Long-Term High-Efficient Cus and Cu2s Cathodes for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) based on intercalation, such as C/LiCoO₂, are dominant in consumer electronics, mainly ascribed to their superiority over their competitors in energy density. To meet our expectations for use in electrical vehicles (EVs), however, LIBs need to further improve their capability in energy density. In this context, intensive investigation has been undertaking for new battery materials of high capacities. A new reactivity concept named “conversion reaction” was first reported with transition metal oxides ¹ at the very beginning of the 21^st century. Since then, more and more binary compounds were discovered having the similar electrochemical reactions in LIBs, such as metal sulfides, metal fluorides, and metal nitrides ². In comparison to the intercalation-based materials, the conversion-based materials can generally provide much higher capacities and this makes these new classes of materials important candidates for new battery technologies.

CuS has been regarded as one promising cathode material via conversion reactions, featuring a theoretical capacity of 560 mAh/g, flat discharge plateaus, and good electrical conductivity. In spite of these advantages, CuS was reported with severe capacity fading ³. To circumvent this technical hurdle, Chung and Sohn ⁴ discovered that narrowing voltage window could help improve cycleability of CuS in LIBs, but CuS still could not sustain long-term high-efficient discharge-charge cycling. In comparison to CuS, there were even fewer studies reported on Cu₂S. In this talk, we are going to present our recent progress on both CuS and Cu₂S cathodes. We confirmed that a suitable selection on voltage windows is essential for securing reliable cycleability of the CuS and Cu₂S cathodes. On the other hand, we found current collectors also have some effects on the LIB cathodes. To explore the underlying mechanism, we applied advanced synchrotron-based techniques of in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to track time-resolved structural changes of CuS and Cu₂S during discharge-charge cycles. Based on all these efforts, we developed a set of conditions for achieving long-term high-efficient CuS (see figure 1) and Cu₂S cathodes in LIBs. In addition, the electrochemical characteristics of CuS and Cu₂S also will be comparatively discussed. This work is potentially significant for developing next-generation high-energy batteries for EVs.

 

References:

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