Preparation process of fast-charging negative electrode material

Abstract

The application relates to a preparation process of a fast-charging negative electrode material, which comprises the following steps: preparation of mesophase pitch, preparation of artificial graphite material, preparation of pitch-coated silicon-carbon composite particles, preparation of carbon nanotube conductive agent, preparation of glucose-based hard carbon precursor, preparation of a silicon-carbon composite fast-charging negative electrode material and the like. The fast-charging negative electrode material prepared by creatively combining a thermal polycondensation reaction, a granulation process, a water-assisted chemical vapor deposition method, a hydrothermal method and the like has the advantages of more stable electrochemical performance, excellent rate performance and the like, can be applied to multiple fields such as power batteries and energy storage batteries, has a wide application field, and has a more promising application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to a new material, in particular to a preparation process of a fast-charging negative electrode material. BACKGROUND

[0002] At present, although the graphite negative electrode material has high specific capacity and stable cycle performance, the large-current charge-discharge performance is relatively poor, which limits the development of new application fields of the graphite negative electrode material, therefore, developing a negative electrode material suitable for fast-charging lithium ion batteries is the key to keeping the graphite negative electrode material in a dominant position in the field of negative electrode materials, in addition, the specific capacity of the graphite material has approached the theoretical specific capacity, therefore, developing a new negative electrode material with high specific capacity to meet new high-energy-density lithium batteries is an important development direction of the negative electrode material at present, the silicon negative electrode has extremely high theoretical specific capacity and is relatively stable, but the silicon negative electrode often has serious volume expansion and shrinkage during the charge-discharge process, and the electronic conductivity is poor, which greatly limits the development of the silicon negative electrode in the field of negative electrode materials.

[0003] The application is just based on the consideration of the above problems, the graphite preparation process is controlled, the material is modified by using nano-carbon, the graphite negative electrode material with excellent rate and cycle performance is obtained, and the silicon material is compounded to obtain a new negative electrode material with high specific capacity, and the silicon-carbon composite fast-charging negative electrode material has the following advantages: (1) high energy density; (2) excellent conductivity; (3) good cycle stability; (4) excellent specific capacity. The silicon-carbon composite fast-charging negative electrode material is composed of silicon and carbon, and combines the high energy density of silicon and the good conductivity and structural stability of carbon, the negative electrode material in the prior art is mainly modified natural graphite and artificial graphite, although the technology is mature, the theoretical specific capacity is limited, and the theoretical specific capacity of the silicon-carbon composite negative electrode material is much higher than that of the graphite negative electrode material in the prior art, so that higher energy density can be provided, and the demand of consumer electronic products for longer endurance is met. SUMMARY

[0004] In view of the above problems, the application provides a preparation process of a fast-charging negative electrode material.

[0005] The preparation process of the fast-charging negative electrode material provided by the application comprises the following steps: preparation of mesophase pitch, preparation of artificial graphite material, preparation of pitch-coated silicon-carbon composite particles, preparation of carbon nanotube conductive agent, preparation of glucose-based hard carbon precursor, and preparation of a silicon-carbon composite fast-charging negative electrode material.

[0006] In the step (5), the preparation of the glucose-based hard carbon precursor comprises the following steps:

[0007] Mixing glucose and water to obtain a glucose solution, then adding the glucose solution and water into a stainless steel high-pressure reaction kettle, hydrothermal reaction at a certain temperature, natural cooling to room temperature, washing with deionized water and suction filtration to neutral, drying the obtained solid precipitate in a blast drying oven to obtain a glucose-based hard carbon precursor;

[0008] Step (6) preparation of the silicon-carbon composite fast-charging negative electrode material includes:

[0009] Coating the pitch-coated silicon-carbon composite material of step (3) with the glucose-based hard carbon precursor of step (5), and finally adding the carbon nanotube conductive agent of step (4) to sinter in a tube furnace (pre-carbonization at medium-low temperature after heating the precursor, then heating, holding, grinding and sieving to obtain the silicon-carbon composite fast-charging negative electrode material.

[0010] As preferred, the preparation of the mesophase pitch in step (1)

[0011] After grinding and crushing the raw pitch, heat conversion experiments are carried out in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, under N2 atmosphere protection, autogenous pressure, stirring, constant temperature for a certain time, discharging the system pressure, and natural cooling to room temperature to obtain the mesophase pitch.

[0012] Step (2) preparation of the artificial graphite material

[0013] Take the needle coke powder, add the mesophase pitch of step (1) to it, mix the two in a VC mixer, stir for a certain time, set the frequency, place the mixture in a self-made converter under N2 protection for granulation, heat to a specified temperature at a certain heating rate, then place the granulated mixture in a graphitization furnace, and after high-temperature graphitization, the artificial graphite material is obtained.

[0014] Step (3) preparation of pitch-coated silicon-carbon composite particles

[0015] Mix the artificial graphite of step (2) with the silicon material, then add the pitch of step (1), add a certain amount of anhydrous ethanol, then use a planetary ball mill for wet mixing, pour the mixed material into a beaker and dry it in a blast drying oven to obtain a silicon-carbon composite precursor, pre-carbonize under argon atmosphere, then heat and carbonize, grind and sieve the carbonized material to obtain pitch-coated silicon-carbon composite particles.

[0016] Step (4) preparation of the carbon nanotube conductive agent

[0017] Put the silicon substrate with the catalyst system into a tube furnace, pass Ar, clean the quartz tube, start temperature rising while passing hydrogen, as the temperature gradually rises, the iron film slowly cracks, the temperature is raised, and the iron film is cracked into uniform size iron nanoparticles, then carbon nanotube conductive agent is prepared under a certain atmosphere and for a certain time, and the product is taken out after natural cooling, and mechanically peeled off;

[0018] Step (5) preparation of glucose-based hard carbon precursor

[0019] Mixing glucose and water to obtain a glucose solution, then adding the glucose solution and water into a stainless steel high-pressure reaction kettle, and then performing hydrothermal reaction at a certain temperature, and then naturally cooling to room temperature, washing with deionized water and suction filtering to neutral, drying the obtained solid precipitate in a blast drying oven to obtain a glucose-based hard carbon precursor;

[0020] Step (6) preparation of silicon-carbon composite fast-charging negative electrode material

[0021] Adding the glucose-based hard carbon precursor of step (5) to the pitch-coated silicon-carbon composite material of step (3) for coating, and finally adding the carbon nanotube conductive agent of step (4) for sintering in a tube furnace (pre-carbonization of the precursor at medium-low temperature after heating, re-heating, holding, grinding and sieving to obtain a silicon-carbon composite fast-charging negative electrode material.

[0022] As preferred, preparation of mesophase pitch in step (1)

[0023] After grinding and crushing the raw pitch, performing a thermal conversion experiment in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, at a heating rate of 5-8℃ / min, under N2 atmosphere protection and self-generated pressure, stirring, constant temperature for 2-10h at a predetermined temperature of 385-445℃, discharging the system pressure, and naturally cooling to room temperature to obtain the mesophase pitch.

[0024] The present application has the advantages that purified coal pitch is used as raw material to prepare mesophase pitch by a thermal polymerization method, greatly shortening the mesophase conversion time, and the thermal polymerization time greatly influences the optical organization structure of the mesophase pitch, and as the time prolongs, the mesophase continuously fuses and merges.

[0025] As preferred, preparation of artificial graphite material in step (2)

[0026] Take 300~400g of needle-shaped coke powder and add the meso phase (mass fraction of 0~20%) from step (1). Mix the two thoroughly in a mixer for 1~2 hours at a frequency of 50~100Hz. Place the mixture in a self-made converter for granulation under N2 protection at a frequency of 20~30Hz and a heating rate of 3~5℃ / min to 650~700℃. Then place the granulated mixture in a graphitization furnace and graphitize it at a high temperature of 2800~3000℃ to obtain artificial graphite material.

[0027] The advantages of this invention are that by mixing needle-shaped coke powder and binder pitch powder, and then granulating and graphitizing the mixture, a secondary particle artificial graphite anode material is obtained. Under these conditions, the particle size and tap density of the artificial graphite anode material are significantly improved. The final secondary particle artificial graphite anode material retains the high capacity advantage of the primary particle anode material while compensating for the shortcomings of the primary particle in terms of rate performance. This enables the high-value utilization of coal tar pitch and also demonstrates excellent high-rate charge and discharge capability in rate performance testing.

[0028] Preferably, step (3) involves the preparation of asphalt-coated silicon-carbon composite particles.

[0029] Take 36-42g of artificial graphite from step (2) and mix it with 4-6g of silicon material. Then add the asphalt from step (1), add anhydrous ethanol, and wet mix it for 5-6 hours using a planetary ball mill. Pour the mixed material into a beaker and dry it in a forced-air drying oven to obtain a silicon-carbon composite precursor. Pre-carbonize it at 300-1200℃ for 3-4 hours under an argon atmosphere, and then carbonize it for 6-7 hours. Grind the carbonized material through a 300-350 mesh sieve to obtain asphalt-coated silicon-carbon composite particles.

[0030] The advantages of this invention are that by using asphalt as the coating material and achieving effective coating of silicon-carbon composite particles through low-temperature carbonization, the multi-level coating structure not only improves the cycling stability of the material but also optimizes its electrochemical performance. At the same time, the asphalt carbon coating can reduce the direct contact between silicon nanoparticles and electrolytes, thereby reducing the generation of side reactions and reducing electrolyte consumption.

[0031] Preferably, step (4) involves the preparation of the carbon nanotube conductive agent.

[0032] Put the silicon substrate with the catalyst system into a tube furnace, pass 1000-1200 sccm Ar, clean the quartz tube for 10-20 min, start heating while passing hydrogen, as the temperature gradually rises, the iron film slowly cracks, the temperature rises to 750-800 DEG C, and the iron film is annealed for 5-10 min, then the iron film is cracked into uniform iron nanoparticles, then the carbon nanotube conductive agent is prepared under the conditions of water content of 150-180 ppm, ethylene flow rate of 100-120 sccm, hydrogen flow rate of 700-750 sccm, and control time of 5-30 min, and the product is taken out after natural cooling.

[0033] The present application has the advantages that the present application can realize the directional and positioning growth of the carbon nanotube array by using the water-assisted chemical vapor deposition method (CVD), the array structure is highly ordered, has high stability, excellent mechanical properties and electrical properties, the water-assisted chemical vapor deposition method has low energy consumption and small environmental pollution, and is conducive to promoting the green preparation and sustainable development of the carbon nanotube conductive agent.

[0034] As preferred, the preparation of the glucose-based hard carbon precursor in step (5)

[0035] 2.5-3 g of glucose and 7.5-8 g of water are mixed to obtain a 25-26% glucose solution, then 25-26% of the glucose solution and 56.67-72.12 g of water are added to a stainless steel high-pressure reaction kettle, and hydrothermal reaction is carried out at 240-280 DEG C for 4-5 h, and then the reaction mixture is naturally cooled to room temperature, washed with deionized water, and filtered to neutral, and the obtained solid precipitate is dried in a blast drying oven for 24-26 h to obtain the glucose-based hard carbon precursor.

[0036] The present application has the advantages that the present application adopts the hydrothermal method to prepare the glucose-based hard carbon precursor, compared with the traditional method, has a faster reaction rate, so that the reaction time is shortened, the experimental equipment only needs a simple reaction kettle, the process is easy to control, glucose is a low-cost biomass model compound, has a strong active hydroxyl group in the molecule, and the hydrothermal reaction occurs at a lower temperature.

[0037] As preferred, the preparation of the silicon-carbon composite fast-charging negative electrode material in step (6)

[0038] The pitch-coated silicon-carbon composite material of step (3) is added with the glucose-based hard carbon precursor of step (5) (the addition amount is 10-12% of the mass of the pitch-coated silicon-carbon composite particles) for coating, and finally the carbon nanotube conductive agent of step (4) is added for sintering in a tube furnace (after heating to 350-400 DEG C, the precursor is pre-carbonized at a medium-low temperature for 3-4 h, and then heated to 700-750 DEG C and kept for 6-7 h), ground and sieved to obtain the silicon-carbon composite fast-charging negative electrode material.

[0039] The application has the advantages that: the silicon-carbon negative electrode material is prepared by using silicon, artificial graphite and water glucose as raw materials through a high-temperature pyrolysis method; the silicon-carbon negative electrode material is uniformly mixed with pitch with different contents, and then the composite negative electrode material is obtained through high-temperature carbonization treatment; the thin carbon layer on the surface of the obtained composite material after carbonization can improve the conductivity of the material and relieve the volume expansion of the material to some extent, which helps to improve the charge-discharge performance of the silicon-carbon material, and finally a more stable and excellent rate performance silicon-carbon composite fast-charging negative electrode material is obtained.

[0040] In summary, the application has the following advantages:

[0041] 1. The application has the advantages that: the mesophase pitch is prepared by using purified coal pitch as raw material through a thermal polymerization method, which greatly shortens the time for mesophase conversion, and the thermal polymerization time has a great influence on the optical structure of the mesophase pitch; and as the time is prolonged, the mesophase constantly fuses and merges.

[0042] 2. The application has the advantages that: the needle-shaped coke powder and the binder pitch powder are mixed, and then the secondary granular artificial graphite negative electrode material is obtained through granulation process and graphitization treatment; the particle size and the tap density of the artificial graphite negative electrode material prepared under the condition are obviously improved; the secondary granular artificial graphite negative electrode material is finally prepared, which retains the high capacity advantage of the primary granular negative electrode material and makes up for the insufficient rate performance of the primary granular material; the high value-added utilization of coal pitch can be realized; and excellent high-rate charge-discharge capacity is exhibited in the rate performance test.

[0043] 3. The application has the advantages that: the pitch is used as the coating material to realize effective coating of the silicon-carbon composite particles through low-temperature carbonization; through the design of the multi-level coating structure, the cycle stability of the material is improved, and the electrochemical performance of the material is optimized; and the pitch carbon coating layer can reduce the direct contact between the silicon nanoparticles and the electrolyte, thereby reducing the generation of side reactions and reducing the consumption of electrolyte.

[0044] 4. The application has the advantages that: the water-assisted chemical vapor deposition method (CVD) can realize the directional and positioning growth of the carbon nanotube array, the array structure is highly ordered, has high stability and excellent mechanical and electrical properties; and the water-assisted chemical vapor deposition method has low energy consumption and small environmental pollution, which is conducive to promoting the green preparation and sustainable development of the carbon nanotube conductive agent.

[0045] 5. The application has the advantages that the glucose-based hard carbon precursor is prepared by a hydrothermal method, the reaction rate is faster than that of the traditional method, the reaction time is shortened, the test equipment only needs a simple reaction kettle, the process is easy to control, glucose is a low-cost biomass model compound, the molecule contains a strong active hydroxyl group, the hydrothermal reaction occurs at a lower temperature, and the like.

[0046] 6. The application has the advantages that the silicon-carbon negative electrode material is prepared by a high-temperature pyrolysis method using silicon, artificial graphite and hydrated glucose as raw materials, the silicon-carbon negative electrode material is uniformly mixed with different contents of pitch, and then subjected to high-temperature carbonization treatment to obtain a composite negative electrode material, the thin carbon layer on the surface of the obtained composite material after carbonization can improve the electrical conductivity of the material, and to a certain extent, can relieve the volume expansion of the material, which is helpful to improve the charge-discharge performance of the silicon-carbon material, and finally a more stable and excellent rate performance silicon-carbon composite fast-charging negative electrode material is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is an XRD graph of Example 2 of the application;

[0048] Figure 2 is an SEM graph of Example 2 of the application;

[0049] Figure 3 is a charge-discharge curve graph of Example 2 of the application;

[0050] Figure 4 is a rate performance graph of a preparation process embodiment of the fast-charging negative electrode material of the application;

[0051] Figure 5 is a preparation process flowchart of the fast-charging negative electrode material of the application. DETAILED DESCRIPTION

[0052] The following examples are used to illustrate the application, but are not used to limit the scope of the application. Modifications or replacements of the method, steps or conditions of the application without departing from the spirit and essence of the application shall fall within the scope of the application.

[0053] If not specifically indicated, the technical means used in the examples is the conventional means well known to those skilled in the art. In addition, all the component raw materials used in the examples are known commercially available products.

[0054] Example 1

[0055] Preparation of the mesophase pitch in step (1)

[0056] The raw material pitch is ground and crushed, and then a thermal conversion experiment is carried out in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, under the protection of N2 atmosphere, at a self-generating pressure, stirring, at a predetermined temperature of 385°C, constant temperature for 2h, discharging the system pressure, and natural cooling to room temperature, to obtain the mesophase pitch;

[0057] Step (2) preparation of artificial graphite material

[0058] 300g of needle coke powder is taken, 1% of the mesophase pitch of step (1) is added, and the two are fully mixed in a mixer for 1h at a frequency of 50Hz, and the mixture is placed in a self-made converter under the protection of 0.1L / min N2 for granulation, the converter frequency is 20Hz, the temperature is raised to 650°C at a rate of 3°C / min, and then the granulated mixture is placed in a graphitization furnace for high-temperature graphitization at 2800°C to obtain the artificial graphite material;

[0059] Step (3) preparation of pitch-coated silicon-carbon composite particles

[0060] 36g of the artificial graphite of step (2) is mixed with 4g of silicon material, then the pitch of step (1) is added, after adding anhydrous ethanol, wet mixing is carried out for 5h using a planetary ball mill, the mixed material is poured into a beaker and dried in a forced air drying oven to obtain a silicon-carbon composite precursor, pre-carbonization is carried out at 1000°C for 3h under an argon atmosphere, and then carbonization is carried out for 6h, the carbonized material is ground through a 300 mesh sieve to obtain pitch-coated silicon-carbon composite particles;

[0061] Step (4) preparation of carbon nanotube conductive agent

[0062] The silicon substrate with a catalyst system is placed in a tube furnace, 1000sccm of Ar is introduced, the quartz tube is cleaned for 10min, hydrogen is introduced while the temperature is rising, the iron film is slowly cracked as the temperature gradually rises, the temperature is raised to 750°C, and annealing is carried out for 5min, the iron film is cracked into uniform-sized iron nanoparticles, then the carbon nanotube conductive agent is prepared under the conditions of a water content of 150ppm, an ethylene flow of 100sccm, a hydrogen flow of 700sccm, and a control time of 5min, the product is taken out after natural cooling, and mechanical peeling is carried out;

[0063] Step (5) preparation of glucose-based hard carbon precursor

[0064] Mix 2.5 g of glucose and 7.5 g of water to obtain a 25% glucose solution, then add the 25-26% glucose solution and 56.67 g of water into a stainless steel high-pressure reaction kettle, and hydrothermally react at 240°C for 4 h, naturally cool to room temperature, wash with deionized water and filter to neutral, dry the obtained solid precipitate in a blast drying oven for 24 h to obtain a glucose-based hard carbon precursor;

[0065] Step (6) Preparation of silicon-carbon composite fast-charging negative electrode material

[0066] Add the glucose-based hard carbon precursor of step (5) (the addition amount is 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material of step (3), and then add the carbon nanotube conductive agent of step (4) to sinter in a tube furnace (after heating to 350°C, pre-carbonize the precursor at medium-low temperature for 3 h, then heat to 700°C and keep for 6 h), grind and sieve to obtain a silicon-carbon composite fast-charging negative electrode material.

[0067] Example 2

[0068] Step (1) Preparation of mesophase pitch

[0069] After grinding and crushing the raw pitch, perform a thermal conversion experiment in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, with a heating rate of 5°C / min, self-generated pressure under N2 atmosphere, stirring, constant temperature at a predetermined temperature of 385°C for 2 h, discharge the system pressure, and naturally cool to room temperature to obtain mesophase pitch;

[0070] Step (2) Preparation of artificial graphite material

[0071] Take 300 g of needle coke powder, add 8% of the mesophase pitch of step (1) to it, mix the two in a mixer for 1 h at a frequency of 50 Hz, and then place the mixture in a self-made converter under the protection of 0.1 L / min N2 to perform granulation, with a converter frequency of 20 Hz and a heating rate of 3°C / min to heat to 650°C, and then place the granulated mixture in a graphitization furnace to obtain an artificial graphite material after high-temperature graphitization at 2800°C;

[0072] Step (3) Preparation of pitch-coated silicon-carbon composite particles

[0073] Take 36 g of the artificial graphite of step (2) and 4 g of silicon material, then add the pitch of step (1), add anhydrous ethanol, and then use a planetary ball mill to wet mix for 5 h, pour the mixed material into a beaker and dry in a blast drying oven to obtain a silicon-carbon composite precursor, pre-carbonize at 1000°C for 3 h under an argon atmosphere, and then carbonize at a higher temperature for 6 h, grind the carbonized material through a 300-mesh sieve to obtain pitch-coated silicon-carbon composite particles.

[0074] Step (4) Preparation of carbon nanotube conductive agent

[0075] Put the silicon substrate with catalyst system into the tube furnace, pass 1000 sccm Ar, clean the quartz tube for 10 min, start heating while passing hydrogen, as the temperature gradually rises, the iron film slowly cracks, the temperature rises to 750℃, annealing for 5 min, the iron film cracks into uniform size iron nanoparticles, then under the conditions of water content 150 ppm, ethylene flow 100 sccm, hydrogen flow 700 sccm, control time for 5 min, prepare carbon nanotube conductive agent, take out the product after natural cooling, and mechanically peel off;

[0076] Step (5) Preparation of glucose-based hard carbon precursor

[0077] Mix 2.5 g of glucose and 7.5 g of water to obtain a 25% glucose solution, then add 25% glucose solution and 56.67 g of water into a stainless steel high-pressure reaction kettle, hydrothermal reaction at 240℃ for 4h, natural cooling to room temperature, washed with deionized water and suction filtered to neutral, the obtained solid precipitate is dried in a blast drying oven for 24h to obtain a glucose-based hard carbon precursor;

[0078] Step (6) Preparation of silicon-carbon composite fast-charging negative electrode material

[0079] Add the glucose-based hard carbon precursor of step (5) (the addition amount is 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material of step (3) for coating, and finally add the carbon nanotube conductive agent of step (4) to sinter in a tube furnace (after heating to 350℃, the precursor is pre-carbonized at medium-low temperature for 3h, and then heated to 700℃ and kept for 6h), ground and sieved to obtain a silicon-carbon composite fast-charging negative electrode material.

[0080] The XRD of the prepared silicon-carbon composite fast-charging negative electrode material is shown in Figure 1 As can be seen from the figure, a characteristic diffraction peak appears at 26.39, which corresponds to the (111) crystal plane of silicon. Figure 2 The SEM of the silicon-carbon composite fast-charging negative electrode material is shown in

[0081] From Figure 3In the charge-discharge curve, we can see that the prepared silicon-carbon composite fast-charging negative electrode material has a reversible capacity of 480.53 mAh / g. In combination with Table 1, the charge-discharge specific capacity of Example 2 is the best, and the reversible capacity of Comparative Example 2 is relatively poor, and the reversible capacity as a whole shows a trend of first increasing and then decreasing, and the electrochemical performance is better when the carbonization temperature is 1000℃, and the interface resistance of the material continuously decreases as the heat treatment temperature increases, and the interface resistance reaches the minimum when the heat treatment temperature is 1000℃, and continues to increase when the temperature continues to rise, so the charge-discharge specific capacity performance of the material obtained by heat treatment at 1000℃ is the best, and it has great advantages in the field of fast-charging negative electrode materials.

[0082] From Figure 4 In the rate performance graph, in combination with Table 2, the electrochemical performance of Example 2 is the best, and the performance of Comparative Example 2 is relatively poor, so it is concluded that the mass fraction of adding pitch in artificial graphite material is most appropriate at 8%, and continuing to increase or decrease will only cause the specific capacity to deteriorate, at this time the performance of the secondary particles formed by the granulation process is good, the tap density of the negative electrode material is improved, the specific capacity of the negative electrode material is improved, the specific capacity is optimal, the large particle capacity is high, and it has great potential in the preparation of composite negative electrode materials.

[0083] Example 3

[0084] Step (1) Preparation of mesophase pitch

[0085] After the raw pitch was ground and crushed, a heat conversion experiment was carried out in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, the heating rate was 5℃ / min, the self-generated pressure was protected under N2 atmosphere, stirring, constant temperature at 385℃ for 2h, the system pressure was discharged, and the temperature was naturally cooled to room temperature, and the mesophase pitch was obtained.

[0086] Step (2) Preparation of artificial graphite material

[0087] Take 300g of needle coke powder, add 10% of mesophase pitch of step (1) to it, mix the two in a mixer for 1h at a frequency of 50Hz, and place the mixture in a self-made converter under the protection of 0.1 L / min N2 for granulation, the converter frequency is 20Hz, the temperature is raised to 650℃ at a rate of 3℃ / min, and then the granulated mixture is placed in a graphitization furnace, and the artificial graphite material is prepared after high-temperature graphitization at 2800℃.

[0088] Step (3) Preparation of pitch-coated silicon-carbon composite particles

[0089] Mix 36 g of artificial graphite from step (2) with 4 g of silicon material, then add the pitch from step (1), and after adding anhydrous ethanol, use a planetary ball mill to wet mix for 5 h. Pour the mixed material into a beaker and dry it in a forced air drying oven to obtain a silicon-carbon composite precursor. Pre-carbonize the precursor at 1000°C for 3 h in an argon atmosphere, and then carbonize it at a higher temperature for 6 h. Grind the carbonized material through a 300-mesh sieve to obtain pitch-coated silicon-carbon composite particles.

[0090] Step (4) Preparation of carbon nanotube conductive agent

[0091] Place the silicon substrate with the catalyst system into a tube furnace, and purge the quartz tube with 1000 sccm of Ar for 10 min. Start heating while purging with hydrogen. As the temperature gradually increases, the iron film slowly cracks. When the temperature reaches 750°C, anneal for 5 min. The iron film cracks into uniform-sized iron nanoparticles. Then, under the conditions of a water content of 150 ppm, an ethylene flow rate of 100 sccm, and a hydrogen flow rate of 700 sccm, control the time for 5 min to prepare the carbon nanotube conductive agent. After natural cooling, remove the product and mechanically peel it off.

[0092] Step (5) Preparation of glucose-based hard carbon precursor

[0093] Mix 2.5 g of glucose and 7.5 g of water to obtain a 25% glucose solution. Then, add the 25% glucose solution and 56.67 g of water to a stainless steel high-pressure reaction kettle, and hydrothermally react at 240°C for 4 h. After natural cooling to room temperature, wash and suction-filter the product until it is neutral. Dry the obtained solid precipitate in a forced air drying oven for 24 h to obtain a glucose-based hard carbon precursor.

[0094] Step (6) Preparation of silicon-carbon composite fast-charging negative electrode material

[0095] Add the glucose-based hard carbon precursor from step (5) (added in an amount of 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material from step (3), and then add the carbon nanotube conductive agent from step (4). Sinter the mixture in a tube furnace (pre-carbonize the precursor at a medium-low temperature for 3 h after heating to 350°C, and then heat it to 700°C and maintain the temperature for 6 h). Grind the sintered product through a sieve to obtain a silicon-carbon composite fast-charging negative electrode material.

[0096] Example 4

[0097] Step (1) Preparation of mesophase pitch

[0098] The raw material pitch is ground and crushed, and then a thermal conversion experiment is carried out in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, under the protection of N2 atmosphere, at a self-generating pressure, stirring, at a predetermined temperature of 385°C, constant temperature for 2h, discharging the system pressure, and natural cooling to room temperature, to obtain the mesophase pitch;

[0099] Step (2) preparation of artificial graphite material

[0100] 300g of needle coke powder is taken, and the mesophase pitch of step (1) (mass fraction of 8%) is added thereto, and the two are fully mixed in a mixer for 1h at a frequency of 50Hz, and the mixture is placed in a self-made converter under the protection of N2 at a flow rate of 0.1L / min, and granulation is carried out at a converter frequency of 20Hz, and the mixture after granulation is placed in a graphitization furnace, and an artificial graphite material is prepared after high-temperature graphitization at 2800°C;

[0101] Step (3) preparation of pitch-coated silicon-carbon composite particles

[0102] 36g of artificial graphite of step (2) is mixed with 4g of silicon material, and then the pitch of step (1) is added, and after adding anhydrous ethanol, wet mixing is carried out for 5h using a planetary ball mill, and the mixed material is poured into a beaker and dried in a forced air drying oven to obtain a silicon-carbon composite precursor, and argon atmosphere is used, pre-carbonization is carried out at 900°C for 3h, and then carbonization is carried out for 6h, and the material after carbonization is ground through a 300 mesh sieve to obtain pitch-coated silicon-carbon composite particles;

[0103] Step (4) preparation of carbon nanotube conductive agent

[0104] The silicon substrate with a catalyst system is placed in a tube furnace, 1000sccm of Ar is introduced, the quartz tube is cleaned for 10min, hydrogen is introduced while the temperature is rising, the iron film is slowly cracked as the temperature gradually rises, the temperature is raised to 750°C, and annealing is carried out for 5min, the iron film is cracked into uniform iron nanoparticles, and then the carbon nanotube conductive agent is prepared under the conditions of a water content of 150ppm, an ethylene flow rate of 100sccm, a hydrogen flow rate of 700sccm, and a control time of 5min, and the product is taken out after natural cooling and mechanical peeling;

[0105] Step (5) preparation of glucose-based hard carbon precursor

[0106] Mix 2.5 g of glucose and 7.5 g of water to obtain a 25% glucose solution, then add the 25% glucose solution and 56.67 g of water into a stainless steel autoclave, and hydrothermally react at 240℃ for 4-5 h, naturally cool to room temperature, wash with deionized water and filter to neutral, dry the obtained solid precipitate in a blast drying oven for 24 h to obtain a glucose-based hard carbon precursor;

[0107] Step (6) Preparation of silicon-carbon composite fast-charging negative electrode material

[0108] Add the glucose-based hard carbon precursor of step (5) (the addition amount is 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material of step (3) for coating, and finally add the carbon nanotube conductive agent of step (4) for sintering in a tube furnace (after heating to 350℃, pre-carbonize the precursor at medium-low temperature for 3 h, and then heat to 700℃ and keep for 6 h), grind and sieve to obtain a silicon-carbon composite fast-charging negative electrode material.

[0109] Example 5

[0110] Step (1) Preparation of mesophase pitch

[0111] After grinding and crushing the raw pitch, perform a thermal conversion experiment in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, with a heating rate of 5℃ / min, self-generated pressure under N2 atmosphere protection, stirring, constant temperature at a predetermined temperature of 385℃ for 2 h, discharge the system pressure, and naturally cool to room temperature to obtain mesophase pitch;

[0112] Step (2) Preparation of artificial graphite material

[0113] Take 300 g of needle coke powder, add 8% of the mesophase pitch of step (1) to it, mix the two in a mixer for 1 h at a frequency of 50 Hz, and place the mixture in a self-made converter under the protection of 0.1 L / min N2 for granulation, with a converter frequency of 20 Hz and a heating rate of 3℃ / min to heat to 650℃, then place the granulated mixture in a graphitization furnace for high-temperature graphitization at 2800℃ to obtain an artificial graphite material;

[0114] Step (3) Preparation of pitch-coated silicon-carbon composite particles

[0115] Take 36 g of the artificial graphite of step (2) and 4 g of silicon material, then add the pitch of step (1), add anhydrous ethanol, and use a planetary ball mill for wet mixing for 5 h, pour the mixed material into a beaker and dry in a blast drying oven to obtain a silicon-carbon composite precursor, pre-carbonize at 1100℃ for 3 h under an argon atmosphere, and then carbonize at a higher temperature for 6 h, grind the carbonized material through a 300 mesh sieve to obtain pitch-coated silicon-carbon composite particles.

[0116] Step (4) Preparation of carbon nanotube conductive agent

[0117] Put the silicon substrate with catalyst system into the tube furnace, pass 1000 sccm Ar, clean the quartz tube for 10 min, start heating while passing hydrogen, as the temperature gradually rises, the iron film slowly cracks, the temperature rises to 750℃, and the iron film is cracked into uniform size iron nanoparticles, then under the conditions of water content 150 ppm, ethylene flow 100 sccm, hydrogen flow 700 sccm, control time 5 min, prepare carbon nanotube conductive agent, take out the product after natural cooling, and mechanically peel off;

[0118] Step (5) Preparation of glucose-based hard carbon precursor

[0119] Mix 2.5 g of glucose and 7.5 g of water to obtain a 25% glucose solution, then add 25% glucose solution and 56.67 g of water into a stainless steel high-pressure reaction kettle, hydrothermal reaction at 240℃ for 4-5 h, natural cooling to room temperature, washing with deionized water and suction filtration to neutral, drying the obtained solid precipitate in a blast drying oven for 24 h to obtain a glucose-based hard carbon precursor;

[0120] Step (6) Preparation of silicon-carbon composite fast-charging negative electrode material

[0121] Add the glucose-based hard carbon precursor of step (5) (the addition amount is 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material of step (3) for coating, and finally add the carbon nanotube conductive agent of step (4) for sintering in a tube furnace (after heating to 350℃, the precursor is pre-carbonized at medium-low temperature for 3 h, and then heated to 700℃ and kept for 6 h), ground and sieved to obtain a silicon-carbon composite fast-charging negative electrode material.

[0122] Comparative Example 1

[0123] Step (1) Preparation of artificial graphite material

[0124] Take 300 g of needle coke powder, add mesophase pitch (mass fraction 5%) to it, mix the two in a mixer for 1 h at a frequency of 50 Hz, and place the mixture in a self-made rotary furnace under the protection of 0.1 L / min N2 for granulation, the rotary furnace frequency is 20 Hz, and the temperature is raised to 650℃ at a rate of 3℃ / min, then the granulated mixture is placed in a graphitization furnace for high-temperature graphitization at 2800℃ to obtain an artificial graphite material;

[0125] Step (2) Preparation of pitch-coated silicon-carbon composite particles

[0126] Mix 36 g of artificial graphite from step (1) with 4 g of silicon material, then add pitch, add anhydrous ethanol, and use a planetary ball mill for wet mixing for 5 h. Pour the mixed material into a beaker and dry it in a forced air drying oven to obtain a silicon-carbon composite precursor. Pre-carbonize at 1000°C for 3 h under an argon atmosphere, and then carbonize at a higher temperature for 6 h. Grind the carbonized material through a 300 mesh sieve to obtain pitch-coated silicon-carbon composite particles.

[0127] Step (3) Preparation of carbon nanotube conductive agent

[0128] Place the silicon substrate with the catalyst system into a tube furnace, purge the quartz tube with 1000 sccm of Ar for 10 min, and start heating while introducing hydrogen. As the temperature gradually increases, the iron film slowly cracks. When the temperature reaches 750°C, anneal for 5 min. The iron film cracks into uniform-sized iron nanoparticles. Then, under the conditions of a water content of 150 ppm, an ethylene flow rate of 100 sccm, and a hydrogen flow rate of 700 sccm, control the time for 5 min to prepare the carbon nanotube conductive agent. After natural cooling, remove the product and mechanically peel it off.

[0129] Step (4) Preparation of glucose-based hard carbon precursor

[0130] Mix 2.5 g of glucose and 7.5 g of water to obtain a 25% glucose solution. Then, add the 25% glucose solution and 56.67 g of water to a stainless steel high-pressure reaction kettle. Hydrothermal reaction is carried out at 240°C for 4 h. After natural cooling to room temperature, wash with deionized water and suction filter until neutral. Dry the obtained solid precipitate in a forced air drying oven for 24 h to obtain a glucose-based hard carbon precursor.

[0131] Step (5) Preparation of silicon-carbon composite fast-charging negative electrode material

[0132] Add the glucose-based hard carbon precursor of step (4) (added amount is 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material of step (2) for coating. Finally, add the carbon nanotube conductive agent of step (3) and sinter in a tube furnace (pre-carbonize the precursor at a medium-low temperature for 3 h after heating to 350°C, and then heat to 700°C and maintain for 6 h). Grind and sieve to obtain a silicon-carbon composite fast-charging negative electrode material.

[0133] Comparative Example 2

[0134] Step (1) Preparation of mesophase pitch

[0135] After grinding and crushing the raw pitch, perform a thermal conversion experiment in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller. The heating rate is 5°C / min, and the experiment is carried out under N2 atmosphere protection with self-generated pressure and stirring. At the predetermined temperature of 385°C, maintain the temperature for 2 h, release the system pressure, and naturally cool to room temperature to obtain mesophase pitch.

[0136] Step (2) Preparation of artificial graphite material

[0137] Take 300g needle coke powder, add step (1) mesophase pitch (mass fraction of 12%) to it, mix the two in a mixer for 1h at a frequency of 50Hz, place the mixture in a self-made converter under the protection of 0.1L / min N2, carry out granulation at a converter frequency of 20Hz, and heat to 650℃ at a heating rate of 3℃ / min, then place the granulated mixture in a graphitization furnace, and prepare an artificial graphite material after high-temperature graphitization at 2800℃;

[0138] Step (3) Preparation of pitch-coated silicon-carbon composite particles

[0139] Take 36g of the artificial graphite of step (2) and 4g of silicon material, then add the pitch of step (1), add anhydrous ethanol, and use a planetary ball mill for wet mixing for 5h, pour the mixed material into a beaker and dry it in a forced air drying oven to obtain a silicon-carbon composite precursor, pre-carbonize it at 1200℃ for 3h in an argon atmosphere, and then carbonize it at a higher temperature for 6h, grind the carbonized material through a 300 mesh sieve to obtain pitch-coated silicon-carbon composite particles;

[0140] Step (4) Preparation of glucose-based hard carbon precursor

[0141] Mix 2.5g of glucose and 7.5g of water to obtain a 25% glucose solution, then add the 25% glucose solution and 56.67g of water to a stainless steel high-pressure reaction kettle, hydrothermally react at 240℃ for 4-5h, naturally cool to room temperature, wash with deionized water and suction filter to neutral, dry the obtained solid precipitate in a forced air drying oven for 24h to obtain a glucose-based hard carbon precursor;

[0142] Step (5) Preparation of silicon-carbon composite fast-charging negative electrode material

[0143] Add the glucose-based hard carbon precursor of step (5) (added amount is 10% of the mass of the pitch-coated silicon-carbon composite particles) to the pitch-coated silicon-carbon composite material of step (3) for coating, and finally add carbon nanotube conductive agent for sintering in a tube furnace (pre-carbonize the precursor at a medium-low temperature for 3h after heating to 350℃, then heat to 700℃ and keep for 6h), grind and sieve to obtain a silicon-carbon composite fast-charging negative electrode material.

[0144] Detection experiment comparison:

[0145] The silicon-carbon composite fast-charging negative electrode materials obtained in Examples 1-5 and the products of Comparative Examples 1 and 2 were detected, and the specific detection methods are as follows:

[0146] Charge-discharge test

[0147] The LAND battery test system is used to test the charge-discharge and rate performance of the button lithium ion battery, the discharge cut-off voltage is set to 0.005V, and the charge cut-off voltage is set to 2V.

[0148] Electrochemical performance characterization

[0149] 1) After the button battery is aged for 12h, it is used for electrochemical performance test, and the test equipment is a new battery performance detector. The specific test steps are as follows: constant current discharge condition: 0.1C, cut-off voltage 0.005V, 0.05C, cut-off voltage 0.005V, 0.02C, cut-off voltage 0.005V, static: 5min, constant current charging condition: 0.1C, cut-off voltage 2.0V, static: 5min, all tests are completed at 25℃;

[0150] 2) After the button battery is subjected to the above test, the rate performance test is carried out, and the test equipment is a new battery performance detector. The specific test steps are as follows: constant current discharge: 0.1C, cut-off voltage 0.005V, static: 5min, constant current charging condition: 0.1C, cut-off voltage 2.0V, static: 5min, the repeated charge-discharge rate is from low to high, 0.2, 0.5, 1, 2C, all tests are completed at 25℃

[0151] The specific embodiment is only an explanation of the present application, and is not a limitation of the present application. Those skilled in the art can make modifications to the embodiment without creative contribution according to the needs after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

[0152] Table 1: initial charge-discharge specific capacity test results

[0153] Example Asphalt mass fraction / % Heat treatment temperature / °C Discharge specific capacity / mAh.g -1 ]] Charge specific capacity / mAh.g -1 ]] Coulomb efficiency / % 1 1 1000 550.06 461.72 83.94 2 8 1000 536.67 480.53 89.54 3 10 1000 543.39 475.25 87.46 4 8 900 553.20 473.82 85.65 5 8 1100 538.10 475.20 88.31 Comparative Example 1 5 1000 544.73 470.1 86.30 Comparative Example 2 12 1200 540.49 473.9 87.68

[0154] Table 2: rate performance test results

[0155] Example Asphalt mass fraction / % Heat treatment temperature / °C Charge specific capacity / mAh.g -1 ]] 0.2 C specific capacity / mAh g -1 ]] 1 1 1000 461.72 325.65 2 8 1000 480.53 423.35 3 10 1000 475.25 410.71 4 8 900 473.82 405.02 5 8 1100 475.20 409.57 Comparative Example 1 5 1000 470.1 371.33 Comparative Example 2 12 1200 473.9 401.49

Claims

1. A preparation process of a fast-charging negative electrode material, characterized in that Comprising: Step (1) preparation of mesophase pitch After the raw pitch is ground and crushed, a heat conversion experiment is carried out in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, under self-generated pressure in a N2 atmosphere, stirring, constant temperature for a certain time, discharging the system pressure, and natural cooling to room temperature to obtain the mesophase pitch. Step (2) preparation of artificial graphite material Take needle coke powder, add the mesophase pitch of step (1) to it, mix the two in a mixer until they are evenly mixed, stir for a certain time, set the frequency, and place the mixture in a self-made converter under N2 protection to granulate. Heat to the specified temperature at a certain heating rate, then place the granulated mixture in a graphitization furnace, and after high-temperature graphitization, an artificial graphite material is obtained. The mass fraction of the mesophase pitch is 8%. Step (3) preparation of pitch-coated silicon-carbon composite particles Take the artificial graphite of step (2) and mix it with the silicon material, then add the mesophase pitch of step (1). After adding a certain amount of anhydrous ethanol, wet mix using a planetary ball mill. Pour the mixed material into a beaker and dry it in a forced air drying oven to obtain a silicon-carbon composite precursor. Pre-carbonize in an argon atmosphere, then carbonize at a higher temperature. Grind and sieve the carbonized material to obtain pitch-coated silicon-carbon composite particles. Step (4) preparation of carbon nanotube conductive agent Place the silicon substrate with a catalyst system into a tube furnace, purge the quartz tube with Ar, and start heating while purging with hydrogen. As the temperature gradually rises, the iron film slowly cracks. Increase the temperature and anneal for a certain time. The iron film cracks into uniform-sized iron nanoparticles. Then, under a certain atmosphere, control the time to prepare the carbon nanotube conductive agent. After natural cooling, remove the product and mechanically peel it off. Step (5) preparation of glucose-based hard carbon precursor Mix glucose and water to obtain a glucose solution. Add the glucose solution and water to a stainless steel high-pressure reaction kettle. After hydrothermal reaction at a certain temperature, naturally cool to room temperature. Wash with deionized water and filter until neutral. Dry the obtained solid precipitate in a forced air drying oven to obtain a glucose-based hard carbon precursor. Step (6) preparation of silicon-carbon composite fast-charging negative electrode material Add the glucose-based hard carbon precursor of step (5) to the pitch-coated silicon-carbon composite material of step (3) for coating. Finally, add the carbon nanotube conductive agent of step (4) and sinter in a tube furnace. Pre-carbonize the precursor at medium-low temperature, then heat and hold, grind and sieve to obtain a silicon-carbon composite fast-charging negative electrode material.

2. The preparation process of a fast-charging negative electrode material according to claim 1, characterized in that: Step (1) preparation of mesophase pitch After the raw pitch is ground and crushed, a heat conversion experiment is carried out in a stainless steel high-temperature high-pressure reaction kettle equipped with a temperature controller, at a heating rate of 5-8 ℃ / min, under self-generated pressure in a N2 atmosphere, stirring, constant temperature for 2-10 h at a predetermined temperature of 385-445 ℃, discharging the system pressure, and natural cooling to room temperature to obtain the mesophase pitch.

3. The preparation process of a fast-charging negative electrode material according to claim 2, characterized in that: Step (2) preparation of artificial graphite material Take 300~400g needle coke powder, add step (1) mesophase pitch to it, mix the two in a mixer for 1~2h at a frequency of 50~100Hz, and then place the mixture in a self-made rotary furnace under the protection of 0.1~0.3L / min N2, heat it to 650~700℃ at a heating rate of 3~5℃ / min, and then place the granulated mixture in a graphitization furnace, and graphitize it at a high temperature of 2800~3000℃ to obtain the artificial graphite material.

4. The preparation process of the fast-charging negative electrode material according to claim 3, characterized in that: Step (3) preparation of pitch-coated silicon-carbon composite particles Take 36~42g of the artificial graphite of step (2) and 4~6g of silicon material, then add the pitch of step (1), add anhydrous ethanol, and then use a planetary ball mill to wet mix for 5~6h, pour the mixed material into a beaker and dry it in a forced air drying oven to obtain a silicon-carbon composite precursor, pre-carbonize it at 900~1200℃ for 3~4h in an argon atmosphere, and then carbonize it at a higher temperature for 6~7h, grind the carbonized material through a 300~350 mesh sieve to obtain pitch-coated silicon-carbon composite particles.

5. The preparation process of the fast-charging negative electrode material according to claim 4, characterized in that: Step (4) preparation of carbon nanotube conductive agent Put the silicon substrate with a catalyst system into a tube furnace, purge the quartz tube with 1000~1200sccm Ar for 10~20min, start heating while purging with hydrogen, as the temperature gradually rises, the iron film slowly cracks, the temperature rises to 750~800℃, and the iron film cracks into uniform-sized iron nanoparticles after annealing for 5~10min, then prepare the carbon nanotube conductive agent by controlling the time to be 5~30min under the conditions of a water content of 150~180ppm, an ethylene flow rate of 100~120sccm, and a hydrogen flow rate of 700~750sccm, and then mechanically peel off the product after natural cooling.

6. The preparation process of the fast-charging negative electrode material according to claim 5, characterized in that: Step (5) preparation of glucose-based hard carbon precursor Mix 2.5~3g of glucose and 7.5~8g of water to obtain a 25~26% glucose solution, then add 25~26% glucose solution and 56.67~72.12g of water to a stainless steel high-pressure reaction kettle, and hydrothermally react at 240~280℃ for 4~5h, then naturally cool to room temperature, wash with deionized water and suction filter to neutral, and then dry the obtained solid precipitate in a forced air drying oven for 24~26h to obtain a glucose-based hard carbon precursor.

7. The preparation process of the fast-charging negative electrode material according to claim 6, characterized in that: Step (6) preparation of silicon-carbon composite fast-charging negative electrode material The pitch-coated silicon-carbon composite material of step (3) is coated with the glucose-based hard carbon precursor of step (5) in an additive amount of 10-12% of the mass of the pitch-coated silicon-carbon composite particles, and finally the carbon nanotube conductive agent of step (4) is added and sintered in a tube furnace, the precursor is pre-carbonized at a low temperature for 3-4 h after being heated to 350-400 DEG C, and then heated to 700-750 DEG C, and kept for 6-7 h, ground and sieved to obtain a silicon-carbon composite fast-charging negative electrode material.

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