Studies of Li2Fe0.9M0.1SO Antiperovskite Materials for Lithium–Ion Batteries: The Role of Partial Fe2+ to M2+ Substitution

Abstract

Cubic Li2Fe0.9M0.1SO antiperovskites with M–Co2+, or Mn2+ were successfully synthesized by a solid-state technique, and studied as cathode materials in Li-batteries. The influence of the Co, and Mn cation substitution of Fe in Li2FeSO on the resulting electrochemical performance was evaluated by galvanostatic cycling, while the reaction mechanism was explored by applying operando X-ray absorption and X-ray diffraction techniques using synchrotron radiation facilities. Even 10% Fe-substitution by these metals completely changes the structural behavior of the material upon Li-removal and insertion, in comparison to Li2FeSO. The Co-substitution significantly improves cyclability of the material at high current densities in comparison to the non-substituted material, reaching a specific capacity of 250 mAh/g at 1C current density. In contrast, the Mn-substitution leads to deterioration of the electrochemical performance because of the impeded kinetics, which may be caused by the appearance of a second isostructural phase due to formation of Jahn-Teller Mn3+ cations upon delithiation.

Anti-perovskites for solid-state batteries: recent developments, current challenges and future prospects

“…Beyond the preliminary studies of Li 2 FeSO, anti-perovskite cathodes would be expected to benefit from the chemical flexibility of the structure to tune their properties via substitutions. 119,[169][170][171] Any transition metal with an accessible M 2+ -M 3+ redox pair is in principle usable, with Li 2 MnOS and Li 2 CoOS having already been synthesised 119 and the properties of the Cr, Cu, Mo, Ni and V analogues having been probed through DFT calculations. 169 Careful optimisation of the composition is expected to allow for the tailoring of properties, including the average operating voltage, electronic conductivity and phase stability, 169 in close analogy with commercial NMC electrodes.…”

“…For example, small amounts of Co incorporation were shown to dramatically increase the accessible capacity to >250 mAh/g. 171 No reports of sodium equivalent versions (e.g., Na 2 FeOS) currently exist yet, with the exception of the recently discovered anti-Ruddlesden-Popper phase Na 2 Fe 2 OS 2 . 172 Moreover, anti-perovskite cathode materials possess certain intrinsic advantages with respect to their application in solid-state batteries.…”

“…Furthermore, anti-perovskite cathodes have shown minimal and isotropic electrochemical expansion upon cycling; as lithium is reversibly (de)inserted, the cubic lattice parameter varies by less than 1%. 100,166,171 This is especially relevant for solid-state batteries where mechanical degradation mechanisms (e.g., interface delamination, loss of contact and cracking) are exacerbated and directly linked to localised stresses generated by the large electrochemical expansion of the layered cathode materials typically used. Finally, although the utilisation of M 2+ -M 3+ redox pairs and the inclusion of sulphur tend to limit the operating voltage to ~2.5 V vs. Li + /Li 0 , this can enable the use of solid electrolytes with limited electrochemical stability in oxidation.…”

Tuning the electrochemical properties by anionic substitution of Li-rich antiperovskite (Li2Fe)S1−xSexO cathodes for Li-ion batteries

“…6 Recently, a novel class of Li-rich antiperovskite cathodes with a general formula (Li 2 TM)ChO (TM ¼ Fe, Mn, Co; Ch ¼ S, Se) was discovered and its electrochemical performance was evaluated. [7][8][9][10] These antiperovskite cathodes display a multielectron storage merit with a reversible transfer of 1.2 Li + per formula unit, resulting in an outstanding specic capacity. Besides, they offer other advantages such as reasonable working voltage ($1.2-3 V) and 3-dimensional (3D) Li + diffusion with a low diffusion barrier ($0.32 eV).…”

Antiperovskite Superionic Conductors: A Critical Review

“…The Co substitution improves the cyclability, whereas Mn substitution deteriorates the cycling performance. 70,71 Theoretical study shows the Li-ion diffusion barrier in (Li 2 Fe)SO is only 0.32 eV, which may explain its good rate capacity. 72 73 For the Na-ion, although Na-containing analogues (Li 2−n Na n Fe)SO cannot be synthesized through solid-state reaction, Na 2 Fe 2 OS 2 with anti-RP structure can be synthesized through solid-state or mechanochemical synthesis.…”