Effective thermal management of batteries is critical to maximise performance & durability. The first mass market HEVs and EV batteries used passive or forced air thermal management. As vehicle performance requirements have increased most current electric vehicles use a water glycol based thermal management system. As this medium is electrically conductive it must be separated from the electrical components, commonly achieved either using a heat exchanger under the cells or tubes woven between the cells. This approach is known as indirect thermal management and has several limitations. Firstly, proximity of the thermal management fluid to the cells is limited. This reduces the available heat paths to the fluid which limits the total heat flux rates and biases the heat path to one side or area of a cell leading to high inter-cell temperatures. In order to achieve higher energy density there is an industry trend towards larger format cells which results in increased volume to surface area ratio and makes cell thermal management ever more challenging. Since 2017 Castrol has been investigating direct thermal management technology using a dielectric fluid which can be in direct contact with the electrical components. This approach can achieve more uniform inter- & intra- cell temperatures contributing to cell longevity & performance. In addition, it can increase heat removal and enable faster charging. In 2019 Castrol ON introduced to the market EV Thermal Fluids for direct battery cooling technology and the brand currently offers a range of fluids tailored to meet customer requirements. The test rig & direct cooled module presented here have been codeveloped with a Battery Electric Vehicle Automotive Partner. Direct thermal management was applied to large format cylindrical cells, represented by aluminium cylinders containing heater cartridges, in conjunction with Castrol ON EV Thermal Fluids. Testing Concept Castrol have developed an in-house rig to test EV Thermal Fluids in interchangeable battery modules that don’t include live cell chemistry or any combustible materials. Cells are replaced with representative units that feature internal electrical heating to mimic cell thermal behaviour and thermistors to measure surface temperature. The units are carefully engineered to replicate the thermal characteristics of the cells they are representing. While battery system validation testing will normally need to be completed with real hardware, for the purposes of developing thermal management systems and fluids Castrol has found the thermal rig approach offers several key advantages over live cell testing. Live Li-ion cells are subject to both calendar and cycle aging which makes obtaining precise repeatable results over time very challenging. In addition, cell piece to piece variation reduces test reproducibility and can result in an imbalance of cell voltages within a Advanced techniques for selection of battery thermal management fluids Why Direct Thermal Management? Figure 1 – Castrol On Thermal Rig in temperature-controlled test chamber Advertising feature
RkJQdWJsaXNoZXIy MjI2Mzk4