Recycling the anode from electric vehicle lithium ion batteries for a circular economy

Sargent, Alexander Thomas ORCID: 0000-0002-8301-0938 (2024). Recycling the anode from electric vehicle lithium ion batteries for a circular economy. University of Birmingham. Ph.D.

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Abstract

Lithium ion batteries are a vital part towards a decarbonised future. However, contained within are materials of critical importance, these include: cobalt, nickel, lithium, phosphorous and graphite (both synthetic and natural). Recycling of lithium ion batteries is essential to both ease the pressure on these unstable feedstocks and to ensure lithium ion batteries are sustainable. An often overlooked critical material within industry is graphite. This is due to the current economically low value of the material, however it’s monopolised supply chain and large greenhouse output warrants the case for graphite recycling. Another sentiment for graphite recycling is the specialist grade required for lithium ion batteries, requiring many energy taxing processing steps to create spherical, pitch coated particles for the anode. Academic research on graphite recovery mainly focuses on the extraction of graphite for use in alternative applications despite it being the active anode material in the vast majority of lithium-ion batteries. This is derived from the concept that use within a battery induces significant deterioration, including particle cracking and exfoliation.

Within this thesis, the quality of anode material recovered from cells of various states of health will be analysed in order to determine whether this material could act as a future source for battery-grade graphite. After which, a method to reclaim and reuse this graphite
will be developed.

Cells used within this work include quality control rejected, Envision AESC, first generation lithium ion pouch cells, and used (to various states of health) end of life lithium ion pouch cells obtained from a first generation electric Nissan Leaf.

The findings show that under normal and over-normal use, the graphite shows no substantial ageing. Degradation on the anode primarily occurs via solid electrolyte interface growth, metal deposition and particle disconnection. These factors can be easily addressed by recycling, rejuvenating and re-coating the anode. Therefore further focus was given to establishing a sustainable, quick and cost effective technique to extract and reuse the graphite for electrochemical use.

The difficulty in recycling graphite lies with the poly(vinylidene difluoride) binder. Poly(vinylidene difluoride) lacks solubility in non-harmful solvents making it difficult to separate the graphite from the other anode components. Within this work, it was found that when a discharged cell is dismantled, trace amounts of lithiated graphite remained in the anode. This lithiated graphite will react with water to produce hydrogen when submerged in water, which creates localised area of heat and pressure that can cleave the active material away from the current collector. The technique requires only water and its efficiency can be altered by increasing the time the anode is exposed to air. With increased air exposure, lithiated graphite will react with the moisture in the air and reduce the amount of hydrogen gas produced when submerged in water, decreasing the effectiveness of the delamination.

After delamination, the copper current collector was left bare and ready to collect, although with an oxidised surface. Anode active material (containing the graphite) could also be collected as large sheets. Lithium could be extracted from the delamination solution using sodium carbonate and phosphoric acid. As a proof of concept, (0.14 g of Li2CO3 and 0.34 g of Li3PO4 were extracted from an end of life anode weighing 13.5 g.

Water delamination also cleaned the graphite surface of most contaminates, although the poly(vinylidene difluoride) binder and metal contamination still remained. Annealing to 500 ◦C removed the binder and produced graphitic material similar to virgin batterygrade
graphite. This recovered graphite was used to create second-life anodes, whose electrochemical performance was tested. Half cell performance showed that graphite recovered from a cell with only 30% of its original capacity could perform close to the theoretical capacity of graphite after water delamination and annealing. This demonstrates that End-of-Life lithium ion batteries can provide high-performing battery-grade graphite,
helping to secure future supplies of this critical raw material and alleviating concerns over future accumulation of battery waste.

Water delamination was ineffective after exposing the anodes to air for more than four weeks. It was found that the use of acids allowed for an extended period of delamination that provided graphite of similar quality.

Up-cycling of the graphite material was attempted via delamination within colloidal silica. Here, nanoparticles of silica would coat the graphite allowing for increased capacity during second life use. However, the deposited silica particles were too large to be electrochemically active and therefore future avenues for optimising this procedure are suggested.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):