Diethylzinc-Assisted Atomic Surface Reduction to Stabilize Li and Mn-Rich NCM

Abstract

Li and Mn-rich nickel cobalt manganese oxide (LMR-NCM) is one of the most promising cathode materials for realizing next-generation Li-ion batteries due to its high specific capacity of >250 mA h g −1 and operating potential > 4.5 V. Nevertheless, being plagued by severe capacity fading and voltage decay, the commercialization of LMR-NCM appears to be a distant goal. The anionic activity of oxygen and associated phase transformations are the reasons behind the unstable electrochemical performance. The tendency of LMR-NCM to react with CO 2 and moisture further makes it prone to interfacial instability and degradation. Here, we report a neoteric method to mitigate the stability issues and improve the electrochemical performance of LMR-NCM by changing the electronic configuration of constituting O and transition metals via diethylzinc-assisted atomic surface reduction (Zn-ASR) using an extremely facile protocol. With the proposed Zn-ASR, a 2−3 nm thin layer of a reduced surface enriched with complex ZnO x or ZnO x Ry was obtained on the LMR-NCM particles. X-ray photoelectron spectroscopy suggested the transfer of ethyl groups of diethylzinc to O atoms on the LMR-NCM surface, which ultimately led to the reduction of near-surface Mn and Ni atoms and impeded irreversible anionic activity. The presence of ZnO x / ZnO x Ry also resulted in superior charge transfer and resistance against HF. As a result, in contrast to LMR-NCM, the Zn-ASRtreated sample exhibited substantially improved rate capabilities, facilitated charge transfer, enhanced capacity retention, reduced parasitic reactions, and long-term stability as reflected from in-depth electrochemical analysis, in operando gaseous evolution studies, and post-mortem microscopic analysis.

Investigating the Temperature Dependency of Trimethyl Aluminum Assisted Atomic Surface Reduction of Li and Mn-Rich NCM

“…Recently, we explored the application of ASR using different metals-namely zinc instead of aluminum-to further enhance the performance of specific electrode materials like NCM811, LNMO. [30][31][32] The density functional theory calculations we reported for TMA-ASR predicted that in the presence of TMA, the surface reduction can essentially occur at room temperature. 28 Therefore, in this work, we build upon our ASR method and present a case study investigating the impact of low temperatures on ASR efficiency using TMA vapor treatment on Li and Mn-rich NCM.…”