Electrochimica Acta 95 (2013) 295–300 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Optimization of electrophoretic suspension to fabricate Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 based positive electrode for Li-ion batteries K. Prasanna, T. Subburaj, Yong Nam Jo, Chang Woo Lee ∗ Department of Chemical Engineering, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Gihung, Yongin, Gyeonggi 446-701, South Korea a r t i c l e i n f o Article history: Received 5 December 2012 Received in revised form 12 January 2013 Accepted 21 January 2013 Available online 13 February 2013 Keywords: Li-ion batteries Positive electrode Electrophoretic deposition Box-Bhenken design a b s t r a c t A direct deposition technique based on electrophoresis is employed to prepare positive electrode for Li- ion batteries. Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 (active material), denka black (conductive agent) and PVDF (binder) is dispersed in the solvent and used as a suspension for electrophoretic deposition (EPD) process. The Box-Bhenken design is made to optimize the EPD suspension, by varying three controllable input factors namely weight of active material, conductive agent and binder. The output responses are initial discharge capacity and capacity retention ratio. There is a good agreement between the actual and predicted values. The adequacies of the models are established with analysis of variance. The response surface methodology with desirability function is used to determine the optimum deposition condition to obtain maximum initial discharge capacity and capacity retention ratio for the EPD prepared positive electrode. The devel- oped design predicts the 500 mg of active material, 10 mg of conductive agent and 30 mg of binder as an optimum condition for maximum discharge capacity of 152 mAh/g and capacity retention ratio of 93%. For confirmation, the electrode prepared with these optimum parameters gives discharge capacity of 147.18 mAh/g and capacity retention ratio of 97.11%. EPD process is suggested to be efficient for fabrica- tion of positive electrode under the predicted optimal condition in accordance to the positive electrode prepared by Doctor blade method. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction EPD the most popular manufacturing methods of engineering materials have been chosen for this study due to its low cost, flexi- bility and efficiency [1,2]. EPD have been applied to the well-known positive electrodes in Li-ion batteries such as LiCoO 2 and LiMn 2 O 4 [3]. EPD process begins with well dispersed powder material in a solvent and uses an electric field to move the powder particles into a desired arrangement on an electrode surface. Compared to the commonly used Doctor blade method of preparing electrode, EPD have several advantageous factors like shorter duration for preparation of electrode, uniform distribution of materials, uniform thickness of electrode and proper density of electrode [4]. EPD pro- cess is carried out in the suspension consisting of active materials, conductive agents and binder. During the EPD process these three materials deposits simultaneously on a substrate by applying a high voltage to a simple electrochemical cell. The composition of the suspension should be optimized to obtain high-performance elec- trodes for Li-ion batteries. The deposition depends on the surface characteristics, molecular weight and percentage of each material in the EPD suspension [5]. Therefore the amount of active material, ∗ Corresponding author. Tel.: +82 31 201 3825; fax: +82 31 204 8114. E-mail address: cwlee@khu.ac.kr (C.W. Lee). conductive agent and binder in the suspension should be opti- mized. Optimization is practically difficult using the conventional experimentation; it could be achieved with the help of experi- mental design tool. In the present investigation, it is attempted to evaluate the materials involved in the suspension for EPD pro- cess using the response surface methodology (RSM) [6]. RSM is a statistical and mathematical technique used for modeling and optimization of processes in which a response of interest is influ- enced by several variables. The RSM has important application in the design, development and formulation of new products, as well as in the improvement of existing product designs. It defines the effect of the input variables on the process, either individually or collectively. Further, the experimental methodology generates a mathematical model, which describes the chemical or biochemical processes. RSM design is made keeping all the variables constant except the variables to be evaluated. RSM reveals the effect of the chosen parameters under set conditions, assuming that variables are independent and that the effect will be the same at other values of the remaining variables [7]. In this experiment the widely used Li[Ni 1/3 Co 1/3 Mn 1/3 ]O 2 have been chosen as active material, due to its high theoretical capacity, zero phase change during charge/discharge cycles, good thermal stability and high safety [8,9]. It had been dispersed in the EPD solution along with denka black and PVDF. RSM procedures were employed in modeling and optimization of materials used in the 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.01.102