A gel electrolyte, a preparation method thereof, a battery cell, and a battery

Abstract

The present application relates to the technical field of electrolyte, in particular to a kind of gel electrolyte and its preparation method, battery cell, battery.The gel electrolyte includes at least from the structural unit of crosslinking monomer, the crosslinking monomer includes repeating unit and the number of the repeating unit is 2-8, and the gel electrolyte lock liquid rate and liquid retention rate are preferably.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, specifically to a gel electrolyte and its preparation method, a battery cell, and a battery. Background Technology

[0002] Bipolar batteries allow cell-to-cell connections without additional electrical links, shortening electron transport paths while achieving high output voltage and energy density. This assembly method also reduces the use of foil and cover plates, lowering battery costs. However, bipolar batteries are prone to short circuits caused by electrolyte leakage between cells.

[0003] Gel polymer electrolytes (GPEs) are gel network structures containing electrolyte salts. Their core function is ion conduction, offering advantages such as high ionic conductivity, high safety, and good processability. They can be used in bipolar batteries to reduce electrolyte flow. However, when existing GPEs are subjected to pressure on the battery cell, the liquid contained within the GPE is easily squeezed out, potentially causing short circuits due to leakage from adjacent cell current collectors or edge sealing defects.

[0004] Therefore, effectively reducing electrolyte leakage from the electrolyte is of great significance for improving the safety performance of bipolar batteries. Summary of the Invention

[0005] The gel electrolyte provided by this invention, by controlling the number of repeating units from cross-linked monomers in the structural unit, makes the structure of the gel electrolyte more stable and less susceptible to damage by external forces, thereby improving the liquid retention rate and liquid holding rate of the gel electrolyte, and effectively improving the short circuit phenomenon caused by leakage.

[0006] The present invention achieves the above-mentioned technical objectives through the following technical solutions:

[0007] A gel electrolyte comprising at least structural units derived from a crosslinking monomer, wherein the crosslinking monomer includes repeating units and the number of repeating units is 2-8.

[0008] In the gel electrolyte described above, the molecular weight of the crosslinking monomer is 190-1000 g / mol.

[0009] In the gel electrolyte described above, the molecular weight of the crosslinking monomer is 190-600 g / mol.

[0010] The structural unit of the gel electrolyte described above is derived from the crosslinking monomer and other monomers, wherein the other monomers are monomers containing only one chemically reactive functional group.

[0011] The gel electrolyte described above includes repeating units in the other units, and the number of repeating units is no more than 9.

[0012] In the gel electrolyte described above, the proportion of the other monomers in the total mass of the crosslinking monomers and other monomers is no more than 60%.

[0013] In the gel electrolyte described above, the molecular weight of the other monomers is 100-500 g / mol.

[0014] In the gel electrolyte described above, the number of repeating units in the other monomers is no more than 5.

[0015] The crosslinking monomers in the gel electrolyte described above are one or more of polyethylene glycol dimethacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and polyethylene glycol diglycidyl ether.

[0016] In the gel electrolyte described above, the other monomers are one or more of polyethylene glycol methyl ether methacrylate, polyethylene glycol methacrylate, hexafluorobutyl methacrylate, and acrylonitrile.

[0017] The gel electrolyte described above also includes an initiator and an electrolyte solution, wherein the mass ratio of the electrolyte solution to other monomers to crosslinking monomers to initiator is (90-97):(0-6):(3-10):(0.02-0.1).

[0018] This invention also provides a method for preparing a gel electrolyte, comprising at least the step of polymerizing a raw material including a crosslinking monomer; wherein the crosslinking monomer comprises repeating units and the number of repeating units is 2-8. This preparation method is simple, easy to implement, and yields a gel electrolyte with good liquid retention and liquid locking properties.

[0019] In the preparation method of the gel electrolyte described above, the polymerization reaction temperature is 45-60℃.

[0020] The preparation method of the gel electrolyte described above also includes the step of injecting the raw material into the battery matrix and then carrying out the polymerization reaction.

[0021] The present invention also provides a battery cell comprising the above-described gel electrolyte or the gel electrolyte prepared by the above method. This battery cell is less prone to short circuits due to electrolyte leakage.

[0022] The present invention also provides a battery comprising the above-described battery cell, which is less prone to short circuit problems.

[0023] The battery described above is a bipolar battery. Attached Figure Description

[0024] Figure 1 The images shown are SEM images of the gel electrolytes in Example 2 and Comparative Example 1, along with corresponding deformation demonstration diagrams. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] In view of the problem that free electrolyte can easily seep out and cause internal short circuits when gel electrolytes are squeezed by external force, the present invention provides a gel electrolyte, which includes at least structural units from crosslinking units, and the crosslinking units include repeating units and the number of repeating units is 2-8.

[0027] To better understand this invention, some key terms are explained below:

[0028] Gel electrolytes are materials that fall between liquid and solid electrolytes. They are semi-solid materials composed of a polymer network and a liquid electrolyte. The polymer network is a three-dimensional network structure formed through chemical or physical cross-linking, providing mechanical strength and stability. The liquid electrolyte fills the polymer network, providing ionic conductivity.

[0029] Crosslinking monomers are small organic molecules that have two or more chemically reactive functional groups and can react with other monomers or polymer chains in polymers to form a three-dimensional network structure.

[0030] Other monomers in this invention refer to small organic molecules possessing a single functional group capable of undergoing a chemical reaction. More specifically, this means that the monomer possesses only one functional group capable of chemically reacting with the crosslinking monomer; it can be either a monomer including repeating units or a non-repeating monomer without repeating units.

[0031] Liquid retention rate: refers to the percentage of the mass of free electrolyte to the mass of gel electrolyte after the gel electrolyte has solidified.

[0032] Liquid retention rate: refers to the percentage of free electrolyte that seeps out after the gel electrolyte has solidified and is subjected to external pressure, relative to the total mass of the gel electrolyte.

[0033] This invention improves the liquid retention and liquid holding rates of the gel electrolyte by controlling the number of repeating units derived from crosslinking monomers within the structural unit, making the gel electrolyte structure more stable and less susceptible to damage from external forces. The reason for this might be that... Figure 1 As shown, when the number of repeating units from cross-linking monomers in the structural unit of the gel electrolyte is greater, the intersegmental spacing of the molecular chains is larger, the van der Waals forces between the molecular chains are weaker, and the deformability is stronger. Macroscopically, this means that the structure will not be destroyed after external force stimulation, and therefore the contained electrolyte will not be squeezed out, resulting in a high liquid retention rate. Conversely, the smaller the intersegmental spacing of the molecular chains, the stronger the van der Waals forces between the molecular chains, the weaker the deformability, and the more fragile the structure will be after external force stimulation. The contained electrolyte will be squeezed out under certain pressure, resulting in a poor liquid retention rate.

[0034] When the number of repeating units is 2-8, such as 2, 3, 4, 5, 6, 7, or 8, the gel electrolyte exhibits good liquid retention and locking rates, and the overall electrolyte viscosity is not too high, which is beneficial for cell wetting. Therefore, in practical applications, crosslinking monomers with a molecular weight of 190-1000 g / mol are typically selected, such as 190 g / mol, 250 g / mol, 300 g / mol, 500 g / mol, 600 g / mol, 700 g / mol, 800 g / mol, 900 g / mol, 1000 g / mol, or any range between these values. When crosslinking monomers with a molecular weight of 190-600 g / mol are used, the performance of the gel electrolyte is relatively better.

[0035] In some embodiments of the present invention, the structural units in the gel electrolyte are derived from crosslinking monomers and other monomers, wherein the other monomers are monomers containing only one chemically reactive functional group. By introducing other monomers, the number of sites capable of chemical crosslinking increases, and the liquid retention and liquid locking rates of the gel electrolyte can be further improved.

[0036] It should be noted that other monomers may or may not contain repeating units. When other monomers also contain repeating units, the number of repeating units should not exceed 9, such as 2, 3, 4, 5, 6, 7, 8, or 9. When the number of repeating units is too high (>9), the overall viscosity of the electrolyte will increase, which is not conducive to cell wetting.

[0037] Understandably, the types of repeating units in other monomers are not restricted; they can be the same as or different from the repeating units in the crosslinking monomers.

[0038] When other monomers account for too much of the total mass, the gel skeleton cannot hold a large amount of electrolyte (≥94%). Therefore, the proportion of other monomers in the total mass of crosslinking monomers and other monomers is usually controlled to be no more than 60%.

[0039] Studies have found that gel electrolytes exhibit better performance when the molecular weight of other monomers is between 100 and 500 g / mol. Further research revealed that gel electrolytes demonstrate better liquid retention and liquid locking rates when other monomers contain repeating units of 1-5 units.

[0040] There are no specific limitations on the crosslinking monomers and other monomers used in this invention. For example, the crosslinking monomer may be one or more of polyethylene glycol dimethacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and polyethylene glycol diglycidyl ether, and other monomers may be one or more of polyethylene glycol methacrylate, fluoromethacrylate, and acrylonitrile.

[0041] Specifically, when the crosslinking monomer is polyethylene glycol dimethacrylate, its repeating unit is -CH2-CH2-O-, and the number of repeating units is 2-8. When the crosslinking monomer is ethoxylated trimethylolpropane triacrylate, its repeating unit is -CH2-CH2-O-, and the number of repeating units is 2-8. When the crosslinking monomer is pentaerythritol tetraacrylate, its repeating unit is -CH2-CH2-O-, and the number of repeating units is 2-8.

[0042] When other monomers are polyethylene glycol methacrylate, the repeating unit is -CH2-CH2-O-, and the number of repeating units is no more than 9. When other monomers are fluoromethacrylate, fluoromethacrylate with a fluorination number of 3-12 is preferred.

[0043] It is easy to understand that most polymerization reactions require the addition of an initiator to initiate or start the polymerization process. Furthermore, as a gel electrolyte, to fulfill its ion-conducting function, the gel electrolyte also includes an electrolyte, which fills the three-dimensional cross-linked structure of the gel electrolyte. There are no specific limitations on the amount of initiator and electrolyte added. However, when the mass ratio of electrolyte:other monomers:crosslinking monomers:initiator is (90-97):(0-6):(3-10):(0.02-0.1), the prepared gel electrolyte exhibits better performance, with a liquid retention rate ≥99% and a liquid holding rate ≥95%.

[0044] There are no special restrictions on the initiator and electrolyte. For example, the initiator can be one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and lithium difluorooxalate borate. The electrolyte includes an electrolyte salt and a solvent, which are also not particularly limited. The electrolyte salt can be a lithium salt, such as lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium tetrafluoroborate (LiBF4); or a sodium salt, such as sodium hexafluorophosphate (NaPF6) or sodium perchlorate (NaClO4); or other materials suitable for battery electrolytes, such as potassium hydroxide (KOH) or tetraethylammonium tetrafluoroborate (TEABF4). The solution can use solvents commonly used in the preparation of gel electrolytes, such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), tetrahydrofuran (THF), or 1,3-dioxolane (DOL). The concentration of the electrolyte salt in the electrolyte is 0.65-1.5M.

[0045] In this invention, the number of repeating units of cross-linked monomers in the finished end-gel electrolyte can be measured by mass spectrometry, and the ratio of other monomers to cross-linked monomers can be detected by infrared and nuclear magnetic resonance spectrometry.

[0046] The present invention also provides a method for preparing the above-mentioned gel electrolyte, which includes at least the step of polymerizing a raw material comprising a crosslinking monomer. The crosslinking monomer comprises repeating units, and the number of repeating units is 2-8.

[0047] The above-mentioned preparation can be carried out using either in-situ or non-in-situ methods. Non-in-situ methods include solution coating, phase transfer, and electrospinning, while in-situ preparation involves polymerization under specific external conditions, such as ultraviolet light and heat treatment, after injection into the battery. In-situ preparation can solve problems such as the difficulty of gel electrolytes penetrating porous electrodes, poor electrode / electrolyte contact, and high interfacial impedance. Therefore, in-situ preparation methods are preferred in actual preparation.

[0048] There are no special restrictions on the polymerization reaction conditions; both photopolymerization and thermal polymerization can be used. In some specific embodiments of the present invention, the polymerization reaction temperature is 45-60°C.

[0049] For example, the preparation method is as follows: the monomer, crosslinking agent and initiator are added to the electrolyte one by one, stirred at 200-400 rpm for 1 h under argon protection atmosphere, and then injected into the battery cell. After standing at room temperature for 24-48 h, it is heated at 45-60 ℃ for 4-8 h for curing, and then cooled to obtain the product.

[0050] The present invention also provides a battery cell comprising the above-described gel electrolyte or a gel electrolyte prepared by the above method.

[0051] The present invention also provides a battery comprising the aforementioned battery cell. This battery can be either a unipolar or a bipolar battery. Furthermore, the battery is preferably a bipolar battery, meaning that the gel electrolyte is suitable not only for general unipolar batteries but also for bipolar batteries.

[0052] The gel electrolyte and its preparation method described in this invention will be described in detail below with reference to specific embodiments.

[0053] Example 1

[0054] Monomer: 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, with the following structure: It has 2 repeating units and a molecular weight of 188 g / mol.

[0055] Crosslinking agent: polyethylene glycol dimethacrylate, with the following structure: The number of repeating units is 3, and its molecular weight is 330 g / mol.

[0056] Initiator: Azobisisobutyronitrile (AIBN).

[0057] Electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) are mixed with 1M LiPF6 in a 1:1:1 mass ratio.

[0058] Step 1: Mix monomer, crosslinking agent, initiator and electrolyte in a mass ratio of 1.25:3.75:0.025:95 and stir at 300 rpm for 1 h in a glove box under argon protection to obtain a prepolymer solution.

[0059] Step 2: Inject the well-mixed prepolymer solution into the battery in a glove box. The battery is vacuum sealed with a vacuum degree of 70 kPa and then immersed at room temperature for 30 hours.

[0060] Step 3: Place the battery clamp obtained in Step 2 with a clamping pressure of 3N, and then place it in a 60℃ oven for 2 hours to solidify the electrolyte by heating, thus completing the preparation of the gel electrolyte. The number of repeating units of the monomer in the obtained gel electrolyte is the same as the number of repeating units of the corresponding small molecule.

[0061] Example 2

[0062] The difference between this embodiment and Example 1 is that the number of repeating units of the crosslinking agent is 4, and its molecular weight is 374 g / mol.

[0063] Example 3

[0064] The difference between this embodiment and Example 1 is that the number of repeating units of the crosslinking agent is 7, and its molecular weight is 506 g / mol.

[0065] Example 4

[0066] The difference between this embodiment and Example 1 is that the number of repeating units of the crosslinking agent is 2, and its molecular weight is 286 g / mol.

[0067] Example 5

[0068] The difference between this embodiment and Example 1 is that the number of repeating units of the crosslinking agent is 8, and its molecular weight is 550 g / mol.

[0069] Example 6

[0070] The difference between this embodiment and Example 1 is that the monomer has 9 repeating units and a molecular weight of 496 g / mol.

[0071] Example 7

[0072] The difference between this embodiment and Example 1 is that the monomer has 5 repeating units and a molecular weight of 320 g / mol.

[0073] Example 8

[0074] The difference between this embodiment and Embodiment 1 is that the monomer, crosslinking agent, initiator and electrolyte are mixed in a mass ratio of 2.5:2.5:0.025:95.

[0075] Example 9

[0076] The difference between this embodiment and Embodiment 1 is that the monomer, crosslinking agent, initiator and electrolyte are mixed in a mass ratio of 1.67:3.33:0.025:95.

[0077] Example 10

[0078] The difference between this embodiment and Embodiment 1 is that it does not contain monomers, and the crosslinking agent, initiator and electrolyte are mixed in a mass ratio of 5:0.025:95.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that the crosslinking agent component has 1 repeating unit and a molecular weight of 242 g / mol.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that the crosslinking agent component has 9 repeating units and a molecular weight of 594 g / mol.

[0083] Comparative Example 3

[0084] The difference from Example 1 is that the proportions of monomer and crosslinking agent components are different, that is, the monomer, crosslinking agent, initiator and electrolyte are mixed in a ratio of 5:0:0.025:95.

[0085] Performance testing:

[0086] (1) The prepared gel prepolymer solution was dropped onto the surface of a stainless steel electrode. After adding a separator, the solution was dropped again, and then a stainless steel sheet was added to the solution surface to assemble a symmetrical stainless steel coin cell. After heating and curing, the EIS impedance spectrum of the coin cell was tested on an electrochemical workstation to obtain its ionic conductivity. The test results are shown in Table 1.

[0087] (2) Liquid retention rate test

[0088] The liquid retention rate y is defined as the ratio of the difference between the mass m1 of the gel electrolyte after being compressed under a certain pressure and the mass m0 before compression, to the mass m1 before compression. This value reflects the ability of the gel electrolyte to retain liquid when subjected to external pressure. It can prevent the free electrolyte from being squeezed out by the expansion force during cycling, which would then lead to leakage through defects in the current collector, resulting in performance degradation and short circuits in the bipolar battery. The test results are shown in Table 1.

[0089] The specific test method is as follows: A certain mass of gel electrolyte m0 is placed in a container with a cylindrical inner wall. The container is open at both the top and bottom, and the tightness of the bottom gasket is adjusted so that the liquid can flow down but the gel cannot. A pressure of 1.2 MPa is applied above the container through a plunger of a similar size, and the constant pressure is applied for 10 minutes. Then, the mass m1 of the gel electrolyte after extrusion is weighed. The ratio of the mass difference of the gel electrolyte before and after the test to the initial mass m0 is the liquid retention rate.

[0090] (3) Liquid retention rate test:

[0091] The test method is as follows: a certain mass of prepolymer solution m0 is placed in a bottle for polymerization. After polymerization, the mass of free liquid that is not locked is m1, and the liquid lock-in rate is defined as (m0-m1) / m0.

[0092] Table 1

[0093]

[0094] As shown in Table 1, the number of repeating units from crosslinking monomers in the electrolyte has a significant impact on the liquid retention and liquid locking rates (especially the liquid retention rate) of the gel electrolyte. When the number of repeating units increases from 1 to 4 to 9, the liquid retention rate of the gel electrolyte decreases from 84.2% to 99.1% to 80.5%. In terms of battery performance, gel electrolytes with a liquid retention rate below 90% exhibit short circuits within 100 cycles. When the number of repeating units from crosslinking monomers in the electrolyte is 2-8, the electrolyte exhibits better liquid retention and liquid locking rates. When the crosslinking agent component accounts for 0% of the electrolyte, the gel electrolyte cannot solidify. Furthermore, the elongation of the crosslinking agent chain segments in the electrolyte improves the ionic conductivity; when the number of crosslinking agent repeating units is 2-8, the ionic conductivity of the gel electrolyte is also relatively good.

[0095] As shown in Examples 1-9 and Example 10, when the structural units of the gel electrolyte are derived from both the aforementioned crosslinking agent and other monomers, its liquid retention and liquid locking rates are better. Furthermore, as shown in Examples 1, 6, and 7, when the number of repeating units of other monomers increases from 2 to 5, its liquid retention and liquid locking rates are relatively better, and the ionic conductivity increases by approximately 7.2%. When the number of repeating units of other monomers further increases, its liquid retention, liquid locking rate, and ionic conductivity all decrease.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gel electrolyte, characterized in that, The gel electrolyte comprises at least structural units derived from crosslinked monomers, wherein the crosslinked monomers include repeating units and the number of repeating units is 2-8.

2. The gel electrolyte according to claim 1, characterized in that, The molecular weight of the crosslinking monomer is 190-1000 g / mol.

3. The gel electrolyte according to claim 2, characterized in that, The molecular weight of the crosslinking monomer is 190-600 g / mol.

4. The gel electrolyte according to any one of claims 1-3, characterized in that, The structural unit is derived from the crosslinking monomer and other monomers, wherein the other monomers are monomers containing only one chemically reactive functional group.

5. The gel electrolyte according to claim 4, characterized in that, The other monomers include repeating units and the number of repeating units is no more than 9; and / or The proportion of the other monomers in the total mass of the crosslinking monomers and other monomers is no more than 60%; and / or The molecular weight of the other monomers is 100-500 g / mol.

6. The gel electrolyte according to claim 5, characterized in that, The number of repeating units in the other monomers is no more than 5.

7. The gel electrolyte according to any one of claims 4-6, characterized in that, The crosslinking monomer is one or more selected from polyethylene glycol dimethacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and polyethylene glycol diglycidyl ether; and / or The other monomers are one or more of polyethylene glycol methacrylate, fluoromethacrylate, and acrylonitrile.

8. The gel electrolyte according to any one of claims 1-7, characterized in that, It also includes an initiator and an electrolyte, wherein the mass ratio of the electrolyte to other monomers to crosslinking monomers to initiator is (90-97):(0-6):(3-10):(0.02-0.1).

9. A method for preparing a gel electrolyte according to any one of claims 1-8, characterized in that, It includes at least the step of polymerizing raw materials, including crosslinking monomers; The crosslinking monomer includes repeating units, and the number of repeating units is 2-8.

10. The method for preparing a gel electrolyte according to claim 9, characterized in that, The polymerization reaction is carried out at a temperature of 45-60℃.

11. The method for preparing the gel electrolyte according to claim 10, characterized in that, It also includes the step of injecting the raw material into the battery matrix before carrying out the polymerization reaction.

12. A battery cell, characterized in that, The battery cell includes the gel electrolyte as described in any one of claims 1-8 or the gel electrolyte prepared by the preparation method described in any one of claims 9-11.

13. A battery, characterized in that, Includes the battery cell as described in claim 12.

14. The battery according to claim 13, characterized in that, The battery is a bipolar battery.

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