Preparation method of positive electrode lithium supplement material, positive electrode lithium supplement material, preparation method of positive electrode lithium supplement pole piece, positive electrode lithium supplement pole piece and secondary battery

Abstract

The invention relates to the technical field of new energy batteries, in particular to a preparation method of a positive lithium supplement material, the positive lithium supplement material, a preparation method of a positive lithium supplement pole piece, the positive lithium supplement pole piece and a secondary battery. According to the preparation method of the positive electrode lithium supplementing material, the lithium supplementing agent and the inorganic oxide are mixed, and then the surface of the mixed material is modified in a chemical reaction mode, so that a passivated hydrophobic self-assembly layer is constructed on the surface of the mixed material; the problem of residual alkali of the lithium supplementing material is solved, the dispersity of inorganic oxide and the processability of coating slurry prepared subsequently are improved, and the internal resistance is reduced. And then in the preparation method of the positive electrode lithium supplementing pole piece, adding a positive electrode lithium supplementing material in a homogenizing process, and improving the process to obtain a positive electrode composite lithium supplementing coating with uniform and controllable thickness. When the positive electrode lithium supplementing pole piece is applied to a secondary battery, lithium can be removed during first-circle discharge of the battery, lithium loss is relieved, wettability is improved, and electrochemical performance, cycle performance and safety performance are improved.

Description

Technical Field

[0001] This application relates to the field of new energy battery technology, specifically to a method for preparing a positive electrode lithium replenishment material, a positive electrode lithium replenishment material, a method for preparing a positive electrode lithium replenishment sheet, a positive electrode lithium replenishment sheet, and a secondary battery. Background Technology

[0002] Energy density and safety are crucial performance characteristics of lithium-ion batteries. Lithium replenishment technology is an effective means to improve energy density, such as negative electrode pre-lithiation. However, negative electrode pre-lithiation suffers from drawbacks such as high difficulty, high cost, and difficulty in control. Therefore, positive electrode pre-lithiation is also under development, involving the incorporation of lithium replenishment materials into the positive electrode sheet, such as coating the surface of the positive electrode with lithium replenishment materials. Compared with negative electrode pre-lithiation, positive electrode pre-lithiation has advantages such as ease of synthesis, low cost, and higher lithium replenishment capacity. Furthermore, positive electrode pre-lithiation is compatible with most current lithium-ion battery production lines, providing a more practical solution for the industrial application of lithium replenishment technology.

[0003] However, the lithium-replenishing material coated on the positive electrode surface increases the difficulty of ion transport, resulting in increased cell impedance and a tendency to overheat, which in turn negatively impacts safety. Furthermore, due to their high lithium content, lithium-replenishing additives easily generate residual alkali on the surface, affecting processing and deteriorating the electrode's electrochemical performance. Moreover, in batteries using lithium-replenished positive electrode sheets, after the first cycle, the lithium-replenishing agent inside the positive electrode becomes passivated, affecting the battery's electronic and ionic conductivity and causing a deterioration in electrochemical performance.

[0004] Therefore, improving the poor electrochemical performance, poor safety, and poor cycle stability of pre-lithiation of the cathode is an important research and development direction in this field. Summary of the Invention

[0005] This application aims to provide a method for preparing a positive electrode lithium replenishment material, a positive electrode lithium replenishment material, a method for preparing a positive electrode lithium replenishment electrode sheet, a positive electrode lithium replenishment electrode sheet, and a secondary battery, so as to improve the problems of poor electrochemical performance, poor safety, and poor cycle stability of positive electrode pre-lithiation.

[0006] The embodiments of this application are implemented as follows:

[0007] In a first aspect, embodiments of this application provide a method for preparing a positive electrode lithium supplementation material, including:

[0008] S1, Dissolve the self-assembled molecular material in a first solvent to obtain a self-assembled molecular solution, wherein the self-assembled molecular material includes long-chain phosphonic acid;

[0009] S2, the lithium supplement is mixed with inorganic oxide to obtain a mixed powder;

[0010] S3, the mixed powder is immersed in the self-assembled molecular solution for surface modification treatment, and a suspension is obtained;

[0011] S4, separate the insoluble matter from the suspension, dry the insoluble matter, and obtain the surface self-assembled modified positive electrode lithium replenishment material.

[0012] In one embodiment of this application, in S1:

[0013] The self-assembled molecular material has a mass fraction of (0.05-0.5%) in the self-assembled molecular solution; and / or

[0014] The long-chain phosphonic acid has the molecular formula RP(O)(O)=O, where R is a C10-C18 alkyl group; and / or

[0015] The first solvent includes at least one of dichloromethane, N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran; and / or

[0016] The method of "dissolving self-assembled molecular materials in a first solvent" includes ultrasonic dispersion, wherein the ultrasonic dispersion has an ultrasonic frequency of 20-100 kHz and a duration of 5-30 min.

[0017] In one embodiment of this application, in S2:

[0018] The mass ratio of the lithium supplement to the inorganic oxide is in the range of (1-11):(89-99); and / or

[0019] The lithium supplement includes at least one of lithium nickel oxide, lithium iron phosphate rich in lithium, lithium cobalt oxide rich in lithium, and lithium zirconate; and / or

[0020] The inorganic oxide includes at least one of silicon dioxide, aluminum oxide, titanium dioxide, and boehmite; and / or

[0021] The inorganic oxide is particulate matter with a particle size range of 50-300 nm.

[0022] In one embodiment of this application, in step S3, the mixed powder is immersed in the self-assembled molecular solution and then stirred continuously for 3-10 hours.

[0023] In one embodiment of this application, in step S4, the insoluble matter is first centrifuged, washed, and then dried, wherein:

[0024] Centrifugation rate: 1000-8000 rpm; and / or

[0025] Washing time is 1-15 minutes; and / or

[0026] The number of washes is 0-8 times; and / or

[0027] The cleaning agents used for washing include at least one of ethanol and ethylene glycol.

[0028] In one embodiment of this application, in step S4, drying the insoluble substance includes placing the insoluble substance in an environment with a temperature of 60-100°C and a vacuum degree of ≤133Pa for more than 2 hours.

[0029] Secondly, embodiments of this application provide a positive electrode lithium replenishment material, which is prepared by the positive electrode lithium replenishment material preparation method described in any one of the first aspects; or, the positive electrode lithium replenishment material comprises a lithium replenishment agent modified by a solution of a long-chain phosphonic acid self-assembled molecular material and an inorganic oxide.

[0030] Thirdly, embodiments of this application provide a method for preparing a positive lithium-added electrode sheet, which includes:

[0031] S5, the positive electrode lithium replenishing material, conductive agent and binder described in the second aspect are added to the second solvent, and after stirring and mixing, a mixed slurry is obtained;

[0032] S6, the mixed slurry is coated on the surface of the positive electrode material, baked and dried to obtain a positive electrode with a positive composite lithium coating.

[0033] In one embodiment of this application, in S5:

[0034] The mass ratio of the positive electrode lithium replenishment material, the conductive agent, and the binder ranges from (85.5-95.5):(2-6.5):(2.5-8); and / or

[0035] The second solvent includes N-methyl-2-pyrrolidone; and / or

[0036] The conductive agent includes at least one of conductive carbon black, graphene, carbon nanotubes, carbon nanofibers, and expanded graphite; and / or

[0037] The adhesive comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, epoxy resin, polypropylene carbonate, polyacrylonitrile, and polyurethane; and / or

[0038] The solids content of the mixed slurry is 15-25%; and / or

[0039] Mix at a speed of 200-2500 r / min for 60-180 min; and / or

[0040] Perform step S5 in an environment where the dew point is below -40°C.

[0041] In one embodiment of this application, in S5:

[0042] After stirring and mixing, a thickener is added to the mixed slurry to make the viscosity of the mixed slurry ≥600mPa·S.

[0043] In one embodiment of this application, the thickener includes at least one of a cross-linked polymeric thickener and a polymeric anionic associative thickener; and / or

[0044] The thickener is added at a mass fraction of 0.05-3%; and / or

[0045] After adding the thickener to the mixture, stir at a speed of 100-2000 r / min for 60-120 min.

[0046] In one embodiment of this application, in S6:

[0047] The positive electrode material includes at least one of lithium cobalt oxide, high-nickel ternary lithium, lithium iron phosphate, or lithium manganese iron phosphate; and / or

[0048] Baking time is 1-10 minutes; and / or

[0049] The drying process includes drying for at least 12 hours in a vacuum environment with a vacuum degree ≤133 Pa; and / or

[0050] Perform step S6 in an environment with a dew point below -40°C.

[0051] Fourthly, embodiments of this application provide a positive lithium-filling electrode sheet, which is prepared using the positive lithium-filling electrode sheet preparation method described in any one of the third aspects. The positive lithium-filling electrode sheet includes a positive electrode sheet raw material and a positive composite lithium-filling coating.

[0052] Fifthly, embodiments of this application provide a secondary battery comprising the positive lithium-filled electrode sheet described in the fourth aspect.

[0053] The beneficial effects of this application are:

[0054] The positive electrode lithium replenishment material and its preparation method provided in this application involve first mixing a lithium replenishing agent with an inorganic oxide, and then modifying the surface of the mixed material through a chemical reaction. A self-assembled molecular solution containing long-chain phosphonic acid constructs a passivated hydrophobic self-assembled layer on the surface of the mixed material, which effectively reduces the residual alkali value of the lithium replenishment material, improves the dispersibility of nano-inorganic oxide particles, improves the processability of the coating slurry, and inhibits the occurrence of interfacial side reactions. It also increases the wettability of the ester-based electrolyte to the electrode and its coating. As a result, the prepared positive electrode lithium replenishment material can alleviate the problem of electrochemical performance deterioration caused by positive electrode lithium replenishment, as well as the safety problem caused by high cell impedance.

[0055] The positive electrode sheet with a positive electrode composite lithium replenishment coating provided in this application embodiment has a hydrophobic self-assembled layer on the surface of the lithium replenishment material that can reduce the residual alkali value in the lithium replenishment material. This balances lithium replenishment and improved battery cycle life with optimal electrochemical performance, reduced internal resistance, and enhanced electrode wettability, thereby further improving safety performance while increasing energy density. Simultaneously, the self-assembled modified inorganic components in the positive electrode composite lithium replenishment coating can significantly increase the uniformity of viscositant dispersion during the composite coating mixing process, preventing burrs from piercing the separator during subsequent slitting of the positive electrode sheet, thus improving the safety performance of the lithium battery, refining the battery manufacturing process, and increasing energy density.

[0056] The positive electrode sheet with a positive composite lithium replenishment coating provided in this application embodiment is used in a lithium battery. After the first charge and discharge cycle of the battery, the lithium replenishment material in the composite coating undergoes irreversible delithiation. The remaining self-assembled modified inactive part and inorganic oxide part can be used as a passivation barrier layer to enhance the safety performance of the battery cell. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of this application, 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 this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a flowchart of a method for preparing a positive electrode lithium replenishment material according to an embodiment of this application;

[0059] Figure 2 This is a flowchart illustrating a method for preparing a positive lithium-filled electrode according to an embodiment of this application. Detailed Implementation

[0060] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0061] Unless otherwise defined, 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. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0062] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish a numerical order.

[0063] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0064] In this application, "at least one" means one or more, and "more than one" means two or more. "One or more", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0065] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0066] In the current lithium-ion battery system, energy density can be improved by optimizing the battery structure, or by iterating on the positive and negative electrode materials and selecting materials with higher capacity, thus achieving a significant increase in battery energy density. Furthermore, lithium-ion battery replenishment technology is also an important means of improving battery energy density.

[0067] During the first charge of a lithium-ion battery, the organic electrolyte undergoes reduction and decomposition on the negative electrode surface, forming a solid electrolyte interphase (SEI) film. This consumes a significant amount of lithium from the positive electrode, resulting in a low coulombic efficiency (ICE) for the first cycle and reducing the battery's capacity and energy density. Additionally, processes such as the deactivation of negative electrode material particles due to detachment and irreversible lithium metal deposition also consume active lithium from the positive electrode, further reducing the battery's capacity and energy density.

[0068] In related technologies, lithium replenishment at the negative electrode is often used to alleviate this problem. This involves pre-lithiating or pre-intercalating the negative electrode, for example, by adding lithium powder or lithium foil to the negative electrode before the lithium-ion battery operates, thereby offsetting irreversible lithium loss and improving the battery's total capacity and energy density. Lithium powder replenishment typically involves adding an appropriate amount of lithium powder to the negative electrode through processes such as spraying and slurry addition. Lithium foil replenishment typically involves rolling metallic lithium foil to a thickness of several micrometers, then combining it with the negative electrode and rolling it again. After the battery is filled with electrolyte, this metallic lithium rapidly reacts with the negative electrode and intercalates into the negative electrode material, thereby improving the material's initial efficiency. However, because metallic lithium is a highly reactive alkali metal that reacts violently with water, it has very high environmental requirements; otherwise, serious safety accidents can easily occur. This necessitates significant investment in production line upgrades and the purchase of expensive replenishment equipment for negative electrode lithium replenishment processes. Furthermore, to ensure the replenishment effect, adjustments to existing production processes are also required.

[0069] To address the challenges of controlling, being difficult, and costly in negative electrode pre-lithiation, research is now underway on positive electrode pre-lithiation. This involves incorporating lithium-replenishing materials into the positive electrode sheet, such as coating the surface of the positive electrode with these materials. Compared to negative electrode pre-lithiation, positive electrode pre-lithiation does not require metallic lithium. Instead, it uses lithium-containing compounds or lithium-containing complexes—substances with good environmental stability—as lithium-replenishing materials. This offers advantages such as ease of synthesis, low cost, and high lithium-replenishing capacity. Furthermore, positive electrode pre-lithiation is compatible with most current lithium-ion battery production lines, generally requiring no additional process modifications. However, coating the positive electrode surface with lithium-replenishing materials increases ion transport difficulty, leading to increased cell impedance and potentially causing overheating, which negatively impacts safety. Additionally, the high lithium content of lithium-replenishing additives can easily generate residual alkali on the surface, affecting processing and deteriorating electrode electrochemical performance. Moreover, in batteries using lithium-replenished positive electrode sheets, after the first cycle, the lithium-replenishing agent inside the positive electrode becomes passivated, affecting the battery's electronic and ionic conductivity and causing electrochemical performance degradation.

[0070] In view of this, the present application provides a technical solution to improve the problems of poor electrochemical performance, poor safety and poor cycle stability of positive electrode pre-lithiation.

[0071] In a first aspect, embodiments of this application provide a method for preparing a positive electrode lithium replenishment material, the steps of which include:

[0072] S1, Dissolve the self-assembled molecular material in a first solvent to obtain a self-assembled molecular solution, wherein the self-assembled molecular material includes long-chain phosphonic acid;

[0073] S2, the lithium supplement is mixed with inorganic oxide to obtain a mixed powder;

[0074] S3, the mixed powder is immersed in a self-assembled molecular solution for surface modification treatment, and a suspension is obtained;

[0075] S4. Separate the insoluble matter from the suspension, dry the insoluble matter, and obtain the surface self-assembled modified positive electrode lithium replenishment material.

[0076] In some embodiments, in S1, the mass fraction of the self-assembled molecular material in the self-assembled molecular solution is (0.05-0.5%). For example, the mass fraction of the self-assembled molecular material in the self-assembled molecular solution is 0.05%, 0.06%, 0.07%, 0.08%, 0.10%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.23%, 0.25%, 0.27%, 0.29%, 0.30%, 0.31%, 0.33%, 0.35%, 0.37%, 0.39%, 0.40%, 0.42%, 0.45%, 0.48%, or 0.50%, etc.

[0077] In some embodiments, in S1, the molecular formula of the long-chain phosphonic acid is RP(O)(O)=O, where R is a C10-C18 alkyl group.

[0078] In some embodiments, in S1, the first solvent includes at least one of dichloromethane (DCM), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF).

[0079] In some embodiments, in S1, the method of "dissolving the self-assembled molecular material in a first solvent" includes ultrasonic dispersion, wherein the ultrasonic dispersion has an ultrasonic frequency of 20-100 kHz and a duration of 5-30 min.

[0080] In some embodiments, in S2, the mass ratio of the lithium supplement to the inorganic oxide ranges from (1-11):(89-99). For example, the mass ratios of the lithium supplement to the inorganic oxide are 1:89, 1:90, 1:92, 1:95, 1:97, 1:98, 2:89, 2:95, 2:96, 2:98, 2:99, 3:90, 3:92, 3:93:3:95, 3:97:3:98, 4:90, 4:91, 4:92, 4:95, 4:96, 4:98, 5:90, 5:91, 5:93, 5:95, 5:97, 5:98, 6:92, 6:95, 6:96, 6:9 8, 7:90, 7:91, 7:93, 7:94, 7:95, 7:97, 7:98, 8:90, 8:91, 8:92, 8:95, 8:97, 8:98, 9:89, 9:90, 9:91, 9:93, 9:95, 9:97, 9:98, 10:89, 10:90, 10:91, 10:93, 10:95, 10:97, 11:89, 11:90, 11:91, 11:92, 11:95, 11:96, or 11:98, etc.

[0081] In some embodiments, in S2, the lithium supplement includes at least one of lithium nickel oxide, lithium iron phosphate, lithium cobalt oxide, lithium zirconate, and lithium molybdate.

[0082] In some embodiments, in S2, the inorganic oxide includes at least one of silicon dioxide, aluminum oxide, titanium dioxide, and boehmite.

[0083] In some embodiments, in S2, the inorganic oxide is particulate matter with a particle size range of 50-300 nm. For example, the particle size of the inorganic oxide is configured to be approximately uniformly around 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 150 nm, 180 nm, or 200 nm, or the inorganic oxide is configured as a variety of particles of different sizes within the 50-300 nm range.

[0084] In some embodiments, in S3, after immersing the mixed powder in the self-assembled molecular solution, the mixture is continuously stirred for 3-10 hours. For example, the mixed powder is immersed in the self-assembled molecular solution and then continuously mechanically stirred for 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or 9 hours to ensure that the mixed powder and the self-assembled molecular solution are uniformly mixed and fully chemically reacted, thereby completing the surface modification process of the mixed powder by the self-assembled molecular solution.

[0085] In some embodiments, in S4, the insoluble matter is first centrifuged, washed, and then dried, wherein:

[0086] Centrifugation rate is 1000-8000 rpm;

[0087] Washing time is 1-15 minutes;

[0088] The number of washes is 0-8 times;

[0089] The cleaning agents used for washing include at least one of ethanol and ethylene glycol.

[0090] In some embodiments, in S4, "drying the insoluble matter" includes placing the insoluble matter in an environment with a temperature of 60-100°C and a vacuum degree of ≤133Pa for more than 2 hours. This vacuum high-temperature baking process removes as much of the first solvent as possible, resulting in a purer positive electrode lithium replenishment material.

[0091] This application modifies the surface of the mixed material by first mixing the lithium supplementing agent with inorganic oxides before compounding the active component lithium supplementing agent, and then using a chemical reaction. The self-assembled molecular solution containing long-chain phosphonic acid constructs a hydrophobic self-assembled layer on the surface of the mixed material, which effectively reduces the residual alkali value of the lithium supplementing material, improves the dispersibility of nano-inorganic oxide particles, improves the processability of coating slurry, and inhibits the occurrence of interfacial side reactions. It also increases the wettability of ester-based electrolytes to the electrode and its coating. The resulting positive electrode lithium supplementing material can alleviate the problem of electrochemical performance deterioration caused by positive electrode lithium supplementation and alleviate the safety problem caused by high cell impedance.

[0092] Secondly, embodiments of this application provide a positive electrode lithium replenishment material, which is prepared using any of the positive electrode lithium replenishment material preparation methods in the first aspect; or, the positive electrode lithium replenishment material comprises a lithium replenishing agent modified from a long-chain phosphonic acid self-assembled molecular material solution and an inorganic oxide.

[0093] Thirdly, embodiments of this application provide a method for preparing a positive lithium-added electrode sheet, the steps of which include:

[0094] S5, the positive electrode lithium replenishing material, conductive agent and binder from the second aspect are added to the second solvent, and after stirring and mixing, a mixed slurry is obtained;

[0095] S6. The mixed slurry is coated on the surface of the positive electrode material, baked and dried to obtain a positive electrode with a positive composite lithium coating.

[0096] In some embodiments, in S5, the mass ratio of the positive electrode lithium replenishment material, the conductive agent, and the binder ranges from (85.5-95.5):(2-6.5):(2.5-8). For example, the mass ratio of the positive electrode lithium replenishment material, the conductive agent, and the binder is 85.5:6.5:8, or 86:7:7, or 88:6:6, or 88:5:7, or 90:5:5, or 90:4:6, or 90:3:7, or 92:3:5, or 95:2:3, etc.

[0097] In some embodiments, in S5, the second solvent comprises N-methyl-2-pyrrolidone (NMP).

[0098] In some embodiments, in S5, the conductive agent includes at least one of conductive carbon black (SP), graphene, carbon nanotubes, carbon nanofibers (VGCF), and expanded graphite.

[0099] In some embodiments, in S5, the adhesive includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, epoxy resin, polypropylene carbonate, polyacrylonitrile, and polyurethane.

[0100] In some embodiments, in S5, the solid content of the mixed slurry is 15-25%. For example, after mixing the positive electrode lithium supplement material, conductive agent, and binder in the specified mass ratio, a certain amount of NMP solvent is added to adjust the solid content of the slurry to 15%, 16%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%, in order to balance the fluidity and film-forming properties of the mixed slurry.

[0101] In some embodiments, in S5, the mixture is stirred at a speed of 200-2500 r / min for 60-180 min. For example, the mixture is stirred at a speed of 2000 r / min for 120 min.

[0102] In some embodiments, step S5 is performed in an environment where the dew point is below -40°C.

[0103] In some embodiments, in S5, after stirring and mixing, a thickener is added to the mixed slurry to make the viscosity of the mixed slurry ≥ 600 mPa·S.

[0104] Optionally, the thickener includes at least one of cross-linked polymeric thickeners and polymeric anionic associative thickeners.

[0105] Optionally, the amount of thickener added is 0.05-3% by mass.

[0106] Optionally, after adding a thickener to the mixed slurry, stir at a speed of 100-2000 r / min for 60-120 min.

[0107] For example, a thickener is added to the mixed slurry at a mass fraction of 0.05%, 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.70%, 0.80%, 0.90%, 1.0%, 1.1%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5%, 2.8%, or 3.0%, and then stirred at 2000 r / min for 100 min to ensure that the mixed slurry with the added thickener is fully dispersed and that the viscosity of the mixed slurry is 800 Pa·s.

[0108] In some embodiments, in S6, the positive electrode material includes at least one of lithium cobalt oxide, high-nickel ternary lithium, lithium iron phosphate, or lithium manganese iron phosphate.

[0109] In some embodiments, step S6 is performed in an environment where the dew point is below -40°C.

[0110] In some embodiments, the baking time in S6 is 1-10 minutes.

[0111] In some embodiments, in S6, the drying step includes drying for more than 12 hours in a vacuum environment with a vacuum degree ≤133 Pa.

[0112] The positive electrode sheet with a positive electrode composite lithium replenishment coating provided in this application embodiment includes a modified lithium replenishment material, a modified nano-inert inorganic oxide, and an oil-based binder. The modified lithium replenishment material can release active lithium to replenish the active lithium consumed by the negative electrode interface reaction during the first charge cycle of the battery, and at the same time replenish the active lithium consumed by the side reaction during the battery cycle. The modified nano-inert inorganic oxide can significantly increase the viscosity of the composite coating slurry during the mixing process, avoid burrs generated during the cutting of the positive electrode material electrode sheet from piercing the separator, improve the safety performance of the lithium battery, improve the battery manufacturing process, and increase the energy density. The oil-based binder PVDF has the characteristics of good adhesion and high tensile strength, good dispersibility in the slurry medium, and can provide good processing performance and high adhesion strength, suppressing the problem of coating falling off the electrode surface and failing during the charge and discharge process.

[0113] Fourthly, embodiments of this application provide a positive lithium supplement electrode sheet, which is prepared using any of the positive lithium supplement electrode sheet preparation methods in the third aspect. The positive lithium supplement electrode sheet includes a positive electrode sheet raw material and a positive composite lithium supplement coating.

[0114] Fifthly, embodiments of this application provide a secondary battery, which includes the positive lithium-filled electrode sheet described in the fourth aspect.

[0115] When the positive electrode sheet with a positive electrode composite lithium replenishment coating provided in this application embodiment is applied in a lithium-ion battery, the lithium replenishment component in the composite lithium replenishment coating can release more irreversible capacity in the first cycle to replenish the amount of active lithium consumed by the negative electrode in the first cycle and to replenish the amount of active lithium consumed by side reactions during the cycle, thereby improving the battery cycle life. In addition, the hydrophobic self-assembled layer on the surface of its lithium replenishment material can reduce the residual alkali value in the lithium replenishment material, reduce internal resistance, and improve the wettability of the electrode sheet, thereby further improving safety performance on the basis of increasing energy density.

[0116] Meanwhile, the self-assembled modified inorganic components in the positive electrode composite lithium replenishment coating can significantly increase the viscosity dispersion uniformity during the composite coating mixing process, avoid the problem of burrs piercing the separator during the subsequent slitting process of the positive electrode sheet, improve the safety performance of lithium batteries, improve battery production processes, and increase energy density.

[0117] In addition, after the first charge and discharge cycle of the battery, the lithium replenishment material in the composite coating undergoes irreversible delithiation, and the remaining self-assembled modified inactive part and inorganic oxide part can serve as a passivation barrier layer to enhance the safety performance of the cell.

[0118] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0119] Example 1

[0120] Preparation of solution:

[0121] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0122] Modification treatment:

[0123] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed at 7.5g, and the inorganic oxide particles were boehmite, weighed at 142.5g. The mixture was mechanically stirred to obtain a uniform powder.

[0124] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0125] Preparation of coating slurry:

[0126] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0127] Battery fabrication with coating:

[0128] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0129] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0130] Example 2

[0131] Preparation of solution:

[0132] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0133] Modification treatment:

[0134] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium cobalt oxide rich in lithium, weighed at 7.5g, and the inorganic oxide particles were boehmite, weighed at 142.5g. The mixture was mechanically stirred to obtain a uniform powder.

[0135] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0136] Preparation of coating slurry:

[0137] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0138] Battery fabrication with coating:

[0139] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0140] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0141] Example 3

[0142] Preparation of solution:

[0143] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0144] Modification treatment:

[0145] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed at 7.5g, and the inorganic oxide particles were silicon dioxide, weighed at 142.5g. The mixture was mechanically stirred to obtain a uniform powder.

[0146] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0147] Preparation of coating slurry:

[0148] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0149] Battery fabrication with coating:

[0150] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0151] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0152] Example 4

[0153] Preparation of solution:

[0154] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0155] Modification treatment:

[0156] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 10:90. 15g of lithium nickelate was selected as the lithium supplement, and 135g of alumina was selected as the inorganic oxide particles. The mixture was mechanically stirred to obtain a uniform powder.

[0157] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0158] Preparation of coating slurry:

[0159] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0160] Battery fabrication with coating:

[0161] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0162] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0163] Example 5

[0164] Preparation of solution:

[0165] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0166] Modification treatment:

[0167] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 2:98. The lithium supplement was lithium nickelate, weighed at 3g, and the inorganic oxide particles were alumina, weighed at 147g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0168] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0169] Preparation of coating slurry:

[0170] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0171] Battery fabrication with coating:

[0172] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0173] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0174] Example 6

[0175] Preparation of solution:

[0176] Weigh 0.15 g of octadecylphosphonic acid and 249.85 g of tetrahydrofuran solvent at a mass fraction of 0.06%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0177] Modification treatment:

[0178] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed in as 7.5g, and the inorganic oxide particles were alumina, weighed in as 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0179] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 5 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, washed five times by centrifugation, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0180] Preparation of coating slurry:

[0181] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0182] Battery fabrication with coating:

[0183] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0184] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0185] Example 7

[0186] Preparation of solution:

[0187] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of N,N-dimethylformamide solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0188] Modification treatment:

[0189] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed in as 7.5g, and the inorganic oxide particles were alumina, weighed in as 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0190] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 100℃ and a vacuum degree ≤133Pa to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0191] Preparation of coating slurry:

[0192] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0193] Battery fabrication with coating:

[0194] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0195] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0196] Example 8

[0197] Preparation of solution:

[0198] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0199] Modification treatment:

[0200] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed in as 7.5g, and the inorganic oxide particles were alumina, weighed in as 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0201] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0202] Preparation of coating slurry:

[0203] In an environment with a dew point below -40°C, weigh 86g of self-assembled modified positive electrode lithium replenishment material, 6g of conductive agent SP, and 8g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0204] Battery fabrication with coating:

[0205] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0206] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0207] Example 9

[0208] Preparation of solution:

[0209] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0210] Modification treatment:

[0211] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed in as 7.5g, and the inorganic oxide particles were alumina, weighed in as 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0212] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0213] Preparation of coating slurry:

[0214] In an environment with a dew point below -40°C, weigh 95g of self-assembled modified positive electrode lithium replenishment material, 2g of conductive agent SP, and 3g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0215] Battery fabrication with coating:

[0216] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0217] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0218] Example 10

[0219] Preparation of solution:

[0220] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0221] Modification treatment:

[0222] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed in as 7.5g, and the inorganic oxide particles were alumina, weighed in as 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0223] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0224] Preparation of coating slurry:

[0225] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder polypropylene carbonate, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0226] Battery fabrication with coating:

[0227] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0228] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0229] Comparative Example 1

[0230] Preparation of solution:

[0231] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0232] Modification treatment:

[0233] 125g of silica was weighed and immersed in a self-assembling molecular solution, and mechanically stirred for 4 hours to perform surface self-assembly modification treatment. After modification, the silica was separated by vacuum filtration, washed five times by centrifugation, and dried at 80℃.

[0234] Preparation of coating slurry:

[0235] In an environment with a dew point below -40°C, weigh 90.5g of modified silica, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0236] Battery fabrication with coating:

[0237] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0238] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0239] Comparative Example 2

[0240] Preparation of active materials:

[0241] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed at 7.5g, and the inorganic oxide particles were alumina, weighed at 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder, which is a positive electrode lithium supplement material.

[0242] Preparation of coating slurry:

[0243] In an environment with a dew point below -40°C, weigh 90.5g of positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0244] Battery fabrication with coating:

[0245] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0246] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0247] Comparative Example 3

[0248] Preparation of solution:

[0249] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0250] Modification treatment:

[0251] Lithium nickelate was selected as the lithium supplement agent. 100g of the sample was immersed in a self-assembled molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification treatment. After modification, the sample was separated by vacuum filtration, washed five times by centrifugation, and dried at 80℃ to obtain the positive electrode lithium supplement material.

[0252] Preparation of coating slurry:

[0253] In an environment with a dew point below -40°C, weigh 90.5g of positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0254] Battery fabrication with coating:

[0255] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0256] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0257] Comparative Example 4

[0258] Preparation of solution:

[0259] Weigh 2.04 g of stearic acid into 300 ml of ethanol solvent, and sonicate it in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until it is fully dissolved to obtain a modified monomer solution.

[0260] Modification treatment:

[0261] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed at 7.5g, and the inorganic oxide particles were silicon dioxide, weighed at 142.5g. The mixture was mechanically stirred to obtain a uniform powder.

[0262] 125g of the mixed powder was immersed in the modified monomer molecular solution and mechanically stirred at 45℃ for 100min to allow for a complete reaction. After surface modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface-modified positive electrode lithium replenishment material.

[0263] Preparation of coating slurry:

[0264] In an environment with a dew point below -40°C, weigh 90.5g of surface-modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0265] Battery fabrication with coating:

[0266] The mixed slurry was scraped onto the surface of the octet ternary cathode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0267] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated ternary cathode, silicon-carbon anode, Celgard separator, and carbonate electrolyte prepared above.

[0268] Comparative Example 5

[0269] Preparation of solution:

[0270] Weigh 0.5 g of octadecylphosphonic acid and 249.5 g of tetrahydrofuran solvent at a mass fraction of 0.2%, mix them, and sonicate them in an ultrasonic instrument at a frequency of 80 kHz for 30 minutes until they are fully dissolved to obtain a self-assembled molecular solution.

[0271] Modification treatment:

[0272] The lithium supplement and inorganic oxide particles were weighed at a mass ratio of 5:95. The lithium supplement was lithium nickelate, weighed in as 7.5g, and the inorganic oxide particles were alumina, weighed in as 142.5g. The particles were mixed evenly by mechanical stirring to obtain a mixed powder.

[0273] 125g of the mixed powder was immersed in a self-assembly molecular solution and mechanically stirred for 4 hours to perform surface self-assembly modification. After modification, the mixture was separated by filtration, centrifuged and washed five times, and dried at 80℃ to obtain the surface self-assembly modified positive electrode lithium replenishment material.

[0274] Preparation of coating slurry:

[0275] In an environment with a dew point below -40°C, weigh 90.5g of self-assembled modified positive electrode lithium replenishment material, 4.5g of conductive agent SP, and 5g of binder PVDF, then add 305g of NMP solvent to adjust the slurry solid content to 20%. Stir at 2500r / min for 150min until fully dispersed to obtain a mixed slurry.

[0276] Battery fabrication with coating:

[0277] The mixed slurry was coated onto the surface of the lithium cobalt oxide positive electrode material. After coating, it was baked in a segmented oven for 2 minutes, and then transferred to a vacuum oven with a vacuum degree ≤133Pa to dry at 100℃ for 12 hours.

[0278] The electrodes are rolled and cut to a certain size for battery assembly. The battery assembly includes the composite-coated lithium cobalt oxide positive electrode, silicon-carbon negative electrode, Celgard separator, and carbonate electrolyte prepared above.

[0279] The pouch cells assembled in Examples 1-10 and Comparative Examples 1-5 were subjected to half-resistance tests after formation and capacity testing, high-temperature storage tests, and cycle tests. The pouch cells had a capacity of 2.5 Ah, a formation current of 0.1 C, and a formation cutoff voltage of 4.1 V. The cycle test voltage range was 2.7 V to 4.3 V. The half-resistance of the cells after formation and capacity testing, the capacity retention rate after 300 cycles at 0.5 C / 1 C, and the capacity retention and recovery rate of the fully charged cells after 14 days of storage at 60 °C were tested.

[0280] The test results are shown in Table 1.

[0281] Table 1

[0282]

[0283] Therefore, we can conclude that:

[0284] Compared with Example 1, Example 2 uses a different lithium replenishing agent (lithium-rich cobalt oxide). The lithium replenishing effect and electrochemical stability of this lithium replenishing agent are relatively poor. However, a lithium-replenishing battery with better performance can still be obtained in the technical solution provided in the embodiments of this application. This shows that when different lithium replenishing agents are selected within the scope provided in this application, the technical solution provided in the embodiments of this application can achieve a good improvement effect.

[0285] Compared with Example 1, Example 3 uses a different inorganic oxide (silicon dioxide). Although silicon dioxide has the problem of high internal resistance, a lithium battery with better performance can still be obtained in the technical solution provided in this application. This shows that when different inorganic oxides are selected within the scope provided in this application, the technical solution provided in this application can achieve a good improvement effect.

[0286] Compared with Example 1, Examples 4 and 5 show that by adjusting the ratio of lithium replenishing agent to inorganic oxide within a certain range, high energy density, cycle performance, electrochemical performance and battery internal resistance can still be maintained, and good safety can be achieved.

[0287] Compared with Example 1, Examples 6 and 7 show that adjusting the solute mass fraction of the self-assembled molecular solution within a certain range, and changing the first solvent of the self-assembled molecular solution within a certain range, can maintain high energy density, cycle performance, electrochemical performance, and battery internal resistance, and have good safety.

[0288] Compared with Example 1, Examples 8 and 9 show that the proportions of conductive agent, binder and lithium replenishment material can be adjusted within a certain range when preparing the coating slurry. Furthermore, within the limited proportion range of this application, the higher the proportion of conductive agent and binder, the lower the internal resistance of the battery and the better the lithium replenishment effect. Although the energy density decreases accordingly, it can still maintain a certain improvement effect.

[0289] Compared with Example 1, Example 10 uses a different binder. The polypropylene carbonate used in Example 10 has a poorer bonding effect than the PVDF used in Example 1. However, the application of polypropylene carbonate in the technical solutions provided in the embodiments of this application can still produce lithium-ion batteries with good energy density, cycle performance and electrochemical stability. For example, Example 10 shows improvement compared with Comparative Examples 2, 3 and 4, which did not use the lithium-ion material preparation method of this application. This shows that when different binders are selected within the scope provided in this application, the technical solutions provided in the embodiments of this application can all achieve good improvement effects.

[0290] Compared with Example 1, Comparative Example 5 uses a positive electrode sheet made of a different battery positive electrode material. The battery in Comparative Example 5 has a lower internal resistance, better first-time efficiency and cycle performance. It can be seen that the technical solution of this application can achieve a high lithium replenishment effect, cycle stability and electrochemical stability for different positive electrode materials.

[0291] In summary, by comparing Examples 1-10 and Comparative Examples 1-5, the improved cathode pre-lithiation technology using the technical solution provided in this application can enhance the lithium replenishment effect, maintain a high battery energy density, improve cycle stability, maintain a low internal resistance, and improve electrochemical and safety performance.

[0292] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a positive electrode lithium supplement material, characterized in that, include: S1, Dissolve the self-assembled molecular material in a first solvent to obtain a self-assembled molecular solution, wherein the self-assembled molecular material includes long-chain phosphonic acid; S2, the lithium supplement is mixed with inorganic oxide to obtain a mixed powder; S3, the mixed powder is immersed in the self-assembled molecular solution for surface modification treatment, and a suspension is obtained; S4, separate the insoluble matter from the suspension, dry the insoluble matter, and obtain the surface self-assembled modified positive electrode lithium replenishment material.

2. The method for preparing the positive electrode lithium replenishment material according to claim 1, characterized in that, In S1: The self-assembled molecular material has a mass fraction of (0.05-0.5%) in the self-assembled molecular solution; and / or The long-chain phosphonic acid has the molecular formula RP(O)(O)=O, where R is a C10-C18 alkyl group; and / or The first solvent includes at least one of dichloromethane, N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran; and / or The method of dissolving the self-assembled molecular material in the first solvent includes ultrasonic dispersion, wherein the ultrasonic dispersion has an ultrasonic frequency of 20-100 kHz and a duration of 5-30 min.

3. The method for preparing the positive electrode lithium replenishment material according to claim 1, characterized in that, In S2: The mass ratio of the lithium supplement to the inorganic oxide is in the range of (1-11):(89-99); and / or The lithium supplement includes at least one of lithium nickel oxide, lithium iron phosphate rich in lithium, lithium cobalt oxide rich in lithium, and lithium zirconate; and / or The inorganic oxide includes at least one of silicon dioxide, aluminum oxide, titanium dioxide, and boehmite; and / or The inorganic oxide is particulate matter with a particle size range of 50-300 nm.

4. The method for preparing the positive electrode lithium replenishment material according to claim 1, characterized in that, In step S3, the mixed powder is immersed in the self-assembled molecular solution and stirred continuously for 3-10 hours.

5. The method for preparing the positive electrode lithium replenishment material according to claim 1, characterized in that, In step S4, the insoluble matter is first centrifuged, washed, and then dried, wherein: Centrifugation rate: 1000-8000 rpm; and / or Washing time is 1-15 minutes; and / or The number of washes is 0-8 times; and / or The cleaning agents used for washing include at least one of ethanol and ethylene glycol.

6. The method for preparing the positive electrode lithium replenishment material according to claim 1, characterized in that, In step S4, drying the insoluble substance includes placing the insoluble substance in an environment of 60-100°C and a vacuum degree ≤133Pa for more than 2 hours.

7. A positive electrode lithium replenishment material, characterized in that, The cathode lithium replenishing material is prepared by any one of the methods described in claims 1-6; or, the cathode lithium replenishing material comprises a lithium replenishing agent modified from a solution of a long-chain phosphonic acid self-assembled molecular material and an inorganic oxide.

8. A method for preparing a positive lithium-filled electrode, characterized in that, include: S5, the positive electrode lithium replenishing material, conductive agent and binder described in claim 7 are added to the second solvent, and after stirring and mixing, a mixed slurry is obtained; S6, the mixed slurry is coated on the surface of the positive electrode material, baked and dried to obtain a positive electrode with a positive composite lithium coating.

9. The method for preparing a positive lithium-filled electrode according to claim 8, characterized in that, In S5: The mass ratio of the positive electrode lithium replenishment material, the conductive agent, and the binder ranges from (85.5-95.5):(2-6.5):(2.5-8); and / or The second solvent includes N-methyl-2-pyrrolidone; and / or The conductive agent includes at least one of conductive carbon black, graphene, carbon nanotubes, carbon nanofibers, and expanded graphite; and / or The adhesive comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, epoxy resin, polypropylene carbonate, polyacrylonitrile, and polyurethane; and / or The solids content of the mixed slurry is 15-25%; and / or Mix at a speed of 200-2500 r / min for 60-180 min; and / or Perform step S5 in an environment where the dew point is below -40°C.

10. The method for preparing a positive lithium-filled electrode according to claim 8 or 9, characterized in that, In S5: After stirring and mixing, a thickener is added to the mixed slurry to make the viscosity of the mixed slurry ≥600mPa·S.

11. The method for preparing a positive lithium-filled electrode according to claim 10, characterized in that, The thickener includes at least one of cross-linked polymeric thickeners and polymeric anionic associative thickeners; and / or The thickener is added at a mass fraction of 0.05-3%; and / or After adding the thickener to the mixture, stir at a speed of 100-2000 r / min for 60-120 min.

12. The method for preparing a positive lithium-filled electrode according to claim 8, characterized in that, In S6: The positive electrode material includes at least one of lithium cobalt oxide, high-nickel ternary lithium, lithium iron phosphate, or lithium manganese iron phosphate; and / or Baking time is 1-10 minutes; and / or The drying process includes drying for at least 12 hours in a vacuum environment with a vacuum degree ≤133 Pa; and / or Perform step S6 in an environment where the dew point is below -40°C.

13. A positive lithium-filling electrode, characterized in that, The positive electrode is prepared by the method of any one of claims 8-12, wherein the positive electrode comprises positive electrode raw material and positive electrode composite lithium supplementation coating.

14. A secondary battery, characterized in that, Including the positive lithium-filling electrode sheet as described in claim 13.

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