Interfacial synthesis of strongly-coupled δ-MnO2/MXene heteronanosheets for stable zinc ion batteries with Zn2+-exclusive storage mechanism

Low-cost and nontoxic manganese dioxide (MnO2) cathodes have shown promising application in high-capacity and high-voltage rechargeable zinc ion batteries (ZIBs), but suffer from limited cycling life and energy density mainly due to poor electrical conductivity and structural failure induced by manganese dissolution and H+/Zn2+ co-intercalation in traditional aqueous electrolytes. Herein, two-dimensional strongly-coupled δ-MnO2/MXene heteronanosheets are efficiently developed for high-performance ZIBs, which mainly includes an in-situ polymerization of dopamine on Ti3C2 MXene surface and subsequent redox reaction between KMnO4 and polydopamine. Benefited from the conductive MXene nanosheets for fast electron transfer, and the thin thickness of δ-MnO2 nanosheets for improved Zn2+ insertion kinetics and structural stability, the δ-MnO2/MXene heteronanosheets exhibit unique Zn2+-exclusive storage mechanism without proton storage induced disadvantages (e.g., Mn dissolution in traditional aqueous electrolytes) and superior zinc storage performance in 0.5 M zinc triflate in triethyl phosphate organic electrolyte (Zn(OTf)2/TEP), offering a capacity of ∼163 mAh g−1 at 100 mA g−1, a high capacity retention of 84.5 % after 1000 cycles, and an areal capacity of 1.9 mAh cm−2 when the mass loading is up to 10.5 mg cm−2. This work provides unique Zn2+-exclusive storage mechanism of δ-MnO2 in organic electrolyte and opens up a new approach for building high-performance ZIBs.