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Open Access Publications from the University of California

Phase transformation mechanism in lithium manganese nickel oxide revealed by single-crystal hard X-ray microscopy

  • Author(s): Kuppan, S
  • Xu, Y
  • Liu, Y
  • Chen, G
  • et al.

© 2017 The Author(s). Understanding the reaction pathway and kinetics of solid-state phase transformation is critical in designing advanced electrode materials with better performance and stability. Despite the first-order phase transition with a large lattice mismatch between the involved phases, spinel LiMn 1.5 Ni 0.5 O 4 is capable of fast rate even at large particle size, presenting an enigma yet to be understood. The present study uses advanced two-dimensional and three-dimensional nano-Tomography on a series of well-formed Li x Mn 1.5 Ni 0.5 O 4 (0≤x≤1) crystals to visualize the mesoscale phase distribution, as a function of Li content at the sub-particle level. Inhomogeneity along with the coexistence of Li-rich and Li-poor phases are broadly observed on partially delithiated crystals, providing direct evidence for a concurrent nucleation and growth process instead of a shrinking-core or a particle-by-particle process. Superior kinetics of (100) facets at the vertices of truncated octahedral particles promote preferential delithiation, whereas the observation of strain-induced cracking suggests mechanical degradation in the material.

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