Breaking the battery barrier
A multi-disciplinary team of Argonne MSD and CSE researchers are working together to explore the uncharted territory of lithium-ion-battery cathode materials to improve battery storage and technology. The team’s research has been published in the Journal of Materials Chemistry A.
Layered–layered composite cathode materials for lithium ion batteries with composition xLi2MnO3·(1 − x)LiMO2 have attracted enormous attention because of their high capacities and energy densities. Because microstructural features are expected to influence battery performance, a better characterization of the material structure and transformations would be valuable. Experimental observation shows evidence of fine scale phase separation into Li- and Mn-rich domains and transition metal (TM)-rich domains (Long et al. 2014). TEM indicates that the Li- and Mn-rich domains exhibit the ordering of the LiMn2 layers characteristic of pure Li2MnO3. Furthermore, modeling suggests that the solubility of Li2MnO3 in LiMO2 is negligible, which implies that phase separation would occur at thermodynamic equilibrium.
Layered lithium ion battery cathode materials have been extensively investigated, of which layered–layered composites xLi2MnO3·(1 − x)LiMO2 (M = Mn, Co, Ni) are of particular interest, owing to their high energy density. Before the structural transformations that occur in these materials with cycling can be understood, the structure of the pristine material must be established. In this work, NMR spectra are measured for the model layered–layered system xLi2MnO3·(1 − x)LiCoO2 and Bond-Pathway-model analysis is applied to elucidate the atomic arrangement and domain structure of this material in its pristine state, before electrochemical cycling. The simplest structural element of an Li2MnO3 domain consists of a stripe of composition LiMn2 parallel to a crystallographic axis in a metal layer of the composite. A simple model of the composite structure may be constructed by a superposition of such stripes in an LiCoO2 background. We show that such a model can account for most of the features of the observed NMR spectra.
Hakim Iddir, Baris Key, Fulya Dogan, John T. Russell, Brandon R. Long, Javier Bareño, Jason R. Croy and Roy Benedek, “Pristine-state Structure of Lithium-ion-battery Cathode Material Li1.2Mn0.4Co0.4O2 Derived from NMR Bond Pathway Analysis,” Journal of Materials Chemistry A, Advance Article. DOI: 10.1039/C5TA01510C, Published May 1, 2015.