High-Entropy Na-Deficient Layered Oxides for Sodium-Ion Batteries.
basic_science · Level V
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- Record sourced from PubMed, PMID 37382902.
- Also identified by DOI 10.1021/acsnano.3c02290.
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Abstract
Sodium layered oxides always suffer from sluggish kinetics and deleterious phase transformations at deep-desodiation state (<i>i.e</i>., >4.0 V) in O3 structure, incurring inferior rate capability and grievous capacity degradation. To tackle these handicaps, here, a configurational entropy tuning protocol through manipulating the stoichiometric ratios of inactive cations is proposed to elaborately design Na-deficient, O3-type Na<sub><i>x</i></sub>TmO<sub>2</sub> cathodes. It is found that the electrons surrounding the oxygen of the TmO<sub>6</sub> octahedron are rearranged by the introduction of MnO<sub>6</sub> and TiO<sub>6</sub> octahedra in Na-deficient O3-type Na<sub>0.83</sub>Li<sub>0.1</sub>Ni<sub>0.25</sub>Co<sub>0.2</sub>Mn<sub>0.15</sub>Ti<sub>0.15</sub>Sn<sub>0.15</sub>O<sub>2-δ</sub> (MTS15) with expanded O-Na-O slab spacing, giving enhanced Na<sup>+</sup> diffusion kinetics and structural stability, as disclosed by theoretical calculations and electrochemical measurements. Concomitantly, the entropy effect contributes to the improved reversibility of Co redox and phase-transition behaviors between O3 and P3, as clearly revealed by <i>ex situ</i> synchrotron X-ray absorption spectra and <i>in situ</i> X-ray diffraction. Notably, the prepared entropy-tuned MTS15 cathode exhibits impressive rate capability (76.7% capacity retention at 10 C), cycling stability (87.2% capacity retention after 200 cycles) with a reversible capacity of 109.4 mAh g<sup>-1</sup>, good full-cell performance (84.3% capacity retention after 100 cycles), and exceptional air stability. This work provides an idea for how to design high-entropy sodium layered oxides for high-power density storage systems.