Positive pole piece, preparation method and application thereof and lithium ion battery

Abstract

The invention provides a positive pole piece, a preparation method and application thereof and a lithium ion battery. The positive pole piece comprises a current collector, and a transition layer and an active material layer which are sequentially arranged on the surface of the current collector, wherein the transition layer comprises a carrier layer, a reduction state heteropolyacid layer and an aluminum layer which are sequentially stacked, and the carrier layer is located between the current collector and the reduction state heteropolyacid layer; raw materials of the active material layer comprise a positive electrode active material and a lithium supplement agent. The reduction-state heteropolyacid reacts with oxygen free radicals released in the lithium removal process of the lithium supplement agent, generation of side reaction gas is remarkably inhibited, and the reduction-state heteropolyacid has multi-electron oxidation-reduction capacity and can participate in the charge-discharge process, so that the electrochemical performance of the positive pole piece is further improved.

Description

Technical Field

[0001] This invention relates to the technical field of positive electrode sheets, and more specifically, to a positive electrode sheet, its preparation method, application, and lithium-ion batteries. Background Technology

[0002] Most existing high-specific-capacity electrode materials lose a significant amount of active lithium during the first charge-discharge cycle due to the formation of the SEI film, resulting in a low coulombic efficiency (ICE) for the first cycle and thus reducing the capacity and energy density of lithium-ion batteries. The most widely used graphite anode has an irreversible capacity loss exceeding 6%, while for silicon-based and tin-based alloy anodes with high specific capacity, the irreversible capacity loss can even reach 10%–20% or more. To compensate for the active lithium loss during the film formation process and improve the utilization efficiency of active lithium in the cathode material, researchers have proposed lithium replenishment techniques. Compared to anode lithium replenishment techniques such as lithium powder or lithium strips, cathode lithium replenishment processes offer advantages such as simpler equipment, a relatively milder and less hazardous environment, and better battery consistency.

[0003] Lithium-rich oxide systems, as an important class of cathode lithium replenishing agents, have attracted widespread attention from researchers due to their good compatibility with battery systems, low production cost, non-toxicity, and high lithium replenishing capacity. However, they also have many drawbacks in application. The most significant problem is that the oxygen free radicals released by the delithiation of lithium-rich lithium oxide cathode lithium replenishing agents can easily cause side reactions in the electrolyte, leading to problems such as cell gas expansion and valve opening hazards in the battery.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] The main objective of this invention is to provide a positive electrode sheet, its preparation method, application, and lithium-ion battery, in order to solve the problem in the prior art where the oxygen free radicals generated by the delithiation of lithium-rich oxides used as positive electrode lithium replenishment agents easily cause side reactions in the electrolyte, generating a large amount of gas, leading to cell swelling or reduced battery capacity.

[0006] To achieve the above objectives, according to one aspect of the present invention, a positive electrode sheet is provided, comprising: a current collector, and a transition layer and an active material layer sequentially disposed on the surface of the current collector; wherein the transition layer comprises a carrier layer, a reduced heteropolyacid layer and an aluminum layer sequentially stacked, and the carrier layer is located between the current collector and the reduced heteropolyacid layer; the raw materials of the active material layer include a positive electrode active material and a lithium supplement agent.

[0007] Furthermore, the mass ratio of the reduced heteropolyacid layer to the aluminum layer is 1:(0.15~0.5).

[0008] Furthermore, the mass ratio of the reduced heteropolyacid layer to the support layer is 1:(0.5~1).

[0009] Furthermore, the thickness of the current collector is 5–20 μm.

[0010] Furthermore, the current collector is aluminum foil.

[0011] Furthermore, the raw materials for the reduced heteropolyacid layer include heteropolyacids, including H4SiW 12 O 40 H3PW 12 O 40 K6P2W 18 O 62 H4SiMo 12 O 40 H3PMo 12 O 40 At least one of them.

[0012] Furthermore, the raw material of the carrier layer includes an imide polymer, which includes at least one of polypropyleneimide, branched polyethyleneimine, linear polyethyleneimine, and polyacrylamide.

[0013] Furthermore, the mass ratio of the positive electrode active material to the lithium supplement is (95-98):(1-4).

[0014] Furthermore, the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0015] Furthermore, the particle size of the positive electrode active material is ≤1μm.

[0016] Furthermore, the lithium supplement includes at least one of Li5FeO4, Li2NiO2, Li2CuO2, Li6CoO4, and Li5ReO6.

[0017] Furthermore, the average particle size of the lithium supplement is ≤5μm.

[0018] According to another aspect of the present invention, a method for preparing a positive electrode sheet is provided, comprising the following steps: Step S1, immersing a current collector in a polymer solution, such that the polymer adheres to the surface of the current collector to form a carrier layer; subsequently immersing it in a heteropoly acid solution, such that the heteropoly acid adheres to the surface of the carrier layer to form a heteropoly acid layer; Step S2, depositing an aluminum layer on the heteropoly acid layer, and causing the heteropoly acid in the heteropoly acid layer to undergo a redox reaction to form a reduced heteropoly acid layer, thereby obtaining a transition layer current collector; Step S3, coating an active material slurry onto the transition layer current collector to form an active material layer, thereby obtaining a positive electrode sheet.

[0019] Furthermore, in step S1, the polymer solution is an imine polymer solution, and the concentration of the imine polymer solution is 5–20 mg / mL.

[0020] Furthermore, the concentration of the heteropolyacid solution is 5–20 mg / mL.

[0021] Furthermore, in step S2, the redox conditions are: a temperature of 1200–1400 °C and a vacuum degree of 1 × 10⁻⁶. -3 ~1×10 -2 Pa.

[0022] Furthermore, in step S3, the thickness of the active material slurry coating is 200–400 μm.

[0023] Further, in step S3, the preparation method of the active material slurry includes the following steps: mixing the positive electrode active material, lithium supplementer, binder and solvent to obtain the active material slurry;

[0024] Furthermore, the mass ratio of the positive electrode active material, lithium supplementer, and binder is (95-98):(1-4):1.

[0025] Furthermore, the adhesive includes at least one of polyvinylidene fluoride, polyacrylic acid, polyvinylpyrrolidone, polyimide, and polyamide-imide.

[0026] Furthermore, the solvent is N-methylpyrrolidone.

[0027] According to a third aspect of the present invention, an application of a positive electrode sheet in a lithium-ion battery is provided, wherein the positive electrode sheet is the positive electrode sheet provided in the first aspect or the positive electrode sheet obtained by the preparation method provided in the second aspect.

[0028] According to a fourth aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, wherein the positive electrode sheet is the positive electrode sheet provided in the first aspect above or the positive electrode sheet obtained by the preparation method provided in the second aspect above.

[0029] By applying the technical solution of the present invention, (1) the positive electrode provided by the present invention utilizes the oxygen free radical reaction released during the delithiation process of reduced heteropolyacid and lithium supplementation agent to significantly suppress the generation of gas, thereby effectively solving the safety hazards of cell gas expansion and valve opening.

[0030] (2) By utilizing the multi-electron redox properties of reduced heteropolyacids, Keggin-type heteropolyacids with oxidation potential (>3.6V) are selected to match the delithiation and deoxygenation potential of lithium supplementation agents, which can rapidly, efficiently and fully absorb oxygen free radicals. Furthermore, the reduced heteropolyacids have multi-electron redox capabilities and can participate in the charging and discharging process, thereby further improving the electrochemical performance of the positive electrode.

[0031] (3) In addition, a multilayer electric field structure is constructed by sequentially arranging a carrier layer, a reduced heteropolyacid layer, an aluminum layer, and an active material layer on the surface of the current collector. The interfacial electric field formed between each layer helps to promote the Li + This improves electron transport and thus significantly increases the battery's specific capacity. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0033] As described in the background section of this application, the oxygen free radicals generated during the delithiation of lithium-rich oxides used as positive electrode lithium replenishers can easily cause side reactions in the electrolyte, producing a large amount of gas, leading to cell swelling or reduced battery capacity. To solve this problem, this application provides a positive electrode sheet, its preparation method, its application, and a lithium-ion battery.

[0034] In a first typical embodiment of this application, a positive electrode sheet is provided, comprising: a current collector, and a transition layer and an active material layer sequentially disposed on the surface of the current collector; wherein, the transition layer comprises a carrier layer, a reduced heteropolyacid layer and an aluminum layer sequentially stacked, and the carrier layer is located between the current collector and the reduced heteropolyacid layer; the active material layer comprises a positive electrode active material and a lithium supplement agent.

[0035] Applying the technical solution of this invention, (1) this application first attaches a carrier layer to the surface of the current collector, and then attaches a heteropolyacid layer to the surface of the carrier layer. Utilizing the positive ions in the carrier layer, the heteropolyacid negative ion clusters are electrostatically adsorbed, thereby improving the binding ability of the heteropolyacid on the current collector. Subsequently, an aluminum layer is deposited on the surface of the heteropolyacid layer. Using the aluminum in the aluminum layer as a reducing agent, the heteropolyacid is reduced to a reduced state heteropolyacid. The reduced state heteropolyacid reacts with the oxygen free radicals released during the lithium removal process of the lithium replenishing agent, significantly suppressing the generation of side reaction gases, thereby effectively solving the safety hazards of cell gas expansion and valve opening.

[0036] (2) By utilizing the multi-electron redox properties of reduced heteropolyacids, Keggin-type heteropolyacids with oxidation potential (>3.6V) are selected to match the delithiation and deoxygenation potential of lithium supplementation agents. This allows for rapid, efficient, and sufficient absorption of oxygen free radicals. Furthermore, the reduced heteropolyacids possess multi-electron redox capabilities and participate in the charging and discharging process, further enhancing the electrochemical performance of the positive electrode.

[0037] (3) A multi-layer electric field structure is constructed by sequentially placing a carrier layer, a reduced heteropolyacid layer, an aluminum layer, and an active material layer on the surface of the current collector. The interfacial electric field formed between each layer helps to promote the Li + This improves electron transport and thus significantly increases the battery's specific capacity.

[0038] In this application, the heteropolyacid reacts with excess aluminum, reducing the heteropolyacid to a reduced state, while the aluminum in contact with the reduced heteropolyacid is oxidized to aluminum oxide. Furthermore, the heteropolyacid and the imine polymer are electrostatically bonded; to ensure sufficient adsorption of the heteropolyacid onto the electrode surface, the imine polymer is in excess relative to the charge of the heteropolyacid.

[0039] To more effectively reduce heteropolyacids and better promote the reaction between the reduced heteropolyacids and the oxygen free radicals released during the delithiation process of the lithium supplement, while further suppressing the generation of side reaction gases, the preferred mass ratio of the reduced heteropolyacid layer to the aluminum layer is 1:(0.15–0.5), such as 1:0.15, 1:0.25, 1:0.3, 1:0.4, 1:0.5, or any range of two values. If the aluminum layer mass is too small, the reduction of heteropolyacids will be incomplete; if the aluminum layer mass is too large, it will be detrimental to the processing and result in higher preparation costs.

[0040] To further improve the binding ability of reduced heteropolyacids on the current collector, the preferred mass ratio of the reduced heteropolyacid layer to the carrier layer is 1:(0.5~1), such as 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1 or any range of two values.

[0041] In order to give the positive electrode sufficient mechanical strength and electronic conductivity, and thus make the structure of the positive electrode more stable, the thickness of the current collector is preferably 5 to 20 μm (such as 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm or any two of these values), and the current collector is more preferably aluminum foil.

[0042] To further reduce the generation of side reaction gases, the raw material for the reduced heteropolyacid layer preferably includes heteropolyacids, such as H4SiW. 12 O 40 H3PW 12 O 40 K6P2W 18 O 62 H4SiMo 12 O 40 H3PMo 12 O 40 Any one or more of the following.

[0043] To enhance the electrostatic adsorption of heteropoly acids and ensure a more stable adhesion of the heteropoly acid layer, the raw material of the carrier layer is preferably an imine polymer, which includes any one or more of polypropyleneimide, branched polyethyleneimine, linear polyethyleneimine, and polyacrylamide.

[0044] In some embodiments, the mass ratio of the positive electrode active material to the lithium replenishing agent is (95-98):(1-4), and the mass ratio of the two is, for example, 95:4, 96:3, 97:2, 98:1 or any two of these values, to ensure the efficiency and balance of the lithium replenishment process, and to avoid excessive lithium replenishing agent leading to gas generation and a decrease in electrochemical performance while replenishing active lithium ions.

[0045] To further improve the rate performance and cycle stability of the battery, the preferred positive electrode active material includes any one or more of lithium iron phosphate and lithium iron manganese phosphate, and the particle size of the positive electrode active material is preferably ≤1μm.

[0046] To more effectively compensate for lithium loss during the first charge and discharge of the battery and improve the first coulombic efficiency, the preferred lithium replenishing agent includes any one or more of Li5FeO4, Li2NiO2, Li2CuO2, Li6CoO4, and Li5ReO6, and preferably the average particle size of the lithium replenishing agent is ≤5μm.

[0047] In a second typical embodiment provided in this application, a method for preparing a positive electrode sheet is provided, comprising the following steps: Step S1, immersing a current collector sequentially in a polymer solution, such that the polymer adheres to the surface of the current collector to form a carrier layer; then immersing it in a heteropoly acid solution, such that the heteropoly acid adheres to the surface of the carrier layer to form a heteropoly acid layer; Step S2, depositing an aluminum layer on the heteropoly acid layer, and causing the heteropoly acid in the heteropoly acid layer to undergo a redox reaction to form a reduced heteropoly acid layer, thereby obtaining a transition layer current collector; Step S3, coating an active material slurry onto the transition layer current collector to form an active material layer, thereby obtaining a positive electrode sheet.

[0048] The preparation method described in this application significantly reduces gas generation from the application of lithium supplementation by constructing a reduced heteropolyacid layer and an active material layer containing lithium supplementation agent on the current collector, thereby enhancing the safety of lithium-ion batteries. Simultaneously, the multilayer structure on the positive electrode promotes Li-ion battery performance. + The efficient transfer of electrons effectively improves the electrochemical performance of the battery.

[0049] In order to optimize the loading of imine polymer and improve its uniform distribution, in step S1, the polymer solution is preferably an imine polymer solution, and the concentration of the imine polymer solution is 5-20 mg / mL, and the immersion time in the imine polymer solution is preferably 10-30 min.

[0050] In some embodiments, the mass of the imine polymer in the carrier layer can be controlled by adjusting the concentration of the imine polymer solution and the impregnation time. To further improve the static adsorption efficiency of the imine polymer and the heteropolyacid and achieve stable adhesion of the heteropolyacid to the current collector, the mass ratio of the heteropolyacid in the heteropolyacid layer to the mass of the imine polymer in the carrier layer is preferably 1:(0.5~1).

[0051] To further enhance the electrostatic adsorption properties of the imine polymer and heteropolyacid, the imine polymer is preferably of a number-average molecular weight of 1000–4000.

[0052] In some embodiments, step S1 further includes performing a first drying after immersion in the heteropoly acid solution. To further improve drying efficiency, the first drying method preferably includes freeze drying and / or nitrogen flow drying, and more preferably, the freeze drying temperature is -40 to -60°C; the nitrogen flow drying temperature is 120 to 200°C.

[0053] In some embodiments, the concentration of the heteropolyacid solution is 5–20 mg / mL, and the immersion time in the heteropolyacid solution is preferably 10–30 min. The amount of heteropolyacid adhering can be controlled by adjusting the concentration of the heteropolyacid solution and the immersion time. The amount of aluminum adhering can be controlled by adjusting the deposition time of the aluminum layer in the vacuum thermal evaporation equipment. To ensure that the heteropolyacid is fully reduced to form a reduced heteropolyacid, thereby more effectively improving its reaction efficiency with oxygen free radicals, suppressing the generation of side reaction gases, and further improving the safety and energy density of the battery, the mass ratio of heteropolyacid in the heteropolyacid layer to aluminum in the aluminum layer is preferably 1:(0.15–0.5). This prevents insufficient reduction due to an excessively small aluminum layer thickness ratio, and also prevents increased internal resistance, decreased lithium-ion transport efficiency, and processing difficulties due to an excessively large aluminum layer thickness ratio.

[0054] To further improve the reduction rate of heteropolyacids, the preferred redox conditions are: a temperature of 1200–1400 °C and a vacuum degree of 1 × 10⁻⁶. -3 ~1×10 -2 Pa.

[0055] In some embodiments, the thickness of the active material slurry coating is 200–400 μm (e.g., 200 μm, 250 μm, 300 μm, 350 μm, 400 μm or any combination of two values). The coating thickness of the active material slurry within the above range helps to improve the loading and compaction density of the positive electrode active material, thereby ensuring that the battery has better electrochemical performance and avoiding uneven compaction caused by excessive thickness and insufficient active material caused by excessive thinness.

[0056] In some embodiments, step S3 further includes coating the active material slurry onto the transition layer current collector, followed by a second drying process. To further improve the drying rate of the positive electrode sheet, the second drying method is preferably vacuum drying, and the preferred vacuum drying conditions are: vacuum degree ≤ 0.02 MPa, temperature 80–120 °C, and time 8–24 h.

[0057] In some embodiments, the preparation method of the active material slurry in step S3 includes the following steps: mixing the positive electrode active material, lithium replenishing agent, binder and solvent to obtain the active material slurry. In order to replenish the active lithium ions appropriately while avoiding excessive gas generation, the preferred mass ratio of the positive electrode active material, lithium replenishing agent and binder is (95-98):(1-4):1, such as 95:4:1, 96:3:1, 97:2:1, 98:1:1 or any range of two values.

[0058] In this application, the type of adhesive is not specifically limited, and any adhesive that can be used is acceptable, including but not limited to any one or more of polyvinylidene fluoride, polyacrylic acid, polyvinylpyrrolidone, polyimide, and polyamide-imide.

[0059] In this application, no specific limitation is made on the type of solvent; any solvent commonly used in the art may be used, including but not limited to N-methylpyrrolidone.

[0060] In a third typical embodiment of this application, an application is provided of the positive electrode sheet provided in the first typical embodiment above, or the positive electrode sheet obtained by the preparation method provided in the second typical embodiment above, in a lithium-ion battery.

[0061] In a fourth typical embodiment of this application, a lithium-ion battery is provided, which includes a positive electrode sheet, which is the positive electrode sheet provided in the first typical embodiment above, or the positive electrode sheet obtained by the preparation method provided in the second typical embodiment above.

[0062] The reaction between the reduced heteropolyacid in the positive electrode and the oxygen free radicals released during the lithium removal process by the lithium supplement significantly inhibits the generation of side reaction gases, and the interfacial electric field formed between the layers promotes the lithium removal process. + The electron transport and electron transfer enable lithium-ion batteries containing this positive electrode to significantly suppress cell gas expansion and valve opening safety hazards, as well as to have high energy density.

[0063] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0064] Example 1

[0065] The positive electrode sheet provided in this embodiment is prepared according to the following steps:

[0066] (1) A 10 μm thick aluminum foil was first immersed in a 10 mg / mL polypropylene imide solution (the number average molecular weight of polypropylene imide is 2000) for 10 min to form a carrier layer; then it was immersed in a 10 mg / mL H3PMo solution. 12 O 40The sample is immersed in a heteropolyacid solution for 10 min, and then dried at 180°C by a nitrogen stream to form a heteropolyacid layer, thus obtaining a pretreated current collector; wherein the mass ratio of the heteropolyacid layer to the polyimide layer is 1:0.6.

[0067] (2) Place the pretreated current collector in a vacuum thermal evaporation equipment to deposit an aluminum layer at a temperature of 1200℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, to obtain the transition layer current collector; wherein, the mass ratio of the heteropolyacid layer and the aluminum layer is 1:0.2;

[0068] (3) Lithium iron phosphate (particle size ≤ 1 μm), lithium supplementer Li5FeO4 (average particle size ≤ 5 μm), polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed to prepare an active material slurry; wherein, the mass ratio of lithium iron phosphate, Li5FeO4 and polyvinylidene fluoride is 96:3:1, and the active material slurry is coated on the transition layer current collector with a coating thickness of 200 μm, and vacuum dried at 80℃ for 8 h under a pressure ≤ 0.02 MPa to obtain a positive electrode sheet.

[0069] Example 2

[0070] The positive electrode sheet provided in this embodiment is prepared according to the following steps:

[0071] (1) A 12 μm thick aluminum foil was first immersed in a 20 mg / mL polypropylene imide solution (the number average molecular weight of polypropylene imide is 2000) for 20 min to form a carrier layer; then it was immersed in a 10 mg / mL H4SiW solution. 12 O 40 The sample is immersed in a heteropolyacid solution for 20 min, and then dried at 160 °C with a nitrogen stream to form a heteropolyacid layer, thus obtaining a pretreated current collector; wherein the mass ratio of the heteropolyacid layer to the polyimide layer is 1:0.7.

[0072] (2) Place the pretreated current collector in a vacuum thermal evaporation equipment to deposit an aluminum layer at a temperature of 1300℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, to obtain the transition layer current collector; wherein the mass ratio of the heteropolyacid layer and the aluminum layer is 1:0.3;

[0073] (3) Lithium iron phosphate (particle size ≤ 1 μm), lithium supplementer Li5FeO4 (average particle size ≤ 5 μm), polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed to prepare an active material slurry; wherein, the mass ratio of lithium iron phosphate, Li5FeO4 and polyvinylidene fluoride is 96:3:1; the active material slurry is coated on the transition layer current collector with a coating thickness of 300 μm, and vacuum dried at 80℃ for 8 h under a pressure ≤ 0.02 MPa to obtain a positive electrode sheet.

[0074] Example 3

[0075] The positive electrode sheet provided in this embodiment is prepared according to the following steps:

[0076] (1) First, immerse a 12μm thick aluminum foil in a 10mg / mL polypropylene imide solution (the number average molecular weight of polypropylene imide is 2000) for 10min to form a carrier layer; then immerse it in a 5mg / mL H3PW solution. 12 O 40 The sample is immersed in a heteropolyacid solution for 10 minutes, and then dried at 200°C with a nitrogen stream to form a heteropolyacid layer, thus obtaining a pretreated current collector; wherein the mass ratio of the heteropolyacid layer to the polyimide layer is 1:0.8.

[0077] (2) Place the pretreated current collector in a vacuum thermal evaporation equipment to deposit an aluminum layer at a temperature of 1200℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, to obtain the transition layer current collector; wherein the mass ratio of the heteropolyacid layer and the aluminum layer is 1:0.4;

[0078] (3) Lithium iron phosphate (particle size ≤ 1 μm), lithium supplementer Li6CoO4 (average particle size ≤ 5 μm), polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed to prepare an active material slurry; wherein, the mass ratio of lithium iron phosphate, Li6CoO4 and polyvinylidene fluoride is 96:3:1, and the active material slurry is coated on the transition layer current collector with a coating thickness of 200 μm, and vacuum dried at 80℃ for 8 h under a pressure ≤ 0.02 MPa to obtain a positive electrode sheet.

[0079] Example 4

[0080] The difference from Example 1 is that the heteropoly acid in step (1) of this example is adjusted to be K6P2W. 18 O 62 .

[0081] Example 5

[0082] The difference from Example 1 is that the heteropoly acid in step (1) of this example is adjusted to be H4SiMo. 12 O 40 .

[0083] Example 6

[0084] The difference from Example 1 is that this example keeps the mass ratio of the heteropolyacid layer to the polypropylene imine layer unchanged, and adjusts the mass ratio of the heteropolyacid layer to the aluminum layer to 1:0.5.

[0085] Example 7

[0086] The difference from Example 1 is that this example keeps the mass ratio of the heteropolyacid layer to the polypropylene imine layer unchanged, and adjusts the mass ratio of the heteropolyacid layer to the aluminum layer to 1:0.15.

[0087] Example 8

[0088] The difference from Example 1 is that this example maintains the same mass ratio of the heteropolyacid layer to the polypropylene imine layer, but adjusts the mass ratio of the heteropolyacid layer to the aluminum layer to 1:0.1.

[0089] Example 9

[0090] The difference from Example 1 is that this example keeps the mass ratio of the heteropolyacid layer to the polypropylene imine layer unchanged, and adjusts the mass ratio of the heteropolyacid layer to the aluminum layer to 1:0.8.

[0091] Example 10

[0092] The difference from Example 1 is that in this example, the mass ratio of lithium iron phosphate, Li5FeO4 and polyvinylidene fluoride in step (3) is adjusted to 95:4:1.

[0093] Example 11

[0094] The difference from Example 1 is that in this example, the mass ratio of lithium iron phosphate, Li5FeO4 and polyvinylidene fluoride in step (3) is adjusted to 98:1:1.

[0095] Comparative Example 1

[0096] The difference from Example 1 is that the aluminum foil in this comparative example was not immersed in H3PMo. 12 O 40 In heteropolyacid solutions, the specific steps include:

[0097] (1) A 10 μm thick aluminum foil was immersed in a 10 mg / mL polypropylene imine solution (the number average molecular weight of polypropylene imine is 2000) for 10 min, and then dried at 180 °C by a nitrogen stream to obtain a pretreated current collector.

[0098] (2) Place the pretreated current collector in a vacuum thermal evaporation equipment to deposit an aluminum layer at a temperature of 1200℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, to obtain the transition layer current collector;

[0099] (3) Lithium iron phosphate (particle size ≤ 1 μm), lithium supplementer Li5FeO4 (average particle size ≤ 5 μm), polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed to prepare an active material slurry; wherein, the mass ratio of lithium iron phosphate, Li5FeO4 and polyvinylidene fluoride is 96:3:1, and the active material slurry is coated on the current collector of the transition layer with a coating thickness of 200 μm, and vacuum dried at 80℃ for 8 h under a pressure ≤ 0.02 MPa to obtain the positive electrode sheet.

[0100] Comparative Example 2

[0101] The difference from Example 1 is that this comparative example did not involve vacuum thermal evaporation deposition of an aluminum layer, but specifically included the following steps:

[0102] (1) A 10 μm thick aluminum foil was first immersed in a 10 mg / mL polypropylene imide solution (the number average molecular weight of polypropylene imide is 2000) for 10 min to form a carrier layer; then it was immersed in a 10 mg / mL H3PMo solution. 12 O 40 The sample is immersed in a heteropolyacid solution for 10 min, and then dried at 180°C by a nitrogen stream to form a heteropolyacid layer, thus obtaining a pretreated current collector; wherein the mass ratio of the heteropolyacid layer to the polyimide layer is 1:0.6.

[0103] (2) Lithium iron phosphate (particle size ≤ 1 μm), lithium supplementer Li5FeO4 (average particle size ≤ 5 μm), polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed to prepare an active material slurry; wherein, the mass ratio of lithium iron phosphate, Li5FeO4 and polyvinylidene fluoride is 96:3:1, and the active material slurry is coated on the pretreated current collector with a coating thickness of 200 μm, and vacuum dried at 80℃ for 8 h under a pressure ≤ 0.02 MPa to obtain a positive electrode sheet.

[0104] Comparative Example 3

[0105] The difference from Example 1 is that this comparative example did not include the lithium supplementer Li5FeO4, and specifically includes the following steps:

[0106] (1) A 10 μm thick aluminum foil was first immersed in a 10 mg / mL polypropylene imide solution (the number average molecular weight of polypropylene imide is 2000) for 10 min to form a carrier layer; then it was immersed in a 10 mg / mL H3PMo solution. 12 O 40 The sample is immersed in a heteropolyacid solution for 10 min, and then dried at 180°C by a nitrogen stream to form a heteropolyacid layer, thus obtaining a pretreated current collector; wherein the mass ratio of the heteropolyacid layer to the polyimide layer is 1:0.6.

[0107] (2) Place the pretreated current collector in a vacuum thermal evaporation equipment to deposit an aluminum layer at a temperature of 1200℃ and a vacuum degree of 1×10⁻⁶. -2 Pa, to obtain the transition layer current collector; wherein, the mass ratio of the heteropolyacid layer and the aluminum layer is 1:0.2;

[0108] (3) Lithium iron phosphate (particle size ≤ 1 μm), polyvinylidene fluoride binder and N-methylpyrrolidone solvent are mixed to prepare an active material slurry; wherein the mass ratio of lithium iron phosphate to polyvinylidene fluoride is 99:1, the active material slurry is coated on the transition layer current collector with a coating thickness of 200 μm, and vacuum dried at 80℃ for 8 h under a pressure ≤ 0.02 MPa to obtain a positive electrode sheet.

[0109] Test case

[0110] The positive electrode, graphite negative electrode, and separator provided in the above embodiments and comparative examples were used to prepare soft-pack batteries with a nominal capacity of approximately 3.2 Ah using the stacking method.

[0111] The graphite negative electrode sheet is prepared as follows: Super-P (superconducting carbon black), SBR (styrene-butadiene rubber), carboxymethyl cellulose (CMC), and graphite are dissolved in deionized water at a mass ratio of 1.5:2.3:1.5:94.7, and mixed evenly to form a negative electrode slurry. This slurry is then uniformly coated onto a copper current collector foil. After drying, rolling, die-cutting, and further drying, the graphite negative electrode sheet is obtained. The electrolyte is 1.0M LiPF6, with a solvent ratio of EC (ethylene carbonate):DMC (dimethyl carbonate) = 3:7, and an additive of 1 wt.% FEC (fluoroethylene carbonate). The separator is a PE separator.

[0112] 1. Electrochemical performance testing

[0113] The battery's initial charge / discharge current rate is 0.1C, with a voltage range of 2.5–4.2V. The cycle current rate is 0.2C, with a voltage range of 2.5–3.65V. The battery's design capacity is 3.2Ah. The initial charge capacity is calculated based on the first cycle, and the discharge capacity is calculated based on the second cycle.

[0114] 2. Gas production test

[0115] The gas production of the battery after 10 cycles was measured using the water displacement method.

[0116] ① Fill a container that can completely hold a pouch battery with water, put an unactivated battery into the container, and completely submerge the battery in water. Record the volume of water that overflows as V0.

[0117] ② Refill the container with water, and put the battery that did not release gas after the transformation is completed back into the container, so that it is completely submerged in water. The volume of water that overflows is recorded as V1.

[0118] ③ Gas production = V1 - V0.

[0119] Table 1

[0120]

[0121] Comparing the results of Examples 1-3 and Examples 6-9, it can be seen that the mass ratio of the heteropolyacid layer to the aluminum layer is 1:(0.15-0.5), which is beneficial to the reduction of heteropolyacid, thereby promoting the reaction between the reduced heteropolyacid and the oxygen free radicals released during the lithium removal process of the lithium replenishing agent, further suppressing the generation of side reaction gases, and thus reducing the amount of gas generated by the cell during application; at the same time, it can also further improve the specific capacity of the battery, thereby improving the electrochemical performance.

[0122] Comparing the results of Example 1, Examples 10-11 and Comparative Example 3, it can be seen that, compared with the absence of lithium supplementation, the addition of lithium supplementation to the positive electrode active material can exert the lithium supplementation function and thus improve the specific capacity. However, the gas production does not increase significantly, but remains relatively small. This indicates that the reaction between the reduced heteropolyacid in the transition layer and the oxygen free radicals released during the lithium supplementation process can significantly suppress gas generation.

[0123] Comparing the results of Example 1 and Comparative Examples 1-2, it can be seen that by sequentially arranging a carrier layer, a reduced heteropolyacid layer, an aluminum layer, and an active material layer on the surface of the current collector, a multi-layer electric field structure is constructed. The interfacial electric field formed between each layer helps to promote Li+ and electron transport, thereby significantly improving the specific capacity of the battery. Furthermore, the reduced heteropolyacid reacts with the oxygen free radicals released during the lithium removal process of the lithium replenishment agent, further suppressing the generation of side reaction gases. Conversely, the absence of the heteropolyacid layer or the aluminum layer not only leads to a decrease in specific capacity but also a significant increase in gas production.

[0124] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0125] The positive electrode provided in this application not only significantly suppresses the generation of side reaction gases through the reaction of oxygen free radicals released during the delithiation process of reduced heteropolyacids and lithium supplementation agents, but also utilizes the multi-electron redox properties of heteropolyacids to participate in the charge and discharge process. Furthermore, it constructs a multi-layer electric field structure through a carrier layer, a reduced heteropolyacid layer, an Al aluminum layer, and an active material layer sequentially arranged on the current collector surface, promoting the lithium... + This facilitates electron transport, thereby increasing the specific capacity of the positive electrode.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized by, Comprising: a current collector, and a transition layer and an active material layer arranged on the surface of the current collector in sequence; wherein the transition layer comprises a carrier layer, a reduced state heteropoly acid layer and an aluminum layer arranged in sequence, and the carrier layer is located between the current collector and the reduced state heteropoly acid layer; the raw material of the active material layer comprises a positive electrode active material and a lithium supplement agent.

2. The cathode electrode of claim 1, wherein, The mass ratio of the reduced state heteropoly acid layer to the aluminum layer is 1: (0.15～0.5)； And / or, the mass ratio of the reduced state heteropoly acid layer to the carrier layer is 1:(0.5-1); And / or, the thickness of the current collector is 5-20 μm, preferably the current collector is an aluminum foil.

3. The cathode electrode of claim 1, wherein The raw material of the reduced heteropoly acid layer includes a heteropoly acid including at least one of H4SiW 12 O 40 , H3PW 12 O 40 , K6P2W 18 O 62 , H4SiMo 12 O 40 , H3PMo 12 O 40 ​ And / or, the raw material of the carrier layer comprises an imine polymer, and the imine polymer comprises at least one of polypropylene imine, branched polyethylene imine, linear polyethylene imine, and polyacrylamide.

4. The cathode electrode of claim 1, wherein The mass ratio of the positive electrode active material to the lithium supplement agent is (95-98):(1-4); And / or, the positive electrode active material comprises at least one of lithium iron phosphate and lithium iron manganese phosphate; And / or, the particle size of the positive electrode active material is ≤1 μm; And / or, the lithium supplement agent comprises at least one of Li5FeO4, Li2NiO2, Li2CuO2, Li6CoO4, and Li5ReO6; And / or, the average particle size of the lithium supplement agent is ≤5 μm.

5. A method of producing the positive electrode sheet according to any one of claims 1 to 4, characterized by, Comprising the following steps: Step S1, dipping the current collector in a polymer solution so that the polymer adheres to the surface of the current collector to form a carrier layer; then dipping in a heteropoly acid solution, and the heteropoly acid adheres to the surface of the carrier layer to form a heteropoly acid layer; Step S2, depositing an aluminum layer on the heteropoly acid layer, and the heteropoly acid in the heteropoly acid layer undergoes a redox reaction to form a reduced state heteropoly acid layer, to obtain a transition layer current collector; Step S3, coating an active material slurry on the transition layer current collector to form an active material layer, to obtain the positive electrode sheet.

6. The production method according to claim 5, wherein In the step S1, the polymer solution is an imine polymer solution, and the concentration of the imine polymer solution is 5-20 mg / mL; And / or, the concentration of the heteropoly acid solution is 5-20 mg / mL.

7. The preparation method according to claim 5, characterized in that, The temperature is 1200-1400℃ and the vacuum degree is 1x10 -3 ~1x10 -2 Pa. And / or, in the step S3, the thickness of the active material slurry coating is 200-400 μm.

8. The production method according to any one of claims 5 to 7, characterized by, In the step S3, the preparation method of the active material slurry comprises the following steps: mixing a positive electrode active material, a lithium supplement agent, a binder and a solvent to obtain the active material slurry; Preferably, the mass ratio of the positive electrode active material, the lithium supplement agent and the binder is (95-98): (1～4)：1； Preferably, the binder comprises at least one of polyvinylidene fluoride, polyacrylic acid, polyvinyl pyrrolidone, polyimide, and polyamide imide; Preferably, the solvent is N-methyl pyrrolidone.

9. Use of the positive electrode sheet of any one of claims 1-4 or the positive electrode sheet obtained by the preparation method of any one of claims 5-8 in a lithium ion battery.

10. A lithium-ion battery, characterized by, Comprising a positive electrode sheet, which is the positive electrode sheet of any one of claims 1-4 or the positive electrode sheet obtained by the preparation method of any one of claims 5-8.

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