Journal of Power Sources 195 (2010) 4318–4321 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Electrochemical instability of LiV 3 O 8 as an electrode material for aqueous rechargeable lithium batteries A. Caballero, J. Morales ∗ , O.A. Vargas Departamento de Química Inorgánica e Ingeniería Química, Universidad de Córdoba, Edificio Marie Curie, Campus de Rabanales, 14071 Córdoba, Spain article info Article history: Received 11 November 2009 Accepted 17 January 2010 Available online 25 January 2010 Keywords: Vanadium oxide Lithium cells Aqueous batteries abstract We demonstrate the unsuitability of LiV 3 O 8 as an electrode material for aqueous rechargeable lithium batteries on simple but solid grounds: the compound is unstable under typical battery operation condi- tions, where it slowly dissolves as reflected in the yellow color acquired by the electrolyte. This can be the origin of the poor performance of the aqueous batteries based on this compound. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The outstanding papers by Dahn et al. [1,2] on aqueous rechargeable lithium batteries (ARLB) encouraged research into ways of improving their poor performance by increasing their delivered capacity and life cycle [3–7]. Using an appropriate electrode material is obviously an essential pre-requisite to succeed in this respect. Several years ago, the layered phase LiV 3 O 8 was proposed by Köhler et al. [8] as anode material for these electrochemical devices. Recently, Wu and coworkers have emphasized the suitability of this compound against a wide vari- ety of cathodic materials such as LiCoO 2 [9,10], LiMn 2 O 4 [11] and LiNi 1/3 Co 1/3 Mn 1/3 O 2 [12] . The results, however, were some- what disappointing since the capacity faded continuously upon cycling. In order to shed some light on the origin of this shortcoming, we performed a systematic study of the influence of different variables starting from particle size. However, we found the origin of the poor battery performance to be related neither with this nor with any other structural property, but rather with the instability of this lay- ered oxide in contact with water. In fact, LiV 3 O 8 tends to dissolve under the battery operating conditions. Our results are consistent with the observations made by Li and Dahn [13], who ascribed capacity fading in an aqueous lithium ion battery to dissolution of the active material. ∗ Corresponding author. Tel.: +34 957 218620; fax: +34 957 218621. E-mail address: iq1mopaj@uco.es (J. Morales). 2. Experimental LiV 3 O 8 was obtained in two particle sizes: micrometric (m- LiVO) and submicrometric (sm-LiVO). The micrometric sample was prepared from a mixture of Li 2 CO 3 and V 2 O 5 (both from Merck). 10% excess of Li precursor was used and the product calcined at 600 ◦ C for 48 h. On the other hand, sm-LiV 3 O 8 , was synthesized from pre- cursors Li(CH 3 -COO) (also in a 10% in excess) and VO(C 5 H 8 O 2 ) 2 (both from Aldrich). Oxalic acid from Aldrich was added to the pre- cursor mixture in a 2:1 mole ratio in order to reduce particle size [14]. The final mixture was heated at 120 ◦ C for 5 h and then at 500 ◦ C for a further 5 h. LiMn 2 O 4 was also obtained in two differ- ent particle sizes. The method used to prepare highly crystalline nanometric particles around 40 nm in size (n-LMO) is described elsewhere [15]. The spinel with micrometric particle size (1–2 m) was obtained by applying a conventional ceramic procedure to a stoichiometric mixture of Li 2 CO 3 (Fluka) and Mn(C 5 H 7 O 2 ) 3 (Strem Chemicals) that was then calcined in the air at 900 ◦ C for 24 h. Both samples were obtained as highly pure spinels, as revealed by their XRD patterns (not shown). XRD patterns were recorded on a Siemens D5000 X-ray diffrac- tometer using non-monochromated Cu K radiation and a graphite monochromator for the diffracted beam. The scanning conditions were 5–90 ◦ (2), a 0.03 ◦ step size and 12 s per step. Transmission electron microscopy (TEM) images were obtained with a Phillips TEM instrument operating at 100 keV and SEM images with a Jeol 6400 scanning electron microscope. Electrochemical measurements were carried out in a three- electrode cell with Pt wire as counterelectrode and saturated calomelane (SCE) (supplied by CHI Instruments) as reference elec- trode. The working electrode was prepared by mixing 80 wt% 0378-7753/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2010.01.030