Construction of Multishelled Binary Metal Oxides via Coabsorption of Positive and Negative Ions as a Superior Cathode for Sodium-Ion Batteries

Abstract

Multishelled binary metal oxide, which can exert a synergetic effect of different oxides, is a promising electrochemical electrode material. However, it is challenging to synthesize this kind of binary metal oxide due to the severe hydrolysis and/or precipitation reactions of the precursors between cations and anions of different metals. Herein, by using citric acid as a chelating agent to inhibit hydrolysis and precipitation, a series of multishelled binary metal oxide hollow spheres (Fe 2 (MoO 4 ) 3 , NiMoO 4 , MnMoO 4 , CoWO 4 , MnWO 4 , etc.) were obtained via coabsorption of negative and positive metal ions. In addition, the chelation between a metal ion and citric acid is systematically validated by NMR, MS, Raman, and UV−vis. In particular, multishelled Fe 2 (MoO 4 ) 3 hollow spheres show excellent electrochemical performance as cathode material for sodium-ion batteries benefited from their structural superiorities. Especially, the quintuple-shelled Fe 2 (MoO 4 ) 3 hollow sphere shows the highest specific capacity (99.03 mAh g −1 ) among all Fe 2 (MoO 4 ) 3 hollow spheres, excellent stability (85.6 mAh g −1 was retained after 100 cycles at a current density of 2.2 C), and outstanding rate capability (67.4 mAh g −1 can be obtained at a current density of 10 C). This general approach can be extended to the synthesis of other multishelled multielement metal oxides and greatly enrich the diversity of hollow multishelled structures.

Heterostructured TiO2 Spheres with Tunable Interiors and Shells toward Improved Packing Density and Pseudocapacitive Sodium Storage

“…Mater. 2019, 31,1904589 www.advmat.de www.advancedsciencenews.com of 162 mAh g −1 than that of heterostructured TiO 2 -HS, thus further proving the favorable synergetic effect of bronze and anatase phases ( Figure S10, Supporting Information). Furthermore, TiO 2 -HS and TiO 2 -YB anodes are selected and tested at higher rate of 1 A g −1 and the results are shown in Figure 3e.…”

“…2019, 31,1904589 understand these facts, detailed DFT simulations of the Na storage and diffusion based on the first principles are employed. Mater.…”

“…On the other hand, compared to solid particles, the empty spaces exist in hollow and hierarchical structures are capable of decreasing the material packing densities, thus leading to low volumetric energy densities. [29][30][31][32] Until now, multishelled and asymmetric particles are designed to solve this drawback caused by the "hollow characteristic," but the extra and wasted space generated by the "hierarchical characteristic" has rarely been noticed to best of our knowledge.…”

“…Mater. 2019, 31,1904589 Figure S8 of the Supporting Information to show the formation processes of final TiO 2 spheres. The weight-loss during the heating process can be ascribed to the conversion of H 2 TiO 3 to TiO 2 and the decomposition of involatile organic substances.…”

“…Mater. 2019, 31,1904589 Figure 5. Theoretical calculations of Na storage and diffusion in anatase TiO 2 .…”