Synthesis of Nanosized Lithium Manganate For Lithium-ion Secondary Batteries
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Synthesis of Nanosized Lithium Manganate For Lithium-ion Secondary Batteries Hsien-Cheng Wang, Yueh Lin, Ming-Chang Wen, and Chung-Hsin Lu Department of Chemical Engineering, National Taiwan University. Taipei, Taiwan ABSTRACT Nanosized lithium manganate powders are successfully synthesized via a newly developed reverse-microemulsion (RµE) process. Monophasic LiMn2O4 powders are obtained after calcining the precursor powders at 700oC. The particle size of the spinel compound significantly depends on the concentration of the aqueous phase. Increasing the water-to-oil volume ratio results in an increase in the particle size. While the aqueous phase is equal to 0.5 M, the size of the obtained LiMn2O4 powder is around 60-70 nm. It is found that the specific capacity of nanosized LiMn2O4 particles is greater than that of submicron particles. The large surface area of ultrafine particles is considered to facilitate the intercalation and deintercalation of lithium ions during the cycling test. INTRODUCTION Lately, lithium-ion secondary batteries have became one of the most promising candidates in the field of rechargeable batteries owing to their high working voltage, high energy density, steady discharging properties, and long cycle life. For perfecting the performance of lithium ion batteries, the electrochemical characteristics of cathode materials have been intensively investigated. A variety of lithiated transition metal oxides including LiCoO2, LiNiO2, and LiMn2O4 have been explored for utilizing as cathode electrodes in lithium-ion secondary batteries [1-4]. Among these cathode materials, lithium manganate with a spinel structure is of particular interest for using in the rechargeable cells because of its inexpensive material cost, acceptable environmental characteristics, and better safety compared to LiCoO2. However, LiMn2O4 suffers the disadvantages of relatively low discharge capacity and serious capacity fading during the cycling process [6-8]. For optimizing the electrochemical performance of LiMn2O4, a great deal of efforts have been devoted to synthesize LiMn2O4 powders with a controlled morphology [9,10]. A new reverse-microemulsion (RµE) process was thus to control the morphology and particle size of LiMn2O4 powders,developed in this study, and the electrochemical performance of the obtained powders was also evaluated. EXPERIMENTAL DETAILS Lithium nitrate (LiNO3) and manganese nitrate (Mn(NO3)2) were chosen as the starting V6.31.1
materials. The well-dispersed aqueous phase was mixed with the continuous phase that comprised oil and surfactant. After emulsifying these starting compounds, a transparent RµE system was successfully obtained. The RµE system was heated and dried for preparing the precursors of the target spinel compound. The precursor powders were calcined in a tube furnace at 350oC with a heating rate of 10oC /min to obtain the LiMn2O4 powders. The powders prepared at the cationic concentration of 0.5 M and 2.0 M were named as sample A and B, respectively. The crystallinity of the formed prod
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