Cooling regimes for electric vehicle battery packs in vehicle-to-grid scenarios

In the coming decade, the world-wide fleet of electric vehicles is forecast to number in the tens of millions. At the same time, the ever increasing decentralization of power grids from increased small-scale renewable sources will require a renewed effort to balance supply and demand on the grid. EVs are viewed as a potentially cost effective alternative to grid stabilization by making available energy stored in their batteries to the distribution grid, known as Vehicle-to-Grid (V2G) applications. Supplemental use of an EV beyond driving will inflict additional wear on the battery pack. In the present work, electrochemical inputs from Doyle's classical battery model were applied to an prismatic automotive battery cell simulation to provide thermal profiles of EV driving and associated V2G operations to enable battery pack lifetime estimates to be made. Boundary conditions reflecting air and liquid cooled systems were compared. To obtain these estimates, a coupled electrochemical-thermal model was developed and applied to a range of test scenarios to demonstrate the effects of driving behaviour, charger level, extent of V2G service as well as the type of cooling system employed. The study was able to estimate EV battery pack lifetimes for a range of scenarios. Aggressive driving behaviour and fast charging were the most costly factors for loss of battery life, and it was shown that for these cases, a liquid cooled system can appreciably mitigate this lifetime losses compare to an air cooled system.