A modified natural rubber-based composite film, its preparation method and application

Abstract

The present invention provides a modified natural rubber-based composite film, a preparation method and an application thereof, relating to battery materials. By utilizing the excellent resilience and film-forming property of natural rubber, the mechanical strength after vulcanization can meet the mechanical property requirements of solid electrolytes. Based on the excellent comprehensive properties of natural rubber, the present invention constructs a modified natural rubber-based composite film by combining the connectivity and porosity of an electrospun porous fiber membrane. Among them, the side groups of natural rubber molecules modified with unsaturated carboxylic esters and / or unsaturated carboxylic ester salts contain carboxyl groups, which can bind lithium ions and serve as an ion conduction pathway for lithium ions; the nano conductive fillers uniformly dispersed in the unsaturated carboxyl group-modified natural rubber form a conductive pathway, thereby forming a "dual conduction" pathway with conductivity and ion conduction. The modified natural rubber-based composite film has a high conductivity, a high ion transference number, and greatly reduces the cost, providing an effective way for the comprehensive promotion of all-solid-state lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and particularly relates to a modified natural rubber-based composite film and a preparation method and application thereof. Background Art

[0002] The use of lithium metal anodes in solid-state batteries has become one of the most promising technologies to replace traditional lithium-ion batteries. Solid electrolytes are a key technology for the safe operation of lithium metal batteries because they inhibit the uncontrollable growth of lithium dendrites. However, the mechanical and electrochemical properties of current solid electrolytes still cannot meet the requirements of the practical application of lithium metal batteries. To prepare high-performance solid electrolytes, Korean scholars (M. Lee; J. Han; K. Lee; Y. Lee; B. Kim; K.-N. Jung; B. Kim. Elastomeric electrolytes for high-energy solid-state lithium batteries. Nature, 2022, 601, 217-222.) reported plastic crystal-embedded elastomeric electrolytes (PCEEs) with a bicontinuous structure and their role in simultaneously optimizing their mechanical and electrochemical properties to enable the reliable operation of the resulting solid-state lithium-ion batteries. However, the film-forming properties of the above solid electrolytes are not good enough. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a modified natural rubber-based composite film and a preparation method and application thereof. The modified natural rubber-based composite film provided by the present invention has good uniformity, high conductivity, high ion transference number, and low cost.

[0004] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a modified natural rubber-based composite film, comprising an electrospun porous fiber membrane and natural rubber attached to the surface of the electrospun porous fiber membrane; the electrospun porous fiber membrane is composed of unsaturated carboxylic acid group-modified natural rubber and nano conductive fillers dispersed in the unsaturated carboxylic acid group-modified natural rubber.

[0006] Preferably, the unsaturated carboxylic acid group-modified natural rubber has the structure shown in Formula I:

[0007]

[0008] Wherein, R is an aliphatic hydrocarbon group, and R' is an aliphatic hydrocarbon group or a metal.

[0009] Preferably, the aliphatic hydrocarbon group includes C1-C4 alkyl groups;

[0010] The metal includes zinc, lithium, sodium, magnesium, calcium or rare earth metals.

[0011] Preferably, the nano conductive filler includes one or more of carbon nanotubes, carbon black, copper powder and silver powder.

[0012] Preferably, the mass ratio of the unsaturated carboxyl group modified natural rubber to the nano conductive filler is 5-20:20-30.

[0013] Preferably, the average pore diameter of the electrospun porous fiber membrane ≤ 0.3 μm;

[0014] The thickness of the modified natural rubber-based composite film is 5-30 μm.

[0015] The present invention provides a method for preparing the modified natural rubber-based composite film described in the above technical solution, including the following steps:

[0016] Mix the unsaturated carboxyl group modified natural rubber, nano conductive filler and organic solvent to obtain a mixed spinning solution;

[0017] Perform electrospinning on the mixed spinning solution to obtain an electrospun porous fiber membrane;

[0018] Place the electrospun porous fiber membrane in natural rubber and impregnate it to obtain a modified natural rubber-based composite film.

[0019] Preferably, the organic solvent includes one or more of tetrahydrofuran, toluene, chloroform, n-hexane and gasoline;

[0020] In the mixed spinning solution, the content of the unsaturated carboxyl group modified natural rubber is 5-20 wt%, and the content of the nano conductive filler is 20-30 wt%.

[0021] Preferably, the process conditions of the electrospinning include: using a glass syringe to push the mixed spinning solution, the rate of the mixed spinning solution is 0.02-1 mL / h, the spinning voltage is 12-20 kV, the distance between the spinning plates is 15-30 cm, the humidity of the spinning is ≤ 50%, and the temperature is room temperature.

[0022] The present invention provides the application of the modified natural rubber-based composite film described in the above technical solution or the modified natural rubber-based composite film prepared by the preparation method described in the above technical solution as a composite solid electrolyte.

[0023] The present invention provides a modified natural rubber-based composite film, which comprises an electrospun porous fiber membrane and natural rubber attached to the surface of the electrospun porous fiber membrane; the electrospun porous fiber membrane is composed of unsaturated carboxylic acid group-modified natural rubber and nano conductive fillers dispersed in the unsaturated carboxylic acid group-modified natural rubber. The present invention utilizes the excellent resilience and film-forming property of natural rubber, and the mechanical strength after vulcanization can meet the mechanical property requirements of solid electrolytes. Based on the excellent comprehensive properties of natural rubber, combined with the connectivity and porosity of the electrospun porous fiber membrane, a modified natural rubber-based composite film with good film uniformity is constructed. Among them, the side groups of natural rubber molecules modified by unsaturated carboxylic esters and / or unsaturated carboxylic ester salts contain carboxylic acid groups, which can bind lithium ions and serve as an ion conduction pathway for lithium ions; nano conductive fillers uniformly dispersed in the unsaturated carboxylic acid group-modified natural rubber form a conductive pathway, thereby forming a "dual conduction" pathway with conductivity and ion conduction. The modified natural rubber-based composite film has high conductivity and high ion transference number, providing an effective way for the comprehensive promotion of all-solid-state lithium-ion batteries. Moreover, the price of natural rubber is relatively low, greatly reducing the cost of the modified natural rubber-based composite film. As a composite solid electrolyte of lithium-ion batteries, the modified natural rubber-based composite film reduces the production cost of lithium-ion batteries and provides assistance for the comprehensive promotion of lithium-ion batteries.

[0024] The preparation method of the modified natural rubber-based composite film provided by the present invention has simple process, convenient operation, is green and environmentally friendly, has low cost, and is suitable for industrial production. Brief Description of the Drawings

[0025] Figure 1 It is a schematic diagram of an electrospun porous fiber membrane for preparing a "dual conduction" pathway with conductivity and ion conduction by electrospinning;

[0026] Figure 2 It is an infrared spectrum diagram of natural rubber (NR) and unsaturated carboxylic ester salt-modified natural rubber (modified NR) in Example 1;

[0027] Figure 3 It is a cross-sectional SEM diagram of the modified natural rubber-based composite film prepared in Example 1. Among them, a and b are top views of the cross-section, and c and d are front views of the cross-section;

[0028] Figure 4 It is an SEM diagram of the electrospun porous fiber membrane in Example 2; Detailed Description of the Invention

[0029] The present invention provides a modified natural rubber-based composite film, which includes an electrospun porous fiber membrane and natural rubber attached to the surface of the electrospun porous fiber membrane; the electrospun porous fiber membrane is composed of unsaturated carboxylic acid group-modified natural rubber and nano conductive fillers dispersed in the unsaturated carboxylic acid group-modified natural rubber.

[0030] In the present invention, the unsaturated carboxylic acid group-modified natural rubber preferably has the structure shown in Formula I:

[0031]

[0032] Wherein, R is an aliphatic hydrocarbon group, and R' is an aliphatic hydrocarbon group or a metal; the aliphatic hydrocarbon group preferably includes C1-C4 alkyl groups, more preferably includes methyl, ethyl, propyl or butyl; the metal preferably includes zinc, lithium, sodium, magnesium, calcium or rare earth metals; the rare earth metals preferably include one or more of gadolinium, samarium, cerium and zirconium; the unsaturated carboxylic acid group-modified natural rubber is preferably a single unsaturated carboxylic acid group-modified natural rubber or a mixture of multiple unsaturated carboxylic acid group-modified natural rubbers.

[0033] In the present invention, the unsaturated carboxylic acid group-modified natural rubber preferably includes natural rubber modified by unsaturated carboxylic acid esters and / or unsaturated carboxylic acid ester salts.

[0034] In the present invention, the mass of the unsaturated carboxylic acid esters and / or unsaturated carboxylic acid ester salts in the unsaturated carboxylic acid group-modified natural rubber is preferably 5-25% of the mass of the natural rubber, more preferably 10-20%, and further preferably 12-15%. In the present invention, the natural rubber preferably includes one or more of concentrated natural latex, Tianjia latex and epoxy latex, more preferably a mixture of concentrated natural latex and Tianjia latex, or a mixture of concentrated natural latex and epoxy latex; the mass ratio of concentrated natural latex to Tianjia latex in the mixture of concentrated natural latex and Tianjia latex is preferably 1:0.05-0.5, more preferably 1:0.1-0.2; the mass ratio of concentrated natural latex to epoxy latex in the mixture of concentrated natural latex and epoxy latex is preferably 1:0.05-0.5, more preferably 1:0.1-0.2; the solid content of the concentrated natural latex is preferably 30-60%, more preferably 50-60%; the solid content of the Tianjia latex is preferably 20-50%, more preferably 25-40%; the solid content of the epoxy latex is preferably 20-50%, more preferably 25-40%.

[0035] In the present invention, the unsaturated carboxylic acid esters preferably include one or more of methyl esters, ethyl esters, butyl esters and isopentyl esters of unsaturated carboxylic acids.

[0036] In the present invention, the carboxylic acids in the unsaturated carboxylic acid esters and unsaturated carboxylic acid ester salts preferably independently include one or more of maleic acid, acrylic acid, methacrylic acid, itaconic acid, and sorbic acid.

[0037] In the present invention, the metals in the unsaturated carboxylic acid ester salts preferably include one or more of zinc, lithium, sodium, magnesium, and rare earth metals, that is, the unsaturated carboxylic acid ester salts preferably include one or more of zinc salts, lithium salts, sodium salts, magnesium salts, and rare earth metal salts of unsaturated carboxylic acids.

[0038] In the present invention, the preparation method of the unsaturated carboxylic acid ester salt preferably includes the following steps: mixing an unsaturated carboxylic acid ester, a metal carbonate, and water, and performing an acid-base neutralization reaction to obtain an unsaturated carboxylic acid ester salt.

[0039] In the present invention, the mass ratio of the unsaturated carboxylic acid ester to the metal carbonate is preferably 1:1 to 3, more preferably 1:2. In the present invention, the mass ratio of the unsaturated carboxylic acid ester to water is preferably 1:10 to 20, more preferably 1:10 to 15.

[0040] In the present invention, the temperature of the acid-base neutralization reaction is preferably room temperature, the time is preferably ≤2 h, more preferably 0.5 to 2 h, and further preferably 1 to 1.5 h.

[0041] After completing the acid-base neutralization reaction, the present invention preferably further includes: filtering the obtained acid-base neutralization reaction system, concentrating the obtained liquid component and then crystallizing, and drying the obtained crystals to obtain an unsaturated carboxylic acid ester salt. The present invention has no special limitation on the concentration, and a concentration method well-known to those skilled in the art can be used. In the present invention, the solvent for crystallization preferably includes water; the temperature of crystallization is preferably 25 to 60 °C, more preferably 25 °C. In the present invention, the unsaturated carboxylic acid group-modified natural rubber preferably includes gadolinium monoethyl maleate-modified natural rubber, samarium monoethyl maleate-modified natural rubber, or calcium monomethyl maleate-modified natural rubber latex.

[0042] In the present invention, the preparation method of the unsaturated carboxylic acid group-modified natural rubber preferably includes the following steps: mixing a modifier, natural rubber latex, persulfate, an emulsifier, and water, and performing graft modification to obtain an unsaturated carboxylic acid group-modified natural rubber; the modifier is an unsaturated carboxylic acid ester and / or an unsaturated carboxylic acid ester salt.

[0043] In the present invention, the mass ratio of the natural rubber to the modifier is preferably 100:5 to 25, more preferably 100:10 to 20, and further preferably 100:12 to 15.

[0044] In the present invention, the persulfate preferably includes potassium persulfate; the mass ratio of the natural rubber to the persulfate is preferably 100:0.5 - 2, more preferably 100:0.9 - 1.5.

[0045] In the present invention, the emulsifier preferably includes one or more of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, Peregal 'O', and Tween 80; the mass ratio of the natural latex to the emulsifier is preferably 100:0.5 - 5, more preferably 100:0.9 - 1.5.

[0046] In the present invention, the mass ratio of the natural latex to water is preferably 1:0.7 - 2, more preferably 1:0.9 - 1.5.

[0047] In the present invention, the mixing of the modifier, natural latex, persulfate, emulsifier, and water is preferably as follows: the modifier and persulfate are dissolved in water to obtain a mixed solution; the mixed solution is dropped into the natural latex, and then the emulsifier is added and mixed.

[0048] In the present invention, the emulsification preferably includes thermal stirring and standing in sequence; the temperature of the thermal stirring is preferably 50 - 90°C, more preferably 60 - 70°C; the heat preservation time of the thermal stirring is preferably 1 - 4 h, more preferably 2 - 3 h; the temperature of the standing is preferably 25 - 60°C, more preferably 25°C, and the standing time is preferably 8 - 48 h, more preferably 15 - 24 h.

[0049] In the present invention, the temperature of the graft modification is preferably 50 - 80°C, more preferably 60 - 70°C; the heat preservation time of the graft modification is preferably 8 - 24 h, more preferably 12 - 15 h; the modified system obtained by the graft modification is directly used as unsaturated carboxylic acid group modified natural rubber without post-treatment.

[0050] In the present invention, the nano conductive filler preferably includes one or more of carbon nanotubes, carbon black, copper powder, and silver powder.

[0051] In the present invention, the mass ratio of the unsaturated carboxylic acid group modified natural rubber to the nano conductive filler is preferably 5 - 20:20 - 30, more preferably 10 - 15:22 - 28, and further preferably 12 - 14:25 - 26.

[0052] In the present invention, the average pore diameter of the electrospun porous fiber membrane is preferably ≤0.3 μm, more preferably 0.228 - 0.25 μm. In the present invention, the thickness of the electrospun porous fiber membrane in the modified natural rubber-based composite film is preferably 1 - 15 μm, more preferably 5 - 10 μm.

[0053] In the present invention, the thickness of the modified natural rubber-based composite film is preferably 5-30 μm, more preferably 10-25 μm, and further preferably 15-20 μm; the conductivity of the modified natural rubber-based composite film is preferably > 2.5×10 -4 S·cm -1 , and the ion transference number is preferably > 0.56.

[0054] The present invention provides a method for preparing the modified natural rubber-based composite film described in the above technical solution, comprising the following steps:

[0055] Mix unsaturated carboxylic acid group-modified natural rubber, nano conductive filler and organic solvent to obtain a mixed spinning solution;

[0056] Perform electrospinning on the mixed spinning solution to obtain an electrospun porous fiber membrane;

[0057] Place the electrospun porous fiber membrane in natural rubber and impregnate it to obtain a modified natural rubber-based composite film.

[0058] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0059] The present invention mixes unsaturated carboxylic acid group-modified natural rubber, nano conductive filler and organic solvent to obtain a mixed spinning solution.

[0060] In the present invention, the organic solvent preferably includes one or more of tetrahydrofuran, toluene, chloroform, n-hexane and gasoline.

[0061] In the present invention, in the mixed spinning solution, the content of unsaturated carboxylic acid group-modified natural rubber is preferably 5-20 wt%, more preferably 10-15 wt%, and further preferably 12-14 wt%; the content of nano conductive filler is preferably 20-30 wt%, more preferably 22-28 wt%, and further preferably 25-26 wt%.

[0062] After obtaining the mixed spinning solution, the present invention performs electrospinning on the mixed spinning solution to obtain an electrospun porous fiber membrane.

[0063] In the present invention, the process conditions of the electrospinning preferably include: using a glass syringe to push the mixed spinning solution, with the rate of the mixed spinning solution being 0.02 - 1 mL / h, more preferably 0.3 - 0.5 mL / h; the receiving plate being a metal plate, more preferably a copper plate, an aluminum plate or a tin plate; the spinning voltage being 12 - 20 kV, more preferably 12 - 15 kV; the distance between the spinning plates being 15 - 30 cm, more preferably 20 - 25 cm; the humidity during spinning ≤ 50%, and the temperature being room temperature. In the present invention, the electrospun porous fiber membrane prepared by electrospinning has a "dual-conducting" path for electricity and ions. A schematic diagram of the electrospun porous fiber membrane prepared by electrospinning with a "dual-conducting" path is as shown in Figure 1 shown.

[0064] After completing the electrospinning, the present invention preferably further includes drying the obtained electrospun porous fiber wet membrane to obtain an electrospun porous fiber membrane. In the present invention, the temperature of the drying is preferably 50 - 80 °C, more preferably 60 - 70 °C; the time of the drying is preferably 8 - 48 h, more preferably 15 - 24 h; the drying is preferably vacuum drying, and the vacuum degree of the vacuum drying is preferably < 1 torr.

[0065] After obtaining the electrospun porous fiber membrane, the present invention places the electrospun porous fiber membrane in natural rubber and impregnates it to obtain a modified natural rubber-based composite film.

[0066] In the present invention, the natural rubber preferably includes concentrated natural latex, and the solid content is preferably 60%.

[0067] In the present invention, the number of times of the impregnation is preferably 2 - 3 times, and the time of a single impregnation is preferably 1 - 2 s.

[0068] After completing the impregnation, the present invention preferably further includes air-drying the obtained impregnated film and then vacuum drying it to obtain a modified natural rubber-based composite film. In the present invention, the temperature of the vacuum drying is preferably 50 - 80 °C, more preferably 60 - 70 °C; the time of the vacuum drying is preferably 2 - 24 h, more preferably 15 - 24 h.

[0069] The present invention provides the application of the modified natural rubber-based composite film described in the above technical solution or the modified natural rubber-based composite film prepared by the preparation method described in the above technical solution as a composite solid electrolyte.

[0070] In order to further illustrate the present invention, the following examples are used to describe in detail a modified natural rubber-based composite film provided by the present invention, its preparation method and application, but they should not be construed as limiting the protection scope of the present invention.

[0071] The parts in the following examples are parts by mass.

[0072] Example 1

[0073] Add 10 parts of monoethyl maleate to 100 parts of water, add 20 parts of gadolinium carbonate, stir for 2 h at room temperature, filter to remove the solid residue, concentrate the filtrate, crystallize by natural evaporation, and dry the obtained crystals at 60 °C to obtain gadolinium monoethyl maleate salt. Dissolve 15 parts of gadolinium monoethyl maleate salt and 1 part of potassium persulfate in 100 parts of water, drop the obtained solution into a mixture containing 100 parts of concentrated natural rubber latex and 10 parts of Tianjia rubber latex, add 1 part of sodium dodecyl sulfonate, heat to 60 °C, keep stirring for 2 h, stand for 24 h, and react at 60 °C for 12 h to obtain gadolinium monoethyl maleate-modified natural rubber. Among them, the solid content of the concentrated natural rubber latex is 60%, and the solid content of the Tianjia rubber latex is 25%.

[0074] Add 5 parts of gadolinium monoethyl maleate-modified natural rubber to 100 parts of toluene and stir evenly to obtain a modified natural rubber toluene solution. Mix 10 parts of the modified natural rubber toluene solution and 1 part of ground carbon nanotubes (particle size is), stir, let stand for 2 h, filter, electrospin the obtained mixed spinning solution, and dry the obtained electrospun porous fiber wet film at 0.9 torr and 60 °C for 24 h, then immerse it in concentrated natural rubber latex with a solid content of 60%, immerse it continuously 2 times, the single immersion time is 1 s, air dry and then vacuum dry at 60 °C for 24 h to obtain a modified natural rubber-based composite film. Among them, the process conditions of electrospinning: use a glass syringe to push the mixed spinning solution, the rate of the mixed spinning solution is 0.5 mL / h, use a metal copper plate as the receiving plate, the spinning voltage is 12 kV, the distance between the spinning plates is 25 cm, the humidity of spinning is 50%, and the temperature is room temperature.

[0075] The ionic conductivity is measured by an AC impedance spectrometer, the frequency is 1 - 5 MHz, and the voltage amplitude is 10 mV; the electrochemical impedance spectrometer and chronoamperometry are used to measure the lithium ion transfer number T of the fiber membrane Li+ . Assemble lithium / modified natural rubber-based composite film / LiFePO₄ in a CR2016 type button battery. The measured ion transfer number is: 0.58, and the ionic conductivity is 2.61×10 -4 S·cm -1 .

[0076] Example 2

[0077] Add 10 parts of monoethyl maleate to 100 parts of water, add 20 parts of samarium carbonate, stir for 2 h at room temperature, filter to remove the solid residue, concentrate the filtrate, crystallize by natural evaporation, and dry the obtained crystals at 60 °C to obtain samarium monoethyl maleate salt. Dissolve 10 parts of samarium monoethyl maleate salt and 1 part of potassium persulfate in 100 parts of water, drop the obtained solution into a mixture containing 100 parts of concentrated natural rubber latex and 10 parts of epoxy rubber latex, add 1 part of sodium dodecyl sulfonate, heat to 60 °C, keep stirring for 2 h, stand for 24 h, and react at 60 °C for 12 h to obtain samarium monoethyl maleate-modified natural rubber. Among them, the solid content of the concentrated natural rubber latex is 60%, and the solid content of the natural methyl rubber latex is 25%.

[0078] Add 6 parts of samarium monoethyl maleate-modified natural rubber to 100 parts of chloroform and stir evenly to obtain a chloroform solution of modified natural rubber. Stir 10 parts of the chloroform solution of modified natural rubber and 0.5 part of silver nanoparticles, let stand for 2 h, filter, subject the obtained mixed spinning solution to electrospinning, dry the obtained electrospun porous fiber wet film at 0.9 torr and 60 °C for 24 h, then impregnate it with concentrated natural rubber latex with a solid content of 60%, impregnate it continuously 2 times, with each impregnation time being 1 s, and dry it in vacuum at 60 °C for 24 h after air drying. A modified natural rubber-based composite film is obtained. Among them, the process conditions of electrospinning: use a glass syringe to push the mixed spinning solution, the rate of the mixed spinning solution is 0.5 mL / h, use a metal copper plate as the receiving plate, the spinning voltage is 12 kV, the distance between the spinning plates is 25 cm, the humidity of spinning is 50%, and the temperature is room temperature.

[0079] The ionic conductivity is measured by an alternating current impedance spectrometer, the frequency is in the range of 1 - 5 MHz, and the voltage amplitude is 10 mV; the electrochemical impedance spectrometer and chronoamperometry are used to measure the lithium ion transfer number T of the fiber membrane Li+ 。Assemble lithium / modified natural rubber-based composite film / lithium iron phosphate in a CR2016 type button battery. The measured ion transfer number is: 0.56, and the ionic conductivity is 2.55×10 -4 S·cm -1 。

[0080] Example 3

[0081] Add 10 parts of monomethyl maleate to 100 parts of water, add 20 parts of calcium carbonate, stir for 2 h at room temperature, filter to remove the solid residue, concentrate the filtrate, crystallize by natural evaporation, and dry the obtained crystals at 60 °C to obtain calcium monomethyl maleate. Dissolve 15 parts of calcium monomethyl maleate and 0.8 part of potassium persulfate in 100 parts of water, drop the obtained solution into a mixture containing 100 parts of concentrated natural latex and 10 parts of epoxy latex, add 1 part of sodium dodecyl sulfonate, heat to 60 °C, keep stirring for 2 h, stand for 24 h, and react at 60 °C for 12 h to obtain calcium monomethyl maleate-modified natural rubber. Among them, the solid content of the concentrated natural latex is 60%, and the solid content of the epoxy latex is 25%.

[0082] Add 5 parts of calcium monomethyl maleate-modified natural rubber to 100 parts of tetrahydrofuran and stir evenly to obtain a modified natural rubber tetrahydrofuran solution. Add 10 parts of the modified natural rubber tetrahydrofuran solution and 5 parts of ground carbon nanotubes (particle size is, stir, stand for 2 h, filter, electrospin the obtained mixed spinning solution, dry the obtained electrospun porous fiber wet film at 0.9 torr and 60 °C for 24 h, then impregnate it with concentrated natural latex with a solid content of 60%, impregnate continuously 2 times, the single impregnation time is 1 s, air dry and then vacuum dry at 60 °C for 24 h to obtain a modified natural rubber-based composite film. Among them, the process conditions of electrospinning: use a glass syringe to push the mixed spinning solution, the rate of the mixed spinning solution is 0.5 mL / h, use a metal copper plate as the receiving plate, the spinning voltage is 12 kV, the distance between the spinning plates is 25 cm, the humidity of spinning is 50%, and the temperature is room temperature.

[0083] The ionic conductivity is measured by an alternating current impedance spectrometer, the frequency is 1 - 5 MHz, and the voltage amplitude is 10 mV; the electrochemical impedance spectrometer and chronoamperometry are used to measure the lithium ion transfer number T of the fiber membrane Li+ 。The lithium / modified natural rubber-based composite film / lithium iron phosphate is assembled in a CR2016 type button battery. The measured ion transfer number is: 0.60, and the ionic conductivity is 2.68×10 -4 S·cm -1 。

[0084] Figure 2 Fig. 16 is the infrared spectra of natural rubber (NR) and unsaturated carboxylate salt-modified natural rubber (modified NR) in Example 1. As can be seen from the figure, in addition to retaining the characteristic peaks of natural rubber, the modified natural rubber has obvious absorption peaks at 1548 cm -1 , 1780 cm -1 which are the characteristic peaks of monoethyl maleate salt.

[0085] Figure 3SEM cross-sectional view of the modified natural rubber-based composite film prepared in Example 1. Among them, a and b are the top views of the cross-section, and c and d are the front views of the cross-section. It can be seen from the figure that the modified rubber fibers are wrapped by natural rubber, and the thickness of the composite film is about 50 μm.

[0086] Figure 4 SEM image of the electrospun porous fiber membrane in Example 2. It can be seen from the figure that the conductive filler silver nanoparticles are embedded on the surface of the modified rubber fibers, causing unevenness and non-uniformity of the fibers.

[0087] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A modified natural rubber-based composite film, comprising an electrospun porous fiber membrane and natural rubber attached to the surface of the electrospun porous fiber membrane; the electrospun porous fiber membrane is composed of unsaturated carboxylic acid group-modified natural rubber and nano conductive fillers dispersed in the unsaturated carboxylic acid group-modified natural rubber; the unsaturated carboxylic acid group-modified natural rubber is natural rubber modified by unsaturated carboxylic acid esters and / or unsaturated carboxylic acid ester salts; the unsaturated carboxylic acid esters in the unsaturated carboxylic acid esters and unsaturated carboxylic acid ester salts are independently one or more of methyl ester, ethyl ester, propyl ester and butyl ester of unsaturated carboxylic acid, and the unsaturated carboxylic acid is maleic acid.

2. The modified natural rubber-based composite film according to claim 1, wherein The metals in the unsaturated carboxylic acid ester salts include zinc, lithium, sodium, magnesium, calcium or rare earth metals.

3. The modified natural rubber-based composite film according to claim 1, wherein The nano conductive fillers include one or more of carbon nanotubes, carbon black, copper powder and silver powder.

4. The modified natural rubber-based composite film according to any one of claims 1 to 3, characterized in that, The mass ratio of the unsaturated carboxylic acid group-modified natural rubber to the nano conductive fillers is 5-20:20-30.

5. The modified natural rubber-based composite film according to any one of claims 1 to 3, characterized in that The average pore diameter of the electrospun porous fiber membrane is ≤0.3 μm; The thickness of the modified natural rubber-based composite film is 5-30 μm.

6. The preparation method of the modified natural rubber-based composite film according to any one of claims 1-5, comprising the following steps: Mix the unsaturated carboxylic acid group-modified natural rubber, nano conductive fillers and organic solvent to obtain a mixed spinning solution; Perform electrospinning on the mixed spinning solution to obtain an electrospun porous fiber membrane; Place the electrospun porous fiber membrane in natural rubber and impregnate it to obtain a modified natural rubber-based composite film.

7. The preparation method according to claim 6, characterized in that, The organic solvent includes one or more of tetrahydrofuran, toluene, chloroform, n-hexane and gasoline; In the mixed spinning solution, the content of the unsaturated carboxylic acid group-modified natural rubber is 5-20 wt%, and the content of the nano conductive fillers is 20-30 wt%.

8. The preparation method according to claim 6 or 7, characterized in that, The process conditions of the electrospinning include: using a glass syringe to push the mixed spinning solution, the rate of the mixed spinning solution is 0.02-1 mL / h, the spinning voltage is 12-20 kV, the distance between the spinning plates is 15-30 cm, the humidity of the spinning is ≤50%, and the temperature is room temperature.

9. The application of the modified natural rubber-based composite film according to any one of claims 1-5 or the modified natural rubber-based composite film prepared by the preparation method according to any one of claims 6-8 as a composite solid electrolyte.

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