Antiperovskite Superionic Conductors: A Critical Review

Abstract

Antiperovskites of composition M 3 AB (M = Li, Na, K; A = O; B = Cl, Br, I, NO 2 , etc.) have recently been investigated as solid-state electrolytes for all-solid-state batteries. Inspired by the impressive ionic conductivities of Li 3 OCl 0.5 Br 0.5 and Na 3 OBH 4 as high as 10 −3 S/cm at room temperature, many variants of antiperovskite-based Li-ion and Na-ion conductors have been reported, and K-ion antiperovskites are emerging. These materials exhibit low melting points and thus have the advantages of easy processing into films and intimate contacts with electrodes. However, there are also issues in interpreting the stellar materials and reproducing their high ionic conductivities. Therefore, we think a critical review can be useful for summarizing the current results, pointing out the potential issues, and discussing best practices for future research. In this critical review, we first overview the reported compositions, structural stabilities, and ionic conductivities of antiperovskites. We then discuss the different conduction mechanisms that have been proposed, including the partial melting of cations and the paddlewheel mechanism for cluster anions. We close by reviewing the use of antiperovskites in batteries and suggest some practices for the community to consider.

All-Solid-State Lithium-Ion Batteries Using the Li3AlF6-Based Composite as the Solid Electrolyte

“…One possible explanation is the increase of the Li + -deficient region due to the introduction of the aliovalent anion, SO 4 2− , which maintains charge neutrality. Although the substitution of AlF 6 3− ions with SO 4 2− ions in the host β-Li 3 AlF 6 crystal lattice was not confirmed by XRD, the STEM-EDS results indicated the coexistence of AlF 6 3− and SO 4 2− ions in the amorphous phase. It can be said that charge neutrality should be maintained locally in the case where aliovalent anions are mixed in the amorphous phase.…”

“…High Li + conductivity has been reported for several Li compounds, such as oxides, sulfides, , oxyhalides, , and chloride materials. , Recently, mixed alkali compounds, such as NaI-NaBH 4 -LiI and KLiTaO 6 , wherein other alkali cations coexist with Li + ions, have been reported to be promising solid electrolytes. , For solid electrolytes, high Li + conductivity, high electrochemical stability, air stability, and superior mechanical properties are required for their practical applications in all-solid-state LIBs. Fluoride compounds are a new class of materials that are expected to meet these requirements. − The wide electrochemical stability window of fluorides ensures the use of high-voltage cathodes together with anode materials with low operating voltages, such as graphite and Li metal .…”

“…High Li + conductivity has been reported for several Li compounds, such as oxides, 1 sulfides, 2,3 oxyhalides, 4,5 and chloride materials. 6,7 Recently, mixed alkali compounds, such as NaI-NaBH 4 -LiI and KLiTaO 6 , wherein other alkali cations coexist with Li + ions, have been reported to be promising solid electrolytes.…”

Accelerated Autonomous Workflow For Antiperovskite-based Solid State Electrolytes

“…Recently a new class of materials, denoted charge inverted crystals, obtained by swapping positive and negative ions in the crystal structure, have shown exceptional properties. [16] This in-cludes superionic- [17] and super-conductivity, [18,19] giant magnetoresistance, [20] negative thermal expansion, [21] luminescence, [22] and electrochemical energy conversion. [23] Perovskites, with general formula ABX 3 , are composed of two cations (A and B) and three anions (X) forming an octahedron, and have the charge inverted version, antiperovskites.…”

Theoretical insights into interfacial stability and ionic transport of Li2OHBr solid electrolyte for all-solid-state batteries

“…One promising class of ISEs is antiperovskites Li 3− n OH n X ( n = 0–1, X = Cl, Br) for ASSLIBs. 7 For example, Zhao et al first experimental reported that Li 3 OCl and Li 3 O(Cl 0.5 Br 0.5 ) showed a high ion-conductivity (>10 −3 S cm −1 at 300 K) with low activation energies (0.18–0.26 eV). 8 Subsequently, a good stability and low Li + vacancy migration barrier of Li 3 OX (X = Cl, Br) was verified by first-principles calculations.…”