Phosphoryl isocyanate additive, preparation method thereof, electrolyte, additive and lithium ion battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a phosphoryl isocyanate additive, a preparation method of the phosphoryl isocyanate additive, an electrolyte, the additive and a lithium ion battery. The structure of the phosphoryl isocyanate additive is shown as the following formula (A): # imgabs0 #, R1 is one of alkyl, alkoxy, phenoxyl, alkenyl, alkynyl, phenyl and substitutes thereof with the carbon atom number of 1-6, and R2 is one of isocyanate, alkyl, alkenyl, alkynyl, phenyl and substitutes thereof with the carbon atom number of 1-6. By adding a small amount of phosphoryl isocyanate additive into the electrolyte, a CEI structure which is relatively low in resistance and stable under a high-voltage condition is formed on the surface of a positive electrode, so that the rate capability and the high-voltage cycle stability of the battery can be improved.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a phosphoryl isocyanate additive and a preparation method thereof, an electrolyte and the additive, and a lithium ion battery. Background Art

[0002] In recent years, in order to alleviate mileage anxiety, the energy density and rate charge and discharge performance of lithium-ion batteries have become key indicators for the development of power batteries. Among them, the use of high-voltage positive electrode materials can significantly improve the energy density of batteries. However, in high-voltage battery systems, the commonly used lithium hexafluorophosphate / carbonate electrolyte has poor compatibility with battery systems equipped with high-voltage positive electrode materials. The CEI structure formed on the surface of the positive electrode material is unstable. As the number of cycles increases, the CE I formed on the positive electrode surface continues to reconstruct and thicken, causing the battery impedance to continue to grow, hindering the transmission of lithium ions, and ultimately leading to a decrease in battery rate performance and a decrease in cycle life; in addition, PF5 generated by lithium hexafluorophosphate is prone to trigger a series of side reactions, such as causing carbonate ring opening, forming HF with trace water, corroding CE I and positive electrode materials, and ultimately causing battery life to decay. At present, the cycle life and rate performance of the battery are generally improved by adding additives to the electrolyte, but the commonly used additives still have limited effect on improving the cycle and rate performance. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a phosphoryl isocyanate additive and a preparation method thereof, an electrolyte and the additive, and a lithium ion battery.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A phosphoryl isocyanate additive, the structure of which is shown in the following formula (A):

[0006]

[0007] Among them, R1 is one of the alkyl, alkoxy, phenoxy, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms, preferably alkyl, alkoxy, phenoxy; R2 is one of the isocyanate, alkyl, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms, preferably isocyanate and alkyl.

[0008] Preferably, the structure is one of the following formulas A1, A2, A3, A4, A5, A6;

[0009]

[0010]

[0011] The present invention also includes a method for preparing the phosphoryl isocyanate additive, which is prepared by the following formula (I):

[0012]

[0013] Among them, R1 is one of alkyl, alkoxy, phenoxy, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms, R2 is one of isocyanate, alkyl, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms; the catalyst is one of MgCl2, FeCl3 and CaCl2.

[0014] The method specifically comprises the following steps: mixing cyanate and compound B and adding them into an organic solvent, performing a reflux reaction under the catalytic action of a catalyst, separating the reactants, and obtaining the target phosphoryl isocyanate additive.

[0015] The molar ratio of the cyanate to the compound B is (1-5):1; preferably 3:1; preferably, the organic solvent is one of acetonitrile, acetone, cyclohexane, ethanol, tetrahydrofuran, and ethyl acetate.

[0016] The present invention also includes an electrolyte additive, including the phosphoryl isocyanate additive and other additives; the other additives are one or more of fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, lithium difluorooxalatoborate, and lithium difluorophosphate.

[0017] The present invention also includes an electrolyte, including a solvent, a lithium salt and the electrolyte additive.

[0018] The phosphoryl isocyanate additive accounts for 0.1wt%-2wt%; preferably 0.5wt%;

[0019] Fluorinated ethylene carbonate accounts for 0.1wt%-1wt%, 1,3-propane sultone accounts for 0.1wt%-3wt%, vinyl sulfate accounts for 0.1wt%-3wt%, lithium difluorooxalatoborate accounts for 0.1wt%-1wt%, and lithium difluorophosphate accounts for 0.1wt%-1wt%.

[0020] Preferably, 0.3 wt% of fluoroethylene carbonate, 0.3 wt% of lithium difluorooxalatoborate, 0.5 wt% of lithium difluorophosphate, 1.5 wt% of 1,3-propane sultone, and 1.0 wt% of vinyl sulfate;

[0021] The solvent is two or more of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethylene carbonate, and propylene carbonate;

[0022] Preferably, ethylene carbonate accounts for 5wt%-30wt%, ethyl methyl carbonate accounts for 20wt%-60wt%, and diethyl carbonate accounts for 2wt%-10wt%; preferably: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1t%, and diethyl carbonate accounts for 8.2wt%;

[0023] The lithium salt is one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide;

[0024] Preferably, lithium hexafluorophosphate accounts for 8wt%-15wt%, and lithium bis(fluorosulfonyl)imide accounts for 0.1wt%-6wt%. Preferably, lithium hexafluorophosphate accounts for 13.0wt%, and lithium bis(fluorosulfonyl)imide accounts for 1wt%;

[0025] The present invention also includes a lithium-ion battery, including the electrolyte, positive electrode, negative electrode and separator; preferably, the positive electrode is a high-voltage positive electrode, and the upper limit of the working voltage is greater than 4V; preferably, the positive electrode active material of the positive electrode is one of the quaternary materials of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and NCMA.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a simple method for improving battery rate performance and high-voltage cycle stability. By adding a small amount of phosphoryl isocyanate additive to the electrolyte, a CEI structure with low resistance and stable under high-voltage conditions is formed on the positive electrode surface, thereby improving the battery rate performance and high-voltage cycle stability. This method is simple and easy to operate, has low energy consumption, and has good application prospects.

[0028] The phosphoryl isocyanate additive of the present invention has the following characteristics:

[0029] (1) The additive molecules have a high HOMO energy level and can be preferentially oxidized before the carbonate solvent decomposes. They can synergize with the components of the electrolyte to improve the CEI structure and composition, forming a layer of low-resistance and stable CEI structure on the positive electrode surface, improving the battery rate performance, while inhibiting the structural damage of the positive electrode material and improving the battery cycle stability;

[0030] (2) By reacting -NCO with trace H2O molecules in the electrolyte, the side reaction between PF5 and H2O can be weakened, the decomposition of LiPF6 lithium salt can be inhibited, and the battery cycle life can be improved;

[0031] (3) The additive molecules are weakly alkaline under the action of P=O and -NCO, which interacts with the acidic PF5, weakening the reactivity of PF5, thereby inhibiting the formation of HF and the ring-opening reaction of cyclic carbonates such as EC, and avoiding side reactions;

[0032] (4)-NCO can react with HF molecules in the electrolyte to remove acid, thereby preventing HF from etching LiF and alkyl lithium carbonate in the formed CEI structure, inhibiting the repeated formation of CEI, thereby reducing the growth of battery impedance and weakening battery polarization; in addition, it can also reduce HF etching of the layered oxide positive electrode and maintain stable battery cycling.

[0033] (5) At an addition amount of 0.1%-2%, the additive molecules can form a stable CEI structure on the surface of the layered metal oxide positive electrode, which works together with the components in the electrolyte to significantly improve the battery cycle and storage stability and improve the battery rate performance. DETAILED DESCRIPTION

[0034] In order to make those skilled in the art better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the embodiments. Unless otherwise specified in this application, the percentage content is by mass percentage.

[0035] A phosphoryl isocyanate additive, the structure of which is shown in the following formula (A):

[0036]

[0037] Among them, R1 is one of alkyl, alkoxy, phenoxy, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms, and R2 is one of isocyanate, alkyl, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms.

[0038] Preferably, the structure is one of the following formulas A1, A2, A3, A4, A5, A6;

[0039]

[0040]

[0041] The preparation method of the phosphoryl isocyanate additive is prepared by the following formula (I):

[0042]

[0043] Among them, R1 is one of alkyl, alkoxy, phenoxy, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms, R2 is one of isocyanate, alkyl, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms; the catalyst is one of MgCl2, FeCl3 and CaCl2.

[0044] The method specifically comprises the following steps: mixing cyanate and compound B and adding them into an organic solvent, performing a reflux reaction under the catalytic action of a catalyst, separating the reactants, and obtaining the target phosphoryl isocyanate additive.

[0045] The molar ratio of the cyanate to the compound B is (1-5):1; preferably 3:1; preferably, the organic solvent is one of acetonitrile, acetone, cyclohexane, ethanol, tetrahydrofuran, and ethyl acetate.

[0046] The specific preparation method is described below. In the process of synthesizing the phosphoryl isocyanate, 6 mol sodium cyanate and 2 mol reaction substrate compound B are mixed in 30 mL acetonitrile solvent, and refluxed at 85°C for 1 hour under the catalytic action of 0.05 mol MgCl2. The reactants are separated to obtain the target phosphoryl isocyanate additive compound A. Compounds A1, A2, A3, A4, A5, and A6 are prepared by this method.

[0047] Example 1

[0048] An electrolyte comprising a solvent, a lithium salt and an additive;

[0049] The solvent includes: ethylene carbonate accounts for 24.7wt%, ethyl methyl carbonate accounts for 49.4wt%, and diethyl carbonate accounts for 8.2wt%;

[0050] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0051] The additives include: 0.3 wt% of fluoroethylene carbonate, 0.3 wt% of lithium difluorooxalatoborate, 0.5 wt% of lithium difluorophosphate, 1.5 wt% of 1,3-propane sultone, 1.0 wt% of vinyl sulfate, and 0.1 wt% of phosphoryl isocyanate additive A1.

[0052] Example 2

[0053] An electrolyte comprising a solvent, a lithium salt and an additive;

[0054] The solvent includes: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1wt%, and diethyl carbonate accounts for 8.2wt%;

[0055] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0056] The additives include: 0.3 wt% of fluoroethylene carbonate, 0.3 wt% of lithium difluorooxalatoborate, 0.5 wt% of lithium difluorophosphate, 1.5 wt% of 1,3-propane sultone, 1.0 wt% of vinyl sulfate, and 0.5 wt% of phosphoryl isocyanate additive A1.

[0057] Example 3

[0058] An electrolyte comprising a solvent, a lithium salt and an additive;

[0059] The solvent includes: ethylene carbonate accounts for 24.1wt%, ethyl methyl carbonate accounts for 48.3wt%, and diethyl carbonate accounts for 8.0wt%;

[0060] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0061] The additives include: 0.3 wt% of fluoroethylene carbonate, 0.3 wt% of lithium difluorooxalatoborate, 0.5 wt% of lithium difluorophosphate, 1.5 wt% of 1,3-propane sultone, 1.0 wt% of vinyl sulfate, and 2 wt% of phosphoryl isocyanate additive A1.

[0062] Example 4

[0063] An electrolyte comprising a solvent, a lithium salt and an additive;

[0064] The solvent includes: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1wt%, and diethyl carbonate accounts for 8.2wt%;

[0065] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0066] The additives include: 0.3wt% of fluoroethylene carbonate, 0.3wt% of lithium difluorooxalatoborate, 0.5wt% of lithium difluorophosphate, 1.5wt% of 1,3-propane sultone, 1.0wt% of vinyl sulfate, and 0.5wt% of phosphoryl isocyanate additive A2.

[0067] Example 5

[0068] An electrolyte comprising a solvent, a lithium salt and an additive;

[0069] The solvent includes: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1wt%, and diethyl carbonate accounts for 8.2wt%;

[0070] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0071] The additives include: 0.3 wt% of fluoroethylene carbonate, 0.3 wt% of lithium difluorooxalatoborate, 0.5 wt% of lithium difluorophosphate, 1.5 wt% of 1,3-propane sultone, 1.0 wt% of vinyl sulfate, and 0.5 wt% of phosphoryl isocyanate additive A3.

[0072] Example 6

[0073] An electrolyte comprising a solvent, a lithium salt and an additive;

[0074] The solvent includes: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1wt%, and diethyl carbonate accounts for 8.2wt%;

[0075] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0076] The additives include: 0.3wt% of fluoroethylene carbonate, 0.3wt% of lithium difluorooxalatoborate, 0.5wt% of lithium difluorophosphate, 1.5wt% of 1,3-propane sultone, 1.0wt% of vinyl sulfate, and 0.5wt% of phosphoryl isocyanate additive A4.

[0077] Example 7

[0078] An electrolyte comprising a solvent, a lithium salt and an additive;

[0079] The solvent includes: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1wt%, and diethyl carbonate accounts for 8.2wt%;

[0080] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0081] The additives include: 0.3wt% of fluoroethylene carbonate, 0.3wt% of lithium difluorooxalatoborate, 0.5wt% of lithium difluorophosphate, 1.5wt% of 1,3-propane sultone, 1.0wt% of vinyl sulfate, and 0.5wt% of phosphoryl isocyanate additive A5.

[0082] Example 8

[0083] An electrolyte comprising a solvent, a lithium salt and an additive;

[0084] The solvent includes: ethylene carbonate accounts for 24.6wt%, ethyl methyl carbonate accounts for 49.1wt%, and diethyl carbonate accounts for 8.2wt%;

[0085] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0086] The additives include: 0.3wt% of fluoroethylene carbonate, 0.3wt% of lithium difluorooxalatoborate, 0.5wt% of lithium difluorophosphate, 1.5wt% of 1,3-propane sultone, 1.0wt% of vinyl sulfate, and 0.5wt% of phosphoryl isocyanate additive A6.

[0087] Comparative Example 1

[0088] An electrolyte comprising a solvent, a lithium salt and an additive;

[0089] The solvent includes: ethylene carbonate accounts for 24.7wt%, ethyl methyl carbonate accounts for 49.4wt%, and diethyl carbonate accounts for 8.3wt%;

[0090] The lithium salt includes: lithium hexafluorophosphate accounting for 13.0wt% and lithium bis(fluorosulfonyl)imide accounting for 1wt%;

[0091] The additives include: 0.3 wt % of fluoroethylene carbonate, 0.3 wt % of lithium difluorooxalatoborate, 0.5 wt % of lithium difluorophosphate, 1.5 wt % of 1,3-propane sultone, and 1.0 wt % of vinyl sulfate.

[0092] Based on the electrolytes described in the above embodiments and comparative examples, high-voltage and high-rate lithium-ion batteries were further prepared. The batteries in the embodiments and comparative examples were prepared according to the following method except that the electrolyte formulas were different:

[0093] The positive electrode active material lithium nickel cobalt manganese oxide, conductive agent CNT, conductive agent carbon black and binder PVDF were uniformly dispersed in NMP solvent at a mass ratio of 96.0:0.8:1.7:1.5, and the solid content of the slurry was controlled at 70%. The slurry was fully stirred in a dry environment filled with nitrogen to make it uniformly mixed. The uniformly mixed slurry was coated on both sides of the Al foil, and then dried and coated at 3.4 g / cm 3 The positive electrode sheet is rolled with a compaction density to obtain the required positive electrode sheet.

[0094] Artificial graphite, binder CMC, binder SBR and conductive agent carbon black are uniformly dispersed in deionized water solvent at a mass ratio of 96:1.0:1.5:1.5, and the solid content of the slurry is controlled to be 50%. The slurry is fully stirred and mixed evenly, and the mixed slurry is coated on both sides of the Cu foil, and then dried and coated at 1.5g / cm 3 The negative electrode sheet is rolled with a compaction density to obtain the desired negative electrode sheet.

[0095] The negative electrode sheet, polyethylene separator, and positive electrode sheet are stacked in order, ensuring that the separator separates the positive and negative electrodes, and the effective area of ​​the positive electrode sheet corresponds to the effective area of ​​the negative electrode sheet. The stacked battery cell is subjected to lug welding and encapsulation with an aluminum-plastic film. After the above-mentioned electrode group is dried, the electrolyte described in the embodiment and comparative example is injected, and then the battery is subjected to static, packaging, formation, exhaust, and aging treatment in sequence to obtain the corresponding lithium-ion battery.

[0096] The obtained lithium-ion batteries injected with the electrolyte solutions of different embodiments were subjected to performance tests according to the following test methods:

[0097] Rate charge and discharge performance test: Rate discharge test: At room temperature, charge to 4.4V at 0.33C constant current, charge to 0.05C at 4.4V constant voltage, and then discharge to 2.8V at 3C; Rate charge test: charge to 4.4V at 3C, charge to 0.05C at 4.4V constant voltage, and then discharge to 2.8V at 0.33C.

[0098] High voltage resistance test: At room temperature, the batteries in the embodiments and comparative examples were charged and discharged in a 1C / 1C charge and discharge mode: 1C constant current charging to 4.4V, 4.4V constant voltage charging to 0.05C, then standing for 10 minutes, 1C discharge to 2.8V, and standing for 10 minutes; the test was repeated according to the above charge and discharge mode, and the discharge capacity retention rate of the battery in each cycle was recorded.

[0099] High temperature storage performance test: At room temperature, discharge at 1C to 2.8V, let stand for 10 minutes; charge at 1C constant current to 4.4V, let stand for 10 minutes; charge at 4.4V constant voltage to 0.05C, charge and discharge for 3 cycles according to this charging and discharging mode, finally charge the battery to full power, and store the battery in a 60℃ oven for 7 days. After 7 days of storage, remove the battery and charge and discharge for 3 cycles at room temperature according to the same charging and discharging mode, and record the residual capacity and recovery capacity after storage.

[0100] The test results of lithium-ion batteries injected with different electrolyte solutions are shown below.

[0101] Table 1 Rate test results of lithium ion batteries in various comparative examples and embodiments

[0102] plan 3C constant current charging ratio / % 3C discharge capacity retention rate Comparative Example 1 83.2 81.6 Example 1 83.8 79.1 Example 2 86.5 88.6 Example 3 82.8 80.8 Example 4 86.2 87.4 Example 5 85.8 86.6 Example 6 85.3 86.2 Example 7 86.6 87.9 Example 8 86.1 88.4

[0103] It can be found from Table 1 that the constant current charging ratio under 3C rate charging conditions and the discharge capacity under 3C rate discharging conditions of Examples 2, 4, 5, 6, 7 and 8 are better than those of Comparative Example 1. This shows that the phosphoryl isocyanate additive can be preferentially oxidized on the surface of the positive electrode to form a CEI structure with lower resistance, reduce the lithium ion transfer impedance, and thus improve the battery rate charge and discharge performance. Among them, the constant current charging during 3C rate charging and the discharge capacity during 3C rate discharging of Example 2 are higher than those of Examples 1 and 3, indicating that the amount of additive A1 is 0.1wt%, which has limited effect on the CEI structure; and when the amount of additive is increased to 2wt%, the film formed on the surface of the positive electrode material is too thick, and the lithium ion transmission is hindered. The effective amount of additive A1 is between 0.1wt% and 2wt%.

[0104] Table 2 High voltage cycle test results of lithium ion batteries in comparative examples and embodiments

[0105] plan 25℃ cycle 500 cycles capacity retention rate / % Comparative Example 1 86.2 Example 1 88.5 Example 2 96.7 Example 3 84.3 Example 4 93.8 Example 5 94.4 Example 6 93.5 Example 7 95.1 Example 8 94.4

[0106] From the results shown in Table 2, it can be found that the capacity retention rates of Example 2, Example 4, Example 5, Example 6, Example 7 and Example 8 after 500 cycles in the voltage range of 2.8-4.4V are all better than those of the comparative example, indicating that the phosphoryl isocyanate additive can form a stable CE I structure under high pressure conditions on the surface of the positive electrode material, and at the same time, relying on the effects of P=O and -NCO groups in the additive molecule, the etching of HF on the layered oxide positive electrode material and the Li F and alkyl lithium carbonate in the formed CE I structure is weakened, and the battery can be maintained in a stable cycle in the voltage range of 2.8-4.4V. The capacity retention rates of Example 1 and the comparative example after 500 cycles are slightly different, indicating that when the amount of additive A1 is 0.1wt%, the ability to optimize the high-voltage resistance of the battery is limited. The capacity retention rate of Example 3 after 500 cycles is inferior to that of the comparative example, further indicating that the effective amount of additive A1 is between 0.1wt% and 2wt%.

[0107] Table 3 Residual and recovery results of lithium ion batteries in various comparative examples and embodiments

[0108]

[0109]

[0110] From the results shown in Table 3, it can be seen that the residual and recovery capacity retention rates of Examples 2, 4, 5, 6, 7 and 8 after battery storage are better than those of the comparative example, indicating that the phosphoryl isocyanate additive can form a stable CE I structure under high temperature and high pressure conditions on the surface of the positive electrode material, thereby improving the high temperature storage performance of the battery. The difference between the residual and recovery capacity retention rates of Example 1 and the comparative example is small, indicating that when the amount of additive A1 is 0.1wt%, the optimized battery has limited high temperature and high pressure tolerance. The residual and recovery capacity retention rates of Example 3 are inferior to those of the comparative example, indicating that when the amount of additive A1 is higher than 2wt%, the battery's high temperature and high pressure tolerance deteriorates, and the effective amount of additive A1 is between 0.1wt% and 2wt%.

[0111] It can be seen from the above embodiments and comparative examples that the effective amount of the phosphoryl isocyanate additive is between 0.1wt% and 2wt%, which can be preferentially oxidized before the carbonate solvent decomposes, and synergistically act with the components of the electrolyte to improve the CE I structure and composition, forming a layer of CE I structure with low resistance and stable under high voltage on the surface of the positive electrode, improving the battery rate performance, and enhancing the high voltage cycle stability and high temperature storage performance of the battery.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A phosphoryl isocyanate additive, characterized in that: The structure is shown in the following formula (A): Among them, R1 is one of the alkyl, alkoxy, phenoxy, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms; preferably alkyl, alkoxy and phenoxy; R2 is one of the isocyanate, alkyl, alkenyl, alkynyl, phenyl and their substituents having 1-6 carbon atoms; preferably isocyanate and alkyl.

2. The phosphoryl isocyanate additive according to claim 1, characterized in that: The structure is one of the following formulas A1, A2, A3, A4, A5, A6; 3. A method for preparing the phosphoryl isocyanate additive according to any one of claims 1 to 2, characterized in that: Prepared by the following formula (I): Among them, R1 is one of alkyl, alkoxy, phenoxy, alkenyl, alkynyl, phenyl and their substituents with a carbon number of 1-6, R2 is one of isocyanate, alkyl, alkenyl, alkynyl, phenyl and their substituents with a carbon number of 1-6; the catalyst is one of MgCl2, FeCl3, and CaCl2.

4. The preparation method according to claim 3, characterized in that: The method specifically comprises the following steps: mixing cyanate and compound B and adding them into an organic solvent, performing a reflux reaction under the catalytic action of a catalyst, separating the reactants, and obtaining the target phosphoryl isocyanate additive.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the cyanate to the compound B is (1-5):1; preferably 3:1; preferably, the organic solvent is one of acetonitrile, acetone, cyclohexane, ethanol, tetrahydrofuran, and ethyl acetate.

6. An additive, characterized in that It comprises the phosphoryl isocyanate additive according to any one of claims 1 to 2 and other additives; the other additives are one or more of fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, lithium difluorooxalatoborate and lithium difluorophosphate.

7. An electrolyte, characterized in that: The invention comprises a solvent, a lithium salt and the additive according to claim 6.

8. The electrolyte according to claim 7, characterized in that The phosphoryl isocyanate additive accounts for 0.1wt%-2wt%; fluoroethylene carbonate accounts for 0.1wt%-1wt%, 1,3-propane sultone accounts for 0.1wt%-3wt%, vinyl sulfate accounts for 0.1wt%-3wt%, lithium difluorooxalatoborate accounts for 0.1wt%-1wt%, and lithium difluorophosphate accounts for 0.1wt%-1wt%.

9. The electrolyte according to claim 7, characterized in that The solvent is two or more of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethylene carbonate, and propylene carbonate; Preferably, ethylene carbonate accounts for 5wt%-30wt%, ethyl methyl carbonate accounts for 20wt%-60wt%, and diethyl carbonate accounts for 2wt%-10wt%; The lithium salt is one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; Preferably, lithium hexafluorophosphate accounts for 8wt%-15wt%, and lithium bis(fluorosulfonyl)imide accounts for 0.1wt%-6wt%.

10. A lithium ion battery, characterized in that: It comprises the electrolyte, positive electrode, negative electrode and separator as described in any one of claims 7-9; preferably, the positive electrode is a high-voltage positive electrode, and the upper limit of the working voltage is greater than 4V; preferably, the positive electrode active material of the positive electrode is one of the quaternary materials of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and NCMA.

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