Heat-conducting fireproof solid electrolyte based on functionalized heterogeneous nanostructure and preparation method and application of heat-conducting fireproof solid electrolyte

Abstract

The invention discloses a heat-conducting fireproof solid electrolyte based on a functionalized heterogeneous nanostructure and a preparation method and application thereof, and through surface amino-phosphorus functionalized modification of an MXene / BN heterojunction and in combination with the molecular design of a phosphorus flame retardant PD, the construction of an ionic conduction channel and the synergistic effect of a flame-retardant network are realized. The preparation method comprises the steps of electrostatic spinning of the fiber membrane, heterostructure functionalization, flame retardant synthesis and composite electrolyte casting. The ionic conductivity of the obtained electrolyte at 60 DEG C reaches 9.6 * 10 <-4 > S / cm, the thermal conductivity is 0.65 W / m.K, the growth of lithium dendrites can be inhibited, the thermal runaway temperature of the battery is increased by 89.7 DEG C, and the electrolyte is suitable for a high-safety lithium metal battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solid electrolytes, and particularly relates to a heat-conducting fireproof solid electrolyte based on functionalized heterogeneous nanostructures and a preparation method and application thereof. BACKGROUND

[0002] With the development of high-energy-density energy storage devices, lithium metal batteries have become the research focus due to their high theoretical capacity. However, traditional liquid electrolytes have problems such as flammability, leakage and lithium dendrite growth. Although solid electrolytes can partially solve the above problems, they still face the following technical bottlenecks:

[0003] 1) Insufficient thermal stability and flame retardancy: Most polymer-based solid electrolytes (such as PEO) have low thermal decomposition temperatures (less than 200℃), lack active flame retardant mechanisms, and are prone to thermal runaway;

[0004] 2) Conflict between ionic conductivity and mechanical strength: Improving ionic conductivity often sacrifices mechanical strength, leading to easy penetration of lithium dendrites through the electrolyte membrane;

[0005] 3) Weak thermal management capability: Traditional electrolytes have low thermal conductivity (less than 0.5 W / m.K), and heat is easily accumulated;

[0006] 4) Poor interface compatibility: Rigid electrolytes have poor contact with electrodes, and interface side reactions are serious during cycling.

[0007] Existing solutions mainly focus on optimizing a single performance, such as adding flame retardants to reduce ion mobility, introducing inorganic fillers to increase interface impedance, and uneven dispersion of heat-conducting nanosheets. Therefore, it is urgent to improve the flame retardancy, thermal conductivity, dendrite suppression and interface stability simultaneously through material design and process innovation. SUMMARY

[0008] The application aims to provide a heat-conducting fireproof solid electrolyte based on functionalized heterogeneous nanostructures and a preparation method and application thereof, which improves the thermal stability, flame retardancy and ionic conductivity of the solid electrolyte, thereby comprehensively improving the electrochemical and safety performance of the battery.

[0009] To achieve the above-mentioned purposes, the technical scheme adopted by the application is as follows:

[0010] A preparation method of a heat-conducting fireproof solid electrolyte, comprising the following steps:

[0011] Step S1: preparing a polymer fiber membrane by using an electrospinning technology:

[0012] The PVDF-HFP is dissolved in a mixture of N,N-dimethylformamide and acetone to prepare a spinning solution with a mass concentration of 10wt%-18wt%, and then the polymer fiber membrane is obtained by spinning under the conditions of a voltage of 20±0.1kV and a push-in speed of 0.5mL / h.

[0013] Step S2: preparing a functionalized hetero-nanostructure: the heterojunction is formed by self-assembly of the nanosheet MXene and BN / graphite, and then modified by a silane coupling agent and phenyl dichlorophosphine to form a functionalized hetero-nanostructure P-Ti3C2T n / BN.

[0014] Step S3: preparing a high-efficiency phosphorus-based flame retardant PD: a phosphorus-oxygen-carbon covalent chain is introduced by reacting DOPO with propylene oxide and chlorosulfonic acid to obtain PEG-P-DOPO (PD).

[0015] Step S4: PEO, LiTFSI, functionalized hetero-nanostructure, and PD are dissolved in acetonitrile according to a mass ratio of (330:100:7:7)-(180:50:14:14), and then poured into the polymer fiber membrane after ultrasonic stirring for 24 hours. The solid-state electrolyte is obtained after drying in a vacuum oven at 60°C for 24 hours, and the obtained electrolyte membrane is cut into a 19mm round piece for use.

[0016] The ether oxygen group of the PEO forms a solvation structure with Li+, and LiTFSI provides an ion source (Li+ concentration of 1-2mol / L). The mass ratio can ensure that the lithium salt is fully dissociated, while avoiding crystallization caused by excessive lithium salt.

[0017] Acetonitrile as a polar aprotic solvent has a higher dielectric constant than PEO, which promotes the dissociation of LiTFSI into free ions; low boiling point is easy to remove under vacuum, avoiding the influence of solvent residue on the electrochemical stability of the electrolyte. Magnetic stirring ensures uniform distribution of components to form a "nanosheet-polymer-flame retardant" three-dimensional interpenetrating network, which improves the interface bonding strength.

[0018] Further optimization, in the step S1, the mass ratio of N,N-dimethylformamide and acetone mixture is (1-4):1.

[0019] Further optimization, in the step S2, the preparation of the functionalized hetero-nanostructure includes:

[0020] Step S2.1: MXene nanosheets are prepared by etching Ti3AlC2 with a mixture of LiF dissolved in a 1-10 M HCl solution; BN nanosheets are prepared by mixing boron nitride (BN) powder with N-methyl pyrrolidone, ultrasonic treatment under argon protection, and centrifugal collection of the supernatant; and the MXene nanosheets and the BN nanosheets are mixed in a mass ratio of 2:1, stirred, and then left to stand for 24 hours to form a heterojunction driven by van der Waals forces, and Ti3C2T2 / BN heterojunctions are obtained by freeze-drying.

[0021] Step S2.2: The heterojunctions are mixed with silane coupling agent KH550 in a mass ratio of 10:1, then refluxed at 80°C for 12 hours in a reflux condenser, and washed by centrifugation to obtain amino-functionalized heterojunctions NH2-Ti3C2T2 / BN; the NH2-Ti3C2T2 / BN is dispersed in tetrahydrofuran (THF), and phenyldichlorophosphine is added, and the mixture is reacted at 60°C for 8 hours under nitrogen protection, and washed by centrifugation with THF three times to obtain functionalized hetero-nanostructures P-Ti3C2T2 / BN.

[0022] Further optimization is that the amino-functionalized heterojunctions NH2-Ti3C2T2 / BN are mixed with phenyldichlorophosphine in a molar ratio of 1:1.2.

[0023] MXene (Ti3C2T n ) is a two-dimensional metal carbide with -OH and -O functional groups on the surface, a high thermal conductivity of 1000 W / m·K, and excellent electrical conductivity, which can build an efficient heat conduction path; the negative charge surface adsorbs Li+ through electrostatic attraction, guiding uniform migration of lithium ions and inhibiting dendrite growth.

[0024] BN nanosheets are two-dimensional insulating materials with a thermal conductivity of 400 W / m·K and excellent flame retardant performance (decomposition temperature > 900°C), and can form a "heat conduction-flame retardant" dual-functional network structure with MXene through van der Waals forces. MXene dominates the in-plane heat conduction, and BN blocks the heat diffusion path, thereby synergistically improving the heat management capability.

[0025] The amino group (-NH2) of KH550 condenses with the hydroxyl group (-OH) on the surface of MXene / BN to form a Si-O-C covalent bond, solving the problem of interfacial compatibility between the nanosheets and the polymer matrix (interface impedance is reduced by 40%-60%); the amino group coordinates with Li+ (N→Li+) to form an ion transport "high-speed channel", thereby improving the number of ion migrations. The reaction of phenyldichlorophosphine with the amino group generates a P-N bond, covalently grafting the flame-retardant element (P) onto the surface of the nanosheets, releasing PO· free radicals at high temperatures to capture H·, OH·, and other combustion chain reaction free radicals, thereby achieving gas-phase flame retardation; at the same time, the phosphorus compound decomposes to form a glassy carbon layer (containing P2O5 and B2O3), blocking the transmission of oxygen and heat, and strengthening the condensed-phase flame retardation.

[0026] Further optimization, in step S3, the preparation of high-efficiency phosphorus-based flame retardant PD includes:

[0027] Step 3.1: Mix 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO with propylene oxide in a molar ratio of (1-3):1 in THF, add boron trifluoride ether BF3·Et2O and polyethylene glycol PEG, and react at 60℃ for 24 hours. The product is precipitated with ethanol and vacuum dried to obtain the DOPO-PEG intermediate.

[0028] Step 3.2: Mix the intermediate with chlorosulfonic acid in a molar ratio of 1:(2-4) in dichloromethane, add dropwise at 0℃ and then warm to 25℃ for 12 hours. After dialysis purification, PEG-P-DOPO (PD) is obtained.

[0029] Wherein, DOPO is a phosphorus-oxygen heterocyclic structure, which decomposes at high temperature to produce strong dehydrating agents such as phosphoric acid and metaphosphoric acid, promoting the carbonization of the polymer matrix to form a carbon layer and inhibiting the release of pyrolysis products; at the same time, the bond energy of P-O-C is higher than that of C-C, which improves the thermal stability and increases the decomposition temperature from 180℃ of PEO to above 250℃.

[0030] The flexible PEG chain (-O-CH2-CH2-) improves the compatibility of the flame retardant with the PEO matrix, avoiding the phase separation problem caused by the poor polarity of traditional phosphorus-based flame retardants (such as phosphate esters); at the same time, the ether oxygen atoms of the PEG segment coordinate with Li+, promoting the dissociation of lithium salt and maintaining high ionic conductivity.

[0031] By adding chlorosulfonic acid, sulfonic acid groups (-SO3H) are introduced, which stabilize the lithium salt anion through hydrogen bonding (-SO3H···TFSI-), reduce the anion migration resistance, and further improve the ion conduction efficiency.

[0032] In addition, PD decomposes to produce PO· and HPO· free radicals, which capture H· and OH· in the combustion reaction to terminate the chain reaction; at the same time, it releases N2, CO2 and other non-combustible gases to dilute the oxygen concentration. A glassy carbon layer containing P2O5 and B2O3 is formed to block heat and mass transfer; MXene / BN heterojunctions are embedded in the carbon layer to enhance the mechanical strength of the carbon layer and inhibit the phenomenon of molten droplets.

[0033] A heat-conducting fireproof solid-state electrolyte prepared based on the above method, which contains PEO, LiTFSI matrix, functionalized hetero-nanostructure and PD flame retardant, has an ionic conductivity of ≥9.6×10 -4 S / cm at 60℃; thermal conductivity ≥0.6 W / m·K at 60℃.

[0034] A lithium ion battery comprising the solid electrolyte described above, the positive electrode is LFP, the negative electrode is lithium sheet, and the assembly sequence of the battery is: negative electrode shell-lithium sheet-solid electrolyte-positive electrode sheet-stainless steel gasket-spring sheet-positive electrode shell, and the assembly pressure is 5MPa.

[0035] Compared with the prior art, the beneficial effects of the present application are:

[0036] The novel composite solid electrolyte prepared by the method has excellent flame retardant performance, high ionic conductivity, strong lithium dendrite inhibition capacity, and improved thermal management and safety. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The figure is the cycle performance test diagram of the battery assembled with the solid electrolytes of Comparative Examples 1-5, MTPD-1, MTPD-2 and MTPD-3;

[0038] Figure 2 The figure is the ionic conductivity diagram of the solid electrolyte with different contents at different temperatures;

[0039] Figure 3 The figure is the Li / / Li cycle test diagram of the battery assembled with the solid electrolytes of Comparative Example 1 and MTPD-3;

[0040] Figure 4 The figure is the ARC test result of the battery assembled with the solid electrolytes of Comparative Example 1, MTPD-1, MTPD-2 and MTPD-3: (a) is the thermal runaway temperature parameter test result diagram, (b) is the thermal runaway time parameter test result diagram, (c) is the temperature rise rate test result diagram, and (d) is the activation energy columnar diagram.

[0041] Figure 5 The figure is the thermal conductivity test result diagram of the solid electrolytes of Comparative Example 1, MTPD-1, MTPD-2 and MTPD-3 at different temperatures. DETAILED DESCRIPTION

[0042] In order to further illustrate the technical solutions of the present application, the preferred embodiments of the present application are described below in combination with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not limitations on the claims of the present application. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0043] Meanwhile, the raw materials or reagents mentioned below without detailed description are all commercially available products, and the process steps or methods not mentioned in detail are all known to those skilled in the art.

[0044] The sources of some raw materials and reagents involved in the following examples, comparative examples and test examples are shown as follows:

[0045] Raw material name Purchase source Purity Polyvinylidene fluoride-hexafluoropropylene Mcclin Biochemical Technology Co., Ltd. AR, 99wt% Boron nitride Mcclin Biochemical Technology Co., Ltd. AR, 98.5wt% DOPO-HQ Hubei Meibaixinnu Material Co., Ltd. AR, 99wt% Propylene oxide Mcclin Biochemical Technology Co., Ltd. AR, 99wt% Tetrahydrofuran Mcclin Biochemical Technology Co., Ltd. AR, 99wt% Boron trifluoride ether Mayrl Biochemical Technology Co., Ltd. AR, 99wt% Chlorosulfonic acid Mcclin Biochemical Technology Co., Ltd. AR, 99wt% Dichloromethane Mayrl Biochemical Technology Co., Ltd. AR, 99wt% PEO Mcclin Biochemical Technology Co., Ltd. AR, 99wt% Carbon aluminum titanium Jilin Yi Yi Technology Co., Ltd. AR, 98wt% Bistrifluoromethanesulfonylimide lithium Mayrl Biochemical Technology Co., Ltd. AR, 99wt% Concentrated hydrochloric acid (HCl, 37%) National Pharmaceutical Group Chemical Reagent Co., Ltd. (China) AR, 99wt% Lithium fluoride (LiF) Aladdin Reagent Co., Ltd. (China) AR, 98wt% Polyethylene oxide (PEO) Dongguan Kelude New Energy Technology Co., Ltd. AR, 99wt% Acetonitrile Mcclin Biochemical Technology Co., Ltd. AR, 99wt%

[0046] Example 1:

[0047] Mix 3.30 g of polyethylene oxide PEO, 1.0 g of lithium bis-trifluoromethanesulfonimide LiTFSI, 0.07 g of functionalized hetero-nanostructure P-Ti3C2T2 / BN and 0.07 g of high-efficiency phosphorus-based flame retardant powder PD, and then dissolve them in 100 ml of acetonitrile. Stir continuously for 24 hours. Pour the obtained uniform solution into a polytetrafluoroethylene mold with polymer fiber membranes arranged in it. Place it at room temperature for 24 hours to volatilize the solvent. Then place it in a vacuum oven at 60°C for 24 hours. Take it out and quickly move it into an argon atmosphere glove box. Cut the obtained solid electrolyte membrane into a 19 mm round piece for use. The solid electrolyte is simply referred to as MTPD-1.

[0048] Among them, the mixed powder of the functionalized hetero-nanostructure P-Ti3C2T2 / BN and the high-efficiency phosphorus-based flame retardant powder PD, with a mass ratio of 1:1, is simply referred to as TPD.

[0049] Example 2:

[0050] The difference between this example and Example 1 is only that the mass percentage of the mixture powder in this example is 5.86wt%, specifically 3.50g PEO, 1.0g LiTFSI, 0.28g TPD powder. The solid electrolyte prepared is simply referred to as MTPD-2.

[0051] Example 3:

[0052] The difference between this example and Example 1 is only that the mass percentage of the TPD powder in this example is 10.85wt%, specifically 3.60g PEO, 1.0g LiTFSI, 0.56g TPD powder. The solid electrolyte prepared is simply referred to as MTPD-3.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is only that no TPD powder is added in this comparative example.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is only that the mass percentage of the TPD powder in this example is 1.60wt%, specifically 3.30g PEO, 1.0g LiTFSI, 0.07g TPD powder. The solid electrolyte prepared is simply referred to as Comparative Example 2.

[0057] Comparative Example 3

[0058] The difference between the present comparative example and Example 1 is only that the mass percentage of TPD powder in the present example is 0.80wt%, specifically 3.30g PEO, 1.0g LiTFSI, 0.035g TPD powder, and the prepared solid-state electrolyte is referred to as Comparative Example 3.

[0059] Comparative Example 4

[0060] The difference between the present comparative example and Example 1 is only that the mass percentage of TPD powder in the present example is 19.60wt%, specifically 3.60g PEO, 1.0g LiTFSI, 1.12g TPD powder, and the prepared solid-state electrolyte is referred to as Comparative Example 4.

[0061] Comparative Example 5

[0062] The difference between the present comparative example and Example 1 is only that the mass percentage of TPD powder in the present example is 30.30wt%, specifically 3.60g PEO, 1.0g LiTFSI, 2.00g TPD powder, and the prepared solid-state electrolyte is referred to as Comparative Example 5.

[0063] Table 1 Composition of different solid-state electrolytes

[0064]

[0065]

[0066] The solid-state electrolytes prepared in Examples 1-3 and Comparative Examples 1-5 were first subjected to electrochemical performance test. Electrochemical performance is the most basic performance of solid-state electrolyte, so the examples or comparative examples with good electrochemical performance (stable cycle more than 100 cycles or more) were subjected to combustion test, cone calorimetry test, ionic conductivity test, Li / / Li cycle test, ARC test and thermal conductivity test.

[0067] 1. Electrochemical performance test after battery assembly

[0068] Batteries were assembled using Comparative Examples 1-5, MTPD-1, MTPD-2 and MTPD-3 solid-state electrolytes, respectively. The positive electrode of the battery was LFP, and the negative electrode was lithium sheet. The assembly sequence of the battery was: negative electrode shell-lithium sheet-solid-state electrolyte-positive electrode sheet-stainless steel gasket-spring sheet-positive electrode shell. Finally, it was put into a packaging machine, and the battery was completed after 5s under the action of 5MPa pressure. The cycle performance at 1C was tested. Figure 1The right side coulombic efficiency represents coulombic efficiency, and the left side specific capacity represents specific capacity. It can be seen that the battery assembled with MTPD-3 exhibits good cycle performance, and the initial discharge specific capacity of the battery is as high as 161.42 mAh g -1 , and still retains 143.95 mAh g -1 after 200 cycles. Similarly, the batteries assembled with MTPD-1 and MTPD-2 also exhibit excellent electrochemical performance and have high coulombic efficiency.

[0069] The initial discharge specific capacity of the battery assembled with Comparative Example 1 is 117.79 mAh g -1 , and can cycle 200 times. However, Comparative Examples 2-5 do not exhibit good electrochemical performance. Because electrochemical performance is the basis, when the electrochemical performance is not good, the corresponding solid electrolyte will not be used to assemble the battery in actual production. Therefore, only MTPD-1, MTPD-2 and MTPD-3, and Comparative Example 1 need to be subjected to subsequent experiments.

[0070] 2. Combustion and cone calorimeter test

[0071] 1) Combustion test

[0072] MTPD-1, MTPD-2 and MTPD-3, and Comparative Example 1 were subjected to combustion performance test by vertical combustion method in a fume hood, and the combustion phenomenon was observed and the sample's off-fire self-extinguishing time was recorded with a stopwatch.

[0073] 2) Cone calorimeter test

[0074] MTPD-1, MTPD-2 and MTPD-3, and Comparative Example 1 were subjected to cone calorimeter test. Specifically, a Tech-GBT16172 type cone calorimeter was used, with a working voltage of 230V, a power of 5000W, and a heat output of 0-120kW / m 2 . The main working principle of the cone calorimeter is the oxygen consumption principle. When the sample is combusted under the heat radiation of the conical electric heater, the flame will consume a certain concentration of oxygen in the air and release a certain combustion heat value. The cone calorimeter can be used to measure the heat release rate / total amount, smoke release rate / total amount, CO toxic gas generation rate and other parameters of the material, and is used to evaluate the fire hazard of the material.

[0075] Table 2 Test results of combustion and cone calorimeter of different solid state electrolytes

[0076]

[0077] As can be seen from Table 2, the solid-state electrolyte prepared in Examples 1-3 has very strong flame retardant performance. In the combustion performance test, it is found that the prepared electrolyte does not burn in the flame and no smoke is generated. However, the solid-state electrolyte prepared in Comparative Example 1 burns violently and a large amount of smoke is generated under the same test conditions. It is shown that the flame retardant performance of the flame-retardant solid-state electrolyte prepared in Examples 1-3 is greatly improved.

[0078] Further analysis of the test of the cone calorimeter is shown in Table 2. Table 2 shows the data of total heat release, total smoke production, total CO release and peak heat release rate. It can be found from Table 2 that the total heat release and the peak heat release rate of the solid-state electrolyte prepared in Examples 1-3 are significantly reduced during the combustion process. The peak heat release rate and the total heat release of Comparative Example 1 are 590.12 kW / m 2 , 66.12 MJ / m 2 , respectively. After adding 12wt% of TPD particles, the heat release rate and the total heat release are reduced to 450.01 kW / m 2 , 33.12 MJ / m 2 , respectively, which are reduced by 23.7% and 49.9%, respectively. It is shown that MTPD1-3 can control the heat release rate to a certain extent, and has a significant inhibitory effect on the total heat release. At the same time, the total smoke production and the total CO production of Comparative Example 1 are 0.95 m 2 and 0.80 g, respectively. After adding 12wt% of TPD particles, the total smoke production and the total CO production are reduced to 0.39 m 2 and 0.25 g, respectively. It can be seen that the solid-state electrolyte of the present application has excellent flame retardant and smoke suppression performance.

[0079] 3. Ion conductivity test

[0080] The solid-state electrolytes prepared from MTPD-1, MTPD-2 and MTPD-3, and Comparative Example 1 are assembled into SS / SPE / SS button cells using stainless steel gaskets (SS). The test equipment is Chenhua CHI660E electrochemical workstation, the frequency range is 10 -2 -10 5 Hz, and the test is carried out at 20-80℃ after 1 hour of temperature holding at each temperature. The ion conductivity (σ) calculation formula is as follows:

[0081]

[0082] L is the thickness of the electrolyte, R is the resistance value of the electrolyte film, and S is the contact area between the electrolyte and the stainless steel sheet.

[0083] Figure 2The ion conductivity values of the solid-state electrolytes with different TPD contents and at different temperatures are shown. It can be clearly found that the ion conductivity of all solid-state electrolytes gradually increases with the increase of temperature. Between 50-60℃, due to the melting of PEO, the crystalline phase in the polymer is converted to amorphous phase, thus promoting the flowability of PEO segments at high temperature, and therefore the ion conductivity is significantly improved. At all temperatures, the ion conductivity of the MTPD-3 sample is the highest among all solid-state electrolytes, which is 9.6 x 10 -4 S / cm at 60℃, higher than 9.91 x 10 -5 S / cm of the pure PEO / LiTFSI electrolyte of Comparative Example 1. It can be clearly found that the ion conductivity of Examples 1-3 is improved by one order of magnitude compared with Comparative Example 1 with the increase of TPD. This is due to the formation of Ti3C2T n / BN hetero-nanostructure by liquid-phase ultrasonic exfoliation and van der Waals self-assembly of titanium carbide (Ti3C2T n ) and boron nitride (BN). At the same time, the surface of the heterojunction is hydroxylated with a silane coupling agent, and a covalent bond is formed by the reaction of phenyl dichlorophosphine with amine groups, thereby obtaining a functionalized hetero-nanostructure. The residual amine groups on the surface are coordinated with lithium salts to form an ion-selective transport layer. Thus, while achieving good flame retardant performance, the ion conductivity is also improved.

[0084] 4. Symmetric lithium cycling test

[0085] In order to evaluate the interfacial compatibility of the solid-state electrolyte with lithium metal, the solid-state electrolytes prepared from MTPD-3 with excellent electrochemical performance and Comparative Example 1 were assembled into Li / SPE / Li coin cells, respectively, and a constant current density was applied in a 60℃ environment for cycling test, and the voltage curve during the cycling of the battery was recorded to analyze the influence of the polymer electrolyte on the lithium ion deposition stripping behavior and the ability to suppress lithium dendrites.

[0086] The interfacial stability of the polymer electrolyte with the Li metal negative electrode was evaluated by assembling Li / SPE / Li symmetric cells and performing constant current cycling test at a current density of 0.05 mA cm -2 at 60℃. As shown in Figure 3 , the symmetric cell of MTPD-3 stably cycled for 1200 hours, and the lithium deposition overpotential was about 35-40 mV, while the overpotential of Comparative Example 1 was about 40-45 mV. The greater the overpotential, the more likely it is to cause unstable lithium deposition and induce lithium dendrite growth. The voltage of the symmetric cell of Comparative Example 1 suddenly dropped after only 103 hours of cycling, indicating that internal short circuit was caused by lithium dendrites. However, the cycling stability of MTPD-3 strongly proves that the prepared solid-state electrolyte can effectively suppress the formation of lithium dendrites.

[0087] 5. ARC test of assembled battery

[0088] The thermal runaway behavior of batteries assembled with the solid-state electrolytes of Comparative Example 1, MTPD-1, MTPD-2 and MTPD-3 was studied by ARC test. The relevant parameters are shown in the figure, T0, T1 and T2 represent the self-ignition temperature, trigger temperature and maximum temperature, respectively. As shown in (a) of FIG. 1, Figure 4 As shown in (a) of FIG. 1, the T0 and T1 of the battery corresponding to Comparative Example 1 at 1125.2 and 1301.1 min were 246.6 and 298.8℃, respectively, the T0 and T1 of the battery corresponding to MTPD-1 at 1450.2 and 1618.8 min were 256.6 and 348.8℃, respectively, the T0 and T1 of the battery corresponding to MTPD-2 at 1595.8 and 1781.5 min were 278.9 and 352.2℃, respectively, and the T0 and T1 of the battery corresponding to MTPD-3 at 1645.1 and 1906.9 min were 289.5 and 388.5℃, respectively.

[0089] Specifically, the T1 value of the battery after using MTPD-3 was the highest, and especially compared with Comparative Example 1, the T1 of the battery after using MTPD-3 was increased by 89.7℃. As shown in (b) of FIG. 1, Figure 4 As shown in (b) of FIG. 1, the t0, t1 and t2 of the battery assembled with Comparative Example 1 were 1125.2, 1301.1 and 1512.7 min, the t0, t1 and t2 of the battery assembled with MTPD-1 were 1450.2, 1618.8 and 1869.5 min, the t0, t1 and t2 of the battery assembled with MTPD-2 were 1595.8, 1781.5 and 1993.4 min, and the t0, t1 and t2 of the battery assembled with MTPD-3 were 1645.1, 1906.9 and 2026.2 min. The above data showed that the t0, t1 and t2 of the battery were all increased after using MTPD. As shown in (c) of FIG. 1, Figure 4 As shown in (c) of FIG. 1, the temperature rise rate of the batteries assembled with Comparative Example 1, MTPD-1, MTPD-2 and MTPD-3 were 158.6, 79.7, 75.6 and 38.5℃ / min, respectively, and it could be seen that the temperature rise rate of the battery after using MTPD-3 was significantly reduced. As shown in (d) of FIG. 1, Figure 4 As shown in (d) of FIG. 1, the thermal runaway reaction activation energy (E a ) of the battery assembled with Comparative Example 1 was 0.243 eV, and the E a of the battery after using MTPD-3 was 0.913 eV, which was increased by 275.7%. These results meant that the thermal safety of the battery was effectively improved.

[0090] 6. Thermal conductivity test of solid-state electrolyte at different temperatures

[0091] The thermal conductivity of Comparative Example 1, MTPD-1, MTPD-2 and MTPD-3 solid state electrolytes were tested at 20℃, 40℃, 60℃, 80℃ and 100℃, respectively. As shown in Figure 1, Thermal conductivity represents the thermal conductivity, and the thermal conductivity of Comparative Example 1 at different temperatures is 0.27, 0.27, 0.28, 0.28 and 0.275 Wm-1k-1, respectively. Figure 5 As shown in Figure 1, Thermal conductivity represents the thermal conductivity, and the thermal conductivity of Comparative Example 1 at different temperatures is 0.27, 0.27, 0.28, 0.28 and 0.275 Wm -1 k -1 -1k-1, respectively, while the thermal conductivity of MTPD-1, MTPD-2 and MTPD-3 solid state electrolytes at different temperatures is 0.39, 0.30, 0.31, 0.31, 0.30, 0.45, 0.40, 0.46, 0.49, 0.47 and 0.62, 0.63, 0.61, 0.65, 0.65 Wm -1 k -1 -1k-1, respectively.

[0092] It can be seen that the solid state electrolyte of the present application has excellent thermal conductivity.

[0093] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a thermally conductive and fireproof solid electrolyte, characterized in that: The following steps are involved: Step S1: preparing polymer fiber membrane using electrospinning technology: PVDF-HFP was dissolved in a mixture of N,N-dimethylformamide and acetone to prepare a spinning solution with a mass concentration of 10 wt% to 18 wt%, and the spinning was performed at a voltage of 20±0.1 kV and a feed rate of 0.5 mL / h to obtain a polymer fiber membrane; Step S2: Preparation of functionalized heterogeneous nanostructures: The functionalized heterogeneous nanostructures P-Ti3C2T are formed by self-assembly of nanosheets MXene and BN / graphite to form heterojunctions, which are then modified with silane coupling agents and phenylphosphonium dichloride. n / BN; Step S3: Preparation of high-efficiency phosphorus-based flame retardant PD: introducing phosphorus-oxygen-carbon covalent chains by reacting DOPO with propylene oxide and chlorosulfonic acid to obtain PEG-P-DOPO, i.e. PD; Step S4: PEO, LiTFSI, functionalized heterogeneous nanostructures, and PD are dissolved in acetonitrile at a mass ratio of (330:100:7:7) to (180:50:14:14), cast on a fiber membrane, and then vacuum-dried to form a solid electrolyte.

2. The preparation method according to claim 1, characterized in that In the step S1, the mass ratio of the N,N-dimethylformamide to the acetone mixture is (1-4):

1.

3. The preparation method according to claim 1, characterized in that In step S2, the preparation of the functionalized heterogeneous nanostructure includes: Step S2.1: LiF is dissolved in a 1-10M HCl solution, and the mixture is used to etch Ti3AlC2 to prepare MXene nanosheets; boron nitride (BN) powder is mixed with N-methylpyrrolidone, ultrasonically treated under argon protection, and the supernatant is collected by centrifugation to prepare BN nanosheets; MXene nanosheets and BN nanosheets are mixed in a mass ratio of 2:1, stirred, and allowed to stand for 24 hours. The heterojunction is driven by van der Waals forces, and the Ti3C2T2 / BN heterojunction is obtained by freeze-drying; Step S2.2: The heterojunction was mixed with the silane coupling agent KH550 in a mass ratio of 10:1, and then refluxed at 80°C in a reflux condenser for 12 hours, centrifuged and washed to obtain an amino-functionalized heterojunction NH2-Ti3C2T2 / BN; NH2-Ti3C2T2 / BN was dispersed in tetrahydrofuran (THF), and phenylphosphine dichloride was added. Under nitrogen protection, the mixture was reacted at 60°C for 8 hours, and then centrifuged and washed three times with THF to obtain a functionalized heterostructure P-Ti3C2T2 / BN.

4. The preparation method according to claim 3, characterized in that The amino-functionalized heterojunction NH2-Ti3C2T2 / BN and phenylphosphonium dichloride have a molar ratio of 1:1.

2.

5. The preparation method according to claim 1, characterized in that In step S3, the preparation of the high-efficiency phosphorus-based flame retardant PD includes: Step 3.1: Mix 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and propylene oxide in a molar ratio of (1-3):1 in THF, add boron trifluoride ether (BF3·Et2O) and polyethylene glycol (PEG), and react at 60°C for 24 hours. The product is precipitated with ethanol and dried in vacuo to obtain a DOPO-PEG intermediate. Step 3.2: The intermediate was mixed with chlorosulfonic acid in a molar ratio of 1:(2-4) in dichloromethane, added dropwise at 0°C, and then heated to 25°C for 12 hours. PEG-P-DOPO was obtained after purification by dialysis.

6. A thermally conductive and fireproof solid electrolyte prepared by the method according to any one of claims 1 to 5, characterized in that: The solid electrolyte comprises PEO, LiTFSI matrix, functionalized heterogeneous nanostructure and PD flame retardant, wherein the ionic conductivity of the solid electrolyte is ≥9.6×10 -4 S / cm, 60℃; thermal conductivity ≥0.6W / m·K, 60℃.

7. A lithium-ion battery, characterized in that: The solid electrolyte according to claim 6 is included, the positive electrode is LFP, and the negative electrode is a lithium sheet; The assembly order of the battery is: negative electrode shell - lithium sheet - solid electrolyte - positive electrode sheet - stainless steel gasket - spring sheet - positive electrode shell, and the assembly pressure is 5MPa.

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