A polymer electrolyte precursor solution, a polymer electrolyte, and a polymer battery

Abstract

This invention discloses a polymer electrolyte precursor, a polymer electrolyte, and a polymer battery. The polymer electrolyte precursor comprises the following components in parts by mass: 8-12 parts electrolyte salt, 75-85 parts organic solvent, 4-6 parts polymerizable monomer, 2-4 parts prepolymer, and 0.2-1 parts initiator. The polymerizable monomer is a (meth)acrylate compound containing a cyclic structure and ether bonds. The prepolymer has a number average molecular weight of 600-2000 and contains at least two (meth)acrylate groups. This invention uses (meth)acrylate compounds containing both rigid rings and ether bonds as monomer molecules, combined with a prepolymer of a specific number average molecular weight, to prepare a polymer electrolyte precursor. The resulting polymer electrolyte possesses both high strength and flexibility, improving the lifespan of the polymer battery. Polymer batteries using this gel electrolyte maintain high coulombic efficiency, high capacity, and stable internal resistance during long-term cycling.

Description

Technical Field

[0001] This invention belongs to the field of polymer electrolytes, specifically relating to a polymer electrolyte precursor solution, a polymer electrolyte, and a polymer battery. Background Technology

[0002] Lithium-ion and sodium-ion batteries are widely used as core energy storage devices in renewable energy storage, electric vehicles, and portable electronic devices. In lithium (sodium)-ion batteries, the electrolyte is a key component that connects the positive and negative electrodes and is responsible for ion conduction; its performance directly determines the overall energy density, cycle life, and safety of the battery.

[0003] Polymer electrolytes, as a type of "solid-liquid composite" material, fix liquid electrolyte (lithium salt and organic solvent) in a three-dimensional polymer network, thus combining safety and high ionic conductivity. Therefore, they have unique advantages compared to traditional solid electrolytes or liquid electrolytes. For example, a Chinese patent for a novel gel polymer electrolyte with an interpenetrating network structure, its preparation method and application, uses acrylate compounds as monomers to synthesize a polymer electrolyte that can be used in lithium batteries.

[0004] However, existing polymer electrolytes still suffer from drawbacks such as low mechanical strength and high brittleness (i.e., insufficient toughness). This can lead to lithium (sodium) dendrite growth at the electrode-electrolyte interface during long-term charge-discharge cycles, resulting in a shorter lifespan for polymer batteries. In the long-term cycle process, problems such as excessively rapid decrease in coulombic efficiency and capacity, and excessively rapid increase in internal resistance may occur. Summary of the Invention

[0005] To address the problem that existing polymer electrolytes cannot simultaneously possess high mechanical strength and toughness, leading to a shorter lifespan for polymer batteries and significant decreases in coulombic efficiency and capacity, as well as a significant increase in internal resistance during long-term cycling, this invention provides a polymer electrolyte precursor solution. This polymer electrolyte combines high strength and flexibility, thereby improving the lifespan of polymer batteries. Polymer batteries using this gel electrolyte can maintain high coulombic efficiency, high capacity, and relatively stable internal resistance during long-term cycling.

[0006] Another object of the present invention is to provide a polymer electrolyte.

[0007] Another object of the present invention is to provide a method for preparing a polymer electrolyte.

[0008] Another object of the present invention is to provide a polymer battery.

[0009] The above-mentioned objective of the present invention is achieved through the following technical solution: A polymer electrolyte precursor solution comprises the following components in parts by mass: 8-12 parts electrolyte salt, 75-85 parts organic solvent; 4-6 parts of monomer can be polymerized. 2-4 parts of prepolymer Initiator 0.3~1 part, The polymerizable monomer is a (meth)acrylate compound containing a cyclic structure and ether bonds; the number average molecular weight of the prepolymer is 600-2000, and the prepolymer contains at least two (meth)acrylate groups.

[0010] It should be noted that: The inventors of this invention discovered through research that simultaneously introducing cyclic and ether bond structures into the monomer molecules forming the polymer electrolyte provides the polymer electrolyte with a robust physical barrier. The rigid cyclic structure acts as a "reinforcing point" in the polymer chain, offering high local modulus and dimensional stability. The ether bonds and connected flexible segments endow the network with excellent segmental mobility and toughness. This not only buffers volumetric stress during electrode cycling under large deformation and maintains tight interfacial contact, but the ether oxygen atoms also efficiently complex and transport electrolyte ions, promoting uniform deposition. This, in turn, improves the lifespan of the polymer battery made from the polymer electrolyte, enabling the polymer battery to maintain high coulombic efficiency, high capacity, and stable internal resistance during long-term cycling. When the two structures are covalently integrated into the same monomer, the resulting polymer molecular chain contains alternating "hard-soft" microregions, improving the stability of various performance characteristics of the polymer electrolyte during long-term cycling. Furthermore, controlling the number-average molecular weight of the prepolymer within a specific range ensures both its own mechanical properties and good polymerization and cross-linking with polymerizable monomers, forming a stable three-dimensional network with moderate cross-linking density and segmental flexibility, thereby improving the polymer electrolyte's resistance to dendrite formation. If the molecular weight of the prepolymer is too large or too small, it will lead to an imbalance between the strength and flexibility of the polymer electrolyte, resulting in a shorter lifespan of the polymer battery, a significant decrease in coulombic efficiency and capacity, and a significant increase in internal resistance during long-term cycling.

[0011] Preferably, the electrolyte salt is a lithium salt or a sodium salt; the lithium salt is at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium trifluoromethanesulfonate; the sodium salt is at least one selected from sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium tetrafluoroborate, and sodium trifluoromethanesulfonate.

[0012] Preferably, the organic solvent is at least one selected from ethylene carbonate, diethyl carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, and dipropyl carbonate.

[0013] More preferably, the organic solvent is a mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1:(0.9~1.1).

[0014] In this invention, the cyclic structure includes, but is not limited to, isoborneol, cyclohexyl, benzene ring, and cyclopentenyl.

[0015] Preferably, the polymerizable monomer is at least one of 2-phenoxyethyl acrylate, dicyclopentenoxyethyl methacrylate, and tetrahydropyran acrylate.

[0016] More preferably, the polymerizable monomer is 2-phenoxyethyl acrylate and dicyclopentenoxyethyl methacrylate.

[0017] When the polymerizable monomers are a combination of 2-phenoxyethyl acrylate and dicyclopentenoxyethyl methacrylate, the cycle life and electrical performance of the battery made from the polymer electrolyte can be improved.

[0018] More preferably, the mass ratio of 2-phenoxyethyl acrylate to dicyclopentenoxyethyl methacrylate is 1:(0.8~1.2).

[0019] Preferably, the prepolymer is at least one of polyurethane acrylate, polyurethane methacrylate, polyester acrylate, polyester methacrylate, epoxy acrylate, epoxy methacrylate, and acrylated polybutadiene.

[0020] Preferably, the number-average molecular weight of the prepolymer is 1000-1500. Controlling the number-average molecular weight of the prepolymer within this range can improve the cycle life and electrical performance of the battery made from the polymer electrolyte.

[0021] Preferably, the initiator is at least one of di-tert-butyl hydroperoxide and dicumyl peroxide.

[0022] The present invention also protects a polymer electrolyte prepared from the above-mentioned polymer electrolyte precursor solution.

[0023] Preferably, the preparation method of the above-mentioned polymer electrolyte includes the following steps: allowing the above-mentioned precursor liquid to stand and soak, and then subjecting it to heat treatment to undergo a polymerization reaction, thereby obtaining the polymer electrolyte.

[0024] Preferably, the temperature for static soaking is 35~65℃ and the time is 12~48h.

[0025] Preferably, before the standing soaking, the process further includes the step of injecting the precursor solution into the battery cell.

[0026] Preferably, the heat treatment temperature is 70~120℃ and the time is 6~48h.

[0027] The present invention also protects a polymer battery comprising the above-mentioned polymer electrolyte; the battery is a lithium-ion battery or a sodium-ion battery.

[0028] Compared with the prior art, the beneficial effects of the present invention are: This invention uses (meth)acrylate compounds containing both rigid rings and ether bonds as monomer molecules, and combines them with prepolymers of a specific number-average molecular weight to prepare a polymer electrolyte precursor. The polymer electrolyte prepared from this polymer electrolyte precursor has both high strength and flexibility, which can improve the service life of polymer batteries. Polymer batteries using this gel electrolyte can maintain high coulombic efficiency, high capacity and stable internal resistance during long-term cycling. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0030] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0031] The reagents used in the various embodiments and comparative examples of this invention are described below: Polyurethane acrylate 1#: molecular weight 1000, Kunshan Castel Polymer, U-Cure 9100; Polyurethane acrylate 2#: molecular weight 700, Changxing Chemical Industry (China) Co., Ltd., 6153-3; Polyurethane acrylate 3#: molecular weight 1500, Jiangsu Sanmu Chemical, SM6240; Polyurethane acrylate 4#: molecular weight 500, Jiangsu Sanmu Chemical, SM6330; Polyurethane acrylate 5#: molecular weight 5000, Kunshan Castel Polymer Materials Co., Ltd., U-CURE 9571; Polyester acrylate: molecular weight 1000, Allnex China Co., Ltd., EBECRYL® 810; Acrylated polybutadiene: molecular weight 1200, Nisso Corporation, NISSO-PB B-1000; 2-Phenoxyethyl acrylate (CAS: 48145-04-6): Commercially available; Dicyclopentenoxyethyl methacrylate (CAS: 68586-19-6): Commercially available; Phenyl acrylate (CAS: 937-41-7): Commercially available; Polyethylene glycol methyl ether acrylate (CAS: 32171-39-4): Commercially available; Di-tert-butyl hydroperoxide (CAS: 75-91-2): Commercially available.

[0032] The polymer electrolyte precursor solutions of the embodiments and comparative examples of the present invention were prepared by the following method: The components are mixed in proportion in an argon glove box with both moisture and oxygen content below 0.1 ppm, and magnetically stirred until no insoluble matter remains, resulting in a clear and transparent mixture, which is the precursor solution.

[0033] The polymer batteries of the present invention and comparative examples are prepared by the following method: the obtained polymer electrolyte precursor liquid is injected into a soft-pack battery cell with lithium iron phosphate as the positive electrode and graphite as the negative electrode, and then the injected battery is placed in a constant temperature chamber at 45°C and kept at the temperature for 12 hours; then the battery is transferred to a constant temperature chamber at 85°C and kept at the temperature for 6 hours to allow the polymer electrolyte precursor liquid to polymerize and form a polymer electrolyte, thus obtaining the polymer battery.

[0034] Examples 1-9 Examples 1-9 provide a series of polymer electrolyte precursor solutions and polymer batteries, wherein the formulations of the polymer electrolyte precursor solutions are shown in Table 1.

[0035] Table 1. Formulations (parts by weight) of the Examples

[0036] Comparative Examples 1-5 Comparative Examples 1-5 provide a series of polymer electrolyte precursor solutions and polymer batteries, wherein the formulations of the polymer electrolyte precursor solutions are shown in Table 2.

[0037] Table 2. Comparative formulations (parts by weight)

[0038] Performance testing (1) Cycle life of symmetrical cells: The polymer cells of each embodiment or comparative example at a current density of 0.5 mA / cm² 2 The battery was subjected to constant current cycling at 25°C, and the battery voltage was read every 10 minutes. When the battery voltage dropped to 0 V, it was determined to be a short circuit. The cycle time at this point is the cycle life of the symmetrical battery.

[0039] (2) Capacity retention rate after 300 cycles: The polymer batteries in each embodiment or comparative example are used in constant current charge and discharge mode, with a charging rate of 1C (100 mA) and a charging cut-off voltage of 3.65 V; a discharging rate of 1C (100 mA) and a discharging cut-off voltage of 2.0 V; the capacity retention rate after 300 cycles is calculated according to the following formula: Capacity retention rate after 300 cycles = (300th discharge capacity / initial discharge capacity) × 100%; where the initial discharge capacity is the discharge capacity of the battery during the first charge and discharge.

[0040] (3) Initial Coulomb Efficiency and Coulomb Efficiency after 300 Cycles: In the charge-discharge experiment of (2), the initial Coulomb Efficiency and Coulomb Efficiency after 300 Cycles were calculated based on the discharge capacity and charge capacity of the first and 300th charge-discharge cycles: Initial Coulomb Efficiency = (First Discharge Capacity / First Charge Capacity) × 100%; Coulomb Efficiency after 300 Cycles: The ratio of discharge capacity to charge capacity in the 300th charge-discharge cycle, i.e., Coulomb Efficiency after 300 Cycles = (300th Discharge Capacity / 300th Charge Capacity) × 100%.

[0041] (4) Initial battery internal resistance and battery internal resistance after 300 cycles: In the charge and discharge experiment of (2), the battery internal resistance was measured after the first and 300 cycles. The test method was AC impedance method (EIS), the test frequency range was 0.01 Hz~100kHz, the AC signal amplitude was 5 mV, and the Nyquist spectrum was analyzed by electrochemical workstation. The impedance value of the intersection of the spectrum and the real axis was taken as the total internal resistance of the battery.

[0042] The performance test results (symmetric battery cycle life, capacity retention after 300 cycles, initial coulombic efficiency, coulombic efficiency after 300 cycles, initial battery internal resistance, and battery internal resistance after 300 cycles) of each embodiment and comparative example are shown in Table 3.

[0043] Table 3 Performance test results of each embodiment and comparative example

[0044] Table 3 shows the symmetrical battery cycle life, capacity retention after 300 cycles, initial coulombic efficiency, coulombic efficiency after 300 cycles, initial battery internal resistance, and battery internal resistance after 300 cycles for the polymer batteries of each embodiment and comparative example. As shown in Table 3, the symmetrical battery cycle life of the polymer batteries in each embodiment is not less than 1400 hours, the capacity retention after 300 cycles is not less than 88%, the initial coulombic efficiency and the coulombic efficiency after 300 cycles are not less than 99%, and the battery internal resistance after 300 cycles is not greater than 4.4 Ω. This indicates that the polymer electrolyte of the present invention can effectively suppress dendrite formation, thereby improving the cycle life and electrical performance of the prepared battery under long-term use.

[0045] The polymerizable monomer molecules in Comparative Example 1 do not contain ether bonds, resulting in a shorter cycle life of the symmetrical polymer battery. The capacity retention and coulombic efficiency after 300 cycles are both low, and the battery internal resistance also increases significantly after 300 cycles. The polymerizable monomer molecules in Comparative Example 2 do not contain cyclic structures, resulting in a shorter cycle life for the symmetrical polymer battery. The capacity retention and coulombic efficiency after 300 cycles are both low, and the internal resistance of the battery also increases significantly after 300 cycles. The molecular weight of the prepolymer in Comparative Example 3 was too low, resulting in a short cycle life of the symmetrical polymer battery. The capacity retention and coulombic efficiency after 300 cycles were both low, and the internal resistance of the battery also increased significantly after 300 cycles. The prepolymer of Comparative Example 4 has an excessively high molecular weight, which results in a short cycle life of the symmetrical polymer battery. The capacity retention and coulombic efficiency are both low after 300 cycles, and the internal resistance of the battery also increases significantly after 300 cycles. Comparative Example 5, which did not add prepolymer, resulted in a shorter cycle life for the symmetric polymer battery, with lower capacity retention and coulombic efficiency after 300 cycles, and a significant increase in internal resistance after 300 cycles.

[0046] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polymer electrolyte precursor solution, characterized in that, The components comprise the following parts by mass: 8-12 parts electrolyte salt, 75-85 parts organic solvent; 4-6 parts of monomer can be polymerized. 2-4 parts of prepolymer Initiator 0.2~1 part, The polymerizable monomer is a (meth)acrylate compound containing a cyclic structure and ether bonds; the number average molecular weight of the prepolymer is 600-2000, and the prepolymer contains at least two (meth)acrylate groups.

2. The polymer electrolyte precursor solution according to claim 1, characterized in that, The polymerizable monomer is at least one of 2-phenoxyethyl acrylate, dicyclopentenoxyethyl methacrylate, and tetrahydropyran acrylate.

3. The polymer electrolyte precursor solution according to claim 2, characterized in that, The polymerizable monomers are 2-phenoxyethyl acrylate and dicyclopentenoxyethyl methacrylate.

4. The polymer electrolyte precursor solution according to claim 1, characterized in that, The prepolymer is at least one of polyurethane acrylate, polyurethane methacrylate, polyester acrylate, polyester methacrylate, epoxy acrylate, epoxy methacrylate, and acrylated polybutadiene.

5. The polymer electrolyte precursor solution according to claim 1, characterized in that, The number-average molecular weight of the prepolymer is 1000~1500.

6. A polymer electrolyte, characterized in that, It is prepared from the polymer electrolyte precursor solution according to any one of claims 1 to 5.

7. The method for preparing the polymer electrolyte of claim 6, characterized in that, The process includes the following steps: allowing the polymer electrolyte precursor solution of any one of claims 1 to 5 to stand and soak, then subjecting it to heat treatment to induce a polymerization reaction, thereby obtaining the polymer electrolyte.

8. The preparation method according to claim 7, characterized in that, The temperature for static soaking is 35~65℃, and the time is 12~48h.

9. The preparation method according to claim 7, characterized in that, The heat treatment temperature is 70~120℃, and the time is 6~48h.

10. A polymer battery, characterized in that, It includes the polymer electrolyte of claim 6.