Mechanism of the Salt Anions Impacting on the Interface Chemistry of the Anode During High‐Temperature Calendar Ageing

The calendar ageing has long plagued practical realization of long‐life lithium‐ion batteries (LIBs), and the interfacial ageing significantly affects electrochemical performances compared with bulk electrolyte hydrolysis, while its mechanism remains insufficiently elucidated. We found electron‐tunneling‐induced interfacial electrochemical degradation of solid electrolyte interphase (SEI) is widespread in most electrode interfacial processes, unlike interfacial chemical etching caused by high‐temperature hydrolysis in LiPF 6 ‐based electrolytes. During this electrochemical degradation, LiFSI‐based electrolytes will undergo solvent reduction to reconfigure inorganic‐rich SEI (LiF/Li 3 N/Li 2 S) to organics (RCO 3 Li/RCO 2 Li/RCOLi), leading to active lithium consumption and hindering ion transport. Oppositely, the polymeric SEI (boron‐crosslinked polyether) will evolve from long‐chain ─B─F bonds into ─B─O and LiF in LiDFOB‐based electrolytes via thermally‐induced ageing, effectively suppressing subsequent solvent decomposition. Furthermore, through electrolyte‐exchange experiments, we reveal graphite anode operating via Li + intercalation/deintercalation, behaves as a “Solvation‐Structure‐Restricted Mechanism” and exhibits low dependence on the pristine SEI and can be rehabilitated by replacing electrolytes after ageing; whereas SiO x anode governed by Li + ‐alloying reaction, acts as an “Interface‐Restricted Mechanism” that suffers irreversible capacity decay due to electrochemical degradation, thus being more reliant on the reconstructed polymer‐based SEI enabled by LiDFOB. Our research provides original insights for salt anion selection and interfacial design for high‐energy and long‐cycle‐life LIBs.