(Invited) Influence of Salt Anion on the Electrochemical and Thermal Stability of Electrolyte

Abstract

Electrolytes for Lithium ion batteries mainly consist carbonate solvents and lithium salt. It has been well known that the species and component of solvents greatly affect the stability of electrolyte. While the role of salt anion in electrolyte stability has been neglected. In this presentation, we will reveal the influence of salt anion, mainly PF6 -, on the electrochemical stability and thermal stability of electrolyte. Specifically, on the anode surface, PF6 - shows great influence on the reduction stability and passivation capability of the induced solid electrolyte interphase (SEI) film; on the cathode surface, especially at high voltage, PF6 - affects the oxidation stability of solvent. Moreover, co-oxidation of PF6 - would generate HF. On the other hand, PF6 - reduces the thermal stability of the carbonate-based electrolyte, which would be significantly exacerbated when there are transition metal ions dissolved from cathode in the electrolyte. This overlooked effect is mainly due to the high catalytic effect of transition metal ions on the thermal decomposition of PF6 - to produce PF5. Understanding the mechanisms of the effect of salt anion on the stability of the electrolyte would provide a strong theoretical guidance for the design and development of the next generation lithium-ion battery electrolyte.