Effect Of Film Morphology On The Li Ion Intercalation Kinetics In Anodic Porous Manganese Dioxide Thin Films

Electrolytic manganese dioxide (EMD) films are electrodeposited from acid MnSO4 solution, targeting equivalent film thicknesses between 25 and 100 nm onto silicon substrates coated with Pt and TiN seed layers. The structure and morphology of the deposited EMD films are characterized and tied to the observed electrochemical performance. Deposition efficiencies as large as 80% are achieved, as determined from Rutherford back scattering (RBS). TEM and SEM show that our EMD films are highly porous. The degree of porosity is dependent on the deposition current density and also the deposition time. The electrochemical activity of the EMD films for lithium ion intercalation is investigated in propylene carbonate solvent with 1 M LiClO4. Reversible insertion and extraction of Li+ follows after removing water from the films by annealing and subsequent electrochemical cycling. The porous EMD thin films show a Li ion capacity up to 90% of the theoretical capacity at 0.8 C rate, based on the Mn content from RBS data and assuming one Li ion per MnO2 unit. The effect of film thickness and film porosity on the rate of Li+ intercalation (and thus accessible capacity) is discussed.