High-performance composite solid electrolyte and preparation method and application thereof

Abstract

The invention discloses a high-performance composite solid electrolyte as well as a preparation method and application thereof, and belongs to the technical field of solid lithium batteries. The high-performance composite solid electrolyte provided by the invention is formed by curing a modified polymer solution on a diaphragm, the modified polymer solution comprises a lithium salt, N, N-dimethylformamide, a polymer and an amino-functionalized metal organic framework. The high-performance composite solid electrolyte provided by the invention can adsorb a residual DMF solvent and inhibit decomposition of the residual DMF solvent, and meanwhile, can induce rearrangement of a Li < + > solvation structure and can promote dissociation of lithium salt. The high-performance composite solid electrolyte can be used for preparing a lithium metal battery, and under different current density application conditions, a lithium negative electrode can be continuously kept to achieve stable lithium ion deposition behavior and efficient cycle performance in the cycle process, and side reaction and dendritic crystal formation under a low current condition are inhibited.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state lithium batteries, and in particular relates to a high-performance composite solid-state electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used in consumer electronics and electric vehicles. However, current battery systems have difficulty meeting consumers' continued demand for high energy density and safety. Among various new battery systems, lithium metal batteries (LMBs) have attracted widespread attention due to their high energy density. In particular, lithium metal batteries based on solid-state electrolytes are considered to be one of the most promising next-generation battery systems.

[0003] Among solid electrolytes, solid polymer electrolytes (SPEs) have great application potential due to their high flexibility and interface compatibility. So far, a large number of solid polymer electrolyte systems have been developed, such as polyethylene oxide (PEO)-based SPEs, polyethylene-based SPEs, polyacrylonitrile-based SPEs, polyvinylidene fluoride (PVDF)-based SPEs, polypropylene carbonate-based SPEs, etc. Among them, PVDF-based SPEs have excellent thermal stability, mechanical properties, a wide electrochemical window and unique Li + transport mechanism, which is compatible with high-voltage cathode materials, has attracted extensive attention in recent years.

[0004] The residual N,N-dimethylformamide (DMF) solvent in PVDF-based SPEs can form [Li(DMF)x] + Solvation structure, through the interaction with the F atoms on the polymer chain to achieve Li + Transmission. This is where the gains and losses come from, which brings the following problems: i) The residual DMF solvent also undergoes irreversible side reactions with the lithium metal anode, gradually thickening the solid electrolyte interface (SEI) during the cycle, leading to increased interfacial impedance and dendritic lithium growth.

[0005] ii) DMF has poor antioxidant capacity, which reduces the electrochemical window of SPE.

[0006] iii) The porous structure of PVDF polymer leads to the Li + The uneven flux distribution induces uneven lithium deposition and the formation of dendritic lithium.

[0007] iv) PVDF has a weak ability to dissociate lithium salts and its ionic conductivity is still low.

[0008] Therefore, it is urgent to develop new strategies to solve the above problems. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a high-performance composite solid electrolyte capable of absorbing residual DMF solvent and inhibiting its decomposition, and a preparation method and application thereof.

[0010] In order to solve the above technical problems, the technical solution adopted by the present invention is: a high-performance composite solid electrolyte, formed by solidifying a modified polymer solution on a diaphragm; The modified polymer solution includes lithium salt, N,N-dimethylformamide, PVDF-based polymer and amino-functionalized metal organic framework.

[0011] A method for preparing the above-mentioned high-performance composite solid electrolyte comprises the following steps: S1, completely dissolving the lithium salt and the PVDF-based polymer in N,N-dimethylformamide to obtain a precursor solution, and then adding the amino-functionalized metal organic framework and stirring until no precipitation is observed to obtain a modified polymer solution; S2. Add the modified polymer solution dropwise onto the diaphragm and obtain a high-performance composite solid electrolyte after drying.

[0012] The application of the above-mentioned high-performance composite solid electrolyte in the preparation of lithium metal batteries.

[0013] The beneficial effects of the present invention are as follows: the high-performance composite solid electrolyte provided by the present invention can adsorb the residual DMF solvent and inhibit its decomposition, while inducing Li + The solvation structure is rearranged, which promotes the dissociation of lithium salts. Under different current density application conditions, the lithium negative electrode can sustainably maintain stable lithium ion deposition behavior and efficient cycle performance during the cycle, and inhibit the occurrence of side reactions and the formation of dendrites under low current conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a graph showing the electrical performance test of a lithium / lithium iron phosphate full battery of Example 2 of the present invention at a charge and discharge rate of 5 C; Figure 2 The lithium / lithium symmetric battery of Example 3 of the present invention is shown in FIG. -2 Electrical performance test diagram under charge and discharge conditions; Figure 3 The figure shows the lithium / lithium symmetric battery in Example 3 of the present invention at 0.1 mA, 0.1 mAh cm -2 SEM deposition morphology of lithium negative electrode under charge and discharge conditions; Figure 4 Shown are infrared spectra of the solid electrolytes of Comparative Example 1 and Example 1 of the present invention; Figure 5Shown are nuclear magnetic resonance spectra of the solid electrolytes of Comparative Example 1 and Example 1 of the present invention; Figure 6 The figure shows the electrical performance test diagram of the lithium / lithium iron phosphate full battery of Comparative Example 2 of the present invention at a charge and discharge rate of 5 C; Figure 7 The lithium / lithium symmetric battery of Comparative Example 3 of the present invention is shown in FIG. -2 Electrical performance test diagram under charge and discharge conditions; Figure 8 The results are shown in Table 2. The results are shown in Table 2. The results are shown in Table 2. The results are shown in Table 2. -2 SEM deposition morphology of lithium negative electrode under charge and discharge conditions. DETAILED DESCRIPTION

[0015] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0016] A high-performance composite solid electrolyte formed by curing a modified polymer solution on a separator; The modified polymer solution includes lithium salt, N,N-dimethylformamide, PVDF-based polymer and amino-functionalized metal-organic framework.

[0017] From the above description, it can be seen that the beneficial effects of the present invention are: the high-performance composite solid electrolyte provided by the present invention adopts an amino-functionalized metal organic framework as a modified filler, and the amino-functionalized metal organic framework contains Lewis-acidic zinc metal sites and positively charged amino groups, which can double-adsorb the residual DMF solvent and induce Li + The rearrangement of the solvation structure inhibits the adverse decomposition of DMF, thereby protecting the lithium anode and greatly improving the cycle life of the solid-state lithium metal battery.

[0018] In one or more embodiments, the amino-functionalized metal organic framework is ZIF-90-NH2. On the one hand, the unsaturated Zn metal sites in ZIF-90 can adsorb residual DMF solvent through ion-dipole interaction, and the functionalized amino groups can further anchor the DMF solvent through electrostatic interaction, inducing Li + The rearrangement of the solvation structure allows more anions to participate in it, thereby generating a stable SEI layer rich in LiF and inhibiting the side reaction between DMF and the lithium metal anode; on the other hand, under these two interactions, ZIF-90-NH2 can fix lithium salt anions, promote their dissociation, and accelerate Li + Competitive Li +The synergistic effect of coordination and fixed anions has greatly improved the cycle performance of lithium metal batteries. Compared with other metal organic framework materials, ZIF-90 is a dodecahedral structure with a larger specific surface area, which can better adsorb DMF solvent. At the same time, the aldehyde group in ZIF-90 is highly active and easier to graft functional groups.

[0019] In one or more embodiments, the PVDF-based polymer is preferably polyvinylidene fluoride-co-trifluoroethylene (P(VDF-TrFE)). The polymer P(VDF-TrFE) is different from the traditional PVDF electrolyte. P(VDF-TrFE) has a special all-trans conformation, and all F atoms are uniformly arranged on the same side of the carbon chain, constructing a straight and fast Li + Transmission channel.

[0020] In one or more embodiments, the mass ratio of the amino-functionalized metal organic framework to the PVDF-based polymer is 1:50-200, preferably 1:100.

[0021] In one or more embodiments, the molar ratio of the lithium salt to the PVDF-based polymer is 1:3-10, preferably 1:6.

[0022] In one or more embodiments, the lithium salt is at least one of lithium sulfate, lithium chloride, lithium imide bistrifluoromethanesulfonate, lithium tetrafluoroborate, and lithium hexafluorophosphate.

[0023] In one or more embodiments, the separator is a cellulose separator.

[0024] A method for preparing the above-mentioned high-performance composite solid electrolyte comprises the following steps: S1, completely dissolving the lithium salt and the PVDF-based polymer in N,N-dimethylformamide to obtain a precursor solution, and then adding the amino-functionalized metal organic framework and stirring until no precipitation is observed to obtain a modified polymer solution; S2. Add the modified polymer solution dropwise onto the diaphragm and obtain a high-performance composite solid electrolyte after drying.

[0025] In one or more embodiments, the drying temperature in S2 is 20-30° C., preferably 25° C. Drying at a lower temperature can ensure that the performance of the solid-state lithium battery is not affected.

[0026] Application of any of the above-mentioned high-performance composite solid electrolytes in the preparation of lithium metal batteries.

[0027] In one or more embodiments, the lithium metal battery uses lithium metal material as the negative electrode, and uses any of the above-mentioned high-performance composite solid electrolytes to separate the positive electrode and the negative electrode.

[0028] The high-performance composite solid electrolyte of the present invention is used to prepare lithium metal batteries. By utilizing the characteristics of the amino-functionalized metal organic framework surface with abundant positive charges, lithium salt anions can be anchored under electrostatic interaction to promote the dissociation of lithium salts. At the same time, hydrogen bonds can be formed between P(VDF-TrFE) and ZIF-90-NH2, stabilizing Li + The transmission channel improves the antioxidant performance of the electrolyte, allowing the assembled lithium / lithium iron phosphate full battery to achieve extremely excellent long-term cycling effect at a high rate of 5 C.

[0029] Embodiment 1: The method for preparing a high-performance composite solid electrolyte comprises the following steps: S1. P(VDF-TrFE) and LiTFSI were completely dissolved in DMF solvent at a molar ratio of 6:1 to obtain a P(VDF-TrFE) precursor solution; ZIF-90-NH2 powder was weighed at a mass ratio of P(VDF-TrFE): ZIF-90-NH2=100:1 and added to the P(VDF-TrFE) precursor solution, and stirred for 12 hours until no precipitation was observed to obtain a modified polymer solution; S2. The modified polymer solution was dropped onto a 30 μm thick cellulose membrane and dried in a glove box for 24 hours to obtain a high-performance composite solid electrolyte, namely, composite solid electrolyte membrane A.

[0030] Embodiment 2: A button cell CR2025 system was used to simulate the cycle performance of a full battery. The electrolyte separator in the button cell was the composite solid electrolyte membrane A of Example 1, the negative electrode was lithium foil, and the positive electrode was lithium iron phosphate.

[0031] The battery was tested for electrical performance under 5 C charge and discharge conditions. The test results are shown in Figure 1 shown.

[0032] Embodiment three: A button cell CR2025 system was used to simulate the cycle performance of a symmetrical battery. The electrolyte separator in the button cell was the composite solid electrolyte membrane A of Example 1, the negative electrode was lithium foil, and the positive electrode was lithium foil.

[0033] The battery has a capacity of 0.2 mA and 0.2 mAh cm -2 The electrical performance test was carried out under the charge and discharge conditions. The test results are shown in Figure 2 As shown; the battery has a current of 0.1 mA and 0.1 mAh cm -2 The surface deposition morphology of the lithium negative electrode after 50 cycles under the charge and discharge conditions is shown in Figure 3 shown.

[0034] Comparative Example 1: A method for preparing a conventional solid-state lithium metal battery comprises the following steps: S1, completely dissolving P(VDF-TrFE) and LiTFSI in a DMF solvent at a molar ratio of 6:1 to obtain a P(VDF-TrFE) precursor solution; S2. Use a pipette to draw 100 μL of the precursor solution and drop it onto a 30 μm thick cellulose membrane. Dry it in a glove box for 24 hours to obtain a conventional solid electrolyte membrane B.

[0035] The button cell CR2025 system is used to simulate the cycle performance of the full battery. The electrolyte separator in the button cell is the solid electrolyte membrane in S1, the negative electrode is lithium foil, and the positive electrode is lithium iron phosphate. The battery is tested for electrical performance under 5 C charge and discharge conditions. The test results are shown in Figure 6 .

[0036] The composite solid electrolyte membrane A and solid electrolyte membrane B of Comparative Example 1 and Example 1 were taken and their surfaces were subjected to infrared and nuclear magnetic resonance tests respectively. The infrared test results are shown in Figure 4 The results of the nuclear magnetic resonance test are shown in Figure 5 shown. Depend on Figure 4 It can be seen that DMF solvent molecules can be strongly adsorbed by ZIF-90-NH2. Figure 5 It can be seen that hydrogen bonding interaction is formed between P(VDF-TrFE) and ZIF-90-NH2.

[0037] Comparative Example 2: A button cell CR2025 system was used to simulate the cycle performance of a full battery. The electrolyte separator in the button cell was the solid electrolyte membrane B of Comparative Example 1, the negative electrode was lithium foil, and the positive electrode was lithium iron phosphate.

[0038] The battery was tested for electrical performance under 5 C charge and discharge conditions. The test results are shown in Figure 6 .

[0039] Comparative Example 3: A button cell CR2025 system was used to simulate the cycle performance of a symmetrical battery. The electrolyte separator in the button cell was the solid electrolyte membrane B of Comparative Example 1, the negative electrode was lithium foil, and the positive electrode was lithium foil.

[0040] The battery has a capacity of 0.2 mA and 0.2 mAh cm -2 The electrical performance test was carried out under the charge and discharge conditions. The test results are shown in Figure 7 ; The battery has a current of 0.1 mA and 0.1 mAh cm -2 The surface deposition morphology of the lithium negative electrode after 50 cycles under the charge and discharge conditions is shown in Figure 8 .

[0041] contrast Figure 1 and Figure 6 It can be seen that the full battery assembled with the conventional solid electrolyte short-circuited after only 260 cycles, while the full battery assembled with the composite solid electrolyte of the present invention can stably cycle 400 times and still have a high specific capacity; Figure 2 and Figure 7 It can be seen that the polarization voltage of the symmetrical battery assembled with the conventional solid electrolyte drops sharply after about 460 hours, and the battery short-circuits, while the battery assembled with the composite solid electrolyte of the present invention still has a stable voltage after about 1000 hours. It can be seen that the present invention can improve the cycle performance of the battery by adding an amino-functionalized metal organic framework as a modified filler in P(VDF-TrFE).

[0042] contrast Figure 3 and 8 It can be seen that during the charge and discharge cycle of the battery assembled with the conventional solid electrolyte, the lithium morphology is uneven; during the charge and discharge cycle of the battery assembled with the composite solid electrolyte of the present invention, the lithium morphology always remains uniform and flat.

[0043] Embodiment 4: The only difference between Example 4 and Example 1 is that the lithium salt is LiCl.

[0044] Embodiment five: The only difference between Example 5 and Example 1 is that the lithium salt is Li2SO4; the molar ratio of the lithium salt to the PVDF-based polymer is 1:10, and the mass ratio of ZIF-90-NH2 to the PVDF-based polymer is 1:50.

[0045] Embodiment six: The only difference between Example 6 and Example 1 is that the lithium salt is LiPF6, and the mass ratio of ZIF-90-NH2 to PVDF-based polymer is 1:200.

[0046] Embodiment seven: The only difference between Example 7 and Example 1 is that the lithium salt is LiBF4, and the molar ratio of the lithium salt to the PVDF-based polymer is 1:3.

[0047] In summary, the composite solid electrolyte provided by the present invention achieves the effect of protecting the lithium anode and greatly improves the cycle life of the solid-state lithium metal battery by adding an amino-functionalized metal organic framework as a modified filler and using P(VDF-TrFE) with a special all-trans conformation as a polymer. The composite solid electrolyte provided by the present invention can achieve excellent long-term cycle effect after being used to assemble a solid-state lithium metal battery.

[0048] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A high-performance composite solid electrolyte, characterized in that: It is formed by solidifying the modified polymer solution on the diaphragm; The modified polymer solution includes lithium salt, N,N-dimethylformamide, PVDF-based polymer and amino-functionalized metal organic framework.

2. The high performance composite solid electrolyte according to claim 1, characterized in that: The amino-functionalized metal organic framework is ZIF-90-NH2.

3. The high performance composite solid electrolyte according to claim 1, characterized in that: The mass ratio of the amino-functionalized metal organic framework to the PVDF-based polymer is 1:50-200.

4. The high performance composite solid electrolyte according to claim 1, characterized in that: The molar ratio of the lithium salt to the PVDF-based polymer is 1:3-10.

5. The high performance composite solid electrolyte according to claim 1, characterized in that: The lithium salt is at least one of lithium sulfate, lithium chloride, lithium imide bis(trifluoromethanesulfonate), lithium tetrafluoroborate and lithium hexafluorophosphate.

6. The high performance composite solid electrolyte according to claim 1, characterized in that: The separator is a cellulose separator.

7. A method for preparing a high-performance composite solid electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Completely dissolving the lithium salt and the PVDF-based polymer in N,N-dimethylformamide to obtain a precursor solution, and then adding the amino-functionalized metal organic framework and stirring until no precipitation is observed to obtain a modified polymer solution; S2. Add the modified polymer solution dropwise onto the diaphragm and obtain a high-performance composite solid electrolyte after drying.

8. The preparation method according to claim 7, characterized in that: The drying temperature is 20-30°C.

9. Use of the high-performance composite solid electrolyte according to any one of claims 1 to 6 in the preparation of a lithium metal battery.

10. The use according to claim 9, characterized in that: The lithium metal battery uses lithium metal material as the negative electrode, and uses the high-performance composite solid electrolyte described in any one of claims 1 to 5 to separate the positive electrode and the negative electrode.

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