Preparation method of low-expansion silicon-carbon negative electrode material

Abstract

The invention discloses a preparation method of a low-expansion silicon-carbon negative electrode material. The method comprises the following steps: filling a fluidized bed reactor with porous carbon, heating to 460-500 DEG C, mixing a silicon source and carrier gas, introducing the mixture from the bottom of a bed, mixing a carbon source and the carrier gas after 3-5 hours, introducing the mixture from the top of the bed, stopping gas introduction of the silicon source and the carbon source after the reaction is completed, cooling and discharging. Meanwhile, the low-expansion silicon-carbon material is obtained after silicon deposition and carbon coating, the production efficiency of a modified product is improved by 20% or above, silicon and carbon are repeatedly deposited in the reaction, a formed silicon-carbon deposition layer is more uniform, mixed C1 and C3 gas can improve the generation efficiency of carbon nuclei, more five-membered rings can be formed when the C1 and C3 gas is added on aromatic hydrocarbon, the C-C network bond energy is higher, and the carbon-carbon deposition layer is more uniform. And the inhibition effect on the change of the silicon crystal product is better, and the first-time full-charge expansion of the material is reduced to be below 40%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials, and particularly relates to a preparation method of a low-expansion silicon-carbon negative electrode material. BACKGROUND

[0002] Lithium batteries, as a common type of rechargeable batteries, have a structure including a positive electrode, a negative electrode, and an electrolyte. The negative electrode (also known as a negative electrode material) plays an important role in storing and releasing lithium ions.

[0003] Traditional negative electrode materials for lithium batteries are usually graphite, but as the demand for battery capacity and performance continues to increase, the current graphite products have approached their theoretical capacity. Therefore, scientists are looking for new materials to improve battery performance. Among them, silicon-carbon composite materials have attracted attention as a potential alternative material.

[0004] Silicon-carbon negative electrodes have multiple advantages. First, silicon has a higher specific capacity and can store more lithium ions, increasing the energy density of the battery. Second, carbon can provide good electrical conductivity and structural stability, helping to alleviate the problems caused by the volume expansion of silicon materials and prolonging the life of the battery. Therefore, silicon-carbon composite materials combine the advantages of silicon and carbon and have the potential to become an ideal choice for future lithium battery negative electrodes.

[0005] However, silicon-carbon negative electrodes still face some challenges. For example, the current production process involves multiple stages of reaction. For example, in patent CN102598373B, silicon crystals are first deposited in a carbon scaffold and then coated with a carbon layer. Since the optimal decomposition temperature range of the selected carbon source is different from that of silane, the two-stage process is not compatible, and the overall production time is longer. Compared with patent CN116613299B, the process designed in this paper can control the reaction temperature of the silicon source gas and the carbon source gas below 500°C, eliminating the occurrence of abnormal reactions. The use of diacetylene mixed with C1 or C3 alkenyl gas and the partitioning of silicon source gas can ensure that a dense carbon layer can be formed at low temperatures, effectively reducing the specific surface area of the material and preventing the infiltration of electrolyte, which affects the cycling performance of the product. SUMMARY

[0006] In this paper, the use of C1 and C3 gases with low carbon formation temperature and diacetylene mixed to improve carbon formation efficiency can reduce the carbon coating temperature to the silicon deposition temperature range, while performing the silicon deposition and carbon coating reaction, improving production efficiency. The mixed carbon source gas can deposit a denser carbon coating layer at a lower temperature, improving the electrochemical performance while inhibiting material expansion and ensuring the cycling performance of the product.

[0007] Therefore, the present application provides a preparation method of a low-expansion silicon-carbon negative electrode material, which comprises the following steps:

[0008] In the fluidized bed reactor, fill in the porous carbon, heat to 460℃-500℃, first mix the silicon source with the carrier gas, then pass it from the bottom of the bed, after 3-5h, mix the carbon source with the carrier gas, then pass it from the top of the bed, after the reaction is completed, stop the silicon source and carbon source, then cool down and discharge.

[0009] Preferably, the Dv50 of the porous carbon is 8-9μm, the span is 1.0-1.3, and the specific surface area is 1600±100m 3 / g.

[0010] Preferably, the carrier gas is one or more of nitrogen, argon, and helium, the silicon source is one or more of monosilane, disilane, and trisilane, the carrier gas in the silicon source is referred to as carrier gas 1, the carrier gas in the carbon source is referred to as carrier gas 2, the volume flow rate ratio of carrier gas 1 to monosilane is 1:1-2:1, and the volume flow rate ratio of carrier gas 2 to the carbon source is 5:1-5:4.

[0011] Preferably, the total time of passing in the carbon source gas is 20%-40% of the total reaction time, and the total reaction time is 3.75-8.5h.

[0012] Preferably, when the carbon source gas and the silicon source gas are passed in at the same time, the volume flow rate ratio of the carbon source gas to the silicon source gas is 2:5-4:5.

[0013] Preferably, the carbon source gas is a mixture of diacetylene and C1 or C3 alkene gas, and the volume flow rate ratio is 9:1-7:3, for example, diacetylene 90%vol, methane 10%vol; diacetylene 70%vol, propyne 30%vol, etc.

[0014] The C1 or C3 alkene gas is selected from one or more of methane, propane, propylene, and propyne.

[0015] The beneficial effects of the present application are:

[0016] 1. There is a sufficient overlap interval between the silicon deposition temperature and the diacetylene carbon formation temperature, the silicon source and the carbon source are passed in at the same time, the overall reaction time is shortened, and the silicon-carbon deposition layer formed is more uniform. The carbon source gas such as diacetylene is passed in after a period of time, and its larger molecular diameter can inhibit the migration of the carbon source gas in the pore channel of the porous carbon, preventing the carbon layer from blocking the silicon deposition pore channel.

[0017] 2. The C1 and C3 gas added in the carbon source gas can improve the generation efficiency of carbon nuclei, more five-membered rings will be formed in the carbon network, the C-C bond energy is stronger, and it has a better inhibiting effect on the volume change of the silicon crystal. DETAILED DESCRIPTION

[0018] Test method:

[0019] The material BET is measured by a specific surface area instrument.

[0020] The half cell is buckled, the voltage window is 0-2V, the first charge and discharge test condition is that the control temperature is 25 DEG C, the cut-off voltage is 0-2V, and the current density is 0.1C. The charge capacity is the gram capacity of the material, and the ratio of the charge capacity to the discharge capacity is the first efficiency of the material. The material is mixed with graphite to form a full cell (the designed capacity is 600mAh / g), and the ratio of the charge capacity of 50 cycles to the first cycle capacity is the 50 cycle efficiency of the material after doping. th The cycle retention rate is the full expansion rate of the material according to the overall deformation of the first cycle discharge.

[0021] Raw materials and sources

[0022] The porous carbon is YJ-03 produced by Henan Dachaocanneng Technology Co., Ltd., the specific surface area is 1669m 2 / g, and the Dv50 is 8.15um.

[0023] The application will be further described in combination with examples, but the application is not limited to the following examples.

[0024] Example 1:

[0025] The process for improving the existing low-expansion silicon-carbon negative electrode material in this embodiment includes the following steps:

[0026] 5kg of porous carbon base material is transported into a fluidized bed, heated to 480 DEG C to start the reaction, nitrogen gas 20L / min and methylsilane 10L / min are introduced into the bed bottom, after 5h, nitrogen gas 25L / min, diacetylene 4.5L / min and methane 0.5L / min are introduced into the bed top to continue the reaction for 2h, and then the product is obtained after cooling and discharging.

[0027] Example 2:

[0028] The process for improving the existing low-expansion silicon-carbon negative electrode material in this embodiment includes the following steps:

[0029] 5kg of porous carbon base material is transported into a fluidized bed, heated to 480 DEG C to start the reaction, nitrogen gas 20L / min and methylsilane 10L / min are introduced into the bed bottom, after 5h, nitrogen gas 25L / min, diacetylene 4.5L / min and methane 0.5L / min are introduced into the bed top to continue the reaction for 2h, and then the product is obtained after cooling and discharging.

[0030] Example 3:

[0031] The process for improving the existing low-expansion silicon-carbon negative electrode material in this embodiment includes the following steps:

[0032] 5kg porous carbon substrate was transported into the fluidized bed, the temperature was raised to 480℃ to start the reaction, the bottom of the bed was introduced with nitrogen 15L / min, silane 15L / min, after 3.7h, the top of the bed was introduced with nitrogen 20.5L / min, diacetylene 8.5L / min, propyne 1L / min to continue the reaction for 1h, then the temperature was lowered to discharge the product.

[0033] Example 4:

[0034] The process for improving the existing low-expansion silicon-carbon negative electrode material in this example includes the following steps:

[0035] 5kg porous carbon substrate was transported into the fluidized bed, the temperature was raised to 480℃ to start the reaction, the bottom of the bed was introduced with nitrogen 15L / min, silane 15L / min, after 3.7h, the top of the bed was introduced with nitrogen 20.5L / min, diacetylene 8.5L / min, propyne 1L / min to continue the reaction for 1h, then the temperature was lowered to discharge the product.

[0036] Example 5:

[0037] The process for improving the existing low-expansion silicon-carbon negative electrode material in this example includes the following steps:

[0038] 5kg porous carbon substrate was transported into the fluidized bed, the temperature was raised to 480℃ to start the reaction, the bottom of the bed was introduced with nitrogen 15L / min, silane 15L / min, after 3.7h, the top of the bed was introduced with nitrogen 20.5L / min, diacetylene 8.5L / min, propyne 1L / min to continue the reaction for 1h, then the temperature was lowered to discharge the product.

[0039] Comparative Example 1:

[0040] The process for improving the existing low-expansion silicon-carbon negative electrode material in this example includes the following steps:

[0041] 5kg porous carbon substrate was transported into the fluidized bed, the temperature was raised to 480℃ to start the reaction, the bottom of the bed was introduced with nitrogen 15L / min, silane 15L / min, after 3.7h, the top of the bed was introduced with nitrogen 20.5L / min, diacetylene 8.5L / min, propyne 1L / min to continue the reaction for 1h, then the temperature was lowered to discharge the product.

[0042] Comparative Example 2:

[0043] The process for improving the existing low-expansion silicon-carbon negative electrode material in this example includes the following steps:

[0044] 1. 5kg porous carbon substrate was transported into the modified fluidized bed, the temperature was raised to 480℃ to start the reaction, the bottom of the bed was introduced with nitrogen 20L / min, silane 10L / min, after 5h, the top of the bed was introduced with nitrogen 25L / min, diacetylene 5L / min to continue the reaction for 2h, then the temperature was lowered to discharge the product.

[0045] Comparative Example 3:

[0046] The process for improving the existing low-expansion silicon-carbon negative electrode material in this embodiment includes the following steps:

[0047] 1. Transport 5 kg of porous carbon substrate into the modified fluidized bed, heat to 480°C to start the reaction, introduce nitrogen gas 20 L / min and silane 10 L / min at the bottom of the bed, after 5 h introduce nitrogen gas 25 L / min and methane 5 L / min at the top of the bed to continue the reaction for 2 h, cool down and discharge to obtain the silicon-carbon finished product.

[0048] Table 1

[0049]

[0050] As shown in the above table, after reducing the carbon coating temperature by using the new process, the carbon source gas is introduced synchronously during the silicon deposition stage to improve the production efficiency. Mixing methane, propyne and other gases in diacetylene can promote carbon deposition, reduce the specific surface area, perfect the carbon coating layer structure and improve the electrochemical performance of the material. The denser carbon coating layer can also enhance the restriction on the silicon particles, inhibit the swelling of the material during the charge and discharge process, and improve the long cycle performance of the product.

Claims

1. A method for preparing a low-expansion silicon-carbon negative electrode material, the method comprising the following steps: a fluidized bed reactor is filled with porous carbon, heated to 460-500°C, a silicon source is first mixed with a carrier gas and introduced from the bottom of the bed, 3-5 hours later a carbon source is mixed with a carrier gas and introduced from the top of the bed, after the reaction is complete, the silicon source and carbon source are stopped, and the reactor is cooled and discharged.

2. The production method according to claim 1, wherein The porous carbon has a Dv50 of 8-9 pm, a span of 1.0-1.3, and a specific surface area of 1600±100 m2 / g. 3 / g.

3. The production method according to claim 1 or 2, characterized by, The carrier gas is one or more of nitrogen, argon, and helium, and the silicon source is one or more of monosilane, disilane, and trisilane.

4. The production method according to any one of claims 1 to 3, characterized by, The volume flow ratio of carrier gas to monosilane is 1:1-2:1, and the volume flow ratio of carrier gas to carbon source is 5:1-5:

4.

5. The production method according to any one of claims 1 to 4, wherein The total carbon source gas introduction time is 20-40% of the total reaction time.

6. The production method according to any one of claims 1 to 5, wherein The volume flow ratio of carbon source gas to silicon source gas is 2:5-4:

5.

7. The production method according to any one of claims 1 to 6, wherein The carbon source gas is a mixture of diacetylene and a C1 or C3 alkene-yne gas, and the volume flow ratio is 9:1-7:

3.

8. The production method according to any one of claims 1 to 7, wherein The C1 or C3 alkene-yne gas is one or more of methane, propane, propylene, and propyne.

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