High-temperature and high-pressure electrolyte and application thereof

Abstract

The invention discloses a high-temperature and high-pressure electrolyte and application thereof, and belongs to the technical field of lithium ion batteries. The high-temperature and high-pressure electrolyte comprises a lithium salt, an organic solvent and an additive, the additive at least comprises a compound Y shown as a formula I or a formula II, R1, R2, R4, R5 and R6 are respectively and independently selected from one of substituted or unsubstituted C1-C12 alkyl, alkoxy, amido, substituted or unsubstituted C2-C12 alkenyl, alkynyl and heterocyclic radical, and R1, R2, R4, R5 and R6 are respectively and independently selected from one of substituted or unsubstituted C1-C12 alkyl, alkoxy, amido, substituted or unsubstituted C2-C12 alkenyl, alkynyl and heterocyclic radical. And R3 is selected from one of an isocyanate group, an isothiocyano group, a cyano group, an imidazolyl group and a phosphate group. The high-temperature and high-voltage electrolyte can adapt to a high-voltage and high-nickel system, can form a stable SEI / CEI film on the surfaces of positive and negative electrode materials, keeps good interface stability at high temperature, and can effectively inhibit gas production and volume expansion, so that the cycle performance of the high-nickel system lithium ion battery at high pressure and high temperature is improved.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, specifically relating to a high-temperature, high-pressure electrolyte and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) are rechargeable secondary batteries that primarily store and release energy by the movement of lithium ions between the positive and negative electrodes. Due to their high energy density, long cycle life, and low self-discharge rate, they are widely used in portable electronic devices, electric vehicles, and energy storage systems. With the increasing demands for energy storage, lithium-ion batteries are gradually developing towards higher voltage or higher nickel content to improve energy density. However, the positive electrode materials in these battery systems are highly susceptible to the dissolution of transition metal elements. These dissolved transition metal ions migrate to the negative electrode interface, damaging the solid electrolyte interface (SEI) film formed on the negative electrode surface, thus severely affecting the battery's cycle performance.

[0003] To improve battery cycle performance, a common approach is to add film-forming additives to the electrolyte of lithium-ion batteries, such as vinylene carbonate (VC) and additives that can form films on both the positive and negative electrode surfaces, such as propylene sulfite (PS) and ethylene sulfate (DTD). However, these traditional additives still have significant limitations under high-voltage or high-nickel systems: on the one hand, the interfacial film they form on the positive electrode surface is not dense and stable enough to effectively suppress the dissolution of transition metals and interfacial side reactions of high-voltage or high-nickel positive electrode materials during long-term cycling, especially under high-temperature conditions; on the other hand, under harsh conditions of high temperature and high voltage, the electrolyte itself is very prone to oxidative decomposition, exacerbating gas production, causing battery volume expansion, and further accelerating battery performance degradation. In addition, high-temperature environments also accelerate the rupture and reconstruction of the SEI film, leading to a significant decrease in cycle capacity retention and posing safety hazards. Summary of the Invention

[0004] In view of this, the primary objective of this application is to provide a high-temperature and high-pressure electrolyte that is suitable for high-voltage and high-nickel systems, maintains good interfacial stability at high temperatures, effectively suppresses gas generation and volume expansion, and improves the cycle performance of high-nickel lithium-ion batteries under high voltage and high temperature.

[0005] To achieve the above objectives, this application adopts the following technical solution: One aspect of this application discloses a high-temperature, high-pressure electrolyte, comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises at least compound Y represented by formula I or formula II:

[0006] R1, R2, R4, R5, and R6 are each independently selected from one of the following groups: substituted or unsubstituted C1-C12 alkyl, alkoxy, amino, substituted or unsubstituted C2-C12 alkenyl, alkynyl, and heterocyclic groups. R3 is selected from one of the following groups: isocyanate, isothiocyanate, cyano, imidazole, and phosphate ester.

[0007] This application also discloses the application of high-temperature and high-pressure electrolytes as described in this application in the preparation of lithium-ion batteries.

[0008] Another aspect of this application discloses a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and the high-temperature, high-pressure electrolyte described in this application.

[0009] The beneficial effects of this application are: In this application, a compound Y with a molecular structure as shown in Formula I or Formula II is introduced into the electrolyte. On the one hand, the carbon-carbon double bond in its molecular structure acts as a strong electron-withdrawing group, which can reduce the lowest unoccupied molecular orbital (LUMO) energy of compound Y, thereby increasing the reduction potential of compound Y and allowing it to form an SEI film on the negative electrode surface before carbonate / carboxylic acid ester electrolyte solvents. On the other hand, in high-nickel battery systems, the positive electrode active material is prone to react with the electrolyte during high-temperature cycling, exacerbating battery gas production and metal ion dissolution. Compound Y contains independent functional groups such as isocyanate, isothiocyanate, cyano, imidazole, and phosphate groups, which make it easy to complex transition metals under high temperature and high voltage conditions. This suppresses the dissolution of transition metal ions such as manganese and cobalt ions in the positive electrode of the high-nickel system, avoids damage to the negative electrode, and improves the cycle performance of lithium-ion batteries under harsh high-temperature and high-pressure conditions. Detailed Implementation

[0010] The embodiments of this application will be clearly and completely described below. The technical solutions in the embodiments described below are exemplary and only possible technical implementations of this application, not all possible implementations. Those skilled in the art can combine the embodiments of this application to obtain other embodiments without creative effort, and these embodiments are also within the protection scope of this application.

[0011] The first aspect of this application discloses a high-temperature, high-pressure electrolyte, comprising a lithium salt, an organic solvent, and an additive, wherein the additive comprises at least compound Y represented by formula I or formula II: ; R1, R2, R4, R5, and R6 are independently selected from one of the following groups: substituted or unsubstituted C1-C12 alkyl, alkoxy, amino, substituted or unsubstituted C2-C12 alkenyl, alkynyl, and heterocyclic groups; R3 is selected from one of the following groups: isocyanate (-N=C=O), isothiocyanate (-N=C=S), cyano (-CN), imidazole, and phosphate ester.

[0012] In this application, the substituent group includes at least one of a halogen atom (such as Cl, F, Br, I, etc.), a carboxyl group (-COOH), and a hydroxyl group (-OH).

[0013] In some specific examples, the compound Y has any one of the molecular structures described in Y1-Y10: .

[0014] This application involves adding compound Y to a lithium-ion battery electrolyte for use in high-voltage lithium-ion batteries. This allows the formation of a high-temperature stable inorganic SEI film rich in elements such as S and N at the positive and negative electrode interfaces. Furthermore, compound Y exhibits a certain complexing effect on transition metal ions, effectively reducing the damage to the negative electrode caused by the dissolution of transition metal ions from the positive electrode under high voltage conditions. This improves the high-voltage and high-temperature stability of the lithium-ion battery and enhances its cycle performance. Specifically, the carbon-carbon double bond in compound Y, as a strong electron-withdrawing group, lowers the lowest unoccupied molecular orbital (LUMO) energy of compound Y, thereby increasing its reduction potential. This allows it to form an SEI film on the negative electrode surface before carbonate and carboxylic acid ester electrolyte solvents. Moreover, the additive contains independent functional groups such as isocyanate, isothiocyanate, cyano, imidazole, and phosphate groups, which readily complex with transition metals under high voltage conditions. This inhibits the dissolution of transition metal ions such as manganese and cobalt ions from the positive electrode, thus preventing damage to the negative electrode and improving the battery's cycle performance.

[0015] The preparation of compound Y in this application can be carried out with reference to the processes in the prior art, which will not be described in detail here.

[0016] An appropriate amount of compound Y can ensure that it can form films on the positive / negative electrode surfaces and reduce the dissolution of transition metal ions from the positive electrode, while avoiding excessively thick films that would increase battery impedance. The specific amount can be determined experimentally and is not particularly limited. In some specific examples, the mass percentage of compound Y in the electrolyte is 0.1%-10%, for example, any value or range between 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. Preferably, the mass percentage of compound Y in the electrolyte is 1%-3%, and more preferably, the mass percentage of compound Y in the electrolyte is 3%.

[0017] In this application, the lithium salt is not particularly limited, and any electrolyte conductive lithium salt commonly used in electrolytes that is well known in the art can be used. Specific examples include, but are not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium perchlorate (LiClO4), lithium dioxolaneborate (LiBOB), lithium difluorooxolaneborate (LiODFB), lithium trifluoromethanesulfonate (LiCF3SO3), lithium perfluorobutylsulfonate (LiC4F9SO3), and bis(perfluoroethylsulfonyl)imide (LiN(SO2C2F5)2).

[0018] It is understood that the concentration of lithium salt in the electrolyte is not particularly limited and can be an empirical value in the art or determined experimentally. A suitable lithium salt concentration helps to improve the overall performance of the electrolyte. In some specific examples, the concentration of lithium salt is 0.1-5 mol / L, for example, it can be any concentration or a range between 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, and 5 mol / L.

[0019] In this application, there is no particular limitation on the type of organic solvent, and conventional types in the art can be used. Specifically, the organic solvent can be at least one of carbonates, carboxylic esters, or their derivatives. Carbonate organic solvents can be cyclic and / or chain-like, while carboxylic ester organic solvents can be linear and / or branched. In some specific examples, the organic solvent is at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl acetate (EA), propyl acetate (PA), ethyl propionate (EP), and ethyl butyrate (EB).

[0020] Furthermore, this application may also contain other common additives in the art, such as at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), propylene sulfite (PS), and vinyl sulfate (DTD). In some specific examples, the other additives are at least one of fluoroethylene carbonate (FEC) and vinyl sulfate (DTD). The specific content of the other additives can be determined using empirical values ​​in the art or through experimental methods. Those skilled in the art have the ability to do so. As an example, the content of the additives accounts for 0.01-10% of the total mass of the electrolyte.

[0021] The second aspect of this application discloses the application of the high-temperature and high-pressure electrolyte as described in the first aspect of this application in the preparation of lithium-ion batteries.

[0022] The third aspect of this application discloses a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and the high-temperature and high-pressure electrolyte described in the first aspect of this application.

[0023] It is understood that there are no particular limitations on the positive electrode, negative electrode and separator in this application, and all can be conventional types in the field or types independently developed.

[0024] The positive electrode sheet includes a positive electrode active material, which can be any known or independently developed positive electrode active material in the art, without any particular limitations. Given the excellent performance of the electrolyte in this application, its effect on positive electrode materials in high-nickel systems is even more pronounced. As an example, the positive electrode active material is... 0≤x≤1, 0≤y≤1, where, for high-nickel material systems, x≥0.8, preferably, the positive electrode active material is LiNi. 0.8 Co 0.1 Mn 0.1 O2 cathode material.

[0025] The negative electrode sheet includes a negative electrode active material, which includes one or a combination of two or more of the following: soft carbon, hard carbon, artificial graphite, natural graphite, silicon-oxygen negative electrode, silicon-carbon negative electrode, lithium metal, and lithium alloy.

[0026] The membrane can be made of porous membranes composed of polyethylene, polypropylene, glass fiber, nylon, etc., or composite membranes of these membranes, or modified membranes of these membranes. The modification includes, but is not limited to, surface coatings such as ceramics or fast ion conductors.

[0027] The assembly method for lithium-ion batteries can be any method well known in the art. For example, in a glove box that is isolated from water and oxygen, the positive electrode, separator and negative electrode are assembled in sequence, and then the high-temperature and high-pressure electrolyte of this application is injected to complete the assembly.

[0028] The present application will be further illustrated below with reference to specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present application in any way.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0030] In addition, unless otherwise specified, methods without detailed conditions or steps are conventional methods, and the reagents and materials used are commercially available.

[0031] Example 1 This embodiment discloses a high-temperature, high-pressure electrolyte, the preparation steps of which are as follows: In an argon-filled glove box (H2O < 10 ppm, O2 < 1 ppm), fluoroethylene carbonate and ethylene sulfate were added sequentially to an organic solvent, followed by the slow addition of lithium salt LiPF6. After thorough mixing, a basic electrolyte was obtained. Finally, compound Y was added to the basic electrolyte to obtain a high-temperature, high-pressure electrolyte.

[0032] The addition relationship of each component in the electrolyte in this embodiment is as follows:

[0033] Example 2 This embodiment discloses another high-temperature and high-pressure electrolyte, which adopts the same implementation method as in Example 1, except that the amount of compound Y added is 1 wt%. Other process steps and condition parameters are the same as in Example 1.

[0034] Example 3 This embodiment discloses another high-temperature and high-pressure electrolyte, which adopts the same implementation method as in Example 1, except that the amount of compound Y added is 3wt%. Other process steps and condition parameters are the same as in Example 1.

[0035] Example 4 This embodiment discloses another high-temperature and high-pressure electrolyte, which adopts the same implementation method as in Example 1, except that the amount of compound Y added is 5 wt%. Other process steps and condition parameters are the same as in Example 1.

[0036] Example 5 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y2. All other process steps and condition parameters are the same as in Example 3.

[0037] Example 6 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y3. All other process steps and condition parameters are the same as in Example 3.

[0038] Example 7 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y4. All other process steps and condition parameters are the same as in Example 3.

[0039] Example 8 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y5. All other process steps and condition parameters are the same as in Example 3.

[0040] Example 9 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y6. All other process steps and condition parameters are the same as in Example 3.

[0041] Example 10 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y7. All other process steps and condition parameters are the same as in Example 3.

[0042] Example 11 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y8. All other process steps and condition parameters are the same as in Example 3.

[0043] Example 12 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y9. All other process steps and condition parameters are the same as in Example 3.

[0044] Example 13 This embodiment discloses another high-temperature, high-pressure electrolyte, which adopts the same implementation method as in Example 3, except that compound Y is Y10. All other process steps and condition parameters are the same as in Example 3.

[0045] Comparative Example This comparative example discloses another electrolyte, which adopts the same implementation method as Example 1, except that: the electrolyte is only a basic electrolyte and no compound Y is added.

[0046] Performance testing The electrolytes from Examples 1-13 and the comparative examples were assembled into lithium-ion batteries, and their relevant performance was tested.

[0047] 1. The composition and assembly of lithium-ion batteries are as follows: (1) Preparation of positive electrode: The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black SP, and binder PVDF are dispersed in NMP solvent at a mass ratio of 98:1:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode current collector aluminum foil, dried, cold-pressed, and slit to obtain a positive electrode sheet. The coating amount per unit area on both sides is 180 g / m². 2 .

[0048] (2) Preparation of negative electrode sheet: Graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), styrene-butadiene rubber (adhesive), and acetylene black (conductive agent) were mixed in a mass ratio of 96:1:1:1. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. The negative electrode slurry was uniformly coated on the surface of the copper foil of the negative electrode current collector. After drying, cold pressing, and slitting, a negative electrode sheet was obtained, wherein the coating amount per unit area on both sides was 110 g / m². 2 .

[0049] (3) Separator: Polypropylene diaphragm with a thickness of 14μm.

[0050] (4) Electrolyte: Electrolytes in Examples 1-13 and Comparative Examples.

[0051] (5) Assembly of stacked batteries: The prepared positive / negative electrode sheets and separators are stacked in the order of positive electrode sheet, separator and negative electrode sheet, ensuring that the separator is between the positive / negative electrode sheets. Then, they are wound, hot-pressed and shaped, and the tabs are welded to obtain the bare cell. The top and side are sealed with aluminum-plastic film. After the process, the cell is baked and injected with electrolyte. After negative pressure encapsulation, standing, formation and shaping, lithium-ion battery is obtained.

[0052] 2. Testing Methods (1) Cyclic performance test The battery cell was first charged and discharged at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, at 45℃, the battery cell was charged at a constant current rate of 1C to a voltage of 4.45V, then charged at a constant voltage until the current was ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. Its actual capacity was recorded as C0. Then, the battery cell was charged at a constant current of 1.0C0, with a charging cutoff voltage of 4.45V. After each charging, it was discharged at 1C0 to the full cell discharge cutoff voltage of 2.8V.

[0053] (2) Volume expansion rate test After completing the cycle life test, the battery thickness at fixed points was measured and the volume expansion rate of the battery after cycling was calculated according to formula (1):

[0054] The test results are shown in Table 1.

[0055] Table 1 Battery cycle performance and volume expansion rate

[0056] The test results in Table 1 show that adding an appropriate compound Y to the electrolyte can effectively improve the capacity retention of lithium-ion batteries after 500 cycles at 45°C, and also significantly reduce the volume expansion rate of the battery after high-temperature cycling.

[0057] Therefore, the high-temperature and high-pressure electrolyte proposed in this application can reduce gas production, suppress lithium battery expansion, improve the safety performance of lithium-ion batteries under high voltage and high temperature conditions, and improve the cycle performance of lithium batteries.

[0058] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A high-temperature, high-pressure electrolyte, characterized in that, It includes lithium salts, organic solvents, and additives, wherein the additives include at least compound Y represented by formula I or formula II: ； R1, R2, R4, R5, and R6 are each independently selected from one of the following groups: substituted or unsubstituted C1-C12 alkyl, alkoxy, amino, substituted or unsubstituted C2-C12 alkenyl, alkynyl, and heterocyclic groups. R3 is selected from one of the following groups: isocyanate, isothiocyanate, cyano, imidazole, and phosphate ester.

2. The high-temperature, high-pressure electrolyte as described in claim 1, characterized in that, The substituent group includes at least one of halogen atom, carboxyl group, and hydroxyl group.

3. The high-temperature, high-pressure electrolyte as described in claim 1, characterized in that, The mass percentage of compound Y in the electrolyte is 0.1%-10%.

4. The high-temperature, high-pressure electrolyte as described in claim 3, characterized in that, The mass percentage of compound Y in the electrolyte is 1%-3%.

5. The high-temperature, high-pressure electrolyte as described in claim 1, characterized in that, The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluoroantimonyate, lithium perchlorate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethyl sulfonate, lithium perfluorobutyl sulfonate, and bis(perfluoroethyl)sulfonyl)imide.

6. The high-temperature, high-pressure electrolyte as described in claim 1, characterized in that, The concentration of lithium salt in the electrolyte is 0.1-5 mol / L.

7. The high-temperature, high-pressure electrolyte as described in claim 1, characterized in that, The organic solvent is selected from at least one of carbonates, carboxylic esters and their derivatives.

8. The high-temperature, high-pressure electrolyte as described in claim 7, characterized in that, The organic solvent is at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl acetate, propyl acetate, ethyl propionate, and ethyl butyrate.

9. The application of the high-temperature and high-pressure electrolyte as described in any one of claims 1-8 in the preparation of lithium-ion batteries.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the high-temperature, high-pressure electrolyte as described in any one of claims 1-9.

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