Effects of Li Content on Structure and Electrochemical Properties of Li1 + x ( Ni0.5Mn0.5 ) 1 − x O2 ( 0 ≤ x ≤ 0.15 ) Electrodes in Lithium Cells ( 1.0 – 4.8 V )

Layered Li 1+x (Ni 0.5 Mn 0.5 ) 1-x O 2 (0 ≤ x ≤ 0.15) materials have been synthesized using Li 2 CO 2 and coprecipitated (Ni 0.5 Mn 0.5 )(OH) 2 . The materials with increased lithium content (x ≥ 0.10) showed distinct differences in particle morphology, which is attributed to the melting of excess Li 2 CO 3 during calcination. The powder XRD patterns and the initial charging curves to 4.8 V indicated that the excess lithium resides in the transition metal layer to form Li 2 MnO 2 -like domains in the electrode structure such that these compounds can be reformulated in a two-component composite notation as 2xLi 2 MnO 3 .(1 - 3x)Li(Ni y Mn 1-y )O 2 {y = (1-x)/[2(1- 3x)]) with some cation disorder between the two components. The excess lithium significantly affected the charge/discharge behaviors in the low-voltage range (<2 V) and the rate capability of the electrode materials, which is attributed to increasing Ni 3+ content and decreasing Li/Ni disorder (i.e., Ni content in the lithium layer) in the materials.