Thermal response current collector, preparation method thereof and battery pole piece

Abstract

The invention discloses a thermal response current collector, a preparation method thereof and a battery pole piece, and belongs to the technical field of lithium battery current collectors. A first polymer, namely a low-melting-point polymer and a second polymer, namely a high-melting-point polymer, are jointly used as a polymer matrix, and the polymer matrix and a conductive filler are subjected to melt blending and film drawing to form a thermal response layer; and thus, the thermal response current collector is constructed. The two polymers are used as matrixes, the relation of room temperature resistance, resistance change temperature and PTC strength is balanced, the prepared reversible thermal response layer has a high resistance state at high temperature in a wide temperature range, and the NTC appearance temperature is increased. The battery using the reversible thermal response layer as a current collector can be effectively turned off in a wide temperature range at a high temperature, so that thermal runaway is avoided. In addition, the polymer and the conductive filler both adopt commercialized raw materials which can be massively produced, that is, the reversible thermal response layer can be massively prepared, so that the cost is relatively low.

Description

Technical Field

[0001] This invention relates to the field of lithium battery current collector technology, specifically to a thermally responsive current collector and its preparation method, and battery electrodes. Background Technology

[0002] Lithium-ion batteries are prone to thermal anomalies under high temperatures or abnormal operating conditions, which can lead to thermal runaway and even a chain reaction of thermal propagation within the battery pack, seriously endangering the lives of users. Currently, batteries primarily rely on temperature monitoring systems such as Battery Management Systems (BMS) for passive safety protection. To further improve battery safety, it is necessary to optimize internal battery components to proactively prevent thermal runaway at its source.

[0003] As a key component of a battery, the current collector primarily functions to conduct electricity and support the positive and negative electrode materials. However, the current collector does not participate in the internal electrochemical reactions of the battery and makes no contribution to the battery's energy density. Nevertheless, the current collector is one of the main factors influencing internal short circuits in a battery. By specially designing the current collector to give it functionality, the intrinsic safety performance of the battery's current collector can be achieved. Designing a reversible thermally responsive layer on or inside the current collector is a reliable solution. This reversible thermally responsive layer can conduct electrons at the battery's normal operating temperature; as the temperature rises, the reversible thermally responsive layer becomes an electronic insulator, preventing further battery discharge; and when the temperature returns to the battery's normal operating temperature, it transforms back into an electronic conductor, restoring battery performance.

[0004] Currently, reversible thermally responsive layers in existing technologies primarily utilize PTC (positive temperature coefficient) materials. In battery safety protection, PTC materials achieve current limiting and circuit shutdown by causing a sharp increase in resistance at excessively high temperatures. However, many PTC materials, such as the high-PTC strength conductive composite material with an isolation-double percolation structure disclosed in patent application CN109762277A, exhibit a negative temperature coefficient (NTC) effect after the temperature exceeds its melting point. This means that the resistance decreases with increasing temperature, making it impossible to maintain a high-resistance state at high temperatures, thus hindering effective circuit shutdown over a wide temperature range. Furthermore, high temperatures significantly increase the ionic conductivity inside the battery and exacerbate side reactions, making the battery more susceptible to thermal runaway.

[0005] To effectively suppress the NTC effect of PTC materials at high temperatures, existing technologies, such as the invention patent application CN117186629A, disclose an irradiated nylon 12 / carbon black PTC composite material and its preparation method. This method primarily involves radiation crosslinking to form a stable three-dimensional network structure within the PTC material, thereby suppressing the disordered rearrangement of polymer chains above the melting point and preventing the resistivity from decreasing with increasing temperature, thus achieving the goal of suppressing the NTC effect. Another example is the invention patent application CN118085478A, which discloses a solution-based PTC thin film material and its preparation method. This method designs special conductive particles with composite core-shell structures or surface coatings, enabling them to maintain a stable dispersed state and form a more robust conductive network at high temperatures. This limits particle aggregation and migration even after the polymer matrix melts, effectively suppressing the NTC effect. However, all of the above methods for suppressing the NTC effect increase additional costs. Summary of the Invention

[0006] This invention provides a thermally responsive current collector and its preparation method, as well as a battery electrode. It effectively solves the technical problems of existing PTC materials having an NTC effect that prevents the battery from being turned off over a wide temperature range, thus leading to thermal runaway, and the high cost of existing methods for suppressing the NTC effect. At the same time, it provides a thermally responsive current collector that has a high resistance state at high temperatures and over a wide temperature range, increases the temperature at which the NTC effect occurs, and thus effectively turns off the battery at high temperatures.

[0007] The first objective of this invention is to provide a thermally responsive current collector, characterized in that the thermally responsive current collector comprises a thermally responsive layer formed by melt blending a first polymer and a second polymer as the matrix and a conductive filler as the conductive phase, and then stretching the mixture into a film.

[0008] The melting point of the first polymer is 60℃~120℃, and the melting point of the second polymer is 80℃~150℃; the full width at half maximum (FWHM) of the DSC melting peaks of both the first and second polymers is ≥2.5℃, and the DSC melting peak termination temperature (T) of the first polymer is... L3 ) ≥ the onset temperature of the DSC melting peak of the second polymer (T) H1 The peak temperature difference (T) between the DSC melting peak of the first polymer and the DSC melting peak of the second polymer. L2 – T H2 The temperature range is 10℃ to 50℃, meaning that the DSC melting peaks of the first polymer and the second polymer are adjacent or overlap.

[0009] The mass ratio of the first polymer to the second polymer is 0.5 to 10:1.

[0010] In a preferred embodiment, the initial temperature response range of the thermal response layer is 70°C to 130°C.

[0011] In a preferred embodiment, the mass ratio of the matrix to the conductive filler is 1:0.1~0.5.

[0012] In a preferred embodiment, the thermally responsive current collector is formed from a thermally responsive layer, or it is a composite material consisting of a thermally responsive layer and a conductive layer alternately stacked between two adjacent thermally responsive layers.

[0013] In a preferred embodiment, the thickness of the thermally responsive layer is 1 μm to 30 μm.

[0014] In a preferred embodiment, the first polymer is selected from at least one of low-density polyethylene, polypropylene, polyolefin elastomers, ethylene-vinyl acetate copolymers, polyurethane elastomers, thermoplastic elastomers, and polyester materials; the second polymer is selected from at least one of polyethylene, low-density linear polyethylene, high-density polyethylene, ultra-high-density polyethylene, polyvinyl chloride, copolyamide elastomers, and phosphorus-containing flame-retardant copolyesters; the conductive filler is selected from at least one of conductive carbon, conductive metals, conductive ceramics, and conductive polymers. Of the above raw materials, the low-density polyethylene, polypropylene, polyolefin elastomers, and thermoplastic elastomers in the first polymer are purchased from ExxonMobil Chemicals, the polyurethane elastomer is purchased from Dongguan Jinheng Plastics Co., Ltd., and the ethylene-vinyl acetate copolymer and polyester materials are purchased from Mitsui Chemicals, Japan, and the melting point of each raw material in the first polymer is 60°C to 120°C. The polyethylene in the second polymer was purchased from Maclean's Reagents, the low-density linear polyethylene, high-density polyethylene, ultra-high-density polyethylene, and polyvinyl chloride were purchased from Dow Chemical Company of the United States, and the copolyamide elastomer and phosphorus-containing flame-retardant copolyester were purchased from Shanghai Showa Chemical Co., Ltd. The melting point of each raw material in the second polymer is 80℃~150℃.

[0015] A second objective of this invention is to provide a method for preparing the aforementioned thermally responsive current collector, comprising the following steps: The first polymer and the second polymer are melt-blended at a mass ratio of 0.5 to 10:1, and then conductive filler is added for a second melt-blending to obtain PTC masterbatch. The masterbatch is then stretched into a film to form a thermally responsive layer, thus obtaining a thermally responsive current collector.

[0016] Alternatively, the first polymer and the second polymer are melt-blended at a mass ratio of 0.5 to 10:1, and then conductive filler is added for a second melt-blending to obtain PTC masterbatch. The masterbatch is then stretched into a film to form a thermally responsive layer. The two thermally responsive layers are then composited onto the upper and lower surfaces of the conductive layer to obtain a thermally responsive current collector.

[0017] In a preferred embodiment, the temperature of the first melt blend is 100℃~150℃; the temperature of the second melt blend is 120℃~180℃.

[0018] In a preferred embodiment, the composite is hot-pressed at 100°C to 160°C.

[0019] A third objective of this invention is to provide a battery electrode sheet, which is obtained by coating the surface of the aforementioned thermally responsive current collector with a battery positive or negative electrode material.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a thermally responsive current collector. It uses a first polymer (a low-melting-point polymer) and a second polymer (a high-melting-point polymer) as the polymer matrix, which are melt-blended with conductive fillers and then stretched into a film to form a thermally responsive layer, thus constructing the thermally responsive current collector. By using the two polymers as the matrix, the relationship between room temperature resistance, resistive switching temperature, and PTC intensity is balanced. The thermally responsive layer prepared by this invention has excellent reversibility; it can normally transport electrons at room temperature, blocks electron transport at high temperatures, and can transport electrons again after returning to room temperature from high temperature, ensuring that the battery stops working at high temperatures and resumes normal operation after returning to room temperature. The thermally responsive current collector provided by this invention has a high resistive state at high temperatures and over a wide temperature range, increasing the temperature at which NTC occurs, without requiring additional complex processes. Batteries using this reversible thermally responsive layer as the current collector can effectively shut down at high temperatures and over a wide temperature range, thereby avoiding thermal runaway. Furthermore, the polymers and conductive fillers mentioned above are commercially available raw materials that can be mass-produced, meaning that the above-mentioned thermally responsive layer current collector can be mass-produced, thus reducing costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the thermally responsive current collector of the present invention, wherein 1 is a conductive layer and 2 is a thermally responsive layer.

[0022] Figure 2 The DSC curves are for two polymers with different melting points used in this invention: the first polymer (low melting point polymer) and the second polymer (high melting point polymer).

[0023] Figure 3 These are the resistance-temperature curves of two polymers with different melting points and their thermal response layers used in this invention, where a represents the two polymers with different melting points and b represents the thermal response layer.

[0024] Figure 4 The resistance-temperature curves of the thermally responsive current collectors prepared in Examples 1, 1, and 2 of this invention are shown.

[0025] Figure 5 The resistance-temperature curve of the thermally responsive current collector prepared in Comparative Example 3 of this invention.

[0026] Figure 6 The charge-discharge curves of SiC || NCM811 batteries using the thermally responsive current collectors of Example 1 and Comparative Example 3 of the present invention are shown at different temperatures (the black line represents the charge-discharge curves at room temperature, and the red line represents the charge-discharge curves at high temperature, where a is Example 1 and b is Comparative Example 3). Detailed Implementation

[0027] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0028] For existing thermally responsive current collectors in batteries, the reversible thermally responsive layer in current-generated technologies mainly uses PTC (positive temperature coefficient) materials. In battery safety protection, PTC materials achieve current limiting and circuit shutdown by rapidly increasing resistance at excessively high temperatures. However, many PTC materials exhibit a negative temperature coefficient (NTC) effect after exceeding their melting point, meaning their resistance decreases with increasing temperature. This characteristic prevents them from maintaining a high-resistance state at high temperatures, making it difficult to effectively shut down the circuit over a wide temperature range. Furthermore, high temperatures significantly increase the ionic conductivity inside the battery and exacerbate side reactions, making the battery more susceptible to thermal runaway. Existing methods for suppressing the NTC effect of PTC materials at high temperatures all increase costs. Based on the above technical problems, this invention provides a thermally responsive current collector, its preparation method, and a battery electrode.

[0029] The technical solution of the present invention will be described below.

[0030] The present invention provides a thermally responsive current collector, characterized in that the thermally responsive current collector comprises a thermally responsive layer formed by melt blending a first polymer and a second polymer as the matrix and a conductive filler as the conductive phase, and stretching the mixture into a film.

[0031] The melting point of the first polymer is 60℃~120℃, and the melting point of the second polymer is 80℃~150℃; the full width at half maximum (FWHM) of the DSC melting peaks of both the first and second polymers is ≥2.5℃, and the DSC melting peak termination temperature (T) of the first polymer is... L3 ) ≥ the onset temperature of the DSC melting peak of the second polymer (T) H1 The peak temperature difference (T) between the DSC melting peak of the first polymer and the DSC melting peak of the second polymer. L2 – T H2 The temperature range is 10℃ to 50℃, meaning that the DSC melting peaks of the first polymer and the second polymer are adjacent or overlap.

[0032] In the above technical solution, a low-melting-point polymer and a high-melting-point polymer are used together as the polymer matrix. These are melt-blended with conductive fillers and then stretched into a film to form a thermally responsive layer, thereby constructing a thermally responsive current collector. Using these two polymers as the matrix balances the relationship between room temperature resistance, resistive switching temperature, and PTC strength. The thermally responsive layer prepared by this invention exhibits excellent reversibility; it can normally transport electrons at room temperature, blocks electron transport at high temperatures, and can transport electrons again after returning to room temperature from high temperature. This ensures that the battery stops working at high temperatures and resumes normal operation after returning to room temperature. The thermally responsive current collector provided by this invention has a high resistivity state at high temperatures and over a wide temperature range, increasing the temperature at which NTC occurs, without requiring additional complex processes. Batteries using this reversible thermally responsive layer as the current collector can effectively shut down at high temperatures and over a wide temperature range, thereby avoiding thermal runaway.

[0033] The technical effects of the present invention will be described below through specific embodiments and comparative examples.

[0034] Example 1 A thermally responsive current collector includes a conductive layer and thermally responsive layers disposed on the upper and lower surfaces of the conductive layer. The conductive layer is aluminum foil with a thickness of 15 μm; the single-layer thickness of the thermally responsive layer is 5 μm. Polyolefin elastomer (POE, melting point 94°C) is used as the first polymer, purchased from ExxonMobil Chemicals; linear low-density polyethylene (LLDPE, melting point 122°C) is used as the second polymer, purchased from Dow Chemical; and acetylene black (ACET) is used as the conductive filler, purchased from DENKA, Japan.

[0035] The above-mentioned method for preparing thermally responsive current collectors includes the following steps: S1, POE and LLDPE are melt-blended in an internal mixer at a mass ratio of 6:4. The mixing temperature is set to 150°C and the mixing time is 20 minutes to obtain the blended polymer matrix masterbatch.

[0036] S2, ACET at a mass ratio of 50% of the blended polymer matrix masterbatch is added to the above-mentioned internal mixer for further blending. The mixing temperature is set to 160°C and the mixing time is 20 minutes to obtain PTC masterbatch. Film is then stretched at a temperature of 230°C, a winding speed of 10 m / min, a contact pressure of 50 N, a winding-unwinding stretching speed difference of 0.1 m / min, and a winding-unwinding tension of 30 N to form a thermally responsive layer.

[0037] S3. The two thermally responsive layers are hot-pressed on the upper and lower surfaces of the aluminum foil respectively. The hot-pressing temperature is 150℃ and the hot-pressing time is 10 minutes to obtain the thermally responsive current collector, which is denoted as POE\LLDPE\ACET-Al current collector.

[0038] Example 2 A thermally responsive current collector includes a conductive layer and thermally responsive layers disposed on the upper and lower surfaces of the conductive layer. The conductive layer is a PI / CNTs composite film with a thickness of 10 μm; the single-layer thickness of the thermally responsive layer is 5 μm. Ethylene-vinyl acetate copolymer (EVA, melting point 86℃) is used as the first polymer, purchased from Mitsui Chemicals, Japan; polybutylene succinate (PBS, melting point 115℃) is used as the second polymer, purchased from Shanghai Showa Chemicals Co., Ltd.; and carbon black (CB) is used as the conductive filler, purchased from Guangdong Zhuguang New Energy Technology Co., Ltd.

[0039] The above-mentioned method for preparing thermally responsive current collectors includes the following steps: S1. EVA and PBS are melt-blended in a mixer at a mass ratio of 9:1. The mixing temperature is set to 140°C and the mixing time is 25 minutes to obtain the blended polymer matrix masterbatch.

[0040] S2, CB at 35% by mass of the blended polymer matrix masterbatch is added to the above-mentioned internal mixer for further blending. The mixing temperature is set to 150°C and the mixing time is 25 minutes to obtain PTC masterbatch. Film is then stretched at a temperature of 230°C, a winding speed of 10 m / min, a contact pressure of 50 N, a winding-unwinding stretching speed difference of 0.1 m / min, and a winding-unwinding tension of 30 N to form a thermally responsive layer.

[0041] S3. The two thermally responsive layers are hot-pressed on the upper and lower surfaces of the PI\CNTs composite film at a temperature of 140℃ for 10 minutes to obtain the thermally responsive current collector, denoted as EVA\PBS\CB-PI\CNTs current collector.

[0042] Example 3 A thermally responsive current collector includes a conductive layer and thermally responsive layers disposed on the upper and lower surfaces of the conductive layer. The conductive layer is battery-grade carbon cloth; the thickness of a single thermally responsive layer is 5 μm. Thermoplastic polyurethane elastomer (TPU, melting point 94°C) is used as the first polymer, purchased from Dongguan Jinheng Plastics Co., Ltd.; low-density polyethylene (LDPE, melting point 115°C) is used as the second polymer, purchased from Sinopec Maoming; and carbon black of grade BP2000 is used as the conductive filler, purchased from Cabot Corporation.

[0043] The above-mentioned method for preparing thermally responsive current collectors includes the following steps: S1, TPU and LDPE are melt-blended in an internal mixer at a mass ratio of 5:5. The mixing temperature is set to 140℃ and the mixing time is 25 minutes to obtain the blended polymer matrix masterbatch.

[0044] S2, BP2000 carbon black, accounting for 40% of the mass of the blended polymer matrix masterbatch, is added to the above-mentioned internal mixer for further blending. The internal mixing temperature is set to 150°C and the internal mixing time is 25 minutes to obtain PTC masterbatch. Film is then stretched at a temperature of 260°C, a winding speed of 10m / min, a contact pressure of 50N, a winding-unwinding stretching speed difference of 0.1m / min, and a winding-unwinding tension of 30N to form a thermally responsive layer.

[0045] S3. The two thermally responsive layers are hot-pressed onto the upper and lower surfaces of the battery-specific carbon cloth. The hot-pressing temperature is 140℃ and the hot-pressing time is 10 minutes to obtain the thermally responsive current collector, which is denoted as TPU\LDPE\BP2000-carbon cloth current collector.

[0046] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows.

[0047] Comparative Example 1 The difference compared to Example 1 is that the second polymer is removed.

[0048] A thermally responsive current collector includes a conductive layer and thermally responsive layers disposed on the upper and lower surfaces of the conductive layer. The conductive layer is an aluminum foil with a thickness of 15 μm; the single-layer thickness of the thermally responsive layer is 5 μm. Polyolefin elastomer (POE, melting point 94°C) is used as the polymer matrix, purchased from ExxonMobil Chemicals, and acetylene black (ACET) is used as the conductive filler, purchased from DENKA, Japan.

[0049] The above-mentioned method for preparing thermally responsive current collectors includes the following steps: S1, POE and ACET are melt-blended in an internal mixer at a mass ratio of 1:1. The mixing temperature is set to 150℃ and the mixing time is 30 minutes to obtain PCT masterbatch. Film is then stretched at a temperature of 230℃, a winding speed of 10m / min, a contact pressure of 50N, a winding-unwinding stretching speed difference of 0.1 m / min, and a winding-unwinding tension of 30N to form a thermally responsive layer.

[0050] S3. The two thermally responsive layers are hot-pressed on the upper and lower surfaces of the aluminum foil respectively. The hot-pressing temperature is 150℃ and the hot-pressing time is 10 minutes to obtain the thermally responsive current collector, which is denoted as POE\ ACET-Al current collector.

[0051] Comparative Example 2 Compared to Example 1, the first polymer was removed.

[0052] A thermally responsive current collector includes a conductive layer and thermally responsive layers disposed on the upper and lower surfaces of the conductive layer. The conductive layer is aluminum foil with a thickness of 15 μm; the thermally responsive layers have a thickness of 5 μm. Linear low-density polyethylene (LLDPE, melting point 122°C) is used as the polymer matrix, purchased from Dow Chemical Company, USA, and acetylene black (ACET) is used as the conductive filler, purchased from DENKA, Japan.

[0053] The above-mentioned method for preparing thermally responsive current collectors includes the following steps: S1. LLDPE and ACET are melt-blended in an internal mixer at a mass ratio of 1:1. The mixing temperature is set to 150℃ and the mixing time is 30 minutes to obtain PTC masterbatch. Film is then stretched at a temperature of 260℃, a winding speed of 10 m / min, a contact pressure of 50 N, a winding-unwinding stretching speed difference of 0.1 m / min, and a winding-unwinding tension of 30 N to form a thermally responsive layer.

[0054] S3. The two thermally responsive layers are hot-pressed on the upper and lower surfaces of the aluminum foil respectively. The hot-pressing temperature is 150℃ and the hot-pressing time is 10 minutes to obtain the thermally responsive current collector, which is denoted as LLDPE\ACET-Al current collector.

[0055] Comparative Example 3 A thermally responsive current collector includes a conductive layer and thermally responsive layers disposed on the upper and lower surfaces of the conductive layer. The conductive layer is aluminum foil with a thickness of 15 μm; the thermally responsive layers have a thickness of 5 μm. Polyethylene (PE, melting point 102℃) is used as the polymer matrix, purchased from Maclean's reagents, and carbon black (CB) is used as the conductive filler, purchased from Guangdong Candlelight New Energy Technology Co., Ltd.

[0056] The above-mentioned method for preparing thermally responsive current collectors includes the following steps: S1, PE and CB are melt-blended in an internal mixer at a mass ratio of 6.5:3.5. The mixing temperature is set at 140℃ and the mixing time is 30 minutes to obtain PTC masterbatch. Film is then stretched at a temperature of 260℃, a winding speed of 10 m / min, a contact pressure of 50 N, a winding-unwinding stretching speed difference of 0.1 m / min, and a winding-unwinding tension of 30 N to form a thermally responsive layer.

[0057] S3. The two thermally responsive layers are hot-pressed on the upper and lower surfaces of the aluminum foil respectively. The hot-pressing temperature is 140℃ and the hot-pressing time is 10 minutes to obtain the thermally responsive current collector, which is denoted as PE\CB-Al current collector.

[0058] The structure and performance of the thermally responsive current collectors provided in the above embodiments and comparative examples of the present invention were characterized and tested, and the results are as follows.

[0059] Figure 1The diagram illustrates the structure of the thermally responsive current collector of this invention. 1 is a conductive layer (metal or other conductive layer), which can be a single-layer or multi-layer structure. This invention does not impose any particular restrictions on its form or material; it primarily serves to conduct electricity or provide support. 2 is a thermally responsive layer, which can be used alone as a battery current collector or mounted on 1.

[0060] Because high-melting-point polymers have high crystallinity, and conductive particles are mainly distributed in the amorphous phase, their conductive networks are more easily formed under the same conductive particle content, playing a dominant role at room temperature and achieving low room temperature resistance. Figure 2 As shown, when the temperature reaches T L1 At this point, the crystalline phase in the first polymer (low-melting-point polymer) begins to melt and transform into the amorphous phase, meaning the thermally responsive layer resistance begins to increase, achieving a low resistance transition temperature; when the temperature further increases to T... H1 At this point, the crystalline phase in the second polymer (high-melting-point polymer) begins to melt and transform into the amorphous phase. At this time, the resistivity of the thermally responsive layer further increases, achieving high PTC strength. Since the thermally responsive layer is composed of two polymers, when the temperature exceeds T... H3 Only when the resistance drops significantly will the NTC effect be delayed, allowing the battery to shut off over a wide temperature range. Figure 3 As shown.

[0061] Compared to traditional current collectors and ordinary composite current collectors, this invention provides a thermally responsive layer for a wide-temperature-range two-stage PTC, thereby constructing a thermally responsive current collector. For example... Figure 2 As shown, the DSC melting peak onset temperature T of the second polymer (high melting point polymer) is... H1 Satisfy T L1 ≤T H1 ≤T L3 The DSC melting peak end temperature T of the first polymer (low melting point polymer) L1 Satisfy T H1 ≤T L1 ≤T H3This means that the melting peaks of the two polymers partially overlap or connect, thus achieving low room temperature resistance, low resistance switching temperature, high PTC strength, and a wide high resistance temperature range at high temperatures, delaying the onset of NTC. Batteries using this thermally responsive current collector exhibit superior safety performance at high temperatures, avoiding the severe NTC effect of traditional PTC materials after the temperature exceeds the melting point. This allows the thermally responsive current collector to shut off the battery over a wide temperature range, ensuring battery safety. Based on the fundamental characteristics of positive temperature coefficient thermistors, the onset response temperature of the thermally responsive current collector is defined as twice the resistance value at room temperature (25℃~30℃). When the temperature exceeds this response temperature, the resistance value increases exponentially. The thermally responsive current collector prepared in Example 1 of this invention has an initial response temperature of approximately 80°C, the thermally responsive current collector prepared in Example 2 has an initial response temperature of approximately 70°C, the thermally responsive current collector prepared in Example 3 has an initial response temperature of approximately 90°C, the thermally responsive current collector prepared in Comparative Example 1 has an initial response temperature of approximately 80°C, the thermally responsive current collector prepared in Comparative Example 2 has an initial response temperature of approximately 100°C, and the thermally responsive current collector prepared in Comparative Example 3 has an initial response temperature of approximately 85°C.

[0062] Because the resistance-temperature curve of PTC materials has a strong correlation with the DSC curve, the resistance-temperature curve can be used to directly indicate the performance of PTC. For example... Figure 4 As shown, Example 1 uses a matrix formed by blending POE and LLDPE, Comparative Example 1 uses POE as the matrix, and Comparative Example 2 uses LLDPE as the matrix. With the same proportion of conductive filler added, the resistance-temperature curve of Example 1 is a chelation of Comparative Example 1 and Comparative Example 2. At room temperature, the resistance of Comparative Example 2 is lower than that of Comparative Example 1, while the resistance of Example 1 is close to the room temperature resistance of Comparative Example 2. When the temperature approaches the melting point of POE, the resistance of both Comparative Example 1 and Example 1 begins to rise; when the temperature reaches the melting point of POE, the resistance of Comparative Example 1 reaches a maximum, at which point Example 1 exhibits a local maximum in the first PTC stage; as the temperature rises further, the resistance of Comparative Example 1 begins to decrease, while the resistance of the LLDPE component in Example 1 begins to rise, offsetting the decreasing trend of the POE component resistance; when the temperature rises further to near the melting point of LLDPE, a local maximum appears in the second PTC stage of Example 1; after the temperature rises further, the resistance of Example 1 and Comparative Example 2 begin to show the same decreasing trend.

[0063] The resistance-temperature curve of Comparative Example 3, which has a narrower DSC peak and higher crystallinity, is shown below. Figure 5As shown, when the temperature reaches near the melting point, the resistance increases sharply, exhibiting a significant PTC effect; when the temperature exceeds the melting point, the resistance decreases sharply, exhibiting a significant NTC effect. In summary, Example 1 achieves low room temperature resistance, low resistance switching temperature, high PTC intensity, and a wide high resistance temperature range at high temperatures, thus delaying the onset of NTC.

[0064] The battery prepared using the thermally responsive current collector of Example 1 of this invention is specifically prepared as follows: NCM811 ternary cathode slurry (mass ratio of NCM811 ternary material: conductive carbon black: binder = 97:1.5:1.5) is coated on the upper and lower surfaces of the POE / LLDPE / ACET-Al current collector, with a single-sided loading of 10 mg / cm³. 2 The negative electrode uses copper foil as the current collector, and graphite negative electrode slurry (graphite:CMC:SBR:conductive carbon black mass ratio = 95:1.5:2.5:1) is coated on both the upper and lower surfaces of the copper foil, with a single-sided loading of 6.2 mg / cm³. 2 The processing technology and process control of the positive and negative electrodes both adopt currently industrialized technologies. The processed positive and negative electrode materials are cut into 6cm × 8cm pieces. A mixed solution of 1mol / L LiPF6 ethylene carbonate and dimethyl carbonate (volume ratio = 1:1) is used as the electrolyte at a concentration of 2.5g / Ah. A Celgard 2400 polypropylene porous membrane is used as the separator. The cells are assembled into a full cell in an argon-filled glove box to obtain the battery sample. The battery prepared in this embodiment has a designed capacity of 0.57Ah, using four layers of positive electrode sheets containing POE, LLDPE, and ACET-Al current collectors and three layers of negative electrode sheets, stacked in a positive-negative-positive-negative-positive-negative-positive configuration. Constant current charging is performed at room temperature, and constant current discharge is performed at 80°C. The battery cannot discharge normally, i.e., the battery is turned off. After the battery returns to room temperature, constant current discharge is performed, and the battery discharges normally, indicating that the battery is usable. Change the high-temperature discharge temperature and repeat the above steps. If the battery cannot discharge within the range of 80℃~120℃, but can charge and discharge normally at room temperature, it indicates that it has a wide temperature range for high-temperature shutdown. Figure 6 As shown in a.

[0065] The battery prepared using the current collector from Comparative Example 3 was fabricated in the same way as above, except that the current collector used at the positive electrode was a PE / CB-Al current collector. When subjected to constant current charging at room temperature and constant current discharging at 100°C, the battery could not discharge normally, i.e., the battery was shut off. However, when the battery returned to room temperature and was subjected to constant current discharging again, it discharged normally, meaning the battery could be used normally. Figure 6As shown in b. By changing the high-temperature discharge temperature and repeating the above steps, the battery was able to discharge within the range of 110℃ to 130℃, indicating that the comparison battery could not be shut down at higher temperatures, meaning that it could not be shut down at high temperatures and over a wide temperature range.

[0066] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A thermally responsive current collector, characterized in that, The thermally responsive current collector comprises a thermally responsive layer formed by melt blending and film stretching of a first polymer and a second polymer as the matrix and a conductive filler as the conductive phase. The melting point of the first polymer is 60℃~120℃, and the melting point of the second polymer is 80℃~150℃; the half-width of the DSC melting peak of the first polymer and the second polymer is ≥2.5℃, the end temperature of the DSC melting peak of the first polymer is ≥ the start temperature of the DSC melting peak of the second polymer, and the peak temperature difference between the DSC melting peak of the first polymer and the DSC melting peak of the second polymer is 10℃~50℃. The mass ratio of the first polymer to the second polymer is 0.5 to 10:

1.

2. The thermally responsive current collector according to claim 1, characterized in that, The initial temperature response range of the thermal response layer is 70℃~130℃.

3. The thermally responsive current collector according to claim 1, characterized in that, The mass ratio of the matrix to the conductive filler is 1:0.1~0.

5.

4. The thermally responsive current collector according to claim 1, characterized in that, The thermally responsive current collector is formed by a thermally responsive layer, or by a thermally responsive layer and a conductive layer alternately stacked between two adjacent thermally responsive layers.

5. The thermally responsive current collector according to claim 1, characterized in that, The thickness of the thermally responsive layer is 1 μm to 30 μm.

6. The thermally responsive current collector according to claim 1, characterized in that, The first polymer is selected from at least one of low-density polyethylene, polypropylene, polyolefin elastomers, ethylene-vinyl acetate copolymers, polyurethane elastomers, thermoplastic elastomers, and polyester materials; The second polymer is selected from at least one of polyethylene, low-density linear polyethylene, high-density polyethylene, ultra-high-density polyethylene, polyvinyl chloride, copolyamide elastomer, and phosphorus-containing flame-retardant copolyester; the conductive filler is selected from at least one of conductive carbon, conductive metal, conductive ceramic, and conductive polymer.

7. A method for preparing the thermally responsive current collector according to claim 4, characterized in that, Includes the following steps: The first polymer and the second polymer are melt-blended at a mass ratio of 0.5 to 10:1, and then conductive filler is added for a second melt-blending to obtain PTC masterbatch. The masterbatch is then stretched into a film to form a thermally responsive layer, thus obtaining a thermally responsive current collector. Alternatively, the first polymer and the second polymer are melt-blended at a mass ratio of 0.5 to 10:1, and then conductive filler is added for a second melt-blending to obtain PTC masterbatch. The masterbatch is then stretched into a film to form a thermally responsive layer. The two thermally responsive layers are then composited onto the upper and lower surfaces of the conductive layer to obtain a thermally responsive current collector.

8. The method for preparing a thermally responsive current collector according to claim 7, characterized in that, The temperature of the first melt blend is 100℃~150℃; the temperature of the second melt blend is 120℃~180℃.

9. The method for preparing a thermally responsive current collector according to claim 7, characterized in that, The composite process involves hot pressing at 100℃~160℃.

10. A battery electrode, characterized in that, The battery electrode is obtained by coating the surface of the thermally responsive current collector as described in any one of claims 1 to 6 with the battery positive or negative electrode material.

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