Silicon oxide powder

Abstract

The present invention addresses the problem of providing a silicon oxide powder that can be used as a negative electrode active material, for lithium ion secondary batteries, which is effective in improving the retention rate of discharge capacity through charge-discharge cycles (cycle characteristics). The silicon oxide powder (which includes metal-element-containing silicon oxide) according to the present invention is a silicon oxide powder expressed as SiOx (0.5<x<1.5), and when the volume-based median diameter of the silicon oxide powder is measured using a laser diffraction particle size measurement device, the median diameter is in the range of 1 μm to 30 μm, and when a dispersion of the silicon oxide powder is passed through a filter having a pore size of 1 μm and the volume-based median diameter of the silicon oxide powder in the dispersion is measured thereafter using a dynamic light-scattering particle size measurement device, the median diameter is in the range of 150 nm to 750 nm.

Description

[Technical Field]

[0001] This invention relates to silicon dioxide powder, particularly silicon dioxide powder (including silicon dioxide containing metal elements) used as a negative electrode active material for lithium-ion secondary batteries. [Background technology]

[0002] In recent years, with growing interest in lithium-ion secondary batteries, the development of high-energy-density lithium-ion batteries has accelerated. While various high-capacity materials have been developed and put into practical use as cathode materials, carbon materials, including graphite, are still commonly used as anode materials. However, with the recent increase in cathode capacity, increasing the anode capacity has become increasingly important. Silicon oxide (SiO₂) is being considered as a high-capacity anode forming material. x Expectations for silicon dioxide are rising. However, silicon dioxide has a problem in that its capacity decreases significantly with charge-discharge cycles due to reasons such as a large irreversible capacity due to the formation of an excessive film at the interface with the electrolyte and large volume changes during charge and discharge. In order to solve this problem, various proposals have been made in the past to improve the retention rate of discharge capacity during charge-discharge cycles (hereinafter sometimes referred to as "cycle characteristics") (see, for example, Japanese Patent Publication No. 2011-60610 and Japanese Patent Publication No. 2021-52014). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2011-60610 [Patent Document 2] Japanese Patent Publication No. 2021-52014 [Overview of the project] [Problems that the invention aims to solve]

[0004] Today, the market scale of lithium-ion secondary batteries is on an expanding trend, and their applications are diverse. In such circumstances, further improving the cycle characteristics of lithium-ion secondary batteries becomes extremely important.

[0005] An object of the present invention is to provide a powder of silicon oxide that can be used as a negative electrode active material for a lithium-ion secondary battery, which is effective in improving the retention rate of discharge capacity (cycle characteristics) by charge-discharge cycles.

Means for Solving the Problems

[0006] The powder of silicon oxide (including silicon oxide containing a metal element) according to the present invention is represented by SiO x (0.5 < x < 1.5). And the volume-based median diameter of this powder of silicon oxide measured by a laser diffraction particle size distribution measuring device is within the range of 1 μm or more and 30 μm or less. And when the volume-based median diameter of the powder of silicon oxide in the dispersion liquid of the powder of silicon oxide according to the present invention is measured by a dynamic light scattering particle size distribution measuring device after passing through a filter with a pore diameter of 1 μm, the median diameter is within the range of 150 nm or more and 750 nm or less.

[0007] As a result of the intensive studies by the present inventors, when a powder of silicon oxide satisfying the above conditions is used as a negative electrode active material for a lithium-ion secondary battery, the capacity retention rate of the coin cell produced by the negative electrode active material after 50 cycles is improved. This is because the powder of silicon oxide (main particles) with a volume-based median diameter within the range of 1 μm or more and 30 μm or less and the powder of silicon oxide (fine particles) with a volume-based median diameter within the range of 150 nm or more and 750 nm or less are mixed, so that the fine particles adhere to the surface of the main particles and the fine particles enter the gaps between the main particles, thereby suppressing a decrease in Coulomb efficiency due to the reaction between the fine particles with a large surface area and the electrolyte, the formation of an excessive film at the interface between the main particle surface and the electrolyte, and the breakage of the conduction path due to the expansion and contraction of Si during charge and discharge.

[0008] In addition, in the above-described silicon oxide powder, it is preferable that a metal element is doped. In such a case, the metal element is preferably at least one metal element of Li and Mg. This is because when the silicon oxide powder is used as a negative electrode active material, a remarkable decrease in the initial discharge capacity of a lithium ion secondary battery produced by the negative electrode active material can be suppressed.

[0009] Furthermore, in the above-described silicon oxide powder, it is preferable that at least a part of the surface is covered with a conductive carbon film. In such a case, the mass ratio of carbon in the conductive carbon film to the mass of the silicon oxide powder is preferably within the range of 0.5 mass% or more and 20 mass% or less. This is because when the silicon oxide powder is used as a negative electrode active material, it is possible to impart good conductivity to the silicon oxide powder while maintaining the charge-discharge capacity well, and to suppress side reactions of the silicon oxide powder.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic diagram of a manufacturing apparatus for a powdery silicon oxide powder according to an embodiment of the present invention.

Explanation of Signs

[0011] 5 Vacuum chamber 6 Raw material chamber 7 Precipitation chamber 8 Raw material container 9 Mixed granulation raw material 10 Heat source 11 Precipitation substrate 12 Silicon oxide

Embodiments for Carrying Out the Invention

[0012] The silicon oxide powder according to an embodiment of the present invention is represented by SiO x (0.5 < x < 1.5).

[0013] Furthermore, the silicon dioxide powder according to the embodiment of the present invention has a volume-based median diameter (hereinafter referred to as "D50") measured by a laser diffraction particle size distribution analyzer. S It is sometimes referred to as ". The particle size is preferably in the range of 1.0 μm to 30 μm, more preferably in the range of 1.0 μm to 20 μm, and even more preferably in the range of 1.5 μm to 10 μm. When this silicon dioxide powder is used as a negative electrode active material, it is possible to suppress not only the decrease in the Coulomb rate but also the decrease in the cycle characteristics of the negative electrode by suppressing pulverization.

[0014] Furthermore, in the embodiment of the present invention, when the median diameter of the silicon oxide powder in the dispersion of the silicon oxide powder is measured using a dynamic light scattering particle size distribution analyzer after passing the dispersion of the silicon oxide powder through a filter with a pore size of 1 μm, the median diameter (hereinafter referred to as "D50") is D It is sometimes referred to as ". The wavelength is preferably in the range of 150 nm to 750 nm, more preferably in the range of 200 nm to 750 nm, and even more preferably in the range of 350 nm to 750 nm.

[0015] The above D50 D This can be adjusted by methods such as adjusting the amount of grinding aid in the dry grinding process or performing sedimentation classification during drainage in the liquid phase doping process. To adjust the amount of grinding aid, in the case of a batch-type grinding apparatus, a certain proportion of the grinding aid is added to the material to be ground along with the material to be ground. In the case of a continuous grinding apparatus, the material to be ground is continuously fed in, and the grinding aid is added dropwise to maintain a constant weight ratio using a quantitative liquid delivery pump or the like. In such cases, water, alcohols, alkoxides, etc., are preferably used as grinding aids, and these grinding aids can be appropriately selected according to the grinding method and grinding apparatus. Furthermore, as a method of preparation by sedimentation classification during drainage, the silicon dioxide powder after grinding is uniformly dispersed in a suitable solvent, allowed to stand for a certain period of time to settle and classify the powder, and then the solvent is removed. This allows the desired D50 to be obtained. DParticles having the following can be obtained. The sedimentation time and classification point in sedimentation classification during liquid drainage can be calculated by the following Formula 1 and Formula 2.

[0016]

Formula

[0017]

Formula

[0018] In the above Formula 1 and Formula 2, ·u: Terminal velocity [m / s] ·ρ p : Particle density [kg / m 3 ·ρ f : Fluid density [kg / m 3 ·d: Particle diameter [m] ·η: Viscosity of fluid [Pa·s] ·l: Distance [m] ·t: Time [s] taken to fall through l (distance [m]) is meant.

[0019] Also, in the silicon oxide powder according to the embodiment of the present invention, it is preferable that a metal element is doped. In such a case, the metal element is preferably at least one metal element of Li and Mg. As the Li source when performing Li doping, lithium hydride (LiH), lithium oxide (Li2O), lithium hydroxide (LiOH), lithium carbonate (Li2CO¬3), etc. are used. As the Mg source when performing Mg doping, magnesium hydride (MgH2), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), magnesium carbonate (MgCO3), etc. are used.

[0020] ​Furthermore, it is preferable that the silicon dioxide powder according to the embodiment of the present invention has at least a portion of its surface covered with a conductive carbon coating (hereinafter sometimes referred to as "C-coat"). In such cases, the mass ratio of carbon in the conductive carbon coating to the mass of the silicon dioxide powder (hereinafter sometimes referred to as "carbon coating amount" or "C-coat amount") is preferably in the range of 0.5% by mass or more and 20% by mass or less, more preferably in the range of 0.5% by mass or more and 10% by mass or less, and even more preferably in the range of 0.5% by mass or more and 5% by mass or less. If the carbon coating amount is less than 0.5% by mass, the effect of imparting conductivity is poor and sufficient charge-discharge characteristics cannot be obtained. On the other hand, if the carbon coating amount exceeds 20% by mass, the SiO2 content in the entire powder is x A decrease in volume due to the reduced weight of the powder is a concern. Methods for forming a conductive carbon film on at least a portion of the surface of silicon dioxide powder include, but are not limited to, the CVD method.

[0021] Furthermore, forming a conductive carbon film on at least a portion of the surface of the silicon dioxide powder described above can be appropriately carried out for silicon dioxide before doping with Li and Mg, silicon dioxide after Li doping, silicon dioxide after Mg doping, or silicon dioxide after Li and Mg doping.

[0022] Furthermore, the silicon dioxide powder mentioned above has a BET specific surface area of ​​1 m². 2 / g or more 6m 2 It is preferable that the range be less than or equal to / g, and 1.5m 2 / g or more 5m 2 It is more preferable that the range be less than or equal to / g, and 1.5m 2 / g or more 4m 2 It is even more preferable that the range be within / g or less, and 1.5m 2 / g or more 3m 2It is particularly preferable that the amount be within the range of / g or less. This is because when this silicon dioxide powder is used as the negative electrode active material, it is possible to suppress the decrease in Coulomb efficiency while maintaining good output characteristics. The BET specific surface area can be measured using, for example, the Mascorb HM-1201 manufactured by Mountec Co., Ltd. In this measurement, nitrogen is used as the adsorbate, helium is used as the carrier gas, and liquid nitrogen is used as the cooling medium.

[0023] (Regarding the manufacturing method of silicon dioxide) The silicon dioxide according to the embodiment of the present invention is produced using a silicon dioxide production apparatus as shown in Figure 1. This apparatus consists of a vacuum chamber 5, a raw material chamber 6 located inside the vacuum chamber 5, and a deposition chamber 7 located above the raw material chamber 6.

[0024] The raw material chamber 6 is cylindrical in shape, and a cylindrical raw material container 8 and a heating source 10 surrounding the raw material container 8 are placed in its center. For example, an electric heater can be used as the heating source 10.

[0025] The deposition chamber 7 is composed of a cylindrical body positioned so as to align with the axis of the raw material container 8. A deposition substrate 11 made of stainless steel is provided on the inner circumferential surface of the deposition chamber 7 for depositing gaseous silicon oxide generated by sublimation in the raw material chamber 6.

[0026] A vacuum device (not shown) for discharging atmospheric gas is connected to the vacuum chamber 5, which houses the raw material chamber 6 and the deposition chamber 7, and the gas is discharged in the direction of arrow A.

[0027] When producing silicon oxide using the manufacturing apparatus shown in Figure 1, a mixed granulated raw material 9 is used, which consists of silicon powder and silicon dioxide powder, which are blended, mixed, granulated, and dried. This mixed granulated raw material 9 is filled into a raw material container 8 and heated in an inert gas atmosphere such as argon gas or in a vacuum to generate SiO (sublimation). In this case, heating is preferably carried out in the range of 1000°C to 1600°C, and more preferably in the range of 1200°C to 1400°C. The gaseous SiO gas generated by sublimation rises from the raw material chamber 6 and enters the deposition chamber 7, where it is deposited onto the surrounding deposition substrate 11 and precipitates as silicon oxide 12. Subsequently, the silicon oxide 12 precipitated from the deposition substrate 11 is removed to obtain the desired silicon oxide.

[0028] Examples and comparative examples are shown below to illustrate the present invention in more detail, but the present invention is not limited to these examples. [Examples]

[0029] 1. Manufacturing of silicon dioxide powder The target silicon dioxide powder was produced by sequentially carrying out the following steps.

[0030] (1) Preparation process for silicon dioxide powder Following the method described above, bulk silicon oxide was obtained using the manufacturing apparatus shown in Figure 1. Specifically, silicon (Si) powder and silicon dioxide (SiO2) powder were mixed as raw materials to create a mixed granulation material with a molar ratio of Si:O = 1:1. This mixed granulation material was then filled into a raw material container and heated at 1400°C under an argon atmosphere to sublimate the SiO. The gaseous SiO gas generated by sublimation was deposited onto the surrounding deposition substrate to precipitate silicon oxide. Subsequently, bulk silicon oxide was obtained by removing the silicon oxide.

[0031] (2) Grinding process The above-mentioned lump of silicon dioxide was pulverized in air using a bead mill until the median diameter was approximately 5 μm to obtain the desired silicon dioxide powder. At this time, 0.5% by weight of ethanol was added to the bead mill as a pulverizing aid relative to the silicon dioxide.

[0032] (3) Measurement of the median diameter of silicon dioxide powder using a laser diffraction particle size distribution analyzer. Median diameter D50 of silicon dioxide powder obtained in the above-described grinding process S When measured using a laser diffraction particle size distribution analyzer (Malvern Mastersizer3000), the D50 S The particle size was 7.5 μm (see Table 2). The measurement conditions were as follows:

[0033] • Dispersion medium: Isopropyl alcohol (2-propanol) Particle refractive index: 3.500 • Particle absorption rate: 1.000 • Refractive index of dispersion medium: 1.390

[0034] (4) Measurement of the median diameter of silicon dioxide powder using a dynamic light scattering particle size distribution analyzer. 10 g of the silicon dioxide powder after the grinding process described above was added to 100 mL of isopropyl alcohol (2-propanol), and dispersed for 10 minutes using an ultrasonic cleaner (Honda Electronics Co., Ltd. W-113MkII) to obtain a dispersion. The dispersion was then filtered using a 1 μm pore size filter, and the filtered dispersion was used as the sample solution for measurement. Using this sample solution, the median diameter D50 of the silicon dioxide powder in the sample solution was measured using a dynamic light scattering particle size distribution analyzer (NanoTrack particle size distribution analyzer UPA-EX150, Nikkiso Co., Ltd.). D When measured, the D50 D The wavelength was 351 nm (see Table 2). The measurement conditions were as follows:

[0035] • Measurement time: 180 seconds ·Particle permeability: Transmission ·Particle shape: non-spherical • Particle refractive index: 1.47 ·Particle density: 1.00 • Dispersion medium: Isopropyl alcohol (2-propanol) • Refractive index of dispersion medium: 1.38

[0036] 2. Cycle characteristics of a battery equipped with a negative electrode made of lithium-containing silicon oxide powder. (1) Battery production (1-1) Negative electrode fabrication As described above, the silicon dioxide powder and natural graphite (median diameter 12 μm) were mixed in a mass ratio of 10:90 to prepare the negative electrode active material. Next, the negative electrode active material, sodium polyacrylate (binder), and Denka Black (registered trademark) (acetylene black as a conductive additive) were added to Awatori Rentaro (registered trademark) (ARE-310, manufactured by Thinky Co., Ltd.) in a mass ratio of 92:3:5, and then mixed to prepare a slurry. Subsequently, the slurry was coated onto a 10 μm thick copper foil, and the coating was pre-dried in air at 80°C. Then, the slurry-coated copper foil was punched out into a disc shape with a diameter of 11 mm. Finally, the disc-shaped slurry-coated copper foil was dried in a vacuum at 150°C for 12 hours to obtain the desired negative electrode.

[0037] (1-2) Battery construction A coin cell was fabricated using the above-mentioned negative electrode, Li foil as the counter electrode, separator, and electrolyte. A 20 μm thick porous polyethylene film was used as the separator, and a solution of lithium hexafluoride phosphate (LiPF6) at a concentration of 1 mol / L was used as the electrolyte, which was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 volume ratio.

[0038] (2) Cycle characteristics Using a secondary battery charge / discharge test device manufactured by Electrofield Co., Ltd., the above coin cell was subjected to charge / discharge tests, and the capacity retention rate after 50 cycles (the capacity retention rate after 50 cycles is calculated by dividing the discharge capacity at the 50th cycle by the discharge capacity at the first cycle and multiplying by 100) was determined to be 79.2% (see Table 2). In this charge / discharge test, during the first charge / discharge, charging was performed with a constant current of 0.2C until the voltage between the two electrodes of the battery reached 0.01V, and then with constant potential charging until the current reached 0.01C (CC-CV 0.2C, 0.01V-0.01C) (see Table 1). Also, during the first charge / discharge, discharging was performed with a constant current of 0.2C until the voltage between the two electrodes of the battery reached 1.5V (CC 0.2C, 1.5V cut-off) (see Table 1). Furthermore, during the second and subsequent charge-discharge cycles, charging was performed with a constant current of 1.0C until the voltage between the battery electrodes reached 0.01V, and then with constant potential charging until the current reached 0.01C (CC-CV 1.0C, 0.01V-0.01C) (see Table 1). Also, during the second and subsequent charge-discharge cycles, discharging was performed with a constant current of 1.0C until the voltage between the battery electrodes reached 1.5V (CC 1.0C, 1.5V cut-off) (see Table 1). Here, the current at 1C was calculated using the theoretical capacity calculated assuming a discharge capacity of 360mAh / g for natural graphite and 1900mAh / g for silicon dioxide powder.

[0039] [Table 1]

[0040] (Comparative Example 1) Except for changing the amount of grinding aid added to 1.0% by weight of ethanol relative to the silicon dioxide put into the bead mill, the target silicon dioxide powder was obtained according to the method of Example 1, and the D50 of the same silicon dioxide powder was obtained by the same method as in Example 1. S and D50 D When measured, D50 S It is 7.3 μm, D50 D The wavelength was 131 nm. Also described in Example 1. of A negative electrode was manufactured from the silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 77.2% (see Table 2).

[0041] (Comparative Example 2) Except for not adding a grinding aid, the target silicon dioxide powder was obtained according to the method described in Example 1, and the D50 of the same silicon dioxide powder was obtained by the same method as in Example 1. S and D50 D When measured, D50 S It is 7.7 μm, D50 D The wavelength was 802 nm. Also described in Example 1. of A negative electrode was manufactured from the silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 77.1% (see Table 2).

[0042] [Table 2] [Examples]

[0043] Bulk silicon dioxide was produced using the same method as in Example 1, and silicon dioxide powder was produced by grinding the bulk silicon dioxide using a bead mill without adding any grinding aids. Subsequently, after the following liquid-phase lithium doping step, fine powder was removed by sedimentation classification to obtain lithium-containing silicon dioxide powder. The liquid-phase lithium doping step and the sedimentation classification step are described in detail below.

[0044] (Liquid-phase lithium doping process) A mixed solution was prepared by dissolving naphthalene in tetrahydrofuran (hereinafter referred to as "THF") solvent at a concentration of 0.2 mol / L, and then adding 6.0% by mass of lithium pieces to this solution. Subsequently, the silicon dioxide powder obtained above was immersed in this mixed solution at atmospheric pressure and a temperature of 20°C for 20 hours.

[0045] (Sedimentation classification process) The silicon dioxide powder immersion solution obtained above was stirred to uniformly disperse the silicon dioxide powder in the solution, thereby obtaining a dispersion. The dispersion was then transferred to a graduated cylinder to a level of 10 cm and allowed to stand for 191.3 hours to allow the dispersed silicon dioxide powder to settle. Afterward, the supernatant was removed, and the settled silicon dioxide powder was recovered.

[0046] (Heat treatment process) The obtained silicon dioxide compound particles were heat-treated at 600°C for 24 hours under an argon atmosphere to obtain lithium-containing silicon dioxide powder.

[0047] The lithium-containing silicon dioxide powder obtained as described above was processed according to the method described in Example 1, and D50 S and D50 D When measured, D50 S It is 7.7 μm, D50 D The wavelength was 198 nm. Furthermore, a negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method described in Example 1. Subsequently, a coin cell was fabricated using the negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 82.4% (see Table 3). [Examples]

[0048] Except for changing the settling time in the sedimentation classification process to 93.7 hours, lithium-containing silicon oxide powder was obtained according to the method of Example 2, and the D50 of the same lithium-containing silicon oxide powder was obtained by the same method as in Example 2. S and D50 D When measured, D50 S It is 7.7 μm, D50 D The wavelength was 429 nm. Also described in Example 2. ofA negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 2, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 82.5% (see Table 3). [Examples]

[0049] Except for changing the settling time in the sedimentation classification process to 23.4 hours, lithium-containing silicon oxide powder was obtained according to the method of Example 2, and the D50 of the same lithium-containing silicon oxide powder was obtained by the same method as in Example 2. S and D50 D When measured, D50 S It is 7.9 μm, D50 D The wavelength was 750 nm. Also described in Example 2. of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 2, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 82.6% (see Table 3).

[0050] (Comparative Example 3) Except for changing the settling time in the sedimentation classification process to 240 hours, lithium-containing silicon oxide powder was obtained according to the method of Example 2, and the D50 of the same lithium-containing silicon oxide powder was obtained by the same method as in Example 2. S and D50 D When measured, D50 S It is 7.6 μm, D50 D The wavelength was 121 nm. Also described in Example 2. of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 2, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 81.1% (see Table 3).

[0051] (Comparative Example 4) Except for omitting the sedimentation classification step, the target lithium-containing silicon oxide powder was obtained according to the method described in Example 2, and the D50 of the lithium-containing silicon oxide powder obtained by the same method as in Example 2 S and D50 D When measured, D50 S It is 7.9 μm, D50 D The wavelength was 883 nm. Also described in Example 2. of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 2, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 80.9% (see Table 3).

[0052] [Table 3] [Examples]

[0053] In the "Process for Preparing Lithium-Containing Silicon Oxide Powder" described above, lithium-containing silicon oxide powder was obtained by the same method as in Example 2, except that 10.0% by mass of lithium pieces was added to a solution of naphthalene dissolved in THF solvent at a concentration of 0.2 mol / L. Furthermore, D50 of the same lithium-containing silicon oxide powder was obtained by the same method as in Example 2. S and D50 D When measured, D50 S It is 7.7 μm, D50 D The wavelength was 158 nm. Furthermore, as described in Example 2... of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 2, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 81.5% (see Table 4). [Examples]

[0054] Except for changing the settling time in the sedimentation classification process to 93.7 hours, lithium-containing silicon oxide powder was obtained according to the method of Example 5, and the D50 of the lithium-containing silicon oxide powder obtained by the same method as in Example 5 S and D50 D When measured, D50 S It is 7.7 μm, D50 D The wavelength was 521 nm. Also described in Example 5. of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 5, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 81.6% (see Table 4). [Examples]

[0055] Except for changing the settling time in the sedimentation classification process to 23.4 hours, lithium-containing silicon oxide powder was obtained according to the method of Example 5, and the D50 of the lithium-containing silicon oxide powder obtained by the same method as in Example 5 S and D50 D When measured, D50 S It is 7.8 μm, D50 D The wavelength was 735 nm. Also described in Example 5. of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 5, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 81.9% (see Table 4).

[0056] (Comparative Example 5) Except for changing the settling time in the sedimentation classification process to 240 hours, lithium-containing silicon oxide powder was obtained according to the method of Example 5, and the D50 of the lithium-containing silicon oxide powder obtained by the same method as in Example 5 S and D50 D When measured, D50 S It is 7.5 μm, D50 D The wavelength was 124 nm. Also described in Example 5. ofA negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 5, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 80.3% (see Table 4).

[0057] (Comparative Example 6) Except for omitting the sedimentation classification step, lithium-containing silicon oxide powder was obtained according to the method of Example 5, and the D50 of the lithium-containing silicon oxide powder obtained by the same method as in Example 5 was obtained. S and D50 D When measured, D50 S is 8.0 μm, D50 D The wavelength was 901 nm. Also described in Example 5. of A negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 5, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 79.9% (see Table 4).

[0058] [Table 4] [Examples]

[0059] A carbon-coated (hereinafter sometimes referred to as "C-coated") silicon oxide powder was obtained by the same method as in Example 1, except that a "conductive carbon coating process" was added after the "1.(2) grinding process" described in Example 1. The "conductive carbon coating process" will be described in detail below.

[0060] (Conductive carbon coating process) The silicon dioxide powder obtained by the "1.(2) Grinding Process" described in Example 1 was placed in a rotary kiln and heated to 700°C under an argon atmosphere. Subsequently, propane gas was injected into the rotary kiln as a carbon source, and the surface of the silicon dioxide powder was coated with a carbon film to obtain C-coated silicon dioxide powder. The mass ratio of carbon in the conductive carbon film to the mass of the C-coated silicon dioxide powder was measured by oxygen-flow combustion-infrared absorption spectroscopy. A Leco CS-400 carbon concentration analyzer was used for this measurement. As a result, the mass ratio of carbon in the conductive carbon film to the mass of the C-coated silicon dioxide powder ("carbon coating amount" or "C-coat amount") was 3.0% by mass.

[0061] The D50 of the C-coated silicon dioxide powder obtained above was obtained by the same method as in Example 1. S and D50 D When measured, D50 S It is 6.6 μm, D50 D The wavelength was 275 nm. Furthermore, a negative electrode was manufactured from the lithium-containing silicon oxide powder according to the method described in Example 1. Subsequently, a coin cell was fabricated using the negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 81.0% (see Table 5).

[0062] (Comparative Example 7) Except for changing the amount of grinding aid added to 1.0% by weight of ethanol relative to the silicon dioxide put into the bead mill, C-coated silicon dioxide powder was obtained in the same manner as in Example 8, and the D50 of the C-coated silicon dioxide powder was obtained according to the method of Example 8. S and D50 D When measured, D50 S 6.4 μm, D50 D The wavelength was 102 nm. Also described in Example 8. ofA negative electrode was manufactured from the C-coated silicon dioxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 8, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 79.6% (see Table 5).

[0063] [Table 5] [Examples]

[0064] Following the "conductive carbon coating process" described in Example 8, a powder of C-coated silicon oxide was obtained. The amount of C-coating was measured in the same manner as in Example 8 and was found to be 3.0% by mass. Subsequently, following the "manufacturing process for lithium-containing silicon oxide powder" described in Example 2, lithium was doped into the C-coated silicon oxide powder to obtain a powder of C-coated lithium-containing silicon oxide.

[0065] According to the method described in Example 1, the D50 of the C-coated lithium-containing silicon oxide powder S and D50 D When measured, D50 S It is 6.8 μm, D50 D The wavelength was 164 nm. Also described in Example 2. of A negative electrode was manufactured from the C-coated lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 2, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 85.8% (see Table 6). [Examples]

[0066] Except for changing the standing time in the sedimentation classification process to 93.7 hours, a powder of C-coated lithium-containing silicon oxide was obtained according to the method described in Example 9, and the amount of C-coating was measured in the same manner as in Example 9, and it was 3.0% by mass. Furthermore, the D50 of the same C-coated silicon oxide powder was obtained according to the method described in Example 9. S and D50 DWhen measured, D50 S was 6.8 μm, and D50 D was 374 nm. Also, according to the method described in Example 9, a negative electrode was manufactured from the powder of the same C-coated silicon oxide. Then, a coin cell was fabricated in the same manner as in Example 9 using the obtained negative electrode, and the capacity retention rate after 50 cycles was measured using the coin cell. As a result, the capacity retention rate was 85.9% (see Table 6). of

Example

Example

[0067] A powder of C-coated lithium-containing silicon oxide was obtained according to the method described in Example 9, except that the standing time in the sedimentation classification step was changed to 23.4 hours. When the C-coating amount was measured in the same manner as in Example 9, it was 3.0% by mass. Also, according to the method described in Example 9, D50 S and D50 D of the powder of silicon oxide after the C-coating were measured. As a result, D50 S was 6.9 μm, and D50 D was 720 nm. Also, according to the method described in Example 9, a negative electrode was manufactured from the powder of the same C-coated lithium-containing silicon oxide. Then, a coin cell was fabricated in the same manner as in Example 9 using the obtained negative electrode, and the capacity retention rate after 50 cycles was measured using the coin cell. As a result, the capacity retention rate was 86.1% (see Table 6). of

[0068] (Comparative Example 8)(Comparative Example 8) A powder of C-coated lithium-containing silicon oxide was obtained according to the method described in Example 9, except that the standing time in the sedimentation classification step was changed to 240 hours. When the C-coating amount was measured in the same manner as in Example 9, it was 3.0% by mass. Also, according to the method described in Example 9, D50 S and D50 D of the powder of the same C-coated lithium-containing silicon oxide were measured. As a result, D50 S was 6.9 μm, and D50 D was 796 nm. Also, according to the method described in Example 9, ofA negative electrode was produced from the powder of the C-coated lithium-containing silicon oxide according to the method. Then, a coin cell was fabricated in the same manner as in Example 9 using the negative electrode, and the capacity retention rate after 50 cycles was measured using the coin cell. As a result, the capacity retention rate was 84.3% (see Table 6).

[0069] (Comparative Example 9) A powder of C-coated lithium-containing silicon oxide was obtained according to the method described in Example 9 except that the sedimentation classification step was omitted, and the C-coating amount was measured in the same manner as in Example 9. As a result, it was 3.0% by mass. Also, according to the method described in Example 9, the D50 S and D50 D of the powder of the C-coated lithium-containing silicon oxide were measured. As a result, D50 S was 6.8 μm and D50 D was 144 nm. Also, as described in Example 9 of A negative electrode was produced from the powder of the C-coated lithium-containing silicon oxide according to the method. Then, a coin cell was fabricated in the same manner as in Example 9 using the negative electrode, and the capacity retention rate after 50 cycles was measured using the coin cell. As a result, the capacity retention rate was 83.9% (see Table 6).

[0070]

Table 6

Examples

[0071] According to the "conductive carbon film coating step" described in Example 8, a powder of C-coated silicon oxide was obtained. Also, when the C-coating amount was measured in the same manner as in Example 8, it was 3.0% by mass. Then, according to the "manufacturing step of lithium-containing silicon oxide powder" described in Example 5, the powder of the C-coated silicon oxide was doped with lithium. Then, the powder of the lithium-doped C-coated silicon oxide was sedimentation classified and heat-treated according to the method described in Example 5 to obtain a powder of C-coated lithium-containing silicon oxide.

[0072] According to the method described in Example 1, the D50 of the powder of the C-coated lithium-containing silicon oxideS and D50 D When measured, D50 S It is 6.7 μm, D50 D The wavelength was 150 nm. Furthermore, a negative electrode was manufactured from the C-coated lithium-containing silicon oxide powder according to the method described in Example 1. Subsequently, a coin cell was fabricated using the negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 84.8% (see Table 7). [Examples]

[0073] Except for changing the standing time in the sedimentation classification process to 93.7 hours, a powder of C-coated lithium-containing silicon oxide was obtained according to the method of Example 12, and the amount of C-coating was measured in the same manner as in Example 12, and it was 3.0% by mass. Furthermore, the D50 of the same C-coated lithium-containing silicon oxide powder was obtained according to the method of Example 12. S and D50 D When measured, D50 S It is 6.8 μm, D50 D The wavelength was 374 nm. Also described in Example 12. of A negative electrode was manufactured from the C-coated lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 12, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 84.6% (see Table 7). [Examples]

[0074] Except for changing the standing time in the sedimentation classification process to 23.4 hours, a powder of C-coated lithium-containing silicon oxide was obtained according to the method of Example 12, and the amount of C-coating was measured in the same manner as in Example 12, and it was 3.0% by mass. Furthermore, the D50 of the same C-coated lithium-containing silicon oxide powder was obtained according to the method of Example 1. S and D50 D When measured, D50 S It is 6.9 μm, D50 DThe wavelength was 736 nm. Furthermore, a negative electrode was manufactured from the C-coated lithium-containing silicon oxide powder according to the method described in Example 1. Subsequently, a coin cell was fabricated using the negative electrode in the same manner as in Example 12, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 84.7% (see Table 7).

[0075] (Comparative Example 10) Except for changing the standing time in the sedimentation classification process to 240 hours, a powder of C-coated lithium-containing silicon oxide was obtained according to the method of Example 12, and the amount of C-coating was measured in the same manner as in Example 12, and it was 3.0% by mass. Furthermore, according to the method of Example 12, the D50 of the same C-coated lithium-containing silicon oxide powder was obtained. S and D50 D When measured, D50 S It is 6.6 μm, D50 D The wavelength was 112 nm. Also described in Example 12. of A negative electrode was manufactured from the C-coated lithium-containing silicon oxide powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 12, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 82.5% (see Table 7).

[0076] (Comparative Example 11) Except for omitting the sedimentation classification step, a powder of C-coated lithium-containing silicon oxide was obtained according to the method described in Example 12, and the amount of C-coating was measured in the same manner as in Example 12, and it was 3.0% by mass. Furthermore, the D50 of the same C-coated lithium-containing silicon oxide powder was obtained according to the method described in Example 1. S and D50 D When measured, D50 S It is 6.9 μm, D50 D The wavelength was 770 nm. Furthermore, a negative electrode was manufactured from the C-coated lithium-containing silicon oxide powder according to the method described in Example 1. Subsequently, a coin cell was fabricated using the negative electrode in the same manner as in Example 12, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 82.3% (see Table 7).

[0077] [Table 7] [Examples]

[0078] Mg2SiO4 was prepared according to the following "Mg2SiO4 preparation process".

[0079] (Mg2SiO4 fabrication process) Si powder, MgO powder, and SiO2 powder were mixed in a molar ratio of 7:4:3 (Si:Mg:O = 1:0.4:1). This mixed powder was heated to 1350°C at 1 Pa under an argon gas atmosphere, and the generated gas was cooled to 400°C on a deposition plate placed above it to precipitate and recover.

[0080] When the resulting powder was subjected to XRD measurements using CuKα radiation, crystal peaks for Si, MgSiO3, and Mg2SiO4 were confirmed, but crystal peaks for MgO, amorphous and crystalline peaks for SiO2, and crystalline peaks for metallic Mg and MgSi alloys could not be confirmed.

[0081] Similar to Example 1, 0.5% by weight of ethanol was added to the silicon dioxide fed into the bead mill as a grinding aid, and the Mg2SiO4 obtained as described above was ground to obtain Mg2SiO4 powder. Then, using the same Mg2SiO4 powder, C-coated Mg2SiO4 powder was obtained according to the "conductive carbon coating process" described in Example 8, and the amount of C-coating was measured in the same manner as in Example 8, and the amount of C-coating was found to be 3.0% by mass. Furthermore, the D50 of the same C-coated Mg2SiO4 powder was measured in the same manner as in Example 1. S and D50 D When measured, D50 S It is 5.2 μm, D50 D The wavelength was 374 nm. Also described in Example 1. ofA negative electrode was manufactured from the C-coated Mg2SiO4 powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 82.1% (see Table 8).

[0082] (Comparative Example 12) Except for changing the amount of grinding aid added to 1.0% by weight of ethanol relative to the silicon dioxide put into the bead mill, C-coated Mg2SiO4 powder was obtained according to the method of Example 15, and the amount of C-coating was measured in the same way as in Example 15, and the amount of C-coating was 3.0% by mass. Furthermore, according to the method of Example 15, the D50 of the same C-coated Mg2SiO4 powder was obtained. S and D50 D When measured, D50 S It is 5.1 μm, D50 D The wavelength was 112 nm. Also described in Example 15. of A negative electrode was manufactured from the C-coated Mg2SiO4 powder according to the method. Subsequently, a coin cell was prepared using the negative electrode in the same manner as in Example 15, and the capacity retention rate after 50 cycles was measured using the coin cell, which was found to be 80.3% (see Table 8).

[0083] [Table 8] [Examples]

[0084] The following "Li x Mg y SiO z According to the "Manufacturing Process", Li x Mg y SiO z We manufactured it. Note that Li x Mg y SiO z SiO is used to form the negative electrode of lithium secondary batteries that are doped with both Li and Mg. x The system is a powder in which x, y, and z are positive real numbers and satisfy the following conditions. 0.5 ≤ z ≤ 1.5 ·z / 5≦x+y≦z z / 100 ≤ x and z / 100 ≤ y

[0085] (Li x Mg y SiO z Manufacturing process) A mixed powder was obtained by mixing Si powder, SiO2 powder, Li source LiO2 powder, and Mg source MgO powder in a molar ratio of 13:7:2:4. This mixed powder was calcined at 1 Pa and 1400°C to sublimate and generate gas. The gas generated from the sublimation was deposited onto a quartz substrate, and the deposited material was recovered to obtain a lithium-magnesium-containing silicon oxide compound. Subsequently, as a grinding aid, 0.5 wt% ethanol was added to the silicon oxide fed into the bead mill, and the lithium-magnesium-containing silicon oxide compound was ground in the same manner as in Example 1 to obtain a ground powder. Here, the ground powder was analyzed for the elements Si, O, and Li. The content of Si and Li was determined by ICP emission spectroscopy (PS3520VDD II, Hitachi High-Tech Corporation). The content of O was measured by inert gas fusion infrared absorption method (GFA) using a Leco TC-436. As a result, the composition of the deposited material is Li x Mg y SiO z It was found that (x=0.2, y=0.2, z=1).

[0086] The pulverized powder obtained as described above is subjected to carbon coating (C-coat) at 850°C by thermal CVD using a mixed gas of argon and propane as the carbon source, and C-coat Li x Mg y SiO z (x=0.2, y=0.2, z=1) powder was obtained. The same C-coated Li x Mg y SiO zWhen the amount of C-coating was measured for the powder (x=0.2, y=0.2, z=1) using the same method as in Example 8, the amount of C-coating was found to be 3.0% by mass.

[0087] Next, using the same method as in Example 1, the C-coated Li obtained above was processed. x Mg y SiO z (x=0.2, y=0.2, z=1) Powder D50 S and D50 D When measured, D50 S 5.0 μm, D50 D The wavelength was 153 nm. Also described in Example 1. of According to the method, the same C-coated Li x Mg y SiO z A negative electrode was manufactured from powder (x=0.2, y=0.2, z=1). Subsequently, a coin cell was fabricated using this negative electrode in the same manner as in Example 1, and the capacity retention rate after 50 cycles was measured using this coin cell, which was found to be 82.5% (see Table 9).

[0088] (Comparative Example 13) Except for changing the amount of grinding aid added to 1.0% by weight of ethanol relative to the silicon dioxide put into the bead mill, the method for C-coated Li was followed according to the method in Example 16. x Mg y SiO z A powder was obtained with x=0.2, y=0.2, z=1, and the amount of C-coating was measured in the same manner as in Example 16, and the amount of C-coating was found to be 3.0% by mass. Furthermore, according to the method described in Example 16, the same C-coating Li x Mg y SiO z (x=0.2, y=0.2, z=1) Powder D50 S and D50 D When measured, D50 S 5.0 μm, D50 D The wavelength was 135 nm. Also described in Example 16. of According to the method, the same C-coated Li x Mg y SiO zA negative electrode was manufactured from powder (x=0.2, y=0.2, z=1). Subsequently, a coin cell was fabricated using this negative electrode in the same manner as in Example 16, and the capacity retention rate after 50 cycles was measured using this coin cell, which was found to be 80.5% (see Table 9).

[0089] [Table 9]

[0090] (summary) As is clear from Tables 2 to 9 above, the capacity retention rate after 50 cycles of a coin cell using a negative electrode formed from silicon dioxide powder according to the present invention was improved.

Claims

1. SiO ｘ (0.5<x<1.5), wherein when a volume-based median diameter of the silicon oxide powder is measured with a laser diffraction particle size distribution analyzer, the median diameter is in the range of 1 μm or more and 30 μm or less, and when a dispersion of the silicon oxide powder is passed through a filter having a pore size of 1 μm and then the volume-based median diameter of the silicon oxide powder in the dispersion is measured with a dynamic light scattering particle size distribution analyzer, the median diameter is in the range of 150 nm or more and 750 nm or less.

2. The silicon oxide powder according to claim 1, which is doped with a metal element.

3. The silicon oxide powder according to claim 2, wherein the metal element is at least one of Li and Mg.

4. The silicon oxide powder according to claim 1 or 2, at least a portion of the surface of which is covered with a conductive carbon coating.

5. Silicon oxide powder according to claim 4, wherein the mass ratio of carbon in the conductive carbon coating to the mass of the silicon oxide powder is within the range of 0.5 mass % to 20 mass %.

Images