Structural and electrochemical characterization of the layered LiNi 0.5− yMn 0.5− yCo 2 yO 2 (0 ≤ 2 y ≤ 1) cathodes

Abstract

The crystal chemistry and electrochemical performance of the layered LiNi 0.5− y Mn 0.5− y Co 2 y O 2 oxide cathodes for the entire range of 0 ≤ 2 y ≤ 1 have been investigated. Compositions with 0.33 ≤ 2 y ≤ 0.5 are found to exhibit a combination of high capacities (> 170 mAh/g at 3.0–4.5 V and C/5 rate) and good cyclability (> 90% retention in 50 cycles). The electrochemical rate capability is found to decrease with decreasing Co content 2 y. While no obvious correlation is found with the electrical conductivity, the rate capability bears a clear relationship to the chemical lithium extraction rate, which decreases with decreasing Co content due to an increasing cation disorder. Additionally, the lithium extraction rate is found to influence the structure of the chemically delithiated end members Ni 0.5− y Mn 0.5− y Co 2 y O 2− δ ; the structure changes from P3 to O1 to O3 with decreasing Co content 2 y.