Composition, negative electrode active material, negative electrode for lithium secondary battery, lithium secondary battery, and method for producing composition

Abstract

This composition contains a phosphorus-carbon composite negative electrode material that contains phosphorus atoms and carbon atoms, and a radical scavenger. The radical scavenger preferably contains a phenolic compound. The radical scavenger content relative to the total amount of the composition is preferably 5-30 mass%. Furthermore, the present invention relates to a method for producing a composition, the method comprising a step for obtaining a phosphorus-carbon composite negative electrode material that contains phosphorus atoms and carbon atoms, and a step for mixing the phosphorus-carbon composite negative electrode material and a radical scavenger.

Description

Composition, negative electrode active material, negative electrode for lithium secondary battery, lithium secondary battery, and method for producing the composition

[0001] The present invention relates to a composition, a negative electrode active material, a negative electrode for a lithium secondary battery, a lithium secondary battery, and a method for producing the composition. This application claims priority based on Japanese Patent Application No. 2024-104949, filed on June 28, 2024, 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 uses a black phosphorus carbon composite, which is a composite of a carbon material and phosphorus, as the negative electrode active material, thereby achieving a negative electrode with excellent charge / discharge capacity.

[0004] JP 2009-184861 A

[0005] Lithium secondary batteries require further safety measures, and the negative electrode active material described in Patent Document 1 has ample room for improvement in terms of safety measures. The black phosphorus used in Patent Document 1 has high chemical stability among phosphorus allotropes, and black phosphorus alone is excellent in safety. However, the present inventors have discovered that when black phosphorus is combined with carbon, the chemical stability and safety tend to decrease.

[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 composition containing 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 composition.

[0007] In order to solve the above-mentioned problems, one aspect of the present invention includes the following: [1] A composition comprising a phosphorus-carbon composite negative electrode material containing a phosphorus atom and a carbon atom, and a radical scavenger. [2] The composition according to [1], wherein the radical scavenger contains a compound having a phenol skeleton. [3] The composition according to [1] or [2], wherein the content of the radical scavenger relative to the total amount of the composition is 5% by mass or more and 30% by mass or less. [4] A negative electrode active material comprising the composition according to any one of [1] to [3]. [5] A negative electrode for a lithium secondary battery, comprising the negative electrode active material according to [4]. [6] A lithium secondary battery, comprising the negative electrode active material according to [4]. [7] A method for producing a composition, comprising the steps of obtaining a phosphorus-carbon composite negative electrode material containing a phosphorus atom and a carbon atom, and mixing the phosphorus-carbon composite negative electrode material with a radical scavenger. [8] The method for producing the composition according to [7], wherein the radical scavenger contains a compound having a phenol skeleton.

[0008] According to the present invention, it is possible to provide a highly safe composition containing 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 composition.

[0009] FIG. 1 shows XPS spectra of a PC anode material and a PC mixture. FIG. 2 shows transmission electron microscope (TEM) photographs of the PC material. FIG. 3 shows XRD profiles of a PC anode material and a PC mixture. FIG. 4 is a schematic diagram showing an all-solid-state lithium secondary battery, which is an example of a battery. FIG. 5 is a schematic diagram showing an all-solid-state lithium secondary battery, which is an example of a battery. FIG. 6 shows ESR spectra of the compositions of Example 2 and Comparative Example 1. A diagram for explaining the line width of the ESR spectrum.

[0010] <Composition> The composition of this embodiment includes a phosphorus-carbon composite negative electrode material containing phosphorus atoms and carbon atoms, and a radical scavenger. The composition of this embodiment is suitable for use in producing a negative electrode active material used in a lithium secondary battery. In this embodiment of the present invention, the composition is a negative electrode composition for a lithium secondary battery. In the following description, the "phosphorus-carbon composite negative electrode material" may be simply abbreviated as "P-C negative electrode material."

[0011] The composition of this embodiment has high safety. In this embodiment, whether or not a composition has high safety is evaluated by repeatedly applying a spark to the composition using the cerium-iron spark method described in the Examples below, and checking the number of times the spark is applied before ignition. The greater the number of times the spark is applied before ignition, the higher the safety is evaluated.

[0012] As described below, PC negative electrode materials are manufactured by mixing and grinding a phosphorus raw material and a carbon raw material, which involves compression. Black phosphorus, the phosphorus raw material, is chemically stable among phosphorus allotropes, and black phosphorus alone is unlikely to generate heat or ignite in the atmosphere. Furthermore, carbon raw materials alone are unlikely to generate heat or ignite in the atmosphere.

[0013] However, the present inventors have confirmed that PC negative electrode materials, which are composites of a phosphorus raw material and a carbon raw material through a mixing and grinding process involving compression, tend to have reduced chemical stability and safety. The present inventors speculate as follows about the reason why PC negative electrode materials become unstable.

[0014] First, the P-C negative electrode material composited by a mixing and grinding process involving compression has "isolated" carbon radicals (unpaired electrons). "Isolated" carbon radicals are unstable carbon radicals present in the P-C negative electrode material. The fact that the carbon radicals are "isolated" can be confirmed from the shape of the peak obtained by measuring electron spin resonance (hereinafter referred to as "ESR"). It has been confirmed by ESR that the carbon raw material does not contain isolated carbon radicals.

[0015] If the ESR spectrum obtained by measuring ESR has a broad peak with a wide peak width, it means that "isolated" carbon radicals are present. In contrast, if the "isolated" carbon radicals are reduced, a spectrum with a sharp peak width is observed. Here, in this specification, "sharp peak" means a peak with a line width of 5 mT or less, and "broad peak" means a peak with a line width of more than 5 mT. The ESR spectrum can be measured by the following method.

[0016] [ESR Spectrum Measurement Method] The ESR spectrum is measured using an "X-band ESR measurement device" manufactured by JEOL Ltd. The line width of the ESR signal is measured using a standard sample (Mn ２＋ / MgO).

[0017] For the obtained ESR spectrum, the line width of the peak is calculated from the difference in magnetic field values ​​at which the fitting curve takes a peak. The line width means the distance between peaks in the ESR spectrum, as shown in FIG.

[0018] The isolated carbon radicals contained in the PC negative electrode material are thought to be generated when the carbon-carbon bonds contained in the carbon material are cleaved by mechanical stimulation during the process of mixing and grinding the phosphorus raw material and the carbon raw material, which involves compression. The isolated carbon radicals that are generated are highly reactive (active) and easily bond with oxygen. Therefore, it is thought that the PC negative electrode material is prone to heat generation and ignition.

[0019] Based on the above measurement results and considerations, the present inventors believed that a highly safe composition could be obtained by reducing the carbon radicals contained in the composition, and thus completed the present invention.

[0020] The composition of the present embodiment contains a radical scavenger together with the P-C negative electrode material, and thus can reduce the isolated carbon radicals that were revealed by the above measurements. This suppresses the reaction between the isolated carbon radicals in the P-C negative electrode material and the unpaired electrons in oxygen molecules, resulting in a P-C negative electrode material that is less flammable in the atmosphere and highly safe.

[0021] [Radical Scavenger] In this embodiment, the "radical scavenger" is a compound capable of capturing an isolated carbon radical. In one aspect of the present invention, the radical scavenger is a carbon radical scavenger.

[0022] The carbon radical scavenger refers to a compound that captures carbon radicals and gives a stable product that does not undergo subsequent reactions such as polymerization after the addition of the carbon radicals. The carbon radical scavenger is preferably a compound having a phenol skeleton or a compound having a pyrrolidine skeleton, and more preferably a compound having a phenolic hydroxyl group.

[0023] The compound having a phenol skeleton preferably has a hindered phenol skeleton represented by the following general formula (1).

[0024]

[0025] The compound having a phenol skeleton is more preferably a compound represented by the following general formula (1)-1.

[0026]

[0027] In the general formulas (1) to (1)-1, R is an optional substituent, and R １ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ２ and R ３ are each independently an alkyl group having 1 to 8 carbon atoms. １ The alkyl group having 1 to 10 carbon atoms represented by the formula (I) may be a linear, branched or cyclic alkyl group.

[0028] R ２ is preferably a t-butyl group, a t-amyl group, or a t-octyl group. ３ is preferably a t-butyl group or a t-amyl group. ２ and R ３ is "*-(CH ３ ) ２ -R ４ " (* indicates the linking site to the aromatic ring, R ４ represents an alkyl group having 1 to 5 carbon atoms.

[0029] Of the compounds represented by the general formula (1)-1 above, Sumilizer GM is preferred as a commercially available product. Furthermore, compounds represented by the general formula (1)-1 above can also be used, such as those represented by the following formula (1)-1-1. Examples of compounds represented by the following formula (1)-1-1 include Sumilizer GS.

[0030]

[0031] The above-mentioned radical scavengers may be used alone or in combination of two or more.

[0032] In this embodiment, the content of the radical scavenger relative to the total amount of the composition is preferably 5% by mass or more and 30% by mass or less, and more preferably 8% by mass or more and 25% by mass or less. When the content of the radical scavenger is equal to or greater than the above-mentioned lower limit, the carbon radical scavenging effect of the radical scavenger is fully exerted, and a highly safe composition is likely to be obtained. When the content of the radical scavenger is equal to or less than the above-mentioned upper limit, the content of the P-C negative electrode material can be sufficiently ensured, and the capacity is less likely to decrease when used as a negative electrode active material.

[0033] [Phosphorus-Carbon Composite Negative Electrode Material] The PC negative electrode material used in this embodiment contains phosphorus atoms and carbon atoms. In one aspect of the present invention, the PC negative electrode material is in the form of a powder.

[0034] When the P-C negative electrode 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.

[0035] When the content ratio of the other components is within the above range, the movement of lithium ions is less likely to be hindered, and the initial capacity of the secondary battery is more likely to be improved.

[0036] The PC negative electrode 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 contained in the PC negative electrode material other than phosphorus atoms and carbon atoms include transition metals such as lithium, silicon, germanium, tin, aluminum, magnesium, zinc, niobium, and titanium, as well as nitrogen, oxygen, fluorine, silicon, 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.

[0037] The content of phosphorus atoms, the content of carbon atoms, and the contents of other atoms that may be contained in the PC negative electrode material can be determined by known ICP analysis.

[0038] In the PC negative electrode 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 negative electrode 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.

[0039] In the PC negative electrode 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 negative electrode 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.

[0040] As will be described in detail later, the P-C negative electrode material can be produced by mixing a phosphorus material and a carbon material using a ball mill. The inventors conducted a detailed analysis and study of the obtained P-C negative electrode material and confirmed that the P-C negative electrode material is not a simple mixture of the raw materials, phosphorus and carbon material, but is a novel material in which phosphorus atoms and carbon atoms are chemically bonded (covalently bonded) to each other and have physical properties different from those of the raw materials, phosphorus and carbon materials.

[0041] 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").

[0042] 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 negative electrode material and the PC mixture, CSCNT (cup-stacked carbon nanotubes) are used as the carbon material.

[0043] [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."

[0044] Figure 1 shows XPS spectra of the PC negative electrode material and the PC mixture. In Figure 1, the horizontal axis represents binding energy (eV) and the vertical axis represents the number of detected photoelectrons (cps (counts per second)). In Figure 1, symbol A represents the PC negative electrode material, and symbol X represents the PC mixture.

[0045] (XPS Spectrum Measurement Conditions) XPS spectra are measured under the following measurement conditions: Measuring instrument: XPS apparatus, ESCA-3400 (manufactured by Shimadzu Corporation) Radiation source: Mg Kα radiation (20 mA, 10 kV) When a peak is detected in the range of 132 to 136 eV, it is determined that a P—C bond is present.

[0046] As shown in FIG. 1, 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.

[0047] From the results shown in FIG. 1, it is believed that the PC negative electrode material is a substance having a chemical bond between the phosphorus atom and the carbon atom.

[0048] [Appearance] The PC negative electrode material preferably has a core particle containing a phosphorus atom and a carbon coating covering the surface of the core particle.

[0049] Fig. 2 is a transmission electron microscope (TEM) photograph of the PC negative electrode material. As shown in Fig. 2, particles 50 of the PC negative electrode 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.

[0050] The presence of phosphorus atoms and carbon atoms in the PC negative electrode material can be confirmed by using EDX (Energy Dispersive X-ray Spectroscopy).

[0051] Furthermore, when the PC negative electrode 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 negative electrode material has a core-shell structure in which core particles 51 contain phosphorus atoms and are covered with carbon coatings 52 containing carbon atoms.

[0052] (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.

[0053] According to the above TEM photographing conditions, the core-shell structure of the PC negative electrode material can be confirmed.

[0054] In addition to satisfying the above-mentioned requirements for thermal behavior, the PC negative electrode material preferably has a core-shell structure.

[0055] [Crystalline state] Figure 3 shows XRD profiles of the PC negative electrode material and the PC mixture. In Figure 3, the horizontal axis represents the diffraction angle (2θ, °) and the vertical axis represents the diffracted X-ray intensity (a.u.). In Figure 3, symbol A represents the PC negative electrode material, and symbol X represents the PC mixture.

[0056] (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 ray Measurement range (2θ): 10° to 90° Scan speed: 4° / min Sampling: 0.02° Voltage: 40 kV, current: 40 mA

[0057] As shown in Figure 3, 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 3, it is believed that in the PC negative electrode 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.

[0058] 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)

[0059] 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.

[0060] "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.

[0061] "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.

[0062] 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.

[0063] 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).

[0064] 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 3) and a carbon material in terms of its thermal behavior, bonding state, appearance, and crystalline state.

[0065] (Method for Producing PC Negative Electrode Material) The PC negative electrode material is obtained by mixing a phosphorus material and a carbon material. The phosphorus material and the carbon material are preferably mixed by a mixing and grinding process accompanied by compression.

[0066] 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.

[0067] Examples of amorphous carbon include carbon black (CB), acetylene black (AB), ketjen black, hard carbon, and soft carbon.

[0068] As fullerenes, C ６０ , C ７２ , C ８４ The following can be mentioned:

[0069] 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).

[0070] 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).

[0071] 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.

[0072] 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.

[0073] 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.

[0074] "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 the carbon material and phosphorus to mixed and crushed processing with compression, a strong impact force is applied to the carbon material 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 negative electrode material that does not exhibit the crystalline state seen in the raw materials is obtained.

[0075] 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.

[0076] 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 negative electrode 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.

[0077] 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.

[0078] 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.

[0079] 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 negative electrode material.

[0080] 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, or lengthening the mixing time, the mixing of phosphorus and the carbon material is promoted, making it easier to obtain a P-C negative electrode material.

[0081] 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.

[0082] The diameter of the balls is preferably larger than the average particle size of the pulverized PC negative electrode material. 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.

[0083] 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.

[0084] 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 material powder of the PC negative electrode material can be efficiently pulverized.

[0085] The weight ratio of the balls to the raw material powder of the PC negative electrode material is called the ball powder ratio. By increasing the ball powder ratio, a strong impact force can be applied to the raw material powder of the PC negative electrode material with high frequency, thereby further promoting 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.

[0086] After the ball mill mixing is completed, the balls are separated from the PC negative electrode material using a filter or the like.

[0087] The fact that the above-described PC negative electrode 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 1. 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.

[0088] 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.

[0089] 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 unclear, it is believed that the application of such impacts causes chemical changes that cannot be achieved with ordinary mixtures, forming P-C bonds that are not present in the raw materials, resulting in a P-C negative electrode material that does not exhibit the crystalline state seen in the raw materials.

[0090] <Method for Producing the Composition> The composition of the present invention can be produced by mixing a PC negative electrode material and a radical scavenger. The method for producing the composition of the present invention includes a step of obtaining a PC negative electrode material and a step of mixing the PC negative electrode material and the radical scavenger.

[0091] The step of obtaining a PC negative electrode material can be carried out by the same method as described above (Method of producing a PC negative electrode material). In the step of mixing the PC negative electrode material and the radical scavenger, the PC negative electrode material and the radical scavenger may be mixed directly, or the radical scavenger may be dissolved in a solvent and mixed in order to uniformly disperse the radical scavenger in the composition.

[0092] The solvent for dissolving the radical scavenger may be a known solvent, and examples thereof include halogenated hydrocarbons such as toluene, dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, and o-dichlorobenzene; halogenated phenols such as p-chlorophenol, pentachlorophenol, and pentafluorophenol; ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; ketones such as acetone and cyclohexanone; esters such as ethyl acetate and γ-butyrolactone; carbonates such as ethylene carbonate and propylene carbonate; amines such as triethylamine; nitrogen-containing heterocyclic aromatic compounds such as pyridine; nitriles such as acetonitrile and succinonitrile; amide solvents (organic solvents having an amide bond) such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, urea compounds such as tetramethylurea; nitro compounds such as nitromethane and nitrobenzene; sulfur compounds such as dimethyl sulfoxide and sulfolane; and phosphorus compounds such as hexamethylphosphoramide and tri-n-butylphosphate.

[0093] Of the above solvents, the amide solvents are preferred as the solvent for dissolving the radical scavenger, and N-methylpyrrolidone is more preferred.

[0094] A compound having a phenol skeleton that can be mixed with the PC negative electrode material is preferred, and the explanation of the compound having a phenol skeleton is the same as that in the above [Radical Scavenger].

[0095] When mixing a solution of a radical scavenger dissolved in a solvent with a PC negative electrode material, a drying step for removing the solvent is preferably carried out after mixing. The drying step is preferably carried out at a temperature of 50° C. or higher and 100° C. or lower for 5 hours or longer and 10 hours or shorter.

[0096] <Negative Electrode Active Material> The negative electrode active material of this embodiment includes the composition described above.

[0097] The negative electrode active material may be the above-described P-C negative electrode material alone, or may contain other known materials used as negative electrode active materials in addition to the P-C negative electrode 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.

[0098] (i) Examples of carbon materials include graphite, hard carbon, soft carbon, and carbon nanotubes.

[0099] (ii) Examples of alloy-based negative electrode active materials include metals such as silicon, germanium, tin, aluminum, zinc, and magnesium, and alloys thereof.

[0100] (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).

[0101] (iv) Examples of oxides or composite oxides include titanium oxide, lithium titanate, and silicon oxide.

[0102] <Negative electrode for lithium secondary battery> The negative electrode for lithium secondary battery of this embodiment contains the above-mentioned negative electrode active material. The negative electrode for lithium secondary battery has a current collector in addition to the negative electrode active material. Known materials can be used as the current collector material, and copper or a copper alloy can be preferably used.

[0103] The negative electrode for a lithium secondary battery of this embodiment may or may not have a binder for binding the negative electrode active material to the current collector. When a binder is used, a known structure can be adopted, and one or a mixture of two or more of polyvinylidene fluoride (hereinafter sometimes referred to as PVdF), polyimide, polyamideimide, styrene-butadiene rubber, carboxymethyl cellulose, and acrylic resin can be suitably used.

[0104] <Lithium Secondary Battery> The lithium secondary battery of this embodiment includes the above-described negative electrode for lithium secondary batteries (hereinafter, negative electrode).

[0105] 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.

[0106] 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.

[0107] 4 is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0108] First, as shown in the partially enlarged view of FIG. 4 , 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] <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.

[0117] Fig. 5 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. 5 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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 .

[0122] 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.

[0123] 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).

[0124] 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.

[0125] 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.

[0126] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0127] Example 1 [Manufacturing Process for PC Negative Electrode Material] Black phosphorus manufactured by Rasa Industries and CSCNT (cup-stacked carbon nanotubes: manufactured by GSI Creos Co., Ltd.) were weighed 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 PC Negative Electrode Material 1. (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

[0128] A TEM photograph was taken of the obtained PC negative electrode material 1, and it was confirmed that the material had a core-shell structure in which the surface of a core particle containing phosphorus atoms was covered with a carbon film.

[0129] The obtained P-C 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 average charge potential of P-C negative electrode material 1 relative to the capacity (mAh / g) during charging was 0.1 V or higher. It was confirmed that the obtained P-C negative electrode material 1 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 higher is applied.

[0130] 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.

[0131] 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.

[0132] 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 I at 2θ=20° ２０ is 3063, and the intensity at 2θ = 26.3° is I ２６．３ is 2603, and the intensity at 2θ = 40° is I４０ 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)

[0133] [Step of Mixing P-C Negative Electrode Material 1 and Radical Scavenger] SUMILIZER GM (manufactured by Sumitomo Chemical Co., Ltd.), a radical scavenger, was dissolved in N-methylpyrrolidone to prepare Solution 1 containing 11.11 mass% of the radical scavenger. P-C Negative Electrode Material 1 and Solution 1 were mixed, and after mixing, the mixture was dried at 70°C for 8 hours to obtain Composition 1 containing 10 mass% of the radical scavenger relative to the total amount of the composition.

[0134] Example 2 A PC negative electrode material was produced in the same manner as in Example 1, to obtain PC negative electrode material 1. SUMILIZER GM (manufactured by Sumitomo Chemical Co., Ltd.), a radical scavenger, was dissolved in N-methylpyrrolidone to prepare solution 2 containing 5.26 mass% of the radical scavenger, and PC negative electrode material 1 and solution 2 were mixed. After mixing, the mixture was dried at 70°C for 8 hours to obtain composition 2, which contained 20 mass% of the radical scavenger relative to the total amount of the composition.

[0135] Comparative Example 1 A PC negative electrode material was produced in the same manner as in Example 1 to obtain a PC negative electrode material 1. The PC negative electrode material 1 was designated as composition 11.

[0136] [Ignition Test] Compositions 1 and 2 produced in Examples 1 and 2 and composition 11 produced in Comparative Example 1 were subjected to an ignition test by the cerium-iron spark method described below.

[0137] (Cerium-iron spark method) 0.3 g of each composition was placed in a cone shape on an insulating board (Isowool board 1300S), and a spark was applied to each composition from a distance of about 1 cm using a rock lighter (cerium-iron) manufactured by Shoei Sangyo, and the number of times it took for the composition to ignite was counted. For example, if the composition was ignited by a single spark, the number of times it ignited was recorded as "1," and if the composition was ignited by 10 sparks, the number of times it ignited was recorded as "10," and these are recorded in Table 1. The higher the number of times it ignited, the more difficult it was to burn and the higher its stability was evaluated to be.

[0138] [Evaluation of Discharge Capacity] (Preparation of Evaluation Battery) (1) Preparation of Negative Electrode Each composition, conductive material, and binder were weighed to prepare a mixture of [each composition]:[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).

[0139] 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%.

[0140] 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.

[0141] 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.

[0142] (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.

[0143] Metallic lithium foil was used as the counter electrode.

[0144] 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.

[0145] 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.

[0146] As the separator, a laminated film separator (16 μm thick) was used, in which a heat-resistant porous layer was laminated on a polyethylene porous film.

[0147] (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. The definition of 1C in the examples is the same hereinafter. Minimum charge voltage: 0.005 V Charging current: 0.1 C (1C = 1800 mA / g) Maximum discharge voltage: 2.0 V Discharge current: 0.1 C (1C = 1800 mA / g)

[0148]

[0149] As shown in Table 1, the compositions of Examples 1 and 2, which contain a radical scavenger, ignited more frequently than the composition of Comparative Example 1, which did not contain a radical scavenger, confirming that the compositions contain a phosphorus-carbon composite negative electrode material and are highly safe. Furthermore, when Example 2 is compared with Comparative Example 1, it was confirmed that Example 2 has a higher ignition frequency than Comparative Example 1, making it safer and also providing a larger discharge capacity.

[0150] <Reference Experiment> ESR spectra were measured for the composition of Example 2 and the composition of Comparative Example 1 by the following method. The results are shown in Fig. 6. In the ESR spectrum shown in Fig. 6, the vertical axis represents "Signal Intensity" and the horizontal axis represents "Magnetic Field (mT)."

[0151] [ESR spectrum measurement method] The ESR spectrum was measured using an "X-band ESR measurement device" manufactured by JEOL Ltd. Approximately 20 mg of powder of the composition was placed in a sample tube for ESR spectrum measurement under an argon atmosphere. There were no particular restrictions on other measurement conditions as long as the ESR spectrum could be accurately measured. The line width of the ESR signal was measured using the standard sample (Mn ２＋ / MgO).

[0152] The line width of the peaks in the obtained ESR spectrum was calculated from the difference in magnetic field values ​​at which the fitting curves reached their peaks. The line width was calculated as the distance between peaks in the ESR spectrum, as shown in FIG.

[0153] In Fig. 6, the results of measuring the composition of Example 2 are shown by a solid line, and the results of measuring the composition of Comparative Example 1 are shown by a dashed line. The spectrum obtained by measuring the composition of Example 2 had a peak with a line width of 0.6 mT, confirming that "isolated" carbon radicals were reduced. The spectrum obtained by measuring the composition of Comparative Example 1 had a peak with a line width of 7.5 mT, confirming the presence of "isolated" carbon radicals.

[0154] From the above, it was confirmed that the present invention is useful.

[0155] 50...particle, 51...core particle, 52...carbon film, 100...laminated body, 120...negative electrode, 121...negative electrode active material layer, 130...solid electrolyte layer

Claims

1. A composition comprising: a phosphorus-carbon composite negative electrode material containing phosphorus atoms and carbon atoms; and a radical scavenger.

2. The composition of claim 1, wherein the radical scavenger comprises a compound having a phenol skeleton.

3. The composition according to claim 1 or 2, wherein the content of the radical scavenger relative to the total amount of the composition is 5% by mass or more and 30% by mass or less.

4. A negative electrode active material comprising the composition according to claim 1 or 2.

5. A negative electrode for a lithium secondary battery, comprising the negative electrode active material according to claim 4.

6. A lithium secondary battery comprising the negative electrode active material according to claim 4.

7. A method for producing a composition, comprising the steps of: obtaining a phosphorus-carbon composite negative electrode material containing phosphorus atoms and carbon atoms; and mixing the phosphorus-carbon composite negative electrode material with a radical scavenger.

8. The method for producing the composition according to claim 7, wherein the radical scavenger comprises a compound having a phenol skeleton.

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