Analysis of Thermal Reduction of Mixture of Organic Components on Cathode Materials of Spent Ternary Lithium-Ion Battery

Abstract

Spent ternary lithium-ion batteries, containing PVDF binder and acetylene black as conductive agents, have the potential to destroy the stable layered structure of cathode materials during heat treatment due to their reducibility. However, the reduction mechanism of two of the organic components and their mixtures on cathode materials remains unclear. In this work, the in situ thermal reduction of transition metals using inherent organic components is conducted and the reduction mechanisms of mixtures are analyzed deeply. Results revealed that PVDF mainly relies on high-temperature pyrolysis to generate reducing gases along with a small amount of pyrolysis residual carbon. Acetylene black primarily achieves cathode material reduction through carbothermal reduction within a solid−solid reaction system. The temperature for the thermal reduction of PVDF is about 500 °C, which is lower than that of acetylene black (575 °C). PY-GC-MS testing confirmed that the pyrolysis products of mixtures were completely consistent with those of PVDF, indicating that PVDF and acetylene black did not chemically react during thermal reduction. Furthermore, the addition of acetylene black to PVDF had a positive effect on the thermal reduction reaction, enhancing the reduction effect. However, in mixtures with higher acetylene black content and lower PVDF content, increased PVDF emission created greater separation between acetylene black and the cathode materials, negatively affecting the solid−solid reaction and reducing the overall reduction efficiency.