Zwitterionic polymer-based lithium-ion battery electrolyte and method of making the same

Abstract

The application belongs to the technical field of lithium ion battery electrolyte, and particularly relates to a zwitterionic polymer-based lithium ion battery electrolyte and a preparation method thereof. The electrolyte material can be prepared on a battery negative electrode material through free radical in-situ polymerization, greatly reducing the interface impedance and improving the rate performance and cycle performance of the battery. In addition, an organic solvent is introduced as a plasticizer, so that the battery has high conductivity; the zwitterion is introduced, so that the lithium salt is solvated and the lithium is dendrite-free deposited; and the glass fiber is introduced, so that the lithium transference number is improved. The electrolyte as a whole uses carbonate compounds, has high chemical stability, and can be applied to high-voltage lithium batteries; and the preparation process is conducive to battery integration and large-scale production; no solvent exists in the production process, environmental pollution is reduced, and the cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte technology, specifically relating to a zwitterionic polymer-based lithium-ion battery electrolyte and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in commercial portable electronic devices, but extending their application to air transport such as electric vehicles and drones requires significant improvements in safety and energy density. This is a major challenge currently facing battery systems because they contain volatile and flammable liquid carbonate electrolytes. While these liquid electrolytes have high ionic conductivity, their high flammability, low thermal stability, and inability to suppress lithium dendrite growth are causes of battery fires and explosions. Furthermore, the low energy density of liquid electrolytes hinders the development of lightweight battery systems. Replacing traditional liquid electrolytes with polymer electrolytes has been recognized as an effective way to overcome the safety and energy density problems of lithium-based batteries. For polymer electrolytes to be used in lithium-based batteries, they need to meet high performance requirements, such as high ionic conductivity, high lithium-ion transport number, good mechanical strength, wide electrochemical window, and excellent chemical and thermal stability. However, existing materials and technologies struggle to simultaneously meet these requirements.

[0003] Zwitterions are a unique class of molecules that are locally charged but globally neutral, with cation and anion groups covalently linked. Due to their unique molecular structure, zwitterionic electrolytes possess many advantages. First, the strong dipole moment generated by the molecular structure can promote the dissolution of lithium salts. Second, the cation component of zwitterionic compounds can significantly inhibit the movement of anions in the electrolyte, preventing anion depletion near the anode region. Furthermore, the uniformly arranged anion component in zwitterionic compounds can effectively regulate the lithium content of lithium. + Flux distribution, anion immobilization and regulation of Li + The synergistic effect of these compounds can achieve dendrite-free deposition. However, the molecular structures of zwitterions are still very limited. The cationic groups are mainly heterocyclic imidazoles, and the anionic groups are mainly sulfonate and carboxylate groups; unfortunately, these negatively charged groups have too strong a Coulomb interaction with lithium ions in the electrolyte, which severely hinders the migration of lithium ions under potential and leads to a rather low transference number. Summary of the Invention

[0004] To address the aforementioned problems or shortcomings and to solve the cycle stability issue of polymer-based semi-solid electrolyte batteries, this invention provides a zwitterionic polymer-based lithium-ion battery electrolyte and its preparation method.

[0005] A zwitterionic polymer-based lithium-ion battery electrolyte, composed of an organic polymer, an organic solvent, and a lithium salt, exhibits an ionic conductivity of 8 × 10⁻⁶ at 30°C. -4 ~1.15×10 -3 S / cm.

[0006] The organic polymer is obtained by double-bond free radical polymerization of zwitterionic monomers (15-20 wt.%), carbonate monomers (70-80 wt.%) and polyethylene glycol acrylate monomers (8-15 wt.%), and the total content of the polymer is 1%.

[0007] Among them, the zwitterionic monomer is 3-(N,N-diallyl-N-methylammonium)propanesulfonate (DMA-SO3) with a double bond. - ) or ((3-(diallyl(methyl)amino)propyl)sulfonyl)(trifluoromethyl)sulfonyl)amide (DMA-SO2N) - One or more of SO2CF3, with the following specific structure:

[0008]

[0009] Furthermore, the polyethylene glycol acrylate monomers are one or more selected from polyethylene glycol dimethacrylate (PEGDMA), polyethylene glycol diacrylate (PEGDA), ethoxylated trimethylolpropane triacrylate (ETPTA), and pentaerythritol triacrylate (PETA). Moreover, the relative molecular mass of the monomers used is between 400 and 1500 g / mol.

[0010] Furthermore, the carbonate ester monomer is one or more of ethylene ethylene carbonate (VEC) and divinyl ethylene carbonate.

[0011] Furthermore, the organic solvent is one or more of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and dimethyl carbonate (DMC).

[0012] Furthermore, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium difluorooxalate borate (LiDFOB).

[0013] The preparation method of the above-mentioned zwitterionic polymer-based lithium-ion battery electrolyte includes the following steps:

[0014] Step 1: Preparation of zwitterionic monomers:

[0015] The N,N-diallyl-N-methylamine and 1,3-propanesulfonyl lactone were quaternized in acetonitrile to give the zwitterionic monomer DMA-SO3. - It is 3-(N,N-diallyl-N-methylammonium)propanesulfonate, which has a double bond.

[0016] zwitterionic monomer (DMA-SO2N) - The synthesis of SO2CF3 involves first reacting CF3SO2NH2 with K2CO3 to generate CF3SO2NHK, then reacting it with 1-propanesulfonyl chloride to generate Cl-SO2NSO2CF3. Finally, N,N-diallyl-N-methylamine and Cl-SO2NSO2CF3 are quaternized in acetonitrile to yield the zwitterionic monomer DMA-SO2N. - SO2CF3.

[0017] Prepare an organic solution with a concentration of 0.5-2 mol / L by mixing lithium salt with an organic solvent.

[0018] Step 2: Mix the zwitterionic monomers, carbonate monomers, polyethylene glycol acrylate monomers, the organic solution obtained in Step 2, and the free radical initiator together to form a homogeneous and transparent solution.

[0019] The components in the homogeneous and transparent solution are expressed as mass fractions as follows: zwitterionic monomers 3%–6%, carbonate monomers 15%–25%, polyethylene glycol acrylate monomers 1%–2.5%, organic solutions 65%–80%, and free radical initiators 1%–2%.

[0020] Step 3: The uniform and transparent solution obtained in Step 2 is dropped onto a glass fiber membrane from Whatman or Millipore, then encapsulated. Free radical polymerization is initiated by a thermal initiator within a temperature range of 50℃ to 80℃, achieving in-situ curing on the surface of the lithium-ion battery negative electrode, resulting in a thin film of composite semi-solid lithium-ion battery electrolyte with a thickness of 100 to 200 μm.

[0021] Furthermore, in step 3, the thermal initiator is one or more of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), and benzoyl peroxide (BPO).

[0022] Furthermore, a semi-solid-state lithium-ion battery is provided, wherein the electrolyte is a polymer-based lithium-ion battery electrolyte of the aforementioned zwitterionic composition prepared in situ on the negative electrode. The advantages of the electrolyte material of this invention compared to existing electrolytes are:

[0023] 1. The electrolyte of this invention can be obtained by in-situ polymerization on the negative electrode of the battery, which promotes the interfacial contact between the electrolyte and the electrode, greatly reduces the interfacial impedance of the battery, and improves the rate performance and cycle performance of the battery.

[0024] 2. The present invention introduces an organic solvent as a plasticizer into the electrolyte, resulting in high battery conductivity; introduces zwitterions, enabling lithium salt solvation and dendrite-free lithium deposition; and introduces glass fibers, increasing the lithium transference number. This achieves a lithium-ion battery with better performance.

[0025] 3. The electrolyte of this invention uses carbonate compounds as the whole, which have high chemical stability and can be applied to high-voltage lithium batteries; the preparation process is conducive to battery integration and large-scale production; there are no solvents in the production process, which reduces environmental pollution and lowers costs. Attached Figure Description

[0026] Figure 1 The proton NMR spectrum of the zwitterionic monomer prepared for the example.

[0027] Figure 2 Fourier transform infrared spectra of the electrolytes prepared in Examples 1 and 2.

[0028] Figure 3 Nyquist impedance diagrams of stainless steel (SS) symmetric cells with electrolytes prepared in Examples 1 and 2 at 30°C.

[0029] Figure 4 The linear sweep voltammetry results of the Li / SS batteries with electrolytes prepared in Examples 1 and 2 at 30°C are shown.

[0030] Figure 5 The Li / LFP batteries with electrolytes prepared in Examples 1 and 2 have cycle performance at 30°C with a cutoff voltage of 2.5–3.9 V and a rate of 1C. Detailed Implementation

[0031] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following detailed description of the invention is provided with reference to the accompanying drawings and embodiments. It should be noted that the given embodiments should not be construed as limiting the invention. Non-essential improvements and adjustments made to this invention by those skilled in the art based on its description should still fall within the scope of protection of this invention.

[0032] First, the preparation of the zwitterionic monomer 3-(N,N-diallyl-N-methylammonium)propanesulfonate:

[0033] N,N-diallyl-N-methylamine (0.09 mol) and 1,3-propanesulfonyl lactone (0.1 mol) were reacted in 40 mL of acetonitrile at room temperature with stirring for 5 hours. During this time, a white precipitate formed. The precipitate was then filtered and washed with three 40 mL aliquots of diethyl ether.

[0034] Secondly, the preparation of the positive electrode of the button cell: the positive electrode active materials are lithium iron phosphate (LiFePO4), lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), and layered high-nickel material (LiNi). 0.8 Co 0.15 Al 0.05 One or more of O2. The negative electrode material is one or more of lithium metal, silicon-carbon negative electrode material, and graphite.

[0035] In this embodiment: 0.16 g of LiFePO4, 0.02 g of Super-P, and 0.02 g of PVDF were weighed and 1 ml of N-methylpyrrolidone was added. The mixture was magnetically stirred at 120 r / min for 12 h. The resulting slurry was then coated onto aluminum foil using a spatula, and the aluminum foil was dried in a vacuum oven at 80 °C for 12 h to obtain the positive electrode material. The resulting positive electrode active material had a surface density of 1.13 mg / cm³. 2 .

[0036] Example 1

[0037] Step 1: Place the Whatman fiberglass membrane in a vacuum drying oven at 60°C for 12 hours to remove adsorbed water. Then, cut the dried fiberglass membrane into 16mm diameter discs and store them in an argon-filled glove box for later use.

[0038] Step 2: Prepare an organic solution with LiTFSI as the solute, FEC / DMC (1:4 Vol.%) as the solvent, and a concentration of 1 mol / L. Weigh 0.058 g of LiTFSI and dissolve it in a mixed solution of 0.4 ml FEC and 1.6 ml DMC. Shake to form a homogeneous and transparent solution for later use.

[0039] Step 3: Weigh 0.005g of DMA-SO3 into a glove box filled with argon gas. - 0.016g VEC, 0.002g PEGDMA and 0.002g azobisisobutyronitrile (AIBN) were added to 0.75g of the solution prepared in step 2, and the solution was shaken to dissolve and form a transparent solution.

[0040] Step 4: In an argon-filled glove box, the electrolyte is polymerized in situ to assemble a stainless steel / electrolyte / stainless steel CR2030 coin cell. First, a stainless steel gasket is placed in the positive electrode shell, then the glass fiber membrane from step 1 is placed on top of the gasket. The transparent solution from step 3 is then dropped onto the glass fiber membrane, followed by the stainless steel sheet, spring sheet, and negative electrode shell. Next, using insulated tweezers, the coin cell is placed with the negative electrode side facing up on a coin cell hydraulic press at a pressure of 800 psi for 20 seconds. It is then placed in a vacuum drying oven and reacted at 60°C for 8 hours. Finally, a zwitterionic polymer-based lithium-ion battery is obtained.

[0041] Similarly, the methods for preparing lithium / electrolyte / stainless steel batteries and lithium / electrolyte / lithium iron phosphate batteries are the same. The difference lies in:

[0042] Place a stainless steel gasket and a lithium negative electrode sheet into the positive electrode shell in sequence, then align the gasket and cover it with the glass fiber membrane from step 1. Drop the transparent solution from step 3 onto the glass fiber membrane, and then cover it with a stainless steel sheet (or lithium iron phosphate positive electrode sheet), a spring sheet, and the negative electrode shell in sequence.

[0043] Example 2

[0044] The difference between this embodiment and Embodiment 1 is that:

[0045] Step 3: In an argon-filled glove box, weigh 0.021 g VEC, 0.002 g PEGDMA, and 0.002 g azobisisobutyronitrile (AIBN) and add them to 0.75 g of the solution prepared in Step 2. Shake to dissolve and form a clear solution. Example 2 synthesized a polymer-based electrolyte without the addition of zwitterionic monomers, which was used as a control experimental group.

[0046] Figure 1 The proton NMR spectra of the prepared zwitterionic monomers are shown below, with the peak assignments as follows: ¹H NMR (400 MHz, D₂O) δ 6.03 (ddt, J = 17.4, 10.3, 7.4 Hz, 2H), 5.78–5.57 (m, 4H), 4.02–3.84 (m, 4H), 3.48–3.34 (m, 2H), 3.02 (s, 3H), 2.96 (t, J = 7.2 Hz, 2H), 2.32–2.16 (m, 2H). These results indicate that DMA-SO₃ - Successful synthesis.

[0047] Figure 2 Fourier transform infrared (FTIR) spectra of the electrolytes prepared in Examples 1 and 2. The FTIR spectra of the polymer electrolytes containing zwitterionic monomers show values ​​at 1030 and 1151 cm⁻¹. -1 Sulfonate SO3 - The successful emergence of [something], and its location at 1600–1680 cm -1 Between, DMA-SO3 - The disappearance of carbon-carbon double bonds in VEC and PEGDMA indicates that the monomers have successfully polymerized to form an electrolyte.

[0048] Figure 3 Nyquist impedance diagrams of stainless steel (SS) symmetric cells with electrolytes prepared in Examples 1 and 2 at 30°C. According to the formula:

[0049]

[0050] Where l is the electrolyte thickness, Rb Let S be the resistance of the electrolyte, and S be the effective contact area between the electrode and the electrolyte.

[0051] Example 2 (0wt.% DMA-SO3) - The conductivity at 30℃ is 2.09 × 10⁻⁶. -3 S / cm, Example 1 (5wt.% DMA-SO3) - The conductivity at 30℃ is 1.15 × 10⁻⁶. -3 S / cm. The results show that DMA-SO3 - The addition of monomers reduces conductivity due to DMA-SO3. - Acting as a crosslinking agent increases the degree of crosslinking in polymers, making it more difficult for chain segments to move.

[0052] Figure 4 Linear sweep voltammetry results of Li / SS batteries with electrolytes prepared in Examples 1 and 2 at 30°C. Example 2 (0 wt.% DMA-SO3) - The oxidation potential reaches 4.6V at 30℃ after the introduction of 5wt.% DMA-SO3. - The oxidation potential increased to 5.15V, indicating that it has good electrochemical stability.

[0053] Figure 5 (a) A Li / LFP battery with the electrolyte prepared in Example 2. Figure 5 (b) is the cycling performance graph for Example 1 at 30°C with a cutoff voltage of 2.5–3.9 V and a rate of 0.5C. It can be seen that Examples 1 and 2 have a capacity of 160 mAh g at 0.5C. -1 The average coulombic efficiency exceeds 99.7%, demonstrating excellent battery performance. However, Example 2 (0 wt.% DMA-SO3) - After 200 cycles, the capacity retention was 96.58%, while in Example 1 (5 wt.% DMA-SO3)... - After 200 cycles, the capacity retention was 99.18%. This is due to the uniform distribution of zwitterions, which regulates the uniform deposition of lithium.

[0054] Based on the test results of the above embodiments and comparative examples, it is evident that the electrolyte material of this invention can be prepared on the negative electrode material of a battery through free radical in-situ polymerization, significantly reducing interfacial impedance and improving battery rate performance and cycle performance. Furthermore, the introduction of organic solvents as plasticizers results in high battery conductivity; the introduction of zwitterions enables lithium salt solvation and dendrite-free lithium deposition; and the introduction of glass fibers increases the lithium transference number. Moreover, the electrolyte of this invention uses carbonate compounds throughout, exhibiting high chemical stability and making it suitable for use in high-voltage lithium batteries. The results also confirm that the electrolyte of this invention possesses excellent performance, with a conductivity of 1.15 × 10⁻⁶ at 30°C. -3 S / cm, oxidation potential 5.15V, capacity 160mAhg at 0.5C -1 The average coulomb efficiency exceeds 99.7%, and the capacity retention rate is 99.18% after 200 cycles.

Claims

1. A zwitterionic polymer-based lithium-ion battery electrolyte, characterized in that: Composed of organic polymers, organic solvents, and lithium salts, its ionic conductivity at 30°C is 8 × 10⁻⁶. -4 ~1.15×10 -3 S / cm; The organic polymer is obtained by double-bond free radical polymerization using 15-20 wt.% zwitterionic monomers, 70-80 wt.% carbonate monomers and 8-15 wt.% polyethylene glycol acrylate monomers. Here, the total content is 1. Among them, the zwitterionic monomer is 3-(N,N-diallyl-N-methylammonium)propanesulfonate (DMA-SO3) with a double bond. - ) or ((3-(diallyl(methyl)amino)propyl)sulfonyl)(trifluoromethyl)sulfonyl)amide (DMA-SO2N) - One or more of SO2CF3, with the following specific structure: 。 2. The zwitterionic polymer-based lithium-ion battery electrolyte as described in claim 1, characterized in that: The polyethylene glycol acrylate monomers are one or more of polyethylene glycol dimethacrylate (PEGDMA), polyethylene glycol diacrylate (PEGDA), ethoxylated trimethylolpropane triacrylate (ETPTA), and pentaerythritol triacrylate (PETA); and the relative molecular mass of the monomers used is between 400 and 1500 g / mol.

3. The zwitterionic polymer-based lithium-ion battery electrolyte as described in claim 1, characterized in that: The carbonate ester monomer is one or more of ethylene ethylene carbonate (VEC) and divinyl ethylene carbonate.

4. The zwitterionic polymer-based lithium-ion battery electrolyte as described in claim 1, characterized in that: The organic solvent is one or more of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and dimethyl carbonate (DMC).

5. The zwitterionic polymer-based lithium-ion battery electrolyte as described in claim 1, characterized in that: The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium difluorooxalate borate (LiDFOB).

6. The method for preparing the zwitterionic polymer-based lithium-ion battery electrolyte as described in claim 1, characterized in that, Includes the following steps: Step 1: Prepare zwitterionic monomers and organic solutions; The N,N-diallyl-N-methylamine and 1,3-propanesulfonyl lactone were quaternized in acetonitrile to give the zwitterionic monomer DMA-SO3. - That is, 3-(N,N-diallyl-N-methylammonium)propanesulfonate with double bonds; zwitterionic monomer DMA-SO2N - The synthesis of SO2CF3 involves first reacting CF3SO2NH2 with K2CO3 to generate CF3SO2NHK, then reacting it with 1-propanesulfonyl chloride to generate Cl-SO2NSO2CF3; finally, quaternizing N,N-diallyl-N-methylamine and Cl-SO2NSO2CF3 in acetonitrile yields the zwitterionic monomer DMA-SO2N. - SO2CF3; Prepare an organic solution with a concentration of 0.5-2 mol / L by mixing lithium salt with an organic solvent; Step 2: Mix the zwitterionic monomers, carbonate monomers, polyethylene glycol acrylate monomers, organic solution, and free radical initiator together to form a homogeneous and transparent solution; The components in the homogeneous and transparent solution are expressed as mass fractions as follows: zwitterionic monomers 3%–6%, carbonate monomers 15%–25%, polyethylene glycol acrylate monomers 1%–2.5%, organic solutions 65%–80%, and free radical initiators 1%–2%. Step 3: The uniform and transparent solution obtained in Step 2 is dropped onto a glass fiber membrane from Whatman or Millipore, then encapsulated. Free radical polymerization is initiated by a thermal initiator within a temperature range of 50℃ to 80℃, achieving in-situ curing on the surface of the lithium-ion battery negative electrode, resulting in a thin film of composite semi-solid lithium-ion battery electrolyte with a thickness of 100 to 200 μm.

7. The method for preparing the zwitterionic polymer-based lithium-ion battery electrolyte as described in claim 6, characterized in that: In step 3, the thermal initiator is one or more of azobisisobutyronitrile (AIBN), azobisisobutyronitrile (ABVN), and benzoyl peroxide (BPO).

8. A semi-solid-state lithium-ion battery, characterized in that: Its electrolyte is a polymer-based lithium-ion battery electrolyte of zwitterions as described in claim 1, which is prepared in situ on the negative electrode.

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