Thermally encapsulated phenothiazine@MWCNT cathode for aqueous zinc ion battery

Abstract

Phenothiazine is a p-type cathode that follows the anion pairing mechanism, where the electrode undergoes extensive expansion and contraction during cycling, which deleteriously affects the battery performance. Herein, we tried to improve the electrode stability without compensating the electrical conductivity and the redox properties of the material. We followed the low-temperature solution-phase thermal encapsulation of the molecules inside the multi-walled carbon nanotubes (MWCNT). This method effectively improved the electrical conductivity, inhibited the massive loss of the active material, and alleviated the adverse effects on the cathode. The initial specific capacitance for the neat phenothiazine was found to be 145.2 mA h g⁻¹ at the current density of 100 mA g⁻¹versus Zn/Zn²⁺. The electrode was modified by low-tsemperature solution-phase thermal encapsulation and the specific capacities were found to be 239.5, 177.1, 151.1, 123.5, 90.0, 42.02 mA h g⁻¹ at the respective current densities of 50, 100, 200, 300, 400 and 500 mA g⁻¹. The battery performance was further improved by suppressing dendrite formation at the anode using an ethylene glycol additive. In 2000 charging-discharging cycles at a current density of 300 mA g⁻¹, the encapsulated material with a 1 : 1 water ethylene glycol mixture showed a specific capacity of 123.5 mA h g⁻¹. Thus, we inferred that low-temperature thermal encapsulation is an efficient, non-destructive, and green method for acquiring excellent electrode stability for small organic molecules.