Interfacial Behavior of a Thio-LISICON Solid-State Electrolyte under External Pressure

Abstract

External pressure can greatly affect the cycling performance of solid-state batteries, although pressure-driven changes in electrochemical processes are still not fully understood. For instance, Li 10 GeP 2 S 12 (LGPS) is known to strongly react with lithium metal. However, under external pressure, with the use of additional Li 6 PS 5 Cl (LPSCl) outer layers forming a sandwich structure, stable cycling over 1800 cycles can be achieved (Ye and Li. Nature, 2021, 593, 218−222). This finding motivated us to investigate the interfacial behavior of Li/LGPS under external pressure (i.e., 7.5 MPa) to shed light on the improved electrochemical performance. Our results indicate that the growth rate of the interfacial resistance is substantially decreased while the cycle life before open-circuit failure is substantially extended under the MPa-scale external pressure. The reactivity between lithium metal and LGPS is extremely severe, forming island features upon cycling. Using selected area Raman spectroscopy, these "islands" were confirmed to be interfacial decomposition products, in line with the expected volume expansion of LGPS when reacting with lithium metal. Under 7.5 MPa external pressure, the interface products were formed in a densely packed and homogeneously distributed manner after 10 cycles. While the application of external pressure did not alter the types of interface components, the MPa-level pressure functioned in improving physical contact of the interface and homogenizing the interface reactions. In addition, a lithium depletion layer was formed in the interface region, which can contribute to extra interfacial resistance. Our work marks an important step to understanding the interfacial electrochemical behavior of the Li/LGPS interface under an MPa-scale external pressure.

Pressure Effects and Countermeasures in Solid‐State Batteries: A Comprehensive Review

“…For example, Wu et al investigated the morphology and constituents on the LGPS-Li surface at a moderate stack pressure of 7.5 MPa. [55] While this pressure could not hinder the decomposition process of LGPS, it was found to incubate densely packed "islands" region. The chemical composition of island-featured regions is different from the flat regions, which is believed to suppress the interfacial side reactions by forming an insulating layer.…”

External Pressure in Polymer-Based Lithium Metal Batteries: An Often-Neglected Criterion When Evaluating Cycling Performance?

“…Insufficient contacts within the solid–solid interphases between the ceramic electrolyte and electrode materials may result in larger interfacial resistances coupled with inhomogeneous Li deposition. While there have been efforts to reduce interface resistances by addition of small amounts of liquid electrolytes, , the most effective and common method to improve the interfacial contacts represents the application of a reasonably large external pressure (up to 50 MPa). , The benefits of external pressure could be demonstrated for ceramic electrolytes, including lower interfacial resistances, − reduced overpotentials, , and enhanced limiting current densities, thus enabling prolonged cycle life of the cells. In academia, a press is utilized to apply external pressures to the cells (e.g., in a range of 1–10 MPa, depending on the ceramic material), but it remains a critical factor for large battery packs necessary for electric vehicle applications, thus constraining design opportunities and the energy density of the considered battery packs.…”

Pressure Dependence of Solid Electrolyte Ionic Conductivity: A Particle Dynamics Study

“…An important factor for the SE global conductivity is the applied pressure between the particles. High pressurization levels during fabrication (fabrication pressure) leads to better densification and packing of the SE and consequently can substantially improve the global conductivity together with extending the cycling performance and the overall electrochemical performance . During battery operation, stack pressure can be applied for better contact between SE and the battery electrodes, and in some cases, it was found to improve utilization .…”