Atomic Structural Features of Stacking Faults and Domain Connections in the Li- and Mn-Rich Cathode.
basic_science · Level V
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- Record sourced from PubMed, PMID 40156543.
- Also identified by DOI 10.1021/acsnano.5c02110.
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Abstract
Li- and Mn-rich layered oxides (LMRs), a class of earth-abundant materials for rechargeable Li-ion battery cathodes, crystallize into layered structures of two different symmetries: <i>C</i>2/<i>m</i> represented by Li<sub>2</sub>MnO<sub>3</sub> and <i>R</i>3̅<i>m</i> represented by LiMn<sub>0.5</sub>Ni<sub>0.5</sub>O<sub>2</sub>. Fundamental questions about how the <i>C</i>2/<i>m</i> and <i>R</i>3̅<i>m</i> domains spatially correlate within the same oxide grain and how the <i>C</i>2/<i>m</i> stacking faults arrange themselves when this happens still remain. Here, by using integrated differential phase contrast imaging in scanning transmission electron microscopy (STEM-iDPC), we probe the structural and compositional details of a prototypical, cobalt-free LMR material, 0.3Li<sub>2</sub>MnO<sub>3</sub>·0.7LiMn<sub>0.5</sub>Ni<sub>0.5</sub>O<sub>2</sub> (Li<sub>1.13</sub>Mn<sub>0.57</sub>Ni<sub>0.3</sub>O<sub>2</sub>). The connection between the <i>C</i>2/<i>m</i> and <i>R</i>3̅<i>m</i> domains is found to be abrupt, facilitated by the small lattice mismatch between the two structures. Stacking faults in the <i>C</i>2/<i>m</i> domains feature atomic plane shifting that accommodates stacking sequence changes, which explains why the stacking faults form in a random manner. Furthermore, a local disordering mechanism was identified to correlate with the <i>C</i>2/<i>m</i> stacking faults. Chemically, it is found that Ni coexists with Mn at the transition metal sites within the nominal Li<sub>2</sub>MnO<sub>3</sub> domain. This study demonstrates that STEM-iDPC is a very useful tool for capturing all the elements in a single image, revealing atomic details on domain connections and stacking faults in the LMRs.