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 first active material layer arranged on the surface of a current collector and a barrier layer. The first active material layer comprises a ternary material, and the ternary material is a lithium compound containing at least one of nickel, cobalt and manganese. The barrier layer comprises nanofibers and a solid electrolyte, and the nanofibers are uniformly dispersed in the barrier layer. The application can greatly improve the cycle performance of the battery, 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 in the electrolyte and migrate towards the negative electrode during the charge and discharge 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 first active material layer disposed on the surface of a current collector and a barrier layer;

[0009] The first active material layer includes a ternary material, which is a lithium compound containing at least one of the three metals: nickel, cobalt, and manganese.

[0010] In one specific embodiment, the molecular formula of the ternary material is Li(Ni) a Co b X c O2, where a+b+c=1, and X is selected from one of Mn or Al or a mixture thereof;

[0011] The barrier layer comprises nanofibers and a solid electrolyte, wherein the nanofibers are uniformly dispersed in the barrier layer;

[0012] Nanofibers can prevent the dissolution of metal ions from the composite cathode after long-term battery cycling.

[0013] The nanofibers include polyacrylonitrile fibers;

[0014] The solid electrolyte comprises a block polymer, which includes soft segments and hard segments, wherein the soft segments are composed of polyester or polyether polyol.

[0015] Preferably, the solid electrolyte is a gel electrolyte.

[0016] To further enhance the overall performance of the composite cathode in this application, the composite cathode of this application also includes at least one second active material layer.

[0017] In one specific embodiment, the second active material layer comprises lithium iron manganese phosphate, wherein the molecular formula of the lithium iron manganese phosphate is LiMn. d Fe 1-d PO4, where d is 0.4-0.6.

[0018] It is understood that the composite cathode of this application may include multiple first active material layers and second active material layers.

[0019] In one specific embodiment, the nanofibers comprise -NH2-grafted modified polyacrylonitrile fibers.

[0020] In one specific embodiment, the solid electrolyte is polyurethane.

[0021] In one specific embodiment, the solid electrolyte is a water-soluble polyurethane, and the water-soluble polyurethane and the polyacrylonitrile fiber are combined by dispersing the polymer solution after blending with the polyacrylonitrile fiber.

[0022] In one specific embodiment, the barrier layer further includes a lithium salt.

[0023] In one specific embodiment, the ionic conductivity of the barrier layer is (6.0-7.0)×10⁻⁶. -5 S·cm -1 Preferably, the ionic conductivity of the barrier layer is 6.6 × 10⁻⁶. -5 S·cm -1 .

[0024] In one specific embodiment, the first active material layer accounts for 70-80% of the total thickness of the composite positive electrode.

[0025] In one specific embodiment, the second active material layer accounts for 20-30% of the total thickness of the composite positive electrode.

[0026] In one specific embodiment, the first active material layer further includes a first binder and a first conductive agent.

[0027] In one specific embodiment, the second active material layer further includes a second binder and a second conductive agent.

[0028] 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 and / or solid electrolyte membrane disposed between the composite positive electrode and the negative electrode as described above.

[0029] In one specific embodiment, the lithium-ion battery further includes an electrolyte.

[0030] 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.

[0031] Beneficial effects:

[0032] The composite cathode and lithium-ion battery provided in this application include a composite cathode comprising at least one first active material layer and a barrier layer disposed on the surface of a current collector; the first active material layer comprises a ternary material, wherein the ternary material is a lithium compound containing at least one of nickel, cobalt, and manganese metals; the barrier layer comprises nanofibers and a solid electrolyte, wherein the nanofibers are uniformly dispersed in the barrier layer. 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

[0033] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0034] This application provides a composite positive electrode in one embodiment, comprising at least one active material layer disposed on the surface of a current collector and a barrier layer disposed on the surface of the active material layer. The composite positive electrode structure provided by this application significantly improves the cycle performance of the battery and substantially reduces the deposition of transition metals on the negative electrode.

[0035] The active substance layer includes a first active substance layer.

[0036] In one embodiment of this application, the first active material layer comprises a ternary material. Specifically, the ternary material refers to a lithium compound containing at least one of the three metals: nickel, cobalt, and manganese. Using a ternary material as the positive electrode active material helps to improve the overall energy density of the battery.

[0037] As a preferred example, in this embodiment, the molecular formula of the ternary material is Li(Ni) a Co b X c O2, where a+b+c=1, and X is selected from one of Mn or Al or a mixture thereof.

[0038] In this application, a barrier layer is provided on the surface of the active material layer to prevent metal ions in the ternary material from dissolving out of the positive electrode, thereby effectively solving the problems of capacity decay and metal ion deposition on the negative electrode in batteries made of ternary materials during long-term cycling.

[0039] In one embodiment of this application, the barrier layer comprises nanofibers and a solid electrolyte, wherein the nanofibers are uniformly dispersed in the barrier layer.

[0040] In a preferred embodiment of this application, the nanofibers comprise polyacrylonitrile fibers. Polyacrylonitrile fibers can effectively prevent metal ions from the ternary material from dissolving and entering the negative electrode during long-term cycling of the battery cell, thereby preventing capacity decay. Specifically, the polyacrylonitrile fibers can effectively adsorb transition metal ions. More specifically, the cyano groups of polyacrylonitrile can electrostatically attract transition metal ions.

[0041] More preferably, the nanofibers include -NH2-grafted modified polyacrylonitrile fibers, which can effectively enhance the adsorption capacity for transition metals.

[0042] For example, the content of nanofibers in the barrier layer is 0.1%-20%, preferably 0.5%-10%, and more preferably 1%-5%. If the content of nanofibers is too low, the barrier effect on transition metal ions is limited; if the content is too high, it is not conducive to improving the transport rate of lithium ions inside the battery.

[0043] It is understood that this application does not impose specific restrictions on nanofibers, and any nanofibers that can adsorb transition metal ions can be used as nanofibers in this application.

[0044] The nanofibers can be polymer nanofibers or inorganic compound nanofibers.

[0045] Polymers used to prepare polymer nanofibers include polyacrylonitrile (PAN), cellulose acetate, polyvinylidene fluoride (PVDF), polypropylene (PP), polyethersulfone (PES), and polysulfone (PSF).

[0046] Inorganic compounds used to prepare inorganic compound nanofibers include alumina, zirconium oxide, silicon dioxide, and titanium dioxide.

[0047] In one specific embodiment, the nanofibers have a porous structure.

[0048] When the nanofibers are polymer nanofibers, transition metal ions undergo electrostatic adsorption with the functional groups of the polymer and pore adsorption with the pores on the polymer nanofibers. When the nanofibers are inorganic compound nanofibers, transition metal ions are adsorbed by the pores of the inorganic compound nanofibers. The above are merely the applicant's possible speculations on the principle of the technical solution of this application and do not constitute a limitation on the scope of protection of this application.

[0049] In a preferred embodiment, the polymer nanofibers include functional groups such as cyano, amino, and thiol groups.

[0050] The barrier layer also includes a solid electrolyte, which can further improve the transport efficiency of lithium ions on the composite cathode.

[0051] Preferably, the solid electrolyte is a gel electrolyte.

[0052] In a preferred embodiment of this application, the solid electrolyte comprises a block polymer, including soft segments and hard segments. The soft segments are composed of polyester or polyether polyols. The hard segments are composed of aromatic hydrocarbons, exhibiting greater rigidity, while the soft segments are composed of aliphatic hydrocarbons, exhibiting greater flexibility. This results in the block copolymer possessing both rigidity and flexibility.

[0053] For example, in this embodiment, the solid electrolyte is polyurethane. Polyurethane has a special 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.

[0054] Preferably, in this embodiment of the application, the solid electrolyte is a water-soluble polyurethane, and the water-soluble polyurethane and the polyacrylonitrile fiber are combined by dispersing the polymer solution after blending with the polyacrylonitrile fiber.

[0055] Specifically, 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 lithium manganese iron phosphate is not sensitive to moisture. A water-based polyurethane solid electrolyte layer can be formed on the surface of lithium manganese iron phosphate by a simple method, and the preparation process has excellent environmental friendliness.

[0056] In one embodiment, when the solid electrolyte contained in the barrier layer is 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 anhydride, adiponitrile, fumaric acid, and combinations thereof.

[0057] In a preferred embodiment of this application, the barrier layer further includes a lithium salt.

[0058] Specifically, this application does not impose any particular limitation on the type of lithium salt contained in the polymer 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 barrier layer.

[0059] 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.

[0060] In one embodiment, the lithium salt content in the barrier 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.

[0061] In a preferred embodiment of this application, the ionic conductivity of the barrier layer is (6.0-7.0)×10⁻⁶. -5 S·cm⁻¹; for example, 6.0 × 10⁻¹ -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, which will not be listed one by one here.

[0062] Preferably, the ionic conductivity of the barrier layer is 6.6 × 10⁻⁶. -5 S·cm -1 .

[0063] To further enhance the safety performance of the composite cathode in this application, the composite cathode also includes a second active material layer.

[0064] Specifically, the composite cathode further includes at least one second active material layer.

[0065] In a preferred embodiment, the second active material layer is disposed on the side of the first active material layer away from the current collector.

[0066] In one embodiment of this application, the second active material layer comprises lithium iron manganese phosphate, wherein the molecular formula of the lithium iron manganese phosphate is LiMndFe. 1-d PO4, where d is 0.4-0.6, for example 0.4, 0.45, 0.5, 0.55 or 0.6, etc.

[0067] Specifically, lithium iron manganese phosphate is chosen for the second active material layer because this material offers higher safety performance. Lithium iron manganese phosphate can improve the battery's nail penetration test pass rate and, to some extent, can also block some transition metal ions. Lithium iron manganese phosphate is a novel phosphate-based lithium-ion battery cathode material formed by doping lithium iron phosphate with a certain proportion of manganese (Mn). Through manganese doping, the advantages of both iron and manganese can be effectively combined. Furthermore, manganese and iron are both located in the fourth period of the periodic table and are adjacent to each other, possessing similar ionic radii and some chemical properties; therefore, doping does not significantly affect the original structure. Compared to lithium iron phosphate, the high voltage characteristic of manganese gives lithium iron manganese phosphate a higher voltage platform, resulting in a higher energy density at the same specific capacity—10%-20% higher than lithium iron phosphate under the same conditions. It is understood that the composite cathode of this application may include multiple first and second active material layers. The number of first and second active material layers is not specifically limited here; users can set it according to their actual needs.

[0068] In a preferred embodiment, the thickness of the first active material layer is greater than the thickness of the second active material layer.

[0069] In a preferred embodiment of this application, the first active material layer further includes a first binder and a first conductive agent.

[0070] It is understood that the first binder is a substance used to bond the ternary material, the first conductive agent, 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 the first binder; any known type of binder can be used in the first active material layer.

[0071] Specifically, the first adhesive may comprise a mixture selected 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.

[0072] Conductive agents are mainly used to assist and improve the conductivity in secondary batteries. This application does not impose any particular limitations on the first conductive agent, as long as it has electronic conductivity without causing chemical changes. Specifically, the first 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 powder, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives. From the perspective of improving conductivity, carbon black is preferred.

[0073] In a preferred embodiment of this application, the amount of the first conductive agent in the first active 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%.

[0074] In a preferred embodiment of this application, the amount of the first binder in the first active 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%.

[0075] In a preferred embodiment of this application, the first active material layer accounts for 70-80% of the total thickness of the composite positive electrode. For example, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%, etc., which will not be listed exhaustively here.

[0076] 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 first active material layer, the second active material layer, and the barrier layer.

[0077] In a preferred embodiment of this application, the second active material layer further includes a second binder and a second conductive agent.

[0078] It is understood that the second binder is a substance used to bind the lithium manganese iron phosphate, the second conductive agent, and other components together. Without departing from the inventive concept of this application, this application also does not have any particular requirements on the type of the second binder; any known type of binder can be used in the second active material layer.

[0079] The second adhesive may be the same as or different from the first adhesive. In one embodiment, the second adhesive comprises a material selected 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.

[0080] This application also does not impose any particular limitations on the second conductive agent, as long as it has electronic conductivity without causing a chemical change. Specifically, the second conductive agent may be the same as or different from the first conductive agent. In one embodiment, the second 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 thermal cracking 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, and preferably includes carbon black from the perspective of improving conductivity.

[0081] In a preferred embodiment of this application, the amount of the second conductive agent in the second active 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%.

[0082] In a preferred embodiment of this application, the amount of the second binder in the second active 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%.

[0083] In a preferred embodiment of this application, the second active material layer accounts for 20-30% of the total thickness of the composite positive electrode. For example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, etc., which will not be listed exhaustively here.

[0084] It is understandable that the total thickness of the composite cathode here has the same meaning as the total thickness of the composite cathode mentioned above, neither of which includes the thickness of the current collector.

[0085] In one embodiment, the first active material layer and the second active material layer are obtained by coating with a corresponding positive electrode slurry, followed by drying and rolling.

[0086] 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:

[0087] S100: A first active material layer is coated on the surface of the current collector and dried once;

[0088] S200: A second active material layer is coated on the surface of the first active material layer formed after one drying, followed by a second drying.

[0089] S300: A barrier layer is coated on the surface of the second active material layer formed after secondary drying, followed by three drying cycles and pressing to obtain the positive electrode.

[0090] Preferably, the coating in steps S200 and S300 can be performed while the layers are not completely dry during the corresponding drying process, thereby improving the adhesion between the two layers.

[0091] 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 and / or a solid electrolyte membrane between the composite positive electrode and the negative electrode.

[0092] In a preferred embodiment of this application, the lithium-ion battery further includes an electrolyte.

[0093] 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.

[0094] 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).

[0095] 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.

[0096] 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.

[0097] 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)).

[0098] 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.

[0099] 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.

[0100] The following embodiments will be used to illustrate the present application and its effects in more detail.

[0101] Example 1

[0102] A composite positive electrode is provided, comprising a first active material disposed on the surface of a current collector, a second active material layer and a barrier layer disposed sequentially along a direction away from the first active material layer.

[0103] The first active material layer is composed of 96 wt% NCM811, 2 wt% super-P and 2 wt% PVDF;

[0104] The second active material layer consists of 96 wt% LiMn 0.5 Fe 0.5 PO4, 2wt% super Composed of P and 2wt% PVDF;

[0105] The barrier layer comprises 3 wt% polyacrylonitrile fiber, 87 wt% water-soluble polyurethane and 10 wt% lithium bis(trifluoromethanesulfonylimide) (LITFSI).

[0106] Example 2

[0107] A composite positive electrode is provided, which differs from Example 1 in that the barrier layer comprises 5 wt% polyacrylonitrile fiber, 85 wt% water-soluble polyurethane and 10 wt% lithium bis(trifluoromethanesulfonylimide) (LITFSI).

[0108] Comparative Example 1

[0109] A composite positive electrode is provided, comprising an active material layer disposed on the surface of a current collector, the active material layer being composed of 96 wt% NCM811, 2 wt% super-P and 2 wt% PVDF.

[0110] Comparative Example 2

[0111] A composite positive electrode is provided, comprising a first active material disposed on the surface of a current collector, and a second active material layer disposed on the first active material layer;

[0112] The first active material layer is composed of 96 wt% NCM811, 2 wt% super-P and 2 wt% PVDF;

[0113] The second active material layer consists of 96 wt% LiMn 0.5 Fe 0.5 PO4, 2wt% super It consists of P and 2wt% PVDF.

[0114] Comparative Example 3

[0115] A composite positive electrode is provided, comprising a first active material disposed on the surface of a current collector and a barrier layer disposed on the first active material layer;

[0116] The first active material layer is composed of 96 wt% NCM811, 2 wt% super-P and 2 wt% PVDF;

[0117] The barrier layer comprises 3 wt% polyacrylonitrile fiber, 87 wt% water-soluble polyurethane and 10 wt% lithium bis(trifluoromethanesulfonylimide) (LITFSI).

[0118] Comparative Example 4

[0119] A composite positive electrode is provided, comprising a first active material disposed on the surface of a current collector and a barrier layer disposed on the first active material layer;

[0120] The first active material layer is composed of 96 wt% NCM811, 2 wt% super-P and 2 wt% PVDF;

[0121] The barrier layer consists of 90 wt% water-soluble polyurethane and 10 wt% lithium bis(trifluoromethanesulfonylimide) (LITFSI).

[0122] 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, lithium manganese iron phosphate is from Zhongyue Chemical, ternary cathode material is from Dangsheng Technology; lithium bis(trifluoromethanesulfonylimide) (LITFSI) is from Sigma-Aldrich.

[0123] Battery manufacturing:

[0124] 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.

[0125] test:

[0126] 1. Cycle life test at room temperature with a cutoff of 80% capacity

[0127] (1) Charge at 1C to the termination voltage, cut-off current 0.05C, and let stand for 30 minutes;

[0128] (2) Discharge at 1C to the final discharge voltage, record the discharge capacity, and let stand for 30 minutes;

[0129] Loop (1) (2) The cycle life at room temperature up to 80% capacity was tested. The test results are shown in Table 1.

[0130] 2. Needle prick test

[0131] (1) Fully charge the battery;

[0132] (2) Use a φ3mm or φ5mm high temperature resistant steel needle (the cone angle of the needle tip is 45°~60°, the surface of the needle is smooth, free of rust, oxide layer and oil stains), and penetrate from the direction perpendicular to the electrode plate of the battery cell at a speed of (25±5)mm / s. The penetration position should be close to the geometric center of the pierced surface, and the steel needle stays in the battery cell.

[0133] (3) Observe for 1 hour.

[0134] Record the cell safety level; the test results are shown in Table 1.

[0135] 3. Regarding ICP testing

[0136] 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.

[0137] Table 1

[0138]

[0139] Comparative examples show that sequentially depositing a first active material layer, a second active material layer, and a barrier layer on the surface of the current collector helps improve battery safety and cycle performance, and reduces the deposition of transition metals on the negative electrode. Further comparisons of Examples 1-2 and 1-4 show that depositing a barrier layer containing polyacrylonitrile fibers on the surface of the active material layer allows the polyacrylonitrile fibers to effectively adsorb transition metal ions, thereby effectively preventing metal ions from the ternary material from dissolving and entering the negative electrode during long-term cycling, thus preventing capacity decay.

[0140] Furthermore, the lithium manganese iron phosphate layer, with its high safety performance, serves as a protective layer, enhancing battery safety while maintaining high energy density. Simultaneously, aqueous polyurethane, as the polymer matrix of the solid electrolyte, utilizes the soft segments of polyurethane to dissolve a large amount of lithium salt and exhibits good flexibility, providing excellent ion conductivity. Additionally, the abundant hydrogen-bonding groups in aqueous polyurethane provide the polymer electrolyte with excellent mechanical properties through strong hydrogen bonding. The aqueous polyurethane-based solid polymer electrolyte layer demonstrates good mechanical strength and thermal stability, further improving the cell's safety performance.

[0141] 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 positive electrode includes at least one first active material layer and a barrier layer sequentially disposed on the surface of the current collector; The first active material layer comprises a ternary material, wherein the molecular formula of the ternary material is Li(Ni) a Co b X c O2, where a+b+c=1, and X is selected from one of Mn or Al or a mixture thereof; The barrier layer comprises nanofibers and a solid electrolyte, wherein the nanofibers are uniformly dispersed in the barrier layer; The nanofibers include -NH2-grafted modified polyacrylonitrile fibers; The solid electrolyte includes a block polymer, which includes soft segments and hard segments, wherein the soft segments are composed of polyester or polyether polyol; The composite positive electrode further includes at least one second active material layer, which is disposed between the first active material layer and the barrier layer. The second active material layer comprises lithium manganese iron phosphate, wherein the molecular formula of lithium manganese iron phosphate is LiMn. d Fe 1-d PO4, where d is 0.4-0.

6.

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, and the water-soluble polyurethane and the polyacrylonitrile fiber are combined by dispersing the polymer solution after blending with the polyacrylonitrile fiber.

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

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

6. The composite positive electrode according to claim 1, characterized in that, The second active material layer accounts for 20-30% of the total thickness of the composite positive electrode.

7. The composite positive electrode according to claim 1, characterized in that, The first active material layer accounts for 70-80% of the total thickness of the composite positive electrode.

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

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