Origin of Fast Ion Conduction in Li₁₀GeP₂S₁₂, a Superionic Conductor

Abstract

The discovery of additional sites has revealed important insights into the possibility of cross-channel ionic diffusion in Li10GeP2S12 (LGPS). Here, we present an ab initio study of a Li diffusion mechanism in LGPS. The presence of fractional occupancy for Li sites leads to different c channel population of Li and different local environment for Li hop both along the c-directional channels and in the ab plane. We perform a rigorous computation of the energy barriers with different population of Li and different environment of Li surrounding the c channels. It is found that the diffusion energy barrier in LGPS depends significantly on channel population, local environment, and the type of hop which leads to a range of relative diffusivity along different directions. A novel mechanism of correlated diffusion between the c channel and the ab plane is found with significantly low energy barrier. The relative frequency of occurrence of the novel hop mechanism critically controls the degree of anisotropy in LGPS. Moreover, low activation barrier associated with this hop leads to high diffusivity which is sustained even after repeated cycling due to the presence of cross-channel pathways.

Li10GeP2S12‐Type Superionic Conductors: Synthesis, Structure, and Ionic Transportation

“…In addition, the possibility of cooperative motion of the [001] and [110] jumps was reported by Bhandari et al. [ 120 ] Using the nudged elastic band (NEB) method, different energy barriers were observed depending on the neighboring situation. When a lithium at 4 c attempts to jump to the neighboring site (16 h ) that is occupied, then a 4 c →16 h and 16 h →4 c cooperative jump occurs with the barrier of 0.3 eV.…”

Crystal and Electronic Structure and Optical Properties of AE2SiP4 (AE = Sr, Eu, Ba) and Ba4Si3P8

“…With the discovery of Li 10 GeP 2 S 12 , a remarkable solid Li‐ion conductor, there have been numerous studies to understand and improve various aspects of the solid ionic conductors based on tetrel‐pnictide‐chalcogenides . The crystal structure of Li 10 GeP 2 S 12 is formed by [PS 4 ] 3– and [GeS 4 ] 4– clusters surrounded by mobile Li + counterions .…”

LiSi3As6and Li2SiAs2with flexible SiAs2polyanions: synthesis, structure, bonding, and ionic conductivity

“…Both As-As distances are within reported lengths observed for As-As bonds. 41,42,[48][49][50][51] The plane of Si 2 As 6 antiprisms is formed through isolated Si 2 As 6 units, which are surrounded by 6 Li atoms in the abplane, shown in Fig. 3C.…”

“…[1][2][3][4][5] Recent discovery of the novel crystalline phase Li 10 GeP 2 S 12 with extraordinary ionic conductivity pointed out the potential of non-oxide systems. [6][7][8][9][10][11][12][13] Indeed, a reduction of the ionicity of the Li-X bonds (where Li is surrounded by X atoms) should result in easier Li transport, as shown through comparing oxides vs. phosphides. 14 This pointed to the necessity to study complex Li…”