Research Article Synthesis and Electrochemical Performance of LiMnPO 4 by Hydrothermal Method Daichi Fujimoto, 1,2 Yu Lei, 1 Zheng-Hong Huang, 1 Feiyu Kang, 1 and Junichi Kawamura 2 1 Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 2 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan Correspondence should be addressed to Feiyu Kang; fykang@tsinghua.edu.cn Received 14 March 2014; Accepted 4 June 2014; Published 8 July 2014 Academic Editor: Shengshui Hu Copyright © 2014 Daichi Fujimoto et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. LiMnPO 4 with olivinestructure which is the promising candidate for high voltage cathode material was synthesized by hydrothermal method. In order to synthesize high purity and well-defned LiMnPO 4 , several precursors for Li, Mn, and P sources and hydrothermal reaction parameters including temperature and [H 2 O]/[Mn] value are optimized. By analyzing the structure, Mn valence, morphology, and chemical ratio via XRD, XPS, Raman, SEM, and ICP LiMnPO 4 synthesized from manganese acetate tetrahydrate have single phase of LiMnPO 4 without impurity and showed charge and discharge reaction caused by Mn 2+ /Mn 3+ redox. Specifc capacity of synthesized LiMnPO 4 grew up during cycling. Moreover, when hydrothermal temperature was set at 150 ∘ C and [H 2 O]/[Mn] value was set at 15, discharge capacity as high as 70 mAh/g was obtained at 1/20  rate. 1. Introduction Lithium-ion batteries are used widely as mobile devices like cellphone and notebook. Recently, researchers are actively devoted into the lithium-ion battery research for high energy conversion system, such as electric vehicle. Most of present lithium-ion batteries have used LiCoO 2 as cathode which was discovered in 1980 [1]. However, LiCoO 2 which includes rare- metal Co has irreversible structure shif at discharging over 0.6 Li from LiCoO 2 that cause discharge capacity limited to 120∼130 mAh/g instead of theoretical capacity of 270 mAh/g [2]. Several alternative materials are proposed as cathode materials. In 1997, Padhi et al. reported that phospho-olivine can work as promising cathode materials for lithium-ion battery [3, 4]. Among phospho-olivine LiFePO 4 , LiMnPO 4 , LiCoPO 4 , and LiNiPO 4 are considered to be possible can- didates for lithium-ion battery. Compared to LiFePO 4 and LiCoPO 4 , LiMnPO 4 is a cathode material with high redox potential which can be used with presently available liquid electrolyte so that LiMnPO 4 exceeds the energy density of LiFePO 4 which is the most investigated electrode among LiMPO 4 family [5]. Te characteristic of this olivine structure is an inductive efect which appears due to a strong covalent bond of PO 4 − to rise up redox potential [3]. However, the strong covalent bond causes poor conductivity, decelerating the charge and discharge processes. So far, several approaches have been used to solve this problem, such as controlling the particle size, morphology, and carbon coating [6]. Solid state reaction is generally used to prepare LiMnPO 4 [7, 8]. Besides this, other approaches such as sol-gel method [9, 10], precipitation [11–13], hydrothermal [10, 14–19], solvothermal method [14, 20–22], spray pyrolysis [23], and polyol process [24, 25] are also used. Te hydrothermal method is a simple synthesis method in which precursors are put into autoclave with water and seal and heat at around 200 ∘ C. Te advantages of hydrothermal method are the capability of synthesizing at low temperature, obtaining high crystallinity, high purity material, and controlling particle size and morphology. Terefore, in this work, we further optimized synthesis parameters of hydrothermal method for LiMnPO 4 synthesis and investigated their electrochemical performance. 2. Experimental 2.1. Preparation of LiMnPO 4 . Te hydrothermal reaction of LiMnPO 4 was carried out under various conditions at 150 ∘ C Hindawi Publishing Corporation International Journal of Electrochemistry Volume 2014, Article ID 768912, 9 pages http://dx.doi.org/10.1155/2014/768912