Insight 10: Why Batteries Fail and How to Improve Them – Understanding Degradation to Advance Lithium-ion Battery Performance
Summary
Fundamental research on lithium-ion batteries (LIBs) dates to the 1970s, with their successful commercialisation delivered by Sony in 1991. Since then, LIBs have revolutionised the world of portable electronics, owing to their high energy density and long lifespan. Whilst LIB uptake initially powered small devices, they are now enabling global growth in electric vehicles, as well as having an increasing presence in new areas such as grid storage. Whilst LIBs will continue to lead electrification in multiple sectors, there are still requirements for improvements in lifetime, performance and safety. To achieve these researchers need to better understand – and find ways to mitigate – the many causes of battery degradation.
Focus of the Insight
Over the past decade, the battery research agenda has been predominantly led by the needs of the automotive industry. The main focus has centered on improving energy density to provide a driving range that is competitive with vehicles powered by internal combustion engines. With the sale of new petrol and diesel vehicles in the UK ending by 2030, there is a need to further reduce costs and improve performance to convince consumers that electrification can meet their usage requirements. Improvements are needed in the EV range, to increase the speed with which batteries can be charged and deliver power (which is enabled by power density levels) and, of course, to safety during both operation and storage. Suppressing and ultimately circumventing the degradation of LIB technology is critical for achieving the performance and safety demands required over the next decade.
Conclusion
In this Insight, we have explored the operation of LIBs and mapped out the key degradation modes that lead to capacity fade. We have outlined how an understanding of degradation mechanisms is critical for the design of next-generation LIBs with improved components. However, to achieve deeper understanding of degradation mechanisms, effective characterisation (from microscopic to macroscopic scales) is key and there is still room for improvement. This will benefit technical usage needs; an example of this would be a widening of the usable ‘state of charge’ window, which is presently restricted to protect the battery. Enabling a widening of these limits during use would, for example, enable an increase in EV range whilst maintaining lifetime for a low-cost automotive cell.
To repurpose LIBs in a second life application, effective characterisation will also be required to assess the battery’s SoH. For meaningful re-deployment, this will need to resolve features, timescales and underlying causes of degradation as accurately as possible.
There are also opportunities in developing techniques for the early detection of degradation ‘signatures’ in real world applications outside of a lab environment i.e., during deployment. Innovation is still required in the field to support both the evolution of existing lithium-ion chemistries and the emergence of novel chemistries.
This Insight considers present and future performance benchmarks and what is required at component level to meet these targets. As the world continues to electrify, we will continue to see a diversification of energy density and power needs and the development of batteries tailored to meet those needs. A deeper understanding of the battery degradation signatures of each of these battery types, facilitated by continued high quality research and innovation, will be required to ensure their successful deployment in commercial applications.