Impact of Water on Structure Stabilization in Layered Manganese-Oxide for High-Voltage Zinc Storage in Non-Aqueous Electrolyte: Experimental and Theoretical Aspects

In this work, we suggest layered K0.32MnO2·0.15H2O as a promising high-energy cathode material for non-aqueous zinc-ion batteries (ZIBs). Electrochemical cycling tests indicate acceptable electrode performance with a capacity of 194 mAh (g-oxide)−1 at 0.2 C (40 mA g−1) in the voltage range of 0.6 – 2 V. This performance is achieved via a single-phase reaction accompanied by a Mn4+/Mn3+ redox pair. Further tests validate the availability of the reaction at higher currents, namely, capacity retention of 88 % after 200 cycles at 0.5 C and 54 % after 700 cycles at 2 C. Structural analysis using operando X-ray diffraction confirms a small volume change of ∼1.1% during de/zincation, of which water molecules act as pillars that support the layered structure for long-term cycling stability. The beneficial impact of water within the K0.32MnO2·0.15H2O structure has been validated through density functional theory calculation. Accordingly, the use of a non-aqueous electrolyte yields not only widening of the operating window compared with conventional aqueous solutions but also, more importantly, prevention of cell swelling and bulging caused by H2 generation in an aqueous system. The above findings provide possible solutions toward the practical application of non-aqueous rechargeable ZIBs with high energy.