Effects of Electrical Contact Resistance on External Energy Losses in Lithium-ion Battery Packs for Hybrid and Electric Vehicles

Lithium-ion (Li-ion) batteries are favored in hybrid-electric vehicles and electric vehicles for their outstanding power characteristics. In this paper the energy loss due to electrical contact resistance (ECR) at the interface of electrodes and currentcollector bars in Li-ion battery assemblies is investigated for the first time. ECR is a direct result of contact surface imperfections and acts as an ohmic resistance at the electrode-collector joints. ECR is measured at electrode connections of a sample Li-ion battery, and a straightforward analysis is presented to evaluate the relevant energy loss. Through the experiments, it is observed that ECR is an important issue in energy management of Li-ion batteries. Effects of surface imperfection, contact pressure, joint type, collector bar material, and interfacial materials on ECR are highlighted. The obtained data show that in the considered battery, the energy loss due to ECR can be as high as 20% of the total energy flow in and out of the battery under normal operating conditions. However, ECR loss can be reduced to 6% when proper joint pressure and/or surface treatment are used. A poor connection at the electrode-collector interface can lead to a significant battery energy loss as heat generated at the interface. At sever conditions, heat generation due to ECR might cause serious safety issues, thermal runaway, sparks, and even melting of the electrodes. ∗Address all correspondence to this author. NOMENCLATURE Aa apparent contact area [m2] Ar real contact area [m2] BMS battery management system ECR electrical contact resistance EV electric vehicle F force [N] HEV hybrid-electric vehicle I electrical current [A] ICE internal combustion engine IECM interfacial electrically conductive material Li-ion lithium-ion n number of contact spots N number of surface measurement readings