Europe plans to reduce greenhouse gas emissions from transport by 90% by 2050[1]. Reaching this goal will necessarily involve a profound transformation of our society, which has been shaped by and for the combustion engine car.

Transports electrification appears to be the option promoted by public authorities. Although electromobility has major advantages such as urban air quality improvement and greenhouse gas
emissions reduction, this technology is not the ideal solution that would alone transform human
mobility habits into sustainable [2]. The high cost of this technology also raises questions about its
ability to meet the travel needs of the entire population [3].

With the announced end of combustion engines by 2035, the question of the technological choice
for tomorrow’s mobility cannot be postponed. [4]. To date, the electric vehicle is by far the most mature alternative to the combustion engine. It is now necessary to to make this choice relevant to make our mobility more sustainable and accessible to all.

In an electric vehicle, the battery is the element that requires the most attention from the point of
view of environmental impact. Numerous studies analyzing the life cycle of electric vehicles show
the influence of the battery on the environmental impact that factors such as [5]:

In order to decarbonize individual mobility, it would be wise to promote the use of low-carbon energies, to favour vehicles with a reduced range and to adapt their use in order to extend their life span as much as possible.

Public authorities and individuals alike have a role to play in this quest for sustainable mobility. The circular economy as a solution for sustainable mobility for all. According to the French Environment and Energy Management Agency (ADEME) [6], the circular economy is an economic system that aims to:

In the automotive sector, vehicle end-of-life management plays a central role in increasing efficiency while reducing the cost of these vehicles and creating local employment. A vehicle is
considered “end-of-life” when it no longer has sufficient performance to meet the needs of motorists. When this vehicle is electric, the battery’s ageing can lead to a range deterioration that is no longer acceptable.

In a 2020 report, ADEME indicated that in France 549 electric vehicles had reached “end of life” in
2018, which represents 0.0005% of the french end-of-life vehicles over that same year [7]. These
low volumes are a hindrance to the achievement of economic balance by recyclers [8]. While
waiting for larger volumes and considering the technical limits inherent to recycling, the various
players in the electric vehicle market are devising alternatives to the alternatives to the traditional
end-of-life management strategy: all-recycling [9] [10].

From an environmental point of view, reuse is preferable to recycling since this end-of-life
management strategy allows to extend the life of products and therefore to increase the efficiency of resource use [11]. Legally, reuse is defined as the operation by which an object that is not waste can be used again for its original purpose. In concrete terms, reuse consists in giving a second life to objects [12].

This strategy also has an economic interest. Firstly, it responds to an issue of economic sovereignty
by saving critical imported mining resources (lithium, cobalt, nickel, etc). Secondly, the revenues
generated by the sale of batteries at the end of their life may enable car manufacturers to reduce the sales price of their vehicles. Reuse therefore facilitates access to electric mobility for as many
people as possible. Finally, this strategy can be deployed at the local level, which ensures the
creation of jobs that cannot be relocated.

If this practice is popular for clothes and everyday objects, reuse is still in its infancy for is still in its infancy for batteries [13]. The first hundreds of batteries available for a second life are exploited in different pilot projects involving industrial and academic actors [14]. These projects
aim to evaluate the economic interest and technical feasibility of reuse of used lithium-ion batteries.

The first conclusions of the pilot projects show that the second life use and the degree of
collaboration of the companies involved in the project have a significant impact on the economic
interest of this market. Stationary energy storage applications have been largely favored in
these projects. However, some smaller-scale projects have also tested the use of second-life batteries in mobile applications such as electric boats or electric vehicle charging robots [16] [17].
The results of these pilot projects seem to have removed the economic uncertainties about the reuse of batteries, since large since major groups such as Daimler and Renault have announced the setting up of factories dedicated to plants dedicated to second life [18].

The reuse of batteries also raises questions about technical feasibility. Three scientific barriers
remain to be overcome to facilitate the deployment of of second life batteries:

Rapid estimation of the battery’s state of health is a prerequisite for second life use. On On a new
battery, the state of health does not need to be assessed at reception. Whereas on a battery that has been used in a first application and that one wishes to reuse, the state of health is not known. In order to preserve the economic interest of this second life battery, the characterization method must be as fast as possible and require the least amount of human and experimental resources [19].

Assessing the remaining lifetime allows to anticipate the failure of monitored batteries and to refine economic models for insurance, for example. This information is crucial to evaluate the long-term economic interest of the second life battery compared to the new one.

Given the prohibitive costs of disassembly and reassembly, second life batteries are generally
reused without major structural modifications. However, the aged elements constituting a battery
can be particularly heterogeneous in terms of health status.

These differences can force the user to limit the load according to the characteristics of the less
performing cells. To facilitate the use of batteries containing heterogeneous elements, balancing is
commonly used.

This solution aims at homogenizing the state of charge of the different cells, to allow their use over
the whole operating range [20]. The implementation of a balancing strategy allows to some extent to avoid the long and expensive process of characterization and sorting of cells.

Our mobility will not become sustainable simply by being electric. The principles of the circular
economy can help to achieve this ideal, but a number of economic and technical obstacles remain to be overcome. Ongoing research to reduce the environmental impact of electric cars should help us move towards more sustainable mobility. Nevertheless, in view of the climate emergency, more immediate solutions could be implemented. The filling of vehicles, the modal shift towards soft mobility, the reduction of vehicle mass or the reduction of the need for transport are undoubtedly levers that are just as relevant as the electrification of vehicles [21].