Electrolyte and secondary battery

Abstract

The invention discloses an electrolyte and a secondary battery, and belongs to the technical field of new energy. Wherein the electrolyte comprises a triazine ring compound, and the triazine ring compound comprises one or a combination of more of compounds shown in a formula 1, and in the formula 1, R1, R2 and R3 independently meet any one of the following conditions: (1) a hydrogen atom; (2) an alkyl group having 1 to 9 carbon atoms substituted or unsubstituted with a substituent; (3) alkenyl and alkynyl which are substituted or not substituted by substituent groups and have 2-9 carbon atoms; and (4) a cyano group having 1 to 9 carbon atoms substituted or unsubstituted by a substituent. When the triazine ring compound is used as an additive, the rate capability and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] This application belongs to the field of new energy technology, and in particular relates to an electrolyte and a secondary battery. Background Technology

[0002] Amid the booming development of the global new energy industry, electrolytes, as a key component of lithium-ion batteries, can inhibit decomposition by forming a passivation film after additives are added to the electrolyte.

[0003] In related technologies, the addition of additives to the electrolyte affects the high-temperature performance of the battery. Summary of the Invention

[0004] This application provides an electrolyte and a secondary battery, aiming to solve the aforementioned technical problems.

[0005] This application provides an electrolyte comprising: a triazine cyclic compound, wherein the triazine cyclic compound comprises one or more combinations of compounds shown in [Formula 1]: Formula 1 , Among them, R1, R2, and R3 each independently satisfy any one of the following conditions: (1) Hydrogen atom; (2) Alkyl groups having 1 to 9 carbon atoms, substituted or unsubstituted; (3) Alkenyl or ynyl groups having 2 to 9 carbon atoms, substituted or unsubstituted; (4) A cyano group having 1 to 9 carbon atoms, substituted or unsubstituted.

[0006] Optionally, in some embodiments of this application, any one of R1, R2, and R3 includes one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, and a halocyano group.

[0007] Optionally, in some embodiments of this application, the compound represented by [Formula 1] is any one of the following compounds:

[0008] Optionally, in some embodiments of this application, any one of R1 and R2 includes one or more of halogen substituents, haloalkyl groups, haloalkenyl groups, haloalkynyl groups, and halocyanyl groups.

[0009] Optionally, in some embodiments of this application, the compound represented by [Formula 1] is any one of the following compounds:

[0010] Optionally, in some embodiments of this application, either R1 or R2 includes at least one unsaturated bond.

[0011] Optionally, in some embodiments of this application, the unsaturated bond includes one or more of carbon-carbon double bonds, carbon-carbon triple bonds, and carbon-nitrogen triple bonds.

[0012] Optionally, in some embodiments of this application, the compound represented by [Formula 1] is any one of the following compounds:

[0013] Optionally, in some embodiments of this application, R1 includes at least one unsaturated bond, and R2 includes at least one or more of halogen substituents, haloalkyl groups, haloalkenyl groups, haloalkynyl groups, and halocyanyl groups; Alternatively, R1 may include at least one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, or a halocyano group, and R2 may include at least one unsaturated bond.

[0014] Optionally, in some embodiments of this application, the compound represented by [Formula 1] is any one of the following compounds:

[0015] Optionally, in some embodiments of this application, the ratio of the triazine cyclic compound to the total mass of the electrolyte ranges from 0.1 wt% to 2.0 wt%.

[0016] Accordingly, this application also provides a secondary battery, including the aforementioned electrolyte.

[0017] This application uses triazine ring compounds as additives. The nitrogen atoms on the triazine ring are arranged in meta positions, which makes their electron-withdrawing effect on the cyclic π-electron system more uniform and symmetrically distributed throughout the entire triazine ring. This effectively reduces the LUMO energy level of the compound, increases the reduction potential, and preferentially reduces and decomposes it on the graphite anode surface before the solvent, forming a stable, dense, and LiF-rich SEI film, thus reducing the anode interface impedance. Under high voltage conditions, this additive can preferentially undergo oxidation reaction before the basic electrolyte. The amide bond structure can undergo ring-opening polymerization reaction on the cathode surface to form a uniformly covered and dense CEI interface film. This CEI film can effectively inhibit the catalytic oxidation and decomposition of the electrolyte by the high-voltage cathode material, reducing battery gas production. The nitrogen element in the additive molecule can generate components such as Li3N during the reaction. Li3N is a superionic conductor with extremely high lithium-ion conductivity. Its presence can significantly reduce the cathode interface impedance and improve the rate performance of the battery. The nitrogen atoms in the triazine ring and amide group possess lone pairs of electrons, which can act as Lewis bases to actively capture and bond Lewis acids present in the electrolyte, reduce the acidity of the electrolyte, slow down the corrosion and damage of acidic substances to the positive and negative electrode interface films, and thus improve the cycle performance of the battery. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 These are the redox potential test results of the batteries provided in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] This application provides an electrolyte. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0022] This application provides an electrolyte comprising: a triazine cyclic compound, wherein the triazine cyclic compound comprises one or more combinations of compounds shown in [Formula 1]: Formula 1 , Among them, R1, R2, and R3 each independently satisfy any one of the following conditions: (1) Hydrogen atom; (2) Alkyl groups having 1 to 9 carbon atoms, substituted or unsubstituted; (3) Alkenyl or ynyl groups having 2 to 9 carbon atoms, substituted or unsubstituted; (4) A cyano group having 1 to 9 carbon atoms, substituted or unsubstituted.

[0023] Triazine ring compounds are used as additives. The nitrogen atoms on the triazine ring are arranged in meta positions, which makes their electron-withdrawing effect on the cyclic π-electron system more uniform and symmetrically distributed throughout the triazine ring. This effectively reduces the LUMO energy level of the compound, increases the reduction potential, and preferentially reduces and decomposes it on the graphite anode surface before the solvent, forming a stable, dense, and LiF-rich SEI film, thus reducing the anode interface impedance. Under high voltage conditions, this additive preferentially undergoes oxidation reaction before the basic electrolyte. The amide bond structure can undergo ring-opening polymerization on the cathode surface to form a uniformly covered and dense CEI interface film. This CEI film can effectively inhibit the catalytic oxidation and decomposition of the electrolyte by the high-voltage cathode material, reducing battery gas production. The nitrogen element in the additive molecule can generate components such as Li3N during the reaction. Li3N is a superionic conductor with extremely high lithium-ion conductivity. Its presence can significantly reduce the cathode interface impedance and improve the battery rate performance. The nitrogen atoms in the triazine ring and amide group possess lone pairs of electrons, which can act as Lewis bases to actively capture and bond Lewis acids present in the electrolyte, reduce the acidity of the electrolyte, slow down the corrosion and damage of acidic substances to the positive and negative electrode interface films, and thus improve the cycle performance of the battery.

[0024] In some embodiments of this application, any one of R1, R2, and R3 includes one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, and a halocyano group.

[0025] It can be understood that any one of R1, R2, and R3 on the triazine ring includes one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, or a halocyano group. The halogen substituent or the halogen substituent on the alkyl, alkenyl, alkynyl, or cyano group has strong electron-withdrawing properties, which is beneficial for lowering the LUMO energy level of the molecule, increasing the reduction potential, and preferentially reducing and decomposing it on the graphite anode surface before the solvent, forming a stable, dense, and LiF-rich SEI film, thus reducing the anode interfacial impedance.

[0026] In some examples, the halogen substituents include one or more of F, Cl, Br, I, and At.

[0027] In some examples, the haloalkyl group includes alkyl groups substituted with one or more of F, Cl, Br, I, and At.

[0028] In some examples, the halogenated alkenyl group includes an alkenyl group that is substituted by one or more of F, Cl, Br, I, and At.

[0029] In some examples, the halogenated alkynyl group includes an alkynyl group that has been substituted by one or more of F, Cl, Br, I, and At.

[0030] In some examples, the halocyano group includes a cyano group substituted by one or more of F, Cl, Br, I, and At.

[0031] It is understandable that the steric hindrance of alkyl halogens, alkenyl halogens, alkynyl halogens, and cyano halogens is greater than that of halogen substituents, which can inhibit the excessive growth of SEI films. At the same time, their strong polarity makes the film layer more tightly bonded to the electrode surface, reducing the risk of SEI film rupture at high temperatures.

[0032] Specifically, any one of R1, R2, and R3 includes one or more fluorine substituents or trifluoromethyl groups.

[0033] Understandably, trifluoromethyl groups are polyatomic, strongly electron-withdrawing groups. The combined electron-withdrawing effects of the three F atoms result in a much stronger electron-withdrawing ability than a single trifluoromethyl group. Fluorine substituents, on the other hand, only induce electron withdrawal at a single atom. This strong electron-withdrawing property further lowers the molecular LUMO energy level, enabling more efficient initiation of reduction reactions on the negative electrode surface. Simultaneously, trifluoromethyl groups provide a greater fluorine source, leading to a denser SEI film with a higher LiF content. The steric hindrance of trifluoromethyl groups is greater than that of fluorine substituents, which can inhibit excessive SEI film growth. Furthermore, its strong polarity ensures a tighter bond between the film and the electrode surface, reducing the risk of SEI film rupture at high temperatures.

[0034] In some embodiments of this application, the compound represented by Formula 1 is any one of the following compounds:

[0035] In some embodiments of this application, any one of R1 and R2 includes one or more of halogen substituents, haloalkyl groups, haloalkenyl groups, haloalkynyl groups, and halocyanyl groups.

[0036] It is understandable that R1 and R2 are connection sites close to the amide bond. When either R1 or R2 includes one or more of a halogen substituent, haloalkyl, haloalken, haloalkynyl, or halocyano group, the electron-withdrawing effect of the halogen substituent, haloalkyl, haloalkenyl, haloalkynyl, or halocyano group at the connection site close to the amide bond can be directly transferred to the amide bond, lowering the LUMO energy level and making the reduction reaction more likely to occur at the positive and negative electrode interfaces, resulting in more complete film formation and higher cycle retention. The halogen substituent, haloalkyl, haloalkenyl, haloalkynyl, or halocyano group on R3 also has an electron-withdrawing effect, but its electron-withdrawing effect needs to be indirectly transferred through the triazine ring conjugation system, which weakens the efficiency, results in a higher reduction potential, delayed film formation, slightly poorer SEI / CEI film coverage, and a reduced cycle retention.

[0037] In some embodiments of this application, the compound represented by Formula 1 is any one of the following compounds:

[0038] In some embodiments of this application, either R1 or R2 includes at least one unsaturated bond.

[0039] It is understandable that R1 and R2 are connection sites close to the amide bond. When R1 or R2 includes an unsaturated bond, the unsaturated bond has an electron-withdrawing effect, which can be directly transferred to the amide bond, lowering the LUMO energy level, making the reduction reaction easier to occur at the positive and negative electrode interface, resulting in more complete film formation and higher cycle retention.

[0040] In some embodiments of this application, the unsaturated bond includes one or more of carbon-carbon double bonds, carbon-carbon triple bonds, and carbon-nitrogen triple bonds.

[0041] Understandably, compared to carbon-carbon triple bonds, carbon-carbon double bonds form a larger π-conjugated system with triazine rings, resulting in a more stable molecular structure and easier cross-linking with other polymer chains. The resulting CEI film possesses both density and toughness, buffering the volume expansion of the electrode during battery cycling (such as the lithium intercalation expansion of graphite anodes) and reducing film rupture. In contrast, the conjugation effect of acetylene groups is weaker, and triazine ring compounds are prone to excessive decomposition during film formation. The film formed after the polymerization of acetylene triple bonds is more brittle and easily cracks during cycling, leading to the consumption of active lithium and thus affecting cycle performance. Cyano groups, through their electron-withdrawing properties, assist the positive electrode in forming a simple complex layer, initially inhibiting electrolyte oxidation and thus improving battery cycle performance and high-temperature cycle performance.

[0042] In some embodiments of this application, the compound represented by Formula 1 is any one of the following compounds:

[0043] In some embodiments of this application, R1 includes at least one unsaturated bond, and R2 includes at least one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, and a halocyano group; or, R1 includes at least one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, and a halocyano group, and R2 includes at least one unsaturated bond.

[0044] In some embodiments of this application, the compound represented by Formula 1 is any one of the following compounds:

[0045] In some embodiments of this application, the ratio of the triazine cyclic compound to the total mass of the electrolyte ranges from 0.1 wt% to 2.0 wt%.

[0046] In some embodiments of this application, the electrolyte further includes auxiliary additives, which include one or more of vinylene carbonate, vinyl sulfate, fluorovinyl carbonate, 1,3-propane sulpholactone, methane disulfonate, or tris(trimethylsilane)borate.

[0047] In some embodiments of this application, the mass of the auxiliary additives accounts for 0.1 wt% to 3.0 wt% of the total mass of the electrolyte.

[0048] In some embodiments of this application, the electrolyte comprises a lithium salt. The lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0049] In some embodiments of this application, the molar concentration of the lithium salt is from 0.5 M to 1.5 M.

[0050] In some embodiments of this application, the electrolyte comprises an organic solvent. The organic solvent includes one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, or ethyl butyrate.

[0051] Accordingly, this application also provides a secondary battery, including the aforementioned electrolyte.

[0052] In some embodiments of this application, the secondary battery includes a lithium-ion battery.

[0053] In some embodiments of this application, the lithium-ion battery includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, a separator, and an electrolyte.

[0054] In some embodiments of this application, the negative electrode active material includes at least one or more of carbon-based negative electrode materials, silicon-based negative electrode materials, tin-based negative electrode materials, silicon-containing alloy negative electrode materials, and tin-containing alloy negative electrode materials.

[0055] In some embodiments, the negative electrode active material includes one or more of graphite and silicon.

[0056] In some embodiments of this application, the positive electrode active material includes LiNi. (1-x-y) Co x Mn y Or LiMn a Fe1 a One or more of PO4, wherein 0≤x≤1, 0≤y≤1, and x+y≤1, 0≤a≤1.

[0057] In some examples, the positive electrode active material is lithium iron phosphate (LFP).

[0058] The present application will be further described below through specific embodiments.

[0059] Example 1 Prepare the electrolyte according to the following steps: Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a weight ratio of EC:DMC:EMC = 3:2:5 to obtain a mixed organic solvent system. 1.2 M lithium hexafluorophosphate (LiPF6) was added to the system, and after the lithium salt was completely dissolved, 1.0 wt% of a triazine ring compound of formula 1 and 2.0 wt% of vinylene carbonate (VC) were added to the system.

[0060] Example 2 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 2.

[0061] Example 3 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 3.

[0062] Example 4 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 4.

[0063] Example 5 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 5.

[0064] Example 6 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 6.

[0065] Example 7 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 7.

[0066] Example 8 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 8.

[0067] Example 9 The difference between this embodiment and Embodiment 1 is that the triazine ring compound of structural formula 1 is replaced with the triazine ring compound of structural formula 9.

[0068] Example 10 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structural formula 6 is 0.05 wt%.

[0069] Example 11 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structure 6 is 0.1 wt%.

[0070] Example 12 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structural formula 6 is 0.3 wt%.

[0071] Example 13 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structural formula 6 is 0.5 wt%.

[0072] Example 14 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structural formula 6 is 1.5 wt%.

[0073] Example 15 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structure 6 is 2.0 wt%.

[0074] Example 16 The difference between this embodiment and Example 6 is that the mass fraction of the triazine ring compound of structural formula 6 is 2.5 wt%.

[0075] Comparative Example 1 The difference between this comparative example and Example 1 is that no triazine cyclic compounds were added.

[0076] Comparative Example 2 The difference between this comparative example and Example 1 is that it uses 1,2,3-triazine cyclic compounds.

[0077] Comparative Example 3 The difference between this comparative example and Example 1 is that it uses 1,2,4-triazine cyclic compounds.

[0078] Comparative Example 4 The difference between this comparative example and Example 1 is that it uses a 1,3,4-triazine cyclic compound.

[0079] Comparative Example 5 The difference between this comparative example and Example 1 is that it uses a 1,2,5-triazine cyclic compound.

[0080] Comparative Example 6 The difference between this comparative example and Example 1 is that the amide bond is replaced with an ester group.

[0081] Battery manufacturing: Preparation of positive electrode sheet: Lithium iron phosphate (LFP), conductive agent SuperP, binder PVDF and carbon nanotubes (CNT) are mixed evenly in a weight ratio of 96.5:1.5:1:1 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The slurry is coated on current collector aluminum foil, dried at 85°C and then cold-pressed. After slitting and cutting, it is baked in a vacuum oven at 85°C for 4 hours to prepare the lithium-ion battery positive electrode sheet.

[0082] Preparation of negative electrode sheet: Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR are mixed in a weight ratio of 96:1.2:1.3:1.5 to form a slurry. After being mixed evenly, the slurry is coated on both sides of the copper foil current collector. After drying, rolling, and cutting, the negative electrode sheet of lithium-ion battery is formed.

[0083] Preparation of lithium-ion batteries: The above positive electrode, negative electrode and separator are stacked to form a soft pack battery with a capacity of 2Ah. The battery is then vacuum baked at 85°C for 48h and injected with the electrolyte from the above examples and comparative examples to complete the battery fabrication.

[0084] Battery performance test Redox potential (RPP) testing: Electrolytes prepared in Example 1 and Comparative Example 1 were selected as experimental groups, and the electrolyte of the comparative example without the above additives was used as the base electrolyte. Subsequently, the two electrolytes were assembled into graphite half-cell coin cells, and CV tests were performed. The obtained curves are shown below. Figure 1 As shown.

[0085] Ion conductivity test: Ambient temperature: 25℃±1℃ (conducted in a constant temperature chamber to avoid temperature fluctuations affecting test results); Test equipment: Electrochemical workstation (supports AC impedance testing function); Test electrode: Platinum sheet electrode (the distance between the two electrodes L is fixed at 1.0 cm, the effective area of ​​the electrode A is 1.0 cm², and it is cleaned and dried with anhydrous ethanol before testing). Electrolyte samples: Electrolytes prepared in each example and comparative example (sealed and stored after preparation, and equilibrated at 25°C for 2 hours before testing to avoid the generation of bubbles).

[0086] Test steps Electrode calibration: Plating the platinum electrode into a standard KCl solution with known conductivity (1413 μS / cm at 25℃) and performing AC impedance testing to verify the accuracy of the electrode and equipment; Sample loading: Take 5 mL of the electrolyte to be tested and inject it into the special electrolytic cell. Immerse the calibrated platinum sheet electrode into the electrolyte, ensuring that the electrode is completely submerged and that the two electrodes are not in contact. Seal the electrolytic cell to prevent the electrolyte from evaporating. Impedance test: Set the test parameters of the electrochemical workstation to a frequency range of 1Hz to 100kHz and an AC signal amplitude of 10mV. Perform an AC impedance scan and record the impedance value R (Ω) corresponding to the intersection of the high-frequency band and the real axis in the impedance spectrum. Parallel testing: Each electrolyte sample was tested three times, and the average impedance value R was used for subsequent calculations; Sample replacement: Before testing different samples, thoroughly clean the electrolytic cell and electrodes with anhydrous ethanol, and dry them before testing the next sample to avoid cross-contamination.

[0087] 25℃ Cycling Performance: Under 25℃ conditions, the above-mentioned lithium-ion batteries were charged to 3.65V at a constant current and constant voltage of 1C, and then discharged to 2.5V at a constant current of 1C. This charge / discharge cycle was repeated 800 times, and the capacity retention rate of the lithium-ion batteries was measured. Table 1 is referred to as "25℃ Capacity Retention Rate".

[0088] 45℃ Cycling Performance: The above-mentioned lithium-ion batteries were placed at a high temperature of 45℃ for 3 hours, then charged at 1C constant current and constant voltage to 3.65V, and discharged at 1C constant current to 2.5V. This charge / discharge cycle was repeated 500 times, and the capacity retention rate of the lithium-ion batteries was measured. Table 1 is referred to as "45℃ Capacity Retention Rate".

[0089] The capacity retention rate (%) of a lithium-ion battery after N cycles = discharge capacity of the Nth cycle / initial discharge capacity * 100%.

[0090] 25℃ DCIR Test: Under 25℃ conditions, the above lithium-ion battery was charged to 3.65V using a 1C constant current and constant voltage method, then adjusted to 50% SOC, allowed to stand for 10 minutes, and then charged at 4C for 10 seconds. The DCIR of the lithium-ion battery at 25℃ was measured. Lithium-ion battery DCIR (Ω) = (Voltage after 4C charging - Static voltage before 4C charging) / 4C current.

[0091] Ratio performance: Test conditions Ambient temperature: 25℃±1℃ (conducted in a constant temperature environment chamber); Testing equipment: Battery charge / discharge tester; Test subjects: 2Ah soft-pack lithium-ion batteries prepared in each embodiment and comparative example (the batteries were placed at 25°C for 12 hours before testing to ensure their stability). Charge / discharge voltage range: 3.65V (charging cut-off voltage) ~ 2.5V (discharge cut-off voltage).

[0092] Test steps Battery activation: Charge the battery under test to 3.65V at a constant current and constant voltage of 0.2C (stop charging when the current drops to 0.05C during the constant voltage stage), and let it stand for 30 minutes; then discharge it to 2.5V at a constant current of 0.2C, and let it stand for 30 minutes; repeat this activation process twice to ensure that the active materials of the battery are fully activated. Discharge rate test: The discharge test is conducted in the order of "low rate → high rate", and the specific procedure is as follows: 0.2C discharge: Charge at 0.2C constant current and constant voltage to 3.65V (constant voltage cutoff current 0.05C), let stand for 30 minutes, discharge at 0.2C constant current to 2.5V, and record the discharge capacity C0.2C; 0.5C discharge: Repeat the above charging process, let stand for 30 minutes, discharge at a constant current of 0.5C to 2.5V, and record the discharge capacity of 0.5C; Perform discharge tests at 1C, 2C, 5C, and 10C rates in sequence, and record the discharge capacity at each rate (1C, 2C, 5C, and 10C respectively) (test once for each rate to ensure data stability). Parallel Testing: Three batteries of the same specifications were selected for parallel testing for each example and comparative example. The average discharge capacity at each rate was used for subsequent calculations. Rate Performance Calculation: The ratio of 10C discharge capacity to 0.2C discharge capacity is expressed as a percentage. The calculation formula is as follows: 10C rate discharge performance (%) = (Average discharge capacity at 10C / Average discharge capacity at 0.2C) × 100%.

[0093] The battery test performance of the embodiments and comparative examples of this application is detailed in Table 1.

[0094] Table 1 Battery test performance of embodiments and comparative examples of this application

[0095] As demonstrated in Examples 1 and 2, 4 and 5, and 6 and 7, trifluoromethyl is a polyatomic strong electron-withdrawing group. The induced electron-withdrawing effect of the three F atoms is superimposed, making its electron-withdrawing ability far stronger than that of a single trifluoromethyl group. The fluorine substituent induces electron withdrawal only at a single atom. This strong electron-withdrawing property further lowers the LUMO energy level of the molecule, enabling more efficient initiation of reduction reactions on the negative electrode surface. At the same time, trifluoromethyl provides more fluorine sources, resulting in a denser SEI film with a higher LiF content. The steric hindrance of trifluoromethyl is greater than that of fluorine substituents, which can inhibit the excessive growth of the SEI film. In addition, its strong polarity makes the film layer adhere more tightly to the electrode surface, reducing the risk of SEI film rupture at high temperatures.

[0096] A comparison of Examples 1 and 3 shows that the electron-withdrawing properties of Example 3 are superimposed, resulting in more complete film formation. The electron-withdrawing effect of two F atoms (superimposed inductive effect) is stronger than that of one F atom, leading to a lower LUMO energy level in the molecule and a reduction potential of 1.491V, which is 0.032V lower than that of Example 1. This makes it easier for the SEI film to be preferentially reduced at the negative electrode than the solvent. The SEI film forms earlier and has more comprehensive coverage, and provides more fluorine source to generate LiF. LiF is the core inorganic component of SEI, which can reduce impedance and improve film stability, thus resulting in a slightly better cycle retention rate. At the same time, the uniformity of electron distribution affects the consistency of the film. The two fluorine substituents in Example 3 are set in the meta position, which makes the molecular electron cloud distribution more uniform. The reduction reaction occurs "uniformly at multiple points" on the negative electrode surface, avoiding local films that are too thick or too thin. As can be seen from the comparison between Example 1 and Example 4, and Example 2 and Example 5, the cyano group assists the positive electrode in forming a simple complex layer through electron-withdrawing properties, which initially inhibits electrolyte oxidation and thus improves the cycle performance and high-temperature cycle performance of the battery.

[0097] A comparison of Examples 4 and 5 shows that the cyano group in Example 4 has strong electron-withdrawing properties but low steric hindrance, resulting in a thinner film. In contrast, the trifluoromethyl group in Example 5, in addition to electron withdrawal, provides more fluorine sources, generating a richer LiF layer and a more stable film. Example 5 outperforms Example 4 in high-temperature cycling and rate performance.

[0098] As shown in Examples 6 and 9, the core reaction site of the triazine ring is the N atom connected by the amide bond, which directly participates in the film formation reaction. In Example 6, the trifluoromethyl group of the triazine ring compound is located on the carbon atom adjacent to the amide bond, and its electron-withdrawing effect can be directly transferred to the amide bond, effectively reducing the LUMO energy level and making the reduction reaction easier to occur at the positive and negative electrode interfaces, resulting in more complete film formation. However, in Example 9, the trifluoromethyl group of the triazine ring compound is located far from the amide bond, and the electron-withdrawing effect needs to be indirectly transferred through the triazine ring conjugated system, which weakens the efficiency, leading to an increase in reduction potential, a delayed film formation time, slightly poorer SEI / CEI film coverage, and a decrease in cycle retention rate.

[0099] As can be seen from Examples 7 and 8, compared with carbon-carbon triple bonds, carbon-carbon double bonds form a larger π-conjugated system with triazine rings, resulting in a more stable molecular structure and easier cross-linking with other polymer chains. The resulting CEI film has both density and toughness, which can buffer the volume expansion of the electrode during battery cycling, such as the expansion of lithium intercalation in graphite anodes, and reduce film rupture. In contrast, the conjugation effect of acetylene groups is weaker, and triazine ring compounds are prone to excessive decomposition during film formation. The film formed after the polymerization of acetylene triple bonds is more brittle and prone to cracking during cycling, leading to the consumption of active lithium and thus affecting cycle performance.

[0100] A comparison of Examples 1 and 10 to 16 shows that an appropriate amount of triazine cyclic compound additive can form a uniform, dense, and LiF-rich SEI / CEI film on the electrode surface, improving interfacial stability and lithium-ion conductivity. Secondly, the triazine cyclic compound molecules need to reach a sufficient concentration in the electrolyte to preferentially decompose before the solvent (e.g., EC, DMC) or lithium salt, forming a continuous and dense SEI / CEI film on the electrode surface. Furthermore, the number of active sites on the electrode surface (e.g., edge defects in the graphite anode and transition metal ion exposure sites in the cathode) is fixed; only when the additive molecule concentration matches the number of active sites can "preferential reaction of additive molecules at each active site" be achieved, forming a film layer. When the amount of triazine cyclic compound added is below the scope of this application, film formation is insufficient, SEI / CEI coverage is incomplete, and capacity retention and rate performance significantly decrease. When the amount of triazine cyclic compound added is above the scope of this application, excessive additive may lead to an overly thick film, increased impedance, or even participation in side reactions, resulting in decreased performance.

[0101] like Figure 1 As shown, a comparison between Example 1 and Comparative Example 1 reveals that the triazine cyclic compound in Example 1, due to its higher reduction potential, preferentially reduces to form a film on the negative electrode surface. The resulting SEI film is richer in LiF and has a denser structure, effectively inhibiting the continuous decomposition of the electrolyte and the growth of lithium dendrites, reducing interfacial resistance, and thus improving battery performance. A comparison between Example 1 and Comparative Examples 2 to 5 shows that Comparative Examples 2 to 5 use asymmetric triazine cyclic compounds, resulting in uneven nitrogen distribution and poor electronic effects. A comparison between Example 1 and Comparative Example 6 shows that the amide bond is replaced by an ester group, and the additive lacks the Lewis base effect of nitrogen atoms, resulting in poor film stability.

[0102] The electrolyte and secondary battery provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrolyte, characterized in that, This includes triazine cyclic compounds, which include one or more combinations of compounds shown in Formula 1: Formula 1 ， Among them, R1, R2, and R3 each independently satisfy any one of the following conditions: (1) Hydrogen atom; (2) Alkyl groups having 1 to 9 carbon atoms, substituted or unsubstituted; (3) Alkenyl or ynyl groups having 2 to 9 carbon atoms, substituted or unsubstituted; (4) A cyano group having 1 to 9 carbon atoms, substituted or unsubstituted.

2. The electrolyte according to claim 1, characterized in that, Any one of R1, R2, and R3 includes one or more of halogen substituents, haloalkyl groups, haloalkenyl groups, haloalkynyl groups, and halocyanyl groups.

3. The electrolyte according to claim 1 or 2, characterized in that, The compound represented by Formula 1 is any one of the following compounds: 。 4. The electrolyte according to claim 1, characterized in that, R1 and R2 each include one or more of halogen substituents, haloalkyl groups, haloalkenyl groups, haloynyl groups, and halocyano groups.

5. The electrolyte according to claim 1 or 4, characterized in that, The compound represented by Formula 1 is any one of the following compounds: 。 6. The electrolyte according to claim 1, characterized in that, Either R1 or R2 includes at least one unsaturated bond.

7. The electrolyte according to claim 6, characterized in that, The unsaturated bonds include one or more of the following: carbon-carbon double bonds, carbon-carbon triple bonds, and carbon-nitrogen triple bonds.

8. The electrolyte according to any one of claims 1, 6, or 7, characterized in that, The compound represented by Formula 1 is any one of the following compounds: 。 9. The electrolyte according to claim 1, characterized in that, R1 includes at least one unsaturated bond, and R2 includes at least one or more of halogen substituents, haloalkyl groups, haloalken groups, haloalkyn groups, and halocyanin groups. Alternatively, R1 may include at least one or more of a halogen substituent, a haloalkyl group, a haloalkenyl group, a haloalkynyl group, or a halocyano group, and R2 may include at least one unsaturated bond.

10. The electrolyte according to claim 9, characterized in that, The compound represented by Formula 1 is any one of the following compounds: 。 11. The electrolyte according to claim 1, characterized in that, The ratio of the triazine cyclic compound to the total mass of the electrolyte ranges from 0.1 wt% to 2.0 wt%.

12. A secondary battery, characterized in that, The electrolyte includes any one of claims 1 to 11.

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