Kinetic Study and Pyrolysis Behaviors of Spent LiFePO₄ Batteries

Abstract

Pyrolysis is an important way to deal with spent lithium ion batteries (LIBs). This study investigated the pyrolysis process and pyrolysis behaviors of the main components in spent LIBs. Kinetic studies on the pyrolysis process of spent LIBs were conducted using isoconversional method. The pyrolysis process of spent LIBs could be classified into four stages and the average of active energy was 85.36 kJ/mol. After the pyrolysis process, more than 96 wt % electrolyte, about 88 wt % separator, and 50 wt % poly(vinylidene difluoride) were converted into pyrolytic gas and oil, which were mainly composed of small molecular compounds, such as short-chain hydrocarbons and HF. Most of the harmful element fluorine contained in spent LIBs was converted into HF gas, which can be adsorbed by alkaline solution. Meanwhile, the pyrolysis residues of spent LIBs were mainly composed of carbon powder, fluorocarbon, hydrocarbons, active materials, copper, and aluminum foils. The active materials containing LiFePO 4 and C were not destroyed after the pyrolysis; thus, they can be reused as raw materials for producing new LIBs.

Environmental impacts, pollution sources and pathways of spent lithium-ion batteries

“…In landfills, batteries may be damaged during compacting and hence ignite either immediately or after burial: in the latter case, serious fires could result due to surrounding flammable materials and existing methane in the landfill environment. Even if damaged batteries do not ignite, the pyrolysis that accompanies thermal runaway will generate significant heat and toxic and potentially explosive gases 92 . It should be noted that fires caused by batteries may occur months or even years after they were buried.…”

High-Temperature Behavior of Spent Li-Ion Battery Black Mass in Inert Atmosphere

“…The literature mentions that heating the LFP cathode material (LiFePO 4 ) at 450-650 ℃ would remove PVDF (up to 96.85 wt%), in which the F content decreases from 8.51 wt% (before pyrolysis) to 1.67% (collected oil after pyrolysis). In this study, the decrease in F content was attributed to the evaporation of HF [13].…”

“…According to the literature, thermal pretreatment at 500-600 ℃ can be used to evaporate organic materials in BM (e.g., electrolyte, separator, and PVDF residuals) that contain F, which is known as a hazardous and corrosive element [10,[12][13][14]. Chemical and thermal procedures can be employed separately to remove binders and facilitate BM particle separation.…”

Oxidizing Roasting Behavior and Leaching Performance for the Recovery of Spent LiFePO4 Batteries

“…Correspondingly, the surface corrosion and unevenness of the Al foils increased. This can be attributed to the effective oxidative decomposition of binder PVDF during the higher temperature oxidizing roasting process, which released fluorine-containing gases such as hydrogen fluoride (HF), that could corrode the Al foils [31]. Figure 4 presents the recovery efficiency of cathode materials, weight loss rate of spent LiFePO 4 cathode plates and element content in calcined cathode materials at different roasting temperatures.…”