A solid-state electrolyte based on cellulose derivatives and a preparation method and application thereof

Abstract

The application discloses a cellulose derivative-based solid-state electrolyte and a preparation method and application thereof. The preparation method of the cellulose derivative-based solid-state electrolyte comprises the following steps: S1, cellulose and an acylating agent are subjected to an acylation reaction in an ionic liquid or a mixed solution of an ionic liquid and an organic solvent to obtain a cellulose derivative; S2, a reaction solution after the reaction in the step S1 is added into a precipitant, and the cellulose derivative is obtained through precipitation; S3, the cellulose derivative and a lithium salt are dissolved in a solvent to obtain an electrolyte solution, the electrolyte solution is scraped and coated into a film, and the film is dried to obtain the cellulose derivative-based solid-state electrolyte. Through the extension of the chemical structure of the cellulose skeleton, the transportation of lithium ions is improved by the introduction and regulation of effective functional groups, the ionic conductivity is improved, the mechanical performance is not damaged, the surface stability of the solid-state electrolyte is improved, and the cycle performance and service life of the solid-state battery are improved. The thickness of the solid-state electrolyte is controllable, and the solid-state electrolyte can be thinned.

Description

Technical Field

[0001] This invention relates to a solid electrolyte based on cellulose derivatives, its preparation method and application, belonging to the field of lithium metal battery technology. Background Technology

[0002] The development of lithium battery technology is revolutionizing human life. Lithium-ion batteries, due to their superior performance compared to lead-acid, nickel-cadmium, and nickel-metal hydride batteries, have achieved successful and widespread commercial applications, such as in portable electronic devices and electrically powered vehicles. Using lithium metal instead of the graphite anode in lithium-ion batteries will result in higher energy density, but will also introduce safety issues such as flammability. Solid-state electrolytes offer advantages such as high mechanical strength, non-flammability, a wide operating temperature range, and a large electrochemical stability window. All-solid-state lithium batteries assembled from solid-state electrolytes hold the promise of solving the safety and lithium dendrite problems associated with traditional organic liquid electrolytes. Therefore, due to their combination of high energy density and high safety, solid-state lithium metal batteries have become the most promising next-generation energy storage system.

[0003] Solid-state electrolytes are crucial components of solid-state lithium metal batteries, and their development has a vital impact on their practical applications. Currently, solid-state electrolytes mainly include polymer solid-state electrolytes, oxide solid-state electrolytes, sulfide solid-state electrolytes, and halide solid-state electrolytes. Among them, polymer solid-state electrolytes, with their low cost, ease of preparation, and high flexibility, exhibit unique application advantages. Ether-based polymer electrolytes, represented by PEO, have already been successfully applied in lithium-ion batteries.

[0004] Polymer solid electrolytes typically suffer from low room-temperature conductivity. This is because lithium ions are primarily transported in amorphous regions via the movement and relaxation of polymer chains. Methods to improve the room-temperature conductivity of polymer solid electrolytes generally focus on: 1. reducing polymer crystallinity and increasing the proportion of amorphous regions (block copolymers, inorganic fillers, plasticizers); 2. introducing fast lithium-ion transport regions (gel electrolytes, electrolyte fillers). However, while these methods improve room-temperature conductivity, they also reduce the strength of the polymer electrolyte, posing safety risks and compromising electrochemical stability. The trade-off between room-temperature conductivity and mechanical properties remains a key factor limiting the development of polymer solid electrolytes.

[0005] Therefore, developing a polymer solid electrolyte that combines high room temperature conductivity, high mechanical strength, and high electrochemical stability is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a cellulose derivative-based solid electrolyte to obtain a polymer solid electrolyte that combines high room temperature conductivity, high mechanical strength, and high electrochemical stability. This invention is based on the extended chemical structure of the polymer backbone, and improves lithium ion transport by introducing effective functional groups, thereby increasing ionic conductivity without compromising mechanical properties.

[0007] This invention uses cellulose as a polymer matrix and prepares a series of cellulose derivatives with different side chain functional groups through homogeneous derivatization. The cellulose derivatives are compounded with lithium salts and plasticizers to obtain cellulose derivative-based solid electrolytes with high room temperature conductivity, high electrochemical stability and high mechanical strength.

[0008] The method for preparing the cellulose derivative-based solid electrolyte provided by this invention includes the following steps:

[0009] S1. In an ionic liquid or a mixture of an ionic liquid and an organic solvent, cellulose is reacted with an acylation reagent to obtain a cellulose derivative.

[0010] S2. The reaction solution after step S1 is added to the precipitant, and the cellulose derivative is obtained by precipitation.

[0011] S3. Dissolve the cellulose derivative and lithium salt in a solvent to obtain an electrolyte solution, coat it into a film, and dry it to obtain the cellulose derivative-based solid electrolyte.

[0012] In the above preparation method, in step S1, the cellulose is selected from at least one of the following: microcrystalline cellulose, cotton pulp, cotton, wood pulp fiber, wood pulp, bamboo pulp, cellulose filter paper, newspaper, defatted cotton, bagasse, wood, bacterial cellulose, plant straw, and cellulose obtained from plant straw.

[0013] The mass ratio of the ionic liquid to the organic solvent is 1:0.01 to 1, preferably 1:0.5 to 1;

[0014] The organic solvent is selected from one or more combinations of the following: N,N-dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone;

[0015] The ionic liquid is a molten salt with a melting point below 100°C formed by substituted or unsubstituted imidazole cations or pyridine cations and anions.

[0016] The substituents on the imidazole cation or the pyridine cation are: C1-6 alkyl or C1-6 alkenyl;

[0017] The anions are halide ions, alkyl acid ions (formate ions, acetate ions, etc.), and organophosphate ions (alkyl phosphate ions, dialkyl phosphate ions, etc.).

[0018] In the above preparation method, in step S1, the ionic liquid is selected from at least one of the following: 1-ethyl-3-methylimidazolium chloride ionic liquid (EMIMCl), 1-ethyl-3-methylimidazolium bromide ionic liquid (EMIMBr), 1-allyl-3-methylimidazolium chloride ionic liquid (AMIMCl), 1-allyl-3-methylimidazolium bromide ionic liquid (AMIMBr), 1-butyl-3-methylimidazolium chloride ionic liquid (BMIMCl), 1-butyl-3-methylimidazolium bromide ionic liquid (BMIMBr), 1-ethyl-3-methylimidazolium acetate ionic liquid (EMIMAc), 1-allyl-3-methylimidazolium acetate ionic liquid (AMIMAc), 1-butyl-3-methylimidazolium acetate ionic liquid (BMIMAc), N-ethylpyridine chloride ionic liquid (EPyCl), N-ethylpyridine bromide ionic liquid (EPyBr), 1,3-dimethylimidazolium dimethyl phosphate ionic liquid (MMIM). DMP, 1-ethyl-3-methylimidazolium diethyl phosphate ionic liquid (EMIM DEP), 3-methylimidazolium carboxylate ionic liquid (MIMHCOO), N-methylpyridine carboxylate ionic liquid (MPy HCOO), 1-ethyl-3-methylimidazolium carboxylate ionic liquid (EMIMHCOO) and 1-butyl-3-methylimidazolium carboxylate ionic liquid (BMIM HCOO).

[0019] In the above preparation method, in step S1, the acylation reagent is selected from at least one of acetyl chloride, benzoyl chloride, cinnamoyl chloride, N-(chloroacetoxy)succinimide, p-methoxybenzoyl chloride, 3-nitrobenzoyl chloride, acetyl bromide, benzoyl bromide, cinnamoyl bromide, p-methoxybenzoyl bromide, 3-nitrobenzoyl bromide, benzoic anhydride, phthalic anhydride, trimellitic anhydride, succinic anhydride, maleic anhydride, p-toluenesulfonic anhydride, and 3-nitrophthalic anhydride;

[0020] In the above preparation method, in step S1, the molar ratio of the acylation reagent to the glucose unit in the cellulose is 1:0.1-2, preferably 1:0.3-1.

[0021] The acylation reaction is carried out at a temperature of 30–120°C, preferably 60–100°C, for a time of 0.5–12 h, preferably 6–10 h.

[0022] In the above preparation method, in step S2, the precipitant is selected from at least one of water, methanol, ethanol, isopropanol, acetone, a mixed solvent of water and methanol, a mixed solvent of water and ethanol, and a mixed solvent of water and isopropanol.

[0023] The method further includes the step of washing the cellulose derivative with a cleaning agent;

[0024] The cleaning agent is selected from at least one of water, methanol, ethanol, isopropanol, acetone, a mixed solvent of water and methanol, a mixed solvent of water and ethanol, and a mixed solvent of water and isopropanol.

[0025] In the above preparation method, in step S3, the lithium salt is selected from at least one of lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate.

[0026] The solvent is selected from at least one of N,N-dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, toluene, dichloromethane, tetrahydrofuran, chloroform, N,N-dimethylimidazolinone, and N-methylpyrrolidone.

[0027] In the above preparation method, in step S3, the mass ratio of the lithium salt to the cellulose derivative is 1:0.2 to 10, preferably 1:0.5 to 5 or 1:0.5 to 1.

[0028] In the above preparation method, in step S3, the mass ratio of the solvent to the cellulose derivative is 1:0.01 to 0.3.

[0029] In the above preparation method, step S3 further includes the following step (a) or (b):

[0030] (a) Immerse a cellulose derivative-based solid electrolyte in a plasticizing bath, remove it and heat it to evaporate the solvent to obtain a plasticized solid electrolyte membrane, which increases flexibility, improves the interfacial contact with the electrode, and provides space for ion movement within the electrolyte, thereby improving ionic conductivity.

[0031] The plasticizing bath is a mixed solution of acetonitrile and carbonate or a mixed solution of acetonitrile and phosphate, with a mass ratio of 1:0.05 to 5, preferably 1:1 to 2.

[0032] Preferably, the plasticizing bath is selected from at least one of the following: a mixed solution of acetonitrile and ethylene carbonate, a mixed solution of acetonitrile and propylene carbonate, a mixed solution of acetonitrile and dimethyl carbonate, a mixed solution of acetonitrile and diethyl carbonate, a mixed solution of acetonitrile and methyl ethyl carbonate, a mixed solution of acetonitrile and trimethyl phosphate, and a mixed solution of acetonitrile and triethyl phosphate.

[0033] (b) Add the composite component to the electrolyte solution in step (3), coat it into a film, and dry it to prepare a composite solid electrolyte membrane;

[0034] The composite components are selected from, but are not limited to, homopolymers, copolymers or mixtures of polymers such as polyvinylidene fluoride, polyimide, polyacrylate, polyacrylonitrile, and polyether, as well as nanoparticles.

[0035] Preferably, the nanoparticles include, but are not limited to, one or more of the following: nano-silica, nano-zirconium dioxide, nano-titanium dioxide, nano-montmorillonite, carbon nanotubes, carbon nanofibers, graphene, and nano-apatite, with a particle size of 5 nanometers to 50 micrometers.

[0036] Based on the cellulose derivative-based solid electrolyte provided by the present invention, a further all-solid-state lithium battery is provided, comprising a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode, wherein the solid electrolyte is the cellulose derivative-based solid electrolyte provided by the present invention.

[0037] The thickness of the cellulose derivative-based solid electrolyte is 10–500 micrometers;

[0038] The positive electrode is made of a positive electrode active material, a binder, and a conductive agent;

[0039] The positive electrode active material may be LiFePO4, LiCoO2, LiNiO2, LiMn2O4, or LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2;

[0040] The adhesive may be polyvinylidene fluoride (PVDF), homopolymer of vinylidene fluoride and copolymer of vinylidene fluoride, homopolymer of vinylidene fluoride and copolymer of hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene, polyamide, polyethylene oxide, and a mixture of two or three of the above adhesives.

[0041] The conductive agent may be carbon black, conductive graphite, carbon fiber, carbon nanotubes, graphene, or a mixture of two or three of the above conductive agents.

[0042] The negative electrode is made of elemental lithium metal or a lithium metal alloy.

[0043] The present invention has the following beneficial technical effects:

[0044] (1) This invention improves lithium-ion transport by expanding the chemical structure of the cellulose skeleton and by introducing and regulating effective functional groups, thereby increasing ionic conductivity without damaging mechanical properties, improving the surface stability of solid electrolytes, and improving the cycle performance and lifespan of solid batteries.

[0045] (2) The preparation method of the present invention is simple and easy to combine with existing battery production processes for large-scale production.

[0046] (3) The thickness of the solid electrolyte of the present invention is controllable, which can realize the ultra-thin solid electrolyte. Attached Figure Description

[0047] Figure 1 The impedance spectrum is shown for the cellulose phthalate electrolyte film prepared in Example 1 of this invention.

[0048] Figure 2 The stress-strain curve of the cellulose phthalate electrolyte film prepared in Example 1 of the present invention.

[0049] Figure 3 The charge-discharge curves of the cellulose phthalate electrolyte film Li||Li symmetric battery prepared in Example 1 of this invention are shown.

[0050] Figure 4 The charge-discharge curves of the all-solid-state lithium battery prepared in Example 4 of this invention are shown.

[0051] Figure 5 The linear voltammetric scan curve is shown for the cellulose phthalate electrolyte membrane prepared in Example 1 of this invention. Detailed Implementation

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0053] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0054] Example 1: Preparation of cellulose phthalate solid electrolyte

[0055] 1. Preparation of cellulose phthalates

[0056] 5g of cotton pulp was weighed and dissolved in a mixed solution of 57g of ionic liquid (AMIMCl) and 38g of DMF. 10g of phthalic anhydride (PAA, in which the molar ratio of PAA to glucose units in cotton pulp is 1:0.5) was weighed and dissolved in the above mixed solution. The mixture was stirred at 80°C for 10h to prepare a cellulose derivative solution.

[0057] The cellulose derivative solution was precipitated in isopropanol and washed five times alternately with isopropanol and water.

[0058] The washed product was dried in an oven at 60°C to obtain cellulose phthalate, a cellulose derivative.

[0059] 2. Preparation of cellulose derivative electrolytes

[0060] Weigh 0.5 g of cellulose phthalate and 1 g of lithium bis(trifluoromethanesulfonyl)imide (mass ratio of which to cellulose phthalate is 1:0.5) and dissolve them in 8.5 g of DMF. Stir at room temperature to obtain a homogeneous and transparent solution. Coat the solution onto a flat aluminum foil to form a film thickness of 1000 micrometers. Evaporate the solvent in a 100°C forced-air oven until the electrolyte membrane is completely dry, then transfer it to a glove box and continue drying on a 100°C hot plate for 2 hours.

[0061] Weigh 4g of acetonitrile and 6g of ethylene carbonate in a glove box, mix them at room temperature to prepare a plasticizing bath, immerse the above electrolyte membrane in the plasticizing bath, remove it after 10 minutes, and evaporate the acetonitrile solvent on a 60℃ hot plate to obtain a cellulose phthalate electrolyte membrane.

[0062] 3. Performance testing of cellulose phthalate electrolyte membranes

[0063] 1) Ionic conductivity

[0064] In the glove box, steel sheet button batteries are assembled using plasticized cellulose phthalate electrolyte membranes. The specific method is as follows: two steel sheets are placed on the upper and lower sides of the cellulose phthalate electrolyte membrane to form a sandwich-like structure. The sandwich-like structure is then placed in the electrode shell to assemble the steel sheet button battery.

[0065] Impedance spectra of cellulose phthalate electrolyte films were obtained at room temperature and analyzed using the formula... Calculate, where σ is the conductivity, d is the film thickness, and R is the capacitance. b Let S be the bulk resistance of the thin film, and S be the area of ​​the thin film. The results are as follows: Figure 1 As shown in the figure, the cellulose phthalate electrolyte film prepared by this invention has a room temperature conductivity as high as 1.09 × 10⁻⁶. -3 S cm -1 .

[0066] 2) Mechanical properties

[0067] The film sample was cut into strips of 1cm × 5cm and vertically clamped in the tensile fixture of a universal testing machine for mechanical tensile property testing. The results are as follows: Figure 2 As shown, the tensile strength of the cellulose phthalate electrolyte film can reach 12 MPa, and the elongation at break can reach 80%. This indicates that the cellulose phthalate electrolyte film prepared by this invention has high mechanical strength and good flexibility.

[0068] 3) Cyclic charge-discharge performance

[0069] Assemble a lithium symmetric battery: In a glove box, assemble a lithium symmetric battery using a plasticized cellulose phthalate electrolyte film. The specific method is as follows: place two lithium metal sheets on the upper and lower sides of the cellulose phthalate electrolyte film respectively, and place the other side of the lithium metal sheet in contact with a stainless steel sheet (the stainless steel sheet is slightly smaller than the lithium sheet) to form a sandwich-like structure. Place the sandwich-like structure into the electrode shell to assemble a lithium symmetric battery.

[0070] Lithium-ion symmetric battery testing: The lithium-ion symmetric battery was tested at 25℃ with a constant current of 0.1mA / cm². 2 The device is charged and discharged, with an alternating time interval of 2 hours.

[0071] Figure 3 The cyclic charge-discharge curves of the cellulose phthalate electrolyte film Li||Li symmetric battery prepared in this embodiment show that at 0.1 mA / cm 2 At the specified current density, the voltage of the symmetric cell remained stable throughout the 1000-hour test, with an overpotential of only 25 mV. This indicates that the electrolyte film can promote a homogeneous and stable deposition process of Li and effectively suppress the growth of Li dendrites in the Li symmetric cycling experiment.

[0072] Example 2: Preparation of cellulose acetate solid electrolyte

[0073] 1. Preparation of cellulose acetate

[0074] Weigh 5g of cotton pulp and dissolve it in a mixed solution of 57g of ionic liquid (AMIMCl) and 38g of DMF. Weigh 10g of acetic anhydride (with a molar ratio of 1:0.3 to glucose units in cotton pulp) and dissolve it in the above mixed solution. Stir the mixture at 80°C for 10h to prepare a cellulose derivative solution.

[0075] The cellulose derivative solution was precipitated in isopropanol and washed five times alternately with isopropanol and water.

[0076] The washed product was dried in an oven at 60°C to obtain cellulose acetate, a cellulose derivative.

[0077] 2. Preparation of cellulose acetate electrolyte

[0078] Weigh 0.5g of cellulose acetate and 1g of lithium bis(trifluoromethanesulfonyl)imide and dissolve them in 8.5g of DMF. Stir at room temperature to obtain a homogeneous and transparent solution. Coat the solution onto a flat aluminum foil to form a film thickness of 1000 micrometers. Evaporate the solvent in a 100°C forced-air oven until the electrolyte membrane is completely dry. Transfer the membrane to a glove box and continue drying on a 100°C hot plate for 2 hours.

[0079] Weigh 4g of acetonitrile and 6g of ethylene carbonate in a glove box, mix them at room temperature to prepare a plasticizing bath, immerse the above electrolyte membrane in the plasticizing bath, remove it after 10 minutes, and evaporate the acetonitrile solvent on a 60℃ hot plate to obtain a cellulose acetate electrolyte membrane.

[0080] 3. Performance of cellulose acetate electrolyte membranes

[0081] The room temperature conductivity of the cellulose acetate electrolyte membrane is 1.45 × 10⁻⁶. -4 S cm -1 It can operate stably for 50 hours in a Li symmetric cell with a mechanical strength of 1 MPa.

[0082] Example 3: Preparation of cellulose benzoate solid electrolyte

[0083] 1. Preparation of cellulose benzoate

[0084] Weigh 5g of cotton pulp and dissolve it in a mixed solution of 57g of ionic liquid (AMIMCl) and 38g of DMF. Weigh 8g of benzoyl chloride (with a molar ratio of 1:0.6 to glucose units in cotton pulp) and dissolve it in the above mixed solution. Stir the reaction at 80℃ for 10h to prepare a cellulose derivative solution.

[0085] The cellulose derivative solution was precipitated in isopropanol and washed five times alternately with isopropanol and water.

[0086] The washed product was dried in an oven at 60°C to obtain cellulose benzoate, a cellulose derivative.

[0087] 2. Preparation of cellulose benzoate electrolyte

[0088] Weigh 0.5 g of cellulose benzoate and 1 g of lithium bis(trifluoromethanesulfonyl)imide and dissolve them in 8.5 mL of DMF. Stir at room temperature to obtain a homogeneous and transparent solution. Coat the solution onto a flat aluminum foil to form a film thickness of 1000 micrometers. Evaporate the solvent in a 100°C forced-air oven until the electrolyte membrane is completely dry. Transfer the membrane to a glove box and continue drying on a 100°C hot plate for 2 hours.

[0089] Weigh 4g of acetonitrile and 6g of ethylene carbonate in a glove box, mix them at room temperature to prepare a plasticizing bath, immerse the above electrolyte membrane in the plasticizing bath, remove it after 10 minutes, and evaporate the acetonitrile solvent on a 60°C hot plate to obtain a cellulose benzoate electrolyte membrane.

[0090] 3. Performance of cellulose benzoate electrolyte membranes

[0091] The room temperature conductivity of the cellulose benzoate electrolyte membrane is 2.10 × 10⁻⁶. -4 S cm -1It can operate stably for 100 hours in a Li symmetric cell with a mechanical strength of 5 MPa.

[0092] Comparative Example 1: Preparation of Cellulose Solid Electrolytes

[0093] 1. Preparation of cellulose solid electrolyte

[0094] Weigh 0.5g of microcrystalline cellulose and 1g of lithium bis(trifluoromethanesulfonyl)imide and dissolve them in 8.5g of DMF. Stir at room temperature to obtain a suspension. Coat the solution onto a flat aluminum foil to form a film thickness of 1000 micrometers. Evaporate the solvent in a 100°C forced-air oven until the electrolyte membrane is completely dry. Transfer the membrane to a glove box and continue drying on a 100°C hot plate for 2 hours.

[0095] Weigh 4g of acetonitrile and 6g of ethylene carbonate in a glove box, mix them at room temperature to prepare a plasticizing bath, immerse the above electrolyte membrane in the plasticizing bath, remove it after 10 minutes, and evaporate the acetonitrile solvent on a 60℃ hot plate to obtain a cellulose solid electrolyte membrane.

[0096] 2. Performance of cellulose solid electrolyte membranes

[0097] The room temperature conductivity of cellulose electrolyte membranes is less than 1×10⁻⁶. -6 S cm -1 It cannot operate in Li-symmetric cells and has a mechanical strength of 10 MPa.

[0098] Example 4: Preparation of all-solid-state lithium batteries

[0099] 1. Preparation of positive electrode

[0100] The positive electrode material LiFePO4, conductive agent SP, and binder PVDF were mixed in a commercial mass ratio of LiFePO4:SP:PVDF = 8:1:1. N-methylpyrrolidone (NMP) was added to prepare a slurry. The slurry was coated on aluminum foil (the aluminum foil was used as the current collector) and dried at 60°C for 24 hours to prepare the positive electrode.

[0101] 2. Assemble all-solid-state lithium batteries

[0102] Assemble an all-solid-state lithium battery in a glove box. Place the positive electrode sheet into the positive electrode shell, and stack the cellulose phthalate electrolyte film prepared in Example 1 on top of it in direct contact with it. Place a lithium metal sheet on the other side of the cellulose derivative electrolyte film, and place a stainless steel sheet (slightly smaller than the lithium sheet) on the lithium sheet to form a sandwich-like structure. Cover with the negative electrode shell and assemble into a full battery.

[0103] 3. Testing of all-solid-state lithium batteries

[0104] The solid-state lithium battery was tested at a temperature of 25°C, and the constant charge-discharge test voltage range was 2.4–4.0V.

[0105] Figure 4 The charge-discharge curves of the all-solid-state lithium battery prepared in this embodiment are shown. The positive electrode active material is LiFePO4, the negative electrode material is metallic lithium, and the charge-discharge current density is 0.1C. It can be seen that the all-solid-state lithium battery prepared by the cellulose phthalate electrolyte film of this invention has small internal polarization and high discharge specific capacity (165mAh / g), and the coulombic efficiency is close to 100%. The stable cycle can reach up to 1000 cycles.

[0106] 4. Testing the electrochemical window

[0107] The electrochemical temperature window of the battery gel electrolyte was constructed by placing a cellulose phthalate electrolyte film between a lithium sheet and a stainless steel sheet, with a scanning voltage range of 0-6V and a scanning speed of 1mV / s.

[0108] Figure 5 The linear voltammetric scan curve of the cellulose phthalate electrolyte film prepared in Example 1 shows that the cellulose phthalate electrolyte film of the present invention can be stabilized up to 4.3V.

Claims

1. A method for preparing a cellulose derivative-based solid electrolyte, comprising the following steps S1-S3-a or S1-S3-b: S1. In an ionic liquid or a mixture of an ionic liquid and an organic solvent, cellulose is reacted with an acylation reagent to obtain a cellulose derivative. The acylation reagent is selected from at least one of benzoyl chloride, cinnamoyl chloride, N-(chloroacetoxy)succinimide, p-methoxybenzoyl chloride, 3-nitrobenzoyl chloride, benzoyl bromide, cinnamoyl bromide, p-methoxybenzoyl bromide, 3-nitrobenzoyl bromide, benzoic anhydride, phthalic anhydride, trimellitic anhydride, succinic anhydride, maleic anhydride, p-toluenesulfonic anhydride, and 3-nitrophthalic anhydride; S2. The reaction solution after step S1 is added to the precipitant, and the cellulose derivative is obtained by precipitation. S3-a. Dissolve the cellulose derivative and lithium salt in a solvent to obtain an electrolyte solution, coat it into a film, dry it, immerse it in a plasticizing bath, remove it, and heat it to evaporate the solvent to obtain a plasticized solid electrolyte membrane. The plasticizing bath is a mixed solution of acetonitrile and carbonate or a mixed solution of acetonitrile and phosphate, with a mass ratio of 1:0.1~10. S3-b: Dissolve the cellulose derivative, lithium salt and composite components in a solvent to obtain an electrolyte solution, coat it into a film and dry it to obtain the cellulose derivative-based solid electrolyte; The composite component is selected from homopolymers, copolymers, or mixtures of polyvinylidene fluoride, polyimide, polyacrylate, polyacrylonitrile, and polyether polymers.

2. The preparation method according to claim 1, characterized in that: In step S1, the cellulose is selected from at least one of the following: microcrystalline cellulose, cotton pulp, cotton, wood pulp fiber, wood pulp, bamboo pulp, cellulose filter paper, newspaper, defatted cotton, bagasse, wood, bacterial cellulose, plant straw, and cellulose obtained from plant straw. The mass ratio of the ionic liquid to the organic solvent is 1:0.01~1; The organic solvent is selected from one or more combinations of the following: N,N-dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; The ionic liquid is a molten salt with a melting point below 100 °C formed by substituted or unsubstituted imidazole cations or pyridine cations and anions; The substituents on the imidazole cation or the pyridine cation are: C1-6 alkyl or C1-6 alkenyl; The anion is a halide ion, an alkyl acid ion, or an organophosphate ion.

3. The preparation method according to claim 2, characterized in that: In step S1, the ionic liquid is selected from at least one of the following ionic liquids: 1-ethyl-3-methylimidazolium chloride ionic liquid, 1-ethyl-3-methylimidazolium bromide ionic liquid, 1-allyl-3-methylimidazolium chloride ionic liquid, 1-allyl-3-methylimidazolium bromide ionic liquid, 1-butyl-3-methylimidazolium chloride ionic liquid, 1-butyl-3-methylimidazolium bromide ionic liquid, 1-ethyl-3-methylimidazolium acetate ionic liquid, 1-allyl-3-methylimidazolium chloride ionic liquid, 1-butyl-3-methylimidazolium bromide ionic liquid, 1-ethyl-3-methylimidazolium acetate ionic liquid, 1-allyl-3-methylimidazolium chloride ionic liquid, 1-butyl-3-methylimidazolium bromide ionic liquid, 1-ethyl-3-methylimidazolium acetate ionic liquid, 1-allyl-3-methylimidazolium chloride ionic liquid, 1-ethyl ... Ionic liquids of 1-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, N-ethylpyridine chloride, N-ethylpyridine bromide, 1,3-dimethylimidazolium dimethyl phosphate, 1-ethyl-3-methylimidazolium diethyl phosphate, 3-methylimidazolium carboxylate, N-methylpyridine carboxylate, 1-ethyl-3-methylimidazolium carboxylate, and 1-butyl-3-methylimidazolium carboxylate.

4. The preparation method according to any one of claims 1-3, characterized in that: In step S1, the acylation reaction is carried out at a temperature of 30~120℃ for a time of 0.5~12 h.

5. The preparation method according to any one of claims 1-3, characterized in that: In step S2, the precipitant is selected from at least one of water, methanol, ethanol, isopropanol, acetone, a mixed solvent of water and methanol, a mixed solvent of water and ethanol, and a mixed solvent of water and isopropanol. The method further includes the step of washing the cellulose derivative with a cleaning agent; The cleaning agent is selected from at least one of water, methanol, ethanol, isopropanol, acetone, a mixed solvent of water and methanol, a mixed solvent of water and ethanol, and a mixed solvent of water and isopropanol.

6. The preparation method according to any one of claims 1-3, characterized in that: In step S3, the lithium salt is selected from at least one of lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(difluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium hexafluorophosphate. The solvent is selected from at least one of N,N-dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, toluene, dichloromethane, tetrahydrofuran, chloroform, N,N-dimethylimidazolinone, and N-methylpyrrolidone.

7. A cellulose derivative-based solid electrolyte prepared by the method of any one of claims 1-6.

8. The application of the cellulose derivative-based solid electrolyte of claim 7 in the preparation of all-solid-state lithium batteries.

9. An all-solid-state lithium battery, comprising a positive electrode, a negative electrode, and a solid electrolyte disposed between the positive electrode and the negative electrode, wherein the solid electrolyte is the cellulose derivative-based solid electrolyte of claim 8; The thickness of the cellulose derivative-based solid electrolyte is 10-500 micrometers.

10. The all-solid-state lithium battery according to claim 9, characterized in that: The positive electrode is made of a positive electrode active material, a binder, and a conductive agent; The positive electrode active material is LiFePO4, LiCoO2, LiNiO2, LiMn2O4, or LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2; The negative electrode is made of elemental lithium metal or a lithium metal alloy.

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