Lithium-ion battery second life: pathways, challenges and outlook

Abstract

Net zero targets have resulted in a drive to decarbonise the transport sector worldwide through electrification. This has, in turn, led to an exponentially growing battery market and, conversely, increasing attention on how we can reduce the environmental impact of batteries and promote a more efficient circular economy to achieve real net zero. As these batteries reach the end of their first life, challenges arise as to how to collect and process them, in order to maximise their economical use before finally being recycled. Despite the growing body of work around this topic, the decision-making process on which pathways batteries could take is not yet well understood, and clear policies and standards to support implementation of processes and infrastructure are still lacking. Requirements and challenges behind recycling and second life applications are complex and continue being defined in industry and academia. Both pathways rely on cell collection, selection and processing, and are confronted with the complexities of pack disassembly, as well as a diversity of cell chemistries, state-of-health, size, and form factor. There are several opportunities to address these barriers, such as standardisation of battery design and reviewing the criteria for a battery's end-of-life. These revisions could potentially improve the overall sustainability of batteries, but may require policies to drive such transformation across the industry. The influence of policies in triggering a pattern of behaviour that favours one pathway over another are examined and suggestions are made for policy amendments that could support a second life pipeline, while encouraging the development of an efficient recycling industry. This review explains the different pathways that end-of-life EV batteries could follow, either immediate recycling or service in one of a variety of second life applications, before eventual recycling. The challenges and barriers to each pathway are discussed, taking into account their relative environmental and economic feasibility and competing advantages and disadvantages of each. The review identifies key areas where processes need to be simplified and decision criteria clearly defined, so that optimal pathways can be rapidly determined for each end-of-life battery.

Keywords: end-of-life; lithium-ion battery; policy; regulation; repurposing; safety; second life; state-of-health.

FIGURE 1

A flowchart showing the end-of-life (EoL) pathways for the battery lifecycle, including decisions which need to be made at specific stages. Qualitative ranges have been selected, as the actual figures may change over time. For example, at present, when deciding which route to choose for an EoL battery pack, based on the state-of-health (SoH) check, those which exceed 80% (“above”) are suitable for reuse in another automotive application; those which demonstrate 50% or less (“below”) must be dismantled and those which lie between these limits (“mid-range”) can be considered for repurposing. Reprinted with permission from Edge, J. S., DOI:10.5281/zenodo.10257443 Preprint at 2023.

FIGURE 2

State-of-health (SoH) estimation methods.

FIGURE 3

Simple example of an Electrochemical Impedance Spectroscopy plot used alongside an appropriate Equivalent Circuit Model to determine resistance mechanisms and parameters, CPE represents constant phase elements for the Solid Electrolyte Interphase (SEI) and charge transfer mechanisms.

FIGURE 4

Summary of the costs involved in the refurbishment of EV batteries from the collection to the selling. Reprinted from Martinez-Laserna et al. Renew. Sust. Energ. Rev. 93, 701–718, 2018.

FIGURE 5

Cost of battery disassembly (in $/kWh) showing the individual cost of each step and the cumulative cost up to the respective disassembly stage. Reprinted with permission from Rallo et al. Resour. Conserv. Recycl. 159, 104785, 2020.

FIGURE 6

Quantity sold into second-life applications under different recycling net credit scenarios, shown in comparison to the total used EV batteries produced. Reprinted with permission from Sun et al. J. Energy Storage 19, 41–51, 2018.

FIGURE 7

Global warming potential (GWP) for each configuration at 100 kW charging power for five U.S. Cities [DET, Detroit; LA, Los Angeles; NYC, New York City; PHX, Phoenix; POR, Portland. Adapted from Kamath et al. Environ. Sci. Technol. 54, 6878–6887, 2020.