Achieving Stable Molybdenum Oxide Cathodes for Aqueous Zinc-Ion Batteries in Water-in-Salt Electrolyte

Layered MoO3 represents a promising cathode for aqueous rechargeable Zn-ion batteries, but the implementation of this material is limited due to the low conductivity and poor structural stability. A 30 m ZnCl2 water-in-salt electrolyte (WISE) is introduced to a MoO3 nanobelt cathode for the first time, significantly increasing the stability of MoO3 cathodes compared to those in 3 m ZnSO4 and 3 m ZnCl2. The Zn/MoO3 cell in WISE unambiguously demonstrate significantly improved rate performance delivering 349, 253, and 222 mAh g(-1) at 100, 500, and 1000 mA g(-1), denoting a 12x capacity increase of those achieved in 3 m electrolytes at 1000 mA g(-1). A capacity retention rate of 73% is achieved after (dis)charging at 100 mA g(-1) for 100 cycles, and no obvious capacity fading is observed at higher current densities of 500 mA g(-1) and 2 A g(-1). Specifically, the data suggest that the drastic fading in 3 m electrolytes can be attributed to the parasitic surface deposits on Zn originated from Mo dissolution and H-2 formation due to Zn corrosion and hydrogen evolution reaction, which are significantly suppressed in the WISE. The direct visualization of these side reactions is achieved for the first time in the Zn-MoO3 system, using an in situ optoelectrochemical measurement.

Automated summary

Introducing a 30 m ZnCl2 water-in-salt electrolyte (WISE) to a MoO3 nanobelt cathode significantly enhances the stability and rate performance of MoO3 cathodes. The Zn/MoO3 cell in WISE demonstrates superior capacity retention and lower capacity fading at higher current densities.