Variation in structure and Li+-ion migration in argyrodite-type Li6PS5X (X = Cl, Br, I) solid electrolytes

• DOI: 10.1007/s10008-011-1572-8
• Publication Date: 2011-10-27T07:15:07Z
• Authors: Prasada Rao Rayav...; Neeraj Sharma; Vanessa K. Peterson; Stefan Adams
• Keywords: IONS; Valence; Chemical bonds; 02 engineering and technology; Lithium; 540; 0210 nano-technology; 01 natural sciences; 7. Clean energy; Lithium ions; Neutron diffraction; 0104 chemical sciences; 3. Good health

All-solid-state rechargeable lithium-ion batteries (AS-LIBs) are attractive power sources for electrochemical applications due to their potentiality in improving safety and stability over conventional batteries with liquid electrolytes. Finding a solid electrolyte with high ionic conductivity and compatibility with other battery components is a key factor in raising the performance of AS-LIBs. In this work, we prepare argyrodite-type Li6PS5X (X = Cl, Br, I) using mechanical milling followed by annealing. X-ray diffraction characterization reveals the formation and growth of crystalline Li6PS5X in all cases. Ionic conductivity of the order of 7 × 10−4 S cm−1 in Li6PS5Cl and Li6PS5Br renders these phases suitable for AS-LIBs. Joint structure refinements using high-resolution neutron and laboratory X-ray diffraction provide insight into the influence of disorder on the fast ionic conductivity. Besides the disorder in the lithium distribution, it is the disorder in the S2−/Cl− or S2−/Br− distribution that we find to promote ion mobility, whereas the large I− cannot be exchanged for S2− and the resulting more ordered Li6PS5I exhibits only a moderate conductivity. Li+ ion migration pathways in the crystalline compounds are modelled using the bond valence approach to interpret the differences between argyrodites containing different halide ions.