Room temperature reversible Ca-metal chemistry in commercial fluorinated calcium salt ester electrolytes enabled by a compact N-rich interphase layer

Abstract

Multivalent metal batteries serve as crucial complements to lithium-ion batteries. Nevertheless, fluorinated anions designed for energy storage at high voltages readily passivate the metal anodes in common ester electrolytes, particularly for Ca-metal batteries (CMBs). Ca plating/stripping can hardly occur continuously in common fluorinated calcium salt ester electrolytes due to severe corrosion at room temperature. To address the challenging issue, a uniform artificial interface of calcium fluoride nitride nanocrystals (Ca2NF) and amorphous organic species is engineered in the top of Ca-metal electrodes. The compact inorganic/organic hybrid solid electrolyte interphase (SEI) layer avoided the direct reaction of Ca-metal and corrosive fluorinated anions, effectively preventing the continuous passivation of Ca-metal and expediting the diffusion kinetics of calcium ions at the interface. Therefore, for the first time, stable Ca plating/stripping at 0.005 mA cm−2 over 420 h in a commercial fluorinated calcium salt ester electrolyte is achieved for the Ca-metal electrode with the protective SEI, far superior to that of mere hours for the pristine Ca-metal. The enhanced reversibility is also substantiated in Ca-metal full batteries with biomass-derived carbon cathode, delivering stable cycling performance. This work underscores the importance of interface and interphase engineering as an effective avenue for advancing the development of CMBs.