Controllable fabrication of two-dimensional layered transition metal oxides through electrochemical exfoliation of non-van der Waals metals for rechargeable zinc-ion batteries

Abstract

Electrochemical exfoliation of layered van der Waals solids is becoming a promising method for the fabrication of two-dimensional (2D) materials beyond graphene. Nevertheless, most of bulk layered starting solids are semiconductive or even nonconductive, which will reduce the exfoliation efficiency. In addition, the strong bonding interaction between the layers of van der Waals crystal will lead to the incomplete exfoliation. These deficiencies will hinder the application of this method in the synthesis of two-dimensional semiconductive and insulating materials. Herein, one-pot electrochemical potential-cycles exfoliation has been introduced to fabricate nonconductive 2D layered birnessite-type manganese oxide utilizing non-layered metal as starting precursor, demonstrating that monolayer and few layer birnessite sheets can be obtained through tuning the potential sweep rate. More importantly, this strategy promotes a high exfoliation yield up to 96%, which is much higher than that of electrochemical exfoliation of layered precursors. Additionally, this method can overwhelm the drawbacks such as hindrance of intrinsic/contact high resistance and incomplete exfoliation of the layered starting material presented by electrochemical exfoliation of bulk layered van der Waals solids. When utilized as cathode material for Zn-ion batteries, the exfoliated birnessite can deliver a capacity of 325 mAh g−1 at a current density of 200 mA g−1 and achieved capacity retention of 84% over 1000 cycles at 1000 mA g−1. As exfoliation parameters can be manipulated, this effective method is applicable to producing various 2D layered transition metal oxides and layered double hydroxides regardless of electric conductivity, which will contribute to plentiful applications.