Stress-Engineered SS/LiCoO₂ Thin-Film Electrodes With Enhanced Structural Integrity and Electrochemical Performance

Area of Science:

• Materials Science
• Electrochemistry
• Thin Film Technology

Background:

• Delamination of lithium cobalt oxide (LCO) films on stainless steel (SS) substrates is a major obstacle for all-solid-state thin-film lithium batteries (TFLBs).
• Existing TFLBs face challenges with mechanical integrity and long-term stability due to film delamination.
• Understanding and controlling film stress is crucial for developing durable TFLB devices.

Purpose of the Study:

• To introduce and validate a stress-engineering strategy for mitigating LCO film delamination on SS substrates.
• To elucidate the mechanisms behind residual stress development in LCO thin films during deposition.
• To develop a scalable fabrication process for mechanically robust and high-performance TFLBs.

Main Methods:

• In situ stress measurements during LCO film deposition.
• Systematic variation of deposition parameters, particularly working pressure.
• Substrate pre-annealing and LCO film post-annealing treatments.
• Fabrication and testing of large-area all-solid-state TFLB cells.

Main Results:

• Identified a universal tensile-to-compressive stress transition in LCO films, with amorphous films exhibiting compressive stress due to atomic pinning.
• Working pressure was found to be the dominant parameter for controlling film stress evolution.
• Optimized annealing strategies (substrate pre-annealing and film post-annealing) effectively suppressed delamination and cracking.
• Successfully fabricated meter-scale TFLB cells with robust SS/LCO/LiPON multilayers, achieving high areal capacity and excellent cycle stability (97.1% retention after 1000 cycles).

Conclusions:

• The developed stress-engineering approach effectively resolves the delamination issue in LCO thin films for TFLBs.
• Precise control over film stress through deposition parameters and annealing is key to achieving mechanically resilient thin-film electrodes.
• This work provides a scalable and promising pathway for the commercialization of high-performance all-solid-state TFLBs.