Aqueous lithium supplementing diaphragm, preparation method and application thereof

Abstract

This invention discloses an aqueous lithium-ion replenishing separator, its preparation method, and its application, belonging to the field of lithium battery technology. The aqueous lithium-ion replenishing separator includes a base film and a coating. The coating is applied to one or both surfaces of the base film and includes a lithium replenishing agent-conductive agent-catalyst composite material, binder, dispersant, thickener, wetting agent, etc. The lithium-ion replenishing separator prepared by this invention allows lithium ions to be released from the lithium replenishing layer in the separator at a charging voltage of 3.7V to replenish the battery cell, improving the capacity and cycle life of lithium-ion batteries. The lower lithium replenishing voltage is suitable for lithium replenishing of lithium iron phosphate and ternary systems. Furthermore, the preparation of the lithium-ion replenishing separator in an aqueous solution offers advantages such as environmental insensitivity and low cost.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to an aqueous lithium-replenishing separator, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used due to their high capacity and long lifespan, but capacity decay still limits their development. Research has found that the fundamental reason for the cycle decay of lithium-ion batteries is the consumption of active lithium. To solve this problem, pre-lithiation has been proven to be an effective method, which can compensate for the loss of initial active lithium by providing an additional lithium source.

[0003] Currently, most research on lithium-ion battery cells focuses on adding lithium-adding agents to the positive and negative electrodes. However, this method faces numerous challenges that hinder industrialization. The negative electrode typically uses lithium powder or lithium sheets, which imposes stringent requirements on processes and environmental conditions, and poses safety risks. In positive electrode lithium-ion addition, the lithium-adding agent is susceptible to water and oxygen damage, is unstable, and increases the viscosity of the positive electrode slurry, resulting in harder decomposition products that can easily cause problems such as membrane puncture.

[0004] To address the above issues, existing patent CN117936757A provides a lithium replenishment material, a lithium replenishment membrane, and its preparation method. It uses Li₂O, Li₂S, LFO, or LNO lithium replenishing agents as the core, ternary or quaternary active materials (such as NCM and NCA) as the coating layer, and NMP, DMC, etc., as solvents to prepare the lithium replenishment membrane. This allows the lithium replenishment layer to conduct electricity and ions, enhancing the conductivity of the lithium replenishment material and providing sufficient lithium replenishment by supplying active Li ions, thus achieving excellent and stable lithium replenishment effects. However, the lithium replenishing agents and ternary coating layers involved in the slurry are highly sensitive to water and oxygen, severely limiting production due to environmental constraints. Furthermore, byproducts from the decomposition of the lithium replenishing agents can easily cause interface problems, making the membrane difficult to preserve and resulting in excessively high costs.

[0005] CN118249037A discloses a method for preparing Li2C4O4-MXene composite material and a lithium-supplementing separator, along with their applications. The method involves dissolving 3,4-dihydroxy-3-cyclobutene-1,2-dione and lithium carbonate in water at a molar ratio of 1:(0.6-1.4), followed by stirring to prepare Li2C4O4. The Li2C4O4 and MXene solution are then mixed and spray-dried to form the Li2C4O4-MXene composite material. This composite material is then mixed with SuperP and PVDF in NMP to form a slurry. This slurry is coated onto a separator and dried to obtain the lithium-supplementing separator. However, in actual production, oil-based coatings significantly increase costs. Furthermore, lithium succinate (Li2C4O4) as a lithium supplement produces more CO2 gas during decomposition, which can severely cause cell abnormalities. The actual decomposition voltage is much higher than the theoretical decomposition voltage, reaching approximately 4.9V when lithium ions are released for lithium supplementation. Therefore, the lithium-supplementing separator prepared in this way is difficult to apply to current cell systems. Summary of the Invention

[0006] The purpose of this invention is to provide an aqueous lithium-supplementing separator, its preparation method, and its application, in order to solve the problems in the background art.

[0007] To achieve the above objectives, the present invention provides a method for preparing an aqueous lithium-supplementing separator, specifically comprising the following steps:

[0008] S1. Ball milling: Add lithium supplement, catalyst MX and conductive agent into a ball milling jar and ball mill for 12 hours to allow the catalyst and conductive agent to effectively adhere to the surface of the lithium supplement. The mixed slurry is then spray-dried to obtain composite material powder.

[0009] S2. Preparation of lithium-replenishing coating slurry: The composite material powder obtained above is added to deionized water containing dispersant and dispersed. The binder and thickener are added in sequence and stirred evenly to obtain lithium-replenishing coating slurry.

[0010] S3. Coating: The lithium-replenishing coating slurry is coated on at least one side of the base film, and after curing and drying, a lithium-replenishing separator is obtained.

[0011] Preferably, in S1, by mass percentage, the lithium replenishing agent accounts for 65-95%, the catalyst MX accounts for 1-20%, and the conductive agent accounts for 1-20%; the particle size of the lithium replenishing agent is 0.5-2 μm, the particle size of the catalyst MX is 0.1-1 μm, and the particle size of the conductive agent is 0.01-0.2 μm.

[0012] Preferably, in step S2, by mass percentage, the proportion of composite material powder is 60-95%, the proportion of dispersant is 0.1-10%, the proportion of binder is 1-20%, and the proportion of thickener is 1-20%.

[0013] Preferably, in S1, the lithium supplement is Li. a H b C c O d Wherein, 1≤a≤2, 0≤b≤3, 1≤c≤4, 2≤d≤4; M in catalyst MX is one of Ni, Fe, Mo, Ti and their binary or ternary components; X is one or more elements of O, Se, S; and the conductive agent is one or more of carbon nanotubes, graphene, acetylene black, and Ketjen black.

[0014] Preferably, the lithium supplement is lithium oxalate (Li2C2O4), the conductive agent is carbon nanotubes, and the catalyst is NiO.

[0015] Preferably, in S2, the dispersant is a modified styrene-maleic acid copolymer; the binder is polyacrylamide; and the thickener is sodium carboxymethyl cellulose.

[0016] The present invention also provides an aqueous lithium replenishment separator prepared by the above preparation method, wherein the aqueous lithium replenishment separator comprises a base film and a coating.

[0017] The present invention also provides the application of the above-mentioned aqueous lithium-ion separator in a lithium-ion battery pack, wherein the lithium-ion battery pack includes a battery module, the battery module includes a lithium-ion battery, and the lithium-ion battery includes a positive electrode, a negative electrode, the aqueous lithium-ion separator, and an electrolyte.

[0018] This invention controls the amounts of catalyst and conductive agent to the above-mentioned ratio, resulting in a higher content of MX metal compound as both catalyst and conductive agent, which is beneficial to Li a H b C c O d Lithium supplement decomposes into Li at low voltage + Adding lithium to the battery cell improves its energy density and cycle life. a H b C c O d As a lithium replenisher, its theoretical capacity is over 500 mAh / g, showing great potential for lithium replenishment. However, in practical applications, Li... a H b C c O d A significant problem with lithium oxalate as a lithium supplement is its high decomposition voltage, typically above 4.9V. Compared to the theoretical decomposition voltage of 3.0V, the overpotential is as high as approximately 2V. This is because, during charging, the insulating nature of lithium oxalate hinders the transport of electrons at the interface, and the interface charge transfer process is the main cause of the high overpotential. Regarding Li... a H b C c O dThe problem of excessively high decomposition voltage caused by the insulating properties of lithium supplements can be addressed by mixing lithium supplement powder, catalyst powder, and conductive agent together, ball milling, and then spray drying to obtain lithium supplement-conductive agent-catalyst composite nanoparticles. This can significantly increase the specific surface area of ​​lithium oxalate, improve interfacial electron transport, reduce overpotential, and accelerate electrochemical decomposition, ultimately leading to the development of a functional membrane with highly efficient lithium supplementation performance.

[0019] Therefore, the aqueous lithium-supplementing membrane, its preparation method, and its application, as disclosed in this invention, have the following beneficial effects:

[0020] (1) The present invention selects Li a H b C c O d As a lithium supplement, it is combined with catalyst MX and conductive agent to form lithium supplement-conductive agent-catalyst nanoparticles. It is then dispersed in water with dispersant, binder, thickener and other additives to form an aqueous dispersion, which is uniformly coated on porous PE and PP base membranes to prepare an aqueous lithium supplement membrane. Starting from the aqueous coating process, it has significant effects on environmental protection and cost reduction, and achieves green and low cost.

[0021] (2) This lithium replenishment membrane, through the synergistic effect of nanoscale catalyst and single-walled carbon nanotube conductive agent, successfully reduced the delithiation voltage of the lithium replenishment agent from 4.9V to below 3.7V, meeting the requirements of current lithium iron phosphate and ternary systems, and solving the problem of excessively high lithium voltage. This lithium replenishment membrane has the ability to decompose Li at a lower voltage. + Replenishing the battery cell with lithium can effectively improve the cell's cycle life and capacity.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a water-based lithium replenishment diaphragm according to the present invention;

[0024] Figure 2 This is a morphology diagram of the aqueous lithium replenishment coating in Embodiment 1 of the present invention;

[0025] Figure 3 This is a finished product image of the water-based lithium replenishment separator of this invention;

[0026] Figure 4 This is a graph showing the verification results of the lithium replenishment performance of the aqueous lithium replenishment separator in the battery cell in Embodiment 3 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0028] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0029] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0030] Unless otherwise specified, the reagents, instruments, and equipment used in this invention are all commonly used by those skilled in the art.

[0031] Figure 1 This is a schematic diagram of the structure of the aqueous lithium replenishment membrane prepared by the present invention.

[0032] Example 1

[0033] This embodiment provides a method for preparing an aqueous lithium-supplementing separator, specifically including the following steps:

[0034] S1, Preparation of Li2C2O4-carbon nanotube-NiO composite material: 89g Li2C2O4, 5g NiO and 6g carbon nanotubes were added to a ball mill jar and ball milled for 12h to allow NiO and carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0035] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-carbon nanotube-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-carbon nanotube-NiO composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0036] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0037] Figure 2 This is a SEM image of the aqueous lithium-supplemented separator prepared in this embodiment. Figure 2 It can be seen that the three components, Li2C2O4, carbon nanotubes, and NiO, were eventually combined to obtain a composite material with a smaller particle size through ball milling and spraying. The carbon nanotubes and NiO were better integrated with Li2C2O4, which was beneficial to reducing the delithiation voltage of Li2C2O4.

[0038] Example 2

[0039] This embodiment provides a method for preparing an aqueous lithium-supplementing separator, specifically including the following steps:

[0040] S1, Preparation of Li2C2O4-carbon nanotube-NiO composite material: 92g Li2C2O4, 2g NiO and 6g carbon nanotubes were added to a ball mill jar and ball-milled for 12h to allow NiO and carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0041] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-carbon nanotube-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-carbon nanotube-NiO composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0042] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0043] Example 3

[0044] This embodiment provides a method for preparing an aqueous lithium-supplementing separator, specifically including the following steps:

[0045] S1, Preparation of Li2C2O4-carbon nanotube-NiO composite material: 86g Li2C2O4, 8g NiO and 6g carbon nanotubes were added to a ball mill jar and ball milled for 12h to allow NiO and carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0046] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-carbon nanotube-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-carbon nanotube-NiO composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0047] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0048] Example 4

[0049] This embodiment provides a method for preparing an aqueous lithium-supplementing separator, specifically including the following steps:

[0050] S1, Preparation of Li2C2O4-carbon nanotube-NiO composite material: 92g Li2C2O4, 5g NiO and 3g carbon nanotubes were added to a ball mill jar and ball milled for 12h to allow NiO and carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0051] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-carbon nanotube-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-carbon nanotube-NiO composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0052] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0053] Example 5

[0054] This embodiment provides a method for preparing an aqueous lithium-supplementing separator, specifically including the following steps:

[0055] S1, Preparation of Li2C2O4-carbon nanotube-NiO composite material: 86g Li2C2O4, 5g NiO and 9g carbon nanotubes were added to a ball mill jar and ball milled for 12h to allow NiO and carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0056] S2. Preparation of aqueous lithium-based slurry: 100g of the above-mentioned Li2C2O4-carbon nanotube-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred until homogeneous to obtain the lithium-based slurry. The lithium-carbon nanotube-NiO composite material accounted for 93.5% of the coating by mass, the modified styrene-maleic acid copolymer accounted for 0.93% by mass, the polyacrylamide accounted for 4.67% by mass, and the sodium carboxymethyl cellulose accounted for 0.9% by mass.

[0057] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0058] Comparative Example 1

[0059] This comparative example provides a method for preparing a lithium-supplemented separator, specifically including the following steps:

[0060] Preparation of S1, Li2C2O4-carbon nanotube composite material: 97g Li2C2O4 and 3g carbon nanotubes were added to a ball mill jar and ball milled for 12h to allow the carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0061] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-carbon nanotube nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-carbon nanotube composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0062] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing an aqueous lithium-supplemented separator, specifically including the following steps:

[0065] Preparation of S1, Li2C2O4-NiO composite material: 95g Li2C2O4 and 5g NiO were added to a ball mill jar and ball milled for 12h to allow NiO to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0066] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-NiO composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0067] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0068] Comparative Example 3

[0069] This comparative example provides a method for preparing an aqueous lithium-supplemented separator, specifically including the following steps:

[0070] Preparation of S1, Li2C2O4-NiO composite material: 100g Li2C2O4 and 0g NiO were added to a ball mill jar and ball milled for 12h to allow NiO to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0071] S2. Preparation of aqueous lithium replenishment slurry: 100g of the above-mentioned Li2C2O4-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 5g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-NiO composite material in the coating was 93.5%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 4.67%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0072] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0073] Comparative Example 4

[0074] This comparative example provides a method for preparing an aqueous lithium-supplemented separator, specifically including the following steps:

[0075] S1, Preparation of Li2C2O4-carbon nanotube-NiO composite material: 84.55g Li2C2O4, 4.75g NiO and 5.7g carbon nanotubes were added to a ball mill jar and ball-milled for 12h to allow NiO and carbon nanotubes to effectively adhere to the surface of Li2C2O4. The mixed slurry was then spray-dried to obtain nano-composite powder.

[0076] S2. Preparation of aqueous lithium replenishment slurry: 95g of the above-mentioned Li2C2O4-carbon nanotube-NiO nanocomposite powder was added to 249.9g of water containing 1g of modified styrene-maleic acid copolymer and dispersed at high speed. 10g of polyacrylamide and 0.96g of sodium carboxymethyl cellulose were added sequentially in proportion, and the mixture was stirred evenly to obtain the lithium replenishment slurry. The mass percentage of Li2C2O4-carbon nanotube-NiO composite material in the coating was 88.83%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 9.34%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0077] S3. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0078] Comparative Example 5

[0079] This comparative example provides a method for preparing an aqueous lithium-supplemented separator, specifically including the following steps:

[0080] S1. Preparation of aqueous lithium-based slurry: 89g Li₂C₂O₄, 5g NiO, and 6g carbon nanotube (CNT) aqueous slurry were sequentially added to 249.9g water containing 1g modified styrene-maleic acid copolymer and dispersed at high speed. 10g polyacrylamide and 0.96g sodium carboxymethyl cellulose were then added sequentially according to the specified proportions, and the mixture was stirred until homogeneous to obtain the lithium-based slurry. The mass percentage of Li₂C₂O₄ in the coating was 88.83%, the mass percentage of modified styrene-maleic acid copolymer was 0.93%, the mass percentage of polyacrylamide was 9.34%, and the mass percentage of sodium carboxymethyl cellulose was 0.9%.

[0081] S2. Slurry coating: The above-mentioned lithium replenishing slurry is uniformly coated on at least one side of a 12μm PE base film using a coating machine, and then baked and dried to obtain a lithium replenishing separator.

[0082] Figure 3 The images show the finished aqueous lithium-ion membrane rolls, from left to right: Example 5, Comparative Example 3, and Example 3. Example 5 has the highest conductive agent dosage, resulting in a darker membrane color. Comparative Example 3, without any conductive agent or catalyst, is pure white. Example 3, with the addition of appropriate amounts of conductive agent and catalyst, is gray in color.

[0083] Performance testing

[0084] The aqueous lithium-replenishing separators, electrodes, and electrolytes prepared in Examples 1-5 and Comparative Examples 1-5 were combined to form lithium-ion batteries, and overcharge tests were performed on the assembled lithium-ion batteries. Empty aluminum foil was used as the positive electrode, lithium sheets as the negative electrode, and 1.15 mol of lithium hexafluorophosphate dissolved in a mixed organic solvent of EC:DEC:VEC:PC:PS was used as the electrolyte. The positive and negative electrodes, lithium-replenishing separator, and electrolyte were assembled into coin cells. The testing method involved charging the coin cell at 0.1C to 4.99V, and the charging capacity data of the cell is shown in Table 1.

[0085] Table 1. Test data for lithium-ion coin cell battery replenishment

[0086]

[0087] Table 1 shows that the aqueous lithium-replenishing membrane provided by this invention enables lithium replenishment of the battery cell. A comparison of Example 1 with Comparative Examples 1-3 shows that the catalyst and conductive agent play a crucial role in the complete decomposition of the lithium replenishing agent at low voltage. A comparison of Example 1 with Comparative Example 4 shows that the amount of binder has no effect on the decomposition voltage and capacity of the lithium replenishing agent. A comparison of Example 1 with Comparative Example 5 shows that the combination of ball milling and spray drying processes has a significant impact on the decomposition voltage and capacity of the lithium replenishing agent, allowing the lithium oxalate lithium replenishing agent to replenish the battery cell at even lower voltages.

[0088] As can be seen from the comparison of Examples 1-5, the higher the amount of catalyst added, the lower the delithiation voltage of the lithium replenishing agent. The optimal addition amount of catalyst MX in the coating is 7.8%. The addition amount of conductive agent has little effect on further reducing the delithiation voltage of the lithium replenishing agent. The conductive agent affects whether its lithium replenishment capacity is fully released. The optimal addition amount of conductive agent in the coating is 5.6%.

[0089] Figure 4 This is a graph showing the verification results of the lithium replenishment performance of the aqueous lithium replenishment separator in the cell in Example 4. Empty aluminum foil was used as the positive electrode, lithium metal as the negative electrode, and the electrolyte was 1.15 mol of lithium hexafluorophosphate dissolved in a mixed organic solvent of EC:DEC:VEC:PC:PS. A coin cell was assembled using the positive and negative electrodes, the lithium replenishment separator from Example 4, and the electrolyte. The testing method involved charging the coin cell to 3.8V at 0.1C and observing the cell's charging capacity; this capacity represents the capacity released by the lithium replenishment separator.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an aqueous lithium-supplementing separator, characterized in that: Specifically, the following steps are included: S1. Ball milling: Add lithium supplement, catalyst MX and conductive agent into a ball milling jar and ball mill for 12 hours to allow the catalyst and conductive agent to effectively adhere to the surface of the lithium supplement. The mixed slurry is then spray-dried to obtain composite material powder. Lithium supplement is Li a H b C c O d Wherein, 1≤a≤2, 0≤b≤3, 1≤c≤4, 2≤d≤4; M in catalyst MX is one of Ni, Fe, Mo, Ti and their binary or ternary components; X is one or more elements of O, Se, and S; and the conductive agent is one or more of carbon nanotubes, graphene, acetylene black, and Ketjen black. S2. Preparation of lithium-replenishing coating slurry: The composite material powder obtained above is added to deionized water containing dispersant and dispersed. The binder and thickener are added in sequence and stirred evenly to obtain lithium-replenishing coating slurry. S3. Coating: The lithium-replenishing coating slurry is coated on at least one side of the base film to form a coating, and after curing and drying, a lithium-replenishing separator is obtained.

2. The method for preparing an aqueous lithium-supplementing separator according to claim 1, characterized in that: In S1, by mass percentage, the lithium replenishing agent accounts for 60-98%, the catalyst MX accounts for 1-20%, and the conductive agent accounts for 1-20%; the particle size of the lithium replenishing agent is 0.5-2 μm, the particle size of the catalyst MX is 0.1-1 μm, and the particle size of the conductive agent is 0.01-0.2 μm.

3. The method for preparing an aqueous lithium-supplementing separator according to claim 1, characterized in that: In S2, by mass percentage, the proportion of composite material powder is 40-97%, the proportion of dispersant is 0.1-15%, the proportion of binder is 1-30%, and the proportion of thickener is 1-20%.

4. The method for preparing an aqueous lithium-supplementing separator according to claim 1, characterized in that: The lithium supplement is lithium oxalate (Li₂C₂O₄), the conductive agent is carbon nanotubes, and the catalyst is NiO.

5. The method for preparing an aqueous lithium-supplementing separator according to claim 1, characterized in that: In S2, the dispersant is a modified styrene-maleic acid copolymer; the binder is polyacrylamide; and the thickener is sodium carboxymethyl cellulose.

6. A water-based lithium replenishment diaphragm, characterized in that: The aqueous lithium replenishment membrane is prepared by any one of the preparation methods of claims 1-5, and the aqueous lithium replenishment membrane includes a base film and a coating.

7. The application of the aqueous lithium replenishment diaphragm as described in claim 6, characterized in that: The aqueous lithium-ion replenishing separator is used in a lithium-ion battery pack, which includes a battery module, a lithium-ion battery, and a positive electrode, a negative electrode, the aqueous lithium-ion replenishing separator, and an electrolyte.

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