Rubidium and cesium ions as electrolyte additive for improving performance of hard carbon anode in sodium-ion battery

•Rubidium and cesium ions are used as electrolyte additives for sodium-ion battery.•Rb+ and Cs+ ions modify the solid electrolyte interphase.•The performance of Na/HC(hard carbon) is improved by addition of Rb+ and Cs+ ions.

In this work, rubidium and cesium ions are studied as electrolyte additives for sodium-ion batteries. It is shown that adding small amount of Rb+ and Cs+ into the electrolyte significantly modifies the chemical composition of solid electrolyte interphase (SEI) on hard carbon (HC) surfaces, which results in a significant increase in the ionic conductivity and stability of the SEI. The results of this work show that a 0.05 M addition in the form of MPF6 (M = Rb or Cs) can increase the capacity retention of the Na/HC cells to 95.3% and 97.1% by the Rb+ and Cs+ ions, respectively, from 80.6% of the control cell after 100 cycles.

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