Structural evolution of disordered LiCo1/3Fe1/3Mn1/3PO4 in lithium batteries uncovered

In this study we address the Li-ion de-insertion/insertion mechanisms from/into the lattice of the mixed olivine LiCo1/3Fe1/3Mn1/3PO4 (LCFMP). This mechanism is driven by a subtle interplay of structural, electronic and thermodynamic features. We aim at dissecting this complex landscape that is tightly connected to the long-term electrochemical performance of this material as a positive electrode in lithium-ion cells. To this end, we report advanced structural characterization, based on ex situ synchrotronradiation diffraction on samples at different lithium contents. We couple this analysis with first-principles simulations, for a direct vis-à-vis comparison. Our results show that (1) the mixing of the three transition-metal (TM) cations in the olivine lattice leads to a solid solution, providing the olivine lattice with the necessary flexibility to retain its single-phase structure during cell operation; (2) the electronic features of the three TMs are responsible for the observed electrochemical performance; (3) the de-lithiation of the olivine lattice is a thermodynamically driven process. Last but not least, our integrated experimental and theoretical results reveal the subtle features behind the formation of antisite defects that selectively involve Li-Co couples. In conclusion, our study provides the necessary scientific foundations to understand the structure-property-function relationships in LCFMP olivines, paving the way for further development and optimization of this material for application in Li-ion batteries.