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Download fileUnusual Spinel-to-Layered Transformation in LiMn2O4 Cathode Explained by Electrochemical and Thermal Stability Investigation
journal contribution
posted on 21.09.2017, 00:00 authored by Liubin Ben, Hailong Yu, Bin Chen, Yuyang Chen, Yue Gong, Xinan Yang, Lin Gu, Xuejie HuangDistorted
surface regions (5–6 nm) with an unusual layered-like structure
on LiMn2O4 cathode material were directly observed
after it was cycled (3–4.9 V), indicating a possible spinel-to-layered
structural transformation. Formation of these distorted regions severely
degrades LiMn2O4 cathode capacity. As we attempt
to get a better understanding of the exact crystal structure of the
distorted regions, the structural transformation pathways and the
origins of the distortion are made difficult by the regions’
nanoscopic size. Inspired by the reduction of Mn4+ to Mn3+ in surface electronic structures that might be associated
with oxygen loss during cycling, we further investigated the atomic-level
surface structure of LiMn2O4 by heat-treatments
between 600 and 900 °C in various atmospheres, finding similar
surface spinel-to-layered structural transformation only for LiMn2O4 heat-treated in argon atmosphere for a few minutes
(or more). Controllable and measurable oxygen loss during heat-treatments
result in Mn3+ for charge compensation. The ions then undergo
a disproportionation reaction, driving the spinel-to-layered transformation
by way of an intermediate LiMn3O4-like structure.
The distortion of the surface regions can be extended to the whole
bulk by heat-treatment for 300–600 min, ultimately enabling
us to identify the bulk-level structure as layered Li2MnO3 (C2/m). This work demonstrates
the critical role of Mn3+ in controlling the kinetics of
the structural transformation in spinel LiMn2O4 and suggests heat-treatment in argon as a convenient method to control
the surface oxygen loss and consequently reconstruct the atomic-level
surface structure.
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transformationspinel LiMn 2 O 4LiMn 2 O 4 heat-treatedLiMn 2 O 4 cathode materialregionUnusual Spinel-to-Layered Transformationsurface oxygen lossLiMn 2 O 4 Cathode Explainedspinel-to-layeredLi 2 MnO 3degrades LiMn 2 O 4 cathode capacityoxygen lossLiMn 2 O 4LiMn 3 O 4atomic-level surface structureheat-treatment