Positive pole piece and preparation method thereof, lithium ion battery and electric equipment

Abstract

The invention discloses a positive pole piece and a preparation method thereof, a lithium ion battery and electric equipment, and relates to the technical field of lithium ion batteries. The positive temperature coefficient functional layer is introduced between the positive electrode current collector and the positive electrode active coating, and the positive temperature coefficient functional layer has the characteristic that the specific value of the resistivity at the temperature of more than 80 DEG C to the resistivity at the temperature of 25 DEG C is more than 400%. The positive temperature coefficient functional layer can maintain a stable electron conduction state at normal temperature, and generates controllable volume expansion when the temperature exceeds about 80 DEG C, so that a conductive network is damaged, the resistivity is obviously increased, an electron transmission path is actively interrupted, thermal runaway can be inhibited from the source, and the safety performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a positive electrode sheet and its preparation method, a lithium-ion battery, and an electrical device. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles, portable electronic devices, and energy storage systems, their energy density continues to increase. Consequently, thermal safety issues under abnormal operating conditions such as overcharging, internal short circuits, mechanical damage, and localized overheating are becoming increasingly prominent. Existing safety strategies mainly rely on diaphragm thermal shutdown, electrolyte flame-retardant additives, or external thermal management systems. However, these solutions are mostly passive responses or external controls, making it difficult to promptly suppress localized abnormal heat sources within the electrodes. In particular, they cannot actively cut off electron conduction paths in the early stages of the cell, thus failing to prevent further amplification of thermal runaway.

[0003] Existing positive electrode plates are typically composed of aluminum current collectors and positive electrode active material layers directly composited. They maintain continuous conductivity even when the temperature rises abnormally, which can easily lead to continuous abnormal current flow and exacerbate heat accumulation. Although PTC elements have been used for circuit-level protection, they are usually located outside the cell or at the module level, making it difficult to precisely couple with the thermal evolution process at the electrode scale. Furthermore, they suffer from problems such as response hysteresis and integration difficulties.

[0004] Therefore, there is an urgent need to develop functional structures that can rapidly and actively trigger resistive transitions and interrupt electron channels under high-temperature conditions, so as to suppress the source of thermal runaway at the material and structural levels.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a positive electrode sheet and its preparation method, a lithium-ion battery, and an electrical device, aiming to provide a functional structure that can quickly and actively trigger resistance transitions and interrupt electron channels, so as to suppress the occurrence of thermal runaway at the source and improve battery safety performance.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a positive electrode sheet, including a positive current collector, and a positive temperature coefficient functional layer and a positive active material layer are disposed on at least one side surface of the positive current collector, the positive temperature coefficient functional layer being located between the positive current collector and the positive active material layer; the ratio of the resistivity of the positive temperature coefficient functional layer at a temperature greater than 80°C to the resistivity at 25°C is greater than 400%.

[0008] In an optional embodiment, the positive temperature coefficient functional layer contains 30%-40% carbon-coated lithium iron phosphate, 50%-60% first binder, and 5%-15% first conductive agent by mass fraction.

[0009] In an optional embodiment, the first adhesive is selected from at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide; And / or, the first conductive agent is selected from at least one of conductive carbon black, carbon nanotubes and conductive graphene; And / or, the carbon layer thickness in carbon-coated lithium iron phosphate is 2.5nm-5.0nm, and the average particle size of carbon-coated lithium iron phosphate particles is 100nm-500nm; And / or, the thickness of the positive temperature coefficient functional layer is 1μm-3μm.

[0010] In an optional embodiment, the positive electrode active material in the positive electrode active material layer is selected from at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide. And / or, by mass fraction, the positive electrode active material layer contains 95%-97% positive electrode active material, 1%-3% second binder, and 1%-3% second conductive agent; preferably, the second conductive agent includes conductive carbon black and carbon nanotubes, and the mass ratio of conductive carbon black to carbon nanotubes is 1:(0.5-1.5); preferably, the second binder is selected from at least one of polyvinylidene fluoride and polyacrylic acid.

[0011] In an optional embodiment, the thickness of the positive electrode active material layer is 40 μm-80 μm; And / or, the thickness of the positive electrode current collector is 3μm-10μm; And / or, the positive current collector is made of aluminum.

[0012] Secondly, the present invention provides a method for preparing a positive electrode sheet according to any of the foregoing embodiments, comprising: sequentially forming a positive temperature coefficient functional layer and a positive active material layer on a positive current collector.

[0013] In an optional embodiment, the preparation process of the positive temperature coefficient functional layer includes: mixing carbon-coated lithium iron phosphate, a first binder, a first conductive agent, and a solvent to obtain a functional layer slurry; coating the functional layer slurry onto the positive electrode current collector and drying it; preferably, the solid content of the functional layer slurry is 25wt%-35wt%; preferably, when preparing the positive temperature coefficient functional layer, the drying temperature is controlled at 90℃-110℃ and the drying time is 1h-3h. And / or, before preparing the positive temperature coefficient functional layer, the positive electrode current collector is surface cleaned; preferably, the surface cleaning includes: sequentially performing alkaline washing, acid washing, water washing and drying; more preferably, alkaline washing is performed using sodium hydroxide solution and acid washing is performed using nitric acid solution.

[0014] In an optional embodiment, the preparation process of the positive electrode active material layer includes: coating a positive electrode slurry onto a positive temperature coefficient functional layer, drying it, and then rolling it to control the compaction density to 3.3 mg / cm³. 3 -3.8mg / cm 3 ; Preferably, the preparation process of the positive electrode slurry includes mixing the positive electrode active material, the second binder, the second conductive agent and the solvent.

[0015] Thirdly, the present invention provides a lithium-ion battery, comprising a positive electrode sheet prepared by any of the foregoing embodiments or a positive electrode sheet prepared by any of the foregoing embodiments; Preferably, the lithium-ion battery further includes a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains a flame retardant; more preferably, the flame retardant is selected from at least one of triethyl phosphate, dimethyl methylphosphonate, and ammonium trifluorophosphate; and the mass fraction of the flame retardant in the electrolyte is 1.0%-3.0%. Preferably, the lithium-ion battery was subjected to a needle penetration test, and no fire or explosion occurred under the conditions of a steel nail diameter of 3mm and a penetration speed of 10mm / s, and the maximum surface temperature was ≤110℃. Preferably, in the 70% deformation compression test, the battery did not catch fire or explode, and the highest surface temperature was ≤100℃.

[0016] Fourthly, the present invention provides an electrical device including the lithium-ion battery of the aforementioned embodiments.

[0017] This invention offers the following advantages: A positive temperature coefficient (PTC) functional layer is introduced between the positive electrode current collector and the positive electrode active coating. This PTC functional layer exhibits a resistivity ratio greater than 400% at temperatures above 80°C compared to its resistivity at 25°C. At room temperature, the PTC functional layer maintains a stable electron conduction state. However, at temperatures exceeding approximately 80°C, controllable volume expansion occurs, disrupting the conductive network and causing a significant increase in resistivity. This actively interrupts the electron transport path, suppressing thermal runaway at its source and improving battery safety. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the positive electrode sheet provided by the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] To achieve source-level thermal self-protection, this invention constructs an embedded, temperature-triggered PTC functional layer (i.e., a positive temperature coefficient functional layer) between the positive current collector and the positive active coating. This functional layer maintains a stable electron conduction state at room temperature, while undergoing controllable volume expansion when the temperature exceeds approximately 80°C, which destroys the conductive network and causes a significant increase in resistivity, thereby achieving active interruption of the electron transport path.

[0022] like Figure 1 As shown, an embodiment of the present invention provides a positive electrode sheet, including a positive current collector, and a positive temperature coefficient functional layer is disposed on at least one side surface of the positive current collector. Figure 1 The positive temperature coefficient functional layer is located between the positive current collector and the positive current collector. The positive temperature coefficient functional layer maintains a stable electron conduction state at room temperature. The resistivity at temperatures above 80°C is greater than 400% compared to the resistivity at 25°C, which enables active interruption of the electron transport path.

[0023] Specifically, the resistivity of the positive temperature coefficient functional layer at temperatures above 80°C is more than four times that at 25°C.

[0024] In some embodiments, the positive temperature coefficient functional layer contains, by mass fraction, 30%-40% carbon-coated lithium iron phosphate (C-LFP), 50%-60% first binder, and 5%-15% first conductive agent. In this embodiment, lithium iron phosphate particles with a stable carbon-coated structure are introduced into the functional layer, allowing them to simultaneously act as conductive fillers and mechanically reinforcing phases. This maintains low interfacial impedance while improving the coating's resistance to deformation and interlayer bonding strength during rolling, thereby achieving a synergy between high-temperature response characteristics and engineering processability. At temperatures above 80°C, the carbon-coated lithium iron phosphate undergoes physical displacement due to the dramatic volume expansion of the first binder matrix, causing rapid separation / disconnection of conductive contact points between particles. This thermally induced volume expansion can disrupt the original conductive network structure, triggering significant resistive transitions.

[0025] Specifically, in the positive temperature coefficient functional layer, the mass fraction of carbon-coated lithium iron phosphate can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc.; the mass fraction of the first binder can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc.; and the mass fraction of the first conductive agent can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.

[0026] In some embodiments, the first binder is selected from at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide, and the first binder may be any one or more of the above. The first conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, and conductive graphene, and the first conductive agent may be any one or more of the above.

[0027] In some embodiments, the thickness of the carbon layer in carbon-coated lithium iron phosphate is 2.5 nm-5.0 nm, such as 2.5 nm, 2.8 nm, 3.0 nm, 3.3 nm, 3.5 nm, 3.8 nm, 4.0 nm, 4.3 nm, 4.5 nm, 4.8 nm, 5.0 nm, etc. The average particle size of the carbon-coated lithium iron phosphate particles is 100 nm-500 nm, such as 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc. The average particle size and carbon layer thickness of carbon-coated lithium iron phosphate particles should be controlled within the above-mentioned range. If the carbon layer thickness is too large, the particles themselves will have excessive conductivity and the conductive network will be too "rigid". When heated and expanded, it will be difficult to completely cut off the electron path, thereby reducing the resistivity switching rate (PTC intensity) at high temperature and weakening the safety protection effect. If the carbon layer thickness is too small, it will be difficult to form a continuous and complete conductive coating layer on the surface of lithium iron phosphate, resulting in a significant increase in the contact resistance between particles, causing the initial interface impedance of the functional layer to be too high, which will affect the normal rate performance of the battery.

[0028] Furthermore, the thickness of the positive electrode current collector is 3μm-10μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., and the material of the positive electrode current collector can be aluminum, such as aluminum foil, but is not limited to this. The thickness of the positive electrode active material layer is 40μm-80μm, such as 40μm, 50μm, 60μm, 70μm, 80μm, etc.; the thickness of the positive temperature coefficient functional layer is 1μm-3μm, such as 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, etc. The thickness of each layer should preferably be within the above range. If the thickness of the positive temperature coefficient functional layer is too thin, it will affect the thermal self-protection effect; if the thickness of the positive temperature coefficient functional layer is too thick, it will affect the electrochemical performance of the battery.

[0029] In some embodiments, the positive electrode active material (positive electrode main material) in the positive electrode active material layer is selected from at least one of lithium nickel cobalt manganese oxide (NCM), lithium cobalt oxide (LCO), and lithium nickel cobalt aluminum oxide (NCA). The positive electrode active material can be any one or more of the above. All of the above positive electrode active materials are suitable for the positive electrode sheet provided in the embodiments of the present invention and can all be used as active materials of the positive electrode active material layer.

[0030] Furthermore, by mass fraction, the positive electrode active material layer contains 95%-97% positive electrode active material, 1%-3% second binder, and 1%-3% second conductive agent. By adjusting the content of each component, the electrochemical performance of the battery can be improved. Specifically, the mass fraction of the positive electrode active material can be 95%, 96%, 97%, etc.; the mass fraction of the second binder can be 1%, 2%, 3%, etc.; and the mass fraction of the second conductive agent can be 1%, 2%, 3%, etc.

[0031] Furthermore, the second binder is selected from at least one of polyvinylidene fluoride and polyacrylic acid, and the second binder can be any one or more of the above. The second conductive agent includes conductive carbon black and carbon nanotubes, and the mass ratio of conductive carbon black to carbon nanotubes is 1:(0.5-1.5), such as 1:0.5, 1:0.8, 1:1.0, 1:1.2, 1:1.5, etc. Using a combination of conductive carbon black and carbon nanotubes as the second conductive agent is beneficial to further optimize conductivity and improve battery performance.

[0032] This invention provides a method for preparing a positive electrode sheet, comprising: sequentially forming a positive temperature coefficient functional layer and a positive electrode active material layer on a positive electrode current collector, the specific steps of which are as follows: S1. Fabrication of a positive temperature coefficient functional layer The preparation process of the positive temperature coefficient functional layer includes: coating lithium iron phosphate with carbon, a first binder, a first conductive agent, and a solvent to obtain a functional layer slurry; coating the functional layer slurry onto the positive electrode current collector, and drying it to form the positive temperature coefficient functional layer. The specific types and amounts of the carbon-coated lithium iron phosphate, the first binder, and the first conductive agent are as described above in the instruction manual. The type of solvent is not limited, and can be N-methylpyrrolidone (NMP).

[0033] In some embodiments, the solid content of the functional layer slurry is adjusted to 25wt%-35wt% by controlling the amount of solvent used, such as 25wt%, 28wt%, 30wt%, 32wt%, 35wt%, etc. When preparing the positive temperature coefficient functional layer, the drying temperature is controlled to be 90℃-110℃, such as 90℃, 95℃, 100℃, 105℃, 110℃, etc.; the drying time is 1h-3h, such as 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, etc.

[0034] In some embodiments, before fabricating the positive temperature coefficient functional layer, the positive electrode current collector is surface-cleaned to remove surface oil and oxide layers. The surface cleaning method is not limited. In a preferred embodiment, surface cleaning includes sequentially performing alkaline washing, acid washing, water washing, and drying to thoroughly remove surface oil and oxide layers. Alkaline washing can be performed using sodium hydroxide solution, but is not limited to this. Acid washing uses nitric acid solution, but is not limited to this.

[0035] S2, Preparation of the positive electrode active material layer The preparation process of the positive electrode active material layer includes: coating the positive electrode slurry onto the positive temperature coefficient functional layer, drying and then rolling to control the compaction density to 3.3 mg / cm³. 3 -3.8mg / cm 3 For example, it could be 3.3 mg / cm³ 3 3.4 mg / cm 3 3.5 mg / cm 3 3.6 mg / cm 3 3.7 mg / cm 3 3.8 mg / cm 3 wait.

[0036] In some embodiments, the preparation process of the positive electrode slurry includes mixing a positive electrode active material, a second binder, a second conductive agent, and a solvent. The specific types and amounts of the positive electrode active material, the second binder, and the second conductive agent are as described above. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0037] This invention provides a lithium-ion battery, including a positive electrode sheet as provided in this embodiment, and may also include a negative electrode sheet, electrolyte, separator, and casing. Based on the improvement of the positive electrode sheet, the propagation of battery thermal runaway can be effectively curbed, and the cycle stability of the battery can be improved.

[0038] In some embodiments, the electrolyte contains a flame retardant, a lithium salt, and a solvent, the types of which are not limited. The flame retardant is selected from at least one of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), and ammonium trifluorophosphate (TFPA), and can be any one or more of these. The mass fraction of the flame retardant in the electrolyte is 1.0%-3.0%, such as 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc.

[0039] It should be added that, when the lithium-ion battery is subjected to a nail penetration test, it does not catch fire or explode under the conditions of a steel nail diameter of 3mm and a penetration speed of 10mm / s, and the highest surface temperature is ≤110℃; in the 70% deformation compression test, the battery does not catch fire or explode, and the highest surface temperature is ≤100℃.

[0040] This invention proposes a dual protection scheme combining a PTC functional layer and an electrolyte containing a flame retardant. The PTC functional layer is integrated between the aluminum current collector and the positive electrode active material layer. When the internal temperature of the battery exceeds approximately 80°C, the PTC layer causes a significant increase in resistivity due to volume expansion, actively interrupting the electron transport path, blocking the propagation of heat sources, and preventing the spread of thermal runaway. This invention also introduces a flame retardant into the electrolyte to improve its thermal stability. The flame retardant effectively inhibits the thermal decomposition and combustion reaction of the electrolyte when the battery temperature is too high, mitigating the occurrence of thermal runaway. Combined with the temperature response mechanism of the PTC functional layer, the addition of the flame retardant further enhances the overall thermal safety of the battery, especially under extreme conditions such as high-temperature overcharging or internal short circuits, effectively curbing the spread of thermal runaway.

[0041] This invention enables lithium-ion batteries to actively adjust their internal resistance and limit the continuous flow of current under abnormally high temperature conditions through the synergistic effect of these two thermal self-protection mechanisms. At the same time, it suppresses thermal runaway reactions through flame-retardant electrolyte, making it a more efficient and multi-layered thermal management solution than traditional single protection strategies.

[0042] This invention also provides an electrical device, including the aforementioned lithium-ion battery and the electrical device, wherein the lithium-ion battery is used to supply power to the electrical device, and the specific form of the electrical device is not limited.

[0043] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0044] Example 1 This embodiment provides a method for preparing a positive electrode sheet, the steps of which are as follows: (1) Pretreatment of aluminum current collector Aluminum foil with a thickness of about 6μm was selected, and the surface oil and oxide layer were removed by alkaline washing + acid washing process: first, it was soaked in a 5% NaOH solution for 30s (25℃), then neutralized with a 10% HNO3 solution for 30s, and finally rinsed with deionized water until neutral, and dried in a vacuum drying oven at 80℃ for 2h for later use.

[0045] (2) Preparation of PTC functional layer slurry Weigh out carbon-coated lithium iron phosphate (C-LFP, 35%), polyvinylidene fluoride (PVDF, 55%), and conductive carbon black (Super P, 10%) according to the specified mass ratio. Add them to N-methylpyrrolidone (NMP) solvent, with a solid content of 30 wt%. Disperse the mixture using a high-speed disperser (3000 rpm) for 30 min to form a uniform, agglomerated slurry. The average particle size of the carbon-coated lithium iron phosphate is 260 nm, and the carbon layer thickness is 4 nm.

[0046] (3) Primer coating A slot coating process was used to uniformly coat the slurry onto both sides of the pretreated aluminum foil. The wet film thickness was calculated based on the target thickness of the dried base coating (2.0 μm) and the solid content of the slurry (when the solid content is 30%, the wet film thickness = target dry film thickness / 0.3, i.e., 6.7 μm). The sample was then placed in a vacuum oven at 100℃ for 2 hours to ensure complete solvent evaporation. The total thickness of the aluminum current collector after the base coating was 10 μm (2.0 μm + 6 μm + 2.0 μm).

[0047] This embodiment also utilizes the above-mentioned positive electrode sheet to prepare a lithium-ion battery, the steps of which are as follows: Method for manufacturing positive electrode sheets The above-mentioned positive electrode active material (NCM811), conductive carbon black (Super P), multi-walled carbon nanotubes (HCNT), and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone (NMP) solvent system at a mass ratio of 96:1:1:2 to obtain a positive electrode coating material with a solid content of 40%. This positive electrode coating material was then coated onto the above-mentioned PTC functional coating aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained with a compaction density of 3.5 mg / cm³. 3 The thickness of the formed positive electrode active material layer is 60 μm.

[0048] Negative electrode manufacturing method The negative electrode sheet includes a copper foil current collector and a negative electrode coating material coated on both sides of the current collector. The negative electrode coating material includes 20.0 wt% deposited silicon carbon (purchased from Ningbo Shanshan Co., Ltd.), 76.0 wt% artificial graphite, 0.5 wt% single-walled carbon nanotubes (SWCNTs), 0.9 wt% conductive carbon black (Super P), 1.0 wt% sodium carboxymethyl cellulose (CMC), 0.8 wt% polyacrylic acid (PAA), and 0.8 wt% styrene-butadiene rubber (SBR). These substances are added to deionized water and stirred to form the negative electrode coating material. The negative electrode coating material is then coated on both sides of the current collector. After drying and cold pressing, the negative electrode sheet is formed with a compaction density of 1.6 g / cm³. 3 .

[0049] Preparation of electrolyte An electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), triethyl phosphate (TEP, flame retardant), and vinylene carbonate (VC) in a mass percentage ratio of 11.5:21.6:52.1:2.95:4.88:2.0:4.97, with a LiPF6 concentration of 1 mol / L.

[0050] Selection of diaphragm A high-porosity membrane was selected, in which the thickness of the PE base membrane is 9μm, the thickness of the ceramic coating on both sides of the base membrane is 1.0μm, and the porosity is 40.5%.

[0051] Assembly of lithium-ion batteries After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0052] Example 2 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 30%, 60% and 10%, respectively, while all other aspects are the same as in Embodiment 1.

[0053] Example 3 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 40%, 50% and 10%, respectively, while all other aspects are the same as in Embodiment 1.

[0054] Example 4 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 35%, 60% and 5%, respectively, while all other aspects are the same as in Embodiment 1.

[0055] Example 5 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 35%, 50% and 15%, respectively, while all other aspects are the same as in Embodiment 1.

[0056] Example 6 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 40%, 50% and 10%, respectively, while all other aspects are the same as in Embodiment 1.

[0057] Example 7 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 30%, 60% and 10%, respectively, while all other aspects are the same as in Embodiment 1.

[0058] Example 8 The difference between this embodiment and Embodiment 1 is that the thickness of the PTC functional layer on the aluminum current collector is 1.0 μm, while all other aspects are the same as in Embodiment 1.

[0059] Example 9 The difference between this embodiment and Embodiment 1 is that the thickness of the PTC functional layer on the aluminum current collector is 3.0 μm, while all other aspects are the same as in Embodiment 1.

[0060] Example 10 The difference between this embodiment and Embodiment 1 is that the thickness of the carbon coating layer on C-LFP is 2.5 nm, while all other aspects are the same as in Embodiment 1.

[0061] Example 11 The difference between this embodiment and Embodiment 1 is that the thickness of the carbon coating layer on C-LFP is 3.5 nm, while all other aspects are the same as in Embodiment 1.

[0062] Example 12 The difference between this embodiment and Embodiment 1 is that the thickness of the carbon coating layer on C-LFP is 5.0 nm, while all other aspects are the same as in Embodiment 1.

[0063] Example 13 The difference between this embodiment and Embodiment 1 is that the C-LFP particle size is 100nm, while all other aspects are the same as in Embodiment 1.

[0064] Example 14 The difference between this embodiment and Embodiment 1 is that the C-LFP particle size is 485nm, while all other aspects are the same as in Embodiment 1.

[0065] Example 15 The difference between this embodiment and Embodiment 1 is that the flame retardant in the electrolyte is DMMP, while everything else is the same as in Embodiment 1.

[0066] Example 16 The difference between this embodiment and Embodiment 1 is that the flame retardant in the electrolyte is TFPA, while everything else is the same as in Embodiment 1.

[0067] Comparative Example 1 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 45%, 50% and 5%, respectively, while all other aspects are the same as in Embodiment 1.

[0068] Comparative Example 2 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 30%, 65% and 5%, respectively, while all other aspects are the same as in Embodiment 1.

[0069] Comparative Example 3 The difference between this embodiment and Embodiment 1 is that the mass ratio of C-LFP, PVDF and Super P in the PTC functional layer slurry is 30%, 50% and 20%, respectively, while all other aspects are the same as in Embodiment 1.

[0070] Comparative Example 4 The difference between this embodiment and Embodiment 1 is that the PTC functional layer is not provided on the aluminum current collector; otherwise, they are the same as in Embodiment 1.

[0071] Comparative Example 5 The difference between this embodiment and Embodiment 1 is that the thickness of the PTC functional layer on the aluminum current collector is 5 μm, while all other aspects are the same as in Embodiment 1.

[0072] Comparative Example 6 The difference between this embodiment and Embodiment 1 is that the LFP is not coated with carbon, but otherwise it is the same as Embodiment 1.

[0073] Comparative Example 7 The difference between this embodiment and Embodiment 1 is that the thickness of the C-LFP carbon coating layer is 5.0 μm, while all other aspects are the same as in Embodiment 1.

[0074] Comparative Example 8 The difference between this embodiment and Embodiment 1 is that the C-LFP particle size is 35nm, while all other aspects are the same as in Embodiment 1.

[0075] Comparative Example 9 The difference between this embodiment and Embodiment 1 is that the C-LFP particle size is 760nm, while all other aspects are the same as in Embodiment 1.

[0076] Comparative Example 10 The difference between this embodiment and Embodiment 1 is that no flame retardant is added to the electrolyte, and the missing flame retardant is replaced with the same mass of EC. Everything else is the same as in Embodiment 1.

[0077] Experimental Example 1 The performance of the lithium-ion batteries prepared in the test examples and comparative examples is shown in Tables 1-6.

[0078] The testing method is as follows: PTC functional layer resistivity temperature response test method: First, cut a 1cm × 3cm PTC functional layer sample from the positive electrode (if the electrode contains an active material layer, the active layer must be peeled off first, leaving only the aluminum current collector and PTC layer). Clean the surface with anhydrous ethanol and then dry it. Next, fix the sample on the test stage of a four-probe tester and record the initial resistivity at room temperature (25°C) (repeat the measurement 3 times and take the average value). Then, transfer the sample to a temperature-controlled oven, heat it to 85°C and keep it at that temperature for 30 minutes. After removing it, immediately remeasure the resistivity using a four-probe tester (repeat 3 times as well). Finally, calculate the ratio of the resistivity at 85°C to the resistivity at room temperature (i.e., ρ). 85 / ρ 25 If the percentage is greater than 400%, then it meets the technical requirements.

[0079] Cyclic performance testing methods: Place the battery in a 25°C constant temperature chamber for 6 hours and test it according to the following steps: (1) First round of constant current and constant voltage charging: Charge at a constant current of 1C to 4.2V, then switch to constant voltage charging until the current drops to 0.1C.

[0080] (2) Let it stand for 30 minutes after charging is complete.

[0081] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 1.0C.

[0082] (4) Cyclic charge and discharge process: Charge at a constant current rate of 1.0C to 4.2V. Let stand for 30 minutes again. Discharge at a constant current rate of 1.0C to 2.5V.

[0083] (5) Repeat the above charging and discharging process for a total of 600 cycles.

[0084] The discharge capacities Q1 and Q600 of the battery after 1 cycle and 600 cycles were calculated, and the capacity retention rate of the battery was calculated as: (Q600-Q1) / Q1×100%.

[0085] 70% Deformation Extrusion Test: After charging the lithium-ion battery to 100% state of charge, it is placed horizontally on an extrusion test platform. A cylindrical steel rod with a diameter of 32mm is used as the extrusion head, and extrusion force is applied to the battery thickness at a rate of 10mm / min. Simultaneously, a displacement sensor monitors the battery thickness change in real time. Extrusion is stopped immediately when the battery deformation reaches 70% of its original thickness. The test standard is: the battery must not catch fire or explode during a short circuit.

[0086] Needle penetration test: The battery to be tested was fully charged to 100% SOC and placed in a 25℃ environment for 2 hours to stabilize. Then, the battery was fixed on an insulating clamp, ensuring that its positive and negative terminals were horizontal. Using a 3mm diameter stainless steel needle, perpendicular to the battery surface and along the direction between the positive and negative terminals, the needle was inserted into the battery at a constant speed of 10±1mm / s until it was completely penetrated (the penetration depth should exceed 90% of the battery thickness). After insertion, the needle was kept still, and the battery status was continuously observed for 5 minutes. Any abnormal phenomena such as fire, explosion, or smoke were recorded, and temperature changes were monitored using a thermocouple attached to the battery surface.

[0087] Table 1. Influence of PTC Functional Layer Composition

[0088] Note: ρ 85 ρ represents the resistivity at 85℃. 25 This indicates the resistivity at 25℃.

[0089] Table 1 systematically investigates the effects of the ratio of C-LFP, PVDF and Super P in the PTC functional layer on the normal electrochemical performance and thermal safety behavior of the battery under extreme conditions.

[0090] The results show that within the ratio range of 30-40 wt% C-LFP, 50-60 wt% PVDF, and 5-15 wt% Super P, all embodiments can pass the needle penetration and 70% deformation extrusion tests. The maximum surface temperature of the battery after needle penetration is effectively limited to about 80-95°C, and the resistivity is more than 400% of that at room temperature. This indicates that the PTC functional layer can destroy the original conductive network structure through thermally induced volume expansion under abnormal heating conditions, triggering significant resistance transitions, thereby actively suppressing the continuous flow of abnormal current and the resulting Joule heat accumulation.

[0091] Further comparison revealed that when the ratio of C-LFP to PVDF was in a relatively balanced state (as in Examples 1 and 3), the battery maintained a high 1C / 1C cycle capacity retention rate (approximately 85%) while still exhibiting excellent temperature-triggered response capability, indicating a synergistic optimization between conductive framework stability and thermal trigger sensitivity. However, when the Super P content was too high or too low, although the safety test could still be passed, the cycle capacity retention rate decreased, reflecting that an imbalance in conductive filler content weakens the structural reversibility and interface stability of the PTC network. The mechanism is that under normal temperature conditions, C-LFP and Super P jointly construct a continuous multi-scale conductive network, ensuring low impedance and stable electron transport at the electrode interface. When the temperature rises abnormally, the PVDF matrix undergoes significant thermal expansion and chain relaxation, causing the continuous conductive channels to be broken and decoupled. The conductive network changes from a continuous state to a discrete state, resulting in a transition in bulk resistivity, thereby achieving rapid suppression of abnormal currents. Meanwhile, the rigid particle structure of C-LFP acts as a mechanical support point under rolling and extrusion conditions, suppressing the irreversible collapse of the PTC layer and ensuring the repeatability of temperature response behavior and structural stability. The Super P content determines the initial density of the conductive network; an excess or deficiency will disrupt the balance between room-temperature conductivity and high-temperature on / off ratio. Overall, the reasonable three-phase synergistic ratio enables this PTC functional layer to actively cut off the electronic pathway under high-temperature conditions without significantly sacrificing cycle performance, thus suppressing the occurrence and propagation of thermal runaway from the source.

[0092] Table 2. Influence of PTC functional layer thickness

[0093] Table 2 systematically examines the impact of the thickness of the PTC functional layer on aluminum foil on the normal cycle performance and thermal safety behavior of the battery under extreme conditions.

[0094] It can be seen that when the thickness of the PTC functional layer is in the range of 1.0μm-3.0μm, all embodiments can pass the needle punch and 70% deformation extrusion tests, indicating that the PTC layer in this thickness range can achieve effective thermal response and electronic pathway regulation under abnormal working conditions.

[0095] However, different thicknesses significantly affect the balance between room temperature conduction stability and high temperature triggering efficiency: when the thickness is 1.0 μm (Example 8), the PTC layer is thinner, the interface impedance at room temperature is lower, which is conducive to electron transport, so the 1C / 1C cycle capacity retention rate is the highest (86.7%). However, its volume expansion and ability to damage the conductive network during abnormal temperature rise are relatively limited, which reduces the resistance transition amplitude, resulting in a relatively high maximum surface temperature after needle penetration (96.6 ℃). When the thickness increases to 3.0 μm (Example 9), the expansion effect of the PTC layer at high temperature is more significant, which can more fully destroy the through conductive channels and form a higher resistance transition amplitude. Therefore, the temperature rise under abnormal conditions is further suppressed (78.6 ℃). However, due to the introduction of a larger electron transport path and interface impedance by the thicker layer, its normal cycle capacity retention rate decreases (81.8%). In comparison, a thickness of 2.0 μm (Example 1) achieves a better balance between room-temperature conductivity and high-temperature response sensitivity, enabling the battery to maintain high cycle stability while effectively limiting temperature rise under extreme conditions such as nail penetration and compression. This result indicates that the thickness of the PTC functional layer is not necessarily better the thinner or thicker it is, but rather requires synergistic optimization among electron transport impedance, structural stability, and temperature triggering efficiency.

[0096] Table 3. Effect of carbon coating thickness on C-LFP

[0097] Table 3 systematically investigates the influence of the thickness of the carbon coating layer on the surface of C-LFP particles on the electrochemical performance and thermal safety behavior of the PTC functional layer under extreme operating conditions.

[0098] It can be seen that within the range of 2.5nm-5.0nm carbon coating thickness, all embodiments can pass the needle penetration and 70% deformation extrusion tests, indicating that C-LFP particles within this size range can participate in the construction of a conductive network with temperature-triggered response capability and achieve effective electronic pathway regulation under abnormal operating conditions. However, different carbon coating thicknesses significantly affect the balance between room temperature conduction stability and high temperature triggering sensitivity: when the carbon layer is thin (2.5 nm, Example 10), its continuous coating of the C-LFP particle body is limited, and the stability of the conductive network and its resistance to interface polarization are relatively insufficient. Although it is more easily destroyed by PVDF expansion at high temperatures, it exhibits a lower maximum needle penetration temperature (89.9 °C), but the normal cycle capacity retention rate is relatively low (84.5%). When the carbon layer thickness is moderate (3.5 nm, Example 11), the coating layer can build a stable electron transport channel at room temperature without excessively enhancing the continuity of the conductive network at high temperatures, making it easier for the conductive channel to decouple when temperature is triggered. Therefore, the temperature rise after needle penetration is further reduced to 79.8 °C, showing higher thermal response efficiency. In contrast, when the carbon layer was further thickened to 4.0-5.0 nm (Examples 1 and 12), the continuous and dense carbon coating significantly enhanced the electronic coupling and network connectivity between particles, improving the conductivity at room temperature (88.5% cycle retention rate in Example 1). However, it also increased the threshold for the conductive network to be destroyed at high temperatures, thereby weakening the “on / off ratio” of the PTC layer and reducing the ability to suppress current when triggered at high temperatures, resulting in an increase in the highest surface temperature after needle penetration.

[0099] Table 4. Effect of C-LFP Particle Size

[0100] Table 4 systematically examines the influence of C-LFP particle size on the normal electrochemical performance and thermal safety behavior of the PTC functional layer under extreme conditions. It can be seen that within the particle size range of 100-485 nm, all examples passed the needle penetration and 70% deformation compression tests, indicating that C-LFP particles within this size range can participate in the construction of a conductive network with temperature-triggered response capability and achieve effective control of electronic pathways under abnormal conditions. However, different particle sizes show significant differences in conductive framework construction methods, interface stability, and thermal triggering destructibility, leading to variations in cycling performance and high-temperature response behavior. When the particle size is small (100 nm, Example 13), the particle specific surface area increases significantly, and the number of contact points between particles increases, which is beneficial for constructing a denser conductive network. This makes it easier for the network to undergo overall decoupling and breakage during high-temperature expansion, thus significantly reducing the maximum temperature after needle penetration (78.7 °C). However, the high specific surface area also introduces greater interfacial impedance and side reaction interfaces, thereby reducing the normal cycling capacity retention to 80.5%. When the particle size is large (485 nm, Example 14), the number of contact points between particles decreases, the continuity and structural uniformity of the conductive network decline, and the electron transport path is not stable enough at room temperature, resulting in a low cycle retention rate (81.4%). However, because the network itself is relatively loose, it is more easily destroyed by PVDF expansion during temperature triggering, thus exhibiting a low needle penetration peak temperature (78.6 °C). In contrast, medium particle size (approximately 260 nm, Example 1) achieves a better balance between conductive connectivity and thermally triggered destructibility, enabling the battery to maintain high cycle stability (88.5%) while still possessing reliable temperature response capabilities.

[0101] Table 5. Effect of Flame Retardant Type

[0102] Table 5 systematically examines the effects of different types of flame retardants on the normal cycle performance and thermal safety behavior of batteries under extreme operating conditions.

[0103] It can be seen that when TEP, DMMP, or TFPA are used as the flame retardant components of the electrolyte, all embodiments can pass the needle penetration and 70% deformation extrusion tests, indicating that all three flame retardants can play a role in inhibiting the spread of combustion and thermal reaction under abnormal operating conditions. However, the differences in molecular structure, thermal decomposition pathway, and compatibility with the electrolyte system of different flame retardants lead to different trade-offs between room temperature electrochemical stability and high temperature inhibition efficiency.

[0104] Specifically, the TEP system (Example 1) exhibited the highest 1C / 1C cycle capacity retention rate (88.5%), indicating that it had minimal disturbance to the electrolyte solvation structure and the interface SEI / CEI, maintaining a low side reaction rate while ensuring good ion transport kinetics. However, at high temperatures, it mainly exerted its flame-retardant effect through endothermic decomposition and dilution of flammable components, with relatively limited ability to suppress transient heat release. Therefore, the highest surface temperature after needle puncture was slightly higher (98.0 °C). In contrast, DMMP and TFPA (Examples 13 and 14) contain more reactive phosphorus functional groups, making them more prone to gas-phase free radical capture or the formation of phosphate ester flame-retardant intermediates at high temperatures. This effectively inhibits chain combustion reactions and reduces the heat release rate, resulting in a significant reduction in their peak temperature after needle puncture to approximately 90 °C. However, at the same time, these molecules have a stronger disturbance to the electrolyte system's solvation structure and interface film composition, easily introducing additional interfacial impedance or side reaction channels, thus slightly decreasing the cycle capacity retention rate. In general, the type of flame retardant determines the balance between cycle performance and thermal suppression capability under extreme conditions by regulating the free radical quenching pathway at high temperatures, the exothermic reaction rate, and the interfacial chemical stability at room temperature. When working in synergy with the embedded PTC functional layer, different flame retardants further constitute a dual safety barrier of "electronic-level cutoff + chemical-level flame suppression," enabling the system to suppress abnormal currents at the source while delaying and weakening the subsequent chemical reaction propagation of thermal runaway, thereby achieving a higher level of overall thermal safety.

[0105] Table 6 Performance Comparison of Example 1 and Comparative Example

[0106] Table 6, through a systematic comparison of Example 1 with a series of comparative examples, comprehensively verifies the synergistic mechanism of the key structural parameters and component design of the present invention on the normal performance and thermal safety behavior of the battery under extreme conditions. It can be seen that Example 1 exhibits the best overall characteristics in terms of cycle retention, needle penetration safety, temperature rise control, and extrusion resistance. However, when any key factor deviates from the reasonable design range, the "source-level thermal suppression capability" and structural reversibility of the system both decrease significantly.

[0107] Specifically, in Comparative Examples 1-3, the imbalance in the ratio of C-LFP, PVDF, and Super P disrupts the coupling between the continuity of the conductive framework, its thermally destructible nature, and interface stability. The conductive network becomes either too dense to be effectively destroyed at high temperatures, or its structure is loose, resulting in excessive interface impedance at room temperature. This ultimately leads to PTC response failure, continuous abnormal current flow, and consequently, severe temperature rises or even failure to pass safety tests. In Comparative Example 4, the absence of a PTC functional layer means the electrode remains continuously conductive at high temperatures, lacking a source-level electronic pathway cutoff mechanism. Consequently, continuous Joule heat accumulation occurs under needle penetration and extrusion conditions, causing a rapid rise in surface temperature. In Comparative Example 5, the PTC layer thickness is excessive. Although the resistive transition at high temperatures is sufficient to limit the temperature rise, the excessively thick functional layer significantly increases the room-temperature transmission impedance, weakening cycle performance. This demonstrates that the PTC layer thickness must be synergistically optimized between "high-temperature response capability" and "room-temperature conductivity." Comparative Examples 6 and 7 demonstrate that the carbon coating of C-LFP is crucial for ensuring the stability of the conductive network and the reversibility of thermal triggering: without coating, severe interface polarization leads to an unstable conductive network, while excessively thick coating enhances the "resistance to destruction" of the conductive channels at high temperatures and reduces the PTC on / off ratio. Comparative Examples 8 and 9 further illustrate that the C-LFP particle size determines the topology of the conductive network and its thermal triggering decoupling behavior; particle sizes that are too small or too large disrupt the balance between room-temperature stability and high-temperature response sensitivity, leading to the failure of the safety mechanism. Finally, in Comparative Example 10, no flame retardant was introduced. Although the PTC layer could still suppress abnormal current to some extent, the lack of suppression for subsequent exothermic chemical reactions allowed thermal runaway to be further amplified at high temperatures, ultimately resulting in the failure of the safety test. In summary, the results show that the present invention is not effective due to a single factor. Rather, it works by the synergistic effect of the electronic active cutoff mechanism of the PTC functional layer and the chemical flame-retardant mechanism of the flame-retardant electrolyte. At the same time, it achieves fine control at multiple levels such as material ratio, thickness, particle size and interface structure. Only in this way can abnormal heat generation be suppressed from the source and the cascading amplification process of thermal runaway be blocked without significantly sacrificing cycle performance.

[0108] In summary, this invention introduces an embedded PTC functional layer within the positive electrode and synergistically optimizes the ratio of C-LFP, PVDF, and Super P, the thickness of the functional layer, the carbon coating structure and particle size of C-LFP, and the type of flame retardant in the electrolyte. This allows the electrode to maintain a stable and continuous electronic conduction network at room temperature, while triggering volume expansion and decoupling of conductive channels under abnormal temperature conditions, inducing resistivity transitions, thereby actively cutting off abnormal current and suppressing the accumulation of continuous Joule heat. Simultaneously, the flame retardant further inhibits subsequent exothermic reactions and combustion expansion at high temperatures, constructing a dual safety barrier of "electronic-level cutoff + chemical-level flame suppression." This multi-scale, multi-mechanism synergistic design enables the battery to achieve source-level suppression and cascade amplification blocking of thermal runaway without significantly sacrificing cycle performance, significantly improving overall thermal safety and engineering adaptability under extreme conditions such as nail penetration and extrusion.

[0109] 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 plate, characterized in that, The device includes a positive current collector, and a positive temperature coefficient functional layer and a positive active material layer are disposed on at least one side surface of the positive current collector, wherein the positive temperature coefficient functional layer is located between the positive current collector and the positive active material layer; the ratio of the resistivity of the positive temperature coefficient functional layer at a temperature greater than 80°C to the resistivity at 25°C is greater than 400%.

2. The positive electrode sheet according to claim 1, characterized in that, By mass fraction, the positive temperature coefficient functional layer contains 30%-40% carbon-coated lithium iron phosphate, 50%-60% first binder, and 5%-15% first conductive agent.

3. The positive electrode sheet according to claim 2, characterized in that, The first adhesive is selected from at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide; And / or, the first conductive agent is selected from at least one of conductive carbon black, carbon nanotubes and conductive graphene; And / or, the carbon layer thickness in the carbon-coated lithium iron phosphate is 2.5nm-5.0nm, and the average particle size of the carbon-coated lithium iron phosphate particles is 100nm-500nm; And / or, the thickness of the positive temperature coefficient functional layer is 1μm-3μm.

4. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material in the positive electrode active material layer is selected from at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide; And / or, by mass fraction, the positive electrode active material layer contains 95%-97% positive electrode active material, 1%-3% second binder, and 1%-3% second conductive agent; preferably, the second conductive agent includes conductive carbon black and carbon nanotubes, and the mass ratio of conductive carbon black to carbon nanotubes is 1:(0.5-1.5); preferably, the second binder is selected from at least one of polyvinylidene fluoride and polyacrylic acid.

5. The positive electrode sheet according to claim 1 or 4, characterized in that, The thickness of the positive electrode active material layer is 40μm-80μm; And / or, the thickness of the positive current collector is 3μm-10μm; And / or, the positive current collector is made of aluminum.

6. A method for preparing the positive electrode sheet according to any one of claims 1-5, characterized in that, include: The positive temperature coefficient functional layer and the positive electrode active material layer are sequentially formed on the positive electrode current collector.

7. The preparation method according to claim 6, characterized in that, The preparation process of the positive temperature coefficient functional layer includes: coating lithium iron phosphate with carbon, a first binder, a first conductive agent and a solvent to obtain a functional layer slurry; coating the functional layer slurry onto the positive electrode current collector and drying it; preferably, the solid content of the functional layer slurry is 25wt%-35wt%; preferably, when preparing the positive temperature coefficient functional layer, the drying temperature is controlled at 90℃-110℃ and the drying time is 1h-3h. And / or, before preparing the positive temperature coefficient functional layer, the positive electrode current collector is surface-cleaned; preferably, the surface cleaning includes: sequentially performing alkaline washing, acid washing, water washing and drying; more preferably, the alkaline washing is performed using sodium hydroxide solution and the acid washing is performed using nitric acid solution.

8. The preparation method according to claim 6, characterized in that, The preparation process of the positive electrode active material layer includes: coating the positive temperature coefficient functional layer with a positive electrode slurry, drying it, and then rolling it to control the compaction density to 3.3 mg / cm³. 3 -3.8mg / cm 3 ; Preferably, the preparation process of the positive electrode slurry includes: mixing a positive electrode active material, a second binder, a second conductive agent, and a solvent.

9. A lithium-ion battery, characterized in that, This includes the positive electrode sheet according to any one of claims 1-5 or the positive electrode sheet prepared by the preparation method according to any one of claims 6-8; Preferably, the lithium-ion battery further includes a negative electrode, a separator, and an electrolyte, wherein the electrolyte contains a flame retardant; More preferably, the flame retardant is selected from at least one of triethyl phosphate, dimethyl methylphosphonate, and ammonium trifluorophosphate; in the electrolyte, the mass fraction of the flame retardant is 1.0%-3.0%; Preferably, the lithium-ion battery is subjected to a needle penetration test. Under the conditions of a steel nail diameter of 3mm and a penetration speed of 10mm / s, no fire or explosion occurs, and the maximum surface temperature is ≤110℃. Preferably, in the 70% deformation compression test, the battery did not catch fire or explode, and the highest surface temperature was ≤100℃.

10. An electrical appliance, characterized in that, Including the lithium-ion battery as described in claim 9.

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