Transmission Line Model Impedance Analysis of Lithium Sulfur Batteries: Influence of Lithium Sulfide Deposit Formed During Discharge and Self-Discharge

The effect of Li2S deposition on the impedance response of Li-S battery cells is investigated using a simplified cell design, systematic impedance spectroscopy measurements combined with transmission line modeling, and a complementary microscopy analysis. Glassy carbon cathodes are employed to build and validate the proposed transmission line model, which is later on employed to investigate the effect of various parameters of Li2S deposit (coverage, thickness, porosity) on cell’s impedance. Among others, the model is applied to study the effect of discharge and self-discharge. Finally, the simplified planar cathode is exchanged with a more conventional mesoporous carbon cathode to determine the effect of Li2S deposition on the impedance of a commercially viable cell design. We have found that Li2S deposit has little effect on the impedance response, owing to its porous structure. The most noticeable change stemming from the process of Li2S deposition is due to the depletion of polysulfide species concentration in the electrolyte, which decreases the chemical capacitance and increases the tail height in the low frequency region of the impedance spectra.

Compact, flexible and highly selective wideband complementary FSS with high angular stability

This article presents a novel miniaturized (0.105λ0 × 0.105λ0) flexible complementary frequency selective surfaces (CFSS) structure with sharp band edge selectivity and very high angular stability. To explore two diverse applications as a passband and stopband filter, a novel complementary convoluted square loop (CCSL) type structure has been designed and investigated on ultrathin dielectric material of thickness 0.0023λ0. The second-order wide controllable passband with fractional bandwidth of 19.23% (−3 dB) and remarkably wide stopband of 64.7% (−10 dB) and 54.8% (−20 dB) respectively have been achieved by using a cascaded resonating structure which is composed of asymmetrical meandered CCSL array, arranged on two ultrathin dielectric layers with air foam separation. This particular format would lead to sharp band edge selectivity with steep roll-off (72.43 dB/GHz) and an excellent passband selectivity factor (0.731). An equivalent lumped LC circuit in conjunction with the transmission line model has also been adopted to comprehend the physical mechanism of the proposed single layer and double layer structures. Further, better passband and stopband angular stability at an oblique incident angle of 45° and the bending characteristics have also been investigated thoroughly for the proposed flexible CFSS to check their employability in different conformal structures with WiMAX passband and WLAN stopband application.

Heterogeneity in MacMullin Number of Li-ion Battery Electrodes Studied by Means of an Aperture Probe

Heterogeneity of MacMullin number within battery electrodes is a key metric affecting cell performance. To characterize this heterogeneity, an aperture probe was developed. This probe, coupled with a newly developed transmission-line model, allows for measurements of tortuosity, represented by the MacMullin number, on millimeter length scales. Local MacMullin number values of seven electrodes were measured, and the ionic resistance profiles of these electrodes are given through contour maps of the MacMullin number. The method is validated by comparing the average MacMullin number to the value obtained through other measurement methods. The results show significant local MacMullin number variation in such electrodes on a millimeter length scale. This method will allow battery manufacturers and researchers to better quantify sources of heterogeneity and improve electrode quality.

Investigation and Development of a Three-Dimensional Transmission Tower-Line System Model Using Nonlinear Truss and Elastic Catenary Elements for Wind Loading Dynamic Simulation

The accuracy of transmission tower-line system simulation is highly impacted by the transmission line model and its coupling with the tower. Owing to the high geometry nonlinearity of the transmission line and the complexity of the wind loading, such analysis is often conducted in the commercial software. In most commercial software packages, nonlinear truss element is used for cable modeling, whereas the initial strain condition of the nonlinear truss under gravity loading is not directly available. Elastic catenary element establishes an analytical formulation for cable structure under distributed loading; however, the nonlinear iteration to reach convergence can be computational expensive. To derive an optimal transmission tower-line model solution with high fidelity and computational efficiency, an open-source three-dimensional model is developed. Nonlinear truss element and elastic catenary element are considered in the model development. The results of the study imply that both elements are suitable for the transmission line model; nevertheless, the initial strain in nonlinear truss element largely impacts the model accuracy and should be calibrated from the elastic catenary model. To cross-validate the developed models on the coupled transmission tower and line, a one-span eight-line system is modeled with different elements and compared with several state-of-the-art commercial packages. The results indicate that the displacement time-history root-mean-square error (RMSE) of the open-source transmission tower-line model is less than 1 % and with a 66 % computational time reduction compared with the ANSYS model. The application of the open-source package transmission tower-line model on extreme wind speed considering the aerodynamic damping is further implemented.