Challenges in Recycling Spent Lithium-Ion Batteries: Spotlight on Polyvinylidene Fluoride Removal

Abstract

In the recycling of retired lithium-ion batteries (LIBs), the cathode materials containing valuable metals should be first separated from the current collector aluminum foil to decrease the difficulty and complexity in the subsequent metal extraction. However, strong the binding force of organic binder polyvinylidene fluoride (PVDF) prevents effective separation of cathode materials and Al foil, thus affecting metal recycling. This paper reviews the composition, property, function, and binding mechanism of PVDF, and elaborates on the separation technologies of cathode material and Al foil (e.g., physical separation, solid-phase thermochemistry, solution chemistry, and solvent chemistry) as well as the corresponding reaction behavior and transformation mechanisms of PVDF. Due to the characteristic variation of the reaction systems, the dissolution, swelling, melting, and degradation processes and mechanisms of PVDF exhibit considerable differences, posing new challenges to efficient recycling of spent LIBs worldwide. It is critical to separate cathode materials and Al foil and recycle PVDF to reduce environmental risks from the recovery of retired LIBs resources. Developing fluorine-free alternative materials and solid-state electrolytes is a potential way to mitigate PVDF pollution in the recycling of spent LIBs in the EV era.

Keywords: EV battery recycling; cathode materials; circular economy; lithium recovery; sustainable waste management.

Figure 1

Structure diagrams of LIBs. a) Main components. Reproduced with permission.^{[ 17 ]} Copyright 2018, Elsevier. b) Internal structure. Reproduced with permission.^{[ 21 ]} Copyright 2022, John Wiley and Sons. c) Structure of cathode materials and Al foil (Yellow coating represents PVDF film). Reproduced with permission.^{[ 23 ]} Copyright 2019, American Chemical Society.

Figure 2

a) Different crystal types of PVDF α, β, and γ. Reproduced under the terms of the open access Creative Common CC BY license.^{[ 41 ]} Copyright 2019, Molecular Diversity Preservation International (MDPI). b) Application process of PVDF. Reproduced with permission.^{[ 44 ]} Copyright 2022, Elsevier. c) Bonding mechanism of PVDF in different LIBs. Reproduced with permission.^{[ 53 ]} Copyright 2021, Elsevier.

Figure 3

Principles of different systems for the separation of the cathode materials from Al foil.^{[ 63} , ⁶⁴ , ^{66 ]}

Figure 4

Tracing PVDF in the process of dismantling–crushing–grinding–flotation of spent LIBs.^{[ 71} , ^{75 ]}

Figure 5

Degradation products and occurrence forms of PVDF in solid phase thermochemical media at different temperatures.^{[ 23} , ⁸² , ⁸⁴ , ⁹⁰ , ^{91 ]}

Figure 6

Mechanisms and reactive species of separation of cathode material and Al foil with different solution systems.^{[ 124} , ^{125 ]}