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

The rise of flexible electronics calls for efficient microbatteries (MBs) with requirements in energy/power density, stability, and flexibility simultaneously. However, the ever‐reported flexible MBs only display progress around certain aspects of energy loading, reaction rate, and electrochemical stability, and it remains challenging to develop a micro‐power source with excellent comprehensive performance. Herein, a reconstructed hierarchical Ni–Co alloy microwire is designed to construct flexible Ni–Zn MB. Notably, the interwoven microwires network is directly formed during the synthesis process, and can be utilized as a potential microelectrode which well avoids the toxic additives and the tedious traditional powder process, thus greatly simplifying the manufacture of MB. Meanwhile, the hierarchical alloy microwire is composed of spiny nanostructures and highly active alloy sites, which contributes to deep reconstruction (≈100 nm). Benefiting from the dense self‐assembled structure, the fabricated Ni–Zn MB obtained high volumetric/areal energy density (419.7 mWh cm−3, 1.3 mWh cm−2), and ultrahigh rate performance extending the power density to 109.4 W cm−3 (328.3 mW cm−2). More surprisingly, the MB assembled by this inherently flexible microwire network is extremely resistant to bending/twisting. Therefore, this novel concept of excellent comprehensive micro‐power source will greatly hold great implications for next‐generation flexible electronics.

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Aqueous rechargeable batteries have received widespread attention due to their excellent power density, simple manufacturing process, and inexpensive electrolyte. Iron-ion batteries are expected to meet the goals of high safety, low cost, and non-toxicity pursued in the field of rechargeable batteries. However, passivation, parasitic hydrogen evolution reaction (HER), and low electroplating efficiency (50%-70%) limit the improvement of electrochemical performance, which greatly restricts their practical application. In this study, a high-performance electrolyte for iron-ion batteries was prepared, and the effect of zinc chloride (ZnCl2) additives on inhibiting HER and the improvement of coulomb efficiency in ferrous chloride (FeCl2) electrolyte was explored. Additionally, the effect of the addition of complexing agents in the electrolyte on the coulomb efficiency of the electrodes was studied. It’s demonstrated that the electrode can still obtain a coulomb efficiency of nearly 100% after 20 hours cycling in the electrolyte containing ZnCl2 additive and FeCl2, while in FeCl2 electrolyte, its coulomb efficiency after 20 hours of cycling is only 65%.