A composite negative electrode material for lithium ion batteries, a preparation method and a lithium ion battery

Abstract

The application discloses a kind of composite negative material for lithium ion battery, preparation method and lithium ion battery.The preparation method of composite negative material Si-xSiO2@EG@C for lithium ion battery of the application includes the following steps: S1, in expanded stone graphite, join water ultrasonic stirring, then sequentially add silicone and ethanol to carry out first reaction, adjust pH value to carry out second reaction, obtain first precursor H2SiO3@EG;S2, after the first precursor and magnesium powder are mixed, carry out calcination treatment under inert atmosphere, obtain second precursor Si@EG;S3, the second precursor is carried out 60 Co irradiation source irradiation, obtain third precursor Si-xSiO2@EG;S4, the third precursor is carried out chemical vapor deposition in ethylene atmosphere, to carry out carbon coating, obtain the composite negative material for lithium ion battery.The composite negative material for lithium ion battery of the application effectively alleviates the volume expansion and poor conductivity problem of Si material, and lithium ion battery prepared using the material exhibits good electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material preparation, and particularly relates to a composite anode material for lithium-ion batteries, a preparation method thereof, and a lithium-ion battery. Background Technology

[0002] The development of electric vehicles and large-scale energy storage networks has placed higher demands on the performance (capacity, cycle life, safety, etc.) of lithium-ion batteries. While commercially available graphite anode materials currently possess good first-cycle coulombic efficiency and rate performance, their specific capacity limits their further development. Therefore, the search for anode materials with high capacity and high cycle stability has become a key research focus.

[0003] Silicon is considered the most promising anode material for lithium-ion batteries due to its high theoretical specific capacity, suitable lithium intercalation platform, and large storage capacity. However, silicon has several drawbacks: significant volume expansion during cycling damages the electrode structure, leading to a continuous decline in discharge capacity. Effectively addressing these issues has become a hot research topic. Conventional methods, such as carbon coating, have limited effectiveness due to the substantial expansion of silicon. Summary of the Invention

[0004] The purpose of this invention is to provide a composite anode material for lithium-ion batteries, a preparation method thereof, and a lithium-ion battery. Nano-silicon particles are inserted into an expanded graphite layer to form Si@EG. 60 Co irradiation source forms Si-xSiO2@EG, and then C layer is uniformly coated on the surface of Si-xSiO2@EG by CVD to form Si-xSiO2@EG@C composite material. The SiO2 layer formed on the Si surface reduces volume expansion, and the expansion is constrained by the expanded graphite layer and carbon coating. This structure effectively alleviates the problems of volume expansion and poor conductivity of Si material. Lithium-ion batteries prepared using this material exhibit good electrochemical performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a composite anode material for lithium-ion batteries, wherein the composite material is Si-xSiO2@EG@C, comprising the following steps:

[0007] S1. Water was added to expanded graphite and ultrasonically stirred. Then, organosilicon and ethanol were added in sequence for the first reaction. The pH value was adjusted for the second reaction to obtain the first precursor H2SiO3@EG.

[0008] S2. The first precursor and magnesium powder are mixed and calcined under an inert atmosphere to obtain the second precursor Si@EG;

[0009] S3, Perform the second precursor... 60 Irradiation with a Co irradiation source yielded the third precursor Si-xSiO2@EG;

[0010] S4. The third precursor is subjected to chemical vapor deposition in an ethylene atmosphere to perform carbon coating, thereby obtaining the composite negative electrode material for lithium-ion batteries.

[0011] In the above preparation method, the organosilicon can be one or more of tetraethyl orthosilicate and silicon tetrachloride, preferably silicon tetrachloride.

[0012] In the above preparation method, the expanded graphite (EG) is a loose, porous, worm-like material obtained from natural graphite flakes through intercalation, washing, drying, and high-temperature expansion. The expansion ratio of the expanded graphite is generally 100 to 300 times. Expanded graphite can be prepared according to methods disclosed in the literature or purchased commercially. In a specific embodiment of the present invention, the expanded graphite is expanded graphite produced by Qingdao Jinrilai Graphite Co., Ltd.

[0013] In the above preparation method, the molar ratio of the organosilicon to the expanded graphite can be 1:(0.1-20), specifically 1:(2-4), 1:4 or 1:2, preferably 1:(3-4), more preferably 1:4;

[0014] The mass ratio of the expanded graphite to water can be (1-20):100, specifically 12:100;

[0015] The ratio of expanded graphite to ethanol can be 1 mol: (0.2-20) mL, specifically 1 mol: 1 mL.

[0016] The ethanol is anhydrous ethanol.

[0017] In the above preparation method, the reaction temperature in step (1) can be 40-100℃, specifically 80℃, and the time can be 2-8h, specifically 4h;

[0018] The first reaction is carried out under stirring conditions, with a stirring speed of 500-1000 r / min, specifically 500 r / min, 800 r / min or 1000 r / min.

[0019] In the above preparation method, adjusting the pH value can be done by using ammonia water to adjust the pH value to 3-8, preferably 4-6, such as pH value 5;

[0020] The temperature of the second reaction is 40-100℃, specifically 80℃, and the time is 2-12h, specifically 5h, 6h, 2h, 4h or 12h;

[0021] The second reaction is carried out under stirring conditions, with a stirring speed of 500-1000 r / min, specifically 500 r / min, 800 r / min or 1000 r / min.

[0022] The method further includes, after the second reaction in step (1), the steps of filtration, washing and drying in sequence.

[0023] In the above preparation method, the mass ratio of the first precursor to the magnesium powder can be 1:(0.1-2), specifically 1:(0.25-1), 1:1 or 1:0.25;

[0024] The calcination treatment can be a pre-calcination at 150–250°C for 4–8 hours, followed by calcination at 800–1200°C for 8–24 hours. Specifically, it can be a pre-calcination at 250°C for 5 hours, followed by calcination at 1200°C for 20 hours. The heating rate can be 1–10°C / min, such as 5°C / min.

[0025] The inert atmosphere may specifically be an argon atmosphere.

[0026] The method further includes the steps of washing, filtering, and drying with dilute hydrochloric acid after the calcination treatment.

[0027] In the above preparation method, the 60 The dose of Co irradiation source can be 10–1000 kGy, specifically 400–600 kGy, 500 kGy, 400 kGy, or 600 kGy; the irradiation time can be 0.1–10 h, specifically 1–3 h, 2 h, 1 h, or 3 h; preferably 2 h at a dose of 500 kGy or 3 h at a dose of 600 kGy.

[0028] In the above preparation method, the flow rate of ethylene can be 0.1 to 1 L / min, specifically 0.3 to 1 L / min, 0.5 L / min, 0.3 L / min, 1 L / min or 0.56 L / min, preferably 0.5 L / min or 0.56 L / min;

[0029] The temperature of the chemical vapor deposition can be 600–1000℃, specifically 750–950℃, 950℃, or 750℃; the time can be 1–12h, specifically 1–8h, 1h, 8h, or 6h; preferably, the reaction is carried out at 950℃ for 6h or 8h.

[0030] The chemical vapor deposition is performed in a CVD furnace.

[0031] In a second aspect, the present invention provides a composite negative electrode material for lithium-ion batteries prepared by any of the preparation methods described above.

[0032] Thirdly, the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a current collector and a composite negative electrode material for lithium-ion batteries loaded on the current collector.

[0033] In the aforementioned lithium-ion battery, the negative electrode sheet is made by coating a slurry composed of a composite negative electrode material, a conductive agent, a binder, and an organic solvent onto a current collector.

[0034] In an embodiment of the present invention, the conductive agent is carbon black (SP);

[0035] The adhesive may be carboxymethyl cellulose (CMC) and styrene-butadiene rubber latex (SBR). In an embodiment of the present invention, the adhesive is a carboxymethyl cellulose and styrene-butadiene rubber latex in a mass ratio of 1:1.5.

[0036] In an embodiment of the present invention, the mass ratio of the composite negative electrode material for lithium-ion batteries, the conductive agent, and the binder is 8:1:1;

[0037] In an embodiment of the present invention, the organic solvent is N-methyldipyrrolidone;

[0038] The thickness of the slurry can be 5 to 100 micrometers, such as 35 micrometers; in the embodiments of the present invention, the coating thickness is 50 to 100 micrometers.

[0039] The active material in the positive electrode sheet can be any one of lithium intercalation material, lithium alloy material, or lithium metal, such as lithium metal.

[0040] The electrolyte includes electrolyte salts, organic solvents, and additives, such as 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0041] The diaphragm is any one of polyethylene, polypropylene and related composite or modified polymer microporous membranes, such as Celgard 2400.

[0042] The present invention has the following beneficial effects:

[0043] The inventors of this invention, through careful research, discovered that in the material prepared by the above method, nano-silicon particles are inserted into the expanded graphite layer to form Si@EG, through... 60Co irradiation source forms Si-xSiO2@EG, and then a C layer is uniformly coated onto the surface of Si-xSiO2@EG using CVD to form a Si-xSiO2@EG@C composite material. Since SiO2 expands less than Si, this structure more effectively alleviates the volume expansion and poor conductivity problems of Si materials compared to Si@EG@C. Therefore, lithium-ion batteries prepared with this material exhibit excellent electrochemical performance. This negative electrode material was then combined with widely used positive electrode materials, separators, and non-aqueous electrolytes in lithium-ion batteries to form a high-performance lithium-ion battery, achieving the results of this invention. Attached Figure Description

[0044] Figure 1 Electrical properties of the Si-xSiO2@EG@C composite material in Example 1 of this invention. Detailed Implementation

[0045] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0046] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; and the materials and reagents used are commercially available unless otherwise specified.

[0047] The expanded graphite in the following examples was produced by Qingdao Jinrilai Graphite Co., Ltd., and the product name is Expanded Graphite (Worm) 9980300.

[0048] Example 1

[0049] 1. Preparation of composite materials:

[0050] (a) Weigh 12g (1mol) of expanded graphite and place it in a beaker. Add 100mL of water and stir ultrasonically for 4h. Add organosilicon tetraethyl orthosilicate to the expanded graphite at a molar ratio of 1:4. Add 1mL of anhydrous ethanol and heat to 80℃. Then stir at 500r / min for 4h. Add ammonia to adjust the pH to 5 and continue stirring for 5h. After filtration, washing and drying, the first precursor H2SiO3@EG is obtained.

[0051] (b) The first precursor H2SiO3@EG and magnesium powder were mixed evenly at a mass ratio of 1:1 and placed in a ceramic boat in an Ar atmosphere furnace. The mixture was pre-fired at 250℃ for 5 hours and then calcined at 1200℃ for 20 hours (heating rate of 5℃ / min). After cooling, the mixture was washed with dilute hydrochloric acid, filtered and dried to obtain the second precursor Si@EG.

[0052] (c) The second precursor Si@EG was administered via a 500 kJ dose. 60 After irradiation with a Co irradiation source for 2 hours, the third precursor Si-xSiO2@EG was obtained;

[0053] (d) The third precursor Si-xSiO2@EG was placed in a CVD furnace and reacted at 950℃ for 6h in a C2H4 atmosphere at a flow rate of 0.5L / min to obtain the Si-xSiO2@EG@C composite material.

[0054] 2. Preparation of lithium-ion batteries:

[0055] 80 parts by weight of the above-prepared composite material and 10 parts by weight of conductive agent SP, 10 parts by weight of binder CMC and SBR (mass ratio 1:1.5) were mixed, and an appropriate amount of N-methyldipyrrolidone was added and stirred until the slurry was uniform. The slurry was prepared and coated onto copper foil current collector using an automatic coating machine (coating thickness of 50-100 μm). The slurry was then placed in an 80°C oven and vacuum dried for 12 hours to remove N-methyldipyrrolidone, thus obtaining the negative electrode of the lithium-ion battery.

[0056] A coin cell lithium-ion battery (LR2032) is assembled with the above-prepared negative electrode using a positive electrode, a separator, an electrolyte, and the above-prepared negative electrode. The positive electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0057] Example 2

[0058] 1. Material preparation:

[0059] (a) Weigh 12g (1mol) of expanded graphite and place it in a beaker. Add 100mL of water and stir ultrasonically for 4h. Add organosilicon tetraethyl orthosilicate to the expanded graphite at a molar ratio of 1:2. Add 1mL of anhydrous ethanol and heat to 80℃. Stir at 800r / min for 4h. Add ammonia to adjust the pH to 5 and continue stirring for 6h. After filtration, washing and drying, the first precursor H2SiO3@EG is obtained.

[0060] (b) The first precursor H2SiO3@EG and magnesium powder were mixed evenly at a mass ratio of 1:1 and placed in a ceramic boat in an Ar atmosphere furnace. The mixture was pre-fired at 250℃ for 5 hours and then calcined at 1200℃ for 20 hours (heating rate was 5℃ / min). After cooling, the mixture was washed with dilute hydrochloric acid, filtered and dried to obtain the second precursor Si@EG.

[0061] (c) The second precursor Si@EG was administered via a 400 kJ dose. 60 After irradiation with a Co irradiation source for 1 hour, the third precursor Si-xSiO2@EG was obtained;

[0062] (d) The third precursor Si-xSiO2@EG was placed in a CVD furnace and reacted at 950℃ for 1 h in a C2H4 atmosphere at a flow rate of 0.3 L / min to obtain the Si-xSiO2@EG@C composite material.

[0063] 2. Preparation of lithium-ion batteries:

[0064] 80 parts by weight of the above-prepared composite material and 10 parts by weight of conductive agent SP, 10 parts by weight of binder CMC and SBR (mass ratio 1:1.5) were mixed, and an appropriate amount of N-methyldipyrrolidone was added and stirred until the slurry was uniform. The slurry was prepared and coated onto copper foil current collector using an automatic coating machine (coating thickness of 50-100 μm). The slurry was then placed in an 80°C oven and vacuum dried for 12 hours to remove N-methyldipyrrolidone, thus obtaining the negative electrode of the lithium-ion battery.

[0065] A coin cell lithium-ion battery (LR2032) is assembled with the above-prepared negative electrode using a positive electrode, a separator, an electrolyte, and the above-prepared negative electrode. The positive electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0066] Example 3

[0067] 1. Material preparation:

[0068] (a) Weigh 12g (1mol) of expanded graphite and place it in a beaker. Add 100mL of water and stir ultrasonically for 4h. Add organosilicon tetraethyl orthosilicate to the expanded graphite at a molar ratio of 1:4. Add 1mL of anhydrous ethanol and heat to 80℃. Then stir at 1000r / min for 4h. Add ammonia to adjust the pH to 5 and continue stirring for 2h. After filtration, washing and drying, the first precursor H2SiO3@EG is obtained.

[0069] (b) The first precursor H2SiO3@EG and magnesium powder were mixed evenly at a mass ratio of 4:1 and placed in a ceramic boat in an Ar atmosphere furnace. The mixture was pre-fired at 250℃ for 5 hours and then calcined at 1200℃ for 20 hours (heating rate was 5℃ / min). After cooling, the mixture was washed with dilute hydrochloric acid, filtered and dried to obtain the second precursor Si@EG.

[0070] (c) The second precursor Si@EG was administered via a 600 kJ dose. 60 After irradiation with a Co irradiation source for 3 hours, the third precursor Si-xSiO2@EG was obtained;

[0071] (d) The third precursor Si-xSiO2@EG was placed in a CVD furnace and reacted at 950℃ for 6h in a C2H4 atmosphere at a flow rate of 0.5L / min to obtain the Si-xSiO2@EG@C composite material.

[0072] 2. Preparation of lithium-ion batteries:

[0073] 80 parts by weight of the above-prepared composite material and 10 parts by weight of conductive agent SP, 10 parts by weight of binder CMC and SBR (mass ratio 1:1.5) were mixed, and an appropriate amount of N-methyldipyrrolidone was added and stirred until the slurry was uniform. The slurry was prepared and coated onto copper foil current collector using an automatic coating machine (coating thickness of 50-100 μm). The slurry was then placed in an 80°C oven and vacuum dried for 12 hours to remove N-methyldipyrrolidone, thus obtaining the negative electrode of the lithium-ion battery.

[0074] A coin cell lithium-ion battery (LR2032) is assembled with the above-prepared negative electrode using a positive electrode, a separator, an electrolyte, and the above-prepared negative electrode. The positive electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0075] Example 4

[0076] 1. Material preparation:

[0077] (a) Weigh 12g (1mol) of expanded graphite and place it in a beaker. Add 100mL of water and stir ultrasonically for 4h. Add organosilicon tetraethyl orthosilicate to the expanded graphite at a molar ratio of 1:2. Add 1mL of anhydrous ethanol and heat to 80℃. Stir at 500r / min for 4h. Add ammonia to adjust the pH to 5 and continue stirring for 4h. After filtration, washing and drying, the first precursor H2SiO3@EG is obtained.

[0078] (b) The first precursor H2SiO3@EG and magnesium powder were mixed evenly at a mass ratio of 4:1 and placed in a ceramic boat in an Ar atmosphere furnace. The mixture was pre-fired at 250℃ for 5 hours and then calcined at 1200℃ for 20 hours (heating rate was 5℃ / min). After cooling, the mixture was washed with dilute hydrochloric acid, filtered and dried to obtain the second precursor Si@EG.

[0079] (c) The second precursor Si@EG was administered via a 400 kJ dose. 60 After irradiation with a Co irradiation source for 1 hour, the third precursor Si-xSiO2@EG was obtained;

[0080] (d) The third precursor Si-xSiO2@EG was placed in a CVD furnace and reacted at 750℃ for 8h in a C2H4 atmosphere at a flow rate of 1L / min to obtain the Si-xSiO2@EG@C composite material.

[0081] 2. Preparation of lithium-ion batteries:

[0082] 80 parts by weight of the above-prepared composite material and 10 parts by weight of conductive agent SP, 10 parts by weight of binder CMC and SBR (mass ratio 1:1.5) were mixed, and an appropriate amount of N-methyldipyrrolidone was added and stirred until the slurry was uniform. The slurry was prepared and coated onto copper foil current collector using an automatic coating machine (coating thickness of 50-100 μm). The slurry was then placed in an 80°C oven and vacuum dried for 12 hours to remove N-methyldipyrrolidone, thus obtaining the negative electrode of the lithium-ion battery.

[0083] A coin cell lithium-ion battery (LR2032) is assembled with the above-prepared negative electrode using a positive electrode, a separator, an electrolyte, and the above-prepared negative electrode. The positive electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0084] Example 5

[0085] 1. Material preparation:

[0086] (a) Weigh 12g (1mol) of expanded graphite and place it in a beaker. Add 100mL of water and stir ultrasonically for 4h. Add organosilicon tetraethyl orthosilicate to the expanded graphite at a molar ratio of 1:4. Add 1mL of anhydrous ethanol and heat to 80℃. Stir at 500r / min for 4h. Add ammonia to adjust the pH to 5 and continue stirring for 12h. After filtration, washing and drying, the first precursor H2SiO3@EG is obtained.

[0087] (b) The first precursor H2SiO3@EG and magnesium powder were mixed evenly at a mass ratio of 1:1 and placed in a ceramic boat in an Ar atmosphere furnace. The mixture was pre-fired at 250℃ for 5 hours and then calcined at 1200℃ for 20 hours (heating rate of 5℃ / min). After cooling, the mixture was washed with dilute hydrochloric acid, filtered and dried to obtain the second precursor Si@EG.

[0088] (c) The second precursor Si@EG was administered via a 500 kJ dose. 60 After irradiation with a Co irradiation source for 2 hours, the third precursor Si-xSiO2@EG was obtained;

[0089] (d) The third precursor Si-xSiO2@EG was placed in a CVD furnace and reacted at 950℃ for 8 hours in a C2H4 atmosphere at a flow rate of 0.56 L / min to obtain the Si-xSiO2@EG@C composite material.

[0090] 2. Preparation of lithium-ion batteries:

[0091] Mix 80 parts by weight of the above-prepared composite material with 10 parts by weight of conductive agent SP and 10 parts by weight of binder CMC, add an appropriate amount of N-methyldipyrrolidone and continue stirring until the slurry is uniform, prepare a slurry, and use an automatic coating machine to coat the slurry onto a copper foil current collector (coating thickness is 50-100μm), place it in an 80℃ oven and vacuum dry for 12 hours to remove N-methyldipyrrolidone, and obtain the negative electrode of the lithium-ion battery.

[0092] A coin cell lithium-ion battery (LR2032) is assembled with the above-prepared negative electrode using a positive electrode, a separator, an electrolyte, and the above-prepared negative electrode. The positive electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0093] Comparative Example 1

[0094] 1. Material preparation:

[0095] Commercially available nano-silicon is used as the anode material.

[0096] 2. Preparation of lithium-ion batteries:

[0097] Mix 80 parts by weight of the above-mentioned negative electrode material with 10 parts by weight of conductive agent SP and 10 parts by weight of binder CMC, add an appropriate amount of N-methyldipyrrolidone and continue stirring until the slurry is uniform to prepare a slurry. Use an automatic coating machine to coat the slurry onto a copper foil current collector (coating thickness is 50μm-100μm), place it in an 80℃ oven and vacuum dry for 12 hours to remove N-methyldipyrrolidone, and obtain the negative electrode of the lithium-ion battery.

[0098] A coin cell lithium-ion battery (LR2032) is assembled with the above-prepared negative electrode using a positive electrode, a separator, an electrolyte, and the above-prepared negative electrode. The positive electrode is a lithium metal sheet, the separator is Celgard 2400, and the electrolyte is 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0099] Comparative Example 2

[0100] 1. Preparation of composite materials:

[0101] (a) Weigh 12g (1mol) of expanded graphite and place it in a beaker. Add 100mL of water and stir ultrasonically for 4h. Add tetraethyl orthosilicate and 1mL of anhydrous ethanol at a molar ratio of 1:4. Heat to 80℃ and stir at 500r / min for 4h. Add ammonia to adjust the pH to 5 and continue stirring for 2h. After filtration, washing and drying, the first precursor H2SiO3@EG is obtained.

[0102] (b) The first precursor H2SiO3@EG and magnesium powder were mixed evenly at a mass ratio of 1:1 and placed in a ceramic boat in an Ar atmosphere furnace. The mixture was pre-fired at 250℃ for 5 hours and then calcined at 1200℃ for 20 hours (heating rate of 5℃ / min). After cooling, the mixture was washed with dilute hydrochloric acid, filtered and dried to obtain the second precursor Si@EG.

[0103] (c) The third precursor Si@EG was placed in a CVD furnace and reacted at 950℃ in a C2H4 atmosphere at a flow rate of 0.5 L / min for 6 h to obtain the Si@EG@C composite material.

[0104] 2. Preparation of lithium-ion batteries:

[0105] 80 parts by weight of the above-prepared composite material and 10 parts by weight of conductive agent SP, 10 parts by weight of binder CMC and SBR (mass ratio 1:1.5) were mixed, and an appropriate amount of N-methyldipyrrolidone was added and stirred until the slurry was uniform. The slurry was prepared and coated onto copper foil current collector using an automatic coating machine (coating thickness of 50-100 μm). The slurry was then placed in an 80°C oven and vacuum dried for 12 hours to remove N-methyldipyrrolidone, thus obtaining the negative electrode of the lithium-ion battery.

[0106] An LR2032 coin cell lithium-ion battery was assembled with a positive electrode, a separator, an electrolyte, and the negative electrode prepared above. The positive electrode was a lithium metal sheet, the separator was Celgard 2400, and the electrolyte was 1M LiPF6 EC / DMC / FEC (volume ratio 1:1:0.1).

[0107] Test case

[0108] The lithium-ion batteries assembled in Examples 1-5 and Comparative Examples 1-2 were subjected to electrochemical performance tests at voltages of 0-2.0V and currents of 0.1C / 0.1C.

[0109] The electrical properties of the Si-xSiO2@EG@C composite material in Example 1 are shown in the figure. Figure 1 .

[0110] The test results for each embodiment and comparative example are shown in Table 1:

[0111] Table 1. Comparison of Electrochemical Performance Results

[0112]

[0113] Comparing Example 1 and Comparative Example 1, it can be concluded that the lithium-ion battery assembled according to the present invention can significantly improve the capacity retention rate after cycling and has excellent electrochemical performance. Comparing Example 1 and Comparative Example 2, it can be seen that the volume expansion is significantly reduced after the formation of an oxide layer on the silicon surface, and the cycle performance is significantly improved.

[0114] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including modifications made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. A method for preparing a composite negative electrode material for lithium-ion batteries, characterized in that, The composite material is Si-xSiO2@EG@C, and includes the following steps: S1. Water was added to expanded graphite and ultrasonically stirred. Then, organosilicon and ethanol were added in sequence for the first reaction. The pH value was adjusted for the second reaction to obtain the first precursor H2SiO3@EG. S2. The first precursor and magnesium powder are mixed and calcined under an inert atmosphere to obtain the second precursor Si@EG; S3, Perform the second precursor... 60 Irradiation with a Co irradiation source yielded the third precursor Si-xSiO2@EG; The 60 The dose of Co irradiation source is 10–1000 kJ / g, and the irradiation time is 0.1–10 h. S4. The third precursor is subjected to chemical vapor deposition in an ethylene atmosphere to perform carbon coating, thereby obtaining the composite negative electrode material for lithium-ion batteries.

2. The preparation method according to claim 1, characterized in that: The organosilicon is one or more of tetraethyl orthosilicate and silicon tetrachloride.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the organosilicon to the expanded graphite is 1:(0.1~20). The mass ratio of expanded graphite to water is (1-20):100; The ratio of expanded graphite to ethanol is 1 mol: (0.2-20) mL.

4. The preparation method according to claim 1, characterized in that: The temperature of the first reaction in step (1) is 40-100℃, and the time is 2-8h; The first reaction was carried out under stirring conditions, with a stirring speed of 500-1000 r / min.

5. The preparation method according to claim 1, characterized in that: The pH value is adjusted to 3-8 using ammonia water. The second reaction is carried out at a temperature of 40–100°C for a time of 2–12 hours. The second reaction is carried out under stirring conditions, with a stirring speed of 500-1000 r / min.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the first precursor to the magnesium powder is 1:(0.1~2); The calcination process involves pre-calcining at 150–250°C for 4–8 hours, followed by calcination at 800–1200°C for 8–24 hours.

7. The preparation method according to claim 1, characterized in that: The flow rate of the ethylene is 0.1–1 L / min; The chemical vapor deposition temperature is 600–1000℃, and the time is 1–12 h.

8. The composite negative electrode material for lithium-ion batteries prepared by the preparation method according to any one of claims 1-7.

9. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode includes a current collector and a composite negative electrode material for lithium-ion batteries as described in claim 8, loaded on the current collector.

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