Antiperovskite K₃OI for K-Ion Solid State Electrolyte

Abstract

Discovering new K-ion solid-state electrolytes is crucial for the emerging K-batteries to improve energy density, cycle life, and safety. Here, we present a combined experimental and theoretical study of antiperovskite K 3 OI as a K-ion solid-state electrolyte. A solid−solid phase transition at approximately 240 °C induces an increase in ionic conductivity by 2 orders of magnitude. Anion disorder in the I−O sublattice is found to be a potential mechanism for the observed phase transition. The Ba-doped K 3 OI sample K 2.9 Ba 0.05 OI achieves 3.5 mS cm −1 after the phase transition with a low activation energy of 0.36 eV. Stable cycling of K/ K 2.9 Ba 0.05 OI/K symmetric cells are observed with a low overpotential of 50 mV at 0.5 mA/cm 2 at 270 °C. This study not only reports K 3 OI as a promising K-ion solid-state electrolyte that is compatible with reactive K metal but also improves the understanding of alkali antiperovskite solid-state electrolytes in general.

Li-ion conductivity in Li2OHCl1−xBrx solid electrolytes: grains, grain boundaries and interfaces

“…1d, even a partial replacement of the Cl in Li 2 OHCl with Br, stabilizes the bulk structure of the resulting Li 2 -OHCl 0.9 Br 0.1 because the large Br ion lls the cavity in the framework leading to higher symmetry. 41 The synchrotron XRD patterns conrm this observation, demonstrating the ability of Br to act as an effective structure stabilizer, maintaining a cubic structure at room temperature across all of the tested Br/Cl ratios. Even though each composition contains a small amount of impurities, we preferred to prioritize stoichiometry over purity because of its inuence on vacancy concentrations (Fig.…”

“…The presence of two such peaks can be understood as being from two distinct melting points, one at a lower temperature (T 1 ) and another at a higher temperature (T 2 ) ascribed to local disordering and crystal melting, respectively. 41,51 Therefore, the difference between these two points (DT) indicates the extent of lattice mismatch between the local structure and bulk structure. The peaks for Li 2 OHCl 1Àx Br x antiperovskites with high Br/Cl ratios converged, leading to much smaller values of DT, around 5 to 7 C, which indicates an increase in the structural uniformity between the local structure and the crystal lattice of Br-rich antiperovskites (Fig.…”

Antiperovskite Superionic Conductors: A Critical Review

“…Another important advantage is the intrinsic reduction stability of alkali metal oxyhalide antiperovskite (M 3 OX). For example, K 3 OI has been shown to have intrinsic reduction stability toward K metal . The K/K 2.9 Ba 0.05 OI/K symmetric cell shows a consistent low overpotential of 50 mV at 0.5 mA cm –2 at 270 °C.…”

“…The authors suggest the reorientation of the larger B 12 H 12 2– anion is activated at high temperatures and promotes K-ion mobility, while the disorder of the smaller BH 4 – has no obvious effect. More recently, our group reported K-ion antiperovskite K 3 OI . It has a solid–solid phase transition at approximately 240 °C, which induces an increase in ionic conductivity by 2 orders of magnitude.…”

Cobalt Coordinated Cyano Covalent-Organic Framework for High-Performance Potassium-Organic Batteries

“…Due to the rapid development on the portable electronic devices, the requirements for low-cost and high-power energy storage systems of materials are becoming higher and higher. , The scarcity of lithium resources and the increasing cost has limited the further development of lithium-ion batteries, − and other energy storage systems have emerged to be developed and explored with more efforts to achieve high specific capacity, fast power, and excellent stability. − The potassium ion battery has attracted more and more attention as a promising next-generation energy storage system because of the abundant potassium resources, low cost, and redox potential similar to lithium. ,− However, the large ion radius and low melting point of potassium metal pose a huge challenge to its further exploration, and it is necessary to search for suitable anode materials for potassium ion storage. The carbonaceous materials and transition metals with their derivatives have been proposed as the effective electrodes for PIBs. − Carbon materials, including graphite, − hard carbon, , soft carbon, , and their composites, may have some safety hazards due to their low K + insertion voltage (∼0.3 V). Metal particles, such as Bi and Sb, have aroused great interest due to their appropriate potential and higher theoretical specific capabilities.…”