Direct Recycling and Upcycling of Spent Graphite Anodes

Abstract

Lithium-ion batteries (LIBs) have emerged as the battery of choice for rapidly growing markets in electric vehicles (EVs) and energy storage devices. Thus, there is an enormous interest in the development of new technologies for recycling and recovery of valuable materials from secondary resources, such as those from used LIBs. Finding ways to decrease the cost of recycling could significantly reduce the life cycle cost of LIBs, avoid material shortages, lessen the environmental impact of new material production, and provide low-cost active materials for new LIB manufacturing. The recycling of spent LIBs has mainly been focused on the recycling of the cathode, while recycling of the graphite anode has only received limited attention due to its low value and complex recycling process. However, with the recent shortage of resources and the increase in production costs, recycling of the graphite anode from spent batteries can no longer be ignored. There are several challenges associated with recovering spent graphite anodes – mainly, there are a variety of metal impurities in addition to surface impurities from the solid electrolyte interface (SEI) and interior impurities that need to be removed. Conventional recycling methods are unable to solve this issue, especially for the purification process. Most current recycling systems use pyrometallurgical and/or hydrometallurgical methods, which necessitate multi-unit operations, high energy consumption, and high cost. Direct recycling, on the other hand, is a promising solution for overcoming the hurdles involved with recovering spent graphite anodes.Princeton NuEnergy (PNE) has successfully developed a novel low-temperature plasma process to enable purification and direct repair of graphite anode materials from spent LIBs. We also demonstrated a simple but effective surface coating approach to upgrade the spent graphite to produce a graphite-silicon composite that has an improved energy density. Spent graphite is an ideal choice for low-cost production of high-performance silicon-graphite composites because treated spent graphite presents a porous structure that can be combined well with silicon and effectively relieve volume expansion. The recycled graphite and upcycled graphite-silicon composite anode materials outperform the commercially available equivalent materials. The direct recycling/upcycling of graphite anode materials will increase the commercial viability of LIBs and reduce battery cost, thus accelerating the electrification of transportation and large-scale energy storage for renewable energy in the near future. In this presentation, the materials characterization and electrochemical performance of recycled/upcycled anode materials will be discussed.BEK and CY acknowledge support of this research by Princeton University under the Intellectual Property Accelerator Fund.