Superior shuttling of lithium and sodium ions in manganese-doped titania @ functionalized multiwall carbon nanotube anodes

Abstract

In order to improve the electrochemical kinetics of anatase titania (TiO₂), Mn-doped TiO₂ incorporated with functionalized multiwall carbon nanotubes (MWCNTs) has been prepared by a modified hydrothermal method and tested for both lithium (LIB) and sodium-ion battery (SIB) anodes. The size of the TiO₂ particles is controlled to ∼35–40 nm, with almost even distribution on the MWCNTs surface. The nanostructuring and appropriate doping of cost-effective manganese into the TiO₂ host improved the electrochemical performance in terms of high rate capability and specific capacity for both the rechargeable battery systems. For the LIBs, the charge capacity of the 5% Mn-TiO₂/MWCNT anode is 226.3 mA h g⁻¹ in the first cycle, and is retained at 176.4 mA h g⁻¹ after 80 cycles as compared with the SIBs, in which the charge capacity is 152.1 mA h g⁻¹ in the first cycle, and is retained at 121.4 mA h g⁻¹ after 80 cycles. After testing the electrodes at a high current rate of 20C, the nanocomposite electrode can still demonstrate charge capacities of 131.2 and 117.2 mA h g⁻¹ at a 0.1C rate for LIBs and SIBs, respectively. The incorporation of Mn-ions (2+, 4+) is found to play a crucial role in terms of defects and vacancy creation, increasing conduction band electrons and lattice expansion to facilitate alkali metal ion diffusion for superior electrochemical performance. The combination of heteroatom doping and use of a highly conductive additive in the form of MWCNTs has resulted in excellent electrode integrity, high ion accessibility, and fast electron transport. Its outstanding cycling stability and remarkable rate performance make the 5% Mn-TiO₂/MWCNT a promising anode material for high-performance LIBs and SIBs.