*1.3. Hazards of Lithium-Ion Batteries in End-of-Life*

Lithium-ion batteries may undergo thermal runaway and uncontrolled heat release when they are electrically (e.g., over-charged, deep discharged), mechanically (e.g., penetration, crushing, vibration), or thermally (e.g., externally heated) damaged due to the increased energy density [8,9]. Hence, they may act as ignition sources leading to fire incidents during waste management processes, especially in the case of thermal or mechanical abuse [4].

According to [10], even severe crushing of cells that are below approximately 50% state-of-charge (SOC) will not lead to a severe reaction. Golubkov et al. [11] further investigated the influence of SOC on the thermal runaway behaviour of the two lithiumion battery subtypes and found out that, after thermal abuse, lithium-ion cells with Lix(Ni0.80Co0.15Al0.05)O2 cathodes (NCA) displayed an unmistakable thermal runaway when SOC was ≥25%. In the same way, lithium-ion cells with LixFePO4 cathode (LFP) showed mild exothermic reactions when the SOC was ≥25% and pronounced thermal runaway when SOC was ≥50%. Liu et al. [12] revealed that lithium-ion batteries with a lithium nickel manganese cobalt oxide cathode (NMC) show thermal runaway behaviour when the SOC is ≥25%.

Furthermore, due to significant differences in safety performance, waste batteries impose a higher safety hazard than new batteries, the majority of which are thoroughly tested before market input [8].

### *1.4. State-of-Charge*

Based on that, ref. [13,14] shed light on the distribution of SOC in end-of-life portable lithium-based batteries. ref. [13] found out that 11.4% of tested lithium-based batteries showed an SOC that was higher than 25% in the end-of-life. However, it is unknown how many batteries or cells were tested in the study. According to the results of [14], where 980 batteries were analysed, approximately 24% of the tested batteries showed an SOC higher than 25% (Table 2).

**Table 2.** Distribution of state of charge (SOC) of end-of-life lithium-ion batteries.


### *1.5. Risk Analysis and Risk Assessment*

Risk may be defined as consequences and its associated uncertainty or the combination of frequency or probability of occurrence and the severity or extent of damage [15]. When considering waste fires as the generalised hazard, the probability of an occurring fire incident is the first term, the expected financial losses the second term of the equation (Equation (1)):

$$R = \; probability\; of\;\;free\; incident \; \times \; (\text{expected})\; loss\; in\;\;case\; of\;\;the\; incident\tag{1}$$

If not, a single event is considered, but the sum of risks (e.g., for a single waste management company or the whole waste industry), Equation (2) is applied:

*R* = ∑ *f or all incidents probability o f fire incident* × (*expected*) *loss in case o f the incident* (2)
