h i g h l i g h t s g r a p h i c a l a b s t r a c tNanoparticles of LiMnPO 4 were fabricated in rod, elongated as well as cubic shapes. The 1D Li þ preferred diffusion direction for each shape was determined via electron diffraction spot patterns. The shape of nano-LiMnPO 4 varied the diffusion coefficient of Li þ because the Li þ diffusion direction and the path length were different. The particles with the shortest dimension along the b-axis provided the highest diffusion coefficient, resulting in the highest gravimetric capacity of 135, 100 and 60 mAh g À1 at 0.05C, 1C and 10C, respectively. Using ball-milling, a higher loading of nano-LiMnPO 4 in the electrode was achieved, increasing the volumetric capacity to 263 mAh cm À3 , which is ca. 3.5 times higher than the one obtained by hand-mixing of electrode materials. Thus, the electrochemical performance is governed by both the diffusion coefficient of Li þ , which is dependent on the shape of LiMnPO 4 nanoparticles and the secondary composite structure.

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Advanced lithium ion batteries require higher safety, lower cost, longer durability and lower toxicity to apply larger applications [1]. LiMnPO4 can be an alternative cathode material due to its stable structure, low material cost, lower toxicity, high theoretical capacity (170 mAh/g), high operating voltage (4.1 V vs. Li) and good capacity retention. However, it suffers from poor electronic and ionic conductivity [2, 3]. Its poor ionic conductivity can be overcome by employing nano-particles in order to shorten Li-ion path lengths [4, 5]. Enhancement in electron transport is achieved by carbon coated nanocomposite cathode material. Most high-performing LiMnPO4 materials were so far achieved by adding a large amount of carbon (15 – 30 wt%) in order to increase the electronic conductivity [6-9]. Recently, we reported < 30 nm sized nano-LiMnPO4 reached 97 % of theoretical capacity with 10 wt% of carbon additive in total in the electrodes [10]. It shows that controlling the particle size of LiMnPO4 and the construction of nanocomposite of nano-LiMnPO4 and carbon are critical to maximize the electrochemical properties. Therefore, we investigated further to address the following questions; i) which direction is favorable for lithium ions in different shapes of nano-LiMnPO4? ii) What is the desired composite structure to improve the electrochemical properties ? Since olivine LiMnPO4 materials have a preferred direction of lithium ion diffusion in the lattice, it can be different depending on the shapes and sizes of nano-LiMnPO4 shown in Fig. 1. Chemically exfoliated graphene from graphite flake was applied to nano-LiMnPO4, forming a thin coating on the surface of the active material shown in Fig. 2. We determined the lithium ion diffusion coefficients in terms of shapes and sizes of LiMnPO4 nanomaterials. We also studied the influence of nanocomposite structures, which affected significantly the electrochemical behavior of LiMnPO4 cathode. Several processes of making nanocomposites have been investigated to understand the kinetics of diffusivity in LiMnPO4cathode. References: [1] G.-A. Nazri, G. Pistoia, Lithium batteries: science and Technology, Kluwer Academic Publishers, USA, 2004. [2] M. Yonemura, A. Yamada, Y. Takei, N. Sonoyama, R. Kanno, J. Electrochem. Soc. 151 (2004) A1352-A1356. [3] P.P. Prosini, M. Lisi, D. Zane, M. Pasquali, Solid State Ionics 148 (2002) 45-51. [4] N.-H. Kwon, T. Drezen, I. Exnar, I. Teerlinck, M. Isono, M. Graetzel, Elecrochem. Solid State Lett. 9 (2006) A277-A280. [5] D. Wang, H. Buqa, M. Crouzet, G. Deghenghi, T. Drezen, I. Exnar, N.-H. Kwon, J.H. Miners, L. Poletto, M. Grätzel, J. Power Sources 189 (2009) 624-628. [6] S.-M. Oh, S.-W. Oh, C.-S. Yoon, B. Scrosati, K. Amine, Y.-K. Sun, Adv. Funct. Mater. 20 (2010) 3260-3265. [7] P. Barpanda, K. Djellab, N. Recham, M. Armand, J.-M. Tarascon, J. Mater. Chem. 21 (2011) 10143-10152. [8] D. Rangappa, K. Sone, Y. Zhou, T. Kudo, I. Honma, J. Mater. Chem. 21 (2011) 15813-15818. [9] H. Ji, G. Yang, H. Ni, S. Roy, J. Pinto, X. Jiang, Electrochim. Acta 56 (2011) 3093-3100. [10] N.-H. Kwon, K.M. Fromm, Electrochim. Acta 69 (2012) 38-44. Fig. 1. TEM images show the various shapes and sizes of LiMnPO4nanoparticles. Fig. 2. TEM image shows the nanocomposite containing nano-LiMnPO4 in dark color attached on the surface of graphene sheet in light color.