Sodium Ion Pre-Intercalation of delta-MnO2 Nanosheets for High Energy Density Aqueous Zinc-Ion Batteries

With the merits of low cost, environmental friendliness and rich resources, manganese dioxide is considered to be a promising cathode material for aqueous zinc-ion batteries (AZIBs). However, its low ion diffusion and structural instability greatly limit its practical application. Hence, we developed an ion pre-intercalation strategy based on a simple water bath method to grow in situ d-MnO2 nanosheets on flexible carbon cloth substrate (MnO2), while pre-intercalated Na+ in the interlayer of d-MnO2 nanosheets (Na-MnO2), which effectively enlarges the layer spacing and enhances the conductivity of Na-MnO2. The prepared Na-MnO2//Zn battery obtained a fairly high capacity of 251 mAh g(-1) at a current density of 2 A g(-1), a satisfactory cycle life (62.5% of its initial capacity after 500 cycles) and favorable rate capability (96 mAh g(-1) at 8 A g(-1)). Furthermore, this study revealed that the pre-intercalation engineering of alkaline cations is an effective method to boost the properties of d-MnO2 zinc storage and provides new insights into the construction of high energy density flexible electrodes.