A composite polymer solid-state electrolyte and a preparation method, solid-state lithium metal battery

Abstract

The application discloses a kind of composite polymer solid electrolyte and preparation method, solid-state lithium metal battery, belong to solid battery technical field.Aiming at the problems of low room temperature ionic conductivity of existing polyethylene oxide-based solid electrolyte, poor mechanical properties and difficult to balance both, the application introduces the plasticizer of four nitrile diamine with specific structure and nano alumina filler into polyethylene oxide matrix synergistically.The four nitrile diamine is shown in general formula (I), preferably N,N,N',N'-tetra (2-cyanoethyl) -1,3-propanediamine.The room temperature ionic conductivity of the obtained electrolyte membrane can reach 1.0×10 ‑4 S / cm, the tensile strength reaches 1.7MPa, and the elongation at break is as high as 1500%;The migration loss of small molecule plasticizer is eliminated, and high ionic conductivity and excellent mechanical properties are combined, and the capacity retention rate is greater than or equal to 93% after being assembled into solid-state lithium metal battery and being cycled for 100 times at 0.1C rate, suitable for the preparation of solid-state lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, specifically relating to a composite polymer solid electrolyte and its preparation method, and a solid lithium metal battery. Background Technology

[0002] Traditional liquid lithium-ion batteries use flammable carbonate-based organic electrolytes, posing safety hazards such as leakage, combustion, and even explosion. Furthermore, they cannot effectively suppress lithium dendrite growth, hindering the practical application of lithium metal batteries. Solid-state electrolytes, due to their advantages such as non-flammability, wide electrochemical window, and compatibility with lithium metal anodes, are considered a key approach to solving these safety issues.

[0003] Polyethylene oxide (PEO)-based polymer solid electrolytes have become a research hotspot due to their excellent lithium salt solubility, superior flexibility, and ease of processing. The ether oxygen atoms on the PEO segments can react with lithium ions (Li... + Coordination-decoordination occurs, promoting lithium-ion transport, and PEO has good interfacial compatibility with lithium metal anodes. However, PEO-based solid electrolytes face the following technical bottlenecks in practical applications: (1) Low ionic conductivity at room temperature. (2) Insufficient mechanical properties. (3) Existing modification strategies suffer from trade-offs.

[0004] Chinese patent CN118522946A discloses an all-solid-state polymer electrolyte and its preparation method. It uses polymers containing ether bonds or nitrile groups, one-dimensional nanofillers, and lithium sulfonylimide salt as raw materials to prepare a solvent-free electrolyte membrane via a eutectic hot-pressing method. This scheme improves conductivity to some extent by introducing one-dimensional nanofillers to construct ion transport channels. However, this scheme relies on hot-pressing, which requires sophisticated equipment, and the component stability and filler dispersion uniformity of the eutectic system are difficult to control precisely during long-term operation. Furthermore, the nitrile groups introduced as polymer side chains or end groups have limited effectiveness in inhibiting PEO crystallization due to group density and steric hindrance, resulting in a limited improvement in conductivity. Chinese patent CN118263510A discloses a COF composite polymer solid electrolyte and its preparation method. It first synthesizes a covalent organic framework material, then composites it with polyethylene oxide and a zinc salt solution, and dries it to obtain an electrolyte membrane. This scheme utilizes the ordered pore structure and Lewis acid sites of the COF material to improve the ionic conductivity and cycle stability of the PEO-based electrolyte to some extent. However, the synthesis of COF materials is complicated, requiring freezing-vacuuming-thawing cycles and long-term heating reactions, resulting in low yield and high cost, which is not conducive to large-scale preparation. Furthermore, the introduction of zinc salt may trigger electrochemical side reactions, affecting the interfacial compatibility between the electrolyte and the lithium metal anode.

[0005] In summary, how to significantly improve the room-temperature ionic conductivity of PEO-based solid electrolytes while synergistically enhancing their mechanical properties and electrochemical interface stability, thus achieving a balance between high ionic conductivity and high mechanical strength, is a pressing technical challenge in this field. Summary of the Invention

[0006] One of the objectives of this invention is to provide a composite polymer solid electrolyte to solve the technical problems of low ionic conductivity, poor mechanical properties, and insufficient interfacial stability of existing PEO-based solid electrolytes.

[0007] The second objective of this invention is to provide a method for preparing a composite polymer solid electrolyte, which is used to prepare the aforementioned composite polymer solid electrolyte.

[0008] A third objective of this invention is to provide a solid-state lithium metal battery, comprising the aforementioned composite polymer solid electrolyte.

[0009] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a composite polymer solid electrolyte is characterized by comprising, by mass parts: 100 parts of polyethylene oxide; 30-50 parts lithium salt; 5-25 parts of tetranitrile diamine; 5-25 parts of nano-alumina; The tetranitrile diamine has the structure shown in general formula (I): Where n is an integer from 2 to 8.

[0010] Multiple polar nitrile groups on the tetranitrile diamine molecule can insert between PEO segments, disrupting their regular arrangement, significantly reducing crystallinity, and enhancing chain mobility. Nano-alumina, as a rigid filler, provides physical reinforcement. More importantly, the nitrile groups form a hydrogen bond network with the hydroxyl groups on the nano-alumina surface, "anchoring" the plasticizer to the filler surface. This avoids the problem of mechanical property deterioration caused by the release of traditional small-molecule plasticizers and prevents the aggregation of nano-fillers. Thus, high ionic conductivity and excellent mechanical properties are simultaneously achieved in a single electrolyte membrane.

[0011] Furthermore, the preparation method of the tetranitrile diamine is as follows: S1 Under ice-water bath and nitrogen protection conditions, C2-C8 alkylene diamine is added to the reaction vessel, and the first part of acrylonitrile is slowly added dropwise, controlling the dropping rate to keep the temperature of the reaction system below 30°C. In step S2, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is dissolved in the second part of acrylonitrile to form a lithium salt-containing acrylonitrile solution, which is then slowly added dropwise to the reaction system in step S1. After S3 is added, the reaction system is heated to 45-55℃ and the reaction continues for 20-28 hours. After the S4 reaction is completed, excess acrylonitrile and low-boiling-point impurities are removed by vacuum distillation. Water is added to the residue, and after stirring, the mixture is allowed to stand and separate into layers. The aqueous phase is separated, and the organic phase is washed with ethanol and dried to obtain tetranitrile diamine.

[0012] Furthermore, the total molar ratio of the C2-C8 alkylene diamine to acrylonitrile is 1:(4.5-5.5), and the amount of lithium bis(trifluoromethanesulfonyl)imide is 0.8-1.2 mol of the molar amount of the C2-C8 alkylene diamine.

[0013] Based on the Michael nucleophilic addition reaction of aliphatic primary diamines with acrylonitrile, the four active hydrogens of the primary amino groups at both ends of the diamine are used to gradually add to the α,β-unsaturated double bonds of acrylonitrile to generate tetranitrile diamine. Lithium bis(trifluoromethanesulfonyl)imide is used as a Lewis acid catalyst to enhance its electrophilic activity by coordinating with the cyano group of acrylonitrile, thereby reducing the activation energy of the reaction and inhibiting the self-polymerization side reaction. The temperature of the strongly exothermic reaction is controlled by adding acrylonitrile in two stages, while a slight excess of acrylonitrile is used to ensure complete reaction of the active hydrogens of the diamine. Finally, the product is purified by vacuum distillation to remove low-boiling substances, washing with water to remove catalyst and water-soluble impurities, and washing with ethanol to obtain a high-purity product.

[0014] Furthermore, the tetranitrile diamine is N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine. N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine has a molecular structure of a central flexible propyl chain and four terminal strongly polar cyanoethyl groups. The four cyanoethyl groups can disrupt the van der Waals forces between PEO chain segments in multiple directions and at multiple sites, effectively inhibiting crystallization; simultaneously, multiple nitrile groups can form multi-point hydrogen bonds with the surface of nano-alumina, enhancing the anchoring effect and making the synergistic plasticizing effect more stable and durable.

[0015] Furthermore, the polyethylene oxide has a weight-average molecular weight of 400,000 to 800,000. PEO with a weight-average molecular weight of 400,000 to 800,000 has moderate chain entanglement and film-forming properties, which can form a self-supporting film without causing dissolution difficulties or hindering chain segment movement due to excessively high molecular weight.

[0016] Furthermore, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxaborate, lithium hexafluorophosphate, or lithium perchlorate; the molar ratio of the ether oxygen group in the polyethylene oxide to the lithium ion in the lithium salt is (15-25):1. The lithium salt is selected from large anionic salts such as LiTFSI, whose anions are easily dissociated and can effectively coordinate with the PEO ether oxygen chain to transport Li. + At this ratio, the lithium salt can fully dissociate to provide sufficient charge carriers, while avoiding the formation of ion pairs or self-aggregation of excess lithium salt, thus ensuring the free Li...+ Maximize concentration.

[0017] Furthermore, the amount of tetranitrile diamine added is 5-20% of the mass of polyethylene oxide. If the amount added is too small, the effect of inhibiting crystallization will be insignificant and the improvement of electrical conductivity will be limited; if the amount added is too large, it will lead to excessive plasticization, diluting the lithium salt concentration and weakening the mechanical reinforcement effect of the filler network.

[0018] Furthermore, the nano-alumina has a particle size of 30-100 nm and is added at 5-20% of the mass of polyethylene oxide. Nano-alumina possesses a high specific surface area, providing sufficient surface hydroxyl groups to form hydrogen bonds with nitrile groups, while also being easily and uniformly dispersed in the matrix. Insufficient addition makes it difficult to form an effective reinforcing network and hydrogen bond anchoring sites, while excessive addition easily leads to agglomeration and the formation of defects, hindering ion transport.

[0019] Secondly, a method for preparing a composite polymer solid electrolyte includes the following steps: (1) Dissolve the prescribed amount of polyethylene oxide and lithium salt in anhydrous acetonitrile and stir at 15-35℃ until completely dissolved to form a transparent solution; (2) Add the prescribed amount of tetranitrile diamine and nano alumina to the solution obtained in step (1), and continue stirring at 15-35℃ for 8-16 hours to obtain a homogeneous blended slurry; (3) The blended slurry is poured into a mold, and the solvent is allowed to evaporate naturally at room temperature for 12-24 hours. The mixture is then vacuum dried to obtain the composite polymer solid electrolyte.

[0020] Furthermore, in step (3), the vacuum drying temperature is 50-60℃ and the drying time is 24 hours.

[0021] The preparation method employs solution casting, with each component mixed at the molecular level to ensure sufficient contact between tetranitrile diamine and nano-alumina to form a hydrogen bond network. Slow solvent evaporation at room temperature allows the polymer chains to fully extend and arrange themselves, while vacuum drying at 50-60℃ completely removes residual solvent without disrupting the hydrogen bonds, ensuring a uniform structure and stable performance of the final electrolyte membrane.

[0022] Thirdly, a solid-state lithium metal battery comprising the aforementioned composite polymer solid electrolyte.

[0023] Furthermore, the battery also includes a positive electrode and a negative electrode, wherein the active material of the positive electrode is at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium cobalt oxide, and the negative electrode is metallic lithium or a lithium alloy.

[0024] When this composite electrolyte is used in solid-state lithium metal batteries, its high ionic conductivity ensures the battery's rate performance, its excellent mechanical strength effectively inhibits lithium dendrite growth and puncture, its stable interface extends cycle life, and when matched with high-voltage cathodes such as lithium iron phosphate, it can fully utilize its capacity, thus achieving a high-safety, long-cycle solid-state lithium metal battery.

[0025] The beneficial effects of this invention are: (1) The composite polymer solid electrolyte of the present invention contains 100 parts of polyethylene oxide, 30-50 parts of lithium salt, 5-25 parts of tetranitrile diamine and 5-25 parts of nano alumina. By combining a tetranitrile diamine plasticizer with nano alumina filler, the plasticizer molecules are anchored on the filler surface by utilizing the dynamic hydrogen bond network formed by multiple polar nitrile groups (-CN) on the tetranitrile diamine and the hydroxyl groups on the surface of nano alumina. This simultaneously solves the problems of low conductivity caused by high crystallinity of PEO and the deterioration of mechanical properties and migration and loss of single plasticizer.

[0026] (2) The polynitrile group structure of tetranitrile diamine used in this invention can strongly weaken the van der Waals forces between PEO chain segments, significantly inhibit its crystallization, and increase the proportion of amorphous regions; at the same time, the surface energy of nano-alumina can promote the dissociation of lithium salts (especially LiTFSI), generating more free Li + Its synergistic effect with tetranitrile diamine further constructs a continuous ion transport channel. Together, they enable the electrolyte to achieve an ionic conductivity of 1.0 × 10⁻⁶ at room temperature. -4 The S / cm ratio is more than 10 times higher than that of unmodified pure PEO electrolyte, meeting the room temperature operation requirements of solid-state batteries.

[0027] (3) The nano-alumina used in this invention serves as a rigid filler, acting as a physical crosslinking point and reinforcing phase, significantly improving tensile strength. Meanwhile, tetranitrile diamine is linked to the filler network via hydrogen bonds, effectively limiting its plasticizing effect to the filler interface region. This achieves both the softening of the PEO chain segments and avoids excessive plasticizer release leading to overall membrane softening. The resulting electrolyte membrane possesses both high strength and high ductility, with a tensile strength reaching 1.7 MPa and an elongation at break as high as 1500%, solving the technical problem of traditional electrolytes where "strength and flexibility are difficult to achieve simultaneously."

[0028] (4) The lithium-ion symmetric battery using the composite polymer solid electrolyte of this invention exhibits excellent interfacial stability, eliminating plasticizer migration and loss. Because the tetranitrile diamine molecules are effectively anchored through strong hydrogen bonds between the polynitrile groups and the surface of nano-alumina, the migration and volatilization of small-molecule plasticizers during long-term cycling or high-temperature storage are prevented, thereby improving the long-term structural stability, thermal stability, and electrode / electrolyte interfacial compatibility of the electrolyte, and avoiding interfacial degradation caused by plasticizer loss. The lithium-ion symmetric battery using the electrolyte of this invention achieves a performance of 0.1 mA / cm². 2It can cycle stably for more than 2200 hours at current density without any signs of short circuit.

[0029] (5) The composite polymer solid electrolyte prepared by this invention, when matched with a lithium iron phosphate cathode and a lithium metal anode to form an all-solid-state battery, benefits from high ionic conductivity and a stable interface. At 0.1C rate, the initial discharge specific capacity can reach 160 mAh / g, close to the theoretical capacity. After 100 cycles, the capacity retention exceeds 93%, demonstrating excellent cycle stability and reversibility. Furthermore, the preparation method of this invention uses conventional solution casting, a mature process that requires no additional complex steps and is easy to scale up. The "physical synergistic" modification strategy of this invention does not depend on a specific polymer structure and can be extended to other polymer electrolyte systems. Attached Figure Description

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] Figure 1 The proton nuclear magnetic resonance spectrum of N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine (tetranitrile diamine) used in this invention ( 1 H NMR); Figure 2 The DSC curves are of the composite polymer solid electrolytes prepared in Examples 1-4 of this invention; Figure 3 The stress-strain curves are those of the composite polymer solid electrolytes prepared in Examples 1-4 of this invention. Figure 4 The Arrhenius plots show the ionic conductivity of the composite polymer solid electrolytes prepared in Example 3 and Comparative Examples 1-2 of this invention. Figure 5 The voltage-time curves of lithium symmetric batteries with composite polymer solid electrolytes prepared in Example 3 and Comparative Examples 1-2 of this invention are shown. Figure 6 The charge / discharge specific capacity-cycle count curves of the LFP full cell prepared using the composite polymer solid electrolyte of Example 3 of this invention are shown. Figure 7 The charge-discharge plateau curves of the LFP full cell prepared using the composite polymer solid electrolyte in Example 3 of this invention are shown for different number of cycles. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0033] All operations in the examples and comparative examples were performed in a glove box filled with high-purity argon (H2O, O2 < 0.1 ppm). Main raw material: polyethylene oxide (PEO, M... w =600,000), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, purity 99.9%), nano-alumina (γ phase, particle size 50 nm), anhydrous acetonitrile, tetranitrile diamine (N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine).

[0034] Preparation Example 1 Under ice-water bath and nitrogen protection, propylenediamine (7.4 g, 0.1 mol) was added to a 250 mL three-necked flask, and acrylonitrile (21.2 g, 0.4 mol) was slowly added dropwise, controlling the dropping rate to keep the reaction temperature below 30 °C. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 0.29 g, 0.001 mol, 1 mol%) was dissolved in acrylonitrile (5.3 g, 0.1 mol) to form a lithium salt-containing acrylonitrile solution, which was then slowly added dropwise to the above reaction system. The total molar ratio of propylenediamine to acrylonitrile was 1:5. After the addition was complete, the temperature was raised to 50 °C, and the reaction was continued for 24 hours. After the reaction was complete, excess acrylonitrile and low-boiling substances were removed by vacuum distillation. 200 mL of water was added to the residue, and after stirring, the mixture was allowed to stand and separate into layers. The aqueous phase was separated, and the organic phase was washed with ethanol (100 mL × 3). After drying, a pale yellow viscous liquid product was obtained, namely tetranitrile diamine (n = 3,N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine). The 1H NMR spectrum of N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine is shown below. 1 H NMR) such as Figure 1 As shown.

[0035] Preparation Example 2 The preparation process in this example is the same as in Preparation Example 1, except that propylenediamine is replaced with ethylenediamine of the same molar mass to prepare tetranitrile diamine (N,N,N',N'-tetra(2-cyanoethyl)-1,2-ethylenediamine).

[0036] Preparation Example 3 The preparation process in this example is the same as that in Preparation Example 1, except that propylenediamine is replaced with butanediamine of the same molar mass to prepare tetranitrile diamine (N,N,N',N'-tetra(2-cyanoethyl)-1,4-butanediamine).

[0037] Example 1 (alumina content 15 wt%, tetranitrile diamine content 5 wt%) Weigh 1.00 g PEO and 0.333 g LiTFSI (EO:Li = 20:1), dissolve them in 20 mL of anhydrous acetonitrile, and stir at 25 °C for 2 hours until completely dissolved. Add 0.15 g nano-alumina (equivalent to 15 wt% of PEO mass) and 0.05 g tetranitrile diamine (Preparation Example 1, equivalent to 5 wt% of PEO mass), and continue stirring at 25 °C for 12 hours to obtain a homogeneous blended slurry.

[0038] The slurry was cast into a polytetrafluoroethylene mold and allowed to evaporate the solvent naturally at room temperature for 24 hours. It was then transferred to a vacuum drying oven and dried at 55°C and -0.1 MPa for 24 hours to obtain a composite polymer solid electrolyte with a thickness of approximately 150 μm, denoted as PEO-A15-N5. Its DSC curve is shown below. Figure 2 As shown, the stress-strain curve is as follows: Figure 3 As shown.

[0039] The prepared composite polymer solid electrolyte was applied to solid lithium metal batteries.

[0040] Example 2 (alumina content 15 wt%, tetranitrile diamine content 10 wt%) The preparation process in this embodiment is the same as in Example 1, except that the amount of tetranitrile diamine added is 0.10 g (Preparation Example 1, equivalent to 10 wt% of PEO mass). The resulting composite polymer solid electrolyte is designated as PEO-A15-N10; its DSC curve is shown below. Figure 2 As shown, the stress-strain curve is as follows: Figure 3 As shown.

[0041] Example 3 (alumina content 15 wt%, tetranitrile diamine content 15 wt%) The preparation process in this embodiment is the same as in Example 1, except that the amount of tetranitrile diamine added is 0.15 g (Preparation Example 1, equivalent to 15 wt% of PEO mass). The resulting composite polymer solid electrolyte is denoted as A15N15; its DSC curve is shown below. Figure 2 As shown, the stress-strain curve is as follows: Figure 3 As shown, the Arrhenius diagram of ionic conductivity is as follows: Figure 4 As shown, the voltage-time curve of a lithium symmetric battery is as follows: Figure 5 As shown.

[0042] After applying the composite polymer solid electrolyte to a solid lithium metal battery, the charge / discharge specific capacity-cycle count curve of the battery is as follows: Figure 6 As shown; the charge / discharge plateau curves corresponding to different battery cycles are as follows: Figure 7 As shown.

[0043] Example 4 (alumina content 15 wt%, tetranitrile diamine content 20 wt%) The preparation process in this embodiment is the same as in Example 1, except that the amount of tetranitrile diamine added is 0.20 g (Preparation Example 1, equivalent to 20 wt% of PEO mass). The resulting composite polymer solid electrolyte is denoted as A15N20; its DSC curve is shown below. Figure 2 As shown, the stress-strain curve is as follows: Figure 3 As shown.

[0044] Example 5 (alumina content 10 wt%, tetranitrile diamine content 15 wt%) The preparation process in this embodiment is the same as in Example 1, except that the amount of nano-alumina added is 0.10 g (equivalent to 10 wt% of PEO mass), and the amount of tetranitrile diamine (Preparation Example 1) added is 0.15 g. The resulting electrolyte membrane is designated A10N15.

[0045] Example 6 (alumina content 20 wt%, tetranitrile diamine content 15 wt%) The preparation process in this embodiment is the same as in Example 1, except that the amount of nano-alumina added is 0.20 g (equivalent to 20 wt% of PEO mass), and the amount of tetranitrile diamine (Preparation Example 1) added is 0.15 g. The resulting electrolyte membrane is designated as A20N15.

[0046] Example 7 (using N,N,N',N'-tetra(2-cyanoethyl)-1,2-ethylenediamine, i.e., n=2) The preparation process in this embodiment is the same as in Example 3, except that an equal mass of tetranitrile diamine (Preparation Example 2, N,N,N',N'-tetra(2-cyanoethyl)-1,2-ethylenediamine) is used. The resulting electrolyte membrane is designated A15N4-15.

[0047] Example 8 (using N,N,N',N'-tetra(2-cyanoethyl)-1,4-butanediamine, i.e., n=4) The preparation process in this embodiment is the same as in Example 3, except that an equal mass of tetranitrile diamine (Preparation Example 3, N,N,N',N'-tetra(2-cyanoethyl)-1,4-butanediamine) is used. The resulting electrolyte membrane is designated A15N8-15.

[0048] Comparative Example 1 (Pure PEO Electrolyte) Weigh 1.00 g PEO and 0.333 g LiTFSI, dissolve them in 20 mL of anhydrous acetonitrile, stir to dissolve, and then cast into a polytetrafluoroethylene mold. Allow to evaporate at room temperature for 24 hours, then vacuum dry at 55°C for 24 hours to obtain a pure PEO-LiTFSI electrolyte membrane, denoted as PEO. Its ionic conductivity Arrhenius diagram is shown below. Figure 4 As shown, the voltage-time curve of a lithium symmetric battery is as follows: Figure 5 As shown.

[0049] Comparative Example 2 (PEO electrolyte with only tetranitrile diamine added) Weigh 1.00 g PEO, 0.333 g LiTFSI, and 0.15 g tetranitrile diamine (Preparation Example 1), dissolve them in 20 mL anhydrous acetonitrile, stir for 12 hours, and then cast into a film. Drying conditions are the same as above. The resulting electrolyte membrane, denoted as PEO-N15, has the following Arrhenius graph showing its ionic conductivity: Figure 4 As shown, the voltage-time curve of a lithium symmetric battery is as follows: Figure 5 As shown.

[0050] Comparative Example 3 (PEO electrolyte with only nano-alumina added) Weigh 1.00 g PEO, 0.333 g LiTFSI, and 0.15 g nano-alumina, dissolve them in 20 mL of anhydrous acetonitrile, stir for 12 hours, and then cast them into a film. Drying conditions are the same as above. The resulting electrolyte membrane is designated PEO-A15.

[0051] Comparative Example 4 (using the traditional plasticizer succinate instead of tetranitrile diamine) Weigh 1.00 g PEO, 0.333 g LiTFSI, 0.15 g nano-alumina, and 0.15 g succinate (SN), dissolve them in 20 mL anhydrous acetonitrile, stir for 12 hours, and then cast into a film. Dry under the same conditions as above. The resulting electrolyte membrane is designated PEO-A15-SN15.

[0052] Performance testing System performance tests were performed on the electrolyte membranes prepared in all the above embodiments and comparative examples. The specific methods and conditions for each test item are as follows: 1. Ionic Conductivity Testing: Electrochemical impedance spectroscopy (EIS) was used. The electrolyte membrane was cut into circular pieces and sandwiched between two stainless steel (SS) blocking electrodes to assemble an SS / electrolyte / SS symmetrical cell. Testing was conducted using an electrochemical workstation at a constant temperature of 25°C, with a frequency range of 1Hz to 1MHz, and an AC perturbation signal with an amplitude of 10mV applied. The bulk resistance Rb was obtained by fitting the Nyquist plot, and the ionic conductivity was calculated using the formula σ=L / (Rb×S), where L is the membrane thickness and S is the electrode area.

[0053] 2. Mechanical property testing: Using a universal testing machine, the electrolyte membrane was cut into dumbbell-shaped standard strips (total length 35mm, gauge length 20mm, width 2mm), and tested at a constant tensile rate of 150mm / min at room temperature. At least 3 parallel samples were tested for each group of samples, and the average value was taken to obtain the tensile strength and elongation at break.

[0054] 3. Thermal performance testing: Differential scanning calorimetry (DSC) was used to heat the material from -50℃ to 100℃ at a rate of 10℃ / min under a nitrogen atmosphere. The heat flow curve was recorded, and the change in crystallinity was evaluated by the melting peak temperature (Tm).

[0055] 4. Lithium-ion battery interface stability test: Assemble lithium / electrolyte / lithium-ion battery in a glove box, and test at 0.1 mA / cm². 2 Constant current charge-discharge was performed at a constant current density, with a deposition / deposition facet volume of 0.1 mAh / cm³ per cycle. 2 Voltage-time curves were recorded to assess interface stability and the ability to suppress lithium dendrites based on the operating time before a short circuit.

[0056] 5. Full Battery Cycle Performance Test: CR2032 button cells were assembled with lithium iron phosphate (LFP) as the positive electrode, lithium metal sheets as the negative electrode, and an electrolyte membrane. Constant current charge-discharge tests were conducted at 50°C at a rate of 0.1C (1C=170mA / g), with a voltage window of 2.5-3.8V. The initial discharge specific capacity and capacity retention after 100 cycles were recorded.

[0057] The results are shown in Table 1: Table 1

[0058] As can be seen from Table 1 and the accompanying drawings, the electrolyte of this invention contains tetranitrile diamine and nano-alumina, both of which are indispensable. Comparative Example 1 (pure PEO), due to its high crystallinity (Tm=55℃), has an ionic conductivity of only 8.0 × 10⁻⁶. -6 The conductivity was low (S / cm), indicating poor mechanical properties and a capacity retention of only 45.6% after 100 cycles, suggesting severe interfacial degradation. While adding tetranitrile diamine alone (Comparative Example 2) significantly suppressed crystallization (Tm decreased to 45℃) and increased the conductivity to 1.5 × 10⁻⁶, the results were not satisfactory. -4 The strength is high (S / cm), but the membrane has high viscosity, low strength, and low battery cycle life. Adding nano-alumina alone (Comparative Example 3) can improve the strength to 1.8 MPa, but the conductivity only increases slightly to 3.0 × 10⁻⁶. -5 S / cm, 72.3% capacity retention after 100 cycles, limited cycle life.

[0059] Based on the full-cell data, Example 3 exhibited the highest capacity retention (93.4%), corresponding to the longest symmetric cell lifespan (>2200h); Comparative Example 1 showed the lowest retention (45.6%), corresponding to the shortest lifespan (approximately 80h). This positive correlation fully demonstrates that the long-term cycling stability of a full cell directly depends on the stability of the electrolyte / electrode interface. The tetranitrile diamine of this invention is effectively anchored by forming strong hydrogen bonds with the hydroxyl groups on the surface of nano-alumina through polynitrile groups, fundamentally preventing interfacial degradation caused by plasticizer migration and loss. Therefore, Example 3 achieved excellent long-cycle performance.

[0060] Comparing Example 3 and Comparative Example 4 (using the conventional plasticizer succinic anhydride), under the same alumina content, Example 3 showed a significantly higher capacity retention rate (93.4%) over 100 cycles compared to Comparative Example 4 (52.1%). This difference stems from the fundamental difference in interfacial stability. Succinic anhydride lacks a polynitrile structure and cannot form effective hydrogen bonds with alumina, leading to continuous migration and loss during cycling, resulting in ongoing interfacial deterioration. In contrast, the four terminal nitrile groups of tetranitrile diamine provide multi-site anchoring capability, ensuring long-term interfacial integrity.

[0061] In Examples 1-4, the tetranitrile diamine content was increased from 5 wt% to 20 wt%. The 100-cycle capacity initially increased and then decreased, peaking at 15 wt%. This is because an appropriate amount of tetranitrile diamine maximizes the inhibition of crystallization and improves conductivity, while being adequately anchored by alumina; excessive amounts result in partial free plasticization, which slightly affects interfacial stability. In Examples 5 and 6, the alumina content was adjusted to 10 wt% and 20 wt%, respectively, with retention rates of 91.5% and 89.3%. 10 wt% alumina provided slightly fewer anchoring points, and while 20 wt% alumina enhanced mechanical properties, it reduced conductivity, both resulting in slightly lower cycling performance than the optimal Example 3. Examples 7 and 8 used tetranitrile diamines with different chain lengths (n=2 and n=4), with retention rates of 87.0% and 86.3%, respectively. Although slightly lower than Example 3 (n=3), these were still at a high level, demonstrating the universal effectiveness of tetranitrile diamine.

[0062] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A composite polymer solid electrolyte, characterized in that, Based on parts by mass, it includes the following components: 100 parts of polyethylene oxide; 30-50 parts lithium salt; 5-25 parts of tetranitrile diamine; 5-25 parts of nano-alumina; The tetranitrile diamine has the structure shown in general formula (I): Where n is an integer from 2 to 8.

2. The composite polymer solid electrolyte according to claim 1, characterized in that, The preparation method of the tetranitrile diamine is as follows: S1 Under ice-water bath and nitrogen protection conditions, C2-C8 alkylene diamine is added to the reaction vessel, and the first part of acrylonitrile is slowly added dropwise, controlling the dropping rate to keep the temperature of the reaction system below 30°C. S2 dissolves lithium bis(trifluoromethanesulfonyl)imide in the second part of acrylonitrile to form an acrylonitrile solution containing lithium salt, which is then slowly added dropwise to the reaction system in step S1. After S3 is added, the reaction system is heated to 45-55℃ and the reaction continues for 20-28 hours. After the S4 reaction is completed, excess acrylonitrile and low-boiling-point impurities are removed by vacuum distillation. Water is added to the residue, and after stirring, the mixture is allowed to stand and separate into layers. The aqueous phase is separated, and the organic phase is washed with ethanol and dried to obtain tetranitrile diamine.

3. The composite polymer solid electrolyte according to claim 2, characterized in that, The total molar ratio of the C2-C8 alkylene diamine to acrylonitrile is 1:(4.5-5.5), and the amount of lithium bis(trifluoromethanesulfonyl)imide is 0.8-1.2 mol of the molar amount of the C2-C8 alkylene diamine.

4. The composite polymer solid electrolyte according to claim 1, characterized in that, The tetranitrile diamine is N,N,N',N'-tetra(2-cyanoethyl)-1,3-propanediamine.

5. The composite polymer solid electrolyte according to claim 1, characterized in that, The weight-average molecular weight of the polyethylene oxide is between 400,000 and 800,000. The lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxaborate, lithium hexafluorophosphate, or lithium perchlorate; the molar ratio of the ether group in the polyethylene oxide to the lithium ion in the lithium salt is (15-25):

1.

6. The composite polymer solid electrolyte according to claim 1, characterized in that, The amount of tetranitrile diamine added is 5-20% of the mass of polyethylene oxide.

7. The composite polymer solid electrolyte according to claim 1, characterized in that, The nano-alumina has a particle size of 30-100 nm and is added at 5-20% of the mass of polyethylene oxide.

8. A method for preparing a composite polymer solid electrolyte as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Dissolve the prescribed amount of polyethylene oxide and lithium salt in anhydrous acetonitrile and stir at 15-35℃ until completely dissolved to form a transparent solution; (2) Add the prescribed amount of tetranitrile diamine and nano alumina to the solution obtained in step (1), and continue stirring at 15-35℃ for 8-16 hours to obtain a homogeneous blended slurry; (3) The blended slurry is poured into a mold, and the solvent is allowed to evaporate naturally at room temperature for 12-24 hours. The mixture is then vacuum dried to obtain the composite polymer solid electrolyte.

9. The method for preparing the composite polymer solid electrolyte according to claim 8, characterized in that, In step (3), the vacuum drying temperature is 50-60℃ and the drying time is 24 hours.

10. A solid-state lithium metal battery, characterized in that, It comprises the composite polymer solid electrolyte according to any one of claims 1 to 6; The battery also includes a positive electrode and a negative electrode, wherein the active material of the positive electrode is at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium cobalt oxide, and the negative electrode is metallic lithium or a lithium alloy.

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