Lithium Ion Battery for Hybrid and Electric Mobility under Indian Ambient Conditions - A Perspective

Hybrid Electric Vehicles (HEVs), Plug-in Hybrid Electric Vehicles (PHEVs), Extended Range Electric Vehicles (EREVs), Battery Electric Vehicles' (BEVs) development is gaining traction across all geographies to help meet ever increasing fuel economy regulations and as a pathway to offset concerns due to climate change and improve the overall green quotient of automobiles. These technologies have primarily shifted towards Li-ion batteries for Energy Storage (due to energy density and mass). In order to make actual business sense of these technologies, of which, battery is a major cost driver, it is necessary for these batteries to provide similar performance and life expectancy across the operating and soak (storage) range of the vehicles, as well as provide the requirements at a competitive cost. In other words, the Li-ion batteries have to sustain the normal life cycle requirements and withstand wide span of storage temperatures that the conventional vehicles have been good at and still ensure good life.

HEVs and EVs have so far been a nascent market for South-East Asian regions and India in particular. The Indian ambient conditions range from less than −5deg C to greater than 50 deg C with relative humidity up to 100% in most of the coastal areas where there is very high vehicular density. Hence it is reasonable to state that the batteries have to consistently withstand high temperatures with high humidity and still satisfy their calendar life requirements. It is very realistic that the vehicles would be subject to a parking soak of temperatures exceeding 45 deg C during the summer months. This leads to a challenging task of thermal and battery management to maintain battery life under these soaking conditions. The options of passive (when vehicle off) thermal management system and storage strategy is critical to ensure adequate battery life. Passive thermal management strategy calls for innovative solutions especially in the realm of air cooled systems (low cost solution). This paper studies this challenge pertaining to Indian ambient conditions. This includes understanding the actual ambient environment including variations in Relative Humidity, potential impact of this on High Voltage Battery pack calendar life, potential challenges of integrating such a pack with cost effective thermal management to ensure good life and uncompromised performance of the battery pack and the vehicle.