Calcination Heterogeneity in Li-Rich Layered Oxides: A Systematic Study of Li2CO3 Particle Size

Li- and Mn-rich (LMR) layered oxide positive-electrode materials exhibit high energy density and have earth-abundant compositions relative to conventional Ni-, Mn-, and Co-oxides (NMCs). The lithiation of coprecipitated precursors is a key part of the synthesis and offers opportunities for tuning the properties of LMR materials. Whereas the morphology of transition metal precursors has received substantial attention, that of Li sources has not. Using Li1.14Mn0.57Ni0.29O2 as a model system, in this work, we establish a detailed understanding of LMR calcination pathways via in situ and ex situ diffraction, spectroscopy, microscopy, and thermogravimetry. Our work shows that a large Li2CO3 particle size modulates a previously misunderstood thermogravimetric feature present at the Li2CO3 melting point during layered oxide calcination and causes heterogeneity at larger length scales (inter-secondary particle) than previously reported (intra-secondary particle). We found that electrochemical performance is largely insensitive to this heterogeneity. This work highlights the sensitivity of layered oxide calcination pathways to synthesis conditions and suggests design rules to minimize calcination heterogeneity in layered oxides beyond LMR.