There is a constant drive to improve the specific energy and energy density of the state-of-the-art lithium-ion battery. High energy can be achieved by either choosing a cathode material that operates at a higher potential or has a higher specific capacity. Compared with the conventional 4-V cathodes such as LiCoO2
(LMO) and 3.5-V LiFePO4
(LCP) operates at 4.8 V (vs. Li/Li+
) with a theoretic capacity of 167 mAh g-1
, resulting in a specific energy of ~800 Wh kg-1
, which is about 25% higher than those of the conventional LFP and LMO lithium-ion batteries. Although Co is more expensive than the other transition metals, the energy cost of LCP is expected to be cheaper than all commercialized lithium-ion batteries on the market  due to the improved energy density (FIG.1).
However, LCP suffers from severe capacity fade due to the low intrinsic electronic/ionic conductivity, structure deterioration and electrolyte decomposition . In order to improve the cyclability and reduce the cost of LCP, Co ions were partially substituted by cheaper elements such as Fe, Cr and Si etc . Meanwhile, a carbon-coating was used to improve the electronic conductivity of LCP. Electrochemical tests showed that both carbon-coating and substitution greatly improved the cycling performance of LCP, which suggests that the substituted LCP is a very promising cathode candidate for high energy lithium-ion battery.
 S. Brutti, S. Panero, ACS Symposium Series, 1140, Chapter 4, 69 (2013).
 K. Tadanaga, F. Mizuno, A. Hayashi, T. Minami, M. Tatsumisago, Electrochemistry 71, 1192 (2003).
 J. L. Allen, J. L. Allen, T. Thompson, S. A. Delp, J. Wolfenstine, T. Richard Jow, J. Power Sources, 327, 229 (2016).
FIG. 1. Energy density and energy cost of LCP compared with other cathode materials currently used in lithium-ion batteries.