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

Abstract

The present invention belongs to the field of ion battery technology, specifically relating to silicon-based composite materials, their preparation methods and applications, lithium-ion batteries, and their negative electrode materials and negative electrode sheets. In the present invention, nano-silicon material and lithium titanate are ball-milled to obtain a ball-milled product; the mass of the lithium titanate accounts for 1-10% of the mass of the nano-silicon material, and the ball-milling speed is ≤500 rpm. ‑1 , for ≤10 h; and sintering the ball-milled product in a protective gas atmosphere to obtain the silicon-based composite material, wherein the sintering temperature is ≤500°C. The silicon-based composite material provided by the present invention is applied to lithium-ion batteries and exhibits significant initial discharge specific capacity, good rate performance, and excellent first coulombic efficiency. Furthermore, the preparation method is simple and environmentally friendly, making it suitable for large-scale industrial applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion batteries, and specifically relates to silicon-based composite materials and preparation methods and applications thereof, lithium-ion batteries and negative electrode materials and negative electrode sheets thereof. Background Art

[0002] As a rechargeable and efficient energy storage device, lithium-ion batteries play a key role in mobile electronic devices, new energy vehicles, and grid-level energy storage.

[0003] Silicon materials have a high capacity of about 4200 mAh g -1 Theoretical specific capacity, suitable working potential (≈ 0.4 V vs.Li + / Li) and environmental friendliness, and is considered to be an ideal choice for the next generation of high energy density lithium-ion battery anodes.

[0004] However, silicon materials experience a volume expansion of up to 300% during the lithiation / delithiation process. This dramatic volume effect not only causes mechanical damage to the electrode structure but also increases electrolyte consumption, thereby reducing the battery's initial coulombic efficiency and cycling stability. Furthermore, silicon's poor electronic conductivity further restricts its practical application in 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 and a negative electrode sheet thereof. The silicon-based composite material provided by the present invention is applied to lithium-ion batteries, significantly improving the electronic conductivity of the negative electrode sheet, exhibiting 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] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a silicon-based composite material, comprising the following steps:

[0008] The nano-silicon material and lithium titanate are ball-milled to obtain a ball-milled product; the mass of the lithium titanate accounts for 1-10% of the mass of the nano-silicon material, and the rotation speed of the ball-milling is ≤500 r min -1 , time ≤ 10 h;

[0009] The ball milling product is sintered in a protective gas atmosphere to obtain the silicon-based composite material, and the sintering temperature is ≤500°C.

[0010] Preferably, the mass of the lithium titanate accounts for 2-8% of the mass of the nano-silicon material.

[0011] Preferably, the rotation speed of the ball milling is 50-250 r / min. -1 Preferably, the ball milling time is 1-5 h.

[0012] Preferably, the ball milling uses ball milling beads, the ball milling beads are zirconium beads, and the ball-to-material ratio is 10-30:1.

[0013] The ball milling is wet ball milling, the solvent of the wet ball milling is an alcohol solvent, and the mass of the nano-silicon material and the volume of the alcohol solvent are (1-3) g:(10-30) mL.

[0014] Preferably, the sintering temperature is 400-450 ℃, the holding time is 2-4 h, and the heating rate for heating to the sintering temperature is 1-10 ℃ / min. -1 The protective gas comprises a noble gas.

[0015] The application provides a silicon-based composite material prepared by the preparation method.

[0016] The application provides an application of the silicon-based composite material in preparation of a lithium ion battery negative electrode material or a negative electrode sheet.

[0017] The application provides a lithium ion battery negative electrode material, which comprises a negative electrode active component, and the negative electrode active component is the silicon-based composite material.

[0018] The application provides a lithium ion battery negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material arranged on the surface of the negative electrode current collector, and the negative electrode material is the lithium ion battery negative electrode material.

[0019] The application provides a lithium ion battery, which comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, and the negative electrode sheet is the lithium ion battery negative electrode sheet.

[0020] The application provides a preparation method of a silicon-based composite material (denoted as Si / LTO composite material), which comprises the following steps: ball milling of 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 is ≤500 r / min. -1, time <= 10 h; and sintering the ball-milled product in a protective gas atmosphere to obtain the silicon-based composite material, the sintering temperature being <= 500 DEG C. The present application uses nanosilicon material and lithium titanate as raw materials, first mixes them by ball milling, realizes uniform mixing and full contact of Si and LTO by reasonably optimizing the parameters of ball milling mixing, without destroying the original morphology of Si nanoparticles, which is conducive to maintaining the high specific capacity of Si and improving the cycle stability and safety of the overall composite material with the help of LTO; then the present application uniformly composites the mixed Si and LTO by sintering while reasonably optimizing the sintering temperature, which not only helps LTO to provide lithium ions for Si and reduces the irreversible lithium loss in the first cycle, but also forms a good conductive network, optimizes the transmission path of electrons and lithium ions, and reduces the charge transfer impedance. The silicon-based composite material obtained by the preparation method provided by the present application forms a conductive network of Si and LTO, and the optimized conductive network of the present application effectively reduces the side reaction between silicon and electrolyte, suppresses the formation of thick SEI film, reduces the irreversible capacity loss, and further improves the first coulombic efficiency and long-term cycle performance of the lithium ion battery when used as a negative electrode material. Secondly, due to the unique "zero strain" characteristic of LTO, its introduction into the system can effectively alleviate the severe volume expansion of silicon during charging and discharging, avoid the crushing of Si nanoparticles and the collapse of the electrode structure, and thus significantly improve the cycle life and capacity retention rate of the electrode.

[0021] The experimental results show that the Si / LTO material provided by the present application as a negative electrode active component exhibits a significant initial discharge specific capacity (0.1 A g -1 -1 of 3075.5 mAh g -1 -1, good rate performance (2 A g -1 -1 of 1586.5 mAh g -1 -1), the first coulombic efficiency is increased by 4.43% compared with Si electrode, and the capacity retention rate is still maintained at 80.2% after 100 cycles at a current density of 0.5 A g -1 -1. Furthermore, the first coulombic efficiency of the Si / LTO|LFP full battery is also increased by 7.58% compared with Si|LFP, and the capacity retention rate is increased by 10.18%. The preparation method provided by the present application is simple in design, environmentally friendly, and conducive to large-scale industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The first coulombic efficiency and cycle performance of Si and different amounts of composite materials;

[0023] Figure 2 The electrochemical performance of Si and different amounts of composite materials;

[0024] Figure 3 SEM images of Si and Si / LTO materials;

[0025] Figure 4 SEM and EDS images of Si / LTO;

[0026] Figure 5 XRD patterns of Si, LTO and Si / LTO;

[0027] Figure 6 XPS spectra of Si and Si / LTO;

[0028] Figure 7 Electrochemical performance of Si and Si / LTO;

[0029] Figure 8 Electrochemical performance of Si|LFP and Si / LTO|LFP full cell;

[0030] Figure 9 CV curves and I -1 vs. v -1 plots of Si and Si / LTO at 0.2 mV s p and 1.0 mV s 1 / 2 scan rates;

[0031] Figure 10 Charge-discharge curves of Si and Si / LTO during the fourth cycle and corresponding DRT contour plots obtained by in-situ EIS analysis;

[0032] Figure 11 SEM images of Si and Si / LTO electrode surface and cross-section;

[0033] Figure 12 SEM and TEM images of Si and Si / LTO particles after cycling. DETAILED DESCRIPTION

[0034] The present application provides a preparation method of a silicon-based composite material, comprising the following steps:

[0035] ball-milling the nanosilicon material and lithium titanate to obtain a ball-milling product; the mass percentage of the lithium titanate in the nanosilicon material is 1-10%, and the rotation speed of the ball-milling is ≤500 r / min -1 , and the time is ≤10 h;

[0036] sintering the ball-milling product in a protective gas atmosphere to obtain the silicon-based composite material, and the sintering temperature is ≤500℃.

[0037] In the present application, all the preparation raw materials / components are commercially available products well known to those skilled in the art, unless otherwise specified.

[0038] The present application mixes nano-silicon material and lithium titanate by ball milling to obtain a ball milling product; the mass percentage of the lithium titanate in the nano-silicon material is 1-10%, and the rotation speed of the ball milling is ≤500 r / min -1 , and the time is ≤10 h. In the present application, the particle size of the nano-silicon material is preferably 50-100 nm, and the purity is preferably ≥99%, more preferably ≥99.9%, and in the examples, 99.99%. The lithium titanate is preferably lithium titanate powder. The particle size of the lithium titanate is preferably 50-100 nm, and the purity is preferably ≥99%, and in the examples, 99.9%. The mass percentage of the lithium titanate in the nano-silicon material is preferably 2-8%, and in the examples, it can be 2%, 5%, or 8%.

[0039] In the present application, the ball milling 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 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 is preferably 1-5 h, and in the examples, it can be 3 h. The ball milling preferably uses ball milling beads. The ball milling beads are preferably zirconium beads. The ball-to-material ratio of the ball milling 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 the 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 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.

[0040] In the present application, after the ball milling is completed, the present application preferably uses an alcohol solvent to wash the ball milling product out of the ball milling tank, and then sequentially carries out drying and grinding to obtain the ball milling product.

[0041] After obtaining the ball milling product, the present application sintered the ball milling product in a protective gas atmosphere to obtain the silicon-based composite material, and the sintering temperature is ≤500 ℃. In the present application, the sintering is preferably carried out in a tube furnace. The protective gas preferably includes a noble gas, and in the examples, it can be argon. The sintering temperature is preferably 400-450 ℃, and in the examples, it can be 400 ℃. The holding time of the sintering is preferably 2-4 h, and in the examples, it can be 3 h. The heating rate for heating to the sintering temperature is preferably 1-10 ℃ / min -1 , and in the examples, it can be 5 ℃ / min -1After the sintering, a sintered product is obtained. The sintered product is preferably ground to obtain the silicon-based composite material.

[0042] The Si / LTO composite material is prepared by ball milling and sintering. LTO has a stable chemical structure. When LTO is in contact with Si, lithium ions in LTO can diffuse into Si through the contact interface due to the existence of the lithium intercalation potential difference, thereby compensating for the irreversible consumption of lithium ions in the first charge-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.

[0043] The application provides a silicon-based composite material prepared by the preparation method.

[0044] The application provides an application of the silicon-based composite material in the preparation of a lithium ion battery negative electrode material or a negative electrode sheet.

[0045] The application provides a lithium ion battery negative electrode material comprising a negative electrode active component, wherein the negative electrode active component is the silicon-based composite material.

[0046] The application provides a lithium ion battery negative electrode sheet comprising a negative electrode current collector and a negative electrode material arranged on the surface of the current collector, wherein the negative electrode material is the lithium ion battery negative electrode material. -2 The shape of the lithium ion battery negative electrode sheet is preferably a round sheet, and the diameter of the round sheet is preferably 14 mm.

[0047] The present invention provides a method for preparing a negative electrode sheet of a lithium-ion battery according to the above technical solution, which preferably includes the following steps: mixing the negative electrode active component, binder, conductive agent and water, and then stirring and degassing 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, binder and conductive agent and then mixing them with water. The stirring and degassing is preferably carried out in a stirring and degassing machine. The rotation speed of the stirring and degassing is preferably 1000~1500 r min -1 The coating is preferably performed using a scraper with a diameter of 80 μm. Drying is preferably performed in an electric forced air drying oven at a temperature of 65-70°C for 12-24 hours. The lithium-ion battery negative electrode sheet is preferably stored in a drying can.

[0048] The present invention provides a lithium-ion battery comprising 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 comprises a positive electrode current collector and a positive electrode material disposed on the surface of the current collector. The positive electrode current collector is preferably an aluminum foil current collector. The positive electrode material preferably comprises 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 disc, and the diameter of the disc is preferably 13 mm.

[0049] In the present invention, the method for preparing the positive electrode sheet preferably includes the following steps: mixing the positive electrode active component, binder, conductive agent, and 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 sequentially performing a first drying, punching, and second drying to obtain the lithium-ion battery positive electrode sheet. The organic solvent is preferably N-methylpyrrolidone (NMP). The stirring and degassing is preferably performed in a stirring and degassing machine. The stirring and degassing speed is preferably 1000-1500 r / min. -1 The coating is preferably performed using a scraper. The first drying is preferably performed in a vacuum drying oven at a temperature of 75-80°C for a time of 12-24 hours. The second drying is preferably performed in a vacuum drying oven at a temperature of 100-110°C for a time of 4-6 hours.

[0050] In the present application, the total capacity ratio (N / P) of the negative electrode sheet and the positive electrode sheet is preferably 1.2.

[0051] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0052] The raw materials and reagents used in the following examples are shown in Table 1:

[0053] Table 1 Raw materials and reagents used in the examples

[0054]

[0055] Example 1:

[0056] The present example provides a preparation method of Si / LTO composite material, which is specifically as follows:

[0057] (1) 2 g of Si, a certain amount of LTO (the mass percentage of LTO in Si is 2%, 5%, and 8% respectively), and 20 mL of anhydrous ethanol were added into a polytetrafluoroethylene ball mill jar, zirconium beads were used, and the ball-to-material ratio was 20:1. Then the ball mill jar containing the obtained mixed material was placed in a ZQM-P2 planetary ball mill, and the ball milling speed was set to 250 r min -1 for 3 h.

[0058] (2) After ball milling, the product was washed out with anhydrous ethanol, dried, and then fully ground. Then it was placed in a tube furnace, heated to 400℃ at a heating rate of 5℃ min -1 under an argon (Ar) atmosphere, and kept sintering for 3 h. Then it was cooled, taken out, and ground to obtain the Si / LTO composite material.

[0059] Example 2:

[0060] The present example provides a preparation method of Si / LTO electrode, which is specifically as follows:

[0061] In the present example, polyacrylic acid (PAA) is used as a binder, and Super P is used as a conductive agent. The active material (Si / LTO composite material prepared in Example 1), the binder, and the conductive agent were accurately weighed according to the mass ratio of 8:1:1, and then fully ground to uniformity. Then they were transferred to a stirring and defoaming container. Subsequently, deionized water was added as a solvent, and the stirring and defoaming container was placed in an AD-680 stirring and defoaming machine, and stirred at a speed of 1500 r min -1The slurry was stirred at 2000 rpm for 20 min to obtain a uniform mixture. Then, the slurry was uniformly coated on one side of the copper foil current collector using an 80-μm doctor blade. After coating, the electrode was dried in a 70 °C electric heating drying oven for 12 h to remove the water. Finally, the electrode sheet was cut into 14-mm-diameter discs, weighed, and stored in a dry jar. The active material loading of the electrode sheet was about 1 mg cm -2 .

[0062] Example 3:

[0063] This example provides a method for assembling a Si / LTO half-cell, which is as follows:

[0064] This example assembles a CR2032-type button cell using the Si / LTO electrode prepared in Example 2 as the electrode of the half-cell, a lithium sheet with a diameter of 15.4 mm as the negative electrode, and porous polypropylene as the separator. Commercially available battery-grade electrolyte was used in this example. During assembly, 50 μL of electrolyte was added to each side of the separator. The entire assembly process was performed in an argon-protected glove box to ensure an oxygen-free and water-free environment. The specific assembly process of the CR2032-type button half-cell is as follows: first, place the negative electrode shell, spring, gasket, lithium sheet, separator, electrode sheet, and gasket in order, and then cover the positive electrode shell. Next, use a battery packaging machine to seal and package the battery at a pressure of 50 MPa to ensure that the battery is prepared intact. The assembled half-cell was allowed to stand at room temperature for 24 h, and then tested and evaluated at room temperature using a LAND battery test system.

[0065] Example 4:

[0066] This example provides a method for preparing a Si / LTO full cell, which is as follows:

[0067] The positive electrode material of this example is lithium iron phosphate (LiFeO4, abbreviated as LFP). LFP, conductive additive (SuperP), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1, and a certain amount of N-methyl pyrrolidone (NMP) was added as a solvent into a stirring and degassing box. After sealing, the mixture was placed in an AD-680 stirring and degassing machine at 1500 r min -1The slurry was homogenized at a high speed for 20 minutes. The resulting slurry was evenly coated on one side of an aluminum foil current collector using a spatula and then dried in a vacuum oven at 80°C for 12 hours. The dried electrode sheet was punched into 13 mm diameter discs and further dried in a vacuum oven at 110°C for 6 hours to completely remove any residual solvent. LFP was used as the positive electrode active component (LFP electrode sheet), and Si or Si / LTO composite material was used as the negative electrode active component (N / P). The total capacity ratio (N / P) between the negative and positive electrodes was adjusted to approximately 1.2. The full cell was assembled in the following order: negative electrode case, spring, gasket, negative electrode sheet, separator, LFP electrode sheet, gasket, positive electrode case. 50 μL of commercial battery-grade electrolyte was dripped onto each side of the separator. The cells were sealed using a battery encapsulator at a pressure of 50 MPa to prepare CR2032 coin cells. All assembly steps were performed in an argon-protected glove box, where the water and oxygen content was strictly controlled to below 0.1 ppm. After the encapsulated batteries were left standing at room temperature for 30 h, the electrochemical performance was evaluated using the LAND battery testing system.

[0068] Results and Discussion

[0069] (1) Si / LTO key parameter control

[0070] In order to study the effect of LTO addition on the first coulombic efficiency and cycle stability of the composite material during the charge and discharge process, it was made into a negative electrode sheet and matched with a lithium sheet to make a button battery (the detailed steps of battery preparation are shown in Example 3). The charge and discharge cycle performance of the battery made of Si / LTO composite materials prepared with 2%, 5% and 8% LTO addition as the negative electrode active component and Si as the negative electrode active component material was tested. The Si / LTO composite materials prepared with 2%, 5% and 8% LTO addition as the negative electrode active component were recorded as Si / LTO-2%, Si / LTO-5% and Si / LTO-8% respectively. The test results are shown in Figure 3. Figure 1 As shown, Figure 1 The test conditions are: room temperature, at 0.1 A g -1 The negative electrode material was activated and then cycled for 3 cycles under the test conditions of 0.5 A g -1 Long cycle tests were carried out at a current density of 0.01~2.0 V for charge and discharge. Figure 1 (a) is the initial charge and discharge curve of Si and Si / LTO composite materials with different LTO addition amounts. Figure 1 The results in (a) show that at a cutoff voltage of 2.0 V, the first cycle discharge specific capacities of 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 , the first circle specific capacity is 2358.6 mAh g -1 , 2593.5 mAh g -1 , 2845.4 mAh g -1 and 2720.6 mAh g -1 , the corresponding initial coulombic efficiency is 88.09%, 92.17%, 92.52% and 92.04% respectively. It can be found that the first efficiency is obviously improved after adding lithium titanate, and the first efficiency of 2%, 5% and 8% addition amount is increased by 4.08%, 4.43% and 3.95% respectively, among which the first efficiency of 5% addition amount is the most significant. It shows that the introduction of LTO effectively improves the initial coulombic efficiency of the composite material, and the lithium ions in LTO spontaneously migrate into Si due to the difference in lithium intercalation potential, effectively reducing the irreversible loss of lithium ions during the first cycle, and helping to form a more stable SEI layer. Figure 1 (b) of (a) is the cycle performance of Si and Si / LTO composite materials with different LTO addition amounts. Figure 1 (b) of (a) shows that 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, and the capacity retention rate is increased by 11.3% compared with Si electrode. Too much or too little element doping amount usually has different effects on the electrochemical performance of the material. In the 2% LTO composite system, the lithium ion may not be enough to make up for the loss in the first cycle and the stable SEI film is generated due to the low LTO content, so the first efficiency and cycle stability are limited; while in the 8% LTO composite system, the LTO content may be too much, which limits the lithium ion transmission kinetics, and the effect of improving the silicon negative electrode first efficiency and capacity retention rate is general.

[0071] The rate performance of four electrodes Si, Si / LTO-2%, Si / LTO-5% and Si / LTO-8% was systematically studied, and the results are shown in Figure 2 (a). Figure 2 (a) of (a) is the rate performance of Si and Si / LTO composite materials with different LTO addition amounts. Figure 2 (a) of (a) shows that the step test is carried out in the current density range of 0.1~2.0 A g -1 , and 5 cycles are carried out under each current density. The average specific capacity of the four electrode materials is shown in Table 2. From Figure 2From the information in (a) and Table 2, it can be seen that the Si / LTO-5% composite material exhibits the best rate performance. -1 Recover to 0.1 A g -1 When the charge is repeated, the capacity is almost completely restored, showing good electrochemical reversibility. This is due to the fact that LTO has a stable spinel structure and almost no volume change, which not only allows the electrode to maintain structural stability during repeated charge and discharge, but also provides a good lithium ion transmission channel. The interface characteristics of the four electrodes were further analyzed by electrochemical impedance spectroscopy (EIS). The results are as follows Figure 2 As shown in (b), Figure 2 (b) is the electrochemical impedance of Si and Si / LTO composite materials with different LTO addition amounts. Figure 2 (c) in the figure is 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. The charge transfer impedance (R ct ), smaller values ​​indicate lower charge transfer resistance and faster electrochemical 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. The addition of LTO significantly reduces the charge transfer resistance of the composites, indicating that LTO's inherent good electrical conductivity and high ion diffusion capacity help build a uniform and continuous conductive network, significantly reducing the charge transfer resistance within the electrode. Notably, the resistance value is lowest when LTO is added at a 5% concentration.

[0072] Table 2 Average specific capacities of Si and three composite materials at different rates

[0073]

[0074] In summary, experimental investigations have shown that a 5% LTO addition exhibits the best first-efficiency improvement and electrochemical performance (hereinafter referred to as Si / LTO). In order to further study the intrinsic mechanism of LTO composite improvement of silicon negative electrode materials and achieve high first-efficiency and long-cycle stability, a systematic analysis of the materials will be conducted below.

[0075] (2) Structural characterization of Si / LTO composite materials

[0076] As shown in Example 1, the detailed preparation steps of Si / LTO are as follows: First, 2 g Si, 0.1 g LTO and 20 mL of anhydrous ethanol are weighed and added to a polytetrafluoroethylene ball mill, zirconium beads are added according to a ball-to-material ratio of 20:1, and the ball mill is placed in a ZQM-P2 planetary ball mill. The ball milling speed is set to 250 r min-1 3 h ball milling was performed. Secondly, the slurry was washed out with anhydrous ethanol after the ball milling was completed, and after drying, it was placed in a mortar and ground thoroughly. Finally, the material obtained after grinding was placed in a tube furnace, and sintering treatment was performed under an Ar protective atmosphere, with a temperature rising rate of 5 ℃ min -1 -1 to 400 ℃, and kept at this temperature for 3 h. After the furnace body cooled down, the material was taken out and ground thoroughly, and the desired composite material was finally obtained.

[0077] To study the morphology and element distribution characteristics of Si / LTO, SEM and EDS characterization was performed on Si and Si / LTO. Figure 3 The SEM images of Si and Si / LTO materials are shown in FIGS. 1 and 2, respectively. Figure 3 FIG. 1(a) is the SEM image of the Si material, Figure 3 FIG. 1(b) is the SEM image of the Si / LTO material. From Figure 3 FIGS. 1(a) and 1(b), it can be seen that the original particle size and structure of Si are well preserved after ball milling, without excessive fragmentation or particle refinement, indicating that the selected ball milling process conditions are relatively mild, only realizing the uniform mixing and full contact of Si and LTO, without destroying the original morphology of Si particles, which is conducive 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. Figure 4 The SEM and EDS images of Si / LTO are shown in FIGS. 2(a) and 2(b). From the element distribution imaging (mapping image) of the sample, Figure 4 the results show that Ti, Si and O elements are uniformly distributed.

[0078] XRD technology was used to systematically characterize the phase composition and crystal structure of Si, LTO and Si / LTO composite materials. As shown in FIG. 3, Figure 5 Figure 5 the XRD spectra of Si, LTO and Si / LTO are shown in FIG. 3. The three main peaks of the Si / LTO composite material are located at 28°, 47° and 56°, corresponding to the (111), (220) and (311) crystal planes of Si. At the same time, strong peaks from LTO corresponding to PDF #49-0207 were also found. This indicates that Si and LTO in the composite material both maintain their respective crystal structures, without phase change or change in crystal structure. It is shown that after ball milling of Si and LTO, the intrinsic properties of the two materials are preserved, which helps Si / LTO to fully exert the high specific capacity of Si and the high stability, low volume expansion and other advantages of LTO, thereby showing significant improvement in electrochemical performance and cycle stability.

[0079] ​In order to deeply study the chemical environment of related elements in Si / LTO composites, XPS tests were performed on Si and Si / LTO. Figure 6 As shown in (a), Figure 6 Panel (a) shows the full XPS spectra of Si and Si / LTO. Both Si and Si / LTO exhibit characteristic peaks for O 1s, C 1s, Si 2p, and Si 2s. In addition, Si / LTO exhibits a Ti 2p peak around 453 eV. Figure 6 (b) shows the fine spectrum of Ti 2p, with two broad peaks at approximately 463.7 eV and 458.5 eV, corresponding to the Ti 2p in spinel LTO. 1 / 2 and Ti 2p 3 / 2 Combined with the above XRD patterns and EDX mapping analysis results, the successful preparation of Si / LTO composite materials was further confirmed.

[0080] (3) Si / LTO electrochemical characterization

[0081] The electrochemical performance of Si and Si / LTO was tested by assembling button cells in the voltage range of 0.01~2 V. Figure 7 (a) shows Si and Si / LTO at 0.1 A g -1 The initial charge and discharge curves of Si and Si / LTO under 0.1 Ag -1 The first cycle charge and discharge curves and open circuit voltage are compared below. 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 the first efficiency is improved by 4.44% after the addition of LTO for composite, and the open circuit voltage is reduced by 1.48 V. The high lithium insertion voltage of LTO makes the lithium ions spontaneously migrate from the high chemical potential LTO to the low chemical potential Si after the two come into contact, thereby improving the first efficiency of the silicon-based negative electrode. At the same time, the lithium-containing composite material has a lower open circuit voltage. The lower open circuit voltage can reduce the reduction reaction of the electrolyte on the electrode surface and inhibit the formation of an excessively thick SEI film, thereby reducing the lithium consumed in the first charge and discharge cycle and significantly improving the first efficiency. In addition, Si / LTO has a high charge and discharge efficiency of 0.5 A g -1 After 100 cycles ( Figure 7 (b) shows Si and Si / LTO at 0.5 A g -1 Despite the cycling performance under cyclic conditions, LTO still exhibits remarkable cycling stability, with a capacity retention rate of 80.2%, significantly higher than Si's 68.9%. The cycling data reveals that the introduction of LTO effectively suppresses the capacity decay of silicon, imparting it with excellent long-term cycling stability. Figure 7 (c) and Figure 7(d) shows the Si and Si / LTO electrodes at 0.5 A g -1 The evolution of the charge-discharge curves during 100 cycles at the same current density shows that the flat voltage platform around 0.25 V corresponds to the lithiation reaction of amorphous Si. Clearly, the voltage platform of the Si electrode gradually disappears with increasing cycles, and its capacity decays rapidly. However, the capacity of the Si / LTO electrode shows no significant decay, and the voltage platform changes slightly. The polarization voltage is much smaller than that of the Si electrode, indicating that the LTO compound helps reduce polarization during cycling.

[0082] To further evaluate the application effect of Si / LTO in full cells, the electrochemical performance of Si|LFP and Si / LTO|LFP full cells were assembled and evaluated according to the experimental operation of Example 4 ( Figure 8 The corresponding voltage range and N / P ratio are set to 2.2~4.0 V and 1.20, respectively. Figure 8 (a) is the initial charge-discharge curve of Si|LFP and Si / LTO|LFP full battery at 0.1 C, which shows that at 0.1 C (1 C=160 A g -1 ) initial charge and discharge curves at a current density of . The first coulombic efficiency of Si / LTO|LFP is 85.32%, while the first coulombic efficiency of Si|LFP is 77.74%. By comparison, it can be found that the first efficiency has increased by 7.58%. In addition, the cycle performance of Si|LFP and Si / LTO|LFP batteries was compared and analyzed at a current density of 0.33 C ( Figure 8 (b) shows the cycling performance of Si|LFP and Si / LTO|LFP full cells at 0.33 C. After 35 cycles, the capacity retention of Si / LTO|LFP is 66.71%, while that of Si|LFP is only 56.53%. In comparison, the capacity retention has increased by 10.18%. The incorporation of LTO also exhibits excellent first coulombic efficiency and cycling stability in the full cell.

[0083] In order to further analyze the reaction kinetics of Si and Si / LTO, CV tests at different scan rates were performed on these two electrodes. Figure 9 shown. Figure 9 For Si and Si / LTO at 0.2 mV s -1 to 1.0 mV s -1 CV curves and I p With v 1 / 2 Relationship diagram, Figure 9 (a) and (b) are the test results of Si electrode. Figure 9 (c) and (d) are the test results of Si / LTO electrodes. The test was conducted with a 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 The scan rate was 0.01–2 V. Kinetic analysis was performed on peaks 1 and 2, respectively. The slope was obtained by linearly fitting the current i and the square root of the corresponding scan rate ν. A larger slope indicates a larger diffusion coefficient D, indicating better lithium ion diffusion kinetics in the electrode material. Comparison revealed that the slope for Si / LTO was significantly greater than that for Si. This suggests that the volume expansion of Si leads to structural collapse, hindering ion transport. The introduction of LTO, on the other hand, enhances the lithium ion diffusion rate on the electrode surface, further confirming the positive effect of LTO on improving the electrochemical performance of the composite material.

[0084] In order to comprehensively study the interface evolution of Si and Si / LTO electrodes during cycling, in-situ electrochemical impedance spectroscopy (EIS) was used for analysis. -1 Three cycles of activation were performed under the same conditions and the DRT mode was switched to the dynamic relaxation time (DRT) mode ( Figure 10 The charge-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 . The comparison shows 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 ctThe value is also significantly smaller than that of Si, proving that after the introduction of LTO into 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 significantly 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, and thus improving the overall electrochemical performance and cycle stability of the composite electrode.

[0085] (4) Analysis of Si / LTO electrode morphology after cycling

[0086] The key to the excellent electrochemical performance of Si / LTO composites lies in the uniform combination of LTO and Si, which creates an efficient conductive network that promotes the rapid transport of electrons and lithium ions and reduces charge transfer impedance, which helps improve the electrochemical cycling stability of Si / LTO. Furthermore, as a "zero-strain" material, its rigid skeleton effectively suppresses the dramatic volume expansion of silicon during lithium insertion, thereby maintaining the integrity of the electrode structure and endowing the electrode with excellent cycling performance. Figure 11 The SEM images of the surface and cross section of Si and Si / LTO electrodes. -1 After 100 cycles, various large cracks formed on the surface of the Si electrode ( Figure 11 (a) in the figure shows the surface of Si electrode after cycling). However, no obvious cracks were formed on the surface of Si / LTO electrode after cycling under the same conditions ( Figure 11 (b) shows the surface of Si / LTO electrode after cycling. In addition, the expansion rate of Si electrode is as high as 124.5% compared with that before cycling ( Figure 11 (c) and (d) are cross sections of Si electrodes before and after cycling. The expansion of Si / LTO electrodes is significantly reduced ( Figure 11 (e) and (f) are the cross-sections of Si / LTO electrodes before and after cycling. This result further confirms that the introduction of LTO in Si / LTO can alleviate the volume expansion of Si and has better structural stability.

[0087] The microstructure of Si and Si / LTO electrodes after 100 cycles was characterized by TEM. Figure 12 SEM and TEM images of Si particles and Si / LTO particles after cycling. Figure 12 (a) and (b) are SEM images of Si particles and Si / LTO particles after cycling. Figure 12 (c) and (d) are TEM images of Si particles and Si / LTO particles after cycling.

[0088] like Figure 12 As shown in (a), the pure Si electrode can no longer maintain its complete particle morphology after cycling. This is because the repeated volume expansion / contraction of silicon during the lithiation / delithiation process leads to particle breakage and structural collapse. The newly exposed surface continuously participates in side reactions, eventually leading to electrode failure. Figure 12 As shown in (b), the Si / LTO composite material still maintains its complete particle structure after cycling. This is mainly attributed to the "zero strain" property of LTO effectively buffering the volume change of silicon. At the same time, its stable framework structure provides mechanical support for silicon particles, preventing the particles from pulverizing and agglomerating. This structural stability is the key factor that makes the Si / LTO composite material have excellent cycling performance. Analyze the SEM image of the particles after cycling ( Figure 12 It can also be observed in (c) and (d) that the silicon particles have been pulverized after 100 cycles, and many obvious cracks have appeared on the surface, while the Si / LTO particles remain very complete after 100 cycles, and no cracks are formed on the surface. This is consistent with the TEM results, which fully illustrates the role of LTO in the structural stability of the Si / LTO composite material.

[0089] It can be seen from the above examples that the present invention adopts the ball milling method to prepare the Si / LTO lithium-containing composite material, and realizes the uniform compounding of Si and LTO. The uniform compounding between the two not only helps LTO to provide lithium ions to Si and reduce the irreversible lithium loss in the first cycle, but also forms a good conductive network, optimizes the transmission path of electrons and lithium ions, and reduces the charge transfer impedance. This optimized conductive network effectively reduces the side reactions between silicon and the electrolyte, inhibits the formation of thick SEI film, reduces irreversible capacity loss, and further improves the first coulombic efficiency and long-term cycle performance. Secondly, due to the unique "zero strain" characteristics of LTO, its introduction into the system can effectively reduce the violent volume expansion of silicon during the charge and discharge process, avoid particle breakage and electrode structure collapse, and thus significantly improve the cycle life and capacity retention of the electrode. Experimental results show that the Si / LTO electrode exhibits a significant initial discharge specific capacity (0.1 A g -1 3075.5 mAh g -1 ), good rate performance (2A g -1 1586.5 mAh g -1 ), compared with the Si electrode, the first coulombic efficiency is increased by 4.43%, 0.5 A g -1 After 100 cycles at a current density of 1.5 GHz, the capacity retention rate remained at 80.2%. Furthermore, the initial coulombic efficiency of the Si / LTO|LFP full cell was 7.58% higher than that of Si|LFP, and the capacity retention rate increased by 10.18%. This process design is simple and environmentally friendly, making it suitable for large-scale industrial applications.

[0090] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-based composite material, characterized in that: The following steps are involved: The nano-silicon material and lithium titanate are ball-milled to obtain a ball-milled product; the nano-silicon material is Si nanoparticles, the mass of the lithium titanate accounts for 5% of the mass of the nano-silicon material, and the speed of the ball milling is 250 rmin -1 , the time is 1~5 h, the ball milling is wet ball milling, the solvent of the wet ball milling is an alcohol solvent, and the mass of the nano-silicon material and the volume ratio of the alcohol solvent are (1~3) g: (10~30) mL; The ball milled product is sintered in a protective gas atmosphere to obtain the silicon-based composite material. The sintering temperature is 400-450° C. and the holding time is 2-4 h.

2. The preparation method according to claim 1, characterized in that The ball milling mixture uses ball milling beads, which are zirconium beads, and the ball-to-material ratio is 10-30:

1.

3. The preparation method according to claim 1, characterized in that The heating rate to the sintering temperature is 1-10 °C min -1 , the protective gas includes a rare gas.

4. 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 to 3.

5. Application of a silicon-based composite material in preparing a negative electrode material or a negative electrode sheet for a lithium-ion battery, characterized in that: The silicon-based composite material is the silicon-based composite material according to claim 4.

6. A lithium ion battery negative electrode material, characterized in that The negative electrode active component comprises the silicon-based composite material according to claim 4.

7. A lithium-ion battery negative electrode sheet, characterized in that: The negative electrode battery comprises a negative electrode current collector and a negative electrode material arranged on the surface of the negative electrode current collector, wherein the negative electrode material is the negative electrode material for a lithium ion battery according to claim 6.

8. 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 lithium-ion battery negative electrode sheet according to claim 7.

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