Composite polymer solid electrolyte and preparation method thereof

Abstract

The present invention belongs to the technical field of solid-state lithium metal batteries, and in particular to a composite polymer solid electrolyte and a preparation method thereof, comprising: S1: adding benzenesulfonyl chloride to N, N-dimethylformamide under ice bath conditions, adding chitosan to the solution, and dispersing the chitosan in the solution; then adding lithium hydroxide and stirring; the reaction solution is centrifuged to obtain a supernatant, lithium hydroxide is added to the supernatant, acetone is added to precipitate, and the resulting precipitate is dried; S2: the prepared benzenesulfonamidated chitosan and polyvinylidene fluoride and lithium bis(fluorosulfonyl)imide are dissolved 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 to form a film, and dried. Advantages are: the composite polymer solid electrolyte prepared by the present invention has good flame retardancy, increased mechanical strength, and exhibits good lithium dendrite inhibition ability.

Description

Technical Field

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

[0002] Lithium metal anodes have high theoretical specific capacity. The use of lithium metal anodes can effectively increase the energy density of batteries, further meeting the demand for high-energy-density batteries in the energy storage field. Compared with commercial liquid batteries that are flammable and have high reactivity between electrolytes and battery positive and negative electrodes, solid polymer electrolytes have higher thermal stability and electrochemical stability, which makes the battery safer and more stable. 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 give them the potential for application in multiple scenarios.

[0003] Although solid polymer electrolytes and lithium metal anodes are highly anticipated due to their significant advantages, there are still certain difficulties in practical application. 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 lithium metal surface of the lithium metal anode during battery cycling will greatly reduce the performance and cycle life of the battery. Similarly, solid polymer electrolytes have the disadvantages of limited mechanical strength and low room temperature ion conductivity. The above problems limit the practical application of solid polymer lithium metal batteries.

[0004] In order to increase the mechanical strength and room temperature ion 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. Compared with inorganic fillers, organic fillers can be more evenly diffused in the electrolyte, and organic fillers have the advantages of simple preparation and low cost. Biomass organic fillers have the advantages of being green, sustainable, and rich in functional groups compared to common organic fillers (such as succinonitrile). Chitosan is an effective solid electrolyte filler, but in most work, chitosan is dispersed in the electrolyte in the form of insoluble matter. When some chitosan powder agglomerates, it will not only affect the ion transport capacity of the electrolyte, but also the agglomerated chitosan will cause an 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 shortcomings of the prior art, the present invention provides a composite polymer solid electrolyte and a method for preparing the same. This composite polymer solid electrolyte exhibits excellent mechanical strength, flame retardancy, high room-temperature ionic conductivity, and a high ion transference number. Furthermore, the electrolyte exhibits a high anti-oxidation potential and is suitable for use in high-voltage positive electrodes. The electrolyte also exhibits excellent lithium dendrite suppression, resulting in excellent battery cycle stability and lifespan.

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

[0007] A method for preparing a composite polymer solid electrolyte comprises the following steps:

[0008] S1: adding benzenesulfonyl chloride to N,N-dimethylformamide in an ice bath 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 to react; centrifuging the reaction solution to obtain a supernatant, adding lithium hydroxide to the supernatant, and then adding acetone to precipitate, and drying the resulting precipitate to obtain benzenesulfonamidated chitosan;

[0009] 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;

[0010] S3: The polymer solution is evenly spread on a glass culture dish, formed into a film in a fume hood, and vacuum dried to prepare a composite polymer electrolyte.

[0011] 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 of chitosan and benzenesulfonyl chloride in an N,N-dimethylformamide solution under the action of the alkaline catalyst is carried out at a reaction temperature of 28-32°C and a reaction time of 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.

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

[0013] Based on the added mass of the polyvinylidene fluoride described in S2, the mass of the 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.

[0014] In the above-mentioned 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.

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

[0016] The temperature of the ice bath in S1 is 0-1°C.

[0017] 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.

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

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention obtains benzenesulfonamidated chitosan through organic synthesis. It is dissolved in a mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran with polyvinylidene fluoride and lithium bis(fluorosulfonyl)imide to form a uniform polymer solution. The soluble benzenesulfonamidated chitosan can be uniformly distributed in the polymer network of polyvinylidene fluoride and can also interact with lithium bis(fluorosulfonyl)imide intermolecularly, thereby further forming a uniform lithium ion transmission path, which is beneficial to the transmission and uniform deposition of lithium ions. The polymer solution is evenly spread on a glass culture dish, formed into a film in a fume hood, and dried to obtain a composite polymer electrolyte. The electrolyte grows into a uniform film with a smooth surface and can form a good interface 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 size, the benzenesulfonamide chitosan with regular shape and uniform particles fully dissolves in the N,N-dimethylformamide / tetrahydrofuran mixed solvent. After being compounded with polyvinylidene fluoride molecules, it fully contacts the molecular chain and forms fewer defects or stress concentration points in the interface area with the polyvinylidene fluoride molecules, effectively increasing the mechanical strength of the composite electrolyte. The addition of benzenesulfonamide chitosan causes the bis(fluorosulfonamide)imide lithium anion to interact with the benzenesulfonyl group, promoting the dissociation of lithium salts and inhibiting the movement of lithium salt anions, so that the electrolyte has a high ion transfer number and high room temperature ion conductivity. The electrolyte also has a high antioxidant potential and is suitable for high-voltage positive electrodes. The high lithium ion transport capacity of the electrolyte promotes the uniform deposition of lithium ions on the lithium metal negative electrode, so that the battery has good cycle stability and life, and exhibits 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 dendrites from penetrating the electrolyte, and is suitable for high-safety lithium metal batteries; it has high lithium ion conductivity and lithium ion migration number at room temperature, and low battery concentration polarization during application, which helps to achieve high power density; the electrolyte exhibits a wide electrochemical window and is suitable for high-voltage positive electrodes.

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

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

[0025] Figure 1 This is the Fourier infrared spectrum of the soluble benzenesulfonamide chitosan prepared in Example 1.

[0026] Figure 2 This is the SEM image of chitosan used in Example 1.

[0027] Figure 3 This is the SEM image of the soluble benzenesulfonamide chitosan prepared in Example 1.

[0028] Figure 4 This is a surface SEM image of the composite polymer solid electrolyte using soluble benzenesulfonamide chitosan filler prepared in Example 1.

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

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

[0031] Figure 7 The flame retardant performance diagram of the composite polymer solid electrolyte using soluble benzenesulfonamide chitosan filler prepared in Example 1: (a) is before contact with open flame, (b) is contact for 5 seconds, (c) is contact for 10 seconds, and (d) is a visual image of the electrolyte after the flame retardancy test is completed.

[0032] Figure 8 The stress-strain curves of the tensile properties of the composite polymer solid electrolyte using different fillers prepared in Application Example 1 are shown.

[0033] Figure 9 This is an Arrhenius curve obtained by linear fitting of the ion conductance of the composite polymer solid electrolyte using different fillers prepared in Example 1 and different temperatures.

[0034] Figure 10 This is a bar graph of lithium ion transference numbers obtained by steady-state current method testing of lithium ion symmetric batteries assembled with composite polymer solid electrolytes using different fillers prepared in Example 1.

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

[0036] Figure 12 The linear voltammetry (LSV) curves of the SS|Li battery assembled with the composite polymer solid electrolyte using different fillers prepared in Example 1 are shown.

[0037] Figure 13 This is a long cycle charge and discharge test diagram of a lithium symmetrical battery assembled using the composite polymer solid electrolyte prepared in Example 1.

[0038] Figure 14 This is an SEM image of the lithium metal surface morphology of a lithium symmetrical battery assembled with a composite polymer solid electrolyte using a soluble benzenesulfonamide chitosan filler prepared in Example 1 after 125 cycles of long-cycle charge and discharge testing.

[0039] Figure 15 This is the electrochemical impedance spectroscopy diagram of a lithium symmetric battery assembled using the composite polymer solid electrolyte prepared in Example 2.

[0040] Figure 16This is a long cycle charge and discharge test diagram of a lithium symmetrical battery assembled with a composite polymer solid electrolyte using a soluble benzenesulfonamide chitosan filler prepared in Example 2. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solution of the present invention in conjunction with the data in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection 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 scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods. Among them, lithium bis(fluorosulfonyl)imide is LiFSI; chitosan is CS, and benzenesulfonamide chitosan is SCS.

[0043] A method for preparing a composite polymer solid electrolyte comprises dispersing chitosan in a solution of benzenesulfonyl chloride in N,N-dimethylformamide, using lithium hydroxide as an alkaline catalyst to react the sulfonyl chloride with the amino groups in the chitosan to obtain soluble benzenesulfonamide chitosan; dissolving the benzenesulfonamide chitosan, lithium bis(fluorosulfonyl)imide, and polyvinylidene fluoride in a mixed solvent consisting of N,N-dimethylacetamide and tetrahydrofuran, and using a solution casting method to obtain a transparent composite solid electrolyte. The method specifically comprises the following steps:

[0044] S1: adding benzenesulfonyl chloride to N,N-dimethylformamide under ice bath conditions (0-1°C) 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; then 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.

[0045] The volume of the N,N-dimethylformamide solution is 30 ml, the amounts of benzenesulfonyl chloride and chitosan added are 0.059-0.061 mol and 0.009-0.011 mol, respectively, preferably 0.06 mol and 0.01 mol, respectively; the amount of lithium hydroxide added as an alkaline catalyst is 0.0005 mol; the reaction temperature for the reaction of chitosan and benzenesulfonyl chloride in the N,N-dimethylformamide solution under the action of an alkaline 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, and lithium hydroxide is used as an alkaline reagent to adjust the pH of the solution after the reaction. The more lithium hydroxide is added, the more conducive it is to the precipitation of benzenesulfonamide chitosan, but the amount added should not be too much, and an appropriate and sufficient amount of lithium hydroxide is preferably added. The volume ratio of benzenesulfonyl chloride to N,N-dimethylformamide is 51:200; the volume ratio of acetone to N,N-dimethylformamide solution is 1:1.

[0046] 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;

[0047] The amount of polyvinylidene fluoride added is 1% to 10% by weight (based on the mass of the mixed organic solvent of N,N-dimethylacetamide and tetrahydrofuran), preferably 5% by weight. The mass of benzenesulfonamidated chitosan is 1% to 10% by weight, preferably 5% by weight, based on the mass of the polyvinylidene fluoride added to S2. The mass ratio of lithium bis(fluorosulfonyl)imide to polyvinylidene fluoride is (2 to 2.01):(3 to 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: The polymer solution was evenly spread on a glass culture dish and film-formed in a fume hood at a temperature of 25°C and a wind speed of 30 m / s. The film was vacuum-dried to prepare a transparent composite polymer electrolyte with a thickness of 45 to 55 μm and a smooth surface.

[0049] The polymer solution is cast onto a smooth, flat glass petri dish. The film formation time is 24-25 hours, and the vacuum drying temperature is 55-60°C for 27-30 hours. The goal is to remove the solvent from the solution. Increasing or decreasing the film formation time, drying temperature, and drying time will change the solvent content of the final electrolyte. A too low solvent content will reduce the electrolyte's ionic conductivity, causing excessive polarization during battery cycling and shortening battery life. A too high solvent content will increase the ionic conductivity but increase side reactions between the solvent and the electrode, reducing the stability of the electrolyte interface and, consequently, the battery's cycle life. Therefore, controlling the solvent content in the electrolyte is a key factor in electrolyte performance.

[0050] The prepared composite polymer solid electrolyte is used to assemble a solid-state lithium metal battery: in an argon-filled glove box, the negative electrode shell, spring, gasket, and negative lithium sheet are placed in order. The composite polymer solid electrolyte is then applied to the negative lithium sheet. The positive electrode sheet is then placed, covered with the positive electrode shell, and the battery is compressed. The positive electrode sheet can be selected from lithium nickel cobalt manganese oxide or lithium iron phosphate.

[0051] Example 1

[0052] A method for preparing a composite polymer solid electrolyte comprises the following steps:

[0053] S1. In an ice bath, add 7.65 ml of benzenesulfonyl chloride to 30 ml of N,N-dimethylformamide and stir to form a benzenesulfonyl chloride N,N-dimethylformamide solution. Then, add 1.615 g of chitosan powder to this solution and stir to disperse the chitosan in the N,N-dimethylformamide solution. Simultaneously, add 0.012 g of lithium hydroxide as an alkaline catalyst. Under a nitrogen atmosphere, stir at 30°C for 48 hours to carry out the synthesis reaction. Centrifuge the reaction solution to obtain a supernatant. Add 0.96 g of lithium hydroxide to the supernatant until the lithium hydroxide is completely dissolved. Then, add 30 ml of acetone solution to precipitate. The resulting precipitate is vacuum dried at 60°C for 10 hours to obtain soluble benzenesulfonamidated chitosan.

[0054] S2. Prepare a polymer solution in an argon-filled glove box. Dissolve 0.4517 g of polyvinylidene fluoride (PVDF), 0.0226 g of benzenesulfonamide chitosan (5 wt.% of PVDF), and 0.301 g of lithium bis(fluorosulfonamide)imide (LiFSI) in a mixed solvent consisting of 3 ml of N,N-dimethylacetamide and 7 ml of tetrahydrofuran. Stir until the solutes are completely dissolved, forming a composite polymer solution.

[0055] S3. Pour the polymer solution into a smooth, flat glass dish, spreading it evenly across the bottom of the dish. Allow the solution to form a film in a fume hood for 24 hours. Remove the electrolyte membrane from the dish surface before transferring it to a vacuum drying oven. Dry it at 60°C for 27 hours, flipping the electrolyte membrane over after the 24th hour. Once the drying is complete, a composite polymer solid electrolyte is obtained.

[0056] Example 2

[0057] A method for preparing a composite polymer solid electrolyte comprises the following steps:

[0058] S1. In an ice bath, add 7.65 ml of benzenesulfonyl chloride to 30 ml of N,N-dimethylformamide and stir to form a benzenesulfonyl chloride N,N-dimethylformamide solution. Then, add 1.615 g of chitosan powder to this solution and stir to disperse the chitosan in the N,N-dimethylformamide solution. Simultaneously, add 0.012 g of lithium hydroxide as an alkaline catalyst. Under a nitrogen atmosphere, stir at 30°C for 48 hours to carry out the synthesis reaction. Centrifuge the reaction solution to obtain a supernatant. Add 0.96 g of lithium hydroxide to the supernatant until the lithium hydroxide is completely dissolved. Then, add 30 ml of acetone solution to precipitate. The resulting precipitate is vacuum dried at 60°C for 10 hours to obtain soluble benzenesulfonamidated chitosan.

[0059] S2. Prepare a polymer solution in an argon-filled glove box. Dissolve 0.4517 g of polyvinylidene fluoride (PVDF), 0.0226 g of benzenesulfonamide chitosan (5 wt.% of PVDF), and 0.301 g of lithium bis(fluorosulfonamide)imide (LiFSI) in a mixed solvent consisting of 3 ml of N,N-dimethylacetamide and 7 ml of tetrahydrofuran. Stir until the solutes are completely dissolved, forming a composite polymer solution.

[0060] S3. Pour the polymer solution into a smooth, flat glass dish, so that it is evenly distributed and covers the bottom of the glass dish. Place the film in a fume hood for 24 hours. Before transferring to a vacuum drying oven, remove the electrolyte membrane from the surface of the culture dish and dry it at 60°C for 30 hours. At the 27th hour, turn the electrolyte membrane over and wait until drying is complete to obtain a composite polymer solid electrolyte. The charge transfer impedance of this electrolyte is 668Ω (see attached). Figure 15 ); assembled lithium symmetric battery at 0.1mAcm -2 -0.1mAh cm -2 After 200 cycles under the test parameters, the polarization voltage is 125mV (see attached Figure 16 ).

[0061] Solid-state lithium metal battery assembly:

[0062] A battery was assembled using the composite polymer solid electrolyte prepared in Example 1 as the electrolyte:

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

[0064] Figure 1 In the figure, the blue curve is the Fourier transform infrared spectrum of chitosan, and the red curve is the Fourier transform infrared spectrum of benzenesulfonamidated chitosan. Figure 1 The results showed that new absorption peaks appeared at 1500, 1314 and 1196 wavenumbers on the chitosan molecule, corresponding to the benzene ring functional groups, -SO2- and -SN-, respectively, indicating that chitosan was successfully benzenesulfonamidated.

[0065] Depend on Figure 2 The SEM images of chitosan show that the morphology of chitosan is mainly flake-like, with irregular shape and uneven size.

[0066] Depend on Figure 3 The SEM images of the synthesized benzenesulfonamide chitosan showed that the synthesized benzenesulfonamide chitosan powder was in the form of polyhedral particles with a particle size distribution of 8.5 to 50 μm, mainly blocky particles of about 30 μm. Compared with chitosan, it has a more uniform morphology.

[0067] Depend on Figure 4 、 Figure 5 The SEM images of the surface and cross-section of the composite polymer solid electrolyte respectively show that the electrolyte surface is smooth, flat, dense and non-porous, and has a thickness of 50μm. Figure 6 Visual images of the electrolyte show transparent, smooth and soft properties, indicating that the electrolyte can form good contact with the electrode interface.

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

[0069] The tensile properties of the electrolyte were tested using an electronic universal material testing machine (Istron 5965). The dimensions of the tested electrolyte material were: 7 cm long, 1 cm wide, and 0.05 mm thick. The instrument tensile rate was set at 10 mm min. -1 .Depend on Figure 8Mechanical property testing of the electrolyte shows that the SCS composite polymer solid electrolyte has a tensile stress of 1.4 MPa and a tensile strain of 287.8%, while the CS composite polymer solid electrolyte has a tensile stress and strain of 1.3 MPa and 174.8%, respectively. The SCS composite polymer solid electrolyte exhibits excellent mechanical properties. These excellent mechanical properties can effectively inhibit lithium dendrites from penetrating the electrolyte separator, preventing short circuits during battery operation.

[0070] In order to study the effect of composite polymer solid electrolyte on the dynamic characteristics of lithium ion transport, experiments were carried out to measure the ionic conductivity and lithium ion transference number at different temperatures.

[0071] Depend on Figure 9 As shown in the figure, steel symmetrical cells were assembled using composite polymer solid electrolytes with different fillers, and electrochemical impedance spectroscopy was performed on each cell. The test parameters were as follows: frequency range 0.1-100000 Hz, AC voltage amplitude 5 mV. As shown in the figure, the ionic conductivity of the SCS composite polymer solid electrolyte changes linearly with temperature. In addition, the SCS composite polymer solid electrolyte has a 1.35×10 -3 S cm -1 The high lithium ion conductivity is higher than that of CS composite polymer solid electrolyte (1.03×10 -3 S cm -1 .

[0072] Depend on Figure 10 As shown in the figure, the lithium ion migration number of the composite electrolyte was obtained by steady-state current method. The test steps include electrochemical impedance spectroscopy and IT curve test. The electrochemical frequency impedance test range is 0.1~100000Hz, the AC voltage amplitude is 5mV; the IT curve test parameters are as follows: initial voltage 10mV, test time 1000s, sensitivity 10 -3 Electrochemical impedance spectroscopy was measured before and after the IT test, as well as the current before polarization and after planned stabilization. The calculated lithium ion transference number for the SCS composite electrolyte was 0.6, higher than the 0.45 for the CS composite electrolyte. This demonstrates the composite electrolyte's excellent lithium ion transport capability.

[0073] Tafel test Figure 11 As shown in the figure, the test was performed by assembling a lithium symmetric battery (Li|SSE|Li) and performing a linear scan at a scan rate of 10mV / s in the polarization voltage range of -0.2V to 0.2V (relative to the open circuit potential) to obtain the Tafel plots of the anode (lithium stripping) and cathode (lithium deposition). The exchange current density j0 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 good reaction kinetics at the interface between the composite electrolyte and the lithium metal negative electrode.

[0074] LSV curve is as follows Figure 12 As shown, the test was performed on a steel-to-lithium battery with a sweep rate of 1 mV / s over a voltage range of 2 to 6 V. The LSV curve shows a wide electrochemical stability window for 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. This demonstrates that the composite polymer solid electrolyte has good electrochemical stability and is suitable for high-voltage cathodes.

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

[0076] Depend on Figure 13 The results show that the battery using the SCS composite polymer solid electrolyte has a stable overpotential of around 50mV, indicating good interfacial stability between the composite electrolyte and the lithium metal anode. At this current density, lithium ions can be uniformly reduced and deposited on the lithium metal surface. Moreover, after 500 hours of continuous cycling, the battery polarization potential remains relatively stable, indicating good lithium deposition / stripping behavior.

[0077] Depend on Figure 14 SEM images of the lithium metal anode surface after cycling using different composite polymer solid electrolyte batteries show that the lithium metal surface of the battery using the SCS composite polymer solid electrolyte (Figure a) exhibits a smooth morphology, while the lithium metal surface of the battery using the CS composite polymer solid electrolyte (Figure b) is uneven, with large lithium deposits. This demonstrates the excellent lithium dendrite suppression capability of the SCS composite polymer solid electrolyte.

[0078] The composite polymer solid electrolyte produced by the present invention has a uniform material, smooth and soft texture. The addition of benzenesulfonamide chitosan filler increases the mechanical strength of the electrolyte and improves room-temperature ionic conductivity. Furthermore, the composite electrolyte exhibits good interfacial properties with the lithium metal negative electrode, ensuring long-term stable battery cycling.

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 in an ice bath 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 to react; centrifuging the reaction solution to obtain a supernatant, adding lithium hydroxide to the supernatant, and then adding acetone to precipitate, and drying the resulting 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, formed into a film 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 of chitosan and benzenesulfonyl chloride in an N,N-dimethylformamide solution under the action of the alkaline catalyst is carried out at a reaction temperature of 28-32°C and a reaction time of 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 the 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 above-mentioned 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 to 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.

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