Chenglong Zhao

Advanced Nanostructured Anode Materials for Sodium-Ion Batteries

Sodium-ion batteries (NIBs), due to the advantages of low cost and relatively high safety, have attracted widespread attention all over the world, making them a promising candidate for large-scale energy storage systems. However, the inherent lower energy density to lithium-ion batteries is the issue that should be further investigated and optimized. Toward the grid-level energy storage applications, designing and discovering appropriate anode materials for NIBs are of great concern. Although many efforts on the improvements and innovations are achieved, several challenges still limit the current requirements of the large-scale application, including low energy/power densities, moderate cycle performance, and the low initial Coulombic efficiency. Advanced nanostructured strategies for anode materials can significantly improve ion or electron transport kinetic performance enhancing the electrochemical properties of battery systems. Herein, this Review intends to provide a comprehensive summary on the progress of nanostructured anode materials for NIBs, where representative examples and corresponding storage mechanisms are discussed. Meanwhile, the potential directions to obtain high-performance anode materials of NIBs are also proposed, which provide references for the further development of advanced anode materials for NIBs.

An O3‐type Oxide with Low Sodium Content as the Phase‐Transition‐Free Anode for Sodium‐Ion Batteries

Layered transition metal oxides Nax MO2 (M=transition metal) with P2 or O3 structure have attracted attention in sodium-ion batteries (NIBs). A universal law is found to distinguish structural competition between P2 and O3 types based on the ratio of interlayer distances of the alkali metal layer d(O-Na-O) and transition-metal layer d(O-M-O) . The ratio of about 1.62 can be used as an indicator. O3-type Na0.66 Mg0.34 Ti0.66 O2 oxide is prepared as a stable anode for NIBs, in which the low Na-content (ca. 0.66) usually undergoes a P2-type structure with respect to Nax MO2 . This material delivers an available capacity of about 98 mAh g-1 within a voltage range of 0.4-2.0 V and exhibits a better cycling stability (ca. 94.2 % of capacity retention after 128 cycles). In situ X-ray diffraction reveals a single-phase reaction in the discharge-charge process, which is different from the common phase transitions reported in O3-type electrodes, ensuring long-term cycling stability.

A High-Temperature

The high-temperature β-phase NaMnO 2 is a promising material for Na-ion batteries (NIBs) due to its high capacity and abundant resources. However, the synthesis of phase-pure β-NaMnO 2 is burdensome and costineffective because it needs to be sintered under oxygen atmosphere at high temperature and followed by a quenching procedure. Here we first report that the pure β phase can be stabilized by Cu-doping and easily synthesized by replacing a proportion of Mn with Cu via a simplified process including sintering in air and cooling to room temperature naturally. Based on the first-principle calculations, the band gap decreases from 0.7 eV to 0.3 eV, which indicates that the electronic conductivity can be improved by Cu-doping. The designed β-NaCu0.1 Mn 0.9 O 2 is applied as cathode in NIBs, exhibiting an energy density of 419Wh/kg and better performance in terms of rate capability and cycling stability than those in the undoped case.