High-throughput ab initio screening of binary solid solutions in olivine phosphates for Li-ion battery cathodes

Abstract

A promising approach to improving the performance of iron-phosphate FePO4 cathode materials for Li-ion batteries is to partly or fully substitute Fe with other metals. Here, we use high-throughput density-functional theory (DFT) calculations to investigate binary mixtures of metal atoms M and M′ in (Li)MyM′1−yPO4 olivine phosphates. We determine the formation energy for various stoichiometries of different binary combinations of metals for the cases of full lithiation and delithiation. Systematic screening of all combinations of Fe and Mn with elements of the 3d transition-metal (TM) series allows us to identify trends with average band filling and atomic size. We also included compounds that verify the observed relations or that were discussed as cathode materials, particularly Ni–Co, V–Cu and V–Ni, as well as combinations with 4d TMs (Fe–Zr, Fe–Mo, Fe–Ag) and with Mg (Fe–Mg and Ni–Mg). Based on our DFT calculations for each compound, we estimate the volume change during intercalation, the intercalation voltage, the energy density and the thermal stability with respect to reaction with oxygen. Our calculations indicate that the energy density of the binary TM phosphates increases with average band filling while the thermal stability of the compounds decreases.

Topologically close-packed phases in binary transition-metal compounds: matching high-throughputab initiocalculations to an empirical structure map

“…Intermediate and final results are stored in a database to facilitate postprocessing and restarts of interrupted calculations. Our HTE has proven to be stable in earlier work on intermetallics [22,39], elemental transition metals [61], steels [62][63][64] and battery materials [65].…”

Relating voltage and thermal safety in Li-ion battery cathodes: a high-throughput computational study

“…54 Our results pertain to mixed metal systems insofar as each metal acts independently of the other. 69 Finally, we are only evaluating the conditions at which onset of O 2 evolution from the bulk is expected to occur. 68 In addition, recent computational work by Hajiyani et al for the olivine system indicates that the critical oxidation potential for mixed metal compounds may lie in between the oxidation potentials of their single metal end members.…”

“…68 In addition, recent computational work by Hajiyani et al for the olivine system indicates that the critical oxidation potential for mixed metal compounds may lie in between the oxidation potentials of their single metal end members. 69 Finally, we are only evaluating the conditions at which onset of O 2 evolution from the bulk is expected to occur. We do not model the actual heating rate of the cell due to reaction with the electrolyte, nor do we consider the amount of O 2 evolved.…”

The Unified Electrochemical Band Diagram Framework: Understanding the Driving Forces of Materials Electrochemistry

“…Here, the theoretical average discharge voltage () is calculated using the Gibb's free energy (Δ G ) of reaction, for example, the process of lithium intercalation into a host material according to Li x Host + Li δ ⇌ Li x +δ Host. Here, , where z is the unit charge, F is Faraday's constant, and . A key advantage of this technique is that it enables the high‐throughput screening of lithium insertion electrode materials because it only requires total energy calculations of the lithiated and delithiated host materials.…”

“…A key advantage of this technique is that it enables the high‐throughput screening of lithium insertion electrode materials because it only requires total energy calculations of the lithiated and delithiated host materials. These total energy calculations can be performed rapidly at a relatively low level of theory with a good degree of accuracy . However, this approach to derive redox potentials is limited to materials changes which can be coupled with a convenient electrochemical reference reaction at a known potential (here Li + + e − ⇌ Li).…”