Electrospun manganese cobalt oxide/carbon nanofiber composites as a cathode for high performance rechargeable quasi-solid-state zinc ion batteries

Abstract

Transition metal oxides have long been recognized for their potential in energy storage applications, particularly as cathode materials in zinc-ion batteries (ZIBs). These materials are favored for their environmental sustainability, high specific capacities, and cost-effectiveness. This research introduces a novel approach involving nanostructure engineering through the tailored synthesis of MnCo₂O₄ and CoMn₂O₄ entrapped in carbon nanofibers (CNFs) via the electrospinning technique and subsequent post-treatment processes. Both MnCo₂O₄-CNFs (MCO-CNFs) and CoMn₂O₄-CNFs (CMO-CNFs) exhibit excellent performance as zinc-ion cathodes in ZIBs, with initial specific capacities of 501.94 mAh g⁻¹ and 399.32 mAh g⁻¹ at 0.05 A g⁻¹, respectively. In terms of cycle stability, after 500 cycles, the MCO-CNFs cathode maintains a specific capacity of 101 mAh g⁻¹ at 0.2 A g⁻¹, whereas the CMO-CNFs cathode retains only 69 mAh g⁻¹. The influence of the Mn/Co ratio on the crystal evolution and electrochemical storage behavior of ZIBs during the charge/discharge process is convincingly explored through ex-situ techniques such as Scanning Electron Microscopy (SEM) and operando X-ray Absorption Near Edge Structure (XANES), revealing that MCO-CNFs exhibit greater stability and redox reversibility than CMO-CNFs. Furthermore, this work also explores the development of safe quasi-solid-state ZIBs (QZIBs), emphasizing the use of polyacrylamides (PAM) combined with hemp-derived cellulose nanofibers (CENFs) as a quasi-solid electrolyte (QSE) paired with a cobalt-manganese carbon nanofibers (CMO-CENFs) cathode. During plating/stripping tests with a symmetrical zinc cell, the PAM/CENFs at 1.0 wt% (PNC1) exhibit the lowest overpotential and the most effective zinc dendrite suppression. For QZIB performance testing, the innovatively constructed Zn//PNC1//CMO-CNFs configuration achieves remarkable electrochemical performance, including a high discharge specific capacity of 207.84 mA g⁻¹ at a current density of 0.05 A g⁻¹ and outstanding cyclic stability, with 59% capacity retention after 500 cycles. Additionally, the QZIB demonstrates robust stability under various mechanical stresses and maintains seamless operation even at sub-zero temperatures, thereby enhancing its applicability across diverse environmental conditions.