Synergistic Co‐Solvents Enabled Stable Fast‐Kinetics Calcium Plating/Stripping in Electrolytes With Strongly Coordinating Anions

ABSTRACT Calcium (Ca) metal batteries are challenged by sluggish and unstable Ca plating/stripping in electrolytes with strongly coordinating anions. In the conventional calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI) 2 )/dimethoxyethane (DME) electrolyte, the large barriers to shed coordinated TFSI – and traverse the CaF 2 ‐rich interphases lead to a plating overpotential exceeding 1.5 V at 0.02 mA cm −2 . In contrast, this work demonstrates that synergistic tris(trimethylsilyl)borate (TMSB) and 2‐methoxyethylamine (MOEA) co‐solvents effectively weaken Ca 2+ –TFSI − coordination by Lewis acid–base interactions and strong bidentate coordination of MOEA with Ca 2+ , while promoting the formation of Ca 2 Si‐rich, kinetically favorable interphases via electron‐rich Si sites. Consequently, the optimized electrolyte enables substantially improved Ca metal redox kinetics and cycling stability, delivering an initial plating overpotential of 0.3 V and stable plating/stripping for over 350 h at 0.02 mA cm −2 with slight potential drift. It also exhibits good rate capability over 0.02–0.2 mA cm −2 , maintaining overpotentials below 0.8 V. This work highlights the crucial role of multi‐solvent synergy in optimizing interfacial stability and redox kinetics for calcium‐metal anodes.