Gel electrolyte precursor fluid, gel electrolyte, lithium secondary battery and preparation method therefor

Abstract

The present disclosure relates to the field of batteries. Provided are a gel electrolyte precursor fluid, a gel electrolyte solution, a lithium secondary battery and a preparation method therefor. The gel electrolyte precursor fluid comprises a reaction monomer, a cross-linking agent, an initiator and an electrolyte solution, wherein the reaction monomer comprises at least one of the compounds represented by formula 1, and the cross-linking agent comprises at least one of the compounds represented by formula 2-1 and formula 2-2. The gel electrolyte prepared from the gel electrolyte precursor fluid has relatively high oxidation resistance, and also has a relatively high ionic conductivity and a relatively high mechanical strength.

Description

Gel electrolyte precursor liquid, gel electrolyte, lithium secondary battery and preparation method thereof

[0001] Priority information

[0002] This disclosure claims priority to and the benefits of patent application No. 2024102041917 filed with the State Intellectual Property Office of China on February 23, 2024, and patent application No. 2024114548369 filed with the State Intellectual Property Office of China on October 17, 2024, and the entire text of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the field of batteries, and in particular, to a gel electrolyte precursor liquid, a gel electrolyte, a lithium secondary battery, and a preparation method thereof. Background Art

[0004] As the primary power source for new energy vehicles, lithium-ion secondary batteries have driven the rise of new energy. With the rapid development of new energy vehicles, market demand for power batteries is also increasing. Currently, power batteries are continuously developing towards higher capacity, lower price, and greater safety.

[0005] Lithium secondary batteries typically include a positive electrode and a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte that acts as a lithium ion transfer medium. The electrolyte is typically a liquid electrolyte. However, the electrolyte may leak during use, and during the battery's charge and discharge processes, the solvent may decompose, leading to side reactions. During high-temperature storage, side reactions may be further accelerated, increasing gas generation. Continuous gas generation may induce an increase in the battery's internal pressure, resulting in, among other things, expansion of the battery thickness, and raising safety concerns. The use of gel electrolytes can overcome the safety issues of liquid electrolytes. Gel electrolytes offer advantages in processability and lightweighting, and they can form a protective interface with the battery electrodes. However, gel electrolytes have low oxidation resistance and are prone to reacting with oxygen-containing materials in the battery. The gel also has low mechanical strength, provides limited protection for the electrodes, and has room for improvement in ionic conductivity. These factors limit their application in batteries. Furthermore, most existing gel polymer electrolyte power batteries suffer from poor rate capability and high-temperature storage performance.

[0006] Therefore, it is necessary to further improve the gel electrolyte and gel battery. Summary of the Invention

[0007] The present disclosure aims to solve one of the technical problems in the related art at least to a certain extent.

[0008] In a first aspect, the present disclosure provides a gel electrolyte precursor liquid, comprising a reactive monomer, a cross-linking agent, an initiator, and an electrolyte; wherein the reactive monomer comprises at least one of the compounds represented by Formula 1:

[0009] In Formula 1, R1 is methyl or hydrogen; L is a single bond, a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms; R2, R3, and R4 are the same as or different from each other and are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or fluorine, and at least one of R2, R3, and R4 is fluorine; R5 is hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, or fluorine, and the substituent in L and R5 is fluorine;

[0010] The cross-linking agent includes at least one of the compounds represented by Formula 2-1 and Formula 2-2:

[0011] In formula 2-1, R 1 is an alkyl group having 1 to 4 carbon atoms or R 2 、R 3 、R 4 and R a are the same as or different from each other and are each independently hydrogen or methyl, Indicates a connection key;

[0012] In formula 2-2, R 5 and R 6 are the same or different and are each independently an alkyl group having 1 to 4 carbon atoms, R 7 、R 8 、R 9 and R 10 are the same as or different from each other and are each independently hydrogen or methyl.

[0013] In the gel electrolyte precursor liquid disclosed in the present invention, a fluorine-containing acrylate monomer (shown in Formula 1) is used as a functional monomer, which is beneficial to improving the oxidation resistance of the formed gel electrolyte, and forming the fluorine-containing solid electrolyte (SEI) film at the negative electrode can improve the stability of the SEI layer of the negative electrode (such as a silicon-based negative electrode) during the cycle and extend the cycle life. In addition, the cross-linking agent used is a trifunctional and / or tetrafunctional short-chain acrylate monomer. The use of this cross-linking agent can control the degree of cross-linking of the functional monomer, which is beneficial to improving the cross-linking density of the gel electrolyte and forming a stable network structure to improve the mechanical strength. Furthermore, the functional monomer and the cross-linking agent have an appropriate polymerization reaction rate and monomer conversion rate in the electrolyte system in the presence of an initiator, and the process of forming a polymer gel is controllable, which can avoid sudden polymerization, and the system temperature will not rise sharply, thereby ensuring the safety of the reaction.

[0014] In some embodiments of the present disclosure, in Formula 1, L is a single bond, methylene, fluorine-substituted methylene, ethylene, or fluorine-substituted ethylene, wherein the number of fluorine in the fluorine-substituted methylene and fluorine-substituted ethylene is one or more.

[0015] In some embodiments of the present disclosure, in Formula 1, R2, R3, and R4 are each independently hydrogen, methyl, ethyl, or fluorine, and at least two of R2, R3, and R4 are fluorine.

[0016] In some embodiments of the present disclosure, R5 is hydrogen or trifluoromethyl.

[0017] In some embodiments of the present disclosure, the reactive monomer includes at least one of trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, trifluoroethyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, and octafluoropentyl methacrylate.

[0018] In some embodiments of the present disclosure, the reactive monomer includes at least one of trifluoroethyl methacrylate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. The reactivity of fluoroalkyl groups follows the order: -CF > -CF2 > -CF3. The higher the reactivity, the more likely it is to react with lithium ions and consume electrolyte. The two monomers described above contain -CF3 and a double bond connecting the methyl groups, which can reduce electrolyte consumption. The resulting polymer framework forms an in-situ polymerized gel electrolyte, which not only improves ionic conductivity but also stabilizes the negative electrode SEI film and reduces the occurrence of side reactions in the electrolyte.

[0019] In some embodiments of the present disclosure, in Formula 2-1, R 1 is methyl, ethyl or n-propyl.

[0020] In some embodiments of the present disclosure, in Formula 2-2, R 5 and R 6 are the same or different and are each independently methyl, ethyl or n-propyl.

[0021] In some embodiments of the present disclosure, the crosslinking agent includes at least one of pentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, trimethylolpropane triacrylate, and 1,1,1-trimethylolethane triacrylate.

[0022] In some embodiments of the present disclosure, the initiator includes an oil-soluble initiator.

[0023] In some embodiments of the present disclosure, the oil-soluble initiator includes at least one of azobisisobutyronitrile and azobisisoheptanonitrile, thereby further improving the polymerization reaction efficiency.

[0024] In some embodiments of the present disclosure, the mass ratio of the reactive monomer, crosslinker, and initiator is (6-20):1:(0.05-0.1). This allows the formed polymer to have a more appropriate network structure, while ensuring excellent ionic conductivity and mechanical strength while minimizing the inability to form a gel due to excessively low crosslinking and the excessively low ionic conductivity that may result from excessively high crosslinking.

[0025] In some embodiments of the present disclosure, the electrolyte includes a lithium salt, an organic solvent, and optionally an electrolyte additive.

[0026] In some embodiments of the present disclosure, based on the total weight of the electrolyte, the mass content of the lithium salt is 10% to 17%, the mass content of the electrolyte additive is 5% to 15%, and the mass content of the organic solvent is 70% to 85%.

[0027] In some embodiments of the present disclosure, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide).

[0028] In some embodiments of the present disclosure, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, δ-valerolactone and ε-caprolactone.

[0029] In some embodiments of the present disclosure, the electrolyte additive includes a negative electrode film-forming additive.

[0030] In some embodiments of the present disclosure, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0031] In some embodiments of the present disclosure, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, propylene carbonate, and diethyl carbonate in a mass ratio of 1:(4-6):(0.8-1.2):(2.5-4). This helps reduce the viscosity of the electrolyte and improve the ionic conductivity of the system.

[0032] In some embodiments of the present disclosure, based on the total mass of the gel electrolyte precursor liquid being 100 parts, the mass parts a of the reactive monomer, the mass parts b of the electrolyte, the mass parts c of the cross-linking agent, and the mass parts d of the initiator satisfy the following relationship:

[0033] 4≤a≤22,74≤b≤95,0.8≤c≤2,0.01≤d<1.

[0034] In some embodiments of the present disclosure, 6≤a≤17, 82≤b≤93, 0.8≤c≤1.5, and 0.07≤d<1. Thus, the content of the formed polymer can be controlled within an appropriate range, so that the battery has both high ionic conductivity and mechanical strength.

[0035] In some embodiments of the present disclosure, 0.3<a×(0.1-d)×c×(100-b)<6.2.

[0036] In a second aspect, the present disclosure provides a gel electrolyte, which is prepared by a curing reaction of the gel electrolyte precursor liquid described in the first aspect of the present disclosure.

[0037] The gel electrolyte provided by this disclosure combines excellent ionic conductivity with mechanical strength, and exhibits high aging resistance. Its fluorine-containing backbone provides excellent oxidation resistance, enhancing the interfacial stability between the gel electrolyte and the positive electrode. In particular, the gel electrolyte can stably cycle in high-content silicon-based and high-nickel ternary lithium-ion battery systems, effectively maintaining the integrity of the negative electrode structure and inhibiting silicon negative electrode expansion.

[0038] In some embodiments of the present disclosure, the curing reaction temperature is 55° C. to 70° C. Thus, while ensuring the formation of gel, the side reactions caused by high temperature can be suppressed as much as possible, thereby ensuring product performance.

[0039] In a third aspect, the present disclosure provides use of the gel electrolyte precursor liquid described in the first aspect or the gel electrolyte described in the second aspect in a lithium secondary battery.

[0040] In a fourth aspect, the present disclosure provides a lithium secondary battery comprising the gel electrolyte described in the third aspect of the present disclosure.

[0041] In some embodiments of the present disclosure, the lithium secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode film layer located on at least one side thereof, wherein the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. In particular, the gel electrolyte can effectively maintain the integrity of the negative electrode structure and inhibit expansion of the silicon negative electrode in a battery system with a silicon negative electrode.

[0042] In some embodiments of the present disclosure, the lithium secondary battery includes a positive electrode sheet, the positive electrode sheet including a positive electrode current collector and a positive electrode film layer located on at least one side thereof, the positive electrode film layer including a positive electrode active material, and the positive electrode active material including a nickel-containing lithium battery positive electrode material. In particular, the gel electrolyte can improve oxidation resistance in nickel-containing lithium-ion battery systems.

[0043] In some embodiments of the present disclosure, the positive electrode active material includes a nickel ternary positive electrode material, the chemical formula of the nickel ternary positive electrode material is LiNixCo y Mn z O2,x+y+z=1,0.6≤x≤0.9,0 <y<0.2,0<z<0.2。

[0044] In some embodiments of the present disclosure, the negative electrode active material includes a core and a coating layer, the coating layer includes a first coating layer and a second coating layer, the first coating layer is located on at least a portion of the outer surface of the core, the second coating layer is located on the surface of the first coating layer away from the core, or the second coating layer is located on the surface of the first coating layer away from the core and the surface of the core; the gel electrolyte includes an electrolyte and a gel polymer; the core includes a negative electrode material for active ions to be embedded and de-embedded, the first coating layer includes an SEI film, and the second coating layer includes the gel polymer; the thickness of the coating layer is 0.3-0.5 μm.

[0045] Since the negative electrode active material will undergo intercalation or alloying of lithium during the charge and discharge process, there will be a significant volume expansion, especially the volume change of silicon-based negative electrode active material is more significant. In this process, the negative electrode active material will undergo continuous side reactions with the electrolyte, consuming the electrolyte, and the SEI film will continue to grow and rupture, resulting in a sharp decline in battery capacity. In the lithium secondary battery disclosed herein, the use of a gel electrolyte can alleviate this side reaction to a certain extent. Furthermore, by making the negative electrode active material include a core and a first coating layer and a second coating layer, wherein the first coating layer is located on at least part of the outer surface of the core, and the coating layer includes an SEI film, that is, a solid electrolyte film formed by the reaction of the negative electrode active material and the electrolyte, it is beneficial to reduce the interfacial impedance and improve the ionic conductivity and electronic conductivity of the material; at the same time, a second coating layer is provided on the outer surface of the first coating layer or the outer surface of the first coating layer and the core, and the coating layer includes a gel polymer formed by the polymerization of a fluorinated monomer. On the one hand, it can effectively isolate the negative electrode active material from the electrolyte, prevent the continuous growth and rupture of the SEI film under high-temperature storage conditions, and reduce the consumption of the electrolyte; on the other hand, the gel polymer formed by the polymerization of the fluorinated monomer can also effectively improve the stability of the SEI film. Therefore, the rate performance and high-temperature storage performance of the gel battery can be comprehensively improved.

[0046] In a fifth aspect, the present disclosure provides a method for preparing the lithium secondary battery provided in the fourth aspect of the present disclosure, comprising: injecting the gel electrolyte precursor liquid described in the first aspect of the present disclosure into a battery cell to obtain a first battery; cycling the first battery 1 to 2 times according to the following charge and discharge mechanism to obtain a second battery; the charge and discharge mechanism comprises: charging at a constant current and constant voltage of 0.08C to 0.12C at a pressure of 0.1MPa to 1.0MPa and a temperature not higher than 25°C to a battery operating cut-off voltage, with a cut-off current of 0.05C, and after standing, discharging at a constant current of 0.08C to 0.12C to a battery operating cut-off voltage, and standing; reacting the second battery at a pressure of 0.1MPa to 0.5MPa and a temperature of 55°C to 70°C for a reaction time of not less than 24h to obtain the lithium secondary battery.

[0047] The preparation method of the lithium secondary battery disclosed in the present invention is to activate and cure the lithium ion battery injected with the gel electrolyte precursor liquid by using the fluorine-containing monomer shown in Formula 1. Specifically, the battery is first cycled twice under a specific charge and discharge mechanism, and then reacted for a certain period of time under a specific pressure and temperature. The prepared lithium secondary battery has high rate performance and high-temperature storage performance. Based on this phenomenon, the inventor analyzed and believed that the reason may be: by first activating the lithium ion battery after injection, a stable, dense and uniform SEI film (i.e., the first coating layer) can be formed on the surface of the negative electrode active material in advance under a specific charge and discharge mechanism, effectively reducing the interface impedance. Then, the reaction is carried out for a certain period of time at a specific pressure and reaction temperature, and a curing treatment is performed to form a gel polymer (i.e., the second coating layer) around the negative electrode active material coated with the SEI film. This can effectively prevent the side reaction between the electrolyte and the active material under high-temperature storage conditions, improve the problem of continuous decomposition of the electrolyte on the electrode surface, and reduce the loss of irreversible capacity; at the same time, by controlling the thickness of the coating layer to 0.3-0.5μm, the interfacial impedance can be further reduced and the occurrence of side reactions can be reduced, thereby comprehensively improving the battery's rate performance and high-temperature storage performance. When the charging current is too small, the activation time will be too long and the monomers will partially polymerize. When the charging current is too large, a SEI film with more inorganic lithium salt components will be generated accordingly, resulting in a loose SEI film structure, not dense enough, and a large thickness. When the pressure is too high, the electrolyte will be squeezed to the edge of the battery cell. When the pressure is too low, it will cause the electrolyte to be unevenly infiltrated. Therefore, under the aforementioned charge and discharge mechanism and reaction conditions, the battery's rate performance and high-temperature storage performance can be more effectively improved.

[0048] Additional aspects and advantages of the present disclosure will be given in part in the description that follows and, in part, will be obvious from the description that follows, or will be learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The above and / or additional aspects and advantages of the present disclosure will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0050] FIG1 is an electrochemical window diagram of the gel electrolyte of Example 2;

[0051] FIG2 is a graph showing the room temperature cycle performance of a lithium secondary battery prepared using the gel electrolyte of Example 2.

[0052] FIG3 is a schematic diagram of the structure of the negative electrode active material particles disclosed in the present invention;

[0053] FIG4 is a graph showing the discharge capacity changes of the gel batteries in Example 11 and Comparative Example 3 of the present disclosure at different rates;

[0054] FIG5 is a graph showing the discharge capacity changes of the gel batteries in Example 12 and Comparative Example 4 of the present disclosure at different rates;

[0055] FIG6 is an EIS test diagram of the gel battery in Example 11 of the present disclosure before and after high-temperature storage;

[0056] FIG7 is an EIS test diagram of the gel battery in Example 12 of the present disclosure before and after high-temperature storage;

[0057] FIG8 is an EIS test diagram of the gel battery in Comparative Example 3 of the present disclosure before and after high-temperature storage;

[0058] FIG9 is an EIS test diagram of the gel battery in Comparative Example 4 of the present disclosure before and after high-temperature storage;

[0059] FIG10 is a cross-sectional SEM image of the negative electrode active material in the gel battery of Example 12 of the present disclosure at 6.00 K;

[0060] FIG11 is a cross-sectional SEM image of the negative electrode active material in the gel battery of Example 12 of the present disclosure at 10.0 K;

[0061] FIG12 is a cross-sectional SEM image of the negative electrode active material in the gel battery of Comparative Example 4 of the present disclosure at 6.00 K;

[0062] FIG13 is a cross-sectional SEM image of the negative electrode active material in the gel battery in Comparative Example 4 of the present disclosure at 10.0 K.

[0063] Reference numerals: 1-first coating layer; 2-second coating layer; 3-core. DETAILED DESCRIPTION

[0064] The embodiments of the present disclosure are described in detail below. The embodiments described below are exemplary and are only used to explain the present disclosure, and should not be understood as limiting the present disclosure.

[0065] A first aspect of the present disclosure provides a gel electrolyte precursor liquid comprising a reactive monomer, a cross-linking agent, an initiator, and an electrolyte.

[0066] In the present disclosure, the reactive monomer is a fluorine-containing acrylate monomer, including at least one of the compounds shown in Formula 1:

[0067] In Formula 1, R1 is a methyl group (-CH3) or a hydrogen group (-H); L is a single bond, a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms; R2, R3 and R4 are the same as or different from each other and are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms or fluorine (F), and at least one of R2, R3 and R4 is fluorine; R5 is hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms or fluorine, and the substituents in L and R5 are fluorine.

[0068] In Formula 1, when L is a substituted alkylene group, the number of substituents in L may be one or more, for example, 1, 2, 3, 4, 5, etc.

[0069] In Formula 1, the number of carbon atoms in L can be 1 (eg, an alkylene group), 2, 3, or 4.

[0070] In some embodiments, L is a single bond, a methylene group (-CH2-), a fluorine-substituted methylene group, an ethylene group (-CH2CH2-), or a fluorine-substituted ethylene group, wherein the fluorine-substituted methylene group and the fluorine-substituted ethylene group contain one or more fluorine atoms. For example, the fluorine-substituted methylene group may include -CF2-, -CHF-, and the like.

[0071] In some embodiments, R2, R3 and R4 are each independently hydrogen, methyl (-CH3), ethyl (-CH2CH3) or fluorine, and at least two of R2, R3 and R4 are fluorine.

[0072] In some embodiments, R2, R3, and R4 are all fluorine.

[0073] In some embodiments, R5 is hydrogen or trifluoromethyl.

[0074] In some embodiments, the reactive monomer comprises one or more of the following compounds:

[0075] Furthermore, the reactive monomer includes at least one of trifluoroethyl methacrylate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. This reactive monomer is beneficial for improving the ionic conductivity of the gel electrolyte while stabilizing the SEI film of the silicon-based negative electrode and reducing the occurrence of side reactions in the electrolyte.

[0076] In the present disclosure, the crosslinking agent is a trifunctional acrylate compound and / or a tetrafunctional acrylate compound. Specifically, the crosslinking agent includes at least one of the compounds represented by Formula 2-1 and Formula 2-2:

[0077] In formula 2-1, R 1 is an alkyl group having 1 to 4 carbon atoms or R 2 、R 3 、R 4 and R a are the same as or different from each other and are each independently hydrogen or methyl, Indicates a connection key.

[0078] As some examples, R 1 is an alkyl group having 1 to 4 carbon atoms, R 1 The number of carbon atoms in can be 1, 2, 3 or 4.

[0079] As some examples, R 2 、R 3 、R 4 and R a All are hydrogen.

[0080] In some embodiments, R 1 is methyl, ethyl or n-propyl.

[0081] In formula 2-2, R 5 and R 6 are the same or different and are each independently an alkyl group having 1 to 4 carbon atoms, R 7 、R 8 、R 9 and R 10 are the same as or different from each other and are each independently hydrogen or methyl.

[0082] In formula 2-2, R 5 and R 6 The number of carbon atoms in can be distributed independently as 1, 2, 3 or 4.

[0083] In some embodiments, R 5 and R 6 are the same or different and are each independently methyl, ethyl or n-propyl.

[0084] In some embodiments, the cross-linking agent comprises one or more of the following compounds:

[0085] In the present disclosure, the reactive monomer and the cross-linking agent may undergo a polymerization reaction in the presence of an initiator to form a polymer matrix in the gel electrolyte. Generally, the initiator may be a free radical polymerization initiator.

[0086] In some embodiments, the initiator includes an oil-soluble initiator, which can be better dissolved in a non-aqueous electrolyte containing an organic solvent and effectively initiate polymerization of the reaction monomers.

[0087] In some embodiments, the oil-soluble initiator includes at least one of azobisisobutyronitrile (AIBN) and azobisisoheptanenitrile (ABVN). This type of initiator is a thermal initiator. When injected into a battery to react in situ to form a gel electrolyte, its decomposition temperature has little impact on the battery system and can improve polymerization reaction efficiency.

[0088] In some embodiments, the mass ratio of the reactive monomer, crosslinker, and initiator is (6-20):1:(0.05-0.1). In this case, the formed polymer matrix can have a more appropriate network structure, while ensuring excellent ionic conductivity and mechanical strength, while minimizing the failure to form a gel due to excessive crosslinking and the excessively low ionic conductivity caused by excessive crosslinking.

[0089] In some embodiments, the mass ratio of the reactive monomer to the cross-linking agent is (6-17):1, for example, 6:1, 6.5:1, 7:1, 8:1, 9:1, 10:1, 11:1, 11.5:1, 12:1, 13:1, 14:1, 15:1, 16:1, 16.5:1, 17, etc.

[0090] In some embodiments, the mass ratio of the crosslinking agent to the initiator may be 1:(0.06-0.09), for example, 1:0.06, 1:0.07, 1:0.08, 1:0.09, etc.

[0091] In the present disclosure, the electrolyte generally includes a lithium salt and an organic solvent. In some embodiments, the electrolyte further includes electrolyte additives, such as film-forming additives, and additives that can improve certain battery properties, such as additives that improve high-temperature performance of the battery.

[0092] In some embodiments, the electrolyte includes a lithium salt, an organic solvent, and an electrolyte additive.

[0093] In some embodiments, the mass content of the lithium salt is 10% to 17% based on the total weight of the electrolyte, for example, 10%, 11%, 11.5%, 12%, 12.5%, 13%, 14%, 15%, 16%, 17%, etc.;

[0094] The mass content of the electrolyte additive is 5% to 15%, for example, 5%, 7%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, etc.;

[0095] The mass content of the organic solvent is 70% to 85%, for example, 70%, 75%, 77%, 80%, 81%, 82%, 83%, 84%, 85%, etc.

[0096] In the present disclosure, the lithium salt can be selected from the types of electrolytes commonly used in lithium batteries. In some embodiments, the electrolyte lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonyl imide), and lithium bis(fluorosulfonyl imide).

[0097] In some embodiments, the electrolyte additive includes a negative electrode film-forming additive.

[0098] In some embodiments, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0099] In the present disclosure, the organic solvent may generally include one or more of carbonates and carboxylates. In some embodiments, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, δ-valerolactone and ε-caprolactone.

[0100] Furthermore, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, propylene carbonate and diethyl carbonate, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, propylene carbonate and diethyl carbonate is 1:(4-6):(0.8-1.2):(2.5-4), for example 1:5:1:3.

[0101] In some embodiments, based on 100 parts by weight of the gel electrolyte precursor solution, the weight ratios a of the reactive monomer, b of the electrolyte solution, c of the crosslinking agent, and d of the initiator satisfy the following relationship: 4 ≤ a ≤ 22, 74 ≤ b ≤ 95, 0.8 ≤ c ≤ 2, and 0.05 ≤ d < 1. This promotes crosslinking of the reactive monomers and improves oxidation resistance.

[0102] In some embodiments, 6≤a≤17, 82≤b≤93, 0.8≤c≤1.5, and 0.07≤d<1. Thus, the formed gel electrolyte can have both high ionic conductivity and mechanical strength.

[0103] In some embodiments, 0.3<a×(0.1-d)×c×(100-b)<6.2.

[0104] In some embodiments, the gel electrolyte precursor liquid can be obtained by mixing components including a reactive monomer, a cross-linking agent, an initiator, a lithium salt, an organic solvent, and an optional electrolyte additive. It should be noted that the "optional electrolyte additive" described in this disclosure means that the electrolyte or gel electrolyte precursor liquid may contain an electrolyte additive or may not contain an electrolyte additive; in other words, the gel electrolyte precursor liquid can be obtained by mixing components including a reactive monomer, a cross-linking agent, an initiator, a lithium salt, and an organic solvent; it can also be obtained by mixing components including a reactive monomer, a cross-linking agent, an initiator, a lithium salt, an organic solvent, and an electrolyte additive.

[0105] The second aspect of the present disclosure provides a gel electrolyte, which is prepared by curing the gel electrolyte precursor liquid described in the first aspect of the present disclosure. The gel electrolyte exists in the form of a gel, and is based on a polymer formed by the reaction of reactive monomers, a cross-linking agent, and an initiator. The molecular chains of the polymer are chemically cross-linked to form a network structure, and the pores of the structure are filled with a liquid plasticizer (solvent) and a lithium salt.

[0106] The gel electrolyte disclosed herein can effectively inhibit changes in the negative electrode structure, significantly improving battery safety while increasing specific energy. Furthermore, the gel electrolyte exhibits both excellent ionic conductivity and mechanical strength, and its fluorine-containing backbone provides excellent oxidation resistance, enhancing interfacial stability between the gel electrolyte and the positive electrode.

[0107] In some embodiments, the gel electrolyte can be obtained by injecting the gel electrolyte precursor solution into a battery cell and then heating the battery to cause the mixture to undergo a solidification reaction (i.e., cross-linking) to form a gel. This in-situ polymerization method can enhance the contact between the formed gel electrolyte and the positive and negative electrodes, thereby providing protection.

[0108] In some embodiments, the curing reaction temperature is 55° C. to 70° C., such as 55° C., 60° C., 65° C., 70° C., etc. Thus, while ensuring gel formation, side reactions caused by high temperature can be suppressed as much as possible, thereby ensuring product performance.

[0109] In some embodiments, the curing reaction time is 12 hours to 25 hours, for example, 12 hours, 13 hours, 15 hours, 20 hours, 24 hours, 25 hours, etc.

[0110] A third aspect of the present disclosure provides use of the gel electrolyte precursor liquid described in the first aspect or the gel electrolyte described in the second aspect in a lithium secondary battery.

[0111] In some embodiments, the application may include injecting a gel electrolyte precursor into an electrode core during the preparation of a battery, and obtaining the gel electrolyte through in-situ polymerization.

[0112] The fourth aspect of the present disclosure provides a lithium secondary battery, including the gel electrolyte described in the second aspect. The lithium secondary battery may include a semi-solid lithium secondary battery.

[0113] Generally, the lithium secondary battery further includes a positive electrode sheet, a negative electrode sheet, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The gel electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly functioning to prevent short circuit between the positive electrode and the negative electrode, and at the same time allowing ions to pass through.

[0114] In the present disclosure, the positive electrode sheet generally may include a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode sheet. The positive electrode active material layer includes a positive electrode active material (or referred to as a positive electrode active substance).

[0115] In some embodiments, the positive electrode active layer contains a lithium transition metal oxide as the positive electrode active substance.

[0116] In some embodiments, the positive electrode active substance includes a nickel-containing lithium battery positive electrode material, such as a high-nickel layered oxide. Thereby, the specific capacity per gram of the positive electrode active material can be further increased, and the cost of the positive electrode active material can be reduced. "High nickel" means that based on all transition metals, the molar content of Ni is not less than 60%. Particularly, the gel electrolyte is suitable for a battery with a high-nickel layered oxide positive electrode material. Although the high-nickel layered oxide positive electrode material has a high capacity advantage, it also has high oxidizing property, and usually easily causes oxidation and decomposition of the electrolyte, resulting in a rapid decrease in the battery capacity. However, the gel electrolyte of the present disclosure has high oxidation resistance, can form a stable electrolyte / positive electrode interface, and improve the electrochemical window of the battery.

[0117] As some examples, the positive electrode active substance includes a nickel ternary positive electrode material, and the chemical formula of the nickel ternary positive electrode material is LiNixCo y Mn z O2, where x + y + z = 1, 0.6 ≤ x ≤ 0.9, 0 < y < 0.2, 0 < z < 0.2, and specific examples may include LiNi 0.7 Co 0.1 Mn 0.2 O2 (NCM712), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NMC811).

[0118] In some embodiments, the positive electrode active material layer may further include a binder, and specific examples of the binder include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer.

[0119] In some embodiments, the positive electrode active material layer may further include a conductive agent, and specific examples of the conductive agent include, but are not limited to, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and the like.

[0120] In some embodiments, the positive electrode current collector may be a metal foil, such as aluminum foil.

[0121] In the present disclosure, the negative electrode sheet may generally include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material (or negative electrode active material).

[0122] In some embodiments, the negative electrode active material may include at least one of graphite, a silicon-based material, and lithium titanate.

[0123] In some embodiments, the negative electrode active material is a silicon-based material. Specific examples of the silicon-based material include, but are not limited to, silicon-carbon composite materials and silicon-oxygen composite materials. The gel electrolyte is also particularly suitable for batteries containing silicon-based negative electrodes. Silicon-based materials have the characteristics of high theoretical specific capacity and low delithiation potential, but in general, the material undergoes huge volume changes during the charge and discharge process, which can easily lead to mechanical fracture and crushing of the active material, resulting in continuous destruction and formation of the solid electrolyte membrane. The gel electrolyte disclosed in the present invention has high mechanical properties and ionic conductivity, can effectively maintain the integrity of the silicon-based negative electrode structure and enable the battery to maintain high electrochemical performance.

[0124] In some embodiments, the negative electrode active material layer may further include a binder, and specific examples of the binder include, but are not limited to, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0125] In some embodiments, the negative electrode active material layer may further include a conductive agent, and specific examples of the conductive agent include, but are not limited to, superconducting carbon, acetylene black, carbon black, graphene, and the like.

[0126] In some embodiments, the negative active material layer may further include a thickener, such as sodium carboxymethylcellulose (CMC-Na).

[0127] The present disclosure has no particular limitation on the type of diaphragm, and various porous structure diaphragms with good stability can be selected, such as polyethylene diaphragms, polypropylene diaphragms, PE ceramic coated diaphragms, etc.

[0128] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into a battery cell through a winding process or a lamination process.

[0129] In some embodiments, the lithium secondary battery includes an outer packaging. The outer packaging can be used to encapsulate the battery cell and the polymer gel electrolyte. In addition, the outer packaging of the lithium secondary battery can be a hard shell or a soft shell.

[0130] The present disclosure has no particular limitation on the shape of the lithium secondary battery, which may be cylindrical, square, or any other shape.

[0131] In some embodiments, the negative electrode active material includes a core and a coating layer, the coating layer includes a first coating layer and a second coating layer, the first coating layer is located on at least a portion of the outer surface of the core, the second coating layer is located on the surface of the first coating layer away from the core, or the second coating layer is located on the surface of the first coating layer away from the core and the surface of the core; the gel electrolyte includes an electrolyte and a gel polymer; the core includes a negative electrode material for active ions to be embedded and de-embedded, the first coating layer includes an SEI film, and the second coating layer includes a gel polymer; the thickness of the coating layer is 0.3-0.5 μm.

[0132] In some embodiments, the lithium secondary battery may be a gel battery. Specifically, the present disclosure provides a gel battery comprising a negative electrode sheet and a gel electrolyte; the gel electrolyte comprising an electrolyte and a gel polymer, the gel polymer being obtained by polymerization of a raw material system comprising a fluorine-containing monomer; the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising a core and a coating layer, the coating layer comprising a first coating layer and a second coating layer, the first coating layer being located on at least a portion of the outer surface of the core, the second coating layer being located on a surface of the first coating layer away from the core, or the second coating layer being located on a surface of the first coating layer away from the core and on the surface of the core; the core comprising a negative electrode material for active ion embedding and de-embedding, the first coating layer comprising an SEI film formed by reaction with the electrolyte, and the second coating layer comprising a gel polymer; the coating layer having a thickness of 0.3 μm to 0.5 μm.

[0133] In some embodiments, the gel electrolyte in the gel battery is the gel electrolyte described in the second aspect of the present disclosure. Alternatively, the gel battery of the present disclosure comprises a negative electrode sheet and the gel electrolyte described in the second aspect of the present disclosure, wherein the gel electrolyte comprises an electrolyte solution and a gel polymer; the negative electrode sheet comprises a negative electrode active material, wherein the negative electrode active material comprises a core and a coating layer, wherein the coating layer comprises a first coating layer and a second coating layer, wherein the first coating layer is located on at least a portion of the outer surface of the core, and the second coating layer is located on a surface of the first coating layer away from the core, or the second coating layer is located on a surface of the first coating layer away from the core and on the surface of the core; the core comprises a negative electrode material capable of embedding and extracting active ions, wherein the first coating layer comprises an SEI film, and the second coating layer comprises a gel polymer; and the thickness of the coating layer is 0.3-0.5 μm.

[0134] Illustratively, the coating layer has a thickness of 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm or 0.5 μm.

[0135] Figure 3 is a schematic structural diagram of the negative electrode active material particles. As shown in Figure 3, the negative electrode active material includes a core 3, a first coating layer 1 and a second coating layer 2, wherein the first coating layer 1 is located on at least part of the outer surface of the core 3, the second coating layer 2 is located on the outer surface of the first coating layer 1, or the second coating layer 2 is located on the outer surface of the first coating layer 1 and the outer surface of the core 3.

[0136] As used herein, a "fluorinated monomer" refers to a monomeric compound containing fluorine atoms in its molecular structure. The disclosure does not specifically limit the type or source of the fluorinated monomer; commercially available products or products prepared using conventional preparation methods familiar to those skilled in the art may be used. In some embodiments, the "fluorinated monomer" is a compound represented by Formula 1.

[0137] The present disclosure does not specifically limit the type and source of the negative electrode material, and specifically it can be a silicon-based negative electrode material.

[0138] It can be understood that the gel battery also includes a positive electrode sheet and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer. The positive electrode active layer includes a positive electrode active material.

[0139] The present disclosure does not specifically limit the positive electrode active material, positive electrode current collector and separator, which are all conventionally selected in the art.

[0140] Since the negative electrode active material will undergo intercalation or alloying of lithium during the charge and discharge process, there will be a significant volume expansion, especially the volume change of silicon-based negative electrode active material is more significant. In this process, the negative electrode active material will undergo continuous side reactions with the electrolyte, consuming the electrolyte, and the SEI film will continue to grow and rupture, resulting in a sharp decline in battery capacity. In the gel battery disclosed herein, the use of a gel electrolyte can alleviate this side reaction to a certain extent. Furthermore, the negative electrode active material comprises a core, a first coating layer, and a second coating layer, wherein the first coating layer is located on at least a portion of the outer surface of the core. The coating layer comprises an SEI film, i.e., a solid electrolyte film formed by the reaction of the negative electrode active material and the electrolyte, which is beneficial for reducing interfacial impedance and improving the ionic and electronic conductivity of the material. Simultaneously, a second coating layer is provided on the outer surface of the first coating layer or on the outer surfaces of the first coating layer and the core. The second coating layer comprises a gel polymer formed by the polymerization of a fluorinated monomer. This effectively isolates the negative electrode active material from the electrolyte, preventing the continued growth and rupture of the SEI film under high-temperature storage conditions and reducing electrolyte consumption. Furthermore, the gel polymer formed by the polymerization of the fluorinated monomer can effectively improve the stability of the SEI film. Therefore, the rate capability and high-temperature storage performance of the gel battery can be comprehensively improved.

[0141] In one specific embodiment, the fluorine-containing monomer includes at least one of trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, trifluoroethyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, and octafluoropentyl methacrylate. When the aforementioned compound is a mixture of multiple specific compounds, the present disclosure does not impose excessive restrictions on the ratio between the specific compounds.

[0142] In one embodiment, the electrolyte includes an additive; the additive includes fluoroethylene carbonate and / or vinylene carbonate. When the electrolyte includes the additive, a more stable, dense, and uniform SEI film can be formed, stabilizing the electrolyte-electrolyte interface, further reducing interfacial impedance, and further alleviating the problem of continuous electrolyte decomposition on the electrode surface, thereby enabling the battery to have higher rate capability and high-temperature storage performance.

[0143] When the additive is a mixture of multiple specific compounds, the present disclosure does not impose too many restrictions on the ratio between the specific compounds.

[0144] In one specific embodiment, the weight percentage of the additive in the electrolyte is 5wt% to 12wt%. For example, the weight percentage is 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, or 12wt%. In other words, in some embodiments of the present disclosure, the gel electrolyte includes an electrolyte and a gel polymer, the electrolyte includes an electrolyte additive, and the weight percentage of the electrolyte additive in the electrolyte is 5wt% to 12wt%. Within this range, it helps to further improve the rate performance and high-temperature storage performance of the battery.

[0145] In a fifth aspect, the present disclosure provides a method for preparing the lithium secondary battery provided in the fourth aspect of the present disclosure, comprising: 1) injecting a precursor solution comprising an electrolyte and a fluorine-containing monomer into a battery cell to obtain a first battery; 2) cycling the first battery 1 to 2 times according to the following charge and discharge mechanism to obtain a second battery; the charge and discharge mechanism comprises: charging at a constant current and constant voltage of 0.08C to 0.12C at a pressure of 0.1MPa to 1.0MPa and a temperature not higher than 25°C to a battery operating cutoff voltage, the cutoff current being 0.05C, and after standing, discharging at a constant current of 0.08C to 0.12C to a battery operating cutoff voltage, and standing; 3) reacting the second battery at a pressure of 0.1MPa to 0.5MPa and a temperature of 55°C to 70°C for a reaction time of not less than 24h to obtain a lithium secondary battery.

[0146] As mentioned above, the lithium secondary battery can be a gel battery. Therefore, the present disclosure provides a method for preparing a gel battery, comprising: 1) injecting a precursor solution comprising an electrolyte and a fluorine-containing monomer into a battery cell to obtain a first battery; 2) cycling the first battery 1 to 2 times according to the following charge and discharge mechanism to obtain a second battery; the charge and discharge mechanism comprising: charging at a constant current and constant voltage of 0.08C to 0.12C at a pressure of 0.1MPa to 1.0MPa and a temperature not higher than 25°C to a battery operating cutoff voltage, with a cutoff current of 0.05C, allowing the battery to stand, then discharging at a constant current of 0.08C to 0.12C to a battery operating cutoff voltage, and allowing the battery to stand; 3) reacting the second battery at a pressure of 0.1MPa to 0.5MPa and a temperature of 55°C to 70°C for a reaction time of not less than 24 hours to obtain a gel battery.

[0147] In some embodiments, the preparation method of the gel battery provided in the fifth aspect of the present disclosure includes: injecting the gel electrolyte precursor liquid described in the first aspect of the present disclosure into a battery cell to obtain a first battery; cycling the first battery 1 to 2 times according to the following charge and discharge mechanism to obtain a second battery; the charge and discharge mechanism includes: charging at a constant current and constant voltage of 0.08C to 0.12C at a pressure of 0.1MPa to 1.0MPa and a temperature not higher than 25°C to the battery working cut-off voltage, the cut-off current is 0.05C, after standing, discharging at a constant current of 0.08C to 0.12C to the battery working cut-off voltage, and standing; reacting the second battery at a pressure of 0.1MPa to 0.5MPa and a temperature of 55°C to 70°C, and the reaction time is not less than 24h to obtain the gel battery.

[0148] Specifically, in step 1), the electrolyte and the precursor solution including the fluorine-containing monomer are uniformly mixed and then injected into the baked lithium-ion battery cell. After the injection is completed, the mixture is allowed to stand at room temperature to obtain the first battery.

[0149] The present disclosure does not specifically limit the specific composition of the electrolyte, which can be selected conventionally in the art.

[0150] The present disclosure does not specifically limit the standing time. For example, the standing time is 8 hours to 24 hours.

[0151] In step 2), the first battery is charged at a constant current and constant voltage of 0.08C to 0.12C to the battery operating cutoff voltage at a pressure of 0.1MPa to 1.0MPa and a temperature not exceeding 25°C using a battery clamp. The cutoff current is 0.05C. After standing, the battery is discharged at a constant current of 0.08C to 0.12C to the battery operating cutoff voltage and allowed to stand. The battery is then charged and discharged 1 to 2 times according to the above charge and discharge mechanism to obtain a second battery. In step 3), the second battery is cured at a pressure of 0.1MPa to 0.5MPa and a temperature of 55°C to 70°C for a reaction time of not less than 24 hours. After the reaction is completed, the battery is allowed to stand and the volume is divided to obtain a gel battery.

[0152] The present disclosure does not specifically limit the standing time. For example, the standing time is 8 hours to 16 hours.

[0153] The preparation method of the gel battery disclosed in the present invention uses a fluorine-containing monomer (specifically, a fluorine-containing monomer as shown in Formula 1) and simultaneously activates and cures a lithium-ion battery injected with a gel electrolyte precursor liquid. Specifically, the battery is first cycled twice under a specific charge-discharge regime, and then reacted for a certain period of time under a specific pressure and temperature. The resulting gel battery has high rate performance and high-temperature storage performance. Based on this phenomenon, the inventors analyzed and believe that the reason may be that by first activating the lithium-ion battery after injection, a stable, dense, and uniform SEI film (i.e., the first coating layer) can be pre-formed on the surface of the negative electrode active material under a specific charge-discharge regime, effectively reducing the interfacial impedance. Then, the reaction is carried out for a certain period of time at a specific pressure and reaction temperature, and a curing treatment is performed to form a gel polymer (i.e., the second coating layer) around the negative electrode active material coated with the SEI film. This can effectively prevent the side reaction between the electrolyte and the active material under high-temperature storage conditions, improve the problem of continuous decomposition of the electrolyte on the electrode surface, and reduce the loss of irreversible capacity; at the same time, by controlling the thickness of the coating layer to 0.3μm~0.5μm, the interfacial impedance can be further reduced and the occurrence of side reactions can be reduced, thereby comprehensively improving the battery's rate performance and high-temperature storage performance. When the charging current is too small, the activation time will be too long and the monomer will partially polymerize. When the charging current is too large, an SEI film with more inorganic lithium salt components will be generated accordingly, resulting in a loose SEI film structure, insufficient density, and a large thickness. When the pressure is too high, the electrolyte will be squeezed to the edge of the battery cell. When the pressure is too low, it will cause the electrolyte to be unevenly infiltrated. Therefore, under the aforementioned charge and discharge mechanism and reaction conditions, the battery's rate performance and high-temperature storage performance can be more effectively improved.

[0154] In one embodiment, the mass percentage of the fluorinated monomer in the precursor solution is 6.5 wt% to 19.0 wt%. For example, the mass percentage is 6.5 wt%, 8.0 wt%, 10.0 wt%, 12.0 wt%, 14.0 wt%, 16.0 wt%, 18.0 wt%, or 19.0 wt%. In other words, the gel electrolyte precursor solution includes a reactive monomer, and the reactive monomer includes a fluorinated monomer, and the mass percentage of the fluorinated monomer in the gel electrolyte precursor solution is 6.5 wt% to 19.0 wt%. Within this range, the prepared gel electrolyte not only has higher ionic conductivity, improves the diffusion capacity of lithium ions, reduces the internal resistance of the battery, and improves the charge and discharge capacity of the battery, but also effectively improves the mechanical strength of the gel electrolyte, inhibits the volume expansion of the negative electrode material during the cycle, and improves the stability of the electrode structure, thereby enabling the gel battery to have higher rate performance and cycle performance.

[0155] In a specific embodiment, the precursor solution further comprises a crosslinking agent; the crosslinking agent comprises at least one of pentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate;

[0156] In a specific embodiment, the precursor solution further includes an initiator; the initiator includes azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0157] When the aforementioned two types of compounds are mixtures of multiple specific compounds, the present disclosure does not impose too many restrictions on the ratios between the specific compounds.

[0158] In one specific embodiment, the mass percentage of the crosslinker in the precursor solution is 0.8wt% to 2.0wt%. For example, the mass percentage is 0.8wt%, 1.0wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt% or 2.0wt%. In other words, the gel electrolyte precursor solution includes a crosslinker, and the mass percentage of the crosslinker in the gel electrolyte precursor solution is 0.8wt% to 2.0wt%. Within this range, the fluorinated monomer can undergo a better crosslinking reaction, avoiding a decrease in ionic conductivity caused by excessive crosslinking, so that the prepared gel electrolyte has a higher ionic conductivity, further improving the rate performance of the gel battery.

[0159] In one embodiment, the mass percentage of the initiator in the precursor solution is 0.01 wt% to 0.05 wt%. For example, the mass percentage is 0.01 wt%, 0.015 wt%, 0.02 wt%, 0.025 wt%, 0.03 wt%, 0.035 wt%, 0.04 wt%, 0.045 wt%, or 0.050 wt%. In other words, the gel electrolyte precursor solution includes the initiator, and the mass percentage of the initiator in the gel electrolyte precursor solution is 0.01 wt% to 0.05 wt%. Within this range, a high conversion rate of the fluorinated monomer can be ensured, the fluorinated monomer is fully reacted, and residual fluorinated monomer is prevented from affecting battery performance.

[0160] In one embodiment, the precursor solution comprises, by weight percentage, 8-17 wt% fluorinated monomer, 0.8-1.5 wt% cross-linker, 0.01-0.05 wt% initiator, and the balance electrolyte. The fluorinated monomer, initiator, cross-linker, and electrolyte can better cooperate and synergize to form a more stable and dense SEI film, thereby further reducing interfacial impedance. This also better inhibits side reactions between the electrolyte and active materials, further reducing irreversible capacity loss, and thus comprehensively improving the rate capability and high-temperature storage performance of the gel battery.

[0161] The scheme of the present disclosure is described below by specific examples. It should be noted that the following examples are only used to illustrate the present disclosure and should not be regarded as limiting the scope of the present disclosure. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product instructions. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0162] Example 1

[0163] In a glove box filled with argon (moisture <10ppm, oxygen <1ppm), lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) were mixed and stirred in a mass ratio of 12.5:7.75:38.75:7.75:10:23.25 to obtain an electrolyte.

[0164] A parts by mass of trifluoroethyl methacrylate, c parts by mass of pentaerythritol tetraacrylate, and d parts by mass of azobisisobutyronitrile (AIBN) are added to b parts by mass of the electrolyte and stirred uniformly to obtain a gel electrolyte precursor liquid; wherein a=6.49, b=92.42, c=1, and d=0.09.

[0165] Example 2

[0166] In a glove box filled with argon (moisture <10ppm, oxygen <1ppm), lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) were mixed and stirred in a mass ratio of 12.5:7.75:38.75:7.75:10:23.25 to obtain an electrolyte.

[0167] A parts by mass of trifluoroethyl methacrylate, c parts by mass of pentaerythritol tetraacrylate, and d parts by mass of azobisisobutyronitrile are added to b parts by mass of the electrolyte and stirred uniformly to obtain a gel electrolyte precursor liquid; wherein a=8.99, b=89.92, c=1, and d=0.09.

[0168] Examples 3-6

[0169] The gel electrolyte precursor liquid was prepared according to the method of Example 2, except that the amount of trifluoroethyl methacrylate and / or AIBN was adjusted, and the amount of electrolyte was adjusted accordingly to make a+b+d=99. The specific amounts are shown in Table 1.

[0170] Example 7

[0171] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that trifluoroethyl methacrylate was replaced by 1,1,1,3,3,3-hexafluoroisopropyl methacrylate.

[0172] Example 8

[0173] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that pentaerythritol tetraacrylate was replaced by di(trimethylolpropane) tetraacrylate.

[0174] Example 9

[0175] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that pentaerythritol tetraacrylate was replaced by trimethylolpropane triacrylate.

[0176] Example 10

[0177] The gel electrolyte precursor solution was prepared according to the method of Example 2, except that the amounts of the reaction monomer, initiator, cross-linking agent and electrolyte were adjusted. The specific amounts are shown in Table 1.

[0178] Comparative Example 1

[0179] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that trifluoroethyl methacrylate was replaced by methyl methacrylate.

[0180] Comparative Example 2

[0181] A gel electrolyte precursor solution was prepared according to the method of Example 2, except that pentaerythritol tetraacrylate was replaced by poly(ethylene glycol) diacrylate.

[0182] In the above Examples 1 to 10 and Comparative Examples 1 to 2, the types and contents of the main components in the precursor liquid are shown in Table 1.

[0183] Table 1 Note: The amounts in Table 1 are all parts by mass.

[0184] Test Case

[0185] The test examples are used to illustrate the performance of the gel electrolytes prepared from the gel electrolyte precursor solutions of Examples 1 to 10 and Comparative Examples 1 to 2 above.

[0186] 1. Electrochemical performance test

[0187] 1) The specific preparation method of lithium-ion batteries.

[0188] Preparation of positive electrode: ternary nickel-cobalt-manganese LiNi 0.8 Mn0.1 Co 0.1 O2 (NMC811), conductive agent Super P and adhesive PVDF were mixed evenly with solvent NMP in a mass ratio of 92.5:5:2.5 to prepare positive electrode slurry, which was coated on both sides of the positive electrode current collector aluminum foil (thickness 16 μm) and then dried and cold pressed. The compaction density was 3.4 g / cm 3 , made into a positive electrode sheet.

[0189] Preparation of negative electrode sheet: Silicon oxide (theoretical capacity of 550 mAh / g), conductive agent Super P, SWCNT, binder SBR and CMC were mixed evenly with solvent water in a mass ratio of 87.94:6:0.06:4:2 to prepare negative electrode slurry. The negative electrode slurry was coated on both sides of the negative electrode current collector copper foil (thickness 9 μm) and then dried and cold pressed. The compaction density was 1.55 g / cm 3 , made into a negative electrode sheet.

[0190] Diaphragm: PE ceramic diaphragm;

[0191] The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are made into a battery cell by a winding process, placed in an aluminum-plastic packaging bag, and baked to make a soft-pack lithium-ion battery (capacity of 1Ah).

[0192] The gel electrolyte precursor liquid is injected into the lithium-ion battery. After the liquid is sealed, it is kept at room temperature for 3 hours and then pressurized and cured. The pressure is 3MPa and the temperature is 60℃ to allow the precursor liquid to react. The reaction time is 24 hours. After the reaction, it is kept at room temperature for 24 hours and then pressurized and heated to form. The pressure is 3MPa, the temperature is 45℃, the formation current is 0.1C, and the formation time is 390min.

[0193] The semi-solid-state battery is aged at 45°C, 0.3 MPa, and 16 hours. It is then vented and sealed again, with a venting time of 5 seconds and a vacuum of 90-95 Pa, completing the battery packaging.

[0194] The battery was then divided into different capacities with currents of 0.1, 0.3, 0.5C and 1C, followed by performance testing.

[0195] 2) Normal temperature cycle performance test

[0196] At room temperature, the soft-pack battery was charged to 4.25V at a constant current and constant voltage of 0.5A, with a cut-off current of 0.04A. After resting for 5 minutes, it was discharged to 2.75V at a constant current of 0.5A. After resting for 5 minutes, the constant current and constant voltage charging steps were repeated. The cycle performance of the lithium-ion battery was evaluated by cycling 300 times.

[0197] 2. Test method of ionic conductivity

[0198] The gel electrolyte precursor liquid was placed in a 25 mL colorimetric tube, sealed after inserting a conductivity electrode, and reacted and cured at 60°C for 24 hours. After cooling to 25°C and standing for 1 hour, the ionic conductivity of the obtained gel electrolyte was tested using a conductivity meter.

[0199] 3. Test method of electrochemical window

[0200] The gel electrolyte precursor liquid was placed in a three-electrode sealed electrolytic cell and reacted and cured at 60°C for 24 hours. It was tested using an electrochemical testing system with the initial voltage being the open circuit voltage, the scan rate being 0.1mV / s, and the termination voltage being 7V.

[0201] 4. Storage modulus

[0202] The storage modulus of the gel electrolyte was measured using a rheometer (Anton Paar MCR302). The gel electrolyte (prepared by reacting the precursor solution at 60°C for 24 hours) was placed on an aluminum plate at 25°C. A strain sweep was performed at a constant rate of 1 rad / s over a range of 1-100%. The average storage modulus within the linear viscoelastic range was used to determine the gel's storage modulus.

[0203] The test results are shown in Table 2.

[0204] Table 2

[0205] Combined with the data in Table 1, it can be seen from Examples 1-6 that as the polymer content increases, the ionic conductivity gradually decreases and the storage modulus gradually increases. With high ionic conductivity, the diffusion ability of lithium ions will be stronger, the internal resistance of the battery will be smaller, and the charge and discharge capacity of the battery will be better. With a high storage modulus, the energy stored in the material due to elastic deformation during the deformation process is higher, that is, the mechanical strength of the gel electrolyte is higher, which can effectively inhibit the expansion of the silicon negative electrode during the cycle and maintain the electrode structure better. In addition, the ionic conductivity of the gel electrolyte obtained in Examples 1-10 is greater than 2.7mS·cm -1 The electrochemical window reaches 5.4V and above, and the storage modulus reaches 2kPa and above. The carbon-oxygen and carbon-fluorine bonds on the polymer can coordinate with lithium ions, accelerating the rapid movement of lithium ions. At the same time, the fluorinated polymer provides a mechanical support skeleton for the gel electrolyte, and the continuous fluorinated skeleton provides the electrolyte with excellent chemical stability.

[0206] Furthermore, compared to Example 2, with the same polymer content (calculated as reactive monomers), replacing the monomer with methyl methacrylate in Comparative Example 1 resulted in a decreased electrochemical window and inferior ionic conductivity compared to the gel electrolyte in Example 2. This decreased electrochemical window can affect the chemical stability of the gel electrolyte in high-nickel systems, resulting in poor rate performance and unsatisfactory cycling performance. In Comparative Example 2, replacing the crosslinker with poly(ethylene glycol) diacrylate resulted in a decrease in mechanical strength, making it difficult to effectively maintain the integrity of the electrode structure during cycling.

[0207] FIG1 is an electrochemical window diagram of the gel electrolyte of Example 2. As shown in FIG1 , the gel electrolyte has excellent electrochemical stability, and the electrochemical window is as high as 5.4 V, which can match high-energy positive electrode materials and is conducive to improving energy density.

[0208] FIG2 is a diagram showing the room temperature cycling performance of a lithium secondary battery prepared with the gel electrolyte of Example 2. As shown in FIG2 , the lithium ion battery assembled with the gel electrolyte remains stable after 300 cycles, with a capacity retention rate of up to 86%.

[0209] Example 11

[0210] 1) trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile are mixed in a mass ratio of 9:1:89.975:0.025 to obtain a uniform precursor solution, wherein the electrolyte comprises lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) in a mass ratio of 12.5:7.75:38.75:7.75:10:23.25;

[0211] 2) Inject 4g of the precursor solution into a baked lithium-ion battery (capacity of about 1Ah), where the negative electrode active material is silicon carbon (Tianmu Pioneer 550) and the positive electrode active material is ternary nickel-cobalt-manganese LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811, Rongbai S85E), the diaphragm is a PE ceramic diaphragm; after filling and sealing, the first battery is obtained after standing at room temperature of 25°C for 24 hours;

[0212] 3) The first battery was cycled twice according to the following charge-discharge cycle and activated to obtain a second battery, wherein the charge-discharge cycle is as follows: using a battery clamp, under a pressure of 0.3 MPa, at 25°C, charging at a constant current and constant voltage of 0.1C to a battery operating cut-off voltage of 4.25V, with a cut-off current of 0.05C, and resting for 5 minutes, and then discharging at a constant current of 0.1C to a battery operating cut-off voltage of 2.75V, and resting for 5 minutes;

[0213] 4) The second battery was reacted at a pressure of 0.3 MPa and a temperature of 60° C. for 24 hours. After the reaction, the battery was allowed to stand at room temperature for 24 hours. The battery cell was then vented and the secondary venting time was 5 seconds with a vacuum degree of 90-95 Pa to complete the battery packaging. Finally, the battery was divided into different capacities, with the currents of 0.1C, 0.3C, 0.5C, and 1C, respectively, to obtain the gel battery of this embodiment.

[0214] Example 12

[0215] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator is adjusted to 14:1:84.975:0.027.

[0216] Example 13

[0217] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 3), the pressure is adjusted to 0.1 MPa.

[0218] Example 14

[0219] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 3), the pressure is adjusted to 1 MPa.

[0220] Example 15

[0221] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 4), the pressure is adjusted to 0.1 MPa.

[0222] Example 16

[0223] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 4), the pressure is adjusted to 0.5 MPa.

[0224] Example 17

[0225] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 4), the reaction time is adjusted to 28 hours.

[0226] Example 18

[0227] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 4), the reaction time is adjusted to 32 hours.

[0228] Example 19

[0229] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), trifluoroethyl methacrylate is replaced by 1,1,1,3,3,3-hexafluoroisopropyl methacrylate.

[0230] Example 20

[0231] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), trifluoroethyl methacrylate is replaced by hexafluorobutyl methacrylate.

[0232] Example 21

[0233] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), trifluoroethyl methacrylate is replaced by octafluoropentyl methacrylate.

[0234] Example 22

[0235] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of trifluoroethyl methacrylate in the precursor solution is adjusted to 6.5wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 6.5:1:92.475:0.025.

[0236] Example 23

[0237] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of trifluoroethyl methacrylate in the precursor solution is adjusted to 19wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 19:1:79.975:0.025.

[0238] Example 24

[0239] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of trifluoroethyl methacrylate in the precursor solution is adjusted to 11.5wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 11.5:1:87.475:0.025.

[0240] Example 25

[0241] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), pentaerythritol tetraacrylate is replaced by trimethylolpropane triacrylate.

[0242] Example 26

[0243] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), pentaerythritol tetraacrylate is replaced by trimethylolpropane trimethacrylate.

[0244] Example 27

[0245] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), azobisisobutyronitrile is replaced by azobisisoheptanenitrile.

[0246] Example 28

[0247] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of pentaerythritol tetraacrylate in the precursor solution is adjusted to 0.8wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 9:0.8:90.175:0.027.

[0248] Example 29

[0249] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of pentaerythritol tetraacrylate in the precursor solution is adjusted to 2 wt %. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 9:2:88.975:0.025.

[0250] Example 30

[0251] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of azobisisobutyronitrile in the precursor solution is adjusted to 0.01wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 9:1:89.99:0.01.

[0252] Example 31

[0253] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of azobisisobutyronitrile in the precursor solution is adjusted to 0.5wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 9:1:89.95:0.5.

[0254] Example 32

[0255] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that, in step 1), the content of fluoroethylene carbonate (FEC) in the electrolyte is adjusted to 5 wt %. That is, the mass ratio of lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in the electrolyte is 12.5:9:40:9:5:24.5.

[0256] Example 33

[0257] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that, in step 1), the content of fluoroethylene carbonate (FEC) in the electrolyte is adjusted to 12 wt %. That is, the mass ratio of lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in the electrolyte is 12.5:7.25:38.25:7.25:12:22.75.

[0258] Example 34

[0259] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of trifluoroethyl methacrylate in the precursor solution is adjusted to 20wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 20:1:78.975:0.025.

[0260] Example 35

[0261] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of pentaerythritol tetraacrylate in the precursor solution is adjusted to 2.5wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 9:2.5:88.475:0.025.

[0262] Example 36

[0263] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 1), the mass percentage of azobisisobutyronitrile in the precursor solution is adjusted to 0.1wt%. Accordingly, the mass ratio of trifluoroethyl methacrylate, pentaerythritol tetraacrylate, electrolyte, and initiator azobisisobutyronitrile is 9:1:89.9:0.1.

[0264] Example 37

[0265] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 3), the charge and discharge current is adjusted to 0.08C.

[0266] Example 38

[0267] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 3), the charge and discharge current is adjusted to 0.12C.

[0268] Comparative Example 3

[0269] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 11, except that in step 2), after the liquid is injected and sealed, the battery is left to stand at 25° C. for 3 hours to obtain the first battery;

[0270] In step 3), the first battery is reacted at a pressure of 0.3 MPa and a temperature of 60°C for 24 hours. After the reaction is completed, it is allowed to stand at room temperature for 24 hours, and then subjected to a formation treatment at a pressure of 0.3 MPa, a temperature of 45°C, a formation current of 0.1C, and a formation time of 390 min; the battery after formation is aged at an aging temperature of 45°C, a pressure of 3 MPa, and a time of 16 hours; the battery cell is then exhausted, the secondary exhaust time is 5 seconds, the exhaust vacuum degree is 90-95 Pa, and the battery packaging is completed; finally, the battery is divided into different capacities, and the currents of the divided capacities are 0.1C, 0.3C, 0.5C, and 1C, respectively, to obtain the semi-solid-state battery of this comparative example.

[0271] Comparative Example 4

[0272] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 12, except that, in step 2), after the liquid is injected and sealed, the battery is left to stand at 25° C. for 3 hours to obtain the first battery;

[0273] In step 3), the first battery is reacted at a pressure of 3 MPa and a temperature of 60°C for 24 hours. After the reaction is completed, it is allowed to stand at room temperature for 24 hours, and then subjected to a formation treatment at a pressure of 3 MPa, a temperature of 45°C, a formation current of 0.1C, and a formation time of 390 min; the battery after the formation is aged at an aging temperature of 45°C, a pressure of 3 MPa, and a time of 16 hours; the battery cell is then exhausted, the secondary exhaust time is 5 seconds, the exhaust vacuum is 90-95 Pa, and the battery packaging is completed; finally, the battery is divided into different capacities, and the currents of the divided capacities are 0.1C, 0.3C, 0.5C, and 1C, respectively, to obtain the semi-solid-state battery of this comparative example.

[0274] Comparative Example 5

[0275] The preparation method of the gel battery in this comparative example is basically the same as that in Example 11, except that in step 3), the pressure is adjusted to 2 MPa.

[0276] Comparative Example 6

[0277] The preparation method of the gel battery in this comparative example is basically the same as that in Example 11, except that in step 4), the pressure is adjusted to 0 MPa and the temperature is adjusted to 80°C.

[0278] Comparative Example 7

[0279] The preparation method of the gel battery in this comparative example is basically the same as that in Example 11, except that in step 4), the reaction time is adjusted to 48°C.

[0280] Comparative Example 8

[0281] The preparation method of the gel battery in this comparative example is basically the same as that in Example 11, except that in step 1), the reaction monomer is replaced by ethyl acrylate instead of trifluoroethyl methacrylate.

[0282] Comparative Example 9

[0283] The preparation method of the gel battery in this embodiment is basically the same as that in Example 11, except that in step 3), the charge and discharge current is adjusted to 0.2C.

[0284] Test example

[0285] 1. Testing the high temperature storage performance and rate performance of the lithium ion batteries in Examples 11 to 38 and Comparative Examples 3 to 9 comprises the following steps:

[0286] 1) High-temperature storage capacity remaining rate and capacity recovery rate

[0287] The lithium-ion battery was charged to 4.25V at a current density of 1C to obtain a fully charged battery, and the thickness of the fully charged battery was measured to obtain an initial thickness T0; the internal resistance of the battery was measured using a resistance meter to obtain an initial internal resistance R0; at room temperature of 25°C, the fully charged battery was discharged for 30 minutes to 2.75V, left for 1 hour, and then discharged for 10 seconds to 2.75V to obtain an initial DC resistance DCR0; the discharge capacity obtained by 1C discharge during capacity division was defined as the initial discharge capacity C0;

[0288] The fully charged battery was stored in a constant temperature oven at 60°C for 14 days. After the storage period, the thickness of the battery after storage was measured to obtain the battery thickness T1. The internal resistance of the battery after storage was tested using a resistance meter to obtain the battery internal resistance R1. At room temperature of 25°C, the stored battery was discharged for 30 minutes to 2.75V, left for 1 hour, and then discharged for 10 seconds to 2.75V to obtain the DC resistance DCR1 of the battery after storage.

[0289] At room temperature (25°C), the stored battery was discharged at 1C to 2.75V to obtain a discharge capacity of C1. The battery was then charged and discharged for three cycles at 1C between 2.75V and 4.25V to obtain a discharge capacity of C2.

[0290] Then the high temperature storage capacity retention rate, high temperature storage capacity recovery rate, high temperature storage internal resistance change rate, high temperature storage thickness expansion rate, and DC resistance change rate are calculated by formula a, formula b, formula c, formula d, and formula e, respectively.

[0291] High temperature storage capacity retention rate (%) = (C1 / C0) × 100% Formula a

[0292] High temperature storage capacity recovery rate (%) = (C2 / C1) × 100% Formula b

[0293] High temperature storage internal resistance change rate (%) = (R1 / R0) × 100% Formula c

[0294] High temperature storage thickness expansion rate (%) = (T1 / T0) × 100% Formula d

[0295] High-temperature storage DC resistance change rate (%) = (DCR1 / DCR0) × 100% Formula e.

[0296] The test and calculation results are shown in Table 3.

[0297] 2) Rate performance

[0298] A high-precision battery performance testing system was used to perform rate performance testing on the lithium-ion batteries in the above embodiments and comparative examples. The specific method was as follows: 10 cycles were performed at 1C, 2C, 3C, and 1C at 2.75-4.25V, respectively. The average discharge capacity during the initial 10 cycles at 1C was recorded as C3, and the average discharge capacity during the final 10 cycles at 1C was recorded as C4. The 1C capacity recovery rate (%) was calculated as (C4 / C3)×100%. On this basis, the batteries were cycled at 1C for 200 cycles at 2.75-4.25V. The test results are shown in Table 4 and Figures 3 and 4.

[0299] Figure 4 shows the discharge capacity changes of the gel batteries in Example 11 and Comparative Example 3 at different discharge rates, and Figure 5 shows the discharge capacity changes of the gel batteries in Example 12 and Comparative Example 4 at different discharge rates. Figures 4 and 5 show that Example 11 and Example 12 have higher rate discharge performance than Comparative Example 4, respectively.

[0300] Table 3

[0301] Table 4

[0302] From Table 3 and Table 4, we can see that:

[0303] Compared to Comparative Examples 3-9, Examples 11-38 exhibited higher high-temperature storage performance and rate performance. The lithium-ion battery in Example 12 exhibited a capacity retention rate of 70.5%, a capacity recovery rate of 74.3%, an internal resistance change rate of 45.7%, and a resistance change rate of 40.3% under high-temperature storage. Correspondingly, the thickness expansion rate during high-temperature storage was 10.3%, and the 1C capacity recovery rate was as high as 98.6%. While the expansion rate was relatively high, it was still within an acceptable range, and the overall performance was significantly higher than that of the lithium-ion batteries in Comparative Examples 3-9. Therefore, the gel batteries of the present disclosure exhibited higher rate performance and higher-temperature storage performance.

[0304] 2. AC impedance test was performed on the gel batteries in Examples 11 and 12, Comparative Examples 3 and 4, and on the gel batteries in Examples 11 and 12, Comparative Examples 3 and 4 after storage according to the above-mentioned high temperature storage method. The test conditions were: AC impedance test was performed using an electrochemical workstation at a frequency of 0.04 Hz to 10 5 Hz, the AC amplitude was 10mV, and the AC impedance spectrum (EIS) was obtained. The test results are shown in Figures 6 to 9.

[0305] Figure 6 shows the EIS test graph of the gel battery in Example 11 before and after high-temperature storage, Figure 7 shows the EIS test graph of the gel battery in Example 12 before and after high-temperature storage, Figure 8 shows the EIS test graph of the gel battery in Comparative Example 3 before and after high-temperature storage, and Figure 9 shows the EIS test graph of the gel battery in Comparative Example 4 before and after high-temperature storage. In the EIS test, the larger the radius of the first arc in the curve, the more intense the interfacial reaction. Comparing Figures 6-7 and 8-9, it can be seen that the radius of the first arc in the EIS test curves of Comparative Examples 3 and 4 is significantly larger than that of Examples 11 and 12. This shows that the gel battery prepared by the preparation method of the present disclosure can effectively reduce the SEI film impedance, and the fluorine-containing polymer helps stabilize the SEI film, further reducing the interfacial impedance and battery internal resistance.

[0306] 3. SEM tests were performed on the cross sections of the negative electrode active materials in the gel batteries of Example 12 and Comparative Example 4. The test results are shown in Figures 10 to 13.

[0307] Figure 10 is a cross-sectional SEM image of the negative electrode active material in the gel battery in Example 12 at 6.00K, Figure 11 is a cross-sectional SEM image of the negative electrode active material in the gel battery in Example 12 at 10.0K, Figure 12 is a cross-sectional SEM image of the negative electrode active material in the gel battery in Comparative Example 4 at 6.00K, and Figure 13 is a cross-sectional SEM image of the negative electrode active material in the gel battery in Comparative Example 4 at 10.0K. As can be seen from Figures 10 to 13, the surface of the negative electrode active material in Example 12 contains a coating layer with a small thickness of about 0.42 μm, and in Figure 11 at a high rate, it can be seen that the coating layer contains obvious light and dark irregular areas; although the surface of the negative electrode active material in Comparative Example 4 also contains a coating layer, the thickness is relatively thick, about 0.58 μm, and in Figure 13 at a high rate, it can be seen that there are almost no obvious light and dark irregular areas in the coating layer, and only a very small part exists; combined with the internal resistance and DC impedance data of the lithium ion batteries in Example 12 and Comparative Example 4 in Table 3 above, it can be inferred that the bright areas therein may be SEI films, and the dark areas may be polymers. It is precisely because more SEI films are formed on the surface of the negative electrode active material in Example 12 and almost no SEI film is formed in the coating layer on the surface of the negative electrode active material in Comparative Example 4 that the DC impedance and internal resistance of the battery in Comparative Example 4 are significantly higher than those in Example 12.

[0308] Unless otherwise specified, all technical terms used in this disclosure have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. The terms "comprise" or "include" are open-ended expressions, i.e., include the contents specified in this disclosure, but do not exclude contents in other aspects.

[0309] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0310] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are exemplary and are not to be construed as limitations on the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims

1. A gel electrolyte precursor liquid, comprising a reactive monomer, a crosslinking agent, an initiator and an electrolyte; wherein: The reactive monomer includes at least one of the compounds shown in Formula 1: In Formula 1, R1 is methyl or hydrogen; L is a single bond, a substituted or unsubstituted alkylene group having 1 to 4 carbon atoms; R2, R3, and R4 are the same as or different from each other and are each independently hydrogen, an alkyl group having 1 to 4 carbon atoms, or fluorine, and at least one of R2, R3, and R4 is fluorine; R5 is hydrogen, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, or fluorine, and the substituent in L and R5 is fluorine; The cross-linking agent includes at least one of the compounds represented by Formula 2-1 and Formula 2-2: In formula 2-1, R 1 is an alkyl group having 1 to 4 carbon atoms or R 2 、R 3 、R 4 and R a are the same as or different from each other and are each independently hydrogen or methyl, Indicates a connection key; In formula 2-2, R 5 and R 6 are the same or different and are each independently an alkyl group having 1 to 4 carbon atoms, R 7 、R 8 、R 9 and R 10 are the same as or different from each other and are each independently hydrogen or methyl.

2. The gel electrolyte precursor solution according to claim 1, wherein In Formula 1, at least one of the following conditions is satisfied: L is a single bond, methylene, fluorine-substituted methylene, ethylene, or fluorine-substituted ethylene, wherein the number of fluorine atoms in the fluorine-substituted methylene and fluorine-substituted ethylene groups is one or more; R2, R3 and R4 are each independently hydrogen, methyl, ethyl or fluorine, and at least two of R2, R3 and R4 are fluorine; R5 is hydrogen or trifluoromethyl.

3. The gel electrolyte precursor solution according to claim 1 or 2, wherein The reactive monomer includes at least one of trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, trifluoroethyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate and octafluoropentyl methacrylate.

4. The gel electrolyte precursor solution according to any one of claims 1 to 3, wherein The cross-linking agent satisfies at least one of the following conditions: In formula 2-1, R 1 is methyl, ethyl or n-propyl; In formula 2-2, R 5 and R 6 are the same or different and are each independently methyl, ethyl or n-propyl.

5. The gel electrolyte precursor solution according to any one of claims 1 to 4, wherein The crosslinking agent includes at least one of pentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, trimethylolpropane triacrylate, and 1,1,1-trimethylolethane triacrylate.

6. The gel electrolyte precursor solution according to any one of claims 1 to 5, wherein The mass ratio of the reaction monomer, the crosslinking agent and the initiator is (6-20):1:(0.05-0.1).

7. The gel electrolyte precursor solution according to any one of claims 1 to 6, wherein The electrolyte includes a lithium salt, an organic solvent and an optional electrolyte additive; based on the total weight of the electrolyte, the mass content of the lithium salt is 10% to 17%, the mass content of the electrolyte additive is 5% to 15%, and the mass content of the organic solvent is 70% to 85%.

8. The gel electrolyte precursor solution according to any one of claims 1 to 7, wherein Based on the total mass of the gel electrolyte precursor liquid being 100 parts, the mass parts a of the reaction monomer, the mass parts b of the electrolyte, the mass parts c of the cross-linking agent, and the mass parts d of the initiator satisfy the following relationship: 4≤a≤22, 74≤b≤95, 0.8≤c≤2, 0.01≤d<1.

9. The gel electrolyte precursor solution according to claim 8, wherein 6≤a≤17,82≤b≤93,0.8≤c≤1.5,0.07≤d<1.

10. The gel electrolyte precursor solution according to claim 8 or 9, wherein 0.3<a×(0.1-d)×c×(100-b)<6.

2.

11. A gel electrolyte prepared by curing the gel electrolyte precursor liquid according to any one of claims 1 to 10; wherein: The curing reaction satisfies at least one of the following conditions: The curing reaction temperature is 55°C to 70°C; The curing reaction time is 12 hours to 25 hours.

12. A lithium secondary battery, wherein: comprising the gel electrolyte according to claim 11; The lithium secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer located on at least one side thereof, wherein the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; The lithium secondary battery includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer located on at least one side thereof, wherein the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a nickel-containing lithium battery positive electrode material.

13. The lithium secondary battery according to claim 12, wherein The positive electrode active material includes a nickel ternary positive electrode material, the chemical formula of which is LiNixCo y Mn z O2,x+y+z=1,0.6≤x≤0.9,0 <y<0.2,0<z<0.2。 14. The lithium secondary battery according to claim 12 or 13, wherein The negative electrode active material includes a core and a coating layer, the coating layer includes a first coating layer and a second coating layer, the first coating layer is located on at least a portion of the outer surface of the core, the second coating layer is located on a surface of the first coating layer away from the core, or the second coating layer is located on a surface of the first coating layer away from the core and on the surface of the core; The gel electrolyte comprises an electrolyte solution and a gel polymer; The core includes a negative electrode material that can be used for active ion embedding and extraction, the first coating layer includes an SEI film, and the second coating layer includes the gel polymer; The coating layer has a thickness of 0.3-0.5 μm.

15. A method for preparing a lithium secondary battery according to any one of claims 12 to 14, comprising: injecting the gel electrolyte precursor solution according to any one of claims 1 to 10 into a battery cell to obtain a first battery; Cycling the first battery 1-2 times according to the following charge-discharge mechanism to obtain a second battery; The charge and discharge mechanism includes: charging at a constant current and constant voltage of 0.08C to 0.12C to the battery working cut-off voltage at a pressure of 0.1MPa to 1.0MPa and a temperature not higher than 25°C, with a cut-off current of 0.05C, and then discharging at a constant current of 0.08C to 0.12C to the battery working cut-off voltage after standing still; The second battery is reacted at a pressure of 0.1 MPa to 0.5 MPa and a temperature of 55° C. to 70° C. for a reaction time of not less than 24 hours to obtain the lithium secondary battery.

Images