Silicon composite containing metallic element

Abstract

One of the problems addressed by the present invention is to provide a negative electrode active material for a lithium-ion battery whereby initial efficiency is improved while maintaining the rate characteristics of the lithium-ion battery. A silicon composite containing a metallic element according to a first aspect of the present invention comprises a silicon phase and a silicate phase. The silicon phase is formed from silicon (Si). The silicate phase is adjacent to the silicon phase. The silicon composite containing a metallic element has a composition of LixMgySiOz (where x > 0, y > 0, and z > 0). The composition satisfies all of the following conditions: (a) (2.5x + 2y) / z > 1; (b) (1.5x + y) / z < 1; and (c) (x + 2y) / z < 1.

Description

Silicon-based composites containing metal elements

[0001] The present invention relates to a metal element-containing silicon-based composite.

[0002] Silicon-based compounds are used as high-capacity negative electrode active materials in lithium-ion batteries. Examples of silicon-based compounds as negative electrode active materials include silicon oxide (SiO) (see, for example, JP-A-6-325765), lithium-doped silicon oxide (see, for example, JP-A-6-325765), magnesium-doped silicon oxide (see, for example, JP-A-2018-519648), and lithium-magnesium-doped silicon oxide (see, for example, JP-A-2017-204374).

[0003] Japanese Patent Laid-Open No. 6-325765 Japanese Patent Laid-Open No. 2017-204374 Special Publication No. 2018-519648

[0004] However, none of the above-mentioned silicon-based compounds has been able to simultaneously satisfy the initial efficiency and rate characteristics of lithium ion batteries.

[0005] An object of the present invention is to provide a negative electrode active material for a lithium ion battery that improves the initial efficiency while maintaining the rate characteristics of the lithium ion battery.

[0006] A metal element-containing silicon-based composite according to one aspect of the present invention comprises a silicon phase and a silicate phase. The silicon phase is formed from silicon (Si). The silicate phase is adjacent to the silicon phase. The metal element-containing silicon-based composite contains Li ｘ Mg ｙ SiO ｚ It has a composition of (x>0, y>0, z>0), where the composition satisfies the following conditions: (a) (2.5x+2y) / z>1, (b) (1.5x+y) / z<1, and (c) (x+2y) / z<1.

[0007] As a result of extensive research by the present inventors, it has become clear that when the above-mentioned metal element-containing silicon-based composite is used as the negative electrode active material of a lithium ion battery, the initial efficiency of the lithium ion battery is improved while maintaining the rate characteristics of the battery.

[0008] In the metal element-containing silicon-based composite described above, it is preferable that z satisfies 0.5<z<1.5, because when this metal element-containing silicon-based composite is used as the negative electrode active material of a lithium ion battery, it is possible to suppress a decrease in the life characteristics of the lithium ion battery and also to suppress a decrease in the charge / discharge capacity of the lithium ion battery due to an excess silicate phase.

[0009] In the metal element-containing silicon-based composite, it is preferable that x > 0.1 and y > 0.05. If x and y satisfy these conditions, when the metal element-containing silicon-based composite is used as the negative electrode active material of a lithium ion battery, the crystal growth of silicon can be suppressed, thereby suppressing a decrease in the initial efficiency of the lithium ion battery, and good water resistance can be exhibited during electrode assembly.

[0010] In the above-mentioned metal element-containing silicon-based composite, the silicate phase is composed of Li as a crystal. ４ SiO ４ and Li ２ It is preferable that the material does not contain O. This is because these substances react with carbon dioxide and moisture in the atmosphere to produce lithium carbonate and lithium hydroxide, which are chemically unstable, and also have poor water resistance, which may cause problems during the production of lithium-ion batteries.

[0011] It is also preferable that at least a portion of the surface of the metal element-containing silicon-based composite be covered with a conductive carbon coating, because when this metal element-containing silicon-based composite is used as a negative electrode active material, the charge / discharge capacity of the lithium ion battery can be maintained at a good level, good electrical conductivity can be imparted to the metal element-containing silicon-based composite, and side reactions of silicon oxide can be suppressed.

[0012] 1 is a triangular phase diagram of a metal element-containing silicon-based composite according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a manufacturing apparatus for a metal element-containing silicon-based composite according to an embodiment of the present invention.

[0013] REFERENCE SIGNS LIST 100 Vapor deposition apparatus 110 Crucible 120 Heater 130 Vapor deposition drum 141 Scraper 143 Particle guide 150 Chamber 151 Chamber body 152 Recovery section 153 Exhaust pipe 160 Raw material supply hopper 170 Raw material introduction pipe 180 Recovery container 190 Recovery pipe Gg Gas guide OP Opening RM Deposition chamber Sr Molten metal VL1 First valve VL2 Second valve

[0014] The metal element-containing silicon-based composite according to the embodiment of the present invention comprises a silicon phase and a silicate phase. The silicon phase is formed from silicon (Si). The silicate phase is adjacent to the silicon phase. The metal element-containing silicon-based composite contains Li ｘ Mg ｙ SiO ｚ (x>0, y>0, z>0). In the above composition, Li ２ Si ２ O ５ , Li ２ SiO ３ , Mg ２ SiO ４ and Li ２ MgSiO ４ It is presumed that any one of the three phases is in equilibrium. This equilibrium relationship can be expressed as a triangular phase diagram as shown in FIG. 1. That is, the hatched area in FIG. 1 is the equilibrium region. Here, the composition satisfies all of the conditions: (a) (2.5x + 2y) / z > 1, (b) (1.5x + y) / z < 1, and (c) (x + 2y) / z < 1. Here, by satisfying (a), excellent initial efficiency and rate characteristics can be exhibited in a lithium ion battery, and by satisfying (b) and (c), Li ４ SiO ４ and Li ２The formation of chemically unstable phases such as .O can be suppressed. Here, (2.5x + 2y) / z may be greater than 1 and less than 1.75, or greater than 1.1 and less than 1.5. Furthermore, (1.5x + y) / z may be greater than 0.5 and less than 1, or greater than 0.5 and less than 0.9. Furthermore, (x + 2y) / z may be greater than 0.4 and less than 1, greater than 0.5 and less than 0.9, or greater than 0.6 and less than 0.8. The silicate phase may exist in a crystalline state, an amorphous state, or a partially crystalline state (partially amorphous state). Incidentally, the silicate phase does not necessarily coincide with the equilibrium phase in terms of composition. For example, between Li silicate and Mg silicate, Li silicate is more likely to crystallize at low temperatures, so both a Li silicate crystalline phase and a Mg-rich amorphous phase may occur. Furthermore, although the cause is unclear, MgSiO, which is not included in the equilibrium phase, may occur. ３ In particular, when the recovery temperature or heat treatment temperature of the metal element-containing silicon-based composite is low, a part of it may become an amorphous phase, or there may be slight variations in the concentration of the silicate phase, resulting in the formation of MgSiO as a metastable phase. ３ It is presumed that crystals are formed.

[0015] The composition of the silicate phase according to the embodiment of the present invention is m (Li ２ O)・n(MgO)・SiO ２ It can also be expressed as follows. In this composition, it is preferable that all of the following conditions be satisfied: (e) 2m + 0.5n > 1, (f) m < 1, and (g) m + n < 2. Here, 2m + 0.5n may be greater than 1 and less than 1.7, or greater than 1.1 and less than 1.7. Furthermore, m may be greater than 0.45 and less than 1, greater than 0.45 and less than 0.9, or greater than 0.45 and less than 0.8. Furthermore, m + n may be greater than 0.9 and less than 2, greater than 0.9 and less than 1.9, greater than 0.9 and less than 1.7, greater than 0.9 and less than 1.5, or greater than 0.9 and less than 1.3.

[0016] The shape of the metal element-containing silicon-based composite according to the embodiment of the present invention is not limited, and may be powder, granules, blocks, or other shapes. However, when the metal element-containing silicon-based composite is used as a negative electrode active material for a lithium ion battery, it is preferably in powder form.

[0017] Incidentally, when the above-mentioned metal element-containing silicon-based composite is used as the negative electrode active material of a lithium ion battery, it is possible to obtain an initial efficiency higher than that of conventional lithium ion batteries while maintaining the rate characteristics of the lithium ion battery equivalent to those of conventional lithium ion batteries.

[0018] When the metal-element-containing silicon-based composite is used as a negative electrode active material for a lithium-ion battery, it is preferable that z be in the range of 0.5<z<1.5. This is because it is possible to suppress a decrease in the life characteristics of the lithium-ion battery and to suppress a decrease in the charge / discharge capacity of the lithium-ion battery due to an excessive silicate phase. Furthermore, z is preferably in the range of more than 0.6 and less than 1.4, more preferably in the range of more than 0.7 and less than 1.3, even more preferably in the range of more than 0.8 and less than 1.2, and particularly preferably in the range of more than 0.9 and less than 1.1.

[0019] Furthermore, when the metal element-containing silicon-based composite is used as a negative electrode active material for a lithium ion battery, it is preferable that x > 0.1 and y > 0.05. When x and y satisfy these conditions, silicon crystal growth can be suppressed, thereby suppressing a decrease in the initial efficiency of the lithium ion battery, and good water resistance can be exhibited during electrode assembly. Note that x may be greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.8, or greater than 0.9. Furthermore, y may be greater than 0.1, greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, or greater than 0.7.

[0020] Furthermore, when the metal element-containing silicon-based composite is used as the negative electrode active material of a lithium ion battery, it is preferable that m>0.1 and n>0.1. When m and n satisfy these conditions, it is possible to suppress the crystal growth of silicon, thereby suppressing the decrease in the initial efficiency of the lithium ion battery, and also to exhibit good water resistance during electrode assembly. Note that m may be greater than 0.2, may be greater than 0.3, may be greater than 0.4, may be greater than 0.5, may be greater than 0.6, may be greater than 0.7, may be greater than 0.8, or may be greater than 0.9. Furthermore, n may be greater than 0.2, may be greater than 0.3, may be greater than 0.4, may be greater than 0.5, may be greater than 0.6, may be greater than 0.7, may be greater than 0.8, or may be greater than 0.9. Furthermore, when the composition is m(Li ２ O)・n(MgO)・SiO ２ Even when the O / Si ratio is expressed as follows, it is preferable to satisfy the relationship 0.5<O / Si<1.5. This is because it is possible to suppress a decrease in the life characteristics of the lithium ion battery and to suppress a decrease in the charge / discharge capacity of the lithium ion battery due to an excessive silicate phase. Furthermore, the O / Si ratio is preferably in the range of more than 0.6 and less than 1.4, more preferably in the range of more than 0.7 and less than 1.3, even more preferably in the range of more than 0.8 and less than 1.2, and particularly preferably in the range of more than 0.9 and less than 1.1.

[0021] In addition, when the metal element-containing silicon-based composite is used as a negative electrode active material for a lithium ion battery, the silicate phase is a crystalline Li ４ SiO ４ and Li ２ It is preferable that the material does not contain O. This is because these substances react with carbon dioxide and moisture in the atmosphere to produce lithium carbonate and lithium hydroxide, which are chemically unstable, and also have poor water resistance, which may cause problems during the production of lithium-ion batteries.

[0022] Furthermore, when the metal-element-containing silicon-based composite described above is used as a negative electrode active material for a lithium-ion battery, it is preferable to cover at least a portion of the surface of the metal-element-containing silicon-based composite with a conductive carbon coating. This is because it is possible to impart good conductivity to the metal-element-containing silicon-based composite and suppress side reactions of silicon oxide while maintaining good charge / discharge capacity of the lithium-ion battery. To achieve this effect, the mass ratio of carbon in the conductive carbon coating to the mass of the metal-element-containing silicon-based composite is preferably in the range of 0.5% by mass to 20% by mass, more preferably in the range of 0.5% by mass to 10% by mass, and even more preferably in the range of 0.5% by mass to 5% by mass.

[0023] Hereinafter, a method for producing a metal element-containing silicon-based composite according to an embodiment of the present invention will be described in detail.

[0024] Examples of methods for producing a metal element-containing silicon-based composite according to an embodiment of the present invention include (i) a method of doping silicon oxide with lithium and magnesium, (ii) a method of compounding silicon and silicate by mechanical milling, and (iii) a method of mixed vapor deposition of SiO gas, Li gas, and Mg gas (hereinafter sometimes referred to as a "mixed vapor deposition method"). However, it is preferable to adopt the mixed vapor deposition method in terms of productivity of the metal element-containing silicon-based composite and uniformity of the obtained metal element-containing silicon-based composite.

[0025] The raw materials used in producing metal element-containing silicon oxide are silicon and metal silicate. Here, the metal silicate contains lithium (Li) and magnesium (Mg). That is, as the metal silicate, a metal silicate containing both lithium and magnesium may be used alone, or a lithium-containing silicate and a magnesium-containing silicate may be used in combination. Incidentally, as the lithium-containing silicate, for example, lithium disilicate Li ２ Si ２ O ５ Examples of silicates containing magnesium include magnesium silicate MgSiO ３The metal silicate may be a mixture of a metal oxide and silicon oxide. For example, lithium disilicate Li ２ Si ２ O ５ Li ２ O and 2SiO ２ or a mixture of magnesium silicate MgSiO ３ is MgO and SiO ２ and a mixture of these. Furthermore, in order to incorporate metal elements other than lithium and magnesium into the metal-element-containing silicon-based composite, the metal silicate phase of the raw material may contain an oxide having a metal element other than lithium and magnesium. Such metal elements are not particularly limited, but when a mixed vapor deposition method is employed as a method for producing metal-element-containing silicon oxide, examples include alkali metals, alkaline earth metals, zinc, boron, etc., depending on the vapor pressure of the metal elements and oxides. The silicon and metal silicate may be in the form of powder, granules, blocks, or other shapes.

[0026] In addition, from the viewpoint of reducing manufacturing costs, the above-mentioned mixed vapor deposition method is preferably carried out using a vapor deposition apparatus 100 as shown in Fig. 2. Therefore, first, this vapor deposition apparatus 100 will be described, and then the above-mentioned mixed vapor deposition method will be described in detail.

[0027] As shown in FIG. 2, the vapor deposition apparatus 100 is mainly composed of a crucible 110, a heater 120, a vapor deposition drum 130, a scraper 141, a particle guide 143, a chamber 150, a raw material supply hopper 160, a raw material introduction pipe 170, a recovery container 180, a first valve VL1, and a second valve VL2.

[0028] As shown in FIG. 2 , the crucible 110 is a heat-resistant container whose top wall is open at the center, and is installed in the chamber 150. A through-hole (not shown) is formed in one location on the periphery of the top wall of the crucible 110, and a raw material introduction pipe 170 is inserted through this through-hole. That is, raw material in the raw material supply hopper 160 is supplied to the crucible 110 through the raw material introduction pipe 170. A gas guide Gg is disposed above the top wall of the crucible 110. The gas guide Gg is a member that guides the raw material gas generated in the crucible 110 to the evaporation drum 130, and is installed on the upper surface of the top wall so as to surround the central portion of the top wall, as shown in FIG. 2 .

[0029] The heater 120 is for heating the crucible 110 to a high temperature, and is disposed so as to surround the outer periphery of the crucible 110 .

[0030] The evaporation drum 130 is, for example, a cylindrical horizontal drum. As shown in FIG. 2 , it is disposed above the opening OP in the top wall of the crucible 110, with its lower portion surrounded by a gas guide Gg. The evaporation drum 130 is driven to rotate in one direction by a drive mechanism (not shown). The evaporation drum 130 is equipped with a temperature regulator (not shown) for maintaining a constant temperature on its outer circumferential surface. This temperature regulator uses an externally supplied cooling medium to cool the outer circumferential surface temperature of the evaporation drum 130 to a temperature suitable for the evaporation of the evaporation source gas. The outer circumferential surface temperature of the evaporation drum 130 can also affect the crystallinity of the precipitate deposited on the precipitate remaining on the evaporation drum. By controlling the outer circumferential surface temperature of the evaporation drum 130 within an appropriate range, the progression of crystal growth due to the disproportionation reaction can be suppressed. The outer circumferential surface temperature of the evaporation drum 130 is preferably 900°C or less, more preferably 800°C or less, and particularly preferably 700°C or less.

[0031] The scraper 141 is a member that serves to scrape the thin film formed on the deposition drum 130 from the deposition drum 130, and is disposed near the deposition drum 130 as shown in FIG. 2 . The thin film pieces (metal-element-containing silicon-based composite particles) scraped off by the scraper 141 fall into a particle guide 143. The material of the scraper 141 affects impurity contamination of the metal-element-containing silicon-based composite particles. To suppress this effect, the material of the scraper 141 is preferably a high-hardness metal or ceramic, and particularly preferably ceramic. The scraper 141 is preferably not brought into contact with the outer peripheral surface of the deposition drum 130. This is because this prevents impurity contamination that may occur due to direct contact between the deposition drum 130 and the scraper 141 from being mixed into the recovered metal-element-containing silicon-based composite particles.

[0032] The particle guide 143 is, for example, a vibrating conveying member, and as shown in Figure 2, is arranged so that it slopes downward as it moves from the vicinity of the evaporation drum toward the collection section 152 of the chamber 150.It receives thin film fragments scraped off by the scraper 141 arranged above it and sends them to the collection section 152 of the chamber 150.

[0033] As shown in Fig. 2, the chamber 150 is mainly composed of a chamber main body 151, a recovery section 152, and an exhaust pipe 153. As shown in Fig. 2, the chamber main body 151 is a box-shaped section having a deposition chamber RM therein, and accommodates the crucible 110, the heater 120, the evaporation drum 130, the scraper 141, and the particle guide 143. As shown in Fig. 2, the recovery section 152 is a section that protrudes outward from the side wall of the chamber main body 151 and has a space that communicates with the deposition chamber RM of the chamber main body 151. As described above, the tip of the particle guide 143 is located in the recovery section 152.

[0034] The raw material supply hopper 160 is a raw material supply source, and as shown in Fig. 2, its outlet is connected to a raw material introduction pipe 170. That is, the raw material charged into the raw material supply hopper 160 is supplied to the crucible 110 via the raw material introduction pipe 170 at an appropriate timing. The raw material supplied to the crucible 110 becomes molten Sr and then vaporizes to become raw material gas.

[0035] The raw material introduction pipe 170 is a round-hole nozzle for supplying the solid raw material placed in the raw material supply hopper 160 to the crucible 110, and is arranged in the center of the top plate of the crucible 110 with its mouth facing upward.

[0036] The collection container 180 is a container for collecting thin film pieces that have passed through the first valve VL1 and the second valve VL2.

[0037] The first valve VL1 and the second valve VL2 are used to adjust the amount of thin film pieces collected into the collection container 180 by opening and closing them, and are provided on a collection pipe 190 connecting the collection section 152 of the chamber 150 and the collection container 180.

[0038] The raw material (mixed powder or granulated material) is fed from a raw material supply hopper 160 into the crucible 110 via a raw material introduction pipe 170, or the raw material is fed directly into the crucible 110. As described above, the raw material for the metal element-containing silicon-based composite is heated to a temperature in the range of 1200°C or higher and 1400°C or lower to generate raw material gases of SiO gas, Li gas, and Mg gas.

[0039] After the raw materials are loaded into the crucible 110, the pressure in the precipitation chamber RM is reduced while the crucible 110 is heated by the heater 120. If the pressure in the precipitation chamber RM is too high, the reaction that generates SiO gas from the raw materials becomes difficult to occur. Therefore, the pressure in the precipitation chamber RM is preferably 1000 Pa or less, more preferably 750 Pa or less, and particularly preferably 20 Pa or less. The temperature in the precipitation chamber RM also affects the SiO reaction rate. If the temperature is too low, the reaction rate slows, while if the temperature is too high, there are concerns about side reactions due to melting of the raw materials and reduced energy efficiency. Furthermore, there is also a concern that the temperature may damage the crucible 110. From this perspective, the temperature in the precipitation chamber RM is preferably in the range of 1000°C to 1600°C, more preferably 1100°C to 1500°C, and particularly preferably 1100°C to 1400°C.

[0040] By heating the raw material under reduced pressure as described above, raw material gas is generated from the raw material in the crucible 110, and the raw material gas is supplied to the evaporation drum 130 through the gas guide Gg. At this time, the evaporation drum 130 is rotated by a drive source. The temperature of the outer circumferential surface of the evaporation drum 130 is set lower than the temperature in the deposition chamber RM. More specifically, this temperature is set lower than the condensation temperature of the raw material gas. This setting allows the raw material gas generated from the crucible 110 to be evaporated, precipitated, and deposited on the outer circumferential surface of the rotating evaporation drum 130. Here, the evaporation drum 130 is rotated multiple times while the scraper 141 is kept waiting above, forming a laminated film on the evaporation drum 130. Thereafter, when the rotation speed of the evaporation drum 130 reaches a predetermined number, the scraper 141 is moved downward, and the laminated film is scraped off from the evaporation drum 130 by the scraper 141. The scraped off pieces of the laminated film fall along the outer peripheral surface of the deposition drum 130 into the particle guide 143. Finally, the pieces of the laminated film are pulverized to obtain the target metal element-containing silicon-based composite.

[0041] The metal-element-containing silicon-based composite obtained as described above may be heat-treated. Heat-treating the metal-element-containing silicon-based composite under reduced pressure or an inert gas atmosphere can stabilize the crystalline state of the metal-element-containing silicon-based composite. The heat treatment is preferably carried out at 500°C or higher and 900°C or lower. Treatment at 500°C or higher promotes crystallization of the silicate phase contained in the metal-element-containing silicon-based composite, stabilizing the crystal structure and physical properties. Furthermore, setting the heat treatment temperature to 900°C or lower suppresses excessive crystallization of the silicon phase contained in the metal-element-containing silicon-based composite, thereby maintaining good battery characteristics. The heat treatment may be carried out at any time after the fragments of the laminated film are recovered and after the fragments are crushed. In particular, heat treatment without exposure to the atmosphere after the fragments of the laminated film are recovered is desirable because it suppresses oxidation reactions and deterioration during atmospheric storage and crushing of the fragments. Furthermore, a conductive carbon coating can be formed simultaneously with the heat treatment.

[0042] EXAMPLES In the following, examples and comparative examples will be shown to explain the present invention in more detail, but the present invention is not limited to these examples.

[0043] 1. Production of Li-Mg-containing silicon oxide composite powder The target Li-Mg-containing silicon oxide composite powder was produced by carrying out the following steps in order. (1) Raw material powder preparation step: 1 mol of metallic silicon was mixed with 1 mol of lithium oxide (Li ２ O) 0.3 mol, magnesium oxide (MgO) 0.25 mol, silicon dioxide (SiO ２ ) was mixed with lithium oxide, lithium silicate, magnesium silicate, and silicon dioxide to obtain Li ０．４１ Mg ０．１７ A raw material powder having a composition of SiO was obtained.

[0044] (2) Li·Mg-containing silicon oxide composite production process: A Li·Mg-containing silicon oxide composite was produced according to the above-mentioned method for producing a metal element-containing silicon-based composite using a vapor deposition apparatus 100 shown in Figure 1. During production, the heater 120 was controlled so that the heater temperature, i.e., the raw material heating temperature, was 1200°C to 1400°C, and the pressure reducing device was controlled so that the internal pressure of the chamber 150 was 100 Pa or less. The recovered fragments of the laminated film were heat-treated at 600°C to 700°C in an argon atmosphere to stabilize their crystal structure.

[0045] (3) Pulverization Step The Li-Mg-containing silicon oxide composite obtained as described above was pulverized in air using a bead mill until the average particle size D50 reached approximately 9 μm, and then the particle size was adjusted to obtain the desired Li-Mg-containing silicon oxide composite powder. The average particle size D50 was measured using a laser diffraction particle size distribution analyzer (Malvern Mastersizer 3000) and found to be 9.04 μm. The measurement conditions were as follows: Dispersion medium: isopropyl alcohol (2-propanol); Particle refractive index: 3.500; Particle absorption coefficient: 1.000; Dispersion medium refractive index: 1.390

[0046] 2. Composition Analysis The Li-Mg-containing silicon oxide composite powder obtained as described above was analyzed using an inductively coupled plasma atomic emission spectrometer (ICP-AES) to determine the silicon, lithium, and magnesium contents. The oxygen content can be determined using an inert gas fusion oxygen analyzer or the like, but since the Li-Mg-containing silicon oxide composite powder contains almost no elements other than silicon, lithium, magnesium, and oxygen, and almost no impurities were detected even with the ICP atomic emission spectrometer, the oxygen content was determined assuming that all other contained elements were oxygen.

[0047] As a result, the composition of the obtained Li·Mg-containing silicon oxide composite powder was Li ０．４６ Mg ０．１９ SiO １．１１ Therefore, Li ｘ Mg ｙ SiO ｚIn this case, (2.5x+2y) / z=1.39, (1.5x+y) / z=0.80, and (x+2y) / z=0.77.

[0048] In addition, the composition is m (Li ２ O)・n(MgO)・SiO ２ In this case, m was 0.674 and n was 0.569. Therefore, 2m + 0.5n was 1.632, and m + n was 1.243. In addition, the atomic number of oxygen to silicon (O / Si) was 1.11.

[0049] In addition, the Li·Mg-containing silicon oxide composite powder contains Li as a crystal. ４ SiO ４ and Li ２ The absence of O was confirmed by an X-ray diffractometer (XRD). At that time, the measurement was carried out using Cu-Kα rays as characteristic X-rays with a diffraction angle interval of 0.13°.

[0050] 3. Characteristics of a Battery Equipped with a Negative Electrode Composed of a Li-Mg-Containing Silicon Oxide Composite Powder (1) Battery Fabrication (1-1) Negative Electrode Fabrication The Li-Mg-containing silicon oxide composite powder obtained as described above was loaded into a rotary kiln, and carbon coating was performed on the Li-Mg-containing silicon oxide composite powder by thermal CVD in which argon gas and propane gas were passed through at 700°C. The mass ratio of carbon to the mass of the Li-Mg-containing silicon oxide composite powder was 2.31% by mass. This mass ratio was calculated from the carbon content quantitatively evaluated by analyzing carbon dioxide gas using an oxygen stream combustion-infrared absorption method using a carbon concentration analyzer (CS400 manufactured by Leco). Next, the carbon-coated Li-Mg-containing silicon oxide composite powder (hereinafter simply referred to as "carbon-coated powder") and graphite powder were mixed in a mass ratio of 4:1 to prepare the negative electrode active material. Next, in a Thinky Corporation AWATORI MIXER (registered trademark) ARE-310, the negative electrode active material, styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a binder, and carbon nanotubes (CNT) as a conductive additive were added to a solid mass ratio of 89.8: 9: 1: 0.2. The negative electrode active material, an aqueous dispersion of styrene butadiene rubber (SBR), an aqueous dispersion of carboxymethyl cellulose (CMC), and carbon nanotubes (CNT) were then kneaded to prepare an aqueous slurry. Subsequently, the slurry was applied to a 10 μm thick copper foil, and the coating was pre-dried at 80 ° C. in air. The slurry-coated copper foil was then punched into a disk having a diameter of 11 mm. The disk-shaped slurry-coated copper foil was then dried in a vacuum at 150 ° C. for 12 hours to obtain the desired negative electrode.

[0051] (1-2) Battery Fabrication A coin cell was fabricated using the above-mentioned negative electrode, a lithium iron phosphate positive electrode material as a counter electrode, a separator, and an electrolyte. A 20 μm-thick polyethylene porous film was used as the separator, and the electrolyte was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1, to which lithium hexafluorophosphate (LiPF ６ ) was dissolved at a concentration of 1 mol / L.

[0052] (2) Rate Characteristics A charge / discharge test of the coin cell was performed using a secondary battery charge / discharge tester manufactured by Electrofield Co., Ltd. to determine the initial efficiency (%), and the charge / discharge efficiency (%) of each cycle during 10 charge / discharge cycles was determined, and the average value was used as the rate characteristics. During the charge / discharge test, the conditions for the first charge were "CC-CV 0.2C" and "10mV-0.01C," the conditions for the first discharge were "CC 0.2C" and "1.5V cut-off," the conditions for the second and subsequent charge were "CC-CV 1C" and "10mV-0.5C," and the conditions for the second and subsequent discharge were "CC 0.5C" and "1.5V cut-off." Here, the discharge capacity of natural graphite was assumed to be 360 ​​mAh / g, and the discharge capacity of the Li·Mg-containing silicon oxide composite powder was assumed to be 1900 mAh / g, and the theoretical capacity was used to calculate the current at 1 C. The initial efficiency of this coin cell was 86.0%, and the rate characteristic was 99.4%.

[0053] For 1 mol of metallic silicon, lithium oxide (Li ２ O) 0.35 mol, magnesium oxide (MgO) 0.15 mol, silicon dioxide (SiO ２ ) was mixed with lithium oxide, lithium silicate, magnesium silicate, and silicon dioxide to obtain Li ０．４７ Mg ０．１ A Li-containing silicon oxide composite powder was obtained in the same manner as in Example 1, except that a raw material powder having a composition of SiO was obtained, and composition analysis was performed in the same manner as in Example 1. Furthermore, a coin cell was produced in the same manner as in Example 1, and the initial efficiency (%) and rate characteristics (%) of the coil cell were measured. As a result, the composition of the obtained Li-Mg-containing silicon oxide composite powder was Li. ０．５４ Mg ０．１１ SiO １．０８ Therefore, Li ｘ Mg ｙ SiO ｚ In this case, (2.5x+2y) / z=1.45, (1.5x+y) / z=0.85, and (x+2y) / z=0.71.

[0054] In addition, the composition is m (Li ２ O)・n(MgO)・SiO ２ In this case, m was 0.786 and n was 0.324. Therefore, 2m + 0.5n was 1.698, and m + n was 1.092. In addition, the atomic number of oxygen to silicon (O / Si) was 1.08.

[0055] In addition, the Li·Mg-containing silicon oxide composite powder contains Li as a crystal. ４ SiO ４ and Li ２ The absence of O was confirmed by X-ray diffraction (XRD). The initial efficiency of this coin cell was 85.6%, and the rate characteristic was 99.5%.

[0056] For 1 mol of metallic silicon, lithium oxide (Li ２ O) 0.25 mol, magnesium oxide (MgO) 0.25 mol, silicon dioxide (SiO ２ ) was mixed with lithium oxide, lithium silicate, magnesium silicate, and silicon dioxide to obtain Li ０．３３ Mg ０．１７ A Li-containing silicon oxide composite powder was obtained in the same manner as in Example 1, except that a raw material powder having a composition of SiO was obtained, and composition analysis was performed in the same manner as in Example 1. Furthermore, a coin cell was produced in the same manner as in Example 1, and the initial efficiency (%) and rate characteristics (%) of the coil cell were measured. As a result, the composition of the obtained Li-Mg-containing silicon oxide composite powder was Li. ０．３６ Mg ０．１８ SiO １．１５ Therefore, Li ｘ Mg ｙ SiO ｚ In this case, (2.5x+2y) / z=1.11, (1.5x+y) / z=0.63, and (x+2y) / z=0.63.

[0057] In addition, the composition is m (Li ２ O)・n(MgO)・SiO ２In this case, m was 0.463 and n was 0.464. Therefore, 2m + 0.5n was 1.158, and m + n was 0.927. In addition, the atomic number of oxygen to silicon (O / Si) was 1.15.

[0058] In addition, the Li·Mg-containing silicon oxide composite powder contains Li as a crystal. ４ SiO ４ and Li ２ The absence of O was confirmed by X-ray diffraction (XRD). The initial efficiency of this coin cell was 86.1%, and the rate characteristic was 99.5%.

[0059] (Comparative Example 1) A lithium oxide (Li ２ O) 0.33 mol, silicon dioxide (SiO ２ ) was 0.67 mol by mixing lithium oxide, lithium silicate, and silicon dioxide (i.e., magnesium silicate was not added) to obtain Li ０．４ A Li-containing silicon oxide composite powder was obtained in the same manner as in Example 1, except that a raw material powder having a composition of SiO was obtained, and composition analysis was performed in the same manner as in Example 1. Furthermore, a coin cell was produced in the same manner as in Example 1, and the initial efficiency (%) and rate characteristics (%) of the coil cell were measured. As a result, the composition of the obtained Li-Mg-containing silicon oxide composite powder was Li. ０．４０ SiO ０．９３ Therefore, Li ｘ Mg ｙ SiO ｚ When (y=0), (2.5x+2y) / z=1.07, (1.5x+y) / z=0.64, and (x+2y) / z=0.43.

[0060] In addition, the composition is m (Li ２ O)・n(MgO)・SiO ２ In this case, m was 0.548 and n was 0.000. Therefore, 2m + 0.5n was 1.096, and m + n was 0.548. In addition, the atomic number of oxygen to silicon (O / Si) was 0.93.

[0061] In addition, the Li·Mg-containing silicon oxide composite powder contains Li as a crystal. ４ SiO ４ and Li ２ The absence of O was confirmed by X-ray diffraction (XRD). The initial efficiency of this coin cell was 82.8%, and the rate characteristic was 99.1%.

[0062] (Comparative Example 2) A lithium oxide (Li ２ O) is 0.2125 mol, magnesium oxide (MgO) is 0.2125 mol, silicon dioxide (SiO ２ ) was mixed with lithium oxide, lithium silicate, magnesium silicate, and silicon dioxide to obtain Li ０．２７ Mg ０．１３ A Li-containing silicon oxide composite powder was obtained in the same manner as in Example 1, except that a raw material powder having a composition of SiO was obtained, and composition analysis was performed in the same manner as in Example 1. Furthermore, a coin cell was produced in the same manner as in Example 1, and the initial efficiency (%) and rate characteristics (%) of the coil cell were measured. As a result, the composition of the obtained Li-Mg-containing silicon oxide composite powder was Li. ０．３１ Mg ０．１６ SiO １．２９ Therefore, Li ｘ Mg ｙ SiO ｚ In this case, (2.5x+2y) / z=0.85, (1.5x+y) / z=0.49, and (x+2y) / z=0.49.

[0063] In addition, the composition is m (Li ２ O)・n(MgO)・SiO ２ In this case, m was 0.322 and n was 0.324. Therefore, 2m + 0.5n was 0.806, and m + n was 0.646. In addition, the atomic number of oxygen to silicon (O / Si) was 1.29.

[0064] In addition, the Li·Mg-containing silicon oxide composite powder contains Li as a crystal. ４ SiO ４ and Li２ The absence of O was confirmed by an X-ray diffraction (XRD) device. The initial efficiency of this coin cell was 84.7%, and the rate characteristic was 99.4%.

[0065] The results shown in Examples 1 to 3 and Comparative Examples 1 and 2 are summarized in Tables 1 to 3 below.

[0066] As is clear from Table 3, the coin cells shown in Examples 1 to 3 exhibit better initial efficiency and rate characteristics than the coin cell of Comparative Example 1 having a negative electrode made of a negative electrode active material that does not contain magnesium, and also exhibit better initial efficiency than the coin cell of Comparative Example 2 having a negative electrode made of a negative electrode active material with low lithium and magnesium contents.

[0067]

[0068]

[0069]

Claims

1. A method for producing a composite material comprising the steps of: a silicon phase formed from silicon; and a silicate phase adjacent to the silicon phase; ｘ Mg ｙ SiO ｚ A metal-element-containing silicon-based composite having a composition of (x>0, y>0, z>0), which satisfies the following conditions: (a) (2.5x+2y) / z>1, (b) (1.5x+y) / z<1, and (c) (x+2y) / z<1.

2. The metal element-containing silicon-based composite according to claim 1, wherein 0.5<z<1.

5.

3. The metal element-containing silicon-based composite according to claim 1, wherein x>0.1 and y>0.

05.

4. The silicate phase is composed of crystalline Li ４ SiO ４ and Li ２ The metal element-containing silicon-based composite according to claim 1 , which does not contain O.

5. The metal element-containing silicon-based composite according to claim 1, at least a portion of the surface of which is covered with a conductive carbon coating.

Images