SMaRT research reveals new role for carbon storage for lithium-ion batteries

UNSW SMaRT Centre researchers' have demonstrated a new role for waste carbon as a key storage factor for lithium-ion (Li-ion) batteries, not just using carbon for existing sodium-ion (Na-ion) batteries.

Traditionally used for Na-ion systems, carbon electrodes when sythesised across a broad range of temperatures reveal a clear, superior performance in Li-ion batteries.

The novel findings, in the new study published by Advanced Science Journal, show that carbon derived from waste compact disks (CDs) has promising potential to be used in the much more common and versatile Li-ion packs.

These dual findings - using waste for energy storage and for Li-ion batteries - builds on a strong line of research by the SMaRT centre on repurposing waste materials as feedstock for remanufacturing and new products as part of genuinely creating a more sustainable energy system transition.

Summary

The dumping of e-waste has become an increasingly serious global issue, largely due to the short service life of modern electronic devices. To achieve sustainable development, responsible consumption and production must address the growing challenges associated with e-waste by adopting sustainable strategies for its management. Efficient recycling and proper handling of e-waste are crucial, as improper disposal continues to contribute significantly to landfill growth. Currently, only about 20% of e-waste is recycled, while approximately 80% remains uncollected due to high processing costs and a lack of adequate infrastructure. Among various forms of e-waste, compact discs (CDs) present a notable concern. 

The end-of-life scenario for CD waste remains ambiguous. As society increasingly transitions to digital platforms and embraces circular economy principles, questions arise about the ultimate fate of these CDs. Improper disposal of CDs is particularly problematic, as the polycarbonate used in their production can depolymerize into bisphenol A, a compound associated with environmental and health risks. Therefore, exploring efficient recycling strategies for CD waste is essential. Continued research into the recovery and transformation of such materials can play a critical role in promoting sustainable waste management practices and advancing the circular economy.

Graphite has been the dominant anode material since the commercialization of lithium-ion batteries (LIBs). For sustainable post-lithium technologies, sodium-ion batteries (NIBs) have emerged as a promising alternative. In the search for suitable anode materials for NIBs, carbon has been considered one of the most viable candidates. However, the commonly used graphite cannot be directly applied in NIBs. Although graphite performs satisfactorily as an anode in LIBs, it fails to deliver acceptable electrochemical performance in NIBs—primarily due to its microstructural morphology. 

As a result, other forms of carbon, particularly hard carbon (e.g., biochar), have been extensively investigated for use in sodium-ion batteries. For NIBs, the anodic behavior of a material must exhibit a lower sodium-ion insertion and extraction potential than that of metallic sodium. While highly ordered graphitic carbon meets this criterion effectively for LIBs, they fall short in delivering comparable performance for sodium-ion systems. In contrast, disordered carbonaceous materials present a promising alternative for NIB anodes. These materials are characterized by a highly disordered structure with nanoscale porosity, formed by stacked and twisted graphene sheets. This unique architecture facilitates efficient sodium-ion storage during electrochemical cycling, making them well-suited for use as anode materials in sodium-ion batteries.

In this study, we aimed to elucidate how the hybrid microstructure of carbon electrodes influences their capacitive energy storage performance in lithium-ion (Li-ion) and sodium-ion (Na-ion) systems. Electrochemical measurements conducted on carbon materials synthesized across a broad temperature range (1200°C–1600°C) revealed a clear correlation between storage capacity and the physicochemical properties of the carbon. Our findings indicate that micro-regional structural features—previously considered advantageous primarily for Na-ion storage—exhibit superior performance in Li-ion systems. 

This enhanced performance is likely attributed to a combination of factors, including the formation of larger hexagonally bonded carbon domains via phase clustering, the annealing of structural defects, and the elimination of surface functional groups during high-temperature annealing. Notably, carbons with progressively ordered domains demonstrated improved long-term storage capacity in Li-ion batteries compared to Na-ion batteries. We attribute this to the more efficient ion accommodation within the hybrid carbon matrix, which is better suited to the smaller ionic radius and higher mobility of lithium ions. Overall, this work highlights a previously underappreciated microstructural parameter—namely, the hybrid configuration of carbon—as a key determinant of superior electrochemical performance in Li-ion systems.

 These insights offer valuable guidance for the rational design and synthesis of high-performance, sustainable electrode materials tailored for rechargeable Li-ion and Na-ion batteries.

The research was undertaken under SMaRT’s Australian Research Council Industrial Transformation Research Hub into Microrecycling of Batteries and Other Consumer Wastes.