Porous polymer electrolyte and preparation method thereof

Abstract

The invention relates to the field of lithium ion batteries, and particularly discloses a porous polymer electrolyte and a preparation method thereof. According to the preparation method, a polyHIPE film is prepared by adopting a high internal phase emulsion polymerization system and applying a reversible addition fragmentation chain transfer free radical polymerization technology, and the polyHIPE film is immersed into an electrolyte solution in which lithium salt is dissolved so as to prepare the porous polymer electrolyte. Aiming at the key bottleneck problem that a traditional gel type polymer electrolyte is difficult to have both ionic conductivity and mechanical property, a phase separation structure is constructed through a polyHIPE film, and an internal highly-communicated porous channel adsorbs an electrolyte to serve as a lithium ion transmission path to ensure high ionic conductivity; an external polymer skeleton prepared based on reversible addition fragmentation chain transfer free radical polymerization has a uniform chemical cross-linked network structure and basically does not swell electrolyte to ensure good mechanical properties, the discharge specific capacity of a LiFePO4 / / Li button cell assembled based on the porous polymer electrolyte is 95mAh / g at 25C multiplying power, and the cycle performance test is carried out at 4C multiplying power. After 200 times of circulation, the material still keeps the specific discharge capacity of 131.48 mAh / g, the capacity retention rate is 96.1%, the coulombic efficiency is 90.3%, and excellent electrochemical performance is shown.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, in particular to a porous polymer electrolyte and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have become an ideal power source for various electronic devices due to their high energy density, long cycle stability and lack of memory effect. Currently, most commercial lithium-ion batteries use liquid electrolyte systems, which pose a safety hazard of leakage and flammability. In contrast, polymer electrolytes can replace both the diaphragm and the electrolyte at the same time, and have the advantages of high safety and strong plasticity. The room temperature ionic conductivity of all-solid-state polymer electrolytes is not enough to meet production needs. Gel polymer electrolytes have the advantages of both high ionic conductivity and safety and no leakage, but their biggest drawback is that the improvement in ionic conductivity requires the swelling of a large amount of electrolyte at the expense of mechanical strength. Therefore, how to decouple the contradictory relationship between ionic conductivity and mechanical properties has become a key bottleneck problem in the industrial application of polymer electrolytes. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In view of the deficiencies in the prior art, the present invention provides a porous polymer electrolyte and a preparation method thereof.

[0005] (2) Technical solution

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted:

[0007] A porous polymer electrolyte, characterized by comprising the following raw materials in the following weight ratios: 1-10 parts of a polyHIPE membrane, 3-60 parts of an electrolyte, and 0.2-5 parts of a lithium salt; the polyHIPE membrane is prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, and the preparation method is as follows:

[0008] 0.1-0.5 parts by weight of a thiocarbonate compound, 0.1-0.5 parts by weight of an initiator, 3-10 parts by weight of a soft monomer, 0.5-5 parts by weight of a hard monomer, 0.2-4 parts by weight of a crosslinking monomer, and 1-5 parts by weight of an oil-soluble emulsifier are mixed to form an oil phase;

[0009] Dissolving 0.1-0.5 parts by weight of an electrolyte salt and 0.1-0.5 parts by weight of an ionic emulsifier in 20-100 parts by weight of deionized water to form an aqueous phase;

[0010] The oil phase and the water phase are mixed and then stirred and emulsified to form a high internal phase emulsion;

[0011] The high internal phase emulsion is poured into a mold, and the temperature is raised to 50-90° C. under nitrogen protection. The reaction is stopped after polymerization for 36-96 hours, and the product is dried to obtain a polyHIPE film.

[0012] The electrolyte is one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0013] The lithium salt is one or more of lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), and perfluoroalkylsulfonylmethyl lithium (LiC(CF3SO2)3).

[0014] The structural formula of the thiocarbonate compound used in the polyHIPE film preparation method is shown in formula (I):

[0015]

[0016] The structures of the Z group are shown in formulas (II), (III), and (IV):

[0017] C12H25S-(III)C4H9S-(IV)

[0018] The structures of the R groups are shown in formulas (V), (VI), and (VII):

[0019]

[0020] The initiator used in the polyHIPE film preparation method is one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dibenzoyl peroxide.

[0021] The soft monomers used in the polyHIPE film preparation method are one or more of methyl acrylate, butyl acrylate, and isooctyl acrylate.

[0022] The hard monomers used in the polyHIPE film preparation method are one or more of styrene, methyl methacrylate, methacrylonitrile and acrylonitrile.

[0023] The cross-linking monomers used in the polyHIPE film preparation method are one or more of divinylbenzene, ethylene glycol dimethacrylate, butanediol dimethacrylate, triethylene glycol dimethacrylate, and tetraethylene glycol dimethacrylate.

[0024] The oil-soluble emulsifier used in the polyHIPE film preparation method is one or more of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate.

[0025] The electrolyte salt used in the polyHIPE film preparation method is one or more of sodium chloride, calcium chloride, magnesium chloride and aluminum chloride.

[0026] The ionic emulsifier used in the polyHIPE film preparation method is one or more of sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and hexadecyltrimethylammonium chloride.

[0027] (3) Beneficial effects

[0028] Compared with the prior art, the present invention provides a porous polymer electrolyte and a preparation method thereof, which have the following beneficial effects: the present invention addresses the key bottleneck problem that traditional gel-type polymer electrolytes are difficult to achieve both ionic conductivity and mechanical properties. A phase separation structure is constructed through a polyHIPE membrane, and the highly interconnected porous channels inside adsorb the electrolyte as a lithium ion transmission path to ensure high ionic conductivity. The external polymer skeleton prepared based on reversible addition-fragmentation chain transfer radical polymerization has a uniform chemically cross-linked network structure and basically does not swell with the electrolyte to ensure good mechanical properties. The LiFePO4 / / Li button battery assembled based on the porous polymer electrolyte has a discharge specific capacity of 95mAh / g at a rate of 25C. In a cycle performance test at a rate of 4C, the discharge specific capacity of 131.48mAh / g is still maintained after 200 cycles, the capacity retention rate is 96.1%, and the coulombic efficiency is 90.3%, showing excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 are optical photographs of the porous polymer electrolytes obtained in Examples 1 and 2 of the present invention;

[0030] Figure 2 is an ionic conductivity-liquid absorption rate curve of the porous polymer electrolyte obtained in Example 1 and Example 2 of the present invention;

[0031] Figure 3 This is a rate performance diagram of a LiFePO4 / / Li button cell assembled with a porous polymer electrolyte obtained in Example 2 of the present invention;

[0032] Figure 4 This is a cycle performance diagram of a LiFePO4 / / Li button battery assembled with a porous polymer electrolyte obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are further described in detail below.

[0034] The porous polymer electrolyte was placed between two stainless steel sheets (SS) to assemble a CR2025 button cell. The ionic conductivity of the porous polymer electrolyte at different liquid absorption rates was tested using the electrochemical impedance spectroscopy (EIS) technique in the Shanghai Chenhua CHI 660E electrochemical workstation at a test frequency of 10 -2 -10 5 Hz, the test temperature is 25℃. The calculation formula of ionic conductivity σ is as follows:

[0035] σ=d / (R e ×S)

[0036] Where d is the thickness of the porous polymer film, R e is the body resistance, and S is the area of ​​the stainless steel electrode.

[0037] Lithium-ion battery performance evaluation was conducted on a Neware BTS battery testing system. The cathode material, composed of lithium iron phosphate (LiFePO4) as the active material, carbon black as the conductive agent, and polyvinylidene fluoride (PVDF) as the adhesive, was coated on an aluminum foil current collector in a mass ratio of 8:1:1. The anode material, a lithium sheet, was assembled with a porous polymer electrolyte into a lithium-ion battery for performance testing at 25°C.

[0038] Example 1:

[0039] A porous polymer electrolyte comprises the following raw materials in the following weight ratios: 1 part polyHIPE membrane, 6 parts electrolyte, and 0.2 parts lithium salt; the polyHIPE membrane is prepared by reversible addition fragmentation chain transfer (RAFT) polymerization, and the preparation method is as follows:

[0040] 0.1 parts by weight of a thiocarbonate compound, 0.1 parts by weight of an initiator, 3 parts by weight of a soft monomer, 0.5 parts by weight of a hard monomer, 0.2 parts by weight of a crosslinking monomer, and 1 part by weight of an oil-soluble emulsifier are mixed to form an oil phase;

[0041] Dissolve 0.1 parts by weight of an electrolyte salt and 0.1 parts by weight of an ionic emulsifier in 20 parts by weight of deionized water to form an aqueous phase;

[0042] The oil phase and the water phase are mixed and then stirred and emulsified to form a high internal phase emulsion;

[0043] The high internal phase emulsion was poured into a mold, and the temperature was raised to 50° C. under nitrogen protection. The reaction was stopped after polymerization for 96 hours, and the product was dried to obtain a polyHIPE film.

[0044] The electrolyte is ethylene carbonate (EC).

[0045] The lithium salt is lithium perchlorate (LiClO4).

[0046] The structural formula of the thiocarbonate compound used in the polyHIPE membrane preparation method is shown in formula (I).

[0047] The structure of the Z group is shown in formula (II).

[0048] The structure of the R group is shown in formula (V).

[0049] The initiator used in the polyHIPE film preparation method is azobisisoheptanonitrile.

[0050] The soft monomer used in the polyHIPE film preparation method is methyl acrylate.

[0051] The hard monomer used in the polyHIPE film preparation method is styrene.

[0052] The cross-linking monomer used in the polyHIPE film preparation method is divinylbenzene.

[0053] The oil-soluble emulsifier used in the polyHIPE film preparation method is sorbitan monolaurate.

[0054] The electrolyte salt used in the polyHIPE film preparation method is sodium chloride.

[0055] The ionic emulsifier used in the polyHIPE film preparation method is sodium dodecylbenzenesulfonate.

[0056] Example 2:

[0057] A porous polymer electrolyte comprises the following raw materials in the following weight ratios: 10 parts of a polyHIPE membrane, 60 parts of an electrolyte, and 5 parts of a lithium salt; the polyHIPE membrane is prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, and the preparation method is as follows:

[0058] 0.5 parts by weight of a thiocarbonate compound, 0.5 parts by weight of an initiator, 10 parts by weight of a soft monomer, 5 parts by weight of a hard monomer, 4 parts by weight of a crosslinking monomer, and 5 parts by weight of an oil-soluble emulsifier are mixed to form an oil phase;

[0059] Dissolve 0.5 parts by weight of an electrolyte salt and 0.5 parts by weight of an ionic emulsifier in 100 parts by weight of deionized water to form an aqueous phase;

[0060] The oil phase and the water phase are mixed and then stirred and emulsified to form a high internal phase emulsion;

[0061] The high internal phase emulsion was poured into a mold, and the temperature was raised to 90° C. under nitrogen protection. The reaction was stopped after polymerization for 36 hours, and the product was dried to obtain a polyHIPE film.

[0062] The electrolyte is propylene carbonate (PC) and dimethyl carbonate (DMC), and the mass ratio of the two is 1:1.

[0063] The lithium salts are lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4), and the mass ratio of the two is 1:1.

[0064] The structural formula of the thiocarbonate compound used in the polyHIPE membrane preparation method is shown in formula (I).

[0065] The structure of the Z group is shown in formula (III).

[0066] The structure of the R group is shown in formula (VI).

[0067] The initiator used in the polyHIPE film preparation method is azobisisobutyronitrile.

[0068] The soft monomer used in the polyHIPE film preparation method is butyl acrylate.

[0069] The hard monomer used in the polyHIPE film preparation method is methyl methacrylate.

[0070] The cross-linking monomers used in the polyHIPE film preparation method are ethylene glycol dimethacrylate and butanediol dimethacrylate, and the mass ratio of the two is 1:1.

[0071] The oil-soluble emulsifier used in the polyHIPE film preparation method is sorbitan monopalmitate.

[0072] The electrolyte salt used in the polyHIPE film preparation method is calcium chloride.

[0073] The ionic emulsifier used in the polyHIPE film preparation method is sodium lauryl sulfate.

[0074] Example 3:

[0075] A porous polymer electrolyte comprises the following raw materials in the following weight ratios: 1 part polyHIPE membrane, 3 parts electrolyte, and 1 part lithium salt; the polyHIPE membrane is prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, and the preparation method is as follows:

[0076] 0.3 parts by weight of a thiocarbonate compound, 0.3 parts by weight of an initiator, 8 parts by weight of a soft monomer, 3 parts by weight of a hard monomer, 1 part by weight of a crosslinking monomer, and 2 parts by weight of an oil-soluble emulsifier are mixed to form an oil phase;

[0077] Dissolve 0.3 parts by weight of an electrolyte salt and 0.3 parts by weight of an ionic emulsifier in 50 parts by weight of deionized water to form an aqueous phase;

[0078] The oil phase and the water phase are mixed and then stirred and emulsified to form a high internal phase emulsion;

[0079] The high internal phase emulsion was poured into a mold, and the temperature was raised to 70° C. under nitrogen protection. The reaction was stopped after polymerization for 72 hours, and the product was dried to obtain a polyHIPE film.

[0080] The electrolyte is ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and the mass ratio of the two is 1:1.

[0081] The lithium salts are lithium trifluoromethanesulfonate (LiCF3SO3) and perfluoroalkylsulfonylmethyl lithium (LiC(CF3SO2)3), and the mass ratio of the two is 1:1.

[0082] The structural formula of the thiocarbonate compound used in the polyHIPE membrane preparation method is shown in formula (I).

[0083] The structure of the Z group is shown in formula (IV).

[0084] The structure of the R group is shown in formula (VII).

[0085] The initiator used in the polyHIPE film preparation method is dibenzoyl peroxide.

[0086] The soft monomer used in the polyHIPE film preparation method is isooctyl acrylate.

[0087] The hard monomers used in the polyHIPE film preparation method are methacrylonitrile and acrylonitrile, and the mass ratio of the two is 1:1.

[0088] The cross-linking monomers used in the polyHIPE film preparation method are triethylene glycol dimethacrylate and tetraethylene glycol dimethacrylate, and the mass ratio of the two is 1:1.

[0089] The oil-soluble emulsifiers used in the polyHIPE film preparation method are sorbitan monostearate and sorbitan monooleate, and the mass ratio of the two is 1:1.

[0090] The electrolyte salts used in the polyHIPE membrane preparation method are magnesium chloride and aluminum chloride, and the mass ratio of the electrolyte salts is 1:1.

[0091] The ionic emulsifier used in the polyHIPE film preparation method is hexadecyltrimethylammonium chloride.

[0092] The optical photographs of the porous polymer electrolytes described in Example 1 and Example 2 are as follows: Figure 1 As shown, the performance test results of the porous polymer electrolytes and LiFePO4 / / Li button batteries assembled therewith described in Examples 1 and 2 are as follows: Figure 2-4 shown.

[0093] Depend on Figure 1 It can be seen that the porous polymer electrolyte has a white appearance, indicating that the polymer skeleton and the pores of the adsorbed liquid electrolyte form a clear phase separation structure, and no cracks occur when bent, indicating that the porous polymer electrolyte has good flexibility. Figure 2 It can be seen that the ionic conductivity of the porous polymer electrolyte increases with the increase of the liquid absorption rate. When the liquid absorption rate is 600%, the ionic conductivity exceeds 2.5×10 -3 S / cm. Figure 3 It can be seen that as the rate increases, the discharge capacity of the LiFePO4 / / Li button battery assembled with porous polymer electrolyte shows a downward trend, but the discharge capacity still reaches 95mAh / g at a rate of 25C. When the rate is restored to 0.1C, the discharge capacity of the battery basically returns to the initial value, indicating that the battery has no structural damage during the cycle. Figure 4 The LiFePO4 / / Li button cell assembled with the porous polymer electrolyte achieved a discharge capacity of 131.48 mAh / g, a capacity retention of 96.1%, and a coulombic efficiency of 90.3% after 200 cycles at a 4C rate. These results demonstrate that the LiFePO4 / / Li button cell assembled with the all-solid-state polymer electrolyte prepared by reversible addition-fragmentation chain transfer polymerization possesses excellent electrochemical performance. Therefore, the porous polymer electrolyte prepared by this invention has broad application prospects.

[0094] The above embodiments are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A porous polymer electrolyte, characterized in that The invention comprises the following raw materials in the following weight ratios: 1-10 parts of polyHIPE membrane, 3-60 parts of electrolyte, and 0.2-5 parts of lithium salt; the polyHIPE membrane is prepared by reversible addition fragmentation chain transfer (RAFT) polymerization, and the preparation method is as follows: 0.1-0.5 parts by weight of a thiocarbonate compound, 0.1-0.5 parts by weight of an initiator, 3-10 parts by weight of a soft monomer, 0.5-5 parts by weight of a hard monomer, 0.2-4 parts by weight of a crosslinking monomer, and 1-5 parts by weight of an oil-soluble emulsifier are mixed to form an oil phase; Dissolving 0.1-0.5 parts by weight of an electrolyte salt and 0.1-0.5 parts by weight of an ionic emulsifier in 20-100 parts by weight of deionized water to form an aqueous phase; The oil phase and the water phase are mixed and then stirred and emulsified to form a high internal phase emulsion; The high internal phase emulsion is poured into a mold, and the temperature is raised to 50-90° C. under nitrogen protection. The reaction is stopped after polymerization for 36-96 hours, and the product is dried to obtain a polyHIPE film.

2. A porous polymer electrolyte according to claim 1, characterized in that: The electrolyte is one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

3. A porous polymer electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), and perfluoroalkylsulfonylmethyl lithium (LiC(CF3SO2)3).

4. The porous polymer electrolyte according to claim 1, characterized in that The structural formula of the thiocarbonate compound used in the polyHIPE film preparation method is shown in formula (I): The structures of the Z group are shown in formulas (II), (III), and (IV): C 12 H 25 S—— (III)C4H9S—— (IV) The structures of the R groups are shown in formulas (V), (VI), and (VII):

5. The porous polymer electrolyte according to claim 1, characterized in that: The initiator used in the polyHIPE film preparation method is one or more of azobisisobutyronitrile, azobisisoheptanenitrile and dibenzoyl peroxide.

6. The porous polymer electrolyte according to claim 1, characterized in that: The soft monomers used in the polyHIPE film preparation method are one or more of methyl acrylate, butyl acrylate, and isooctyl acrylate.

7. The porous polymer electrolyte according to claim 1, characterized in that: The hard monomers used in the polyHIPE film preparation method are one or more of styrene, methyl methacrylate, methacrylonitrile and acrylonitrile.

8. The porous polymer electrolyte according to claim 1, characterized in that: The cross-linking monomers used in the polyHIPE film preparation method are one or more of divinylbenzene, ethylene glycol dimethacrylate, butanediol dimethacrylate, triethylene glycol dimethacrylate, and tetraethylene glycol dimethacrylate.

9. The porous polymer electrolyte according to claim 1, characterized in that: The oil-soluble emulsifier used in the polyHIPE film preparation method is one or more of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate.

10. The porous polymer electrolyte according to claim 1, characterized in that: The electrolyte salt used in the polyHIPE film preparation method is one or more of sodium chloride, calcium chloride, magnesium chloride and aluminum chloride.

11. The porous polymer electrolyte according to claim 1, characterized in that: The ionic emulsifier used in the polyHIPE film preparation method is one or more of sodium dodecylbenzenesulfonate, sodium lauryl sulfate, and hexadecyltrimethylammonium chloride.

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