Phosphorus-carbon composite negative electrode material, negative electrode active material, negative electrode for lithium secondary battery, lithium secondary battery, and method for producing phosphorus-carbon composite negative electrode material

Abstract

This phosphorus-carbon composite negative electrode material comprises a phosphorus-carbon material containing phosphorus atoms and elemental carbon, and a coating material that coats at least a portion of one particle of the phosphorus-carbon material, wherein the coating material contains a polymer compound, and has a coverage rate measured by an energy-dispersive X-ray spectroscopy method of 0.1% to 5%. In the phosphorus-carbon composite negative electrode material, a ratio WL620 / WL780 between a weight reduction rate WL620 at a measurement temperature of 620°C determined by a prescribed thermal weight measurement and a weight reduction rate WL780 at a measurement temperature of 780°C is preferably 0.1 to 0.9.

Description

Phosphorus-carbon composite negative electrode material, negative electrode active material, negative electrode for lithium secondary battery, lithium secondary battery, and method for producing phosphorus-carbon composite negative electrode material

[0001] The present invention relates to a phosphorus-carbon composite negative electrode material, a negative electrode active material, a negative electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing the phosphorus-carbon composite negative electrode material. This application claims priority based on Japanese Patent Application No. 2023-127804, filed on August 4, 2023, the contents of which are incorporated herein by reference.

[0002] Lithium secondary batteries are used as power sources for small electronic devices such as mobile phones and laptops. In recent years, lithium secondary batteries have also been put to practical use as medium- to large-sized power sources for automobiles and power storage applications.

[0003] Carbon materials are known as negative electrode active materials for lithium secondary batteries. Conventionally, negative electrode active materials in which phosphorus is further added to a carbon material have been known for the purpose of improving battery performance (see, for example, Patent Document 1). The negative electrode active material described in Patent Document 1, which is a composite of a carbon material and phosphorus, can be used to provide a negative electrode with excellent charge / discharge capacity.

[0004] JP 2009-184861 A

[0005] Further safety measures are required for lithium secondary batteries, and the negative electrode active material described in Patent Document 1 has ample room for improvement from the viewpoint of safety measures. Specifically, the black phosphorus used in Patent Document 1 has high chemical stability and excellent safety among phosphorus allotropes. However, the present inventors have found a problem in that the chemical stability and safety of black phosphorus are easily reduced depending on the processing method.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly safe phosphorus-carbon composite negative electrode material, a negative electrode active material, a negative electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing the phosphorus-carbon composite negative electrode material.

[0007] In order to solve the above problems, one aspect of the present invention includes the following: [1] A phosphorus-carbon composite negative electrode material comprising a phosphorus-carbon material containing phosphorus atoms and carbon elements, and a coating that coats at least a portion of one particle of the phosphorus-carbon material, wherein the coating contains a polymer compound, and the coating has a coverage of 0.1% or more and 5% or less as measured by energy dispersive X-ray spectroscopy. [2] A weight loss rate WL at a measurement temperature of 620°C determined by thermogravimetry under the following conditions: ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Relative to WL ６２０ / WL ７８０ The phosphorus-carbon composite negative electrode material according to [1], wherein the value of σ is 0.1 or more and 0.9 or less. (Thermogravimetry) 10 mg of the phosphorus-carbon composite negative electrode material is precisely weighed out to prepare a sample, and a thermogravimetry device is used to measure the change in weight when heated in a nitrogen stream from 50°C to 780°C at a temperature increase rate of 10°C / min. (Weight loss rate) The ratio of the weight of the sample at the measurement temperature to the weight of the precisely weighed sample is taken as the weight loss rate (wt%) at the measurement temperature. [3] The phosphorus-carbon composite negative electrode material according to [1] or [2], which has a peak in its XPS spectrum indicating a bond between a phosphorus atom and a carbon atom. [4] In an XRD profile measured using CuKα radiation, the intensity I at 2θ=20° is ２０ , intensity I at 2θ=26.3° ２６．３ , and the intensity at 2θ=40° I ４０ The phosphorus-carbon composite negative electrode material according to any one of [1] to [3], wherein |P| / |B|<2 (1) satisfies the following formulas (1) to (3): ２６．３ -I ４０ ...(2) B = (I ２０ -I ４０)×(26.3−40) / (20−40) ... (3) [5] The phosphorus-carbon composite negative electrode material according to any one of [1] to [4], wherein the phosphorus-carbon material has a core particle containing a phosphorus atom and a carbon coating covering the surface of the core particle. [6] A negative electrode active material comprising the phosphorus-carbon composite negative electrode material according to any one of [1] to [5]. [7] A negative electrode for a lithium secondary battery comprising the negative electrode active material according to [6]. [8] A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to [7]. [9] A method for producing a phosphorus-carbon composite negative electrode material, comprising: a step of obtaining a phosphorus-carbon material containing a phosphorus atom and elemental carbon; a step of mixing the phosphorus-carbon material with a binder resin to obtain a mixed powder; a step of mixing the mixed powder with a solvent; and a subsequent drying step.

[10] A method for producing a phosphorus-carbon composite negative electrode material, comprising the steps of: mixing a phosphorus material, a carbon material, and a binder resin to obtain a mixed powder; mixing the mixed powder with a solvent; and then drying the mixed powder.

[11] The method for producing a phosphorus-carbon composite negative electrode material according to [9] or

[10] , wherein the mixing ratio of the binder resin is 0.5 mass % or more and 15 mass % or less with respect to the total amount of the mixed powder.

[12] The method for producing a phosphorus-carbon composite negative electrode material according to any one of [9] to

[11] , wherein the binder resin is polyvinylidene fluoride.

[0008] According to the present invention, it is possible to provide a highly safe phosphorus-carbon composite negative electrode material, a negative electrode active material, a negative electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing the phosphorus-carbon composite negative electrode material.

[0009] FIG. 1 is a graph showing the results of thermogravimetry of a PC anode material and a PC mixture. FIG. 2 is an XPS spectrum of the PC anode material and the PC mixture. FIG. 3 is a transmission electron microscope (TEM) photograph of a phosphorus-carbon material. FIG. 4 is an XRD profile of the PC anode material and the PC mixture. FIG. 5 is a schematic diagram showing an all-solid-state lithium secondary battery, which is an example of a battery. FIG. 6 is a schematic diagram showing an all-solid-state lithium secondary battery, which is an example of a battery.

[0010] <Phosphorus-carbon composite negative electrode material> The phosphorus-carbon composite negative electrode material of this embodiment comprises a phosphorus-carbon material containing phosphorus atoms and carbon elements, and a coating that coats at least a portion of one particle of the phosphorus-carbon material. In the following description, the "phosphorus-carbon composite negative electrode material" may be simply abbreviated as "P-C negative electrode material." The "phosphorus-carbon material" may be referred to as "P-C material." In one aspect of the present invention, the P-C negative electrode material is a powder.

[0011] In this embodiment, whether or not a PC negative electrode material is highly safe is evaluated by checking for the presence or absence of odor through a moisture resistance test described in the Examples below. If there is no odor, phosphine, which can cause ignition, is not generated, and the material is evaluated as being highly safe.

[0012] In a P-C negative electrode material provided with a coating, the P-C material is protected by the coating. This makes it difficult for phosphorus to react with moisture in the air, and it is difficult for phosphine, which can cause ignition, to be generated. As a result, a P-C negative electrode material that is difficult to ignite and highly safe can be provided. As an example, phosphorus that has been processed into a fine powder and has a large surface area is prone to react with moisture in the air. Even with phosphorus that has been processed into a fine powder, providing a coating makes this reaction less likely to occur, and a P-C negative electrode material that is highly safe can be provided. The example of phosphorus processed into a fine powder is just one example, and the above-mentioned effect of being protected by a coating is exerted regardless of the processing mode of the phosphorus.

[0013] The coating contains a polymer compound. The polymer compound contained in the coating is preferably a material used as a binder in secondary batteries. Specifically, a thermoplastic resin binder can be used.

[0014] Examples of the thermoplastic binder include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, hexafluoropropylene-vinylidene fluoride copolymers, and tetrafluoroethylene-perfluorovinyl ether copolymers; polyolefin resins such as polyethylene and polypropylene; and amide resins such as polyimide and polyamideimide.

[0015] The polymer compound is preferably a fluorine-based resin, more preferably polyvinylidene fluoride. That is, the coating preferably contains fluorine. The coating may contain chlorine, bromine, or iodine in addition to fluorine. That is, the coating may contain one or more elements selected from the group consisting of fluorine, chlorine, bromine, and iodine.

[0016] The PC negative electrode material has a coverage of 0.1% or more and 5% or less as measured by energy dispersive X-ray spectroscopy. The method for measuring the coverage is described below. Hereinafter, energy dispersive X-ray spectroscopy will be referred to as "EDX analysis." EDX analysis can measure the types and amounts of elements present on the surface of the PC negative electrode material.

[0017] [Method for Measuring Coverage Ratio] When measuring the coverage ratio, specific elements contained in the coating are measured and measured as the surface abundance ratio of the specific elements. Examples of specific elements include fluorine, chlorine, bromine, and iodine. Hereinafter, these specific elements may be referred to as coating elements.

[0018] For PC negative electrode materials, the abundance ratio of coating elements is calculated from the EDX spectrum obtained by performing EDX analysis during scanning electron microscope (hereinafter referred to as SEM) observation. Specifically, SEM observation of the PC negative electrode material is performed under the following conditions, and the EDX spectrum is analyzed. SEM / EDX device: JEOL JCM-7000 tabletop scanning electron microscope, accelerating voltage: 5 kV, working distance: 12.6 mm, observation magnification: 5000x, field of view area: 489.4 μm ２

[0019] Under the above conditions, the abundance of elements near the surface of the PC negative electrode material can be analyzed by setting the acceleration voltage to a low voltage of 5 kV. In areas of the PC negative electrode material where the coating is thin or absent, not only the coating but also the surface of the PC material is analyzed.

[0020] The peaks corresponding to each element can be identified using an existing database, or the abundance ratio of each element can be calculated automatically using the included software.

[0021] The coverage, specifically the surface abundance of the coating element, is calculated from the abundance ratio of the coating element, carbon, and phosphorus using the following formula.

[0022] Coverage (%) = [covering element / (covering element + C + P)] x 100

[0023] The coverage of the PC negative electrode material is preferably 0.15% to 4.5%, more preferably 0.2% to 4%, even more preferably 0.25% to 3.5%, and particularly preferably 0.3% to 2%. When the coverage is equal to or greater than the lower limit, the PC material is protected from moisture in the air, making it less susceptible to hygroscopic reactions and phosphine-generating reactions, resulting in a highly safe PC negative electrode material. When the coverage is equal to or less than the upper limit, lithium ion migration is less likely to be hindered, resulting in high safety, and in addition, the discharge capacity and cycle characteristics of the secondary battery are more likely to be improved.

[0024] When the PC material contains components other than phosphorus atoms and carbon atoms, the content of the other components is preferably 1 mass % or more and 15 mass % or less, more preferably 2 mass % or more and 12 mass % or less, and even more preferably 2.5 mass % or more and 8 mass % or less, based on the total amount of the components other than phosphorus atoms and carbon atoms.

[0025] When the content ratio of the other components is within the above range, the movement of lithium ions is not easily hindered, and in addition to the effect of high safety, the discharge capacity and cycle characteristics of the secondary battery are likely to be improved.

[0026] The content of phosphorus atoms in the PC material is preferably 10% by mass or more and 95% by mass or less. Furthermore, the content of carbon atoms in the PC material is preferably 5% by mass or more and 90% by mass or less. When the PC material is composed of phosphorus atoms and carbon atoms, the sum of the carbon atom content and the phosphorus atom content in the PC material is 100% by mass. Even when the PC material is composed of carbon atoms and phosphorus atoms, impurities inevitably mixed in from the raw materials and manufacturing process of the PC material are acceptable.

[0027] The PC material is composed of 60 mass% or more of phosphorus atoms and carbon atoms, and may further contain elements other than phosphorus atoms and carbon atoms. Examples of elements other than phosphorus atoms and carbon atoms contained in the PC material include lithium, silicon, germanium, tin, aluminum, zinc, magnesium, transition metals, nitrogen, oxygen, fluorine, silicon, titanium, niobium, sulfur, and chlorine. These can be obtained from metal oxides, composite metal oxides, metal fluorides, metal sulfides, metal chlorides, silicon oxides, silicates, titanates, and aluminates.

[0028] The content of phosphorus atoms, the content of carbon atoms, and the content of other atoms that may be contained in the PC material can be determined by known ICP analysis.

[0029] In the PC material, the content of the phosphorus atoms is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more. A higher phosphorus content increases the initial charge / discharge capacity of the PC negative electrode material. Furthermore, in the PC material, the content of the phosphorus atoms is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. This is because if the content of phosphorus atoms is too high, the cycle characteristics of the PC negative electrode material will deteriorate. The upper and lower limits of the content of phosphorus atoms can be combined arbitrarily.

[0030] In the PC material, the carbon atom content is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. A higher carbon atom content improves the cycle characteristics of the PC negative electrode material. Furthermore, in the PC material, the carbon atom content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less. This is because if the carbon atom content is too high, the initial charge / discharge capacity of the PC negative electrode material decreases. The upper and lower limits of the carbon atom content can be combined arbitrarily.

[0031] As will be described in detail later, the PC negative electrode material can be produced by ball milling phosphorus, a carbon material, and a polymer compound. The inventors conducted a detailed analysis and study of the obtained PC negative electrode material and confirmed that the PC negative electrode material is not simply a mixture of the raw materials, phosphorus, a carbon material, and a polymer compound, but is a novel material in which phosphorus atoms and carbon atoms are chemically bonded (covalently bonded) in the PC material and have physical properties different from those of the raw materials, phosphorus and carbon materials. Even when the phosphorus material, carbon raw material, and binder resin are ball milled, a negative electrode active material in which the phosphorus atoms and carbon atoms are chemically bonded (covalently bonded) is produced.

[0032] The physical properties of the PC negative electrode material will be described in detail below, comparing it with a mixture of phosphorus and a carbon material (hereinafter sometimes referred to as a "PC mixture").

[0033] The following description compares an example of a PC negative electrode material with an example of a mixture obtained by mixing the same raw materials as the PC negative electrode material in a mortar. In the example shown below, the raw materials for the PC negative electrode material and the raw materials for the PC mixture both contain black phosphorus and a carbon material in a mass ratio of 6:4. In both the PC material and the PC mixture, CSCNT (cup-stacked carbon nanotubes) are used as the carbon material.

[0034] [Heat behavior] The PC negative electrode material has a weight loss rate WL at a measurement temperature of 620°C, which is determined by thermogravimetry under the following conditions: ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Relative to WL ６２０ / WL ７８０ is preferably 0.1 or more and 0.9 or less. (Thermogravimetric Measurement) 10 mg of the phosphorus-carbon composite negative electrode material is precisely weighed out to prepare a sample, and a thermogravimetric measuring device is used to measure the change in weight when the sample is heated from 50°C to 780°C at a temperature increase rate of 10°C / min in a nitrogen stream. (Weight Loss Rate) The ratio of the weight of the sample at the measurement temperature to the weight of the precisely weighed sample is defined as the weight loss rate (wt %) at the measurement temperature.

[0035] Figure 1 is a graph showing the results of the thermogravimetric measurements of the PC negative electrode material and the PC mixture. In Figure 1, the horizontal axis represents the heating temperature (°C), and the vertical axis represents the weight loss rate (wt%) relative to the sample weight. In Figure 1, the symbol A represents the behavior of the PC negative electrode material, and the symbol X represents the behavior of the PC mixture.

[0036] As shown in FIG. 1, for the PC mixture, the weight loss rate WL at the measurement temperature of 620°C was ６２０ (Indicated by symbol X1 in FIG. 1) and the weight loss rate WL at a measurement temperature of 780°C ７８０ (indicated by symbol X2 in FIG. 1) ６２０ / WL ７８０ The PC mixture exhibited a steep weight loss at measurement temperatures of around 350°C to 450°C, and at 620°C, the sample had lost approximately 60% of its initial weight.

[0037] This weight loss is thought to correspond to the weight of the raw material black phosphorus. In the case of the PC mixture, it is thought that the black phosphorus contained in the PC mixture was lost due to heating. It is known that black phosphorus changes into its allotrope, red phosphorus, when heated to 125°C. It is also known that red phosphorus sublimes at 416°C under normal pressure.

[0038] On the other hand, the weight loss rate of the PC negative electrode material at a measurement temperature of 620°C is WL ６２０ (Indicated by symbol A1 in FIG. 1) and the weight loss rate WL at a measurement temperature of 780°C ７８０ (indicated by symbol A2 in FIG. 1) ６２０ / WL ７８０ is included in the range of 0.1 to 0.9.

[0039] In addition, the PC negative electrode material has a weight loss rate WL at a measurement temperature of 300°C obtained by the above thermogravimetry. ３００ (Indicated by symbol A3 in FIG. 1) and the weight loss rate WL at a measurement temperature of 600°C ６００ (shown as symbol A4 in FIG. 1) ３００ / WL ６００ is preferably in the range of −0.1 to 0.15.

[0040] That is, unlike the PC mixture, the PC negative electrode material shows almost no weight loss up to a measurement temperature of 300°C and is thermally stable at the measurement temperature of 300°C.

[0041] W.L. ６２０ / WL ７８０ is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. ６２０ / WL ７８０ is preferably 0.9 or less, more preferably 0.8 or less. ６２０ / WL ７８０ The upper and lower limits can be combined arbitrarily.

[0042] W.L. ３００ / WL ６００ is preferably −0.1 or more, more preferably −0.08 or more. ３００ / WL ６００ is preferably 0.15 or less, more preferably 0.10 or less. ３００ / WL ６００ The upper and lower limits can be combined arbitrarily.

[0043] From the results shown in FIG. 1, it is believed that in the PC negative electrode material, the black phosphorus used as a raw material changes, becoming a substance that behaves differently from black phosphorus in response to heat.

[0044] [Presence or absence of P-C bond] P-C negative electrode materials have a peak indicative of a bond between a phosphorus atom and a carbon atom in an XPS spectrum. It is known that the "peak indicative of a bond between a phosphorus atom and a carbon atom" appears in the range of 132 to 136 eV in an XPS spectrum. In the following description, the bond between a phosphorus atom and a carbon atom may be simply referred to as a "P-C bond."

[0045] Figure 2 shows XPS spectra of the PC negative electrode material and the PC mixture. In Figure 2, the horizontal axis represents binding energy (eV) and the vertical axis represents the number of detected photoelectrons (cps (counts per second)). In Figure 2, the symbol A represents the PC material, and the symbol X represents the PC mixture.

[0046] (XPS Spectrum Measurement Conditions) XPS spectra are measured under the following measurement conditions: Measuring instrument: XPS device, ESCA-3400 (manufactured by Shimadzu Corporation) Radiation source: Mg Kα radiation (20 mA, 10 kV) If a peak is detected in the range of 132 to 136 eV, it is determined that a P—C bond is present.

[0047] As shown in FIG. 2, no peak indicating a P—C bond was detected in the range of 132 to 136 eV in the P—C mixture, but a peak indicating a P—C bond (denoted by the symbol α) was detected in the P—C negative electrode material.

[0048] From the results shown in FIG. 2, it is believed that the PC material contained in the PC negative electrode material is a substance having a chemical bond between a phosphorus atom and a carbon atom.

[0049] [Appearance] The PC material preferably has a core particle containing a phosphorus atom and a carbon coating covering the surface of the core particle.

[0050] Fig. 3 is a transmission electron microscope (TEM) photograph of the PC material contained in the PC negative electrode material. As shown in Fig. 3, particles 50 of the PC material have a core-shell structure in which the surface of a core particle 51 containing phosphorus atoms is covered with a carbon coating 52.

[0051] The presence of phosphorus atoms and carbon atoms in the PC material can be confirmed by using EDX (Energy Dispersive X-ray Spectroscopy).

[0052] Furthermore, when the PC material is composed only of phosphorus atoms and carbon atoms, the heavier phosphorus atoms appear darker in the TEM photograph, and therefore, based on the TEM photograph, it can be easily determined that the PC material has a core-shell structure in which core particles 51 contain phosphorus atoms and are covered with carbon coatings 52 containing carbon atoms.

[0053] (TEM Photographing Conditions) TEM photographs are taken under the following photographing conditions: TEM device: Transmission electron microscope H-9000NAR (manufactured by Hitachi, Ltd.) Field of view: maximum 500 nm x 500 nm At least a portion of the particles of the PC negative electrode material is included in the field of view when photographing.

[0054] According to the above-described TEM photographing conditions, the core-shell structure can be similarly confirmed whether the PC negative electrode material is made of a phosphorus-carbon material containing a phosphorus atom and a carbon element or a composite material containing a PC material and a resin component.

[0055] The PC negative electrode material preferably satisfies the above-mentioned requirements for [thermal behavior] and also has the above-mentioned core-shell structure.

[0056] [Crystalline state] Figure 4 shows XRD profiles of the PC negative electrode material and the PC mixture. In Figure 4, the horizontal axis represents the diffraction angle (2θ, °) and the vertical axis represents the diffracted X-ray intensity (a.u.). In Figure 4, symbol A represents the PC negative electrode material, and symbol X represents the PC mixture.

[0057] (XRD Profile Measurement Conditions) The XRD profile is measured under the following measurement conditions: Measurement equipment: horizontal sample multipurpose X-ray diffractometer Ultima IV (manufactured by Rigaku Corporation) Radiation source: Cu Kα radiation Measurement range (2θ): 10° to 90° Scan speed: 4° / min Sampling: 0.02° Voltage: 40 kV, current: 40 mA

[0058] As shown in Figure 4, in the PC mixture, the carbon material and black phosphorus each have a certain degree of crystallinity and exhibit diffraction peaks. In contrast, in the PC negative electrode material, the diffraction peaks seen in the PC mixture were not observed, and only noise was observed throughout the measurement range. In other words, from the results shown in Figure 4, it is believed that in the PC material, the crystallinity of the carbon material used as a raw material has been lost and it has become amorphous, or the carbon material has become so fine that the crystalline state cannot be confirmed.

[0059] Here, when the XRD profile of the PC negative electrode material is measured under the above conditions, the intensity I at 2θ=20° in the XRD profile measured under the above conditions is ２０ , intensity I at 2θ=26.3° ２６．３ , and the intensity at 2θ=40° I ４０ It is preferable that |P| / |B|<2 (1) P=I ２６．３ -I ４０ ...(2) B = (I ２０ -I ４０ ) × (26.3 - 40) / (20 - 40) ... (3)

[0060] When the XRD profile of a raw carbon material is measured, a peak of the carbon material appears at 2θ = 26.3°, which corresponds to the graphite (002) peak. On the other hand, the XRD profile of a normal carbon material does not have peaks at 2θ = 20° or 2θ = 40°. Therefore, in the above formula (1), 2θ = 40°, where no peak of the carbon material exists, is set as the reference point, and the state of the carbon material can be determined by comparing the intensity of the reference point in the XRD profile with the intensity at the position (2θ = 26.3°) where the peak of the raw carbon material exists.

[0061] "P" expressed in the above formula (2) is the intensity I of the reference point ４０ and the intensity I at the position where the peak of the carbon material exists. ２６．３ and indicates the difference of the peak from the reference point.

[0062] "B" in the above formula (3) indicates the baseline intensity at 2θ=26.3°, estimated from two positions (2θ=20° and 2θ=40°) where there are no peaks.

[0063] The ratio of the baseline intensity from the reference point to the peak intensity can be calculated from the ratio of the absolute values ​​of P and B (|P| / |B|) expressed by the above formula (1). When |P| / |B| is 2 or more, it indicates the presence of a peak of the carbon material.

[0064] On the other hand, when |P| / |B| is less than 2 and satisfies formula (1), the peak of the carbon material is reduced, and it can be determined that the crystallinity of the carbon material is reduced and the carbon material is amorphous or so fine that the crystalline state cannot be confirmed. Therefore, it is preferable that the P-C negative electrode material satisfies the above-mentioned requirements for [thermal behavior] as well as the above-mentioned relational expressions (1) to (3).

[0065] As described above, the PC anode material is a novel substance that differs from the mixture of the raw material phosphorus (black phosphorus in Figures 1 to 4) and a carbon material in terms of its thermal behavior, bonding state, appearance, and crystalline state.

[0066] <<Production Method 1 of Phosphorus-Carbon Composite Negative Electrode Material>> The P-C negative electrode material can be produced by a production method including a step of producing a P-C material containing a phosphorus material and a carbon material, a step of mixing the obtained P-C material with a binder resin to obtain a mixed powder, a step of mixing the mixed powder with a solvent, and a subsequent drying step.

[0067] [Step of Obtaining PC Material] In this step, the phosphorus material and the carbon material are mixed to obtain the PC material. The phosphorus material and the carbon material are preferably mixed by a mixing and grinding process accompanied by compression.

[0068] The raw carbon materials include amorphous carbon, graphite, porous carbon, mesocarbon microbeads (MCMB), fullerene, carbon nanotubes, graphene, graphene oxide, and carbon nitrite (C ３ N ４ ), and laminated carbon nanofibers (Carbon nanofiber platelets). All of these carbon materials have a graphite structure.

[0069] Examples of amorphous carbon include carbon black (CB), acetylene black (AB), ketjen black, hard carbon, and soft carbon.

[0070] As fullerenes, C６０ , C ７２ , C ８４ The following can be mentioned:

[0071] Examples of carbon nanotubes include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), cup-stacked carbon nanotubes (CSCNTs), and vapor-grown carbon fibers (VGCFs).These have a structure extending in one axial direction (one-dimensional structure).

[0072] Graphene, graphene oxide, carbon nitrite (C ３ N ４ ), laminated carbon nanofibers (carbon nanofiber platelets) have a structure that extends in the plane direction (two-dimensional structure).

[0073] In carbon materials, the edges (edge ​​sites) of the graphite structure are more active than non-edge sites. Therefore, it is assumed that most of the P-C bonds are formed at the edge sites of the carbon material. Therefore, from the viewpoint of facilitating the formation of P-C bonds, it is preferable to use a carbon material that has many edge sites.

[0074] Carbon materials with many edge sites include CSCNT, graphite, mesocarbon microbeads (MCMB), graphene, graphene oxide, and carbon nitrite (C ３ N ４ Among them, CSCNT is preferred as the carbon material.

[0075] Any of the known phosphorus allotropes can be used as the raw material phosphorus, and black phosphorus is preferred as it is the most chemically stable of the phosphorus allotropes and is a good conductor of electricity.

[0076] "Mixed and crushed processing with compression" is a process in which a compressive force is applied to multiple types of powdered raw materials, mixing and crushing the raw materials. By subjecting carbon materials and phosphorus to mixed and crushed processing with compression, a strong impact force is applied to the carbon materials and phosphorus, which is thought to cause a chemical change that cannot be achieved with a normal mixture while mixing and crushing the raw material powders. As a result, it is thought that a P-C bond that is not present in the raw materials is formed as a product, and a P-C material that does not exhibit the crystalline state seen in the raw materials is obtained.

[0077] The "mixing and grinding treatment accompanied by compression" may be carried out until the peaks derived from the raw materials disappear in the XRD profile of the mixed material, or until the formation of P-C bonds can be confirmed in the XPS spectrum of the mixed material.

[0078] Examples of processing devices (pulverizers) capable of performing mixing and pulverization accompanied by compression include roller mills, jet mills, hammer mills, pin mills, disk mills, rod mills, ball mills, vibration mills, attritors, and bead mills. In the production of PC materials, it is preferable to use an agitation type pulverizer equipped with a grinding vessel and a rotor, particularly because mixing and pulverization can be performed simultaneously. Examples of agitation type pulverizers include pin mills, disk mills, rod mills, ball mills, vibration mills, attritors, and bead mills.

[0079] Furthermore, as the processing device, a media-agitation type mill is preferred because it can mix and pulverize the raw material powder while simultaneously applying a strong impact force to the carbon material and phosphorus. Examples of media-agitation type mills include a ball mill, a vibration mill, an attritor, and a bead mill. Among these, a ball mill is particularly preferred from the viewpoint of easily controlling the property conditions.

[0080] It is believed that the ball mill mixing first causes atomization of phosphorus and decomposition of the carbon material, followed by the formation of P—C bonds. During this ball mill mixing process, phosphorus becomes the core particles described above.

[0081] It is believed that the carbon film is then formed around the core particles containing phosphorus atoms, resulting in a composite, thereby obtaining a PC material.

[0082] During ball mill mixing, the production conditions can be controlled by adjusting the rotation speed of the ball mill, the amount of media (balls) relative to the raw materials (ball powder ratio), and the mixing time. That is, by adjusting the conditions such as increasing the rotation speed of the ball mill, increasing the amount of media relative to the raw materials, and lengthening the mixing time, the mixing of phosphorus and carbon material is promoted, making it easier to obtain a P-C material. By controlling the above production conditions, the formation of P-C bonds is promoted, and WL ６２０ / WL ７８０ Therefore, it is easy to produce a PC negative electrode material that satisfies the condition of 0.1 or more and 0.9 or less.

[0083] Balls are grinding media for grinding metal materials. The diameter of the balls is the average particle size of the balls. The balls flow at high speed within the grinding container as the grinding container of the grinder rotates, colliding with the powder raw material containing the carbon material and phosphorus, thereby grinding the raw material into particles with a smaller average particle size. In the grinding process, it is preferable that the grinding container and beads are not excessively worn. Therefore, the shape of the balls is preferably spherical or ellipsoidal.

[0084] The diameter of the balls is preferably larger than the average particle size of the PC material after pulverization. By using such balls, a large amount of pulverization energy can be applied to the metal material, allowing metal particles to be obtained efficiently in a short time.

[0085] The diameter of the balls is preferably 0.1 to 10 mm, more preferably 1 to 10 mm. When the diameter of the balls is within this range, the formation of P—C bonds is promoted and re-agglomeration can be suppressed. The diameter of the balls placed in the grinding container may be uniform or may vary.

[0086] Examples of materials for the balls include glass, agate, alumina, zirconia, stainless steel, chrome steel, tungsten carbide, silicon carbide, and silicon nitride. Among these, zirconia is preferred because it has a relatively high hardness and is therefore resistant to wear, and its relatively high specific gravity allows for the generation of large pulverization energy. By using these balls, the raw powder of the PC material can be pulverized efficiently.

[0087] The weight ratio of the balls to the raw powder of the PC material is called the ball powder ratio. By increasing the ball powder ratio, a strong impact force can be applied to the raw powder of the PC material with high frequency, which further promotes the formation of PC bonds. If the ball powder ratio is too high, the production amount of PC negative electrode material per unit operation decreases. Therefore, the ball powder ratio is preferably 0.5 to 500, more preferably 1 to 200, and even more preferably 10 to 200.

[0088] After the ball mill mixing is completed, the balls are separated from the PC material using a filter or the like.

[0089] The fact that the above-described PC material has been obtained by ball mill mixing can be confirmed by measuring the XRD profile of the mixed material and checking that the peaks derived from the raw materials disappear, as shown in Figure 3. The duration of ball mill mixing can be determined by conducting a preliminary experiment to determine the correspondence between the mixing time and the time until the peaks derived from the raw materials disappear. In other words, ball mill mixing should be carried out until the peaks derived from the raw materials disappear in the XRD profile of the mixed material.

[0090] Alternatively, the formation of P-C bonds may be confirmed by measuring the XPS spectrum of the mixed material, as shown in Figure 1. In this case, the duration of ball mill mixing may be determined by conducting a preliminary experiment to determine the relationship between the mixing time and the time required for the formation of P-C bonds. In other words, ball mill mixing may be carried out until the formation of P-C bonds can be confirmed in the XPS spectrum of the mixed material.

[0091] During ball mill mixing, strong localized impacts (pressure) are applied to the carbon material and phosphorus due to collisions between media and between the media and the ball mill container. Although the details are unknown, it is thought that the application of such impacts causes chemical changes that cannot be achieved with normal mixtures, forming P-C bonds that are not present in the raw materials, resulting in a P-C material that does not exhibit the crystalline state seen in the raw materials.

[0092] [Step of Obtaining Mixed Powder] The obtained PC material and binder resin are mixed to obtain a mixed powder. The step of mixing the PC material and binder resin is preferably carried out using a mixer such as a Henschel mixer, a planetary mixer, a microspeed mixer, or a Loedige mixer, or by a method similar to the mixing and grinding process accompanied by compression described above.

[0093] Examples of the binder resin include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride-propylene hexafluoride-vinylidene fluoride copolymers, propylene hexafluoride-vinylidene fluoride copolymers, and ethylene tetrafluoride-perfluorovinyl ether copolymers; and polyolefin resins such as polyethylene and polypropylene.

[0094] The binder resin is preferably a fluorine-based resin, more preferably polyvinylidene fluoride.

[0095] The mixing ratio of the PC material and the binder resin is preferably adjusted so that the mixing ratio of the binder resin to the total amount of the mixed powder is in the range of 0.5% by mass or more and 15% by mass or less, more preferably 1.0% by mass or more and 15% by mass or less.

[0096] [Step of Mixing Mixed Powder with Solvent] The obtained mixed powder is mixed with a solvent. The solvent is preferably an organic solvent, and examples of the organic solvent include amine solvents such as N,N-dimethylaminopropylamine and diethylenetriamine, ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate, and amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).

[0097] The mixing ratio of the mixed powder to the solvent can be adjusted appropriately within the range of 1:9 to 9:1.

[0098] [Drying Step] After mixing with the solvent, the PC negative electrode material is dried to obtain a coverage of 0.1% to 5%. The drying conditions are a drying temperature of 40°C to 280°C and a drying time of 1 minute to 24 hours.

[0099] By mixing with a solvent and then drying, the binder resin is easily fixed, and the coverage rate is easily set to 0.1% or more and 5% or less.

[0100] <<Production Method 2 of Phosphorus-Carbon Composite Negative Electrode Material>> The P-C negative electrode material can be produced by a production method including a step of producing a mixed powder containing a phosphorus material, a carbon material, and a binder resin, a step of mixing the obtained mixed powder with a solvent, and a subsequent drying step.

[0101] The explanations regarding the phosphorus material, the carbon material, and the binder resin in the second method for producing a phosphorus-carbon composite negative electrode material are the same as those in the first method for producing a phosphorus-carbon composite negative electrode material.

[0102] [Step of Obtaining Mixed Powder] The phosphorus material, the carbon material, and the binder resin are mixed by the method described above in "Mixing and Grinding Treatment with Compression" to obtain a mixed powder. At this time, the mixing ratio of the binder resin to the total amount of the mixed powder is adjusted to be preferably in the range of 0.5% by mass to 15% by mass, more preferably 1.0% by mass to 15% by mass.

[0103] [Step of Mixing Mixed Powder and Solvent] This step is carried out in the same manner as the [Step of Mixing Mixed Powder and Solvent] described in the above-mentioned method 1 for producing a phosphorus-carbon composite negative electrode material.

[0104] [Drying Step] This is carried out in the same manner as the [Drying Step] described in the above-mentioned Method 1 for producing a phosphorus-carbon composite negative electrode material.

[0105] <<Method 3 for Producing a Phosphorus-Carbon Composite Negative Electrode Material>> In the method for producing a phosphorus-carbon composite negative electrode material, an aqueous binder resin can be used as the binder resin. The aqueous binder resin is an aqueous dispersion of a binder resin, such as styrene-butadiene rubber (SBR).

[0106] When an aqueous binder is used, the coverage of the PC material can be controlled to 0.1% or more and 5% or less by producing a PC material by the method described in the above-mentioned <<Production Method 1 of Phosphorus-Carbon Composite Negative Electrode Material>> and then coating the PC material with an aqueous binder. In this case, a high concentration of the aqueous binder resin dispersion is preferable because it shortens the drying time, but it is also preferable to adjust the concentration of the aqueous binder resin dispersion to a viscosity that allows it to be easily mixed with the admixture.

[0107] The mixing ratio of the mixed powder to the aqueous binder resin can be adjusted appropriately within the range of 1:99 to 90:10. The higher the solvent ratio, the more uniform the coating can be. From the viewpoint of shortening the drying time, the mixing ratio of the mixed powder to the aqueous binder resin is preferably within the range of 2:8 to 6:4.

[0108] [Drying Step] After mixing with the solvent, the PC negative electrode material is dried to obtain a coverage of 0.1% to 5%. The drying conditions are, for example, a drying temperature of 40°C to 280°C and a drying time of 1 minute to 24 hours.

[0109] By mixing with a solvent and then drying, the binder resin is easily fixed, and the coverage rate is easily set to 0.1% or more and 5% or less.

[0110] <Negative Electrode Active Material> The negative electrode active material of this embodiment includes the above-described PC negative electrode material.

[0111] The negative electrode active material may be the above-mentioned PC material alone, or may contain other known materials used as negative electrode active materials in addition to the PC material. Examples of such materials include (i) carbon materials capable of inserting and extracting lithium ions, (ii) alloy-based negative electrode active materials that form a lithium alloy phase, (iii) transition metal oxides that undergo a decomposition and regeneration reaction (conversion reaction) with lithium ions, and (iv) oxides or composite oxides that have activity as negative electrode active materials.

[0112] (i) Examples of carbon materials include graphite, hard carbon, soft carbon, and carbon nanotubes.

[0113] (ii) Examples of alloy-based negative electrode active materials include metals such as silicon, germanium, tin, aluminum, zinc, and magnesium, and alloys thereof.

[0114] (iii) Examples of transition metal oxides include manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, and magnesium oxide. These oxides may be composite metal oxides further containing other metals (e.g., lithium).

[0115] (iv) Examples of oxides or composite oxides include titanium oxide, lithium titanate, and silicon oxide.

[0116] <Negative electrode for lithium secondary battery> The negative electrode for lithium secondary battery of this embodiment contains the above-mentioned negative electrode active material. In addition to the negative electrode active material, the negative electrode for lithium secondary battery also has a current collector and a binder for binding the negative electrode active material to the current collector. The current collector and binder can have known configurations.

[0117] As the material for the current collector, copper or a copper alloy can be suitably used.

[0118] As the binder, polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) can be suitably used.

[0119] <Lithium Secondary Battery> The lithium secondary battery of this embodiment includes the above-described negative electrode for lithium secondary batteries (hereinafter, negative electrode).

[0120] An example of a suitable lithium secondary battery when using the negative electrode active material of this embodiment has a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

[0121] An example of a lithium secondary battery has a positive electrode, a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

[0122] 5 is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0123] First, as shown in the partially enlarged view of FIG. 5 , a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are stacked in this order: separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0124] The positive electrode 2 includes, for example, a positive electrode active material layer 2 a containing a positive electrode active material (hereinafter, referred to as CAM) and a positive electrode current collector 2 b having the positive electrode active material layer 2 a formed on one surface thereof. The positive electrode 2 can be manufactured by first preparing a positive electrode mixture containing the CAM, a conductive material, and a binder, and then supporting the positive electrode mixture on one surface of the positive electrode current collector 2 b to form the positive electrode active material layer 2 a.

[0125] Examples of the negative electrode 3 include an electrode in which a negative electrode mixture containing a negative electrode active material (not shown) is supported on a negative electrode current collector, and an electrode made of a negative electrode active material alone, and can be manufactured in the same manner as the positive electrode 2.

[0126] Next, the electrode group 4 and an insulator (not shown) are housed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with an electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing member 8, whereby a lithium secondary battery 10 can be manufactured.

[0127] The shape of the electrode group 4 can be, for example, a columnar shape such that the cross-sectional shape when the electrode group 4 is cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0128] The shape of a lithium secondary battery having such an electrode group 4 can be any shape specified in IEC 60086, which is a standard for batteries established by the International Electrotechnical Commission (IEC), or JIS C 8500. Examples of shapes include a cylindrical shape and a rectangular shape.

[0129] Furthermore, the lithium secondary battery is not limited to the above-mentioned wound type configuration, and may be a stacked type configuration in which a stacked structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly stacked. Examples of stacked lithium secondary batteries include so-called coin type batteries, button type batteries, and paper type (or sheet type) batteries.

[0130] The positive electrode, separator, negative electrode, and electrolyte constituting the lithium secondary battery can be those described in, for example,

[0113] to

[0140] of WO2022 / 113904A1, and the materials and manufacturing methods therefor.

[0131] <All-Solid-State Lithium Secondary Battery> Next, an all-solid-state lithium secondary battery having the above-described negative electrode will be described while explaining the configuration of the all-solid-state lithium secondary battery.

[0132] Fig. 6 is a schematic diagram showing an example of an all-solid-state lithium secondary battery. The all-solid-state lithium secondary battery 1000 shown in Fig. 6 includes a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an exterior body 200 that houses the laminate 100. The all-solid-state lithium secondary battery 1000 may also have a bipolar structure in which a CAM and a negative electrode active material are disposed on both sides of a current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400.

[0133] The positive electrode 110 includes a positive electrode active material layer 111 and a positive electrode current collector 112. The positive electrode active material layer 111 includes the above-described CAM and solid electrolyte. The positive electrode active material layer 111 may also include a conductive material and a binder.

[0134] The negative electrode 120 includes a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 contains a negative electrode active material. The negative electrode active material layer 121 may also contain a solid electrolyte and a conductive material.

[0135] The laminate 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may have a separator between the positive electrode 110 and the negative electrode 120.

[0136] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the exterior body 200 , and a sealing body (not shown) that seals the opening 200 a of the exterior body 200 .

[0137] The exterior body 200 may be a container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel. Alternatively, the exterior body 200 may be a bag-shaped container made of a laminate film having corrosion resistance on at least one surface.

[0138] The shape of the all-solid-state lithium secondary battery 1000 may be, for example, a coin type, a button type, a paper type (or a sheet type), a cylindrical type, a square type, or a laminate type (pouch type).

[0139] Although the all-solid-state lithium secondary battery 1000 is illustrated as having one laminate 100 as an example, the present embodiment is not limited to this. The all-solid-state lithium secondary battery 1000 may have a configuration in which the laminate 100 is used as a unit cell, and a plurality of unit cells (laminated bodies 100) are sealed inside an exterior body 200.

[0140] For the all-solid-state lithium secondary battery, for example, the configuration, materials and manufacturing method described in paragraphs

[0141] to

[0181] of WO2022 / 113904A1 can be used.

[0141] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0142] Example 1 Black phosphorus manufactured by Rasa Kogyo, CSCNT (cup-stacked carbon nanotubes manufactured by GSI Creos Co., Ltd.), and PVdF (KF polymer #9300 manufactured by Kureha) were weighed out in a mass ratio of P:C:PVdF = 59:40:1 (total amount 1.26 g) and mixed using a ball mill under the following conditions to obtain a PVdF-containing PC negative electrode material. The proportion of PVdF relative to the total amount of black phosphorus, CSCNT, and PVdF was 1 mass%. (Ball mill mixing conditions) Apparatus: Retsch PM-100 Container: ZrO ２ 125mL container Media: ZrO２ 8 mm diameter ball manufactured by 150 g Atmosphere: Argon gas sealed Sample amount: 1.26 g as a mixture of raw materials Ball / powder ratio: 120 (weight ratio) Mixing time: 12 hours

[0143] 0.2 g of NMP was added to the obtained PVdF-containing PC negative electrode material, and the mixture was kneaded in an agate mortar so that the PVdF was dissolved and uniformly mixed, and then vacuum dried at 80°C to obtain a powdered PC negative electrode material 1 coated with PVdF.

[0144] The surface abundance rate of fluorine atoms in PC negative electrode material 1 was measured by the method described in the above [Method for measuring coverage rate] and was found to be 0.28%.

[0145] A TEM photograph was taken of the negative electrode active material contained in the obtained PC negative electrode material 1. As a result, it was confirmed that the negative electrode active material had a core-shell structure in which the surface of a core particle containing phosphorus atoms was covered with a carbon film.

[0146] The obtained PC negative electrode material 1 was charged at a charge rate of 0.2 C using lithium metal as the counter electrode. As a result, the PC material had an average charge potential of 0.1 V or more relative to the capacity (mAh / g) during charging. It was confirmed that the obtained PC material is a material that absorbs lithium ions when lithium (alkali metal) is used as the counter electrode and a voltage of 0.1 V or more is applied.

[0147] The resulting P-C negative electrode material 1 had a phosphorus atom content of 60 mass % and a carbon atom content of 40 mass %. Because the container used in the above-mentioned production was extremely airtight, it was determined that the content of each atom in the P-C negative electrode material 1 was equal to the raw material ratio.

[0148] The obtained PC negative electrode material 1 has a weight loss rate WL at a measurement temperature of 620°C determined by thermogravimetry under the following conditions: ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Relative to WL ６２０ / WL ７８０was 0.29. (Thermogravimetric Measurement) 10 mg of the PC negative electrode material 1 was precisely weighed out to prepare a sample, and the change in weight was measured using a thermogravimetric measuring device when the sample was heated from 50°C to 780°C at a temperature increase rate of 10°C / min in a nitrogen stream. (Weight Loss Rate) The ratio of the weight of the sample at the measurement temperature to the weight of the precisely weighed sample was taken as the weight loss rate (wt %) at the measurement temperature.

[0149] Furthermore, the obtained PC negative electrode material 1 has a weight loss rate WL at a measurement temperature of 300°C determined by the above thermogravimetry. ３００ and the weight loss rate WL at a measurement temperature of 600 ° C. ６００ Ratio to WL ３００ / WL ６００ However, it was 0.04.

[0150] The obtained PC negative electrode material 1 was measured according to the above-mentioned (XPS spectrum measurement conditions), and a peak indicating a bond between a phosphorus atom and a carbon atom was confirmed.

[0151] The obtained PC negative electrode material 1 was measured according to the above-mentioned (XRD profile measurement conditions), and in the XRD profile, the intensity I20 at 2θ=20° was 3063, the intensity I26.3 at 2θ=26.3° was 2603, and the intensity I40 at 2θ=40° was 1917. In addition, |P| / |B| was 0.87. PC negative electrode material 1 exhibiting these values ​​satisfies the following formulas (1) to (3). |P| / |B|<2 ... (1) P=I ２６．３ -I ４０ ...(2) B = (I ２０ -I ４０ ) × (26.3 - 40) / (20 - 40) ... (3)

[0152] Example 2 A PC negative electrode material 2 was produced in the same manner as in Example 1, except that the proportion of PVdF relative to the total amount of black phosphorus, CSCNT, and PVdF was changed to 3 mass %. The surface abundance ratio of fluorine atoms in PC negative electrode material 2 was 0.76%.

[0153] The obtained P-C negative electrode material 2 was charged at a charge rate of 0.2 C using lithium metal as the counter electrode. As a result, the average charge potential of P-C negative electrode material 2 relative to the capacity (mAh / g) during charging was 0.1 V or more. It was confirmed that the obtained P-C negative electrode material 2 is a material that absorbs lithium ions when lithium (alkali metal) is used as the counter electrode and a voltage of 0.1 V or more is applied.

[0154] The resulting P-C negative electrode material 2 had a phosphorus atom content of 60 mass % and a carbon atom content of 40 mass %. Because the container used in the above-mentioned production was extremely airtight, it is determined that the content of each atom in the P-C negative electrode material 2 was equal to the raw material ratio.

[0155] The obtained PC negative electrode material 2 had a weight loss rate WL at a measurement temperature of 620° C., which was determined by thermogravimetry in the same manner as in Example 1. ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Ratio to WL ６２０ / WL ７８０ However, it was 0.52.

[0156] Furthermore, the obtained PC negative electrode material 2 has a weight loss rate WL at a measurement temperature of 300° C. obtained by the above-mentioned thermogravimetry. ３００ and the weight loss rate WL at a measurement temperature of 600 ° C. ６００ Ratio to WL ３００ / WL ６００ However, it was 0.06.

[0157] The obtained PC negative electrode material 2 was measured according to the above-mentioned (XPS spectrum measurement conditions), and a peak indicating a bond between a phosphorus atom and a carbon atom was confirmed.

[0158] The obtained PC negative electrode material 2 was measured according to the above-mentioned (XRD profile measurement conditions), and in the XRD profile, the intensity I20 at 2θ = 20° was 3280, the intensity I26.3 at 2θ = 26.3° was 2663, and the intensity I40 at 2θ = 40° was 1873. In addition, |P| / |B| was 0.82. PC negative electrode material 2 exhibiting these values ​​satisfies the above formulas (1) to (3).

[0159] Example 3 A PC negative electrode material 3 was produced in the same manner as in Example 1, except that the proportion of PVdF relative to the total amount of black phosphorus, CSCNT, and PVdF was changed to 6 mass %. The surface abundance ratio of fluorine atoms in PC negative electrode material 3 was 1.54%.

[0160] The obtained P-C negative electrode material 3 was charged at a charge rate of 0.2 C using lithium metal as the counter electrode. As a result, the average charge potential of P-C negative electrode material 3 relative to the capacity (mAh / g) during charging was 0.1 V or more. It was confirmed that the obtained P-C negative electrode material 3 is a material that absorbs lithium ions when lithium (alkali metal) is used as the counter electrode and a voltage of 0.1 V or more is applied.

[0161] The resulting P-C negative electrode material 3 had a phosphorus atom content of 60 mass % and a carbon atom content of 40 mass %. Because the container used in the above-described production was extremely airtight, it is determined that the content of each atom in the P-C negative electrode material 3 was equal to the raw material ratio.

[0162] The obtained PC negative electrode material 3 had a weight loss rate WL at a measurement temperature of 620° C., which was determined by thermogravimetry in the same manner as in Example 1. ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Ratio to WL ６２０ / WL ７８０ However, it was 0.38.

[0163] Furthermore, the obtained PC negative electrode material 3 has a weight loss rate WL at a measurement temperature of 300° C. obtained by the above-mentioned thermogravimetry. ３００ and the weight loss rate WL at a measurement temperature of 600 ° C. ６００ Ratio to WL ３００ / WL ６００ However, it was 0.12.

[0164] The obtained PC negative electrode material 3 was measured according to the above-mentioned (XPS spectrum measurement conditions), and a peak indicating a bond between a phosphorus atom and a carbon atom was confirmed.

[0165] The obtained PC negative electrode material 3 was measured according to the above-mentioned (XRD profile measurement conditions), and in the XRD profile, the intensity I20 at 2θ = 20° was 2993, the intensity I26.3 at 2θ = 26.3° was 2500, and the intensity I40 at 2θ = 40° was 1707. In addition, |P| / |B| was 0.90. PC negative electrode material 3 exhibiting these values ​​satisfies the above formulas (1) to (3).

[0166] Example 4 A PC negative electrode material 4 was produced in the same manner as in Example 1, except that the proportion of PVdF relative to the total amount of black phosphorus, CSCNT, and PVdF was changed to 10 mass %. The surface abundance ratio of fluorine atoms in PC negative electrode material 4 was 2.14%.

[0167] The obtained P-C negative electrode material 4 was charged at a charge rate of 0.2 C using lithium metal as the counter electrode. As a result, the average charge potential of P-C negative electrode material 4 relative to the capacity (mAh / g) during charging was 0.1 V or more. It was confirmed that the obtained P-C negative electrode material 4 is a material that absorbs lithium ions when lithium (alkali metal) is used as the counter electrode and a voltage of 0.1 V or more is applied.

[0168] The resulting P-C negative electrode material 4 had a phosphorus atom content of 60 mass % and a carbon atom content of 40 mass %. Because the container used in the above-described production was extremely airtight, it was determined that the content of each atom in the P-C negative electrode material 4 was equal to the raw material ratio.

[0169] The obtained PC negative electrode material 4 had a weight loss rate WL at a measurement temperature of 620° C., which was determined by thermogravimetry in the same manner as in Example 1. ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Relative to WL ６２０ / WL ７８０ However, it was 0.53.

[0170] Furthermore, the obtained PC negative electrode material 4 has a weight loss rate WL at a measurement temperature of 300° C. obtained by the above-mentioned thermogravimetry. ３００ and the weight loss rate WL at a measurement temperature of 600 ° C. ６００ Relative to WL ３００ / WL ６００ However, it was 0.08.

[0171] When the obtained PC negative electrode material 4 was measured according to the above-mentioned (XPS spectrum measurement conditions), a peak indicating a bond between a phosphorus atom and a carbon atom was confirmed.

[0172] The obtained PC negative electrode material 4 was measured according to the above-mentioned (XRD profile measurement conditions), and in the XRD profile, the intensity I20 at 2θ = 20° was 3240, the intensity I26.3 at 2θ = 26.3° was 2680, and the intensity I40 at 2θ = 40° was 1900. In addition, |P| / |B| was 0.85. PC negative electrode material 4 exhibiting these values ​​satisfies the above formulas (1) to (3).

[0173] Production Example 1 Black phosphorus manufactured by Rasa Industries and CSCNT (cup-stacked carbon nanotubes manufactured by GSI Creos Co., Ltd.) were weighed out in a mass ratio of P:C = 6:4 (total amount 1.25 g) and mixed using a ball mill under the following conditions to obtain a PC negative electrode material. (Ball mill mixing conditions) Apparatus: Retsch PM-100 Container: ZrO ２ 125mL container Media: ZrO ２ 8 mm diameter ball manufactured by SANYO, 1500 g Atmosphere: Argon gas sealed Sample amount: 1.25 g as a mixture of raw materials Ball / powder ratio: 120 (weight ratio) Mixing time: 12 hours

[0174] 0.13 g of 48% SBR latex solution was added to 1 g of the obtained PC negative electrode material, and the mixture was kneaded in an agate mortar and then vacuum dried at 80°C to obtain a powdered PC negative electrode material 5 coated with SBR. The proportion of SBR relative to the total amount of black phosphorus, CSCNT, and SBR was 6 mass%. As a result, a PC negative electrode material 5 having a coating containing SBR was produced.

[0175] Comparative Example 1 Black phosphorus manufactured by Rasa Industries was used as the PC negative electrode material 11. The surface abundance rate of fluorine atoms in the PC negative electrode material 11 was 0%.

[0176] The PC negative electrode material 11 thus obtained had a weight loss rate WL at a measurement temperature of 620° C., which was determined by thermogravimetry in the same manner as in Example 1. ６２０and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Relative to WL ６２０ / WL ７８０ However, it was 0.99.

[0177] Furthermore, the obtained PC negative electrode material 11 has a weight loss rate WL at a measurement temperature of 300° C. obtained by the above-mentioned thermogravimetry. ３００ and the weight loss rate WL at a measurement temperature of 600 ° C. ６００ Relative to WL ３００ / WL ６００ However, it was 0.01.

[0178] Comparative Example 2 Black phosphorus manufactured by Rasa Industries and CSCNT (cup-stacked carbon nanotubes: manufactured by GSI Creos Co., Ltd.) were weighed out in a mass ratio of P:C = 6:4 (total amount 1.25 g) and mixed using a ball mill under the following conditions to obtain a PC negative electrode material 12. (Ball mill mixing conditions) Apparatus: Retsch PM-100 Container: ZrO ２ 125mL container Media: ZrO ２ 8 mm diameter ball manufactured by 150 g Atmosphere: Argon gas sealed Sample amount: 1.25 g as a mixture of raw materials Ball / powder ratio: 120 (weight ratio) Mixing time: 12 hours

[0179] The surface abundance rate of fluorine atoms in P-C negative electrode material 12 was 0%. The obtained P-C negative electrode material 12 was charged at a charge rate of 0.2 C using lithium metal as the counter electrode. As a result, the average charge potential of P-C negative electrode material 5 relative to the capacity (mAh / g) during charging was 0.1 V or more. It was confirmed that the obtained P-C negative electrode material 5 is a material that absorbs lithium ions when lithium (alkali metal) is used as the counter electrode and a voltage of 0.1 V or more is applied.

[0180] The resulting P-C negative electrode material 12 had a phosphorus atom content of 60 mass % and a carbon atom content of 40 mass %. Because the container used in the above-described production was extremely airtight, it was determined that the content of each atom in the P-C negative electrode material 12 was equal to the raw material ratio.

[0181] The PC negative electrode material 12 thus obtained had a weight loss rate WL at a measurement temperature of 620° C., which was determined by thermogravimetry in the same manner as in Example 1. ６２０ and the weight loss rate WL at a measurement temperature of 780 ° C. ７８０ Ratio to WL ６２０ / WL ７８０ However, it was 0.51.

[0182] Furthermore, the obtained PC negative electrode material 12 has a weight loss rate WL at a measurement temperature of 300° C. obtained by the above-mentioned thermogravimetry. ３００ and the weight loss rate WL at a measurement temperature of 600 ° C. ６００ Ratio to WL ３００ / WL ６００ However, it was 0.06.

[0183] The obtained PC negative electrode material 12 was measured according to the above-mentioned (XPS spectrum measurement conditions), and a peak indicating a bond between a phosphorus atom and a carbon atom was confirmed.

[0184] The obtained PC negative electrode material 12 was measured according to the above-mentioned (XRD profile measurement conditions), and in the XRD profile, the intensity I20 at 2θ = 20° was 3662, the intensity I26.3 at 2θ = 26.3° was 2949, and the intensity I40 at 2θ = 40° was 1864. In addition, |P| / |B| was 0.88. PC negative electrode material 12 exhibiting these values ​​satisfies the above formulas (1) to (3).

[0185] [Moisture Resistance Test] A moisture resistance test was conducted to determine the presence or absence of odor using the following method for PC negative electrode materials 1 to 4 produced in Examples 1 to 4 and PC negative electrode materials 11 to 12 produced in Comparative Examples 1 and 2. 0.1 g of the PC negative electrode material was placed in a Petri dish and placed in a constant temperature and humidity chamber controlled at a room temperature of 25°C and a humidity of 50%, and after 5 to 10 seconds, the odor was detected at a distance of approximately 30 cm directly above the sample. If a characteristic garlic-like odor was detected, it was determined that an odor was present; if not, it was determined that no odor was present.

[0186] The results of the moisture resistance test and the values ​​of the coverage for Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1. The coverage shown in Table 1 is the surface abundance rate of fluorine when fluorine is used as the covering element.

[0187]

[0188] As shown in Table 1, Examples 1 to 4, which had a coverage rate of 0.1% or more and 5% or less, did not generate any odor, confirming that they were highly safe phosphorus-carbon composite anode materials. Comparative Example 1 was not a phosphorus-carbon composite anode material, but contained black phosphorus alone, which reacted with moisture in the air to generate phosphine, thereby generating an odor. Comparative Example 2 was a phosphorus-carbon composite anode material, but because it did not have a coating, it reacted with moisture in the air to generate phosphine, thereby generating an odor.

[0189] (Preparation of Evaluation Battery) (1) Preparation of Negative Electrode The PC negative electrode material, conductive material, and binder were weighed to prepare a mixture of [PC negative electrode material]:[conductive material]:[binder] = 80:10:10 (mass ratio). The materials used were as follows. Binder: vinylidene fluoride PVdF Kureha KF Polymer #1100 (manufactured by Kureha Corporation) Conductive material: acetylene black, Denka Black HS100 (manufactured by Denka Company Limited)

[0190] The mixture was kneaded with a solvent (NMP (N-methyl-2-pyrrolidone)) using an agate mortar to prepare a negative electrode slurry. At this time, the slurry concentration was adjusted so that the content of the negative electrode active material (the total of the P-C negative electrode material or the P-C mixture, the conductive material, and the binder) in the negative electrode slurry was 30 to 60 mass%.

[0191] The negative electrode slurry was applied to a copper foil current collector using a doctor blade, and then the resulting laminate was dried with air at 120°C for 1 hour to remove the solvent, yielding a laminate. The resulting laminate was pressed at 10 MPa for 10 seconds and then further dried in vacuum at 120°C for 12 hours to obtain a negative electrode.

[0192] The preparation of the negative electrode slurry and the preparation of the negative electrode were carried out in a glove box in an argon atmosphere.

[0193] (2) Preparation of Lithium-ion Secondary Battery The negative electrode, counter electrode, electrolyte, and separator prepared in (1) were combined to prepare a lithium-ion secondary battery (coin-type battery R2032). The battery was assembled in a glove box under an argon atmosphere.

[0194] Metallic lithium foil was used as the counter electrode.

[0195] As the electrolyte, LiPF ６ A mixed solution prepared by adding 10% by mass of fluoroethylene carbonate (FEC) to a solution (manufactured by Kishida Chemical Co., Ltd.) was used.

[0196] LiPF ６ The solution was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35, with LiPF ６ A solution in which the above was dissolved at a concentration of 1 mol / L was used.

[0197] As the separator, a laminated film separator (16 μm thick) was used, which was made by laminating a heat-resistant porous layer on a polyethylene porous film.

[0198] (Evaluation 1. Discharge Capacity) Using the above evaluation battery, a charge / discharge test was carried out under the following conditions while maintaining the temperature at 25°C. Here, the theoretical capacity of phosphorus was 2600 mAh / g, the actual capacity of the P-C negative electrode material was 1800 mAh / g, and the 1C current for charging or discharging the electrode capacity in 1 hour was 1800 mA / g. In the charge / discharge test, the 1C current was calculated from the mass of phosphorus contained in the negative electrode. The definition of 1C in the examples is the same hereinafter. Minimum charge voltage: 0.010 V Charging current: 0.1 C (1C = 1800 mA / g) Maximum discharge voltage: 2.5 V Discharge current: 0.1 C (1C = 1800 mA / g)

[0199] In Evaluation 1, a battery with a discharge capacity of 500 mAh / g or more was judged to be good, and a battery with a discharge capacity of less than 500 mAh / g was judged to be bad. For reference, the theoretical discharge capacity of graphite, which is a carbon material, is 372 mAh / g.

[0200] (Evaluation 2. Cycle Characteristics) Using the above evaluation battery, cycle characteristics were evaluated by repeatedly charging and discharging under the following conditions while maintaining the temperature at 25°C. The cycle characteristics were evaluated using the ratio (D100 / D1) of the discharge capacity D100 at the 100th cycle at a 1C rate current to the charge capacity D1 at the 1st cycle. The larger D100 / D1 indicates a higher retention rate of discharge capacity with cycling, and therefore can be judged to be an excellent negative electrode active material. Minimum charge voltage: 0.005V Charging current: 1C (1C = 1800mA / g) Maximum discharge voltage: 2.0V Discharge current: 1C (1C = 1800mA / g)

[0201] The discharge capacity and cycle characteristics were evaluated for the PC negative electrode materials of Example 3, Example 4, Comparative Example 1, and Comparative Example 2. As a result, the discharge capacity of PC negative electrode material 3 of Example 3 was 1800 mAh / g, and the cycle characteristics (D100 / D1) were 33%. The discharge capacity of PC negative electrode material 4 of Example 4 was 800 mAh / g, and the cycle characteristics (D100 / D1) were 26%.

[0202] The discharge capacity of the PC negative electrode material 11 of Comparative Example 1 was 1950 mAh / g, and the cycle characteristic (D100 / D1) was 11%. The discharge capacity of the PC negative electrode material 12 of Comparative Example 2 was 1800 mAh / g, and the cycle characteristic (D100 / D1) was 85%.

[0203] From the results of the battery evaluation, the P-C negative electrode material 3 of Example 3 had a capacity similar to that of the P-C negative electrode material 11 of Comparative Example 1. It was also confirmed that the P-C negative electrode material 3 of Example 3 had cycle characteristics three times higher than those of the P-C negative electrode material 11 of Comparative Example 1. It was also confirmed that the P-C negative electrode material 4 of Example 4 was a good product with a discharge capacity of 500 mAh / g or more, and that its cycle characteristics were more than twice as high as those of the P-C negative electrode material 11 of Comparative Example 1.

[0204] The PC negative electrode material 12 of Comparative Example 2 had no problem in terms of battery characteristics, but was insufficient in terms of safety.

[0205] From the above results, it was confirmed that the PC negative electrode material of this embodiment is highly safe and can provide good battery characteristics.

[0206] From the above, it was confirmed that the present invention is useful.

[0207] 50: particle, 51: core particle, 52: carbon coating, 100: laminate, 120: negative electrode, 121: negative electrode active material layer, 130: solid electrolyte layer

Claims

1. A phosphorus-carbon composite negative electrode material comprising: a phosphorus-carbon material containing phosphorus atoms and carbon elements; and a coating that coats at least a portion of a particle of the phosphorus-carbon material, wherein the coating contains a polymer compound, and the coating has a coating rate of 0.1% or more and 5% or less as measured by energy dispersive X-ray spectroscopy.

2. Weight loss rate WL at a measurement temperature of 620°C obtained by thermogravimetry under the following conditions ６２０ and the weight loss rate WL at a measurement temperature of 780°C ７８０ Relative to WL ６２０ / WL ７８０ The phosphorus-carbon composite negative electrode material according to claim 1, wherein is 0.1 or more and 0.9 or less. (Thermogravimetric measurement) 10 mg of the phosphorus-carbon composite negative electrode material is precisely weighed out to prepare a sample, and a thermogravimetric measuring device is used to measure the change in weight when the sample is heated from 50° C. to 780° C. at a temperature increase rate of 10° C. / min in a nitrogen stream. (Weight reduction rate) The ratio of the weight of the sample at the measurement temperature to the weight of the precisely weighed sample is defined as the weight reduction rate (wt %) at the measurement temperature.

3. The phosphorus-carbon composite negative electrode material according to claim 1 or 2, which has a peak in an XPS spectrum indicating a bond between a phosphorus atom and a carbon atom.

4. In the XRD profile measured using CuKα radiation, the intensity I at 2θ = 20° ２０ , Intensity I at 2θ=26.3° ２６．３ , and the intensity I at 2θ=40° ４０ The phosphorus-carbon composite negative electrode material according to claim 1 or 2, wherein |P| / |B|<2 ... (1) P=I satisfies the following formulas (1) to (3). ２６．３ -I ４０ ... (2) B = (I ２０ -I ４０ ) × (26.3 − 40) / (20 − 40) … (3) 5. The phosphorus-carbon composite negative electrode material according to claim 1 or 2, wherein the phosphorus-carbon material has a core particle containing a phosphorus atom, and a carbon coating covering the surface of the core particle.

6. A negative electrode active material comprising the phosphorus-carbon composite negative electrode material according to claim 1 or 2.

7. A negative electrode for a lithium secondary battery comprising the negative electrode active material according to claim 6.

8. A lithium secondary battery comprising the negative electrode for lithium secondary batteries according to claim 7.

9. A method for producing a phosphorus-carbon composite negative electrode material, comprising: obtaining a phosphorus-carbon material containing phosphorus atoms and carbon elements; mixing the phosphorus-carbon material with a binder resin to obtain a mixed powder; mixing the mixed powder with a solvent; and then drying the resulting mixture.

10. A method for producing a phosphorus-carbon composite negative electrode material, comprising: mixing a phosphorus material, a carbon material, and a binder resin to obtain a mixed powder; mixing the mixed powder with a solvent; and then drying the mixed powder.

11. The method for producing a phosphorus-carbon composite negative electrode material according to claim 9 or 10, wherein the mixing ratio of the binder resin is 0.5 mass % or more and 15 mass % or less with respect to the total amount of the mixed powder.

12. The method for producing a phosphorus-carbon composite negative electrode material according to claim 9 or 10, wherein the binder resin is polyvinylidene fluoride.

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