Electric vehicles have gained increasing interest due to their potential to lower environmental pollution and demand for energy. However, EVs remain uncompetitive with traditional internal combustion engine vehicles, in terms of range ability; limited energy density and high cost of battery technology present a bottleneck for wide adaptation. Therefore, with limited energy storage capacity, efficiency in managing power flow is crucial. This thesis presents a methodology to realize design optimization of a multi-energy storage system for an all-wheel EV. This study looks into utilizing multiple energy storage technologies to capitalize on performance characteristics to increase driving range. The optimization objectives are to efficiently manage power flow between a lithium-ion battery pack and a supercapacitor bank to prolong the driving range and increase the life cycle of the lithium-ion battery pack without compromising the vehicle performance. The driving performance requirements are formulated as the constraint conditions, while the range is set as the optimization variable. Simulation results show that electric vehicles can be designed with supercapacitor banks in complementary to batteries to match cost, range and life time of internal combustion engine vehicles without sacrificing vehicle performance.