The need for environmentally friendly, safe, stable, and low cost materials for application in lithium-ion batteries has led to strong interest in developing olivine-type LiMPO₄ (M = Fe, Mn, Co, Ni) cathode materials. Among them, LiFePO₄ (LFP) has been extensively studied and commercialized. However, LFP has some special shortcomings in practical applications, such as low potential plateau (3.4 V vs. Li/Li⁺) and small packing density (due to the inclusion of large-volume carbon), which lead to relatively low specific energy density (580 Wh kg^-1). Whereas LiCoPO₄ (LCP) in the olivine family has been considered as an attractive cathode candidate due to the large theoretical capacity (167 mAh g^-1), high operating voltage (4.8 V vs. Li/Li⁺) and high specific energy density (800 Wh kg^-1).

However, LCP suffers from severe capacity fade due to the low intrinsic electronic/ionic conductivity, structure deterioration and electrolyte decomposition [1]. In this work, Hydro Quebec and US Army Research Laboratory dedicated to develop the high voltage olivine cathode. Specifically, partially Co-substitution strategy with a carbon coating was successfully used to improve the cycling stability of LCP cathode [2]. FIG. 1 shows the cyclability of substituted-LCP olivine cathode at room temperature under C/3 rate, from which no obvious capacity loss was observed in 100 cycles. Moreover, phosphate based cathodes may provide higher abuse tolerance than oxides at a given voltage due the strong covalent band of P-O. Therefore, the substituted high voltage LCP olivine cathode has the apparent potential to be a next decade success story in lithium-ion technologies and to find large application in the next generation lithium-ion batteries.

References

[1] K. Tadanaga, F. Mizuno, A. Hayashi, T. Minami, M. Tatsumisago, Electrochemistry 71, 1192 (2003).

[2] J. L. Allen, J. L. Allen, T. Thompson, S. A. Delp, J. Wolfenstine, T. Richard Jow, J. Power Sources, 327, 229 (2016).