Silicon-based composite material, preparation method and application thereof, lithium ion battery, negative electrode material of lithium ion battery and negative electrode plate of lithium ion battery

Abstract

The invention belongs to the technical field of ion batteries, and particularly relates to a silicon-based composite material, a preparation method and application thereof, a lithium ion battery, a negative electrode material of the lithium ion battery and a negative electrode plate. The preparation method comprises the following steps: ball-milling and mixing a nano silicon material and lithium titanate to obtain a ball-milled product; the mass of the lithium titanate accounts for 1-10% of the mass of the nano silicon material, the rotating speed of the ball-milling mixing is less than or equal to 500 r min <-1 >, and the time is less than or equal to 10 h; and sintering the ball-milled product in a protective gas atmosphere at the temperature of less than or equal to 500 DEG C to obtain the silicon-based composite material. The silicon-based composite material provided by the invention is applied to the lithium ion battery, and shows remarkable initial discharge specific capacity, good rate capability and excellent first coulombic efficiency; meanwhile, the preparation method is simple, environment-friendly and beneficial to large-scale industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion batteries, and particularly relates to a silicon-based composite material, a preparation method and application thereof, a lithium-ion battery, a negative electrode material thereof, and a negative electrode sheet. Background Art

[0002] As a rechargeable and efficient energy storage device, lithium-ion batteries play a crucial role in the fields of mobile electronic devices, new energy vehicles, and grid-scale energy storage.

[0003] Silicon materials are considered to be an ideal choice for the negative electrodes of next-generation high-energy-density lithium-ion batteries due to their theoretical specific capacity of up to about 4200 mAh g -1 , suitable working potential (≈ 0.4 V vs. Li + / Li), and environmental friendliness.

[0004] However, silicon materials will undergo a volume expansion of up to 300% during the lithiation / delithiation process. This severe volume effect will not only cause mechanical damage to the electrode structure but also increase the consumption of the electrolyte, thereby weakening the initial Coulombic efficiency and cycle stability of the battery. In addition, the electronic conductivity of silicon is poor, which further restricts its practical application in the field of lithium-ion batteries. Summary of the Invention

[0005] The purpose of the present invention is to provide a silicon-based composite material, a preparation method and application thereof, a lithium-ion battery, a negative electrode material thereof, and a negative electrode sheet. The silicon-based composite material provided by the present invention is applied to a lithium-ion battery, significantly improving the electronic conductivity of the negative electrode sheet, showing a high initial discharge specific capacity, good rate performance, and excellent first Coulombic efficiency; at the same time, the preparation method is simple and environmentally friendly, which is conducive to large-scale industrial application.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: The present invention provides a preparation method of a silicon-based composite material, comprising the following steps: Ball-milling and mixing nano-silicon materials and lithium titanate to obtain a ball-milled product; the percentage of the mass of lithium titanate in the mass of the nano-silicon materials is 1-10%, and the rotation speed of the ball-milling and mixing ≤ 500 r min -1 , and the time ≤ 10 h; Sintering the ball-milled product in a protective gas atmosphere to obtain the silicon-based composite material, and the sintering temperature ≤ 500 °C.

[0007] Preferably, the percentage of the mass of lithium titanate in the mass of the nano-silicon materials is 2-8%.

[0008] Preferably, the rotation speed of the ball milling and mixing is 50 - 250 r min -1 ; the time of the ball milling and mixing is 1 - 5 h.

[0009] Preferably, the ball milling and mixing uses ball milling beads, the ball milling beads are zirconium beads, and the ball-to-material ratio is 10 - 30:1; The ball milling is wet ball milling, the solvent of the wet ball milling is an alcohol solvent, and the mass ratio of the nano-silicon material to the volume of the alcohol solvent is (1 - 3) g : (10 - 30) mL.

[0010] Preferably, the sintering temperature is 400 - 450 °C, the heat preservation time is 2 - 4 h, and the heating rate for heating to the sintering temperature is 1 - 10 °C min -1 , and the protective gas includes noble gases.

[0011] The present invention provides a silicon-based composite material, which is prepared by the preparation method described in the above technical solution.

[0012] The present invention provides an application of a silicon-based composite material in the preparation of a negative electrode material or a negative electrode sheet of a lithium-ion battery, and the silicon-based composite material is the silicon-based composite material described in the above technical solution.

[0013] The present invention provides a negative electrode material for a lithium-ion battery, including a negative electrode active component, and the negative electrode active component is the silicon-based composite material described in the above technical solution.

[0014] The present invention provides a negative electrode sheet for a lithium-ion battery, including a negative electrode current collector and a negative electrode material provided on the surface of the negative electrode current collector, and the negative electrode material is the negative electrode material for a lithium-ion battery described in the above technical solution.

[0015] The present invention provides a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, and the negative electrode sheet is the negative electrode sheet for a lithium-ion battery described in the above technical solution.

[0016] The present invention provides a preparation method of a silicon-based composite material (denoted as Si / LTO composite material), including the following steps: ball milling and mixing a nano-silicon material (Si-NPs, Si) and lithium titanate (LTO) to obtain a ball milling product; the mass percentage of the lithium titanate in the mass of the nano-silicon material is 1 - 10%, and the rotation speed of the ball milling and mixing ≤500 r min -1, time ≤ 10 h; in a protective gas atmosphere, sinter the ball-milled product to obtain the silicon-based composite material, and the sintering temperature ≤ 500°C. The present invention uses nano-silicon material and lithium titanate as raw materials. First, the ball-milling method is adopted for mixing. By reasonably optimizing the parameters of ball-milling mixing, uniform mixing and sufficient contact of Si and LTO are achieved without destroying the original morphology of Si nanoparticles, which is beneficial to maintaining the high specific capacity of Si while improving the cycle stability and safety of the overall composite material with the help of LTO; then, through sintering and reasonably optimizing the sintering temperature, the mixed Si and LTO are uniformly compounded, which not only helps LTO provide lithium ions to Si, reducing the irreversible lithium loss in the first cycle, but also forms a good conductive network, optimizing the transmission paths of electrons and lithium ions and reducing the charge transfer impedance. In the silicon-based composite material obtained by the preparation method provided by the present invention, a conductive network of Si and LTO is formed. The optimized conductive network of the present invention effectively reduces the side reaction between silicon and the electrolyte, inhibits the formation of a thick SEI film, reduces the irreversible capacity loss, and further improves the initial Coulombic efficiency and long-term cycle performance of the lithium-ion battery when it is used as the active component of the negative electrode material. Secondly, due to the unique "zero strain" characteristic of LTO, introducing it into the system can effectively alleviate the severe volume expansion of silicon during charge and discharge, avoiding the fragmentation of Si nanoparticles and the collapse of the electrode structure, and thus significantly improving the cycle life and capacity retention rate of the electrode.

[0017] The experimental results show that using the Si / LTO material provided by the present invention as the negative electrode active component exhibits a significant initial discharge specific capacity (3075.5 mAh g -1 at 0.1 A g -1 ), good rate performance (1586.5 mAh g -1 at 2 A g -1 ). Compared with the Si electrode, the initial Coulombic efficiency is increased by 4.43%. After 100 cycles at a current density of 0.5 A g -1 , the capacity retention rate still remains at 80.2%. Moreover, the initial Coulombic efficiency of the Si / LTO|LFP full battery is also increased by 7.58% compared with that of the Si|LFP, and the capacity retention rate is increased by 10.18%. The preparation method provided by the present invention has a simple design and is environmentally friendly, which is beneficial to large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 shows the initial Coulombic efficiency and cycle performance of the composite materials of Si and different addition amounts; Figure 2 shows the electrochemical performance of the composite materials of Si and different addition amounts; Figure 3 shows the SEM images of Si and Si / LTO materials; Figure 4 SEM and EDS diagrams of Si / LTO; Figure 5 XRD spectra of Si, LTO and Si / LTO; Figure 6 XPS spectra of Si and Si / LTO; Figure 7 Electrochemical performance of Si and Si / LTO; Figure 8 Electrochemical performance of Si|LFP and Si / LTO|LFP full cells; Figure 9 For Si and Si / LTO at 0.2 mV s -1 to 1.0 mV s -1 CV curves and I p versus v 1 / 2 relationship diagrams; Figure 10 Charge-discharge curves of Si and Si / LTO during the fourth cycle and the corresponding DRT contour plots obtained by in-situ EIS analysis; Figure 11 SEM diagrams of the surface and cross-section of Si and Si / LTO electrodes; Figure 12 SEM and TEM diagrams of Si and Si / LTO particles after cycling. Detailed implementation mode

[0019] The present invention provides a preparation method of a silicon-based composite material, comprising the following steps: Ball-milling and mixing nano-silicon material and lithium titanate to obtain a ball-milled product; the mass percentage of the lithium titanate in the nano-silicon material is 1-10%, and the rotation speed of the ball-milling and mixing ≤ 500 r min -1 , and the time ≤ 10 h; Sintering the ball-milled product in a protective gas atmosphere to obtain the silicon-based composite material, and the sintering temperature ≤ 500 °C.

[0020] In the present invention, without special instructions, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0021] The present invention ball-mills and mixes nano-silicon material and lithium titanate to obtain a ball-milled product; the mass percentage of the lithium titanate in the nano-silicon material is 1-10%, and the rotation speed of the ball-milling and mixing ≤ 500 r min -1, time ≤ 10 h. In the present invention, the particle size of the nano-silicon material is preferably 50 - 100 nm, the purity is preferably ≥ 99%, more preferably ≥ 99.9%, and in the examples it is 99.99%. The lithium titanate is preferably lithium titanate powder. The particle size of the lithium titanate is preferably 50 - 100 nm, the purity is preferably ≥ 99%, and in the examples it is 99.9%. The percentage of the mass of the lithium titanate in the mass of the nano-silicon material is preferably 2 - 8%, and in the examples it can be 2%, 5% or 8%.

[0022] In the present invention, the ball milling and mixing is preferably carried out in a planetary ball mill, and in the examples, the model of the planetary ball mill is ZQM-P2. The rotation speed of the ball milling and mixing is preferably 50 - 250 r min -1 , preferably 150 - 250 r min -1 , and in the examples it can be 250 r min -1 . The time of the ball milling and mixing is preferably 1 - 5 h, and in the examples it can be 3 h. The ball milling and mixing preferably uses ball milling beads. The ball milling beads are preferably zirconium beads. The ball-to-material ratio of the ball milling and mixing is preferably 10 - 30:1, more preferably 20:1. The ball-to-material ratio is the ratio of the mass of the ball milling to the total mass of the nano-silicon material and lithium titanate. The ball milling is preferably wet ball milling, and the solvent of the wet ball milling is preferably an alcohol solvent, and in the examples it can be ethanol. The mass ratio of the nano-silicon material to the volume of the alcohol solvent is preferably (1 - 3) g:(10 - 30) mL, and in the examples it can be 2 g:20 mL.

[0023] In the present invention, after the ball milling and mixing is completed, the present invention preferably uses an alcohol solvent to wash out the ball milling product from the ball milling tank, and then dries and grinds it in sequence to obtain the ball milling product.

[0024] After obtaining the ball milling product, in an inert gas atmosphere, the ball milling product is sintered to obtain the silicon-based composite material, and the sintering temperature ≤ 500 °C. In the present invention, the sintering is preferably carried out in a tube furnace. The inert gas preferably includes noble gases, and in the examples it can be argon. The sintering temperature is preferably 400 - 450 °C, and in the examples it can be 400 °C. The heat preservation time of the sintering is preferably 2 - 4 h, and in the examples it can be 3 h. The heating rate of heating to the sintering temperature is preferably 1 - 10 °C min -1 , and in the examples it can be 5 °C min -1 . After the sintering is completed, a sintered product is obtained. The present invention preferably grinds the sintered product to obtain the silicon-based composite material.

[0025] The present invention prepares the Si / LTO composite material by ball milling and sintering. LTO has a stable chemical structure. When LTO contacts with Si, due to the existence of the lithium intercalation potential difference, lithium ions in LTO can diffuse into Si through the contact interface, thereby compensating for the irreversible consumption of lithium ions during the first charge and discharge process of the Si negative electrode. In addition, the unique "zero strain" property of LTO can provide physical constraints for the volume expansion of silicon, reducing the irreversible consumption of lithium ions caused by the repeated rupture of the SEI film.

[0026] The present invention provides a silicon-based composite material, which is prepared by the preparation method described in the above technical solution. In the present invention, the silicon-based composite material includes nano-silicon and lithium titanate, and the nano-silicon and lithium titanate are in full contact and mixing to form a conductive network structure. The crystal forms of nano-silicon and lithium titanate in the silicon-based composite material remain unchanged.

[0027] The present invention provides an application of the silicon-based composite material in preparing a negative electrode material or a negative electrode sheet of a lithium-ion battery, and the silicon-based composite material is the silicon-based composite material described in the above technical solution.

[0028] The present invention provides a negative electrode material of a lithium-ion battery, including a negative electrode active component, and the negative electrode active component is the silicon-based composite material described in the above technical solution. In the present invention, the negative electrode material of the lithium-ion battery preferably further includes a binder and a conductive agent. The binder is preferably polyacrylic acid (PAA). The conductive agent is preferably Super P. The mass ratio of the negative electrode active component, the binder and the conductive agent is preferably 8:1:1.

[0029] The present invention provides a negative electrode sheet of a lithium-ion battery, including a negative electrode current collector and a negative electrode material disposed on the surface of the current collector, and the negative electrode material is the negative electrode material of the lithium-ion battery described in the above technical solution. In the present invention, the negative electrode current collector is preferably a copper foil current collector. The loading amount of the negative electrode active component in the negative electrode material on the negative electrode sheet of the lithium-ion battery is preferably 1 mg cm -2 . The shape of the negative electrode sheet of the lithium-ion battery is preferably a circular sheet, and the diameter of the circular sheet is preferably 14 mm.

[0030] The present invention provides a preparation method of the negative electrode sheet of the lithium-ion battery described in the above technical solution, preferably including the following steps: mixing the negative electrode active component, the binder, the conductive agent and water, and then stirring and defoaming to obtain a negative electrode slurry; coating the negative electrode slurry on the surface of the negative electrode current collector, and then drying and cutting in sequence to obtain the negative electrode sheet of the lithium-ion battery. The water is preferably deionized water. The mixing preferably includes: grinding the negative electrode active component, the binder and the conductive agent and then mixing with water. The stirring and defoaming is preferably carried out in a stirring and defoaming machine. The rotation speed of the stirring and defoaming is preferably 1000~1500 r min-1 Preferably, the time is 20 to 25 minutes. The coating is preferably carried out using a doctor blade with a specification of 80 μm. The drying is preferably carried out in an electrothermal forced-air drying oven, and the drying temperature is preferably 65 to 70 °C; the time is preferably 12 to 24 hours. The negative electrode sheet of the lithium-ion battery is preferably stored in a drying tank.

[0031] The present invention provides a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The negative electrode sheet is the negative electrode sheet of the lithium-ion battery described in the above technical solution. In the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode material provided on the surface of the current collector. The positive electrode current collector is preferably an aluminum foil current collector. The positive electrode material preferably includes a positive electrode active component, a binder and a conductive agent. The positive electrode active component is preferably lithium iron phosphate (LiFeO4, abbreviated as LFP). The binder is preferably polyvinylidene fluoride (PVDF). The conductive agent is preferably Super P. The mass ratio of the positive electrode active component, the conductive agent and the binder is preferably 8:1:1. The shape of the positive electrode sheet is preferably a circular sheet, and the diameter of the circular sheet is preferably 13 mm.

[0032] In the present invention, the preparation method of the positive electrode sheet preferably includes the following steps: mixing the positive electrode active component, the binder, the conductive agent and an organic solvent, and then stirring and degassing to obtain a positive electrode slurry; coating the positive electrode slurry on the surface of the positive electrode current collector, and then successively performing first drying, blanking and second drying to obtain the positive electrode sheet of the lithium-ion battery. The organic solvent is preferably N-methylpyrrolidone (NMP). The stirring and degassing is preferably carried out in a stirring and degassing machine. The rotation speed of the stirring and degassing is preferably 1000 to 1500 r min -1 Preferably, the time is 20 to 25 minutes. The coating is preferably carried out using a doctor blade. The first drying is preferably carried out in a vacuum drying oven, and the first drying temperature is preferably 75 to 80 °C; the time is preferably 12 to 24 hours. The second drying is preferably carried out in a vacuum drying oven, and the second drying temperature is preferably 100 to 110 °C; the time is preferably 4 to 6 hours.

[0033] In the present invention, the total capacity ratio (N / P) of the negative electrode sheet and the positive electrode sheet is preferably 1.2.

[0034] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0035] The raw materials and reagents used in the following examples are shown in Table 1: Table 1 Raw materials and reagents used in the examples

[0036] Example 1: This example provides a preparation method for Si / LTO composite materials, which is as follows: (1) Add 2 g of Si, a certain mass of LTO (the mass percentage of LTO in Si is 2%, 5%, and 8% respectively), and 20 mL of absolute ethanol into a polytetrafluoroethylene ball milling tank. Use zirconium beads with a ball-to-material ratio of 20:1. Then place the ball milling tank containing the obtained mixed material into a ZQM-P2 type planetary ball mill, and set the ball milling speed to 250 r min -1 Keep ball milling for 3 h.

[0037] (2) After ball milling, wash out the product with absolute ethanol, dry it, and then grind it thoroughly. Then place it in a tube furnace. Under the argon (Ar) atmosphere, heat the material to 400 °C at a heating rate of 5 °C min -1 and keep sintering for 3 hours. Then cool it down. After taking it out and grinding it, finally obtain the Si / LTO composite material.

[0038] Example 2: This example provides a preparation method for Si / LTO electrodes, which is as follows: In this example, polyacrylic acid (PAA) is used as the binder, and Super P is selected as the conductive agent. Weigh accurately according to the mass ratio of the active material (the Si / LTO composite material prepared in Example 1), the binder, and the conductive agent of 8:1:1, and grind it thoroughly until it is uniform. Then transfer it to a stirring and degassing container. Subsequently, add deionized water as the solvent, and place the stirring and degassing container in an AD-680 type stirring and degassing machine, and stir at a speed of 1500 r min -1 for 20 minutes to obtain a uniformly mixed slurry. Then, use an 80 μm scraper to uniformly coat the slurry on the copper foil current collector on one side. After coating, place the electrode in an electrothermal blast drying oven at 70 °C and dry it for 12 h to remove moisture. Finally, cut the electrode sheet into 14 mm circular pieces, weigh them, and store them in a drying tank. The active material loading of the electrode sheet is about 1 mg cm -2 .

[0039] Example 3: This example provides an assembly method for Si / LTO half-cells, which is as follows: In this example, a CR2032 button battery is assembled. The Si / LTO electrode prepared in Example 2 is used as the electrode of the half-cell. A lithium sheet with a diameter of 15.4 mm is used as the negative electrode, and porous polypropylene is selected as the separator. In this example, a commercial battery-grade electrolyte is used. During assembly, 50 μL of the electrolyte is dropped on each side of the separator. The entire battery assembly process is completed in a glove box under argon protection to ensure an oxygen-free and water-free environment. The specific assembly process of the CR2032 button half-cell is as follows: First, the negative electrode case, shrapnel, gasket, lithium metal sheet, separator, electrode sheet, and gasket are placed in sequence, and finally the positive electrode case is covered. Then, a pressure of 50 MPa is applied to the battery using a battery encapsulation machine for sealed packaging to ensure the battery is well-prepared. The assembled half-cell is left standing at room temperature for 24 h, and then tested and evaluated using a LAND battery test system under normal temperature conditions.

[0040] Example 4: This example provides a method for preparing a Si / LTO full cell, and the specific steps are as follows: The positive electrode material in this example is lithium iron phosphate (LiFeO4, abbreviated as LFP). LFP, conductive additive (SuperP), and polyvinylidene fluoride (PVDF) are proportioned according to a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone (NMP) is added as a solvent and placed in a stirring and degassing box. After sealing, it is put into an AD-680 stirring and degassing machine and homogenized at a high speed of 1500 r min -1 for 20 minutes. The obtained slurry is evenly coated on one side of the aluminum foil current collector using a scraper, and then treated in a vacuum drying oven at 80 °C for 12 h. The dried electrode sheet is punched into a circular sheet with a diameter of 13 mm and placed in a vacuum oven at 110 °C for further drying for 6 h to completely remove the residual solvent. A positive electrode sheet (LFP electrode sheet) is obtained using LFP as the positive electrode active component material, and a negative electrode sheet is obtained using Si or Si / LTO composite material as the negative electrode active component material. The total capacity ratio (N / P) between the negative electrode and the positive electrode is adjusted to be approximately 1.2. The assembly sequence of the full cell is as follows: negative electrode case, shrapnel, gasket, negative electrode sheet, separator, LFP electrode sheet, gasket, positive electrode case, and 50 μL of commercial battery-grade electrolyte is dropped on each side of the separator. A CR2032 button battery is prepared by sealing under a pressure of 50 MPa using a battery encapsulation machine. All assembly steps are completed in a glove box under argon protection, and the water and oxygen content in the box is strictly controlled below 0.1 ppm. After the packaged battery is left standing at room temperature for 30 h, the electrochemical performance is evaluated using a LAND battery test system.

[0041] Results and Discussion (1) Regulation of key parameters of Si / LTO To study the effect of the addition amount of LTO on the initial Coulombic efficiency and cycle stability of the composite material during charge and discharge, the composite material was made into a negative electrode sheet, and a coin cell was made by matching it with a lithium sheet as the counter electrode (for the detailed steps of cell fabrication, see Example 3). The charge-discharge cycle performance of the Si / LTO composite materials prepared with 2%, 5%, and 8% LTO addition amounts as the negative active component and the cell made with Si as the negative active component material was tested. The Si / LTO composite materials prepared with 2%, 5%, and 8% LTO addition amounts as the negative active component were denoted as Si / LTO-2%, Si / LTO-5%, and Si / LTO-8%, respectively. The test results are as Figure 1 shown, Figure 1 The test conditions were as follows: at room temperature, cycle for 3 cycles under the test condition of 0.1 A g -1 , perform activation treatment on the negative electrode material, and then conduct long-cycle tests at a current density of 0.5 A g -1 . The charge-discharge voltage range was 0.01~2.0 V. Figure 1 In (a) of Figure 1 are the initial charge-discharge curves of Si and Si / LTO composite materials with different LTO addition amounts. -1 The results in (a) of -1 show that at a cut-off voltage of 2.0 V, the first-cycle discharge specific capacities of the four different materials, Si, Si / LTO-2%, Si / LTO-5%, and Si / LTO-8%, are 2677.4 mAh g -1 , 2813.8 mAh g -1 , 3075.5 mAh g -1 , and 2955.8 mAh g -1 , respectively, and the first-cycle charge specific capacities are 2358.6 mAh g -1 , 2593.5 mAh g -1 , 2845.4 mAh g Figure 1 In (b) of Figure 1As shown in (b) of [reference], the capacity retention rates after 100 cycles are 68.9%, 79.6%, 80.2% and 76.6% respectively, and Si / LTO-5% also shows the best cycle stability, with the capacity retention rate increased by 11.3% compared with the Si electrode. More or less element doping amount usually has different effects on the electrochemical performance of materials. In the 2% LTO composite system, due to the relatively low LTO content, there are not enough lithium ions to make up for the loss in the first cycle and the formation of a stable SEI film, so the first efficiency and cycle stability are improved limitedly; while in the 8% LTO composite system, the excessive LTO content may lead to restricted lithium ion transport kinetics, and the effect is average in improving the first efficiency and capacity retention rate of the silicon anode.

[0042] The rate performance of four electrodes Si, Si / LTO-2%, Si / LTO-5% and Si / LTO-8% was systematically studied below, and the results are as Figure 2 shown in (a) of [reference]. Figure 2 As shown in (a) of [reference], it is the rate performance of Si and Si / LTO composites with different LTO addition amounts. Figure 2 As shown in (a) of [reference], it shows that a step test was carried out in the current density range of 0.1~2.0 A g -1 , and 5 cycles were carried out at each current density. The average specific capacities of the four electrode materials are shown in Table 2. From Figure 2 the information in (a) of [reference] and Table 2, it can be seen that the Si / LTO-5% composite material shows the best rate performance. When the current density returns from 2.0 A g -1 to 0.1 A g -1 , its capacity almost completely recovers, showing good electrochemical reversibility. This benefits from the stable spinel structure of LTO and almost no volume change, which can not only keep the structure stable during repeated charge and discharge processes of the electrode, but also provide a good lithium ion transport channel. The interfacial characteristics of the four electrodes were further analyzed by electrochemical impedance spectroscopy (EIS), and the results are as Figure 2 shown in (b) of [reference], Figure 2 As shown in (b) of [reference], it is the electrochemical impedance of Si and Si / LTO composites with different LTO addition amounts. Figure 2 As shown in (c) of [reference], the data was fitted using ZView software. The semicircle diameter in the high-frequency region of the AC impedance spectrum reflects the charge transfer process at the electrode / electrolyte interface. After software fitting, the charge transfer resistance (R ct), the smaller the value, the smaller the charge transfer resistance of the material, indicating faster electrochemistry reaction kinetics. The fitted impedances of Si, Si / LTO-2%, Si / LTO-5%, and Si / LTO-8% are 197 Ω, 147.2 Ω, 103.8 Ω, and 165.3 Ω respectively. Adding LTO significantly reduces the charge transfer resistance of the composite material, indicating that the good conductivity and high ion diffusion ability of LTO itself contribute to constructing a uniform and continuous conductive network, thus significantly reducing the charge transfer resistance inside the electrode. It should be noted that the resistance value of the 5% LTO addition amount is the smallest.

[0043] Table 2 Average specific capacities of Si and three composite materials at different rates In summary, through experimental exploration, the 5% LTO addition amount shows the best initial efficiency improvement and electrochemical performance (subsequently named Si / LTO). In order to deeply study the internal mechanism of LTO composite improving silicon anode materials and achieving high initial efficiency and long cycle stability, the materials will be systematically analyzed below.

[0044] (2)Structure characterization of Si / LTO composite material As shown in Example 1, the detailed preparation steps of Si / LTO: First, weigh 2 g of Si, 0.1 g of LTO, and 20 mL of absolute ethanol and add them to a polytetrafluoroethylene ball milling tank. Add zirconium beads according to a ball-to-material ratio of 20:1. Place the ball milling tank in a ZQM-P2 type planetary ball mill, and set the ball milling speed to 250 r min -1 for 3 h of ball milling. Secondly, after the ball milling is completed, wash out the slurry with absolute ethanol, dry it, and put it into a mortar for sufficient grinding. Finally, place the ground material in a tube furnace, under an Ar protective atmosphere, heat it to 400 °C at a heating rate of 5 °C min -1 and hold it at this temperature for 3 h for sintering treatment. After the furnace body cools down, take out the material and grind it sufficiently to finally obtain the required composite material.

[0045] To study the morphology and element distribution characteristics of Si / LTO, SEM and EDS characterizations were carried out on Si and Si / LTO. Figure 3 Figure (a) in is the SEM image of Si material, Figure 3 Figure (b) in is the SEM image of Si / LTO material. From Figure 3 Figure 3As can be seen from (a) and (b) in [reference], the original particle size and structure of Si remain intact after ball milling, without excessive fragmentation or particle refinement. This indicates that the selected ball milling process conditions are relatively mild, only achieving uniform mixing and sufficient contact between Si and LTO, without damaging the original morphology of Si particles. This is beneficial for maintaining the high specific capacity of Si while improving the cycle stability and safety of the overall composite material with the help of LTO. Figure 4 SEM and EDS images of Si / LTO. The elemental composition and distribution of the sample can be further analyzed from the elemental distribution imaging map (mapping map) ( Figure 4 ), and the results show that Ti, Si, and O elements are uniformly distributed.

[0046] The XRD technique was used to systematically characterize the phase composition and crystal structure of Si, LTO, and Si / LTO composites. As Figure 5 shown, Figure 5 are the XRD patterns of Si, LTO, and Si / LTO. The three main peaks of the Si / LTO composite are located at 28°, 47°, and 56°, corresponding to the (111), (220), and (311) crystal planes of Si, respectively. At the same time, strong peaks from LTO corresponding to PDF#49-0207 were also found. This indicates that both Si and LTO in the composite material maintain their respective crystal structures without phase transformation or change in crystal structure. It shows that after compounding Si and LTO by ball milling, the intrinsic properties of the two materials are retained, which helps Si / LTO give full play to the advantages of the high specific capacity of Si and the high stability and low volume expansion of LTO, and thus shows a significant improvement in electrochemical performance and cycle stability.

[0047] To deeply study the chemical environment of relevant elements in the Si / LTO composite material, XPS tests were carried out on Si and Si / LTO. As Figure 6 shown in (a) of [reference], Figure 6 in (a) are the full XPS spectra of Si and Si / LTO. Both Si and Si / LTO show characteristic peaks of O 1s, C 1s, Si 2p, and Si 2s in the full spectra. In addition, a signal peak of Ti 2p appears at around 453 eV in Si / LTO. Figure 6 In (b) of [reference], the fine spectrum of Ti 2p is shown, and the two broad peaks are located at about 463.7 eV and 458.5 eV, corresponding to the signals of Ti 2p 1 / 2 and Ti 2p 3 / 2 in spinel LTO. Combining the previous XRD pattern and EDX mapping analysis results, it further confirms the successful preparation of the Si / LTO composite material.

[0048] (3) Electrochemical characterization of Si / LTO In the voltage range of 0.01 - 2 V, button cells were assembled to test the electrochemical performance of Si and Si / LTO. Figure 7 Figure (a) in [reference] shows the initial charge-discharge curves of Si and Si / LTO at 0.1 A g -1 -1, showing the comparison of the first charge-discharge curves and open-circuit voltages of Si and Si / LTO at 0.1 A g -1 -1. The first Coulombic efficiency of Si is 88.08% and the open-circuit voltage is 2.26 V. The first Coulombic efficiency of Si / LTO is 92.52% and the open-circuit voltage is 0.78 V. It is obvious that after the addition of LTO for composite, the first efficiency is increased by 4.44% and the open-circuit voltage is decreased by 1.48 V. The high lithium intercalation voltage of LTO enables lithium ions to spontaneously migrate from LTO with high chemical potential to Si with low chemical potential after the two come into contact, thus improving the first efficiency of the silicon-based anode. At the same time, the lithium-containing composite material has a lower open-circuit voltage, and the lower open-circuit voltage can reduce the reduction reaction of the electrolyte on the electrode surface, inhibit the formation of an overly thick SEI film, thereby reducing the lithium consumed in the first charge-discharge cycle and significantly improving the first efficiency. In addition, after 100 cycles of Si / LTO at 0.5 A g -1 -1 ( Figure 7 Figure (b) in [reference] shows the cycling performance of Si and Si / LTO at 0.5 A g -1 -1), it still shows significant cycling stability, with a capacity retention rate of 80.2%, significantly higher than 68.9% of Si. The cycling data reveals that the introduction of LTO effectively inhibits the capacity decay of silicon and endows it with excellent long-term cycling stability. Figure 7 Figures (c) in [reference] and Figure 7 Figures (d) in [reference] show the evolution of the charge-discharge curves of Si and Si / LTO electrodes during 100 cycles at a current density of 0.5 A g -1 -1. The flat voltage plateau that appears near 0.25 V corresponds to the lithiation reaction process of amorphous Si. Obviously, the voltage plateau of the Si electrode gradually disappears with the increase of the number of cycles, and at the same time, the capacity decays rapidly, while the capacity of Si / LTO does not decay significantly, the change of the voltage plateau is also small, and the polarization voltage is much smaller than that of the Si electrode, indicating that the composite of LTO helps to reduce the polarization reaction during cycling.

[0049] To further evaluate the application effect of Si / LTO in full cells, the electrochemical performance of Si|LFP and Si / LTO|LFP full cells was assembled and evaluated according to the experimental operation of Example 4 ( Figure 8 ). The corresponding voltage range and N / P ratio were set to 2.2 - 4.0 V and 1.20, respectively. Figure 8(a) shows the initial charge-discharge curves of the Si|LFP and Si / LTO|LFP full cells at 0.1 C, indicating the initial charge-discharge curves at a current density of 0.1 C (1 C = 160 A g -1 ). The first Coulombic efficiency of Si / LTO|LFP is 85.32%, and that of Si|LFP is 77.74%. By comparison, the first efficiency is improved by 7.58%. In addition, at a current density of 0.33 C, the cycling performance of the Si|LFP and Si / LTO|LFP cells was compared and analyzed ( Figure 8 (b) in shows the cycling performance of the Si|LFP and Si / LTO|LFP full cells at 0.33 C). After 35 cycles, the capacity retention rate of Si / LTO|LFP is 66.71%, while that of Si|LFP is only 56.53%. In contrast, the capacity retention rate is increased by 10.18%. The incorporation of LTO also exhibits excellent first Coulombic efficiency and cycling stability in the full cell.

[0050] To further analyze the reaction kinetic information of Si and Si / LTO, CV tests were carried out on these two electrodes at different scan rates, and the results are as Figure 9 shown. Figure 9 are the CV curves of Si and Si / LTO at scan rates from 0.2 mV s -1 to 1.0 mV s -1 and the I p vs. v 1 / 2 relationship diagrams. Figure 9 (a) and (b) in show the test results of the Si electrode, Figure 9 (c) and (d) in show the test results of the Si / LTO electrode. Scan rates of 0.2 mV s -1 , 0.4 mV s -1 , 0.6 mV s -1 , 0.8 mV s -1 and 1.0 mV s -1 were used, and the voltage range was 0.01~2 V. Kinetic analysis was performed on its peak 1 and peak 2 respectively. After linearly fitting the current i and the square root of the corresponding scan rate ν to obtain the slope, the larger the slope, the larger the diffusion coefficient D, that is, the better the diffusion kinetics of lithium ions in the electrode material. By comparison, it can be found that the slope of Si / LTO is significantly greater than that of Si, which indicates that the volume expansion of Si will cause structural collapse and hinder ion transport, while the introduction of LTO improves the diffusion rate of lithium ions on the electrode surface, further confirming the positive effect of LTO on improving the electrochemical performance of the composite material.

[0051] In order to comprehensively study the interface evolution of Si and Si / LTO electrodes during the cycling process, in-situ electrochemical impedance spectroscopy (EIS) test analysis was used. -1 3 cycles of activation and conversion to dynamic relaxation time (DRT) mode ( Figure 10 The charge and discharge curves of Si and Si / LTO during the fourth cycle and the corresponding DRT contours obtained by in-situ EIS analysis are shown in Figure 2. Figure 10 (a) is the test result of Si electrode. Figure 10 (b) is the test result of Si / LTO electrode. DRT results show that at about 10 -5 , 10 -3 and 10 0 There are three different relaxation times in seconds, corresponding to R s , R SEI , R ct . By comparison, it is found that the R s The value is significantly smaller than that of Si, which indicates that after the introduction of LTO into the composite system, a more continuous and efficient conductive network is constructed, thereby significantly reducing the internal resistance of the overall electrode. It is worth noting that the R SEI The value is significantly lower than that of Si, indicating that the formed SEI is thinner. This is because the introduced LTO plays a role in buffering the volume expansion of silicon, making the SEI protective layer formed during the charge and discharge process thinner, denser and more stable. In addition, the R ct The value is also significantly smaller than that of Si, proving that after the introduction of LTO in the composite system, the charge transfer process at the electrode / electrolyte interface has been significantly improved. The good ionic and electronic conductivity of LTO itself helps to build a uniform and continuous conductive network, while improving the contact and ion transport at the electrode / electrolyte interface, thereby greatly reducing the interfacial polarization. Lower charge transfer impedance and internal resistance mean that during the charge and discharge process, the transmission of lithium ions in the composite material is smoother, which helps to inhibit the repeated rupture and regeneration of the SEI film caused by the drastic volume expansion of silicon, thereby reducing the irreversible consumption of lithium in the first cycle, thereby improving the overall electrochemical performance and cycle stability of the composite electrode.

[0052] (4) Morphology analysis of Si / LTO electrode after cycling The reason why Si / LTO composite materials exhibit excellent electrochemical performance is that the uniform composite of LTO and Si constructs an efficient conductive network, which promotes the rapid transport of electrons and lithium ions, reduces the charge transfer impedance, and is conducive to improving the electrochemical cycle stability of Si / LTO. In addition, as a "zero-strain" material, its rigid skeleton can effectively inhibit the severe volume expansion of silicon during lithium intercalation, thereby maintaining the integrity of the electrode structure and endowing the electrode with excellent cycle performance. Figure 11 Figure 2 shows the SEM images of the surface and cross-section of Si and Si / LTO electrodes. After cycling 100 times at 0.5 A g -1 , various large cracks formed on the surface of the Si electrode ( Figure 11 Figure 2(a) shows the surface of the Si electrode after cycling), however, no obvious cracks formed on the surface of the Si / LTO electrode after cycling under the same conditions ( Figure 11 Figure 2(b) shows the surface of the Si / LTO electrode after cycling). In addition, compared with before cycling, the electrode expansion rate of Si was as high as 124.5% ( Figure 11 Figures 2(c) and (d) show the cross-section of the Si electrode before and after cycling), and the electrode expansion of Si / LTO decreased significantly ( Figure 11 Figures 2(e) and (f) show the cross-section of the Si / LTO electrode before and after cycling, and this result further confirms that the introduction of LTO in Si / LTO can alleviate the volume expansion of Si and has better structural stability.

[0053] The microstructures of the Si and Si / LTO electrodes after cycling 100 times were characterized by TEM. Figure 12 Figure 3 shows the SEM and TEM images of the Si particles and Si / LTO particles after cycling. Figure 12 Figures 3(a) and (b) show the SEM images of the Si particles and Si / LTO particles after cycling, Figure 12 Figures 3(c) and (d) show the TEM images of the Si particles and Si / LTO particles after cycling.

[0054] As shown in Figure 12 Figure 3(a), the pure Si electrode could not maintain a complete particle morphology after cycling, which was due to the repeated volume expansion / contraction of silicon during lithiation / delithiation, resulting in particle fragmentation and structural collapse. The newly exposed surface continuously participated in side reactions, ultimately leading to electrode failure. In contrast, as shown in Figure 12 Figure 3(b), the Si / LTO composite material still maintained a complete particle structure after cycling, which was mainly attributed to the "zero-strain" property of LTO effectively buffering the volume change of silicon. At the same time, its stable framework structure provided mechanical support for the silicon particles, preventing particle pulverization and agglomeration. This structural stability is the key factor for the excellent cycle performance of the Si / LTO composite material. Analyzing the SEM images of the particles after cycling ( Figure 12In (c) and (d) as well, it can be observed that after 100 cycles, the silicon particles have pulverized and many obvious cracks have appeared on the surface, while the particles of Si / LTO still remain very intact after 100 cycles and no cracks have formed on the surface. This is consistent with the TEM results, fully demonstrating the role of LTO in stabilizing the structure of the Si / LTO composite material.

[0055] As can be seen from the above embodiments, the present invention uses the ball milling method to prepare the Si / LTO lithium-containing composite material, realizing the uniform composite of Si and LTO. The uniform composite between the two not only helps LTO provide lithium ions to Si, reducing the irreversible lithium loss in the first cycle, but also can form a good conductive network, optimizing the transmission paths of electrons and lithium ions and reducing the charge transfer impedance. This optimized conductive network effectively reduces the side reaction between silicon and the electrolyte, inhibits the formation of a thick SEI film, reduces the irreversible capacity loss, and further improves the first Coulombic efficiency and long-term cycling performance. Secondly, due to the unique "zero strain" characteristic of LTO, introducing it into the system can effectively alleviate the severe volume expansion of silicon during charge and discharge, avoiding particle fragmentation and electrode structure collapse, and thus significantly improving the cycle life and capacity retention rate of the electrode. The experimental results show that the Si / LTO electrode exhibits a remarkable initial discharge specific capacity (3075.5 mAh g -1 at 0.1 A g -1 ), good rate performance (1586.5 mAh g -1 at 2 A g -1 ). Compared with the Si electrode, the first Coulombic efficiency has increased by 4.43%, and the capacity retention rate still remains at 80.2% after 100 cycles at a current density of 0.5 A g -1 . Moreover, the first Coulombic efficiency of the Si / LTO|LFP full cell has also increased by 7.58% compared with that of the Si|LFP, and the capacity retention rate has increased by 10.18%. This process design is simple and environmentally friendly, which is conducive to large-scale industrial application.

[0056] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of a silicon-based composite material, characterized in that Comprising the following steps: Mix nano-silicon material and lithium titanate by ball milling to obtain a ball-milled product; the percentage of the mass of the lithium titanate in the mass of the nano-silicon material is 1 to 10%, and the rotation speed of the ball milling is ≤ 500 r min -1 , and the time is ≤ 10 h; In a protective gas atmosphere, sinter the ball-milled product to obtain the silicon-based composite material, and the sintering temperature ≤ 500 °C.

2. The preparation method according to claim 1, wherein The mass percentage of the lithium titanate in the mass of the nanosilicon material is 2-8%.

3. The preparation method according to claim 1 or 2, characterized in that, The rotation speed of the ball milling and mixing is 50 - 250 r / min -1 ; The time of the ball milling and mixing is 1 - 5 h.

4. The preparation method according to claim 1, characterized in that, The ball milling uses milling beads, the milling beads are zirconium beads, and the ball-to-material ratio is 10-30:1; The ball milling is wet ball milling, the solvent for the wet ball milling is an alcohol solvent, and the mass ratio of the nanosilicon material to the volume of the alcohol solvent is (1-3) g:(10-30) mL.

5. The preparation method according to claim 1, characterized in that, The sintering temperature is 400~450 °C, the heat preservation time is 2~4 h, and the heating rate to the sintering temperature is 1~10 °C / min -1 , and the protective gas includes noble gases.

6. A silicon-based composite material, characterized in that, The silicon-based composite material is prepared by the preparation method according to any one of claims 1-5.

7. Use of a silicon-based composite material in preparing an anode material or an anode sheet of a lithium-ion battery, characterized in that, The silicon-based composite material is the silicon-based composite material according to claim 6.

8. An anode material for a lithium-ion battery, characterized in that, Comprising a negative electrode active component, and the negative electrode active component is the silicon-based composite material according to claim 6.

9. A negative electrode sheet of a lithium-ion battery, characterized in that, Comprising a negative electrode current collector and a negative electrode material provided on the surface of the negative electrode current collector, and the negative electrode material is the negative electrode material for a lithium-ion battery according to claim 8.

10. A lithium-ion battery, comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, characterized in that, The negative electrode sheet is the negative electrode sheet for a lithium-ion battery according to claim 9.

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