Gel electrolyte precursor fluid, gel electrolyte, and lithium secondary battery

Abstract

The invention relates to the field of batteries, and provides a gel electrolyte precursor liquid, a gel electrolyte and a lithium secondary battery. The gel electrolyte precursor liquid comprises a reactive monomer, a cross-linking agent, an initiator and an electrolyte, the reactive monomer comprises at least one of compounds shown as a formula 1, and the cross-linking agent comprises at least one of compounds shown as a formula 2-1 and a formula 2-2; the gel electrolyte prepared from the gel electrolyte precursor solution has relatively high oxidation resistance, and also has relatively high ionic conductivity and mechanical strength. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a gel electrolyte precursor liquid, a gel electrolyte and a lithium secondary battery. Background Art

[0002] As the main power source of new energy vehicles, lithium secondary batteries have promoted the rise of new energy. With the rapid development of new energy vehicles, the market demand for power batteries is also increasing. At present, power batteries are developing in the direction of high capacity, low price and greater safety.

[0003] Lithium secondary batteries generally include a positive electrode and a negative electrode, a separator inserted between the positive electrode and the negative electrode, and an electrolyte as a transfer medium for lithium ions, wherein the electrolyte generally uses a liquid electrolyte. However, the electrolyte may leak during use, and may also cause the solvent to be decomposed and produce side reactions during the battery charging and discharging process. During high-temperature storage, side reactions may be further accelerated, increasing the amount of gas generated. The continuously generated gas may induce an increase in the internal pressure of the battery, thereby causing the battery thickness to expand, causing safety issues. The use of gel electrolytes can overcome the safety issues of liquid electrolytes, and gel electrolytes have advantages in processability and lightweight, and they can form a protective interface with the battery electrodes. However, the oxidation resistance of gel electrolytes is not high, it is easy to react with oxygen-containing materials in the battery, the mechanical strength of the gel is not high, the protection of the electrodes is limited, and the ionic conductivity needs to be improved, all of which limit the application of gel electrolytes in batteries. Summary of the invention

[0004] The present application aims to solve one of the technical problems in the related art at least to some extent.

[0005] In a first aspect, the present application 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 shown in Formula 1:

[0006]

[0007] 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 or different from each other and are 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;

[0008] The cross-linking agent includes at least one of the compounds represented by Formula 2-1 and Formula 2-2:

[0009]

[0010] 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 the connection key;

[0011] 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.

[0012] In the gel electrolyte precursor liquid of the present application, the fluorine-containing acrylate monomer (shown in Formula 1) is used as a functional monomer, which is beneficial to improve the oxidation resistance of the formed gel electrolyte, and the fluorine-containing solid electrolyte (SEI) film is formed at the negative electrode, which 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 the cross-linking agent can control the degree of cross-linking of the functional monomer, which is beneficial to improve the cross-linking density of the gel electrolyte and form 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 violent polymerization, and the system temperature will not rise sharply, ensuring the safety of the reaction.

[0013] In some embodiments of the present application, in Formula 1, L is a single bond, a methylene group, a fluorine-substituted methylene group, an ethylene group, or a fluorine-substituted ethylene group, wherein the number of fluorine in the fluorine-substituted methylene group and the fluorine-substituted ethylene group is one or more, respectively.

[0014] In some embodiments of the present application, 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.

[0015] In some embodiments of the present application, R5 is hydrogen or trifluoromethyl.

[0016] In some embodiments of the present application, 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.

[0017] Optionally, the reactive monomer includes at least one of trifluoroethyl methacrylate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. The order of reactivity in the fluoroalkyl group is: -CF>-CF2>-CF3. The higher the activity, the easier it is to react with lithium ions and consume electrolyte. The above two monomers have -CF3 and are combined with double bonds to connect methyl groups, which can reduce the degree of consumption of electrolyte. The formed polymer framework constructs an in-situ polymerized gel electrolyte, which is more conducive to stabilizing the SEI film of the negative electrode and reducing the occurrence of side reactions in the electrolyte while improving the ionic conductivity.

[0018] In some embodiments of the present application, in Formula 2-1, R 1 It is methyl, ethyl or n-propyl.

[0019] In some embodiments of the present application, in Formula 2-2, R 5 and R 6 are the same or different and are each independently methyl, ethyl or n-propyl.

[0020] In some embodiments of the present application, the cross-linking agent includes at least one of pentaerythritol tetraacrylate, di(trimethylolpropane) tetraacrylate, trimethylolpropane triacrylate and 1,1,1-trimethylolethane triacrylate.

[0021] In some embodiments of the present application, the initiator includes an oil-soluble initiator.

[0022] Optionally, the oil-soluble initiator includes at least one of azobisisobutyronitrile and azobisisoheptanitrile. Thus, the polymerization reaction efficiency can be further improved.

[0023] In some embodiments of the present application, the mass ratio of the reaction monomer, the crosslinking agent and the initiator is (6-20):1:(0.05-0.1). Thus, the formed polymer can have a more appropriate network structure, while ensuring excellent ionic conductivity and mechanical strength, while avoiding the inability to form a gel due to too low a crosslinking degree and the possibility of too low an ionic conductivity due to too high a crosslinking degree.

[0024] In some embodiments of the present application, the electrolyte includes a lithium salt, an organic solvent, and an optional electrolyte additive.

[0025] Optionally, 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%.

[0026] In some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

[0027] In some embodiments of the present application, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl 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.

[0028] In some embodiments of the present application, the electrolyte additive includes a negative electrode film-forming additive.

[0029] Optionally, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0030] In some embodiments of the present application, 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 is beneficial to reduce the viscosity of the electrolyte and improve the ionic conductivity of the system.

[0031] In some embodiments of the present application, based on the total mass of the gel electrolyte precursor liquid as 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:

[0032] 4≤a≤22, 74≤b≤95, 0.8≤c≤2, 0.05≤d<1.

[0033] Optionally, 6≤a≤17, 82≤b≤93, 0.8≤c≤1.5, 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.

[0034] Optionally, 0.3<a·(0.1-d)·c·(100-b)<6.2.

[0035] In a second aspect, the present application provides a gel electrolyte obtained by subjecting the gel electrolyte precursor liquid described in the first aspect of the present application to a curing reaction.

[0036] The gel electrolyte provided by the present application has both excellent ionic conductivity and mechanical strength, and has high aging resistance. Its fluorine-containing skeleton provides excellent oxidation resistance and improves the interface stability between the gel electrolyte and the positive electrode. In particular, the gel electrolyte can be stably cycled in a high-content silicon-based and high-nickel ternary lithium-ion battery system, and can effectively maintain the integrity of the negative electrode structure and inhibit the expansion of the silicon negative electrode.

[0037] In some embodiments of the present application, the temperature of the curing reaction 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 to ensure product performance.

[0038] In a third aspect, the present application provides an application of the gel electrolyte precursor liquid described in the first aspect of the present application or the gel electrolyte described in the second aspect in a lithium secondary battery.

[0039] In a fourth aspect, the present application provides a lithium secondary battery, comprising the gel electrolyte described in the third aspect of the present application.

[0040] In some embodiments of the present application, 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. In particular, the gel electrolyte can effectively maintain the integrity of the negative electrode structure in a battery system with a silicon negative electrode and inhibit the expansion of the silicon negative electrode.

[0041] In some embodiments of the present application, the lithium secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on at least one side thereof, 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. In particular, the gel electrolyte can improve oxidation resistance in a nickel-containing lithium ion battery system.

[0042] Optionally, the positive electrode active material includes a nickel ternary positive electrode material, and 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。

[0043] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0045] Figure 1 is the electrochemical window diagram of the gel electrolyte of Example 2;

[0046] Figure 2 This is a diagram of the room temperature cycle performance of a lithium secondary battery prepared with the gel electrolyte of Example 2. DETAILED DESCRIPTION

[0047] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0048] A first aspect of the present application provides a gel electrolyte precursor liquid, comprising a reactive monomer, a cross-linking agent, an initiator and an electrolyte.

[0049] In the present application, the reactive monomer is a fluorinated acrylic ester monomer, including at least one of the compounds shown in Formula 1:

[0050]

[0051] In Formula 1, R1 is methyl (-CH3) or hydrogen (-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 substituent in L and R5 is fluorine.

[0052] 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.

[0053] In Formula 1, L may have 1 (eg, alkylene), 2, 3, or 4 carbon atoms.

[0054] 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 number of fluorine in the fluorine-substituted methylene group and the fluorine-substituted ethylene group is one or more. For example, the fluorine-substituted methylene group may include -CF2-, -CHF-, etc.

[0055] 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.

[0056] Optionally, R2, R3 and R4 are all fluorine.

[0057] Alternatively, R5 is hydrogen or trifluoromethyl.

[0058] Optionally, the reactive monomer includes one or more of the following compounds:

[0059]

[0060]

[0061] Furthermore, the reactive monomer includes at least one of trifluoroethyl methacrylate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate. The reactive monomer is beneficial for improving the ionic conductivity of the gel electrolyte, stabilizing the SEI film of the silicon-based negative electrode, and reducing the occurrence of side reactions in the electrolyte.

[0062] In the present application, 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 shown in Formula 2-1 and Formula 2-2:

[0063]

[0064] 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.

[0065] 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.

[0066] As some examples, R 2 , R 3 , R 4 and R a All are hydrogen.

[0067] Optionally, R 1 It is methyl, ethyl or n-propyl.

[0068] 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.

[0069] In formula 2-2, R 5 and R 6 The number of carbon atoms in can be independently distributed as 1, 2, 3 or 4.

[0070] Optionally, R 5 and R 6 are the same or different and are each independently methyl, ethyl or n-propyl.

[0071] In some embodiments, the cross-linking agent includes one or more of the following compounds:

[0072]

[0073]

[0074] In the present application, 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.

[0075] In some embodiments, the initiator includes an oil-soluble initiator, which can be better dissolved in a non-aqueous electrolyte containing an organic solvent as a solvent, and effectively initiate polymerization of the reaction monomers.

[0076] Optionally, 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 the battery to react in situ to form a gel electrolyte, its decomposition temperature has little effect on the battery system and can improve the polymerization reaction efficiency.

[0077] In some embodiments, the mass ratio of the reaction monomer, the crosslinking agent and the 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 avoiding the inability to form a gel due to too low crosslinking and the low ionic conductivity caused by too high crosslinking.

[0078] Optionally, 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.

[0079] Optionally, 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.

[0080] In the present application, the electrolyte may generally include a lithium salt and an organic solvent. Optionally, the electrolyte may also include an electrolyte additive, such as a film-forming additive, or an additive capable of improving certain battery properties, such as an additive capable of improving high temperature performance of the battery.

[0081] In some embodiments, the electrolyte includes a lithium salt, an organic solvent, and an electrolyte additive.

[0082] Optionally, based on the total weight of the electrolyte, the mass content of the lithium salt is 10% to 17%, for example, 10%, 11%, 11.5%, 12%, 12.5%, 13%, 14%, 15%, 16%, 17%, etc.;

[0083] The mass content of the electrolyte additive is 5% to 15%, such as 5%, 7%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, etc.;

[0084] The mass content of the organic solvent is 70% to 85%, for example, 70%, 75%, 77%, 80%, 81%, 82%, 83%, 84%, 85%, etc.

[0085] In the present application, the lithium salt can be selected from the types of electrolytes commonly used in lithium batteries. As some embodiments, the electrolyte lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide.

[0086] In some embodiments, the electrolyte additive includes a negative electrode film-forming additive.

[0087] Optionally, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0088] In the present application, the organic solvent may generally include one or more of carbonates and carboxylates. As 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.

[0089] 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.

[0090] In some embodiments, 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 crosslinking agent, and the mass parts d of the initiator satisfy the following relationship: 4≤a≤22, 74≤b≤95, 0.8≤c≤2, 0.05≤d<1. Thus, the crosslinking reaction of the reactive monomer can be promoted and the oxidation resistance can be improved.

[0091] Optionally, 6≤a≤17, 82≤b≤93, 0.8≤c≤1.5, 0.07≤d<1. Thus, the formed gel electrolyte can have both high ion conductivity and mechanical strength.

[0092] Optionally, 0.3<a·(0.1-d)·c·(100-b)<6.2.

[0093] As some embodiments, the gel electrolyte precursor liquid can be obtained by mixing various components including a reactive monomer, a cross-linking agent, an initiator, a lithium salt, an organic solvent, and optional electrolyte additives.

[0094] The second aspect of the present application provides a gel electrolyte, which is obtained by curing the gel electrolyte precursor liquid described in the first aspect of the present application. The gel electrolyte exists in the form of a gel, with a polymer formed by the reaction of a reaction monomer, a cross-linking agent, and an initiator as a matrix, and the molecular chains of the polymer form a network structure through chemical cross-linking, and the pores in the structure are filled with a liquid plasticizer (solvent) and a lithium salt.

[0095] The gel electrolyte of the present application can effectively inhibit the change of the negative electrode structure, and can greatly improve the safety of the battery while increasing the specific energy. In addition, the gel electrolyte has both excellent ionic conductivity and mechanical strength, and its fluorine-containing skeleton provides excellent oxidation resistance, which improves the interface stability between the gel electrolyte and the positive electrode.

[0096] In some embodiments, the gel electrolyte can be obtained by injecting the gel electrolyte precursor liquid into the battery cell, and heating the battery to cause the mixed liquid to undergo a curing reaction (i.e., cross-linking) to form a gel state. This in-situ polymerization method can enhance the contact between the formed gel electrolyte and the positive and negative electrodes, and play a protective role.

[0097] 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 the formation of gel, the side reactions caused by high temperature can be suppressed as much as possible, thereby ensuring product performance.

[0098] 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.

[0099] The third aspect of the present application provides the 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.

[0100] In some embodiments, the application may include, during the process of preparing the battery, injecting a gel electrolyte precursor into a battery cell, and obtaining the gel electrolyte through in-situ polymerization.

[0101] The fourth aspect of the present application provides a lithium secondary battery, comprising the gel electrolyte described in the second aspect. The lithium secondary battery may include a semi-solid lithium secondary battery.

[0102] Generally, the lithium secondary battery also includes a positive electrode sheet, a negative electrode sheet and a separator. During the battery charging and discharging process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The gel electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the short circuit between the positive electrode and the negative electrode, and at the same time to allow ions to pass through.

[0103] In the present application, the positive electrode plate may generally include a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode plate. The positive electrode active material layer includes a positive electrode active material.

[0104] In some embodiments, the positive electrode active layer includes a transition metal oxide of lithium as the positive electrode active material.

[0105] Optionally, the positive electrode active material includes a nickel-containing lithium battery positive electrode material, such as a high-nickel layered oxide. Thereby, the gram capacity of the positive electrode active material is further increased and the cost of the positive electrode active material is reduced. "High nickel" means that the molar content of Ni is not less than 60% based on all transition metals. In particular, the gel electrolyte is suitable for batteries with high-nickel layered oxide positive electrode materials. Although high-nickel layered oxide positive electrode materials have a higher capacity advantage, they also have high oxidizability, which usually easily leads to electrolyte oxidation and decomposition, causing the battery capacity to drop rapidly. The gel electrolyte of the present application has a higher oxidation resistance, can form a stable electrolyte / positive electrode interface, and improve the electrochemical window of the battery.

[0106] As some examples, the positive electrode active material 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. 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).

[0107] In some embodiments, the positive electrode active material layer may further contain a binder. Specific examples of the binder include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, etc.

[0108] In some embodiments, the positive electrode active material layer may further include a conductive agent. 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, etc.

[0109] In some embodiments, the positive electrode current collector may be made of a metal foil, such as aluminum foil.

[0110] In the present application, the negative electrode sheet generally may include a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0111] In some embodiments, the negative electrode active material may include at least one of graphite, a silicon - based material, and lithium titanate.

[0112] Optionally, 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 with silicon - based material negative electrodes. The silicon - based material has the characteristics of high theoretical specific capacity and low de - lithium potential. However, in general, this material will undergo a huge volume change during charge and discharge, which easily leads to mechanical fracture and pulverization of the active material, causing continuous damage and formation of the solid electrolyte membrane. While the gel electrolyte of the present application has high mechanical properties and ionic conductivity, which can effectively maintain the integrity of the silicon - based negative electrode structure and enable the battery to maintain high electrochemical performance.

[0113] In some embodiments, the negative electrode active material layer may further include a binder. Specific examples of the binder include, but are not limited to, styrene - butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0114] 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.

[0115] In some embodiments, the negative active material layer may further include a thickener, such as sodium carboxymethylcellulose (CMC-Na).

[0116] The present application has no particular restriction 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.

[0117] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into a battery cell by a winding process or a lamination process.

[0118] In some embodiments, the lithium secondary battery includes an outer package. The outer package can be used to encapsulate the battery core and the polymer gel electrolyte. In addition, the outer package of the lithium secondary battery can be a hard shell or a soft shell.

[0119] The present application has no particular limitation on the shape of the lithium secondary battery, which may be cylindrical, square, or any other shape.

[0120] The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained commercially.

[0121] Example 1

[0122] In a glove box filled with argon (water <10ppm, oxygen <1ppm), lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) are mixed and stirred in a mass ratio of 12.5:7.75:38.75:7.75:10:23.25 to obtain an electrolyte.

[0123] 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 evenly to obtain a gel electrolyte precursor liquid; wherein a=6.49, b=92.42, c=1, and d=0.09.

[0124] Example 2

[0125] In a glove box filled with argon (water <10ppm, oxygen <1ppm), lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and diethyl carbonate (DEC) are mixed and stirred in a mass ratio of 12.5:7.75:38.75:7.75:10:23.25 to obtain an electrolyte.

[0126] 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 evenly to obtain a gel electrolyte precursor liquid; wherein a=8.99, b=89.92, c=1, and d=0.09.

[0127] Embodiment 3-6

[0128] 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.

[0129] Example 7

[0130] 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.

[0131] Example 8

[0132] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that pentaerythritol tetraacrylate was replaced by di(trimethylolpropane) tetraacrylate.

[0133] Example 9

[0134] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that pentaerythritol tetraacrylate was replaced by trimethylolpropane triacrylate.

[0135] Example 10

[0136] The gel electrolyte precursor liquid was prepared according to the method of Example 2, except that the amounts of the reaction monomer, initiator, crosslinking agent and electrolyte were adjusted. The specific amounts are shown in Table 1.

[0137] Comparative Example 1

[0138] A gel electrolyte precursor liquid was prepared according to the method of Example 2, except that trifluoroethyl methacrylate was replaced by methyl methacrylate.

[0139] Comparative Example 2

[0140] 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.

[0141] In the above embodiments and comparative examples, the types and contents of the main components in the precursor liquid are shown in Table 1.

[0142] Table 1

[0143]

[0144]

[0145] Note: The amounts in Table 1 are all parts by mass.

[0146] Test Case

[0147] The test examples are used to illustrate the performance of the gel electrolytes prepared from the gel electrolyte precursor solutions of the above embodiments and comparative examples.

[0148] 1. Electrochemical performance test

[0149] 1) The specific preparation method of lithium-ion batteries.

[0150] Preparation of positive electrode: ternary nickel-cobalt-manganese LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811), conductive agent Super P and adhesive PVDF were mixed with solvent NMP in a mass ratio of 92.5:5:2.5 to form positive electrode slurry, which was coated on both sides of positive electrode current collector aluminum foil (thickness 16 μm) and cold pressed after drying. The compaction density was 3.4 g / cm 3 , made into the positive electrode sheet.

[0151] Preparation of negative electrode sheet: Silicon oxide (theoretical capacity of 550 mAh / g), conductive agent Super P, SWCNT, adhesive SBR and CMC were mixed evenly with solvent water in a mass ratio of 87.94:6:0.06:4:2 to form negative electrode slurry. The negative electrode slurry was coated on both sides of the negative electrode current collector copper foil (thickness 9 μm), dried and cold pressed, and the compaction density was 1.55 g / cm 3 , to make the negative electrode sheet.

[0152] Diaphragm: PE ceramic diaphragm;

[0153] 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).

[0154] 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 for curing. The pressure is 3MPa and the temperature is 60°C 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 for formation. The pressure is 3MPa, the temperature is 45°C, the formation current is 0.1C, and the formation time is 390min.

[0155] The semi-solid battery is aged at 45°C, 0.3MPa and 16h. Then, it is vented and sealed again, with 5s venting time and 90Pa~95Pa venting vacuum to complete the battery packaging.

[0156] The batteries were then divided into different capacities with currents of 0.1, 0.3, 0.5C and 1C, followed by performance testing.

[0157] 2) Normal temperature cycle performance test

[0158] 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 standing for 5 minutes, it was discharged to 2.75V at a constant current of 0.5A. After standing 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.

[0159] 2. Test method of ionic conductivity

[0160] The gel electrolyte precursor liquid was placed in a 25 mL colorimetric tube, and the conductivity electrode was inserted and sealed. The tube was 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 with a conductivity meter.

[0161] 3. Test method of electrochemical window

[0162] 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 an initial voltage of open circuit voltage, a scan rate of 0.1 mV / s, and a termination voltage of 7V.

[0163] 4. Storage modulus

[0164] The storage modulus of the gel electrolyte was tested using a rheometer (model Anton Paar MCR302). The gel electrolyte (precursor liquid was reacted at 60°C for 24 hours) was placed on an aluminum plate at 25°C, and a strain scan was performed using a constant rate of 1 rad / s. The scan range was 1-100%, and the average storage modulus within the linear viscoelastic range was taken to determine the storage modulus of the gel.

[0165] The test results are shown in Table 2.

[0166] Table 2

[0167]

[0168] 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 capacity 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 bonds and carbon-fluorine bonds on the polymer can coordinate with lithium ions to accelerate 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 excellent chemical stability for the electrolyte.

[0169] In addition, compared with Example 2, when the polymer content is the same (calculated as the reactive monomer), after the monomer is replaced with methyl methacrylate in Comparative Example 1, the electrochemical window decreases, and the ionic conductivity is not as good as the gel electrolyte in Example 2. The decrease in electrochemical window will affect the chemical stability of the gel electrolyte in the high nickel system, the rate performance is poor, and the cycle effect is not ideal. After the cross-linking agent is replaced with poly (ethylene glycol) diacrylate in Comparative Example 2, the mechanical strength decreases, and it is difficult to effectively maintain the complete structure of the electrode during the cycle of the battery.

[0170] Figure 1 is the electrochemical window diagram of the gel electrolyte of Example 2, Figure 1 It can be seen that the gel electrolyte has excellent electrochemical stability and an electrochemical window of up to 5.4V, which can match high-energy positive electrode materials and is beneficial to improving energy density.

[0171] Figure 2 The room temperature cycle performance diagram of the lithium secondary battery prepared by the gel electrolyte of Example 2 is shown in FIG. Figure 2 It can be seen that the lithium-ion battery assembled with gel electrolyte remains stable after 300 cycles, with a capacity retention rate of up to 86%.

[0172] Unless otherwise specified, all technical terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs. The term "comprising" or "including" is an open expression, that is, including the content specified in this application, but not excluding other aspects.

[0173] In the description of this specification, the description of reference terms "some embodiments", "other embodiments" and the like 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 application. 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 may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory. Although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and cannot be construed as limitations on the present application. Those of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A gel electrolyte precursor liquid, characterized in that: It includes a reactive monomer, a cross-linking 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 or different from each other and are 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 the 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 liquid according to claim 1, characterized in that: In Formula 1, L is a single bond, a methylene group, a fluorine-substituted methylene group, an ethylene group, or a fluorine-substituted ethylene group, wherein the number of fluorine atoms in the fluorine-substituted methylene group and the fluorine-substituted ethylene group is one or more; Optionally, R2, R3 and R4 are each independently hydrogen, methyl, ethyl or fluorine, and at least two of R2, R3 and R4 are fluorine; Alternatively, R5 is hydrogen or trifluoromethyl.

3. The gel electrolyte precursor liquid according to claim 1, characterized in that: The reactive monomers include at least one of trifluoroethyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, trifluoroethyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate and octafluoropentyl methacrylate; Optionally, the reactive monomer includes at least one of trifluoroethyl methacrylate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate.

4. The gel electrolyte precursor liquid according to claim 1, characterized in that: In formula 2-1, R 1 is methyl, ethyl or n-propyl; and / or 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 liquid according to claim 1, characterized in that: 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 liquid according to claim 1, characterized in that: The initiator includes an oil-soluble initiator; Optionally, the oil-soluble initiator includes at least one of azobisisobutyronitrile and azobisisoheptanenitrile.

7. The gel electrolyte precursor liquid according to claim 1, characterized in that: The mass ratio of the reaction monomer, the crosslinking agent and the initiator is (6-20):1:(0.05-0.1).

8. The gel electrolyte precursor liquid according to any one of claims 1 to 7, characterized in that: The electrolyte comprises a lithium salt, an organic solvent and an optional electrolyte additive; Optionally, 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%.

9. The gel electrolyte precursor liquid according to claim 8, characterized in that: The lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide; Optionally, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl 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; Optionally, the electrolyte additive includes a negative electrode film-forming additive; More optionally, the negative electrode film-forming additive includes at least one of fluoroethylene carbonate and vinylene carbonate.

10. The gel electrolyte precursor liquid according to claim 9, characterized in that: The organic solvent comprises 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).

11. The gel electrolyte precursor liquid according to any one of claims 1 to 7, characterized in that: Taking the total mass of the gel electrolyte precursor liquid as 100 parts, the mass parts a of the reaction monomer, the mass parts b of the electrolyte, the mass parts c of the crosslinking agent, and the mass parts d of the initiator satisfy the following relationship: 4≤a≤22, 74≤b≤95, 0.8≤c≤2, 0.05≤d<1; Optionally, 6≤a≤17, 82≤b≤93, 0.8≤c≤1.5, 0.07≤d<1; Optionally, 0.3<a·(0.1-d)·c·(100-b)<6.

2.

12. A gel electrolyte, characterized in that: The gel electrolyte precursor liquid is prepared by curing reaction.

13. The gel electrolyte according to claim 12, characterized in that: The curing reaction temperature is 55°C to 70°C, and / or The curing reaction time is 12h to 25h.

14. Use of the gel electrolyte precursor liquid according to any one of claims 1 to 11 or the gel electrolyte according to any one of claims 12 to 13 in a lithium secondary battery.

15. A lithium secondary battery, characterized in that: Comprising the gel electrolyte according to claim 12 or 13.

16. The lithium secondary battery according to claim 15, characterized in that: The lithium secondary battery comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer located on at least one side thereof, wherein the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material.

17. The lithium secondary battery according to claim 15 or 16, characterized in that: The lithium secondary battery comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer located on at least one side thereof, wherein the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a nickel-containing lithium battery positive electrode material; Optionally, the positive electrode active material includes a nickel ternary positive electrode material, and 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。

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