A high-safety, high-cycle-life in-situ cured gel polymer electrolyte and its preparation method

Abstract

This invention discloses a high-safety, high-cycle-life in-situ cured gel polymer electrolyte and its preparation method, belonging to the field of lithium-ion battery technology. The electrolyte is formed by in-situ polymerization of a gel precursor solution inside the battery triggered by an energy field. The precursor solution contains acrylamide and / or methacrylamide polymerizable monomers, multifunctional acrylate and / or methacrylate crosslinking agents, phosphorus-containing polymerizable flame-retardant components, an initiator, lithium salt, and an organic solvent. The preparation method includes preparing the precursor solution, injecting it into the pores of the battery cell, and in-situ curing triggered by heat or ultraviolet light. Through the synergistic effect of in-situ gelation and gradient electrodes, continuous and stable ion transport channels and flame-retardant networks are constructed within the electrode pores, thereby simultaneously improving the battery's abuse safety and low-temperature cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an in-situ cured gel polymer electrolyte with high safety and high cycle life, and its preparation method. Background Technology

[0002] Lithium-ion batteries, as highly efficient electrochemical energy storage devices, have been widely used in consumer electronics, electric vehicles, and large-scale energy storage systems. Their performance and safety are highly dependent on the electrolyte system. Currently, commercial lithium-ion batteries mainly use liquid organic electrolytes. While this system has high ionic conductivity and good electrode wettability, it also has inherent safety risks and performance bottlenecks.

[0003] In terms of safety, traditional liquid electrolytes are typically based on flammable organic solvents such as carbonates. When the battery experiences a sudden temperature rise due to internal short circuits, mechanical abuse (such as puncture or crushing), or thermal abuse, it is highly susceptible to combustion or even explosion. Although the industry has attempted to improve safety by adding liquid flame retardants (such as phosphorus-based and halogen-based compounds), these additives often undergo irreversible decomposition or migration during cycling, leading to a significant decline in electrochemical performance (such as cycle life and rate performance), and have limited effectiveness in suppressing the root cause of thermal runaway.

[0004] In terms of cycle performance, especially low-temperature cycle life, the viscosity of liquid electrolytes increases sharply at low temperatures, and the ion conductivity decreases significantly, leading to a surge in battery interfacial impedance and increased polarization. This not only significantly reduces the usable capacity of the battery at low temperatures but also triggers side reactions such as uneven lithium-ion deposition (lithium plating) on ​​the electrode surface, accelerating capacity decay and introducing new safety risks. Although developing new lithium salts, low-freezing-point solvents, or low-temperature additives can improve low-temperature performance to some extent, these improvements often come at the cost of sacrificing the thermal or chemical stability of the electrolyte, making it difficult to fundamentally achieve a synergy between high safety and excellent low-temperature cycle life.

[0005] In recent years, solid-state or gel polymer electrolytes have been considered an important direction for improving safety due to their non-flammability and lack of leakage risk. However, traditional pre-prepared gel electrolytes or inorganic solid electrolytes generally suffer from poor contact with porous electrodes, low room-temperature ionic conductivity, and complex and costly large-scale production processes. In particular, rigid solid-solid interface contacts lead to extremely high interfacial impedance, severely degrading the rate performance and low-temperature performance of batteries. In-situ gelation technology, which injects liquid precursor liquid into the battery and then triggers solidification, is expected to improve electrode / electrolyte interface contact. However, most existing in-situ gelation systems focus on improving mechanical strength or room-temperature ionic conductivity, and their component design often does not systematically integrate flame retardancy and low-temperature performance optimization functions. Simple gel networks may not be able to effectively suppress heat and current concentration under abuse conditions, and their chain segment mobility at low temperatures may be insufficient to ensure continuous rapid ion transport.

[0006] Therefore, developing a novel electrolyte system that can fundamentally integrate high flame retardancy with excellent low-temperature ion transport capabilities, and achieving a balance between safety and long cycle life (especially in harsh low-temperature environments) through an in-situ curing method compatible with battery manufacturing processes, has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide an in-situ cured gel polymer electrolyte and method with high safety and long cycle life, so as to solve the problem mentioned in the background art that the existing lithium-ion batteries cannot simultaneously achieve both safety and long cycle life.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A high-safety, high-cycle-life in-situ cured gel polymer electrolyte is formed by in-situ polymerization of a gel precursor solution inside a battery triggered by an energy field. The gel precursor solution comprises, by mass percentage: 0.01-10 wt% of acrylamide and / or methacrylamide polymerizable monomers, 0.01-10 wt% of multifunctional acrylate and / or methacrylate crosslinking agents, wherein the crosslinking agent has at least three polymerizable double bonds, 0.1-20 wt% of phosphorus-containing polymerizable flame retardant components, 0.001-5 wt% of initiator, lithium salt, and the balance being an organic solvent.

[0009] Furthermore, the phosphorus-containing polymerizable flame-retardant component is selected from at least one of vinyl phosphate, acryloyloxyalkyl phosphate and / or methacryloyloxyalkyl phosphate, phosphorus-containing acrylate and / or phosphorus-containing methacrylate monomer.

[0010] Furthermore, the multifunctional acrylate and / or methacrylate crosslinking agent is selected from at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate.

[0011] Furthermore, the initiator is a thermal initiator or a photoinitiator; the thermal initiator is selected from at least one of azobisisobutyronitrile and benzoyl peroxide; the photoinitiator is selected from at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, and benzophenone.

[0012] A method for preparing the in-situ cured gel polymer electrolyte includes the following steps: S1: Under an inert atmosphere, lithium salt is dissolved in an organic solvent to form a basic electrolyte; S2: Add acrylamide and / or methacrylamide polymerizable monomers, multifunctional acrylate and / or methacrylate crosslinking agents, phosphorus-containing polymerizable flame retardant components and initiators to the basic electrolyte in sequence, mix evenly, and obtain a gel precursor solution. S3: Inject the gel precursor solution into the battery cell to wet the pores of the electrodes and separator. S4: By applying an energy field, the gel precursor liquid is triggered to polymerize and crosslink in situ within the pores to form the gel polymer electrolyte.

[0013] Furthermore, in step S4, the energy field is a thermal field or an ultraviolet light field; When thermosetting is used, the conditions are: heating at 60~100℃ for 2~8 hours; When using ultraviolet light curing, the conditions are: irradiation for 1 to 5 minutes under ultraviolet light with a wavelength of 320~400nm and an intensity of 10~100mW / cm².

[0014] Furthermore, the gel polymer electrolyte is injected in the form of a liquid precursor during battery assembly and then solidifies in situ inside the battery.

[0015] A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an in-situ cured gel polymer electrolyte, wherein the electrolyte fills the pores of the electrodes and the separator; the positive electrode and / or the negative electrode is a gradient structure electrode, which includes a current collector and a first active layer and a second active layer sequentially stacked on the same side of the current collector, wherein the electronic conductivity of the first active layer is greater than 10. -3 S / m, the electronic conductivity of the second active layer is less than 10. -8 S / m.

[0016] Furthermore, the lithium-ion battery containing the electrolyte retains a capacity of not less than 60% after 600 cycles at 1C rate at -40°C.

[0017] Furthermore, batteries containing electrolytes can pass the UL1642 standard nail penetration test.

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) Improve the intrinsic safety of the battery: The phosphorus flame retardant components in the electrolyte are polymerized in situ to form a stable flame retardant network, giving the system long-lasting flame retardancy; gel curing eliminates the risk of electrolyte leakage, and the low conductivity gradient outer layer can suppress current concentration during short circuit, enabling the battery to pass the UL1642 nail penetration test, fundamentally improving the safety of abuse.

[0019] (2) Improved low-temperature cycling performance: The in-situ formed gel network ensures continuous ion channels within the electrode pores, effectively reducing interfacial impedance; combined with the optimization of ion / electron transport by the gradient electrode, low-temperature polarization is significantly mitigated. After 600 cycles at -40℃ and 1C rate, the battery retains more than 72% of its capacity, and the interfacial impedance increases slowly.

[0020] (3) Good process compatibility and comprehensive performance: The "pre-wetting and then curing" process is compatible with existing battery production lines and is easy to scale up. While achieving high safety and excellent low-temperature performance, this system maintains good room temperature ionic conductivity and cycle stability, providing a reliable solution for expanding the application of lithium-ion batteries in harsh environments. Attached Figure Description

[0021] Figure 1 This is a comparison chart of the capacity retention rates of Comparative Example 1 and Example 3 of the present invention after 600 cycles at a low temperature of -40°C. Figure 2 This is a flowchart illustrating the preparation method of an in-situ cured gel polymer electrolyte with high safety and high cycle life according to the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise stated, the "mass percentage (wt%)" mentioned in this invention is based on the total mass of the corresponding formulation system (such as gel precursor liquid); the "electronic conductivity" is determined by the standard four-probe method at room temperature (25±2℃); the "residual conductive agent content is less than 0.05 wt%" means that the mass fraction of the conductive agent in the active layer formulation does not exceed 0.05%.

[0024] Example 1: Battery fabrication based on gradient cathode and thermally triggered in-situ gel electrolyte Preparation of gradient structure cathode: Current collector: Aluminum foil.

[0025] First active layer (high conductivity layer): Lithium cobalt oxide ( A mixture of 93 wt% conductive carbon black (Super P, 5 wt%) and polyvinylidene fluoride (PVDF, 2 wt%) was prepared by adding N-methylpyrrolidone (NMP) solvent, with the solid content controlled to approximately 60%. This slurry was coated onto aluminum foil, and after drying, its density was 15 mg / cm². Its electronic conductivity was greater than 10. -3 S / m.

[0026] Second active layer (low conductivity layer): Lithium manganese iron phosphate (… The slurry was prepared by mixing PVDF (1.5 wt%) with a conductive agent without adding any conductive agent. This slurry was coated onto the surface of the first active layer and dried to a density of 3 mg / cm². Its electronic conductivity is less than [missing value]. .

[0027] The above-mentioned double-layer structure electrode sheet was rolled and the overall compaction density was controlled at 3.5 g / cm³.

[0028] Conventional negative electrode preparation: Current collector: copper foil.

[0029] Artificial graphite (97 wt%), sodium carboxymethyl cellulose (CMC, 1.5 wt%) and styrene-butadiene rubber (SBR, 1.5 wt%) were mixed to form a slurry, which was then coated onto copper foil. The areal density was 10 mg / cm², and the compacted density after roller pressing was 1.7 g / cm³.

[0030] Preparation of heat-triggered gel precursor solution: Basic solution: LiPF6 lithium salt was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1 to prepare an electrolyte with a concentration of 1 mol / L.

[0031] Under an inert atmosphere, the following components (based on the total mass of the gel precursor solution) were added to the above-mentioned basic electrolyte: 1.5 wt% N,N′-methylenebisacrylamide (MBA), 0.5 wt% pentaerythritol tetraacrylate (PETEA), 1.0 wt% dimethyl vinyl phosphate, and 0.03 wt% azobisisobutyronitrile (AIBN) as a thermal initiator, and mixed thoroughly.

[0032] Battery assembly and curing: The positive electrode, polyethylene separator, and negative electrode are stacked together to form a battery cell.

[0033] Inject the gel precursor solution into the battery cell and let it stand to fully wet the electrodes and pores of the separator.

[0034] The battery cell was heated in an oven at 60°C for 6 hours, which triggered the decomposition of AIBN and the in-situ polymerization and cross-linking of the precursor liquid in the pores to form a flame-retardant gel polymer electrolyte.

[0035] The subsequent processes include routine packaging, formation, and capacity testing.

[0036] Example 2: Battery fabrication based on gradient negative electrode and thermally triggered in-situ gel electrolyte Conventional positive electrode preparation: Similar to the conventional negative electrode preparation method described in Example 1, NCM622 (96wt%) was used as the active material, combined with SuperP (2wt%) and PVDF (2wt%), with an areal density of 18mg / cm² and a compaction density of 3.4g / cm³.

[0037] Fabrication of gradient structure negative electrode: Current collector: copper foil.

[0038] First active layer (high conductivity layer): Artificial graphite (98 wt%), Super P (0.8 wt%), CMC (0.6 wt%) and SBR (0.6 wt%) are mixed and slurried, and coated on copper foil with an areal density of 8 mg / cm².

[0039] Second active layer (low conductivity layer): Niobium oxide ( The mixture of 98.5 wt% CMC (0.75 wt%) and SBR (0.75 wt%) was prepared without the addition of conductive agents. It was then coated onto the surface of the first active layer, with an areal density of 2 mg / cm². After roller pressing, the overall compacted density was 2.0 g / cm³.

[0040] Preparation of gel precursor solution, battery assembly and curing: Same as in Example 1.

[0041] Example 3: Battery fabrication based on gradient positive and negative electrodes and UV-triggered in-situ gel electrolyte Preparation of gradient structure positive and negative electrodes: Same as in Example 1 and Example 2, respectively.

[0042] Preparation of UV-triggered gel precursor solution: Basic solution: The electrolyte was prepared by dissolving EC and ethyl methyl carbonate (EMC) in a mixed solvent with a volume ratio of 3:7 to obtain an electrolyte with a concentration of 1 mol / L.

[0043] Add the following components: MBA 1.2 wt%, PETEA 0.8 wt%, dimethyl vinyl phosphate 1.2 wt%, and 2-hydroxy-2-methyl-1-phenyl-1-propanone (Irgacure 1173) 0.5 wt% as a photoinitiator, and mix thoroughly.

[0044] Battery assembly and curing: The assembly and impregnation steps are the same as in Example 1.

[0045] The impregnated battery cells were placed in a UV curing device and irradiated for 3 minutes under UV light with a wavelength of 365 nm and an intensity of 50 mW / cm² to trigger in-situ polymerization.

[0046] The subsequent processes include packaging and formation.

[0047] Comparative Example 1: Conventional Liquid Electrolyte Battery Conventional NCM622 positive and graphite negative electrodes were prepared without using a gradient structure. The electrolyte was a commercially available 1 mol / L LiPF6 / carbonate solution (EC:DMC:EMC = 1:1:1, volume ratio), free of any polymerizable monomers, crosslinking agents, or flame retardant components. The assembly, encapsulation, and formation processes were the same as in the previous examples.

[0048] Performance Tests and Results Low-temperature cycling test: After the battery is placed in an environment of -40℃ until the temperature reaches equilibrium, it is subjected to constant current charge-discharge cycle at a rate of 1C (charge upper limit voltage 4.2 V, discharge cut-off voltage 3.0 V), and the discharge capacity retention rate (relative to the first discharge capacity) is recorded after the 600th cycle.

[0049] Needle penetration test: According to UL1642 standard, a fully charged battery is punctured and observed to see if it catches fire or explodes.

[0050] Interface impedance testing: Electrochemical impedance spectroscopy (EIS) was used to test the initial charge transfer impedance (Rct) of the battery at -40℃ and the Rct after 600 cycles.

[0051] Test Results: Sample -40℃, 1C 600-cycle capacity retention UL1642 needle penetration test initial Rct (mΩ) after 600 cycles Rct (mΩ)

[0052] As shown in the table above, Examples 1-3, employing the in-situ cured gel polymer electrolyte and gradient electrode structure described in this invention, exhibit a significant advantage in capacity retention (more than 10 percentage points higher) in low-temperature cycling performance at -40°C compared to Comparative Example 1, which uses a conventional liquid electrolyte. Furthermore, they show lower interfacial impedance and slower impedance growth after cycling. All examples passed the UL1642 needle penetration test, demonstrating their high safety. In particular, Example 3 (UV cured) exhibits the best overall performance.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-safety, high-cycle-life in-situ cured gel polymer electrolyte, characterized in that, It is formed by in-situ polymerization of a gel precursor solution inside the battery triggered by an energy field; the gel precursor solution contains, by mass percentage: 0.01~10wt% of acrylamide and / or methacrylamide polymerizable monomers, 0.01~10wt% of multifunctional acrylate and / or methacrylate crosslinking agents, wherein the crosslinking agent has not less than 3 polymerizable double bonds, 0.1~20wt% of phosphorus-containing polymerizable flame retardant components, 0.001~5wt% of initiator, lithium salt, and the balance being organic solvent.

2. The in-situ cured gel polymer electrolyte according to claim 1, characterized in that, The phosphorus-containing polymerizable flame-retardant component is selected from at least one of vinyl phosphate, acryloyloxyalkyl phosphate and / or methacryloyloxyalkyl phosphate, phosphorus-containing acrylate and / or phosphorus-containing methacrylate monomer.

3. The in-situ cured gel polymer electrolyte according to claim 1, characterized in that, The multifunctional acrylate and / or methacrylate crosslinking agent is selected from at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and trimethylolpropane triacrylate.

4. The in-situ cured gel polymer electrolyte according to claim 1, characterized in that, The initiator is a thermal initiator or a photoinitiator; the thermal initiator is selected from at least one of azobisisobutyronitrile and benzoyl peroxide; the photoinitiator is selected from at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, and benzophenone.

5. A method for preparing an in-situ cured gel polymer electrolyte as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Under an inert atmosphere, lithium salt is dissolved in an organic solvent to form a basic electrolyte; S2: Add acrylamide and / or methacrylamide polymerizable monomers, multifunctional acrylate and / or methacrylate crosslinking agents, phosphorus-containing polymerizable flame retardant components and initiators to the basic electrolyte in sequence, mix evenly, and obtain a gel precursor solution. S3: Inject the gel precursor solution into the battery cell to wet the pores of the electrodes and separator. S4: By applying an energy field, the gel precursor liquid is triggered to polymerize and crosslink in situ within the pores to form the gel polymer electrolyte.

6. The method according to claim 5, characterized in that, In step S4, the energy field is a thermal field or an ultraviolet light field; When thermosetting is used, the conditions are: heating at 60~100℃ for 2~8 hours; When using ultraviolet light curing, the conditions are: irradiation for 1 to 5 minutes under ultraviolet light with a wavelength of 320~400nm and an intensity of 10~100mW / cm².

7. The application of the in-situ cured gel polymer electrolyte according to claim 1 in lithium-ion batteries, characterized in that, The gel polymer electrolyte is injected as a liquid precursor during battery assembly and then solidified in situ inside the battery.

8. A lithium-ion battery, characterized in that, The electrode comprises a positive electrode, a negative electrode, a separator, and an in-situ cured gel polymer electrolyte as described in any one of claims 1 to 4, wherein the electrolyte fills the pores of the electrodes and the separator; the positive electrode and / or the negative electrode is a gradient structure electrode, the gradient structure electrode comprising a current collector and a first active layer and a second active layer sequentially stacked on the same side of the current collector, wherein the electronic conductivity of the first active layer is greater than 10. -3 S / m, the electronic conductivity of the second active layer is less than 10. -8 S / m.

9. The lithium-ion battery according to claim 8, characterized in that, After the battery containing the electrolyte is cycled 600 times at 1C rate at -40°C, the capacity retention rate is not less than 60%.

10. The lithium-ion battery according to claim 8 or 9, characterized in that, Batteries containing the electrolyte are able to pass the UL1642 standard nail penetration test.

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