Sodium Ion Pre-Intercalation of δ-MnO 2 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 δ-MnO 2 nanosheets on flexible carbon cloth substrate (MnO 2 ), while pre-intercalated Na + in the interlayer of δ-MnO 2 nanosheets (Na-MnO 2 ), which effectively enlarges the layer spacing and enhances the conductivity of Na-MnO 2 . The prepared Na-MnO 2 //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 δ-MnO 2 zinc storage and provides new insights into the construction of high energy density flexible electrodes.