Li Biao, Zhuo Zengqing, Zhang Leiting, Iadecola Antonella, Gao Xu, Guo Jinghua, Yang Wanli, Morozov Anatolii V, Abakumov Artem M, Tarascon Jean-Marie
Chimie du Solide-Energie, UMR 8260, Collège de France, Paris, France.
Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, Amiens, France.
Nat Mater. 2023 Nov;22(11):1370-1379. doi: 10.1038/s41563-023-01679-x. Epub 2023 Oct 5.
Li[LiNiMnCo]O (lithium-rich NMCs) are benchmark cathode materials receiving considerable attention due to the abnormally high capacities resulting from their anionic redox chemistry. Although their anionic redox mechanisms have been much investigated, the roles of cationic redox processes remain underexplored, hindering further performance improvement. Here we decoupled the effects of nickel and cobalt in lithium-rich NMCs via a comprehensive study of two typical compounds, LiNiMnO and LiCoMnO. We discovered that both Ni and Co, generated during cationic redox processes, are actually intermediate species for triggering oxygen redox through a ligand-to-metal charge-transfer process. However, cobalt is better than nickel in mediating the kinetics of ligand-to-metal charge transfer by favouring more transition metal migration, leading to less cationic redox but more oxygen redox, more O release, poorer cycling performance and more severe voltage decay. Our work highlights a compositional optimization pathway for lithium-rich NMCs by deviating from using cobalt to using nickel, providing valuable guidelines for future high-capacity cathode design.
富锂层状氧化物Li[LiNiMnCo]O（富锂镍锰钴氧化物）由于其阴离子氧化还原化学导致的异常高容量而成为备受关注的基准正极材料。尽管对其阴离子氧化还原机制进行了大量研究，但阳离子氧化还原过程的作用仍未得到充分探索，这阻碍了性能的进一步提升。在此，我们通过对两种典型化合物LiNiMnO和LiCoMnO的全面研究，解耦了富锂镍锰钴氧化物中镍和钴的影响。我们发现，在阳离子氧化还原过程中产生的镍和钴实际上都是通过配体到金属的电荷转移过程触发氧氧化还原的中间物种。然而，钴在介导配体到金属电荷转移的动力学方面比镍更好，因为它有利于更多的过渡金属迁移，导致较少的阳离子氧化还原但更多的氧氧化还原、更多的氧释放、较差的循环性能和更严重的电压衰减。我们的工作突出了一条通过从使用钴转向使用镍来优化富锂镍锰钴氧化物组成的途径，为未来高容量正极设计提供了有价值的指导方针。
