Pre-lithiation agent and preparation method thereof, negative plate and lithium ion battery

Abstract

The invention provides a pre-lithiation agent, a preparation method of the pre-lithiation agent, a negative plate and a lithium ion battery. The pre-lithiation agent comprises porous carbon, a lithium-silicon alloy, amorphous silicon and a carbon layer, the lithium-silicon alloy and the amorphous silicon are located in pores of the porous carbon, the surface of the lithium-silicon alloy is coated with the amorphous silicon, and the outer surface of the porous carbon is coated with the carbon layer. The porous carbon serves as a carrier, and the high specific surface area of the porous carbon provides sufficient space for reacting and storing the lithium-silicon alloy. The lithium-silicon alloy can provide a large amount of active lithium for compensating for lithium ions consumed by SEI film formation in the first charge-discharge cycle of the battery. And the existence of the amorphous silicon is beneficial to sealing of the lithium silicon alloy with relatively strong activity. The carbon layer has a good isolation effect on the external environment, especially air and water. Therefore, the pre-lithiation agent provided by the invention has relatively high stability and consistency, and is beneficial to improving the consistency and stability of the lithium ion battery when being applied to the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a pre-lithiation agent and a preparation method thereof, a negative electrode sheet and a lithium ion battery. Background Art

[0002] The application range of lithium-ion batteries is becoming increasingly wider, and the requirements for battery energy density are also increasing. During the initial charging process of a lithium-ion battery, the lithium ions released from the positive electrode react on the surface of the negative electrode to form a SEI film, which consumes active lithium ions, reduces the number of lithium ions returning to the positive electrode during discharge, reduces the battery's initial coulombic efficiency, and thus reduces the battery's cycle energy density. In the face of the loss caused by the reaction of lithium ions at the negative electrode to form SEI, the most effective and direct solution is to pre-lithiate the battery with a pre-lithiation agent to compensate for the lithium ion loss caused by SEI and improve the battery's cycle energy density.

[0003] Using a negative electrode pre-lithiation agent to compensate for lost lithium ions is an effective way to replenish lithium. The most common methods include pre-lithiation using lithium powder / lithium ribbon, chemical pre-lithiation, electrochemical pre-lithiation, and lithium-silicon alloy pre-lithiation. The lithium powder / lithium ribbon pre-lithiation method primarily uses lithium powder or lithium ribbon as a pre-lithiation agent. Chinese patent application publication number CN117476877A composites lithium ribbon with copper foil to produce a copper-lithium composite ribbon, which is then coated on the negative electrode for pre-lithiation. Due to the high chemical activity of lithium ribbon, this method has high requirements for the negative electrode coating environment and slurry type, a narrow range of applications, and cannot be applied to conventional wet coating equipment. Chinese patent application publication number CN117393705A uses biphenyl lithium for chemical pre-lithiation. Since the pre-lithiation agent is an aromatic hydrocarbon, its raw materials are highly toxic. Furthermore, the pre-lithiation method uses a pre-lithiation agent solution to impregnate the electrode to achieve pre-lithiation, which can easily lead to poor consistency in large-scale production. The Chinese patent application with patent application publication number CN118448584A generates a lithium-silicon alloy by reacting molten lithium with silicon. However, this method has the problem of difficulty in accurately controlling the degree of lithium-silicon reaction and poor consistency. Summary of the Invention

[0004] The main purpose of the present invention is to provide a pre-lithiation agent and its preparation method, a negative electrode sheet and a lithium-ion battery, so as to solve the problems of complex preparation process, high cost, poor stability and consistency of the pre-lithiation agent in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a pre-lithiation agent is provided, which includes porous carbon, lithium-silicon alloy, amorphous silicon and a carbon layer, wherein the lithium-silicon alloy and amorphous silicon are located in the pores of the porous carbon, the amorphous silicon is coated on the surface of the lithium-silicon alloy, and the carbon layer is coated on the outer surface of the porous carbon.

[0006] Furthermore, the D50 of the porous carbon is 1 to 8 μm; and / or the mass ratio of the porous carbon to the lithium silicon alloy is 1:(2 to 4); and / or the thickness of the carbon layer is 1 to 10 nm.

[0007] Furthermore, the specific surface area of ​​the porous carbon is 2100-2700 m 2 / g; and / or, the average pore diameter of the porous carbon is 0.1 to 2.5 nm.

[0008] Furthermore, the molar ratio of lithium element to silicon element in the above lithium-silicon alloy is (1.5-5):1.

[0009] Furthermore, the ratio of the mass of silicon element to the mass of amorphous silicon in the lithium-silicon alloy is 1:(0.001-1).

[0010] According to another aspect of the present invention, a method for preparing the aforementioned pre-lithiation agent is provided, which comprises placing porous carbon in a fluidized bed, sequentially introducing a first silane-containing gas, lithium vapor, a second silane-containing gas, and a carbon-containing source gas to carry out a deposition reaction to obtain a pre-lithiation agent.

[0011] Furthermore, the ratio of the mass of the above-mentioned porous carbon, the volume of the first silane-containing gas, the volume of lithium vapor, the volume of the second silane-containing gas, and the volume of the carbon source gas is (0.5~1kg):(522~900L):(1216~3200L):150L:(102~960L); and / or, the temperature of the deposition reaction is 350~800℃.

[0012] Furthermore, the preparation method includes: placing porous carbon in a fluidized bed, sequentially introducing a first silane-containing gas to perform a first deposition reaction, introducing lithium vapor to perform a second deposition reaction to form a lithium-silicon alloy, introducing a second silane-containing gas to perform a third deposition reaction to form amorphous silicon, and introducing a carbon source gas to perform a fourth deposition reaction to form a carbon layer to obtain a pre-lithiation agent; preferably, the temperature of the first deposition reaction, the temperature of the second deposition reaction, and the temperature of the third deposition reaction are each independently 350-700°C; and / or, the temperature of the fourth deposition reaction is 500-800°C; preferably, the first silane-containing gas includes a first carrier gas and a first silane gas, and the volume ratio of the first carrier gas to the first silane gas is (1-4):( 1~4); and / or, the second silane-containing gas includes a second carrier gas and a second silane gas, and the volume ratio of the second carrier gas and the second silane gas is (1~4):(1~4); and / or, the carbon source gas includes a third carrier gas and a carbon source gas, and the volume ratio of the third carrier gas to the carbon source gas is (1~4):(1~4); further preferably, the first silane gas and the second silane gas are each independently selected from any one or more of monosilane, disilane and trisilane; and / or, the carbon source gas is a hydrocarbon gas, preferably a hydrocarbon gas is selected from any one or more of methane, ethane, ethylene and acetylene; and / or, the first carrier gas, the second carrier gas and the third carrier gas are each independently selected from any one or more of argon, nitrogen and helium.

[0013] According to another aspect of the present invention, a negative electrode sheet is provided, comprising a negative electrode active layer and a current collector, wherein the negative electrode active layer contains the aforementioned pre-lithiation agent.

[0014] According to another aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet.

[0015] Applying the technical solution of the present invention, porous carbon is used as a carrier, and its high specific surface area provides sufficient space for reaction and storage of lithium-silicon alloy, which is conducive to the rapid diffusion and storage of lithium ions, thereby helping to enhance the pre-lithiation effect of the pre-lithiation agent. The lithium-silicon alloy can provide a large amount of active lithium to compensate for the lithium ions consumed by the formation of the SEI film in the first charge and discharge cycle of the battery, thereby helping to improve the cycle stability of the battery. The presence of amorphous silicon helps to seal the lithium-silicon alloy with strong activity, thereby helping to improve the structural stability of the lithium-silicon alloy. The carbon layer has a good insulating effect on the external environment, especially air and water, and can effectively protect the lithium-silicon alloy and the silicon layer to avoid reaction with oxygen and water vapor in the air, thereby helping to improve the air stability of the pre-lithiation agent, which is beneficial to its safety and long-term storage during production and use. Therefore, the pre-lithiation agent of the present application has high stability and consistency, and its application in lithium-ion batteries helps to improve the consistency and stability of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 The SEM image of the pre-lithiation agent in Example 1 of the present application is shown. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0019] As analyzed in the background technology of this application, the existing technology has problems such as complex preparation process, high cost, poor stability and consistency of pre-lithiation agents. In order to solve the above problems, this application provides a pre-lithiation agent and its preparation method, a negative electrode sheet and a lithium-ion battery.

[0020] In a typical embodiment of the present application, a pre-lithiation agent is provided, which includes porous carbon, a lithium-silicon alloy, amorphous silicon and a carbon layer, wherein the lithium-silicon alloy and the amorphous silicon are located in the pores of the porous carbon, the amorphous silicon is coated on the surface of the lithium-silicon alloy, and the carbon layer is coated on the outer surface of the porous carbon.

[0021] Porous carbon acts as a carrier, and its high specific surface area provides sufficient space for reaction and storage of lithium-silicon alloy, which contributes to the rapid diffusion and storage of lithium ions, thereby helping to enhance the pre-lithiation effect of the pre-lithiation agent. Lithium-silicon alloy can provide a large amount of active lithium to compensate for the lithium ions consumed by SEI film formation in the first charge and discharge cycle of the battery, thereby helping to improve the cycle stability of the battery. The presence of amorphous silicon helps to seal the lithium-silicon alloy with strong activity, thereby helping to improve the structural stability of the lithium-silicon alloy. The carbon layer has a good insulating effect on the external environment, especially air and water, and can effectively protect the lithium-silicon alloy and the silicon layer, avoiding reaction with oxygen and water vapor in the air, thereby helping to improve the air stability of the pre-lithiation agent, which is beneficial to its safety and long-term storage during production and use. Therefore, the pre-lithiation agent of the present application has high stability and consistency, and its application in lithium-ion batteries helps to improve the consistency and stability of lithium-ion batteries.

[0022] In one embodiment of the present application, the D50 of the porous carbon is 1 to 8 μm; and / or the mass ratio of the porous carbon to the lithium silicon alloy is 1:(2 to 4); and / or the thickness of the carbon layer is 1 to 10 nm.

[0023] Controlling the D50 of the porous carbon within the above range helps provide more efficient lithium ion transmission channels, accelerates the diffusion of lithium ions in the material, and thus improves the pre-lithiation efficiency. Controlling the mass ratio of the porous carbon to the lithium-silicon alloy within the above range helps optimize the lithium compensation effect, thereby helping to improve the cycle stability of the battery. Controlling the thickness of the carbon layer within the above range helps to improve the inertness of the pre-lithiation agent to air and water during production and use, thereby helping to improve the stability and consistency of the pre-lithiation agent.

[0024] In one embodiment of the present application, the specific surface area of ​​the porous carbon is 2100-2700 m 2 / g; and, the average pore diameter of the porous carbon is 0.1 to 2.5 nm.

[0025] Controlling the specific surface area of ​​the porous carbon within the above range helps to provide more surfaces and pores, which is beneficial to improving the deposition efficiency of the lithium-silicon alloy and the uniformity of the distribution of the lithium-silicon alloy, thereby helping to improve the lithium storage capacity and lithium ion transmission rate of the pre-lithiation agent, thereby helping to improve the cycle stability of the lithium-ion battery, and also helps to make the lithium-silicon alloy, amorphous silicon and carbon layer more uniformly deposited inside the pores of the porous carbon, thereby helping to improve the lithium ion compensation efficiency of the pre-lithiation agent, while reducing internal stress and helping to enhance the structural stability of the entire material. Controlling the average pore size of the porous carbon within the above range helps to promote the formation of the lithium-silicon alloy and can also provide channels suitable for the rapid diffusion of lithium ions, thereby helping to optimize the transmission efficiency of lithium ions during the charge and discharge process.

[0026] In one embodiment of the present application, the molar ratio of lithium element to silicon element in the lithium-silicon alloy is (1.5-5):1.

[0027] Controlling the molar ratio of lithium to silicon in the lithium-silicon alloy within the above range helps to maintain structural stability while increasing the specific capacity, thereby helping to optimize the pre-lithiation effect and improve the cycle stability of the lithium-ion battery.

[0028] In one embodiment of the present application, the ratio of the mass of silicon element to the mass of amorphous silicon in the lithium-silicon alloy is 1:(0.001-1).

[0029] Controlling the ratio of the mass of silicon element to the mass of amorphous silicon in the lithium-silicon alloy within the above range helps the lithium-silicon alloy provide sufficient lithium ions during the first charge and discharge process. At the same time, amorphous silicon can serve as an additional lithium ion storage reservoir and provide a stable charge and discharge platform during the cycle.

[0030] In another typical embodiment of the present application, a method for preparing the aforementioned pre-lithiation agent is provided, which comprises: placing porous carbon in a fluidized bed, sequentially introducing a first silane-containing gas, lithium vapor, a second silane-containing gas and a carbon-containing source gas to carry out a deposition reaction to obtain a pre-lithiation agent.

[0031] The use of a fluidized bed helps to make the gas contact with the porous carbon material evenly, which helps to improve the efficiency of the deposition reaction. A first silane-containing gas is introduced to deposit a layer of silicon in the pores of the porous carbon, and then lithium vapor is introduced. The lithium vapor combines with the silicon to form a lithium-silicon alloy. Then a second silane-containing gas is introduced to form amorphous silicon on the surface of the lithium-silicon alloy, which helps to seal the lithium-silicon alloy with strong activity, thereby helping to improve the structural stability of the lithium-silicon alloy. Finally, a carbon-containing source gas is introduced to form a carbon layer on the outer surface of the porous carbon, which helps to protect the internal lithium-silicon alloy and avoid it from reacting with oxygen and water vapor in the air, thereby helping to improve the air stability of the pre-lithiation agent, which is beneficial to its safety and long-term storage during production and use. The preparation method of the present application is simple and low in cost, and the prepared pre-lithiation agent has high stability and consistency.

[0032] In one embodiment of the present application, the ratio of the mass of the above-mentioned porous carbon, the volume of the first silane-containing gas, the volume of lithium vapor, the volume of the second silane-containing gas, and the volume of the carbon source gas is (0.5~1kg):(522~900L):(1216~3200L):150L:(102~960L); and / or, the temperature of the deposition reaction is 350~800℃.

[0033] Controlling the ratios of the porous carbon mass, the volume of the first silane-containing gas, the volume of the lithium vapor, the volume of the second silane-containing gas, and the volume of the carbon-containing source gas within the aforementioned ranges helps control the ratios of the porous carbon, lithium-silicon alloy, amorphous silicon, and carbon layer within an appropriate range, thereby helping to improve the stability and consistency of the pre-lithiation agent, and thus, the consistency and stability of the lithium-ion battery. Controlling the deposition reaction temperature within the aforementioned range helps to improve the efficiency of the formation of the lithium-silicon alloy, amorphous silicon, and carbon layer, as well as the structural stability.

[0034] In order to further improve the stability and consistency of the pre-lithiation agent, thereby improving the cycle stability of the lithium-ion battery, in one embodiment of the present application, the above-mentioned preparation method preferably includes: placing porous carbon in a fluidized bed, sequentially introducing a first silane-containing gas to perform a first deposition reaction, introducing lithium vapor to perform a second deposition reaction to form a lithium-silicon alloy, introducing a second silane-containing gas to perform a third deposition reaction to form amorphous silicon, and introducing a carbon source gas to perform a fourth deposition reaction to form a carbon layer to obtain a pre-lithiation agent; preferably, the temperature of the first deposition reaction, the temperature of the second deposition reaction, and the temperature of the third deposition reaction are each independently 350 to 700°C; and / or, the temperature of the fourth deposition reaction is 500 to 800°C; preferably, the first silane-containing gas includes a first carrier gas and a first silane gas, and the first carrier gas includes a first carrier gas and a first silane gas. The volume ratio of the first silane-containing gas and the first silane-containing gas is (1-4):(1-4); and / or the second silane-containing gas includes a second carrier gas and a second silane-containing gas, and the volume ratio of the second carrier gas and the second silane-containing gas is (1-4):(1-4); and / or the carbon source gas includes a third carrier gas and a carbon source gas, and the volume ratio of the third carrier gas to the carbon source gas is (1-4):(1-4); further preferably, the first silane-containing gas and the second silane-containing gas are each independently selected from any one or more of monosilane, disilane and trisilane; and / or the carbon source gas is a hydrocarbon gas, preferably a hydrocarbon gas is selected from any one or more of methane, ethane, ethylene and acetylene; and / or the first carrier gas, the second carrier gas and the third carrier gas are each independently selected from any one or more of argon, nitrogen and helium.

[0035] In another typical embodiment of the present application, a negative electrode sheet is provided, comprising a negative electrode active layer and a current collector, wherein the negative electrode active layer contains the aforementioned pre-lithiation agent.

[0036] Since the negative electrode sheet contains the pre-lithiation agent of the present application, the negative electrode sheet has high stability and consistency.

[0037] In another typical embodiment of the present application, a lithium-ion battery is provided, comprising a positive electrode sheet, an electrolyte, and a negative electrode sheet, wherein the negative electrode sheet is the aforementioned negative electrode sheet.

[0038] Since the negative electrode sheet of the lithium-ion battery contains the pre-lithiation agent of the present application, the lithium-ion battery has high consistency, cycle stability and safety.

[0039] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0040] Example 1

[0041] 1 kg of porous carbon (D50 is 8 μm, specific surface area is 2100 m 2 / g, with an average pore size of 2.5 nm) was put into a fluidized bed, the temperature was raised to 500°C at 5°C / min, and a first argon gas + silane gas (argon volume: silane volume = 2:3) with a flow rate of 5 L / min was continuously introduced for 180 min, and then lithium vapor with a flow rate of 5 L / min was introduced for 640 min, and then a second argon gas + silane gas (argon volume: silane volume = 2:3) with a flow rate of 5 L / min was introduced for 30 min, and then the temperature was raised to 600°C at 5°C / min, and argon gas + silane gas with a flow rate of 5 L / min was introduced. The pre-lithiation agent is obtained by adding acetylene gas (argon volume: acetylene volume = 2:3) for 60 minutes, and the pre-lithiation agent includes porous carbon, lithium-silicon alloy, amorphous silicon and a carbon layer. The lithium-silicon alloy and the amorphous silicon are located in the pores of the porous carbon, and the amorphous silicon is coated on the surface of the lithium-silicon alloy. The carbon layer is coated on the outer surface of the porous carbon. The mass ratio of the porous carbon to the lithium-silicon alloy is 1:2, the molar ratio of the lithium element to the silicon element in the lithium-silicon alloy is 4:1, the ratio of the mass of the silicon element in the lithium-silicon alloy to the mass of the amorphous silicon is 1:0.125, and the thickness of the carbon layer is 3 nm.

[0042] Example 2

[0043] The difference from Example 1 is that the D50 of the porous carbon is 1 μm, the average pore size is 0.1 nm, and the specific surface area is 2700 m 2 / g, and finally a pre-lithiation agent was obtained, and the thickness of the carbon layer was 2.7nm.

[0044] Example 3

[0045] The difference from Example 1 is that the D50 of the porous carbon is 9 μm, the average pore size is 3 nm, and the specific surface area is 2000 m 2 / g, and finally a pre-lithiation agent was obtained, and the thickness of the carbon layer was 3.5nm.

[0046] Example 4

[0047] The difference from Example 1 is that the mass of the porous carbon is 1.3 kg, and the pre-lithiation agent is finally obtained, wherein the mass ratio of the porous carbon to the lithium silicon alloy is 1:1.5, and the thickness of the carbon layer is 1.5 nm.

[0048] Example 5

[0049] The difference from Example 1 is that the mass of the porous carbon is 0.5 kg, and the pre-lithiation agent is finally obtained, wherein the mass ratio of the porous carbon to the lithium silicon alloy is 1:4, and the thickness of the carbon layer is 5 nm.

[0050] Example 6

[0051] The difference from Example 1 is that the flow rate of the first argon + silane gas is 5 L / min, and the flow rate of lithium vapor is 1.9 L / min, and a pre-lithiation agent is finally obtained, wherein the molar ratio of lithium element to silicon element in the lithium silicon alloy is 1.5:1, and the ratio of the mass of silicon element in the lithium silicon alloy to the mass of amorphous silicon is 1:0.001.

[0052] Example 7

[0053] The difference from Example 1 is that the flow rate of the first argon + silane gas is 2.9 L / min, and the flow rate of lithium vapor is 3.5 L / min, and a pre-lithiation agent is finally obtained, wherein the molar ratio of lithium element to silicon element in the lithium silicon alloy is 5:1, and the ratio of the mass of silicon element in the lithium silicon alloy to the mass of amorphous silicon is 1:1.

[0054] Example 8

[0055] The difference from Example 1 is that the flow rate of the first argon + silane gas is 0.625 L / min, and the flow rate of lithium vapor is 0.625 L / min, and finally a pre-lithiation agent is obtained, wherein the molar ratio of lithium element to silicon element in the lithium silicon alloy is 1:1, and the ratio of the mass of silicon element in the lithium silicon alloy to the mass of amorphous silicon is 1:2.

[0056] Example 9

[0057] The difference from Example 1 is that the flow rate of argon gas + acetylene gas is 1.7 L / min, and the pre-lithiation agent is finally obtained, wherein the thickness of the carbon layer is 1 nm.

[0058] Example 10

[0059] The difference from Example 1 is that the flow rate of argon gas + acetylene gas is 16 L / min, and the pre-lithiation agent is finally obtained, wherein the thickness of the carbon layer is 10 nm.

[0060] Example 11

[0061] The difference from Example 1 is that the flow rate of argon gas + acetylene gas is 25 L / min, and the pre-lithiation agent is finally obtained, wherein the thickness of the carbon layer is 15 nm.

[0062] Example 12

[0063] The difference from Example 1 is that the first deposition reaction temperature, the second deposition reaction temperature and the third deposition reaction temperature are all 350° C., and the temperature of the fourth deposition reaction is 500° C., and finally a pre-lithiation agent is obtained.

[0064] Example 13

[0065] The difference from Example 1 is that the first deposition reaction temperature, the second deposition reaction temperature and the third deposition reaction temperature are all 700° C., and the temperature of the fourth deposition reaction is 800° C., and finally a pre-lithiation agent is obtained.

[0066] Example 14

[0067] The difference from Example 1 is that the first deposition reaction temperature, the second deposition reaction temperature and the third deposition reaction temperature are all 800° C., and the temperature of the fourth deposition reaction is 900° C., and finally a pre-lithiation agent is obtained.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that the introduction of the second argon gas + monosilane gas is eliminated, and a pre-lithiation agent is finally obtained.

[0070] Performance Testing

[0071] Three batches of pre-lithiation agents were prepared according to the methods of the examples and comparative examples. The three batches of pre-lithiation agents were added to the graphite negative electrode slurry and mixed. The mixture was coated on a copper foil to form a negative electrode sheet. The negative electrode sheet, the lithium iron phosphate positive electrode sheet and the lithium hexafluorophosphate electrolyte were assembled into a battery for the first charge specific capacity test (the discharge step was 0.1C discharge, which was changed to 0.05C discharge after reaching the cut-off voltage of 0.05V, and then changed to 0.02C discharge after reaching the cut-off voltage of 0.05V again, with a cut-off voltage of 50mV; and 0.1C charging to a cut-off voltage of 1.5V). The standard deviation of the three batches of first charge specific capacities was calculated, and the results are shown in Table 1.

[0072] Table 1

[0073]

[0074]

[0075] It can be seen from the results in Table 1 that the pre-lithiation agent prepared by the preparation method of the present application has good stability and consistency, and is more suitable for use in batteries.

[0076] Figure 1 This is an SEM image of the pre-lithiation agent in Example 1 of the present application. It can be seen from the image that the morphology of the pre-lithiation agent is well uniform.

[0077] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0078] Porous carbon acts as a carrier, and its high specific surface area provides sufficient space for reaction and storage of lithium-silicon alloy, which contributes to the rapid diffusion and storage of lithium ions, thereby helping to enhance the pre-lithiation effect of the pre-lithiation agent. Lithium-silicon alloy can provide a large amount of active lithium to compensate for the lithium ions consumed by SEI film formation in the first charge and discharge cycle of the battery, thereby helping to improve the cycle stability of the battery. The presence of amorphous silicon helps to seal the lithium-silicon alloy with strong activity, thereby helping to improve the structural stability of the lithium-silicon alloy. The carbon layer has a good insulating effect on the external environment, especially air and water, and can effectively protect the lithium-silicon alloy and the silicon layer, avoiding reaction with oxygen and water vapor in the air, thereby helping to improve the air stability of the pre-lithiation agent, which is beneficial to its safety and long-term storage during production and use. Therefore, the pre-lithiation agent of the present application has high stability and consistency, and its application in lithium-ion batteries helps to improve the consistency and stability of lithium-ion batteries.

[0079] The above are merely embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A pre-lithiation agent, characterized in that The pre-lithiation agent includes porous carbon, lithium-silicon alloy, amorphous silicon and a carbon layer. The lithium-silicon alloy and the amorphous silicon are located in the pores of the porous carbon, the amorphous silicon is coated on the surface of the lithium-silicon alloy, and the carbon layer is coated on the outer surface of the porous carbon.

2. The pre-lithiation agent according to claim 1, wherein The D50 of the porous carbon is 1 to 8 μm; and / or the mass ratio of the porous carbon to the lithium silicon alloy is 1:(2 to 4); And / or, the carbon layer has a thickness of 1 to 10 nm.

3. The pre-lithiation agent according to claim 1 or 2, characterized in that The specific surface area of ​​the porous carbon is 2100-2700 m 2 / g; and / or, the average pore diameter of the porous carbon is 0.1 to 2.5 nm.

4. The pre-lithiation agent according to any one of claims 1 to 3, characterized in that The molar ratio of lithium element to silicon element in the lithium-silicon alloy is (1.5-5):

1.

5. The pre-lithiation agent according to any one of claims 1 to 4, characterized in that The ratio of the mass of silicon element in the lithium silicon alloy to the mass of the amorphous silicon is 1:(0.001-1).

6. A method for preparing a pre-lithiation agent according to any one of claims 1 to 5, characterized in that: The preparation method comprises: The porous carbon is placed in a fluidized bed, and a first silane-containing gas, lithium vapor, a second silane-containing gas and a carbon-containing source gas are introduced in sequence to carry out a deposition reaction to obtain the pre-lithiation agent.

7. The preparation method according to claim 6, characterized in that The ratio of the mass of the porous carbon, the volume of the first silane-containing gas, the volume of the lithium vapor, the volume of the second silane-containing gas, and the volume of the carbon-containing source gas is (0.5-1 kg):(522-900 L):(1216-3200 L):150 L:(102-960 L); And / or, the temperature of the deposition reaction is 350-800°C.

8. The preparation method according to claim 7, characterized in that The preparation method comprises: The porous carbon is placed in the fluidized bed, and the first silane-containing gas is introduced in sequence to perform a first deposition reaction, the lithium vapor is introduced to perform a second deposition reaction to form a lithium-silicon alloy, the second silane-containing gas is introduced to perform a third deposition reaction to form amorphous silicon, and the carbon source gas is introduced to perform a fourth deposition reaction to form a carbon layer, thereby obtaining the pre-lithiation agent; Preferably, the temperature of the first deposition reaction, the temperature of the second deposition reaction, and the temperature of the third deposition reaction are each independently 350-700° C.; and / or, the temperature of the fourth deposition reaction is 500-800° C.; Preferably, the first silane-containing gas includes a first carrier gas and a first silane gas, and the volume ratio of the first carrier gas to the first silane gas is (1-4):(1-4); And / or, the second silane-containing gas includes a second carrier gas and a second silane-based gas, and the volume ratio of the second carrier gas to the second silane-based gas is (1-4):(1-4); And / or, the carbon source-containing gas includes a third carrier gas and a carbon source gas, and the volume ratio of the third carrier gas to the carbon source gas is (1-4):(1-4); Further preferably, the first silane gas and the second silane gas are independently selected from any one or more of monosilane, disilane and trisilane; And / or, the carbon source gas is a hydrocarbon gas, preferably the hydrocarbon gas is selected from any one or more of methane, ethane, ethylene and acetylene; And / or, the first carrier gas, the second carrier gas and the third carrier gas are each independently selected from any one or more of argon, nitrogen and helium.

9. A negative electrode sheet comprising a negative electrode active layer and a current collector, characterized in that: The negative electrode active layer contains the pre-lithiation agent according to any one of claims 1 to 5.

10. A lithium-ion battery comprising a positive electrode, an electrolyte and a negative electrode, characterized in that: The negative electrode sheet is the negative electrode sheet according to claim 9.

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