The continuous expansion of smart microelectronics puts forward higher requirements for energy conversion, mechanical performance, and biocompatibility of micro energy storage devices (MESDs). Unique porosity, superior flexibility and comfortable breathability...

The demand for green and efficient energy storage devices in daily life is constantly rising, which is caused by the global environment and energy problems. Lithium-ion batteries (LIBs), an important kind of energy storage devices, are attracting much attention. Graphite is used as LIBs anode, however, its theoretical capacity is low, so it is necessary to develop LIBs anode with higher capacity. Application strategies and research progresses of novel iron oxides and their composites as LIBs anode in recent years are summarized in this review. Herein we enumerate several typical synthesis methods to obtain a variety of iron oxides based nanostructures, such as gas phase deposition, co-precipitation, electrochemical method, etc. For characterization of the iron oxides based nanostructures, especially the in-situ X-ray diffraction and 57Fe Mössbauer spectroscopy are elaborated. Furthermore, the electrochemical applications of iron oxides based nanostructures and their composites are discussed and summarized.Graphic Abstract

Nitrogen‐doped carbon‐coated transition‐metal sulfides (TMS@NCs) have been considered as efficient anodes for sodium‐ion batteries. However, the uncontrollable morphology and weak core–shell binding forces significantly limit the sodium storage performance and life. Herein, based on the reversible ring‐opening reaction of the epoxy group of the tertiary amino group‐rich epoxide cationic polyacrylamide (ECP) at the beginning of hydrothermal process (acidic environment) and the irreversible ring‐opening (cross‐linking reactions) at the late hydrothermal period (alkaline environment), 47 nm‐sized ZnS@NCs were prepared via a one‐pot hydrothermal process. During this process, the covalent bonds formed between the ZnS core and elastic carbon shell significantly improved the mechanical and chemical stabilities of ZnS@NC. Benefiting from the nanosize, fast ion/electron transfer, and high stability, ZnS@NC exhibited a high reversible capacity of 421.9 mAh g−1 at a current density of 0.1 A g−1 after 1000 cycles and a superior rate capability of 273.8 mAh g−1 at a current density of 5 A g−1. Moreover, via this universal synthesis strategy, a series of TMS@NCs, such as MoS2@NC, NiS@NC, and CuS@NC were developed with excellent capacity and cyclability.