Composite solid electrolyte, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a composite solid electrolyte, a preparation method thereof and a lithium ion battery. The composite solid electrolyte comprises a polyimide nanofiber membrane, an inorganic solid electrolyte, a lithium salt and a binder, wherein the polyimide nanofiber membrane contains a repetitive unit A as shown in a formula (1) and a repetitive unit B as shown in a formula (2). The composite solid electrolyte takes the polyimide nanofiber membrane as a framework and the inorganic solid electrolyte as a filling medium, and has relatively high room-temperature ionic conductivity and lithium ion transference number, and the obtained lithium ion battery has relatively high cycling stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite solid electrolyte, its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, commercially available lithium-ion batteries are increasingly unable to meet demand due to their limited energy density. Existing lithium-ion batteries mainly use anode materials based on artificial graphite, which have a low theoretical capacity (not exceeding 372 mAh / g), limiting the improvement of lithium-ion battery energy density.

[0003] Traditional lithium-ion batteries use a liquid electrolyte solution, primarily consisting of organic solvents and lithium salts, which pose risks of leakage, combustion, and short circuits during long-term use. Solid-state electrolytes, a rapidly developing type of solid electrolyte material in recent years, do not contain liquid organic solvents, overcoming the drawbacks of traditional batteries such as leakage, flammability, and short circuits. They also utilize lithium metal, which has a higher theoretical specific capacity, as the negative electrode, offering advantages such as high energy density and high safety. Furthermore, solid-state electrolytes can simultaneously function as both an electrolyte and a separator, eliminating the need for a separate separator and the need for overcharge protection as with liquid electrolyte batteries, making battery manufacturing relatively easier.

[0004] Solid-state electrolytes can be classified into three main categories: inorganic, organic, and inorganic / organic composite solid-state electrolytes. Pure inorganic solid-state electrolytes have high conductivity but are fragile; pure organic solid-state electrolytes have good machinability and high flexibility but low conductivity; inorganic / organic composite solid-state electrolytes combine high conductivity and flexibility, and can further improve the energy density of lithium-ion batteries, making them the most promising research direction for current applications. However, the room temperature conductivity of existing inorganic / organic composite solid-state electrolytes is less than 10. -5 mS / cm, while the room temperature conductivity of liquid electrolytes is greater than 10. -3 In comparison, existing inorganic / organic composite solid electrolytes have low room temperature conductivity (mS / cm) and low lithium-ion transference number.

[0005] Therefore, developing a solid electrolyte that combines high room temperature conductivity and lithium-ion transference number is of great significance and application value. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low room temperature conductivity and low lithium-ion transference number in existing solid electrolytes, and to provide a composite solid electrolyte, its preparation method, and a lithium-ion battery thereof. This composite solid electrolyte exhibits high room temperature ionic conductivity and high lithium-ion transference number, and the resulting lithium-ion battery demonstrates high capacity retention.

[0007] To achieve the above objectives, the first aspect of the present invention provides a composite solid electrolyte, wherein the composite solid electrolyte comprises a polyimide nanofiber membrane, an inorganic solid electrolyte, a lithium salt, and a binder;

[0008] The polyimide nanofiber membrane contains repeating unit A as shown in formula (1) and repeating unit B as shown in formula (2).

[0009]

[0010] Where R1 is Where R is R2 is

[0011] A second aspect of the present invention provides a method for preparing a composite solid electrolyte, wherein the method includes the following steps:

[0012] (1) In the presence of a polar solvent, a monomer mixture is subjected to a polymerization reaction to obtain a polyamic acid precursor solution; wherein the monomer mixture contains 3,5-diaminobenzoic acid, monomer X and monomer Y, wherein monomer X has the structure shown in formula (3) and monomer Y has the structure shown in formula (4).

[0013] H2N-R2′-NH2 equation (4), where R1′ is Where R' is R2' is

[0014] (2) The precursor solution is electrospun to obtain a polyamic acid nanofiber membrane;

[0015] (3) The polyamic acid nanofiber membrane was thermally imidized to obtain a polyimide nanofiber membrane;

[0016] (4) The inorganic solid electrolyte, lithium salt, additives, binder and solvent are mixed to obtain a slurry;

[0017] (5) The slurry is impregnated with a polyimide nanofiber membrane and dried to obtain the composite solid electrolyte.

[0018] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes a positive electrode material, a negative electrode material and a composite solid electrolyte, wherein the solid composite electrolyte is the composite solid electrolyte described in the first aspect or the composite solid electrolyte prepared by the method described in the second aspect.

[0019] Through the above technical solution, the present invention can achieve the following technical effects:

[0020] (1) The composite solid electrolyte provided by the present invention uses a polyimide nanofiber membrane as a skeleton and an inorganic solid electrolyte as a filling medium. The flexible skeleton of the polyimide nanofiber membrane gives the composite solid electrolyte good mechanical properties, and the inorganic solid electrolyte gives the composite solid electrolyte lower interfacial impedance. Moreover, the polyimide nanofiber membrane has a 3D porous skeleton structure. The continuous inorganic / polymer electrolyte interface constructed in the composite solid electrolyte forms a continuous and interconnected fast lithium-ion transport path, which promotes the rapid transfer of lithium ions and thus improves the room temperature lithium-ion conductivity of the composite solid electrolyte.

[0021] (2) The composite solid electrolyte provided by the present invention has a polyimide nanofiber membrane containing carboxyl groups, which coordinate with the negative ions of lithium salt, promote the dissolution and ionization of lithium salt in the composite solid electrolyte, fix the negative ions, thereby increasing the lithium ion transference number of the composite solid electrolyte. The composite solid electrolyte is used to prepare lithium-ion batteries, which improves the cycle stability of lithium-ion batteries. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of the present invention provides a composite solid electrolyte, wherein the composite solid electrolyte comprises a polyimide nanofiber membrane, an inorganic solid electrolyte, a lithium salt, and a binder;

[0024] The polyimide nanofiber membrane contains repeating unit A as shown in formula (1) and repeating unit B as shown in formula (2).

[0025]

[0026] Where R1 is Where R is R2 is

[0027] The inventors of this invention discovered in their research that simultaneously introducing repeating unit A and repeating unit B into the macromolecular structure of polyimide nanofiber membranes is beneficial for obtaining polyimide nanofiber membranes containing carboxyl groups. Furthermore, the obtained polyimide nanofiber membranes have a 3D porous framework structure with interconnected channels, which helps to enable the prepared composite solid electrolyte to have higher ionic conductivity at room temperature (25°C) and improve the ion transference number of the composite solid electrolyte.

[0028] In this invention, when R1 is When, the repeating unit A shown in equation (1) is as follows: The repeating unit B shown in equation (2) is as follows:

[0029] In this invention, preferably, R1 is R2 is

[0030] In this invention, the polyimide nanofiber membrane contains repeating units A and B. The polyimide nanofiber membrane can be obtained by polymerization and thermal imidization of 3,5-diaminobenzoic acid monomer, monomer X, and monomer Y, which are used in the following methods to provide repeating units A and B. Preferably, the polyimide nanofiber membrane has the following general structural formula:

[0031]

[0032] In this invention, by means of 13 C NMR, 1 ¹H NMR, elemental analysis, and NMR analysis of the residue from the separated polymerization product to determine the proportion of unpolymerized monomers, thus comprehensively demonstrating that the polyimide nanofiber membrane is a material with the above-mentioned structure.

[0033] In this invention, the content of each repeating unit in the polyimide nanofiber membrane is sufficient to achieve the purpose of this invention. Preferably, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 1:9-9:1. More preferably, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:7-7:3.

[0034] In this invention, conventional methods in the prior art can be used to test the content of each repeating unit in the polyimide nanofiber membrane, such as infrared spectroscopy, nuclear magnetic resonance, and the amount of monomers fed during polymerization. In this invention, the percentage content of each repeating unit in the polymer is determined by the actual feeding ratio of each monomer participating in the polymerization.

[0035] In this invention, preferably, the number-average molecular weight of the polyimide nanofiber membrane is 100,000-200,000.

[0036] In some embodiments of the present invention, preferably, based on the total amount of the composite solid electrolyte, the content of the inorganic solid electrolyte is 80-95 wt%, for example, 80 wt%, 83 wt%, 86 wt%, 89 wt%, 90 wt%, 92 wt%, 95 wt%, and any value within any range of any two values, preferably 83-90 wt%; the polyimide nanofiber membrane is 1-5 wt%, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, and any value within any range of any two values, preferably 1.5-4.5 wt%.

[0037] In this invention, the composite solid electrolyte uses a polyimide nanofiber membrane as a skeleton and an inorganic solid electrolyte as a filling medium. The flexible skeleton of the polyimide nanofiber membrane gives the composite solid electrolyte good mechanical properties, while the inorganic solid electrolyte gives the composite solid electrolyte lower interfacial impedance.

[0038] In this invention, the inorganic solid electrolyte is a conventionally used inorganic solid electrolyte in the art. Preferably, the inorganic solid electrolyte is selected from NASICON-type solid electrolytes, garnet-type solid electrolytes, perovskite-type solid electrolytes, and LiAl(PO4)(OH)2. 1-z F z At least one of z, where 0 ≤ z ≤ 1.

[0039] In some embodiments of the present invention, preferably, the NASICON-type solid electrolyte is selected from Li 1+ x Al x Ti 2-x (PO4)3 and / or Li 1+y Al y Ge 2-y (PO4)3, where 0≤x≤2, 0≤y≤1, more preferably selected from Li 1.4 Al 0.4 Ti 1.6 (PO4)3 and / or Li 1.5 Al 0.5 Ge 1.5 (PO4)3.

[0040] In some embodiments of the present invention, preferably, the garnet-type solid electrolyte is Li 7-m La3Zr 2- m Tam O 12 Where 0≤m≤2, preferably Li7La3Zr2O 12 .

[0041] In some embodiments of the present invention, preferably, the perovskite solid electrolyte is Li 3a La 2 / 3-a TiO3, wherein 0 < a ≤ 0.16, preferably Li 0.33 La 0.557 TiO3.

[0042] In some embodiments of the present invention, preferably, the LiAl(PO4)(OH) 1-z F z Selected from LiAl(PO4)(OH) 0.5 F 0.5 ) and / or LiAl(PO4)(OH 0.3 F 0.7 ).

[0043] In this invention, the lithium salt is beneficial for further improving the ionic conductivity of the composite solid electrolyte. This invention allows for a wide range of lithium salt selection, as long as the above-mentioned objective is achieved; various lithium salts conventionally used in the art can be used. Preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorooxalateborate, and lithium bis(oxalateborate). The lithium salt in this preferred embodiment is more beneficial for improving the room-temperature ionic conductivity of the composite solid electrolyte; and the negative ions of the lithium salt can coordinate with the carboxyl groups of the polyimide nanofiber membrane provided in this invention, promoting the dissolution and ionization of the lithium salt in the composite solid electrolyte and increasing the lithium-ion transference number of the composite solid electrolyte.

[0044] In this invention, the room-temperature ionic conductivity (σ) is calculated according to the following formula:

[0045] σ=L / (R b ·A)

[0046] Where L is the thickness of the diaphragm (cm); A is the measured area of ​​the diaphragm (cm²). 2 ); R b The battery's intrinsic resistance (Ω) was measured using an electrochemical workstation.

[0047] In this invention, the lithium-ion transference number is determined using an electrochemical workstation.

[0048] t + =Is(ΔV-I0R0) / I0(ΔV-I S RS )

[0049] In the formula, t + I0 is the lithium-ion transference number, I0 is the initial state current (A), and I0 is the initial state current (A). S R0 is the steady-state current (A), V is the polarization voltage (V), R0 is the initial state interface resistance of the cell (Ω), and R0 is the steady-state current (A). S The value is the interface resistance (Ω) of the battery in steady state.

[0050] In this invention, the binder can be any binder known to those skilled in the art for use in the preparation of composite solid electrolytes. Preferably, the binder is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinyl alcohol, and more preferably polyvinylidene fluoride.

[0051] In some embodiments of the present invention, preferably, the mass ratio of the inorganic solid electrolyte, lithium salt and binder is 1:0.02-0.15:0.01-0.05, more preferably 1:0.05-0.12:0.02-0.04.

[0052] In some embodiments of the present invention, preferably, the composite solid electrolyte further includes additives.

[0053] In this invention, the additive can be any additive known to those skilled in the art for use in the preparation of composite solid electrolytes. Preferably, the additive is selected from at least one of the following: succinate, adiponitrile, 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,4-butanesulfonate lactone, cyclohexylbenzene, ethyl 4,4,4-trifluorobutyrate, 1,1,2,2-tetrafluoroethyl, 2,2,3,3-tetrafluoropropyl ether, ethylene glycol dipropionitrile ether, pentafluoroalkoxycyclotriphosphazene, 1,3,6-hexanetrionitrile, fluorobenzene, boron trifluoride, tetrahydrofuran, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, and methanedisulfonate.

[0054] In some embodiments of the present invention, preferably, the mass ratio of the additive to the composite solid electrolyte is 0.005-0.1:1, more preferably 0.01-0.06:1.

[0055] The sources of the 3,5-diaminobenzoic acid, monomer X, monomer Y, inorganic solid electrolyte, lithium salt, additives and binders described in this invention are not particularly limited, and can be obtained commercially or prepared by existing methods.

[0056] In a preferred embodiment of the present invention, the composite solid electrolyte comprises: a polyimide nanofiber membrane and a garnet-type solid electrolyte (preferably Li7La3Zr2O). 12), lithium salts and binders;

[0057] The polyimide nanofiber membrane contains repeating unit A as shown in formula (1) and repeating unit B as shown in formula (2).

[0058]

[0059] The inventors of this invention discovered that, using a polyimide nanofiber membrane containing the aforementioned repeating unit A and repeating unit B as a framework, and a garnet-type solid electrolyte (preferably Li7La3Zr2O) can be used... 12 When used as a filling medium, in combination with lithium salts, binders and additives, it is more conducive to the preparation of composite solid electrolytes with higher ionic conductivity and higher ion transference number at room temperature (25℃), and the prepared lithium-ion batteries have better electrochemical performance.

[0060] A second aspect of the present invention provides a method for preparing a composite solid electrolyte, wherein the method includes the following steps:

[0061] (1) In the presence of a polar solvent, a monomer mixture is subjected to a polymerization reaction to obtain a polyamic acid precursor solution; wherein the monomer mixture comprises 3,5-diaminobenzoic acid, monomer X and monomer Y, monomer X having the structure shown in formula (3), and monomer Y having the structure shown in formula (5).

[0062] H2N-R2′-NH2 equation (4), where R1′ is Where R' is R2' is

[0063] (2) The precursor solution is electrospun to obtain a polyamic acid nanofiber membrane;

[0064] (3) The polyamic acid nanofiber membrane was thermally imidized to obtain a polyimide nanofiber membrane;

[0065] (4) The inorganic solid electrolyte, lithium salt, additives, binder and solvent are mixed to obtain a slurry;

[0066] (5) The slurry is impregnated with a polyimide nanofiber membrane and dried to obtain the composite solid electrolyte.

[0067] In some embodiments of the present invention, preferably, in step (1), the molar ratio of monomer Y and 3,5-diaminobenzoic acid is 1:9-9:1, more preferably 3:7-7:3.

[0068] In some embodiments of the present invention, preferably, in step (1), the molar ratio of monomer X to monomer Y is 1:0.9-1.03, more preferably 1:0.97-1.01. In the present invention, the amount of each monomer is such that the obtained polyimide nanofiber membrane has the required repeating unit composition.

[0069] In this invention, in step (1), the polar solvent can be any polar solvent known to those skilled in the art. Preferably, the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0070] In some embodiments of the present invention, preferably, the content of the polar solvent is 82-90 wt%, based on the total amount of the polyamic acid precursor solution.

[0071] In this invention, in step (1), 3,5-diaminobenzoic acid, monomer X, monomer Y, and solvent are added to a reactor and stirred under a protective atmosphere. The stirring conditions are not specifically limited; for example, stirring can be performed at room temperature (25°C) at a speed of 100-300 r / min for 3-6 h. In this invention, the protective atmosphere can be any atmosphere conventional in the art that provides an inert environment, such as nitrogen.

[0072] In some embodiments of the present invention, preferably, in step (2), the electrospinning process conditions include: needle nozzle diameter of 0.2-3 mm, spinning voltage of 5-30 kV, receiving distance of 10-20 cm, spinning solution injection speed of 0.02-0.2 mm / min, ambient temperature of 10-35 °C, and relative humidity of 15-40%.

[0073] In this invention, the electrospinning is carried out in an electrospinning machine. By controlling the electrospinning process conditions within the above-mentioned range, it is easy to spin the film, which is beneficial for the thermal imidization of the carboxyl-containing polyamic acid nanofiber membrane, thereby obtaining a carboxyl-containing polyimide nanofiber membrane.

[0074] In this invention, the polyimide nanofiber membrane is a 3D porous framework structure formed by overlapping and spun fibers, with a porosity of 70-95%. The pores are interconnected, resulting in a continuous inorganic-polymer composite solid electrolyte with a continuous inorganic-polymer interface. This forms a continuous and interconnected rapid ion transport pathway, promoting rapid lithium-ion transport and improving the room-temperature conductivity of the composite solid electrolyte. The preferred porosity of the polyimide nanofiber membrane in this invention is 80-90%. The porosity can be determined using a mercury porosimeter method.

[0075] In some embodiments of the present invention, preferably, the thermal imidization method includes: performing a heating process under a protective atmosphere, first heating to 100-140°C for 1-2 hours, then heating to 180-220°C for 1-1.5 hours, and then heating to 300-450°C for 1-1.5 hours; the heating rate is 3-6°C / min. In this invention, the thermal imidization method provided by the present invention is beneficial for obtaining the desired polyimide nanofiber membrane. The high temperature of the third heat treatment in the thermal imidization process inevitably leads to structural collapse of the polyimide nanofiber membrane, and cross-linking of the membrane surface, resulting in reduced membrane porosity. This slightly reduces the ionic conductivity and lithium-ion transference number of the resulting composite solid electrolyte at room temperature, leading to poorer electrochemical performance of the resulting lithium-ion battery. The protective atmosphere can be a conventional atmosphere in the art that provides an inert environment, such as nitrogen.

[0076] In this invention, in step (4), the solvent can be any volatile solvent known to those skilled in the art. Preferably, the solvent is an organic solvent, more preferably selected from at least one of acetone, acetonitrile, ethanol, and benzene, and even more preferably acetone.

[0077] In some embodiments of the present invention, preferably, in step (4), the solvent content is 70-90 wt% based on the total amount of the slurry.

[0078] In this invention, the method of impregnating the polyimide nanofiber membrane with the slurry in step (5) is not particularly limited, as long as the slurry can fill the polyimide nanofiber membrane. Preferably, the impregnation includes pouring the slurry into a mold containing the polyimide nanofiber membrane. The material and size of the mold are not particularly limited, as long as it ensures that the obtained composite solid electrolyte can be easily removed. For example, it can be polytetrafluoroethylene.

[0079] In some embodiments of the present invention, preferably, the mass ratio of the inorganic solid electrolyte, lithium salt, binder and additive is 1:0.02-0.15:0.01-0.05:0.005-0.1, more preferably 1:0.05-0.12:0.02-0.04:0.01-0.06.

[0080] In some embodiments of the present invention, preferably, based on the total amount of the composite solid electrolyte, the content of the inorganic solid electrolyte is 80-95 wt%, for example, 80 wt%, 83 wt%, 86 wt%, 89 wt%, 90 wt%, 92 wt%, 95 wt%, and any value within the range of any two values, more preferably 83-90 wt%; the polyimide nanofiber membrane is 1-5 wt%, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, and any value within the range of any two values, more preferably 1.5-4.5 wt%.

[0081] In a preferred embodiment of the present invention, the method for preparing the composite solid electrolyte includes:

[0082] (1) Add 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether and solvent to the reactor and stir and mix under a protective atmosphere. While stirring, add 3,3',4,4'-biphenyltetracarboxylic acid dianhydride to obtain a polyamic acid precursor solution.

[0083] (2) Electrospinning the polyamic acid precursor solution to prepare a polyamic acid nanofiber membrane;

[0084] (3) The polyamic acid nanofiber membrane is subjected to thermal imidization treatment. The nanofiber membrane is placed in a hot oven under a nitrogen atmosphere for programmed heating to obtain a polyimide nanofiber membrane.

[0085] (4) Dissolve the lithium salt and binder in a solvent, and then add the additives and garnet-type solid electrolyte (preferably Li7La3Zr2O). 12 Mix thoroughly to obtain a slurry;

[0086] (5) Place the polyimide nanofiber membrane in a mold, then pour the slurry into the mold, demold and dry to obtain the composite solid electrolyte.

[0087] A third aspect of the present invention provides a lithium-ion battery, wherein the lithium-ion battery includes a positive electrode material, a negative electrode material and a composite solid electrolyte, wherein the solid composite electrolyte is the solid composite electrolyte described in the first aspect above or the solid composite electrolyte prepared by the method described in the second aspect above.

[0088] In this invention, the positive electrode is made of a positive electrode material for lithium-ion batteries, a conductive agent, and a binder. The positive electrode material can be any existing material, such as at least one selected from lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA). The negative electrode can be made of any negative electrode material, a conductive agent, and a binder. The negative electrode material can be any negative electrode material, such as at least one selected from graphite, soft carbon, hard carbon, silicon carbon, silicon-oxygen carbon, and metallic lithium.

[0089] In this invention, the lithium-ion battery possesses all the characteristics and advantages of the aforementioned composite solid electrolyte, and exhibits excellent cycle stability, with a capacity retention of not less than 57% after 200 cycles. The lithium-ion battery is cycle-tested at 0.5C, and the ratio of the discharge capacity after 200 cycles to the discharge capacity after the first cycle is used as the capacity retention rate.

[0090] The present invention will be described in detail below through embodiments.

[0091] Battery capacity retention: Lithium-ion batteries are manufactured using lithium nickel cobalt manganese oxide (NMC622) as the positive electrode, lithium foil as the negative electrode, and a composite solid electrolyte to replace the traditional separator or organic liquid electrolyte.

[0092] The lithium-ion battery was subjected to a 0.5C cycle test, and the ratio of the discharge capacity after 200 cycles to the discharge capacity after the first cycle was used as the capacity retention rate.

[0093] The raw materials used in the following examples and comparative examples are as follows:

[0094] Unless otherwise specified, all raw materials were purchased commercially. Polyvinylidene fluoride (PVDF) was purchased from Arkema, France, grade HSV900.

[0095] Example 1

[0096] (1) Mix 3.791 g (18.9 mmol) of 4,4'-diaminodiphenyl ether, 1.922 g (12.6 mmol) of 3,5-diaminobenzoic acid and 85 g of N-methylpyrrolidone, stir under a nitrogen atmosphere, and add 9.287 g (31.5 mmol) of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride while stirring. Stir at room temperature (25 °C) for 4 h to obtain polyamic acid precursor spinning solution;

[0097] (2) The polyamic acid precursor spinning solution is electrospun to prepare a polyamic acid nanofiber membrane. The electrospinning process conditions include: using a disposable syringe to draw 5 mL of spinning solution, using a flat stainless steel needle nozzle with a diameter of 0.5 mm, controlling the spinning voltage of the electrospinning machine to be 20 kV, the spinning environment temperature to be 10 °C, the relative humidity of the air to be 38%, the injection speed of the spinning solution to be 0.15 mm / min, and the receiving distance to be 12 cm.

[0098] (3) The polyamic acid nanofiber membrane is subjected to thermal imidization treatment. The nanofiber membrane is placed in a hot oven under a nitrogen atmosphere and subjected to programmed temperature rise. The temperature rise conditions include: heating from room temperature (25°C) to 140°C at a heating rate of 3°C / min, holding at this temperature for 2 hours, then heating to 200°C at a heating rate of 3°C / min, holding at this temperature for 1 hour, then heating to 300°C at a heating rate of 3°C / min, holding at this temperature for 1 hour, then stopping the heating and cooling to room temperature to obtain a polyimide nanofiber membrane with a porosity of 88%.

[0099] (4) In a glove box, dissolve 0.2g of polyvinylidene fluoride and 1g of lithium bis(oxalato)borate in 30g of acetone and stir for 24h. Then add 0.5g of succinic anionyl and 10g of Li7La3Zr2O. 12 The powder was stirred at 25°C for 24 hours and mixed evenly to obtain a slurry.

[0100] (5) In a glove box, place 0.2g of polyimide nanofiber membrane in a polytetrafluoroethylene mold, then pour the slurry into the mold. After the solvent evaporates, remove the composite solid electrolyte precursor from the mold and dry it in a vacuum oven at 60℃ for 8h to obtain the composite solid electrolyte.

[0101] In this process, 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The polyamic acid precursor solution is completely reacted to obtain a polyimide nanofiber membrane by electrospinning.

[0102] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 185,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:2.

[0103] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the composite solid electrolyte are shown in Table 1.

[0104] Example 2

[0105] The method is the same as in Example 1, except that...

[0106] In step (1), the masses of 4,4'-diaminodiphenyl ether, 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride added are 1.802 g, 3.195 g and 8.827 g, respectively;

[0107] In step (2), the porosity of the obtained polyimide nanofiber membrane is 87%.

[0108] In this process, 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The polyamic acid precursor solution is completely reacted to obtain a polyimide nanofiber membrane by electrospinning.

[0109] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 180,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:7.

[0110] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0111] Example 3

[0112] The method is the same as in Example 1, except that...

[0113] In step (1), the masses of 4,4'-diaminodiphenyl ether, 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride added are 4.205 g, 1.369 g and 8.827 g, respectively;

[0114] In step (2), the porosity of the obtained polyimide nanofiber membrane is 86%.

[0115] In this process, 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The polyamic acid precursor solution is completely reacted to obtain a polyimide nanofiber membrane by electrospinning.

[0116] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 188,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 7:3.

[0117] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0118] Example 4

[0119] The method is the same as in Example 1, except that...

[0120] In step (1), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is replaced with pyromellitic dianhydride, and the masses of p-4,4'-diaminodiphenyl ether, 3,5-diaminobenzoic acid and pyromellitic dianhydride added are 2.044 g, 1.922 g and 6.871 g, respectively.

[0121] In step (2), the porosity of the obtained polyimide nanofiber membrane is 83%.

[0122] In this process, 4,4'-diaminodiphenyl ether and pyromellitic dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and pyromellitic dianhydride provide structural unit B. 4,4'-diaminodiphenyl ether, 3,5-diaminobenzoic acid and pyromellitic dianhydride react completely, and the resulting polyamic acid precursor solution is electrospun to obtain a polyimide nanofiber membrane.

[0123] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 180,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:2.

[0124] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0125] Example 5

[0126] The method is the same as in Example 1, except that...

[0127] In step (1), 4,4'-diaminodiphenyl ether is replaced with p-phenylenediamine, and the masses of the added p-phenylenediamine, 3,5-diaminobenzoic acid and 3,3,4,4-biphenyltetracarboxylic acid dianhydride are 2.044 g, 1.922 g and 9.268 g, respectively;

[0128] In step (2), the porosity of the obtained polyimide nanofiber membrane is 83%.

[0129] In this process, p-phenylenediamine and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The p-phenylenediamine, 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride react completely, and the resulting polyamic acid precursor solution is electrospun to obtain a polyimide nanofiber membrane.

[0130] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 155,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:2.

[0131] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0132] Example 6

[0133] The method is the same as in Example 1, except that...

[0134] In step (1), 4,4'-diaminodiphenyl ether is replaced with 4,4'-diaminodibenzophenone, and the masses of the added 4,4'-diaminodibenzophenone, 3,5-diaminobenzoic acid and 3,3,4,4-biphenyltetracarboxylic acid dianhydride are 4.011 g, 1.922 g and 9.268 g, respectively;

[0135] In step (2), the porosity of the obtained polyimide nanofiber membrane is 81%.

[0136] 4,4'-diaminobenzophenone and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The polyamic acid precursor solution obtained by the complete reaction of 4,4'-diaminobenzophenone, 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is electrospun to obtain a polyimide nanofiber membrane.

[0137] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 185,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:2.

[0138] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0139] Example 7

[0140] The method is the same as in Example 1, except that...

[0141] In step (1), the masses of 4,4'-diaminodiphenyl ether, 3,5-diaminobenzoic acid and 3,3,4,4-biphenyltetracarboxylic acid dianhydride added are 5.52 g, 0.466 g and 9.021 g, respectively;

[0142] In step (2), the porosity of the obtained polyimide nanofiber membrane is 75%.

[0143] In this process, 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The polyamic acid precursor solution is completely reacted to obtain a polyimide nanofiber membrane by electrospinning.

[0144] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 192,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 9:1.

[0145] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0146] Example 8

[0147] The method is the same as in Example 1, except that...

[0148] In step (3), the heating conditions include: heating from room temperature (25°C) to 140°C at a heating rate of 3°C / min, holding at that temperature for 2 hours, then heating to 200°C at a heating rate of 3°C / min, holding at that temperature for 1 hour, and then heating to 450°C at a heating rate of 3°C / min, holding at that temperature for 1 hour; the porosity of the resulting polyimide nanofiber membrane is 78%.

[0149] In this process, 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit A, and 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride provide structural unit B. The polyamic acid precursor solution is completely reacted to obtain a polyimide nanofiber membrane by electrospinning.

[0150] The number-average molecular weight of the polyimide nanofiber membrane described in this embodiment is 185,000; based on the amount of material fed, the molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 3:2.

[0151] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0152] Comparative Example 1

[0153] The method is the same as in Example 1, except that...

[0154] In step (1), 3,5-diaminobenzoic acid is not added, and the masses of 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride added are 6.11 g and 8.89 g, respectively;

[0155] In step (2), the porosity of the obtained polyamic acid nanofiber membrane is 83%.

[0156] The obtained polyimide nanofiber membrane does not simultaneously contain repeating unit A and repeating unit B.

[0157] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the obtained composite solid electrolyte are shown in Table 1.

[0158] Comparative Example 2

[0159] The method is the same as in Example 1, except that...

[0160] In step (1), 4,4'-diaminodiphenyl ether is not added, and the added 3,5-diaminobenzoic acid and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride are 0.466 g and 9.853 g, respectively.

[0161] Due to the poor reactivity of 3,5-diaminobenzoic acid, the resulting polyamic acid has a low relative molecular weight and poor film-forming properties. Furthermore, the resulting polyimide nanofiber membrane does not simultaneously contain repeating unit A and repeating unit B.

[0162] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the composite solid electrolyte are shown in Table 1.

[0163] Comparative Example 3

[0164] (1) In a glove box, 0.2g of polyvinylidene fluoride and 1g of lithium bis(oxalato)borate were dissolved in 12g of acetone and stirred for 24 hours. Then, 0.5g of succinic anionyl and 10g of Li7La3Zr2O were added respectively. 12 The powder was stirred at room temperature for 24 hours to obtain a slurry.

[0165] (2) In a glove box, the slurry is poured into a mold. After the solvent evaporates, the composite solid electrolyte precursor is removed from the mold and dried in a vacuum oven at 60°C for 8 hours to obtain a solid electrolyte film.

[0166] The conductivity, ion transport number, and discharge capacity retention after 200 cycles of the composite solid electrolyte are shown in Table 1.

[0167] Table 1

[0168]

[0169]

[0170] As can be seen from the results in Table 1, the polyimide nanofiber membrane with repeating unit A and repeating unit B provided by the present invention, combined with inorganic solid electrolyte, lithium salt, binder and additives, results in a composite solid electrolyte with high ionic conductivity and high ion transference number at room temperature (25°C), and the prepared lithium-ion battery has excellent electrochemical performance.

[0171] As can be seen from Examples 1-8 and Table 1 of this application, the composite solid electrolyte obtained by using the polyimide nanofiber membrane with repeating unit A and repeating unit B provided by this invention has an ionic conductivity of 0.37-0.69 mS / cm and an ion transference number of 0.44-0.7 at room temperature, and the capacity retention rate of the prepared lithium-ion battery is 57-81% after 200 cycles.

[0172] Based on the results of Examples 1, Comparative Examples 1 and 2, and Table 1, it can be seen that, since the polyimide nanofiber membranes used in Comparative Examples 1 and 2 do not simultaneously possess repeating units A and B, the composite solid electrolyte obtained in Comparative Example 1 has a lower lithium-ion transference number and a lower capacity retention rate of the lithium-ion battery after 200 cycles; the polyimide nanofiber membrane in Comparative Example 2 has poor film-forming properties and cannot be used for performance testing; based on the results of Examples 1, Comparative Example 3, and Table 1, it can be seen that, since Comparative Example 3 did not use the polyimide nanofiber membrane specified in this invention, the room temperature ionic conductivity and ion transference number of the obtained composite solid electrolyte are lower, and the capacity retention rate of the prepared lithium-ion battery is lower.

[0173] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite solid electrolyte, characterized in that, The composite solid electrolyte comprises a polyimide nanofiber membrane, an inorganic solid electrolyte, a lithium salt, and a binder; The polyimide nanofiber membrane contains repeating unit A as shown in formula (1) and repeating unit B as shown in formula (2). Where R1 is Where R is R2 is 2. The composite solid electrolyte according to claim 1, wherein, The molar ratio of repeating unit A to repeating unit B in the polyimide nanofiber membrane is 1:9-9:1; preferably 3:7-7:

3.

3. The composite solid electrolyte according to claim 1 or 2, wherein, Based on the total amount of the composite solid electrolyte, the content of the inorganic solid electrolyte is 80-95 wt%, and the content of the polyimide nanofiber membrane is 1-5 wt%.

4. The composite solid electrolyte according to any one of claims 1-3, wherein, The inorganic solid electrolyte is selected from NASICON-type solid electrolyte, garnet-type solid electrolyte, perovskite-type solid electrolyte, and LiAl(PO4)(OH)2. 1-z F z At least one of the following, where 0 ≤ z ≤ 1; Preferably, the NASICON-type solid electrolyte is selected from Li 1+x Al x Ti 2-x (PO4)3 and / or Li 1+y Al y Ge 2-y (PO4)3, where 0≤x≤2, 0≤y≤1, preferably selected from Li 1.4 Al 0.4 Ti 1.6 (PO4)3 and / or Li 1.5 Al 0.5 Ge 1.5 (PO4)3; Preferably, the garnet-type solid electrolyte is Li 7-m La3Zr 2-m Ta m O 12 Where 0≤m≤2, preferably Li7La3Zr2O 12 ; Preferably, the perovskite solid electrolyte is Li 3a La 2 / 3-a TiO3, wherein 0 < a ≤ 0.16, preferably Li 0.33 La 0.557 TiO3; Preferably, the LiAl(PO4)(OH) 1-z F z Selected from LiAl(PO4)(OH) 0.5 F 0.5 ) and / or LiAl(PO4)(OH 0.3 F 0.7 ); Preferably, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium difluorooxalate borate, and lithium bis(oxalate borate). Preferably, the adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyvinyl alcohol, and is preferably polyvinylidene fluoride; Preferably, the mass ratio of the inorganic solid electrolyte, lithium salt and binder is 1:0.02-0.15:0.01-0.

05.

5. The composite solid electrolyte according to any one of claims 1-4, wherein, The composite solid electrolyte also includes additives.

6. The composite solid electrolyte according to claim 5, wherein, The additive is selected from at least one of succinate, adiponitrile, 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,4-butanesulfonate lactone, cyclohexylbenzene, ethyl 4,4,4-trifluorobutyrate, 1,1,2,2-tetrafluoroethyl, 2,2,3,3-tetrafluoropropyl ether, ethylene glycol dipropionitrile ether, pentafluoroalkoxycyclotriphosphazene, 1,3,6-hexanetrionitrile, fluorobenzene, boron trifluoride, tetrahydrofuran, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, and methanedisulfonate. Preferably, the mass ratio of the additive to the composite solid electrolyte is 0.005-0.1:

1.

7. A method for preparing a composite solid electrolyte, characterized in that, The method includes the following steps: (1) In the presence of a polar solvent, a monomer mixture is subjected to a polymerization reaction to obtain a polyamic acid precursor solution; wherein the monomer mixture contains 3,5-diaminobenzoic acid, monomer X and monomer Y, wherein monomer X has the structure shown in formula (3) and monomer Y has the structure shown in formula (4). H2N-R2′-NH2 equation (4), where R1′ is Where R' is R2' is (2) The precursor solution is electrospun to obtain a polyamic acid nanofiber membrane; (3) The polyamic acid nanofiber membrane was thermally imidized to obtain a polyimide nanofiber membrane; (4) The inorganic solid electrolyte, lithium salt, additives, binder and solvent are mixed to obtain a slurry; (5) The slurry is impregnated with a polyimide nanofiber membrane and dried to obtain the composite solid electrolyte.

8. The method according to claim 7, wherein, The molar ratio of monomer Y to 3,5-diaminobenzoic acid is 1:9-9:1; preferably 3:7-7:

3. Preferably, the molar ratio of monomer X to the total molar ratio of monomer Y and 3,5-diaminobenzoic acid is 1:0.9-1.03, more preferably 1:0.97-1.01; Preferably, the polar solvent is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; Preferably, the content of the polar solvent is 82-90 wt%, based on the total amount of the polyamic acid precursor solution; Preferably, the mixing conditions in step (1) include stirring for 3-6 hours under a protective atmosphere.

9. The method according to claim 7 or 8, wherein, In step (2), the electrospinning process conditions include: needle nozzle diameter of 0.2-3mm, spinning voltage of 5-30kV, receiving distance of 10-20cm, spinning solution injection speed of 0.02-0.2mm / min, ambient temperature of 10-35℃, and relative humidity of 15-40%. Preferably, in step (3), the porosity of the polyimide nanofiber membrane is 70-95%, more preferably 80-90%; Preferably, the thermal imidization method includes: performing a heating program under a protective atmosphere, first heating to 100-140℃ for 1-2 hours, then heating to 180-220℃ for 1-1.5 hours, and then heating to 300-450℃ for 1-1.5 hours; the heating rate is 3-6℃ / min. Preferably, in step (4), the solvent is an organic solvent, preferably selected from at least one of acetone, acetonitrile, ethanol, and benzene, with acetone being the most preferred; Preferably, in step (4), the solvent content is 70-90 wt%, based on the total amount of the slurry; Preferably, in step (5), the impregnation includes pouring the slurry into a mold containing a polyamide nanofiber membrane; Preferably, the mass ratio of the inorganic solid electrolyte, lithium salt, binder, and additive is 1:0.02-0.15:0.01-0.05:0.005-0.1; Preferably, based on the total amount of the composite solid electrolyte, the content of the inorganic solid electrolyte is 80-95 wt%, and the content of the polyimide nanofiber membrane is 1-5 wt%.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode material, a negative electrode material, and a composite solid electrolyte, wherein the solid composite electrolyte is the composite solid electrolyte according to any one of claims 1-6 or the composite solid electrolyte prepared by the method according to any one of claims 7-9.

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