Silicon-oxygen composite material, preparation method thereof, negative electrode material and lithium ion battery

Abstract

The present application relates to a silicon-oxygen composite material, a preparation method thereof, a negative electrode material and a lithium ion battery. The silicon-oxygen composite material comprises a core and a carbon layer formed on the surface of the core, the core comprises a lithium-containing compound and a non-metallic silicon-containing material, the non-metallic silicon-containing material comprises at least one of nano-silicon and silicon oxide, and the non-metallic silicon-containing material is dispersed in the lithium-containing compound; and the size D10 of the silicon-oxygen composite material is 3.0-8.2 mu m. By controlling the particle size D10 of the silicon-oxygen composite material to be between 3.0-8.2 mu m, on the one hand, the pre-lithium uniformity can be improved, the nano-silicon is not exposed on the surface of the particles, the expected initial efficiency is improved, and good cycle stability is obtained; on the other hand, the silicon-oxygen composite material has a suitable electronic and ionic conduction path, the internal impedance of the particles is small, and the rate performance and cycle performance of the material are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a silicon-oxygen composite material, a preparation method thereof, a negative electrode material and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have been widely applied in portable electronic products and electric vehicles due to high working voltage, long cycle service life, no memory effect, small self-discharge and environmental friendliness.

[0003] At present, commercial lithium ion batteries mainly use graphite-based negative electrode materials, but the theoretical specific capacity thereof is only 372 mAh / g, which cannot meet the demand of future lithium ion batteries for high energy density. Although the existing Si has a theoretical capacity of 4200 mAh / g, its expansion reaches 300%, which affects the cycle performance and leads to constraints in market promotion and application. The corresponding silicon-oxygen material has better cycle performance, but has low initial efficiency. During the first charging, 20% to 50% of lithium needs to be consumed for SEI film formation, which greatly reduces the initial coulombic efficiency.

[0004] The method for improving the initial efficiency of the silicon-oxygen material is currently pre-lithiation, but the pre-lithiation brings cycle degradation of the silicon-oxygen material. In order to improve the application value of the pre-lithiation material, it is of great significance to improve the cycle performance of the pre-lithiation material. At the same time, the development and application of the silicon-based material are also greatly promoted.

[0005] A method for pre-lithiating a silicon-based negative electrode of a battery and simultaneously forming an SEI film is disclosed. The method includes the following steps: using silicon monoxide, inert lithium powder and 1-fluorodecane as raw materials to prepare a pre-lithiated negative electrode; the surface of the pre-lithiated negative electrode is uniformly pre-lithiated, and the SEI film uniformly and densely covers the material. However, this method forms an artificial SEI film by doping lithium, and the cycle effect of the obtained silicon-based negative electrode is improved.

[0006] For example, a Si-O-C-Li composite is disclosed, which includes nano-silicon, a lithium-containing compound and a carbon coating. Although the initial efficiency is improved by doping lithium, the cycle degradation of the silicon-oxygen material is also brought. SUMMARY

[0007] In view of this, it is necessary to provide a silicon-oxygen composite material with good cycle performance after doping lithium, excellent initial coulombic efficiency and specific capacity, a preparation method thereof, a negative electrode material and a lithium ion battery.

[0008] In a first aspect, a silicon-oxygen composite material is provided, which comprises a core and a carbon layer formed on a surface of the core, the core comprising a lithium-containing compound and a non-metallic silicon-containing material, the non-metallic silicon-containing material comprising at least one of nano-silicon and silicon oxide, the non-metallic silicon-containing material being dispersed in the lithium-containing compound; the silicon-oxygen composite material having a size D10 of 3.0 μm to 8.2 μm.

[0009] Preferably, the lithium-containing compound comprises at least one of lithium silicate, lithium carbonate, lithium aluminate and lithium nitrate.

[0010] Preferably, the silicon oxide has a chemical formula of SiO x, wherein 0 < x ≤ 1.8. x

[0011] Preferably, the nano-silicon is dispersed in the silicon oxide and / or the nano-silicon is dispersed in the lithium-containing compound.

[0012] Preferably, a mass ratio of the nano-silicon dispersed in the silicon oxide to the nano-silicon dispersed in the lithium-containing compound is (15-46):(54-75).

[0013] Preferably, the nano-silicon has a size D50 of 0-15 nm, and the 0 is excluded.

[0014] Preferably, a molar ratio of the nano-silicon to the lithium-containing compound is (0.5-10):1.

[0015] Preferably, a molar ratio of the silicon oxide to the lithium-containing compound is (0.2-2):1.

[0016] Preferably, the carbon layer comprises at least one of amorphous carbon, graphene sheets, soft carbon capable of graphitization, carbon fibers, carbon nanotubes and conductive carbon black.

[0017] Preferably, a mass content of the carbon layer is 1% to 15% based on 100% of a mass of the silicon-oxygen composite material.

[0018] Preferably, in the silicon-oxygen composite material, the carbon layer has a thickness of 200 nm to 1000 nm.

[0019] In a second aspect, a method for preparing a silicon-oxygen composite material is provided, which comprises the following steps:

[0020] adjusting a particle size of a silicon source to have a particle size D10 of 2.5 μm to 7.5 μm;

[0021] performing carbon coating on the silicon source after the particle size adjustment to obtain a carbon-containing silicon-oxygen precursor; and

[0022] ​mixing the carbon-containing silicon-oxygen precursor with a lithium source, and baking to obtain the silicon-oxygen composite material.

[0023] Preferably, the particle size D10 of the silicon-oxygen composite material is 3.0 μm to 8.2 μm.

[0024] Preferably, the preparation process of the silicon source comprises heating a raw material capable of generating silicon oxide gas under an inert atmosphere to generate silicon oxide gas, and cooling to obtain the silicon source.

[0025] Preferably, the silicon source is silicon monoxide.

[0026] Preferably, the inert atmosphere comprises at least one of helium, neon, argon, krypton, xenon, and nitrogen.

[0027] Preferably, the heating temperature is 900°C to 1500°C.

[0028] Preferably, the raw material capable of generating silicon oxide gas is a mixture of Si and SiO2.

[0029] Preferably, the particle size adjustment method comprises at least one of crushing, ball milling, and classification.

[0030] Preferably, the carbon coating method comprises at least one of a gas phase carbon coating method and a solid phase carbon coating method.

[0031] Preferably, the gas phase carbon coating method comprises mixing the particle size-adjusted silicon source with an organic carbon source under a protective atmosphere, and heating to obtain the carbon-containing silicon-oxygen precursor.

[0032] Preferably, the gas in the protective atmosphere comprises at least one of hydrogen, nitrogen, helium, neon, argon, krypton, and xenon.

[0033] Preferably, the organic carbon source comprises at least one of methane, ethylene, acetylene, acetone, and benzene.

[0034] Preferably, the heating temperature is 600°C to 1000°C.

[0035] Preferably, the solid phase carbon coating method comprises fusing the particle size-adjusted silicon source with a carbon coating source, and carbonizing to obtain the carbon-containing silicon-oxygen precursor.

[0036] Preferably, the fusing time is 0.2 h to 1 h.

[0037] Preferably, the carbon coating source comprises at least one of coal coke, petroleum coke, a sugar, an organic acid, and pitch.

[0038] Preferably, the carbonizing temperature is 600°C to 1000°C.

[0039] Preferably, the carbonization time is 3h-10h.

[0040] Preferably, the carbon-containing silicon-oxygen precursor has a particle size D10 of 3.0-8.2μm.

[0041] Preferably, the lithium source comprises a lithium compound free of oxygen.

[0042] Preferably, the lithium source comprises at least one of lithium hydride, lithium amide, lithium alkyl, lithium aluminum hydride, lithium monomer and lithium borohydride.

[0043] Preferably, the lithium source has a particle size D10 of 0.5-10μm.

[0044] Preferably, the molar ratio of the carbon-containing silicon-oxygen precursor to the lithium source is (1.4-3):1.

[0045] Preferably, the mixing of the carbon-containing silicon-oxygen precursor and the lithium source comprises at least one of VC mixing, kneading, fusion, mixing, dispersion and stirring.

[0046] Preferably, the calcination is performed in a non-oxygen environment.

[0047] Preferably, the non-oxygen environment comprises at least one of vacuum atmosphere, hydrogen atmosphere, nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere and xenon atmosphere.

[0048] Preferably, the calcination temperature is 300-1000℃, preferably 450-800℃.

[0049] In one possible implementation, the method for preparing the silicon-oxygen composite material comprises the following steps:

[0050] heating a mixture of Si and SiO2 to 900-1500℃ in an inert atmosphere to produce silicon oxide gas, cooling, adjusting the particle size, and obtaining a silicon source having a particle size D10 of 2.5-7.5μm;

[0051] carbon-coating the silicon source after the particle size adjustment to obtain a carbon-containing silicon-oxygen precursor having a particle size D10 of 3.0-8.2μm; and

[0052] mixing the carbon-containing silicon-oxygen precursor with a lithium source, and performing calcination at a temperature of 450-800℃ in a non-oxygen environment to obtain a silicon-oxygen composite material having a particle size D10 of 3.0-8.2μm.

[0053] In a third aspect, a negative electrode material is provided, comprising the silicon-oxygen composite material of the first aspect.

[0054] Preferably, the negative electrode material is a composite of graphite and the silicon-oxygen composite material of the first aspect.

[0055] Preferably, the negative electrode material is a composite of lithium titanate and the silicon-oxygen composite material of the first aspect.

[0056] In a fourth aspect, there is provided a lithium ion battery comprising the silicon-oxygen composite material of the first aspect.

[0057] Advantages of the present application will be set forth in part in the description which follows, and in part will be obvious from the description or can be learned by practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a SEM image of the silicon-oxygen composite material provided by specific embodiment 1 of the present application.

[0059] Figure 2 is a comparison chart of capacity retention rate of half-cell cycling for 50 cycles of the silicon-oxygen composite material provided by specific embodiment 1, comparative example 1 and comparative example 2 of the present application.

[0060] Figure 3 is a process flow chart of the preparation method of the silicon-oxygen composite material in an embodiment of the present application. DETAILED DESCRIPTION

[0061] The technical solutions of the present application will be further described below in combination with the drawings and through specific embodiments.

[0062] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other. Without departing from the principles of the embodiments of the present application, several improvements and refinements can also be made, which are also considered within the protection scope of the embodiments of the present application.

[0063] An embodiment provides a silicon-oxygen composite material to solve the problem of poor cycle performance of pre-lithium materials in the prior art, thereby obtaining a silicon-oxygen composite material with excellent cycle performance, first coulomb efficiency and gram capacity. Another embodiment provides a preparation method of the above-mentioned silicon-oxygen composite material. Still another embodiment provides a negative electrode material comprising the above-mentioned silicon-oxygen composite material. Yet another embodiment provides a battery comprising the above-mentioned silicon-oxygen composite material.

[0064] The silicon-oxygen composite material of one embodiment includes a core and a carbon layer formed on a surface of the core, the core includes a lithium-containing compound and a non-metallic silicon-containing material, the non-metallic silicon-containing material is dispersed in the lithium-containing compound, the non-metallic silicon-containing material includes at least one of nanosilicon and silicon oxide, and the non-metallic silicon-containing material is dispersed in the lithium-containing compound.

[0065] The size D10 of the silicon-oxygen composite material is 3.0 μm to 8.2 μm, and more specifically, can be 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 7 μm, 7.2 μm, 7.5 μm, 7.8 μm, or 8 μm.

[0066] The silicon-oxygen composite material of one embodiment includes a core and a carbon layer formed on a surface of the core, the core includes a lithium-containing compound and a non-metallic silicon-containing material, the non-metallic silicon-containing material is dispersed in the lithium-containing compound, the non-metallic silicon-containing material includes at least one of nanosilicon and silicon oxide, and the non-metallic silicon-containing material is dispersed in the lithium-containing compound.

[0067] The silicon-oxygen composite material of one embodiment includes a core and a carbon layer formed on a surface of the core, the core includes a lithium-containing compound and a non-metallic silicon-containing material, the non-metallic silicon-containing material is dispersed in the lithium-containing compound, the non-metallic silicon-containing material includes at least one of nanosilicon and silicon oxide, and the non-metallic silicon-containing material is dispersed in the lithium-containing compound.

[0068] In some embodiments, the lithium-containing compound includes at least one of lithium silicate, lithium carbonate, lithium aluminate, and lithium nitrate.

[0069] In some embodiments, the silicon oxide has a chemical formula of SiOx, where 0 < x ≤ 1.8, and more specifically, can be 0.2, 0.5, 0.8, 1, 1.2, or 1.5.

[0070] In some embodiments, the nanosilicon is dispersed in the silicon oxide and / or the nanosilicon is dispersed in the lithium-containing compound.

[0071] In some embodiments, the mass ratio of the nano-silicon dispersed in the silicon oxide and the nano-silicon dispersed in the lithium-containing compound is (15-46):(54-75), and more specifically, can be 15:75, 20:75, 25:75, 35:75, 20:70, 20:60, 20:50, 40:54, 40:60, or 40:73, etc.

[0072] In some embodiments, the size D50 of the nano-silicon is 0-15 nm, and more specifically, can be 0.5 nm, 1 nm, 2 nm, 3 nm, 5 nm, 8 nm, 9 nm, 10 nm, 12 nm, or 15 nm, etc.

[0073] In some embodiments, the molar ratio of the nano-silicon and the lithium-containing compound is (0.5-10):1, and more specifically, can be 0.5:1, 1:1, 2:1, 3:1, 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 10:1, etc. If the content of the nano-silicon is too high and the content of the lithium-containing compound is too low, the material expansion increases, causing the cycle performance to deteriorate. If the content of the nano-silicon is too low and the content of the lithium-containing compound is too high, the electronic conductivity of the material is weakened, the battery is polarized seriously, and the performance of the material is not good.

[0074] In some embodiments, the molar ratio of the silicon oxide and the lithium-containing compound is (0.2-2):1, and more specifically, can be 0.2:1, 0.4:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.6:1, 1.8:1, or 2:1, etc. If the content of the silicon oxide is too high, the first efficiency of the material is improved little, resulting in a low first efficiency of the battery cell prepared therefrom, and the positive electrode capacity in the corresponding battery is blocked. If the content of the silicon oxide is too low, the cycle performance of the material deteriorates.

[0075] In some embodiments, the carbon layer includes at least one of amorphous carbon, graphene sheet, soft carbon that can be graphitized, carbon fiber, carbon nanotube, and conductive carbon black.

[0076] In some embodiments, the mass content of the carbon layer is 1%-15% based on 100% of the mass of the silicon-oxygen composite material, and more specifically, can be 1%, 2%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8%, 10%, 11.5%, 13%, or 15%, etc.

[0077] In some embodiments, the thickness of the carbon layer in the silicon-oxygen composite material is 200 nm-1000 nm, and more specifically, can be 200 nm, 300 nm, 350 nm, 400 nm, 450 nm, 550 nm, 600 nm, 700 nm, 800 nm, or 1000 nm, etc.

[0078] The preparation method of the silicon-oxygen composite material is shown in the following process flow chart Figure 3 , and includes steps S100-S300.

[0079] In step S100, the particle size of the silicon source is adjusted to have a D10 of 2.5-7.5 μm.

[0080] In some embodiments, the silicon source is silicon monoxide.

[0081] In some embodiments, the method of adjusting the particle size includes at least one of crushing, ball milling, and grading.

[0082] It can be understood that by controlling the particle size D10 of the silicon source to be 2.5-7.5 μm, and more specifically, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, or 7 μm, etc., not only can the final silicon-oxygen composite material have a D10 of 3.0-8.2 μm, but also the silicon-oxygen composite material has excellent electrochemical performance. When the particle size D10 of the silicon source is less than 2.5 μm, the phenomenon of over-lithiation of small-particle nano-silicon during the subsequent pre-lithiation process is prone to occur, leading to the deterioration of the cycle performance of the final product; when the particle size D10 of the silicon source is greater than 7.5 μm, the large particle size leads to a long electron and ion transport path, which is not conducive to the overall performance of the silicon-oxygen composite material.

[0083] In some embodiments, the silicon source is silicon monoxide.

[0084] In some embodiments, the silicon source can be prepared by step S110.

[0085] In step S110, a raw material capable of generating a silicon oxide gas is heated under an inert atmosphere to generate the silicon oxide gas, and the silicon source is obtained after cooling.

[0086] In some embodiments, the method of adjusting the particle size includes at least one of crushing, ball milling, and grading.

[0087] In some embodiments, the inert atmosphere includes at least one of a helium atmosphere, a neon atmosphere, an argon atmosphere, a krypton atmosphere, a xenon atmosphere, and a nitrogen atmosphere.

[0088] In some embodiments, the temperature of the heating is 900-1500 °C, and more specifically, 950 °C, 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, or 1450 °C, etc.

[0089] In some embodiments, the raw material capable of generating a silicon oxide gas is a mixture of Si and SiO2.

[0090] It can be understood that the ratio of Si and SiO2 in the raw material capable of producing silicon oxide gas is not specifically limited, and can be selected by those skilled in the art according to actual experience. Exemplary molar ratio of Si and SiO2 is 2:1.

[0091] In step S200, the silicon source with adjusted particle size is carbon-coated to obtain a carbon-containing silicon-oxygen precursor.

[0092] In some embodiments, the carbon-coating method comprises at least one of a gas-phase carbon-coating method and a solid-phase carbon-coating method.

[0093] In some embodiments, the gas-phase carbon-coating method comprises: mixing the silicon source with adjusted particle size with an organic carbon source under a protective atmosphere, and heating to obtain a carbon-containing silicon-oxygen precursor.

[0094] In some embodiments, the gas in the protective atmosphere comprises at least one of hydrogen, nitrogen, helium, neon, argon, krypton, and xenon.

[0095] In some embodiments, the organic carbon source comprises at least one of methane, ethylene, acetylene, acetone, and benzene.

[0096] In some embodiments, the heating temperature is 600-1000°C, and more specifically, can be 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, or 950°C, etc.

[0097] In some embodiments, the solid-phase carbon-coating method comprises: fusing the silicon source with adjusted particle size with a carbon-coating source, and carbonizing to obtain a carbon-containing silicon-oxygen precursor.

[0098] In some embodiments, the fusing time is 0.2-1h, and more specifically, can be 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, or 0.9h, etc.

[0099] In some embodiments, the fusing is performed in a fusing machine, and preferably, the rotation speed of the fusing machine is 500-3000r / min, and more specifically, can be 800r / min, 1000r / min, 1200r / min, 1500r / min, 1800r / min, 2000r / min, 2200r / min, 2500r / min, or 2800r / min, etc.

[0100] In some embodiments, the carbon-coating source comprises at least one of coal coke, petroleum coke, sugar, organic acid, and pitch.

[0101] In some embodiments, the carbonization temperature is 600-1000℃, more specifically, it can be 650℃, 700℃, 750℃, 800℃, 850℃, 900℃ or 950℃, etc.

[0102] In some embodiments, the carbonization time is 3-10h, more specifically, it can be 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h or 9.5h, etc.

[0103] In some embodiments, the particle size D10 of the carbon-containing silicon-oxygen precursor is 3.0-8.2μm, more specifically, it can be 3.2μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 5.2μm, 5.5μm, 5.8μm, 6μm, 6.2μm, 6.5μm, 7μm, 7.2μm, 7.5μm, 7.8μm or 8μm, etc.

[0104] Step S300, mixing the carbon-containing silicon-oxygen precursor with the lithium source, and calcining to obtain a silicon-oxygen composite material.

[0105] In some embodiments, the lithium source is an oxygen-free lithium compound.

[0106] In some embodiments, the lithium source includes at least one of lithium hydride, lithium amide, alkyl lithium, lithium aluminum hydride, lithium monomer and lithium borohydride.

[0107] In some embodiments, the particle size D10 of the lithium source is 0.5-10μm, more specifically, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc. If the particle size D10 of the lithium source is <0.5um, it is high in safety risk during use and prone to deterioration; if the particle size D10 is >10um, it is too large to cause a decrease in pre-lithium uniformity, and some particles are excessively pre-lithiated, resulting in a decrease in the comprehensive performance of the material after pre-lithiation.

[0108] In some embodiments, the molar ratio of the carbon-containing silicon-oxygen precursor to the lithium source is (1.4-3):1, more specifically, it can be 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1 or 3:1, etc.

[0109] In some embodiments, the mixing method of the carbon-containing silicon-oxygen precursor and the lithium source includes at least one of VC mixing, kneading, fusion, mixing, dispersion and stirring.

[0110] In some embodiments, the calcination is performed in a non-oxygen environment.

[0111] In some embodiments, the non-oxygen environment includes at least one of a vacuum atmosphere, a hydrogen atmosphere, a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, an argon atmosphere, a krypton atmosphere, and a xenon atmosphere.

[0112] In some embodiments, the temperature of the calcination is 300-1000℃ (more specifically, it can be 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, or 950℃, etc.), and too low a temperature will result in incomplete reaction, and too high a temperature will cause the nano-silicon to grow rapidly, resulting in a decrease in cycle performance. The temperature range that can achieve optimal performance is 450-800℃.

[0113] In the above embodiments, the silicon source is first coated with carbon, and then mixed with the lithium source to react, which can consume the irreversible lithium consumption phase in the silicon source in advance by the lithium source, on the one hand, to improve the initial coulombic efficiency of the silicon-oxygen material, and on the other hand, to effectively buffer the volume change of the internal nano-silicon, to improve the cycle performance of the material. At the same time, the carbon layer coated in advance can alleviate the severity of the pre-lithium reaction, and avoid the rapid growth of the nano-silicon grains during the pre-lithium process.

[0114] In some embodiments, the method for preparing the silicon-oxygen composite material includes the following steps:

[0115] The mixture of Si and SiO2 is heated to 900-1500℃ under an inert atmosphere, to produce a silicon oxide gas, which is then cooled and adjusted in particle size, to obtain a silicon source with a particle size D10 of 2.5-7.5μm;

[0116] The silicon source adjusted in particle size is coated with carbon, to obtain a carbon-containing silicon-oxygen precursor with a particle size D10 of 3.0-8.2μm; and

[0117] The carbon-containing silicon-oxygen precursor is mixed with a lithium source, and calcined at a temperature of 450-800℃ under a non-oxygen environment, to obtain a silicon-oxygen composite material with a particle size D10 of 3.0-8.2μm.

[0118] A negative electrode material comprising the above silicon-oxygen composite material.

[0119] In some embodiments, the negative electrode material is a composite of graphite and the silicon-oxygen composite material of the first aspect.

[0120] In some embodiments, the negative electrode material is a composite of lithium titanate and the silicon-oxygen composite material of the first aspect.

[0121] A lithium ion battery comprising the above silicon-oxygen composite material.

[0122] The above embodiments have and are not limited to the following beneficial effects:

[0123] The above embodiment can improve the pre-lithium uniformity, and the first coulomb efficiency and the cycle stability are improved, on the one hand, and the silicon-oxygen composite material has a suitable electron and ion conduction path, the internal impedance of the material is small, and the rate performance and cycle performance of the silicon-oxygen composite material are improved.

[0124] The following is a typical but non-limiting embodiment of the present application:

[0125] Example 1

[0126] A preparation method of a silicon-oxygen composite material, comprising the following steps:

[0127] 1 kg of silicon powder and 2.1 kg of silicon dioxide were weighed and placed in a vacuum reaction furnace, and heated to 1300 DEG C under argon atmosphere for 10 h, and then cooled to room temperature. The material was taken out and crushed, ball milled and classified to obtain silicon monoxide particles with D10 = 2.6 μm.

[0128] The silicon monoxide particles 1 kg were placed in a CVD rotary kiln and heated to 800 DEG C, and acetylene gas was introduced at a flow rate of 0.5 L / min. After 100 min of reaction, the material was cooled to room temperature to obtain carbon-containing silicon monoxide particles with D10 = 3.2 μm.

[0129] The carbon-containing silicon monoxide 1 kg and 200 g of lithium hydride with a particle size D10 of 0.5 μm were placed in a fusion machine with a rotation speed of 1000 r / min for 20 min, and then taken out and loaded into a graphite crucible and placed in an atmosphere furnace. The gas introduced was argon, and the calcination temperature was 600 DEG C. After 2 h of heat preservation, the temperature was cooled to room temperature to obtain a silicon-oxygen composite material.

[0130] The particle size D10 of the silicon-oxygen composite material prepared in this example is 3.2 μm, which includes SiO x , x = 0.8, nano-silicon, lithium silicate and a carbon layer, the silicon oxide is dispersed in the lithium silicate, a part of the nano-silicon is dispersed in the silicon oxide, and another part of the nano-silicon is dispersed in the lithium silicate. The molar ratio of nano-silicon and lithium silicate is 6:1; the molar ratio of silicon oxide and lithium silicate is 0.2:1.

[0131] Figure 1 The SEM photo of the silicon-oxygen composite material of this example is shown in the figure, and it can be seen that the particle size uniformity of the silicon-oxygen composite material is high.

[0132] Example 2

[0133] A method for preparing a silicon-oxygen composite material, comprising the following steps:

[0134] 1 kg of silicon powder and 2.1 kg of silicon dioxide are weighed and placed in a vacuum reaction furnace respectively, heated to 1300℃ under argon atmosphere for 10 h, then cooled to room temperature, and the material is taken out for crushing, ball milling and grading to obtain silicon monoxide particles with D10=5.6 μm.

[0135] The silicon monoxide particles 1 kg are placed in a CVD rotary kiln, heated to 800℃, and acetylene gas is introduced at a flow rate of 0.5 L / min. After 100 min of reaction, the material is cooled to room temperature to obtain carbon-containing silicon monoxide particles with D10=6.0 μm.

[0136] The carbon-containing silicon monoxide 1 kg and 380 g of lithium aluminum hydride are placed in a fusion machine with a rotation speed of 2000 r / min for 20 min, taken out, loaded into a graphite crucible, and placed in an atmosphere furnace for calcination. Argon gas is introduced, the calcination temperature is 600℃, and the material is cooled to room temperature after 2 h of heat preservation to obtain a silicon-oxygen composite material.

[0137] The silicon-oxygen composite material prepared in this example has a particle size D10 of 6 μm, and the silicon oxide is SiO x , x=0.2, nanosilicon, lithium silicate, and a carbon layer. The silicon oxide is dispersed in the lithium silicate, a part of the nanosilicon is dispersed in the silicon oxide, and another part of the nanosilicon is dispersed in the lithium silicate. The mass ratio of the nanosilicon dispersed in the silicon oxide to the nanosilicon dispersed in the lithium-containing compound is 1:1. The molar ratio of the nanosilicon to the lithium silicate is 3:1, and the molar ratio of the silicon oxide to the lithium silicate is 0.8:1.

[0138] Example 3

[0139] A method for preparing a silicon-oxygen composite material, comprising the following steps:

[0140] 1 kg of silicon powder and 2.1 kg of silicon dioxide are weighed and placed in a vacuum reaction furnace respectively, heated to 1300℃ under argon atmosphere for 10 h, then cooled to room temperature, and the material is taken out for crushing, ball milling and grading to obtain silicon monoxide particles with D10=5.6 μm.

[0141] The silicon monoxide particles 1 kg are placed in a CVD rotary kiln, heated to 800℃, and acetylene gas is introduced at a flow rate of 0.5 L / min. After 100 min of reaction, the material is cooled to room temperature to obtain carbon-containing silicon monoxide particles with D10=6.0 μm.

[0142] Take 1 kg of carbon-containing silicon monoxide and 220 g of lithium amide into a fusion machine with a rotation speed of 1500 r / min and fuse for 20 min, take out and load into a graphite crucible, and place in an atmosphere furnace, the gas introduced is argon, the baking temperature is 600℃, and after holding for 2 h, cool to room temperature, and take out to obtain a silicon-oxygen composite material.

[0143] The particle size D10 of the silicon-oxygen composite material prepared in this example is 8.1 μm, including silicon oxide SiO x , x = 1.6, nano-silicon, lithium silicate, and a carbon layer. The molar ratio of nano-silicon to lithium silicate is 1.1:1; the molar ratio of silicon oxide to lithium silicate is 2:1.

[0144] Example 4

[0145] The difference from Example 1 is that the baking temperature is 200℃.

[0146] The particle size D10 of the silicon-oxygen composite material prepared in this example is 3.2 μm, including silicon oxide SiO x , x = 1.8, nano-silicon, lithium silicate, and a carbon layer. The molar ratio of nano-silicon to lithium silicate is 2.3:1; the molar ratio of silicon oxide to lithium silicate is 1:1.

[0147] Example 5

[0148] The difference from Example 1 is that the baking temperature is 1100℃.

[0149] The particle size D10 of the silicon-oxygen composite material prepared in this example is 3.2 μm, including silicon oxide SiO x , x = 0.6, nano-silicon, lithium silicate, and a carbon layer. The molar ratio of nano-silicon to lithium silicate is 0.8:1; the molar ratio of silicon oxide to lithium silicate is 1.4:1.

[0150] Example 6

[0151] The difference from Example 1 is that the silicon monoxide particle D10 = 2.2 μm, and the particle size D10 of the carbon-containing silicon monoxide particles is the same as in Example 1.

[0152] The particle size D10 of the silicon-oxygen composite material prepared in this example is 3.2 μm, including silicon oxide SiO x , x = 0.9, nano-silicon, lithium silicate, and a carbon layer. The molar ratio of nano-silicon to lithium silicate is 2.3:1; the molar ratio of silicon oxide to lithium silicate is 1:1.

[0153] Example 7

[0154] The difference from Example 3 is that the particle size D10 of the silicon monoxide particles is 7.8 μm, and the particle size D10 of the carbon-containing silicon monoxide particles is the same as in Example 3.

[0155] The particle size D10 of the silicon-oxygen composite material prepared in this example is 8.1 μm, and the silicon oxide is SiO x wherein x = 1.1, nanosilicon, lithium silicate, and a carbon layer. The molar ratio of nanosilicon to lithium silicate is 1.1:1, and the molar ratio of silicon oxide to lithium silicate is 2:1.

[0156] Example 8

[0157] The difference from Example 1 is that the particle size D10 of the lithium hydride is 0.2 μm, and the other conditions are the same as in Example 1.

[0158] The particle size D10 of the silicon-oxygen composite material prepared in this example is 3.2 μm, and the silicon oxide is SiO x wherein x = 0.5, nanosilicon, lithium silicate, and a carbon layer. The molar ratio of nanosilicon to lithium silicate is 10:1, and the molar ratio of silicon oxide to lithium silicate is 0.005:1.

[0159] Example 9

[0160] The difference from Example 1 is that the particle size D10 of the lithium hydride is 15 μm, and the other conditions are the same as in Example 1.

[0161] The particle size D10 of the silicon-oxygen composite material prepared in this example is 3.2 μm, and the silicon oxide is SiO x wherein x = 1.85, nanosilicon, lithium silicate, and a carbon layer. The molar ratio of nanosilicon to lithium silicate is 0.12:1, and the molar ratio of silicon oxide to lithium silicate is 5:1.

[0162] Comparative Example 1

[0163] The difference from Example 1 is that the particle size D10 of the silicon monoxide particles is 2.0 μm, and the particle size D10 of the carbon-containing silicon monoxide particles is 2.5 μm.

[0164] Comparative Example 2

[0165] The difference from Example 1 is that the particle size D10 of the silicon monoxide particles is 10 μm, and the particle size D10 of the carbon-containing silicon monoxide particles is 10.5 μm.

[0166] Figure 2The capacity retention rate of the half cells of the silicon-oxygen composite materials obtained in Example 1, Comparative Example 1 and this comparative example after 50 cycles is compared in the following graph. As can be seen from the graph, the silicon-oxygen composite material obtained in Example 1 has stable post-cycle performance and reduced capacity attenuation, while the silicon-oxygen composite materials obtained in Comparative Example 1 and this comparative example have low capacity retention rate and poor cycle performance.

[0167] Performance test:

[0168] The silicon-oxygen composite materials obtained in each example and comparative example are subjected to the following performance tests:

[0169] (1) The surface morphology of the sample is observed using a Hitachi S4800 scanning electron microscope;

[0170] (2) The particle size of the material is tested using a Malvern 2000 laser particle size analyzer. The specific testing method is as follows: a dispersant and the sample to be tested are placed in a 50 mL beaker, a certain amount of pure water is added, and the mixture is stirred thoroughly with a glass rod. The uniformly dispersed sample is introduced into the measuring cup, and the measurement is started. Each sample is measured three times, and the average value is taken as the particle size of the sample;

[0171] (3) Cycle performance test: the silicon-oxygen composite materials obtained in each example and comparative example are mixed with graphite at a mass ratio of 1:9 to obtain active material. The active material: conductive agent (conductive carbon black): binder (SBR+CMC) = 85:15:10. Lithium metal is used as the counter electrode, PP / PE is used as the separator, LiPF6 / EC+DEC+DMC (EC, DEC and DMC are in a volume ratio of 1:1:1) is used as the electrolyte, and a button cell is assembled in an argon-filled glove box. The electrochemical performance of the battery after 50 cycles is tested using a blue electric 5V / 10mA type battery tester. The charging voltage is 1.5V, the discharge is to 0.01V, and the charge / discharge rate is 0.1C;

[0172] (4) First cycle performance test: the silicon-oxygen composite materials obtained in each example and comparative example are used as active material, SBR+CMC is used as binder, and conductive carbon black is added and stirred to form a slurry, which is coated on a copper foil. Finally, the negative electrode sheet is obtained by drying and rolling. The active material: conductive agent: binder = 85:15:10. Lithium metal is used as the counter electrode, PP is used as the separator, LiPF6 / EC+DEC+DMC (EC, DEC and DMC are in a volume ratio of 1:1:1) is used as the electrolyte, and a simulated battery is assembled in an argon-filled glove box. The first coulombic efficiency and the first charge specific capacity of the button cell are tested using a blue electric 5V / 10mA type battery tester. The charging voltage is 1.5V, the discharge is to 0.01V, and the charge / discharge rate is 0.1C.

[0173] The test results are shown in Table 1:

[0174] Table 1

[0175]

[0176] As can be seen from the data in Table 1, the silicon-oxygen composite material prepared by the method according to the embodiment has good capacity, first coulombic efficiency and cycle performance.

[0177] As can be seen from the comparison between Example 1 and Examples 4-5, the pre-lithiation reaction temperature has a great influence on the cycle performance of the material. If the temperature is too high, the cycle capacity retention rate of the material is low. If the temperature is too low, the first efficiency of the material is low.

[0178] As can be seen from the comparison between Example 1 and Examples 6-7, the particle size D10 of the silicon monoxide particles has a significant influence on the performance of the material. If the particle size is too large, the first efficiency and cycle performance of the material are poor. If the particle size is too small, the cycle performance of the material is poor.

[0179] As can be seen from the comparison between Example 1 and Examples 8-9, the D10 particle size of the lithium source is too large or too small, which is not conducive to the improvement of the performance of the material after pre-lithiation. Reason: When the D10 particle size of the lithium source is 0.2 um, the particle size is too small, and the performance is too active, which is easy to deteriorate. When the D20 particle size is 15 um, the particle size is too large, and the pre-lithiation uniformity is reduced, which is easy to cause the phenomenon that some particles are excessively pre-lithiated, resulting in a decrease in the performance of the material after pre-lithiation.

[0180] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, when the D10 particle size is greater than 8.2 um or less than 3 um, the cycle retention rate of the corresponding material is low. Reason: When the D10 particle size is less than 3.0 um, the small particles are easy to be excessively pre-lithiated during the pre-lithiation process, so that the silicon contained therein is exposed on the surface. The volume change caused by repeated charge and discharge cannot be alleviated and inhibited, resulting in poor cycle performance. When the D10 particle size is greater than 8.2 um, the overall particle size is too large, the electron and ion conduction path in the particle is long, the electrode polarization is intensified, the internal impedance of the particle is increased, and finally the cycle life of the material is short. Therefore, the performance of Comparative Examples 1-2 is poorer than that of Example 1.

[0181] The applicant declares that the detailed process equipment and process flow of the present application are illustrated by the above examples, but the present application is not limited to the above detailed process equipment and process flow, that is, it does not mean that the present application must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A silicon-based composite material, characterized by, The silicon-based composite material comprises an inner core and a carbon layer formed on the surface of the inner core, the inner core comprises a lithium-containing compound and a non-metallic silicon-containing material, the non-metallic silicon-containing material comprises nano-silicon and silicon oxide, the silicon oxide is dispersed in the lithium-containing compound, a part of the nano-silicon is dispersed in the silicon oxide, and another part of the nano-silicon is dispersed in the lithium-containing compound; the molar ratio of the nano-silicon and the lithium-containing compound is (1-10):

1. The particle size D10 of the silicon-based composite material is 3.0 μm-8.2 μm.

2. The silicon-based composite material of claim 1, wherein, The lithium-containing compound comprises at least one of lithium silicate, lithium carbonate, lithium aluminate and lithium nitrate.

3. The silicon-based composite material of claim 1, wherein, The silicon oxide has the chemical formula SiO x wherein 0 < x < 1.

8.

4. The silicon-based composite material of claim 1, wherein The mass ratio of the nano-silicon dispersed in the silicon oxide and the nano-silicon dispersed in the lithium-containing compound is (15-46):(54-75).

5. The silicon-based composite material of claim 1, wherein, The particle size D50 of the nano-silicon is 0-15 nm, and 0 is not included.

6. The silicon-based composite material of claim 1, wherein, The molar ratio of the silicon oxide and the lithium-containing compound is (0.2-2):

1.

7. The silicon-based composite material of claim 1, wherein The carbon layer comprises at least one of amorphous carbon, graphene sheet, graphitizable soft carbon, carbon fiber, carbon nanotube and conductive carbon black.

8. The silicon-based composite material of claim 1, wherein, The mass content of the carbon layer is 1%-15% based on 100% of the mass of the silicon-based composite material.

9. The silicon-based composite material of claim 1, wherein The thickness of the carbon layer in the silicon-based composite material is 200 nm-1000 nm.

10. A method of preparing a silicon-based composite material according to any one of claims 1 to 9, characterized in that, The method comprises the following steps: The particle size of the silicon source is adjusted to have a particle size D10 of 2.5 μm-7.5 μm; The silicon source after the particle size adjustment is carbon-coated to obtain a carbon-containing silicon-oxygen precursor; And The carbon-containing silicon-oxygen precursor is mixed with a lithium source, and then is calcined to obtain the silicon-based composite material; The particle size D10 of the silicon-based composite material is 3.0 μm-8.2 μm.

11. The method of claim 10, wherein, The preparation process of the silicon source comprises: heating raw materials capable of generating silicon oxide gas under an inert atmosphere to generate silicon oxide gas, and obtaining the silicon source after cooling.

12. The method of claim 10, wherein, The silicon source is silicon monoxide.

13. The method of claim 11, wherein, The inert atmosphere comprises at least one of helium gas atmosphere, neon gas atmosphere, argon gas atmosphere, krypton gas atmosphere, xenon gas atmosphere and nitrogen gas atmosphere.

14. The method of claim 11, wherein, The heating temperature is 900°C-1500°C.

15. The method of claim 11, wherein, The raw materials capable of generating silicon oxide gas are a mixture of Si and SiO2.

16. The method of claim 10, wherein, The particle size adjustment method comprises at least one of crushing, ball milling and classification.

17. The method of claim 10, wherein, The carbon-coating method comprises at least one of a gas phase carbon-coating method and a solid phase carbon-coating method.

18. The method of claim 17, wherein, The gas phase carbon-coating method comprises: mixing the silicon source after the particle size adjustment with an organic carbon source under a protective atmosphere, and then heating to obtain the carbon-containing silicon-oxygen precursor.

19. The method of claim 18, wherein, The gas in the protective atmosphere comprises at least one of hydrogen, nitrogen, helium, neon, argon, krypton and xenon.

20. The method of claim 18, wherein, The organic carbon source comprises at least one of methane, ethylene, acetylene, acetone and benzene.

21. The method of claim 18, wherein, The heating temperature is 600°C-1000°C.

22. The method of claim 17, wherein, The solid phase carbon-coating method comprises: fusing the silicon source after the particle size adjustment with a carbon-coating source, and then carbonizing to obtain the carbon-containing silicon-oxygen precursor.

23. The method of claim 22, wherein, The fusing time is 0.2 h-1 h.

24. The method of claim 22, wherein, The carbon-coating source comprises at least one of coal coke, petroleum coke, sugar, organic acid and pitch.

25. The method of claim 22, wherein, The carbonization temperature is 600-1000℃.

26. The method of claim 22, wherein, The carbonization time is 3-10 hours.

27. The method of claim 10, wherein, The particle size D10 of the carbon-containing silicon-oxygen precursor is 3.0-8.2 μm.

28. The method of claim 10, wherein, The lithium source comprises a lithium compound without oxygen.

29. The method of claim 10, wherein, The lithium source comprises at least one of lithium hydride, lithium amide, alkyl lithium, lithium aluminum hydride, lithium monomer and lithium borohydride.

30. The method of claim 10, wherein, The particle size D10 of the lithium source is 0.5-10 μm.

31. The method of claim 10, wherein, The molar ratio of the carbon-containing silicon-oxygen precursor to the lithium source is (1.4-3):

1.

32. The method of claim 10, wherein, The mixing method of the carbon-containing silicon-oxygen precursor and the lithium source comprises at least one of VC mixing, kneading, fusion, mixing, dispersion and stirring.

33. The method of claim 10, wherein, The calcination is performed in a non-oxygen environment.

34. The method of claim 33, wherein, The non-oxygen environment comprises at least one of vacuum atmosphere, hydrogen atmosphere, nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere and xenon atmosphere.

35. The method of claim 10, wherein, The calcination temperature is 300-1000℃.

36. The method of claim 10, wherein, The method comprises the following steps: a mixture of Si and SiO2 is heated to 900-1500℃ in an inert atmosphere to produce a silicon oxide gas, and then cooled to adjust the particle size, to obtain a silicon source with a particle size D10 of 2.5-7.5 μm; the silicon source after the particle size adjustment is carbon-coated to obtain a carbon-containing silicon-oxygen precursor with a particle size D10 of 3.0-8.2 μm; and the carbon-containing silicon-oxygen precursor is mixed with a lithium source, and calcined at a temperature of 450-800℃ in a non-oxygen environment to obtain a silicon-based composite material with a particle size D10 of 3.0-8.2 μm.

37. A negative electrode material, characterized by comprising: The silicon-based composite material of any one of claims 1-9.

38. The anode material of claim 37, wherein, The negative electrode material is a composite of graphite and the silicon-based composite material of any one of claims 1-9.

39. The anode material of claim 37, wherein, The negative electrode material is a composite of lithium titanate and the silicon-based composite material of any one of claims 1-9.

40. A lithium-ion battery, characterized by, The silicon-based composite material of any one of claims 1-9. The silicon-based composite material of any one of claims 1-9.

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