Composite polymer solid electrolyte and preparation method thereof

Abstract

The invention belongs to the technical field of solid-state lithium metal batteries, and particularly relates to a composite polymer solid-state electrolyte and a preparation method thereof.The preparation method comprises the steps that S1, benzene sulfonyl chloride is added into N, N-dimethylformamide under the ice bath condition, chitosan is added into the solution, and the chitosan is dispersed in the solution; then adding lithium hydroxide and stirring; centrifuging the reaction solution to obtain supernate, adding lithium hydroxide into the supernate, adding acetone for precipitation, and drying the obtained precipitate; s2, dissolving the prepared benzene sulfonamide chitosan, polyvinylidene fluoride and bis (fluorosulfonyl) lithium imide in a mixed organic solvent of N, N-dimethylacetamide and tetrahydrofuran to form a uniform polymer solution; and S3, uniformly spreading the polymer solution on a glass culture dish to form a film, and drying. The composite polymer solid electrolyte has the advantages that the prepared composite polymer solid electrolyte has good flame resistance, mechanical strength is improved, and good lithium dendrite inhibition capability is shown.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lithium metal batteries, and particularly relates to a composite polymer solid electrolyte and a preparation method thereof. Background Art

[0002] Lithium metal anodes have a high theoretical specific capacity. Using lithium metal anodes can effectively increase the energy density of batteries, further meeting the requirements of the energy storage field for high-energy density batteries. Compared with commercial liquid batteries that are flammable and have high reactivity between the electrolyte and the battery anode and cathode, solid polymer electrolytes have higher thermal stability and electrochemical stability, thus enabling the battery to have better safety and stability performance. Similarly, solid polymer electrolytes have better interfacial contact with lithium metal anodes, which is conducive to the formation of a more stable solid electrolyte interface layer and uniform lithium ion deposition. In addition, the flexibility and easy processability of solid polymer electrolytes endow them with the potential for multi-scenario applications.

[0003] Although solid polymer electrolytes and lithium metal anodes are highly anticipated due to their significant advantages, there are still certain difficulties at the practical application level. Specifically, the main problems faced by solid polymer electrolytes include low room-temperature lithium ion conductivity, which directly limits their application in high-power density batteries; the formation of lithium dendrites on the surface of lithium metal during the battery cycling process, which will cause a significant reduction in the battery performance and cycle life. Similarly, solid polymer electrolytes have limited mechanical strength and low room-temperature ionic conductivity. These above problems limit the practical application of solid polymer lithium metal batteries.

[0004] In order to increase the mechanical strength and room-temperature ionic conductivity of solid polymer electrolytes and inhibit the growth of lithium dendrites in lithium metal batteries, relevant researchers have proposed a strategy of adding fillers to modify polymer electrolytes. Adding organic fillers can diffuse more uniformly in the electrolyte compared with inorganic fillers, and organic fillers have the advantages of simple production and low cost. Biomass organic fillers have the advantages of green sustainability and rich functional groups compared with common organic fillers (such as succinonitrile). Chitosan is an effective solid electrolyte filler, but in most works, chitosan is dispersed in the electrolyte in the form of insoluble substances. When partial chitosan powder agglomerates, it will not only affect the ion transport ability of the electrolyte, but also the agglomerated chitosan will cause the uneven surface of the polymer electrolyte, further affecting the contact effect between the electrolyte and the electrode. Summary of the Invention

[0005] To overcome the deficiencies of the prior art, the object of the present invention is to provide a composite polymer solid electrolyte and a preparation method thereof. The composite polymer solid electrolyte has good mechanical strength, flame retardancy resistance, high room temperature ionic conductivity, high ion migration number. Also, this electrolyte has a high oxidation potential and can be applied to high-voltage positive electrodes. This electrolyte has good lithium dendrite inhibition ability, enabling the battery to have good cycle stability and lifespan.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] A preparation method of a composite polymer solid electrolyte, comprising the following steps:

[0008] S1: Under ice bath conditions, add benzenesulfonyl chloride to N,N-dimethylformamide to prepare a solution of benzenesulfonyl chloride in N,N-dimethylformamide; add chitosan to this solution to disperse chitosan in the N,N-dimethylformamide solution of benzenesulfonyl chloride; then add lithium hydroxide as an alkaline catalyst and carry out a stirring reaction; the reaction solution is centrifuged to obtain a supernatant, lithium hydroxide is added to the supernatant, and then acetone is added for precipitation. The obtained precipitate is dried to obtain benzenesulfonamidated chitosan;

[0009] S2: Dissolve the prepared benzenesulfonamidated chitosan, polyvinylidene fluoride, and lithium bis(fluorosulfonyl)imide in a mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran to form a homogeneous polymer solution;

[0010] S3: Uniformly spread the polymer solution on a glass petri dish, form a film in a fume hood, and carry out vacuum drying to prepare a composite polymer electrolyte.

[0011] The addition amount of the benzenesulfonyl chloride is 0.059 - 0.061 mol, the addition amount of chitosan is 0.009 - 0.011 mol; the addition amount of lithium hydroxide as an alkaline catalyst is 0.0005 mol; the reaction temperature for the reaction of chitosan and the N,N-dimethylformamide solution of benzenesulfonyl chloride under the action of the alkaline catalyst is 28 - 32 °C, and the reaction time is 46 - 48 h; 0.03 - 0.06 mol of lithium hydroxide is added to the supernatant; the volume ratio of benzenesulfonyl chloride to N,N-dimethylformamide is 51:200; the volume ratio of acetone to N,N-dimethylformamide is 1:1.

[0012] The addition amount of the polyvinylidene fluoride is 1% - 10 wt.% of the mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran;

[0013] Based on the mass of polyvinylidene fluoride described in S2, the mass of benzenesulfonamidated chitosan is 1% to 10% of it, and the mass ratio of lithium bis(fluorosulfonyl)imide to polyvinylidene fluoride is (2 to 2.01):(3 to 3.01); the volume ratio of N,N-dimethylacetamide to tetrahydrofuran is 3:7.

[0014] In the S3 described above, the film-forming time is 24 to 25 h, the vacuum drying temperature is 55 to 60 °C, and the vacuum drying time is 27 to 28 h.

[0015] The thickness of the composite polymer solid electrolyte is 45 to 55 μm.

[0016] In the S1 described above, the temperature of the ice bath is 0 to 1 °C.

[0017] In the S3 described above, the film-forming temperature is 24 to 27 °C, and the wind speed in the fume hood is 28 to 32 m / s.

[0018] The composite polymer solid electrolyte is prepared by the described preparation method and is a smooth, transparent film with a flat surface.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. In the present invention, benzenesulfonamidated chitosan is obtained through organic synthesis. It, polyvinylidene fluoride, and lithium bis(fluorosulfonyl)imide are dissolved in a mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran to form a homogeneous polymer solution. The soluble benzenesulfonamidated chitosan can be uniformly distributed in the polymer network of polyvinylidene fluoride, and at the same time, it can have an intermolecular interaction with lithium bis(fluorosulfonyl)imide, thereby further forming a uniform lithium ion transport path, which is beneficial to the transport and uniform deposition of lithium ions. The polymer solution is uniformly spread on a glass petri dish, and film-forming and drying are carried out in a fume hood to obtain a composite polymer electrolyte. The electrolyte has a uniform film and a smooth surface, and can form a good interfacial contact with the electrode.

[0021] 2. The composite polymer solid electrolyte prepared by the present invention has good flame retardancy; compared with insoluble chitosan powder with irregular particle shapes and larger sizes, the regularly shaped and uniformly sized benzenesulfonamidated chitosan is fully dissolved in the mixed solvent of N,N-dimethylformamide / tetrahydrofuran. After being compounded with polyvinylidene fluoride molecules, it is in full contact with the molecular chains, forming fewer defects or stress concentration points in the interface region with polyvinylidene fluoride molecules, effectively increasing the mechanical strength of the composite electrolyte; the addition of benzenesulfonamidated chitosan enables the lithium anion of bis(fluorosulfonamide) imide to have an intermolecular interaction with the benzenesulfonyl group, promoting the dissociation of the lithium salt and inhibiting the movement of the lithium salt anion, making the electrolyte have a high ion migration number and high room-temperature ionic conductivity. Similarly, this electrolyte has a high oxidation potential and is applicable to high-voltage positive electrodes. The high lithium ion transport ability of this electrolyte promotes the uniform deposition of lithium ions on the lithium metal negative electrode, enabling the battery to have good cycle stability and lifespan, and showing good lithium dendrite inhibition ability.

[0022] The composite polymer solid electrolyte prepared by the present invention has good flame retardant properties and mechanical properties, can effectively prevent battery thermal runaway and lithium dendrite piercing the electrolyte, and is applicable to lithium metal batteries with high safety; it has high lithium ion conductivity and lithium ion migration number at room temperature, has low concentration polarization of the battery during application, and helps to achieve a high power density; this electrolyte exhibits a wide electrochemical window and is applicable to high-voltage positive electrodes.

[0023] 3. The preparation method of the present invention is simple and easy to operate. Except for the synthesis of benzenesulfonamidated chitosan, the preparation of the electrolyte only includes operations such as solution preparation, casting, film formation, and drying, which is suitable for large-scale industrial production.

[0024] 4. The composite polymer solid electrolyte of the present invention has good film-forming properties, has good contact with the electrode, has good interfacial compatibility with the lithium metal negative electrode, and can effectively inhibit the growth of lithium dendrites. Description of the Drawings

[0025] Figure 1 It is the Fourier infrared spectrum diagram of the soluble benzenesulfonamidated chitosan prepared in Example 1.

[0026] Figure 2 It is the SEM diagram of the chitosan used in Example 1.

[0027] Figure 3 It is the SEM diagram of the soluble benzenesulfonamidated chitosan prepared in Example 1.

[0028] Figure 4 It is the surface SEM diagram of the composite polymer solid electrolyte prepared in Example 1 using soluble benzenesulfonamidated chitosan as a filler.

[0029] Figure 5SEM image of the surface of the composite polymer solid electrolyte prepared in Example 1 using soluble benzenesulfonamide chitosan filler.

[0030] Figure 6 Images of the uniformity and transparency of the composite polymer solid electrolyte prepared in Example 1 using soluble benzenesulfonamide chitosan filler.

[0031] Figure 7 Flame retardant resistance graph of the composite polymer solid electrolyte prepared in Application Example 1 using soluble benzenesulfonamide chitosan filler: (a) before contacting an open flame, (b) after contacting for 5 seconds, (c) after contacting for 10 seconds, (d) visual image of the electrolyte after the flame retardancy test is completed.

[0032] Figure 8 Stress-strain curve graph of the tensile properties of the composite polymer solid electrolyte prepared in Application Example 1 using different fillers.

[0033] Figure 9 Arrhenius curve graph obtained by linearly fitting the ionic conductivity of the composite polymer solid electrolyte prepared in Application Example 1 using different fillers with different temperatures.

[0034] Figure 10 Histogram of the lithium ion transference number obtained by the steady-state current method for the lithium symmetric battery assembled with the composite polymer solid electrolyte prepared in Application Example 1 using different fillers.

[0035] Figure 11 Tafel curve graph of the lithium symmetric battery assembled with the composite polymer solid electrolyte prepared in Application Example 1 using different fillers.

[0036] Figure 12 Linear sweep voltammetry (LSV) curve graph of the SS|Li battery assembled with the composite polymer solid electrolyte prepared in Application Example 1 using different fillers.

[0037] Figure 13 Long cycle charge-discharge test graph of the lithium symmetric battery assembled with the composite polymer solid electrolyte prepared in Application Example 1.

[0038] Figure 14 SEM image of the lithium metal surface morphology after 125 cycles of long cycle charge-discharge test for the lithium symmetric battery assembled with the composite polymer solid electrolyte prepared in Application Example 1 using soluble benzenesulfonamide chitosan filler.

[0039] Figure 15 Electrochemical impedance graph of the lithium symmetric battery assembled with the composite polymer solid electrolyte prepared in Application Example 2.

[0040] Figure 16Long cycle charge-discharge test chart of a lithium symmetric battery assembled with a composite polymer solid electrolyte using the soluble benzenesulfonamide chitosan filler prepared in Application Example 2. Detailed implementation manners

[0041] The technical solutions of the present invention will be clearly and completely described below in combination with the data in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0042] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be obtained through market purchase or prepared by existing methods. Among them, lithium bis(fluorosulfonyl)imide is LiFSI; chitosan is CS, and benzenesulfonamide chitosan is SCS.

[0043] A preparation method of a composite polymer solid electrolyte is as follows: chitosan is dispersed in an N,N-dimethylformamide solution of benzenesulfonyl chloride, and lithium hydroxide is used as a basic catalyst. Through the reaction of sulfonyl chloride and the amino group in chitosan, soluble benzenesulfonamide chitosan is obtained; benzenesulfonamide chitosan, lithium bis(fluorosulfonyl)imide, and polyvinylidene fluoride are dissolved in a mixed solvent composed of N,N-dimethylacetamide and tetrahydrofuran, and the mixed solution is made into a transparent composite solid electrolyte by the solution casting method. Specifically, it includes the following steps:

[0044] S1: Under ice bath conditions (0-1 °C), benzenesulfonyl chloride is added to N,N-dimethylformamide to prepare an N,N-dimethylformamide solution of benzenesulfonyl chloride; chitosan is added to this solution to disperse chitosan in the N,N-dimethylformamide solution of benzenesulfonyl chloride; then lithium hydroxide is added as a basic catalyst and stirred for reaction; the reaction solution is centrifuged to obtain a supernatant, lithium hydroxide is added to the supernatant, and then acetone is added for precipitation, and the obtained precipitate is dried to obtain benzenesulfonamidated chitosan.

[0045] Among them, the volume of the N,N-dimethylformamide solution is 30 ml, and the addition amounts of benzenesulfonyl chloride and chitosan are 0.059 - 0.061 mol and 0.009 - 0.011 mol respectively, preferably 0.06 mol and 0.01 mol respectively; the addition amount of lithium hydroxide as the basic catalyst is 0.0005 mol; the reaction temperature of the reaction between chitosan and the N,N-dimethylformamide solution of benzenesulfonyl chloride under the action of the basic catalyst is 28 - 32 °C, preferably 30 °C, and the reaction time is 46 - 50 h; 0.036 - 0.04 mol of lithium hydroxide is added to the supernatant. Lithium hydroxide is used as the basic reagent to adjust the pH of the solution after the reaction. The more it is added, the more beneficial it is to the precipitation of chitosan benzenesulfonamide, but the addition amount should not be too much, and an appropriate sufficient addition amount of lithium hydroxide is preferred. The volume ratio of benzenesulfonyl chloride to N,N-dimethylformamide is 51:200; the volume ratio of acetone to the N,N-dimethylformamide solution is 1:1.

[0046] S2: Dissolve the prepared chitosan benzenesulfonamide, polyvinylidene fluoride, and lithium bis(fluorosulfonyl)imide in a mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran to form a homogeneous polymer solution;

[0047] The addition amount of polyvinylidene fluoride is 1% - 10 wt.% (accounting for the mass of the mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran), preferably 5 wt.%. Based on the mass of polyvinylidene fluoride added in S2, the mass of chitosan benzenesulfonamide is 1% - 10 wt.% of it, preferably 5 wt.%, and the mass ratio of lithium bis(fluorosulfonyl)imide to polyvinylidene fluoride is (2 - 2.01):(3 - 3.01), preferably 2:3; the volume ratio of N,N-dimethylacetamide to tetrahydrofuran is 3:7, and the total volume is 10 ml.

[0048] S3: Spread the polymer solution evenly on a glass petri dish, form a film in a fume hood at a temperature of 25 °C, set the wind speed in the fume hood to 30 m / s, and dry it under vacuum to prepare a transparent composite polymer electrolyte with a smooth and flat surface and a thickness of 45 - 55 μm.

[0049] Among them, the polymer solution is cast on a smooth and flat glass petri dish. The film-forming time is 24 - 25 h, the vacuum drying temperature is 55 - 60 °C, and the vacuum drying time is 27 - 30 h. The purpose is to remove the solvent in the solution. Increasing or decreasing the film-forming time, drying temperature, and time will change the solvent content of the final electrolyte. Among them, too low solvent content will reduce the ionic conductivity of the electrolyte, resulting in excessive polarization during the battery cycle and reducing the battery life; too high solvent content will increase the ionic conductivity, but will increase the side reaction between the solvent and the electrode, reducing the stability of the electrolyte interface, thereby reducing the cycle life of the battery. Therefore, controlling the solvent content in the electrolyte is a key factor in the electrolyte performance.

[0050] Assemble a solid-state lithium metal battery with the prepared composite polymer solid electrolyte: In a glove box filled with argon, place the negative electrode case, shrapnel, gasket, negative lithium electrode in sequence, cover the negative lithium electrode with the composite polymer solid electrolyte, then put in the positive electrode sheet, cover the positive electrode case and press the battery tightly. The positive electrode sheet is selected from lithium nickel cobalt manganese oxide electrode sheet or lithium iron phosphate electrode sheet.

[0051] Example 1

[0052] A preparation method of a composite polymer solid electrolyte includes the following steps:

[0053] S1. Under ice bath conditions, add 7.65 ml of benzenesulfonyl chloride to 30 ml of N,N-dimethylformamide, stir to form a solution of benzenesulfonyl chloride in N,N-dimethylformamide, then add 1.615 g of chitosan powder to this solution, and stir to disperse chitosan in the N,N-dimethylformamide solution. At the same time, add 0.012 g of lithium hydroxide as an alkaline catalyst, and under a nitrogen atmosphere, stir at 30 °C for 48 h for the synthesis reaction. The reaction solution is centrifuged to obtain the supernatant. Add 0.96 g of lithium hydroxide to the supernatant until lithium hydroxide is completely dissolved, then add 30 ml of acetone solution for precipitation, and vacuum dry the obtained precipitate at 60 °C for 10 h to obtain soluble benzenesulfonamidated chitosan.

[0054] S2. Prepare a polymer solution in a glove box filled with an argon atmosphere. Dissolve 0.4517 g of polyvinylidene fluoride (PVDF), 0.0226 g of benzenesulfonamidated chitosan accounting for 5 wt.% of its mass, and 0.301 g of lithium bis(fluorosulfonimide) (LiFSI) in a mixed solvent composed of 3 ml of N,N-dimethylacetamide and 7 ml of tetrahydrofuran. Stir until the solute is completely dissolved to form a composite polymer solution.

[0055] S3. Pour the polymer solution onto a smooth and flat glass dish, and spread it evenly to cover the bottom of the glass dish. Let it form a film in the fume hood for 24 h. Before transferring it to the vacuum drying oven, peel the electrolyte membrane from the surface of the culture dish, dry it at 60 °C for 27 h, and turn the electrolyte membrane over at the 24th h. After drying, a composite polymer solid electrolyte is obtained.

[0056] Example 2

[0057] A preparation method of a composite polymer solid electrolyte includes the following steps:

[0058] S1. Add 7.65 ml of benzenesulfonyl chloride to 30 ml of N,N-dimethylformamide under ice bath conditions, stir to form a solution of benzenesulfonyl chloride in N,N-dimethylformamide, then add 1.615 g of chitosan powder to this solution, and stir to disperse chitosan in the N,N-dimethylformamide solution. At the same time, add 0.012 g of lithium hydroxide as a basic catalyst, and carry out a synthesis reaction with stirring at 30 °C for 48 h under a nitrogen atmosphere. The reaction solution is centrifuged to obtain the supernatant. Add 0.96 g of lithium hydroxide to the supernatant until it is completely dissolved, then add 30 ml of acetone solution for precipitation. The obtained precipitate is vacuum dried at 60 °C for 10 h to obtain soluble benzenesulfonamidated chitosan.

[0059] S2. Prepare a polymer solution in a glove box filled with an argon atmosphere. Dissolve 0.4517 g of polyvinylidene fluoride (PVDF), 0.0226 g of benzenesulfonamidated chitosan accounting for 5 wt.% of its mass, and 0.301 g of lithium bis(fluorosulfonimide) (LiFSI) in a mixed solvent composed of 3 ml of N,N-dimethylacetamide and 7 ml of tetrahydrofuran. Stir until the solute is completely dissolved to form a composite polymer solution.

[0060] S3. Pour the polymer solution onto a smooth and flat glass dish, and spread it evenly to cover the bottom of the glass dish. Let it form a film in the fume hood for 24 h. Before transferring it to the vacuum drying oven, peel the electrolyte membrane from the surface of the culture dish, dry it at 60 °C for 30 h, and turn the electrolyte membrane over at the 27th h. After drying, a composite polymer solid electrolyte is obtained. The charge transfer resistance of this electrolyte is 668 Ω (see attached Figure 15 ); The assembled lithium symmetric battery has a polarization voltage of 125 mV after cycling 200 times under the test parameters of 0.1 mA cm -2 -0.1 mAh cm -2 (see attached Figure 16 ).

[0061] Assembly of solid-state lithium metal battery:

[0062] Use the composite polymer solid electrolyte prepared in Example 1 as the electrolyte to assemble a battery:

[0063] Taking the CR2032 button battery as an example, in a glove box filled with argon, a negative electrode case, a shrapnel, a gasket, a negative lithium sheet are sequentially placed, the composite polymer solid electrolyte is covered on the negative lithium sheet, then a positive lithium sheet is put in, the positive electrode case is covered and the battery is pressed tightly to obtain the battery.

[0064] Figure 1 Among them, the blue curve is the Fourier infrared spectrum of chitosan, and the red curve is the Fourier infrared modified spectrum of phenylsulfonamide chitosan. Observe Figure 1 It is concluded that new absorption peaks appear at wavenumbers of 1500, 1314, and 1196 on the chitosan molecule, corresponding to the benzene ring functional group, -SO 2 -, -S-N-, indicating that chitosan has been successfully phenylsulfonamidated.

[0065] From Figure 2 The SEM image of chitosan shows that the morphology of chitosan is mainly flaky, with irregular shapes and non-uniform sizes.

[0066] From Figure 3 The SEM image of phenylsulfonamide chitosan shows that the synthesized phenylsulfonamide chitosan powder is in the shape of polyhedral particles, and the particle size distribution is 8.5 - 50 μm, mainly blocky particles of about 30 μm. It has a more uniform morphology compared to chitosan.

[0067] From Figure 4 、 Figure 5 The SEM images of the surface and cross-section of the composite polymer solid electrolyte respectively show that the surface of the electrolyte is smooth, flat, dense and pore-free, and the thickness is 50 μm. Figure 6 The visual image of the electrolyte shows the characteristics of transparency, smoothness and softness, indicating that the electrolyte can form good contact with the electrode interface.

[0068] The flame retardant performance of the composite electrolyte was tested. As shown in Figure 7 (a), before the electrolyte contacts the fire source, the morphology of the electrolyte is a flat circle. After contacting the fire source for 5 s and 10 s, Figure 7 (d) the electrolyte still almost maintains its original morphology, indicating the good flame retardant performance of the composite polymer solid electrolyte.

[0069] The tensile properties of the electrolyte were tested using an electronic universal material testing machine (Istron 5965). The dimensions of the electrolyte material tested were: length 7 cm, width 1 cm, thickness 0.05 mm; the stretching rate of the instrument was set at 10 mm min -1 . From Figure 8As shown, the mechanical property tests of the electrolyte indicate that the tensile stress of the SCS composite polymer solid electrolyte is 1.4 MPa and the tensile strain is 287.8%, while those of the CS composite polymer solid electrolyte are 1.3 MPa and 174.8% respectively. The SCS composite polymer solid electrolyte exhibits good mechanical properties. Good mechanical properties can effectively inhibit the penetration of lithium dendrites through the electrolyte diaphragm and prevent short circuits during battery operation.

[0070] To study the influence of the composite polymer solid electrolyte on the dynamic characteristics of lithium-ion transport, measurement experiments of ionic conductivity and lithium-ion transference number at different temperatures were carried out.

[0071] As Figure 9 shown, steel symmetric batteries assembled with composite polymer solid electrolytes using different fillers were subjected to electrochemical impedance tests respectively. The test parameters are as follows: the frequency range is 0.1 - 100000 Hz and the AC voltage amplitude is 5 mV. As shown in the figure, the ionic conductivity of the SCS composite polymer solid electrolyte changes linearly with temperature. And the SCS composite polymer solid electrolyte has a high lithium-ion conductivity of 1.35×10 -3 S cm -1 at 25 °C, which is higher than 1.03×10 -3 S cm -1 of the CS composite polymer solid electrolyte.

[0072] As Figure 10 shown, the lithium-ion transference numbers of the composite electrolytes obtained by the steady-state current method testing, the test steps include electrochemical impedance testing and i-t curve testing. The electrochemical frequency impedance test range is 0.1 - 100000 Hz and the AC voltage amplitude is 5 mV; the i-t curve test parameters are as follows: the initial voltage is 10 mV, the test time is 1000 s, and the sensitivity is 10 -3 . The electrochemical impedance before and after the i-t test was tested respectively, and the currents before polarization and after polarization stabilization were obtained through the i-t test. After calculation, the lithium-ion transference number of the SCS composite electrolyte is 0.6, which is higher than 0.45 of the CS composite electrolyte. It shows the good lithium-ion transport ability of the composite electrolyte.

[0073] The Tafel test is as Figure 11 shown. This test was carried out by assembling a lithium symmetric battery (Li|SSE|Li) and performing a linear sweep at a sweep rate of 10 mV / s within a polarization voltage range of -0.2 V to 0.2 V (relative to the open circuit potential) to obtain the Tafel curves of the anode (lithium stripping) and the cathode (lithium deposition). The exchange current density j 0 of the composite polymer solid electrolyte is 4.45×10 -2 mAcm -2The size of this value is related to the interface between the electrolyte and the lithium metal electrode. The high exchange current density indicates that the interface between the composite electrolyte and the lithium metal negative electrode has good reaction kinetics.

[0074] LSV curve Figure 12 As shown, the test was performed by assembling a steel-to-lithium battery with a scan rate of 1 mV / s in the voltage range of 2 to 6 V. The LSV curve shows a wide electrochemical stability window of the SCS composite polymer solid electrolyte, extending to 4.85 V, which is higher than the oxidation potential of the CS composite polymer solid electrolyte of 4.77 V, indicating that the composite polymer solid electrolyte has good electrochemical stability and can be used for high-voltage positive electrodes.

[0075] In order to further study the low interfacial compatibility between the composite polymer solid electrolyte and the lithium metal anode, at 0.1 mA cm -1 The current density and 0.1 mAh cm -1 Charge and discharge tests were carried out at a unit area capacity of .

[0076] Depend on Figure 13 The results show that the overpotential of the battery using the SCS composite polymer solid electrolyte is stable at about 50mV, indicating that the composite electrolyte has good interfacial stability with the lithium metal negative electrode, and that lithium ions can be uniformly reduced and deposited on the lithium metal surface at this current density. And after 500h of continuous cycling, the battery polarization potential still fluctuates little, indicating the good lithium deposition / stripping behavior of the battery.

[0077] Depend on Figure 14 The SEM images of the lithium metal negative electrode surface after cycling using different composite polymer solid electrolyte batteries show that the lithium metal surface of the SCS composite polymer solid electrolyte battery in Figure a shows a flat and smooth morphology, while the lithium metal surface of the CS composite polymer solid electrolyte battery in Figure b is uneven, with large lithium deposits. This shows that the SCS composite polymer solid electrolyte has good lithium dendrite inhibition ability.

[0078] The composite polymer solid electrolyte prepared by the present invention has uniform material, smooth and soft texture, and the mechanical strength of the electrolyte is increased by adding benzenesulfonamide chitosan filler, and the room temperature ion conductivity is improved. In addition, the composite electrolyte has good interface properties with the lithium metal negative electrode, which provides conditions for the long-term stable cycle of the battery.

Claims

1. A method for preparing a composite polymer solid electrolyte, characterized in that: The following steps are involved: S1: adding benzenesulfonyl chloride to N,N-dimethylformamide under ice bath conditions to prepare a benzenesulfonyl chloride N,N-dimethylformamide solution; adding chitosan to the solution to disperse the chitosan in the benzenesulfonyl chloride N,N-dimethylformamide solution; adding lithium hydroxide as an alkaline catalyst and stirring the reaction; centrifuging the reaction solution to obtain a supernatant, adding lithium hydroxide to the supernatant, and then adding acetone to precipitate, and drying the obtained precipitate to obtain benzenesulfonamidated chitosan; S2: dissolving the prepared benzenesulfonamidated chitosan, polyvinylidene fluoride and lithium bis(fluorosulfonyl)imide in a mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran to form a uniform polymer solution; S3: The polymer solution is evenly spread on a glass culture dish, film-formed in a fume hood, and vacuum-dried to prepare a composite polymer electrolyte.

2. The method for preparing a composite polymer solid electrolyte according to claim 1, characterized in that: The amount of benzenesulfonyl chloride added is 0.059-0.061 mol, the amount of chitosan added is 0.009-0.011 mol; the amount of lithium hydroxide added as an alkaline catalyst is 0.0005 mol; the reaction temperature of chitosan and benzenesulfonyl chloride in N, N-dimethylformamide solution under the action of the alkaline catalyst is 28-32°C, and the reaction time is 46-48 hours; 0.03-0.06 mol of lithium hydroxide is added to the supernatant; the volume ratio of benzenesulfonyl chloride to N, N-dimethylformamide is 51:200; and the volume ratio of acetone to N, N-dimethylformamide is 1:

1.

3. The method for preparing a composite polymer solid electrolyte according to claim 1, characterized in that: The amount of polyvinylidene fluoride added is 1% to 10wt.% of the mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran; Based on the added mass of the polyvinylidene fluoride described in S2, the mass of benzenesulfonamidated chitosan is 1% to 10%, the mass ratio of lithium bis(fluorosulfonyl)imide to polyvinylidene fluoride is (2 to 2.01):(3 to 3.01); the volume ratio of N,N-dimethylacetamide to tetrahydrofuran is 3:

7.

4. The method for preparing a composite polymer solid electrolyte according to claim 1, characterized in that: In the S3, the film forming time is 24 to 25 hours, the vacuum drying temperature is 55 to 60° C., and the vacuum drying time is 27 to 28 hours.

5. The method for preparing a composite polymer solid electrolyte according to claim 1, characterized in that: The thickness of the composite polymer solid electrolyte is 45-55 μm.

6. The method for preparing a composite polymer solid electrolyte according to claim 1, characterized in that: The temperature of the ice bath in S1 is 0-1°C.

7. The method for preparing a composite polymer solid electrolyte according to claim 1, characterized in that: In the above-mentioned S3, the film forming temperature is 24-27° C., and the wind speed of the fume hood is 28-32 m / s.

8. A composite polymer solid electrolyte obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The composite polymer solid electrolyte is prepared by the preparation method and is a transparent film with a flat and smooth surface.

Images