Search

CN-122025818-A - Low-temperature safe lithium iron phosphate battery electrolyte and preparation method thereof

CN122025818ACN 122025818 ACN122025818 ACN 122025818ACN-122025818-A

Abstract

The invention discloses a low-temperature safe lithium iron phosphate battery electrolyte and a preparation method thereof, and belongs to the technical field of lithium battery electrolytes. The electrolyte consists of three parts, namely a ternary composite solvent consisting of an ether-based solvent, a phosphate solvent and a carbonate solvent, a ternary composite lithium salt consisting of lithium hexafluorophosphate, lithium difluorosulfimide and lithium difluorooxalato borate, and a functional composite additive. The preparation method adopts a step-by-step feeding process, sequentially adds solvent, lithium salt and additive according to a specific sequence, and prepares the finished product through ageing, inspection, filtration and filling. According to the invention, the low-temperature ion conduction and flame-retardant safety is improved through the synergy of the ternary composite solvent, the wide temperature range, the high conductivity and the aluminum foil compatibility are considered through the ternary composite lithium salt, the gradient double-layer interface film with the internal inorganic and external organic is constructed through the reduction potential gradient difference of the functional additive so as to reduce the low-temperature interface impedance, and the lithium ion solvation structure is regulated and controlled through the step-by-step preparation process so as to improve the low-temperature performance and the batch stability.

Inventors

  • CHEN XIAOYANG
  • LIU FENG
  • LI SHICHANG

Assignees

  • 桐芯锂创绿色能源科技(济南)有限公司

Dates

Publication Date
20260512
Application Date
20260320

Claims (9)

  1. 1. The low-temperature safe lithium iron phosphate battery electrolyte is characterized by comprising, by mass, 13-22 parts of 2-methyltetrahydrofuran, 8-15 parts of cyclopentyl methyl ether, 8-16 parts of triethyl phosphate, 16-27 parts of methyl ethyl carbonate, 16-27 parts of dimethyl carbonate, 5-8 parts of lithium hexafluorophosphate, 3-5 parts of lithium difluorosulfimide, 1.1-2.3 parts of lithium difluorooxalato borate, 1.2-2.5 parts of vinylene carbonate, 0.5-1.5 parts of fluoroethylene carbonate, 0.4-1.0 parts of trimethylsilyl phosphate and 1.0-3.0 parts of fluoroethyl methyl carbonate.
  2. 2. The electrolyte for a low-temperature safety lithium iron phosphate battery according to claim 1, wherein the 2-methyltetrahydrofuran and the cyclopentyl methyl ether are prepared by adding the 2-methyltetrahydrofuran or the cyclopentyl methyl ether into a sealed glass container pre-filled with an activated 3 a molecular sieve, and sealing and standing at 20-25 ℃ for at least 16 hours under the protection of argon, wherein the sealed glass container is a glass container Filtering with polytetrafluoroethylene filter membrane to remove molecular sieve, collecting filtrate, transferring filtrate into round bottom flask with distillation device, performing atmospheric distillation under argon protection, and collecting fraction with 2-methyltetrahydrofuran boiling range of 79-81 ℃ and fraction with cyclopentyl methyl ether boiling range of 105-107 ℃ to obtain the prepared 2-methyltetrahydrofuran and cyclopentyl methyl ether.
  3. 3. The electrolyte for a low-temperature safety type lithium iron phosphate battery according to claim 1, wherein the triethyl phosphate, the methylethyl carbonate and the dimethyl carbonate are prepared by respectively adding the triethyl phosphate, the methylethyl carbonate or the dimethyl carbonate into a sealed container pre-filled with an activated 4 a molecular sieve, sealing and standing for at least 12 hours at 20-25 ℃ under the protection of argon gas, and then subjecting the mixture to a process of preparing the electrolyte Filtering with polytetrafluoroethylene membrane to remove molecular sieve, and collecting filtrate to obtain the final product.
  4. 4. The low-temperature safe lithium iron phosphate battery electrolyte according to claim 1, wherein the lithium hexafluorophosphate, the lithium difluorosulfonimide and the lithium difluorooxalato borate are dried in a vacuum drying oven for 10-12 hours at 80-90 ℃ before use.
  5. 5. A method for preparing the low-temperature safe lithium iron phosphate battery electrolyte according to any one of claims 1 to 4, which is characterized by comprising the following steps in a closed inert atmosphere environment: S1, sequentially adding dried and pretreated 2-methyltetrahydrofuran, cyclopentyl methyl ether, triethyl phosphate, methyl ethyl carbonate and dimethyl carbonate into a reaction kettle with a sealing and stirring device according to the formula amount, and mixing to obtain a clear and uniform mixed solvent; s2, sequentially adding dried and pretreated lithium hexafluorophosphate, lithium difluorosulfimide and lithium difluorooxalato borate serving as main lithium salt into the mixed solvent obtained in the step S1, and fully stirring after each lithium salt is added until the lithium salt is completely dissolved to obtain a composite lithium salt solution; S3, adding lithium difluoroborate, trimethylsilyl phosphate, fluoroethylene carbonate, vinylene carbonate and fluoroethyl methyl carbonate serving as film forming additives into the composite lithium salt solution obtained in the step S2 in sequence, and stirring until each component is completely mixed with the solution after adding to obtain a crude electrolyte product; And S4, standing and aging the electrolyte crude product obtained in the step S3 under a sealed inert atmosphere, and filtering and filling the electrolyte crude product through a microporous filter membrane after the moisture and free acid content are checked to be qualified, thus obtaining the low-temperature safe lithium iron phosphate battery electrolyte.
  6. 6. The method of claim 5, wherein S1 comprises the following operations: s11, adding 2-methyltetrahydrofuran and cyclopentyl methyl ether into a reaction kettle at the same time, starting stirring until the 2-methyltetrahydrofuran and the cyclopentyl methyl ether are completely mixed, and visually clarifying the liquid without layering to obtain an ether group mixed solvent; S12, slowly adding the formula amount of triethyl phosphate into the ether-based mixed solvent obtained in the step S11, and stirring until the liquid is clear and uniform and has no oil beads or turbidity to obtain an ether-phosphate mixed solution; And S13, adding the methyl ethyl carbonate with the formula amount into the ether-phosphate mixed solution obtained in the step S12, stirring until the mixture is clear and uniform, adding the dimethyl carbonate with the formula amount, and continuing stirring until the mixture is completely mixed, and visually free from turbidity or layering, so as to obtain the mixed solvent.
  7. 7. The method of claim 5, wherein S2 comprises the following operations: s21, dividing the formula amount of lithium hexafluorophosphate into 3-5 equal parts, adding the first part into the mixed solvent obtained in the step S1, stirring until solid particles completely disappear, adding the next part after the solution is clarified, and the like until all lithium hexafluorophosphate is completely added and completely dissolved, so as to obtain a solution containing lithium hexafluorophosphate; S22, adding the formula amount of lithium bis (fluorosulfonyl) imide into the solution obtained in the step S21 at one time, and stirring until the solid completely disappears, and clarifying the solution to obtain a mixed lithium salt solution containing lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate; And S23, adding 0.8-1.5 parts of lithium difluoro oxalate borate into the solution obtained in the step S22, and stirring until the solid completely disappears, and obtaining the compound lithium salt solution after the solution is clear and yellowish.
  8. 8. The method of claim 5, wherein S3 comprises the following operations: S31, adding 0.3-0.8 part of lithium difluoro oxalate borate into the composite lithium salt solution obtained in the step S2, stirring until the solid is completely dissolved, and keeping the solution clear and transparent; s32, dropwise adding the trimethyl silicon-based phosphate with the formula amount into the solution obtained in the step S31, and stirring until the solution is clear and uniform and is free of oil beads or suspended matters; S33, adding the fluoroethylene carbonate with the formula amount into the solution obtained in the S32, stirring until the fluoroethylene carbonate is completely dissolved, adding the vinylene carbonate with the formula amount, and stirring until the solution is clear and uniform; and S34, adding the fluoroethyl methyl carbonate with the formula amount into the solution obtained in the step S33, and stirring until the liquid is completely mixed, and clarifying the solution to obtain the crude electrolyte.
  9. 9. The method of claim 5, wherein S4 comprises the following operations: S41, transferring the electrolyte crude product obtained in the step S3 into a sealed inert atmosphere container for standing and aging, wherein the judgment standard of aging completion is that no solid is separated out from the bottom of the container, the liquid is clear and transparent, and the upper layer and the lower layer are uniform in color; S42, sampling from the electrolyte after aging, and detecting the moisture content and the free hydrogen fluoride content; s43, passing the electrolyte qualified in the inspection under the protection of dry inert gas atmosphere in turn And The polytetrafluoroethylene filter membranes with the apertures are connected in series for filtration, and the filtrate is filled in the channels And (5) drying the electrolyte in a sealed container to obtain the finished product of the low-temperature safe lithium iron phosphate battery electrolyte.

Description

Low-temperature safe lithium iron phosphate battery electrolyte and preparation method thereof Technical Field The invention belongs to the technical field of lithium battery electrolyte, and particularly relates to low-temperature safe lithium iron phosphate battery electrolyte and a preparation method thereof. Background The lithium iron phosphate battery has been widely used in the fields of power batteries and energy storage systems because of the advantages of good thermal stability, long cycle life, lower raw material cost and the like. The electrolyte is used as an ion transmission medium for connecting the anode and the cathode in the lithium battery, and the performance of the electrolyte directly determines the electrochemical performance of the battery under different working conditions. The conventional commercial electrolyte generally takes a carbonic ester solvent as a main body and lithium hexafluorophosphate as a lithium salt, and the system can provide good ionic conductivity and electrochemical stability in a normal temperature range and can meet the requirements of general use scenes. However, with the popularization and application of new energy automobiles and energy storage technologies to extremely low-temperature environments such as high latitude, high altitude and the like, the performance deficiency of the traditional carbonate-based electrolyte under the low-temperature condition gradually becomes a core bottleneck for restricting the application range of the lithium iron phosphate battery. The viscosity of the carbonic ester solvent is increased sharply at low temperature, the ion migration rate is reduced remarkably, the ion conductivity of the electrolyte is greatly attenuated, and serious polarization phenomenon and capacity loss of the battery occur. In order to improve the low-temperature performance of the electrolyte, various improvement ideas appear in the prior art. One idea is to introduce low freezing point ester or ether solvents into carbonate systems to reduce the viscosity and freezing point of the electrolyte, but such low freezing point solvents tend to have lower flash points and insufficient oxidation stability, and the safety of the electrolyte is sacrificed while the low temperature performance is improved. Another idea is to replace or partially replace traditional lithium hexafluorophosphate with new lithium salts, for example, using lithium bis (fluorosulfonyl) imide to improve low temperature ion conductivity, but lithium bis (fluorosulfonyl) imide can corrode aluminum foil current collectors at higher usage ratios, affecting long-term reliability of the battery. In addition, there is also a study to optimize the structure of a solid electrolyte interfacial film on the surface of a negative electrode by adding a film-forming additive to an electrolyte solution, but it is difficult to construct a high quality interfacial film having a low temperature ion rapid transport capability on the surface of a negative electrode with a single kind or a simple combination of additives. In the aspect of the preparation process of the electrolyte, the prior art generally adopts a conventional preparation method of mixing and stirring all solvents, lithium salts and additives at one time. The one-step preparation process ignores the influence of different lithium salt dissolution and heat release differences and coordination competition relationship between anions and lithium ions on a solvation structure, so that the solvation shell structure of lithium ions in the electrolyte is not uniform enough, the performance fluctuation among batches is large, and the optimal low-temperature ion transmission characteristic is difficult to obtain stably. In summary, in the prior art, there is a lack of a solution for preparing lithium iron phosphate battery electrolyte capable of simultaneously satisfying low-temperature ion conductivity, flame-retardant safety, aluminum foil compatibility and cycle stability, and a lack of a method for preparing electrolyte capable of precisely controlling lithium ion solvation structure to improve low-temperature performance and batch stability. Disclosure of Invention The invention provides a low-temperature safe lithium iron phosphate battery electrolyte which is prepared from the following components, by mass, 13-22 parts of 2-methyltetrahydrofuran, 8-15 parts of cyclopentyl methyl ether, 8-16 parts of triethyl phosphate, 16-27 parts of methyl ethyl carbonate, 16-27 parts of dimethyl carbonate, 5-8 parts of lithium hexafluorophosphate, 3-5 parts of lithium difluorosulfimide, 1.1-2.3 parts of lithium difluorooxalato borate, 1.2-2.5 parts of vinylene carbonate, 0.5-1.5 parts of fluoroethylene carbonate, 0.4-1.0 parts of trimethylsilyl phosphate and 1.0-3.0 parts of fluoromethyl ethyl carbonate. In a preferred scheme, the 2-methyltetrahydrofuran and the cyclopentyl methyl ether are prepared by adding the 2-methyltetrahydrofuran or the cyclopen