Production process and device for preparing silicon-carbon negative electrode material from self-bonding coke

Abstract

A production process and device for preparing a silicon-carbon negative electrode material from self-bonding coke, comprising the following steps: 1) preparation of a silicon-carbon negative electrode precursor, silicon powder and graphite are uniformly mixed in a mixer; 2) preparation of self-bonding coke, using pitch as raw material, a coke with a certain range of volatile matter is prepared in a coking tower and crushed to a certain particle size; 3) preparation of a silicon-carbon negative electrode material, the self-bonding coke and the silicon-carbon negative electrode precursor are uniformly mixed in a certain proportion, and are placed in a carbonization furnace for carbonization to form a silicon-carbon negative electrode material. The self-bonding coke prepared in the present application can realize bonding and coating without adding another binder during the mixing and carbonization process of the silicon-carbon negative electrode precursor, solving the problems of uneven mixing of the binder and the silicon-carbon precursor and the non-compact carbon coating of silicon in the preparation process of the existing method, and the obtained silicon-carbon material has high tap density and compactness, good processability, high reversible specific capacity and excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode material production, and particularly relates to a production process and device for preparing silicon-carbon negative electrode material from self-bonding coke. BACKGROUND

[0002] Lithium ion batteries have been widely used in 3C electronic products, electric tools, medical electronics, energy storage equipment and other fields due to their high energy density, high power density, long service life, low self-discharge rate, no memory effect, safety, low pollution and other advantages, and gradually popularized in pure electric vehicles, hybrid electric vehicles, rail transportation, aerospace and other transportation fields. At present, China has become the world's largest lithium ion battery production and manufacturing base and the second largest lithium ion battery production and export country. With the rapid increase of battery energy density requirements in various fields, high energy density lithium ion batteries are the focus of research and development.

[0003] In the current negative electrode system, the theoretical lithium intercalation capacity of silicon (3500-4200 mAh / g) is about 10 times that of graphite (372 mAh / g), and silicon is abundant, non-toxic, non-polluting, and has a low lithium intercalation platform (about 0.37 V), making it a widely studied negative electrode material for lithium ion batteries. However, silicon has low electrical conductivity and undergoes significant volume expansion when lithium is intercalated or deintercalated, making it difficult to maintain the capacity advantage of the silicon negative electrode. Silicon-carbon composite negative electrode materials can effectively solve the problems of volume change, material structure damage, irreversible consumption of electrolyte, and negative electrode function failure of elemental silicon negative electrodes, and achieve significantly improved lithium storage performance.

[0004] Patent document CN111725507A discloses a high-compactness silicon-carbon negative electrode material for lithium ion batteries and a preparation method thereof. The method controls the furnace pressure of the nitrogen atmosphere protection furnace to form a gas-solid two-phase interface on the surface of the silicon-carbon negative electrode with the smoke volatilized from the pitch, thereby reducing the amount of pitch used and obtaining a silicon-carbon negative electrode material with high compactness and excellent cycle performance. This method improves the unevenness of the surface carbon coating to some extent, but still requires the addition of a binder, which is difficult to control during the mixing process and may result in uneven mixing. Moreover, after the addition of pitch, the graphitization degree of the obtained silicon-carbon negative electrode material decreases, resulting in a decrease in capacity. Patent document CN109920982A discloses a preparation method for a silicon-carbon negative electrode material for lithium ion batteries. The method involves crushing active carbon material, mixing it with nano-silicon slurry and soft pitch, coking and carbonizing, and then crushing and sieving the product to obtain a 5-30 μm product as a silicon-carbon negative electrode material. This method is simple, but the soft pitch has a low coking value, and the light components are lost during coking and carbonization after mixing with the carbon source and silicon source, resulting in an unstable coating layer on the surface, low tap density, and poor processing performance. SUMMARY

[0005] The application provides a production process and device for preparing a silicon-carbon negative electrode material from self-bonding coke.

[0006] To achieve the above object, the application adopts the following technical solutions:

[0007] The production process for preparing the silicon-carbon negative electrode material from the self-bonding coke specifically comprises the following steps:

[0008] 1) Preparation of a silicon-carbon negative electrode precursor: uniformly mix nano-silicon and graphite in a mixer;

[0009] 2) Preparation of self-bonding coke: melt solid pitch or send liquid pitch into a heating furnace for heating, then send it into a coking tower from the bottom of the coking tower for coking reaction to obtain self-bonding coke, and send the oil gas generated at the top of the coking tower into a flash distillation tower, cool the oil gas at the top of the flash distillation tower, send the light components at the top of the flash distillation tower into a light oil receiving tank, and send the heavy distillates at the bottom of the flash distillation tower to a heavy oil receiving tank or circulate to a pitch raw material tank to realize partial reflux;

[0010] 3) Preparation of a silicon-carbon negative electrode material: crush and sieve the self-bonding coke obtained in step 2) to D50 of 2-3 microns, uniformly mix the self-bonding coke with the silicon-carbon negative electrode precursor prepared in step 1) in a mixer, and send the mixture to a carbonization furnace to prepare the silicon-carbon negative electrode material.

[0011] In step 1) above, the mass ratio of the nano-silicon is 10%-50%, and the mass ratio of the graphite is 50%-90%.

[0012] In step 3) above, the mass ratio of the silicon-carbon negative electrode precursor is 70%-90%, and the mass ratio of the self-bonding coke is 10%-30%.

[0013] The pitch is one or more of coal pitch, petroleum pitch, spinnable pitch and mesophase pitch.

[0014] The preparation process conditions of the self-bonding coke in the coking tower are as follows: a temperature rising rate of 2-8 ℃ / min at 400-520 ℃, a constant temperature time of 2-5 h at 520 ℃, and a pressure of 0.2-0.5 MPa; and the volatile content of the self-bonding coke is 10%-20%.

[0015] In step 1) above, the mixer is a VC mixer, and the motor frequency during mixing is 50-60 HZ.

[0016] In step 3) above, the carbonization process conditions are as follows: a temperature of 500-1200 ℃, and a temperature rising rate of 2-5 ℃ / min.

[0017] The prepared silicon-carbon negative electrode material has a capacity of 700 mAh / g to 1800 mAh / g, a first coulombic efficiency of 83% to 92%, and a capacity retention rate of 65% to 95% after 0.1C cycles for 100 times.

[0018] The device for the production process of the self-bonding coke for preparing the silicon-carbon negative electrode material comprises a pitch melting tank, a liquid pitch storage tank, a heating furnace, a coking tower, a crusher, a screening machine, a mixer I, a mixer II, a carbonization furnace, a disperser, a magnetic field eliminator, a finished product bin and a flash distillation tower.

[0019] The graphite raw material and the silicon raw material are mixed in the mixer I, the mixer I feeds the mixer II, the mixer II feeds the carbonization furnace, and the outlet of the carbonization furnace is sequentially connected with the disperser, the magnetic field eliminator and the finished product bin.

[0020] Compared with the prior art, the self-bonding coke for preparing the silicon-carbon negative electrode material has the following beneficial effects:

[0021] 1) The self-bonding coke prepared by controlling the preparation process has a volatile content within a certain range, the raw material is easy to obtain, the coke is crushed to a certain particle size and then mixed with a silicon-carbon precursor, and the carbonization process is controlled to uniformly coat the coke and the precursor, so that the volume expansion of silicon in the silicon-carbon negative electrode material is reduced.

[0022] 2) The self-bonding coke is mixed with the precursor without introducing a binder, the whole material preparation process is simple to operate, the equipment is common industrial equipment, the raw material is economical, the pollution is small, and the industrialization is easy.

[0023] 3) The physicochemical index test of the self-bonding coke for preparing the silicon-carbon negative electrode material shows that the tap density is greater than or equal to 1.1 g / cm 3 , the compacted density is greater than or equal to 1.25 g / cm 3 , which is higher than the first-class standard in the national standard GB / T38823-2020 of the silicon-carbon, and the processing performance is excellent.

[0024] 4) Electrochemical tests of the self-adhesive coke-coated silicon-carbon anode material prepared by the present invention show that the reversible capacity of the material reaches 700 mAh / g to 1800 mAh / g, the initial coulombic efficiency is 83% to 92%, and the capacity retention rate is 65% to 95% after 100 cycles at 0.1C, which shows good cycling performance.

[0025] 5) This invention obtains self-adhesive coke with volatile content of 10% to 20% by controlling the process. This ensures that it can be bonded and coated with silicon-carbon anode precursor without the need for additional binder during mixing and carbonization. It also avoids reducing the capacity of the material due to the high light component content when making anode material. This solves the problems of uneven mixing of binder and silicon-carbon precursor and poor carbon coating of silicon in the preparation process of existing methods. Attached Figure Description

[0026] Figure 1 This is the process route diagram of the present invention.

[0027] Figure 2 This is the XRD pattern of the silicon-carbon anode material prepared in Example 1.

[0028] Figure 3 This is a SEM image of the silicon-carbon anode material prepared in Example 1.

[0029] Figure 4 This is a charge-discharge curve of the silicon-carbon anode material prepared in Example 1.

[0030] Figure 5 This is a comparison chart of the cycling curves of the silicon-carbon anode material prepared in Example 1 and the silicon-carbon material prepared in Comparative Example 1.

[0031] Figure 1 In the middle: 1-Asphalt raw material silo, 2-1 Asphalt melting tank, 2-2 Liquid asphalt storage tank, 3-Heating furnace, 4-Coking tower, 5-Crusher, 6-Screwing machine, 7-Screw feeder, 8-Mixer I, 9-Mixer II, 10-Carbonization furnace, 11-Disperser, 12-Demagnetizer, 13-Finished product silo, 14-Flash distillation tower, 15-Light oil receiving tank, 16-Heavy oil receiving tank, 17-Graphite silo, 18-Silicon silo. Detailed Implementation

[0032] The implementation of the present invention will be further described below with reference to specific embodiments:

[0033] like Figure 1 As shown, a production process for preparing silicon-carbon anode materials using self-adhesive coke specifically includes the following steps:

[0034] 1) Preparation of silicon-carbon anode precursor: Nano-silicon and graphite are mixed evenly in a mixer;

[0035] 2) Self-bonding coke preparation: melt solid pitch or send liquid pitch into a heating furnace for heating, then send into a coking tower from the bottom for coking reaction, control the reaction conditions to obtain self-bonding coke, and the oil gas generated at the top of the coking tower enters a flash distillation tower, and the light components at the top of the flash distillation tower enter a light oil receiving tank, and the heavy fraction at the bottom of the flash distillation tower is transported to a heavy oil receiving tank or a circulating tank.

[0036] 3) Silicon-carbon negative electrode material preparation: crush and sieve the self-bonding coke obtained in step 2) to D50 of 2-3 μm, mix the self-bonding coke with the silicon-carbon negative electrode precursor prepared in step 1) in a mixer, transport the mixture to a carbonization furnace, and control the carbonization program to obtain the silicon-carbon negative electrode material.

[0037] The mass ratio of the nano-silicon in step 1) is 10%-50%, and the mass ratio of the graphite is 50%-90%.

[0038] The mass ratio of the silicon-carbon negative electrode precursor in step 3) is 70%-90%, and the mass ratio of the self-bonding coke is 10%-30%.

[0039] The pitch is one or more of coal pitch, petroleum pitch, spinnable pitch, and mesophase pitch.

[0040] The preparation process conditions of the self-bonding coke in the coking tower are: a temperature rising rate of 2-8 ℃ / min at 400 ℃-520 ℃, a constant temperature time of 2-5 h at 520 ℃, and a pressure of 0.2-0.5 MPa; and the volatile content of the self-bonding coke is 10%-20%.

[0041] The mixer in step 1) is a VC mixer, and the motor frequency during mixing is 50-60 HZ.

[0042] The carbonization process conditions in step 3) are: a temperature of 500 ℃-1200 ℃, and a temperature rising rate of 2-5 ℃ / min.

[0043] The tap density of the prepared silicon-carbon negative electrode material is ≥1.1 g / cm 3 , the compacted density is ≥1.25 g / cm 3 , the capacity is 700-1800 mAh / g, the first coulombic efficiency is 83%-92%, and the capacity retention rate after 0.1 C cycle for 100 times is 65%-95%.

[0044] The apparatus used in a process for preparing silicon-carbon anode materials from self-adhesive coke includes an asphalt raw material silo 1, an asphalt melting tank 2-1, a liquid asphalt storage tank 2-2, a heating furnace 3, a coking tower 4, a crusher 5, a screening machine 6, a screw feeder 7, a mixer I 8, a mixer II 9, a carbonization furnace 10, a dispersant 11, a demagnetizer 12, a finished product silo 13, a flash distillation tower 14, a light oil receiving tank 15, a heavy oil receiving tank 16, a graphite silo 17, and a silicon material silo 18. The asphalt raw material enters the asphalt melting tank 2-1 from the asphalt raw material silo 1 via a bucket elevator. The asphalt melting tank 2-1 and / or the liquid asphalt storage tank 2-2... The outlet of the heating furnace 3 is connected to the inlet of the heating furnace 3. The outlet of the heating furnace 3 is connected to the coking tower 4. The light phase outlet of the coking tower 4 is connected to the flash distillation tower 14. The heavy phase outlet of the coking tower 4 feeds to the crusher 5. The crusher 5 feeds to the screening machine 6. The graphite silo 17 and the silicon silo 18 are connected to the mixer I 8. The screening machine 6 and the mixer I 8 feed to the mixer II 9. The mixer II 9 feeds to the carbonization furnace 10. The material in the carbonization furnace 10 is sent to the finished product silo 13 after passing through the disperser 11 and the demagnetizer 12. The light phase outlet of the flash distillation tower 14 is connected to the light oil receiving tank 15. The heavy phase outlet of the flash distillation tower 14 is connected to the heavy oil receiving tank 16.

[0045] Example 1:

[0046] Nano-silicon and artificial graphite were mixed in a mixer at a ratio of 20 wt%: 80 wt% and set aside. Coal-based medium-temperature pitch was conveyed to a melting tank via a bucket elevator for melting, then pumped into a heating furnace for heating, and finally conveyed to a coking tower. The temperature was increased from 410℃ to 520℃ at a rate of 3℃ / h, with a pressure of 0.2 MPa and a holding time of 2 hours, yielding self-adhesive coke with a measured volatile content of 12.3%. The self-adhesive coke was crushed to obtain coke powder, which was then sieved to a particle size of D. 50 The particle size is 2-3 μm. The sieved self-adhesive coke and silicon-carbon precursor are mixed in a mixer at a ratio of 15 wt% to 85 wt% with a motor frequency of 50 Hz. After mixing for 2 hours, the mixture is conveyed to a carbonization furnace and carbonized under inert gas protection at a temperature range of 500℃ to 1200℃ with a heating rate of 3℃ / min. After carbonization, the material is dispersed and demagnetized before entering the finished product silo. A battery is assembled using this material as the negative electrode and lithium foil as the positive electrode for testing. The electrochemical performance is shown in Table 1.

[0047] The XRD pattern of the prepared silicon-carbon anode material is shown in the figure. Figure 2 As shown in the figure, typical diffraction peaks of graphite and silicon can be observed, while self-adhesive coke transforms into amorphous soft carbon. Figure 3 The image shows the SEM pattern of the prepared silicon-carbon anode material, which reveals that nano-silicon and self-adhesive coke are uniformly loaded or bonded to the surface of graphite particles.

[0048] from Figure 4 Charge and discharge curves and Figure 5From the contrastive graph of cycle curves, it can be seen that the tap density of the silicon-carbon negative material prepared by self-bonding coke is 1.1190 g / cm 3 , the compacted density is ≥1.2828 g / cm 3 , the reversible capacity reaches 921.9 mAh / g, the first efficiency is 89.3%, after 0.1C cycle for 100 weeks, the capacity retention rate is 90.6%, and the cycle performance is better than that of the conventional pitch-coated silicon-carbon composite material.

[0049] Example 2:

[0050] The nano-silicon and artificial graphite are mixed at 30wt%:70wt% in a mixer for standby; the petroleum-based medium-temperature pitch is conveyed to a melting tank by an elevator for melting, is pumped into a heating furnace for heating, and is conveyed to a coking tower, the temperature is raised from 410°C to 520°C at a temperature raising rate of 5°C / h, the pressure is 0.2MPa, the constant temperature time is 4h, and the self-bonding coke is obtained, and the volatile matter is 16.7% measured. The self-bonding coke is crushed to obtain coke powder, and the coke powder is screened, the screening particle size is D 50 2-3μm; the screened self-bonding coke and the silicon-carbon precursor are mixed at 20wt%:80wt% in the mixer, the motor frequency is 50Hz; after mixing for 2h, the mixture is conveyed to a carbonization furnace, and is subjected to carbonization treatment under inert gas protection, the temperature interval is controlled to be 500°C-1200°C, the temperature raising rate is 4°C / min, after the carbonization is completed, the material is subjected to magnetic removal by being scattered, and is conveyed to a finished product bin; the battery is assembled by taking the material as a negative electrode and taking lithium sheet as a positive electrode, and the electrochemical performance is shown in Table 1.

[0051] Example 3:

[0052] The nano-silicon and artificial graphite are mixed at 40wt%:60wt% in a mixer for standby; the mesophase pitch is conveyed to a melting tank by an elevator for melting, is pumped into a heating furnace for heating, and is conveyed to a coking tower, the temperature is raised from 410°C to 520°C at a temperature raising rate of 5°C / h, the pressure is 0.3MPa, the constant temperature time is 4h, and the self-bonding coke is obtained, and the volatile matter is 14.1% measured. The self-bonding coke is crushed to obtain coke powder, and the coke powder is screened, the screening particle size is D 50 2-3μm; the screened self-bonding coke and the silicon-carbon precursor are mixed at 50wt%:75wt% in the mixer, the motor frequency is 60Hz; after mixing for 2h, the mixture is conveyed to a carbonization furnace, and is subjected to carbonization treatment under inert gas protection, the temperature interval is controlled to be 500°C-1200°C, the temperature raising rate is 5°C / min, after the carbonization is completed, the material is subjected to magnetic removal by being scattered, and is conveyed to a finished product bin; the battery is assembled by taking the material as a negative electrode and taking lithium sheet as a positive electrode, and the electrochemical performance is shown in Table 1.

[0053] Comparative Example 1:

[0054] The nano-silicon, artificial graphite and 2.8 μm coal pitch are mixed in a mixer at 17 wt%: 68 wt%: 15 wt% with a motor frequency of 50 Hz; after mixing for 2 h, the mixture is delivered to a carbonization furnace, and carbonization treatment is carried out under inert gas protection, with a temperature range of 500-1200 ℃ and a heating rate of 3 ℃ / min; after the carbonization is completed, the material is dispersed and demagnetized to enter a finished product bin; the product is used as a negative electrode, and a lithium sheet is used as a positive electrode to assemble a battery for testing, and the electrochemical performance is shown in Table 1.

[0055] Table 1 Performance indicators of the self-bonding coke and silicon-carbon negative electrode material after discharging

[0056]

[0057] As shown in Table 1, the reversible capacity of the negative electrode material of the present application is 921.9 mAh / g, the initial efficiency is 89.3%, and after 100 cycles at 0.1 C, the capacity remains 835.6 mAh / g, and the capacity retention rate is 90.6%, which has good cycle performance. The silicon-carbon negative electrode material prepared by simply coating with coal pitch has a reversible capacity of 972.9 mAh / g, but after 100 cycles, only 633.7 mAh / g remains, and the capacity retention rate is only 65.1%. It can be seen that the silicon-carbon negative electrode material prepared by coating with the self-bonding coke of the present application has better cycle performance than the silicon-carbon negative electrode material prepared by coating with conventional pitch.

Claims

1. A production process for the preparation of a self-binding pitch-derived silicon-carbon anode material, characterized in that, Specifically comprising the following steps: 1) Preparation of silicon-carbon negative electrode precursor: uniformly mix nano-silicon and graphite in a mixer; 2) Preparation of self-bonding coke: melt solid pitch or send liquid pitch into a heating furnace for heating, then send into a coking tower for coking reaction to obtain self-bonding coke, the oil gas generated at the top of the coking tower enters a flash distillation tower, and the oil gas at the top of the flash distillation tower is cooled, the light components at the top of the flash distillation tower enter a light oil receiving tank, and the heavy fraction at the bottom of the flash distillation tower is transported to a heavy oil receiving tank or recycled to a pitch raw material tank; The preparation process conditions of the self-bonding coke in the coking tower are: a temperature rising rate of 2-8℃ / min at 400-520℃, a constant temperature time of 2-5h at 520℃, and a pressure of 0.2-0.5MPa; the volatile matter of the self-bonding coke is 10%-20%; 3) Preparation of silicon-carbon negative electrode material: crush and sieve the self-bonding coke obtained in step 2) to D50 of 2-3μm, uniformly mix with the silicon-carbon negative electrode precursor prepared in step 1) in a mixer, and transport the mixture to a carbonization furnace to prepare the silicon-carbon negative electrode material.

2. The process for producing a self-bonding silicon-carbon negative electrode material according to claim 1, characterized in that, The mass ratio of nano-silicon in step 1) above is 10%-50%, and the mass ratio of graphite is 50%-90%.

3. The process for producing a self-bonding silicon-carbon negative electrode material according to claim 1, characterized in that, The mass ratio of the silicon-carbon negative electrode precursor in step 3) above is 70%-90%, and the mass ratio of the self-bonding coke is 10%-30%.

4. The process for producing a self-bonding silicon-carbon negative electrode material according to claim 1, characterized in that, The pitch is one or more of coal pitch, petroleum pitch, spinnable pitch, and mesophase pitch.

5. The process for producing a self-bonding silicon-carbon negative electrode material according to claim 1, characterized in that, The mixer in step 1) above is a VC mixer, and the motor frequency during mixing is 50-60HZ.

6. The process for producing a self-bonding silicon-carbon negative electrode material according to claim 1, characterized in that, The carbonization process conditions in step 3) above are: 500-1200℃, and a temperature rising rate of 2-5℃ / min.

7. The process for producing a self-bonding silicon-carbon negative electrode material according to claim 1, characterized in that, The prepared silicon-carbon negative electrode material has a capacity of 700-1800mAh / g, a first coulombic efficiency of 83%-92%, and a capacity retention rate of 65%-95% after 0.1C cycle for 100 times.

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