Vehicle battery monitoring

Today, the battery status in electric vehicles is measured with voltammetry, which means that the voltage and current drawn from the battery is also used to identify state of charge (SOC) and state of health (SOH). However, the open circuit voltage of batteries changes during the charge and discharge processes, over time, and with temperature, which makes voltammetry an insufficient measurement tool. This uncertainty forces manufacturers to use oversized batteries and perform service earlier than what is actually needed. Due to the safety margins built into the battery management systems the full battery capacity is not utilized, energy is wasted and the use of natural resources is not efficient. It has been shown that by basing the battery control system on the chemical and structural processes rather than the voltage limits, the available energy of Li-ion cells can be improved by 212 %, the power density by 22 %, and the charging rate by 50 % (Smith & Wang, 2006). Also, the possibility of a catastrophic failure due to an exothermic chemical chain reaction inside the battery which cause explosion or fire (Tesla Motors – Quarterly Report, 2013) can be reduced significantly when the internal state of the battery is known more accurately.

Insplorion’s NPS technology allows highly sensitive in-situ monitoring of structural and chemical changes and temperature shifts. It has the potential to significantly reduce several inherent problems related to voltammetry by measuring directly inside each battery cell. The chemical composition of the battery cell changes during charge and discharge processes and can be measured by the Insplorion’s patented sensor, which in laboratory settings has been shown to allow at least 25 % more of the power density. Additionally, measuring chemical and physical processes inside the battery cells can be used to detect early warning sign of catastrophic failure (explosion).

The project has proven successful in laboratory scale battery cells both for led and Li-ion based batteries. Insplorion has recently implemented the NPS sensor in a commercial prototype in collaboration with AGM batteries Ltd in Thurso, UK. Read more about the project in the Horizon 2020 projects issue 13 here.