A high-safety coating current collector for new energy electric vehicles and lithium battery

Abstract

The application discloses a high-safety coating current collector for new energy electric vehicles and a lithium battery. The high-safety coating current collector for new energy electric vehicles comprises a conductive base material and a temperature response coating coated on at least one surface of the conductive base material, wherein the temperature response coating comprises a fusible polymer, a conductive agent and a binder; the fusible polymer is one of polyethylene, polypropylene, polyethylene oxide, polymethyl methacrylate or a copolymer thereof, and the melting point of the fusible polymer is between 130 DEG C and 180 DEG C. In the early stage when a thermal runaway chain reaction is ignited, that is, at the initial moment when the temperature abnormally rises, the internal resistance is automatically and rapidly increased to a large extent, and even the current loop is cut off, by virtue of the material characteristics, so that the safety risk of the battery system is suppressed in the budding state, and the battery safety level is improved.

Description

Technical Field

[0001] This application relates to the field of energy storage applications in new energy vehicles, and in particular to a high-safety coated current collector and lithium battery for new energy electric vehicles. Background Technology

[0002] Lithium-ion batteries and other rechargeable batteries have been widely used in new energy electric vehicles and other fields due to their advantages such as high energy density and long cycle life. However, their safety issues, especially the risk of thermal runaway, remain a key challenge restricting their further development. Thermal runaway is usually triggered by abuse conditions such as internal short circuits, overcharging, and overheating, leading to a chain of exothermic reactions that may ultimately result in serious consequences such as fires and explosions.

[0003] To improve battery safety, existing technologies mainly focus on two levels: external management and internal passive protection. At the external management level, a Battery Management System (BMS) is commonly used. This system monitors parameters such as voltage, current, and temperature in real time, issuing alarms or cutting off circuits when abnormalities occur. However, the response of a BMS depends on the accuracy of the sensors and the speed of signal transmission and processing, exhibiting a certain degree of lag, and it cannot prevent violent chemical reactions already occurring inside the battery. At the internal passive protection level, functional separators are primarily used, such as ceramic coatings on polyolefin separators or thermal shutdown separators. Thermal shutdown separators melt and close pores when the temperature exceeds the melting point of their polymer substrate, thus blocking electron transport. However, this protection is inherently "passive," as its response occurs after a thermal runaway chain reaction has begun, and the battery permanently fails after pore closure. Furthermore, the mechanical strength of the separator decreases at high temperatures, posing a risk of shrinkage and rupture, which could exacerbate internal short circuits.

[0004] In summary, existing mainstream safety technologies such as BMS and functional diaphragms are "passive" or "external" strategies that intervene or remedy during or after thermal runaway. They are unable to provide immediate, intrinsic blocking at the earliest critical point of the thermal runaway chain reaction, and cannot break the vicious cycle from the source electrode reaction of energy supply.

[0005] Therefore, developing an intrinsic safety technology that can be built into key battery components and can actively, spontaneously, and quickly cut off the current path in the early stages of overheating to prevent thermal runaway has become an urgent need to improve battery safety. Summary of the Invention

[0006] The purpose of this application is to overcome the shortcomings of existing battery safety technologies that rely heavily on external management systems or passive protection measures such as separators, and to provide a high-safety coated current collector and lithium battery for new energy electric vehicles.

[0007] The first inventive objective of this invention is achieved through the following technical solution: A high-safety coated current collector for new energy electric vehicles includes a conductive substrate and a temperature-responsive coating applied to at least one surface of the conductive substrate. The temperature-responsive coating comprises a fusible polymer, a conductive agent, and a binder; The meltable polymer is one of polyethylene, polypropylene, polyethylene oxide, polymethyl methacrylate or copolymers thereof, and the melting point of the meltable polymer is between 130°C and 180°C.

[0008] By adopting the above technical solution, a porous composite coating consisting of a fusible polymer, a conductive agent, and a binder is coated on the surface of the current collector. When the battery is working normally (usually -20℃ to 60℃), the fusible polymer in the coating is solid and forms a stable composite structure rich in ion transport channels together with the conductive agent, ensuring efficient conduction of electrons and ions. However, when the battery experiences localized overheating due to misuse, and the temperature rises to a first threshold near the melting point of the selected polymer (e.g., >130°C), the mobility of the polymer molecular chain segments increases dramatically. The material begins to soften and expand in volume, leading to irreversible deformation of the coating's microstructure—pores are compressed and connectivity decreases. This process significantly increases the migration resistance of lithium / sodium ions within the coating, manifesting as a sharp increase in the battery's internal resistance, thus forming a warning signal. If the temperature continues to rise to the second threshold (e.g., >150℃), the polymer completely melts and flows. Driven by capillary action and interfacial tension, it redistributes and fills the remaining pores of the coating, eventually forming a continuous and dense insulating film on the surface of the current collector. This film physically blocks the electron transport path between the active material and the current collector, while its dense structure also completely isolates the passage of ions, thereby forcibly terminating the electrochemical reaction inside the battery and achieving a controllable and non-destructive "soft failure". By incorporating the safety response function into the current collector coating, the material's own properties drive the automatic and rapid increase in internal resistance and even the interruption of the current loop in the early stages of the thermal runaway chain reaction, i.e., the initial moment of abnormal temperature rise. By eliminating the source of electrical energy required to maintain thermal runaway, the positive feedback loop of "heat generation - temperature rise - reaction intensification" is blocked, thereby curbing the safety risks of the battery system in their infancy and improving the battery safety level.

[0009] Optionally, the adhesive is one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid resin, and polyolefin resin.

[0010] By adopting the above technical solution, the binder forms a stable three-dimensional network skeleton in the coating, "anchoring" the functional components (fusible polymer and conductive agent) and ensuring their strong bond with the current collector substrate. Among them, one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid are used as binders. The resulting high-safety coating current collector for new energy electric vehicles is stable under normal working conditions, and does not affect the melting change of the fusible polymer when local overheating occurs, ensuring the operation of the rapid response mechanism.

[0011] Optionally, the adhesive accounts for 3-15% of the total mass of the temperature-responsive coating.

[0012] By adopting the above technical solution, the amount of binder is controlled to avoid excessively low binder content, ensuring that the coating can form a continuous and complete adhesive network, effectively coating and fixing the conductive agent particles and fusible polymer, and ensuring sufficient adhesion between the coating and the current collector substrate to withstand the rolling stress during electrode manufacturing and the shear force generated by the volume change of active material during battery cycling. On the other hand, excessive binder is prevented from overfilling the inherent pores in the coating or covering the conductive agent surface too thickly, avoiding overfilling that reduces the effective channels required for lithium-ion transport and increases the transport distance, ensuring the ionic conductivity and electronic conductivity of the coating at normal operating temperature, and maintaining the rate performance of the battery.

[0013] Optionally, the conductive agent is one or more of carbon black, graphene, and carbon nanotubes, and its mass accounts for 5-30% of the total mass of the temperature-responsive coating.

[0014] By adopting the above technical solution, the conductive agent in the coating plays the role of forming a continuous and highly permeable three-dimensional electronic conduction network. When its total mass ratio is precisely controlled between 5% and 30%, it can ensure that the content of the conductive agent exceeds the "penetration threshold" for forming a continuous conductive network, thereby obtaining a stable high electronic conductivity. At the same time, this upper limit prevents excessive conductive agent from overcrowding the volume share of the fusible polymer and binder, avoiding the obstruction of ion transport due to excessively low coating porosity, or the impact on temperature response characteristics due to changes in mechanical properties.

[0015] Optionally: the conductive agent is composed of carbon black and graphene, wherein graphene accounts for 10-60% of the total mass of the conductive agent.

[0016] By adopting the above technical solution, the conductive agent is composed of carbon black and graphene composite, thereby adjusting the structural characteristics of the three-dimensional electronic conduction network in the coating, making the formed three-dimensional electronic conduction network more sensitive to the microscopic deformation of the coating substrate. In a three-dimensional electronic conduction network, two-dimensional sheet-like graphene forms a dominant layered electron transport path through the stacking and overlapping of surfaces. When the battery is at its normal operating temperature, this composite network provides excellent electronic conductivity. However, once the battery overheats locally, causing the coating temperature to rise to the softening point of the fusible polymer, the polymer matrix melts and undergoes considerable microscopic deformation. This deformation affects the graphene sheets embedded within (the flow of the polymer matrix, the convergence and shunting of the polymer matrix due to surface tension), leading to nanoscale slippage, warping, or separation between the layers. This causes the three-dimensional electronic conduction network to rearrange, resulting in a nonlinear and sharp increase in the electronic resistance of the coating. This, in turn, coordinates with the melt-blocking effect of the fusible polymer to form a multi-level safety protection against battery overheating that is more timely and reliable, further enhancing battery safety.

[0017] Optionally, the temperature-responsive coating may further contain a dielectric constant abrupt change filler; the dielectric constant abrupt change filler is strontium (Sr)-doped barium titanate (Ba). 0.85 Sr 0.15 TiO3 nanoparticles, wherein the phase transition point of the dielectric constant abrupt change filler is 147±5℃.

[0018] By adopting the above technical solution, a dielectric constant abrupt change filler is added to the coating. This dielectric constant abrupt change filler is in the ferroelectric phase at the battery operating temperature and has an extremely high dielectric constant. It will form an enhanced local electric field in the surrounding micro-region, which is beneficial for attracting and guiding lithium ions in the electrolyte, reducing the energy barrier for lithium ions to cross the interfacial double layer and undergo charge transfer, thus having a reducing or stabilizing effect on the interfacial impedance. When the battery is locally overheated and the temperature rises to near the phase transition point of the designed filler, the filler undergoes a rapid transformation from a ferroelectric phase to a paraelectric phase. The change in its crystal structure leads to the disappearance of spontaneous polarization, and the dielectric constant drops sharply by orders of magnitude. Its polarization ability disappears, and the surrounding local enhanced electric field also weakens or even disappears sharply. This significantly increases the energy barrier for lithium ion migration at the interface, resulting in a sharp increase in the interfacial charge transfer impedance. By disabling the "switch" of this property through phase transition, a "high-energy barrier region" for ion migration is rapidly created at the interface, enabling rapid and sensitive regulation of the "field effect" electrochemical safety response and further improving battery safety.

[0019] Furthermore, when the conductive agent contains graphene, it also exhibits a synergistic effect with sheet-like graphene in terms of microstructure. The two-dimensional sheet structure of graphene can physically block the aggregation of dielectric filler nanoparticles, allowing them to be more uniformly dispersed in the polymer matrix. During phase transitions, its perturbation effect on the local electric field can be more uniformly distributed throughout the entire coating, avoiding "hot spots" and "blind spots" caused by aggregation, thus making the "field effect" impedance mechanism more sensitive and consistent. At the same time, the filler particles may also act as spacers between graphene sheets, optimizing the structure of the conductive network.

[0020] Optional: The mass of the filler with a dielectric constant abrupt change accounts for 2-8% of the total mass of the temperature-responsive coating.

[0021] By adopting the above technical solution, the mass ratio of filler with abrupt change in dielectric constant in this application is controlled at 0.5-10%, which can achieve the regulation effect of "local electric field environment" on the coating system, while avoiding negative impact on the basic performance of the coating. When the filler content is not less than 0.5%, it achieves a certain spatial distribution density in the coating, ensuring that a sufficient number of filler particles simultaneously experience a sharp drop in dielectric constant when the temperature reaches its phase transition point. These dispersed, drastically changing "points" can effectively interfere with the overall ion migration environment of the coating through percolation effects or long-range interactions, making the local "field effect" impedance enhancement mechanism macroscopically measurable, thereby contributing significantly to the overall internal resistance of the battery. When the filler content is not higher than 10%, it can prevent the introduction of excessive filler from occupying too much volume, thus avoiding its potential adverse effects on the continuity of the conductive network, the uniformity of the polymer matrix, and the pore structure of the coating. This ensures that the electronic conductivity, ionic conductivity, and mechanical properties of the coating are not significantly impaired at normal operating temperatures.

[0022] A lithium battery, comprising the aforementioned high-safety coated current collector for new energy electric vehicles.

[0023] By adopting the above technical solution, the battery can quickly respond and block as its temperature rises, resulting in high safety.

[0024] In summary, this application has at least the following beneficial effects: 1. By synergistically implementing three mechanisms—conductive network creep, dielectric mutation, and polymer melting blockage—in terms of time and effect, multi-level protection from early warning to final cut-off is achieved, resulting in a more sensitive and reliable response. The three main response mechanisms are independent of each other in terms of physical and electrical dimensions, yet they also serve as backups for each other. Even if a single mechanism fails partially, the other mechanisms can still provide effective protection, greatly enhancing the overall reliability of the system. 2. Through the optimized design of the types and contents of each component, the coating is ensured to have excellent electronic conductivity, ion permeability and structural stability at normal temperatures, without affecting the basic electrochemical performance of the battery. Detailed Implementation

[0026] raw material Low-density polyethylene (LDPE) powder, commercially available product Sinopec Yanshan Petrochemical LD607, density 0.915–0.925 g / cm³, D 50 Particle size 5μm, melting range 130–134℃, melt index (MI) 7–10g / 10min (190℃ / 2.16kg), crystallinity approximately 45–55%; The carbon black is a conductive carbon black (Swiss Temiko Super P Li), with a particle size of 45±5nm, purity ≥99.5%, and loss on drying ≤0.5%. Graphene nanosheets with a diameter of 5–10 μm (D 50 The thickness is 3-5 layers, the specific surface area is about 150-300 m² / g, the carbon content is ≥97wt%, the oxygen content is ≤2wt%, and the electrical conductivity is ≥1000 S / cm (compacted state). It is prepared by redox method. Polyvinylidene fluoride (PVDF), commercially available products include Arkema Kynar® HSV900 and Arkema Kynar® 761A; The filler with abrupt change in dielectric constant is strontium-doped barium titanate (Ba0). 85 Sr0. 15 TiO3 nanoparticles were prepared by a solid-state reaction method: BaCO3, SrCO3, and TiO2 were used as raw materials and mixed in a molar ratio of Ba:Sr:Ti = 0.85:0.15:1. After ball milling and mixing, the mixture was pre-calcined at 1200–1250℃ for 2–4 hours, and then ground and sieved to obtain perovskite phase BST powder. The true density of the powder was 5.9 g / cm³, and the average particle size D was [missing information]. 50 ≈100nm (particle size distribution 60–150nm), its ferroelectric-paraelectric phase transition point (Curie temperature) was measured to be Tc=150±3℃; strontium-doped barium titanate (Ba0). 85 Sr0. 15 TiO3 is in the ferroelectric phase at room temperature with a dielectric constant εᵣ≈1500–2500@1kHz. When the temperature exceeds the phase transition point, a ferroelectric to paraelectric phase transition occurs, and the dielectric constant drops sharply to εᵣ≈200–500. N-Methylpyrrolidone (NMP), CAS 872-50-4, electronic grade, purity ≥99.9wt%, moisture ≤100ppm, total metal ions ≤1ppm; BASF Ultrason® E-series 2020 P polyethersulfone has a glass transition temperature (Tg) of approximately 220–225°C (DSC method) and a heat distortion temperature (1.8 MPa) of approximately 203°C. The particle size D is obtained by grinding and sieving. 50 5μm; Styrene-butadiene rubber (SBR), BASF Styrofan® ND 656, ground to an average particle size D 50 5μm, vacuum dry at 60℃ for 8h before use to remove residual moisture, moisture content ≤0.5 wt; Sodium carboxymethyl cellulose, Ashland CMC 7HF, degree of substitution 0.8, purity ≥99.0 wt%, average particle size D 50 30μm, vacuum dried at 80℃ for 12h before use until moisture content ≤1.0wt%; Low-neutralization polyacrylic acid (PAA), neutralization degree 30 mol%, number average molecular weight Mn 110,000 Acid value 712 mg KOH / g, Tg 106℃, average particle size D 50 20μm, moisture content ≤2.0wt%, vacuum dried to ≤0.5wt% at 80℃ before use; Multi-walled carbon nanotubes, Nanocyl NC7000, carbon content ≥95wt%, ash content ≤1.5wt%, total metal impurities ≤0.5wt%; Ternary cathode active material, NCM523, chemical formula LiNi0.5Co0.2Mn0.3O2, such as Ningbo Ronbay R523; Artificial graphite, BTR S360, D50=15μm; SBR emulsion, BASF Styrofan® ND 656, solids content 50 wt%.

[0027] Example 1 A high-safety coated current collector for new energy electric vehicles includes a conductive substrate and a temperature-responsive coating applied to both surfaces of the conductive substrate.

[0028] The conductive substrate is an electrolytic copper foil with a thickness of 12μm; Temperature-responsive coatings consist of a fusible polymer, a conductive agent, a binder, and a filler with a dielectric constant abrupt change.

[0029] The meltable polymer is low-density polyethylene (LDPE) powder with an average particle size of 5 μm and a melting range of 130-134℃.

[0030] The conductive agent is a mixture of carbon black and graphene nanosheets, with graphene accounting for 30% of the total mass and carbon black accounting for 70% of the total mass. The graphene nanosheets have a diameter of 5-10 μm and a thickness of 3-5 layers.

[0031] The adhesive is polyvinylidene fluoride (PVDF, HSV900).

[0032] The filler with a sudden change in dielectric constant is strontium (Sr)-doped barium titanate (Ba). 0.85 Sr 0.15 TiO3 nanoparticles with an average particle size of 100 nm were found to have a ferroelectric-paraelectric phase transition point (Curie temperature) of 150 °C.

[0033] A method for preparing a high-safety coated current collector for new energy electric vehicles is as follows: Dissolve 9g of adhesive in 250g of NMP solvent to form a homogeneous adhesive solution; Under stirring, 25g of conductive agent and 6g of dielectric constant change filler are added to the above adhesive solution in sequence and dispersed at high speed to obtain mixed slurry A; Add 60g of the fusible polymer to 56g of NMP solvent and stir at low speed until the powder is fully wetted and initially dispersed to obtain slurry B. Slowly add slurry B to slurry A and continuously stir planetarily until all components are mixed evenly to form a stable and uniform temperature-responsive coating slurry. Using a precision coating machine, the temperature-responsive coating slurry is uniformly coated on both surfaces of a clean and dry conductive substrate, with the wet film thickness controlled at 100 μm. The coated current collector was transferred to a vacuum drying oven at 80°C and dried for 12 hours to completely remove the NMP solvent. After drying, the coating thickness was 10±1μm. The dried coated current collector is cut into the required size using a punching machine to obtain a high-safety coated current collector for new energy electric vehicles.

[0034] Comparative Example 1 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that it uses polyethersulfone with a melting point greater than 180°C in an equal mass to replace low-density polyethylene (LDPE) powder. Specifically, the polyethersulfone is BASF Ultrason® E series 2020 P.

[0035] Example 2 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the binder is styrene-butadiene rubber.

[0036] Example 3 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the binder is sodium carboxymethyl cellulose.

[0037] Example 4 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the binder is low-neutralization polyacrylic acid.

[0038] Example 5 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the binder is a mixture of styrene-butadiene rubber and polyacrylic acid in a mass ratio of 1:0.65.

[0039] Example 6 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of binder used is 1.73g.

[0040] Example 7 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of binder used is 2.82g.

[0041] Example 8 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of binder used is 16.1g.

[0042] Example 9 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of binder used is 23.2g.

[0043] Example 10 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the conductive agent is a single carbon black.

[0044] Example 11 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the conductive agent is a single type of graphene.

[0045] Example 12 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the conductive agent is a single multi-walled carbon nanotube (Nanocyl NC700).

[0046] Example 13 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of conductive agent used is 2.32g.

[0047] Example 14 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of conductive agent used is 3.95g.

[0048] Example 15 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of conductive agent used is 32.2g.

[0049] Example 16 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of conductive agent used is 75g.

[0050] Example 17 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the proportion of graphene in the conductive agent is 5wt%.

[0051] Example 18 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the proportion of graphene in the conductive agent is 10wt%.

[0052] Example 19 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the proportion of graphene in the conductive agent is 60wt%.

[0053] Example 20 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the proportion of graphene in the conductive agent is 70wt%.

[0054] Example 21 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of filler with a dielectric constant abrupt change is 0, the amount of fusible polymer in slurry B is 66g, ensuring that the solid content in the temperature-responsive coating slurry is stable, and the proportion of other components in the coating remains unchanged.

[0055] Example 22 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of filler with a dielectric constant abrupt change is 0.5g.

[0056] Example 23 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of filler with a dielectric constant abrupt change is 2g.

[0057] Example 24 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of filler with a dielectric constant abrupt change is 8g.

[0058] Example 25 A high-safety coated current collector for new energy electric vehicles differs from Example 1 in that the amount of filler with a dielectric constant abrupt change is 11g.

[0059] The coated current collectors and assembled batteries of Examples 1-25 and Comparative Example 1 were tested, and the test items are as follows.

[0060] Coated current collector - resistance test: Semi-automatic equipment was used for testing. The pre-cut coated current collector was placed between copper electrodes with a diameter of 14 mm. The pressure increase rate was controlled at 2 MPa / s. After the pressure was applied to 20-25 MPa, it was held for 10 seconds. During the pressure holding phase, the resistance value was measured using the current commutation method. Subsequently, the pressure was reduced at a rate of 5 MPa / s to complete the test, and R was obtained. 室温 .

[0061] Coated current collector - resistivity change ratio (R) during heating to 200℃ ratio ) Detection: The test was conducted using semi-automatic equipment. The cut rectangular foil was placed between copper electrodes (with heating and temperature control functions) with a diameter of 14 mm. The pressure increase rate was controlled at 2 MPa / s. After the pressure was applied to 20-25 MPa, the pressure was maintained. The heating program was started to raise the electrode temperature from room temperature to 200°C at a heating rate of 2°C / min. During the heating process, the resistance value is recorded every 5°C, or continuous recording is achieved if the equipment allows. Pay special attention to the resistance changes near the melting point of fusible polymers (130–150℃) and near the phase transition point of dielectric fillers (147±5℃), and increase the recording frequency if necessary (record once every 1℃). Continue monitoring until the temperature reaches 200℃, and record the maximum resistance value that occurs during the entire heating process, denoted as R. max (Unit: mΩ), and record R simultaneously. max1 The corresponding temperature T at which it occurs peak ; Calculate the resistance jump ratio for each sample: R ratio =R max1 ÷R 25 Repeat the test 8 times and take the average value.

[0062] Battery assembly method: 1) Slurry preparation Cathode slurry: Ternary cathode active material (NCM523), carbon black, polyvinylidene fluoride (Arkema Kynar®761A) are mixed with NMP at a mass ratio of 96:2:2; the process maintains a vacuum of -0.09MPa, a temperature of 25℃, a slurry solid content of 62%, and a viscosity of 5000mPa·s (25℃). Before discharge, the slurry is passed through a 200-mesh sieve to remove agglomerated particles, and vacuum degassing is performed for 45 minutes. The target for solvent residue is NMP ≤ 500ppm. Negative electrode slurry: Artificial graphite (D...)50 =15μm), carbon black, sodium carboxymethyl cellulose (Ashland CMC 7HF), and SBR emulsion were mixed with deionized water at a mass ratio of 96:1.2:1.2:1.6. The slurry had a solid content of 50% and a viscosity of 3000 mPa·s (25℃). It was then passed through a 120-mesh sieve and degassed for later use. 2) Coating and drying Positive electrode coating: The positive electrode slurry is uniformly coated on both sides of a 14μm thick aluminum foil using a slit extrusion coating method. The coating speed is 12m / min, the die lip gap is 0.3 mm, the design value of the single-sided coating surface density is 24mg / cm², and the total surface density of the double-sided coating is 48mg / cm². After coating, it is dried in a multi-section gradient oven. After drying, the residual NMP of the electrode is ≤500ppm, and the surface is free of cracks and orange peel. Negative electrode coating: The negative electrode slurry is uniformly coated on the current collector with the temperature-responsive safety coating. The coating speed is 10m / min, the single-sided surface density design value is 12mg / cm², and the moisture content after drying is ≤1000ppm. The electrode sheet has no bulging edges and no powder shedding. 3) Roll pressing and slitting The dried positive and negative electrode sheets were separately fed into a two-roll cold press for compaction. The target compaction density of the positive electrode (NCM523) was 3.6 g / cm³, the linear rolling pressure was 150 kN / m, and the porosity after compaction was 32%. The target compaction density of the negative electrode (graphite-based) was 1.60 g / cm³, the linear rolling pressure was 10 kN / m, and the porosity after compaction was 35%. The cells are longitudinally slit and cut according to the battery specifications (width 58 mm). The edges of the electrode sheets are chamfered / rounded, and the edges of the coating are flush with or slightly recessed by 0.3 mm from the edges of the foil. 4) Electrode die-cutting / film preparation Remove the uncoated areas at the beginning and end of the electrode sheet, and use a die-cutting machine to cut out the tab window (U-shaped cut). Positive electrode: Aluminum electrode tabs (0.15 mm thick, 1070 aluminum alloy) are ultrasonically welded in the blank area. Negative electrode: Nickel-plated copper tabs (0.12 mm thick) are ultrasonically welded in the blank area, and insulating tape is attached to the base of the tabs to prevent short circuits; 5) Winding The positive electrode, porous polyolefin separator (PP / PE / PP three-layer composite separator, 16μm thick, 132℃ closed-cell temperature), and negative electrode are sequentially wound into a battery cell by a fully automatic winding machine, and the tabs are welded on. Winding tension: 20N on the positive electrode side, 15N on the negative electrode side, with tension fluctuation within ±5%; diaphragm tension: 8N; winding alignment tolerance: misalignment between electrode and diaphragm ≤0.3 mm, misalignment between electrode pieces ≤0.5 mm. After winding, the two ends of the cell are hot-pressed for shaping (temperature 70℃, pressure 0.3 MPa, holding pressure for 5 s), and then inserted into the steel shell; 6) Assembly and injection The battery cell is placed into the battery casing, the top cover is welded, and a suitable lithium salt electrolyte is injected under low dew point conditions. The electrolyte formula is: 1.0 mol / L LiPF6 dissolved in a mixed solvent of EC / EMC / DMC at a volume ratio of 3:5:2, with additives containing 1.5% VC, 3% FEC, and 0.8% PS. The injection volume is based on an excess coefficient of 1.3× the design capacity. The entire process is carried out in a low dew point environment with a workshop dew point of -38℃ and moisture content controlled to ≤40ppm. 7) Formation and Division After electrolyte injection, the cell was left to stand at 45°C for 24 hours, then charged at a constant current of 0.08C to 3.5V, then charged at 0.15C to 3.8V, and then held at a constant voltage of 3.8V for 45 minutes. The cell temperature was controlled at 25°C during the process for formation. After formation, the battery cells are aged at 45℃ for 24 hours; Charge at a constant current of 0.5C to 4.20V, then at a constant voltage until the current drops to 0.05C, and record the charging capacity; let stand for 20 minutes; discharge at a constant current of 0.5C to 2.80V, and record the discharge capacity (i.e., the capacity rating). Group and classify the cells according to capacity, voltage (≥4.15V), and internal resistance ≤40mΩ. The consistency requirements for cells in the same group are: capacity difference ≤±2%, voltage difference ≤±10mV, and internal resistance difference ≤±5mΩ.

[0063] Battery room temperature internal resistance (1kHz AC internal resistance) testing method The coated current collectors were assembled into finished batteries using conventional battery fabrication methods; at least three parallel batteries were fabricated for each type of coated current collector for statistical analysis. After the AC internal resistance tester (HIOKI BT3562) has been powered on and warmed up for 15 minutes, it should be calibrated using a standard resistor (such as 1mΩ or 10mΩ) to ensure that the error is within ±0.5%. Connect the red and black clips of the four-wire Kelvin clamp to the positive and negative terminals of the battery, ensuring good contact and no looseness. Note that the red and black clips should be placed as close as possible to the base of the terminals, avoiding clamping on the wires or extensions of the terminals; Set the test mode to AC four-wire method, frequency 1kHz, test current 50mA (or device default), and sampling frequency 3 times. Take the arithmetic mean of the three measurements as the battery's internal resistance value R0 (unit: mΩ). Battery thermal chamber testing method The coated current collectors were assembled into finished batteries according to the battery assembly method group; at least 3 parallel batteries were prepared for each type of coated current collector for statistical purposes; Place the battery on a special clamp inside the temperature-controlled chamber, ensuring it does not come into contact with the chamber walls.

[0064] A type K thermocouple is attached to the center of the battery surface and secured with high-temperature resistant tape.

[0065] Connect the positive and negative terminals of the battery to the data acquisition system for real-time monitoring of open circuit voltage (OCV). Connect the clamp of the AC internal resistance tester to the battery terminals and set it to timed measurement mode (automatic measurement every 10 seconds) to record the battery's initial voltage V0, initial internal resistance R0 and initial surface temperature T0 at room temperature (25℃). The constant temperature chamber was set to heat up from room temperature (25°C) at a heating rate of 2°C / min, with a target temperature of 200°C. During the heating process, the following data were continuously recorded: battery surface temperature (°C), battery open circuit voltage (V), and battery AC internal resistance at 1kHz (mΩ). When any of the following phenomena are observed, mark the corresponding temperature and time: Voltage drop: A momentary drop in battery open-circuit voltage of ≥0.1V; Internal resistance surge: The battery's internal resistance increases sharply by ≥10 times its initial value; Surface temperature inflection point: The slope of the battery surface temperature curve changes abruptly (e.g., due to accelerated heating caused by internal exothermic reactions). Continue heating to 200°C or until the battery experiences thermal runaway (voltage drops to zero, temperature rises sharply, smoke or fire). The test results are presented as follows: Safety response trigger temperature (Ttrip): Defined as the battery surface temperature (°C) when the battery internal resistance first appears to be ≥10 times the initial value R0. Response time tresponse: defined as the time (s) from when the battery surface temperature reaches 100℃ (as the overheating initiation reference point) to when a safety response is triggered (internal resistance ≥ 10 × R0); Maximum internal resistance ratio Rmax2 / R0: Record the ratio of the maximum internal resistance value that occurs during the heating process to the initial internal resistance; Voltage holding time: Record the total duration (in seconds) during which the battery voltage is maintained above 3.0V to assess the normal operating time of the battery before a safety response.

[0066] The test results are shown in Table 1-2 below.

[0067] Table 1. Test Results of Coated Current Collector

[0068] Table 2. Test Results of Assembled Batteries

[0069] Comparing Example 1 and Comparative Example 1, the film resistances of Example 1 and Comparative Example 1 are similar, but the Rratio of Example 1 is significantly greater than that of Comparative Example 1; the trigger temperature of the assembled battery in Example 1 is lower than that in Comparative Example 1; the response time of Example 1 is significantly shorter than that in Comparative Example 1; the maximum internal resistance ratio of the assembled battery in Example 1 is significantly greater than that in Comparative Example 1; and the voltage holding time of Example 1 is shorter than that in Comparative Example 1.

[0070] Therefore, this application coats a porous composite coating consisting of a fusible polymer, a conductive agent, and a binder onto the surface of the current collector. When the battery is operating normally, the fusible polymer in the coating is solid and forms a stable composite structure rich in ion transport channels together with the conductive agent, ensuring efficient conduction of electrons and ions. However, when the battery is abused (such as overcharging or short circuit) and local overheats, and the temperature rises to a first threshold near the melting point of the selected polymer (e.g., >130°C), the mobility of the polymer molecular chain segments increases dramatically, the material begins to soften and expand in volume, resulting in irreversible deformation of the coating's microstructure—pores are squeezed and connectivity decreases. This process significantly increases the migration resistance of lithium / sodium ions within the coating, manifesting as a sharp increase in the battery's internal resistance, thus forming a warning signal. If the temperature continues to rise to the second threshold (e.g., >150℃), the polymer completely melts and flows, redistributing and filling the remaining pores in the coating under the drive of capillary action and interfacial tension. Ultimately, a continuous and dense insulating film is formed on the surface of the current collector. This film physically blocks the electron transport path between the active material and the current collector, while its dense structure also completely isolates the passage of ions, thereby forcibly terminating the electrochemical reaction inside the battery and achieving a controllable, non-destructive "soft failure." By "shaping" the safety response function into the current collector coating, in the early stage of the thermal runaway chain reaction ignited, i.e., at the beginning of the abnormal temperature rise, the material's own characteristics drive it to automatically and rapidly increase the internal resistance and even cut off the current loop. By eliminating the source of electrical energy required to maintain thermal runaway, the positive feedback loop of "heat generation - temperature rise - reaction intensification" is blocked, thereby curbing the safety risks of the battery system in their infancy and improving the battery's safety level.

[0071] Comparing Examples 2-5 and Comparative Example 1, Examples 2-5 differ from Example 1 in that they use different adhesives. The Rratio of Examples 2-5 is significantly greater than that of Comparative Example 1, the trigger temperature of Examples 2-5 is significantly lower than that of Comparative Example 1, the response time of Examples 2-5 is significantly shorter than that of Comparative Example 1, the maximum internal resistance ratio of Examples 2-5 is greater than that of Comparative Example 1, and the voltage holding time of Examples 2-5 is shorter than that of Comparative Example 1. Therefore, the adhesive used in this application is one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid resin, and polyolefin resin.

[0072] Comparing Examples 1 and 6-9, the Rratio of Examples 1, 7, and 8 is significantly greater than that of Examples 6 and 9. The triggering temperatures of Examples 1, 7, and 8 are lower than those of Examples 6 and 9. The response times of Examples 1, 7, and 8 are shorter than those of Examples 6 and 9. The maximum internal resistance ratio of Examples 1, 7, and 8 is greater than that of Examples 6 and 9. The voltage holding time of Examples 1, 7, and 8 is shorter than that of Examples 6 and 9. Therefore, in this application, it is preferable that the binder mass accounts for 3-15% of the total mass of the temperature-responsive coating, which controls the adhesion... The amount of binder used should be carefully controlled to avoid excessively low binder content. This ensures that the coating can form a continuous and complete adhesive network, effectively encapsulating and fixing the conductive agent particles and fusible polymers. It also ensures sufficient adhesion between the coating and the current collector substrate to withstand the rolling stress during electrode manufacturing and the shear force generated by the volume change of active materials during battery cycling. On the other hand, excessive binder should be prevented from overfilling the inherent pores in the coating or excessively covering the conductive agent surface. Overfilling reduces the effective channels required for lithium-ion transport and increases the transport distance, ensuring the ionic and electronic conductivity of the coating at normal operating temperatures and maintaining the rate performance of the battery.

[0073] The Rratio and maximum internal resistance ratio of Examples 10-12 are greater than those of Comparative Example 1. However, based on the test results of Example 1, the Rratio and maximum internal resistance ratio of Examples 1 and 11 are greater than those of Examples 10 and 12. The trigger temperature, response time, and voltage holding time of Examples 1 and 11 are also less than those of Examples 10 and 12. Therefore, the conductive agent in this application is one or more of carbon black, graphene, and carbon nanotubes, with carbon black and graphene being preferred. This is related to the structural distribution of the conductive agent in the coating.

[0074] In Example 1, the conductive agent is composed of carbon black and graphene composites. The resulting three-dimensional electronic conduction network is highly sensitive to the microscopic deformation of the coating matrix. In the three-dimensional electronic conduction network, the two-dimensional sheet-like graphene forms a dominant layered electron transport path through the stacking and overlapping of surfaces. When the battery is at normal operating temperature, this composite network provides excellent electronic conductivity. Once the battery is locally overheated and the coating temperature rises to the softening point of the fusible polymer, the polymer matrix melts and undergoes considerable microscopic deformation. This deformation affects the graphene sheets embedded within (the flow of the polymer matrix, the convergence and shunting of the polymer matrix due to surface tension), causing nanoscale slippage, warping, or separation between the layers. This rearrangement of the three-dimensional electronic conduction network leads to a nonlinear and sharp increase in the electronic resistance of the coating. This, in turn, coordinates with the melt-blocking effect of the fusible polymer to form a more timely and reliable multi-level safety protection against battery overheating, further improving battery safety.

[0075] Comparing Example 1 and Examples 13-16, the diaphragm resistance R of Examples 1, 15, and 16 is... 25 Compared to Examples 13-14, the Rratio of Examples 1, 14, and 15 is greater than that of Examples 13 and 16. The trigger temperature and response time of Examples 1, 15, and 16 are lower than those of Examples 6 and 9. The maximum internal resistance ratio of Examples 1 and 15 is greater than that of Examples 13, 14, and 16. The voltage holding time of Examples 1 and 15 is shorter than that of Examples 13, 14, and 16. Therefore, a conductive agent content of 5-30 wt% is preferred in this application. This ensures that the conductive agent content exceeds the "penetration threshold" for forming a continuous conductive network, thereby obtaining a stable high electronic conductivity. At the same time, this upper limit prevents excessive conductive agent from over-crowding the volume share of the fusible polymer and binder, avoiding the obstruction of ion transport due to excessively low coating porosity, or the impact on temperature response characteristics due to changes in mechanical properties.

[0076] Comparing Examples 1 and 17-20, the Rratio and maximum internal resistance ratio of Examples 1, 19, and 20 are greater than those of Examples 17-18. However, the Rratio and maximum internal resistance of Example 20 are lower than those of Example 19. Therefore, when the conductive agent in this application is composed of carbon black and graphene, it is preferable that graphene accounts for 10-60% of the total mass of the conductive agent.

[0077] Comparing Example 1 and Example 21, Example 1 has a significantly higher Rratio and maximum internal resistance ratio than Example 21, a shorter voltage holding time than Example 21, and a trigger temperature similar to Example 21. Therefore, this application incorporates a dielectric constant abrupt change filler into the coating. This filler, which is in the ferroelectric phase at the battery operating temperature, possesses an extremely high dielectric constant and forms an enhanced local electric field in its surrounding micro-region. This facilitates the attraction and guidance of lithium ions in the electrolyte, reducing the energy barrier for lithium ions to cross the interfacial double layer and undergo charge transfer, thus reducing or stabilizing the interfacial impedance. When the battery is locally overheated and the temperature rises to near the phase transition point of the designed filler, the filler undergoes a rapid transition from the ferroelectric phase to the paraelectric phase. The change in its crystal structure leads to the disappearance of spontaneous polarization, resulting in a sharp drop in dielectric constant by orders of magnitude. Its polarization ability disappears, and the surrounding enhanced local electric field weakens or even disappears, significantly increasing the energy barrier for lithium ion migration at the interface, thereby causing a sharp increase in interfacial charge transfer impedance. By disabling this characteristic "switch" through the phase transition, a "high energy barrier region" for ion migration is rapidly created at the interface, achieving rapid and sensitive "field effect" electrochemical safety response regulation, further improving battery safety.

[0078] Furthermore, when the conductive agent contains graphene, it also exhibits a synergistic effect with sheet-like graphene in terms of microstructure. The two-dimensional sheet structure of graphene can physically block the aggregation of dielectric filler nanoparticles, allowing them to be more uniformly dispersed in the polymer matrix. During phase transitions, its perturbation effect on the local electric field can be more uniformly distributed throughout the entire coating, avoiding "hot spots" and "blind spots" caused by aggregation, thus making the "field effect" impedance mechanism more sensitive and consistent. At the same time, the filler particles may also act as spacers between graphene sheets, optimizing the structure of the conductive network.

[0079] Comparing Example 1 and Examples 22-25, the R values ​​of Examples 1, 23, and 24 are... ratio The maximum internal resistance ratio is greater than that of Examples 22 and 25, while the trigger temperature, response time, and voltage holding time of Examples 1, 23, and 24 are less than those of Examples 22 and 25. Therefore, it is preferable to control the mass ratio of filler with abrupt changes in dielectric constant in this application at 0.5-10%. This achieves the effect of regulating the "local electric field environment" of the coating system while avoiding negative impacts on the basic properties of the coating.

[0080] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of protection claimed by the present invention, they are protected by patent law.

Claims

1. A high-safety coated current collector for new energy electric vehicles, comprising a conductive substrate and a temperature-responsive coating applied to at least one surface of the conductive substrate, characterized in that: The temperature-responsive coating comprises a fusible polymer, a conductive agent, and a binder; The meltable polymer is one of polyethylene, polypropylene, polyethylene oxide, polymethyl methacrylate or copolymers thereof, and the melting point of the meltable polymer is between 130°C and 180°C.

2. The high-safety coated current collector for new energy electric vehicles according to claim 1, characterized in that, The adhesive is one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid resin, and polyolefin resin.

3. The high-safety coated current collector for new energy electric vehicles according to claim 2, characterized in that, The adhesive accounts for 3-15% of the total mass of the temperature-responsive coating.

4. The high-safety coated current collector for new energy electric vehicles according to claim 1, characterized in that, The conductive agent is one or more of carbon black, graphene, and carbon nanotubes, and its mass accounts for 5-30% of the total mass of the temperature-responsive coating.

5. A high-safety coated current collector for new energy electric vehicles according to claim 4, characterized in that, The conductive agent is composed of carbon black and graphene, wherein graphene accounts for 10-60% of the total mass of the conductive agent.

6. A high-safety coated current collector for new energy electric vehicles according to claim 1 or 5, characterized in that, The temperature-responsive coating also contains a dielectric constant abrupt change filler; the dielectric constant abrupt change filler is strontium (Sr)-doped barium titanate (Ba). 0.85 Sr 0.15 TiO3 nanoparticles, wherein the phase transition point of the dielectric constant abrupt change filler is 147±5℃.

7. A high-safety coated current collector for new energy electric vehicles according to claim 6, characterized in that, The mass of the filler with a sudden change in dielectric constant accounts for 2-8% of the total mass of the temperature-responsive coating.

8. A lithium battery, characterized in that, The high-safety coated current collector for new energy electric vehicles is described in any one of claims 1-5 or 7.

9. A lithium battery, characterized in that, This includes a high-safety coated current collector for new energy electric vehicles as described in claim 6.

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