**5. Conclusion**

In conclusion, this work has shown that kinetic analysis can be employed in optimising the thermal processing of positive electroactive materials. As an example, kinetic analysis using a first-order kinetic analysis method and an incremental integral approach was performed for the water loss process from electrolytic manganese dioxide, the precursor material for use in non-aqueous Li/MnO2 cells. Both methods determined the pre-exponential factor and the activation energy for this process as a function of the extent of conversion, hence allowing for variation in the values over the process studied, while the incremental integral method also varied with heating rate.

Comparison and investigation of the two methods revealed the incremental integral method as the preferred means for obtaining the kinetic parameters describing this process. This result stems back to the use of a single TG experiment and the exclusive use of a slower scan rate using the incremental integral method (multiple scan rates, and thus experiments, are required in the first order kinetic analysis method). A single experiment avoids inherent variability between multiple experiments and limits errors induced in the somewhat arbitrary application of the background correction. Using slower scan rates reduces the possible undesired effects arising from thermal gradients across the sample as a result of the thermal conductivity of the material.

Using the kinetic parameters determined for this process, and assuming first order kinetics, a family of thermal treatment regimes based on heating temperature and duration were calculated to, in theory, completely remove water from the manganese dioxide structure.

Characterization of the resulting HEMD materials revealed considerable differences in their properties. It was found that materials undergo a mainly kinetically limited thermal conversion from γ-MnO2 towards β-MnO2. The material surface area generally decreases with heating temperature, although noticeably, the pore collapse process is thermally limited at lower temperatures, while at the higher temperatures the reaction kinetics dictate the extent to which this process proceeds. Despite the theoretical expectation of complete water removal from the EMD, experimental results demonstrate that thermal and kinetic limitations present under these heating conditions prevent the completion of the water loss process. In general, however, as heating temperature increases there is a decrease in cation vacancy fraction and amount of structural water, while Mn(III) and Mn(IV) increase and remain relatively steady, respectively.

Electrochemical performance of the HEMD materials generated in this work revealed they are superior in terms of specific energy, and comparable in terms of specific power, to recent reports in the literature for the primary Li/MnO2 system. Greatest differentiation of materials was noted at the low discharge rates, where materials prepared at 300°C and 350°C demonstrated best performance.

Finally, it is important to note that the method of kinetic analysis outlined here is not limited to only mass loss processes. It can in fact be employed to monitor the progress of any thermally based reaction which undergoes changes measurable by TG, DTA, DSC, etc. Therefore, the method of kinetic analysis outlined here could be applied in optimising the preparation and electrochemical performance of numerous other positive electroactive materials with similar improvements to performance anticipated.
