Journal
CHEMISTRY OF MATERIALS
Volume 28, Issue 2, Pages 534-542Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.chemmater.5b03983
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Funding
- Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences
- Chemical Imaging Initiative conducted under the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL)
- DOE's Office of Biological and Environmental Research
- Department of Energy [DE-AC05-76RLO1830]
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Magnesium batteries are an energy storage system that potentially offers high energy density, but development of new high voltage cathode materials and understanding of their electrochemical mechanism are critical to realize its benefits. Herein, we synthesize the layered MnO2 polymorph (the birnessite phase) as a nanostructured phase supported on conductive carbon cloth and compare its electrochemistry and structural changes when it is cycled as a positive electrode material in a Mg-ion battery under nonaqueous or aqueous conditions. X-ray photoelectron spectroscopy and transmission electron microscopy studies show that a conversion mechanism takes place during cycling in a non-aqueous electrolyte, with the formation of MnOOH, MnO, and Mg(OH)(2) upon discharge. In aqueous cells, on the other hand, intercalation of Mg2+ ions takes place, accompanied by expulsion of interlayer water and transformation to a spinel-like phase as evidenced by X-ray diffraction. Both systems are structurally quasireversible. The sharp contrast in behavior in the two electrolytes points to the important role of the desolvation energy of the Mg2+ cation in nonaqueous systems.
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