Facet-Dependent Thermal Instability in LiCoO<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 28230376.
- Also identified by DOI 10.1021/acs.nanolett.6b04502.
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Abstract
Thermal runaways triggered by the oxygen release from oxide cathode materials pose a major safety concern for widespread application of lithium ion batteries. Utilizing in situ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) at high temperatures, we show that oxygen release from Li<sub>x</sub>CoO<sub>2</sub> cathode crystals is occurring at the surface of particles. We correlated this local oxygen evolution from the Li<sub>x</sub>CoO<sub>2</sub> structure with local phase transitions spanning from layered to spinel and then to rock salt structure upon exposure to elevated temperatures. Ab initio molecular dynamics simulations (AIMD) results show that oxygen release is highly dependent on Li<sub>x</sub>CoO<sub>2</sub> facet orientation. While the [001] facets are stable at 300 °C, oxygen release is observed from the [012] and [104] facets, where under-coordinated oxygen atoms from the delithiated structures can combine and eventually evolve as O<sub>2</sub>. The novel understanding that emerges from the present study provides in-depth insights into the thermal runaway mechanism of Li-ion batteries and can assist the design and fabrication of cathode crystals with the most thermally stable facets.