The surface science of titanium dioxide

Research Development on Sodium-Ion Batteries

Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.

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Sodium-ion batteries: present and future

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Density functional theory (DFT) computations were performed to investigate the electronic properties and Li storage capability of Ti3C2, one representative MXene (M represents transition metals, and X is either C or/and N) material, and its fluorinated and hydroxylated derivatives. The Ti3C2 monolayer acts as a magnetic metal, while its derived Ti3C2F2 and Ti3C2(OH)2 in their stable conformations are semiconductors with small band gaps. Li adsorption forms a strong Coulomb interaction with Ti3C2-based hosts but well preserves its structural integrity. The bare Ti3C2 monolayer exhibits a low barrier for Li diffusion and high Li storage capacity (up to Ti3C2Li2 stoichiometry). The surface functionalization of F and OH blocks Li transport and decreases Li storage capacity, which should be avoided in experiments. The exceptional properties, including good electronic conductivity, fast Li diffusion, low operating voltage, and high theoretical Li storage capacity, make Ti3C2 MXene a promising anode material for...

Are MXenes Promising Anode Materials for Li Ion Batteries? Computational Studies on Electronic Properties and Li Storage Capability of Ti3C2 and Ti3C2X2 (X = F, OH) Monolayer

Diffusion of Li and Na ions in TiO2, anatase, has been studied using theoretical (quantum chemical ab initio periodic Hartree−Fock and a modified semiempirical INDO) as well as electrochemical (chronocoloumetry) methods. On the basis of the theoretical calculations, the geometry of equilibrium and transition states for the impurities as well as the crystalline framework are analyzed and discussed. The calculated activation energies for Li+ and Na+ diffusion were found to be only slightly higher than 0.5 eV by both theoretical methods. The agreement of either theoretical method with the electrochemical experiments, 0.60 and 0.52 eV for Li+ and Na+, respectively, is also remarkably good.

Li and na diffusion in tio2 from quantum chemical theory versus electrochemical experiment

Motivated by recent developments concerning coloration and energy storage in lithium intercalated nanostructural TiO2, quantum chem. Hartree-Fock calcns. have been carried out to study lithium atom intercalation in rutile and anatase. Equil. geometries and effective at. charge were obtained for the rutile (110) and anatase (101) clean surfaces. Li-induced local one-electron energy levels were found in the gap between the upper valence band and the conduction band and could be attributed to Ti3+ states. The absorption energies obtained are compared with available exptl. data. The equil. positions of the Li atom and its surrounding host atoms have been calcd. for both structures. The results predict a higher possibility of lithium intercalation in the anatase structure than in rutile.

Theoretical study of lithium intercalation in rutile and anatase

Bi-isonicotinic acid ~2,28-bipyridine–4,48-dicarboxylic acid! is the ligand of several organometallic
dyes, used in photoelectrochemical applications. Therefore the atomic scale understanding of the
bonding of this molecule to rutile TiO2(110) should give insight into the crucial dye–surface
interaction. High resolution x-ray photoelectron spectroscopy ~XPS!, near edge x-ray absorption
fine structure ~NEXAFS!, and periodic intermediate neglect of differential overlap ~INDO!
calculations were carried out on submonolayer bi-isonicotinic acid rutile TiO2(110). Data from
multilayers is also presented to support the submonolayer results. For a multilayer, XPS shows that
the carboxyl groups remain in the ~pristine! protonated form, and NEXAFS show that the molecular
plane is tilted by 57° with respect to the surface normal. For the submonolayer, the molecule bonds
to the rutile TiO2(110) surface via both deprotonated carboxyl groups, with a tilt angle of 25°, and
additionally an azimuthal orientation of 44° with respect to the @001# crystallographic direction. The
adsorbant system was also investigated by quantum mechanical calculations using a periodic INDO
model. The most stable theoretical adsorption geometry involves a twist around the molecular axis,
such that the pyridine rings are tilted in opposite directions. Both oxygen atoms of each carboxyl
group are bonded to five-fold coordinated Ti atoms ~2M-bidentate!, in excellent agreement with the
experimental results.

Adsorption of Bi-Isonicotinic Acid on Rutile TiO2 (110)

Al-doped ZnO: Electronic, electrical and structural properties

The semiempirical intermediate neglect of differential overlap method was used for calculating optical properties of ${\mathit{F}}^{+}$ and F centers (oxygen vacancy trapped one and two electrons, respectively) embedded into large quantum clusters, ${\mathrm{Al}}_{26}$${\mathrm{O}}_{39}$. The geometry was optimized for both the ground and excited states of defects. Calculated absorption and luminescence energies obtained for ${\mathit{F}}^{+}$ and F centers are in good agreement with experimental data. Their energy levels lie in the gap between the upper valence band and conduction band, like for similar centers in MgO and alkali halides. It is shown that the oxygen vacancy in corundum crystals is able also to trap a third electron; experimental evidence for this is discussed.

Arvids Stashans

Papers

Li and na diffusion in tio2 from quantum chemical theory versus electrochemical experiment

Theoretical study of lithium intercalation in rutile and anatase

Adsorption of Bi-Isonicotinic Acid on Rutile TiO2 (110)

Al-doped ZnO: Electronic, electrical and structural properties

Calculations of the ground and excited states of F-type centers in corundum crystals.