Synthesis, Crystal Structure and Performance of Solid Electrolytes for Lithium and Sodium Solid-State Batteries

Abstract

The world is realizing the significance of clean energy technologies for green house gas emission reduction. To pave the path to electrification across multiple sectors including transportation, quality energy storage materials must be developed for supplying global market clean energy demands. All-solid-state batteries (ASSBs) have garnered immense attention as a potential avenue for improving the safety and energy density of battery platforms. Large-scale application of ASSBs in electric and hybrid vehicle technologies requires new electrode materials especially solid electrolytes with excellent Li-ion transport properties. This thesis presents an in-depth study of novel solid electrolytes for lithium and sodium solid-state batteries, their crystal structure, and methods to modify their composition and enhance their electrochemical performance. In chapter 1, a brief introduction of batteries and different kinds of solid electrolytes are described in detail. In chapter 2, the various characterization techniques that were applied throughout this thesis are described. In chapter 3, the synthesis, structure, and electrochemical performance of new halide-rich solid solution phases in the argyrodite Li6PS5Cl family, Li6-xPS5-xCl1+x, are reported. The limit of the solid solution range, Li5.5PS4.5Cl1.5, exhibits quadrupled ionic conductivity (compared to Li6PS5Cl) of 9.4 ± 0.1 mS.cm-1 at room temperature. The ionic conductivity goes up to 12 mS.cm-1 for sintered materials, approaching the best benchmarks in the field. The structure of single-phase Li5.5PS4.5Cl1.5 argyrodite was elucidated by neutron diffraction and refinement results suggest that only one Li (48h) site is present, with no Li present on the 24g site. In chapter 4, synthesis, and characterization of solid solution series Li6PS5-xSexCl electrolytes are discussed. Single crystals of chalcogenohalides were grown and systematically studied via single-crystal X-ray diffraction to understand the effect of Se substitution. Material transport properties were studied via electrochemical impedance spectroscopy and correlated to the underlying structure. In chapter 5, the synthesis procedure for argyrodites were optimized and novel series of highly conductive sulfide-based compounds, Li6+2*n-x-m*yMyPS5+n-xX1+x (m = 1,2; M= Ca, Ga, Al) which were prepared by a rapid method are presented. The “super Cl-rich” composition Li5.35Ca0.1PS4.5Cl1.55 was reported for the first time. This material possesses a high room temperature ionic conductivity of 10.2 mS cm-1 in the cold-pressed state. Rietveld refinement of the “super Cl-rich” phase was performed against neutron diffraction data and the results show a refined composition of Li5.36Ca0.08PS4.47Cl1.54 that is almost identical to targeted Li5.35Ca0.1PS4.5Cl1.55. Furthermore, an adaptable approach for designing future solid electrolytes is provided. Finally, in chapter 6, novel glassy materials including LiAl0.33S (σ = 0.08 mS.cm-1) are presented.