As-grown vertically aligned amorphous TiO2 nanotube arrays as high-rate Li-based micro-battery anodes with improved long-term performanceElectrochimica Acta

About

Authors
Andrea Lamberti, Nadia Garino, Adriano Sacco, Stefano Bianco, Angelica Chiodoni, Claudio Gerbaldi
Year
2015
DOI
10.1016/j.electacta.2014.10.150
Subject
Electrochemistry / Chemical Engineering (all)

Text

s b egl 10 h

Electrochimica Acta 151 (2015) 222–229

Contents lists available at ScienceDirect

Electrochim journal homepa ge: www.elseReceived 30 June 2014

Received in revised form 27 October 2014

Accepted 29 October 2014

Available online 3 November 2014

Keywords: amorphous TiO2 nanotube anodic oxidation lithium battery rate capability cycling stability 2 anodic oxidation of a titanium foil. The formation of well-defined one-dimensional nanotubular carpets is assessed by means of morphological Field Emission Scanning Electron Microscopy characterisation, while X-ray diffraction analysis and Transmission Electron Microscopy imaging confirm the amorphous nature of the samples. The electrochemical response evaluated in lab-scale lithium cells is highly satisfying with near-theoretical initial specific capacity and remarkable rate capability, noteworthy in the absence of binders and conductive agents, which would affect the overall energy density. A specific capacity exceeding 200 mAh g1 is observed at very high 24 C and approx. 80 mAh g1 are retained even at very high 96 C rate, thus accounting for the promising prospects in storage devices conceived for high power applications. Moreover, the NTs can perform with good cycling stability and capacity retention approaching 50% of the initial value after very long-term operation along with improved durability (> 2000 cycles). ã 2014 Elsevier Ltd. All rights reserved. 1. Introduction

Microbatteries with improved storage capacity, thanks to a three dimensional (3D) electrode design, have promising prospects to be implemented in the next future Li-ion battery (LiB) market [1]. This is due to the urgent demand of on-board power supplies for smart technologies, such as smart medicine and implantable medical tools, micro-electromechanical systems (MEMS) and for many others autonomous devices [2,3].

On the anode side, LiB research and development is mainly focused on the replacement of the commercially used graphite with novel materials having higher energy density, improved rate capability and higher intrinsic safety [4,5]. Transition metal oxides (MOs, where M=Sn, Cu, Fe, Zn, etc.) have the advantages of high capacity and safety compared to conventional carbonaceous materials [6], but they suffer from severe degradation upon long-term cycling, which limits their practical application. In such a scenario, titanium dioxide (titania, TiO2) may represent an interesting alternative thanks to a high number of attractive characteristics [7]. Indeed, it has a theoretical specific capacity of about 330 mAh g1 which is only slightly lower than graphite, an outstanding structural stability upon lithium insertion/deinsertion process with a limited volume change of < 4%, and a high operating potential which assures an enhanced battery safety. Significant drawbacks of titania in its bulk form are the poor lithium diffusion rate and electronic conductivity. It has been well established that the lithium intercalation activity and cycling stability strongly depend on the electrode material morphology, and nanostructuration has been found to drastically improve these features [8,9].

An interesting approach is the preparation of nanotubular electrode films [9–14].

Among the amount of approaches for the synthesis of TiO2 ordered nanostructures, anodic oxidation is now a well-established technique as it can provide large area uniform nanotubular arrays with relatively high specific surface and interesting characteristics in various applications [15–19]. The quasi onedimensional structure coupled with the vertical arrangement of the anodically grown nanotubes (NTs) can improve the charge carrier transport exploiting the unidirectional path along the tube. * Corresponding author . Tel.: +39 011 090 7394; fax: +39 011 090 7399. ** Corresponding author.: Tel. +39 011 090 4643/4638; fax: +39 011 090 4699.

E-mail addresses: andrea.lamberti@polito.it (A. Lamberti), claudio.gerbaldi@polito.it (C. Gerbaldi). http://dx.doi.org/10.1016/j.electacta.2014.10.150 0013-4686/ã 2014 Elsevier Ltd. All rights reserved.As-grown vertically aligned amorphou high-rate Li-based micro-battery anodes performance

Andrea Lamberti a,b,*, Nadia Garino b, Adriano Sacco

Angelica Chiodoni b, Claudio Gerbaldi a,b,** aDepartment of Applied Science and Technology – DISAT, Politecnico di Torino, C.so Duca d bCenter for Space Human Robotics @Polito, Istituto Italiano di Tecnologia, Corso Trento 21,

A R T I C L E I N F O

Article history:

A B S T R A C T

Vertically oriented arrays of TiO2 nanotube arrays as with improved long-term , Stefano Bianco b, i Abruzzi 24, 10129 Torino, Italy 129 Torino, Italy igh surface area TiO nanotubes (NTs) are fabricated by the fast and facile ica Acta v ier .com/locate /e lectacta

Moreover the nanopores (inner space of the tubes) may provide preferential channels for the quick diffusion of the electrolyte, simplifying the Li+ ions insertion/deinsertion at the inner NT surface with a consequent improvement of the overall electrochemical performances [20,21].

As-grown anodically oxidized TiO2 nanotubular carpets are fully amorphous in nature [22]. As recently demonstrated [23–26], this may not be a drawback when their application in Li- or Nabased secondary batteries is envisaged. Since amorphous titania has poor semiconducting characteristics, its interesting electrochemical behaviour may be related to its defective nature and intrinsic structural features. Indeed, the nanotubular amorphous structure is more disordered than the crystalline one obtained upon annealing, thereby resulting in a higher number of defects (e.g., oxygen vacancies which exist in n-type semiconducting titania acting as donors) [27], that can provide higher carrier concentration [27] and more active sites [26,28]. Moreover, asgrown NTs are composed by two distinct walls (i.e., a porous inner core and a more compact outer shell), but the two walls are well interpenetrated with very good interfacial characteristics thus, in principle, resulting in an efficient electron exchange. On the contrary, when the samples are crystallized into their anatase phase upon annealing, a partial separation between these two walls may occur, thus increasing the transport resistance from one to the other and, eventually, resulting in a progressive performance decay upon very long-term cycling [29,30].