Flux growth and enhanced electrochemical properties of LiNi0.5Co0.2Mn0.3O2 cathode material by excess lithium carbonate for lithium-ion batteries

Abstract

Layered LiNi0.5Co0.2Mn0.3O2 (LNCM) cathode material is synthesized via an assisted molten salt method with different amounts of Li2CO3 in this work. Rietveld refinements of X-ray diffraction reveal that the samples treated using excess lithium have better crystalline structures with lower cation mixing than pristine LNCM. With variations in Li/transition metal (TM) molar ratio, the morphology changes from aggregations consisting of primary particles (with a size around 500 nm) to dispersed micron particles (with a size around 2 μm) as characterized by scanning electron microscopy (SEM) results. The sample with a Li/TM ratio of 2.1 has excellent cycling capability at 1 C in the voltage range of 2.8–4.4 V, and has a 97.5% capacity retention with an initial capacity of 143.8 mAh g−1 after 100 cycles. The rate capability is also enhanced, exhibiting 89.5% of the first discharge capacity at 5 C after 200 cycles. The Li diffusion coefficients are collected using the galvanostatic intermittent titration technique (GITT) and increase with an increase in the lithium content. In-situ X-ray diffraction confirms that molten salt leads to less change in the crystal structural volume, thus providing sustainable evolution of structure against repeated cycling.