Cellulose acetate modified PEO-based solid electrolyte membrane, solid lithium battery and preparation method of cellulose acetate modified PEO-based solid electrolyte membrane

Abstract

The invention relates to the technical field of solid-state lithium batteries, in particular to a cellulose acetate modified PEO-based solid-state electrolyte membrane, a solid-state lithium battery and a preparation method thereof.The preparation method comprises the steps that lithium bis (trifluoromethanesulfonyl) imide, cellulose acetate and polyethylene oxide are dissolved in a solvent, and a mixed solution is obtained; and curing the mixed solution in a mold to obtain the cellulose acetate modified PEO-based solid electrolyte membrane. According to the invention, the cellulose acetate is introduced to modify the polyethylene oxide solid electrolyte, and the prepared cellulose acetate modified PEO-based solid electrolyte membrane can generate a stable solid electrolyte interface rich in Li2O and LiF on the surface of a lithium negative electrode in situ in the application of a solid lithium battery, so that the growth ability of lithium dendrites is effectively inhibited, and the performance of the lithium battery is improved. The interface impedance is reduced, and the operating temperature range of the solid-state lithium battery is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lithium batteries, and in particular to a cellulose acetate-modified PEO-based solid electrolyte membrane, a solid-state lithium battery and a preparation method thereof. Background Art

[0002] Lithium metal is considered to be an ideal choice for the next generation of high energy density negative electrode materials due to its high theoretical capacity of 3860 mAh / g and extremely low electrochemical potential, which is -3.04 V compared to the standard hydrogen electrode. Unlike the lithium ion insertion mechanism used in traditional lithium-ion batteries, lithium metal batteries use Li + / Li 0 Energy conversion is achieved through the direct deposition and dissolution process. This feature makes it far exceed the theoretical specific capacity of commercial graphite negative electrodes, almost 10 times that of commercial graphite negative electrodes.

[0003] However, in the process of electrochemical reduction, the traditional polyethylene oxide-based solid electrolyte, namely PEO-based solid electrolyte, tends to react violently and spontaneously with almost all organic electrolytes due to the high reactivity of lithium metal, and continuously forms an irreversible solid electrolyte interface at the interface between the electrode and the electrolyte, which not only leads to a large loss of active lithium substances, but also significantly reduces the coulombic efficiency of the battery. Most importantly, the disordered deposition of lithium will induce uncontrollable lithium dendrite growth and penetrate the battery separator, causing internal short circuits, thereby causing serious safety problems such as battery spontaneous combustion or explosion. In addition, the disordered deposition and dissolution process of lithium will aggravate the fluctuation of the lithium electrode surface, further promote the growth of lithium dendrites, and produce a large amount of electrically insulating "dead lithium" and accelerate the consumption of electrolyte. The combined effect of these factors will aggravate the battery polarization phenomenon, leading to rapid decline in battery capacity and even serious safety problems. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a cellulose acetate modified PEO-based solid electrolyte membrane, a solid-state lithium battery and a preparation method thereof. The present invention adopts a solvent casting method, uses lithium bis(trifluoromethanesulfonyl)imide, cellulose acetate and polyethylene oxide as raw materials, and prepares a cellulose acetate modified PEO-based solid electrolyte membrane. The present invention introduces cellulose acetate to modify the polyethylene oxide solid electrolyte, and the obtained cellulose acetate modified PEO-based solid electrolyte membrane can generate Li-rich in situ on the surface of the lithium negative electrode in the application of solid-state lithium batteries. 2 The stable solid electrolyte interface of O and LiF not only effectively inhibits the growth of lithium dendrites and reduces the interface impedance, but also broadens the operating temperature range of solid-state lithium batteries.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: The first object of the present invention is to provide a method for preparing a cellulose acetate modified PEO-based solid electrolyte membrane, comprising the following steps: Lithium bis(trifluoromethanesulfonyl)imide, cellulose acetate and polyethylene oxide are dissolved in a solvent. Through electrostatic interaction, the carbonyl groups in cellulose acetate strongly adsorb TFSI. - , accelerating the decomposition of LiTFSI into TFSI - , and obtain a mixed solution; the mass ratio of polyethylene oxide to cellulose acetate is 2:0.01~0.6; among them, cellulose acetate, as a reinforcing agent, can improve the mechanical strength of the cellulose acetate-modified PEO-based solid electrolyte membrane; if its content is too low, the mechanical properties of the cellulose acetate-modified PEO-based solid electrolyte membrane will deteriorate; and because cellulose acetate itself is a non-conductive polymer, if its content is too high, it will dilute the conductive part in polyethylene oxide and reduce Li + migration capabilities.

[0006] The mixed solution is placed in a mold and solidified to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane; during the electrochemical reduction process of the cellulose acetate-modified PEO-based solid electrolyte membrane, the carbonyl group in the cellulose acetate strongly adsorbs TFSI in lithium bistrifluoromethanesulfonyl imide. - , promoting the decomposition of lithium bis(trifluoromethanesulfonyl)imide into TFSI - And form LiF deposition, while TFSI - Directly react with lithium metal to generate Li-rich 2 O and LiF solid electrolyte interface layer.

[0007] Preferably, the mass ratio of polyethylene oxide to cellulose acetate is 2:0.2.

[0008] Preferably, the ethoxy unit EO in polyethylene oxide and the Li + The molar ratio of EO and Li is 14~18:1; if + The molar ratio of EO to Li is lower than this range, which will lead to a significant decrease in the conductivity of the cellulose acetate modified PEO-based solid electrolyte membrane. + Coordinate to form an ionic complex that can migrate; if Li + If the concentration is too high, insufficient EO can provide coordination and form polymers or ineffective coordination, thus limiting the Li + Migration ability; if EO and Li + The molar ratio of Li is higher than this range, which leads to an increase in the crystallinity of the cellulose acetate modified PEO-based solid electrolyte membrane. + Too low a concentration will increase the crystallization tendency of polyethylene oxide and inhibit the amorphous region of polyethylene oxide, which is the Li + The main channel of migration.

[0009] Preferably, the ethoxy unit EO in polyethylene oxide and the Li + The molar ratio is 14~18:1.

[0010] Preferably, the curing conditions are: drying at 50° C. to 60° C. for 48 h to 60 h.

[0011] Preferably, the solvent is selected from anhydrous acetonitrile or N,N-dimethylformamide.

[0012] The second object of the present invention is to provide a cellulose acetate-modified PEO-based solid electrolyte membrane prepared by the above preparation method.

[0013] Preferably, the thickness of the cellulose acetate modified PEO-based solid electrolyte membrane is 50 μm to 500 μm; wherein, if the thickness is less than 50 μm, the mechanical stability of the cellulose acetate modified PEO-based solid electrolyte membrane is reduced, the risk of short circuit is increased, and the interface heterogeneity between the cellulose acetate modified PEO-based solid electrolyte membrane and the solid-state lithium battery electrode is aggravated; on the contrary, if the thickness exceeds 500 μm, the Li + The resistance to migration reduces the energy density of the battery and brings additional challenges to the processing process.

[0014] The third object of the present invention is to provide a solid-state lithium battery, which is made of the following raw materials: a negative electrode shell, a positive electrode sheet, a negative electrode sheet, a positive electrode shell, a spring, a gasket and a cellulose acetate-modified PEO-based solid electrolyte membrane.

[0015] Preferably, the preparation method of the solid-state lithium battery is: Place the negative electrode shell, spring, gasket, and negative electrode sheet in sequence, then cover the negative electrode sheet with the cellulose acetate-modified PEO-based solid electrolyte membrane, then place the positive electrode sheet, and cover with the positive electrode shell.

[0016] Preferably, the positive electrode sheet is selected from a lithium sheet or a lithium iron phosphate sheet, and the negative electrode sheet is selected from a lithium sheet.

[0017] Preferably, the solid-state lithium battery is a lithium iron phosphate battery or a lithium symmetrical battery.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a method for preparing a cellulose acetate modified PEO-based solid electrolyte membrane, wherein the PEO group refers to polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, cellulose acetate and polyethylene oxide are dissolved in a solvent, and the carbonyl group in the cellulose acetate strongly adsorbs TFSI through electrostatic interaction. - , accelerating the decomposition of LiTFSI into TFSI -, obtaining a mixed solution; wherein the mass ratio of polyethylene oxide to cellulose acetate is 2:0.01-0.6; the mixed solution is placed in a mold for solidification to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane; during the electrochemical reduction process of the cellulose acetate-modified PEO-based solid electrolyte membrane, the carbonyl group in the cellulose acetate adsorbs TFSI in the lithium bistrifluoromethanesulfonyl imide - , accelerating the decomposition of lithium bis(trifluoromethanesulfonyl)imide into TFSI - And form LiF deposition, while TFSI - Directly react with lithium metal to generate Li-rich 2 The present invention introduces cellulose acetate to modify the polyethylene oxide solid electrolyte to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane, which can generate Li-rich in-situ on the surface of the lithium negative electrode in the application of solid-state lithium batteries. 2 The stable solid electrolyte interface of O and LiF not only effectively inhibits the growth of lithium dendrites and reduces the interface impedance, but also broadens the operating temperature range of solid-state lithium batteries. At the same time, it overcomes the problems of low conductivity and poor safety performance of traditional polyethylene oxide solid electrolytes at room temperature.

[0019] 2. During the electrochemical reduction process of the cellulose acetate modified PEO-based solid electrolyte membrane of the present invention, lithium bis(trifluoromethanesulfonyl)imide, i.e., TFSI in LiTFSI - Directly react with lithium metal to generate Li 2 O; At the same time, TFSI in LiTFSI - Under reducing conditions, it decomposes to generate LiF with high mechanical hardness, and finally obtains Li-rich 2 O and LiF solid electrolyte interface layer. 2 O and LiF are chemically inert substances that can effectively prevent side reactions between lithium and solid electrolytes and reduce electrolyte decomposition. Among them, LiF has high mechanical hardness and can form a dense solid electrolyte interface layer on the lithium surface, which helps to inhibit the growth of lithium dendrites. The formation of this dense solid electrolyte interface layer can maintain the flatness of the electrode surface during multiple charge and discharge cycles, thereby reducing the risk of short circuits. Secondly, Li 2 Both O and LiF have low lithium ion migration barriers, especially Li 2 O can improve the migration efficiency of lithium ions, help improve the lithium ion conductivity of the battery, reduce the interface resistance, and enhance the overall electrochemical performance of the solid-state lithium battery.

[0020] With other lithium salts such as LiClO 4 and LiPF 6 In contrast, LiTFSI can not only provide the transferred Li +, and can also show good compatibility with polyethylene oxide. This compatibility effectively reduces the crystalline area of ​​polyethylene oxide, thereby promoting the migration efficiency of lithium ions in the amorphous area. In addition, LiTFSI also has excellent thermal stability and chemical stability, can maintain its performance stable over a wide temperature range, and is not prone to decomposition. At the same time, LiTFSI has a wide electrochemical stability window and can adapt to a variety of electrode materials, thereby improving the safety performance of solid-state batteries.

[0021] 3. The cellulose ether modified PEO-based solid electrolyte membrane prepared by the present invention is applied to solid-state lithium batteries to generate Li-rich 2 O and LiF-rich solid electrolyte interface layer not only improves the cycle performance of solid-state lithium batteries at high temperatures, but also significantly broadens the operating temperature range of solid-state lithium batteries, that is, it exhibits excellent stability and conductivity regardless of room temperature or low temperature conditions, proving its excellent operating capability in a wide temperature range.

[0022] Compared with the limitation that traditional PEO-based solid-state lithium batteries can only operate in a high-temperature environment of 60°C, the battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane prepared by the present invention successfully achieved stable operation at room temperature of 25°C or even as low as -10°C, significantly broadening its applicable temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 ] are SEM images of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1, wherein a is a surface SEM image of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1, and b is a cross-sectional SEM image of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1.

[0024] Figure 2 The TGA curves of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 are shown.

[0025] Figure 3 The XRD patterns of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1.

[0026] Figure 4 The ATR-FTIR graphs of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1.

[0027] Figure 5 The tensile stress-strain curves of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1.

[0028] Figure 6 The resistance and ion conductivity diagrams of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1, wherein a is the resistance of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1, the inset in Figure a is an enlarged diagram of the resistance of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 when the resistance value is 0Ω~40Ω, and b is the resistance and ion conductivity diagram of the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1.

[0029] Figure 7 The Tafel curves of the stainless steel symmetrical battery assembled with the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1.

[0030] Figure 8 The resistance diagrams of the lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 before and after cycling, wherein: Figure 8 The illustration in the figure is the resistance diagram of the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 before and after cycling.

[0031] Fig. 9 The lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 were tested at 0.1 mA / cm 2 、0.1mAh / cm 2 The voltage distribution diagram below.

[0032] Fig.10 The lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 were tested at a current density of 0.1 mA / cm 2 , area capacity is 0.1-1mAh / cm 2 Voltage distribution diagram when .

[0033] Fig.11 The cycling performance diagram of the lithium iron phosphate metal battery assembled with the PEO-based solid electrolyte membrane modified with cellulose acetate in Example 1 and the lithium iron phosphate metal battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1 at 60°C with a rate of 0.5C.

[0034] Fig.12The cycling performance diagram of the lithium iron phosphate metal battery assembled with the PEO-based solid electrolyte membrane modified with cellulose acetate in Example 1 and the lithium iron phosphate metal battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1 at a rate of 1C at 60°C.

[0035] Fig.13 Cycling performance diagram of the lithium iron phosphate metal battery assembled with the PEO-based solid electrolyte membrane modified with cellulose acetate in Example 1 and the lithium iron phosphate metal battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1 at room temperature 25°C and low temperature -10°C with a rate of 0.1C. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are conventional methods unless otherwise specified.

[0037] 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 bistrifluoromethanesulfonyl imide, namely LiTFSI, is purchased from MacLean reagent; polyethylene oxide, namely PEO, is purchased from Aladdin reagent; cellulose acetate, namely CA, is purchased from Aladdin reagent.

[0038] In the prior art, traditional polyethylene oxide electrolytes are prone to crystallization at room temperature. This crystallization phenomenon will severely limit the internal lithium ion transmission channel, making ion migration difficult, resulting in low ion conductivity. At the same time, crystallization will also affect the mechanical properties of polyethylene oxide solid electrolytes, making them more brittle and easy to break, thereby deteriorating the safety performance of polyethylene oxide electrolytes.

[0039] In view of the problems existing in the prior art, the present invention provides a method for preparing a cellulose acetate modified PEO-based solid electrolyte membrane, comprising the following steps: dissolving lithium bis(trifluoromethanesulfonyl)imide, cellulose acetate and polyethylene oxide in a solvent, and strongly adsorbing TFSI to the carbonyl group in the cellulose acetate through electrostatic interaction. - , accelerating the decomposition of LiTFSI into TFSI -, obtaining a mixed solution; wherein the mass ratio of polyethylene oxide to cellulose acetate is 2:0.01-0.6; the mixed solution is placed in a mold for solidification to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane; during the electrochemical reduction process of the cellulose acetate-modified PEO-based solid electrolyte membrane, the carbonyl group in the cellulose acetate adsorbs TFSI in the lithium bistrifluoromethanesulfonyl imide - , accelerating the decomposition of lithium bis(trifluoromethanesulfonyl)imide into TFSI - And form LiF deposition, while TFSI - Directly react with lithium metal to generate Li-rich 2 O and LiF solid electrolyte interface layer.

[0040] The present invention introduces cellulose acetate to modify the polyethylene oxide solid electrolyte, which not only significantly reduces the crystallinity of the polyethylene oxide solid electrolyte, but also improves the ionic conductivity of the cellulose acetate-modified PEO-based solid electrolyte membrane and enhances its mechanical strength. In addition, the cellulose acetate-modified PEO-based solid electrolyte membrane prepared by the present invention is applied to a solid-state lithium battery, which can generate Li-rich in-situ on the surface of the lithium negative electrode. 2 The formation of a stable solid electrolyte interface between LiO and LiF not only effectively inhibits the growth of lithium dendrites and significantly reduces the interface impedance, but also broadens the operating temperature range of solid-state lithium batteries, overcoming the problems of low conductivity and poor safety performance of traditional polyethylene oxide solid electrolytes at room temperature.

[0041] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0042] Example 1 A method for preparing a cellulose acetate-modified PEO-based solid electrolyte membrane comprises the following steps: S1. Dissolve 0.8146 g of LiTFSI in 20 mL of anhydrous acetonitrile. After LiTFSI is completely dissolved, add 0.2 g of CA powder and stir. After it is completely dissolved, add 2 g of PEO and stir to obtain a mixed solution.

[0043] S2. The mixed solution was poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55° C. for 48 h to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane, which was recorded as CA-0.2.

[0044] Example 2 A method for preparing a cellulose acetate-modified PEO-based solid electrolyte membrane comprises the following steps: S1. Dissolve 0.8 g of LiTFSI in 20 mL of anhydrous acetonitrile. After LiTFSI is completely dissolved, add 0.1 g of CA powder and stir. After it is completely dissolved, add 2 g of PEO and stir to obtain a mixed solution.

[0045] S2. The mixed solution is poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 60° C. for 48 h to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane.

[0046] Example 3 A method for preparing a cellulose acetate-modified PEO-based solid electrolyte membrane comprises the following steps: S1. Dissolve 1 g of LiTFSI in 20 mL of anhydrous acetonitrile. After LiTFSI is completely dissolved, add 0.3 g of CA powder and stir. After it is completely dissolved, add 2 g of PEO and stir to obtain a mixed solution.

[0047] S2. The mixed solution is poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 58° C. for 48 h to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane.

[0048] Example 4 A method for preparing a cellulose acetate-modified PEO-based solid electrolyte membrane comprises the following steps: S1. Dissolve 1 g of LiTFSI in 20 mL of anhydrous acetonitrile. After LiTFSI is completely dissolved, add 0.15 g of CA powder and stir. After it is completely dissolved, add 2 g of PEO and stir to obtain a mixed solution.

[0049] S2. The mixed solution is poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55° C. for 48 h to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane.

[0050] Example 5 A method for preparing a cellulose acetate-modified PEO-based solid electrolyte membrane comprises the following steps: S1. Dissolve 0.9 g of LiTFSI in 20 mL of anhydrous acetonitrile. After LiTFSI is completely dissolved, add 0.2 g of CA powder and stir. After it is completely dissolved, add 2 g of PEO and stir to obtain a mixed solution.

[0051] S2. The mixed solution is poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55° C. for 48 h to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane.

[0052] Example 6 A method for preparing a cellulose acetate-modified PEO-based solid electrolyte membrane comprises the following steps: S1. Dissolve 0.8146 g of LiTFSI in 20 mL of anhydrous acetonitrile. After LiTFSI is completely dissolved, add 0.01 g of CA powder and stir. After it is completely dissolved, add 2 g of PEO and stir to obtain a mixed solution.

[0053] S2. The mixed solution is poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55° C. for 48 h to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane.

[0054] Comparative Example 1 A method for preparing a PEO-based solid electrolyte membrane comprises the following steps: Using a typical solvent casting method, 0.8146 g of LiTFSI was dissolved in 20 mL of anhydrous acetonitrile. After LiTFSI was completely dissolved, 2 g of PEO was added and stirred. After stirring evenly, the mixed solution was poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55 ° C for 48 hours to obtain a PEO-based solid electrolyte membrane.

[0055] Comparative Example 2 A method for preparing a PEO-based solid electrolyte membrane comprises the following steps: Using a typical solvent casting method, 0.8 g of LiTFSI was dissolved in 20 mL of anhydrous acetonitrile. After LiTFSI was completely dissolved, 2 g of PEO was added and stirred. After stirring evenly, the mixed solution was poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 60 ° C for 48 hours to obtain a PEO-based solid electrolyte membrane.

[0056] Comparative Example 3 A method for preparing a PEO-based solid electrolyte membrane comprises the following steps: Using a typical solvent casting method, 1g of LiTFSI was dissolved in 20mL of anhydrous acetonitrile. After LiTFSI was completely dissolved, 2g of PEO was added and stirred. After stirring evenly, the mixed solution was poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 58°C for 48h to obtain a PEO-based solid electrolyte membrane.

[0057] Comparative Example 4 A method for preparing a PEO-based solid electrolyte membrane comprises the following steps: Using a typical solvent casting method, 1g of LiTFSI was dissolved in 20mL of anhydrous acetonitrile. After LiTFSI was completely dissolved, 2g of PEO was added and stirred. After stirring evenly, the mixed solution was poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55°C for 48h to obtain a PEO-based solid electrolyte membrane.

[0058] Comparative Example 5 A method for preparing a PEO-based solid electrolyte membrane comprises the following steps: Using a typical solvent casting method, 0.9 g of LiTFSI was dissolved in 20 mL of anhydrous acetonitrile. After LiTFSI was completely dissolved, 2 g of PEO was added and stirred. After stirring evenly, the mixed solution was poured into a polytetrafluoroethylene mold and formed in a glove box, and then vacuum dried at 55 ° C for 48 hours to obtain a PEO-based solid electrolyte membrane.

[0059] In Examples 1 to 5 of the present invention, cellulose acetate modified PEO-based solid electrolyte membranes were prepared, and the effects were similar. The following batteries were assembled using the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1, respectively, and were denoted as CA-0.2 and Bare PEO. The specific research methods and results are as follows: a.Battery assembly: A CA-0.2 battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1: Taking a CR2032 button battery as an example, in a glove box filled with argon, a negative electrode shell, a spring, a gasket, a negative electrode lithium sheet, and the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 are placed in sequence on the negative electrode lithium sheet, and then a positive electrode lithium sheet or a lithium iron phosphate electrode sheet is placed, the positive electrode shell is covered and the battery is pressed to obtain a CA-0.2 battery, recorded as CA-0.2.

[0060] Bare PEO battery assembled with PEO-based solid electrolyte membrane: Taking CR2032 button battery as an example, in a glove box filled with argon, the negative electrode shell, spring, gasket, negative electrode lithium sheet, the PEO-based solid electrolyte membrane prepared in Example 1 are placed in sequence on the negative electrode lithium sheet, and then the positive electrode lithium sheet or lithium iron phosphate sheet is placed, the positive electrode shell is covered and the battery is pressed to obtain a Bare PEO battery, which is recorded as Bare PEO.

[0061] Results and Discussion observe Figure 1 Figure a shows that the surface of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 has texture and rough structure, which is caused by the doping of cellulose acetate. This structure provides an additional path for the conduction of lithium ions and can also reduce the interface resistance by enhancing the contact with the electrode. Figure 1As shown in Figure b, the cross section of the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 shows a relatively uniform thickness and structure. Figure 1 The thickness of the membrane is marked as 108µm in Figure b, which is one of the key parameters of the solid electrolyte membrane. This thickness can provide good mechanical support and stability for the battery in solid-state batteries, while allowing effective lithium ion conduction. It shows that CA and PEO are mixed together more evenly. In addition, there seem to be tiny rough structures or undulations on the upper and lower surfaces of the membrane, which is due to the influence of cellulose introduced during the preparation process. These surface undulations increase the contact area between the electrode and the electrolyte and improve the interfacial conductivity.

[0062] Figure 2 1 is a TGA curve diagram of the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1. Figure 2 As shown, the thermal degradation temperature of CA powder is 314°C, and the thermal degradation temperature of the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 is 370°C, which is mainly due to the pyrolysis of the PEO matrix. It is worth noting that below 300°C, the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 did not undergo any obvious thermal degradation, indicating that the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 have excellent thermal stability and can meet the practical application requirements of solid-state batteries. In addition, the weight loss of the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 at the end of the test is 3.4% less than that of the PEO-based solid electrolyte membrane of Comparative Example 1. This is because the CA powder generates a stable carbon material after pyrolysis, which does not pyrolyze at 650°C.

[0063] Figure 3 The XRD patterns of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 are shown in FIG. Figure 3 It is concluded that the crystallinity of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 is reduced, which is beneficial to the migration of lithium ions in the amorphous region, thereby improving the ionic conductivity of the cellulose acetate-modified PEO-based solid electrolyte membrane. And no new diffraction peaks are generated after adding cellulose acetate, indicating that the doping of CA does not destroy the original crystalline structure of PEO.

[0064] Figure 4 The ATR-FTIR graphs of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 are shown. Figure 4It is found that compared with the PEO-based solid electrolyte membrane of Comparative Example 1, the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 has a higher -1 A significant characteristic peak appeared at , which corresponds to the absorption peak of carbonyl in cellulose acetate. The appearance of this absorption peak indicates that cellulose acetate has been successfully doped into the PEO matrix without destroying the structure of the PEO matrix, thus maintaining the overall chemical stability of the electrolyte membrane.

[0065] Figure 5 1 is the tensile stress-strain curve of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1. Figure 5 As shown. After the addition of cellulose acetate, the tensile strength, related fracture strain and toughness of the solid electrolyte membrane are significantly improved. Specifically, the maximum tensile stress of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 reached 1801KPa, and the strain reached 1849%. This excellent mechanical property means that the addition of CA enhances the deformation resistance of the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1, which helps to inhibit the growth of lithium dendrites during battery operation, thereby improving the cycle stability and safety of the battery. In summary, the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 not only exhibits appropriate thickness, uniform mixing and optimized surface morphology in microstructure, but also shows significant improvements in thermal stability, crystallinity and mechanical properties, which can provide guarantees for the long-life cycle and safety of solid-state lithium batteries.

[0066] In order to further evaluate the effect of CA addition on the electrochemical properties of cellulose acetate modified PEO-based solid electrolyte membrane, a stainless steel symmetrical cell was assembled using the cellulose acetate modified PEO-based solid electrolyte membrane in Example 1, and an AC impedance test was performed using an electrochemical workstation at 60°C~30°C.

[0067] The cellulose acetate modified PEO-based solid electrolyte membrane in Example 1 was used as a diaphragm, and stainless steel sheets were used as positive and negative electrodes. A stainless steel symmetrical battery was assembled and electrically connected to an electrochemical workstation. The test results were tested under different temperature conditions. The results are shown below: Figure 6 The resistance and ion conductivity diagram of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 are as follows: Figure 6As shown in the inset of Figure a, at 60°C, 50°C, 40°C and 30°C, the corresponding resistances of the stainless steel symmetric cell assembled with the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 are 5.16Ω, 7.266Ω, 18.15Ω and 26.46Ω, respectively. By fitting these resistance data, the ionic conductivity is calculated to be 1.0415mS•cm -1 、0.7396mS•cm -1 、0.2961mS•cm -1 and 0.2031mS•cm -1 ,like Figure 6 As shown in Figure b in . In comparison, the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 exhibits higher resistance and lower ionic conductivity, which indicates that the addition of CA effectively reduces the interfacial resistance of the electrolyte and significantly improves the lithium ion conductivity of the battery, thereby improving the electrochemical performance and stability of the battery as a whole.

[0068] First, a Tafel test was performed on the lithium symmetric battery assembled with the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 at 60° C. using an electrochemical workstation.

[0069] Figure 7 The Tafel curves of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 are shown in FIG. Figure 7 As shown, the corrosion potential of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane in Example 1 is higher than that of the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1, indicating that it has stronger corrosion resistance. The exchange current density of the stainless steel symmetrical battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane in Example 1 obtained by fitting calculation is 0.173 mA cm -2 , which is higher than 0.0762 mA cm of the stainless steel symmetrical battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1. -2 , which shows that compared with PEO-based electrolytes, the addition of cellulose acetate significantly increased the overall current density and improved its conductivity and electrochemical stability, which is crucial for the application of solid-state batteries.

[0070] Figure 8 The resistance diagrams of the lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 before and after cycling are as follows: Figure 8As shown, the lithium metal symmetric battery assembled with the cellulose acetate-modified PEO-based solid electrolyte membrane in Example 1 exhibited lower resistance before and after cycling, indicating its excellent electrochemical stability during cycling.

[0071] In order to further evaluate the cross-sectional stability of the cellulose acetate modified PEO-based solid electrolyte membrane, a lithium symmetric constant current charge-discharge cycle test was performed on the cellulose acetate modified PEO-based solid electrolyte membrane in Example 1 at 60°C.

[0072] Fig. 9 The lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 were tested at 0.1 mA / cm 2 、0.1mAh / cm 2 The voltage distribution diagram under Fig. 9 As shown. The lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 exhibits an overpotential of about 37mV, and the overpotential drops rapidly after only 62h of cycling, indicating that lithium dendrites gradually form at the electrode interface or unnecessary side reactions occur. In contrast, the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane modified with cellulose acetate in Example 1 can be stably cycled for more than 2300h, and as shown in the voltage distribution enlargement diagram, its overpotential at 2300h is only 35mV, indicating better cycle stability. This is attributed to the formation of a dense LiF solid electrolyte interface layer on the surface of lithium metal after the addition of cellulose acetate. It is a chemically inert product that can effectively prevent side reactions between lithium metal and solid electrolytes and reduce the possibility of electrolyte decomposition. Because it has a high mechanical hardness, it can form a dense and stable protective layer on the surface of lithium metal. This dense protective film not only prevents further side reactions, but also provides uniform lithium nucleation sites on the electrode surface, significantly inhibiting the formation of lithium dendrites, enabling uniform lithium deposition during multiple charge and discharge cycles, reducing the risk of short circuits, and thus significantly improving the safety and life of the battery.

[0073] Fig.10 The lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane of Example 1 and the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane of Comparative Example 1 were tested at a current density of 0.1 mA / cm 2 , the area capacity is 0.1 -1 mAh / cm 2 The voltage distribution diagram when Fig.10As shown in the figure, under different area capacities, the lithium metal symmetric battery assembled with the cellulose acetate modified PEO-based solid electrolyte membrane in Example 1 always exhibits excellent plating / stripping behavior compared with the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1, and its overpotential is always maintained at about 20mV. However, the overpotential of the lithium metal symmetric battery assembled with the PEO-based solid electrolyte membrane in Comparative Example 1 increases continuously with the increase of area capacity, especially when the cycle reaches 1mAh / cm 2 When the area capacity returned to 1 mAh / cm 2 , its overpotential increases significantly, indicating inhomogeneous lithium deposition and short circuiting at high areal capacity.

[0074] In summary, the addition of cellulose acetate effectively improves the electrical conductivity, ion conductivity and electrochemical stability of the solid electrolyte membrane, significantly reduces the interfacial impedance, and enhances the corrosion resistance of the battery. These characteristics enable the CA-0.2 electrolyte membrane to exhibit better lithium ion transmission capacity and long-term stability in solid-state battery applications, demonstrating its great application potential in high-performance solid-state lithium batteries.

[0075] Fig.11 and Fig.12 The cycle performance of the battery assembled with the cellulose acetate-modified PEO-based solid electrolyte membrane of Example 1 and the PEO-based solid electrolyte membrane of Comparative Example 1 at a rate of 0.5C and 1C at 60°C is respectively demonstrated. The results show that CA-0.2 exhibits better cycle performance at both 0.5C and 1C rates, and the higher the rate, the more obvious the contrast. This shows that the addition of cellulose acetate significantly enhances the cycle capacity of the entire battery, enabling the cellulose acetate-modified PEO-based solid electrolyte membrane to maintain stable electrochemical performance at higher rates. At the same time, in order to further evaluate the application potential of CA-0.2 solid electrolyte under different temperature conditions, we conducted operation tests on LFP batteries assembled with CA-0.2 electrolyte at 25°C and low temperature -10°C.

[0076] Fig.13The cycle curve of the battery at a rate of 0.1C is shown. It can be seen from the figure that at room temperature 25°C, the CA-0.2 battery can stably cycle 150 times and maintain a high capacity; even at a low temperature of -10°C, the battery can continue to cycle stably for 80 times, and the capacity retention rate is also excellent. Such performance proves the superior performance of the CA-0.2 electrolyte under wide temperature conditions, especially under low temperature conditions, it can still maintain good electrochemical stability and conductivity. These test results fully demonstrate that the addition of cellulose acetate not only improves the cycle performance of solid-state batteries at high temperatures, but also significantly broadens the operating temperature range of the battery. Whether at room temperature or low temperature, the CA-0.2 battery exhibits excellent stability and conductivity, proving its excellent operating ability under a wide temperature range. It can be concluded that the optimized design of the CA-0.2 electrolyte is of great significance to improving the performance of the entire battery, and provides a solid technical foundation for the practical application of solid-state batteries.

[0077] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a cellulose acetate modified PEO-based solid electrolyte membrane, characterized in that: The following steps are involved: Dissolving lithium bis(trifluoromethanesulfonyl)imide, cellulose acetate and polyethylene oxide in a solvent to obtain a mixed solution; wherein the mass ratio of polyethylene oxide to cellulose acetate is 2:0.01-0.6; The mixed solution is placed in a mold for solidification to obtain a cellulose acetate-modified PEO-based solid electrolyte membrane; During the electrochemical reduction process of cellulose acetate modified PEO-based solid electrolyte membrane, the carbonyl groups in cellulose acetate adsorb TFSI from lithium bis(trifluoromethanesulfonyl)imide - , accelerating the decomposition of lithium bis(trifluoromethanesulfonyl)imide into TFSI - And form LiF deposition, while TFSI - It reacts directly with lithium metal to form a solid electrolyte interfacial layer rich in Li2O and LiF.

2. The method for preparing a cellulose acetate modified PEO-based solid electrolyte membrane according to claim 1, characterized in that: The ethoxy unit EO in polyethylene oxide reacts with Li in lithium bis(trifluoromethanesulfonyl)imide + The molar ratio is 14~18:

1.

3. The method for preparing a cellulose acetate modified PEO-based solid electrolyte membrane according to claim 1, characterized in that: The curing conditions are: drying at 50℃~60℃ for 48h~60h.

4. A cellulose acetate-modified PEO-based solid electrolyte membrane prepared by the preparation method according to any one of claims 1 to 3.

5. The cellulose acetate modified PEO-based solid electrolyte membrane according to claim 4, characterized in that: The thickness of the cellulose acetate modified PEO-based solid electrolyte membrane is 50 μm~500 μm.

6. A solid-state lithium battery, characterized in that: The invention is made of the following raw materials: a negative electrode shell, a positive electrode sheet, a negative electrode sheet, a positive electrode shell, a spring, a gasket and the cellulose acetate-modified PEO-based solid electrolyte membrane according to claim 4.

7. The solid-state lithium battery according to claim 6, characterized in that: Solid-state lithium batteries are lithium iron phosphate batteries or lithium symmetrical batteries.

8. The method for preparing a solid-state lithium battery according to claim 7, characterized in that: The following steps are involved: In a glove box filled with argon, the negative electrode shell, spring, gasket, and negative electrode sheet are placed in sequence, and then the cellulose acetate-modified PEO-based solid electrolyte membrane is covered on the negative electrode sheet, and then the positive electrode sheet is placed and covered with the positive electrode shell.

9. The method for preparing a solid-state lithium battery according to claim 8, characterized in that: The positive electrode sheet is selected from a lithium sheet or a lithium iron phosphate sheet, and the negative electrode sheet is selected from a lithium sheet.

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