High Rate Performance of Nano-Structured LiFePO 4 /C Cathode Material Prepared by a Polymer-Assisted Method from Inexpen
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h Rate Performance of Nano-Structured LiFePO4/C Cathode Material Prepared by a Polymer-Assisted Method from Inexpensive Iron(III) Raw Material Wenjing Pua, b, *, Wei Lua, **, Zhipeng Chena, Kai Xiec, and Chunman Zhengc aInstitutes
of Physical Scicence and Information Technology, Anhui University, Hefei, 230601 China Institute of Applied Physics, PLA Army Academy of Artillery and Air Defense, Hefei, 230031 China c Department of Material Science and Engineering, School of Aerospace Science and Engineering, National University of Defense Technology, Changsha, 410073 China *e-mail: [email protected] **e-mail: [email protected]
b
Received April 22, 2019; revised July 2, 2019; accepted July 29, 2019
Abstract—A spherical carbon coated nano-structured LiFePO4 composite is synthesized by a polymerassisted method from inexpensive iron(III) raw material. The synthesis process includes two steps: (1) nanoFePO4/polyaniline composites with core–shell structure are synthesized through the in-situ polymerization of aniline; (2) LiFePO4/C composites are prepared through carbothermal reduction with the nanoFePO4/polyaniline and sucrose as raw materials. The structure, surface morphology of the materials and the properties of the coated carbon are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The obtained nano-structured LiFePO4/carbon composite has a spherical morphology compose of ordered olivine structure, which is coated with 2 nm thick amorphous layer of carbon. At the same time, the materials are linked together by amorphous carbon from sucrose decomposition. The aniline plays an important role during the synthesis process. The electrochemical properties of the materials are tested by charge–discharge measurements. The obtained nano-structured LiFePO4/carbon composite shows excellent electrochemical properties, especially its high rate performance. It exhibits initial discharge capacities of 138, 136, 118, 103, and 92 mA h g–1 at 0.2, 1, 10, 20, and 30 C rate between 3.65 and 2.0 V, respectively. That makes it a promising cathode material for advanced power Li-ion batteries. The excellent electrochemical properties of the materials can be ascribed to the two different amorphous carbons. The carbon coated on the surface of LiFePO4 effectively reduces interparticle agglomeration of the LiFePO4 particles. The carbon interlinked between the composite improve the electronic conductivity. Those shorten the lithium ions diffusion length and improve the electric contact between LiFePO4 particles. Keywords: LiFePO4, lithium-ion batteries, high rate, carbon coating DOI: 10.1134/S1023193520050092
INTRODUCTION With the increasing concerns about environmental protection and energy saving, rechargeable lithiumion batteries have been extensively used in a wide variety of portable electric devices owing to their high energy densities, high voltage and portability [1–3]. In recent years, there has been a dramatic increase in research and comme
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