Fabrication of controllable electrode materials MnOx-PTh for high-performance asymmetric supercapacitors

Abstract

Aiming at the structure instability of polythiophene (PTh) caused by expansion/contraction in the processes of charging and discharging leading to the loss of capacitance after moderate cycling, the combination of transition metal oxides (TMOs) obtained from metal-organic frameworks (MOFs) and PTh in electrode materials is applied to overcome the limitations. TMOs/PTh composite electrode materials were successfully synthesized using Mn-MOF as a sacrificial template through in-situ growth of PTh using electrodeposition method. This method not only effectively mitigated the volumetric changes of TMOs but also prevented the loss of active species. In a three-electrode system, the MnOx-PTh-2 composite demonstrated exceptional specific capacitance of 602.5 F·g−1 at a current density of 1 A·g−1, along with excellent cycling stability with a capacitance retention rate of 83.2% even after 10,000 charge-discharge cycles under high current density. It was because that MnOx-PTh-2 exhibited lower resistance of charge transfer and resistance of diffusion. Furthermore, the synergistic effect of the composite material enhanced the ability for charge transfer, facilitated the dynamic response of ions, and enabled rapid ion transport. In addition, the MnOx-PTh-2 electrode predominantly operated under diffusion-controlled processes, and the pseudocapacitive properties of PTh facilitated the diffusion-control behavior of MnOx, thereby enhancing the ion-electrode interaction and improving the electrochemical performance of the material. Similarly, the asymmetric supercapacitor (MnOx-PTh-2//AC) assembled with the positive electrode of MnOx-PTh-2 and the negative electrode of activated carbon (AC)exhibited an energy density of 41.5 Wh·kg−1 when the power density was 498 W·kg−1. Additionally, it maintained 80.2% capacitance retention after 5000 cycles.