Alleviating Mn<sup>3+</sup> Dissolution in ZnMn<sub>2</sub>O<sub>4</sub> Cathode for the Extended Cyclability via Particle Size Increase

Abstract

ZnMn<sub>2</sub>O<sub>4</sub> (ZMO) cathode possesses a high theoretical capacity of 224 mAh g<sup>-1</sup> and high operating voltage (1.9 V vs. Zn<sup>2+</sup>/Zn) for aqueous Zn–ion batteries. However, the disproportionation reaction of Mn<sup>3+</sup> leads to Mn dissolution in the ZMO cathode, deteriorating lifespan. In this study, we attempted to reduce Mn dissolution by enlarging the particle size, thereby diminishing the electrode/electrolyte interfacial area. The ZMO particle grew with increasing the calcination temperatures of 400℃, 500℃, and 600℃. Higher calcination temperature created oxygen vacancies within the lattice, thereby increasing the contents of Mn<sup>3+</sup> for charge neutrality. The rate capability decreased with the increase in particle size, which is presumed to be due to the lengthening of the diffusion path of Zn ions. After a long–cycle experiment of Zn–ion batteries assembled with ZMO cathode and Zn anode, the Mn deposit amount on the anode was measured to reveal the Mn dissolution from the ZMO cathode based on the disproportionation reaction. The ZMO particle synthesized at 600℃ with the largest particle size demonstrated the highest cyclability of 48.1% at 1.0 A g<sup>-1</sup> based on the lowest Mn deposit on the anode. Hence, the ZMO electrode with a larger particle size exhibited improved cycle stability by alleviating of the disproportionation reaction from the reduced electrode/electrolyte interfacial area.