Abstract:

All-solid-state thin film lithium batteries (TFBs) are regarded as the ideal power source for microelectronics in the upcoming era of the Internet of Things, owing to their solid-state architecture, flexible size and shape, long cycle life, low self-discharge rate, and facile miniaturization. Even though tremendous improvements have been made in TFBs in the last decades, recycling of TFBs, which is supposed to be a serious issue in the future, is rarely studied. With continuous TFB market expansion, the sustainable development of TFBs is becoming an increasingly important research topic. To date, Li anode failure has been regarded as the most common reason for the failure of TFBs due to the following aspects of Li metal anode: strong reactivity with moisture, large volume change during cycling, and inevitable dendrite growth during Li plating. In this work, a facile recycling strategy is developed based on the most commonly used TFBs of LiCoO₂ (LCO)/lithium phosphorus oxynitride (LiPON)/Li (F-TFB). Our findings indicate that the Li anode in F-TFB is partially oxidized during cycling with noticeable surface morphology change, which leads to an obvious increase in Li/LiPON interfacial resistance associated with rapid capacity loss. To directly recycle the F-TFB, we developed a simple method to remove the spent Li anode by dissolving the metallic Li metal of the F-TFB in an ethanol solution. The efficient dissolution of metallic Li allows the oxidized Li residues to be easily wiped away from the surface of the LiPON electrolyte film with the assistance of a dust-free cloth, resulting in the rapid recycling of the underlying LCO/LiPON film. Structural and surface characterization results indicate that the obtained LCO/LiPON which was part of the failed F-TFB remains in a good condition without structural degradation, which enables its direct reuse in fabricating new TFBs. Consequently, a recycled LCO/LiPON/Li TFB (R-TFB) is constructed by sequentially depositing new LiPON and Li films on the used LCO/LiPON film, exhibiting a small interfacial resistance, recovered Li anode morphology and surface, and restorative electrochemical performance. Specifically, the R-TFB delivers a specific capacity of 0.223 mAh·cm⁻² at 0.1 mA·cm⁻², acceptable rate performance (0.120 mAh·cm⁻² at 0.8 mA·cm⁻²), and good cycle performance (77.3% capacity retention after 500 cycles), which are very close to those of a newly fabricated TFB, demonstrating the feasibility of this direct recycling approach. Such a simple yet efficient recycling approach may effectively extend the lifespan of solid-state batteries and provide important insights to develop sustainable TFBs for microelectronic devices.

Key words: Solid-state lithium battery, Thin film battery, Lithium anode failure, Recycling, Sustainability