High-Energy and Stable Subfreezing Aqueous Zn-MnO Batteries with Selective and Pseudocapacitive Zn-Ion Insertion in MnO.

One major challenge of aqueous Zn-MnO batteries for practical applications is their unacceptable performance below freezing temperatures. Here the use of simple Zn(ClO ) aqueous electrolytes is described for all-weather Zn-MnO batteries even down to -60 °C. The symmetric, bulky ClO anion effectively disrupts hydrogen bonds between water molecules and provides intrinsic ion diffusion even while frozen, and enables ≈260 mAh g on MnO cathodes at -30 °C . It is identified that subfreezing cycling shifts the reaction mechanism on the MnO cathode from unstable H insertion to predominantly pseudocapacitive Zn insertion, which converts MnO nanofibers into complicated zincated MnO that are largely disordered and appeared as crumpled paper sheets. The Zn insertion at -30 °C is faster and much more stable than at 20 °C, and delivers ≈80% capacity retention for 1000 cycles without Mn additives. In addition, simple Zn(ClO ) electrolyte also enables a nearly fully reversible and dendrite-free Zn anode at -30 °C with ≈98% Coulombic efficiency. Zn-MnO prototypes with an experimentally verified unit energy density of 148 Wh kg at a negative-to-positive ratio of 1.5 and an electrolyte-to-capacity ratio of 2.0 are further demonstrated.