Abstract
A new mesoporous carbon (MC) is obtained from pyrolysis of resorcinol/formaldehyde resin, polymerized in the presence of tetraethoxysilane and Pluronic F108, followed by pyrolysis at 800 °C and silica removal. The reaction mixture in a molar ratio of 1F108/60resorcinol/292 formaldehyde/16900 H2O/50 tetraethoxysilane heated at 67 °C produces MC nanoparticles (200 nm average size) exhibiting 3D bimodal mesopores (3.9 and 8.2 nm), 1198 m2/g surface area, 1.8 cm3/g pore volume, and important graphitic character for use as a conductive material. Composites LiFePO4/carbon prepared with MC or commercial Super P, by the slurry method, were tested as coin Li-ion battery (LiB) cathodes. Super P (40 nm average particle size) exhibits better graphitic character, but lower porosity than MC. LiFePO4/MC shows better specific capacity (161 mAhg−1) than LiFePO4/Super P (126 mAhg−1), with a retention capacity (RC) after cycling at C/10 of 81%. Both composites with MC and Super P show well-distributed particles. According to impedance analysis, MC mesoporosity improves the charge transfer kinetics (CTK) more than Super P, producing a cathode with higher efficiency, although lithium ions’ diffusion decreases because larger MC particles form longer diffusion paths. Owing to the good specific capacity of the LiB cathode prepared with MC, research looking into improving its retention capacity should be a focus.
Highlights
The lithium insertion compounds, with an olivine structure, are considered as potential positive electrode materials of large-scale lithium-ion rechargeable batteries (LIBs) for electric vehicles because of their high operative voltage and energy density
We developed a new method for the synthesis of mesoporous carbon as an additive for LiFePO4
H1 hysteresis loop corresponding to materials with cylindrical of mesoporous carbon (MC) and Super P, respectively, and Table 1 presents their porous characteristics
Summary
The lithium insertion compounds, with an olivine structure, are considered as potential positive electrode materials of large-scale lithium-ion rechargeable batteries (LIBs) for electric vehicles because of their high operative voltage and energy density. LiFePO4 as a cathode material in lithium ion batteries is important because it exhibits low toxicity and is obtained at a relatively low cost It has a high lithium intercalation voltage of 3.4 V, which is compatible with most existing organic electrolytes; a high theoretical capacity of 170 mAhg−1 ; and safety when compared with cobalt oxide-based olivine materials for large-scale applications [1]. LiFePO4 , when cycled, has a practical capacity much lower than the theoretical capacity This limitation for commercial applications has mainly been attributed to the low intrinsic electronic conductivity 10−11 Scm−1 (compared with 10−3 Scm−1 for LiCoO2 ) and low Li+ diffusion coefficient through the LiFePO4 /FePO4 interface [2,3]. To overcome these drawbacks and to improve the electrochemical performance of LiFePO4 , many studies have been conducted involving reduction of
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