An acidic polymer / lithium supplement multifunctional composite additive for positive electrode slurry and a preparation method thereof

Abstract

This invention discloses a multifunctional composite additive of acidic polymer / lithium replenishment agent for positive electrode slurry and its preparation method, relating to the field of lithium-ion battery technology. The multifunctional composite additive is prepared by modifying a lithium replenishment agent with an acidic polymer; the ratio of acidic polymer to lithium replenishment agent is (0.02-0.1):1; wherein the acidic polymer undergoes an acid-base neutralization reaction with residual lithium compounds on the surface of the lithium replenishment agent, and the resulting product coats the lithium replenishment agent, effectively removing residual lithium compounds and improving the stability of the lithium replenishment agent. The multifunctional composite additive provided by this invention has high pre-lithiation efficiency and high compatibility with existing lithium-ion battery manufacturing processes, which is beneficial for improving the subsequent slurry processing performance and the performance of the positive electrode sheet. The preparation method is simple and highly operable, and is expected to achieve industrial production and engineering applications.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a multifunctional composite additive for positive electrode slurry, consisting of an acidic polymer / lithium supplement, and its preparation method. Background Technology

[0002] During the first charge of a lithium-ion battery, some Li₂ will be released from the positive electrode. + Instead of embedding itself in the negative electrode, it participates in the formation of the SEI film on the negative electrode surface. This process is irreversible and consumes some active lithium, thus reducing the battery's initial coulombic efficiency and energy density. Currently widely used graphite negative electrodes experience more than 10% irreversible consumption of the positive electrode lithium source during the first charge, resulting in an initial coulombic efficiency of less than 90%. Therefore, it is necessary to introduce an additional active lithium source into the battery to compensate for the irreversible consumption of the positive electrode active lithium.

[0003] The common solution currently is to add lithium-replenishing additives to compensate for the loss of active lithium, effectively improving the battery's initial coulombic efficiency and energy density, and fully utilizing the performance of the cathode material. Among them, lithium iron ferrite (Li5FeO4) is inexpensive and safe, making it a promising lithium-replenishing agent. However, it is very sensitive to moisture and carbon dioxide, and cannot maintain its stability in air. The alkaline residual lithium compounds formed on its surface affect the subsequent slurry processing performance and electrode performance, making Li5FeO4 difficult to mass-produce and apply in engineering.

[0004] Therefore, how to efficiently remove residual lithium compounds and improve the stability of lithium supplementation additives has become one of the technical challenges that urgently need to be solved in this field.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a multifunctional composite additive for positive electrode slurry, consisting of an acidic polymer and a lithium supplement, and a method for preparing the same, in order to solve or improve the aforementioned technical problems.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a multifunctional composite additive of acidic polymer / lithium supplement for positive electrode slurry, wherein the multifunctional composite additive is prepared by modifying a lithium supplement additive with an acidic polymer. The ratio of acidic polymer to lithium supplementation additive is (0.02-0.1):1; The acidic polymer is selected from at least one of poly(2-acrylamide-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) copolymer, poly(2-acrylamide-2-methylpropanesulfonic acid), and polyacrylic acid.

[0008] In a second aspect, the present invention provides a method for preparing a multifunctional composite additive as described in any of the foregoing embodiments, comprising the following preparation steps: Preparation of acidic polymers; A suspension was prepared by mixing the acidic polymer with the lithium supplementation additive in a certain proportion and reacting at room temperature for 0.1 h to 3.0 h. After the suspension was filtered, the resulting filter cake was vacuum dried at 70℃-110℃ to obtain a multifunctional composite additive of acid polymer / lithium supplement.

[0009] Thirdly, the present invention provides a positive electrode sheet, wherein the positive electrode slurry used includes a multifunctional composite additive as described in any of the foregoing embodiments or a multifunctional composite additive prepared by any of the foregoing embodiments.

[0010] Fourthly, the present invention provides a lithium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0011] The present invention has the following beneficial effects: The multifunctional composite additive for acidic polymers / lithiation supplements provided in this invention exhibits high stability, high pre-lithiation efficiency, and high compatibility with existing lithium-ion battery manufacturing processes, which is beneficial for improving the performance of subsequent slurry processing and the performance of the positive electrode sheet. The preparation method is simple and highly operable, and it holds promise for industrial production and engineering applications. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 The charging curves are for the batteries manufactured in Examples 1, 3, 5, 7, and 8. Figure 2 The charging curves are for the batteries manufactured in Examples 2, 4, and 6. Figure 3 The charging curves of the batteries corresponding to Comparative Examples 1-4 are shown. Figure 4 The results are SEM morphology analysis of Examples 1, 9, and the lithium supplementation additive LFO. Figure 5 The XRD test analysis results are for Examples 1, 9, and the lithium supplement additive LFO; Figure 6The results are infrared test analysis results for Examples 1, 9, and the lithium supplementation additive LFO. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0015] In a first aspect, the present invention provides a multifunctional composite additive of acidic polymer / lithium supplement for positive electrode slurry and a method for preparing the same, wherein the multifunctional composite additive is prepared by modifying a lithium supplement additive with an acidic polymer. The ratio of acidic polymer to lithium supplementation additive is (0.02-0.1):1; The acidic polymer is selected from at least one of poly(2-acrylamide-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) copolymer (P(AMPS-co-AA-co-AM)), poly(2-acrylamide-2-methylpropanesulfonic acid) (PAMPS), and polyacrylic acid (PAA).

[0016] It should be noted that the acidic polymer in the multifunctional composite additive undergoes an acid-base neutralization reaction with the residual lithium compounds on the surface of the lithium replenishing additive. The resulting product coats the lithium replenishing additive, effectively removing the residual lithium compounds and improving the stability of the lithium replenishing additive, thereby enhancing the subsequent slurry processing performance and electrode performance.

[0017] For example, the ratio of acidic polymer to lithium-replenishing additive can be selected from any one of 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.08:1, and 0.1:1, or other values ​​within the range of (0.02-0.1):1. If the ratio exceeds this range, when the ratio of acidic polymer to lithium-replenishing additive is less than 0.02, the acidic polymer cannot completely react with the residual lithium on the surface, the slurry viscosity remains high, and the processing performance is not significantly improved; when the ratio of acidic polymer to lithium-replenishing additive is greater than 0.1, the acidic polymer will react with the lithium ions in the bulk phase of the lithium-replenishing additive, affecting the lithium-replenishing efficiency.

[0018] In an optional embodiment, the lithium supplementing additive is selected from at least one of lithium iron ferrite (Li5FeO4, denoted as LFO), lithium nickel ferrite (LiNiO2, denoted as LNO), and lithium manganese ferrite. And / or, the monomer raw materials of the acid polymer are selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), polyacrylic acid (PAA), and acrylamide (AM); Furthermore, when the acidic polymer is a poly(2-acrylamide-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) copolymer, the monomer raw materials used include 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide in a mass ratio of (1.8-2.3):(0.8-1.2):(0.8-1.2).

[0019] For example, the mass ratio of the monomer raw materials 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide can be selected from any one of 1.8:0.8:0.8, 1.8:1.0:1.0, 1.0:1.0:1.0, 2.0:1.0:1.0, 2.0:1.2:1.2, 2.3:1.0:1.0 and 1.3:1.2:1.2, or other values ​​within the range of (1.8-2.3):(0.8-1.2):(0.8-1.2).

[0020] In a second aspect, the present invention provides a method for preparing a multifunctional composite additive as described in any of the foregoing embodiments, comprising the following preparation steps: Preparation of acidic polymers; A suspension was prepared by mixing the acidic polymer with the lithium supplementation additive in a certain proportion and reacting at room temperature for 0.1 h to 3.0 h. After the suspension was filtered, the resulting filter cake was vacuum dried at 70℃-110℃ to obtain a multifunctional composite additive of acid polymer / lithium supplement.

[0021] In an optional embodiment, the preparation of the acidic polymer further includes the addition of an initiator and a first solvent; wherein the mass of the initiator is 1.0%-2.5% of the mass of the acidic polymer; and the mass of the first solvent is 3-5 times the total mass of the acidic polymer monomer raw materials. The free radicals generated by the initiator interact with the carbon-carbon double bonds in the monomer raw materials to form monomer free radicals, which is beneficial for initiating the activity of the monomer raw materials and controlling the polymerization process.

[0022] Furthermore, after adding an initiator, the reaction is carried out at a temperature of 50℃-65℃ for 20 h-25 h to obtain an acidic polymer.

[0023] Further, the initiator is selected from at least one of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), dimethyl azobisisobutyrate (MAIB or AIBME), azobiscyclohexylformonitrile (ACCN or ABCN), benzoyl peroxide (BPO), di-tert-butyl peroxide (DTBP or TBP), and dilauryl peroxide (LPO); the first solvent is selected from at least one of N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF).

[0024] In an optional embodiment, a first stirring treatment is performed during the preparation of the acidic polymer, wherein the stirring speed is 600 rpm-1200 rpm and the time is 0.1 h-1.0 h; And / or, a second stirring treatment is performed during the preparation of the suspension, wherein the second stirring treatment speed is 300 rpm-600 rpm.

[0025] It should be noted that the purpose of stirring is to accelerate the dissolution of materials and to quickly mix the reaction system to a homogeneous state. The stirring process should be adjusted according to the actual amount of materials being processed.

[0026] For example, the rotation speed of the first stirring treatment can be selected from any one of 600 rpm, 800 rpm, 1000 rpm and 1200 rpm, or other values ​​in the range of 600 rpm to 1200 rpm; the time can be selected from any one of 0.1 h, 0.2 h, 0.5 h and 1.0 h, or other values ​​in the range of 0.1 h to 1.0 h.

[0027] The second stirring speed can be selected from any one of 300 rpm, 400 rpm, 500 rpm, and 600 rpm, or other values ​​within the range of 300 rpm to 600 rpm; the time can be selected from any one of 0.1 h, 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, and 3.0 h, or other values ​​within the range of 0.1 h to 3.0 h.

[0028] In an optional embodiment, during the preparation of the suspension, a second solvent is added, the mass of which is 5 to 20 times the mass of the lithium supplement additive; for example, the mass of the second solvent can be selected from any one of 5, 6, 8, 10, 18, and 20 times the mass of the lithium supplement additive, or other values ​​within the range of 5 to 20 times.

[0029] Furthermore, the second solvent is selected from at least one of N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide; Furthermore, the second solvent is the same type as the first solvent.

[0030] It should be noted that, in the embodiments of the present invention, the type of the second solvent used is consistent with that of the first solvent, so as to ensure good contact between the acidic polymer and the lithium supplementation additive.

[0031] In an optional embodiment, the filtration process is vacuum filtration, with a temperature of 15°C to 40°C and a filtration pressure of -0.06 MPa to -0.10 MPa.

[0032] It should be noted that lithium supplementation additives have extremely high chemical activity (especially towards water and CO2), and their physicochemical properties (such as solubility, phase stability, and particle size) are temperature-sensitive. To prevent side reactions, the filtration process needs to be carried out at a temperature slightly above room temperature. Specifically, since the detergent used in the filtration process is an organic solvent, such as anhydrous ethanol, it boils very easily under vacuum conditions, causing the filter cake to break down and subsequently damaging the filter paper or membrane, resulting in detergent loss and impurity residue. Therefore, it is necessary to control the temperature during the filtration process. The filtration pressure is negative to accelerate the filtration process and facilitate rapid solid-liquid separation.

[0033] In one embodiment of the invention, the temperature of the filtration process is 20°C and the pressure is -0.08 MPa. In other embodiments of the invention, the filtration temperature is adjusted according to the actual ambient temperature, and the filtration pressure is adjusted according to the actual amount of material being processed.

[0034] In an optional embodiment, the vacuum drying process is carried out at a temperature of 85°C-100°C for a time of 4 h-24 h.

[0035] In this embodiment of the invention, the temperature of the vacuum drying process is 90°C, and the time is not particularly limited, but can be reasonably adjusted according to the actual amount of material being processed.

[0036] Specifically, the preparation method of the multifunctional composite additive of acidic polymer / lithium supplement includes the following preparation steps: (1) Preparation of acidic polymers After mixing the monomer raw materials of the acid polymer with the first solvent in proportion, the mixture is stirred for the first time. After the system is completely dissolved, the initiator is added, and the reaction is carried out at a temperature of 50℃-65℃ for 20 h-25 h to obtain the acid polymer.

[0037] The first stirring treatment was carried out at a speed of 600 rpm to 1200 rpm for a time of 0.1 h to 1.0 h.

[0038] The initiator has a mass of 1.0%-2.5% of the acid polymer mass; the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobiscyclohexylformonitrile, benzoyl peroxide, di-tert-butyl peroxide and dilauryl peroxide.

[0039] The mass of the first solvent used is 3 to 5 times the total mass of the acidic polymer monomer raw materials; the first solvent is selected from at least one of N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide and N,N-dimethylformamide.

[0040] The monomer raw materials of the acid polymer are selected from at least one of 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide; further, when the acid polymer is a poly(2-acrylamide-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) copolymer, the monomer raw materials used include 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide in a mass ratio of (1.8-2.3):(0.8-1.2):(0.8-1.2).

[0041] (2) Preparation of suspension The acidic polymer, lithium supplementation additive, and second solvent obtained in step (1) are mixed in proportion and then subjected to a second stirring treatment. After reacting at room temperature for 0.1h-3.0h, a suspension is obtained.

[0042] Specifically, the lithium-supplementing additive and the second solvent are first mixed evenly, and then the acidic polymer is added to continue the reaction.

[0043] The second stirring process involves a rotation speed of 300 rpm to 600 rpm.

[0044] The mass of the second solvent used is 5 to 20 times the mass of the lithium supplement additive; the second solvent is selected from at least one of N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide and N,N-dimethylformamide.

[0045] The ratio of acidic polymer to lithium supplementation additive is (0.02-0.1):1; the lithium supplementation additive is selected from at least one of lithium iron ferrite, lithium nickel ferrite, and lithium manganese ferrite.

[0046] (3) Preparation of multifunctional composite additives of acid polymer / lithium supplement After the suspension obtained in step (2) is filtered, the resulting filter cake is vacuum dried at 70℃-110℃ to obtain a multifunctional composite additive of acid polymer / lithium supplement.

[0047] The filtration process is vacuum filtration, with a temperature of 15℃-40℃ and a filtration pressure of -0.06 MPa to -0.10 MPa.

[0048] The vacuum drying process is carried out at a temperature of 85℃-100℃ for 4 h-24 h.

[0049] Thirdly, the present invention provides a positive electrode sheet, wherein the positive electrode slurry used includes a multifunctional composite additive as described in any of the foregoing embodiments or a multifunctional composite additive prepared by any of the foregoing embodiments.

[0050] It should be noted that the preparation of the positive electrode sheet can be reasonably configured as needed. Specifically, in the embodiments of the present invention, the preparation of the positive electrode sheet includes the following steps: A multifunctional composite additive was used as the active material, and was mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) at a mass ratio of 50:45:5. NMP was added dropwise to adjust the consistency of the slurry, so that the solid content was controlled within a suitable range of 35%-45%. The above slurry was placed in a high-speed disperser to obtain a uniform positive electrode slurry. The positive electrode slurry was evenly coated onto the surface of a cleaned aluminum foil using a scraper, and then placed in an 80℃ vacuum drying oven for 12 hours to dry. After drying, it was cut into the required size to obtain the positive electrode sheet.

[0051] Fourthly, the present invention provides a lithium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0052] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0053] Example 1 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, specifically including the following preparation steps: (1) Preparation of acidic polymer P(AMPS-co-AA-co-AM) After mixing the monomer raw materials of the acid polymer with the first solvent in proportion, the mixture is stirred for the first time. After the system is completely dissolved, the initiator is added and the reaction is carried out at a temperature of 60°C for 24 h to obtain the acid polymer P (AMPS-co-AA-co-AM).

[0054] The first stirring treatment was carried out at 800 rpm for 10 minutes.

[0055] The initiator was 2.0% of the mass of the acid polymer; the initiator was 0.02 g of azobisisobutyronitrile.

[0056] The mass of the first solvent used is 4 times the total mass of the acidic polymer monomer raw materials; the first solvent is 4g of N-methylpyrrolidone.

[0057] The monomer raw materials of the acid polymer include 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide in a mass ratio of 2:1:1, wherein the mass of 2-acrylamide-2-methylpropanesulfonic acid is 0.5 g.

[0058] (2) Preparation of suspension Inside a glove box, 0.05 g of the acidic polymer obtained in step (1), 1 g of lithium-rich lithium iron ferrite (Li5FeO4) and 10 g of N-methylpyrrolidone were mixed in proportion, and then subjected to a second stirring treatment. After reacting at room temperature for 1.0 h, a suspension was obtained. Specifically, the lithium-rich additive and the second solvent were first mixed evenly, and then the acidic polymer was added to continue the reaction.

[0059] The second stirring process was carried out at a speed of 500 rpm.

[0060] (3) Preparation of multifunctional composite additives of acid polymer / lithium supplement After the suspension obtained in step (2) is filtered, the resulting filter cake is vacuum dried at 90°C for 6 hours to obtain a multifunctional composite additive of acid polymer / lithium supplement.

[0061] The filtration process is vacuum filtration, with a temperature of 20℃ and a filtration pressure of -0.08 MPa.

[0062] Example 2 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (2) Preparation of suspension The lithium supplement additive is 1 g of lithium-rich nickel oxide (LiNiO2).

[0063] Example 3 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (1) Preparation of acidic polymer PAMPS The monomer raw material for the acid polymer is 1 g of 2-acrylamide-2-methylpropanesulfonic acid.

[0064] Example 4 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (1) Preparation of acidic polymer PAMPS The monomer raw material for the acid polymer is 1 g of 2-acrylamide-2-methylpropanesulfonic acid.

[0065] (2) Preparation of suspension The lithium supplement additive is 1 g of lithium-rich nickel oxide (LiNiO2).

[0066] Example 5 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (1) Preparation of acidic polymer PAA The monomer raw material for the acid polymer is 1 g of acrylamide.

[0067] Example 6 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (1) Preparation of acidic polymer PAA The monomer raw material for the acid polymer is 1 g of acrylamide.

[0068] (2) Preparation of suspension The lithium supplement additive is 1 g of lithium-rich nickel oxide (LiNiO2).

[0069] Example 7 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (2) Preparation of suspension The acidic polymer is 0.02 g.

[0070] Example 8 This embodiment provides a method for preparing a multifunctional composite additive of acidic polymer / lithium supplement, which differs from Example 1 only in that it specifically includes the following preparation steps: (2) Preparation of suspension The acidic polymer is 0.1 g.

[0071] Example 9 This embodiment provides a method for preparing a lithium supplement additive, which specifically includes the following preparation steps: The lithium supplement additive (1 g of lithium-rich lithium iron oxide (Li5FeO4)) was exposed to room temperature air for 4.0 h to obtain the exposure-deterioration lithium supplement additive.

[0072] Comparative Example 1 This embodiment provides a method for preparing a lithium supplement additive, which specifically includes the following preparation steps: Inside a glove box, a lithium supplement additive (1 g of lithium-rich lithium iron ferrite (Li5FeO4) and 10 g of N-methylpyrrolidone) were mixed in proportion and stirred. The mixture was reacted at room temperature for 1.0 h to obtain a suspension. The stirring speed was 500 rpm.

[0073] The obtained suspension was filtered, and the resulting filter cake was vacuum dried at 90°C for 6 hours to obtain a lithium supplement additive. The filtration process was vacuum filtration at a temperature of 20°C and a pressure of -0.08 MPa.

[0074] Comparative Example 2 This embodiment provides a method for preparing a lithium supplement additive, which differs from Comparative Example 1 only in that it specifically includes the following preparation steps: The lithium supplement additive is 1 g of lithium-rich nickel oxide (LiNiO2).

[0075] Comparative Example 3 This embodiment provides a method for preparing a lithium supplement additive, which specifically includes the following preparation steps: (1) Preparation of polymer solution A polymer solution was prepared by mixing 1 g of polyvinylpyrrolidone (PVP) and a first solvent (4 g of N-methylpyrrolidone) in a specified ratio and then stirring. The stirring time was 800 rpm for 10 min.

[0076] (2) Preparation of suspension Inside a glove box, 0.05 g of the polymer solution obtained in step (1), 1 g of lithium-rich lithium iron ferrite (Li5FeO4) and 10 g of N-methylpyrrolidone were mixed in proportion, and then subjected to a second stirring treatment. After reacting at room temperature for 1.0 h, a suspension was obtained. Specifically, the lithium additive and the second solvent were first mixed evenly, and then the polymer solution obtained in step (1) was added to continue the reaction. The stirring speed for the second stirring treatment was 500 rpm.

[0077] (3) Preparation of lithium supplementation additives After the suspension obtained in step (2) is filtered, the resulting filter cake is vacuum dried at 90°C for 6 hours to obtain a lithium supplement additive.

[0078] The filtration process is vacuum filtration, with a temperature of 20℃ and a filtration pressure of -0.08 MPa.

[0079] Comparative Example 4 This embodiment provides a method for preparing a lithium supplement additive, which differs from Comparative Example 3 only in that it specifically includes the following preparation steps: (1) Preparation of polymer solution A polymer solution is prepared by mixing 1 g of citric acid and 4 g of N-methylpyrrolidone in a certain proportion and then performing a first stirring treatment.

[0080] The first stirring treatment was carried out at 800 rpm for 10 minutes.

[0081] (2) Preparation of suspension Inside a glove box, 0.05 g of the polymer solution obtained in step (1), 1 g of lithium-rich lithium iron ferrite (Li5FeO4) and 10 g of N-methylpyrrolidone were mixed in proportion, and then subjected to a second stirring treatment. After reacting at room temperature for 1.0 h, a suspension was obtained. Specifically, the lithium additive and the second solvent were first mixed evenly, and then the polymer solution obtained in step (1) was added to continue the reaction. The stirring speed for the second stirring treatment was 500 rpm.

[0082] (3) Preparation of lithium supplementation additives After the suspension obtained in step (2) is filtered, the resulting filter cake is vacuum dried at 90°C for 6 hours to obtain a lithium supplement additive.

[0083] The filtration process is vacuum filtration, with a temperature of 20℃ and a filtration pressure of -0.08 MPa.

[0084] Experimental Example 1 In this experiment, the processing performance and electrochemical performance of the multifunctional composite additives prepared in Examples 1-8 and the lithium supplementation additives prepared in Comparative Examples 1-4 were tested.

[0085] (a) The specific methods are as follows: (1) Determination of slurry viscosity LiCoO2 was used as the active material and mixed with conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) at a mass ratio of 95:2:1:2. Lithium-supplementing additives (the multifunctional composite additives prepared in Examples 1-8 and the lithium-supplementing additives prepared in Comparative Examples 1-4) were added to the slurry at a ratio of 3 wt% relative to LiCoO2. NMP was added dropwise to adjust the slurry consistency, controlling the solid content at 60%. The above materials were placed in a high-speed disperser to obtain a homogeneous positive electrode slurry. The viscosity of the prepared positive electrode slurry was measured using a rotational rheometer, and the results are summarized in Table 1.

[0086] It should be noted that if the viscosity of the positive electrode slurry is too high, it cannot be used for the next coating process, meaning it has poor processing performance.

[0087] (2) Determination of charging specific capacity Using lithium-supplementing additives (the multifunctional composite additives prepared in Examples 1-8 and the lithium-supplementing additives prepared in Comparative Examples 1-4) as active materials, they were mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) at a mass ratio of 50:45:5. NMP was added dropwise to adjust the consistency of the slurry, so that the solid content was controlled at 40%. The above materials were placed in a high-speed disperser to obtain a uniform positive electrode slurry. The positive electrode slurry was then coated onto a clean aluminum foil using a scraper and placed in a vacuum drying oven at 80°C for 12 h. After drying, it was cut into circular electrode sheets with a diameter of 12 mm.

[0088] For half-cell assembly, the prepared circular electrode sheet is used as the positive electrode and the lithium sheet is used as the negative electrode. The circular electrode sheet is placed in the center of the positive electrode shell, and then 40 μL of electrolyte (1.0 M LiPF6 dissolved in a 1:1 volume ratio of EC and DEC mixed solution, the volume of the mixed solution is 1 L) is added. Then the separator is placed, and another 40 μL of electrolyte is added to wet the separator onto the electrode sheet. Then the lithium sheet is placed to correspond with the electrode sheet. Finally, the spacer spring and the negative electrode shell are placed. The battery is pressed tightly using a press and left to stand for 5 h before subsequent electrochemical tests are performed.

[0089] Constant current charge-discharge test records the potential change of the battery under a fixed current: The Xinwei testing system tested a coin cell at 30℃, and the theoretical specific capacity of the lithium replenishment material was 867 mAh·g. -1 The voltage range was 2.5 V-4.3 V, and the specific charging capacity of the battery was measured at a current density of 0.1 C. The test results of the relevant specific charging capacity are summarized in Table 1. The charging curves of the batteries corresponding to Examples 1, 3, 5, 7, and 8 are shown in [Table 1]. Figure 1 The charging curves of the batteries corresponding to Examples 2, 4, and 6 are shown below. Figure 2 The charging curves of the batteries corresponding to Comparative Examples 1-4 are shown in [reference needed]. Figure 3 .

[0090] Table 1 Test Results

[0091] Combining the data in Table 1 and Figures 1-3 As can be seen, the specific analysis is as follows: Comparing Examples 1-6, it can be seen that the slurry viscosity of Example 1 is lower than that of Examples 3 and 5, while the charge specific capacity is higher than that of Examples 3 and 5; the slurry viscosity of Example 2 is lower than that of Examples 4 and 6, while the charge specific capacity is higher than that of Examples 4 and 6. The above results indicate that the multifunctional composite additive prepared by treating with acidic polymer P (AMPS-co-AA-co-AM) is better than acidic polymers PAMPS and PAA in removing residual lithium on the surface, and can effectively improve the processing performance and pre-lithiation efficiency of the cathode slurry.

[0092] Comparing Examples 1, 7, and 8, it can be seen that the slurry viscosity of Example 8 is lower than that of Examples 1 and 7, and the charge specific capacity of Example 1 is higher than that of Examples 7 and 8. This result indicates that increasing the amount of P(AMPS-co-AA-co-AM) can more effectively remove residual lithium on the surface, but it will affect the electrochemical performance.

[0093] Comparative Examples 1-4 show that the effects of acid-free polymers, non-acidic polymers, and small molecule organic acids in removing residual lithium from the surface are not as good as those of P(AMPS-co-AA-co-AM) acidic polymers.

[0094] Test Example 1 This test case performs SEM morphology analysis on the products obtained in Example 1 and Example 9, respectively. See details below. Figure 4 .

[0095] from Figure 4 It can be seen that the surface of the lithium-replenishing additive prepared in Example 9 became extremely rough, exhibiting significant agglomeration. In contrast, the surface of the multifunctional composite additive prepared in Example 1 was covered by a smooth and dense layer, with significantly improved particle dispersibility and the disappearance of agglomeration. This result indicates that P(AMPS-co-AA-co-AM) treatment not only removes residual lithium from the surface but also forms a uniform and dense coating layer in situ, effectively repairing surface degradation caused by air exposure.

[0096] Test Example 2 This test case presents XRD analysis of Examples 1 and 9, and the lithium-rich lithium iron phosphate (LFO) additive. See details in the attached table. Figure 5 .

[0097] from Figure 5It can be seen that all samples exhibit similar diffraction peak shapes and positions, indicating that the material has good crystallinity and a typical lithium iron ferrite crystal structure. In the XRD pattern of the lithium-replenishing additive prepared in Example 9, obvious Li₂CO₃ characteristic peaks appeared at approximately 32° and 43°, proving that air exposure led to the formation of a large amount of lithium carbonate on the surface. The intensity of the Li₂CO₃ characteristic peak of the multifunctional composite additive prepared in Example 1 was significantly reduced, while the diffraction peaks of the LFO bulk remained intact, further verifying that the multifunctional composite additive prepared by treating the lithium-replenishing additive with P(AMPS-co-AA-co-AM) effectively removed the surface-generated Li₂CO₃ without destroying the bulk crystal structure of the LFO.

[0098] Test Example 3 This test example performs infrared spectroscopy analysis on the products obtained in Example 1, Example 9, and the lithium-rich lithium iron phosphate (LFO) additive. See details below. Figure 6 .

[0099] from Figure 6 It can be seen that the characteristic peak of Li2CO3 is located at 863 cm⁻¹. -1 The intensity of the Li₂CO₃ characteristic peak of the lithium-replenishing additive prepared in Example 9 was significantly higher than that of the original sample, confirming that air exposure led to the formation of surface lithium carbonate. The intensity of the Li₂CO₃ characteristic peak of the multifunctional composite additive prepared in Example 1 was significantly reduced, further demonstrating that P(AMPS-co-AA-co-AM) treatment effectively removed residual lithium from the surface. Furthermore, no new characteristic peaks were observed in the sample after P(AMPS-co-AA-co-AM) treatment, indicating that no new impurity phase was introduced.

[0100] In summary, the embodiments of this invention involve a neutralization reaction between an acidic polymer and residual lithium compounds on the surface of a lithium-replenishing additive. The resulting product coats the lithium-replenishing additive, effectively removing residual lithium compounds and improving the stability of the additive. The multifunctional composite additive provided by this invention exhibits high stability, high pre-lithiation efficiency, and high compatibility with existing lithium-ion battery manufacturing processes, which is beneficial for improving the performance of subsequent slurry processing and the performance of the positive electrode. The preparation method is simple, highly operable, and holds promise for industrial production and engineering applications.

[0101] 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. An acidic polymer / lithium supplement multifunctional composite additive for a positive electrode slurry, characterized by, The multifunctional composite additive is prepared by modifying a lithium-supplementing additive with an acidic polymer. The ratio of the acidic polymer to the lithium supplementation additive is (0.02-0.1):1; The acidic polymer is selected from at least one of poly(2-acrylamide-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) copolymer, poly(2-acrylamide-2-methylpropanesulfonic acid), and polyacrylic acid.

2. The multifunctional complex additive according to claim 1, characterized in that, The lithium supplementation additive is selected from at least one of lithium iron ferrite, lithium nickel ferrite, and lithium manganese ferrite. And / or, the monomer raw material of the acid polymer is selected from at least one of 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide; Preferably, when the acidic polymer is a poly(2-acrylamide-2-methylpropanesulfonic acid-co-acrylic acid-co-acrylamide) copolymer, the monomer raw materials used include 2-acrylamide-2-methylpropanesulfonic acid, polyacrylic acid and acrylamide in a mass ratio of (1.8-2.3):(0.8-1.2):(0.8-1.2).

3. A method of preparing a multifunctional complex additive as claimed in any one of claims 1-2, characterized by, The preparation steps include the following: Preparation of acidic polymers; The acidic polymer was mixed with the lithium supplementation additive in a certain proportion and reacted at room temperature for 0.1 h to 3.0 h to obtain a suspension. After the suspension is filtered, the resulting filter cake is vacuum dried at 70℃-110℃ to obtain a multifunctional composite additive of acid polymer / lithium supplement.

4. The production method according to claim 3, characterized by, The preparation of the acidic polymer also includes the addition of an initiator and a first solvent; wherein the mass of the initiator is 1.0%-2.5% of the mass of the acidic polymer; and the mass of the first solvent is 3-5 times the total mass of the acidic polymer monomer raw materials. Preferably, after adding the initiator, the reaction is carried out at a temperature of 50℃-65℃ for 20 h-25 h to obtain the acidic polymer; Preferably, the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azobiscyclohexylformitrile, benzoyl peroxide, di-tert-butyl peroxide, and dilauryl peroxide; the first solvent is selected from at least one of N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide.

5. The preparation method according to claim 3, characterized in that, During the preparation of the acidic polymer, a first stirring treatment is performed, with a stirring speed of 600 rpm-1200 rpm and a time of 0.1 h-1.0 h. And / or, a second stirring treatment is performed during the preparation of the suspension, wherein the second stirring treatment is performed at a speed of 300 rpm-600 rpm.

6. The preparation method according to claim 3, characterized in that, In the process of preparing the suspension, a second solvent is added, and the mass of the second solvent used is 5 to 20 times the mass of the lithium supplementation additive. Preferably, the second solvent is selected from at least one of N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide; Preferably, the second solvent is the same type as the first solvent.

7. The preparation method according to claim 3, characterized in that, The filtration process is vacuum filtration, with a temperature of 15℃-40℃ and a filtration pressure of -0.06 MPa to -0.10 MPa.

8. The preparation method according to claim 3, characterized in that, The vacuum drying process is carried out at a temperature of 85℃-100℃ for 4 h-24 h.

9. A positive electrode sheet characterized by comprising: The positive electrode slurry used includes the multifunctional composite additive as described in any one of claims 1-2 or the multifunctional composite additive prepared by the preparation method described in any one of claims 3-8.

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

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