DOI:
Authors:
Madison Olson
Abstract:
Developing an alternative to traditional lithium-ion batteries has been heavily researched to enable safe, cost-effective, and more energy dense technology. Sodium solid-state electrolytes (SSEs) are of particular interest due to their potential to lower the cost and environmental risks of lithium systems. While there are many classes of sodium SSEs, glassy solid electrolytes (GSEs) have been heavily researched due to their beneficial properties. GSEs can be studied over a wide compositional space, where small changes can be made in the structure to achieve the desired changes in properties. GSEs can also be processed in unique ways compared to other classes of material systems due to their ability to exhibit viscous flow past their glass transition temperature (Tg). This thesis explores two series of GSEs, one a single glass former system mixed oxy-sulfide-nitride (MOSN) series, and one a mixed glass former (MGF) mixed oxy-sulfide (MOS) series. The first series, Na4P2S7-6xO4.62xN0.92x, 0 ≤ x ≤ 0.5 (NaPSON), was studied for its short range order (SRO) structures and properties. The nitrogen incorporated into the NaPSON series showed a positive effect on the ionic conductivity and thermal properties compared to glasses without nitrogen. Further, the x = 0.2 glass in the NaPSON series, Na4P2S5.8O0.92N0.18 (NaPSON-2), was found to be uncrystallizable allowing it to be processed into thin film. The electrochemical properties of NaPSON-2 thin film were determined and showed the glass could cycle at 5 A/cm2 at room temperature. However, NaPSON-2 exhibited an increase in resistance over 200 cycles due to a decomposition reaction of the main phosphate network, where the P2S74- and PS43- SRO units were found to decompose to P2S64- and Na3P. With this limitation in pure phosphate glasses determined, a second series of GSEs was developed to combat this (0.6-0.08y)Na2S+(0.4-0.08y)[(1- y)[(1-x)SiS2+xPS5/2]+yNaPO3], 0 ≤ x ≤ 0.35 and 0.15 ≤ y ≤ 0.35 (NaPSiSO). This second series was also studied for its SRO structures and properties to determine a composition for high performance all solid-state sodium batteries (ASSSBs). These complex GSEs were found to be highly processable, and an ideal composition was determined, x = 0.15 and y = 0.15 (NaPSiSO-15), to be stable under an applied voltage and sustained current vs. Na-metal. The electrochemical behavior of NaPSiSO-15 was studied and found to show stability up to 4 V and stable cycling at 0.1 mA cm-2 for > 500 h.