Lithium (Li) deposition is a problem in Li batteries (LB) – both Li metal (LMB) and Li-ion (LIB) batteries – which limits their performance in terms of power and energy density. Two trends can be identified in the advancement of LBs concerning the problem of Li deposition: optimization of the existing system (the state-of-the-art LIBs) and further development of cell components such as electrolytes. This work addresses both approaches. In the first part, this study investigates Li deposition in LMB and LIBs. A novel method to study the Li-based transport mechanisms in LIBs is introduced. Later the kinetic deviations between anode and cathode as a consequence of aging and the relation of these deviations to the occurrence of Li-plating are discussed. In the second part, the applicability of PEO-based solid polymer electrolytes for LMBs to overcome the Li plating issue is investigated. The introduction of various interfacial interlayers at the cathode/electrolyte interphase was studied to improve the electrochemical stability of the cells. Cells with an in-situ electro-deposited interlayer showed the best cyclability.