Alleviating Structure Collapse of Polycrystalline LiNi<sub><i>x</i></sub>Co<sub><i>y</i></sub>Mn<sub>1-<i>x</i>-<i>y</i></sub>O<sub>2</sub> via Surface Co Enrichment.
basic_science · Level V
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- Record sourced from PubMed, PMID 38900971.
- Also identified by DOI 10.1021/acsnano.4c03128.
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Abstract
The structure collapse issues have long restricted the application of polycrystalline LiNi<sub><i>x</i></sub>Co<sub><i>y</i></sub>Mn<sub>1-<i>x</i>-<i>y</i></sub>O<sub>2</sub> (NCM) at high voltages beyond 4.4 V vs Li/Li<sup>+</sup>. Herein, for LiNi<sub>0.55</sub>Co<sub>0.12</sub>Mn<sub>0.33</sub>O<sub>2</sub> (P-NCM), rapid surface degradation is observed upon the first charge, along with serious particle fragmentation upon repeated cycles. To alleviate these issues, a surface Co enrichment strategy is proposed [i.e., Co-enriched NCM (C-NCM)], which promotes the in situ formation of a robust surface rock-salt (RS) layer upon charge, serving as a highly stable interface for effective Li<sup>+</sup> migration. Benefiting from this stabilized surface RS layer, Li<sup>+</sup> extraction occurs mainly through this surface RS layer, rather than along the grain boundaries (GBs), thus reducing the risk of GBs' cracking and even particle fragmentation upon cycles. Besides, O loss and TM (TM = Ni, Co, and Mn) dissolution are also effectively reduced with fewer side reactions. The C-NCM/graphite cell presents a highly reversible capacity of 205.1 mA h g<sup>-1</sup> at 0.2 C and a high capacity retention of 86% after 500 cycles at 1 C (1 C = 200 mA g<sup>-1</sup>), which is among the best reported cell performances. This work provides a different path for alleviating particle fragmentation of NCM cathodes.