AbstractLi₂MnO₃ has been contemplated as a high‐capacity cathode candidate for Li‐ion batteries; however, it evolves oxygen during battery charging under ambient conditions, which hinders a reversible reaction. However, it is unclear if this irreversible process still holds under subambient conditions. Here, the low‐temperature electrochemical properties of Li₂MnO₃ in an aqueous LiCl electrolyte are evaluated and a reversible discharge capacity of 302 mAh g⁻¹ at a potential of 1.0 V versus Ag/AgCl at −78 °C with good rate capability and stable cycling performance, in sharp contrast to the findings in a typical Li₂MnO₃ cell cycled at room temperature, is observed. However, the results reveal that the capacity does not originate from the reversible oxygen oxidation in Li₂MnO₃ but the reversible Cl₂(l)/Cl⁻(aq.) redox from the electrolyte. The results demonstrate the good catalytic properties of Li₂MnO₃ to promote the Cl₂/Cl⁻ redox at low temperatures.