A lithium-ion battery anode material, its preparation method and application

Abstract

This invention provides a lithium-ion battery anode material, its preparation method, and its application. The lithium-ion battery anode material is a porous silicon-carbon material coated with lithium phosphate. The preparation method is simple and efficient, using a solvent wet coating process to uniformly distribute lithium phosphate on the surface of the porous silicon-carbon material, followed by sintering and heating to decompose the lithium phosphate into LiF and Li. 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 P y O z Coating layer, thus obtaining LiF and Li x P y O z Uniformly coated porous silicon-carbon material, combining LiF and Li x P y O z The advantages of both are combined, resulting in high strength, high stability, and high ionic conductivity. This effectively suppresses the volume expansion of silicon-carbon materials during charging and discharging, blocks electron penetration, and reduces capacity loss during the reaction process. When used in the manufacture of lithium-ion batteries, it significantly improves the cycle stability of the batteries.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in 3C electronics, new energy vehicles and energy storage fields due to their excellent comprehensive performance. However, with the increasing demand for battery capacity in various fields, the traditional graphite negative electrode (theoretical specific capacity is only 372 mAh / g) cannot meet the requirements. Silicon-carbon negative electrode material has become a potential next-generation negative electrode material due to its extremely high theoretical specific capacity (4200 mAh / g), low cost and environmental friendliness. However, the volume expansion of silicon-carbon material during charging and discharging will cause structural damage and electrode fracture, leading to continuous cracking and growth of SEI film, continuous consumption of lithium, and reduction of battery capacity and cycle stability. At the same time, silicon-carbon material is sensitive to temperature, and at high temperature, it is easy to generate insulating SiC to reduce the initial capacity, and at low temperature, it is easy to cause the attenuation of discharge capacity and cycle performance due to the slow migration rate of lithium ions and the increase of SEI film impedance, and safety hazards such as lithium precipitation.

[0003] The patent document CN20211114995.9 reports a lithium battery negative electrode material preparation method by reacting lithium hexafluorophosphate and lithium carbonate to generate a lithium difluorophosphate coating layer on the surface of the material in situ, but the high hydrolysis sensitivity of lithium hexafluorophosphate leads to the generation of a large amount of HF and PF5 and other by-products, which will significantly reduce the quality of the coating layer, increase the interface impedance, and the coating layer generated by direct reaction is only physically adsorbed and combined with the substrate, and the strength is weak, which is easy to locally peel off during the reaction process, and loses the original modification effect. CN202410038500.8 proposes a method of dissolving a solid-state electrolyte in a solvent and mixing and stirring with porous silicon-carbon, drying and then laser sintering to obtain a porous silicon-carbon coated with a solid-state electrolyte. The oxide solid-state electrolyte is easy to have side reactions in the solvent, and LLZO (lithium lanthanum zirconium oxide) is easy to hydrolyze in water or alcohol solvent to generate Li2CO3 and La(OH)3 and other impurities, reducing the ionic conductivity, and LATP (lithium aluminum titanium phosphate) contains variable valence element Ti 4+ , which is reduced to Ti 3+ during heating and stirring, resulting in an increase in electronic conductivity and causing battery short circuit. The generated solid-state electrolyte coating layer is in the form of non-continuous island distribution, which exposes the negative electrode material surface locally and directly contacts the electrolyte, generates unstable SEI film, continuously consumes active lithium, and reduces the charging and discharging efficiency of the battery.

[0004] Therefore, it is urgent to find a method with simple process, controllable cost and avoiding side reactions of pre-prepared materials to construct a dense, uniform and high ionic conductive and mechanically stable composite coating layer on the surface of silicon-carbon negative electrode material in situ to improve the initial efficiency and long cycle stability. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a lithium ion battery negative electrode material.

[0006] Another technical problem to be solved by the present application is to provide a preparation method of the lithium ion battery negative electrode material.

[0007] Another technical problem to be solved by the present application is to provide an application of the lithium ion battery negative electrode material.

[0008] To solve the above technical problems, the technical solution of the present application is as follows:

[0009] A lithium ion battery negative electrode material, comprising a coating layer composed of LiF (lithium fluoride) and Li x P y O z and a porous silicon-carbon material prepared by CVD deposition of nano-silicon particles in porous carbon; the coating layer is LiF and Li x P y O z uniformly distributed on the outer surface layer of the porous carbon negative electrode material, which is formed in situ after the decomposition of lithium phosphate salt during sintering.

[0010] Preferably, the lithium ion battery negative electrode material, the LiF and Li x P y O z are obtained by sintering lithium phosphate salt.

[0011] Preferably, the lithium ion battery negative electrode material, the sintering temperature of lithium phosphate salt is 300-400℃, and the holding time is 4-8h. The ratio between the LiF and Li x P y O z changes according to the temperature and holding time during sintering of lithium phosphate salt. The higher the temperature and the longer the time, the more Li x P y O z is obtained. For example, the mass ratio of LiF and Li x P y O z obtained after sintering at 400℃ for 8h is about 1:1.

[0012] Preferably, the lithium ion battery negative electrode material has the following performance parameters:

[0013] Physical properties Standard Tap density (g / m 3 )]]> ＞0.8 Specific surface (m 2 / g) ≤2 Resistance (Ω•cm) ≤3 dQ / dV (mAh / V) 1.6-1.9 Magnetic substance (Fe+Cr+Ni+Zn) (ppm) ≤5 Gas production at 45℃ for 24h (mL / g) ≤1

[0014] The preparation method of the lithium ion battery negative electrode material is specifically as follows:

[0015] S1, dissolving a lithium phosphate salt in a solvent to obtain a fluorine-containing lithium salt solution by stirring;

[0016] S2, adding porous silicon-carbon powder into the fluorine-containing lithium salt solution, and after preliminary drying by heating and stirring, completely drying in a drying box, and then sintering the powder in an inert gas to obtain LiF and Li x P y O z The porous silicon-carbon material uniformly coated.

[0017] Preferably, in the preparation method of the lithium ion battery negative electrode material, the lithium phosphate salt in step S1 is one or more of LiPO2F2 (lithium difluorophosphate), LiODFP (lithium difluorobisoxalate phosphate), and LiFOP (lithium tetrafluorooxalate phosphate). Further preferably, it is LiPO2F2 (lithium difluorophosphate).

[0018] Preferably, in the preparation method of the lithium ion battery negative electrode material, the solvent in step S1 is one or more of an alcohol, an ester, a ketone, an ether, and a liquid alkane.

[0019] Preferably, in the preparation method of the lithium ion battery negative electrode material, the mass ratio of the lithium phosphate salt to the solvent in step S1 is about 1: (40-800).

[0020] Preferably, in the preparation method of the lithium ion battery negative electrode material, the porous silicon-carbon powder in step S2 is prepared by chemical vapor deposition (CVD) 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 μm. Further preferably, the particle size of the porous silicon-carbon powder is 6-8 μm.

[0021] Preferably, in the preparation method of the lithium ion battery negative electrode material, the specific steps of preparing the porous silicon-carbon powder by chemical vapor deposition method are as follows:

[0022] (1) Preparation of porous carbon: placing raw materials in a continuous atmosphere rotary furnace, introducing inert gas as protective gas, heating and holding to carbonize organic material raw materials to form a preliminary porous structure, after carbonization, cooling for pore expansion reaction and again heating, activating and expanding pores, after cooling, taking out, washing with deionized water until neutral, and drying for standby;

[0023] (2) CVD deposition: the porous carbon matrix is loaded into the reaction device, uniformly spread, inert gas is introduced to remove air, heated and stabilized, silane and carbon source gas are introduced, and the deposition process begins; after deposition, the reaction gas is turned off, and inert gas continues to be introduced to purge the pipeline; under the protection of the atmosphere, it is naturally cooled to room temperature, and the deposition sample is taken out; the airflow pulverizer is used for micronization treatment of the material.

[0024] Preferably, in the preparation method of the lithium ion battery negative electrode material, the mass ratio of the porous silicon-carbon powder to the lithium phosphate salt in step S2 is 100: (0.5-5).

[0025] Preferably, in the preparation method of the lithium ion battery negative electrode material, the mass ratio of the porous silicon-carbon powder to the solvent in step S2 is 1: (2-4).

[0026] Preferably, in the preparation method of the lithium ion battery negative electrode material, the heating and stirring temperature in step S2 is 60-100°C, and the stirring time is 6-12h.

[0027] Preferably, in the preparation method of the lithium ion battery negative electrode material, the drying temperature of the drying box in step S2 is 80-120°C, and the drying time is 4-10h.

[0028] Preferably, in the preparation method of the lithium ion battery negative electrode material, the heating rate in the sintering process in step S2 is 2-5°C / min, the temperature is 300-400°C, and the holding time is 4-8h.

[0029] Preferably, in the preparation method of the lithium ion battery negative electrode material, the inert gas in step S2 is one or more of nitrogen, argon, and helium, and the gas flow rate is 30-70cm 3 / min. Further preferably, the gas flow rate is 40-60cm 3 / min.

[0030] The application of the lithium ion battery negative electrode material in the manufacture of lithium ion batteries.

[0031] Beneficial effects:

[0032] The lithium ion battery negative electrode material is a porous silicon-carbon material coated with lithium phosphate salt, which solves the problems of interface stability of silicon-carbon materials and capacity decay of batteries under long cycle; the preparation method is simple and efficient, the cost is controllable, and the side reactions of the pre-prepared material in the prior art can be avoided; the lithium phosphate salt is uniformly distributed on the surface of the porous silicon-carbon material through solvent wet coating, and the lithium phosphate salt is decomposed into LiF and Li x P y O z , and Li xP y O z coated layer, thereby obtaining LiF and Li x P y O z The uniformly coated porous silicon-carbon material has a dense and strong-bonding coated layer composed of LiF and Li x P y O z The coated silicon-carbon material combines the advantages of LiF and Li x P y O z The coated silicon-carbon material combines the advantages of LiF and Li x P y O z has high ionic conductivity, and the two are synergistic, having high strength, high mechanical stability and high ionic conductivity characteristics, which can effectively inhibit the volume expansion of the silicon-carbon material during the charging and discharging process, block the penetration of electrons, reduce side reactions, inhibit the growth of SEI to stabilize the interface of the silicon-carbon negative electrode material, effectively reduce the lithium loss in the initial reaction, improve the first coulombic efficiency and lithium ion diffusion rate, enhance the material stability under high and low temperature conditions, reduce the capacity loss of the silicon-carbon material during the reaction process, synergistically improve the first efficiency, and significantly improve the long cycle stability of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the morphology scanning and fluorine and phosphorus element distribution diagram of the unmodified material of the present application comparative example 1.

[0034] Figure 2 is the morphology scanning and fluorine and phosphorus element distribution diagram of the coated material in the present application example 1.

[0035] Figure 3 is the morphology scanning and fluorine and phosphorus element distribution diagram of the coated material in the present application example 2.

[0036] Figure 4 is the morphology scanning and fluorine and phosphorus element distribution diagram of the coated material in the present application example 3. DETAILED DESCRIPTION

[0037] The lithium ion battery negative electrode material and the preparation method and application thereof described in the present application will be described in detail below in combination with examples and drawings.

[0038] The preparation method of the porous silicon-carbon powder in the following examples is as follows:

[0039] 1. Raw materials: select one of resin-based, biomass-based and pitch-based as raw material, ensure low impurity content and uniform structure. If the raw material is in block or granular form, it needs to be crushed and sieved to a suitable particle size (usually 0.5-3 mm) first.

[0040] 2. Inert gas (Ar or N2) is introduced as a protective atmosphere, with a flow rate controlled at 5-15 L / min.

[0041] 3. The temperature is raised to 800-1200°C at a rate of 5-10°C / min, and maintained for 1-3 hours to carbonize the organic matter and form a preliminary porous structure.

[0042] 4. After carbonization, the temperature is lowered to 500-700°C, and activating gas (such as CO2) is introduced or the powder is immersed in KOH solution before being heated again. Activation is carried out at 700-900°C for 1-2 hours to further expand the pores and increase the specific surface area to >1000 m 2 / g, with a porosity of >60% and a pore size mainly in the micropore to mesopore range.

[0043] 5. The deposition reaction equipment is a rotary kiln or a fluidized bed. The total gas flow rate is set to be in the range of 100-500 sccm, adjusted according to the volume of the reaction chamber.

[0044] 7. After removing air by introducing inert gas, the temperature is first raised to 700-1000°C and stabilized for 30 minutes.

[0045] 8. Deposition process: the target silicon content is 40%-50%, the molar ratio of silane (SiH4) to carbon source gas (C2H2 or CH4) is 1:1-2:1, and 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.

[0046] 9. The material is micronized using an air jet mill. The final particle size D50 is controlled to be in the range of 2-15 μm by using a classification screen.

[0047] Comparative Example 1

[0048] Resin-based 8 μm porous silicon-carbon powder, Super P conductive carbon, carboxymethyl cellulose sodium (CMC), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 7:1:1:1 in deionized water, then stirred to obtain a uniform slurry (as shown in Figure 1 , the particle surface is smooth and there is no distribution of F and P elements), the electrode sheet is prepared and dried, and the battery is assembled and tested for performance.

[0049] Example 1

[0050] 1 g of LiPO2F2 (lithium difluorophosphate) is dissolved in 300 g of dimethyl ether solvent to obtain a fluorine-containing lithium salt solution; 100 g of resin-based 8 μm porous silicon-carbon powder is added to the fluorine-containing lithium salt solution, heated and stirred at 60°C for 12 h for preliminary drying, then dried at 80°C in a drying oven for 10 h, and then sintered in an argon atmosphere, with a gas flow rate of 50 cm3 / min, and then increased to 300°C at a heating rate of 5°C / min, and then naturally cooled after being kept at 300°C for 6h to obtain the fluorinated lithium and Li x P y O z The uniformly coated porous silicon-carbon material (such as Figure 2 As shown in FIG. 1, small particles appear on the surface of the particles, and element scanning shows that F and P elements are distributed, indicating that the F and P-containing substance is successfully coated on the surface of the porous silicon-carbon, and the distribution is uniform.

[0051] The fluorinated lithium and Li x P y O z The uniformly coated porous silicon-carbon material, Super P conductive carbon, carboxymethyl cellulose sodium (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 7:1:1:1 in deionized water, and then stirred to obtain a uniform slurry, to prepare a pole piece, dry the pole piece, assemble a button cell, and test the battery performance.

[0052] Example 2

[0053] 3g of LiODFP (lithium difluorobisoxalate phosphate) was dissolved in 350g of an ethanol solvent to obtain a fluorine-containing lithium salt solution; 100g of resin-based 8μm porous silicon-carbon powder was added to the fluorine-containing lithium salt solution, and then heated and stirred at 80°C for 8h for preliminary drying, and then dried in a drying oven at 100°C for 8h, and then the powder was sintered in an argon atmosphere, with a gas flow rate of 60 cm 3 / min, and then increased to 350°C at a heating rate of 2°C / min, and then naturally cooled after being kept at 350°C for 4h to obtain the fluorinated lithium and Li x P y O z The uniformly coated porous silicon-carbon material (such as Figure 3 As shown in FIG. 1, small particles appear on the surface of the particles, and element scanning shows that F and P elements are distributed, indicating that the F and P-containing substance is successfully coated on the surface of the porous silicon-carbon, and the distribution is uniform.

[0054] The negative pole piece was prepared according to the same method as in Example 1, the button cell was assembled, and the battery performance was tested.

[0055] Example 3

[0056] 5g of LiFOP (lithium tetrafluorophosphate oxalate) was dissolved in 400g of a dimethyl carbonate solvent to obtain a fluorine-containing lithium salt solution; 100g of biomass-based 6μm porous silicon-carbon powder was added to the fluorine-containing lithium salt solution, and then heated and stirred at 100°C for 6h for preliminary drying, and then dried in a drying oven at 120°C for 6h, and then the powder was sintered in a nitrogen atmosphere, with a gas flow rate of 40 cm 3 / min, and then increased to 400℃ at a rate of 5℃ / min, and then naturally cooled after being kept at 400℃ for 4h to obtain the LiF and Li x P y O z The uniformly coated porous silicon-carbon material (such as Figure 4 As shown, small particles appear on the surface of the particles, and element scanning shows that F and P elements are distributed, indicating that the F and P containing substance is successfully coated on the surface of the porous silicon-carbon, and is uniformly distributed.

[0057] The negative electrode sheet was prepared according to the same method as in Example 1, and the battery performance was tested after the battery was assembled.

[0058] The test method of the cycle performance of the lithium ion battery: after being activated by being cycled at 0.1C for 5 times at 25℃, the lithium ion battery was cycled at 1.0C rate for 200 times. The initial efficiency of the battery was: the first charge capacity / the first discharge capacity x 100%, and the cycle capacity retention rate of the battery after being cycled for 200 times was: the 200th charge capacity / the first charge capacity x 100%. The test data are shown in Table 1.

[0059] The test method of the tap density (g / m 3 ) of the negative electrode material of the lithium ion battery:

[0060] 1. The silicon-carbon negative electrode material is easy to absorb moisture and agglomerate, and therefore needs to be dried in a vacuum drying box at 100℃ for 4h before being tested. The test environment temperature is controlled at 25±2℃, and the relative humidity is ≤60%,

[0061] 2. 5g of the pretreated silicon-carbon powder was weighed by using an analytical balance, and the accurate mass value was recorded. A clean and dry 10mL measuring cylinder was fixed on the clamp of the tap density instrument to ensure that the measuring cylinder was vertical and had no inclination. The weighed silicon-carbon powder was slowly poured into the measuring cylinder by using a medicine spoon to avoid splashing and stratification of the powder; after the sample was loaded, the surface of the powder at the top of the measuring cylinder was scraped flat by using a spatula, and the loose volume of the powder at this time was recorded.

[0062] 3. The vibration program was started, and the parameters of the tap density instrument were set: amplitude 3mm, vibration frequency 100 times / min, and vibration times 1000 times. After the vibration was terminated and the volume was read, the measuring cylinder was left to stand for 1min until the powder was completely stable. The volume Vt of the powder in the measuring cylinder after being vibrated was read, and the reading was accurate to 0.1mL when the line of sight was horizontal to the scale line of the measuring cylinder; if the surface of the powder was uneven, the average value of the highest and lowest points was taken.

[0063] The tap density value of each test was calculated according to the formula ρ t = m / V t , wherein ρ t is the tap density (g / cm 3 ), m is the mass of the silicon-carbon powder (g), and Vt Bulk volume of powder after tapping (cm 3 ). Test data are shown in Table 2.

[0064] Test method of specific surface area (m 2 / g) of lithium ion battery negative electrode material:

[0065] 1. Pretreatment of silicon-carbon negative electrode: 0.5 g of silicon-carbon powder was weighed and the mass m was accurately recorded. The sample tube was loaded into the degassing station of the analyzer, and the degassing parameters were set as follows: temperature 150°C, vacuum degree ≤10 Pa, and degassing time 3 h. After degassing, the vacuum system was turned off, and the sample tube was quickly transferred to a dry dish after cooling to room temperature. The laboratory temperature was controlled at 25°C±2°C, and the relative humidity was ≤50%.

[0066] 2. The pretreated sample tube was connected to the test station of the analyzer, and the interface was sealed to ensure no gas leakage. At the same time, an empty sample tube was installed as a blank control for background adsorption deduction.

[0067] The analyzer was started, and the system was checked for leakage to ensure that the vacuum degree met the requirements. The adsorption isotherm measurement range was set as follows: P / P0=0.05:0.35, and the adsorption equilibrium time was 5 min to 10 min at each partial pressure point to ensure that the adsorption reached a stable state.

[0068] 3. The sample tube was immersed in a liquid nitrogen bath (temperature about 77 K), and the test program was started. The analyzer automatically introduced nitrogen-helium mixed gas. The system adjusted different P / P0 partial pressures in turn, and the nitrogen adsorption amount at each partial pressure was recorded until the adsorption test at all set partial pressure points was completed. After adsorption, the sample tube was taken out and warmed up to room temperature for desorption operation to recover the adsorbed nitrogen. The analyzer automatically recorded the difference between the adsorption data of the blank tube and the sample tube to obtain the actual nitrogen adsorption amount of the silicon-carbon sample.

[0069] 4. Data processing and result calculation

[0070] BET equation fitting: The analyzer software performed linear fitting according to the collected P / P0 and P / [V(P0-P)] data to obtain the slope k=(C-1) / (V m C) and the intercept b=1 / (V m C) of the fitting straight line.

[0071] Single-layer saturated adsorption amount calculation: V m m=1 / (k+b). Specific surface area calculation: S BET =(V BET ·N m ·A A ·A m) / (m·V0). In the formula:

[0072] N A : Avogadro's number (6.022 x 10 23 mol -1 ), A m : cross-sectional area of a nitrogen molecule (usually taken as 0.162 nm 2 ), V0: molar volume of a gas at standard state (22414 mL / mol), m: sample mass (g). Test data are shown in Table 2.

[0073] Method for testing resistance (Ω•cm) of lithium ion battery negative electrode material (four-probe method):

[0074] 1. Sample preparation: 1 g of silicon-carbon negative electrode powder was accurately weighed using a balance, and the specific value was recorded. The powder was uniformly filled into a cylindrical mold with a standard inner diameter of 10 mm. Gently shake or scrape to ensure that the powder surface is flat and there are no obvious voids or accumulations.

[0075] 2. Pressurized molding and testing: a powder resistivity tester was used. The mold containing the powder was placed on the testing platform, and the program was set for pressure testing. The pressure was gradually increased from 10 MPa to 200 MPa, with an increase of 20 MPa at each step, and the pressure was maintained for 10 seconds at each pressure point to stabilize the readings. The instrument automatically applies a test current and measures the voltage at each pressure holding stage, and calculates and records the resistivity at that pressure in real time. The instrument usually directly displays or outputs the resistivity (Ω•cm). Test data are shown in Table 2.

[0076] Method for testing dQ / dV (mAh / V) of lithium ion battery negative electrode material:

[0077] 1. The silicon-carbon material was assembled into a button cell with lithium sheet, and the constant current charge and discharge was carried out at 25°C in the voltage range of 0-1.5V using 0.1C current, and the voltage (V) and cumulative capacity (Q, mAh / g) data were recorded.

[0078] 2. The data processing software numerically differentiates 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.

[0079] 3. Plotting voltage (V) as the horizontal coordinate and dQ / dV as the vertical coordinate, the differential capacity curve can be obtained. Taking the dQ / dV data at 0.45V, the dQ / dV value to be obtained is obtained. Test data are shown in Table 2.

[0080] Method for testing magnetic substances (Fe+Cr+Ni+Zn) (ppm) of lithium ion battery negative electrode material:

[0081] 1. Sample pretreatment: Silicon-carbon negative electrode contains silicon phase (SiO x ) and carbon phase, silicon phase needs to be digested with hydrofluoric acid, and carbon phase needs to be oxidized with nitric acid + perchloric acid. 0.5 g of silicon-carbon negative electrode powder (accurate to 0.0001 g) is weighed with an electronic balance and placed in a polytetrafluoroethylene digestion tank. The mass of the sample m is recorded. 5 mL of concentrated nitric acid + 2 mL of concentrated hydrofluoric acid is added, shaken gently, and placed in a fume hood for pre-reaction for 30 min. The digestion tank is sealed and placed in a microwave digestion instrument. After digestion is completed, it is cooled to room temperature, the digestion tank is opened, 1 mL of perchloric acid is added, and it is heated to white smoke on a graphite digestion instrument until the solution is clear and transparent. The digestion solution is transferred to a 50 mL polytetrafluoroethylene volumetric flask, the digestion tank is washed several times with ultrapure water, the washing liquid is added to the volumetric flask, and the volume is adjusted to the mark with ultrapure water, shaken well, and the sample solution to be tested is obtained. Preparation of blank solution: without adding silicon-carbon sample, the same acid digestion and constant volume steps are followed to prepare the reagent blank solution.

[0082] 2. Test: Standard solution preparation: dilute single-element standard solution or mixed standard stock solution with ultrapure water to prepare 5 concentration gradients of standard working solution (such as 0, 0.1, 0.5, 1.0, 5.0 μg / L), and add the same amount of internal standard solution (usually 10 μg / L) to the standard working solution and the sample solution to be tested. Start ICP-MS and set the optimal working parameters of the instrument (radio frequency power, nebulizer gas flow, sampling depth, etc.). The blank solution and standard working solution are sequentially introduced into the sample system. The element concentration is taken as the abscissa and the ion count intensity is taken as the ordinate. The standard curve is drawn. The linear correlation coefficient R2 is required to be ≥0.999. The reagent blank solution and the sample solution to be tested are sequentially introduced into the ICP-MS sample system, and the ion count intensity of Fe, Cr, Ni, and Zn is automatically collected by the instrument. The concentration Ci of each element in the sample solution is calculated by the standard curve (unit: μg / L).

[0083] 3. Data calculation and result determination:

[0084] Single-element content calculation formula: wi (ppm) = m (Ci - C 0i ) × V × 10 -3 , where:

[0085] wi: the content of element i (Fe / Cr / Ni / Zn) in the sample, unit ppm; Ci: the concentration of element i in the sample solution, μg / L; C 0i : the concentration of element i in the reagent blank solution, μg / L; V: the constant volume of the sample, mL; m: the mass of the silicon-carbon sample, g; 10 -3 : unit conversion coefficient (1 μg / L × 1 mL = 10 -3 μg = 10 -6 mg).

[0086] Total magnetic substance content: total content = w Fe +w Cr +w Ni +w Zn . Test data are shown in Table 2.

[0087] Test method for gas production amount (mL / g) of lithium ion battery negative electrode material at 45°C for 24h:

[0088] 1. Accurately weigh 1g±0.1g of sample and 2g±0.5g of deionized water into an aluminum plastic bag, heat seal the aluminum plastic bag by hand pressing type sealing machine for 5-10 seconds, and seal for standby. After sealing, shake the aluminum plastic film manually to mix the powder sample and deionized water completely and uniformly, without obvious caking phenomenon.

[0089] 2. Add water to the solid density meter until the fixed frame is covered, turn on the solid density meter switch, and wait for use. Place the sample gas production aluminum plastic bag on the solid density meter, press the ENTER key to record the mass of the aluminum plastic bag. Place the sample gas production aluminum plastic bag into the water tank test fixture, press the ENTER key again to record the buoyancy. Take the sample gas production aluminum plastic bag, press the MODE key, and calculate the gas production amount.

[0090] 3. After placing the sample gas production aluminum plastic bag in a 45°C oven for 24h, take it out and test the gas production amount again, and record the difference as the 24h gas production amount of the material. Test data are shown in Table 2.

[0091] Table 1

[0092]

[0093] Table 2 Material property test data

[0094]

[0095] From Table 1, it can be seen that, for Comparative Examples 1, 2, 3 and Comparative Example 1, the first discharge efficiency of lithium ion battery is increased from 93.4% to 94.1%, 94.2%, and 93.7%, and the capacity retention rate after 200 cycles is increased from 82.4% to 90.6%, 90.8%, and 87.7%. It can be seen that LiF and Li x P y O z uniformly coated porous silicon-carbon negative electrode material can effectively improve the cycle stability of the porous silicon-carbon negative electrode material. x P y O z

[0096] ​As can be seen from Table 2, compared with Comparative Example 1, the tap density of Example 1, 2 and 3 has a slight decrease, and the specific surface area is obviously reduced, which is beneficial to reduce the side reaction and improve the material stability; dQ / dV, magnetic journal, gas production and the like are all in the normal range, and there is no obvious difference; the resistance is obviously reduced, which indicates that the synthesis of high-conductivity material is successful, and is beneficial to the fast charge and discharge of the battery.

[0097] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, the construction steps of the present application do not have a specific order, and the improvements and refinements made by those skilled in the art based on the method of the present application or the structure modification based on the method are all considered to be within the protection scope of the present application.

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 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 silicon-carbon 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 area < 2 m 2 / g; electrical resistance < 3 Ω-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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