Rational H2O deintercalation effects on cobalt vanadium oxide hydrates for ultrafast energy storage devices

Abstract

Pseudocapacitive materials have been employed in supercapacitors owing to their high specific capacitance. Nevertheless, high-level ultrafast capabilities are emphasized to overcome their rapid capacitance degradation under ultrafast-rate ion diffusion conditions. We demonstrated rational H₂O deintercalation effects on cobalt vanadium oxide hydrate (CVOH) with increasing temperature. As the temperature increases to 200 ℃, CVOH undergoes a partial amorphization and exists in a mixed state of hydrated and dehydrated phases. As the temperature increases to 500 ℃, CVOH recrystallizes into the CVO phase through a complete deintercalation of H₂O molecules. Such acceleration of H₂O deintercalation leaves functionalized hydroxyl groups at the vertex oxygens, promoting binding affinity with electrolyte ions. Moreover, the crack propagation is accelerated on the CVO surface, resulting in a nano-split morphology from the surface to the interior of CVO particles that enlarges the contact area between the CVO and electrolyte. As the temperature increases to 800 ℃, H₂O molecules re-intercalate and carbon bridged covalent bonds are formed between the CVO interlayers, resulting in particle coarsening. Owing to the rational H₂O deintercalation effects on CVOH, CVO subjected to temperature at 500 ℃ maintained notable specific capacitance retention even under the ultrafast ion diffusion conditions (137.9 F/g at 500 mV/s).