Electric vehicles (EVs) can significantly reduce the greenhouse gas emission from the transportation sector and thus can have positive impact on the climate change. Now-a-days, the majority of the electric vehicles (EV) relies on the Li-ion batteries (LIB) for energy storage. High energy and power density and low maitenance is the main reason behind it. However, the popularity o EVs is hindered by the limited electric driving range and high cost of the battery. To overcome this limitation, the energy density of the LIBs has to be increased while maintaining the high safety. In the pursuit of a low cost, higher energy density safer battery, research and development has been spread over different size scale level of the component. While new materials are being developed at the material scale, cell, module and pack design are being improved at the higher scale of the development processes. The main objective of this PhD is to contribute in the multiscale development process of LIB. First, the study focuses on the temperature inhomogeneity of conventional LIB pouch cell. Then the study focuses on the understabding of the operation mechanism of Li-Sulfur batteries (LSB). In both cases, a combination of in-depth experimental characterizations and continuum mathematical models are employed to elucidate the mechanisms.