An Active Strategy to Reduce Residual Alkali for High-Performance Layered Oxide Cathode Materials of Sodium-Ion Batteries.

Residual alkali is one of the biggest challenges for the commercialization of sodium-based layered transition metal oxide cathode materials since it can even inevitably appear during the production process. Herein, taking O3-type Na0.9Ni0.25Mn0.4Fe0.2Mg0.1Ti0.05O2 as an example, an active strategy is proposed to reduce residual alkali by slowing the cooling rate, which can be achieved in one-step preparation method. It is suggested that slow cooling can significantly enhance the internal uniformity of the material, facilitating the reintegration of Na+ into the bulk material during the calcination cooling phase, therefore substantially reducing residual alkali. The strategy can remarkably suppress the slurry gelation and gas evolution and enhance the structural stability. Compared to naturally cooled cathode materials, the capacity retention of the slowly cooled electrode material increases from 76.2% to 85.7% after 300 cycles at 1 C. This work offers a versatile approach to the development of advanced cathode materials toward practical applications.

Mechanisms underlying enhanced Cd translocation and tolerance in roots of Populus euramericana in response to nitrogen fertilization.

A pot experiment was conducted to evaluate how nitrogen (N) availability influences cadmium (Cd) absorption, translocation and stress tolerance in roots of Populus euramericana. Seedling growth was sensitive to N deficiency, but it was unaltered by Cd exposure. Cadmium absorption by roots was promoted by N deficiency, resulting in a higher root Cd concentration compared to the N-sufficient condition. Fine-root length was tightly correlated (R2 = 0.73) with Cd concentration in roots, indicating that vigorous fine-root proliferation under N deficiency contributed to active absorption and accumulation of Cd in roots. Despite accumulation in roots, Cd translocation from roots to shoots was less active under N deficiency compared to N sufficiency. This was related to elevated glutathione reductase (GR) activity and glutathione (GSH) levels in roots after N application, which may not only promote antioxidant defence, but also facilitate the formation of GSH-Cd complexes that are uploaded into root cylinders. Nitrogen application also promoted antioxidant defense in roots via increased production of phytohormones and the level of enzymatic and non-enzymatic antioxidants. Transcript levels for genes responsible for antioxidant defense, Cd detoxification and Cd uploading were increased in roots by N application. The N-stimulated Cd tolerance, detoxification and uploading in roots are factors likely to promote Cd translocation from roots to shoots, which may enhance the biological capacity of this poplar species for phytoremediation of Cd pollution.