Polymer solid electrolyte membranes, their preparation methods and applications

Abstract

This disclosure provides a method for preparing a polymer solid electrolyte membrane, comprising: adding polyethylene oxide, lithium salt, and plasticizer to an organic solvent in a certain proportion, stirring and dissolving evenly to obtain an electrolyte solution; pouring the electrolyte solution into a mold, completely immersing a polymer separator in the electrolyte solution; waiting for the organic solvent in the electrolyte solution to evaporate, and then drying to obtain the polymer solid electrolyte membrane, wherein the molar ratio of the ether oxygen segment of polyethylene oxide to the lithium salt is (10-20):1; the molar ratio of the ether oxygen segment of polyethylene oxide to the plasticizer is (3-7):1; the plasticizer is selected from one or more of succinic anionyl nitrile, adiponitrile, and sebacate; and the polymer separator is selected from one of polypropylene wet-process separator, polypropylene dry-process separator, polyethylene separator, and polyimide separator. This disclosure also provides a polymer solid electrolyte membrane and its application in lithium metal batteries.

Description

Technical Field

[0001] This disclosure belongs to the field of all-solid-state lithium metal batteries and polymer solid electrolyte technology, and particularly relates to a polymer solid electrolyte membrane, its preparation method and application. Background Technology

[0002] Lithium metal batteries have broad application prospects in new energy vehicles, portable electronic devices, and large-scale energy storage systems due to their high energy density, excellent cycle stability, and light weight. However, traditional lithium battery systems use organic electrolytes as electrolytes, which suffer from problems such as electrolyte leakage, flammability, narrow electrochemical window, and poor chemical compatibility with lithium metal anodes. Compared with liquid electrolytes, solid-state electrolytes possess the characteristics of being non-flammable, heat-resistant, and relatively stable in lithium metal systems. In addition, they have a certain degree of mechanical strength, which can better suppress lithium dendrite growth, resist external stress impacts, and reduce the risk of thermal runaway, thereby significantly improving battery safety performance. Furthermore, solid-state electrolytes can be compatible with higher specific capacity positive and negative electrode materials, opening up room for increasing energy density. Therefore, developing all-solid-state electrolytes can fundamentally solve the intrinsic safety problems of liquid electrolytes and is one of the key factors in realizing next-generation power batteries and energy storage devices.

[0003] Polyethylene oxide (PEO) electrolytes have attracted much attention due to their advantages such as low cost, flexibility, good processability, and good chemical compatibility with lithium metal, making them one of the earliest commercially applied solid-state electrolytes. However, pure PEO polymer electrolytes exhibit high crystallinity at low temperatures, a high degree of coupling between lithium-ion transport and chain segment movement, and poor high-voltage stability and mechanical strength, resulting in poor electrochemical performance at low temperatures. This makes them unsuitable for high-voltage cathodes and leads to safety issues such as short circuits caused by lithium dendrite growth, hindering their commercial application in high-performance power batteries. Currently, the field often employs composite techniques with ceramic electrolytes or other polymer electrolytes to improve the overall performance of PEO electrolytes. However, these modification methods often only address one of the aforementioned shortcomings while also negatively impacting other properties. Therefore, developing a PEO polymer solid-state electrolyte with both excellent electrochemical performance and good mechanical strength remains essential. Summary of the Invention

[0004] In view of this, the present disclosure provides a polyoxyethylene polymer solid electrolyte membrane, its preparation method and application, in order to at least partially solve the above-mentioned technical problems.

[0005] In one aspect of this disclosure, a method for preparing a polyoxyethylene polymer solid electrolyte membrane is provided, comprising:

[0006] Polyethylene oxide, lithium salt and plasticizer are added to an organic solvent in a certain proportion and stirred until dissolved to obtain an electrolyte solution.

[0007] The electrolyte solution is poured into the mold, and the polymer diaphragm is completely immersed in the electrolyte solution.

[0008] After waiting for the organic solvent in the electrolyte solution to evaporate, the membrane is dried to obtain a solid electrolyte membrane.

[0009] The molar ratio of the ether oxygen segment of polyethylene oxide to the lithium salt is (10-20):1;

[0010] The molar ratio of the ether oxygen segment of polyethylene oxide to the plasticizer is (3-7):1;

[0011] The plasticizer is selected from one or more of succinic anhydride, adiponitrile, and sebacate.

[0012] The polymer membrane is selected from one of the following: polypropylene wet-process membrane, polypropylene dry-process membrane, polyethylene membrane, and polyimide membrane.

[0013] According to embodiments of this disclosure, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium bis(fluorosulfonyl)imide, and the organic solvent is acetonitrile.

[0014] According to embodiments of this disclosure, the molecular weight of the polyethylene oxide is 300,000 to 1,000,000.

[0015] According to embodiments of this disclosure, the mold is a polytetrafluoroethylene mold.

[0016] According to embodiments of this disclosure, the polymer diaphragm thickness is 12 μm to 25 μm.

[0017] According to embodiments of this disclosure, the evaporation method is natural evaporation, the evaporation time is 12h to 24h, and the drying method is vacuum heating drying, the drying temperature is 50℃ to 60℃, and the drying time is 12h to 24h.

[0018] In another aspect of this disclosure, a solid electrolyte membrane prepared by the above-described preparation method is provided.

[0019] According to embodiments of this disclosure, the thickness of the solid electrolyte membrane is 70 μm to 120 μm, the solid electrolyte membrane is suitable for environments ranging from 0°C to 60°C, the tensile modulus of the solid electrolyte membrane is 6 MPa to 12 MPa, and the ionic conductivity of the solid electrolyte membrane is 1 × 10⁻⁶. -4 S·cm -1 ~1×10 -3 S·cm -1 .

[0020] In another aspect of this disclosure, an application of the aforementioned solid electrolyte membrane in a lithium metal battery is provided.

[0021] According to embodiments of this disclosure, a lithium metal battery includes a solid electrolyte membrane, which is suitable for a cathode material selected from lithium iron phosphate cathode, nickel-cobalt-manganese ternary cathode, and lithium cobalt oxide cathode.

[0022] Based on the above technical solution, the solid electrolyte membrane, its preparation method, and its application provided by the present invention have at least one of the following beneficial effects:

[0023] (1) According to the embodiments of this disclosure, a polymer separator is introduced during the preparation of the solid electrolyte membrane to improve the mechanical strength of the solid electrolyte membrane. Simultaneously, a large amount of plasticizer is added to reduce the crystallinity of the polyethylene oxide (PEO) and the activation energy of lithium-ion transport, partially decoupling the dependence of lithium-ion transport on the ether oxygen segment kinetics. By controlling the ratio of the ether oxygen segments of the PEO to the lithium salt and plasticizer in the electrolyte membrane, a balance between electrochemical performance and mechanical strength is achieved, resulting in a solid electrolyte membrane with both excellent low-temperature electrochemical performance and mechanical strength, and broadening its electrochemical window. The preparation process uses a solution casting method, which is simple, low-cost, and compatible with commercially mature polymer separator and lithium battery production processes.

[0024] (2) According to the embodiments of this disclosure, the solid electrolyte membrane prepared by the solid electrolyte membrane preparation method proposed in this disclosure has a wide applicable temperature range, especially suitable for low temperature environment (0℃~25℃), and at the same time exhibits good low temperature ion conduction performance and good mechanical strength. Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation method of the solid electrolyte membrane in this disclosure;

[0026] Figure 2 This is a graph showing the conductivity changes of solid electrolyte membranes with different plasticizer contents prepared in Examples 1-3 of this disclosure at different temperatures;

[0027] Figure 3 These are stress-strain curves of the solid electrolyte membranes prepared in Example 1, Comparative Example 1, and Comparative Example 4 of this disclosure.

[0028] Figure 4 These are the electrochemical impedance spectra of the solid electrolyte membranes prepared in Examples 1, 1, and 4 of this disclosure at 25°C.

[0029] Figure 5 These are the electrochemical impedance spectra of the solid electrolyte membranes prepared in Examples 1, 1, and 4 of this disclosure at 0°C.

[0030] Figure 6 These are the linear voltammetric scan curves of the solid electrolyte membranes prepared in Examples 1, 1, and 4 of this disclosure. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments.

[0032] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] In the process of developing this disclosure, it was discovered that pure polyethylene oxide polymer solid electrolytes (PEOs) suffer from several drawbacks. These include high crystallinity, low ionic conductivity at both room and low temperatures, low transport number, and poor electrochemical performance; poor mechanical strength, making them susceptible to lithium dendrite growth and short circuits; and a narrow electrochemical window, hindering compatibility with high-voltage (4.2V and above) cathodes such as nickel-cobalt-manganese. Current modification techniques for solid electrolytes only address one aspect of these defects and inevitably affect other properties. For example, adding plasticizers can inhibit ethylene oxide crystallization, promote ether oxygen chain movement and lithium-ion transport, and improve ionic conductivity, thereby enhancing electrochemical performance. However, this further degrades the mechanical strength of the solid electrolyte membrane, leading to short circuits and other safety issues. While introducing a polymer separator can significantly improve the mechanical strength of the solid electrolyte, the ion-insulating polymer framework hinders lithium-ion transport, reducing electrochemical performance. Therefore, neither approach meets commercially viable performance requirements for solid electrolytes.

[0035] This disclosure proposes a method for preparing a solid electrolyte membrane. By introducing a polymer separator with certain mechanical strength and toughness, the mechanical strength of the solid electrolyte membrane is improved. Furthermore, the polymer separator can, to a certain extent, block the penetration and growth of lithium dendrites and, through its internal microporous structure, serve as a template for ion transport channels within the electrolyte, thereby improving ionic conductivity and electrochemical performance. Simultaneously, a large amount of plasticizer is added, enabling it to play a plasticizing role throughout the electrolyte membrane, reducing the crystallinity of the polyethylene oxide (PEO) and partially decoupling the dependence of lithium-ion transport on the ether oxygen chain kinetics of PEO, thus improving the ionic conductivity of the electrolyte. By controlling the ratio of ether oxygen chains to lithium salt and plasticizer in the solid electrolyte membrane, a compatibility and balance between electrochemical performance and mechanical strength is achieved, resulting in a solid electrolyte membrane with excellent low-temperature electrochemical performance and mechanical strength, while also broadening its electrochemical window. The prepared solid electrolyte membrane can be matched with cathode materials for lithium metal batteries, which is of great significance for the development of solid electrolyte and lithium metal battery technologies.

[0036] Figure 1 This is a flowchart of the preparation method of the solid electrolyte membrane in this disclosure.

[0037] like Figure 1 As shown, this disclosure proposes a method for preparing a solid electrolyte membrane, comprising the following steps S1 to S3:

[0038] Step S1: Add polyethylene oxide, lithium salt and plasticizer to an organic solvent in proportion, stir and dissolve evenly to obtain an electrolyte solution;

[0039] Step S2: Pour the electrolyte solution into the mold, and then completely immerse the polymer diaphragm in the electrolyte solution;

[0040] Step S3: Wait for the organic solvent in the electrolyte solution to evaporate, and then dry to obtain a solid electrolyte membrane. The molar ratio of the ether oxygen segment of polyethylene oxide to the lithium salt is (10-20):1; the molar ratio of the ether oxygen segment of polyethylene oxide to the plasticizer is (3-7):1; the plasticizer is selected from one or more of succinic anionyl nitrile, adiponitrile, and sebacate; and the polymer membrane is selected from one of polypropylene wet-process membrane, polypropylene dry-process membrane, polyethylene membrane, and polyimide membrane.

[0041] According to embodiments of this disclosure, a polymer separator is introduced during the preparation of the solid electrolyte membrane to improve its mechanical strength. Simultaneously, a large amount of plasticizer is added to reduce its crystallinity and the activation energy of lithium-ion transport, thereby increasing ionic conductivity and ultimately improving electrochemical performance. By controlling the ratio of the ether oxygen segments of polyethylene oxide to lithium salt and plasticizer in the solid electrolyte membrane, a balance between electrochemical performance and mechanical strength is achieved, resulting in a solid electrolyte membrane with both excellent low-temperature electrochemical performance and mechanical strength, and its electrochemical window is broadened.

[0042] According to embodiments of this disclosure, in step S1, the plasticizer is selected from one or more of succinic anionyl nitrile, adiponitrile, and sebacate, with succinic anionyl nitrile being preferred. Plasticizers with smaller molecular weights and volumes are more likely to enter the molecular chains of the polymer and can be more uniformly distributed in the polyethylene oxide, thereby reducing the crystallinity of the polyethylene oxide and partially decoupling the dependence of lithium-ion transport on polymer chain segment kinetics, thus improving the ionic conductivity of the electrolyte. Furthermore, the distance between the plasticizer and the oxygen (i.e., adjacent binding sites of lithium ions) in different ether oxygen segments of the polyethylene oxide is relatively small, which facilitates the formation of ion transport channels, thereby improving ionic conductivity and electrochemical performance. The polymer membrane is selected from one of polypropylene wet-process membranes, polypropylene dry-process membranes, polyethylene membranes, and polyimide membranes. The polymer membrane can serve as a framework, improving the mechanical strength of the solid electrolyte membrane and its ability to inhibit lithium dendrite growth, and its internal microporous structure provides a template for ion transport channels within the electrolyte. Furthermore, the polymer membrane thickness is 12–25 μm, for example, 12 μm, 15 μm, 20 μm, 23 μm, 25 μm, etc., and the pore size is 50–200 nm, for example, 80 nm, 100 nm, 120 nm, 140 nm, 150 nm, etc. A thinner membrane and smaller pore size can reduce ion transport obstacles, lower resistance, and thus improve ionic conductivity. The molar ratio of the ether oxygen segment of polyethylene oxide to the lithium salt is (10–20):1, for example, 10:1, 12:1, 15:1, 18:1, 20:1, etc. If there is too little lithium salt, the electrochemical performance of the electrolyte is poor, and the ionic conductivity decreases; if there is too much lithium salt, the mechanical properties of the solid electrolyte membrane deteriorate, and a complete electrolyte membrane cannot be formed. The molar ratio of the ether oxygen segment of polyethylene oxide to the plasticizer is (3-7):1, for example, 3:1, 4:1, 5:1, 6:1, 7:1, etc. Excessive plasticizer hinders ion movement within the polymer network, leading to decreased ion transport performance and also reducing the membrane's mechanical properties. Insufficient plasticizer results in only a slight improvement in electrochemical performance, making it difficult for the electrolyte membrane to meet the requirements of practical applications. This disclosure, in the preparation of the solid electrolyte membrane, ensures that the solid electrolyte membrane maintains both superior electrochemical performance and sufficient mechanical strength by adjusting the appropriate ratio between the ether oxygen segment of polyethylene oxide, the lithium salt, and the plasticizer, thus achieving compatibility and balance in all aspects of the solid electrolyte membrane's performance.

[0043] According to embodiments of this disclosure, the above preparation process is carried out in an argon-protected glove box, where the water and oxygen content is less than 0.01 ppm. This prevents the lithium salt from reacting with water, oxygen, and other impurities in the air, which could affect the quality and stability of the solid electrolyte membrane.

[0044] According to embodiments of this disclosure, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), and lithium bis(fluorosulfonyl)imide (LiFSI), with LiTFSI being preferred due to its excellent thermal stability, high ionic conductivity, and the absence of corrosive gases such as hydrogen fluoride during the reaction. Furthermore, the relatively difficult migration of the larger anion (TFSI-) in LiTFSI contributes to increasing the lithium ion transference number, further enhancing lithium ion transport performance. The organic solvent is acetonitrile, which effectively dissolves polyethylene oxide, the lithium salt, and the plasticizer, facilitating the preparation of a homogeneous electrolyte solution.

[0045] According to embodiments of this disclosure, the molecular weight of the polyethylene oxide is 300,000 to 1,000,000, and the molecular weight can be, for example, 300,000, 600,000, 900,000, or 1,000,000. A moderate molecular weight (300,000 to 1,000,000) of polyethylene oxide ensures that the solid electrolyte membrane possesses both excellent electrochemical and mechanical properties. The moderate molecular weight promotes appropriate chain segment movement and improves ionic conductivity. Simultaneously, an appropriate molecular weight helps to form a uniform polymer solution, resulting in a structurally uniform solid electrolyte membrane.

[0046] According to embodiments of this disclosure, the mold is a polytetrafluoroethylene (PTFE) mold. PTFE is a hydrophobic material with low surface energy, which can prevent polymer residues from remaining on the mold, maintain dimensional stability, and withstand high temperatures and various chemical environments.

[0047] According to embodiments of this disclosure, the evaporation method is natural evaporation, with an evaporation time of 12h to 24h, for example, 12h, 18h, 20h, 22h, 24h, etc. The drying method is vacuum heating drying, with a drying temperature of 50℃ to 60℃, for example, 50℃, 55℃, 60℃, etc., and a drying time of 12h to 24h, for example, 12h, 18h, 20h, 22h, 24h, etc.

[0048] In another aspect of this disclosure, a solid electrolyte membrane prepared by the above-described preparation method is provided.

[0049] According to embodiments of this disclosure, the prepared solid electrolyte membrane includes an electrolyte and a polymer membrane. During the preparation process, the electrolyte solution fully penetrates into the polymer membrane, and after solvent evaporation and drying, a uniform solid electrolyte membrane is formed.

[0050] According to embodiments of this disclosure, the thickness of the solid electrolyte membrane is 70 μm to 120 μm, for example, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, etc. The solid electrolyte membrane is suitable for environments ranging from 0℃ to 60℃, for example, 0℃, 25℃, 30℃, 40℃, 50℃, 60℃, etc., and is particularly suitable for low-temperature environments (0℃ to 25℃). The tensile modulus of the solid electrolyte membrane is 6 MPa to 12 MPa, for example, 6 MPa, 8 MPa, 10 MPa, 12 MPa, etc., and the ionic conductivity of the solid electrolyte membrane is 1×10⁻⁶. - 4 S·cm -1 ~1×10 -3 S·cm -1 For example, at 0°C, the ionic conductivity of a solid electrolyte membrane can reach 1.03 × 10⁻⁶. -4 S·cm -1 At 25℃, the ionic conductivity of the solid electrolyte membrane can reach 3.33 × 10⁻⁶. -4 S·cm -1 The ionic conductivity of the solid electrolyte membrane can reach 9.63 × 10⁻⁶ at 50℃. -4 S·cm -1 .

[0051] According to embodiments of this disclosure, the prepared solid electrolyte membrane has a wide applicable temperature range and is suitable for low-temperature environments, while exhibiting good low-temperature ion conductivity and good mechanical strength. This disclosure introduces a large amount of plasticizer, resulting in numerous plasticizer-modified regions throughout the electrolyte membrane, enabling them to function effectively across the entire membrane. Furthermore, the nitrile groups in the plasticizer can complex with lithium ions, thereby partially decoupling lithium-ion transport from its dependence on the movement of polyethylene oxide chain segments, further improving the low-temperature performance of the solid electrolyte membrane.

[0052] In a further aspect of this disclosure, an application of the above-described solid electrolyte membrane in a lithium metal battery is provided.

[0053] According to embodiments of this disclosure, a lithium metal battery includes a solid electrolyte membrane. The solid electrolyte membrane is suitable for use as a cathode material, and the solid electrolyte membrane is matched with a high-voltage cathode material to prepare the lithium metal battery. The cathode material in the lithium metal battery is selected from one of lithium iron phosphate cathode, nickel-cobalt-manganese ternary cathode, and lithium cobalt oxide cathode. It plays a role in storing and releasing lithium ions in the lithium metal battery and has a significant impact on the battery's energy density, charge / discharge efficiency, and safety.

[0054] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments. Unless otherwise specified, the experimental materials and reagents used in the following embodiments are commercially available. Methods not specifically described in the embodiments are conventional methods and can be performed according to the techniques or conditions described in the literature in this field or according to the product instructions.

[0055] Example 1:

[0056] This embodiment provides a polyethylene oxide composite solid electrolyte membrane, prepared in an argon-protected glove box, wherein the water and oxygen content is less than 0.01 ppm. The preparation method of the polyethylene oxide composite solid electrolyte membrane includes the following steps:

[0057] Step S1: Add polyethylene oxide (PEO, Mw = 600000), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), and succinate (SN) to 15 ml of acetonitrile (ACN) solvent, wherein the molar ratio of the ether oxygen segment of polyethylene oxide to lithium bis(trifluoromethanesulfonylimide) is 10:1, and the molar ratio of the ether oxygen segment (EO) of polyethylene oxide to succinate is 3:1. Stir magnetically until dissolved and homogeneous to obtain an electrolyte solution.

[0058] Step S2: Pour the electrolyte solution into a polytetrafluoroethylene (PTFE) mold, and then completely immerse the wet-process polypropylene diaphragm (PP) in the electrolyte solution;

[0059] Step S3: Allow the acetonitrile solvent in the electrolyte solution to evaporate naturally for 12 hours, then vacuum dry at 50°C for 12 hours to obtain a circular transparent solid electrolyte membrane with a diameter of 16 mm and a thickness of 100–120 μm, labeled as PP-PEO. 10 -LiTFSI-SN.

[0060] Example 2:

[0061] Compared with Example 1, the only difference in Example 2 is that in step S1, the molar ratio of the ether oxygen segment of polyethylene oxide to succinic acid is 5:1. All other preparation processes are the same as in Example 1, and a solid electrolyte membrane is prepared.

[0062] Example 3:

[0063] Compared with Example 1, the only difference in Example 3 is that in step S1, the molar ratio of the ether oxygen segment of polyethylene oxide to succinic acid is 7:1. All other preparation processes are the same as in Example 1, and a solid electrolyte membrane is prepared.

[0064] Comparative Example 1:

[0065] Compared with Example 1, the only difference in Comparative Example 1 is that succinic anionylene was not added in step S2; all other preparation processes were the same as in Example 1. The solid electrolyte membrane prepared was labeled as PP-PEO. 10 -LiTFSI.

[0066] Comparative Example 2:

[0067] Compared with Example 1, the only difference in Comparative Example 2 is that a wet-process polypropylene membrane was not used in step S2. All other preparation processes were the same as in Example 1, and the resulting solid electrolyte membrane was labeled as PEO. 10 -LiTFSI-SN.

[0068] Comparative Example 3:

[0069] Compared with Example 1, the only difference in Comparative Example 3 is that in step S2, no plasticizer and polypropylene membrane were used. All other preparation processes were the same as in Example 1, and the resulting solid electrolyte membrane was labeled as PEO. 10 -LiTFSI.

[0070] Comparative Example 4:

[0071] The conventional method for preparing polyethylene oxide solid electrolyte membranes is carried out in an argon-protected glove box, where the water and oxygen content is less than 0.01 ppm. The conventional method for preparing polyethylene oxide solid electrolyte membranes includes the following steps:

[0072] Step S1: Add polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide and succinate to 15 ml of acetonitrile solvent, wherein the molar ratio of the ether oxygen segment of polyethylene oxide to lithium bis(trifluoromethanesulfonyl)imide is 18:1. Stir magnetically until dissolved and homogeneous to obtain an electrolyte solution.

[0073] Step S2: Pour the electrolyte solution into a polytetrafluoroethylene mold;

[0074] Step S3: Allow the acetonitrile solvent in the electrolyte solution to evaporate naturally for 12 hours, then vacuum dry at 60°C for 12 hours to obtain a solid electrolyte membrane, labeled as PEO. 18 -LiTFSI.

[0075] The solvent was removed by natural evaporation for 12 hours and vacuum drying at 60°C for 12 hours, resulting in a polyoxyethylene solid electrolyte membrane, labeled PEO. 18 -LiTFSI.

[0076] The ionic conductivity values ​​of Examples 1 to 3 were tested, and the results are recorded in Table 1. Table 1 shows the ionic conductivity values ​​of three solid electrolyte membranes with different plasticizer contents prepared in Examples 1 to 3 of this disclosure at different temperatures.

[0077] Table 1

[0078]

[0079] Figure 2 This is a graph showing the conductivity changes of three solid electrolyte membranes with different plasticizer contents prepared in Examples 1-3 of this disclosure at different temperatures.

[0080] Based on the data in Table 1 and Figure 2 It is known that the ionic conductivity of the solid electrolyte membrane increases with increasing ambient temperature. Lithium ions in the solid electrolyte membrane coordinate with the oxygen in the ether oxygen segments of polyethylene oxide (PEO). Accompanying the chain movement of PEO, lithium ions continuously coordinate and decoordinate, moving forward. Therefore, at higher ambient temperatures, the crystallinity of PEO decreases, chain movement is enhanced, and lithium ion transport is also strengthened. With increasing temperature, the electrochemical performance becomes more excellent. Increasing the amount of succinate, when the molar ratio of PEO ether oxygen segments to succinate is 3:1, the ionic conductivity of the solid electrolyte membrane at 0℃ can reach 1.03081 × 10⁻⁶. -4 S·cm -1 It exhibits excellent low-temperature electrochemical performance. The introduction of a large amount of plasticizer significantly reduces the crystallinity of the polyethylene oxide matrix, improving polymer chain segment kinetics and enabling succinic anhydride to play a plasticizing role throughout the electrolyte membrane. Furthermore, the nitrile groups in the succinic anhydride complex with lithium ions, partially decoupling the dependence of lithium ion transport on the kinematics of the polyethylene oxide chain segments. This results in the solid electrolyte membrane prepared in the embodiments of this disclosure exhibiting good low-temperature ion transport performance, such as at 0°C.

[0081] Table 2 shows the composition, proportion, and ionic conductivity values ​​of the solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-4 of this disclosure at 25°C.

[0082] Table 2

[0083]

[0084] Table 2 shows that when the molar ratio of ethylene oxide ether oxygen segments to lithium salt is 10:1, without the addition of plasticizers and polymer separators, the solid electrolyte membrane prepared has poor strength (Comparative Example 3) and can hardly form a film. When the molar ratio of ethylene oxide ether oxygen segments to lithium salt is adjusted to 18:1, the solid electrolyte membrane prepared without the addition of plasticizers and polymer separators (Comparative Example 4) can form a film, but the ionic conductivity at 25°C is only 7.65 × 10⁻⁶. -6 S·cm -1The electrochemical performance was not improved. Even with a 10:1 molar ratio of ethylene oxide ether oxygen segments to lithium salt and a 3:1 molar ratio of ethylene oxide ether oxygen segments to succinic anhydride, the solid electrolyte membrane prepared without a polymer separator (Comparative Example 2) still failed to form a film, despite the addition of a large amount of accelerator to improve electrochemical performance. Therefore, in the preparation of solid electrolyte membranes, the ratio of ethylene oxide ether oxygen segments to lithium salt and plasticizer has a significant impact on the mechanical strength and ionic conductivity of the solid electrolyte membrane. Excessive lithium salt content leads to a decrease in the mechanical properties of the solid electrolyte, preventing the formation of a complete solid electrolyte membrane. On the other hand, while the addition of plasticizer can improve the electrochemical performance of the solid electrolyte, it is difficult to form a solid electrolyte membrane with only plasticizer added. Therefore, in the preparation of solid electrolyte membranes, it is necessary to comprehensively consider the ratio of ethylene oxide ether oxygen segments, lithium salt, and plasticizer to ensure that the solid electrolyte membrane has good mechanical strength and ionic conductivity.

[0085] Figure 3 This is Embodiment 1 of the present disclosure (PP-PEO) 10 -LiTFSI-SN), Comparative Example 1 (PP-PEO) 10 -LiTFSI) and Comparative Example 4 (PEO) 18 Stress-strain curves of three solid electrolyte membranes prepared in LiTFSI.

[0086] Combined Table 2 and Figure 3 It can be seen that in the system without polymer membrane reinforcement (i.e., comparative example 4PEO), 18 -LiTFSI), the tensile modulus of the solid electrolyte membrane is in the range of 0.3MPa to 0.6MPa, while in the system with polymer membrane reinforcement but without plasticizer (i.e., comparative example 1PP-PEO) 10 LiTFSI), the tensile modulus of the solid electrolyte membrane can be increased to 6MPa~12MPa, but its ionic conductivity at room temperature is low. Example 1 of this disclosure (PP-PEO) 10 The solid electrolyte membrane prepared in LiTFSI-SN can achieve a tensile modulus of 6.715 MPa, while also possessing good mechanical strength and electrochemical performance. It can resist battery short circuit problems caused by lithium dendrite growth and penetration, thus improving battery safety during application.

[0087] Figure 4 This is Embodiment 1 of the present disclosure (PP-PEO) 10 -LiTFSI-SN), Comparative Example 1 (PP-PEO) 10 -LiTFSI) and Comparative Example 4 (PEO) 18Electrochemical impedance spectroscopy of three solid electrolyte membranes prepared in LiTFSI at 25 °C.

[0088] Depend on Figure 4 As can be seen, Embodiment 1 of this disclosure (PP-PEO) 10 The solid electrolyte membrane prepared in LiTFSI-SN can achieve an ionic conductivity of 4.25 × 10⁻⁶ at 25 °C. -4 S·cm -1 It was significantly higher than that of Comparative Example 1 and Comparative Example 4.

[0089] Figure 5 This is Embodiment 1 of the present disclosure (PP-PEO) 10 -LiTFSI-SN), Comparative Example 1 (PP-PEO) 10 -LiTFSI) and Comparative Example 4 (PEO) 18 Electrochemical impedance spectroscopy of three solid electrolyte membranes prepared in LiTFSI at 0 °C.

[0090] Depend on Figure 5 As can be seen, Embodiment 1 of this disclosure (PP-PEO) 10 The solid electrolyte membrane prepared in LiTFSI-SN still maintains an ionic conductivity of 1.03 × 10⁻⁶ at 0 °C. -4 S·cm -1 Comparative Example 1 (PP-PEO) 10 -LiTFSI) and Comparative Example 4 (PEO) 18 The ionic conductivity of the solid electrolyte membrane prepared in LiTFSI can only reach 1.33 × 10⁻⁶. -6 S·cm -1 and 4.13×10 -7 S·cm -1 This demonstrates that Example 1 of this disclosure still exhibits excellent electrochemical performance at low temperatures.

[0091] Figure 6 This is Embodiment 1 of the present disclosure (PP-PEO) 10 -LiTFSI-SN), Comparative Example 1 (PP-PEO) 10 -LiTFSI) and Comparative Example 4 (PEO) 18 Linear voltammetric scan curves of three solid electrolyte membranes prepared in LiTFSI.

[0092] Depend on Figure 6 As can be seen, Embodiment 1 of this disclosure (PP-PEO) 10The solid electrolyte membrane prepared in the LiTFSI-SN process exhibits a broadened electrochemical window (4.7V vs. Li+ / Li). The physical entanglement between the introduced polypropylene wet-process separator and the electrolyte (polyethylene oxide, lithium salt, and plasticizer) inhibits the decomposition of the electrolyte at high voltages (4.2V and above), resulting in a broadened electrochemical window. This allows the solid electrolyte membrane to be matched with high-voltage cathode materials and applied to lithium metal batteries, which is beneficial for improving the energy density of the battery.

[0093] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for preparing a polymer solid electrolyte membrane, comprising: Polyethylene oxide, lithium salt and plasticizer are added to an organic solvent in a certain proportion and stirred until dissolved to obtain an electrolyte solution. The electrolyte solution is poured into a mold, and the polymer diaphragm is completely immersed in the electrolyte solution. After waiting for the organic solvent in the electrolyte solution to evaporate, the membrane is dried to obtain a solid electrolyte membrane. The molar ratio of the ether oxygen segment of the polyethylene oxide to the lithium salt is (10~15):1; The molar ratio of the ether oxygen segment of the polyethylene oxide to the plasticizer is (3~4):1; The plasticizer is selected from one or more of succinic acid, adiponitrile, and sebacate. The polymer membrane is selected from one of the following: polypropylene wet-process membrane, polypropylene dry-process membrane, polyethylene membrane, and polyimide membrane; The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium bis(fluorosulfonyl)imide.

2. The preparation method according to claim 1, wherein, The organic solvent is acetonitrile.

3. The preparation method according to claim 1, wherein, The molecular weight of the polyoxyethylene is 300,000 to 1,000,000.

4. The preparation method according to claim 1, wherein, The mold is a polytetrafluoroethylene mold.

5. The preparation method according to claim 1, wherein, The thickness of the polymer membrane is 12 μm to 25 μm.

6. The preparation method according to claim 1, wherein, The volatilization method is natural volatilization, and the volatilization time is 12 h to 24 h; The drying method is vacuum heating drying, with a drying temperature of 50 ℃~60 ℃ and a drying time of 12 h~24 h.

7. A polymer solid electrolyte membrane prepared by any one of claims 1 to 6.

8. The polymer solid electrolyte membrane according to claim 7, wherein, The thickness of the polymer solid electrolyte membrane is 70 μm to 120 μm; The polymer solid electrolyte membrane is suitable for environments ranging from 0 ℃ to 60 ℃; The tensile modulus of the polymer solid electrolyte membrane is 6 MPa ~ 12 MPa; The polymer solid electrolyte membrane has an ionic conductivity of 1×10⁻⁶. -4 S·cm⁻¹~1×10⁻¹ -3 S·cm⁻¹.

9. The application of a polymer solid electrolyte membrane as described in claim 7 or 8 in a lithium metal battery.

10. The application according to claim 9, wherein, The lithium metal battery includes a polymer solid electrolyte membrane, a positive electrode, and a lithium metal negative electrode. The polymer solid electrolyte membrane is suitable for the positive electrode material, which is selected from lithium iron phosphate positive electrode, nickel-cobalt-manganese ternary positive electrode, and lithium cobalt oxide positive electrode.

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