Figure 1.1. A schematic showing the construction of cylindrical
LIB and the constituent elements used in each component (Kim, et al.,
2021).
EOL Management
Most LIBs have a lifespan of between 3 and 8 years (Mossali, et al.,
2020), after which they reach their so-called end-of-life (EOL).
Individual cells from EOL LIBs, and particularly those from electric
vehicles (EVs), can be reused for applications such as backup power and
stationary energy storage units (Kim, et al., 2021). At present, this is
feasible because the demand for used batteries far outweighs the supply
of used batteries (Harper, et al., 2019). However, as the uptake of EVs
increases, it is anticipated that the supply of cells (new and reused)
will eventually outweigh the demand. At this point, recycling will
become a necessity. Furthermore, a percentage of cells from EOL
batteries cannot be reused due to irreversible damage that can occur.
These have a final fate of recycling, regardless of the route they take
to arrive there (Harper, et al., 2019). Currently, only a small
percentage of the batteries that are produced are being recycled at EOL
(Velázquez-Martinez, et al., 2019), with estimates that 95% of the LIBs
that were produced globally in 2016 remaining stockpiled in old devices
(Heelan, et al., 2016). This is predominantly due to most people not
knowing how to safely manage EOL LIBs and being ignorant of the risks
resulting from poor management (Mossali, et al., 2020).
Although recycling is a necessary treatment process for EOL LIBs, it is
also a source of secondary raw materials (Velázquez-Martinez, et al.,
2019; Harper, et al., 2019). Raw materials of particular interest from
recycling include Co, Cu, Ni, Al, and Li, due to their high value (Li,
et al., 2018; Zhang, et al., 2021). This is of importance due to the
potential of demand outstripping supply for some materials, such as Li
(Sonoc, et al., 2015). Additionally, in comparison to the production of
virgin Li, in which ± 250 tons of feedstock are needed to produce 1 ton
of Li, recycling can recover 1 ton of Li from ± 28 tons of feedstock
(Harper, et al., 2019). Furthermore, the production of some virgin
materials, such as Co, raise numerous social and ethical concerns
(Harper, et al., 2019). More importantly, the recycling of LIBs prevents
hazardous materials from entering the environment.
The two commonly used categories of LIB recycling are pyrometallurgical
and hydrometallurgical processes (Kim, et al., 2021). Newer direct
recycling processes are also under development, but these are not widely
operated on an industrial scale yet. Pyrometallurgical processes are the
most prevalent because they can handle large volumes of LIBs without
need for pre-treatment and regardless of their state-of-charge (SOC)
(Zheng, et al., 2018; Kim, et al., 2021; Rouhi, et al., 2021). When
using pyrometallurgical processes, Ni, Co, and Cu are recovered from the
batteries, but other materials such as the Li, Al and Mn are lost in the
slag, while the graphite burns (Yi, et al., 2021). Hydrometallurgical
processes are generally better equipped to enable the recovery of
materials; however, they require shredding of the LIBs as a first step
in the process (Wuschke, et al., 2019). The shredding processes must
have a means of damping explosions and preventing fires or else
additional stabilisation of the LIBs is required before shredding
(Segura-Bailón, et al., 2024).
Discharging
(stabilisation)
For LIBs, discharging process refers to processes where the amounts of
metallic Li present in the cells are oxidised, preventing any violent
reactions which occur when the Li is exposed to oxygen and/or water in
the air (Duan, et al., 2022; Yang, et al., 2022). The discharging
process (also referred to as stabilisation) forces the
Li+ ions to move from being absorbed by the graphite
anode back to a stable cathode material. This means that lithium is
thermodynamically stable and will not react violently if exposed to air
or water (Punt, et al., 2022). This also allows to maximise the recovery
of the lithium from the cathode by removing it from the anode. It also
prevents short-circuits leading to thermal runaway (TR) events (Perea,
et al., 2018; Sahraei, et al., 2012), as this would lead to the
self-ignition of the metallic lithium present in the graphite anodes of
the cells (Jena, et al., 2021; Zheng, et al., 2023) without the need for
an external fuel source or oxygen once they have reached a certain
temperature (Sommerville, et al., 2020)
Thermal runaway
Thermal runaway (TR) events in batteries can lead to major dangers,
including the formation of hydrogen fluoride (HF) from the
polyvinylidene fluoride (PVDF) binder, formation of carcinogenic nickel
oxide, and exothermic decomposition of the conducting salt,
LiPF6 to form hydrogen fluoride (Hanisch, et al., 2015;
Lee, et al., 2023). Nedjalkov et al. (2016) identified 11 different
hazardous gases being released from a LIB while in TR. These include
styrene, hydrogen fluoride and acrolein.
An oft-neglected fact is that the danger of TR exists even in stockpiled
batteries awaiting processing (Harper, et al., 2019). It was reported
that 50 % of all recycling and waste fires in the United Kingdom were
due to stockpiled LIBs (Brown, et al., 2021). It is therefore important
that these stockpiled LIBs be made safe to prevent TR. LIBs that are no
longer susceptible to TR have the added advantage of significantly
reduced transportation costs (Larouche, et al., 2020).
Stabilisation processes
There are several different techniques used for the stabilisation of
LIBs. These techniques are listed in Table 1.2. There is limited
research that has been undertaken on the stabilisation of LIBs. Of the
346 articles reviewed by Gao et al. (2024) only 75 even considered the
discharge methods utilised as information worth mentioning, and even
fewer of these gave more than a cursory mention of these discharge
methods. This has led to an incomplete picture of the best methods of
stabilisation (Fang, et al., 2022).
Table 1.2. Stabilisation techniques used for LIBs.