Lithium ion solid electrolyte as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of solid-state batteries, and provides a lithium-ion solid-state electrolyte and a preparation method and application thereof. The electrolyte comprises a polymer matrix, a lithium salt and a polar organic compound, the polymer matrix includes a first monomer and a second monomer. The preparation method comprises the following steps: mixing a lithium salt and a polar organic compound to obtain a eutectic mixture; mixing a first monomer and a second monomer with the eutectic mixture to obtain a precursor solution; and coating a mold with the precursor solution, and curing. The invention also discloses a solid-state lithium ion battery comprising the electrolyte. The lithium ion solid electrolyte disclosed by the invention is high in room-temperature ionic conductivity, excellent in stretchability, high in breaking strength and tensile elongation and incombustibility. And by introducing the composite material into a porous electrode and tightly combining the composite material with active material particles in the electrode, the problem of stress failure of the electrode under low stacking pressure is solved, and good cycling stability of the all-solid-state battery under the low stacking pressure or even under the condition that no external pressure is applied is realized.

Description

Technical Field

[0001] This disclosure relates to the field of solid-state battery technology, and in particular to a lithium-ion solid electrolyte, its preparation method, and its application. Background Technology

[0002] With the booming development of the new energy market, traditional lithium-ion batteries containing organic liquid electrolytes can no longer meet the increasingly urgent demands for high energy density and safety. Solid-state batteries, due to their high energy density and high safety, have received much attention from the industry in recent years. Currently, the most prominent lithium-ion solid electrolytes mainly include oxide, sulfide, halide lithium-ion solid electrolytes and polymer lithium-ion solid electrolytes. However, these lithium-ion solid electrolytes still encounter many problems in practical applications that need to be solved. For example, sulfide lithium-ion solid electrolytes have a narrow voltage window, are prone to side reactions at the electrode interface, and are very sensitive and unstable to air / moisture; oxide lithium-ion solid electrolytes have a large Young's modulus, low room temperature ionic conductivity, and poor interfacial contact with electrode materials, resulting in high interfacial impedance; halide lithium-ion solid electrolytes cannot be used on a large scale due to poor compatibility with the negative electrode and easy hydrolysis. Polymer lithium-ion solid electrolytes (such as PEO-based) have limitations in practical applications due to their low room temperature conductivity and poor oxidation resistance (difficult to match high-voltage positive electrodes). Meanwhile, the practical application of solid-state batteries is currently hampered by other technical issues, including the need for extremely high stacking pressure. Reducing the operating pressure typically leads to a decrease in the cycle stability of solid-state batteries. The main reason is that without sufficient external pressure, the repeated expansion and contraction of the active material can loosen the contact between the active material and the lithium-ion solid electrolyte, thus hindering lithium-ion transport and causing cycle capacity decay. However, providing such high stacking pressure in practical applications presents significant challenges; the addition of extra pressurization equipment greatly reduces the battery's energy density and increases production costs. Summary of the Invention

[0003] This disclosure provides a lithium-ion solid electrolyte, its preparation method, and its application, to at least solve the above-mentioned technical problems existing in the prior art.

[0004] According to a first aspect of this disclosure, a lithium-ion solid electrolyte is provided, comprising a polymer matrix, a lithium salt, and a polar organic compound; said polymer matrix comprises a first monomer and a second monomer.

[0005] In one embodiment, the first monomer includes at least one of acrylamide (AM) and its derivatives.

[0006] In one embodiment, the acrylamide derivative is selected from... At least one of them.

[0007] In one embodiment, the second monomer includes at least one of dimethylacrylamide (DMAM) and its derivatives.

[0008] In one embodiment, the dimethacrylamide derivative is selected from... At least one of them.

[0009] In one embodiment, the molar ratio of the first monomer to the second monomer is (0.3-5):1.

[0010] In one embodiment, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiTf), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), lithium perchlorate (LiClO4), lithium chloride (LiCl), lithium iodide (LiI), and lithium bromide (LiBr).

[0011] In one embodiment, the polar organic compound is selected from at least one of N-methylacetamide (NMA), N-ethylacetamide (NEA), 2-methylpropionamide, 1-methyl-3-propylimidazolium, triethylene glycol dimethyl ether, lactic acid, triethanolamine, glycerol, and urea.

[0012] Specifically, the aforementioned lithium salt and polar organic compound can form a eutectic mixture that is liquid at room temperature through strong interactions (Lewis acid-base interactions). The melting point of the resulting eutectic mixture is lower than that of each component. Specifically, Li in the lithium salt... + Lithium salts coordinate with highly electronegative atoms in polar organic compounds, while hydrogen bonds form between the groups in the polar organic compounds and the highly electronegative atoms in the lithium salt. This results in strong interactions between different proportions of polar organic compounds and lithium salts, forming eutectic mixtures. As the lithium salt concentration decreases, the degree of lithium salt dissociation increases, leading to higher ionic conductivity in the eutectic mixture. However, excessively low lithium salt proportions will result in low ionic conductivity due to low carrier concentration.

[0013] In one embodiment, the molar ratio of the lithium salt to the polar organic compound is 1:(1 to 10).

[0014] In one embodiment, the lithium-ion solid electrolyte further includes a crosslinking agent and an initiator; the crosslinking agent is selected from at least one of N,N'-methylenebisacrylamide (MBA), polyethylene glycol diacrylate (PEGDA), trimethylolpropane triacrylate (TMPTA), 1,6-hexanediol diacrylate (HDDA), pentaerythritol triacrylate (PETRA), polyethylene glycol dimethacrylate (PEGDMA), divinylbenzene (DVB), triallylamine (TAA), bisacryloylcysteine ​​(BAC), triacryloylhexahydro-1,3,5-triazine (TAT), and pentaerythritol tetraacrylate; the initiator is selected from at least one of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, 2-hydroxy-2-methylphenylacetone, benzoin dimethyl ether, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and lithium phenyl-2,4,6-trimethylbenzoylphosphonate.

[0015] In one embodiment, the molar ratio of the polymer matrix to the crosslinking agent is (0.5-4):1.

[0016] Specifically, the molar amount of the polymer matrix refers to the total molar amount of the first monomer and the second monomer.

[0017] In one embodiment, the molar ratio of the crosslinking agent to the initiator is (0.5-3):1.

[0018] According to a second aspect of this disclosure, a method for preparing the above-mentioned lithium-ion solid electrolyte is provided, comprising the following steps:

[0019] S1: A lithium salt and a polar organic compound are mixed to obtain a eutectic mixture;

[0020] S2: Mix the first monomer and the second monomer with the eutectic mixture to obtain the precursor liquid;

[0021] S3: After coating the precursor liquid onto the mold, it is cured to obtain the lithium-ion solid electrolyte.

[0022] In one embodiment, the mixing temperature in step S1 is 20–40°C.

[0023] In one embodiment, step S2 involves mixing the first monomer, the second monomer, the crosslinking agent, and the initiator with the eutectic mixture to obtain the precursor liquid.

[0024] Specifically, lithium-ion solid electrolytes with different soft and hard phase ratios can be prepared by adjusting the molar ratio of the first monomer to the second monomer. The first monomer, after polymerization, is immiscible with the eutectic mixture. Due to its abundant hydrogen bonds, the first monomer forms a hard phase after polymerization. The second monomer, after polymerization, is miscible with the eutectic mixture and forms a uniform soft phase. The soft and hard phases randomly copolymerize in the lithium-ion solid electrolyte. Due to the different miscibility of the first and second monomer polymers with the eutectic mixture, a bicontinuous phase separation network is formed. Different ratios of soft and hard phases also affect the Tg of the copolymer; the Tg decreases with increasing proportion of the first monomer polymer. All materials have a Tg below room temperature, giving them excellent ion transport capabilities at room temperature. After being combined with the copolymer network, the eutectic mixture is constrained and coordinated by the macromolecular chains within the polymer, making it different from traditional free-state liquid additives and exhibiting a tendency towards solid-state properties.

[0025] The pure second monomer polymer exhibits excellent tensile strength but low fracture strength. This low fracture strength is due to a lack of interchain interactions, as the second monomer polymer is miscible with the eutectic mixture, resulting in highly solvated molecular chains. In contrast, the pure first monomer polymer exhibits extremely low elongation at break and high fracture strength. Under low stacking pressure, the mechanical properties of lithium-ion solid-state electrolytes significantly affect the cycle stability of the battery. To optimize the mechanical properties of lithium-ion solid-state electrolytes, the proportions of the first monomer polymer (hard phase) and the second monomer polymer (soft phase) are adjusted to combine the tensile strength of the soft phase (second monomer polymer) with the strength of the hard phase (first monomer polymer).

[0026] In one embodiment, the mixing temperature in step S2 is 20–40°C.

[0027] In one embodiment, step S3 involves curing under ultraviolet light irradiation for a time of 5 to 8 minutes.

[0028] In one embodiment, steps S1 to S3 are all performed under an inert atmosphere, which is selected from an argon atmosphere or a nitrogen atmosphere.

[0029] In one embodiment, the thickness of the lithium-ion solid electrolyte film is 10–120 μm.

[0030] According to a third aspect of this disclosure, a solid-state lithium-ion battery is provided, comprising a positive electrode, a negative electrode, and the aforementioned lithium-ion solid electrolyte.

[0031] In one embodiment, the positive electrode comprises, by weight percentage, 90-96% of the positive electrode active material, 0-5% of the positive electrode conductive agent, and 0-5% of the positive electrode binder.

[0032] Typically, but not limitingly, the mass percentage of the positive electrode active material can be 90%, 91%, 92%, 93%, 94%, 95%, or 96%, or any value within the range of 90% to 96%.

[0033] Typically, but not limitingly, the mass percentage of the positive conductive agent can be 1%, 2%, 3%, 4%, or 5%, or any value in the range of 0 to 5%.

[0034] Typically, but not limitingly, the mass percentage of the positive electrode binder can be 1%, 2%, 3%, 4%, or 5%, or any value in the range of 0 to 5%.

[0035] In one embodiment, the positive electrode active material includes lithium iron phosphate, lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NCM), and lithium-rich manganese-based crystalline oxide (Li). 1+x [NiMnCo] 1-x At least one of O2, LMR-NMC, lithium cobalt oxide (LCO), and lithium manganese oxide (LMO).

[0036] In one embodiment, the positive electrode conductive agent includes at least one of VGCF, carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0037] In one embodiment, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride hexafluoropropylene, polypropylene, polyethylene, and polyimide.

[0038] In one embodiment, the negative electrode comprises, by weight percentage, 90-96% of the negative electrode active material, 0-5% of the negative electrode conductive agent, and 0-5% of the negative electrode binder.

[0039] Typically, but not limitingly, the mass percentage of the negative electrode active material can be 90%, 91%, 92%, 93%, 94%, 95%, or 96%, or any value within the range of 90% to 96%.

[0040] Typically, but not limitingly, the mass percentage of the negative electrode conductive agent can be 1%, 2%, 3%, 4%, or 5%, or any value in the range of 0 to 5%.

[0041] Typically, but not limitingly, the mass percentage of the negative electrode binder can be 1%, 2%, 3%, 4%, or 5%, or any value in the range of 0 to 5%.

[0042] In one embodiment, the negative electrode active material includes at least one of artificial graphite, natural graphite, silicon (Si), silicon suboxide (SiO), pre-lithiated silicon suboxide, silicon carbide (SiC), lithium, aluminum-silicon alloy, lithium-indium alloy, lithium-tin alloy, and lithium-aluminum alloy.

[0043] In one embodiment, the negative electrode conductive agent includes at least one of VGCF, carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0044] In one embodiment, the negative electrode binder includes at least one of sodium carboxymethyl cellulose, carboxymethyl cellulose, methyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymers, cyclodextrin, styrene-butadiene rubber (SBR), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), polymethyl methacrylate (PMMA), styrene-butadiene block copolymer (SBS), styrene-ethylene-butene-styrene block copolymer (SEBS), and polyisobutylene (PIB).

[0045] According to one possible implementation of this disclosure, at least the following beneficial effects are achieved:

[0046] This disclosure presents an elastic lithium-ion solid electrolyte composed of a polymer matrix, a lithium salt, and a polar organic compound (the lithium salt and the polar organic compound are mixed to form a eutectic mixture). This electrolyte exhibits high ionic conductivity at room temperature, excellent tensile strength, high tensile strength and elongation at break, and non-flammability. The eutectic mixture is a mixture of two strongly interacting chemical substances with a melting point much lower than that of a single component, possessing high ionic conductivity, non-toxicity, and environmental friendliness. The elastic lithium-ion solid electrolyte is constructed by polymerizing a copolymer matrix containing a soft phase (the second monomer polymer) and a hard phase (the first monomer polymer) within the eutectic mixture. The copolymer material composed of the soft and hard phases possesses excellent mechanical properties, including high strength and good deformation resilience. This copolymer achieves high ionic conductivity without sacrificing mechanical properties. Furthermore, the eutectic mixture, due to its non-flammability and low vapor pressure, offers superior safety compared to traditional liquid organic electrolytes, providing strong protection for battery safety and making it an ideal choice for preparing safe electrolytes. Based on the aforementioned advantageous characteristics, the excellent reliability of this lithium-ion solid electrolyte ensures battery safety and is expected to become an excellent electrolyte for solid-state batteries operating under low stacking pressure.

[0047] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0048] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of this disclosure are illustrated in the drawings by way of example and not limitation, in which:

[0049] In the accompanying drawings, the same or corresponding reference numerals indicate the same or corresponding parts.

[0050] Figure 1 A schematic diagram of the structure of the first monomer of this disclosure is shown;

[0051] Figure 2 A schematic diagram of the structure of the second monomer of this disclosure is shown;

[0052] Figure 3 A schematic diagram of the structure of the polar organic compound disclosed herein is shown;

[0053] Figure 4 A schematic diagram of the process for preparing a lithium-ion solid electrolyte according to Embodiment 1 of this disclosure is shown;

[0054] Figure 5 A schematic diagram of the molecular design of the lithium-ion solid electrolyte in Embodiment 1 of this disclosure is shown. Detailed Implementation

[0055] To make the objectives, features, and advantages of this disclosure more apparent and understandable, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0056] This disclosure develops a multifunctional elastic lithium-ion solid electrolyte with high lithium-ion mobility, a certain degree of flexibility, and strong compatibility with both positive and negative electrodes. This multifunctional elastic lithium-ion solid electrolyte can penetrate and occupy the internal pores of a porous electrode, and can encapsulate irregularly shaped active material particles within the electrode structure. The lithium-ion solid electrolyte acts as a rapid ion transport channel between the active material particles. By introducing an elastic lithium-ion solid electrolyte with high room temperature ionic conductivity, significant tensile and compressive resilience, and non-flammability into the internal structure of a porous electrode, and achieving tight bonding with the active material particles within the electrode, the problem of electrode stress failure under low stacking pressure is solved. By applying this elastic lithium-ion solid electrolyte in solid-state lithium-ion batteries, good cycle stability of solid-state lithium-ion batteries is achieved under low stacking pressure or even without external pressure.

[0057] The lithium-ion solid electrolyte disclosed herein includes a polymer matrix, a lithium salt, and a polar organic compound; the polymer matrix includes a first monomer and a second monomer.

[0058] The first monomer includes at least one of acrylamide (AM) and its derivatives, and the structures of each compound are as follows: Figure 1 As shown.

[0059] The second monomer includes at least one of dimethylacrylamide (DMAM) and its derivatives, the structures of which are as follows: Figure 2 As shown.

[0060] Lithium salts include at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiTf), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), lithium perchlorate (LiClO4), lithium chloride (LiCl), lithium iodide (LiI), and lithium bromide (LiBr).

[0061] The polar organic compound is selected from at least one of N-methylacetamide (NMA), N-ethylacetamide (NEA), 2-methylpropionamide, 1-methyl-3-propylimidazolium, triethylene glycol dimethyl ether, lactic acid, triethanolamine, glycerol, and urea, and the structure of each compound is shown in the figure. Figure 3 As shown.

[0062] The following examples illustrate this in detail.

[0063] Example 1

[0064] This embodiment prepares a lithium-ion solid electrolyte, the flowchart of which is shown below. Figure 4 As shown in the diagram, the design schematic is as follows: Figure 5 As shown. Specifically:

[0065] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.6 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0066] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0067] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0068] Example 2

[0069] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0070] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.5 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0071] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0072] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0073] Example 3

[0074] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0075] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.4 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0076] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0077] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0078] Example 4

[0079] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0080] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.3 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0081] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0082] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0083] Example 5

[0084] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0085] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.7 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0086] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0087] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0088] Example 6

[0089] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0090] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.8 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0091] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0092] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0093] Example 7

[0094] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0095] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.9 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0096] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0097] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0098] Example 8

[0099] This embodiment prepares a lithium-ion solid electrolyte, as detailed below:

[0100] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 1.0 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0101] (2) Add 4.8 mol acrylamide, 1.2 mol N-methyl-N-ethylacrylamide (DMAM-1), 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0102] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0103] Comparative Example 1

[0104] This comparative example prepared a lithium-ion solid electrolyte. The difference from Example 1 is that no second monomer was added in this comparative example. Details are as follows:

[0105] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.6 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0106] (2) Add 4.8 mol acrylamide, 3 mol crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0107] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0108] Comparative Example 2

[0109] This comparative example prepared a lithium-ion solid electrolyte, which differs from Example 1 in that the first monomer was not added. Details are as follows:

[0110] (1) Under an argon atmosphere, 2.4 mol of N-ethylacetamide and 0.6 mol of LiTFSI were poured into a 500 mL glass beaker and stirred at 25 °C for 30 min to form a homogeneous mixture.

[0111] (2) Add 1.2 mol of N-methyl-N-ethylacrylamide (DMAM-1), 3 mol of crosslinking agent N,N'-methylenebisacrylamide and 1.6 mol of photoinitiator 2-hydroxy-2-methylphenylacetone to the above eutectic mixture and stir at 25°C for 30 min to form a homogeneous precursor solution.

[0112] (3) The above homogeneous precursor liquid was coated onto a polytetrafluoroethylene mold and then irradiated under ultraviolet light (365nm) for 6 minutes to solidify into a film. The film thickness was controlled to be 10μm by a doctor blade to obtain a lithium-ion solid electrolyte.

[0113] Comparative Example 3

[0114] This comparative example prepared a lithium-ion solid electrolyte, which differs from Example 1 in that it prepared a halide lithium-ion solid electrolyte. Details are as follows:

[0115] Li3InCl6 and PTFE were added to a mortar at a mass ratio of 96:4, mixed evenly, and rolled to obtain a halide lithium-ion solid electrolyte with a thickness of 10 μm.

[0116] Test case

[0117] 1. Tensile strength test: The solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-3 were subjected to tensile stress-strain tests. To prepare samples for tensile testing, a homogeneous precursor solution was poured into a dumbbell-shaped polytetrafluoroethylene mold with effective dimensions of 16×4×2mm, followed by UV polymerization for 5min, with the tensile deformation rate set at 100mm / min.

[0118] 2. Ionic Conductivity Test: The ionic conductivity of the solid electrolyte was obtained by assembling a symmetrical cell with a steel sheet as the blocking electrode and measuring the electrochemical impedance spectroscopy on an electrochemical workstation at a frequency range of 0.1 Hz to 10 MHz, an amplitude of 10 mV, and a temperature of 25 °C. The calculation formula is as follows:

[0119] σ=L / (R b ·S)

[0120] Where S represents the effective contact area (cm²) between the electrolyte and the occluded electrode. 2 L represents the thickness (cm) of the solid polymer electrolyte membrane, and R represents the thickness of the solid polymer electrolyte membrane. b This represents the total impedance of the electrolyte (Ω).

[0121] 3. Electrical performance test: The solid electrolytes prepared in Examples 1-8 and Comparative Examples 1-3 were used to prepare cells for charge and discharge tests: the mold half-cell was charged at a constant current of 0.1C to 4.25V, charged at a constant voltage to 0.05C, and discharged at a constant current of 0.1C to 0.05V.

[0122] 4. Discharge capacity and cycle performance:

[0123] Solid-state lithium-ion batteries were prepared using the solid-state electrolytes prepared in Examples 1-8 and Comparative Examples 1-2. The specific steps are as follows:

[0124] (1) NCM811, VGCF and PVDF in a mass ratio of 96:2:2 were added to N-methylpyrrolidone (NMP), mixed to form a slurry, and then coated onto carbon-coated aluminum foil. The mixture was then vacuum dried at 92°C for 18 hours to obtain a positive electrode sheet. (2) A lithium metal sheet was used as the negative electrode. (3) The solid electrolyte prepared in Examples 1 to 8 or Comparative Examples 1 to 2 was placed directly between the negative and positive electrodes, allowing the solid electrolyte to penetrate and occupy the pores inside the porous electrode. The electrolyte was then heated and cured at 60°C for 12 hours. Finally, after electrode tab welding and vacuum encapsulation, an NCM811||Li all-solid-state lithium-ion battery was obtained.

[0125] Solid-state lithium-ion batteries were prepared using the solid electrolyte prepared in Comparative Example 3. The specific steps are as follows:

[0126] (1) NCM811, Li3InCl6, VGCF and PVDF in a mass ratio of 96:2:2 were added to N-methylpyrrolidone (NMP), mixed to form a slurry, and then coated onto carbon-coated aluminum foil. After the NMP evaporated naturally, it was vacuum dried at 92°C for 18 hours to obtain the positive electrode sheet. (2) A lithium metal sheet was used as the negative electrode. (3) The solid electrolyte prepared in Comparative Example 3 was directly placed between the negative and positive electrode sheets and stacked and bonded. After tab welding and vacuum sealing, the NCM811|Li3InCl6|Li all-solid-state lithium-ion battery was obtained.

[0127] Cyclic tests were conducted on the all-solid-state lithium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-3. At a temperature of 25±2°C, the batteries were first charged at 0.1C or a specified current to a termination voltage of 4.25V, with a cutoff current of 0.01C, and then allowed to rest for 30 minutes. The second step involved discharging at 0.1C to a final discharge voltage of 0.05V, recording the discharge capacity, and allowing the batteries to rest for 30 minutes. The cycle of steps one and two was repeated for 500 cycles to test the battery's cycle performance. All tests were conducted under a specific stacking pressure (50 kPa) load condition.

[0128] The test results are shown in Table 1.

[0129] Table 1

[0130]

[0131] Table 1 shows that, comparing Examples 1-8, the ionic conductivity of the eutectic mixture reaches its maximum when the molar ratio of NMA:LiTFSI is 4:1 (Example 1). As the lithium salt concentration decreases, the degree of lithium salt dissociation increases, leading to higher ionic conductivity in the eutectic mixture. However, excessively low lithium salt ratios result in lower ionic conductivity due to lower carrier concentrations. Comparing Examples 1, 1, and 2, the pure second monomer polymer exhibits excellent tensile strength but low fracture strength. The low fracture strength is due to the lack of interchain interactions, as the second monomer is miscible with the eutectic mixture, resulting in highly solvated molecular chains. The pure first monomer polymer exhibits extremely low elongation at break and high fracture strength. Copolymerizing the first monomer polymer (hard phase) and the second monomer polymer (soft phase) at a molar ratio of 4:1 results in a polymer that combines the tensile strength of the soft phase (second trimer polymer) and the strength of the hard phase (first monomer polymer).

[0132] In Example 1, the lithium-ion solid electrolyte with high room temperature ionic conductivity and good tensile properties is introduced into the internal structure of the porous electrode and tightly bonded with the active material particles inside the electrode, which solves the problem of electrode stress failure under low stacking pressure and achieves good cycle stability of the all-solid-state battery under low stacking pressure or even without external pressure.

[0133] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this is not limited herein.

[0134] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise explicitly specified.

[0135] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A lithium-ion solid electrolyte, characterized in that, The lithium-ion solid electrolyte comprises a polymer matrix, a lithium salt, and a polar organic compound; the polymer matrix comprises a first monomer and a second monomer.

2. The lithium-ion solid electrolyte according to claim 1, characterized in that, The first monomer includes at least one of acrylamide and its derivatives; Preferably, the second monomer comprises at least one of dimethacrylamide and its derivatives; Preferably, the molar ratio of the first monomer to the second monomer is (0.3-5):

1.

3. The lithium-ion solid electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium bis(oxalate)borate, lithium difluoromethanesulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium bis(fluorosulfonylimide), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium nitrate, lithium perchlorate, lithium chloride, lithium iodide, and lithium bromide. Preferably, the polar organic compound is selected from at least one of N-methylacetamide, N-ethylacetamide, 2-methylpropionamide, 1-methyl-3-propylimidazolium, triethylene glycol dimethyl ether, lactic acid, triethanolamine, glycerol, and urea; Preferably, the molar ratio of the lithium salt to the polar organic compound is 1:(1 to 10).

4. The lithium-ion solid electrolyte according to claim 1, characterized in that, The lithium-ion solid electrolyte further includes a crosslinking agent and an initiator; the crosslinking agent is selected from at least one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, trimethylolpropane triacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, polyethylene glycol dimethacrylate, divinylbenzene, triallylamine, bisacryloylcysteine, triacryloylhexahydro-1,3,5-triazine, and pentaerythritol tetraacrylate; the initiator is selected from at least one of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone, 2-hydroxy-2-methylphenylacetone, benzoin dimethyl ether, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and lithium phenyl-2,4,6-trimethylbenzoylphosphonate. Preferably, the molar ratio of the polymer matrix to the crosslinking agent is (0.5-4):1; Preferably, the molar ratio of the crosslinking agent to the initiator is (0.5-3):

1.

5. The method for preparing the lithium-ion solid electrolyte according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: A lithium salt and a polar organic compound are mixed to obtain a eutectic mixture; S2: Mix the first monomer and the second monomer with the eutectic mixture to obtain the precursor liquid; S3: After coating the precursor liquid onto the mold, it is cured to obtain the lithium-ion solid electrolyte.

6. The preparation method according to claim 5, characterized in that, Step S2 involves mixing the first monomer, the second monomer, the crosslinking agent, and the initiator with the eutectic mixture to obtain the precursor solution.

7. The preparation method according to claim 5, characterized in that, Step S3 involves curing under ultraviolet light for 5-8 minutes. Preferably, the thickness of the lithium-ion solid electrolyte film is 10–120 μm.

8. A solid-state lithium-ion battery, characterized in that, The solid-state lithium-ion battery includes a positive electrode, a negative electrode, and a lithium-ion solid electrolyte as described in any one of claims 1 to 4.

9. The solid-state lithium-ion battery according to claim 8, characterized in that, The positive electrode comprises, by weight percentage, 90-96% positive electrode active material, 0-5% positive electrode conductive agent and 0-5% positive electrode binder; The positive electrode active material includes at least one of lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium nickel manganese cobalt oxide, lithium-rich manganese base oxide, lithium cobalt oxide, and lithium manganese oxide. The positive electrode conductive agent includes at least one of VGCF, carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene. The positive electrode binder includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride hexafluoropropylene, polypropylene, polyethylene, and polyimide.

10. The solid-state lithium-ion battery according to claim 8, characterized in that, The negative electrode comprises, by weight percentage, 90-96% of the negative electrode active material, 0-5% of the negative electrode conductive agent and 0-5% of the negative electrode binder; The negative electrode active material includes at least one of the following: artificial graphite, natural graphite, silicon, silicon suboxide, pre-lithiated silicon suboxide, silicon carbide, lithium, aluminum-silicon alloy, lithium-indium alloy, lithium-tin alloy, and lithium-aluminum alloy. The negative electrode conductive agent includes at least one of VGCF, carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene. The negative electrode binder includes at least one of sodium hydroxymethyl cellulose, carboxymethyl cellulose, methyl cellulose, styrene-butadiene latex, polyacrylic acid, acrylic copolymers, cyclodextrin, styrene-butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polymethyl methacrylate, styrene-butadiene block copolymer, styrene-ethylene-butene-styrene block copolymer, and polyisobutylene.

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