Effects of Lithium Content and Surface Area on the Electrochemical Performance of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂

Abstract

Lithium-rich, layered composites of xLi2MnO3•(1-x)LiNi1/3Mn1/3Co1/3O2 have been extensively studied for PHEVs and EVs. To ensure complete lithiation, most synthesis methods require the addition of excess lithium compared to the stoichiometric composition. In this study lithium enriched, layered composites of Li1.2Mn0.54Ni0.13Co0.13O2 were synthesized in a spray pyrolysis process. Spray pyrolysis allows for excellent control of composition and in this work the lithium content was systematically varied between 3.3 wt% excess and 3.3 wt% deficient compared to Li1.2Mn0.54Ni0.13Co0.13O2. The as-synthesized powders were annealed at 900°C for 2, 5 and 20 hours. Results indicate that as the annealing time is increased the surface areas is reduced from 9 to ∼2 m2 g−1. No new phases form during the annealing process although changes in the relative intensity of the (018) and (110) peaks imply a reorganization between the transition metal and lithium layers. An excess Li of 3.3 wt% is sufficient to counter these structural rearrangements and maintain discharge capacities close to 200 mAhg−1 after 100 cycles at C/3. Samples with a smaller surface area do not lead to improved capacity retention. The results also suggest that the Li2MnO3 structural component has a key role in the voltage fade for these materials.