MnS/MnO heterostructures with dual ion defects for high-performance aqueous magnesium ion capacitors
Minghui Liu, Mudi Li, Siwen Zhang, Yaxi Ding, Ying Sun, Jiazhuo Li, Haixi Gu, Bosi Yin, Hui Li, Tianyi Ma
Abstract
The advancement of aqueous magnesium ion energy storage devices encounters limitations due to the substantial hydration radius of magnesium ions (Mg2+) and their strong electrostatic interaction with the primary material. Consequently, this study successfully developed a MnS/MnO heterostructure through a straightforward hydrothermal and annealing method, marking its initial application in aqueous magnesium ion capacitors (AMICs). The fabricated MnS/MnO heterostructure, characterized by S defects, also generates Mn defects via in-situ initiation of early electrochemical processes. This unique dual ion defects MnS/MnO heterostructure (DID-MnS/MnO) enables the transformation of MnS and MnO, initially not highly active electrochemically for Mg2+, into cathode materials exhibiting high electrochemical activity and superior performance. Moreover, DID-MnS/MnO enhances conductivity, improves the kinetics of surface redox reactions, and increases the diffusion rate of Mg2+. Furthermore, this study introduces a dual energy storage mechanism for DID-MnS/MnO, which, in conjunction with dual ion defects, offers additional active sites for Mg2+ insertion/deinsertion in the host material, mitigating volume expansion and structural degradation during repeated charge-discharge cycles, thereby significantly enhancing cycling reversibility. As anticipated, using a three-electrode system, the developed DID-MnS/MnO demonstrated a discharge specific capacity of 237.9 mAh/g at a current density of 0.1 A/g. Remarkably, the constructed AMIC maintained a capacity retention rate of 94.3 % after 10000 cycles at a current density of 1.0 A/g, with a specific capacitance of 165.7 F/g. Hence, DID-MnS/MnO offers insightful perspectives for designing alternative clean energy sources and is expected to contribute significantly to the advancement of the clean energy sector.