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Using high resolution computed tomography (CT) the change of the morphometric parameters in depth of electrodes for lithium ion batteries with aging has been examined. Commercially available 2 Ah Li-ion cells were continuously cycled to different state of health (SOH). The cathodes were subsequently analyzed using CT with voxel size resolution of about 400 nm. For a quantitative analysis binarized images were evaluated and various properties such as the size distribution of active particles analyzed. Using this technique a decrease in the average particle size and an increase in number of particles of LiCoO2 with decreasing SOH of the battery is confirmed experimentally for the first time.
Polymer grafting from graphitic carbon materials has been explored for several decades. Currently existing methods mostly employ harsh chemical treatment to generate defect site in graphitic carbon plane, which are used as active site for polymerization of precursors. Unfortunately, the treatment cause serious degradation of chemical structure and material properties. Here, we present a straightforward route for growth of polyaniline chain from nitrogen (N)-sites of carbon nanotubes. N site in the CNT wall initiates the polymerization of aniline monomer, which generates seamless hybrids composed of polyaniline directly grafted onto the CNT walls. The synthesized hybrids show excellent synergistic electrochemical performance, and are employed for electrodes of pseudo-capacitor. This approach offers an efficient way to obtain hybrid system consisting of conducting polymers directly grafted from graphitic dopant sites.
Use of spark plasma sintering (SPS) allows improving thermoelectric figure of merit Z of bulk nanothermoelectrics but required parameters of SPS process for achievement of best Z can be defined only empirically.
In the present study the finite elements method for investigation of electric and thermal processes which occur in volume and on boundaries of sintering particles is applied. As a geometrical model a structural cell of a sintered sample, containing contact “a truncated cone - a plate” has been chosen. Temperature distributions in the volume of a sample depending on amplitude, on-off time ratio and duration of impact of the electric current has been obtained for solid solution based on bismuth telluride using the energy balance equation and the equation of electric current continuity. Under certain conditions nonlinear and nonlocal processes start to arise.
The calculated temperature distributions at different sintering conditions were comparing with empirically defined experimental parameters that lead to improved value of Z. The comparison allows formulating recommendations to achieve best conditions of SPS process for increase of Z. The present method can be used for management of SPS fabrication process for different application, not only for thermoelectrics.
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