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

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.