Lithium battery silicon-carbon anode material, its preparation method and application

Abstract

The present invention provides a silicon-carbon anode material for lithium batteries, a preparation method thereof, and an application thereof. The preparation method includes: self-assembling polyvinylpyrrolidone into hollow microspheres PVP; in-situ growing silica on the inner surface of the hollow microspheres PVP to obtain a hollow microsphere PVP@SiO2 material; sintering the hollow microsphere PVP@SiO2 material to obtain a hollow microsphere C@Si material; coating the hollow microsphere C@Si material with lithium titanate to obtain a silicon-carbon anode material for lithium batteries. The hollow LTO-C@Si material is obtained by an in-situ growth method, and its hollow structure can effectively alleviate the impact of the volume expansion of silicon on the electrode structure during cycling, ensuring the continuity of lithium-ion transmission and the integrity of the SEI film. The outer layer of lithium titanate provides a fast lithium-ion transmission channel, improving the electronic conductivity of the electrode material. The lithium titanate layer can balance the surface potential of the electrode, enabling uniform deposition of lithium ions and avoiding the formation of lithium dendrites.

Description

Technical Field

[0001] The present invention relates to the field of anode materials for lithium batteries, and more particularly, to a silicon-carbon anode material for lithium batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Silicon (Si) is considered to replace or supplement the graphite anode of next-generation lithium-ion batteries (LIBs) due to its extremely high theoretical capacity (4200 mAh / g), and has received extensive attention from the scientific and industrial communities, and efforts have been made to commercialize silicon-based anode materials.

[0003] However, silicon as a Li storage material inevitably faces two major challenges: firstly, serious volume expansion occurs during repeated lithiation / delithiation processes; secondly, it has poor electronic conductivity compared with graphite. The former leads to hindrance of electron transport in the electrode and continuous rupture of the solid electrolyte interphase (SEI), and the latter strictly limits the loading amount of silicon-based materials in the electrode.

[0004] At present, by preparing silicon-carbon anode materials through methods such as combining silicon with porous materials (mesoporous carbon) and secondary granulation coating, the volume expansion of silicon-carbon materials on the electrode structure can be effectively alleviated, and the conductivity of the electrode material can be improved, which is a beneficial attempt for the commercialization of silicon-carbon materials. However, the improvement of the conductivity of the silicon-carbon anode materials prepared by existing methods is limited, and further improvement is still needed. Summary of the Invention

[0005] The main object of the present invention is to provide a silicon-carbon anode material for lithium batteries, a preparation method thereof, and an application thereof, so as to solve the problem that the improvement of the conductivity of the silicon-carbon anode materials prepared by existing methods is limited.

[0006] To achieve the above object, according to one aspect of the present invention, a preparation method of a silicon-carbon anode material for lithium batteries is provided. The preparation method includes: self-assembling polyvinylpyrrolidone into hollow microspheres PVP; in-situ growing silica on the inner surface of the hollow microspheres PVP to obtain a hollow microsphere PVP@SiO2 material; sintering the hollow microsphere PVP@SiO2 material to obtain a hollow microsphere C@Si material; coating the hollow microsphere C@Si material with lithium titanate to obtain a silicon-carbon anode material for lithium batteries.

[0007] Further, self-assembling polyvinylpyrrolidone into hollow microspheres PVP includes: mixing an aqueous solution of cetyltrimethylammonium bromide and deionized water with absolute ethanol to obtain a first solution; mixing an aqueous solution of polyvinylpyrrolidone with the first solution to obtain hollow microspheres PVP.

[0008] Further, the mass-volume ratio of cetyltrimethylammonium bromide to deionized water is: (0.2 - 5) g : 80 mL; preferably, the mass-volume ratio of cetyltrimethylammonium bromide to absolute ethanol is (0.2 - 5) g : 16 mL.

[0009] Further, the molar concentration of polyvinylpyrrolidone in the polyvinylpyrrolidone aqueous solution is 0.2 - 0.8 M; preferably, the average molecular weight of polyvinylpyrrolidone is 38000 - 42000.

[0010] Further, in-situ growth of silica on the inner surface of the hollow microsphere PVP to obtain the hollow microsphere PVP@SiO2 material includes: subjecting the hollow microsphere PVP to ultrasonic treatment to obtain treated microspheres; adding lithium hydroxide to the treated microspheres to obtain alkaline microspheres; adding tetraethyl orthosilicate dropwise to the alkaline microspheres to obtain the hollow microsphere PVP@SiO2 material; preferably, the time for ultrasonic treatment is 10 - 20 min; preferably, the addition amount of lithium hydroxide is 20 - 100 mg; preferably, the molar concentration of tetraethyl orthosilicate is 0.1 - 1 M, and the addition amount is 0.2 - 5 ml.

[0011] Further, adding tetraethyl orthosilicate dropwise to the alkaline microspheres to obtain the hollow microsphere PVP@SiO2 material includes: adding tetraethyl orthosilicate dropwise to the alkaline microspheres and stirring during the dropping process to obtain a reaction product; successively washing the reaction product with a PVP aqueous solution and absolute ethanol, and drying to obtain the hollow microsphere PVP@SiO2 material; preferably, the dropping rate is 5 - 30 drops / min; preferably, the stirring is carried out at 25 - 80 °C, more preferably the stirring speed is 200 - 500 rpm, and the stirring time is 2 - 8 h; preferably, the molar concentration of the PVP aqueous solution is 0.2 - 2 M, and more preferably the reaction product is centrifuged at 5500 - 6200 rpm for 8 - 12 min and washed 1 - 2 times with the PVP aqueous solution; preferably, the reaction product washed with the PVP aqueous solution is centrifuged at 7500 - 8500 rpm for 10 - 20 min and washed 3 - 5 times with absolute ethanol.

[0012] Furthermore, the hollow microsphere PVP@SiO2 material is sintered to obtain a hollow microsphere C@Si material, which includes: placing the hollow microsphere PVP@SiO2 material at 500 - 1000 °C, preferably 750 - 1000 °C, for heat preservation for 2 - 8 h, preferably 4 - 6 h, and then cooling to obtain a hollow microsphere C@SiO2 material; placing the hollow microsphere C@SiO2 material and magnesium powder at 500 - 1000 °C, preferably 550 - 700 °C, for heat preservation for 5 - 10 h, preferably 5 - 8 h, and then cooling to obtain a sintered product; placing the sintered product in a hydrochloric acid solution, and successively performing ultrasonic treatment and stirring to obtain a treated product; centrifugally washing the treated product with hexanol and deionized water 4 - 6 times each, and then drying to obtain a hollow microsphere C@Si; preferably, the heat preservation is carried out under the protection of an inert gas, and more preferably the inert gas is argon; preferably, the mass ratio of the hollow microsphere C@SiO2 material to magnesium powder is 0.5 - 5 g:0.5 - 5 g; preferably, the molar concentration of hydrochloric acid is 0.2 - 2 M, more preferably 0.75 - 1.25 M; preferably, the time of ultrasonic treatment is 10 - 20 min; preferably, the time of stirring is 45 - 75 min; preferably, the centrifugation is carried out at 5000 - 7000 rpm for 5 - 15 min.

[0013] Furthermore, the hollow microsphere C@Si material is coated with lithium titanate to obtain a lithium battery silicon-carbon anode material, which includes: grinding the hollow microsphere C@Si material and lithium titanate to obtain an LTO-C@Si material, and the LTO-C@Si material is the lithium battery silicon-carbon anode material; preferably, the mass ratio of the hollow microsphere C@Si material to lithium titanate is 2 - 10 g:0.2 - 5 g; preferably, the grinding duration is 0.5 - 4 h, and preferably, the particle size after grinding is 15 - 20 μm.

[0014] To achieve the above object, according to the second aspect of the present invention, there is provided a lithium battery silicon-carbon anode material, which is prepared by any of the above preparation methods.

[0015] According to the third aspect of the present invention, there is provided a lithium battery silicon-carbon anode material, which includes a hollow microsphere C layer, a Si layer provided on the inner surface of the hollow microsphere C layer, and a lithium titanate layer coated on the outer surface of the hollow microsphere C layer.

[0016] Furthermore, the inner diameter of the hollow of the hollow microsphere is 9 - 19 times the thickness of the C layer.

[0017] Furthermore, the inner diameter of the hollow of the hollow microsphere is 5 - 15 μm; preferably, the thickness of the lithium titanate layer is 1 - 10 μm; more preferably, the particle size of the lithium battery silicon-carbon anode material is 15 - 20 μm.

[0018] According to the fourth aspect of the present invention, a lithium battery is provided, including a negative electrode, which uses any one of the above-mentioned lithium battery silicon-carbon negative electrode materials.

[0019] Further, when cycling 500 weeks at 45 °C, the discharge capacity retention rate of the lithium battery is 90-96%.

[0020] Applying the technical solution of the present invention, a hollow LTO-C@Si material is prepared by an in-situ growth method. The hollow structure of the LTO-C@Si material can effectively alleviate the impact of the volume expansion of silicon on the electrode structure during cycling, ensuring the continuity of lithium-ion transmission and the integrity of the SEI film. In addition, the lithium titanate (LTO) on the outer layer of the LTO-C@Si material can provide a fast lithium-ion transmission channel, improving the electronic conductivity of the electrode material. At the same time, the large-area lithium titanate layer can balance the electrode surface potential, enabling uniform lithium-ion deposition and avoiding the formation of lithium dendrites. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0022] Figure 1 Shows the AC impedance curve diagrams of the batteries using the negative electrode materials of Example 1, Example 2 and Comparative Example 1 of the present invention.

[0023] Figure 2 Shows that when the battery cycles 500 weeks, the discharge capacity retention rates of the batteries using the negative electrode materials of Example 1, Example 2 and Comparative Example 1 at room temperature (25 °C) are 96.759%, 92.384% and 85.724% respectively.

[0024] Figure 3 Shows that when the battery cycles 500 weeks, the discharge capacity retention rates of the batteries using the negative electrode materials of Example 1, Example 2 and Comparative Example 1 at high temperature (45 °C) are 95.268%, 88.271% and 81.032% respectively. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0026] It should be noted that the expression a@b in this application represents a core-shell structure, b after @ represents the core structure component, a before @ represents the shell structure component. In the expression d-a@b, b also represents the core structure component, d-a represents the shell structure component, and the d layer is on the outer layer of the a layer.

[0027] Polyvinylpyrrolidone: The English abbreviation is PVP.

[0028] Lithium titanate: The English abbreviation is LTO.

[0029] Cetyltrimethylammonium bromide: The English abbreviation is CTAB.

[0030] As mentioned in the background art, there have been various attempts to prepare silicon-carbon anode materials in the prior art. However, the existing methods have limited improvement on battery performance, and it is necessary to further improve. On this basis, the applicant proposes an improved solution for this application.

[0031] In a typical embodiment, a method for preparing a silicon-carbon anode material for a lithium battery is provided. The preparation method includes: self-assembling polyvinylpyrrolidone into hollow microspheres PVP; in-situ growing silica on the inner surface of the hollow microspheres PVP to obtain a hollow microsphere PVP@SiO2 material; sintering the hollow microsphere PVP@SiO2 material to obtain a hollow microsphere C@Si material; coating the hollow microsphere C@Si material with lithium titanate to obtain a silicon-carbon anode material for a lithium battery.

[0032] Compared with the prior art methods of coating a silica layer on the surface of ready-made carbon nanotubes and then coating a carbon layer on the outer layer, or coating a silica layer on the surface of carbon nanotubes, then reducing it to a Si layer, and then coating a carbon layer on the outer layer, the above preparation method of this application forms hollow microspheres PVP by utilizing the advantages of self-assembly of PVP, and then prepares a hollow LTO-C@Si material by in-situ growth on the inner wall surface of the hollow microspheres PVP by utilizing the non-polarity of silica. The hollow structure of the LTO-C@Si material can effectively alleviate the impact of the volume expansion of silicon on the electrode structure during cycling, ensuring the continuity of lithium-ion transport and the integrity of the SEI film. In addition, the lithium titanate (LTO) on the outer layer of the LTO-C@Si material can provide a fast lithium-ion transport channel, improving the electronic conductivity of the electrode material. At the same time, the large-area lithium titanate layer can balance the electrode surface potential, enabling uniform deposition of lithium ions and avoiding the formation of lithium dendrites.

[0033] The advantage of self-assembly is that the internal space of the hollow structure is larger than that of carbon nanotubes, and the hollow structure is not airtight, enabling such a structure to conveniently and quickly load more SiO2 particles. Relatively speaking, more carbon nanotubes are loaded at both ends, and the loading amount of SiO2 in the remaining space may be relatively small, that is, the uneven distribution affects the uniformity of the position of silicon during volume expansion during cycling, thereby affecting battery performance. And the existence of Si in the form of Si on the inner surface of the hollow microspheres has a relatively smaller impact on battery performance than in the form of SiO2, while improving the initial efficiency of the battery.

[0034] The above-mentioned self-assembly of polyvinylpyrrolidone into hollow microspheres PVP includes: mixing an aqueous solution of cetyltrimethylammonium bromide in deionized water with absolute ethanol to obtain a first solution; mixing an aqueous solution of polyvinylpyrrolidone with the first solution to obtain hollow microspheres PVP. As a cationic surfactant, cetyltrimethylammonium bromide can play a good dispersing role in PVP. PVP is soluble in water and ethanol.

[0035] In the above preparation method, the mass-volume ratio of cetyltrimethylammonium bromide to deionized water is: (0.2 - 5) g : 80 mL; preferably, the mass-volume ratio of cetyltrimethylammonium bromide to absolute ethanol is (0.2 - 5) g : 16 mL. Within this dosage range, it has the beneficial effects of facilitating the dissolution and dispersion of PVP and promoting the self-assembly of PVP into monolayer ordered microspheres.

[0036] Preferably, the molar concentration of polyvinylpyrrolidone in the aqueous solution of polyvinylpyrrolidone is 0.2 - 0.8 M, such as 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, or 0.8 M. PVP at this concentration has the advantages of facilitating the dissolution and dispersion of PVP.

[0037] Preferably, the average molecular weight of polyvinylpyrrolidone is 38000 - 42000, such as 38000, 39000, 40000, 41000, or 42000. PVP with a molecular weight in this range has the beneficial effect of forming hollow microspheres with a diameter of 5 - 15 μm compared to PVP with a larger or smaller molecular weight.

[0038] Since PVP is small particles (PVP is a long-chain polymer that self-assembles into hollow microspheres after decomposition, and here the particle size is not limited as long as there is a molecular weight limit), it can connect and self-assemble into large hollow spherical particles (with an average particle size of 5 - 15 μm) one by one in an aqueous solution. There are gaps between each small particle, so subsequently under alkaline conditions, SiO2 can preferentially grow in situ on the hydrophobic inner surface of the hollow microspheres due to its non-polarity. When PVP self-assembles, it can be carried out according to the existing self-assembly conditions or reasonably adjusted according to actual needs on the existing conditions. The addition amount of each raw material is based on the amount of Si generated, that is, the expanded volume of Si after cycling does not exceed the internal hollow volume of the hollow microspheres.

[0039] In a preferred embodiment of the present application, the in-situ growth of silica on the inner surface of the hollow microsphere PVP to obtain the hollow microsphere PVP@SiO2 material includes: subjecting the hollow microsphere PVP to ultrasonic treatment to obtain treated microspheres; adding lithium hydroxide to the treated microspheres to obtain alkaline microspheres; and dropping tetraethyl orthosilicate into the alkaline microspheres to obtain the hollow microsphere PVP@SiO2 material. Preferably, the time of ultrasonic treatment is 10-20 min; preferably, the addition amount of lithium hydroxide is 20-100 mg; preferably, the molar concentration of tetraethyl orthosilicate is 0.1-1 M, and the addition amount is 0.2-5 ml. When the amount of tetraethyl orthosilicate used is more than this range, relatively more Si is generated, resulting in a relatively smaller inner intermediate space. In the case of excessive use, even Si particles will be generated outside the microspheres, which will affect the material and battery performance.

[0040] The ultrasonic treatment of the hollow microsphere PVP is to make the hollow microsphere PVP disperse evenly, so that SiO2 grows in-situ on the inner wall of the hollow microsphere, and SiO2 is evenly dispersed and free of agglomeration. Lithium hydroxide provides an alkaline environment to enable tetraethyl orthosilicate to generate SiO2 under alkaline conditions. Among them, the time of ultrasonic treatment is based on uniform dispersion, and the effect of uniform dispersion can usually be achieved within the above preferred time range. The addition amount of tetraethyl orthosilicate is calculated based on the volume of the hollow microsphere, and the converted volume of Si after expansion should not exceed the hollow volume inside the hollow microsphere. Denote the inner hollow inner diameter of the innermost layer as r1 and the thickness of the C layer as r2, then r1=(9-19)r2. The purpose of such a design ratio is to make the hollow volume 3-5 times that of the C layer volume. Because the volume expansion of silicon carbide is close to 300%, the reserved space volume is at least 3 times that of the C layer volume, and too large will result in too little silicon loading, and the specific capacity of the negative electrode material will not increase significantly.

[0041] In a preferred embodiment, the method of adding tetraethyl orthosilicate to alkaline microspheres to obtain the hollow microsphere PVP@SiO2 material includes: adding tetraethyl orthosilicate to alkaline microspheres and stirring during the addition to obtain a reaction product; successively washing the reaction product with a PVP aqueous solution and absolute ethanol, and drying to obtain the hollow microsphere PVP@SiO2 material. Further preferably, the dropping rate is 5 to 30 drops / min, and this dropping rate helps the reaction to be more complete. Preferably, the stirring is carried out at 25 - 80 °C, more preferably the stirring speed is 200 - 500 rpm, and the stirring time is 2 - 8 h. The higher the temperature, the faster the speed, and the longer the time, the more beneficial it is for the complete reaction to decompose the molecular weight of orthosilicic acid into silicon dioxide. Preferably, the molar concentration of the PVP aqueous solution is 0.2 - 2 M. At this concentration, it is beneficial for PVP to dissolve and disperse. More preferably, the reaction product is washed by centrifugation at 5500 - 6200 rpm for 8 - 12 min with the PVP aqueous solution for 1 - 2 times; preferably, the reaction product washed with the PVP aqueous solution is washed by centrifugation at 7500 - 8500 rpm for 10 - 20 min with absolute ethanol for 3 - 5 times.

[0042] The washing method of first centrifuging and washing with a PVP aqueous solution and then using absolute ethanol for centrifuging and washing has the advantages of removing the excess unassembled PVP and separating more quickly and thoroughly compared with the existing method of only washing with deionized water. Compared with the washing method using deionized water and alcohol, it has the advantage of removing the excess unassembled PVP. The centrifugation speed during PVP washing is lower than that during absolute ethanol washing, considering that too high a centrifugation speed during PVP washing will damage the self-assembled hollow microspheres. The number of washing times is determined according to the amount of impurities in the product. The more times, the cleaner the removal of the excess unassembled PVP molecules, which is beneficial to ensuring the integrity and purity of the particles in the composite material, increasing the silicon content, and improving the battery performance.

[0043] The above-mentioned method of sintering the hollow microsphere PVP@SiO2 material can adopt a known sintering method to carbonize the carbon source PVP into a C layer and sinter and reduce the SiO2 layer into an Si layer, thereby obtaining the hollow microsphere C@Si material. The specific sintering conditions can be reasonably set according to the actual situation. In a preferred embodiment of the present application, the sintering step includes: placing the hollow microsphere PVP@SiO2 material at 500-1000 °C, preferably 750-1000 °C, more preferably 800 °C, 850 °C, 900 °C or 950 °C for heat preservation for 2-8 h, preferably 4-6 h, and then cooling to obtain the hollow microsphere C@SiO2 material; placing the hollow microsphere C@SiO2 material and magnesium powder at 500-1000 °C, preferably 550-700 °C, more preferably 600 °C, 650 °C, 700 °C for heat preservation for 5-10 h, preferably 5-8 h, more preferably 5 h, 6 h, 7 h or 8 h, and then cooling to obtain a sintered product; placing the sintered product in a hydrochloric acid solution, and performing ultrasonic treatment and stirring in sequence to obtain a treated product; centrifugally washing the treated product with hexanol and deionized water 4-6 times each, and then drying to obtain the hollow microsphere C@Si. Further, preferably, the heat preservation is carried out under the protection of an inert gas, more preferably the inert gas is argon; preferably, the mass ratio of the hollow microsphere C@SiO2 material to magnesium powder is 0.5-5 g:0.5-5 g; preferably, the molar concentration of hydrochloric acid is 0.2-2 M, more preferably 0.75-1.25 M; preferably, the time of ultrasonic treatment is 10-20 min; preferably, the time of stirring is 45-75 min; preferably, the centrifugation is carried out at 5000-7000 rpm for 5-15 min.

[0044] The specific coating method for coating lithium titanate on the hollow microsphere C@Si material can adopt an existing method for secondary coating. In the present application, the preferred step of coating lithium titanate includes: grinding the hollow microsphere C@Si material and lithium titanate to obtain the LTO-C@Si material, and the LTO-C@Si material is the silicon-carbon negative electrode material for lithium batteries. Further preferably, the mass ratio of the hollow microsphere C@Si material to lithium titanate is 2-10 g:0.2-5 g. Grinding according to this mass ratio helps to improve the coating effect of LTO. Preferably, the grinding duration is 0.5-4 h, more preferably 1-2 h. If the grinding time is too long, the core-shell structure of the material may be damaged, and if the grinding time is too short, the coating effect of LTO may be poor. After grinding, the particle size is preferably controlled at 15-20 μm. If the particles are too large, it is not conducive to the preparation of the negative electrode slurry and the coating effect is poor. If the particles are too small, it means that the LTO coating is incomplete, which will reduce the conductivity of the material and affect the performance of the composite material and the battery.

[0045] In the second typical embodiment of the present application, a silicon-carbon negative electrode material for a lithium battery is provided, and the silicon-carbon negative electrode material for a lithium battery is prepared by using any one of the above preparation methods.

[0046] In the third typical embodiment of the present application, a silicon-carbon anode material for lithium batteries is provided. The silicon-carbon anode material for lithium batteries includes a hollow microsphere C layer, a Si layer disposed on the inner surface of the hollow microsphere C layer, and a lithium titanate layer coated on the outer surface of the hollow microsphere C layer.

[0047] Preferably, the inner hollow diameter of the hollow microsphere is 9 to 19 times the thickness of the C layer. Denote the innermost hollow diameter as r1 and the thickness of the C layer as r2, then r1 = (9 - 19)r2. The purpose of such a design ratio is to make the hollow volume 3 to 5 times the volume of the C layer. Since the volume expansion of silicon-carbon is close to 300%, the reserved space volume is at least 3 times the volume of the C layer, while being too large will result in too little silicon loading and an insignificant increase in the specific capacity of the anode material.

[0048] Preferably, the thickness of the lithium titanate layer is 1 to 10 μm.

[0049] In the fourth typical embodiment of the present application, a lithium battery is provided, including a negative electrode. Among them, the negative electrode uses the above-mentioned silicon-carbon anode material for lithium batteries. Preferably, when cycled 500 weeks at 45 °C, the discharge capacity retention rate of the lithium battery of the present application is 90 - 96%.

[0050] The beneficial effects of the present application will be further described below in conjunction with specific embodiments.

[0051] Example 1

[0052] Take a mixed solution of deionized water and absolute ethanol containing 0.5 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL) and mix it with an aqueous solution of polyvinylpyrrolidone (PVP) (Mw: ~40,000) (0.4 M, 50 mL). After ultrasonic treatment for 15 min, add 50 mg of lithium hydroxide and stir to dissolve. Then, measure 0.8 mL of tetraethyl orthosilicate (0.3 M) and add it dropwise to the above solution, and stir at 40 °C for 6 h. Finally, wash the solution with an aqueous solution of PVP (0.8 M) by centrifugation (6,000 rpm, 10 min) once, and then wash it repeatedly with absolute ethanol by centrifugation (8,000 rpm, 15 min) four times. After drying, hollow microspheres PVP@SiO2 are obtained.

[0053] Put the above sample into a tubular furnace, keep it at 800 °C for 5 h under an argon protection atmosphere, and obtain a hollow microsphere C@SiO2 sample after cooling.

[0054] Weigh 1.5 g of the C@SiO2 sample and 1 g of magnesium powder according to the reaction equation ratio of silicon dioxide to magnesium. After fully grinding, transfer them into a tubular furnace and keep them at 650 °C for 6 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (1 M), ultrasonicate for 15 min, and then stir for 1 h. Then, centrifuge the residue with hexanol and deionized water (6,000 rpm, 10 min) and wash it five times each, and finally dry it to obtain the hollow C@Si sample.

[0055] Take 5 g of the prepared hollow C@Si sample and 2 g of lithium titanate (LTO), put them into a mortar and grind for 2 h, and finally prepare the sample material, denoted as LTO-C@Si-1.

[0056] Example 2

[0057] Mix the mixed solution of deionized water and absolute ethanol containing 0.2 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL) with an aqueous solution of polyvinylpyrrolidone (PVP) (Mw: ~40,000) (0.2 M, 30 mL). After ultrasonication for 15 min, add 30 mg of lithium hydroxide and stir to dissolve. Then, measure 0.2 mL of tetraethyl orthosilicate (0.1 M) and add it dropwise to the above solution, and stir at 30 °C for 2 h. Finally, wash the solution with an aqueous PVP solution (0.5 M) by centrifugation (6,000 rpm, 10 min) once, and then wash it repeatedly with absolute ethanol by centrifugation (8,000 rpm, 15 min) four times. After drying, obtain the hollow microsphere PVP@SiO2.

[0058] Put the above sample into a tubular furnace and keep it at 700 °C for 2 h under an argon protection atmosphere. After cooling, obtain the hollow microsphere C@SiO2 sample.

[0059] Weigh 0.5 g of the C@SiO2 sample and 0.5 g of magnesium powder according to the reaction equation ratio of silicon dioxide to magnesium. After fully grinding, transfer them into a tubular furnace and keep them at 500 °C for 5 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (0.5 M), ultrasonicate for 15 min, and then stir for 1 h. Then, centrifuge the residue with hexanol and deionized water (6,000 rpm, 10 min) and wash it five times each, and finally dry it to obtain the hollow C@Si sample.

[0060] Take 2 g of the prepared hollow C@Si sample and 0.2 g of lithium titanate (LTO), put them into a mortar and grind for 0.5 h, and finally prepare the sample material, denoted as LTO-C@Si-2.

[0061] Comparative Example 1

[0062] Mix deionized water and absolute ethanol mixed solution containing 0.5 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL). After ultrasonic treatment for 15 min, add 50 mg of lithium hydroxide and stir to dissolve. Then, measure 0.8 mL of tetraethyl orthosilicate (0.3 M) and add it dropwise to the above solution, and stir at 40 °C for 6 h. Finally, wash it four times by repeated centrifugation (8,000 rpm, 15 min) with absolute ethanol, and obtain nano-SiO2 particles after drying.

[0063] Weigh 1.5 g of SiO2 sample and 1 g of magnesium powder according to the reaction equation ratio of silicon dioxide and magnesium. After thorough grinding, transfer them into a tube furnace and keep them at 650 °C for 6 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (1 M), perform ultrasonic treatment for 15 min, and then stir for 1 h. Then, wash the residue five times each by centrifugation (6,000 rpm, 10 min) with hexanol and deionized water, and finally dry to obtain a hollow Si sample.

[0064] Take 5 g of the prepared hollow Si sample, 1 g of lithium titanate (LTO), and 1 g of graphite, put them into a mortar, and grind for 2 h to finally prepare a sample material, denoted as LTO-C-Si.

[0065] For the anode materials of the above Examples 1 and 2 and Comparative Example 1, under the condition that other battery components are the same, assemble them into batteries for performance testing. Among them, Figure 1 are the AC impedance curves of the batteries with LTO-C@Si-1, LTO-C@Si-2, and LTO-C-Si as the anode materials. It can be clearly seen from Figure 1 that the impedance of the anode material of LTO-C@Si-1 is significantly lower than that of the other two materials.

[0066] Figure 2 and Figure 3 are the cycling curves of the three anode materials at room temperature (25 °C) and high temperature (45 °C) respectively. It can be seen from Figure 2 that when the battery is cycled 500 times, the discharge capacity retention rates of the batteries with LTO-C@Si-1, LTO-C@Si-2, and LTO-C-Si as the materials are 96.759%, 92.384%, and 85.724% respectively. It can be seen from Figure 3 that when the battery is cycled 500 times, the discharge capacity retention rates of the batteries with LTO-C@Si-1, LTO-C@Si-2, and LTO-C-Si as the materials are 95.268%, 88.271%, and 81.032% respectively. By comparison, it is found that the LTO-C@Si-1 material has better electrochemical performance.

[0067] Example 3

[0068] A deionized water and absolute ethanol mixed solution containing 1 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL) was mixed with an aqueous solution of polyvinylpyrrolidone (PVP) (Mw: 38,000) (0.2 M, 200 mL). After ultrasonic treatment for 15 min, 20 mg of lithium hydroxide was added and stirred until dissolved. Then, 3 mL of tetraethyl orthosilicate (0.1 M) was added dropwise to the above solution and stirred at 25 °C for 8 h. Finally, the solution was washed once with an aqueous PVP solution (0.2 M) by centrifugation (6,500 rpm, 5 min), and then repeatedly washed with absolute ethanol by centrifugation (8,500 rpm, 5 min) four times. After drying, hollow microspheres PVP@SiO2 were obtained.

[0069] The above sample was placed in a tube furnace and kept at 500 °C for 8 h under an argon protective atmosphere. After cooling, a hollow microsphere C@SiO2 sample was obtained.

[0070] According to the reaction equation ratio of silicon dioxide and magnesium, 0.5 g of the C@SiO2 sample and 0.6 g of magnesium powder were weighed, thoroughly ground and then transferred into a tube furnace. It was kept at 500 °C for 10 h under an argon protective atmosphere. After cooling, the product was placed in a dilute hydrochloric acid solution (0.2 M), ultrasonicated for 15 min and then stirred for 1 h. Then, the residue was washed five times each with hexanol and deionized water by centrifugation (5,800 rpm, 14 min). Finally, after drying, hollow C@Si samples were obtained.

[0071] 2 g of the prepared hollow C@Si sample and 0.2 g of lithium titanate (LTO) were taken and placed in a mortar and ground for 0.5 h. Finally, the sample material was prepared and denoted as LTO-C@Si-3.

[0072] Example 4

[0073] A deionized water and absolute ethanol mixed solution containing 2.5 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL) was mixed with an aqueous solution of polyvinylpyrrolidone (PVP) (Mw: ~41,000) (0.6 M, 250 mL). After ultrasonic treatment for 15 min, 75 mg of lithium hydroxide was added and stirred until dissolved. Then, 1 mL of tetraethyl orthosilicate (0.5 M) was added dropwise to the above solution and stirred at 60 °C for 4 h. Finally, the solution was washed once with an aqueous PVP solution (1 M) by centrifugation (5,500 rpm, 15 min), and then repeatedly washed with absolute ethanol by centrifugation (7,500 rpm, 20 min) four times. After drying, hollow microspheres PVP@SiO2 were obtained.

[0074] The above sample was placed in a tube furnace and kept at 700 °C for 6 h under an argon protective atmosphere. After cooling, a hollow microsphere C@SiO2 sample was obtained.

[0075] Weigh 3.5 g of the C@SiO2 sample and 3 g of magnesium powder according to the reaction equation ratio of silicon dioxide to magnesium. After thorough grinding, transfer them into a tube furnace and keep them at 850 °C for 7 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (1 M), sonicate for 15 min, and then stir for 1 h. Then, wash the residue five times each with hexanol and deionized water by centrifugation (6,000 rpm, 10 min), and finally dry to obtain the hollow C@Si sample.

[0076] Take 6 g of the prepared hollow C@Si sample and 4 g of lithium titanate (LTO), put them into a mortar, and grind for 1 h to finally obtain the sample material, denoted as LTO-C@Si-4.

[0077] Example 5

[0078] Mix a mixed solution of deionized water and absolute ethanol containing 5 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL) with an aqueous solution of polyvinylpyrrolidone (PVP) (Mw: ~42,000) (0.8 M, 300 mL). After sonication for 15 min, add 100 mg of lithium hydroxide and stir to dissolve. Then, measure 0.4 mL of tetraethyl orthosilicate (1 M) and add it dropwise to the above solution, and stir at 80 °C for 2 h. Finally, wash the solution with an aqueous PVP solution (2 M) by centrifugation (6,000 rpm, 8 min) once, and then wash it repeatedly with absolute ethanol by centrifugation (8,200 rpm, 13 min) four times, and obtain the hollow microspheres PVP@SiO2 after drying.

[0079] Put the above sample into a tube furnace and keep it at 1000 °C for 5 h under an argon protection atmosphere, and obtain the hollow microspheres C@SiO2 sample after cooling.

[0080] Weigh 5 g of the C@SiO2 sample and 4.8 g of magnesium powder according to the reaction equation ratio of silicon dioxide to magnesium. After thorough grinding, transfer them into a tube furnace and keep them at 1000 °C for 5 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (2 M), sonicate for 15 min, and then stir for 1 h. Then, wash the residue five times each with hexanol and deionized water by centrifugation (6,500 rpm, 6 min), and finally dry to obtain the hollow C@Si sample.

[0081] Take 10 g of the prepared hollow C@Si sample and 5 g of lithium titanate (LTO), put them into a mortar, and grind for 4 h to finally obtain the sample material, denoted as LTO-C@Si-5.

[0082] Example 6

[0083] Take a mixed solution of deionized water and anhydrous ethanol containing 5g of hexadecyltrimethylammonium bromide (80mL of deionized water and 16mL of anhydrous ethanol) and mix it with a polyvinylpyrrolidone (PVP) (Mw: ~50,000) aqueous solution (0.8M, 50mL). After ultrasonication for 15min, add 100mg of lithium hydroxide and stir to dissolve. Then, add 0.4mL of tetraethyl orthosilicate (1M) dropwise to the above solution and stir at 80℃ for 2h. Finally, wash the solution (2M) with PVP aqueous solution by centrifugation (6,000rpm, 8min) once, and then wash it four times with anhydrous ethanol by repeated centrifugation (8,200rpm, 13min)), and obtain hollow microspheres PVP@SiO2 after drying.

[0084] The above sample was placed in a tubular furnace and kept at 1000°C for 5 h under an argon protective atmosphere. After cooling, a hollow microsphere C@SiO2 sample was obtained.

[0085] According to the reaction equation of silicon dioxide and magnesium, 5g C@SiO2 sample and 4.8g magnesium powder were weighed, fully ground and moved into a tube furnace, and kept at 1000℃ for 5h under argon protection atmosphere. After cooling, the product was placed in a dilute hydrochloric acid solution (2M), ultrasonicated for 15min, and stirred for 1h. Then, the residue was washed five times each with hexanol and deionized water by centrifugation (6,500rpm, 6min), and finally dried to obtain a hollow C@Si sample.

[0086] 10 g of the prepared hollow C@Si sample and 5 g of lithium titanate (LTO) were put into a mortar and ground for 4 h to finally prepare the sample material, which was recorded as LTO-C@Si-6.

[0087] Example 7

[0088] Take a mixed solution of deionized water and anhydrous ethanol containing 5g of hexadecyltrimethylammonium bromide (80mL of deionized water and 16mL of anhydrous ethanol) and mix it with a polyvinylpyrrolidone (PVP) (Mw: ~42,000) aqueous solution (0.8M, 25mL). After ultrasonication for 15min, add 100mg of lithium hydroxide and stir to dissolve. Then, measure 1mL of tetraethyl orthosilicate (1.1M) and add it dropwise to the above solution, stirring at 80℃ for 2h. Finally, wash the solution (2M) with PVP aqueous solution by centrifugation (6,000rpm, 8min) once, and then wash it four times with anhydrous ethanol by repeated centrifugation (8,200rpm, 13min)), and obtain hollow microspheres PVP@SiO2 after drying.

[0089] The above sample was placed in a tubular furnace and kept at 1000°C for 5 h under an argon protective atmosphere. After cooling, a hollow microsphere C@SiO2 sample was obtained.

[0090] Weigh 5 g of the C@SiO2 sample and 4.8 g of magnesium powder according to the reaction equation ratio of silicon dioxide to magnesium. After thoroughly grinding, transfer them into a tubular furnace and keep them at 1000 °C for 5 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (2 M), sonicate for 15 min, and then stir for 1 h. Then, centrifuge the residue with hexanol and deionized water (6,500 rpm, 6 min) and wash it five times each. Finally, dry it to obtain the hollow C@Si sample.

[0091] Take 10 g of the prepared hollow C@Si sample and 5 g of lithium titanate (LTO), put them into a mortar, and grind for 4 h. Finally, prepare the sample material, denoted as LTO-C@Si-7.

[0092] Example 8

[0093] Mix the deionized water and anhydrous ethanol mixed solution containing 5 g of cetyltrimethylammonium bromide (where the deionized water is 80 mL and the anhydrous ethanol is 16 mL) with an aqueous solution of polyvinylpyrrolidone (PVP) (Mw: ~42,000) (0.8 M, 300 mL). After sonication for 15 min, add 100 mg of lithium hydroxide and stir to dissolve. Then, measure 0.1 mL of tetraethyl orthosilicate (1 M) and add it dropwise to the above solution, and stir at 80 °C for 2 h. Finally, wash the solution with an aqueous PVP solution (2 M) by centrifugation (6,000 rpm, 8 min) once, and then wash it repeatedly with anhydrous ethanol by centrifugation (8,200 rpm, 13 min) four times. After drying, obtain the hollow microspheres PVP@SiO2.

[0094] Put the above sample into a tubular furnace and keep it at 1000 °C for 5 h under an argon protection atmosphere. After cooling, obtain the hollow microspheres C@SiO2 sample.

[0095] Weigh 5 g of the C@SiO2 sample and 4.8 g of magnesium powder according to the reaction equation ratio of silicon dioxide to magnesium. After thoroughly grinding, transfer them into a tubular furnace and keep them at 1000 °C for 5 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (2 M), sonicate for 15 min, and then stir for 1 h. Then, centrifuge the residue with hexanol and deionized water (6,500 rpm, 6 min) and wash it five times each. Finally, dry it to obtain the hollow C@Si sample.

[0096] Take 1 g of the prepared hollow C@Si sample and 5 g of lithium titanate (LTO), put them into a mortar, and grind for 4 h. Finally, prepare the sample material, denoted as LTO-C@Si-8.

[0097] Comparative Example 2

[0098] Mix a mixed solution of deionized water and absolute ethanol containing 0.5 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL). After ultrasonic treatment for 15 min, add 50 mg of lithium hydroxide and stir to dissolve. Add carbon nanotubes to the above solution in a mass ratio of carbon nanotubes:ethanol solution of 1:1000 and stir evenly. Then, measure 0.8 mL of tetraethyl orthosilicate (0.3 M) and add it dropwise to the above solution, and stir at 40 °C for 6 h. Finally, wash the solution with an aqueous PVP solution (0.8 M) by centrifugation (6,000 rpm, 10 min) once, and then wash it repeatedly with absolute ethanol by centrifugation (8,000 rpm, 15 min) four times. After drying, carbon nanotube / SiO2 is obtained.

[0099] Mix carbon nanotube / SiO2 and sucrose evenly in a mass ratio of 1:1, and put them into deionized water to form a sucrose solution, and stir evenly. Then dry at 110 °C to remove moisture. Subsequently, sinter at 700 °C for 3 h under the protection of an argon atmosphere, and a carbon nanotube / SiO2 / carbon composite anode material is obtained after cooling.

[0100] Comparative Example 3

[0101] Mix a mixed solution of deionized water and absolute ethanol containing 0.5 g of cetyltrimethylammonium bromide (where deionized water is 80 mL and absolute ethanol is 16 mL). After ultrasonic treatment for 15 min, add 50 mg of lithium hydroxide and stir to dissolve. Add carbon nanotubes to the above solution in a mass ratio of carbon nanotubes:ethanol solution of 1:1000 and stir evenly. Then, measure 0.8 mL of tetraethyl orthosilicate (0.3 M) and add it dropwise to the above solution, and stir at 40 °C for 6 h. Finally, wash the solution with an aqueous PVP solution (0.8 M) by centrifugation (6,000 rpm, 10 min) once, and then wash it repeatedly with absolute ethanol by centrifugation (8,000 rpm, 15 min) four times. After drying, carbon nanotube / SiO2 is obtained.

[0102] Weigh 1.5 g of carbon nanotube / SiO2 sample and 1 g of magnesium powder according to the reaction equation ratio of silicon dioxide and magnesium. After sufficient grinding, transfer them into a tubular furnace and keep them at 650 °C for 6 h under an argon protection atmosphere. After cooling, put the product into a dilute hydrochloric acid solution (1 M), ultrasonic for 15 min, and then stir for 1 h. Then, wash the residue with hexanol and deionized water by centrifugation (6,000 rpm, 10 min) five times each, and finally dry to obtain carbon nanotube / Si sample.

[0103] Take 5 g of the prepared carbon nanotube / Si sample and 2 g of lithium titanate (LTO), put them into a mortar and grind for 2 h, and finally prepare a carbon nanotube / Si / LTO composite anode material.

[0104] For the negative electrode materials of the above Examples 3-9 and Comparative Examples 2 and 3, under the condition that other battery components are the same, batteries were assembled for performance testing. The test results are shown in Table 1.

[0105] Table 1:

[0106] Performance parameters Discharge capacity retention rate after 500 cycles at 25°C Discharge capacity retention rate after 500 cycles at 45°C Example 1 96.759 95.268 Example 2 92.384 88.271 Example 3 90.256 87.496 Example 4 91.232 89.179 Example 5 89.939 87.396 Example 6 88.633 86.278 Example 7 88.535 86.265 Example 8 94.813 90.378 Comparative example 1 85.724 81.032 Comparative example 2 87.223 83.578 Comparative example 3 88.001 84.714

[0107] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: The hollow LTO-C@Si material is prepared by an in-situ growth method. The hollow structure of the LTO-C@Si material can effectively alleviate the impact of the volume expansion of silicon on the electrode structure during cycling, ensuring the continuity of lithium-ion transmission and the integrity of the SEI film. In addition, the lithium titanate (LTO) on the outer layer of the LTO-C@Si material can provide a fast lithium-ion transmission channel, improving the electronic conductivity of the electrode material. At the same time, the large-area lithium titanate layer can balance the electrode surface potential, enabling uniform lithium-ion deposition and avoiding the formation of lithium dendrites.

[0108] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a silicon-carbon anode material for a lithium battery, characterized in that, The preparation method includes: Self-assembling polyvinylpyrrolidone into hollow microspheres PVP; In-situ growing silica on the inner surface of the hollow microspheres PVP to obtain a hollow microsphere PVP@SiO2 material; Sintering the hollow microsphere PVP@SiO2 material to obtain a hollow microsphere C@Si material; Coating lithium titanate on the hollow microsphere C@Si material to obtain the silicon-carbon anode material for lithium batteries.

2. The preparation method according to claim 1, characterized in that, Self-assembling polyvinylpyrrolidone into hollow microspheres PVP includes: Mixing an aqueous solution of cetyltrimethylammonium bromide with deionized water and absolute ethanol to obtain a first solution; Mixing an aqueous solution of polyvinylpyrrolidone with the first solution to obtain the hollow microspheres PVP.

3. The preparation method according to claim 2, wherein The mass-volume ratio of the cetyltrimethylammonium bromide to deionized water is: (0.2~5) g: 80 mL.

4. The preparation method according to claim 3, characterized in that, The mass-volume ratio of the cetyltrimethylammonium bromide to the absolute ethanol is (0.2~5) g: 16 mL.

5. The preparation method according to claim 2, characterized in that, The molar concentration of polyvinylpyrrolidone in the aqueous solution of polyvinylpyrrolidone is 0.2~0.8 M.

6. The preparation method according to claim 5, wherein The average molecular weight of the polyvinylpyrrolidone is 38000~42000.

7. The preparation method according to claim 1, characterized in that, In-situ growing silica on the inner surface of the hollow microspheres PVP to obtain a hollow microsphere PVP@SiO2 material includes: Subjecting the hollow microspheres PVP to ultrasonic treatment to obtain treated microspheres; Adding lithium hydroxide to the treated microspheres to obtain basic microspheres; Adding tetraethyl orthosilicate dropwise to the basic microspheres to obtain the hollow microsphere PVP@SiO2 material.

8. The preparation method according to claim 7, characterized in that, The time for the ultrasonic treatment is 10~20 min.

9. The preparation method according to claim 7, characterized in that, The addition amount of the lithium hydroxide is 20~100 mg.

10. The preparation method according to claim 7, characterized in that, The molar concentration of the tetraethyl orthosilicate is 0.1~1 M, and the addition amount is 0.2~5 mL.

11. The preparation method according to claim 7, characterized in that, Adding tetraethyl orthosilicate dropwise to the basic microspheres to obtain the hollow microsphere PVP@SiO2 material includes: Adding tetraethyl orthosilicate dropwise to the basic microspheres and stirring during the dropping process to obtain a reaction product; Washing the reaction product successively with an aqueous solution of PVP and absolute ethanol, and drying to obtain the hollow microsphere PVP@SiO2 material.

12. The preparation method according to claim 11, wherein, The dropping rate is 5~30 drops / min.

13. The preparation method according to claim 11, wherein The stirring is carried out at 25 - 80 °C.

14. The preparation method according to claim 13, wherein The stirring speed is 200~500 rpm, and the stirring time is 2~8 h.

15. The preparation method according to claim 11, characterized in that, The molar concentration of the aqueous solution of PVP is 0.2 - 2 M.

16. The preparation method according to claim 15, wherein, Washing the reaction product with an aqueous solution of PVP by centrifugation at 5500 - 6200 rpm for 8 - 12 min for 1~2 times.

17. The preparation method according to claim 11, wherein, Washing the reaction product after being washed with the aqueous solution of PVP with absolute ethanol by centrifugation at 7500~8500 rpm for 10 - 20 min for 3~5 times.

18. The preparation method according to claim 1, characterized in that, Sintering the hollow microsphere PVP@SiO2 material to obtain a hollow microsphere C@Si material includes: Placing the hollow microsphere PVP@SiO2 material at 500~1000 °C for heat preservation for 2 - 8 h and then cooling to obtain a hollow microsphere C@SiO2 material; Put the hollow microsphere C@SiO2 material and magnesium powder at 500-1000 °C for heat preservation for 5-10 h and then cool to obtain a sintered product; Put the sintered product into a hydrochloric acid solution, and perform ultrasonic treatment and stirring in sequence to obtain a treated product; Centrifuge and wash the treated product with hexanol and deionized water 4-6 times each, and then dry to obtain the hollow microsphere C@Si.

19. The preparation method according to claim 18, characterized in that, Keep the hollow microsphere PVP@SiO2 material at 750-1000 °C for heat preservation.

20. The preparation method according to claim 18 or 19, characterized in that, After heat preservation for 4-6 h, cool to obtain the hollow microsphere C@SiO2 material.

21. The preparation method according to claim 20, characterized in that, Put the hollow microsphere C@SiO2 material and magnesium powder at 550-700 °C for heat preservation.

22. The preparation method according to claim 21, characterized in that, After heat preservation for 5-8 h, cool to obtain the sintered product.

23. The preparation method according to claim 18, wherein The heat preservation is carried out under the protection of an inert gas.

24. The preparation method according to claim 23, wherein The inert gas is argon.

25. The preparation method according to claim 18, characterized in that, The mass ratio of the hollow microsphere C@SiO2 material to magnesium powder is 0.5-5 g: 0.5-5 g.

26. The preparation method according to claim 18, wherein, The molar concentration of the hydrochloric acid is 0.2-2 M.

27. The preparation method according to claim 26, wherein The molar concentration of the hydrochloric acid is 0.75-1.25 M.

28. The preparation method according to claim 18, wherein, The time of the ultrasonic treatment is 10-20 min.

29. The preparation method according to claim 18, characterized in that, The time of the stirring is 45-75 min.

30. The preparation method according to claim 18, characterized in that, The centrifugation is carried out at 5000-7000 rpm for 5-15 min.

31. The preparation method according to claim 1, characterized in that, Coat the hollow microsphere C@Si material with lithium titanate to obtain the lithium battery silicon-carbon negative electrode material, including: Grind the hollow microsphere C@Si material and lithium titanate to obtain the LTO-C@Si material, and the LTO-C@Si material is the lithium battery silicon-carbon negative electrode material.

32. The preparation method according to claim 31, wherein The mass ratio of the hollow microsphere C@Si material to lithium titanate is 2-10 g: 0.2-5 g.

33. The preparation method according to claim 31, wherein, The duration of the grinding is 0.5-4 h.

34. The preparation method according to claim 31, characterized in that, The particle size after grinding is 15-20 μm.

35. A silicon-carbon anode material for lithium batteries, characterized in that, The lithium battery silicon-carbon negative electrode material is prepared by using the preparation method described in any one of claims 1 to 34.

36. A silicon-carbon anode material for lithium batteries, characterized in that, The lithium battery silicon-carbon negative electrode material includes a C layer of hollow microspheres, a Si layer provided on the inner surface of the C layer of the hollow microspheres, and a lithium titanate layer coated on the outer surface of the C layer of the hollow microspheres.

37. The silicon-carbon anode material for lithium batteries according to claim 36, characterized in that, The inner diameter of the hollow of the hollow microspheres is 9-19 times the thickness of the C layer.

38. The silicon-carbon anode material for lithium batteries according to claim 37, wherein The inner diameter of the hollow of the hollow microspheres is 5-15 μm.

39. The silicon-carbon anode material for lithium batteries according to claim 38, wherein The thickness of the lithium titanate layer is 1-10 μm.

40. The silicon-carbon anode material for lithium batteries according to claim 39, wherein The particle size of the lithium battery silicon-carbon negative electrode material is 15-20 μm.

41. A lithium battery, comprising a negative electrode, characterized in that, The negative electrode uses the lithium battery silicon-carbon negative electrode material described in any one of claims 35-40.

42. The lithium battery according to claim 41, characterized in that, When cycling 500 weeks at 45 °C, the discharge capacity retention rate of the lithium battery is 90-96%.

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