Composite ‘Layered-Layered-Spinel’ Cathode Structures for Lithium-Ion Batteries

The concept of embedding a spinel component in high capacity, composite xLi 2 MnO 3 •(1−x)LiMO 2 (M = Mn, Ni) 'layered-layered' structures to improve their electrochemical properties and cycling stability has been exploited. In this paper, we report the preparation and electrochemical characterization of three-component 'layered-layered-spinel' electrodes, synthesized by lowering the lithium content of a parent 'layered-layered' 0.3Li 2 MnO 3 •0.7LiMn 0.5 Ni 0.5 O 2 material while maintaining a Mn:Ni ratio of 0.65:0.35; such compounds can be designated generically by the system, Li x Mn 0.65 Ni 0.35 O y , for which the end members are 0.3Li 2 MnO 3 •0.7LiMn 0.5 Ni 0.5 O 2 (x = 1.3; y = 2.3), in which the average manganese and nickel oxidation states are 4+ and 2+, respectively, and LiMn 1.3 Ni 0.7 O 4 (x = 0.5; y = 2) in which the corresponding average oxidation states are expected to lie between 4+ and 3.77+ for Mn, and 2.57+ and 3+ for Ni, respectively. For this study, compounds with a lithium content of x = 1.3, i.e., the parent 'layered-layered' composition, and 1.25 were selected for detailed and comparative investigation, the latter value corresponding to a targeted spinel content of 6%. The beneficial effects of 1) using Mg 2+ as a dopant ion and 2) treating the electrode particle surface with an acidic solution of AlF 3 to enhance cycling stability, reduce first-cycle capacity loss, and to slow voltage decay on cycling are discussed.