Cr and Si Substituted-LiCo0.9Fe0.1PO4: Structure, full and half Li-ion cell performance

Abstract The use of LiCoPO 4 as a Li-ion cathode material can enable high energy 5 V batteries. However, LiCoPO 4 shows limited cycle life and much less than theoretical energy density. In order to address these shortcomings, Fe, Cr and Si substituted-LiCoPO 4 ( Cr,Si-LiCo 0.9 Fe 0.1 PO 4 ) was investigated as an improved LiCoPO 4 based cathode material. Fe substitution greatly improves the cycle life and increases the energy density. Cr substitution further increases the energy density, cycle life and rate capability. Si substitution reduces the reactivity of the cathode with electrolyte thereby increasing cycle life. In combination, the substituents lead to a LiCoPO 4 based cathode material with no capacity fade over 250 cycles in Li/Cr,Si-LiCo 0.9 Fe 0.1 PO 4 half cells, a discharge capacity of 140 mAh g −1 at C/3 at an average discharge voltage of 4.78 V giving an energy density of 670 Wh per kg of cathode. In graphite/Cr,Si-LiCo 0.9 Fe 0.1 PO 4 full Li-ion cells, the cathode material shows an energy density of 550 Wh per kg of cathode material at 1C rate for the initial cycles and 510 Wh per kg of cathode material at the 250th cycle.