Pre-lithiated silicon-based negative electrode sheet and method for manufacturing the same, secondary battery
By combining electrochemical and mechanical pre-lithiation, ion transport channels were constructed and the pre-lithiation process was optimized, solving the problem of poor cycle performance of silicon-based anode sheets and achieving higher pre-lithiation uniformity and improved battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI XUANYI NEW ENERGY DEV CO LTD
- Filing Date
- 2026-04-22
- Publication Date
- 2026-07-24
AI Technical Summary
In the existing technology, silicon-based anode electrode sheets have poor cycle performance and poor pre-lithiation uniformity during the pre-lithiation process, which leads to a decrease in battery consistency and cycle performance.
Electrochemical pre-lithiation technology is employed, which involves constructing ion transport channels, combining mechanical pre-lithiation processes, spraying lithium trifluoromethane sulfinate electrolyte and covering with lithium strips, and combining rolling and heat treatment to optimize the pre-lithiation process.
It significantly improves the pre-lithiation uniformity and depth of silicon-based anode sheets, enhances battery first-efficiency and cycle performance, and reduces cell consistency issues.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of secondary batteries, and more specifically, to a pre-lithiated silicon-based negative electrode sheet, its preparation method, and a secondary battery. Background Technology
[0002] In recent years, the new energy industry has developed rapidly, and research and development on the material and cell systems are in full swing. The demand for energy density in the lithium battery industry has been increasing year by year. From cells to modules, everyone is pursuing the ultimate in lightweighting, but the use of positive and negative electrode material systems is still stuck ten years ago.
[0003] Currently, silicon-based materials are the most popular anode materials in solid-state, semi-solid-state, and liquid-state batteries. Silicon-based anodes possess extremely high lithium storage capacity, theoretically reaching 4200 mAh / g, and are abundant in resources. The specific capacity of silicon suboxide can also reach over 1400 mAh / g, making it the most promising material to replace graphite as the next-generation lithium-ion battery anode. Silicon-based anodes may be the key to improving energy density in the future, becoming the preferred anode material for current ternary high-energy-density battery cells.
[0004] However, the initial efficiency of silicon-oxygen anodes is far inferior to that of graphite systems. Even after years of dedicated research by material manufacturers, pre-lithiation cannot compensate for the nearly 15% capacity loss, and the cycle performance of high-silicon systems still lags significantly behind that of graphite systems. The low initial efficiency of anodes continues to hinder energy density improvements, while pre-lithiation offers new hope for improving the initial efficiency and cycle performance of silicon-based anode systems. In the field of pre-lithiation technology, mechanical pre-lithiation is currently one of the more efficient methods, but it suffers from inaccurate pre-lithiation control and poor pre-lithiation uniformity. This not only affects battery consistency but may also lead to localized over-lithiation, further exacerbating the volume expansion and cycle performance degradation of silicon-based anodes.
[0005] Therefore, how to provide a new method for preparing pre-lithiated silicon-based anode electrode sheets to improve the uniformity and depth of pre-lithiation of silicon-based anodes, thereby obtaining silicon-based anode electrode sheets with superior cycle performance, is one of the technical problems to be solved in this field. Summary of the Invention
[0006] The main objective of this invention is to provide a pre-lithiated silicon-based anode electrode sheet and its preparation method, as well as a secondary battery, to solve the problem of poor cycle performance of silicon-based anode electrode sheets in the prior art.
[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a pre-lithiated silicon-based negative electrode sheet, comprising: step S1, preparing a negative electrode active material, a conductive agent, a binder, and a dispersant into a negative electrode slurry; step S2, coating the negative electrode slurry onto both sides of a negative electrode current collector and drying it to form a first material layer and a second material layer on both sides of the negative electrode current collector, respectively, to obtain a first electrode sheet; step S3, preparing an electrolyte containing lithium trifluoromethanesulfinate, and spraying the electrolyte onto the surfaces of the first material layer and the second material layer away from the negative electrode current collector, respectively, to form a first material layer on both sides of the negative electrode current collector. A first activation layer is formed on the surface of the first material layer, and a second activation layer is formed on the surface of the second material layer to obtain a second electrode sheet; in step S4, along the direction away from the negative electrode current collector, a first lithium strip is covered on the surface of the first activation layer, and a second lithium strip is covered on the surface of the second activation layer to obtain a third electrode sheet; in step S5, along the direction away from the negative electrode current collector, a first fabric layer is covered on the surface of the first lithium strip, and a second fabric layer is covered on the surface of the second lithium strip to obtain a fourth electrode sheet; in step S6, the fourth electrode sheet is sequentially subjected to rolling and heat treatment to obtain a pre-lithiated silicon-based negative electrode sheet.
[0008] Further, in step S1, the negative electrode slurry comprises, by weight, 10 to 13 parts of negative electrode active material, 2 to 5 parts of conductive agent, 2 to 5 parts of binder, and 75 to 80 parts of dispersant; and / or, the solid content of the negative electrode slurry is 15% to 25%, and the viscosity is 3000 mPa·s to 8000 mPa·s.
[0009] Further, in step S2, a transfer coating machine is used for coating, and the roll gap width of the transfer coating machine is 320μm~350μm; and / or, the coating surface density is 160g / m³. 2 ~260g / m 2 ; and / or, the drying temperature is 90±10℃; and / or, the thickness of the first material layer and the second material layer are each independently 45μm~160μm, preferably 85±5μm.
[0010] Further, in step S3, the electrolyte also includes lithium salt, additives, and solvent, and the molar ratio of lithium salt, additives, solvent, and lithium trifluoromethanesulfinate is 1:3:14:(0.16~0.32); and / or, on the surfaces of the first material layer and the second material layer, the spraying amount of electrolyte is independently 0.1mL~0.5mL, and the spraying surface density is independently 0.005mL / cm². 2 ~0.04mL / cm 2 Preferably, the lithium salt is lithium hexafluorophosphate and / or lithium bisfluorosulfonyl imide; and / or, the additive is fluoroethylene carbonate and / or vinylene carbonate; and / or, the solvent is a carbonate.
[0011] Further, in step S4, the thickness of the first lithium strip and the second lithium strip are each independently 4μm~8μm; and / or, the first lithium strip completely covers the first activation layer, and the surface of the first lithium strip opposite to the first activation layer is denoted as surface A1, and the projection surface of the first activation layer on surface A1 is denoted as surface B1, with the area ratio of surface A1 to surface B1 being (1.0~1.2):1; and / or, the second lithium strip completely covers the second activation layer, and the surface of the second lithium strip opposite to the second activation layer is denoted as surface A2, and the projection surface of the second activation layer on surface A2 is denoted as surface B2, with the area ratio of surface A2 to surface B2 being (1.0~1.2):1.
[0012] Furthermore, in step S5, both the first fabric layer and the second fabric layer are flexible screen fabrics, preferably with a mesh size of 100 to 300 mesh; and / or, the thickness of each of the first fabric layer and the second fabric layer is independently 100 μm to 125 μm.
[0013] Further, in step S6, the rolling pressure of the rolling process is 160MPa~200MPa; and / or, the heat treatment temperature is 60℃~75℃, and the heat treatment time is 4h~24h; and / or, before the heat treatment, step S6 further includes a preservation treatment of the fourth electrode sheet after the rolling process for 12h~72h, preferably the preservation treatment is carried out under a vacuum of -0.08Mpa~-0.1Mpa.
[0014] Furthermore, the negative electrode active material is a silicon-carbon composite material, and the silicon-carbon composite material is selected from one or more of biomass silicon-carbon and resin-type silicon-carbon; and / or, the conductive agent is selected from one or more of single-walled carbon nanotubes, conductive carbon black, multi-walled carbon nanotubes, graphene and carbon fibers, preferably a mixture obtained by mixing single-walled carbon nanotubes and conductive carbon black in a weight ratio of (1~3):(1~2); and / or, the binder is selected from one or more of polyacrylic acid binder, polymethyl methacrylate binder and polyacrylonitrile binder; and / or, the dispersant is water; and / or, the negative electrode current collector is copper foil, and the thickness of the negative electrode current collector is 4.5μm~7μm.
[0015] A second aspect of the present invention provides a pre-lithiated silicon-based negative electrode sheet, which is prepared by the above-described method for preparing a pre-lithiated silicon-based negative electrode sheet.
[0016] A third aspect of the present invention provides a secondary battery comprising the aforementioned pre-lithiated silicon-based negative electrode sheet.
[0017] By applying the technical solution of this invention, electrochemical pre-lithiation technology is employed, and by constructing ion transport channels and simultaneously optimizing the pre-lithiation process, the uniformity and depth of pre-lithiation in silicon-based anodes are improved. This results in significantly enhancing the first-cycle efficiency of the battery, improving cycle performance, and reducing cell consistency issues caused by mechanical pre-lithiation. Detailed Implementation
[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.
[0019] As described in the background section, existing silicon-based anode electrode sheets suffer from poor cycle performance. To address this problem, a first aspect of the present invention provides a method for preparing a pre-lithiated silicon-based anode electrode sheet, comprising: step S1, preparing an anode active material, a conductive agent, a binder, and a dispersant into a anode slurry; step S2, coating the anode slurry onto both sides of a negative electrode current collector and drying it to form a first material layer and a second material layer on both sides of the negative electrode current collector, respectively, to obtain a first electrode sheet; and step S3, preparing an electrolyte containing lithium trifluoromethanesulfinate and spraying the electrolyte onto the surfaces of the first and second material layers away from the negative electrode current collector, respectively, to... A first activation layer is formed on the surface of a first material layer, and a second activation layer is formed on the surface of a second material layer to obtain a second electrode sheet; in step S4, a first lithium strip is covered on the surface of the first activation layer and a second lithium strip is covered on the surface of the second activation layer in a direction away from the negative electrode current collector to obtain a third electrode sheet; in step S5, a first fabric layer is covered on the surface of the first lithium strip and a second fabric layer is covered on the surface of the second lithium strip in a direction away from the negative electrode current collector to obtain a fourth electrode sheet; in step S6, the fourth electrode sheet is subjected to rolling and heat treatment in sequence to obtain a pre-lithiated silicon-based negative electrode sheet.
[0020] This invention improves the uniformity and depth of pre-lithiation in silicon-based anodes by constructing ion transport channels and optimizing the pre-lithiation process. Specifically, in steps S1 and S2, an anode slurry is prepared, coated onto both sides of the anode current collector, and dried to obtain a first electrode sheet containing a first material layer and a second material layer. Then, an electrolyte containing lithium trifluoromethanesulfinate (LiOTf) is prepared and sprayed onto the surfaces of the first and second material layers away from the anode current collector, resulting in a second electrode sheet containing a first activation layer and a second activation layer. As a highly efficient lithium salt, LiOTf not only improves the conductivity of the electrolyte but also promotes lithium ion diffusion in the electrode material, accelerating the pre-lithiation process. Furthermore, LiOTf reacts with silicon materials during pre-lithiation to form a stable and efficient SEI film, significantly improving the battery's initial efficiency and cycle stability. Compared to traditional coating, spraying the electrolyte provides a more uniform coverage of the electrode surface, avoiding localized over-lithiation or insufficient pre-lithiation, and improving the consistency of pre-lithiation. In steps S4 and S5, a third and fourth electrode sheet are formed by sequentially covering the activation layer with a lithium strip and a fabric layer. The lithium strip provides a sufficient lithium source, while the fabric layer not only provides additional mechanical support, preventing electrode deformation caused by uneven pressure during pre-lithiation, but also increases surface roughness, which is beneficial for further lithium ion intercalation. In step S6, the fourth electrode sheet undergoes roll forming and heat treatment to obtain a pre-lithiated silicon-based negative electrode sheet. Roll forming ensures close contact between the lithium strip and the negative electrode material, promoting contact self-discharge pre-lithiation, and also appropriately compresses the fabric layer, improving its bonding force with the lithium strip. Heat treatment promotes lithium ion intercalation in the silicon-based material and ensures that the remaining lithium metal in the outer layer is completely ionized and fully introduced into the silicon-based material, further improving the pre-lithiation efficiency and the initial efficiency of the silicon-oxygen negative electrode.
[0021] The preparation method provided by this invention uses self-discharge electrochemical pre-lithiation to catalyze mechanical pre-lithiation kinetics, improving the depth and uniformity of mechanical pre-lithiation by constructing ion transport channels. The addition of lithium trifluoromethane sulfinate further enhances the initial efficiency of the resulting battery electrode sheet. Mechanical rolling tightly bonds the lithium metal to the wetted negative electrode, facilitating self-discharge pre-lithiation. Furthermore, after the self-discharge at the lithium metal liquid-solid interface, a heat treatment process is introduced to improve the kinetics of lithium-ion intercalation in the silicon-oxygen negative electrode. Ionizing the remaining lithium metal in the outer layer and completely introducing it into the silicon-oxygen structure effectively enhances the initial efficiency of the small-particle silicon-based negative electrode. Introducing a pre-lithiation process during the development of the negative electrode sheet ensures that the particles are charged and discharged under relatively low stress (material-end pre-lithiation requires high-temperature sintering, and material expansion affects cycle performance), while also achieving controllable pre-lithiation based on the lithium strip thickness.
[0022] In summary, the above preparation method, through the combination of electrochemical pre-lithiation and mechanical pre-lithiation, constructs an effective lithium-ion transport channel, optimizes the pre-lithiation process, significantly improves the pre-lithiation efficiency and uniformity of silicon-based anode sheets, and thus improves their electrical performance, especially significantly enhancing their cycle stability.
[0023] In step S1, to ensure the obtained negative electrode sheet has a higher lithium storage capacity, the obtained negative electrode slurry preferably includes 10 to 13 parts by weight of negative electrode active material, 2 to 5 parts by weight of conductive agent, 2 to 5 parts by weight of binder, and 75 to 80 parts by weight of dispersant. Furthermore, the obtained negative electrode slurry preferably has a solid content of 15% to 25% and a viscosity of 3000 mPa·s to 8000 mPa·s (more preferably 4500 ± 500 mPa·s), which facilitates the coating process by ensuring that it is neither too thin nor too viscous, thus promoting the formation of a more uniform, denser active material layer with better electrochemical performance.
[0024] Further, in step S2, preferably: a transfer coating machine is used for coating, and the roll gap width of the transfer coating machine is 320μm~350μm; and / or, the coating surface density is 160g / m³. 2 ~260g / m 2 The drying temperature is 90±10℃; and / or the thickness of the first material layer and the second material layer are each independently 45μm~160μm (preferably 85±5μm). The preferred coating density combined with the roll gap width promotes a more suitable thickness and compositional distribution in the formed material layers, resulting in a more uniform thin electrode structure, which is beneficial for further improving the energy density and cycle performance of the final negative electrode. The preferred drying temperature allows the coated wet film to cure more effectively, reducing excessive expansion and microcracks.
[0025] In step S3, the electrolyte preferably further includes lithium salt, additives, and solvent, and the molar ratio of lithium salt, additives, solvent, and lithium trifluoromethanesulfinate is 1:3:14:(0.16~0.32) to further improve the stability of the prepared electrolyte and promote a more effective reaction between pre-lithiated lithium ions and the active material. Regarding the spraying amount and spraying density, preferably, the spraying amount of electrolyte on the surfaces of the first and second material layers is independently 0.1 mL~0.5 mL, and the spraying density is independently 0.005 mL / cm². 2 ~0.04mL / cm 2This is to ensure uniform wetting of the active material layer surface, thereby more effectively reducing uneven lithium-ion deposition and improving pre-lithiation efficiency, ultimately enhancing the electrical and cycling performance of the resulting electrode sheet. In practical applications, the lithium salt is lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide; and / or, the additive is fluoroethylene carbonate and / or vinylene carbonate; and / or, the solvent is a carbonate.
[0026] In step S4, the thickness of the first and second lithium strips is preferably 4 μm to 8 μm, each independently. The thickness of the lithium strips used in the preparation method provided by this invention directly affects the lithium ion transport pathway and the degree of pre-lithiation. An excessively thin lithium strip may lead to insufficient lithium ion supply during the pre-lithiation process, while an excessively thick lithium strip may cause unnecessary lithium ion waste and even damage to the electrode structure. Therefore, the preferred thickness ensures a sufficient but not excessive lithium source during the mechanical pre-lithiation process, thereby achieving a more efficient pre-lithiation process. Ultimately, while reducing or avoiding localized overlithiation problems, it provides more ion transport channels for the resulting negative electrode sheet, thus significantly improving its first-efficiency and cycle performance. To further improve pre-lithiation efficiency, preferably: the first lithium strip completely covers the first activation layer, the surface of the first lithium strip opposite to the first activation layer is denoted as surface A1, the projection surface of the first activation layer on surface A1 is denoted as surface B1, and the area ratio of surface A1 to surface B1 is (1.0~1.2):1; and / or, the second lithium strip completely covers the second activation layer, the surface of the second lithium strip opposite to the second activation layer is denoted as surface A2, the projection surface of the second activation layer on surface A2 is denoted as surface B2, and the area ratio of surface A2 to surface B2 is (1.0~1.2):1.
[0027] In step S5, preferably, both the first and second fabric layers are flexible screen fabrics (specifically, nylon screen fabrics or other types of screen fabrics commonly used in the art can be selected), and more preferably, the mesh size of the flexible screen fabric is 100 mesh to 300 mesh, so as to further enhance the ion transport path while providing mechanical strength. Specifically, the thickness of the first and second fabric layers is independently 100 μm to 125 μm.
[0028] Further, in step S6, the rolling pressure of the rolling process is preferably 160MPa~200MPa, thereby promoting a tighter bond between the activation layer and the lithium strip and optimizing the mechanical pre-lithiation process. Subsequently, to further accelerate the lithium-ion insertion into the active material layer in the lithium strip and significantly improve the pre-lithiation efficiency, the heat treatment temperature is preferably 60℃~75℃, and the holding time is 4h~24h, so as to obtain an electrode sheet with better electrical and cycling performance. Before the heat treatment, in order to better protect the lithium strip and reduce its oxidation in air, and also to provide a purer environment for lithium-ion insertion during the heat treatment process, step S6 preferably also includes a storage treatment of the fourth electrode sheet after the rolling process for 12h~72h, more preferably, the storage treatment is carried out under a vacuum of -0.08Mpa~-0.1Mpa.
[0029] In several typical embodiments, the negative electrode active material is a silicon-carbon composite material, and the silicon-carbon composite material is selected from one or more of biomass silicon-carbon and resin-type silicon-carbon; and / or, the conductive agent is selected from one or more of single-walled carbon nanotubes, conductive carbon black, multi-walled carbon nanotubes, graphene, and carbon fibers; and / or, the binder is selected from one or more of polyacrylic acid binder, polymethyl methacrylate (PMMA) binder, and polyacrylonitrile (PAN) binder; and / or, the dispersant is water; and / or, the negative electrode current collector is copper foil, and the thickness of the negative electrode current collector is 4.5 μm to 7 μm. In order to form a more efficient three-dimensional conductive network in the material layer before pre-lithiation and ultimately obtain an electrode sheet with higher electrical performance, the conductive agent is further preferably a mixture of single-walled carbon nanotubes and conductive carbon black in a weight ratio of (1~3):(1~2).
[0030] A second aspect of this invention provides a pre-lithiated silicon-based anode electrode sheet, which is prepared by the aforementioned method for preparing pre-lithiated silicon-based anode electrodes. The resulting pre-lithiated silicon-based anode electrode sheet, obtained based on electrochemical pre-lithiation technology, possesses optimized ion transport channels, high pre-lithiation effect, and uniformity, thus exhibiting excellent electrical and cycling performance. It should be noted that due to the complex structural formation and compositional changes during the preparation process, and the limitations of the specific characteristics of electrode materials and existing testing and characterization methods, a comprehensive quantitative characterization of the complex microstructure of the aforementioned pre-lithiated electrode sheet is difficult. However, performance test results have already shown that the anode electrode sheet obtained by this invention possesses superior cycling stability.
[0031] A third aspect of the present invention provides a secondary battery comprising the aforementioned pre-lithiated silicon-based negative electrode sheet. The resulting pre-lithiated silicon-based negative electrode sheet exhibits superior cycle performance, significantly improving the overall performance of the secondary battery, particularly its first-efficiency and cycle performance, reducing cell consistency issues, and providing strong technical support for the development and application of high-energy-density, long-cycle secondary batteries.
[0032] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.
[0033] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.
[0034] Example 1
[0035] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0036] (1-1) Take 10 parts by weight of non-pre-lithiated silicon carbon anode powder (manufacturer model BTR-SiC450), 2 parts by weight of single-walled carbon nanotubes and 1 part by weight of conductive carbon black and mix them dry until the powder is uniform.
[0037] (1-2) Add 3 parts by weight of solid polyacrylic adhesive (manufacturer model PAA-200K) and 20 parts by weight of deionized water to knead the dry matter until the powder is completely wetted and presents a dry paste.
[0038] (1-3) Add 60 parts by weight of deionized water to the kneaded slurry and disperse it at high speed under vacuum until the slurry is uniform;
[0039] (1-4) Vacuum defoaming was performed by low-speed homogenization, and the mixture was stirred slowly in reverse until there were no large number of fine air bubbles in the slurry. The slurry was then sieved through a 150-mesh sieve to obtain a negative electrode slurry with a solid content of 16% and a viscosity of 4500±500 mPa·s.
[0040] (2) Apply coating to the copper foil surface using a transfer coating machine with a roll gap width of 340 μm and a coating surface density of 125 g / m². 2 After drying in a forced-air oven at 90℃, the low-efficiency silicon anode, namely the first electrode sheet, is obtained by winding. A first material layer with a thickness of 85±5μm and a second material layer with a thickness of 85±5μm are formed on the two opposite surfaces.
[0041] (3) Fluoroethylene carbonate (FEC) and carbonate solvent were mixed at a molar ratio of 3:14. After being magnetically stirred at low temperature until homogeneous, 1 molar of lithium hexafluorophosphate and 0.28 molar of lithium trifluoromethanesulfinate were added. The mixture was then magnetically stirred until the solution was colorless and clear, resulting in a low-lithium salt concentration electrolyte (the molar ratio of lithium salt, FEC additive, carbonate solvent, and lithium trifluoromethanesulfinate was 1:3:14:0.28). The dried electrode rolls were die-cut, with a die-cut size of 126×96mm. The obtained low-lithium salt concentration electrolyte was evenly sprayed onto the surface of the die-cut negative electrode sheet for wetting. Before spraying, the tabs were covered with PET film. The single-sided negative electrode spraying amount was 0.3mL, and the spraying surface density was 0.0248mL / cm². 2 Subsequently, electrode sheets with a first activation layer and a second activation layer respectively coated with electrolyte were obtained;
[0042] (4) Die-cut the lithium strips. Based on the die-cut size of the electrode sheet, the die-cut size of the two lithium strips, each with a thickness of 6μm, is slightly larger than the negative electrode material area, and the area of each is 130×100mm. Along the direction away from the negative electrode current collector, cover the surface of the first activation layer with the first lithium strip and cover the surface of the second activation layer with the second lithium strip to obtain the third electrode sheet. The first lithium strip completely covers the first activation layer. Let the surface of the first lithium strip opposite to the first activation layer be A1, and let the projection surface of the first activation layer on the A1 surface be B1. The area ratio of the A1 surface to the B2 surface is 1.07:1. The second lithium strip completely covers the second activation layer. Let the surface of the second lithium strip opposite to the second activation layer be A2, and let the projection surface of the second activation layer on the A2 surface be B2. The area ratio of the A2 surface to the B2 surface is 1.07:1.
[0043] (5) Then, two 100μm thick, 200-mesh flexible nylon sieves are used as the outermost layer to provide toughness and roughness, and the interior is a three-layer structure of lithium strip, negative electrode and lithium strip.
[0044] (6) Perform cold rolling. The diameter of the rolling roller is 1.5 meters and the pressure is 160 MPa. During the rolling process, the lithium strip must completely cover the material area and the negative electrode tab must be exposed. The composite five-layer structure is stored in a nitrogen atmosphere for 12 hours until the lithium strip on the negative electrode surface is completely without metallic luster. Then, it is vacuum heated at 60°C for 12 hours (vacuum degree is -0.1 MPa).
[0045] Example 2
[0046] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0047] The only difference between this embodiment and Embodiment 1 is that in step (2), the roll gap width is changed to 300 μm, and the coating surface density is changed to 150 g / m². 2 .
[0048] Example 3
[0049] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0050] The only difference between this embodiment and Embodiment 1 is that in step (2), the roll gap width is changed to 400 μm, and the coating surface density is changed to 280 g / m². 2 .
[0051] Example 4
[0052] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0053] The only difference between this embodiment and Example 1 is that in step (3), the molar ratio of lithium salt, FEC additive, carbonate solvent and lithium trifluoromethane sulfinate is changed to 1:3:14:0.1.
[0054] Example 5
[0055] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0056] The only difference between this embodiment and Example 1 is that in step (3), the molar ratio of lithium salt, FEC additive, carbonate solvent and lithium trifluoromethane sulfinate is changed to 1:3:14:0.5.
[0057] Example 6
[0058] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0059] The only difference between this embodiment and Embodiment 1 is that in step (3), the amount of single-sided negative electrode coating is changed by 0.05 mL, and the coating density is changed to 0.0041 mL / cm². 2 .
[0060] Example 7
[0061] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0062] The only difference between this embodiment and Embodiment 1 is that in step (3), the amount of single-sided negative electrode coating is changed by 0.5 mL, and the coating density is changed to 0.041 mL / cm². 2 .
[0063] Example 8
[0064] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0065] The only difference between this embodiment and embodiment 1 is that the roller pressure in step (6) is changed to 150MPa, and the vacuum heating temperature is changed to 80℃.
[0066] Example 9
[0067] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0068] The only difference between this embodiment and embodiment 1 is that the roller pressure in step (6) is changed to 250MPa, and the vacuum heating temperature is changed to 50℃.
[0069] Example 10
[0070] A method for preparing a pre-lithiated silicon-based negative electrode sheet:
[0071] The only difference between this embodiment and embodiment 1 is that in step (6), no preservation treatment in a nitrogen atmosphere was performed.
[0072] Comparative Example 1
[0073] A method for preparing a silicon-based negative electrode sheet:
[0074] The only difference between this comparative example and Example 1 is that steps (3) to (6) were not performed; instead, the first electrode sheet obtained in step (2) was directly used as the final electrode sheet sample.
[0075] Comparative Example 2
[0076] A method for preparing a silicon-based negative electrode sheet:
[0077] The only difference between this comparative example and Example 1 is that step (3) was not performed. Instead, two lithium strips were directly applied to the two sides of the first electrode sheet obtained in step (2) and the subsequent steps were performed.
[0078] Comparative Example 3
[0079] A method for preparing a silicon-based negative electrode sheet:
[0080] The only difference between this comparative example and Example 1 is that lithium trifluoromethanesulfinate was not added to the electrolyte prepared in step (3).
[0081] Comparative Example 4
[0082] A method for preparing a silicon-based negative electrode sheet:
[0083] The only difference between this comparative example and Example 1 is that, in the electrolyte prepared in step (3), lithium difluorooxalate borate is used instead of lithium trifluoromethane sulfinate in an equimolar amount.
[0084] Comparative Example 5
[0085] A method for preparing a silicon-based negative electrode sheet:
[0086] The only difference between this comparative example and Example 1 is that step (4) was not performed. Instead, two flexible screens were directly applied to the two sides of the electrode sheet obtained in step (3) and subsequent rolling and pressing steps were performed.
[0087] Test methods
[0088] A positive electrode sheet was prepared by coating-rolling-slitting, using lithium nickel cobalt manganese oxide as the positive electrode active material. Using the negative electrode sheet samples obtained in the above examples and comparative examples as negative electrodes, a polyethylene (PE) porous membrane coated with an alumina ceramic layer as a separator, a 1.0 M LiPF6 EC / EMC / DMC (volume ratio 1:1:1) solution, and 2 wt.% VC as an electrolyte, battery cell samples with a capacity of 2 Ah were assembled.
[0089] Cycling performance of each cell sample was tested at room temperature, and the capacity retention rate after 100, 150, and 300 cycles was obtained. The test results are shown in Table 1.
[0090] Table 1
[0091]
[0092] As can be seen from the above description, the embodiments of the present invention have achieved the preparation of a high-performance negative electrode sheet. Thanks to the mechanical pre-lithiation and electrochemical pre-lithiation processes, the resulting electrode sheet possesses superior electrical properties, especially long-cycle performance.
[0093] Specifically, in each embodiment:
[0094] Comparing Examples 2 and 3 with Example 1, it can be seen that by optimizing the roll gap width and coating density in step S2, the formed material layer can have a more suitable thickness and composition distribution, resulting in a more uniform thin electrode structure, which is beneficial to further improve the energy density and cycle performance of the final negative electrode sheet.
[0095] Comparing Examples 4 and 5 with Example 1, it can be seen that by optimizing the molar ratio of lithium salt, additives, solvent, and lithium trifluoromethanesulfinate, the stability of the prepared electrolyte can be further improved, and the reaction between pre-lithiated lithium ions and active materials can be promoted more effectively.
[0096] Comparing Examples 6 and 7 with Example 1, it can be seen that by optimizing the amount and density of single-sided negative electrode spraying in step S3, the phenomenon of uneven lithium-ion deposition can be reduced more effectively under the condition of uniform wetting of the surface of the active material layer, thereby more effectively improving the pre-lithiation efficiency and further improving the electrical performance and cycle performance of the final electrode sheet.
[0097] Comparing Examples 8 and 9 with Example 1, it can be seen that by optimizing the rolling pressure and vacuum heating temperature in step S6, the activation layer and lithium strip can be more tightly bonded, optimizing the mechanical pre-lithiation process; at the same time, it further accelerates the embedding of lithium ions in the active material layer in the lithium strip, and significantly improves the pre-lithiation efficiency.
[0098] Comparing Example 10 with Example 1, it can be seen that by preferably performing preservation treatment in a nitrogen atmosphere, the lithium strip can be better protected, its oxidation in the air can be reduced, and a purer environment can be provided for lithium ion intercalation during the heat treatment process, ultimately resulting in an electrode sheet with better electrical and cycle performance.
[0099] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.
[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a pre-lithiated silicon-based negative electrode sheet, characterized in that, include: Step S1: Prepare a negative electrode slurry by combining the negative electrode active material, conductive agent, binder and dispersant; Step S2: The negative electrode slurry is coated on both sides of the negative electrode current collector and dried to form a first material layer and a second material layer on both sides of the negative electrode current collector, respectively, to obtain the first electrode sheet. Step S3: Prepare an electrolyte containing lithium trifluoromethane sulfinate, and spray the electrolyte onto the surfaces of the first material layer and the second material layer away from the negative electrode current collector, respectively, to form a first activation layer on the surface of the first material layer and a second activation layer on the surface of the second material layer, thereby obtaining a second electrode sheet; Step S4: Along the direction away from the negative electrode current collector, cover the surface of the first activation layer with the first lithium strip and cover the surface of the second activation layer with the second lithium strip to obtain the third electrode sheet; Step S5: Along the direction away from the negative electrode current collector, cover the surface of the first lithium strip with the first fabric layer, and cover the surface of the second lithium strip with the second fabric layer to obtain the fourth electrode sheet. In step S6, the fourth electrode sheet is subjected to rolling and heat treatment in sequence to obtain the pre-lithiated silicon-based negative electrode sheet.
2. The method for preparing the pre-lithiated silicon-based negative electrode sheet according to claim 1, characterized in that, In step S1 By weight, the negative electrode slurry comprises 10 to 13 parts of the negative electrode active material, 2 to 5 parts of the conductive agent, 2 to 5 parts of the binder, and 75 to 80 parts of the dispersant; and / or, The negative electrode slurry has a solid content of 15% to 25% and a viscosity of 3000 mPa·s to 8000 mPa·s.
3. The method for preparing a pre-lithiated silicon-based negative electrode sheet according to claim 1 or 2, characterized in that, In step S2 The coating is performed using a transfer coating machine, wherein the roll gap width of the transfer coating machine is 320 μm to 350 μm; and / or, The surface density of the coating is 160 g / m³. 2 ~260g / m 2 ; and / or, The drying temperature is 90±10℃; and / or, The thickness of the first material layer and the second material layer are each independently 45μm~160μm, preferably 85±5μm.
4. The method for preparing a pre-lithiated silicon-based negative electrode sheet according to any one of claims 1 to 3, characterized in that, In step S3 The electrolyte further includes lithium salt, additives, and solvent, and the molar ratio of the lithium salt, the additives, the solvent, and the lithium trifluoromethanesulfinate is 1:3:14:(0.16~0.32); and / or, On the surfaces of the first material layer and the second material layer, the amount of electrolyte sprayed is independently 0.1 mL to 0.5 mL, and the spray density is independently 0.005 mL / cm². 2 ~0.05mL / cm 2 ; Preferably, the lithium salt is lithium hexafluorophosphate and / or lithium bisfluorosulfonylimide; and / or, the additive is fluoroethylene carbonate and / or vinylene carbonate; and / or, the solvent is a carbonate.
5. The method for preparing a pre-lithiated silicon-based negative electrode sheet according to any one of claims 1 to 4, characterized in that, In step S4 The thickness of the first lithium strip and the second lithium strip are each independently 4μm~8μm; and / or, The first lithium strip completely covers the first activation layer. Let the surface of the first lithium strip opposite the first activation layer be surface A1, and let the projection of the first activation layer onto surface A1 be surface B1. The area ratio of surface A1 to surface B1 is (1.0~1.2):1; and / or, The second lithium strip completely covers the second activation layer. The surface of the second lithium strip opposite to the second activation layer is denoted as surface A2, and the projection surface of the second activation layer on surface A2 is denoted as surface B2. The area ratio of surface A2 to surface B2 is (1.0~1.2):
1.
6. The method for preparing a pre-lithiated silicon-based negative electrode sheet according to any one of claims 1 to 5, characterized in that, In step S5 Both the first fabric layer and the second fabric layer are flexible screen fabrics, preferably with a mesh size of 100 to 300 mesh; and / or, The thickness of the first fabric layer and the second fabric layer are each independently 100μm~125μm.
7. The method for preparing a pre-lithiated silicon-based negative electrode sheet according to any one of claims 1 to 6, characterized in that, In step S6 The rolling pressure of the rolling process is 160MPa~200MPa; and / or, The heat treatment is performed at a holding temperature of 60℃~75℃ for 4h~24h; and / or, Before the heat treatment, step S6 further includes storing the fourth electrode sheet after the roll forming process for 12h to 72h, preferably under a vacuum of -0.08Mpa to -0.1Mpa.
8. The method for preparing a pre-lithiated silicon-based negative electrode sheet according to any one of claims 1 to 7, characterized in that, The negative electrode active material is a silicon-carbon composite material, and the silicon-carbon composite material is selected from one or more of biomass silicon-carbon and resin-type silicon-carbon; and / or, The conductive agent is selected from one or more of single-walled carbon nanotubes, conductive carbon black, multi-walled carbon nanotubes, graphene, and carbon fibers, preferably a mixture obtained by mixing the single-walled carbon nanotubes and the conductive carbon black in a weight ratio of (1~3):(1~2); and / or, The adhesive is selected from one or more of polyacrylic acid adhesives, polymethyl methacrylate adhesives, and polyacrylonitrile adhesives; and / or, The dispersant is water; and / or, The negative electrode current collector is a copper foil, and the thickness of the negative electrode current collector is 4.5μm~7μm.
9. A pre-lithiated silicon-based negative electrode sheet, characterized in that, The pre-lithiated silicon-based negative electrode sheet is prepared by the method for preparing the pre-lithiated silicon-based negative electrode sheet according to any one of claims 1 to 8.
10. A secondary battery, characterized in that, The secondary battery includes the pre-lithiated silicon-based negative electrode sheet as described in claim 9.