Excess-Li Localization Triggers Chemical Irreversibility in Li- and Mn-Rich Layered Oxides.
basic_science · Level V
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- Record sourced from PubMed, PMID 32656860.
- Also identified by DOI 10.1002/adma.202001944.
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Abstract
Li- and Mn-rich layered oxides (LMRs) have emerged as practically feasible cathode materials for high-energy-density Li-ion batteries due to their extra anionic redox behavior and market competitiveness. However, sluggish kinetics regions (<3.5 V vs Li/Li<sup>+</sup> ) associated with anionic redox chemistry engender LMRs with chemical irreversibility (first-cycle irreversibility, poor rate properties, voltage fading), which limits their practical use. Herein, the structural origin of this chemical irreversibility is revealed through a comparative study involving Li<sub>1.15</sub> Mn<sub>0.51</sub> Co<sub>0.17</sub> Ni<sub>0.17</sub> O<sub>2</sub> with relatively localized and delocalized excess-Li in its lattice system. Operando fine-interval X-ray absorption spectroscopy is used to simultaneously observe the interplay between transition-metal-oxygen (TM-O) redox chemistry and TM migration behavior in real time. Density functional theory calculations show that excess-Li localization in the LMR structure attenuates TM-O covalency and stability, leading to overall chemical irreversibility. Hence, the delocalized excess-Li system is proposed as an alternative design for practically feasible LMR cathodes with restrained TM migration and sustainable O-redox chemistry.