Electrical and dielectric behavior of manganese-dioxide electrochemical electrodes
MetadataShow full item record
Manganese dioxide (MnO 2 ) is widely used in battery electrodes. The dielectric and electrical conduction properties of MnO 2 electrochemical electrodes with and without carbon black (CB, an electrically conductive additive), with and without an electrolyte (15 vol.% sulfuric acid), have been studied for various volume fractions of MnO 2 and CB. The case without the electrolyte pertains to MnO 2 particle compacts (40-75 vol.% MnO 2 ). The case with the electrolyte pertains to MnO 2 particle pastes (30-83 vol.% MnO 2 ). As the MnO 2 volume fraction increases from 40% to 75%, the relative dielectric constant increases from 58 to 72 for the MnO 2 compact and from 61 to 75 for the MnO 2 solid in the compact, and the resistivity decreases from 18000 to 11000 ohm.cm for the compact and from 9700 to 8100 ohm.cm for the MnO 2 solid in the compact. Increase in the MnO 2 volume fraction increases the relative dielectric constant of the MnO 2 solid in both compacts and pastes, due to the increasing dielectric connectivity of the MnO 2 particles. However, it decreases the resistivity of the MnO 2 solid in compacts and increases this resistivity in pastes. The presence of the electrolyte has negligible effect on the relative dielectric constant of the MnO 2 solid, but significantly decreases the resistivity of the MnO 2 solid. The interparticle interface enhances the compact resistivity, but reduces the paste resistivity. The compacts are effectively modeled as MnO 2 and air in parallel electrically, whereas the pastes are effectively modeled as MnO 2 and the electrolyte in series. The CB resistivity is significantly decreased and the CB relative dielectric constant is increased by the presence of the electrolyte, indicating that the electrolyte helps the CB electrical/dielectric connectivity. The CB resistivity in the presence of MnO 2 is higher than that in the absence of MnO 2 , indicating that the CB electrical connectivity is reduced by the presence of MnO 2 . The resistivity of CB in an MnO 2 compact (without electrolyte) decreases from 236 to 165 Ω.cm as the CB volume fraction increases from 13.5 to 29.5% and the MnO 2 volume fraction decreases from 68.6% to 58.7%, indicating increasing CB electrical connectivity. This is accompanied by decrease of the relative dielectric constant of CB from 53 to 12, suggesting decreasing CB polarizability as the CB is less squished by the lesser amount of MnO 2 . For similar reasons, the resistivity of CB in the MnO 2 paste (with electrolyte) decreases from 49 to 34 Ω.cm and the relative dielectric constant of CB decreases from 29 to 22 as the CB volume fraction increases from 18% to 25%. This thesis research has provided new information on the effects of the MnO 2 volume fraction, the CB volume fraction and the presence of the electrolyte, and has provided decoupling and determination of the contributions from the MnO 2 , CB and electrolyte to the electrical resistance and capacitance. The decoupled information on the MnO 2 and CB and the effect of the electrolyte on the properties of MnO 2 and CB have not been previously reported. The new information strengthens the science base needed for the design of electrode materials. The methodology demonstrated in this thesis may be applied to the study of a large variety of electrochemical devices.