In one embodiment, the blending amount of material B is preferably 20 to 200 parts by mass based on 100 parts by mass of material A, as described above.
Further, the amount of the sulfide solid electrolyte to be blended is preferably 5 to 200 parts by mass based on the total of 100 parts by mass of material A, material B, and elemental sulfur.

As for mixing conditions, for example, when a planetary ball mill is used, the rotation speed may be several tens to several hundreds of revolutions/minute, and the treatment may be performed for 0.5 hours to 100 hours. More specifically, in the case of the planetary ball mill (manufactured by Fritsch, model number P-5) used in the Examples of the present application, the rotation speed of the planetary ball mill is preferably 100 rpm or more and 600 rpm or less, and more preferably 150 rpm or more and 400 rpm or less.
For example, when a zirconia ball is used as the grinding media, the diameter thereof is preferably 0.2 to 20 mm.

In one embodiment, the positive electrode composite material can be manufactured by mixing the material A-elementary sulfur composite powder and material B, and then adding a sulfide solid electrolyte and mixing them again.

In one embodiment, the positive electrode mixture may be heated after the step of mixing the material A-elementary sulfur composite powder and material B. It is possible to improve battery characteristics by improving ionic conductivity by crystallizing the solid electrolyte whose crystallinity has decreased in the mixing process again or by forming an interface by heating.

Although the heating temperature and time can be adjusted as appropriate depending on the type of solid electrolyte, for example, when the crystallization temperature of the solid electrolyte is 200° C. or lower, the heat treatment is performed in accordance with the crystallization temperature of the solid electrolyte. If the intercrystalline temperature of the solid electrolyte is high, such as 300°C or higher, heating at around 200°C, where excessive sulfur evaporation does not occur, will reform the interface, although it will not result in crystallization. I can.

The heating temperature is not limited as it varies depending on the type of solid electrolyte as described above, but is, for example, 250°C or lower, preferably 200°C or lower. The lower the temperature, the more suppressed sulfur transpiration can be. The heating temperature is 50°C or higher, preferably 100°C or higher, and more preferably 120°C or higher. The heating time is not particularly limited, but is, for example, 1 minute to 99 hours, preferably 10 minutes to 10 hours, particularly preferably 30 minutes to 3 hours.

Further, the timing of heating may be immediately after forming the composite material, or heating may be performed after the composite material is processed into an electrode sheet by a method such as slurry casting using a solvent or electrostatic coating. In the case of production by slurry casting, it is also possible to reduce the number of steps by heating for crystallization at the same time as removing the solvent.

3. Lithium Ion Battery A lithium ion battery according to one embodiment of the present invention includes the positive electrode composite material of the present invention described above. For example, by using a solid electrolyte in place of a liquid electrolyte, an all-solid-state lithium ion battery can be manufactured. By using the positive electrode mixture of the present invention, an all-solid-state lithium ion battery with good rate characteristics can be produced.

An all-solid-state lithium ion battery mainly consists of a positive electrode layer, a negative electrode layer, and an electrolyte layer, and the positive electrode composite material of the present invention is suitable as a constituent material of the positive electrode layer. The negative electrode layer and the electrolyte layer can be manufactured by known methods. Further, in addition to the positive electrode layer, negative electrode layer, and electrolyte layer, a current collector is preferably used, and a known current collector is also used.
Although the solid electrolyte is not particularly limited, examples thereof include the sulfide solid electrolyte described above.

Hereinafter, the present invention will be specifically explained based on Examples. The invention is not limited to the examples.
The ratio of the area of the G band to the area of the D band (G/D) in Raman measurements of materials A and B was determined under the following conditions.
<Measurement conditions>
Equipment: DXR2 (Thermo Fisher Scientific Co., Ltd.)
Exposure time: 10 seconds Integration number: 20 times Background: 20 times Laser wavelength: 532 nm
Laser power: 3.0mW
Pinhole: 25μm pinhole Resolution: HIGH RES GRATING
Measurement range: 50-1800cm ^-1
Measurement magnification: 50x objective lens

The baseline was a straight line passing through two points near 700 and 1800 cm ⁻¹ that had no structure-derived peaks. If there is a peak at the above wave number, a nearby wave number that does not have a peak can be used as the starting point of the baseline.
For 1475 cm ^-1 , which separates the G band and D band, the wave number that takes the minimum value of each Raman spectrum from 1400 to 1550 cm ^-1 was calculated, and the wave number was adopted as the average value.

(Example 1)
(1) Preparation of activated carbon-elementary sulfur composite powder In a glass bottle, activated carbon (manufactured by Kansai Thermal Chemical Co., Ltd., MSC-30, pore volume 1.67 cc/g, average pore radius 1.12 nm) as material A, Elemental sulfur was added at a mass ratio of 1:5 and sealed in a SUS tube container. The mixture was heated in an electric furnace at 150°C for 6 hours and at 300°C for 2.75 hours to obtain activated carbon-elementary sulfur composite powder.
The pore volume of activated carbon is 1.67 cc/g, and when calculated assuming that the density of elemental sulfur is 2 g/cc, the content of elemental sulfur per 1 g of activated carbon is 2.5 cc. From the above, the content (amount) of elemental sulfur is 150% (volume) of the total pore volume of activated carbon.
Regarding the activated carbon-elementary sulfur composite powder, a particle cross section was formed by ion milling, and the cross section was observed using SEM-EDS. As a result, sulfur element was observed in the carbon, indicating that elemental sulfur was impregnated into the pores of the activated carbon. It was confirmed that
The average pore radius and pore volume of the activated carbon were measured using a pore distribution measuring device (Autosorb-3) manufactured by Quantacrome.

(2) Preparation of solid electrolyte Lithium sulfide 0.4127g, diphosphorus pentasulfide 0.6655g, lithium iodide 0.2137g, lithium bromide 0.2080g, 10 zirconia balls with a diameter of 10 mm, and 45 mL of zirconia balls. Pour it into a pot and seal it. Using a planetary ball mill (manufactured by Fritsch, model number P-7), the mixture was mixed (mechanical milling) for 40 hours at a rotation speed of 370 rpm to obtain a powder. The obtained powder was heated at 195° C. for 3 hours to obtain a solid electrolyte.

(3) Preparation of positive electrode mixture 0.45 g of activated carbon-elementary sulfur composite powder obtained in (1) above, 0.5 g of solid electrolyte obtained in (2) above, and vapor-grown multi-walled carbon nanotubes (VGCF (registered) Trademark), manufactured by Showa Denko K.K., average fiber length 6 μm, average fiber diameter 150 nm, aspect ratio 40, micropore amount by t-plot method 0 cc/g) 0.05 g, along with 10 zirconia balls with a diameter of 10 mm. , into a 45 mL zirconia pot and sealed (Material A + Material B: Sulfur = 1:3 (mass ratio), Material A: Material B: Sulfur = 7.5:5:37.5 (mass ratio)) .
Mixing was performed using a planetary ball mill (manufactured by Fritsch, model number P-7) at a rotation speed of 370 rpm for 20 hours at room temperature to obtain a positive electrode composite powder.

(4) Preparation of all-solid-state lithium ion battery 100 mg of the solid electrolyte prepared in the above (2) was charged into a Macol (registered trademark) cylinder having a diameter of 10 mm, and the battery was pressure-molded. The positive electrode composite powder prepared in (3) above was placed on the pressurized surface so that the content of elemental sulfur was 1.75 mg, and pressure molding was performed again. An all-solid-state battery was fabricated by placing indium foil and lithium foil on the pressurized side opposite to the positive electrode mixture and applying pressure.

(Example 2)
Except that the activated carbon (MSC-30) in Example 1 was changed to a porous carbon material (CNovel (registered trademark), manufactured by Toyo Tanso Co., Ltd., pore volume 3.09 cc/g, average pore radius 4.27 nm). A positive electrode composite powder was obtained in the same manner as in Example 1.
The content of elemental sulfur is 81% of the total pore volume.
As a result of observing the cross section of the porous carbon material-elementary sulfur composite powder using SEM-EDS in the same manner as in Example 1, it was confirmed that elemental sulfur was impregnated into the pores of the porous carbon material.
An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Example 3)
Example 1 except that the activated carbon (MSC-30) in Example 1 was changed to carbon black (Ketjen Black (registered trademark), KB, pore volume 4.33 cc/g, average pore radius 6.64 nm). Similarly, a positive electrode composite powder was obtained. The content of elemental sulfur is 58% of the pore volume.
As a result of observing the cross section of the carbon black-elementary sulfur composite powder using SEM-EDS in the same manner as in Example 1, it was confirmed that elemental sulfur was impregnated into the pores of the carbon black.
An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Comparative example 1)
In Example 1 (3), without adding vapor grown multi-walled carbon nanotubes (VGCF (registered trademark)), 0.5 g of activated carbon-elementary sulfur composite powder, 0.5 g of solid electrolyte, and zirconia with a diameter of 10 mm were used. A positive electrode composite powder was obtained in the same manner as in Example 1 except that it was placed in a zirconia pot together with 10 balls (Material A + Material B: Sulfur = 1:5 (mass ratio), Material A: Material B: Sulfur = 8.3:0:41.7 (mass ratio)). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Comparative example 2)
In Example 1 (3), without using activated carbon-elementary sulfur composite powder, 0.125 g of VGCF, 0.375 g of sulfur, 0.5 g of solid electrolyte, and 10 zirconia balls with a diameter of 10 mm were used together with zirconia. A positive electrode composite powder was obtained in the same manner as in Example 1 except that it was put into a pot for making (material A + material B: sulfur = 1:3 (mass ratio), material A: material B: sulfur = 0:12. 5:37.5 (mass ratio)). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Comparative example 3)
In Example 1 (3), 0.075 g of acetylene black (AB, carbon material without pores, granular Denka Black manufactured by Denka Co., Ltd.) and 0.0 g of VGCF were used without using the activated carbon-elementary sulfur composite powder. A positive electrode composite powder was obtained in the same manner as in Example 1, except that 050 g of sulfur, 0.375 g of sulfur, and 10 zirconia balls each having a diameter of 10 mm were added to a zirconia pot (Material A + Material B: Sulfur = 1: 3 (mass ratio), material A: material B: sulfur = 0:12.5:37.5 (mass ratio)). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Comparative example 4)
In Example 1 (1), the activated carbon (MSC-30) was changed to carbon black (Ketjen Black (registered trademark), KB, pore volume 4.33 cc/g, average pore radius 6.64 nm). A carbon black-sulfur composite powder was produced in the same manner. The content of elemental sulfur is 58% of the total pore volume.
In Example 1 (3), 0.5 g of carbon black-elementary sulfur composite powder, 0.5 g of solid electrolyte, and zirconia with a diameter of 10 mm were used without adding vapor-grown multi-walled carbon nanotubes (VGCF (registered trademark)). A positive electrode composite powder was obtained in the same manner except that it was put into a zirconia pot together with 10 balls (Material A + Material B: Sulfur = 1:5 (mass ratio), Material A: Material B: Sulfur = 8 .3:0:41.7 (mass ratio)). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Example 4)
In Example 1 (3), acetylene black (AB, carbon material without pores, Denka Black granules manufactured by Denka Co., Ltd., t-plot method) was used instead of vapor-grown multi-walled carbon nanotubes (VGCF (registered trademark)). 0.05 g of micropore volume (0 cc/g), 0.45 g of activated carbon-elementary sulfur composite powder, 0.5 g of solid electrolyte, and 10 zirconia balls with a diameter of 10 mm were placed in a zirconia pot. obtained a positive electrode composite powder in the same manner (Material A + Material B: Sulfur = 1:3 (mass ratio), Material A: Material B: Sulfur = 7.5:5:37.5 (mass ratio)) . An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used. Acetylene black is said to have a structural structure made up of carbon particles without pores, and can be expected to have essentially the same effect as adding carbon with a high aspect ratio.

(Example 5)
In Example 1 (3), carbon nanofibers (manufactured by Merck & Co., Ltd., Carbon nanofibers, width 100 nm, length 20-200 μm, nominal aspect ratio 200 ～2000, PR-25-XT-HHT, 0.05 g of micropore amount (0 cc/g) by t-plot method, 0.45 g of activated carbon-elementary sulfur composite powder, 0.5 g of solid electrolyte, diameter 10 mm A positive electrode composite powder was obtained in the same manner except that it was put into a zirconia pot together with 10 zirconia balls (Material A + Material B: Sulfur = 1:3 (mass ratio), Material A: Material B: Sulfur) =7.5:5:37.5 (mass ratio)). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(Example 6)
In Example 1 (3), 0.025 g of vapor-grown multi-walled carbon nanotubes (VGCF (registered trademark)), 0.475 g of activated carbon-elementary sulfur composite powder, 0.5 g of solid electrolyte, and zirconia balls with a diameter of 10 mm were used. A positive electrode composite powder was obtained in the same manner except that it was put into a zirconia pot together with 10 pieces (Material A + Material B: Sulfur = 1:3.2 (mass ratio), Material A: Material B: Sulfur = 9 .5:2.5:38 (mass ratio)). An all-solid-state battery was produced in the same manner as in Example 1, except that the obtained positive electrode composite powder was used.

(evaluation)
[Scanning microscope (SEM)]
FIG. 1 is a SEM image of the positive electrode composite material obtained in Example 1 (3). It was confirmed that VGCF was well dispersed in the positive electrode mixture.

[Evaluation of battery characteristics]
Constant current charging and discharging tests were conducted on the all-solid-state batteries produced in each example. The cutoff potential of the constant current test is 0.8-2.2V vs. Li--In was used, and the current density was set as shown in Table 1.

Table 2 shows the physical properties of materials A and B. Table 3 also shows the sulfur content of Examples 1 to 6 and Comparative Examples 1 to 4 at the second cycle (current density during discharge: 0.147 mA) and at the fifth cycle (current density during discharge: 0.586 mA). The discharge capacity per gram (mAh/g) is shown.

From Table 3, it can be confirmed that when materials A and B are used in combination as in the example, the discharge capacity is large and the rate characteristics are excellent. It can also be confirmed that the presence or absence of pores in material A influences the rate characteristics. Furthermore, it can be confirmed that even if the type and content of material B were changed, the discharge capacity was larger than that of Comparative Examples 1 and 2, and the rate characteristics were excellent.

The positive electrode mixture of the present invention is suitable for a positive electrode of a lithium ion battery. Furthermore, the lithium ion battery of the present invention is suitably used in, for example, batteries used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, and vehicles such as electric cars.

Claims (13)

sulfide solid electrolyte,
An electronically conductive material A having an average pore radius of 10 nm or less;
Material B is conductive carbon with a ratio of G band area to D band area (G/D) in Raman measurement of 0.6 or more;
At least one of elemental sulfur and discharge products of elemental sulfur present in at least a portion of the pores of the material A,
A positive electrode, wherein the ratio [S/(A+B)] of the total mass (S) of the elemental sulfur and the sulfur of the discharge product of elemental sulfur to the total mass (A+B) of the materials A and B is 2.5 or more. Composite material. The ratio of the total mass of the material A, the material B, the elemental sulfur and the sulfur of the discharge product of the elemental sulfur (A:B:S) is 5 to 15:1 to 10:30 to 50. The positive electrode composite material according to claim 1. The positive electrode composite material according to claim 1 or 2, wherein the material A has an average pore radius of less than 5 nm. The positive electrode composite material according to any one of claims 1 to 3, wherein the material A is a porous carbon material. The positive electrode composite material according to any one of claims 1 to 4, wherein the material B has a micropore amount of 0.1 cc/g or less. The positive electrode composite material according to any one of claims 1 to 5, wherein the material B is carbon fiber. The positive electrode composite material according to any one of claims 1 to 6, wherein the ratio of the area of the G band to the area of the D band (G/D) in Raman measurement of the material A is less than 0.6. The positive electrode composite material according to any one of claims 1 to 7, wherein the total pore volume of the material A and the material B is 1.0 cc/g or more. The positive electrode according to any one of claims 1 to 8, wherein the total sulfur content of the elemental sulfur and the discharge product of the elemental sulfur is 1.0 cc or more per 1 g of the total mass of the material A and the material B. Composite material. The positive electrode composite according to any one of claims 1 to 9, wherein the total sulfur content of the elemental sulfur and the discharge product of the elemental sulfur is 70% or more of the total pore volume of the material A and the material B. Material. A positive electrode for a lithium ion battery, comprising the positive electrode composite material according to any one of claims 1 to 10. A lithium ion battery comprising the positive electrode for a lithium ion battery according to claim 11. A step of heating material A having electronic conductivity with an average pore radius of 10 nm or less and elemental sulfur at a temperature equal to or higher than the melting point of the elemental sulfur to form a material A-elementary sulfur composite powder;
The material A - elemental sulfur composite powder, the material B which is conductive carbon with a G band area/D band area of 0.6 or more in Raman measurement, and a sulfide solid electrolyte are mixed, and a positive electrode is formed. A method for producing a positive electrode composite material, including a step of making it into a material.

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