Novel electrode materials for thin-film ultracapacitors: Comparison of electrochemical properties of sol-gel-derived and electrodeposited manganese dioxide

Thin films of manganese dioxide were formed on nickel foils by electrodepos ition and by both dip-coating and drop-coating with manganese dioxide suspe nsions (sols) and their subsequent gelation and calcination. The performanc e of these films as ultracapacitors was studied by cyclic voltammetry in th e range 0.0-0.9 V (SCE) and by chronopotentiometry in unbuffered Na2SO4 sol ution. The cyclic voltammograms of ultrathin, dip-coated sol-gel-derived fi lms indicated better capacitive behavior and gave differential specific cap acitance values as high as 698 F/g compared to values half to two-thirds as great for the electrodeposited films. Multilayer drop-coated sol-gel films were prepared to attain film thicknesses comparable to the electrodeposite d mms, and these were found to provide charge-storage capacity as high as 1 .5 mC/cm(2), more than three limes greater than that of the electrodeposite d films. All films, except electrodeposited films that were not thermally c ured, exhibited good cycling stability, losing not much more than 10% of ca pacity after 1500 cycles. (C) 2000 The Electrochemical Society. S0013-4651( 99)04-063-X. All rights reserved.