Journal of Energy Chemistry 24(2015)157–170 Enhanced electrochemical performance of Li-ion batteries with nanoporous titania as negative electrodes Md. Arafat Rahman a , Xiaojian Wang a , Cuie Wen a,b∗ a. Faculty ofScience, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia; b. School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University Bundoora, Victoria 3083, Australia [ Manuscript received September 15, 2014; revised November 9, 2014 ] Abstract Nanoporous anatase TiO 2 (np-TiO 2 ) electrodes have been developed via the anodization of titanium foils in fluoride containing electrolytes, and its application in rechargeable lithium-ion batteries (LIBs) was investigated. Four different types of np-TiO 2 electrodes with different pore diameters of 14.7±8.2 nm, 12.8±6.8 nm, 11.0±5.5, and 26.7±13.6 nm were fabricated for evaluating the effect of nanoporous characteristics on the LIB performance. The discharge capacity of the four battery types 1, 2, 3, and 4 were 132.7 mAh·g −1 , 316.7 mAh·g −1 , 154.3 mAh·g −1 , and 228.4 mAh·g −1 , respectively. In addition, these electrodes 1, 2, 3, and 4 exhibited reversible capacity of 106.9 mAh·g −1 after 295th, 180.9 mAh·g −1 after 220th, 126.1 mAh·g −1 after 150th, and 206.7 mAh·g −1 after 85th cycle at a rate of 1 C, respectively. It was noted that the cyclic life of the batteries had an inverse relationship, and the capacity had a proportional relationship to the pore diameter. The enhanced electrochemical performance of the nanoporous electrodes can be attributed to the improved conductivity and the enhanced kinetics of lithium insertion/extraction at electrode/electrolyte interfaces because of the large specific surface area of np-TiO 2 electrodes. Key words nanoporous TiO 2 ; negative electrode; capacity; lithium-ion batteries 1. Introduction Lithium-ion batteries (LIBs) are one of the most promis- ing energy storage systems for the portable power market [1], which have attracted enormous attention for several years be- cause of their large-scale energy storage applications, such as for solar and wind power [2], electric vehicles (EV) and hy- brid electric vehicles (HEV) [3]. LIBs have been very suc- cessful in the division of portable electronics since their first commercialization by Sony in the early 1990s [4]. However, further improvements in terms of power densities, safety, cost effectiveness, and lifetime require new materials or new struc- tures with a higher storage capacity, faster charge/discharge rates and desirable potential for wider applications [5,6]. In principle, the thermodynamics of lithium insertion into the electrochemically active phase is affected by the nanosized structure of the host materials [7−9]. Extensive investigations have been carried out on the nanostructured materials because of their beneficial properties, such as shortened diffusion paths for both electronic and ionic transport, and also a large electrode-electrolyte contact area [10−12]. Among various kinds of nanostructured materials, nanoporous materials have received particular attention since they can be more effective in increasing the electrode stability and Li intercalation ca- pacity, especially at high charge/discharge rates. Electrodes of nanoporous, especially mesoporous (2−50 nm) materi- als for lithium batteries have short transport lengths for Li + ions due to their nanosized grains (10−20 nm), and easy ac- cess for electrolytes due to their nanopores (5−10 nm) [13]. Therefore, attempts have been made to synthesize hierarchi- cal, porous, nanometer-sized materials for applications in neg- ative electrode materials for stationary energy storages with high discharging potential [14−18]. Transition-metal oxides (TMOs) have been extensively studied as negative electrodes since the reaction of nanosized TMOs with Li + in the solid state was reported [19]. The nano- sized pores play a considerable role in shortening the lithium- diffusion length in the solid phase, as long as the electrolytes can penetrate the pores, thus enabling fast transport towards the interior of the solid. Among various TMOs, TiO 2 has been considered as one of the promising electrode materials for LIBs. Various polymorphs of titania such as rutile [20], anatase [18,21] and TiO 2 (B) [22−25] have been studied as ∗ Corresponding author. Tel: +61-3-92145651; Fax: +61-3-92145050; E-mail: cwen@swin.edu.au This work was supported by the Australia-India Strategic Research Fund (AISRF, ST060048). Copyright©2015, Science Press and Dalian Institute of Chemical Physics. All rights reserved. doi: 10.1016/S2095-4956(15)60296-0