Gel electrolyte, preparation method, negative pole piece, electrochemical device and device

Abstract

The invention provides a gel electrolyte, a preparation method, a negative pole piece, an electrochemical device and a device. The composition comprises a gel skeleton, a conductive additive and a first lithium salt, the gel skeleton is formed by polymerizing monomers in the presence of an initiator, the monomers comprise at least one of compounds as shown in a formula I-1 and a formula I-2, and the conductive additive comprises dinitrile and / or fluorine-containing ionic liquid. The gel electrolyte formed by the composition is arranged on a negative electrode plate (especially a silicon-carbon negative electrode plate or a silicon-oxygen negative electrode plate), so that the cycle life and the safety of the battery can be greatly improved. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the field of preparation of gel electrolytes, and in particular, to a gel electrolyte, a preparation method, a negative electrode sheet, an electrochemical device and an apparatus. Background Art

[0002] Existing liquid electrolytes and solid electrolytes are extremely prone to decomposition under high-voltage conditions, which will affect the performance and cycle life of the battery. To solve the above technical problems, existing work mainly focuses on how to improve the high-voltage resistance performance and long-cycle performance of the positive electrode material.

[0003] Existing literature provides a gel electrolyte precursor, including monomers, flexible additives, polymerization initiators and lithium salts, wherein the monomers include acrylonitrile monomers. The polyacrylonitrile-based gel electrolyte prepared by this method has a good effect on improving the high-voltage resistance performance of the positive electrode material. However, since it cannot form a protective film on the surface of the negative electrode, the improvement effect on the high-voltage resistance performance and long-cycle performance of the negative electrode material is very limited.

[0004] Another piece of existing literature reports a solid polymer electrolyte with high-voltage resistance, including a polymer matrix and a lithium salt contained in the polymer matrix. The polymer matrix is prepared by polymerizing a fluorinated organic monomer under the action of a catalyst. The fluorinated organic monomer is a fluorinated cyclic or unsaturated chain organic monomer, such as fluoroethylene carbonate. After directly applying the above solid polymer electrolyte to the negative electrode material, the resistance of the negative electrode is very large, resulting in poor conductivity of the electrode. Therefore, the solid polymer electrolyte prepared by this method is mainly aimed at the positive electrode material. At the same time, since a certain amount of hydrofluoric acid will be generated after the fluorinated ethylene carbonate monomer is mixed with the electrolyte, it will damage the positive electrode material. At the same time, considering the protection of the electrode sheet, it is mainly applied to the field of solid electrolytes.

[0005] Since the long-cycle performance of the negative electrode material also has a great impact on the performance and cycle performance of the battery, it is necessary to develop a gel electrolyte that can improve the long-cycle performance of the negative electrode material (especially silicon-carbon negative electrode and silicon-oxygen negative electrode materials). Summary of the Invention

[0006] The present invention aims to provide a gel electrolyte, a preparation method, a negative electrode sheet, an electrochemical device and an apparatus to solve the problem that existing gel electrolyte materials are mainly aimed at the positive electrode material and are not suitable for improving the long-cycle performance of the negative electrode material (especially silicon-carbon negative electrode and silicon-oxygen negative electrode materials).

[0007] The first aspect of the present application provides a gel electrolyte, comprising a gel framework, a conductive additive, and a first lithium salt. The gel framework is formed by polymerization of a monomer in the presence of an initiator. The monomer comprises at least one of the compounds represented by Formula I-1 and Formula I-2. The conductive additive comprises dinitrile and / or a fluorinated ionic liquid;

[0008]

[0009] In Formula I-1, R1, R2, R3, and R4 are each independently selected from a hydrogen atom, a fluorine atom, and a fluorine-substituted or unsubstituted C1-C6 alkyl group, and at least one of R1, R2, R3, and R4 is a fluorine atom or a fluorine-substituted C1-C6 alkyl group. Q1 is absent or Q1 is selected from a C1-C6 alkylene group; in Formula I-2, R5 and R6 are each independently selected from a fluorine-substituted or unsubstituted C1-C6 alkyl group, and at least one of R5 and R6 is a fluorine-substituted C1-C6 alkyl group.

[0010] The second aspect of the present application provides a method for preparing a gel electrolyte. The method for preparing the gel electrolyte comprises: (i) mixing the aforementioned monomer, conductive additive, first lithium salt, and initiator to form a first solution; (ii) mixing the aforementioned non-aqueous solvent and second lithium salt to form a second solution; (iii) mixing the first solution and the second solution to obtain a gel electrolyte forming composition, and polymerizing the gel electrolyte forming composition at 50-100 °C to obtain the gel electrolyte.

[0011] The third aspect of the present application provides a negative electrode sheet, which comprises a negative electrode active material layer and the gel electrolyte provided by the present application on the surface of the negative electrode active material layer or obtained by polymerizing the aforementioned gel electrolyte forming composition on the negative electrode active material layer.

[0012] The fourth aspect of the present application provides an electrochemical device, comprising a positive electrode sheet and the negative electrode sheet provided by the present application.

[0013] The fifth aspect of the present application further provides a device, comprising the above-mentioned electrochemical device.

[0014] Beneficial effects:

[0015] During polymerization, after adding dinitrile and / or a conductive additive such as a fluorinated ionic liquid, such substances can break the grain boundaries to form a non-crystalline phase, thereby improving the lithium-ion conduction performance of the gel electrolyte and enhancing the migration rate of lithium ions. At the same time, compared with the traditional acrylonitrile gel electrolyte, the polyfluoride gel electrolyte formed from the above raw materials has better high-voltage stability, and it can form a stable SEI film on the negative electrode, thereby greatly improving the long-cycle performance of the negative electrode (especially the silicon-carbon negative electrode or the silicon-oxygen negative electrode). In summary, by providing the gel electrolyte formed from the above composition on the negative electrode sheet (especially the silicon-carbon negative electrode sheet or the silicon-oxygen negative electrode sheet), the cycle life and safety of the battery can be significantly improved. Detailed Embodiments

[0016] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0017] In the description herein, unless otherwise specified, "above" and "below" include the recited number.

[0018] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application). It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0019] As described in the background art, the existing gel electrolyte materials mainly target the positive electrode materials and are not suitable for improving the long-cycle performance of the negative electrode materials (especially the silicon-carbon negative electrode and the silicon-oxygen negative electrode materials). To solve the above technical problems, this application provides a gel electrolyte, including a gel framework, a conductive additive, and a first lithium salt. The gel framework is formed by the polymerization of monomers in the presence of an initiator. The monomers include at least one of the compounds represented by Formula I-1 and Formula I-2. The conductive additive is dinitrile and / or a fluorinated ionic liquid;

[0020]

[0021] In formula I-1, R1, R2, R3 and R4 are each independently selected from a hydrogen atom, a fluorine atom, and a fluorine-substituted or unsubstituted C1-C6 alkyl group, and at least one of R1, R2, R3 and R4 is a fluorine atom or a fluorine-substituted C1-C6 alkyl group. Q1 is absent or Q1 is selected from C1-C6 alkylene groups; in formula I-2, R5 and R6 are each independently selected from fluorine-substituted or unsubstituted C1-C6 alkyl groups, and at least one of R5 and R6 is a fluorine-substituted C1-C6 alkyl group.

[0022] When a polymer formed from an unsaturated fluorinated vinyl ester is directly used as an electrolyte, it has a relatively large resistance, which will seriously affect the electrochemical performance of the electrode. To solve this problem, the inventors conducted experiments and mechanism studies from multiple perspectives and found that the fluorinated vinyl ester is prone to form a crystalline phase after polymerization, which results in a relatively high resistance and thus has a great impact on the migration of lithium ions. When a conductive additive such as dinitrile and / or fluorinated ionic liquid is added during polymerization, such substances can break the grain boundaries to form a non-crystalline phase, thereby improving the lithium ion conduction performance of the gel electrolyte and enhancing the migration rate of lithium ions. At the same time, compared with traditional acrylonitrile gel electrolytes, the polyfluoride gel electrolyte formed from the above raw materials has better high-voltage stability, and it can form a stable SEI film on the negative electrode, thereby greatly improving the long-cycle performance of the negative electrode (especially silicon-carbon negative electrode or silicon-oxygen negative electrode). In summary, setting the gel electrolyte formed from the above composition on the negative electrode sheet (especially silicon-carbon negative electrode sheet or silicon-oxygen negative electrode sheet) can significantly improve the cycle life and safety of the battery.

[0023] In some embodiments of the present application, the above monomers include one or more of fluorinated ethylene carbonate, difluorinated ethylene carbonate, fluorinated propylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl 2-(trifluoromethyl)acrylate, and trifluoroethyl methacrylate. More preferably, the above monomers include one or more of 3,3,3-trifluoropropylene carbonate, methyl 2-(trifluoromethyl)acrylate, and trifluoroethyl methacrylate. Compared with other monomers, the gel electrolyte formed from the fluoropolymer formed by the above several monomers has more excellent antioxidant performance, which is beneficial to further improving the capacity retention rate of the battery and extending the cycle life. In some embodiments of the present application, when the monomer is a mixture of the compound represented by formula I-1 and the compound represented by formula I-2, the weight ratio of the two is (4-9):1.

[0024] In some embodiments of the present application, the dinitrile includes one or more of succinonitrile, trans-butenedinitrile, adiponitrile, glutaronitrile, suberonitrile, and sebaconitrile, and more preferably trans-butenedinitrile containing both a nitrile group and an alkene group.

[0025] In some embodiments of the present application, the fluorine-containing ionic liquid includes one or more of 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide, 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0026] In some embodiments of the present application, the conductive additive includes dinitrile and a fluorine-containing ionic liquid, and the weight ratio of the two is 1:(0.1 - 3). Further limiting the composition of the conductive additive is beneficial to further improving the electrochemical performance of the battery cell during application.

[0027] In some embodiments of the present application, the initiator includes, but is not limited to, one or more of stannous octoate, dibutyltin dilaurate, triethylenediamine, dimethylcyclohexylamine, and dimethylaminoethoxyethanol.

[0028] In some embodiments of the present application, the electrolyte can be of the types commonly used in the art. The solvent of the electrolyte includes, but is not limited to, a mixed solution (for example, EC:DMC:EMC = 2:4:4), and the content of lithium hexafluorophosphate (LiPF6) is 1 mol / L.

[0029] In some embodiments of the present application, by weight, the raw materials for forming the gel electrolyte include: 20 - 60 parts of monomer, 20 - 60 parts of conductive additive, 1 - 5 parts of initiator, and 5 - 20 parts of the first lithium salt. Exemplarily, among the above raw materials, the dosage of the monomer can be selected from 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, or the range formed by any two of the above values; the dosage of the conductive additive can be selected from 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, or the range formed by any two of the above values; the dosage of the initiator can be selected from 1 part, 2 parts, 3 parts, 4 parts, 5 parts, or the range formed by any two of the above values; the dosage of the first lithium salt can be selected from 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, or the range formed by any two of the above values.

[0030] Exemplarily, the weight ratio of the monomer to the conductive additive is 1:(0.5 - 3).

[0031] In some embodiments of the present application, the gel electrolyte further includes a non-aqueous solvent and a second lithium salt. The non-aqueous solvent is selected from at least one of linear carbonates; when the ratio of the total mass A of the gel framework, the conductive additive, and the first lithium salt to the total mass B of the non-aqueous solvent and the second lithium salt is 1:9 to 7:3. Exemplarily, the ratio of A to B is 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, or the range formed by any two of the above values.

[0032] In some embodiments of the present application, the first lithium salt and the second lithium salt each include one or more of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium tetrafluoroborate, preferably lithium bis(trifluoromethanesulfonyl)imide.

[0033] The second aspect of the present application further provides a method for preparing a gel electrolyte, including:

[0034] (i) Mixing the aforementioned monomer, conductive additive, first lithium salt, and initiator to form a first solution;

[0035] (ii) Mixing the aforementioned non-aqueous solvent and second lithium salt to form a second solution;

[0036] (iii) Mixing the first solution and the second solution to obtain a gel electrolyte forming composition, and polymerizing the gel electrolyte forming composition at 50 - 100 °C to obtain the gel electrolyte.

[0037] In some embodiments of the present application, the above-mentioned negative electrode sheet is prepared by the following method:

[0038] 1) Uniformly spraying the above-mentioned gel electrolyte forming composition on the negative electrode sheet, and waiting for the surface of the sheet to dry. This operation can be carried out at room temperature, and the humidity should be maintained at a dew point of -40 °C.

[0039] 2) Subjecting the sprayed sheet to in-situ polymerization. The humidity should be maintained at a dew point of -40 °C.

[0040] 3) After polymerization, a negative electrode sheet containing a gel electrolyte can be obtained, and the sheet is sealed in an inert gas (N2) storage cabinet.

[0041] The third aspect of the present application further provides a negative electrode sheet, which includes a negative electrode active material layer and a gel electrolyte on the surface of the negative electrode active material layer. The gel electrolyte includes the gel electrolyte provided by the present application or is obtained by polymerizing the aforementioned gel electrolyte forming composition on the negative electrode active material layer.

[0042] In some embodiments of the present application, the semi-solid battery cell is prepared by the following method: a gel electrolyte and an electrolyte solution are mixed to form a semi-solid gel, and then the prepared positive electrode sheet or negative electrode sheet is immersed therein and then taken out; in-situ polymerization is carried out to form a gel electrolyte layer on the positive electrode sheet or negative electrode sheet; and the semi-solid battery cell is prepared by stacking assembly.

[0043] In some other embodiments of the present application, the semi-solid battery cell is prepared by the following method: after the negative electrode sheet and the positive electrode sheet are stacked and assembled, a mixture of a gel electrolyte precursor solution and an electrolyte solution is injected into the battery cell, and polymerization is carried out in the formation step to form a gel electrolyte, and then a semi-solid battery cell is made.

[0044] In some embodiments of the present application, the negative electrode active material includes a silicon-based material, and the silicon-based material includes silicon oxide and / or silicon carbide. Based on the mass of the negative electrode active material, the mass percentage content g of the silicon-based material satisfies: 1% ≤ g ≤ 35%.

[0045] The fourth aspect of the present application further provides an electrochemical device including the negative electrode sheet provided by the present application.

[0046] In some embodiments of the present application, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes at least one selected from lithium nickel transition metal oxides represented by the formula LiNi m Co n A (1-m-n) O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium, and tungsten, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1.

[0047] In some embodiments of the present application, the above-mentioned electrochemical device includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.

[0048] In a specific example of the present invention, the electrochemical device is a lithium ion battery. The present application does not specifically limit the type of the lithium ion battery, and it can be any type of lithium ion battery, such as button-type, cylindrical, soft-pack lithium ion batteries, etc.

[0049] The fifth aspect of the present application further provides a device including the above-mentioned electrochemical device provided by the present application.

[0050] In some embodiments, the above-mentioned electrical devices include, but are not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. In order to meet the high power and high energy density requirements of the device for secondary batteries, battery packs or battery modules can be used.

[0051] In other embodiments, the above-mentioned electrical devices can be mobile phones, tablet computers, laptop computers, etc. This device usually requires being thin and light, and secondary batteries can be used as the power source.

[0052] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0053] Example 1

[0054] Mix the following components to form a first solution: 42 wt% of monomer, 42 wt% of conductive additive, 0.5 wt% of polymerization initiator, and 15.5 wt% of first lithium salt. The monomer is fluoroethylene carbonate, the conductive additive is succinonitrile, the polymerization initiator is stannous octoate, and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0055] The second solution includes a non-aqueous solvent with a volume ratio of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate of 2:4:4 and a second lithium salt lithium hexafluorophosphate (LiPF6) with a molar concentration of 1.00 mol / L.

[0056] At room temperature, mix the first solution with the second solution to obtain a gel electrolyte forming composition. The weight ratio of the first solution to the second solution is 4:6.

[0057] The preparation steps of the positive electrode plate are as follows: Mix the positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive agent carbon nanotubes (CNT) / acetylene black (Super-P), and binder polyvinylidene fluoride PVDF in a weight ratio of LiNi 0.9 Co 0.05 Mn 0.05 O2﹕CNT / Super-P﹕PVDF = 95﹕2.0 / 1.0﹕2 and homogenize well in an N-methylpyrrolidone NMP solvent system, then coat it on a 12-μm-thick aluminum-coated current collector, dry and roll it to obtain the positive electrode plate.

[0058] The preparation steps of the negative electrode plate are as follows: Mix the negative electrode active material silicon oxide (SiO x, 0.5 ≤ x ≤ 1.5) - graphite composite (the mass ratio of silicon oxide to graphite in the composite is 30:70), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickener sodium carboxymethyl cellulose CMCNa, and polyacrylic acid PAA are homogenized in deionized water at a weight ratio of 96:1:1.5:1:0.5, then coated on the surface of an 8-μm-thick copper current collector, dried, rolled, and slit to obtain a negative electrode sheet. The gel electrolyte forming composition is coated on the negative electrode active material layer of the negative electrode sheet and heated at 80 °C for 24 h, and after polymerization gelation, a negative electrode sheet containing the gel electrolyte is obtained.

[0059] Preparation of a lithium-ion secondary battery: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed in the middle of the positive and negative electrode sheets, and wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum-plastic film outer package, and after liquid injection, formation, secondary sealing, and grading, a lithium-ion secondary battery (battery cell) with a rated capacity of 75 Ah is obtained.

[0060] Example 2

[0061] The difference from Example 1 is that the following components are mixed to form a first solution: monomer 42.2 wt%, conductive additive 42.2 wt%, polymerization initiator 0.1 wt%, first lithium salt 15.5 wt%, and the mass ratio of the first solution to the second solution is 4:6.

[0062] The monomer is: fluoroethylene carbonate and fluoropropylene carbonate (the weight ratio of the two components is 5:1); the conductive additive is: succinonitrile; the polymerization initiator is: stannous octoate; the first lithium salt is: lithium bis(trifluoromethanesulfonyl)imide.

[0063] Example 3

[0064] The difference from Example 1 is that the following components are mixed to form a first solution: monomer 42 wt%, conductive additive 42 wt%, polymerization initiator 0.5 wt%, first lithium salt 15.5%, and the mass ratio of the first solution to the second solution is 4:6. The monomer is fluoroethylene carbonate and fluoropropylene carbonate (the weight ratio of the two components is 1:1); the conductive additive is succinonitrile; the polymerization initiator is stannous octoate; the first lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0065] Example 4

[0066] The difference from Example 1 is as follows: The following components are mixed to form a first solution: 42.2 wt% of monomer, 42.2 wt% of conductive additive, 0.1 wt% of polymerization initiator, 15.5 wt% of first lithium salt, and the mass ratio of the first solution to the second solution is 4:6. Among them, the monomer is vinylidene fluoride carbonate and propylene fluoride carbonate (weight ratio of the two components is 9:1), the conductive additive is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the polymerization initiator is stannous octoate, and the first lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0067] Example 5

[0068] The difference from Example 3 is that the monomer is 3,3,3-trifluoropropylene carbonate.

[0069] Example 6

[0070] The difference from Example 3 is that the monomer is methyl 2-(trifluoromethyl)acrylate.

[0071] Example 7

[0072] The difference from Example 3 is that the monomer is trifluoroethyl methacrylate.

[0073] Example 8

[0074] The difference from Example 3 is that the dinitrile is trans-butenedinitrile.

[0075] Example 9

[0076] The difference from Example 3 is that the dinitrile is adiponitrile.

[0077] Example 10

[0078] The difference from Example 3 is that the dinitrile is suberonitrile.

[0079] Example 11

[0080] The difference from Example 3 is that the conductive additive is 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (Moni Chemical Technology Co., Ltd., [Pi13]TFSI).

[0081] Example 12

[0082] The difference from Example 3 is that the conductive additive is 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Moni Chemical Technology Co., Ltd., [BMPy]TFSI).

[0083] Example 13

[0084] The difference from Example 3 is that the conductive additive is trans-butenedinitrile and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (Moni Chemical Technology Co., Ltd., [EMlm]TFSI), and the weight ratio is 1:1.

[0085] Example 14

[0086] The difference from Example 3 is:

[0087] Mix the following components to form a first solution: 12 wt% of monomer, 72 wt% of conductive additive, 0.5 wt% of polymerization initiator, 15.5% of first lithium salt, and the mass ratio of the first solution to the second solution is 4:6.

[0088] Example 15

[0089] The difference from Example 3 is:

[0090] Mix the following components to form a first solution: 55 wt% of monomer, 35 wt% of conductive additive, 1 wt% of polymerization initiator, 9% of first lithium salt, and the mass ratio of the first solution to the second solution is 4:6.

[0091] Example 16

[0092] The difference from Example 3 is:

[0093] Mix the following components to form a first solution: 45 wt% of monomer, 40 wt% of conductive additive, 1 wt% of polymerization initiator, 14% of first lithium salt, and the mass ratio of the first solution to the second solution is 4:6.

[0094] Comparative Example 1

[0095] Composition of the electrolyte: The solvent is EC:DMC:EMC = 2:4:4 in volume ratio, and the LiPF6 content is 1.00 mol / L.

[0096] Cell preparation method: Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive and negative electrode sheets, and wind to obtain a bare cell; place the bare cell in an aluminum-plastic film outer package, and after injection, formation, secondary sealing, and grading, obtain a lithium-ion secondary battery (cell) with a rated capacity of 75 Ah.

[0097] Testing method

[0098] 1. Standard capacity:

[0099] (a) At 25 ± 2 °C, let it stand for 5 min;

[0100] (b) At 25 ± 2 °C, at 1 / 3 C, at the rated power, charge at constant current and constant voltage until 4.25 V, and the cut-off current is 1 / 20 C rated;

[0101] (c) At 25 ± 2 °C, let it stand for 30 min;

[0102] (d) At 25 ± 2 °C, discharge at 1 / 3 C rated until 2.5 V;

[0103] (e) At 25 ± 2 °C, let it stand for 30 min;

[0104] (f) Repeat steps (b) to (e); (Take the calibrated discharge capacity in the second week as C0);

[0105] (g) At 25 ± 2 °C, charge with 1 / 3 C0 CC - CV to 4.25 V, and the cut-off current is 1 / 20 C0;

[0106] (h) End.

[0107] 2. Number of cycles:

[0108] (j) At 25 ± 2 °C, discharge at 1 C0 constant current until Vmin;

[0109] (k) At 25 ± 2 °C, let it stand still for 30 min;

[0110] (l) At 25 ± 2 °C, charge at 1 C0 constant current until Vmax;

[0111] (m) At 25 ± 2 °C, charge at constant voltage until C0 / 20;

[0112] (n) At 25 ± 2 °C, let it stand still for 30 min;

[0113] (o) Repeat steps (j) to (n) for 1600 times.

[0114] Note: If the discharge capacity during the cycling process reaches 80% of the standard discharge capacity, stop the charge - discharge cycle at this time. This is the number of cycles with a capacity retention rate of 80%. This value is used to evaluate the number of cycles of the battery cell.

[0115] 3. Method for the lithium - ion conductivity of the electrolyte (liquid):

[0116] Button battery assembly:

[0117] Separate two stainless - steel sheets with a glass - fiber non - woven fabric with a thickness of 100 μm, add 100 μl of electrolyte, and assemble into a button battery. After standing still for 24 h, place the button battery at 70 °C and keep it at a constant temperature for 10 h, then cool it to room temperature to provide a test sample for AC impedance.

[0118] Test conditions:

[0119] Temperature: Keep at 25 °C for 1 h, AC impedance frequency: 1 MHz - 100 mHz, and the lithium - ion conductivity can be calculated through the formula ​

[0120] R: The body impedance of the AC impedance test;

[0121] L: The thickness of the glass fiber non-woven fabric;

[0122] S: The area of the stainless steel sheet;

[0123] After testing, the capacity retention rate of the solidified battery cell is more than 10% higher than that of the non-solidified battery cell.

[0124] Other test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] Comparing Examples 1 to 16 with Comparative Example 1, it can be seen that compared with the existing electrolyte, after applying the gel electrolyte provided in this application to the battery cell, the battery cell has better conductivity and cycling performance. At the same time, optimizing parameters such as the type of monomer, the type of conductive additive, and the composition of the first solution is beneficial to further improving the electrochemical performance of the battery cell.

[0128] It should be noted that the terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that these terms can be interchanged under appropriate circumstances so that the embodiments of this application described here can be implemented in an order other than those described here, for example.

[0129] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A gel electrolyte, comprising a gel framework, a conductive additive, and a first lithium salt, wherein the gel framework is formed by polymerization of a monomer in the presence of an initiator, the monomer comprises at least one of the compounds represented by Formula I-1 and Formula I-2, and the conductive additive comprises dinitrile and / or a fluorinated ionic liquid; In Formula I-1, R1, R2, R3, and R4 are each independently selected from a hydrogen atom, a fluorine atom, and a fluorine-substituted or unsubstituted C1-C6 alkyl group, and at least one of R1, R2, R3, and R4 is a fluorine atom or a fluorine-substituted C1-C6 alkyl group, and Q1 is absent or Q1 is selected from a C1-C6 alkylene group; in Formula I-2, R5 and R6 are each independently selected from a fluorine-substituted or unsubstituted C1-C6 alkyl group, and at least one of R5 and R6 is a fluorine-substituted C1-C6 alkyl group.

2. The gel electrolyte according to claim 1, wherein, The gel electrolyte satisfies at least one of the following conditions: (a) The monomer includes one or more of fluorinated ethylene carbonate, difluorinated ethylene carbonate, fluorinated propylene carbonate, 3,3,3-trifluorinated propylene carbonate, methyl 2-(trifluoromethyl)acrylate, and trifluoroethyl methacrylate; (b) The dinitrile includes one or more of succinonitrile, trans-butenedinitrile, adiponitrile, glutaronitrile, suberonitrile, and sebaconitrile; (c) The fluorinated ionic liquid includes one or more of 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide, 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium tetrafluoroborate; 3. The gel electrolyte according to claim 2, wherein, The gel electrolyte satisfies at least one of the following conditions: (d) The monomer includes one or more of 3,3,3-trifluorinated propylene carbonate, methyl 2-(trifluoromethyl)acrylate, and trifluoroethyl methacrylate; (e) The dinitrile includes trans-butenedinitrile; (g) The conductive additive includes the dinitrile and the fluorinated ionic liquid, and the weight ratio of the dinitrile to the fluorinated ionic liquid is 1:(0.1 - 3); 4. The gel electrolyte according to any one of claims 1 to 3, wherein, The gel electrolyte satisfies at least one of the following conditions: (h) By weight, the raw materials for forming the gel electrolyte include: 20 - 60 parts of the monomer, 20 - 60 parts of the conductive additive, 1 - 5 parts of the initiator, and 5 - 20 parts of the first lithium salt; (i) The weight ratio of the monomer to the conductive additive is 1:(0.5 - 3); (j) The gel electrolyte further includes a non-aqueous solvent and a second lithium salt, the non-aqueous solvent includes at least one of linear carbonates and cyclic carbonates; the ratio of the total mass A of the gel framework, the conductive additive, and the first lithium salt to the total mass B of the non-aqueous solvent and the second lithium salt is 1:9 - 7:

3.

5. A method for preparing a gel electrolyte, the method for preparing the gel electrolyte comprising: (i) Mix the monomer, conductive additive, first lithium salt, and initiator described in any one of claims 1 to 4 to form a first solution; (ii) Mix the non-aqueous solvent and the second lithium salt described in condition (j) of claim 4 to form a second solution; (iii) Mix the first solution and the second solution to obtain a gel electrolyte forming composition, and polymerize the gel electrolyte forming composition at 50 - 100 °C to obtain the product.

6. A negative electrode sheet, wherein, The negative electrode sheet includes a negative electrode active material layer and a gel electrolyte on the surface of the negative electrode active material layer. The gel electrolyte includes the gel electrolyte described in any one of claims 1 to 4 or is obtained by polymerizing the gel electrolyte forming composition described in claim 5 on the negative electrode active material layer.

7. The negative electrode sheet according to claim 6, wherein, The negative electrode active material contains a silicon-based material, and the silicon-based material includes a silicon oxide compound and / or a silicon carbide compound. Based on the mass of the negative electrode active material, the mass percentage g of the silicon-based material satisfies: 1% ≤ g ≤ 35%.

8. An electrochemical device, comprising a positive electrode sheet and the negative electrode sheet according to claim 6 or 7.

9. The electrochemical device according to claim 8, wherein, The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes at least one selected from lithium nickel transition metal oxides represented by the formula LiNi m Co n A (1-m-n) O2, where A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium, and tungsten, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1.

10. An apparatus comprising the electrochemical apparatus according to claim 8 or 9.

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