Ambient Temperature Sodium–Sulfur Batteries

Ambient‐ or room‐temperature sodium–sulfur batteries (RT Na–S) are gaining much attention as a low‐cost option for large‐scale electrical energy storage applications. However, their adoption is hampered by severe challenges. This concept paper summarizes first the operating principles, history, recent progress, and challenges of RT Na–S battery technology, and then suggests future directions towards enhancing performance in order for it to be a viable technology.     

Lithium–Sulfur Batteries: Progress and Prospects

Development of advanced energy‐storage systems for portable devices, electric vehicles, and grid storage must fulfill several requirements: low‐cost, long life, acceptable safety, high energy, high power, and environmental benignity. With these requirements, lithium–sulfur (Li–S) batteries promise great potential to be the next‐generation high‐energy system. However, the practicality of Li–S technology is hindered by technical obstacles, such as short shelf and cycle life and low sulfur content/loading, arising from the shuttling of polysulfide intermediates between the cathode and anode and the poor electronic conductivity of S and the discharge product Li₂S. Much progress has been made during the past five years to circumvent these problems by employing sulfur–carbon or sulfur–polymer composite cathodes, novel cell configurations, and lithium‐metal anode stabilization. This Progress Report highlights recent developments with special attention toward innovation in sulfur‐encapsulation techniques, development of novel materials, and cell‐component design. The scientific understanding and engineering concerns are discussed at the end in every developmental stage. The critical research directions needed and the remaining challenges to be addressed are summarized in the Conclusion.     

Recent Progress in Electrically Rechargeable Zinc–Air Batteries

Over the past decade, the surging interest for higher‐energy‐density, cheaper, and safer battery technology has spurred tremendous research efforts in the development of improved rechargeable zinc–air batteries. Current zinc–air batteries suffer from poor energy efficiency and cycle life, owing mainly to the poor rechargeability of zinc and air electrodes. To achieve high utilization and cyclability in the zinc anode, construction of conductive porous framework through elegant optimization strategies and adaptation of alternate active material are employed. Equally, there is a need to design new and improved bifunctional oxygen catalysts with high activity and stability to increase battery energy efficiency and lifetime. Efforts to engineer catalyst materials to increase the reactivity and/or number of bifunctional active sites are effective for improving air electrode performance. Here, recent key advances in material development for rechargeable zinc–air batteries are described. By improving fundamental understanding of materials properties relevant to the rechargeable zinc and air electrodes, zinc–air batteries will be able to make a significant impact on the future energy storage for electric vehicle application. To conclude, a brief discussion on noteworthy concepts of advanced electrode and electrolyte systems that are beyond the current state‐of‐the‐art zinc–air battery chemistry, is presented.     

Self‐Catalyzed Growth of Co–N–C Nanobrushes for Efficient Rechargeable Zn–Air Batteries

Highly efficient and stable bifunctional electrocatalysts for oxygen reduction and evolution are essential for aqueous rechargeable Zn–air batteries, which require highly active sites as well as delicate structural design for increasing effective active sites and facilitating mass/electron transfer. Herein, a scalable and facile self‐catalyzed growth strategy is developed to integrate highly active Co–N–C sites with 3D brush‐like nanostructure, achieving Co–N–C nanobrushes with Co,N‐codoped carbon nanotube branches grown on Co,N‐codoped nanoparticle assembled nanowire backbones. Systematic investigations suggest that nanobrushes deliver significantly improved electrocatalytic activity compared with nanowire or nanotube counterparts and the longer nanotube branches give the better performance. Benefiting from the increase of accessible highly active sites and enhanced mass transfer and electron transportation, the present Co–N–C nanobrush exhibits superior electrocatalytic activity and durability when used as a bifunctional oxygen catalyst. It enables a rechargeable Zn–air battery with a high peak power density of 246 mW cm^?2 and excellent cycling stability. These results suggest that the reported synthetic strategy may open up possibilities for exploring efficient electrocatalysts for diverse applications.     

Advanced Technologies for High‐Energy Aluminum–Air Batteries

Aluminum–air batteries are considered as next‐generation batteries owing to their high energy density with the abundant reserves, low cost, and lightweight of aluminum. However, there are several hurdles to be overcome, such as the sluggish rate of the oxygen reduction reaction (ORR) at the air electrode, precipitation of aluminum hydroxides and oxides at the anode, and severe hydrogen evolution problems at the interface of the anode and the electrolyte. Here, recent advances in silver metal and metal–nitrogen–carbon‐based ORR electrocatalysts, aluminum anodes, electrolytes, and the requirements of future research directions are mainly summarized.     

Ternary Sn–Ti–O Based Nanostructures as Anodes for Lithium Ion Batteries

SnO_x (x = 0, 1, 2) and TiO₂ are widely considered to be potential anode candidates for next generation lithium ion batteries. In terms of the lithium storage mechanisms, TiO₂ anodes operate on the base of the Li ion intercalation–deintercalation, and they typically display long cycling life and high rate capability, arising from the negligible cell volume change during the discharge–charge process, while their performance is limited by low specific capacity and low electronic conductivity. SnO_x anodes rely on the alloying–dealloying reaction with Li ions, and typically exhibit large specific capacity but poor cycling performance, originating from the extremely large volume change and thus the resultant pulverization problems. Making use of their advantages and minimizing the disadvantages, numerous strategies have been developed in the recent years to design composite nanostructured Sn–Ti–O ternary systems. This Review aims to provide rational understanding on their design and the improvement of electrochemical properties of such systems, including SnO_x–TiO₂ nanocomposites mixing at nanoscale and nanostructured Sn_xTi_1‐xO₂ solid solutions doped at the atomic level, as well as their combinations with carbon‐based nanomaterials.