Synthesis and Characterization of Silica-LiMn 2 O 4 Core-Shell Nanosphere Cathodes
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Synthesis and Characterization of Silica-LiMn2O4 Core-Shell Nanosphere Cathodes Jong-Moon Lee1, Soon-Kie Hong1, Won Il Cho2, In-Hyeong Yeo3 and Sun-il Mho1 1
Division of Energy Systems Research, Ajou University, Suwon 443-749, Korea
2
Center for Energy Convergence, Korea Institute of Science and Technology, Seoul 136-791,
Korea 3
Department of Chemistry, Dongguk University, Seoul 100-715, Korea
ABSTRACT In order to improve the charge/discharge cycling performance of the LiMn2O4 cathode, the spinel LiMn2O4 is coated on the structurally stable SiO2 nanosphere cores, LiMn2O4@SiO2. The core-shell LiMn2O4@SiO2 nanosphere cathodes are prepared by the MnCO3 precipitation on the silica surface and the following solid state reaction of MnCO3@SiO2 with a lithium salt. The charge/discharge cycle stability has improved by the nanostructural characteristics of the LiMn2O4@ shell on the SiO2 core. The cathode composed of LiMn2O4@SiO2 nanospheres exhibits higher capacity retention of 97% than that of LiMn2O4 nanoparticles of 89%, after 100 battery cycles at a 10C rate. INTRODUCTION The spinel-structured LiMn2O4 is of great interest as a cathode material for lithium ion batteries because of the structural characteristics with the 3-D path of lithium ion, high operating voltages, moderate theoretical capacities, and acceptable environmental friendliness [1-11]. In the case of LiMn2O4 spinel, the cathodes suffer from poor cycling performance for long life operating, especially at high temperatures, which is caused by the dissolution of Mn2+ formed from the disproportion reaction of Mn3+ and the structural deformation resulted from the JahnTeller effect of Mn3+ formed by the Mn4+/Mn3+ redox reaction at discharged states. Much effort has made to diminish the Mn2+ dissolution at the interface and to reduce the structural deformation during the charge/discharge process by surface modifications[2-7], by doping with various materials [8,9], and by reducing the LiMn2O4 particle sizes[9-11]. By coating various oxides, such as Al2O3, ZrO2, SiO2, and ZnO, the Mn dissolution during cycling test can be decreased as a result of retarding the interface reaction between the electrode and electrolyte [6,7]. In addition, structural instability was able to be reduced by incorporating cations (Al, Ni, Mg, etc.) into the Mn3+ lattice sites [8,9]. Long-term cyclability and high specific capacities were also able to obtain by utilizing the advantage of nanomaterials [9-11]. The high specific capacity certainly results from the large specific surface area and the reduced Li+ diffusion path lengths in the materials. In this work, spinel LiMn2O4 was formed on the surface of structurally stable SiO2 nanosized sphere cores, LiMn2O4@SiO2 nanosphere, as a nanoengineered cathode material.
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EXPERIMENTAL Firstly, SiO2 nanosph
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