Improved Lithium Storage Performance of a TiO2 Anode Material Doped by Co

TiO₂ is a promising anode material for lithium-ion batteries (LIBs) due to its low cost, suitable operating voltage, and excellent structural stability. The inherent poor electron conductivity and low ion diffusion coefficient, however, severely limit its application in lithium storage. Here, Co-doped TiO₂ is synthesized by a hydrothermal method as an anode material since Co@TiO₂ possesses a large specific surface area and high electronic conductivity. Thanks to the Co dopants, the ion diffusion and electron transport are both greatly improved, which is very beneficial for cycle stability, coulombic efficiency (CE), reversible capacity, and rate performance. As a result, Co@TiO₂ shows a high reversible capacity of 227 mAh g^-1 at 3 C, excellent rate performance, and cycling stability with a capacity of about 125 mAh g^-1 at 10C after 600 cycles (1 C = 170 mA g^-1).

Vertically Aligned Binder-Free TiO2 Nanotube Arrays Doped with Fe, S and Fe-S for Li-ion Batteries

Vertically aligned Fe, S, and Fe-S doped anatase TiO₂ nanotube arrays are prepared by an electrochemical anodization process using an organic electrolyte in which lactic acid is added as an additive. In the electrolyte, highly ordered TiO₂ nanotube layers with greater thickness of 12 μm, inner diameter of approx. 90 nm and outer diameter of approx. 170 nm are successfully obtained. Doping of Fe, S, and Fe-S via simple wet impregnation method substituted Ti and O sites with Fe and S, which leads to enhance the rate performance at high discharge C-rates. Discharge capacities of TiO₂ tubes increased from 0.13 mAh cm⁻²(bare) to 0.28 mAh cm⁻² for Fe-S doped TiO₂ at 0.5 C after 100 cycles with exceptional capacity retention of 85 % after 100 cycles. Owing to the enhancement of thermodynamic and kinetic properties by doping of Fe-S, Li-diffusion increased resulting in remarkable discharge capacities of 0.27 mAh cm⁻² and 0.16 mAh cm⁻² at 10 C, and 30 C, respectively.

Improvement of Na Ion Electrode Activity of Metal Oxide via Composite Formation with Metal Sulfide

The composite formation with a conductive metal sulfide domain can provide an effective methodology to improve the Na-ion electrode functionality of metal oxide. The heat treatment of TiO₂(B) under CS₂ flow yields an intimately coupled TiO₂(B)-TiS₂ nanocomposite with intervened TiS₂ domain, since the reaction between metal oxide and CS₂ leads to the formation of metal sulfide and CO₂. The negligible change in lattice parameters and significant enhancement of visible light absorption upon the reaction with CS₂ underscore the formation of conductive metal sulfide domains. The resulting TiO₂(B)-TiS₂ nanocomposites deliver greater discharge capacities with better rate characteristics for electrochemical sodiation-desodiation process than does the pristine TiO₂(B). The ²³Na magic angle spinning nuclear magnetic resonance analysis clearly demonstrates that the electrode activities of the present nanocomposites rely on the capacitive storage of Na⁺ ions, and the TiS₂ domains in TiO₂(B)-TiS₂ nanocomposites play a role as mediators for Na⁺ ions to and from TiO₂(B) domains. According to the electrochemical impedance spectroscopy, the reaction with CS₂ leads to the significant enhancement of charge transfer kinetics, which is responsible for the accompanying improvement in electrode performance. The present study provides clear evidence for the usefulness in composite formation between the semiconducting metal oxide and metal sulfide in exploring new efficient NIB electrode materials.