Low-Cost High-Energy Potassium Cathode

Potassium
has as rich an abundance as sodium in the earth, but
the development of a K-ion battery is lagging behind because of the
higher mass and larger ionic size of K+ than that of Li+ and Na+, which makes it difficult to identify
a high-voltage and high-capacity intercalation cathode host. Here
we propose a cyanoperovskite KxMnFe­(CN)6 (0 ≤ x ≤ 2) as a potassium
cathode: high-spin MnIII/MnII and low-spin FeIII/FeII couples have similar energies and exhibit
two close plateaus centered at 3.6 V; two active K+ per
formula unit enable a theoretical specific capacity of 156 mAh g–1; Mn and Fe are the two most-desired transition metals
for electrodes because they are cheap and environmental friendly.
As a powder prepared by an inexpensive precipitation method, the cathode
delivers a specific capacity of 142 mAh g–1. The
observed voltage, capacity, and its low cost make it competitive in
large-scale electricity storage applications.