Use of boron trifluoride pyrosulfate complex metal salt in electrolyte and method for preparing same

Abstract

The present invention discloses the use of boron trifluoride pyrosulfate complex metal salt in an electrolyte. Adding at least one structural boron trifluoride pyrosulfate complex metal salt in an amount of 0.1 to 15.0 wt% to an electrolyte can simultaneously improve the cycle performance, high-temperature storage performance, and low-temperature performance of a battery. The boron trifluoride pyrosulfate complex metal salt can be obtained by reacting a pyrosulfate with boron trifluoride gas or a boron trifluoride complex. When a pyrosulfate salt with an SO3 content of 500 ppm or less is used as a raw material, a clear, transparent, and low-color boron trifluoride pyrosulfate complex metal salt can be obtained. Using this in an electrolyte improves the discoloration problem during long-term storage and further improves the high-temperature performance of the battery. Furthermore, adding a lithium boron trifluoride pyrosulfate complex salt with a specific surface area of ​​0.1 to 20 m2 can improve the battery's cycle performance, high-temperature storage performance, and low-temperature performance. 2 / g of negative electrode active material, the interaction between the electrolyte and the negative electrode material creates a low-impedance lithium ion transport channel, further improving the battery's fast charging and low-temperature performance.

Description

[Technical Field]

[0001] The present invention relates to the field of electrolytes for lithium / sodium ion batteries, and in particular to the use of a novel compound, boron trifluoride pyrosulfate complex metal salt (lithium boron trifluoride pyrosulfate complex salt or sodium boron trifluoride pyrosulfate complex salt), in an electrolyte and a method for preparing the same. [Background technology]

[0002] As an essential component of batteries, electrolyte additives primarily play a role in establishing a stable electrode / electrolyte interfacial film, achieving electronic insulation, and facilitating the movement of lithium ions and sodium ions. The various functional groups contained in the additives affect both the composition and structure of the interfacial film, ultimately affecting the battery's performance, including cycle life, high-temperature storage, and low-temperature discharge.

[0003] As the demand for volumetric energy density of batteries continues to increase, the current mainstream approach is to improve the operating voltage of batteries and develop high-voltage electrolytes. However, high voltages result in a deterioration of the electrochemical properties of batteries, which places increasing demands on the performance of electrolyte additives. Furthermore, to simultaneously meet battery operating performance requirements in both high and low temperature environments, electrolytes are required to have both excellent high-temperature and low-temperature performance. Currently, most electrolyte additives only have either high-temperature or low-temperature performance. To achieve both high-temperature and low-temperature performance in batteries, practical application often involves compensating for each additive's shortcomings. That is, the simultaneous addition of high-temperature and low-temperature additives to the electrolyte formulation is not only cumbersome, but also leads to adverse effects of each additive on battery performance, to a greater or lesser extent. Furthermore, the interaction of multiple additives may lead to further performance degradation, necessitating the addition of an additional additive to improve the performance. Therefore, the development of novel metal salt-based products that simultaneously offer both high-temperature and low-temperature performance is an important direction in electrolyte research.

[0004] Lithium boron trifluoride pyrosulfate complex salt is a novel electrolyte additive developed by Jiangsu Provincial Chemical Research Institute Co., Ltd., which combines high-temperature and low-temperature performance. Patent application CN202211375099.4 discloses a method for preparing lithium pyrosulfate using disilyl sulfate ester and lithium hexafluorophosphate as raw materials. Subsequent patent application CN202211583064.X further discloses a method for obtaining lithium boron pyrosulfate complex salt by reacting the lithium pyrosulfate with boron trifluoride gas or a boron trifluoride complex. This additive can simultaneously improve the cycle performance, high-temperature storage performance, and low-temperature performance of batteries. Summary of the Invention

[0005] In order to solve the above technical problems, the first aspect of the present invention provides the use of boron trifluoride pyrosulfate complex metal salt in an electrolyte, thereby improving the battery cycle and high-temperature storage performance, and also improving the low-temperature performance of the battery.

[0006] The objective of the first aspect of the present invention is achieved by the following technical solutions. There is provided a use of a boron trifluoride pyrosulfate complex metal salt in an electrolyte solution, which comprises adding a boron trifluoride pyrosulfate complex metal salt having a structure represented by the following formula (I) and / or (II) to the electrolyte solution: JPEG2025538745000002.jpg32170In formula (I), M is Li or Na, and X is independently F or a substituent represented by the following formula (A): JPEG2025538745000003.jpg22170, wherein in formula (A), M is similarly Li or Na, and X is similarly independently selected from F or formula (A) repeated until X is finally F; The mass percentage of the boron trifluoride pyrosulfate complex metal salt in the electrolytic solution is 0.1 to 15.0 wt %, and preferably the mass percentage is 0.2 to 3.0 wt %.

[0007] In the compound having the structure represented by formula (I), Xs above and below the B atom are F, and Xs to the right of the B atom are a substituent represented by formula (A). Similarly, in the substituent represented by formula (A), Xs above and below the B atom are F, and Xs to the right of the B atom are again substituted with a substituent represented by formula (A). In this case, the structure of the boron trifluoride pyrosulfate complex metal salt is as follows: It can also be expressed as JPEG2025538745000004.jpg18170. Here, M is similarly Li or Na, and m is an integer selected from 1 to 100. Preferably, m is an integer selected from 1 to 50.

[0008] Preferably, the boron trifluoride pyrosulfate complex metal salt has the following structure: JPEG2025538745000005.jpg28170JPEG2025538745000006.jpg32170JPEG2025538745000007.jpg28170JPEG2025538745000008.jpg28170JPEG2025538745000009.jpg62170JPEG2025538745000010.jpg96170, where M is Li or Na.

[0009] The boron trifluoride pyrosulfate complex metal salt of the present invention, when added to an electrolyte, not only improves the oxidation resistance of the electrolyte inherent to the pyrosulfate compound itself, but also improves room temperature / high temperature cycle performance and high temperature storage performance. Furthermore, the -SOB- group in its structure forms an interfacial film with a crosslinked network structure containing S and B at the electrode interface during the charge / discharge process of the battery, thereby reducing the content of inorganic lithium salts such as M2SO4 and M2SO3 in the interfacial film and effectively reducing the internal resistance of the battery. Furthermore, this interfacial film with a crosslinked network structure allows for the absorption of more Li. + / Na + The conductive vacancies provide high ionic conductivity and significantly improve the low-temperature performance of the battery. Therefore, when the boron trifluoride pyrosulfate composite metal salt of the present invention is used in an electrolyte, the high-temperature and low-temperature performance of the battery can be improved at the same time.

[0010] The boron trifluoride pyrosulfate complex metal salt can be obtained by the following steps: In a reaction solvent, lithium pyrosulfate / sodium pyrosulfate is reacted with boron trifluoride gas and / or a boron trifluoride complex to obtain a reaction solution of boron trifluoride pyrosulfate complex metal salt. The lithium pyrosulfate / sodium pyrosulfate refers to lithium pyrosulfate or sodium pyrosulfate.

[0011] The reaction solvent is at least one selected from 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, phenylacetonitrile, and propionitrile. Considering the use of boron trifluoride pyrosulfate complex metal salt in an electrolyte solution, the reaction solvent is preferably at least one selected from solvents commonly used in electrolyte solutions, such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0012] The boron trifluoride reacting with lithium pyrosulfate / sodium pyrosulfate may be boron trifluoride gas or a boron trifluoride complex. Optionally, the boron trifluoride complex is at least one selected from the group consisting of boron trifluoride etherate, boron trifluoride ethylene glycol dimethyl etherate, boron trifluoride dimethyl carbonate, boron trifluoride pyridine, boron trifluoride ethylamine, boron trifluoride butyl etherate, boron trifluoride methyl etherate, boron trifluoride acetonitrile, boron trifluoride piperidine, boron trifluoride phenol, boron trifluoride tetrahydrofuran, boron trifluoride dimethyl sulfide, and boron trifluoride morpholine. Preferably, the boron trifluoride complex is at least one selected from a boron trifluoride dimethyl carbonate complex, a boron trifluoride ether complex, and a boron trifluoride acetonitrile complex.

[0013] In the reaction process, the molar ratio of lithium pyrosulfate / sodium pyrosulfate to boron trifluoride gas or boron trifluoride complex is (0.2-1.2):1, and preferably the molar ratio is (0.33-1.0):1.

[0014] The reaction temperature is 10 to 90°C and the reaction time is 1 to 48 hours, preferably 20 to 50°C and 5 to 24 hours.

[0015] The reaction solution of boron trifluoride pyrosulfate complex metal salt prepared as described above contains the reaction solvent and unreacted boron trifluoride, so the reaction solvent and unreacted boron trifluoride are removed from the reaction solution by atmospheric distillation or reduced pressure distillation to obtain boron trifluoride pyrosulfate complex metal salt.

[0016] When the reaction temperature is 10 to 40°C, the mass percentage of compound (2) in the boron trifluoride pyrosulfate complex metal salt is 50% or more, preferably 80% or more, with the remainder being at least one selected from compounds (1), (3), (4), (5), and (6).When the reaction temperature is 40 to 90°C, the mass percentage of compound (1) in the boron trifluoride pyrosulfate complex metal salt is 50% or more, preferably 80% or more, with the remainder being at least one selected from compounds (2), (3), (4), (5), and (6).

[0017] Because the reaction solution cannot be completely removed by distillation due to the solvation effect, the boron trifluoride pyrosulfate complex metal salt obtained after distillation is a concentrated solution containing ≦60% of the reaction solvent. If the reaction solvent is a solvent commonly used in electrolytes, the concentrated solution can be added directly to the electrolyte. If the reaction solvent is not a solvent commonly used in electrolytes, an electrolyte solvent is added, and the reaction solvent is removed by atmospheric or reduced pressure distillation before being added to the electrolyte.

[0018] The boron trifluoride pyrosulfate complex metal salt obtained after distillation was analyzed by nuclear magnetic resonance. The results showed that when the reaction temperature was low, the main product was cyclic compounds, and as the reaction temperature increased, chain compounds were more easily formed. With the reaction temperature and reaction time increasing at the same time, the polymer content in the composition gradually increased, and branched polymers were gradually formed.

[0019] The electrolyte according to the present invention further comprises a main salt, an organic solvent and a basic additive. The main salt is a main lithium salt or a main sodium salt, and the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, and lithium difluorobisoxalatephosphate. The main sodium salt is at least one selected from sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonimide), and sodium difluorophosphate. The main salt has a molar concentration in the electrolyte of 0.1 to 4.0 mol / L. The organic solvent is at least one selected from the group consisting of C3 to C6 carbonate compounds, C3 to C8 carboxylic acid ester compounds, sulfone compounds, and ether compounds. The base additive is at least one selected from sulfonic acid ester compounds, sulfate ester compounds, fluorinated carbonate compounds, unsaturated carbonate compounds, and fluorine-containing lithium / sodium salt compounds.

[0020] Preferably, the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and has a molar concentration in the electrolyte of 0.8 to 1.5 mol / L. The main sodium salt is at least one selected from sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonimide), and has a molar concentration in the electrolyte of 0.8 to 1.5 mol / L. The organic solvent is at least one selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, acetonitrile, ether, and ethylene glycol dimethyl ether. The base additive is at least one selected from vinylene carbonate, fluorinated ethylene carbonate, vinyl sulfate, 1,3-propane sultone, tris(trimethylsilyl)phosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalato)phosphate, lithium difluoro(oxalato)borate, sodium difluoro(oxalato)borate, sodium difluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium difluorobis(oxalato)phosphate. The mass percentage of any of the base additives in the electrolyte is 0.1 to 5.0 wt %, and the base additive is different from the main salt.

[0021] In a first embodiment of the present invention, in the process of preparing the lithium pyrosulfate complex salt of boron trifluoride, the starting material lithium pyrosulfate is prepared from disilyl sulfate ester and lithium hexafluorophosphate. The lithium pyrosulfate complex salt of boron trifluoride prepared from this lithium pyrosulfate starting material is reddish-brown in color. Its use in an electrolyte solution affects the color stability of the electrolyte solution to some extent.

[0022] In the present invention, further research has revealed that lithium boron trifluoride pyrosulfate complex salts prepared using lithium pyrosulfate prepared by different preparation methods have different chromaticities. Further research has revealed that the SO3 contained in the lithium pyrosulfate raw material increases the chromaticity of the product, affecting the electrochemical performance of batteries using lithium boron trifluoride pyrosulfate complex salt. This is thought to be due to the following two reasons: On the one hand, the SO3 contained in the lithium pyrosulfate raw material decomposes the lithium boron trifluoride pyrosulfate salt product during the synthesis and preparation process, thereby increasing the chromaticity of the product. On the other hand, the SO3 contained in the lithium pyrosulfate raw material will inevitably be transferred to the boron trifluoride pyrosulfate complex lithium salt product during the synthesis and preparation process. Due to the relatively strong oxidizing properties of SO3, when the boron trifluoride pyrosulfate complex lithium salt is used in the electrolyte, the oxidizing substance will catalyze the fluorination of the solvent molecules, producing higher molecular weight fluorinated polymers, which will accelerate the discoloration of the electrolyte and cause deterioration of the electrochemical performance of the battery, resulting in a significant decrease in the battery's cycle performance and high-temperature storage performance.

[0023] In addition, the present invention has further researched and verified that boron trifluoride pyrosulfate complex sodium salt and boron trifluoride pyrosulfate complex lithium salt have the same properties and phenomena.

[0024] Therefore, in a second aspect of the present invention, a method for preparing a low-color boron trifluoride pyrosulfate complex metal salt is provided. The boron trifluoride pyrosulfate complex metal salt prepared by this method is clear, transparent, and highly pure. When used in an electrolyte, the problem of discoloration of the electrolyte is alleviated, and the high-temperature performance of the battery is further improved.

[0025] The objective of the second aspect of the present invention is achieved by the following technical solutions. A method for preparing a low-color boron trifluoride pyrosulfate complex metal salt includes reacting a pyrosulfate having an SO content of ≦500 ppm with boron trifluoride gas or a boron trifluoride complex in a reaction solvent to obtain a reaction solution having a color of ≦50 Hazen. The reaction solution contains at least a boron trifluoride pyrosulfate complex metal salt having a structure represented by the following formula (I-1): JPEG2025538745000011.jpg28170In formula (I-1), M is Li or Na, and preferably, M is Li.

[0026] For example, the preparation of boron trifluoride pyrosulfate complex lithium salt is carried out by the following reaction scheme: JPEG2025538745000012.jpg26170Preferably, pyrosulfate having an SO3 content of ≦200 ppm is used as the raw material to obtain a reaction liquid having a color of ≦20 Hazen.

[0027] Generally, by ensuring that the SO3 content in the pyrosulfate raw material is ≦200 ppm and controlling the content of acid gas impurities such as POF3 and fluorosilane, low color boron trifluoride pyrosulfate complex metal salt can be obtained.

[0028] In a preferred embodiment, the pyrosulfate raw material of the present invention is prepared by the following steps: (1) Preparation of hydrogen sulfate: An inorganic salt is reacted with dilute sulfuric acid to obtain hydrogen sulfate. The inorganic salt is at least one selected from sulfates, metal oxides, carbonates, metal hydroxides, and hydrogen carbonates. The hydrogen sulfate is lithium hydrogen sulfate or sodium hydrogen sulfate. Taking lithium sulfate as an example, the reaction scheme is as follows: (2) Pyrosulfate Preparation Step: The hydrogen sulfate solid is thermally decomposed to obtain a pyrosulfate, which may be lithium pyrosulfate or sodium pyrosulfate. Using lithium hydrogen sulfate as an example, the reaction is as follows: JPEG2025538745000014.jpg15170

[0029] In step (1), the present invention uses dilute sulfuric acid as the raw material, thereby avoiding the corrosive problem associated with using SO3, concentrated sulfuric acid, fuming sulfuric acid, etc. as raw materials, and reducing the SO3 content in the prepared pyrosulfate raw material. Specifically, the mass concentration of the dilute sulfuric acid is 10 to 65 wt%. In actual operation, dilute sulfuric acid of the corresponding concentration may be used, or sulfuric acid with a slightly higher concentration may be used after diluting it with deionized water. Preferably, the mass concentration of the dilute sulfuric acid is 15 to 40 wt%.

[0030] In step (1), the molar ratio of inorganic salt to dilute sulfuric acid is (0.8-1.2):1, preferably (0.9-1.1):1, and more preferably about 1:1. The reaction temperature in step (1) is controlled to 0-80°C, and the reaction time is 0.5-24 hours. Preferably, the reaction temperature is 20-45°C, and the reaction time is 2-4 hours. By controlling the molar ratio of sulfate to dilute sulfuric acid, the reaction temperature, and the reaction time, the reaction product of step (1) is essentially hydrogen sulfate. This reaction product can be used in the next step simply by heating and drying it to remove moisture.

[0031] In step (2), the hydrogen sulfate solid is calcined at 100-300°C for 0.5-72 hours to obtain pyrosulfate. Preferably, the hydrogen sulfate solid is calcined at 130-250°C for 2-36 hours to obtain pyrosulfate. More preferably, the hydrogen sulfate solid is heated at 160-200°C for 4-12 hours to obtain pyrosulfate. The purity of the resulting pyrosulfate varies depending on the calcination temperature. If the calcination temperature is too high, the product will contain relatively large amounts of sulfate impurities and will have a high SO3 content. If the calcination temperature is too low, the conversion of hydrogen sulfate will be incomplete and the sample will contain relatively large amounts of HO.

[0032] In the specific operation, to improve the reaction efficiency, before the hydrogen sulfate is heated and decomposed, the hydrogen sulfate solid obtained in step (1) is pulverized to obtain a uniform white powder, which is then placed in a heating device (e.g., a muffle furnace) for calcination and decomposition to obtain the pyrosulfate raw material.

[0033] In the process of preparing the boron trifluoride pyrosulfate complex metal salt, the reaction solvent is at least one selected from 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, phenylacetonitrile, and propionitrile. Considering the use of the boron trifluoride pyrosulfate complex metal salt in an electrolyte solution, the reaction solvent is preferably at least one selected from solvents commonly used in electrolyte solutions, such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0034] The substance that reacts with the pyrosulfate may be boron trifluoride gas or a boron trifluoride complex, and the boron trifluoride complex is at least one selected from the group consisting of a boron trifluoride ether complex, a boron trifluoride ethylene 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, and a boron trifluoride morpholine complex.

[0035] In the reaction process between pyrosulfate and boron trifluoride gas or boron trifluoride complex, the molar ratio of pyrosulfate to boron trifluoride gas or boron trifluoride complex is (0.33-1.0):1, the reaction temperature is 40-70°C, and the reaction time is 5-24 hours. Preferably, the reaction temperature is 50-70°C, and the reaction time is 5-12 hours. In this way, the boron trifluoride pyrosulfate complex metal salt prepared in the second embodiment of the present invention is mainly a chain product.

[0036] In the preparation process of the second aspect of the present invention, depending on factors such as different reaction temperatures and different material mixing ratios, the reaction solution may contain at least one compound selected from the compounds represented by the following formulas (I-2), (I-3), (I-4), (I-5), and (I-6) in addition to the boron trifluoride pyrosulfate complex metal salt having a structure represented by formula (I-1). JPEG2025538745000015.jpg32170JPEG2025538745000016.jpg28170JPEG2025538745000017.jpg28170JPEG2025538745000018.jpg61170JPEG2025538745000019.jpg95170In formulas (I-2), (I-3), (I-4), (I-5), and (I-6), M is Li or Na.

[0037] Specifically, the reaction solution contains at least 80 wt % or more of the boron trifluoride pyrosulfate complex metal salt having the structure represented by the formula (I-1). Preferably, the reaction solution contains 80 to 95 wt % of the boron trifluoride pyrosulfate complex metal salt having the structure represented by the formula (I-1), with the remainder being at least one compound selected from the compounds represented by the formulas (I-2), (I-3), (I-4), (I-5), and (I-6).

[0038] The present invention further provides use of a low-color boron trifluoride pyrosulfate complex metal salt prepared by any of the above preparation methods in an electrolyte. The use includes adding the prepared low-color boron trifluoride pyrosulfate complex metal salt to an electrolyte so that the mass percentage in the electrolyte is 0.01 to 15.0 wt%. In a preferred embodiment, the mass percentage of the prepared boron trifluoride pyrosulfate complex metal salt in the electrolyte is 0.1 to 10.0 wt%, more preferably 0.1 to 5.0 wt%, and even more preferably 0.1 to 3.0 wt%.

[0039] The electrolyte obtained by adding the boron trifluoride pyrosulfate complex metal salt can be used in lithium ion secondary batteries or sodium ion secondary batteries, and can improve the high voltage, high-temperature cycle performance, high-temperature storage performance, and low-temperature cycle performance of the battery.

[0040] In a specific embodiment, the boron trifluoride pyrosulfate complex metal salt is a lithium boron trifluoride pyrosulfate complex salt, which is added to a lithium ion battery electrolyte for use. The positive electrode active material of the lithium ion secondary battery is selected from a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobalt oxide material, or a lithium iron phosphate material. The negative electrode active material is selected from graphite, silicon carbon, silicon monoxide, silicon, tin, metallic lithium, or a composite thereof.

[0041] In another specific embodiment, the boron trifluoride pyrosulfate complex metal salt is a boron trifluoride pyrosulfate complex sodium salt, which is added to a sodium ion battery electrolyte for use. The active material of the positive electrode sheet of the sodium ion secondary battery is NaMn (1-x-y) Ni y M x O2 (0≦x, y≦1, M is Cu, Fe, Co), sodium manganate, sodium vanadium phosphate, sodium fluorovanadium phosphate, sodium iron phosphate, sodium manganese phosphate, Nax At least one selected from MnFe(CN)6 (0 < x ≦ 2), and the active material of the negative electrode sheet is at least one selected from hard carbon, carbon black, amorphous carbon, graphite, SnS2, Na2Ti3O7, silicon-based materials, metal oxides, metal sulfides or metallic sodium.

[0042] Specifically, in the present invention, the use of boron trifluoride pyrosulfate complex lithium salt in a high-voltage rapid-charging lithium-ion secondary battery was further studied. As a result, it was found that the boron trifluoride pyrosulfate complex lithium salt has the effect of reducing the liquid-solid interface impedance and charge transfer impedance inside the battery, but when used simultaneously with different negative electrode active materials, there are significant differences in the improvement effects of the rapid-charging performance and low-temperature performance of the battery.

[0043] Therefore, in the third aspect of the present invention, there is provided a high-voltage rapid-charging lithium-ion secondary battery in which the boron trifluoride pyrosulfate complex lithium salt and a specific negative electrode active material interact with each other. It can construct a low-impedance lithium-ion migration channel to improve the rapid-charging performance and low-temperature performance of the battery.

[0044] The object of the third aspect of the present invention is achieved by the following technical solutions. The high-voltage rapid-charging lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator and an electrolyte. The electrolyte includes a main lithium salt, a non-aqueous solvent and an additive. The additive includes a novel composite lithium salt. The novel composite lithium salt includes at least a boron trifluoride pyrosulfate complex lithium salt having a structure represented by the following formula (II-1). JPEG2025538745000020.jpg28170 The novel composite lithium salt is 0.02 to 5.0 wt% of the total mass of the electrolyte, preferably 0.1 to 2.0 wt% of the total mass of the electrolyte. The negative electrode includes an active material capable of reversibly absorbing and releasing lithium ions. The specific surface area of the active material is 0.1 to 20.0 m 2 / g. Preferably, the specific surface area of the active material is 0.5 to 10.0 m 2 / g.

[0045] When the active material is a single material, the specific surface area of ​​the single material must satisfy the above-mentioned limitations. When the active material is two or more kinds of substances, the specific surface area of ​​any of the substances must satisfy the above-mentioned limitation.

[0046] The novel composite lithium salt, combined with a negative electrode active material with the above specific surface area, can achieve the goal of establishing low-impedance, stable, and smooth lithium ion migration channels, thereby improving the fast-charging performance and low-temperature performance of the battery. If the specific surface area of ​​the negative electrode active material is too small, the lithium ion migration path within the negative electrode active material becomes long, making solid-state diffusion of the lithium ions difficult, increasing the battery's diffusion impedance and internal impedance, and degrading the fast-charging performance and low-temperature performance of the battery. If the specific surface area of ​​the negative electrode active material is too large, excess electrolyte is more likely to be involved in the liquid-solid interface formation process, increasing side reactions, increasing the number of irreversible lithium ions, thickening the interfacial layer, increasing the battery's internal impedance, and degrading the fast-charging performance and low-temperature performance of the battery.

[0047] The active material of the negative electrode is selected from a carbon material and / or a silicon material, where the carbon material is at least one selected from natural graphite, artificial graphite, and hard carbon, and the silicon material is selected from silicon and / or silicon monoxide.

[0048] The specific types of carbon materials described in the present invention are materials commonly used in the field of secondary batteries. Here, natural graphite refers to graphite material with non-uniform particle diameters or a wide particle diameter distribution, and generally has defects on its surface. Lithium-ion secondary batteries manufactured using natural graphite generally have many side reactions and relatively poor cycle performance, but have the advantages of low cost and wide commercial application. Artificial graphite refers to artificially produced or selected graphite material with approximately uniform particle diameters or a narrow particle diameter distribution compared to natural graphite, and has good compatibility with electrolytes and excellent usability, but is expensive and is commonly used in the field of high-performance lithium-ion secondary batteries, such as high-end new energy vehicles. Hard carbon refers to a carbon material that is difficult to graphitize even at temperatures above 2500°C, and its interior has a highly disordered carbon layer structure and an open void structure. All three can be purchased directly on the market.

[0049] Furthermore, the active material of the negative electrode contains at least hard carbon, and the mass content of the hard carbon is 0.1 to 100%. Preferably, the mass content of the hard carbon in the active material of the negative electrode is 1 to 50%. More preferably, the mass content of the hard carbon in the active material of the negative electrode is 5 to 20%.

[0050] The inclusion of hard carbon in the negative electrode active material significantly improves the diffusion ability of lithium ions in the negative electrode, resulting in excellent reaction kinetics. At the same time, the electrolyte of the present invention has good compatibility with the negative electrode material, contributing to the formation of a stable and smooth liquid-solid interface during the initial charge-discharge process of the battery, thereby improving the rapid charge performance of the battery.

[0051] Further research has shown that the magnitude of the diffusion resistance is primarily determined by the state of the solid-phase material in lithium-ion secondary batteries, and that its distribution spans the entire frequency range, but its main component is distributed in the low-frequency range (1-0.01 Hz frequency range). Therefore, the ratio of the AC impedance in the low-frequency range (1-0.01 Hz) to the AC impedance in the full frequency range (10,000-0.01 Hz) is an important means of measuring the proportion of the diffusion impedance in the overall internal impedance of the battery, and is also an important indicator for evaluating the battery's fast charging performance.

[0052] Due to the interaction between the boron trifluoride pyrosulfate composite lithium salt of the present invention and the specific negative electrode active material, the AC impedance of the lithium ion secondary battery in the 1 to 0.01 Hz frequency range accounts for 40 to 80% of the AC impedance in the 10,000 to 0.01 Hz frequency range, and further accounts for 60 to 70% of the AC impedance in the 10,000 to 0.01 Hz frequency range.

[0053] Specifically, the AC impedance is measured at a temperature range of 0 to 45° C. with the battery state of charge at 20% to 80%. In a specific embodiment, AC impedance values ​​in different frequency ranges can be measured at room temperature with the battery state of charge at approximately 50%.

[0054] In addition, the battery's positive electrode, negative electrode, separator, and liquid-solid interface formed by the interaction between the electrolyte and the positive and negative electrodes all affect the charge transport resistance. Because the separator has little effect on the charge transport resistance, the present invention can employ a separator commonly used in lithium-ion secondary batteries. Preferably, the separator is at least one selected from the group consisting of polyolefin-based separators, polyester-based separators, cellulose-based separators, and polyimide-based separators, and can be further processed using ceramic coating technology. The present invention employs a positive electrode material commonly used in lithium-ion secondary batteries. While the positive electrode material has a certain effect on the charge transport resistance, the present invention employs a high-voltage battery system to improve the battery's energy density, which places certain limitations on the selection of the positive electrode material. Preferably, the positive electrode active material is at least one selected from the group consisting of lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, layered lithium manganese oxide, spinel lithium manganese oxide, and lithium nickel manganese oxide materials.

[0055] Generally, the electrolyte additive and the liquid-solid interface formed by the interaction of the additive with the negative electrode have a significant impact on the magnitude of the charge transport resistance of lithium-ion secondary batteries. The process of lithium ions migrating from the liquid-solid interface to the solid phase of the negative electrode material is the main component of the charge transport impedance. The generated AC impedance is partially distributed in the low-frequency range of 1-0.1 Hz and partially overlaps with the diffusion impedance. The decoupling data mentioned in this invention show that within the above-mentioned test temperature and charge state range of this invention, the charge transport impedance accounts for 20-40% of the AC impedance in the entire frequency range of 10,000-0.01 Hz.

[0056] Due to the different parameters of the preparation process of the novel composite lithium salt, the novel composite lithium salt further comprises at least one compound selected from the group consisting of compounds represented by the following formulas (II-2), (II-3), (II-4), (II-5) and (II-6): JPEG2025538745000021.jpg32170JPEG2025538745000022.jpg29170JPEG2025538745000023.jpg25170JPEG2025538745000024.jpg83170 The novel composite lithium salt contains at least 80.0 wt% or more of the boron trifluoride pyrosulfate composite lithium salt having a structure represented by formula (II-1). Preferably, the novel composite lithium salt contains 80.0 to 95.0 wt% of the boron trifluoride pyrosulfate composite lithium salt having a structure represented by formula (II-1), with the remainder being at least one selected from compounds (II-2), (II-3), (II-4), (II-5), and (II-6).

[0057] In the high-voltage rapid charge lithium-ion secondary battery, the additive further includes a base additive. The base additive is at least one selected from vinylene carbonate, fluorinated ethylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)phosphate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, succinic anhydride, hexadionitrile, cyclohexylbenzene, lithium difluorobis(oxalato)phosphate, and lithium difluoro(oxalato)borate. The mass percentage of any of the base additives in the electrolyte solution is 0.1 to 5.0 wt%, preferably 0.1 to 2.0 wt%.

[0058] In a specific embodiment, the base additives are lithium difluoro(oxalato)borate (LiDFOB) and lithium difluorophosphate (LiDFP), each of which accounts for 0.1% to 2.0% of the total mass of the electrolyte. The novel composite lithium salt interacts with the negative electrode active material to improve the fast charging performance and low temperature performance of the lithium ion secondary battery.

[0059] In another embodiment, the base additives are fluorinated ethylene carbonate (FEC), vinyl sulfate (DTD), and tris(trimethylsilyl)phosphate (TMSP), each of which accounts for 0.1% to 2.0% of the total mass of the electrolyte. The interaction between the novel composite lithium salt and the negative electrode active material can further improve the fast charging performance and low temperature performance of the lithium ion secondary battery.

[0060] In the high-voltage rapid charge lithium-ion secondary battery, the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, and lithium difluorobisoxalatephosphate, and its molar concentration is 0.1 to 4.0 mol / L.

[0061] According to the high-voltage rapid charging lithium-ion secondary battery, the non-aqueous solvent is at least one selected from the group consisting of C3 to C6 carbonate compounds, C3 to C8 carboxylic acid ester compounds, sulfone compounds, ether compounds, and nitrile compounds. Preferably, the C3-C6 carbonate compound is at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl-2,2,2-trifluoroethyl. The C3-C8 carboxylic acid ester compound is at least one selected from γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, and 2,2-difluoroethyl acetate. The sulfone compound is at least one selected from sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone. The ether compound is selected from triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether. The nitrile compound is at least one selected from acetonitrile, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 4-fluorobenzonitrile, and 1,2-bis(cyanoethoxy)ethane.

[0062] Preferably, the non-aqueous solvent is a mixture of at least two solvents selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, ethyl acetate, ethyl propionate, propyl propionate, succinonitrile, adiponitrile, and 1,3,6-hexanetricarbonitrile.

[0063] According to the high-voltage fast charging lithium-ion secondary battery, the negative electrode further includes auxiliary materials such as a current collector, a conductive agent, an adhesive, etc. The selection of the auxiliary materials does not significantly affect the interaction between the electrolyte solution and the negative electrode described in the present invention, so the present invention is not limited to the type of the auxiliary materials, and any known auxiliary materials can be used.

[0064] The positive electrode active material described in the present invention can be any positive electrode material commonly used in lithium-ion secondary batteries. Preferably, the positive electrode active material is at least one selected from lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, layered lithium manganese oxide, spinel lithium manganese oxide, and lithium nickel manganese oxide materials. More preferably, the positive electrode active material is at least one selected from lithium nickel manganese cobalt oxide, lithium cobalt oxide, and lithium nickel oxide materials.

[0065] The high-voltage rapid charge lithium ion secondary battery described in the present invention has excellent low-temperature rapid charge performance, and has a constant current charge ratio of 75% or more at a charge rate of 1 to 6 C and a cutoff operating voltage of 4.2 to 5.0 V. Furthermore, the lithium ion secondary battery has a constant current charge ratio of 90% or more at a charge rate of 2 to 4 C and a cutoff operating voltage of 4.25 to 4.45 V.

[0066] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides, for the first time, a salt-based additive with a novel structure, such as boron trifluoride pyrosulfate complex metal salt, which, when applied to an electrolyte, can simultaneously achieve high-temperature and low-temperature performance. The pyrosulfate structure can improve the oxidation resistance of the electrolyte and significantly improve its ambient / high-temperature cycling performance and high-temperature storage performance. The -SOB- group effectively controls the interfacial film components, forming an interfacial film with a crosslinked network structure containing S and B, reducing the content of inorganic lithium salts in the interfacial film and effectively reducing the internal resistance of the battery. At the same time, the interfacial film with a crosslinked network structure contains more voids, improving ionic conductivity and improving the low-temperature performance of the battery. 2. The present invention provides a pyrosulfate salt with a low SO3 content, which is then used as a raw material to prepare a clear and transparent boron trifluoride pyrosulfate composite metal salt with a color value of 50 Hazen or less. The use of this boron trifluoride pyrosulfate composite metal salt as an additive in an electrolyte alleviates the discoloration of the electrolyte and improves the electrochemical performance of the battery, particularly by suppressing gas generation during high-temperature storage and significantly improving high-temperature performance such as high-temperature capacity maintenance and recovery rate. Furthermore, the pyrosulfate salt prepared by the process of the present invention not only has a low SO3 content, but is also free of substances such as POF3 and fluorosilane, making the overall process simple, requiring low raw material costs, and being safe and environmentally friendly, making it suitable for industrial applications. 3. The present invention employs boron trifluoride pyrosulfate composite lithium salt and a specific negative electrode to strengthen the interaction between the electrolyte and the negative electrode, thereby solving the problem of excessively high solid-state impedance formed by the reaction between the electrolyte, the negative electrode, and the electrolyte and the negative electrode, and improving the fast charging performance and low-temperature performance of lithium-ion secondary batteries. 4. By using the relaxation time distribution function to decouple the various components and their magnitudes of the internal resistance of a lithium ion secondary battery, the present invention has verified that only when the electrolyte and anode of the present invention are used simultaneously can the resulting lithium secondary battery simultaneously achieve the effects of reducing both charge transport resistance and diffusion resistance. Although the mechanism by which the electrolyte and anode affect charge transport resistance and diffusion resistance is currently unclear, analysis of experimental results has shown that the novel composite lithium salt of the present invention and the specific anode act synergistically during the battery manufacturing process to form a stable, highly ion-permeable electrolyte-anode channel, thereby improving the electrochemical performance of the lithium ion secondary battery. [Brief explanation of the drawings]

[0067] [Figure 1] 19F-NMR spectrum of 2.1# lithium salt prepared in Example 2.1 of the present invention. [Figure 2] FIG. 11B-NMR spectrum of the 2.1# lithium salt prepared in Example 2.1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0068] The present invention will be further described below with reference to specific examples, but the present invention is not limited to these specific embodiments. Those skilled in the art should understand that the present invention covers all alternatives, modifications, and equivalents that may fall within the scope of the claims. A first embodiment of the present invention provides a method for preparing boron trifluoride pyrosulfate complex metal salt, in which lithium pyrosulfate / sodium pyrosulfate are prepared from disilyl sulfate and lithium hexafluorophosphate / sodium hexafluorophosphate as raw materials.

[0069] 1. Preparation of additives Preparation Example 1 This preparation example provides a method for preparing an electrolyte additive, boron trifluoride pyrosulfate complex lithium salt, which specifically includes the following steps: S1: In a dry room with a dew point of -40°C, 0.2 mol of lithium pyrosulfate (purity 99%) was added to a reaction flask, and dimethyl carbonate was used as a solvent. The reaction system was stirred to mix uniformly, and then 0.4 mol of boron trifluoride gas was introduced into the reaction flask. The reaction was carried out at 25°C for 5 hours, yielding a boron trifluoride pyrosulfate complex lithium salt reaction solution. S2: The reaction solvent and remaining unreacted boron trifluoride in the crude product were removed by vacuum distillation. The temperature of the vacuum distillation was controlled at 60°C and the time was controlled at 0.5 hours to obtain boron trifluoride pyrosulfate complex lithium salt, which was recorded as 1.1# lithium salt. 1.1#About lithium salts 19 F-NMR and 11B-NMR measurements were performed to obtain NMR spectra. Peaks were observed at δ = -150.78 ppm in the F spectrum and δ = -1.17 ppm in the B spectrum, confirming that this substance was compound I-1 (M is Li). Peaks were observed at δ = -144.21 ppm in the F spectrum and δ = -0.81 ppm in the B spectrum, confirming that this substance was compound I-2 (M is Li). The integrated area ratio of δ = -1.17 ppm and δ = -0.81 ppm in the B spectrum was 8.9:1. Analysis confirmed that the 1.1# lithium salt contained 90.0% compound I-2 (M is Li) and 10.0% compound I-1 (M is Li).

[0070] Preparation Example 2 The procedure of this Preparation Example was the same as Preparation Example 1, except that the reaction temperature in step S1 was increased to 50°C and the resulting product was a 1.2# lithium salt. 1.2#About lithium salts 19 F-NMR and 11 B-NMR measurement was performed to obtain an NMR spectrum. The same peaks as in Preparation Example 1 were observed, but the integrated area ratio of the B spectrum δ = -1.17 ppm and δ = -0.81 ppm was 1:9. Analysis revealed that the 2# lithium salt was 9.9% compound (I-2, M is Li) and 90.1% compound (I-1, M is Li).

[0071] Preparation Example 3 The procedure of this preparation example was the same as that of Preparation Example 2, except that the reaction time in step S1 was extended to 8 hours and the resulting product was a 1.3# lithium salt. 1.3#About lithium salts 19 F-NMR and 11B-NMR measurement was performed to obtain an NMR spectrum. The peaks of compound I-1 (M is Li) were observed (they coincided with those of compound I-1 (M is Li) in Preparation Example 1). Furthermore, peaks were observed in the F spectrum at δ = -150.38 ppm and δ = -144.25 ppm, with a peak area integral ratio of 3:1. The peaks were observed in the B spectrum at δ = -1.12 ppm and δ = -0.78 ppm, with a peak area integral ratio of 2:1. This substance was confirmed to be compound I-3 (M is Li). The ratio of the integrated areas of the B spectrum δ = -1.17 ppm and δ = -0.78 ppm was 6.19: 1. Analysis confirmed that the 1.3# lithium salt contained 86.1% of compound I-1, M is Li, and 13.9% of compound I-3, M is Li.

[0072] Preparation Example 4 The procedure of this preparation example was the same as that of Preparation Example 2, except that the reaction time in step S1 was extended to 12 hours and the resulting product was a 1.4# lithium salt. 1.4#About lithium salts 19 F-NMR and 11 B-NMR measurements were performed to obtain NMR spectra. Peaks corresponding to compound (I-1, M is Li) and compound (I-3, M is Li) were observed (they matched those of compound (I-1, M is Li) and compound (I-3, M is Li) in Preparation Example 3). Furthermore, peaks were observed in the F spectrum at δ = -150.12 ppm and δ = -143.73 ppm, with a peak area integral ratio of 1.5:1. Nuclear magnetic resonance B spectrum showed peaks at δ = -1.10 ppm and δ = -0.71 ppm, with a peak area integral ratio of 1:1. This substance was confirmed to be compound (I-4, M is Li). The integrated area ratio of the B spectrum δ = -1.17 ppm, δ = -0.78 ppm, and δ = -0.71 ppm was 16.11:1.75:1. Analysis confirmed that the 1.4# lithium salt contained 85.4% of compound I-1, M is Li, 9.3% of compound I-3, M is Li, and 5.3% of compound I-4, M is Li.

[0073] Preparation Example 5 The procedure of this preparation example was the same as that of Preparation Example 2, except that the reaction time in step S1 was extended to 20 hours and the resulting sign product was a 1.5# lithium salt. 1.5#About lithium salts 19 F-NMR and 11 B-NMR measurements were performed to obtain NMR spectra. Peaks corresponding to compound (1), compound (I-3, M is Li), and compound (I-4, M is Li) were observed (these peaks coincided with those of compound (I-1, M is Li), compound (I-3, M is Li), and compound (I-4, M is Li) in Preparation Example 4). Furthermore, peaks were observed in the F spectrum at δ = -149.36 ppm and δ = -141.12 ppm, with a peak area integral ratio of 6.1:1. Nuclear magnetic resonance B spectrum showed peaks at δ = -1.01 ppm and δ = -0.63 ppm, with a peak area integral ratio of 2.9:1. This substance was confirmed to be compound (I-5, M is Li). The integrated area ratios of the B spectrum δ = -1.17 ppm, δ = -0.78 ppm, δ = -0.71 ppm, and δ = -0.63 ppm were 28.2:3.17:2.1:1. Analysis confirmed that the 1.5# lithium salt contained 81.8% of compound I-1, M is Li, 9.2% of compound I-3, M is Li, 6.1% of compound I-4, M is Li, and 2.9% of compound I-5, M is Li.

[0074] Preparation Example 6 The procedure of this preparation example was the same as that of Preparation Example 2, except that the reaction time in step S1 was extended to 24 hours and the resulting product was a 1.6# lithium salt. 1.6#About lithium salts 19 F-NMR and 11B-NMR measurements were performed to obtain NMR spectra. Peaks corresponding to compound (1), compound (I-3, M is Li), compound (I-4, M is Li), and compound (I-5, M is Li) were observed (these peaks coincided with those of compound (I-1, M is Li), compound (I-3, M is Li), compound (I-4, M is Li), and compound (I-5, M is Li) in Preparation Example 5). Furthermore, a peak was observed at δ = -147.21 ppm in the F spectrum, and peaks were observed at δ = -0.89 ppm and δ = -0.56 ppm in the nuclear magnetic resonance B spectrum, with a peak area integral ratio of 4.2:1. This substance was confirmed to be compound (I-6, M is Li). The integrated area ratios of the B spectrum δ = -1.17 ppm, δ = -0.78 ppm, δ = -0.71 ppm, δ = -0.63 ppm, and δ = -0.56 ppm were 36.18:3.72:2.23:1. Analysis confirmed that the 1.6# lithium salt contained 79.6% of compound I-1, M is Li, 8.2% of compound I-3, M is Li, 5.1% of compound I-4, M is Li, 4.9% of compound I-5, M is Li, and 2.2% of compound I-6, M is Li.

[0075] Preparation Example 7 The procedure of this Preparation Example was the same as Preparation Example 2, except that the reaction temperature in step S1 was changed to 70°C and the resulting product was a 1.7# lithium salt. 1.7#About lithium salts 19 F-NMR and 11 B-NMR measurement was performed to obtain an NMR spectrum. Peaks corresponding to Compound (I-1, M is Li), Compound (I-3, M is Li), and Compound (I-4, M is Li) were observed (these peaks coincided with those of Compound (I-1, M is Li), Compound (I-3, M is Li), and Compound (I-4, M is Li) in Preparation Example 4). The integrated area ratio of the B spectrum δ = -1.17 ppm, δ = -0.78 ppm, and δ = -0.71 ppm was 13.41:1.44:1. Analysis confirmed that the 1.7# lithium salt contained 84.6% of compound I-1, M is Li, 9.1% of compound I-3, M is Li, and 6.3% of compound I-4, M is Li.

[0076] Preparation Example 8 The procedure of this Preparation Example was the same as Preparation Example 2, except that the reaction temperature in step S1 was changed to 90°C and the resulting product was a 1.8# lithium salt. 1.8#About lithium salts 19 F-NMR and 11 B-NMR measurements were performed to obtain NMR spectra. Peaks corresponding to compound (I-1, M is Li), compound (I-3, M is Li), compound (I-4, M is Li), and compound (I-5, M is Li) were observed. The peaks matched those of compound (I-1, M is Li), compound (I-3, M is Li), compound (I-4, M is Li), and compound (I-5, M is Li) from Preparation Example 5. The integrated area ratios of the B spectrum δ = -1.17 ppm, δ = -0.78 ppm, δ = -0.71 ppm, and δ = -0.63 ppm were 20.74:2.28:1.62:1. Analysis confirmed that the 1.8# lithium salt contained 80.9% of compound I-1, M is Li, 8.9% of compound I-3, M is Li, 6.3% of compound I-4, M is Li, and 3.9% of compound I-5, M is Li.

[0077] Preparation Example 9 The procedure of this preparation example is the same as that of Preparation Example 1, except that lithium pyrosulfate in step S1 is changed to sodium pyrosulfate, and the resulting product is 1.1# sodium salt. 1.1#About sodium salts 19 F-NMR and 11B-NMR measurements were performed to obtain NMR spectra. Peaks were observed at δ = -153.28 ppm in the F spectrum and δ = -1.01 ppm in the B spectrum, confirming that this substance was compound I-1 (M is Na). Peaks were observed at δ = -148.18 ppm in the F spectrum and δ = -0.69 ppm in the nuclear magnetic resonance B spectrum, confirming that this substance was compound I-2 (M is Na). The integrated area ratio of δ = -1.05 ppm and δ = -0.77 ppm in the B spectrum was 9.1:1. Analysis confirmed that the 1.1# sodium salt contained 91.1% compound I-2 (M is Na) and 8.9% compound I-1 (M is Na).

[0078] Preparation Example 10 The procedure of this preparation example was the same as that of Preparation Example 9, except that the reaction temperature in step S1 was changed to 50°C. The prepared boron trifluoride pyrosulfate complex sodium salt was recorded as 1.2% sodium salt. 1.2#About sodium salts 19 F-NMR and 11 B-NMR measurements were performed to obtain an NMR spectrum. The same peaks as in Preparation Example 9 were observed, except that the integrated area ratio of the B spectrum δ = -1.05 ppm to δ = -0.77 ppm was 1:8.35. Analysis confirmed that the 1.2# sodium salt contained 89.3% of compound I-1, M is Na, and 10.7% of compound I-2, M is Na.

[0079] 2, Electrolyte Preparation of Basal Electrolyte Solution 1 In an argon-filled glove box (water content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:EMC:DEC = 3:5:2, and lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution until the molar concentration of LiPF6 reached 1.2 mol / L, yielding base electrolyte 1. Preparation of base electrolyte 2 In an argon-filled glove box (moisture < 5 ppm, oxygen < 10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:EMC:DEC = 3:5:2, and sodium hexafluorophosphate (NaPF6) was slowly added to the mixed solution until the molar concentration of NaPF6 reached 1.2 mol / L, yielding base electrolyte 2.

[0080] Example 1.1 0.2 wt % of 1.2# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0081] Example 1.2 1 wt % of 1.2# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0082] Example 1.3 2 wt % of 1.2# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0083] Example 1.4 3 wt % of 1.2# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0084] Example 1.5 1 wt % of 1.1# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0085] Example 1.6 1 wt % of 1.3# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0086] Example 1.7 1 wt % of 1.4# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0087] Example 1.8 1 wt % of 1.5# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0088] Example 1.9 1 wt % of 1.6# lithium salt was added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0089] Example 1.10 1 wt % of 1.2# lithium salt and 1% wt of vinylene carbonate (VC) were added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0090] Example 1.11 1 wt % of 1.2# lithium salt and 1% wt % of 1,3-propane sultone (PS) were added to the base electrolyte solution 1 to obtain the electrolyte solution of this example.

[0091] Example 1.12 0.2 wt % of 1.2# sodium salt was added to the base electrolyte 2 to obtain the electrolyte of this example.

[0092] Example 1.13 1.0 wt % of 1.2# sodium salt was added to the base electrolyte 2 to obtain the electrolyte of this example.

[0093] Comparative Example 1.1 0.2 wt % lithium pyrosulfate was added to the base electrolyte solution 1 to obtain the electrolyte solution of this comparative example.

[0094] Comparative Example 1.2 The electrolyte of this comparative example was obtained by adding 1 wt% lithium pyrosulfate to the base electrolyte 1. A large amount of insoluble matter was generated in this electrolyte, making it impossible to carry out the subsequent battery assembly test. The lithium pyrosulfate did not dissolve completely, and the solubility was found to be 0.2 wt%.

[0095] Comparative Example 1.3 The electrolyte solution of this comparative example was obtained without any treatment of the base electrolyte solution 1.

[0096] Comparative Example 1.4 The electrolyte solution of this comparative example was obtained without any treatment from the base electrolyte solution 2.

[0097] 2. Electrochemical performance test Using the electrolyte solutions of Examples 1.1 to 1.11 and Comparative Examples 1.1 to 1.3, soft-pack capacity 1260 mAh lithium ion batteries were fabricated. The lithium ion batteries comprised a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte solution, and battery auxiliary materials. The positive electrode active material was a ternary positive electrode LiNi 0.6 Co 0.2 Mn 0.2 The negative electrode active material is high-capacity graphite. The preparation process is as follows: the positive electrode sheet, separator, and negative electrode sheet are wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrode meets the required level. After baking, the cell is filled with electrolyte, and the process involves leaving it to stand, chemical treatment, capacity grading, and aging to obtain the finished soft-pack cell.

[0098] Using the electrolytes of Examples 1.12 to 1.13 and Comparative Example 1.4, soft-pack capacity 1260 mAh sodium ion batteries were fabricated. The sodium ion batteries included a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material was a ternary positive electrode NaNi 0.33 Fe 0.33 Mn 0.33 The active material is O2, and the negative electrode active material is hard carbon. The preparation process is as follows: the positive electrode sheet, separator, and negative electrode sheet are wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrode meets the required level. After baking, the cell is filled with electrolyte, and the cell is left to stand, undergoes chemical conversion treatment, capacity grading, and aging processes to obtain the finished sodium soft-pack cell.

[0099] The lithium-ion batteries and sodium-ion batteries prepared as described above were subjected to performance tests (test voltage 2.8 to 4.2 V). The main test contents are as follows: (1) 60°C high-temperature storage test: The battery was charged to 100% SOC and stored in an oven at 60±2°C for 28 days. The volume was measured before and after storage to obtain the volume expansion rate of the battery cell before and after storage at 60°C. The DCR value after storage at room temperature was measured, and the percentage value of the initial DCR was calculated and recorded as the discharge DCR change rate. (2) 25°C room temperature cycle test: The battery was cycled in an oven at 25±1°C with a charge / discharge current of 1C / 1C, and the discharge capacity of each cycle was calculated. After 500 cycles, the cycling was stopped and the capacity retention rate after cycling was calculated. (3) -20°C low-temperature discharge: The battery was discharged to 80% of the lower limit voltage at a discharge current of 1 C in an oven at -20±1°C, and the low-temperature discharge capacity was determined. The percentage of the 1 C discharge capacity at 25°C was calculated and recorded as the low-temperature discharge capacity retention rate.

[0100] The test results are shown in Table 1 below.

[0101] JPEG2025538745000026.jpg138170

[0102] As can be seen from Table 1 above, adding boron trifluoride pyrosulfate complex lithium salt to the electrolyte can reduce the initial battery impedance, improve low-temperature discharge performance, inhibit gas release and impedance increase during high-temperature storage of the battery, improve cycle performance, and achieve both high and low-temperature performance.

[0103] Comparing Examples 1.2, 1.5, 1.6, 1.7, 1.8, and 1.9, we find that a composition containing primarily monomeric linear compounds can more effectively reduce the internal resistance of the battery and improve cycling and storage capabilities. When a composition contains primarily cyclic compounds, the electrochemical activity is improved and the proportion of boron atoms is significantly reduced, resulting in an increase in initial impedance compared to linear compounds, but slightly improved storage performance. As the content of dimers in the composition increases, the proportion of boron atoms in the structure decreases, resulting in an increase in initial internal resistance and a decrease in low-temperature performance compared to linear compounds, but the film formation quality is better, resulting in slightly improved storage and cycling performance. As the polymerization unit increases, for example, the content of trimers or tetramers in the composition increases, the proportion of boron atoms further decreases, further increasing the initial internal resistance of the battery. If the degree of polymerization is too high, the film formed becomes thick and not dense, resulting in poor cycling and storage performance.

[0104] A comparison of Examples 1.2 and 1.8 shows that adding 1.2# lithium salt and VC to the electrolyte not only avoids the problem of VC increasing the initial battery impedance, but also further improves high-temperature storage performance and cycle performance. A comparison of Examples 1.2 and 1.9 shows that adding 1.2# lithium salt and PS to the electrolyte not only significantly reduces gas release during high-temperature storage, but also avoids the problems of PS increasing the initial battery impedance and degrading low-temperature performance.

[0105] As can be seen from Examples 1.1 to 1.4, the overall performance of the battery improved with increasing amounts of 1.2# lithium salt, but further increases in the amount did not result in continued improvement in battery performance. The optimal amount was approximately 1 wt%. In sodium-ion batteries, 1.2# sodium salt has similar properties to 1.2# lithium salt, and can more effectively reduce the internal resistance of the battery and improve cycle and storage capacity.

[0106] A second embodiment of the present invention provides a method for preparing low-color boron trifluoride pyrosulfate composite metal salt, which is prepared by adding lithium sulfate to lithium pyrosulfate as a starting material to obtain lithium hydrogen sulfate, which is then decomposed to obtain solid lithium pyrosulfate.

[0107] Example 2.1 This example provides a method for preparing boron trifluoride pyrosulfate complex lithium salt, which specifically includes the following steps: S1. 1 mol of Li2SO4 (purity 99.5%) was added to a reaction flask, and 491.27 g of 20 wt% H2SO4 was further added to the reaction flask. The reaction system was stirred to mix uniformly and reacted at 25°C for 4 hours to obtain a LiHSO4 reaction solution. The LiHSO4 reaction solution was rotary evaporated and heated to dryness to remove moisture, obtaining a LiHSO4 solid. S2. LiHSO4 solid was uniformly pulverized to obtain a white powdery solid. The LiHSO4 powder was placed in a crucible, placed in a muffle furnace, and calcined at 150°C for 10 hours to obtain lithium pyrosulfate solid. The SO3 content in the lithium pyrosulfate solid was measured using IC (ion chromatography). The test method was performed in accordance with the industry standard SJ / T11723-2018. The SO3 content in the prepared lithium pyrosulfate solid was found to be 124 ppm. S3. In a dry room with a dew point of -40°C, 0.2 mol of lithium pyrosulfate (99% purity) prepared in step S2 was added to the reaction flask, and dimethyl carbonate was used as the solvent. The reaction system was stirred to homogeneity. 0.4 mol of boron trifluoride gas was then introduced into the reaction flask, and the reaction was allowed to proceed at 50°C for 5 hours, yielding a boron trifluoride pyrosulfate complex lithium salt reaction solution. The reaction solvent and any remaining unreacted boron trifluoride were removed by vacuum distillation. The vacuum distillation temperature was controlled at 60°C for 0.5 hours, yielding a boron trifluoride pyrosulfate complex lithium salt. This was recorded as 2.1% lithium salt.

[0108] According to the test method described in the SJ / T11723-2018 industry standard document, the color was detected by a colorimeter. The detection result shows that the color of 2.1# lithium salt is 15.6 Hazen.

[0109] The composition of the product was also determined by nuclear magnetic resonance F and B spectroscopy, and compared with that of a LiBF4 standard sample. 19 The nuclear magnetic resonance B spectrum measured by F-NMR is 11 The nuclear magnetic resonance (NMR) spectrum was measured by B-NMR. Figures 1 and 2 show the F and B spectra of the 2.1# lithium salt, respectively. As shown in Figures 1 and 2, the peak positions of the F spectrum were as follows: Compound (I-1, M is Li): δ = -151.05 ppm Compound (I-2, M is Li): δ = -146.83 ppm The peak positions of the nuclear magnetic resonance B spectrum were as follows: Compound (I-1, M is Li): δ = -0.75 ppm Compound (I-2, M is Li): δ = -1.12 ppm The nuclear magnetic resonance F spectrum of the standard sample LiBF4 has a peak δ=-156.69 ppm; the nuclear magnetic resonance B spectrum has a peak δ=-1.02 ppm.

[0110] To verify and confirm the compounds, theoretical calculations and analyses were performed on compound (I-1, M is Li) and compound (I-2, M is Li), as well as LiBF4. The structures of the compounds were optimized using DFT / B3 LYP functions and the 6-31** basis set. Nuclear magnetic resonance peak position calculations were performed on the above compounds using DFT / B3 LYP functions and the 6-311** basis set. The calculation results were analyzed by comparing them with the test results and the nuclear magnetic resonance peak positions of a LiBF4 standard sample (F: δ = -156.69 ppm, B: δ = -1.02 ppm). The results were consistent with the above nuclear magnetic resonance spectrum results, demonstrating high reliability. This confirmed that the 2.1# lithium salt is composed primarily of compound I-1 (M is Li), with compound I-2 (M is Li) also present.

[0111] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Li) in the 2.1# lithium salt, excluding the amount of dimethyl carbonate, was 95.84 wt%, and the mass content of compound I-2 (M is Li) was 4.16 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0112] Example 2.2 The procedure of this example was the same as in Example 2.1, except that the reaction temperature in step S3 was changed from 50°C to 70°C. Step S3 yielded a lithium salt of boron trifluoride pyrosulfate, which was recorded as 2.2# lithium salt.

[0113] According to IC test, the SO3 content in the lithium pyrosulfate solid was 189 ppm, and the color of the 2.2# lithium salt was 25.1 Hazen as measured by a colorimeter.

[0114] 2.2#About lithium salts 19 F-NMR and 11 The F and B nuclear magnetic resonance spectra were measured by B-NMR and compared with a LiBF4 standard sample. The peak positions of the F and B spectra were as follows: Compound (I-1, M is Li): A peak was observed at δ=−151.05 ppm in the nuclear magnetic resonance F spectrum and at δ=−0.75 ppm in the nuclear magnetic resonance B spectrum.

[0115] Compound I-3 (M is Li): In the F nuclear magnetic resonance spectrum, peaks were observed at δ = -150.65 ppm and δ = -144.52 ppm, with a peak area integral ratio of 3:1. In the B nuclear magnetic resonance spectrum, peaks were observed at δ = -0.67 ppm and δ = -0.36 ppm, with a peak area integral ratio of 2:1.

[0116] Compound I-4 (M is Li): In the nuclear magnetic resonance F spectrum, peaks were observed at δ = -150.39 ppm and δ = -144.0 ppm, with a peak area integral ratio of 1.5:1. In the nuclear magnetic resonance B spectrum, peaks were observed at δ = -0.65 ppm and δ = -0.26 ppm, with a peak area integral ratio of 1:1.

[0117] Standard sample LiBF4: A peak was observed at δ=-156.69 ppm in the nuclear magnetic resonance F spectrum, and a peak was observed at δ=-1.02 ppm in the nuclear magnetic resonance B spectrum.

[0118] To verify and confirm the compounds, theoretical calculations and analyses were carried out on the compounds (I-1, I-3, I-4, M is Li for all) and LiBF4. The compounds were optimized using the DFT / B3 LYP function and 6-31** basis set, and the nuclear magnetic resonance peak position of the above compounds was calculated using the DFT / B3 LYP function and 6-311** basis set. The calculation results were analyzed by comparing them with the test results and the nuclear magnetic resonance peak position of the LiBF4 standard sample (F: δ = -156.69 ppm, B: δ = -1.02 ppm). The results were consistent with the above nuclear magnetic resonance results, demonstrating high reliability. Based on this, Product 2.2 # It was confirmed that the compound I-1 (M is Li) was the main component, and that compounds I-3 (M is Li) and I-4 (M is Li) were also contained.

[0119] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, in the 2.2# lithium salt, the mass content of compound I-1 (M is Li) excluding the amount of dimethyl carbonate was 84.6 wt%, the mass content of compound I-3 (M is Li) was 9.1 wt%, and the mass content of compound I-4 (M is Li) was 6.3 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0120] Example 2.3 The procedure of this example was the same as in Example 2.1, except that 1 mol of Li2CO3 (purity 99.5%) was used instead of 1 mol of Li2SO4 in step S1. The prepared boron trifluoride pyrosulfate complex lithium salt was recorded as 2.3# lithium salt.

[0121] According to IC test, the SO3 content in the lithium pyrosulfate solid was 177 ppm, and when measured by a colorimeter, the color of the 2.3# lithium salt was 23.5 Hazen.

[0122] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Li) excluding the amount of dimethyl carbonate in the 2.3# lithium salt was 92.6 wt%, and the mass content of compound I-2 (M is Li) was 7.4 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0123] Example 2.4 The procedure of this example was the same as in Example 2.1, except that the baking temperature in step S2 was changed from 150 ° C to 190 ° C. The prepared boron trifluoride pyrosulfate complex lithium salt was recorded as 2.4# lithium salt.

[0124] According to IC test, the SO3 content in the lithium pyrosulfate solid was 372 ppm, and when measured by a colorimeter, the color of the 2.4# lithium salt was 45.1 Hazen.

[0125] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Li) in the 2.4# lithium salt, excluding the amount of dimethyl carbonate, was 90.3 wt% and the mass content of compound I-2 (M is Li) was 9.7 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0126] Example 2.5 The procedure of this example was the same as in Example 2.1, except that in step S1, the concentration of dilute sulfuric acid was adjusted by adding 270.21 g of 40 wt% H2SO4. The prepared boron trifluoride pyrosulfate complex lithium salt was recorded as 2.5# lithium salt. According to IC test, the SO3 content in the lithium pyrosulfate solid was 316 ppm, and the color of the 2.5# lithium salt was 42.6 Hazen as measured by a colorimeter. The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Li) in the 2.5# lithium salt, excluding the amount of dimethyl carbonate, was 94.3 wt% and the mass content of compound I-2 (M is Li) was 5.7 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0127] Example 2.6 The procedure of this example was the same as in Example 2.1, except that NaSO was used instead of LiSO. Sodium pyrosulfate solid was prepared in steps S1 and S2. Boron trifluoride pyrosulfate complex sodium salt was obtained in step S3. This was recorded as 2.1# sodium salt.

[0128] According to IC testing, the SO3 content in the solid sodium pyrosulfate was 154 ppm, and when tested with a colorimeter, the color of the 2.1# sodium salt was 21.1 Hazen.

[0129] 2.1#About sodium salts 19 F-NMR and 11 The results were measured by B-NMR and compared with a standard NaBF4 sample. The peak positions of the nuclear magnetic resonance F spectrum were as follows: Compound (I-1, M is Na): δ = -154.24 ppm Compound (I-2, M is Na): δ = -150.21 ppm The peak positions of the nuclear magnetic resonance B spectrum were as follows: Compound (I-1, M is Na): δ = -0.64 ppm Compound (I-2, M is Na): δ = -1.01 ppm The nuclear magnetic resonance F spectrum of the standard sample NaBF4 had a peak at δ=-159.94 ppm, and the nuclear magnetic resonance B spectrum had a peak at δ=-0.89 ppm.

[0130] To verify and confirm the compounds, theoretical calculations and analyses were performed on compounds (I-1, M is Na) and (I-2, M is Na), as well as NaBF4. The structures of the compounds were optimized using DFT / B3 LYP functions and the 6-31** basis set. Nuclear magnetic resonance peak position calculations were performed on the above compounds using DFT / B3 LYP functions and the 6-311** basis set. The calculation results were analyzed by comparing them with the test results and the nuclear magnetic resonance peak positions of a LiBF4 standard sample (F: δ = -159.94 ppm, B: δ = -0.89 ppm). The results were consistent with the above nuclear magnetic resonance spectrum results, demonstrating high reliability. This confirmed that the 2.1# sodium salt is composed primarily of compound I-1 (M is Na), with compound I-2 (M is Na) also present.

[0131] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound (I-1) in the 2.1# sodium salt, excluding the amount of dimethyl carbonate, was 92.72 wt% and the mass content of compound (I-2) was 7.28 wt%. Furthermore, the area integration conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0132] Comparative Example 2.1 In this comparative example, lithium pyrosulfate was prepared using disilyl sulfate ester and lithium hexafluorophosphate as raw materials, and this lithium pyrosulfate was used to prepare a lithium boron trifluoride pyrosulfate complex salt. The specific steps are as follows: S1. In a dry room with a dew point of -40°C, 1.0 mol of lithium hexafluorophosphate (LiPF6, purity 99.9%) was added to a reaction flask, and ethyl methyl carbonate was added as a solvent. The mass ratio of ethyl methyl carbonate to LiPF6 was 6:1. After stirring to uniformly mix the reaction system, bistrimethylsilyl sulfate was added to the reaction flask in batches (controlling the reaction temperature below approximately 25°C), venting after each addition. A total of 1.5 mol of bistrimethylsilyl sulfate was added, and the reaction was allowed to proceed at 25°C for 1 hour to obtain the reaction product. S2. The reaction product was degassed under reduced pressure for 0.5 hours to remove sulfur trioxide, phosphoryl fluoride, and fluorosilane gases, yielding a crude product. Isopropyl ether was added to the crude product as a crystallization solvent, and the mixture was stirred at 25°C for 1.5 hours to precipitate crystals. The mixture was then left to stand and filtered. The filter cake was washed two or three times with isopropyl ether and then dried under reduced pressure at 60°C, yielding 94.5 g of powdered lithium pyrosulfate product. The product yield was 99.47%. Step S3 is the same as in Example 2.1. The obtained boron trifluoride pyrosulfate complex lithium salt was recorded as 2.6# lithium salt.

[0133] According to IC test, the SO3 content in the lithium pyrosulfate solid was 3512 ppm, and the color of the 2.6# lithium salt was 546 Hazen as measured by a colorimeter.

[0134] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Li) in the 2.6# lithium salt, excluding the amount of dimethyl carbonate, was 90.1 wt%, and the mass content of compound I-2 (M is Li) was 8.9 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0135] Comparative Example 2.2 The procedure of this comparative example is the same as that of Example 2.1, except that the baking temperature in step S2 is adjusted from 150 ° C to 320 ° C. The prepared boron trifluoride pyrosulfate complex lithium salt was recorded as 2.7# lithium salt.

[0136] According to IC test, the SO3 content in the lithium pyrosulfate solid was 721 ppm, and when measured by a colorimeter, the color of the 2.7# lithium salt was 89.3 Hazen.

[0137] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Li) in the 2.7# lithium salt, excluding the amount of dimethyl carbonate, was 89.5 wt%, and the mass content of compound I-2 (M is Li) was 10.5 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0138] Comparative Example 2.3 The procedure of this comparative example was the same as that of Example 2.6, except that the baking temperature in step S2 was changed from 150°C to 320°C. The prepared boron trifluoride pyrosulfate complex sodium salt was recorded as 2.2# sodium salt.

[0139] According to IC test, the SO3 content in the solid sodium pyrosulfate was 813 ppm, and when measured by a colorimeter, the color of the 2.2# sodium salt was 98.4 Hazen.

[0140] The peak areas of the nuclear magnetic resonance F spectrum were integrated and calculated. As a result, the mass content of compound I-1 (M is Na) excluding the amount of dimethyl carbonate in the 2.2# sodium salt was 80.2 wt%, and the mass content of compound I-2 (M is Na) was 19.8 wt%. Furthermore, the area integral conversion using the B spectrum agreed with the calculated results of the F spectrum, confirming the high reliability of the calculation.

[0141] Comparing the experimental results of Examples 2.1 to 2.5 and Comparative Example 2.1 above, it can be seen that compared with the preparation route using disilyl sulfate ester and lithium hexafluorophosphate as raw materials, the SO content in the lithium pyrosulfate boron trifluoride complex salt prepared using lithium sulfate as raw material was low (SO in the lithium pyrosulfate solid was transferred to the lithium pyrosulfate boron trifluoride complex salt product during the synthesis process), and the color of the product was low.

[0142] 2, Electrolyte 2.1 Preparation of basal electrolyte solution In an argon-filled glove box (water content <5 ppm, oxygen content <10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:EMC:DEC = 4:4:2. Lithium hexafluorophosphate (LiPF6) was then slowly added to the mixed solution until the molar concentration reached 1.0 mol / L, yielding base electrolyte 2.1.

[0143] 2.2 Preparation of Basal Electrolyte In an argon-filled glove box (moisture < 5 ppm, oxygen < 10 ppm), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:EMC:PC = 7:10:1, and sodium hexafluorophosphate (NaPF6) was slowly added to the mixed solution until the molar concentration of NaPF6 reached 1.0 mol / L, yielding base electrolyte 2.2.

[0144] Application Example 2.1 The electrolyte of this application example was obtained by adding 0.2 wt% of 2.1# lithium salt to the base electrolyte 2.1.

[0145] Application example 2.2 The electrolyte for this application example was obtained by adding 1 wt% of 2.1# lithium salt to the basic electrolyte 2.1.

[0146] Application Example 2.3 The electrolyte of this application example was obtained by adding 2 wt% of 2.1# lithium salt to the base electrolyte 2.1.

[0147] Application Example 2.4 The electrolyte for this application example was obtained by adding 3 wt% of 2.1# lithium salt to the base electrolyte 2.1.

[0148] Application Example 2.5 The electrolyte for this application example was obtained by adding 1 wt% of 2.2# lithium salt to the base electrolyte 2.1.

[0149] Application Example 2.6 The electrolyte for this application example was obtained by adding 1 wt% of 2.3# lithium salt to the base electrolyte 2.1.

[0150] Application Example 2.7 The electrolyte for this application example was obtained by adding 1 wt% of 2.4# lithium salt to the base electrolyte 2.1.

[0151] Application Example 2.8 The electrolyte for this application example was obtained by adding 1 wt% of 2.5# lithium salt to the base electrolyte 2.1.

[0152] Application Example 2.9 The electrolyte of this application example was obtained by adding 1 wt% of 2.1# lithium salt and 1% wt% vinylene carbonate (VC) to the base electrolyte 2.1.

[0153] Application Example 2.10 The electrolyte of this application example was obtained by adding 1 wt% of 2.1# lithium salt and 1% wt% of 1,3-propane sultone (PS) to the base electrolyte 2.1.

[0154] Application Example 2.11 The electrolyte of this application example was obtained by adding 1 wt% of 2.1# lithium salt and 1% wt% vinyl sulfate (DTD) to the base electrolyte 2.1.

[0155] Application Example 2.12 The electrolyte for this application example was obtained by adding 1 wt% of 2.1# sodium salt to the base electrolyte 2.2.

[0156] Application comparison example 2.1 1 wt% of 2.6# lithium salt was added to the base electrolyte 2.1 to obtain the electrolyte of this comparative application example.

[0157] Application comparison example 2.2 1 wt% of 2.7# lithium salt was added to the base electrolyte 2.1 to obtain the electrolyte of this comparative application example.

[0158] Application comparison example 2.3 The base electrolyte 2.1 was not treated in any way to obtain the electrolyte of this comparative application example.

[0159] Application comparison example 2.4 1 wt% of 2.2# sodium salt was added to the base electrolyte 2.2 to obtain the electrolyte of this comparative application example.

[0160] Application comparison example 2.5 The base electrolyte 2.2 was not treated in any way to obtain the electrolyte of this comparative application example.

[0161] 2. Electrochemical performance test Using the electrolytes of Application Examples 2.1 to 2.11 and Application Comparative Examples 2.1 to 2.3, lithium ion batteries with a soft pack capacity of 1260 mAh were fabricated. The lithium ion batteries comprised a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material was a ternary positive electrode LiNi 0.6 Co 0.2 Mn 0.2 The cathode active material was O2, and the anode active material was high-capacity graphite. The preparation process was as follows: the cathode sheet, separator, and anode sheet were wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrodes met the required level. After baking, the cell was filled with electrolyte, and the cells were left to stand, underwent chemical conversion treatment, capacity grading, and aging processes to obtain the finished lithium-ion soft pack cells.

[0162] Using the electrolytes of Application Example 2.12 and Application Comparative Examples 2.4 to 2.5, sodium ion batteries with a soft pack capacity of 1260 mAh were fabricated. The sodium ion batteries comprised a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material was a ternary positive electrode NaNi 0.33 Fe 0.33 Mn 0.33 The active material was O2, and the negative electrode active material was hard carbon. The preparation process was as follows: the positive electrode sheet, separator, and negative electrode sheet were wound together on a core, sealed with aluminum plastic film, and then baked to ensure the moisture content of the electrode met the required level. After baking, the cell was filled with electrolyte, and the cells were left to stand, underwent chemical conversion treatment, capacity grading, and aging processes to obtain the finished sodium-ion soft pack cell.

[0163] The lithium-ion batteries and sodium-ion batteries prepared as described above were subjected to performance tests (test voltage: 2.8 to 4.2 V). The following performance tests were mainly carried out. (1) 60°C high-temperature storage test: The battery was charged to 100% SOC and stored in an oven at 60±2°C for 28 days. The volume was measured before and after storage, and the volume expansion rate of the battery cell before and after storage at 60°C was obtained. The DCR value after storage at room temperature was calculated, and the percentage value of the initial DCR was calculated and recorded as the discharge DCR change rate. (2) 45°C high temperature cycle test: The battery was cycled in an oven at 45±1°C with a charge / discharge current of 1C / 1C, and the discharge capacity was calculated for each cycle. After 500 cycles, the cycling was stopped and the capacity retention rate after cycling was calculated. (3) -20°C low-temperature discharge: The battery was discharged in an oven at -20±1°C with a discharge current of 1C to 80% of the lower limit voltage, and the low-temperature discharge capacity was determined. The percentage of the 1C discharge capacity at 25°C was calculated and recorded as the low-temperature discharge capacity retention rate.

[0164] JPEG2025538745000027.jpg132170

[0165] As can be seen from Table 2 above, comparing Application Examples 2.2, 2.5-2.8 and Comparative Application Examples 2.1-2.3, or Application Example 2.12 and Comparative Application Examples 2.4 and 2.5, the boron trifluoride pyrosulfate complex metal salt prepared using pyrosulfate with a low SO3 content as the raw material has low color, suppresses gas release and impedance increase during high-temperature storage, and has the effect of improving low-temperature performance.

[0166] Furthermore, comparing Application Example 2.2, Application Example 2.7, and Comparative Application Example 2.2, it can be seen that with increasing calcination temperature, the SO3 content of lithium pyrosulfate and the color of the prepared boron trifluoride pyrosulfate complex lithium salt both increase, and the electrochemical performance used in lithium-ion battery electrolytes tends to decrease. This is because, as the calcination temperature increases, some of the lithium pyrosulfate decomposes to generate SO3, which increases the SO3 content in the prepared boron trifluoride pyrosulfate complex salt. The SO3 promotes the occurrence of electrolyte / electrode side reactions in the battery, thereby reducing its electrochemical performance.

[0167] As can be seen from a comparison of Application Examples 2.2 and 2.9, adding 2.1# lithium salt and VC to the electrolyte simultaneously avoids the increase in battery initial impedance caused by VC and improves high-temperature storage performance and cycle performance. As can be seen from a comparison of Application Examples 2.2 and 2.10, adding 2.1# lithium salt and PS to the electrolyte simultaneously demonstrates the advantage of PS in suppressing gas release during high-temperature storage and avoids the defects of PS increasing initial impedance and deteriorating low-temperature performance.

[0168] Comparing Application Examples 2.1 to 2.4, it can be seen that as the amount of lithium salt added in 2.1# increases, the overall battery performance gradually improves within a certain range of addition. However, as the amount of added increases further, the battery performance cannot be further improved. The optimal amount of added lithium salt is about 1 wt% to 2 wt%.

[0169] A third embodiment of the present invention provides a high-voltage rapid charging lithium ion secondary battery in which boron trifluoride pyrosulfate complex lithium salt interacts with a specific negative electrode active material.

[0170] In the following examples and comparative examples of the present invention, the types of novel composite lithium salts are as follows: Composite lithium salt A1: containing 95 wt % of compound II-1 and 5 wt % of compound II-2. Composite lithium salt A2: containing 90 wt% of compound II-1, 6 wt% of compound II-2, and 4 wt% of compound II-3.

[0171] JPEG2025538745000028.jpg10170

[0172] Example 3.1 This embodiment provides a method for preparing a lithium ion secondary battery, which specifically includes the following steps: Preparation of positive electrode sheet The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi) 0.7 Co 0.2 Mn 0.1 O2, conductive carbon black Super-P, and adhesive polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 93:4:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry was uniformly applied to both sides of an aluminum foil current collector, dried, rolled, and vacuum-dried, and an aluminum lead wire was welded to it using an ultrasonic welder to obtain a positive electrode sheet.

[0173] Preparation of negative electrode sheet Conductive carbon black, the negative electrode active material, and styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC), the adhesives, were mixed in a mass ratio of 92:2:3:3 and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was applied to both sides of a copper foil current collector, dried, rolled, and vacuum-dried, and a nickel lead wire was welded to it using an ultrasonic welder to obtain a negative electrode sheet. The negative electrode active material was a copper foil with a specific surface area of ​​20 m. 2 / g of hard carbon was used.

[0174] Cell preparation A 20 μm-thick polyethylene microporous membrane was placed between the positive electrode sheet and the negative electrode sheet as a separator. The sandwich structure consisting of the positive electrode sheet, negative electrode sheet, and separator was then wound up, the tab was pulled out, and the structure was sealed in aluminum plastic film to obtain a soft-pack lithium-ion battery cell with an unfilled capacity of 1000 mAh.

[0175] Preparation of electrolyte Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 3:2:5, and then lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) were added to the mixture to a molar concentration of 0.75 mol / L and 0.25 mol / L, respectively, to form a base electrolyte. 5.0% of the composite lithium salt A1 was added to the total mass of the electrolyte.

[0176] Cell filling and chemical treatment The electrolyte prepared in this example was poured into a cell in a glove box containing less than 10 ppm of moisture. The amount of electrolyte must be sufficient to fill the gaps within the cell. The cell was then subjected to a chemical conversion treatment according to the following steps: 30 min of constant current charging at 0.01 C, 60 min of constant current charging at 0.02 C, 90 min of constant current charging at 0.05 C, and 240 min of constant current charging at 0.1 C. After 1 hour of static charging, the cell was shaped and sealed. It was then charged at a constant current of 0.2 C to 4.40 V, allowed to stand at room temperature for 24 hours, and then discharged at a constant current of 0.2 C to 3.0 V.

[0177] Based on Example 3.1, the composite lithium salt and its content in the electrolyte, and the negative electrode active material and its content were changed, and other operations were the same. A lithium ion secondary battery was prepared according to the electrolyte and negative electrode active material formulations in Table 3 below.

[0178] JPEG2025538745000029.jpg137170

[0179] Based on Example 3.6, the electrolyte formulation was changed, and the negative electrode active material, content and other operations were kept the same, and a lithium ion secondary battery was prepared according to the following Table 4: Electrolyte Formulation Table.

[0180] JPEG2025538745000030.jpg64170

[0181] 2. Electrochemical performance test The lithium secondary battery was tested for various performance characteristics, including the following: (1) AC impedance test This test was carried out at room temperature of 25°C, with the secondary battery being charged to 50% SOC (state of charge). An AC impedance test was carried out on the secondary battery using an electrochemical workstation with an electrochemical impedance spectrum test function. The initial frequency of the test was 10,000 Hz, the cutoff frequency was 0.01 Hz, the disturbance voltage was ±0.01 V, and the test points were 60 or more. The impedance data Z at each test frequency was n (n is the test frequency) was obtained, and the ratio c% of the 1-0.01 Hz AC impedance to the 10,000-0.01 Hz AC impedance was calculated according to the following formula. c%=(Z 0.01 -Z1) / (Z 0.01 -Z 10000 )×100% This ratio reflects the situation where the diffusion impedance dominates the cell impedance, but also includes the situation where a portion of the charge transfer impedance dominates the cell impedance.

[0182] (2) Low-temperature performance test Low-temperature discharge capacity: At room temperature (25°C), the battery was charged at a constant current of 1C to 4.45V, then charged at a constant voltage until the current decreased to 0.05C. It was then discharged at a constant current of 1C to 2.8V, and the room-temperature discharge capacity C1 was recorded. The above charging steps were repeated until the battery reached 4.45V. The ambient temperature was then lowered to -20°C, and the battery was left at ambient temperature for 5 hours to cool. It was then discharged at a constant current of 0.5C to 2.5V, and the discharge capacity C2 and capacity retention rate R1 were recorded. R1=C2 / C1*100% Low-temperature DCIR impedance: Fast charging performance test: After adjusting the battery to 50% SOC at room temperature (25°C) with a current of 0.2C, the ambient temperature was lowered to -20°C and the battery was left at that temperature for 5 hours to cool the battery down. After that, it was discharged at a constant current of 1C I1 for 30 seconds, and the voltage value V1 at the last 1 second of discharge and the voltage value V2 at 30 seconds of discharge were recorded. The low-temperature DCIR impedance R2 was calculated using the following formula: R2 = (V1 - V2) / I1.

[0183] (3) Multiplier charging performance test The battery was charged at a constant current of 4C at room temperature (25°C) up to a charge end voltage of 4.45V, and then charged at a constant voltage until the current dropped to 0.1C. The total charge capacity C3 and the charge capacity C4 in the constant current section were recorded, and the constant current charge ratio R3 of the battery was calculated according to the following formula. R3 = C4 / C3 × 100%.

[0184] The specific results are shown in Table 5 below.

[0185] JPEG2025538745000031.jpg236170

[0186] As can be seen from a comparison of Examples 3.1 to 3.2 with Comparative Examples 3.1 to 3.2 in Table 5 above, when using a negative electrode material with a specific specific surface area in a secondary battery, only by using an electrolyte containing 0.02 to 5.0 wt% of the new composite lithium salt can a specific negative electrode-electrolyte interaction be achieved, reducing the diffusion impedance and charge transport impedance of the battery and improving the battery's high-voltage rapid charging performance and low-temperature performance.

[0187] As can be seen from the comparison between Example 3.6 and Comparative Example 3.5 in Table 5 above, only when the lithium salt additive used is the composite lithium salt additive described in the present invention, the effect of improving the fast charging performance and low temperature performance of the secondary battery can be obtained.

[0188] As can be seen from a comparison of Examples 3.1 to 3.4 and Comparative Examples 3.3 to 3.4 in Table 5 above, a specific electrolyte additive was used in the secondary battery, and the specific surface area was 0.1 to 20.0 m 2 When using a negative electrode active material with a specific specific surface area of ​​1 / g, the interaction between the specific negative electrode and the electrolyte reduces the diffusion impedance and charge transport impedance of the battery, improving the battery's high-voltage rapid charging performance and low-temperature performance. If the specific surface area is too small, there are too few active sites on the negative electrode active material, which is unfavorable for the occurrence of negative electrode-electrolyte interactions. If the specific surface area is too large, there is insufficient new composite lithium salt to participate in the negative electrode-electrolyte interfacial interactions, affecting the stability of the interfacial phase.

[0189] As can be seen from a comparison of Examples 3.1 to 3.4 or Examples 3.10 to 3.12 in Table 5 above, when the amount of the novel composite lithium salt used is further reduced to 0.1 to 2.0 wt%, the rapid charging performance and low temperature performance of the secondary battery are further improved.

[0190] As can be seen from a comparison of Examples 3.1 to 3.4 or Examples 3.10, 3.13 to 3.14 in Table 5 above, the specific surface area of ​​the negative electrode active material is further increased to 0.5 to 10.0 m 2 / g, the rapid charging performance and low temperature performance of the secondary battery are further improved.

[0191] In the present invention, the novel composite lithium salt interacts with the negative electrode active material, and therefore the amount of the novel composite lithium salt used and the specific surface area of ​​the negative electrode active material affect each other. When the specific surface area of ​​the negative electrode active material varies within the range of the present invention, the amount of the novel composite lithium salt used must also vary within the range of the present invention in order to obtain optimal performance effects.

[0192] As can be seen from a comparison between Example 3.10 and Comparative Examples 3.5 to 3.6 in Table 5 above, when using a negative electrode material of a specific type and specific surface area, if the amount of novel composite lithium salt added is too small, it becomes difficult to form a dense, highly permeable interfacial phase, and other lithium salts and / or solvents in the electrolyte are involved in the interfacial phase film formation reaction, increasing the interfacial impedance and deteriorating fast charge performance and low temperature performance.If the amount of novel composite lithium salt added is too large, it itself forms an interfacial phase that is too dense during the battery production process, which is detrimental to lithium ion transport and is also detrimental to fast charge performance and low temperature performance.

[0193] As can be seen from a comparison of Examples 3.5 to 3.9 and Examples 3.15 to 3.18 in Table 5 above, when hard carbon is used as one of the negative electrode active materials, it is advantageous to further improve the ion conduction ability of the negative electrode, and forms a stable and highly ion-permeable lithium ion transmission channel with the novel composite lithium salt, thereby improving the fast charging performance and low-temperature performance of the battery.

[0194] As can be seen from a comparison of Example 3.6 with Examples 3.19 to 3.21 in Table 5 above, adding 0.1% to 2.0 wt% of a different type of other lithium salt to the base electrolyte is advantageous for further improving the fast charging performance and low temperature performance of the battery.

[0195] As can be seen from the comparison of Example 3.6 with Examples 3.22 to 3.23 in Table 5 above, adding 0.1% to 2.0 wt% of different types of basic additives to the base electrolyte is advantageous for further improving the fast charging performance and low temperature performance of the battery.

Claims

1. Use of boron trifluoride pyrosulfate complex metal salt in an electrolyte solution, Adding boron trifluoride pyrosulfate complex metal salt having a structure represented by the following formula (I) and / or (II) to an electrolytic solution, In formula (I), M is Li or Na, and X is independently selected from F or a substituent represented by the following formula (A): In formula (A), M is similarly Li or Na, and X is similarly independently selected from F or a substituent represented by formula (A), and is repeated until X finally becomes F. The mass percentage of the boron trifluoride pyrosulfate complex metal salt in the electrolyte is 0.1 to 15.0 wt %.

2. The use according to claim 1, characterized in that the mass percentage of the boron trifluoride pyrosulfate complex metal salt in the electrolyte is 0.2 to 3.0 wt%.

3. The boron trifluoride pyrosulfate complex metal salt has the following structure:

2. The use according to claim 1, characterized in that the compound is at least one selected from the group consisting of compounds represented by the formula: (wherein M is Li or Na).

4. The boron trifluoride pyrosulfate complex metal salt can be obtained by the following steps: The use according to any one of claims 1 to 3, characterized in that lithium pyrosulfate / sodium pyrosulfate is reacted with boron trifluoride gas and / or a boron trifluoride complex in a reaction solvent to obtain a boron trifluoride pyrosulfate complex metal salt reaction solution.

5. The use according to claim 4, characterized in that the reaction solvent is at least one selected from 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, phenylacetonitrile, and propionitrile.

6. 5. The use according to claim 4, wherein the boron trifluoride complex is at least one selected from the group consisting of boron trifluoride ether complex, boron trifluoride ethylene glycol dimethyl ether complex, boron trifluoride dimethyl carbonate complex, boron trifluoride pyridine complex, boron trifluoride ethylamine complex, boron trifluoride butyl ether complex, boron trifluoride methyl ether complex, boron trifluoride acetonitrile complex, boron trifluoride piperidine complex, boron trifluoride phenol complex, boron trifluoride tetrahydrofuran complex, boron trifluoride dimethyl sulfide complex, and boron trifluoride morpholine complex.

7. 5. The use according to claim 4, characterized in that the molar ratio of lithium pyrosulfate / sodium pyrosulfate to boron trifluoride gas and / or boron trifluoride complex is (0.2-1.2):

1.

8. The use according to claim 4, characterized in that the reaction temperature is 10-90°C and the reaction time is 1-48h.

9. The use according to claim 4, characterized in that the reaction solvent and unreacted boron trifluoride are removed from the reaction solution of boron trifluoride pyrosulfate complex metal salt by atmospheric distillation or reduced pressure distillation to obtain boron trifluoride pyrosulfate complex metal salt.

10. The use according to any one of claims 4 to 9, characterized in that when the reaction temperature is 10 to 40°C, the mass percentage of compound (2) in the boron trifluoride pyrosulfate complex metal salt is 50% or more, and when the reaction temperature is 40 to 90°C, the mass percentage of compound (1) in the boron trifluoride pyrosulfate complex metal salt is 50% or more.

11. The electrolyte further comprises a main salt, an organic solvent and a basic additive; the main salt is selected from a main lithium salt or a main sodium salt, the main lithium salt being at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, and lithium difluorobisoxalate phosphate; and the main sodium salt being at least one selected from sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonimide), and sodium difluorophosphate; the organic solvent is at least one selected from the group consisting of a C3 to C6 carbonate compound, a C3 to C8 carboxylic acid ester compound, a sulfone compound, and an ether compound; 11. The use according to any one of claims 1 to 10, characterized in that the base additive is at least one selected from sulfonate ester compounds, sulfate ester compounds, fluorinated carbonate compounds, unsaturated carbonate compounds, and fluorine-containing lithium / sodium salt compounds.

12. the main lithium salt is at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and has a molar concentration in the electrolyte solution of 0.1 to 4.0 mol / L; the main sodium salt is at least one selected from sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonimide), and has a molar concentration in the electrolyte of 0.1 to 4.0 mol / L; the C3 to C6 carbonate compound is at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; the C3 to C8 carboxylic acid ester compound is at least one selected from γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, and propyl propionate; the sulfone compound is at least one selected from sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone; and the ether compound is selected from triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether, 12. The use according to claim 11, wherein the base additive is at least one selected from the group consisting of vinylene carbonate, fluorinated ethylene carbonate, vinyl sulfate, 1,3-propane sultone, tris(trimethylsilyl)phosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalato)phosphate, lithium difluoro(oxalato)borate, sodium difluoro(oxalato)borate, sodium difluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium difluorobis(oxalato)phosphate, wherein the mass percentage of any one of the base additives in the electrolyte is 0.1 to 5.0 wt %, and the base additive is different from the main salt.

13. 1. A method for preparing a low color boron trifluoride pyrosulfate complex metal salt, comprising: The preparation method includes adding SO ３ The method includes using a pyrosulfate having a content of ≦500 ppm as a raw material and reacting the pyrosulfate with boron trifluoride gas or a boron trifluoride complex to obtain a reaction solution having a color of ≦50 Hazen, wherein the reaction solution contains at least a boron trifluoride pyrosulfate complex metal salt having a structure represented by the following formula (I-1): wherein M is Li or Na.

14. The pyrosulfate raw material is obtained by the following steps: (1) preparing a hydrogen sulfate salt: reacting an inorganic salt with dilute sulfuric acid to obtain a hydrogen sulfate salt, the inorganic salt being at least one selected from sulfate salts, metal oxides, carbonate salts, metal hydroxides, and hydrogen carbonate salts, and the hydrogen sulfate salt being sodium hydrogen sulfate or lithium hydrogen sulfate; (2) preparing pyrosulfate salt: the hydrogen sulfate solid is thermally decomposed to obtain pyrosulfate salt, and the pyrosulfate salt is lithium pyrosulfate or sodium pyrosulfate, according to claim 13.

15. The preparation method according to claim 14, characterized in that in step (1), the mass concentration of dilute sulfuric acid is 10% to 65 wt%.

16. The preparation method according to claim 14, characterized in that in step (1), the molar ratio of inorganic salt to dilute sulfuric acid is (0.8-1.2):

1.

17. The preparation method according to claim 14, characterized in that in step (1), the reaction temperature is 0-80°C and the reaction time is 0.5-24h.

18. The preparation method according to claim 14, characterized in that in step (2), the hydrogen sulfate solid is calcined at 100-300°C for 0.5-72h to obtain pyrosulfate.

19. The preparation method according to claim 18, characterized in that in step (2), the hydrogen sulfate solid is calcined at 130-250°C for 2-36h to obtain pyrosulfate.

20. SO in pyrosulfate raw material ３ 20. A process according to any one of claims 13 to 19, characterized in that the content is ≦200 ppm.

21. 14. The method according to claim 13, wherein the reaction solvent is at least one selected from the group consisting 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, phenylacetonitrile, and propionitrile.

22. 14. The method according to claim 13, wherein the boron trifluoride complex is at least one selected from the group consisting of boron trifluoride etherate complex, boron trifluoride ethylene glycol dimethyl etherate complex, boron trifluoride dimethyl carbonate complex, boron trifluoride pyridine complex, boron trifluoride ethylamine complex, boron trifluoride butyl etherate complex, boron trifluoride methyl etherate complex, boron trifluoride acetonitrile complex, boron trifluoride piperidine complex, boron trifluoride phenol complex, boron trifluoride tetrahydrofuran complex, boron trifluoride dimethyl sulfide complex, and boron trifluoride morpholine complex.

23. 14. The method of claim 13, wherein in the reaction of pyrosulfate with boron trifluoride gas or boron trifluoride complex, the molar ratio of pyrosulfate to boron trifluoride gas or boron trifluoride complex is (0.33-1.0):1, the reaction temperature is 40-70°C, and the reaction time is 5-24 hours.

24. The reaction solution contains at least 80 wt % or more of the boron trifluoride pyrosulfate complex metal salt having a structure represented by the formula (I-1), and the remainder is the salt of the following formulas (I-2), (I-3), (I-4), (I-5), and (I-6): (wherein M is Li or Na).

25. The preparation method according to claim 24, characterized in that the reaction solution contains 80 to 95 wt % of the boron trifluoride pyrosulfate complex metal salt having a structure represented by formula (I-1).

26. Use of the boron trifluoride pyrosulfate complex metal salt with low color obtained by the preparation method according to any one of claims 13 to 25 in an electrolyte solution, The method according to any one of claims 13 to 25, characterized in that the prepared low-color boron trifluoride pyrosulfate complex metal salt is added to an electrolytic solution so that the mass percentage of the boron trifluoride pyrosulfate complex metal salt in the electrolytic solution is 0.01 to 15 wt %.

27. A high-voltage rapid charging lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte solution, The electrolyte solution includes a main lithium salt, a non-aqueous solvent, and an additive. The additive includes a novel composite lithium salt. The novel composite lithium salt includes at least a boron trifluoride pyrosulfate composite lithium salt having a structure represented by the following formula (II-1): The novel composite lithium salt is present in an amount of 0.02 to 5.0 wt % of the total mass of the electrolyte; The negative electrode contains an active material that can reversibly absorb and release lithium ions, and the specific surface area of ​​the active material is 0.1 to 20.0 m ２ / g.

28. The specific surface area of ​​the active material is 0.5 to 10.0 m ２ 28. The high-voltage rapid charging lithium ion secondary battery according to claim 27, wherein the Cr content is 0.15 / g.

29. 28. The high-voltage fast charging lithium-ion secondary battery according to claim 27, wherein the active material of the negative electrode is selected from a carbon material and / or a silicon material, the carbon material being at least one selected from natural graphite, artificial graphite, and hard carbon, and the silicon material being selected from silicon and / or silicon monoxide.

30. 30. The high-voltage rapid charging lithium-ion secondary battery according to claim 29, wherein the active material of the negative electrode contains at least hard carbon, and the mass content of the hard carbon is 0.1 to 100%.

31. 31. The high-voltage rapid charging lithium-ion secondary battery according to claim 30, wherein the mass content of the hard carbon in the active material of the negative electrode is 5 to 20%.

32. The high-voltage rapid charging lithium-ion secondary battery of claim 27, wherein the novel composite lithium salt is 0.1 to 2.0 wt% of the total mass of the electrolyte.

33. The high-voltage rapid charging lithium-ion secondary battery according to any one of claims 27 to 32, characterized in that the AC impedance of the lithium-ion secondary battery in the 1 to 0.01 Hz frequency range is 40 to 80% of the AC impedance in the 10,000 to 0.01 Hz frequency range.

34. The high-voltage rapid charging lithium-ion secondary battery according to claim 33, wherein the AC impedance of the lithium-ion secondary battery in the 1 to 0.01 Hz frequency range is 60 to 70% of the AC impedance in the 10,000 to 0.01 Hz frequency range.

35. The novel composite lithium salts are represented by the following formulae (II-2), (II-3), (II-4), (II-5), and (II-6): The novel composite lithium salt is at least one selected from compounds represented by the formula (II-1), and the novel composite lithium salt contains at least 80.0 wt% or more of the boron trifluoride pyrosulfate composite lithium salt having a structure represented by the formula (II-1). The high-voltage rapid charging lithium ion secondary battery according to claim 27.

36. The novel composite lithium salt contains 80.0 to 95.0 wt % of the boron trifluoride pyrosulfate composite lithium salt having a structure represented by formula (II-1), and the remainder is at least one selected from compounds (II-2), (II-3), (II-4), (II-5), and (II-6). The high-voltage rapid charging lithium ion secondary battery according to claim 35.

37. 28. The high-voltage fast charging lithium-ion secondary battery of claim 27, wherein the additives further include a base additive, the base additive being at least one selected from vinylene carbonate, fluorinated ethylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)phosphate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, succinic anhydride, hexadionitrile, cyclohexylbenzene, lithium difluorobis(oxalato)phosphate, and lithium difluoro(oxalato)borate, and the mass percentage of any one base additive in the electrolyte is 0.1 to 5.0 wt %.

38. 28. The high-voltage fast charging lithium-ion secondary battery of claim 27, wherein the main lithium salt is at least one selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, and lithium difluorobisoxalatephosphate, and has a molar concentration of 0.1 to 4.0 mol / L.

39. the non-aqueous solvent is at least one selected from the group consisting of a C3 to C6 carbonate compound, a C3 to C8 carboxylic acid ester compound, a sulfone compound, an ether compound, and a nitrile compound; The C3 to C6 carbonate compound is at least one selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl-2,2,2-trifluoroethyl; the C3 to C8 carboxylic acid ester compound is at least one selected from γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, and 2,2-difluoroethyl acetate; and the sulfone compound is at least one selected from γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl propionate, and 2,2-difluoroethyl acetate.

28. The high-voltage rapid charging lithium-ion secondary battery according to claim 27, wherein the compound is at least one selected from the group consisting of sulfolane, dimethyl sulfoxide, dimethyl sulfone, and diethyl sulfone; the ether-based compound is selected from triethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether; and the nitrile-based compound is at least one selected from the group consisting of acetonitrile, succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 4-fluorobenzonitrile, and 1,2-bis(cyanoethoxy)ethane.

40. 28. The high-voltage fast charging lithium-ion secondary battery according to claim 27, wherein the positive electrode active material is at least one selected from the group consisting of lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, layered lithium manganese oxide, spinel lithium manganese oxide, and lithium nickel manganese oxide materials.

41. The high-voltage rapid-charge lithium-ion secondary battery according to any one of claims 27 to 40, characterized in that the lithium-ion secondary battery has a constant current charge ratio of 75% or more when constant current and constant voltage charging is performed at a charge rate of 1 to 6C and a cutoff operating voltage of 4.2 to 5.0V.

42. 42. The high-voltage fast-charging lithium-ion secondary battery of claim 41, wherein the lithium-ion secondary battery has a constant current charge ratio of 90% or more at a charge rate of 2 to 4 C and a cutoff operating voltage of 4.25 to 4.45 V.

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