Magnetic and structural approach for understanding the electrochemical behavior of LiNi0.33Co0.33Mn0.33O2 positive electrode material

• LixNi0.33Mn0.33Co0.33O2 samples were chemically prepared.
• No structural transition was evidenced during delithiation (ΔV ≤ 1%).
• EPR and SQUID studies show a simultaneous redox activity of Ni2+ and Co3+.
• More pronounced antiferromagnetic interaction were evidenced upon lithium extraction.

A systematic study has been performed to investigate the structural and magnetic changes in LiNi0.33Mn0.33Co0.33O2, a member of the LiNiyMnyCo1–2yO2 series, upon chemical lithium deintercalation. Structural characterization of the chemically delithiated LixNi0.33Mn0.33Co0.33O2 samples indicates that the initial rhombohedral symmetry (α-NaFeO2 type structure) is maintained in the whole 0.3 ≤ x ≤ 1.0 composition 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 LixNi0.33Mn0.33Co0.33O2 compounds 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.

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