As a Li-ion battery ages, it loses capacity and its internal resistance increases. We investigate different contributions to aging effects on the anode and the cathode side. SEI growth as well as Li-plating are discussed in detail. State of Health estimation methods and State of Health prediction are addressed as well. We look into the heat production of a Li-ion battery and how it changes as the battery ages. We also address the influence of aging on the safety of the battery.