Electrolyte additive as well as preparation method and application thereof

Abstract

The invention provides an electrolyte additive and a preparation method and application thereof, the electrolyte additive comprises at least one of trifluoromethyl phosphoric acid silane compounds, the trifluoromethyl phosphoric acid silane compounds have a structure as shown in a formula I: # imgabs0 #, and R1 and R2 are independently selected from methyl or halogen atom substituted methyl. The electrolyte additive provided by the invention has high thermal stability and excellent interface film-forming characteristic, and can improve the stability of the electrolyte and reduce the risk of thermal runaway under a high-temperature condition, so that the safety of the lithium ion battery is remarkably improved; and meanwhile, the ion transmission efficiency is not influenced.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to an electrolyte additive, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion batteries are widely used in electronic devices, electric vehicles, and energy storage systems, and their advantages include high energy density and long life. However, with the improvement of battery energy density and charge-discharge rate, the safety issues of lithium-ion batteries have attracted increasing attention. Especially under extreme conditions (such as overcharging, over-discharging, high temperature, etc.), lithium-ion batteries may experience a "thermal runaway" phenomenon, resulting in electrolyte decomposition, increased internal pressure, and even explosion or fire, posing significant safety hazards.

[0003] Among the components of the electrolyte, although carbonate solvents have high ionic conductivity, their thermal stability is poor and they are prone to decomposition at high temperatures, leading to safety problems. To address this issue, the industry generally adds some substances that inhibit thermal runaway to the electrolyte, including phosphate esters, sulfides, etc. However, although traditional additives can improve the thermal safety of lithium-ion batteries to a certain extent, they all have their own disadvantages, mainly including:

[0004] 1. Poor thermal stability: Many additives are prone to decomposition or phase change at high temperatures, unable to form a stable protective film, affecting the safety of the battery.

[0005] 2. Affecting ionic conductivity: Most flame retardant or thermal runaway-inhibiting additives often significantly reduce the ionic conductivity of the electrolyte when improving the thermal stability of the electrolyte, affecting the normal charge-discharge efficiency of the battery.

[0006] 3. Limited inhibition effect: Some traditional additives are difficult to effectively inhibit electrolyte decomposition at high temperatures, resulting in the still existing risk of thermal runaway.

[0007] 4. Decline in electrochemical performance: Some flame retardants have poor stability to electrode materials, and long-term use will lead to capacity attenuation and shortened cycle life.

[0008] 5. High cost: Some highly efficient additives, such as solid electrolytes or compounds containing rare metals, have high costs and are difficult to be applied on a large scale.

[0009] In summary, traditional additives are either costly, or the improvement of the safety of lithium-ion batteries needs to be enhanced, or the ionic conductivity often decreases while improving safety, thereby affecting the rate performance and cycle life of the battery.

[0010] Therefore, developing an additive that can at least improve the thermal stability of the electrolyte without significantly affecting ion transport is of great significance for the safety of lithium-ion batteries. Summary of the Invention

[0011] In view of this, an object of the present application is to provide an electrolyte additive, which has high thermal stability and excellent interfacial film-forming characteristics, can improve the stability of the electrolyte under high-temperature conditions, reduce the risk of thermal runaway, and thus significantly enhance the safety of lithium-ion batteries; at the same time, it does not affect the ion transport efficiency.

[0012] Another object of the present application is to provide a preparation method of the electrolyte additive.

[0013] Another object of the present application is to provide an electrolyte.

[0014] Another object of the present application is to provide a lithium-ion battery.

[0015] Another object of the present application is to provide an electrical device.

[0016] To achieve the above object, the first aspect of the present application provides an electrolyte additive, including at least one of trifluoromethylphosphine silane compounds, and the trifluoromethylphosphine silane compound has the structure shown in Formula I:

[0017]

[0018] Wherein, R 1 and R 2 are each independently selected from methyl or methyl substituted by a halogen atom.

[0019] The second aspect of the present application provides a preparation method of the electrolyte additive, including:

[0020] Performing a first reaction on a silane compound and a metal phosphate to obtain a phosphorus-containing silane compound;

[0021] Performing a second reaction on the phosphorus-containing silane compound and a fluoride to obtain the trifluoromethylphosphine silane compound.

[0022] The third aspect of the present application provides an electrolyte, including a lithium salt, a non-aqueous organic solvent, and an additive, and the additive includes the electrolyte additive described in the present application or the electrolyte additive prepared by the preparation method of the electrolyte additive described in the present application.

[0023] The fourth aspect of the present application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, and the electrolyte is the electrolyte described in the present application.

[0024] The fifth aspect of the present application provides an electrical device, including the lithium-ion battery described in the present application.

[0025] The electrolyte additive described in this application can at least bring the following beneficial effects:

[0026] In the molecule of the trifluoromethylphosphorosilane compound, a phosphate group and a silyl group structure are simultaneously introduced, enabling the electrolyte additive to have high thermal stability and excellent interfacial film-forming characteristics. It can inhibit the decomposition of the electrolyte under high-temperature conditions, improve the stability of the electrolyte, alleviate the thermal runaway phenomenon, and thus reduce the risk of thermal runaway, significantly enhancing the safety of lithium-ion batteries. At the same time, it does not significantly affect the ion transport efficiency of the electrolyte (i.e., does not affect ion conductivity), so it does not reduce the rate performance of the battery. In addition, since the protective layer formed by the electrolyte additive described in this application on the electrode surface can prevent the occurrence of side reactions, it can reduce the decomposition of the electrolyte, enabling the battery to maintain good performance under high-rate and long-term cycling conditions.

[0027] Specifically, compared with the electrolyte without the electrolyte additive described in this application under the same conditions:

[0028] 1. Improvement in thermal safety: At high temperatures, the thermal decomposition temperature of the electrolyte with the electrolyte additive described in this application increases by about 25%, and the potential safety hazards caused by electrolyte decomposition are greatly reduced.

[0029] 2. Conductivity retention rate: The ionic conductivity of the electrolyte with the electrolyte additive described in this application remains above 4.5 mS / cm, showing no significant decrease compared to the base electrolyte (i.e., the electrolyte without the electrolyte additive described in this application under the same conditions).

[0030] 3. Extension of cycle life: Under the 1C rate cycling test, the capacity retention rate of the battery using the electrolyte with the electrolyte additive described in this application can reach over 90% after 500 cycles, far superior to the electrolyte without the electrolyte additive described in this application under the same conditions.

[0031] The preparation method of the electrolyte additive described in this application, in addition to having the beneficial effects of the electrolyte additive described in this application, can at least bring the following beneficial effects: The synthesis steps are simple and easy to operate, and the pollution is relatively lower than that of the prior art.

[0032] The electrolyte, lithium-ion battery, and electrical device described in this application all at least have the beneficial effects of the electrolyte additive and the preparation method of the electrolyte additive described in this application.

[0033] The additional aspects and advantages of this application will be partially given in the following description, partially become apparent from the following description, or be understood through the practice of this application. Detailed implementation manners

[0034] Embodiments of the present application will be described in detail below. The embodiments are exemplary and are intended to explain the present application, but should not be construed as limiting the present application.

[0035] In the present application, the disclosure of a numerical range includes all values within the entire range and the disclosure of further sub-ranges, including the endpoints and sub-ranges given for these ranges.

[0036] In the present application, raw materials, equipment, etc. involved, unless otherwise specified, are raw materials and equipment that can be obtained through commercial channels or prepared by known methods; methods involved, unless otherwise specified, are conventional methods.

[0037] When the term "and / or" is used in a list containing two or more items, it means that any one of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression "A and / or B" is intended to mean A or B or A and B, that is, it only means A, only means B, or means the combination of A and B.

[0038] In the present application, normal pressure refers to one standard atmosphere (1.01325×10 5 Pa).

[0039] In the present application, room temperature refers to 20 - 30 °C.

[0040] <Electrolyte additive>

[0041] The electrolyte additive of the embodiment of the present application includes at least one of trifluoromethylphosphinosilane compounds, and the trifluoromethylphosphinosilane compound has the structure shown in Formula I:

[0042]

[0043] Wherein, R 1 , R 2 are each independently selected from methyl or methyl substituted by a halogen atom.

[0044] The electrolyte additive of the embodiment of the present application simultaneously introduces a phosphate group and a silyl group structure into the trifluoromethylphosphinosilane compound molecule, making the electrolyte additive have good thermal stability and interfacial film-forming ability, significantly improving the overall performance of the electrolyte; at the same time, the phosphorus-containing structure generates a chemically inert layer under high-temperature conditions, which can inhibit the decomposition of the electrolyte, reduce the decomposition risk of the electrolyte at high temperature, and reduce the occurrence of thermal runaway; in addition, the protective layer formed by the trifluoromethylphosphinosilane compound at the negative electrode interface enhances the stability of the electrode interface, thereby effectively inhibiting the side reaction between the electrolyte and the electrode material and improving the cycle stability of the battery.

[0045] In some embodiments, the halogen atom includes, but is not limited to, a fluorine atom (F), a chlorine atom (Cl), a bromine atom (Br), or an iodine atom (I), etc.

[0046] As an alternative example, the R 1 , R 2 are both methyl groups. At this time, the structural formula of the trifluoromethylphosphinosilane compound is:

[0047]

[0048] <Preparation Method of Electrolyte Additive>

[0049] The preparation method of the electrolyte additive in the embodiments of the present application can be used to prepare the electrolyte additive in the embodiments of the present application.

[0050] The preparation method of the electrolyte additive in the embodiments of the present application includes the following steps:

[0051] S101. Perform a first reaction on a silane compound and a metal phosphate to obtain a phosphorus-containing silane compound.

[0052] S102. Perform a second reaction on the phosphorus-containing silane compound obtained in step S101 and a fluoride to obtain the trifluoromethylphosphinosilane compound.

[0053] In some embodiments, in step S101, the silane compound includes, but is not limited to, at least one of trimethylsilane, triethylsilane, etc.

[0054] In some embodiments, in step S101, the metal phosphate includes, but is not limited to, at least one of tricalcium phosphate, magnesium phosphate, aluminum phosphate, etc.

[0055] In some embodiments, taking the case where the silane compound is trimethylsilane and the metal phosphate is tricalcium phosphate as an example, in step S101, the reaction equation of the first reaction is:

[0056] Ca 3 (PO 4 ) 2 +6HSi(CH 3 ) 3 →2[(CH 3 ) 3 SiO] 3 PO+3Ca+3H 2 ↑

[0057] In some embodiments, in step S101, the reaction temperature of the first reaction is 400 - 600 °C. In the examples of the present application, when the reaction temperature of the first reaction is within the above range, the reaction rate is fast enough, and at the same time, side reactions dominated by thermodynamics are avoided; when it is lower than 400 °C, the reaction rate decreases, the reaction is incomplete, the amount of by-products increases, the difficulty of subsequent purification steps increases, and the fluorination reaction may be interfered; when it is higher than 600 °C, there is a possibility of thermal decomposition of the silane compound and the metal phosphate, and at the same time, the metal phosphate particles are sintered, reducing the contact area with the silane, thereby reducing the efficiency.

[0058] Exemplarily, in step S101, the reaction temperature of the first reaction includes but is not limited to 425 °C, 450 °C, 475 °C, 500 °C, 525 °C, 550 °C or 575 °C, etc., and is preferably 500 - 550 °C.

[0059] In some embodiments, in step S101, the reaction time of the first reaction is 4 - 8 h, including but not limited to 5 h, 6 h or 8 h, etc.

[0060] In some embodiments, in step S101, the reaction pressure of the first reaction is normal pressure.

[0061] In some embodiments, in step S101, the first reaction is carried out in an inert gas atmosphere. Exemplarily, the inert gas atmosphere includes but is not limited to at least one of nitrogen, argon, etc.

[0062] In some embodiments, in step S102, the fluoride includes but is not limited to at least one of hydrogen fluoride (HF), ammonium fluoride (NH 4 F), potassium fluoride (KF), etc.

[0063] In some embodiments, in step S102, the second reaction is a fluorination reaction.

[0064] In some embodiments, taking the case where the silane compound is trimethylsilane, the metal phosphate is tricalcium phosphate, and the fluoride is hydrogen fluoride as an example, in step S102, the reaction equation of the second reaction is:

[0065] [(CH 3 ) 3 SiO] 3 PO + 3HF → [CF3-(CH 3 ) 2 SiO] 3 PO + 3H 2 ↑

[0066] In some embodiments, in step S102, the reaction temperature of the second reaction is 200 - 300 °C, including but not limited to 225 °C, 250 °C, 275 °C, etc.

[0067] Exemplarily, in step S102, the reaction temperature of the second reaction includes but not limited to 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, etc., and is preferably 250 - 280 °C.

[0068] In some embodiments, in step S102, the reaction time of the second reaction is 2 - 4 h, including but not limited to 2.5 h, 3 h, 3.5 h, etc.

[0069] In some embodiments, in step S102, the reaction pressure of the second reaction is normal pressure.

[0070] In some embodiments, in step S102, the second reaction is carried out in an inert gas atmosphere. Exemplarily, the inert gas includes but not limited to at least one of argon, nitrogen, etc.

[0071] In some embodiments, the molar ratio of the silane compound, the metal phosphate, and the fluoride is (3 - 4):1:(3 - 6), including but not limited to 3:1:3, 3:1:5, 3:1:6, 4:1:3.5, 4:1:5, etc., and is preferably 4:1:3.5, etc.

[0072] In some embodiments, the preparation method of the electrolyte additive further includes a step of purifying the product of the second reaction.

[0073] Exemplarily, the above purification method includes: cooling the product of the second reaction, then washing with dilute alkali solution and filtering, and retaining the liquid phase product, which is the electrolyte additive.

[0074] Optionally, the dilute alkali solution for washing includes at least one of saturated sodium bicarbonate solution, dilute ammonia water, etc.

[0075] As an alternative example, the above purification method includes: cooling the product of the second reaction to room temperature, washing the product of the second reaction with saturated sodium bicarbonate solution or dilute ammonia water, and then separating the solid residue by a centrifuge to retain the liquid phase product.

[0076] <Electrolyte>

[0077] The electrolyte of the embodiment of the present application includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes the electrolyte additive of the embodiment of the present application, or an electrolyte additive prepared by the preparation method of the electrolyte additive of the embodiment of the present application.

[0078] In some embodiments, the mass content of the silicon trifluoromethylphosphate compound in the electrolyte is 0.5-2%. In the examples of the present application, when the mass content of the silicon trifluoromethylphosphate compound in the electrolyte is within the above range, it can ensure that while improving the thermal stability, it does not affect the ionic conductivity of the electrolyte; if it is less than 0.5%, the thermal stability is insufficient, the SEI film has defects, and the antioxidant ability is weak; if it is higher than 2%, the electrochemical polarization increases, the kinetic performance deteriorates, the side reactions intensify, and the economy deteriorates.

[0079] Exemplarily, the mass content of the silicon trifluoromethylphosphate compound in the electrolyte includes but is not limited to 0.75%, 1%, 1.25%, 1.5% or 1.75%, etc., and is preferably 0.75-1%.

[0080] It should be noted that in some cases, in the electrolyte of the embodiments of the present application, in addition to the electrolyte additives of the embodiments of the present application or the electrolyte additives prepared by the preparation method of the electrolyte additives of the embodiments of the present application, the additives may also include other additives well-known in the art that can improve the performance of the electrolyte, such as at least one of 4-cyano-3-(trimethylsilyl)pyridine, tris(2,2,2-trifluoroethyl) phosphate, etc. The dosages of these other additives that can improve the performance of the electrolyte are not limited and can be any dosages well-known in the art.

[0081] In some embodiments, the non-aqueous organic solvent includes but is not limited to at least one of carbonate compounds, carboxylate compounds, nitrate compounds, etc.

[0082] Exemplarily, the carbonate compounds include but are not limited to at least one of ethylene carbonate (EC), diethyl carbonate (DEC), trifluoroethyl carbonate, etc.

[0083] Exemplarily, the carboxylate compounds include but are not limited to at least one of ethyl acetate, propyl propionate, ethyl trifluoroacetate, etc.

[0084] As an alternative example, the non-aqueous organic solvent is a carbonate compound.

[0085] Exemplarily, when the non-aqueous organic solvent is a plurality of carbonate compounds, the mass ratio of the plurality of carbonate compounds is not limited.

[0086] In some embodiments, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF 6 )、lithium bisimide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), etc.

[0087] Exemplarily, the concentration of the lithium salt in the electrolyte is about 1.0 mol / L, such as 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L or 1.2 mol / L, etc.

[0088] As an alternative example, the electrolyte is composed of a lithium salt, a non-aqueous organic solvent and an additive, wherein the lithium salt is lithium hexafluorophosphate (LiPF 6 ), the non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), and the additive is the electrolyte additive of the embodiment of the present application or the electrolyte additive prepared by the preparation method of the electrolyte additive of the embodiment of the present application.

[0089] In some embodiments, the preparation method of the electrolyte of the embodiment of the present application includes the following steps:

[0090] 1) Add the lithium salt to the non-aqueous organic solvent and mix evenly to obtain a basic electrolyte.

[0091] 2) Add the electrolyte additive of the embodiment of the present application or the electrolyte additive of the embodiment of the present application to the basic electrolyte, and then stir under constant temperature conditions to make it fully mixed to ensure that each component is evenly distributed, so as to obtain the electrolyte of the embodiment of the present application.

[0092] In some embodiments, when the non-aqueous organic solvent is a mixed solvent of multiple (more than two) substances, the preparation method of the electrolyte of the embodiment of the present application further includes:

[0093] Before adding the electrolyte, mix the multiple substances to obtain a mixed solvent, and use this mixed solvent as the non-aqueous organic solvent.

[0094] <Lithium-ion battery>

[0095] The lithium-ion battery of the embodiment of the present application includes a positive electrode, a negative electrode, a separator and an electrolyte, and the electrolyte is the electrolyte of the embodiment of the present application.

[0096] In the embodiments of the present application, the selection of the positive electrode, the negative electrode and the separator is not limited, and it can be any positive electrode, negative electrode or separator that is well known in the art and can be used for lithium-ion batteries.

[0097] <Electrical device>

[0098] The electrical device of the embodiment of the present application includes the lithium-ion battery of the embodiment of the present application.

[0099] In some embodiments, the above-mentioned electrical device can be electronic products such as mobile phones and tablet computers, or vehicles such as new energy electric vehicles and cars, or lighting devices such as table lamps and flashlights, etc.

[0100] Certain features of the present technology are further illustrated in the following non-limiting examples.

[0101] The trifluoromethylphosphinosilane compounds involved in the following examples and the additives involved in some of the comparative examples are all selected from Table 1.

[0102] Table 1 Trifluoromethylphosphinosilane compounds involved in each example and additives involved in some comparative examples

[0103]

[0104] Example 1

[0105] (Electrolyte additive)

[0106] The electrolyte additive of this example is a trifluoromethylphosphinosilane compound, specifically Compound 1. Its preparation method includes the following steps:

[0107] (1) React 4 mol of trimethylsilane (CAS No.: 993-07-7) with 1 mol of tricalcium phosphate (Ca 3 (PO 4 ) 2 ) in a nitrogen gas atmosphere at 500 °C and atmospheric pressure for 5 h to obtain a phosphorus-containing silane compound.

[0108] (2) React the phosphorus-containing silane compound obtained in step (1) with 3.5 mol of hydrogen fluoride (HF) in a nitrogen gas atmosphere at 250 °C and atmospheric pressure for 3 h. Then cool the reaction product to room temperature (25 °C), wash the reaction product with saturated sodium bicarbonate solution, and finally separate the solid residue by centrifuge to retain the liquid phase product, thus obtaining Compound 1.

[0109] (Electrolyte)

[0110] The electrolyte of this example consists of a lithium salt, a non-aqueous organic solvent, and an additive. Among them, the lithium salt is LiPF 6 , and its concentration in the electrolyte is 1 mol / L; the non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed in a volume ratio of 3:7; the additive is the electrolyte additive Compound 1 of this example, and its mass content in the electrolyte is 0.7%.

[0111] (Preparation method of electrolyte)

[0112] Mix ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7 to obtain a mixed solvent; then add LiPF 6 to the mixed solvent and mix well to obtain a basic electrolyte; then, add Compound 1 to the basic electrolyte and stir at a constant temperature of 25 °C for 4 h to make it fully mixed, thus obtaining the electrolyte of this example.

[0113] Example 2 (the electrolyte contains 0.5% of silane trifluoromethylphosphate compound)

[0114] This example is basically the same as Example 1, except that:

[0115] In the electrolyte, the mass content of Compound 1 in the electrolyte is 0.5%.

[0116] Example 3 (the electrolyte contains 1% of silane trifluoromethylphosphate compound)

[0117] This example is basically the same as Example 1, except that:

[0118] In the electrolyte, the mass content of Compound 1 in the electrolyte is 1%.

[0119] Example 4 (the electrolyte contains 1.5% of silane trifluoromethylphosphate compound)

[0120] This example is basically the same as Example 1, except that:

[0121] In the electrolyte, the mass content of Compound 1 in the electrolyte is 1.5%.

[0122] Example 5 (the electrolyte contains 2% of silane trifluoromethylphosphate compound)

[0123] This example is basically the same as Example 1, except that:

[0124] In the electrolyte, the mass content of Compound 1 in the electrolyte is 2%.

[0125] Example 6 (compared with Example 1, the raw materials of the first reaction are different)

[0126] This example is basically the same as Example 1, except that:

[0127] In the preparation method of the electrolyte additive Compound 1, trimethylsilane in step (1) is replaced by methyldichlorosilane (CAS No.: 617-86-7).

[0128] Example 7 (compared with Example 1, the raw materials of the second reaction are different)

[0129] This example is basically the same as Example 1, except that:

[0130] In the preparation method of the electrolyte additive Compound 1, hydrogen fluoride (HF) in step (2) is replaced by ammonium fluoride (NH 4 F).

[0131] Example 8 (compared with Example 1, the lower limit of the temperature of the first reaction)

[0132] This example is basically the same as Example 1, except that:

[0133] In the preparation method of the electrolyte additive compound 1, the reaction temperature in step (1) is 400 °C.

[0134] Example 9 (upper limit of the temperature of the first reaction compared with Example 1)

[0135] This example is basically the same as Example 1, except that:

[0136] In the preparation method of the electrolyte additive compound 1, the reaction temperature in step (1) is 600 °C.

[0137] Example 10 (lower limit of the temperature of the second reaction compared with Example 1)

[0138] This example is basically the same as Example 1, except that:

[0139] In the preparation method of the electrolyte additive compound 1, the reaction temperature in step (2) is 200 °C.

[0140] Example 11 (upper limit of the temperature of the second reaction compared with Example 1)

[0141] This example is basically the same as Example 1, except that:

[0142] In the preparation method of the electrolyte additive compound 1, the reaction temperature in step (2) is 300 °C.

[0143] Example 12 (the electrolyte additive is compound 2 compared with Example 1)

[0144] This example is basically the same as Example 1, except that:

[0145] The electrolyte additive of this example is a trifluoromethylphosphinosilane compound, specifically compound 2, and its preparation method includes the following steps:

[0146] (1) React 4 mol of trimethylsilane (CAS No.: 993-07-7) with 1 mol of tricalcium phosphate (Ca 3 (PO 4 ) 2 ) in a nitrogen gas atmosphere at 500 °C and atmospheric pressure for 5 h to obtain a phosphorus-containing silane compound.

[0147] (2) React the phosphorus-containing silane compound obtained in step (1) with 5 mol of hydrogen fluoride (HF) in a nitrogen gas atmosphere at 250 °C and atmospheric pressure for 4 h to obtain compound 2.

[0148] Example 13 (compared with Example 1, the electrolyte additive is Compound 3)

[0149] This example is basically the same as Example 1, except that:

[0150] The electrolyte additive in this example is a trifluoromethylphosphinosilane compound, specifically Compound 3, and its preparation method includes the following steps:

[0151] (1) React 4 mol of trimethylsilane (CAS No.: 993-07-7) with 1 mol of tricalcium phosphate (Ca 3 (PO 4 ) 2 ) in a nitrogen gas atmosphere at 500 °C and atmospheric pressure for 5 h to obtain a phosphorus-containing silane compound.

[0152] (2) React the phosphorus-containing silane compound obtained in step (1) with 6 mol of hydrogen fluoride (HF) in a nitrogen gas atmosphere at 250 °C and atmospheric pressure for 4 h. Then cool the reaction product to room temperature (25 °C), wash the reaction product with saturated sodium bicarbonate solution, and finally separate the solid residue by centrifuge and retain the liquid phase product to obtain Compound 3.

[0153] In the electrolyte and its preparation method, the additive is Compound 3.

[0154] Example 14 (compared with Example 1, the electrolyte additive is Compound 4)

[0155] This example is basically the same as Example 1, except that:

[0156] The electrolyte additive in this example is a trifluoromethylphosphinosilane compound, specifically Compound 4, and its preparation method includes the following steps:

[0157] (1) React 4 mol of trimethylsilane (CAS No.: 993-07-7) with 1 mol of tricalcium phosphate (Ca 3 (PO 4 ) 2 ) in a nitrogen gas atmosphere at 500 °C and atmospheric pressure for 5 h to obtain a phosphorus-containing silane compound.

[0158] (2) React the phosphorus-containing silane compound obtained in step (1) with 3.5 mol of hydrogen fluoride and 1 mol of hydrogen bromide (HBr) in a nitrogen gas atmosphere at 250 °C and atmospheric pressure for 3 h. Then cool the reaction product to room temperature (25 °C), wash the reaction product with saturated sodium bicarbonate solution, and finally separate the solid residue by centrifuge and retain the liquid phase product to obtain Compound 4.

[0159] In the electrolyte and its preparation method, the additive is Compound 4.

[0160] Comparative Example 1

[0161] This comparative example is basically the same as Example 1, except that:

[0162] No electrolyte additives and method for preparing the same;

[0163] The electrolyte does not contain additives;

[0164] In the preparation method of the electrolyte, remove "; in Example 1, add compound 1 to the basic electrolyte, stir at a constant temperature of 25°C for 4 hours to fully mix, and obtain the electrolyte of this example."

[0165] Comparative Example 2

[0166] The electrolyte of this comparative example is composed of a lithium salt, a non-aqueous organic solvent and an additive. Among them, the lithium salt is LiPF 6 , its concentration in the electrolyte is 1 mol / L; the non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7; the additive is compound 5, and its mass content in the electrolyte is 0.7%.

[0167] The preparation method of the electrolyte is as follows: ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3:7 to obtain a mixed solvent; then LiPF is added to the mixed solvent. 6 The mixture was mixed to obtain a basic electrolyte solution; then, compound 5 was added to the basic electrolyte solution, and the mixture was stirred at a constant temperature of 25° C. for 4 h to fully mix the mixture, thereby obtaining the electrolyte solution of this comparative example.

[0168] Comparative Example 3

[0169] The electrolyte of this comparative example is composed of a lithium salt, a non-aqueous organic solvent and an additive. Among them, the lithium salt is LiPF 6 , its concentration in the electrolyte is 1 mol / L; the non-aqueous organic solvent is a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7; the additive is compound 6, and its mass content in the electrolyte is 0.7%.

[0170] The preparation method of the electrolyte is as follows: ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3:7 to obtain a mixed solvent; then LiPF is added to the mixed solvent. 6 The mixture was mixed to obtain a basic electrolyte solution; then, compound 6 was added to the basic electrolyte solution, and the mixture was stirred at a constant temperature of 25° C. for 4 h to fully mix the mixture, thereby obtaining the electrolyte solution of this comparative example.

[0171] 2. Performance Test

[0172] 1. Thermal decomposition temperature test

[0173] The thermal decomposition temperature of the electrolytes in each example and comparative example was tested by Accelerating Rate Calorimetry (ARC). The specific test method was as follows: The electrolyte sample was placed in a sealed reactor, and the onset temperature of thermal decomposition was determined by monitoring the changes in temperature and pressure in real time. When the sample underwent exothermic decomposition, the instrument captured the inflection point of its temperature-pressure curve to calibrate the onset temperature of thermal decomposition.

[0174] 2. Ionic conductivity test

[0175] The ionic conductivity of the electrolytes in each example or comparative example was tested. The test method was as follows: Two electrodes were inserted into the electrolyte, and a DC voltage was applied to make the ions in the electrolyte move directionally to form an electric current. By measuring the potential difference and current between the electrodes, the resistance of the electrolyte was calculated according to Ohm's law, and then the ionic conductivity was obtained.

[0176] 3. Flame retardancy test

[0177] The flame retardancy of the electrolytes in each example or comparative example was tested. The test method was as follows: After measuring the initial mass of a glass cotton ball with a diameter of 0.3 cm, the glass cotton ball was immersed in the electrolytes of each example or comparative example. After being fully wetted, it was taken out and weighed. An igniter was used to ignite the wetted glass cotton ball, and the time from when the igniter was removed to when the flame went out was recorded, and this was used as the extinguishing time to calculate the self-extinguishing time per unit mass of the electrolyte:

[0178] Self-extinguishing time per unit mass of electrolyte = Extinguishing time / (Wetted mass - Initial mass).

[0179] The longer the self-extinguishing time per unit mass of the electrolyte, the worse the flame retardancy and the worse the ability to slow down thermal runaway; the shorter the self-extinguishing time per unit mass of the electrolyte, the better the flame retardancy and the better the ability to slow down thermal runaway.

[0180] 4. Charge-discharge cycle test and rate performance test

[0181] The electrolytes of each example and comparative example were respectively used in lithium-ion batteries, and the charge-discharge cycle performance and rate performance of their corresponding lithium-ion batteries were tested.

[0182] Among them:

[0183] The assembly method of the lithium-ion battery included the following steps:

[0184] (1) Preparation of the positive electrode sheet: Lithium iron phosphate (LiFePO 4) The positive electrode paste is prepared by mixing SP conductive agent (i.e., conductive carbon black super p), polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2. The positive electrode paste is uniformly coated on the opposite two side surfaces of a carbon-coated aluminum foil with a thickness of 13 μm by a transfer coater to obtain a positive electrode plate.

[0185] (2) Preparation of the negative electrode plate: The artificial graphite, SP conductive agent (i.e., conductive carbon black super p), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96.2:1:1.2:1.6 to prepare a negative electrode paste. The negative electrode paste is uniformly coated on the opposite two side surfaces of a copper foil with a thickness of 4.5 μm by a transfer coater to obtain a negative electrode plate.

[0186] (3) Separator selection: The separator uses a 7 + 1 + 2 separator (7 μm polyethylene (PE) base film, 1 μm ceramic, 2 μm glue).

[0187] (4) Assembly: The positive electrode plate, negative electrode plate, electrolyte, separator, etc. are assembled into a lithium-ion battery, where the electrolyte is the electrolyte of each example or comparative example.

[0188] Test of charge and discharge cycle performance Test the charge and discharge cycle life. The specific test method is as follows: (1) Leave it at 25°C ± 2°C for 120 min; (2) Charge it at 1 / 3C CCCV (constant current constant voltage) to 3.65V, with a cut-off current of 0.05C; (3) Discharge it at 1 / 3C CC (constant current) to 2.5V; (4) Leave it for 30 min; (5) Repeat steps 2 - 4 for two weeks; (6) Charge it at 1 / 3C constant current constant voltage to 3.65V, with a cut-off current of 0.05C; (7) Leave it for 30 min; (8) Discharge it at 1 / 3C constant current to 2.5V; (9) Leave it for 30 min; (Record the capacity as C0, and correct the capacity every 100 weeks); (10) Charge it at 1C0 constant current constant voltage to 3.65V, with a cut-off current of 0.05C0; Leave it for 30 min; (11) Discharge it at 1C0 constant current to 2.5V; Leave it for 30 min; (12) Repeat steps 10 - 11 for 100 cycles; (13) Leave it for 24 h; (14) Repeat steps 6 - 13 until 500 cycles stop. The charge capacity of the 500th cycle / the charge capacity of the 1st cycle is the 500-cycle capacity retention rate.

[0189] The test method for rate performance is rate discharge. The specific method is as follows: 1) Leave it standing for 10 min; 2) Constant current discharge at 1 / 3C to 2.0V (time limit 4h); 3) Leave it standing for 30 min; 4) Constant current and constant voltage charge at 1 / 3C to 3.65V, cut-off current 0.05C (time limit 4h); 5) Leave it standing for 30 min; 6) Constant current discharge at 5C to 2.0V respectively; 7) Leave it standing for 30 min / 60 min; (when the discharge rate ≥ 1C, the standing time is changed to 60 min) 8) Repeat steps 2) to 7) and discharge at 5C rate respectively, record the discharge capacity; 9) End.

[0190] The quality of rate performance is expressed by the capacity retention rate. The higher the capacity retention rate, the better the rate performance; the lower the capacity retention rate, the worse the rate performance. Among them, the calculation formula for the capacity retention rate used to express rate performance is:

[0191] Capacity retention rate = 5C discharge capacity / 1C discharge capacity * 100%.

[0192] The performance test results of the electrolytes of each example and comparative example and their corresponding lithium-ion batteries are shown in Table 2.

[0193] Table 2 Performance test results

[0194]

[0195] As can be seen from Table 1, the thermal decomposition temperature and ionic conductivity of the electrolytes containing the electrolyte additives of each example of the present application are significantly higher than those of the electrolytes containing the electrolyte additives of each comparative example, and at the same time, the flame retardant performance is better. In addition, the rate performance and cycle performance of the lithium-ion batteries containing the electrolyte additives of each example of the present application are also significantly better than those of the lithium-ion batteries containing the electrolyte additives of each comparative example. In particular, Example 1 performs the best in various performances - the initial thermal decomposition temperature of the electrolyte added with the electrolyte additive of the present application in Example 1 is 24% higher than that of the electrolyte without adding the electrolyte additive of the present application in Comparative Example 1, which proves that the electrolyte additive of the present application effectively enhances the thermal stability of the electrolyte by inhibiting the high-temperature decomposition reaction; at the same time, compared with Comparative Example 1, the ionic conductivity of Example 1 is increased by 81.25%, the flame retardant performance is increased by 91.89%, the rate performance is increased by 36.39%, the 200-cycle capacity retention rate is increased by 21.95%, and the 500-cycle capacity retention rate is increased by 40.83%.

[0196] In this application, terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0197] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of this application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0198] Although the embodiments of this application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting this application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. An electrolyte additive, characterized in that: Including at least one of trifluoromethyl silane phosphate compounds, wherein the trifluoromethyl silane phosphate compound has a structure shown in Formula I: Wherein, R1 and R2 are each independently selected from a methyl group or a methyl group substituted by a halogen atom.

2. The electrolyte additive according to claim 1, characterized in that: The R1 and R2 are both methyl groups.

3. A method for preparing an electrolyte additive according to any one of claims 1 or 2, characterized in that: include: The silane compound is first reacted with the metal phosphate to obtain a phosphorus-containing silane compound; The phosphorus-containing silane compound is subjected to a second reaction with a fluoride to obtain the trifluoromethylphosphoric acid silane compound.

4. The electrolyte additive according to claim 3, characterized in that: The silane compound includes at least one of trimethylsilane and triethylsilane; and / or, The metal phosphate includes at least one of tricalcium phosphate, magnesium phosphate and aluminum phosphate; and / or, The fluoride includes at least one of hydrogen fluoride, ammonium fluoride or potassium fluoride.

5. The electrolyte additive according to claim 3, characterized in that: The molar ratio of the silane compound, the metal phosphate and the fluoride is (3-4):1:(3-6).

6. The electrolyte additive according to claim 3, characterized in that: The reaction temperature of the first reaction is 400-600° C.; and / or, The reaction time of the first reaction is 4-8h; The second reaction is a fluorination reaction; and / or, The reaction temperature of the second reaction is 200-300° C.; and / or, The reaction time of the second reaction is 2-4h; and / or, The second reaction and the first reaction are both carried out under an inert gas atmosphere, and the reaction pressure is both normal pressure.

7. An electrolyte, characterized in that: The invention comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises the electrolyte additive as claimed in claim 1 or 2 or the electrolyte additive prepared as claimed in any one of claims 3 to 6.

8. The electrolyte additive according to claim 7, characterized in that: The mass content of the trifluoromethylsilylphosphophosphate compound in the electrolyte is 0.5-2%; and / or, The non-aqueous organic solvent includes at least one of carbonate compounds, carboxylate compounds, and nitropropyl ethyl ester.

9. A lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, characterized in that: The electrolyte is the electrolyte according to claim 7 or 8.

10. An electrical device, characterized in that: Comprising the lithium ion battery as claimed in claim 9.

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