Positive electrode lithium supplementing conductive agent, preparation method thereof and lithium ion battery

Abstract

The invention discloses a positive electrode lithium supplement conductive agent, a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The preparation method provided by the invention comprises the following steps: placing graphene in an acid solution for reaction, then placing the reacted graphene in a lithium salt solution for ion exchange, and performing plasma treatment on a solid product after ion exchange to obtain the positive electrode lithium supplementing conductive agent. The stable negative charge layer is constructed on the surface of the graphene, the electrostatic adsorption effect is utilized, the Li < + > anchoring capacity is enhanced, and ion / electron double channels are formed, so that efficient lithium ion release and electron / ion cooperative transmission are synchronously realized in the same material system, irreversible lithium loss is effectively compensated, and the lithium ion battery performance is improved. And the transmission efficiency of the conductive network is also remarkably improved, and the technical problem that the lithium supplement function and the conductivity are difficult to consider at the same time is fundamentally solved. And the assembled battery has high first efficiency and good rate capability, cycle performance and safety.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode lithium-replenishing conductive agent, its preparation method, and a lithium-ion battery. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In the field of lithium-ion batteries, a large amount of active lithium is irreversibly consumed during the first charge and discharge cycle to form a solid electrolyte interphase (SEI) film. This process directly leads to a reduction in the battery's usable capacity, energy density, and cycle life. To compensate for this irreversible lithium loss, pre-lithiation technology has become one of the industry's important solutions.

[0004] Currently, pre-lithiation technologies mainly include two routes: negative electrode pre-lithiation and positive electrode pre-lithiation. Negative electrode pre-lithiation involves methods such as using lithium-rich additives, chemical pre-lithiation, or electrochemical pre-lithiation; positive electrode pre-lithiation relies on pre-lithiation additives or overlithiated positive electrode materials. However, these methods generally suffer from a series of common problems: such as high safety risks, high process complexity, difficulty in cost control, and the introduction of inactive substances into the electrode leading to a decrease in the proportion of active materials, thereby affecting the overall conductivity and energy density.

[0005] On the other hand, conductive additives are indispensable in the manufacture of lithium-ion batteries, among which graphene is widely used due to its excellent conductivity and mechanical properties. However, graphene itself also has certain limitations. The oxygen-containing functional groups on its surface can easily capture lithium ions, causing irreversible capacity loss. At the same time, graphene sheets are prone to recombination, which hinders the lithium ion transport path and leads to a decrease in ionic conductivity.

[0006] Therefore, the core contradiction facing current technology lies in the fact that while lithium replenishing agents can provide high lithium content, they often come at the cost of conductivity; while conductive agents, although possessing good electron migration capabilities, lack lithium replenishment functionality. How to simultaneously achieve efficient lithium-ion release and synergistic electron / ion transport within a single material system has become a critical challenge that urgently needs to be overcome in existing technologies. Summary of the Invention

[0007] In view of this, the present invention provides a positive electrode lithium-conducting agent and its preparation method, as well as a lithium-ion battery. The present invention enhances the lithium-ion battery by constructing a stable negative charge layer on the graphene surface and utilizing electrostatic adsorption. +The anchoring capability forms a dual ion / electron channel, thereby simultaneously achieving efficient lithium-ion release and synergistic electron / ion transport within the same material system. This not only effectively compensates for irreversible lithium loss but also significantly improves the transmission efficiency of the conductive network, fundamentally solving the technical challenge of balancing lithium replenishment and conductivity.

[0008] In a first aspect, the present invention provides a method for preparing a positive electrode lithium-supplementing conductive agent, comprising the following steps: Graphene is reacted in an acid solution, and then the reacted graphene is placed in a lithium salt solution for ion exchange. The solid product after ion exchange is subjected to plasma treatment to obtain a positive electrode lithium-replenishing conductive agent.

[0009] Preferably, the acid solution is selected from one or more of sulfuric acid, nitric acid, or phosphoric acid; the lithium salt is selected from one or more of LiClO4, LiCH3COO, LiCl, Li3C6H5O7, LiOH, Li2SO4, or Li2C2O4.

[0010] Preferably, in the step of reacting graphene in acid, the reaction temperature is 30~100℃ and the reaction time is 0.5~10h; the ratio of graphene to acid is (0.1~0.5)g : (80~300)mL.

[0011] Preferably, the concentration of the lithium salt solution is 0.05~1M, and the ratio of graphene to lithium salt solution is (0.1~0.5)g : (80~300)mL.

[0012] Preferably, the ion exchange process is carried out under ultrasonic conditions, with the ultrasonic time being 2-8 hours and the ultrasonic power being 300-800W.

[0013] Preferably, the plasma treatment time is 0.5 to 5 hours, and the ambient temperature during the plasma treatment process is controlled below 80°C; the working gas during the plasma treatment process is a mixture of nitrogen and hydrogen, or a mixture of argon and hydrogen.

[0014] Secondly, the present invention provides a positive electrode lithium-supplementing conductive agent prepared by the above preparation method.

[0015] Thirdly, the present invention provides a positive electrode sheet, comprising a current collector and a positive active material, a binder and a positive lithium-ion conductive agent disposed on the current collector, wherein the positive lithium-ion conductive agent is the aforementioned positive lithium-ion conductive agent.

[0016] Preferably, the mass ratio of the positive electrode active material, binder and positive electrode lithium-supplementing conductive agent is (7~9): (0.5~1.5): (0.5~1.5).

[0017] Fourthly, the present invention provides a lithium-ion battery comprising the above-mentioned positive electrode sheet.

[0018] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) This invention successfully prepares a positive electrode lithium-replenishing conductive agent that combines lithium replenishment and conductivity by reacting graphene in a specific acid solution to covalently graft negatively charged functional groups onto its surface, then introducing lithium ions through ion exchange and stabilizing the structure through plasma treatment. This method innovatively constructs a stable negatively charged layer on the graphene surface, achieving efficient anchoring of lithium ions through electrostatic adsorption, forming a unique ion / electron dual-channel structure, fundamentally solving the technical problem of the difficulty in synergistic function of lithium replenishment agents and conductive agents in traditional technologies.

[0019] (2) The lithium content of the positive electrode lithium replenishing conductive agent powder prepared by the present invention is as high as 10~16%, which provides a solid foundation for efficient lithium replenishment. At the same time, it has excellent electronic conductivity. The positive electrode sheet prepared by it exhibits a low electrode resistivity, proving that it can construct an efficient conductive network.

[0020] (3) The lithium-ion battery assembled using the positive electrode sheet of the present invention achieves an initial charge-discharge efficiency of over 92%, effectively compensating for irreversible lithium loss caused by SEI film formation. Simultaneously, the battery exhibits low charge transfer impedance in electrochemical tests. More importantly, thanks to the unique ion / electron dual-channel structure of the positive electrode lithium replenishing conductive agent of the present invention, the assembled battery achieves a capacity retention rate of over 89% at high rate (3C), and a capacity retention rate of over 92% after 100 cycles at 1C. Furthermore, since there are no inactive, non-conductive residues after lithium replenishment, the battery effectively avoids safety risks such as gas generation and metal dissolution common with traditional lithium replenishing agents during cycling or storage. Attached Figure Description

[0021] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0022] Figure 1This is a Zeta potential diagram of the untreated graphene (GN) of the present invention, the sulfonic acid functionalized graphene (S-GN) of Example 1, the carboxyl functionalized graphene (C-GN) of Example 2, the phosphoric acid functionalized graphene (P-GN) of Example 3, the sulfonic acid functionalized lithium graphene (Li@S-GN) of Example 1, the carboxyl functionalized lithium graphene (Li@C-GN) of Example 2, and the phosphoric acid functionalized lithium graphene (Li@P-GN) of Example 3. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] This invention provides a method for preparing a positive electrode lithium-supplementing conductive agent, comprising the following steps: Graphene is reacted in an acid solution, and then the reacted graphene is placed in a lithium salt solution for ion exchange. The solid product after ion exchange is subjected to plasma treatment to obtain a positive electrode lithium-replenishing conductive agent.

[0025] This invention constructs modified graphene that integrates lithium replenishment and conductivity through surface chemical design and physical treatment. First, the graphene is reacted in an acidic solution to covalently graft highly negatively charged functional groups onto its surface, thereby constructing a stable negatively charged interface layer. This interface layer, through its strong electrostatic adsorption capacity, lays the structural foundation for the subsequent efficient and reversible anchoring of lithium ions.

[0026] Subsequently, in the ion exchange step, lithium ions in the solution are selectively adsorbed onto the negatively charged graphene surface. This process achieves stable fixation of lithium ions through electrostatic interactions, thereby avoiding the safety risks and uncontrollable side reactions associated with violent chemical reactions.

[0027] This invention introduces a plasma treatment step after the ion exchange step. Its core function is to bombard and modify the material surface with high-energy particles, thereby further stabilizing the interaction between adsorbed lithium ions and negatively charged groups and optimizing the surface charge distribution. This treatment effectively prevents unintended desorption of lithium ions during subsequent processing or use, ensuring the chemical stability and functional reliability of the lithium replenisher under battery manufacturing conditions, while also helping to maintain the graphene sp. 2 The integrity of the conjugated structure ensures that its basic electrical conductivity is not compromised.

[0028] The above-mentioned technical solution of the present invention creatively solves the industry problem that the conductivity of lithium replenishing agents is impaired due to the introduction of inactive substances or irreversible structural changes, and achieves the technical effect of constructing a highly efficient ion / electron dual channel while compensating for the loss of active lithium.

[0029] This invention does not impose special restrictions on the source of graphene; it can be obtained through commercial channels or prepared in-house. The graphene can be obtained through methods such as electrochemical exfoliation, chemical redox, chemical vapor deposition, liquid phase exfoliation, and mechanical exfoliation.

[0030] In an optional embodiment of the present invention, the acid solution is selected from one or more of sulfuric acid, nitric acid, or phosphoric acid. Sulfuric acid is used to introduce the highly electronegative sulfonate ion (-SO3). - Nitric acid treatment is used to introduce carboxyl groups (-COO). - Phosphoric acid is used to introduce phosphate ions (-PO3). 2- These specific groups have low pKa values, allowing for complete dissociation in the system and providing stable and strong electronegativity, making them highly efficient at adsorbing Li. + The key point is that the present invention does not impose special restrictions on the concentration of the acid solution. Preferably, when the acid solution is sulfuric acid, the concentration of sulfuric acid is 95~98wt%; when the acid solution is nitric acid, the concentration of nitric acid is 40~70wt%, more preferably 45~60wt%; and when the acid solution is phosphoric acid, the concentration of phosphoric acid is 10~30wt%, more preferably 15~25wt%.

[0031] In optional embodiments of the present invention, the lithium salt is selected from one or more of LiClO4, LiCH3COO, LiCl, Li3C6H5O7, LiOH, Li2SO4, or Li2C2O4. The present invention does not impose special limitations on the type of solvent used for the lithium salt solution, as long as it can fully dissolve the lithium salt and does not cause harmful reactions with the lithium salt, graphene, or the newly introduced negatively charged functional groups on its surface. Examples of solvents include ethanol, methanol, isopropanol, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), ethylene carbonate (EC), and dimethyl carbonate (DMC). In one or more embodiments of the present invention, the lithium salt solvent solution is ethanol.

[0032] In an optional embodiment of the present invention, in the step of reacting graphene in acid, the reaction temperature is 30-100℃, more preferably 30-90℃, and even more preferably 40-80℃; the reaction time is 0.5-10h, more preferably 4-8h, and even more preferably 5-7h. The ratio of graphene to acid is (0.1-0.5)g : (80-300)mL, more preferably (0.1-0.3)g : (80-150)mL. Suitable temperature, time, and ratio are beneficial for promoting the functional group modification reaction on the graphene surface without adversely affecting the graphene structure.

[0033] In an optional embodiment of the present invention, the concentration of the lithium salt solution is 0.05~1M, more preferably 0.1~0.5M, and even more preferably 0.15~0.45M; the ratio of graphene to lithium salt solution is (0.1~0.5)g : (80~300)mL; more preferably (0.1~0.3)g : (80~150)mL. The concentration and ratio together determine the amount of Li available for exchange. + The total amount directly affects the lithium content of the final product. If the concentration is too low or the amount used is too small, the lithium loading will be insufficient; if the concentration is too high, it may lead to lithium salt precipitation or uneven adsorption.

[0034] In an optional embodiment of the present invention, the ion exchange process is carried out under ultrasonic conditions for 2-8 hours, more preferably 4-6 hours. The ultrasonic power is 300-800W, more preferably 400-500W. Too low a power will result in poor dispersion and activation, while too high a power may cause the graphene sheets to break. Ultrasonic treatment serves two purposes: firstly, to disperse and prevent the graphene sheets from recombinizing, thus exposing all active sites; secondly, it serves as an energy input, utilizing the energy provided by the cavitation effect to promote Li... + Overcoming the energy barrier, it diffuses and firmly adsorbs onto negatively charged sites.

[0035] Following the ion exchange step, this invention further includes solid-liquid separation and drying to obtain a solid product. The specific steps of solid-liquid separation are not particularly limited; for example, centrifugation or filtration can be used. Centrifugation is preferred. Following the plasma treatment step, this invention also includes washing and drying steps to finally obtain a positive electrode lithium-conducting agent.

[0036] In optional embodiments of the present invention, the plasma treatment time is 0.5~5h, more preferably 1~3h, and even more preferably 1.5~2.5h; the ambient temperature during the plasma treatment process is controlled below 80℃ to ensure that the entire process is carried out at a low temperature, avoiding thermal desorption of lithium or thermal damage to the graphene structure; more preferably 25~70℃, and even more preferably 30~60℃ (controlled by water cooling). The working gas during the plasma treatment process is a mixture of nitrogen and hydrogen, or a mixture of argon and hydrogen, to prevent the lithium salt from being oxidized. The high-energy particles and active species in the plasma bombard the material surface, which mainly has the following three effects: First, cross-linking and curing: to make the adsorbed Li + The binding between functional groups is more stable, preventing them from falling off during drying and battery fabrication; second, slight etching and pore creation: increase ion transport channels; third, surface cleaning: remove weakly adsorbed impurities.

[0037] The present invention also provides a positive electrode lithium-replenishing conductive agent prepared by the above preparation method, wherein the lithium element mass content is 10~16wt%.

[0038] The present invention also provides a positive electrode sheet, comprising a current collector and a positive active material, a binder and a positive lithium-ion conductive agent disposed on the current collector, wherein the positive lithium-ion conductive agent is the aforementioned positive lithium-ion conductive agent.

[0039] In an optional embodiment of the present invention, the mass ratio of the positive electrode active material, the binder and the positive electrode lithium-supplementing conductive agent is (7~9): (0.5~1.5): (0.5~1.5).

[0040] In the positive electrode sheet of this invention, the conductive agent can be limited to the aforementioned positive electrode lithium-supplementing conductive agent, or it can include other commonly used conductive agents, such as conductive carbon black (e.g., Super P, acetylene black, Ketjen black), carbon nanotubes, carbon fibers, or graphite. This invention does not impose any special limitations on the positive electrode active material, including but not limited to lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, or their doped and modified materials. This invention also does not impose any special limitations on the binder; commonly used binders in the art can be used, including but not limited to polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, and their salts. This invention also does not impose any special limitations on the current collector used; for example, it can be aluminum foil or carbon-coated aluminum foil. This invention does not impose any special limitations on the preparation method of the positive electrode sheet; commonly used methods in the art can be used.

[0041] The present invention also provides a lithium-ion battery, including the above-mentioned positive electrode, as well as a negative electrode, a separator, an electrolyte, etc. The present invention does not impose any special restrictions on its preparation method.

[0042] The lithium-ion battery prepared by this invention has comprehensive advantages such as high initial coulombic efficiency (greater than 92%), excellent rate performance (capacity retention rate of more than 89% at 3C rate), long cycle life (capacity retention rate of more than 92% after 100 cycles at 1C rate) and higher safety, effectively avoiding the risks of gas expansion and thermal runaway caused by gas generation and metal dissolution of traditional lithium replenishment agents.

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0044] The graphene in the following examples was prepared by electrochemical exfoliation, with 3-5 layers and a specific surface area >500 m². 2 / g.

[0045] Example 1 This embodiment provides a method for preparing sulfonic acid-functionalized lithium graphene (Li@S-GN) and the corresponding positive electrode.

[0046] (1) Surface functionalization: Accurately weigh 0.2g of graphene and disperse it in 100 mL of 98% sulfuric acid. Stir the mixture continuously at 80℃ for 6 hours.

[0047] (2) Washing and drying: After the reaction was completed, the product was centrifuged and washed repeatedly with deionized water until the filtrate was neutral. The obtained solid was dried in a vacuum drying oven at 80°C for 12 hours to obtain sulfonic acid functionalized graphene (S-GN).

[0048] (3) Ion exchange and lithium loading: The dried S-GN (approximately 0.13 g) was redispersed in 100 mL of 0.2 mol / L lithium perchlorate (LiClO4) anhydrous ethanol solution. The solution was ultrasonically treated at 25°C for 4 hours in an ultrasonic cell disruptor with a power of 500 W to complete the ion exchange and lithium loading process.

[0049] (4) Plasma stabilization treatment: The above slurry is centrifuged and dried, and the resulting solid is transferred to a plasma treatment device. Under a mixed atmosphere of argon / hydrogen volume ratio of 4:1, the ambient temperature of the reaction chamber is controlled at 60°C, the power is applied at 300W, and the treatment lasts for 2 hours.

[0050] (5) Post-treatment: The plasma-treated sample was washed twice with anhydrous ethanol and then dried in a vacuum environment at 80°C for 12 hours to obtain the final product, sulfonic acid functionalized lithium graphene Li@S-GN.

[0051] (6) Preparation of positive electrode sheet: Dry Li@S-GN, ternary positive electrode active material (NCM811), and polyvinylidene fluoride (PVDF) binder are mixed at a mass ratio of 1:8:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred in a vacuum mixer for 4 hours to form a uniform slurry. Subsequently, the slurry is coated onto an aluminum foil current collector and vacuum dried at 120°C for 12 hours. After rolling and stamping, the positive electrode sheet is formed.

[0052] Example 2 This embodiment provides a method for preparing carboxyl-functionalized lithium graphene (Li@C-GN) and the corresponding positive electrode.

[0053] (1) Surface functionalization: 0.2g of graphene was accurately weighed and dispersed in 100 mL of 50wt% nitric acid. The mixture was then mechanically stirred at 80℃ for 6 hours.

[0054] (2) Washing and drying: After the reaction was completed, the product was centrifuged and washed repeatedly with deionized water until the filtrate was neutral. The obtained solid was dried in a vacuum drying oven at 80°C for 12 hours to obtain carboxyl-functionalized graphene (C-GN).

[0055] (3) Ion exchange and lithium loading: The dried C-GN (approximately 0.15 g) was redispersed in 100 mL of 0.2 mol / L lithium perchlorate (LiClO4) anhydrous ethanol solution. The solution was ultrasonically treated at 25°C for 4 hours in an ultrasonic cell disruptor with a power of 500 W to complete the ion exchange and lithium loading process.

[0056] (4) Plasma stabilization treatment: The above slurry is centrifuged and dried, and the resulting solid is transferred to a low-temperature plasma treatment device. Under a mixed atmosphere of argon and hydrogen with a volume ratio of 4:1, the ambient temperature of the reaction chamber is controlled at 60°C, the power is applied at 300W, and the treatment lasts for 2 hours.

[0057] (5) Post-treatment: The plasma-treated sample was washed twice with anhydrous ethanol and then dried in a vacuum environment at 80°C for 12 hours to obtain the final product, carboxyl-functionalized lithium graphene Li@C-GN.

[0058] (6) Preparation of positive electrode sheet: Dry Li@C-GN, ternary positive electrode active material (NCM811), and polyvinylidene fluoride (PVDF) binder are mixed at a mass ratio of 1:8:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred in a vacuum mixer for 4 hours to form a uniform slurry. Subsequently, the slurry is coated onto an aluminum foil current collector and vacuum dried at 120°C for 12 hours. After rolling and stamping, the positive electrode sheet is formed.

[0059] Example 3 This embodiment provides a method for preparing phosphoric acid-functionalized lithium graphene (Li@P-GN) and the corresponding positive electrode.

[0060] (1) Surface functionalization: Accurately weigh 0.2g of graphene and disperse it in 100 mL of 20wt% phosphoric acid solution. Stir the mixture continuously at 80℃ for 6 hours.

[0061] (2) Washing and drying: After the reaction was completed, the product was centrifuged and washed repeatedly with deionized water until the filtrate was neutral. The obtained solid was dried in a vacuum drying oven at 80°C for 12 hours to obtain phosphate-functionalized graphene (P-GN).

[0062] (3) Ion exchange and lithium loading: The dried P-GN (approximately 0.15 g) was redispersed in 100 mL of 0.2 mol / L lithium perchlorate (LiClO4) anhydrous ethanol solution. The solution was ultrasonically treated at 25°C for 4 hours in a 500 W ultrasonic cell disruptor to complete the ion exchange and lithium loading process.

[0063] (4) Plasma stabilization treatment: The above slurry is centrifuged and dried, and the resulting solid is transferred to a plasma treatment device. Under a mixed atmosphere of argon and hydrogen with a volume ratio of 4:1, the ambient temperature of the reaction chamber is controlled at 60°C, the power is applied at 300W, and the treatment lasts for 2 hours.

[0064] (5) Post-processing: The plasma-treated sample was washed twice with anhydrous ethanol and then dried in a vacuum environment at 80°C for 12 hours to obtain the final product, phosphoric acid functionalized lithium graphene Li@P-GN.

[0065] (6) Preparation of positive electrode sheet: Dry Li@P-GN, ternary positive electrode active material (NCM811), and polyvinylidene fluoride (PVDF) binder are mixed at a mass ratio of 1:8:1. An appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred in a vacuum mixer for 4 hours to form a uniform slurry. Subsequently, the slurry is coated onto an aluminum foil current collector and vacuum dried at 120°C for 12 hours. After rolling and stamping, the positive electrode sheet is formed.

[0066] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example does not process the graphene, but directly uses untreated graphene as a conductive agent to prepare the positive electrode sheet.

[0067] The preparation process of the positive electrode sheet in this comparative example is as follows: Graphene, ternary positive electrode active material (NCM811), and polyvinylidene fluoride (PVDF) binder are mixed at a mass ratio of 1:8:1, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added. The mixture is stirred in a vacuum mixer for 4 hours until a uniform slurry is formed. Subsequently, the slurry is coated onto an aluminum foil current collector and vacuum dried at 120°C for 12 hours. After rolling and stamping, the positive electrode sheet is formed.

[0068] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example uses a traditional lithium replenishing agent. Li5FeO4 and conductive carbon black (Super P) are pre-mixed at a mass ratio of 2:8 to form a mixed lithium replenishing conductive agent. The mixed lithium replenishing conductive agent, ternary cathode active material (NCM811), and polyvinylidene fluoride (PVDF) binder are mixed at a mass ratio of 1:8:1, and an appropriate amount of N-methylpyrrolidone (NMP) solvent is added. The mixture is stirred in a vacuum mixer for 4 hours until a uniform slurry is formed. Subsequently, the slurry is coated onto an aluminum foil current collector, vacuum dried at 120°C for 12 hours, and then rolled and stamped to form a cathode sheet.

[0069] Comparative Example 3 The difference between this comparative example and Example 1 is that steps (3) to (5) are not performed in this comparative example. In this comparative example, dry sulfonic acid functionalized graphene (S-GN), ternary positive electrode active material (NCM811), and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 1:8:1 to prepare a positive electrode sheet. The preparation method of the positive electrode sheet is the same as that in Example 1.

[0070] Comparative Example 4 The difference between this comparative example and Example 1 is that step (4) is not performed in this comparative example. In this comparative example, sulfonic acid functionalized graphene (Non-PT-S-GN), ternary positive electrode active material (NCM811), and polyvinylidene fluoride (PVDF) binder without plasma treatment are mixed in a mass ratio of 1:8:1 to prepare a positive electrode sheet. The preparation method of the positive electrode sheet is the same as that in Example 1.

[0071] Test case Assembly of coin cells: The positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-4 were used to assemble CR2025 coin cells. The specific steps are as follows: In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the positive electrode shell, positive electrode sheet, separator (Celgard 2400), electrolyte, lithium sheet (counter electrode), gasket, spring, and negative electrode shell were assembled in that order. The electrolyte used was 1 M LiPF6 dissolved in a mixed solvent of EC / DMC (volume ratio 1:1). After assembly, the cells were sealed and allowed to stand for 24 hours before electrochemical testing.

[0072] The test methods and test results are as follows: 1. Initial charge / discharge efficiency and specific capacity test: The prepared coin cell half-cells were charged at a constant current of 0.1C to 4.3V at 25℃, then switched to constant voltage charging until the current dropped to 0.05C. After resting for 5 minutes, they were discharged at a constant current of 0.1C to the cutoff voltage of 2.75V, completing the first charge-discharge cycle. The initial charge capacity (Q) was recorded. c ) and initial discharge capacity (Q d The first-time Coulomb efficiency (first-efficiency) is expressed by the formula "(Q)". d / Q c The initial discharge specific capacity is calculated using the formula "Q × 100%". d The value is calculated from the "mass of positive electrode active material", with the unit being mAh / g.

[0073] 2. Cyclic performance test: The battery was first charged and discharged at 0.1C at 25°C (method as above). Then, a cycle test was performed at a charge / discharge rate of 1C within a voltage range of 2.75~4.35V, and the discharge capacity C of the 100th cycle was recorded. 100 The formula for calculating capacity retention rate is: Capacity Retention Rate = (C... 100 / C1) × 100%, where C1 is the discharge capacity of the first 1C cycle. The nominal specific capacity is 1C = 210mAh / g.

[0074] 3. Ratio Performance Test: At 25°C, the battery was charged to 4.3V at a constant current and constant voltage of 0.2C, and then discharged to 2.75V at constant current rates of 0.2C, 0.5C, 1C, 2C, and 3C, respectively. The discharge capacity at each rate was recorded. Rate performance is expressed as the percentage of discharge capacity at 3C to discharge capacity at 0.2C, i.e., 3C / 0.2C rate capacity retention.

[0075] 4. Electrochemical Impedance Spectroscopy (EIS) Test The battery was charged to 50% state of charge (SOC) and tested using an electrochemical workstation. The test frequency range was 100 kHz to 10 mHz, with a perturbation voltage of 5 mV. The charge transfer impedance (Ro) of the battery was obtained by fitting. ct ).

[0076] 5. Electrode resistivity test The sheet resistance of the dried positive electrode was directly measured using the four-probe method, and the volume resistivity (Ω·cm) of the electrode was calculated based on the electrode thickness. 2 ).

[0077] 6. Lithium content test The mass percentage (wt%) of lithium in the prepared lithium-replenishing conductive agent was measured using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0078] 7. Zeta potential The Zeta potentials of untreated graphene (GN), sulfonate-functionalized graphene (S-GN) from Example 1, carboxyl-functionalized graphene (C-GN) from Example 2, phosphate-functionalized graphene (P-GN) from Example 3, sulfonate-functionalized lithium graphene (Li@S-GN) from Example 1, carboxyl-functionalized lithium graphene (Li@C-GN) from Example 2, and phosphate-functionalized lithium graphene (Li@P-GN) from Example 3 were measured using a Zeta potential analyzer. The results are summarized in... Figure 1 .

[0079] The results of the above electrochemical performance tests are summarized in Table 1.

[0080] Table 1. Electrochemical performance test results of the examples and comparative examples.

[0081] from Figure 1 The Zeta potential diagram shows that untreated graphene is negatively charged. This is because oxygen-containing functional groups on the graphene surface dissociate in solution and carry a negative charge. After surface treatment, the GN charge is further reduced to -75.1 to -67.5 mV, which is beneficial for cations (Li). + GN has strong electrostatic interactions. - Through electrostatic interaction with Li + Combined, forming a load Li + The graphene conductive agent has a zeta potential of 13.2~15.4mV.

[0082] As shown in Table 1, the initial coulombic efficiency of all embodiments exceeded 92%, significantly higher than Comparative Example 1 (pure graphene, 83.3%) and Comparative Example 2 (traditional Li5FeO4 lithium supplement, 87.5%). This directly proves that the lithium loaded by electrostatic adsorption in this invention is efficiently released in the first cycle, effectively compensating for the irreversible lithium loss caused by SEI formation. Meanwhile, the electrode resistivity of the embodiments is comparable to that of pure graphene (Comparative Example 1) and much lower than that of Comparative Example 2, indicating that this invention, while introducing a high content of active lithium, does not sacrifice its conductivity, successfully solving the industry problem of increased internal resistance caused by the introduction of inactive residues or damage to the conductive network in traditional lithium supplements.

[0083] Examples 1-3 all exhibited extremely high 3C / 0.2C rate capacity retention (>89%) and low EIS impedance. This is mainly due to the graphene sp... 2 The conjugated framework ensures rapid electron transport, while the surface-grafted negatively charged groups (-SO3) - -COO - -PO3 2- This formed a favorable environment for Li + The "ion channels" facilitate rapid ion / electron transport. In contrast, Comparative Example 1 lacks ion channels, and in Comparative Example 2, Fe catalyzes the decomposition of the electrolyte, forming a loose and thick SEI that hinders lithium-ion migration. This leads to increased ion concentration polarization at high rates, resulting in a significant deterioration in rate performance. Furthermore, the residual inactive metal oxides in Comparative Example 2 after the first charge-discharge cycle may affect the battery's energy density and rate performance.

[0084] The first-cycle efficiency of Comparative Example 3 was slightly lower than that of pure graphene and significantly lower than that of Example 1. This strongly demonstrates that "surface functionalization" and "lithium loading" are two closely related and indispensable steps. A surface with only a negative charge and no lithium loading cannot achieve lithium replenishment and will consume more active lithium due to electrostatic effects, further reducing the first-cycle efficiency. The cycle retention rate of Comparative Example 4 was lower than that of Example 1, proving that plasma treatment plays a crucial role in stabilizing the electrode structure and improving long-term cycling performance. This may be achieved by stabilizing Li... + Adsorption and optimized interfaces reduce the degradation of active lithium and conductive networks during cycling.

[0085] Example 1 (Li@S-GN, sulfonic acid group) showed the best performance in terms of first-efficiency, rate capability, and cycle life, which may be due to the -SO3 group. - The group exhibits stronger acidity and electronegativity, and is more effective against Li. + Its electrostatic adsorption effect is stronger and more stable.

[0086] In summary, the positive electrode lithium replenishing conductive agent and its preparation method provided by this invention solve the synergistic problem of lithium replenishment and conductivity by constructing an integrated structure of "electrostatic anchoring of lithium in a negative charge layer", thus endowing lithium-ion batteries with high initial efficiency, excellent rate performance and long cycle life.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode lithium-supplementing conductive agent, characterized in that, Includes the following steps: Graphene is reacted in an acid solution, and then the reacted graphene is placed in a lithium salt solution for ion exchange. The solid product after ion exchange is subjected to plasma treatment to obtain a positive electrode lithium-replenishing conductive agent.

2. The preparation method according to claim 1, characterized in that, The acid solution is selected from one or more of sulfuric acid, nitric acid, or phosphoric acid; the lithium salt is selected from one or more of LiClO4, LiCH3COO, LiCl, Li3C6H5O7, LiOH, Li2SO4, or Li2C2O4.

3. The preparation method according to claim 1, characterized in that, In the step of reacting graphene in acid, the reaction temperature is 30~100℃ and the reaction time is 0.5~10h; the ratio of graphene to acid is (0.1~0.5)g: (80~300)mL.

4. The preparation method according to claim 1, characterized in that, The concentration of the lithium salt solution is 0.05~1M, and the ratio of graphene to lithium salt solution is (0.1~0.5)g : (80~300)mL.

5. The preparation method according to claim 1, characterized in that, The ion exchange process is carried out under ultrasonic conditions for 2 to 8 hours, with an ultrasonic power of 300 to 800 W.

6. The preparation method according to claim 1, characterized in that, The plasma treatment time is 0.5 to 5 hours, the ambient temperature during the plasma treatment process is controlled below 80°C, and the working gas during the plasma treatment process is a mixture of nitrogen and hydrogen, or a mixture of argon and hydrogen.

7. The positive electrode lithium-replenishing conductive agent prepared by the preparation method according to any one of claims 1 to 6.

8. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode active material disposed on the current collector, a binder, and a positive electrode lithium-replenishing conductive agent, wherein the positive electrode lithium-replenishing conductive agent is the positive electrode lithium-replenishing conductive agent as described in claim 7.

9. The positive electrode sheet as described in claim 8, characterized in that, The mass ratio of the positive electrode active material, binder, and positive electrode lithium-supplementing conductive agent is (7~9): (0.5~1.5): (0.5~1.5).

10. A lithium-ion battery, characterized in that, Including the positive electrode sheet as described in claim 8 or 9.

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