Pyrolyzed "Black Mass" Feedstocks and Their Synthetic Proxies Relevant to Li-Ion Battery Recycling

Lithium-ion battery (LIB) recycling aims to recover valuable materials present within end-of-life electrochemical cells. Industrial recycling processes produce "black mass" from recycling feedstock from which desirable materials can be recollected. Spent cells first undergo mechanical shredding and sieving, and organic components are removed by thermal treatment (pyrolysis) before hydrometallurgical processing is employed to recover the constituent elements. Black mass may contain a range of reaction products, formed at high temperature during pyrolysis, due to the compositionally complex and inhomogeneous nature of recycling feedstock. These products, however, may have different elemental compositions, ratios, and structures, making efficient hydrometallurgical recovery difficult. Here, we present three distinct, industrially sourced black mass samples containing Li-(Ni _x Mn _y Co _z )-O₂ (x + y + z = 1) positive electrodes of varying composition. We employ a suite of structural and compositional characterization techniques, including synchrotron X-ray and neutron powder diffraction and element specific analysis (X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma optical emission spectroscopy), to identify phases formed during commercial treatment of recycling feedstocks and how their relative quantities are affected by process order. Additionally, we also present results of studies on simpler model systems to better identify minor phases present within the complex recycling feedstocks and to direct the efficient recovery of valuable components.