Improved cycling and high rate performance of core-shell LiFe1/3Mn1/3Co1/3PO4/carbon nanocomposites for lithium-ion batteries: Effect of the carbon source

Abstract

Core-shell type olivine solid solutions, LiFe1/3Mn1/3Co1/3PO4/C, are synthesized via a very simple and rapid microwave heating route with different carbon sources. The obatined LiFe1/3Mn1/3Co1/3PO4/C materials are characterized thoroughly by various analytical techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy-dispersive spectroscopy instrument. The particle sizes and distribution of the carbon layer of BP2000 carbon black coated LiFe1/3Mn1/3Co1/3PO4 (LiFe1/3Mn1/3Co1/3PO4/BP) are more uniform than that obtained from acetylene black (LiFe1/3Mn1/3Co1/3PO4/AB) and Super P (LiFe1/3Mn1/3Co1/3PO4/SP). Moreover, the LiFe1/3Mn1/3Co1/3PO4/BP nanocomposite shows superior electrochemical properties such as high discharge capacity of 160mAhg−1 at 0.1C, excellent cyclic stability (143mAhg−1 at 0.1C after 30 cycles) and rate capability (76mAhg−1 at 20C), which are better than other two samples. Cyclic voltammetric and electrical tests disclose that the Li-ion diffusion, the reversibility of lithium extraction/insertion and electrical conductivity are significantly improved in LiFe1/3Mn1/3Co1/3PO4/BP composite. Electrochemical impedance spectroscopy illustrates that LiFe1/3Mn1/3Co1/3PO4/BP composite electrode possesses low contact and charge-transfer impedances, which can lead to rapid electron transport during the electrochemical lithium insertion/extraction reaction. It is believed that olivine solid solution LiFe1/3Mn1/3Co1/3PO4 decorated with carbon from appropriate carbon source is a promising cathode for high-performance lithium-ion batteries.