Preparation method of alpha-olefin cross-linked copolymer gel electrolyte and lithium ion battery

Abstract

The invention discloses a preparation method of an alpha-olefin cross-linked copolymer gel electrolyte and a lithium ion battery, and the method comprises the following steps: mixing alpha-olefin, acrylate, a lithium salt, a carbonate plasticizer and an azo initiator to obtain a gel electrolyte precursor solution; and heating and curing the gel electrolyte precursor solution to obtain the cross-linked copolymer gel electrolyte. By introducing alpha-olefin, not only is the crystallinity of the polymer reduced, but also the dissociation and transmission capability of the cross-linked copolymer gel electrolyte to lithium ions can be enhanced; the alpha-olefin, the acrylate, the lithium salt, the carbonate plasticizer and the azo initiator have a synergistic effect, so that the lithium ion transmission performance of the cross-linked copolymer gel electrolyte at room temperature can be further enhanced, and the performance of a battery adopting the cross-linked copolymer gel electrolyte is also remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of gel electrolytes, and more specifically to a preparation method of an alpha-olefin cross-linked copolymer gel electrolyte and a lithium electronic battery. Background Art

[0002] With the rapid development of new energy technologies and electric vehicles, energy storage equipment has increasingly stringent performance requirements, especially in terms of safety, charge and discharge platform and energy density. To meet these requirements, high-voltage lithium metal batteries have attracted much attention. High-voltage lithium metal batteries are composed of high-voltage positive electrode materials, lithium metal negative electrode materials and high-performance electrolyte materials. High-voltage positive electrode materials stand out with their high charge and discharge voltage and energy density, while lithium metal negative electrode materials stand out with their ultra-high specific capacity (3860mAh g -1 ) and extremely low electrochemical potential (-3.04V vs. standard hydrogen electrode) have attracted much attention. Despite the excellent performance of these two materials, there are few electrolyte materials designed for high-voltage lithium metal batteries in practical applications. Among them, liquid electrolytes perform poorly in terms of high voltage resistance and inhibition of lithium dendrite growth, and are prone to fire; all-solid-state electrolytes are difficult to promote and apply due to their high cost, environmentally unfriendly preparation process, poor electrode wetting performance, and narrow electrochemical window.

[0003] Acrylate cross-linked gel electrolytes have attracted more research attention in recent years due to their strong high-voltage resistance, stability to lithium metal, and high designability. However, acrylate cross-linked gel electrolytes still face some challenges in practical applications: poor mechanical properties, high crystallinity and high cross-linking point density limit the transmission channel of lithium ions, affecting their high-rate performance; at the same time, their low lithium ion dissociation ability restricts the ion transmission rate, resulting in low room temperature ionic conductivity.

[0004] In order to improve the lithium ion transmission capacity and room temperature ionic conductivity of acrylate cross-linked gel electrolytes, researchers currently generally use methods such as adding inorganic fillers, blending with polymers, and increasing the content of liquid electrolytes. For example, Chinese patent application document 1 (application number: 202010484928.7, application date: 2018.05.13) proposes a method for enhancing the lithium ion transmission capacity of acrylate-based gel electrolytes by adding a large amount of inorganic active fillers. This method uses a non-in-situ method to prepare a gel electrolyte. First, a composite electrolyte membrane containing a large amount of fast ion conductors is prepared, and then it is immersed in a gel electrolyte, and finally a composite gel electrolyte is obtained by a non-in-situ preparation method. However, the process of this method requires a lot of energy consumption and is accompanied by the generation of a large amount of industrial waste, which is not green and environmentally friendly. In addition, Chinese patent application document 2 (application number: 202010713118.4, application date: 2020.07.22) discloses a method for preparing a cross-linked polymer gel electrolyte containing a large amount of liquid components, but the excessively high liquid electrolyte content limits its application scenarios and is accompanied by safety risks.

[0005] Therefore, in view of the problems of high crystallinity and poor lithium ion dissociation ability of acrylate cross-linked gel electrolytes, the present invention provides a method for preparing an α-olefin cross-linked copolymer gel electrolyte and a lithium electronic battery. Summary of the invention

[0006] In view of this, the present invention provides a method for preparing an α-olefin cross-linked copolymer gel electrolyte and a lithium electronic battery.

[0007] In one aspect, the present invention provides a method for preparing an α-olefin cross-linked copolymer gel electrolyte, comprising:

[0008] Mixing an α-olefin, an acrylate, a lithium salt, a carbonate plasticizer and an azo initiator to obtain a gel electrolyte precursor solution, wherein the carbon chain length of the α-olefin ranges from 6 to 10;

[0009] The gel electrolyte precursor solution is heated and solidified to obtain a cross-linked copolymer gel electrolyte.

[0010] Optionally, the α-olefin is one of 1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene.

[0011] Optionally, the α-olefin, the acrylate, the lithium salt, the carbonate plasticizer and the azo initiator are mixed to obtain the gel electrolyte precursor solution, comprising:

[0012] dissolving the lithium salt in the carbonate plasticizer to obtain a first clear solution;

[0013] adding the α-olefin to the first clear solution and stirring to obtain a second clear solution;

[0014] adding the acrylic acid ester to the second clear solution and stirring to obtain a third clear solution;

[0015] The azo initiator is added to the third clear solution and stirred to obtain the gel electrolyte precursor solution.

[0016] Optionally, the gel electrolyte precursor solution is heated and cured to obtain the cross-linked copolymer gel electrolyte, comprising:

[0017] Injecting the gel electrolyte precursor solution into the battery and leaving it to stand;

[0018] After the positive electrode and the negative electrode of the battery are both infiltrated by the gel electrolyte precursor solution, they are heated and cured at a heating temperature ranging from 45° C. to 60° C. to obtain the cross-linked copolymer gel electrolyte.

[0019] Optionally, the mass of the α-olefin accounts for 10% to 40% of the total mass of the cross-linked copolymer gel electrolyte.

[0020] Optionally, the acrylate is an acrylate containing two carbon-carbon double bonds.

[0021] Optionally, the acrylic acid ester containing two carbon-carbon double bonds is one of 1,4-bis(acryloxy)butane, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,6-bis(methacryloxy)hexane, 1,3-butanediol diacrylate, vinyl diacrylate, 1,3-butanediol dimethacrylate, and 1,4-butanediol dimethacrylate.

[0022] Optionally, the lithium salt is a fluorine-containing lithium salt, and the fluorine-containing lithium salt is one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium difluorooxalatoborate, lithium hexafluorophosphate, and lithium tetrafluoroborate; and / or, the carbonate plasticizer is a fluorine-containing carbonate plasticizer, and the fluorine-containing carbonate plasticizer is one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0023] Optionally, the azo initiator is one or more of dimethyl azobisisobutyrate, azobisisoheptanenitrile, and azobisisobutyronitrile.

[0024] On the other hand, the present invention also provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an α-olefin cross-linked copolymer gel electrolyte, wherein the α-olefin cross-linked copolymer gel electrolyte is prepared by any of the above-mentioned preparation methods.

[0025] Compared with the prior art, the preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention achieve at least the following beneficial effects:

[0026] 1. The preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention are as follows: α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator are mixed to obtain a gel electrolyte precursor solution; the gel electrolyte precursor solution is heated and cured to obtain a cross-linked copolymer gel electrolyte. By introducing α-olefin, not only the crystallinity of the polymer is reduced, but also the dissociation and transmission capacity of the cross-linked copolymer gel electrolyte for lithium ions can be enhanced; the synergistic effect of α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator can further enhance the lithium ion transmission performance of the cross-linked copolymer gel electrolyte at room temperature, and the performance of the battery using the cross-linked copolymer gel electrolyte is also significantly improved.

[0027] 2. The preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention enhance the contact performance of the electrode-electrolyte interface in the high-voltage lithium metal battery by combining in-situ preparation, artificial solid electrolyte interface membrane and cross-linking copolymerization methods, and improve the stability of the cross-linked copolymer gel electrolyte to the high-voltage positive electrode and lithium negative electrode.

[0028] 3. The preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention are simple and easy to operate, have low raw material costs, are safe and environmentally friendly, and are suitable for large-scale batch production.

[0029] Of course, any product implementing the present invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0030] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0032] Figure 1 The present invention is a schematic flow chart of a method for preparing an α-olefin cross-linked copolymer gel electrolyte.

[0033] Figure 2 It is a schematic diagram of a process for mixing α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator.

[0034] Figure 3 The present invention is a schematic diagram of a process for heating and curing a gel electrolyte precursor solution.

[0035] Figure 4 It is a structural diagram of a battery.

[0036] In the figure: 1, positive electrode; 2, cross-linked copolymer gel electrolyte; 3, separator; 4, negative electrode. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0038] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0039] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0040] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0041] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0042] Example 1

[0043] Reference Figure 1 , Figure 1 The present invention provides a schematic flow chart of a method for preparing an α-olefin cross-linked copolymer gel electrolyte, which is used to illustrate a specific embodiment of the method for preparing an α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0044] S1: mixing α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator to obtain a gel electrolyte precursor solution, wherein the carbon chain length of the α-olefin ranges from 6 to 10;

[0045] S2: heating and curing the gel electrolyte precursor solution to obtain a cross-linked copolymer gel electrolyte.

[0046] It should be noted that lithium salts are the main source of active lithium ions in cross-linked copolymer gel electrolytes, and lithium salts can participate in the construction of artificial solid electrolyte interface films, thereby optimizing the electrode-electrolyte interface performance. Carbonates, as film-forming additives and plasticizers, can form solid electrolyte interface films with lithium salts and acrylates. This film can induce uniform deposition and stripping of lithium ions, inhibit the formation of lithium dendrites, and alleviate the volume expansion of lithium metal negative electrodes. At the same time, small molecular carbonates can participate in the transmission of lithium ions, thereby improving the lithium ion transmission performance of cross-linked copolymer gel electrolytes. α-olefins, as the second monomer, can reduce the crystallinity of cross-linked copolymer gel electrolytes, enhance the flexibility of cross-linked copolymer gel electrolytes, and thereby enhance the lithium ion transmission capacity and electrolyte anti-dendrite capacity of cross-linked copolymer gel electrolytes. In addition, α-olefins include alkyl chains, and the introduction of alkyl chains can enhance the electrochemical stability of the positive electrode. The polymer matrix obtained by copolymerization of α-olefin and acrylate has a higher elastic modulus. If the length of the main carbon chain of α-olefin is too long, it is easy to reduce the reactivity of some carbon-carbon double bonds of acrylate and fail to fully participate in the copolymerization. On the contrary, if the main carbon chain of α-olefin is too short, olefin is a gas, the process is difficult, and it is difficult to obtain a copolymer product. Therefore, it is better to set the carbon chain length of α-olefin to 6 to 10. Acrylate can spontaneously form a cross-linked structure during the polymerization process. This cross-linked structure can more effectively fix carbonate plasticizers, inhibit the side reactions of cross-linked copolymer gel electrolytes on the positive and negative electrode surfaces, and enhance the electrochemical stability of batteries using cross-linked copolymer gel electrolytes. In addition, the cross-linked structure gel electrolyte has stronger mechanical properties and better anti-dendritic ability. Azo initiators are used as polymerization initiators to realize the polymerization process.

[0047] It can be understood that in this embodiment, carbonate is used as a film-forming additive and plasticizer, acrylate and α-olefin are used as polymer monomers, and a cross-linked copolymer gel electrolyte is prepared by in-situ polymerization. By introducing α-olefin, not only the crystallinity of the cross-linked copolymer gel electrolyte is reduced, but also the dissociation and transmission capacity of the cross-linked copolymer gel electrolyte for lithium ions can be enhanced; the synergistic effect of α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator can further enhance the lithium ion transmission performance of the cross-linked copolymer gel electrolyte at room temperature, and the performance of the battery using the cross-linked copolymer gel electrolyte is also significantly improved. The method of the present invention is simple and easy to operate, with low raw material cost, safety and environmental protection, and is suitable for large-scale batch production.

[0048] Example 2

[0049] Reference Figure 1 , Figure 2 and Figure 3 , Figure 2It is a schematic diagram of a process for mixing α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator. Figure 3 The present invention is a schematic flow chart of heating and curing a gel electrolyte precursor solution to illustrate another specific embodiment of the method for preparing an α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0050] S1: Mixing α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator to obtain a gel electrolyte precursor solution, wherein the carbon chain length of the α-olefin ranges from 6 to 10, including:

[0051] S11: dissolving a lithium salt in a carbonate plasticizer to obtain a first clear solution;

[0052] S12: adding α-olefin to the first clear solution and stirring to obtain a second clear solution;

[0053] S13: adding acrylate to the second clear solution and stirring to obtain a third clear solution;

[0054] S14: adding an azo initiator to the third clear solution and stirring to obtain a gel electrolyte precursor solution;

[0055] S2: heating and curing the gel electrolyte precursor solution to obtain a cross-linked copolymer gel electrolyte, wherein the mass of the α-olefin accounts for 10% to 40% of the total mass of the cross-linked copolymer gel electrolyte, comprising:

[0056] S21: injecting the gel electrolyte precursor solution into the battery and letting it stand;

[0057] S22: After the positive electrode and the negative electrode of the battery are both infiltrated with the gel electrolyte precursor solution, they are heated and cured at a temperature ranging from 45° C. to 60° C. to obtain a cross-linked copolymer gel electrolyte.

[0058] It should be noted that, in the present embodiment, the lithium salt adopts a fluorine-containing lithium salt, and the fluorine-containing lithium salt is one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium difluorooxalate borate, lithium hexafluorophosphate, and lithium tetrafluoroborate. The carbonate plasticizer adopts a fluorine-containing carbonate plasticizer, and the fluorine-containing carbonate plasticizer is one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate. The α-olefin is one of 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. The acrylate uses an acrylate containing two carbon-carbon double bonds, and the acrylate containing two carbon-carbon double bonds is one of 1,4-bis(acryloxy)butane, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,6-bis(methacryloxy)hexane, 1,3-butanediol diacrylate, vinyl diacrylate, 1,3-butanediol dimethacrylate, and 1,4-butanediol dimethacrylate. The azo initiator is one or more of dimethyl azobisisobutyrate, azobisisoheptanenitrile, and azobisisobutyronitrile. The material of the positive electrode is one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, and nickel cobalt manganese. If the material of the positive electrode is nickel cobalt manganese, nickel cobalt manganese 811 can be specifically selected, that is, nickel cobalt manganese with a ratio of 8:1:1 for nickel, cobalt, and manganese; the current collector of the positive electrode is carbon-coated aluminum foil, which is of course not limited to this and can be adjusted according to actual needs; the material of the negative electrode is lithium metal. The battery also includes a diaphragm, which is a cellulose diaphragm, a polyethylene battery diaphragm, a polypropylene battery diaphragm, or a polyethylene / polypropylene composite battery diaphragm. When both the positive electrode and the negative electrode are infiltrated with the gel electrolyte precursor solution, the diaphragm is also infiltrated with the gel electrolyte precursor solution. In this embodiment, the gel electrolyte precursor solution is prepared in the order of steps S11 to S14, and the azo initiator is added last to avoid unnecessary reactions between the free radicals generated by its decomposition and other components, which may affect the normal progress of the polymerization reaction. In step S22, the temperature range of heating and curing is 45°C to 60°C. Specifically, the temperature of heating and curing can be 45°C, 50°C, 55°C, or 60°C.

[0059] Fluorinated carbonates are used as film-forming additives and plasticizers to form solid electrolyte interface films rich in lithium fluoride together with fluorinated lithium salts and acrylates. The solid electrolyte interface films rich in lithium fluoride can induce uniform deposition and stripping of lithium ions, inhibit the formation of lithium dendrites, and alleviate the volume expansion of lithium metal negative electrodes. In addition, small-molecule fluorinated carbonates can participate in the transmission of lithium ions, further improving the lithium ion transmission performance of cross-linked copolymer gel electrolytes. Acrylates containing two carbon-carbon double bonds can spontaneously form cross-linked structures during the polymerization process. This cross-linked structure can more effectively fix the fluorinated carbonate plasticizer and inhibit the side reactions of the cross-linked copolymer gel electrolyte on the surfaces of the positive and negative electrodes. It is understandable that α-olefins include alkyl chains, and the content of alkyl chains in the gel electrolyte is directly related to the performance of the gel electrolyte. Too low a content of alkyl chains will lead to a decrease in the lithium ion transmission capacity of the gel electrolyte, aggravate the internal polarization phenomenon of the battery during the charge and discharge process, and weaken the charge and discharge performance of the battery; a high content of alkyl chains will lead to poor solubility of lithium salts, making the overall performance of the battery worse. Therefore, it is better to set the ratio of the mass of α-olefin to the total mass of the cross-linked copolymer gel electrolyte to a range of 10% to 40%. Specifically, the mass of α-olefin accounts for The mass of the cross-linked copolymer gel electrolyte is 10%, 15%, 20%, 25%, 30%, 35% or 40% of the total mass of the cross-linked copolymer gel electrolyte; the mass of the fluorine-containing lithium salt accounts for 1% to 20% of the total mass of the cross-linked copolymer gel electrolyte, specifically, the mass of the fluorine-containing lithium salt accounts for 1%, 5%, 10%, 15% or 20% of the total mass of the cross-linked copolymer gel electrolyte; the mass of the fluorine-containing carbonate plasticizer accounts for 40% to 50% of the total mass of the cross-linked copolymer gel electrolyte, specifically, the mass of the fluorine-containing carbonate plasticizer accounts for 50% to 60% of the total mass of the cross-linked copolymer gel electrolyte. The mass of the acrylic ester containing two carbon-carbon double bonds accounts for 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50% of the total mass of the cross-linked copolymer gel electrolyte; the mass of the acrylic ester containing two carbon-carbon double bonds accounts for 10% to 40% of the total mass of the cross-linked copolymer gel electrolyte, specifically, the mass of the acrylic ester containing two carbon-carbon double bonds accounts for 10%, 15%, 20%, 25%, 30%, 35% or 40% of the total mass of the cross-linked copolymer gel electrolyte; the mass of the azo initiator accounts for 0% of the total mass of the cross-linked copolymer gel electrolyte .001% to 0.045%, specifically, the mass of the azo initiator accounts for 0.001%, 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, 0.030%, 0.035%, 0.040% or 0.045% of the total mass of the cross-linked copolymer gel electrolyte. Of course, the specific contents of the fluorine-containing lithium salt, the fluorine-containing carbonate plasticizer, the α-olefin, the acrylate containing two carbon-carbon double bonds and the azo initiator can be adjusted according to actual needs, and this embodiment does not make any specific limitation to this.In this embodiment, the carbonate plasticizer itself is a clear solution, and the added lithium salt can be completely dissolved in the carbonate plasticizer in step S11. There is no specific time limit for the time required for dissolution, and the stirring time range of steps S12 to S14 is 10 minutes to 120 minutes, because stirring time less than 10 minutes may result in insufficient dissolution, and stirring time greater than 120 minutes will waste time and material resources.

[0060] The preparation method of the α-olefin cross-linked copolymer gel electrolyte provided in this embodiment uses fluorinated carbonate as a film-forming additive and plasticizer, and uses acrylate with two carbon-carbon double bonds and α-olefin as polymer monomers, and obtains a cross-linked copolymer gel electrolyte by in-situ polymerization. The cross-linked copolymer gel electrolyte has good room temperature lithium ion transmission capacity, high voltage resistance, and helps to improve the stability of lithium metal and electrode-electrolyte interface performance. In addition, the preparation method of the α-olefin cross-linked copolymer gel electrolyte provided in this embodiment is compatible with existing battery injection, battery formation and other process equipment, has broad application prospects, is simple and easy to operate, has low raw material cost, is safe and environmentally friendly, and is suitable for large-scale batch production.

[0061] Example 3

[0062] This embodiment illustrates another specific embodiment of the method for preparing the α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0063] Dissolving 0.2 g of lithium tetrafluoroborate in 2.0 g of trifluoropropylene carbonate, stirring continuously at room temperature for 30 minutes until the mixture is completely dissolved, to obtain a first clear solution;

[0064] Add 1.0 g of 1-hexene to the first clear solution and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0065] Add 1.0 g of 1,4-bis(acryloyloxy)butane to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0066] Add 0.06 mg of dimethyl azobisisobutyrate to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0067] The fourth clarified solution is injected into the battery, the battery separator uses a polyethylene battery separator, the battery positive electrode material is a lithium iron phosphate positive electrode, and the battery negative electrode material is lithium metal. The battery is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0068] Example 4

[0069] This embodiment illustrates another specific embodiment of the method for preparing the α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0070] Dissolving 0.2 g of lithium bis(fluorosulfonyl)imide in 2.0 g of difluoroethylene carbonate, stirring continuously at room temperature for 30 minutes until the mixture is completely dissolved, to obtain a first clear solution;

[0071] Add 1.0 g of 1-heptene to the first clear solution and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0072] Add 1.0 g of neopentyl glycol dimethacrylate to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0073] Add 0.06 mg of azobisisoheptanenitrile to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0074] The fourth clarified solution is injected into the battery, the battery separator uses a polyethylene battery separator, the battery positive electrode material is a lithium iron phosphate positive electrode, and the battery negative electrode material is lithium metal. The battery is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0075] Example 5

[0076] This embodiment illustrates another specific embodiment of the method for preparing the α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0077] Dissolving 0.2 g of lithium bis(trifluoromethanesulfonyl)imide in 2.0 g of trifluoropropylene carbonate, stirring continuously at room temperature for 30 minutes until the mixture is completely dissolved, to obtain a first clear solution;

[0078] Add 1.0 g of 1-octene to the first clear solution and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0079] Add 1.0 g of tetraethylene glycol dimethacrylate to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0080] Add 0.06 mg of dimethyl azobisisobutyrate to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0081] The fourth clarified solution is injected into the battery, the battery separator uses a polypropylene battery separator, the battery positive electrode material is a lithium cobalt oxide positive electrode, and the battery negative electrode material is lithium metal. The battery is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0082] Example 6

[0083] This embodiment illustrates another specific embodiment of the method for preparing the α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0084] Dissolving 0.2 g of lithium difluorooxalatoborate in 2.0 g of fluoroethylene carbonate, stirring continuously at room temperature for 30 minutes until the solution is completely dissolved, to obtain a first clear solution;

[0085] Add 1.0 g of 1-nonene to the first clear solution and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0086] Add 1.0 g of 1,6-bis(methacryloyloxy)hexane to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0087] Add 0.06 mg of azobisisobutyronitrile to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0088] The fourth clarified solution is injected into the battery, the battery separator uses a polyethylene / polypropylene composite battery separator, the battery positive electrode material is a nickel-cobalt-manganese 811 positive electrode, and the battery negative electrode material is lithium metal. It is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0089] Example 7

[0090] This embodiment illustrates another specific embodiment of the method for preparing the α-olefin cross-linked copolymer gel electrolyte provided by the present invention, comprising:

[0091] Dissolving 0.2 g of lithium hexafluorophosphate in 2.0 g of difluoroethylene carbonate, stirring continuously for 30 minutes at room temperature until the mixture is completely dissolved, to obtain a first clear solution;

[0092] Add 1.0 g of 1-decene to the first clear solution and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0093] Add 1.0 g of 1,3-butanediol diacrylate to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0094] Add 0.06 mg of azobisisoheptanenitrile to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0095] The fourth clarified solution is injected into the battery, the battery separator uses a cellulose separator, the battery positive electrode material is a lithium manganese iron phosphate positive electrode, and the battery negative electrode material is lithium metal. The battery is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0096] The present invention also provides two comparative examples, as follows:

[0097] Comparative Example 1

[0098] Dissolving 0.2 g of lithium bis(trifluoromethanesulfonyl)imide in 2.0 g of fluoroethylene carbonate, stirring continuously at room temperature for 30 minutes until the mixture is completely dissolved, to obtain a first clear solution;

[0099] Add 1.5 g of 1-heptene to the first clear solution and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0100] Add 0.5 g of neopentyl glycol dimethacrylate to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0101] Add 0.06 mg of azobisisobutyronitrile to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0102] The fourth clarified solution is injected into the battery, the battery separator is a cellulose separator, the positive electrode material of the battery is a lithium manganese iron phosphate positive electrode, and the negative electrode material of the battery is lithium metal. The battery is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0103] Comparative Example 2

[0104] Dissolving 0.2 g of lithium bis(trifluoromethanesulfonyl)imide in 2.0 g of fluoroethylene carbonate, stirring continuously at room temperature for 30 minutes until the mixture is completely dissolved, to obtain a first clear solution;

[0105] Add 0.5 g of 1-heptene to the first clear solution, and continue stirring at room temperature for 30 minutes to obtain a second clear solution;

[0106] Add 1.5 g of neopentyl glycol dimethacrylate to the second clear solution, and continue stirring at room temperature for 30 minutes to obtain a third clear solution;

[0107] Add 0.06 mg of azobisisobutyronitrile to the third clear solution, and continue stirring at room temperature for 30 minutes to obtain a fourth clear solution, i.e., a gel electrolyte precursor solution;

[0108] The fourth clarified solution is injected into the battery, the battery separator uses a cellulose separator, the battery positive electrode material is a lithium manganese iron phosphate positive electrode, and the battery negative electrode material is lithium metal. The battery is allowed to stand until it is completely soaked, and finally heated and cured to obtain a cross-linked copolymer gel electrolyte.

[0109] The formulas of Examples 3 to 7, Comparative Examples 1 and 2 are summarized in Table 1. The numbers in Table 1 are reserved to 2 decimal places, so the azo initiator is not shown in Table 1, as follows:

[0110] Table 1. Cross-linked copolymer gel electrolyte formula

[0111]

[0112] Table 1. Cross-linked copolymer gel electrolyte formula

[0113]

[0114] Examples 3 to 7, Comparative Examples 1 and 2 were all prepared according to the specifications of button cells, and the entire preparation process was carried out in a glove box environment. The button cell materials used included: battery positive and negative electrode shells with specifications of CR2025, composite positive electrode plates with a diameter of 12 mm, diaphragms with a diameter of 19 mm, stainless steel plates with a diameter of 15.8 mm, stainless steel spring plates with an outer diameter of 15.8 mm, and gel electrolyte precursor solutions obtained corresponding to Examples 3 to 7, Comparative Examples 1 and 2. In the gel electrolyte performance test, the following three batteries can be used according to different performance requirements:

[0115] The double-blocking battery comprises a positive electrode shell, a stainless steel sheet, an electrolyte, a diaphragm, an electrolyte, a stainless steel sheet, a spring sheet and a negative electrode shell.

[0116] A single blocking battery comprises a positive electrode shell, a lithium sheet, an electrolyte, a separator, an electrolyte, a stainless steel sheet, a spring sheet and a negative electrode shell.

[0117] A lithium symmetrical battery comprises a positive electrode shell, a lithium sheet, an electrolyte, a separator, an electrolyte, a lithium sheet, a stainless steel sheet, a spring sheet and a negative electrode shell.

[0118] After selecting the type of battery to be used, assemble the button cells in the order corresponding to the battery type, and use a battery sealer to pressurize and seal until the inner circle scale reaches 500 pounds per square inch.

[0119] Seven batteries were tested to obtain a comparison table of electronic conductivity, a comparison table of electrochemical window upper limit, and a comparison table of lithium ion migration number, as shown in Table 2, Table 3 and Figure 4 As shown:

[0120] Table 2. Comparison of electronic conductivity

[0121] Ionic conductivity (Scm-1) Example 3 <![CDATA[3.43×10 -4 ]]> Example 4 <![CDATA[2.73×10 -4 ]]> Example 5 <![CDATA[3.81×10 -4 ]]> Example 6 <![CDATA[4.20×10 -4 ]]> Example 7 <![CDATA[5.38×10 -4 ]]> Comparative Example 1 <![CDATA[2.34×10 -4 ]]> Comparative Example 2 <![CDATA[3.37×10 -4 ]]>

[0122] It can be concluded from Table 2 that by adjusting the type and content of raw materials of the composite gel electrolyte, its room temperature ionic conductivity will change. The use of fluorine-containing lithium salts with strong dissociation ability, low-viscosity fluorine-containing carbonate plasticizers, and long alkyl chain α-olefins can improve the ionic conductivity of the cross-linked copolymer gel electrolyte at room temperature. Compared with Example 1, the difference between Example 4 and Comparative Example 1 lies in the content of α-olefin. Since the content of α-olefin in Comparative Example 1 is too high, the solubility of the lithium salt in Comparative Example 1 is reduced, and the lithium ion transmission capacity is reduced, which is manifested as low ionic conductivity.

[0123] Table 3. Comparison of electrochemical window upper limits

[0124] Electrochemical window upper limit (V) Example 3 5.10 Example 4 5.19 Example 5 5.25 Example 6 5.34 Example 7 5.37 Comparative Example 1 5.32 Comparative Example 2 5.15

[0125] As shown in Table 3, the upper limits of the electrochemical windows of Examples 3 to 7 are all higher than 5.0 V, showing good electrochemical stability and being able to adapt to high-voltage positive electrode materials. The difference between Example 4 and Comparative Example 2 is the content of α-olefin. Since the content of α-olefin compounds in Comparative Example 2 is too low, the high-voltage resistance of Comparative Example 2 is weakened, which is manifested as a low upper limit of the electrochemical window.

[0126] Table 4. Lithium ion migration number comparison table

[0127] Lithium ion migration number Example 3 0.26 Example 4 0.24 Example 5 0.29 Example 6 0.25 Example 7 0.30 Comparative Example 1 0.16 Comparative Example 2 0.27

[0128] Referring to Table 4, the difference between Example 4 and Comparative Example 1 lies in the content of α-olefin substances. Since the content of α-olefin substances in Comparative Example 1 is too high, the solubility of the lithium salt in the gel electrolyte is reduced and it cannot migrate quickly in the gel electrolyte, resulting in a lower lithium ion migration number.

[0129] In summary, α-olefins combined with fluorine-containing lithium salts, fluorine-containing carbonate plasticizers, acrylates containing two carbon-carbon double bonds, and azo initiators can effectively solve the problems of high crystallinity and poor lithium ion dissociation ability of acrylate cross-linked gel electrolytes. The cross-linked copolymer gel electrolyte obtained by the method of the present invention has excellent lithium ion transmission performance at room temperature, good high voltage resistance, and can also increase the stability of lithium metal and have excellent electrode-electrolyte interface performance. By regulating the content of α-olefins, the specific properties of the cross-linked copolymer gel electrolyte can be further enhanced to achieve the preparation of multi-type and multi-purpose electrolytes. In addition, the preparation method of the α-olefin cross-linked copolymer gel electrolyte provided in this embodiment is compatible with existing battery injection, battery formation and other process equipment, has broad application prospects, is simple and easy to operate, has low raw material cost, is safe and environmentally friendly, and is suitable for large-scale batch production.

[0130] Example 8

[0131] Based on the same invention idea, refer to Figure 4 , Figure 4 1 is a schematic diagram of the structure of a battery, which illustrates a specific embodiment of the lithium-ion battery provided by the present invention, including a positive electrode 1, a negative electrode 4, a separator 3 and an α-olefin cross-linked copolymer gel electrolyte 2, wherein the α-olefin cross-linked copolymer gel electrolyte 2 is prepared by the preparation method of the α-olefin cross-linked copolymer gel electrolyte 2 in any one of the above embodiments.

[0132] It should be noted that the material of the positive electrode 1 is one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, and nickel cobalt manganese. If the material of the positive electrode 1 is nickel cobalt manganese, nickel cobalt manganese 811 can be specifically selected, that is, nickel cobalt manganese with a ratio of nickel, cobalt, and manganese of 8:1:1; the current collector of the positive electrode 1 is carbon-coated aluminum foil, of course, it is not limited to this and can be adjusted according to actual needs. The material of the negative electrode 4 is lithium metal. The separator 3 is a cellulose separator, a polyethylene battery separator, a polypropylene battery separator, and a polyethylene / polypropylene composite battery separator.

[0133] It is understandable that the introduction of α-olefin not only reduces the crystallinity of the polymer, but also enhances the dissociation and transmission capacity of the cross-linked copolymer gel electrolyte 2 for lithium ions; the synergistic effect of α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator can further enhance the lithium ion transmission performance of the cross-linked copolymer gel electrolyte 2 at room temperature. The application of the cross-linked copolymer gel electrolyte 2 containing α-olefin to lithium-ion batteries can significantly improve the performance of the lithium-ion batteries using the cross-linked copolymer gel electrolyte 2.

[0134] It can be seen from the above embodiments that the preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention achieve at least the following beneficial effects:

[0135] 1. The preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention are as follows: α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator are mixed to obtain a gel electrolyte precursor solution; the gel electrolyte precursor solution is heated and cured to obtain a cross-linked copolymer gel electrolyte. By introducing α-olefin, not only the crystallinity of the polymer is reduced, but also the dissociation and transmission capacity of the cross-linked copolymer gel electrolyte for lithium ions can be enhanced; the synergistic effect of α-olefin, acrylate, lithium salt, carbonate plasticizer and azo initiator can further enhance the lithium ion transmission performance of the cross-linked copolymer gel electrolyte at room temperature, and the performance of the battery using the cross-linked copolymer gel electrolyte is also significantly improved.

[0136] 2. The preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention enhance the contact performance of the electrode-electrolyte interface in the high-voltage lithium metal battery by combining in-situ preparation, artificial solid electrolyte interface membrane and cross-linking copolymerization methods, and improve the stability of the cross-linked copolymer gel electrolyte to the high-voltage positive electrode and lithium negative electrode.

[0137] 3. The preparation method of the α-olefin cross-linked copolymer gel electrolyte and the lithium electronic battery provided by the present invention are simple and easy to operate, have low raw material costs, are safe and environmentally friendly, and are suitable for large-scale batch production.

[0138] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for preparing an α-olefin cross-linked copolymer gel electrolyte, characterized in that: include: Mixing an α-olefin, an acrylate, a lithium salt, a carbonate plasticizer and an azo initiator to obtain a gel electrolyte precursor solution, wherein the carbon chain length of the α-olefin ranges from 6 to 10; The gel electrolyte precursor solution is heated and solidified to obtain a cross-linked copolymer gel electrolyte.

2. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The α-olefin is one of 1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene.

3. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The α-olefin, the acrylate, the lithium salt, the carbonate plasticizer and the azo initiator are mixed to obtain the gel electrolyte precursor solution, comprising: dissolving the lithium salt in the carbonate plasticizer to obtain a first clear solution; adding the α-olefin to the first clear solution and stirring to obtain a second clear solution; adding the acrylic acid ester to the second clear solution and stirring to obtain a third clear solution; The azo initiator is added to the third clear solution and stirred to obtain the gel electrolyte precursor solution.

4. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The gel electrolyte precursor solution is heated and solidified to obtain the cross-linked copolymer gel electrolyte, comprising: Injecting the gel electrolyte precursor solution into the battery and leaving it to stand; After the positive electrode and the negative electrode of the battery are both infiltrated by the gel electrolyte precursor solution, they are heated and cured at a heating temperature ranging from 45° C. to 60° C. to obtain the cross-linked copolymer gel electrolyte.

5. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The ratio of the mass of the α-olefin to the total mass of the cross-linked copolymer gel electrolyte ranges from 10% to 40%.

6. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The acrylic ester is acrylic ester containing two carbon-carbon double bonds.

7. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 6, characterized in that: The acrylic acid ester containing two carbon-carbon double bonds is one of 1,4-bis(acryloxy)butane, neopentyl glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,6-bis(methacryloxy)hexane, 1,3-butanediol diacrylate, vinyl diacrylate, 1,3-butanediol dimethacrylate and 1,4-butanediol dimethacrylate.

8. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The lithium salt is a fluorine-containing lithium salt, and the fluorine-containing lithium salt is one or more of lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium difluorooxalatoborate, lithium hexafluorophosphate, and lithium tetrafluoroborate; and / or, the carbonate plasticizer is a fluorine-containing carbonate plasticizer, and the fluorine-containing carbonate plasticizer is one or more of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

9. The method for preparing the α-olefin cross-linked copolymer gel electrolyte according to claim 1, characterized in that: The azo initiator is one or more of dimethyl azobisisobutyrate, azobisisoheptanenitrile and azobisisobutyronitrile.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an alpha-olefin cross-linked copolymer gel electrolyte, wherein the alpha-olefin cross-linked copolymer gel electrolyte is prepared by the preparation method according to any one of claims 1 to 9.

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