A Study on Combined Lithium and Sodium-Ion Hybrid Energy Storage Systems in Battery Electric Vehicles

Abstract With an end-goal of carbon neutrality set by many nations across the world, various industries face the challenging task of incorporating novel technologies in their products while remaining economically sustainable. This is particularly evident in the automotive sector, where diversifying the product portfolio of many Original Equipment Manufacturers to meet carbon emission targets is a primary goal, investing in research ranging from hydrogen fuel propulsion to energy storage systems. It is in this latter area in which this paper provides an insightful analysis in the coupling of two rechargeable energy storage systems based on different chemical technologies. The work herein evaluates a hybrid energy storage system for a subcompact crossover sport utility vehicle that includes a lithium-ion (LIB) and sodium-ion battery (NaIB) pack, with varying divisions of the total energy between the two. The aim is to exploit the NaIB pack to the greatest possible degree such that the longevity of the LIB pack is extended, given that NaIBs are more forgiving in their response to high C-rates. The division is performed on the basis of two methodologies: 1) maintaining a constant mass of the combined battery pack and 2) maintaining a constant energy of the hybrid energy storage system. The analysis considers two energy management strategies that are both deterministic rule-based, the first termed as a Load Follower and the second as a Range Extender. The analysis of a selection of energy division and energy management strategies shows that a hybrid battery system comprising of 70% of energy provided by a LIB and 30% by a NaIB coupled with a Range Extender energy management provides the best trade-off between C-rate reduction, range penalization and cost reduction. Such a solution allows for up to 46% reduction in LIB C-rate and 7.6% reduction in cost with respect to the vehicle mounted with the baseline LIB.