Direct Recycling of LiNixMnyCozO2 (NMC) Cathode Materials in Molten Salts
Authors: Wang Tao , Luo Huimin , Dai Sheng 
Published: December 2024

Direct recycling is an emerging technology to retrain the added value of compound structure by healing the compositional and structural defects in spent cathode materials. In our previous work, we developed a successful lithiation via ionothermal synthesis using a cost-effective Li halide as Li source and recyclable ILs as solvents for the direct recycling of LiNi1/3Mn1/3Co1/3O2 (NMC 111) cathodes.[1] Compared to the classic solid-state sintering approach, the flux synthesis in ionic liquids can achieve high-temperature phase products under a lower temperature and ambient pressure. The relithiated NMC 111 exhibited excellent electrochemical performance as a pristine NMC 111 in both half-cell and full-cell tests. For the direct recycling of commercial Ni-rich NMC cathodes, Li containing reciprocal ternary molten salts (RTMS) flux media can serve as both Li sources and solvents to restore Li in spent NMC under relatively low temperatures (below 300 °C).[2] Surpassing the traditional binary or ternary molten salts, the reciprocal ternary molten salts (RTMS) feature two cation species and two anion species, and a lower eutectic temperature. In addition, the highly charged flux media offered by molten salts provide efficient environments for transporting ionic reaction precursors for a successful direct recycling of spent NMC cathodes.Beyond direct recycling, direct upcycling of spent cathodes to the next-generation cathodes can maximize the value of EOL LIBs (Figure 1a). In a typical Li+, Na+||Cl-, NO3
- RTMS system, the reversible reaction: NaNO3 + LiCl ⇌ LiNO3 + NaCl enables a low eutectic melting point for the effective flux process under 300 °C and can provide an oxygen-rich environment, which are critical indexes for a low-temperature upcycling of spent NMC 111 to Ni-rich NMCs (eg. NMC 622).[3] After upcycling, the chemical composition of Up-NMC 622 is Li1.08Ni0.63Co0.19Mn0.18O2, having a restored Li content and higher Ni content compared to spent NMC 111 (Li0.93Ni0.33Co0.33Mn0.33O2), suggesting the successful upcycling in chemical composition. In the half-cell battery tests, the first charge/discharge capacities of Up-NMC 622 are larger than those of spent NMC 111 (charge capacity: 188.6 vs 140.1 mAh/g; discharge capacity: 153.6 vs 119.5 mAh/g at 20 mA/g). Thus, molten salts are promising and effective for the direct recycling/upcycling of spent NMC cathodes.

References:

1. Wang, T., Luo, H. M., Bai, Y. C., Li, J. L., Belharouak, I., Dai, S., Direct Recycling of Spent NCM Cathodes through Ionothermal Lithiation. Adv. Energy Mater. 2020, 10, 2001204.

2. Wang, T., Luo, H., Bai, Y., Belharouak, I., Jayanthi, K., Paranthaman, M.P., Manard, B.T., Wang, E.T.H., Dogan, F., Son, S.B., Ingram, B.J., Direct recycling of spent nickel-rich cathodes in reciprocal ternary molten salts. Journal of Power Sources, 2024, 593, 233798.

3. Wang, T., Luo, H., Fan, J., Thapaliya, B.P., Bai, Y., Belharouak, I., Dai, S., Flux upcycling of spent NMC 111 to nickel-rich NMC cathodes in reciprocal ternary molten salts. Iscience, 2022, 25(2), 103801.