Enhancing Shelf-Life of Electrolytes with LiPF₆ By Increasing Stability Under Commercially Relevant Storage Conditions

Lithium hexafluorophosphate (LiPF 6 ) salt is the most commonly used lithium salt in commercial Li-ion batteries due to its high conductivity, passivation of Al current collectors for positive electrodes, and participation in SEI layer formation at graphite anodes. 1 However, LiPF 6 suffers from poor thermal stability and poor stability toward protic species (like water) leading to decomposition that can significantly reduce Li-ion battery performance especially under the extreme conditions demanded by today’s industrial applications. Specifically, LiPF 6 decomposition leads to HF generation, especially in the presence of water 2 , which results in multiple negative outcomes in Li-ion cells including dissolution of cathode materials and gas generation. 3 Conditions during electrolyte blending, transport, and/or storage often exacerbate LiPF 6 instability and increase HF generation. To date, efforts to replace LiPF 6 have not proven to be commercially successful, therefore strategies to improve the stability of LiPF 6 electrolytes under relevant storage conditions are critical to support the deployment of Li-ion batteries. Koura has extensively characterized the degradation of LiPF 6 as a function of multiple conditions, including temperature, water content, and electrolyte composition to inform the design of strategies to improve stability. This presentation will summarize Koura’s efforts to understand LiPF6 decomposition under conditions relevant to the Li-ion electrolyte supply chain. Specifically, we will present data showing a series of fluorinated materials that improve the thermal stability of LiPF 6 electrolyte through the elimination of existing HF and suppression of additional formation. References: Sascha Nowak and Martin Winter 2015 J. Electrochem. Soc. 162 A2500 Hui Yang et al 2006 J. Power Sources 161 573 Weishan Li 2020 J. Electrochem. Soc. 167 090514