A gel electrolyte, a preparation method, and a solid-state lithium battery

Abstract

The present invention belongs to the technical field of new energy materials and devices, and relates to a gel electrolyte, a preparation method, and a solid-state lithium battery. A liquid novel initiator with a lower freezing point, a cyclic ether-based polymerizable monomer, and a plasticizer are mixed to form a homogeneous precursor solution. The precursor solution is injected into a battery casing and left to stand at room temperature (20°C - 35°C) for in-situ polymerization, and a gel electrolyte-based solid-state battery can be obtained. This gel electrolyte is initiated by a novel initiator and has better low-temperature performance compared with that initiated by a common initiator, forming a high-performance solid-state lithium battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials and devices, and in particular relates to a gel electrolyte, a preparation method, and a solid-state lithium battery. Background Art

[0002] At present, most of the liquid electrolytes used on a large scale have the risks of leakage and flammability. Therefore, developing high-safety lithium batteries with solid-state and quasi-solid-state electrolytes as the core is a necessary means for the upgrading of battery systems.

[0003] The gel electrolyte is composed of a polymer matrix and a liquid plasticizer, combining the advantages of all-solid-state electrolytes and liquid electrolytes. In the gel polymer electrolyte, the polymer matrix provides certain mechanical strength and flexibility, while the liquid-phase component can improve the ionic conductivity and interface stability. The polymer skeleton locks the organic liquid-phase component, making the whole electrolyte a non-flowing gel state, avoiding the leakage risk of the liquid electrolyte. It is the most promising solid electrolyte at present. In-situ polymerization can enable the solid electrolyte to have good contact with the positive and negative electrodes and form an ionic pathway to match the high-loading positive electrode, and it is a gel electrolyte preparation method with great potential.

[0004] However, although the ionic conductivity of many gel polymer electrolyte films can reach a level close to that of liquid electrolytes at room temperature (10 -3 S cm -1 ), at low temperatures, the Li + kinetics is slow, the ionic conductivity of the gel polymer electrolyte drops significantly, the interfacial charge transfer rate decreases, and at the same time, the organic liquid-phase components may also solidify, making it difficult to meet the actual application requirements in low-temperature environments.

[0005] Therefore, it is particularly important to improve the low-temperature performance of the gel electrolyte by various means.

[0006] There are two common methods to improve the low-temperature performance of gel electrolytes. One is to improve the contact between the electrode and the electrolyte interface through in-situ polymerization, accelerate the interfacial charge transfer rate, and avoid the low-temperature solidification of organic electrolyte components, thereby ensuring the rapid transport of ions between liquid-phase molecules at low temperatures. The other is to select an organic solvent with a lower freezing point as a plasticizer component. Researchers often combine these two methods to achieve better low-temperature performance. At present, most domestic and foreign experts and scholars choose to regulate the plasticizer component for research. However, to achieve ideal low-temperature performance, an excessive amount of liquid-phase plasticizer needs to be added to the system (often more plasticizer than the amount of polymerization monomer is required). For example, a liquid-phase plasticizer with a dosage of 150% of the cyclic ether monomer (DOL) is selected, and there are reports of excellent low-temperature performance at -20°C (Ciucci et al., Advanced Energy Materials, 2022, 12, 2102.). Such an excessive amount of liquid-phase plasticizer will inevitably cause a loss of energy density, and may also lead to a higher leakage risk and certain safety hazards. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a gel electrolyte, a preparation method, and a solid-state lithium battery. A gel electrolyte with good low-temperature performance is prepared for assembling a high-performance solid-state lithium battery.

[0008] The technical solution to achieve the present invention is as follows:

[0009] The first aspect of the present invention provides a gel electrolyte, which is composed of a polymerization monomer solution, an initiator, and a plasticizer in a volume ratio of 50 - 300:5 - 100:0 - 100.

[0010] The polymerization monomer has a cyclic ether structure. The polymerization monomer solution is obtained by adding a lithium salt to the polymerization monomer, and the initiator is methyl difluorofluorosulfonylacetate (MDFSA).

[0011] The polymerization monomer is one or more of 1,3-dioxolane (DOL), 1,3,5-trioxane (TXE), ethylene oxide, propylene oxide, oxolane, and tetrahydrofuran (THF). The lithium salt in the polymerization monomer solution is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluoro(oxalato)borate (LiDFOB), lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), and lithium perchlorate (LiClO4), and the lithium salt concentration is 0.1 - 10 mol / L.

[0012] The present invention prepares a gel electrolyte by in-situ polymerization of a cyclic ether monomer initiated by a novel initiator, which has good low-temperature performance.

[0013] Furthermore, the polymerizable monomer solution, initiator, and plasticizer are composed in a volume ratio of 100:10-50:30-70.

[0014] Preferably, the polymerizable monomer solution, initiator, and plasticizer are composed in a volume ratio of 100:30:30-70.

[0015] Furthermore, the plasticizer composition includes a lithium salt and an organic solvent, and can be mixed with the polymerizable monomer to form a homogeneous solution.

[0016] Furthermore, the plasticizer is obtained by adding lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to fluoroethylene carbonate (FEC), and the concentration of lithium bis(trifluoromethanesulfonyl)imide is 0.5-3 mol / L.

[0017] The second aspect of the present invention is to provide a method of mixing and dissolving a cyclic ether-based polymerizable monomer, an initiator, and a plasticizer to form a homogeneous precursor solution; and subjecting the precursor solution to in-situ polymerization by standing at 20°C-35°C for 3 h-48 h.

[0018] The third aspect of the present invention is to provide a solid-state lithium battery including the above gel electrolyte.

[0019] Furthermore, the positive electrode of the solid-state lithium battery is any one of lithium-rich manganese-based, nickel cobalt manganese-based, lithium cobaltate, and lithium iron phosphate, and the negative electrode is any one of lithium metal, lithium-based alloy, silicon carbon, and graphite.

[0020] Furthermore, the housing of the solid-state lithium battery is one of a soft-pack battery, a square battery, a cylindrical battery, a stacked battery, and a wound battery.

[0021] Preferably, the battery housing includes but is not limited to a commercial XR2032 assembled battery, and the amount of the electrolyte precursor solution used is 10 μL-100 μL.

[0022] Advantages and beneficial effects of the present invention:

[0023] 1. The present invention develops a liquid-phase initiator with low-temperature performance. When the liquid-phase component in the system is only 80% of the amount of the cyclic ether-based monomer (DOL), excellent low-temperature performance at -20°C is also achieved, greatly reducing the amount of the liquid-phase component in the gel electrolyte.

[0024] 2. The present invention selects to develop a new liquid initiator with a lower freezing point to initiate the ring-opening polymerization of the cyclic ether-based polymerizable monomer. When other conditions such as the plasticizer are the same, it has better low-temperature performance than the commonly used initiator, and is a highly potential preparation method for the gel electrolyte of low-temperature solid-state batteries. Description of the Drawings

[0025] Figure 1It is the optical picture of the gel electrolyte after polymerization in Example 1;

[0026] Figure 2 It is the infrared (FT-IR) spectrum test chart of the gel electrolyte after polymerization in Example 1 and the comparative samples DOL + 1M LiTFSI, FEC / 1M LiTFSI;

[0027] Figure 3 It is the Raman spectrum test chart of the gel electrolyte after polymerization in Example 1 and the comparative samples DOL + 1M LiTFSI, FEC / 1M LiTFSI;

[0028] Figure 4 It is the ionic conductivity at different temperatures of the SS-SS half-cell test assembled in Example 1;

[0029] Figure 5 It is the charge-discharge curves of the 3rd cycle at room temperature and -20 °C in Example 2;

[0030] Figure 6 It is the charge-discharge curves of the 3rd cycle at room temperature and -20 °C in Comparative Example 1;

[0031] Figure 7 It is the graph of the capacity change with cycle at -20 °C for Example 2 (blue) and Comparative Example 1 (red). Detailed implementation mode

[0032] The present invention will be further illustrated below through the accompanying drawings and specific examples. The following examples are only for illustration and should not be construed as limiting the scope of the present invention. The protection scope of the present invention is not limited to the following examples either.

[0033] Example 1

[0034] First, dissolve 1M LiTFSI in the polymerization monomer (DOL), then take out 100 μL of this solution and mix it with 30 μL of MDFSA (novel initiator) and 50 μL of FEC / 1M LiTFSI (plasticizer) for dissolution to form a homogeneous precursor solution;

[0035] Let the precursor solution in the vial stand at room temperature (20 °C - 35 °C) until in-situ polymerization is completed to obtain the optical picture of the gel electrolyte. At the same time, perform infrared (FT-IR) spectrum and Raman spectrum tests on the comparative samples of the polymerization monomer DOL + 1M LiTFSI and the plasticizer FEC / 1M LiTFSI;

[0036] The unprecipitated precursor solution in Example 1 was assembled into a half-cell. An SS-SS half-cell was assembled with both the positive and negative electrodes being stainless steel gaskets (SS). The amount of the precursor solution used was 50 μL. After the battery was assembled with a pressure of 0.85 tons, it was left standing at room temperature (20 °C - 35 °C) for 24 h until in-situ polymerization was completed. The separator was Celgard 2500, and the injection tool was a pipette gun with a measuring range of 100 μL.

[0037] Figure 1 Figure 4 shows the polymerization situation of the precursor solution in the vial of Example 1 after standing at room temperature for 24 h. The flowing liquid in the vial became a gel state and could not flow, indicating the completion of the polymerization reaction. Figure 2 Figure 6 is the infrared (FT-IR) spectrogram of Example 1 and the comparative samples (polymerization monomer, plasticizer). The characteristic peak of the monomer at ~915 cm -1 disappeared, and the characteristic peak of the polymer at ~848 cm -1 appeared, indicating the completion of the polymerization reaction. Figure 3 Figure 12 is the Raman spectrogram of Example 1 and the comparative samples (polymerization monomer, plasticizer). The C-O-C characteristic peak of the monomer at ~937 cm -1 disappeared, and the characteristic peak of the polymer at ~845 cm -1 appeared, also indicating the completion of the polymerization reaction. Figure 4 Figure 18 shows the ion conductivity test of the SS-SS half-cell in Example 1 at different temperatures after standing at room temperature for 24 h. The ionic conductivity of the gel electrolyte was still ~0.1 mS / cm at -20 °C, indicating its potential for low-temperature operation.

[0038] Example 2

[0039] First, 1 M LiTFSI was dissolved in the polymerization monomer (DOL), and then 100 μL of this solution was taken and mixed with 30 μL of MDFSA (novel initiator) and 50 μL of FEC / 1 M LiTFSI (plasticizer) and dissolved to form a homogeneous precursor solution;

[0040] The unprecipitated precursor solution in Example 2 was assembled into a battery. The battery case was a commercial XR2032 assembled battery. The positive electrode was lithium iron phosphate, and the negative electrode was lithium metal. The diameter of the full-cell positive electrode was 10 mm and the loading was ~2 mg cm -2 , the negative electrode was a Li sheet with a diameter of 14 mm and a thickness of 450 μm. The amount of the precursor solution added was 50 μL. After the battery was assembled with a pressure of 0.85 tons, it was left standing at room temperature (20 °C - 35 °C) for 24 h until in-situ polymerization was completed. The separator was Celgard 2500, and the injection tool was preferably a pipette gun with a measuring range of 100 μL.

[0041] After the assembled half-cell was activated at 0.1C and 2.5 - 4.0V for 3 cycles at room temperature, it was then charged and discharged cyclically at 0.1C and 2.5 - 4.0V at -20°C. 1C = 170 mAh g -1 . Figure 5 Figure 3 shows the charge-discharge curves of the 3rd cycle at room temperature and -20°C for Example 2. The discharge capacity of the 3rd cycle at room temperature is 161.3 mAh g -1 , and the discharge capacity of the 3rd cycle at -20°C is 87.1 mAh g -1 , which is 54.0% of the room temperature capacity.

[0042] Comparative Example 1

[0043] A method for preparing a cyclic ether-based gel electrolyte using a common initiator: First, 1M LiTFSI was dissolved in the polymerization monomer (DOL), and then 100 μL of this solution was taken and mixed with 80 μL of FEC / 1M LiDFOB (plasticizer, and LiDFOB can also be used as an initiator) and dissolved to form a homogeneous precursor solution;

[0044] The battery was assembled using the non-static precursor solution in Comparative Example 1. The battery case was a commercial XR2032 assembled battery. The positive electrode was lithium iron phosphate, and the negative electrode was lithium metal. The diameter of the full battery positive electrode was 10 mm and the loading was ~2 mg cm -2 , the negative electrode was a Li sheet with a diameter of 14 mm and a thickness of 450 μm. The amount of the precursor solution added was 50 μL. After the battery was assembled using a pressure of 0.85 tons, it was left standing at room temperature (20°C - 35°C) for 24 h until in-situ polymerization was completed. The separator was Celgard 2500, and the injection tool was preferably a pipette with a measuring range of 100 μL;

[0045] After the assembled half-cell was activated at 0.1C and 2.5 - 4.0V for 3 cycles at room temperature, it was then charged and discharged cyclically at 0.1C and 2.5 - 4.0V at -20°C. 1C = 170 mAh g -1 . Figure 6 Figure 3 shows the charge-discharge curves of the 3rd cycle at room temperature and -20°C for Comparative Example 1. The discharge capacity of the 3rd cycle at room temperature is 156.7 mAh g -1 , and the discharge capacity of the 3rd cycle at -20°C is 71.0 mAh g -1 , which is only 45.3% of the room temperature capacity.

[0046] Figure 7 Figure 4 shows the cycle-capacity change diagrams of Example 2 and Comparative Example 1 at -20°C. The capacity retention ability of Example 2 at low temperature (the capacity retention rate after 100 cycles is 93.3%) is significantly higher than that of Comparative Example 1 (the capacity retention rate after 100 cycles is 63.2%).

[0047] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and optimizations can be made, including the improvement and optimization of the polymerizable monomer with a cyclic ether group, plasticizer, lithium salt, and the novel liquid initiator with a lower freezing point. These improvements and optimizations should also be regarded as the protection scope of the present invention.

Claims

1. A gel electrolyte, characterized in that, The preparation method is as follows: A polymerization monomer solution, an initiator, and a plasticizer are mixed and dissolved in a volume ratio of 50 - 300:5 - 100:0 - 100 to form a homogeneous precursor solution; the homogeneous precursor solution is allowed to stand at 20°C - 35°C for 3h - 48h for in-situ polymerization to obtain a gel electrolyte. The polymerization monomer solution is obtained by adding a lithium salt to a polymerization monomer, and the polymerization monomer has a cyclic ether structure. The initiator is methyl fluorosulfonyldifluoroacetate.

2. The gel electrolyte according to claim 1, wherein The polymerization monomer is one or more of 1,3-dioxolane, 1,3,5-trioxane, ethylene oxide, propylene oxide, oxolane, and tetrahydrofuran; the lithium salt in the polymerization monomer solution is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium perchlorate, and the lithium salt concentration is 0.1 - 10 mol / L.

3. The gel electrolyte according to claim 1, characterized in that, The plasticizer is composed of a lithium salt and an organic solvent. The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium perchlorate, and the organic solvent is one or more of fluoroethylene carbonate, dimethyl carbonate, 1,2-dimethoxyethane, and methyl propionate.

4. The gel electrolyte according to claim 3, characterized in that, The plasticizer is obtained by adding lithium bis(trifluoromethanesulfonyl)imide to fluoroethylene carbonate, and the concentration of lithium bis(trifluoromethanesulfonyl)imide is 0.5 - 3 mol / L.

5. A solid-state lithium battery comprising the gel electrolyte according to any one of claims 1 - 4.

6. The solid-state lithium battery according to claim 5, wherein The positive electrode of the solid-state lithium battery is any one of lithium-rich manganese-based, nickel cobalt manganese-based, lithium cobaltate, and lithium iron phosphate, and the negative electrode is any one of lithium metal, lithium-based alloy, silicon-carbon, and graphite.

7. The solid-state lithium battery according to claim 5, characterized in that, The housing of the solid-state lithium battery is one of a soft-pack battery, a square battery, a cylindrical battery, a stacked battery, and a wound battery.

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