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Open Access Publications from the University of California

Effect of composition on the structure of lithium- and manganese-rich transition metal oxides

  • Author(s): Shukla, AK
  • Ramasse, QM
  • Ophus, C
  • Kepaptsoglou, DM
  • Hage, FS
  • Gammer, C
  • Bowling, C
  • Gallegos, PAH
  • Venkatachalam, S
  • et al.

© 2018 The Royal Society of Chemistry. The choice of chemical composition of lithium- and manganese-rich transition metal oxides used as cathode materials in lithium-ion batteries can significantly impact their long-term viability as storage solutions for clean energy automotive applications. Their structure has been widely debated: conflicting conclusions drawn from individual studies often considering different compositions have made it challenging to reach a consensus and inform future research. Here, complementary electron microscopy techniques over a wide range of length scales reveal the effect of lithium-to-transition metal-ratio on the surface and bulk structure of these materials. We found that decreasing the lithium-to-transition metal-ratio resulted in a significant change in terms of order and atomic-level local composition in the bulk of these cathode materials. However, throughout the composition range studied, the materials consisted solely of a monoclinic phase, with lower lithium content materials showing more chemical ordering defects. In contrast, the spinel-structured surface present on specific crystallographic facets exhibited no noticeable structural change when varying the ratio of lithium to transition metal. The structural observations from this study warrant a reexamination of commonly assumed models linking poor electrochemical performance with bulk and surface structure.

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