context: However, in the extreme case, when Qm of a dual-ion battery cathode is 300 mA h g−1 and the average potential is 5.0 V, Ecorrm is only ∼500 W h kg−1 if KPF6 is used as the supporting salt (Chart 2b). Switching to lighter salts, such as KClO4, KBF4 and particularly KF might significantly boost the energy density (Chart 2c). For potassium fluoride, an Ecorrm of ∼500 W h kg−1 is achieved already at a reasonable ∼200 mA h g−1 and 3.6 V. Optimization of the salt composition, however, has not been reported yet. Considering low solubility of KF in aprotic electrolytes, it is especially intriguing if it may succeed as the supporting salt.