Fine Li(4-x)/3Ti(2-2x)/3FexO2 (0.18 <= x <= 0.67) powder with cubic rock-salt structure as a positive electrode material for rechargeable lithium batteries

摘要

Li4/3Ti2/3O2 - LiFeO2 solid solution, Li(4 - x)/3Ti(2 - 2x)/3FexO2 (0.18 less than or equal to x less than or equal to 0.67), which has the cubic rock-salt structure (Fm (3) over barm, average particle size less than 100 nm), was synthesized from Fe-Ti co-precipitates by hydrothermal reaction with excess LiOH and KClO3 at 220 degreesC. Calcination of the products with lithium hydroxide in an oxidative atmosphere leads to the oxidation of trivalent iron to a 3+/4+ mixed valence state. Hydrothermally-obtained Li1.2Ti0.4Fe0.4O2 gave maximum initial charge (266 mA h g(-1)) and discharge capacities (153 mA h g(-1) around 3 V) between 2.5 and 4.8 V. Calcination enabled us not only to improve the crystallinity, but also suppress the discharge capacity fading with cycle number. Two plateaus around 3 and 4 V were observed on discharging by decreasing the amount of Li extraction (0.4 Li per chemical formula). Although the cubic rock-salt structure was retained during both charge and discharge processes, a partial 3d-cation displacement from octahedral 4a to tetrahedral 8c sites and some oxygen loss were observed after electrochemical delithiation. In-situ Fe-57 Mossbauer spectroscopy showed evidence of the Fe3+/Fe4+ redox only around the 4 V region. [References: 29]