Gel electrolyte and preparation method and application thereof

Abstract

The invention relates to a gel electrolyte and a preparation method and application thereof. The gel electrolyte is prepared from the following raw materials: a nitrogen heterocyclic gel monomer, an electrolyte and an initiator, the nitrogen heterocyclic gel monomer is prepared from the following raw materials: a nucleophilic reagent and an epoxy compound. The gel electrolyte provided by the invention is high in conductivity and good in uniformity, can realize stable circulation under 5C multiplying power, and can be well applied to a quick-charge type gel battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a gel electrolyte and a preparation method and application thereof. Background Art

[0002] With the rapid growth in market demand for portable consumer electronics, energy storage products, and electric vehicles, there is an increasing demand for gel electrolyte lithium-ion batteries. The polymer matrix in traditional gel electrolytes is mostly linear monomers, such as pentaerythritol tetraacrylate (PETEA), pentaerythritol triacrylate (PETA), polymethyl methacrylate (PMMA), polyethylene glycol diacrylate (PEGDMA), etc. The uncontrolled polymerization of linear monomers leads to large cross-linking disorder and freedom, which hinders ion migration. As the molecular weight increases during the polymerization process, the conductivity continues to decrease and the battery consistency becomes poor. In addition, during the polymerization process, the disordered entanglement of the linear monomer polymer chains causes stress concentration, resulting in over-polymerization and matrix cracking. Therefore, due to the lack of effective ion transport channels, traditional gel electrolytes suffer from the problem of deteriorated lithium ion transport kinetics after solidification.

[0003] Specifically, traditional gel electrolytes have the following main problems:

[0004] (1) The gel electrolyte is not uniformly distributed. Currently, the commonly used gel monomers contain at least one propylene (CH2=) double bond and one ester group. The monomers containing olefinic bond structures are converted into free radicals by initiators and heating, and then form macromolecular polymers through further chain growth reactions, completing the gelation process. However, under no constraints, the cross-linking disorder of the gel skeleton is high, and different polymer chains are easily entangled due to van der Waals interactions / hydrogen bond interactions, showing the heterogeneity of the spatial distribution of the gel electrolyte; secondly, the spatial freedom of the connecting bonds between the polymerized monomers is high, and the polymerization process can rotate without restriction in space, resulting in inconsistent microscopic orientation of the gel electrolyte, further aggravating the heterogeneity of the gel electrolyte distribution.

[0005] (2) The poor kinetic performance of gel electrolytes. On the one hand, gel monomers have an adsorption effect on lithium ions, and the key factor determining the conductivity of the gel is gel polymerization. Excessive polymerization blocks the ion mass transfer pathways inside the gel, resulting in a continuous decrease in conductivity. On the other hand, uncontrolled polymerization will cause different stresses in different regions, thereby destroying the matrix. Ultimately, the battery is manifested as inconsistent impedance at various locations, resulting in a large polarization voltage and poor kinetic performance.

[0006] Therefore, it is of great significance to design and provide a gel electrolyte with high conductivity and uniform distribution suitable for fast charging battery systems. Summary of the Invention

[0007] To address the above technical problems, the present invention provides a gel electrolyte, its preparation method, and its application. The gel electrolyte provided by the present invention has good uniformity and low conductivity variation during the polymerization process. This enables the resulting gel battery to exhibit stable cycling performance and good charge-discharge performance at a 5C rate, making it well suited for fast-charging gel batteries.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a gel electrolyte, wherein raw materials for preparing the gel electrolyte include a nitrogen heterocyclic gel monomer, an electrolyte, and an initiator;

[0010] The raw materials for preparing the nitrogen heterocyclic gel monomer include a nucleophilic reagent and an epoxy compound.

[0011] The present invention replaces traditional linear monomers with nitrogen heterocyclic gel monomers. These monomers work well with the electrolyte and initiator, significantly reducing the restrictions on the free movement of lithium ions in the resulting network gel polymer matrix, thereby increasing the transference number of lithium ions and resulting in a higher conductivity for the resulting gel electrolyte. Furthermore, the network gel polymer matrix is ​​uniformly distributed within the battery, free of cracks, minimizing electrode polarization and imparting high conductivity to the resulting gel electrolyte system, enabling fast charging. This enables the resulting gel battery to exhibit stable cycling performance and good charge-discharge performance at a 5C rate, making it well-suited for fast-charging gel batteries.

[0012] The polymerization process of gel electrolyte is complex. The gel macromolecules are formed by the continuous opening and recombination of carbon-carbon double bonds between monomers under the initiation of free radicals. If no restrictions are given, the polymerization process is random, and the degree of polymerization and spatial orientation are uncontrollable. This will lead to increased disorder of the gel skeleton, a continuous decrease in the conductivity of the electrolyte, and obstructed lithium ion transmission, which in turn affects the consistency and electrochemical performance of the battery.

[0013] In the gel electrolyte of the present invention, the nitrogen heterocyclic gel monomer prepared from a nucleophilic reagent and an epoxy compound is a monomer molecule having intramolecular hydrogen bonds and chelating sites. The internal hydrogen bonds can limit the spatial rotation of the monomer itself, thereby reducing the degree of freedom of site orientation, thereby obtaining a monomer arrangement with consistent orientation, which helps to improve the conduction of lithium ions; at the same time, the electrostatic repulsion of the chelating sites can limit the increased adsorption of lithium ions and the entanglement of the chain due to the continuous growth of the gel polymer matrix, thereby solving the problem of continuous decrease in conductivity during the polymerization process, reducing the cross-linking disorder of the gel polymer matrix skeleton, and facilitating the precise control of the monomer polymerization process, thereby obtaining a uniform gel electrolyte with a concentrated molecular weight distribution, which is well suitable for fast-charging lithium batteries.

[0014] The key to the electrochemical performance of high-performance, highly stable fast-charge lithium-ion batteries lies in the performance of the electrode materials and the electrolyte-electrode interface structure. The polymerization process of hard in-situ gel electrolytes is uncontrollable, making it extremely difficult to construct an electrolyte-electrode interface with a clear structure and high compatibility. The electrolyte-electrode interface in a gel-state battery includes both a polymer skeleton structure and the decomposition products of related components in the liquid electrolyte. It is a complex system. The electrochemical process and phase evolution occurring at the electrolyte-electrode interface are relatively complex, and it is difficult to clearly define the role played by each system. The present invention, through the use of nitrogen heterocyclic gel monomers, can accurately control the electrolyte / electrode interface structure during the polymerization process, thereby achieving the purpose of accurate control of the highly compatible electrolyte-electrode interface, which is conducive to establishing a correlation between the controllable polymerization process and the electrolyte-electrode interface structure, and thus has important significance for the study of the evolution law and mechanism of each component in the battery charging and discharging process.

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0016] As a preferred technical solution of the present invention, based on the mass percentage of the electrolyte as 100%, the mass percentage of the nitrogen heterocyclic gel monomer is 0.6-20%, for example, it can be 0.6%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.5%, 2%, 5%, 10%, 15% or 20%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and is further preferably 0.8-1.2%.

[0017] A reasonable gel monomer content is the key to ensuring a uniform and complete gel matrix. The compatible fusion of the gel phase and the liquid electrolyte is the basis for achieving a macroscopically and microscopically uniform electrolyte and is also a necessary condition for ensuring the normal operation of the battery. The present invention can improve the uniformity of the resulting gel electrolyte and the stability of the conductivity during the polymerization process by controlling the mass percentage of the nitrogen heterocyclic gel monomer within a specific range, thereby making the resulting gel battery have better cycle performance and rate performance. If its content is too low, a complete gel matrix cannot be formed, and the overall electrolyte will become a macroscopically and microscopically heterogeneous phase, resulting in an uneven distribution of lithium ions and severe concentration polarization, which will cause a sharp decline in battery performance; if its content is too high, the polymer matrix will dominate, causing the lithium ions transmitted in the liquid matrix to be blocked by the gel solid phase matrix, thereby affecting the lithium ion transmission performance, and significantly reducing the rate capability of the gel electrolyte. In severe cases, it can cause the battery to fail to operate normally. Furthermore, when its content is 0.8-1.2%, the comprehensive performance of the resulting gel electrolyte is even better.

[0018] As a preferred technical solution of the present invention, the molar ratio of the nucleophilic reagent and the epoxy compound in the raw material for preparing the nitrogen heterocyclic gel monomer is 1:(3-6), wherein (3-6) can be 3, 3.5, 4, 4.5, 5, 5.5 or 6, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0019] The present invention regulates the structure of the obtained nitrogen heterocycle gel monomer by controlling the molar ratio of nucleophilic reagent and epoxy compound, and under alkaline or neutral conditions, the nitrogen atom of amine group (-NH, -NHR, -NR2) carries lone pair electrons and is activated as nucleophilic reagent. Its lone pair electron attacks the carbon atom with partial positive charge in the epoxy ring due to ring tension to form a CN bond, while the CO bond of the epoxy oxygen atom begins to break, and the ring is opened to generate an alkoxide anion intermediate, thereby completing the preparation of the novel nitrogen heterocycle gel monomer. Reasonable molar ratio is the basis for forming a pure substance, and its molar ratio is calculated based on the number ratio of amine group and epoxy, and then the nitrogen heterocycle gel electrolyte with more excellent comprehensive performance is obtained. If the two molar ratios are too low, then epoxide is in surplus, cannot fully react, and the nitrogen heterocycle gel monomer with high purity is not obtained; If the two molar ratios are too high, amine group will not be fully added by epoxy, and the formed substance must also have various by-products, thereby affecting the performance of the obtained gel electrolyte.

[0020] Preferably, the nucleophile comprises a nitrogen heterocyclic epoxide.

[0021] Preferably, the nitrogen heterocyclic compound includes any one or a combination of at least two of 1,4,7,10-tetraazacyclododecane (Cyclen), indole, imidazole, benzimidazole, purine or 1,2,3-triazole.

[0022] When the nitrogen heterocyclic compound in the present invention is 1,4,7,10-tetraazacyclododecane (Cyclen), the nitrogen heterocyclic gel monomer obtained is a monomer molecule with intramolecular hydrogen bonds and chelating sites. It has a spatially symmetrical monomer molecule, which can better reduce the cross-linking disorder of the gel polymer matrix skeleton, and is more conducive to achieving precise control of the monomer polymerization process, thereby obtaining a uniform gel electrolyte with a concentrated molecular weight distribution, which is better applied to fast-charging lithium batteries.

[0023] Preferably, the epoxy compound includes glycidyl methacrylate (GMA) and / or glycidyl acrylate.

[0024] Preferably, the nitrogen heterocyclic gel monomer is prepared by the following method, which comprises the following steps:

[0025] The nucleophilic reagent and the epoxy compound are reacted to obtain the nitrogen heterocyclic gel monomer.

[0026] Preferably, the reaction temperature is 50-100°C, for example, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C or 90°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0027] Preferably, the reaction time is 6-18 h, for example, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h or 18 h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0028] Preferably, the reaction is carried out in a solvent.

[0029] Preferably, the solvent includes any one of propylene carbonate, ethylene carbonate or butylene carbonate, or a combination of at least two of them.

[0030] Preferably, based on the mass percentage of the raw materials for preparing the nitrogen heterocyclic gel monomer as 100%, the mass percentage of the solvent is 30-80%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0031] Preferably, the reaction is carried out under a protective gas atmosphere.

[0032] Preferably, the protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them.

[0033] Preferably, the reaction further comprises a post-treatment step. Preferably, the post-treatment method comprises purifying the mixed solution after the reaction by precipitation using a precipitant.

[0034] It should be noted that there is no particular limitation on the type of precipitant selected in the present invention, as long as the nitrogen heterocyclic gel monomer can be precipitated from the mixed solution. Examples include but are not limited to diethyl ether, n-hexane, petroleum ether, pentane, dichloromethane, chloroform, 2-methyltetrahydrofuran, cyclopentyl methyl ether, or a combination of acetonitrile and tert-butyl methyl ether, a combination of acetone and brine (saturated NaCl), a combination of tetrahydrofuran (THF) and methanol, etc.

[0035] It should be noted that, in the actual production of the gel electrolyte, no post-processing step is required, and the mixed solution containing the nitrogen heterocyclic gel monomer is directly mixed with the electrolyte and the initiator.

[0036] Preferably, the electrolyte comprises a lithium salt and a non-aqueous solvent.

[0037] It should be noted that there is no special limitation on the type of lithium salt selected in the present invention, and all commonly used lithium salts in the art are applicable, including but not limited to lithium perchlorate (LiClO4), lithium difluorophosphate (LiPO2F2), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium difluorosulfonimide (LiFSi), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), bisoxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) or lithium hexafluorophosphate (LiPF6).

[0038] Preferably, the non-aqueous solvent includes any one or a combination of at least two of cyclic carbonate, chain carbonate, aliphatic carboxylate, γ-lactone, chain ether or cyclic ether, more preferably a combination of cyclic carbonate and chain carbonate.

[0039] It should be noted that, in the present invention, there is no special limitation on the selection of the types of cyclic carbonates, chain carbonates, aliphatic carboxylates, γ-lactones, chain ethers and cyclic ethers, and the cyclic carbonates, chain carbonates, aliphatic carboxylates, γ-lactones, chain ethers and cyclic ethers commonly used in this area are all applicable.

[0040] The cyclic carbonate esters illustratively include, but are not limited to, ethylene carbonate (EC), fluoroethylene carbonate, difluoroethylene carbonate, propylene carbonate (PC), butylene carbonate (BC), and the like.

[0041] The chain carbonates illustratively include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, dibutyl carbonate, divinyl carbonate, diallyl carbonate, diphenyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl butyl carbonate, methyl vinyl carbonate, methyl allyl carbonate, methyl phenyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, ethyl vinyl carbonate, ethyl allyl carbonate, ethyl phenyl carbonate, and the like.

[0042] The aliphatic carboxylic acid esters illustratively include, but are not limited to, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl n-butyrate, and the like.

[0043] The γ-lactones illustratively include but are not limited to γ-butyrolactone, γ-valerolactone, and the like.

[0044] The chain ethers illustratively include but are not limited to: 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, etc.; the cyclic ethers illustratively include but are not limited to: tetrahydrofuran, 2-methyltetrahydrofuran, etc.

[0045] It should be noted that the volume ratio of the cyclic carbonate to the linear carbonate in the present invention is not particularly limited, and any conventional volume ratio in the art can be applied, including but not limited to: EC:DMC=1:1, EC:EMC=3:7, etc.

[0046] Preferably, the concentration of the lithium salt in the electrolyte is 0.5-6 mol / L, for example, it can be 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L or 6 mol / L, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0047] Preferably, based on the mass percentage of the electrolyte as 100%, the mass percentage of the initiator is 0.01-4%, for example, it can be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.5%, 1%, 2%, 3% or 4%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0048] Preferably, the initiator includes any one of an azo initiator, a peroxide initiator or a persulfate, or a combination of at least two of them.

[0049] In a second aspect, the present invention provides a method for preparing the gel electrolyte according to the first aspect, the preparation method comprising the following steps:

[0050] The nitrogen heterocyclic gel monomer, electrolyte and initiator are mixed and heated to obtain the gel electrolyte.

[0051] The present invention mixes nitrogen heterocyclic gel monomers, an electrolyte and an initiator, and after heating, the nitrogen heterocyclic gel monomers can be further polymerized to form a network gel polymer matrix skeleton. While reducing the restriction on the free movement of lithium ions, it also has the characteristics of good uniformity inside the battery, so that the obtained gel electrolyte has good cycle performance.

[0052] Preferably, the heating temperature is 50-75°C, for example, it can be 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C or 75°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0053] Preferably, the heating time is 0.5-6h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0054] Specifically, the preparation method of the gel electrolyte comprises the following steps:

[0055] A nitrogen heterocyclic gel monomer, an electrolyte and an initiator are mixed to obtain an electrolyte precursor solution, which is then heated at 50-75° C. for 0.5-6 hours to obtain the gel electrolyte.

[0056] In a third aspect, the present invention provides a use of the gel electrolyte as described in the first aspect in a gel battery.

[0057] Compared with the prior art, the present invention has at least the following beneficial effects:

[0058] (1) The gel electrolyte provided by the present invention uses nitrogen heterocyclic gel monomers to replace traditional linear monomers. It can reduce the cross-linking disorder and degree of freedom of the gel polymer matrix skeleton through chelation and internal hydrogen bonding, forming a regular porous network structure, thereby improving the solubility of lithium salts, so that the adsorption of lithium by the gel polymer matrix skeleton is weakened, and effectively avoiding the problem of the conductivity of the obtained gel electrolyte decreasing with the excessive polymerization of gel molecules; in addition, the molecular chain of the nitrogen heterocyclic gel monomer can also form high-density charge groups and lithium ion transmission channels, which well meet the needs of rapid lithium ion conduction and further improve the conductivity of the gel electrolyte. Furthermore, when applied to gel batteries, the gel electrolyte provided by the present invention can achieve controllable and precise polymerization, present uniformity in the electrodes and the entire battery, and can ensure the uniform transmission of lithium ions without causing battery polarization, thus well achieving the purpose of improving battery rate performance and consistency.

[0059] (2) The gel electrolyte provided by the present invention has good uniformity and will not crack due to the high degree of disorder and freedom of the gel polymer matrix skeleton. The conductivity is stable during the polymerization process (the change rate is 1.0-14.6%), which can enable the obtained gel battery to have good cycle performance (capacity retention rate after 1000 cycles is 48.4-87.0%) and rate performance (discharge rate at 5C is 58.2-94.5%). BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 is the H NMR spectrum of the CCGM monomer obtained in Preparation Example 1;

[0061] Figure 2 is the carbon NMR spectrum of the CCGM monomer obtained in Preparation Example 1;

[0062] Figure 3 is a graph showing changes in conductivity of the gel electrolyte obtained in Example 1 during the polymerization process;

[0063] Figure 4 This is a physical picture of the gel electrolyte obtained in Example 1 during the polymerization process;

[0064] Figure 5 is a reaction diagram of the gel electrolyte obtained in Example 1;

[0065] Figure 6 This is a graph showing the change in conductivity of the gel electrolyte obtained in Comparative Example 1 during the polymerization process;

[0066] Figure 7 This is a physical picture of the gel electrolyte obtained in Comparative Example 1 during the polymerization process;

[0067] Figure 8 is a mechanism diagram of the gel electrolyte of the present invention;

[0068] Figure 9 1 is a schematic diagram of charging the gel battery obtained in Application Example 1;

[0069] Figure 10 Schematic diagram of charging of the gel battery obtained in comparative application example 1. DETAILED DESCRIPTION

[0070] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0071] Unless otherwise specified, the raw materials and reagents used in the following examples and comparative examples are commercially available.

[0072] Preparation Example 1

[0073] This preparation example provides a nitrogen heterocyclic gel monomer 1 (CCGM monomer), and its preparation method specifically includes the following steps:

[0074] Under nitrogen protection, 1,4,7,10-tetraazacyclododecane (Cyclen) and glycidyl methacrylate (GMA) at a molar ratio of 1:4 were added to PC solvent (the mass percentage of PC solvent was 40%). After stirring at 70° C. for 12 h, the reaction solution was purified by ether precipitation to obtain the nitrogen heterocyclic gel monomer 1.

[0075] like Figure 1 and Figure 2 As shown, 1 In the H NMR, the δ4.1-4.3ppm signal disappears, that is, the characteristic peak of the epoxy ring methylene proton completely disappears, indicating that the epoxy group has been ring-opened; a new peak appears in the δ3.5-4.0ppm region, indicating that a β-hydroxyamine structure (-CH2-CH(OH)-CH2-) is formed after the corresponding ring opening; the signal in the δ2.5-3.5ppm region changes, that is, the signal of the methylene proton (-CH2-NH-) of Cyclen is weakened or broadened, indicating that the hydrogen on the nitrogen is replaced; the δ5.5-6.5ppm (double bond hydrogen) and δ1.8-2.0ppm (double bond methyl) signals are retained, indicating that the methacrylate double bond has not been polymerized.

[0076] 13In C NMR, the δ44-48 ppm signal disappears: the signal corresponding to the epoxy ring carbon disappears, further confirming the ring opening; a new peak appears in the δ65-75 ppm region, indicating that -CH(OH)- carbon is formed after the corresponding ring opening; the signal shift in the δ45-55 ppm region, that is, the methylene carbon of Cyclen shifts to the downfield due to the change in the electronic environment of the nitrogen atom (from -NH- to -N-CH2-); the δ125-140 ppm (double bond carbon) signal is retained, further confirming that the double bond does not participate in the reaction.

[0077] Preparation Example 2

[0078] This preparation example provides a nitrogen heterocyclic gel monomer 2, and its preparation method specifically includes the following steps:

[0079] Under nitrogen protection, 1,4,7,10-tetraazacyclododecane (Cyclen) and glycidyl acrylate in a molar ratio of 1:3 were added to EC solvent (the mass percentage of EC solvent was 30%), and the mixture was stirred at 50° C. for 18 h. The reaction solution was then purified by pentane precipitation to obtain the nitrogen heterocyclic gel monomer 2.

[0080] Preparation Example 3

[0081] This preparation example provides a nitrogen heterocyclic gel monomer 3, and its preparation method specifically includes the following steps:

[0082] Under nitrogen protection, 1,4,7,10-tetraazacyclododecane (Cyclen) and glycidyl methacrylate (GMA) at a molar ratio of 1:6 were added to BC solvent (the mass percentage of BC solvent was 80%). After stirring at 100° C. for 6 h, the reaction solution was purified by precipitation with petroleum ether to obtain the nitrogen heterocyclic gel monomer 3.

[0083] Preparation Example 4

[0084] This preparation example provides a nitrogen heterocyclic gel monomer 4, and its preparation method specifically includes the following steps:

[0085] Under nitrogen protection, melamine and glycidyl methacrylate (GMA) at a molar ratio of 1:3 were added to PC solvent (the mass percentage of PC solvent was 40%), and the mixture was stirred at 70° C. for 12 h. The reaction solution was then purified by ether precipitation to obtain the nitrogen heterocyclic gel monomer 4.

[0086] Example 1

[0087] This embodiment provides a gel electrolyte, and its preparation method specifically includes the following steps:

[0088] 0.8% of CCGM monomer (Preparation Example 1) and 0.016% of azobisisobutyronitrile (AIBN) were added to 1 mol / L LiPF6 / EC:DMC electrolyte (EC:DMC=1:1, vol:vol) to obtain an electrolyte precursor solution, which was then heated at 60°C for 3 hours to obtain the gel electrolyte.

[0089] Example 2

[0090] This embodiment provides a gel electrolyte, and its preparation method specifically includes the following steps:

[0091] 0.8% of nitrogen heterocyclic gel monomer 2 (Preparation Example 2) and 0.02% of dibenzoyl peroxide were added to 0.5 mol / L LiPF6 / EC:EMC electrolyte (EC:EMC=3:7, vol:vol) to obtain an electrolyte precursor solution, which was then heated at 75°C for 0.5 h to obtain the gel electrolyte.

[0092] Example 3

[0093] This embodiment provides a gel electrolyte, and its preparation method specifically includes the following steps:

[0094] 0.8% of nitrogen heterocyclic gel monomer 3 (Preparation Example 3) and 4% of azobisisobutyronitrile were added to 6 mol / L LiPF6 / EC:PC electrolyte (EC:PC=1:1, vol:vol) to obtain an electrolyte precursor solution, which was then heated at 50°C for 0.5h to obtain the gel electrolyte.

[0095] Example 4

[0096] This embodiment provides a gel electrolyte, which differs from Example 1 in that the content of CCGM monomer (Preparation Example 1) is adjusted from 0.8% by mass of the electrolyte to 0.6%. Other raw materials, contents and preparation methods are the same as those in Example 1.

[0097] Example 5

[0098] This embodiment provides a gel electrolyte, which differs from Example 1 in that the content of CCGM monomer (Preparation Example 1) is adjusted from 0.8% by mass of the electrolyte to 1.2%. Other raw materials, contents and preparation methods are the same as those in Example 1.

[0099] Example 6

[0100] This embodiment provides a gel electrolyte, which differs from Example 1 in that the content of CCGM monomer (Preparation Example 1) is adjusted from 0.8% by mass of the electrolyte to 2.0%. Other raw materials, contents and preparation methods are the same as those in Example 1.

[0101] Example 7

[0102] This embodiment provides a gel electrolyte, which differs from Example 1 in that the content of CCGM monomer (Preparation Example 1) is adjusted from 0.8% by mass of the electrolyte to 20%. Other raw materials, contents and preparation methods are the same as those in Example 1.

[0103] Example 8

[0104] This embodiment provides a gel electrolyte, which differs from Example 1 in that the content of CCGM monomer (Preparation Example 1) is adjusted from 0.8% by mass of the electrolyte to 25%. Other raw materials, contents and preparation methods are the same as those in Example 1.

[0105] Example 9

[0106] This embodiment provides a gel electrolyte, which differs from Example 1 in that the CCGM monomer (Preparation Example 1) is replaced with an equal mass of nitrogen heterocyclic gel monomer 4 (Preparation Example 4), and other raw materials, contents and preparation methods are the same as those in Example 1.

[0107] Comparative Example 1

[0108] This comparative example provides a gel electrolyte, which differs from Example 1 in that the CCGM monomer (Preparation Example 1) is replaced with an equal mass of PETEA monomer (pentaerythritol tetraacrylate), and the other raw materials, contents and preparation methods are the same as those in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a gel electrolyte, which differs from Example 1 in that the CCGM monomer (Preparation Example 1) is replaced with an equal mass of PETA monomer (pentaerythritol triacrylate) monomer, and the other raw materials, contents and preparation methods are the same as those in Example 1.

[0111] Application Example 1

[0112] This application example provides a gel battery, and the preparation process of the gel battery includes:

[0113] NCM811 was used as the positive electrode of the battery, silicon carbon was used as the negative electrode, and the electrolyte precursor solution in Example 1 was injected. The battery was allowed to stand at 25° C. for 48 h, and then hot-pressed at 0.2 MPa and 60° C. for 3 h to obtain the gel battery in situ.

[0114] Application Example 2

[0115] This application example provides a gel battery, and the preparation process of the gel battery includes:

[0116] NCM811 was used as the positive electrode of the battery, silicon carbon was used as the negative electrode, and the electrolyte precursor solution in Example 2 was injected. The battery was allowed to stand at 25° C. for 48 h, and then hot-pressed at 0.2 MPa and 75° C. for 0.5 h to obtain the gel battery in situ.

[0117] Application Example 3

[0118] This application example provides a gel battery, and the preparation process of the gel battery includes:

[0119] NCM811 was used as the positive electrode of the battery, silicon carbon was used as the negative electrode, and the electrolyte precursor solution in Example 3 was injected. The battery was allowed to stand at 25°C for 48 hours, and then hot-pressed at 0.1 MPa and 50°C for 6 hours to obtain an in-situ gel battery.

[0120] Application Examples 4-9 and Comparative Application Examples 1-2

[0121] Application Examples 4-9 and Comparative Application Examples 1-2 respectively provide a gel battery, which differs from Application Example 1 only in that the electrolyte precursor solution in Example 1 used in Application Example 1 is replaced by the electrolyte precursor solutions in Examples 4-9 and Comparative Examples 1-2, respectively. The other preparation processes and parameter settings are the same as those in Application Example 1.

[0122] The performance of the gel electrolytes obtained in Examples 1-9 and Comparative Examples 1-2 was tested using the following test methods / standards:

[0123] (1) Conductivity test: using an electrochemical workstation, the applicable standard is NB / T 10827-2021 (power battery film);

[0124] (2) Uniformity test: Ultrasonic fingerprint technology is used to obtain uniformity information by utilizing the propagation characteristics of ultrasound in gel electrolyte;

[0125] (3) Cycling performance test: Refer to GB / T 31484-2015 to test the capacity retention rate (%) of gel battery after 200 and 1000 cycles;

[0126] (4) Rate performance test: At 25°C, the gel battery was discharged at a constant current of 1.0 CmA to 3.0 V. After fully charged, discharge tests at different rates were performed.

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] The test results show that:

[0132] (1) It can be seen from Examples 1 to 9 that the present invention introduces nitrogen heterocyclic gel monomers into the electrolyte. The gel electrolyte prepared by combining the nitrogen heterocyclic gel monomers with the electrolyte and the initiator has good uniformity, no cracks or even cracking, and stable conductivity during the polymerization process (the change rate is 1.0-14.6%). The obtained gel battery can have good cycle performance (capacity retention rate after 1000 cycles is 48.4-87.0%) and rate performance (discharge rate at 5C is 58.2-94.5%).

[0133] (2) It can be seen from Example 1 and Examples 4-8 that compared with Example 8, Examples 4-7 have better comprehensive performance. Furthermore, compared with Examples 1 and 5, the comprehensive performance of Examples 4 and 6 is worse, indicating that the present invention can improve the uniformity of the obtained gel electrolyte and the stability of the conductivity during the polymerization process by limiting the content of nitrogen heterocyclic gel monomer in the gel electrolyte, thereby making the obtained gel battery have better cycle performance and rate performance, and excellent comprehensive performance.

[0134] (3) By comparing Example 1 with Example 9, it can be seen that Example 9 uses a non-specific nitrogen heterocyclic gel monomer, and the conductivity of the resulting gel electrolyte changes greatly during the polymerization process, and the cycle performance and rate performance of the resulting gel battery are both deteriorated. This shows that the present invention can obtain a gel electrolyte with better comprehensive performance by further optimizing the type of nitrogen heterocyclic gel monomer.

[0135] (4) By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that, compared with the polymer matrix commonly used in the prior art, the nitrogen heterocyclic gel monomer provided by the present invention can make the obtained gel electrolyte have good uniformity, no cracks or even cracks, and stable conductivity during the polymerization process (the maximum change rate is only 14.6%), and can also make the obtained gel battery have good cycle performance and rate performance.

[0136] pass Figure 3 and Figure 6 From the comparison of the conductivity change graphs during the polymerization process, it can be clearly seen that the conductivity of the gel electrolyte provided by the present invention does not change much during the polymerization process, while the conductivity of the linear monomer gel electrolyte continues to decrease during the polymerization process, and the matrix electrolyte is destroyed when over-polymerization occurs. This shows that the use of nitrogen heterocyclic gel monomers in the gel electrolyte provided by the present invention can significantly reduce the cross-linking disorder of the gel polymer matrix skeleton, thereby achieving precise control of the monomer polymerization process and obtaining a uniform gel electrolyte with a concentrated molecular weight distribution.

[0137] Further, through Figure 4 and Figure 7 From the comparison, it can be seen that the gel electrolyte provided by the present invention has good uniformity, which is beneficial to improving the consistency of the obtained gel battery; while the linear monomer gel electrolyte has obvious cracks, which seriously affects the consistency of the obtained gel battery.

[0138] like Figure 5 As shown, in Example 1, a spatially symmetrical monomer molecule nitrogen heterocyclic gel monomer having intramolecular hydrogen bonds and chelating sites is preferentially formed by a nucleophilic reagent and an epoxy compound, and then polymerized under the action of an initiator to obtain a gel electrolyte having a regular network gel polymer matrix skeleton, thereby making it have excellent comprehensive performance and can be well applied to fast-charging gel batteries.

[0139] like Figure 8 The diagram shows the mechanism of the gel electrolyte of the present invention. The presence of intramolecular hydrogen bonds and chelating sites in the nitrogen heterocyclic gel monomer structure of the present invention can reduce the cross-linking disorder and freedom of the gel polymer matrix skeleton, thereby improving the comprehensive performance of the obtained gel electrolyte.

[0140] pass Figure 9 and Figure 10 It can be seen from the comparison that the gel electrolyte provided by the present invention can be well applied to fast-charging gel batteries.

[0141] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A gel electrolyte, characterized in that: The raw materials for preparing the gel electrolyte include nitrogen heterocyclic gel monomer, electrolyte and initiator; The raw materials for preparing the nitrogen heterocyclic gel monomer include a nucleophilic reagent and an epoxy compound.

2. The gel electrolyte according to claim 1, wherein Based on the mass percentage of the electrolyte being 100%, the mass percentage of the nitrogen heterocyclic gel monomer is 0.6-20%, preferably 0.8-1.2%.

3. The gel electrolyte according to claim 1 or 2, characterized in that The molar ratio of the nucleophilic reagent to the epoxy compound in the raw materials for preparing the nitrogen heterocyclic gel monomer is 1:(3-6).

4. The gel electrolyte according to any one of claims 1 to 3, characterized in that The nucleophile comprises a nitrogen heterocyclic compound; Preferably, the nitrogen heterocyclic compound includes any one or a combination of at least two of 1,4,7,10-tetraazacyclododecane, indole, imidazole, benzimidazole, purine or 1,2,3-triazole; Preferably, the epoxy compound includes glycidyl methacrylate and / or glycidyl acrylate.

5. The gel electrolyte according to any one of claims 1 to 4, characterized in that: The nitrogen heterocyclic gel monomer is prepared by the following method, which comprises the following steps: The nucleophilic reagent and the epoxy compound are reacted to obtain the nitrogen heterocyclic gel monomer.

6. The gel electrolyte according to claim 5, characterized in that The reaction temperature is 50-100°C; Preferably, the reaction time is 6-18h; Preferably, the reaction is carried out in a solvent; Preferably, the solvent comprises any one of propylene carbonate, ethylene carbonate or butylene carbonate, or a combination of at least two thereof; Preferably, based on the mass percentage of the raw material for preparing the nitrogen heterocyclic gel monomer being 100%, the mass percentage of the solvent is 30-80%; Preferably, the reaction is carried out under a protective gas atmosphere; Preferably, the protective gas includes any one of nitrogen, argon or helium, or a combination of at least two of them.

7. The gel electrolyte according to any one of claims 1 to 6, characterized in that: The electrolyte includes a lithium salt and a non-aqueous solvent; Preferably, the non-aqueous solvent comprises any one or a combination of at least two of cyclic carbonate, chain carbonate, aliphatic carboxylate, γ-lactone, chain ether or cyclic ether, more preferably a combination of cyclic carbonate and chain carbonate; Preferably, the concentration of the lithium salt in the electrolyte is 0.5-6 mol / L.

8. The gel electrolyte according to any one of claims 1 to 7, characterized in that: Based on the mass percentage of the electrolyte being 100%, the mass percentage of the initiator is 0.01-4%; Preferably, the initiator includes any one of an azo initiator, a peroxide initiator or a persulfate, or a combination of at least two of them.

9. A method for preparing a gel electrolyte according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: The nitrogen heterocyclic gel monomer, electrolyte and initiator are mixed and heated to obtain the gel electrolyte.

10. Use of the gel electrolyte according to any one of claims 1 to 8 in a gel battery.

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