Structural Evidence for High Ionic Conductivity of Li₇P₃S₁₁ Metastable Crystal

Electrical conductivity, time-of-flight neutron diffraction (TOF-ND), and synchrotron X-ray diffraction (SXRD) measurements were carried out for 7 Li 7 P 3 S 11 metastable crystal and ( 7 Li 2 S) 70 (P 2 S 5 ) 30 glass. Reverse Monte Carlo modeling based on the TOF-ND and SXRD data showed three-dimensional structures of 7 Li 7 P 3 S 11 metastable crystal and ( 7 Li 2 S) 70 (P 2 S 5 ) 30 glass. A detailed polyhedral analysis of the three-dimensional atomic configuration yielded the spatial distribution of [LiS 4 ] tetrahedra ([LiS 4 ] units) and S 4 tetrahedra (without Li + ion; [S 4 ] units) in 7 Li 7 P 3 S 11 metastable crystal and ( 7 Li 2 S) 70 (P 2 S 5 ) 30 glass. When an a c -[S 4 ] unit is recognized as a fully acceptable unit of the Li + ion, the coordination number of a c -[S 4 ] units around a [LiS 4 ] unit for 7 Li 7 P 3 S 11 metastable crystal was estimated to be 3.9 on average, whereas it was 1.9 for ( 7 Li 2 S) 70 (P 2 S 5 ) 30 glass. Such structural characteristics in 7 Li 7 P 3 S 11 metastable crystal and ( 7 Li 2 S) 70 (P 2 S 5 ) 30 glass are deeply associated with electrochemical properties.