Silicon-carbon composite negative electrode material and preparation method thereof

Abstract

The invention belongs to the field of battery materials, discloses a silicon-carbon composite negative electrode material and a preparation method thereof, and aims to solve the technical problems of poor conductivity and poor cycling stability of a lithium ion battery negative electrode material. Fluorine doping is carried out on the nano-crystalline cellulose, so that the fluorinated nano-crystalline cellulose is obtained. The preparation method comprises the following steps: taking fluorinated nano cellulose as a structural unit, taking graphene oxide as a template, forming hydrogen bonds by fluorine ions and hydroxyl groups on the surface of the graphene oxide, performing defect modification on the graphene oxide to obtain high-conductivity graphene composite carbon fiber coated nano silicon, and performing spray drying and sintering to obtain the silicon-carbon negative electrode material. The preparation method is mild in synthesis condition and simple in synthesis step, and the technological process for preparing the silicon-carbon composite material is effectively shortened. According to the prepared silicon-carbon composite negative electrode material, due to higher conductivity, a stable graphene coating layer and uniform distribution of nanoparticles, the volume expansion effect of silicon in the charging and discharging process is greatly relieved, and the performance of the material in a lithium ion battery is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and particularly to a silicon-carbon anode material. Background Art

[0002] With the rapid development of the mobile electronic product and new energy vehicle industries, the market's demand for the energy density of lithium-ion batteries is increasing day by day. As a key material of lithium-ion batteries, the anode material plays a decisive role in the performance of the battery. The theoretical specific capacity of the traditional anode material graphite is only 372 mAh / g, which can no longer meet the requirements of high-energy-density lithium-ion batteries. The theoretical capacity of silicon is as high as 4200 mAh / g, which is more than ten times that of graphite. To achieve the goal of higher energy density, it has been a consensus in the industry to develop silicon-based anodes for use in lithium-ion battery systems.

[0003] Although silicon-based anode materials have broad application prospects, there are still technical barriers to be broken through in the actual use of silicon-based materials. The most important problems are as follows: 1) The volume expansion reaches 320% after lithium intercalation, and the volume expansion will further lead to material pulverization, electrode structure change, and continuous formation of the solid electrolyte interface (SEI) film; 2) It is intrinsically a semiconductor material with poor conductivity. Due to the limitations of the above bottleneck problems, silicon materials cannot be used alone as anode materials. Currently, the main approach of battery material enterprises is to combine silicon with graphite, conductive agents, and other carbon materials for use. The introduction of carbon materials can improve the conductivity of silicon-carbon anodes.

[0004] Chinese Patent CN 108091866 A provides a preparation method for a silicon-carbon anode material for lithium-ion batteries. A cellulose raw material solution is added to a solution of elemental silicon material to obtain a cellulose-silicon powder mixture, and after regeneration treatment, a cellulose-elemental silicon composite material is formed; the cellulose-elemental silicon composite material is calcined and carbonized to obtain a silicon-carbon anode material for lithium-ion batteries. This process uses renewable and inexpensive cellulose raw materials. During the preparation process, silicon dioxide can be generated simultaneously, forming a multi-layer structure of the electrode material, further enhancing the cycle stability of the electrode material. The method is simple and non-toxic. However, the appearance of the silicon dioxide layer results in a low initial efficiency and low capacity performance of the silicon-carbon material, unable to meet the performance requirements of the anode material. In addition, the application with the publication number CN116130628A discloses a coated silicon anode material, its preparation method and application. Surface-modified nanocellulose is used to coat nanosilicon to further improve the adhesion between the nanocellulose and the surface of the silicon-containing active material, thereby further improving the swelling and aging problems of the silicon-containing active material during cycling and enhancing the comprehensive performance of the material in the battery. However, the structure of cellulose itself is fragile, and relying solely on the amorphous carbon after cellulose sintering cannot effectively ensure the cycle stability of the nanosilicon material. Summary of the Invention

[0005] In view of the technical problems of poor electrical conductivity and poor cycle stability of the anode material of lithium-ion batteries, the present invention proposes a silicon-carbon composite anode material and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is realized as follows:

[0007] A preparation method of a silicon-carbon composite anode material, the steps are as follows:

[0008] (1) Add microcrystalline cellulose, ionic liquid, and fluoride to deionized water, heat and stir to obtain a fluorinated nanocellulose suspension. By treating microcrystalline cellulose with ionic liquid and fluoride, on the one hand, cellulose hydrolysis can be realized to obtain nanocellulose; on the other hand, fluoride ion doping of nanocellulose can be carried out.

[0009] (2) Add graphene oxide slurry to the fluorinated nanocellulose suspension A, stir for a certain time at room temperature, and then obtain sample A through freeze-drying. By stirring the fluorinated nanocellulose and graphene oxide, it is beneficial for the hydroxyl groups on the surfaces of the fluorinated nanocellulose and graphene oxide to form hydrogen bonds, which is beneficial for the cellulose to tightly coat the surface of graphene; on the other hand, freeze-drying is beneficial for better retention of the fiber morphology, so as to ensure that the nanocellulose becomes carbon cellulose in shape after carbonization, and can also better repair the defects of graphene oxide.

[0010] (3) Disperse and stir sample A and nanosilicon in deionized water, and finally obtain the silicon-carbon anode material through spray drying and sintering. In sample A, graphene oxide serves as a template for the carbonization of nanocellulose. Graphene oxide improves the carbonization degree of nanocellulose. Nanocellulose effectively repairs the defects of graphene oxide and connects them. The template carbonization and highly ordered construction of nanocellulose produce a highly conductive graphene composite carbon fiber material; the carboxyl groups on the surface of graphene can also form hydrogen bonds with silicon, and the modified graphene oxide provides a dense and stable coating layer for nanosilicon. Such a structure not only improves the cycle stability of silicon-carbon, but also inhibits the volume expansion of silicon during the cycle, and improves the electrochemical performance of the material.

[0011] In the above step (1), the mass ratio of microcrystalline cellulose, ionic liquid, and fluoride is 1:(0.5 - 5):(0.1 - 1).

[0012] In the above step (1), the diameter of the microcrystalline cellulose is 1 - 20 μm, and the length is 5 - 20 μm; the ionic liquid is at least one of 1-hexylimidazole acetate, 1-butyl-3-methylimidazolium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-hexylimidazole acetate, tetrabutylammonium fluoride, and tetraethylammonium chloride; the fluoride is ammonium fluoride, lithium fluoride, etc.

[0013] In the above step (1), the heating temperature is 40 - 120 °C and the time is 1 - 10 h.

[0014] In the above step (2), the solid content of the graphene oxide slurry is 1 - 5 wt%, and the mass ratio of graphene oxide to microcrystalline cellulose is (0.1 - 2):1; the temperature of freeze-drying is -60 to -80 °C and the time is 48 h.

[0015] In the above step (3), the mass ratio of sample A to nanosilicon is 1:(0.5 - 2).

[0016] In the above step (3), the particle size of the nanosilicon is 10 - 100 nm.

[0017] In the above step (3), the temperature of spray drying is 150 - 190 °C; the sintering is carried out in an inert atmosphere, heated to 200 °C at a heating rate of 2 - 5 °C / min, sintered for 1 - 2 h, and then heated to 600 - 900 °C at a heating rate of 2 - 5 °C / min and sintered for 1 - 4 h.

[0018] The silicon-carbon composite anode material prepared by the above preparation method.

[0019] The application of the above silicon-carbon composite anode material in a lithium-ion battery.

[0020] The beneficial effects of the present invention are:

[0021] (1) The present invention prepares fluorinated nanocellulose by the method of ionic liquid hydrolysis and fluoride doping. On the one hand, hydrogen bonds are formed between the fluorinated nanocellulose and the hydroxyl groups on the surface of graphene oxide, which is beneficial for the cellulose to densely coat on the surface of graphene and modify the defects; on the other hand, graphene oxide serves as a template for the carbonization of nanocellulose, and graphene oxide improves the degree of carbonization of nanocellulose. The nanocellulose effectively repairs the defects of graphene oxide and connects them. The template carbonization and highly ordered construction of nanocellulose produce a highly conductive graphene composite carbon fiber material. The carboxyl groups on the surface of graphene can also form hydrogen bonds with silicon, and the highly conductive modified graphene oxide provides a dense and stable coating layer for nanosilicon. Such a structure not only improves the cycling stability of silicon-carbon but also inhibits the volume expansion of silicon during cycling and improves the electrochemical performance of the material.

[0022] (2) When the silicon-carbon composite anode material prepared by the preparation method of the present invention is applied to a lithium-ion battery, the capacity of the battery can reach more than 1780 mAh / g, the initial efficiency ≥ 87%, and after 50 cycles, the capacity retention rate can reach 89 - 95%. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0024] Figure 1 Flow chart for preparing the silicon-carbon composite anode material of the present invention.

[0025] Figure 2 Scanning electron micrograph of the silicon-carbon composite anode material prepared in Example 1.

[0026] Figure 3 Charge-discharge test graphs of the silicon-carbon materials prepared in Example 1 and Comparative Examples 1-3. Detailed implementation manners

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0028] Example 1

[0029] The preparation method of the silicon-carbon composite anode material in this embodiment, the preparation flow chart is as Figure 1 shown, and the steps are as follows:

[0030] (1) Add 5 g of microcrystalline cellulose (with a diameter of 1-20 μm and a length of 5-20 μm), 3 g of 1-butyl-3-methylimidazolium chloride, and 1 g of ammonium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 4 h to obtain a fluorinated nanocellulose suspension.

[0031] (2) Add 100 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nanocellulose suspension, stir for 2 h, and then freeze-dry at -70 °C for 48 h to obtain sample A.

[0032] (3) Take 1 g of nanosilicon (particle size 10-100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C, then obtain a silicon-carbon precursor, and then put it into a tubular furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. When calcining, introduce the protective gas argon, and the heating rate is 5 °C / min, and finally obtain the silicon-carbon composite anode material.

[0033] Figure 2 Scanning electron micrograph of the silicon-carbon composite anode material prepared in this example. It can be seen from the figure that the nano-silicon particles are coated with highly conductive graphene material.

[0034] Example 2

[0035] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0036] (1) Add 5 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of 1-butyl-1-methylpyrrolidinium chloride, and 1 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 2 h to obtain a fluorinated nano-cellulose suspension.

[0037] (2) Add 100 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nano-cellulose suspension, stir for 1 h, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0038] (3) Take 1 g of nano-silicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C, then obtain a silicon-carbon precursor, and then put it into a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. Argon is introduced as a protective gas during calcination, and the heating rate is 5 °C / min. Finally, the silicon-carbon composite anode material is obtained.

[0039] Example 3

[0040] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0041] (1) Add 5 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of tetraethylammonium chloride, and 1 g of ammonium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 4 h to obtain a fluorinated nano-cellulose suspension.

[0042] (2) Add 100 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nano-cellulose suspension, stir for 2 h, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0043] (3) Take 1 g of nanosilicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C to obtain a silicon-carbon precursor, then place it in a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min to finally obtain the silicon-carbon composite anode material.

[0044] Example 4

[0045] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0046] (1) Add 5 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of 1-butyl-1-methylpyrrolidinium chloride, and 1 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 2 h to obtain a fluorinated nanocellulose suspension.

[0047] (2) Add 100 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nanocellulose suspension, stir for 2 h, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0048] (3) Take 1 g of nanosilicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C to obtain a silicon-carbon precursor, then place it in a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min to finally obtain the silicon-carbon composite anode material.

[0049] Example 5

[0050] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0051] (1) Add 3 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of 1-butyl-1-methylimidazolium chloride, and 0.5 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 2 h to obtain a fluorinated nanocellulose suspension.

[0052] (2) Add 100 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nanocellulose suspension, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0053] (3) Take 1 g of nano-silicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C to obtain a silicon-carbon precursor, then place it in a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min. Finally, a silicon-carbon composite anode material is obtained.

[0054] Example 6

[0055] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0056] (1) Add 3 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of 1-butyl-1-methylimidazolium chloride, and 0.5 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 2 h to obtain a fluorinated nano-cellulose suspension.

[0057] (2) Add 50 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nano-cellulose suspension, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0058] (3) Take 1 g of nano-silicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C to obtain a silicon-carbon precursor, then place it in a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min. Finally, a silicon-carbon composite anode material is obtained.

[0059] Example 7

[0060] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0061] (1) Add 5 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of 1-hexylimidazolium acetate, and 1 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 2 h to obtain a fluorinated nano-cellulose suspension.

[0062] (2) Add 50 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nano-cellulose suspension, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0063] (3) Take 1 g of nanosilicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C to obtain a silicon-carbon precursor, then place it in a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min to finally obtain the silicon-carbon composite anode material.

[0064] Example 8

[0065] The preparation method of the silicon-carbon composite anode material of this example is as follows:

[0066] (1) Add 3 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 3 g of 1-hexylimidazole acetate, and 0.5 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 2 h to obtain a fluorinated nanocellulose suspension.

[0067] (2) Add 50 g of graphene oxide slurry (solid content 3.5 wt%) to the fluorinated nanocellulose suspension, stir for 4 h, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0068] (3) Take 1 g of nanosilicon (particle size 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C to obtain a silicon-carbon precursor, then place it in a tube furnace and calcine at 200 °C for 2 h, then raise the temperature to 800 °C and calcine for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min to finally obtain the silicon-carbon composite anode material.

[0069] Example 9

[0070] The preparation method of the silicon-carbon composite anode material of this example is as follows:

[0071] (1) Add 5 g of microcrystalline cellulose (diameter 1 - 20 μm, length 5 - 20 μm), 2.5 g of 1-hexylimidazole acetate, and 0.5 g of lithium fluoride into a flask, add 300 mL of deionized water, heat and stir at 40 °C for 10 h to obtain a fluorinated nanocellulose suspension.

[0072] (2) Add 50 g of graphene oxide slurry (solid content 1 wt%) to the fluorinated nanocellulose suspension, stir for 3 h, and then freeze-dry at -60 °C for 48 h to obtain graphene sample A.

[0073] (3) Take 1 g of nanosilicon (particle size of 10 - 100 nm) and 0.5 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 150 °C, then obtain a silicon-carbon precursor, and then place it in a tube furnace for high-temperature calcination at 200 °C for 1.5 h, and then raise the temperature to 900 °C for calcination for 1 h. During calcination, introduce the protective gas argon, and the heating rate is 2 °C / min. Finally, obtain the silicon-carbon composite anode material.

[0074] Example 10

[0075] The preparation method of the silicon-carbon composite anode material in this example is as follows:

[0076] (1) Add 3 g of microcrystalline cellulose (diameter of 1 - 20 μm, length of 5 - 20 μm), 15 g of 1-butyl-1-methylpyrrolidinium chloride, and 3 g of lithium fluoride into a flask, add 400 mL of deionized water, heat and stir at 120 °C for 1 h to obtain a fluorinated nanocellulose suspension.

[0077] (2) Add 120 g of graphene oxide slurry (solid content of 5 wt%) to the fluorinated nanocellulose suspension, stir for 4 h, and then freeze-dry at -80 °C for 48 h to obtain graphene sample A.

[0078] (3) Take 0.5 g of nanosilicon (particle size of 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 190 °C, then obtain a silicon-carbon precursor, and then place it in a tube furnace for high-temperature calcination at 200 °C for 1 h, and then raise the temperature to 600 °C for calcination for 4 h. During calcination, introduce the protective gas argon, and the heating rate is 4 °C / min. Finally, obtain the silicon-carbon composite anode material.

[0079] Comparative Example 1

[0080] The preparation method of the silicon-carbon composite anode material in this comparative example is different from that of Example 1 in that ammonium fluoride is not added in step (1). The specific steps are as follows:

[0081] (1) Add 5 g of microcrystalline cellulose (diameter of 1 - 20 μm, length of 5 - 20 μm) and 3 g of 1-butyl-1-methylpyrrolidinium chloride into a flask, add 300 mL of deionized water, heat and stir at 90 °C for 4 h to obtain a nanocellulose suspension.

[0082] (2) Add 100 g of graphene oxide slurry (solid content of 3.5 wt%) to the nanocellulose suspension, and then freeze-dry at -70 °C for 48 h to obtain graphene sample A.

[0083] (3) Take 1 g of nanosilicon (particle size of 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C, then obtain a silicon-carbon precursor, then place it in a tube furnace and calcine it at 200 °C for 2 h, then raise the temperature to 800 °C and calcine it for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min. Finally, obtain a silicon-carbon composite anode material.

[0084] Comparative Example 2

[0085] The preparation method of the silicon-carbon composite anode material in this comparative example is different from that of Example 1 in that step (1) is not carried out and the fluorinated nanocellulose suspension is not added. The specific steps are as follows:

[0086] (1) Take 30 g of graphene oxide slurry (solid content 3.5 wt%) and freeze-dry it at -70 °C for 48 h to obtain graphene sample A.

[0087] (2) Take 1 g of nanosilicon (particle size of 10 - 100 nm) and 1 g of sample A in a beaker, add 200 mL of deionized water, stir for 4 h, spray-dry the sample at a temperature of 180 °C, then obtain a silicon-carbon precursor, then place it in a tube furnace and calcine it at 200 °C for 2 h, then raise the temperature to 800 °C and calcine it for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min. Finally, obtain a silicon-carbon composite anode material.

[0088] Comparative Example 3

[0089] The preparation method of the silicon-carbon composite anode material in this comparative example is different from that of Example 1 in that graphene oxide is not added and freeze-drying treatment is not carried out. The specific steps are as follows:

[0090] (1) Add 5 g of microcrystalline cellulose (diameter of 1 - 20 μm, length of 5 - 20 μm), 3 g of 1-butyl-3-methylimidazolium chloride, and 1 g of ammonium fluoride to 300 mL of deionized water, heat and stir at 90 °C for 4 h to obtain a fluorinated nanocellulose suspension.

[0091] (2) According to the solid content of the fluorinated nanocellulose suspension, add an equal mass of nanosilicon (particle size of 10 - 100 nm) to its suspension, stir for 4 h, spray-dry the sample at a temperature of 180 °C, then obtain a silicon-carbon precursor, then place it in a tube furnace and calcine it at 200 °C for 2 h, then raise the temperature to 800 °C and calcine it for 2 h. During calcination, introduce the protective gas argon, and the heating rate is 5 °C / min. Finally, obtain a silicon-carbon composite anode material.

[0092] Application Example

[0093] The negative electrode materials prepared in the embodiments and comparative examples of the present invention were assembled into half-cells and subjected to electrochemical performance tests. The silicon-carbon negative electrode material, Super P, and the binder were homogenized and coated in a mass ratio of 8:1:1. Among them, the binder was a solution with a mass ratio of sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR): polyacrylic acid (PAA) of 1:1:1, and the electrolyte was LiPF 6 conventional electrolyte. A lithium sheet was used as the counter electrode to assemble a CR2025 button cell. Under normal temperature conditions, a LANHE CT2001A blue battery test system was used to conduct charge-discharge tests at a current density of 100 mA / g, and the voltage range was 0.005 - 2.0 V. The specific electrochemical performance is shown in Table 1 and Figure 3 as follows.

[0094] Table 1 Electrochemical performance data

[0095]

[0096]

[0097] Figure 3 Figures for charge-discharge tests of the negative electrode materials prepared in Example 1 and Comparative Examples 1 - 3 are shown. It can be seen that the performance of the silicon-carbon material in Example 1 is the best. In Comparative Example 1, the nanofibrillated cellulose was not doped with fluoride ions, resulting in a lower initial efficiency and a poorer capacity retention rate of the silicon-carbon. In Comparative Example 2, the graphene oxide was not modified by nanofibrillated cellulose, and although the cycle stability was good, the capacity utilization was low. In Comparative Example 3, due to the lack of graphene oxide as a template, the cycle performance was poor. As can be seen from Table 1, the materials prepared by the process of the present invention have excellent electrochemical performance. Specifically, the capacity can reach over 1780 mAh / g, the initial efficiency is ≥ 87%, and after 50 cycles, the capacity retention rate can reach 89 - 95%.

[0098] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite negative electrode material, characterized in that: Here are the steps: (1) adding microcrystalline cellulose, ionic liquid and fluoride into deionized water, heating and stirring to obtain a fluorinated nanocellulose suspension; (2) adding graphene oxide slurry to the fluorinated nanocellulose suspension, stirring for a certain period of time and then freeze-drying to obtain sample A; (3) Dispersing and stirring sample A and nano-silicon in deionized water, and finally spray drying and sintering to obtain a silicon-carbon composite negative electrode material.

2. The method for preparing a silicon-carbon composite negative electrode material according to claim 1, characterized in that: In the step (1), the mass ratio of microcrystalline cellulose, ionic liquid and fluoride is 1:(0.5-5):(0.1-1).

3. The method for preparing the silicon-carbon composite negative electrode material according to claim 2, characterized in that: In the step (1), the diameter of the microcrystalline cellulose is 1-20 μm and the length is 5-20 μm; the ionic liquid is at least one of 1-hexylimidazole acetate, 1-butyl-3-methylimidazolium chloride, 1-butyl-1-methylpyrrolidium chloride, 1-hexylimidazole acetate, tetrabutylammonium fluoride and tetraethylammonium chloride.

4. The method for preparing the silicon-carbon composite negative electrode material according to claim 3, characterized in that: The heating temperature in step (1) is 40-120° C. and the heating time is 1-10 h.

5. The method for preparing the silicon-carbon composite negative electrode material according to claim 4, characterized in that: In the step (2), the solid content of the graphene oxide slurry is 1-5 wt %, and the mass ratio of graphene oxide to microcrystalline cellulose is (0.1-2):

1.

6. The method for preparing the silicon-carbon composite negative electrode material according to claim 5, characterized in that: In the step (3), the mass ratio of sample A to nano-silicon is 1:(0.5-2).

7. The method for preparing a silicon-carbon composite negative electrode material according to claim 6, characterized in that: The nano silicon particle size in step (3) is 10-100 nm.

8. The method for preparing the silicon-carbon composite negative electrode material according to claim 7, characterized in that: The spray drying temperature in step (3) is 150-190°C; the sintering is carried out in an inert atmosphere, the temperature is increased to 200°C at a heating rate of 2-5°C / min, sintered for 1-2 h, and then increased to 600-900°C at a heating rate of 2-5°C / min, and sintered for 1-4 h.

9. A silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the silicon-carbon composite negative electrode material according to claim 9 in lithium-ion batteries.

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