HQ - US Army Development of High Voltage Olivine Cathode

Abstract

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.