Among various electrical energy storage devices the recent advances in Li-ion battery technology has made this technology very promising. Li-ion batteries can be used in stationary applications such as conventional or renewable energy power plants or also in development of electric vehicles. The advantage of these batteries is high energy and power density. As these batteries are deployed in various applications there is a need to understand the aging mechanisms of these batteries to improve the cycle life. Aging of the cells at the macroscopic or system level is quantied by the change in the internal resistance measured by impedance techniques. To understand the related loss of capacity, it is imperative to understand the degradation of the electrode materials of the battery. The degradation of the material is caused by several simultaneous physiochemical processes that occur within the batteries which makes material characterization of the electrodes a challenging task.
Performance of any new electrode material is investigated by testing the materials in a small experimental (so-called coin) cell. In commercial batteries the electrodes are made up of nanomaterials to leverage the eects of high surface area. Thus commercial batteries are larger in size as they provide the necessary building blocks for the battery packs. The eects of scaling in the commercial cell might be overlooked if the results of the so-called coin cell experiments are to be believed alone. This further adds to the complexity of analyzing the degradation mechanisms in commercial batteries.
As such a systematic multi-scale characterization plan has been developed to understand the degradation mechanisms of the battery. Various materials characterization techniques have been chosen to understand the degradation at a particular length scale and providing a direction for higher length scales. Along with certain physical and morphological characterization, techniques that characterize the functional properties such as resistance and surface potential has also been included in this scheme of multi-scale techniques. Certain chemical characterization techniques are also included to understand the chemical changes during the life of the battery. This thesis provides an discussion of these various techniques and an overview of the degradation studies of Li-ion batteries.