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 MnO2/CB/C nanocomposites films are prepared by direct electrophoretic deposition (EPD) process on nickel plates in an aqueous solution containing of MnO2 nanoparticles, carbon black (CB) and sodium alginate (SA), followed by carbonization of SA to carbon layer. The nanocomposites of MnO2/CB/C films are prepared from different electrolytic solutions with mass ratios of MnO2 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 MnO2 nanoparticles, carbon black with polyvinylidene fluoride (PVDF) are used. From scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) images, the MnO2/CB/C shows a uniform aggregation of MnO2 and carbon nanoparticles covered with carbon layers. In the case of the MnO2/CB/PVDF from DB process, the MnO2 nanoparticles are separately clustered, and the clusters are adhered to CB together with PVDF. More uniform film and better contact of MnO2 with CB by carbon layer can be obtained from EPD/Carbonization process. The electrochemical performances of MnO2/CB/C and MnO2/CB/PVDF nanocomposites in different mass ratios are compared by areal specific capacitances (Ca), charge transfer resistance of films and retention of capacitance after 1500 cycles of charge/discharge to test stability respectively. The nanocomposites of MnO2/CB/C show better areal specific capacitances and smaller charge transfer resistances at each ratio. The carbon layer coating on surface of MnO2 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.