Page 400 - Handbook of Battery Materials

References 371

energy densities, but the long-term cycling stability of these high-voltage cathodes
has yet to be established, and their successful application requires the development
of more stable high-voltage electrolytes.
In recent years, the phospho-olivine LiFePO 4 cathode has attracted much at-
tention because of its excellent cycle life, high chemical stability, and good safety
characteristics compared to the layered and spinel oxide cathodes. However, its
lower cell voltage (3.45 V) and crystallographic density limit the energy density.
Although other olivines like LiCoPO 4 and LiNiPO 4 offer higher energy densities
due to higher voltages (4.8–5.1 V), the instability of conventional electrolytes at
these higher voltages limits their adoptability. In this regard, the challenge is to
develop a polyanion-containing framework that can allow for extraction/insertion
of more than one lithium ion per transition metal ion with a voltage around 4 V
without undergoing any major structural changes during cycling.
Overall, there is immense interest in lowering the cost, improving the safety,
and increasing the energy and power densities so that the lithium-ion technology
can be successfully employed for vehicle and stationary storage applications. The
development of (a) new materials that can allow the insertion/extraction of more
than one lithium per transition metal ion without unduly increasing the insertion
host weight or (b) more stable, robust electrolytes to utilize the high-voltage (>4.3 V)
cathodes is needed to move the field forward.

Acknowledgments

This work was supported by the Welch Foundation grant F-1254,Office of
Vehicle Technologies of the U.S. Department of Energy under Contract No.
DE-AC02-05CH11231, and NASA contract NNC09CA08C.

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