A High-Entropy Multicationic Substituted Lithium Argyrodite Superionic Solid Electrolyte

Abstract

Bulk-type solid-state batteries (SSBs) constitute a promising next-generation technology for electrochemical energy storage. However, in order for SSBs to become competitive with mature battery technologies, (electro)chemically stable, superionic solid electrolytes are much needed. Multicomponent or high-entropy lithium argyrodites have recently attracted attention for their favorable material characteristics. In the present work, we report on increasing the configurational entropy of the Li 6+a P 1−x M x S 5 I solid electrolyte system and examine how this affects the structureconductivity/stability relationships. Using electrochemical impedance spectroscopy and 7 Li pulsed field gradient nuclear magnetic resonance (NMR) spectroscopy, multicationic substitution is demonstrated to result in a very low activation energy for Li diffusion of ∼0.2 eV and a high room-temperature ionic conductivity of ∼13 mS cm −1 (for Li 6.5 [P 0.25 Si 0.25 Ge 0.25 Sb 0.25 ]S 5 I). The transport properties are rationalized from a structural perspective by means of complementary neutron powder diffraction and magic-angle spinning NMR spectroscopy measurements. The Li 6.5 [P 0.25 Si 0.25 Ge 0.25 Sb 0.25 ]S 5 I solid electrolyte was also tested in high-loading SSB cells with a Ni-rich layered oxide cathode and found by X-ray photoelectron spectroscopy to suffer from interfacial side reactions during cycling. Overall, the results of this study indicate that optimization of conductivity is equally important to optimization of stability, and compositionally complex lithium argyrodites represent a new playground for a rational design of (potentially advanced) superionic solid electrolytes.

Understanding the limits to Short-range order Suppression in Many-Component Disordered Rock Salt Lithium-ion Cathode Materials

“…It is worth noting that there may be beneficial effects in high-entropy disordered rock salt cathode materials with respect to lithium mobility. A "more disordered" system will likely see a wider range of site energies within the lithium transport network improving the conductivity as has been observed in as range of solid electrolyte materials [64][65][66]. However, we postulate that any increase in mobility will also be minimal at high fluorine and lithium contents as the formation of Li-F rich regions will minimise the impact of any local distortions that influence the site energies in the lithium diffusion pathway from introducing more transition metals.…”

Understanding the limits to short-range order suppression in many-component disordered rock salt lithium-ion cathode materials

“…It is worth noting that there may be beneficial effects in high-entropy disordered rock salt cathode materials with respect to lithium mobility. A “more disordered” system will likely see a wider range of site energies within the lithium transport network improving the conductivity as has been observed in a range of solid electrolyte materials; 65–68 these concepts are clearly extensible to intercalation cathodes. 69,70 However, we postulate that any increase in mobility will also be minimal at high fluorine and lithium contents as the formation of Li–F rich regions will minimise the impact of any local distortions that influence the site energies in the lithium diffusion pathway from introducing more transition metals.…”

Configurational and Dynamical Heterogeneity in Superionic Li5.3PS4.3Cl1.7−xBrx

“…[7,20] To understand the origin of Li redistribution in Li 5.3 PS 4.3 Cl 1.7−x Br x and fast Li + conduction, interrogation of its anion sublattice is carried out with multinuclear 31 P, 35 Cl, and 79 Br NMR. 31 P NMR is a sensitive probe to uncover the local disorder within the anion sublattice induced by other anion species. [7,8] As shown in Figure 4a, the complexity of the 31 31 P resonances, attributed to different nS(4−n)X combinations occupying 4d sites of the argyrodite structure.…”