Mechanical Failure of Solid‐State Electrolyte Rooted in Synergy of Interfacial and Internal Defects

Abstract

The mechanical failure of solid‐state electrolytes induced by the growth of the lithium metal anode hinders the development of solid‐state Li metal batteries with good safety and high energy density, and thus the understanding of the failure mechanism is of high importance for the application of solid‐state lithium‐metal batteries. Herein, a modified electro‐chemo‐mechanical model is built to bridge the dynamic relationship between the mechanical failure of solid‐state electrolytes and the electrodeposition of lithium metal. The results, visualize evolution of local stress fields and the corresponding relative damage, and indicate that the generation of damage inside the solid‐state electrolyte is rooted in a synergy of interfacial and internal defects. Compression by electrodeposited lithium inside interfacial defects and further transmission of stress inward in the electrolyte causes catastrophic damage, which is determined by the geometry of interfacial defects. Moreover, the internal defects of the solid‐state electrolyte from sintering can influence the pathway of damage and work as the inner fountainhead for further damage propagation, and as such, the position and amount of the internal voids exhibit a more competitive role in the mechanical failure of solid‐state electrolyte. Thus, the synergetic failure mechanism of solid‐state electrolytes raised in this work provides a modeling framework to design effective strategies for state‐of‐the‐art solid‐state lithium‐metal batteries.

Electro‐Chemo‐Mechanical Failure Mechanisms of Solid‐State Electrolytes

“…The mechanical failure of SSEs mainly results from crack infiltration, interface delamination, and void/pore formation, which, on one hand, promote Li dendrite propagation eventually causing short circuit, on the other hand, cause contact loss increasing the overpotential and resulting in capacity decay. [52] The process of crack formation and interface delamination occurs as follows. Nonuniform Li deposition leads to severe fluctuation of the Li/SSEs interfaces due to the rigidity of SSEs compared to liquid electrolytes.…”

“…The interfacial and internal defects and voids of SSEs also induces nonuniform electrodeposition of Li and trigger mechanical degradation of SSEs. [52] Liu et al built a modified electro-chemo-mechanical model to describe the interplay of interfacial and internal defects on mechanical failure, which provides the relationship between mechanical failure of SSEs and electrodeposition of Li metal. [23] Stress transmits through the SSE due to Li deposition at the Li/SSE interface, thus generating damage inside the SSE, which is governed by the morphology of interfacial defects.…”

“…The larger number of internal voids lead to the shorter damaging time, and the shorter distance between internal voids also shortens the damage time. [52] The formation of voids/pores is another source of mechanical failure. Voids form in the Li anode at the surface when the stripping current density removes Li from the interface faster than it can be replenished, which leads to contact loss, increased impedance, and locally increased current density, promoting formation of Li dendrites.…”

“…The interfacial and internal defects and voids of SSEs also induces nonuniform electrodeposition of Li and trigger mechanical degradation of SSEs [52] . Liu et al.…”

PEO/PVDF–HFP/LLZTO Composite Solid Polymer Electrolyte for High-Performance All-Solid-State Lithium Metal Batteries

“…Nowadays, all-solid-state lithium metal batteries (ASSLMBs) have become the promising candidates due to the high safety of the solid-state electrolyte (SSE) and high energy density of the lithium metal. − SSEs are an important component in ASSLMBs, which can be categorized into three types: solid inorganic electrolytes (SIEs), solid polymer electrolytes (SPEs), and composite SPEs (CSPEs). − SIEs present high ionic conductivity, a wide electrochemical stability window (ESW), high mechanical strength, incombustibility, and a superior lithium-ion (Li + ) transfer number ( t Li + ). Unfortunately, SIEs are more brittle and exhibit poor interfacial contact with electrodes.…”