Composite positive electrode and lithium ion battery

Abstract

The application provides a composite positive electrode and a lithium ion battery, the composite positive electrode comprises at least one layer of ternary positive electrode material layer arranged on the surface of a current collector, and a protective layer is arranged on the side of the composite positive electrode in contact with an electrolyte; the protective layer comprises an acrylic copolymer containing at least one functional group of a hydroxyl group, an amine group and a carboxyl group and a solid-state electrolyte; the copolymer comprises a benzene ring structure, and a hydroxyl group structure is connected to at least adjacent substitution positions of the same benzene ring; the solid-state electrolyte is a block polymer comprising a soft segment and a hard segment; and the ternary positive electrode material layer accounts for 70-80% of the total thickness of the composite positive electrode. According to the application, the cycle performance of the battery can be greatly improved, and the precipitation of transition metals in the negative electrode is obviously improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a composite cathode and a lithium-ion battery. Background Technology

[0002] In today's society, lithium-ion batteries have gradually become the primary portable energy source due to their excellent cycle performance and environmental friendliness. Correspondingly, the safety and energy density of lithium-ion batteries are receiving increasing attention.

[0003] Lithium-ion batteries using ternary materials as electrode materials have attracted widespread attention due to their high energy density and long driving range in new energy devices. However, on the one hand, the safety of ternary batteries is worse than that of other batteries (such as lithium iron phosphate batteries), which prevents ternary batteries from being used on a larger scale.

[0004] On the other hand, ternary batteries exhibit poor cycle performance and rapid capacity decay, which is related to the dissolution of transition metal ions. The dissolution of transition metals is an inherent defect of ternary materials. In lithium batteries made primarily of nickel, cobalt, and manganese, deposits of nickel, cobalt, and manganese were found in the negative electrode after failure. The speculated reason is that trace amounts of water inside the battery react with lithium salt LiPF6 to generate HF, which then reacts with transition metal ions on the electrode surface to form products with high impedance, such as MF2 (where M represents the transition metal), leading to loss of positive electrode material. (Transition metal ions M...) 2+ It will dissolve and migrate towards the negative electrode during the charging and discharging process, depositing as a metal on the negative electrode surface. Under the principle of charge balance, this behavior will inevitably cause the Li already embedded in the negative electrode to... + Forced to detach and enter the middle, it forms the so-called negative electrode "self-discharge" process, causing battery capacity loss.

[0005] Therefore, there is an urgent need to develop a new positive electrode for lithium-ion batteries to solve the above problems. Summary of the Invention

[0006] To address one or more of the aforementioned technical problems in the prior art, embodiments of this application provide a composite positive electrode and a lithium-ion battery, thereby resolving the issue of Li-ion batteries using ternary materials as electrode materials in the prior art having Li-ion batteries with embedded negative electrodes. + Forced to detach and enter the middle, it forms the so-called negative electrode "self-discharge" process, causing problems such as battery capacity loss.

[0007] To address the above problems, this application provides the following technical solution:

[0008] In a first aspect, a composite positive electrode is provided, the composite positive electrode comprising at least one ternary positive electrode material layer disposed on the surface of the current collector, and a protective layer disposed on the side of the composite positive electrode in contact with the electrolyte;

[0009] The protective layer comprises an acrylic acid copolymer containing at least one functional group selected from hydroxyl, amine, and carboxyl groups, and a solid electrolyte;

[0010] The copolymer comprises a benzene ring structure, and a hydroxyl structure is attached at at least adjacent substitution sites on the same benzene ring;

[0011] The solid electrolyte is a block polymer, comprising soft segments and hard segments;

[0012] The ternary cathode material layer accounts for 70-80% of the total thickness of the composite cathode.

[0013] Preferably, the solid electrolyte is a gel polymer electrolyte.

[0014] It is understood that the composite cathode of this application may include multiple ternary cathode material layers.

[0015] In one specific embodiment, the monomer unit of the copolymer simultaneously contains hydroxyl, amine, and carboxyl functional groups.

[0016] In one specific embodiment, the monomer unit of the copolymer contains two or more hydroxyl, amine, and carboxyl functional groups.

[0017] In one specific embodiment, the copolymer is a copolymer of epoxy succinic acid containing catechol groups and acrylic acid.

[0018] In one specific embodiment, the solid electrolyte is polyurethane, preferably water-soluble polyurethane.

[0019] In one specific embodiment, the content ratio of the copolymer to the solid electrolyte is (1-5):(5-9).

[0020] Preferably, the content ratio of the copolymer to the solid electrolyte is (1.5-3):(7-8.5).

[0021] In one specific embodiment, the protective layer further includes a lithium salt.

[0022] In one specific embodiment, the ionic conductivity of the protective layer is (6.0-7.0)×10⁻⁶. -5 S·cm -1 .

[0023] Preferably, the ionic conductivity of the protective layer is 6.6 × 10⁻⁶. -5S·cm -1 .

[0024] In one specific embodiment, the ternary cathode material layer further includes a binder and a conductive agent.

[0025] Secondly, corresponding to the above-mentioned composite positive electrode, a lithium-ion battery is also provided, including the composite positive electrode, negative electrode, and a separator disposed between the composite positive electrode and the negative electrode as described above.

[0026] In one specific embodiment, the lithium-ion battery further includes an electrolyte.

[0027] In another specific embodiment, when the battery containing the composite positive electrode as described above is a solid-state lithium-ion battery, the barrier layer also includes a plasticizer.

[0028] Beneficial effects:

[0029] The composite cathode and lithium-ion battery provided in this application include a composite cathode comprising at least one ternary cathode material layer disposed on the surface of a current collector, and a protective layer disposed on the side of the composite cathode in contact with the electrolyte. The protective layer comprises an acrylic acid copolymer containing at least one functional group selected from hydroxyl, amine, and carboxyl groups, and a solid electrolyte. The copolymer contains a benzene ring structure, and a hydroxyl structure is attached to at least adjacent substitution sites on the same benzene ring. The solid electrolyte is a block polymer, including soft segments and hard segments. The ternary cathode material layer accounts for 70-80% of the total thickness of the composite cathode. This application can significantly improve the cycle performance of the battery and significantly improve the precipitation of transition metals on the negative electrode. Detailed Implementation

[0030] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0031] This application provides a composite positive electrode in one embodiment. The composite positive electrode includes at least one ternary positive electrode material layer disposed on the surface of the current collector, and a protective layer is disposed on the side of the composite positive electrode in contact with the electrolyte. The composite positive electrode structure provided by this application significantly improves the cycle performance of the battery and significantly improves the deposition of transition metals on the negative electrode.

[0032] It is understood that the composite cathode of this application may include multiple ternary cathode material layers. The number of ternary cathode material layers is not specifically limited here, and users can set it according to their actual needs.

[0033] In one embodiment of this application, the ternary cathode material layer includes a ternary cathode material. A ternary material refers to a material composition consisting of three chemical components (elements), elements (simple substances and compounds), or parts (components), including alloys, inorganic non-metallic materials, organic materials, and polymer composite materials, and is widely used in industries such as mineral extraction, metal smelting, materials processing, and new energy. Specifically, the ternary cathode material in this application refers to a lithium compound containing at least one of the three metals: nickel, cobalt, and manganese. Setting a ternary cathode material layer with a ternary cathode material in a composite cathode helps to improve the overall energy density of the battery.

[0034] In this application, no specific limitation is made to the ternary cathode material. Any known ternary cathode material can be used in this application without departing from the inventive concept. As an exemplary and not restrictive illustration, the ternary cathode material in this application includes lithium nickel cobalt manganese oxide (LCO). LCO is a key ternary cathode material for lithium-ion batteries, possessing higher specific capacity and lower cost than single-cell cathode materials. LCO features high energy density, good cycle performance, high voltage platform, and good thermal stability. Moreover, it replaces more than two-thirds of the cobalt in lithium cobalt oxide with relatively inexpensive nickel and manganese, resulting in a significant cost advantage. Compared with other lithium-ion battery cathode materials such as lithium manganese oxide and lithium iron phosphate, LCO is very close to lithium cobalt oxide in terms of electrochemical and processing performance, making it a new battery material that is gradually replacing lithium cobalt oxide.

[0035] Optionally, the ternary cathode material includes any one or a combination of at least two of NCM532, NCM811, and NCM333.

[0036] In one embodiment of this application, the ternary cathode material layer accounts for 70-80% of the total thickness of the composite cathode. For example, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%, etc., which will not be listed exhaustively here.

[0037] It is understandable that the total thickness of the composite cathode does not include the thickness of the current collector; the total thickness of the composite cathode is the total thickness of the ternary cathode material layer and the protective layer.

[0038] In a preferred embodiment, the ternary cathode material layer further includes a binder and a conductive agent.

[0039] It is understood that an adhesive is a substance used to bind ternary materials, conductive agents, and other components together. Without departing from the inventive concept of this application, this application does not have any particular requirements on the type of adhesive; any known type of adhesive can be used in the ternary cathode material layer.

[0040] Specifically, the adhesive may comprise a selection from polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, and ethylene. propylene Diene monomers, styrene At least one of the group consisting of butadiene rubber and fluororubber, preferably polyvinylidene fluoride.

[0041] Conductive agents are mainly used to assist and improve the conductivity of secondary batteries. This application does not impose any particular limitations on the conductive agent, as long as it possesses electronic conductivity without causing chemical changes. Specifically, the conductive agent may independently comprise graphite, such as natural or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders, such as fluorocarbon powders, aluminum powders, and nickel powders; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxides; and polyphenylene derivatives. From the perspective of improving conductivity, carbon black is preferred.

[0042] In a preferred embodiment, in this application, the amount of the conductive agent in the ternary cathode material layer can be 1... 20wt%, for example 1wt%, 3wt%, 5wt%, 7wt%, 10wt%, 12.5wt%, 15wt%, 16wt%, 18wt%, or 20wt%, etc., preferably 1.2wt%. 10wt%.

[0043] In a preferred embodiment, in this application, the amount of binder in the ternary cathode material layer can be 1... 20wt%, for example 1wt%, 3wt%, 5wt%, 7wt%, 10wt%, 12.5wt%, 15wt%, 16wt%, 18wt%, or 20wt%, etc., preferably 1.2wt%. 10wt%.

[0044] In one embodiment of this application, the protective layer comprises an acrylic acid copolymer containing at least one functional group selected from hydroxyl, amino, and carboxyl groups. As a preferred embodiment, in this application, the copolymer comprises a benzene ring structure, and a hydroxyl structure (similar to an ortho-diphenol structure) is attached to at least adjacent substitution sites on the same benzene ring. The protective layer is disposed on the side of the composite cathode in contact with the electrolyte, thereby effectively preventing transition metal ions from the ternary cathode material from entering the electrolyte.

[0045] In a preferred embodiment, the monomer units of the copolymer in this application simultaneously contain hydroxyl, amino, and carboxyl functional groups. Preferably, the monomer units of the copolymer simultaneously contain two or more hydroxyl, amino, and carboxyl functional groups.

[0046] On the one hand, the copolymer possesses numerous active functional groups, including hydroxyl, amino, and carboxyl groups. These functional groups provide a large number of active sites, which can interact with nickel, manganese, and cobalt ions through various mechanisms such as coordination, chelation, hydrogen bonding, or π-π stacking. This prevents transition metal ions dissolved during the ternary cathode recycling process from depositing on the anode and causing capacity decay. On the other hand, the polyhydroxy polymer has a high affinity for transition metal ions, enabling rapid adsorption of these ions through coordination.

[0047] In a preferred embodiment, the copolymer in this application is a copolymer of epoxy succinic acid containing catechol groups and acrylic acid.

[0048] In one embodiment, the ternary cathode material layer is obtained by coating a corresponding cathode slurry and then drying it.

[0049] In one embodiment of this application, the protective layer further includes a solid electrolyte, which can further improve the lithium-ion transport efficiency on the composite cathode. The solid electrolyte is preferably a gel polymer electrolyte.

[0050] In a preferred embodiment of this application, the solid electrolyte comprises a block polymer, including soft segments and hard segments. The hard segments are composed of aromatic hydrocarbons, exhibiting high rigidity, while the soft segments are composed of aliphatic hydrocarbons, exhibiting high flexibility. This combination allows the block copolymer to possess both rigidity and flexibility.

[0051] Preferably, in this embodiment, the solid electrolyte is polyurethane. Polyurethane has a unique hard-soft segment structure, and its molecules are highly designable, allowing it to be prepared into materials with different mechanical properties according to application requirements. The soft segments of polyurethane can dissolve a large amount of lithium salt and have good flexibility, providing excellent ion conductivity. The hard segments can form hydrogen bonds with each other and with the soft segments, and the strong hydrogen bonding provides the polymer electrolyte with good mechanical properties.

[0052] More preferably, in this embodiment of the application, the solid electrolyte is water-soluble polyurethane. Water-soluble polyurethane has good mechanical strength and thermal stability, which further improves the safety performance of the battery cell. In addition, polyurethane is water-soluble, and water-based polyurethane-based solid electrolyte has excellent environmental friendliness in the preparation process.

[0053] In one embodiment of this application, when the solid electrolyte included in the protective layer is a water-soluble polyurethane, it also includes a solid plasticizer, which is substantially miscible with the overall structure of the water-based polyurethane. This application does not impose any particular requirements on the type of plasticizer; any known plasticizers suitable for water-based polyurethanes can be used in this application without departing from the inventive concept. As merely an illustrative example, at least one solid plasticizer may include organic materials (e.g., small solid organic molecules) and / or oligomer materials; for example, the at least one solid plasticizer may be selected from glutaronitrile, succinic anionyl nitrile, adiponitrile, fumaric acid, and combinations thereof.

[0054] In a preferred embodiment of this application, the content ratio of the copolymer to the solid electrolyte is (1-5):(5-9), and more preferably, the content ratio of the copolymer to the solid electrolyte is (1.5-3):(7-8.5). This arrangement is intended to ensure that the protective layer does not affect the lithium-ion transport rate at the composite cathode.

[0055] In a preferred embodiment of this application, the protective layer further includes a lithium salt.

[0056] Specifically, this application does not particularly limit the type of lithium salt included in the protective layer. Any known type of lithium salt can be used in this application without departing from the inventive concept. Under the action of water-soluble polyurethane and lithium salt, lithium ions can pass smoothly through the protective layer.

[0057] As an illustrative example only, and not a limitation on the scope of protection, the lithium salt can be lithium hexafluorophosphate (LiPF6). Lithium perchlorate () Lithium tetrachloroaluminate ( ) Lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate ( Lithium difluorooxalate borate ( ) (LiODFB), Lithium tetraphenylborate ( ), Lithium bis(oxalate)borate ( (LiBOB), lithium tetrafluorooxalate phosphate ( (LiFOP), Lithium nitrate ( Lithium hexafluoroarsenate ( ) Lithium trifluoromethanesulfonate ( ), Lithium bis(trifluoromethanesulfonylimide) (LITFSI) Lithium difluorosulfonylimide () (LIFSI) and combinations thereof. In some variants, the lithium salt is selected from lithium hexafluorophosphate (LIFSI). ), Lithium bis(trifluoromethanesulfonylimide) (LiTFSI) Lithium difluorosulfonylimide () (LiFSI), lithium fluoroalkylphosphonate (LiFAP), lithium phosphate ( One or more of them.

[0058] In one embodiment, the lithium salt content in the protective layer is 10. 60wt%, for example 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, or 60wt%, etc.; it is understood that there are no special requirements for the lithium salt content, and it is known in the art to adjust the ionic conductivity of the solid electrolyte layer by adjusting the lithium salt content.

[0059] In a preferred embodiment of this application, the ionic conductivity of the protective layer is (6.0-7.0)×10⁻⁵ S·cm⁻¹; for example, 6.0×10⁻⁵ S·cm⁻¹. -5 S·cm -1 6.1×10 -5 S·cm -1 6.2×10 -5 S·cm -1 6.3×10 -5 S·cm -1 6.4×10 -5 S·cm -1 6.5×10 -5 S·cm -1 6.6×10 -5 S·cm -1 6.7×10 -5 S·cm -1 6.8×10 -5 S·cm -1 6.9×10 -5 S·cm -1 7.0×10 -5 S·cm -1 And so on, not all of them will be listed here. Preferably, the ionic conductivity of the protective layer is 6.6 × 10⁻⁶. -5 S·cm -1 .

[0060] It is understood that the present application does not particularly limit the type of current collector in the composite positive electrode. Any known positive electrode current collector can be used in this application without departing from the inventive concept. As an exemplary and not restrictive description, in the embodiments of this application, the current collector in the composite positive electrode includes, but is not limited to, any one of aluminum, nickel, or stainless steel. Optionally, the current collector is elemental aluminum, such as aluminum foil.

[0061] Corresponding to the above-described composite positive electrode, in one embodiment of the present invention, a method for preparing the above-described composite positive electrode is also provided, the method comprising the following steps:

[0062] S100: A ternary cathode material layer is coated on the surface of the current collector and dried in one step;

[0063] S200: A protective layer is coated on the surface of the ternary cathode material layer formed after a first drying, followed by a second drying and roll pressing to obtain the cathode.

[0064] Preferably, the coating in step S200 can be performed while the material is not completely dry during the corresponding drying process, thereby improving the adhesion between the two layers.

[0065] In another embodiment of the present invention, a lithium-ion battery is provided, the lithium-ion battery comprising a composite positive electrode as described above, a negative electrode, and a separator between the composite positive electrode and the negative electrode.

[0066] In a preferred embodiment of this application, the lithium-ion battery further includes an electrolyte.

[0067] This application does not have any special requirements for electrolyte materials. Without departing from the inventive concept of this application, known non-aqueous electrolyte systems, solid electrolyte systems, gel electrolyte systems, and solid-liquid mixed electrolyte systems can all be used in this application.

[0068] It is understood that any suitable electrolyte capable of conducting lithium ions between the composite positive and negative electrodes can be used in the lithium-ion battery of this application, and can be in solid, liquid, or gel form. As an illustrative example, the electrolyte can be a non-aqueous liquid electrolyte solution comprising a lithium salt dissolved in an organic solvent or a mixture of organic solvents; when using a non-aqueous electrolyte solution, a separator must be used, which can be formed of a microporous insulating material, wherein the non-aqueous liquid can wet the pore structure of the separator. The electrolyte can also be a solid electrolyte material, which can serve both as an ion conductor (e.g., to transport lithium ions) and as an electrical insulator (e.g., to prevent charge or current from flowing from the negative electrode to the composite positive electrode).

[0069] In another specific embodiment, when the battery containing the composite positive electrode as described above is a solid-state lithium-ion battery, the protective layer also includes a plasticizer.

[0070] This application does not specifically limit the negative electrode; as an illustrative example, the negative electrode comprises a negative electrode active material. In some embodiments, the negative electrode may be composed of multiple negative electrode active materials. Such negative electrode active materials may be disposed in one or more layered structures. In some variations, the negative electrode may also include an electrolyte.

[0071] The negative electrode active material can be a lithium-based negative electrode active material, comprising, for example, lithium metal and / or lithium alloys. In other embodiments, the negative electrode is a silicon-based negative electrode active material, comprising silicon, such as silicon alloys, silicon oxide, or combinations thereof, and in some cases may also be mixed with graphite. In other embodiments, the negative electrode may include a carbon-based negative electrode active material, comprising one or more of graphite, graphene, carbon nanotubes (CNTs), and combinations thereof. In yet another embodiment, the negative electrode includes one or more lithium-accepting negative electrode active materials, such as lithium titanium oxide (Li4Ti5O). 12 One or more transition metals (e.g., tin (Sn)), one or more metal oxides (e.g., vanadium oxide (V₂O₅), tin oxide (SnO), titanium dioxide (TiO₂)), titanium niobium oxide (TiO₂) x Nb y O z , where 0≤x≤2, 0≤y≤24 and 0≤z≤64, metal alloys (such as copper-tin alloy (Cu6Sn5)) and one or more metal sulfides (such as iron sulfide (FeS)).

[0072] Optionally, the negative electrode active material in the negative electrode may be doped with one or more conductive agents that provide an electron conduction path and / or at least one polymer binder material that improves the structural integrity of the negative electrode. For example, the negative electrode active material may optionally be doped with binders such as: poly(tetrafluoroethylene) (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and combinations thereof. Conductive agents may include carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Carbon-based materials may include particles such as carbon black, graphite, superP, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fibers and nanotubes, graphene, etc. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4) Ethylene dioxythiophene (EDT) polysulfonated styrene, etc.

[0073] The negative electrode may include more than or equal to about 50% by weight to less than or equal to about 97% by weight of a negative electrode active material, optionally include more than or equal to about 0% by weight to less than or equal to about 60% by weight of a solid electrolyte, optionally include more than or equal to about 0% by weight to less than or equal to about 15% by weight of a conductive agent, and optionally include more than or equal to about 0% by weight to less than or equal to about 10% by weight of a binder.

[0074] The following embodiments will be used to illustrate the present application and its effects in more detail.

[0075] Example 1

[0076] A composite cathode is provided, comprising a ternary cathode material layer disposed on the surface of a current collector, the ternary cathode material layer being composed of 96 wt% NCM811, 2 wt% super-P and 2 wt% PVDF.

[0077] Example 2

[0078] A composite positive electrode is provided, comprising a ternary positive electrode material layer disposed on the surface of a current collector, wherein a protective layer is disposed on the side of the composite positive electrode that is in contact with the electrolyte;

[0079] The ternary cathode material layer is composed of 96wt% NCM811, 2wt% super-P and 2wt% PVDF;

[0080] The protective layer comprises a waterborne polyurethane-based composite solid electrolyte containing a catechol-containing epoxy succinic acid and an acrylic copolymer, which consists of 30 wt% of a catechol-containing epoxy succinic acid and an acrylic copolymer, 60 wt% of a water-soluble polyurethane, and 10 wt% of lithium bis(trifluoromethanesulfonylimide) (LITFSI).

[0081] The preparation process of the copolymer of catechin-containing epoxysuccinic acid and acrylic acid is as follows:

[0082] Step 1: Synthesis of epoxy succinic acid and acrylic acid copolymer:

[0083] 0.2 mol of epoxysuccinic acid was added to a three-necked flask, followed by 30 g of deionized water to completely dissolve it. While maintaining mechanical stirring at 30 rpm / min, a 40% NaOH aqueous solution was slowly added to adjust the pH to approximately 10. Then, 2% potassium persulfate was added. Acrylic acid was then added dropwise using a constant-pressure dropping funnel, while simultaneously adding 40% NaOH aqueous solution to control the pH. After the acrylic acid addition was complete, the temperature was raised to 90°C in a water bath and the reaction was allowed to proceed overnight. Throughout the reaction, the viscosity of the reaction system gradually increased, and the color changed from colorless to yellow. After the reaction was complete, the mixture was cooled to room temperature in a water bath, diluted with a small amount of ethanol to reduce the viscosity, allowed to settle and precipitate, and finally, a 1 mol / L HCl aqueous solution was added to adjust the pH to 3. The mixture was then dried under vacuum to obtain the intermediate product.

[0084] Step 2: Synthesis of epoxy succinic acid containing catechol groups and acrylic acid copolymer:

[0085] The intermediate product synthesized in step one was dissolved in deionized water in a three-necked flask. The pH of the solution was adjusted to between 5 and 6 with dilute hydrochloric acid. An amidation reagent (EDC) was added under ice bath conditions. After reacting for one hour, dopamine was added in multiple batches. After the dopamine was completely added, the ice bath was maintained for another 10 hours. Then, the copolymer of epoxy succinic acid and acrylic acid containing catechol groups was obtained by dialysis.

[0086] Example 3

[0087] A composite positive electrode is provided, comprising a ternary positive electrode material layer disposed on the surface of a current collector, wherein a protective layer is disposed on the side of the composite positive electrode that is in contact with the electrolyte;

[0088] The ternary cathode material layer is composed of 96wt% NCM811, 2wt% super-P and 2wt% PVDF;

[0089] The protective layer comprises an aqueous polyurethane-based composite solid electrolyte consisting of 90 wt% water-soluble polyurethane and 10 wt% lithium bis(trifluoromethanesulfonylimide) (LITFSI).

[0090] In this embodiment, the PVDF is from Arkema HSV1810, and the waterborne polyurethane is from McLean Reagents Company's waterborne polyurethane A909856. P is from Cabot's LITX300, the ternary cathode material is from Dangsheng Technology, and the lithium bis(trifluoromethanesulfonylimide) (LITFSI) is from Sigma-Aldrich.

[0091] Battery manufacturing:

[0092] The composite positive electrode prepared in each embodiment is combined with the negative electrode and electrolyte to obtain a lithium-ion battery. The composition of the negative electrode active material layer is 95wt% graphite, 2wt% conductive carbon black and 3wt% binder composed of CMC and SBR.

[0093] test:

[0094] 1. Cycle life test at room temperature with 80% capacity cutoff

[0095] (1) Charge at 1C to the termination voltage, cut-off current 0.05C, and let stand for 30 minutes;

[0096] (2) Discharge at 1C to the final discharge voltage, record the discharge capacity, and let stand for 30 minutes;

[0097] Loop (1) (2) The cycle life at room temperature up to 80% capacity was tested. The test results are shown in Table 1.

[0098] 3. Regarding ICP testing

[0099] A: Weigh two portions of approximately 0.1 g of negative electrode powder (accurate to ±0.0003 g) from each example, place them in a 100 ml beaker, add a small amount of distilled water to moisten the bottom of the beaker, then add 5 ml of 12 mol / L HCl (Shandong-made, GR) to dissolve, heat on an electric heating plate for 20 min, remove and cool, dilute and then test. Introduce the prepared series of standard solutions into an iCAP7000 inductively coupled plasma optical transilluminator (ICP) (made in the USA), and measure the intensity of each element in the standard solution at the wavelength of the element to be tested (lithium, nickel, cobalt, and manganese). When the linear correlation coefficient r of the working curve is ≥0.9995, the measurement can be performed. The test results are shown in Table 1.

[0100] Table 1

[0101]

[0102] Comparative examples show that depositing a ternary cathode material layer on the current collector surface and a protective layer on the side of the composite cathode in contact with the electrolyte helps improve battery safety and cycle performance, and reduces the deposition of transition metals on the negative electrode. Further comparisons of Examples 1-3 reveal that depositing a protective layer of an acrylic copolymer containing at least one functional group such as hydroxyl, amino, or carboxyl groups on the side of the composite cathode in contact with the electrolyte provides numerous active sites. These sites can interact with nickel, manganese, and cobalt ions through coordination, chelation, hydrogen bonding, or π-π stacking, preventing transition metal ions dissolved during ternary cathode recycling from depositing on the negative electrode and causing capacity decay. Furthermore, the high affinity between the polyhydroxy polymer and transition metal ions allows for rapid adsorption of transition metal ions through coordination.

[0103] Furthermore, by using waterborne polyurethane as the polymer matrix of the solid electrolyte, the soft segments of polyurethane can dissolve a large amount of lithium salt and have good flexibility, providing excellent ion conductivity. At the same time, waterborne polyurethane contains a large number of hydrogen-bonded groups, and the strong hydrogen bonding provides the polymer electrolyte with good mechanical properties. The waterborne polyurethane-based solid polymer electrolyte layer exhibits good mechanical strength and thermal stability, further improving the safety performance of the battery cell.

[0104] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite positive electrode, characterized in that, The composite cathode includes at least one ternary cathode material layer disposed on the surface of the current collector, and a protective layer is disposed on the side of the composite cathode that is in contact with the electrolyte. The protective layer comprises an acrylic acid copolymer containing at least one functional group selected from hydroxyl, amine, and carboxyl groups, and a solid electrolyte; The copolymer comprises a benzene ring structure and has hydroxyl structures attached to at least adjacent substitution sites on the same benzene ring. The copolymer is a copolymer of epoxy succinic acid containing catechol groups and acrylic acid. The solid electrolyte is a block polymer, comprising soft segments and hard segments; The ternary cathode material layer accounts for 70-80% of the total thickness of the composite cathode.

2. The composite positive electrode according to claim 1, characterized in that, The solid electrolyte is polyurethane.

3. The composite positive electrode according to claim 2, characterized in that, The solid electrolyte is water-soluble polyurethane.

4. The composite positive electrode according to claim 1, characterized in that, The content ratio of the copolymer to the solid electrolyte is (1-5):(5-9).

5. The composite positive electrode according to claim 1, characterized in that, The protective layer also includes lithium salt.

6. The composite positive electrode according to claim 1, characterized in that, The ionic conductivity of the protective layer is (6.0-7.0)×10⁻⁶. -5 S·cm -1 .

7. The composite positive electrode according to claim 1, characterized in that, The ternary cathode material layer also includes a binder and a conductive agent.

8. A lithium-ion battery, characterized in that, It includes a composite positive electrode, a negative electrode, and a separator disposed between the composite positive electrode and the negative electrode as described in any one of claims 1 to 7.

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