MXene / PTC composite current collector, preparation method and application thereof

Abstract

The application discloses a kind of MXene / PTC composite current collector and its preparation method and application, belong to new energy battery key material and intelligent monitoring technical field, intelligent perception composite current collector includes polymer support base film and functional conductive sensing layer;The functional conductive sensing layer is by two-dimensional layered Ti3C2T x The MXene material, the conductive particles with the positive temperature coefficient effect and the polymer binder are compounded.The application utilizes the unique two-dimensional interlayer spacing pressure-sensitive characteristic of MXene and the thermal resistance mutation characteristic of PTC material, so that the current collector has the electronic bus function, can in-situ perceive the battery pole piece expansion pressure and carry out blocking response to local overheating.The design realizes the decoupling monitoring of multiple physical fields in the battery, solves the technical problem that the traditional current collector has single function and cannot perceive internal state.

Description

Technical Field

[0001] This invention relates to the field of key materials and intelligent monitoring technology for new energy batteries, and in particular to an MXene / PTC composite current collector, its preparation method, and its application. Background Technology

[0002] In high-energy chemical power systems such as lithium-ion batteries and solid-state batteries, current collectors play a crucial role. They are both the hub for collecting and conducting electrons generated by electrochemical reactions and the mechanical support framework for the coatings of positive and negative electrode active materials. For a long time, commercial batteries have mainly used copper foil (for the negative electrode) and aluminum foil (for the positive electrode) as current collectors. However, with the continuous pursuit of battery energy density, traditional solid metal foils, due to their high density and high mass ratio, have gradually become a bottleneck restricting further improvement in battery specific energy. In addition, under extreme operating conditions (such as abusive needle puncture), traditional metal foils are prone to generating sharp burrs that can cause serious internal short circuits. To overcome these defects, in recent years, composite current collectors with a typical "sandwich" structure of "metal-polymer-metal" (such as copper or aluminum plated on the surface of PET, PP, or PI base films) have emerged. Composite current collectors, with their lightweight design that significantly improves battery mass energy density and the inherent safety advantage brought by the thermal shrinkage and circuit breaking of the polymer substrate during needle puncture, are becoming a hot research and application area in the power battery field.

[0003] While existing composite current collectors have made progress in terms of lightweighting and safety, they are essentially still single-function "passive" conductive components, unable to sense the complex electrochemical and mechanical evolution within the battery. Especially in the design of next-generation high-energy-density batteries, silicon-based anode materials are widely used due to their ultra-high theoretical specific capacity. However, silicon materials undergo significant volume expansion and contraction (breathing effect) during lithium insertion / extraction cycles. This drastic mechanical deformation generates enormous internal stress within the electrode, leading to the pulverization of active material particles, delamination of the electrode layer from the current collector interface, and ultimately, rapid capacity decay. Current composite current collectors lack the ability to monitor this internal mechanical stress in situ and in real time, making it impossible for battery management systems to accurately predict the risk of structural failure due to stress accumulation.

[0004] Thermal safety is another major challenge facing high-energy-density batteries. When a battery experiences an internal micro-short circuit due to manufacturing defects, or when localized overheating occurs during high-rate charging and discharging, traditional composite current collectors still maintain a highly efficient conductive path. This causes the short-circuit current to continuously generate Joule heat, which rapidly accumulates and induces irreversible thermal runaway. Although there have been attempts in the industry to introduce a positive temperature coefficient (PTC) coating onto the current collector surface to increase resistance and suppress current at high temperatures, existing PTC material systems often suffer from poor conductivity, significantly increasing the battery's internal resistance and sacrificing power performance. Furthermore, their slow thermal response makes it difficult to effectively block current within milliseconds of a short circuit, failing to meet extreme safety protection requirements.

[0005] In summary, future high-performance batteries urgently require a "smart current collector" that integrates electronic conduction, mechanical stress sensing, and active thermal safety protection, upgrading it from a mere "skeleton" to the "nervous system" and "fuse" within the battery. However, achieving this goal faces numerous materials science challenges. For example, traditional carbon nanotube (CNT)-based strain sensors often exhibit severe nonlinear responses under high pressure, making it difficult to accurately quantify the expansion stress of the silicon anode. Furthermore, achieving both highly sensitive pressure monitoring and extremely sensitive temperature cutoff control within a single material system, while effectively decoupling the signals from these two different physical fields, is a key technical challenge that urgently needs to be addressed in the current field of composite current collector technology. Summary of the Invention

[0006] This invention discloses an MXene / PTC composite current collector, its preparation method, and its application. This composite current collector not only retains the basic functions of traditional current collectors in collecting and transmitting electrons and the lightweight advantages of composite current collectors, but also integrates a microscopic intelligent response system. While undertaking efficient electron transmission, it can achieve in-situ, high-sensitivity monitoring of the expansion pressure of battery electrodes and provide instantaneous, blocking response to local overheating. This significantly improves the intelligent management level and intrinsic safety of high-energy-density batteries, thereby solving the technical problems of existing composite current collectors having single functions, being unable to perceive the evolution of mechanical stress inside the battery in real time, and lacking a rapid active thermal safety protection mechanism.

[0007] To achieve the above objectives, this invention discloses an MXene / PTC composite current collector, comprising: Polymer supporting base film; A functional conductive sensing layer is attached to a polymer support base film; The functional conductive sensing layer comprises a micro / nano composite conductive network and a polymer binder. The micro / nano composite conductive network consists of two-dimensional layered Ti3C2T x It is composed of cross-linked MXene nanosheets and conductive particles.

[0008] Preferably, it further includes a metal conductive layer, which is deposited on the surface of the functional conductive sensing layer away from the polymer support base film; or, the functional conductive sensing layer directly serves as the outermost conductive interface.

[0009] Preferably, the conductive particles with positive temperature coefficient characteristics are any one of grafted modified conductive carbon black, graphene microflakes, or nickel-plated carbon fibers. The polymer binder is a thermally expanding polymer matrix, which is any one of high-density polyethylene, polypropylene, polyamide, polyimide, polyurethane, polyethylene oxide, polyvinyl alcohol, and polyethylene terephthalate.

[0010] Preferably, the polymer support base film is any one of PET film, PP film or PI film.

[0011] Preferably, the conductive metal layer is a nanoscale aluminum metal film or a nanoscale copper metal film.

[0012] Preferably, the thickness of the polymer support film is 2-12 micrometers; The thickness of the functional conductive sensing layer is 0.5-3 micrometers, and its sheet resistance is adjustable from 10-100 milliohms / □.

[0013] In this functional conductive sensing layer, two-dimensional layered transition metal carbide / nitride (MXene) nanosheets serve as the pressure-sensitive core component, while conductive particles with a positive temperature coefficient (PTC) effect serve as the temperature-sensitive core component. This material combination endows the current collector with a completely new working mechanism: MXene-based pressure-sensitive mechanism: utilizing Ti3C2T x The unique two-dimensional "accordion"-shaped multilayer microstructure of MXene material, especially when using silicon-based anodes, results in out-of-plane pressure from electrode expansion acting on the current collector surface during battery charging and discharging. This compresses the van der Waals force gaps between MXene layers, reducing the interlayer distance and significantly lowering the barrier and resistance for interlayer electron hopping conduction. Macroscopically, this microstructural change manifests as a highly sensitive linear decrease in the conductive layer resistance with increasing pressure (piezoresistive effect).

[0014] The thermosensitive mechanism based on PTC composite particles: PTC components (e.g., conductive carbon black particles dispersed in a polymer matrix with a high coefficient of thermal expansion) are uniformly distributed in an MXene network, forming parallel or percolating conductive pathways. Under normal operating temperatures, the conductive particles maintain good contact, ensuring low resistivity. Once the temperature at the monitoring point abnormally rises due to internal short circuits or overcharging and exceeds a critical threshold (e.g., 100℃-120℃), the polymer matrix encapsulating the particles undergoes a rapid volume phase transition expansion, physically widening the gap between the conductive particles and disrupting the conductive network. This process causes the local resistance of the functional layer to increase exponentially within milliseconds, thereby rapidly cutting off the abnormal current path and providing microscopic-level "self-melting" protection.

[0015] This invention also provides a method for preparing the above-mentioned intelligent sensing composite current collector based on the MXene / PTC synergistic effect, comprising the following steps: S1. Preparation of sensitive slurry: Add 1~10 mg / mL of Ti3C2T x MXene nanosheet dispersion, conductive particles and polymer binder were rapidly shear-mixed in NMP solvent at a solid-phase mass ratio of 1:(2~5):(3~8) to construct a conductive slurry with dual percolation thresholds; S2. Precision Coating: A functional conductive sensing layer is formed on the surface of a polymer support base film using micro-gravure coating or magnetron sputtering-assisted coating processes. S3. Interface modification and metallization: A 10-200 nm metal conductive layer is deposited on the surface of the functional conductive sensing layer by vacuum evaporation.

[0016] Therefore, the present invention, employing the above-mentioned MXene / PTC composite current collector, its preparation method, and its application, possesses the following beneficial effects: 1. Decoupled Monitoring of Multiple Physics Fields Inside the Battery: This invention utilizes the stark differences in signal change direction, linearity, and magnitude between the MXene piezoresistive effect (resistance decreases linearly with increasing pressure, typically by 10%–50%) and the PTC thermistor effect (resistance increases exponentially with increasing temperature, with extremely large changes). The response signals from these two sensing mechanisms exhibit significant intrinsic physical differences in polarity, linearity, magnitude, and response time scale. This allows external monitoring circuits to directly distinguish and identify abnormal pressure and temperature events based on these differences, without the need for complex signal decoupling algorithms. It can accurately distinguish and decouple mechanical expansion signals and abnormal temperature signals inside the battery, avoiding the signal confusion problem associated with single-material sensors. This truly upgrades the current collector into a system capable of sensing multi-dimensional information within the battery.

[0017] 2. Imparting intrinsically safe active protection to the current collector: Compared to traditional PTC coatings with slow response and limited resistance changes, the micro-nano composite structure of this invention, combined with a thin-layer design, achieves an extremely fast thermal response speed (<1 second). In the initial stage of an internal short circuit caused by needle penetration or impact, the functional layer can quickly transform from a good conductor to a high-resistivity material, instantaneously blocking the Joule heat accumulation generated by the short-circuit current and significantly suppressing the occurrence of thermal runaway.

[0018] 3. Excellent mechanical adaptability and high sensitivity: MXene materials not only possess excellent conductivity, but their two-dimensional layered structure also endows the coating with excellent flexibility and mechanical strength, enabling it to adapt to the huge volume breathing effect of next-generation silicon-carbon anodes without easily cracking or detaching. Furthermore, compared to the nonlinear sensitivity of one-dimensional materials such as carbon nanotubes under high pressure, MXene's interlayer compression mechanism provides superior linear response sensitivity over a wide pressure range, ensuring accurate monitoring of stress evolution throughout the battery's lifecycle.

[0019] 4. Lightweight structure and process compatibility: This technical solution retains the advantages of the composite current collector’s “metal-polymer-metal” sandwich structure, which can significantly reduce weight and improve battery mass energy density. At the same time, its core functional layer can be prepared by a mature precision coating process, which is highly compatible with the existing lithium battery electrode manufacturing process. It does not require disruptive modifications to the production line and has good prospects for large-scale industrial application.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the microscopic response mechanism of the functional conductive sensing layer of the present invention when subjected to external pressure; Figure 2 This is a schematic diagram of the microscopic response mechanism of the functional conductive sensing layer of the present invention when the local temperature rises abnormally; Figure 3 The figure shows typical resistance response characteristic curves of the intelligent sensing composite current collector of the present invention, wherein (a) is the linear response curve of resistance with pressure change, and (b) is the PTC nonlinear response curve of resistance with temperature change. Figure 4 A schematic diagram of the micro-section structure of the intelligent sensing composite current collector provided in Example 1; Figure 5 The Ti3C2T prepared in Example 2 x XRD patterns of MXene nanosheets; Figure 6 The surface morphology of the functional conductive sensing layer prepared in Example 3; Figure 7The image shows the cross-sectional morphology of the liquid nitrogen-frozen brittle fracture of the intelligent sensing composite current collector prepared in Example 3. Figure 8 Pressure-resistance response tests were conducted on the intelligent sensing composite current collectors prepared in Example 3 and Comparative Example 1. Figure 9 Temperature-resistance response tests were conducted on the intelligent sensing composite current collectors prepared in Example 3 and Comparative Example 1. Figure 10 This is a comparison graph showing the changes in voltage and surface temperature over time between the experimental and control groups of batteries during the needle penetration process in the application example. Figure Labels 1. Polymer supporting base film; 2. Functional conductive sensing layer; 3. Metal conductive layer; 2-1. Ti3C2T x MXene nanosheets; 2-2, conductive particles. Detailed Implementation

[0022] This invention discloses an MXene / PTC composite current collector, which employs a layered composite structure. It comprises: The polymer support base film is an insulating material (such as PET, PP or PI film), which has excellent mechanical strength and insulation properties, and serves as the supporting skeleton of the overall structure.

[0023] The functional conductive sensing layer is coated and attached to one or both surfaces of a polymer support film using a precision coating process. This functional conductive sensing layer is not a single component, but a complex micro / nano composite conductive network: within it, a two-dimensional Ti3C2T layer with an accordion-like multilayer structure... x MXene nanosheets serve as pressure-sensitive units to construct the basic conductive framework, while conductive particles (PTC particles) with a significant positive temperature coefficient effect are dispersed within them as thermosensitive units. The two are cross-linked and fixed together by a flexible polymer binder matrix.

[0024] To further optimize the interfacial contact resistance with the active material layers of the positive and negative electrodes of the battery, an ultrathin metal conductive layer (such as a nano-aluminum layer or copper layer formed by vacuum evaporation) can be selectively deposited on the outermost surface of the functional conductive sensing layer.

[0025] The varistor response mechanism of the functional conductive sensing layer based on MXene composition is as follows: Figure 1As shown in the figure, the left side of the figure illustrates the stretched two-dimensional multilayer structure of MXene nanosheets under no external pressure or low initial pressure. A certain van der Waals force gap exists between the layers, requiring electrons to hop between them for conduction, resulting in a relatively high overall resistance. The right side of the figure shows the situation when the current collector is applied to a battery (especially a silicon-based anode battery), and the electrode expands in volume and is subjected to out-of-plane pressure during charging. Under pressure, the flexible MXene layers are compressed, significantly reducing the interlayer spacing, lowering the barrier for electron hopping, and making the conductive path smoother. This microstructural change manifests macroscopically as a highly sensitive linear decrease in the resistance of the sensing layer with increasing pressure, thus enabling real-time monitoring of the mechanical stress inside the battery.

[0026] Functional conductive sensing layer based on the thermal active blocking mechanism of PTC composite particles, such as Figure 2 As shown in the figure. The left side of the figure illustrates that within the normal operating temperature range, conductive carbon black and other PTC particles dispersed in a polymer matrix with a high coefficient of thermal expansion are in close contact with each other, forming a good permeation conductive network, ensuring the efficient electron transport capability of the intelligent sensing composite current collector. The right side of the figure shows that when a micro-short circuit or local overheating occurs inside the battery, causing the temperature at the monitoring point to exceed a preset critical threshold (e.g., 110°C), the polymer matrix encapsulating the conductive particles undergoes a rapid volume phase change expansion. This expansion physically forces the distance between the conductive particles apart, disrupting the original conductive network. This process causes the resistance of the local area to surge exponentially, thereby rapidly cutting off the abnormal short-circuit current and providing microscopic self-fusing protection.

[0027] Based on the above principle, the typical resistance response characteristic curves of this composite current collector differ under different physical fields, such as... Figure 3 As shown, this demonstrates its key signal decoupling capability. Figure 3 Figure (a) shows that the current collector resistance decreases linearly with increasing pressure (piezoresistive effect). This highly linear change is very suitable for precise quantitative monitoring of the breathing process of electrode expansion. Figure 3 Figure (b) shows that the current collector resistance remains low and stable within the normal temperature range, but increases sharply and significantly once a certain threshold temperature is exceeded (PTC effect). These two distinct signal characteristics enable the backend battery management system to clearly distinguish whether the battery is in a normal mechanical expansion state or facing the risk of thermal runaway through simple algorithmic logic, thereby making accurate judgments and responses.

[0028] The technical solution of the present invention will be further described below through embodiments and accompanying drawings.

[0029] To more clearly illustrate the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are merely some embodiments of the present invention, and are only used to illustrate the present invention, and do not limit the scope of the present invention.

[0030] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0031] Example 1 This embodiment provides an MXene / PTC composite current collector, whose microstructure is as follows: Figure 4 As shown, the intelligent sensing composite current collector adopts a layered composite structure. The middle layer is a polymer support base film 1 with excellent mechanical strength and insulation properties, serving as the supporting framework of the overall structure. On both sides of the polymer support base film 1, the core functional conductive sensing layer 2 is attached through a precision coating process.

[0032] The functional conductive sensing layer 2 has a micro-nano composite conductive network and a polymer binder filling the space between them. The micro-nano composite conductive network includes a two-dimensional Ti3C2T structure with an accordion-like multilayer structure. x MXene nanosheets 2-1, serving as pressure-sensitive units, form the basic conductive framework, while conductive particles 2-2, exhibiting a significant positive temperature coefficient effect, serve as thermosensitive units. The two are cross-linked and fixed together by a flexible polymer binder matrix.

[0033] An ultrathin metal conductive layer 3 is deposited on the outermost surface of both functional conductive sensing layers 2 to further optimize the interfacial contact resistance with the active material layers of the positive and negative electrodes of the battery.

[0034] Example 2 This embodiment provides a two-dimensional layered Ti3C2T x The preparation method of MXene nanosheets includes the following steps: (1) Preparation of etching solution: Weigh 1.6g of lithium fluoride powder and slowly add it to 20mL of 9mol / L hydrochloric acid solution. Stir for 30 minutes to ensure thorough mixing and dissolution, resulting in a homogeneous etching solution. Weigh 1.0g of Ti3C2T x The ceramic powder was slowly added in batches to the prepared etching solution under ice-water bath cooling conditions to prevent violent exothermic reactions. After the powder addition was complete, the reaction vessel was sealed and transferred to a constant temperature water bath at 35°C and stirred for 24 hours.

[0035] (3) Washing: After the reaction is complete, transfer the acidic suspension to a centrifuge tube and add deionized water for dilution and washing. Centrifuge at 3500 rpm for 5 minutes using a high-speed centrifuge, then discard the supernatant. Repeat the above steps 6 times until the pH of the supernatant rises and stabilizes at around 6.0.

[0036] (4) Ultrasonic stripping: The precipitate, which has been cleaned to near neutral, is redispersed in 50 mL of deionized water and placed in an ultrasonic cleaner. Under the protection of an ice-water bath environment, it is continuously ultrasonically treated at a power of 250 W for 1 hour to utilize the ultrasonic cavitation effect to destroy the residual van der Waals forces and further expand the interlayer spacing.

[0037] (5) Collection and drying: The ultrasonically treated suspension was centrifuged again at 3500 rpm for 1 hour to allow the incompletely separated multilayered MXene and impurity particles at the bottom to settle. The dark green supernatant was collected. The dispersion was pre-frozen in a -80℃ low-temperature chamber for 12 hours, and then placed in a vacuum freeze dryer and dried for 48 hours under the conditions of cold trap temperature -50℃ and vacuum degree <10Pa to finally obtain a well-formed two-dimensional layered Ti3C2T x MXene nanosheet powder.

[0038] First, the phase composition of the prepared Ti3C2Tx MXene nanosheets was analyzed using X-ray diffraction. The test results are as follows: Figure 5 As shown, the original Ti3AlC2MAX phase material exhibits a significant characteristic diffraction peak at approximately 39° 2θ, corresponding to the Al atomic layer in its crystal structure. After LiF / HCl etching, this Al peak completely disappeared, indicating that the Al atomic layer was successfully and selectively removed. Simultaneously, the (002) main peak, originally located at approximately 9.5° 2θ, shifted significantly to a lower angle to approximately 6.8° 2θ, and the peak shape became more broadened. This result strongly demonstrates that Ti3AlC2 has been successfully transformed into an accordion-like multilayer Ti3C2T x MXene, after ultrasonic exfoliation, effectively expands the interlayer spacing, laying the structural foundation for achieving a highly sensitive piezoresistive response.

[0039] Example 3 This embodiment provides a method for preparing a smart sensing composite current collector as shown in Embodiment 1, including the following steps: (1) Ti3C2T was prepared using the same preparation method as in Example 2. xMXene nanosheets were dissolved in 100 mL of N-methylpyrrolidone solvent and ultrasonically dispersed to obtain a dispersion with a concentration of 5 mg / mL. Then, 1.5 g of polyethylene-grafted conductive carbon black and 3.0 g of polyvinylidene fluoride were added sequentially to the dispersion and mixed at 3500 rpm for 60 minutes to construct a conductive slurry with dual percolation thresholds, a solid content of approximately 12 wt.%, and a viscosity of approximately 2500–5000 mPa·s.

[0040] (2) A micro-gravure coating process is adopted, with a coating line speed of 1m / min. The coating is then placed in a multi-stage oven for gradient drying. The temperatures of the three ovens are set to 85℃, 100℃, and 120℃, respectively. After drying and roll forming, a functional conductive sensing layer with a thickness of about 1 micrometer is formed on both sides of the 6-micrometer-thick PET base film.

[0041] (3) Place the PET film with the functional conductive sensing layer attached in the vacuum chamber of the vacuum coating machine and evacuate it to below 5.0 × 10⁻⁶. -3 A high-purity aluminum wire was heated to a pressure of 2 nm / s, and an Al conductive layer with a thickness of approximately 50 nm was deposited on the surface of the functional conductive sensing layer by vacuum evaporation, thus preparing the intelligent sensing composite current collector. The resistivity of the intelligent sensing composite current collector prepared in this embodiment was measured to be 45 mΩ / m using the four-probe method. 2 In the actual preparation process, the deposition thickness of the metal conductive layer (e.g., 10–200 nm) is adjusted by changing the belt speed of the coating machine or the power of the evaporation source, and the Ti3C2T content in the sensitive slurry is fine-tuned. x The mass ratio of MXene nanosheets can determine the final resistivity of this composite current collector, which is between 10 and 100 mΩ / m. 2 The settings are flexible and adjustable to meet the customized needs of batteries with different power densities.

[0042] The surface microstructure and cross-sectional layered structure of the final prepared intelligent sensing composite current collector were observed using field emission scanning electron microscopy. The results are as follows: Figure 6 as well as Figure 7 As shown. Figure 6 The surface morphology of the functional conductive sensing layer is shown. The large-sized, lamellar distribution is Ti3C2T. x MXene nanosheets; the tiny spherical particles scattered between these sheets and on their surface are PTC conductive particles (modified conductive carbon black). This interwoven structure of MXene sheets and PTC particles ensures that this functional layer simultaneously possesses a pressure sensing path and a heat-sensitive cutoff mechanism. Figure 7The liquid nitrogen cryogenic fracture morphology of the intelligent sensing composite current collector was demonstrated, clearly showing its typical "sandwich" multilayer structure. The innermost layer is a PET polymer support film with a thickness of approximately 6 micrometers, and its cross-section is smooth and flat. On the upper and lower sides of the support film, a functional conductive sensing layer with a thickness of approximately 1 micrometer is uniformly attached. This layer exhibits rich layered texture and granularity, corresponding to the stacking of MXene and the filling of PTC particles. On the outermost side of the functional conductive layer, an extremely thin and dense bright layer can be observed, which is a metallic aluminum conductive layer with a thickness of approximately 50 nm deposited by vacuum evaporation. The interfaces between the layers are tightly bonded, with no obvious pores or peeling, indicating that the fabrication process has good interlayer bonding force and can meet the mechanical requirements of battery winding and charge-discharge cycling.

[0043] Example 4 This embodiment uses the same preparation method as in Example 3 to prepare the intelligent sensing composite current collector. The composite current collector in this embodiment is also provided with an edge signal extraction area, which is used to export the resistance change signal sensed by the functional conductive sensing layer to the external battery management system.

[0044] Comparative Example 1 This comparative example provides a method for preparing an intelligent sensing composite current collector, which is the same as Example 3, except that the conductive slurry in step (1) of this comparative example contains only modified conductive carbon black and polymer binder.

[0045] To evaluate the sensing and protection capabilities of the smart composite current collector prepared in Example 3 under actual battery conditions, a systematic pressure-resistance response test and temperature-resistance response test were conducted on the smart sensing composite current collectors prepared in Example 3 and Comparative Example 1.

[0046] The smart sensing composite current collector samples prepared in Example 3 and Comparative Example 1 were all cut into standard dimensions of 20mm × 20mm and placed between the upper and lower pressure plates of a high-precision universal testing machine. A digital multimeter was used to record the resistance change of the smart sensing composite current collector in real time during the application of pressure in the vertical direction. The test pressure range was set from 0MPa to 2.0MPa to simulate the typical expansion stress range generated by a silicon-based anode during charge-discharge cycles.

[0047] Test results are as follows Figure 8 As shown in the figure, the curve of the relative resistance change rate as applied pressure changes is displayed. Positive values ​​indicate the magnitude of the resistance decrease.

[0048] Figure 8It can be seen that the slope of the curve (square) representing the sample of Example 3 is significantly greater than that of the curve (circle) representing the sample of Comparative Example 1. Under a pressure of 2.0 MPa, the resistance of the sample of Example 3 decreased by approximately 25%, while the pure carbon black control sample only decreased by approximately 8%. This indicates that the current collector's sensitivity to pressure (strain coefficient) is significantly improved after introducing two-dimensional layered MXene. This is because the contact area of ​​the two-dimensional sheets increases significantly with increasing pressure, and compared to the point contact of zero-dimensional carbon black particles, the construction of its conductive pathway is more sensitive to pressure. The response curve of the sample of Example 3 exhibits excellent linearity throughout the entire test range. In contrast, the curve of the control sample shows some nonlinearity in both the low-pressure and high-pressure regions. High linearity is crucial for the accurate calibration and quantification of the internal stress of the battery in the back-end BMS system, demonstrating the superiority of the material system of this invention in sensing applications.

[0049] To verify the active circuit breaking capability of the current collector under abnormal high-temperature conditions, samples from Example 3 and Comparative Example 1 were placed on a heating stage with precise temperature control. They were heated from room temperature to 150°C at a rate of 5°C / min, while the change in their sheet resistivity was continuously monitored. The test results are as follows: Figure 9 As shown, the vertical axis in the figure uses a logarithmic coordinate axis to clearly present the dramatic changes in resistance.

[0050] It is clearly observable that the Sample 3 exhibits a typical positive temperature coefficient (PTC) effect: within the range of room temperature (25°C) to approximately 100°C, the resistance of the intelligent sensing composite current collector remains at a low and stable level, with the slight increase being due to the inherent temperature coefficient of resistance of the metal and semiconductor materials. This region ensures the battery's high conductivity under normal operating temperature and general abuse temperature (e.g., 85°C hot box testing). At room temperature, thanks to MXene's excellent two-dimensional conductive network construction capability, the initial sheet resistance of Sample 3 is significantly lower than that of the pure carbon black PTC coating. When the temperature exceeds the critical threshold (approximately 110°C in this example), the resistance curve shows a near-vertical steep rise. Within a short temperature rise range of 10°C-15°C, the resistance of the current collector increases instantaneously by more than four orders of magnitude, rapidly transforming from a good conductor to a high-resistivity material. Sample 3 exhibits a steeper resistance jump than the pure carbon black PTC coating, with a larger order of magnitude increase in resistance. The study demonstrated an excellent synergistic effect between MXene and PTC particles: the dual percolation conductive network constructed by the interweaving of MXene two-dimensional sheets and carbon black particles is more easily and completely cut off when the polymer matrix is ​​heated and expanded, thus achieving more rapid and thorough active circuit breaking protection than PTC material alone.

[0051] Application examples In this application example, the intelligent sensing composite current collector prepared in Example 3 is used as the positive electrode current collector. A conventional NCM811 positive electrode slurry is coated onto its surface, and the positive electrode sheet is prepared by drying, rolling, and die-cutting. The negative electrode uses conventional copper foil coated with graphite slurry. The separator is a PP / PE / PP composite microporous membrane. The electrolyte is a conventional lithium hexafluorophosphate carbonate system. The above components are wound into a cell, filled with electrolyte, sealed, and then formed to obtain a 5Ah soft-pack battery. Except for using ordinary commercial aluminum foil of the same thickness instead of the intelligent composite current collector as the positive electrode current collector, the other materials and preparation processes are completely consistent with the experimental group, and a 5Ah soft-pack battery is also prepared as the experimental group battery.

[0052] After fully charging the batteries in both the experimental and control groups (100% SOC, cutoff voltage 4.2V), they were left to stand for 2 hours. A needle penetration test was then conducted inside an explosion-proof enclosure. The test conditions were as follows: a 3mm diameter high-temperature resistant steel needle was used to vertically pierce the center of the battery at a speed of 25mm / s, penetrating the entire battery and remaining inside. During the test, a data acquisition device was used to simultaneously record the voltage changes across the battery terminals, and a thermocouple attached to the battery surface near the piercing point was used to record the temperature changes.

[0053] Test results are as follows Figure 10 The figure shows a comparison of the voltage and surface temperature changes over time for the experimental and control groups of batteries during the nail penetration process. The figure shows that the control group battery (gray curve) experienced a rapid voltage drop to 0V at the moment of nail penetration, and its surface temperature soared to over 450°C within a short period, resulting in severe thermal runaway and fire. In contrast, the experimental group battery (black curve), after being triggered by nail penetration, exhibited slight voltage fluctuations but ultimately maintained a stable voltage of approximately 3.0V, and its highest surface temperature was successfully suppressed to around 120°C, effectively avoiding the dangerous area of ​​thermal runaway. This comparative result intuitively demonstrates that the intelligent composite current collector described in this invention can actively disconnect the circuit at the moment of short circuit occurrence through the sensitive thermal response mechanism (PTC effect) of the functional layer, thereby ensuring the inherent safety of high-energy-density batteries under extreme abuse conditions.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An MXene / PTC composite current collector, characterized in that, include: Polymer supporting base film; A functional conductive sensing layer is attached to a polymer support base film; The functional conductive sensing layer comprises a micro / nano composite conductive network and a polymer binder. The micro / nano composite conductive network is a two-dimensional layered Ti3C2T x The structure of MXene nanosheets interwoven with conductive particles; The conductive particles are coated with a polymer binder, thus exhibiting PTC properties. The conductive particles are any one of grafted and modified conductive carbon black, graphene microflakes, or nickel-plated carbon fiber. The polymer binder is a thermally expanding polymer matrix, which is any one of high-density polyethylene, polypropylene, polyamide, polyimide, polyurethane, polyethylene oxide, polyvinyl alcohol, and polyethylene terephthalate.

2. The MXene / PTC composite current collector according to claim 1, characterized in that: It also includes a metal conductive layer, which is deposited on the surface of the functional conductive sensing layer away from the polymer support base film.

3. The MXene / PTC composite current collector according to claim 1, characterized in that: The functional conductive sensing layer directly serves as the outermost conductive interface.

4. The MXene / PTC composite current collector according to claim 1, characterized in that: The functional conductive sensing layer is configured to respond to external pressure applied to the composite current collector, Ti3C2T x The change in the interlayer spacing of MXene nanosheets causes the resistance of the functional conductive sensing layer to change negatively with external pressure.

5. The MXene / PTC composite current collector according to claim 1, characterized in that: The functional conductive sensing layer is configured such that, in response to the ambient temperature exceeding a critical threshold, the polymer binder encapsulating the conductive particles undergoes a volume phase transition expansion to increase the volume between and / or between the conductive particles and Ti3C2T. x The spacing between MXene nanosheets interrupts at least part of the conductive pathway, causing the local resistance of the functional conductive sensing layer to increase.

6. The MXene / PTC composite current collector according to claim 1, characterized in that: The polymer support film can be any one of PET film, PP film or PI film.

7. The MXene / PTC composite current collector according to claim 2, characterized in that: The conductive metal layer is a nanoscale aluminum metal film or a nanoscale copper metal film.

8. The MXene / PTC composite current collector according to claim 1, characterized in that: The thickness of the polymer support film is 2-12 micrometers; The thickness of the functional conductive sensing layer is 0.5-3 micrometers, and its sheet resistance is 10-100 milliohms / □.

9. A method for preparing the MXene / PTC composite current collector as described in any one of claims 1-2 and 4-8, characterized in that: Includes the following steps: S1. Preparation of sensitive slurry: Add 1~10 mg / mL of Ti3C2T x MXene nanosheet dispersion, conductive particles and polymer binder were rapidly shear-mixed in NMP solvent at a solid-phase mass ratio of 1:(2~5):(3~8) to construct a conductive slurry with dual percolation thresholds; S2. Precision Coating: A functional conductive sensing layer is formed on the surface of a polymer support base film using micro-gravure coating or magnetron sputtering-assisted coating processes. S3. Interface modification and metallization: A 10-200 nm metal conductive layer is deposited on the surface of the functional conductive sensing layer by vacuum evaporation.

10. An application of the MXene / PTC composite current collector as described in any one of claims 1-8, characterized in that, The composite current collector is used in batteries.

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