Influence of chromium doping on the electrochemical performance of the 5 V spinel cathode LiMn1.5Ni0.5O4

With an aim to improve the 5 V capacity and cyclability of the LiMn1.5Ni0.5O4 spinel oxide, three series of Cr substitutions have been pursued with y ≤ 0.2: LiMn1.5Ni0.5−yCryO4, LiMn1.5−0.5yNi0.5−0.5yCryO4, and LiMn1.5−0.33yLi0.33yNi0.5−yCryO4. While the first series involves an increase in the Mn3+ content, the second and third series are designed to maintain charge neutrality (Mn4+, Ni2+, Cr3+, and Li+) without introducing Mn3+ ions. The LiMn1.5Ni0.5−yCryO4 series experiences a widening of the 4 V plateau and a decrease in the 5 V capacity compared to LiMn1.5Ni0.5O4 due to an increase in the Mn3+ content. On the other hand, the LiMn1.5−0.5yNi0.5−0.5yCryO4 series shows a suppression of the 4 V plateau and an increase in the 5 V capacity due to the elimination of the Mn3+ions. The LiMn1.5−0.33yLi0.33yNi0.5−yCryO4 series shows a suppression of the 4 V plateau at low Cr contents, but an increase in the 4 V plateau as the Cr content increases above 0.1. Among the various compositions investigated, LiMn1.45Ni0.45Cr0.1O4 exhibits the best combination of high 5 V capacity (128 mAh/g at 5–4.2 V) and excellent capacity retention (98% in 50 cycles) compared to 118 mAh/g and 92% for LiMn1.5Ni0.5O4.