Monoclinic Cu3(OH)2V2O7·2H2O nanobelts/reduced graphene oxide: A novel high-capacity and long-life composite for potassium-ion battery anodes

Developing suitable anode materials for potassium-ion batteries (PIBs) remains a great challenge owing to the limited theoretical capacity of active materials and large radius of K+ ion (1.38 Å). To solve these obstacles, by integrating the principles of multielectron transfer and rational porous crystal framework, we creatively propose the monoclinic Cu3(OH)2V2O7·2H2O (CVO) as a novel anode for PIBs. Furthermore, inspired by the metastable nature of CVO under high temperature/pressure, we skillfully design a facile hydrothermal recrystallization strategy without the phase change and surfactants addition. Thus, for the first time, the porous composite of Cu3(OH)2V2O7·2H2O nanobelts covered in situ by reduced graphene oxide (CVO NBs/rGO) was assembled, greatly improving the deficiencies of CVO. When used as a novel anode for PIBs, CVO NBs/rGO delivers large specific capacity (up to 551.4 mAh g−1 at 50 mA g−1), high-rate capability (215.3 mAh g−1 at 2.5 A g−1) and super durability (203.6 mAh g−1 at 500 mA g−1 even after 1000 cycles). The outstanding performance can be ascribed to the synergistic merits of desirable structural features of monoclinic CVO nanobelts and the highly conductive graphene 3D network, thus promoting the composite material stability and electrical/ionic conductivity. This work reveals a novel metal vanadate-based anode material for PIBs, would further motivate the subsequent batteries research on M3(OH)2V2O7·nH2O (M; Co, Ni, Cu, Zn), and ultimately expands valuable fundamental understanding on designing other high-performance electrode materials, including the combined strategies of multielectron transfer with rational porous crystal framework, and the composite fabrication of 1D electrode nanostructure with conductive carbon matrix.