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 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 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 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 4 such a unique material and ideally shaping future discourse of LiFePO 4 research.

We have investigated Mg intercalation into orthorhombic V 2 O 5 , one of only three cathodes known to reversibly intercalate Mg ions. By calculating the ground-state Mg x V 2 O 5 configurations and by developing a cluster expansion for the configurational disorder in δ-V 2 O 5 , a full temperature− composition phase diagram is derived. Our calculations indicate an equilibrium phase-separating behavior between fully demagnesiated α-V 2 O 5 and fully magnesiated δ-V 2 O 5 , but also motivate the existence of potentially metastable solid solution transformation paths in both phases. We find significantly better mobility for Mg in the δ polymorph, suggesting that better performance can be achieved by cycling Mg in the δ phase.

Cation disorder is an important design criterion for technologically relevant transition-metal (TM) oxides, such as radiation-tolerant ceramics and Li-ion battery electrodes. In this Letter, we use a combination of first-principles calculations, normal mode analysis, and band-structure arguments to pinpoint a specific electronic-structure effect that influences the stability of disordered phases. We find that the electronic configuration of a TM ion determines to what extent the structural energy is affected by site distortions. This mechanism explains the stability of disordered phases with large ionic radius differences and provides a concrete guideline for the discovery of novel disordered compositions.

also been experimentally verifi ed. [ 1,7 ] This is in line with the general strategy to utilize Li-excess chemistries to achieve higher energy densities. [13][14][15] However, Li-excess materials often suffer from structural instabilities that give rise to phase transitions and degradation upon repeated cycling. [16][17][18][19] As a possible remedy, cation disorder was found to enhance the structural stability upon Li extraction, which makes it possible to achieve high reversible capacities and reduces the overall volume change with varying lithium content. [ 1 ] Minimizing volume fl uctuations is benefi cial for all electrodes, but is especially important for solid-state batteries in order to prevent fracturing of the solid/solid electrode/electrolyte interfaces, [ 20,21 ] and as such cation-disordered electrodes are particularly attractive for all-solid batteries.The stringent electronic structure requirements on TM ions in structures that need to remain well layered [ 22,23 ] have limited the active chemistry of cathode oxides to just a few elements such as Co and Ni. On the other hand, the composition space for potential cation-disordered oxides is vast, as TM mobility is not a constraint. Indeed, many of the new disordered cathodes contain elements such as Cr, Mo, Ti, and Nb, which were usually not used in well-ordered cathodes. Because of this, identifying the compositions of new cation-disordered oxides is a critical bottleneck for the discovery of improved disordered cathode materials. One successful strategy for the rational design of new cation-disordered Li-excess cathode materials has been to introduce excess Li into known stoichiometric disordered compositions, such as LiTi 0.5 Ni 0.5 O 2 [ 8,24,25 ] and LiTi 0.5 Fe 0.5 O 2 . [ 7,26,27 ] This approach is, however, limited by the small number of presently known cation-disordered Li-TM oxides. While it is in some cases possible to impose cation disorder to otherwise ordered crystal structures by means of mechanochemical synthesis routes, [ 28 ] a complete library of materials that potentially form in the disordered rocksalt structure would accelerate the development of cation-disordered cathode materials.With this motivation in mind, the objective of the present work is to introduce a straightforward methodology for the computational prediction of new disordered rocksalts and to demonstrate its practicality by identifying and synthesizing a novel cation-disordered oxide. In the following Section 2 the computational methods, synthesis procedures, and characterization techniques are outlined. This is followed by a report of Cation-disordered lithium-excess metal oxides have recently emerged as a promising new class of high-energy-density cathode materials for Li-ion batteries, but the exploration of disordered materials has been hampered by their vast and unexplored composition space. This study proposes a practical methodology for the identifi cation of stable cation-disordered rocksalts. Here, it is established that the effi cient method, which makes...

Cation disorder is a phenomenon that is becoming increasingly important for the design of high-energy lithium transition metal oxide cathodes (LiMO2) for Li-ion batteries. Disordered Li-excess rocksalts have recently been shown to achieve high reversible capacity, while in operando cation disorder has been observed in a large class of ordered compounds. The voltage slope is a critical quantity for the design of cation-disordered rocksalts, as it controls the Li capacity accessible at voltages below the stability limit of the electrolyte (∼4.5–4.7 V). In this study, we develop a lattice model based on first principles to understand and quantify the voltage slope of cation-disordered LiMO2. We show that cation disorder increases the voltage slope of Li transition metal oxides by creating a statistical distribution of transition metal environments around Li sites, as well as by allowing Li occupation of high-voltage tetrahedral sites. We further demonstrate that the voltage slope increase upon disorder is generally smaller for high-voltage transition metals than for low-voltage transition metals due to a more effective screening of Li–M interactions by oxygen electrons. Short-range order in practical disordered compounds is found to further mitigate the voltage slope increase upon disorder. Finally, our analysis shows that the additional high-voltage tetrahedral capacity induced by disorder is smaller in Li-excess compounds than in stoichiometric LiMO2 compounds.