Positive pole piece and preparation method thereof, diaphragm-free battery and battery

Abstract

The invention discloses a positive pole piece and a preparation method thereof, a diaphragm-free battery and a battery. The positive pole piece comprises a positive pole current collector and a positive pole active material layer arranged on at least one side of the positive pole current collector, the positive pole active material layer comprises a polymer, and the polymer is formed by polymerizing at least one of small molecules of the following raw material components: vinylethylene carbonate, vinylene carbonate, 2, 3, 4-trimethyl-1, 3-pentanedione, 2, 3, 4-trimethyl-1, 3-pentanedione and 2, 3, 4-trimethyl-1, 3-pentanedione. The adhesive is prepared from 2, 4-hexadienoic acid, allyl trifluoroacetate, diethyl allylmalonate, allyl methacrylate, allyl chloroformate, allyl phenylacetate, allyl acetate, allyl 4-hydroxybenzoate and allyl phenoxyacetate. The adhesive is prepared from the following raw materials: 1, 4-hexadienoic acid, allyl trifluoroacetate, diethyl allylmalonate, allyl methacrylate, allyl chloroformate, allyl phenylacetate, allyl acetate, allyl 4-hydroxybenzoate and allyl phenoxyacetate. The positive pole piece provided by the invention comprises the polymer, so that the interface impedance can be reduced, and the rate capability of the battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a positive electrode sheet and its preparation method, a battery, and a membrane-free battery. Background Technology

[0002] With the ever-growing energy demands of the consumer electronics and electric vehicle markets, there is an urgent need to develop energy storage devices with sustainable high energy density and high safety. Among all energy storage devices, lithium batteries have been widely studied due to their excellent reversible capacity. However, traditional lithium batteries use PE or PP separators, which have poor thermal stability, are prone to shrinkage at high temperatures causing short circuits, and are not resistant to lithium dendrite penetration.

[0003] Solid-state and semi-solid-state electrolytes have advantages such as high temperature resistance and resistance to lithium dendrite penetration, and are considered the most promising direction for improving the safety performance of lithium batteries in the future. However, due to the introduction of solid-state or semi-solid-state electrolytes, there will be uneven point contact at the solid-solid contact interface between the electrode active material and the solid electrolyte layer, resulting in large interfacial impedance or polarization, which leads to reduced interface stability and thus reduces the cycle stability and rate performance of the battery.

[0004] The related technology utilizes a method for preparing lithium-ion battery electrodes containing an interface-stabilizing polymer material and its application in solid-state lithium-ion batteries. The interface-stabilizing polymer material is polyvinyl carbonate (PVC) or a copolymer thereof. The polymer is obtained by bulk polymerization of monomers initiated by free radicals. The interface-stabilizing polymer material can form a coating film on the electrode surface, effectively suppressing the damage to the electrode material and the decomposition of the solid electrolyte on the positive and negative electrode surfaces during charging and discharging. Simultaneously, this polymer material can form a stable protective layer on the lithium metal surface, inhibiting the growth of lithium dendrites, thereby improving the cycle performance of the solid-state lithium-ion battery. However, using PVC or the block copolymer containing VC units described in the patent directly with lithium salt as the solid electrolyte layer may result in problems such as hardness and low ionic conductivity, leading to poor rate performance of the battery. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a positive electrode sheet and its preparation method, a membrane-free battery, and a battery, wherein the positive electrode sheet comprises a polymer, which can reduce interfacial impedance and improve the rate performance of the battery.

[0006] In a first aspect, the present invention provides a positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising a polymer formed by polymerization of at least one of the following raw material components:

[0007] Ethylene carbonate, vinylene carbonate, 2,4-hexadienoic acid, allyl trifluoroacetate, diethyl allyl malonate, allyl methacrylate, allyl chloroformate, allyl phenylacetate, allyl acetate, allyl 4-hydroxybenzoate, and allyl phenoxyacetate.

[0008] According to the above embodiments of the present invention, the positive electrode active material layer comprises a polymer, which is formed by the polymerization of at least one of the small molecules. The small molecules can be uniformly polymerized around the positive electrode active material to form a flexible interface layer. On the one hand, the flexible interface layer has high lithium-ion dissociation capability and high ionic conductivity, which can effectively alleviate the polarization caused by the agglomeration of positive electrode active material particles and effectively reduce the overall interface impedance of the electrode. On the other hand, the flexible interface layer formed by the polymer can effectively contact the subsequent solid electrolyte layer or semi-solid electrolyte layer, reduce the solid-solid interface impedance, and the abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution and alleviate the structural stress changes caused by phase transition, thereby improving the electrochemical performance of the electrode and improving the rate performance of the battery.

[0009] In addition, the method for preparing the positive electrode sheet according to the above embodiments of the present invention may also have the following additional technical features:

[0010] In some embodiments of the present invention, the degree of polymerization of the polymer is 10-10. 5 This can improve the rate performance of the battery.

[0011] In some embodiments of the present invention, the positive electrode active material layer further includes the following raw material components: crosslinking agent, initiator, binder, positive electrode active material, and conductive agent. This improves the rate performance of the battery.

[0012] In some embodiments of the present invention, based on the total mass of the effective components of the adhesive solution in the positive electrode active material layer, the mass percentage of each component is: small molecules 10%-90%, crosslinking agent 4.8%-50%, initiator 0.2%-1%, and binder 5%-80%; the effective components of the adhesive solution include small molecules, crosslinking agent, initiator, and binder. This can improve the rate performance of the battery.

[0013] In some embodiments of the present invention, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode active material is 60%-95%, and the mass percentage of the conductive agent is 1%-20%.

[0014] In some embodiments of the present invention, the crosslinking agent includes at least one selected from pentaerythritol triacrylate, triallyl isocyanurate, triallyl isocyanurate, and 2,5-dimethyl-2,5-di-tert-butylperoxide. This improves the rate performance of the battery.

[0015] In some embodiments of the present invention, the initiator includes at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diethylhexyl percarbonate, cumene hydroperoxide, tert-butyl hydroperoxide, dodecyl peroxide, tert-butyl peroxide, tert-butyl peroxybenzoate, diisopropyl peroxide, potassium persulfate, and ammonium persulfate. This improves the rate performance of the battery.

[0016] In some embodiments of the present invention, the binder includes at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, and polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer. This can improve the rate performance of the battery.

[0017] In some embodiments of the present invention, the positive electrode active material includes at least one of lithium iron phosphate, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium-rich manganese-based positive electrode materials, and lithium manganese iron phosphate. This can improve the rate performance of the battery.

[0018] In some embodiments of the present invention, the conductive agent includes at least one selected from conductive carbon black, carbon nanotubes, and graphene. This can improve the rate performance of the battery.

[0019] In some embodiments of the present invention, the raw material components of the positive electrode active material layer further include lithium salt and inorganic additives. This can improve the rate performance of the battery.

[0020] In some embodiments of the present invention, the lithium salt includes at least one of LiODFB, LiBOB, LiPO2F2, and LiNO3. This improves the rate performance of the battery.

[0021] In some embodiments of the present invention, the inorganic additive includes at least one selected from LLZO, LLZTO, LATP, TiO2, and SiO2. This can improve the rate performance of the battery.

[0022] In some embodiments of the present invention, based on the total mass of the effective components of the adhesive in the positive electrode active material layer, the mass ratio of the lithium salt and the inorganic additive is: lithium salt 0%-10% and inorganic additive 0%-3%; the effective components of the adhesive include small molecules, crosslinking agents, initiators, binders, lithium salt, and the additives. This can improve the rate performance of the battery.

[0023] In a second aspect, the present invention provides a method for preparing the positive electrode sheet described in the first aspect. The method includes: polymerizing small molecules in a slurry containing a positive electrode active material layer into a polymer, and then coating the polymer onto at least one side of a positive electrode current collector to obtain a positive electrode sheet; or, coating a slurry containing a small molecule positive electrode active material layer onto at least one side of a positive electrode current collector, and then polymerizing the small molecules to form a polymer to obtain a positive electrode sheet. Therefore, the positive electrode sheet prepared by the present invention can improve the rate performance of a battery.

[0024] In some embodiments of the present invention, the slurry of the positive electrode active material layer includes an organic solvent, which includes at least one selected from diethyl ether, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, malononitrile, succinic anionizer, glutaronitrile, adiponitrile, heptacyanide, octanoic anionizer, azelaic anionizer, and sebacate. Therefore, the prepared positive electrode sheet can improve the rate performance of the battery.

[0025] In some embodiments of the present invention, the slurry of the positive electrode active material layer further includes a crosslinking agent, an initiator, a binder, a positive electrode active material, and a conductive agent. Based on the total mass of the slurry of the positive electrode active material layer, the mass percentage of the effective components in the adhesive solution is 4%-39%, and the effective components in the adhesive solution include small molecules, a crosslinking agent, an initiator, and a binder. Therefore, the prepared positive electrode sheet can improve the rate performance of the battery.

[0026] In some embodiments of the present invention, the method includes: first heating a slurry containing a layer of small-molecule positive electrode active material to polymerize the small molecules into a polymer, then coating the polymer onto at least one side of a positive electrode current collector, and finally drying it to obtain a positive electrode sheet. The resulting positive electrode sheet can improve the rate performance of the battery.

[0027] In some embodiments of the present invention, the method includes: coating a slurry containing a layer of small-molecule positive electrode active material onto at least one side of a positive electrode current collector, subjecting it to a second heating process to polymerize the small molecules into a polymer, and then drying the polymer to obtain a positive electrode sheet. The resulting positive electrode sheet can improve the rate performance of the battery.

[0028] In some embodiments of the present invention, the temperature of the first heating is 55°C-80°C. Therefore, the prepared positive electrode sheet can improve the rate performance of the battery.

[0029] In some embodiments of the present invention, the first heating time is 0.5h-8h. Therefore, the prepared positive electrode sheet can improve the rate performance of the battery.

[0030] In some embodiments of the present invention, the temperature of the second heating is 55°C-80°C. Therefore, the prepared positive electrode sheet can improve the rate performance of the battery.

[0031] In some embodiments of the present invention, the second heating time is 0.5h-8h. Therefore, the prepared positive electrode sheet can improve the rate performance of the battery.

[0032] In a third aspect, the present invention provides a separatorless battery comprising the aforementioned positive electrode. Compared with the prior art, the battery containing this positive electrode exhibits superior rate performance.

[0033] In a fourth aspect, the present invention provides a battery. This battery includes a positive electrode sheet as described in the first aspect of the invention or a positive electrode sheet prepared using the method described in the second aspect, and the battery containing this positive electrode sheet exhibits superior rate performance compared to the prior art.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0035] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] Solid-state and semi-solid-state electrolytes have advantages such as high temperature resistance and resistance to lithium dendrite penetration, and are considered the most promising direction for improving the safety performance of lithium batteries in the future. However, due to the introduction of solid-state or semi-solid-state electrolytes, there will be uneven point contact at the solid-solid contact interface between the electrode active material and the solid electrolyte layer, resulting in large interfacial impedance or polarization, which leads to reduced interface stability and thus reduces the cycle stability and rate performance of the battery.

[0037] In view of this, in a first aspect, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising a polymer, the polymer being formed by polymerization of at least one of the following raw material components:

[0038] Ethylene carbonate, vinylene carbonate, 2,4-hexadienoic acid, allyl trifluoroacetate, diethyl allyl malonate, allyl methacrylate, allyl chloroformate, allyl phenylacetate, allyl acetate, allyl 4-hydroxybenzoate, and allyl phenoxyacetate.

[0039] The positive electrode sheet of this invention includes a positive electrode active material layer comprising a polymer. The polymer is formed by the polymerization of at least one of the above-mentioned small molecules. The small molecule monomers have the characteristic of promoting lithium-ion dissociation and transport, and the small molecules can uniformly polymerize around the positive electrode active material to form a flexible interface layer. On the one hand, the flexible interface layer has high lithium-ion dissociation capability and high ionic conductivity, effectively alleviating the polarization caused by the agglomeration of positive electrode active material particles, and can effectively reduce the overall interface impedance of the positive electrode sheet. On the other hand, the flexible interface layer formed by the polymer can effectively contact the solid electrolyte layer or the semi-solid electrolyte layer, reducing the solid-solid interface impedance. Moreover, the abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate the structural stress changes caused by phase transition, thereby improving the electrochemical performance of the electrode and improving the rate performance of the battery.

[0040] It is understood that the polymers formed by the aforementioned small molecules, including polymers formed by the polymerization of small molecules themselves, as well as copolymers formed by the polymerization of two or more small molecules, are all within the protection scope of this invention.

[0041] According to some embodiments of the present invention, the degree of polymerization of the polymer is 10-10. 5 For example, the degree of polymerization of the polymer can be 10, 100, or 10-1. 3 10 4 10 5 By controlling the degree of polymerization of the polymer within the above range, the flexible interface layer in the positive electrode active material layer has excellent lithium-ion dissociation ability and ionic conductivity, and can effectively contact the positive electrode active material layer with the solid electrolyte layer, reducing interface impedance and improving the rate performance of the battery.

[0042] According to some embodiments of the present invention, the positive electrode active material layer further includes the following raw material components: a crosslinking agent, an initiator, a binder, a positive electrode active material, and a conductive agent. Specifically, the crosslinking agent can form bridging bonds between the polymer molecular chains formed by the above-mentioned small molecules, the initiator can cause the small molecules to polymerize or copolymerize, the binder can ensure that the positive electrode active material and the polymer do not detach from the positive electrode sheet, and the conductive agent can ensure the conductivity.

[0043] Specifically, the positive electrode active material layer uses the above-mentioned raw material components, directly mixing small molecules, crosslinking agents, and initiators with the components of the positive electrode active material layer. The small molecule monomers have stronger van der Waals interactions with the surface of the positive electrode active material, which can be better and more uniformly dispersed around the positive electrode active material particles. After in-situ polymerization, a flexible composite interface coating layer (flexible interface layer) with high lithium-ion dissociation capability and high ionic conductivity is formed on the surface of the positive electrode active material, effectively alleviating the polarization caused by the agglomeration of positive electrode active material particles. The abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate structural stress changes caused by phase transition, thereby improving the electrochemical performance of the electrode. It also forms a good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery.

[0044] According to some embodiments of the present invention, based on the total mass of the effective components of the adhesive in the positive electrode active material layer, the mass percentage of each component is as follows:

[0045] The adhesive consists of 10%-90% small molecules, 4.8%-50% crosslinking agents, 0.2%-1% initiators, 5%-80% binders, 60%-95% positive electrode active materials, and 1%-20% conductive agents; the effective components of the adhesive include small molecules, crosslinking agents, initiators, and binders.

[0046] As examples, the mass percentage of small molecules can be 10%, 30%, 50%, 70%, 90%, etc.; the mass percentage of crosslinking agents can be 10%, 20%, 30%, 40%, 50%, etc.; the mass percentage of initiators can be 0.2%, 0.4%, 0.5%, 0.7%, 0.9%, 1%, etc.; the mass percentage of binders can be 5%, 10%, 30%, 50%, 70%, 80%, etc.; the mass percentage of positive electrode active materials can be 60%, 70%, 80%, 90%, 95%, etc.; and the mass percentage of conductive agents can be 1%, 5%, 10%, 15%, 20%, etc.

[0047] Specifically, by controlling the mass ratio of each raw material component in the positive electrode active material layer within the above range, the decrease in battery energy density caused by insufficient positive electrode active material can be reduced, as can the decrease in conductivity and wettability of the positive electrode sheet caused by excessive positive electrode active material. Furthermore, the decrease in conductivity and rate performance of the positive electrode sheet caused by insufficient conductive agent can be reduced, as can the decrease in battery energy density caused by excessive conductive agent.

[0048] According to some embodiments of the present invention, the crosslinking agent includes at least one of pentaerythritol triacrylate, triallyl isocyanurate, triallyl isocyanurate, and 2,5-dimethyl-2,5-di-tert-butylperoxide. Using at least one of the above substances as a crosslinking agent, under heating conditions, the polymer chains can be crosslinked, which can improve the various properties of the obtained polymer, improve the stability of the positive electrode active material layer and the effective contact between it and the solid electrolyte, and improve the rate performance of the battery.

[0049] According to some embodiments of the present invention, the initiator includes at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diethylhexyl percarbonate, cumene hydroperoxide, tert-butyl hydroperoxide, dodecyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyvalerate, diisopropyl peroxide, potassium persulfate, and ammonium persulfate. Under heating conditions, the above initiators can initiate in-situ polymerization of small molecules to form a flexible composite interface coating layer (flexible interface layer) with high lithium-ion dissociation capacity and high ionic conductivity on the surface of the positive electrode active material, effectively alleviating the polarization caused by particle agglomeration of the positive electrode active material; the abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate structural stress changes caused by phase transition, thereby improving the electrochemical performance of the electrode; and form good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery.

[0050] According to some embodiments of the present invention, the binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, and polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer. The above-mentioned binder has good bonding effect and can ensure that the positive electrode active material and polymer do not fall off from the positive electrode sheet.

[0051] According to some embodiments of the present invention, the positive electrode active material includes at least one of lithium iron phosphate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese-based positive electrode material, and lithium manganese iron phosphate.

[0052] According to some embodiments of the present invention, the conductive agent includes at least one selected from conductive carbon black, carbon nanotubes, and graphene. The aforementioned conductive agent can improve the conductivity of the positive electrode and enhance the rate performance of the battery.

[0053] According to some embodiments of the present invention, the raw material components of the positive electrode active material layer further include lithium salt and inorganic additives. The role of lithium salt is mainly in all-solid-state batteries. Since all-solid-state batteries do not have electrolyte and cannot wet the positive electrode active material, additional lithium salt needs to be added to the positive electrode active material to form a complete lithium-ion migration circuit. The role of inorganic additives is mainly twofold: first, they can improve the lithium-ion migration capability of the solid electrolyte system by changing the lithium-ion migration mechanism in the solid electrolyte; second, they can play a role in more efficiently constructing lithium-ion conduction circuits for active inorganic fillers (LLZO, LLZTO, LATP).

[0054] According to some embodiments of the present invention, the lithium salt includes at least one of LiODFB (lithium difluorooxalate borate), LiBOB (lithium dioxalate borate), LiPO2F2, and LiNO3. The above lithium salts are used in all-solid-state batteries to form a complete lithium-ion migration circuit and improve the rate performance of the battery.

[0055] According to some embodiments of the present invention, the inorganic additives include LLZO (lithium lanthanum zirconium oxide) and (lithium lanthanum zirconium tantalum oxide Li... 6.5 La3Zr 1.5 Ta 0.5 O 12 LATP (lithium aluminum titanium phosphate Li) 1.5 Al 0.5 Ti 1.5 At least one of (PO4)3), TiO2, and SiO2. The above-mentioned inorganic additives can further enhance the lithium-ion migration capability of the solid electrolyte system and ensure that the inorganic filler forms a lithium-ion conduction circuit, thereby improving the rate performance of the battery.

[0056] According to some embodiments of the present invention, based on the total mass of the effective components of the adhesive in the positive electrode active material layer, the mass ratio of the lithium salt and the inorganic additive is: 0%-10% lithium salt and 0%-3% inorganic additive; the effective components of the adhesive include small molecules, crosslinking agents, initiators, binders, lithium salt, and the additives. As an example, the mass ratio of lithium salt can be 0%, 2%, 4%, 5%, 7%, 10%, etc., and the mass ratio of inorganic additives can be 0%, 1%, 3%, etc. When this type of electrode is used in all-solid-state batteries, lithium salt is essential, and the addition of inorganic additives can improve the electrochemical performance of the all-solid-state battery.

[0057] In a second aspect of the invention, a method for preparing the positive electrode sheet described in the first aspect is provided, the method comprising:

[0058] S1. The small molecules in the slurry containing the positive electrode active material layer are polymerized into a polymer, which is then coated onto at least one side of the positive electrode current collector to obtain a positive electrode sheet; or,

[0059] A slurry containing a layer of small-molecule positive electrode active material is applied to at least one side of a positive electrode current collector, and the small molecules are polymerized to form a polymer to obtain a positive electrode sheet.

[0060] Specifically, small polymer monomers with lithium-ion dissociation and transport properties are used in combination with crosslinking agents (and initiators, etc.) dissolved in organic solvents, and binders are added to ensure bonding effect. This mixture is used directly as a slurry for the positive electrode active material layer. Thermal initiation and in-situ polymerization are carried out during the mixing or coating drying stage. Compared with directly adding the above polymers, the small monomers have stronger van der Waals interactions with the surface of the positive electrode active material, which can be better and more uniformly dispersed around the positive electrode active material particles. After in-situ polymerization, a flexible composite interface coating layer with high lithium-ion dissociation capacity and high ionic conductivity is formed on the surface of the positive electrode active material, which effectively alleviates the polarization caused by the agglomeration of positive electrode active material particles. The abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution and alleviate structural stress changes caused by phase transition, thereby improving the electrochemical performance of the electrode. It also forms a good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery.

[0061] It is understood that, in the embodiments of the present invention, a slurry containing a positive electrode active material layer of small molecules may be first applied to at least one side of the positive electrode current collector, and then the small molecules may be polymerized to form a polymer; alternatively, the small molecules may be polymerized to form a polymer first, and then a slurry containing a positive electrode active material layer of the polymer formed by the small molecules may be applied to at least one side of the positive electrode current collector. Both preparation methods are within the scope of protection of this application.

[0062] According to some embodiments of the present invention, the slurry of the positive electrode active material layer includes an organic solvent, which includes at least one selected from diethyl ether, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, malononitrile, succinic anionizer, glutaronitrile, adiponitrile, heptacyanide, octanoic anionizer, azelaic anionizer, and sebacate. The above-mentioned organic solvents have good dispersibility and stability, and can be used to prepare a uniform positive electrode active material layer.

[0063] According to some embodiments of the present invention, the slurry of the positive electrode active material layer further includes a crosslinking agent, an initiator, a binder, a positive electrode active material, and a conductive agent. Based on the total mass of the slurry of the positive electrode active material layer, the mass percentage of the effective adhesive component is 4%-39%. The effective adhesive component includes small molecules, a crosslinking agent, an initiator, and a binder. For example, based on the total mass of the slurry of the positive electrode active material layer, the mass percentage of the effective adhesive component can be 4%, 10%, 20%, 30%, 39%, etc. Controlling the mass percentage of the effective adhesive component in the slurry of the positive electrode active material layer within the above range can reduce the decrease in electrode peeling force caused by insufficient effective adhesive component, ensure low interfacial impedance, and also ensure the conductivity of the electrode and the energy density of the battery.

[0064] It is understandable that in the slurry of the positive electrode active material layer, when the raw materials of the positive electrode active material layer also include lithium salt and inorganic additives, the effective components of the adhesive also include lithium salt and inorganic additives.

[0065] According to some embodiments of the present invention, step S1 includes:

[0066] S11. The slurry containing a small molecule positive active material layer is heated to polymerize the small molecules to form a polymer, which is then coated on at least one side of the positive current collector and dried to obtain a positive electrode sheet.

[0067] This step first polymerizes small molecules through heating, then coats the polymer-containing slurry onto the positive electrode current collector. Compared to directly adding the polymer, the small molecule monomers have stronger van der Waals interactions with the surface of the positive electrode active material, allowing for better and more uniform dispersion around the positive electrode active material particles. After in-situ polymerization, a flexible composite interface coating layer with high lithium-ion dissociation capacity and high ionic conductivity is formed on the surface of the positive electrode active material, effectively alleviating polarization caused by particle agglomeration. The abundant hydrogen bonds in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate structural stress changes caused by phase transitions, thereby improving the electrochemical performance of the electrode. Furthermore, it forms a good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery.

[0068] According to some embodiments of the present invention, the temperature of the first heating is 55°C-80°C. For example, the temperature of the first heating can be 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc. Specifically, by controlling the temperature of the first heating within the above range, the above-mentioned small molecule polymerization reaction can be controlled, thereby achieving control over the degree of polymerization of the polymer. This results in the flexible interface layer in the positive electrode active material layer having excellent lithium-ion dissociation ability and ionic conductivity, and also allows the positive electrode active material layer to effectively contact the solid electrolyte layer, reducing interface impedance and improving the rate performance of the battery.

[0069] According to some embodiments of the present invention, the first heating time is 0.5h-8h. For example, it can be 0.5h, 1h, 3h, 5h, 7h, 8h, etc. Controlling the first heating time within the above range can control the above-mentioned small molecule polymerization reaction, thereby achieving control over the degree of polymerization of the polymer, so that the polymer has a suitable degree of polymerization, and the flexible interface layer in the positive electrode active material layer has excellent lithium-ion dissociation ability and ionic conductivity, and can effectively contact the positive electrode active material layer with the solid electrolyte layer, reduce interface impedance, and improve the rate performance of the battery.

[0070] According to other embodiments of the present invention, step S1 includes:

[0071] S12. A slurry containing a small molecule positive electrode active material layer is applied to at least one side of the positive electrode current collector, and then heated a second time to polymerize the small molecules into a polymer and dry it to obtain a positive electrode sheet.

[0072] This step first involves coating a slurry containing small molecules onto the positive electrode current collector, and then heating it to polymerize the small molecules. Compared to directly adding the polymer, the small molecule monomers have stronger van der Waals interactions with the surface of the positive electrode active material, allowing for better and more uniform dispersion around the positive electrode active material particles. After in-situ polymerization, a flexible composite interface coating layer with high lithium-ion dissociation capability and high ionic conductivity is formed on the surface of the positive electrode active material, effectively alleviating the polarization caused by the agglomeration of positive electrode active material particles. The abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate structural stress changes caused by phase transitions, thereby improving the electrochemical performance of the electrode. Furthermore, it forms a good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery.

[0073] It is understood that steps S11 and S12 are parallel technical solutions. In actual operation, only step S11 or only step S12 can be used.

[0074] According to some embodiments of the present invention, the temperature of the second heating is 55°C-80°C. For example, the temperature of the second heating can be 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc. Specifically, by controlling the temperature of the second heating within the above range, the above-mentioned small molecule polymerization reaction can be controlled, thereby achieving control over the degree of polymerization of the polymer. This results in the flexible interface layer in the positive electrode active material layer having excellent lithium-ion dissociation ability and ionic conductivity, and also allows the positive electrode active material layer to effectively contact the solid electrolyte layer, reducing interface impedance and improving the rate performance of the battery.

[0075] According to some embodiments of the present invention, the second heating time is 0.5h-8h. For example, it can be 0.5h, 1h, 3h, 5h, 7h, 8h, etc. By controlling the second heating time within the above range, the above-mentioned small molecule polymerization reaction can be controlled, thereby achieving control over the degree of polymerization of the polymer. This allows the polymer to have a suitable degree of polymerization, resulting in the flexible interface layer in the positive electrode active material layer having excellent lithium-ion dissociation ability and ionic conductivity. Furthermore, it allows the positive electrode active material layer to effectively contact the solid electrolyte layer, reducing interface impedance and improving the rate performance of the battery.

[0076] In summary, in this embodiment of the invention, a pre-mixing followed by polymerization method is adopted during the preparation of the positive electrode sheet. Small molecule monomers are effectively dispersed around the positive electrode active material particles and then uniformly polymerized to form a flexible coating layer, which can effectively reduce the overall interfacial impedance of the positive electrode sheet. This method for preparing the positive electrode sheet is compatible with existing battery coating processes and will not significantly reduce production capacity. The prepared positive electrode active material layer contains a flexible interface layer, which can effectively contact the subsequent solid electrolyte layer, reducing solid-solid interface impedance. Furthermore, the abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate structural stress changes caused by phase transitions, thereby improving the electrochemical performance of the electrode and the rate performance of the battery.

[0077] In a third aspect, this invention proposes a separatorless battery, comprising the aforementioned positive electrode sheet or a positive electrode sheet prepared using the method described above. A separatorless battery is a battery that replaces the traditional separator with a solid electrolyte. It exhibits extremely high thermal stability and effectively suppresses lithium dendrite growth during reversible charge-discharge processes, significantly improving battery safety. Given that separatorless batteries often exhibit uneven point contact at the solid-solid interface between the positive electrode active material layer and the solid electrolyte layer, leading to significant interfacial impedance or polarization, this application demonstrates even better performance in separatorless batteries.

[0078] In some embodiments of the present invention, the membraneless battery further includes an electrolyte.

[0079] In some embodiments of the present invention, the electrolyte comprises a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium trifluoromethanesulfonate.

[0080] In some embodiments of the present invention, the membrane-free battery includes a solid electrolyte, which comprises inorganic particles, including LLZO (lithium lanthanum zirconium oxide) and LLZTO (lithium lanthanum zirconium tantalum oxide). 6.5 La3Zr 1.5 Ta 0.5 O12 LATP (lithium aluminum titanium phosphate Li) 1.5 Al 0.5 Ti 1.5 (PO4)3), LAGP (lithium aluminum germanium phosphate Li) 1.5 Al 0.5 Ge 1.5 (PO4)3), LLTO (lithium lanthanum tantalum oxide Li) 0.33 La 0.56 At least one of TiO3, SiO2, TiO2, Al2O3, and BN.

[0081] In a fourth aspect, the present invention provides a battery comprising the positive electrode sheet described in the first aspect or a positive electrode sheet prepared using the method described in the second aspect. According to embodiments of the present invention, compared with the prior art, in this battery, after in-situ polymerization of small molecules, a flexible composite interface coating layer with high lithium-ion dissociation capability and high ionic conductivity is formed on the surface of the positive electrode active material, effectively alleviating polarization caused by particle agglomeration of the positive electrode active material; the abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition, transition metal dissolution, and alleviate structural stress changes caused by phase transition, thereby improving the electrochemical performance of the electrode; and it forms good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery. It should be noted that the features and advantages described above for the positive electrode sheet and its preparation method also apply to this battery, and will not be repeated here.

[0082] In some embodiments of the present invention, the battery includes at least one of a lithium-ion battery, a lithium metal battery, a lithium-sulfur battery, a lithium-ion solid-state battery, and a membrane-free battery. Thus, the positive electrode of the battery contains a flexible interface layer, which has high lithium-ion dissociation capability and high ionic conductivity, effectively mitigating polarization caused by the agglomeration of positive electrode active material particles. The abundant hydrogen bonding in the flexible interface layer can hinder electrolyte decomposition and transition metal dissolution, and alleviate structural stress changes caused by phase transitions, improving the electrochemical performance of the electrode. Furthermore, it forms a good solid-solid interface contact with the solid electrolyte layer, effectively reducing interface impedance and improving the rate performance of the battery.

[0083] In some embodiments of the present invention, the battery further includes a negative electrode sheet, which also includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer including a negative active material.

[0084] In some embodiments of the present invention, the negative electrode active material is at least one of graphite, silicon oxide, silicon carbon, lithium titanate, or metallic lithium.

[0085] In some embodiments of the present invention, the negative electrode active material layer further includes a binder and a conductive agent, wherein the conductive agent includes at least one selected from conductive carbon black, carbon nanotubes, and graphene. The binder includes at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyethylene oxide, and polyvinylidene fluoride-chlorotrifluoroethylene copolymer.

[0086] In some embodiments of the present invention, the negative electrode sheet is prepared in the following manner:

[0087] The components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent to form a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0088] In some embodiments of the present invention, the solvent includes at least one selected from diethyl ether, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, malononitrile, succinic anionyl nitrile, adiponitrile, heptacyanide, octanoic anionyl nitrile, azelaic anionyl nitrile, and sebacate.

[0089] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0090] Example 1

[0091] 1. Preparation of positive electrode sheet with flexible interface layer:

[0092] 8g of small molecule vinylene carbonate, 1g of crosslinking agent pentaerythritol triacrylate, 1g of binder PVDF (polyvinylidene fluoride) and 0.045g of initiator AIBN (azobisisobutyronitrile) were dissolved in organic solvent NMP (N-methylpyrrolidone) and stirred to form a homogeneous solution. 39g of positive electrode active material LiFePO4 and 1g of conductive agent conductive carbon black were added to form a uniform slurry. The stirring temperature (the temperature of the first heating) was set to 70℃ and kept at that temperature (the time of the first heating) for 2h. The slurry was then coated onto aluminum foil and dried to form a positive electrode sheet with a flexible interface layer.

[0093] Based on the total mass of the effective components of the positive electrode active material layer adhesive, the mass percentages of each component are as follows: small molecules 79.64%, crosslinking agent 9.96%, binder 9.96%, and initiator 0.44%.

[0094] 2. Preparation of composite positive electrode:

[0095] LLZO, PVDF, and LiTFSI (lithium bis(trifluoromethanesulfonylimide)) were dispersed in DMF in a ratio of 6:3:1 to achieve a solid content of 50%. The dispersion was then introduced onto the positive electrode sheet prepared in step 1 by ultrasonic spraying, dried, and rolled to obtain a composite positive electrode sheet.

[0096] 3-1 (Solid-state battery negative electrode, corresponding to Table 1), the negative electrode uses lithium metal sheet, step 4 is omitted. All-solid-state batteries are tested using coin cells.

[0097] 3-2 (Preparation of semi-solid negative electrode, see Table 2 for examples): Preparation of negative electrode sheet: Graphite, conductive carbon, CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber) were dissolved in water at a mass percentage of 95:3:1:1 to prepare a negative electrode slurry. This slurry was then coated onto a copper current collector, dried at 100°C, and rolled. It was then matched with the positive electrode material to prepare a 2Ah soft-pack battery.

[0098] 4. The composite positive and negative electrode sheets are stacked, tabs are welded on, and the cells are encapsulated in an aluminum-plastic film. Then, electrolyte injection and vacuum sealing are performed, followed by formation and capacity testing to obtain a membrane-free battery. The electrolyte injection volume is 1.1 g / Ah.

[0099] Example 2

[0100] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode sheet, 8g of vinylene carbonate is replaced with 8g of ethylene ethylene carbonate.

[0101] Example 3

[0102] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode sheet, 8g of vinylene carbonate is replaced with 8g of allyl phenylacetate.

[0103] Example 4

[0104] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode sheet, 1g of pentaerythritol triacrylate is replaced with 1g of triallyl isocyanurate.

[0105] Example 5

[0106] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode, 8g of vinylene carbonate is replaced with 7g of vinylene carbonate, 0.5g of inorganic additive LLZO and 0.5g of lithium salt LiODFB.

[0107] Based on the total mass of the effective components of the positive electrode active material layer adhesive, the mass percentage of each component is as follows: small molecules 69.69%, crosslinking agent 9.96%, binder 9.96%, initiator 0.44%, inorganic additives 4.98%, and lithium salt 4.98%.

[0108] Example 6

[0109] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode sheet, the positive electrode slurry stirring step is not heated, and in the positive electrode slurry coating and drying stage, the drying temperature (second heating temperature) is set to 75°C and the holding time (second heating time) is 2h.

[0110] Example 7

[0111] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode sheet, 8g of vinylene carbonate is replaced with 8g of allyl trifluoroacetate.

[0112] Example 8

[0113] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode sheet, 8g of vinylene carbonate is replaced with 4g of 2,4-hexadienoic acid and 4g of diethyl allyl malonate.

[0114] Example 9

[0115] The process is basically the same as in Example 1, except that the stirring temperature is set to 55°C and the temperature is maintained for 8 hours.

[0116] Example 10

[0117] It is basically the same as Example 1, except that the stirring temperature is set to 80°C and kept warm for 0.5 hours.

[0118] Comparative Example 1

[0119] The method is basically the same as in Example 1, except that the crosslinking agent is replaced with the same mass of vinylene carbonate in the preparation method of the composite positive electrode sheet.

[0120] Comparative Example 2

[0121] The method is basically the same as in Example 1, except that no small molecules, crosslinking agents and initiators are added in the preparation method of the composite positive electrode sheet.

[0122] Comparative Example 3

[0123] The method is basically the same as in Example 1, except that in the preparation method of the composite positive electrode, 8g of vinylene carbonate is replaced with less than 8g of small molecules with the following structural formula:

[0124]

[0125] Testing and Analysis

[0126] The membrane-free battery prepared above was subjected to charge-discharge rate performance tests at room temperature: the battery was tested at rates of 0.33C, 0.5C, 1C and 2C.

[0127] The test results are shown in Table 1.

[0128] Table 1 (All Solid-State Batteries)

[0129]

[0130] Table 2 (Semi-solid membrane-free batteries)

[0131]

[0132]

[0133] As shown in Table 1, in Examples 1-10 of this application, the addition of small molecules to the positive electrode active material layer to form a polymer can significantly improve the rate performance of the battery containing it. Comparative Examples 1-3 are not within the scope of this application, and their battery rate performance is significantly reduced. Therefore, the technical solution of this application can significantly improve the rate performance of the battery.

[0134] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "some implementations," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0135] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a polymer, which is formed by the polymerization of at least one of the following raw material components: Ethylene carbonate, vinylene carbonate, 2,4-hexadienoic acid, allyl trifluoroacetate, diethyl allyl malonate, allyl methacrylate, allyl chloroformate, allyl phenylacetate, allyl acetate, allyl 4-hydroxybenzoate, and allyl phenoxyacetate.

2. The positive electrode sheet according to claim 1, characterized in that, The degree of polymerization of the polymer is 10-10. 5 .

3. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material layer also includes the following raw material components: Crosslinking agents, initiators, binders, positive electrode active materials, and conductive agents.

4. The positive electrode sheet according to claim 3, characterized in that, Based on the total mass of the effective components of the adhesive solution in the positive electrode active material layer, the mass percentage of each component is as follows: The adhesive consists of 10%-90% small molecules, 4.8%-50% crosslinking agents, 0.2%-1% initiators, and 5%-80% binders. The effective components of the adhesive include small molecules, crosslinking agents, initiators, and binders. Optionally, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode active material is 60%-95%, and the mass percentage of the conductive agent is 1%-20%.

5. The positive electrode sheet according to claim 3, characterized in that, The crosslinking agent includes at least one of pentaerythritol triacrylate, triallyl isocyanurate, triallyl isocyanurate and 2,5-dimethyl-2,5-di-tert-butylperoxide. Preferably, the initiator includes at least one selected from azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, diethylhexyl peroxide dicarbonate, cumene hydroperoxide, tert-butyl hydroperoxide, dodecyl peroxide, tert-butyl peroxide, tert-butyl peroxybenzoate, diisopropyl peroxide, potassium persulfate, and ammonium persulfate. Preferably, the adhesive comprises at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, and polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer; Preferably, the positive electrode active material includes at least one of lithium iron phosphate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese-based positive electrode material, and lithium manganese iron phosphate; Preferably, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene.

6. The positive electrode sheet according to any one of claims 3-5, characterized in that, The raw material components of the positive electrode active material layer also include lithium salt and inorganic additives; Preferably, the lithium salt includes at least one of LiODFB, LiBOB, LiPO2F2, and LiNO3; Preferably, the inorganic additive includes at least one of LLZO, LLZTO, LATP, TiO2 and SiO2.

7. The positive electrode sheet according to claim 6, characterized in that, Based on the total mass of the effective components of the adhesive in the positive electrode active material layer, the mass ratio of the lithium salt and the inorganic additive is: lithium salt 0%-10% and inorganic additive 0%-3%. The effective components of the adhesive include small molecules, crosslinking agents, initiators, binders, lithium salts, and inorganic additives.

8. A method for preparing a positive electrode sheet according to any one of claims 1-7, characterized in that, include: The small molecules in the slurry containing the positive electrode active material layer are polymerized into a polymer, which is then coated onto at least one side of the positive electrode current collector to obtain a positive electrode sheet; or, A slurry containing a layer of small-molecule positive electrode active material is applied to at least one side of a positive electrode current collector, and the small molecules are polymerized to form a polymer to obtain a positive electrode sheet.

9. The method according to claim 8, characterized in that, The slurry of the positive electrode active material layer includes an organic solvent, which includes at least one of diethyl ether, ethanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, malononitrile, succinic anionyl nitrile, glutaronitrile, adiponitrile, heptacyanide, octanoic anionyl nitrile, azelaic anionyl nitrile, and sebacate.

10. The method according to claim 8, characterized in that, The slurry of the positive electrode active material layer also includes a crosslinking agent, an initiator, a binder, a positive electrode active material, and a conductive agent. Based on the total mass of the slurry of the positive electrode active material layer, the mass ratio of the effective components of the adhesive is 4%-39%, and the effective components of the adhesive include small molecules, crosslinking agents, initiators, and binders.

11. The method according to claim 8 or 9, characterized in that, include: A slurry containing a layer of small-molecule positive electrode active material is first heated to polymerize the small molecules into a polymer, which is then coated onto at least one side of the positive electrode current collector and dried to obtain a positive electrode sheet; or, A slurry containing a layer of small-molecule positive electrode active material is applied to at least one side of the positive electrode current collector, and then subjected to a second heating process to polymerize the small molecules into a polymer and dry it to obtain a positive electrode sheet.

12. The method according to claim 11, characterized in that, The temperature of the first heating is 55℃-80℃; Preferably, the first heating time is 0.5h-8h; Preferably, the temperature of the second heating is 55℃-80℃; Preferably, the second heating time is 0.5h-8h.

13. A separatorless battery, characterized in that, The membraneless battery includes a positive electrode sheet according to any one of claims 1-7, or a positive electrode sheet prepared by any one of claims 8-12.

14. A battery, characterized in that, The battery includes a positive electrode sheet according to any one of claims 1-7, or a positive electrode sheet prepared by any one of claims 8-12.

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