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Lithium metal has been deemed the most attractive anode for high-energy-density batteries due to its high theoretical capacity and low anode potential. Unfortunately, its development still faces various challenges, mainly including dendritic Li growth and low Coulombic efficiency. Here, we constructed a flexible and free-standing 3D hollow carbon fiber container with porous skeleton, which can suppress Li dendrite growth and bring about high Coulombic efficiency, large areal capacity, long lifespan, and good full cell performance.

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Rechargeable magnesium (Mg) batteries have been attracting increasing attention recently because of the abundance of the raw material, their relatively low price and their good safety characteristics. However, rechargeable Mg batteries are still in their infancy. Therefore, alternate Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg batteries. In this study, we introduce the spinel Li 4 Ti 5 O 12 as an Mg-ion insertion-type anode material with a high reversible capacity of 175 mA h g À1 . This material possesses a low-strain characteristic, resulting in an excellent long-term cycle life. The proposed Mg-storage mechanism, including phase separation and transition reaction, is evaluated using advanced atomic scale scanning transmission electron microscopy techniques. This unusual Mg storage mechanism has rarely been reported for ion insertion-type electrode materials for rechargeable batteries. Our findings offer more options for the development of Mg-ion insertion materials for long-life rechargeable Mg batteries. NPG Asia Materials (2014) 6, e120; doi:10.1038/am.2014.61; published online 22 August 2014 INTRODUCTIONWith growing concern about the environment, climate change and a sustainable energy supply, studies have been focused on the development of green energy storage systems with high volumetric energy density, low price and improved safety. Compared to lithium battery systems, 1-6 rechargeable magnesium (Mg) batteries are considered to be a prospective candidate for reversible energy storage because of the great abundance of Mg resources, better chemical stability of metallic Mg in humid and oxygen-containing environments and higher volumetric capacity. [7][8][9] In particular, the increasing attention to rechargeable Mg batteries is due to the pioneering work of Aurbach's group. 10-14 Some progress has been achieved toward designing electrode materials 10,15-24 and electrolytes 25-29 for rechargeable Mg batteries. Nevertheless, rechargeable Mg batteries are still in their infancy. Therefore, alternative Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg-ion batteries. Recently, we have discovered the feasibility of utilizing spinel Li 4 Ti 5 O 12 , which is well known as a 'zero-strain' anode material for long-life stationary lithium-ion batteries, as an anode material for rechargeable Mg batteries. In this work, we further show that spinel Li 4 Ti 5 O 12 nanoparticles (LTO NPs) can exhibit excellent Mg storage performance under optimized conditions for rechargeable Mg batteries. This material shows a high reversible capacity of B175 mA h g À1 and superior cycling performance. By using an advanced atomic resolution scanning transmission electron

Developing high-voltage layered cathodes for sodium-ion batteries (SIBs) has always been a severe challenge. Herein, a new family of honeycomb-layered Na3Ni1.5M0.5BiO6 (M = Ni, Cu, Mg, Zn) with a monoclinic superstructure has been shown to combine good Na+ (de)­intercalation activity with a competitive 3.3 V high voltage. By coupling the electrochemical process with ex situ X-ray absorption spectroscopy as well as in situ X-ray diffraction, the charge compensation mechanism and structural evolution of these new cathodes are clearly investigated. Interestingly, both Ni2+/Ni3+ and Cu2+/Cu3+ participate in the redox reaction upon cycling, and the succession of single-phase, two-phase, or three-phase regions upon Na+ extraction/insertion were identified with rather good accuracy. This research strategy could provide insights into the structure–function–property relationships on a new series of honeycomb-ordered materials with the general formula Na3Ni1.5M0.5BiO6 and also serve as a bridge to guide future design of high-performance cathodes for SIBs.