Heterojunction design of ZnO/α-Fe2O3 with dual enhancement of ion/electron transport for energy storage

Abstract Transition metal oxides (TMOs), such as Fe2O3 and ZnO, are attractive as anode materials for battery application due to the high theoretical specific capacity, environmental friendliness, and low price. However, poor electron conductivity or poor ion migration rate significantly limit the application of TMOs in lithium-ion batteries. To overcome both challenges, a heterostructured construction consisting of two different transition metal oxides proves to be effective for cycling stability and rate performance. In the present work, high-capacity α-Fe2O3 and ZnO are combined into a nanocomposite with heterojunction by facile wet ball-milling process. Microstructural observation shows that the irregular ZnO surface is tightly wrapped by needle-like Fe2O3, and the interface of the two phases is in close contact at the atomic level. According to the energy band theory, heterojunction is formed at the interface. Electrochemical tests showed that the construction of heterojunction promotes the release of inert lithium from the inner ZnO, thus improving the initial Coulombic efficiency (ICE). The two phases synergistically regulate the electron/ion transport of the composites. In addition, The heterojunction at the interface of the two phases achieved rapid electron transport, resulting in excellent cycling and rate perfomance (∼472 mA h/g at 200 mA/g after 270 cycles). In fact, the straightforward and scalable technique without carbon which is used on this heterostructured metal oxide anodes provides a viable solution for future industrial-grade preparations.