Mechanical Homogenization Promoting Dual-Directional Upcycling of Layered Oxide Cathodes

Abstract

Upcycling is regarded as a sustainable and promising recycling solution for spent lithium-ion batteries (LIBs). However, current upcycling strategies such as converting Ni-lean to Ni-rich cathodes struggle to change the composition of the spent cathodes to meet the diverse market demands. In addition, the commonly employed molten-salts method requires tens of hours of high-temperature treatment, restricting its sustainability. Herein, this study reports an efficient, flexible dual-directional upcycling strategy to upcycle a broad family of layered oxide cathodes into fresh LiNi_xCo_yMn_zO₂ (NCM) cathodes with tailored Ni-contents—either increased or decreased—in just 4 h via mechanical homogenization pretreatment. This study confirms that the bulk diffusion of transition metals (TMs) is the rate-determining step in the resynthesis process, and the mechanical homogenization can shorten the diffusion pathway of TMs, thus reducing the sintering duration effectively. The as-upcycled NCM cathodes can deliver electrochemical performance on par with commercial counterparts. Notably, a systematic technoeconomic analysis shows that upcycling spent LiCoO₂ into NCM622 can yield a profit up to 35 US$/kg, 30% higher than the conventional acid-leaching resynthesis approach. This work provides an energy-saving, widely adaptable, flexible, and cost-efficient method for regenerating spent cathode materials, paving the way for the sustainable recycling of LIBs.