Nano-particle Li 4 Ti 5 O 12 spinel as electrode for electrochemical generators A. Guerfi a , S. Se ´vigny a , M. Lagace ´ a , P. Hovington a , K. Kinoshita b , K. Zaghib a,* a Institut de Recherche d’Hydro-Que ´bec, 1800 Boul., Lionel-Boulet, Varennes, Que., Canada J3X 1S1 b Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Abstract Li 4 Ti 5 O 12 was obtained by solid-state reaction of a ternary precursor mixture, TiO 2 , Li 2 CO 3 and carbon. The influences of the reaction time, temperature and mixing method on the electrochemical performance of Li 4 Ti 5 O 12 were investigated. Electrochemical measurements and XRD diffraction characterization were used to determine the reversible capacity and TiO 2 residue in the final powder, respectively. Between 1.2 and 2.0 V versus Li, a reversible capacity as high as 165 mAh/g at 7.3 mA/g was obtained. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Electrochemical generators; Solid-state reaction; Zero strain; Nano particles; Li 4 Ti 5 O 12 1. Introduction Electrodes containing Li 4 Ti 5 O 12 have good Li-ion inter- calation and de-intercalation reversibility and exhibit no structural change (zero-strain insertion material) during charge–discharge cycling. Thus, Li 4 Ti 5 O 12 is a interesting candidate in negative electrodes for solid-state [1–13] and liquid-type [1–6] lithium-ion batteries. This active material has a mid-discharge voltage close to 1.55 V versus Li þ /Li, which is very promising for electrodes in a large number of battery applications [4,5]. It can be used as an anode combined with: (a) high-voltage cathodes for Li-ion bat- teries and (b) carbon electrodes in hybrid supercapacitors suggested for the first time by Zaghib et al. [3,4]. In addition, Li 4 Ti 5 O 12 can be used as a cathode with lithium metal in primary rechargeable batteries (Fig. 1). In this paper, we report on the results obtained with a zero- stain insertion material produced by a new synthesis process. This process is based on the use of a ternary precursor material [12,14]. The intent of the present paper is to extend these studies by providing a systematic analysis of a series of Li 4 Ti 5 O 12 samples obtained by several methods. The dif- ferent parameters affecting the material performance, par- ticle size and shape were investigated. The Li 4 Ti 5 O 12 powder was characterized by X-ray diffraction (XRD) ana- lysis and scanning electron microscopy (SEM) observations. The electrochemical discharge and charge behavior was determined in a liquid electrolyte. 2. Experimental The starting materials, TiO 2 -anatase and Li 2 CO 3 , were commercially available with purities of 99 and 99.5%, respectively. A mixture of TiO 2 and Li 2 CO 3 (molar ratio Ti/Li of 2.27) was prepared by two methods. In the con- ventional method, a binary mixture of TiO 2 and Li 2 CO 3 was heated at 850 8C for 12 h in an air steam. In the second method, carbon was added to the starting materials (TiO 2 , Li 2 CO 3 ) to make a ternary mixture. Homogeneous mixed phases of the binary and ternary compositions were obtained by high-energy ball-milling. After mixing, the powders were heat treated to form the desired phases. The samples were characterized by X- ray diffraction and scanning electron microscopy. The dis- charge (intercalation)–charge (de-intercalation) cycling of Li 4 Ti 5 O 12 was carried out in 4 cm 2 laboratory cells (two electrodes) with lithium metal as the counter electrode. The initial cell chemistry is based on the following configuration: Li metal()/electrolyte/Li 4 Ti 5 O 12 (þ) with a liquid electro- lyte (EC/DMC þ LiClO 4 ). The working electrode was pre- pared from a paste mixture of Li 4 Ti 5 O 12 , carbon black for an electronic conductor additive and PVDF binder mixed in NMP. The paste was coated on aluminum Exmet. The electrode was dried under vacuum at 85 8C for 24 h before electrochemical evaluation. The discharge–charge cycling Journal of Power Sources 119–121 (2003) 88–94 * Corresponding author. Tel.: þ1-450-652-8019; fax: þ1-450-652-8424. E-mail address: karimz@ireq.ca (K. Zaghib). 0378-7753/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-7753(03)00131-9