SAFETY concerns surrounding lithium-ion batteries dominated a recent IChemE-hosted roundtable discussion on the state of the UK’s battery energy storage systems (BESS).
Taking place in London, and with a virtual presence, the discussion was chaired by Mark Apsey MBE, IChemE deputy president and UK managing director for renewable energy firm Ameresco, and featured contributors from industry and academia.
BESS are seen as key in the decarbonisation of the UK’s electricity supply, but some well-publicised examples of lithium-ion batteries (LIBs) catching fire in recent years have led to safety fears.
According to statistics discussed by one member of the group, around 68 grid-scale battery systems have exploded or burned since 2010 – the majority within the last four years.
Fires generally result from thermal runaway. This occurs when components in the battery break down due to heat, causing an uncontrollable, self-heating state to propagate. Energy stored in the battery is then released very suddenly, which in turn can cause combustion and fire, and the expulsion of toxic gases, including carbon monoxide and hydrogen fluoride.
While there are ways to reduce the risk of thermal runaway in batteries, such as storing batteries at the correct temperature, and providing adequate ventilation, if a grid-scale battery did catch fire, then letting it burn itself out was seen as one way to deal with the problem. One participant with experience in utility-scale power station batteries – around 35 MW – said that was how their company dealt with it. “Our view of safety was, if it catches fire, it’s dead to us. Let it burn out, make sure it’s safe and contained, and no one can go near it.” Batteries targeted for residential use were a different matter, but utility-scale batteries, in their opinion, were being designed to do just that, burn out in isolation so that remaining assets were not affected.
Different battery types were also discussed, and some were deemed safer than others. Lithium iron phosphate (LFP) batteries were viewed as less likely to experience thermal runaway compared with NMC batteries, which contain nickel, manganese, and cobalt. This is due to the strong covalent P–O bonds in the cathode, and because it can withstand high voltages for longer periods. Would sodium ion batteries turn out to be the better solution? Possibly, said one participant. Still the same safety issues as lithium iron, said another.
However, a researcher at the discussion pointed out that other materials inside the battery also need to be taken into consideration when it comes to safety. Electrolyte material, the organic solvent that is the carrier of ion transmission in the battery, is most often in non-aqueous solutions, and is flammable. This has led to developments in highly concentrated “water-in-salt” (WIS) electrolytes that could be a potential alternative. Some new types of batteries also incorporate silicon material in with the graphite anode, and this too poses safety concerns.
Overall, issues surrounding safety boil down to a lack of understanding, the researcher said. It was a view shared by many. It was not just a lack of knowledge on the actual chemical reactions taking place, but a failure to understand the risks and hazards of LIBs from all stakeholders involved, including planning officials, that posed a problem. “We need to educate everybody, and have more standards,” one participant said. “Otherwise, we will keep seeing the same knee-jerk reaction which we see now from some groups, where as soon as a grid-scale system is proposed, an opposition group forms and immediately opposes it.”
A handful of safety guidelines are currently in use, including NFPA 855, a systems level safety group, NFPA 68, a standard on explosion protection by deflagration venting, and NFPA 69, the standard on explosion prevention systems. However, often changes in safety information come about following an incident, said a contributor, leading to reactionary guidelines. “You either get drastic super safety in a battery system that is needed, but then from a project point of view it no longer becomes feasible, or it goes the other way. Then it becomes not safe enough, and the system is in danger of causing a real hazard,” they explained.
It was also mentioned that a lot of safety information was written by academia. Though not problematic, it highlighted a divide between academia and industry whereby companies were doing one thing, and research groups another. Researchers in academia said industry tends to be tight-lipped about what they are working on, even when it comes to safety issues, so they end up reinventing the wheel, time and time again. It was agreed that a repository of anonymised data or more cross collaboration to avoid duplication was required.
A division was also seen in the way academia and small and medium enterprises (SMEs) approach a battery project compared with large, established companies. Often people do not have an understanding of how manufacturing works, one person said. It’s relatively easy to change an electrolyte for instance, but once you invest in machinery, it needs to stay in for at least ten years. That’s why Tesla keeps building batteries with cylindrical lithium-ion cells – they can't simply change all their machines overnight when a new technology becomes available, they added.
Both participants and IChemE noted how the institute could help by being a bridge between academia and industry and provide safety information and/or guidelines that approach BESS methodically, and with scientific understanding, as well as helping researchers to understand how products are mass produced.
Questions on topics such as recycling, flow batteries, and even data control philosophies, remained unanswered due to time constraints. All the more reason to have another roundtable, it was concluded.
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