Polyanionic compounds have large compositional flexibility, which creates a growing interest in exploring the property limits of electrode materials of rechargeable batteries. The realization of multisodium storage in the polyanionic electrodes can significantly improve capacity of the materials, but it often causes irreversible capacity loss and crystal phase evolution, especially under high-voltage operation, which remain important challenges for their application. Herein, it is shown that the multisodium storage in the polyanionic cathode can be enhanced and stabilized by increasing the entropy of the polyanionic host structure. The obtained polyanionic Na 3.4 Fe 0.4 Mn 0.4 V 0.4 Cr 0.4 Ti 0.4 (PO 4 ) 3 cathode exhibits multicationic redox property to achieve high capacity with good reversibility under the high voltage of 4.5 V (vs Na/Na + ). Exploring the underlying mechanism through operando characterizations, a stable trigonal phase with reduced volume change during the multisodium storage process is disclosed. Besides, the enhanced performance of the HE material also derives from the synergistic effect of the diverse TM species with suitable molarity. These results reveal the effectiveness of high-entropy concept in expediting high-performance polyanionic cathodes discovery.
As an attractive cathode candidate for sodium-ion batteries, P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 is famous for its high stability in humid air, attractive capacity, and high operating voltage. However, the low Na + transport kinetics, oxygen-redox reactions, and irreversible structural evolution at high-voltage areas hinder its practical application. Herein, a comprehensive study of a microbar P2-type Ni 2/3 Ni 1/4 Mg 1/12 Mn 2/3 O 2 material with {010} facets is presented, which exhibits high reversibility of structural evolution and anionic redox activity, leading to outstanding rate capability and cyclability. The notable rate performance (53 mA h g −1 at 20 C, 2.0− 4.3 V) contributed to the high exposure of {010} facets via controlling the growth orientation of the precursor, which is certified by density functional theory calculation and lattice structural analysis. Mg substitution strengthens the reversibility of anionic oxygen redox and structural evolution in high-voltage areas that was confirmed by the in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy tests, leading to outstanding cyclic reversibility (68.9% after 1000 cycles at 5 C) and slowing down the voltage fading. This work provides new insights into constructing electrochemically active planes combined with heteroatom substitution to improve the Na + transport kinetics and structural stability of layered oxide cathodes for sodium storage.
The spent cathode carbon (SCC) from aluminum electrolysis was subjected to caustic leaching to investigate the different effects of ultrasound-assisted and traditional methods on element fluorine (F) leaching rate and leaching residue carbon content. Sodium hydroxide (NaOH) dissolved in deionized water was used as the reaction system. Through single-factor experiments and a comparison of two leaching techniques, the optimum F leaching rate and residue carbon content for ultrasound-assisted leaching process were obtained at a temperature of 70°C, residue time of 40min, initial mass ratio of alkali to SCC (initial alkali-to-material ratio) of 0.6, liquid-to-solid ratio of 10mL/g, and ultrasonic power of 400W, respectively. Under the optimal conditions, the leaching residue carbon content was 94.72%, 2.19% larger than the carbon content of traditional leaching residue. Leaching wastewater was treated with calcium chloride (CaCl) and bleaching powder and the treated wastewater was recycled caustic solution. All in all, benefiting from advantage of the ultrasonication effects, ultrasound-assisted caustic leaching on spent cathode carbon had 55.6% shorter residue time than the traditional process with a higher impurity removal rate.
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