Facile synthesis of the sandwich-structured germanium/reduced graphene oxide hybrid: an advanced anode material for high-performance lithium ion batteries

Abstract

A sandwich-structured reduced graphene oxide/germanium/reduced graphene oxide hybrid (denoted as rGO/Ge/rGO) is successfully synthesized through a facile thermal reduction method for the first time. The rGO/Ge/rGO hybrid, with submicron Ge crystals (200–600 nm) uniformly encapsulated in a conductive rGO matrix, offers several favorable features: enough void space to accommodate the volume change, fast electrons and lithium ions transport, and superior structural stability. When acting as the anode in lithium ion batteries (LIBs), rGO/Ge/rGO exhibits significantly improved electrochemical performance compared to that of pure Ge, owing to the sufficient wrapping of Ge by rGO and strong chemical interaction between Ge and rGO. Enhanced reversible specific capacity of 1085 mA h g⁻¹ after 500 cycles can be achieved at 1C rate (1C = 1600 mA g⁻¹) with the capacity loss of ∼0.017% per cycle. Furthermore, the coin-type full cell composed of the rGO/Ge/rGO anode and the LiNi_0.5Co_0.2Mn_0.3O₂ cathode delivers a high specific capacity of 940 mA h g⁻¹ with a capacity retention of 93.6% after 100 cycles at 1C rate. Such a sandwich-type rGO/Ge/rGO hybrid, which presents excellent cycle life and remarkably high capacity, is expected to be a promising anode material candidate for further application in next-generation high energy density LIBs and other electrochemical devices.