Preparation method of difluorophosphoric acid alkali metal salt

Abstract

The invention discloses a preparation method of difluorophosphoric acid alkali metal salt. In the method, the difluorophosphoric acid alkali metal salt is produced through a reaction of hexafluorophosphates of alkali metals and corresponding phosphates of the alkali metals in a solid phase or in a non-aqueous solvent, wherein the reaction equation is MPF6+M3PO4=2MPO2F2+2MF (M=Li, Na, K, Rb, Cs), the molar ratio of MPF6 to M3PO4 is 0.8-1.5:1, preferably 1.1-1.2:1, namely, the hexafluorophosphates of alkali metals is excessive properly to ensure reaction of the phosphates to be carried completely. The method can be used for preparing the difluorophosphoric acid alkali metal salt under safe situations, thereby improving safety of the preparation process and ensuring safety of preparation operators. The difluorophosphoric acid alkali metal salt is produced through a reaction of the hexafluorophosphates and the phosphates of the alkali metals, and the target product can be produced whether the reaction is carried out in solid phases or liquid phases under mild conditions without dangerous gas raw materials and generation of acidic gas or water which may damage performances of an electrolyte.

Description

technical field [0001] The invention is applicable to the preparation of electrolyte salt or additive—difluorophosphate alkali metal salt in the field of lithium ion battery materials. Background technique [0002] With the promotion of the application of lithium-ion batteries, the market has put forward higher requirements for the capacity, cycle performance, rate performance, and high and low temperature performance of lithium-ion batteries. Lithium difluorophosphate as an electrolyte additive can significantly improve the cycle stability of lithium-ion batteries and has attracted much attention. [0003] Patent Document 1 Japanese Patent "JP-P-11-67270" first mentions adding LiPO to the electrolyte 2 f 2 It can improve the high-temperature cycle performance of the battery, which has triggered people's interest in LiPO 2 f 2 attention, and various preparation methods have been developed. [0004] The current preparation method is to use the existing electrolyte soluti...

AI Technical Summary

Problems solved by technology

However, the above three methods all have the following defects: (1) During the preparation process, LiPO 2 f 2 There is no strict stoichiometric relationship between the formation of silicon dioxide and lithium carbonate and other materials added, and the final concentration still needs to be determined by methods such as ion chromatography, which is inconvenient for actual use; (2) Secondly, LiPF in the electrolyte 6 The decomposition and conversion of lithium hexafluorophosphate is also difficult to control. If the reaction temperature is too high (such as higher than 70°C), the decomposition of lithium hexafluorophosphate will be accelerated, and excessive high-reactivity phosphorus pentafluoride will be decomposed, resulting in an increase in reaction by-products and affecting the quality of the electrolyte; (3) In addition , the above methods generally have water or acid gas (such as hydrogen chloride, carbon dioxide, silicon tetrafluoride, etc.), the existence of these impurities is not only difficult to post-processing, but also will lead to the decomposition of lithium hexafluorophosphate or solvent, affecting the capacity and life

The technical routes adopted in the two documents both use expensive, highly toxic, and high-risk phosphorus pentafluoride and phosphorus oxyfluoride gases. The requirements for production equipment and process safety are strict, and the product cost is relatively high.

Images