such as elements, alloys, and oxides, have been investigated for anodic use in Li-ion batteries. [ 5,6 ] Among these materials, elemental Si has received distinctive attention because of its huge theoretical capacity coming up to 4200 mA h g −1 , which is greater than those of any other materials. [ 7,8 ] Improving the Li storage properties of Si has been of great signifi cance for commercializing high energy-density batteries incorporating Si-based anodes. However, the enormous volume change during lithiation/delithiation induces a critical mechanical strain on Si particles, thus causing pulverization and the loss of electrical contact, which have been recognized as the major reasons for the rapid capacity fading of Si-based anodes.Extensive efforts have been made to solve the aforementioned problems and obtain highly reversible Si-based anodes. One effective approach is to utilize an electronically conductive carbon matrix, [ 9,10 ] which not only helps to maintain the electrical conductivity around Si parts but also reduces or relieves its huge volume change. Recent studies have shown that graphene can greatly improve cycling stability and rate capability of Li-ion battery electrodes as a conducting and buffering matrix. [11][12][13] However, it is well known that graphene has been diffi cult to be utilized in Si-based anodes [14][15][16] because of its complex, expensive, and non-environment friendly synthetic route. Luo et al. [ 17 ] prepared micrometer-sized Si nanoparticles (NPs) wrapped in graphene shells by a one-step rapid capillary-driven assembly route with improved cycling stability and descent initial coulombic effi ciency. However, an ultrasonic atomizer was used to disperse Si NPs onto the graphene layer, thus rendering the process complex and costly. Zhou et al. [ 18 ] developed nitrogen-doped carbon-coated graphene/Si NPs composites using ionic liquid 1-ethyl-3-methylimidazolium dicyanamide as a carbon precursor. It showed a decent reversible capacity of 902 mA h g −1 after 100 cycles but a very low initial coulombic effi ciency of 57.3%, which renders it not suitable for the commercial full cell application. Although Yi et al. [ 19 ] recently reported an initial coulombic effi ciency of over 60% for graphene/Si-carbon composite and an impressive areal capacity Improving the lithium (Li) storage properties of silicon (Si)-based anode materials is of great signifi cance for the realization of advanced Li-ion batteries. The major challenge is to make Si-based anode materials maintain electronic conduction and structural integrity during cycling. Novel carboncoated Si nanoparticles (NPs)/reduced graphene oxides (rGO) composites are synthesized through simple solution mixing and layer-by-layer assembly between polydopamine-coated Si NPs and graphene oxide nanosheets by fi ltration, followed by a thermal reduction. The anodic properties of this composite demonstrate the potency of the novel hybrid design based on two dimensional materials for extremely reversible energy conversion and storage. A high...

The development of next-generation energy-storage devices with high power, high energy density, and safety is critical for the success of large-scale energy-storage systems (ESSs), such as electric vehicles. Rechargeable sodium-oxygen (Na-O ) batteries offer a new and promising opportunity for low-cost, high-energy-density, and relatively efficient electrochemical systems. Although the specific energy density of the Na-O battery is lower than that of the lithium-oxygen (Li-O ) battery, the abundance and low cost of sodium resources offer major advantages for its practical application in the near future. However, little has so far been reported regarding the cell chemistry, to explain the rate-limiting parameters and the corresponding low round-trip efficiency and cycle degradation. Consequently, an elucidation of the reaction mechanism is needed for both lithium-oxygen and sodium-oxygen cells. An in-depth understanding of the differences and similarities between Li-O and Na-O battery systems, in terms of thermodynamics and a structural viewpoint, will be meaningful to promote the development of advanced metal-oxygen batteries. State-of-the-art battery design principles for high-energy-density lithium-oxygen and sodium-oxygen batteries are thus reviewed in depth here. Major drawbacks, reaction mechanisms, and recent strategies to improve performance are also summarized.

Development of high performance electrode materials for energy storage is one of the most important issues for our future society. However, a lack of clear analytical views limits critical understanding of electrode materials. This review covers useful analytical work using X-ray diffraction, X-ray absorption spectroscopy, microscopy and neutron diffraction for ion storage systems. The in situ observation facilitates comprehending real-time ion storage behaviour while the ion storage system is operating, which help us to understand detailed physical and chemical properties. We will discuss how the tools have been used to reveal detailed reaction mechanisms and underlying properties of electrode materials.

An effective chemical way to optimize the oxygen electrocatalyst and Li‐O2 electrode functionalities of metal oxide can be developed by the control of chemical bond nature with the surface anchoring of highly oxidized selenate (SeO42−) clusters. The bond competition between (Se6+−O) and (Mn−O) bonds is quite effective in stabilizing Jahn–Teller‐active Mn3+ state and in increasing oxygen electron density of α‐MnO2 nanowire (NW). The selenate‐anchored α‐MnO2 NW shows excellent oxygen electrocatalytic activity and electrode performance for Li‐O2 batteries, which is due to the improved charge transfer kinetics and reversible formation/decomposition of Li2O2. The present study underscores that the surface anchoring of highly oxidized cluster can provide a facile, effective way of improving the oxygen electrocatalyst and electrochemical performances of nanostructured metal oxide in Li‐O2 cells.