Elucidating the Role of Defects for Electrochemical Intercalation in Sodium Vanadium Oxide

Na_{1.25+<i>x</i>}V₃O₈ (with <i>x</i> < 0, = 0, and > 0) was synthesized via a wet chemical route involving the reduction of V₂O₅ in oxalic acid and NaNO₃ followed by calcination. It was possible to control the sodium composition in the final product by adjusting the amount of sodium precursor added during synthesis. It was revealed that deficient and excessive sodium contents, with respect to the ideal stoichiometry, are accommodated or compensated by the respective generation of oxygen vacancies and partial transition metal reduction, or cation disordering. When examined as NIB electrode material, the superior performance of the cation disordered material with excessive sodium was clearly demonstrated, with more than 50% higher storage capacity and superior rate capacity and cyclic stability. The formation of oxygen vacancies initially seemed promising but was coupled with stability issues and capacity fading upon further cycling. The disparity in electrochemical performance was attributed to variations in the electronic distribution as promoted through Na–ion interactions and the direct influence of such on the oxygen framework (sublattice); these factors were determined to have significant impact on the migration energy and diffusion barriers

Study of the Tribological Properties of Modified Potassium Titanate Whisker-Reinforced Resin-Based Friction Composites

The surface modifications of reinforcing components have significant influence on the tribological performance of resin-based friction composites. In this work, 3-aminopropyltriethoxysilane coupling agent (KH550) and octadecyltrichlorosilane (OTS) were used to modify nanosized potassium titanate whiskers (PTW). Subsequently, the modified potassium titanate whiskers were used as reinforcing components in phenolic resin-based friction composites. The tribological behavior and wear mechanism of the composites were studied. The results show that the surface free energy of 5% OTS-modified potassium titanate whiskers is the closest to that of the resin matrix, which is 26.4 mJ/m2. Moreover, the OTS-modified PTW-reinforced composites possess a more stable friction coefficient and a lower wear rate at high temperature. The OTS-modified PTW-reinforced composite (O-C) has a 19% lower total wear rate than the unmodified PTW-reinforced composite (P-C). That is mainly because the modified potassium titanate whisker is more evenly distributed in the resin matrix and tightly bonded to the resin. Results demonstrate that OTS-modified PTW-reinforced composites displayed preferable tribological performance. This article provides a new method for PTW modifications in improving the tribological performance of the resin-based friction composites.</p