Wei Lin,Wenxue Min,Qimeng Zhang,Shunzhang You,Song Han,Chenghao Yang
O3-type layered oxides have become a research hotspot in the development of sodium-ion batteries owing to their simple synthesis method and competitive theoretical capacity. However, their practical applications still face enormous challenges, especially concerning insufficient cyclic stability and poor kinetic performance. Herein, the Sb/Al co-doping NaNi 0.48 Mn 0.49 Sb 0.01 Al 0.02 O 2 (NMSA) material was produced via sol-gel process. Sodium-ion kinetics were investigated through Cyclic Voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT), while the charge compensation mechanism was examined via ex-situ X-ray Photoelectron Spectroscopy (XPS). The successful doping of Al improves the stability of the transition metal oxide layer (TMO 2 ), thereby extending the cycle life of material. In-situ X-ray Diffraction (XRD) analysis reveals successful inhibition of the irreversible O3-P3 phase transition. In addition, Sb-doping increases the number of ions involved in charge compensation, thereby elevating the discharge specific capacity. Therefore, the NMSA material can provide a discharge specific capacity of 128.5 mAh g −1 at 0.1C and a capacity retention rate of 85 % after 100 cycles at 1C. Finally, the interface stability of the cycled material was studied to investigate the stability of the cathode/electrolytes interface (CEI) layer. This study provides new innovative views on proposing advanced cathode for high-energy sodium-ion batteries.
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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