Method for manufacturing phosphorus-carbon composite materials

Abstract

To provide a novel phosphorus-carbon composite material containing phosphorus and carbon, a manufacturing method of the phosphorus-carbon composite material, a negative electrode active material containing phosphorus-carbon composite material, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery.SOLUTION: A phosphorus-carbon composite material containing phosphorus atoms and carbon atoms, wherein a content of phosphorus atoms in the phosphorus-carbon composite material is 10 to 95 mass%, and the content of carbon atoms in the phosphorus-carbon composite material is 5 to 90 mass%, and a ratio WL620 / WL780 between the weight loss rate WL620 at 620°C and the weight loss rate WL780 at 780°C obtained by thermogravimetry under the following conditions is 0.1 to 0.9. (Thermogravimetry) 10 mg of the phosphorus-carbon composite material is heated from 50°C. to 780°C. at 10°C. / min under N2 using a thermogravimetry device to measure the change in weight. (Weight reduction rate) The ratio of the weight of the sample at the measurement temperature to the weight of the accurately weighed sample is defined as the weight reduction rate (% by weight) at the measurement temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a phosphorus-carbon composite material, a method for producing a phosphorus-carbon composite material, a negative electrode active material, a negative electrode for a lithium secondary battery, and a lithium secondary battery. [Background technology]

[0002] Lithium-ion batteries are used as power sources for small electronic devices such as mobile phones and laptop computers. In recent years, lithium-ion batteries have also been increasingly put into practical use in medium- and large-scale power sources for applications such as automobiles and power storage.

[0003] Carbon materials are known as negative electrode active materials for lithium secondary batteries. Conventionally, negative electrode active materials containing phosphorus in addition to carbon materials have been known for the purpose of improving battery performance (see, for example, Patent Document 1). In the negative electrode active material described in Patent Document 1, by further containing phosphorus in a negative electrode active material containing carbon material, a negative electrode with excellent charge and discharge capacity can be made. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-67207 [Overview of the project] [Problems that the invention aims to solve]

[0005] To obtain highly reliable and high-performance lithium-ion secondary batteries, negative electrode active materials are required to be not only capable of charging and discharging but also possess excellent durability. Conventional negative electrode active materials still have room for improvement in order to enhance the performance of lithium-ion secondary batteries.

[0006] The present invention has been made in view of these circumstances, and aims to provide a novel phosphorus-carbon composite material containing phosphorus and carbon. It also aims to provide a method for producing such a novel phosphorus-carbon composite material that can be suitably manufactured. Furthermore, it aims to provide a negative electrode active material, a negative electrode for a lithium secondary battery, and a lithium secondary battery containing such a novel phosphorus-carbon composite material. [Means for solving the problem]

[0007] To solve the above problems, one aspect of the present invention includes the following aspects.

[0008] [1] A phosphorus-carbon composite material comprising phosphorus atoms and carbon atoms, wherein the phosphorus content in the phosphorus-carbon composite material is 10% by mass or more and 95% by mass or less, and the carbon content in the phosphorus-carbon composite material is 5% by mass or more and 90% by mass or less, wherein the weight loss rate WL at a measurement temperature of 620°C is determined by thermogravimetric analysis under the following conditions. 620 And, the weight loss rate WL at a measurement temperature of 780°C 780 Comparison with WL 620 / WL 780 However, it is a phosphorus-carbon composite material with a ratio between 0.1 and 0.9. (Thermogravimetric measurement) A 10 mg phosphorus-carbon composite material is accurately weighed and used as a sample. The weight change is measured when the material is heated from 50°C to 780°C at a heating rate of 10°C / min under a nitrogen atmosphere using a thermogravimetric analyzer. (Weight reduction rate) The ratio of the sample weight at the measurement temperature to the weight of the precisely weighed sample is defined as the weight loss rate (weight %) at the measurement temperature.

[0009] [2] Weight loss rate WL at a measurement temperature of 300°C, determined by the above thermogravimetric measurement. 300 And the weight loss rate WL at a measurement temperature of 600°C. 600 Comparison with WL 300 / WL 600 However, the phosphorus-carbon composite material described in [1] is between -0.1 and 0.1.

[0010] [3] The phosphorus-carbon composite material according to [1] or [2], which has a peak indicating the bond between a phosphorus atom and a carbon atom in the XPS spectrum.

[0011] [4] In the XRD profile measured using CuKα radiation, the intensity I at 2θ = 20° 20 , the intensity I at 2θ = 26.3° 26.3 , and the intensity I at 2θ = 40° 40 satisfy the following formulas (1) to (3), and the phosphorus-carbon composite material according to any one of [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)

[0012] [5] The phosphorus-carbon composite material according to any one of [1] to [4], which has core particles containing phosphorus atoms and a carbon film covering the surface of the core particles.

[0013] [6] A method for producing a phosphorus-carbon composite material, which includes a step of compounding a carbon material and phosphorus by a mixed grinding process with compression.

[0014] [7] A method for producing a phosphorus-carbon composite material, which includes a step of mixing a carbon material and phosphorus in a ball mill.

[0015] [8] The method for producing a phosphorus-carbon composite material according to [6] or [7], wherein the carbon material is at least one selected from the group consisting of amorphous carbon, graphite, porous carbon, mesocarbon microbeads, fullerene, carbon nanotube, graphene, graphene oxide, carbon nitride (C3N4), and laminated carbon nanofiber.

[0016] [9] The method for producing a phosphorus-carbon composite material according to any one of [6] to [8], wherein the phosphorus is black phosphorus.

[0017] A negative electrode active material comprising a phosphorus-carbon composite material as described in any one of items

[10] , [1] to [5].

[0018] A negative electrode for a lithium secondary battery, comprising the negative electrode active material described in

[11]

[10] .

[0019] A lithium secondary battery including the negative electrode for lithium secondary batteries described in

[12]

[11] . [Effects of the Invention]

[0020] According to the present invention, a novel phosphorus-carbon composite material containing phosphorus and carbon can be provided. Furthermore, a method for producing such a novel phosphorus-carbon composite material can be provided that allows for the suitable production of such a material. In addition, a negative electrode active material, a negative electrode for a lithium secondary battery, and a lithium secondary battery containing such a novel phosphorus-carbon composite material can be provided. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 is a graph showing the results of thermogravimetric measurements for PC materials and PC mixtures. [Figure 2] Figure 2 shows the XPS spectra of PC material and PC mixture. [Figure 3] Figure 3 is a transmission electron microscope (TEM) image of the PC material. [Figure 4] Figure 4 shows the XRD profiles of PC material and PC mixture. [Figure 5] Figure 5 is a schematic diagram showing an example of a lithium-ion secondary battery. [Figure 6] Figure 6 is a schematic diagram showing an example of an all-solid-state lithium secondary battery. [Figure 7] Figure 7 is a graph showing the thermogravimetric analysis results of the PC materials prepared in Examples 1, 4-7, and the PC mixture prepared in Comparative Example 2. [Figure 8] Figure 8 shows the XPS spectra of the PC materials prepared in Examples 1-5 and 7. [Figure 9] Figure 9 shows the XRD profiles of the PC materials prepared in Examples 1-7 and the PC mixtures prepared in Comparative Examples 1 and 2. [Figure 10] Figure 10 is a graph showing the discharge capacity up to 100 cycles of lithium secondary batteries using PC materials in Examples 1-7 and Comparative Example 2. [Modes for carrying out the invention]

[0022] The following description will explain the method for manufacturing the phosphorus-carbon composite material, the negative electrode active material, the negative electrode for the lithium secondary battery, and the lithium secondary battery according to this embodiment, with reference to Figures 1 to 6. Note that in all the following drawings, the dimensions and proportions of each component have been appropriately altered for clarity.

[0023] Phosphorus-carbon composite materials The phosphorus-carbon composite material of this embodiment contains phosphorus atoms and carbon atoms. In the following description, "phosphorus-carbon composite material" may be simply abbreviated as "PC material".

[0024] PC materials have a phosphorus content of 10% to 95% by mass. Furthermore, the carbon atom content of the PC material is 5% to 90% by mass. If the PC material consists of both phosphorus and carbon atoms, the sum of the carbon atom and phosphorus atom content must be 100% by mass. Even if the PC material consists of both carbon and phosphorus atoms, impurities inevitably introduced from the raw materials or manufacturing process are permitted.

[0025] PC materials are composed of more than 60% by mass of phosphorus and carbon atoms, and may also contain elements other than phosphorus and carbon atoms. Elements other than phosphorus and carbon atoms that PC materials contain include lithium, silicon, germanium, tin, aluminum, zinc, magnesium, transition metals, nitrogen, oxygen, fluorine, silicon, titanium, niobium, sulfur, and chlorine. These can be used as raw materials in the form of metal oxides, composite metal oxides, metal fluorides, metal sulfides, metal chlorides, silicon oxide, silicates, titanates, and aluminates.

[0026] The phosphorus atom content, carbon atom content, and other possible atom content in PC materials can be determined by known ICP analysis.

[0027] In PC materials, the phosphorus atom content 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 material. Furthermore, in PC materials, the phosphorus atom content 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 phosphorus atom content is too high, the cycle characteristics of the PC material deteriorate. The upper and lower limits of the phosphorus atom content can be arbitrarily combined.

[0028] In PC materials, 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 material. Furthermore, in PC materials, 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 material decreases. The upper and lower limits of the carbon atom content can be arbitrarily combined.

[0029] As will be explained in more detail later, PC material can be manufactured by ball-milling phosphorus and carbon material. The inventors conducted a detailed analysis and examination of the obtained PC material and confirmed that it is not simply a mixture of the raw materials phosphorus and carbon material, but rather a novel material in which phosphorus atoms and carbon atoms are chemically bonded (covalently bonded), and which has different physical properties from the raw materials phosphorus and carbon material.

[0030] The following section details the physical properties of PC materials, comparing them with mixtures of phosphorus and carbon materials (hereinafter sometimes referred to as "PC mixtures").

[0031] The following explanation compares an example of a PC material with an example of a mixture obtained by mixing the same raw materials as the PC material in a mortar. In the examples shown below, both the raw materials for the PC material and the PC mixture contain black phosphorus and carbon material in a 6:4 (mass ratio). In both the PC material and the PC mixture, the carbon material used is CSCNT (Cup-Laminated Carbon Nanotube).

[0032] [Behavior in response to heat] The weight loss rate (WL) of the PC material at a measurement temperature of 620°C is determined by thermogravimetric analysis under the following conditions. 620 And, the weight loss rate WL at a measurement temperature of 780°C 780 Comparison with WL 620 / WL 780 However, it is between 0.1 and 0.9. (Thermogravimetric measurement) A 10 mg phosphorus-carbon composite material is accurately weighed and used as a sample. The weight change is measured when the material is heated from 50°C to 780°C at a heating rate of 10°C / min under a nitrogen atmosphere using a thermogravimetric analyzer. (Weight reduction rate) The ratio of the sample weight at the measurement temperature to the weight of the precisely weighed sample is defined as the weight loss rate (weight %) at the measurement temperature.

[0033] Figure 1 is a graph showing the results of the thermogravimetric measurements performed on PC material and PC mixture. In Figure 1, the horizontal axis represents the heating temperature (°C), and the vertical axis represents the weight loss rate (weight %) relative to the weight of the sample. In Figure 1, the graph labeled A represents the behavior of PC material, and the graph labeled X represents the behavior of PC mixture.

[0034] As shown in Figure 1, the weight loss rate WL for the PC mixture at a measurement temperature of 620°C is 620 (Shown as X1 in Figure 1), the weight loss rate WL at a measurement temperature of 780°C. 780 The ratio WL (shown as X2 in Figure 1) 620 / WL 780 However, the value is less than 0.58. The PC mixture showed a steep weight loss at measurement temperatures between 350°C and 450°C, and at 620°C, approximately 60% of the sample's initial weight was lost.

[0035] This weight reduction 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.

[0036] In contrast, the PC material showed a weight loss rate WL at a measurement temperature of 620°C. 620 (Shown as symbol A1 in Figure 1), the weight loss rate WL at a measurement temperature of 780°C. 780 The ratio WL (shown as symbol A2 in Figure 1) 620 / WL 780 However, it falls within the range of 0.1 to 0.9.

[0037] Furthermore, the weight loss rate WL of the PC material at a measurement temperature of 300°C, as determined by the above thermogravimetric analysis, is 300 (Shown as symbol A3 in Figure 1) and the weight loss rate WL at a measurement temperature of 600°C. 600 The ratio WL (shown as symbol A4 in Figure 1) 300 / WL 600 However, it is preferable that the value falls within the range of -0.1 to 0.1.

[0038] In other words, unlike PC mixtures, PC material exhibits almost no weight loss up to a measurement temperature of 300°C and is thermally stable at 300°C.

[0039] WL 620 / WL 780 Preferably, it is 0.1 or higher, more preferably 0.3 or higher, and even more preferably 0.5 or higher. 620 / WL 780 WL is preferably 0.9 or less, and more preferably 0.8 or less. 620 / WL 780 The upper and lower limits can be combined in any way.

[0040] WL 300 / WL 600 A value of -0.1 or higher is preferred, and -0.08 or higher is more preferred. 300 / WL 600 WL is preferably 0.1 or less, and more preferably 0.08 or less. 300 / WL 600 The upper and lower limits can be combined in any way.

[0041] The results shown in Figure 1 suggest that in PC materials, the black phosphorus used as a raw material undergoes a transformation, resulting in a substance that behaves differently from black phosphorus in response to heat.

[0042] [Presence or absence of PC integration] PC materials exhibit a peak in their XPS spectrum indicating a bond between phosphorus and carbon atoms. This "peak indicating a phosphorus-carbon bond" is known to appear in the 132–136 eV range in the XPS spectrum. In the following explanation, this bond between phosphorus and carbon atoms may be simply referred to as a "PC bond."

[0043] Figure 2 shows the XPS spectra of PC material and PC mixture. In Figure 2, the horizontal axis represents the binding energy (eV), and the vertical axis represents the number of photoelectrons detected (cps (count per second)). In Figure 2, the symbol A represents PC material, and the symbol X represents PC mixture.

[0044] (XPS spectral measurement conditions) The XPS spectrum is measured under the following conditions. • Measuring equipment: XPS device, ESCA-3400 (manufactured by Shimadzu Corporation) ·Radiation source: Mg Kα radiation (20mA, 10kV) If a peak is detected in the range of 132-136 eV, it is determined that PC binding is present.

[0045] As shown in Figure 2, no peaks indicating PC bonding in the 132-136 eV range were detected in the PC mixture, but peaks indicating PC bonding (indicated by the sign α) were detected in the PC material.

[0046] The results shown in Figure 2 suggest that the PC material is a substance that has a chemical bond between phosphorus atoms and carbon atoms.

[0047] [exterior] The PC material comprises core particles containing phosphorus atoms and a carbon film covering the surface of the core particles.

[0048] Figure 3 is a transmission electron microscope (TEM) image of the PC material. As shown in Figure 3, the PC material particles 50 exhibit a core-shell structure in which a carbon film 52 covers the surface of a core particle 51 containing phosphorus atoms.

[0049] The presence of phosphorus and carbon atoms in PC materials can be confirmed using EDX (Energy Dispersive X-ray Spectroscopy).

[0050] Furthermore, if the PC material consists only of phosphorus and carbon atoms, the heavier phosphorus atoms will appear more densely in the TEM image. Therefore, based on the TEM image, it can be easily determined that the core particle 51 contains phosphorus atoms and is covered by a carbon film 52 containing carbon atoms, forming a core-shell structure.

[0051] (TEM imaging conditions) TEM images are acquired under the following imaging conditions. • TEM equipment: Transmission electron microscope H-9000NAR (manufactured by Hitachi, Ltd.) • Field of view: Maximum 500nm x 500nm. Capture images with at least a portion of the PC material particles within the field of view.

[0052] In addition to satisfying the requirements regarding the thermal behavior described above, the PC material is preferably of the core-shell structure described above.

[0053] [Crystalline state] Figure 4 shows the XRD profiles of PC material and PC mixture. In Figure 4, the horizontal axis represents the diffraction angle (2θ, °), and the vertical axis represents the diffracted X-ray intensity (au). In Figure 4, the symbol A represents PC material, and the symbol X represents PC mixture.

[0054] (XRD profile measurement conditions) The XRD profile is measured under the following measurement conditions. • Measuring instrument: Sample horizontal type multi-purpose X-ray diffractometer Ultima IV (manufactured by Rigaku Corporation) ·Radiation source: Cu Kα radiation • Measurement range (2θ): 10°~90° • Scan speed: 4° / min • Sampling: 0.02° • Voltage 40kV, Current 40mA

[0055] As shown in Figure 4, in the PC mixture, the carbon material and black phosphorus each exhibit a certain degree of crystallinity and show diffraction peaks. In contrast, the PC material did not show the diffraction peaks seen in the PC mixture, and only noise was detected throughout the measurement range. In other words, from the results shown in Figure 4, it is thought 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.

[0056] Here, when the XRD profile of the PC 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 intensity I at 2θ=40° 40 However, the following relationships (1) to (3) are satisfied. |P| / |B|<2 …(1) P=I 26.3 -I 40 …(2) B=(I 20 -I 40 ) × (26.3 - 40) / (20 - 40) … (3)

[0057] When the XRD profile of the raw material carbon is measured, the peak of the carbon material appears at 2θ=26.3°, which corresponds to the peak of graphite (002). On the other hand, in the XRD profile of a typical carbon material, there are no peaks at 2θ=20° or 2θ=40°. Therefore, in the above equation (1), 2θ=40°, where no peak of the carbon material exists, is used 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 where the peak of the raw material carbon material exists (2θ=26.3°).

[0058] The "P" represented by the above formula (2) is the intensity I of the reference point. 40 And the intensity I at the location where the carbon material peak exists. 26.3 This represents the difference, indicating the difference in peaks from the reference point.

[0059] The "B" represented by equation (3) above indicates the baseline intensity at 2θ=26.3°, estimated from two positions where there are no peaks (2θ=20° and 2θ=40°).

[0060] The ratio of the absolute values ​​of P and B (|P| / |B|), expressed by equation (1) above, can be used to determine the ratio of the baseline intensity from the reference point to the peak intensity. When |P| / |B| is 2 or greater, it indicates the presence of a peak for carbon material.

[0061] On the other hand, when |P| / |B| is less than 2 and equation (1) is satisfied, the peak of the carbon material has decreased, and it can be determined that the crystallinity of the carbon material has decreased, resulting in an amorphous carbon material or a carbon material so fine that the crystalline state cannot be confirmed. Therefore, in addition to satisfying the requirements for [behavior with respect to heat] described above, it is preferable that the PC material also satisfies the above relationships (1) to (3).

[0062] As described above, PC material is a novel substance that differs from a mixture of phosphorus (black phosphorus in Figures 1-4) and carbon material in terms of its behavior with respect to heat, bonding state, appearance, and crystalline state.

[0063] Method for manufacturing phosphorus-carbon composite materials As described above, PC material can be manufactured by a manufacturing method that includes a step of compounding carbon material and phosphorus through a mixed pulverization process accompanied by compression.

[0064] In the above manufacturing method, at least one material selected from the group consisting of amorphous carbon, graphite, porous carbon, mesocarbon microbeads (MCMB), fullerene, carbon nanotubes, graphene, graphene oxide, carbon nitride (C3N4), and layered carbon nanofibers (carbon nanofibers platelets) can be used as the raw material carbon material. All of these carbon materials have a graphite structure.

[0065] Examples of amorphous carbon include carbon black (CB), acetylene black (AB), Ketjenblack, hard carbon, and soft carbon.

[0066] As for fullerenes, C 60 , C 72 , C 84 Examples include:

[0067] 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 that extends in one axial direction (one-dimensional structure).

[0068] Graphene, graphene oxide, carbon nitride (C3N4), and layered carbon nanofibers (carbon nanofibers platelets) have a structure that extends in the planar direction (two-dimensional structure).

[0069] In carbon materials, the edges (edge ​​sites) of the graphite structure are more reactive than other areas. Therefore, it is assumed that most PC bonds are formed at the edge sites of the carbon material. Consequently, from the viewpoint of facilitating PC bond formation, it is preferable to use a carbon material that has many edge sites.

[0070] Carbon materials with many edge sites include CSCNTs, graphite, mesocarbon microbeads (MCMBs), graphene, graphene oxide, carbon nitride (C3N4), and multilayer carbon nanofibers. Among these, CSCNTs are preferred as carbon materials.

[0071] Furthermore, in the above manufacturing method, any known phosphorus allotrope can be used as the phosphorus raw material. Among the phosphorus allotropes, black phosphorus is preferred because it is the most chemically stable and also a good electrical conductor.

[0072] In the above manufacturing method, "compression-assisted mixing and grinding treatment" refers to a process in which compressive force is applied to multiple types of powdered raw materials to mix and grind them. By applying compression-assisted mixing and grinding treatment to carbon material and phosphorus, a strong impact force is applied to the carbon material and phosphorus, which is thought to mix and grind the raw material powders and simultaneously cause chemical changes that cannot be obtained with ordinary mixtures. As a result, it is thought that a PC material is obtained in which PC bonds that were not present in the raw materials are formed, and the crystalline state observed in the raw materials is not seen.

[0073] The "compression-assisted mixing and grinding process" should be carried out until the peaks originating from the raw materials disappear from the XRD profile of the mixed materials. Alternatively, it should be carried out until the presence of PC bonding can be confirmed in the XPS spectrum of the mixed materials.

[0074] Examples of processing equipment (grinders) capable of mixed grinding with compression include roller mills, jet mills, hammer mills, pin mills, disc mills, rod mills, ball mills, vibratory mills, attritors, and bead mills. In the manufacture of PC materials, it is particularly preferable to use an agitated grinder equipped with a grinding container and a rotating body, as it can perform mixing and grinding simultaneously. Examples of agitated grinders include pin mills, disc mills, rod mills, ball mills, vibratory mills, attritors, and bead mills.

[0075] Furthermore, as the processing apparatus, a media-stirring type pulverizer is preferred because it can mix and pulverize the raw material powder while simultaneously applying strong impact force to the carbon material and phosphorus. Examples of media-stirring type pulverizers include ball mills, vibratory mills, attritors, and bead mills. Among these, a ball mill is particularly preferred in terms of its ability to easily control the properties of the material.

[0076] During ball milling, it is believed that phosphorus is first atomized and carbon material is decomposed, followed by the formation of PC bonds. In these ball milling processes, phosphorus becomes the core particles mentioned above.

[0077] Subsequently, it is believed that a PC material is obtained by compounding the core particles containing phosphorus atoms while forming the aforementioned carbon film around them.

[0078] During ball mill mixing, manufacturing conditions can be controlled by adjusting the rotation speed of the ball mill equipment, the amount of media (balls) relative to the raw material (ball powder ratio), and the mixing time. Specifically, by adjusting conditions such as increasing the rotation speed of the ball mill equipment, increasing the amount of media relative to the raw material, or lengthening the mixing time, the mixing of phosphorus and carbon materials is promoted, making it easier to obtain PC material. By controlling the above manufacturing conditions, the formation of PC bonds is promoted, and WL (Whole Life Form) is produced. 620 / WL 780 It is easier to generate PC materials that satisfy the condition of being between 0.1 and 0.9.

[0079] The balls are a grinding medium for crushing 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 due to the rotation of the grinding container itself, and collide with the powder raw material containing carbon material and phosphorus, thereby crushing it into particles with a smaller average particle size. In the grinding process, it is preferable that the grinding container and beads do not wear excessively. For this reason, the shape of the balls is preferably spherical or ellipsoidal.

[0080] The diameter of the balls should preferably be larger than the average particle size of the PC material after grinding. Using such balls allows for greater grinding energy to be imparted to the metal material, enabling the efficient production of metal particles in a short time. On the other hand, if the diameter of the balls is too large, it promotes the re-aggregation of the PC material, resulting in PC material with a wide particle size distribution.

[0081] The diameter of the balls is preferably 0.1 to 10 mm, and more preferably 1 to 10 mm. When the diameter of the balls is within this range, the formation of PC bonds can be promoted while re-aggregation can be suppressed. The diameters of the balls placed in the grinding container may be uniform or varied.

[0082] Suitable 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 relatively high hardness, making it resistant to wear, and its relatively high specific gravity allows for obtaining large pulverizing energy. By using these balls, the raw material powder of PC materials can be efficiently pulverized.

[0083] The weight ratio of balls to the raw material powder of the PC material is defined as the ball-powder ratio. Increasing the ball-powder ratio allows for a stronger impact force to be applied to the raw material powder of the PC material at a higher frequency, thereby further promoting the formation of PC bonds. If the ball-powder ratio is too high, the amount of PC material produced per unit operation decreases. Therefore, a preferred ball-powder ratio is 0.5 to 500, more preferably 1 to 200, and even more preferably 10 to 200.

[0084] Furthermore, after the ball milling is complete, the balls are removed from the PC material using filters, etc. They separate.

[0085] The fact that the aforementioned PC material is obtained by ball mill mixing can be confirmed by measuring the XRD profile of the mixed material and observing that the peaks originating from the raw materials disappear, as shown in Figure 4. The duration of ball mill mixing should be determined by conducting preliminary experiments to determine the relationship between mixing time and the time it takes for the peaks originating from the raw materials to disappear. In other words, ball mill mixing should be continued until the peaks originating from the raw materials disappear from the XRD profile of the mixed material.

[0086] Alternatively, the XPS spectrum of the mixed materials can be measured to confirm the presence of PC bonding, as shown in Figure 2. In this case, the duration of ball mill mixing should be determined by conducting preliminary experiments to determine the relationship between mixing time and the time it takes for PC bonding to occur. In other words, ball mill mixing should be continued until the presence of PC bonding can be confirmed in the XPS spectrum of the mixed materials.

[0087] In ball mill mixing, the presence of carbon materials and phosphorus in collisions between media and between media and the ball mill container applies locally strong impacts (pressure) to the carbon materials and phosphorus. Although the details are unclear, it is thought that such impacts cause chemical changes not obtained in ordinary mixtures, leading to the formation of PC bonds that are not present in the raw materials, and resulting in a PC material that does not exhibit the crystalline state seen in the raw materials.

[0088] Therefore, according to the manufacturing method of this embodiment, the above-mentioned PC material can be easily produced by performing a mixed grinding treatment involving compression on the carbon material and phosphorus.

[0089] Furthermore, according to the manufacturing method of this embodiment, the above-mentioned PC material can be easily produced by a simple method of ball-milling carbon material and phosphorus.

[0090] 《Negative electrode active material》 The negative electrode active material of this embodiment includes the PC material described above.

[0091] The negative electrode active material may be the PC material described above alone, or it may include other known materials used as negative electrode active materials. Examples of such materials include (i) carbon materials that can insert and remove lithium ions, (ii) alloy-based negative electrode active material materials that involve the formation of a lithium alloy phase, (iii) transition metal oxides that undergo decomposition and regeneration reactions (conversion reactions) with lithium ions, and (iv) oxides or composite oxides that have activity as negative electrode active materials.

[0092] (i) Examples of carbon materials include graphite, hard carbon, soft carbon, and carbon nanotubes.

[0093] (ii) Examples of alloy-based negative electrode active materials include silicon, germanium, tin, aluminum, zinc, magnesium, or alloys thereof.

[0094] (iii) Examples of transition metal oxides include manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, and magnesium oxide. These oxides may also be composite metal oxides further containing other metals (e.g., lithium).

[0095] (iv) Examples of oxides or composite oxides include titanium dioxide, lithium titanate, and silicon dioxide.

[0096] Negative electrode for lithium secondary batteries The negative electrode for the lithium secondary battery of this embodiment includes the negative electrode active material described above. In addition to the negative electrode active material, the negative electrode for the lithium secondary battery also includes a current collector and a binder for attaching the negative electrode active material to the current collector. The current collector and binder can employ known configurations.

[0097] Copper or a copper alloy can be suitably used as the material for the current collector.

[0098] Polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) can be suitably used as a binder.

[0099] Lithium-ion rechargeable battery The lithium secondary battery of this embodiment includes the above-described negative electrode for lithium secondary batteries (hereinafter referred to as the negative electrode).

[0100] A suitable example of a lithium secondary battery using the negative electrode active material of this embodiment includes a positive electrode and a negative electrode, a separator sandwiched between the positive electrode and the negative electrode, and an electrolyte placed between the positive electrode and the negative electrode.

[0101] An example of a lithium secondary battery includes a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte placed between the positive and negative electrodes.

[0102] Figure 5 is a schematic diagram showing an example of a lithium secondary battery. The cylindrical lithium secondary battery 10 of this embodiment is manufactured as follows.

[0103] First, as shown in Figure 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 the order of separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0104] Next, the electrode group 4 and an insulator (not shown) are placed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with electrolyte 6, and the electrolyte is placed 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 body 8 to manufacture the lithium secondary battery 10.

[0105] As for the shape of the electrode group 4, for example, a columnar shape can be given 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.

[0106] Furthermore, the shape of the lithium secondary battery having such electrode group 4 can be one of those specified in IEC60086 or JIS C 8500, which are battery standards established by the International Electrotechnical Commission (IEC). For example, cylindrical or prismatic shapes can be used.

[0107] Furthermore, lithium secondary batteries are not limited to the wound configuration described above; they may also have a stacked configuration in which a stacked structure of positive electrode, separator, negative electrode, separator is repeatedly stacked. Examples of stacked lithium secondary batteries include so-called coin-type batteries, button-type batteries, or paper-type (or sheet-type) batteries.

[0108] The following describes each component in turn. (positive electrode) A positive electrode can be manufactured by preparing a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder, and then supporting the positive electrode mixture on a positive electrode current collector.

[0109] (Cathode active material) Lithium-containing compounds or other metallic compounds can be used as the positive electrode active material. Examples of lithium-containing compounds include lithium cobalt composite oxide having a layered structure, lithium nickel composite oxide having a layered structure, lithium manganese composite oxide having a spinel structure, and lithium iron phosphate having an olivine-type structure.

[0110] Other metal compounds include, for example, oxides such as titanium oxide, vanadium oxide, or manganese dioxide, or sulfides such as titanium sulfide or molybdenum sulfide.

[0111] (Conductive material) Carbon materials can be used as the conductive material for the positive electrode. Examples of carbon materials include graphite powder, carbon black (e.g., acetylene black), and fibrous carbon materials.

[0112] The proportion of conductive material in the positive electrode mixture is preferably 5 to 20 parts by mass per 100 parts by mass of positive electrode active material.

[0113] (binder) A thermoplastic resin can be used as the binder for the positive electrode. Examples of such thermoplastic resins include polyimide resins; fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; polyolefin resins such as polyethylene and polypropylene; and resins described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0114] (Positive electrode current collector) As the positive electrode current collector, a strip-shaped member made of a metal material such as Al, Ni, or stainless steel can be used.

[0115] One method for supporting the positive electrode mixture on a positive electrode current collector is to paste the positive electrode mixture using an organic solvent, apply the resulting paste to at least one side of the positive electrode current collector, dry it, and then fix it in place by performing an electrode pressing process.

[0116] When forming the positive electrode mixture into a paste, N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) is one of the organic solvents that can be used.

[0117] Methods for applying the positive electrode mixture paste to the positive electrode current collector include, for example, slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying. The positive electrode can be manufactured using the methods described above.

[0118] (Negative electrode) The negative electrode of the lithium secondary battery is the negative electrode for lithium secondary batteries described above.

[0119] (Separator) As the separator in a lithium secondary battery, for example, a material having the form of a porous membrane, nonwoven fabric, or woven fabric can be used, made of materials such as polyethylene and polypropylene polyolefin resins, fluororesins, or nitrogen-containing aromatic polymers. Furthermore, two or more of these materials may be used to form the separator, or these materials may be laminated to form the separator. Alternatively, the separator described in JP-A-2000-030686 or US20090111025A1 may be used.

[0120] (electrolyte) The electrolyte in a lithium secondary battery contains an electrolyte and an organic solvent.

[0121] The electrolytes contained in the electrolyte solution include LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(COCF3), Li(C4F9SO3), LiC(SO2CF3)3, and Li2B 10 Cl 10 Examples of lithium salts include LiBOB (where BOB is bis(oxalato)borate), LiFSI (where FSI is bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylates, and LiAlCl4, and mixtures of two or more of these may be used. In particular, it is preferable to use an electrolyte that contains at least one selected from the group consisting of fluorine-containing LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(SO2CF3)2, and LiC(SO2CF3)3.

[0122] Furthermore, the organic solvents contained in the electrolyte include, for example, carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one and 1,2-di(methoxycarbonyloxy)ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran and 2-methyltetrahydrofuran. Any ether; esters such as methyl formate, methyl acetate, propyl propionate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propanesalton; or these organic solvents into which a fluoro group has been further introduced (one or more hydrogen atoms in the organic solvent have been replaced with a fluorine atom) can be used.

[0123] The electrolyte may contain additives such as tris(trimethylsilyl) phosphate and tris(trimethylsilyl) borate.

[0124] As the organic solvent, it is preferable to use a mixture of two or more of these. Among these, a mixed solvent containing carbonates is preferred, and a mixed solvent of cyclic carbonates and acyclic carbonates and a mixed solvent of cyclic carbonates and ethers are even more preferred.

[0125] Furthermore, as the electrolyte, it is preferable to use an electrolyte containing a fluorine-containing lithium salt such as LiPF6 and an organic solvent having a fluorine substituent, in order to enhance the safety of the resulting lithium secondary battery. The electrolyte and organic solvent contained in the electrolyte may be those described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0126] <All-solid-state lithium secondary battery> Next, we will describe the all-solid-state lithium secondary battery having the aforementioned negative electrode, while explaining the configuration of the all-solid-state lithium secondary battery.

[0127] Figure 6 is a schematic diagram showing an example of an all-solid-state lithium secondary battery of this embodiment. The all-solid-state lithium secondary battery (lithium secondary battery) 1000 shown in Figure 6 has a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer casing 200 that houses the laminate 100. The all-solid-state lithium secondary battery 1000 may also have a bipolar structure in which the positive electrode active material and the negative electrode active material are arranged on both sides of the current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400. The materials constituting each component will be described later.

[0128] The laminated body 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.

[0129] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the outer casing 200 and a seal (not shown) that seals the opening 200a of the outer casing 200.

[0130] The outer casing 200 can be a container formed from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel. Alternatively, the outer casing 200 can be a container made by processing a laminate film with corrosion-resistant treatment applied to at least one side into a bag shape.

[0131] Examples of shapes for the all-solid-state lithium secondary battery 1000 include coin-shaped, button-shaped, paper-shaped (or sheet-shaped), cylindrical, rectangular, or laminated (pouch-shaped).

[0132] Although the all-solid-state lithium secondary battery 1000 is shown in one example configuration having a single stacked body 100, this embodiment is not limited to this configuration. The all-solid-state lithium secondary battery 1000 may also have a configuration in which the stacked body 100 is used as a unit cell, and multiple unit cells (stacked bodies 100) are sealed inside the outer casing 200.

[0133] The following describes each component in turn.

[0134] (positive electrode) The positive electrode 110 comprises a positive electrode active material layer 111 and a positive electrode current collector 112.

[0135] The positive electrode active material layer 111 contains a positive electrode active material and a solid electrolyte. The positive electrode active material layer 111 may also contain a conductive material and a binder.

[0136] (solid electrolyte) As the solid electrolyte contained in the positive electrode active material layer 111, a solid electrolyte having lithium ion conductivity and used in a known all-solid-state lithium secondary battery can be adopted. Examples of such solid electrolytes include inorganic electrolytes and organic electrolytes. Examples of inorganic electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hydride-based solid electrolytes. Examples of organic electrolytes include polymer-based solid electrolytes. Examples of each electrolyte include the compounds described in WO2020 / 208872A1, US2016 / 0233510A1, US2012 / 0251871A1, and US2018 / 0159169A1, and for example, the following compounds can be mentioned.

[0137] (Oxide-based solid electrolyte) Examples of oxide-based solid electrolytes include perovskite-type oxides, NASICON-type oxides, LISICON-type oxides, garnet-type oxides, and the like. Specific examples of each oxide include the compounds described in WO2020 / 208872A1, US2016 / 0233510A1, and US2020 / 0259213A1, and for example, the following compounds can be mentioned.

[0138] As perovskite-type oxides, Li a La 1-a TiO3 (0 < a < 1) and other Li-La-Ti-based oxides, Li b La 1-b TaO3 (0 < b < 1) and other Li-La-Ta-based oxides, and Li c La 1-c NbO3 (0 < c < 1) and other Li-La-Nb-based oxides, etc. can be mentioned.

[0139] As NASICON-type oxides, Li 1+d Al d Ti 2-d (PO4)3 (0 ≤ d ≤ 1) and the like can be mentioned. NASICON-type oxides refer to Li m M 1 n M 2 o P p O q (In the formula, M1 is one or more elements selected from the group consisting of B, Al, Ga, In, C, Si, Ge, Sn, Sb, and Se. 2 It is an oxide represented by , where m, n, o, p, and q are any positive numbers.

[0140] Li4M is an example of a LISICON-type oxide. 3 O4-Li3M 4 O4(M 3 is one or more elements selected from the group consisting of Si, Ge, and Ti. 4 This is one or more elements selected from the group consisting of P, As, and V. Examples include oxides represented by ).

[0141] As for garnet-type oxides, Li7La3Zr2O 12 Examples include Li-La-Zr oxides such as (also known as LLZ).

[0142] The oxide-based solid electrolyte may be a crystalline material or an amorphous material.

[0143] (Sulfide solid electrolyte) Examples of sulfide-based solid electrolytes include Li2S-P2S5 compounds, Li2S-SiS2 compounds, Li2S-GeS2 compounds, Li2S-B2S3 compounds, LiI-Si2S-P2S5 compounds, LiI-Li2S-P2O5 compounds, LiI-Li3PO4-P2S5 compounds, and Li 10 GeP2S 12 Examples include compound systems.

[0144] In this specification, the term "system compound" referring to sulfide-based solid electrolytes is used as a general term for solid electrolytes that mainly contain the raw materials such as "Li2S" and "P2S5" listed before the term "system compound." For example, Li2S-P2S5 system compounds include solid electrolytes that mainly contain Li2S and P2S5, and also contain other raw materials. The proportion of Li2S in a Li2S-P2S5 system compound is, for example, 50 to 90% by mass of the entire Li2S-P2S5 system compound. The proportion of P2S5 in a Li2S-P2S5 system compound is, for example, 10 to 50% by mass of the entire Li2S-P2S5 system compound. In addition, the proportion of other raw materials in a Li2S-P2S5 system compound is, for example, 0 to 30% by mass of the entire Li2S-P2S5 system compound. Furthermore, Li2S-P2S5 system compounds also include solid electrolytes in which the mixing ratio of Li2S and P2S5 is different.

[0145] Li2S-P2S5 compounds include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiI-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, and Li2S-P2S5-Z m S n Examples include: (m and n are positive numbers. Z is Ge, Zn, or Ga.)

[0146] Li2S-SiS2 compounds include Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-SiS2-P2S5-LiCl, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li2SO4, and Li2S-SiS2-Li x MO y Examples include: (x and y are positive numbers. M is P, Si, Ge, B, Al, Ga, or In.)

[0147] Examples of Li2S-GeS2-based compounds include Li2S-GeS2 and Li2S-GeS2-P2S5.

[0148] The sulfide-based solid electrolyte may be a crystalline material or an amorphous material.

[0149] (Hydroxide-based solid electrolytes) Examples of hydride-based solid electrolyte materials include LiBH4, LiBH4-3KI, LiBH4-PI2, LiBH4-P2S5, LiBH4-LiNH2, 3LiBH4-LiI, LiNH2, Li2AlH6, Li(NH2)2I, Li2NH, LiGd(BH4)3Cl, Li2(BH4)(NH2), Li3(NH2)I, and Li4(BH4)(NH2)3.

[0150] (Polymer-based solid electrolyte) Examples of polymer-based solid electrolytes include organic polymer electrolytes such as polyethylene oxide-based polymer compounds and polymer compounds containing one or more selected from the group consisting of polyorganosiloxane chains and polyoxyalkylene chains. Furthermore, so-called gel-type electrolytes, in which a non-aqueous electrolyte is held within a polymer compound, can also be used.

[0151] Two or more solid electrolytes can be used in combination, as long as they do not impair the effects of the invention.

[0152] (Conductive materials and binders) The conductive material in the positive electrode active material layer 111 can be any of the materials described above under (Conductive Material). Similarly, the proportion of conductive material in the positive electrode mixture can also be the proportion described above under (Conductive Material). Furthermore, the binder in the positive electrode can be any of the materials described above under (Binder).

[0153] (Positive electrode current collector) The positive electrode current collector 112 of the positive electrode 110 can be made from the material described above in (Positive Electrode Current Collector).

[0154] One method for supporting the positive electrode active material layer 111 on the positive electrode current collector 112 is to pressure-molde the positive electrode active material layer 111 on the positive electrode current collector 112. Cold pressing or hot pressing can be used for pressure molding.

[0155] Alternatively, a mixture of positive electrode active material, solid electrolyte, conductive material, and binder may be formed into a paste using an organic solvent to form a positive electrode mixture, and the resulting positive electrode mixture may be applied to at least one surface of the positive electrode current collector 112, dried, and pressed to fix it, thereby supporting the positive electrode active material layer 111 on the positive electrode current collector 112.

[0156] Alternatively, a mixture of positive electrode active material, solid electrolyte, and conductive material may be formed into a paste using an organic solvent to create a positive electrode mixture. This mixture may then be applied to at least one surface of the positive electrode current collector 112, dried, and sintered to support a positive electrode active material layer 111 on the positive electrode current collector 112.

[0157] The positive electrode active material that can be used in the positive electrode mixture is the same as the positive electrode active material described above (positive electrode active material).

[0158] The organic solvent that can be used in the positive electrode mixture is the same organic solvent that can be used when the positive electrode mixture described above (positive electrode current collector) is made into a paste.

[0159] One method for applying the positive electrode mixture to the positive electrode current collector 112 is the method described above in the section on (positive electrode current collector).

[0160] The positive electrode 110 can be manufactured using the methods described above. Specific material combinations used for the positive electrode 110 include the positive electrode active material and the combinations listed in Table 1.

[0161] [Table 1]

[0162] [Table 2]

[0163] [Table 3]

[0164] (Negative electrode) The negative electrode 120 comprises a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 contains the negative electrode active material of this embodiment.

[0165] (Solid electrolyte layer) The solid electrolyte layer 130 has the solid electrolyte described above.

[0166] One example of a method for producing the solid electrolyte layer 130 is to apply an inorganic solid electrolyte to the surface of the positive electrode active material layer 111 of the positive electrode 110 described above by sputtering, or by applying a paste-like mixture containing a solid electrolyte and drying it. In the latter case, after drying, the material may be press-molded and then pressurized by cold isostatic pressing (CIP) to form the solid electrolyte layer 130.

[0167] The laminate 100 can be manufactured by laminating the negative electrode 120 onto the solid electrolyte layer 130 provided on the positive electrode 110, using a known method, such that the negative electrode active material layer 121 is in contact with the surface of the solid electrolyte layer 130.

[0168] A lithium secondary battery with the above configuration uses a negative electrode active material containing the aforementioned PC material, resulting in a lithium battery with high capacity and excellent cycle characteristics.

[0169] As one aspect, the present invention also encompasses the following aspects.

[0170] <1> A phosphorus-carbon composite material containing phosphorus atoms and carbon atoms, The phosphorus atom content in the phosphorus-carbon composite material is 10% by mass or more and 95% by mass or less, The carbon atom content in the phosphorus-carbon composite material is 5% by mass or more and 90% by mass or less, A phosphorus-carbon composite material having a peak indicating the bond between phosphorus atoms and carbon atoms in the XPS spectrum.

[0171] <2>A phosphorus-carbon composite material containing phosphorus atoms and carbon atoms, The phosphorus atom content in the phosphorus-carbon composite material is 10% by mass or more and 95% by mass or less, The carbon atom content in the phosphorus-carbon composite material is 5% by mass or more and 90% by mass or less, In the XRD profile measured using CuKα rays, the intensity I at 2θ = 20°, 20 the intensity I at 2θ = 26.3°, 26.3 and the intensity I at 2θ = 40°, 40 satisfy the following formulas (1) to (3) for the phosphorus-carbon composite material. |P| / |B| < 2 …(1) P = I 26.3 - I 40 …(2) B = (I 20 - I 40 ) × (26.3 - 40) / (20 - 40) …(3)

[0172] <3>A phosphorus-carbon composite material containing phosphorus atoms and carbon atoms, The phosphorus atom content in the phosphorus-carbon composite material is 10% by mass or more and 95% by mass or less, The carbon atom content in the phosphorus-carbon composite material is 5% by mass or more and 90% by mass or less, core particles containing phosphorus atoms, and a carbon film covering the surface of the core particles, for the phosphorus-carbon composite material.

[0173] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but the present invention is not limited to these examples. The shapes and combinations of the constituent members shown in the above examples are merely examples, and can be modified in various ways based on design requirements, etc., without departing from the spirit of the present invention. [Examples]

[0174] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Examples 2-6 are for reference only.

[0175] In this embodiment, the physical properties were measured by the following method.

[0176] [Thermogravimetry] A 10 mg phosphorus-carbon composite material is accurately weighed and used as a sample. The weight change is measured when the material is heated from 50°C to 780°C at a heating rate of 10°C / min under a nitrogen atmosphere using a thermogravimetric analyzer.

[0177] [XPS spectrum] The measurement was performed according to the above-mentioned (XPS spectral measurement conditions).

[0178] [Raman spectrum] The measurement was performed according to the (Raman spectrum measurement conditions) described above.

[0179] [TEM photo] Images were acquired according to the above-mentioned (TEM imaging conditions).

[0180] [XRD Profile] The measurements were taken according to the (XRD profile measurement conditions) described above.

[0181] [Raw materials] The following materials were used in the examples and comparative examples.

[0182] (Lin) Black phosphorus manufactured by Rasa Industries

[0183] (Carbon materials) CSCNT: Manufactured by GSI Creos Corporation MCMB1:MG10, manufactured by China Steelchemical Co., Ltd. MCMB2:MG11, manufactured by China Steelchemical Co., Ltd. MCMB3:MG12, manufactured by China Steel Chemical Co., Ltd. Graphite: SNO15, manufactured by SEC Carbon. AB: Denka Black HS100, manufactured by Denka Co., Ltd. SWCNT: Manufactured by GSI Creos Corporation

[0184] [Examples 1-7] Black phosphorus and carbon material were weighed in the ratios shown in Table 4 (total amount 0.5g), and mixed using a ball mill under the following conditions to obtain the PC material. (Ball mill mixing conditions) Equipment:Retsch PM-100 Container: 50mL container made of ZrO2 Media: ZrO2 5mm diameter ball, 60g Atmosphere: Argon gas filled Sample quantity: 0.5g as a mixture of raw materials Ball / powder ratio: 120 (by weight) Mixing time: 12 hours

[0185] [Comparative Examples 1, 2] Black phosphorus and carbon material were weighed in the ratios shown in Table 4 (total amount 0.5g), and mixed using a mortar and pestle to obtain a PC mixture.

[0186] [Table 4]

[0187] [evaluation] Using the obtained materials, evaluation batteries were fabricated and evaluated using the following method. The evaluation results are shown in Table 5.

[0188] (Preparation of evaluation batteries) (1) Fabrication of the negative electrode The PC material or PC mixture, conductive material, and binder were weighed and a mixture was prepared with the ratio [PC material or PC mixture]:[conductive material]:[binder] = 80:10:10 (by mass). The materials used are as follows: Binder: Vinylidene fluoride (PVdF), Kureha KF Polymer #1100 (manufactured by Kureha Corporation) Conductive material: Acetylene black, Denka Black HS100 (manufactured by Denka Co., Ltd.)

[0189] The above mixture and solvent (NMP (N-methyl-2-pyrrolidone)) were kneaded 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 (total of PC material or PC mixture, conductive material and binder) in the negative electrode slurry was 30 to 60% by mass.

[0190] The negative electrode slurry was applied to the copper foil current collector using a doctor blade, and then the solvent was removed by blow-drying at 120°C for 1 hour to obtain a laminate. M The negative electrode was obtained by pressurizing it at Pa for 10 seconds, and then vacuum drying it at 120°C for 12 hours.

[0191] The preparation of the negative electrode slurry and the negative electrode itself was carried out in a glove box under an argon atmosphere.

[0192] (2) Fabrication of lithium-ion secondary batteries A lithium-ion secondary battery (coin-type battery R2032) was fabricated by combining the negative electrode, counter electrode, electrolyte, and separator prepared in (1). The battery was assembled in a glove box under an argon atmosphere.

[0193] As a counterpoint, metallic lithium foil was used.

[0194] As the electrolyte, a mixture of LiPF6 solution (manufactured by Kishida Chemical Co., Ltd.) with 10% by mass of fluoroethylene carbonate (FEC) added was used.

[0195] As the LiPF6 solution, a solution was used in which LiPF6 was dissolved to a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35.

[0196] As a separator, a laminated film separator (16 μm thick) was used, which consisted of a heat-resistant porous layer laminated on top of a porous polyethylene film.

[0197] (Evaluation 1. Discharge capacity) Using the evaluation battery described above, charge-discharge tests were conducted under the following conditions while maintained at 25°C. Here, the theoretical capacity of phosphorus was assumed to be 2600 mAh / g, and the 1C current used to charge or discharge the electrode capacity in 1 hour was set to 2600 mA / g. In the charge-discharge tests, 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 as below. Minimum charging voltage: 0.005V Charging current: 0.1C (1C=2600mA / g) Maximum discharge voltage: 2.0V Discharge current: 0.1C (1C=2600mA / g)

[0198] In Evaluation 1, products with a discharge capacity of 500 mAh / g or more were judged as good, and those with a discharge capacity of less than 500 mAh / g were judged as defective. For reference, the theoretical discharge capacity of graphite, a carbon material, is 372 mAh / g.

[0199] (Evaluation 2. Cycle characteristics) Using the evaluation battery described above, the cycle characteristics were evaluated by repeatedly charging and discharging under the following conditions while maintaining a temperature of 25°C. The cycle characteristics were evaluated using the ratio (D100 / D1) of the discharge capacity D100 at the 100th cycle and the charge capacity D1 at the 1st cycle at a 1C rate current. A larger D100 / D1 indicates a higher retention rate of discharge capacity with each cycle, and therefore, it can be judged that the material is superior as a negative electrode active material. Minimum charging voltage: 0.005V Charging current: 1C (1C = 2600 mA / g) Maximum discharge voltage: 2.0 V Discharge current: 1C (1C = 2600 mA / g)

[0200] In Evaluation 2, those with D100 / D1 of 50% or more were judged as good products, and those with D100 / D1 less than 50% were judged as defective.

[0201]

Table 5

[0202] Figure 7 is a graph showing the results of thermogravimetric measurements of the P-C materials prepared in Examples 1, 4 to 7 and the P-C mixture prepared in Comparative Example 2. As shown in Figure 7, all the P-C materials satisfied WL 620 / WL 780 being 0.1 or more and 0.9 or less.

[0203] Also, the P-C material of Example 7 had WL 620 / WL 780 of 0.75, which was larger than that of the P-C materials of other examples. The SWCNT, which is the carbon material used in Example 7, is considered to have a smaller amount of edge sites relative to the carbon atomic weight compared to other carbon materials. Thus, in a carbon material with fewer edge sites, it is considered that the amount of P-C bonds formed is less than that in a carbon material with more edge sites. Such a difference in the amount of P-C bonds is considered to be manifested in the difference in the results of thermogravimetric measurements between the P-C material of Example 7 and the P-C materials of other examples.

[0204] In contrast, the P-C mixtures of Comparative Examples 1 and 2 had WL 620 / WL 780 greater than 0.9, showed a sharp weight loss around the measurement temperature of 350°C to 450°C, and almost no weight loss was observed at temperatures of 500°C or higher. Therefore, it can be said that the P-C mixtures of Comparative Examples 1 to 2 do not form new bonds that can withstand high temperatures of 620°C or higher and are in the state of a mixture of phosphorus and carbon material as raw materials.

[0205] Figure 8 shows the XPS spectra of the P-C materials prepared in Examples 1 to 5 and 7. As shown in Figure 8, a peak appears in the range of 132 to 136 eV in any of the P-C materials, and it can be confirmed that a P-C bond is formed.

[0206] On the other hand, although not shown in Figure 8, the P-C mixtures of Comparative Examples 1 and 2 had no peak in the range of 132 to 136 eV in the XPS spectrum, and a P-C bond could not be confirmed.

[0207] Figure 9 shows the XRD profiles of the P-C materials prepared in Examples 1 to 7 and the P-C mixtures prepared in Comparative Examples 1 and 2. As shown in Figure 9, in any of the P-C materials, no peak can be confirmed at the position of 2θ = 26.3°, and it can be judged that the carbon material is amorphous or a very fine carbon material whose crystalline state cannot be confirmed.

[0208] On the other hand, in the P-C mixtures of Comparative Examples 1 and 2, since a peak could be confirmed at the position of 2θ = 26.3°, it can be judged that the amorphization of the carbon material was insufficient.

[0209] Figure 10 is a graph showing the discharge capacity up to 100 cycles of a lithium secondary battery using the P-C materials of Examples ۱ to ۷ and Comparative Example ۲. When evaluating the battery performance, it was found that the P-C materials of Examples 1 to 7 had a high discharge capacity and excellent cycle characteristics when used as the negative electrode active material. On the other hand, the P-C mixture of Comparative Example 2 could not obtain a sufficient discharge capacity, and the cycle characteristics were extremely low compared with the examples.

[0210] From the above results, it was confirmed that the present invention is useful.

Explanation of symbols

[0211] 3,120... negative electrode, 10... lithium secondary battery, 50... particles, 51... core particles, 52... carbon film, 1000... all-solid lithium secondary battery (lithium secondary battery)

Claims

1. The process involves compounding carbon material and phosphorus through a mixed pulverization process accompanied by compression. The carbon material is a carbon nanotube, A method for producing a phosphorus-carbon composite material, comprising the compounding process performed until the peaks originating from the raw materials disappear in the XRD profile of the mixed materials.

2. The process involves ball-milling carbon material and phosphorus. The carbon material is a carbon nanotube, A method for producing a phosphorus-carbon composite material, comprising the step of ball milling the mixed materials until the peaks originating from the raw materials disappear in the XRD profile of the mixed materials.

3. The method for producing a phosphorus-carbon composite material according to claim 1 or 2, wherein the carbon nanotube is a cup-stacked carbon nanotube.

4. A method for producing a phosphorus-carbon composite material according to any one of claims 1 to 3, wherein the phosphorus is black phosphorus.

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