YIG-Inspired Fe 3d Spin Rearrangement to Construct Built-In Electric Field Achieving Fast-Charging Layered Cathode for Wide-Temperature Sodium-Ion Battery
O3-NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathodes are promising candidates for sodium-ion batteries benefited of the high theoretical capacity. However, the inherently poor electronic conductivity limits rate performance and aggravates O3-P3 phase transition, further weakens phase transition reversibility and results in structural degradation. Herein, a localized electronic regulation strategy inspired by yttrium iron garnet (YIG) is employed to address the issue of sluggish electron transport. Specifically, Y 3+ ions are utilized to partially substitute Ni 2+ to rearrange the electronic configuration of Fe 3 d orbitals, which could trigger a transition from high-spin state ( t 2 g 3 e g 2 ) to low-spin state ( t 2 g 5 e g 0 ) as well as narrow the band gap due to the asymmetric splitting of the t 2 g ∗ band near the Fermi level. Moreover, the large ionic radius tends to construct a concentration gradient of Y 3+ , thereby generating a long-range built-in electric field. Benefiting from the improved electrical conductivity, Y0.25-NFM performs 64 mAh g −1 reversible capacity at 20 C, also the enhanced reversible phase transitions assist Y0.25-NFM maintains 80.9% of initial capacity at 1 C for 500 cycles (44.7% for baseline NFM). The thorough understanding of the dual regulatory effects for Y 3+ doping on short & long-range electronic interactions provides a novel strategy to construct outstanding layered oxide cathodes for advanced SIBs.
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