Oral Probing of the Sodium Intercalation mechanism into Nano-sized V2O5 for Sodium-ion Batteries
In recent years, numerous efforts have been made to develop high performance rechargeable batteries to use for large scaleapplications such as electrical energy storage systems (ESS). Lithium ion batteries have been the most popular and widely usedbatteries in portable devices like cell phones, laptops, etc. However, it has some constraints to be used for large scale applicationsas the cost for the raw materials for lithium is expensive. There have been ongoing studies searching for alternative shuttle ionsand sodium can be one of the possible substitutes since it is more abundant and cheaper. High performance materials with largesodium storage capacities are required for the realization of sodium-ion batteries. Vanadium pentoxide (V2O5) is consideredas promising active material due to its unique crystal structure with large interlayer spacing of 4.4 Å. It is known that layeredV2O5 is electrochemically active when the electrode was applied in NIBs but exhibiting less noticeable performances. Herein, wedesigned the novel composite electrodes which consist of V2O5 nanoparticles and carbon and investigated the electrochemicalenergy storage mechanism of the electrode materials. Due to the incorporation of carbon-based material, the charge transferresistance was significantly improved compared to the electrode with V2O5 alone. Accordingly, the nano sized V2O5/C compositehas shown a superior reversible capacity as well as high rate capability. The electrodes with fully charged-discharged states havebeen further investigated by ex situ XRD and the result reveals the reversible sodium de/intercalation. Ex situ TEM analysis ofthe fully discharged electrode shows both crystalline and amorphous phases of Na2V2O5. In addition, NEXAFS spectroscopy isemployed to monitor the oxidation stage changes of vanadium ions upon Na+ insertion/extraction and it is found that the redox(V4+/V5+) is responsible of the delivered capacity.