On the Influence of Recycled Graphite Properties for Anode Preparation and Efficiency in LIBs
Authors: Briqueleur Elsa , Rica Brunilda , Bogaert Antonin , Waldron Karen , Dolle Mickael 
Published: December 2024

The consumption of rechargeable batteries, and especially lithium-ion batteries (LIBs) has exponentially grown since their first commercialization. They are currently dominating the market, both for stationary and mobile applications: from one LIB to power a cellphone to a pack of six cells in a laptop or thousands in an electric vehicle (E.V.). In short, the number of LIBs currently in use and in need for end-of-life management in the coming years is tremendous. Furthermore, considering the new regulations following commitments to allow for the energy transition, the E.V. market is expected to continue to grow, which on one hand implies a surge in the international battery demand, which incidentally puts pressure on the stock and on the availability of the valuable elements composing the battery, and on the other hands, requires solving their end-of-life management. For both these reasons, the LIBs recycling became a necessity as it offers several advantages, including: (i) providing a sustainable feedstock of battery components; (ii) avoiding mining of raw limited minerals; (iii) adding value to a system (i.e. the battery pack) that was meant to be discarded; (iv) avoiding the creation of waste.

At the end of life, the LIBs are usually crushed to obtain a “black mass” from which minerals must be extracted. Nowadays, most of the spent batteries actually end their life in China, where pyrometallurgy is used (i.e. heating up the batteries to high temperature (e.g. 1000°C)) to recover cobalt, and nickel. However, lithium can not be recovered using the pyro-metallurgical process as it will be lost in the slag, as well as aluminium. Graphite is also destroyed in this process. Another technique is hydrometallurgy to recover the valuable metals in solution as well as the graphite as a solid. Moreover, lithium can also be recovered in this recycling process, by precipitation of lithium carbonate. However, the currently used hydrometallurgy processes often imply the use of H2SO4/H2O2 mixture which is detrimental to the graphitic structure and lead to acidic wastewater generation.

Even though graphite was recently classified as “critical” by Canada, so far, the focus in the LIBs recycling field wad mainly placed on the recovery and regeneration of the critical minerals that compose the cathode (Lithium, Cobalt, Nickel), due to their high value on the market. This explains the currently developed methods that were detrimental to this long forgotten critical mineral. Therefore, we hereby present a recycling process that, in addition to being efficient for the recovery of transition metals, takes into account the regeneration of graphite. As demonstrated with XRD, Raman and analytical results, by developing and tailoring a soft hydrometallurgy leaching treatment of black mass, the graphitic structure of the residues was preserved while still being purified from their contaminants. In addition, the large acidic wastewater usually generated by hydrometallurgy was avoided. It was also demonstrated that thanks to the preservation of the graphitic structure during its purification, the material only needed low temperature and soft conditions for its refinement. The physico-chemical properties of this new graphite feedstock were thoroughly evaluated and compared to battery-grade graphite to understand their implications in both the electrode making and LIB efficiency.