Effect of Different Calcination Temperatures and Carbon Coating on the Characteristics of LiFePO4 Prepared by Hydrothermal Route (original) (raw)

2017, International Journal of Engineering and Technology

The characteristics of lithium iron phosphate (LiFePO 4) prepared via hydrothermal route and calcined at various temperatures have been examined. Calcinations were performed at temperature variations of 500, 600, and 750C for 5 hours. The properties were characterized through thermal decomposition, structure, morphological and electrical properties. Flake-shaped pure LiFePO 4 and LiFePO 4 /C was successfully synthesized with the addition of 5 wt.% carbon black. The results showed that the addition of carbon effectively protected the material from oxidation and grain growth. The optimum calcination temperature was obtained at 750C with flake diameter of 80 nm and average length of 427 nm. The measured conductivity of the carbon coated LiFePO 4 (2.23 x 10-4 S/cm) was much higher than that of the as-synthesized LiFePO 4 (5 x 10-7 S/cm). The battery performance was obtained with a stable voltage ranging from 3.3 to 3.4 volts. Keyword-Carbon coating. Hydrothermal, LiFePO 4 , Cathode, Lithium ion battery I. INTRODUCTION Lithium ferro phosphate (LiFePO 4) has attracted many investigators since the reversibility of intercalationdeintercalation lithium ion in electrochemical process was observed [1], primarily as a promising candidate for lithium ion battery cathode. Many advantages of this material have been reviewed such as low production cost, environmental friendly and high capacity and stability cycle [2]. Despite its many advantageous, however, LiFePO 4 also has a drawback in that its electronic conductivity is low, measured only 10-9 S/cm [3]. This low electronic conductivity could lead to a low rate capability. Because of that, several approaches have been proposed by many investigators to improve this conductivity, e.g. refining the grain to nanoscale [4], [5], metal doping [6], [7], carbon coating [2], and co-synthesis with carbon in powder metallurgy method [8]. The synthesis routes of LiFePO 4 are mainly divided into two categories. The first route is a solid-state reaction, which involves a combination of mechanical alloying and solid reaction at high temperature [9]-[11]. The second route is a wet chemical approach, which involves utilization of chemical reaction solution followed by crystallization. This approach includes sol-gel [12], [13], hydrothermal [14]-[18], and solvothermal [19], [20]. Solid state route has attracted many investigators due to the ease of the process; however, solid state synthesis needs high temperature for sintering process in addition to the impurity problems dominated by Li 3 PO 4 and Fe 2 O 3 [21]. In the electrochemical reaction during charge-discharge process, the material containing these impurities will degrade and reduce the capacity of the active material [22]. The alternative is to synthesize LiFePO 4 by using hydrothermal route, which involves wet chemical process at low temperature followed by purifying process at relatively high temperature. This route has some advantages such as simple process and relatively low crystallization temperature and thus energy consumption [23]. In addition, the impurities could also be controlled during the reaction process [24]. In this work, LiFePO 4 was prepared using the hydrothermal route. The characteristics of the material after calcination at various different temperatures are presented. Further, the effect of carbon coating on the LiFePO 4 performance in a lithium ion battery cathode is also examined and discussed.