Environmental life cycle impacts of lithium-sulfur and sodium-ion batteries

Licentiate thesis, 2024

Mitigating climate change and other environmental problems will require a transition away from fossil fuels. Batteries can be part of such a transition as they enable a cleaner energy system by providing energy storage for intermittent energy sources such as wind and solar power, as well as a cleaner transport system by replacing internal combustion engine vehicles with electric vehicles. Globally, battery demand is projected to increase 6-20 times in the coming 15 years. If batteries are to become sustainability enablers globally, a large-scale diffusion of these technologies must be possible. To achieve such a diffusion, batteries should preferably contain few metals and materials connected to resource availability issues to reduce the risk of resource-related bottlenecks. Furthermore, battery technologies should be as environmentally benign as possible. The lithium-ion battery (LIB) is currently the dominating rechargeable battery technology, and while having high technical performance, it contains metals and materials connected to resource availability issues. However, there are several next-generation batteries (NGBs) that might be able to outperform LIBs from a life cycle environmental and resource perspective. The aim of this thesis is therefore to investigate the environmental and resource impacts of two NGBs, lithium-sulfur (Li-S) batteries and sodium-ion batteries (SIBs), with the overall goal of providing technology guidance.
 
To fulfil this aim, three studies have been included in the thesis. Two of them address the life cycle environmental and resource impacts of Li-S and SIBs, respectively. Furthermore, as lithium is a key metal for Li-S batteries, it is important to understand the environmental implications of extracting lithium from various sources with different ore grades. Therefore, in the third study, several lithium sources and their corresponding lithium production routes were assessed. Life cycle assessment (LCA) was applied in all studies, as comparing environmental and resource impacts of products in a holistic manner requires a life cycle perspective. Additionally, as Li-S batteries and SIBs are emerging technologies and not yet produced at large scale, prospective LCA was applied. Prospective aspects that were considered include production scale-up and accounting for potential future changes to the batteries as well as some supplies of materials and energy.
 
The results show that SIBs are on par with LIBs regarding climate change and perform better regarding mineral resource scarcity. Li-S batteries can perform similarly to LIBs for the same impact categories, but the results are uncertain as the future values of several Li-S design parameters are based on estimations. Furthermore, the environmental and resource performance of Li-S batteries is sensitive towards the lithium source and grade. Several lessons have been learned regarding Li-S battery and SIB impacts as well as the methodology applied. It is concluded that of the investigated NGBs, SIBs show the largest potential from an environmental and resource perspective. Furthermore, due to uncertainties inherent to prospective LCA, results should be seen as indicative rather than absolute. Additionally, involving a technology expert in prospective LCA projects can enhance the understanding of the future technical NGB systems.