Preparation method of silicon negative electrode lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a preparation method of a silicon negative electrode lithium ion battery, which comprises the following steps: 1) coating a carbon layer on the surface of a silicon material, performing fluorine doping on the carbon layer by using a fluorine-containing substance in a calcining manner, performing charge modification on the surface of the carbon layer by using a cationic surface active agent, and then coating by using MXene to obtain a silicon negative electrode lithium ion battery; a carbon-coated silicon material of a fluorine-doped carbon layer coated with MXene is used as a negative electrode active material, a negative electrode plate is prepared from the negative electrode active material, and then the lithium ion battery containing the negative electrode plate is prepared. 2) performing vacuum baking on the lithium ion battery to enable the moisture of the lithium ion battery to be less than 200ppm; 3) injecting a conventional electrolyte into the lithium ion battery, and fully standing; 4) carrying out pressurized formation on the lithium ion battery; and 5) charging the lithium ion battery to a fully charged state, and standing to prepare the high-performance silicon negative electrode lithium ion battery. Compared with the prior art, the lithium ion battery prepared by the method is good in cycle performance and rate capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for preparing a silicon negative electrode lithium ion battery. Background Art

[0002] With the development of new energy technologies, advanced energy storage devices with high specific energy have attracted increasing attention. However, existing lithium-ion secondary batteries cannot meet the specific energy requirements of advanced energy storage devices.

[0003] Among the many alternative anode materials to graphite, silicon (Si) is considered one of the most promising. Its unique advantages include: ① high theoretical specific capacity. When Si is fully lithiated to Li4.4Si, the theoretical specific capacity can reach 4200mAh / g (approximately 10 times that of graphite); ② suitable operating voltage (approximately 0.2-0.3V vs. Li / Li+), which can be directly matched with commercial cathode materials (such as LiCoO2 and nickel-cobalt-manganese ternary materials) to produce full batteries; and ③ abundant natural resources, low price, and environmental protection. Despite these many advantages, silicon anodes also have some limitations that limit their commercial application.

[0004] The lithium storage mechanism of silicon-based negative electrodes is an alloying reaction mechanism. During the lithiation process, the silicon material will undergo severe volume expansion. During the operation of the battery, repeated volume changes will lead to the collapse of the electrode material structure and the repeated formation of the solid electrolyte interphase (SEI), resulting in the active Li + Irreversible losses and rapid capacity decay reduce the first coulombic efficiency and cycle life of silicon-based LIBs.

[0005] Therefore, it is of great significance to realize the practical application of silicon-based electrode materials to study how to improve the rate performance and cycle life of electrode materials through other means, such as: composite of silicon-based materials and carbon materials, nano-sizing of silicon-based materials, coating with metal oxides (such as Fe2O3, TiO2, Al2O3, etc.), surface modification, etc. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a silicon negative electrode lithium ion battery in order to improve the cycle performance and rate performance of the battery.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a silicon negative electrode lithium ion battery comprises the following steps:

[0009] 1) coating the surface of the silicon material with a carbon layer;

[0010] 2) fluorine-doping the carbon layer by calcining with a fluorine-containing substance;

[0011] 3) using cationic surfactants to modify the charge of the carbon layer surface;

[0012] 4) Coating with MXene;

[0013] 5) Using a carbon-coated silicon material coated with a fluorine-doped carbon layer of MXene as the negative electrode active material to prepare a negative electrode sheet, and then preparing a lithium-ion battery containing the negative electrode sheet;

[0014] 6) vacuum baking the lithium-ion battery to reduce the moisture content of the lithium-ion battery to less than 200 ppm;

[0015] 7) Inject conventional electrolyte into the lithium-ion battery and let it stand for a long time;

[0016] 8) Pressurizing the lithium-ion battery;

[0017] It should be noted that if the pressure is too low, the positive and negative electrodes and the separator will not fit well together, affecting the interface and causing uneven current density. Furthermore, the gas generated during formation can easily damage the interface. Excessive pressure can force the electrolyte out of the gaps, affecting the transport of lithium ions. Furthermore, if the formation current is too low, the formation time will be too long, affecting production efficiency. If the formation current is too high, the reaction will be too intense, such as gas generation, which can damage the interface.

[0018] 9) Charging the lithium-ion battery to a fully charged state at a pressure of 0.6 to 1.2 MPa to obtain a silicon negative electrode lithium-ion battery.

[0019] Preferably, in step 1), the silicon material has a particle size of 1 to 10 μm. The optimal particle size is 5 μm. If the silicon material particle size is too small, the specific surface area is large, processing performance is poor, and electrolyte consumption is rapid. If the silicon material particle size is too large, the material expands significantly and the cycle performance is poor.

[0020] Preferably, in step 1), coating methods include but are not limited to pyrolysis and vapor deposition carbon.

[0021] Preferably, in step 2), the calcination temperature is 400-1000° C., and the fluorine-containing substance includes but is not limited to tetrafluoroterephthalic acid, PVDF and octafluoronaphthalene.

[0022] Preferably, in step 3), the cationic surfactant includes but is not limited to CTAB and PDDA.

[0023] Preferably, in step 5), the mass ratio of the silicon material MXene to the negative electrode active material is 1 to 99%.

[0024] Preferably, the porosity of the negative electrode sheet is 5-40%. More preferably, the porosity of the negative electrode sheet is 20%. If the porosity is too small, the electrolyte loading amount is too small, the internal resistance is large, and the cycle performance is poor; if the porosity is too large, the effective active material is small and the energy density is low.

[0025] Preferably, in step 6), the temperature of vacuum baking is 85-120° C., and the vacuum degree is less than -85 KPa.

[0026] Preferably, in step 7), the standing time is 24 to 96 hours.

[0027] Preferably, in step 8), the pressure is 0.6-1.2 MPa, and the formation current is 0.02C-0.5C.

[0028] Preferably, in step 9), the current of constant current charging is 0.01 to 0.5 C, the current of constant voltage charging is 0.005 to 0.05 C, and the battery is left to stand for 1 to 24 hours.

[0029] The present invention also provides a silicon negative electrode lithium ion battery obtained by the method.

[0030] Compared with the prior art, the preparation method of the present invention has at least the following beneficial effects:

[0031] 1) The present invention coats the surface of the silicon material with a carbon layer. On the one hand, the carbon coating can significantly improve the overall conductivity of the silicon material, thereby reducing the internal impedance of the battery and improving the battery's charge and discharge performance. On the other hand, the elastic structure formed by the carbon coating can act as a buffer, helping to maintain the structural stability of the material and extend the cycle life of the battery.

[0032] 2) The present invention dopes the carbon layer with fluorine by calcining it with a fluorine-containing substance. The fluorine element promotes the formation of a fluoride-enriched SEI film (such as LiF) with excellent electronic insulation and ionic conductivity, thereby reducing side reactions and improving interfacial stability. Fluorine doping also inhibits side reactions between the negative electrode and the electrolyte, reducing electrolyte decomposition and consumption, and slowing capacity decay.

[0033] 3) The present invention utilizes a carbon-coated silicon material coated with a fluorine-doped carbon layer using MXene. MXene is a two-dimensional transition metal carbide or nitride with excellent electrical conductivity. Using MXene as a coating material significantly improves the electronic conductivity of the composite material. The carbon coating provides mechanical support to a certain extent, buffering volume expansion. The MXene coating further enhances structural stability, prevents cracking of the electrode material, and improves cycling stability.

[0034] 4) The structure produced by the present method combines the high conductivity and mechanical stability of MXene with the chemical stability of fluorine-doped carbon. The MXene and fluorine-doped carbon layers reduce irreversible capacity loss while retaining the high theoretical specific capacity of silicon, resulting in a material with high capacity, long life, and high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 : Comparative Examples 1-3 and Example 1 prepared silicon negative electrode lithium ion batteries at 0.2Ag -1 Next 100 laps of the cycle diagram;

[0036] Figure 2 : Charge and discharge diagram of the lithium-ion battery prepared in Comparative Examples 1-3. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below in conjunction with specific implementation examples, but the protection scope of the present invention is not limited to the following embodiments.

[0038] The various raw materials used in the embodiments of the present invention are all commercially available.

[0039] Comparative Example 1

[0040] 1) coating a silicon material with a carbon layer (coating methods include but are not limited to pyrolysis and vapor deposition carbon) as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet;

[0041] 2) vacuum baking the lithium ion battery obtained in step 1), wherein the vacuum baking temperature is 85° C. and the vacuum degree is less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0042] 3) injecting a conventional electrolyte into the lithium-ion battery obtained in step 2) and allowing it to stand for 48 hours;

[0043] 4) pressurizing the lithium-ion battery obtained in step 3) at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0044] 5) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to prepare a silicon negative electrode lithium-ion battery.

[0045] Comparative Example 2

[0046] 1) Coating the silicon material surface with a carbon layer (coating methods include but are not limited to pyrolysis and vapor deposition carbon)

[0047] 2) fluorine-doping the carbon layer of the material obtained in step 1) by calcining with a fluorine-containing substance at a calcination temperature of 1000° C. (the fluorine-containing substance includes but is not limited to tetrafluoroterephthalic acid, PVDF, and octafluoronaphthalene) as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet;

[0048] 3) vacuum baking the lithium ion battery obtained in step 2), wherein the vacuum baking temperature is 85° C. and the vacuum degree is less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0049] 4) injecting a conventional electrolyte into the lithium-ion battery obtained in step 3) and allowing it to stand for 48 hours;

[0050] 5) pressurizing the lithium-ion battery obtained in step 4) at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0051] 6) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0052] Comparative Example 3

[0053] 1) Coating the silicon material surface with a carbon layer (coating methods include but are not limited to pyrolysis and vapor deposition carbon)

[0054] 2) The material obtained in step 1) is fluorine-doped with a fluorine-containing substance by calcining the carbon layer at a temperature of 1000° C. (The fluorine-containing substance includes but is not limited to tetrafluoroterephthalic acid, PVDF, and octafluoronaphthalene).

[0055] 3) using a cationic surfactant to modify the charge of the carbon layer surface of the material obtained in step 2) (cationic surfactants include but are not limited to CTAB and PDDA) to prepare a negative electrode active material, and then preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet;

[0056] 4) vacuum baking the lithium ion battery obtained in step 3) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0057] 5) injecting a conventional electrolyte into the lithium-ion battery obtained in step 4) and allowing it to stand for 48 hours;

[0058] 6) pressurizing the lithium-ion battery obtained in step 5) at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0059] 7) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to prepare a silicon negative electrode lithium-ion battery.

[0060] Comparative Example 4

[0061] 1) Coating the silicon material surface with a carbon layer (coating methods include but are not limited to pyrolysis and vapor deposition carbon)

[0062] 2) The material obtained in step 1) is fluorine-doped with a fluorine-containing substance by calcining the carbon layer at a temperature of 1000° C. (The fluorine-containing substance includes but is not limited to tetrafluoroterephthalic acid, PVDF, and octafluoronaphthalene).

[0063] 3) Using a cationic surfactant to modify the surface charge of the carbon layer of the material obtained in step 2) (cationic surfactants include but are not limited to CTAB and PDDA)

[0064] 4) The material obtained in step 3) is coated with MXene, and the mass ratio of the obtained material to MXene is 99%

[0065] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0066] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0067] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0068] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0069] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0070] Example 1

[0071] 1) coating the surface of the silicon material with a carbon layer by pyrolysis;

[0072] 2) calcining the material obtained in step 1) with tetrafluoroterephthalic acid (a fluorine-containing substance) to fluorine-dope the carbon layer at a temperature of 1000° C.;

[0073] 3) using a cationic surfactant CTAB to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0074] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 99% of the mass of the obtained material;

[0075] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0076] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0077] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0078] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0079] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0080] Example 2

[0081] 1) coating the surface of the silicon material with a carbon layer by pyrolysis;

[0082] 2) fluorine-doping the carbon layer of the material obtained in step 1) with fluorine-containing material PVDF by calcining at a temperature of 1000° C.;

[0083] 3) using a cationic surfactant CTAB to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0084] 4) coating the material obtained in step 3) with MXene, wherein the mass ratio of the obtained material to MXene is 10%;

[0085] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0086] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0087] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0088] 8) The lithium ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C.

[0089] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0090] Example 3

[0091] 1) coating the surface of the silicon material with a carbon layer by vapor deposition;

[0092] 2) calcining the material obtained in step 1) with fluorine-containing substance octafluoronaphthalene to fluorine-dope the carbon layer at a temperature of 800° C.;

[0093] 3) using a cationic surfactant CTAB to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0094] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 20% of the mass of the obtained material;

[0095] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0096] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0097] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0098] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0099] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0100] Example 4

[0101] 1) coating the surface of the silicon material with a carbon layer by vapor deposition;

[0102] 2) calcining the material obtained in step 1) with tetrafluoroterephthalic acid (a fluorine-containing substance) to fluorine-dope the carbon layer at a temperature of 800° C.;

[0103] 3) using a cationic surfactant PDDA to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0104] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 30% of the mass of the obtained material;

[0105] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0106] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0107] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0108] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0109] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0110] Example 5

[0111] 1) coating the surface of the silicon material with a carbon layer by pyrolysis;

[0112] 2) fluorine-doping the carbon layer of the material obtained in step 1) with fluorine-containing material PVDF by calcining at a temperature of 700° C.;

[0113] 3) using a cationic surfactant PDDA to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0114] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 99% of the mass of the obtained material;

[0115] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0116] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0117] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0118] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0119] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0120] Example 6

[0121] 1) coating the surface of the silicon material with a carbon layer by vapor deposition;

[0122] 2) calcining the material obtained in step 1) with fluorine-containing substance octafluoronaphthalene to fluorine-dope the carbon layer at a temperature of 700° C.;

[0123] 3) using a cationic surfactant PDDA to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0124] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 15% of the mass of the obtained material;

[0125] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0126] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0127] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0128] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0129] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0130] Example 7

[0131] 1) coating the surface of the silicon material with a carbon layer by pyrolysis;

[0132] 2) calcining the material obtained in step 1) with tetrafluoroterephthalic acid (a fluorine-containing substance) to fluorine-dope the carbon layer at a temperature of 600° C.;

[0133] 3) using a cationic surfactant CTAB to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0134] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 25% of the mass of the obtained material;

[0135] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0136] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 105° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0137] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0138] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0139] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0140] Example 8

[0141] 1) coating the surface of the silicon material with a carbon layer by pyrolysis;

[0142] 2) fluorine-doping the carbon layer of the material obtained in step 1) with fluorine-containing material PVDF by calcining at a temperature of 500° C.;

[0143] 3) using a cationic surfactant CTAB to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0144] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 35% of the mass of the obtained material;

[0145] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0146] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 150° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0147] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0148] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0149] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0150] Example 9

[0151] 1) coating the surface of the silicon material with a carbon layer by vapor deposition;

[0152] 2) calcining the material obtained in step 1) with fluorine-containing substance octafluoronaphthalene to fluorine-dope the carbon layer at a temperature of 500° C.;

[0153] 3) using a cationic surfactant CTAB to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0154] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 5% of the mass of the obtained material;

[0155] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0156] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 125° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0157] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0158] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0159] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0160] Example 10

[0161] 1) coating the surface of the silicon material with a carbon layer by vapor deposition;

[0162] 2) calcining the material obtained in step 1) with tetrafluoroterephthalic acid (a fluorine-containing substance) to fluorine-dope the carbon layer at a temperature of 800° C.;

[0163] 3) using a cationic surfactant PDDA to charge-modify the surface of the carbon layer of the material obtained in step 2);

[0164] 4) coating the material obtained in step 3) with MXene, wherein the mass of MXene accounts for 50% of the mass of the obtained material;

[0165] 5) Using a carbon-coated silicon material having a fluorine-doped carbon layer coated with MXene as a negative electrode active material, preparing a negative electrode sheet using the negative electrode active material, and then preparing a lithium-ion battery containing the negative electrode sheet.

[0166] 6) vacuum baking the lithium ion battery obtained in step 5) at a temperature of 85° C. and a vacuum degree of less than -85 kPa, so that the moisture content of the lithium ion battery is less than 200 ppm;

[0167] 7) injecting a conventional electrolyte into the lithium-ion battery obtained in step 6) and allowing it to stand for 48 hours;

[0168] 8) The lithium-ion battery obtained in step 7) was pressurized at a pressure of 0.8 MPa and a formation current of 0.1 C;

[0169] 9) The lithium-ion battery was charged to a full charge state at a pressure of 0.8 MPa, a charging current of 0.1 C, a constant voltage charge of 0.02 C, and allowed to stand for 12 h to obtain a silicon negative electrode lithium-ion battery.

[0170] Under the conditions of Comparative Example 1-2, Figure 1 and Figure 2 have to:

[0171] Batteries with Si@C at 0.2Ag -1 The initial discharge capacity is 2134.5 mAh g -1 , which is higher than the initial discharge capacity of original Si (1738.8 mAh g -1 ), Figure 1 shows that Si anode is 0.2Ag -1The Si@C anode showed a high capacity of 514.73 mAh g after 100 cycles. -1 reversible capacity, while the original Si only retained 323.7 mAh g -1 ;

[0172] Data shows that by coating the surface of silicon materials with a carbon layer, on the one hand, the carbon coating can significantly improve the overall conductivity of the silicon material, thereby reducing the internal impedance of the battery and improving the battery's charge and discharge performance. On the other hand, the elastic structure formed by the carbon coating can act as a buffer, helping to maintain the structural stability of the material and extend the cycle life of the battery.

[0173] Comparative Example 3 and Example 1, Figure 1 and Figure 2 have to:

[0174] Data comparison 1: Batteries with Si@CF-MXene at 0.2Ag -1 The Si@CF-MXene anode showed 1184.53 mAh g after 100 cycles. -1 reversible capacity, while the original Si only retained 323.7 mAh g -1 , Si@C retained 514.73mAh g -1 , Si@CF retained 734.54 mAh g -1 All are lower than Si@CF-MXene;

[0175] Data comparison 2: The specific data in comparison 1 and Figure 1-2 The Si@CF batteries are also higher than the original Si and Si@C batteries;

[0176] Data comparison 2 shows that fluorine-doping the carbon layer with fluorine-containing substances through calcination promotes the formation of a fluoride-enriched SEI film (such as LiF). This film has excellent electronic insulation and ionic conductivity, thereby reducing side reactions and improving interfacial stability. Fluorine doping can also inhibit side reactions between the negative electrode and the electrolyte, reducing electrolyte decomposition and consumption, and delaying capacity decay.

[0177] Data comparison 1 demonstrates the potential of carbon-coated silicon materials coated with fluorine-doped carbon layers using MXene. MXene is a two-dimensional transition metal carbide or nitride with excellent electrical conductivity. Using MXene as a coating significantly improves the electronic conductivity of the composite material. The carbon coating provides mechanical support and mitigates volume expansion. The MXene coating further enhances structural stability, prevents cracking in the electrode material, and improves cycling stability.

[0178] Data comparison 1 shows that the structure prepared by the preparation method of the present invention combines the high conductivity and mechanical stability of MXene with the chemical stability of fluorine-doped carbon. The MXene and fluorine-doped carbon layers reduce irreversible capacity loss while retaining the high theoretical specific capacity of silicon, resulting in a material with high capacity, long life, and high stability.

Claims

1. A method for preparing a silicon negative electrode lithium ion battery, characterized in that: The following steps are involved: 1) coating the surface of the silicon material with a carbon layer; 2) fluorine-doping the carbon layer by calcining with a fluorine-containing substance; 3) using cationic surfactants to modify the charge of the carbon layer surface; 4) Coating with MXene; 5) Using a carbon-coated silicon material coated with a fluorine-doped carbon layer of MXene as the negative electrode active material to prepare a negative electrode sheet, and then preparing a lithium-ion battery containing the negative electrode sheet; 6) vacuum baking the lithium-ion battery to reduce the moisture content of the lithium-ion battery to less than 200 ppm; 7) Inject conventional electrolyte into the lithium-ion battery and let it stand for a long time; 8) Pressurizing the lithium-ion battery; 9) Charging the lithium-ion battery to a fully charged state at a pressure of 0.6 to 1.2 MPa to obtain a silicon negative electrode lithium-ion battery.

2. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 1), the particle size of the silicon material is 1 to 10 μm; the coating method includes but is not limited to pyrolysis and vapor deposition carbon.

3. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 2), the calcination temperature is 400-1000° C., and the fluorine-containing substance includes but is not limited to tetrafluoroterephthalic acid, PVDF and octafluoronaphthalene.

4. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 3), the cationic surfactant includes but is not limited to CTAB and PDDA.

5. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 5), the mass ratio of the silicon material MXene to the negative electrode active material is 1 to 99%; the porosity of the negative electrode sheet is 5 to 40%.

6. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 6), the temperature of vacuum baking is 85-120° C., and the vacuum degree is less than -85 KPa.

7. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 7), the standing time is 24 to 96 hours.

8. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 8), the pressure is 0.6-1.2 MPa, and the formation current is 0.02C-0.5C.

9. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, wherein: In step 9), the current of constant current charging is 0.01 to 0.5C, the current of constant voltage charging is 0.005 to 0.05C, and the battery is left to stand for 1 to 24 hours.

10. A lithium-ion battery with a silicon negative electrode obtained by the method according to any one of claims 1 to 9.

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