Solid polymer electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of all-solid-state lithium metal batteries, in particular to a preparation method of a solid polymer electrolyte, which comprises the following steps: S1, fully mixing polyethylene glycol dimethyl ether with a lithium salt by adopting a solvent-free method, heating and stirring until the polyethylene glycol dimethyl ether is completely molten and the lithium salt is completely dissolved, thereby obtaining a polyethylene glycol dimethyl ether-based electrolyte; and S2, adding the lithium carboxymethyl cellulose powder into the polyethylene glycol dimethyl ether-based electrolyte, continuously stirring at constant temperature until the lithium carboxymethyl cellulose powder is completely dissolved, and cooling to obtain the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte. The solid polymer electrolyte CMC-Li-PEGDME is obtained by introducing the carboxymethyl cellulose lithium into the polyethylene glycol dimethyl ether based electrolyte, so that the ionic conductivity, the interface stability and the cycle life of the electrolyte are remarkably improved. And the problems of unstable interface and dendritic crystal growth of the traditional solid polymer electrolyte in the lithium metal battery are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state lithium metal batteries, and particularly relates to a method for preparing a solid polymer electrolyte by introducing lithium carboxymethyl cellulose into a polyethylene glycol dimethyl ether-based electrolyte and its application. Background Art

[0002] With the rapid development of renewable energy, the demand for efficient and safe energy storage technologies is increasing day by day. Lithium metal is regarded as an ideal anode material for high-energy-density batteries due to its extremely high theoretical specific capacity (3860 mAh g-1), low mass density (0.59 g cm-3), and extremely negative reduction potential (-3.04 V vs. standard hydrogen electrode). However, despite the many advantages of lithium metal anodes, solid polymer electrolytes (SPEs) still face severe challenges in practical applications, mainly including low lithium salt dissociation degree and poor electrolyte-electrode interface stability.

[0003] Firstly, the dissociation degree of lithium salts in solid polymer electrolytes is relatively low, resulting in a limited number of free lithium ions available for transport, thus significantly reducing the ionic conductivity and affecting the rate performance and cycle stability of the battery. Secondly, solid polymer electrolytes are prone to interfacial side reactions with lithium metal anodes and high-voltage cathodes during cycling, leading to unstable interfacial layers and shortening the battery life. Especially under high-voltage conditions, the interfacial side reactions are aggravated to generate unstable SEI and CEI, reducing the Coulombic efficiency and cycle life of the battery. Therefore, improving the dissociation degree of lithium salts and optimizing the interfacial compatibility between the electrolyte and the electrode are crucial for enhancing the performance of all-solid-state lithium metal batteries. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a solid polymer electrolyte and its application, which can enhance the lithium ion coordination ability and the dissociation degree of lithium salts by introducing lithium carboxymethyl cellulose CMC@Li. As a functional additive, CMC@Li can form a stable coordination with lithium ions, weaken the strong interaction between lithium ions and polyethylene glycol dimethyl ether PEGDME, thereby promoting the dissociation of lithium salts and enhancing the ionic conductivity of the electrolyte.

[0005] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] A method for preparing a solid polymer electrolyte, comprising the following steps:

[0007] S1. Preparation of polyethylene glycol dimethyl ether-based electrolyte: By a solvent-free method, polyethylene glycol dimethyl ether PEGDME and a lithium salt are fully mixed, and then heated and stirred until polyethylene glycol dimethyl ether PEGDME is completely melted and the lithium salt is completely dissolved, thereby obtaining a polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME;

[0008] S2. Preparation of solid polymer electrolyte: Add lithium carboxymethyl cellulose CMC@Li powder to polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME, and continue stirring at a constant temperature until the lithium carboxymethyl cellulose CMC@Li powder is completely dissolved. After cooling, lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME is obtained.

[0009] Preferably, the lithium salt is composed of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, and lithium nitrate LiNO3.

[0010] Preferably, the mass ratio of polyethylene glycol dimethyl ether PEGDME to lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, and lithium nitrate LiNO3 in the lithium salt is 3: 1.152 - 1.402: 0.187 - 0.229: 0.083 - 0.1014.

[0011] Preferably, the mass ratio of polyethylene glycol dimethyl ether PEGDME to lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, and lithium nitrate LiNO3 in the lithium salt is 3: 1.28: 0.208: 0.092.

[0012] Preferably, the mass ratio of lithium carboxymethyl cellulose CMC@Li powder to polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME is 1: 40 - 50.

[0013] Preferably, the temperature of the heating and stirring and the constant temperature stirring is 110 - 120 °C.

[0014] A solid polymer electrolyte is prepared by the above method.

[0015] An application of a solid polymer electrolyte, an application of lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME in all-solid-state lithium metal batteries.

[0016] Preferably, the application method is as follows: Inside a glove box filled with argon, heat the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME to 60 - 70 °C until it is completely molten. Then, place the negative electrode case, shrapnel, and gasket in sequence, and place the lithium metal negative electrode sheet on them. Subsequently, fully soak the molten solid polymer electrolyte CMC@Li-PEGDME with a 3501 battery separator and cover the lithium metal negative electrode sheet. Then, place the positive electrode sheet, and finally cover the positive electrode case and press the battery tightly.

[0017] Compared with the existing technology, the beneficial effects of the present invention are:

[0018] 1. This application introduces lithium carboxymethyl cellulose (CMC@Li) into polyethylene glycol dimethyl ether (PEGDME)-based electrolytes, which significantly improves the performance of all-solid-state lithium metal batteries (ASSLMBs) in all-solid-state lithium metal batteries.

[0019] As the matrix material, PEGDME, with its excellent flexibility and high mechanical modulus, can not only improve the mechanical strength of the electrolyte but also enhance the interfacial compatibility with the lithium metal anode. Meanwhile, the ether oxygen groups (-O-) in PEGDME provide abundant lithium ion migration channels, which play an important role in enhancing lithium ion conduction.

[0020] As a functional additive, CMC@Li can form strong interactions with Li in the lithium salt through polar groups such as carboxyl (-COO-) and hydroxyl (-OH) in its molecular structure, forming stable coordination. This coordination can effectively reduce the Coulomb interaction barrier between anions and cations in the lithium salt, promote the dissociation of the lithium salt, and thus enhance the ionic conductivity of the electrolyte. In addition, good interactions are formed between CMC@Li molecules and the PEGDME matrix through hydrogen bonds and van der Waals forces, making the system more uniform and improving the structural stability of the electrolyte and the continuity of the ion migration channels. + More importantly, the introduction of CMC@Li forms a stable solid electrolyte interface (SEI) with high ionic conductivity and high mechanical modulus between the solid electrolyte and the lithium metal anode. During the battery cycling process, the carboxyl group of CMC@Li can directly react with metallic lithium on the lithium metal surface to generate lithium-containing organic compounds (such as RCOOLi), while the hydroxyl group further combines with lithium ions to generate inorganic products (such as Li2CO3 and LiOH). These products form a dense and stable SEI layer on the lithium metal surface, which can not only block the further diffusion of side reaction substances but also significantly inhibit the growth of lithium dendrites.

[0021] At the same time, at the cathode interface (CEI), the polar groups in CMC@Li can cooperate with the active substances on the surface of the cathode material to regulate the interfacial electrochemical reaction kinetics and reduce the occurrence of interfacial side reactions. This optimized CEI layer has excellent stability, which can inhibit the over-oxidation of the cathode material and the decomposition of the electrolyte, thus improving the cycling performance of the battery.

[0022]

[0023] ​In summary, by introducing lithium carboxymethyl cellulose CMC@Li into polyethylene glycol dimethyl ether PEGDME-based electrolytes to obtain a solid polymer electrolyte CMC@Li-PEGDME, the ionic conductivity, interfacial stability, and cycle life of the electrolyte are significantly improved. It effectively solves the key problems such as unstable interfaces and dendrite growth existing in traditional solid polymer electrolytes (SPEs) in lithium metal batteries, providing a new idea for the development of high-performance all-solid-state lithium metal batteries.

[0024] 2. The all-solid-state lithium metal symmetric battery prepared by using the CMC@Li-PEGDM solid polymer electrolyte of the present invention has a cycle life of up to 4000 h at a current density / capacity of 0.1 mA cm -2 / 0.5 mAh cm -2 , and a cycle life of 3200 h is achieved at a current density / capacity of 0.1 mA cm -2 / 1 mAh cm -2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of the CMC@Li-PEGDME electrolyte.

[0026] Figure 2 is an infrared thermal imaging image of different electrolytes under the same heating conditions.

[0027] Figure 3 is the cycle stability test of the lithium symmetric battery assembled with the solid polymer electrolyte of Example 1 of the present invention and the comparative sample at 0.1 mA cm -2 , 0.5 mAh cm -2 .

[0028] Figure 4 is the cycle stability test of the lithium symmetric battery assembled with the solid polymer electrolyte of Example 1 of the present invention and the comparative sample at 0.1 mA cm -2 , 1 mAh cm -2 .

[0029] Figure 5 is the test of the lithium symmetric battery assembled with two electrolytes of the present invention at different rates.

[0030] Figure 6 a is the XPS F1s spectrum of the interface between the lithium metal electrode and the Bare-PEGDME electrolyte.

[0031] Figure 6 b is the XPS F1s spectrum of the interface between the lithium metal electrode and the CMC@Li-PEGDME electrolyte.

[0032] Figure 7a is the XPS Li 1s spectrum of the lithium metal electrode and the interface of Bare-PEGDME and electrolyte.

[0033] Figure 7 b is the XPS Li 1s spectrum of the lithium metal electrode and the interface of CMC@Li-PEGDME electrolyte.

[0034] Figure 8 It is the cycle performance test of the full cell assembled with the lithium iron phosphate cathode material under the condition of 0.2C using two different electrolytes.

[0035] Figure 9 It is the rate performance test of the full cell assembled with the lithium iron phosphate cathode material under different rate conditions using two different electrolytes. Detailed implementation mode

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "plurality" is more than two.

[0037] Unless otherwise clearly specified and defined, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0038] A preparation method of a solid polymer electrolyte includes the following steps:

[0039] S1. Preparation of polyethylene glycol dimethyl ether-based electrolyte: Using a solvent-free method, after fully mixing polyethylene glycol dimethyl ether PEGDME and a lithium salt, heat and stir until polyethylene glycol dimethyl ether PEGDME is completely melted and the lithium salt is completely dissolved, thereby obtaining polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME.

[0040] S2. Preparation of solid polymer electrolyte: Lithium carboxymethyl cellulose CMC@Li powder is added to polyethylene glycol dimethyl ether-based electrolyte, and stirring is continued at a constant temperature until the lithium carboxymethyl cellulose CMC@Li powder is completely dissolved. After cooling, lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME is obtained.

[0041] Since PEGDME contains ethylene glycol and dimethyl ether groups, it has good dissolution characteristics and coordination ability, so that it can form stable coordination interaction with CMC@Li, promote its uniform dispersion in PEGDME, and finally form a stable composite electrolyte.

[0042] The lithium salt is composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide salt (LiFSI), and lithium nitrate (LiNO3).

[0043] The mass ratio of polyethylene glycol dimethyl ether to lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt, and lithium nitrate is 3: 1.152 - 1.402: 0.187 - 0.229: 0.083 - 0.1014.

[0044] The mass ratio of lithium carboxymethyl cellulose CMC@Li powder to polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME is 1: 40 - 50.

[0045] The temperature of the heating and stirring and the constant temperature stirring is 110 - 120 °C.

[0046] An application of a solid polymer electrolyte, the application of lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME in all-solid-state lithium metal batteries.

[0047] The application method is as follows: In a glove box filled with argon, the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME is heated to 60 - 70 °C to be completely melted, and then the negative electrode case, shrapnel and gasket are placed in turn, and the lithium metal negative electrode sheet is placed on them. Subsequently, the 3501 battery separator is fully wetted with the molten solid polymer electrolyte and covered on the lithium metal negative electrode sheet, then the positive electrode sheet is placed, and finally the positive electrode case is covered and the battery is pressed tightly.

[0048] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Additionally, it should be noted that in the above specific embodiments, the various specific technical features described can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods. Furthermore, any combination can be made between different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

[0049] To make the objectives, technical solutions, and technical effects of the present invention clearer, the technical solutions in the embodiments of the present invention will now be described clearly and completely. However, the embodiments described below are only a part of the embodiments of the present invention, rather than all of the embodiments. Combining the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0050] Example 1:

[0051] A method for preparing a solid polymer electrolyte, comprising the following steps:

[0052] (1) Preparation of a polyethylene glycol dimethyl ether-based electrolyte: The electrolyte is prepared by a solvent-free method. 3 g of polyethylene glycol dimethyl ether (PEGDME), 1.28 g of lithium bis(trifluoromethanesulfonyl)imide, 0.208 g of lithium bis(fluorosulfonyl)imide salt, and 0.092 g of lithium nitrate are uniformly mixed. Subsequently, the mixture is heated to 120 °C and continuously stirred until the polyethylene glycol dimethyl ether is completely melted and the lithium bis(trifluoromethanesulfonyl)imide is fully dissolved, thereby preparing a polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME;

[0053] (2) Preparation of a solid polymer electrolyte: 0.115 g of lithium carboxymethyl cellulose CMC@Li powder is added to 4.58 g of the polyethylene glycol dimethyl ether-based electrolyte, and the mixture is continuously stirred at 120 °C until the lithium carboxymethyl cellulose CMC@Li is completely dissolved. Subsequently, the mixture is cooled to room temperature, and finally, a lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME is obtained.

[0054] Example 2:

[0055] A method for preparing a solid polymer electrolyte, comprising the following steps:

[0056] (1) Preparation of polyethylene glycol dimethyl ether-based electrolyte: The electrolyte was prepared by a solvent-free method. 3 g of polyethylene glycol dimethyl ether, 1.312 g of lithium bis(trifluoromethanesulfonyl)imide, 0.216 g of lithium bis(fluorosulfonyl)imide salt, and 0.096 g of lithium nitrate were uniformly mixed. Subsequently, the mixture was heated to 110 °C and continuously stirred until the polyethylene glycol dimethyl ether was completely melted and the lithium bis(trifluoromethanesulfonyl)imide was fully dissolved, thereby preparing the polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME;

[0057] (2) Preparation of solid polymer electrolyte: 0.115 g of CMC@Li powder was added to 4.624 g of polyethylene glycol dimethyl ether-based electrolyte and continuously stirred at 110 °C until the CMC@Li was completely dissolved. Subsequently, the mixture was cooled to room temperature, and finally, the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME was obtained.

[0058] Example 3:

[0059] A method for preparing a solid polymer electrolyte, comprising the following steps:

[0060] (1) Preparation of polyethylene glycol dimethyl ether-based electrolyte: The electrolyte was prepared by a solvent-free method. 3 g of polyethylene glycol dimethyl ether, 1.36 g of lithium bis(trifluoromethanesulfonyl)imide, 0.196 g of lithium bis(fluorosulfonyl)imide salt, and 0.089 g of lithium nitrate were uniformly mixed. Subsequently, the mixture was heated to 115 °C and continuously stirred until the polyethylene glycol dimethyl ether was completely melted and the lithium bis(trifluoromethanesulfonyl)imide was fully dissolved, thereby preparing the polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME;

[0061] (2) Preparation of solid polymer electrolyte: 0.115 g of CMC@Li powder was added to 4.645 g of polyethylene glycol dimethyl ether-based electrolyte and continuously stirred at 115 °C until the CMC@Li was completely dissolved. Subsequently, the mixture was cooled to room temperature, and finally, the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME was obtained.

[0062] Application example:

[0063] The all-solid-state lithium metal battery was fabricated using the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME prepared in Example 1. Taking the CR2032 coin cell as an example, inside a glove box filled with argon, the solid polymer electrolyte CMC@Li-PEGDME prepared in Example 1 was heated at 70 °C until it was completely melted. Then, the negative electrode case, shrapnel, gasket, and lithium metal negative electrode were placed in sequence, and the 3501 battery separator was fully immersed in the molten electrolyte CMC@Li-PEGDME and then covered on the surface of the lithium metal negative electrode. Then, according to the battery type, a lithium positive electrode or a lithium iron phosphate positive electrode was placed, and then the positive electrode case was covered and pressed and fixed. Finally, the CMC@Li-PEGDME coin cell was assembled.

[0064] Comparative example:

[0065] The all-solid-state lithium metal battery was fabricated using the polyethylene glycol dimethyl ether PEGDME-based solid polymer electrolyte. Taking the CR2032 coin cell as an example, inside a glove box filled with argon, the polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME obtained after cooling in Step 1 of Example 1 was heated at 70 °C until it was completely melted. Then, the negative electrode case, shrapnel, gasket, and lithium metal negative electrode were placed in sequence, and the 3501 separator was fully immersed in the molten electrolyte Bare-PEGDME and then covered on the surface of the lithium sheet. Then, according to the battery type, a lithium positive electrode or a lithium iron phosphate positive electrode was placed, and then the positive electrode case was covered and pressed and fixed. Finally, the Bare-PEGDME coin cell was assembled.

[0066] To study the effect of CMC@Li on the electrochemical performance, Figure 1 The structural schematic diagram of the CMC@Li-PEGDME electrolyte is shown. Compared with traditional polymer electrolytes, the CMC@Li-PEGDME solid polymer electrolyte exhibits significant advantages in many aspects.

[0067] Firstly, this system constructs a better lithium-ion transport path through the polymer matrix, thereby improving the ionic conductivity. Secondly, the introduction of CMC@Li effectively promotes the dissociation of the lithium salt, increases the concentration of migratory free lithium ions, and further enhances the overall ionic conductivity. In addition, this composite electrolyte can optimize the stability of the solid electrolyte interface (SEI) and the cathode electrolyte interface (CEI), inhibit side reactions, reduce the interfacial impedance, and thus significantly improve the cycle life and long-term stability of the battery.

[0068] To evaluate the thermal properties of the two solid polymer electrolytes, we applied a 10 W light-emitting diode (LED) chip to each electrolyte and monitored its temperature distribution and cooling efficiency. As Figure 2As shown, when the LED operates for 15 s, 30 s, and 60 s, the highest central temperatures of the Bare-PEGDME electrolyte reach 63.7 °C, 100.9 °C, and 140.6 °C, respectively. Under the same conditions, the central temperatures of the CMC@Li-PEGDME solid polymer electrolyte are significantly reduced, being 61.0 °C, 79.7 °C, and 119.6 °C, respectively. This result indicates that the CMC@Li-PEGDME solid polymer electrolyte has excellent thermal management capabilities and can maintain a more uniform temperature distribution in high-temperature environments. In addition, after the LED is turned off and naturally cooled for 30 seconds, the surface temperature of the CMC@Li-PEGDME solid polymer electrolyte drops to 78.9 °C, while the surface temperature of the Bare-PEGDME polyethylene glycol dimethyl ether-based electrolyte remains at 90.0 °C, indicating that the CMC@Li-PEGDME solid polymer electrolyte has a higher heat dissipation efficiency. This phenomenon further proves that the introduction of CMC@Li significantly improves the thermal conductivity and heat dissipation ability of the electrolyte, thereby effectively reducing the operating temperature and enhancing the safety and stability of all-solid-state lithium metal batteries.

[0069] To verify the positive effect of lithium salt dissociation on electrochemical performance, we conducted electrochemical tests, such as Figure 3 As shown, at a current density of 0.1 mA cm-2, the CMC@Li-PEGDME solid polymer electrolyte exhibits significantly enhanced long-term stability, maintaining a low polarization within 4000 hours. In contrast, the Bare-PEGDME polyethylene glycol dimethyl ether-based electrolyte shows obvious polarization. In addition, as Figure 4 shown, under the constant current cycling conditions of 0.1 mA cm-2 and 1 mAh cm-2, the CMC@Li-PEGDME button battery operates stably with extremely low polarization for more than 3200 hours, while the Bare-PEGDME button battery shows obvious polarization aggravation after 2800 hours. Thanks to these advantages, the CMC@Li-PEGDME solid polymer electrolyte exhibits excellent cycle stability during fast charging. To further explore its critical current density, we tested the Li symmetric battery in the current density range of 0.1 to 0.75 mA cm-2. The results show that the CMC@Li-PEGDME solid polymer electrolyte can effectively reduce polarization and significantly improve the stability of lithium metal batteries, further verifying its application potential in all-solid-state lithium metal batteries. As Figure 5As shown, the overpotential gradually increases with the increase of current density. However, even at higher current densities, the CMC@Li-PEGDME solid polymer electrolyte still does not show a short-circuit phenomenon, indicating its excellent electrochemical stability. This stable electrochemical cycling performance is mainly attributed to the role of CMC@Li in the electrolyte, which can improve the lithium-ion coordination ability, promote the dissociation of lithium salts, and optimize the interface stability, thereby enhancing the uniformity of lithium deposition and inhibiting the formation of lithium dendrites. In addition, the introduction of CMC@Li helps to form a stable SEI layer, reduce interfacial side reactions, and improve electrode stability. To deeply explore the influence of SEI composition on electrochemical performance, we carried out XPS analysis on the lithium metal anode after cycling (as Figure 6 and Figure 7 shown) to analyze the regulation effect of CMC@Li-PEGDME solid polymer electrolyte on the SEI structure and composition. The XPS analysis results show that the CMC@Li-PEGDME electrolyte has significant advantages in SEI composition. The presence of LiF and other inorganic components indicates that a stable inorganic interfacial layer is formed by the decomposition of the electrolyte during cycling. Further analysis reveals that with the increase of sputtering depth, the organic components (such as C-F) gradually decrease, while the intensity of inorganic components (such as LiF and Li2O) increases, indicating that the CMC@Li-PEGDME solid polymer electrolyte helps to form a richer inorganic SEI layer. Compared with the Bare-PEGDME polyethylene glycol dimethyl ether-based electrolyte, the inorganic components on the surface of the CMC@Li-PEGDME solid polymer electrolyte electrode are more significant. This stable inorganic SEI layer can effectively regulate the lithium-ion deposition process, reduce the growth of lithium dendrites, and thus improve the cycle life of all-solid-state lithium metal batteries.

[0070] To evaluate the practical applicability of the CMC@Li-PEGDME solid polymer electrolyte in full cells, we assembled Li-LFP batteries. Compared with traditional solid electrolytes, the CMC@Li-PEGDME solid polymer electrolyte realizes more efficient ion transport and interface stability by enhancing the lithium-ion coordination ability and promoting the dissociation of lithium salts. These advantages effectively improve the cycle performance and rate performance of the battery, showing excellent application potential in all-solid-state lithium metal batteries (ASSLB). As Figure 8As shown, when cycling at a rate of 0.2C, the initial capacity of the lithium iron phosphate battery using the CMC@Li-PEGDME solid polymer electrolyte is 146.81 mAh g-1, which is significantly better than 116.97 mAh g-1 of the battery using the Bare-PEGDME dimethoxyethane-based electrolyte. After 220 cycles, the battery with the CMC@Li-PEGDME solid polymer electrolyte still maintains a capacity of 136.72 mAh g-1, while the specific capacity of the Bare-PEGDME button battery decreases significantly. To further evaluate the effect of the electrolyte on the rate performance, we conducted rate tests in the range of 0.1C to 1C. As Figure 9 shown, the lithium metal battery using the CMC@Li-PEGDME solid polymer electrolyte exhibits better discharge capacity at different rates. Specifically, at 0.1C, 0.2C, 0.5C, and 1C, the corresponding specific capacities of this electrolyte are 160.9 mAh g-1, 145.1 mAh g-1, 119.1 mAh g-1, and 71.1 mAh g-1, respectively, while the batteries with the Bare-PEGDME dimethoxyethane-based electrolyte are only 145.6 mAh g-1, 146.1 mAh g-1, 112.9 mAh g-1, and 34.7 mAh g-1. In addition, after returning to the 0.1C charging rate, the CMC@Li-PEGDME solid polymer electrolyte can still provide a reversible capacity of 156.7 mAh g-1, further demonstrating its excellent cycle stability and reversibility. This excellent performance can be attributed to the introduction of CMC@Li, which can effectively enhance the lithium ion coordination ability and promote the dissociation of lithium salts, thus optimizing ion transport and interfacial stability.

[0071] In summary, this study provides important guidance for achieving stable cycle performance and high energy density ASSLBs.

[0072] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and basic spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a solid polymer electrolyte, characterized in that, Including the following steps: S1. Preparation of polyethylene glycol dimethyl ether-based electrolyte: By using a solvent-free method, after fully mixing polyethylene glycol dimethyl ether (PEGDME) with a lithium salt, heat and stir until PEGDME is completely melted and the lithium salt is completely dissolved, thereby obtaining a polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME; S2. Preparation of solid polymer electrolyte: Add lithium carboxymethyl cellulose CMC@Li powder into the polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME, continue stirring at a constant temperature until the lithium carboxymethyl cellulose CMC@Li powder is completely dissolved, and obtain a lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME after cooling.

2. The preparation method of a solid polymer electrolyte according to claim 1, characterized in that, The lithium salt consists of lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, and lithium nitrate LiNO3.

3. The preparation method of a solid polymer electrolyte according to claim 1, wherein, The mass ratio of polyethylene glycol dimethyl ether PEGDME to lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, and lithium nitrate LiNO3 in the lithium salt is 3: 1.152 - 1.402: 0.187 - 0.229: 0.083 - 0.1014.

4. The preparation method of a solid polymer electrolyte according to claim 1, characterized in that, The mass ratio of polyethylene glycol dimethyl ether PEGDME to lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide salt LiFSI, and lithium nitrate LiNO3 in the lithium salt is 3: 1.28: 0.208: 0.

092.

5. The preparation method of a solid polymer electrolyte according to claim 1, wherein The mass ratio of lithium carboxymethyl cellulose CMC@Li powder to the polyethylene glycol dimethyl ether-based electrolyte Bare-PEGDME is 1: 40 - 50.

6. The preparation method of a solid polymer electrolyte according to claim 1, characterized in that, The temperature of the heating and stirring and the constant-temperature stirring is 110 - 120 °C.

7. A solid polymer electrolyte, characterized in that, Prepared by the method according to any one of claims 1 - 6.

8. The application of a solid polymer electrolyte according to claim 7, characterized in that, Application of lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME in all-solid-state lithium metal batteries.

9. The application of a solid polymer electrolyte according to claim 8, wherein, The application method is as follows: Inside a glove box filled with argon, heat the lithium carboxymethyl cellulose-polyethylene glycol dimethyl ether solid polymer electrolyte CMC@Li-PEGDME to 60 - 70 °C until it is completely melted, then successively place the negative electrode case, spring washer, and gasket, and place the lithium metal negative electrode sheet thereon. Subsequently, fully soak the molten solid polymer electrolyte CMC@Li-PEGDME with a 3501 battery separator and cover the lithium metal negative electrode sheet. Then place the positive electrode sheet, and finally cover the positive electrode case and press the battery tightly.

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