Promoting the Selective Intercalation of Lithium in the Olivine FePO₄ Host

The lithium supply challenge predominantly stems from the limitations of existing mining techniques in accessing lithium sources with intricate chemistry and low concentrations. Electrochemical intercalation presents an avenue for extracting lithium from diluted water sources. However, during the extraction process, the co-intercalation of lithium and its primary competitor, sodium ions, occurs. The comprehensive understanding of how host materials respond to this co-intercalation process remains an ongoing pursuit. Moreover, despite the well-acknowledged potential for lithium extraction, the reported selectivity for lithium can exhibit considerable disparity. This discrepancy in selectivity, as observed with olivine-type FePO₄, can span nearly three orders of magnitude, potentially arising from the diverse particle forms adopted (e.g., sizes, morphology, dominant facets, etc.).<br/> <br/>In this talk, using one-dimensional (1D) olivine iron phosphate (FePO₄) as a model host, I will first introduce the co-intercalation behavior of lithium and sodium ions and the control of lithium selectivity through intercalation kinetic manipulations. By combining computational and experimental investigations, we noticed that lithium- and sodium-rich phases tend to separate in the host. Exploiting this mechanism, I will discuss how the sodium-ion intercalation energy barrier can be increased using partially filled 1D lithium channels, generated via non-equilibrium solid-solution lithium seeding or remnant lithium in the solid solution phases. Furthermore, the lithium selectivity enhancement during co-intercalation shows a strong correlation with the fractions of solid-solution phases with high lithium content (i.e., Li_xFePO₄ with 0.5 ≤ x &lt; 1). Finally, I will delve into the impact of different structural forms of the host material. Specifically, I will discuss how these structural variations can influence particle kinetics and chemo-mechanical responses during Li/Na intercalation, ultimately affecting the preference for lithium.