A Critical Review of the Li Insertion Mechanisms in LiFePO[subscript 4] Electrodes

With the ever-growing public and now commercial sentiment supporting the widespread adoption of low and zero-emission vehicles, it is unsurprising that Li-ion batteries which currently assume the bulk of the cost of electrified vehicles (a significant proportion coming from cost of battery materials) have become prolific not only in the primary research literature but have also entered the general public consciousness. Since the initial work in 1997, over 2000 research publications have been authored on lithium iron phosphate (LiFePO[subscript 4]), one of only a handful of commercially viable Li-ion battery cathode materials currently used in electrified vehicles. Despite the sheer quantity of research devoted to the subject and the well-demonstrated excellent battery performance of LiFePO[subscript 4], what is surprising are the number of apparent discrepancies and ensuing contention in the literature regarding its (de)lithiation kinetics. This Review forgoes re-summarizing the well-accepted materials properties of LiFePO[subscript 4] and instead seeks to address headlong the specific areas of dispute in the field, specifically by considering how the thermodynamics and kinetics of Li intercalation are modified from the bulk to single-particle to multi-particle scales, shedding light on what makes LiFePO[subscript 4] such a unique material and ideally shaping future discourse of LiFePO[subscript 4] research.