DataSheet1_Hydrogen reduction of spent lithium-ion battery cathode material for metal recovery: Mechanism and kinetics.docx

Hydrogen reduction is becoming a promising method for recycling lithium-ion battery cathode materials. However, the reaction mechanism and kinetics during hydrogen reduction are unclear, requiring further investigation. Therefore, non-isothermal and isothermal reduction experiments were conducted to evaluate the temperature dependence of the hydrogen reduction kinetics using simultaneous thermogravimetric and differential thermal analysis equipped with mass spectrometry. XRD and SEM were used to characterize the reduction products to understand the underlying reduction mechanisms. The hydrogen reduction profile could be divided into three main stages: decomposition of cathode materials, reduction of the resultant nickel and cobalt oxides, and reduction of LiMnO2 and residual nickel and cobalt oxides. The hydrogen reduction rate increased with increasing temperature, and 800°C was the optimum temperature for separating the magnetic Ni-Co alloy from the non-magnetic manganese oxide particles. The apparent activation energy for the isothermal tests in the range of 500–700°C was 84.86 kJ/mol, and the rate-controlling step was the inward diffusion of H2(g) within each particle. There was an downward progression of the reduction through the material bed for the isothermal tests in the range of 700–900°C, with an apparent activation energy of 51.82 kJ/mol.

氢还原法正成为锂离子电池正极材料回收的极具潜力的技术手段。然而，氢还原过程中的反应机理与动力学特性尚未明确，仍需开展深入研究。为此，本研究开展了非等温与等温还原实验，采用配备质谱检测器的同步热重-差热分析仪，评估氢还原动力学的温度依赖性；同时借助X射线衍射（XRD）与扫描电子显微镜（SEM）对还原产物进行表征，以揭示氢还原的内在机制。氢还原过程可分为三个主要阶段：正极材料的分解、生成的镍钴氧化物的还原，以及LiMnO₂与残留镍钴氧化物的还原。氢还原速率随温度升高而增大，且800℃为磁性镍钴合金与非磁性氧化锰颗粒实现有效磁分离的最优温度。在500~700℃区间的等温还原实验中，表观活化能为84.86 kJ/mol，速率控制步骤为氢气（H₂(g)）在单个颗粒内部的向内扩散。在700~900℃区间的等温还原实验中，还原反应沿物料床层自上而下逐步推进，表观活化能为51.82 kJ/mol。