Improving the Electrochemical Properties of Self-Organized Titanium Dioxide Nanotubes in Lithium Batteries by Surface Polyacrylonitrile Electropolymerization

Abstract

The surface of the amorphous TiO 2 nanotubes is critical to achieve high capacity, cycling stability and high rate performance. In order to improve the stability of nanotubular titanium dioxide electrodes in lithium batteries, polyacrylonitrile (PAN) has been deposited by electropolymerization. Self-organized TiO 2 nanotubes were prepared by titanium anodization with different aspect ratios. After electropolymerization, electron microscopy, composition mapping and XPS data confirmed that electrododeposited PAN covered the complete surface of open ends of the nanotubes, exclusively. The resulting electrode material was tested in lithium cells, and showed reversible areal capacities in the order of 0.5 mAhcm −2 and good cycling behavior and within a wide potential window (0.0-3.0 V). The improvement of the electrochemistry is more evident for the lower aspect ratio nt-TiO 2 , with capacity values normalized by the nanotubes length of around 0.25 mAh cm −2 μm -1 at slow rate. An areal capacity of 0.26 mAh cm −2 is delivered at 75C rate. The ion-conducting PAN layer ensures lithium ion access to the nanotubes, protects the open end surface from undesirable reactions with the electrolyte and provides enhanced mechanical stability to the electrode and lower charge transfer resistance. It is well known that self-organized titanium dioxide nanotubes (nt-TiO 2 ) can be grown by anodization of a titanium flat surface without the need of templates. 1,2 In recent years, the use of nt-TiO 2 in field of lithium ion batteries was found to be particularly promising. 3,4 Besides the lower theoretical capacity for lithium intercalation into TiO 2 (335 mAhg −1 for a maximum LiTiO 2 stoichiometry) as compared with graphite (372 mAhg −1 ), the higher voltage for Li intercalation could avoid lithium electroplating processes and thus increase the safety of current lithium-ion batteries. In addition to the insertion of Li into TiO 2 by a faradaic-type reaction involving the Ti 4+ /Ti 3+ redox pair, lithium ions may also be stored in the surface of the TiO 2 nanoparticles and increase the overall capacity by pseudocapacitive reactions and double layer phenomena. 5,6 In this line, Borghols et al.proposed that part of the extra capacity for amorphous TiO 2 nanoparticles may be due to the reversible lithium storage in the form of Li 2 O at the TiO 2 surface. 7 For nt-TiO 2 , a greater proportion of surface sites for reaction with lithium and a smaller proportion of interstitial sites for lithium insertion into bulk TiO 2 would be expected. Moreover, the high aspect ratio of nt-TiO 2 , defined as the nanotube length-to-outer diameter ratio, allows achieving higher areal capacities, which is particularly useful for the development of 3D microbatteries with high power density and fast charge properties. 4,8 On the other hand, some limitations are inherent to the use of TiO 2 electrodes. Both the Jahn-Teller effect of Ti 3+ ions and phase transitions can produce strains in crystalline TiO 2 and capacity fade on electrochemical charge-discharge ...

Controlled Growth and Application in Lithium and Sodium Batteries of High-Aspect-Ratio, Self-Organized Titania Nanotubes

“…2 The possible formation of a passivating film that avoids the consumption of electrolyte on the surface of nt-TiO 2 is not wholly confirmed, but several studies have inferred its existence. 2,37 In order to achieve high power batteries, the retention of the capacity at high current density is critical. Thus, we have studied the cycling at several current densities (Figs.…”

“…Two main mechanisms can contribute to the reversible capacity of amorphous nt-TiO 2 . 2,6 One of these mechanisms is the lithium insertion into TiO 2 with the consequent reduction from Ti 4+ to Ti 3+ , typically up to x = 0.5 in anatase-type Li x TiO 2 although x may be larger for amorphous titania. The electrochemical Li insertion into anatase leads to two two-phase regions: first the anatase/Lititanate (α/β) coexistence, and second the phase coexistence between Li-titanate and the Li 1 TiO 2 phase (β/γ).…”

Self‐Organised TiO2 Nanotubes for 2D or 3D Li‐Ion Microbatteries

“…Djenizian and co‐workers have studied the lithium storage behaviour of self‐organised TiO 2 nanotubes coated with a layer of room‐temperature Li + ‐conducting gel‐type PEO‐PMMA copolymer (see Figure 33 a–d) 39b. 149b, 156 Nacimiento et al 157. have shown that improvements in the lithium storage behaviour of self‐organised TiO 2 nanotubes can be obtained by coating the nanotubes with Li + ‐conducting polyacrylonitrile through the use of electropolymerisation.…”

Strain‐Driven Formation of Multilayer Graphene/GeO2 Tubular Nanostructures as High‐Capacity and Very Long‐Life Anodes for Lithium‐Ion Batteries

“…The plots clearly show that the diameter of the semicircle of the graphene/GeO 2 microtubes is much smaller than that of the pure GeO 2 electrode, indicating that the presence of graphene enhances the charge transfer process compared to pure GeO 2 . The results are fitted according to an equivalent circuit [Re (Rct CPE1) CPE2], where Re represents the effective series resistances of the electrode, electrolyte and separator, Rct is the Faradic charge‐transfer resistance, and CPE1 and CPE2 are constant phase elements 32, 34. The fitting results yield effective series resistances of graphene/GeO 2 and pure GeO 2 electrodes of 16 and 22 Ω, respectively.…”