Artificial Hybrid Solid Electrolyte-Mediated Ca Metal for Ultradurable Room Temperature 5 V Calcium Batteries

The anodic stability and reversibility of Ca metal electrodeposition/dissolution have always been hampered by surface passivation and anion corrosion, especially in F-based carbonate ester electrolytes at high device voltages. To avoid direct Ca metal/electrolyte reactions, an artificial hybrid solid electrolyte layer (AHSEL), which is characteristic of sodium/calcium carbonate and calcium hydride nitride nanocrystals of size <10 nm encapsulated by amorphous C, N species, is constructed on calcium with good ion conductivity (≈0.01 mS cm⁻¹) and uniform coating of thickness ≈20 μm. After cycling in the KPF₆ electrolyte, AHSEL is transformed into Na/K/Ca hybrid solid electrolyte interphases (SEIs), which is a compact layer composed of monodisperse nanocrystals (mostly Ca₂NH) and small amorphous zones, thus greatly suppressing the fluoridation of the Ca deposit. Consequently, the plating/stripping performance of AHSEL-modified Ca (AHSEL-Ca) is markedly improved compared with that of pristine Ca, lasting for >1400 h at a polarization shift of <0.4 mV/h. The AHSEL-Ca anode also endows Ca batteries with superior anodic stability with a ceiling voltage of up to 5.0 V, a high discharge voltage (>3.3 V), a large capacity of ≈80 mAh g⁻¹ at 200 mA g⁻¹, and an ultralong lifespan ≈5000 cycles.