The crystal structure and Li storage properties of Cu-doped rutile TiO2 after a phase change caused by lithiation were investigated for the first time. Structural analysis results confirmed that undoped rutile TiO2 was transformed to a disordered layered rock-salt LixTiO2 structure with a small volume expansion of only 1 % when cycled in a potential range of 1.0−3.0 V vs. Li + /Li. A substitutional solid solution of Cu 2+ was formed in layered LixTiO2. The Cu doping increased both the interlayer distance and electronic conductivity of the layered LixTiO2. As an Li-ion battery anode, a Cu-doped TiO2 electrode exhibited a long cycle life, maintaining a reversible capacity of 120 mAh g −1 over 10000 cycles at 5C and an excellent rate capability of 108 mAh g −1 at 50C. Furthermore, this electrode could also be potentially used as a Na storage material. These attractive properties demonstrate high applicability of Cu-doped rutile TiO2 as a novel anode material.

We hydrothermally synthesized In-doped rutile TiO 2 particles in an anionic surfactant solution and investigated the influences of In doping and the particle morphology on the Na + storage properties. The solid solubility limit was found to be 0.8 atom % in In-doped TiO 2 . In the case where no surfactant was used, the best anode performance was obtained for 0.8 atom % In-doped TiO 2 electrode by the benefits of three doping effects: (i) expanded diffusionpath size, (ii) improved electronic conductivity, and (iii) reduced electron charge density in the path. Further enhancement in the performance was achieved for the In-doped TiO 2 with a reduced particle length by the synthesis in the surfactant solution. This electrode exhibited a better cycle stability and maintained a high discharge capacity of 240 mA h g −1 for 200 cycles. The reason is probably that Na + can be inserted in the inner part of TiO 2 particles because of its reduced particle length.

We attempted to improve electrochemical performances of a rutile TiO 2 electrode as a Li-ion battery anode by doping with two kinds of elements with different ionic sizes. When Nb 5+ and Fe 3+ were doped into TiO 2 , the total doping amount could be increased up to 11 at.% because the doping amounts of Nb 5+ (9 at. %) and Fe 3+ (2 at.%) could exceed their solubility limits. It is considered that the compressive strain caused by the doping of larger Nb 5+ than Ti 4+ could be partially offset by the tensile strain induced by the doping of smaller Fe 3+ . The Fe−Nb-doped TiO 2 anode exhibited an excellent cycle performance and a good highrate performance. We consider that these performances are attributed to the lattice parameter expansion and the electronic conductivity enhancement based on the increasing doping amount.

Assessing the recovery of Vietnam's economy, domestic and international experts said that Vietnam's economy is "resilient and recovering", gradually becoming a destination of interest for foreign investors. Evidence of the recovery of Vietnam's economy are economic indicators such as GDP growth rate, total retail sales of consumer goods and services, number of newly registered enterprises, production and business situation... of the first quarter of 2022 all increased compared to the first quarter of 2021. However, according to experts, Vietnam's economy has not yet maximized resource efficiency. The article mentions the recovery results of Vietnam's economy and solutions for Vietnam's economic development after the Covid-19 pandemic.