(Digital Presentation) Lifsi Based Electrolyte Corrosion Study on Al Current Collector and Its Effect on Cu Side

High energy density Li-ion battery with ultra-stable electrolyte is essential to facilitate the massive application of electric vehicles. Despite being used ubiquitously in Li-ion batteries, lithium hexafluorophosphate (LiPF6) is not stable both chemical and electrochemically, rendering the battery using LiPF6 based electrolyte. While lithium bis(fluorosulfonyl)imide (LiFSI) based electrolyte possesses both higher conductivity and better compatibility with the electrode materials compared to the traditional LiPF6 electrolyte, the high cost and the inability to suppress aluminum corrosion hinder its application in Li-ion batteries. In this work, we developed a bi-salt electrolyte by blending LiPF6 and LiFSI, as well as introducing Lithium difluoroborate (LiDFOB) as the anti-corrosion additive to mitigate the Al corrosion. Although the newly formulated electrolyte shows promising result at coin cell level, the big format pouch cell using the new electrolyte failed after prolonged cycling due to the detachment of the Cu tab. Based on the NMR results, we revealed that Al corrosion was accelerated by the change in the electrolyte formulation during cycling, and the situation was further escalated by the high state of charge (SOC). Most importantly, the Al3+ ions dissolved from the cathode side migrated to the anode side and formed alloy with Li and Cu, triggering the detachment of Cu tab, which was confirmed by SEM, ICP-MS and HRXRD. Owing to the higher current density and temperature on the tab region, it has significantly higher chance to be torn apart. In sum, it is imperative to precisely control both the SOC and the amount of LiFSI added to minimize the corrosion problem.