Preparation method and application of silicon-carbon lithium ion battery negative electrode

Abstract

The invention discloses a preparation method and application of a silicon-carbon lithium ion battery negative electrode, and the preparation method comprises the following steps: carrying out carbon coating on a single-walled carbon nanotube through a hydrothermal reaction to obtain a carbon-coated single-walled carbon nanotube; performing chemical etching and pore forming on the carbon-coated single-walled carbon nanotube to obtain a porous carbon-coated single-walled carbon nanotube; and adding the porous carbon coated single-walled carbon nanotube into a lithium ion battery negative electrode material containing a silicon negative electrode to obtain the silicon-carbon lithium ion battery negative electrode. Volume expansion is inhibited through the porous carbon coated silicon negative electrode, the micro-mesopore composite porous carbon coated single-walled carbon nanotube is prepared to replace a pure single-walled carbon nanotube to serve as a main conductive agent in a silicon-doped negative electrode formula, the cycle life of a lithium battery is prolonged, and the rate capability of the lithium battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and more specifically, to a method for preparing a negative electrode of a silicon-carbon lithium-ion battery and applications thereof. Background Art

[0002] With the rapid development of lithium-ion batteries, more stringent requirements have been put forward for the energy density of lithium-ion batteries. Currently, the negative electrode material of commercial lithium-ion batteries is mainly graphite material, and its theoretical gram capacity is only 372mAh / g, which greatly limits the energy density of the battery.

[0003] Silicon has a theoretical capacity of up to 4200mAh / g, and is currently the most widely studied and most promising negative electrode material for mass production. However, silicon materials expand in volume by up to 300% during the charging process, causing damage to the pole piece structure, leading to a series of problems such as battery capacity attenuation and reduced cycle life. In view of this, many researchers have studied silicon-carbon materials or silicon-oxygen materials to suppress the volume expansion problem of silicon materials and achieve mass production. Of course, due to the extremely poor conductivity of silicon materials themselves, single-walled carbon nanotubes with high conductivity, high flexibility, and high aspect ratio are usually selected in the current mass-produced negative electrode silicon-doped system formula, supplemented with other conductive carbon black as a conductive agent. Considering the actual volume expansion problem that still exists, even in the formula with low silicon doping, the cycle life and rate performance of the battery still face severe challenges.

[0004] Therefore, there is an urgent need for a method for preparing a negative electrode for a silicon-carbon lithium-ion battery that can improve the battery energy density and ensure the battery cycle life and rate performance. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing a negative electrode of a silicon-carbon lithium-ion battery and its application, so as to improve the energy density of the battery and at the same time ensure the cycle life and rate performance of the battery.

[0006] In one aspect, the present invention provides a method for preparing a negative electrode of a silicon-carbon lithium-ion battery, comprising:

[0007] Carbon-coating single-walled carbon nanotubes by hydrothermal reaction to obtain carbon-coated single-walled carbon nanotubes;

[0008] Chemically etching the carbon-coated single-walled carbon nanotubes to form pores to obtain porous carbon-coated single-walled carbon nanotubes;

[0009] The porous carbon-coated single-walled carbon nanotubes are added to a lithium-ion battery negative electrode material containing a silicon negative electrode to obtain a silicon-carbon lithium-ion battery negative electrode.

[0010] Optionally, the carbon-coating of single-walled carbon nanotubes by hydrothermal reaction to obtain carbon-coated single-walled carbon nanotubes comprises:

[0011] Weigh the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate and the glucose reagent respectively and disperse them uniformly by ultrasonication to obtain a mixed solution;

[0012] The mixed solution is subjected to a hydrothermal reaction to obtain hydrothermal carbon, which is then washed and dried for standby use to obtain single-walled carbon nanotubes coated with hydrothermal carbon, wherein the hydrothermal reaction temperature is 180° C. to 200° C., and the hydrothermal reaction time is 5 h to 20 h;

[0013] The dried hydrothermal carbon is subjected to a carbonization experiment to obtain the carbon-coated single-walled carbon nanotubes, wherein the carbonization temperature is 600° C. to 800° C., the carbonization time is 1 h to 2 h, the protective gas is high-purity argon gas, and the purity of the high-purity argon gas reaches 99.999%.

[0014] Optionally, the mass ratio of the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate, and the glucose reagent is 250:0.1:(5-20).

[0015] Optionally, the step of chemically etching the carbon-coated single-walled carbon nanotubes to form pores to obtain porous carbon-coated single-walled carbon nanotubes comprises:

[0016] The carbon-coated single-walled carbon nanotubes and potassium hydroxide are weighed respectively, ground evenly and chemically etched to form pores to obtain porous carbon-coated single-walled carbon nanotube materials, which are washed and dried for later use. The activation reaction temperature is 800° C. to 1000° C., the activation time is 1 h to 2 h, and the protective gas is high-purity argon gas, the purity of which reaches 99.999%.

[0017] Optionally, the mass ratio of the carbon-coated single-walled carbon nanotubes to the potassium hydroxide is 1:(5-10).

[0018] Optionally, the porous carbon-coated single-walled carbon nanotubes are added to a lithium-ion battery negative electrode material containing a silicon negative electrode to obtain a silicon-carbon lithium-ion battery negative electrode, comprising:

[0019] The porous carbon-coated single-walled carbon nanotubes, pure silicon-based negative electrode materials, conductive carbon black, polyacrylic acid and styrene-butadiene rubber are weighed and added into deionized water, and the negative electrode slurry is obtained after being fully stirred. The negative electrode slurry is obtained after coating and drying.

[0020] Optionally, the mass ratio of the porous carbon-coated single-walled carbon nanotubes to the negative electrode slurry is 0.01 to 0.20.

[0021] Optionally, in the carbon-coated single-walled carbon nanotube, the carbon coating thickness is 10 nm to 30 nm.

[0022] On the other hand, the present invention also provides a silicon-carbon lithium-ion battery negative electrode, which is prepared by the above-mentioned method for preparing the silicon-carbon lithium-ion battery negative electrode.

[0023] On the other hand, the present invention also provides a lithium-ion battery, including a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the negative electrode is the negative electrode of the silicon-carbon lithium-ion battery described above.

[0024] Compared with the prior art, the preparation method and application of the silicon-carbon lithium-ion battery negative electrode provided by the present invention achieve at least the following beneficial effects:

[0025] The present invention suppresses volume expansion by coating a silicon negative electrode with porous carbon, and prepares a micro-mesoporous composite porous carbon-coated single-walled carbon nanotube to replace pure single-walled carbon nanotube as the main conductive agent in the silicon-doped negative electrode formula, thereby improving the cycle life and rate characteristics of the lithium battery.

[0026] The present invention prepares a single-walled carbon nanotube material coated with porous carbon, and applies it as a conductive agent in a silicon-doped negative electrode formula. On the one hand, through the advantages of high conductivity, high flexibility, and high aspect ratio of the single-walled carbon nanotube itself, a developed, dense, conductive, and tough connection is established between the silicon particles, thereby improving the conductivity of the negative electrode sheet of the lithium battery; at the same time, the porous carbon material coated on the single-walled carbon nanotube material is loose and porous, which can effectively inhibit the volume expansion and contraction of the silicon material during the charging and discharging process, slow down the pulverization of the electrode sheet, and improve the cycle life. In addition, the porous carbon mesopores of the micro-mesoporous composite in the negative electrode formula can absorb electrolyte and serve as a transmission channel for lithium ions, shortening the transmission path of lithium ions and improving the rate characteristics of the battery, while the micropores can store a small amount of lithium ions and improve the charge and discharge capacity of the battery.

[0027] Of course, any product implementing the present invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0028] Other features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0030] Figure 1 This is a flow chart of a method for preparing a negative electrode of a silicon-carbon lithium-ion battery provided by the present invention;

[0031] Figure 2 This is a diagram of the structure of porous carbon-coated single-walled carbon nanotubes. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0033] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0034] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0035] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0036] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0037] Combination Figure 1 , Figure 1 The present invention provides a flow chart of a method for preparing a negative electrode of a silicon-carbon lithium-ion battery, which specifically comprises the following steps:

[0038] S1, carbon-coating single-walled carbon nanotubes by hydrothermal reaction to obtain carbon-coated single-walled carbon nanotubes;

[0039] S2, chemically etching the carbon-coated single-walled carbon nanotubes to form pores to obtain porous carbon-coated single-walled carbon nanotubes;

[0040] S3, adding the porous carbon-coated single-walled carbon nanotubes into a lithium-ion battery negative electrode material containing a silicon negative electrode to obtain a silicon-carbon lithium-ion battery negative electrode.

[0041] By preparing porous carbon-coated single-walled carbon nanotube materials and applying them as conductive agents in silicon-doped negative electrode formulations, the negative electrode material combines the excellent conductivity of single-walled carbon nanotubes and the high capacity characteristics of silicon. At the same time, the porous carbon coating layer improves the cycle stability and rate performance of the material.

[0042] Optionally, the carbon-coating of single-walled carbon nanotubes by hydrothermal reaction to obtain carbon-coated single-walled carbon nanotubes comprises:

[0043] Weigh the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate and the glucose reagent respectively and disperse them uniformly by ultrasonication in a beaker to obtain a mixed solution;

[0044] The mixed solution is poured into a hydrothermal kettle for hydrothermal reaction to obtain hydrothermal carbon, and then washed and dried for standby use to obtain hydrothermal carbon-coated single-walled carbon nanotubes, wherein the hydrothermal reaction temperature is 180° C. to 200° C., and the hydrothermal reaction time is 5 h to 20 h;

[0045] The dried hydrothermal carbon is transferred into a tubular furnace for carbonization experiment to obtain the carbon-coated single-walled carbon nanotubes, wherein the carbonization temperature is 600° C. to 800° C., the carbonization time is 1 h to 2 h, the protective gas is high-purity argon, and the purity of the high-purity argon reaches 99.999%.

[0046] The aqueous slurry of single-walled carbon nanotubes is used as the core material to provide conductivity and structural support. The surfactant sodium dodecylbenzene sulfonate (SDBS) is used to improve the dispersibility of single-walled carbon nanotubes in water and prevent agglomeration. Glucose reagent: As a carbon source, it is used to form a carbon coating in the hydrothermal reaction. Under high temperature and pressure, glucose molecules will decompose and deposit on the surface of single-walled carbon nanotubes to form a preliminary carbon coating. The SDBS surfactant helps to maintain the dispersion state of the single-walled carbon nanotubes and prevent agglomeration during the reaction. After the reaction is completed, the product is washed to remove unreacted glucose and SDBS. The washed product is dried to obtain hydrothermal carbon-coated single-walled carbon nanotubes for use.

[0047] The mixture was ultrasonically dispersed using an ultrasonic processor to ensure that each component was evenly dispersed in the solution.

[0048] The hydrothermal reaction temperature is 180°C to 200°C. For example, the hydrothermal reaction temperature can be 180°C, 185°C, 190°C, 185°C, 200°C, or any temperature value between 180°C and 200°C. This temperature range is conducive to the decomposition of glucose and the formation of the carbon coating layer.

[0049] The hydrothermal reaction time can be set to 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or any time value between 5h and 20h. There is no specific limitation here. The length of the reaction time will affect the thickness and uniformity of the carbon coating layer. The hydrothermal reaction time is 5h to 20h, which makes the carbon coating layer more uniform and can ensure that the carbon coating thickness is between 10nm and 30nm, which is beneficial to improve the conductivity of the negative electrode sheet of the lithium battery.

[0050] The dried hydrothermal carbon is transferred to a tube furnace for carbonization experiments. At high temperatures, the hydrothermal carbon undergoes a carbonization reaction to form a more stable carbon structure. After the carbonization is completed, the product is taken out of the tube furnace and cooled. The cooled product is a carbon-coated single-walled carbon nanotube, which can be used for subsequent chemical etching pore formation and the preparation of negative electrode materials for lithium-ion batteries.

[0051] The carbonization temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, or any temperature value between 600°C and 800°C. This temperature range can further carbonize the hydrothermal carbon to form a more stable carbon coating.

[0052] The carbonization time can be 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, or any time value between 1h and 2h. The carbonization time of 1h to 2h can ensure that the carbonization process is fully carried out.

[0053] Of course, high-purity argon is used as an inert gas and as a protective gas to prevent oxidation reactions during the carbonization process. The purity of high-purity argon reaches 99.999% to ensure the purity of the carbonization environment.

[0054] Optionally, the mass ratio of the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate, and the glucose reagent is 250:0.1:(5-20).

[0055] The mass ratio of single-walled carbon nanotube aqueous slurry, surfactant sodium dodecylbenzene sulfonate, and glucose reagent is very important for the preparation of carbon-coated single-walled carbon nanotubes, which will directly affect the formation, thickness and performance of the carbon coating layer of the final product. The single-walled carbon nanotube aqueous slurry is the core material, providing conductivity and structural support. Its mass occupies a dominant position in this ratio, ensuring the presence and performance of single-walled carbon nanotubes in the final product. The surfactant sodium dodecylbenzene sulfonate (SDBS) is used to improve the dispersibility of single-walled carbon nanotubes in water and prevent agglomeration. Although its mass ratio is small, its role is crucial because it directly affects the uniformity of the dispersion of single-walled carbon nanotubes in the reaction system. Glucose reagent is used as a carbon source to form a carbon coating layer in the hydrothermal reaction. Its mass ratio is within a certain range (5 to 20), which allows the thickness and properties of the carbon coating layer to be adjusted according to specific needs. The decomposition products of glucose will be deposited on the surface of the single-walled carbon nanotubes to form a carbon coating layer, thereby improving the stability and conductivity of the material.

[0056] In the present invention, the mass ratio of the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate, and the glucose reagent can be 250:0.1:5, 250:0.1:10, 250:0.1:15, 250:0.1:20, and of course other ratios can also be used, which are not specifically limited here. The mass ratio of the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate, and the glucose reagent is 250:0.1:(5-20). Within this range, combined with the process conditions of the hydrothermal reaction and the carbonization reaction, the carbon coating thickness can be ensured to be 10nm-30nm, which is beneficial to improving the conductivity of the negative electrode sheet of the lithium battery.

[0057] Optionally, the step of chemically etching the carbon-coated single-walled carbon nanotubes to form pores to obtain porous carbon-coated single-walled carbon nanotubes comprises:

[0058] The carbon-coated single-walled carbon nanotubes and potassium hydroxide are weighed separately, put into a mortar, grind evenly, and transferred into a tube furnace for chemical etching to form pores to obtain a porous carbon-coated single-walled carbon nanotube material, which is washed and dried for use. The activation reaction temperature is 800° C. to 1000° C., the activation time is 1 h to 2 h, the protective gas is high-purity argon, and the purity of the high-purity argon reaches 99.999%.

[0059] Chemical etching pore formation can improve the electrochemical performance of single-walled carbon nanotube materials by increasing their specific surface area and pore structure.

[0060] A certain amount of carbon-coated single-walled carbon nanotubes and potassium hydroxide (KOH) were weighed into a mortar, and the mixture was fully ground using a pestle to ensure that potassium hydroxide particles were evenly distributed on the surface of the carbon-coated single-walled carbon nanotubes.

[0061] The activation reaction temperature can be 800°C, 850°C, 900°C, 950°C, 1000°C, or any temperature between 800°C and 1000°C. Within this temperature range, potassium hydroxide will react with carbon to generate products such as potassium carbonate, hydrogen and water vapor. The escape of these products will form pores in the carbon material.

[0062] The activation time is 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, or any time value between 1h and 2h. The length of the activation time will affect the formation of pores and the structural stability of the material. An activation time of 1h to 2h can form a porous carbon coating with uniform pore size and stable material structure.

[0063] In the activation reaction, high-purity argon is used as a protective gas to prevent oxidation reaction during the activation process. The purity of high-purity argon reaches 99.999% to ensure the purity of the activation environment.

[0064] Optionally, after activation, the product is taken out of the tube furnace and cooled. The product is washed with an appropriate washing liquid (such as dilute hydrochloric acid or deionized water) to remove impurities such as residual potassium hydroxide and potassium carbonate generated by the reaction. The washed product is dried to obtain a porous carbon-coated single-walled carbon nanotube material for standby use.

[0065] Optionally, the mass ratio of the carbon-coated single-walled carbon nanotubes to the potassium hydroxide is 1:(5-10).

[0066] The mass ratio of carbon-coated single-walled carbon nanotubes to potassium hydroxide determines the relative content of carbon nanotubes and potassium hydroxide in the reaction system, which in turn affects the pore structure, specific surface area and electrochemical properties of the final porous carbon nanotube material. As the main material of the reaction, the carbon-coated single-walled carbon nanotubes provide structural support and conductivity. Their mass is used as a benchmark in this ratio to ensure the presence and performance of carbon nanotubes in the final product. Potassium hydroxide (KOH) acts as an etchant and reacts with the carbon on the surface of the carbon tube to generate products such as potassium carbonate, hydrogen and water vapor. The escape of these products will form pores on the surface and inside of the carbon tube. The mass ratio of potassium hydroxide is 5 to 10 times that of the mass of the carbon tube, and the size, quantity and distribution of the pores can be adjusted according to specific needs. Of course, as the reaction proceeds, the carbon on the surface of the carbon tube is gradually consumed to form pores. The size, quantity and distribution of the pores also depend on factors such as the concentration of potassium hydroxide, reaction temperature and time.

[0067] Optionally, the porous carbon-coated single-walled carbon nanotubes are added to a lithium-ion battery negative electrode material containing a silicon negative electrode to obtain a silicon-carbon lithium-ion battery negative electrode, comprising:

[0068] The porous carbon-coated single-walled carbon nanotubes, pure silicon-based negative electrode materials, conductive carbon black, polyacrylic acid and styrene-butadiene rubber are weighed and added into deionized water, and the negative electrode slurry is obtained after being fully stirred. The negative electrode slurry is obtained after coating and drying.

[0069] Specifically, accurately weigh the required mass of porous carbon tubes, pure silicon-based negative electrode materials, conductive carbon black, polyacrylic acid and styrene-butadiene rubber. The selection and proportion of these materials can be optimized according to the specific battery performance requirements. Add the weighed materials to a container filled with an appropriate amount of deionized water, and use a stirrer or disperser to fully stir the mixture to ensure that all materials are evenly dispersed in the water to form a stable slurry. The stirring time and speed can be adjusted according to the characteristics of the material and the required slurry viscosity. The stirred negative electrode slurry is evenly coated on the current collector. The coating thickness and uniformity should be controlled during the coating process to ensure the performance consistency of the final negative electrode material.

[0070] Optionally, the mass ratio of the porous carbon-coated single-walled carbon nanotubes in the negative electrode material is 0.01 to 0.20.

[0071] The mass ratio of porous carbon-coated single-walled carbon nanotubes in the negative electrode material is 0.01-0.20, for example, 0.01, 0.05, 0.1, 0.15, 0.2. Although its content in the negative electrode material is relatively small, it plays a key role in conductivity and enhancement.

[0072] Optionally, in the carbon-coated single-walled carbon nanotube, the carbon coating thickness is 10 nm to 30 nm.

[0073] The carbon coating thickness needs to be appropriate. If the carbon coating layer is too thin, it will not be conducive to improving the conductivity. If the carbon coating layer is too thick, it will increase the resistance and reduce the conductivity efficiency. In the present invention, the carbon coating thickness can be 10nm, 15nm, 20nm, 25nm, 30nm, which can improve the conductivity without reducing the conductivity efficiency.

[0074] On the other hand, the present invention also provides a silicon-carbon lithium-ion battery negative electrode, which is prepared by the above-mentioned method for preparing the silicon-carbon lithium-ion battery negative electrode.

[0075] On the other hand, the present invention also provides a lithium-ion battery, including a positive electrode, an electrolyte, a separator, and a negative electrode, wherein the negative electrode is the above silicon-carbon lithium-ion battery negative electrode.

[0076] Embodiment 1:

[0077] This embodiment is a method for preparing a lithium ion battery, comprising:

[0078] The porous carbon-coated single-walled carbon nanotubes are prepared as follows: (1) 0.4 wt.% of single-walled carbon nanotube aqueous slurry produced by OCSiAl, surfactant sodium dodecylbenzene sulfonate, and glucose reagent are weighed in a beaker in a mass ratio of 250:0.1:5, and ultrasonically dispersed uniformly; (2) the ultrasonically dispersed mixed solution is poured into a hydrothermal kettle for hydrothermal reaction at 180°C for 8 hours to obtain hydrothermal carbon, which is washed and dried for standby use to obtain hydrothermal carbon-coated single-walled carbon nanotubes; (3) the hydrothermal carbon-coated single-walled carbon nanotubes are transferred into a tubular furnace and carbonized at 800°C for 1 hour to obtain carbon-coated single-walled carbon nanotubes, and high-purity argon is selected as the protective gas; (4) the carbon-coated single-walled carbon nanotubes and potassium hydroxide are weighed in a mass ratio of 1:5, put into a mortar and grind evenly, and then transferred into a tubular furnace for activation reaction at 800°C for 1 hour, and the protective gas is high-purity argon, to obtain a porous carbon-coated single-walled carbon nanotube material (such as Figure 2 As shown), washing and drying for later use;

[0079] Pure silicon-based negative electrode material, porous carbon-coated single-walled carbon nanotubes, conductive carbon black, polyacrylic acid PAA, and styrene-butadiene rubber SBR are weighed in a mass ratio of 95:0.05:1.95:2:1, and deionized water is added. After fully stirring, a negative electrode slurry is obtained, and after coating and drying, a negative electrode sheet for a lithium-ion battery is obtained.

[0080] Metal lithium was used as the counter electrode and assembled with the above negative electrode to form a button half-cell, wherein Celgard2400 was selected as the separator and 1M LiPF6 was dissolved in EC:EMC:DEC (1:1:1 Vol.%) for electrochemical testing. The charge and discharge window was 0.005V~1.5V.

[0081] The above batteries were evaluated, and the main items were:

[0082] Cyclic gram capacity and first efficiency test: After leaving the battery unpowered for 12 hours, discharge the battery to 0.005V at a constant current and voltage of 0.1C (the gram capacity of the silicon negative electrode is calculated as 2000mAh / g), with a cut-off current of 0.05C, and record the discharge (lithium insertion) capacity as Q1; charge the battery to 1.5V at a constant current of 0.1C, and record the charge (lithium removal) capacity as Q2. The first lithium removal gram capacity is the gram capacity of the battery material, and the first coulombic efficiency of the battery = (first lithium removal capacity / first lithium insertion capacity) × 100%.

[0083] Capacity retention rate test: After the above test steps, the battery is left for 3 minutes, discharged at 1 / 3C constant current and constant voltage to 0.005V, the cut-off current is 0.05C, left for 3 minutes, and charged at 1 / 3C constant current to 1.5V, the first cycle of lithium-free capacity is recorded as SP.C1, the above steps are repeated 100 times, and the 100th cycle of lithium-free capacity is recorded as SP.C100. The capacity retention rate of the 100th cycle = (the 100th cycle of lithium-free capacity is recorded as SP.C100 / the one-cycle lithium-free capacity is recorded as SP.C1) × 100%.

[0084] Pole expansion rate test: After the button half-cell is assembled, let it stand for 12 hours, and discharge it to 0.005V at a constant current and constant voltage of 0.1C, with a cut-off current of 0.05C. Disassemble the button cell in the glove box, clean the pole piece with DEC solvent, and measure the thickness of the negative pole piece in the fully charged state. Pole expansion rate = (thickness of the negative pole piece in the fully charged state - thickness of the fresh pole piece) / thickness of the fresh pole piece × 100%.

[0085] Embodiment 2:

[0086] This embodiment is a method for preparing a lithium ion battery, comprising:

[0087] The porous carbon-coated single-walled carbon nanotubes are prepared, specifically as follows: (1) 0.4wt.% of single-walled carbon nanotube aqueous slurry produced by OCSiAl, surfactant sodium dodecylbenzene sulfonate, and glucose reagent are weighed in a beaker in a mass ratio of 250:0.1:8, and ultrasonically dispersed uniformly; (2) the ultrasonically dispersed mixed solution is poured into a hydrothermal kettle for hydrothermal reaction at 190°C for 8h to obtain hydrothermal carbon, which is then washed and dried for use to obtain hydrothermal carbon-coated single-walled carbon nanotubes; (3) the hydrothermal carbon-coated single-walled carbon nanotubes are transferred into a tubular furnace, and carbonized at 800°C for 1h to obtain carbon-coated single-walled carbon nanotubes, with high-purity argon being the protective gas; (4) the carbon-coated single-walled carbon nanotubes and potassium hydroxide are weighed in a mass ratio of 1:8, put into a mortar and grind evenly, and then transferred into a tubular furnace for activation reaction at 800°C for 1h, with high-purity argon being the protective gas, to obtain porous carbon-coated single-walled carbon nanotube materials, which are then washed and dried for use;

[0088] The slurry preparation of the above materials as conductive agents, the assembly of button half-cells and the testing of the cells are the same as those in Example 1.

[0089] Embodiment 3:

[0090] This embodiment is a method for preparing a lithium ion battery, comprising:

[0091] The porous carbon-coated single-walled carbon nanotubes were prepared by: (1) weighing 0.4 wt.% of single-walled carbon nanotube aqueous slurry produced by OCSiAl, a surfactant sodium dodecylbenzene sulfonate, and a glucose reagent in a mass ratio of 250:0.1:10 respectively and ultrasonically dispersing them uniformly in a beaker; (2) pouring the ultrasonically dispersed mixed solution into a hydrothermal reactor and hydrothermally reacting it at 190°C for 10 hours to obtain hydrothermal carbon, which was washed and dried for later use to obtain hydrothermal carbon-coated Single-walled carbon nanotubes; (3) transferring the hydrothermal carbon-coated single-walled carbon nanotubes into a tubular furnace and carbonizing them at 800°C for 1 h to obtain carbon-coated single-walled carbon nanotubes, with high-purity argon as the protective gas; (4) weighing the carbon-coated single-walled carbon nanotubes and potassium hydroxide in a mass ratio of 1:10, putting them into a mortar and grinding them evenly, and then transferring them into a tubular furnace for activation reaction at 800°C for 2 h, with high-purity argon as the protective gas, to obtain porous carbon-coated single-walled carbon nanotube materials, which were washed and dried for later use;

[0092] The slurry preparation of the above materials as conductive agents, the assembly of button half-cells and the testing of the cells are the same as those in Example 1.

[0093] Embodiment 4:

[0094] This embodiment is a method for preparing a lithium ion battery, comprising:

[0095] The porous carbon-coated single-walled carbon nanotubes were prepared by: (1) weighing 0.4 wt.% of single-walled carbon nanotube aqueous slurry produced by OCSiAl, a surfactant sodium dodecylbenzene sulfonate, and a glucose reagent in a mass ratio of 250:0.1:20 respectively and ultrasonically dispersing them uniformly in a beaker; (2) pouring the ultrasonically dispersed mixed solution into a hydrothermal reactor and hydrothermally reacting it at 190°C for 10 hours to obtain hydrothermal carbon, which was washed and dried for later use to obtain hydrothermal carbon-coated Single-walled carbon nanotubes; (3) transferring the hydrothermal carbon-coated single-walled carbon nanotubes into a tubular furnace and carbonizing them at 800°C for 2h to obtain carbon-coated single-walled carbon nanotubes, with high-purity argon as the protective gas; (4) weighing the carbon-coated single-walled carbon nanotubes and potassium hydroxide at a mass ratio of 1:20, putting them into a mortar and grinding them evenly, and then transferring them into a tubular furnace for activation reaction at 800°C for 2h, with high-purity argon as the protective gas, to obtain porous carbon-coated single-walled carbon nanotube materials, which were washed and dried for later use;

[0096] The slurry preparation of the above materials as conductive agents, the assembly of button half-cells and the testing of the cells are the same as those in Example 1.

[0097] Comparative Example 1:

[0098] Pure silicon-based negative electrode material, single-walled carbon nanotubes, conductive carbon black, polyacrylic acid PAA, and styrene-butadiene rubber SBR were weighed in a mass ratio of 95:0.05:1.95:2:1, and deionized water was added, and the mixture was stirred thoroughly to obtain a negative electrode slurry, which was then coated and dried to obtain a negative electrode sheet for a lithium-ion battery. The assembly of the button half-cell and the test of the battery were the same as in Example 1.

[0099] Comparative Example 2:

[0100] Pure silicon-based negative electrode material, multi-walled carbon nanotubes, conductive carbon black, polyacrylic acid PAA, and styrene-butadiene rubber SBR were weighed in a mass ratio of 95:1.5:0.5:2:1, and deionized water was added, and the mixture was stirred thoroughly to obtain a negative electrode slurry, which was then coated and dried to obtain a negative electrode sheet for a lithium-ion battery. The assembly of the button half-cell and the test of the battery were the same as in Example 1.

[0101] Table 1 Battery performance of various embodiments and comparative examples

[0102]

[0103]

[0104] Combined with Table 1, it can be seen that, compared with Comparative Example 1 and Comparative Document 2, in Examples 1 to 4 of the present invention, the gram capacity is significantly increased, the capacity retention rate at 100 cycles is also significantly increased, and the pole piece expansion rate is reduced. A higher gram capacity means that the battery can store more electrical energy, thereby providing a longer use time or higher energy output; the increase in the capacity retention rate at 100 cycles indicates that the high-quality lithium-ion battery can ensure that the battery can maintain stable performance during long-term use; the pole piece expansion rate reflects the change in the thickness of the pole piece during the battery's charge and discharge cycle. A reduced pole piece expansion rate can improve the battery's cycle stability and safety.

[0105] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for preparing a negative electrode of a silicon-carbon lithium-ion battery, characterized in that: include: Carbon-coating single-walled carbon nanotubes by hydrothermal reaction to obtain carbon-coated single-walled carbon nanotubes; Chemically etching the carbon-coated single-walled carbon nanotubes to form pores to obtain porous carbon-coated single-walled carbon nanotubes; The porous carbon-coated single-walled carbon nanotubes are added to a lithium-ion battery negative electrode material containing a silicon negative electrode to obtain a silicon-carbon lithium-ion battery negative electrode.

2. The method for preparing a negative electrode for a silicon-carbon lithium-ion battery according to claim 1, characterized in that: The method of carbon-coating single-walled carbon nanotubes by hydrothermal reaction to obtain carbon-coated single-walled carbon nanotubes comprises: Weigh the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate and the glucose reagent respectively and disperse them uniformly by ultrasonication to obtain a mixed solution; The mixed solution is subjected to a hydrothermal reaction to obtain hydrothermal carbon, which is then washed and dried for standby use to obtain single-walled carbon nanotubes coated with hydrothermal carbon, wherein the hydrothermal reaction temperature is 180° C. to 200° C., and the hydrothermal reaction time is 5 h to 20 h; The dried hydrothermal carbon is subjected to a carbonization experiment to obtain the carbon-coated single-walled carbon nanotubes, wherein the carbonization temperature is 600° C. to 800° C., the carbonization time is 1 h to 2 h, the protective gas is high-purity argon gas, and the purity of the high-purity argon gas reaches 99.999%.

3. The method for preparing a negative electrode of a silicon-carbon lithium-ion battery according to claim 2, characterized in that: The mass ratio of the single-walled carbon nanotube aqueous slurry, the surfactant sodium dodecylbenzene sulfonate, and the glucose reagent is 250:0.1:(5-20).

4. The method for preparing a negative electrode for a silicon-carbon lithium-ion battery according to claim 1, characterized in that: The step of chemically etching the carbon-coated single-walled carbon nanotubes to form pores to obtain porous carbon-coated single-walled carbon nanotubes comprises: The carbon-coated single-walled carbon nanotubes and potassium hydroxide are weighed respectively, ground evenly and chemically etched to form pores to obtain porous carbon-coated single-walled carbon nanotube materials, which are washed and dried for later use. The activation reaction temperature is 800° C. to 1000° C., the activation time is 1 h to 2 h, and the protective gas is high-purity argon gas, the purity of which reaches 99.999%.

5. The method for preparing a negative electrode for a silicon-carbon lithium-ion battery according to claim 4, characterized in that: The mass ratio of the carbon-coated single-walled carbon nanotube to the potassium hydroxide is 1:(5-10).

6. The method for preparing a negative electrode for a silicon-carbon lithium-ion battery according to claim 1, characterized in that: The method of adding the porous carbon-coated single-walled carbon nanotubes to a lithium-ion battery negative electrode material containing a silicon negative electrode to obtain a silicon-carbon lithium-ion battery negative electrode comprises: The porous carbon-coated single-walled carbon nanotubes, pure silicon-based negative electrode materials, conductive carbon black, polyacrylic acid and styrene-butadiene rubber are weighed and added into deionized water, and the negative electrode slurry is obtained after being fully stirred. The negative electrode slurry is obtained after coating and drying.

7. The method for preparing a negative electrode for a silicon-carbon lithium-ion battery according to claim 6, characterized in that: The mass ratio of the porous carbon-coated single-walled carbon nanotubes to the negative electrode slurry is 0.01 to 0.

20.

8. The method for preparing a negative electrode for a silicon-carbon lithium-ion battery according to claim 1, characterized in that: In the carbon-coated single-walled carbon nanotube, the carbon coating thickness is 10nm to 30nm.

9. A silicon-carbon lithium-ion battery negative electrode, characterized in that: The method is prepared by the method for preparing a silicon-carbon lithium-ion battery negative electrode according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: It comprises a positive electrode, an electrolyte, a separator and a negative electrode, wherein the negative electrode is the negative electrode of the silicon-carbon lithium-ion battery mentioned above.

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