Fast-charging high-entropy O3-type layered cathodes for sodium-ion batteries

Abstract

Sodium-ion batteries (SIBs) are considered as the most promising complementary energy storage system for large-scale application due to the high abundance of sodium. However, the irreversible phase transition and slow diffusion kinetics in O3-type layered transition metals oxides cathodes impede the development of advanced SIBs. Here we address this issue by introducing high-entropy doping regulation strategies, a series of NaNi_0.4Mn_0.3-xFe_0.1Ti_0.1Sn_xLi_0.05Sb_0.05O₂ cathodes exhibit an excellent rate performance (>60 mAh/g at 6 A/g) and prolonged cycle performance (capacity retention >80 % after 300 cycles, at 120 mA/g). The correlations between the chemical compositions and the electrochemical properties in the designed high-entropy transition metal oxides cathodes were elucidated using a combination of analytical tools including all kinds of electrochemical techniques including galvanostatic intermittent titration technique (GITT) and density functional theory (DFT) calculations, in conjunction with in-situ X-ray diffraction (XRD). These studies revealed a P3-phase dominated solid-solution reaction during the charge/discharge process that boosts the sodium ions migration in the structure. This study provides a model for effective simultaneous electrochemical evaluation and structure evolution analysis of the multi-elements high-entropy metal oxide cathodes. The understanding gained, enables to apply a successful doping regulation procedure, thus paving the way for a rational design of optimal high-entropy multi-component NaTMO₂ cathodes for rechargeable Na ions batteries.