Composite material and method for manufacturing the same

Abstract

Prepare a compound A containing Li, S, and M elements (M is phosphorus, etc.) and containing a crystal phase having an argyrodite-type crystal structure, and mix the compound A with a conductive material to obtain a composite material formed by compounding the two. In the XRD pattern of the compound A, the intensity of peak A observed at 2θ = 29.7° ± 1.00° is set as I0, and in the XRD pattern of the composite material, the intensity of peak B observed at 2θ = 29.7° ± 1.00° is set as I t When, the degree of amorphization N obtained by 100×(I0 - I t ) / I0 is mixed in such a way that it becomes 97% or more. It is suitable that the atomic ratio of the halogen (X) element contained in the compound A to the phosphorus (P) element is less than 1.0.

Description

Technical Field

[0001] The present invention relates to a composite material and a method for producing the same. The composite material of the present invention can be suitably used as a battery material. Background Art

[0002] Lithium-ion batteries are widely used as power sources for portable electronic devices such as laptop computers and mobile phones due to their high energy density and ease of miniaturization and lightness. In addition, the development of high-output, high-capacity lithium-ion batteries for electric vehicles, hybrid electric vehicles, etc. has been progressing recently.

[0003] For example, Patent Document 1 proposes a composite positive electrode material, which is produced by mixing a sulfide electrolyte of a silver vanadium sulfide crystal structure type with a conductive carbon material in a dry ball mill. Furthermore, Non-Patent Document 1 proposes a positive electrode active material, which is a composite of Li3PS4 glass as a sulfide solid electrolyte and a carbon-based conductive additive.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent document 1: CN109256555A

[0007] Non-patent literature

[0008] Non-patent document 1: Journal of Power Sources 293 (2015) 721-725 Summary of the invention

[0009] The present inventors have conducted research aimed at improving the performance of lithium-ion batteries and have found that a more excellent positive electrode active material is required in order to further improve the performance of lithium-ion batteries.

[0010] Therefore, an object of the present invention is to provide a material capable of improving the performance of lithium-ion batteries and a method suitable for producing the same.

[0011] The present invention solves the above-mentioned technical problems by providing the following method for manufacturing a composite material:

[0012] A method for manufacturing a composite material, comprising the following steps:

[0013] A preparation step of preparing a compound A containing lithium (Li), sulfur (S) and M (M is at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co) and manganese (Mn) and containing a crystal phase having an argyrodite-type crystal structure; and

[0014] A mixing step, mixing the aforementioned compound A with a conductive material to obtain a composite material of the two.

[0015] The aforementioned manufacturing method carries out the aforementioned mixing step in the following manner:

[0016] In the X-ray diffraction pattern of the compound A measured by an X-ray diffractometer using CuKα1 rays, a diffraction peak observed at a position of 2θ=29.7°±1.00° is defined as peak A.

[0017] In the X-ray diffraction pattern of the composite material measured by an X-ray diffractometer using CuKα1 rays, a diffraction peak observed at a position of 2θ=29.7°±1.00° is defined as Peak B.

[0018] The intensity of the peak A is denoted as I0, and the intensity of the peak B is denoted as I t When , the amorphization degree N obtained by the following formula (1) becomes 97% or more.

[0019] Amorphization degree N (%) = 100 × (I0-I t ) / I0(1) BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Example 1.

[0021] Figure 2 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Example 2.

[0022] Figure 3 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Example 3.

[0023] Figure 4 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Example 4.

[0024] Figure 5 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Example 5.

[0025] Figure 6 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Comparative Example 1.

[0026] Figure 7 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Comparative Example 2.

[0027] Figure 8 : is the X-ray diffraction pattern of the composite material of compound A and conductive material used in Reference Example 1.

[0028] Fig. 9 1 is a charge and discharge curve of a battery obtained by using the positive electrode active material prepared in Example 1.

[0029] Fig.10 1 is a charge and discharge curve of a battery obtained by using the positive electrode active material prepared in Example 3.

[0030] Fig.11 : This is a charge and discharge curve of a battery obtained using the positive electrode active material prepared in Comparative Example 1.

[0031] Fig.12 : This is a charge and discharge curve of a battery obtained using the positive electrode active material prepared in Comparative Example 2.

[0032] Fig.13 : This is a charge and discharge curve of a battery obtained using the positive electrode active material prepared in Reference Example 1. DETAILED DESCRIPTION

[0033] The present invention is described below based on its preferred embodiments. The present invention relates to a method for producing a composite material. The composite material is a composite material of the compound A described below and a conductive material. The composite material is particularly suitable for use as an active material for a battery.

[0034] The production method of the present invention can be roughly divided into the following steps (1) and (2).

[0035] (1) A step of preparing compound A (hereinafter also referred to as a "preparation step").

[0036] (2) A step of mixing compound A and a conductive material to obtain a composite material of the two (hereinafter also referred to as a "mixing step").

[0037] Each process is described below.

[0038] 〔Preparation process〕

[0039] In this process, compound A is prepared. Compound A preferably comprises lithium (Li) element, sulfur (S) element and M element. M element is preferably at least one of phosphorus (P) element, germanium (Ge) element, antimony (Sb) element, silicon (Si) element, tin (Sn) element, aluminum (Al) element, titanium (Ti) element, iron (Fe) element, nickel (Ni) element, cobalt (Co) element and manganese (Mn) element. In particular, M element preferably includes at least phosphorus (P) element, and further preferably M element is only P element. Thus, the discharge capacity of the battery using the composite material obtained by the present manufacturing method as the active material can be further improved.

[0040] Examples of compounds containing Li, S, and M include Li7PS6, Li 7+3x (P 5+ 1-x Fe 2+ x )S6、Li 7+x (P 5+ 1-x Si 4+ x )S6 etc. (wherein, x represents a number greater than 0.1 and less than 1.0.). In addition, as a compound comprising Li element, S element and M element, a compound comprising other elements on the basis of these three elements can also be used. As the other element, for example, a halogen (X) element can be listed. By using a compound further comprising an X element on the basis of Li element, S element and M element, the properties of the composite material obtained by the present manufacturing method as an active material can be further improved. As the X element, at least one element selected from fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) can be used.

[0041] From the viewpoint of further improving the properties of the composite material obtained by the present production method as an active material, the aforementioned compound containing the Li element, the S element, the M element and the X element is preferably a compound having the composition formula (1): Li a MS b X c (In the formula, M is at least one element selected from P, Ge, Sb, Si, Sn, Al, Ti, Fe, Ni, Co and Mn. X is at least one element selected from F, Cl, Br and I.)

[0042] In the aforementioned composition formula (1), from the viewpoint of improving lithium ion conductivity, a is preferably 3.0 or more, and more preferably 3.5 or more. On the other hand, a is preferably 9.0 or less, and more preferably 8.0 or less. In particular, when the M element is P, the atomic ratio of Li relative to P, i.e., the value of a, is preferably 5.0 or more, preferably 5.5 or more, and particularly preferably 6.0 or more. On the other hand, a is preferably 8.0 or less, preferably 7.8 or less, and particularly preferably 7.5 or less. By making a within the aforementioned range, the composite of compound A and the conductive material can be smoothly carried out.

[0043] Moreover, b is preferably 4.0 or more, more preferably 4.5 or more, and even more preferably 5.0 or more. On the other hand, b is preferably 7.5 or less, more preferably 7.0 or less, and even more preferably 6.5 or less.

[0044] Furthermore, c is preferably 0.1 or more, more preferably 0.2 or more. On the other hand, c is preferably less than 1.0, more preferably less than 0.8, and more preferably less than 0.6. By making b within the aforementioned range, the compound A and the conductive material can be smoothly composited, and an amorphous compound A can be suitably obtained. In particular, when the M element is P, when the atomic ratio of X to P is within the aforementioned range, the amorphization of the compound A occurs smoothly, and therefore it is preferred.

[0045] The M element in the aforementioned composition formula (1) is particularly preferably at least one of P element, Ge element, Sb element, Sn element and Si element, particularly preferably including P element, and more preferably only P element. Thus, when the composite material obtained by the present manufacturing method is used as an active material of a battery, the discharge capacity of the battery can be increased.

[0046] In the case where the M element is P, the value of the atomic ratio c of X relative to P is preferably, for example, 0.10 or more, preferably 0.2 or more. On the other hand, the value of c is preferably, for example, less than 1.0, preferably 0.8 or less, and particularly preferably 0.6 or less. By making the value of c within the aforementioned range, the compound A and the conductive material can be smoothly composited, and amorphous compound A can be suitably obtained. In addition, in the case where the M element is P, the atomic ratio of Li relative to P is preferably, for example, 5.0 or more, preferably 5.5 or more, and particularly preferably 6.0 or more. On the other hand, the atomic ratio of Li relative to P is preferably, for example, 9.0 or less, preferably 8.0 or less, and further preferably 7.5 or less. By making the atomic ratio of Li relative to P within the aforementioned range, the compound A and the conductive material can be smoothly composited. It should be noted that, in the case where the M element includes P element and elements other than P, the atomic ratio of Li relative to P can be, for example, 20.0 or less, 15.0 or less, or 9.0 or less.

[0047] From the viewpoint of further improving the properties of the composite material obtained by the present production method as an active material, the compound A is particularly preferably a compound of the composition formula (2): Li 7-d MS 6-d X d In the case where the M element is P, the atomic ratio of X to P, that is, the value of d, may be the same as the value of c in the above-mentioned composition formula (1), and thus the description thereof is omitted. In addition, in the case where the M element is P, the atomic ratio of Li to P may also be the same as that in the above-mentioned composition formula (1), and thus the description thereof is omitted.

[0048] When the M element in the above composition formula (1) is an M1 element and an M2 element that are different from each other, the compound A can be Li a (M1 1-y M2 y )S b X c In addition, when the M element in the composition formula (2) is an M1 element and an M2 element that are different from each other, the compound A can be represented by Li 7-d (M1 1-y M2 y )S 6-d X d y is preferably greater than 0.010, more preferably greater than 0.020, and more preferably greater than 0.050. On the other hand, y is preferably less than 0.70, more preferably less than 0.40, and more preferably less than 0.20. It should be noted that the M1 element and the M2 element may be the same as the M element described in the composition formula (1), and therefore the description here is omitted.

[0049] The composition of each element in the compound A can be measured by, for example, ICP emission spectrometry.

[0050] Compound A preferably includes a crystalline phase having a argyrodite-type crystal structure on the basis of including the above-mentioned elements. Thus, the characteristics of the composite material obtained by the present manufacturing method as an active material can be further improved. The results of the inventors' research show that even when compound A contains the above-mentioned elements, when compound A is amorphous, specifically, when it does not contain a crystalline phase having a argyrodite-type crystal structure, when the composite material formed by compounding compound A with a conductive material is used as an active material of a battery, its performance is difficult to improve. Compound A particularly preferably includes a crystalline phase having a cubic or orthorhombic argyrodite-type crystal structure. Whether a crystalline phase having a argyrodite-type crystal structure is included can be determined by analyzing the active material of the present invention using an X-ray diffraction method or an X-ray total scattering method. As a ray source in the X-ray diffraction method, CuKα rays, such as CuKα1 rays, can be used.

[0051] When compound A has a cubic argyrodite type crystal structure, it preferably has peaks at positions of 2θ=25.19°±1.00° and 29.62°±1.00° in an X-ray diffraction pattern measured using CuKα1 rays.

[0052] In the case where compound A has a cubic argyrodite type crystal structure, in the X-ray diffraction pattern measured with CuKα1 rays, it is further preferred that in addition to the positions of 2θ=25.19°±1.00° and 29.62°±1.00°, a position selected from the group consisting of 2θ=15.34°±1.00°, 17.74°±1.00°, 30.97°±1.00°, 44.37°±1.00°, 47.22°±1.00° and 51 .70°±1.00° has peaks at one or more positions, and further preferably has peaks at all positions of 2θ=15.34°±1.00°, 17.74°±1.00°, 30.97°±1.00°, 44.37°±1.00°, 47.22°±1.00° and 51.70°±1.00° in addition to the positions of 2θ=25.19°±1.00° and 29.62°±1.00°.

[0053] When compound A has an orthorhombic argyrodite-type crystal structure, it preferably has two peaks at 2θ=25.38°±1.00° and four peaks at 29.77°±1.00° in the X-ray diffraction pattern measured using CuKα1 rays.

[0054] In addition, when compound A has an orthorhombic argyrodite type crystal structure, in the X-ray diffraction pattern measured with CuKα1 rays, it is further preferred that in addition to the two peaks at 2θ=25.38°±1.00° and the four peaks at 29.77°±1.00°, there are also two peaks selected from 2θ=15.40°±1.00°, two peaks at 17.86°±1.00°, two peaks at 31.25°±1.00°, four peaks at 44.40°±1.00°, four peaks at 47.20°±1.00° and 52.00°. It has peaks at one or more of the two peaks at 2θ=25.38°±1.00° and four peaks at 29.77°±1.00°, and it is further preferred that, in addition to the two peaks at 2θ=25.38°±1.00° and the four peaks at 29.77°±1.00°, it also has peaks at all of the positions of 2θ=15.40°±1.00°, 2 peaks at 17.86°±1.00°, 2 peaks at 31.25°±1.00°, 4 peaks at 44.40°±1.00°, 4 peaks at 47.20°±1.00° and 2 peaks at 52.00°±1.00°.

[0055] It should be noted that the above-mentioned peak position is represented by a central value ±1.00°, but is preferably a central value ±0.800°, and more preferably a central value ±0.500°.

[0056] Compound A may contain other materials and other components as needed. Therefore, compound A may be a compound formed by a single phase composed of a crystalline phase of a argyrodite-type crystal structure, or may contain other phases on the basis of this phase. For example, compound A may contain Li2S phase, Li3PS4 phase, Li4P2S6 phase, LiCl or LiBr phase, etc. on the basis of a crystalline phase of a argyrodite-type crystal structure. From the viewpoint that the capacity of the composite material obtained by the present manufacturing method as the active material is further improved, compound A is particularly preferably composed of a Li2S phase on the basis of a crystalline phase of a argyrodite-type crystal structure. Compound A is particularly preferably composed of a compound containing Li element, S element, M element and X element, and containing a crystalline phase having a argyrodite-type crystal structure as the main material. In addition, in addition to the above-mentioned other materials and other components, compound A may also contain unavoidable impurities that have a small adverse effect on the effect of the present invention, for example, less than 5% by mass, especially less than 3% by mass.

[0057] Compound A is a substance in the form of particles, and its particle size D1 is a volume cumulative particle size D1 at a cumulative volume of 50% by volume based on a laser diffraction scattering particle size distribution measurement method. 50It is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. Also, D1 is preferably 20.0 μm or less, more preferably 10.0 μm or less, and even more preferably 5.0 μm or less.

[0058] Compound A can be manufactured by a known method. When compound A contains, for example, Li element, P element, S element, Cl element and Br element, lithium sulfide (Li2S) powder, phosphorus pentasulfide (P2S5) powder, lithium chloride (LiCl) powder and lithium bromide (LiBr) powder can be mixed and calcined to obtain particles of the aforementioned compound. As a mixing method for these powders, it is preferred to use, for example, a ball mill, a bead mill, a homogenizer, etc.

[0059] After mixing as described above, drying is performed as needed, and then the mixed powder is calcined in an inert atmosphere or under the circulation of hydrogen sulfide gas (H2S), crushed and pulverized and classified as needed, thereby obtaining compound A. The calcination temperature when calcining in an atmosphere containing hydrogen sulfide gas is preferably, for example, 350°C or more, and more preferably 450°C or more. On the other hand, the calcination temperature is preferably, for example, 650°C or less, more preferably 600°C or less, and more preferably 500°C or less. On the other hand, the calcination temperature when calcining in an inert atmosphere is preferably, for example, 350°C or more. On the other hand, the calcination temperature is preferably, for example, 550°C or less, more preferably 500°C or less, and more preferably 450°C or less.

[0060] Compound A can also be manufactured by amorphizing the raw material powder by mechanical grinding, and then heat treating the amorphized raw material powder to crystallize it. In this case, as long as the raw material powder can be fully mixed and amorphized, the processing device and processing conditions are not particularly limited. In particular, when a planetary ball mill is used, since the container filled with the raw material powder revolves at a high speed, high impact energy is generated between the balls that serve as the pulverizing medium placed in the container together with the raw material powder, and the raw material powder can be efficiently and uniformly amorphized. The mechanical grinding method can be dry or wet.

[0061] The processing conditions based on the mechanical grinding method can be appropriately set according to the processing device used, for example, the processing time can be set to more than 0.1 hours and less than 100 hours. By making the processing time within the range, the raw material powder can be more efficiently and uniformly amorphized. The ball as the grinding medium is preferably made of ZrO2, Al2O3, Si3N4 (silicon nitride) or WC (tungsten carbide), and the ball diameter is preferably, for example, more than 0.2 mm and less than 10 mm.

[0062] The raw material powder that has been mechanically ground and rendered amorphous can be crystallized by heat treatment under the same calcination conditions as above to obtain compound A. The raw material powder that has been mechanically ground is in a more uniformly mixed state than the raw material powder obtained by conventional pulverization and mixing, so the heat treatment temperature can be further lowered.

[0063] Compound A can also be produced by a liquid phase method using an organic solvent. In this case, the compound A can be obtained by dissolving the sulfide or halide as the raw material of compound A in a solvent such as tetrahydrofuran or ethanol, and precipitating compound A using the solvent as a reaction field. Compound A can also be obtained by synthesizing compound A by other means in advance, dissolving it in a solvent such as ethanol, and then precipitating it. This liquid phase method can produce compound A in a shorter time and with less energy than other methods, and it is also easier to reduce the particle size of the particles.

[0064] After the particles of compound A are obtained in this way, they are preferably sized to a suitable particle size. The preferred particle size of compound A may be the same as that described above, and therefore, the description thereof is omitted here.

[0065] 〔Mixing process〕

[0066] In this process, the above-mentioned compound A is mixed with a conductive material to obtain a composite material formed by combining the two. As the conductive material used together with compound A, a material having electronic conductivity can be used without particular limitation. As the conductive material, for example, various metal materials and conductive non-metal materials can be listed. The metal material and the conductive non-metal material can use any one of these, or use the two in combination.

[0067] As the aforementioned metal material, various precious metal elements can be listed, such as gold (Au) element, silver (Ag) element, platinum (Pt) element, palladium (Pd) element, rhodium (Rh) element, iridium (Ir) element, ruthenium (Ru) element and osmium (Os) element. In addition, various transition metal elements can be listed, such as copper (Cu) element, iron (Fe) element and tin (Sn) element. These metal elements can be used alone or in combination of two or more. As the aforementioned conductive non-metallic material, for example, carbon materials can be used. As examples thereof, graphite, acetylene black, carbon black, carbon nanofibers, carbon nanotubes, nanographene and fullerene nanowhiskers can be listed. These carbon materials can be used alone or in combination of two or more. Among these carbon materials, when carbon black is used, the initial capacity and discharge rate characteristics of the battery using the composite material obtained by the present manufacturing method as the active material can be further improved. From the viewpoint of making this advantage more significant, furnace black is preferably used as the carbon black, among which oil furnace black is preferably used, and Ketjen black is particularly preferably used.

[0068] The conductive material is a substance having a particle form, and its particle diameter D2 is preferably, for example, 1 nm or more, more preferably 10 nm or more, and more preferably 20 nm or more. In addition, D2 is preferably, for example, 500 nm or less, more preferably 300 nm or less, and more preferably 200 nm or less. The particle diameter D2 of the conductive material can be the average particle diameter (average value of more than 100 particles) of the Feret diameter measured by directly observing the particles using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0069] It should be noted that, when the conductive material is in a fibrous shape such as the above-mentioned carbon nanotubes and carbon nanofibers, the fiber diameter can be used instead of the particle diameter. The fiber diameter D3 is preferably, for example, 50 nm or more, more preferably 100 nm or more, and more preferably 150 nm or more. In addition, D3 is preferably, for example, 10000 nm or less, more preferably 5000 nm or less, and more preferably 2000 nm or less.

[0070] From the viewpoint of smoothly compounding the conductive material and the compound A, the size of the conductive material is preferably smaller than the size of the compound A. Specifically, the value of the ratio D1 / D2 of the particle size D1 of the compound A to the particle size D2 of the conductive material is preferably, for example, 2 or more, more preferably 5 or more, and further preferably 10 or more. On the other hand, the value of D1 / D2 is preferably, for example, 1000 or less, more preferably 500 or less, and further preferably 10 or more and 100 or less.

[0071] In addition, the size of the fibrous conductive material is also preferably smaller than that of the compound A. Specifically, the value of the ratio D1 / D3 of the particle size D1 of the compound A to the fiber diameter D3 of the conductive material is preferably, for example, 1 or more, more preferably 2 or more, and further preferably 5 or more. On the other hand, the value of D1 / D3 is preferably, for example, 1000 or less, more preferably 500 or less, and further preferably 100 or less.

[0072] Compound A and the conductive material can be combined by, for example, applying mechanical energy to particles of compound A and particles of the conductive material. To achieve this, it is preferred that a compressive / impact force or a shearing / friction force be applied to compound A and the conductive material in a mixed state.

[0073] In order to apply mechanical energy such as compression / impact force, shear / friction force to compound A and conductive material in a mixed state to make them composite, it is preferred to use a device mainly used when stirring, mixing, kneading, granulating, crushing, dispersing and / or surface modification of powder. For example, planetary ball mill, ball mill, jet mill, bead mill, stirring type crusher, vibration mill, hammer mill, roller mill and atomizer can be used. The main types of mechanical energy that can be applied using these devices vary according to each device. For example, when a planetary ball mill is used, by mainly applying compression / impact force to compound A and conductive material in a mixed state, the two can be composited. The centrifugal acceleration obtained when the device rotates is not particularly limited as long as it is the degree to which compound A and conductive material can be composited, but for example, it is preferably more than 10G, more preferably more than 15G, and more preferably more than 18G. In addition, the aforementioned centrifugal acceleration is, for example, preferably less than 40G, more preferably less than 30G, and more preferably less than 25G. By setting the centrifugal acceleration within the above range, when the composite material obtained by the present invention is used as an active material for a battery, the discharge capacity of the battery can be further increased.

[0074] For the mixing of compound A and conductive material, the conductive material is preferably set to 1 mass part or more, more preferably 2 mass parts or more, and more preferably 5 mass parts or more relative to 100 mass parts of compound A. On the other hand, the conductive material is preferably set to 50 mass parts or less, more preferably 20 mass parts or less, and more preferably 10 mass parts or less relative to 100 mass parts of compound A. By mixing compound A with a conductive material within this range, a battery having a composite material obtained by the present manufacturing method as an active material can significantly exhibit a high discharge capacity.

[0075] The compound A and the conductive material are preferably composited in a manner that reduces the crystallinity of the compound A. The properties of the composite material obtained by the present production method as an active material can be further improved. The degree of reduction in the crystallinity of the compound A can be evaluated by the amorphization degree N represented by the following formula (1).

[0076] Amorphization degree N (%) = 100 × (I0-I t ) / I0(1)

[0077] In the formula, I0 represents the intensity of peak A. Peak A is a diffraction peak observed at 2θ=29.7°±1.00° in an X-ray diffraction pattern when compound A is measured by an X-ray diffraction device using CuKα1 rays. trepresents the intensity of peak B. Peak B is a diffraction peak observed at a position of 2θ=29.7°±1.00° in an X-ray diffraction pattern when the composite material is measured by an X-ray diffractometer using CuKα1 rays.

[0078] The closer the value of the degree of amorphization N is to 100%, the lower the crystallinity.

[0079] It should be noted that, when there are two or more diffraction peaks observed at the position of 2θ=29.7°±1.00° in the X-ray diffraction diagram when measuring compound A, the diffraction peak with the highest peak intensity is taken as I0. Similarly, when there are two or more diffraction peaks observed at the position of 2θ=29.7°±1.00° in the X-ray diffraction diagram when measuring the composite material, the diffraction peak with the highest peak intensity is taken as I t It should be noted that when the crystallinity of the composite material decreases, the half-height width of each diffraction peak in the X-ray diffraction pattern becomes wider, and sometimes multiple diffraction peaks overlap. In this case, the overlapping multiple diffraction peaks are regarded as one diffraction peak and set to I t .

[0080] The mixing step of compound A and the conductive material is preferably carried out in such a manner that the above-mentioned amorphization degree N reaches, for example, 97% or more, preferably 98% or more, and more preferably 99% or more. By making the amorphization degree N within the above-mentioned range, the discharge capacity of the battery using the composite material obtained by the present invention as an active material can be increased.

[0081] As a method for mixing compound A and a conductive material so that the degree of amorphization N becomes greater than the above value to composite the two, for example, a method of adjusting the impact force to a specified range can be cited. The specific impact force is preferably, for example, greater than 0.50N, particularly preferably greater than 0.70N, and particularly preferably greater than 0.90N. It should be noted that the impact force refers to the force generated when a mass object collides, and is represented by the following formula (2).

[0082] Impact force (F) = m × G (2)

[0083] Where m is the weight of the object that collides (kg), G is the acceleration (m / s 2 ), in the case of a planetary ball mill, the total weight of the balls placed in the container containing compound A and the conductive material is m, and G is the centrifugal acceleration.

[0084] As a method for mixing compound A and the conductive material in a manner such that the impact force becomes equal to or greater than the above-mentioned value so as to completely composite the two, for example, a method of adjusting the mixing conditions of the two can be cited. For example, the following method can be cited: as conditions for mixing compound A and the conductive material using a planetary ball mill, the revolution and / or rotation speed of the device, the diameter, material and number of balls, and the mixing time can be adjusted.

[0085] When compound A is composited with a conductive material in such a way that compound A is amorphized, lithium sulfide (Li2S) may be generated from the elements contained in compound A, depending on the composite conditions. Lithium sulfide functions as a positive electrode active material of a battery and has the effect of increasing the discharge capacity of the battery, so it is desirable to generate lithium sulfide as a result of composite.

[0086] As described above, when compound A and the conductive material are composited so that compound A becomes amorphous in the mixing step, whether the conductive material becomes amorphous is not particularly limited.

[0087] The composite material thus obtained is preferably a particle composed of a main body part and a conductive part, wherein the main body part includes particles of compound A, and the conductive part includes a conductive material dispersed on the surface and / or inside the main body part and providing electronic conductivity. In particular, the conductive part serves as an electron conduction path when lithium is inserted and removed from the main body part, so it is ideal to be uniformly dispersed and closely attached on the surface and inside.

[0088] The argyrodite formation ratio of the composite material obtained by the present production method is not particularly limited as long as it is a degree that the effects of the present invention can be obtained. The argyrodite formation ratio is preferably, for example, 40 or less, preferably 30 or less, particularly preferably 10 or less, further preferably 5 or less, and most preferably 0. It should be noted that the argyrodite formation ratio may be the same as that described in the examples described later, and therefore, the description here is omitted.

[0089] According to the method of the present invention, compound A and a conductive material are "compounded" to preferably the following state: the conductive part is dispersed on the surface and inside of the main part, and is integrally and inseparably bonded to the main part. As the "compounding" method, for example, the method in which particles of the conductive material are inseparably dispersed on the surface and / or inside of the particles of compound A, and the method in which the particles of compound A constituting the main part and the particles of the conductive material constituting the conductive part undergo a chemical reaction and combine. The particles of the conductive material are inseparably dispersed on the surface and inside of the compound particles constituting the main part refers to the following state: for example, when the composite material obtained by the present manufacturing method is observed using a scanning electron microscope (SEM-EDS) equipped with an energy dispersive X-ray spectrometer, when the constituent elements of compound A constituting the main part (such as sulfur element) and the constituent elements of the conductive material constituting the conductive part are mapped, the constituent elements of compound A constituting the main part and the constituent elements of the conductive material constituting the conductive part exist in an overlapping manner. Alternatively, it refers to the following state: when observing the cross section of the positive electrode layer of a battery using the composite material obtained by the present manufacturing method as the active material, the constituent elements of the compound A constituting the main part and the constituent elements of the conductive material constituting the conductive part exist in an overlapping manner on the surface and inside of the active material. It should be noted that in the case where the main part and the conductive part undergo a chemical reaction to form a composite, for example, when the conductive material is a carbon material, it can also be confirmed by analyzing the presence of a C-S bond using Raman spectroscopy or photoelectron spectroscopy.

[0090] When the composite material obtained by the present manufacturing method is used as an active material, the active material obtains conductivity in a manner that the exchange of electrons between the outside of the active material and the main part is smoothly carried out via the conductive part, and also obtains the function of lithium ion insertion and extraction. Furthermore, by using a compound A having an argyrodite-type crystal structure with a high lithium content and high lithium ion conductivity in the main part, a battery having the composite material obtained by the present manufacturing method as an active material can exhibit a high discharge capacity. In particular, the composite material obtained by the present manufacturing method is useful as a positive electrode active material for a lithium ion battery.

[0091] When the composite material obtained by the manufacturing method is used as an active material, the active material can be mixed with an electrolyte, a conductive material, a binder, etc. to form an electrode mixture. The electrode mixture using the composite material obtained by the manufacturing method as a positive electrode active material is a positive electrode mixture constituting a positive electrode layer.

[0092] The aforementioned electrolyte may be, for example, a solid electrolyte. The solid electrolyte preferably has ionic conductivity such as lithium ion conductivity. Specifically, inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, and organic polymer electrolytes such as polymer electrolytes may be cited. From the viewpoint of making the effect of the present invention more significant, the solid electrolyte is preferably a sulfide solid electrolyte. Regarding the sulfide solid electrolyte, it may be the same as the sulfide solid electrolyte used in conventional solid-state batteries. The sulfide solid electrolyte may be, for example, a substance containing Li and S and having lithium ion conductivity.

[0093] The sulfide solid electrolyte may be any of a crystalline material, glass ceramics, and glass. The sulfide solid electrolyte may have an argyrodite-type crystal structure. Examples of such sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX ("X" represents one or more halogen elements), Li2S-P2S5-P2O5, Li2S-Li3PO4-P2S5, Li3PS4, Li4P2S6, Li 10 GeP2S 12 , Li 3.25 Ge 0.25 P 0.75 S4、Li7P3S 11 , Li 3.25 P 0.95 S4, Li a PS b X c ("X" represents one or more halogen elements. a represents a number greater than 3.0 and less than 9.0. b represents a number greater than 3.5 and less than 6.0. c represents a number greater than 0.1 and less than 3.0.) In addition, sulfide solid electrolytes described in International Publication No. 2013 / 099834 and International Publication No. 2015 / 001818 can be cited.

[0094] The active material contained in the electrode mixture can only be the composite material obtained by this manufacture method, or this composite material can be combined with other active materials and used. As other active materials, known sulfur simple substance, active materials comprising sulfur can be listed. The ratio of the composite material in the electrode mixture can be, for example, more than 20 mass %, can also be more than 30 mass %, can also be more than 40 mass %. On the other hand, the aforementioned ratio can be, for example, below 70 mass %, can also be below 60 mass %.

[0095] A battery containing a composite material obtained by the present manufacturing method as an active material comprises: a positive electrode layer containing a positive electrode active material, a negative electrode layer containing a negative electrode active material, and a solid electrolyte layer containing a solid electrolyte, wherein the positive electrode active material is preferably a composite material obtained by the present manufacturing method. The battery can be manufactured by, for example, stacking and press-molding the three layers of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer obtained as described above.

[0096] The battery having the composite material obtained by the present manufacturing method as the active material is preferably a lithium ion battery, wherein preferably a lithium sulfur battery. As the battery here, a solid-state battery having a solid electrolyte layer, in particular an all-solid-state battery, can be cited. In addition, the battery having the composite material obtained by the present manufacturing method as the active material can be a primary battery or a secondary battery, but it is preferably used in a secondary battery, and is particularly preferably used in a lithium secondary battery. The meaning of "lithium secondary battery" broadly includes secondary batteries that are charged and discharged by the movement of lithium ions between the positive electrode and the negative electrode.

[0097] The solid-state battery has a positive electrode layer, a negative electrode layer, and a solid electrolyte layer between the positive electrode layer and the negative electrode layer. The active material of the present invention is preferably contained in the positive electrode layer. "Solid-state battery" refers to: not only a solid-state battery that does not contain any liquid substance or gel-like substance as an electrolyte, but also a form that contains, for example, less than 50 mass%, less than 30 mass%, or less than 10 mass% of a liquid substance or a gel-like substance as an electrolyte.

[0098] Regarding the above-mentioned embodiment, the present invention further discloses the following method for producing a composite material.

[0099] [1] A method for producing a composite material, comprising the following steps:

[0100] A preparation step of preparing a compound A containing lithium (Li), sulfur (S) and M (M is at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co) and manganese (Mn) and containing a crystal phase having an argyrodite-type crystal structure; and

[0101] A mixing step, mixing the aforementioned compound A with a conductive material to obtain a composite material of the two.

[0102] The aforementioned manufacturing method carries out the aforementioned mixing step in the following manner:

[0103] In the X-ray diffraction pattern of the compound A measured by an X-ray diffractometer using CuKα1 rays, a diffraction peak observed at a position of 2θ=29.7°±1.00° is defined as peak A.

[0104] In the X-ray diffraction pattern of the composite material measured by an X-ray diffractometer using CuKα1 rays, a diffraction peak observed at a position of 2θ=29.7°±1.00° is defined as Peak B.

[0105] The intensity of the peak A is denoted as I0, and the intensity of the peak B is denoted as I t When , the amorphization degree N obtained by the following formula (1) becomes 97% or more.

[0106] Amorphization degree N (%) = 100 × (I0-I t ) / I0(1)

[0107] [2] The production method according to [1], wherein the element M contained in the compound A includes at least phosphorus (P).

[0108] [3] The production method according to [1] or [2], wherein the atomic ratio of the halogen (X) element to the phosphorus (P) element contained in the compound A is less than 1.0.

[0109] [4] The production method according to any one of [1] to [3], wherein the atomic ratio of the lithium (Li) element to the phosphorus (P) element contained in the compound A is 5.0 or more and 9.0 or less.

[0110] [5] The production method according to any one of [1] to [4], wherein the conductive material is a carbon material or a metal material.

[0111] [6] A composite material produced by the method described in any one of [1] to [5].

[0112] Example

[0113] The present invention will be described in more detail below based on examples. However, the scope of the present invention is not limited to the examples. Unless otherwise specified, "%" and "parts" represent "mass %" and "mass parts", respectively.

[0114] [Example 1]

[0115] (1) Preparation process

[0116] Compound A and a conductive material having the composition shown in Table 1 below were prepared.

[0117] (2) Mixing process

[0118] Compound A and the conductive material were mixed in the amounts shown in Table 1. A planetary ball mill (Fritsch, P-7) was used for the mixing. The balls used were zirconia balls with a diameter of 5 mm. The mixing was carried out at a rotation speed of 500 rpm for 10 hours. The impact force applied at this time is shown in Table 1. In this way, a composite material of compound A and the conductive material was obtained. The obtained composite material was crushed with a mortar and sized with a sieve with a mesh size of 53 μm to obtain a particle size D 50 The particle size is 6.6 μm.

[0119] All the above operations were carried out in a glove box replaced with sufficiently dry argon (dew point -60°C or less).

[0120] [Example 2]

[0121] As compound A and conductive material, the substances shown in Table 1 were used. A composite material was obtained in the same manner as in Example 1 except for the above. It should be noted that in this example, the "X / P atomic ratio" shown in Table 1 represents the ratio of the number of atoms of the X (halogen) element to the number of atoms of the phosphorus element. In addition, the "Li / P atomic ratio" represents the ratio of the number of atoms of the Li element to the number of atoms of the phosphorus element.

[0122] [Examples 3 and 4]

[0123] Compounds shown in Table 1 were used as compound A. A composite material was obtained in the same manner as in Example 1 except for the above.

[0124] [Example 5]

[0125] Compound A was a compound shown in Table 1. Mixing was performed for 10 hours using a planetary ball mill using zirconia balls with a diameter of 10 mm at a rotation speed of 600 rpm. The impact force applied at this time is shown in Table 1. A composite material was obtained in the same manner as in Example 1 except for the above.

[0126] [Comparative Example 1]

[0127] Compound A was a compound shown in Table 1. Mixing was performed for 10 hours using a planetary ball mill using zirconia balls with a diameter of 10 mm at a rotation speed of 600 rpm. The impact force applied at this time is shown in Table 1. A composite material was obtained in the same manner as in Example 1 except for the above.

[0128] [Comparative Example 2]

[0129] Compound A and the conductive material used were those shown in Table 1. Mixing was performed with a planetary ball mill at a rotation speed of 300 rpm for 1 hour. The impact force applied at this time is shown in Table 1. A composite material was obtained in the same manner as in Example 1 except for the above.

[0130] 〔Reference Example 1〕

[0131] As compound A and conductive material, the materials shown in Table 1 were used. Otherwise, the same procedure as in Example 1 was carried out to obtain a composite material.

[0132] 〔evaluate〕

[0133] XRD measurement was performed on the compound A used in the examples, comparative examples and reference examples and the prepared composite materials to measure the intensities I0 and I1 of peak A and peak B. t , the amorphization degree N is calculated. The results are shown in Table 1. In addition, the XRD spectrum is shown in Figures 1 to 8 The conditions for XRD measurement are as follows.

[0134] 〔XRD measurement〕

[0135] In a glove box substituted with sufficiently dry argon (dew point -60°C or less), the composite materials obtained in Examples, Comparative Examples and Reference Examples were filled in an airtight holder not exposed to the atmosphere and XRD measurement was performed. The measurement conditions were as follows.

[0136] Device name: Fully automatic multifunctional X-ray diffraction device SmartLab SE (manufactured by Rigaku Co., Ltd.)

[0137] · Radiation source: CuKα1

[0138] Tube voltage: 40kV

[0139] Tube current: 50mA

[0140] ·Measurement method: Concentration method (reflection method)

[0141] Optical system: Multilayer mirror divergent beam method (CBO-α)

[0142] Detector: One-dimensional semiconductor detector

[0143] ·Incident sunlight slit: Sunlight slit 2.5°

[0144] · Longitudinal limiting slit: 10mm

[0145] ·Slit for receiving sunlight: 2.5°

[0146] Entrance slit: 1 / 6°

[0147] Receiving slit: 2mm (open)

[0148] ·Measurement range: 2θ=10~120°

[0149] Step length: 0.02°

[0150] Scanning speed: 1.0° / min

[0151] In addition, the argyrodite formation ratio of the composite materials produced in Examples, Comparative Examples and Reference Examples was measured by the following method. The results are shown in Table 1.

[0152] [Germanite formation ratio]

[0153] In the X-ray diffraction pattern of the composite material, when compound A has a cubic argyrodite-type crystal structure, the intensity of the diffraction peak observed at 29.62°±1.00° is set as I a When the diffraction peak has an orthorhombic argyrodite crystal structure, the intensity of the diffraction peak observed at 29.77°±1.00° is set to I a In addition, the diffraction peak intensity of lithium sulfide observed at the position of 2θ = 27.00° ± 1.00° is set as I b The composite material can be evaluated by the argyrodite formation ratio represented by the following formula (3).

[0154] Argentum formation ratio (%) = 100 × I a / (I a +I b )(3)

[0155] It should be noted that impurity phases other than compound A and lithium sulfide may be confirmed in the composite material in some cases, but their generation ratio is very small, so the generation ratio of the impurity phase may not be considered in the argyrodite generation ratio.

[0156] Furthermore, solid-state battery cells were prepared using the composite materials prepared in the examples, comparative examples and reference examples as positive electrode active materials, and the initial discharge capacities were measured by the following method. The results are shown in Table 1.

[0157] <Production of all-solid-state battery cells>

[0158] As the positive electrode active material, the composite materials prepared in the examples, comparative examples and reference examples were used, and as the solid electrolyte powder for the positive electrode layer and the solid electrolyte layer, Lithium argyrodite-type crystal structure was used. 5.4 PS 4.4 Cl 0.8 Br 0.8 , In-Li alloy is used as the negative electrode active material of the negative electrode layer to make an all-solid-state battery.

[0159] (Preparation of positive electrode mixture)

[0160] The composite material powders obtained in the examples and comparative examples and the solid electrolyte powders were mixed in a mortar at a mass ratio of 60:40 to prepare positive electrode mixture powders for positive electrode layers.

[0161] (Fabrication of all-solid-state battery cells)

[0162] The lower opening of the polypropylene cylinder (opening diameter 10.5mm, height 18mm) with upper and lower openings is closed with a negative electrode (made of SUS), a solid electrolyte powder is placed on it, and after being closed with a positive electrode (made of SUS), it is pressed unidirectionally at 200MPa to form a solid electrolyte layer. Next, the positive electrode is temporarily removed, the positive electrode mixture powder is placed on the solid electrolyte layer, and after being closed with the positive electrode again, it is pressed unidirectionally at 560MPa to stack the positive electrode layer and the solid electrolyte layer. After that, the above-mentioned cylinder is turned upside down, the negative electrode is temporarily removed, In-Li foil is placed on the solid electrolyte layer, and it is closed with the negative electrode again. Finally, a G-shaped clamp is used to clamp the positive and negative electrodes with a load of 6N·m to make a fully solid-state battery cell with a positive electrode layer, a solid electrolyte layer and a negative electrode layer stacked. It should be noted that with respect to the thickness of each layer, the positive electrode layer is about 40μm, the solid electrolyte layer is about 600μm, and the negative electrode layer is about 400μm. The production of the all-solid-state battery cell was carried out in a glove box replaced with argon gas with a dew point temperature of -60°C. In an environmental tester maintained at 25°C, the produced all-solid-state battery was connected to a charge and discharge measurement device for battery characteristic evaluation. It should be noted that the current of 2.0 mA during charge and discharge was taken as 1C rate.

[0163] 〔Initial capacity〕

[0164] In the first charge and discharge (first cycle), in order to efficiently extract and embed the lithium ions contained in the positive electrode active material, the battery was charged to 3.0V at 0.03C in CC-CV mode, and discharged to 0.38V at 0.03C in CC mode. In the second cycle, the battery was charged to 3.0V at 0.1C in CC-CV mode, and discharged to 0.38V at 0.1C in CC mode. Here, the charge and discharge capacity of the second cycle is taken as the initial charge and discharge capacity. The measurement results of Examples 1 and 3, Comparative Examples 1 and 2, and Reference Example 1 are shown in Figure 1. Figures 9 to 13 shown.

[0165] [Table 1]

[0166]

[0167] It is clear from the results shown in Table 1 that the initial discharge capacity of the battery using the composite material prepared in each example as the positive electrode active material is improved.

[0168] Industrial Applicability

[0169] As described above in detail, according to the present invention, a method for suitably producing a material capable of improving the performance of a lithium ion battery can be provided.

Claims

1. A method for manufacturing a composite material, comprising the following steps: A preparation step of preparing a compound A containing lithium (Li) element, sulfur (S) element and M element and containing a crystal phase having an argyrodite-type crystal structure, wherein: M is at least one of phosphorus (P), germanium (Ge), antimony (Sb), silicon (Si), tin (Sn), aluminum (Al), titanium (Ti), iron (Fe), nickel (Ni), cobalt (Co), and manganese (Mn); as well as A mixing step, mixing the compound A with a conductive material to obtain a composite material of the two. The M element contained in the compound A at least includes phosphorus (P) element, The atomic ratio of the halogen (X) element contained in the compound A to the phosphorus (P) element is less than 1.0, The atomic ratio of lithium (Li) element contained in the compound A to phosphorus (P) element is 5.0 or more and 9.0 or less, The conductive material is a carbon material, The manufacturing method carries out the mixing step in the following manner: In the X-ray diffraction pattern of the compound A measured by an X-ray diffractometer using CuKα1 rays, a diffraction peak observed at a position of 2θ=29.7°±1.00° is defined as peak A. In the X-ray diffraction pattern of the composite material measured by an X-ray diffraction device using CuKα1 rays, a diffraction peak observed at a position of 2θ=29.7°±1.00° is defined as Peak B, The intensity of the peak A is set to I0, and the intensity of the peak B is set to I t When the amorphization degree N obtained by the following formula (1) becomes 97% or more, Amorphization degree N (%) = 100 × (I0-I t ) / I0(1).

2. The manufacturing method according to claim 1, wherein: The atomic ratio of the halogen (X) element contained in the compound A to the phosphorus (P) element is 0.8 or less.

3. The manufacturing method according to claim 1, wherein: The atomic ratio of the lithium (Li) element contained in the compound A to the phosphorus (P) element is 6.0 or more and 9.0 or less. 4 . A composite material produced by the method according to claim 1 .

Images