Magnetic and structural approach for understanding the electrochemical behavior of LiNi0.33Co0.33Mn0.33O 2positive electrode material

Abstract

A systematic study has been performed to investigate the structural and magnetic changes in LiNi0.33Mn0.33Co0.33O 2, a member of the LiNiyMnyCo 1-2yO2series, upon chemical lithium deintercalation. Structural characterization of the chemically delithiated LixNi 0.33Mn0.33Co0.33O2samples indicates thatthe initial rhombohedral symmetry (α-NaFeO2type structure) is maintained in the whole 0.3 ≤ x ≤ 1.0composition range. Less than 1% variation in the hexagonal unit cell volume was evidenced showing a good structural stability of this sample. SEM pictures of the delithiated phases confirm this stability. Indeed, the particle size average undergoes a small decrease (from 180 nm at x = 1.0-130 nm for x = 0.3).The magnetic properties (SQUID and EPR) of LixNi0.33Mn0.33Co0.33O 2compounds were also investigated. A simultaneous oxidation of Ni2+to Ni4+via Ni3+and Co3+to Co4+was observed upon lithium removal. EPR signals registered at 100 K, coupled to SQUID measurements, revealed strong antiferromagnetic interactions within the structure of this sample which became more pronounced by the delithiation process. © 2013 Elsevier Ltd. All rights reserved.