Is proton a charge carrier for δ-MnO2 cathode in aqueous rechargeable magnesium-ion batteries?

• Published in: Journal of energy chemistry 2022-05, Vol.68, p.572-579
• Main Authors: Liu, Zhenzhen, Li, Xiang, He, Jian, Wang, Qian, Zhu, Ding, Yan, Yigang, Chen, Yungui
• Format: Article
• Language: English
• Subjects: Cathode; Magnesium-ion batteries; Mg ion insertion/extraction; Proton insertion/extraction; δ-MnO2
• ISSN: 2095-4956
• DOI: 10.1016/j.jechem.2021.12.016

Highly porous δ-MnO2 delivers a high specific capacity of 252.1 mAh g−1 and an excellent rate capability. It endures the consequent H+ and Mg2+ insertion during discharging in MgCl2 aqueous electrolyte. [Display omitted] Manganese dioxide (MnO2) is considered as a potential cathode material for aqueous magnesium-ion batteries. However, the charge/discharge mechanism of MnO2 in aqueous electrolyte is still unclear. In present study, highly porous δ-MnO2 is investigated, which delivers a high capacity of 252.1 mAh g−1 at 0.05 A g−1 and excellent rate capability, i.e., 109.7 mAh g−1 at 1 A g−1, but a low-capacity retention of 54.4% after 800 cycles at 1 A g−1. The two-step discharging process, namely a consequent H+ and Mg2+ insertion reaction, is verified, by comparing the electrochemical performance of δ-MnO2 in 1 M MgCl2 and 1 M MnCl2 aqueous electrolyte and analyzing detailedly the Mg content and the bonding state of Mn at different charge/discharge state. Furthermore, partial irreversibility of Mg2+ ion insertion/extraction is observed, which may be one of the major reasons leading to capacity decay.