An electrochemical investigation of rutile TiO₂ microspheres anchored by nanoneedle clusters for sodium storage

Abstract

Rutile TiO2 microspheres anchored by nanoneedle clusters, as a new class of anode materials, are successfully employed for sodium-ion batteries and manifested good energy storage behavior. The initial discharge capacity of 308.8 mA h g(-1) is obtained and a high reversible capacity of 121.8 mA h g(-1) is maintained after 200 cycles at a current density of 0.1 C, exhibiting a high capacity retention of 83.1%. All these merits are not only ascribed to the rutile TiO2 crystal structure, but also thanks to the porous morphology of hundreds of nanoneedle clusters in favor of sodium diffusion and accommodating the strain during the sodiation and desodiation processes. Therefore, it is highly expected that rutile TiO2, as a feasible electrochemical sodium storage material, can be a new promising candidate as an anode for sodium-ion batteries.

Insertion of Mono- vs. Bi- vs. Trivalent Atoms in Prospective Active Electrode Materials for Electrochemical Batteries: An ab Initio Perspective

“…We considered (100) and (111) reconstructed surfaces. We found that Li insertion barriers into (100) and (111) bare surfaces are about 1 and 1.1 eV, respectively. These are much larger barriers than the well-studied diffusion barriers of Li in bulk Si, which are on the order of 0.5 eV, and could be the kinetic bottleneck in initial stages of lithiation.…”

“…These barriers can be significantly changed by the presence of EC: the EC molecule can adsorb on these surfaces in a molecular, semi-dissociated (SD) configuration or a ketone-like configuration, with a preference for SD. The SD configuration, whose formation is very exothermic, lowers the insertion barrier of a neighboring Li atom by about 0.2 eV on the (100) surface but raises it by a similar amount on (111). The ketone-like configuration, however, which is only by about 0.2 eV less stable on the (111) surface, raises the barrier by 0.4 eV.…”

“…Our estimated voltage for magnesiation of the anatase phase (about 0.9 V, note that the numbers in Figure 9 are for defect formation energies and expected voltage is −E f /q) was shortly after confirmed experimentally [113]. For cases where there were no measurements or where the experimental results in different publications are contradictory (e.g., Na in rutile where both activity and lack of activity were reported [108,109,111]), our calculations provided practically useful information on the contribution to voltage due to the properties of the material itself, which is not directly accessible in experiments which compound contributions from interfaces, nanosizing, binders etc. An important finding is that amorphization of TiO 2 strengthens binding of Li, Na, and Mg vs any crystalline phase and can be used to control voltage.…”

“…The ketone-like configuration, however, which is only by about 0.2 eV less stable on the (111) surface, raises the barrier by 0.4 eV. Focusing on the (111) surface, in Ref. [11], we compared insertion barriers of Li, Na, and Mg.…”

“…We have produced the first comparative computational study [22] of Li, Na, and Mg interaction with four phases of titania which are intensely studied by experimentalists as potential electrode materials: anatase, rutile, (B), and amorphous TiO2 [39,[100][101][102][103][104][105][106][107][108][109][110][111][112]. Interaction energies were mapped for the first time among the three types of inserted metal atoms and four phases.…”