Entropy and crystal-facet modulation of P2-type layered cathodes for long-lasting sodium-based batteries.

P2-type sodium manganese-rich layered oxides are promising cathode candidates for sodium-based batteries because of their appealing cost-effective and capacity features. However, the structural distortion and cationic rearrangement induced by irreversible phase transition and anionic redox reaction at high cell voltage (i.e., >4.0 V) cause sluggish Na-ion kinetics and severe capacity decay. To circumvent these issues, here, we report a strategy to develop P2-type layered cathodes via configurational entropy and ion-diffusion structural tuning. In situ synchrotron X-ray diffraction combined with electrochemical kinetic tests and microstructural characterizations reveal that the entropy-tuned Na _0.62 Mn _0.67 Ni _0.23 Cu _0.05 Mg _0.07 Ti _0.01 O ₂ (CuMgTi-571) cathode possesses more {010} active facet, improved structural and thermal stability and faster anionic redox kinetics compared to Na _0.62 Mn _0.67 Ni _0.37 O ₂ . When tested in combination with a Na metal anode and a non-aqueous NaClO ₄ -based electrolyte solution in coin cell configuration, the CuMgTi-571-based positive electrode enables an 87% capacity retention after 500 cycles at 120 mA g ^-1 and about 75% capacity retention after 2000 cycles at 1.2 A g ^-1 .
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