Preparation method and application of novel annular boron-containing metal salt compound

Abstract

The invention discloses a preparation method and application of a novel annular boron-containing metal salt compound, and the preparation method comprises the following steps: (1) salinization: in a first solvent, squaric acid and inorganic metal salt react to obtain lithium squarate or sodium squarate; (2) complexing: in a second solvent, reacting lithium squarate or sodium squarate with a boron trifluoride / boron trifluoride complex to obtain a reaction solution of a novel annular boron-containing metal salt compound at least containing a structure shown as a formula (I): in a # imgabs0 # formula, M is Li or Na, and n is a positive integer selected from 1-6; the reaction liquid comprises at least one novel annular boron-containing metal salt compound with a structure shown in a formula (I). The novel annular boron-containing metal salt compound provided by the invention simultaneously contains a squaric acid four-membered ring and a boron-oxygen structure-containing multi-membered ring, has a stable film-forming structure and more lithium / sodium ion holes, not only remarkably improves the high-temperature performance of the battery, but also can effectively inhibit impedance increase in the cycle process of the battery, and is obvious in low-temperature performance advantage.

Description

Technical Field

[0001] The invention relates to the field of metal ion battery electrolytes, and in particular to a preparation method of a novel cyclic boron-containing metal salt compound and an application thereof as an electrolyte additive. Background Art

[0002] The new energy industry is developing rapidly, and good high-temperature and low-temperature performance of batteries are of great significance to electric vehicles. As an indispensable component of metal-ion batteries, electrolyte additives are mainly responsible for building a stable electrode / electrolyte interface film to achieve electronic insulation and facilitate ion transmission. Under the influence of different functional groups of additives, the composition and structure of the battery interface film change, ultimately affecting the high-temperature and low-temperature performance of the battery.

[0003] Organic ester additives significantly improve the high-temperature performance of batteries. Among them, sulfur-containing organic ester additives such as 1,3-propane sultone and methylene disulfonate have excellent effects in inhibiting gas production and improving high-temperature performance, and have been widely used. Its reduction products include Li 2 SO 3 、(CH-CH 2 -CH 2 -OSO 3 Li) 2 The passivation layer composed of these substances has strong polarity and can improve the stability of the SEI film of the graphite negative electrode. However, this type of additive significantly increases the impedance of the negative electrode, especially when the addition amount reaches more than 1%, it has a relatively large impact on the battery's rate amplification, low-temperature charging and discharging performance.

[0004] Salt additives significantly improve the low temperature performance of batteries, among which P-containing salt additives such as lithium difluorophosphate and lithium difluorobisoxalate phosphate have the best effect. x PF y O z (M is Li or Na) and other ions have high conductivity, which can effectively improve the cycle stability, rate performance and low temperature performance of the battery. However, P-salt additives also have many limitations in the application process, such as low solubility, low film toughness and flatness, and poor high temperature performance.

[0005] The above-mentioned existing single additive cannot meet the high temperature performance and low temperature performance of the battery at the same time. In order to meet the high and low temperature performance of the battery at the same time, the above-mentioned two types of additives are generally used in combination to solve the problem of balancing high and low temperature performance. However, the combined effect is still not as expected. Therefore, it is necessary to develop an additive with both high and low temperature performance.

[0006] Patent CN114230586A of Beijing Weilan New Energy Technology Co., Ltd. discloses the synthesis and application of an unsaturated carbon ring boron trifluoride salt electrolyte. In Example 2, the raw material 3,4-dihydroxy-3-cyclobutene-1,2-dione is first complexed with a boron trifluoride ether complex and then reacted with butyl lithium to obtain a chain boron trifluoride lithium squarate, which can reduce battery impedance and improve battery low-temperature performance, but is detrimental to battery high-temperature performance.

[0007] Ube Industries' patent JP2015138662 A discloses cyclic lithium boron trifluoride squarate, which can be used in electrolytes to improve the properties of batteries used under high temperature and high voltage conditions, and can inhibit gas generation and capacity loss during storage, but the preparation method of the substance is not disclosed.

[0008] Therefore, developing new additives that take into account both high-temperature and low-temperature performance remains an important direction of electrolyte research. Summary of the invention

[0009] In order to solve the above technical problems, the present invention proposes a preparation method of a novel cyclic boron-containing metal salt compound and its application in an electrolyte, which can significantly improve the high-temperature performance of the battery, especially inhibit gas production during high-temperature storage, while also improving the low-temperature performance of the battery.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] A method for preparing a novel cyclic boron-containing metal salt compound, the preparation method comprising:

[0012] (1) a salification step: in a first solvent, a squaric acid and an inorganic metal salt react to obtain lithium squarate or sodium squarate, wherein the inorganic metal salt is selected from at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, sodium carbonate, sodium bicarbonate or sodium hydroxide;

[0013] The chemical reaction formula using lithium carbonate as an inorganic metal salt is as follows:

[0014]

[0015] The chemical reaction formula using lithium carbonate as an inorganic metal salt is as follows:

[0016]

[0017] (2) Complexation step: In a second solvent, lithium squarate or sodium squarate and boron trifluoride / boron trifluoride complex react to obtain a reaction solution containing at least a novel cyclic boron-containing metal salt compound having a structure represented by the following formula (I):

[0018]

[0019] In the formula, M is Li or Na, and n is a positive integer selected from 1 to 6;

[0020] The reaction solution comprises at least one novel cyclic boron-containing metal salt compound having a structure shown in formula (I), specifically, at least one of the novel cyclic boron-containing metal salt compounds having the following structures:

[0021]

[0022]

[0023] In formulas (I-1), (I-2), (I-3), (I-4), (I-5), and (I-6), M is Li or Na.

[0024] The chemical reaction formula with the above compound (I-1) as the main product is exemplified as follows:

[0025]

[0026] Wherein, M is Li or Na.

[0027] In step (2), boron trifluoride / boron trifluoride complex represents boron trifluoride or boron trifluoride complex. The boron trifluoride complex is selected from at least one of boron trifluoride ether complex, boron trifluoride glycol dimethyl ether complex, boron trifluoride dimethyl carbonate complex, boron trifluoride ethylamine complex, boron trifluoride butyl ether complex, boron trifluoride methyl ether complex, boron trifluoride acetonitrile complex or boron trifluoride tetrahydrofuran complex. Preferably, the boron trifluoride / boron trifluoride complex is selected from boron trifluoride gas, boron trifluoride dimethyl carbonate complex or boron trifluoride ether complex. More preferably, squarate and boron trifluoride gas are reacted.

[0028] Furthermore, the reaction solution in step (2) may also contain at least one of the compounds having structures represented by the following formula (II), (III) or (IV):

[0029]

[0030] In formula (II), (III) and (IV), M is Li or Na.

[0031] In step (1), the first solvent is selected from water or a second solvent; the second solvent is selected from at least one of ethylene carbonate, propylene carbonate, 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.

[0032] The first solvent is preferably water. In this case, the squarate obtained in step (1) is dried to remove water and then used in the reaction of step (2). Of course, the first solvent can also be directly selected as the second solvent. In this case, after step (1) is completed, boron trifluoride / boron trifluoride complex can be directly added to carry out complex reaction.

[0033] Due to the solvation of the novel cyclic boron-containing metal salt compound, a second solvent generally exists in the product. Therefore, the second solvent is preferably a solvent available in the electrolyte, and specifically preferably at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate or propylene carbonate.

[0034] In the salting reaction of step (1) of the preparation method of the present invention, the molar ratio of squaric acid to inorganic metal salt is 1:(0.8-5); the reaction temperature is -20-90°C, and the reaction time is 1-24h. Preferably, the molar ratio of squaric acid to inorganic metal salt is 1:(1.5-3); the reaction temperature is 20-45°C, and the reaction time is 1-3h.

[0035] In the complexation reaction of step (2) of the preparation method of the present invention, the molar ratio of lithium squarate or sodium squarate to boron trifluoride / boron trifluoride complex is 1:(0.3-4), the reaction temperature is -20-90°C, and the reaction time is 1-24h. During the complexation reaction of lithium squarate or sodium squarate and boron trifluoride, a variety of different cyclic boron-containing salt compounds may be produced, including the above-mentioned compounds (I-1)-(I-6) and compound (II), compound (III), etc. By adjusting the reaction temperature, molar ratio, and reaction time, the product can be adaptively regulated.

[0036] For example, when the reaction temperature of step (2) is -20 to 45°C, especially -20 to 25°C, the reaction solution is mainly composed of oligomeric products (n value is small), especially compound (I-1) when n=1; specifically, based on the cyclic boron-containing metal salt compound (the content of the second solvent is not included), the reaction solution contains at least 85% by mass of the compound (I-1), preferably at least 95% by mass of the compound (I-1).

[0037] When the reaction temperature in step (2) is high, such as 45-90°C, especially 60-90°C, the content of highly polymerized products (with larger n value) in the reaction solution increases, such as the content of the above-mentioned compound (I-3) significantly increases to more than 2%.

[0038] According to the preparation steps of the novel cyclic boron-containing metal salt compounds, although the reaction solution of step (2) is mainly composed of cyclic boron-containing salt compounds, some chain boron-containing salt compounds (IV) are inevitably present. In order to further improve the product purity of the cyclic boron-containing salt compounds, the preparation method further includes:

[0039] (3) Crystallization step: After removing the second solvent and possible excess boron trifluoride in the reaction solution of step (2) by vacuum distillation, a concentrated solution is obtained, and a third solvent is added to the concentrated solution, and the solution is kept at -60 to 20°C for 0.5 to 144 hours to precipitate LiBF 4 or NaBF 4 The product is crystallized and filtered to obtain a novel cyclic boron-containing metal salt compound solution.

[0040] The concentrated solution is obtained by vacuum distillation, which can reduce the boiling point and prevent the product from decomposing. The third solvent is selected from at least one of dichloromethane, chloroform, tetrachloroethane, isopropanol, methyl tert-butyl ether or toluene, preferably dichloromethane and toluene.

[0041] Under the action of the third solvent, the chain boron-containing metal salt compound in the reaction solution undergoes cyclization and is transformed into a cyclic boron-containing metal salt compound, as shown in the following reaction formula:

[0042]

[0043] Wherein, M is Li or Na.

[0044] Preferably, the crystallization step can be completed by keeping warm at -20 to 0°C for 0.5 to 10 hours.

[0045] The new cyclic boron-containing metal salt compound solution obtained after crystallization and filtration contains a second solvent and a third solvent. For the convenience of product use, the third solvent can be removed by rotary evaporation 1 to 5 times to obtain a new cyclic boron-containing metal salt compound. Due to the solvation effect, the product contains a new cyclic boron-containing metal salt compound and a second solvent, and the mass concentration of the new cyclic boron-containing metal salt compound is between 5 and 70wt%. When the second solvent is a non-aqueous solvent commonly used in electrolytes, the product can be directly used in the preparation of electrolytes.

[0046] The present invention also proposes the application of the novel cyclic boron-containing metal salt compound prepared as above in an electrolyte, and the application comprises: adding the novel cyclic boron-containing metal salt compound into the electrolyte in a mass content of 0.1 to 15 wt % of the total mass of the electrolyte, preferably the mass content in the electrolyte is 0.2 to 10.0 wt %, more preferably the mass content in the electrolyte is 0.2 to 5.0 wt %, and most preferably the mass content in the electrolyte is 0.2 to 3.0 wt %.

[0047] Specifically, the electrolyte further includes:

[0048] An electrolyte salt, wherein the electrolyte salt is mainly a lithium salt or a mainly sodium salt, and the molar concentration in the electrolyte is 0.1 to 4.0 mol / L; the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, or lithium difluorobisoxalate phosphate; the main sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium perchlorate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium bisfluorosulfonyl imide, sodium bistrifluoromethylsulfonyl imide, sodium tetrafluorooxalate phosphate, sodium trioxalate phosphate, or sodium difluorobisoxalate phosphate;

[0049] A non-aqueous solvent, wherein the non-aqueous solvent is selected from at least one of C3-C6 carbonate or fluorinated carbonate compounds, C3-C8 carboxylic acid ester or fluorinated carboxylic acid ester compounds, sulfone compounds or ether compounds;

[0050] The basic additive is selected from at least one of sulfonate compounds, sulfate compounds, fluorocarbonate compounds, unsaturated carbonate compounds or fluorine-containing salt compounds.

[0051] Specifically, the sulfonate compound is selected from at least one of 1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1,4-butane sultone, methyl ethylene sulfonate, methyl fluorosulfonate or methylene bis(thienyl sulfonic acid) ester.

[0052] The sulfate compound is selected from vinyl sulfate and / or vinylidene sulfate;

[0053] The fluorinated carbonate compound is selected from at least one of fluorinated ethylene carbonate, trifluoropropylene carbonate or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0054] The unsaturated carbonate compound is selected from at least one of vinylene carbonate, ethyl acrylate, butyl acrylate or ethyl methacrylate;

[0055] The fluorine-containing salt compound is selected from at least one of difluorophosphate, bis(fluorosulfonyl)imide salt, and bis(difluoromethanesulfonyl)imide salt, and is different from the electrolyte salt.

[0056] Preferably, the base additive is selected from at least one of vinylene carbonate, vinyl sulfate or 1,3 propane sultone.

[0057] The present invention also provides a metal ion secondary battery, including a positive electrode, a negative electrode, a separator and an electrolyte. In particular, the electrolyte is an electrolyte formed by adding any one of the above-mentioned novel cyclic boron-containing metal salt compounds into the electrolyte with a mass content of 1-15 wt% based on the total mass of the electrolyte. Preferably, any one of the above-mentioned novel cyclic boron-containing metal salt compounds is added into the electrolyte with a mass content of 0.2-10 wt%, more preferably 0.2-5.0 wt%, and most preferably 0.2-3.0 wt% based on the total mass of the electrolyte.

[0058] In a specific embodiment, the cyclic boron-containing metal salt compound is a cyclic boron-containing lithium salt, which is added to the electrolyte of a lithium ion battery for application. The active material of the positive electrode of the lithium ion secondary battery is selected from nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium cobaltate materials or lithium iron phosphate materials, and the active material of the negative electrode is selected from graphite, silicon-carbon, silicon monoxide, silicon, tin, metallic lithium or their composite materials.

[0059] In another specific embodiment, the cyclic boron-containing metal salt compound is a cyclic boron-containing sodium salt, which is added to the electrolyte of a sodium ion battery for application. The active material of the positive electrode plate of the sodium ion secondary battery is selected from at least one of NaMn (1-x-y) Ni y M x O 2 (0≤x, y≤1, M is Cu, Fe, Co), sodium manganate, sodium vanadium phosphate, sodium fluorovanadate, sodium iron phosphate, sodium manganese phosphate, Na x MnFe(CN) 6 (0<x≤2), and the active material of the negative electrode plate is selected from at least one of hard carbon, carbon black, amorphous carbon, graphite, SnS 2 、Na 2 Ti 3 O 7 , silicon-based materials, metal oxides, metal sulfides or metallic sodium.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0061] 1. The present invention realizes the preparation of the novel cyclic boron-containing metal salt compound through a salification step and a complexation step in sequence, with simple operation, mild reaction and high yield.

[0062] 2. The present invention obtains a novel cyclic boron-containing metal salt compound mainly composed of compound (I-1) (≥85%) with high selectivity through the steps of salification, complexation and crystallization, and through reaction temperature control and reaction solvent selection. When the compound is used in an electrolyte, an armor structure interface film can be formed through the dual synergistic effect of the four-membered ring of the square acid and the multi-membered ring containing a boron-oxygen structure. The film has a strong film-forming ability, a stable film structure and a large number of ion holes, which can significantly improve the battery cycle and high-temperature storage performance, inhibit battery gas production, and improve the low impedance effect, effectively inhibit the impedance growth during the battery cycle, and improve the low temperature performance and initial DCR of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Attached Figure 1 The product 1 prepared in Example 1 of the present invention # of 19 F-NMR spectrum;

[0064] Attached Figure 2 The product 1 prepared in Example 1 of the present invention # of 11 B-NMR spectrum. DETAILED DESCRIPTION

[0065] 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.

[0066] Example 1

[0067] This embodiment provides a method for preparing a cyclic boron-containing lithium salt, which specifically comprises the following steps:

[0068] S1. Add 1 mol of squaric acid (purity 99%) to the reaction flask, add 100 mL of water as a solvent, start stirring to mix the system evenly; then add 1 mol of lithium carbonate to the reaction flask, react at 25 ° C for 4 hours, and dry and remove water to obtain lithium squarate;

[0069] S2. In a dry room with a dew point of -40°C, add 1 mol of lithium squarate (purity 99%) to a reaction bottle, use dimethyl carbonate as a solvent, start stirring to mix the system evenly; then pass 2 mol of boron trifluoride gas into the reaction bottle, react at 25°C for 1 hour, and obtain a reaction solution;

[0070] S3. Remove dimethyl carbonate and unreacted boron trifluoride from the reaction solution by vacuum distillation at a pressure of 2.67 kPa, control the vacuum distillation temperature to 60°C, and control the time to 0.5 h, and obtain a reaction concentrate due to solvation; add dichloromethane as the third solvent to the reaction concentrate, keep it at 0°C for 5 h, and precipitate LiBF 4 The crystals were filtered. The product 1 was obtained by repeated rotary evaporation at 40°C for 3 times to remove the third solvent. # .

[0071] Attached Figure 1 and attached Figure 2 Given product 1 # The NMR F spectrum and NMR B spectrum are shown in Figure 2. The NMR F spectrum is obtained by using LiBF 4 As a reference, the NMR F spectrum is shown below:

[0072] Cyclic boron salt compound (I-1, M is Li): δ = -152.34 ppm

[0073] Cyclic boron salt compound (I-2, M is Li): δ = -151.30 ppm

[0074] Cyclic boron salt compound (I-3, M is Li): δ = -150.98 ppm

[0075] Chain boron salt compounds (IV, M is Li): δ = -151.80 ppm

[0076] LiBF 4 :δ=-156.39ppm

[0077] NMR B spectrum using LiBF 4 As a reference, the NMR B spectrum is shown below:

[0078] Cyclic boron salt compound (I-1, M is Li): δ = -0.84 ppm

[0079] Cyclic boron salt compound (I-2, M is Li): δ = 1.98 ppm

[0080] Cyclic boron salt compound (I-3, M is Li): δ = 2.01 ppm

[0081] Chain boron salt compounds (IV, M is Li): δ = -1.79 ppm

[0082] LiBF 4 :δ=0.89ppm

[0083] In order to verify and confirm the compounds, theoretical calculations were performed on cyclic boron salt compounds (I-1, I-2, I-3, M is Li) and chain boron salt compounds (IV, M is Li), as well as compounds (II, M is Li) and compounds (III, M is Li). The DFT / B3LYP function and 6-31** basis set were used to optimize the structures of the compounds, and the DFT / B3LYP function and 6-311** basis set were used to calculate the nuclear magnetic peak positions of the above compounds. The calculation results were compared with the test results, as well as LiBF 4 The NMR peak position of the standard sample (F: δ = 156.39ppm, B: δ = 0.89ppm) was analyzed in tandem. It matches the above NMR results and has a high degree of credibility. Therefore, it can be confirmed that product 1 # The main compound is compound (I-1, M is Li), and it also includes compound (I-2, M is Li), compound (I-3, M is Li), compound (IV, M is Li), etc.

[0084] By integrating and calculating the peak area of ​​the NMR F spectrum, we can know that: Product 1 # In the above analysis, excluding the amount of dimethyl carbonate, the mass content of the cyclic boron-containing lithium salt (I-1) is 95.2wt%, the mass content of the chain boron-containing lithium salt (IV) is 2.7wt%, and the mass content of the remaining impurities (including compound (I-2, M is Li), compound (I-3, M is Li), etc.) is 2.1wt%.

[0085] Further area integral conversion was performed using the B spectrum, and it was found that the calculation results were consistent with those of the F spectrum, and the calculation credibility was high.

[0086] Example 2

[0087] The operation of this example is the same as that of Example 1, except that in the complexation step S2, the reaction temperature is increased from 25°C to 45°C, and other operations remain unchanged. The cyclic boron-containing lithium salt obtained is recorded as Product 2 # .

[0088] For product 2 # The nuclear magnetic F spectrum and nuclear magnetic B spectrum were tested, and the nuclear magnetic F spectrum is as follows:

[0089] Cyclic boron salt compound (I-1, M is Li): δ = -152.34 ppm

[0090] Cyclic boron salt compound (I-2, M is Li): δ = -151.30 ppm

[0091] Cyclic boron salt compound (I-3, M is Li): δ = -150.98 ppm

[0092] Chain boron salt compounds (IV, M is Li): δ = -151.80 ppm

[0093] LiBF4: δ = -156.39 ppm

[0094] The NMR B spectrum is shown below:

[0095] Cyclic boron salt compound (I-1, M is Li): δ = -0.84 ppm

[0096] Cyclic boron salt compound (I-2, M is Li): δ = 1.98 ppm

[0097] Cyclic boron salt compound (I-3, M is Li): δ = 2.01 ppm

[0098] Chain boron salt compounds (IV, M is Li): δ = -1.79 ppm

[0099] LiBF4: δ = 0.89 ppm

[0100] By integrating and calculating the peak area of ​​the NMR F spectrum, we can know that: Product 2 # In the above, excluding the amount of dimethyl carbonate, the mass content of the cyclic boron-containing lithium salt (I-1) is 90.2wt%, the mass content of the cyclic boron-containing lithium salt (I-2) is 4.8wt%, the content of the chain boron-containing lithium salt (IV) is 3.5wt%, and the content of the remaining impurities (compound I-3, etc., M is Li) is 1.5wt%. Further area integral conversion is performed through the B spectrum, and it is found that the results are consistent with the F spectrum, and the calculation reliability is high.

[0101] Example 3

[0102] The operation of this example is the same as that of Example 1, except that in the complexation step S2, the reaction temperature is increased from 25°C to 60°C, and other conditions remain unchanged. The cyclic boron-containing lithium salt is prepared and recorded as product 3 # .

[0103] The NMR F spectrum is shown below:

[0104] Cyclic boron salt compound (I-1, M is Li): δ = -152.34 ppm

[0105] Cyclic boron salt compound (I-2, M is Li): δ = -151.30 ppm

[0106] Cyclic boron salt compound (I-3, M is Li): δ = -150.98 ppm

[0107] Cyclic boron salt compound (I-4, M is Li): δ = -149.88 ppm

[0108] Chain boron salt compounds (IV, M is Li): δ = -151.80 ppm

[0109] Compound III (M is Li): δ 1 =-151.78ppm

[0110] δ 2 =-152.51ppm

[0111] LiBF 4 :δ=-156.39ppm

[0112] The NMR B spectrum is shown below:

[0113] Cyclic boron salt compound (I-1, M is Li): δ = -0.84 ppm

[0114] Cyclic boron salt compound (I-2, M is Li): δ = 1.98 ppm

[0115] Cyclic boron salt compound (I-3, M is Li): δ = 2.01 ppm

[0116] Cyclic boron salt compound (I-4, M is Li): δ = 2.5 ppm

[0117] Compound II (M is Li): δ = 3.01 ppm

[0118] Compound III (M is Li): δ = -0.54 ppm

[0119] δ=-1.75ppm

[0120] Chain boron salt compounds (IV, M is Li): δ = -1.79 ppm

[0121] LiBF4: δ = 0.89 ppm

[0122] For product 3 # By performing NMR F spectrum and NMR B spectrum detection and integrating the peak area of ​​NMR F spectrum, we can know that: Product 3 # In the above, excluding the amount of dimethyl carbonate, the cyclic boron-containing lithium salt (I-1) contains 82.4wt%, the cyclic boron-containing lithium salt (I-2) contains 6.8wt%, the cyclic boron-containing lithium salt (I-3) contains 4.4wt%, the cyclic boron-containing lithium salt (I-4) contains 2.1wt%, the chain boron-containing lithium salt (IV) contains 2.5wt%, and the content of other impurities (including compound (II, M is Li), compound (III, M is Li), etc.) is 1.8wt%.

[0123] Further area integral conversion was performed using the B spectrum, and it was found that the results were consistent with those of the F spectrum, and the calculation credibility was high.

[0124] Example 4

[0125] The operation of this embodiment is the same as that of embodiment 1, except that: in step S2, 3 mol of boron trifluoride gas is introduced, and other conditions remain unchanged, and the cyclic boron-containing lithium salt is prepared and recorded as product 4 # .

[0126] For product 4 # By performing NMR F spectrum and NMR B spectrum detection and integrating the peak area of ​​NMR F spectrum, we can know that: Product 4 # In the above, excluding the amount of dimethyl carbonate, the cyclic boron-containing lithium salt (I-1) contains 87.3wt%, the chain boron-containing lithium salt compound (IV) contains 9.8wt%, and the content of other impurities (compound (II, M is Li), compound (III, M is Li), etc.) is 2.9wt%.

[0127] Further area integral conversion was performed using the B spectrum, and it was found that the results were consistent with those of the F spectrum, and the calculation credibility was high.

[0128] Example 5

[0129] The operation of this example is the same as that of Example 1, except that in step S2, the reaction is carried out at 25° C. for 2 h, and other conditions remain unchanged, to prepare a cyclic boron-containing lithium salt, which is recorded as product 5. # .

[0130] By integrating and calculating the peak area of ​​the NMR F spectrum, we know that: Product 5 # In the above analysis, excluding the amount of dimethyl carbonate, the mass content of the cyclic boron-containing lithium salt (I-1) is 96.3wt%, the mass content of the chain boron-containing lithium salt (IV) is 2.5wt%, and the mass content of the remaining impurities (including compound (I-2, M is Li), compound (I-3, M is Li), etc.) is 1.2wt%.

[0131] Further area integral conversion was performed using the B spectrum, and it was found that the calculation results were consistent with those of the F spectrum, and the calculation credibility was high.

[0132] Example 6

[0133] The operation of this embodiment is the same as that of embodiment 1, except that in step S2, the reaction is carried out at 25° C. for 10 h, and other conditions remain unchanged, to prepare a cyclic boron-containing lithium salt, which is recorded as product 6. # .

[0134] By integrating and calculating the peak area of ​​the NMR F spectrum, we know that: Product 6 #In the above analysis, excluding the amount of dimethyl carbonate, the mass content of the cyclic boron-containing lithium salt (I-1) is 97.2wt%, the mass content of the chain boron-containing lithium salt (IV) is 1.5wt%, and the mass content of the remaining impurities (including compound (I-2, M is Li), compound (I-3, M is Li), etc.) is 1.3wt%.

[0135] Further area integral conversion was performed using the B spectrum, and it was found that the calculation results were consistent with those of the F spectrum, and the calculation credibility was high.

[0136] Example 7

[0137] The operation of this embodiment is the same as that of embodiment 1, except that in step S1, lithium carbonate is replaced with sodium carbonate, and other conditions remain unchanged, and the cyclic boron-containing sodium salt is prepared and recorded as product 7. # .

[0138] The product 7# sodium salt was tested by nuclear magnetic resonance and NaBF 4 Compare with standard samples;

[0139] Using NaBF 4 As a reference, the NMR F spectrum is shown below:

[0140] Cyclic boron salt compounds (I-1, M is Na): δ = -155.44 ppm

[0141] Cyclic boron salt compound (I-2, M is Na): δ = -153.31 ppm

[0142] Cyclic boron salt compound (I-3, M is Na): δ = -153.95 ppm

[0143] Chain boron salt compounds (IV, M is Na): δ = -154.78 ppm

[0144] NaBF 4 :δ=-159.99ppm

[0145] NMR B spectrum was obtained using NaBF 4 As a reference, the NMR B spectrum is shown below:

[0146] Cyclic boron salt compounds (I-1, M is Na): δ = -0.75 ppm

[0147] Cyclic boron salt compound (I-2, M is Na): δ = 1.83 ppm

[0148] Cyclic boron salt compound (I-3, M is Na): δ = 1.89 ppm

[0149] Chain boron salt compounds (IV, M is Na): δ = -1.63 ppm

[0150] NaBF 4 :δ=0.84ppm

[0151] Standard NaBF 4 The NMR F spectrum peak δ = -159.94ppm; the NMR B spectrum peak δ = 0.84ppm.

[0152] To verify and confirm the compounds, compound (I-1, M is Na) and compound (I-2, M is Na), as well as NaBF 4 Theoretical calculations were performed. The DFT / B3LYP function and 6-31** basis set were used to optimize the structure of the compound, and the DFT / B3LYP function and 6-311** basis set were used to calculate the NMR peak position of the above compound. The calculation results were compared with the test results, as well as NaBF 4 The NMR peak position of the standard sample (F: δ = -159.99ppm, B: δ = 0.84ppm) was analyzed in coordination, and it matched the above NMR results, which had a high degree of credibility. # The main compound is compound (I-1, M is Na), and it also includes compound (I-2, M is Na), compound (I-3, M is Na), compound (IV, M is Na), etc.

[0153] By integrating and calculating the peak area of ​​the NMR F spectrum, we know that: Product 7 # In the above analysis, excluding the amount of dimethyl carbonate, the mass content of the cyclic boron-containing sodium salt (I-1) is 95.8wt%, the mass content of the chain boron-containing sodium salt (IV) is 2.2wt%, and the mass content of the remaining impurities (including compound (I-2, M is Na), compound (I-3, M is Na), etc.) is 2.0wt%.

[0154] Further area integral conversion was performed using the B spectrum, and it was found that the calculation results were consistent with those of the F spectrum, and the calculation credibility was high.

[0155] Comparative Example 1

[0156] This comparative example provides a method for changing the reaction order and regulating the product ratio, which specifically comprises the following steps:

[0157] S1. Add 1 mol of squaric acid (purity 99%) to a reaction flask, add 100 mL of tetrahydrofuran as a solvent, start stirring to mix the system evenly; then pass 2 mol of boron trifluoride gas into the reaction flask, react at 60° C. for 1 h to obtain a reaction solution intermediate product, remove the tetrahydrofuran solvent by vacuum distillation to obtain a boron trifluoride squaric acid complex;

[0158] S2. In a dry room with a dew point of -40°C, add 14 ml of a hexane solution of butyl lithium (c = 1.6 mol / L) to a reaction bottle, use dimethyl carbonate as a solvent, start stirring to mix the system evenly; then add 1 mol of squaric acid (purity 99%) to the reaction bottle, react at 25°C for 1 hour, and obtain a reaction solution;

[0159] S3. Under the condition of 2.67 kPa, the dimethyl carbonate in the reaction solution was removed by vacuum distillation, the vacuum distillation temperature was controlled to 50 ° C, the time was controlled to 0.5 h, and the reaction concentrate was obtained by solvation; dichloromethane was added to the reaction concentrate as a third solvent, kept at 0 ° C for 5 h, and the third solvent was removed by evaporation and drying, recorded as control sample 1 # .

[0160] Integrate the peak area of ​​the NMR F spectrum and convert it to the reference sample 1 # It contains 15.2wt% of cyclic boron-containing lithium salt (I-1), 82.5wt% of chain boron-containing lithium salt (IV), and 2.3wt% of compound (II, M is Li), compound (III, M is Li), etc. Further area integration conversion by B spectrum was found to be consistent with the calculation results of F spectrum, and the calculation credibility was high.

[0161] Comparative Example 2

[0162] The operation of this comparative example is the same as that of Example 1, except that in the complexation step S2, the temperature is changed to 100°C, and other conditions remain unchanged. The product is recorded as control sample 2 # .

[0163] Ignoring the amount of dimethyl carbonate, control sample 2 # Among them, the cyclic boron-containing lithium salt (I-1) contains 72.4wt%, the cyclic boron-containing lithium salt (I-2) contains 12.8wt%, the cyclic boron-containing lithium salt (I-3) contains 7.4wt%, the cyclic boron-containing lithium salt (I-4) contains 3.1wt%, the chain boron-containing lithium salt (IV) contains 2.5wt%, and the content of other impurities (compound (II, M is Li), compound (III, M is Li), etc.) is 1.8wt%.

[0164] Comparative Example 3

[0165] The operation of this comparative example is the same as that of Example 1, except that: in step S2, 0.1 mol of boron trifluoride gas is introduced, and other conditions remain unchanged. A large amount of insoluble lithium squarate is found, and the product is recorded as control sample 3 # .

[0166] The peak area of ​​the NMR F spectrum was integrated and converted to the control sample 3 #It contains 91.3wt% of cyclic boron-containing lithium salt (I-1), 5.6wt% of chain boron-containing lithium salt (IV) and 3.1% of other impurities (compound (II, M is Li), compound (III, M is Li), etc.). And through the area integration conversion of B spectrum, it is found that the results are uniform and the calculation credibility is high.

[0167] Comparative Example 4

[0168] The operation of this comparative example is the same as that of comparative example 1, except that butyl lithium is replaced by butyl sodium, and other conditions remain unchanged.

[0169] The peak area of ​​the NMR F spectrum was integrated and converted to the control sample 4 # It contains 14.2wt% of cyclic boron-containing sodium salt (I-1), 83.4wt% of chain boron-containing sodium salt (IV), and 2.4wt% of other impurities (compound (II, M is Na), compound (III, M is Na), etc.). Further area integration conversion was performed through B spectrum, and it was found that the calculation results were consistent with those of F spectrum, and the calculation reliability was high.

[0170] Application Examples

[0171] Preparation of basic electrolyte 1: In a glove box filled with argon (water content <5ppm, oxygen content <10ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of EC:EMC:DEC=4:4:2, and then lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution. 6 ) to a molar concentration of 1.0 mol / L to obtain basic electrolyte 1.

[0172] Preparation of basic electrolyte 2: In a glove box filled with argon (water content <5ppm, oxygen content <10ppm), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of PC:EMC:DEC = 7:10:1, and sodium hexafluorophosphate (NaPF 6 ) to NaPF 6 The molar concentration is 1.0 mol / L, and basic electrolyte 2 is obtained.

[0173] Application Example 1

[0174] Add 0.2wt% of product 1 into the basic electrolyte 1 # , and obtain the electrolyte of this embodiment.

[0175] Application Example 2

[0176] Add 1wt% product 1 to the base electrolyte # , the electrolyte of this embodiment is obtained.

[0177] Application Example 3

[0178] Add 2wt% product 1 to the base electrolyte # , and obtain the electrolyte of this embodiment.

[0179] Application Example 4

[0180] Add 3wt% product 1 to the base electrolyte # , and obtain the electrolyte of this embodiment.

[0181] Application Example 5

[0182] Add 1wt% product 2 to the base electrolyte 1 # , and obtain the electrolyte of this embodiment.

[0183] Application Example 6

[0184] Add 1wt% product 3 to the base electrolyte # , and obtain the electrolyte of this embodiment.

[0185] Application Example 7

[0186] Add 1wt% product 4 to the base electrolyte # , and obtain the electrolyte of this embodiment.

[0187] Application Example 8

[0188] Add 1wt% product 1 to the base electrolyte # and 1%wt of vinylene carbonate (VC) to obtain the electrolyte of this embodiment.

[0189] Application Example 9

[0190] Add 1wt% product 1 to the base electrolyte # and 1%wt of diethyl sulfate (DTD) to obtain the electrolyte of this embodiment.

[0191] Application Example 10

[0192] Add 1wt% product 1 to the base electrolyte 1 # and 1%wt of 1,3-propane sultone (PS) to obtain the electrolyte of this embodiment.

[0193] Application Example 11

[0194] Add 1wt% product 7 to the base electrolyte 2 # , and obtain the electrolyte of this embodiment.

[0195] Application Comparative Example 1

[0196] Add 0.2 wt% of control sample 1 to the basic electrolyte 1 # , and obtain the electrolyte of this comparative example.

[0197] Application Comparative Example 2

[0198] Add 1 wt% of control sample 1 to the basic electrolyte 1 # , and obtain the electrolyte of this comparative example.

[0199] Application Comparative Example 3

[0200] Add 1 wt% of control sample 2 to the basic electrolyte 1 # , and obtain the electrolyte of this comparative example.

[0201] Application Comparative Example 4

[0202] Add 1 wt% of control sample 4 to the basic electrolyte 1 # , and obtain the electrolyte of this comparative example.

[0203] Application Comparative Example 5

[0204] The basic electrolyte 1 was prepared without any other treatment to obtain the electrolyte of this comparative example.

[0205] Application Comparative Example 6

[0206] The basic electrolyte 2 was prepared without any other treatment to obtain the electrolyte of this comparative example.

[0207] 2. Electrochemical performance test

[0208] The electrolytes of the above-mentioned application examples 1 to 10 and the application comparative examples 1 to 5 are respectively made into soft-pack lithium-ion batteries with a capacity of 1260 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 ternary positive electrode LiNi 0.6 Co 0.2 Mn 0.2 O 2 The negative electrode active material is high-capacity graphite. The preparation process is as follows: the positive electrode sheet, the separator and the negative electrode sheet are wound together into a roll core, sealed with an aluminum plastic film and then baked to make the electrode moisture meet the requirements, and the battery cell is injected with electrolyte after baking, and the finished lithium-ion battery soft pack battery cell is obtained through the steps of standing, forming, capacity separation and aging.

[0209] The electrolytes of the above-mentioned application example 11 and the application comparative example 6 are respectively made into soft-pack sodium ion batteries with a capacity of 1260 mAh. The sodium 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 ternary positive electrode NaNi 0.33 Fe 0.33 Mn 0.33 O2 The negative electrode active material is hard carbon. The preparation process is as follows: the positive electrode sheet, the separator and the negative electrode sheet are wound together into a roll core, sealed with an aluminum plastic film and then baked to make the electrode moisture meet the requirements, and the battery cell is injected with electrolyte after baking, and the finished sodium ion soft-pack battery cell is obtained through the steps of standing, forming, volume separation and aging.

[0210] The performance tests (test voltage 2.8-4.2V) of the lithium-ion battery and the sodium-ion battery prepared above were carried out, mainly including: (1) 60°C high temperature storage test: the battery was charged to 100% SOC, stored in a 60±2°C oven for 28 days, and the volume before and after storage was tested to obtain the volume expansion rate of the single battery before and after 60°C storage; the DCR value after storage was tested at room temperature, and the percentage value of the initial DCR was calculated and recorded as the discharge DCR change rate;

[0211] (2) 25°C room temperature cycle test: The battery is cycled at 25±1°C in an oven at a charge and discharge current of 1C / 1C. The discharge capacity per week is calculated. The cycle is stopped after 500 cycles, and the capacity retention rate after the cycle is calculated.

[0212] (3) -20℃ low-temperature discharge: The battery is discharged in a -20±1℃ oven at a discharge current of 1C to 80% of the lower limit voltage. The low-temperature discharge capacity is taken as the percentage of the 1C discharge capacity at 25℃, which is recorded as the low-temperature discharge capacity retention rate.

[0213] The test results are shown in Table 1 below:

[0214] Table 1 Electrochemical performance test results

[0215]

[0216]

[0217] According to Table 1 above, adding cyclic boron-containing lithium salt or cyclic boron-containing sodium salt to the electrolyte can reduce the initial impedance of the battery, improve the low-temperature discharge performance, inhibit the gas production and impedance growth of the battery during high-temperature storage, and improve the cycle performance, thereby achieving the effect of taking into account both high and low temperature performance.

[0218] By comparing Application Examples 2, 5, 6 and 7, it can be found that when the proportion of chain boron-containing lithium salt (IV) in the compound increases, the internal resistance of the battery can be more effectively reduced. When the cyclic compound is mainly used, the electrochemical activity is enhanced and the proportion of boron atoms is significantly reduced, so compared with the chain boron-containing lithium salt, the initial impedance will increase, but the storage and cycle performance will be improved.

[0219] By comparing Application Example 2 and Application Example 8, it can be found that adding VC to the cyclic boron-containing lithium salt can further improve the high-temperature storage performance and cycle performance; by comparing Application Example 2 and Application Example 9, it can be found that adding DTD to the cyclic boron-containing lithium salt can further reduce the battery impedance performance and improve the high-temperature storage performance and cycle performance; by comparing Application Example 2 and Application Example 10, it can be found that adding PS to the cyclic boron-containing lithium salt can further improve the high-temperature storage performance and inhibit battery gas production.

[0220] Through application examples 1 to 4, it can be found that as the amount of cyclic boron-containing lithium salt added gradually increases, the overall performance of the battery improves first, but as the amount added further increases, the effect of further improving the battery performance is not significant. The optimal addition amount of the cyclic boron-containing lithium salt is around 1wt% to 2wt%.

Claims

1. A method for preparing a novel cyclic boron-containing metal salt compound, the preparation method comprising: (1) a salification step: in a first solvent, a squaric acid and an inorganic metal salt react to obtain lithium squarate or sodium squarate, wherein the inorganic metal salt is selected from at least one of lithium carbonate, lithium bicarbonate, lithium hydroxide, sodium carbonate, sodium bicarbonate or sodium hydroxide; (2) Complexation step: In a second solvent, lithium squarate or sodium squarate and boron trifluoride / boron trifluoride complex react to obtain a reaction solution containing at least a novel cyclic boron-containing metal salt compound having a structure represented by the following formula (I): In the formula, M is Li or Na, and n is a positive integer selected from 1 to 6; the reaction solution contains at least one novel cyclic boron-containing metal salt compound having a structure represented by formula (I).

2. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 1, characterized in that: The reaction solution of step (2) further comprises at least one of the compounds represented by the following formula (II), (III) or (IV): In formula (II), (III) and (IV), M is Li or Na.

3. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 1 or 2, characterized in that: In step (1), the first solvent is selected from water or a second solvent; the second solvent is selected from at least one of ethylene carbonate, propylene carbonate, 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.

4. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 3, characterized in that: The first solvent is water, and the lithium squarate or sodium squarate obtained in step (1) is used for the reaction in step (2) after being dried and dehydrated.

5. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 4, characterized in that: The second solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate or propylene carbonate.

6. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 1, characterized in that: 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 ethylamine complex, a boron trifluoride butyl ether complex, a boron trifluoride methyl ether complex, a boron trifluoride acetonitrile complex or a boron trifluoride tetrahydrofuran complex.

7. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 1, characterized in that: In step (1), the molar ratio of the squaric acid to the inorganic metal salt is 1:(0.8-5); the reaction temperature is -20-90°C, and the reaction time is 1-24h.

8. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 1, characterized in that: In step (2), the molar ratio of lithium squarate or sodium squarate to boron trifluoride / boron trifluoride complex is 1:(0.3-4), the reaction temperature is -20-90°C, and the reaction time is 1-24h.

9. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 8, characterized in that: In step (2), when the reaction temperature is -20 to 45°C, the reaction solution contains at least 85% by mass of a novel cyclic boron-containing metal salt compound having a structure represented by the following formula (I-1): Wherein, M is Li or Na.

10. The method for preparing the novel cyclic boron-containing metal salt compound according to any one of claims 1 to 9, characterized in that: The preparation method further comprises: (3) a crystallization step: removing the second solvent in the reaction solution of step (2) by vacuum distillation to obtain a concentrated solution, adding a third solvent to the concentrated solution, and keeping the temperature at -60 to 20° C. for 0.5 to 144 hours to precipitate LiBF4 or NaBF4 crystals, and filtering to obtain a novel cyclic boron-containing metal salt compound solution; The third solvent is selected from at least one of dichloromethane, chloroform, tetrachloroethane, isopropanol, methyl tert-butyl ether or toluene.

11. The method for preparing the novel cyclic boron-containing metal salt compound according to claim 10, characterized in that: The novel cyclic boron-containing metal salt compound solution is subjected to 1 to 5 rotary evaporations to remove the third solvent, thereby obtaining the novel cyclic boron-containing metal salt compound.

12. Use of the novel cyclic boron-containing metal salt compound prepared according to claim 11 in an electrolyte, characterized in that: The novel cyclic boron-containing metal salt compound is added into the electrolyte at a mass content of 0.1 to 15 wt % of the total mass of the electrolyte.

13. Use of the novel cyclic boron-containing metal salt compound prepared according to claim 12 in an electrolyte, characterized in that: The electrolyte also includes: An electrolyte salt, wherein the electrolyte salt is mainly a lithium salt or a mainly sodium salt, and the molar concentration in the electrolyte is 0.1 to 4.0 mol / L; the main lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, or lithium difluorobisoxalate phosphate; the main sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium perchlorate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium bisfluorosulfonyl imide, sodium bistrifluoromethylsulfonyl imide, sodium tetrafluorooxalate phosphate, sodium trioxalate phosphate, or sodium difluorobisoxalate phosphate; A non-aqueous solvent, wherein the non-aqueous solvent is selected from at least one of C3-C6 carbonate or fluorinated carbonate compounds, C3-C8 carboxylic acid ester or fluorinated carboxylic acid ester compounds, sulfone compounds or ether compounds; The basic additive is selected from at least one of sulfonate compounds, sulfate compounds, fluorocarbonate compounds, unsaturated carbonate compounds or fluorine-containing salt compounds.

14. A metal ion secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, characterized in that: The electrolyte is formed by adding the novel cyclic boron-containing metal salt compound described in claim 12 or 13 into the electrolyte at a mass content of 0.1 to 15 wt % of the total mass of the electrolyte.

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