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Lithium-rich antiperovskites (APs) have attracted significant research attention due to their ionic conductivity above 1 mS cm −1 at room temperature. However, recent experimental reports suggest that proton-free lithium-rich APs, such as Li 3 OCl, may not be synthesized using conventional methods. While Li 2 OHCl has a lower conductivity of about 0.1 mS cm −1 at 100 °C, its partially fluorinated counterpart, Li 2 (OH) 0.9 F 0.1 Cl, is a significantly better ionic conductor. In this article, using density functional theory simulations, we show that it is easier to synthesize Li 2 OHCl and two of its fluorinated variants, i.e., Li 2 (OH) 0.9 F 0.1 Cl and Li 2 OHF 0.1 Cl 0.9 , than Li 3 OCl. The transport properties and electrochemical windows of Li 2 OHCl and the fluorinated variants are also studied. The ab initio molecular dynamics simulations suggest that the greater conductivity of Li 2 (OH) 0.9 F 0.1 Cl is due to structural distortion of the lattice and correspondingly faster OH reorientation dynamics. Partially fluorinating the Cl site to obtain Li 2 OHF 0.1 Cl 0.9 leads to an even greater ionic conductivity without impacting the electrochemical window and synthesizability of the materials. This study motivates further research on the correlation between local structure distortion, OH dynamics, and increased Li mobility. Furthermore, it introduces Li 2 OHF 0.1 Cl 0.9 as a novel Li conductor.

The oxygen evolution reaction (OER) is the bottleneck of many sustainable energy conversion systems, including water splitting technologies. The kinetics of the OER is generally sluggish unless precious metal‐based catalysts are used. Perovskite oxides have shown promise as alternatives to these expensive materials. However, for several perovskites, including SrCoO3−δ, the rate‐limiting step is proton‐transfer. In this study, it is shown that such a kinetic limitation can be overcome by coupling those perovskites with MoS2 mechanochemically. By studying composites of SrMO3−δ (M = Co, Fe, Ti) and MoS2, the role that the formed heterointerfaces play in enhancing the activity is investigated. Mechanochemically mating SrCoO3−δ and MoS2 increases the mass activity toward OER by a factor of ten and led to a Tafel slope of only 37 mV dec−1. In contrast, combining MoS2 with SrFeO3−δ or SrTiO3−δ, two materials whose OER is not limited by proton‐transfer, does not result in an improvement of the performance. The experimental measurements and first‐principle calculations reveal that the MoS2 at the MoS2@SrCoO3−δ heterointerfaces is both an electron and a proton acceptor, thereby facilitating deprotonation of the perovskite and resulting in faster OER kinetics.