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A newly prepared type of carbon felt with oxygen-rich phosphate groups is proposed as a promising electrode with good stability for all-vanadium redox flow batteries (VRFBs). Through direct surface modification with ammonium hexafluorophosphate (NH4PF6), phosphorus can be successfully incorporated onto the surface of the carbon felt by forming phosphate functional groups with −OH chemical moieties that exhibit good hydrophilicity. The electrochemical reactivity of the carbon felt toward the redox reactions of VO2+/VO2+ (in the catholyte) and V3+/V2+ (in the anolyte) can be effectively improved owing to the superior catalytic effects of the oxygen-rich phosphate groups. Furthermore, undesirable hydrogen evolution can be suppressed by minimizing the overpotential for the V3+/V2+ redox reaction in the anolyte of the VRFB. Cell-cycling tests with the catalyzed electrodes show improved energy efficiencies of 88.2 and 87.2 % in the 1st and 20th cycles compared with 83.0 and 81.1 %, respectively, for the pristine electrodes at a constant current density of 32 mA cm−2. These improvements are mainly attributed to the faster charge transfer allowed by the integration of the oxygen-rich phosphate groups on the carbon-felt electrode.

Si based anode materials for lithium-ion batteries have gained much attention due to its high theoretical capacity (3,580 mAhg-1). However, Si anode materials have critical limit for their commercial use because of their poor cycle performance associated with severe volume changes during cycling. In this work, we synthesized a two-dimensional(2D) SiOx material by solution evaporation induced interfacial sol-gel reaction. This synthesis method is simple, cost-effective and scalable. The resulting 2D SiOx material showed stable cycle performance with reversible capacity of about 650 mAhg-1 even at a high current density of 50 C (50 A g-1). More detailed analysis of two-dimensional SiOx materials will be discussed in this presentation.

Electrochemical double layer capacitors (EDLCs) are energy storage devices that have been used for a wide range of electronic applications. In particular, the electrolyte is one of the important components, directly related to the capacitance and stability. Herein, we first report a series of the smallest quaternary ammonium salts (QASs), with ether groups on tails and tetrafluoroborate (BF4) as an anion, for use in EDLCs. To find the optimal structure, various QASs with different sized head groups and ether-containing tail groups were systematically compared. Comparing two nearly identical structures with and without ether groups, QASs with oxygen atoms showed improved capacitance, proving that ions with oxygen atoms move more easily than their counterparts at lower electric fields. Moreover, the ether containing QASs showed low activation energy values of conductivities, leading to smaller IR drops during the charge and discharge processes, resulting in an overall higher capacitance.

Non-stoichiometric SiOx based materials have gained much attention as high capacity lithium storage materials. However, their anode performance of these materials should be further improved for their commercial success. A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), is employed as a flexible electrical interconnector to improve the electrochemical performance of Si/SiOx nanosphere anode materials for lithium ion batteries (LIBs). The resulting Si/SiOx-PEDOT:PSS core-shell structured material with the small amount (1 wt %) of PEDOT:PSS shows the improved initial reversible capacity of 968.2 mA h g−1 with excellent long-term cycle performance over 200 cycles. These promising properties can be attributed to the use of the electroconductive and flexible PEDOT:PSS shell layer, which protects the electrical conduction pathways in the electrode from the large volume changes of silicon during cycling.

Carbon nanotubes (CNT) grown on nanoporous carbon (NPC), which yields coexisting amorphous and graphitic nanoarchitectures, have been prepared on a large scale from zeolitic imidazolate framework (ZIF) by introducing bimetallic ions (Co2+ and Zn2+). Interestingly, the hybrid Co/Zn-ZIF-derived NPC showed rich graphitic CNTs on the surface. This NPC was utilized for a coin-type supercapacitor cell with an aqueous electrolyte, which showed enhanced retention at high current density and good stability over 10000 cycles.

Lithium-air battery (LAB) technology is currently being considered as a future technology for resolving energy and environmental issues. During the last decade, much effort has been devoted to realizing state-of-the-art LABs, and remarkable scientific advances have been made in this research field. Although LABs possess great potential for efficient energy storage applications, there are still various technical limitations to be overcome before the full transition. It has been well recognized that the battery performance of LABs is mainly governed by the electrochemical reactions that occur on the surface of the cathode. Thus, the rational design of highly reliable cathodes is essential for building high-performance LABs. In this respect, we introduce recent advances in the development of LABs, particularly focusing on the cathodes based on a fundamental understanding of Li-O2 electrochemistry. Furthermore, we review the remaining technical challenges in order to formulate a strategy for future research and consolidate Li-O2 electrochemistry for successful implementation of LABs in the near future.

The positive effects of incorporating electrically conductive poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT-PSS) into the negative electrode (NE) of a lithium ion capacitor (LIC) is investigated. The binding material of the NE, styrene-butadiene rubber (SBR), is partially substituted by conductive PEDOT-PSS. The soft carbon NE with 1.0 wt% PEDOT-PSS exhibits enhanced capacity retention of 64% at a current density of 5 C by lowering its electrical and electrochemical charge transfer resistance. The rate capability increased with increasing amounts of PEDOT-PSS, with no variation in the Li+ diffusivity. This improved electrochemical performance of the NE is also reflected in the LIC full-cell configuration. An LIC employing a 1.0 wt% PEDOT-PSS NE delivers 6.6 F at a high current density of 100 C, which is higher than the 6.0 F measured for the LIC with a bare NE. Moreover, the LIC with the 1.0 wt% PEDOT-PSS NE retains 85% of its initial capacitance even after 5000 cycles. These results are mainly attributed to the favourable electrical network formed by the incorporation of PEDOT-PSS into the NE. Thus, we believe that the incorporation of conductive PEDOT-PSS is a viable approach for obtaining high-power LICs.

Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries.

Transition metal oxides possessing two kinds of metals (denoted as AxB3-xO4, which is generally defined as a spinel structure; A, B = Co, Ni, Zn, Mn, Fe, etc.), with stoichiometric or even non-stoichiometric compositions, have recently attracted great interest in electrochemical energy storage systems (ESSs). The spinel-type transition metal oxides exhibit outstanding electrochemical activity and stability, and thus, they can play a key role in realising cost-effective and environmentally friendly ESSs. Moreover, porous nanoarchitectures can offer a large number of electrochemically active sites and, at the same time, facilitate transport of charge carriers (electrons and ions) during energy storage reactions. In the design of spinel-type transition metal oxides for energy storage applications, therefore, nanostructural engineering is one of the most essential approaches to achieving high electrochemical performance in ESSs. In this perspective, we introduce spinel-type transition metal oxides with various transition metals and present recent research advances in material design of spinel-type transition metal oxides with tunable architectures (shape, porosity, and size) and compositions on the micro- and nano-scale. Furthermore, their technological applications as electrode materials for next-generation ESSs, including metal-air batteries, lithium-ion batteries, and supercapacitors, are discussed.