Hierarchical Micron-Sized Mesoporous/Macroporous Graphene with Well-Tuned Surface Oxygen Chemistry for High Capacity and Cycling Stability Li–O₂ Battery

Nonaqueous Li–O₂ battery is recognized as one of the most promising energy storage devices for electric vehicles due to its super-high energy density. At present, carbon or catalyst-supporting carbon materials are widely used for cathode materials of Li–O₂ battery. However, the unique electrode reaction and complex side reactions lead to numerous hurdles that have to be overcome. The pore blocking caused by the solid products and the byproducts generated from the side reactions severely limit the capacity performance and cycling stability. Thus, there is a great need to develop carbon materials with optimized pore structure and tunable surface chemistry to meet the special requirement of Li–O₂ battery. Here, we propose a strategy of vacuum-promoted thermal expansion to fabricate one micron-sized graphene matrix with a hierarchical meso-/macroporous structure, combining with a following deoxygenation treatment to adjust the surface chemistry by reducing the amount of oxygen and selectively removing partial unstable groups. The as-made graphene demonstrates dramatically tailored pore characteristics and a well-tuned surface chemical environment. When applied in Li–O₂ battery as cathode, it exhibits an outstanding capacity up to 19 800 mA h g^–1 and is capable of enduring over 50 cycles with a curtaining capacity of 1000 mA h g^–1 at a current density of 1000 mA g^–1. This will provide a novel pathway for the design of cathodes for Li–O₂ battery

Low-Cost Room-Temperature Synthesis of NaV₃O₈·1.69H₂O Nanobelts for Mg Batteries

Potentially safe and economically feasible magnesium batteries (MBs) have attracted tremendous research attention as an alternative to high-cost and unsafe lithium ion batteries. In the current work, for the first time, we report a novel room-temperature approach to dope the atomic species sodium between the vanadium oxide crystal lattice to obtain NaV₃O₈·1.69H₂O (NVO) nanobelts. The synthesized NVO nanobelts are used as electrode materials for MBs. The MB cells demonstrate stable discharge specific capacity of 110 mA h g^–1 at a current density of 10 mA g^–1 and a high cyclic stability, that is 80% capacity retention after 100 cycles, at a current density of 50 mA g^–1. Moreover, the effects of cutoff voltages (ranging from 2 to 2.6 V) on their electrochemical performance were investigated. The reason for the limited specific capacity of MBs is attributed to the trapping of Mg ions inside the NVO lattices. This work opens up a new pathway to explore different electrode materials for MBs with improved electrochemical performance

Carbon-Free CoO Mesoporous Nanowire Array Cathode for High-Performance Aprotic Li–O₂ Batteries

Although various kinds of catalysts have been developed for aprotic Li–O₂ battery application, the carbon-based cathodes are still vulnerable to attacks from the discharge intermediates or products, as well as the accompanying electrolyte decomposition. To ameliorate this problem, the free-standing and carbon-free CoO nanowire array cathode was purposely designed for Li–O₂ batteries. The single CoO nanowire formed as a special mesoporous structure, owing even comparable specific surface area and pore volume to the typical Super-P carbon particles. In addition to the highly selective oxygen reduction/evolution reactions catalytic activity of CoO cathodes, both excellent discharge specific capacity and cycling efficiency of Li–O₂ batteries were obtained, with 4888 mAh g_CoO^–1 and 50 cycles during 500 h period. Owing to the synergistic effect between elaborate porous structure and selective intermediate absorption on CoO crystal, a unique bimodal growth phenomenon of discharge products was occasionally observed, which further offers a novel mechanism to control the formation/decomposition morphology of discharge products in nanoscale. This research work is believed to shed light on the future development of high-performance aprotic Li–O₂ batteries

Layer-by-Layer Assembled C/S Cathode with Trace Binder for Li–S Battery Application

The C/S cathode with only 0.5 wt % binder, composed with Nafion and PVP, was assembled layer-by-layer for lithium–sulfur battery (Li–S) application. It achieved excellent binding strength and battery performance compared to the cathode with 10 wt % PVDF, which is promising to further increase the practical energy density of Li–S batteries