A temperature-controllable polymer composite diaphragm, a preparation method and application thereof

Abstract

The application discloses a temperature-controllable polymer composite diaphragm, which comprises a diaphragm base and a temperature-controlling layer arranged on one side or both sides of the diaphragm base; the diaphragm base is a polymer film; the temperature-controlling layer is a negative electrically-car-coating material layer, and the negative electrically-car-coating material layer is composed of a three-dimensional ceramic framework and a polar polymer material, both of which have a negative electrically-car-coating effect. The application further discloses a preparation method of the temperature-controllable polymer composite diaphragm and application of the temperature-controllable polymer composite diaphragm in a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a temperature-controllable polymer composite diaphragm as well as a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries have been widely used in portable electronic devices, large-scale energy storage systems, electric vehicles and other fields due to their high energy density, long cycle life and low self-discharge; however, the battery thermal runaway phenomenon of electric vehicles and fixed grid-scale energy storage systems is still the primary safety concern and one of the most urgent and challenging tasks. As one of the four key components of lithium ion batteries, the diaphragm can prevent short circuits between the positive and negative electrodes and allow Li + free transmission, which is crucial to the safety and reliability of lithium ion batteries. Currently, porous and thin polyolefin films have become the most mainstream commercial diaphragm due to their low cost, good mechanical properties and electrochemical stability; unfortunately, when lithium ion batteries are overcharged, mechanically extruded or short-circuited, the polyolefin film will significantly shrink at a temperature of 130-150℃, causing direct contact between the anode and the cathode, triggering complex chemical reactions, exacerbating battery temperature rise, and then severe heat accumulation causing the released oxygen from the cathode to react with the combustible materials in the battery, further leading to explosion or even fire.

[0003] Current technical research on lithium battery diaphragms mainly includes enhancing their mechanical stability, improving their electrolyte wettability, improving diaphragm porosity, and improving diaphragm thermal stability. In terms of thermal stability, reasonable doping and coating of the diaphragm can improve the thermal stability of the diaphragm to some extent, thereby improving the safety of the lithium battery, but may affect the overall ionic conductivity of the battery, and cannot cool the battery temperature during the charging and discharging process of the battery to prevent the battery from overheating. For example, Chinese published patent CN112928389A obtains a temperature-regulating diaphragm by coating a phase change material, but the diaphragm can only absorb battery heat to reduce battery temperature when the phase change material undergoes a phase change, and the phase change temperature point of the phase change material is relatively low, which cannot inhibit the thermal shrinkage of the diaphragm in a high-temperature state. For another example, Chinese published patent CN114284640A prepares a thermal switch coating layer to make the diaphragm melt at a high temperature to block the migration of lithium ions, thereby inhibiting heat spread. In summary, none of the existing technologies can reduce the temperature of the battery in real time during the charging and discharging process of the lithium ion battery to ensure that the battery does not overheat and operates normally. SUMMARY

[0004] One of the purposes of the present application is to provide a temperature-controllable polymer composite diaphragm having temperature regulation function and high ionic conductivity.

[0005] The second object of the present application is to provide a preparation method of the temperature-controllable polymer composite separator.

[0006] The third object of the present application is to provide an application of the temperature-controllable polymer composite separator.

[0007] The first object of the present application is achieved by the following technical solutions.

[0008] A temperature-controllable polymer composite separator, characterized in that it comprises a separator substrate and a temperature-regulating layer arranged on one side or both sides of the separator substrate.

[0009] The separator substrate is a polymer film.

[0010] The temperature-regulating layer is a negative electrocaloric material layer composed of a three-dimensional ceramic framework and a polar polymer material, both of which have negative electrocaloric effect.

[0011] The negative electrocaloric material layer, i.e. the temperature-regulating layer, is composed of a three-dimensional ceramic framework and a polar polymer material, both of which have negative electrocaloric effect, so that the temperature-controllable polymer composite separator has temperature-regulating function and high ionic conductivity. When the battery is charging and discharging (i.e. when there is an external voltage), the dipole inside the negative electrocaloric material layer flips or shifts, changing from an ordered state to a disordered state. On the one hand, the disordered dipole provides multiple migration channels for lithium ions, improving the lithium ion migration rate, i.e. improving the ionic conductivity of the separator. On the other hand, the change of the dipole from an ordered state to a disordered state increases the entropy of the negative electrocaloric material layer, absorbing environmental heat, which helps to reduce the temperature of the separator and the battery, preventing the separator from overheating and causing thermal shrinkage or edge curling, which leads to the contact between the positive and negative electrodes of the battery, thereby causing short circuit and avoiding the occurrence of battery thermal runaway. Further, the polar polymer material is filled in the three-dimensional ceramic framework to form an integral body, enhancing the negative electrocaloric effect and producing greater adiabatic temperature change. When there is an external voltage, it can absorb more heat, which is more conducive to regulating the temperature of the separator and the battery. In addition, the polar polymer material has good flexibility and processability, and the three-dimensional ceramic framework has high hardness and thermal conductivity. The combination of the two forms a temperature-regulating layer that is a separator refrigeration material with good flexibility and high conductivity.

[0012] The material of the three-dimensional ceramic framework can be selected from ceramic particles with relaxor ferroelectric or antiferroelectric effect, such as relaxor ferroelectric lead zirconate titanate or its dopant, potassium / sodium / silver-based niobate or its dopant, strontium titanate or its dopant. Preferably, the material of the three-dimensional ceramic framework of the present application is a relaxor ferroelectric lead zirconate titanate dopant, more preferably a relaxor ferroelectric lead zirconate titanate dopant doped with tin, specifically Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 Ti O4.

[0013] The polar polymer material is at least one of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene), poly(vinylidene fluoride-trifluoroethylene), polyurea-based aromatic linear dielectric polymer, perovskite-type relaxor ferroelectric high polymer material, polyimide-based material, polyamide-based material, polystyrene-based material; the present application preferably is poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene), hereinafter referred to as P(VDF-TrFE-CFE).

[0014] The material of the diaphragm substrate can be any conventional polymer used to prepare diaphragms, and can be at least one of polyacrylonitrile, polyethylene, polypropylene, polyvinylidene fluoride, polyvinylpyrrolidone, poly-m-phenylene isophthalamide and polymethyl methacrylate.

[0015] Preferably, the temperature-controllable polymer composite diaphragm has a thickness of 30-200 μm; and the thickness ratio of the diaphragm substrate to the temperature-controlling layer is 5:1-30:1.

[0016] To achieve the second object of the present application, the present application provides a preparation method of the above-mentioned temperature-controllable polymer composite diaphragm, characterized in that it comprises the following steps: preparing a three-dimensional ceramic framework by a sol-gel method; filling a polar polymer material into the three-dimensional ceramic framework, and then performing hot pressing to obtain a temperature-controlling layer; and finally hot pressing the diaphragm substrate and the temperature-controlling layer to obtain the temperature-controllable polymer composite diaphragm.

[0017] As a specific embodiment, the method for preparing the three-dimensional ceramic framework is as follows: uniformly mixing raw materials for preparing the three-dimensional ceramic framework with a solvent to obtain a sol; immersing a polyurethane foam template in the sol, then extruding excess sol from the polyurethane foam template and drying at 35-65℃ to obtain a precursor template; and finally sintering the precursor template at 1000-1400℃ for 1-3h (in this process, the polyurethane foam template is gasified and removed), to obtain the three-dimensional ceramic framework.

[0018] Preferably, the immersing time is 15-20 min, more preferably 10 min.

[0019] Preferably, the solvent is composed of 5-40 mL of ethanol, 1-10 mL of acetylacetone and 5-30 mL of glacial acetic acid; more preferably, it is composed of 15 mL of ethanol, 5 mL of acetylacetone and 20 mL of glacial acetic acid.

[0020] Preferably, the raw materials for preparing the three-dimensional ceramic framework are PbO, La2O3, TiO2, ZrO2 and SnO2, to prepare a relaxor ferroelectric lead zirconate titanate dopant doped with tin. The mass ratio of the raw materials for preparing the three-dimensional ceramic framework to the solvent is 1:5-1:50.

[0021] Preferably, the precursor template is dried at 45℃ to obtain a precursor template, and the precursor template is sintered at 1200℃ for 2h to obtain the three-dimensional ceramic framework.

[0022] As a specific embodiment, the method for preparing the temperature regulating layer is: dissolving the polar polymer material to obtain a polar polymer material solution with a concentration of 5-35wt%; then filling the polar polymer material solution into the three-dimensional ceramic framework prepared above, and heating in an oven at 40-80℃ for 0.1-2h; repeating the filling-heating operation several times until the three-dimensional ceramic framework is completely filled with the polar polymer material to obtain a composite material; drying the obtained composite material, and then hot-pressing the composite material at 0.1-1MPa and 100-150℃ for 10-25min to convert the composite material into a dense body to obtain the temperature regulating layer.

[0023] The concentration of the polar polymer material solution is obtained through a large number of experiments; if the polar polymer material in the temperature regulating layer is too much, it will cause the lithium ion migration channel in the original separator to be blocked, reducing the migration rate of lithium ions, and thus affecting the capacity of the battery; if the polar polymer material in the temperature regulating layer is too little, it will not have a cooling effect, and in the process of battery charging and discharging, it cannot reduce the temperature of the battery, which is not conducive to controlling the occurrence of battery thermal runaway.

[0024] Preferably, a polar polymer material solution with a concentration of 15wt% is used; after the polar polymer material solution is filled into the three-dimensional ceramic framework, it is heated in an oven at 60℃ for 0.5h.

[0025] Preferably, the obtained composite material is dried at 40-60℃ for 8-12h, and then hot-pressed at 120℃ under a pressure of 0.5MPa for 15min.

[0026] As a specific embodiment, the temperature regulating layer is placed on one side of the separator substrate, and a polymer composite separator is obtained by hot-pressing; the pressure of the hot-pressing is 0.5-1MPa, the temperature is 100-200℃, and the time is 1-10h; finally, the obtained polymer composite separator is annealed at 106℃ in a vacuum oven for 10h to improve the crystallinity of the film to obtain the temperature regulating polymer composite separator. If the temperature regulating layer is arranged on both sides of the separator substrate, the temperature regulating layer can be placed on both sides of the separator substrate at the same time and hot-pressed, or the temperature regulating layer is first placed on one side of the separator substrate and hot-pressed, and then the same treatment is performed on the other side.

[0027] Preferably, the pressure of the hot-pressing of the temperature regulating layer and the separator substrate is 0.5MPa, the temperature is 110℃, and the time is 5h.

[0028] Preferably, the preparation method of the diaphragm substrate is: mixing the polymer and N-methyl pyrrolidone into a polymer solution according to a mass ratio of 1:10-1:50; pouring the obtained polymer solution into a mold, and placing it into an oven for drying at 40-60°C for 6-12h to obtain the diaphragm substrate.

[0029] Preferably, the polymer and N-methyl pyrrolidone are stirred at 40-60°C for 6-8h to obtain the polymer solution.

[0030] To achieve the third object of the present application, the present application provides the application of the above-mentioned temperature-controllable polymer composite diaphragm in lithium ion batteries.

[0031] Preferably, the temperature-regulating layer in the temperature-controllable polymer composite diaphragm is on the negative electrode side, which can further inhibit the growth of lithium dendrites.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] The present application combines the conventional polymer film with the negative electric card material layer (temperature-regulating layer) to achieve the regulation and control of the temperature of the diaphragm, so that the temperature-controllable polymer composite diaphragm has high ionic conductivity and good electrolyte wettability.

[0034] When the battery is charged and discharged, i.e. in the presence of an external voltage, the dipole of the negative electric card material inside the diaphragm changes from an ordered state to a disordered state, the material absorbs the heat generated by the battery, and the temperature of the battery is reduced, thereby reducing the thermal runaway of the battery, effectively ensuring the safety of the battery, and improving the thermal safety performance of the battery; at the same time, the disordered dipole can provide more migration channels for lithium ions, promote the migration of lithium ions, and be beneficial to improving the capacity of the battery.

[0035] When the battery is stopped charging and discharging, i.e. the external electric field is removed, the temperature rise of the battery can reduce the polarization inside the battery, the lithium ions can migrate more, the capacity of the battery can be improved, and the growth of lithium dendrites can be inhibited. The temperature-regulating layer in the temperature-controllable polymer composite diaphragm of the present application is arranged on the negative electrode side, which can further inhibit the growth of lithium dendrites and reduce the capacity decay of the battery.

[0036] The temperature-controllable polymer composite diaphragm of the present application has a simple structure and preparation method DETAILED DESCRIPTION

[0037] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0038] Example 1 is prepared by the following steps:

[0039] S1: Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 The TiO4material is prepared from PbO, La2O3, TiO2, ZrO2and SnO2with purity greater than 99.0%, and the above raw materials are weighed according to the stoichiometric ratio; 15 mL of ethanol, 5 mL of acetylacetone and 20 mL of glacial acetic acid are mixed to obtain a co-solvent, and then the above raw materials are sequentially dissolved in the co-solvent and stirred to form a uniform solution, wherein the mass ratio of the raw materials of the three-dimensional ceramic framework to the co-solvent is 1:10, thereby obtaining a PLZST sol.

[0040] S2: soak the polyurethane foam template (TX704, ITW Texwipe) in the PLZST sol for 10 min; then squeeze out the excess sol from the polyurethane foam template and dry at 45°C to obtain a PLZST precursor template; finally, sinter the PLZST precursor template at 1200°C for 2h to obtain a three-dimensional ceramic framework.

[0041] S3: dissolve P(VDF-TrFE-CFE) (62.1 / 30.1 / 7.8 mol%, Piezotech, France) in DMF and stir for 10h to obtain a uniform P(VDF-TrFE-CFE) solution with a concentration of 15wt%.

[0042] S4: place the three-dimensional ceramic framework on a PTFE mold with a length, width and height of 40x40x20 mm, then fill the P(VDF-TrFE-CFE) solution obtained in S3 into the three-dimensional ceramic framework, and then place it in an oven at 60°C for 0.5h. Repeat the above filling-heating process several times until the three-dimensional ceramic framework is completely filled with P(VDF-TrFE-CFE) to obtain a composite material.

[0043] S5: dry the obtained composite material at 50°C for 10h to remove excess solvent, and then convert the above material into a dense body by hot pressing at 0.5MPa and 120°C for 15min to obtain a temperature-regulating layer.

[0044] S6: polyethylene powder and NMP are loaded into a glass container according to a mass ratio of 1:20 and stirred at 50°C for 6h to obtain a polymer solution; pour the polymer solution into a PTFE template and place it in an oven for drying, with a drying temperature of 50°C and a drying time of 8h to obtain a separator base.

[0045] S7: The temperature regulating layer was placed on one side of the separator substrate and hot-pressed at a pressure of 0.5 MPa and a temperature of 110 °C for 5 h; the final polymer composite separator was annealed at 106 °C for 10 h in a vacuum oven to improve the crystallinity of the film, obtaining a temperature regulating polymer composite separator with a thickness of 38 pm, in which the thickness ratio of the separator substrate to the temperature regulating layer was 8:1.

[0046] Example 2 A temperature regulating polymer composite separator was prepared by the following steps:

[0047] S1 : Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 The PbO, La2O3, TiO2, ZrO2, and SnO2 materials with a purity of more than 99.0% were prepared according to the stoichiometric ratio; 13 mL of ethanol, 7 mL of acetylacetone, and 15 mL of glacial acetic acid were mixed to obtain a co-solvent, and then the above-mentioned raw materials were sequentially dissolved in the co-solvent and stirred to form a uniform solution, wherein the mass ratio of the raw materials of the three-dimensional ceramic framework to the co-solvent was 1:7, thereby obtaining a PLZST sol.

[0048] S2: The polyurethane foam template (TX704, ITW Texwipe) was soaked in the PLZST sol for 10 min; then the excess sol was squeezed out of the polyurethane foam template and dried at 45 °C to obtain a PLZST precursor template; finally, the PLZST precursor template was sintered at 1100 °C for 2 h to obtain a three-dimensional ceramic framework.

[0049] S3: P(VDF-TrFE-CFE) (62.1 / 30.1 / 7.8 mol%, Piezotech, France) was dissolved in DMF and stirred for 10 h to obtain a uniform P(VDF-TrFE-CFE) solution with a concentration of 28 wt%.

[0050] S4: The three-dimensional ceramic framework was placed on a PTFE mold with a length, width, and height of 40 x 40 x 20 mm; then the P(VDF-TrFE-CFE) solution obtained in S3 was filled into the three-dimensional ceramic framework, and then placed in an oven at 60 °C for heating for 0.5 h. The above-mentioned filling-heating process was repeated several times until the three-dimensional ceramic framework was completely filled with P(VDF-TrFE-CFE), obtaining a composite material.

[0051] S5: The obtained composite material was dried at 50 °C for 10 h to remove excess solvent, and then the above-mentioned material was converted into a dense body by hot-pressing at 0.5 MPa and 120 °C for 15 min to obtain a temperature regulating layer.

[0052] S6: Polyethylene powder and NMP were loaded into a glassware in a mass ratio of 1:10 for stirring at 50 °C for 6 h to obtain a polymer solution; the polymer solution was poured into a PTFE mold and placed in an oven for drying at a temperature of 50 °C for 8 h to obtain a separator substrate.

[0053] S7: The temperature-regulating layer material was placed on one side of the separator substrate and hot-pressed at a pressure of 0.5 MPa and a temperature of 110 °C for 5 h; the final polymer composite separator was annealed in a vacuum oven at 106 °C for 10 h to improve the crystallinity of the film, obtaining a temperature-regulating polymer composite separator with a thickness of 48 pm, wherein the thickness ratio of the separator substrate to the temperature-regulating layer was 13:1.

[0054] Example 3 A temperature-regulating polymer composite separator was prepared by the following steps:

[0055] S1: Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 The TiO4 material was prepared from PbO, La2O3, TiO2, ZrO2, and SnO2 with a purity greater than 99.0%, and the above raw materials were weighed according to the stoichiometric ratio; 10 mL of ethanol, 7 mL of acetylacetone, and 10 mL of glacial acetic acid were mixed to obtain a co-solvent, and then the above raw materials were sequentially dissolved in the co-solvent and stirred to form a uniform solution, wherein the mass ratio of the raw materials of the three-dimensional ceramic framework to the co-solvent was 1:20, thereby obtaining a PLZST sol.

[0056] S2: A polyurethane foam template (TX704, ITW Texwipe) was soaked in the PLZST sol for 10 min. Then the excess sol was squeezed out of the polyurethane foam template and dried at 45 °C to obtain a PLZST precursor template. Finally, the PLZST precursor template was sintered at 1100 °C for 2 h to obtain a three-dimensional ceramic framework.

[0057] S3: P(VDF-TrFE-CFE) (62.1 / 30.1 / 7.8 mol%, Piezotech, France) was dissolved in DMF and stirred for 10 h to obtain a uniform P(VDF-TrFE-CFE) solution with a concentration of 26 wt%.

[0058] S4: The three-dimensional ceramic framework was placed on a PTFE mold with a length, width, and height of 40 x 40 x 20 mm; then the P(VDF-TrFE-CFE) solution obtained in S3 was filled into the three-dimensional ceramic framework, which was then placed in an oven at 60 °C for heating for 0.5 h. The above filling-heating process was repeated several times until the three-dimensional ceramic framework was completely filled with the polymer matrix, obtaining a composite material.

[0059] S5: The resulting composite material was dried at 50 °C for 10 h to remove excess solvent, followed by converting the above material into a dense body by hot pressing at 0.5 MPa and 120 °C for 15 min to obtain a temperature-regulating layer.

[0060] S6: Polyethylene powder and NMP were loaded into a glassware in a mass ratio of 1 : 15 for stirring at 50 °C for 6 h to obtain a polymer solution; the polymer solution was poured into a PTFE template and placed in an oven for drying at 50 °C for 8 h to obtain a separator substrate.

[0061] S7: The temperature-regulating layer material was placed on one side of the separator substrate and hot-pressed at a pressure of 0.5 MPa and a temperature of 110 °C for 5 h; the final polymer composite separator was annealed at 106 °C for 10 h in a vacuum oven to improve the crystallinity of the film, obtaining a temperature-regulating polymer composite separator with a thickness of 42 pm, wherein the thickness ratio of the separator substrate to the temperature-regulating layer was 11 : 1.

[0062] Example 4: A temperature-regulating polymer composite separator was prepared by the following steps:

[0063] S1 : Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 The PbO, La2O3, TiO2, ZrO2, and SnO2 materials with a purity of more than 99.0% were prepared according to the stoichiometric ratio; 10 mL of ethanol, 3 mL of acetylacetone, and 10 mL of glacial acetic acid were mixed to obtain a co-solvent, and the above-mentioned raw materials were sequentially dissolved in the co-solvent and stirred to form a uniform solution, wherein the mass ratio of the raw materials of the three-dimensional ceramic framework to the co-solvent was 1 : 30, thereby obtaining a PLZST sol.

[0064] S2: A polyurethane foam template (TX704, ITW Texwipe) was soaked in the PLZST sol for 10 min; then the excess sol was squeezed out from the polyurethane foam template and dried at 45 °C to obtain a PLZST precursor template; finally, the PLZST precursor template was sintered at 1100 °C for 2 h to obtain a three-dimensional ceramic framework.

[0065] S3: P(VDF-TrFE-CFE) (62.1 / 30.1 / 7.8 mol%, Piezotech, France) was dissolved in DMF and stirred for 10 h to obtain a uniform P(VDF-TrFE-CFE) solution with a concentration of 30 wt%.

[0066] S4: The three-dimensional ceramic skeleton was placed on a PTFE mold with a length, width, and height of 40x40x20 mm, and then the P(VDF-TrFE-CFE) solution obtained in S3 was filled into the three-dimensional ceramic skeleton, which was then placed in an oven at 60°C for heating for 0.5 h. The above filling-heating process was repeated several times until the three-dimensional ceramic skeleton was completely filled with P(VDF-TrFE-CFE), obtaining a composite material.

[0067] S5: The obtained composite material was dried at 50°C for 10 h to remove excess solvent, and then the above material was converted into a dense body by hot pressing at 0.5 MPa and 110°C for 15 min to obtain a temperature-regulating layer.

[0068] S6: Polyethylene powder and NMP were loaded into a glass container in a mass ratio of 1:8 for stirring at 50°C for 6 h to obtain a polymer solution; the polymer solution was poured into a PTFE mold and placed in an oven for drying at a temperature of 50°C for 8 h to obtain a separator substrate.

[0069] S7: The temperature-regulating layer was placed on one side of the separator substrate and hot-pressed at a pressure of 0.5 MPa and a temperature of 110°C for 5 h; finally, the obtained polymer composite separator was annealed in a vacuum oven at 106°C for 10 h to improve the crystallinity of the film, obtaining a temperature-regulating polymer composite separator with a thickness of 52 μm, wherein the thickness ratio of the separator substrate to the temperature-regulating layer is 16:1.

[0070] Example 5: A temperature-regulating polymer composite separator was prepared by the following steps:

[0071] S1: Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 The PbO, La2O3, TiO2, ZrO2, and SnO2 materials with a purity of greater than 99.0% were prepared according to the stoichiometric ratio; 6 mL of ethanol, 3 mL of acetylacetone, and 10 mL of glacial acetic acid were mixed to obtain a co-solvent, and then the above raw materials were sequentially dissolved in the co-solvent and stirred to form a uniform solution, wherein the mass ratio of the raw materials of the three-dimensional ceramic skeleton to the co-solvent was 1:22, thereby obtaining a PLZST sol.

[0072] S2: A polyurethane foam template (TX704, ITW Texwipe) was immersed in the PLZST sol for 10 min; then the excess sol was squeezed out of the polyurethane foam template and dried at 45°C to obtain a PLZST precursor template; finally, the PLZST precursor template was sintered at 1100°C for 2 h to obtain a three-dimensional ceramic skeleton.

[0073] S3: P(VDF-TrFE-CFE) (62.1 / 30.1 / 7.8 mol%, Piezotech, France) was dissolved in DMF for 10 h with stirring to obtain a homogeneous P(VDF-TrFE-CFE) solution with a concentration of 24 wt%.

[0074] S4: The three-dimensional ceramic framework was placed on a PTFE mold with a length, width, and height of 40 x 40 x 20 mm, and then the P(VDF-TrFE-CFE) solution obtained in S3 was filled into the three-dimensional ceramic framework, which was then placed in an oven at 60°C for 0.5 h. The above filling-heating process was repeated several times until the three-dimensional ceramic framework was completely filled with P(VDF-TrFE-CFE), obtaining a composite material.

[0075] S5: The obtained composite material was dried at 50°C for 10 h to remove excess solvent, and then the above material was converted into a dense body by hot pressing at 0.5 MPa and 110°C for 15 min to obtain a temperature-regulating layer.

[0076] S6: Polyethylene powder and NMP were loaded into a glass container in a mass ratio of 1:13 and stirred at 50°C for 6 h to obtain a polymer solution; the polymer solution was poured into a PTFE mold and placed in an oven for drying at a temperature of 50°C for 8 h to obtain a separator substrate.

[0077] S7: The temperature-regulating layer was placed on one side of the separator substrate and hot-pressed at a pressure of 0.5 MPa and a temperature of 110°C for 5 h; finally, the obtained polymer composite separator was annealed at 106°C for 10 h in a vacuum oven to improve the crystallinity of the film, obtaining a temperature-controlled polymer composite separator with a thickness of 41 μm, wherein the thickness ratio of the separator substrate to the temperature-regulating layer is 12.5:1.

[0078] Example 6: A temperature-controlled polymer composite separator was prepared by the following steps:

[0079] S1: Pb 0.97 La 0.02 Zr 0.91 Sn 0.05 The PbO, La2O3, TiO2, ZrO2, and SnO2 materials with a purity of greater than 99.0% were prepared according to the stoichiometric ratio; 6 mL of ethanol, 3 mL of acetylacetone, and 10 mL of glacial acetic acid were mixed to obtain a co-solvent, and then the above raw materials were sequentially dissolved in the co-solvent and stirred to form a uniform solution, wherein the mass ratio of the raw materials of the three-dimensional ceramic framework to the co-solvent was 1:18, thereby obtaining a PLZST sol.

[0080] S2: soak the polyurethane foam template (TX704, ITW Texwipe) in the PLZST sol for 10 min; then squeeze out the excess sol from the polyurethane foam template and dry at 45℃ to obtain a PLZST precursor template; finally, sinter the PLZST precursor template at 1100℃ for 2h to obtain a three-dimensional ceramic skeleton.

[0081] S3: stir P(VDF-TrFE-CFE) (62.1 / 30.1 / 7.8 mol%, Piezotech, France) in DMF for 10h to obtain a homogeneous P(VDF-TrFE-CFE) solution with a concentration of 32wt%.

[0082] S4: place the three-dimensional ceramic skeleton in a PTFE mold with a length, width and height of 40x40x20 mm, then fill the P(VDF-TrFE-CFE) solution obtained in S3 into the three-dimensional ceramic skeleton, and then place it in an oven at 60℃ for 0.5h. Repeat the above filling-heating process several times until the three-dimensional ceramic skeleton is completely filled with P(VDF-TrFE-CFE) to obtain a composite material.

[0083] S5: dry the obtained composite material at 50℃ for 10h to remove excess solvent, then convert the above material into a dense body by hot pressing at 0.5MPa and 110℃ for 15min to obtain a temperature-regulating layer.

[0084] S6: stir the polyethylene powder and NMP in a glass container according to a mass ratio of 1:11 at 50℃ for 6h to obtain a polymer solution; pour the polymer solution into a PTFE mold and place it in an oven for drying, with a drying temperature of 50℃ and a drying time of 8h to obtain a separator substrate.

[0085] S7: place the temperature-regulating layer on one side of the separator substrate and hot-press it at a pressure of 0.5MPa and a temperature of 110℃ for 5h; finally, anneal the obtained polymer composite separator in a vacuum oven at 106℃ for 10h to improve the crystallinity of the film to obtain a temperature-regulating polymer composite separator, which has a thickness of 55μm, wherein the thickness ratio of the separator substrate to the temperature-regulating layer is 18:3.

[0086] Comparative Example 1

[0087] This comparative example differs from Example 1 in that the concentration of the P(VDF-TrFE-CFE) solution is 2wt%, and the remaining steps are the same as those of Example 1; this comparative example obtains a separator with a thickness of 38μm, wherein the thickness ratio of the separator substrate to the temperature-regulating layer is 40:1.

[0088] Comparative Example 2

[0089] The difference between the present comparative example and Example 1 is that the concentration of the P(VDF-TrFE-CFE) solution is 50 wt%, and the remaining steps are the same as those of Example 1. The present comparative example obtains a separator with a thickness of 200 μm, in which the thickness ratio of the separator substrate to the temperature regulating layer is 2:3.

[0090] Comparative Example 3

[0091] A conventional polymer separator is prepared by a hot-pressing method without a temperature regulating layer. Specifically, polyethylene powder and NMP are loaded into a glassware in a mass ratio of 1:20 for stirring at 50 °C for 6 h, followed by hot-pressing at a pressure of 0.5 MPa and a temperature of 110 °C for 5 h to obtain a conventional polymer separator with a thickness of 40 μm.

[0092] Comparative Example 4

[0093] The polymer separator of the present example is a commercially available polyolefin separator.

[0094] Test Example 1: Separator Ionic Conductivity and Battery Temperature Test

[0095] 1) The separators of Example 1 and Comparative Examples 1-4 are respectively assembled with stainless steel sheets to form symmetrical batteries, and the ionic conductivity of the separators is tested at a voltage of 5 mV and a frequency of 0.01 Hz-1 MHz.

[0096] 2) The separators of Example 1 and Comparative Examples 1-4 are respectively assembled with LFP positive electrodes and graphite negative electrodes to form full batteries, and the battery temperature is tested at a constant current charge and discharge of 0.1 C at room temperature with a charge and discharge voltage range of 2.5 V-3.8 V. Meanwhile, the batteries are also placed in a 130 °C oven and the battery temperature is tested at a constant current charge of 0.1 C with a charge and discharge voltage range of 2.5 V-3.8 V.

[0097] Table 1: Performance Research Results of Example 1 and Its Comparative Examples

[0098]

[0099]

[0100] As can be seen from Example 1 and Comparative Examples 1-4, Example 1 has good ionic conductivity, 8.88 mS / cm, Comparative Example 1 has 1.65 mS / cm, Comparative Example 2 has 0.12 mS / cm, Comparative Example 3 has 0.15 mS / cm, and Comparative Example 4 has 0.58 mS / cm. Thus, the composite separator modified by the negative electrode material layer has good ionic conductivity, and can reduce the temperature of the battery during charging and discharging, so that the temperature of the battery is maintained near room temperature, and the temperature of the battery is prevented from further rising. When the battery is in the charging process, the temperature of the environment caused by external factors such as fire is higher than the melting point temperature of the conventional polyolefin separator 130℃, at this time, the temperature control polymer composite separator of the application can absorb the temperature of the environment, reduce the temperature of the battery, and effectively avoid the occurrence of battery thermal runaway; as shown in the rightmost column of the battery temperature in Table 1, when the battery is being charged and discharged, the temperature of the environment is higher than 130℃, at this time, the temperature of the battery in Example 1 can still be maintained at 50℃, which has very good temperature control effect, while the temperature of the battery of the comparative example is already higher than the temperature of the environment, which will further cause the battery to explode.

[0101] Test Example 2

[0102] Test 1: The temperature control polymer composite separator prepared from Example 2 and Comparative Example 4 was cut into a 19 mm round piece, and assembled with a positive electrode material lithium iron phosphate to form a half battery for electrical performance testing, and cycled 300 times at room temperature at a 2C rate.

[0103] The temperature control composite separator prepared from Example 3 was cut into a 19 mm round piece, and assembled with graphite to form a half battery for electrical performance testing, and cycled 150 times at room temperature at a 4C rate.

[0104] The results are shown in Table 2.

[0105] Table 2: Charge-discharge test results of the half battery assembled with the separator of Example 2-3

[0106] Example Rate Capacity retention Discharge specific capacity (mAh / g) Example 2 2C 99.9％ 155 Example 3 4C No significant attenuation No significant attenuation Comparative Example 4 2C 95.6％ 132

[0107] As can be seen from Table 2, the half battery assembled with Example 2 has good capacity retention rate, 99.9%, and discharge specific capacity, 155 mAh / g, when charged and discharged at a 2C rate, and the graphite half battery in Example 3 has no obvious decay when charged and discharged at a 4C rate, which shows that the separator has good electrical performance. The half battery assembled with the commercial polyolefin separator of Comparative Example 4 has lower capacity retention rate and discharge specific capacity than Example 2 after 2C charge-discharge test, which proves that the temperature control polymer composite separator of the application has good electrical performance.

[0108] Test 2: The temperature-controlling polymer composite separator prepared in Example 4 was cut into a 19 mm round piece, and assembled into a lithium-lithium symmetric battery (wherein the temperature-controlling layer of the separator was arranged at the negative electrode side) to test the electrical performance. At room temperature, the battery was tested at a current density of 2 mA / cm 2 for 4000 cycles.

[0109] The test results of the electrical performance showed that the lithium-lithium symmetric battery assembled with the temperature-controlling polymer composite separator of Example 4 exhibited a polarization voltage of 0.2 V after 4000 cycles at a current density of 2 mA / cm 2 , indicating that the battery still exhibited a small polarization voltage after 4000 cycles, and that the battery had a strong ability to inhibit lithium dendrites. The conventional polyolefin separator was affected by internal impurities during charging and discharging, and the migration speed of lithium ions was slow, which could further block the pores of the separator, increase the internal resistance of the battery, and cause the capacity of the battery to drop sharply and the cycle number to decrease significantly, failing to reach 4000 cycles.

[0110] Meanwhile, the results also showed that when the charging and discharging were stopped and the electric field was removed, the temperature increase of the lithium-lithium symmetric battery assembled with the temperature-controlling polymer composite separator of Example 4 could reduce the internal polarization, effectively reduce the internal resistance of the battery, and improve the capacity of the battery. Taking charging as an example, the conventional polyolefin separator did not have a temperature-controlling function, and could not quickly eliminate the concentration polarization inside the lithium ion battery, which finally led to incomplete embedding of lithium ions in the negative electrode. Then, the lithium ions released from the positive electrode would form lithium single elements or lithium compounds on the surface of the negative electrode, or even dead lithium, which caused the growth of lithium dendrites, leading to the attenuation of the capacity of the battery, and further growth of the lithium dendrites, which could even pierce the separator, causing the positive and negative electrodes of the battery to contact, and leading to thermal runaway. However, in the present application, the temperature-controlling polymer composite separator with a negative electrode card effect could further increase the temperature after the electric field was removed, promote the rapid migration of lithium ions, reduce the internal concentration polarization, and enable the lithium ions to almost 100% embed in the negative electrode, without staying on the surface of the negative electrode. In addition, the temperature-controlling layer with a certain rigidity facing the negative electrode was also beneficial to inhibiting the generation of lithium dendrites, thereby significantly improving the capacity of the battery.

[0111] Test 3: The temperature-controlling polymer composite separator prepared in Example 5 was cut into a 25 mm x 30 mm rectangular piece, and assembled into a soft package battery with a lithium iron phosphate loading of 20 mg / cm 2 and a graphite loading of 8 mg / cm 2 to test the electrical performance. The battery was tested at room temperature and at a 1C rate.

[0112] The test results show that the battery assembled with the temperature control polymer composite separator of Example 5 can be normally cycled and charged and discharged, and the temperature of the battery can be maintained below 40℃; if the battery unfortunately is in a high temperature environment greater than 130℃, the battery can also be "cooled" during charging and discharging, effectively avoiding further thermal runaway of the battery.

[0113] Test IV: The temperature control polymer composite separator prepared in Example 6 was cut into a rectangular piece of 25mm x 30mm, and was assembled into a soft package battery with lithium iron phosphate having a loading amount of 20mg / cm 2 and graphite having a loading amount of 8mg / cm 2 to test the electrical performance. The battery was tested for charging and discharging at room temperature at a 6C rate.

[0114] The test results show that the battery assembled with the temperature control polymer composite separator of Example 6 can be cycled and charged and discharged under fast charging conditions, and the temperature of the battery can still be controlled within 35℃, which shows that the separator can be effectively applied in the field of battery fast charging and has good application prospects.

Claims

1. A temperature-controlling polymer composite diaphragm, characterized in that: It includes a diaphragm base and a temperature regulating layer arranged on one side or both sides thereof; The diaphragm substrate is a polymer film; The temperature regulating layer is a negative electrocaloric material layer, which is composed of a three-dimensional ceramic skeleton and a polar polymer material both having a negative electrocaloric effect; The material of the three-dimensional ceramic skeleton is a relaxor ferroelectric lead zirconate titanate dopant doped with tin; The polar polymer material is poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene); The temperature-controlling polymer composite diaphragm is prepared by the following steps: preparing a three-dimensional ceramic skeleton by a sol-gel method; filling the three-dimensional ceramic skeleton with a polar polymer material, and then hot-pressing to obtain a temperature-controlling layer; and finally hot-pressing the diaphragm base and the temperature-controlling layer to obtain the temperature-controlling polymer composite diaphragm. The method for preparing the three-dimensional ceramic skeleton comprises: uniformly mixing raw materials for preparing the three-dimensional ceramic skeleton with a solvent to obtain a sol; soaking a polyurethane foam template in the sol, then squeezing out excess sol from the polyurethane foam template and drying it to obtain a precursor template; and finally, sintering the precursor template to obtain the three-dimensional ceramic skeleton. The method for preparing the temperature regulating layer is: filling a polar polymer material solution into the three-dimensional ceramic skeleton prepared above until the three-dimensional ceramic skeleton is completely filled with the polar polymer material to obtain a composite material; drying the obtained composite material, and then hot pressing to convert the above composite material into a dense body to obtain a temperature regulating layer.

2. The temperature-controlling polymer composite diaphragm according to claim 1, characterized in that: The material of the diaphragm substrate is selected from at least one of polyacrylonitrile, polyethylene, polypropylene, polyvinylidene fluoride, polyvinyl pyrrolidone, poly(m-phenylene isophthalamide) and polymethyl methacrylate.

3. A method for preparing the temperature-controlling polymer composite diaphragm according to claim 1, characterized in that: The following steps are involved: A three-dimensional ceramic skeleton is prepared by a sol-gel method; a polar polymer material is filled into the three-dimensional ceramic skeleton, and then hot-pressed to obtain a temperature-regulating layer; and finally, the diaphragm base and the temperature-regulating layer are hot-pressed to obtain the temperature-regulating polymer composite diaphragm; The method for preparing a three-dimensional ceramic skeleton comprises: uniformly mixing raw materials for preparing the three-dimensional ceramic skeleton with a solvent to obtain a sol; infiltrating a polyurethane foam template in the sol, then squeezing excess sol from the polyurethane foam template and drying it at 35-65°C to obtain a precursor template; and finally, sintering the precursor template at 1000-1400°C for 1-3 hours to obtain a three-dimensional ceramic skeleton. The method for preparing the temperature control layer is as follows: dissolving the polar polymer material to obtain a polar polymer material solution with a concentration of 5~35 wt%; then filling the polar polymer material solution into the three-dimensional ceramic skeleton prepared above, and then placing it in an oven at 40~80°C and heating it for 0.1~2 h; repeating the above filling-heating operation several times until the three-dimensional ceramic skeleton is completely filled with the polar polymer material to obtain a composite material; drying the obtained composite material at 40~60°C for 8~12 h, and then hot pressing at 0.1~1 MPa and 100~150°C for 10~25 min to convert the above composite material into a dense body to obtain the temperature control layer.

4. The method for preparing the temperature-controlling polymer composite diaphragm according to claim 3, wherein: The infiltration time is 15 to 20 minutes; the solvent is composed of 5 to 40 mL of ethanol, 1 to 10 mL of acetylacetone, and 5 to 30 mL of glacial acetic acid; and the mass ratio of the raw materials for preparing the three-dimensional ceramic skeleton to the solvent is 1:5 to 1:

50.

5. The method for preparing the temperature-controlling polymer composite diaphragm according to claim 4, wherein: placing a temperature-regulating layer on one side of a diaphragm substrate and performing hot pressing to obtain a polymer composite diaphragm, wherein the hot pressing pressure is 0.5-1 MPa, the temperature is 100-200°C, and the time is 1-10 hours; finally, annealing the obtained polymer composite diaphragm in a vacuum oven at 106°C for 10 hours to improve the crystallinity of the membrane, thereby obtaining the temperature-regulating polymer composite diaphragm; The preparation method of the diaphragm substrate comprises: mixing a polymer and N-methylpyrrolidone in a mass ratio of 1:10 to 1:50 to form a polymer solution; pouring the obtained polymer solution into a template, placing the template in an oven at 40 to 60°C for drying for 6 to 12 hours to obtain the diaphragm substrate.

6. Use of the temperature-controlling polymer composite diaphragm according to claim 1 in lithium-ion batteries.

Images