Si / LATP-coated CNT composite material, preparation method and application thereof, lithium ion battery, and negative electrode material and negative electrode plate of lithium ion battery

Abstract

The invention belongs to the technical field of ion batteries, and particularly relates to a Si / LATP-CNT 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 of the lithium ion battery. The preparation method comprises the following steps: mixing a nano silicon material, an organic solvent, lithium titanium aluminum phosphate and carbon nanotubes to obtain a precursor dispersion liquid; carrying out ball milling on the precursor dispersion liquid and then carrying out solid-liquid separation to obtain precursor powder; and carrying out heat treatment on the precursor powder in a protective gas atmosphere to obtain the Si / LATP-coated CNT composite material. The Si / LATP-coated CNT composite material provided by the invention has a dual-channel interface of efficient electron conduction and rapid ion diffusion, has excellent electrochemical performance, and remarkably improves the interface stability and cycling stability of a silicon-based negative electrode.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion batteries, and specifically relates to a Si / LATP@CNT composite material and a preparation method and application thereof, a lithium ion battery and a negative electrode material and a negative electrode sheet thereof. Background Art

[0002] As the global energy structure transformation accelerates, lithium-ion batteries, as the core energy storage carrier of electric vehicles and smart grids, are increasingly in urgent need of increasing their energy density. -1 Theoretical specific capacity (about 10 times that of graphite negative electrode) and 0.4V (vs.Li + / Li) is considered the next-generation anode system with the greatest commercial potential. However, the volume expansion effect of silicon materials, up to 300%, during the charge and discharge process can cause particle pulverization, active material shedding, and continuous reconstruction of the solid electrolyte interface (SEI), leading to electrode structural instability and rapid capacity decay. This bottleneck problem seriously restricts its large-scale application, and how to achieve interfacial stability control of silicon-based anodes has become a key challenge in current research.

[0003] In recent years, researchers have proposed a variety of solutions from the perspectives of material modification and structural design. The related technology uses tin (Sn) with high electronic conductivity to bond the Si negative electrode and copper (Cu) current collector together through hot pressing, achieving an ICE of 82.7% and a current of 300mAg. -1 The company maintained a capacity retention rate of 81.77% after 100 cycles. The related technology combines SiO with graphene (Gr) and graphite (AG) to form an adaptive composite anode material (SiO@Gr / AG). This material, when used with a high-nickel ternary cathode material (NCM) for lithium-ion batteries, increased the capacity retention rate from 37.5% to 69.1% after 300 cycles.

[0004] However, existing strategies still have significant limitations: while conductive network construction schemes (such as carbon coating and metal particle doping) can improve electron transport, they are unable to alleviate the diffusion hysteresis of lithium ions at the silicon / conductive agent interface. This mismatch in electron / ion transport rates can induce local polarization, accelerate electrode performance degradation, and lead to poor interface stability and cycling stability of the negative electrode material. Summary of the Invention

[0005] The purpose of the present invention is to provide a Si / LATP@CNT composite material, a preparation method and application thereof, a lithium-ion battery, a negative electrode material and a negative electrode sheet thereof. The Si / LATP@CNT composite material provided by the present invention has a dual-channel interface with both efficient electron conduction and rapid ion diffusion, has excellent electrochemical properties, and significantly improves the interface stability and cycle stability of the silicon-based negative electrode.

[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 Si / LATP@CNT composite material, comprising the following steps:

[0008] mixing nano-silicon material, organic solvent, lithium aluminum titanium phosphate and carbon nanotubes to obtain a precursor dispersion;

[0009] ball-milling the precursor dispersion and performing solid-liquid separation to obtain a precursor powder;

[0010] The precursor powder is heat-treated in a protective gas atmosphere to obtain the Si / LATP@CNT composite material.

[0011] Preferably, the mass of the lithium titanium aluminum phosphate accounts for 1.5-4.5% of the mass of the nano-silicon material.

[0012] Preferably, the mass of the carbon nanotubes accounts for 1-10% of the mass of the nano-silicon material.

[0013] Preferably, the ball milling speed is 100-250 rmin -1 The ball milling time is 6 to 12 hours;

[0014] The ball mill uses ball milling beads, which are zirconia beads, and the ball-to-material ratio is 20 to 50:1.

[0015] Preferably, the heat treatment temperature is 800-950°C, the holding time is 2-4 hours, and the heating rate to the heat treatment temperature is 1-10°C min -1 , the protective gas includes a rare gas.

[0016] The present invention provides a Si / LATP@CNT composite material prepared by the preparation method described in the above technical solution.

[0017] The present invention provides the use of the Si / LATP@CNT composite material described in the above technical solution in the preparation of lithium-ion battery negative electrode materials or negative electrode sheets.

[0018] The present invention provides a lithium-ion battery negative electrode material, comprising a negative electrode active component, wherein the negative electrode active component is the Si / LATP@CNT composite material described in the above technical solution.

[0019] The present invention 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 negative electrode current collector, wherein the negative electrode material is the lithium ion battery negative electrode material described in the above technical solution.

[0020] The present invention provides a lithium-ion battery comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet is the lithium-ion battery negative electrode sheet described in the above technical solution.

[0021] The present invention provides a method for preparing a Si / LATP@CNT composite material, comprising the following steps: mixing a nano-silicon material (Si-NPs, Si), an organic solvent, lithium aluminum titanium phosphate (LATP) and carbon nanotubes (CNT) to obtain a precursor dispersion; ball-milling the precursor dispersion and performing solid-liquid separation to obtain a precursor powder; and heat-treating the precursor powder in a protective gas atmosphere to obtain the Si / LATP@CNT composite material. The present invention simultaneously introduces LATP and CNT into a nano-silicon material matrix, with LATP serving as an ion conductive enhancement phase. On the one hand, LATP can construct a continuous lithium ion transmission channel on the surface of the silicon matrix, reducing Li + diffusion activation energy; on the other hand, its high modulus characteristics (~120GPa) can play a mechanical supporting role and inhibit the volume expansion of silicon. At the same time, the three-dimensional network construction of carbon nanotubes (CNTs) realizes the optimization of the electronic pathway of the composite material. The present invention first realizes the uniform dispersion of LATP and CNT in the silicon matrix by ball milling, and then through heat treatment, the synergistic effect of LATP and CNT realizes the integrated design of the "ion-electron" dual continuous transmission network, which provides a technical guarantee for the interface stability and long-cycle stable operation of the composite material. In summary, the present invention uses LATP and CNT to collaborate, and forms a "rigid-flexible coupling" composite framework through ball milling and heat treatment, wherein LATP is anchored on the silicon particles through a heterogeneous interface to obtain a Si / LATP matrix, and CNT is interwoven and wound on the Si / LATP matrix to obtain a Si / LATP@CNT composite material. The results of the embodiment show that the high ionic conductivity characteristics of LATP significantly reduce Li + Diffusion barrier ( Increased to 1.63×10 -10 cm 2 s -1 ), optimizing the interface stability and charge transfer efficiency of Si / LATP@CNT composites, which is attributed to the synergistic effect of LATP's sodium fast ion conductor (NASICON, Na Super-ionic Conductor) type fast ion channel and CNT electronic network; at the same time, the dual transport network system makes Si / LATP@CNT composites have stable Li during the process of lithium insertion and extraction. + The resistance across the SEI layer (R SEI ) and a stable interfacial charge transfer resistance (R ct), reflecting that the "ion-electron" dual continuous transport network enhances the ion transport dynamics within the battery. The core mechanism is that LATP induces the formation of a thin layer of LiF-rich SEI, thereby improving the interface stability and cycle performance of the material. In the electrochemical performance test, the initial specific capacity of the Si / LATP@CNT composite material reached 2708mAh g -1 , 0.5Ag -1 After 400 cycles, the lithium insertion capacity is stable at 1093 mAh g -1 , in 2Ag -1 It can still maintain 1553mAh g at a high current density -1 The high capacity is superior to that of traditional Si@CNT materials. This is mainly attributed to the fact that LATP doping can effectively alleviate the structural deformation of the silicon anode during long-term charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the preparation flow chart of Si / LATP@CNT material;

[0023] Figure 2 is the morphological feature of original silicon (Si);

[0024] Figure 3 The morphology and crystal structure characteristics of LATP;

[0025] Figure 4 XRD and Raman spectra of Si / LATP;

[0026] Figure 5 For the electrochemical characterization of Si and Si / LATP;

[0027] Figure 6 It is the CNT morphology and crystal structure characteristics;

[0028] Figure 7 XRD spectra and Raman spectra of Si, CNT, LATP, Si@CNT, Si / LATP@CNT and magnified images;

[0029] Figure 8 SEM images, TEM images and EDS spectra of Si / LATP@CNT;

[0030] Figure 9 The electrochemical performance of Si@CNT and Si / LATP@CNT;

[0031] Figure 10 The electrochemical performance of Si / LATP@CNT-1 and Si / LATP@CNT-2;

[0032] Figure 11CV curves of Si / LATP@CNT and Si@CNT at different scan rates and peak current (I p ) and scanning speed (v 1 / 2 ) relationship diagram;

[0033] Figure 12 Nyquist diagrams of Si / LATP@CNT, Si@CNT, and Si at OCV, 3 cycles, and 100 cycles, as well as Z′ and ω -1 / 2 relationship diagram;

[0034] Figure 13 The Li of Si / LATP@CNT, Si@CNT and Si in OCV, 3 cycles and 100 cycles + Diffusion coefficient;

[0035] Figure 14 In situ electrochemical impedance spectroscopy of Si / LATP@CNT and Si@CNT, as well as the corresponding charge-discharge curves and distribution of relaxation time (DRT);

[0036] Figure 15 XPS spectra of Si / LATP@CNT and Si@CNT;

[0037] Figure 16 Cross-sectional SEM images of Si / LATP@CNT and Si@CNT electrodes before and after 100 cycles, and planar SEM images of electrodes before and after 100 cycles. DETAILED DESCRIPTION

[0038] The present invention provides a method for preparing a Si / LATP@CNT composite material, comprising the following steps:

[0039] mixing nano-silicon material, organic solvent, lithium aluminum titanium phosphate and carbon nanotubes to obtain a precursor dispersion;

[0040] ball-milling the precursor dispersion and performing solid-liquid separation to obtain a precursor powder;

[0041] The precursor powder is heat-treated in a protective gas atmosphere to obtain the Si / LATP@CNT composite material.

[0042] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0043] The present invention mixes nano-silicon material, organic solvent, lithium titanium aluminum phosphate and carbon nanotubes to obtain a precursor dispersion. In the present invention, the nano-silicon material is preferably a nano-powder. The purity of the nano-silicon material is preferably ≥99%, more preferably ≥99.9%, and 99.99% in the embodiment. The particle size of the nano-silicon material is preferably about 300nm. The organic solvent is preferably N-methylpyrrolidone (NMP). The lithium titanium aluminum phosphate is preferably lithium titanium aluminum phosphate powder. The purity of the lithium titanium aluminum phosphate is preferably ≥99%, and 99% in the embodiment. In the present invention, the particle size of the lithium titanium aluminum phosphate is preferably about 300nm. The present invention introduces LATP as an ion conductivity enhancing phase into the silicon-based negative electrode to construct a continuous Li + The carbon nanotubes (CNTs) are preferably used in the form of a carbon nanotube slurry, which preferably includes carbon nanotubes and a solvent. The carbon nanotube content in the slurry is preferably 0.4%, and the solvent in the slurry is preferably N-methylpyrrolidone (NMP). Carbon nanotubes (CNTs) can form a three-dimensional conductive skeleton, and the construction of a three-dimensional network optimizes the electron pathway.

[0044] In the present invention, the mass percentage of the lithium aluminum titanium phosphate to the mass percentage of the nano-silicon material is preferably 1.5-4.5%, and in embodiments, it can be 2%, 3%, or 4%. The mass percentage of the carbon nanotubes to the mass percentage of the nano-silicon material is preferably 1-10%, more preferably 2-8%, and most preferably 4%. The present invention has no particular requirements for the amount of the organic solvent used. In embodiments, the ratio of the mass of the nano-silicon material to the volume of the organic solvent is preferably 2 g:10-15 mL.

[0045] In the present invention, the mixing preferably includes: dispersing the nano-silicon material in an organic solvent to obtain a nano-silicon dispersion; mixing the nano-silicon dispersion with the lithium aluminum titanium phosphate to obtain a mixed solution; and mixing the mixed solution with the carbon nanotubes to obtain a precursor dispersion.

[0046] After obtaining the precursor dispersion, the present invention ball mills the precursor dispersion and then separates the solid and liquid to obtain a precursor powder. In the present invention, the ball milling is preferably carried out in a planetary ball mill. The speed of the ball mill is preferably 100 to 250 rmin -1 , more preferably 150 to 250 rmin -1 In the embodiment, the speed may be 250 rmin -1. The ball milling time is preferably 6 to 12 hours, and in the embodiment it can be 10 hours. The ball milling preferably uses ball milling beads. The ball milling beads are preferably zirconia beads. The diameter of the ball milling beads is preferably 2 mm. The ball-to-material ratio of the ball milling is preferably 20 to 50:1, more preferably 40:1. The ball-to-material ratio is the ratio of the mass of the ball milling beads to the total mass of the nano-silicon, lithium aluminum titanium phosphate and carbon nanotubes.

[0047] In the present invention, after the ball milling is completed, the ball milled product is preferably washed out from the ball milling tank, and then solid-liquid separation and drying are performed in sequence to obtain the precursor powder. The solid-liquid separation is preferably filtration.

[0048] After obtaining the precursor powder, the present invention heat-treats the precursor powder in a protective gas atmosphere to obtain the Si / LATP@CNT composite material. In the present invention, the heat treatment is preferably carried out in a tubular furnace. The protective gas preferably includes a rare gas, which may be argon in the embodiment. The temperature of the heat treatment is preferably 800-950°C, and may be 900°C in the embodiment. The holding time of the heat treatment is preferably 2-4h, and may be 3h in the embodiment. The rate of heating to the temperature of the heat treatment is preferably 1-10°C min -1 In the embodiment, the temperature can be 5°C min -1 After the heat treatment is completed, the present invention preferably cools the mixture naturally to room temperature to obtain the Si / LATP@CNT composite material.

[0049] The present invention provides a Si / LATP@CNT composite material prepared by the preparation method described in the above technical solution.

[0050] In the Si / LATP@CNT composite material provided by the present invention, LATP is anchored on silicon particles through a heterogeneous interface to form a Si / LATP matrix, and CNTs are interwoven and wound on the Si / LATP matrix.

[0051] The synergistic effect of LATP and CNTs in the present invention can achieve the following advantages: (1) the ionic conductivity of LATP reduces the charge transfer impedance; (2) the CNT network maintains the integrity of the electron conduction path; and (3) the synergistic effect of the composite interface inhibits the excessive growth of the SEI film.

[0052] The present invention provides the use of the Si / LATP@CNT composite material described in the above technical solution in the preparation of lithium-ion battery negative electrode materials or negative electrode sheets.

[0053] The present invention provides a lithium-ion battery negative electrode material, comprising a negative electrode active component, wherein the negative electrode active component is the Si / LATP@CNT composite material described in the above technical solution. In the present invention, the lithium-ion battery negative electrode material preferably also includes a binder and a conductive agent. The binder is preferably polyacrylic acid (PAA). The conductive agent is preferably SuperP. The mass ratio of the negative electrode active component, binder, and conductive agent is preferably 8:1:1.

[0054] The present invention provides a lithium-ion battery negative electrode sheet, comprising a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector. The negative electrode material is the lithium-ion battery negative electrode material described in the above technical solution. In the present invention, the negative electrode current collector is preferably a copper foil current collector. The lithium-ion battery negative electrode sheet is preferably in the form of a disc, and the diameter of the disc is preferably 14 mm.

[0055] 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 speed of the stirring and degassing is preferably 1000-1500 rmin -1 The coating is preferably carried out using a scraper. The drying is preferably carried out in a drying oven at a temperature of 75 to 80°C and for a time of 8 to 12 hours.

[0056] The present invention provides a lithium-ion battery comprising a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet is the lithium-ion battery negative electrode sheet described in the above technical solution.

[0057] In the present invention, the electrolyte preferably includes lithium hexafluorophosphate, fluoroethylene carbonate and an organic solvent. The organic solvent preferably includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC). The volume ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) is preferably 1:1. The molar concentration of the lithium hexafluorophosphate in the electrolyte is preferably 1 to 1.5 mol / mL, and in embodiments, it can be 1 mol / L. The volume percentage of the fluoroethylene carbonate to the volume of the organic solvent is preferably 1 to 10%, and in embodiments, it can be 5%.

[0058] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] The raw material information used in the following examples is as follows:

[0060] The silicon nanoparticles (Si, 99.99%) used in the following examples were provided by Shenzhen Eigen Equation Graphene Technology Co., Ltd., with a particle size of 300 nm. Lithium aluminum titanium phosphate (LATP, 99%) powder was purchased from Shenzhen Kejing Zhida Technology Co., Ltd. Carbon nanotube (CNT) slurry was produced by Jiangsu Tiannai Technology Co., Ltd., with a CNT content of 0.4 wt%. The dispersant N-methylpyrrolidone (NMP) was provided by Aladdin Biochemical Technology Co., Ltd. All materials were used directly without any other treatment.

[0061] Example 1:

[0062] This example provides the preparation of Si / LATP@CNT composite materials: the preparation flow chart is as follows Figure 1 shown.

[0063] Weigh 2g of nano-silicon powder and disperse it in 10mL of N-methylpyrrolidone (NMP) to form a uniform dispersion solution to obtain the NMP dispersion of nano-silicon. Next, weigh a certain amount of lithium aluminum titanium phosphate (LATP) powder according to the required addition amount (the mass percentage of LATP powder to the mass of nano-silicon powder is 1%, 2%, and 5%, respectively), mix it with the above-mentioned NMP dispersion of nano-silicon to obtain a mixed solution, weigh carbon nanotube slurry according to the mass of carbon nanotubes accounting for 4wt% of silicon nanopowder, mix it evenly with the above-mentioned mixed solution to obtain a precursor dispersion, and place it in a ball mill, add zirconium oxide beads with a diameter of 2mm to the ball mill, and add zirconium oxide beads at a mass ratio of 40:1 to the active material (including the solid mass of nano-silicon powder, lithium aluminum titanium phosphate powder and carbon nanotubes in the carbon nanotube slurry). Place the ball mill containing the precursor dispersion in a planetary ball mill and pulverize at 250rmin -1 The obtained precursor powder was placed in a square alumina porcelain boat and then placed in a tube furnace, and Ar atmosphere was introduced as a protective gas at 5℃ min -1 The temperature was raised to 900°C at a heating rate and then heat treated for 3 hours. The temperature was naturally cooled and the obtained composite materials were recorded as Si / LATP@CNT-1, Si / LATP@CNT and Si / LATP@CNT-2, among which the LATP powder mass proportion was 1% to obtain Si / LATP@CNT-1, the LATP powder mass proportion was 1% to obtain Si / LATP@CNT, and the LATP powder mass proportion was 5% to obtain Si / LATP@CNT-2.

[0064] Comparative Example 1:

[0065] (1) The detailed preparation method of Si / LATP is as follows: 2 g of nano-silicon powder is weighed and dispersed in 10 mL of N-methylpyrrolidone (NMP) to form a uniform dispersion to obtain the NMP dispersion of nano-silicon. Next, lithium aluminum titanium phosphate (LATP) powder is weighed so as to account for 2 wt% of the nano-silicon powder, and mixed with the above-mentioned NMP dispersion of nano-silicon to obtain a mixed dispersion, which is then placed in a ball mill, and zirconium oxide beads with a diameter of 2 mm are added to the ball mill. The zirconium oxide beads are added in a mass ratio of 40:1 to the active material (nano-silicon powder and LATP powder). The ball mill containing the mixed solution is placed in a planetary ball mill and pulverized at 250 rmin. -1 The mixed powder was placed in a square alumina porcelain boat and then placed in a tube furnace. Ar atmosphere was introduced as a protective gas and the mixture was heated at 5℃ min -1 The temperature was raised to 900 °C at a heating rate of 1000 ℃, heat treated for 3 hours, and then cooled naturally. The obtained composite material was recorded as Si / LATP.

[0066] (2) The detailed preparation method of Si@CNT is as follows: 2g of nano-silicon powder is weighed and dispersed in 10mL of N-methylpyrrolidone (NMP) to form a uniform dispersion to obtain the NMP dispersion of nano-silicon. Next, the carbon nanotube slurry is weighed so that the mass of the carbon nanotubes accounts for 4wt% of the silicon nanopowder, and is evenly mixed with the NMP dispersion of nano-silicon. The mixture is then placed in a ball mill, and zirconium oxide beads with a diameter of 2mm are added to the ball mill. The zirconium oxide beads are added in a mass ratio of 40:1 to the active material (silicon nanopowder and carbon nanotubes). The ball mill containing the mixed solution is placed in a planetary ball mill and pulsated at 250rmin. -1 The mixed powder was placed in a square alumina porcelain boat and then placed in a tube furnace. Ar atmosphere was introduced as a protective gas and the mixture was heated at 5℃ min -1 The temperature was raised to 900 °C at a heating rate of 1000 ℃, heat treated for 3 hours, and then cooled naturally. The obtained composite material was recorded as Si@CNT.

[0067] Examples and effect data

[0068] 1. Electrochemical testing

[0069] (1) Preparation of electrode sheet: After grinding the Si / LATP@CNT composite material for 10 min, polyacrylic acid (PAA) was used as a binder and conductive carbon black (SP) was used as a conductive agent. The Si / LATP@CNT composite material, PAA, and SP were ground and mixed evenly in a mass ratio of 8:1:1. An appropriate amount of deionized water was added and the mixture was placed in a stirring degassing machine and stirred at 1500 rmin. -1Stir at a rate of 10 for 10 minutes to obtain the negative electrode slurry. Use an electrode scraper to evenly coat the negative electrode slurry onto the copper foil current collector and dry it in an 80°C oven for 8 hours to remove moisture. Use a sheet puncher to cut the electrode sheet into 14 mm diameter discs, obtaining the negative electrode sheet composed of the Si / LATP@CNT composite material.

[0070] (2) Assembly of button cells: To test the electrochemical performance of the Si / LATP@CNT composite material, the prepared negative electrode sheet was combined with lithium foil and Celgard-2400 separator to form a half-cell assembly of CR2032 button cells. All cells were assembled in an argon-filled glove box (O2<0.1ppm, H2O<0.1ppm). The negative electrode shell, spring, gasket, Si / LATP@CNT negative electrode sheet, separator, lithium foil, gasket, and positive electrode shell were assembled in this order. An appropriate amount of electrolyte was dripped on both sides of the separator. The electrolyte was LiPF6 dissolved in diethyl carbonate (DEC) and ethylene glycol (EC) (the volume ratio of DEC to EC was 1:1), and fluoroethylene carbonate (FEC) was added at the same time. The molar concentration of LiPF6 in the electrolyte was 1 mol / L, and the volume of fluoroethylene carbonate (FEC) accounted for 5% of the total volume of diethyl carbonate (DEC) and ethylene glycol (EC). The button cells were then packaged using a tablet press. The cells were left to rest for 24 hours before electrochemical testing.

[0071] (3) Electrochemical performance test: Test the constant current charge / discharge cycle performance on the MIHW-200-160CH-B NEWARE button battery test system or the CT3002ALAND battery test system, with a voltage range of 0.001 to 2 V (vs. Li + / Li), 0.1Ag -1 After 3 cycles of activation at a current density of 0.5Ag -1 The constant current charge-discharge cycle test was carried out at a constant current density.

[0072] 2. Study on LATP doping modification

[0073] The microstructure and chemical composition characteristics of the original silicon material are as follows Figure 2 shown. Figure 2 The SEM images in (a) and (b) show that commercial nano-silicon particles have a typical irregular polygonal morphology with an average particle size distribution of around 300 nm. Figure 2 Transmission electron microscopy analysis of (c) and (d) further reveals its crystallographic characteristics. The TEM image clearly shows a lattice spacing of 0.31 nm, corresponding to the (111) crystal plane of silicon (PDF#04-006-6436). In addition, Figure 2The EDS spectra of (e) and (f) show that the silicon element is uniformly dispersed. In summary, it is shown that the original silicon material used in the present invention is a high-purity silicon material.

[0074] The physicochemical properties of LATP additives are as follows: Figure 3 As shown, Figure 3 (a) and (b) are SEM images. Figure 3 (c) and (d) are TEM images. Figure 3 The illustration in (d) is the crystal structure information of the dotted box. Figure 3 (e) is the XRD pattern, Figure 3 (f) is the Raman spectrum. The commercial LATP particles have a polyhedral morphology and a particle size distribution range of about 300nm ( Figure 3 (a) and (b)), TEM analysis ( Figure 3 (c) in the figure further verifies the polyhedral morphology of the LATP particles. In addition, clear lattice fringes were observed in the TEM image. The area within the white dotted box was used as a representative to perform Fourier transform (FFT) and inverse Fourier transform (IFFT) to obtain a clear distribution of interplanar spacing, as shown in Figure 2. Figure 3 As shown in the inset in the upper right corner of (d), the measured interplanar spacing of 0.36 nm corresponds to the (113) crystal plane of the NASICON structure (PDF#97-009-5979). Figure 3 (e)) in the figure shows characteristic diffraction peaks at 2θ = 20.857°, 20.860° and 24.511°, which match the standard card. The Raman spectrum is shown in Figure 3 As shown in (f), 850~1130cm -1 and 400~680cm -1 The characteristic peaks at 200-400 cm-1 are attributed to the stretching vibration and bending vibration of PO. -1 Belong to Ti 4+ The overall translational movement and PO4 3- Free movement.

[0075] In order to explore the effect of the introduction of LATP on the electrochemical performance of silicon negative electrode, Si was mixed with 2 wt% LATP (i.e., the mass of LATP accounted for 2 wt% of the Si material) and uniformly dispersed by high-energy ball milling. Subsequently, Si / LATP was obtained by calcining at 900 °C for 3 h (the detailed preparation method is recorded in Comparative Example 1).

[0076] XRD and Raman spectroscopy were used to study the interaction mechanism between LATP and Si. Figure 4 (a) and (b) are the XRD spectra of Si / LATP. Figure 4(c) and (d) are Raman spectra. XRD patterns ( Figure 4 In (a)), Si / LATP has sharp characteristic peaks at 2θ of 28.495, 47.392 and 56.189, corresponding to the (111), (220) and (311) crystal planes of silicon, respectively, which match the standard card PDF#04-006-6436. Figure 4 As shown in (b), the (111) crystal plane (2θ = 28.563°) shifts slightly (28.495°) after the incorporation of LATP, and the half-peak width narrows slightly, and the diffraction peak becomes sharper. It is worth noting that the diffraction peaks of the (220) and (311) crystal planes split.

[0077] In the present invention, materials with different lattice constants will cause the Si lattice to expand or contract during the doping process, resulting in a stress effect. This stress originates from the difference in atomic radius and lattice coordination of the doping elements. When the doping amount is low, the doping elements may not completely replace the crystal positions in Si, but instead form a certain surface or interface stress, thereby causing strain in the local area of ​​the Si crystal. This stress and strain effect is reflected in the changes in the diffraction peak position and half-height width. Therefore, the shift of the main diffraction peak of the (111) crystal plane indicates that the LATP doping of Si causes its lattice to undergo a slight expansion or contraction. The slight decrease in the half-height width of the Si / LATP material may be attributed to the relief of the local lattice strain of Si after doping with LATP, resulting in a sharper diffraction peak. The splitting of the main diffraction peaks of Si, such as (111) and (220), further confirms the successful doping of LATP. Especially at extremely low doping concentrations (2wt%), LATP may not completely replace the atoms in the Si lattice, but exist as a heterogeneous structure. This structural heterogeneity causes the splitting of the diffraction peak.

[0078] In addition, Raman spectroscopy ( Figure 4 (c) and (d) also confirm the successful doping of LATP at 500 cm -1 The sharp characteristic peak is the Si-Si vibration peak, and Si / LATP appears red-shifted at this main diffraction peak (from 500 cm -1 to 518.4cm -1 ) and splitting phenomena, which are consistent with the XRD patterns, implying that LATP is successfully incorporated into Si and undergoes tiny lattice expansion or contraction, causing local strain or lattice heterogeneity in the structure.

[0079] The effect of LATP doping on the electrochemical performance of silicon electrodes is shown in the following example: Figure 5 As shown, Figure 5 Electrochemical characterization of Si and Si / LATP. Figure 5 (a) is the first cycle charge and discharge curve; Figure 5 (b) in the figure is the reversible capacity, irreversible capacity and ICE; Figure 5 (c) in the figure is the cycle performance; Figure 5 (d) and (e) are the charge and discharge curves of the first 100 cycles; Figure 5 (f) is the rate performance. Initial charge and discharge curve ( Figure 5 (a) shows that the original silicon electrode is -1 The first discharge / charge specific capacities were 3160 / 2247 mAh g -1 The initial coulombic efficiency (ICE) is 71%. After adding 2 wt% LATP, the first discharge / charge specific capacity is 3131 / 2743 mAh g -1 , ICE increased to 87%, indicating that the introduction of LATP effectively suppressed the irreversible decomposition of the electrolyte in the first cycle. This reveals that LATP may induce the formation of a denser and more stable solid electrolyte interface (SEI) on the silicon surface, reducing Li + The irreversible consumption of side reactions (such as the generation of inactive components such as Li2O / LiF). Secondly, the first irreversible capacity is reduced from 913 mAh g -1 Reduced to 388mAh g -1 ( Figure 5 (b) LATP acts as a fast ion conductor. Its rigid structure may buffer the volume expansion (~300%) during silicon lithium insertion through mechanical support, reduce particle breakage and the stripping of active materials from the current collector, thereby reducing the first irreversible capacity loss and maintaining a higher reversible lithium removal capacity (2743 vs. 2247 mAh g -1 Although doping resulted in a slight decrease in discharge capacity (3160→3131 mAh g -1 ), but the delithiation capacity increased (Δ=496mAhg -1 ) is significantly higher than the lithium insertion capacity drop (Δ=29mAh g -1 ), confirming that LATP does not significantly sacrifice silicon's intrinsic lithium storage capacity. Instead, it improves active material utilization by inhibiting the formation of "dead lithium" (e.g., the lithiation of isolated silicon particles). This suggests that LATP may reduce polarization losses during the delithiation process by improving the overall ionic conductivity of the electrode, thereby promoting the diffusion dynamics of lithium ions within silicon particles.

[0080] In order to verify the effect of LATP doping on the cycle performance of silicon-based anode, -1 The Si and Si / LATP were cycled at the current density, as shown in ( Figure 5 As shown in (c)), the original Si is at 0.5Ag -1 The initial discharge capacity is 1261 mAh g -1Due to the rapid volume expansion, Si exhibits rapid capacity decay, and the discharge capacity rapidly decays to 0 mAh g after 60 cycles. -1 On the contrary, even after 100 cycles, the discharge capacity of Si / LATP is 1316 mAh g -1 , the cycle stability is significantly higher than that of Si electrode. Figure 5 Figures (d) and (e) show that the lithiation (~0.149V) and delithiation (~0.403V) platforms of Si / LATP remain clear after 100 cycles, and the voltage hysteresis (ΔV) increases from the initial 0.254mV to 0.257mV; while the ΔV of pure Si increases from 0.232mV to 0.934mV, indicating that the introduction of LATP alleviates electrode polarization, improves the interfacial kinetics, and significantly improves the reversibility of the electrode reaction. Figure 5 (f)) in the figure further reveals the effect of LATP on the improvement of kinetic performance. -1 At current densities of 1, 2, 3, 4, 5, 8, 10, 20, 30, 40, 50, 70, 80, 100, 150, 200, 300, 400, 700, 800, 1000, 1500, 2000, 3000, 4000, 7000, 800 -1 When the current density returns to 0.1Ag -1 The discharge capacity is 2137 mAh g -1 , indicating that Si / LATP has good reversibility. However, Si underwent a huge volume change during the entire rate performance test cycle. -1 Only 275mAh g -1 The discharge capacity of 0.5, 1 and 2Ag -1 At a current density of 100 nm, the discharge specific capacity is close to zero, and the surface silicon particles undergo structural collapse due to the drastic volume expansion, resulting in the separation of the active material from the current collector. At the same time, the continuous rupture / regeneration of SEI causes serious lithium loss. At a high current density, the excessive polarization and collapsed electrode structure result in Si having no electrochemical activity.

[0081] 3. Research on LATP / CNT dual-phase modified silicon-based anode

[0082] Single LATP doping has helped to achieve a breakthrough in the electrochemical performance of silicon anodes and significantly improved the cycle stability of silicon anodes. However, although LATP as a dopant has excellent ionic conductivity, it is not a qualified electronic conductor (<1×10 -5 S cm -1 ). And as a semiconductor, the intrinsic conductivity of silicon anode is also relatively low (10 -4 ~10 -3 S cm -1). Therefore, it is necessary to construct an electron transfer path to reduce the electron transfer barrier between silicon and LATP, thereby further improving the long-cycle stability of the silicon negative electrode. To this end, the present invention introduces carbon nanotubes (CNTs) to construct a three-dimensional conductive network and proposes a "ion-electron dual continuous transmission" synergistic mechanism. First, LATP particles form a continuous Li on the surface of the silicon substrate. + The open three-dimensional channels of its NASICON skeleton enable rapid lithium ion transmission. Secondly, CNT forms close contact with silicon / LATP through physical entanglement, and its sp 2 The hybrid carbon tube network provides a highly conductive path, thereby simultaneously improving the ionic and electronic conduction efficiency of the composite electrode. Finally, the high modulus of LATP (120GPa) and the toughness of CNTs (fracture strain >15%) form a composite support framework, creating a mechanical synergistic effect that limits the anisotropic expansion of silicon particles.

[0083] The carbon nanotubes (CNTs) used in the present invention are CNT slurries dispersed with the assistance of N-methylpyrrolidone (NMP) solvent. To study the composition and structure of CNTs, the slurry is rapidly stirred at 120°C until the NMP is completely volatilized, and then heat-treated at 900°C in an argon atmosphere for 3 h to obtain CNT powder.

[0084] The microscopic morphology and crystal structure characteristics of CNTs are as follows: Figure 6 As shown, Figure 6 (a) is the SEM image; Figure 6 (b) and (c) are TEM images; Figure 6 (d), (e), and (f) are EDS spectra. CNTs exhibit a typical one-dimensional tubular morphology with a diameter of approximately 7 nm. They are composed of multiple layers of rolled-up graphene sheets, with the tube wall consisting of 4 to 6 layers of rolled-up graphene sheets. Their high aspect ratio and low curvature structure are conducive to the construction of a three-dimensional conductive network. EDS element distribution ( Figure 6 (d), (e), and (f) show that the carbon element is evenly distributed, and the residual trace fluorine element comes from the decomposition by-products of the precursor slurry.

[0085] Figure 7 (a) is the XRD spectra of Si, CNT, LATP, Si@CNT, and Si / LATP@CNT. Figure 7 (b) is the Raman spectra and magnified images of Si, CNT, LATP, Si@CNT, and Si / LATP@CNT. Further XRD analysis shows that ( Figure 7In (a), the diffraction peaks at 25.15, 43.75 and 44.71 correspond to the (002), (100) and (101) planes of the graphite structure. Among them, the (002) crystal plane peak is relatively broad, indicating that the CNT may have certain defects or the structure is not completely ordered, which is also a common CNT feature. In order to further determine the structural characteristics of CNT, Raman spectroscopy analysis was performed, such as Figure 7 As shown in (b) in the figure. At ~1342 and ~1596 cm -1 The vibration C—C bonds can be observed at the peaks 1 and 2, which belong to the D peak and G peak of CNT respectively. The D peak represents the disorder degree of CNT, and the G peak is the strongest Raman peak in graphite materials, representing the graphitization degree of CNT. The intensity ratio of the D peak to the G peak is D / I G =0.06, indicating the low defect density and high degree of graphitization of CNTs, which means that CNTs have high electronic conductivity. It is worth noting that the G peak of CNTs is split into G + and G - Peaks (~1572 and ~1596 cm -1 ), which is mainly due to the fact that although CNT has a high degree of crystallinity, it still has local defect structures (I D / I G =0.06), indicating the presence of localized stress distribution on the CNT wall, leading to the broadening and splitting of the G peak. This localized stress may originate from topological defects caused by carbon atom rearrangement during high-temperature annealing, which in turn enhances interfacial charge transfer dynamics.

[0086] The phase composition and crystal structure of Si@CNT and Si / LATP@CNT composites were systematically analyzed by XRD and Raman spectroscopy. The XRD spectrum showed that both composites had sharp diffraction peaks at 2θ=28.5°, 47.4° and 56.3°, corresponding to the (111), (220) and (311) crystal planes of single crystal silicon (PDF#04-006-6436), indicating that the crystal structure of silicon did not undergo significant phase change or lattice distortion during the LATP doping and CNT coating process. However, the (002) characteristic diffraction peak (~26°) of CNT was almost undetectable in the composite material, which was attributed to the low sensitivity of CNT in XRD, resulting in its diffraction signal being masked by the strong peak of silicon. The presence of CNT in the composite material was further verified by Raman spectroscopy. Figure 7 As shown in (b), Si@CNT and Si / LATP@CNT have the peaks at 510 and 938 cm -1 The two peaks at 1591.74 cm are attributed to Si. -1The diffraction peaks that appear in the spectra correspond to the G peaks in CNTs, indicating the presence of CNTs. It is worth noting that although the theoretical Raman characteristic peaks of LATP (such as PO4 3- Tensile vibration, 850~1130cm -1 ) was not detected in Si / LATP@CNT, but by comparing the Si / LATP material doped with single LATP ( Figure 4 ) It can be clearly seen that it is distributed in the silicon matrix in the form of a heterogeneous structure.

[0087] Figure 8 The microstructural characteristics of Si / LATP@CNT composite materials were analyzed in detail. Figure 8 (a) is the SEM image of Si / LATP@CNT; Figure 8 (b), (c), (d), (e), and (f) are TEM images. Figure 8 (d), (e), and (f) are the crystal structure information and SAED patterns of the blue d area and the yellow e area dashed boxes in (c), respectively; Figure 8 (g) is the EDS spectrum. SEM image of Si / LATP@CNT ( Figure 8 Middle (a) shows that CNTs are interwoven into a three-dimensional network structure on the surface of silicon particles, effectively covering the LATP-doped silicon matrix. Its high flexibility can effectively buffer the volume deformation of the silicon matrix during the lithium insertion / extraction process, while providing a fast channel for electron transmission. The corresponding TEM image ( Figure 8 (b) also shows that CNT wraps Si / LATP to form a continuous three-dimensional network skeleton. The interaction between Si and LATP in Si / LATP@CNT was confirmed by TEM analysis. Figure 8 In (c), (d), and (e), Si and LTAP exhibit two-phase coexistence characteristics. The lattice fringes of silicon (0.31 nm, corresponding to the (111) crystal plane) and the characteristic crystal plane of LATP (0.36 nm, (113) crystal plane) form a heterogeneous interface, indicating that Si and LATP coexist in the form of a heterogeneous structure. This has been confirmed in the composition analysis of the Si / LATP material mentioned above ( Figure 4 This strong coupling structure can promote the rapid migration of lithium ions at the interface and inhibit the structural pulverization of silicon particles during cycling. Figure 8 The selected area electron diffraction (SAED) of (f) shows polycrystalline diffraction characteristics, and the EDS spectrum ( Figure 8 The uniform distribution of Ti, Al, and P elements was detected in (g), confirming the uniform composite of LATP and silicon. This microscopic homogeneity provides the structural basis for the long-term cycling stability of the material.

[0088] In order to study the kinetic mechanism of the LATP / CNT dual-channel transport network in improving the electrochemical performance of silicon anode, CV tests were carried out on Si@CNT (prepared in Comparative Example 1) and Si / ALTP@CNT. Figure 9 The electrochemical properties of Si@CNT and Si / LATP@CNT. Figure 9 (a) is at 0.2mV s -1 The CV curve below, Figure 9 (b) is the cycle performance and the corresponding Coulomb efficiency, Figure 9 (c) in the figure is at 0.5Ag -1 The charge and discharge curves of the next 200 cycles, Figure 9 (d) in the figure is the rate performance at different current densities. Figure 9 As shown in (a), at 0.2mV s -1 At a scan rate of 1.5, Si@CNT and Si / LATP@CNT exhibited similar CV curve characteristics in the first three cycles. The sharp reduction peak near 0.01 V corresponds to the phase transition from crystalline Si to amorphous LixSi during the lithiation process, while the oxidation peak near 0.56 V corresponds to the phase transition from Li to Si during the delithiation process. x It is worth noting that Si / LATP@CNT exhibits a higher response current density, indicating that it has better lithium ion transport kinetics, which is mainly attributed to the dual-channel transmission network synergistically constructed by LATP and CNT, which effectively improves the conduction efficiency of lithium ions and electrons.

[0089] Cycle performance ( Figure 9 (b)) shows that at 0.1Ag -1 When initially activated under low temperature, the discharge specific capacities of Si@CNT and Si / ALTP@CNT were 2787 mAh g -1 , 2708mAh g -1 , corresponding to ICE of 88% and 87% respectively. Si / ALTP@CNT exhibits slightly lower discharge capacity and ICE than Si@CNT, which is related to the electronic insulation properties of LTAP. Although LATP has excellent ionic conductivity, its electronic conductivity is poor. -1 Under the condition of high temperature, the discharge capacity of Si / LATP@CNT increased from the initial 1693 mAh g -1 Slowly decreases to 1351mAh g -1 , the capacity retention rate reached 80%. In contrast, Si@CNT quickly decayed to 171mAh g -1, the capacity retention rate is only 0.09%. Although CNTs are entangled on the surface of silicon particles to form a three-dimensional conductive network skeleton, the drastic volume change of silicon particles during the process of lithium insertion and removal causes the internal pores of the electrode to be filled, thereby generating a large charge transfer impedance in the subsequent lithiation process. Si / LATP@CNT benefits from the fact that LATP is evenly dispersed at the interface of silicon particles and is jointly wrapped by the CNT conductive skeleton. LATP inhibits the collapse of electrode pores through its three-dimensional ion transport channels, and the CNT conductive skeleton maintains a continuous electron transport path, reducing the charge transfer impedance during the cycle. Therefore, the interface coupling design of LATP and CNT ensures the complete lithium ion and electron transmission path of Si / LATP@CNT during repeated charge and discharge, thereby effectively solving the kinetic limitations and structural instability problems of silicon-based negative electrodes.

[0090] Charge and discharge curves under different cycle periods ( Figure 9 Figure (c) shows that the voltage curves of Si / ALTP@CNT exhibit good overlap, confirming its excellent cycling stability. The surface dual-phase synergistic effect effectively inhibits electrode structural degradation. Specifically, after 200 cycles, the voltage hysteresis (ΔV) of Si / ALTP@CNT decreases from ~0.39 mV to ~0.26 mV, while that of Si@CNT increases from ~0.26 mV to ~0.97 mV. This voltage hysteresis is primarily due to polarization effects (including ohmic polarization, electrochemical polarization, and concentration polarization) and material phase transition hysteresis. The volume expansion / contraction of the silicon-based anode leads to stress-induced voltage hysteresis. After 200 cycles, the voltage hysteresis of Si / ALTP@CNT changes by only 0.13 mV, and its voltage hysteresis is significantly lower than that of Si@CNT, indicating significantly improved interfacial kinetic stability. This is closely related to the stabilization of the SEI film on the silicon particle surface by LATP.

[0091] Rate performance is another important indicator for evaluating the electrochemical performance of composite materials. Figure 9 As shown in (d), when the current density is from 0.1Ag -1 Gradually increase to 2Ag -1 During the process, Si@CNT and Si / LATP@CNT were -1 and 0.2Ag -1 ) showed similar lithium insertion capacity. However, with the increase of current density, the lithium insertion capacity of Si / LATP@CNT was significantly higher than that of Si@CNT. -1 At a high current density of 1553 mAh g -1 High capacity and recovery at current density down to 0.1A -1 When the capacity is basically restored to 2939mAh g-1 (with the initial 2999mAh g -1 Compared with the previous study, the capacity recovery rate reached 98.0%, which shows that the material has excellent structural reversibility. The LATP / CNT dual-channel network effectively maintains the integrity of the electrode structure and reduces the polarization loss at high rates. Long-term cycle stability is a key challenge in the practical application of silicon-based negative electrodes. Figure 9 As shown in (e), the lithium insertion capacity of Si / LATP@CNT is stable at 1093 mAh g after 400 cycles. -1 , further verifying the effectiveness of the composite structure design.

[0092] In order to explore the regulatory mechanism of LATP doping on the electrochemical performance of Si / LATP@CNT composites, the present invention systematically optimized the LATP addition ratio and designed doping amounts of 0wt%, 1wt%, 2wt% and 5wt%, respectively. The corresponding composite materials are labeled Si@CNT, Si / LATP@CNT-1, Si / LATP@CNT and Si / LATP@CNT-2. Figure 9 The electrochemical cycling performance and rate performance of Si@CNT and Si / LATP@CNT have been discussed in detail, while the performance of Si / LATP@CNT-1 and Si / LATP@CNT-2 are shown in Figure 10 As shown, Figure 10 (a) in the figure is at 0.5Ag -1 Cycling stability at different current densities; Figure 10 (b) shows the rate performance at different current densities. With the increase of LATP, the discharge capacity of Si@CNT, Si / LATP@CNT-1, Si / LATP@CNT and Si / LATP@CNT-2 after 100 cycles is 1200 mAh g -1 , 1525mAh g -1 , 1819mAh g -1 and 954mAh g -1 , and the corresponding capacity retention rates are 61%, 76%, 88% and 47% respectively. Figure 10 The rate test results in (b) also conform to this pattern, demonstrating that the Si / ALTP@CNT electrode has the best cycling stability and rate performance. This suggests that there is an optimal threshold for LATP doping (2 wt%), and that excessive addition of LATP leads to a decrease in electronic conductivity. This non-monotonic variation can be explained by percolation theory: when the LATP content reaches 2 wt%, its percolation network forms an interpenetrating structure with the CNT conductive network, achieving synergistic optimization of ion / electron transport.

[0093] 4. Ion transport kinetics research

[0094] The above optimization of the structural design and electrochemical performance of LATP-doped and LATP / CNT dual-phase modified silicon-based negative electrodes has significantly improved the cycle stability and interface stability of the silicon negative electrode. However, its intrinsic kinetic enhancement mechanism still needs to be further analyzed. The kinetic properties of the electrode material (especially the transport behavior of lithium ions) are the key factors that determine the battery rate performance and cycle life. The capacity decay of traditional silicon-based negative electrodes is often related to Li + Diffusion kinetics hysteresis is closely related to the unstable evolution of SEI film. To further clarify the charge storage mechanism and lithium ion diffusion behavior of the material system, the present invention systematically studied the ion transport kinetics of Si / LATP@CNT through multi-scale kinetic characterization (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS)). Based on the Randle-Sevick (RS) equation and the Warburg impedance model, the effects of different modification strategies on the lithium ion diffusion coefficient were quantitatively analyzed. The regulation rules of the dual-channel transmission network reveal the optimization mechanism of the dynamic process.

[0095] Figure 11 The CV curves of Si / LATP@CNT and Si@CNT at different scan rates and their lithium ion diffusion coefficients are shown. calculate, Figure 11 (a) and (c) are the CV curves of Si / LATP@CNT at different scan rates and the peak current (I p ) and scanning speed (v 1 / 2 ), Figure 11 (b) and (d) are the CV curves of Si@CNT at different scan rates and the peak current (I p ) and scanning speed (v 1 / 2 ). Figure 11 As shown in (a) and (b), the redox peak response current of Si / LATP@CNT increases with the increase of scan rate and is much higher than the redox peak current of Si@CNT, indicating that Si / LATP@CNT has faster interface transmission kinetics. It is worth noting that Si@CNT has a higher redox peak current at high scan rate (>0.8mV s -1 ) shows a peak splitting phenomenon, indicating that the concentration polarization caused by the limited solid-phase diffusion is aggravated, while the peak shape of Si / LATP@CNT remains intact, confirming that the dual-channel design can alleviate the kinetic bottleneck. According to the RS equation, Figure 11 (c) and (d) of the graph, the oxidation peak current (I p ) and the square root of the sweep rate (v 1 / 2 ) showed a good linear relationship (R 2 =0.959), which is consistent with the diffusion-controlled process described by the RS equation. -1Within the scanning rate range, the oxidation peak I of Si / LATP@CNT p / v 1 / 2 The slope is 6.87×10 -4 , significantly higher than Si@CNT (3.29×10 -4 ), indicating that the ion channel constructed by LATP effectively reduced the + Diffusion activation energy. Corresponding lithium ion diffusion coefficient 1.63×10 -10 cm 2 s -1 , which is an order of magnitude higher than that of Si@CNT (3.74×10 -11 cm 2 s -1 This indicates that the introduction of LATP effectively reduces the lithium ion diffusion barrier, and its three-dimensional ion conduction network forms a synergistic effect with the electron transport path of CNT, significantly improving the interfacial reaction kinetics.

[0096] The evolution of electrode interface impedance was systematically analyzed by electrochemical impedance spectroscopy (EIS). Figure 12 (a) and (b) are the Nyquist plots of Si / LATP@CNT at open circuit voltage (OCV), 3 cycles, and 100 cycles, as well as the relationship between Z′ and ω. -1 / 2 relationship diagram; Figure 12 (c) and (d) are the Nyquist plots of Si@CNT at OCV, 3 cycles, and 100 cycles, as well as the relationship between Z′ and ω-1 / 2; Figure 12 (e) and (f) are the Nyquist plots of Si at OCV, 3 cycles, and 100 cycles, as well as the relationship between Z′ and ω-1 / 2. Nyquist plots of Si / LATP@CNT, Si@CNT, and Si at OCV, 3 activations, and 100 cycles ( Figure 12 (a), (c), and (e) all show typical high-frequency semicircle-low-frequency oblique line characteristics, representing the charge transfer resistance (R ct ) and Li + Warburg impedance related to ion diffusion. The results show that at all test stages (OCV, 3 cycles, 100 cycles), the high-frequency semicircle diameter of Si / LATP@CNT is the smallest, followed by Si@CNT and Si, indicating that the Si / LATP@CNT electrode has the lowest charge transfer impedance, which means that the dual transport channels of LATP and CNT help maintain the integrity of the SEI and effectively inhibit the continuous decomposition of the electrolyte.

[0097] Combined with the low-frequency Warburg impedance analysis of lithium ion diffusion dynamics, Figure 12Z′-ω in (b), (d), and (f) -1 / 2 The lithium ion diffusion coefficient calculated by the relationship like Figure 13 As shown ( Figure 13 The Li of Si / LATP@CNT, Si@CNT and Si in OCV, 3 cycles and 100 cycles + Diffusion coefficient), in the OCV state, Si / LATP@CNT, Si@CNT and Si are 2.36×10 -16 , 4.03×10 -16 and 9.64×10 -17 cm 2 s -1 After 3 activation cycles, the three were significantly increased to the maximum, which were 3.83×10 -14 , 3.16×10 -14 and 1.38×10 -15 cm 2 s -1 This is mainly attributed to the formation of SEI film during the initial cycle, which optimizes the interface wettability and reduces the Li + The activation energy barrier for transport across the interface. However, after 100 cycles decayed to 1.59×10 -14 , 7.32×10 -15 and 2.66×10 -17 cm 2 s -1 This kinetic degradation is mainly due to the irreversible collapse of the electrode pore structure, which leads to the + The diffusion path is blocked. It is worth noting that pure Si It is even lower than the initial value, which confirms the severity of its structural instability.

[0098] The above results confirm that the pore structure of the original Si electrode collapses after repeated lithium insertion and removal, resulting in a blockage of the diffusion path. While the silicon anode with a single CNT conductive network can improve the electrode's interfacial diffusion impedance, after long-term cycling, the silicon particles undergo electrochemical sintering, leading to the fusion and growth of the silicon particles, which in turn hinders the transmission of lithium ions and causes a rapid decrease in the lithium ion diffusion coefficient.

[0099] The excellent kinetic stability of Si / LATP@CNT can be attributed to the stabilizing effect of the LATP / CNT dual network on the electrode / electrolyte interface: LATP effectively inhibits the uncontrolled thickening of the SEI film, while the mechanical support provided by its rigid skeleton ensures the long-lasting and effective ion channel during cycling. The three-dimensional interconnected structure of CNT provides a continuous pathway for electron transport, significantly alleviating the kinetic attenuation caused by electrode pulverization during cycling. Therefore, the synergistic modification of LATP / CNT not only optimizes the electrode / electrolyte interface properties, but more importantly, by establishing multi-dimensional transmission channels, it achieves a simultaneous improvement in lithium ion diffusion kinetics and structural stability.

[0100] 5. Long-cycle stability performance improvement mechanism

[0101] Based on an in-depth analysis of the ion transport kinetics at the electrode interface, it is known that the LATP / CNT dual-phase conductive network exhibits excellent ion transport kinetics, but the intrinsic mechanism of its long-cycle stability still needs to be systematically analyzed in combination with the interface chemical evolution and electrode structural integrity. To this end, the present invention reveals the long-cycle performance improvement mechanism of Si / LATP@CNT from three aspects: dynamic interface impedance response, SEI component reconstruction, and electrode structure failure behavior through in situ impedance spectroscopy, surface chemical analysis, and micromorphological characterization.

[0102] Figure 14 The dynamic evolution of the interface impedance of Si / LATP@CNT and Si@CNT after pre-activation was revealed. Figure 14 (a) and (b) are the in-situ electrochemical impedance spectroscopy of Si / LATP@CNT and the corresponding charge-discharge curves and relaxation time distribution (DRT). Figure 14 (c) and (d) are the in-situ electrochemical impedance spectroscopy of Si@CNT and the corresponding charge-discharge curves and relaxation time distribution (DRT). During the lithiation and delithiation processes, the Nyquist plots of Si / LATP@CNT and Si@CNT both show typical high-frequency semicircle and low-frequency oblique line characteristics. Si / LATP@CNT maintains a smaller semicircle diameter during the charge and discharge process, indicating that Si / LATP@CNT has a stable and low interfacial impedance. In contrast, Si@CNT exhibits a larger semicircle diameter during the discharge process and a sudden drop during the charge process, indicating that it undergoes a drastic volume change during the lithiation process, resulting in the rupture and reorganization of the SEI film. This result means that LATP can accelerate the charge transfer process, further confirming the importance of LATP doping. Figure 14 The horizontal coordinates of the three-dimensional graphs in (a) and (c) are Potential (V) and Z' (ohm), respectively.

[0103] However, although EIS is widely used to study the interfacial chemistry of lithium-ion batteries, it is difficult to distinguish effectively because the semicircles in the medium and high frequency regions are usually coupled. In order to further analyze the coupling mechanism of the interface process, the distribution of relaxation time (DRT) can convert the coupled EIS into the relationship between the time constant (τ) and the time constant distribution (γ(τ)), thereby revealing the complex interface dynamics process. The present invention uses the DRT method developed by the Ciucci team to deconvolute the in situ EIS data. The results are as follows Figure 14 As shown in (b) and (d) in Figure 3, three obvious peaks can be observed, located at 10 -5 , 10 -4 ~10 -2 and 1~10s, marked as τ1, τ2 and τ3. τ1 is related to Li + Diffusion related (R SEI ), τ2 and τ3 are assigned to the charge transfer resistance (R ct During the lithiation process, the τ1 and τ2 values ​​of Si@CNT continue to rise, reaching their maximum values ​​at the end of lithiation and gradually decreasing during the subsequent delithiation process. In contrast, Si / LATP@CNT maintains relatively stable τ1 and τ2 peak values ​​during the lithium insertion and delithiation process, indicating that the dynamic reconstruction of the SEI layer in the former leads to a tortuous ion transport path, while the rigid skeleton of LATP in Si / LATP@CNT effectively suppresses the non-uniform stress distribution during the dynamic reconstruction of the SEI film.

[0104] In order to reveal the effect of the dual transport network on the structure and composition of the thin SEI formed on the surface of the Si electrode, X-ray photoelectron spectroscopy (XPS) analysis was performed on the original electrode and the electrode after 100 cycles. Figure 15 shown. Figure 15 XPS spectra of Si / LATP@CNT and Si@CNT, Figure 15 (a) and (e) in are C1s, Figure 15 (b) and (f) are O1s, Figure 15 (c) and (g) in are F1s, Figure 15 (d) and (h) are Li 1s. The typical peaks of C1s spectra at 283.8, 285.7, and 290.0 eV in the original Si / LATP@CNT and Si@CNT electrodes can be attributed to the C=C, CN, and CF bonds in CNTs ( Figure 15(a) and (e) in the figure). After 100 cycles, the typical peaks at 284.8, 286.5 and 288.3 in the C1s spectrum can be attributed to CC, CO and ROCO2Li, which are the main decomposition products of carbonate solvents in the electrolyte. It is worth noting that the characteristic peak intensities of CO and ROCO2Li in the Si / LATP@CNT electrode are significantly lower than those in the Si@CNT electrode, indicating that the decomposition of conventional solvents has been effectively suppressed. In the F1s spectrum ( Figure 15 In (c) and (g), Si / LATP@CNT forms a SEI layer dominated by LiF (684.8eV), while the SEI of Si@CNT is jointly determined by POF (686.0eV), CF (687.1eV) and LiF. Among them, LiF is the main decomposition product of fluoroethylene carbonate (FEC), the POF peak comes from the reduction of lithium hexafluorophosphate (LiPF6) salt, and the CF peak is attributed to the reduction product of CNT and FEC. The SEI film with high LiF content has good electronic insulation, which can effectively prevent electrons from conducting through the SEI film, thereby inhibiting the further decomposition of the electrolyte solution. In addition, it is reported that LiF has higher interfacial energy and lower Li + The LATP / CNT dual transport network significantly promotes the decomposition of FEC to generate more LiF, forming a LiF-rich SEI layer with high mechanical strength, low interfacial energy, and effectively suppresses the volume expansion of the silicon electrode during cycling.

[0105] Electrode microstructure evolution ( Figure 16 ) revealed the structural stability of Si / LATP@CNT during long-term cycling. Figure 16 (a) and (b) are cross-sectional SEM images of Si / LATP@CNT electrodes before and after 100 cycles. Figure 16 (c) and (d) are cross-sectional SEM images of Si@CNT electrodes before and after 100 cycles; Figure 16 (e) and (f) are the SEM images of the electrode sheet before and after 100 cycles of Si / LATP@CNT. Figure 16 (g) and (h) are the plane SEM images of the Si@CNT electrode sheet before and after 100 cycles. Figure 16As can be seen from (a), (b), (c), and (d) in the figure, after 100 cycles, the cross-sectional thickness of the Si / LATP@CNT electrode increased from the initial 13.9μm to 37.1μm after 100 cycles of charge and discharge, with an expansion rate of 266.9%. The Si@CNT electrode increased from the initial 14.2μm to 64.4μm, with an expansion rate of 453.5%, showing more obvious cracks and material expansion. This shows that the rigid framework of LATP and the tough network of CNT synergistically suppress the volume effect. From the planar SEM image ( Figure 16 From (e), (f), (g), and (h) in Figure 3, Si / LATP@CNT maintained a good particle morphology, while Si@CNT showed obvious electrochemical sintering and particle fusion. This difference in structural stability can be attributed to the "dual-phase buffer layer" formed by the rigid skeleton of LATP nanoparticles and the flexible entanglement of CNTs, which inhibited the electrochemical sintering of silicon particles.

[0106] In summary, the dual-channel transport network constructed by LATP-CNT achieves the improvement of the long-cycle performance of silicon-based anode through the following mechanisms: (1) significantly reducing Li + The migration barrier and charge transfer impedance in the SEI enable fast lithium ion diffusion kinetics. (2) The LiF-rich SEI film reduces interfacial impedance and inhibits side reactions; (3) The rigid-flexible composite structure buffers volume expansion and maintains the integrity of the electrode structure.

[0107] As can be seen from the above examples, the present invention reveals the synergistic improvement mechanism of the structural stability and electrochemical performance of silicon-based negative electrodes by constructing a LATP / CNT two-phase transport network through systematic research. Structural characterization (SEM, TEM, XRD) confirmed that LATP particles and CNT three-dimensional networks form a "rigid-flexible coupling" composite framework, in which LATP is anchored to silicon particles through a heterogeneous interface, while CNTs are interwoven and entangled on the Si / LATP matrix. Ion transport kinetic analysis (EIS, CV) shows that the high ionic conductivity characteristics of LATP significantly reduce the Li + Diffusion barrier ( Increased to 1.63×10 -10 cm 2 s -1 ), optimizing the interface stability and charge transfer efficiency of Si / LATP@CNT, which is attributed to the synergistic effect of LATP's NASICON fast ion channel and CNT electronic network. Further in situ electrochemical impedance spectroscopy and relaxation time distribution analysis showed that the dual transport network system makes Si / LATP@CNT have stable Li during the process of lithium insertion and extraction. + The resistance across the SEI layer (R SEI ) and a stable interfacial charge transfer resistance (R ct), reflecting that the "ion-electron" dual continuous transport network enhances the ion transport dynamics within the battery. The core mechanism is that LATP induces the formation of a thin layer of LiF-rich SEI, thereby improving the interface stability and cycle performance of the material. In the electrochemical performance test, the initial specific capacity of the Si / LATP@CNT material reached 2708mAh g -1 , 0.5Ag -1 After 400 cycles, the lithium insertion capacity is stable at 1093 mAh g -1 , in 2Ag -1 It can still maintain 1553mAh g at a high current density -1 The high capacity of the Si@CNT material is superior to that of traditional Si@CNT materials. This is mainly attributed to the fact that LATP doping can effectively alleviate the structural deformation of the silicon anode during long-term charge and discharge cycles. In summary, the synergistic effect of LATP and CNT not only improves the electrochemical performance of silicon-based anodes, but also provides new ideas for the design of high-performance silicon-based anode materials.

[0108] 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 Si / LATP@CNT composite material, characterized in that: The following steps are involved: mixing nano-silicon material, organic solvent, lithium aluminum titanium phosphate and carbon nanotubes to obtain a precursor dispersion; ball-milling the precursor dispersion and performing solid-liquid separation to obtain a precursor powder; The precursor powder is heat-treated in a protective gas atmosphere to obtain the Si / LATP@CNT composite material.

2. The preparation method according to claim 1, characterized in that The mass of the lithium titanium aluminum phosphate accounts for 1.5-4.5% of the mass of the nano-silicon material.

3. The preparation method according to claim 1 or 2, characterized in that The mass of the carbon nanotubes accounts for 1-10% of the mass of the nano-silicon material.

4. The preparation method according to claim 1, characterized in that The ball mill has a rotation speed of 100 to 250 rmin. -1 The ball milling time is 6 to 12 hours; The ball mill uses ball milling beads, which are zirconia beads, and the ball-to-material ratio is 20 to 50:

1.

5. The preparation method according to claim 1, characterized in that The heat treatment temperature is 800-950°C, the holding time is 2-4 hours, and the heating rate to the heat treatment temperature is 1-10°C min -1 , the protective gas includes a rare gas.

6. The Si / LATP@CNT composite material prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the Si / LATP@CNT composite material according to claim 6 in preparing anode materials or cathode sheets for lithium-ion batteries.

8. A lithium ion battery negative electrode material, characterized in that The negative electrode active component comprises the Si / LATP@CNT composite material according to claim 6.

9. 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 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 lithium-ion battery negative electrode sheet according to claim 9.

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