Lithium ion battery negative electrode material and preparation method and application thereof

Abstract

The invention provides a lithium ion battery negative electrode material as well as a preparation method and application thereof. The lithium ion battery negative electrode material is a porous silicon carbon material coated with lithium phosphate. The preparation method is simple and efficient, lithium phosphate salt is uniformly distributed on the surface of the porous silicon carbon material through solvent wet coating, the lithium phosphate salt is decomposed into LiF and LixPyOz through sintering and heating, and LiF and LixPyOz coating layers are generated in situ on the surface of the porous silicon carbon negative electrode material of the lithium ion battery, so that the porous silicon carbon material uniformly coated with LiF and LixPyOz is obtained, the advantages of LiF and LixPyOz are combined, and the porous silicon carbon material has the advantages that the porous silicon carbon material can be used for preparing the lithium ion battery negative electrode material through cooperation of LiF and LixPyOz; the silicon-carbon material prepared by the method has the characteristics of high strength, high stability and high ionic conductivity, can effectively inhibit volume expansion of the silicon-carbon material in the charge-discharge process, block penetration of electrons and reduce capacity loss of the silicon-carbon material in the reaction process, is used for manufacturing a lithium ion battery and remarkably improves the cycling stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-ion battery anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in 3C electronics, new energy vehicles, and energy storage due to their excellent overall performance. However, with the increasing demand for battery capacity in various fields, traditional graphite anodes (theoretical specific capacity of only 372 mAh / g) can no longer meet the requirements. Silicon-carbon anode materials have become a promising next-generation anode material due to their extremely high theoretical specific capacity (4200 mAh / g), low cost, and environmental friendliness. However, the volume expansion of silicon-carbon materials during charge and discharge can lead to structural damage and electrode breakage, causing the SEI film to continuously break and grow, continuously consuming lithium, and reducing battery capacity and cycle stability. At the same time, silicon-carbon materials are temperature sensitive. At high temperatures, insulating SiC is easily formed, reducing the initial capacity. At low temperatures, the lithium-ion migration rate slows down and the SEI film impedance increases, resulting in a decline in discharge capacity and cycle performance, as well as safety hazards such as lithium plating.

[0003] Patent document CN20211114995.9 reports a method for preparing lithium battery anode materials by in-situ generating a lithium difluorophosphate coating layer on the material surface through the reaction of lithium hexafluorophosphate and lithium carbonate. However, the high hydrolysis sensitivity of lithium hexafluorophosphate leads to the generation of a large amount of byproducts such as HF and PF5, which significantly reduces the quality of the coating layer and increases the interfacial impedance. Furthermore, the coating layer generated by the direct reaction only has physical adsorption bonding with the substrate, resulting in weak strength and easy local peeling during the reaction process, thus losing the original modification effect. CN202410038500.8 proposes a method to obtain porous silicon carbon coated with a solid electrolyte by dissolving a solid electrolyte in a solvent, mixing and drying it, and then laser sintering it. The oxide solid electrolytes mentioned in the paper are prone to side reactions in solvents. LLZO (lithium lanthanum zirconium oxide) is prone to hydrolysis in water or alcohol solvents, generating impurities such as Li2CO3 and La(OH)3, which reduces ionic conductivity. LATP (lithium aluminum titanium phosphate) contains the variable valence element Ti. 4+ It is reduced to Ti during heating and stirring. 3+ This leads to an increase in electronic conductivity, causing a short circuit in the battery. The generated solid electrolyte coating layer is distributed in a discontinuous, island-like pattern, causing localized exposure of the negative electrode material surface, which directly contacts the electrolyte, forming an unstable SEI film that continuously consumes active lithium and reduces the battery's charge and discharge efficiency.

[0004] Therefore, there is an urgent need to find a simple, cost-controllable method that can avoid side reactions of pre-fabricated materials to construct a dense, uniform composite coating layer with both high ionic conductivity and high mechanical stability on the surface of silicon-carbon anode materials in situ, so as to synergistically improve its first-cycle efficiency and long-cycle stability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a lithium-ion battery anode material.

[0006] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned lithium-ion battery anode material.

[0007] Another technical problem to be solved by the present invention is to provide the application of the above-mentioned lithium-ion battery anode material.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A lithium-ion battery anode material comprising LiF (lithium fluoride) and Li x P y O z The composition includes a coating layer and a porous silicon-carbon material, wherein the porous silicon-carbon material is prepared by CVD deposition of nano-silicon particles in porous carbon; the coating layer is composed of LiF and Li2, which are formed in situ after the decomposition of lithium phosphate salt during sintering. x P y O z They are uniformly distributed on the outer surface layer of the porous carbon anode material.

[0009] Preferably, in the above-mentioned lithium-ion battery anode material, the LiF and Li x P y O z It is obtained by sintering lithium phosphate salt.

[0010] Preferably, in the above-mentioned lithium-ion battery anode material, the lithium phosphate salt is sintered at a temperature of 300-400℃ and held for 4-8 hours. The LiF and Li... x P y O z The ratio between them will vary depending on the temperature and holding time during the sintering of lithium phosphate salts. The higher the temperature and the longer the holding time, the higher the yield of Li. x P y O z The more, for example, the more LiF and Li obtained after holding at 400℃ for 8 hours. x P y O z The mass ratio is approximately 1:1.

[0011] Preferably, the above-mentioned lithium-ion battery anode material has the following performance parameters: physical properties standard <![CDATA[Vibrating compaction (g / m 3 )]]> ＞0.8 <![CDATA[Specific gravity (m 2 / g)]]> ≤2 Resistance (Ω•cm) ≤3 dQ / dV (mAh / V) 1.6-1.9 Magnetic materials (Fe+Cr+Ni+Zn) (ppm) ≤5 Gas production (mL / g) at 45℃ for 24 hours ≤1 The specific steps for preparing the above-mentioned lithium-ion battery anode material are as follows: S1. Dissolve lithium phosphate in a solvent and stir to obtain a fluorinated lithium salt solution; S2. Porous silicon-carbon powder is added to a fluorine-containing lithium salt solution, and after preliminary drying by heating and stirring, it is thoroughly dried in a drying oven. Then, the powder is sintered in an inert gas atmosphere to obtain LiF and Li. x P y O z Uniformly coated porous silicon-carbon material.

[0012] Preferably, in the above-mentioned method for preparing the lithium-ion battery anode material, the lithium phosphate salt in step S1 is one or more of LiPO2F2 (lithium difluorophosphate), LiODFP (lithium difluorobis(oxalate) phosphate), and LiFOP (lithium tetrafluorooxalate phosphate). More preferably, it is LiPO2F2 (lithium difluorophosphate).

[0013] Preferably, in the above-mentioned method for preparing lithium-ion battery anode materials, the solvent in step S1 is one or more of alcohols, esters, ketones, ethers, and liquid alkanes.

[0014] Preferably, in the above-mentioned method for preparing lithium-ion battery anode material, the mass ratio of lithium phosphate salt to solvent in step S1 is approximately 1:(40-800).

[0015] Preferably, in the above-mentioned method for preparing the lithium-ion battery anode material, in step S2, the porous silicon-carbon powder is obtained by depositing nano-silicon particles in porous carbon using chemical vapor deposition (CVD). The porous carbon is one of resin-based, biomass-based, and pitch-based, and the particle size of the porous silicon-carbon powder is 2-15 μm. More preferably, the particle size of the porous silicon-carbon powder is 6-8 μm.

[0016] Preferably, the specific steps of the above-mentioned method for preparing lithium-ion battery anode material, which involves depositing nano-silicon particles in porous carbon using chemical vapor deposition to obtain porous silicon-carbon powder, are as follows: (1) Preparation of porous carbon: The raw material is placed in a continuous atmosphere rotary furnace, and an inert gas is introduced as a protective gas. The raw material is heated and kept warm to carbonize the organic material to form a preliminary porous structure. After carbonization, the temperature is lowered to carry out the pore expansion reaction and then heated again to activate the pore expansion. After cooling, the material is taken out, washed with deionized water until neutral, and dried for later use. (2) CVD deposition: The porous carbon matrix is ​​loaded into the reaction equipment, spread evenly, and inert gas is introduced to remove air. After heating and stabilizing, silane and carbon source gas are introduced to start the deposition process. After deposition is completed, the reaction gas is turned off and inert gas is introduced to purge the pipeline. The sample is naturally cooled to room temperature under a protective atmosphere and then removed. The material is micronized using an air jet mill.

[0017] Preferably, in the above-mentioned method for preparing the negative electrode material of lithium-ion batteries, the mass ratio of porous silicon-carbon powder to lithium phosphate salt in step S2 is 100:(0.5-5).

[0018] Preferably, in the above-mentioned method for preparing the negative electrode material of lithium-ion batteries, the mass ratio of porous silicon-carbon powder to solvent in step S2 is 1:(2-4).

[0019] Preferably, in the above-mentioned method for preparing lithium-ion battery anode material, the heating and stirring temperature in step S2 is 60-100℃, and the stirring time is 6-12h.

[0020] Preferably, in the above-mentioned method for preparing lithium-ion battery anode material, the drying temperature of the drying oven in step S2 is 80-120℃, and the drying time is 4-10h.

[0021] Preferably, in the above-mentioned method for preparing lithium-ion battery anode material, the sintering process in step S2 has a heating rate of 2-5℃ / min, a temperature of 300-400℃, and a holding time of 4-8h.

[0022] Preferably, in the above-mentioned method for preparing the lithium-ion battery anode material, the inert gas in step S2 is one or more of nitrogen, argon, and helium, and the gas flow rate is 30-70 cm⁻¹. 3 / min. More preferably, the gas flow rate is 40-60 cm⁻¹. 3 / min.

[0023] The above-mentioned lithium-ion battery anode materials are used in the manufacture of lithium-ion batteries.

[0024] Beneficial effects: The lithium-ion battery anode material is a porous silicon-carbon material coated with lithium phosphate, which solves the problems of interface stability of silicon-carbon materials and capacity decay of batteries under long-term cycling. The preparation method is simple and efficient, cost-controllable, and avoids the side reactions of pre-fabricated materials in existing technologies. The lithium phosphate is uniformly distributed on the surface of the porous silicon-carbon material through solvent wet coating, and the lithium phosphate is decomposed into LiF and Li by sintering and heating. x P y O z In-situ generation of LiF and Li on the surface of porous silicon-carbon anode material for lithium-ion batteries x Py O z Coating layer, thus obtaining LiF and Li x P y O z Uniformly coated porous silicon-carbon material with a dense and strongly bonded coating layer, composed of LiF and Li x P y O z The coated silicon-carbon material combines LiF and Li x P y O z The advantages of LiF are good stability and high mechanical strength; Li x P y O z It possesses high ionic conductivity, and the two work synergistically to combine high strength, high mechanical stability and high ionic conductivity characteristics. It can effectively suppress the volume expansion of silicon-carbon materials during charging and discharging, block electron penetration, reduce side reactions, suppress SEI growth to stabilize the silicon-carbon anode material interface, effectively reduce lithium loss in the early stage of reaction, improve the material's initial coulombic efficiency and lithium-ion diffusion rate, enhance the material's stability under high and low temperature conditions, reduce the capacity loss of silicon-carbon materials during the reaction process, synergistically improve the initial efficiency, and significantly improve the long-cycle stability of the battery. Attached Figure Description

[0025] Figure 1 This is a scanning image of the morphology of the unmodified material in Comparative Example 1 of this invention and a distribution map of fluorine and phosphorus elements.

[0026] Figure 2 This is a scanning image of the material morphology and the distribution of fluorine and phosphorus elements after coating in Embodiment 1 of the present invention.

[0027] Figure 3 This is a scan of the material morphology and the distribution of fluorine and phosphorus elements after coating in Embodiment 2 of the present invention.

[0028] Figure 4 This is a scan of the material morphology and the distribution of fluorine and phosphorus elements after coating in Embodiment 3 of the present invention. Detailed Implementation

[0029] The following detailed description of the lithium-ion battery anode material, its preparation method, and its application, in conjunction with embodiments and accompanying drawings, provides a comprehensive overview.

[0030] The preparation method of porous silicon carbide powder in the following examples follows the steps below: 1. Raw materials: Select one of resin-based, biomass-based, or asphalt-based raw materials to ensure low impurity content and uniform structure. If the raw materials are in block or granular form, they need to be crushed and screened to a suitable particle size (usually 0.5-3mm).

[0031] 2. Introduce an inert gas (Ar or N2) as a protective atmosphere, with the flow rate controlled at 5-15 L / min.

[0032] 3. Increase the temperature to 800-1200℃ at a rate of 5-10℃ / min and hold for 1-3 hours to carbonize the organic matter and form a preliminary porous structure.

[0033] 4. After carbonization, cool to 500–700℃, then introduce an activating gas (such as CO2) or impregnate with KOH solution before reheating. Activate at 700–900℃ for 1–2 hours to further expand pores and increase the specific surface area to >1000 μm². 2 / g, porosity >60%, pore size is mainly micropore to mesopore.

[0034] 5. The deposition reaction equipment is a rotary kiln or fluidized bed. The total gas flow rate is set to a range of 100–500 sccm, adjusted according to the volume of the reaction chamber.

[0035] 7. After introducing inert gas to purge air, first raise the temperature to 700-1000℃ and stabilize it for 30 minutes.

[0036] 8. Deposition process: The target silicon content is 40%–50%, and the molar ratio of silane (SiH4) to carbon source gas (C2H2 or CH4) is 1:1–2:1. The reaction pressure is controlled at atmospheric pressure or slightly negative pressure (0.1–0.5 atm) to avoid silane accumulation. The deposition time is 2–6 hours, and the temperature and gas flow rate are continuously monitored during the process.

[0037] 9. Use an air jet mill to micronize the material. Control the final particle size D50 within the range of 2–15 μm using a classifying sieve.

[0038] Comparative Example 1 Resin-based 8μm porous silicon carbide powder, Super P conductive carbon, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in deionized water at a mass ratio of 7:1:1:1, and then stirred to obtain a homogeneous slurry (e.g., Figure 1 As shown, the particles have smooth surfaces and no F or P element distribution. Electrodes are prepared, dried, and cut into sheets, then assembled into coin cells, and the battery performance is tested.

[0039] Example 1 1 g of LiPO2F2 (lithium difluorophosphate) was dissolved in 300 g of dimethyl ether solvent to obtain a fluorinated lithium salt solution. 100 g of resin-based 8 μm porous silicon carbide powder was added to the fluorinated lithium salt solution. After initial drying by heating and stirring at 60 °C for 12 h, the powder was dried in a drying oven at 80 °C for 10 h. The powder was then sintered in an argon atmosphere with a gas flow rate of 50 cm⁻¹. 3The temperature was increased to 300℃ at a rate of 5℃ / min, held at that temperature for 6 hours, and then allowed to cool naturally to obtain the lithium fluoride and Li. x P y O z Uniformly coated porous silicon-carbon materials (such as Figure 2 As shown, small particles appear on the surface of the particles, and elemental scanning shows the distribution of F and P elements, indicating that F- and P-containing materials were successfully coated on the porous silicon-carbon surface and the distribution was uniform.

[0040] LiF and Li x P y O z Uniformly coated porous silicon-carbon material, Super P conductive carbon, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were mixed in deionized water at a mass ratio of 7:1:1:1, and then stirred to obtain a uniform slurry. Electrodes were prepared, dried, and cut into sheets, assembled into coin cells, and the battery performance was tested.

[0041] Example 2 3g of LiODFP (lithium difluorobis(oxalato) phosphate) was dissolved in 350g of ethanol to obtain a fluorinated lithium salt solution. 100g of resin-based 8μm porous silicon carbide powder was added to the fluorinated lithium salt solution. After initial drying by heating and stirring at 80℃ for 8h, the powder was dried in a drying oven at 100℃ for 8h. The powder was then sintered in an argon atmosphere with a gas flow rate of 60 cm⁻¹. 3 The temperature was increased to 350°C at a rate of 2°C / min, held at that temperature for 4 hours, and then allowed to cool naturally to obtain the lithium fluoride and Li. x P y O z Uniformly coated porous silicon-carbon materials (such as Figure 3 As shown, small particles appear on the surface of the particles, and elemental scanning shows the distribution of F and P elements, indicating that F- and P-containing materials were successfully coated on the porous silicon-carbon surface and the distribution was uniform.

[0042] The negative electrode sheet was prepared using the same method as in Example 1, the coin cell assembly was completed, and the battery performance was tested.

[0043] Example 3 5g of LiFOP (lithium tetrafluorooxalate phosphate) was dissolved in 400g of dimethyl carbonate solvent to obtain a fluorinated lithium salt solution. 100g of biomass-based 6μm porous silicon carbide powder was added to the fluorinated lithium salt solution. After initial drying by heating and stirring at 100℃ for 6h, the powder was dried in a drying oven at 120℃ for 6h. The powder was then sintered under a nitrogen atmosphere with a gas flow rate of 40 cm⁻¹. 3 The temperature was increased to 400℃ at a rate of 5℃ / min, held at that temperature for 4 hours, and then allowed to cool naturally to obtain the LiF and Li. x Py O z Uniformly coated porous silicon-carbon materials (such as Figure 4 As shown, small particles appear on the surface of the particles, and elemental scanning shows the distribution of F and P elements, indicating that F- and P-containing materials were successfully coated on the porous silicon-carbon surface and the distribution was uniform.

[0044] The negative electrode sheet was prepared using the same method as in Example 1, the coin cell assembly was completed, and the battery performance was tested.

[0045] Test method for lithium-ion battery cycle performance: After activation at 25℃ by cycling 5 times at 0.1C, the lithium-ion battery is then charged and discharged 200 times at a constant current rate of 1.0C. The initial battery efficiency is calculated as: (initial charge capacity / initial discharge capacity) × 100%. The battery capacity retention rate after 200 cycles is calculated as: (200th charge capacity / 1st charge capacity) × 100%. Test data are shown in Table 1.

[0046] Tap value of lithium-ion battery anode material (g / m) 3 Test method: 1. Silicon-carbon anode materials are prone to moisture absorption and agglomeration. Before testing, they must be placed in a vacuum drying oven at 100℃ for 4 hours to remove moisture. The testing environment temperature should be controlled at 25±2℃, and the relative humidity ≤60%. 2. Weigh 5g of pretreated silicon carbide powder using an analytical balance and record the precise mass value. Fix a clean, dry 10mL graduated cylinder onto the clamp of the tapped density meter, ensuring the cylinder is vertical and not tilted. Slowly pour the weighed silicon carbide powder into the graduated cylinder using a spatula, avoiding powder splashing and stratification; after loading the sample, use a scraper to level the powder surface at the top of the graduated cylinder and record the loose volume of the powder at this point.

[0047] 3. Start the vibration program and set the parameters of the tapped density meter: amplitude 3mm, vibration frequency 100 times / min, number of taps 1000. Stop vibration and read volume. After vibration, let the graduated cylinder stand for 1 minute to allow the powder to stabilize completely. Read the volume Vt of the powder in the graduated cylinder after tapping. When reading, the line of sight should be horizontal with the graduation line of the graduated cylinder, accurate to 0.1mL; if the powder surface is uneven, take the average of the highest and lowest points.

[0048] According to the formula ρ t = m / V t Calculate the tap density value for each test, where ρ t — Tap density (g / cm³) 3 m—mass of silicon carbide powder (g), V t —Volume of powder after compaction (cm³) 3 The test data is shown in Table 2.

[0049] Specific Gravity Table of Lithium-ion Battery Anode Materials (m)2 / g) test method: 1. Silicon-carbon anode pretreatment: Weigh 0.5g of silicon-carbon powder and accurately record the mass m. Load the sample into a sample tube and connect it to the degassing station of the analyzer. Set the degassing parameters as follows: temperature 150℃, vacuum degree ≤10Pa, degassing time 3h. After degassing is complete, turn off the vacuum system and allow the sample tube to cool to room temperature. Then, quickly transfer it to a desiccator for later use. The laboratory temperature should be controlled at 25℃±2℃, and the relative humidity ≤50%.

[0050] 2. Connect the pretreated sample tube to the test station of the analyzer, ensuring the interface is sealed and leak-free; at the same time, install an empty sample tube as a blank control to subtract background adsorption.

[0051] Start the analyzer and perform a system leak check to ensure the vacuum level meets requirements. Set the adsorption isotherm measurement range: P / P0 = 0.05 : 0.35. Adsorption equilibrium time: 5 min to 10 min for each partial pressure point to ensure adsorption reaches a stable state.

[0052] 3. Immerse the sample tube in a liquid nitrogen bath (approximately 77K), start the test program, and the analyzer automatically introduces a nitrogen-helium mixture. The system sequentially adjusts different P / P0 partial pressures, recording the amount of nitrogen adsorbed at each partial pressure, until adsorption tests at all set partial pressure points are completed. After adsorption is complete, remove the sample tube, heat it to room temperature, and perform desorption to recover the adsorbed nitrogen. The analyzer automatically records the difference in adsorption data between the blank tube and the sample tube to obtain the actual amount of nitrogen adsorbed on the silicon-carbon sample.

[0053] 4. Data Processing and Result Calculation BET equation fitting: The analyzer software performs linear fitting based on the collected P / P0 and P / [V(P0-P)] data to obtain the slope of the fitted line k=(C-1) / (V m C) and intercept b=1 / (V m C).

[0054] The saturated adsorption capacity of a monolayer is calculated from the slope and intercept, V. m Vm = 1 / (k + b). Specific surface area is calculated using the formula S. BET :S BET =(V m ·N A ·A m ) / (m·V0). Where: N A Avogadro's constant (6.022 × 10⁻⁶) 23 mol -1 A mThe cross-sectional area of ​​a nitrogen molecule (usually taken as 0.162 nm). 2 V0: Molar volume of gas under standard conditions (22414 mL / mol), m: Sample mass (g). Test data are shown in Table 2.

[0055] Test method for resistivity (Ω•cm) of lithium-ion battery negative electrode material (four-probe method): 1. Sample Preparation: Accurately weigh 1g of silicon-carbon anode powder using a balance and record the exact value. Evenly fill the powder into a cylindrical mold with a standard inner diameter of 10mm. Gently shake or smooth the powder to ensure a flat surface without obvious gaps or accumulations.

[0056] 2. Pressure Molding and Testing: A powder resistivity meter is used. The mold containing powder is placed on the test bench, and the program is set for pressure testing. The pressure is gradually increased from 10 MPa to 200 MPa, increasing by 20 MPa in each step, and held at each pressure point for 10 seconds to allow the reading to stabilize. The instrument automatically applies a test current and measures the voltage during each pressure holding phase, calculating and recording the resistivity at that pressure in real time. The instrument typically displays or outputs the resistivity (Ω·cm) directly. Test data are shown in Table 2.

[0057] Test method for dQ / dV (mAh / V) of lithium-ion battery anode materials: 1. Assemble silicon-carbon materials with lithium sheets into coin cells. At 25℃, in a voltage range of 0-1.5V, use a constant current of 0.1C for charging and discharging, and record the voltage (V) and cumulative capacity (Q, mAh / g) data.

[0058] 2. The data processing software performs numerical differentiation on the discrete data of capacity (Q) with respect to voltage (V) to obtain the dQ / dV (mAh / V / g) value corresponding to each voltage point.

[0059] 3. Plotting voltage (V) on the x-axis and dQ / dV on the y-axis yields the differential capacity curve. The desired dQ / dV value is obtained by taking the dQ / dV data at 0.45V. Test data is shown in Table 2.

[0060] Test method for magnetic materials (Fe+Cr+Ni+Zn) (ppm) in lithium-ion battery anode materials: 1. Sample pretreatment: Silicon-carbon anode contains silicon phase (SiO2) xThe silicon-carbon anode powder consists of a silicon phase and a carbon phase. The silicon phase requires digestion with hydrofluoric acid, while the carbon phase requires oxidation with nitric acid and perchloric acid. Weigh 0.5 g of silicon-carbon anode powder (accurate to 0.0001 g) using an electronic balance and place it in a polytetrafluoroethylene digestion vessel, recording the sample mass m. Add 5 mL of concentrated nitric acid and 2 mL of concentrated hydrofluoric acid, gently shake, and place in a fume hood for pre-reaction for 30 min. Seal the digestion vessel and place it in a microwave digestion apparatus. After digestion, cool to room temperature, open the digestion vessel, add 1 mL of perchloric acid, and heat on a graphite digestion apparatus until white fumes appear and the solution becomes clear and transparent. Transfer the digestion solution to a 50 mL polytetrafluoroethylene volumetric flask, wash the digestion vessel several times with ultrapure water, add the washings to the volumetric flask, and dilute to the mark with ultrapure water. Shake well to obtain the sample solution to be tested. Blank solution preparation: Without silicon-carbon sample, prepare a reagent blank solution following the same acid digestion and dilution steps as described above.

[0061] 2. Testing: Standard Solution Preparation: Dilute the single-element standard solution or mixed standard stock solution with ultrapure water to prepare standard working solutions with five concentration gradients (e.g., 0, 0.1, 0.5, 1.0, 5.0 μg / L). Add an equal volume of internal standard solution (usually 10 μg / L) to both the standard working solutions and the sample solutions to be tested. Start the ICP-MS and set the optimal instrument operating parameters (RF power, nebulizer gas flow rate, sampling depth, etc.). Inject the blank solution and standard working solutions sequentially. Plot a standard curve with element concentration on the x-axis and ion count intensity on the y-axis, requiring a linear correlation coefficient R² ≥ 0.999. Introduce the reagent blank solution and the sample solutions to be tested sequentially into the ICP-MS injection system. The instrument automatically collects the ion count intensities of Fe, Cr, Ni, and Zn. Calculate the concentration Ci (unit: μg / L) of each element in the sample solution using the standard curve.

[0062] 3. Data Calculation and Result Determination: Formula for calculating single element content: wi (ppm) = m (Ci - C) 0i )×V×10 -3 In the formula: wi: Content of element i (Fe / Cr / Ni / Zn) in the sample, in ppm; Ci: Concentration of element i in the sample solution, in μg / L; C 0i : Concentration of element i in the reagent blank solution, μg / L; V: Sample volume, mL; m: Mass of silicon-carbon sample, g; 10 -3 Unit conversion factor (1μg / L×1mL=10) -3 μg=10 -6 mg).

[0063] Total magnetic material content: Total content = w Fe +w Cr +w Ni +wZn The test data is shown in Table 2.

[0064] Test method for gas production (mL / g) of lithium-ion battery anode material at 45℃ for 24 hours: 1. Accurately weigh 1g±0.1g of sample and 2g±0.5g of deionized water into an aluminum-plastic bag. Seal the bag using a hand-operated sealing machine for 5-10 seconds. After sealing, manually shake the aluminum-plastic film to ensure the powder sample and deionized water are completely and evenly mixed without any obvious clumping.

[0065] 2. Add water to the solid density meter until it covers the mounting bracket, turn on the solid density meter, and set aside. Place the gas-producing aluminum-plastic bag sample on the solid density meter and press ENTER to record the mass of the aluminum-plastic bag. Place the gas-producing aluminum-plastic bag sample under the water tank testing bracket and fix it in place, then press ENTER again to record the buoyancy. Remove the gas-producing aluminum-plastic bag sample, press MODE, and calculate the gas production.

[0066] 3. After placing the sample aluminum-plastic bag that produces gas in a 45℃ oven for 24 hours, remove it and test the gas production again. Record the difference, which is the gas production of the material over 24 hours. The test data are shown in Table 2.

[0067] Table 1

[0068] Table 2 Material property test data

[0069] As can be seen from Table 1, compared with Comparative Examples 1, 2, and 3 and Comparative Example 1, the LiF and Li in Examples 1, 2, and 3 are significantly different. x P y O z Uniformly coating porous silicon-carbon anode material improved the first discharge efficiency of lithium-ion batteries from 93.4% to 94.1%, 94.2%, and 93.7%, and the capacity retention after 200 cycles from 82.4% to 90.6%, 90.8%, and 87.7%, respectively. This demonstrates the superior performance of LiF and Li. x P y O z Coating has a significant effect on improving the first discharge efficiency and cycle retention of batteries, and can effectively improve the cycle stability of porous silicon-carbon anode materials.

[0070] As can be seen from Table 2, compared with Comparative Example 1, the tap density of Examples 1, 2, and 3 decreased slightly, and the specific gravity decreased significantly, which is beneficial to reducing side reactions and improving material stability; dQ / dV, magnetic impurities, gas generation, etc. are all within the normal range and there is no significant difference; the resistance decreased significantly, indicating that the synthesis of highly conductive materials was successful, which is beneficial to the rapid charging and discharging of batteries.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention. The construction steps of the structure of the present invention are not in any particular order. All improvements and modifications, such as structural modifications, made by those skilled in the art based on the method of the present invention or based on the method are considered to be within the scope of protection of the present invention.

Claims

1. A lithium-ion battery anode material, characterized in that: comprising a coating layer of LiF and Li x P y O z and a porous silicon-carbon material prepared by CVD deposition of nano-silicon particles in a porous carbon; said coating layer of LiF and Li x P y O z uniformly distributed in the outer layer of said porous carbon anode material.

2. The lithium-ion battery anode material of claim 1, wherein: The lithium phosphate salt sintering temperature is 300-400 DEG C, and the holding time is 4-8h.

3. The lithium-ion battery anode material of claim 1, wherein: tap density > 0.8 g / m 3 specific surface < 2 m 2 / g; electrical resistance < 3 ohm-cm; dQ / dV = 1.6-1.9 mAh / V; magnetic substances < 5 ppm; gas evolution < 1 mL / g at 45°C for 24 h.

4. The method for producing a negative material for lithium ion batteries as claimed in any one of claims 1 to 3, characterized in that: The specific steps are as follows: S1, the lithium phosphate salt is dissolved in a solvent, and stirring is carried out to obtain a fluorine-containing lithium salt solution; S2, the porous silicon-carbon powder is added into a solution containing fluorine-containing lithium salt, and after preliminary drying by heating and stirring, the powder is completely dried in a drying oven, and then sintered in an inert gas to obtain LiF and Li x P y O z The porous silicon-carbon material uniformly coated.

5. The method for preparing the lithium-ion battery anode material according to claim 4, characterized in that: The lithium phosphate salt in the step S1 is one or more of LiPO2F2, LiODFP and LiFOP.

6. The method for preparing the lithium-ion battery anode material according to claim 4, characterized in that: The solvent in the step S1 is one or more of alcohol, ester, ketone, ether and liquid alkane.

7. The method for preparing the lithium-ion battery anode material according to claim 4, characterized in that: The porous silicon-carbon powder in the step S2 is prepared by chemical vapor deposition method, in which nano-silicon particles are deposited in porous carbon, the porous carbon is one of resin-based, biomass-based and pitch-based, and the particle size of the porous silicon-carbon powder is 2-15 mu m.

8. The method for preparing the lithium-ion battery anode material according to claim 4, characterized in that: The mass ratio of the porous silicon-carbon powder to the lithium phosphate salt in the step S2 is 100: (0.5-5), and the mass ratio of the porous silicon-carbon powder to the solvent is 1: (2-4).

9. The method for preparing the lithium-ion battery anode material according to claim 4, characterized in that: The heating and stirring temperature in the step S2 is 60-100℃, the stirring time is 6-12h; the drying box drying temperature is 80-120℃, the drying time is 4-10h; the sintering process heating rate is 2-5℃ / min, the temperature is 300-400℃, the holding time is 4-8h; the inert gas is one or more of nitrogen, argon, helium, and the gas flow rate is 30-70cm 3 / min.

10. The application of the lithium ion battery negative electrode material in the manufacture of lithium ion batteries.

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