Followed
by decades of successful efforts in developing cathode
materials for high specific capacity lithium-ion batteries, currently
the attention is on developing a high-voltage battery (>5 V vs
Li/Li+) with an aim to increase the energy density for
their many
fold advantages over conventional <4 V batteries. Among the various
cathode materials, phosphate polyanion materials (LiMPO4, where M is a single metal or a combination of metals) showed promising
candidacy given their high electrochemical potential (4.8–5
V vs Li/Li+), long cycle stability, low cost, and achieved
specific capacity (∼165 mAh·g–1) near
to its theoretical limit (170 mAh·g–1). In
this review, factors affecting the electrochemical potential of the
cathode materials are reviewed and discussed. Techniques to improve
the electrical and ionic conductivities of phosphate polyanion cathodes,
namely, surface coating, particle size reduction, doping, and morphology
engineering, are also discussed. A processing–property correlation
in phosphate polyanion materials is also undertaken to understand
relative merits and drawbacks of diverse processing techniques to
deliver a material with targeted functionality. Strategies required
for high-voltage phosphate polyanion cathode materials are envisioned,
which are expected to deliver lithium-ion battery cathodes with higher
working potential and gravimetric specific capacity.