Understanding the Stability for LiNi0.5Mn0.5O2 as a Co-free positive electrode material

For understanding the stability of Co-free positive electrode material, LiNi0.5Mn0.5O2 was synthesized with different addition amount of lithium during calcination. The valence states of transition metal in the prepared samples were determined by combining accurate stoichiometry analysis via ICP, magnetic moment measurement via SQUID, and element valence analysis via XPS with Ar ion etching. Unexpectedly, the transition metals, Ni and Mn, at interior and surface of LiNi0.5Mn0.5O2 particles show different electrochemical properties. This answer lingering questions of Li de-intercalation mechanism in LiNi0.5Mn0.5O2.