Synthesis and Electrochemical Properties of Layered Birnessite MnO2/Activated Carbon Nanocomposite

• Published in: Journal of electronic materials Vol. 51; no. 5; pp. 2412 - 2432
• Main Authors: Shaeri, M. A., Bagheri Mohagheghi, M. M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.05.2022; Springer Nature B.V
• Subjects: Activated carbon; Annealing; Anodes; Characterization and Evaluation of Materials; Chemistry and Materials Science; Citric acid; Diffraction patterns; Electrochemical analysis; Electrode materials; Electronics and Microelectronics; Energy gap; Field emission microscopy; Hydrazines; Infrared spectroscopy; Instrumentation; Ion diffusion; Lattice vibration; Lithium-ion batteries; Low conductivity; Manganese dioxide; Mass ratios; Materials Science; Nanocomposites; Nanoparticles; Optical and Electronic Materials; Original Research Article; Pore size; Potassium permanganate; Rechargeable batteries; Solid State Physics; Spectrum analysis; Synthesis; Walnuts; Weight; activated carbon; hydrazine; energy gap; nanocomposites; MnO
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-022-09499-6

Mesoporous MnO 2 /activated carbon (AC) nanocomposites are promising materials as anode material in lithium ion batteries which are being considered by researchers due to their low conductivity and considerable irreversible capacity loss. The porous structures of these nanocomposites can facilitate Li ion diffusion into the porous structure. In this paper, MnO 2 /AC nanocomposites were synthesized by the coating of a MnO 2 layer on AC using the reduction reaction of KMnO 4 with AC and citric acid. The AC in nanocomposites prepared from walnut shell powder, hydrazine hydrate, and NaCl were used as activating agents. The MnO 2 /AC nanocomposites were synthesized with mass ratios of 1:4, 1:1, 4:1, and 1:0 and the effect of the annealing process at the temperature of 300°C was investigated. The x-ray diffraction (XRD) patterns of MnO 2 /AC nanocomposites have shown the growth of the layered birnessite-type MnO 2 nanoparticles on the AC. Field emission-scanning electron microscopy (FE-SEM) images of the AC shows cracked surfaces with pieces of sizes from 20 nm to 100 nm and the pore size in the wide range of 20–200 nm. Based on EDS results, decreasing the AC content in MnO 2 /AC nanocomposites led to the decrease of the weight ratio of carbon before annealing, but increased the weight ratio of carbon after annealing. Fourier-transform infrared (FTIR) spectroscopy results showed the existence of bands attributed to the lattice vibration of Mn−O and the strengthening of the related carbon bands in composites containing AC. The direct and indirect band gaps of MnO 2 /AC nanocomposites were determined by UV-Vis absorption spectroscopy. For the MnO 2 /AC nanocomposites with less or equal MnO 2 content, the indirect energy gap of MnO 2 (≈ 2.4 eV) increases with increasing the MnO 2 /AC ratio before annealing, while this gap disappeared after annealing. The direct energy gap of MnO 2 in the nanocomposites was always larger than 3.09 eV, due to the nanoscale size of the MnO 2 nanoparticles. Comparisons of the direct gaps of 1:4, 1:1, and 4:1 composites before and after annealing imply that the direct gap decreases from 5.88 eV, 5.51 eV, and 6.41 eV before annealing to 5.52 eV, 5.44 eV, and 5.68 eV after annealing, respectively. Electrochemical measurements including voltage capacity and dQ/dV indicate that the MnO 2 /AC (1:4) nanocomposite anodes demonstrate more than 89% coulombic efficiency and a specific capacity of 1495 mAh/g in 20 mA/g in the first cycle.