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...

Fluorophosphate cathodes are currently one of the most promising polyanionic sodium-ion battery cathodes and exhibit specific energies not far below oxide cathodes.To further improve fluorophosphate cathodes their capacity must be increased, which might be possible since some sodium (Na) remains unextracted in these cathodes during cycling. In this study we attempt to answer the question of what specific mechanism limits fluorophosphate cathode capacity, which could stem from either redox-limiting or site-limiting behavior. This paper reports the synthesis, electrochemical characterization, and computational examination of Na 3 GaV(PO 4 ) 2 F 3 . This test system, which was designed explicitly for uncovering the limiting factors in these structures, exhibits reversible insertion of Na + and redox activity for V 2+ through V 5+ during electrochemical cycling, indicating that fluorophosphate cathodes are not fundamentally redox-limited and must be site-limited. First-principles calculations indicate that large diffusion barriers at high sodiations impose a kinetic limit on Na + insertion in fluorophosphate cathodes, but further investigation is needed to determine capacity limits on Na + extraction. From our combined results we also propose possible routes to improve future fluorophosphate cathodes.

Previously conducted high-throughput ab initio calculations have identified carbonophosphates as a new class of polyanion cathode materials. Li 3 MnCO 3 PO 4 is the most promising candidate due to its high theoretical capacity and ideal voltage range. However, a major limitation of this material is its poor cyclability and experimentally observed capacity. In this work we synthesize Li 3 The need for lithium-ion batteries with higher energy density than existing materials has led to significant efforts to discover new cathode materials.1-3 High-throughput ab initio computation is an effective approach employed to accelerate the process of materials discovery. 4 This has led to the identification of several novel lithium intercalation materials. 3,5,6 One class of novel materials that has been predicted to function as intercalation cathodes for Li-ion batteries is the lithium transition metal carbonophosphates. 5 The Li 3 FeCO 3 PO 4 and Li 3 MnCO 3 PO 4 compounds are of particular interest, as shown in Table I, which shows data first reported by Chen et al. 3 Both are predicted to have accessible 2 + to 3 + redox couples, but the 3 + to 4 + couple in the manganese-containing compound is also expected to be active at a voltage compatible with existing electrolytes. As a result, Li 3 MnCO 3 PO 4 is of the greatest interest because it has a high theoretical capacity of 231 mAh/g and average voltage of 3.7 V. As polyanionic cathodes, lithium metal carbonophosphates could also be preferred over oxide cathode materials since they are generally less likely to release oxygen at high voltages. 4 The synthesis and characterization of both Li 3 FeCO 3 PO 4 and Li 3 MnCO 3 PO 4 have been previously reported.3 The lithiumcontaining carbonophosphates are not thermodynamic ground states, so the compounds are synthesized using ion-exchange techniques from the thermodynamically stable sodium carbonophosphates. As reported previously by Chen et al., Li 3 FeCO 3 PO 4 has a theoretical capacity of 115 mAh/g and can be easily synthesized using ion exchange methods. This compound cycles reversibly, close to its theoretical limit at a rate of C/5. In contrast, Li 3 MnCO 3 PO 4 shows a discharge capacity of 135 mAh/g on its first discharge at a rate of C/100, which is only ∼58% of its theoretical capacity. In addition, the capacity of Li 3 MnCO 3 PO 4 degrades in subsequent cycles. The poor performance in Li 3 MnCO 3 PO 4 could be due to many factors. However, we believe one major cause is the residual sodium (∼17%) ions sitting on Li sites as a result of an incomplete ion exchange during synthesis. The better-performing Li 3 FeCO 3 PO 4 shows no residual sodium after synthesis. 3Our approach is to substitute manganese in the Li 3 MnCO 3 PO 4 with iron to improve its performance by imparting the ion-exchangeability and cycling performance of the Li 3 FeCO 3 PO 4 on to Li 3 MnCO 3 PO 4 . Similar mixing techniques have been used in previous attempts to improve the performance of α-LiMnPO 4 . [7][8][9] In this paper we focus specifically...

In article number 1600488, Gerbrand Ceder and co-workers present a computational highthroughput approach to identify novel disordered oxides for high-capacity Li-ion battery cathodes. The image shows the structures of ordered and cation-disordered Li transition metal (TM) oxides. Various TM combinations, predicted to form either ordered or disordered phases are visualized as small and large circles, respectively. LITHIUM BATTERIES

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