High power battery characterization for parameterization of battery management systems

Lithium ion batteries must be carefully measured and managed by the battery management system (BMS) to achieve high performance, safe operations, and accurate reporting of the state of charge (SOC) and state of health (SOH). Each lithium ion cell chemistry and format have unique voltage, current, and thermal response characteristics that are a function of SOC, temperature, operating mode (charge, discharge, or standby), rate (current), and degradation (capacity loss and/or internal resistance growth). Consequently, each lithium ion cell type must be measured in detail to determine its characteristics so as to program the BMS for high performance, but safe operation, of the battery pack. Historically, this has been accomplished by testing lithium ion cells in carefully controlled laboratory air-based thermal chamber environment, which produces reasonable results at low rates where the cell temperature is nearly uniform. However, new battery applications and system designs render this method less accurate because of two reasons: (1) at ultrafast charging rate the cell temperature can deviate substantially from the thermal chamber and also become non uniform throughout and across the cell, and (2) advanced thermal conditioning systems (e.g. immersing the battery in dielectric cooling oil) have much greater thermal convection and conduction capabilities than air based thermal chambers. This project will develop new test protocols and equipment to compare and contrast the fidelity and accuracy of battery testing in isothermal units, air thermal chamber testing, and translate those results practical liquid and immersion style thermal management systems. This technology research will lead to faster charging electric vehicles that perform better in cold climates like Canada.