Negative electrode pre-lithiation method, pre-lithiated negative electrode and battery

Abstract

The invention provides a negative electrode pre-lithiation method, a pre-lithiated negative electrode and a battery, and the negative electrode pre-lithiation method comprises the following steps: forming a groove in an active substance layer on the surface of at least one side of a negative electrode pole piece, then immersing the negative electrode pole piece in a conductive polymer solution, and then immersing the negative electrode pole piece in a lithium salt solution to obtain a one-step pre-lithiated negative electrode pole piece; and placing the one-step pre-lithiated negative electrode piece in a gas environment to adsorb gas, then arranging metal lithium on the surface of the one-step pre-lithiated negative electrode piece adsorbing the gas, and carrying out gas-solid reaction, curing and post-treatment to obtain the pre-lithiated negative electrode. According to the negative electrode pre-lithiation method, a three-dimensional groove network is firstly constructed on the surface of an active material, and a two-step composite pre-lithiation process is combined, so that a composite solid electrolyte interface layer which has gradient distribution and is rich in a lithium source and a buffer skeleton is constructed in situ inside and on the surface of a negative electrode; therefore, the first coulombic efficiency, the cycling stability and the rate capability of the battery are provided at the same time.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a method for pre-lithiation of a negative electrode, a pre-lithiated negative electrode, and a battery. Background Technology

[0002] In lithium-ion batteries, the performance of the anode material is crucial, directly determining core indicators such as energy density and cycle life. However, traditional and next-generation high-capacity anode materials (especially silicon-based materials) face a fundamental challenge during the first charge-discharge cycle: a complex electrochemical reaction occurs between the anode surface and the electrolyte, forming an SEI (solid electrolyte interface) film. This process irreversibly consumes a large amount of lithium ions from the cathode, leading to a significant reduction in the battery's initial coulombic efficiency (typically below 90% for silicon-based anodes), resulting in permanent capacity loss and severely limiting the improvement of battery energy density. Furthermore, the initially formed SEI film often has limited stability and poor ionic conductivity, continuously thickening, breaking, and reconstructing during subsequent cycles, constantly consuming active lithium and electrolyte, thereby exacerbating capacity decay and impedance growth, and affecting cycle life.

[0003] To fundamentally compensate for the irreversible lithium loss during the initial charging cycle and overcome the bottleneck of first-cycle efficiency, pre-lithiation technology has emerged. Pre-lithiation technology can be divided into positive electrode pre-lithiation and negative electrode pre-lithiation based on the location of lithium replenishment. Positive electrode pre-lithiation involves introducing lithium-rich compounds (such as Li₂O, Li₅FeO₄, or Li₂NiO₂) as additives into the positive electrode. During the first charge, the lithium-rich compounds decompose to release active lithium to compensate for the loss. However, this method has inherent limitations. The decomposition process of lithium-rich compounds is often accompanied by electrolyte oxidation and gas generation. The introduced impurity atoms form electrochemically inert byproducts, hindering ion / electron transport within the electrode and increasing internal resistance. Furthermore, its theoretical lithium replenishment capacity (typically <1000 mAh / g) is far lower than that of metallic lithium (3860 mAh / g).

[0004] In contrast, negative electrode pre-lithiation, because it directly replenishes lithium on the negative electrode side, avoids introducing inactive materials into the positive electrode, and is considered a more direct and efficient pathway. It utilizes the strong reducing properties of metallic lithium to chemically react with the negative electrode material, spontaneously completing the lithium replenishment process. This allows lithium to be preferentially used to form a stable SEI film during battery activation, effectively preserving the positive electrode lithium, effectively compensating for initial lithium loss, and significantly improving the first-cycle coulombic efficiency. Therefore, negative electrode pre-lithiation is a key enabling technology for realizing high-energy-density lithium batteries, especially for promoting the commercial application of novel negative electrodes such as silicon-carbon.

[0005] However, the negative electrode pre-lithiation technology still has the following problems:

[0006] 1. Process complexity and high cost: Existing pre-lithiation methods (such as electrochemical pre-lithiation, SLMP spraying and lithium foil bonding) all require additional and complex process steps or special equipment, which are cumbersome to operate, have high production costs, and have poor compatibility with large-scale industrial battery production processes.

[0007] 2. Poor uniformity and consistency of pre-lithiation: It is difficult to achieve uniform and consistent pre-lithiation on the negative electrode sheet on a macroscopic scale. Local over- or under-lithiation will seriously affect the overall performance and safety of the battery.

[0008] 3. Risks of interface stability and structural damage: Existing pre-lithiation methods may form an unstable interface layer, or the structure of the anode material itself may be damaged due to violent reactions during the pre-lithiation process (such as the breakage of silicon particles), affecting the cycle life of the battery.

[0009] 4. Safety and compatibility concerns: Directly using highly active lithium metal powder or lithium foil for pre-lithiation poses safety risks during processing and handling. Furthermore, additives such as SLMP have poor compatibility with existing electrode preparation systems (such as PVDF / NMP slurries), limiting their application.

[0010] Based on the above research, there is a need to provide a negative electrode pre-lithiation method. The negative electrode pre-lithiation method has a simple process, is easy to integrate into existing production lines, has high safety, and has excellent pre-lithiation effect. Summary of the Invention

[0011] The purpose of this invention is to provide a method for pre-lithiation of the negative electrode, a pre-lithiated negative electrode, and a battery. The method for pre-lithiation of the negative electrode involves first constructing a three-dimensional groove network on the surface of the active material, and then combining it with a two-step composite pre-lithiation process to construct a composite solid electrolyte interface layer with a gradient distribution, rich in lithium source and buffer framework, in situ inside and on the surface of the negative electrode. This simultaneously provides the battery's initial coulombic efficiency, cycle stability, and rate performance.

[0012] To achieve this objective, the present invention adopts the following technical solution:

[0013] In a first aspect, the present invention provides a method for pre-lithiation of a negative electrode, the method comprising the following steps:

[0014] (1) Grooves are made on the active material layer on at least one side of the negative electrode sheet to form a groove array on the surface of the active material layer, thereby obtaining a structured negative electrode sheet.

[0015] (2) The negative electrode sheet after the structuring treatment described in step (1) is first immersed in a conductive polymer solution, and then immersed in a lithium salt solution. After the immersion is completed, the obtained negative electrode sheet is dried to obtain a one-step pre-lithiation negative electrode sheet.

[0016] (3) Place the one-step pre-lithiation negative electrode sheet described in step (2) in a gas environment to adsorb gas, and then set metallic lithium on the surface of the one-step pre-lithiation negative electrode sheet that adsorbs gas to carry out a gas-solid reaction to obtain a two-step pre-lithiation negative electrode sheet.

[0017] (4) The two-step pre-lithiation anode sheet described in step (3) is aged and post-treated to obtain a pre-lithiation anode.

[0018] This invention first creates grooves on the surface of the active material layer on one or both sides of the negative electrode sheet. These grooves divide the negative electrode surface into multiple independent active material regions, forming a three-dimensional structural framework. Furthermore, creating these grooves significantly increases the surface porosity of the negative electrode sheet, thereby achieving electrode control, increasing lithium-ion diffusion channels, and shortening the lithium-ion migration path. In addition, the grooves facilitate deeper wetting and penetration of the electrolyte, allowing the capacity of the active material near the current collector to be utilized more effectively. Moreover, the grooves on the electrode surface increase the contact area between the active material and the electrolyte, thereby increasing the lithium-ion insertion / extraction rate and improving the battery's charge / discharge performance.

[0019] In step (2) of this invention, a first step of chemical pre-lithiation is performed: the negative electrode sheet with grooves is first immersed in a conductive polymer solution, and a conductive polymer coating is formed on the surface of the electrode sheet, the inner wall of the groove, and the bottom of the groove through self-polymerization. Subsequently, the electrode sheet is placed in a lithium salt solution, and the reducing and adhesive properties of the conductive polymer are used to preferentially deposit nano-lithium particles in situ inside the groove. The inside of the groove becomes a composite structure enriched with lithium source and polymer. This structure can not only store lithium, but also buffer volume expansion.

[0020] Step (3) of this invention involves a second pre-lithiation step, which constructs a dense inorganic interface layer on the surface. Specifically, it utilizes the strong reducing properties of metallic lithium to induce a gas-solid chemical reaction with a specific gaseous component (such as N2, O2, CO2) that is intentionally introduced or present in the environment. This spontaneously generates a lithium-containing compound interface layer composed of one or more of lithium nitride, lithium oxide, or lithium carbonate on the surface of the negative electrode and the edge of the groove. This spontaneously formed interface layer itself acts as a lithium replenishing agent. Furthermore, due to its excellent ion conductivity, it can also serve as an excellent lithium-ion channel, accelerating the pre-lithiation reaction between the underlying metallic lithium and the negative electrode active material. Moreover, the gas-solid reaction technology in step (3) of this invention does not require any additional complex equipment or artificial deposition steps to pre-manufacture a protective layer. The formation of the entire interface layer is based on a simple chemical reaction, making the process extremely simple and easy to integrate into existing production lines, achieving "unmanned" self-assembly.

[0021] Therefore, this invention constructs a composite solid electrolyte interface layer with a gradient distribution, rich in lithium source and buffer framework, in situ inside and on the surface of the negative electrode, which greatly stabilizes the electrode structure and thus simultaneously improves the battery's initial coulombic efficiency, cycle stability and rate performance.

[0022] Preferably, the negative electrode sheet in step (1) includes a current collector and an active material layer on at least one side of the current collector surface.

[0023] Preferably, the current collector includes any one of copper foil, copper-plated aluminum foil, or stainless steel foil.

[0024] Preferably, the active material layer comprises a negative electrode active material, a conductive agent, and a binder. The negative electrode active material comprises any one or a combination of at least two of elemental silicon, porous silicon-carbon composite, silicon suboxide, silicon oxide, artificial graphite, natural graphite, composite graphite, soft carbon, or hard carbon. The conductive agent comprises any one or a combination of at least two of conductive carbon black, conductive graphite, carbon nanofibers, carbon nanotubes, or graphene. The binder comprises any one or a combination of at least two of polyvinylidene fluoride, polytetrafluoroethylene, polyamide, polyimide, polymethyl methacrylate, carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, polyacrylic acid, or polyvinyl alcohol.

[0025] Preferably, in the active material layer, the mass percentage of the negative electrode active material is 88wt%-98wt%, for example, it can be 88wt%, 90wt%, 92wt%, 94wt%, 96wt% or 98wt%, the mass percentage of the conductive agent is 1wt%-7wt%, for example, it can be 1wt%, 3wt%, 5wt% or 7wt%, and the mass percentage of the binder is 1wt%-5wt%, for example, it can be 1wt%, 2wt%, 3wt%, 4wt% or 5wt%, but it is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] Preferably, the method for creating the groove in step (1) includes laser etching.

[0027] Preferably, after creating the groove in step (1), the weight loss rate of the active material layer is c, where c = k × (w × d × L) / b0, where w is the average width of the groove in μm, d is the average depth of the groove in μm, and L is the total length of the groove per unit area in m / m. 2 k is the conversion factor, and b0 is the areal density of the active material layer before the grooves are created (before etching), in g / cm³. 3 .

[0028] Where k is a conversion coefficient related to the compaction density of the material, obtained by k=10 -6×ρa calculation, where ρa is defined as the mass per unit volume of the active material, ρa=b0 / thickness of the active material layer, and the weight loss rate c of the active material layer, the surface density b of the active material after etching, and the design parameters of the groove satisfy the following relationship: c=k×(w×d×L) / b0 and b=b0×(1-c / 100).

[0029] Preferably, the depth of the groove in step (1) is 30%-80% of the thickness of the active material layer, for example, it can be 30%, 40%, 50%, 60%, 70% or 80%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] It should be noted that the present invention only grooves the active material layer, and the thickness of the groove is less than the thickness of the active material layer, and preferably 30%-80% of the thickness of the active material layer.

[0031] The depth of the grooves in this invention affects the pre-lithiation effect. If the groove depth is too small compared to the thickness of the active material layer, the pre-lithiation effect inside the active material layer will be poor. However, if the groove depth is too large, the etching depth will approach or reach 100% (i.e., there is a risk of etching through to the current collector), which will disrupt the continuity of the conductive network of the current collector, leading to a significant decrease in the electronic conductivity of the electrode, increasing internal resistance, and affecting rate performance. Simultaneously, exposure of the current collector may cause problems such as electrolyte corrosion. Furthermore, excessively deep grooves will reduce the effective carrying capacity of the active material (slightly reducing the capacity per unit area) and may weaken the overall mechanical strength of the electrode, making it more fragile during rolling or assembly.

[0032] Preferably, the shape of the groove in step (1) is any one of the following: strip groove, round hole groove, square groove, grid groove, stepped groove or annular groove.

[0033] The present invention uses laser etching to create multiple grooves on the active material layer. The grooves are one of the following: strip grooves, circular hole grooves, square grooves, grid grooves, stepped grooves, or annular grooves. The multiple grooves are arranged parallel to each other along the width and length of the active material layer to form a grid-like groove.

[0034] Preferably, in the groove array described in step (1), the interval between adjacent grooves is 1mm-5mm, for example, it can be 1mm, 2mm, 3mm, 4mm or 5mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the immersion time in the conductive polymer solution in step (2) is 0.5h-2h, for example, 0.5h, 1h, 1.5h or 2h, and the temperature is 25℃-40℃, for example, 25℃, 30℃, 35℃ or 40℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the conductive polymer solution in step (2) comprises a polydopamine solution.

[0037] Preferably, the pH of the conductive polymer solution in step (2) is 8.5-9.0, for example, it can be 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the concentration of the conductive polymer solution in step (2) is 1.0 mg / mL to 3.0 mg / mL, for example, it can be 1.0 mg / mL, 1.5 mg / mL, 2 mg / mL, 2.5 mg / mL or 3.0 mg / mL, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, after the negative electrode sheet after the structuring treatment in step (1) is immersed in the conductive polymer solution in step (2), the obtained negative electrode sheet is first washed and purged with gas, and then immersed in the lithium salt solution in step (2).

[0040] Preferably, the immersion time in the lithium salt solution in step (2) is 1 min to 5 min, for example, it can be 1 min, 2 min, 3 min, 4 min or 5 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, the concentration of the lithium salt solution in step (2) is 0.03 mol / L-0.1 mol / L, for example, it can be 0.03 mol / L, 0.06 mol / L, 0.09 mol / L or 0.1 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the lithium salt solution in step (2) includes a lithium salt and an organic solvent, wherein the lithium salt includes any one or a combination of at least two of LiCl, LiF, Li2CO3 or LiNO3, and the organic solvent includes tetrahydrofuran;

[0043] Preferably, the gaseous environment in step (3) includes any one or a combination of at least two of N2, O2 or CO2.

[0044] Preferably, the temperature of the gas environment in step (3) is 60℃-80℃, for example, 60℃, 65℃, 70℃, 75℃ or 80℃, and the time is 1h-3h, for example, 1h, 1.5h, 2h, 2.5h or 3h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the method for setting lithium metal in step (3) includes any one or a combination of at least two of the following: vacuum resistance heating evaporation, vacuum electron beam evaporation, vacuum laser heating evaporation, magnetron sputtering, vacuum coating, or atomic layer deposition.

[0046] Preferably, the thickness of the lithium metal in step (3) is set to be 0.5μm-30μm, for example, it can be 0.5μm, 10μm, 20μm or 30μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] The thickness of the lithium metal layer in this invention affects the thickness of the resulting inorganic interface layer. If the lithium metal layer is too thin, the resulting inorganic interface layer will be too thin, affecting its effectiveness. However, if the lithium metal layer is too thick, the resulting inorganic interface layer will be too thick, severely damaging battery performance. First, it will create extremely high ion transport impedance, leading to deterioration in rate performance and irreversible locking of a large amount of active lithium. Second, its brittle nature cannot adapt to changes in electrode volume, making it prone to cracking and peeling during cycling, triggering a vicious cycle of continuous SEI growth. Third, an excessively thick dense layer will destroy the gradient interface structure designed in this invention, not only blocking the internal lithium source diffusion channels but also becoming a stress concentration point due to the huge mechanical mismatch with the underlying flexible buffer layer, ultimately comprehensively degrading the battery's kinetics, cycle life, and structural stability. Therefore, precisely controlling its thickness to obtain a "thin and dense" morphology is key to achieving a high-performance pre-lithiation anode.

[0048] Preferably, the temperature of the gas-solid reaction in step (3) is 20℃-30℃, for example, it can be 20℃, 22℃, 24℃, 26℃, 28℃ or 30℃, and the time is 0.5h-2h, for example, it can be 0.5h, 1h, 1.5h or 2h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the ripening method in step (4) includes placing the two-step pre-lithiation negative electrode sheet in step (3) in an inert gas or vacuum environment for a period of 8h-12h, for example, 8h, 9h, 10h, 11h or 12h, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the post-processing in step (4) includes cold pressing.

[0051] In a second aspect, the present invention provides a pre-lithiated anode, which is obtained by pre-lithiation of the anode as described in the first aspect.

[0052] The pre-lithiated negative electrode of the present invention has a lithium-rich buffer layer and an inorganic interface layer sequentially disposed on the surface, the sidewall of the groove and the bottom (the lithium-rich buffer layer and the inorganic interface layer are interwoven with each other); the lithium-rich buffer layer includes a conductive polymer (such as polydopamine) and lithium metal particles, and the inorganic interface layer includes a lithium-containing compound (such as any one or a combination of at least two of Li3N, Li2O or Li2CO3).

[0053] Thirdly, the present invention provides a battery comprising a pre-lithiated negative electrode as described in the second aspect.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) Stepwise and gradient pre-lithiation mechanism: The first step of this invention is chemical pre-lithiation in the groove, which forms a lithium source reserve point. The second step of pre-lithiation, a gas-solid reaction, forms an interface layer over a larger area. These two steps form a gradient pre-lithiation structure from point (groove) to surface (electrode surface). The pre-lithiation depth and uniformity far exceed any single method, thereby achieving a highly efficient and uniform pre-lithiation effect. Moreover, the interface layer formed by the second step of pre-lithiation (composed of Li3N, Li2O or Li2CO3, etc.) has high chemical and mechanical stability, ensuring close contact and uniform distribution between the lithium source and the negative electrode. It can also serve as a high-quality artificial SEI film to suppress the continuous decomposition of the electrolyte and the damage to the electrode structure during cycling, thus extending the cycle life of the battery.

[0056] (2) Functional Synergy: The conductive polymer coating plus grooves can buffer volume expansion. The groove filling material of conductive polymer and nano-lithium particles intertwines with the subsequently generated interface layer to form a composite SEI film with toughness and high ionic conductivity, which greatly stabilizes the electrode structure. In addition, the grooves greatly shorten the migration path of lithium ions and reduce the ion transport impedance. The grooves promote the rapid and uniform distribution of electrolyte inside the electrode, improve the uniformity of the reaction in the thickness direction of the electrode, help to make full use of the capacity of the active material, and increase the dimension and number of lithium ion diffusion channels, accelerate the pre-lithiation reaction, effectively compensate for the first lithium loss, and significantly improve the first-cycle coulombic efficiency.

[0057] (3) Greatly reduces production costs and process complexity: Since the additional pre-lithiation equipment and complex processes are eliminated, the method described in this invention is simple, low-cost, and has excellent compatibility with large-scale industrial production.

[0058] (4) Ensures the integrity of the electrode structure: The pre-lithiation process is more gentle and controllable, avoiding damage to the microstructure of the negative electrode material (especially brittle silicon) by violent reactions, which is conducive to maintaining the structural stability of the negative electrode and improving electrochemical performance.

[0059] (5) Improved safety: This invention reduces the safety risks during raw material storage, transportation and processing by converting highly active metallic lithium into a relatively stable lithium-containing compound interface layer. Detailed Implementation

[0060] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0061] In the following examples and comparative examples, the preparation method of the negative electrode sheet without pre-lithiation includes the following steps: preparing a silicon-carbon composite material (SiO2)... x -C, where x≈1, particle size D50 is 8μm), acetylene black and polyacrylic acid were weighed in a mass ratio of 90:5:5, and then mixed in a planetary mixer for 4 hours using deionized water as solvent to obtain a negative electrode slurry with a solid content of 45wt%.

[0062] The above-mentioned negative electrode slurry was uniformly coated onto a 10 μm thick copper foil current collector using a coating machine, with the areal density of the coating on one side controlled at 3.0 mg / cm². 2 Subsequently, the electrode was placed in an 85°C forced-air oven for initial drying for 2 hours, and then transferred to a 120°C vacuum oven for drying for 12 hours to completely remove moisture, finally obtaining a negative electrode with an active material layer thickness of 50μm.

[0063] Example 1

[0064] This embodiment provides a method for pre-lithiation of a negative electrode, which includes the following steps:

[0065] (1) Laser etching for structuring:

[0066] The negative electrode sheet is processed using an ultraviolet laser etching machine (wavelength 355nm). A grid-like groove array is etched on the surface of the negative electrode sheet, with a grid line width of 30μm and a grid unit of 1.0mm×1.0mm square. The laser power and scanning speed are controlled to make the groove depth 35μm (70% of the thickness of the active material layer) to ensure that the copper current collector at the bottom is not damaged. After etching, the surface of the electrode sheet is purged with argon gas to remove etching residue.

[0067] After the grooves are created, w represents the average width of the grooves (specifically 30 μm), d represents the average depth of the grooves (35 μm), and L represents the total length of the grooves per unit area (specifically 2000 m / m). 2 ), where k is the conversion factor related to the compaction density of the material, k = 5.4 × 10 -7 By k=10 -6 The calculation is based on ×ρa, where ρa is defined as the mass per unit volume of the active material, ρa = b0 / thickness of the active material layer, and b0 is the density before etching (27 g / cm³). 3 );

[0068] The weight loss rate c of the active material layer (specifically 4.2%) and the areal density b of the active material after etching (specifically 25.9 g / m²) are also mentioned. 2 The design parameters of the groove satisfy the following relationship: c = k × (w × d × L) / b0 and b = b0 × (1 - c / 100);

[0069] (2) First step of pre-lithiation:

[0070] Prepare a 10 mM Tris-HCl buffer solution and adjust its pH to 8.8. Add dopamine hydrochloride to the buffer solution to prepare a polydopamine solution with a concentration of 2.0 mg / mL. Immerse the structured negative electrode obtained in step (1) into the polydopamine solution and let it stand in a constant temperature water bath at 30°C for 1.5 hours. Then take out the electrode, rinse it gently with deionized water to remove physically adsorbed impurities, and then blow away the large droplets on the surface with nitrogen to obtain a negative electrode with a polydopamine coating (in a semi-dry state).

[0071] Prepare a 0.05 mol / L tetrahydrofuran solution of lithium chloride as a lithium source solution. Immerse the negative electrode sheet with polydopamine coating in the lithium source solution for 3 minutes. Then remove the electrode sheet and vacuum dry it at 70°C for 1 hour to completely remove the tetrahydrofuran and obtain a one-step pre-lithiation negative electrode sheet.

[0072] (3) Second step of pre-lithiation:

[0073] The first-step pre-lithiation negative electrode sheet was placed in a sealed vacuum glove box transition chamber and vacuum-baked at 80°C for 2 hours. Subsequently, the electrode sheet was transferred to a sealed reactor filled with high-purity dry carbon dioxide gas at atmospheric pressure (1 atm). It was kept at 80°C for 1 hour to allow for full adsorption of CO2 gas. Then, using a vacuum electron beam evaporation device, metallic lithium was coated onto the surface of the CO2-adsorbed negative electrode sheet with a thickness of 30 μm, ensuring close contact between the metallic lithium and the three-dimensional surface of the negative electrode sheet (including the raised planar areas and the recessed grid areas). It was left at room temperature for 1 hour. During this period, the metallic lithium and the adsorbed CO2 underwent a gas-solid reaction, generating an inorganic interface layer including Li2CO3 at the edges of the grooves, the grid junctions, and the planar areas of the electrode sheet, thus obtaining the second-step pre-lithiation negative electrode sheet.

[0074] (4) The two-step pre-lithiation negative electrode sheet was placed in a glove box under an argon atmosphere and left to stand at room temperature for 10 hours to ripen, allowing lithium ions to diffuse further inward and stabilizing the interfacial components; finally, the electrode sheet was cold-pressed at room temperature using a roller press to control the compaction density of the electrode sheet to 1.65 g / cm³. 3 This yields the final pre-lithiated anode.

[0075] Example 2

[0076] This embodiment provides a method for pre-lithiation of a negative electrode, which includes the following steps:

[0077] (1) Laser etching for structuring:

[0078] The negative electrode sheet is processed using an ultraviolet laser etching machine (wavelength 355nm). A grid-like groove array is etched on the surface of the negative electrode sheet, wherein the grid line width is 30μm and the grid unit is a 1.0mm×1.0mm square. The laser power and scanning speed are controlled so that the depth of the groove is 30% of the thickness of the active material layer, ensuring that the copper current collector at the bottom is not damaged. After etching, the surface of the electrode sheet is purged with argon gas to remove etching residues.

[0079] After the grooves are created, w represents the average width of the grooves (specifically 30 μm), d represents the average depth of the grooves (15 μm), and L represents the total length of the grooves per unit area (specifically 2000 m / m). 2 ), where k is the conversion factor related to the compaction density of the material, k = 5.4 × 10 -7 By k=10 -6 The calculation is based on ×ρa, where ρa is defined as the mass per unit volume of the active material, ρa = b0 / thickness of the active material layer, and b0 is the density before etching (27 g / cm³). 3 );

[0080] The weight loss rate c of the active material layer (specifically 1.8%) and the areal density b of the active material after etching (specifically 26.5 g / m²) are also mentioned. 2 The design parameters of the groove satisfy the following relationship: c = k × (w × d × L) / b0 and b = b0 × (1 - c / 100);

[0081] (2) First step of pre-lithiation:

[0082] Prepare a polydopamine solution with a concentration of 1.0 mg / mL and a pH of 9.0; immerse the structured negative electrode obtained in step (1) into the polydopamine solution, let it stand in a constant temperature water bath at 40°C for 0.5 h, then take out the electrode, rinse it gently with deionized water to remove physically adsorbed impurities, and then blow away the large droplets on the surface with nitrogen to obtain a negative electrode with a polydopamine coating (in a semi-dry state).

[0083] A 0.1 mol / L tetrahydrofuran solution of lithium chloride was prepared as the lithium source solution. The negative electrode with polydopamine coating was immersed in the lithium source solution for 1 min. Then the electrode was removed and vacuum dried at 80 °C for 1 h to completely remove the tetrahydrofuran, thus obtaining a one-step pre-lithiation negative electrode.

[0084] (3) Second step of pre-lithiation:

[0085] The first-step pre-lithiation anode electrode was placed in a sealed vacuum glove box transition chamber and vacuum-baked at 80°C for 2 hours. Subsequently, the electrode was transferred to a sealed reactor filled with high-purity dry N2 at atmospheric pressure (1 atm). It was kept at 60°C for 3 hours, and then lithium metal was coated onto the surface of the N2-adsorbed anode electrode using a vacuum electron beam evaporation device. The thickness of the lithium metal coating was 15 μm. After being placed at 20°C for 2 hours, an inorganic interface layer including lithium nitride was generated, resulting in a second-step pre-lithiation anode electrode.

[0086] (4) The two-step pre-lithiation negative electrode sheet was placed in a glove box under an argon atmosphere and left to stand at room temperature for 12 hours to ripen, allowing lithium ions to diffuse further inward and stabilizing the interfacial components; finally, the electrode sheet was cold-pressed at room temperature using a roller press to control the compaction density of the electrode sheet to 1.65 g / cm³. 3 This yields the final pre-lithiated anode.

[0087] Example 3

[0088] This embodiment provides a method for pre-lithiation of a negative electrode, which includes the following steps:

[0089] (1) Laser etching for structuring:

[0090] The negative electrode sheet is processed using an ultraviolet laser etching machine (wavelength 355nm). A grid-like groove array is etched on the surface of the negative electrode sheet, with a grid line width of 30μm and a grid unit of 1.0mm×1.0mm square. The laser power and scanning speed are controlled so that the depth of the groove is 80% of the thickness of the active material layer, ensuring that the copper current collector at the bottom is not damaged. After etching, the surface of the electrode sheet is purged with argon gas to remove etching residue.

[0091] After the grooves are created, w represents the average width of the grooves (specifically 30 μm), d represents the average depth of the grooves (40 μm), and L represents the total length of the grooves per unit area (specifically 2000 m / m). 2 ), where k is the conversion factor related to the compaction density of the material, k = 5.4 × 10 -7 By k=10 -6 The calculation is based on ×ρa, where ρa is defined as the mass per unit volume of the active material, ρa = b0 / thickness of the active material layer, and b0 is the density before etching (27 g / cm³). 3 );

[0092] The weight loss rate c of the active material layer (specifically 4.8%) and the areal density b of the active material after etching (specifically 25.7 g / m²) are also mentioned. 2 The design parameters of the groove satisfy the following relationship: c = k × (w × d × L) / b0 and b = b0 × (1 - c / 100);

[0093] (2) First step of pre-lithiation:

[0094] Prepare a polydopamine solution with a concentration of 3.0 mg / mL and a pH of 8.5; immerse the structured negative electrode obtained in step (1) into the polydopamine solution, let it stand in a constant temperature water bath at 25°C for 2 hours, then take out the electrode, rinse it gently with deionized water to remove physically adsorbed impurities, and then blow away the large droplets on the surface with nitrogen to obtain a negative electrode with a polydopamine coating (in a semi-dry state).

[0095] A 0.03 mol / L tetrahydrofuran solution of lithium chloride was prepared as the lithium source solution. The negative electrode with polydopamine coating was immersed in the lithium source solution for 5 min. Then the electrode was removed and vacuum dried at 60 °C for 3 h to completely remove the tetrahydrofuran, thus obtaining a one-step pre-lithiation negative electrode.

[0096] (3) Second step of pre-lithiation:

[0097] The first-step pre-lithiation anode sheet was placed in a sealed vacuum glove box transition chamber and vacuum-baked at 80°C for 2 hours. Subsequently, the electrode sheet was transferred to a sealed reactor filled with high-purity dry N2 at atmospheric pressure (1 atm). It was kept at 80°C for 1 hour, and then lithium metal was coated onto the surface of the N2-adsorbed anode sheet using a vacuum electron beam evaporation device. The thickness of the lithium metal coating was 0.5 μm. After being placed at 30°C for 0.5 hours, an inorganic interface layer including lithium nitride was generated, resulting in a second-step pre-lithiation anode sheet.

[0098] (4) The two-step pre-lithiation negative electrode sheet was placed in a glove box under an argon atmosphere and left to stand at room temperature for 8 hours to ripen, allowing lithium ions to diffuse further inward and stabilizing the interfacial components; finally, the electrode sheet was cold-pressed at room temperature using a roller press to control the compaction density of the electrode sheet to 1.65 g / cm³. 3 This yields the final pre-lithiated anode.

[0099] Example 4

[0100] This embodiment provides a negative electrode pre-lithiation method, which is the same as that in Embodiment 1 except that the depth of the groove in step (1) is 20% of the thickness of the active material layer.

[0101] Example 5

[0102] This embodiment provides a negative electrode pre-lithiation method, which is the same as that in Embodiment 1 except that the depth of the groove in step (1) is 85% of the thickness of the active material layer.

[0103] Example 6

[0104] This embodiment provides a negative electrode pre-lithiation method, which is the same as that in Embodiment 1 except that the thickness of the lithium metal coverage in step (3) is 0.2 μm.

[0105] Example 7

[0106] This embodiment provides a negative electrode pre-lithiation method, which is the same as that in Embodiment 1 except that the thickness of the lithium metal coverage in step (3) is 35 μm.

[0107] Comparative Example 1

[0108] This comparative example provides a negative electrode pre-lithiation method, which is the same as Example 1 except that the laser etching structuring process in step (1) is not performed.

[0109] Comparative Example 2

[0110] This comparative example provides a negative electrode pre-lithiation method, which is the same as Example 1 except that the first step of pre-lithiation in step (2) is not performed.

[0111] Comparative Example 3

[0112] This comparative example provides a negative electrode pre-lithiation method, which is the same as Example 1 except that the second pre-lithiation step (3) is not performed.

[0113] The pre-lithiated negative electrodes obtained in the above examples and comparative examples were assembled into CR2032 coin cell half-cells. The positive electrode used was a lithium metal sheet as both the counter and reference electrode. The separator was a Celgard 2325 type (PP / PE / PP) three-layer composite polyolefin separator. The electrolyte used was LiPF6 as the lithium salt, and a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with 10 wt% fluoroethylene carbonate (FEC) and 1 wt% lithium difluorooxalate borate (LiDFOB) added as additives. The electrochemical performance of the assembled battery was tested. All electrochemical tests were conducted at a constant temperature of 25°C using a LAND or Arbin battery testing system. Specific test conditions were as follows:

[0114] (1) Initial charge-discharge efficiency test: The first constant current charge-discharge was performed at a current density of 0.05C (1C = 500 mA / g, calculated based on the mass of the negative electrode active material);

[0115] (2) Cyclic stability test: The battery was activated by cycling at 0.1C rate for 3 weeks, and then a long-term cycle test was conducted at 0.5C rate;

[0116] (3) Rate performance test: The battery was charged (constant current and constant voltage to 0.005V, cutoff current 0.05C) and discharged (constant current to 1.5V) at 0.1C, 0.2C, 0.5C, 1C and 2C rates respectively, for 5 cycles at each rate. The discharge capacity at the 5th cycle at each rate was recorded. The capacity retention rate (%) at other rates was calculated based on the discharge capacity at 0.1C rate (100%).

[0117] (4) Electrochemical impedance spectroscopy (EIS) test: The battery before cycling was tested, with a frequency range of 100 kHz to 10 mHz and an amplitude of 5 mV. The interfacial membrane impedance (R_SEI, Ω) corresponding to the semicircle in the high-frequency region was extracted by equivalent circuit fitting.

[0118] The test results are shown in Table 1 below:

[0119] Table 1

[0120]

[0121] As can be seen from Table 1 above:

[0122] As shown in Example 1 and Comparative Example 1, the present invention, by creating grooves on the surface of the active material layer, can form a gradient pre-lithiation structure from the grooves to the electrode surface, improving the depth and uniformity of pre-lithiation. It also improves the wettability of the electrolyte and increases the lithium-ion insertion / extraction rate, thereby enhancing the battery's initial efficiency, cycle performance, and rate capability. As shown in Example 1 and Comparative Example 2, the first pre-lithiation step of the present invention not only stores lithium but also alleviates negative electrode expansion, thus significantly improving the battery's electrochemical performance. As shown in Example 1 and Comparative Example 3, the second pre-lithiation step of the present invention can construct a highly stable... Furthermore, the inorganic interface layer containing lithium compounds can act as a lithium replenishing agent and accelerate the pre-lithiation reaction between the lower layer of metallic lithium and the negative electrode material, thereby further improving the battery's first efficiency, cycle performance, and rate capability. As can be seen from Examples 1 and 4-5, the depth of the grooves opened on the surface of the active material layer in this invention will affect the depth and uniformity of pre-lithiation, thereby affecting the pre-lithiation effect. Preferably, the depth of the grooves is within a specific range. As can be seen from Examples 1 and 6-7, the thickness of metallic lithium set in step (3) of this invention will affect the pre-lithiation effect in the second step. Preferably, the thickness of metallic lithium is set within a specific range.

[0123] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for pre-lithiation of a negative electrode, characterized in that, The negative electrode pre-lithiation method includes the following steps: (1) Grooves are made on the active material layer on at least one side of the negative electrode sheet to form a groove array on the surface of the active material layer, thereby obtaining a structured negative electrode sheet. (2) The negative electrode sheet after the structuring treatment described in step (1) is first immersed in a conductive polymer solution, and then immersed in a lithium salt solution. After the immersion is completed, the obtained negative electrode sheet is dried to obtain a one-step pre-lithiation negative electrode sheet. (3) Place the one-step pre-lithiation negative electrode sheet described in step (2) in a gas environment to adsorb gas, and then set metallic lithium on the surface of the one-step pre-lithiation negative electrode sheet that adsorbs gas to carry out a gas-solid reaction to obtain a two-step pre-lithiation negative electrode sheet. (4) The two-step pre-lithiation anode sheet described in step (3) is aged and post-treated to obtain a pre-lithiation anode.

2. The negative electrode pre-lithiation method according to claim 1, characterized in that, The method for creating the groove in step (1) includes laser etching; And / or, after creating the grooves in step (1), the weight loss rate of the active material layer is c, c=k×(w×d×L) / b0, where w is the average width of the groove in μm, d is the average depth of the groove in μm, and L is the total length of the groove per unit area in m / m. 2 k is the conversion factor, and b0 is the areal density of the active material layer before the groove is created, in g / cm³. 3 .

3. The negative electrode pre-lithiation method according to claim 1 or 2, characterized in that, The depth of the groove in step (1) is 30%-80% of the thickness of the active material layer; And / or, the shape of the groove in step (1) is any one of the following: strip groove, round hole groove, square groove, grid groove, stepped groove or annular groove; And / or, in the groove array described in step (1), the interval between adjacent grooves is 1mm-5mm.

4. The negative electrode pre-lithiation method according to claim 1 or 2, characterized in that, The immersion time in the conductive polymer solution in step (2) is 0.5h-2h, and the temperature is 25℃-40℃; And / or, the conductive polymer solution in step (2) includes a polydopamine solution; And / or, the pH of the conductive polymer solution in step (2) is 8.5-9.0; And / or, the concentration of the conductive polymer solution in step (2) is 1.0 mg / mL to 3.0 mg / mL.

5. The negative electrode pre-lithiation method according to claim 1 or 2, characterized in that, After the negative electrode sheet after the structuring treatment in step (1) is immersed in the conductive polymer solution in step (2), the obtained negative electrode sheet is first washed and purged with gas, and then immersed in the lithium salt solution in step (2).

6. The negative electrode pre-lithiation method according to claim 1 or 2, characterized in that, The immersion time in the lithium salt solution in step (2) is 1 min to 5 min; And / or, the concentration of the lithium salt solution in step (2) is 0.03 mol / L-0.1 mol / L; And / or, the lithium salt solution in step (2) includes a lithium salt and an organic solvent, wherein the lithium salt includes any one or a combination of at least two of LiCl, LiF, Li2CO3 or LiNO3, and the organic solvent includes tetrahydrofuran.

7. The negative electrode pre-lithiation method according to claim 1 or 2, characterized in that, The gaseous environment described in step (3) includes any one or a combination of at least two of N2, O2, or CO2; And / or, the temperature of the gas environment in step (3) is 60℃-80℃, and the time is 1h-3h; And / or, the method of setting lithium metal in step (3) includes any one or a combination of at least two of the following: vacuum resistance heating evaporation, vacuum electron beam evaporation, vacuum laser heating evaporation, magnetron sputtering, vacuum blade coating, or atomic layer deposition. And / or, in step (3), the thickness of the lithium metal is set to be 0.5 μm-30 μm; And / or, the temperature of the gas-solid reaction in step (3) is 20℃-30℃ and the time is 0.5h-2h.

8. The negative electrode pre-lithiation method according to claim 1 or 2, characterized in that, The ripening method in step (4) includes placing the two-step pre-lithiation negative electrode sheet from step (3) in an inert gas or vacuum environment for 8-12 hours. And / or, the post-processing described in step (4) includes cold pressing.

9. A pre-lithiated anode, characterized in that, The pre-lithiated anode is obtained by pre-lithiation of the anode as described in any one of claims 1-8.

10. A battery, characterized in that, The battery includes the pre-lithiated negative electrode as described in claim 9.

Images