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CN-121990576-A - Preparation method and device of silicon-based negative electrode precursor silicon material of lithium ion battery

CN121990576ACN 121990576 ACN121990576 ACN 121990576ACN-121990576-A

Abstract

The invention discloses a preparation method and a device of a silicon-based negative electrode precursor silicon material of a lithium ion battery. The method comprises the steps of (1) loading and vacuumizing, (2) melting and homogenizing, (3) directional solidification, namely, when the temperature of the silicon material is reduced to the initial solidification temperature of 1410-1420 ℃, starting the active cooling unit, introducing cooling liquid into a cooling flow channel in the water-cooled cooling plate, controlling the instantaneous cooling rate in the process of reducing the solid-phase silicon material from 1410-1420 ℃ to 1240 ℃ to be 3.5-5.5 ℃ per min, finally solidifying the silicon material into a silicon ingot, (4) annealing, and (5) cooling.

Inventors

  • KOU CUIQING
  • LIU MENG

Assignees

  • 宁晋县氢为新能源科技有限公司

Dates

Publication Date
20260508
Application Date
20260122

Claims (10)

  1. 1. A preparation method of a silicon-based negative electrode precursor silicon material of a lithium ion battery based on directional solidification is characterized in that solar-grade silicon material is prepared in a polycrystalline silicon ingot furnace with a heating and heat insulation system modified, wherein, The transformation mode of the heating heat insulation system of the polysilicon ingot furnace is that 4-9 quartz crucibles with the same size are uniformly arranged on a heat exchange table to replace the original standard large-size quartz crucible, and the adjacent quartz crucibles are separated by a heat insulation plate with the height not lower than the top of the quartz crucible to form independent smelting units which are mutually heat-insulated; The preparation method comprises the following steps: (1) Charging and vacuumizing, namely respectively charging solar-grade silicon materials into each small quartz crucible, closing a lifting heat insulation bottom plate and a heat insulation cage, closing a furnace body, and vacuumizing; (2) Melting and homogenizing, namely electrifying and heating to 1420-1450 ℃ to enable the silicon material to be completely melted, and preserving heat for a period of time to ensure that the components are uniform; (3) The directional solidification comprises the steps of starting an active cooling unit when the temperature of the silicon material is reduced to an initial solidification temperature of 1410-1420 ℃, and introducing cooling liquid into a cooling flow channel in a water-cooling cold plate, controlling the instantaneous cooling rate of the solid phase silicon material in the process of reducing the temperature of 1410-1420 ℃ to 1240-1250 ℃ to be maintained within 3.5-5.5 ℃ per minute, and finally solidifying the silicon material into a silicon ingot; (4) Annealing, namely annealing the obtained silicon ingot after solidification is completed; (5) And cooling, namely cooling the silicon ingot to a safe discharging temperature after annealing is finished, and taking out the silicon ingot to obtain the silicon-based negative electrode precursor silicon material of the lithium ion battery.
  2. 2. The preparation method of the polycrystalline silicon ingot furnace is characterized in that in the step (3), when the temperature of a silicon material is reduced to an initial solidification temperature of 1410-1420 ℃, an active cooling unit is synchronously started, cooling liquid is introduced into a cooling flow channel in a water-cooling cold plate and a furnace body jacket, a heat insulation bottom plate is controlled to be reduced from a closed position to a heat dissipation working position 200-250 mm away from a heat exchange table, meanwhile, a control system of the polycrystalline silicon ingot furnace collects the temperature data of the silicon material at a frequency of 10-30 seconds, an instantaneous cooling rate is calculated, and the flow rate/flow rate of the cooling liquid and the power of a heating assembly are dynamically adjusted, so that the instantaneous cooling rate of the silicon material in the process of reducing the temperature of 1410-1420 ℃ to 1240-1250 ℃ is accurately stabilized at 3.5-5.5 ℃/min.
  3. 3. The method according to claim 2, wherein 4 quartz crucibles of the same size are arranged in a2 x 2 array or 8 quartz crucibles of the same size are arranged in a3 x 3 decentered array on the original heat exchange table.
  4. 4. The preparation method of the polycrystalline silicon ingot furnace is characterized in that the water-cooling cold plate is made of high-heat-conductivity metal, a spiral cooling flow passage is arranged in the water-cooling cold plate, a high-emissivity ceramic coating is sprayed on the upper surface of the water-cooling cold plate after precise polishing, a water inlet pipe and a water outlet pipe of the cooling flow passage are connected with a cooling liquid source outside the polycrystalline silicon ingot furnace, and the high-emissivity ceramic coating has full-band infrared emissivity epsilon of more than or equal to 0.90 in an oxidizing atmosphere at 500-1000 ℃ and has a thickness of 20-50 mu m.
  5. 5. The method according to claim 4, wherein the heating elements provided on the side of the quartz crucible are divided into upper, middle and lower sections, each section is independently powered and has adjustable power, and in step (3), the power of the heating elements of the upper, middle and lower sections is maintained to be increased from bottom to top.
  6. 6. A polycrystalline silicon ingot furnace for preparing a silicon-based negative electrode precursor silicon material of a lithium ion battery comprises a furnace body and a heating heat insulation system in the furnace body, wherein the heating heat insulation system comprises a heat insulation cage, a heat insulation bottom plate, a heating assembly, a heat exchange table and a quartz crucible, a parallel driving screw rod system is arranged at the lower part of the heat insulation bottom plate to enable the heat insulation bottom plate to achieve a lifting function, the heat insulation bottom plate is matched with the heat insulation cage arranged above the heat insulation bottom plate when the heat insulation bottom plate operates to the highest position to form a closed cavity, the heat exchange table is fixed at the upper part of the heat insulation bottom plate, the heating assembly is positioned at the inner side of the heat insulation cage and surrounds the upper part and the periphery of the quartz crucible when the heat insulation bottom plate and the heat insulation cage are closed, and is characterized in that 4-9 quartz crucibles with the same size are uniformly arranged on the heat exchange table to replace the original standard large-size quartz crucible, adjacent quartz crucibles are separated by a heat insulation plate with the height not lower than the top of the heat exchange table to form independent units which are mutually thermally isolated, and a water cooling plate is embedded into the upper surface of the heat insulation bottom plate as an active cooling unit, and the area of the water cooling plate is not smaller than the projection scope of the bottom of the quartz crucible.
  7. 7. The polycrystalline silicon ingot furnace according to claim 6, wherein 4 quartz crucibles of the same size are arranged in a2 x 2 array or 8 quartz crucibles of the same size are arranged in a3 x 3 decentration array on a heat exchange table.
  8. 8. The polysilicon ingot furnace of claim 7, wherein a blind hole is formed at the bottom of the heat exchange table corresponding to the bottom center of each quartz crucible, a high temperature resistant thermocouple is embedded in the blind hole, the temperature measuring end of the blind hole is tightly attached to the heat exchange table, meanwhile, a through hole coaxially aligned with the blind hole is correspondingly formed in the heat insulation bottom plate and the water cooling cold plate, a signal lead of the high temperature resistant thermocouple penetrates through the through hole and can adapt to the up-and-down movement of the heat insulation bottom plate, and the signal lead of the high temperature resistant thermocouple is led out of the furnace body through a high temperature vacuum sealing joint and is connected to a control system of the polysilicon ingot furnace.
  9. 9. The polycrystalline silicon ingot furnace of claim 8, wherein the heat insulation plate is made of graphite or carbon fiber composite material, the water-cooling cold plate is made of high-heat-conductivity metal, a spiral cooling flow passage is arranged in the water-cooling cold plate, a water inlet pipe and a water outlet pipe of the cooling flow passage are connected with a cooling liquid source outside the polycrystalline silicon ingot furnace, a high-emissivity ceramic coating is sprayed on the upper surface of the water-cooling cold plate, the full-band infrared emissivity epsilon of the high-emissivity ceramic coating in an oxidizing atmosphere at 500-1000 ℃ is more than or equal to 0.90, and the thickness of the high-emissivity ceramic coating is 20-50 mu m.
  10. 10. The polycrystalline silicon ingot furnace of claim 9, wherein the upper surface of the water-cooling cold plate is flush with or slightly higher than the upper surface of the heat insulation bottom plate by 0.1-0.5 mm, the water-cooling cold plates are arranged into a plurality of small water-cooling cold plates which are respectively in one-to-one correspondence with the quartz crucibles, the small water-cooling cold plates are used for independently cooling the quartz crucibles, the quartz crucibles are coaxially aligned with the corresponding water-cooling cold plates, a through hole is reserved in the geometric center of the water-cooling cold plates, and the through hole is coaxially aligned with the blind hole of the heat exchange table.

Description

Preparation method and device of silicon-based negative electrode precursor silicon material of lithium ion battery Technical Field The invention particularly relates to a preparation method of a silicon-based negative electrode precursor silicon material for a high-energy-density lithium ion battery and a special device thereof, wherein the lithium ion battery comprises, but is not limited to, a solid electrolyte system and a liquid electrolyte system. Background Silicon is considered as an ideal negative electrode material for replacing graphite (372 mAh/g) because of its extremely high theoretical specific capacity (about 4200 mAh/g), proper lithium intercalation potential (0.1-0.4V vs. Li +/Li) and abundant resources. However, silicon has a volume expansion rate of over 300% during charge and discharge, which is prone to electrode pulverization and cycle failure. In order to alleviate this problem, especially for solid-state lithium ion batteries, micron-sized silicon particles (d50=1 to 2 μm) are often used and the Particle size distribution is controlled to improve the cycle stability. Mechanical comminution is the primary means of obtaining the size particles. Researches show that if the Grain size (Grain) of the precursor polysilicon is controlled within the range of 20-50 mu m, the precursor polysilicon is easier to break along Grain boundaries in the subsequent crushing process, so that silicon powder with uniform morphology and fewer defects is obtained, and meanwhile, the energy consumption is remarkably reduced. Currently, the main preparation method of the silicon-based negative electrode precursor silicon material of the lithium ion battery comprises a chemical reduction method (such as Mg reduction SiO 2), a plasma method/vapor deposition method and a ball milling crushing method. However, the above main stream preparation methods have the following problems, respectively: (1) The chemical reduction method is that although submicron to micron-sized powder can be obtained, the content of oxygen and carbon impurities in the product is high (O is more than 2 wt percent, C is more than 0.2 wt percent), so that the first coulomb efficiency of the lithium ion battery is generally lower than 75 percent, and the post-treatment process of the method is complex; (2) The plasma method/vapor deposition method can prepare high-purity nano silicon, but has large equipment investment and high energy consumption, so that the production cost is high, the economic feasibility is not realized, and the large-scale production is difficult to realize; (3) The ball milling crushing method is that the ball milling crushing of the photovoltaic polycrystalline silicon ingots is the route closest to mass production at present, but the particle size of silicon particles is difficult to control, so that the particle size distribution is extremely wide, the inventor adopts the polycrystalline silicon ingots in the photovoltaic industry to carry out ball milling crushing, and finds that the particle size distribution of the crushed silicon particles is extremely wide, particularly D10 is 5 mu m, D90 is 150 mu m, RSD is more than 60% (relative standard Deviation RELATIVE STANDARD devitation, RSD, namely the ratio of standard Deviation to average value is expressed in percentage) and is used for representing the discrete degree of data), and the ball milling process leads the silicon surface to be easily oxidized seriously (O is more than 2 wt percent), acid washing passivation is needed, and further cost is increased and pollution is introduced. In other words, the existing preparation method of the silicon-based negative electrode precursor silicon material of the lithium ion battery cannot be achieved in three aspects of purity, particle size uniformity and cost controllability. Therefore, how to prepare a silicon material with high purity and uniform particle size in a low-cost manner becomes a key technical bottleneck to be solved in the lithium ion battery industry. In the prior art, the main stream method for producing polysilicon in the photovoltaic industry is a directional solidification method, and the whole production process can be completed in one polysilicon ingot furnace. Therefore, the method has the advantages of simple process, low production equipment cost, large grain size and high purity, and is stable in growth, and the method is difficult to meet the core requirements of the lithium ion battery on the fine grain, uniformity and the like of the cathode precursor silicon material due to the characteristics of coarse grain, serious doping segregation and the like, so that reports of preparing the battery-grade silicon material by using the method are not seen. The existing polysilicon ingot furnace generally comprises a furnace body, a heating heat insulation system, a vacuum and air supply system, a cooling system and a power supply and control system, wherein a JJL series polysilicon ingot furnace pro