Application of unsaturated phosphate lithium fluoroborate in electrolyte and preparation method of unsaturated phosphate lithium fluoroborate

Abstract

The invention discloses an application of unsaturated phosphate lithium fluoroborate in an electrolyte and a preparation method of the unsaturated phosphate lithium fluoroborate, and particularly, the unsaturated phosphate lithium fluoroborate is added into the electrolyte in an addition amount which accounts for 0.01-15wt% of the total mass of the electrolyte; the preparation method of the unsaturated phosphate lithium fluoroborate comprises the following steps: reacting unsaturated phosphonic acid with an inorganic lithium salt to obtain an unsaturated lithium phosphate reaction solution, and introducing boron trifluoride gas into the unsaturated lithium phosphate reaction solution or adding a boron trifluoride complex into the unsaturated lithium phosphate reaction solution to react to obtain the unsaturated phosphate lithium fluoroborate. The unsaturated phosphate lithium fluoroborate is applied to an electrolyte, and has the advantages of reducing the initial impedance of a battery, reducing gas production during storage, improving the cycle performance and the like.

Description

Technical Field

[0001] The invention relates to the field of electrolytes, and in particular to a preparation method of unsaturated phosphate-based lithium fluoroborate and application thereof in lithium ion battery electrolytes. Background Art

[0002] As an indispensable component of lithium-ion batteries, electrolyte additives are mainly responsible for constructing a stable electrode / electrolyte interface film to achieve electronic insulation and facilitate lithium ion transmission. Under the influence of different functional groups in the additives, the composition and structure of the battery interface film change, ultimately affecting the battery cycle life, high-temperature storage, and low-temperature discharge performance.

[0003] Compounds with different functional groups or heteroatoms often exhibit different effects. For example, boron-containing additives can dissolve LiF inorganic lithium salts on the surface of the interface film due to the electron-deficient effect of boron atoms, thereby reducing the internal resistance of the battery and improving the low-temperature performance of the battery; the "P=O" of phosphorus-containing additives has a strong interaction with the transition metal elements on the surface of the positive electrode, thereby forming a stable positive electrode interface film on the surface, improving the storage performance and cycle performance of the battery; unsaturated functional groups, such as vinyl and acetylene groups, can be reduced and polymerized at the negative electrode to form a stable interface film, reducing the reduction reaction between the solvent and the negative electrode surface and reducing the gas production of the battery; F atoms in the additives can form LiH at the interface between the positive and negative electrodes, increasing the stability and mechanical strength of the interface film and improving the battery cycle life. However, compounds containing multiple advantageous functional groups or heteroatoms often have complex structures and are difficult to prepare and obtain.

[0004] Chinese patent CN112751080A discloses an unsaturated phosphate compound and a synthesis method thereof, wherein unsaturated vinyl lithium phosphate can be used as an electrolyte additive to reduce battery impedance and improve rate and cycle performance. The patent uses excess LiH to react with unsaturated phosphonic acid to obtain unsaturated phosphate. On the one hand, due to the high reaction activity of LiH, the reaction releases a large amount of heat, and the unsaturated bonds are easily thermally polymerized at high temperatures to generate insoluble impurities; on the other hand, due to the low solubility of LiH and vinyl lithium phosphate in carbonates, it is difficult to effectively separate the reaction product and the raw material, and the reaction yield is low.

[0005] Therefore, developing compounds with multiple advantageous functional groups or heteroatoms, simplifying the synthesis method, and improving the reaction yield and product purity is one of the difficulties in the current development and design of new additives. Summary of the invention

[0006] In order to solve the problems existing in the background technology, the present invention provides a new type of unsaturated phosphate-based lithium fluoroborate for use in an electrolyte, which contains multiple advantageous functional groups such as F, P, B and unsaturated bonds, and can form stable SEI film and CEI film at the positive and negative electrode interfaces, which can effectively reduce the initial impedance of the battery, reduce storage gas production, and further improve the cycle performance of the battery.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] An application of unsaturated phosphate-based lithium fluoroborate in an electrolyte, specifically, adding the unsaturated phosphate-based lithium fluoroborate represented by the following structure (I) into the electrolyte in an amount of 0.01 to 15 wt % of the total mass of the electrolyte:

[0009]

[0010] In the formula, R is selected from C2-C4 alkenyl, C2-C4 alkynyl, C2-C4 haloalkenyl or C2-C4 haloalkynyl; preferably, R is selected from C2-C4 alkenyl or C2-C4 alkynyl; more preferably, the unsaturated phosphate lithium fluoroborate is selected from at least one of the following structures:

[0011]

[0012] Preferably, the unsaturated lithium phosphate fluoroborate of the present invention is added to the electrolyte in an amount of 0.1 to 10 wt % of the total mass of the electrolyte; more preferably, the unsaturated lithium phosphate fluoroborate is added to the electrolyte in an amount of 0.5 to 5.0 wt % of the total mass of the electrolyte.

[0013] The electrolyte of the present invention further comprises:

[0014] A main lithium salt, wherein the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide, and the molar concentration in the electrolyte is 0.4 to 1.6 mol / L; preferably, the main lithium salt is lithium hexafluorophosphate or lithium bis(fluorosulfonyl)imide, and the molar concentration in the electrolyte is 0.6 to 1.2 mol / L;

[0015] A non-aqueous solvent, wherein the non-aqueous organic solvent is a combination of a cyclic solvent and a linear solvent, wherein the cyclic solvent is selected from at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, γ-butyrolactone or δ-valerolactone; and the linear solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, ethyl propionate, n-propyl propionate and methyl propyl carbonate;

[0016] The basic additive is selected from at least one of fluoroethylene carbonate, ethylene carbonate, tris(trimethylsilyl) phosphate, 1,3-propane sultone, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)difluorophosphate or lithium difluorooxalatoborate, and the amount of any basic additive used accounts for 0.1 to 5.0 wt % of the total amount of the electrolyte.

[0017] In a preferred embodiment, the electrolyte comprises: 1.0-1.2 mol / L lithium hexafluorophosphate, 0.2-1.0 wt% 1,3-propane sultone and 1.0-2.0 wt% unsaturated lithium phosphate fluoroborate shown in structural formula I-1. Compared with adding unsaturated lithium phosphate fluoroborate alone, it can not only further reduce the storage gas production of the battery, but also improve the high temperature cycle performance.

[0018] In another preferred embodiment, the electrolyte comprises: 1.0-1.2 mol / L lithium hexafluorophosphate, 0.5-5.0 wt% fluoroethylene carbonate, 0.5-2.0 wt% lithium bis(fluorosulfonyl)imide and 1.0-2.0 wt% unsaturated lithium phosphate fluoroborate shown in structural formula I-1. Compared with the use of unsaturated lithium phosphate fluoroborate alone, it can not only reduce the initial impedance of the battery and improve the normal temperature and high temperature cycle performance, but also can further inhibit high temperature storage gas production and improve the comprehensive performance of the battery.

[0019] The present invention further provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and any one of the above-mentioned electrolytes.

[0020] The positive electrode active material is a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobalt oxide material or a lithium iron phosphate material. The nickel-cobalt-manganese ternary material is Li(Ni x Co y Mn z ) 2 , x>0, y>0, z>0, x+y+z=1, the nickel-cobalt-aluminum ternary material is Li(Ni x Co y Al z ) 2 , x>0, y>0, z>0, x+y+z=1; the negative electrode active material is one of a graphite negative electrode, a silicon-carbon negative electrode, and a lithium metal negative electrode.

[0021] The present invention also provides a method for preparing any of the above-mentioned unsaturated phosphate lithium fluoroborate, the preparation method comprising the following steps:

[0022] (1) in a first solvent, an unsaturated phosphonic acid reacts with an inorganic lithium salt to obtain an unsaturated lithium phosphonate reaction solution, wherein the inorganic lithium salt is selected from at least one of lithium carbonate, lithium bicarbonate, lithium oxide, or lithium hydroxide; preferably lithium bicarbonate, lithium oxide, or lithium hydride, and more preferably lithium carbonate;

[0023] Taking lithium carbonate as an example, the reaction formula is as follows:

[0024]

[0025] Wherein R is defined as above;

[0026] (2) Boron trifluoride gas or a boron trifluoride complex is introduced into the unsaturated lithium phosphonate reaction solution to obtain an unsaturated lithium phosphate fluoroborate reaction solution, and the reaction formula is as follows:

[0027]

[0028] The definition of R in the formula is the same as described above.

[0029] In step (1), inorganic lithium salt and unsaturated phosphonic acid are used as raw materials, and the reaction heat is reduced by controlling the reaction temperature and feed ratio, thereby avoiding thermal polymerization of unsaturated bonds in the raw materials or reaction products to form dimers or even polymers, thereby improving the reaction yield and product purity.

[0030] Therefore, in step (1), the molar ratio of lithium in the inorganic lithium salt to the unsaturated phosphonic acid is (1.6-2.2):1, preferably (1.8-2.1):1, and more preferably about 2:1.

[0031] Meanwhile, the reaction temperature in step (1) is controlled to be -10 to 50°C, and the reaction time is 0.5 to 24 hours; preferably, the reaction temperature is 0 to 10°C, and the reaction time is 10 to 12 hours.

[0032] In step (1), the first solvent is selected from at least one of water, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, ether, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide or propionitrile, preferably at least one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0033] In step (2) of the present invention, unsaturated lithium phosphonate reacts with boron trifluoride gas or boron trifluoride complex to obtain unsaturated lithium phosphate fluoroborate reaction liquid, and the reaction liquid is concentrated by vacuum distillation to obtain unsaturated lithium phosphate fluoroborate, and the vacuum distillation temperature is 0 to 60° C., preferably 20 to 30° C. Due to the solvation of the unsaturated lithium phosphate fluoroborate, the unsaturated lithium phosphate fluoroborate obtained after vacuum distillation and concentration is a concentrated solution.

[0034] Specifically, in step (2), the boron trifluoride complex is selected from at least one of a boron trifluoride ethyl ether complex, a boron trifluoride glycol dimethyl ether complex, a boron trifluoride dimethyl carbonate complex, a boron trifluoride pyridine complex, a boron trifluoride ethylamine complex, a boron trifluoride butyl ether complex, a boron trifluoride methyl ether complex, a boron trifluoride acetonitrile complex, a boron trifluoride piperidine complex, a boron trifluoride phenol complex, a boron trifluoride tetrahydrofuran complex, a boron trifluoride dimethyl sulfide complex or a boron trifluoride morpholine complex.

[0035] In step (2), the molar ratio of unsaturated lithium phosphate to boron trifluoride or boron trifluoride complex is 1:(1.8-3), preferably the molar ratio is 1:(1.9-2.5), and more preferably the molar ratio is 1:(2.0-2.2).

[0036] In step (2), the reaction temperature is 0-50°C, and the reaction time is 0.5-24h; preferably, the reaction temperature is 10-30°C, and the reaction time is 2-4h.

[0037] Compared with the prior art, the present invention has the following technical effects:

[0038] 1. The present invention provides a method for preparing unsaturated lithium phosphate fluoroborate, which has simple process and high reaction yield. By optimizing the reaction conditions, the generation of polymers is reduced, and the reaction yield and product purity are further improved.

[0039] 2. The present invention proposes the use of unsaturated lithium phosphate fluoroborate in lithium ion battery electrolyte, which can form a film on the positive and negative electrodes of the battery, reduce the initial impedance of the battery, reduce the gas production during high-temperature storage, and improve the battery's room-temperature and high-temperature cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the NMR nuclear magnetic hydrogen spectrum of the lithium salt 1# prepared in Example 1 of the present invention;

[0041] Figure 2 This is the NMR nuclear magnetic fluorine spectrum of the lithium salt 1# prepared in Example 1 of the present invention;

[0042] Figure 3 This is the NMR nuclear magnetic phosphorus spectrum of lithium salt 1# prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0044] Example 1

[0045] This embodiment provides a method for preparing lithium ethylene phosphate trifluoroborate (I-1), which specifically comprises the following steps:

[0046] (1) In a drying room with a dew point of -40°C, 0.1 mol (7.40 g) of lithium carbonate and 100 g of DMC solvent were added to a reaction bottle, and then stirred in a 0°C low-temperature cold bath for 30 min to cool the reaction solution to 0°C; 0.1 mol (10.80 g) of vinylphosphonic acid was dissolved in 10 g of DMC, and slowly added to the reaction solution through a constant pressure dropping funnel, and reacted at 0°C for 10 h to obtain a solution containing lithium vinylphosphonate;

[0047] (2) Add 0.21 mol (33.18 g) of dimethyl boron trifluoride carbonate complex to the above solution containing lithium vinyl phosphate, stir at room temperature for 4 h, filter out insoluble solids, and remove excess DMC solvent and BF by vacuum distillation. 3 , and then remove water with a dry molecular sieve for 30 minutes, and finally obtain a DMC concentrate containing compound (I-1), which is recorded as lithium salt 1#.

[0048] Figure 1 , Figure 2 and Figure 3 The NMR spectrum of lithium salt 1# is given, where Figure 1 is the H spectrum, where δ = 5.7-6.2 ppm (m, 3H), corresponding to the H on the vinyl group, and δ = 3.66 ppm (s), corresponding to the methyl hydrogen on the DMC; Figure 2 For the F spectrum, a peak was observed at δ = -148.05 ppm; Figure 3 The peak is observed at δ=11.79ppm for the P spectrum. The structure of the compound was optimized using the DFT / B3LYP function and the 6-31** basis set, and the NMR peak position of the above compound was calculated using the DFT / B3LYP function and the 6-311** basis set. The calculated results were analyzed in coordination with the test results, and matched the above NMR spectrum results with a high degree of credibility. Therefore, it can be confirmed that the compound in lithium salt 1# is compound (I-1).

[0049] Further calculation by H NMR spectrum showed that the concentration of compound (I-1) in DMC solution was 37.6 wt %. A total of 66.73 g of vacuum distillation concentrate was obtained. The actual mass of compound (I-1) was 25.09 g (0.098 mol). The reaction yield was 98%.

[0050] Example 2

[0051] The operation of this example is the same as that of Example 1, except that in step (1), the amount of raw material lithium carbonate is adjusted to 0.08 mol (5.92 g), and finally a DMC concentrate containing compound (I-1) is obtained, which is the same as that of Example 1 and is recorded as lithium salt 1#.

[0052] The mass of the compound (I-1) actually obtained was 19.46 g (0.076 mol), and the reaction yield was 95%.

[0053] Example 3

[0054] The operation of this example is the same as that of Example 1, except that in step (1), the raw material lithium carbonate is replaced by lithium oxide in an amount of 0.1 mol (3.0 g), and finally a DMC concentrate containing compound (I-1) is obtained, which is the same as that of Example 1 and is recorded as lithium salt 1#.

[0055] The mass of the compound (I-1) actually obtained was 24.05 g (0.093 mol), and the reaction yield was 93%.

[0056] Example 4

[0057] The operation of this embodiment is the same as that of embodiment 1, except that in step (2), there is no vacuum distillation to remove excess DMC and BF 3 Operation, to obtain a mixture containing compound (I-1) and BF 3 The DMC mixed solution is recorded as lithium salt 2#.

[0058] The concentration of compound (I-1) in DMC solution was calculated by H NMR spectrum to be 21.02%. After filtering out insoluble matter, 117.76 g of reaction solution was obtained. The actual mass of compound (I-1) was 25.42 g (0.098 mol), and the reaction yield was 98%.

[0059] Example 5

[0060] The operation of this example is the same as that of Example 1, except that in step (1), the DMC used in the reaction is replaced by DEC to obtain a DEC concentrate containing compound (I-1), which is recorded as lithium salt 3#

[0061] The concentration of compound (I-1) in DEC solution was calculated by H NMR spectrum to be 39.4 wt%, and a total of 63.03 g of vacuum distillation concentrate was obtained. The actual mass of compound (I-1) was 24.83 g (0.097 mol), and the reaction yield was 97%.

[0062] Example 6

[0063] The operation of this example is the same as that of Example 1, except that in step (1), the raw material lithium carbonate is replaced by lithium hydroxide in an amount of 0.2 mol (4.8 g), and a DMC concentrate containing compound (I-1) is obtained, which is recorded as lithium salt 4#.

[0064] The mass of the compound (I-1) actually obtained was 24.05 g (0.093 mol), and the reaction yield was 93%.

[0065] Example 7

[0066] The operation of this example is the same as that of Example 1, except that in step (1), the raw material vinyl phosphate is replaced by allyl phosphate in an amount of 0.1 mol (12.20 g), and a DMC concentrate containing compound (I-2) is obtained, which is recorded as lithium salt 5#.

[0067] The actual mass of the compound (I-2) obtained was calculated to be 25.79 g (0.097 mol), and the reaction yield was 97%.

[0068] Example 8

[0069] The operation of this example is the same as that of Example 1, except that in step (1), the raw material vinyl phosphate is replaced by butynyl phosphate in an amount of 0.1 mol (13.40 g), and a DMC concentrate containing compound (I-6) is obtained, which is recorded as lithium salt 6#.

[0070] The actual mass of the compound (I-6) obtained was calculated to be 26.16 g (0.094 mol), and the reaction yield was 94%.

[0071] Comparative Example 1

[0072] The operation of this comparative example is the same as that of Example 1, except that the reaction in step (1) is carried out without a cold bath, and the reaction temperature is about 25° C. However, since the reaction is an exothermic reaction, the temperature rises sharply during the reaction.

[0073] The mass of the compound (I-1) actually obtained was 22.91 g (0.097 mol), and the reaction yield was 89.5%.

[0074] Comparative Example 2

[0075] This comparative example is used to obtain lithium ethylene phosphate. The specific operation is as follows: after the reaction of step (1) of Example 1 is completed, the insoluble matter generated by the reaction is filtered, and washed with DMC, and then dried to obtain lithium ethylene phosphate shown in the following structure (II):

[0076]

[0077] 2. Electrolyte

[0078] Preparation of basic electrolyte 1: In a glove box filled with argon (water content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were evenly mixed in a mass ratio of EC:EMC:DEC=3:5:2, and then lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution to a molar concentration of 1.0 mol / L to obtain a basic electrolyte.

[0079] Application Example 1: In a basic electrolyte, lithium salt 1# is used to add 0.5 wt % of compound (I-1) to obtain an electrolyte.

[0080] Application Example 2: In a basic electrolyte, 1.0 wt% of compound (I-1) is added using lithium salt 1# to obtain an electrolyte.

[0081] Application Example 3: In a basic electrolyte, 2.0 wt% of compound (I-1) is added using lithium salt 1# to obtain an electrolyte.

[0082] Application Example 4: In a basic electrolyte, 5.0 wt % of compound (I-1) was added using lithium salt 1# to obtain an electrolyte.

[0083] Application Example 5: In a basic electrolyte, 1.0 wt% of compound (I-1) and 1.0 wt% of vinylene carbonate (VC) were added using lithium salt 1# to obtain an electrolyte.

[0084] Application Example 6: In a basic electrolyte, 1.0 w% t of compound (I-1) and 1.0 wt% of 1,3-propane sultone (PS) were added using lithium salt 1# to obtain an electrolyte.

[0085] Application Example 7: In a basic electrolyte, 1.0 w% t of compound (I-1) and 2.0 wt% of fluoroethylene carbonate (FEC) were added using lithium salt 1# to obtain an electrolyte.

[0086] Application Example 8: In a basic electrolyte, 1.0 wt% of compound (I-1) is added using lithium salt 2# to obtain an electrolyte.

[0087] Application Example 9: In a basic electrolyte, 1.0 wt% of compound (I-1) is added using lithium salt 3# to obtain an electrolyte.

[0088] Application Example 10: In a basic electrolyte, 1.0 wt% of compound (I-1) is added using lithium salt 4# to obtain an electrolyte.

[0089] Application Example 11: In a basic electrolyte, 1.0 wt% of compound (I-2) is added using lithium salt 5# to obtain an electrolyte.

[0090] Application Example 12: In a basic electrolyte, 1.0 wt% of compound (I-6) is added using lithium salt 6# to obtain an electrolyte.

[0091] Application Example 13: In a basic electrolyte, 1.0 wt% of compound (I-1), 1.0 wt% of fluoroethylene carbonate (FEC) and 1.0 wt% of lithium bis(fluorosulfonyl)imide (LiFSI) are added using lithium salt 1# to obtain an electrolyte.

[0092] Application Example 14: In a basic electrolyte, 2.0 wt% of compound (I-1) is added using lithium salt 4# to obtain an electrolyte.

[0093] In Application Example 15, 5.0 wt% of compound (I-1) is added to a basic electrolyte using lithium salt 4# to obtain an electrolyte.

[0094] Application Comparative Example 1: The basic electrolyte is not treated in any way to obtain an electrolyte.

[0095] Application Comparative Example 2: In the basic electrolyte, 1.0 wt% VC was added to obtain an electrolyte.

[0096] Application Comparative Example 3: In the basic electrolyte, 1.0 wt% of PS was added to obtain an electrolyte.

[0097] Application Comparative Example 4: In the basic electrolyte, 2.0 wt% of FEC was used to obtain an electrolyte.

[0098] Application Comparative Example 4: In the basic electrolyte, 0.2 wt % of lithium ethylene phosphate is added to obtain an electrolyte.

[0099] 2. Electrochemical performance test

[0100] The electrolytes of the above application examples and comparative examples are respectively made into soft-pack lithium-ion batteries with a capacity of 1500 mAh. The lithium-ion batteries include a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and battery auxiliary materials. The positive electrode active material is a nickel-cobalt-manganese ternary material Li (Ni 0.8 Co 0.1 Mn 0.1 ) 2 , the negative electrode active material is artificial graphite.

[0101] The preparation process is as follows: the positive electrode sheet, the separator and the negative electrode sheet are wound together into a core, which is sealed with an aluminum-plastic film and then baked so that the moisture content of the electrode meets the requirements. After baking, the battery cell is injected with electrolyte, and the finished soft-pack battery cell is obtained through the steps of standing, forming, capacity separation and aging.

[0102] The prepared lithium-ion power battery (soft-pack battery cell) was subjected to performance testing. The specific test items and methods are as follows:

[0103] (1) 60℃ high temperature storage test: Before storage, cycle 1 cycle at 0.5C / 0.5C at room temperature, record the discharge capacity, internal resistance and volume of the first cycle, then charge to 4.20V at 0.5C constant current, and charge at constant voltage until the current drops to 0.05C, stand in a 60℃ constant temperature oven for 60 days, then cycle 2 cycles at 0.5C / 0.5C at room temperature, record the discharge capacity of the first cycle after high temperature standing, the discharge capacity of the second cycle, the internal resistance and volume after storage. Calculate the capacity retention rate, capacity recovery rate, internal resistance growth rate and volume expansion rate of the battery after storage according to the following formula:

[0104] Capacity retention rate = discharge capacity of the first cycle after high-temperature standing (after storage) / discharge capacity of the first cycle (before storage) * 100%.

[0105] Capacity recovery rate = discharge capacity of the second cycle after high-temperature standing (after storage) / discharge capacity of the first cycle (before storage) * 100%.

[0106] Volume expansion ratio = (volume after storage - volume before storage) / volume before storage * 100%.

[0107] (2) 25°C high temperature cycle test: The battery is cycled at a charge and discharge current of 1C / 1C in a room temperature environment of 25±1°C, and the discharge capacity per week is calculated. The cycle is stopped when the capacity retention rate is less than 80%.

[0108] (3) 45°C high temperature cycle test: The battery is cycled in a 45±1°C oven at a charge and discharge current of 1C / 1C, and the discharge capacity per week is calculated. The cycle is stopped when the capacity retention rate is less than 80%.

[0109] The test results are shown in Table 1 below:

[0110] Table 1 Battery performance test results

[0111]

[0112]

[0113] According to the data in Table 1 above, by comparing application examples 1 to 4 and comparative application example 1, it can be seen that the use of compound (I-1) as an electrolyte additive can reduce the initial impedance of the battery, improve the normal temperature and high temperature cycle performance, and also has an excellent storage gas generation inhibition effect. As the amount of lithium salt added gradually increases, within a certain range, the overall performance of the battery gradually improves, but as the content further increases, some performance begins to decline, and the optimal usage amount is around 1.0 to 2.0 wt%. In the comparative application example, the solubility of compound (II) in the electrolyte is only 0.2 wt%, and the addition amount of 1.0 wt% cannot be reached, otherwise solids will precipitate, and its effect on improving battery performance is weak, while compound (I-1) has good solubility in the solvents used in the electrolyte, and the improvement of the overall performance of the battery is more obvious, and it has a wider range of applications and practical value.

[0114] By comparing Application Examples 2, 5 to 7, and 13 with Application Comparative Example 1, it can be seen that the combined use of compound (I-1) and basic additives such as VC, PS, FEC, and LiFSI can further improve the overall performance of the battery.

[0115] Comparing application examples 2, 8 and 10, in application example 8, since lithium salt 2# was not subjected to vacuum distillation, a small amount of BF 3 , the H generated by the reaction of lithium hydroxide and acid in Example 10 is used 2 O is large in amount and difficult to remove with molecular sieves, but BF 3 and H 2 The presence of O will deteriorate the storage gas generation inhibition effect and cycle performance. Further comparison of Application Example 10, Application Example 14 and Application Example 15 shows that as the amount of lithium salt 2# used increases, the higher the water content in the electrolyte, the more obvious the deterioration of the battery performance. Therefore, in the preparation process, it is necessary to reduce the presence of impurities as much as possible by selecting suitable raw materials and reasonable post-processing schemes, so as to improve the reaction efficiency and maximize the effect of the substances in the application process.

Claims

1. Application of unsaturated phosphate lithium fluoroborate in electrolyte, Features: Unsaturated lithium phosphate fluoroborate represented by the following structure (I) is added to the electrolyte in an amount of 0.01 to 15 wt % of the total mass of the electrolyte: In the formula, R is selected from C2-C4 alkenyl, C2-C4 alkynyl, C2-C4 haloalkenyl or C2-C4 haloalkynyl.

2. Use of the unsaturated phosphate lithium fluoroborate according to claim 1 in an electrolyte, Features: The unsaturated phosphate lithium fluoroborate is selected from at least one of the following structures:

3. Use of the unsaturated phosphate-based lithium fluoroborate according to claim 1 in an electrolyte, Features: The unsaturated phosphate-based lithium fluoroborate is added to the electrolyte in an amount of 0.5-5.0 wt % of the total mass of the electrolyte.

4. Use of the unsaturated lithium phosphate fluoroborate according to any one of claims 1 to 3 in an electrolyte, Features: The electrolyte also includes: A main lithium salt, wherein the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; A non-aqueous solvent, wherein the non-aqueous organic solvent is a combination of a cyclic solvent and a linear solvent, wherein the cyclic solvent is selected from at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, γ-butyrolactone or δ-valerolactone; and the linear solvent is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, ethyl propionate, n-propyl propionate and methyl propyl carbonate; The basic additive is selected from at least one of fluoroethylene carbonate, ethylene carbonate, tris(trimethylsilyl) phosphate, 1,3-propylene sultone, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)difluorophosphate or lithium difluorooxalatoborate, and the amount of any basic additive used accounts for 0.1 to 5.0% of the total amount of the electrolyte.

5. A lithium ion battery comprising a positive electrode, a negative electrode, and a separator. Features: The lithium-ion battery further comprises the electrolyte according to any one of claims 1-4.

6. The method for preparing the unsaturated lithium phosphate fluoroborate according to any one of claims 1 to 4, Features: The preparation method comprises: (1) in a first solvent, an unsaturated phosphonic acid reacts with an inorganic lithium salt to obtain an unsaturated lithium phosphonate reaction solution, wherein the inorganic lithium salt is selected from at least one of lithium carbonate, lithium bicarbonate, lithium oxide or lithium hydroxide; (2) Boron trifluoride gas or a boron trifluoride complex is introduced into the unsaturated lithium phosphonate reaction solution to obtain an unsaturated lithium phosphate fluoroborate reaction solution.

7. The method for preparing the unsaturated phosphate lithium fluoroborate according to claim 6, Features: In step (1), the molar ratio of lithium in the inorganic lithium salt to the unsaturated phosphoric acid is (1.6-2.2):

1.

8. The method for preparing unsaturated phosphate lithium fluoroborate according to claim 6, Features: In step (1), the reaction temperature is -10 to 50°C and the reaction time is 0.5 to 24 hours.

9. The method for preparing unsaturated phosphate lithium fluoroborate according to claim 6, Features: The first solvent is selected from at least one of water, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, methyl propionate, γ-butyrolactone, ethyl ether, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide or propionitrile.

10. The method for preparing unsaturated phosphate lithium fluoroborate according to claim 6, Features: In step (2), the boron trifluoride complex is selected from at least one of a boron trifluoride ethyl ether complex, a boron trifluoride glycol dimethyl ether complex, a boron trifluoride dimethyl carbonate complex, a boron trifluoride pyridine complex, a boron trifluoride ethylamine complex, a boron trifluoride butyl ether complex, a boron trifluoride methyl ether complex, a boron trifluoride acetonitrile complex, a boron trifluoride piperidine complex, a boron trifluoride phenol complex, a boron trifluoride tetrahydrofuran complex, a boron trifluoride dimethyl sulfide complex or a boron trifluoride morpholine complex.

11. The method for preparing unsaturated phosphate lithium fluoroborate according to claim 6, Features: In step (2), the molar ratio of unsaturated lithium phosphonate to boron trifluoride gas or boron trifluoride complex is 1:(1.8-3).

12. The method for preparing unsaturated phosphate lithium fluoroborate according to claim 6, Features: In step (2), the reaction temperature is 0 to 50° C. and the reaction time is 0.5 to 24 h.

13. The method for preparing unsaturated phosphate lithium fluoroborate according to claim 6, Features: The unsaturated lithium phosphate fluoroborate reaction solution obtained in step (2) is subjected to reduced pressure distillation to obtain unsaturated lithium phosphate fluoroborate, and the reduced pressure distillation temperature is 0 to 60°C.

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