Lithium ion battery

Abstract

The application relates to the technical field of batteries, in particular to a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte; the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating arranged on at least one side surface of the positive electrode current collector; the negative electrode sheet comprises a negative electrode current collector and a negative electrode coating arranged on at least one side surface of the negative electrode current collector; at least one of the positive electrode sheet and the negative electrode sheet further comprises a PTC functional layer arranged between the positive electrode current collector and the positive electrode coating and / or arranged between the negative electrode current collector and the negative electrode coating; the PTC functional layer has a resistivity temperature coefficient greater than 3.5% within 90 DEG C to 130 DEG C; and the electrolyte comprises a flame retardant. Compared with the prior art, the active limiting effect of the PTC functional layer on abnormal current and the inhibiting effect of the flame retardant in the electrolyte on combustion are coordinated, so that the thermal safety of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to lithium-ion batteries. Background Technology

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and high-power electronic devices, their energy density continues to improve. However, the thermal safety issues of batteries under extreme conditions such as overcharging, internal short circuits, puncture, compression, and localized overheating are becoming increasingly prominent. Numerous accidents have shown that battery thermal runaway is often sudden, cascading, and irreversible. Its essence stems from the inability to promptly suppress abnormal localized heat generation, ultimately leading to separator melting, direct contact between positive and negative electrodes, electrolyte decomposition, gas eruption, and even combustion and explosion. Summary of the Invention

[0003] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a lithium-ion battery that achieves rapid limitation of short-circuit transient current by introducing a PTC functional layer in the electrode, while simultaneously introducing a flame retardant in the electrolyte to inhibit the release of flammable components, reduce the combustion enthalpy, and delay the thermal diffusion process. The synergistic effect of these two methods not only reduces the intensity of the heat source but also weakens the propagation path of thermal runaway, thereby significantly improving the intrinsic safety level of the battery under conditions of nail penetration, extrusion, and internal short circuit.

[0004] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a lithium-ion battery is provided, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode includes a positive current collector and a positive coating disposed on at least one side surface of the positive current collector; the negative electrode includes a negative current collector and a negative coating disposed on at least one side surface of the negative current collector; at least one of the positive and negative electrode sheets further includes a PTC functional layer, the PTC functional layer being disposed between the positive current collector and the positive coating, and / or between the negative current collector and the negative coating; the resistivity temperature coefficient of the PTC functional layer is greater than 3.5% within the range of 90℃ to 130℃; The electrolyte includes a flame retardant.

[0005] In some of these embodiments, the resistivity temperature coefficient of the PTC functional layer satisfies: ; Where TCR is the temperature coefficient of resistivity, %; ρ is the resistivity at different temperatures T, Ω·cm; ρ0 is the resistivity at 25℃, Ω·cm; T0 is 25℃.

[0006] In some of these embodiments, the thickness of the PTC functional layer on one side is 1.5µm to 3.5µm.

[0007] In some of these embodiments, the PTC functional layer includes an adhesive and a conductive filler.

[0008] In some embodiments, the mass ratio of the adhesive to the conductive filler is 0.2 to 0.42:1.

[0009] In some embodiments, the adhesive includes one or more of polymethyl methacrylate, polypropylene, and polyvinylidene fluoride.

[0010] In some embodiments, the conductive filler includes at least two of carbon fibers, graphene nanosheets, carbon nanotubes, and conductive carbon black.

[0011] In some embodiments, the conductive filler comprises carbon fibers and graphene nanosheets, wherein the mass ratio of the carbon fibers to the graphene nanosheets is 1:0.2 to 0.4.

[0012] In some embodiments, the positive electrode coating includes a positive electrode active material, which includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide.

[0013] In some embodiments, the negative electrode coating includes a negative electrode active material, which includes one or more of deposited silicon-carbon, silicon-carbon composite materials, natural graphite, artificial graphite, and hard carbon.

[0014] In some embodiments, the flame retardant includes one or more of triethyl phosphate, dimethyl methylphosphonate, tris(2-chloroethyl) phosphate, and hexachlorocyclotriphosphazene.

[0015] In some embodiments, the lithium-ion battery does not catch fire or explode during the nail penetration test, and the highest surface temperature of the lithium-ion battery during the nail penetration test is ≤110℃; wherein the conditions for the nail penetration test are: steel nail diameter 3mm, penetration speed 10mm / s.

[0016] In some embodiments, the lithium-ion battery has a discharge capacity of Q1 at 25°C when discharged at a rate of 1.0C to 2.5V, and a discharge capacity of Q2 at a rate of 10C to 2.5V, wherein Q2 / Q1 ≥ 65%.

[0017] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. This invention introduces a PTC functional layer inside the electrode to respond from an electrical perspective, rapidly increasing resistance during localized overheating and suppressing the initiation of thermal runaway at the energy source, thus quickly limiting short-circuit transient current. Simultaneously, by adding a flame retardant to the electrolyte, it responds from a chemical perspective, inhibiting the release of flammable components, reducing the enthalpy of combustion, and delaying the thermal diffusion process. These two elements work synergistically to construct a multi-dimensional coupled safety control mechanism of "electro-thermal-chemical," which not only reduces the intensity of the heat source but also weakens the propagation path of thermal runaway, effectively improving the safety of lithium-ion batteries under extreme operating conditions.

[0018] 2. By rationally controlling the composition and structure of the PTC functional layer, this invention can not only effectively suppress the excessive increase of short-circuit current and prevent thermal runaway, but also maintain a high discharge capacity and ensure the stability of the battery under high-rate discharge conditions.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 The resistivity-temperature response test diagrams of the PTC functional layer obtained in Embodiment 1 and Comparative Example 1 of the present invention are shown. Detailed Implementation

[0022] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0025] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0027] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0028] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0029] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0030] Currently, with the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and high-power electronic devices, their energy density continues to improve. However, the thermal safety issues of batteries under extreme conditions such as overcharging, internal short circuits, puncture, compression, and localized overheating are becoming increasingly prominent. Numerous accidents have shown that battery thermal runaway is often sudden, cascading, and irreversible. Its essence stems from the inability to promptly suppress abnormal localized heat generation, ultimately leading to separator melting, direct contact between positive and negative electrodes, electrolyte decomposition, gas eruption, and even combustion and explosion.

[0031] From the perspective of failure mechanism, thermal runaway often originates from a positive feedback process of local short circuit—Joule heat accumulation—accelerated side reactions—oxygen release—chain exothermic reaction. Among them, the electrode layer is one of the earliest structural units to participate in thermal evolution: on the one hand, once a short circuit channel is formed in a local area of ​​the electrode, the short circuit current will amplify sharply within milliseconds, resulting in an instantaneous jump in power density; on the other hand, traditional electrode materials themselves lack self-regulation ability and cannot actively suppress current or block heat diffusion when the temperature rises.

[0032] Positive Temperature Coefficient (PTC) materials are considered ideal functional units for constructing the intrinsic safety structure of lithium-ion batteries due to their characteristic of a sharp increase in resistance as temperature rises. PTC materials maintain low impedance at room temperature, not significantly affecting the normal rate performance of the battery; however, under conditions of localized overheating or short circuits, their volume expansion, phase transition, or disruption of the conductive network leads to a sudden increase in resistance, thereby rapidly limiting abnormal current and achieving "self-current limiting" and "self-protection" functions. Compared to traditional passive safety structures, PTC functional layers have advantages such as fast response, strong reversibility, and no need for external control systems, actively suppressing the energy release rate at the initial stage of a short circuit from an electrical perspective.

[0033] However, the single PTC mechanism still has certain limitations: on the one hand, its main target is the current channel, and its ability to suppress the thermal decomposition of the electrolyte, the release of flammable vapors, and the risk of secondary combustion is limited; on the other hand, under extreme mechanical damage or multi-point short circuit conditions, local high-temperature areas may still be generated, inducing electrolyte volatilization, flammable gas accumulation, and open flame propagation. Therefore, relying solely on PTC regulation is insufficient to fundamentally eliminate the risk of thermal runaway chain reactions.

[0034] Building upon this foundation, this invention rapidly limits short-circuit transient current by introducing a PTC functional layer into the electrode. Simultaneously, it introduces a flame retardant with free radical capture, phosphorus-nitrogen synergistic flame retardant, or endothermic decomposition properties into the electrolyte, constructing an "electro-thermal-chemical" multidimensional coupled safety regulation mechanism. This mechanism simultaneously inhibits the release of flammable components, reduces the combustion enthalpy, and slows down the thermal diffusion process. The synergistic effect of these two mechanisms not only reduces the intensity of the heat source but also weakens the propagation path of thermal runaway, thereby significantly improving the intrinsic safety level of lithium-ion batteries under conditions of needle penetration, extrusion, and internal short circuits.

[0035] Specifically, the present invention adopts the following technical solution: According to one aspect of the present invention, a lithium-ion battery is provided, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode includes a positive current collector and a positive coating disposed on at least one side surface of the positive current collector; the negative electrode includes a negative current collector and a negative coating disposed on at least one side surface of the negative current collector; at least one of the positive and negative electrode sheets further includes a PTC functional layer, the PTC functional layer being disposed between the positive current collector and the positive coating, and / or between the negative current collector and the negative coating; the resistivity temperature coefficient of the PTC functional layer is greater than 3.5% within the range of 90℃ to 130℃; The electrolyte includes a flame retardant.

[0036] Specifically, at least one of the positive electrode and the negative electrode further includes a PTC functional layer in three cases: (1) the PTC functional layer is only provided between the positive current collector and the positive electrode coating, and the negative electrode only includes the negative current collector and the negative electrode coating; (2) the PTC functional layer is only provided between the negative current collector and the negative electrode coating, and the positive electrode only includes the positive current collector and the positive electrode coating; (3) the PTC functional layer is provided between the positive current collector and the positive electrode coating, and between the negative current collector and the negative electrode coating. Preferably, providing the PTC functional layer only between the positive current collector and the positive electrode coating is more effective.

[0037] In a specific embodiment of the present invention, the positive electrode sheet includes a positive current collector, a PTC functional layer disposed on at least one side surface of the positive current collector, and a positive electrode coating disposed on the surface of the PTC functional layer. The PTC functional layer has a resistivity temperature coefficient greater than 3.5% within the range of 90°C to 130°C, which can ensure that the impedance of the PTC functional layer is sufficiently low within the normal operating temperature range of the battery, while generating a sufficiently large resistive transition near the thermal runaway trigger temperature to achieve fast and effective current limiting.

[0038] In a specific embodiment of the present invention, the positive electrode coating preferably comprises a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material preferably comprises one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide; the positive electrode binder preferably comprises one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the positive electrode conductive agent preferably comprises one or more of conductive carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The present invention does not impose any special restrictions on the source of the above-mentioned positive electrode active material, positive electrode binder, and positive electrode conductive agent; commercially available products well known to those skilled in the art can be used.

[0039] In a specific embodiment of the present invention, the method for preparing the positive electrode sheet includes: adding positive electrode active material, positive electrode binder, and positive electrode conductive agent to a solvent and mixing them thoroughly to prepare a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector having a PTC functional layer; and drying, cold pressing, and slitting to obtain the positive electrode sheet. The positive electrode current collector can be a metal foil such as aluminum foil, and the solvent can be N-methylpyrrolidone.

[0040] In a specific embodiment of the present invention, the resistivity temperature coefficient (TCR) of the PTC functional layer satisfies: ; Wherein, TCR is the temperature coefficient of resistivity, %; ρ is the resistivity at different temperatures T, Ω·cm; ρ0 is the resistivity at 25℃, Ω·cm; and T0 is 25℃. This invention selects a PTC functional layer that satisfies the specific TCR formula, which exhibits a significant increase in resistivity as temperature rises, thereby actively limiting abnormal current in lithium-ion batteries.

[0041] In a specific embodiment of the present invention, the thickness of one side of the PTC functional layer is preferably 1.5µm to 3.5µm, specifically 1.5µm, 1.7µm, 1.9µm, 2.1µm, 2.3µm, 2.5µm, 2.7µm, 2.9µm, 3.1µm, 3.3µm, 3.5µm, and any value between the two mentioned above. If the thickness is too thin, a continuous and effective current limiting path may not be formed, resulting in insufficient current limiting effect under abnormal conditions; if the thickness is too thick, it will excessively increase the internal resistance of the battery, significantly negatively impacting the high-rate discharge performance under normal operating conditions.

[0042] In a specific embodiment of the present invention, the PTC functional layer preferably includes an adhesive and a conductive filler; the adhesive preferably includes one or more of polymethyl methacrylate (PMMA), polypropylene (PP), and polyvinylidene fluoride (PVDF); the conductive filler preferably includes at least two of carbon fiber (CF), graphene nanosheets (CNPs), carbon nanotubes (CNTs), and conductive carbon black (SP), more preferably carbon fiber and graphene nanosheets. The present invention uses the above-mentioned adhesive and conductive filler, which can form a conductive network between the conductive fillers and cause the adhesive to thermally expand and disrupt the conductive pathway when the temperature rises, thereby achieving the PTC effect. The present invention does not have any special restrictions on the source of the above-mentioned adhesive and conductive filler; commercially available products well known to those skilled in the art can be used.

[0043] In a specific embodiment of the present invention, the preferred mass ratio of the adhesive to the conductive filler is 0.2 to 0.42:1, specifically 0.2:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1, 0.3:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.4:1, 0.42:1, and any value between any two of the above. The present invention selects the above-mentioned suitable mass ratio, which can both tightly bond the PTC functional layer to the current collector and provide a certain mechanical strength.

[0044] In a specific embodiment of the present invention, the conductive filler preferably comprises carbon fibers and graphene nanosheets, and the mass ratio of the carbon fibers to the graphene nanosheets is preferably 1:0.2~0.4, specifically 1:0.2, 1:0.3, 1:0.4, and any value between the two mentioned above. Carbon fibers serve as a long-range conductive framework, while graphene nanosheets effectively fill the gaps between the carbon fibers, forming a dense and efficient three-dimensional conductive network. This not only ensures excellent conductivity at room temperature but also achieves superior PTC response characteristics.

[0045] In a specific embodiment of the present invention, the electrolyte includes a flame retardant, preferably one or more of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tris(2-chloroethyl) phosphate (TCEP), and hexachlorocyclotriphosphazene (HCCP). These flame retardants typically function through gas-phase or condensed-phase flame-retardant mechanisms, such as decomposing at high temperatures to generate free radical scavengers, interrupting the combustion chain reaction; or decomposing to generate a heat-insulating and oxygen-barrier coke layer. When the PTC functional layer limits abnormal current and delays temperature rise, the presence of the flame retardant can further inhibit chemical reactions such as electrolyte decomposition and combustible gas combustion that may be caused by localized hot spots, thereby providing a second layer of protection for the battery from a chemical perspective. The present invention does not impose any special restrictions on the source of the aforementioned flame retardants; commercially available products well known to those skilled in the art can be used.

[0046] In specific embodiments of the present invention, the electrolyte further includes an organic solvent, an electrolyte lithium salt, and additives. Preferably, the electrolyte lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluorosulfonylimide, lithium difluorophosphate, lithium difluorooxalate borate, and lithium bis(trifluoromethanesulfonylimide). The organic solvent preferably comprises one or more of dimethyl carbonate (DMC), diethyl carbonate, ethylene carbonate (EC), and methyl ethyl carbonate. The additives preferably comprise one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate, ethylene sulfate (DTD), ethylene sulfite, vinylene carbonate (VC), and vinyl carbonate. The present invention does not impose any special restrictions on the source of the above-mentioned organic solvent, electrolyte lithium salt, and additives; commercially available products well known to those skilled in the art can be used.

[0047] In a specific embodiment of the present invention, the separator includes a base membrane and a coating disposed on at least one surface of the base membrane. The base membrane preferably includes a polyolefin microporous separator, specifically a polypropylene (PP) membrane, a polyethylene (PE) membrane, or a polypropylene / polyethylene / polypropylene (PP / PE / PP) composite membrane, etc.; the coating is preferably a ceramic coating and / or a PVDF coating. The present invention does not impose any special restrictions on the source of the separator; commercially available products well known to those skilled in the art can be used.

[0048] In a specific embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating disposed on at least one side surface of the negative electrode current collector. The negative electrode coating preferably includes a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a dispersant; wherein, the negative electrode active material preferably includes one or more of deposited silicon carbon, silicon carbon composite materials, natural graphite, artificial graphite, and hard carbon; the negative electrode binder preferably includes one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS); the negative electrode conductive agent preferably includes one or more of conductive carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the dispersant preferably includes sodium carboxymethyl cellulose (CMC) and ammonium polyacrylate (PAA-NH4). + The negative electrode active material, negative electrode binder, negative electrode conductive agent, and dispersant are selected from one or more of the following: nonionic polyacrylamide (NPAM). This invention does not impose any special restrictions on the source of the above-mentioned negative electrode active material, negative electrode binder, negative electrode conductive agent, and dispersant; commercially available products well-known to those skilled in the art can be used.

[0049] In a specific embodiment of the present invention, the method for preparing the negative electrode sheet includes: adding negative electrode active material, negative electrode binder, negative electrode conductive agent and dispersant to a solvent and mixing thoroughly to prepare a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector; drying, cold pressing, and slitting to obtain the negative electrode sheet. The negative electrode current collector can be a metal foil such as copper foil, and the solvent can be deionized water.

[0050] In a specific embodiment of the present invention, the lithium-ion battery is preferably formed by stacking a positive electrode, a separator, and a negative electrode, and then winding them together. In a preferred embodiment of the present invention, the preparation process of the lithium-ion battery includes: sequentially stacking the positive electrode, the separator, and the negative electrode, then winding them together to form an electrode assembly, packaging them with a polymer, filling them with electrolyte, and then forming them into a battery through processes such as formation. The specific conditions and parameters for each step in the above preparation process can be achieved using battery preparation techniques well known to those skilled in the art, and the present invention does not impose any special limitations on them.

[0051] In a specific embodiment of the present invention, the lithium-ion battery does not catch fire or explode during the needle penetration test, and the highest surface temperature of the lithium-ion battery during the needle penetration test is ≤110℃; wherein, the conditions for the needle penetration test are: steel nail diameter 3mm, penetration speed 10mm / s.

[0052] In a specific embodiment of the present invention, the discharge capacity of the lithium-ion battery at 25°C, discharged at a rate of 1.0C to 2.5V, is Q1, and the discharge capacity at a rate of 10C to 2.5V is Q2, where Q2 / Q1 ≥ 65%.

[0053] The following detailed description of this application is based on specific embodiments, but the implementation and protection of this invention are not limited thereto. The following embodiments are only some embodiments of this application and are not intended to limit this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0054] Example 1 (1) Raw material pretreatment: Aluminum foil with a thickness of 6µm was selected, and the surface oil and oxide layer were removed by alkaline washing + acid washing process: first, it was soaked in 5% NaOH solution for 30s (25℃), then neutralized with 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.

[0055] Polymethyl methacrylate (PMMA), graphene nanosheets (CNPs) and carbon fibers (CF) were placed in a vacuum oven and dried continuously at 80°C for 24 hours to remove adsorbed moisture and volatile impurities.

[0056] (2) Preparation of the positive electrode: Weigh PMMA, CF, and CNPs according to a mass ratio of 25:57.5:17.5 and add them to a mixed solvent of acetone and chloroform (V). 丙酮 :V 氯仿 In a solution of 7:3 (cN=7:3), the solid content is 20wt%. The solution is dispersed at 3000rpm for 30min using a high-speed disperser to promote the formation of a uniformly dispersed conductive network structure between CNPs and CF in the solution system, thus obtaining PTC slurry.

[0057] PTC slurry was uniformly coated onto both sides of pretreated aluminum foil using a slot coating process, with a coating thickness of 10µm on each side. The sample was then placed in a vacuum oven at 100℃ for 2 hours to ensure complete solvent evaporation, resulting in aluminum foil with a PTC functional layer. The total thickness of the aluminum foil with the PTC functional layer was 10µm, the total thickness of the PTC functional layer was 4µm, and the thickness of the PTC functional layer on each side was 2µm.

[0058] A positive electrode slurry was prepared by thoroughly mixing NCM811, conductive carbon black, multi-walled carbon nanotubes, and polyvinylidene fluoride in an N-methylpyrrolidone solvent at a mass ratio of 96:1:1:2. The positive electrode slurry was then coated onto both sides of an aluminum foil with a PTC functional layer. After drying and cold pressing, a positive electrode sheet was obtained with a compaction density of 3.5 mg / cm³. 3 .

[0059] (3) Preparation of negative electrode: A negative electrode slurry was prepared by adding 20 wt% deposited silicon carbon, 76 wt% artificial graphite, 0.5 wt% single-walled carbon nanotubes, 0.9 wt% conductive carbon black, 1 wt% sodium carboxymethyl cellulose, 0.8 wt% polyacrylic acid, and 0.8 wt% styrene-butadiene rubber to deionized water and stirring thoroughly. The negative electrode slurry was then coated on both sides of a copper foil, dried, and cold-pressed to obtain a negative electrode sheet with a compaction density of 1.6 g / cm³. 3 .

[0060] (4) 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), and vinylene carbonate (VC) in a mass ratio of 11.5:21.6:52.1:2.95:4.88:2:4.92, wherein the concentration of LiPF6 was 1 mol / L.

[0061] (5) Preparation of lithium-ion batteries: A 9µm thick PE membrane was selected as the base membrane, and a 1.0µm thick ceramic coating was applied to both sides of the base membrane. After drying, a separator was obtained with a porosity of 40.5%.

[0062] The prepared positive and negative electrode sheets are rolled and slit respectively, and then wound together with the separator according to the set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to the 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, a lithium-ion battery 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 specifications.

[0063] Example 2 The difference between Example 2 and Example 1 is that in step (2), the thickness of the PTC slurry coating on each side is 7.5µm, resulting in a total thickness of 9µm for the aluminum foil with the PTC functional layer, a total thickness of 3µm for the PTC functional layer, and a thickness of 1.5µm for the PTC functional layer on one side.

[0064] Example 3 The difference between Example 3 and Example 1 is that in step (2), the thickness of the PTC slurry coating on each side is 12.5µm, resulting in a total thickness of 11µm for the aluminum foil with the PTC functional layer, a total thickness of 5µm for the PTC functional layer, and a thickness of 2.5µm for the PTC functional layer on one side.

[0065] Example 4 The difference between Example 4 and Example 1 is that in step (2), the thickness of the PTC slurry coating on each side is 15µm, resulting in a total thickness of 12µm for the aluminum foil with the PTC functional layer, a total thickness of 6µm for the PTC functional layer, and a thickness of 3µm for the PTC functional layer on one side.

[0066] Example 5 The difference between Example 5 and Example 1 is that in step (2), the thickness of the PTC slurry coating on each side is 17.5µm, resulting in a total thickness of 13µm for the aluminum foil with the PTC functional layer, a total thickness of 7µm for the PTC functional layer, and a thickness of 3.5µm for the PTC functional layer on one side.

[0067] Example 6 The difference between Example 6 and Example 1 is that in step (2) of the PTC slurry composition, polypropylene (PP) is used instead of PMMA.

[0068] Example 7 The difference between Example 7 and Example 1 is that in step (2) of the PTC slurry composition, polyvinylidene fluoride (PVDF) is used instead of PMMA.

[0069] Example 8 The difference between Example 8 and Example 1 is that carbon nanotubes (CNTs) are used instead of CNPs in the composition of the PTC slurry in step (2).

[0070] Example 9 The difference between Example 9 and Example 1 is that in step (2) of the PTC slurry composition, conductive carbon black (SP) is used instead of CNPs.

[0071] Example 10 The difference between Example 10 and Example 1 is that in step (2) of the PTC slurry composition, CNT is used to replace CF, and the mass ratio of PMMA, CNPs and CNT is 25:57.5:17.5.

[0072] Example 11 The difference between Example 11 and Example 1 is that in step (2) of the PTC slurry composition, SP is used to replace CF, and the mass ratio of PMMA, CNPs and SP is 25:57.5:17.5.

[0073] Example 12 The difference between Example 12 and Example 1 is that in step (2) of the PTC slurry composition, CNT and SP are used to replace CF and CNPs, and the mass ratio of PMMA, CNT and SP is 25:57.5:17.5.

[0074] Example 13 The difference between Example 13 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 20:60:20.

[0075] Example 14 The difference between Example 14 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 30:55:15.

[0076] Example 15 The difference between Example 15 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 25:62.5:12.5.

[0077] Example 16 The difference between Example 16 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 25:53.6:21.4.

[0078] Example 17 The difference between Example 17 and Example 1 is that in step (4) of preparing the electrolyte, dimethyl methylphosphonate (DMMP) is used instead of TEP.

[0079] Example 18 The difference between Example 18 and Example 1 is that in step (4) of preparing the electrolyte, tris(2-chloroethyl) phosphate (TCEP) is used instead of TEP.

[0080] Example 19 The difference between Example 19 and Example 1 is that in step (4) of preparing the electrolyte, hexachlorocyclotriphosphazene (HCCP) is used instead of TEP.

[0081] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that PTC slurry is not applied in step (2).

[0082] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in step (2), the thickness of the PTC slurry coating on each side is 25µm, resulting in a total thickness of 16µm for the aluminum foil with the PTC functional layer, a total thickness of 10µm for the PTC functional layer, and a thickness of 5µm for the PTC functional layer on one side.

[0083] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in step (2), no CNPs are added to the PTC slurry composition, and the mass ratio of PMMA to CF is 25:75.

[0084] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that in step (2), no CF is added to the PTC slurry, and the mass ratio of PMMA and CNPs is 25:75.

[0085] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 9.1:69.7:21.2.

[0086] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 33.3:51.1:15.2.

[0087] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 25:68.2:6.8.

[0088] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that in step (2), the mass ratio of PMMA, CF and CNPs in the PTC slurry is 25:50:25.

[0089] Performance testing: The positive electrode sheets and lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to performance tests, and the specific operations are as follows: (1) Temperature response test of PTC functional layer resistivity: First, 1cm×3cm samples were cut from the positive electrode sheet of Example 1 (the positive electrode coating needs to be peeled off first, leaving only the aluminum foil and PTC functional layer) and the positive electrode sheet of Comparative Example 1 (the positive electrode coating needs to be peeled off first, leaving only the aluminum foil). The surfaces were cleaned with anhydrous ethanol and then dried. Next, the samples were fixed on the test stage of a four-probe tester, and the initial resistivity ρ0 was recorded at room temperature (the average value was taken after 3 repeated measurements). Then, the samples were transferred to a temperature-controlled oven, heated to different temperatures and kept at that temperature for 30 minutes. After removal, the resistivity ρ was immediately remeasured using a four-probe tester (the average value was taken after 3 repeated measurements). Finally, the resistivity temperature coefficient was obtained by calculating the ratio of the resistivity ρ at different temperatures to the room temperature resistivity ρ0 according to the following formula: ; Where TCR is the temperature coefficient of resistivity, %; ρ is the resistivity at different temperatures T, Ω·cm; ρ0 is the resistivity at 25℃, Ω·cm; T0 is 25℃.

[0090] (2) 25℃ rate discharge performance test: The battery was placed in a 25℃ constant temperature chamber for 4 hours and tested according to the following steps: ① Charged at 1.0C with constant current and constant voltage to 4.2V, with a cutoff current of 0.1C, and left to stand for 30 minutes; ② Discharged at 1.0C with constant current to 2.5V cutoff, with a capacity of Q1, and left to stand for 30 minutes; ③ Charged at 1.0C with constant current and constant voltage to 4.2V, with a cutoff current of 0.1C, and left to stand for 30 minutes; ④ Discharged at 10C with constant current to 2.5V cutoff, with a capacity of Q2, and left to stand for 30 minutes; ⑤ 10C discharge capacity retention rate (%) = Q2 / Q1 × 100%.

[0091] (3) 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 placed horizontally. A stainless steel needle with a diameter of 3 mm was inserted into the battery at a speed of 10±1 mm / s perpendicular to the surface of the battery and along the direction between the positive and negative terminals 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 the temperature change was monitored by a thermocouple attached to the surface of the battery.

[0092] The test results are shown in Table 1 below.

[0093] Table 1 Test data for the examples and comparative examples Referring to Table 1, Examples 1-5 demonstrate the impact of different PTC functional layer thicknesses on battery performance, particularly in terms of 10C discharge capacity retention, nail penetration test pass rate, and the highest surface temperature of the battery during the nail penetration test. As the thickness of the PTC functional layer on one side increases, from 2.0 µm in Example 1 to 3.5 µm in Example 5, the discharge capacity retention gradually decreases, from 73.6% in Example 1 to 65.4% in Example 5. This phenomenon may be because a thicker PTC functional layer can impede current conduction during normal discharge, thus affecting the battery's performance at high discharge rates. However, a thicker PTC functional layer can more effectively suppress excessive current flow during short circuits or overheating, thereby improving the intrinsic safety of the battery.

[0094] In the nail penetration test, all embodiments passed the test, demonstrating that the PTC functional layer design effectively enhances battery safety under mechanical damage. Specifically, when local overheating or short circuits occur, the resistance of the PTC functional layer increases sharply due to its positive temperature coefficient, limiting the rapid increase of abnormal current and preventing further thermal runaway. With increasing PTC functional layer thickness, the maximum battery surface temperature shows a slight decreasing trend (91.7°C in Example 5 and 95.0°C in Example 1), indicating that a thicker PTC functional layer provides better suppression in thermal management, helping to reduce the generation of localized high-temperature areas and slowing the propagation path of thermal runaway.

[0095] Combining Comparative Examples 1 and 2, in terms of discharge capacity retention, Comparative Example 1 (without the PTC functional layer) exhibited the highest discharge capacity retention (75.9%), but failed the nail penetration test, and the highest surface temperature of the battery was extremely high, reaching 591.8°C, indicating very poor safety. In contrast, Example 1 maintained a higher discharge capacity (73.6%) while exhibiting a lower surface temperature (95.0°C), demonstrating that the introduction of the PTC functional layer significantly improved the battery's safety and thermal management capabilities. In Comparative Example 2 (PTC functional layer thickness of 5µm on one side), although the discharge capacity retention decreased to 60.4% and the highest surface temperature of the battery was 86.7°C, it still passed the nail penetration test, indicating that excessive PTC functional layer thickness may affect discharge performance, but provides a certain degree of thermal stability.

[0096] from Figure 1 It can be seen that Example 1, which is coated with a PTC functional layer, exhibits a significant positive temperature coefficient effect in the range of 80℃ to 120℃. The TCR increases sharply with the increase of temperature, and it has excellent overheat current limiting protection capability. In contrast, Comparative Example 1, which is not coated with a PTC functional layer, shows that the TCR value fluctuates very little with the increase of temperature, indicating that its resistance has almost no response to temperature changes and it completely lacks the ability to regulate under thermal runaway.

[0097] While a thicker PTC functional layer offers better safety, it can also negatively impact overall battery performance. Therefore, balancing the thickness of the PTC functional layer with battery performance is crucial in the design, ensuring both sufficient safety and battery stability under extreme conditions such as high-rate discharge. Overall, by adjusting the thickness of the PTC functional layer, an optimized balance between battery performance and safety can be achieved, aligning with the design philosophy of this invention to enhance the intrinsic safety of the battery.

[0098] Referring to Table 1, Examples 1 and 6-7 demonstrate the impact of different binder types on battery performance, particularly on 10C discharge capacity retention, nail penetration test pass rate, and the highest surface temperature of the battery during the nail penetration test. The three binder materials are PMMA, PP, and PVDF.

[0099] Regarding discharge capacity retention, Example 1, using PMMA, performed best, with a discharge capacity retention rate of 73.6%. Examples 6 and 7, using PP and PVDF respectively, showed discharge capacity retention rates of 66.9% and 67.8%, both lower than PMMA. This difference may be related to the conductivity of the binder itself, its compatibility with conductive fillers, and the influence of the binder on the overall structural stability of the PTC functional layer. PMMA, as a binder, may have better compatibility with conductive fillers (such as carbon fibers and graphene nanosheets), thus effectively maintaining the battery's high-rate discharge performance. PP and PVDF, on the other hand, have poor conductivity, which may lead to greater resistance to current flow through the PTC functional layer during high-rate discharge, thus affecting the discharge capacity retention rate.

[0100] In the nail penetration test, all embodiments passed the test, demonstrating that regardless of the binder used, the design of the PTC functional layer effectively enhances battery safety under extreme mechanical damage. The successful nail penetration test verifies the self-limiting current capability of the PTC functional layer, effectively preventing thermal runaway of the battery during nail penetration or short circuits.

[0101] Regarding the highest surface temperature of the battery during the nail penetration test, Example 1, using PMMA, exhibited a higher temperature (95.0°C), while Examples 6 and 7, using PP and PVDF respectively, showed slightly lower temperatures of 90.7°C and 91.4°C. This result may be related to the thermal conductivity, expansion properties, and structural effects on the PTC functional layer of different binders. The higher temperature of PMMA may be related to its poor thermal stability at high temperatures, while the relatively lower temperatures of PP and PVDF may be due to the stronger phase transition or expansion effects of these materials at high temperatures, thus limiting further increases in current.

[0102] In summary, different binder types have varying degrees of impact on the high-rate discharge capability, thermal management, and safety of batteries. PMMA offers good high-rate discharge performance but is slightly inferior in thermal stability; PP and PVDF perform well in thermal management but may sacrifice some discharge performance. Therefore, when designing the PTC functional layer, the choice of binder needs to strike a balance between safety and battery performance.

[0103] Referring to Table 1, Examples 1 and 8-12 demonstrate the impact of different conductive filler types on battery performance, particularly in terms of 10C discharge capacity retention, nail penetration test pass rate, and the highest surface temperature of the battery during the nail penetration test. The selection of conductive filler in the PTC functional layer directly affects its conductivity, structural stability, and thermal management performance.

[0104] Regarding discharge capacity retention, Example 1 (CF / CNPs) performed best, with a discharge capacity retention of 73.6%. This indicates that the combination of carbon fiber (CF) and graphene nanosheets (CNPs) has good conductivity and good interfacial compatibility, which helps to improve the high-rate discharge performance of the battery. In contrast, Example 8 (CF / CNT) had a retention of 71.4%, and Example 9 (CF / SP) had a retention of 72.1%, with these combinations showing slightly lower discharge capacity retention than CF / CNPs. Although carbon fiber (CF) has certain conductivity with carbon nanotubes (CNT) or conductive carbon black (SP), they may be slightly inferior to graphene nanosheets (CNPs) in terms of electronic conduction efficiency and interfacial contact. The discharge capacity retention of Examples 10 (CNPs / CNT), 11 (CNPs / SP), and 12 (CNT / SP) gradually decreased, with Example 12 (CNT / SP) showing the lowest retention at only 68.6%. This may be because the combination of carbon nanotubes and conductive carbon black has poor conductivity, which inhibits the energy release efficiency of the battery during high-rate discharge.

[0105] In terms of nail penetration testing, all embodiments passed the test, demonstrating that the PTC functional layer effectively enhances battery safety under mechanical damage in various conductive filler combinations. The nail penetration test also verifies the self-current limiting characteristic of the PTC functional layer, i.e., by increasing resistance to limit the increase of short-circuit current, it effectively suppresses thermal runaway.

[0106] Regarding the highest surface temperature of the battery in the nail penetration test, Example 12 (CNT / SP) exhibited the highest temperature (99.6°C). Despite its poor conductivity, the PTC functional layer was able to delay the propagation of thermal runaway under short-circuit and overheating conditions through its self-limiting current function. However, compared to other examples, the higher surface temperature of Example 12 indicates poorer thermal management and a tendency for localized temperature rise. Example 1 (CF / CNPs) exhibited a lower surface temperature (95.0°C), indicating that this combination provides good conductivity while maintaining good thermal stability, helping to prevent localized overheating.

[0107] In summary, the combination of different conductive fillers has a significant impact on battery performance and safety. The CF / CNPs combination exhibits excellent thermal management while maintaining a high discharge capacity retention rate. While the CNT / SP combination still plays a role in safety, it suffers from shortcomings in thermal stability and conductivity. Therefore, selecting an appropriate conductive filler combination requires balancing the demands of thermal management and electrical conductivity while improving battery discharge performance and ensuring safety.

[0108] Referring to Table 1, Examples 1, 13-14, and Comparative Examples 5-6 demonstrate the impact of different binder-to-conductive filler ratios on battery performance, particularly in terms of 10C discharge capacity retention, nail penetration test pass rate, and the highest surface temperature of the battery during the nail penetration test. The binder-to-conductive filler ratio directly affects the conductivity, bond strength, and thermal stability of the PTC functional layer, and is therefore crucial for the overall performance and safety of the battery.

[0109] Regarding discharge capacity retention, Example 13 (binder to conductive filler ratio of 0.25:1) performed best, with a discharge capacity retention of 74.7%. This indicates that a lower binder ratio helps improve the conductivity of the conductive filler in the PTC functional layer, thereby improving the high-rate discharge performance of the battery. In contrast, Examples 1 (ratio of 0.33:1) and 14 (ratio of 0.42:1) showed discharge capacity retention rates of 73.6% and 66.8%, respectively, demonstrating the impact of adjusting the binder and conductive filler ratio on battery discharge performance. A higher binder ratio may lead to uneven dispersion of the conductive filler, increasing resistance and thus affecting the battery's discharge performance.

[0110] In the nail penetration test, all embodiments passed the test, demonstrating that regardless of the binder to conductive filler ratio, the PTC functional layer design effectively enhances battery safety under extreme mechanical damage. The nail penetration test verified the self-current limiting function of the PTC functional layer, which can effectively suppress the growth of short-circuit current and avoid thermal runaway.

[0111] Regarding the highest surface temperature of the battery in the nail penetration test, Example 13 (0.25:1 ratio) exhibited a higher temperature (108.7°C), while Example 14 (0.42:1 ratio) and Example 1 (0.33:1 ratio) reached 100.5°C and 95.0°C, respectively. This indicates that while a lower binder ratio results in better discharge capacity retention, it may lead to a slight decrease in the thermal stability of the PTC functional layer under overheating, causing a faster local temperature rise. A higher binder ratio (such as in Example 14), while resulting in a lower discharge capacity retention, can improve thermal stability to some extent, preventing a drastic temperature rise under overheating.

[0112] In Comparative Example 5 (ratio of 0.1:1) and Comparative Example 6 (ratio of 0.5:1), the discharge capacity retention rates were 75.6% and 65.4%, respectively. Although Comparative Example 5 performed better in terms of discharge capacity, it failed the nail penetration test and the highest surface temperatures were as high as 556℃ and 109.6℃, indicating that too low or too high binder ratios can affect thermal stability and battery safety.

[0113] Referring to Table 1, Examples 1, 15-16, Comparative Examples 3-4, and 7-8 demonstrate the effect of different carbon fiber (CF) to graphene nanosheet (CNPs) mass ratios on battery performance. Example 1 (CF:CNPs=1:0.3) showed the best performance, with a discharge capacity retention rate of 73.6% and a maximum surface temperature of 95.0°C in the nail penetration test, exhibiting good discharge performance and thermal management capabilities. Conversely, Examples 15 (CF:CNPs=1:0.2) and 16 (CF:CNPs=1:0.4) showed a decrease in discharge capacity retention rate and thermal stability, at 71.3% and 70.2%, respectively, and the maximum surface temperatures increased to 109.8°C and 107.5°C, respectively. This indicates that lower or higher CNPs ratios may affect the battery's conductivity and thermal management effectiveness. For Comparative Examples 3 (CF as conductive filler) and 4 (CNPs as conductive filler), although the discharge capacity retention rates were 66.5% and 67.3%, respectively, they failed the nail penetration test, and their surface temperatures both exceeded 500°C, demonstrating significant deficiencies in thermal stability and safety. Excessive concentration of conductive filler may lead to insufficient thermal management capabilities of the PTC functional layer, resulting in ineffective control of local temperatures. Comparative Examples 7 (CF:CNPs=1:0.1) and 8 (CF:CNPs=1:0.5) achieved discharge capacity retention rates of 70.6% and 71.2%, respectively, but failed the nail penetration test, and their highest surface temperatures approached 580°C, indicating disadvantages in thermal management and safety. Therefore, the mass ratio of CF to CNPs has a significant impact on battery performance and safety; the optimal ratio should balance the battery's discharge capacity and thermal stability.

[0114] Referring to Table 1, Examples 1 and Examples 17-19 demonstrate the impact of different flame retardant types on battery performance. Example 1 (TEP flame retardant) performed best, with a discharge capacity retention rate of 73.6% and a maximum surface temperature of 95.0°C in the nail penetration test, showing good high-rate discharge capability and thermal management effect. In contrast, Examples 17 (DMMP) and 18 (TCEP) had slightly lower discharge capacity retention rates of 73.0% and 72.5%, respectively, and surface temperatures increased to 106.7°C and 105.9°C, respectively. Example 19 (HCCP) performed worst, with a discharge capacity retention rate of 71.9% and a surface temperature of 103.8°C. However, all examples passed the nail penetration test, proving that the addition of different flame retardants has a positive effect on battery safety. Overall, TEP flame retardant showed the most outstanding performance in improving battery performance and thermal stability.

[0115] In summary, this invention significantly improves the safety and thermal management capabilities of lithium-ion batteries under extreme operating conditions by optimizing the design of the PTC functional layer in the positive electrode, combined with appropriate PTC functional layer thickness, and the ratio of conductive filler and binder. By rationally controlling the composition and structure of the PTC functional layer, it can not only effectively suppress excessive short-circuit current and prevent thermal runaway, but also maintain a high discharge capacity, ensuring the battery's stability under high-rate discharge conditions. This invention, through a multi-dimensional coupled safety mechanism, combined with the synergistic effect of conductive filler and flame-retardant system, effectively reduces battery temperature rise and improves thermal stability, demonstrating broad application prospects.

[0116] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0117] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0118] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery, characterized in that, include: Positive electrode, negative electrode, separator, and electrolyte; The positive electrode includes a positive current collector and a positive coating disposed on at least one side surface of the positive current collector; the negative electrode includes a negative current collector and a negative coating disposed on at least one side surface of the negative current collector; at least one of the positive and negative electrode sheets further includes a PTC functional layer, the PTC functional layer being disposed between the positive current collector and the positive coating, and / or between the negative current collector and the negative coating; the resistivity temperature coefficient of the PTC functional layer is greater than 3.5% within the range of 90℃ to 130℃; The electrolyte includes a flame retardant.

2. The lithium-ion battery according to claim 1, characterized in that, The resistivity temperature coefficient of the PTC functional layer satisfies: ； Where TCR is the temperature coefficient of resistivity, %; ρ is the resistivity at different temperatures T, Ω·cm; ρ0 is the resistivity at 25℃, Ω·cm; T0 is 25℃.

3. The lithium-ion battery according to claim 1, characterized in that, The thickness of the PTC functional layer on one side is 1.5µm to 3.5µm.

4. The lithium-ion battery according to claim 1, characterized in that, The PTC functional layer includes an adhesive and a conductive filler; the adhesive includes one or more of polymethyl methacrylate, polypropylene, and polyvinylidene fluoride; the conductive filler includes at least two of carbon fiber, graphene nanosheets, carbon nanotubes, and conductive carbon black.

5. The lithium-ion battery according to claim 4, characterized in that, The mass ratio of the adhesive to the conductive filler is 0.2~0.42:

1.

6. The lithium-ion battery according to claim 4, characterized in that, The conductive filler includes carbon fibers and graphene nanosheets, and the mass ratio of the carbon fibers to the graphene nanosheets is 1:0.2~0.

4.

7. The lithium-ion battery according to claim 1, characterized in that, The positive electrode coating includes a positive electrode active material, which includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide. And / or, the negative electrode coating includes a negative electrode active material, which includes one or more of deposited silicon carbon, silicon carbon composite materials, natural graphite, artificial graphite, and hard carbon.

8. The lithium-ion battery according to claim 1, characterized in that, The flame retardant includes one or more of triethyl phosphate, dimethyl methylphosphonate, tris(2-chloroethyl) phosphate, and hexachlorocyclotriphosphazene.

9. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery does not catch fire or explode during the nail penetration test, and the highest surface temperature of the lithium-ion battery during the nail penetration test is ≤110℃; wherein, the conditions for the nail penetration test are: steel nail diameter 3mm, penetration speed 10mm / s.

10. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery has a discharge capacity of Q1 at 25°C when discharged at a rate of 1.0C to 2.5V, and a discharge capacity of Q2 at a rate of 10C to 2.5V, where Q2 / Q1 ≥ 65%.

Images