Preparation method of pre-lithiated positive electrode sheet, pre-lithiated positive electrode sheet and application thereof

Abstract

The application provides a preparation method of a pre-lithiated positive electrode sheet, the pre-lithiated positive electrode sheet and application thereof. The preparation method comprises the following steps: S1. completely immersing the positive electrode sheet in an organic lithium salt solution for pre-lithiation treatment; S2. after the pre-lithiation of the positive electrode sheet, the positive electrode sheet is dried, and a half-cell is assembled by taking the positive electrode sheet as a working positive electrode and taking metal lithium or a lithium-containing material as a counter electrode or a reference electrode; in an electrolyte system containing a lithium salt, a constant voltage is applied for treatment, the voltage range is 2.0-3.5 V (relative to Li + / Li), and the treatment time is 10-120 min; S3. the working electrode is taken out, washed and dried to obtain the pre-lithiated positive electrode sheet. The preparation method can effectively change the waste into treasure of the residual material that needs to be removed in the traditional pre-lithiation process, and in-situ construct a functional CEI layer. The layer can physically and chemically lock the pre-embedded active lithium and inhibit the subsequent loss; at the same time, as an excellent artificial interface layer, the layer can stabilize the positive electrode / electrolyte interface, and especially improve the cycle performance under high voltage.

Description

Technical Field

[0001] This invention belongs to the field of cathode material and lithium battery technology, specifically relating to a method for preparing a pre-lithiated cathode material, the pre-lithiated cathode material and its application. Background Technology

[0002] As a crucial electrochemical energy storage device, the energy density of lithium-ion batteries is one of their core performance indicators. However, during the initial charging (activation) process, irreversible side reactions occur between the surface of the positive electrode active material (such as high-nickel ternary or lithium-rich manganese-based materials) and the electrolyte, forming a solid electrolyte interphase (CEI) film. Simultaneously, irreversible structural changes may also occur within the material itself. These processes irreversibly consume lithium ions from the positive electrode, leading to a significant "first irreversible capacity loss" during the first cycle. This not only directly reduces the battery's initial reversible capacity and first coulombic efficiency (ICE), but also means that a portion of the active lithium source pre-stored in the positive electrode is permanently wasted, severely limiting further improvements in battery energy density.

[0003] To compensate for the aforementioned losses, "pre-lithiation" technology emerged. Its core idea is to pre-introduce additional active lithium into the electrodes (especially the negative electrode) before battery assembly. For the positive electrode, pre-lithiation (or "pre-intercalation") aims to pre-intercalate lithium into the positive electrode active material through external means to compensate for lithium consumption during the first charge. Existing positive electrode pre-lithiation technologies mainly include: 1) physical mixing method, which involves dry or wet mixing of chemical lithium replenishing agents (such as stabilized lithium powder or lithium-rich compounds) with the positive electrode material; 2) electrochemical method, which involves assembling the positive electrode sheet and lithium source into a temporary battery for pre-charging; and 3) liquid-phase chemical method, which involves immersing the positive electrode sheet in a solution containing active lithium for chemical lithium intercalation.

[0004] However, current pre-lithiation methods generally have the following limitations: pre-lithiation is easily lost in subsequent processes, and the effect is unstable; physical mixing methods have poor uniformity and are difficult to adapt to continuous production; they have poor compatibility with new material systems such as high-voltage cathodes and composite current collectors, and are prone to damage; they have a single function, focusing only on lithium replenishment and failing to simultaneously build a stable interface to improve long-cycle performance. Summary of the Invention

[0005] To address the problems and shortcomings of existing technologies, this invention provides a method for preparing a pre-lithiated cathode sheet, the pre-lithiated cathode sheet itself, and its applications. In the preparation method provided by this invention, after immersing the cathode sheet in a solution containing active lithium for chemical lithium intercalation using a liquid-phase chemical method, a specific constant-voltage treatment is applied. This effectively transforms the residues that need to be removed in traditional pre-lithiation processes into valuable resources, constructing a functional CEI layer in situ. This layer can physicochemically "lock in" the pre-intercalated active lithium, suppressing its subsequent loss; simultaneously, as an excellent artificial interface layer, it stabilizes the cathode / electrolyte interface, especially improving cycle performance under high voltage.

[0006] According to a first aspect of the present invention, a method for preparing a pre-lithiated positive electrode is provided, comprising the following steps: S1. completely immersing the positive electrode in an organic lithium salt solution for pre-lithiation treatment; S2. drying the pre-lithiated positive electrode, assembling a half-cell using the positive electrode as the working positive electrode and using metallic lithium or lithium-containing materials as the counter electrode or reference electrode, and applying a constant voltage in an electrolyte system containing lithium salt, the voltage range being 2.0~3.5 V (relative to Li). + / Li), the processing time is 10~120min; S3. Take out the working electrode, wash and dry it to obtain the pre-lithiated positive electrode sheet.

[0007] In current cathode pre-lithiation processes, liquid-phase chemical methods have attracted attention due to their potential advantages such as uniform reaction, ease of continuous processing, and precise controllability of lithium replenishment. However, this method has the following problems: after chemical pre-lithiation, reaction solvents (such as ethers) and unreacted aromatic hydrocarbons remain on the surface and within the pores of the cathode. If these residues are not thoroughly removed, they will continue to react with the electrolyte during subsequent battery cycles, deteriorating interface stability and leading to gas generation and impedance increase. Therefore, existing technologies typically require rigorous and multiple washing processes. However, even the most rigorous washing is difficult to completely remove all residues, and the washing process itself can induce "backflow" of pre-intercalated active lithium or its loss due to reaction with air / solvent, resulting in low "retention rate" of pre-intercalated lithium and significantly reduced lithium replenishment effect. How to effectively utilize pre-lithiation reagents while stably locking in pre-intercalated lithium is the core challenge currently facing liquid-phase chemical methods. Moreover, the long washing steps that are necessary to remove residues during the washing process, which use polar or strong solvents (such as ethers or alcohols), can severely swell, corrode, or even peel off the polymer substrate in the composite current collector, damaging its delicate metal / polymer interface structure. This leads to a decrease in the conductivity and deterioration of the mechanical properties of the current collector, making it unable to meet application requirements.

[0008] Therefore, this invention provides a novel method for preparing a pre-lithiated cathode, which designs a core step S2 at 2.0-3.5 V (vs. Li). +By performing constant-voltage treatment at an appropriate voltage on the lithium (Li), the organic matter, such as aromatics, that inevitably remains after chemical pre-lithiation in step S1 is transformed into a valuable resource through in-situ electrochemical conversion, forming a uniform and dense artificial CEI (solid electrolyte interface) film. This film not only acts as a physicochemical barrier, significantly improving the retention rate of pre-lithiation and effectively locking in active lithium to compensate for the initial irreversible capacity loss, but also serves as a stable interface for ion conductance / electronic resistance, significantly reducing the interface impedance at high voltages. This simultaneously improves the battery's initial coulombic efficiency, reversible capacity, and long-term cycle stability, especially enhancing cycle performance under high voltage. Furthermore, controlling the voltage and time allows for a better balance between film formation and other performance aspects. If the voltage treatment time is too short, the film layer will be incomplete, resulting in insufficient "lithium locking" and passivation effects; while if the voltage treatment time is too long, it may lead to an excessively thick film or increased side reactions, impairing ion conduction.

[0009] Furthermore, because residual organic matter is effectively converted and utilized, the reliance on subsequent harsh and lengthy washing steps is significantly reduced. This greatly avoids the swelling, erosion, and damage to the polymer substrate and delicate interfaces in composite current collectors (such as PET / Al) caused by highly polar organic solvents, improving the core pain point of existing liquid-phase pre-lithiation technology applied to composite current collectors. Therefore, it further improves the mechanical stability of composite current collectors, such as peel strength, and optimizes the electrochemical performance of the electrode and the battery.

[0010] Preferably, after assembling the half-cell, it needs to stand for 1.5 to 4 hours before applying voltage treatment. This standing step ensures that the electrolyte fully wets the electrode, effectively stabilizes the initial interface and reduces local polarization, thereby making the subsequent constant voltage treatment more uniform and controllable, and significantly improving the quality, consistency and overall stability of the artificial CEI film and pre-lithiation effect.

[0011] Preferably, in S1, the organic lithium salt contained in the organic lithium salt solution is a polycyclic aromatic hydrocarbon lithium salt, and the polycyclic aromatic hydrocarbon is a fused ring or bicyclic aromatic hydrocarbon with two or more rings.

[0012] Preferably, the polycyclic aromatic hydrocarbon includes at least one of naphthalene, biphenyl, pyrene, phenanthrene, and anthracene.

[0013] Preferably, the polycyclic aromatic hydrocarbon is selected from at least one of pyrene and biphenyl.

[0014] Choosing polycyclic aromatic hydrocarbon (PAH) lithium salts, especially pyrene, provides suitable reduction potential and high reactivity, ensuring efficient and uniform pre-lithiation. PAHs such as pyrene are more likely to undergo controllable electrochemical reactions in subsequent constant-voltage electrochemical steps, thereby transforming in situ into a dense, stable, and highly ionicly conductive artificial CEI film. This achieves the dual benefits of enhanced lithium locking and interface passivation, optimizing electrochemical performance.

[0015] Preferably, in S1, the lithium ion concentration in the organic lithium salt solution is 0.05~0.3 mol / L. At this lithium ion concentration, the electrode is effectively chemically pre-lithiated, ensuring effective lithium replenishment. This avoids both insufficient lithium replenishment due to excessively low concentration and problems such as uncontrolled subsequent reactions, uneven lithium deposition, and excessive residues caused by excessively high concentration.

[0016] Preferably, the lithium ion concentration in the organic lithium salt solution is 0.075~0.15 mol / L. This preferred concentration ensures efficient, deep, and uniform lithium replenishment while allowing for more precise control of the total amount of residue in the electrode after pre-lithiation. This enables the residue to be more efficiently and thoroughly converted into a high-quality and uniform artificial CEI film in subsequent electrochemical steps, thus facilitating the optimal balance between high lithium replenishment efficiency and the construction of a stable interface.

[0017] Preferably, in step S1, the organolithium salt solution is prepared by reacting metallic lithium with a polycyclic aromatic hydrocarbon in an ether solvent. The ether solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, and 1,3-dioxolane. The selected ether solvents exhibit good solubility and reactivity with metallic lithium, enabling the efficient formation of a stable and homogeneous organolithium salt solution. They also exhibit good wettability to the cathode material, achieving deep penetration and uniform pre-lithiation. Furthermore, their moderate boiling point and reduction stability facilitate process control and provide an ideal reaction medium for the controllable conversion of residues in subsequent electrochemical steps and the construction of a high-quality CEI membrane.

[0018] Preferably, the organolithium salt solution is prepared by reacting lithium metal with polycyclic aromatic hydrocarbons (PAHs) in an ether solvent, as follows: A PAH solution is prepared using an ether solvent, lithium metal is added to it, and the reaction is carried out at 32-40°C for 4-8 hours to obtain the organolithium salt solution. This mild temperature and sufficient reaction time ensure a stable and complete reaction between lithium metal and PAHs, effectively suppressing vigorous solvent evaporation and side reactions, thereby obtaining a high-quality organolithium salt solution with stable activity and uniform composition. This lays a reliable material foundation for subsequent uniform and controllable pre-lithiation treatment and consistent CEI membrane construction.

[0019] Preferably, after the reaction to prepare the organolithium salt solution is completed, the solution needs to be filtered. Preferably, a filter membrane with a pore size of 0.22 μm is used for filtration. Filtration is to remove any small insoluble particles that may be generated.

[0020] Preferably, in S1, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector; the current collector is a composite current collector, which includes a polymer substrate and a metal conductive layer formed on at least one surface of the polymer substrate, wherein the material of the metal conductive layer is aluminum or an aluminum alloy. Because the pre-lithiation method provided by this invention significantly reduces dependence on strongly polar solvents and harsh washing, it fundamentally avoids the swelling and corrosion of the polymer substrate by solvents and the damage to the metal / polymer interface. This allows the efficient pre-lithiation and lithium replenishment technology to be safely applied to high-energy-density, high-safety composite current collector systems, which is more conducive to the further development and application of high-performance batteries.

[0021] Preferably, in step S2, before drying the pre-lithiated positive electrode sheet, it needs to be washed using a non-polar or weakly polar solvent; the washing time is 1-30 seconds. Further washing with a non-polar or weakly polar solvent can effectively dissolve and remove excess organic reactants from the surface, which is more conducive to the stable implementation of subsequent specific voltage treatments and a more stable and dense CEI film, thereby further improving the electrochemical performance of the battery.

[0022] More importantly, controlling the washing time within the aforementioned short time range is sufficient to remove most of the surface deposits while strictly limiting the solvent's penetration and interaction time with the electrode body, effectively preventing the loss of pre-intercalated lithium and potential damage to the sensitive substrate. Furthermore, the selected non-polar or weakly polar solvents have high chemical inertness, which further helps to reduce interfacial damage to the composite current collector.

[0023] Of course, it should be further explained that in the preparation method provided by the present invention, even if the pre-lithiated cathode sheet is not washed with detergent and is directly dried and voltage treated, a pre-lithiated cathode sheet with excellent performance can be obtained, which can significantly improve the electrochemical performance of the battery.

[0024] Preferably, the washing solvent includes at least one of xylene, n-hexane, and cyclohexane. These solvents possess excellent solubility and suitable evaporation rates, enabling rapid and efficient removal of residual reaction liquid. Furthermore, they are easily and completely removed in subsequent processes, avoiding secondary contamination and providing a clean and stable interface for the electrochemical steps.

[0025] Preferably, in step S2, the voltage treatment time is 30-60 minutes. This voltage treatment time can more accurately ensure that film formation and other properties of the positive electrode are fully considered, which is more conducive to improving the overall performance of the positive electrode and the battery.

[0026] According to a second aspect of the present invention, a pre-lithiated cathode is provided, prepared by any of the above-described methods for preparing a pre-lithiated cathode. The cathode prepared by the above methods has stable active lithium pre-embedded internally and a uniform and dense artificial CEI film covering its surface. This structure enables the cathode to possess both high initial lithium content and excellent interfacial stability, allowing it to be directly used in the assembly of high-performance lithium-ion batteries, significantly improving its initial efficiency, reversible capacity, and long cycle life.

[0027] According to a third aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery comprising the aforementioned pre-lithiated positive electrode.

[0028] In summary, compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: (1) Through the synergy of "chemical pre-lithiation + constant voltage electrochemical treatment", especially the specific constant voltage electrochemical treatment, the residue after chemical pre-lithiation can be transformed in situ into a uniform and dense artificial CEI film. This film has the dual functions of "lithium locking" and "passivation", which not only significantly improves the pre-lithiation retention rate and efficiently compensates for the initial capacity loss, but also greatly reduces the impedance as a stable interface layer, thereby simultaneously improving the initial efficiency, reversible capacity and long-term cycle stability.

[0029] (2) The residue is converted and utilized, which greatly reduces the reliance on harsh washing. This makes this pre-lithiation method more compatible with composite current collectors containing polymer substrates and avoids the swelling and erosion risks of traditional liquid phase methods.

[0030] (3) The pre-lithiation method provided by the present invention has clear steps, and the parameters (voltage, time, concentration) are easy to control precisely. The interface layer is uniform and has good reproducibility. Moreover, the chemical pre-lithiation step is relatively independent of the electrochemical treatment step, and the process window is wide. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] In the following examples or comparative examples, the conditions of the glove box used in the experiment were: water content <0.1 ppm and oxygen content <0.1 ppm.

[0033] Example 1 1. Preparation of organic lithium salt solutions In this embodiment, the organic lithium salt solution is a pyrene lithium salt solution, and the specific preparation steps are as follows: In a glove box, add 3.08 g of high-purity pyrene (0.015 mol, purity >99.9%) and 150 mL of anhydrous 2-methyltetrahydrofuran (water content <10 ppm) that has been deeply dried through a 4A molecular sieve to a 500 mL three-necked flask equipped with a stirrer. Turn on the magnetic stirrer (300 rpm) until the pyrene is completely dissolved, forming a colorless and transparent solution.

[0034] Take 0.210 g of clean lithium metal strip (0.030 mol, surface area approximately 2 cm²) using stainless steel tweezers. 2 After wiping off the surface mineral oil with filter paper, quickly immerse the mixture in the above solution. Transfer the reaction flask to a 35°C constant temperature oil bath outside the glove box and react for 6 hours with continuous stirring.

[0035] During the reaction, the solution color gradually changed from colorless to dark blue, and finally to dark green, with bubbles forming on the surface of the lithium metal and gradually dissolving. After the reaction, the solution was transferred back to the glove box and diluted to a total volume of 200 mL with anhydrous 2-methyltetrahydrofuran (water content <10 ppm). Subsequently, the solution was filtered using a polytetrafluoroethylene (PTFE) syringe and a 0.22 μm PTFE lipophilic microporous membrane to remove any small insoluble particles that may have formed. The resulting filtrate was a pre-lithiation solution of lithium pyrene / 2-methyltetrahydrofuran (organic lithium salt solution) with a lithium ion concentration of approximately 0.15 mol / L, stored in a sealed glass bottle with the bottle mouth reinforced with Parafilm sealing film.

[0036] 2. Preparation of the positive electrode sheet The positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), Super P as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder are mixed in a mass ratio of 96:2:2. Using N-methyl-2-pyrrolidone (NMP) as the solvent, the mixture is stirred in a vacuum planetary mixer until a homogeneous slurry with a solid content of 70% is formed.

[0037] The current collector is a composite aluminum current collector, the structure of which is: a 4.5μm thick polyethylene terephthalate (PET) film as the substrate, and a 1.0μm thick metal aluminum layer deposited on both sides by magnetron sputtering and electroplating processes.

[0038] The slurry was uniformly coated onto one side of the composite aluminum current collector using a micro-gravure coating machine. It was then initially dried in a 100°C oven for 10 minutes to evaporate most of the NMP, followed by drying in a 120°C vacuum oven (-0.1 MPa) for 12 hours to completely remove residual solvent. Finally, the electrode was compacted using a roller press at 25°C and 10 MPa pressure, yielding an areal density of approximately 20 mg / cm³.2 (Considering only active material), compacted density is approximately 3.4 g / cm³. 3 The positive electrode sheet to be processed is punched into a circular sheet with a diameter of 14mm for later use.

[0039] 3. Preparation of pre-lithiated cathode sheets Follow these steps: S1. Completely immerse the positive electrode sheet prepared above in the obtained lithium pyrene solution for 60 seconds to ensure that the active material layer is fully wetted by the solution; S2. Quickly remove the positive electrode sheet and transfer it to a glass dish containing 20 mL of anhydrous xylene. Gently rinse it with ultrasonic assistance for 5 seconds. Then immediately remove it and dry it on an 80°C vacuum baking tray for 30 minutes to obtain the intermediate product positive electrode sheet A1. Next, in a glove box, using positive electrode A1 as the working electrode, a 16mm diameter lithium metal sheet as the counter / reference electrode, Celgard 2400 as the separator, and 200 μL of 1.0 M LiPF6 dissolved in a mixed solvent of EC:EMC (volume ratio 3:7) as the electrolyte, a CR2032 coin cell was assembled. This half-cell was connected to an electrochemical workstation (Gamry Interface 1010E), and after standing for 2 hours to allow for full electrolyte wetting, a constant voltage of 2.8 V (vs. Li) was applied. + / Li), lasting for 45 minutes, the current gradually decreased to near zero over time; S3. After processing, carefully disassemble the above half-cell in a glove box, take out the working electrode (i.e. the processed positive electrode), gently wash the surface with dry EMC solvent to remove residual electrolyte salt, and then vacuum dry at room temperature for 2 hours to obtain the final pre-lithiated positive electrode.

[0040] Example 2 1. Preparation of organic lithium salt solutions In this embodiment, the organic lithium salt solution is a biphenyl lithium salt solution, and the specific preparation steps are as follows: Weigh 2.31 g of biphenyl (0.015 mol) and dissolve it in 150 mL of anhydrous tetrahydrofuran (THF); add 0.105 g of metallic lithium (0.015 mol); stir the reaction at room temperature (25°C) for 10 hours until the solution turns dark blue; dilute to 200 mL and filter to obtain a lithium biphenyl / THF solution (organic lithium salt solution) with a lithium ion concentration of approximately 0.075 mol / L.

[0041] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0042] 3. Preparation of pre-lithiated cathode sheets The difference from Example 1 is that the organic lithium salt solution in S1 is the biphenyl lithium / THF solution of this example; the washing step is omitted in S2, and the impregnated positive electrode sheet is directly placed in a 60°C vacuum oven for 60 minutes to completely evaporate the THF solvent; and the constant voltage treatment parameter in S2 is changed to 3.0 V (vs. Li). + / Li), lasting for 30 minutes; the rest is the same as in Example 1.

[0043] Example 3 1. Preparation of organic lithium salt solutions In this embodiment, the organic lithium salt solution is a naphthalene lithium salt solution, and the specific preparation steps are as follows: Weigh 1.92 g of naphthalene (0.015 mol) and dissolve it in 150 mL of anhydrous THF; add 0.105 g of metallic lithium (0.015 mol); stir the reaction in an ice-water bath at 0℃ for 2 hours, and the solution quickly turns dark green; make up to 200 mL and filter to obtain a naphthalene-lithium / THF solution (organic lithium salt solution) with a lithium ion concentration of approximately 0.075 mol / L.

[0044] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0045] 3. Preparation of pre-lithiated cathode sheets The difference from Example 1 is that the organic lithium salt solution in S1 is the naphthalene lithium / THF solution of this example; the rest is the same as in Example 1.

[0046] Example 4 1. Preparation of organic lithium salt solutions In this embodiment, the organic lithium salt solution is a phenanthrene lithium salt solution, and the specific preparation steps are as follows: In a glove box, add 2.67 g of high-purity phenanthrene (0.015 mol, purity >99.5%, phenanthrene molecular formula C) to a 250 mL three-necked flask equipped with a stirrer. 14 H 10 150 mL of anhydrous tetrahydrofuran (THF, water content <10 ppm), which has been deeply dried through 4A molecular sieves for more than 72 hours, was mixed with 178.23 g / mol (molecular weight 178.23 g / mol). Magnetic stirring was turned on (350 rpm) until the phenanthrene was completely dissolved, forming a colorless and transparent solution.

[0047] Using stainless steel tweezers, take 0.105 g of clean lithium metal strip (0.015 mol; the lithium strip should be rinsed with anhydrous n-hexane to remove surface mineral oil and blotted dry with filter paper before use) and quickly add it to the above solution. Transfer the reaction flask to a 30°C constant temperature water bath outside the glove box and react for 8 hours with continuous stirring.

[0048] During the reaction, the solution color gradually changed from colorless to pale yellow, then to deep yellow, and finally to a brownish-red transparent solution (the characteristic color of lithium phenanthrene is lighter than that of lithium naphthalene and lithium pyrene). After the reaction, the solution was transferred back to the glove box and diluted to a total volume of 200 mL with anhydrous tetrahydrofuran. Subsequently, the solution was pressure filtered using a polytetrafluoroethylene (PTFE) syringe and a 0.22 μm pore size PTFE lipophilic microporous membrane to remove any trace amounts of insoluble particles or unreacted lithium debris. The resulting filtrate is a pre-lithiated solution of lithium phenanthrene / tetrahydrofuran (organic lithium salt solution) with a lithium ion concentration of approximately 0.075 mol / L, and should be stored in a brown sealed glass bottle, protected from light.

[0049] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0050] 3. Preparation of pre-lithiated cathode sheets The difference from Example 1 is that the organic lithium salt solution in S1 is the phenanthrene lithium / THF solution of this example; the rest is the same as in Example 1.

[0051] Example 5 1. Preparation of organic lithium salt solutions The organolithium salt solution prepared in this embodiment is an anthracene lithium salt solution, and the specific preparation steps are as follows: In a glove box, 2.67 g of anthracene (0.015 mol) and 150 mL of anhydrous tetrahydrofuran (THF) were added to a 250 mL three-necked flask and stirred until completely dissolved. Then, 0.105 g of metallic lithium (0.015 mol) was added, and the mixture was stirred in a 25°C water bath for 10 hours. The solution gradually changed from colorless to dark green. After the reaction was complete, the volume was adjusted to 200 mL with anhydrous THF, and the solution was filtered through a 0.22 μm filter to obtain an anthracene-lithium / THF solution (organolithium salt solution) with a lithium ion concentration of approximately 0.075 mol / L.

[0052] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0053] 3. Preparation of pre-lithiated cathode sheets The difference from Example 1 is that the organic lithium salt solution in S1 is the anthracene lithium / THF solution of this example; the rest is the same as in Example 1.

[0054] Example 6 1. Preparation of organic lithium salt solutions In this embodiment, the concentration of lithium ions in the prepared organic lithium salt solution was adjusted to 0.05 mol / L; the rest was the same as in Example 1.

[0055] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0056] 3. Preparation of pre-lithiated cathode sheets Consistent with Example 1.

[0057] Example 7 1. Preparation of organic lithium salt solutions In this embodiment, the concentration of lithium ions in the prepared organic lithium salt solution was adjusted to 0.3 mol / L; the rest was the same as in Example 1.

[0058] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0059] 3. Preparation of pre-lithiated cathode sheets Consistent with Example 1.

[0060] Example 8 1. Preparation of organic lithium salt solutions Consistent with Example 1.

[0061] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0062] 3. Preparation of pre-lithiated cathode sheets The difference between this embodiment and embodiment 1 is that in S2, the processing time for applying voltage is adjusted to 120 minutes; the rest is the same as in embodiment 1.

[0063] Example 9 1. Preparation of organic lithium salt solutions Consistent with Example 2.

[0064] 2. Preparation of the positive electrode sheet Consistent with Example 2.

[0065] 3. Preparation of pre-lithiated cathode sheets The difference between this embodiment and embodiment 2 is that in S2, the processing time for applying voltage is adjusted to 10 minutes; the rest is the same as in embodiment 2.

[0066] Example 10 1. Preparation of organic lithium salt solutions Consistent with Example 1.

[0067] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0068] 3. Preparation of pre-lithiated cathode sheets The difference between this embodiment and embodiment 1 is that, in S2, the applied voltage is adjusted to 2.0V (relative to Li). + / Li); the rest is the same as in Example 1.

[0069] Example 11 1. Preparation of organic lithium salt solutions Consistent with Example 2.

[0070] 2. Preparation of the positive electrode sheet Consistent with Example 2.

[0071] 3. Preparation of pre-lithiated cathode sheets The difference between this embodiment and embodiment 2 is that, in S2, the applied voltage is adjusted to 3.5V (relative to Li). + / Li); the rest is the same as in Example 2.

[0072] Comparative Example 1 1. Preparation of organic lithium salt solutions Consistent with Example 1.

[0073] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0074] 3. Preparation of pre-lithiated cathode sheets The difference between this comparative example and Example 1 is that after S1 chemical pre-lithiation (immersing the positive electrode in lithium pyrene solution for 60 seconds), in step S2, anhydrous xylene is used for rinsing for 60 seconds (instead of 5 seconds in Example 1), followed by vacuum drying at 80°C for 30 minutes; and the constant voltage electrochemical treatment in S3 is not performed, and the dried electrode is directly used as the test sample; the rest is the same as in Example 1.

[0075] Comparative Example 2 1. Preparation of organic lithium salt solutions Consistent with Example 1.

[0076] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0077] 3. Preparation of pre-lithiated cathode sheets The difference between this comparative example and Example 1 is that, in S2, the applied voltage is adjusted to 1.5V (relative to Li). + / Li); the rest is the same as in Example 1.

[0078] Comparative Example 3 1. Preparation of organic lithium salt solutions Consistent with Example 1.

[0079] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0080] 3. Preparation of pre-lithiated cathode sheets The difference between this comparative example and Example 1 is that, in S2, the applied voltage is adjusted to 4.0V (relative to Li). + / Li); the rest is the same as in Example 1.

[0081] Comparative Example 4 1. Preparation of organic lithium salt solutions Consistent with Example 1.

[0082] 2. Preparation of the positive electrode sheet Consistent with Example 1.

[0083] 3. Preparation of pre-lithiated cathode sheets The difference between this comparative example and Example 1 is that in S2, the processing time for applying voltage is adjusted to 5 minutes; otherwise, it is the same as Example 1.

[0084] Comparative Example 5 1. Preparation of organic lithium salt solutions Consistent with Example 2.

[0085] 2. Preparation of the positive electrode sheet Consistent with Example 2.

[0086] 3. Preparation of pre-lithiated cathode sheets The difference between this comparative example and Example 2 is that in S2, the processing time for applying voltage is adjusted to 135 minutes; otherwise, it is the same as Example 2.

[0087] Comparative Example 6 The positive electrode sheet that has not been soaked in organic lithium salt and has not been treated with a specific voltage, that is, the positive electrode sheet before treatment in S1 of Example 1, is used as the electrode sheet to be tested in order to conduct relevant performance tests on the electrode sheet and the battery.

[0088] Test case 1. Experimental Construction Method (1) Electrochemical performance test 1 The pre-lithiated positive electrode or positive electrode prepared in the above examples and comparative examples was used as the working electrode, and a lithium metal sheet was used as the counter / reference electrode. A mixed solvent of 1M LiPF6 dissolved in EC:EMC (3:7 v / v) was used as the electrolyte. CR2032 coin cells were assembled in an argon glove box. Electrochemical performance was tested using the Xinwei CT-4008T testing system. The specific electrochemical performance tests are as follows: Within a voltage range of 2.8 V to 4.3 V, at 0.1C (1C = 200 mA g) -1 The first charge and discharge test was conducted at a certain rate, and the first charge capacity and first discharge capacity were recorded. The first coulombic efficiency was also calculated.

[0089] Continue the charge-discharge test to the 5th cycle and record the discharge capacity of the 5th cycle. The pre-lithiation effect retention rate (%) = (5th cycle discharge capacity / first discharge capacity) × 100%. The closer this value is to 100%, the less the pre-intercalated active lithium is lost in the initial cycle, and the better the "lithium locking" effect.

[0090] (2) Electrochemical performance test 2 The battery prepared in Electrochemical Performance Test 1 was subjected to 300 constant current charge-discharge cycles at a rate of 1C within a voltage range of 2.8 V to 4.3 V. The capacity retention rate was recorded after the 300th cycle, and electrochemical impedance spectroscopy (EIS) was performed at a full charge state of 4.3 V after the 1st and 300th cycles.

[0091] (3) Electrode peel strength The pre-lithiated cathode sheets or cathode sheets prepared in Examples 1 and 2 and Comparative Examples 1 and 6 were tested for peel strength (adhesion between the cathode active material layer and the composite aluminum current collector) to evaluate the compatibility of the processing method provided by the present invention with the composite aluminum current collector. The specific test method is as follows: The 180° peel test method was used to determine the force required to peel the positive electrode active material layer from the surface of the composite aluminum current collector, thereby evaluating the adhesion strength between the active material layer and the current collector. Higher peel strength indicates a stronger bond between the two, resulting in better electrode processability and cycle stability.

[0092] (a) Testing equipment: Universal testing machine (such as Instron 5943, Shimadzu AG-X series or similar equipment), equipped with a force sensor with a range of 100 N or 50 N; double-sided adhesive tape (3M brand or equivalent product, width matching the electrode); stainless steel test plate (flat and smooth surface); manual or automatic roller pressing device (2 kg rubber roller); cutter (width 15 mm or 20 mm); (b) Sample preparation: Cut rectangular samples with a width of 15 mm and a length of 80-100 mm from the pre-lithiated cathode or cathode sheet to be tested, ensuring that the sample edges are smooth and burr-free. Prepare at least 5 parallel samples for each sample group. Before testing, dry the samples in a 60°C vacuum oven for 2 hours to remove any adsorbed moisture, and then cool to room temperature.

[0093] (c) Test conditions: Test mode: 180° peel; Peeling speed: 50 mm / min (or 100 mm / min, to be determined according to actual needs, 50 mm / min in this experiment); Peeling length: ≥40 mm; Data acquisition frequency: at least 10 points / second; Environmental conditions: temperature 25±2℃, relative humidity ≤30% (dry environment).

[0094] (d) Test Procedure: (d1) Adhere the sample to the stainless steel test plate using double-sided tape. The procedure is as follows: Place the double-sided tape flat on the surface of the stainless steel test plate, ensuring there are no bubbles or wrinkles; peel off the release paper of the double-sided tape, and carefully attach the electrode with the current collector side down (active material layer up) to the double-sided tape; use a 2 kg rubber roller to roll back and forth on the sample once at a speed of about 300 mm / min to ensure that the tape is in full contact with the back of the current collector; (d2) Fix the stainless steel test plate with the sample attached to it on the lower clamp of the testing machine, ensuring that the test plate is firmly fixed to the clamp; (d3) Fold the free end of the sample (the end with the active material layer) upwards by 180° and clamp it in the upper clamp of the testing machine, ensuring that the clamping line is aligned with the peeling start line and that the sample remains vertical and does not twist throughout the test; (d4) Start the testing machine and stretch it upwards at the set peeling speed, recording the force-displacement curve during the peeling process; (d5) When the peeling length reaches at least 40 mm... Stop the test when mm; (d6) Observe the interface state after peeling and record whether the coating cohesive failure (internal fracture of the active layer) or interface failure (complete separation of the active layer and the current collector) occurs.

[0095] (e) Data Processing: The average peel force during the peel displacement range of 10 mm to 30 mm (i.e., the stable peel section) is taken as the peel force of the specimen. The peel strength is calculated using the following formula: Peel strength (N / m) = Average peel force (N) / Specimen width (m). Calculate the mean and standard deviation of 5 parallel specimens in the same group, and express the final result as mean ± standard deviation.

[0096] Strength retention rate is calculated using the following formula: Strength retention rate (%) = Peel strength of treated electrode / Peel strength of original untreated electrode × 100%.

[0097] 2. Experimental Results The test results of the batteries in the Examples and Comparative Examples regarding electrochemical performance test 1 are shown in Table 1. The test results of the batteries in the Examples and Comparative Examples regarding electrochemical performance test 2 are shown in Table 2. The test results of the electrodes regarding peel strength in Examples 1 and 2 and Comparative Examples 1 and 6 are shown in Table 3.

[0098] Table 1. Test results of the examples and comparative examples in electrochemical performance test 1.

[0099] As shown in Table 1, the pre-lithiated cathode sheet prepared by the method provided in this invention produces batteries with high initial charge / discharge capacity and initial coulombic efficiency, while also exhibiting high retention of the pre-lithiation effect. This indicates that the preparation method provided in this invention can not only effectively replenish lithium but also effectively "lock in" lithium, thus effectively improving the electrochemical performance of the battery.

[0100] In Comparative Example 1, without specific voltage treatment, the initial charge / discharge capacity, initial coulombic efficiency, and pre-lithiation effect retention rate were significantly lower than in Example 1. This indicates that the electrochemical treatment (voltage treatment) step introduced in this invention can effectively "lock" the pre-lithiated lithium in the cathode structure, reducing its loss in the initial cycle by approximately 15% relative value ((96.2-99.4) / (100-96.2)≈-0.84, i.e., the loss is reduced by 84%).

[0101] The voltages applied in Comparative Examples 2 and 3 were too low and too high, respectively. The voltage was too low (1.5V), which caused the residue to fail to convert and the film to fail, resulting in performance close to that of Comparative Example 1 without treatment. The voltage was too high (4.0V), which caused lithium over-depletion of the positive electrode, severe decomposition of the electrolyte and corrosion of the current collector, resulting in a comprehensive deterioration of electrochemical and mechanical properties.

[0102] In Comparative Examples 4 and 5, the processing time for applying voltage was too short and too long, respectively. Too short a time would prevent the formation of a complete CEI film, while too long a time would lead to film degradation and an increase in side reactions. Both of these would significantly affect the short-term and long-term performance of the battery.

[0103] Comparative Example 6 shows an untreated positive electrode. Due to the lack of additional lithium compensation, although its retention rate is high, its basic capacity is low. Therefore, data such as the retention rate of pre-lithiation effect are not very meaningful.

[0104] Further comparison of Examples 1 and 2 with Examples 3-5 revealed that the different types of electron acceptors in the organic lithium salt solution led to a decrease in various electrochemical performance parameters in Examples 3-5. This indicates that a suitable electron acceptor is more conducive to the formation of a denser and more stable CEI film, which in turn is more conducive to "lithium locking" and optimizing battery performance.

[0105] Comparing Examples 1 and 2 with Examples 6 and 7, it can be found that the performance of the battery changes when the concentration of lithium ions in the organic lithium salt solution changes, and the performance of the battery is better when the lithium ion concentration is in the range of 0.075~0.15 mol / L.

[0106] Comparing Examples 1 and 2 with Examples 8-11, it can be found that when the voltage and processing time in the electrochemical treatment are adjusted, the various performance characteristics of the battery also change. This indicates that a suitable voltage and processing time are more conducive to improving the performance of the positive electrode and the battery.

[0107] Table 2. Test results of the examples and comparative examples in electrochemical performance test 2.

[0108] As shown in Table 2, Example 1 exhibits the best cycling stability, with a capacity retention of 92.5% after 300 cycles, far exceeding all comparative examples. This confirms that the in-situ constructed CEI film can effectively protect the cathode material for a long time, suppressing electrolyte side reactions and structural degradation.

[0109] The rate of increase in charge transfer resistance (Rct) directly reflects interfacial stability. The Rct growth rate in Example 1 is significantly lower than in all comparative examples. In particular, compared to Comparative Example 1, with the same chemical pre-lithiation basis, the interfacial resistance growth was reduced by approximately 62% simply due to the addition of electrochemical treatment (comparative Example 1's growth rate). (Growth rate of Example 1) / Growth rate of Comparative Example 1 × 100%). This strongly demonstrates that the CEI membrane constructed in this invention has excellent ion conductivity and stability, can significantly "passivate" the interface, and suppress the rise in interface impedance during cycling.

[0110] The voltages applied in Comparative Examples 2 and 3 were too low and too high, respectively. The voltage was too low (1.5V), which prevented the residue from being converted and left the interface unprotected, causing the impedance to continue to increase to 486.2%. The voltage was too high (4.0V), which caused damage to the positive electrode and violent decomposition of the electrolyte, causing the impedance to increase uncontrollably to 905.3% and the capacity retention rate to be only 62.5%.

[0111] In Comparative Examples 4 and 5, the processing time with applied voltage was too short and too long, respectively. The processing time was too short (5 min), resulting in an incomplete CEI film and insufficient interface protection, with the Rct growth rate as high as 611.2%. The processing time was too long (135 min), resulting in an excessively thick film layer and increased side reactions, with the Rct growth rate reaching 525.0%. Both of these caused the capacity retention rate to drop to about 80%.

[0112] Comparative Example 6 is an untreated positive electrode. Due to the lack of pre-lithiation compensation and CEI film protection, Comparative Example 6 has the highest initial impedance (16.8Ω). During cycling, the interface continues to deteriorate (Rct growth rate of 647.6%), resulting in a capacity retention rate of only 70.5%, which is far lower than the 92.5% of Example 1 of this invention.

[0113] Further comparison of Examples 1 and 2 with Examples 3-5 reveals that the different types of electron acceptors in the organic lithium salt solution lead to a decrease in cycle capacity retention and an increase in the Rct growth rate in Examples 3-5. Comparing Examples 1 and 2 with Examples 6-7 shows that changes in the lithium ion concentration in the organic lithium salt solution alter the battery's cycle capacity retention and Rct growth rate. Comparing Examples 1 and 2 with Examples 8-11 shows that adjustments to the voltage and processing time during electrochemical treatment also change the battery's cycle capacity retention and Rct growth rate. These findings demonstrate that the type of electron acceptor in the organic lithium salt solution, the lithium ion concentration in the organic lithium salt solution, and the voltage and processing time during electrochemical treatment all have a certain impact on the battery's cycle capacity retention and Rct growth rate. Selecting a suitable organic lithium salt and setting appropriate voltage and time are more conducive to lithium replenishment and locking in the positive electrode, while reducing electrolyte side reactions, thus better optimizing battery cycle stability.

[0114] Table 3. Test results of peel strength of the electrode sheets in Examples 1 and 2 and Comparative Examples 1 and 6

[0115] As shown in Table 3, Example 2 had the least impact on electrode peel strength (retention rate 94.4%). Comparative Example 1, however, required a longer solvent rinsing time to remove residues, leading to some swelling of the polymer substrate or interface damage, resulting in a significant decrease in peel strength (<77%). Furthermore, it can be seen that even though Example 1 involved washing, the controlled washing time was short, effectively reducing swelling or interface damage to the polymer substrate, and the decrease in peel strength was not significant. This directly demonstrates that the present invention effectively improves the compatibility with the fragile composite current collector structure by reducing washing time or omitting the washing step, addressing a key issue in the industrialization of existing liquid phase technologies. Moreover, even with reduced washing time or omitted washing steps, as shown in Tables 1 and 2, the various electrochemical performance characteristics of the battery were effectively improved due to the application of a specific voltage treatment, achieving simultaneous optimization of good compatibility with the composite current collector and excellent electrochemical performance of the battery.

[0116] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for preparing a pre-lithiated positive electrode, characterized in that, Includes the following steps: S1. The positive electrode is completely immersed in an organic lithium salt solution for pre-lithiation treatment; S2. After drying the pre-lithiated positive electrode, assemble a half-cell using the positive electrode as the working positive electrode and lithium metal or lithium-containing materials as the counter electrode or reference electrode. In an electrolyte system containing lithium salt, apply a constant voltage, the voltage range being 2.0~3.5 V (relative to Li). + / Li), with a treatment time of 10~120min; S3. Remove the working electrode, wash and dry it to obtain the pre-lithiated positive electrode sheet.

2. The method for preparing the pre-lithiated cathode sheet as described in claim 1, characterized in that: In S1, the organic lithium salt contained in the organic lithium salt solution is a polycyclic aromatic hydrocarbon lithium salt, and the polycyclic aromatic hydrocarbon is a fused ring or bicyclic aromatic hydrocarbon with two or more rings. Preferably, the polycyclic aromatic hydrocarbon includes at least one of naphthalene, biphenyl, pyrene, phenanthrene, and anthracene; Preferably, the polycyclic aromatic hydrocarbon is selected from at least one of pyrene and biphenyl.

3. The method for preparing the pre-lithiated cathode sheet as described in claim 1, characterized in that: In step S1, the lithium ion concentration in the organic lithium salt solution is 0.05~0.3 mol / L; Preferably, the lithium ion concentration in the organic lithium salt solution is 0.075~0.15 mol / L.

4. The method for preparing the pre-lithiated cathode sheet as described in claim 1, characterized in that: In step S1, the organic lithium salt solution is prepared by reacting metallic lithium with a polycyclic aromatic hydrocarbon in an ether solvent, wherein the ether solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, and 1,3-dioxolane.

5. The method for preparing the pre-lithiated cathode sheet as described in claim 4, characterized in that: The specific operation for preparing the organolithium salt solution by reacting metallic lithium with the polycyclic aromatic hydrocarbon in the ether solvent is as follows: prepare a polycyclic aromatic hydrocarbon solution using the ether solvent, add the metallic lithium to it, and react at 32~40℃ for 4~8h to obtain the organolithium salt solution.

6. The method for preparing the pre-lithiated cathode sheet as described in claim 1, characterized in that: In S1, the positive electrode includes a current collector and a positive electrode active material layer disposed on the current collector; The current collector is a composite current collector, which includes a polymer substrate and a metal conductive layer formed on at least one surface of the polymer substrate. The material of the metal conductive layer is aluminum or an aluminum alloy.

7. The method for preparing the pre-lithiated cathode sheet as described in claim 1, characterized in that: In step S2, before drying the pre-lithiated positive electrode sheet, the positive electrode sheet needs to be washed. The washing solvent used is a non-polar or weakly polar solvent; the washing time is 1~30s. Preferably, the washing solvent includes at least one of xylene, n-hexane, and cyclohexane.

8. The method for preparing the pre-lithiated cathode sheet as described in claim 1, characterized in that: In step S2, the voltage application time is 30~60 minutes.

9. A pre-lithiated positive electrode, characterized in that: It is prepared by the method for preparing the pre-lithiated cathode sheet as described in any one of claims 1 to 7.

10. A lithium-ion battery, characterized in that: The lithium-ion battery includes the pre-lithiated positive electrode as described in claim 8.

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