Non-fluidization preparation method of silicon-carbon negative electrode and reactor for method

Abstract

The invention discloses a non-fluidization preparation method of a silicon-carbon negative electrode and a reactor for the method. The preparation method comprises the following steps: in a heating environment, mixing silane gas with a carbon matrix for reaction to obtain silicon-carbon particles; and then carrying out carbon coating on the silicon-carbon particles to obtain the silicon-carbon negative electrode. Wherein the flow velocity V of the silane gas is equal to u * A. The invention discloses a non-fluidized tubular reaction method for the first time, the method has certain advantages, and in a tubular reactor, process parameters are designed, and silicon particles can be deposited in a carbon material through a chemical vapor deposition method to form a silicon-carbon composite structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to a method for producing a silicon-carbon negative electrode, specifically a non-fluidized preparation method and a tubular reactor for a silicon-carbon negative electrode, which discloses for the first time the non-fluidized preparation of a silicon-carbon negative electrode. Background Art

[0002] The rapid development of the new energy industry has driven a research boom in silicon-carbon negative electrode materials. Silicon has the advantage of high specific capacity, while carbon materials can effectively alleviate the volume change of silicon during the charging and discharging process, making silicon-carbon composite materials an ideal choice for negative electrode materials for lithium-ion batteries.

[0003] Common methods for synthesizing silicon-carbon composite materials all use reactors for fluidized deposition. Fluidized bed reactors can achieve full mixing of silicon and carbon materials to form a uniform silicon-carbon composite structure. However, production has found that small-particle carbon materials are prone to channeling in the fluidized bed, affecting the deposition efficiency. Although channeling can be suppressed to a certain extent by adjusting the gas velocity, it leads to poor internal conditions of the fluidized bed and still cannot achieve good technical results.

[0004] In general, the rapid development of the new energy industry has promoted the research of silicon-carbon anode materials. Fluidized bed reaction is a commonly used preparation method, but the problem of fluidization performance needs to be solved. Therefore, it is necessary to further improve the preparation efficiency and performance of silicon-carbon composite materials by optimizing reaction conditions and reactor design. Summary of the invention

[0005] The present invention discloses for the first time a non-fluidized tubular reaction method having certain advantages. In a tubular reactor, by designing process parameters, silicon particles can be deposited in a carbon material by chemical vapor deposition to form a silicon-carbon composite structure.

[0006] The present invention adopts the following technical scheme.

[0007] A non-fluidized preparation method for a silicon-carbon negative electrode comprises the following steps: in a heating environment, silane gas is mixed with a carbon matrix to react to obtain silicon-carbon particles; the silicon-carbon particles are then carbon-coated to obtain a silicon-carbon negative electrode; wherein the flow rate of the silane gas is V=u×A, A is the pipe diameter area, m2, u is the take-out speed m / s, and u is greater than 0.03 m / s.

[0008] In the present invention, the silane gas includes one or more of monosilane, disilane, trisilane and silicon tetrachloride.

[0009] Preferably, silane gas is mixed and reacted with the carbon matrix in a heating environment and in an inert gas to obtain silicon-carbon particles; the inert gas is one or more of nitrogen, helium, xenon, radon, neon and argon.

[0010] Preferably, the sum of the gas flow rates of the silane gas and the inert gas is V, V=u×A, A is the pipe diameter area, m2, u is the take-out speed m / s, and u is greater than 0.03 m / s.

[0011] Preferably, u is greater than 0.03 m / s and less than 0.1 m / s.

[0012] Further preferably, u is greater than 0.03 m / s and less than 0.06 m / s.

[0013] Preferably, the gas flow ratio of silane gas to inert gas is 1: (0.1-10); further preferably, the gas flow ratio of silane gas to inert gas is 1: (0.5-5); even more preferably, the gas flow ratio of silane gas to inert gas is 1: (0.8-2), such as 1:1, 1:1.5, 1:2 or any ratio in the range.

[0014] In the present invention, carbon coating of silicon-carbon particles is to form a coating layer on the surface of the silicon-carbon core, including: carbon coating on the surface of silicon-carbon particles by at least one of ball milling, mechanical stirring, mechanical fusion, atomic layer deposition, vapor deposition, magnetron sputtering, liquid phase reaction, sol-gel, solvent thermal, vacuum thermal deposition, plasma sputtering or melting. Preferably, the coating layer raw material gas is introduced into the silicon-carbon particles, and the core-shell structure silicon-carbon negative electrode material is obtained after the reaction.

[0015] In the present invention, when the silane gas is mixed with the carbon matrix for reaction, the reaction temperature and time can refer to the reaction parameters of existing silicon and carbon materials; when the silicon-carbon particles are carbon-coated, the raw gas flow rate, reaction temperature and time can refer to the reaction parameters of the existing carbon coating layer formed on the surface of the silicon-carbon core.

[0016] As an example, when silane gas is mixed with a carbon matrix for reaction, the temperature of vapor deposition is 400° C.-900° C., and the time is 1-15 hours.

[0017] As an example, when silicon-carbon particles are carbon-coated, the reaction temperature is 500°C-900°C, and the reaction time is 1h-12h; the coating layer raw material gas includes one or more of methane, ethane, propane, acetylene, propyne, butyne, propylene, and ethylene.

[0018] In the present invention, the carbon matrix is ​​porous carbon, preferably, the particle size of the porous carbon is less than 20 microns, and more preferably, the particle size of the porous carbon is less than 10 microns, such as 0.1-10 microns, 0.5-10 microns, 1-10 microns. Porous carbon itself is an existing product. The present invention improves the deposition and coating of small-particle porous carbon, and solves the problem that in the existing sulfurization method, small-particle carbon materials are prone to channeling in the fluidized bed, affecting the deposition efficiency and even causing agglomeration.

[0019] In the present invention, the non-fluidized preparation method of the silicon-carbon negative electrode is carried out in a reaction tube, wherein the reaction tube comprises a reaction zone; an amplification zone is provided at the upper end of the reaction zone, and an air inlet and outlet zone is provided at the lower end. The tube diameter area of ​​the reaction zone is denoted as A.

[0020] The invention discloses a reaction tube for non-fluidized preparation of the silicon-carbon negative electrode. The reaction tube comprises a reaction zone. An amplification zone is arranged at the upper end of the reaction zone and an air inlet and outlet zone is arranged at the lower end.

[0021] As common sense, the reaction zone is a hollow cylindrical structure equipped with a heating device, which itself and its installation are conventional technologies and can provide heat to the reaction zone. Referring to the existing technology, internal heating or external heating can be used. It is the main area for the mixed reaction of silane gas and carbon matrix and the carbon coating of silicon-carbon particles.

[0022] As common sense, the air inlet and outlet area is a hollow cylindrical structure or an (inverted) truncated cone structure. The specific structure does not affect the technical effect of the present invention understood by those skilled in the art. A gas inlet and a powder outlet are provided, which are respectively used for the introduction of functional gas (silane gas, coating layer raw material gas) and protective gas (inert gas), and the unloading of the silicon-carbon negative electrode that forms the coating layer.

[0023] An innovation of the present invention is the enlarged zone, which is a structure disclosed for the first time in the present invention. The enlarged zone refers to a zone where the diameter of the tube is larger than the diameter of the tube in the reaction zone.

[0024] Preferably, in the enlarged area, the largest tube diameter is 1.2 to 2 times the diameter of the reaction zone, and preferably, in the enlarged area, the largest tube diameter is 1.4 to 1.8 times the diameter of the reaction zone.

[0025] Preferably, the height of the enlarged area is 5-15% of the height of the reaction tube, preferably, the height of the enlarged area is 8-12% of the height of the reaction tube; for example, 9%, 10%, 11% or any proportion within the range.

[0026] Preferably, the enlarged area is an inverted frustum structure, wherein the surface with a small area coincides with the upper surface of the reaction area.

[0027] Preferably, the outer wall of the amplification zone is provided with an insulation layer, and the specific insulation layer material and wrapping installation are conventional technologies. The prior art generally provides an insulation layer in the reaction zone, and the heating device is arranged between the insulation layer and the reactor shell in an external heating manner. The present invention innovatively provides an insulation layer on the outside of the amplification zone, thereby improving the reaction effect.

[0028] The invention discloses a silicon-carbon negative electrode prepared according to the non-fluidization preparation method of the silicon-carbon negative electrode.

[0029] The invention discloses a negative electrode sheet, comprising the silicon-carbon negative electrode.

[0030] The invention discloses a lithium ion battery, comprising the negative electrode sheet.

[0031] The invention discloses an electrochemical device, comprising the lithium ion battery.

[0032] The invention discloses the application of the silicon-carbon negative electrode in a lithium ion battery.

[0033] In order to overcome the volume expansion problem of silicon, the strategy of silicon-carbon composite materials is currently widely used, that is, by depositing silicon particles on a porous carbon matrix to form a silicon-carbon composite negative electrode material. As a matrix material, porous carbon has a high specific surface area, good electrical conductivity and a large porosity, which can buffer the volume expansion of silicon to a certain extent and provide an effective channel for the embedding and de-embedding of lithium ions. However, the current porous carbon still has some shortcomings in the process of combining with silicon, including insufficient thermal stability, insufficient electrical conductivity, insufficient pore structure optimization and agglomeration with silicon particles, etc. These shortcomings limit the performance improvement of silicon-carbon composite materials. The present invention provides a method for non-fluidized reaction, in which a sudden enlargement area is designed at the top of a tubular reactor to prevent particles from agglomerating at the top, and further, the sudden enlargement area is insulated to increase the reaction effectiveness. The present invention overcomes the technical prejudice of the prior art that only the fluidization method can be used to prepare silicon-carbon negative electrodes. It adopts a non-fluidization method and realizes non-fluidization, i.e., disorderly gas-solid mixing, by changing the air intake parameters. Combined with the design of the amplification zone, it unexpectedly solves the problem that the prior art is difficult to deposit and coat small-particle carbon materials, mainly avoiding the production problems of agglomeration and pressure release. The prepared silicon-carbon negative electrode has a good silane utilization rate, and especially has excellent electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the reaction tube structure for the non-fluidized preparation of the silicon-carbon negative electrode of the present invention; Among them, 1: air inlet pipe, 2: discharge pipe, 3: feed pipe, 4: exhaust pipe, 5: reaction area, 6: amplification area, 7: heating device, 8: thermal insulation cotton, 9: air inlet and discharge area. DETAILED DESCRIPTION

[0035] In view of the problem that the prior art fluidization method has poor effect on the porous carbon coating of small particles, the present invention adopts a non-fluidization method, through sudden amplification, so that the particles return to the inside of the reaction bed, and the insulation in the suddenly amplified area further improves the effective reaction degree. As common sense, the reaction tube has the basic components and structures of a conventional reactor, such as an air inlet, an air outlet, and a functional port, and the functional port includes a temperature measuring port, a pressure measuring port, and a safety valve port. The air inlet is used to ventilate the reactor cavity to provide the gas required for production; the air outlet is used to discharge the tail gas generated by production. Conventionally, in order to prevent the powder in the reactor from flowing out, a filter element is provided in the air outlet. During actual production, the air outlet is backwashed at intervals to prevent the filter element from being blocked; the temperature measuring port is used to monitor the temperature of different areas inside the reactor in real time, and the temperature of the heating tube is adjusted according to the temperature to ensure that the material is heated evenly, so as to achieve effective management and optimization of the silane cracking reaction; the pressure measuring port is used to monitor the pressure of different areas inside the reactor in real time, and the gas flow is adjusted according to the pressure to ensure that the pressure inside the reactor remains stable to maintain a good fluidized state; when the pressure in the reactor cavity is too high, the gas can be released through the safety valve port.

[0036] The following is a detailed description of the technical progress of the present invention through specific experiments. The raw materials used are existing products, the specific components of the reaction tube and their interconnection and application are conventional technologies, and the specific preparation operations and performance tests are all conventional technologies. The positional relationship involved in the present invention is the positional relationship in actual production. Embodiment 1

[0037] See also Figure 1 The present invention discloses a reaction tube for non-fluidized preparation of silicon-carbon negative electrode, the reaction tube comprising a reaction zone 5; an amplification zone 6 is provided at the upper end of the reaction zone, and an air inlet and outlet zone 9 is provided at the lower end; As with existing technology: The reaction zone is a hollow cylindrical structure with an inner diameter of 260 mm. A heating device 7 is provided. The heating device 7 is installed by conventional technology and can provide heat to the reaction zone. In the figure, external heating is adopted. The reaction zone is provided with a heat preservation (cotton) layer 8. The heating device is arranged between the heat preservation layer and the reactor shell in an external heating manner. The interior of this area is the main area for the mixed reaction of silane gas and carbon matrix and the carbon coating of silicon-carbon particles. The gas inlet and outlet area is a hollow inverted truncated cone structure with an inner diameter of 150 mm at the bottom. It is equipped with a gas inlet 1 (gas inlet pipe) and a powder outlet 2 (discharge pipe), which are used for the introduction of functional gas (silane gas, coating layer raw material gas) and protective gas (inert gas) and the unloading of the silicon-carbon negative electrode forming the coating layer. An innovation of the present invention lies in the enlarged area, which is a structure disclosed for the first time in the present invention. The enlarged area is an inverted frustum structure, in which the surface with a small area coincides with the upper surface of the reaction zone, and the tube diameter of the other side is 390 mm.

[0038] The height of the reaction tube is 3 meters, the height of the enlargement area is 0.3 meters, and the height of the air inlet and outlet area is 0.15 meters.

[0039] As common sense, the reaction tube has the basic components and structure of a conventional reactor, such as 3: feed pipe, 4: exhaust pipe, etc. Embodiment 2

[0040] On the basis of the first embodiment, a heat-insulating cotton layer is also provided on the outer wall of the amplification area, and the specific installation is conventional technology, which can refer to the reaction area.

[0041] Different from the existing fluidized reaction, in the reaction tubes of the first and second embodiments, after the gas is passed through, the porous carbon is in a disordered suspension state, not a fluidized state.

[0042] When the above tubular reactor with an amplification zone is used to prepare a silicon-carbon negative electrode, the process preparation conditions are: (1) Porous carbon is fed into the tubular reactor through a feed tube, wherein the porous carbon can be purchased from the market and has a particle size range of ≤20 μm; (2) A certain flow rate of silane and nitrogen is mixed and introduced into the reactor through the bottom air inlet pipe and reacted under certain conditions, wherein the certain temperature is 400-700° C.; the flow rate range of the silicon source gas and the nitrogen is 0-100 L / min, and the deposition time is 3-6 h; (3) Carbon coating the porous carbon with deposited nano-silicon to prepare a surface carbon layer. The bottom inlet gas is changed from a mixture of silane and nitrogen to a mixture of nitrogen and acetylene. The carbon deposition time is 60-200 minutes, the flow range of acetylene gas and nitrogen is 0-100L / min, and the deposition temperature is 500-850°C.

[0043] Compared with ordinary tubular reactors, this equipment has a sudden expansion area at the top to prevent abnormal phenomena such as material agglomeration and reactor pressure relief. In addition, the sudden expansion area is insulated with thermal insulation cotton, which is conducive to increasing the reactivity of the effective bed, making the silane decomposition more sufficient and the reaction more complete. Embodiment 3

[0044] (1) Place 20 kg of porous carbon substrate (particle size range, 1-10 μm) purchased from the market into a tubular reactor (Example 2); (2) Monosilane and nitrogen were mixed and introduced into the reactor through the bottom inlet pipe, with gas flow rates of 60 L / min and 60 L / min, respectively, and reacted at 540 °C for 300 min to obtain porous carbon with deposited nano-silicon; (3) Carbon coating the porous carbon with deposited nanosilicon to prepare a surface carbon layer: the bottom inlet gas was changed from a mixture of silane and nitrogen to a mixture of nitrogen and acetylene, with gas flow rates of 10 L / min and 50 L / min, respectively, and the reaction was carried out at 580 °C for 120 min.

[0045] The carbon content in the porous silicon-carbon negative electrode material obtained after deposition is 47.6wt%. Embodiment 4

[0046] Refer to Example 3, wherein the reactor is the reaction tube of Example 1. Comparative Example 1

[0047] On the basis of Example 1, the enlarged area was adjusted to a hollow cylinder with an inner diameter of 260 mm, that is, the enlarged area was omitted and the reaction area was filled in. With this reaction tube, the reaction test was carried out according to Example 3. Comparative Example 2

[0048] Referring to Example 3, in step (2), the gas flow rates of monosilane and nitrogen are 40 L / min and 40 L / min, respectively.

[0049] The same as the rest, the porous silicon-carbon negative electrode material obtained after deposition showed agglomeration phenomenon.

[0050] Comparison example The porous carbon matrix (particle size range, 1-10 microns) purchased on the market was placed into the mainstream fluidized bed reactor in existing production, with a mass of 20 kg. The reaction was carried out according to the existing mature process, and the porous silicon-carbon negative electrode material obtained after deposition showed agglomeration. Application Examples

[0051] The particle size of the material was measured by a Malvern laser particle size analyzer, and the specific surface area of ​​the material was measured by a nitrogen adsorption method.

[0052] The obtained material was uniformly mixed with commercial graphite A in a mass ratio of 1:1 as the negative electrode material of lithium-ion batteries. The obtained negative electrode material was uniformly mixed with 2% carbon black, 2% sodium cellulose acid, and 3% styrene-butadiene rubber in a water solvent to form a battery slurry, which was coated on copper foil, dried and cut into 8×8mm square pieces, and then vacuum dried at 110 degrees Celsius for 12 hours. Half-cells were assembled on the lithium sheets in a glove box to evaluate their electrochemical properties. Commercial graphite material A was purchased from Jiangxi Zichen Technology Co., Ltd.

[0053] The electrochemical test mode is 0.1C discharge to 0.005V, 0.05C discharge to 0.005V, and 0.02C discharge to 0.005V in the first week. After standing for 5s, charge at 0.1C to 1V. The subsequent cycles are 0.5C discharge to 0.005V, 0.2C discharge to 0.005V, 0.05C discharge to 0.005V, 0.02C discharge to 0.005V, and charge at 0.5C to 1V after standing for 5s. The full charge expansion rate test is the expansion of the buckled electrode sheet. The calculation method is the ratio of the difference in electrode sheet thickness before and after full charge to the electrode sheet thickness before full charge. The electrode sheet thickness before full charge refers to the electrode sheet thickness when not charged.

[0054] The above-mentioned discharge is a lithium insertion process, corresponding to the charging in the full battery, and the charging is a lithium removal process, corresponding to the discharge of the full battery.

[0055] Table 1 Performance of silicon-carbon negative electrodes prepared in Examples and Comparative Examples

[0056] As can be seen from Table 1, the powder resistance of the sample of the present invention using the sudden expansion area and adding the insulation design is significantly lower than that of the sample without the insulation layer design. The insulation design further increases the effective reactivity and improves the reaction efficiency of silane and porous carbon, thereby reducing the deposition degree of silicon particles on the porous carbon surface. This is conducive to inhibiting the expansion of silicon particles, reducing their rupture, and reducing the frequency of contact with the electrolyte to form the SEI film, thereby improving the cycle performance. In contrast, the reaction efficiency of silane and porous carbon is low due to insufficient reactivity, which makes it easy for silicon particles to deposit on the surface, which easily leads to expansion and rupture, resulting in higher powder resistance and poorer cycle performance.

[0057] In addition, if there is no sudden enlargement area, at a higher gas velocity, the particles will be blown to the top of the reactor by the higher gas velocity, which will cause the particles to gather at the top of the reactor and then react, resulting in agglomeration between the particles, causing serious agglomeration, which will lead to blockage of the filter element and the failure of the pressure inside the reactor to drop, resulting in pressure relief. Reducing the gas velocity may solve this problem, but it must be considered that a smaller gas velocity will cause channeling in the bed. As shown in Comparative Example 2, the same total amount of silane is used, but the smaller gas velocity makes fluidization more difficult, resulting in severe channeling and other abnormal phenomena. Embodiment 5

[0058] On the basis of Example 1, the height of the reaction tube is 3 meters, the height of the enlarged area is 0.28 meters, and the height of the air inlet and outlet area is 0.15 meters. Embodiment 6

[0059] Based on Example 3, the gas flow rates of monosilane and nitrogen are 70 L / min and 70 L / min respectively. Embodiment 7

[0060] Based on Example 3, the gas flow rates of monosilane and nitrogen are 60 L / min and 65 L / min, respectively. Embodiment 8

[0061] Based on Example 3, the gas flow rates of monosilane and nitrogen are 55 L / min and 65 L / min, respectively.

[0062] The present invention improves the conventional tubular reactor and has many advantages in preparing silicon-carbon negative electrode materials. First, the selection of gas velocity can effectively destroy the channeling phenomenon in the furnace and improve the utilization efficiency of the gas. Secondly, a suddenly expanded area is set at the top of the reactor, which can make the reaction particles gather at the top of the furnace, and the effective reactivity is further increased by the insulation design at the top, which is conducive to improving the reaction efficiency of the gas. These innovative structural designs cleverly utilize the characteristics of tubular reactors and effectively solve common problems such as low gas utilization and insufficient reactivity.

Claims

1. A non-fluidized preparation method for a silicon-carbon negative electrode, comprising the following steps: in a heated environment, mixing silane gas with a carbon matrix to react to obtain silicon-carbon particles; and then carbon coating the silicon-carbon particles to obtain a silicon-carbon negative electrode, characterized in that: The flow rate of silane gas is V=u×A, where A is the pipe diameter area, m2, and u is the carry-out velocity in m / s, and u is greater than 0.03 m / s.

2. The non-fluidized preparation method of the silicon-carbon negative electrode according to claim 1, characterized in that: In a heating environment and in an inert gas, silane gas and a carbon matrix are mixed and reacted to obtain silicon-carbon particles; the gas flow ratio of the silane gas to the inert gas is 1: (0.1-10).

3. The non-fluidized preparation method of the silicon-carbon negative electrode according to claim 2, characterized in that: The carbon matrix is ​​porous carbon, and the particle size of the porous carbon is less than 20 microns; the sum of the flow rates of the silane gas and the inert gas is V=u×A.

4. The non-fluidized preparation method of the silicon-carbon negative electrode according to claim 1, characterized in that: The non-fluidized preparation method of the silicon-carbon negative electrode is carried out in a reaction tube, wherein the reaction tube comprises a reaction zone; an amplification zone is provided at the upper end of the reaction zone and an air inlet and outlet zone is provided at the lower end; the tube diameter area of ​​the reaction zone is denoted as A.

5. A reaction tube used in the non-fluidized preparation method of the silicon-carbon negative electrode according to claim 1, wherein the reaction tube comprises a reaction zone, characterized in that: The upper end of the reaction zone is provided with an amplification zone, and the lower end is provided with an air inlet and outlet zone.

6. The reaction tube according to claim 5, characterized in that: In the enlarged area, the largest tube diameter is 1.2 to 2 times the tube diameter of the reaction zone; the height of the enlarged area is 5 to 15% of the height of the reaction tube.

7. The reaction tube according to claim 5, characterized in that: The outer side wall of the enlarged area is provided with a heat-insulating layer.

8. The silicon-carbon negative electrode prepared by the non-fluidized preparation method of the silicon-carbon negative electrode according to claim 1.

9. A negative electrode sheet comprising the silicon-carbon negative electrode according to claim 8; or a lithium-ion battery comprising the negative electrode sheet; or an electrochemical device comprising the lithium-ion battery.

10. Use of the silicon-carbon negative electrode according to claim 8 in a lithium-ion battery.

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