Electrolyte additive, battery electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive, a battery electrolyte and a lithium ion battery, the electrolyte additive comprises an isocyanate group fluorosilane compound with a chemical structure shown in the following formula (I), R1, R2 and R3 are respectively and independently selected from one of C1-C5 alkyl groups, hydrogen atoms in the C1-C5 alkyl groups are optionally substituted by fluorine atoms, the fluorine atoms in the C1-C5 alkyl groups are optionally substituted by fluorine atoms, the fluorine atoms in the C1-C5 alkyl groups are optionally substituted by fluorine atoms, the fluorine atoms in the C1-C5 alkyl groups are optionally substituted by fluorine atoms, and the fluorine atoms in the C1-C5 alkyl groups are optionally substituted by fluorine atoms. R1, R2 and R3 at least contain one fluorine atom. The electrolyte additive structurally comprises an isocyanate group, a trialkylsilyl group and at least one substituted fluorine atom in the trialkylsilyl group, and under the synergistic effect of the functional groups, the electrolyte additive can effectively improve ecological damage to the electrolyte in the battery circulation process and relieve the manganese dissolution phenomenon. When the electrolyte additive is applied to the lithium ion battery, the high-temperature cycling stability of the lithium ion battery can be effectively improved, and the service life of the lithium iron manganese phosphate battery can be prolonged. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte additive, a battery electrolyte and a lithium ion battery. Background Art

[0002] With the rapid development of new energy technologies, lithium-ion batteries, as core energy storage devices, are playing an irreplaceable role in electric vehicles, wearable devices, energy storage systems, and other fields. Among them, lithium iron manganese phosphate (LiMnFePO4), a cathode material with the same olivine-type structure as lithium iron phosphate, has attracted widespread attention due to its high discharge voltage. This property makes LiMnFePO4 promising to significantly improve the energy density of batteries while maintaining the advantages of lithium iron phosphate batteries.

[0003] Despite its numerous advantages, lithium manganese iron phosphate (LMP) faces a significant challenge in practical applications: poor cycling performance. This is because the trace amounts of water that inevitably remain in the electrolyte trigger the decomposition of lithium salts, generating highly corrosive hydrofluoric acid (HF). HF not only accelerates the dissolution of manganese ions in the cathode material, destroying the cathode structure, blocking lithium ion diffusion pathways and increasing battery polarization, but also promotes the migration of manganese ions to the anode surface during charging, catalyzing the further decomposition of solvent molecules and lithium salts in the electrolyte. This process destabilizes the solid electrolyte interface (SEI) film on the anode surface, causing it to continuously thicken, consume more active lithium, and ultimately lead to rapid battery capacity degradation. This phenomenon is particularly pronounced under high temperature conditions, severely restricting the long-term operation and cycling performance of LMP batteries.

[0004] The existing method for solving the above-mentioned problems mainly involves adding electrolyte additives to the battery electrolyte to achieve the purpose of alleviating the above-mentioned adverse effects. However, the electrolyte additives in the existing technology are not very effective in improving the cycle stability of lithium iron manganese phosphate batteries and are also easily restricted by high temperature conditions. Therefore, the development of new electrolyte additives for lithium iron manganese phosphate lithium-ion batteries is of great significance for improving the cycle stability of lithium iron manganese phosphate batteries, especially for improving the cycle performance of lithium iron manganese phosphate lithium-ion batteries in high temperature environments. To this end, the present invention is specially proposed. Summary of the Invention

[0005] The main purpose of the present invention is to provide an electrolyte additive, a battery electrolyte and a lithium-ion battery to solve the problem that the electrolyte additives in the prior art have a poor effect on improving the cycle stability of lithium iron manganese phosphate batteries, and the improvement of the cycle performance of lithium iron manganese phosphate batteries by electrolyte additives in the prior art is limited by high temperature conditions. The purpose is to improve the cycle stability performance of lithium iron manganese phosphate lithium-ion batteries and extend the service life of lithium iron manganese phosphate lithium-ion batteries.

[0006] The electrolyte additive provided by the present invention includes an isocyanate fluorosilane compound having a chemical structure shown in the following formula (I):

[0007] Wherein, R1, R2, and R3 are each independently selected from a C1-C5 alkyl group, the hydrogen atoms in the C1-C5 alkyl group are optionally substituted with fluorine atoms, and at least one fluorine atom is contained in R1, R2, and R3. The isocyanate-based fluorosilane compound provided herein is used as an electrolyte additive in lithium-ion batteries. It can effectively improve the cycling stability of lithium-ion batteries even under high temperature conditions, allowing the batteries to maintain a high capacity retention rate after a long cycle.

[0008] Furthermore, R1, R2, and R3 are each independently selected from a C1-C3 alkyl group, wherein the hydrogen atoms in the C1-C3 alkyl group are optionally substituted with fluorine atoms, and at least one fluorine atom is contained in R1, R2, and R3. Preferably, R1, R2, and R3 are each independently selected from a methyl group, a monofluoromethyl group, a difluoromethyl group, or a trifluoromethyl group, and at least one of R1, R2, and R3 is a monofluoromethyl group, a difluoromethyl group, or a trifluoromethyl group. Limiting the substituents of R1, R2, and R3 in the isocyanate fluorosilane compound to the above range can further improve the cycling stability of the lithium-ion battery.

[0009] Furthermore, the isocyanate fluorosilane compound is selected from one or more of the following compounds S1 to S3:

[0010]

[0011] Furthermore, the electrolyte additive also includes 1,3-propane sultone or vinyl sulfite; preferably, the electrolyte additive includes an isocyanate fluorosilane compound and 1,3-propane sultone, and the weight ratio of the two is (0.1 to 3):1; or, the electrolyte additive includes an isocyanate fluorosilane compound and vinyl sulfite, and the weight ratio of the two is (0.2 to 5):1; more preferably, the electrolyte additive includes an isocyanate fluorosilane compound and 1,3-propane sultone, and the weight ratio of the two is (0.5 to 2):1; or, the electrolyte additive includes an isocyanate fluorosilane compound and vinyl sulfite, and the weight ratio of the two is (0.5 to 3):1. The isocyanate-based fluorosilane electrolyte additive of the present invention is combined with 1,3-propane sultone or vinyl sulfite. Under the synergistic effect of the two types of electrolyte additives, it is beneficial to better inhibit the dissolution of manganese ions during the cycle of the lithium-ion battery, reduce the decomposition of the electrolyte, and improve the high-temperature cycle stability of the battery.

[0012] According to a second aspect of the present invention, a battery electrolyte is also provided, comprising a lithium salt, an organic solvent, and the aforementioned electrolyte additive. The isocyanate-based fluorosilane compound provided herein is used as an electrolyte additive in the battery electrolyte to effectively improve the cycling stability of a lithium-ion battery, enabling the battery to maintain a high capacity retention rate after prolonged cycling, thereby further improving the high-temperature cycling stability of the lithium-ion battery.

[0013] Furthermore, the weight content of the electrolyte additive in the battery electrolyte is 1-8%; preferably, the weight content of the electrolyte additive in the battery electrolyte is 1-4%; preferably, the concentration of the lithium salt in the battery electrolyte is 0.1-3.0 mol / L.

[0014] Furthermore, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; preferably, the organic solvent is one or more of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate.

[0015] Furthermore, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluoroantimonate, lithium bis(fluorooxalatoborate) and lithium hexafluoroarsenate.

[0016] According to a third aspect of the present invention, a lithium-ion battery is further provided, the lithium-ion battery further comprising: a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a battery separator; preferably, the positive electrode active material is a lithium iron manganese phosphate material; preferably, the negative electrode active material is one or more of a natural graphite material, an artificial graphite material, a silicon material, a silicon-oxygen material, and a silicon-carbon and carbon composite material; preferably, the battery separator is at least one of a polypropylene separator, a polyethylene separator, and a polyethylene-polypropylene separator. The electrolyte additive provided by the present invention is used in a lithium iron manganese phosphate battery to effectively alleviate manganese dissolution, improve the battery's interfacial resistance and other properties, and thus further improve the battery's high-temperature cycle stability.

[0017] The present invention provides an electrolyte additive, which is an isocyanate-based fluorosilane compound, which includes an isocyanate group, a trialkylsilyl group, and at least one fluorine atom substituted in the trialkylsilyl group. Under the synergistic effect of the above-mentioned functional groups, the resulting electrolyte additive can effectively improve the ecological damage to the electrolyte during the battery cycle and can effectively alleviate the manganese dissolution phenomenon. The isocyanate-based fluorosilane compound provided by the present application is applied as an electrolyte additive to a lithium-ion battery. Even under high temperature conditions, it can effectively improve the cycle stability of the lithium-ion battery, so that the battery can still maintain a high capacity retention rate after a long cycle, which is significant for extending the service life of the lithium iron manganese phosphate battery. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0019] As described in the background technology section, lithium iron manganese phosphate (LiMnFePO4) has attracted widespread attention due to its advantages in many aspects, including its high discharge voltage and battery energy density. However, in practical applications, the poor cycling performance of LiMnFePO4 batteries has limited their further development. The existing method for solving the electrolyte problem mainly involves adding electrolyte additives to the electrolyte to achieve the purpose of alleviating the above-mentioned effects. However, the additives in the existing technology have a poor effect on improving the cycling stability of LiMnFePO4 batteries and are also limited by high temperature conditions.

[0020] In order to solve the above problems, the present invention provides an electrolyte additive, which includes an isocyanate fluorosilane compound having a chemical structure shown in the following formula (I):

[0021]

[0022] Wherein, R1, R2 and R3 are each independently selected from one of C1 to C5 alkyl groups, the hydrogen atoms in the C1 to C5 alkyl groups are optionally replaced by fluorine atoms, and R1, R2 and R3 contain at least one fluorine atom.

[0023] The electrolyte additive provided by the present invention is an isocyanate-based fluorosilane small molecule compound, which carries an isocyanate group and a trialkylsilyl group substituted with at least one fluorine atom. Under the synergistic effect of the above-mentioned functional groups, the obtained electrolyte additive can effectively improve the ecological damage to the battery electrolyte during the battery cycle. The isocyanate-based fluorosilane compound provided by the present application is applied as an electrolyte additive to lithium-ion batteries, which can effectively improve the cycle stability of lithium-ion batteries, so that the battery can still maintain a high capacity retention rate after a long cycle at a higher temperature. Analysis of the reasons for the above-mentioned beneficial effects mainly includes:

[0024] First, the electrolyte additive with this specific chemical structure improves the ion transport efficiency in the battery electrolyte: The electrolyte additive provided by the present invention has a small molecule structure with high polarity, which not only gives it a low viscosity but also improves wettability with other components in the battery electrolyte (such as lithium salts and organic solvents). These properties can further enhance the ionic conductivity of the battery electrolyte and improve the transport efficiency of lithium ions in the electrolyte, thereby further improving the cycling performance of lithium-ion batteries.

[0025] Secondly, the use of the above-mentioned electrolyte additives inhibits the dissolution of manganese ions in the battery electrolyte: trace amounts of water will inevitably remain in the battery electrolyte, and the presence of trace water will induce the decomposition of lithium salts to generate hydrofluoric acid, which will further lead to the dissolution of manganese ions in the lithium iron manganese phosphate positive electrode material. On the one hand, it will destroy the positive electrode structure, hindering the diffusion of lithium ions, increasing battery polarization, and reducing the battery's capacity and efficiency; on the other hand, during the charging process, manganese ions migrate back to the negative electrode surface, catalyzing the decomposition of solvent molecules and lithium salts in the electrolyte, destroying the stability of the formed SEI, resulting in the consumption of more active lithium in the SEI repair process, thereby causing rapid decay of battery capacity and reducing its cycle performance. The isocyanate and fluorosilane groups in the isocyanate-based fluorosilane electrolyte additive provided by the present invention react with water and HF in the electrolyte, consume the trace water and HF remaining in the battery electrolyte, alleviate the dissolution of manganese ions, and thus improve the resulting damage to the lithium ion transport performance and the damage to the SEI stability, thereby better improving the cycle performance of the lithium ion battery.

[0026] Third, the use of the above-mentioned electrolyte additive reduces the interfacial resistance in the electrolyte: the presence of fluorine atoms in the fluorosilane in the electrolyte additive provided by the present invention will participate in the formation of the SEI film on the surface of the negative electrode, generating an SEI film containing lithium fluoride (LiF). Lithium fluoride is an excellent electronic insulator that can effectively prevent the excessive reaction of lithium ions and reduce the occurrence of side reactions. The formation of lithium fluoride in the SEI film improves the electronic insulation and mechanical stability of the film, reduces the excessive deposition of lithium ions at the interface and the loss of active lithium, while maintaining good ionic conductivity and reducing interfacial impedance, so that the lithium-ion battery still has good cycle efficiency and stability even under high temperature conditions.

[0027] In summary, under the synergistic effect of the isocyanate group, trialkylsilyl group, and at least one fluorine atom substituted in the trialkylsilyl group in the isocyanate-based fluorosilane electrolyte additive provided by the present invention, the electrolyte additive can effectively improve the ecological damage to the battery electrolyte during the battery cycle. The isocyanate-based fluorosilane compound provided by the present application is applied as an electrolyte additive to lithium-ion batteries. Even under high temperature conditions, it can effectively improve the cycle stability of lithium-ion batteries, allowing the battery to maintain a high capacity retention rate after a long cycle at a higher temperature, thereby effectively improving the cycle stability of the battery.

[0028] In a preferred embodiment, R1, R2 and R3 are each independently selected from one of C1 to C3 alkyl groups, the hydrogen atoms in the C1 to C3 alkyl groups are optionally replaced by fluorine atoms, and R1, R2 and R3 contain at least one fluorine atom. By limiting the substituents R1, R2 and R3 in the isocyanate fluorosilane compound having the chemical structure shown in formula (I) to the above range, the electrolyte additive can have a better wetting effect with the lithium salt and organic solvent in the electrolyte, which is conducive to further improving the role of the electrolyte additive in the battery electrolyte, thereby further improving the cycle stability of the lithium ion battery. Preferably, R1, R2 and R3 are each independently selected from methyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one of R1, R2 and R3 is monofluoromethyl, difluoromethyl or trifluoromethyl. Selecting the above specific types of substituents as the substituents R1, R2 and R3 in the isocyanate fluorosilane compound can better exert the above effects.

[0029] By way of example but not limitation, the isocyanate fluorosilane compound is selected from one or more of the following compounds S1 to S3:

[0030]

[0031] Compound S1, compound S2 and compound S3 are used as electrolyte additives in battery electrolytes. Under the action of the above-mentioned functional groups and the synergistic effect of the above-mentioned functional groups, the obtained electrolyte additives can effectively improve the cycle stability of lithium-ion batteries, so that the battery can still maintain a high capacity retention rate after a long cycle.

[0032] In a preferred embodiment, the electrolyte additive also includes 1,3-propane sultone or vinyl sulfite. 1,3-Propane sultone is a type of film-forming electrolyte additive containing a sulfonic acid group, which can synergize with the isocyanate-based fluorosilane electrolyte additive described in the present invention to better alleviate the decomposition of the electrolyte in the battery and inhibit the generation of decomposition gas in the electrolyte, which is beneficial to improving the battery's cycle performance at high temperatures and improving the battery's comprehensive electrochemical performance. Vinyl sulfite is a type of film-forming electrolyte additive containing a sulfite group, which can work together with the isocyanate-based fluorosilane electrolyte additive described in the present invention to form a more stable SEI film at the negative electrode of the battery, further improving the battery's cycle performance. In summary, the compounding of the isocyanate-based fluorosilane electrolyte additive and 1,3-propane sultone or vinyl sulfite in the present invention, under the synergistic effect of the two types of electrolyte additives, is conducive to better inhibiting the dissolution of manganese ions during the cycle of lithium-ion batteries, reducing the decomposition of the electrolyte, and forming a more stable SEI film during the battery cycle, thereby improving the high-temperature cycle stability of the battery.

[0033] Preferably, the electrolyte additive includes an isocyanate fluorosilane compound and 1,3-propane sultone, and the weight ratio of the two is (0.1-3):1, specifically 0.1:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.8:1, 3:1, or any weight ratio between any two of the above; or, the electrolyte additive includes an isocyanate fluorosilane compound and vinyl sulfite, and the weight ratio of the two is (0.2-5):1, specifically 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any weight ratio between any two of the above. After a large number of experiments, the inventors creatively discovered that controlling the addition ratio of the isocyanate fluorosilane provided by the present invention and 1,3-propane sultone or vinyl sulfite when compounded and used within the above range, under the further synergistic effect of the two electrolyte additives, it is beneficial to better improve the cycle stability of the lithium-ion battery. More preferably, the electrolyte additive includes an isocyanate fluorosilane compound and 1,3-propane sultone, and the weight ratio of the two is (0.5-2):1; or, the electrolyte additive includes an isocyanate fluorosilane compound and vinyl sulfite, and the weight ratio of the two is (0.5-3):1. Controlling the addition ratio of the isocyanate fluorosilane provided by the present invention and 1,3-propane sultone or vinyl sulfite when compounded and used within the above preferred range, the above effect is better, which is beneficial to further improve the electrochemical performance of the battery.

[0034] According to a second aspect of the present invention, a battery electrolyte is also provided, comprising a lithium salt, an organic solvent, and the aforementioned electrolyte additive. The isocyanate-based fluorosilane compound provided herein is used as an electrolyte additive in the battery electrolyte to effectively improve the cycling stability of a lithium-ion battery, enabling the battery to maintain a high capacity retention rate after prolonged cycling, thereby further improving the high-temperature cycling stability of the lithium-ion battery.

[0035] In a preferred embodiment, the weight content of the electrolyte additive in the battery electrolyte is 1-8%; preferably, the concentration of the lithium salt in the battery electrolyte is 0.1-3.0 mol / L. Controlling the addition ratio of the electrolyte additive in the battery electrolyte and the concentration of the lithium salt in the battery electrolyte within the above ranges can give full play to the electrolyte additive's improvement effects on the ion transmission efficiency in the battery electrolyte, inhibiting the dissolution of manganese ions in the electrolyte, and reducing the interfacial resistance in the electrolyte, so that the battery electrolyte has good electron transmission performance, conductivity and cycle stability. Preferably, the weight content of the electrolyte additive in the battery electrolyte is 1-4%. Controlling the addition ratio of the electrolyte additive in the battery electrolyte within the above preferred range will result in a better effect of the battery electrolyte and can further improve the cycle stability of the lithium-ion battery.

[0036] In a preferred embodiment, the organic solvent includes but is not limited to one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; preferably, the organic solvent includes but is not limited to one or more of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate; preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluoroantimonate, lithium bis(fluorooxalato)borate and lithium hexafluoroarsenate. Combining the above-mentioned specific organic solvents and lithium salts can further improve the cycle stability of lithium-ion batteries. More preferably, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate are used in combination, and further preferably, the mass fraction of ethylene carbonate is controlled to be 20-30%, the mass fraction of ethyl methyl carbonate carbon is 50-70%, and the mass fraction of diethyl carbonate is 0-20%. Adjusting the ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate to the above-mentioned range can further improve the mutual solubility of the organic solvent with the lithium salt and the electrolyte additive in the battery electrolyte, which is beneficial to further improve the stability of the battery electrolyte and the ion transmission efficiency.

[0037] According to a third aspect of the present invention, a lithium-ion battery is provided, comprising the aforementioned battery electrolyte. The electrolyte in the lithium-ion battery utilizes the aforementioned isocyanate-based fluorosilane compound as an electrolyte additive, resulting in improved cycling stability and the ability to maintain a high capacity after prolonged cycling.

[0038] In a preferred embodiment, the lithium-ion battery further comprises: a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a battery separator; preferably, the positive electrode active material is a lithium iron manganese phosphate material; preferably, the negative electrode active material is one or more of a natural graphite material, an artificial graphite material, a silicon material, a silicon-oxygen material, and a silicon-carbon and carbon composite material; preferably, the battery separator is at least one of a polypropylene separator, a polyethylene separator, and a polyethylene-polypropylene separator. The electrolyte additive provided by the present invention is used in a lithium iron manganese phosphate battery to effectively alleviate manganese dissolution, improve the battery's interfacial resistance and other properties, and thus further improve the high-temperature cycling stability of the battery electrolyte.

[0039] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0040] It should be further explained here that the isocyanate fluorosilane compounds S1, S2 and S3 used in the examples have the following structures:

[0041]

[0042] Example 1

[0043] The preparation of lithium-ion batteries includes the following steps:

[0044] (1) Preparation of battery electrolyte

[0045] In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed in a weight ratio of 3:5:2. Dry lithium hexafluorophosphate, an electrolyte additive comprising an isocyanate-based fluorosilane component having the structure of compound S1, and a 1,3-propane sultone electrolyte additive were quickly added. After thorough mixing, the electrolyte was tested for moisture and free acid levels to yield a battery electrolyte. The electrolyte contained 1.5% by weight of the electrolyte additive, a 1:2 weight ratio of compound S1 to 1,3-propane sultone, a lithium hexafluorophosphate concentration of 1.0 mol / L, and both moisture and free acid levels were less than 100 ppm.

[0046] (2) Preparation of positive and negative electrode sheets

[0047] Preparation of positive electrode: Lithium manganese iron phosphate (LiMn 0.6 Fe 0.4PO4), a conductive agent (PVDF) and conductive carbon black are mixed in a weight ratio of 96.5:1.5:2, and then N-methylpyrrolidone is added and mixed evenly in a vacuum mixer to form a positive electrode slurry with a solid content of 57%; the positive electrode slurry is evenly coated on both sides of the aluminum foil, and after drying, it is rolled and cut to obtain positive electrode sheets.

[0048] Preparation of negative electrode sheets: Graphite, conductive carbon black, binder (CMC), and dispersant (SBR) are mixed in a weight ratio of 96.5:0.5:1.2:1.8, and then deionized water is added and mixed evenly in a vacuum mixer to form a negative electrode slurry with a solid content of 55%; the negative electrode slurry is evenly coated on both sides of the copper foil, dried, rolled, and cut to obtain negative electrode sheets.

[0049] (3) Preparation of lithium-ion batteries

[0050] The positive electrode sheet, battery separator (model: 92211) and the negative electrode sheet obtained above are sequentially subjected to lamination, hot pressing and shaping, tab welding, aluminum-plastic film packaging, battery cell baking, liquid injection and chemical composition to obtain a lithium-ion battery.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is that the electrolyte additives in the battery electrolyte are compound S1 and vinyl sulfite, and the weight ratio of compound S1 to vinyl sulfite is 5:1.

[0053] Example 3

[0054] The difference between Example 3 and Example 1 is that the electrolyte additives in the battery electrolyte are compound S1 and vinyl sulfite, and the weight ratio of compound S1 to vinyl sulfite is 0.2:1.

[0055] Example 4

[0056] The difference between Example 4 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 8%, and the weight ratio of compound S1 to 1,3-propane sultone is 0.1:1.

[0057] Example 5

[0058] The difference between Example 5 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 4%, and the weight ratio of compound S1 to 1,3-propane sultone is 3:1.

[0059] Example 6

[0060] The difference between Example 6 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 2%, and the weight ratio of compound S1 to 1,3-propane sultone is 1:1.

[0061] Example 7

[0062] The difference between Example 7 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 3%, and the weight ratio of compound S1 to 1,3-propane sultone is 2:1.

[0063] Example 8

[0064] The difference between Example 8 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 1.1%, and the weight ratio of compound S1 to 1,3-propane sultone is 0.1:1.

[0065] Example 9

[0066] The difference between Example 9 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 1.5%, and the electrolyte additive is compound S2 and 1,3-propane sultone, and the weight ratio of the two is 1:2.

[0067] Example 10

[0068] The difference between Example 10 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 1.5%, and the electrolyte additive is compound S3 and 1,3-propane sultone, and the weight ratio of the two is 1:2.

[0069] Example 11

[0070] The difference between Example 11 and Example 1 is that in the battery electrolyte, the electrolyte additive has a weight content of 3%, and the electrolyte additive is compound S1.

[0071] Example 12

[0072] The difference between Example 12 and Example 1 is that the weight content of the electrolyte additive in the battery electrolyte is 9%, and the concentration of the lithium salt in the battery electrolyte is 1 mol / L.

[0073] Comparative Example 1

[0074] The difference between Comparative Example 1 and Example 1 is that, when preparing the battery electrolyte, the electrolyte additive used is 1,3-propane sultone, and the isocyanate fluorosilane component having the structure of Compound S1 is not added.

[0075] Comparative Example 2

[0076] The difference between Comparative Example 2 and Example 1 is that, when preparing the battery electrolyte, trimethylsilyl isocyanate is used instead of the isocyanate fluorosilane component having the structure of Compound S1.

[0077] Comparative Example 3

[0078] The difference between Comparative Example 3 and Example 1 is that vinylene carbonate is used as the electrolyte additive when preparing the battery electrolyte.

[0079] Comparative Example 4

[0080] The difference between Comparative Example 4 and Example 1 is that no electrolyte additives are added when preparing the battery electrolyte.

[0081] The lithium-ion batteries prepared in the above examples and comparative examples were tested for manganese dissolution and capacity retention, and the results are shown in Table 1. The specific test methods are:

[0082] (1) Manganese dissolution from the negative electrode: The effectiveness of the electrolyte in inhibiting manganese dissolution was tested by inductively coupled plasma (ICP) to detect the manganese ion content in the negative electrode. After cycling, the Example and Comparative groups of batteries were disassembled after full discharge, and the manganese ion content in the negative electrode was measured. The resulting data is the manganese dissolution from the negative electrode of the battery.

[0083] (2) High-temperature cycle capacity retention rate: At 45°C, first charge the battery to 4.25V at a constant current of 1C, then charge the battery to a current of less than 0.05C at a constant voltage of 4.25V. After standing for 10 minutes, discharge the battery to 2.5V at a constant current of 1C. The discharge capacity of the battery at this time is measured, which is the discharge capacity of the first cycle. The battery is cycled according to the above conditions, and the capacity retention rate of the battery after 300 cycles is calculated. The capacity retention rate after cycling is calculated according to the following formula: Capacity retention rate (%) = (discharge capacity after 300 cycles / discharge capacity of the first cycle) × 100%.

[0084] Table 1

[0085]

[0086]

[0087] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0088] As shown in the table, the use of the isocyanate-based fluorosilane electrolyte additive proposed in the present invention in lithium-ion batteries in Examples 1 to 12 effectively mitigates manganese dissolution in the batteries, significantly improving the cycling stability of lithium-ion batteries under high-temperature conditions and extending the battery life. In particular, controlling parameters such as the ratio of the electrolyte additive in the electrolyte within a preferred range significantly improves the electrochemical performance of the lithium-ion battery. For example, in Examples 6, 7, and 9, the capacity retention rate of the lithium-ion batteries after 300 cycles was above 87%, demonstrating excellent high-temperature cycling stability.

[0089] In Comparative Examples 1 to 3, conventional electrolyte additives were used in lithium-ion batteries, but the improvement in manganese dissolution and battery cycling stability was significantly lower than that achieved in the examples of the present application. In Comparative Example 4, no electrolyte additives were used, and the lithium-ion battery experienced severe manganese dissolution and poor cycling stability, with a capacity retention rate of only 79.85% after 300 cycles.

[0090] In summary, under the synergistic effect of the isocyanate group, trialkylsilyl group, and at least one fluorine atom substituted in the trialkylsilyl group in the isocyanate-based fluorosilane electrolyte additive provided by the present invention, the resulting electrolyte additive can effectively improve the ecological damage to the battery electrolyte during battery cycling. The isocyanate-based fluorosilane compound provided by this application is used as an electrolyte additive in lithium-ion batteries. Even under high temperature conditions, it can effectively improve the cycle stability of lithium-ion batteries, allowing the battery to maintain a high capacity retention rate after a long cycle.

[0091] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An electrolyte additive, characterized in that The electrolyte additive includes an isocyanate-based fluorosilane compound having a chemical structure shown in the following formula (I): Wherein, R1, R2 and R3 are each independently selected from one of C1 to C5 alkyl groups, the hydrogen atoms in the C1 to C5 alkyl groups are optionally substituted by fluorine atoms, and at least one of R1, R2 and R3 contains one fluorine atom.

2. The electrolyte additive according to claim 1, characterized in that R1, R2 and R3 are each independently selected from one of C1 to C3 alkyl groups, the hydrogen atoms in the C1 to C3 alkyl groups are optionally substituted by fluorine atoms, and at least one of R1, R2 and R3 contains a fluorine atom; Preferably, the R1, the R2 and the R3 are each independently selected from methyl, monofluoromethyl, difluoromethyl or trifluoromethyl, and at least one of the R1, the R2 and the R3 is the monofluoromethyl, the difluoromethyl or the trifluoromethyl.

3. The electrolyte additive according to claim 2, characterized in that The isocyanate fluorosilane compound is selected from one or more of the following compounds S1 to S3:

4. The electrolyte additive according to any one of claims 1 to 3, characterized in that The electrolyte additive further includes 1,3-propane sultone or vinyl sulfite; Preferably, the electrolyte additive includes the isocyanate fluorosilane compound and the 1,3-propane sultone, and the weight ratio of the two is (0.1-3):1; or, the electrolyte additive includes the isocyanate fluorosilane compound and the vinyl sulfite, and the weight ratio of the two is (0.2-5):1; More preferably, the electrolyte additive includes the isocyanate fluorosilane compound and the 1,3-propane sultone, and the weight ratio of the two is (0.5-2):1; or, the electrolyte additive includes the isocyanate fluorosilane compound and the vinyl sulfite, and the weight ratio of the two is (0.5-3):

1.

5. A battery electrolyte, characterized in that: The battery electrolyte comprises a lithium salt, an organic solvent and the electrolyte additive according to any one of claims 1 to 4.

6. The battery electrolyte according to claim 5, characterized in that The weight content of the electrolyte additive in the battery electrolyte is 1 to 8%; Preferably, the weight content of the electrolyte additive in the battery electrolyte is 1 to 4%; Preferably, the concentration of the lithium salt in the battery electrolyte is 0.1 to 3.0 mol / L.

7. The battery electrolyte according to claim 5 or 6, characterized in that The organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; preferably, the organic solvent is one or more of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate.

8. The battery electrolyte according to claim 5 or 6, characterized in that The lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluoroantimonate, lithium bis(fluorooxalatoborate) and lithium hexafluoroarsenate.

9. A lithium-ion battery, characterized in that: The lithium-ion battery comprises the battery electrolyte according to any one of claims 5 to 8.

10. The lithium-ion battery according to claim 9, characterized in that The lithium-ion battery further comprises: a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material and a battery separator; Preferably, the positive electrode active material is lithium manganese iron phosphate material; Preferably, the negative electrode active material is one or more of natural graphite material, artificial graphite material, silicon material, silicon-oxygen material, and silicon-carbon and carbon composite materials; Preferably, the battery separator is at least one of a polypropylene separator, a polyethylene separator and a polyethylene-polypropylene separator.

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