Marcus Sampson, Business Line Manager for Transport at TÜV SÜD, says that in European Union Member States and a number of other countries, including the UK, the standard for rechargeable energy storage systems (RESS) used in electric vehicles is UNECE Regulation 100 (R100)
However, while safety, as prescribed in R100, is clearly a critical consideration, it does not encompass the full range of additional considerations applicable to electric vehicle batteries. Some of these considerations may fall under the scope of a voluntary standard adopted by the industry, or under more stringent regulatory requirements imposed in individual countries or legal jurisdictions. But a manufacturer’s failure to evaluate the full range of battery safety and performance issues can lead to battery failures over time that necessitate product recalls, as well as expensive and time-consuming repairs. If this evaluation is left until the end of the product development process, the risk of identifying unexpected safety or performance characteristics that require redesign increases. A thorough evaluation and testing of rechargeable battery systems intended for use in electric vehicles should follow a progressive, multistep approach that begins early in the vehicle design process. This approach consists of the following five phases: Cell evaluation Cell types from several suppliers are subject to initial safety and performance assessments to identify potential weaknesses and vulnerabilities. The goal of this phase is to select battery cells that are suitable for the vehicle. Cell assessment The cells selected by the cell evaluation phase are subject to in-depth safety and performance assessments as well as a lifetime assessment of the cell. Data generated during this phase provides assurances regarding the accuracy of the assessment in the previous phase, and can be used for identifying suitable parameters for battery management system simulation and testing. Module validation This next phase repeats safety, performance and lifetime assessments, but this time at the module level and with a slightly different focus. Cell evaluation and assessment focus primarily on intrinsic safety, while module validation may also include the evaluation of external safety mechanisms. Module validation therefore helps to further affirm the findings of the cell-level assessments and provides important initial insights into battery behaviour that is likely to be observed at the pack level. Pack/system validation Safety and performance assessments are repeated once more at the pack level, again serving to validate earlier testing and to give further assurances regarding battery safety as well as performance under actual use conditions. Testing for the environmental influences is also an important aspect in this phase. Failure analysis Finally, battery packs are subjected to testing to evaluate potential failure modes and to better understand the root causes of such failures. Failure modes are validated, and actual problems observed with prototype vehicle use are examined to determine root causes. This final assessment allows for validation of the safety concept behind the battery pack and helps to complete the refinement of the pack design. This multi-step approach to battery pack assessment and testing has the benefit of validating a rechargeable battery system, layer by successive layer. This enables electric vehicle designers to identify potential battery-related issues as early as possible in the vehicle design process, thereby facilitating design changes without impacting the overall development schedule and reducing the risk of battery failure. Finally, information generated through the validation process can also help support product verification requirements that are necessary to successfully achieve regulatory approval. Innovation in batteries and battery systems will be an essential factor in the development of advanced electric vehicles. The demand for more powerful batteries with faster acceleration and extended vehicle operating ranges is occurring at the same time that battery designs are expected to have lower mass and occupy less vehicle space. Designers are therefore continuously exploring variations of existing lithium-ion battery configurations to increase battery energy and vehicle operating range. However, incorporating advanced battery technologies into the design of new electric vehicles is not without its challenges. While battery safety is of paramount importance, other issues, such as battery performance and reliability, are often beyond the scope of applicable regulations. In a highly competitive market, manufacturers should therefore consider expanding the scope of their evaluation of battery systems beyond mere compliance with applicable regulations and safety requirements. They should undertake a comprehensive approach to battery system testing and validation, beginning at the earliest stages of the vehicle design and development process.
