Mechanism Study of Unsaturated Tripropargyl Phosphate as an Efficient Electrolyte Additive Forming Multifunctional Interphases in Lithium Ion and Lithium Metal Batteries

Electrolytes in modern Li ion batteries (LIBs) rely on additives of various structures to generate key interphasial chemistries needed for desired performances, although how these additives operate in battery environments remains little understood. Meanwhile, these traditional additives face increasing challenges from emerging battery chemistries, especially those based on the nickel cathode (Ni ≥ 50%) or the metallic lithium anode. In this work, we report a new additive structure with the highest unsaturation degree known so far along with the in-depth understanding of its breakdown mechanism on those aggressive electrode surfaces. Tripropargyl phosphate (TPP) containing three carbon-carbon triple bonds was found to form dense and protective interphases on both NMC532 cathode as well as graphitic and metallic lithium anodes, leading to significant improvements in performances of both LIBs and lithium metal batteries (LMBs). Comprehensive characterizations together with calculations reveal how the unsaturation functionalities of TPP interact with these electrode chemistries and establish interphases that inhibit gas generation, suppress lithium dendrite growth, and prevent transition metal ion dissolution and deposition on the anode surface. The correlation established among the additive structure, interphasial chemistries, and cell performance will doubtlessly guide us in designing the electrolytes with atomistic precision for future battery chemistries.