Nasicon based materials for sodium – ion – capacitors

Abstract

Sodium-ion hybrid capacitors (SICs) are a potential class of energy storage devices that combine the best features of high-power capacitors and high-energy batteries while making use of cheap and plentiful sodium resources. However, conventional SICs use organic electrolytes that are highly combustible and show safety hazards, which mandates alternate and safe capacitor systems. Generally, the performance of the SIC device mainly depends on the electrode and electrolyte materials. In this thesis, we focused on engineering electrodes and electrolytes through doping and using high-concentration electrolytes, respectively for sodium-ion capacitors in the environmentally benign aqueous media. The low-concentration electrolytes usually suffer from a low Electrochemical stability window (ESW) of 1.23 V and the strong electrode dissolution in aqueous electrolytes that are barriers to the high energy density and extended lifespan of SICs. Firstly, this thesis introduces the high-concentration electrolytes concept with the concentration ranges from 1-17m NaClO4 for achieving high ESW in SICs. With an ESW of 3.8 V, the 17m (mol kg−1) NaClO4 electrolyte showed remarkable storage performance using NASICON-based polyanionic cathodes Na3V2(PO4)3 (NVP). Additionally, the electrolyte showed a significant reduction in vanadium dissolution and stable charge-storage performance in NVP after using 17m NaClO4.