Ionic liquid-based semi-solid electrolyte and semi-solid secondary battery

Abstract

The invention discloses an ionic liquid-based semi-solid electrolyte and a semi-solid secondary battery, the ionic liquid-based semi-solid electrolyte is obtained by in-situ polymerization of a precursor solution, and the precursor solution comprises fluorine-containing electrolyte salt, quaternary ammonium ionic liquid, an amide monomer and a wetting agent; positive ions of the fluorine-containing electrolyte salt comprise alkali metal ions and / or alkaline earth metal ions, and negative ions comprise negative ions for battery electrolyte; the amide monomer contains a polymerizable unsaturated bond; the wetting agent is polyhalogenated alkane; the structural formula of the quaternary ammonium ionic liquid is A < + > B <->; a < + > is a cyclic quaternary ammonium cation group or a chain quaternary ammonium cation group with N located on a C5-C8 saturated ring; b <-> is a fluorine-containing sulfonic acid anion, a fluorine-containing sulfimide anion, a fluoroborate anion, a fluorine-containing phosphate anion, a difluoro (oxalato) borate anion and a bis (oxalato) borate anion; the semi-solid secondary battery disclosed by the invention has the advantages of no liquid leakage, high thermal stability, high electrochemical stability, high cycle performance and the like.

Description

Technical Field

[0001] The present invention relates to the field of solid electrolytes for lithium-ion batteries, and in particular to an ionic liquid-based semi-solid electrolyte and a semi-solid secondary battery. Background Art

[0002] As a new energy storage device, lithium-ion batteries are widely used in various portable electronic devices, new energy vehicles, aerospace, and other fields due to their advantages such as high energy density, high operating voltage, and good cycle stability. Currently, most commercial lithium-ion batteries use organic liquid electrolytes, which pose a significant safety hazard due to the risks of leakage, gas expansion, combustion, and even explosion.

[0003] To address the volatilization, leakage, gas expansion, and flammability of liquid electrolytes, researchers have attempted to replace traditional organic liquid electrolytes with safer solid-state electrolytes. However, the low ionic conductivity and poor solid-solid interface of solid-state electrolytes severely limit their application. On the other hand, ionic liquid-based electrolytes have the advantages of being non-flammable, having a wide electrochemical window, and excellent thermal stability, and are therefore considered a hot electrolyte material. However, ionic liquid electrolytes also have problems such as low lithium ion transference number and leakage.

[0004] In-situ solidification is a recently emerging technology for preparing solid-state / semi-solid batteries. This technique typically involves thoroughly mixing appropriate polymer monomers, lithium salts, solvents, and initiators to form a precursor solution, which is then injected directly into the battery. Once the precursor has fully soaked the electrodes, in-situ polymerization occurs within the battery under thermal or electrochemical initiation conditions, resulting in the in-situ preparation of solid-state / semi-solid electrolytes. This in-situ solidification technique effectively avoids the leakage issues associated with traditional liquid electrolytes, preserving the electrolyte's high ionic conductivity and electrode compatibility. Furthermore, it seamlessly integrates with existing liquid lithium battery manufacturing processes and equipment, offering the advantages of mature manufacturing processes and low costs. Therefore, the use of in-situ solidification combined with highly safe ionic liquid electrolytes to prepare high-performance ionic liquid-based semi-solid electrolytes holds great promise for enabling lithium batteries to achieve both high safety and excellent electrochemical performance while meeting the requirements for large-scale manufacturing. This holds great commercial value and broad application prospects.

[0005] Most of the in-situ solidification technologies in existing technical solutions are based on the preparation of semi-solid electrolytes based on traditional organic solvent systems. These semi-solid electrolytes still retain highly flammable organic solvents or organic polymer components, which cannot solve the flammability and explosion problems of the electrolytes and make it difficult to ensure the safety of the batteries. The ionic conductivity of the polyionic liquid solid electrolytes in existing technical solutions is generally low, which makes it difficult to meet the application requirements of batteries at room temperature. The lithium ion migration number of the ionic liquid electrolyte in the existing technical solution is low, which can easily lead to uneven deposition of lithium metal; at the same time, the liquid electrolyte also has safety risks such as leakage. In view of this, it is necessary to develop an ionic liquid-based semi-solid electrolyte and a semi-solid secondary battery with low leakage risk, high lithium ion migration number, low interfacial impedance, high electrochemical stability, and good cycle performance. Summary of the Invention

[0006] The present invention addresses the problems of flammability, explosion and leakage of organic electrolytes in the prior art. The ionic liquid-based semi-solid electrolyte prepared by the present invention has the advantages of no leakage, thermal stability and electrochemical stability, and high cycle performance, which can effectively improve the safety and durability of the battery.

[0007] The polymer solid electrolyte prepared by traditional non-in-situ polymerization is difficult to be in close contact with the positive and negative electrodes, resulting in a large interfacial impedance, which limits the transmission of lithium ions and thus affects the electrochemical performance and cycle stability of the battery. The present invention adopts an in-situ curing technology to prepare an ionic liquid-based semi-solid electrolyte. This in-situ curing technology not only ensures the high ionic conductivity of the electrolyte, but also significantly improves the interfacial compatibility, allowing good contact between the electrode and the electrolyte, thereby effectively reducing the interfacial impedance between the electrode and the electrolyte, and further improving the electrochemical performance of the battery. At the same time, it also has the advantages of simple process and low processing cost.

[0008] To address the issues of ionic liquid electrolyte leakage and low lithium ion transference numbers, this technical solution incorporates cross-linkable amide monomers to form a polymer cross-linked network structure. This not only effectively restricts the mobility of the ionic liquid, thereby improving the electrolyte's curing ability, but also allows the amide bonds to form hydrogen bonds and coordination interactions with anions and cations, respectively, restricting their migration and thus increasing the lithium ion transference number. Ultimately, this enables the preparation of highly safe and high-performance semi-solid-state batteries.

[0009] The present invention is achieved through the following technical solutions:

[0010] The present invention first provides an ionic liquid-based semi-solid electrolyte, which is obtained by in-situ polymerization of a precursor solution;

[0011] The precursor solution includes a fluorine-containing electrolyte salt, a quaternary ammonium ionic liquid, an amide monomer, and a wetting agent;

[0012] The cations of the fluorine-containing electrolyte salt include alkali metal ions and / or alkaline earth metal ions, and the anions of the fluorine-containing electrolyte salt include fluorine-containing anions for battery electrolytes;

[0013] The amide monomer contains a polymerizable unsaturated bond;

[0014] The wetting agent is one or more polyhalogenated low-polarity alkanes;

[0015] The structural formula of the quaternary ammonium ionic liquid is A + B - ;

[0016] The A + It is a cyclic quaternary ammonium cationic group in which N is located on a C5-C8 saturated ring, or a chain quaternary ammonium cationic group;

[0017] The B - It is selected from one of the group consisting of fluorine-containing sulfonic acid anion groups, fluorine-containing sulfonimide anion groups, fluorine-containing borate anion groups, fluorine-containing phosphate anion groups, difluorooxalatoborate anion groups (DFOB-), and bisoxalatoborate anion groups (BOB-).

[0018] As a further solution, the A in the quaternary ammonium ionic liquid + Selected from one of the following structural formulas:

[0019]

[0020] (R)m means that there are m substituents R on the saturated ring, wherein the substituents R may be the same or different.

[0021] Wherein n=1-4;

[0022] Wherein m is an integer from 0 to n+3;

[0023] In the formula, R, R1-R6 are each independently selected from a substituted or unsubstituted C1-C8 alkyl group, a substituted or unsubstituted C1-C8 alkoxy group, and when substituted, the substituent is selected from a hydroxyl group, a carboxyl group, an amide group, an acyloxy group, an amino group, an aromatic group, a nitro group, a cyano group, an etheroxy group, a halogen group, and an aromaticoxy group.

[0024] As a further preferred embodiment, A+ in the quaternary ammonium ionic liquid is selected from one of the following structural formulas:

[0025] That is, A in the quaternary ammonium ionic liquid + wherein n=1 or n=2, and m=0; B- in the quaternary ammonium ionic liquid is selected from one of DFOB-, BF4-, TFSI-, FSI-, and PF6-;

[0026] Preferably, A+ in the ionic liquid is preferably a five-membered cyclic quaternary ammonium cationic group That is, A in quaternary ammonium ionic liquids + n = 1, and m = 0;

[0027] Preferably, the B- is preferably FSI-;

[0028] Preferably, said R1 and R2 are each independently an unsubstituted alkyl group;

[0029] Preferably, both R1 and R2 are C1-C6 alkyl groups;

[0030] Preferably, the quaternary ammonium ionic liquid is N-methyl, butylpyrrolidinobis(fluorosulfonyl)imide salt.

[0031] The alkali metal ions in the fluorine-containing electrolyte salt are selected from Li + 、Na + , K + At least one of the alkaline earth metal ions selected from Mg 2+ , Ca 2+ At least one of the 2+ ), aluminum ions (Al 3+ );

[0032] The fluorine-containing anion is selected from fluorine-containing organic anions or fluorine-containing inorganic anions,

[0033] The fluorine-containing organic anion is selected from TFSI - 、FSI - CF3SO3 - DFOB - 、BOB - One of the following;

[0034] The fluorine-containing inorganic anion is selected from PF6 - 、BF4 - PO2F2 - One of them.

[0035] The polyhalogenated low polarity alkane is selected from C1-C10 polyhalogenated low polarity alkane having 3 or more halogen atoms.

[0036] Further preferably, the polyhalogenated low polar alkane is selected from one or more of fluorinated low polar alkanes, chlorinated low polar alkanes, brominated low polar alkanes, fluorinated chlorinated low polar alkanes, fluorinated brominated low polar alkanes, and chlorinated brominated low polar alkanes, with fluorinated chlorinated low polar alkanes and fluorinated brominated low polar alkanes being preferred.

[0037] Further preferably, the carbon atoms of the polyhalogenated low polar alkane are selected from one of C1-C8 fluorinated chlorinated low polar alkane and fluorinated brominated low polar alkane.

[0038] Further preferably, the polyhalogenated low polar alkane is preferably one of C1-C5 fluorinated chlorinated low polar alkane and fluorinated brominated low polar alkane.

[0039] As a further preferred embodiment, the polyhalogenated low-polarity alkane is a halogenated propane.

[0040] As a further preferred embodiment, the number of halogen fluorine, chlorine and bromine atoms in the halopropane is preferably 4-5.

[0041] As a further preferred embodiment, the halogenated propane is selected from one or more of 2,3-dichloro-1,1,1-trifluoropropane, 1-chloro-3,3,3-trifluoropropane, 1,2-dichloro-1,1-difluoropropane, 2,3-dichloro-1,1,1-trifluoropropane, 1-fluoro-1,1,3-trichloropropane, 3-bromo-1,1,1-trifluoropropane and 1,3-dibromo-1,1-difluoropropane.

[0042] As a further preferred embodiment, the polyhalogenated low-polarity alkane is 2,3-dichloro-1,1,1-trifluoropropane.

[0043] The amide monomer is one of N, N-methylenebisacrylamide and its homologues;

[0044] Preferably, the amide monomer is N,N-methylenebisacrylamide.

[0045] As a further solution, the molar ratio of the fluorine-containing electrolyte salt, the amide monomer, the quaternary ammonium ionic liquid, and the wetting agent is (1-8): (1-4): (5-20): (2-10).

[0046] As a further preferred solution, the molar ratio of the fluorine-containing electrolyte salt, the amide monomer, the quaternary ammonium ionic liquid, and the wetting agent is 2:1:6:3.

[0047] The precursor solution further contains an initiator, which is selected from one or more of nitrile compounds, amide compounds, hydrogen peroxide compounds, acid compounds, ester compounds, ketone compounds, persulfate, benzoyl compounds, and hydrochloride;

[0048] As a further preferred embodiment, the initiator is selected from one or more nitrile compounds;

[0049] The initiator is selected from one or more of azobisisobutyronitrile, azoisobutylcyanamide, tert-butyl hydroperoxide, dimethyl azobisisobutyrate, persulfate, dimethyl azobisisobutyrate, methyl ethyl ketone peroxide, azobisisovaleronitrile, cyclohexanone peroxide, azobisisoheptonitrile, azobiscyclohexylcarbonitrile, azobiscyanovaleric acid, tert-butyl perbenzoate, benzoyl peroxide, and azobisisopropylimidazoline hydrochloride;

[0050] As a further preferred embodiment, the initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobiscyclohexylcarbonitrile.

[0051] As a further solution, the initiator is azobisisobutyronitrile.

[0052] As a further preferred example, the molar ratio of the initiator to the amide monomer is (1-2):(100-200).

[0053] As a further preferred example, the molar ratio of the initiator to the amide monomer is 1:100.

[0054] In a second aspect, the present invention further provides a secondary battery, wherein the semi-solid secondary battery includes a precursor solution, a positive electrode material, a separator, and a negative electrode material.

[0055] The active material in the positive electrode material is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium cobaltate, lithium titanate, lithium manganate, lithium nickel cobalt manganate, lithium-rich manganese-based oxide, layered nickel-rich NCM523, NCM811, NCM90, lithium nickelate, sodium vanadium phosphate, sodium vanadium oxyphosphate, layered transition metal oxides containing sodium ions and potassium ions, Prussian blue compounds, zinc salts, magnesium salts, and calcium salts of layered oxides.

[0056] The binder of the positive electrode material is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene glycol, and polyacrylic acid.

[0057] The conductive additive of the positive electrode material is selected from one or more of conductive carbon black, conductive graphite, fullerene, graphene, carbon fiber, and carbon nanotube.

[0058] The negative electrode material is selected from one or more of metallic lithium, graphite negative electrode, silicon-carbon negative electrode, carbon fiber, soft carbon negative electrode, hard carbon negative electrode, metallic magnesium, metallic zinc, metallic calcium, and metallic sodium.

[0059] The separator is selected from one or more of polypropylene membrane, polyethylene membrane, cellulose membrane and glass fiber membrane.

[0060] In a third aspect, the present invention further provides a method for preparing a secondary battery, comprising the following steps:

[0061] (1) Preparation of a precursor solution: fully stirring a fluorine-containing electrolyte salt, an ionic liquid solvent, a wetting agent, and an amide monomer, and then adding an initiator to obtain a precursor solution;

[0062] (2) A semi-solid secondary battery is prepared by adopting an in-situ curing technology: the precursor solution in step (1) is injected into a battery cell composed of a positive electrode material, a separator and a negative electrode material, and then the assembled battery is placed at a low temperature for standing, and the battery is placed at a high temperature for curing, wherein the standing temperature is 5-35°C and the standing time is 6-24 hours; the curing temperature is 40°C-90°C and the curing time is 2-24 hours.

[0063] As a further preferred solution, the standing temperature is 10-30° C., and the standing time is 6-24 hours; the curing temperature is 45° C.-80° C., and the curing time is 2-24 hours.

[0064] The characteristics and beneficial effects of the present invention are:

[0065] The present invention provides a simple ionic liquid-based semisolid electrolyte and semisolid secondary battery, offering advantages such as leak-proofness, high stability, and excellent cycling performance, effectively improving battery safety and durability. By utilizing a quaternary ammonium ionic liquid, an amide monomer, a polyhalogenated low-polarity alkane wetting agent, and a fluorine-containing electrolyte salt, the electrolyte overcomes the inherent contradictions of traditional semisolid electrolytes: high ionic conductivity, low mechanical strength, and low electrochemical stability, achieving a trinity of performance improvements. First, unlike imidazole and carbon-carbon double bond ionic liquids, the present invention adopts quaternary ammonium salt ionic liquids without unsaturated bonds, which can ensure high electrochemical stability and electrode compatibility, thereby improving the electrochemical performance of the battery; amide monomers are used as cross-linking agents to achieve their in situ polymerization, thereby forming a stable cross-linked network structure, and the rich C=O and NH functional groups on the amide monomers can form coordination and hydrogen bond interactions with quaternary ammonium cations, fluorine-containing anions, and polyhalogenated alkanes, respectively, thereby increasing the lithium ion migration number, which is beneficial to promoting the uniform deposition of lithium metal and improving the battery cycle performance; second, polyhalogenated low-polarity alkanes are used as wetting agents, and polyhalogenated solvents can synergistically act with amide monomers, which helps to improve the wettability of the precursor solution in the electrode and improve the consistency of in situ solidification. The NH functional groups on the amide polymer chain segments produce hydrogen bonds with halogen atoms, so after polymerization, the fluidity and reactivity of the solvent can be effectively reduced, thereby further reducing the liquid content of the semi-solid electrolyte and improving its electrochemical performance. At the same time, polyhalogenated low-polarity alkanes also have low reactivity, which can ensure the intrinsic safety and electrochemical stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1The discharge specific capacity and coulombic efficiency of the NCM90||Li semi-solid-state battery assembled in Example 1 at room temperature;

[0067] Figure 2 The battery charge and discharge curve diagram of Example 1 DETAILED DESCRIPTION

[0068] The present invention will be further described below through the accompanying drawings and specific embodiments, but it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, that is, they are not intended to limit the scope of protection of the present invention.

[0069] The polymer solid electrolyte prepared by traditional non-in-situ polymerization is difficult to be in close contact with the positive and negative electrodes, resulting in a large interfacial impedance, which limits the transmission of lithium ions and thus affects the electrochemical performance and cycle stability of the battery. The present invention adopts an in-situ curing technology to prepare an ionic liquid-based semi-solid electrolyte. This in-situ curing technology not only ensures the high ionic conductivity of the electrolyte, but also significantly improves the interfacial compatibility, allowing good contact between the electrode and the electrolyte, thereby effectively reducing the interfacial impedance between the electrode and the electrolyte, and further improving the electrochemical performance of the battery. At the same time, it also has the advantages of simple process and low processing cost.

[0070] To address the issues of ionic liquid electrolyte leakage and low lithium ion transference numbers, this technical solution incorporates cross-linkable amide monomers to form a polymer cross-linked network structure. This not only effectively restricts the mobility of the ionic liquid, thereby improving the electrolyte's solidification ability, but also through amide bonds, hydrogen bonds and coordination with anions and cations, restricting their migration, thereby increasing the lithium ion transference number. Ultimately, this enables the preparation of highly safe and high-performance solid-state batteries.

[0071] The present invention is achieved through the following technical solutions:

[0072] The present invention first provides an ionic liquid-based semi-solid electrolyte, which is obtained by in-situ polymerization of a precursor solution;

[0073] The precursor solution includes a fluorine-containing electrolyte salt, a quaternary ammonium ionic liquid, an amide monomer, and a wetting agent;

[0074] The cations of the fluorine-containing electrolyte salt include alkali metal ions and / or alkaline earth metal ions, and the anions include fluorine-containing anions for battery electrolytes;

[0075] The wetting agent is one or more polyhalogenated low-polarity alkanes;

[0076] The structural formula of the quaternary ammonium ionic liquid is A + B- ;

[0077] The A + It is a cyclic quaternary ammonium cationic group in which N is located on a C5-C8 saturated ring, or a chain quaternary ammonium cationic group;

[0078] The B - Selected from fluorine-containing sulfonic acid anion group, fluorine-containing sulfonimide anion group, fluorine-containing borate anion group, fluorine-containing phosphate anion group, difluorooxalate borate anion group (DFOB - ), bis(oxalatoborate) anion group (BOB - )

[0079] The present invention adopts the in-situ polymerization method of the precursor solution to prepare an ionic liquid-based semi-solid electrolyte. By specially adopting the mutual cooperation of quaternary ammonium ionic liquid, amide monomer, polyhalogenated low-polarity alkane wetting agent and fluorine-containing electrolyte salt, the contradiction of "high ion conductivity-low mechanical strength-low electrochemical stability" of the traditional semi-solid electrolyte is overcome, and the performance improvement of the trinity is achieved. Generally speaking, as the polymerization ability of the polymer electrolyte increases, the active sites available for ion transmission become fewer. At the same time, due to the increase in the compactness of the polymerization degree, the polymer layer tends to provide it with fewer ion transmission channels, so that the polymer electrolyte layer generally has the limitation of low ion conductivity. Although the ion conduction efficiency can be improved by adding some ionic liquid to the polymer layer, the ionic liquid has high fluidity and is prone to leakage and segregation, which puts higher binding requirements on the polymer. On the other hand, the introduction of the ionic liquid also brings about interface problems between the polymer and the active material particles of the electrode. A more complex interface relationship is generated between the two and between the active material particles of the electrode, which easily leads to the complexity of the stable interface construction and needs to take into account the ion transport and mechanical strength problems.

[0080] The present invention first adopts quaternary ammonium ionic liquid, the substitution structure of quaternary ammonium cation is completely saturated, without π electron system, its HOMO energy level is lower than other types (such as imidazole) ionic liquid, oxidation potential is improved, with higher electrochemical stability; simultaneously quaternary ammonium cation and amide monomer have stronger cross-linking polymerization, the alkyl chain of quaternary ammonium cation forms multiple hydrogen bonds with the amide group (-CONH-) of amide monomer, the alkyl in quaternary ammonium cation strengthens interface bonding through van der Waals force, quaternary ammonium cation serves as "cross-linking node", forms three-dimensional interpenetrating network with polyamide chain, limits ionic liquid migration, further reduces the mobility of ionic liquid in electrolyte, strengthens its binding effect in amide polymer, enables it to be better evenly distributed in the cross-linked layer formed by amide monomer polymerization, avoids ionic liquid from gathering in the cross-linked layer, ion conducting ability is more stable; the composite structure greatly strengthens the cross-linked layer composed of amide monomer to the anchoring effect of ionic liquid, prompts ionic liquid to be evenly distributed in the cross-linked layer. This synergistic effect circumvents the phase separation problem caused by aggregation of ionic liquid in traditional system, thereby improving the continuity and stability of ion transmission path.

[0081] Building on the above, the present invention further utilizes polyhalogenated low-polarity alkanes as wetting agents for ionic liquid-based semi-solid electrolytes. The polyhalogenated alkanes, due to their polyhalogen content, possess moderate polarity due to their strong electronegativity, resulting in improved basic wettability. The polyhalogenated polar alkanes selected in the present invention are particularly well-suited for multiple wetting between quaternary ammonium ionic liquids and amide monomers, as well as between these two and the active material particles in the electrode, improving multi-level interfaces and simultaneously enhancing electrochemical performance. Polyhalogenated low-polarity alkanes can effectively dissolve polar amide monomers, while stabilizing monomer molecules through solvation, promoting uniform dispersion, avoiding uneven polymerization caused by excessive local concentration of amide monomers, and improving the consistency of in-situ solidification; the introduction of polyhalogenated low-polarity alkanes regulates the high polarity of quaternary ammonium ionic liquids, and the NH functional groups in them can also produce hydrogen bonds with halogen atoms, thereby effectively reducing the fluidity of the ionic liquid, improving the binding of the ionic liquid in the cross-linked layer formed by the amide monomer, and improving its electrochemical performance, ensuring battery safety and electrochemical stability; halogen atoms can promote the decomposition of initiators, accelerate free radical generation, improve the polymerization efficiency of amide monomers, reduce activation energy by stabilizing transition states, and reduce reaction activation energy by stabilizing polymerization transition states, shortening curing time; halogen-containing low-polarity alkanes have low surface tension, which allows them to spread quickly on the surface of the active material particles of the electrode, enhancing their penetration into the porous electrode.

[0082] The present invention introduces a metal salt containing a halogen anion into the electrolyte salt, wherein the halogen group thereof forms a dynamic coordination effect with the quaternary ammonium cation group and the polyamide main chain, thereby promoting the dissociation of the lithium salt and increasing the number of lithium ion migrations. At the same time, the halogen anion group is preferentially adsorbed at the electrode interface, and can synergistically form a passivation layer rich in halogen elements with the halogen in the polyhalogenated wetting agent, thereby inhibiting the side reaction between the semi-solid electrolyte and the highly active electrode and improving the cycle stability. The anions in the fluorine-containing electrolyte salt can further consolidate the network structure composed of the cross-linked layer and the ionic liquid through electrostatic interaction with the quaternary ammonium cation in the ionic liquid and hydrogen bond cross-linking with the polyamide chain, thereby enhancing the mechanical strength, preventing leakage of the semi-solid electrolyte, and further improving the safety of the battery.

[0083] The present invention prepares an ionic liquid-based semi-solid electrolyte with high stability, high cycle performance and high safety through the synergy of the above-mentioned multiple components, simultaneously improving the ionic conductivity, mechanical strength and safety of the battery, overcoming the contradiction in the comprehensive improvement of the performance of traditional semi-solid electrolytes, and providing an efficient solution for high-safety, long-life semi-solid batteries.

[0084] As a further example, the A in the quaternary ammonium ionic liquid + Selected from one of the following structural formulas:

[0085]

[0086] (R)m means that there are m substituents R on the saturated ring, wherein the substituents R may be the same or different.

[0087] Wherein n=1-4;

[0088] Wherein m is an integer from 0 to n+3.

[0089] In the formula, R, R1-R6 are each independently selected from a substituted or unsubstituted C1-C8 alkyl group, a substituted or unsubstituted C1-C8 alkoxy group, and when substituted, the substituent is selected from a hydroxyl group, a carboxyl group, an amide group, an acyloxy group, an amino group, an aromatic group, a nitro group, a cyano group, an etheroxy group, a halogen group, and an aromaticoxy group.

[0090] As a further preferred example, the A in the quaternary ammonium ionic liquid + Selected from one of the following structural formulas:

[0091] That is, A in the quaternary ammonium ionic liquid + wherein n=1 or n=2, and m=0; wherein B in the quaternary ammonium ionic liquid - Selected from DFOB - 、BF4 - TFSI - 、FSI - PF6- One of the following;

[0092] Preferably, the A in the ionic liquid + Preferably a five-membered cyclic quaternary ammonium cationic group That is, A in quaternary ammonium ionic liquids + where n=1 and m=0;

[0093] Preferably, the B - FSI is preferred - ;

[0094] Preferably, said R1 and R2 are each independently an unsubstituted alkyl group;

[0095] Preferably, both R1 and R2 are C1-C6 alkyl groups;

[0096] Preferably, the quaternary ammonium ionic liquid is N-methyl, butylpyrrolidinobis(fluorosulfonyl)imide salt.

[0097] The quaternary ammonium ionic liquid N-methyl, butylpyrrolidine bis(fluorosulfonyl)imide salt used in the present invention has stronger electronegativity, high bond energy characteristics, and antioxidant properties because it contains 6 fluorine atoms. Compared with other halogen atoms, it has higher ion migration efficiency. Fluorine atoms weaken the Coulomb interaction between anions and lithium ions through the electron-withdrawing effect, promote the dissociation of lithium salts, and improve the lithium ion migration number. Compared with fluoroboric acid and fluorophosphate, fluorosulfonyl has higher thermal stability and high ionic conductivity, making the electrolyte resistant to high pressure and high temperature environments, further improving the safety of the battery. Fluorine atoms form weak hydrogen bonds with the amide group (-CONH-) of the polyamide main chain, further reducing the mobility of the ionic liquid in the electrolyte, and assisting the ionic liquid to build a denser three-dimensional cross-linked network, thereby improving mechanical strength.

[0098] The use of a five-membered saturated cyclic quaternary ammonium cation provides a more rigid structure than chain-type quaternary ammonium cations and six-membered rings. Its ring tension and steric hindrance reduce molecular vibration, resulting in a higher thermal decomposition temperature and greater mechanical strength, making it more suitable for high-temperature battery environments. When R1 and R2 on the ring are different and both are short-chain alkyl groups, the high dissociation degree of the methyl group in the N-methyl-butylpyrrolidinobis(fluorosulfonyl)imide salt ionic liquid works in conjunction with the interfacial stability of the butyl group to achieve a balance between conductivity and cycle life.

[0099] The alkali metal ions in the fluorine-containing electrolyte salt include Li + 、Na + , K + At least one of the alkaline earth metal ions, wherein the alkaline earth metal ions include Mg 2+ , Ca 2+ At least one of the 2+), aluminum ions (Al 3+ );

[0100] The anion is a fluorine-containing anion;

[0101] The fluorine-containing anion is selected from fluorine-containing organic anions or fluorine-containing inorganic anions;

[0102] The fluorine-containing organic anion is selected from TFSI - 、FSI - CF3SO3 - DFOB - 、BOB - One of the following;

[0103] The fluorine-containing inorganic anion is selected from PF6 - 、BF4 - PO2F2 - One of them.

[0104] Preferably, the fluorine-containing electrolyte salt is lithium bis(fluorosulfonyl)imide (LiFSI).

[0105] Lithium bis(fluorosulfonyl)imide (LiFSI) contains a sulfonyl imide group that is shared with quaternary ammonium ionic liquids. The combination can further improve ionic conductivity. Since the bis(fluorosulfonyl)imide group of LiFSI has a strong electron-withdrawing effect, it is easier to dissociate in the electrolyte and release a large amount of free Li + , significantly improving the ionic conductivity.

[0106] The polyhalogenated low-polarity alkane is selected from C1-C10 polyhalogenated alkanes having 3 or more halogen atoms;

[0107] Further preferably, the polyhalogenated low polar alkane is selected from one or more of fluorinated low polar alkanes, chlorinated low polar alkanes, brominated low polar alkanes, fluorinated chlorinated low polar alkanes, fluorinated brominated low polar alkanes, and chlorinated brominated low polar alkanes, with fluorinated chlorinated low polar alkanes and fluorinated brominated low polar alkanes being preferred;

[0108] Further preferably, the carbon atoms of the polyhalogenated low polarity alkane are selected from one of C1-C8 fluorinated chlorinated low polarity alkanes and fluorinated brominated low polarity alkanes;

[0109] Further preferably, the polyhalogenated low polarity alkane is preferably one of C1-C5 fluorinated chlorinated low polarity alkane and fluorinated brominated low polarity alkane;

[0110] Further preferably, the polyhalogenated low-polarity alkane is a halogenated propane;

[0111] Further preferably, the number of halogen fluorine, chlorine, and bromine atoms in the halopropane is preferably 4-5;

[0112] Further preferably, the halogenated propane is selected from one or more of 2,3-dichloro-1,1,1-trifluoropropane, 1-chloro-3,3,3-trifluoropropane, 1,2-dichloro-1,1-difluoropropane, 2,3-dichloro-1,1,1-trifluoropropane, 1-fluoro-1,1,3-trichloropropane, 3-bromo-1,1,1-trifluoropropane and 1,3-dibromo-1,1-difluoropropane;

[0113] More preferably, the polyhalogenated low-polarity alkane is 2,3-dichloro-1,1,1-trifluoropropane.

[0114] The present invention further optimizes the type of halogen atoms, with the optimal halogen atom comprising both fluorine and other halogens, and a total of five halogen atoms. This is because the combination of highly polar fluorine and moderately polar chlorine or bromine prevents swelling or phase separation of the crosslinked layer due to excessive hydrophilicity, the loss of network tightness and mechanical strength due to swelling, and the disruption of electrode uniformity and ion / electron transport pathways due to microscopic or macroscopic phase separation. Furthermore, the molecular size optimizes steric hindrance, balancing permeability and network stability.

[0115] When the polyhalogenated low-polarity alkane is a fluorine-free halogenated alkane, its polarity is too low and its hydrophobicity is too strong. This results in insufficient wetting and spreading ability on the surface and pores of the electrode particles, making it unable to effectively reduce the interfacial tension, resulting in poor contact between the electrode and electrolyte interface, significantly increasing the interfacial impedance, and seriously restricting the battery's rate performance and capacity.

[0116] Since short-chain halogenated alkanes have an optimal carbon chain length—neither too short nor too long, such as methyl halides, which are too polar, or hexane halides, which are too hydrophobic—this moderate polarity provides good compatibility with the polar groups of amide monomers, such as amino and carbonyl groups, enabling them to effectively wet and penetrate the polymer network, promoting uniform dispersion of the monomers and polymerization reactions.

[0117] Compared with long-chain halogenated alkanes, halogenated propanes have smaller molecular sizes and can more effectively penetrate into the porous structure of semi-solid electrolytes, reducing interfacial contact resistance and improving wettability. This property is crucial for the construction of ion transport pathways and the maintenance of interfacial stability. Short-chain halogenated hydrocarbons have lower viscosity and better fluidity, and can diffuse rapidly in the electrolyte to form a uniform solvation layer, reducing local concentration gradients, thereby improving the uniformity of the polymerization reaction and the long-term stability of the electrolyte. It avoids the difficulty of decomposition or increased side reactions caused by the large molecular weight of long-chain halogenated alkanes. In addition, halogenated propanes have good thermal and electrochemical stability and are suitable for use in semi-solid battery systems that require long-term cycling. Halogenated propanes can better penetrate the microporous structure of porous membranes or electrode materials, forming a uniform ion transport network and improving the overall electrochemical performance.

[0118] Therefore, in halogenated propanes, the highly polar fluorine atoms ensure a good wettability and permeability foundation; while the moderately polar chlorine atoms (or larger bromine atoms) play a key balancing role. On the one hand, the synergy of the two enables the overall polarity of the molecule to reach a "golden section point" - sufficient to effectively wet the interface while avoiding the risk of swelling or phase separation of the cross-linked layer caused by excessive hydrophilicity. On the other hand, the introduction of chlorine atoms (or bromine atoms) provides an optimized molecular size and steric hindrance effect, which effectively limits the excessive penetration of solvent molecules into the polymer network and helps maintain the stability of the electrode structure; at the same time, this moderate steric hindrance is combined with the optimized polarity to finely balance the contradiction between the penetration depth of the wetting agent inside the electrode and the disturbance of the electrode skeleton structure at the microscopic level, thereby ensuring excellent interfacial contact (low impedance) while maximizing the maintenance of the overall network stability and long-term cycle performance of the electrode.

[0119] The amide monomer is one of N,N methylene bis acrylamide and its homologues.

[0120] Preferably, the amide monomer is N,N-methylenebisacrylamide.

[0121] The double bonds of this amide monomer can polymerize to form a cross-linked network structure. Furthermore, the C=O and NH functional groups on the monomer chain can form coordination bonds and hydrogen bonds with cations and fluorinated anions, respectively, thereby restricting the migration of cations and anions in the electrolyte and increasing the number of lithium ion transferences. Compared to other amide monomers, acrylamide has a larger spacing between amide groups, resulting in stronger polarity and a linear or cross-linked network. The porosity can be controlled according to the degree of polymerization.

[0122] As a further example, the molar ratio of the fluorine-containing electrolyte salt, the amide monomer, the quaternary ammonium ionic liquid, and the wetting agent is (1-8): (1-4): (5-20): (2-10).

[0123] As a further preferred example, the molar ratio of the fluorine-containing electrolyte salt, the amide monomer, the quaternary ammonium ionic liquid, and the wetting agent is 2:1:6:3.

[0124] When the electrolyte contains excessive fluorine-containing electrolyte salt, the viscosity of the electrolyte may increase. + The migration number is reduced, hindering ion diffusion. When the amount of fluorine-containing electrolyte salt is insufficient, the conductivity decreases due to insufficient ion carrier concentration. When the proportion of amide monomers is low, the cross-linked network formed has larger pores and the structural strength is reduced. If there are too many amide monomers, the cross-linking density is too high, resulting in excessive structural rigidity, which hinders ion diffusion. Therefore, it is necessary to balance the amount of amide monomers so that the cross-linked network formed has a uniform porosity and pore size distribution, providing a rapid migration channel for Li+ and ensuring the mechanical strength of the electrolyte. The appropriate amount of quaternary ammonium ionic liquid allows the ionic liquid to fully fill the cross-linked network formed by the polymerization of amide monomers, avoiding the discontinuity or even absence of the ion migration network caused by insufficient ionic liquid content, and also avoids local aggregation caused by excessive ionic liquid content, reducing the ability of the cross-linked network formed by the polymerization of amide monomers to bind the ionic liquid, which in turn brings the risk of leakage. At the same time, wetting agents play a key role in processes such as interface optimization and polarity adjustment. Therefore, it is necessary to balance the amount to avoid swelling or phase separation of the cross-linked layer caused by excessive hydrophilicity, and to balance permeability and network stability. Only when the molar ratio of fluorine-containing electrolyte salt, amide monomer, quaternary ammonium ionic liquid and wetting agent is under certain conditions, can the halogen metal salt be better dispersed in the cross-linked network formed by the polymerization of amide monomer containing ionic liquid, and the ionic liquid can be better bound, thereby simultaneously meeting higher anti-electrolyte leakage performance, ion transmission efficiency and structural strength.

[0125] The precursor solution further contains an initiator, which is selected from one or more of nitrile compounds, amide compounds, hydrogen peroxide compounds, acid compounds, ester compounds, ketone compounds, persulfate, benzoyl compounds, and hydrochloride;

[0126] The initiator is selected from one or more of azobisisobutyronitrile, azoisobutylcyanamide, tert-butyl hydroperoxide, dimethyl azobisisobutyrate, persulfate, dimethyl azobisisobutyrate, methyl ethyl ketone peroxide, azobisisovaleronitrile, cyclohexanone peroxide, azobisisoheptonitrile, azobiscyclohexylcarbonitrile, azobiscyanovaleric acid, tert-butyl perbenzoate, benzoyl peroxide, azobisisopropylimidazoline hydrochloride and the like;

[0127] As a further preferred example, the initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobiscyclohexylcarbonitrile.

[0128] As a further preferred example, the initiator is azobisisobutyronitrile.

[0129] As a further preferred example, the molar ratio of the initiator to the amide monomer is (1-2):(100-200).

[0130] As a further preferred example, the molar ratio of the initiator to the amide monomer is 1:100.

[0131] The polyhalogenated low polar alkane is selected from one or more of fluorinated low polar alkanes, chlorinated low polar alkanes, brominated low polar alkanes, fluorinated-chlorinated low polar alkanes, fluorinated-brominated low polar alkanes, and chlorinated-brominated low polar alkanes.

[0132] In a second aspect, the present invention further provides a secondary battery, wherein the semi-solid secondary battery comprises a precursor solution, an initiator, a positive electrode material, a separator, and a negative electrode material.

[0133] The active material in the positive electrode material is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, lithium cobaltate, lithium titanate, lithium manganate, lithium nickel cobalt manganate, lithium-rich manganese-based oxide, layered nickel-rich NCM523, NCM811, NCM90, lithium nickelate, sodium vanadium phosphate, sodium vanadium oxyphosphate, layered transition metal oxides containing sodium ions and potassium ions, Prussian blue compounds, zinc salts, magnesium salts, and calcium salts of layered oxides.

[0134] The binder of the positive electrode material is selected from one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyethylene glycol, and polyacrylic acid.

[0135] The conductive additive of the positive electrode material is selected from one or more of conductive carbon black, conductive graphite, fullerene, graphene, carbon fiber, and carbon nanotube.

[0136] The negative electrode material is selected from one or more of metallic lithium, graphite negative electrode, silicon-carbon negative electrode, carbon fiber, soft carbon negative electrode, hard carbon negative electrode, metallic magnesium, metallic zinc, metallic calcium, and metallic sodium.

[0137] The separator is selected from one or more of polypropylene membrane, polyethylene membrane, cellulose membrane and glass fiber membrane.

[0138] In a third aspect, the present invention further provides a method for preparing a secondary battery, comprising the following steps:

[0139] (1) Preparation of a precursor solution: fully stirring a fluorine-containing electrolyte salt, a quaternary ammonium ionic liquid, a wetting agent, and an amide monomer to obtain a uniform precursor solution, and then adding an initiator to obtain a precursor solution;

[0140] (2) A semi-solid secondary battery is prepared by using an in-situ curing technology: the precursor solution in step (1) is injected into a battery cell consisting of a positive electrode material, a separator and a negative electrode material, and the assembled battery is then allowed to stand and cure. The standing temperature is 5-35°C and the standing time is 6-24 hours; the curing temperature is 40°C-90°C and the curing time is 2-24 hours.

[0141] As a further preferred solution, the standing temperature is 10-30° C., and the standing time is 6-24 hours; the curing temperature is 45° C.-80° C., and the curing time is 2-24 hours.

[0142] In order to facilitate understanding of the present invention, the present invention will be described in more detail below, and embodiments of the present invention are given, but the scope of the present invention is not limited thereby.

[0143] Example 1:

[0144] 2 mol of lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) and 1 mol of amide monomer N,N-methylenebis(acrylamide) were dissolved in 6 mol of N-methyl, butylpyrrolidine bis(fluorosulfonyl)imide ionic liquid solvent and 3 mol of 2,3-dichloro-1,1,1-trifluoropropane wetting agent. The mixture was stirred at room temperature for 2 hours to obtain a uniform precursor solution. 0.01 mol of azobis(isobutyronitrile), a thermal initiator, was added to the solution and stirred at room temperature for 10 minutes to obtain a uniform mixed solution. Using NCM90 as the positive electrode material, pure lithium (Li) as the negative electrode material, and polypropylene film as the separator, the positive electrode shell, NCM90, polypropylene film, Li sheet, stainless steel sheet, spring, and negative electrode shell were stacked in sequence, and the mixed solution was then injected to assemble the lithium-ion battery. After assembly, the battery was placed at 20°C for 12 hours to ensure that the solution completely penetrated the interior of the electrode. The battery was then placed in a 60°C oven and heat-cured for 6 hours to obtain a solid-state battery. The battery was placed in a battery test cabinet at 25°C and subjected to charge and discharge cycle testing. The test voltage range was 2.8V-4.3V, and the test rate was 0.1C activation for 5 times and 0.2C cycle for up to 200 times.

[0145] Example 2:

[0146] The only difference from Example 1 is that lithium bis(fluorosulfonyl)imide (LiFSI) is replaced by lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0147] Example 3:

[0148] The only difference from Example 1 is that the N-methyl, butyl pyrrolidine bis(trifluoromethanesulfonyl)imide ionic liquid in Example 1 is replaced by tetraethylammonium bis(trifluoromethanesulfonyl)imide ionic liquid ([N 2222 ][TFSI]), the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0149] Example 4:

[0150] The only difference from Example 1 is that the N-methyl, butylpyrrolidine bis(fluorosulfonyl)imide salt ionic liquid in Example 1 is replaced by N-methyl, butylpiperidinium bis(trifluorosulfonyl)imide salt ionic liquid ([MBPip][TFSI]), and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0151] Example 5:

[0152] The only difference from Example 1 is that the 2,3-dichloro-1,1,1-trifluoropropane wetting agent in Example 1 is replaced with 2,3-dichloro-1,1,1-tribromopropane, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0153] Example 6:

[0154] The only difference from Example 1 is that the 2,3-dichloro-1,1,1-trifluoropropane wetting agent in Example 1 is replaced with 2,2-dichloro-1,1,1-trifluoroethane, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0155] Example 7:

[0156] The only difference from Example 1 is that the 2,3-dichloro-1,1,1-trifluoropropane wetting agent in Example 1 is replaced with 1,1,1,3,3-pentafluoropropane. The remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0157] Example 8:

[0158] The only difference from Example 1 is that the 2,3-dichloro-1,1,1-trifluoropropane wetting agent in Example 1 is replaced by 1-chloro-3,3,3-trifluoropropane. The remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0159] Example 9:

[0160] The only difference from Example 1 is that the initiator azobisisobutyronitrile is replaced by benzoyl peroxide, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0161] Example 10:

[0162] The difference from Example 1 is that the content of the amide monomer is increased from 1 mol to 2 mol. The remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0163] Example 11:

[0164] The difference from Example 1 is that the content of LiFSI salt is increased from 2 mol to 4 mol, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0165] Example 12:

[0166] The difference from Example 1 is that the high-temperature curing temperature is set to 45° C. and the time is 12 hours. The remaining components, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0167] Comparative Example 1:

[0168] The difference from Example 1 is that the amide monomer N,N-methylenebisacrylamide is replaced by methyl methacrylate (CH2=C(CH3)COOCH3), and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0169] Comparative Example 2:

[0170] The difference from Example 1 is that no initiator is added, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0171] Comparative Example 3:

[0172] The difference from Example 1 is that the heating and curing time at 60° C. is 1 hour, and the remaining compositions, preparation methods, battery assembly and testing methods are the same as those in Example 1.

[0173] Comparative Example 4:

[0174] The difference from Example 1 is that the wetting agent 2,3-dichloro-1,1,1-trifluoropropane is replaced by n-butyl ether, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0175] Comparative Example 5: The difference from Example 1 is that the N-methyl, butylpyrrolidine bis(fluorosulfonyl)imide salt ionic liquid in Example 1 is replaced by tetrabutylphosphine bis(trifluoromethanesulfonyl)imide salt ([P4444]NTf2), and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0176] Comparative Example 6:

[0177] The difference from Example 1 is that the N-methyl, butylpyrrolidine bis(fluorosulfonyl)imide salt ionic liquid in Example 1 is replaced by 1-allyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt ionic liquid, and the remaining composition, preparation method, battery assembly and testing methods are the same as those in Example 1.

[0178] To illustrate the effectiveness of the present invention in detail, the electrochemical performance tests were performed on Examples 1-8 and Comparative Examples 1-12:

[0179] Performance test: The lithium ion migration number test method refers to the Bruce-Vincent method, by assembling Li / Li symmetrical batteries and formula The battery coulombic efficiency and capacity retention rate test method is to assemble NCM90 / Li batteries, place the batteries in a 25°C battery test cabinet, and perform charge and discharge cycle tests. The test voltage range is 2.8V-4.3V, and the test rate is 0.1C activation for 5 times and 0.2C cycle for up to 200 times. The specific test items are as follows:

[0180] (1) Lithium ion migration number

[0181] (2) First discharge specific capacity

[0182] (3) First Coulomb efficiency

[0183] (4) Average Coulomb efficiency

[0184] (5) Capacity retention rate at the 200th cycle

[0185] The results of the performance test are shown in the following table:

[0186] Table 1 Electrochemical performance test results

[0187] Serial number Lithium ion migration number First discharge specific capacity (mAh / g) First coulombic efficiency (%) Average Coulombic efficiency (%) Capacity retention rate at the 200th cycle (%) Example 1 0.63 212 90.3 99.9 91.4 Example 2 0.59 204 89.7 99.8 90.2 Example 3 0.55 195 87.1 98.9 90.2 Example 4 0.53 203 86.8 98.7 90.5 Example 5 0.53 189 86.5 95.2 86.8 Example 6 0.55 192 86.8 96.8 89.1 Example 7 0.51 190 86.2 95.9 87.2 Example 8 0.57 206 87.1 97.9 90.1 Example 9 0.5 183 84.1 94.6 86.3 Example 10 0.49 189 83.6 95.7 85.4 Example 11 0.51 179 83.2 94.2 87.3 Example 12 0.55 187 87.2 96.9 88 Comparative Example 1 0.21 162 75.8 90.8 80.2 Comparative Example 2 0.25 154 76.5 91.5 81.6 Comparative Example 3 0.32 173 82.1 93.1 82.1 Comparative Example 4 0.32 169 81.4 92.8 82.5 Comparative Example 5 0.47 176 80.2 93.1 83.2 Comparative Example 6 0.46 174 81.2 93.4 84.6

[0188] The above results fully demonstrate that the ionic liquid-based semi-solid electrolyte of the present invention has good electrode compatibility, can ensure the long-term cycle stability of the battery, has a high cycle capacity retention rate, and has a high coulombic efficiency.

[0189] Table 1 compares the lithium ion transference numbers of the electrolytes of different embodiments and comparative examples and the first discharge specific capacity, first coulombic efficiency, average coulombic efficiency and capacity retention rate after 200 cycles of the NCM90||Li batteries assembled therefrom.

[0190] Figure 1The discharge specific capacity and coulombic efficiency of the NCM90||Li semi-solid-state battery assembled in Example 1 at room temperature are shown. It can be found that the use of the ionic liquid-based semi-solid electrolyte of the present invention can enable the battery to achieve high discharge specific capacity (≥200 mAh / g), high average coulombic efficiency (≥99.9%), and high capacity retention (capacity retention ≥91.4% after 200 cycles).

[0191] Figure 2 The charge-discharge curves for the battery in Example 1 show that this battery also exhibits a small increase in polarization voltage, demonstrating its excellent electrochemical stability. These results fully demonstrate that the ionic liquid-based semi-solid electrolyte of the present invention has good electrode compatibility, ensuring long-term battery cycle stability and high coulombic efficiency.

[0192] By comparing Example 1 and Comparative Example 1, it is found that compared with the addition of methyl methacrylate (CH2=C(CH3)COOCH3), the use of amide monomer N,N-methylenebisacrylamide can polymerize to form a more stable cross-linked network structure. This may be because the C=O and NH functional groups on the monomer chain segments can form coordination bonds and hydrogen bond interactions with cations and fluorine-containing anions, respectively, thereby restraining the migration of cations and anions in the electrolyte and increasing the lithium ion migration number. The lithium ion migration number of the semi-solid electrolyte of the present invention is significantly improved, and the assembled battery has higher coulombic efficiency and capacity retention rate, indicating that it can effectively improve the battery cycle stability.

[0193] Through Comparative Example 2 and Comparative Example 3, compared with Example 1, it can be found that when no initiator is added or the curing time is short, the amide monomer is difficult to polymerize or the degree of polymerization is insufficient, resulting in its residual monomer easily undergoing irreversible side reactions with the electrode, thereby deteriorating the battery performance and ultimately reducing the coulombic efficiency and capacity retention rate of the battery.

[0194] It can be found from Example 1 and Comparative Example 4 that if other wetting agents, such as n-butyl ether, are added, the semi-solid electrolyte may not be evenly distributed due to the inability of the precursor solution to completely infiltrate the diaphragm and the electrode. The lack of the solvation effect of the wetting agent to stabilize the amide monomer will cause the local concentration of the amide monomer to be too high or too low, which will lead to uneven polymerization. At the same time, the binding ability of the ionic liquid in the cross-linked layer is poor, which will affect the transmission path of lithium ions, and ultimately affect the battery capacity and cycle stability.

[0195] Comparative Examples 5 and 6 show that, compared with saturated five-membered rings, imidazole ionic liquids with conjugated structures containing unsaturated bonds are more susceptible to redox reactions. The five-membered ring of the imidazole cation contains both conjugated double bonds C═N and C═C. Its delocalized π electrons are easily oxidized at high voltages, causing the imidazole ring to lose electrons and generate free radical cations, which further decompose into pyridine derivatives and nitrogen-containing gases, consuming active lithium and causing electrolyte failure. At low potentials, the imidazole double bonds can accept electrons and undergo hydrogenation reactions, forming saturated heterocyclic compounds, which destabilize the ionic liquid structure. This results in low battery capacity, low coulombic efficiency, and low capacity retention. This further demonstrates that quaternary ammonium salt-based ionic liquids without unsaturated bonds have higher electrochemical stability, thereby ensuring good electrochemical performance. Using other types of ionic liquids, such as tetrabutylphosphonium bis(trifluoromethanesulfonyl imide), lacks the stronger ion-dipole coordination between the quaternary ammonium cation and the amide monomer, which is not conducive to binding the ionic liquid and results in poorer performance.

[0196] It can be found from Examples 1 to 12 that the semi-solid electrolyte prepared within the conditions specified in the present invention has a high lithium ion transference number (all ≥0.49), and the semi-solid battery can ensure good cycle stability and high coulombic efficiency.

[0197] By comparing Example 1 with Example 2, it can be seen that when lithium bis(trifluoromethylsulfonyl)imide (LiFSI) is replaced by lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), its lithium ion transference number, first coulombic efficiency and 200 cycle capacity retention rate are all lower than those in Example 1. This may be due to the low dissociation degree of lithium bis(trifluoromethylsulfonyl)imide: Li + It is easy to form a compact ion with TFSI-, free Li + The concentration is reduced. The decomposition products of the anion TFSI- in lithium bis(fluorosulfonyl)imide may be different from those of FSI- in LiFSI, which may lead to differences in the density, ionic conductivity, and stability of the SEI film, thereby affecting the coulombic efficiency. Lithium bis(trifluoromethylsulfonyl)imide may be more likely to undergo side reactions at the electrode / electrolyte interface (such as gas production, corrosion of the current collector, and generation of an interface layer with greater impedance) than lithium bis(fluorosulfonyl)imide, or its ion pair structure may be more likely to induce uneven deposition (lithium dendrites) during the cycle. Since lithium bis(fluorosulfonyl)imide contains a sulfonyl imide group shared with quaternary ammonium ionic liquids, its combination can further improve ionic conductivity. Since its bis(fluorosulfonyl)imide group has a strong electron-withdrawing effect, it is easier to dissociate in the electrolyte, releasing a large amount of free Li+, significantly improving ionic conductivity.

[0198] By comparing Example 1 with Example 3 and Example 4, when the ionic liquid is replaced by a six-membered ring N-methyl, butylpiperidinium bis(fluorosulfonyl)imide salt ionic liquid or a linear tetraethylammonium bis(trifluoromethanesulfonyl)imide salt ionic liquid, the lithium ion migration number, the first-round coulombic efficiency and the 200-cycle capacity retention rate are all lower than those in Example 1. This may be because the five-membered ring cyclic quaternary ammonium cation has a certain tension compared to the six-membered ring and chain quaternary ammonium cation, and the thermodynamic stability is higher, it is not easy to cause side reactions due to structural distortion, and the rigid structure has higher mechanical strength.

[0199] Comparing Examples 1, 6, and 8 with Examples 5 and 7, when the wetting agent contains both fluorine and chlorine, or fluorine and bromine, the performance is better than that of halogenated alkanes containing only fluorine or other halogen elements. This is because the strong polarity of fluorine and the moderate polarity of chlorine are balanced, avoiding swelling or phase separation of the cross-linked layer due to excessive hydrophilicity. At the same time, its molecular size can optimize steric hindrance and balance permeability and network stability.

[0200] Comparing Examples 1 and 8 with Example 6, when the halogen atoms include both fluorine and chlorine and are halogenated propanes, the performance is better. This may be because compared with other halogenated alkanes, halogenated propanes have smaller molecular sizes and can more effectively penetrate into the porous structure of the semi-solid electrolyte, reducing the interfacial contact resistance and improving the wettability.

[0201] Comparing Example 1 and Example 8, when the wetting agent is replaced with 1-chloro-3,3,3-trifluoropropane, the lithium ion migration number and the 200-cycle capacity retention rate are lower than those in Example 1. This may be due to the different number of halogen substitutions, resulting in differences in the polarity and hydrophilicity of the wetting agent, and thus leading to differences in its compatibility and wetting ability with the amide monomer.

[0202] Comparing Example 1 with Example 9, when the initiator is azobisisobutyronitrile, the performance is better. Since two stable isobutyronitrile free radicals are generated by homolysis, the free radical activity is moderate, the initiation efficiency is higher, the decomposition temperature is lower, and it is suitable for polymerization reactions under mild conditions; while benzoyl peroxide requires a higher temperature.

[0203] Compared with Example 1, Example 10, and Example 11, when the molar ratio of lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) and amide monomer N,N-methylenebisacrylamide is 2:1, the performance is better. This is because the bis(fluorosulfonyl)imide group of LiFSI has a strong electron-withdrawing effect, which makes it easier to dissociate in the electrolyte and release a large amount of free Li + , significantly improving ionic conductivity. However, excessive LiFSI (such as too high a molar ratio) may increase the viscosity of the electrolyte and hinder ion migration. When the proportion of amide monomers is low, the cross-linked network formed has a moderate porosity and pore size distribution, which is Li +It provides a fast migration channel and ensures the mechanical strength of the electrolyte. If there are too many amide monomers, the cross-linking density will be too high, resulting in excessive structural rigidity and hindering ion diffusion.

[0204] By comparing Example 1 and Example 12, it can be seen that the high-temperature curing temperature and time have an impact on the degree of polymerization and the strength of the polymer. Increasing the curing temperature can accelerate the movement of the molecular chain, significantly increase the rates of initiator decomposition, chain growth and cross-linking reactions, shorten the gelation time, and further affect the cross-linking strength, affecting the lithium ion migration number and 200 cycle capacity retention rate.

[0205] In summary, in response to the problems of flammability, explosion and leakage of organic electrolytes in the prior art, an ionic liquid-based semi-solid electrolyte with the advantages of no leakage, strong thermal stability, strong electrochemical stability and high cycle performance has been invented, which can effectively improve the safety and durability of the battery. The present invention adopts in-situ curing technology to prepare an ionic liquid-based semi-solid electrolyte. Through this in-situ curing technology, not only can the high ionic conductivity of the electrolyte be guaranteed, but also the interfacial compatibility can be significantly improved, so that the contact between the electrode and the electrolyte is good, thereby effectively reducing the interfacial impedance between the electrode and the electrolyte, and further improving the electrochemical performance of the battery. At the same time, it also has the advantages of simple process and low processing cost. In response to the problems of easy leakage and low lithium ion migration number of ionic liquid electrolytes, this technical solution can form a polymer cross-linked network structure by adding a cross-linkable amide monomer. Not only can the mobility of the ionic liquid be effectively restrained to improve the curing ability of the electrolyte, but also the amide bond can generate hydrogen bonds and coordination effects with anions and cations respectively, restraining the migration of anions and cations, thereby increasing the lithium ion migration number. Ultimately, the preparation of a highly safe and high-performance semi-solid battery is achieved.

[0206] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ionic liquid-based semi-solid electrolyte, characterized in that The ionic liquid-based semi-solid electrolyte is obtained by in-situ polymerization of a precursor solution; The precursor solution includes a fluorine-containing electrolyte salt, a quaternary ammonium ionic liquid, an amide monomer, and a wetting agent; The cations of the fluorine-containing electrolyte salt include alkali metal ions and / or alkaline earth metal ions, and the anions include fluorine-containing anions for battery electrolytes; The amide monomer contains a polymerizable unsaturated bond; The wetting agent is one or more polyhalogenated alkanes; The structural formula of the quaternary ammonium ionic liquid is A + B - ; The A + It is a cyclic quaternary ammonium cationic group in which N is located on a C5-C8 saturated ring, or a chain quaternary ammonium cationic group; The B - Selected from fluorine-containing sulfonic acid anion group, fluorine-containing sulfonimide anion group, fluorine-containing borate anion group, fluorine-containing phosphate anion group, difluorooxalate borate anion group (DFOB - ), bis(oxalatoborate) anion group (BOB - ) 2. An ionic liquid-based semi-solid electrolyte according to claim 1, characterized in that The A in the quaternary ammonium ionic liquid + Selected from one of the following structural formulas: Wherein n=1-4; Wherein m is an integer from 0 to n+3; In the formula, R, R1-R6 are each independently selected from a substituted or unsubstituted C1-C8 alkyl group, a substituted or unsubstituted C1-C8 alkoxy group, and when substituted, the substituent is selected from a hydroxyl group, a carboxyl group, an amide group, an acyloxy group, an amino group, an aromatic group, a nitro group, a cyano group, an etheroxy group, a halogen group, and an aromaticoxy group.

3. An ionic liquid-based semi-solid electrolyte according to claim 2, characterized in that: The A in the quaternary ammonium ionic liquid + wherein n=1 or n=2, and m=0; wherein B in the quaternary ammonium ionic liquid - Selected from DFOB - 、BF4 - TFSI - 、FSI - PF6 - One of the following; Preferably, the A in the quaternary ammonium ionic liquid + where n=1 and m=0; Preferably, the B - For FSI - ; Preferably, said R1 and R2 are each independently an unsubstituted alkyl group; Preferably, both R1 and R2 are C1-C6 alkyl groups; Preferably, the quaternary ammonium ionic liquid is N-methyl, butylpyrrolidinobis(fluorosulfonyl)imide salt.

4. The ionic liquid-based semi-solid electrolyte according to claim 1, characterized in that: The alkali metal ions in the fluorine-containing electrolyte salt include Li + 、Na + , K + At least one of the alkaline earth metal ions, wherein the alkaline earth metal ions include Mg 2+ , Ca 2+ At least one of the 2+ ), aluminum ions (Al 3+ ); The fluorine-containing anion is selected from fluorine-containing organic anions or fluorine-containing inorganic anions; The fluorine-containing organic anion is selected from TFSI - 、FSI - CF3SO3 - DFOB - 、BOB - One of the following; The fluorine-containing inorganic anion is selected from PF6 - 、BF4 - PO2F2 - One of them.

5. The ionic liquid-based semi-solid electrolyte according to claim 1, characterized in that: The polyhalogenated alkane is selected from C1-C10 polyhalogenated alkanes having 3 or more halogen atoms; Further preferably, the polyhalogenated alkane is selected from one or more of fluorinated low polar alkanes, chlorinated low polar alkanes, brominated low polar alkanes, fluorinated chlorinated low polar alkanes, fluorinated brominated low polar alkanes, and chlorinated brominated low polar alkanes, with fluorinated chlorinated low polar alkanes and fluorinated brominated low polar alkanes being preferred; Further preferably, the polyhalogenated alkane is selected from one of C1-C8 fluorinated chlorinated low polarity alkanes and fluorinated brominated low polarity alkanes; Further preferably, the polyhalogenated alkane is preferably one of a C1-C5 fluorinated chlorinated low polar alkane and a fluorinated brominated low polar alkane; Further preferably, the polyhalogenated alkane is a halopropane; Further preferably, the number of halogen fluorine, chlorine, and bromine atoms in the halopropane is preferably 4-5; Further preferably, the halogenated propane is selected from one or more of 2,3-dichloro-1,1,1-trifluoropropane, 1-chloro-3,3,3-trifluoropropane, 1,2-dichloro-1,1-difluoropropane, 2,3-dichloro-1,1,1-trifluoropropane, 1-fluoro-1,1,3-trichloropropane, 3-bromo-1,1,1-trifluoropropane and 1,3-dibromo-1,1-difluoropropane; More preferably, the polyhalogenated alkane is 2,3-dichloro-1,1,1-trifluoropropane.

6. The ionic liquid-based semi-solid electrolyte according to claim 1, characterized in that: The amide monomer is one of N, N-methylenebisacrylamide and its homologues; Preferably, the amide monomer is N,N-methylenebisacrylamide.

7. The ionic liquid-based semi-solid electrolyte according to claim 1, characterized in that: The molar ratio of the fluorine-containing electrolyte salt, the amide monomer, the quaternary ammonium ionic liquid, and the wetting agent is (1-8): (1-4): (5-20): (2-10); Preferably, the molar ratio of the fluorine-containing electrolyte salt, the amide monomer, the quaternary ammonium ionic liquid, and the wetting agent is 2:1:6:

3.

8. The ionic liquid-based semi-solid electrolyte according to claim 1, characterized in that: The precursor solution further contains an initiator, which is selected from one or more of nitrile compounds, amide compounds, hydrogen peroxide compounds, acid compounds, ester compounds, ketone compounds, persulfate, benzoyl compounds, and hydrochloride; Preferably, the initiator is selected from one or more nitrile compounds; Preferably, the initiator is selected from one or more of azobisisobutyronitrile, azoisobutylcyanamide, tert-butyl hydroperoxide, dimethyl azobisisobutyrate, persulfate, dimethyl azobisisobutyrate, methyl ethyl ketone peroxide, azobisisovaleronitrile, cyclohexanone peroxide, azobisisoheptonitrile, azobiscyclohexylcarbonitrile, azobiscyanovaleric acid, tert-butyl perbenzoate, benzoyl peroxide, and azobisisopropylimidazoline hydrochloride; Further preferably, the initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azobiscyclohexylcarbonitrile; Further preferably, the initiator is azobisisobutyronitrile; Further preferably, the molar ratio of the initiator to the amide monomer is (1-2):(100-200); More preferably, the molar ratio of the initiator to the amide monomer is 1:

100.

9. A secondary battery, characterized in that: The invention comprises the ionic liquid-based semi-solid electrolyte according to any one of claims 1 to 8, and further comprises a positive electrode material, a separator and a negative electrode material.

10. The method for preparing a secondary battery according to claim 9, wherein: The steps include: S1: Preparation of precursor solution: Fluorine-containing electrolyte salt, quaternary ammonium ionic liquid, wetting agent and amide monomer are thoroughly stirred and then an initiator is added to obtain a precursor solution; S2: preparing a semi-solid secondary battery using an in-situ curing technology: injecting the precursor solution in step S1 into a battery cell comprising a positive electrode material, a separator, and a negative electrode material, and allowing the assembled battery to stand for curing at a temperature of 5-35°C for 6-24 hours; and curing at a temperature of 40-90°C for 2-24 hours. Preferably, the standing temperature is 10-30° C., and the standing time is 6-24 hours; the curing temperature is 45-80° C., and the curing time is 2-24 hours.

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