Controlled Anodic Decomposition Pathway of Supramolecular Lithium Borate for Rationally Tuned Interphase Chemistry

The rational tailoring and molecular-level engineering of stable cathode-electrolyte interphases (CEIs) is paramount to advancing the performance of next-generation high-energy, layered nickel-rich oxide-based lithium metal batteries. However, developing well-tailored electrolyte additives with rationally controlled interfacial chemistry remains highly challenging. Here, two lithium borates: lithium (2-methoxy-15-crown-5)trifluoroborate (C-LiMCFB) and lithium (15-methoxy-2,5,8,11,14-pentaoxahexadecan)trifluoroborate (L-LiMCFB), incorporating cyclic 15-crown-5 (15C5) and linear pentaethylene glycol monomethyl ether (PEGME) as respective host groups tethered to the boron center are designed and synthesized. In C-LiMCFB, the supramolecular polydentate chelation/de-chelation of the 15C5 with Li⁺ can sequentially deactivate/activate the anodic decomposition of the C─O bonds, therefore leading to the controlled cleavage pathway of B─O and C─O bonds. The controlled interfacial chemistry leads to the formation of a uniform CEI layer, rich in lithium boron-oxygen clusters interwoven with LiF, on the NCM811 surface. This novel CEI configuration demonstrates an exceptional balance of mechanical robustness, adhesiveness, and toughness, providing highly desirable protection for the NCM811 cathode. The discovery of these novel supramolecular boron-based lithium salts not only unlocks supramolecular chemistry for rational electrolyte tuning but also provides a deeper understanding of the CEI formation mechanism in high-energy lithium metal batteries.