Feixiang Ding

Sodium-ion batteries have captured widespread attention for grid-scale energy storage owing to the natural abundance of sodium. The performance of such batteries is limited by available electrode materials, especially for sodium-ion layered oxides, motivating the exploration of high compositional diversity. How the composition determines the structural chemistry is decisive for the electrochemical performance but very challenging to predict, especially for complex compositions. We introduce the "cationic potential" that captures the key interactions of layered materials and makes it possible to predict the stacking structures. This is demonstrated through the rational design and preparation of layered electrode materials with improved performance. As the stacking structure determines the functional properties, this methodology offers a solution toward the design of alkali metal layered oxides.

Abstract Material innovation on high‐performance Na‐ion cathodes and the corresponding understanding of structural chemistry still remain a challenge. Herein, we report a new concept of high‐entropy strategy to design layered oxide cathodes for Na‐ion batteries. An example of layered O3‐type NaNi 0.12 Cu 0.12 Mg 0.12 Fe 0.15 Co 0.15 Mn 0.1 Ti 0.1 Sn 0.1 Sb 0.04 O 2 has been demonstrated, which exhibits the longer cycling stability (ca. 83 % of capacity retention after 500 cycles) and the outstanding rate capability (ca. 80 % of capacity retention at the rate of 5.0 C). A highly reversible phase‐transition behavior between O3 and P3 structures occurs during the charge‐discharge process, and importantly, this behavior is delayed with more than 60 % of the total capacity being stored in O3‐type region. Possible mechanism can be attributed to the multiple transition‐metal components in this high‐entropy material which can accommodate the changes of local interactions during Na + (de)intercalation. This strategy opens new insights into the development of advanced cathode materials.

High-capacity anode materials are one of the bottlenecks to further improve the energy density of Na-ion batteries (NIBs). Except for introducing more defects to increase the sloping capacity, tuning the closed porous structure to boost the plateau capacity is another direction. Here by adopting phenol-formaldehyde resin (PF) as the carbon precursor and ethanol (EtOH) as the pore-forming agent, through precise chemical regulation of their relative content during a solvothermal process before further carbonization, carbon anodes with appropriate microstructure are achieved. It is found that the function of EtOH rests on generating steam vapor to create a pore cavity among cross-linked matrixes. The obtained optimal anodes exhibit a high Na storage capacity of ca. 410 mAh/g. When pairing with an O3-NaNi1/3Fe1/3Mn1/3O2 cathode, the full cell delivers a high initial Coulombic efficiency of 83% and energy density of ca. 300 Wh/kg. The proposed chemical regulation approach via a pore-forming strategy is simple and practical to enable high-energy-density NIBs.

Na-ion layered oxide cathodes (NaxTMO2, TM = transition metal ion(s)), as an analogue of lithium layered oxide cathodes (such as LiCoO2, LiNixCoyMn1–x–yO2), have received growing attention with the development of Na-ion batteries. However, due to the larger Na+ radius and stronger Na+–Na+ electrostatic repulsion in NaO2 slabs, some undesired phase transitions are observed in NaxTMO2. Herein, we report a high-entropy configuration strategy for NaxTMO2 cathode materials, in which multicomponent TMO2 slabs with enlarged interlayer spacing help strengthen the whole skeleton structure of layered oxides through mitigating Jahn–Teller distortion, Na+/vacancy ordering, and lattice parameter changes. The strengthened skeleton structure with a modulated particle morphology dramatically improves the Na+ transport kinetics and suppresses intragranular fatigue cracks and TM dissolution, thus leading to highly improved performances. Furthermore, the elaborate high-entropy TMO2 slabs enhance the TM–O bonding energy to restrain oxygen release and thermal runaway, benefiting for the improvement of thermal safety.