Preparation method and application of a polymer electrolyte

Abstract

This invention discloses a method for preparing a polymer electrolyte and its application. The polymer solid-state electrolyte is prepared by free radical thermal polymerization after adding a low-solventization-energy, low-melting-point small-size co-solvent, polymer monomer, and initiator to a deep eutectic electrolyte. The deep eutectic electrolyte is prepared through a eutectic reaction of a hydrogen bond donor and a lithium salt. The low-solventization-energy, low-melting-point small-size co-solvent is one or more of acetonitrile, fluoroacetonitrile, difluoroacetonitrile, and trifluoroacetonitrile. The polymer electrolyte for solid-state batteries provided by this invention has high conductivity, a simple preparation method, good flexibility, and is easy to process. It exhibits good stability to the lithium metal anode while also accommodating the rapid desolvation process of lithium ions, and can be applied in wide-temperature-range solid-state batteries operating at -80 to 120°C.

Description

Technical Field

[0001] This invention relates to the fields of electrolytes and solid-state batteries, and particularly to a method for preparing and applying a polymer electrolyte. Background Technology

[0002] With the rapid development of application demands, people are placing higher requirements on driving range and capacity, and paying increasing attention to high-energy-density electrode materials and highly safe electrolytes. Lithium metal and silicon-based anodes, due to their high theoretical specific capacity, can effectively improve battery energy density when matched with high-voltage cathodes such as nickel-cobalt-manganese ternary, lithium manganese iron phosphate, and lithium cobalt oxide. However, the carbonate electrolyte used in traditional lithium-ion batteries suffers from sluggish lithium plating / stripping kinetics at low temperatures, leading to lithium dendrite growth and lower discharge energy density. At high temperatures, the unstable interface causes continuous consumption of electrolyte and lithium, resulting in a reduced battery life.

[0003] Deep eutectic electrolytes (DEEs) are a novel type of electrolyte material formed by the strong hydrogen-bonding interactions between a solid component hydrogen bond donor and a lithium salt. This strongly interacting network structure remains stable at high temperatures (above 60 °C), effectively suppressing molecular volatilization and decomposition, thereby maintaining the electrolyte's chemical stability and significantly reducing the risk of battery thermal runaway. However, at low temperatures, the electrolyte is prone to freezing, leading to restricted molecular motion, increased ion migration resistance, a sharp drop in ionic conductivity, and a drastic decrease in battery capacity.

[0004] Using low-melting-point solvents as the solvent base for deep eutectic electrolytes can significantly lower the freezing point of the electrolyte and improve ion conductivity at low temperatures. However, some low-melting-point solvents possess high solvation energies, which can compete with hydrogen bond donors in the electrolyte system for lithium ion coordination, reconstructing the solvation structure in the electrolyte and leading to a decrease in the high-temperature performance of the original deep eutectic electrolyte. Simultaneously, low-melting-point solvents are highly susceptible to vaporization at high temperatures, causing battery bulging and posing a safety hazard. Summary of the Invention

[0005] In view of this, the present invention prepares a polymer electrolyte using in-situ polymerization technology. This polymer electrolyte consists of polymer monomers, a deep eutectic electrolyte, and a co-solvent. The polymer monomers, after in-situ polymerization, serve as a mechanical framework, enhancing the film-forming properties of the electrolyte. Simultaneously, the strongly electron-withdrawing atoms in the polymer monomers anchor the co-solvent, preventing its loss at high temperatures. The deep eutectic electrolyte, as the ion-conducting phase, possesses intrinsic safety, good ion conductivity, and efficient ion conduction behavior at the interface. The small-sized co-solvent with low solvation energy and low melting point significantly lowers the solidification point of the electrolyte, improving ion conductivity and battery capacity at low temperatures. The introduction of the co-solvent does not compromise the high-temperature characteristics of the deep eutectic electrolyte and can also lower the lithium-ion desolvation barrier, improving ion conductivity and battery capacity at low temperatures, enabling the solid-state battery to operate normally over a wide temperature range.

[0006] The first aspect of this invention provides a method for preparing a polymer electrolyte, comprising the following steps:

[0007] S1. Lithium salt and hydrogen bond donor are mixed and stirred at 25-100℃ for 0.5-24h to obtain deep eutectic electrolyte;

[0008] S2. The deep eutectic electrolyte obtained in step S1 is mixed with a cosolvent, polymer monomer, and initiator to obtain a polymer electrolyte prepolymer solution; the cosolvent has low solvation energy and low melting point, and the volume of the solvation sheath formed with the lithium-ion solvation structure does not exceed 300 Å. 3 ;

[0009] S3. Inject the polymer electrolyte prepolymer solution obtained in step S2 into the battery and soak it for 2h to 48h. Then heat it at a temperature range of 25 to 120°C for 0.5h to 48h to obtain the polymer electrolyte, which exists in the battery.

[0010] By using small-sized cosolvents with low solvation energy and low melting point to assist in controlling the solvation structure of deep eutectic electrolytes, the viscosity and melting point of the electrolyte are reduced, and the ionic conductivity of the electrolyte is improved. At the same time, the small-sized cosolvents can release Li in the first solvation sheath. + Pulling out forms a rapid ion-conducting ligand channel, promoting Li + The migration of lithium ions is facilitated by the use of small-sized solvents with low solvation energy, which also allow anions to enter the first solvation shell, forming an inorganic-rich interface. Most importantly, the introduction of a co-solvent does not compromise the high-temperature properties of the deep eutectic electrolyte while lowering the lithium-ion desolvation barrier and suppressing a sharp increase in electrolyte viscosity at low temperatures, thus balancing the electrolyte's potential for application in wide-temperature-range batteries.

[0011] Preferably, the mass ratio of the lithium salt and the hydrogen bond donor additive in step S1 is (5~95):(5~95).

[0012] Preferably, the mass ratio of the cosolvent, polymer monomer, and deep eutectic electrolyte in step S2 is (1~95):(5~90):(10~95).

[0013] Preferably, the mass ratio of the polymer monomer to the initiator in step S2 is (90 ~ 99.9):(0.1 ~ 10), and the polymer monomer is one or more of N,N-dimethylacrylamide, N,N-methylenebisacrylamide, and acrylamide.

[0014] Preferably, the lithium salt in step S1 is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalateborate), lithium tetrafluoroborate, lithium difluorooxalateborate, lithium nitrate, and lithium perchlorate.

[0015] Preferably, the hydrogen bond donor in step S1 is one or more of the following: succinate, N-methylacetamide, urea, 1,3-dimethyl-2-imidazolinone, sulfolane, dimethyl sulfoxide, sulfate, 1-propene-1,3-sulfolactone, propane sulfolactone, methane disulfonate methylene sulfonate, 4-vinyl sulfite, vinyl sulfite, and sulfite.

[0016] Preferably, the co-solvent in step S2 is one or more of acetonitrile, fluoroacetonitrile, difluoroacetonitrile, and trifluoroacetonitrile.

[0017] Preferably, the polymer monomer in step S2 is one or more of vinyl polymer monomers such as N,N-dimethylacrylamide, N,N-methylenebisacrylamide, and acrylamide.

[0018] Polymer monomers can anchor more cosolvent molecules through differences in electronegativity, thereby preventing solvent loss at high temperatures. The carbonyl oxygen atom in amide-based polymer monomers has a strong electron-withdrawing ability and can form strong hydrogen bonds with the α-H atoms in acetonitrile, fluoroacetonitrile, difluoroacetonitrile, and trifluoroacetonitrile. The polymer network formed after in-situ polymerization can anchor a large number of cosolvent molecules.

[0019] Preferably, the initiator in step S2 is one or more of azobisisobutyronitrile, benzoyl peroxide, and dimethyl azobisisobutyrate.

[0020] A second aspect of the present invention provides an application of a polymer electrolyte in a solid-state battery, the solid-state battery comprising an electrolyte, a positive electrode, a negative electrode, and a separator, wherein the electrolyte is prepared by an in-situ curing method.

[0021] Preferably, the positive electrode active material of the solid-state battery can be one or more of lithium iron phosphate, high-voltage positive electrode ternary lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium nickel cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese iron phosphate, lithium iron phosphate, sulfur, and lithium sulfide; the negative electrode material is one or more of lithium metal, graphite, silicon negative electrode, silicon carbon negative electrode, silicon suboxide, and lithium titanate; the separator is one or more of commercially available PP, PE, PI, cellulose membrane, PET porous membrane, and ceramic coated membrane.

[0022] The beneficial effects of this invention are:

[0023] (1) The low-melting-point, low-solventization-energy small-size cosolvent introduced in this invention does not damage the high-temperature characteristics of the deep eutectic electrolyte, while significantly reducing the solidification point of the electrolyte and improving the ion conductivity and battery capacity at low temperatures. The polymer electrolyte prepared by this invention can be applied to wide-temperature-range solid-state batteries at -80~120℃.

[0024] (2) The polymer monomer and cosolvent of the present invention form a strong interaction, which enables more cosolvent to be anchored in the skeleton, thus preventing the vaporization loss of cosolvent when used at high battery temperatures.

[0025] (3) The present invention adopts an in-situ curing method to improve the contact between the electrode and the electrolyte and reduce the interfacial impedance between the electrode and the electrolyte. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The image shows the EIS plot of the polymer electrolyte prepared in Example 1 at -20 to -80°C.

[0028] Figure 2 The image shows the EIS diagram of the polymer electrolyte prepared in Example 1 at 40~80℃.

[0029] Figure 3 The graph shows the results of charge-discharge cycle tests of the Li∣NiCoMann solid-state battery assembled with the polymer electrolyte prepared in Example 1 at -20 ~ -80℃.

[0030] Figure 4 The figure shows the charge-discharge cycle test results of the Li|NiCoMann solid-state battery assembled with polymer electrolyte prepared in Example 1 at 40~100℃. Detailed Implementation

[0031] The following are preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0032] Example 1

[0033] S1. Weigh 2.4g of 1-propylene-1,3-sulfonolactone and 2.87g of lithium bis(trifluoromethanesulfonylimide) in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0034] S2. Add 1.18g of fluoroacetonitrile to the deep eutectic electrolyte to obtain a low-viscosity electrolyte.

[0035] S3. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0036] S4. Weigh 1g of polymer elastomer and 10g of low viscosity electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0037] S5. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, lithium metal as the negative electrode, and a commercial PP porous membrane. The polymer electrolyte precursor prepared in step S4 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0038] Example 2

[0039] S1. Weigh 3.2g of succinate and 2.87g of lithium bis(trifluoromethanesulfonylimide) separately in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0040] S2. Add 1.18g of fluoroacetonitrile to the deep eutectic electrolyte to obtain a low-viscosity electrolyte.

[0041] S3. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0042] S4. Weigh 1g of polymer elastomer and 10g of low viscosity electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0043] S5. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, lithium metal as the negative electrode, and a commercial PP porous membrane. The polymer electrolyte precursor prepared in step S4 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0044] Example 3

[0045] S1. Weigh 2.4g of 1-propylene-1,3-sulfonolactone and 2.87g of lithium bis(trifluoromethanesulfonylimide) in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0046] S2. Add 2.06g of trifluoroacetonitrile to the deep eutectic electrolyte to obtain a low-viscosity electrolyte.

[0047] S3. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0048] S4. Weigh 1g of polymer elastomer and 10g of low viscosity electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0049] S5. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, lithium metal as the negative electrode, and a commercial PP porous membrane. The polymer electrolyte precursor prepared in step S4 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0050] Example 4

[0051] S1. Weigh 2.4g of 1-propylene-1,3-sulfonolactone and 2.87g of lithium bis(trifluoromethanesulfonylimide) in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0052] S2. Add 2.06g of trifluoroacetonitrile to the deep eutectic electrolyte to obtain a low-viscosity electrolyte.

[0053] S3. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0054] S4. Weigh 1g of polymer elastomer and 10g of low viscosity electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0055] S5. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, graphite as the negative electrode, and a commercial PP porous membrane. The polymer electrolyte precursor prepared in step S4 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0056] Example 5

[0057] S1. Weigh 2.4g of 1-propylene-1,3-sulfonolactone and 2.87g of lithium bis(trifluoromethanesulfonylimide) in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0058] S2. Add 2.06g of trifluoroacetonitrile to the deep eutectic electrolyte to obtain a low-viscosity electrolyte.

[0059] S3. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0060] S4. Weigh 1g of polymer elastomer and 10g of low viscosity electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0061] S5. In an argon-filled glove box, a battery is assembled using lithium iron phosphate as the positive electrode, graphite as the negative electrode, and a commercial PP porous membrane. The polymer electrolyte precursor prepared in step S4 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0062] Comparative Example 1

[0063] S1. Weigh 3.2g of succinate and 2.87g of lithium bis(trifluoromethanesulfonylimide) separately in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0064] S2. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0065] S3. Weigh 1g of polymer elastomer and 10g of deep eutectic electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0066] S4. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, lithium metal as the negative electrode, and a commercial PP porous membrane. The polymer deep eutectic electrolyte precursor prepared in step S3 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0067] Comparative Example 2

[0068] S1. Weigh 2.4g of 1-propylene-1,3-sulfonolactone and 2.87g of lithium bis(trifluoromethanesulfonylimide) in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0069] S2. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0070] S3. Weigh 1g of polymer elastomer and 10g of deep eutectic electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0071] S4. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, lithium metal as the negative electrode, and a commercial PP porous membrane. The polymer deep eutectic electrolyte precursor prepared in step S3 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0072] Comparative Example 3

[0073] S1. Weigh 2.4g of sulfolane and 2.87g of lithium bis(trifluoromethanesulfonylimide) separately in an argon glove box, mix them, and heat and stir at 80℃ for 6h to obtain a deep eutectic electrolyte.

[0074] S2. Weigh 10g of N,N-dimethylacrylamide and 0.05g of azobisisobutyronitrile in an argon glove box, mix and stir for 6h to obtain a polymer elastomer.

[0075] S3. Weigh 1g of polymer elastomer and 10g of deep eutectic electrolyte in an argon glove box, mix them, and stir for 12h to obtain the polymer electrolyte precursor.

[0076] S4. In an argon-filled glove box, a battery is assembled using nickel-cobalt-manganese as the positive electrode, lithium metal as the negative electrode, and a commercial PP porous membrane. The polymer deep eutectic electrolyte precursor prepared in step S3 is then used as the electrolyte. After assembly, the battery is immersed at room temperature for 24 hours and cured at 70°C for 4 hours to obtain an in-situ polymerized solid-state battery.

[0077] The table below shows the low-temperature ionic conductivity and high and low temperature performance of the polymer electrolytes prepared in Examples 1-5 and Comparative Examples 1-3, as well as the solid-state battery performance.

[0078] As shown in the table above, the polymer electrolytes prepared in Examples 1-5 have ionic conductivity of the same order of magnitude and are significantly better than those in Comparative Examples 1-3. The solid-state batteries assembled from the polymer electrolytes prepared in Examples 1-5 have significantly higher capacity at low temperatures than those in Comparative Examples 1-3. This indicates that the present invention, by introducing one or more co-solvents such as acetonitrile, fluoroacetonitrile, difluoroacetonitrile, and trifluoroacetonitrile, which have low solvation energy, low melting point, and small size, can effectively reduce the viscosity and melting point of the electrolyte and improve the ionic conductivity of the polymer electrolyte at low temperatures. The small-size co-solvent promotes the formation of micro-solvation sheaths and promotes Li... +The migration of lithium ions is facilitated by small-sized solvents with low solvation energy, which promotes inorganic-rich interfaces, reduces the lithium-ion desolvation energy barrier, and ensures rapid lithium-ion conduction at the interface at low temperatures. Simultaneously, the low-solvation-energy co-solvent does not compromise the high-temperature stability of the deep eutectic electrolyte, ensuring that the solid-state batteries assembled with polymer electrolytes prepared in Examples 1-5 exhibit ultra-high capacity performance at high temperatures, comparable to those prepared in Comparative Examples 1-5.

Claims

1. A method for preparing a polymer electrolyte, characterized in that, Includes the following steps: S1. Lithium salt and hydrogen bond donor are mixed and stirred at 25-100℃ for 0.5-24h to obtain deep eutectic electrolyte; S2. The deep eutectic electrolyte obtained in step S1 is mixed with a cosolvent, polymer monomer, and initiator to obtain a polymer electrolyte prepolymer solution; the cosolvent has low solvation energy and low melting point, and the volume of the solvation sheath formed with the lithium-ion solvation structure does not exceed 300 Å. 3 ; The co-solvent is one or more of fluoroacetonitrile, difluoroacetonitrile, and trifluoroacetonitrile; The polymer monomer is one or more of N,N-dimethylacrylamide, N,N-methylenebisacrylamide, and acrylamide; The mass ratio of the cosolvent, polymer monomer, and deep eutectic electrolyte is (1~95):(5~90):(10~95); S3. Inject the polymer electrolyte prepolymer solution obtained in step S2 into the battery and soak it for 2h to 48h. Then heat it at a temperature range of 25 to 120°C for 0.5h to 48h to obtain the polymer electrolyte, which exists in the battery.

2. The method for preparing the polymer electrolyte according to claim 1, characterized in that, The mass ratio of lithium salt to hydrogen bond donor in step S1 is (5~95):(5~95).

3. The method for preparing the polymer electrolyte according to claim 1, characterized in that, The mass ratio of polymer monomer to initiator in step S2 is (90 ~ 99.9):(0.1 ~ 10).

4. The method for preparing the polymer electrolyte according to claim 1, characterized in that, The lithium salt mentioned in step S1 is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(oxalateborate), lithium tetrafluoroborate, lithium difluorooxalateborate, lithium nitrate, and lithium perchlorate.

5. The method for preparing the polymer electrolyte according to claim 1, characterized in that, The hydrogen bond donor in step S1 is one or more of succinate, N-methylacetamide, urea, 1,3-dimethyl-2-imidazolinone, sulfolane, dimethyl sulfoxide, sulfate, 1-propene-1,3-sulcinolone, propane sulcinolone, methane disulfonate methylene sulfonate, 4-vinyl sulfite, vinyl sulfite, and sulfite.

6. The application of the polymer electrolyte prepared by the polymer electrolyte preparation method according to any one of claims 1 to 5 in a wide temperature range solid-state battery.

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