The significance of the Li2MnO3 component in 'composite' xLi2MnO3 • (1-x)LiMn0.5Ni0.5O2 electrodes

The electrochemical behavior of 0.3Li(2)MnO(3) . 0.7LiMn(0.5)Ni(0.5)O(2) 'composite' electrodes, when charged to potentials greater than or equal to4.5 V in lithium cells, has been compared with the behavior of electrodes that were preconditioned by acid treatment. When charged to 5 V, all the lithium can be extracted from 0.3Li(2)MnO(3) . 0.7LiMn(0.5)Ni(0.5)O(2) in two distinct steps to yield a Mn0.65Ni0.35O2 product, the first step corresponding predominantly to lithium extraction from the electrode structure with the concomitant oxidation of Ni2+ to Ni4+, and the second to the electrochemical removal of Li2O from the structure. The electrode delivers a rechargeable capacity >250 mAh/g when cycled between 5.0 and 2.0 V vs. Li-0; the high capacity and cycling stability are attributed to the high manganese (IV) content in the electrode over this voltage range. Acid-treatment significantly reduces the coulombic inefficiency of the initial charge/discharge cycle of the cells. The electrochemical behavior of 0.3Li(2)MnO(3) . 0.7LiMn(0.5)Ni(0.5)O(2) is compared with that of standard Li2MnO3 electrodes. The advantage of using the two-component notation xLi(2)MnO(3) . (1 - x)LiMn0.5Ni0.5O2 instead of the equivalent layered notation Li[Lix/(2 + x)Mn(1 + x)/(2 + x)Ni(1 - x)/(2 + x)]O-2 to monitor the compositional changes that occur in the electrode during electrochemical charge and discharge is highlighted. (C) 2004 Elsevier B.V. All rights reserved.