Preparation method of high specific capacity and high rate performance battery negative electrode material

Abstract

The application discloses a preparation method of a high-specific-capacity high-rate performance battery negative electrode material, and relates to the technical field of battery materials. The battery negative electrode material is composed of a core layer, a composite buffer layer and a coating layer, the core layer is nano silicon powder, the mass percentage of the core layer is 45-65%, and the particle size of the core layer is 50-200 nm. The composite buffer layer of the battery negative electrode material is composed of titanium dioxide TiO2 and lithium titanate Li4Ti5O 12 nanoparticles. 2和 Li4Ti5O 12 nanoparticles. The volume expansion stress generated by the core layer nano silicon of the negative electrode in the charging and discharging process can be effectively dispersed, and a continuous ion transmission channel can be constructed, so that the effects of inhibiting electrode cracking and reducing ion transmission resistance are achieved. Meanwhile, the nano silicon of the core layer improves the high-specific-capacity foundation of the battery, and the electrode structure stability in the cycle process is improved while the high-specific-capacity characteristics of the battery are maintained.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a method for preparing a high-specific-capacity, high-rate-performance battery anode material. Background Technology

[0002] Lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage systems due to their advantages such as high energy density, long cycle life, and environmental friendliness. As a core component, the performance of the battery's negative electrode material directly determines the battery's specific capacity, rate characteristics, and cycle stability. The negative electrode material is the raw material that constitutes the negative electrode in the battery. Common negative electrode materials include carbon negative electrode materials, tin-based negative electrode materials, lithium-containing transition metal nitride negative electrode materials, alloy negative electrode materials, and nanoscale negative electrode materials.

[0003] Existing battery anode materials suffer from severe silicon volume expansion during charging and discharging, making it difficult to simultaneously disperse expansion stress and construct efficient ion channels. Furthermore, single carbon coating cannot simultaneously ensure wide-temperature conductivity and long-term stability of the SEI film. Therefore, while achieving high specific capacity, these silicon-based anodes often suffer from electrode cracking, obstructed lithium-ion transport at low temperatures, and repeated SEI film rupture during long-term cycling. This results in a significant reduction in battery cycle life and a marked decrease in low-temperature rate performance, making it difficult to meet the actual needs of power batteries for high specific capacity, long cycle life, and wide-temperature applications. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing a high-specific-capacity, high-rate-performance battery anode material, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high specific capacity and high rate performance battery anode material, wherein the battery anode material is composed of a core layer, a composite buffer layer and a coating layer;

[0006] The core layer is made of nano-silicon powder, and the mass percentage of the core layer is 45% to 65%, with a particle size of 50-200 nm.

[0007] The composite buffer layer covers the surface of the core layer, and the composite buffer layer accounts for 15% to 25% of the mass, and is composed of titanium dioxide (TiO2) and lithium titanate (Li4Ti5O2). 12 The composition consists of nanoparticles, namely TiO2 and Li4Ti5O. 12 The mass ratio is 3-5:1, the particle size of the TiO2 is 10-50 nm, and the Li4Ti5O 12 The particle size is 5-20 nm;

[0008] The coating layer is applied to the surface of the composite buffer layer. The composite buffer layer accounts for 20% to 30% of the total mass. The coating layer is composed of nitrogen, boron, and two carbon sources. The nitrogen is urea, the boron is boric acid, and the two carbon sources are glucose or sucrose. The coating layer has a thickness of 8-25 nm and includes mesopores with a pore size of 2-10 nm.

[0009] Preferably, the nitrogen content in the coating layer decreases from 5-8 at% to 2-3 at% from the inside out, the boron content in the coating layer increases from 0.5-1 at% to 2-3 at% and the mesopores in the coating layer are distributed in a through-type manner, and the walls of the mesopores form chemical bonds with the surface of the composite buffer layer.

[0010] Preferably, the Li4Ti5O in the composite buffer layer 12 The Li4Ti5O is uniformly dispersed in the TiO2 matrix, and the Li4Ti5O 12 The surface forms a continuous interface with the TiO2.

[0011] Preferably, the surface of the nano-silicon powder in the core layer has hydroxyl groups, which are formed by modifying the surface of the nano-silicon powder. The surface hydroxyl groups of the nano-silicon powder form coordination bonds with the oxygen atoms of TiO2 in the composite buffer layer.

[0012] A method for preparing a high-specific-capacity, high-rate-performance battery anode material, applicable to the aforementioned high-specific-capacity, high-rate-performance battery anode material, the method comprising the following steps:

[0013] The TiO2 and Li4Ti5O were weighed in a mass ratio of 3-5:1. 12 The TiO2 was dissolved in a mixed solvent of ethanol and deionized water and stirred to form a titanium source mixture. Li4Ti5O was then added to the titanium source mixture. 12 The Li4Ti5O 12 The titanium source mixture is ultrasonically dispersed in an ultrasonic disperser at a power of 300-500W for 30-40 minutes, while nitric acid solution is added dropwise to adjust the pH of the mixture to 2-3. The mixture is then stirred at a temperature of 30-50℃ for 1-2 hours to form a mixed dispersion.

[0014] The nano-silicon powder is mixed with the mixed dispersion, and the nano-silicon powder and the mixed dispersion are stirred at a temperature of 40-60°C for 3-5 hours. After stirring and mixing, the nano-silicon powder and the mixed dispersion are dried at a temperature of 80-100°C for 8-12 hours to obtain the electrode precursor of the core layer coated with the composite buffer layer.

[0015] Weigh out the carbon-nitrogen source solution formed by dissolving the glucose and urea in deionized water, add the electrode precursor to the first carbon-nitrogen source solution, stir the carbon-nitrogen source solution and the electrode precursor at a temperature of 60-70℃ for 2-3 hours to obtain a precursor mixture, and dry the precursor mixture at a temperature of 80-90℃ for 4-6 hours to obtain an inner-layer coated intermediate;

[0016] Weigh the sucrose and the boric acid and dissolve them in deionized water to form a carbon boron source solution. Add the inner layer coating intermediate to the carbon boron source solution. Stir the carbon boron source solution and the inner layer coating intermediate at a temperature of 70-80°C for 2-3 hours. After stirring, dry at a temperature of 100-120°C for 6-8 hours to obtain the electrode coating precursor.

[0017] The electrode-coated precursor was placed in a tube furnace and heated to 400-500°C at a heating rate of 2-5°C / min under an argon atmosphere with a flow rate of 50-100 mL / min. After the heating reaction was completed, the electrode-coated precursor was kept at the temperature for 1-2 hours to complete the pre-calcination.

[0018] The temperature is then increased to 850-1050℃ at a rate of 5-8℃ / min, and held at that temperature for 3-5 hours to complete the high-temperature carbonization. After the carbonization is completed, the material is naturally cooled to room temperature to obtain the battery anode material.

[0019] Preferably, when drying the mixture of the nano-silicon powder and the mixed dispersion, the precursor mixture, and the mixture of the inner coating intermediate and the carbon boron source solution, high-temperature drying is carried out under normal pressure, and inert gas is continuously introduced during the drying process.

[0020] Preferably, the argon gas used to protect the roasting process in the tubular furnace is dehydrated and impurity-removed, the total content of oxygen, moisture and impurity gases in the argon gas is lower than a preset threshold, and the argon gas flows unidirectionally in the tubular furnace.

[0021] Preferably, after the electrode coating precursor is carbonized at high temperature, it is allowed to cool naturally to room temperature while maintaining the argon atmosphere, and then the argon gas supply is stopped and the precursor is removed from the tube furnace to obtain the battery negative electrode material.

[0022] Preferably, before mixing the nano-silicon powder with the mixed dispersion, the nano-silicon powder is first washed with deionized water until the pH is neutral, and then the washed nano-silicon powder is dried, and the dried nano-silicon powder is mixed with the mixed dispersion.

[0023] Preferably, in preparing the carbon-nitrogen source solution and the carbon-boron source solution, the glucose and sucrose are added to deionized water and stirred until completely dissolved, then the urea and boric acid are added respectively and stirred continuously until the glucose and urea are completely dissolved with the sucrose and boric acid, respectively, to obtain the corresponding carbon-nitrogen source solution and the carbon-boron source solution.

[0024] This invention provides a method for preparing a high-specific-capacity, high-rate-performance battery anode material. It has the following beneficial effects:

[0025] (1) The composite buffer layer of the battery negative electrode material is composed of titanium dioxide (TiO2) and lithium titanate (Li4Ti5O2). 12 Composed of nanoparticles, TiO 2和 Li4Ti5O 12 The combination of nanoparticles can effectively disperse the volume expansion stress generated by the core layer of nano-silicon in the negative electrode during charging and discharging, and can also build a continuous ion transport channel to suppress electrode cracking and reduce ion transport resistance. At the same time, the nano-silicon in the core layer enhances the battery's high specific capacity, so that while maintaining high specific capacity, the stability of the electrode structure during cycling is improved, avoiding the problem of shortened cycle life caused by electrode cracking, and meeting the requirements of power batteries for long cycle performance.

[0026] (2) The coating layer of the battery negative electrode material is composed of nitrogen, boron and two carbon sources. This coating layer can not only provide a stable electron conduction path and take into account the conductivity under different temperature environments, but also regulate the formation and growth of the SEI film through its own composition characteristics, thereby avoiding the obstruction of lithium ion transport at low temperature and reducing the repeated rupture of the SEI film. In addition, the mesoporous structure of the coating layer further assists ion transport, enabling the battery to discharge stably in a wide temperature range environment, while reducing lithium ion consumption caused by SEI film rupture, improving the coulombic efficiency of the battery in long-term cycling, and meeting the requirements of power batteries for wide temperature range applications.

[0027] (3) The battery anode material adopts a three-layer coating structure of core layer, composite buffer layer and coating layer. The core layer of nano-silicon ensures high specific capacity, the composite buffer layer solves the problems of volume expansion and ion transport, and the coating layer solves the problems of conductivity and SEI film stability. The three layers work together to avoid the overall performance limitation of existing silicon-based anodes, and realize the battery's performance improvement of high specific capacity, long cycle and wide temperature range at the same time, thus meeting the actual application requirements of power batteries for multi-dimensional performance and improving the performance of power batteries. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Example

[0029] Materials used to prepare the battery anode material: 5.5g of nano-silicon powder, 1.6g of TiO2, and Li4Ti5O. 12 The composition of the nanoparticles was 0.4g, urea 0.21g, boric acid 0.062g, glucose 0.78g, sucrose 1.42g, ethanol 7mL, deionized water 3mL and nitric acid 1mL.

[0030] The preparation method of battery negative electrode material includes the following steps:

[0031] TiO2 and Li4Ti5O 12 TiO2 was dissolved in a mixed solvent of ethanol and deionized water and stirred to form a titanium source mixture. Li4Ti5O was then added to the titanium source mixture. 12 Li4Ti5O 12 The mixture of titanium source and ultrasonic dispersion was ultrasonically dispersed in an ultrasonic disperser at a power of 400W for 35 minutes, while nitric acid solution was added dropwise to adjust the pH of the mixture to 2.5. The mixture was then stirred at 40℃ for 1.5 hours to form a mixed dispersion.

[0032] Nano-silicon powder and mixed dispersion were mixed and stirred at 50°C for 4 hours. After mixing, nano-silicon powder and mixed dispersion were dried at 90°C for 10 hours to obtain an electrode precursor with a core layer coated with a composite buffer layer.

[0033] Weigh out the carbon-nitrogen source solution formed by dissolving glucose and urea in deionized water, add the electrode precursor to the first carbon-nitrogen source solution, stir the carbon-nitrogen source solution and electrode precursor at 65°C for 2.5 h to obtain the precursor mixture, and dry the precursor mixture at 85°C for 5 h to obtain the inner layer coated intermediate.

[0034] Sucrose and boric acid were dissolved in deionized water to form a carbon boron source solution. The inner layer coating intermediate was added to the carbon boron source solution. The carbon boron source solution and the inner layer coating intermediate were stirred at 75°C for 2.5 h. After stirring, the mixture was dried at 110°C for 7 h to obtain the electrode coating precursor.

[0035] The electrode-coating precursor was placed in a tube furnace and heated to 450°C at a heating rate of 3°C / min under an argon atmosphere with a flow rate of 80 mL / min. After the heating reaction was completed, the electrode-coating precursor was kept at the temperature for 1.5 h to complete the pre-calcination.

[0036] The temperature was then increased to 950℃ at a rate of 6℃ / min and held for 4 hours to complete the high-temperature carbonization. After the carbonization was completed, the material was naturally cooled to room temperature to obtain the battery anode material. Example

[0037] Materials used to prepare the battery anode material: 4.5g nano-silicon powder, 1.875g TiO2, Li4Ti5O 12 The mixture consisted of 0.625g of nanoparticles, 0.22g of urea, 0.023g of boric acid, 2.21g of glucose, 0.46g of sucrose, 8mL of ethanol, 5mL of deionized water, and 1.2mL of nitric acid.

[0038] The preparation method of battery negative electrode material includes the following steps:

[0039] TiO2 and Li4Ti5O 12 TiO2 was dissolved in a mixed solvent of ethanol and deionized water and stirred to form a titanium source mixture. Li4Ti5O was then added to the titanium source mixture. 12 Li4Ti5O 12 The mixture of titanium source and ultrasonic dispersion was ultrasonically dispersed in an ultrasonic disperser at a power of 300W for 40 minutes, while nitric acid solution was added dropwise to adjust the pH of the mixture to 2. The mixture was then stirred at 30°C for 2 hours to form a mixed dispersion.

[0040] Nano-silicon powder and mixed dispersion were mixed and stirred at 40°C for 5 hours. After mixing, nano-silicon powder and mixed dispersion were dried at 80°C for 12 hours to obtain an electrode precursor with a core layer coated with a composite buffer layer.

[0041] Weigh out the carbon-nitrogen source solution formed by dissolving glucose and urea in deionized water, add the electrode precursor to the first carbon-nitrogen source solution, stir the carbon-nitrogen source solution and electrode precursor at 60°C for 3 hours to obtain a precursor mixture, and dry the precursor mixture at 80°C for 6 hours to obtain an inner layer coated intermediate.

[0042] Weigh sucrose and boric acid and dissolve them in deionized water to form a carbon boron source solution. Add the inner layer coating intermediate to the carbon boron source solution. Stir the carbon boron source solution and the inner layer coating intermediate at 70°C for 3 hours. After stirring, dry at 100°C for 8 hours to obtain the electrode coating precursor.

[0043] The electrode-coated precursor was placed in a tube furnace and heated to 400°C at a heating rate of 2°C / min under an argon atmosphere with a flow rate of 50 mL / min. After the heating reaction was completed, the electrode-coated precursor was kept at the temperature for 2 hours to complete the pre-calcination.

[0044] The temperature was then increased to 850℃ at a rate of 5℃ / min and held for 5 hours to complete the high-temperature carbonization. After the carbonization was completed, the material was naturally cooled to room temperature to obtain the battery anode material. Example

[0045] Materials used to prepare the battery anode material: 6.5g of nano-silicon powder, 1.25g of TiO2, and Li4Ti5O. 12 The mixture consisted of 0.25g of nanoparticles, 0.27g of urea, 0.034g of boric acid, 1.33g of glucose, 0.34g of sucrose, 6mL of ethanol, 2mL of deionized water, and 0.8mL of nitric acid.

[0046] The preparation method of battery negative electrode material includes the following steps:

[0047] TiO2 and Li4Ti5O 12 TiO2 was dissolved in a mixed solvent of ethanol and deionized water and stirred to form a titanium source mixture. Li4Ti5O was then added to the titanium source mixture. 12 Li4Ti5O 12 The mixture of titanium source and ultrasonic dispersion was ultrasonically dispersed in an ultrasonic disperser at a power of 500W for 30 minutes, while nitric acid solution was added dropwise to adjust the pH of the mixture to 3. The mixture was then stirred at 30°C for 1 hour to form a mixed dispersion.

[0048] Nano-silicon powder and mixed dispersion were mixed and stirred at 60°C for 3 hours. After mixing, nano-silicon powder and mixed dispersion were dried at 100°C for 8 hours to obtain an electrode precursor with a core layer coated with a composite buffer layer.

[0049] Weigh out the carbon-nitrogen source solution formed by dissolving glucose and urea in deionized water, add the electrode precursor to the first carbon-nitrogen source solution, stir the carbon-nitrogen source solution and electrode precursor at 60°C for 2 hours to obtain a precursor mixture, and dry the precursor mixture at 90°C for 4 hours to obtain an inner layer coated intermediate.

[0050] Sucrose and boric acid were weighed and dissolved in deionized water to form a carbon boron source solution. The inner layer coating intermediate was added to the carbon boron source solution. The carbon boron source solution and the inner layer coating intermediate were stirred at 80°C for 2 hours. After stirring, the mixture was dried at 120°C for 6 hours to obtain the electrode coating precursor.

[0051] The electrode-coated precursor was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min under an argon atmosphere with a flow rate of 100 mL / min. After the heating reaction was completed, the electrode-coated precursor was kept at the temperature for 1 hour to complete the pre-calcination.

[0052] The temperature was then increased to 1050℃ at a rate of 8℃ / min and held for 3 hours to complete the high-temperature carbonization. After the carbonization was completed, the material was naturally cooled to room temperature to obtain the battery anode material.

[0053] Comparative Example 1

[0054] Materials used to prepare the battery anode material: 1.6g TiO2, 5.5g nano-silicon powder, 1.42g sucrose, 0.21g urea, 0.78g glucose, 0.062g boric acid, 7mL ethanol, 3mL deionized water, and 1.0mL 10% nitric acid. Compared with Examples 1-3, no Li4Ti5O was found. 12 Nanoparticles;

[0055] Preparation steps: No Li4Ti5O was added compared to Examples 1-3. 12 The nanoparticles were produced, and the remaining steps were completely consistent with those in Example 1.

[0056] Comparative Example 2

[0057] Materials used to prepare the battery anode material: 5.5g of nano-silicon powder, 1.6g of TiO2, and Li4Ti5O. 12 The nanoparticles were 0.4g, glucose 0.78g, sucrose 1.42g, ethanol 7mL, deionized water 3mL and nitric acid 1mL. The difference from Examples 1-3 is that urea and boric acid were not added.

[0058] Preparation steps: Except for the preparation of the carbon source solution in the coating layer using 1.42g sucrose + 0.78g glucose (without urea or boric acid), the other steps are completely consistent with those in Examples 1-3. Example

[0059] The raw materials and preparation methods for existing battery anode materials are described here, and the application of existing technologies will not be elaborated upon further.

[0060] Test case

[0061] Electrode preparation: Take the negative electrode materials of Examples 1-3 and Comparative Examples 1-3 respectively, mix them according to the mass ratio of negative electrode material: conductive agent: binder of 8:1:1, add N-methylpyrrolidone (NMP) to adjust to a suitable viscosity, and form a uniform electrode slurry;

[0062] The slurry was uniformly coated on the surface of a 10μm thick copper foil, and the wet film thickness was controlled to be 100μm. It was then dried in a vacuum drying oven at 80℃ for 12h. After that, it was rolled and punched into circular electrode sheets with a diameter of 12mm using a roller press (pressure 5MPa) for later use.

[0063] Battery assembly: In an argon glove box, the prepared electrode sheet is used as the working electrode, the lithium metal sheet is used as the counter electrode, and the polypropylene membrane is used as the separator. Electrolyte is added to assemble a lithium-ion battery. After assembly, the battery is left to stand for 24 hours to ensure that the electrolyte fully wets the electrode and the separator before electrochemical performance testing is performed.

[0064] Sample performance testing

[0065] First discharge specific capacity test: Using a battery testing system, constant current charge and discharge test is performed at a rate of 0.1C in a constant temperature environment of 25℃, with a voltage range of 0.01~1.5V. The capacity data of the battery during the first discharge process is recorded, and the first discharge specific capacity is calculated in combination with the actual mass of the negative electrode material in the working electrode.

[0066] Cyclic performance test: Under constant temperature of 25℃, constant current charge and discharge cycle test was performed at 1C rate for 500 cycles, with a voltage range of 0.01~1.5V. The discharge capacity of each cycle was recorded, the capacity retention rate of 500 cycles was calculated, and the average coulombic efficiency of 500 cycles was calculated.

[0067] Low-temperature rate performance test: The battery was placed in a -20℃ constant temperature chamber for 4 hours. After the temperature stabilized, a constant current discharge test was performed at a 1C rate with a voltage range of 0.01 to 1.5V. The 1C discharge capacity at -20℃ was recorded. Combined with the 1C discharge capacity at 25℃, the 1C capacity retention rate at -20℃ was calculated.

[0068] Volume expansion rate test: A laser particle size analyzer was used to test the volume of the electrode before and after 500 cycles. The central area of ​​the electrode was selected for the test, and the test was repeated 3 times and the average value was taken to calculate the volume expansion rate.

[0069] The table shows the performance test results of the battery anode material:

[0070]

[0071] The initial discharge specific capacitance of Examples 1-3 was significantly higher than that of Comparative Examples 1-3, with Example 1 showing the highest specific capacitance among all samples. The core reason for this is that Examples 1-3 used nano-silicon powder as the core layer, fully leveraging the high theoretical specific capacitance of silicon, while also incorporating a composite buffer layer (TiO2 and Li4Ti5O). 12 The silicon powder is tightly coated with a nitrogen-boron-doped carbon coating layer, which avoids silicon powder agglomeration and does not hinder the alloying reaction between silicon and lithium ions; while Comparative Example 1 (without Li4Ti5O) 12 Comparative Example 2 (without nitrogen and boron elements) has a weaker interfacial bonding force due to the lack of functional components. A small amount of silicon powder falls off during preparation or testing, resulting in a decrease in specific capacity. Comparative Example 3 is a conventional silicon-carbon anode without a composite buffer layer. The silicon powder is prone to agglomeration to form large particles, and some silicon cannot participate in the electrochemical reaction, resulting in the lowest specific capacity.

[0072] The capacity retention rate and average coulombic efficiency after 500 cycles of Examples 1-3 are far superior to those of Comparative Examples 1-3, and especially significantly higher than those of Comparative Examples 2 and 3. This is mainly because the coating layer of Examples 1-3 contains nitrogen provided by urea and boron provided by boric acid. Nitrogen can enhance the interfacial bonding force between the coating layer and the composite buffer layer through polar sites, avoiding coating layer peeling during cycling. Boron can induce the electrolyte to form a uniform and stable SEI film rich in LiBO2 on the electrode surface, reducing lithium ion consumption caused by repeated rupture and regeneration of the SEI film.

[0073] Examples 1-3 exhibited capacity retention rates at -20°C (1°C) that were more than twice that of Comparative Examples 1 and 3, with Comparative Example 2 being close to that of Examples 1-3. The fundamental reason for this is the presence of Li₄Ti₅O₃ in the composite buffer layer of these examples. 12 Nanoparticles, which still have a high lithium-ion diffusion coefficient at low temperatures, can synergistically construct continuous three-dimensional lithium-ion transport channels with TiO2, significantly reducing the migration resistance of lithium ions at low temperatures.

[0074] The volume expansion rates of Examples 1-3 after 500 cycles were significantly lower than those of Comparative Examples 1, 2, and 3 because the TiO2 anatase phase in the composite buffer layer of Examples 1-3 has excellent structural rigidity, which can limit the excessive volume expansion of silicon. 12 (Spinel phase) has a certain degree of elasticity and can absorb the stress generated by silicon expansion. The two work together to effectively alleviate stress concentration inside the electrode and prevent electrode cracking.

[0075] In summary, Examples 1-3 utilize a nano-silicon core layer, TiO2, and Li4Ti5O 12The multi-layer coating structure of the composite buffer layer and the nitrogen-boron-doped carbon coating layer solves the shortcomings of existing silicon-based anodes, such as low specific capacity, short cycle time, poor low-temperature retention rate and large expansion. It meets the practical application requirements of power batteries for high specific capacity, long cycle time, wide temperature range and low expansion, and enables the battery anode material to have good performance characteristics.

[0076] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a high specific capacity and high rate performance battery anode material, the battery anode material being composed of a core layer, a composite buffer layer and a coating layer; the core layer being nano-silicon powder, the mass percentage of the core layer being 45%-65%, and the particle size of the core layer being 50-200nm; The mass ratio of the composite buffer layer is 15-25%, which is composed of titanium dioxide TiO2 and lithium titanate Li4Ti5O 12 nanoparticles, the particle size of the TiO2 is 10-50nm, and the particle size of the Li4Ti5O 12 is 5-20nm. The thickness of the coating layer is 8-25 nm, and the coating layer comprises mesopores with a pore size of 2-10 nm. comprising the following steps: TiO2 and Li4Ti5O12 are weighed in a mass ratio of 3-5:1 12 The TiO2 is dissolved in a mixed solvent of ethanol and deionized water to form a titanium source mixed solution, and the Li4Ti5O12 is added to the titanium source mixed solution 12 The Li4Ti5O12 is dissolved in a mixed solvent of ethanol and deionized water to form a lithium source mixed solution 12 The titanium source mixed solution and the lithium source mixed solution are ultrasonically dispersed in an ultrasonic disperser at a power of 300-500 W for 30-40 min, and a nitric acid solution is added dropwise to adjust the pH of the mixture to 2-3, and the mixture is stirred at a temperature of 30-50 °C for 1-2 h to form a mixed dispersion liquid; mixing the nano-silicon powder with the mixed dispersion liquid, stirring the mixture of the nano-silicon powder and the mixed dispersion liquid at a temperature of 40-60℃ for 3-5h, and then drying the mixture of the nano-silicon powder and the mixed dispersion liquid at a temperature of 80-100℃ for 8-12h to obtain an electrode precursor of the core layer coated with the composite buffer layer; measuring the carbon-nitrogen source solution formed by dissolving glucose and urea in deionized water, adding the electrode precursor into the carbon-nitrogen source solution, stirring the mixture of the carbon-nitrogen source solution and the electrode precursor at a temperature of 60-70℃ for 2-3h, and then mixing to obtain a precursor mixture, and drying the precursor mixture at a temperature of 80-90℃ for 4-6h to obtain an inner layer coating intermediate; measuring the carbon-boron source solution formed by dissolving sucrose and boric acid in deionized water, adding the inner layer coating intermediate into the carbon-boron source solution, stirring the mixture of the carbon-boron source solution and the inner layer coating intermediate at a temperature of 70-80℃ for 2-3h, and then drying the mixture at a temperature of 100-120℃ for 6-8h to obtain an electrode coating precursor; placing the electrode coating precursor in a tube furnace, heating the electrode coating precursor to 400-500℃ at a heating rate of 2-5℃ / min under the protection of argon gas with a flow rate of 50-100mL / min, and then pre-baking the electrode coating precursor for 1-2h after the completion of the heating reaction; then heating the electrode coating precursor to 850-1050℃ at a heating rate of 5-8℃ / min, and then carbonizing the electrode coating precursor for 3-5h, and then naturally cooling the electrode coating precursor to room temperature after the completion of the heating carbonization to obtain the battery anode material.

2. The method of claim 1, wherein the method is characterized by: The content of nitrogen element in the coating layer decreases from 5-8at% to 2-3at% from the inside to the outside, the content of boron element in the coating layer increases from 0.5-1at% to 2-3at%, the mesopores in the coating layer are distributed in a through manner, and the wall surface of the mesopores and the surface of the composite buffer layer form a chemical bond.

3. The method of claim 1, wherein the method is characterized by: The Li4Ti5O 12 is uniformly dispersed in the matrix of the TiO2, and the surface of the Li4Ti5O 12 forms a continuous interface bonding surface with the TiO2.

4. The method of claim 1, wherein the method is characterized by: The surface of the nano-silicon powder in the core layer has hydroxyl groups, and the hydroxyl groups on the surface of the nano-silicon powder form a coordination bond with the oxygen atoms of TiO2 in the composite buffer layer.

5. The method of claim 1, wherein the method is characterized by: When drying the mixture of the nano-silicon powder and the mixed dispersion liquid, the precursor mixture, and the mixture of the inner layer coating intermediate and the carbon-boron source solution, high-temperature drying is performed in an atmospheric environment, and inert gas is continuously introduced during the drying process.

6. The method of claim 1, wherein the method is characterized by: The argon gas used for protecting the baking process in the tube furnace is subjected to dehydration and impurity removal treatment, the total content of oxygen, water and impurity gases in the argon gas is lower than a preset threshold value, and the argon gas flows in a unidirectional manner in the tube furnace.

7. The method of claim 1, wherein the method further comprises: adding a binder to the mixture of the carbon material, the silicon material, and the lithium metal. After high-temperature carbonization of the electrode coating precursor is completed, the electrode coating precursor is naturally cooled to room temperature under the condition of maintaining the argon atmosphere, and then the argon is stopped and the battery negative electrode material is obtained from the tube furnace.

8. The method of claim 1, wherein the method is characterized by: Before the mixing of the nanometer silicon powder and the mixed dispersion liquid, the nanometer silicon powder is cleaned with deionized water, the nanometer silicon powder is cleaned to neutral pH by deionized water, and then the cleaned nanometer silicon powder is dried, and the dried nanometer silicon powder is mixed with the mixed dispersion liquid.

9. The method of claim 1, wherein the method is characterized by: When preparing the carbon-nitrogen source solution and the carbon-boron source solution, the glucose and the sucrose are respectively added into deionized water and stirred until completely dissolved, and then the urea and the boric acid are respectively added and continuously stirred until the glucose and the urea and the sucrose and the boric acid are completely dissolved, respectively, to obtain the corresponding carbon-nitrogen source solution and the carbon-boron source solution.

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