Composite particles and slurries, and secondary batteries using these

Abstract

The object of the present invention is to provide negative electrode active material particles that can suppress the deterioration of the cycle characteristics of a lithium-ion secondary battery when used as a negative electrode active material for the lithium-ion secondary battery. The composite particle according to the first aspect of the present invention comprises a core containing silicon and a coating portion mainly composed of carbon and containing nitrogen, covering at least a part of the core. Furthermore, in the photoelectron spectrum obtained by X-ray electron spectroscopy, the composite particle shows a signal intensity of "N at 398.5 eV". I2 " for "Signal strength N at 400.8eV" I1 The ratio of "N I1 / N I2 ) is within the range of 0.5 to 4.

Description

[Technical Field]

[0001] This invention relates to composite particles and slurries used as negative electrode active material particles in secondary batteries, and to secondary batteries using these. [Background technology]

[0002] In recent years, there has been a growing demand for smaller and lighter mobile devices such as smartphones and laptops, leading to active development of secondary batteries to meet these needs. Furthermore, the development of electric vehicles to address environmental issues has also become more active, creating a demand for higher-capacity secondary batteries. Among these secondary batteries, lithium-ion secondary batteries are attracting attention from the perspective of high capacity. To achieve higher capacity in lithium-ion secondary batteries, development is underway to use silicon-based active materials such as silicon or silicon compounds instead of graphite, which has been conventionally used as the negative electrode active material in lithium-ion secondary batteries. However, silicon-based active materials repeatedly expand and contract during charging and discharging. This expansion and contraction can cause cracks to form in the active material itself or at the interface between the active material and the current collector, or the SEI (Solid Electrolyte Interphase) formed on the negative electrode surface to peel off from the negative electrode surface. For this reason, lithium-ion secondary batteries using silicon or silicon-based compounds as the negative electrode active material may experience a decrease in charge-discharge cycle characteristics.

[0003] Patent Document 1 discloses a technique for pre-coating the active material with polyimide to improve the charge-discharge cycle characteristics of lithium-ion secondary batteries. Patent Document 2 discloses a technique for nitrogen-doped carbon films to provide non-aqueous secondary batteries with high charge-discharge efficiency. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-157652 [Patent Document 2] Japanese Patent Publication No. 2015-035317 [Overview of the project] [Problems that the invention aims to solve]

[0005] The method disclosed in Patent Document 1 did not sufficiently suppress performance degradation due to repeated charge-discharge cycles. Furthermore, the method disclosed in Patent Document 2 could not suppress the expansion of the silicon-based active material, and therefore did not sufficiently suppress the degradation of battery performance during charge-discharge cycles.

[0006] The object of the present invention is to provide negative electrode active material particles that, when used as a negative electrode active material for a lithium-ion secondary battery, can suppress the deterioration of the cycle characteristics of the lithium-ion secondary battery. [Means for solving the problem]

[0007] The composite particle according to the first aspect of the present invention comprises a core portion and a coating portion. The core portion contains silicon (Si). The core portion may consist not only of silicon-containing particles but also of particles containing other elements. Here, carbon is preferred as the other element, and graphite particles are preferred as the carbon-containing particles. The coating portion mainly consists of carbon and also contains nitrogen. Furthermore, the coating portion covers at least a part of the core portion. This composite particle exhibits a signal intensity of "N at 398.5 eV" in the photoelectron spectrum obtained by X-ray electron spectroscopy. I2 " for "Signal strength N at 400.8eV" I1 The ratio of "N I1 / N I2 ) is within the range of 0.5 to 4.

[0008] In the composite particles according to the first aspect of the present invention, it is preferable that nitrogen accounts for a mass within the range of 0.03% by mass or more and 2.8% by mass or less of the total amount of composite particles.

[0009] In the composite particles according to the first aspect of the present invention, it is preferable that carbon occupies a mass within a range of 3% by mass or more and 85% by mass or less with respect to the total amount of the composite particles.

[0010] In the composite particles according to the first aspect of the present invention, in the photoelectron spectrum, the signal intensity C of the peak derived from the carbon existing between 282 eV and 288 eV A The signal intensity N of the peak derived from the nitrogen existing between 397 eV and 404 eV with respect to A The ratio (N A / C A ) is preferably within a range of 0.019 or more and 0.5 or less.

[0011] In the composite particles according to the first aspect of the present invention, in the photoelectron spectrum, the signal intensity Si of the peak derived from the silicon existing between 89 eV and 109 eV A The signal intensity N of the peak derived from the nitrogen existing between 397 eV and 404 eV with respect to A The ratio (N A / Si A ) is preferably within a range of 0.15 or more and 0.7 or less.

[0012] The composite particles according to the second aspect of the present invention are the composite particles according to the first aspect, and it is preferable that the core portion further contains oxygen and lithium. In such a case, it is preferable that the core portion contains lithium metasilicate (Li2SiO3). Note that this core portion may be formed only of lithium metasilicate.

[0013] In the composite particles according to the second aspect, it is preferable that nitrogen occupies a mass within a range of 0.03% by mass or more and 0.2% by mass or less with respect to the total amount of the composite particles.

[0014] In the composite particles according to the second aspect, it is preferable that carbon occupies a mass within a range of 3% by mass or more and 6% by mass or less with respect to the total amount of the composite particles.

[0015] Furthermore, in the composite particles related to the second phase, the signal intensity of the peak originating from carbon, located between 282 eV and 288 eV, is observed in the photoelectron spectrum. A "The signal intensity of the peak originating from nitrogen, located between 397eV and 404eV" A The ratio of "N A / C A It is preferable that the value is within the range of 0.04 to 0.5.

[0016] Furthermore, in the composite particles related to the second phase, the signal intensity of the peak originating from silicon, which is present between 89 eV and 109 eV, is Si in the photoelectron spectrum. A "The signal intensity of the peak originating from nitrogen, located between 397eV and 404eV" A The ratio of "N A / Si A It is preferable that the value is within the range of 0.15 or more and 0.5 or less.

[0017] The composite particle according to the third aspect of the present invention is the composite particle according to the first aspect, wherein the core consists solely of silicon. This core only needs to consist substantially of silicon and may contain impurities to an extent that does not impair the spirit of the invention.

[0018] Furthermore, in the composite particles relating to the third phase, it is preferable that nitrogen accounts for a mass within the range of 1.5% by mass or more and 2.8% by mass or less of the total amount of composite particles.

[0019] Furthermore, in the composite particles relating to the third phase, it is preferable that carbon accounts for a mass within the range of 38% by mass or more and 45% by mass or less of the total amount of composite particles.

[0020] Furthermore, in the composite particles relating to the third phase, the signal intensity C of the peak originating from the carbon, which is located between 282 eV and 288 eV, is observed in the photoelectron spectrum. A "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" A The ratio of "N A / C AIt is preferable that the value is within the range of 0.085 or more and 0.16 or less.

[0021] The composite particle according to the fourth aspect of the present invention is the composite particle according to the first aspect, and the core preferably contains a first core containing silicon and a second core containing carbon. In this case, the second core is preferably formed from graphite.

[0022] Furthermore, in the composite particles relating to the fourth phase, it is preferable that nitrogen accounts for a mass within the range of 0.75% by mass or more and 0.9% by mass or less of the total amount of composite particles.

[0023] Furthermore, in the composite particles relating to the fourth phase, it is preferable that carbon accounts for a mass within the range of 60% by mass or more and 85% by mass or less of the total amount.

[0024] Furthermore, in the composite particles relating to the fourth phase, the signal intensity of the peak originating from carbon, located between 282 eV and 288 eV, is observed in the photoelectron spectrum. A "The signal intensity of the peak originating from nitrogen, located between 397eV and 404eV" A The ratio of "N A / C A It is preferable that the value is within the range of 0.019 or more and 0.05 or less.

[0025] Furthermore, in the composite particles relating to the fourth phase, the signal intensity of the peak originating from silicon, which is present between 89 eV and 109 eV, is Si in the photoelectron spectrum. A "The signal intensity of the peak originating from nitrogen, located between 397eV and 404eV" A The ratio of "N A / Si A It is preferable that the value is within the range of 0.19 or more and 0.7 or less.

[0026] The slurry according to the fifth aspect of the present invention contains one composite particle from any of the composite particles according to the first to fourth aspects, a binder, and a solvent that disperses the composite particle and dissolves the binder.

[0027] The negative electrode for a lithium-ion secondary battery according to the sixth aspect of the present invention mainly consists of one composite particle from the first to fourth aspects of the composite particle. [Effects of the Invention]

[0028] This invention provides composite particles that can be used as a negative electrode material for batteries. By forming the negative electrode of the electrode using these composite particles, the deterioration of the cycle characteristics when the battery is repeatedly charged and discharged can be suppressed. [Modes for carrying out the invention]

[0029] <Configuration of composite particles according to embodiments of the present invention> The composite particles according to an embodiment of the present invention comprise a core portion and a coating portion. The coating portion mainly consists of carbon and contains nitrogen. The coating portion covers at least a part of the core portion. Here, the core portion contains silicon. Here, the core portion may consist only of silicon, or it may contain elements other than silicon. When the core portion consists only of silicon, it may contain impurities to an extent that does not impair the spirit of the invention. When the core portion contains elements other than silicon, it is preferable that the core portion contains silicon, oxygen, and lithium. In this case, the core portion may contain elements other than silicon, oxygen, and lithium, or it may contain only silicon, oxygen, and lithium. It is preferable that the core portion contains lithium metasilicate and silicon. Furthermore, the core portion may contain Li2Si2O5, Li4SiO4, Li8SiO6, SiO2, or an amorphous structure of Si and O. Furthermore, it is preferable that the core portion is lithium-doped silicon oxide. Furthermore, other particles may be used in combination as the core, in addition to the particles mentioned above. Examples of these other particles include graphite particles.

[0030] The presence of lithium metasilicate in the composite particles can be confirmed by using a BRUKER AXS D8 DISCOVER powder X-ray diffraction analyzer to observe peaks appearing around 2θ = 19° and 27° based on the following measurement condition 1. The presence of silicon in the composite particles can also be confirmed by using the same powder X-ray diffraction analyzer to observe peaks appearing around 2θ = 28° to 29° based on the following measurement condition 1.

[0031] (Measurement condition 1) ·Incoming X-ray: Cu-Kα ray ·Optical system: Bragg-Brentano optical system • Tube voltage: 40kV ·Tube current: 40mA • Detector: LYNXEYE detector • Measurement range: 2θ = 15°-35° • Scanning speed: 14.3° / second ·Measurement temperature: Room temperature (25℃) • Measurement pressure: Standard atmospheric pressure (1 atm)

[0032] The coating may partially cover the core or completely cover the core. Preferably, the coating does not contain metallic elements other than lithium, such as iron, cobalt, nickel, or manganese.

[0033] The composite particles according to the embodiment of the present invention exhibit a signal intensity of "N at 398.5 eV" in the photoelectron spectrum obtained by X-ray electron spectroscopy (XPS). I2 " for "Signal strength N at 400.8eV" I1 The ratio of "N I1 / N I2 ) is within the range of 0.5 to 4. Here, N I1 / N I2 It is preferable that the value is within the range of 0.4 to 4, more preferably within the range of 0.45 to 4, and even more preferably within the range of 0.5 to 3.75. Note that these upper and lower limits can be combined in any way. Here, "signal intensity N at 398.5 eV" I2" is the bond energy originating from nitrogen in the photoelectron spectrum obtained by XPS, and this bond energy indicates the presence of pyridine-like nitrogen in which a nitrogen atom is incorporated into a six-membered ring structure. Also, "signal intensity N at 400.8 eV" I1 " is the bond energy originating from nitrogen in the photoelectron spectrum obtained by XPS, and this bond energy indicates the presence of pyrrole-like nitrogen containing a nitrogen atom in a five-membered ring structure. Also, "signal intensity N at 398.5 eV" I2 " and "Signal strength N at 400.8eV I1 The measurement is performed using the JPS-9010MC XPS measurement device manufactured by JEOL Ltd., based on the following measurement condition 2.

[0034] (Measurement condition 2) ·X-ray source: MgKα ray • X-ray irradiation diameter: 10 mm • Power output: 100W (10kV, 10mA) • Binding energy range: 409-389 eV (N1s)

[0035] The composite particles according to the embodiment of the present invention exhibit a signal area intensity of a peak originating from carbon, located between 282 eV and 288 eV, in the photoelectron spectrum obtained by X-ray electron spectroscopy. A " for " the signal area intensity of the peak originating from nitrogen present between 397 eV and 404 eV A The ratio of "N A / C A Preferably, N is in the range of 0.019 or more and 0.5 or less. A / C A It is more preferable that the range is between 0.025 and 0.45, more preferably between 0.025 and 0.4, and even more preferably between 0.025 and 0.375. Furthermore, when the core of the composite particle according to the embodiment of the present invention contains silicon, oxygen, and lithium, in the photoelectron spectrum obtained by X-ray electron spectroscopy, the signal area intensity C of the peak originating from carbon, which is present between 282 eV and 288 eV, is A" for " the signal area intensity of the peak originating from nitrogen present between 397 eV and 404 eV A The ratio of "N A / C A Preferably, N is in the range of 0.04 or more and 0.5 or less. A / C A It is more preferable that the range is between 0.04 and 0.45, more preferably between 0.04 and 0.4, and even more preferably between 0.05 and 0.4. Furthermore, when the core of the composite particle according to the embodiment of the present invention consists only of silicon, in the photoelectron spectrum obtained by X-ray electron spectroscopy, the signal area intensity C of the peak originating from carbon, which is present between 282 eV and 288 eV, is A " for " the signal area intensity of the peak originating from nitrogen present between 397 eV and 404 eV A The ratio of "N A / C A Preferably, N is in the range of 0.085 or more and 0.16 or less. A / C A It is more preferable that the range is between 0.085 and 0.15, more preferably between 0.085 and 0.14, and even more preferably between 0.086 and 0.135. Furthermore, when the core of the composite particle according to the embodiment of the present invention includes a first core containing silicon and a second core containing carbon, in the photoelectron spectrum obtained by X-ray electron spectroscopy, the signal area intensity C of the peak originating from carbon, which is located between 282 eV and 288 eV, is A " for " the signal area intensity of the peak originating from nitrogen present between 397 eV and 404 eV A The ratio of "N A / C A Preferably, N is in the range of 0.019 or more and 0.05 or less. A / C A It is more preferable that the value is within the range of 0.02 to 0.04, and more preferably within the range of 0.025 to 0.035. Note that these upper and lower limits can be combined arbitrarily. Here, "signal area intensity C of the peak originating from carbon present between 282 eV and 288 eV"A " represents the binding energy originating from carbon in the photoelectron spectrum obtained by XPS, and this binding energy indicates the presence of "carbon on the surface of the composite particle." Also, "the signal area intensity of the peak originating from nitrogen, which is between 397 eV and 404 eV" A " is the binding energy originating from nitrogen in the photoelectron spectrum obtained by XPS, and this binding energy indicates the presence of "nitrogen on the surface of the composite particle." Also, "the signal area intensity C of the peak originating from carbon, which is present between 282 eV and 288 eV." A " and "signal area intensity of the nitrogen-derived peak present between 397 eV and 404 eV N A This is measured using XPS based on the following measurement condition 3.

[0036] (Measurement condition 3) ·X-ray source: MgKα ray • X-ray irradiation diameter: 10 mm • Power output: 100,250W (10kV, 10,25mA) • Bond energy range: 294-274 eV (C1s), 409-389 eV (N1s)

[0037] The composite particles according to the embodiment of the present invention exhibit a signal area intensity of a peak originating from silicon, located between 89 eV and 109 eV, in the photoelectron spectrum obtained by X-ray electron spectroscopy. A " for " the signal area intensity of the peak originating from nitrogen present between 397 eV and 404 eV A The ratio of "N A / Si A Preferably, N is in the range of 0.15 or more and 0.7 or less. A / Si AIt is more preferably within the range of 0.16 or more and 0.6 or less, more preferably within the range of 0.19 or more and 0.5 or less, and even more preferably within the range of 0.198 or more and 0.401 or less. Further, when the core part of the composite particles according to the embodiment of the present invention contains silicon, oxygen and lithium, in the photoelectron spectrum by X-ray photoelectron spectroscopy, "the signal area intensity Si of the peak derived from silicon existing between 89 eV and 109 eV" A "to the "signal area intensity N of the peak derived from nitrogen existing between 397 eV and 404 eV" A "The ratio (N A / Si A ) is preferably within the range of 0.15 or more and 0.5 or less, and N A / C A is more preferably within the range of 0.2 or more and 0.45 or less, more preferably within the range of 0.25 or more and 0.4 or less, and even more preferably within the range of 0.3 or more and 0.35 or less. Further, when the core part of the composite particles according to the embodiment of the present invention includes a first core part containing silicon and a second core part containing carbon, in the photoelectron spectrum by X-ray photoelectron spectroscopy, "the signal area intensity Si of the peak derived from silicon existing between 89 eV and 109 eV" A "to the "signal area intensity N of the peak derived from nitrogen existing between 397 eV and 404 eV" A "The ratio (N A / Si A ) is preferably within the range of 0.19 or more and 0.7 or less, and N A / C A is more preferably within the range of 0.2 or more and 0.6 or less, and more preferably within the range of 0.3 or more and 0.5 or less. Here, the upper limit value and the lower limit value can be arbitrarily combined. Here, "the signal area intensity Si of the peak derived from silicon existing between 89 eV and 109 eV" A is the binding energy derived from silicon in the photoelectron spectrum obtained by XPS, and this binding energy indicates the presence of "silicon on the surface of the composite particles". Further, "the signal area intensity N of the peak derived from nitrogen existing between 397 eV and 404 eV" AThe " " represents the binding energy originating from nitrogen in the photoelectron spectrum obtained by XPS, and this binding energy indicates the presence of "nitrogen on the surface of the composite particle." Also, the "signal area intensity of the peak originating from silicon, located between 89 eV and 109 eV, Si A " and "signal area intensity of the nitrogen-derived peak present between 397 eV and 404 eV N A This is measured using XPS based on the following measurement condition 4.

[0038] (Measurement condition 4) ·X-ray source: MgKα ray • X-ray irradiation diameter: 10 mm • Power output: 100,250W (10kV, 10,25mA) • Bonding energy range: 89-109 eV (Si1s), 409-389 eV (N1s)

[0039] In the composite particles according to the embodiment of the present invention, nitrogen preferably accounts for a mass of 0.03% to 2.8% by mass relative to the total amount of composite particles, more preferably 0.03% to 2.6% by mass relative to the total amount of composite particles, even more preferably 0.03% to 2.4% by mass relative to the total amount of composite particles, even more preferably 0.03% to 2.2% by mass relative to the total amount of composite particles, and even more preferably 0.03% to 2.0% by mass relative to the total amount of composite particles. Furthermore, when the core of the composite particles according to the embodiment of the present invention contains silicon, oxygen, and lithium, it is preferable that nitrogen accounts for a mass of 0.03% to 0.2% by mass relative to the total amount of composite particles, more preferably 0.03% to 0.18% by mass relative to the total amount of composite particles, even more preferably 0.03% to 0.16% by mass relative to the total amount of composite particles, even more preferably 0.03% to 0.14% by mass relative to the total amount of composite particles, and even more preferably 0.03% to 0.12% by mass relative to the total amount of composite particles. Furthermore, when the core of the composite particles according to the embodiment of the present invention consists only of silicon, it is preferable that nitrogen accounts for a mass of 1.5% by mass or more and 2.8% by mass or less of the total amount of composite particles, more preferably 1.6% by mass or more and 2.8% by mass or less of the total amount of composite particles, even more preferably 1.7% by mass or more and 2.8% by mass or less of the total amount of composite particles, even more preferably 1.75% by mass or more and 2.8% by mass or less of the total amount of composite particles, and even more preferably 1.8% by mass or more and 2.8% by mass or less of the total amount of composite particles.Furthermore, when the core of the composite particle according to the embodiment of the present invention includes a first core containing silicon and a second core containing carbon, it is preferable that nitrogen accounts for a mass of 0.75% by mass or more and 0.9% by mass or less of the total amount of composite particles, more preferably 0.8% by mass or more and 0.9% by mass or less of the total amount of composite particles, and even more preferably 0.85% by mass or more and 0.9% by mass or less of the total amount of composite particles. These upper and lower limits can be arbitrarily combined. When the nitrogen content in the composite particle is within the above range, the battery characteristics of the lithium-ion secondary battery made using this composite particle can be improved, and the decrease in conductivity between the negative electrode active materials can be suppressed. The nitrogen content is measured by the "inert gas fusion-thermal conductivity method" using an oxygen-nitrogen-hydrogen analyzer, EMGA-930, manufactured by Horiba, Ltd., based on the following measurement conditions 5.

[0040] (Measurement condition 5) • Sample weight: Approximately 0.01g • Type of inert gas: Helium

[0041] In the composite particles according to the embodiment of the present invention, it is preferable that hydrogen is not included, but hydrogen may be included in these composite particles. If hydrogen is included in the composite particles, the amount of hydrogen may be in the range of more than 0% by mass and 1.0% by mass or less of the total amount of composite particles. In this case, the amount of hydrogen may be in the range of 0.01% by mass or more and 1.0% by mass or less of the total amount of composite particles, in the range of 0.05% by mass or more and 1.0% by mass or less of the total amount of composite particles, in the range of 0.1% by mass or more and 0.95% by mass or less of the total amount of composite particles. When the amount of hydrogen in the composite particles is within the above range, the carbonization of the organic compound mainly composed of carbon and containing nitrogen, as described later, is sufficiently advanced, and the residue of the organic compound on the surface of the composite particles can be suppressed. As a result, a decrease in the electronic conductivity between Si particles or between Si particles and the conductive material can be suppressed, and a decrease in charge / discharge capacity and an increase in internal resistance can be suppressed. The hydrogen content is measured using the "inert gas fusion-nondispersive infrared absorption method" with the EMGA-930 oxygen, nitrogen, and hydrogen analyzer manufactured by Horiba, Ltd., based on the above measurement conditions 5.

[0042] In the composite particles according to the embodiment of the present invention, carbon preferably accounts for a mass of 3% to 85% by mass of the total amount of composite particles, more preferably 10% to 80% by mass of the total amount of composite particles, and even more preferably 15% to 75% by mass of the total amount of composite particles. Furthermore, when the core of the composite particles according to the embodiment of the present invention contains silicon, oxygen, and lithium, carbon preferably accounts for a mass of 3% to 6% by mass of the total amount of composite particles, more preferably 3.2% to 6% by mass of the total amount of composite particles, more preferably 3.4% to 6% by mass of the total amount of composite particles, even more preferably 3.6% to 6% by mass of the total amount of composite particles, and even more preferably 3.8% to 6% by mass of the total amount of composite particles. Furthermore, when the core of the composite particles according to the embodiment of the present invention consists only of silicon, it is preferable that carbon accounts for 38% to 45% by mass of the total amount of composite particles, more preferably 38% to 44% by mass of the total amount of composite particles, even more preferably 38.5% to 44% by mass of the total amount of composite particles, even more preferably 39% to 43% by mass of the total amount of composite particles, and even more preferably 39.5% to 43.5% by mass of the total amount of composite particles. Furthermore, when the core of the composite particle according to the embodiment of the present invention includes a first core containing silicon and a second core containing carbon, it is preferable that the carbon accounts for 60% to 85% by mass of the total amount of composite particles, more preferably 65% ​​to 85% by mass of the total amount of composite particles, even more preferably 65% ​​to 80% by mass of the total amount of composite particles, even more preferably 65% ​​to 75% by mass of the total amount of composite particles, and even more preferably 70% to 75% by mass of the total amount of composite particles.These upper and lower limits can be combined arbitrarily. Furthermore, the carbon content is measured using the "combustion in oxygen stream - infrared absorption method" with the Horiba EMIA-920V carbon-sulfur simultaneous quantitative analyzer, based on the following measurement conditions 6.

[0043] (Measurement condition 6) • Sample weight: Approximately 0.15g • Gas carrier: oxygen

[0044] The average particle diameter D50 (median diameter) of the composite particles according to the embodiment of the present invention is preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less, and even more preferably 3 μm or more and 10 μm or less. The average particle diameter D50 referred to herein is measured by laser diffraction and scattering using a particle size distribution analyzer, SYNC, manufactured by Microtrac Bell Co., Ltd.

[0045] <Method for producing composite particles according to an embodiment of the present invention> Examples of methods for producing composite particles according to embodiments of the present invention include: a method for producing composite particles using pre-doped lithium particles (particles containing silicon, oxygen, and lithium) as core particles (composite particle production method 1); a method for producing composite particles by subsequently doping silicon and oxygen-containing particles as core particles with lithium (composite particle production method 2); a method for producing composite particles using particles consisting only of silicon as core particles (composite particle production method 3); and a method for producing composite particles using a mixture of silicon-containing particles and carbon-containing particles as core particles (composite particle production method 4). In any of the composite particle production methods 1 to 3, graphite particles may be used in combination with the various particles (i.e., a mixture of various particles and graphite particles may be used). In such cases, granulated particles made from each particle and graphite particles may be used as core particles. The following describes each of these manufacturing methods.

[0046] 1. Method for producing composite particles 1 The composite particles according to the embodiment of the present invention are obtained by heat-treating composite particles, which are particles containing silicon, oxygen, and lithium coated with an organic compound mainly composed of carbon and containing nitrogen, in an inert atmosphere or in a vacuum.

[0047] Particles containing silicon, oxygen, and lithium may contain elements other than silicon, oxygen, and lithium, or they may contain only silicon, oxygen, and lithium. Preferably, these particles contain lithium metasilicate and silicon. Furthermore, these particles may contain Li2Si2O5, Li4SiO4, Li8SiO6, SiO2, or an amorphous structure of Si and O. Preferably, these particles are lithium-doped silicon oxide. As mentioned above, these particles may be used in combination with graphite particles (i.e., mixed particles of these particles and graphite particles may be used). In such cases, granulated particles made from these particles and graphite particles may be used as core particles.

[0048] Organic compounds that are mainly composed of carbon and also contain nitrogen may be low-molecular-weight compounds or high-molecular-weight compounds. Examples of low-molecular-weight compounds include polyimide precursors (a mixture of tetracarboxylic acid diester and diamine), phthalonitrile polymer precursors, urethane resin precursors, melamine resin precursors, and bismaleimidotriazine resin precursors. Examples of high-molecular-weight compounds include polyimide, polyamide, polyamideimide, bismaleimidotriazine resin, polyacrylonitrile, urethane, melamine, polypyrrole, urea resin, chitin, guanamine resin, cyanate resin, ABS resin, nitrile rubber, polyvinylpyridine, and epoxy resins with amines as curing agents.

[0049] The organic compound, which has carbon as its main component and also contains nitrogen, is preferably a polyimide or a precursor of polyimide. Polyimides can generally be synthesized from tetracarboxylic dianhydrides (or their derivatives) and polyhydric amine compounds. For example, a mixture containing a tetracarboxylic ester compound, such as an ester compound of benzophenonetetracarboxylic acid and an aliphatic alcohol, and a polyhydric amine compound, such as metaphenylenediamine, can be polymerized by heating. The polyimide thus obtained can then be further heat-treated in an inert atmosphere to form a carbon film containing nitrogen.

[0050] Examples of tetracarboxylic dianhydrides include pyromellitic dianhydride (PMDA), 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3'4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), bis(2,3-dicarboxyphenyl)methane dianhydride, and bis(3,4-dicarboxyphenyl)methane dianhydride. Examples include phenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 2,2-bis[3,4-(dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, oxydiphthalic anhydride (ODPA), thiodiphthalic anhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrenetetracarboxylic acid dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, and 9,9-bis[4-(3,4'-dicarboxyphenoxy)phenyl]fluorene dianhydride. Among these tetracarboxylic dianhydrides, pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) are preferred. In addition, in the present invention, asymmetric biphenyltetracarboxylic dianhydrides may be used as tetracarboxylic dianhydrides. A typical example of an asymmetric biphenyltetracarboxylic dianhydride is 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA). Furthermore, these tetracarboxylic dianhydrides may be used individually or in combination of two or more.

[0051] Furthermore, the polyvalent amine compound is preferably a diamine compound or a trivalent amine compound. Examples of such diamine compounds include paraphenylenediamine (PPD), metaphenylenediamine (MPDA), 2,5-diaminotoluene, 2,6-diaminotoluene, 4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 2,2-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane (MDA), 2,2-bis-(4-aminophenyl)propane, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether (34ODA), and 4,4'-diaminodiphenyl ether (ODA). Examples include 1,5-diaminonaphthalene, 4,4'-diaminodiphenyldiethylsilane, 4,4'-diaminodiphenylsilane, 4,4'-diaminodiphenylethylphosphine oxide, 1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene (134APB), 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 2,2-bis(3-aminophenyl)1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)1,1,1,3,3,3-hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, and 2,2',6,6'-tetraethyl(4,4'-methylenedianiline). Among these diamine compounds, it is preferable to use paraphenylenediamine (PPD), metaphenylenediamine (MPDA), 4,4'-diaminodiphenylmethane (MDA), 3,4'-diaminodiphenyl ether (34ODA), 4,4'-diaminodiphenyl ether (ODA), 1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene (134APB), and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP).Furthermore, these diamine compounds may be used individually or in combination of two or more.

[0052] Examples of trivalent amine compounds include 2,4,6-triaminopyrimidine (TAP), 1,3,5-triaminobenzene, 1,3,5-tris(4-aminophenyl)benzene, 3,4,4'-triaminodiphenyl ether, 6-phenylbuteridine-2,4,7-triamine, tris(4-aminophenyl)methanol, melamine, 2',4',4-triaminobenzanilide, 2,5,6-triamino-3-methylpyrimidine-4(3H)-one, 1,4,5,8-tetraaminoanthraquinone, and 3,3'-diaminobenzidine. Among these trivalent amine compounds, 2,4,6-triaminopyrimidine (TAP) and tris(4-aminophenyl)methanol are preferred. These trivalent amine compounds may be used individually or in combination. Diamine compounds and trivalent amine compounds may also be used in combination.

[0053] Furthermore, while this organic compound, which has carbon as its main component and also contains nitrogen, may also contain elements other than carbon and nitrogen, it is preferable that it does not contain any elements other than carbon and nitrogen.

[0054] In the composite particles according to the embodiment of the present invention, the surface of the composite particles may be partially coated, or the surface of the composite particles may be entirely coated.

[0055] The heat treatment temperature is preferably in the range of 500°C to 1000°C, more preferably in the range of 550°C to 900°C, even more preferably in the range of over 600°C and 900°C, and still more preferably in the range of over 600°C and 800°C. If the heat treatment temperature is too low, carbonization will not proceed and sufficient electronic conductivity cannot be obtained. On the other hand, if the heat treatment temperature is too high, the particles containing silicon, oxygen, and lithium will partially melt, and the energy consumption of the manufacturing process will also increase.

[0056] The heat treatment time is preferably between 30 minutes and 100 hours, more preferably between 30 minutes and 50 hours, and even more preferably between 1 hour and 50 hours. If the heat treatment time is too short, carbonization will not proceed sufficiently, and adequate electronic conductivity cannot be obtained. On the other hand, if the heat treatment time is too long, manufacturing energy consumption will increase.

[0057] Furthermore, the composite particles are not heat-treated in an oxidizing atmosphere prior to the above heat treatment.

[0058] 2. Method for manufacturing composite particles 2 The composite particles according to embodiments of the present invention are obtained by heat-treating a mixture of silicon and oxygen-containing particles, a nitrogen-containing organic compound, and a lithium compound, or a mixture obtained by coating silicon and oxygen-containing particles with a nitrogen-containing organic compound and then mixing it with a lithium compound, in an inert atmosphere or in a vacuum.

[0059] Examples of particles containing silicon and oxygen include silicon dioxide (SiO₂). x (x=0.1~1.9)), silicon dioxide (SiO2), a mixture of amorphous silicon and oxygen, and particles in which metallic silicon is embedded within silicon dioxide are used. It is preferable that the silicon oxide particles be silicon monoxide (SiO). Furthermore, as mentioned above, these particles may be used in combination with graphite particles (i.e., a mixture of these particles and graphite particles may be used). In such cases, granulations from these particles and graphite particles may be used as core particles.

[0060] Examples of lithium compounds used include lithium hydride, lithium oxide, lithium carbonate, lithium hydroxide, lithium aluminum hydride, lithium formate, lithium oxalate, lithium acetate, lithium lactate, lithium citrate, methyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium, lithium methoxide, lithium ethoxide, and lithium tert-butoxide. Lithium hydride is preferred as the lithium compound.

[0061] The organic compound containing carbon as the main component and nitrogen, the heat treatment temperature, and the heat treatment time in "Method 2 for Manufacturing Composite Particles" are as described in section "1. Method 1 for Manufacturing Composite Particles".

[0062] 3. Method for producing composite particles 3 The composite particles according to the embodiment of the present invention are obtained by heat-treating composite particles, which consist of silicon only and are coated with an organic compound mainly composed of carbon and containing nitrogen, in an inert atmosphere or in a vacuum.

[0063] The organic compound containing carbon as the main component and nitrogen, the heat treatment temperature, and the heat treatment time in "Method 3 for Manufacturing Composite Particles" are as described in section "1. Method 1 for Manufacturing Composite Particles".

[0064] The composite particles according to the embodiment of the present invention can be used as active material particles for the negative electrode of a lithium-ion secondary battery.

[0065] 4. Method for producing composite particles 4 The composite particles according to the embodiment of the present invention are obtained by heat-treating a composite particle, which is a mixture of silicon-containing particles and carbon-containing particles, coated with an organic compound mainly composed of carbon and containing nitrogen, in an inert atmosphere or in a vacuum.

[0066] Examples of silicon-containing particles include silicon particles, and examples of carbon-containing particles include graphite particles.

[0067] The organic compound containing carbon as the main component and nitrogen, the heat treatment temperature, and the heat treatment time in "Method 4 for Manufacturing Composite Particles" are as described in section "1. Method 1 for Manufacturing Composite Particles".

[0068] The composite particles according to the embodiment of the present invention can be used as active material particles for the negative electrode of a lithium-ion secondary battery.

[0069] <Configuration of the slurry according to an embodiment of the present invention> The slurry according to an embodiment of the present invention contains at least the above-mentioned composite particles, a binder, and a solvent. The binder binds the slurry to the current collector described later. The solvent disperses the composite particles and dissolves the binder.

[0070] The binder is preferably an aqueous binder. This aqueous binder includes not only aqueous binders that are water-soluble, but also aqueous binders that are dispersed in water in an emulsified state (in the form of an emulsion).

[0071] Examples of water-soluble aqueous binders include polyacrylic acid (PAA), carboxymethylcellulose (CMC), polyethylene oxide, or homopolymers or copolymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid. Note that acids such as polyacrylic acid and unsaturated carboxylic acids may also be used after dissolving a salt of them with a metal such as sodium in water.

[0072] Examples of aqueous binders dispersed in emulsion form include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyvinyl chloride, methacrylic resin, modified polyphenylene oxide, polyethylene, polypropylene, ethylene propylene polymer; styrene-butadiene rubber (SBR), isoprene rubber, butyl rubber, acrylic rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer; and ethylenically unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate.

[0073] These aqueous binders may be used individually or in combination of at least two of them.

[0074] It is preferable to use water alone as the solvent. Alternatively, the solvent may include organic solvents such as alcohols (methanol, ethanol, propanol, butanol), amide solvents (N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), 3-methoxy-N,N-dimethylpropanamide, dimethylisobutyric acid amide, hexamethylphosphoric triamide), ester solvents (gammabutyrolactone), ether solvents (1,2-dimethoxyethane, diglyme, triglime, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane), ketone solvents (cyclopentanone), and urea solvents (tetramethylurea, N,N-dimethylethylurea, 1,3-dimethyl-2-imidazolidinone). These solvents may be used individually or in combination.

[0075] Furthermore, this slurry may further contain a conductive additive. Examples of such conductive additives include conductive fillers. Examples of conductive fillers include carbon black, Ketjenblack, acetylene black, carbon whiskers, carbon fibers such as vapor-grown carbon fiber (VGCF), natural graphite, artificial graphite, carbon nanoparticles, carbon nanotubes, graphene, titanium oxide, ruthenium oxide, aluminum, nickel, copper, or other metal powders or metal fibers, or conductive oxides and nitrides. These conductive fillers may be used individually or in combination.

[0076] <Method for producing slurry according to an embodiment of the present invention> The slurry according to the embodiment of the present invention is obtained by mixing the composite particles prepared above with a binder and water. In this case, a conductive additive may be further mixed in.

[0077] Furthermore, the slurry according to the embodiment of the present invention can be used as a slurry for manufacturing the negative electrode of a lithium-ion secondary battery.

[0078] <Configuration of the negative electrode according to an embodiment of the present invention> An embodiment of the present invention comprises a current collector for the negative electrode and a negative electrode active material layer mainly composed of the composite particles.

[0079] The negative electrode current collector is preferably a conductive metal foil. Such a conductive metal foil is formed from, for example, metals such as copper, nickel, iron, titanium, and cobalt, or alloys obtained by combining these metals.

[0080] Furthermore, it is preferable that the negative electrode current collector be roughened in order to improve its bonding with the negative electrode active material layer. The negative electrode current collector can be roughened by applying electrolytic copper or an electrolytic copper alloy to its surface. Alternatively, the negative electrode current collector can be roughened by applying a roughening treatment. Examples of such roughening treatments include vapor deposition, etching, and polishing. Examples of vapor deposition methods include sputtering, CVD, and vapor deposition. Examples of etching methods include physical etching and chemical etching. Examples of polishing methods include polishing with sandpaper and polishing by blasting.

[0081] The surface roughness (arithmetic mean roughness) Rz of the negative electrode current collector is preferably 0.1 μm or more and 5 μm or less, more preferably 0.5 μm or more and 5 μm or less, and even more preferably 0.5 μm or more and 3 μm or less.

[0082] The thickness of the negative electrode active material layer (the thickness of the negative electrode excluding the thickness of the negative electrode current collector) is preferably in the range of 5 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm.

[0083] The performance of the negative electrode according to the embodiment of the present invention can be evaluated by using a half-cell made of lithium metal as the counter electrode, a separator placed between the negative electrode and the lithium metal, and an electrolyte-containing medium filled between the negative electrode and the lithium.

[0084] <Method for manufacturing a negative electrode according to an embodiment of the present invention> The negative electrode according to the embodiment of the present invention can be manufactured by applying the slurry prepared above onto a current collector for the negative electrode, drying the coating film, and then heat-treating the dried coating film. The drying process is preferably carried out at a temperature within the range of 60°C to 140°C. The drying method used in the drying process may be hot air drying, radiant heating, hot plate heating, etc. The heat treatment of the coating film may be carried out in the atmosphere, or in a non-oxidizing atmosphere such as under vacuum, nitrogen atmosphere, or argon atmosphere, or in a reducing atmosphere such as a hydrogen atmosphere. The heat treatment temperature of the coating film according to the present invention is preferably in the range of 100°C to 400°C, more preferably in the range of 100°C to 350°C, even more preferably in the range of 120°C to 200°C, and particularly preferably in the range of 120°C to 160°C. Examples of heat treatment methods include using a conventional constant temperature furnace or the hot press method. Furthermore, a process to increase the electrode density by roll pressing can be included after drying or heat treatment. In this way, a negative electrode active material layer mainly composed of the above composite particles is formed on the negative electrode current collector.

[0085] <Configuration of a lithium-ion secondary battery according to an embodiment of the present invention> A lithium-ion secondary battery according to an embodiment of the present invention comprises a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte-containing medium filled between the positive and negative electrodes. The positive electrode, negative electrode, separator, and electrolyte-containing medium filled between the positive and negative electrodes are enclosed in packaging material.

[0086] For the positive electrode, known positive electrodes for lithium-ion secondary batteries are used. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer.

[0087] The positive electrode current collector may have the same configuration as the negative electrode current collector, except that the materials used may be changed as appropriate. The positive electrode current collector is preferably a conductive metal foil. This conductive metal foil is formed from, for example, metals such as aluminum, aluminum alloys, nickel, and titanium, or alloys such as stainless steel obtained by combining these metals.

[0088] The positive electrode active material layer is formed on the positive electrode current collector. The positive electrode active material layer may have the same configuration as the negative electrode active material layer, except that the material of the active material particles is appropriately changed. Examples of positive electrode active material particles include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO), and ternary (Li(Ni)). x Co y Mn z Lithium-containing transition metal oxides such as 2O can be used.

[0089] For the separator, known separators for lithium-ion secondary batteries are used. Examples of such separators include polyimide resin separators, glass nonwoven fabric separators, pulp separators, aramid separators, polypropylene resin separators, or polyamide-imide resin separators.

[0090] The electrolyte-containing medium can be a known electrolyte-containing medium for lithium-ion secondary batteries. For example, a lithium salt, which is the electrolyte, can be dissolved in an organic solvent as the electrolyte-containing medium. Preferably, the organic solvent is at least one selected from non-aqueous solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl ether, isopropyl methyl carbonate, vinylene carbonate, γ-butyrolactone, and acetonitrile. Multiple types of these organic solvents may be used in mixture form. For example, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiI, and LiClO4 can be used as the electrolyte. The electrolyte-containing medium may also contain additives. Additives that can be used include fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesultone (PS), butylsultone (BS), propa-1-ene-1,3-sultone (PES), propargylmethanesulfonate (PMS), cyclohexylbenzene (CHB), biphenyl (BP), tert-amylbenzene (TAB), lithium difluorooxalatoborate (LiODFB), trimethoxyboroxine (TMOBX), and lithium bis(oxalate)borate (LiBOB).

[0091] The packaging material houses the positive electrode, negative electrode, separator, and electrolyte-containing medium. Examples of packaging materials include polyimide resin film, aromatic polyamide resin film, polyamide-imide resin film, polyalkylene terephthalate resin film, aluminum laminate film, stainless steel, nickel-plated steel sheet, and aluminum alloy.

[0092] <Method for manufacturing a lithium-ion secondary battery according to an embodiment of the present invention> A lithium-ion secondary battery according to an embodiment of the present invention can be manufactured by enclosing a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes in a packaging material, filling the space between the positive and negative electrodes with an electrolyte-containing medium, and then sealing the packaging material.

[0093] <Examples and Comparative Examples> The following describes specific examples and comparative examples, but the present invention is not limited to these examples and comparative examples. [Examples]

[0094] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles A synthesis vessel was formed by attaching a stirring rod fitted with a polytetrafluoroethylene stirring blade to a 500 mL three-necked flask. 115.71 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 49.63 g of ethanol, and 95.83 g of N-methyl-2-pyrrolidone (NMP) were added to the synthesis vessel and stirred at 80°C under atmospheric pressure for 2 hours to carry out the esterification reaction and obtain a reaction solution. Next, after cooling this reaction solution to below 40°C, 38.83 g of metaphenylenediamine (MPDA) was added and stirred again at 80°C under atmospheric pressure for 3 hours to prepare a polyimide precursor composition (a nitrogen-containing organic compound) in which benzophenonetetracarboxylic diethyl ester and metaphenylenediamine with a solid content of 47.2% by mass were dissolved in NMP. All of the above reactions were carried out under an argon atmosphere. Next, the polyimide precursor composition and core particles were mixed in a solid content mass ratio of 4:96, and NMP was added as a solvent and stirred to obtain a homogeneous slurry. In this case, silicon monoxide powder with an average particle size of 5 μm was coated with 4.1% by mass of carbon (hereinafter sometimes referred to as "carbon-coated SiO") as the core particles (here, the silicon monoxide particles form the core and the carbon coating forms the intermediate coating). This carbon-coated SiO is obtained by adding 4.33 g of lithium hydride to 50 g of silicon monoxide powder with an average particle size of 5 μm obtained from Almedio Co., Ltd., under an argon gas atmosphere with a dew point temperature of -50°C or lower, and mixing the mixture in a ball mill using 10 mm diameter zirconia balls. This mixture is heated from room temperature to 600°C over 2 hours under an argon atmosphere, held at 600°C for 10 hours, and then cooled. The resulting calcined product is dispersed in purified water for washing, the washed calcined product is dried, the dried calcined product is ball-milled using 10 mm diameter zirconia balls, and the pulverized calcined product is placed in a tube furnace, acetylene is introduced under an argon atmosphere, and it is held at 600°C for 10 hours. This powder has peaks at approximately 2θ = 18.5° and 26.5° that are attributed to lithium metasilicate and a peak at 2θ = 28° that is attributed to silicon, as measured by a powder X-ray diffraction analyzer.Then, the obtained slurry was spread on a heat-resistant film and dried with hot air at 120 °C to obtain a dried product. After that, the dried product was pulverized and passed through a 0.5-mm mesh sieve to obtain a pulverized product. Next, this pulverized product was heated from room temperature to 600 °C over 2 hours under an argon atmosphere, held at 600 °C for 1 hour, and then cooled to obtain a fired product. Then, using 10-mm diameter zirconia balls, the obtained fired product was ball-milled and passed through a 50-μm mesh sieve to produce composite particles. When these composite particles were analyzed with an oxygen / nitrogen / hydrogen analyzer, it was confirmed that they contained 0.085 mass% nitrogen (see Table 1). Also, as a result of analysis with this oxygen / nitrogen / hydrogen analyzer, since it was confirmed that they contained 0.2 mass% hydrogen, it was confirmed that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles had sufficiently progressed (see Table 1). Furthermore, as a result of analysis with a carbon / sulfur simultaneous quantification analyzer, it was confirmed that they contained 5.8 mass% carbon (see Table 1). Also, when these composite particles were analyzed by XPS, the ratio of the area of the peak showing nitrogen near 400 eV (N A ) to the area of the peak showing carbon near 285 eV (C A ) (N A / C A ) was 0.4 (see Table 1). Also, the intensity ratio of the intensity at 400.8 eV (N I2 ) to the intensity at 398.5 eV (N I1 ) (N I1 / N I2 ) was 3.7 (see Table 1). Furthermore, the ratio of the area of the peak showing nitrogen near 400 eV (N A ) to the area of the peak showing silicon near 100 eV (Si A ) (N A / Si A ) was 0.4 (see Table 1). Also, when these composite particles were analyzed by powder X-ray diffraction measurement, peaks attributed to lithium metasilicate appearing near 2θ = 18.5° and 26.5° and a peak derived from silicon at 2θ = 28° were confirmed. Also, as a result of measurement with a particle size distribution meter, the D50 of these composite particles was 6.1 μm.

[0095] (2) Preparation of slurry In a 24 mL plastic container, 1.35 g of a polyacrylic acid solution (10% by mass solution obtained by dissolving polyacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in purified water as a binder, 0.135 g of acetylene black as a conductive additive, and 1.08 g of the composite particles prepared in (1) above were added. Then, purified water was added to the same plastic container to adjust the solid content of the raw materials in the plastic container to 37.5% by mass. After that, the mixture was mixed at 2000 rpm for 5 minutes using a planetary rotation / revolution type mixer (ARE-310, manufactured by Thinky Co., Ltd.) to obtain a slurry. The solid content mass ratio of this slurry is "binder:conductive additive:composite particles = 10:10:80".

[0096] (3) Fabrication of the negative electrode The slurry prepared in (2) above was coated onto one side of an electrolytic copper foil (thickness 18 μm) with a surface roughness (arithmetic mean roughness) Rz of 1.3 μm using a coater. The electrolytic copper foil coated with the slurry was then dried at 80°C for 30 minutes under normal pressure to obtain a negative electrode intermediate. Next, this negative electrode intermediate was heat-treated in a vacuum furnace at 120°C for 2 hours to produce a negative electrode in close contact with the copper foil. The thickness of the negative electrode (active material layer) excluding the electrolytic copper foil was 17 μm, and the area was 1 cm². 2 The weight per unit was 1.2 mg.

[0097] (4) Fabrication of lithium-ion secondary battery coin cells Using the negative electrode prepared in (3) above, a secondary battery coin cell with a half-cell structure and a lithium metal foil counter electrode was fabricated. Specifically, in an argon gas atmosphere with a dew point temperature of -50°C or lower, a negative electrode made by punching out a φ16 mm circular shape, a φ19 mm circular shape punched out 16 μm thick polypropylene separator (obtained from ATR Corporation), and a φ16 mm circular shape punched out 0.5 mm thick lithium metal foil (manufactured by Honjo Metal Co., Ltd.) as the counter electrode were sequentially layered in a CR2032 type SUS coin cell case. A solution of "ethylene carbonate and diethyl carbonate mixed in a volume ratio of 1:1 with 1 mol / L of LiPF6 dissolved in it (manufactured by Kishida Chemical Co., Ltd.)" and "fluoroethylene carbonate (Sigma Aldrich)" mixed in a mass ratio of 9:1 was injected as an electrolyte-containing medium, and the CR2032 type SUS coin cell case was sealed to fabricate a secondary battery coin cell.

[0098] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed on the lithium-ion secondary battery coin cell fabricated in "1.(4)" above. The charge-discharge cycle test was conducted at an ambient temperature of 25°C, with a cutoff voltage of 0.0V during charging and 1.0V during discharging. The charge capacity (mAh / g) and discharge capacity (mAh / g) were measured after each cycle. In this charge-discharge cycle test, the initial charge was performed with a current of 0.075mA per 1mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.15mA. This charge-discharge cycle test was performed for 100 charge-discharge cycles, and the initial charge-discharge efficiency, the retention rate of discharge capacity after the 10th cycle, the retention rate of discharge capacity after the 50th cycle, and the retention rate of discharge capacity after the 100th cycle were determined. The charge-discharge capacity (mAh / g) was calculated by dividing the amount of charge required for charging and discharging (mAh) by the weight of the composite particles (g).

[0099] As a result, the charge capacity in the first cycle was 1341 mAh / g, the discharge capacity was 1093 mAh / g, and the initial charge / discharge efficiency was 82% (=1093 / 1341 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 1173 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 107% (=1173 / 1093 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 1058 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 97% (=1058 / 1093 × 100) (see Table 3). Finally, the discharge capacity in the 100th cycle was 745 mAh / g, and the retention rate of the discharge capacity in the 100th cycle was 68% (=745 / 1093 × 100) (see Table 3). [Examples]

[0100] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that the pulverized material was heated from room temperature to 1000°C over 2 hours under an argon atmosphere, held at 1000°C for 1 hour, and then cooled to obtain a calcined product. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.033 mass% nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.1 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 5.9 mass% carbon (see Table 1). Additionally, XPS analysis of these composite particles revealed a peak area (C) indicating carbon around a bond energy of 285 eV. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.06 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.8 (see Table 1). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.3 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 6.1 μm.

[0101] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0102] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 1098 mAh / g, the discharge capacity was 877 mAh / g, and the initial charge-discharge efficiency was 80% (=877 / 1098 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 908 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 104% (=908 / 877 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 765 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 87% (=765 / 877 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 705 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 80% (= 705 / 877 × 100) (see Table 3). [Examples]

[0103] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles A polyimide precursor composition (organic compound containing nitrogen) prepared by the same method as shown in Example 1 was mixed with core particles in a solid content mass ratio of 4:96. NMP was added as a solvent and the mixture was stirred to obtain a homogeneous slurry. Silicon monoxide with a particle size of 5 μm, manufactured by Osaka Titanium Technologies Co., Ltd., was used as the core particles. The obtained slurry was spread onto a heat-resistant film and dried with hot air at 120°C to obtain a dried product. This dried product was then pulverized and sieved through a 0.5 mm mesh to obtain a pulverized product. Next, this pulverized product was heat-treated at 350°C for 1 hour under an argon atmosphere to obtain a first calcined product. Subsequently, 5.6 g of this first calcined product was mixed with 0.49 g of lithium hydride under an argon gas atmosphere with a dew point of -50°C or lower, and the mixture was ball-milled using 10 mm diameter zirconia balls to obtain a mixed pulverized product. Next, the mixed pulverized material was heated from room temperature to 800°C over 2 hours under an argon atmosphere, held at 800°C for 5 hours, and then cooled to obtain a second calcined product. The obtained second calcined product was then dispersed in purified water and washed. After washing, the washed second calcined product was ball-milled using 10 mm diameter zirconia balls and sieved through a 50 μm mesh to produce composite particles. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.15 mass% nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.08 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles had progressed sufficiently (see Table 1). In addition, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 3.2 mass% carbon (see Table 1). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.04 (see Table 1). Also, the intensity was 398.5 eV (N I2) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.4 (see Table 1). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.4 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 5.7 μm.

[0104] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0105] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 1194 mAh / g, the discharge capacity was 865 mAh / g, and the initial charge-discharge efficiency was 72% (=865 / 1194 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 1102 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 127% (=1102 / 865 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 930 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 108% (=930 / 865 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 771 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 89% (= 771 / 865 × 100) (see Table 3). [Examples]

[0106] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that a polyimide precursor varnish PYRE-ML® (a polymeric organic compound containing nitrogen), obtained by polymerizing pyromellitic dianhydride and oxydianiline and available from I.S.T. Corporation, was used instead of the polyimide precursor composition (a polymeric organic compound containing nitrogen). Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.12% by mass of nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.1% by mass of hydrogen, indicating that the carbonization of the polyimide precursor varnish PYRE-ML® (a polymeric organic compound containing nitrogen) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 5.6% by mass of carbon (see Table 1). XPS analysis of these composite particles revealed a peak area (C) indicating carbon around a binding energy of 285 eV. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The intensity was 0.3 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.0 (see Table 1). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si AThe ratio was 0.3 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 5.7 μm.

[0107] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0108] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 904 mAh / g, the discharge capacity was 694 mAh / g, and the initial charge-discharge efficiency was 77% (=694 / 904 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 798 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 115% (=798 / 694 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 587 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 85% (=587 / 694 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 526 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 76% (= 526 / 694 × 100) (see Table 3). [Examples]

[0109] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that a polyimide precursor varnish (a polymeric organic compound containing nitrogen) obtained by polymerizing paraphenylenediamine and biphenyltetracarboxylic dianhydride was used instead of the polyimide precursor composition (an organic compound containing nitrogen). Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.18% by mass nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.2% by mass hydrogen, indicating that the carbonization of the polyimide precursor varnish (polymeric organic compound containing nitrogen) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 6.0% by mass carbon (see Table 1). XPS analysis of these composite particles revealed the area of ​​the peak indicating carbon around the bond energy of 285 eV (C). A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.2 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 0.59 (see Table 1). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.2 (see Table 1). Furthermore, analysis of these composite particles by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were attributed to lithium metasilicate, and a peak at 2θ = 28° that was attributed to silicon. In addition, particle size distribution analysis showed that the D50 of these composite particles was 5.5 μm.

[0110] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0111] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 961 mAh / g, the discharge capacity was 754 mAh / g, and the initial charge-discharge efficiency was 79% (=754 / 961 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 1090 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 145% (=1090 / 754 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 860 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 114% (=860 / 754 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 564 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 75% (= 564 / 754 × 100) (see Table 3). [Examples]

[0112] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that a phthalonitrile polymer precursor (a nitrogen-containing organic compound) manufactured by Azista Composites was used instead of the polyimide precursor composition (an organic compound containing nitrogen). Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.12% by mass nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.07% by mass hydrogen, indicating that the carbonization of the phthalonitrile polymer precursor (a nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 5.7% by mass carbon (see Table 1). XPS analysis of these composite particles revealed the area of ​​the peak indicating carbon around a binding energy of 285 eV (C). A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.05 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.0 (see Table 1). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.4 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 5.4 μm.

[0113] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0114] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 1050 mAh / g, the discharge capacity was 820 mAh / g, and the initial charge-discharge efficiency was 78% (=820 / 1050 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 1046 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 128% (=1046 / 820 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 806 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 98% (=806 / 820 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 547 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 67% (= 547 / 820 × 100) (see Table 3). [Examples]

[0115] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles A polyimide precursor composition (organic compound containing nitrogen) prepared by the same method as shown in Example 1 was mixed with core particles in a solid content mass ratio of 62.5:37.5. NMP was added as a solvent and the mixture was stirred to obtain a homogeneous slurry. As the core particles, silicon powder with a particle size of 0.1 μm obtained from Chem-Impex International was used. This powder has a peak originating from silicon at 2θ=28° in a powder X-ray diffraction analyzer. The obtained slurry was spread onto a heat-resistant film and dried with hot air at 120°C to obtain a dried product. This dried product was then pulverized and sieved through a 0.5 mm mesh to obtain a pulverized product. Next, this pulverized product was heated from room temperature to 600°C in an argon atmosphere over 2 hours, held at 600°C for 1 hour, and then cooled to obtain a calcined product. The obtained calcined product was then ball-milled using 10 mm diameter zirconia balls and sieved through a 50 μm mesh to produce composite particles. Analysis of these composite particles using an oxygen, nitrogen, and hydrogen analyzer confirmed that they contained 2.4 mass% nitrogen (see Table 2). Furthermore, analysis using the same analyzer confirmed that they contained 0.9 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 2). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 39.8 mass% carbon (see Table 2). Additionally, XPS analysis of these composite particles revealed a peak area (C) indicating carbon around a binding energy of 285 eV. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.1 (see Table 2). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.1 (see Table 2). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 6.2 μm.

[0116] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0117] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.0875 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.175 mA. As a result, the charge capacity in the first cycle was 2214 mAh / g, the discharge capacity was 1409 mAh / g, and the initial charge-discharge efficiency was 64% (=1409 / 2214 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 1435 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 102% (=1435 / 1409 × 100) (see Table 4). Furthermore, the discharge capacity at cycle 50 was 1003 mAh / g, and the retention rate of the discharge capacity at cycle 50 was 71% (=1003 / 1409 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 750 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 53% (=750 / 1409 × 100) (see Table 4). [Examples]

[0118] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 7, except that instead of silicon powder with a particle size of 0.1 μm, silicon sludge obtained from Almedio Co., Ltd. was wet-cleared with φ1 mm Zircon beads (D50 = 0.46 μm) as the core particle. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 2.6 mass% nitrogen (see Table 2). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.8 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 2). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 42.6 mass% carbon (see Table 2). XPS analysis of these composite particles revealed the area of ​​the peak indicating carbon around the binding energy of 285 eV (C A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.1 (see Table 2). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.0 (see Table 2). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 11.4 μm.

[0119] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0120] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.0875 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.175 mA. As a result, the charge capacity in the first cycle was 1726 mAh / g, the discharge capacity was 1118 mAh / g, and the initial charge-discharge efficiency was 65% (=1118 / 1726 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 1295 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 116% (=1295 / 1118 × 100) (see Table 4). Furthermore, the discharge capacity at cycle 50 was 1139 mAh / g, and the retention rate of the discharge capacity at cycle 50 was 102% (=1139 / 1118 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 999 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 89% (=999 / 1118 × 100) (see Table 4). [Examples]

[0121] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 7, except that the polyimide precursor composition, core particles, and acetylene black were mixed in a solid content mass ratio of 47:41:12, and NMP was added as a solvent and stirred to obtain a homogeneous slurry. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 1.8% by mass nitrogen (see Table 2). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.9% by mass hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 2). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 40.6% by mass carbon (see Table 2). XPS analysis of these composite particles revealed a peak area (C) indicating carbon around a binding energy of 285 eV. AThe area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.1 (see Table 2). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.0 (see Table 2). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 9.0 μm.

[0122] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0123] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.0625 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.125 mA. As a result, the charge capacity in the first cycle was 1985 mAh / g, the discharge capacity was 1310 mAh / g, and the initial charge-discharge efficiency was 66% (=1310 / 1985 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 1273 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 97% (=1273 / 1310 × 100) (see Table 4). Furthermore, the discharge capacity at cycle 50 was 1073 mAh / g, and the retention rate of the discharge capacity at cycle 50 was 82% (=1073 / 1310 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 914 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 70% (=914 / 1310 × 100) (see Table 4). [Examples]

[0124] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 8, except that the heat treatment conditions for the pulverized material involved raising the temperature from room temperature to 1000°C over 2 hours under an argon atmosphere, holding at 1000°C for 1 hour, and then cooling to obtain the calcined product. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 1.8 mass% nitrogen (see Table 2). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.2 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 2). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 43.4 mass% carbon (see Table 2). Additionally, XPS analysis of these composite particles revealed the area of ​​the peak indicating carbon around a bond energy of 285 eV (C). AThe area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.09 (see Table 2). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 0.72 (see Table 2). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 9.0 μm.

[0125] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0126] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.0875 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.175 mA. As a result, the charge capacity in the first cycle was 1631 mAh / g, the discharge capacity was 1135 mAh / g, and the initial charge-discharge efficiency was 70% (=1135 / 1631 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 1424 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 125% (=1424 / 1135 × 100) (see Table 4). Furthermore, the discharge capacity at cycle 50 was 1130 mAh / g, and the retention rate of the discharge capacity at cycle 50 was 100% (=1130 / 1135 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 581 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 51% (=581 / 1135 × 100) (see Table 4). [Examples]

[0127] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 7, except that a polyimide precursor composition (organic compound containing nitrogen) prepared using the same method as shown in Example 1, silicon powder (particle size 0.1 μm, obtained from Chem-Impex International) as the first core particle, and spheroidal graphite (particle size 8 μm, SG-BH8 from Ito Graphite Industry Co., Ltd.) as the second core particle were mixed in a solid content mass ratio of 20:30:50. When these composite particles were analyzed using an oxygen-nitrogen-hydrogen analyzer, it was confirmed that they contained 0.76 mass% nitrogen (see Table 5). Furthermore, the analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.24 mass% hydrogen, confirming that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles had progressed sufficiently (see Table 5). In addition, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 61 mass% carbon (see Table 5). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.04 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 0.90 (see Table 5). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.2 (see Table 5). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 7.8 μm.

[0128] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0129] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.05 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.1 mA. As a result, the charge capacity in the first cycle was 1480 mAh / g, the discharge capacity was 1074 mAh / g, and the initial charge-discharge efficiency was 73% (=1074 / 1480 × 100) (see Table 6). Furthermore, the discharge capacity in the 10th cycle was 1065 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 99% (=1065 / 1074 × 100) (see Table 6). In addition, the discharge capacity in the 50th cycle was 916 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 85% (=916 / 1074 × 100) (see Table 6). Finally, the discharge capacity at cycle 100 was 677 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 63% (= 677 / 1074 × 100) (see Table 6). [Examples]

[0130] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles A polyimide precursor composition (a nitrogen-containing organic compound) prepared by the same method as shown in Example 1, silicon powder as the first core particle (particle size 0.1 μm, obtained from Chem-Impex), and spheroidal graphite as the second core particle (particle size 8 μm, SG-BH8 from Ito Graphite Industry Co., Ltd.) were mixed in a solid content mass ratio of 20:20:60. NMP was added as a solvent and the mixture was stirred to obtain a homogeneous slurry. The obtained slurry was then spread onto a heat-resistant film and dried with hot air at 100°C to obtain a dried product. This dried product was then coarsely ground in a mortar and pestle, and then ball-milled using 10 mm diameter zirconia balls. The resulting pulverized material was placed in a powder molding mold consisting of a cylindrical mold with an inner diameter of φ20 mm and upper and lower punches, and double-screw molding was performed by applying a pressure of 200 MPa to obtain pellets. These pellets were then heated from room temperature to 600°C over 10 hours in an argon atmosphere, held at 600°C for 10 hours, and then cooled to obtain a calcined product. The obtained calcined material was coarsely ground in a mortar, then ball-milled using 10 mm diameter zirconia balls, and finally sieved through a 50 μm mesh to produce composite particles. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.85 mass% nitrogen (see Table 5). Further analysis using the same analyzer confirmed the presence of 0.32 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 5). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 71 mass% carbon (see Table 5). XPS analysis of these composite particles revealed a peak area (C) indicating carbon around a binding energy of 285 eV. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.02 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2The ratio was 1.1 (see Table 5). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.5 (see Table 5). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 8.8 μm.

[0131] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0132] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge in the charge-discharge cycle test was performed with a current of 0.0375 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.075 mA. As a result, the charge capacity in the first cycle was 1095 mAh / g, the discharge capacity was 720 mAh / g, and the initial charge-discharge efficiency was 66% (=720 / 1095 × 100) (see Table 6). Furthermore, the discharge capacity in the 10th cycle was 767 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 107% (=767 / 720 × 100) (see Table 6). In addition, the discharge capacity in the 50th cycle was 743 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 103% (=743 / 720 × 100) (see Table 6). Finally, the discharge capacity at cycle 100 was 613 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 85% (= 613 / 720 × 100) (see Table 6). [Examples]

[0133] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 13, except that a polyimide precursor composition (organic compound containing nitrogen) prepared using the same method as shown in Example 1, silicon powder (particle size 0.1 μm, obtained from Chem-Impex International) as the first core particle, and flake graphite (particle size 7 μm, CNP7 from Ito Graphite Industry Co., Ltd.) as the second core particle were mixed in a solid content mass ratio of 20:30:50. When these composite particles were analyzed using an oxygen-nitrogen-hydrogen analyzer, it was confirmed that they contained 0.86 mass% nitrogen (see Table 5). Furthermore, the analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.3 mass% hydrogen, confirming that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles had progressed sufficiently (see Table 5). In addition, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 62 mass% carbon (see Table 5). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.03 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.1 (see Table 5). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si AThe ratio was 0.3 (see Table 5). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 8.5 μm.

[0134] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0135] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.05 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.1 mA. As a result, the charge capacity in the first cycle was 1261 mAh / g, the discharge capacity was 861 mAh / g, and the initial charge-discharge efficiency was 68% (=861 / 1261 × 100) (see Table 6). Furthermore, the discharge capacity in the 10th cycle was 947 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 110% (=947 / 861 × 100) (see Table 6). In addition, the discharge capacity in the 50th cycle was 924 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 107% (=924 / 861 × 100) (see Table 6). Finally, the discharge capacity at cycle 100 was 625 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 73% (= 625 / 861 × 100) (see Table 6). [Examples]

[0136] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles Coated graphite particles were prepared using the same method as in Example 1, except that a polyimide precursor composition (organic compound containing nitrogen), prepared using the same method as in Example 1, was mixed with spheroidal graphite SG-BH8 with a particle size of 8 μm, obtained from Ito Graphite Industry Co., Ltd., as the core particle, in a solid content mass ratio of 4:96. Analysis of these coated graphite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 2.4 mass% nitrogen (see Table 5). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.9 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles was sufficiently advanced (see Table 5). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 40 mass% carbon (see Table 5). XPS analysis of these coated graphite particles revealed a peak area (C) indicating carbon around a binding energy of 285 eV. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The intensity was 0.1 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The value was 1.1 (see Table 5).

[0137] (2) Fabrication of lithium-ion secondary battery coin cells Using the coated graphite particles prepared in (1) above and the composite particles prepared in Example 7, a slurry was prepared in the same manner as in Example 1 such that the solid content mass ratio of the slurry was "binding agent:conductive additive:coated graphite particles:composite particles = 5:10:64:21". A negative electrode was then prepared using this slurry in the same manner as in Example 1. A lithium-ion secondary battery coin cell was then prepared using this negative electrode in the same manner as in Example 1.

[0138] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in the above “1. (2)”, the first charge in the charge-discharge cycle test was carried out at a current of 0.03575 mA with respect to 1 mg of the composite particles and the coated graphite particles. The charge-discharge cycle test was carried out in the same manner as in Example 1 except that the first discharge and the charge-discharge from the second time onwards were carried out at a current of 0.0715 mA. As a result, the charge capacity in the first cycle was 900 mAh / g, the discharge capacity was 618 mAh / g, and the first charge-discharge efficiency was 69% (= 618 / 900 × 100) (see Table 6). Also, the discharge capacity in the 10th cycle was 627 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 101% (= 627 / 618 × 100) (see Table 6). Furthermore, the discharge capacity in the 50th cycle was 532 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 86% (= 532 / 618 × 100) (see Table 6). Finally, the discharge capacity in the 100th cycle was 428 mAh / g, and the retention rate of the discharge capacity in the 100th cycle was 69% (= 428 / 618 × 100) (see Table 6).

Example

[0139] 1. Preparation of Lithium-Ion Secondary Battery Coin Cell A slurry was prepared in the same manner as in Example 1 except that the composite particles prepared in Example 1 and spherical graphite SG-BH8 with a particle size of 8 μm obtained from Ito Graphite Industry Co., Ltd. were mixed at a mass ratio of 25:75. Using this slurry, a negative electrode was prepared in the same manner as in Example 1. Then, using this negative electrode, a lithium-ion secondary battery coin cell was prepared in the same manner as in Example 1.

[0140] 2. Charge-Discharge Cycle Test of Lithium-Ion Secondary Battery Coin Cell Using the lithium-ion secondary battery coin cell prepared in the above "1.", the first charge in the charge-discharge cycle test was performed at a current of 0.03075 mA with respect to 1 mg of the composite particles and spherical graphite, and the charge-discharge cycle test was performed in the same manner as in Example 1 except that the first discharge and the charge-discharge after the second cycle were performed at a current of 0.0615 mA. As a result, the charge capacity in the first cycle was 683 mAh / g, the discharge capacity was 552 mAh / g, and the first charge-discharge efficiency was 81% (= 552 / 683 × 100) (see Table 6). Also, the discharge capacity in the 10th cycle was 607 mAh / g, and the maintenance rate of the discharge capacity in the 10th cycle was 110% (= 607 / 552 × 100) (see Table 6). Furthermore, the discharge capacity in the 50th cycle was 564 mAh / g, and the maintenance rate of the discharge capacity in the 50th cycle was 102% (= 564 / 552 × 100) (see Table 4). Finally, the discharge capacity in the 100th cycle was 438 mAh / g, and the maintenance rate of the discharge capacity in the 100th cycle was 79% (= 438 / 552 × 100) (see Table 6).

Example

[0141] 1. Preparation of Lithium-Ion Secondary Battery Coin Cell (1) Preparation of Composite Particles For a 50 mL glass bottle, a synthesis container was formed using a stirrer made of polytetrafluoroethylene and a hot magnetic stirrer. Then, 1.364 g of 3,3'-diaminodiphenyl sulfone (33DDS) and 6.865 g of NMP were added to the synthesis container and stirred for 30 minutes at room temperature and normal pressure to dissolve. Next, 1.770 g of BTDA was added, the temperature was gradually raised to 60 °C, and stirred at 60 °C for 6 hours to prepare a polyimide precursor composition (organic compound containing nitrogen and sulfur) in which a polymer of 33DDS and BTDA with a solid content of 29.4 mass% was dissolved in NMP. All the above reactions were carried out under an argon atmosphere.

[0142] The target composite particles were prepared using the same method as shown in Example 13, except that this polyimide precursor was used. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.77 mass% nitrogen (see Table 5). Furthermore, analysis using the same analyzer confirmed the presence of 0.12 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 5). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 73 mass% carbon (see Table 5). XPS analysis of these composite particles revealed the area of ​​the peak indicating carbon around a binding energy of 285 eV (C). A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.05 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.9 (see Table 5). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.2 (see Table 5). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 9.8 μm.

[0143] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0144] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.0375 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.075 mA. As a result, the charge capacity in the first cycle was 1163 mAh / g, the discharge capacity was 783 mAh / g, and the initial charge-discharge efficiency was 67% (=783 / 1163 × 100) (see Table 6). Furthermore, the discharge capacity in the 10th cycle was 788 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 101% (=788 / 783 × 100) (see Table 6). In addition, the discharge capacity in the 50th cycle was 737 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 94% (=737 / 783 × 100) (see Table 6). Finally, the discharge capacity at cycle 100 was 631 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 81% (= 631 / 783 × 100) (see Table 6). [Examples]

[0145] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 7, except that a polyimide precursor composition (organic compound containing nitrogen) prepared using the same method as shown in Example 1, silicon powder (particle size 0.1 μm, obtained from Chem-Impex International) as the first core particle, and flake graphite (particle size 7 μm, CNP7 from Ito Graphite Industry Co., Ltd.) as the second core particle were mixed in a solid content mass ratio of 20:20:60. When these composite particles were analyzed using an oxygen-nitrogen-hydrogen analyzer, it was confirmed that they contained 0.81 mass% nitrogen (see Table 5). Furthermore, the analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.28 mass% hydrogen, confirming that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles had progressed sufficiently (see Table 5). In addition, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 73 mass% carbon (see Table 5). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.02 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.2 (see Table 5). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.4 (see Table 5). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 7.7 μm.

[0146] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0147] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge in the charge-discharge cycle test was performed with a current of 0.0375 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.075 mA. As a result, the charge capacity in the first cycle was 1188 mAh / g, the discharge capacity was 792 mAh / g, and the initial charge-discharge efficiency was 67% (=792 / 1188 × 100) (see Table 6). Furthermore, the discharge capacity in the 10th cycle was 807 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 102% (=807 / 792 × 100) (see Table 6). In addition, the discharge capacity in the 50th cycle was 764 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 96% (=764 / 792 × 100) (see Table 6). Finally, the discharge capacity at cycle 100 was 657 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 83% (= 657 / 792 × 100) (see Table 6). [Examples]

[0148] 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 7, except that a polyimide precursor composition (organic compound containing nitrogen) prepared using the same method as shown in Example 1, silicon powder (particle size 5 μm, obtained from Elkem) as the first core particle, and spheroidal graphite (particle size 8 μm, SG-BH8 from Ito Graphite Industry Co., Ltd.) as the second core particle were mixed in a solid content mass ratio of 20:8:72. When these composite particles were analyzed using an oxygen-nitrogen-hydrogen analyzer, it was confirmed that they contained 0.78 mass% nitrogen (see Table 5). Furthermore, the analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.26 mass% hydrogen, confirming that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles had progressed sufficiently (see Table 5). In addition, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 84 mass% carbon (see Table 5). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.02 (see Table 5). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 1.5 (see Table 5). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.6 (see Table 5). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 12.6 μm.

[0149] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0150] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.025 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.05 mA. As a result, the charge capacity in the first cycle was 804 mAh / g, the discharge capacity was 533 mAh / g, and the initial charge-discharge efficiency was 66% (=533 / 804 × 100) (see Table 6). Furthermore, the discharge capacity in the 10th cycle was 524 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 98% (=524 / 533 × 100) (see Table 6). In addition, the discharge capacity in the 50th cycle was 482 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 91% (=482 / 533 × 100) (see Table 6). Finally, the discharge capacity at cycle 100 was 335 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 63% (= 335 / 533 × 100) (see Table 6).

[0151] (Comparative Example 1) 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that the heat treatment conditions for the pulverized material involved raising the temperature from room temperature to 1100°C over 2 hours under an argon atmosphere, holding at 1100°C for 1 hour, and then cooling to obtain the calcined product. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.07 mass% nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.09 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 5.9 mass% carbon (see Table 1). Additionally, XPS analysis of these composite particles revealed the area of ​​the peak indicating carbon around a binding energy of 285 eV (C). A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.02 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) and strength (N) of 400.8 eV I1 The peak intensity of ) was small, with an intensity of 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 ) could not be determined. Furthermore, the area of ​​the peak indicating silicon around 100 eV of bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.8 (see Table 1). Furthermore, analysis of these composite particles by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were attributed to lithium metasilicate, and a peak at 2θ = 28° that was attributed to silicon. In addition, measurements using a particle size analyzer showed that the D50 of these composite particles was 5.9 μm.

[0152] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared in the same manner as in Example 1 using the composite particles prepared in (1) above, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0153] 2. Charge-discharge cycle test of lithium-ion secondary battery coin cell A charge-discharge cycle test was carried out in the same manner as in Example 1 using the lithium-ion secondary battery coin cell prepared in “1. (2)” above. As a result, the charge capacity in the first cycle was 900 mAh / g, the discharge capacity was 753 mAh / g, and the initial charge-discharge efficiency was 84% (= 753 / 900 × 100) (see Table 3). Also, the discharge capacity in the 10th cycle was 614 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 82% (= 614 / 753 × 100) (see Table 3). Furthermore, the discharge capacity in the 50th cycle was 255 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 34% (= 255 / 753 × 100) (see Table 3). Finally, the discharge capacity in the 100th cycle was 185 mAh / g, and the retention rate of the discharge capacity in the 100th cycle was 25% (= 185 / 753 × 100) (see Table 3).

[0154] (Comparative Example 2) 1. Fabrication of lithium-ion secondary battery coin cell (1) Preparation of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that the heat treatment conditions for the pulverized material involved raising the temperature from room temperature to 350°C over 1 hour under an argon atmosphere, holding at 350°C for 1 hour, and then cooling to obtain the calcined product. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.07 mass% nitrogen (see Table 1). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.2 mass% hydrogen, indicating that the carbonization of the polyimide precursor composition (nitrogen-containing organic compound) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 6.3 mass% carbon (see Table 1). Additionally, XPS analysis of these composite particles revealed a peak area (C) indicating carbon around a bond energy of 285 eV. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.05 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The value was 5.0 (see Table 1). Furthermore, the area of ​​the peak indicating silicon around 100 eV of the bond energy (Si A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.4 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 5.4 μm.

[0155] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0156] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 989 mAh / g, the discharge capacity was 841 mAh / g, and the initial charge-discharge efficiency was 85% (=841 / 989 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 765 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 91% (=765 / 841 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 606 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 72% (=606 / 841 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 245 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 29% (= 245 / 841 × 100) (see Table 3).

[0157] (Comparative Example 3) 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as in Example 1, except that the core particles used in Example 1 were heated from room temperature to 1000°C over 2 hours in an argon atmosphere, held at 1000°C for 1 hour, and then cooled to obtain a calcined product, without using a polyimide precursor composition (organic compound containing nitrogen). Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.00 mass% nitrogen (see Table 1). Analysis using the same oxygen-nitrogen-hydrogen analyzer also confirmed the presence of 0.06 mass% hydrogen (see Table 1). Furthermore, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 3.8 mass% carbon (see Table 1). XPS analysis of these composite particles did not reveal a peak indicating nitrogen around a bond energy of 400 eV. Furthermore, the area of ​​the peak indicating silicon around a bond energy of 100 eV (Si) was not observed. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.06 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 6.2 μm.

[0158] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0159] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 1238 mAh / g, the discharge capacity was 496 mAh / g, and the initial charge-discharge efficiency was 40% (=496 / 1238 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 416 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 84% ​​(=416 / 496 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 248 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 50% (=248 / 496 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 159 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 32% (= 159 / 496 × 100) (see Table 3).

[0160] (Comparative Example 4) 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as in Example 3, except that silicon monoxide with a particle size of 5.0 μm, manufactured by Osaka Titanium Technologies Co., Ltd., was used as the core particle in Example 3 without using a polyimide precursor composition (organic compound containing nitrogen). The first calcined product was obtained by heating the silicon monoxide from room temperature to 600°C in 2 hours under an argon atmosphere, holding it at 600°C for 1 hour, and then cooling it. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.01% by mass nitrogen (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 1.0% by mass carbon (see Table 1). Furthermore, XPS analysis of these composite particles did not reveal a peak indicating nitrogen around a bond energy of 400 eV. Additionally, the area of ​​the peak indicating silicon around a bond energy of 100 eV (Si) was not observed. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si AThe ratio was 0.02 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 6.2 μm.

[0161] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0162] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 619 mAh / g, the discharge capacity was 356 mAh / g, and the initial charge-discharge efficiency was 58% (=356 / 619 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 292 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 82% (=292 / 356 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 133 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 37% (=133 / 356 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 129 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 36% (= 129 / 356 × 100) (see Table 3).

[0163] (Comparative Example 5) 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 1, except that carboxymethylcellulose (CMC) (a nitrogen-free organic compound) was used instead of the polyimide precursor composition (a nitrogen-containing organic compound). Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed the presence of 0.00 mass% nitrogen (see Table 1). Furthermore, analysis using the same analyzer confirmed the presence of 0.07 mass% hydrogen, indicating that the carbonization of the carboxymethylcellulose (nitrogen-free organic compound) in the composite particles was sufficiently advanced (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed the presence of 4.3 mass% carbon (see Table 1). XPS analysis of these composite particles did not reveal a peak indicating nitrogen around a bond energy of 400 eV. Furthermore, the area of ​​the peak indicating silicon around a bond energy of 100 eV (Si) was not observed. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / Si A The ratio was 0.04 (see Table 1). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that were due to lithium metasilicate, and a peak at 2θ = 28° that was due to silicon. In addition, measurements using a particle size analyzer showed that the D50 of this composite particle was 5.1 μm.

[0164] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0165] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells A charge-discharge cycle test was performed using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 1391 mAh / g, the discharge capacity was 1118 mAh / g, and the initial charge-discharge efficiency was 80% (=1118 / 1391 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 914 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 82% (=914 / 1118 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 661 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 59% (=661 / 1118 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 520 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 47% (= 520 / 1118 × 100) (see Table 3).

[0166] (Comparative Example 6) 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles In Example 1, 5 g of core particles and 3.33 g of polyvinylpyrrolidone (K-30) (a nitrogen-containing organic compound) were mixed in a ball mill. The mixture was heated from room temperature to 250°C in air over 2 hours, then held at 250°C for 2 hours (heat treatment in an oxidizing atmosphere), and then cooled to obtain the first calcined product. Next, the first calcined product was heated from room temperature to 1000°C in an argon stream over 2 hours, held at 1000°C for 3 hours, and then cooled to obtain the second calcined product. This second calcined product was then ball-milled using 10 mm diameter zirconia balls and sieved through a 50 μm mesh to produce composite particles. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed that they contained 0.39 mass% nitrogen (see Table 1). Analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 15.0 mass% carbon (see Table 1). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / CA The value was 0.02 (see Table 1). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 0.38 (see Table 1). Furthermore, analysis of these composite particles by powder X-ray diffraction revealed peaks at approximately 2θ = 18.5° and 26.5° that are attributed to lithium metasilicate, and a peak at 2θ = 28° that is attributed to silicon.

[0167] (2) Fabrication of lithium-ion battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0168] 2. Charge-discharge cycle testing of lithium-ion battery coin cells A charge-discharge cycle test was performed using the lithium-ion battery coin cell prepared in "1.(2)" above, in the same manner as in Example 1. As a result, the charge capacity in the first cycle was 724 mAh / g, the discharge capacity was 582 mAh / g, and the initial charge-discharge efficiency was 80% (=582 / 724 × 100) (see Table 3). Furthermore, the discharge capacity in the 10th cycle was 652 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 112% (=652 / 582 × 100) (see Table 3). In addition, the discharge capacity in the 50th cycle was 357 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 61% (=357 / 582 × 100) (see Table 3). Finally, the discharge capacity at cycle 100 was 288 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 49% (= 288 / 582 × 100) (see Table 3).

[0169] (Comparative Example 7) 1. Fabrication of lithium-ion secondary battery coin cells Instead of composite particles, a slurry was prepared using silicon powder with a particle size of 0.1 μm obtained from Chem-Impex International, in the same manner as in Example 7. A negative electrode was then prepared using this slurry in the same manner as in Example 7. A lithium-ion secondary battery coin cell was then prepared using this negative electrode in the same manner as in Example 7. Analysis of this silicon using an oxygen-nitrogen-hydrogen analyzer confirmed that it contained 0.5 mass% nitrogen (see Table 2). Analysis using the same oxygen-nitrogen-hydrogen analyzer also confirmed that it contained 0.15 mass% hydrogen (see Table 2). Furthermore, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that it contained 0.17 mass% carbon (see Table 2). XPS analysis of this silicon did not reveal a peak indicating nitrogen around the bond energy of 400 eV. Powder X-ray diffraction analysis of this silicon (Si) revealed a peak originating from silicon at 2θ=28°.

[0170] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1." above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.175 mA per 1 mg of silicon powder, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.35 mA. As a result, the charge capacity in the first cycle was 2780 mAh / g, the discharge capacity was 1851 mAh / g, and the initial charge-discharge efficiency was 67% (=1851 / 2780 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 1038 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 56% (=1038 / 1851 × 100) (see Table 4). In addition, the discharge capacity in the 50th cycle was 599 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 32% (=599 / 1851 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 310 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 17% (=310 / 1851 × 100) (see Table 4).

[0171] (Comparative Example 8) 1. Fabrication of lithium-ion secondary battery coin cells (1) Fabrication of composite particles The target composite particles were prepared using the same method as shown in Example 8, except that a polyimide precursor composition and core particles were mixed in a solid content mass ratio of 50:50, NMP was added as a solvent and stirred to obtain a homogeneous slurry, and the heat treatment conditions for the pulverized material were raised from room temperature to 350°C over 1 hour under an argon atmosphere, held at 350°C for 1 hour, and then cooled to obtain a calcined product. Analysis of these composite particles using an oxygen-nitrogen-hydrogen analyzer confirmed that they contained 2.8% by mass of nitrogen (see Table 2). Furthermore, analysis using the same oxygen-nitrogen-hydrogen analyzer confirmed that they contained 1.4% by mass of hydrogen, indicating that the carbonization of the polyimide precursor composition (organic compound containing nitrogen) in the composite particles had not progressed sufficiently (see Table 2). In addition, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that they contained 32.9% by mass of carbon (see Table 2). Furthermore, when this composite particle was analyzed by XPS, the area of ​​the peak indicating carbon around a binding energy of 285 eV (C) was found. A The area of ​​the peak showing nitrogen around 400 eV relative to (N A ) ratio (N A / C A The value was 0.2 (see Table 2). Also, the intensity was 398.5 eV (N I2 ) with an intensity of 400.8 eV (N I1 ) Strength ratio (N I1 / N I2 The ratio was 6.3 (see Table 2). Furthermore, analysis of this composite particle by powder X-ray diffraction revealed a peak originating from silicon at 2θ=28°. In addition, particle size distribution analysis showed that the D50 of this composite particle was 15.0 μm.

[0172] (2) Fabrication of lithium-ion secondary battery coin cells A slurry was prepared using the composite particles prepared in (1) above in the same manner as in Example 1, and a negative electrode was prepared using this slurry in the same manner as in Example 1. Then, a lithium-ion secondary battery coin cell was prepared using this negative electrode in the same manner as in Example 1.

[0173] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1.(2)" above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge in the charge-discharge cycle test was performed with a current of 0.0875 mA per 1 mg of composite particles, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.175 mA. As a result, the charge capacity in the first cycle was 2308 mAh / g, the discharge capacity was 1130 mAh / g, and the initial charge-discharge efficiency was 49% (=1130 / 2308 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 936 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 83% (=936 / 1130 × 100) (see Table 4). In addition, the discharge capacity in the 50th cycle was 879 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 78% (=879 / 1130 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 224 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 20% (= 224 / 1130 × 100) (see Table 4).

[0174] (Comparative Example 9) 1. Fabrication of lithium-ion secondary battery coin cells A slurry was prepared in the same manner as in Example 8, except that the silicon sludge used in Example 8 was heated from room temperature to 600°C over 2 hours under an argon atmosphere, held at 600°C for 1 hour, and then cooled, without using a polyimide precursor composition (organic compound containing nitrogen). An anode was then prepared using this slurry in the same manner as in Example 8. A lithium-ion secondary battery coin cell was then prepared using this anode in the same manner as in Example 8. Analysis of the silicon sludge after firing using an oxygen-nitrogen-hydrogen analyzer confirmed that it contained 0.40 mass% nitrogen (see Table 2). Analysis using the same oxygen-nitrogen-hydrogen analyzer also confirmed that it contained 0.3 mass% hydrogen (see Table 2). Furthermore, analysis using a carbon-sulfur simultaneous quantitative analyzer confirmed that it contained 0.12 mass% carbon (see Table 2). XPS analysis of this silicon sludge did not reveal any peaks indicating nitrogen around a binding energy of 400 eV. Furthermore, when this silicon (Si) was analyzed by powder X-ray diffraction, a peak originating from silicon at 2θ = 28° was confirmed.

[0175] 2. Charge-discharge cycle testing of lithium-ion secondary battery coin cells Using the lithium-ion secondary battery coin cell prepared in "1." above, the charge-discharge cycle test was performed in the same manner as in Example 1, except that the initial charge was performed with a current of 0.125 mA per 1 mg of silicon sludge, and the initial discharge and subsequent charge-discharge cycles were performed with a current of 0.25 mA. As a result, the charge capacity in the first cycle was 2476 mAh / g, the discharge capacity was 1510 mAh / g, and the initial charge-discharge efficiency was 61% (=1510 / 2476 × 100) (see Table 4). Furthermore, the discharge capacity in the 10th cycle was 1326 mAh / g, and the retention rate of the discharge capacity in the 10th cycle was 88% (=1326 / 1510 × 100) (see Table 4). In addition, the discharge capacity in the 50th cycle was 1127 mAh / g, and the retention rate of the discharge capacity in the 50th cycle was 75% (=1127 / 1510 × 100) (see Table 4). Finally, the discharge capacity at cycle 100 was 753 mAh / g, and the retention rate of the discharge capacity at cycle 100 was 50% (= 753 / 1510 × 100) (see Table 4).

[0176] [Table 1]

[0177] [Table 2]

[0178] [Table 3]

[0179] [Table 4]

[0180] [Table 5]

[0181] [Table 6]

[0182] (summary) As is clear from Table 3, the "retention rate of discharge capacity at the 50th cycle" in Examples 1 to 6 was higher than that in Comparative Examples 1 to 6. Furthermore, the "retention rate of discharge capacity at the 100th cycle" in Examples 1 to 3 and 5 and 6 was also higher than that in Comparative Examples 1 to 6. Therefore, it has become clear that the lithium-ion secondary battery coin cell using the composite particles according to the present invention can suppress the decline in the cycle characteristics of the lithium-ion secondary battery coin cell, particularly the "retention rate of discharge capacity at the 50th cycle" and the "retention rate of discharge capacity at the 100th cycle."

[0183] Furthermore, as is clear from Table 4, the "retention rate of discharge capacity at the 50th cycle" in Examples 8 to 10 was higher than that in Comparative Examples 7 to 9. Similarly, the "retention rate of discharge capacity at the 100th cycle" in Examples 7 to 10 was also higher than that in Comparative Examples 7 to 9. Therefore, it is suggested that the lithium-ion secondary battery coin cell using the composite particles according to the present invention can suppress the decline in the cycle characteristics of the lithium-ion secondary battery coin cell, particularly the "retention rate of discharge capacity at the 50th cycle" and the "retention rate of discharge capacity at the 100th cycle." [Industrial applicability]

[0184] When the composite particles according to the present invention are used as active material particles for the negative electrode of a lithium-ion secondary battery, the deterioration of the cycle characteristics of the lithium-ion secondary battery can be suppressed.

Claims

1. A silicon-containing core, A coating portion that mainly consists of carbon and contains nitrogen, and covers at least a part of the core portion. Equipped with, In the photoelectron spectrum obtained by X-ray electron spectroscopy, the signal intensity N at 398.5 eV Ｉ２ " for "Signal strength N at 400.8 eV" Ｉ１ The ratio of " (N Ｉ１ / N Ｉ２ ) is within the range of 0.5 or more and 4 or less. composite particles.

2. The nitrogen mentioned above accounts for a mass within the range of 0.03% to 2.8% by mass of the total amount. The composite particle according to claim 1.

3. The carbon in question accounts for a mass within the range of 3% to 85% of the total amount. The composite particle according to claim 1.

4. In the aforementioned photoelectron spectrum, the signal intensity C of the peak originating from carbon, which is located between 282 eV and 288 eV, is Ａ "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" Ａ The ratio of " (N Ａ / C Ａ ) is within the range of 0.019 or more and 0.5 or less. The composite particle according to claim 1.

5. In the photoelectron spectrum, the signal intensity Si of the peak derived from silicon existing between 89 eV and 109 eV Ａ with respect to the signal intensity N of the peak derived from nitrogen existing between 397 eV and 404 eV Ａ The ratio (N Ａ / Si Ａ ) is within the range of 0.15 or more and 0.7 or less The composite particle according to claim 1.

6. A composite particle according to any one of claims 1 to 5, Binding agent and A solvent that disperses the composite particles and dissolves the binder A slurry containing [a specific ingredient].

7. Composite particles as described in any one of claims 1 to 5 Negative electrode for lithium-ion secondary batteries.

8. The core further contains oxygen and lithium. The composite particle according to claim 1.

9. The aforementioned core is lithium metasilicate (Li ２ SiO ３ ) contains The composite particle according to claim 8.

10. The aforementioned core consists solely of silicon. The composite particle according to claim 1.

11. The aforementioned core comprises a first core containing silicon and a second core containing carbon. The composite particle according to claim 1.

12. The nitrogen mentioned above accounts for a mass within the range of 0.03% by mass or more and 0.2% by mass or less of the total amount. The composite particle according to claim 8.

13. The carbon in question accounts for a mass within the range of 3% to 6% by mass of the total amount. The composite particle according to claim 8.

14. In the aforementioned photoelectron spectrum, the signal intensity C of the peak originating from carbon, which is located between 282 eV and 288 eV, is Ａ "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" Ａ The ratio of " (N Ａ / C Ａ ) is within the range of 0.04 or more and 0.5 or less. The composite particle according to claim 8.

15. In the aforementioned photoelectron spectrum, the signal intensity of the peak originating from silicon, located between 89 eV and 109 eV, is Si Ａ "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" Ａ The ratio of " (N Ａ / Si Ａ ) is within the range of 0.15 or more and 0.5 or less. The composite particle according to claim 8.

16. The nitrogen mentioned above accounts for a mass within the range of 1.5% by mass or more and 2.8% by mass or less of the total amount. The composite particle according to claim 10.

17. The carbon in question accounts for a mass within the range of 38% to 45% of the total amount. The composite particle according to claim 10.

18. In the aforementioned photoelectron spectrum, the signal intensity C of the peak originating from carbon, which is located between 282 eV and 288 eV, is Ａ "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" Ａ The ratio of " (N Ａ / C Ａ ) is within the range of 0.085 or more and 0.16 or less. The composite particle according to claim 10.

19. The nitrogen mentioned above accounts for a mass within the range of 0.75% by mass or more and 0.9% by mass or less of the total amount. The composite particle according to claim 11.

20. The carbon in question accounts for a mass within the range of 60% to 85% of the total amount. The composite particle according to claim 11.

21. In the aforementioned photoelectron spectrum, the signal intensity C of the peak originating from carbon, which is located between 282 eV and 288 eV, is Ａ "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" Ａ The ratio of " (N Ａ / C Ａ ) is within the range of 0.019 or more and 0.05 or less. The composite particle according to claim 11.

22. In the aforementioned photoelectron spectrum, the signal intensity of the peak originating from silicon, located between 89 eV and 109 eV, is Si Ａ "The signal intensity of the peak originating from nitrogen that is present between 397 eV and 404 eV" Ａ The ratio of " (N Ａ / Si Ａ ) is within the range of 0.19 or more and 0.7 or less. The composite particle according to claim 11.

23. The composite particles according to claim 8, 10, or 11, Binding agent and A solvent that disperses the composite particles and dissolves the binder A slurry containing [a specific ingredient].

24. Composite particles as described in claim 8, 10, or 11 are the main component Negative electrode for lithium-ion secondary batteries.

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