The search for new electrode materials for lithium-ion batteries (LIBs) has been an important way to satisfy the ever-growing demands for better performance with higher energy/power densities, improved safety and longer cycle life. Nanostructured metal oxides exhibit good electrochemical properties, and they are regarded as promising anode materials for high-performance LIBs. In this feature article, we will focus on three different categories of metal oxides with distinct lithium storage mechanisms: tin dioxide (SnO₂), which utilizes alloying/dealloying processes to reversibly store/release lithium ions during charge/discharge; titanium dioxide (TiO₂), where lithium ions are inserted/deinserted into/out of the TiO₂ crystal framework; and transition metal oxides including iron oxide and cobalt oxide, which react with lithium ions via an unusual conversion reaction. For all three systems, we will emphasize that creating nanomaterials with unique structures could effectively improve the lithium storage properties of these metal oxides. We will also highlight that the lithium storage capability can be further enhanced through designing advanced nanocomposite materials containing metal oxides and other carbonaceous supports. By providing such a rather systematic survey, we aim to stress the importance of proper nanostructuring and advanced compositing that would result in improved physicochemical properties of metal oxides, thus making them promising negative electrodes for next-generation LIBs.

We report a facile way to grow various porous NiO nanostructures including nanoslices, nanoplates, and nanocolumns, which show a structure-dependence in their specific charge capacitances. The formation of controllable porosity is due to the dehydration and re-crystallization of β-Ni(OH)₂ nanoplates synthesized by a hydrothermal process. Thermogravimetric analysis shows that the decomposition temperature of the β-Ni(OH)₂ nanostructures is related to their morphology. In electrochemical tests, the porous NiO nanostructures show stable cycling performance with retention of specific capacitance over 1000 cycles. Interestingly, the formation of nanocolumns by the stacking of β-Ni(OH)₂ nanoslices/plates favors the creation of small pores in the NiO nanocrystals obtained after annealing, and the surface area is over five times larger than that of NiO nanoslices and nanoplates. Consequently, the specific capacitance of the porous NiO nanocolumns (390 F/g) is significantly higher than that of the nanoslices (176 F/g) or nanoplates (285 F/g) at a discharge current of 5 A/g. This approach provides a clear illustration of the process-structure-property relationship in nanocrystal synthesis and potentially offers strategies to enhance the performance of supercapacitor electrodes.