Electrochimica Acta 56 (2011) 3406–3414 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Effect of sintering temperature on microstructure and transport properties of Li 3x La 2/3-x TiO 3 with different lithium contents Hongxia Geng, Jinle Lan, Ao Mei, Yuanhua Lin, C.W. Nan ∗ State Key Laboratory of New Ceramics and Fine Processing and Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China article info Article history: Received 19 March 2010 Received in revised form 10 June 2010 Accepted 11 June 2010 Available online 17 June 2010 Keywords: Li3xLa 2/3-x TiO3 Solid electrolyte Sol–gel Ionic conductivity Ceramics abstract Li 3x La 2/3-x TiO 3 (LLTO) powder with different lithium contents (nominal 3x = 0.03–0.75) was synthesized via a simple sol–gel route and then calcination of gel-derived precursor at 900 ◦ C which was much below the calcination temperature required for synthesizing the LLTO powder via solid state reaction route. The LLTO powder of sub-micron sized particles, derived from such sol–gel method, showed almost no aggregation. Starting from the sol–gel-derived powder, the LLTO ceramics with different lithium contents were prepared at different sintering temperatures of 1250 and 1350 ◦ C. It demonstrated that our sol–gel route is quite simple and convenient compared to the previous sol–gel method and requires lower tem- perature for the LLTO. Our results also illustrated that lithium content significantly affects the structure and ionic conductivity of the LLTO ceramics. The dependence of the ionic conductivity on the lithium content, lattice structure, microstructure and sintering temperature was investigated systematically. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction An inorganic solid state electrolyte with high ionic conductiv- ity would show extensive potential applications in secondary solid state lithium batteries due to high safety and high discharge–charge potential of lithium [1,2]. In the last few years, a lot of attention was paid to the perovskite-type Li 3x La 2/3-x TiO 3 (LLTO), a promis- ing electrolyte material that has an excellent ionic conductivity of up to 10 -3 S/cm at room temperature [3]. However, the total conductivity of such LLTO polycrystalline ceramics is much lower due to the impediment from grain boundaries [4]. So far several approaches, for example, substitution of A and B-sites by other atoms and introduction of a second phase into the LLTO matrix [3,5–11], have been proposed to enhance the ionic conductivity of LLTO ceramics. As well known, LLTO crystal is constructed by TiO 6 octahedra, with Li + and La 3+ occupying in the A-sites. The vacan- cies in the A-sites allow the lithium ions to move throughout the lattice, presenting ionic conductivity over a wide range of com- positions [12]. In addition, the microstructure, e.g., grain size and morphology, as well as the lithium content plays a key role on the ionic conductivity. Thus the processing parameters such as sinter- ing temperature and holding time on which ceramic microstructure is dependent would affect their electrical properties [13]. So it is very useful to investigate the preparation methods so as to enhance the overall ionic conductivity further. However, so far the LLTO ∗ Corresponding author. Tel.: +86 10 62773587; fax: +86 10 62772507. E-mail address: cwnan@mail.tsinghua.edu.cn (C.W. Nan). ceramics have been prepared generally using solid state reaction at high temperature of about 1350 ◦ C [14–16]. The high sintering temperature and long holding time in solid state reaction method could lead to a serious loss of lithium, opposite to the improvement of lithium ionic conductivity. Therefore, the synthesis processing like sol–gel method, pulsed laser deposition, microwave sintering method and so on was applied to prepare LLTO ceramics [17–22]. Among these methods, sol–gel method requires relatively low cal- cination temperature for the powder preparation, contributing to highly stoichiometric composition, less loss of lithium and homoge- neous mixing of the raw materials. The sol–gel method was applied to prepare the LLTO powder using metal alkoxides as starting mate- rials which are unstable in air with serious moisture absorption [23,24], followed by heat treatment at high temperature of 1300 ◦ C. Vijayakumar et al. prepared the LLTO powder using La 2 O 3 , Li 2 CO 3 , H 2 O 2 , NH 3 ·H 2 O, Ti metal powder and citric acid [17]. However, the La 2 O 3 involved needs to be heat-treated in air at 1000 ◦ C for 10 h to remove moisture absorbed. In addition, the preparation process- ing of the polymerized precursor was quite complicated. Recently, Ionela Carazeanu Popovici et al. used citric acid and ethylene glycol to get the condensation polymerization between them in order to obtain LLTO powder [21]. The present work aims to investigate a simple sol–gel route for the preparation of LLTO powder. Using our sol–gel route for LLTO preparation, the sub-micron sized LLTO powder and the dense LLTO ceramics made from sol–gel powder are produced. The procedure is quite convenient and low-cost due to use of trinitrates with com- mercial applicability as raw materials instead of alkoxides or La 2 O 3 and Li 2 CO 3 sensitive to moisture. Furthermore, the influence of the 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.06.031