Nanostructured mesoporous tungsten oxynitride composites for the high-performance advanced secondary batteries

Abstract

The problems of energy depletion and environmental pollution are becoming serious all over the world, and interest in new and renewable energy is increasing as a way to solve them. In addition, the paradigm of the global automobile market is changing from internal combustion engine vehicles to electric vehicles due to the strengthening of international environmental regulations on vehicle exhaust gas, the possibility of oil depletion, and the continuing high oil price. As the penetration rate of new and renewable energy increases due to eco-friendly energy policies announced worldwide, it is necessary to solve load management and stabilization of renewable energy output, and more stable energy storage technology is required. An energy storage system is a key element that enables reliable and effective use of energy. The energy storage device can improve energy efficiency by storing eco-friendly generated power and then supplying it when it is most needed. In addition, it is possible to supplement the disadvantages of the existing power grid system and solve the problem of uneven quality occurring in solar and wind power generation. However, energy storage devices developed so far have problems such as lack of energy efficiency, vulnerability to fire, and high cost. Therefore, many studies on energy storage devices are currently being conducted. In this study, for the first time, porous tungsten oxynitride nanofibers and graphite are used as cathode materials with high activity to improve the efficiency of zinc-bromine flow batteries with low chemical cost and using aqueous electrolytes that are safer against fire than lithium ion batteries. Nanocomposites with graphite felt were synthesized. Porous tungsten oxynitride nanofibers were synthesized by simple heat treatment and ammonia gas treatment after electrospinning a tungsten precursor solution. Compared to conventional methods that require a multi-step process using a template, electrospinning can easily synthesize one-dimensional nanostructures through a fast and large-area process. After preparing the tungsten oxynitride nanofiber solution, it was coated on the surface of the graphite felt and filled inside. The coated tungsten oxynitride nanofiber and graphite felt composite improves current transfer and bromine ion transfer rate generated by rapid reaction, lowers electrochemical polarization, and finally brings an effect of improving energy efficiency. Second, a nanocomposite was synthesized by applying porous tungsten oxynitride nano-filler as a solid electrolyte for a lithium metal battery. Nano tungsten oxynitride serves as a pathway through which lithium ions can move in the solid electrolyte. Ion conductivity is improved, and by applying a reinforcing effect to the polymer matrix with elasticity, it brings about effects such as improvement in mechanical properties. Porous tungsten oxynitride nanocomposites with such excellent functionality can be presented as promising materials for the development of energy storage devices.