The aim of this work is to answer the question: how to realize high energy and high-power lithium-ion batteries. Lithium-metal and graphite anodes with nickel manganese cobalt (NMC) cathodes of varying thickness are investigated with finite element modelling. The overpotential analysis is performed to pinpoint the source of losses and the possible ways to decrease them. The electrolyte overpotential, resulting from the salt concentration gradient and leading to saturation and depletion of lithium in parts of the cell is identified as the main factor causing poor specific capacity at high discharge/charge currents. The influence of various parameters, including concentration and transference number of lithium salt in the electrolyte, NMC particle size, electrolyte conductivity and the exchange current density, on the galvanostatic response of modelled battery cells is discussed. The increase of the transference number would improve the performance as this would decrease the electrolyte salt concentration gradient. Lithium depletion effect can be also minimized by elevating the initial electrolyte salt concentration, as well as by increasing the porosity of the cathode, particularly at the cathode/separator boundary.