PVDF-PMMA piezoelectric sensing composite diaphragm, preparation method and application thereof

Abstract

This invention relates to the field of battery technology, specifically disclosing a PVDF-PMMA piezoelectric sensing composite separator, its preparation method, and its application. The preparation method includes: dissolving poly(vinylidene fluoride-co-hexafluoropropylene) powder in solvent A and stirring until homogeneous to obtain solution A; dissolving polymethyl methacrylate particles in solvent B and stirring until homogeneous to obtain solution B; using solution A as the electrospinning solution for the shell layer and solution B as the electrospinning solution for the core layer, preparing an electrospun composite separator using coaxial electrospinning technology, and drying to obtain the PVDF-PMMA piezoelectric sensing composite separator. The separator prepared by this invention possesses both high specific surface area and porosity, and the PVDF-HFP acts as a positive friction layer in synergy with the negative electrode PMMA, outputting a piezoelectric signal in real time when subjected to external pressure during the charging and discharging process of the pouch battery, thereby achieving timely and effective battery safety monitoring.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a PVDF-PMMA piezoelectric sensing composite separator, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are among the most promising energy storage batteries in battery energy storage systems. However, with the widespread application of lithium-ion batteries, their safety monitoring issues urgently require effective solutions. During operation, lithium-ion batteries are affected by external physical factors, which can cause a series of dangerous reactions internally, such as battery short circuits and electrolyte leakage, leading to more serious fire and explosion incidents.

[0003] Existing battery safety monitoring and early warning systems often rely on sensors. Common sensor systems include non-embedded and embedded types. The measurement results of most non-embedded sensors are easily affected by external factors, impacting their accuracy and stability, and their operation is complex. Embedded sensors require installation inside the battery, which inherently causes unpredictable effects on the battery's electrochemical performance. Furthermore, the cost of using embedded sensors is significantly higher than that of non-embedded sensors.

[0004] Patent CN119372839A discloses a method for preparing and applying a PVDF-PVA piezoelectric sensing composite battery separator. PVDF-HFP and PV are used as friction substrates, and a nanofiber separator capable of sensing properties is prepared by electrospinning. However, this PVDF-PVA piezoelectric sensing composite separator exhibits shortcomings in practical use, including high interfacial impedance, poor electrochemical reaction kinetics, poor rate performance, and significant capacity decay over long cycles. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a PVDF-PMMA piezoelectric sensing composite membrane, its preparation method, and its application. This PVDF-PMMA piezoelectric sensing composite membrane has both high specific surface area and porosity, and the PVDF-HFP acts as a positive friction layer in synergy with the negative electrode PMMA. When the soft-pack battery is subjected to external pressure during charging and discharging, it outputs a piezoelectric signal in real time, thereby achieving timely and effective battery safety monitoring.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a PVDF-PMMA piezoelectric sensing composite diaphragm, which includes the following steps: S1. Dissolve poly(vinylidene fluoride-co-hexafluoropropylene) powder in solvent A and stir until homogeneous to obtain solution A; S2. Dissolve polymethyl methacrylate particles in solvent B and stir until homogeneous to obtain solution B; S3. Using solution A as the electrospinning shell layer spinning solution and solution B as the electrospinning core layer spinning solution, an electrospinning composite membrane is prepared by coaxial electrospinning technology, and dried to obtain a PVDF-PMMA piezoelectric sensing composite membrane.

[0007] As a further improvement to the above-mentioned scheme of the present invention, the mass ratio of poly(vinylidene fluoride-co-hexafluoropropylene) powder in solution A to polymethyl methacrylate particles in solution B is 0.1~1:0.1~1.

[0008] As a further improvement to the above-described scheme of the present invention, in step S1, solvent A is prepared by mixing acetone and N,N-dimethylformamide in a volume ratio of 1~3:7~9. Step S1 involves stirring at room temperature for 5~10 h.

[0009] As a further improvement to the above-described scheme of the present invention, in step S2, solvent B is prepared by mixing acetone and N,N-dimethylacetamide in a volume ratio of 3~5:5~7. Step S2 involves stirring at room temperature for 10~15 h.

[0010] As a further improvement to the above-mentioned scheme of the present invention, the mass percentage of polymethyl methacrylate in solution A is 10%~15%; and the mass percentage of polymethyl methacrylate in solution B is 10%~12%.

[0011] As a further improvement to the above-mentioned solution of the present invention, in step S3, the coaxial electrospinning process parameters are as follows: the electrospinning voltage is set to 18kV, the core spinning solution flow rate is 0.3~0.5mL / h, the shell spinning solution flow rate is 0.4~0.6 mL / h, the rotation speed is 320 rpm, and the distance between the transmitter and the receiving substrate is 15cm.

[0012] As a further improvement to the above-mentioned solution of the present invention, in step S3, the drying is carried out at 90~110°C for 10~15 hours.

[0013] The present invention also provides a PVDF-PMMA piezoelectric sensing composite diaphragm, which is prepared by the preparation method described above.

[0014] As a further improvement to the above-mentioned solution of the present invention, the PVDF-PMMA piezoelectric sensing composite membrane is composed of dense, bead-free nanofibers with an average thickness of 300 nm, and the thickness of the PVDF-PMMA piezoelectric sensing composite membrane is 45~65 μm.

[0015] This invention also provides an application of the PVDF-PMMA piezoelectric sensing composite separator as a separator for lithium-ion pouch batteries, as described above. The PVDF-PMMA piezoelectric sensing composite separator is used for safety monitoring of lithium-ion pouch batteries. PVDF, as a positive electrode material in the triboelectric material series, is paired with PMMA, the negative electrode material. The two effectively generate piezoelectric sensing signals, thereby effectively detecting the voltage generated during the operation of the pouch battery and performing timely and effective safety monitoring.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention is based on the principle that an induced voltage is generated when two different materials come into contact. It utilizes polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with a positive triboelectric charge and polymethyl methacrylate (PMMA) with a negative triboelectric charge. Through coaxial electrospinning, a nanofiber composite separator with sensing function was successfully prepared, suitable for lithium-ion batteries. Batteries assembled using this separator exhibit excellent electrochemical performance: at a current density of 0.5C, the coin cell retains up to 95% of its capacity after 100 cycles, while the pouch cell retains 80% of its capacity after 200 cycles.

[0017] This invention uses coaxial electrospinning to prepare PVDF-PMMA piezoelectric sensing composite battery separators with nanofibers. The preparation process is simple, the reaction conditions are mild, and the cost is low. The morphology of the obtained PVDF-PMMA composite battery separator can be controlled by adjusting the reaction temperature, reactant ratio, and process conditions such as electrospinning spray voltage, flow rate, and spray distance.

[0018] The PVDF-PMMA piezoelectric sensing composite diaphragm of this invention generates voltage signals of 0.78V, 0.33V, 0.05V and 0.48V respectively by pressing with the palm, clicking with the finger, rubbing with the finger and striking with a rubber hammer. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the principle of coaxial electrospinning in an embodiment of the present invention; Figure 2 A scanning electron microscope image of the PVDF-PMMA piezoelectric sensing composite diaphragm prepared according to an embodiment of the present invention; Figure 3 X-ray diffraction comparison images of the diaphragms provided in the embodiments and comparative examples 1-2 of the present invention; Figure 4 A comparison chart of the porosity and liquid absorption rate of the diaphragms provided in the embodiments of the present invention and Comparative Example 3; Figure 5 A comparison chart of the porosity and liquid absorption rate of the diaphragms provided in the embodiments of the present invention and Comparative Example 4; Figure 6 This is a comparison chart of the electrical performance of coin cells assembled using the separators provided in the embodiments of the present invention and Comparative Example 4. Figure 7 The figure shows the test results of the piezoelectric performance of the PVDF-PMMA piezoelectric sensing composite diaphragm provided in the embodiments of the present invention. Figure 8 The figure shows the stability test results of the PVDF-PMMA piezoelectric sensing composite diaphragm provided in the embodiment of the present invention. Figure 9 The image shows the performance of a pouch cell assembled using the PVDF-PMMA piezoelectric sensing composite separator provided in this embodiment of the invention. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0022] Example This embodiment proposes a PVDF-PMMA piezoelectric sensing composite separator that can monitor the internal pressure of a lithium-ion battery. Its preparation method includes the following steps: S1. Add 0.6248 g of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to solvent A (a mixture of 4 mL of N,N-dimethylformamide and 1 mL of acetone) and stir evenly at room temperature for 8 h to obtain a shell spinning solution A with a solid content of 12 wt%.

[0023] S2. Add 0.372 g of polymethyl methacrylate (PMMA) to solvent B (a mixture of 3 mL N,N-dimethylacetamide and 2 mL acetone) and stir evenly at room temperature for 12 h to obtain a core spinning solution B with a solid content of 10 wt%.

[0024] S3. For example Figure 1As shown, shell spinning solution A and core spinning solution B were slowly added to two syringes, respectively. Shell spinning solution A and core spinning solution B were connected to the shell and core layers of a coaxial electrospinning needle, respectively. The flow rate of the core spinning solution was 0.3–0.6 mL / h, and the flow rate of the shell spinning solution was 0.4–0.6 mL / h. A rotating cylinder covered with aluminum foil was used as the receiving device, rotating at 320 rpm, with a spinning distance of 15 cm between the syringe tip and the collector. The spinning solution passed through the spinneret and was stretched into fibers under the action of a high-voltage electrostatic field, with a voltage of 18 kV. After the solvent evaporated, a coaxial electrospinned composite diaphragm was obtained on the receiving device. The diaphragm was placed in a vacuum drying oven at 100 °C overnight, and the PVDF-PMMA piezoelectric sensing composite diaphragm was obtained upon removal.

[0025] Figure 2 This is a scanning electron micrograph of the PVDF-PMMA piezoelectric sensing composite diaphragm prepared in this embodiment. Figure 2 As can be seen, the PVDF-PMMA piezoelectric sensing composite diaphragm prepared in this embodiment is in the form of nanofibers with an average diameter of 300 nm. Its microstructure is dense and free of beads.

[0026] Comparative Example 1 This comparative example presents a PVDF membrane, the preparation method of which includes the following steps: S1. Add 0.6248 g of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to solvent A (a mixture of 4 mL of N,N-dimethylformamide and 1 mL of acetone) and stir evenly at room temperature for 8 h to obtain a spinning solution with a solid content of 12 wt%.

[0027] S2. Two spinning solutions were connected to the shell and core layers of a coaxial electrospinning needle, respectively, with the shell spinning solution flow rate being 0.4–0.6 mL / h. A rotating cylinder covered with aluminum foil was used as the receiving device, rotating at 320 rpm, with a spinning distance of 15 cm between the syringe tip and the collector. The spinning solution passed through the spinneret and was stretched into fibers under the action of a high-voltage electrostatic field, with the electrostatic voltage being 18 kV. After the solvent evaporated, a coaxial electrospinned diaphragm was obtained on the receiving device. The diaphragm was placed in a vacuum drying oven at 100 °C overnight, and after removal, a PVDF diaphragm was obtained.

[0028] Comparative Example 2 This comparative example presents a PMMA membrane, the preparation method of which includes the following steps: S1. Add 0.372 g of polymethyl methacrylate (PMMA) to solvent B (a mixture of 3 mL N,N-dimethylacetamide and 2 mL acetone) and stir evenly at room temperature for 12 h to obtain a spinning solution with a solid content of 10 wt%.

[0029] S3. Two spinning solutions were connected to the shell and core layers of a coaxial electrospinning needle, respectively, with the core layer spinning solution flow rate being 0.3–0.6 mL / h. A rotating cylinder covered with aluminum foil was used as the receiving device, rotating at 320 rpm, with a spinning distance of 15 cm between the syringe tip and the collector. The spinning solution passed through the spinneret and was stretched into fibers under the action of a high-voltage electrostatic field, with the electrostatic voltage being 18 kV. After the solvent evaporated, a coaxial electrospinning diaphragm was obtained on the receiving device. The diaphragm was placed in a vacuum drying oven at 100 °C overnight, and the PMMA diaphragm was obtained after removal.

[0030] Comparative Example 3 This comparative example provides a commercially available PP diaphragm.

[0031] Comparative Example 4 This comparative example proposes a PVDF- The preparation method of the PVA piezoelectric sensing composite diaphragm includes the following steps: S1. 0.6248g of poly(vinylidene fluoride) co Hexafluoropropylene was added to 4 mL of N,N A shell spinning solution A with a solid content of 12 wt% was obtained by uniformly stirring a mixed solution of dimethylformamide and 1 mL of acetone at room temperature for 8 h.

[0032] S2. Add 0.6818g of polyvinyl alcohol to 5mL of deionized water and stir evenly at 90℃ for 12h to obtain a core spinning solution B with a solid content of 10wt%.

[0033] S3. Shell spinning solution A and core spinning solution B are slowly added to two syringes, respectively. Shell spinning solution A and core spinning solution B are connected to the shell and core layers of a coaxial electrospinning needle, respectively. The flow rate of the core spinning solution is 0.2~0.5 mL / h, and the flow rate of the shell spinning solution is 0.3~0.6 mL / h. A rotating cylinder covered with aluminum foil is used as the receiving device, rotating at 320 rpm, with a spinning distance of 15 cm between the syringe tip and the collector. The spinning solution passes through the spinneret and is stretched into fibers under a high-voltage electrostatic field of 18 kV. After the solvent evaporates, a coaxial electrospinned composite diaphragm is obtained on the receiving device. The diaphragm is placed in a vacuum drying oven at 100℃ overnight, and PVDF is obtained upon removal. PVA piezoelectric sensing composite diaphragm.

[0034] Test case (1) The diaphragms prepared in the examples and comparative examples 1-2 were characterized to obtain the following results: Figure 3 The X-ray diffraction comparison diagram shown. From Figure 3 It can be seen that the X-ray diffraction peaks of the PVDF-PMMA piezoelectric sensing composite membrane prepared in the embodiments of the present invention are only the characteristic peaks of PVDF-HFP, indicating that a core-shell structure with PVDF-HFP as the outer shell and PMMA as the core layer has been successfully synthesized.

[0035] (2) The porosity and liquid absorption rate of the diaphragms of the examples and Comparative Examples 3 and 4 were tested. The diaphragm porosity test steps were as follows: the diaphragm was immersed in n-butanol solution for 1 hour, and the n-butanol solution on the surface was wiped off with filter paper. The mass of the sample before soaking. To determine the quality of the sample after soaking, It is the density of n-butanol. This is the volume of the dry sample. The porosity of the membrane is calculated using formula (1): (1) The specific steps for the diaphragm absorbance test are as follows: Immerse the diaphragm in the electrolyte and keep it for 30 minutes to ensure it is fully wetted, then wipe off the electrolyte on the surface with filter paper. Calculate the absorbance of the diaphragm by the difference in mass before and after immersion. Record the initial mass of the diaphragm as m1. Record the mass of the diaphragm after immersion as m2. The absorbance of the diaphragm can be calculated using the following formula (2): (2) The results are as follows Figure 4 , Figure 5 As shown. Among them, Figure 4 a, Figure 5 a is a porosity comparison chart. Figure 4 b、 Figure 5 b is a comparison chart of liquid absorption rates.

[0036] from Figure 4 As can be seen, the PVDF-PMMA piezoelectric sensing composite battery separator prepared in the examples has a better liquid absorption rate and porosity than the traditional PP separator, which are 268.3% and 98.6%, respectively.

[0037] from Figure 5As can be seen, the PVDF-PMMA piezoelectric sensing composite battery separator prepared in the examples exhibits significantly better liquid absorption rate and porosity than the PVDF-PVA separator. Higher porosity means a richer network of channels within the separator, providing more transport pathways for lithium ions, which helps reduce battery internal resistance and improve rate performance. The liquid absorption rate of the PVDF-PMMA separator is nearly 10% higher than that of the PVDF-PVA separator. Liquid absorption rate directly reflects the separator's affinity for the electrolyte; a higher absorption rate means the separator can more fully absorb and retain the electrolyte, which is beneficial for forming a stable solid-liquid interface and improving ionic conductivity. Compared to the PVDF-PVA separator, the PMMA-modified separator shows a positive improvement in both porosity and electrolyte wettability, especially in the liquid absorption rate.

[0038] (3) The separators of Examples 1 and 4 were used to assemble button cells. The specific installation steps are as follows: A CR2025 battery case was used to assemble the button cell, with lithium iron phosphate as the positive electrode and lithium metal as the negative electrode. The prepared composite separator was used for assembly. The assembly sequence was as follows: positive electrode case, positive electrode sheet, separator, electrolyte, negative electrode sheet, nickel foam, and negative electrode case. The assembly of the lithium-ion soft-pack battery was carried out in an argon glove box, with the internal environment maintained at H2O < 0.1 ppm and O2 < 0.1 ppm. The electrolyte was EC / EMC / DMC (volume ratio 1:1:1) + 1 mol·L⁻¹. -1 LiPF6 button cells were sealed using a sealing machine and then left to stand for 24 hours. Electrochemical tests were then conducted, including EIS testing, CV testing, rate performance testing, and long-cycle testing. The results are as follows: Figure 6 As shown.

[0039] Figure 6 Electrochemical impedance spectroscopy (EIS) results show that, compared with PVDF-PVA membranes, the batteries with PVDF-PMMA membranes exhibit lower interfacial impedance and charge transfer impedance. This is attributed to the optimization of electrolyte wettability and interfacial stability by PMMA modification, which effectively reduces the transport resistance of lithium ions at the electrode / electrolyte interface.

[0040] Figure 6 Cyclic voltammetry (CV) curves show that the battery using the PVDF-PMMA separator has higher oxidation / reduction peak currents and better peak shape symmetry, indicating that its electrochemical reaction kinetics are superior.

[0041] Figure 6 The c-rate performance test results show that as the current density increases, the specific capacity of the PVDF-PVA membrane battery decreases significantly, while the PVDF-PMMA membrane battery exhibits higher specific capacity and better capacity recovery capability at different rates.

[0042] Figure 6 Long-cycle performance testing further validated the advantages of the PVDF-PMMA separator: after 100 cycles at a current density of 0.5C, the specific capacity of the PVDF-PMMA separator battery still remained at approximately 169 mAh g⁻¹. -1 The capacity decay is negligible, and the coulombic efficiency remains stable at close to 100%; in contrast, the specific capacity of PVDF-PVA separator batteries shows a more significant decrease.

[0043] In summary, the introduction of PMMA significantly improves the interfacial properties and structural stability of the separator, effectively enhancing the battery's ion transport efficiency, rate performance, and cycle life. (4) The separators from Examples 1 and 4 (Comparative Example 4) were used to assemble soft-pack batteries. The assembly steps were as follows: 0.8 g LFP (active material), 0.1 g Super-P (conductive agent), and 2 g PVDF (5% by mass, binder) were mixed in NMP to form a uniform positive electrode slurry. Separately, 0.8 g graphite, 0.1 g Super-P, and 0.1 g CMC were mixed in deionized water to form a uniform negative electrode slurry. The positive and negative electrode slurries were stretched into films using 200 μm and 150 μm thicknesses, respectively, and then dried in a vacuum drying oven at 80°C for 12 hours. The assembly of the lithium-ion soft-pack battery was carried out in an argon glove box (with the internal environment maintained at H2O < 0.1 ppm and O2 < 0.1 ppm), and the electrolyte was EC / EMC / DMC (volume ratio 1:1:1) + 1 mol·L⁻¹. -1 LiPF6. The cells were sealed at 160°C using a heat sealer and allowed to stand for 24 hours before testing. External pressure was applied to the prepared pouch cells using various methods: slapping with the palm, tapping with the finger, rubbing with the finger, and striking with a rubber mallet, ensuring consistency under the same conditions. Results are as follows... Figure 7 As shown in Table 1.

[0044] Table 1. Piezoelectric performance results

[0045] from Figure 7 It can be seen that when external pressure is applied to the soft-pack battery assembled with the PVDF-PMMA piezoelectric sensing composite separator prepared in the example, the piezoelectric signal generated by the internal PVDF-PMMA separator is transmitted in the form of voltage through the external wire. The voltage results corresponding to the palm slap, finger tap, finger rub, and rubber hammer tap are 0.78V, 0.43V, 0.15V, and 0.48V, respectively.

[0046] As shown in Table 1, under the same operating conditions, the piezoelectric signal output of the PVDF-PMMA diaphragm is significantly stronger.

[0047] In addition, a 30-day stability test was conducted on the PVDF-PMMA separator, and the results were as follows: Figure 8 As shown, the results indicate that the signal strength after 30 days is 0.36V, which is not significantly lower than the signal strength of 0.62V before 30 days, indicating that its long-term sensing stability is better.

[0048] from Figure 9 It can be seen that the pouch cell assembled using the PVDF-PMMA piezoelectric sensing composite separator prepared in the examples has an initial discharge capacity of 162.4 mAh g⁻¹ at a current density of 0.5 C. -1 After 200 cycles, the discharge capacity is approximately 125.1 mAh g. -1 Coulomb efficiency has consistently remained above 98%.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a PVDF-PMMA piezoelectric sensing composite diaphragm, characterized in that, It includes the following steps: S1. Dissolve poly(vinylidene fluoride-co-hexafluoropropylene) powder in solvent A and stir until homogeneous to obtain solution A; S2. Dissolve polymethyl methacrylate particles in solvent B and stir until homogeneous to obtain solution B; S3. Using solution A as the electrospinning shell layer spinning solution and solution B as the electrospinning core layer spinning solution, an electrospinning composite membrane is prepared by coaxial electrospinning technology, and dried to obtain a PVDF-PMMA piezoelectric sensing composite membrane.

2. The method for preparing the PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 1, characterized in that, The mass ratio of poly(vinylidene fluoride-co-hexafluoropropylene) powder in solution A to polymethyl methacrylate particles in solution B is 0.1~1:0.1~1.

3. The method for preparing the PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 1, characterized in that, In step S1, solvent A is prepared by mixing acetone and N,N-dimethylformamide in a volume ratio of 1~3:7~9.

4. The method for preparing the PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 1, characterized in that, In step S2, solvent B is prepared by mixing acetone and N,N-dimethylacetamide in a volume ratio of 3~5:5~7.

5. The method for preparing the PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 1, characterized in that, The mass percentage of polymethyl methacrylate in solution A is 10%~15%; the mass percentage of polymethyl methacrylate in solution B is 10%~12%.

6. The method for preparing the PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 1, characterized in that, In step S3, the coaxial electrospinning process parameters are as follows: the electrospinning voltage is set to 18kV, the core spinning solution flow rate is 0.3~0.5mL / h, the shell spinning solution flow rate is 0.4~0.6 mL / h, the rotation speed is 320 rpm, and the distance between the transmitter and the receiving substrate is 15cm.

7. The method for preparing the PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 1, characterized in that, In step S3, the drying is carried out at 90~110℃ for 10~15 hours.

8. A PVDF-PMMA piezoelectric sensing composite diaphragm, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The PVDF-PMMA piezoelectric sensing composite diaphragm according to claim 8, characterized in that, The PVDF-PMMA piezoelectric sensing composite membrane is composed of dense, bead-free nanofibers with an average diameter of 300 nm, and the thickness of the PVDF-PMMA piezoelectric sensing composite membrane is 45~65 μm.

10. The application of a PVDF-PMMA piezoelectric sensing composite separator as described in any one of claims 8-9 as a separator for lithium-ion pouch batteries.

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