Preparation of supercapacitors based on nanocomposites films of MnO2/CB/C from sodium alginate and MnO2 nanoparticles by direct electrophoretic deposition and carbonization

Supercapacitors based on MnO 2 /CB/C nanocomposites films are prepared by direct electrophoretic deposition (EPD) process on nickel plates in an aqueous solution containing of MnO 2 nanoparticles , carbon black (CB) and sodium alginate (SA), followed by carbonization of SA to carbon layer . The nanocomposites of MnO 2 /CB/C films are prepared from different electrolytic solutions with mass ratios of MnO 2 nanoparticles, CB and SA from 8: 1: 1 to 6: 2: 2. Same mass ratios of nanocomposites are prepared by traditional Doctoral Blade (DB) process for morphologies and performances comparisons, in which mixtures of MnO 2 nanoparticles, carbon black with polyvinylidene fluoride (PVDF) are used. From scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) images, the MnO 2 /CB/C shows a uniform aggregation of MnO 2 and carbon nanoparticles covered with carbon layers. In the case of the MnO 2 /CB/PVDF from DB process, the MnO 2 nanoparticles are separately clustered, and the clusters are adhered to CB together with PVDF. More uniform film and better contact of MnO 2 with CB by carbon layer can be obtained from EPD/Carbonization process. The electrochemical performances of MnO 2 /CB/C and MnO 2 /CB/PVDF nanocomposites in different mass ratios are compared by areal specific capacitances (C a ), charge transfer resistance of films and retention of capacitance after 1500 cycles of charge/discharge to test stability respectively. The nanocomposites of MnO 2 /CB/C show better areal specific capacitances and smaller charge transfer resistances at each ratio. The carbon layer coating on surface of MnO 2 nanoparticles can effectively delay the capacitance loss, which leads to 98% of capacitance after charge/discharge cycles, much better than retention of those from DB process (50%). The EPD/Carbonization is an easy way to make carbon layer on pseudo capacitive materials from sodium alginates , and the carbon layer can effectively improve the charge/discharge stability of supercapacitors.