Multi‐Ions Electrolyte Enabled High Performance Voltage Tailorable Room‐Temperature Ca‐Metal Batteries

Abstract Calcium metal batteries, as one of the promising alternatives beyond Li‐metal technology, is held back by the lack of suitable cathodes of considerable energy storage capability, and Ca anodes of long‐term stability and lower polarization potentials for Ca‐plating/stripping. Here, by recycling cellulose waste paper, feasible cathodes for Ca‐metal batteries of good high‐voltage and wide‐window‐voltage adaptability (0.005–4.9 V versus Ca/Ca 2+ ), and impressive energy density ( ≈ 517.5 Wh kg −1 at 0.1 A g −1 ) are developed. Meanwhile, through tailorable Ca‐plating/stripping potentials ( ∆ V ≈ 0.65 V) realized by a modified electrolyte of Li + , Ca 2+ , , and multi‐ions system, the proof‐of‐concept Ca‐metal batteries not only delivered enhanced storage capability (101 mAh g −1 versus 51 mAh g −1 at 0.1 A g −1 in the window voltage of 2.0–4.7 V) and cycling stability ( ≈ 77% capacity retention for 100 cycles), but also simultaneously show a high output average working voltage of ≈ 3.2 V. The work provides a hint that mixed metal deposition under multi‐ions electrolyte system may address the challenging issues faced by single alkali or alkaline‐earth metal batteries.