Anode materials and batteries

Abstract

The negative electrode material (1000) disclosed herein comprises a negative electrode active material (310), a solid electrolyte (300), and a coating material that covers the negative electrode active material (310). The coating material is represented by the following composition formula (1), wherein a, b, and c are positive real numbers, A is at least one selected from P and S, and X is F and O. a A b X c (1)

Description

Technical Field

[0001] The present disclosure relates to negative electrode materials and batteries. Background Art

[0002] Patent Document 1 discloses a powdery negative electrode active material made of amorphous coated graphite in which at least a portion of the surface of graphite particles is coated with amorphous carbon.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 4729716 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Batteries using solid electrolytes have inferior charging rate characteristics compared to batteries using electrolyte solutions. Therefore, there has been a desire to improve the charging rate characteristics of solid batteries.

[0008] Means for solving problems

[0009] The present disclosure provides a negative electrode material, which contains: a negative electrode active material; a solid electrolyte; and a coating material coating the negative electrode active material.

[0010] The coating material is represented by the following composition formula (1):

[0011] Li a A b X c (1)

[0012] Where a, b, and c are positive real numbers.

[0013] A is at least one selected from P and S,

[0014] X is F and O.

[0015] Effects of the Invention

[0016] According to the present disclosure, the charging rate characteristics of a solid-state battery can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view schematically showing the structure of the negative electrode material 3000 in the first embodiment.

[0018] Figure 2 This is a cross-sectional view schematically showing the structure of a battery 2000 in the second embodiment. DETAILED DESCRIPTION

[0019] (Insights that form the basis of this disclosure)

[0020] In recent years, the development of solid batteries using solid electrolytes has been progressing. Compared with lithium-ion batteries using electrolytes, there is a tendency for the interface area between the negative electrode active material and the electrolyte to be smaller in solid batteries. If the interface area is reduced, the input rate characteristics when lithium ions are embedded in the negative electrode active material, that is, the charging rate characteristics, are reduced. Therefore, the charging rate characteristics of solid batteries tend to be worse than those of lithium-ion batteries using electrolytes. In order to popularize solid batteries, it is expected to improve the charging rate characteristics related to shortening the charging time.

[0021] In the field of lithium-ion liquid batteries using electrolytes, various compounds that can be dissolved in organic electrolytes are being studied. By utilizing these compounds to produce a reduction reaction on the surface of the negative electrode, a coating is formed on the surface of the negative electrode. As a result, attempts have been made to improve the properties of the negative electrode active material. However, in the case of solid-state batteries, since the electrolyte is solid, previous methods cannot be simply applied. In other words, in the field of solid-state batteries, there have been almost no attempts to improve the properties by coating the negative electrode active material with a coating material.

[0022] As a method of improving the charging rate characteristics, there is the following method. That is, reducing the mass of the negative electrode active material, thereby reducing the capacity per unit area. In this way, the current per unit area can be reduced, thereby improving the charging rate characteristics through the hourly rate current. However, if the mass of the negative electrode active material is reduced, the mass of the positive electrode active material must also be reduced. As a result, the capacity of the battery is reduced. Since the volume of components that do not contribute to the capacity, such as the collector and the insulating layer, does not change, the proportion of materials that contribute to the capacity is relatively reduced. Therefore, the energy density of the battery per unit volume or per unit mass is also reduced.

[0023] The present disclosure has been made in view of the above circumstances, and provides a negative electrode material capable of improving the charge rate characteristics of a battery.

[0024] (Summary of one aspect of the present disclosure)

[0025] The negative electrode material of the first embodiment of the present disclosure comprises: a negative electrode active material; a solid electrolyte; and a coating material coating the negative electrode active material.

[0026] The coating material is represented by the following composition formula (1):

[0027] Li a A b X c (1)

[0028] Where a, b, and c are positive real numbers.

[0029] A is at least one selected from P and S,

[0030] X is F and O.

[0031] By coating the negative electrode active material with the coating material represented by formula (1), the charging rate characteristics of the battery can be improved.

[0032] In the second aspect of the present disclosure, for example, in the negative electrode material according to the first aspect, the coating material may contain SO x F y According to such a configuration, since a better coating layer can be formed, degradation of the solid electrolyte can be suppressed, and the charge rate characteristics of the battery can be improved more effectively.

[0033] In the third aspect of the present disclosure, for example, in the negative electrode material according to the second aspect, the coating material may contain Li, S, O, and F. This configuration allows for a better interface between the active material and the solid electrolyte, thereby more effectively improving the battery's charge rate characteristics.

[0034] In the fourth aspect of the present disclosure, for example, in the negative electrode material according to the first aspect, the coating material may also contain PO x F y According to this structure, since a better interface between the active material and the solid electrolyte can be formed, the charging rate characteristics of the battery can be improved more effectively.

[0035] In the fifth aspect of the present disclosure, for example, in the negative electrode material according to the fourth aspect, the coating material may contain Li, P, O, and F. This configuration can form a better interface between the active material and the solid electrolyte, thereby more effectively improving the charge rate characteristics of the battery.

[0036] In the sixth aspect of the present disclosure, for example, in the negative electrode material according to the first aspect, the coating material may contain at least one selected from LiSO3F and LiPO2F2. By using these materials as the coating material, the charge rate characteristics of the battery can be improved.

[0037] In the seventh aspect of the present disclosure, for example, in the negative electrode material according to any one of the first to sixth aspects, the thickness of the coating material layer may be 0.5 nm to 20 nm. Adjusting the thickness of the coating material layer to this range allows for further improvement in the battery's charge rate characteristics while ensuring sufficient Li ion conductivity in the coating material layer.

[0038] In the eighth aspect of the present disclosure, for example, in the negative electrode material according to any one of the first to seventh aspects, the solid electrolyte may include at least one selected from a sulfide solid electrolyte, a halide solid electrolyte, and an oxyhalide solid electrolyte. This configuration can improve the ionic conductivity of the solid electrolyte.

[0039] In the ninth aspect of the present disclosure, for example, in the negative electrode material according to any one of the first to eighth aspects, the negative electrode active material may contain at least one selected from a carbon material and an alloy-type active material that forms an alloy with lithium. The use of an alloy-type active material can increase the energy density of the battery.

[0040] In the tenth aspect of the present disclosure, for example, in the negative electrode material according to any one of the first to ninth aspects, the negative electrode active material may contain graphite. Graphite is suitable as a negative electrode active material because of its low expansion coefficient during lithium ion insertion reaction.

[0041] In the eleventh aspect of the present disclosure, for example, in the negative electrode material according to any one of the first to tenth aspects, the solid electrolyte may also have lithium ion conductivity. With such a configuration, the negative electrode material can be used in a lithium ion battery.

[0042] A battery according to a twelfth aspect of the present disclosure includes: a negative electrode containing the negative electrode material according to any one of the first to eleventh aspects; a positive electrode; and an electrolyte layer provided between the positive electrode and the negative electrode.

[0043] According to the battery of the present disclosure, the above-mentioned benefits can be obtained in the negative electrode.

[0044] A method for producing a negative electrode material according to a thirteenth aspect of the present disclosure is a method for producing a negative electrode material comprising a negative electrode active material and a coating material coating the negative electrode active material, comprising the following steps:

[0045] preparing a solution containing the coating material and a first solvent,

[0046] The solution and the negative electrode active material are mixed to prepare a mixture,

[0047] The negative electrode active material is coated with the coating material by removing the first solvent from the mixture.

[0048] According to the method disclosed herein, the negative electrode active material can be efficiently coated with the coating material, and since high-temperature drying is not required, the method is simple.

[0049] In the fourteenth aspect of the present disclosure, for example, the method for producing a negative electrode material according to the thirteenth aspect may be configured to produce a slurry of the negative electrode material by kneading a solid electrolyte with the negative electrode active material coated with the coating material using a second solvent in which the coating material is insoluble. This configuration allows for efficient production of the negative electrode.

[0050] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0051] (Implementation Method 1)

[0052] Figure 1 This is a cross-sectional view schematically showing the structure of the negative electrode material 3000 in the first embodiment.

[0053] The negative electrode material 3000 in the first embodiment includes a coated active material 330 and a solid electrolyte 300. The coated active material 330 and the solid electrolyte 300 are in contact with each other.

[0054] The coated active material 330 includes the negative electrode active material 310 and the coating layer 320. The coating layer 320 is provided on the surface of the negative electrode active material 310. The coating layer 320 is a layer containing a coating material. The negative electrode active material 310 is coated with the coating material. In the coating layer 320, the coating material is in a solid state.

[0055] The coating material is represented by the following composition formula (1): wherein a, b, and c are positive real numbers. A is at least one selected from P and S. X is F and O.

[0056] Li a A b X c (1)

[0057] By including a coating material represented by formula (1) in the coating layer 320, the battery's charge rate characteristics can be improved. While the principle behind this is not necessarily clear, it is believed that various factors, including the coating material's voltage resistance, the solid electrolyte 300's oxidation resistance, the coating material's reactivity with the negative electrode active material 310, the coating material's reactivity with the solid electrolyte 300, and the physical contact between the negative electrode active material 310 and the solid electrolyte 300, play a complex role. It is believed that the coating material facilitates the transfer of lithium ions between the negative electrode active material 310 and the solid electrolyte 300 on the surface of the negative electrode active material 310. Alternatively, the coating layer 320 may contain only the coating material, excluding unavoidable impurities.

[0058] According to the above configuration, since a better interface between the coated active material 330 and the solid electrolyte 300 can be formed, the charging rate characteristics of the battery can be more effectively improved.

[0059] The coating material may also contain SO x F y x and y are values ​​satisfying x>0, y>0. Even if the stoichiometric composition is x+y=3 or 4, x and y may take a non-stoichiometric ratio according to actual chemical analysis.

[0060] According to the above configuration, since a better coating layer 320 can be formed, degradation of the solid electrolyte 300 can be suppressed, and the charge rate characteristics of the battery can be improved more effectively.

[0061] The coating material may contain Li, S, O, and F.

[0062] The above configuration can effectively improve the battery's charge rate characteristics by forming a better interface between the coated active material 330 and the solid electrolyte 300. The coating material may also be made of Li, S, O, and F, excluding unavoidable impurities.

[0063] The coating material may also contain PO x F y x and y are values ​​satisfying x>0, y>0. Even if the stoichiometric composition is x+y=3 or 4, x and y may take a non-stoichiometric ratio according to actual chemical analysis.

[0064] According to the above configuration, since a better interface between the coated active material 330 and the solid electrolyte 300 can be formed, the charging rate characteristics of the battery can be more effectively improved.

[0065] The coating material may contain Li, P, O, and F.

[0066] The above configuration can effectively improve the battery's charge rate characteristics by forming a better interface between the coated active material 330 and the solid electrolyte 300. The coating material may also be made of Li, P, O, and F, excluding unavoidable impurities.

[0067] The coating material may be a phosphoric acid-based material or a sulfonic acid-based material. The coating material may also contain at least one selected from the group consisting of LiPOF4, LiPO2F2, Li2PO3F, and LiSO3F.

[0068] The coating material may preferably contain at least one selected from LiSO 3 F and LiPO 2 F 2 .

[0069] By using these materials as coating materials, the charging rate characteristics and life characteristics of the battery can be further improved.

[0070] The coating layer 320 may contain only the compound represented by formula (1) excluding unavoidable impurities. With such a configuration, the effect of improving the charging rate characteristics of the battery can be reliably obtained.

[0071] The ratio of the mass of the coating material to the mass of the coated active material 330 may be greater than 0 mass % and less than 10.0 mass %. The ratio of the mass of the coating material to the mass of the coated active material 330 may be greater than 0 mass % and less than 5.0 mass %. The ratio of the mass of the coating material to the mass of the coated active material 330 may be greater than 0 mass % and less than 3.0 mass %.

[0072] If the coating amount is adjusted to such a range, lithium ions can be smoothly transferred between the coated active material 330 and the solid electrolyte 300 , thereby more effectively improving the charge rate characteristics of the battery.

[0073] The ratio of the mass of the coating material to the mass of the coated active material 330 can be obtained, for example, by the following method. The coated active material 330 is dissolved in an acid or the like to prepare an aqueous solution. Then, the elements contained in the aqueous solution are quantified by inductively coupled plasma (ICP) emission spectrometry analysis. Thus, the ratio of the mass of the coating material to the mass of the coated active material 330 can be obtained. At this time, it is also possible to focus on the quantitative value of the element contained only in one of the negative electrode active material 310 and the coating material. After dissolving the coating material in pure water, the elements can also be quantified by detecting the dissolved ions using ion chromatography.

[0074] The coating material can also have a peak in the range of 685±7eV in the XPS spectrum measured using AlKα radiation. A peak originating from the F1s orbital is detected within this range. In particular, the peak centered at 685eV indicates the presence of a Li-F bond. Compared to the bonds between Li and other anions, the bond between Li and F is stronger and therefore more stable. Therefore, a coating material having a peak within this range is less likely to deteriorate even during charge and discharge reactions, enabling continuous improvement in charge rate characteristics.

[0075] The thickness of the coating layer 320 can also be between 0.5 nm and 20 nm. Setting the thickness of the coating layer 320 to 0.5 nm or greater can further improve the battery's charge rate characteristics. Setting the thickness of the coating layer 320 to 20 nm or less can improve Li-ion conductivity. More preferably, the thickness of the coating layer 320 can be between 0.5 nm and 10 nm or less.

[0076] The method for measuring the thickness of the coating layer 320 is not particularly limited. For example, in XPS measurement, the thickness can be estimated by scraping away the surface of the coated active material 330 using ion beam etching while observing specific peaks attributed to the coating material. Alternatively, the thickness of the coating layer 320 can also be measured by direct observation using a transmission electron microscope.

[0077] The coating layer 320 may cover the entire surface of the particles of the negative electrode active material 310. This can suppress direct contact between the particles of the negative electrode active material 310 and the particles of the solid electrolyte 300, thereby suppressing side reactions of the solid electrolyte 300. Consequently, the charge and discharge efficiency can be improved.

[0078] Alternatively, the coating layer 320 may cover only a portion of the surface of the negative electrode active material particles 310. By allowing the plurality of negative electrode active material particles 310 to directly contact each other via the portion without the coating layer 320, the electron conductivity between the particles of the negative electrode active material 310 is improved. Consequently, the battery can operate at a high power.

[0079] The shape of the solid electrolyte 300 in the first embodiment is not particularly limited, and may be, for example, needle-shaped, spherical, or elliptical. For example, the solid electrolyte 300 may be in the form of particles.

[0080] For example, when the solid electrolyte 300 in Embodiment 1 is in a particulate (e.g., spherical) shape, the median particle size can be 100 μm or less. When the median particle size of the solid electrolyte 300 is 100 μm or less, the coated active material 330 and the solid electrolyte 300 can be well dispersed in the negative electrode material 3000. This improves the battery's charge rate characteristics. In Embodiment 1, the median particle size of the solid electrolyte 300 can also be 10 μm or less.

[0081] According to the above configuration, the coated active material 330 and the solid electrolyte 300 can be well dispersed in the negative electrode material 3000 .

[0082] In the first embodiment, the median particle size of the solid electrolyte 300 may be smaller than the median particle size of the coated active material 330 .

[0083] According to the above configuration, the solid electrolyte 300 and the coated active material 330 can be better dispersed in the negative electrode material 3000 .

[0084] The median particle size of the coated active material 330 may be 0.1 μm or more and 100 μm or less.

[0085] When the median particle size of the coated active material 330 is 0.1 μm or greater, the coated active material 330 and the solid electrolyte 300 can be well dispersed in the negative electrode material 3000. As a result, the charge and discharge characteristics of the battery are improved.

[0086] When the median particle size of the coated active material 330 is 100 μm or less, the diffusion rate of lithium in the coated active material 330 can be sufficiently ensured. Therefore, the battery can operate at high power.

[0087] The median particle size of the coated active material 330 may be larger than the median particle size of the solid electrolyte 300. This allows the coated active material 330 and the solid electrolyte 300 to be well dispersed.

[0088] In the negative electrode material 3000 in the first embodiment, the particles of the solid electrolyte 300 and the particles of the coating active material 330 may also be as follows: Figure 1 The solid electrolyte 100 may fill the spaces between the particles of the coating active material 330. In this case, the coating layer 320 and the solid electrolyte 300 are in contact with each other.

[0089] The negative electrode material 3000 in the first embodiment may include a plurality of particles of the solid electrolyte 300 and a plurality of particles coated with the active material 330 .

[0090] The content of the solid electrolyte 300 and the content of the coated active material 330 in the negative electrode material 3000 may be the same as or different from each other.

[0091] In this specification, the "median diameter" refers to the particle diameter at which the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution can be measured, for example, using a laser diffraction analyzer or an image analyzer.

[0092] The solid electrolyte 300 may also have lithium ion conductivity. In this case, the negative electrode material 3000 can be used in a lithium ion battery.

[0093] The solid electrolyte 300 may include at least one selected from the group consisting of a sulfide solid electrolyte, a halide solid electrolyte, and an oxyhalide solid electrolyte.

[0094] According to the above configuration, the ion conductivity of the solid electrolyte 300 can be improved, thereby reducing the resistance of the battery.

[0095] Examples of the halide solid electrolyte include Li3YX'6, Li2MgX'4, Li2FeX'4, Li(Al, Ga, In)X'4, and Li3(Al, Ga, In)X'6.

[0096] Examples of oxyhalide solid electrolytes include Li a (Ta, Nb) b O c X' d a, b, c, and d are each independently a value greater than 0. X' contains at least one selected from F, Cl, Br, and I.

[0097] As sulfide solid electrolytes, Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 LiX', Li2O, MO can also be added to the above q 、Li p MO q etc. Wherein, the element X' in "LiX'" is at least one element selected from F, Cl, Br and I. "MO q ” and “Li p MO q The element M in "MO" is at least one element selected from P, Si, Ge, B, Al, Ga, In, Fe and Zn. q ” and “Li p MO q " where p and q are independent natural numbers.

[0098] In this disclosure, when an element in a formula is represented by "(Al, Ga, In)", this symbol represents at least one element selected from the group of elements enclosed in parentheses. That is, "(Al, Ga, In)" has the same meaning as "at least one selected from Al, Ga, and In." The same applies to other elements.

[0099] Various solid electrolytes can be produced, for example, by the following methods.

[0100] Prepare the raw material powders in a ratio that achieves the desired composition. For example, to produce Li₃YBr₃Cl₃, prepare LiCl and YBr₃ at a molar ratio of 3:1. The composition of the solid electrolyte can be adjusted by adjusting the type of raw material powder, the ratio of the raw material powders, and the synthesis process.

[0101] After the raw material powders are thoroughly mixed, they are then mixed and pulverized using a mechanochemical milling method to allow them to react. Alternatively, after the raw material powders are thoroughly mixed, the resulting mixture can be calcined in an inert atmosphere. This produces the desired solid electrolyte.

[0102] As the negative electrode active material 310 , a material having the property of intercalating and deintercalating metal ions such as lithium ions can be used.

[0103] The negative electrode active material 310 can be at least one selected from a carbon material, a metal material, an oxide, a nitride, a tin compound, silicon, a silicon compound, and a titanium compound. The metal material can be a single metal or an alloy. Examples of the metal material include lithium metal, lithium alloys, tin, and tin alloys. Examples of the carbon material include graphite, coke, graphitized carbon, carbon fibers, spherical carbon, and amorphous carbon.

[0104] The negative electrode active material 310 may also contain at least one selected from a carbon material and an alloy-based active material that forms an alloy with lithium. Since the expansion coefficient of carbon materials during charging is relatively small, the safety of the battery can be improved if a carbon material is used as the negative electrode active material 310. Carbon materials typically include graphite. Graphite is suitable as the negative electrode active material 310 because of its small expansion coefficient during the insertion reaction of lithium ions. The theoretical capacity of alloy-based active materials is large. If an alloy-based active material is used, the energy density of the battery can be improved. Examples of alloy-based active materials include silicon, tin, silicon compounds, and tin compounds.

[0105] The negative electrode active material 310 has a particle shape, for example. The shape of the particles of the negative electrode active material 310 is not particularly limited. The particles of the negative electrode active material 310 may be spherical, ellipsoidal, scaly, or fibrous.

[0106] Next, a method for producing the negative electrode material 3000 will be described.

[0107] First, a solution containing a coating material and a first solvent is prepared. The first solvent is a solvent capable of dissolving the coating material represented by formula (1). Examples of the first solvent include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethanol, methanol, hexanal, N-methylpyrrolidone, acetophenone, tetrahydrofurfuryl alcohol, methyl benzoate, methyl salicylate, isophorone, ethyl cyanoacetate, diethyl malonate, 1,4-dichlorobutane, ethyl acetate, benzaldehyde, chloroacetone, pyridine, butyronitrile, and acrylonitrile. One solvent selected from these solvents may be used alone as the first solvent, or a mixed solvent of two or more solvents selected from these solvents may be used as the first solvent.

[0108] Next, the solution and the negative electrode active material 310 are mixed to form a mixture. The first solvent is removed from the resulting mixture, thereby coating the negative electrode active material 310 with the coating material. The first solvent can be removed from the mixture by leaving it to stand in an atmosphere at room temperature, or by heating the mixture to volatilize the first solvent from the mixture. This results in a powder of the coated active material 330. This method allows the negative electrode active material 310 to be efficiently coated with the coating material. If heating is considered to remove the first solvent, it is recommended to use a first solvent with a boiling point lower than the decomposition temperature of the coating material.

[0109] In addition, a second solvent in which the coating material is insoluble is used to mix the solid electrolyte 300 and the negative electrode active material 310 coated with the coating material, thereby producing a slurry-like negative electrode material 3000. The slurry-like negative electrode material 3000 is applied to the negative electrode collector to form a coating film, and the coating film is dried to obtain the negative electrode of the battery. The coating film can be dried by heating it at a temperature higher than room temperature, or by allowing it to dry in an atmosphere at room temperature. Even in the former method, a drying temperature of less than 300°C is sufficient. According to the method of this embodiment, the negative electrode can be efficiently produced by a wet method such as a coating method. The method of this embodiment is simple because it does not require drying at a high temperature.

[0110] The second solvent has a δp value lower than that of the first solvent. The coating material and solid electrolyte are insoluble in the second solvent. Using the second solvent allows the negative electrode containing the coated active material 330 and solid electrolyte 300 to be fabricated while maintaining the coating layer 320. The "δp value" is a polarization term in the Hansen Solubility Parameter.

[0111] (Implementation Method 2)

[0112] Hereinafter, Embodiment 2 will be described, and descriptions overlapping with those of Embodiment 1 will be omitted as appropriate.

[0113] Figure 2 This is a cross-sectional view schematically showing the structure of a battery 2000 in the second embodiment.

[0114] The battery 2000 in the second embodiment includes a positive electrode 201 , an electrolyte layer 202 , and a negative electrode 203 .

[0115] The negative electrode 203 contains the negative electrode material 3000 in Embodiment 1. The benefits described in Embodiment 1 can be obtained in the negative electrode 203 .

[0116] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0117] According to the above configuration, the charge and discharge efficiency of the battery 2000 can be improved.

[0118] When the volume ratio of the negative electrode active material 310 to the solid electrolyte 300 (first solid electrolyte) in the negative electrode 203 is expressed as "v2:100-v2", the volume ratio v2 of the negative electrode active material 310 may satisfy 30≤v2≤95. When 30≤v2 is satisfied, the energy density of the battery 2000 can be sufficiently ensured. Furthermore, when v2≤95 is satisfied, high power operation is possible.

[0119] The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, the energy density of the battery 2000 can be sufficiently ensured. When the thickness of the negative electrode 203 is 500 μm or less, high power operation is possible.

[0120] The positive electrode 201 contains a positive electrode active material and a solid electrolyte (third solid electrolyte). As the positive electrode active material, a material having the property of inserting and extracting metal ions such as lithium ions can be used. As the positive electrode active material, lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal sulfur oxides, transition metal nitrogen oxides, etc. can be used. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost can be reduced and the average discharge voltage can be increased.

[0121] The positive electrode active material may contain Li and at least one element selected from Mn, Co, Ni, and Al. Examples of such materials include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2.

[0122] The positive electrode active material has a particle shape, for example. The shape of the positive electrode active material particles is not particularly limited. The shape of the positive electrode active material particles can be needle-shaped, spherical, ellipsoidal, or scaly.

[0123] The median particle size of the particles of the positive electrode active material can also be greater than 0.1 μm and less than 100 μm. When the median particle size of the particles of the positive electrode active material is greater than 0.1 μm, the positive electrode active material and the solid electrolyte can form a well-dispersed state in the positive electrode 201. As a result, the charge and discharge characteristics of the battery 2000 are improved. When the median particle size of the particles of the positive electrode active material is less than 100 μm, the diffusion of lithium within the particles of the positive electrode active material is accelerated. Therefore, the battery 2000 can operate at high power.

[0124] As the solid electrolyte for positive electrode 201, at least one selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte may be used. Oxide solid electrolytes have excellent high potential stability. By using an oxide solid electrolyte, the charge and discharge efficiency of battery 2000 can be further improved.

[0125] When the volume ratio of the positive electrode active material to the solid electrolyte in positive electrode 201 is expressed as "v1:100-v1", the volume ratio v1 of the positive electrode active material may satisfy 30≤v1≤95. When 30≤v1 is satisfied, the energy density of battery 2000 can be sufficiently ensured. Furthermore, when v1≤95 is satisfied, high power operation is possible.

[0126] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 is 10 μm or more, the energy density of the battery 2000 can be sufficiently ensured. When the thickness of the positive electrode 201 is 500 μm or less, high power operation is possible.

[0127] When the solid electrolyte contained in positive electrode 201 is in a particulate (e.g., spherical) shape, the median particle size of the solid electrolyte particles can be 100 μm or less. When the median particle size is 100 μm or less, the positive electrode active material and the solid electrolyte are well dispersed in positive electrode 201. Consequently, the charge and discharge characteristics of battery 2000 are improved.

[0128] Electrolyte layer 202 is a layer containing an electrolyte. This electrolyte is, for example, a solid electrolyte. That is, electrolyte layer 202 may also be a solid electrolyte layer. Hereinafter, the solid electrolyte contained in electrolyte layer 202 is also referred to as the "second solid electrolyte."

[0129] As the second solid electrolyte, the materials exemplified in Embodiment 1 may be used. That is, the electrolyte layer 202 may contain a solid electrolyte having the same composition as that of the solid electrolyte 300 contained in the negative electrode material 3000 .

[0130] According to the above configuration, the charge and discharge efficiency of the battery 2000 can be further improved.

[0131] Alternatively, the electrolyte layer 202 may contain a halide solid electrolyte having a composition different from the composition of the solid electrolyte 300 contained in the negative electrode material 3000 .

[0132] According to the above configuration, the power density and charge and discharge efficiency of the battery 2000 can be improved.

[0133] The halide solid electrolyte contained in the electrolyte layer 202 may also contain Y as a metal element.

[0134] According to the above configuration, the power density and charge / discharge efficiency of the battery 2000 can be further improved.

[0135] The electrolyte layer 202 may contain a sulfide solid electrolyte. Examples of the sulfide solid electrolyte include the solid electrolytes described in the first embodiment.

[0136] According to the above configuration, since the sulfide solid electrolyte having excellent reduction stability is contained, a negative electrode material having a low potential, such as graphite or metallic lithium, can be used, and the energy density of the battery 2000 can be increased.

[0137] The electrolyte layer 202 may contain at least one selected from an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0138] As oxide solid electrolytes, for example, NASICON solid electrolytes represented by LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite solid electrolytes, and Li 14 ZnGe4O 16 , LISICON type solid electrolyte represented by Li4SiO4, LiGeO4 and their elemental substitutes, Li7La3Zr2O 12 Garnet-type solid electrolytes represented by Li3N and its H-substituted products, Li3PO4 and its N-substituted products, glass or glass ceramics made by adding Li2SO4, Li2CO3 and other materials to a matrix material containing Li-BO compounds such as LiBO2 and Li3BO3, etc.

[0139] As a polymer solid electrolyte, for example, a polymer compound and a compound with a lithium salt can be used. The polymer compound may also have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain more lithium salt, thereby further improving the ion conductivity. As lithium salts, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. can be used. As the lithium salt, one lithium salt selected from the above may be used alone, or a mixture of two or more lithium salts selected from the above may be used.

[0140] As the complex hydride solid electrolyte, for example, LiBH 4 —LiI, LiBH 4 —P 2 S 5 , or the like can be used.

[0141] The electrolyte layer 202 may contain the second solid electrolyte as a main component. That is, the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio of 50% or more (ie, 50% by mass or more) relative to the total mass of the electrolyte layer 202 .

[0142] According to the above configuration, the charge and discharge characteristics of the battery 2000 can be further improved.

[0143] The electrolyte layer 202 may contain the second solid electrolyte in an amount of 70% or more (ie, 70% by mass or more) relative to the total mass of the electrolyte layer 202 .

[0144] According to the above configuration, the charge and discharge characteristics of the battery 2000 can be further improved.

[0145] The electrolyte layer 202 may contain the second solid electrolyte as a main component and may also contain inevitable impurities, starting materials, by-products, decomposition products, etc. used in synthesizing the second solid electrolyte.

[0146] The electrolyte layer 202 may contain the second solid electrolyte in an amount of 100% (ie, 100% by mass) based on the total mass of the electrolyte layer 202 excluding unavoidable impurities.

[0147] According to the above configuration, the charge and discharge characteristics of the battery 2000 can be further improved.

[0148] As described above, the electrolyte layer 202 may be composed only of the second solid electrolyte.

[0149] Electrolyte layer 202 may contain only one solid electrolyte selected from the aforementioned solid electrolyte group, or may contain two or more solid electrolytes selected from the aforementioned solid electrolyte group. The multiple solid electrolytes may have different compositions. For example, electrolyte layer 202 may contain both a halide solid electrolyte and a sulfide solid electrolyte.

[0150] The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the positive electrode 201 and the negative electrode 203 can be more reliably separated. When the thickness of the electrolyte layer 202 is 300 μm or less, high-power operation can be achieved.

[0151] In at least one of the positive electrode 201, the electrolyte layer 202 and the negative electrode 203, a binder can also be contained for the purpose of improving the adhesion between the particles. The binder is used to improve the cohesiveness of the material constituting the electrode. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aromatic polyamide resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyether, polyether sulfone, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc. can be listed. In addition, as the binder, a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, hexadiene can be used. Furthermore, two or more selected from the above may be mixed and used as the binder.

[0152] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to improve electronic conductivity. Examples of the conductive additive include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and Ketjen black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0153] Each of the positive electrode 201 and the negative electrode 203 may have a current collector. Examples of the material of the current collector include aluminum, aluminum alloys, stainless steel, copper, and nickel.

[0154] The battery 2000 in the second embodiment can be configured as a battery in various shapes, such as a coin-shaped, cylindrical, rectangular, sheet-shaped, button-shaped, flat, and laminated type.

[0155] Example

[0156] Hereinafter, the present disclosure will be described in detail using Examples and Comparative Examples.

[0157] [Preparation of sulfide solid electrolyte]

[0158] In a glove box with an Ar atmosphere at a dew point below -60°C, Li2S and P2S5 are weighed in a molar ratio of Li2S:P2S5=75:25. They are crushed and mixed in a mortar to obtain a mixture. Then, a planetary ball mill (P-7 model manufactured by Fritsch) is used to grind the mixture at 510 rpm for 10 hours to obtain a glassy solid electrolyte. The glassy solid electrolyte is heat-treated at 270 degrees for 2 hours in an inert atmosphere. Thus, a glass-ceramic sulfide solid electrolyte, namely, a powder of Li2S-P2S5, is obtained.

[0159] Example 1

[0160] [Preparation of coated active material]

[0161] In a glove box in an Ar atmosphere with a dew point of -60°C or less, 0.12 g of LiSO3F was dissolved in 9.88 g of dimethyl carbonate to obtain a lithium sulfonate solution with a concentration of 1.2% by mass.

[0162] 10 g of LiSO 3 F solution and 10 g of graphite were mixed, left at room temperature for 24 hours, and then dried at 105° C. for 8 hours. This yielded graphite coated with LiSO 3 F as a coated active material.

[0163] [Production of negative electrode materials]

[0164] In a glove box with an Ar atmosphere having a dew point of -60°C or lower, the coated active material and the sulfide solid electrolyte were mixed at a mass ratio of 7:3. Thus, the negative electrode material of Example 1 was obtained.

[0165] [Battery Production]

[0166] The following steps were carried out using a negative electrode material, a sulfide solid electrolyte, and a copper foil (thickness 12 μm).

[0167] First, 10 mg of a sulfide solid electrolyte and 10 mg of a negative electrode material were stacked in an insulating outer cylinder and press-formed at a pressure of 360 MPa to obtain a stack of negative electrode active material layers and electrolyte layers.

[0168] Next, copper foil was stacked on the negative electrode active material layer and press-formed at 360 MPa to obtain a stack of the negative electrode current collector, the negative electrode active material layer, and the electrolyte layer.

[0169] Next, metal In (200 μm thick), metal Li (300 μm thick), and metal In (200 μm thick) were stacked in this order on the electrolyte layer. These were press-formed at a pressure of 80 MPa to produce a stack consisting of the positive electrode, electrolyte layer, and negative electrode.

[0170] Next, stainless steel current collectors were placed on the upper and lower sides of the stacked body, and current collecting leads were attached to the current collectors.

[0171] Finally, the insulating outer cylinder was sealed using an insulating ferrule to isolate the interior of the insulating outer cylinder from the external atmosphere, thereby producing the battery of Example 1.

[0172] Example 2

[0173] [Preparation of coated active material]

[0174] 10g of LiSO3F solution, 9g of graphite, and 1g of silicon were mixed and left at room temperature for 24 hours, then dried at 105°C for 8 hours. This produced a mixed active material of graphite coated with LiSO3F and silicon coated with LiSO3F. Powdered graphite and silicon were used.

[0175] [Production of negative electrode materials]

[0176] In a glove box with an Ar atmosphere having a dew point of -60°C or lower, the mixed active material and the sulfide solid electrolyte were mixed at a mass ratio of 7:3. Thus, the negative electrode material of Example 2 was obtained.

[0177] [Battery Production]

[0178] A battery of Example 2 was prepared in the same manner as in Example 1, except that 5 mg of the negative electrode material of Example 2 was used instead of the negative electrode material of Example 1.

[0179] Example 3

[0180] [Preparation of coated active material]

[0181] In a glove box with an Ar atmosphere at a dew point of -60°C or lower, 0.6 g of LiPO2F2 was dissolved in 9.94 g of dimethyl carbonate to obtain a LiPO2F2 solution with a concentration of 0.6% by mass.

[0182] [Production of negative electrode materials]

[0183] 10 g of LiPO2F2 solution and 10 g of graphite were mixed, left at room temperature for 24 hours, and then dried at 105°C for 8 hours. In this way, graphite coated with LiPO2F2 was obtained as a coated active material.

[0184] [Battery Production]

[0185] A battery of Example 3 was produced in the same manner as in Example 1, except that the negative electrode material of Example 3 was used instead of the negative electrode material of Example 1.

[0186] Comparative Example 1

[0187] A battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that graphite without a coating layer was used as the negative electrode active material.

[0188] Comparative Example 2

[0189] A battery of Comparative Example 2 was prepared in the same manner as in Example 2, except that a mixture of graphite without a coating layer and silicon without a coating layer was used as the negative electrode active material.

[0190] Comparative Example 3

[0191] A battery of Comparative Example 3 was prepared in the same manner as in Example 1 except that 7.7 mg of graphite without a coating layer was used as the negative electrode active material.

[0192] Comparative Example 4

[0193] [Preparation of coated active material]

[0194] In a glove box of an Ar atmosphere with a dew point of -60°C or lower, graphite was coated with amorphous carbon according to the method disclosed in Patent Document 1 to obtain a coated active material.

[0195] [Production of negative electrode materials]

[0196] In a glove box with an Ar atmosphere having a dew point of -60°C or lower, the coated active material and the sulfide solid electrolyte were mixed at a mass ratio of 7:3. Thus, the negative electrode material of Comparative Example 4 was obtained.

[0197] [Battery Production]

[0198] A battery of Comparative Example 4 was prepared in the same manner as in Example 1, except that 10 mg of the negative electrode material of Comparative Example 4 was used instead of the negative electrode material of Example 1.

[0199] Comparative Example 5

[0200] A battery of Comparative Example 5 was produced in the same manner as in Example 1 except that LiFSI (LiN(SO 2 F) 2 ) was used as the coating material.

[0201] Comparative Example 6

[0202] [Preparation of coated active material]

[0203] In a glove box with an Ar atmosphere at a dew point of -60°C or less, 0.6 g of LiPF6 was dissolved in 9.94 g of dimethyl carbonate to obtain a LiPF6 solution with a concentration of 0.6% by mass.

[0204] [Production of negative electrode materials]

[0205] 10 g of LiPF6 solution and 10 g of graphite were mixed, left at room temperature for 24 hours, and then dried at 105°C for 8 hours. In this way, graphite coated with LiPF6 was obtained as a coated active material.

[0206] [Battery Production]

[0207] A battery of Comparative Example 6 was produced in the same manner as in Example 1, except that the negative electrode material of Comparative Example 6 was used instead of the negative electrode material of Example 1.

[0208] [Charge and discharge test]

[0209] Using the batteries of Examples 1 to 3 and Comparative Examples 1 to 6, charge and discharge tests were carried out under the following conditions.

[0210] The battery was placed in a constant temperature chamber at 25°C.

[0211] Constant current charging was performed at a current value of 380 μA, which gave a 0.05 C rate (20-hour rate) with respect to the theoretical capacity of the battery, and charging was terminated at a voltage of −0.62 V.

[0212] Next, constant current discharge was performed at a current value of 380 μA, which was a rate of 0.05 C (20-hour rate), and the discharge was terminated at a voltage of 1.9 V. However, the current value of the battery of Comparative Example 3 was 292 μA.

[0213] Furthermore, constant current charging was performed at a current value of 380 μA, which is sufficient to achieve a 0.05C rate (20-hour rate) relative to the theoretical capacity of the battery, and charging was terminated at a voltage of -0.62 V. However, for the battery of Comparative Example 3, the current value was 292 μA. The charge capacity at this time is recorded as "0.05C charge capacity."

[0214] Furthermore, after constant current discharge at a current value reaching a 0.05C rate (20-hour rate), the batteries of Examples and Comparative Examples were charged at a constant current value of 3800 μA, 10 times the current value, and the charging was terminated at a voltage of -0.62 V. However, for the battery of Comparative Example 3, the current value was 2920 μA. The charge capacity at this time is recorded as the "0.5C charge capacity."

[0215] The ratio of the 0.5C charge capacity to the 0.05C charge capacity was calculated for the batteries of the examples and comparative examples. The ratio of the 0.05C charge capacity of each battery to the 0.05C charge capacity of the battery of Example 1 was also calculated. The results are shown in Table 1.

[0216] Table 1

[0217]

[0218] Investigation

[0219] The ratio of (0.5C charge capacity) / (0.05C charge capacity) reflects the charging rate characteristics. That is, the higher the value of (0.5C charge capacity) / (0.05C charge capacity), the shorter the charging time.

[0220] As shown in Table 1, the value of (0.5C charge capacity) / (0.05C charge capacity) of the battery of Example 1 is higher than that of Comparative Example 1. The charge rate characteristics are improved by coating the negative electrode active material with LiSO3F.

[0221] Generally speaking, coating the surface of an active material with an inorganic compound that lacks lithium ion conductivity creates a barrier to lithium ion migration, hindering its movement. Therefore, such inorganic compounds are rarely chosen as coating materials for improving charge rate characteristics.

[0222] However, surprisingly, the use of LiSO3F as the coating material in the battery of Example 1 improved the charging rate characteristics. The reason for this is believed to be related to the lithium ion concentration in the coating layer. It is believed that the high lithium concentration in the coating layer of the battery of Example 1 facilitates the incorporation of lithium ions into the negative electrode active material during charging, resulting in improved charging rate characteristics.

[0223] From the comparison results between Example 2 and Comparative Example 2, it can be seen that the same effect can be obtained even when an alloy-based active material is used as the negative electrode active material.

[0224] From the results of Example 3, it can be seen that beneficial effects can also be obtained when LiPO2F2 is used as the coating material.

[0225] On the other hand, the Li source of Comparative Examples 1 and 2 is limited to Li contained in the solid electrolyte. Therefore, it is believed that the charging rate characteristics of the batteries of Comparative Examples 1 and 2 are inferior to the charging rate characteristics of the battery of the example.

[0226] The charging rate characteristics of the battery of Comparative Example 3 were comparable to those of the battery of Example 1. However, due to the reduced amount of negative electrode active material used in Comparative Example 3, the charging capacity of the battery of Comparative Example 3 was significantly lower than that of the battery of Example 1. Comparative Example 3 demonstrates that the charging rate characteristics can be improved at the expense of battery energy density. However, Comparative Example 3 is not preferable from the perspective of battery energy density.

[0227] The charge rate characteristics of the battery of Comparative Example 4 were significantly lower than those of the other batteries. The amorphous carbon coating layer not only failed to improve the charge rate characteristics of the solid battery, but also degraded the charge rate characteristics.

[0228] In the battery of Comparative Example 5, graphite was coated with a lithium salt (LiFSI) containing nitrogen (N) as an anion. Comparison of the results of Comparative Examples 1 and 5 shows that even LiFSI-coated graphite did not improve charging rate performance. This indicates that not all lithium salts produce the same effect.

[0229] In the battery of Comparative Example 6, graphite was coated with LiPF 6. Comparison of the results of Example 1, Comparative Example 1, and Comparative Example 6 shows that the LiPF 6 coating improves the charge rate characteristics, but the effect is limited.

[0230] Industrial applicability

[0231] The battery disclosed herein can be used as, for example, an all-solid-state lithium secondary battery.

Claims

1. A negative electrode material comprising: coating active material; and solid electrolytes, The coated active material includes a negative electrode active material and a coating layer provided on the surface of the negative electrode active material. The coating layer is a layer containing a coating material in a solid state, The coated active material and the solid electrolyte are in contact with each other, The coating material is composed of Li, S, O, and F except for inevitable impurities, and is represented by the following composition formula (1): Li a A b X c (1) in, a, b and c are positive real numbers, A is S, X is F and O, The coating material contains SO x F y base, x and y are values ​​satisfying x>0, y>0.

2. The negative electrode material according to claim 1, wherein The thickness of the coating material layer is 0.5 nm or more and 20 nm or less.

3. The negative electrode material according to claim 1, wherein The solid electrolyte contains at least one selected from the group consisting of a sulfide solid electrolyte, a halide solid electrolyte, and an oxyhalide solid electrolyte.

4. The negative electrode material according to claim 1, wherein The negative electrode active material contains at least one selected from a carbon material and an alloy-type active material that forms an alloy with lithium.

5. The negative electrode material according to claim 1, wherein The negative electrode active material contains graphite.

6. The negative electrode material according to claim 1, wherein The solid electrolyte has lithium ion conductivity.

7. A battery comprising: A negative electrode comprising the negative electrode material according to any one of claims 1 to 6; positive electrode; and An electrolyte layer is provided between the positive electrode and the negative electrode.

8. The method for producing the negative electrode material according to any one of claims 1 to 6, comprising the following steps: preparing a solution containing the coating material and a first solvent, mixing the solution and the negative electrode active material to prepare a mixture, The negative electrode active material is coated with the coating material by removing the first solvent from the mixture.

9. The method for producing a negative electrode material according to claim 8, wherein: The negative electrode material in a slurry form is prepared by kneading a solid electrolyte and the negative electrode active material coated with the coating material using a second solvent in which the coating material is insoluble.

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