Effect of Densification Conditions on the Chemical, Electrochemical, and Mechanical Stability of 75Li2s - 25P2S5 (mol %) As a Potential Solid Electrolyte for Use in Electric Vehicles

Abstract

Solid-state electrolytes have garnered significant attention for their potential to enable solid-state batteries for electric vehicles with metallic Li as an anode. However, the stability between solid-state electrolytes and metallic Li is not well understood. Lithium phosphorous sulfides are a promising class of solid-electrolytes owing to their high ionic conductivity (10-4 – 10-3 S cm-1 at 25 °C), low interface resistance against metallic lithium, and can be consolidated to > 90 % relative density at room temperature1 . In this work, the chemical, electrochemical, and mechanical stability of hot-pressed 75Li2S- 25P2S5 (mol %), or LPS, between 200 and 550 °C was investigated. Hot pressing produced high relative density and crystalline LPS pellets that were characterized using multiple electrochemical techniques. AC impedance measurements were used to characterize the stability of the Li-LPS interface. The electrochemical performance of LPS was analyzed as a function of current density between 0.01 and 1.0 mA cm-2 followed by cross-sectional microstructural analysis. It will be shown that: i) below or equal to 0.05mA cm- 2 ohmic behavior is observed, ii) at 0.1mA cm- 2 a transition behavior occurs identified by an instability in polarization, and iii) above or equal to 0.5mA cm-2 , the potential decreases and is believed to be related to the formation of an electronically conducting phase. Acoustic impulse excitation measurements were used to determine changes in the elastic constants after DC cycling of Li-LPS. Additionally, materials characterization such as Raman, XRD, and SEM will be presented to correlate the densification conditions with DC cycling stability. We believe this is one of the first studies to characterize the chemical, electrochemical, and mechanical stability of a Li-LPS interface. The methodology established in this work could be applied to other solid-state electrolytes as well. Reference Sakuda, Atsushi, Akitoshi Hayashi, and Masahiro Tatsumisago. "Sulfide solid electrolyte with favorable mechanical property for all-solid-state lithium battery."Scientific reports 3 (2013)