Abstract
Most technologically important electrode materials for lithium-ion batteries are essentially lithium ions plus a transition-metal oxide framework. However, their atomic and electronic structure evolution during electrochemical cycling remains poorly understood. Here we report the in situ observation of the three-dimensional structural evolution of the transition-metal oxide framework in an all-solid-state battery. The in situ studies LiNi0.5Mn1.5O4 from various zone axes reveal the evolution of both atomic and electronic structures during delithiation, which is found due to the migration of oxygen and transition-metal ions. Ordered to disordered structural transition proceeds along the <100>, <110>, <111> directions and inhomogeneous structural evolution along the <112> direction. Uneven extraction of lithium ions leads to localized migration of transition-metal ions and formation of antiphase boundaries. Dislocations facilitate transition-metal ions migration as well. Theoretical calculations suggest that doping of lower valence-state cations effectively stabilize the structure during delithiation and inhibit the formation of boundaries.
Highlights
Most technologically important electrode materials for lithium-ion batteries are essentially lithium ions plus a transition-metal oxide framework
By combining focused ion-beam (FIB) milling and a chip-based in situ transmission-electron microscopy (TEM) holder, in situ TEM electrochemical observation is achieved with atomic resolution[22,23]
We investigate the changes of the atomic and electronic structure of spinel P4332 LNMO during delithiation with special attention paid to the behavior of oxygen and transition-metal ions
Summary
Most technologically important electrode materials for lithium-ion batteries are essentially lithium ions plus a transition-metal oxide framework. EELS spectra in Fig. 3h–j show the shift of the L-edge of Ni and Mn in the migration area, indicating a decrease of the valence state of Mn and an increase of the valence state of Ni. Overall, Ni is more likely to occupy the 4a site than Mn during delithiation along with the electronic structural evolution at the same time.
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