Gel electrolyte, preparation method and application thereof

Abstract

The application discloses a kind of gel electrolyte and its preparation method and application, comprising first polymeric network, second polymeric network and lithium salt;The first polymeric network is the first monomer polymerization product gel, the second polymeric network is the second monomer polymerization product, and is formed by crosslinking polymerization of second monomer in the first monomer polymerization product gel;The first monomer is the olefin monomer containing sulfonic acid group, and the monomer is acrylamide monomer and / or acrylic ester monomer.The application further provides a kind of two-step frozen gel preparation above-mentioned gel electrolyte, and the gel electrolyte prepared has double-network sponge structure.The above-mentioned gel electrolyte not only has good solid-solid contact interface compatibility with positive and negative, and has high tensile strength and high ionic conductivity, so that the cycle performance of lithium ion solid-state battery containing the gel electrolyte can reach 1600 cycles @80%SOH.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a gel electrolyte, its preparation method, and its application. Background Technology

[0002] Lithium metal batteries using lithium metal as the negative electrode have a capacity exceeding 350 Wh / kg. -1 With its high specific energy, lithium metal is considered a promising next-generation battery system. However, due to the instability of the lithium metal anode, lithium metal batteries have a short lifespan. In traditional electrolyte-structured lithium batteries, lithium metal anodes suffer from problems such as flammability, volatility, corrosion, and leakage. Solid-state batteries, on the other hand, are non-flammable, heat-resistant, non-corrosive, and non-volatile, effectively avoiding electrolyte leakage problems found in traditional batteries and making them more suitable for the use of high-energy-density lithium metal anodes.

[0003] However, current all-solid-state electrolytes paired with lithium metal anodes suffer from severe lithium dendrite penetration issues. Furthermore, poor contact between the electrode and electrolyte leads to short circuits, poor interface stability, and poor cycle performance. Gel polymer electrolytes offer excellent electrochemical stability and safety, and can also suppress lithium dendrite growth to some extent. However, they also exhibit significant interface problems, affecting battery capacity and rate performance. Moreover, there is a difficulty in simultaneously achieving optimal mechanical properties, conductivity, and ionic conductivity, limiting the practical application of such gel polymer electrolytes in solid-state lithium metal batteries. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a gel electrolyte, its preparation method, and its application. By constructing a gel electrolyte with a double-network sponge-like structure, it achieves both good mechanical strength and excellent electrical and ion-conducting properties, thereby effectively improving the cycle performance of solid-state lithium metal batteries.

[0005] This invention provides the following technical solutions:

[0006] The first aspect of the present invention provides a gel electrolyte comprising a first polymeric network, a second polymeric network, and a lithium salt; wherein the first polymeric network and the second polymeric network form an interpenetrating double network structure, and the lithium salt is uniformly dispersed in the double network structure;

[0007] The first polymer network is a gel of the first monomer polymer product, and the second polymer network is a polymer of the second monomer polymer product.

[0008] Furthermore, the first monomer polymer product gel can be obtained by swelling the first monomer polymer product in a solvent; the second polymer network is formed by cross-linking polymerization of the second monomer in the first monomer polymer product gel.

[0009] Furthermore, the lithium salt exists in the gel electrolyte in the form of free lithium ions.

[0010] Furthermore, the first monomer is an olefin monomer containing a sulfonic acid group, and the second monomer is an acrylamide monomer and / or an acrylate monomer.

[0011] Furthermore, the alkene monomer containing sulfonic acid groups includes one or more of sodium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-dodecylsulfonate, sodium dodecylsulfonate, and sodium 2-acrylamido-octylsulfonate.

[0012] Further, the acrylamide monomers include one or more of acrylamide, methacrylamide, isopropylacrylamide, N,N-diethylacrylamide, isobutoxymethacrylamide, and diacetone acrylamide; the acrylate monomers include one or more of butyl acrylate, methyl acrylate, ethyl acrylate, methyl 2-methacrylate, and isooctyl acrylate.

[0013] Furthermore, the solvent is preferably acetonitrile and / or dimethyl sulfoxide.

[0014] Furthermore, the lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide, lithium perchlorate, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(fluorosulfonate)imide, lithium di(oxalate)borate, and lithium hexafluoroarsenate.

[0015] Furthermore, the mass ratio of the first monomer to the second monomer is preferably (1-10):1; the mass ratio of the lithium salt to the second monomer is preferably in the range of 1:(0.1-1).

[0016] A second aspect of the present invention provides a method for preparing a gel electrolyte, comprising the following steps:

[0017] (1) The first monomer, crosslinking agent and low temperature initiator are pre-cooled respectively, then mixed evenly to obtain the first reaction liquid, and then transferred to the pre-cooled mold for freezing treatment. After thawing, the first monomer polymerization product is obtained.

[0018] (2) The first monomer polymer product prepared in step (1) is immersed in a solvent for gelation treatment to obtain the first monomer polymer product gel;

[0019] (3) Mix the second monomer, crosslinking agent, photoinitiator and lithium salt evenly to obtain the second reaction solution; immerse the first monomer polymerization product gel prepared in step (2) in the second reaction solution and let it stand in the dark;

[0020] (4) Take out the first monomer polymer product gel after impregnation treatment, transfer it to the mold for freezing treatment, wait for ice crystals to form in the gel pores, take it out and perform photo-crosslinking treatment, the second monomer crosslinks and polymerizes in the first monomer polymer product gel to form a second polymer network, and obtain the gel electrolyte.

[0021] Furthermore, the preparation of the second reaction solution in step (3) is not restricted to the order of steps (1) and (2). That is, the second reaction solution can also be prepared when preparing the first reaction solution or when preparing the first monomer polymerization product gel. The prepared second reaction solution can be left to stand in the dark.

[0022] Furthermore, the preparation method is carried out in an environment where O2 ≤ 0.1 ppm and H2O ≤ 0.1 ppm.

[0023] Further, in step (1), the preferred mass ratio of the first monomer to the crosslinking agent and the low-temperature initiator is 100:(0.1-5):(0.01-5); wherein,

[0024] The first monomer is preferably an alkene monomer containing a sulfonic acid group, such as one or more selected from sodium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-dodecylsulfonate, sodium dodecylsulfonate, and sodium 2-acrylamido-octylsulfonate;

[0025] The crosslinking agent is preferably one or more of N,N'-methylenebisacrylamide, epichlorohydrin, benzoyl peroxide, dicumyl peroxide, dicumyl peroxide, diethylenetriamine, 2,5-dimethyl-2,5-di-tert-butylperoxide, and di-tert-butyl peroxide.

[0026] The low-temperature initiator is preferably one or more of ammonium persulfate, benzoyl peroxide, tetramethylethylenediamine, benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptane.

[0027] The preferred temperature for the precooling treatment is -40 to -10°C, and the preferred precooling time is 0.01-0.5 h.

[0028] The preferred temperature for the freezing treatment is -40 to -10°C, and the preferred freezing time is 5-24 hours.

[0029] Further, in step (2), the solvent is preferably acetonitrile and / or dimethyl sulfoxide; the gelation treatment time is preferably 0.5-5 h.

[0030] Further, in step (3), the preferred mass ratio of the second monomer to the crosslinking agent, photoinitiator, and lithium salt is 100:(0.1-5):(0.01-5):(10-100); wherein,

[0031] The second monomer is preferably an acrylamide monomer and / or an acrylate monomer, preferably one or more of acrylamide, methacrylamide, isopropylacrylamide, N,N-diethylacrylamide, isobutoxymethacrylamide, diacetone acrylamide, butyl acrylate, methyl acrylate, ethyl acrylate, 2-methyl methacrylate, and isooctyl acrylate.

[0032] The crosslinking agent is preferably one or more of N,N'-methylenebisacrylamide, epichlorohydrin, benzoyl peroxide, dicumyl peroxide, dicumyl peroxide, diethylenetriamine, 2,5-dimethyl-2,5-di-tert-butylperoxide, and di-tert-butyl peroxide.

[0033] The photoinitiator is preferably one or more of the following: 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, methyl o-benzoylbenzoate, benzophenone, 4-phenylbenzophenone, and ethyl 4-dimethylaminobenzoate.

[0034] The lithium salt is preferably one or more of lithium bis(trifluoromethanesulfonate)imide, lithium perchlorate, lithium tetrafluoroborate, lithium dioxaborate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(fluorosulfonate)imide, lithium dioxaborate, and lithium hexafluoroarsenate.

[0035] The preferred time for the light-protected and static environment is 0.5-10 hours.

[0036] Further, in step (4), the freezing temperature is -40 to -10℃ and the freezing time is 5-24h; during the photo-crosslinking process: the wavelength of the ultraviolet lamp is 300-400nm, the irradiation cycle is 1-15 cycles, each cycle is irradiated for 1-10s, and the cycle interval is 0.1-5s.

[0037] Furthermore, the preparation method further includes the following steps: immersing the product after photocrosslinking treatment in step (4) in a cooling bath at -40 to -10°C, and then removing and thawing it to obtain the gel electrolyte.

[0038] A third aspect of the present invention provides a lithium-ion battery comprising the gel electrolyte described in the first aspect or the gel electrolyte prepared by the preparation method described in the second aspect.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. This invention provides a gel electrolyte with a dual-network sponge-like structure, comprising a lithium salt, a first polymeric network, and a second polymeric network formed within a first monomer polymer product gel. The dual network of this gel electrolyte effectively disperses externally applied stress, resulting in excellent mechanical properties, with a tensile strength reaching 27.3 MPa. Furthermore, the flexible second network formed by the cross-linking polymerization of the second monomer within the first monomer polymer product gel enhances the solid-solid interface compatibility between the prepared gel electrolyte and the positive and negative electrode sheets, thus reducing the interfacial impedance between the gel electrolyte and the electrodes. In addition, the first monomer polymer product gel in the above-mentioned gel electrolyte facilitates lithium-ion migration, thereby reducing the activation energy of lithium-ion migration within the gel electrolyte. The dual-network structure increases lithium-ion migration channels, further improving the ionic conductivity of the electrolyte, enabling the gel electrolyte to achieve an ionic conductivity as high as 4.8 mS·cm. -1 .

[0041] 2. This invention uses a two-step cryogel method to prepare gel electrolytes, so that the prepared gel electrolytes retain the porous structure of the first polymer network while forming the second polymer network. Thus, under the synergistic effect of the porous structure and the dual network structure, the mechanical strength and ionic conductivity of the gel electrolyte are effectively improved.

[0042] 3. The present invention uses the gel electrolyte with high mechanical strength, low impedance and high ionic conductivity to assemble solid-state batteries, which can realize long-term stable cycling of full cells prepared with high nickel ternary cathode and lithium metal anode under high rate and high charging cut-off voltage, with a cycle performance of 1600 cycles @ 80% SOH. Detailed Implementation

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. "Comprising" or "containing" as used herein means that it may include or contain other components in addition to the stated components. "Comprising" or "containing" as used herein may also be replaced with the closed form "is" or "consisting of".

[0044] Currently, gel polymer electrolytes used in solid-state batteries have poor interfacial compatibility with positive and negative electrodes, which affects the battery's capacity and rate performance. Furthermore, it is often difficult to achieve a balance between mechanical properties and electrical and ionic conductivity. Based on these issues, the practical use of such gel polymer electrolytes in solid-state lithium metal batteries is limited.

[0045] To address the aforementioned issues, embodiments of the present invention provide a gel electrolyte having a porous and dual-network structure, comprising a first polymeric network, a second polymeric network, and a lithium salt; the first polymeric network and the second polymeric network form an interpenetrating dual-network structure, and the lithium salt is uniformly dispersed in the dual-network structure; wherein, the first polymeric network is a gel of a first monomer polymer, and the second polymeric network is a gel of a second monomer polymer.

[0046] More preferably, the first monomer is an olefinic monomer containing a sulfonic acid group, and the second monomer is an acrylamide monomer and / or an acrylate monomer; the first monomer polymer product gel is obtained by swelling the first monomer polymer product in a solvent, and the second polymer network is formed by cross-linking polymerization of the second monomer in the first monomer polymer product gel; the lithium salt exists in the gel electrolyte in the form of free lithium ions, for example, the lithium salt can dissociate into free lithium ions in the second monomer polymer product.

[0047] To address the issues of high interfacial impedance between gel polymer electrolytes and electrodes, and the difficulty in simultaneously achieving both mechanical properties and ionic conductivity, this invention provides a gel electrolyte with a dual-network sponge-like structure. This gel electrolyte comprises a first polymeric network and a second polymeric network formed by cross-linking and polymerizing a second monomer within the gel product of the first monomer. The first polymeric network is rigid, while the second polymeric network is flexible. This allows the gel electrolyte to possess excellent mechanical properties while forming a good contact interface with the electrode, thus reducing the interfacial impedance between the gel electrolyte and the electrode. Furthermore, the dual-network structure of the gel electrolyte provided by this invention effectively disperses externally applied stress, resulting in excellent mechanical properties and helping to suppress lithium dendrite formation. Compared to existing gel electrolytes with excellent mechanical properties but poor ionic conductivity, the first monomer polymeric gel product of the gel electrolyte provided by this invention facilitates lithium-ion migration, reducing the activation energy of lithium-ion migration within the gel electrolyte. The dual-network structure also increases lithium-ion migration channels, further improving the ionic conductivity of the electrolyte. The aforementioned gel electrolyte possesses excellent mechanical properties while also exhibiting low impedance and high ionic conductivity, significantly improving upon the current problems of gel electrolytes and facilitating their practical application in solid-state batteries.

[0048] In this invention, the alkene monomers containing sulfonic acid groups include one or more of sodium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-dodecylsulfonate, sodium dodecylsulfonate, and sodium 2-acrylamido-octylsulfonate; the acrylamide monomers include one or more of acrylamide, methacrylamide, isopropylacrylamidamide, N,N-diethylacrylamidamide, isobutoxymethacrylamidamide, and diacetone acrylamide; the acrylate monomers include one or more of butyl acrylate, methyl acrylate, ethyl acrylate, methyl 2-methacrylate, and isooctyl acrylate; more preferably, the first monomer is sodium 2-acrylamido-2-methylpropanesulfonate and the second monomer is acrylamide; or, the first monomer is sodium dodecylsulfonate and the second monomer is methyl 2-methacrylate.

[0049] In this invention, the preferred mass ratio of the first monomer to the second monomer is (1-10):1, such as 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc. The content of the first monomer and the second monomer affects the mechanical properties, interfacial properties and ionic conductivity of the formed gel electrolyte. By controlling the mass ratio of the two to a suitable range, such as (1-10):1, the prepared gel electrolyte can take into account the above-mentioned properties, so as to improve the overall performance of the battery containing the gel electrolyte.

[0050] Lithium salts are essential for lithium ion conduction in gel electrolytes. However, a higher lithium salt content in the gel electrolyte is not necessarily better. The conductivity of the gel electrolyte initially increases and then decreases with increasing lithium salt content. This is because excessive lithium salt content can lead to recrystallization in the gel electrolyte, which hinders ion migration. In this invention, the lithium salt can be selected from one or more of lithium bis(trifluoromethanesulfonate)imide, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(fluorosulfonate)imide, lithium dioxalate borate, and lithium hexafluoroarsenate, but is not limited to the lithium salts listed above. More preferably, the mass ratio of the lithium salt to the second monomer used to prepare the second polymer network is in the range of 1:(0.1-1) to obtain a gel electrolyte with high ionic conductivity.

[0051] This invention provides a method for preparing a gel electrolyte, comprising the following steps:

[0052] (1) The first monomer, crosslinking agent and low temperature initiator are pre-cooled respectively, then mixed evenly to obtain the first reaction liquid, and then transferred to the pre-cooled mold for freezing treatment. After thawing, the first monomer polymerization product is obtained.

[0053] (2) The first monomer polymer product prepared in step (1) is immersed in a solvent for gelation treatment to obtain the first monomer polymer product gel;

[0054] (3) Mix the second monomer, crosslinking agent, photoinitiator and lithium salt evenly to obtain the second reaction solution; immerse the first monomer polymerization product gel prepared in step (2) in the second reaction solution and let it stand in the dark;

[0055] (4) Take out the first monomer polymer product gel after impregnation treatment, transfer it to the mold for freezing treatment, wait for ice crystals to form in the gel pores, take it out and perform photo-crosslinking treatment, the second monomer crosslinks and polymerizes in the first monomer polymer product gel to form a second polymer network, and obtain the gel electrolyte.

[0056] This invention employs a two-step cryogel method to prepare a sponge-like gel electrolyte with a dual-network structure, as follows: In the first step, a cryo-gel treatment causes the first monomer to undergo low-temperature crosslinking polymerization in the presence of a crosslinking agent and a low-temperature initiator, forming a first monomer polymer product with a porous structure. This is followed by gelation treatment to form a gel of the first monomer polymer product with both a porous structure and a single-network structure. This first monomer polymer product gel is then immersed in a reaction solution containing a second monomer, a crosslinking agent, a photoinitiator, and a lithium salt, ensuring that the second monomer, crosslinking agent, initiator, and lithium salt are fully and uniformly dispersed in the gel phase. A second cryo-gel treatment is then performed, causing ice crystals to form in the gel pores. Finally, a light irradiation treatment is applied, causing the second monomer to crosslink and polymerize in the first monomer polymer product gel under the conditions of the crosslinking agent, photoinitiator, and light irradiation, forming a second polymer network. The second monomer in the pore portion of the first monomer polymer product gel does not undergo crosslinking polymerization due to the formation of ice crystals, thus preserving the pore structure of the first monomer polymer product gel and preparing a sponge-like gel electrolyte with a dual-network structure. The porous structure retained in the gel of the first monomer polymerization product can further disperse externally applied stress and increase lithium ion migration channels, thereby improving the mechanical properties and ionic conductivity of the gel electrolyte.

[0057] In this invention, preferably, the above preparation method is carried out in an environment with O2 ≤ 0.1 ppm and H2O ≤ 0.1 ppm, so as to avoid oxygen and water affecting the free radical polymerization reaction and to prevent the lithium salt from absorbing water and reacting with water to deteriorate.

[0058] In this invention, the preferred mass ratio of the first monomer to the crosslinking agent and the low-temperature initiator in step (1) is 100:(0.1-5):(0.01-5), such as 100:0.1:0.01, 100:1:0.1, 100:2:0.2, 100:3:1, 100:4:2, 100:5:5, etc., including but not limited to the mass ratios listed above, and more preferably 100:1:0.1. In the presence of the crosslinking agent and the low-temperature initiator, the first monomer is fully crosslinked and polymerized during the freezing process, and a first monomer polymerization product film is formed after thawing. The first monomer is preferably an olefinic monomer containing a sulfonic acid group, such as one or more selected from sodium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-dodecylsulfonate, sodium dodecylsulfonate, and sodium 2-acrylamido-octylsulfonate; the crosslinking agent is preferably one or more selected from N,N'-methylenebisacrylamide, epichlorohydrin, benzoyl peroxide, dicumyl peroxide, dicumyl hydroperoxide, diethylenetriamine, 2,5-dimethyl-2,5-di-tert-butylperoxide, and di-tert-butyl peroxide; the low-temperature initiator is preferably one or more selected from ammonium persulfate, benzoyl peroxide, tetramethylethylenediamine, benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptane.

[0059] In this invention, the temperature of the pre-cooling treatment in step (1) is preferably -40 to -10°C, and the time of the pre-cooling treatment is preferably 0.01-0.5h. The components in the first reaction liquid and the mold are pre-cooled before freezing treatment to slow down the polymerization process and improve the uniformity of the polymer.

[0060] In this invention, the first monomer is cross-linked polymerized at low temperature. The polymer formed by low-temperature polymerization has a narrow molecular weight distribution, which can improve the uniformity of the polymer molecular weight. Moreover, the low temperature can reduce the decomposition of the polymer and the occurrence of side reactions, thereby ensuring the quality of products prepared in different batches. In step (1), the preferred temperature for freezing treatment is -40 to -10℃, such as -40℃, -35℃, -30℃, -25℃, -20℃, -15℃, -10℃, etc., and the preferred freezing treatment time is 5-24h, such as 10h, 12h, 15h, 18h, 20h, 24h, including but not limited to the listed freezing treatment temperatures and times.

[0061] In this invention, in step (2), the first monomer polymer product prepared in step (1) is immersed in a solvent, such as acetonitrile, dimethyl sulfoxide, etc., to gel the polymer thin film and form a gel of the first monomer polymer product; wherein, the gelation treatment time is preferably 0.5-5h, for example 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h.

[0062] In this invention, in step (3), the preferred mass ratio of the second monomer to the crosslinking agent, photoinitiator, and lithium salt is 100:(0.1-5):(0.01-5):(10-100), for example, 100:1.2:0.11:45, 100:5:0.55:45, etc., including but not limited to the mass ratios listed above; wherein, the second monomer is preferably an acrylamide monomer and / or an acrylate monomer, preferably one or more of acrylamide, methacrylamide, isopropylacrylamide, N,N-diethylacrylamide, isobutoxymethacrylamide, diacetone acrylamide, butyl acrylate, methyl acrylate, ethyl acrylate, 2-methyl methacrylate, and isooctyl acrylate; the preferred crosslinking agent is N,N'-methylenebisacrylamide, The photoinitiator is preferably one or more of the following: epichlorohydrin, benzoyl peroxide, dicumyl peroxide, dicumyl hydroperoxide, diethylenetriamine, 2,5-dimethyl-2,5-di-tert-butylperoxide, and di-tert-butyl peroxide; the photoinitiator is preferably one or more of the following: 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, methyl o-benzoylbenzoate, benzophenone, 4-phenylbenzophenone, and ethyl 4-dimethylaminobenzoate; the lithium salt is preferably one or more of the following: lithium bis(trifluoromethanesulfonate)imide, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, and lithium hexafluoroarsenate.

[0063] In this invention, in step (3), the first monomer polymerization product gel prepared in step (2) is immersed in the second reaction solution and allowed to stand in the dark for 0.5-10 hours to ensure that the second monomer, crosslinking agent, initiator, and lithium salt are fully and uniformly dispersed in the gel phase, while preventing the second monomer from undergoing premature crosslinking polymerization. Furthermore, the preparation of the second reaction solution in step (3) is not restricted by the order of steps (1) and (2), meaning the second reaction solution can be prepared during the preparation of the first reaction solution or during the preparation of the first monomer polymerization product gel; the prepared second reaction solution simply needs to be allowed to stand in the dark.

[0064] In this invention, in step (4), the freezing temperature is preferably -40 to -10°C, for example, freezing at -20°C for 5-24 hours, so that the substances including the second monomer filling the pores of the first monomer polymer product gel form ice crystals, which will not undergo cross-linking polymerization under subsequent light irradiation. After the light irradiation treatment, the thawing treatment is performed to preserve the porous structure in the first monomer polymer product gel. Preferably, during the light cross-linking treatment: the wavelength of the ultraviolet lamp is 300-400nm, for example 312nm, the irradiation cycle is 1-15 cycles, each cycle is irradiated for 1-10s, and the cycle interval is 0.1-5s.

[0065] In this invention, the above preparation method further includes the following operation: immersing the product after photo-crosslinking treatment in step (4) in a cooling bath of -40 to -10°C, and then taking it out to thaw and obtain gel electrolyte; wherein immersing the product after photo-crosslinking treatment in a cooling bath promotes the full polymerization of the second monomer.

[0066] The present invention also provides a lithium-ion battery comprising the above-described gel electrolyte or the gel electrolyte prepared by the above-described preparation method. The gel electrolyte has a double-network sponge structure. Under the synergistic effect of the porous structure and the double-network structure, it not only has excellent mechanical properties, but also has excellent characteristics such as low impedance and high ionic conductivity, so that the lithium-ion battery containing the gel electrolyte has long-term stability.

[0067] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0068] Example 1

[0069] This embodiment relates to the preparation of a dual-network sponge-like structure gel electrolyte, specifically including the following steps:

[0070] (1) Sodium 2-acrylamide-2-methylpropanesulfonate (NaAMPS), N,N'-methylenebisacrylamide (MBAAm), and tetramethylethylenediamine (TEMED) were pre-cooled at -10°C in an ethanol cooling bath, and then mixed evenly at a mass ratio of 100:1:0.1 to obtain the first reaction solution. After pre-cooling the mold in an ethanol cooling bath at -10°C, the first reaction solution was poured into the mold and sealed, and then immediately placed in an ethanol cooling bath at -20°C. The frozen sample was stored at -20°C to promote a high yield of crosslinking polymerization. After 24 hours, the polymerization was basically completed. The mold was removed from the cooling bath and thawed at room temperature to obtain a rigid film of the first monomer polymerization product.

[0071] (2) The prepared rigid film of the first monomer polymerization product was immersed in acetonitrile for 2 hours to gel, and the excess solvent was dried at 30°C to obtain the gel of the first monomer polymerization product.

[0072] (3) Acrylamide (AAm), MBAAm, 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) and lithium bis(trifluoromethanesulfonate)imide (LiTFSI) are mixed evenly in a mass ratio of 100:5:0.55:45 to obtain a second reaction solution. The first monomer polymerization product gel prepared in step (2) is immersed in the second reaction solution and wrapped with aluminum foil to protect it from light. It is left to stand for 10 hours.

[0073] (4) The first monomer polymerization product gel after soaking was transferred to a mold and then cooled in a cooling bath at -20°C for 15 hours. During the cooling process, ice crystals formed in the gel pores. Then, it was taken out and placed under a UV lamp with a wavelength of 312nm for UV periodic radiation crosslinking, 10 cycles, each cycle lasting 10s, with a cycle interval of 1s. After irradiation, the sample was soaked in a cooling bath at -10°C for a certain period of time to achieve a high polymerization yield. After the irradiation was completed, the sample was slowly thawed in cold tap water in the mold to obtain a sponge-like gel electrolyte with a double network structure.

[0074] Example 2

[0075] This embodiment relates to the preparation of a dual-network sponge-like structure gel electrolyte, specifically including the following steps:

[0076] (1) Sodium dodecyl sulfonate (NaSDS), dicumyl peroxide (DBHP), and ammonium persulfate (APS) were pre-cooled at -10°C in an ethanol cooling bath, and then mixed uniformly at a mass ratio of 100:1:0.1 to obtain the first reaction solution. After pre-cooling the mold in an ethanol cooling bath at -10°C, the first reaction solution was poured into the mold and sealed, and immediately placed in an ethanol cooling bath at -20°C. The frozen sample was stored at -20°C to promote a high yield of crosslinking polymerization. After 15 hours, the polymerization was basically completed. The mold was removed from the cooling bath and thawed at room temperature to obtain a rigid film of the first monomer polymerization product.

[0077] (2) The prepared rigid film of the first monomer polymerization product was immersed in dimethyl sulfoxide for 2 hours to gel, and the excess solvent was dried at 30°C to obtain the gel of the first monomer polymerization product.

[0078] (3) Methyl 2-methacrylate (MMA), DBHP, benzophenone (BP) and lithium bis(fluorosulfonyl)imide (LiFSI) are mixed evenly in a mass ratio of 100:1.2:0.11:45 to obtain a second reaction solution. The first monomer polymerization product gel prepared in step (2) is immersed in the second reaction solution and wrapped with aluminum foil to protect it from light. It is then left to stand for 5 hours.

[0079] (4) The first monomer polymerization product gel after soaking was transferred to a mold and then cooled in a cooling bath at -20°C for 10 hours. During the cooling process, ice crystals formed in the gel pores. Then, it was taken out and placed under a UV lamp with a wavelength of 312nm for UV periodic radiation crosslinking, 10 cycles, each cycle lasting 5s with a cycle interval of 1s. After irradiation, the sample was soaked in a cooling bath at -10°C for a certain period of time to achieve a high polymerization yield. After the irradiation was completed, the sample was slowly thawed in cold tap water in the mold to obtain a sponge-like gel electrolyte with a double network structure.

[0080] Example 3

[0081] This embodiment relates to the preparation of a dual-network sponge-like structure gel electrolyte, specifically including the following steps:

[0082] (1) NaAMPS, MBAAm, and TEMED were pre-cooled at -10°C in an ethanol cooling bath, and then mixed uniformly at a mass ratio of 100:1:0.1 to obtain the first reaction solution. After pre-cooling the mold in an ethanol cooling bath at -10°C, the first reaction solution was poured into the mold and sealed, and then immediately placed in an ethanol cooling bath at -20°C. The frozen sample was stored at -20°C to promote a high yield of crosslinking polymerization. After 15 hours, the polymerization was basically completed. The mold was removed from the cooling bath and thawed at room temperature to obtain a rigid film of the first monomer polymerization product.

[0083] (2) The prepared rigid film of the first monomer polymerization product was immersed in acetonitrile for 2 hours to gel, and the excess solvent was dried at 30°C to obtain the gel of the first monomer polymerization product.

[0084] (3) Mix AAm, MBAAm, HMPP and LiTFSI in a mass ratio of 100:1.2:0.11:45 to obtain a second reaction solution. Soak the first monomer polymerization product gel prepared in step (2) in the second reaction solution, wrap it with aluminum foil to protect it from light, and let it stand for 5 hours.

[0085] (4) The first monomer polymerization product gel after soaking was transferred to a mold and then cooled in a cooling bath at -20°C for 10 hours. During the cooling process, ice crystals formed in the gel pores. Then, it was taken out and placed under a UV lamp with a wavelength of 312nm for UV periodic radiation crosslinking, 10 cycles, each cycle lasting 5s with a cycle interval of 1s. After irradiation, the sample was soaked in a cooling bath at -10°C for a certain period of time to achieve a high polymerization yield. After the irradiation was completed, the sample was slowly thawed in cold tap water in the mold to obtain a sponge-like gel electrolyte with a double network structure.

[0086] Comparative Example 1

[0087] This comparative example relates to the preparation of a rigid network structure polymer electrolyte. The difference from Example 1 is that step (2) of gelation treatment is not included. In step (3), the rigid film of the first monomer polymer product prepared in step (1) is directly immersed in the second reaction solution, wrapped with aluminum foil to protect it from light, and left to stand for 10 hours. The remaining operations are the same as in Example 1, and a polymer film with a rigid network structure is obtained.

[0088] Comparative Example 2

[0089] This comparative example relates to the preparation of a polymer electrolyte, which differs from Example 1 in that it does not include the preparation of the first polymer network. Instead, the same amounts of NaAMPS, AAm, MBAAm, HMPP and LiTFSI as in Example 1 are directly mixed and UV polymerized under the same polymerization conditions as in Example 1.

[0090] Application and performance testing

[0091] (1) The tensile properties of the electrolyte materials prepared in the above embodiments and comparative examples were tested. The specific operations are as follows:

[0092] The materials prepared in each embodiment and comparative example were cut into strips of 20×150mm. Tensile tests were performed at room temperature at a rate of 250mm / min, and the tensile strength and elongation at break of the electrolyte were recorded.

[0093] The test results are shown in Table 1 below:

[0094] Table 1

[0095] Example 1 27.3 168 Example 2 15.4 133 Example 3 19.1 124 Comparative Example 1 3.6 57 Comparative Example 2 0.5 165

[0096] As shown in Table 1, compared with the electrolyte materials prepared in Comparative Examples 1 and 2, the gel electrolyte with a double-network sponge structure prepared by the two-step cryogel method of the present invention has better tensile strength and the elongation at break can reach more than 100%, which is significantly better than the rigid network structure polymer electrolyte obtained in Comparative Example 1 without gelation.

[0097] (2) The ionic conductivity of the electrolytes prepared in the above examples and comparative examples was tested using an electrochemical workstation;

[0098] The electrolytes prepared in the above examples and comparative examples were assembled into blocking batteries (except for the electrolyte material, everything else was the same). Then, AC impedance (EIS) tests were performed at room temperature with the initial voltage set to 10mV and the frequency set to 100KHz~0.1mHz. The impedance was recorded.

[0099] The test results are shown in Table 2 below:

[0100] Table 2

[0101] Example 1 3.2 4.8 Example 2 8.4 1.1 Example 3 5.1 3.5 Comparative Example 1 55 0.11 Comparative Example 2 139 0.06

[0102] As shown in Table 2, the gel electrolyte with a double-network sponge structure prepared by the two-step cryogel method of this invention has low impedance and high ionic conductivity. Compared with the polymer electrolyte formed by directly mixing and polymerizing the first monomer, the second monomer, and the lithium salt (Comparative Example 2), the impedance is reduced from 139Ω to below 10Ω, and the ionic conductivity is reduced from 0.06mS·cm. -1Increased to 4.8 mS·cm -1 The impedance of the prepared polymer electrolyte increased by 80 times. The main difference between Comparative Example 1 and Example 1 in preparing the electrolyte material is that no gelation treatment was performed, thus preventing the second monomer from forming a second polymer network in the gel phase of the first polymer network. As a result, the impedance of the prepared polymer electrolyte increased significantly, from 3.2Ω to 55Ω, and its ionic conductivity also decreased significantly. This shows that the cross-linking polymerization of the second monomer in the gel of the first monomer polymerization product has a significant impact on both the impedance and ionic conductivity of the electrolyte.

[0103] (2) The electrolytes prepared in the above examples and comparative examples were used to assemble soft-pack solid-state batteries. The specific operations are as follows:

[0104] Commercial NCM811 positive electrode sheet, gel electrolyte, and lithium copper composite sheet are stacked to obtain a bare cell. Then, positive and negative electrode tabs are welded, the bare cell is installed in an aluminum-plastic film battery case, top and side are sealed, dried to remove moisture, left to stand, formed, and tested for capacity. Finally, the vent is vented and sealed to obtain a lithium metal solid-state battery.

[0105] Under normal temperature conditions, each lithium metal solid-state battery was subjected to cyclic charge-discharge tests between an initial voltage of 2.8V and a cutoff voltage of 4.35V. Specifically, the batteries were charged at 1C to 4.35V, then charged at a constant voltage of 4.35V until the current reached 0.05C cutoff, and discharged at 0.33C to 2.8V. The capacity retention rate of each cycle was recorded.

[0106] The test results are shown in Table 3 below:

[0107] Table 3

[0108] Example 1 96.4 85.1 80.1 Example 2 92.1 81.7 67.2 Example 3 92.9 82.1 75.3 Comparative Example 1 82 / / Comparative Example 2 26 / /

[0109] As shown in Table 3, compared with Comparative Examples 1 and 2, the battery constructed using the gel electrolyte with the double-network sponge structure of the present invention has excellent cycle stability. After 500 charge-discharge cycles, its capacity retention rate is above 90%, and after 1000 charge-discharge cycles, its capacity retention rate is above 80%. Moreover, the battery constructed using the gel electrolyte prepared in Example 1 can still maintain a capacity retention rate of more than 80% after 1600 cycles.

[0110] In summary, the gel electrolyte with a dual-network sponge-like structure described in this invention possesses excellent mechanical properties, low impedance, and high ionic conductivity, enabling batteries containing this gel electrolyte to exhibit excellent cycle stability.

[0111] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A gel electrolyte, characterized in that, The gel electrolyte comprises a first polymeric network, a second polymeric network, and a lithium salt; wherein the first polymeric network and the second polymeric network form an interpenetrating double network structure, and the lithium salt is uniformly dispersed in the double network structure; The first polymeric network is a gel of a first monomer polymer, and the second polymeric network is a polymer of a second monomer; the first monomer is an olefinic monomer containing a sulfonic acid group, and the second monomer is an acrylamide monomer and / or an acrylate monomer; the second polymeric network is formed by cross-linking polymerization of the second monomer in the gel of the first monomer polymer.

2. The gel electrolyte according to claim 1, characterized in that, The lithium salt exists in the gel electrolyte in the form of free lithium ions; The alkene monomers containing sulfonic acid groups include one or more of sodium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-dodecylsulfonate, sodium dodecylsulfonate, and sodium 2-acrylamido-octylsulfonate. The acrylamide monomers include one or more of acrylamide, methacrylamide, isopropylacrylamide, N,N-diethylacrylamide, isobutoxymethacrylamide, and diacetoneacrylamide; The acrylate monomers include one or more of butyl acrylate, methyl acrylate, ethyl acrylate, methyl 2-methacrylate, and isooctyl acrylate; The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(fluorosulfonate)imide, lithium difluorooxalate borate, and lithium hexafluoroarsenate.

3. The gel electrolyte according to claim 2, characterized in that, The mass ratio of the first monomer to the second monomer is (1-10):1; The mass ratio of the lithium salt to the second monomer is in the range of 1:(0.1-1).

4. A method for preparing a gel electrolyte, characterized in that, Includes the following steps: (1) The first monomer, crosslinking agent and low temperature initiator are pre-cooled respectively, then mixed evenly to obtain the first reaction solution, and then transferred to the pre-cooled mold for freezing treatment. After thawing, the first monomer polymerization product is obtained; the first monomer is an alkene monomer containing sulfonic acid groups; (2) The first monomer polymer product prepared in step (1) is immersed in a solvent for gelation treatment to obtain the first monomer polymer product gel; (3) Mix the second monomer, crosslinking agent, photoinitiator and lithium salt evenly to obtain the second reaction solution; immerse the first monomer polymerization product gel prepared in step (2) in the second reaction solution and let it stand in the dark; the second monomer is an acrylamide monomer and / or an acrylate monomer; (4) Take out the first monomer polymer product gel after impregnation treatment, transfer it to the mold for freezing treatment, wait for ice crystals to form in the gel pores, take it out and perform photo-crosslinking treatment, the second monomer crosslinks and polymerizes in the first monomer polymer product gel to form a second polymer network, and obtain the gel electrolyte.

5. The preparation method according to claim 4, characterized in that, The preparation method is carried out in an environment where O2 ≤ 0.1 ppm and H2O ≤ 0.1 ppm.

6. The preparation method according to claim 4, characterized in that, In step (1), the mass ratio of the first monomer to the crosslinking agent and the low-temperature initiator is 100:(0.1-5):(0.01-5). The crosslinking agent is selected from one or more of N,N'-methylenebisacrylamide, epichlorohydrin, benzoyl peroxide, dicumyl peroxide, dicumyl hydroperoxide, diethylenetriamine, 2,5-dimethyl-2,5-di-tert-butylperoxide, and di-tert-butyl peroxide. The low-temperature initiator is selected from one or more of ammonium persulfate, benzoyl peroxide, tetramethylethylenediamine, benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptane; The precooling treatment temperature is -40~-10 ℃, and the precooling treatment time is 0.01-0.5 h; The freezing treatment temperature is -40 to -10 ℃, and the freezing treatment time is 5-24 h.

7. The preparation method according to claim 6, characterized in that, The first monomer is one or more of sodium 2-acrylamido-2-methylpropanesulfonate, sodium 2-acrylamido-dodecylsulfonate, sodium dodecylsulfonate, and sodium 2-acrylamido-octylsulfonate.

8. The preparation method according to claim 4, characterized in that, In step (2), the solvent is acetonitrile and / or dimethyl sulfoxide; The gelation treatment time is 0.5-5 h.

9. The preparation method according to claim 4, characterized in that, In step (3), the mass ratio of the second monomer to the crosslinking agent, photoinitiator, and lithium salt is 100:(0.1-5):(0.01-5):(10-100). The crosslinking agent is selected from one or more of N,N'-methylenebisacrylamide, epichlorohydrin, benzoyl peroxide, dicumyl peroxide, dicumyl hydroperoxide, diethylenetriamine, 2,5-dimethyl-2,5-di-tert-butylperoxide, and di-tert-butyl peroxide. The photoinitiator is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, methyl o-benzoylbenzoate, benzophenone, 4-phenylbenzophenone, and ethyl 4-dimethylaminobenzoate. The lithium salt is selected from one or more of lithium bis(trifluoromethanesulfonate)imide, lithium perchlorate, lithium tetrafluoroborate, lithium dioxaborate, lithium difluorophosphate, lithium hexafluorophosphate, lithium bis(fluorosulfonate)imide, lithium dioxaborate, and lithium hexafluoroarsenate. The time for keeping the plant in the dark is 0.5-10 hours.

10. The preparation method according to claim 9, characterized in that, The second monomer is one or more of acrylamide, methacrylamide, isopropylacrylamide, N,N-diethylacrylamide, isobutoxymethacrylamide, diacetone acrylamide, butyl acrylate, methyl acrylate, ethyl acrylate, 2-methyl methacrylate, and isooctyl acrylate.

11. The preparation method according to claim 4, characterized in that, In step (4), the freezing temperature is -40~-10 ℃, and the freezing time is 5-24 h; During the photo-crosslinking process: the wavelength of the ultraviolet lamp is 300-400 nm, the irradiation cycle is 1-15 cycles, each cycle is irradiated for 1-10 s, and the cycle interval is 0.1-5 s; The preparation method further includes the following operation: the product after photocrosslinking treatment in step (4) is placed in a cooling bath of -40~-10 ℃ and then taken out and thawed to obtain the gel electrolyte.

12. A lithium-ion battery, characterized in that, The gel electrolyte comprises the gel electrolyte according to any one of claims 1-3 or the gel electrolyte prepared by the preparation method according to any one of claims 4-11.