Early Thermal Runaway Detection & Condition Monitoring in Traction Battery Packs through Gas Detection

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The proposed project presents a novel way of monitoring lithium-ion cells inside traction battery packs by using a single gas sensor. Each battery cell in the battery pack will be coated in an agent material which will have a slightly different decomposition signature for each cell. These materials will be designed to "activate" and release gasses at very specific temperatures. By detecting the composition of the released gasses, a single sensor can detect and locate a thermal event occurring at any cell inside the battery pack. Furthermore, the extremely dangerous thermal runaway mechanism that can occur in lithium-ion batteries can be directly characterised by the cell temperature. This new method will allow for early detection of thermal runaway for all cells in a pack, a very difficult task using current monitoring techniques. The data from the gas sensor can be fed directly back into the battery management system (BMS) to shut down the system or activate a prevention system. If there is enough resolution in the 'signature' of each material decomposition, the method could potentially be used to infer the degradation of the cells due to thermal cycling. Existing BMS's fall short when attempting to detect thermal events in a battery pack as they typically rely on discrete temperature sensors such as thermocouples. In large scale battery packs, it is not feasible to monitor each cell with a discrete sensor for various reasons including cost, manufacturing difficulties, computing time etc. Instead, a single sensor is used to monitor groups of cells. This solution is flawed however as any thermal runaway event can go undetected until it is too late if it occurs in a cell which is not directly monitored. Other methods of thermal runaway detection at pack level include gas detection of HF and other gases which are vented from a cell at high temperatures and pressures. The venting event however occurs well into the thermal runaway process and is typically too late to deploy prevention strategies. The proposed method is anticipated to be able to detect thermal runaway at pack level much quicker and more accurately than existing methods.Year 1: The first year will contain mostly research split up into sections which address the distinctive issues of the project. The research will cover battery technology, agent materials, application techniques and gas detection methods. Years 2-3: Years 2-3 will mostly contain experimental work. Depending on the research and available resources in year 1, experiments will need to be carried out to determine the surface temperature characteristics of various lithium-ion batteries under different ageing states. The agent materials researched in year 1 will be manufactured and tested with a gas chromatograph to determine if they function as required in terms of gas decomposition and activation temperature. Once the agent materials are determined, experiments will be carried out to find the best method for applying them to the battery cells. The agent materials will then be applied to dummy batteries which will be heated by a heating element to see if they behave as expected. The gas detection in this stage will be done by both a gas chromatograph and various sensors identified in the research. This will determine which sensors are suitable for the final application. The agent materials will then be applied to real cells which will be purposely put into thermal runaway to assess how effective they are in detecting thermal events. The 'signature' of the gas emitted from the coatings will be investigated through several different cyclic tests on various cells to assess the feasibility of determining the cell degradation. Once optimised, the method will be tested on a commercial EV battery pack to assess the functionality of the method at pack level. Year 4: Year 4 will mostly contain writing up, evaluating, and presenting the results and findings from the experiments in years 2-3.