Electrolyte composition for lithium titanate battery, preparation method thereof and lithium titanate battery

Abstract

The present invention provides an electrolyte composition for lithium titanate batteries, a preparation method thereof and a lithium titanate battery. By weight, the electrolyte composition for lithium titanate batteries includes 70 to 90 parts of an organic solvent, 10 to 20 parts of a lithium salt, 0.1 to 5 parts of a film-forming additive and 0.1 to 5 parts of an organosilicon additive; the organosilicon additive is selected from one or more of 3-isocyanatepropyltriethoxysilane, polydimethylsiloxane and 3-trimethylsilyl-2-oxazolidinone; the film-forming additive includes an organic matter containing a sulfonic acid group and a fluorine-containing salt, and the fluorine-containing salt is selected from one or more of lithium difluorophosphate, lithium difluorooxalate borate and lithium tetrafluorooxalate phosphate. The obtained high-temperature resistant lithium titanate battery electrolyte can participate in the positive and negative electrode film formation, inhibit the dissolution of transition metals, resist the erosion of HF, reduce the interface impedance, inhibit the battery gas production and avoid high-temperature flatulence, and ensure the excellent high-temperature storage and high-temperature cycle performance of lithium titanate batteries.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to an electrolyte composition for a lithium titanate battery, a preparation method thereof, and a lithium titanate battery. Background Art

[0002] Lithium-ion batteries have been widely used in electric vehicles, communications and energy storage due to their high energy density and long cycle life. As the market and users' demands for electric vehicle range and safety increase, the energy density of single cells is getting higher and higher. High-nickel cathode materials have the advantages of high specific capacity and high energy density, making them the preferred materials for high energy density batteries. However, lithium-ion batteries using high-nickel ternary materials as cathode materials still have problems such as poor structural stability, poor cycle performance, poor rate performance and poor thermal stability.

[0003] At the same time, lithium-ion batteries using lithium titanate as the negative electrode material face the problem of flatulence during commercialization, which will cause bubbles to form between the positive and negative electrodes inside the battery, making it difficult for Li+ to migrate, and ultimately leading to problems such as reduced capacity, increased internal resistance, and reduced life. Regarding the flatulence mechanism of lithium titanate, the industry believes that water decomposition and Ti on the surface of lithium titanate materials 3+ The main cause of flatulence in lithium titanate batteries is the production of gas by catalytic decomposition of electrolyte. Therefore, controlling the moisture content in the battery preparation process and adding film-forming additives to the electrolyte to promote the formation of a dense SEI film on the surface of the lithium titanate material are the two main measures to solve the problem of battery flatulence.

[0004] Based on this, how to provide an electrolyte for lithium titanate batteries that can improve the stability of the lithium titanate battery system, inhibit its gas production and high-temperature swelling, and thus ensure its high-temperature storage and high-temperature cyclability, starting from the direction of forming a dense SEI film, is one of the important technical problems that need to be solved in this field. Summary of the invention

[0005] The main purpose of the present invention is to provide an electrolyte composition for lithium titanate batteries, a preparation method thereof and a lithium titanate battery, so as to solve the problem that the electrolyte for lithium titanate batteries in the prior art is difficult to ensure that the corresponding lithium titanate batteries have high-temperature storage and high-temperature cyclability.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides an electrolyte composition for a lithium titanate battery, which comprises, by weight: 70 to 90 parts of an organic solvent, 10 to 20 parts of a lithium salt, 0.1 to 5 parts of a film-forming additive and 0.1 to 5 parts of an organosilicon additive; the organosilicon additive is selected from one or more of 3-isocyanatepropyltriethoxysilane, polydimethylsiloxane and 3-trimethylsilyl-2-oxazolidinone; the film-forming additive comprises an organic matter containing a sulfonic acid group and a fluorine-containing salt, and the fluorine-containing salt is selected from one or more of lithium difluorophosphate, lithium difluorooxalatoborate and lithium tetrafluorooxalatophosphate.

[0007] Furthermore, the weight ratio of the organosilicon additive to the film-forming additive is 1:(1.8-2.0).

[0008] Furthermore, the organosilicon additive includes 3-isocyanatepropyltriethoxysilane and 3-trimethylsilyl-2-oxazolidinone, and the weight ratio of 3-isocyanatepropyltriethoxysilane to 3-trimethylsilyl-2-oxazolidinone is 1:(1.4-1.6).

[0009] Furthermore, in the film-forming additive, the weight ratio of the organic matter containing sulfonic acid groups to the fluorine-containing salt is 1:(0.8-1); preferably, the organic matter containing sulfonic acid groups is 1,3-propanesultone.

[0010] Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium trifluoromethylsulfonate, lithium methanesulfonate and lithium bis(oxalatoborate), preferably lithium hexafluorophosphate; and / or the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, butylene carbonate, methyl acetate, ethyl acetate, propyl acetate and propyl propionate, preferably the group consisting of dimethyl carbonate, ethyl methyl carbonate and ethylene carbonate, and the weight ratio of dimethyl carbonate, ethyl methyl carbonate and ethylene carbonate is (2-2.5):(2-2.5):1.

[0011] Further, the electrolyte composition for lithium titanate battery includes, by weight, 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 0.5 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone; or, the electrolyte composition for lithium titanate battery includes 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone. parts of lithium difluorooxalatoborate, 0.25 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone; or, by weight, the electrolyte composition for lithium titanate battery includes 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 1.0 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone.

[0012] The second aspect of the present invention provides a method for preparing the above-mentioned electrolyte composition for lithium titanate batteries, comprising: adding a film-forming additive and an organosilicon additive to an organic solvent, and obtaining a first solution after a first mixing; adding a lithium salt to the first solution, and obtaining the electrolyte composition for lithium titanate batteries after a second mixing.

[0013] Furthermore, both the first mixing and the second mixing are carried out under the protection of an inert gas, and the time of the first mixing and the second mixing is independently 1 hour to 5 hours; preferably, the inert gas is N2 and / or Ar.

[0014] The third aspect of the present invention provides a lithium titanate battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte is the above-mentioned electrolyte composition for lithium titanate batteries.

[0015] Furthermore, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is LiNi x Co y Mn z O2, x+y+z=1, 0.33≤x≤0.95, y>0, z>0; the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector, the negative electrode active material layer includes a negative electrode active substance, and the negative electrode active substance is lithium titanate; the separator is a polyolefin separator, and the polyolefin separator is a polyethylene film or a polypropylene film.

[0016] By applying the technical solution of the present invention, a high-temperature resistant electrolyte for lithium titanate batteries is designed, which can participate in the film formation of positive and negative electrodes, inhibit the dissolution of transition metals, resist the corrosion of HF, reduce the interface impedance, improve the stability of the battery system, inhibit the gas production of the battery and avoid high-temperature flatulence, thereby ensuring the excellent high-temperature storage and high-temperature cycle performance of lithium titanate batteries. DETAILED DESCRIPTION

[0017] 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 in conjunction with the embodiments.

[0018] As described in the background technology, the electrolyte for lithium titanate batteries in the prior art has the problem that it is difficult to ensure that the corresponding lithium titanate batteries have high temperature storage and high temperature cycling properties. In order to solve the above technical problems, the first aspect of the present invention provides an electrolyte composition for lithium titanate batteries, which comprises, by weight, 70 to 90 parts of an organic solvent, 10 to 20 parts of a lithium salt, 0.1 to 5 parts of a film-forming additive, and 0.1 to 5 parts of an organosilicon additive; the organosilicon additive is selected from one or more of 3-isocyanatepropyltriethoxysilane (IPTS), polydimethylsiloxane (PDMS) and 3-trimethylsilyl-2-oxazolidinone (TMS-ON); the film-forming additive includes an organic matter containing a sulfonic acid group and a fluorine-containing salt, and the fluorine-containing salt is selected from one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiODFB) and lithium tetrafluorooxalatophosphate (LiOTFP).

[0019] The electrolyte composition for lithium titanate battery provided by the present invention contains a special organic silicon additive and a film-forming additive in its formula. The two can synergistically form a stable CEI film containing a small amount of LiF inorganic components on the surface of the positive electrode material, which can serve as a PF6 - and F - At the same time, the above additives can also participate in the negative electrode film formation, effectively reduce the battery self-discharge and impedance, and are beneficial to the high voltage and high temperature cycle of the battery.

[0020] In particular, the inventors have selected one or more of 3-isocyanatepropyltriethoxysilane (IPTS), polydimethylsiloxane (PDMS) and 3-trimethylsilyl-2-oxazolidinone (TMS-ON) as organosilicon additives after a large number of experiments. This is because compared with the borate or phosphate organosilicon commonly used in the art, the above types are more capable of cooperating with film-forming additives composed of organic matter containing sulfonic acid groups and fluoride-containing salts, so as to ensure the film-forming effect of the obtained electrolyte composition in the lithium titanate battery system. Of course, in actual use, the organosilicon additive used in the present invention can also be selected from tris (trimethylsilane) phosphite (TMSPi), tris (trimethylsilane) phosphate (TMSPA), tris (trimethylsilane) borate (TMSB) and dimethyldimethoxysilane (DODSi) commonly used in the art. The above-mentioned organosilicon compounds can also play a similar film-forming role, but the corresponding effect of improving the high temperature resistance of the obtained electrolyte and lithium titanate battery is slightly worse.

[0021] Similarly, the three fluorine-containing salts of lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiODFB) and lithium tetrafluorooxalatophosphate (LiOTFP) in the film-forming additives provided by the present invention are also obtained by the inventors through a large number of experimental comparisons and screening, so as to cooperate with organic matter containing sulfonic acid groups as film-forming additives and better cooperate with silicone additives to achieve the film-forming function.

[0022] Furthermore, in order to achieve a more significant film-forming effect, thereby further improving the performance of the obtained electrolyte composition in lithium titanate batteries, and ultimately making the corresponding lithium titanate batteries exhibit better high temperature resistance, the preferred weight ratio of the silicone additive to the film-forming additive is 1: (1.8~2.0).

[0023] In several preferred embodiments, the organosilicon additive includes 3-isocyanate propyl triethoxysilane and 3-trimethylsilyl-2-oxazolidinone, and the weight ratio of 3-isocyanate propyl triethoxysilane to 3-trimethylsilyl-2-oxazolidinone is 1:(1.4-1.6). The inventors further screened the types of organosilicon additives through a large number of experiments and obtained the above combination scheme, and found that the film-forming effect of the electrolyte composition in the battery operation process is more obvious, so that its chemical stability and thermal stability can be more effectively maintained.

[0024] For the above-mentioned organosilicon additive, the inventors have accordingly preferred through a large number of experiments that the weight ratio of the organic matter containing sulfonic acid groups and the fluorine-containing salt in the film-forming additive is 1: (0.8-1), so that the obtained film-forming additive can better cooperate with it, synergistically strengthen the film-forming effect, and improve the high temperature resistance of the obtained electrolyte composition in lithium titanate batteries. Furthermore, in order to improve the compatibility of the film-forming additive with the electrolyte system, it is preferred that the organic matter containing sulfonic acid groups is 1,3-propane sultone.

[0025] Further, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium methanesulfonate (LiCH3SO3) and lithium bis(oxalatoborate) (LiBOB), preferably lithium hexafluorophosphate (LiPF6). The inventors have selected the type of lithium salt through a large number of experiments to better match the type and amount of the above two additives, and more significantly improve the stability and high temperature resistance of the obtained electrolyte. And / or, the organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), butylene carbonate (BC), methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP) and propyl propionate (PP), preferably a group consisting of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC), and the weight ratio of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC) is (2-2.5): (2-2.5): 1. Theoretically, the organic solvent can be selected from the types commonly used in the art, but the inventors have selected the above-mentioned specific organic solvent composition through a large number of experiments, and found that based on the three-component solvent system, the film-forming additive and the organosilicon additive therein can better synergistically play the role of film-forming, so that the obtained non-aqueous electrolyte exhibits higher high temperature resistance.

[0026] In several typical embodiments, the electrolyte composition for lithium titanate batteries includes, by weight, 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 0.5 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone; or, the electrolyte composition for lithium titanate batteries includes 7.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 0.25 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone; or, by weight, the electrolyte composition for lithium titanate battery includes 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 1.0 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone. After a large number of experiments, the inventors optimized the types and amounts of the components in the provided electrolyte composition for lithium titanate batteries, and obtained the above-mentioned specific formulas, which have better high temperature resistance and can maintain an extremely high capacity retention rate after a long cycle of 30 days at a temperature of 55°C.

[0027] The second aspect of the present invention provides a method for preparing the above-mentioned electrolyte composition for lithium titanate batteries, comprising: adding a film-forming additive and an organosilicon additive to an organic solvent, and obtaining a first solution after a first mixing; adding a lithium salt to the first solution, and obtaining an electrolyte composition for lithium titanate batteries after a second mixing. The present invention provides a preparation method for the above-mentioned electrolyte composition accordingly, so as to successfully obtain an electrolyte with excellent high temperature storage resistance and high temperature stability as mentioned above. In addition, the above-mentioned preparation method strictly controls the order of adding the two additives and the lithium salt to ensure the uniformity of the dispersion of the obtained electrolyte, thereby achieving a long-cycle stability effect.

[0028] Furthermore, the first mixing and the second mixing are both carried out under the protection of an inert gas, and the time for the first mixing and the second mixing is independently 1h to 5h, and the inert gas is preferably N2 and / or Ar. All steps in the preparation process of the electrolyte provided by the present invention are carried out in an environment close to anhydrous and oxygen-free, so as to better improve the purity, inhibit the oxidation denaturation of the components therein, or interfere with the oxygen molecules or water during subsequent applications to cause functional failure. Specifically, the above preparation methods are all carried out in a closed reactor. Furthermore, before adding the lithium salt, step S2 also includes opening cooling water in the outer layer of the reactor to cool the system and maintain the activity of the lithium salt to a greater extent, thereby improving the electrochemical performance of the electrolyte.

[0029] The third aspect of the present invention provides a lithium titanate battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte is the above-mentioned electrolyte composition for lithium titanate batteries. Since the above-mentioned electrolyte composition for lithium titanate batteries provided by the present invention has good high temperature resistance, still maintains good stability after long-term high temperature cycling, and has high ion conductivity, after preparing the lithium titanate battery, the corresponding lithium titanate battery also exhibits excellent high temperature long cycle stability.

[0030] Furthermore, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is LiNi x Co y Mn z O2, x+y+z=1, 0.33≤x≤0.95, y>0, z>0; the negative electrode sheet includes a negative current collector and a negative active material layer coated on the negative current collector, the negative active material layer includes a negative active substance, and the negative active substance is lithium titanate; the separator is a polyolefin separator, and the polyolefin separator is a polyethylene film or a polypropylene film. After a large number of experiments, the inventor optimized and designed the lithium titanate battery environment adapted to the above-obtained lithium titanate battery electrolyte, and obtained the types of the above-mentioned positive electrode sheet, negative electrode sheet and separator. In the lithium titanate battery assembled in this way, the coordination between the components is higher, thereby showing more superior performance.

[0031] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0032] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0033] Example 1

[0034] Preparation of an electrolyte composition for lithium titanate batteries:

[0035] 1. Selection of raw materials: Weigh 17.5 parts by weight of LiPF6 as lithium salt; weigh 33 parts by weight of dimethyl carbonate (DMC), 33 parts by weight of ethyl methyl carbonate (EMC) and 15 parts by weight of ethylene carbonate (EC), and mix the three as an organic solvent; weigh 0.5 parts by weight of lithium difluorooxalatoborate (LiODFB) and 0.5 parts by weight of 1,3-propane sultone (PS), and mix the two as a film-forming additive; weigh 0.2 parts by weight of 3-isocyanatepropyltriethoxysilane (IPTS) and 0.3 parts by weight of 3-trimethylsilyl-2-oxazolidinone (TMS-ON), and mix the two as an organosilicon additive.

[0036] 2. Preparation of electrolyte composition: nitrogen is introduced into a closed reactor, and in this environment, a film-forming additive and an organosilicon additive are added to an organic solvent and mixed for 2.5 hours to obtain a first solution; then cooling water is opened on the outer layer of the reactor, and lithium salt is added to the first solution, and mixed again for 2.5 hours to obtain an electrolyte composition for lithium titanate batteries.

[0037] Examples 2 to 7

[0038] The difference between Examples 2 to 7 and Example 1 is only that the types and amounts of the components are different, as shown in Table 1.

[0039] Example 8

[0040] The only difference between this embodiment and embodiment 1 is that during the preparation of the electrolyte composition, in the step of obtaining the first solution and adding the lithium salt, cooling water is not opened on the outer layer of the reactor; the types and amounts of each component in the electrolyte are the same.

[0041] Comparative Examples 1 to 4

[0042] The difference between Comparative Examples 1 to 4 and Example 1 is only that the types and amounts of each component are different, as shown in Table 1.

[0043] Test Method

[0044] Conductivity test: The conductivity of each electrolyte sample at 25°C was tested by a conductivity instrument.

[0045] Battery sample preparation: A lithium titanate battery with a capacity of 2Ah, including a positive electrode plate, a negative electrode plate, a separator and an electrolyte. The electrolyte used is the electrolyte formula of this embodiment, the active material on the positive electrode plate used is lithium nickel cobalt manganese oxide, the active material on the negative electrode plate used is lithium titanate, and the separator used is a polypropylene separator.

[0046] High temperature storage performance: The following test is performed after storage at 55°C for 30 days.

[0047] 1. Capacity retention rate: Test the capacity change of the battery before and after high-temperature storage.

[0048] 2. Self-discharge performance: Test the change in open circuit voltage of the battery before and after high-temperature storage.

[0049] 3. Internal resistance increase rate: Test the change in internal resistance of the battery before and after high-temperature storage.

[0050] High temperature cycle capacity retention rate: At 45°C, charge and discharge cycles were performed at 1C / 1C, and the discharge capacity retention rate was tested after 3000 cycles.

[0051] The above test results are detailed in Table 1 and Table 2.

[0052] Table 1

[0053]

[0054]

[0055] In Table 1, Example 7 further added 0.5 parts by weight of tris(trimethylsilyl)phosphite (TMSPi), and Comparative Example 3 further added 0.5 parts by weight of trimethyl borate (TMB).

[0056] Table 2

[0057]

[0058] From the above description, it can be seen that the above-mentioned embodiments of the present invention realize the preparation of a high-temperature resistant electrolyte composition for lithium titanate batteries. When it is applied to lithium titanate batteries, the corresponding battery samples show excellent high-temperature storage resistance and high-temperature long cycle resistance.

[0059] Specifically, electrolyte additives can form films synergistically, protecting the stability of electrode materials in high temperature environments and making side reactions less likely to occur.

[0060] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An electrolyte composition for lithium titanate battery, characterized in that: The electrolyte composition for lithium titanate battery comprises, by weight: 70 to 90 parts of organic solvent, 10 to 20 parts of lithium salt, 0.1 to 5 parts of film-forming additive and 0.1 to 5 parts of organosilicon additive; The organosilicon additive is selected from one or more of 3-isocyanatepropyltriethoxysilane, polydimethylsiloxane and 3-trimethylsilyl-2-oxazolidinone; The film-forming additive comprises an organic substance containing a sulfonic acid group and a fluorine-containing salt, wherein the fluorine-containing salt is selected from one or more of lithium difluorophosphate, lithium difluorooxalatoborate and lithium tetrafluorooxalatophosphate.

2. The electrolyte composition for lithium titanate battery according to claim 1, characterized in that: The weight ratio of the organic silicon additive to the film-forming additive is 1:(1.8-2.0).

3. The electrolyte composition for lithium titanate battery according to claim 1 or 2, characterized in that: The organic silicon additive comprises 3-isocyanate propyl triethoxy silane and 3-trimethylsilyl-2-oxazolidinone, and the weight ratio of the 3-isocyanate propyl triethoxy silane to the 3-trimethylsilyl-2-oxazolidinone is 1:(1.4-1.6).

4. The electrolyte composition for lithium titanate batteries according to any one of claims 1 to 3, characterized in that In the film-forming additive, the weight ratio of the organic matter containing sulfonic acid groups to the fluorine-containing salt is 1:(0.8-1); Preferably, the organic compound containing a sulfonic acid group is 1,3-propanesultone.

5. The electrolyte composition for lithium titanate batteries according to any one of claims 1 to 4, characterized in that: The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium methanesulfonate and lithium bis(oxalatoborate), preferably lithium hexafluorophosphate; and / or, The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, butylene carbonate, methyl acetate, ethyl acetate, propyl acetate and propyl propionate, preferably the group consisting of dimethyl carbonate, ethyl methyl carbonate and ethylene carbonate, and the weight ratio of the dimethyl carbonate, the ethyl methyl carbonate and the ethylene carbonate is (2-2.5):(2-2.5):

1.

6. The electrolyte composition for lithium titanate batteries according to any one of claims 1 to 5, characterized in that: In parts by weight, the electrolyte composition for lithium titanate battery includes 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 0.5 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone; or, In parts by weight, the electrolyte composition for lithium titanate battery includes 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 0.25 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone; or, In parts by weight, the electrolyte composition for lithium titanate battery includes 17.5 parts of lithium hexafluorophosphate, 33 parts of dimethyl carbonate, 33 parts of ethyl methyl carbonate, 15 parts of ethylene carbonate, 0.5 parts of lithium difluorooxalatoborate, 1.0 parts of 1,3-propane sultone, 0.2 parts of 3-isocyanatepropyltriethoxysilane and 0.3 parts of 3-trimethylsilyl-2-oxazolidinone.

7. A method for preparing the electrolyte composition for lithium titanate batteries according to any one of claims 1 to 6, characterized in that: The preparation method comprises: Adding a film-forming additive and an organosilicon additive into an organic solvent, and performing a first mixing to obtain a first solution; The lithium salt is added into the first solution, and the electrolyte composition for lithium titanate battery is obtained after a second mixing.

8. The preparation method according to claim 7, characterized in that: The first mixing and the second mixing are both performed under the protection of an inert gas, and the time of the first mixing and the second mixing is independently 1 hour to 5 hours; Preferably, the inert gas is N2 and / or Ar.

9. A lithium titanate battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The electrolyte is the electrolyte composition for lithium titanate batteries according to any one of claims 1 to 6.

10. The lithium titanate battery according to claim 9, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material is LiNi x Co y Mn z O2, x+y+z=1, 0.33≤x≤0.95, y>0, z>0; The negative electrode sheet comprises a negative current collector and a negative active material layer coated on the negative current collector, the negative active material layer comprises a negative active material, and the negative active material is lithium titanate; The diaphragm is a polyolefin diaphragm, and the polyolefin diaphragm is a polyethylene film or a polypropylene film.

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