1 research outputs found
Unexpected Chain of Redox Events in Co-Based Prussian Blue Analogues
The electronic structure of electrode materials for metal-ion
batteries
has a great impact on their charge compensation mechanism and, consequently,
electrochemical behavior. In this paper, we report on the cobalt doping
in the potassium manganese hexacyanoferrate positive electrode material
for potassium-ion batteries, resulting in the formation of a system
of K2−δCoxMn1–x[Fe(CN)6] compounds with x = 0...1 and provide their comprehensive characterization
including crystal structure evolution and charge compensation mechanisms
upon K de/intercalation. Synthesized by a coprecipitation method,
K2−δCoxMn1–x[Fe(CN)6] forms two series
of solid solutions with monoclinic (Co-poor) and cubic (Co-rich) structures.
According to energy-dispersive X-ray analysis, the K content diminishes
with increasing x value. Electrochemical properties
of electrode materials based on K2−δCoxMn1–x[Fe(CN)6] in K-metal half cells are also strongly dependent on Co
doping regarding both specific capacity and redox potential. Attempts
to interpret the results led to an unexpected conclusion that cobalt
has influence on iron and manganese redox potentials, forming the
following oxidation sequence: Co2+/3+, Mn2+/3+, and Fe2+/3+ in K2−δCoxMn1–x[Fe(CN)6], which is inverse to that of Co-free K2−δMn[Fe(CN)6] (Fe2+/3+, Mn2+/3+),
as validated by ex situ, operando X-ray absorption spectroscopy, and 57Fe Mössbauer
spectroscopy