Non-equilibrium thermodynamic modelling of cooling path dependent phase evolution of Li2SiO3 from Li2O-SiO2 melt by considering mixed kinetic phenomena and time-dependent concentration fields

Abstract

Efficient recovery of Li2SiO3 or other Li compounds from slag streams generating from pyrometallurgical treatment of lithium ion batteries (LIBs) requires fundamental understanding of the kinetics that govern slag solidification. In this work, a non-equilibrium thermodynamic model that incorporates mixed internal kinetics of diffusion and interface mobility, influenced by external cooling paths, is developed to investigate for the first time, the dependence of the phase evolution rate of Li2SiO3 from Li2O-SiO2 melt, on the available driving forces and time-dependent concentration fields. Experiments with different thermal profiles were performed for inverse identification of the kinetic coefficients. It turned out that different cooling rates (1.5Kmin−1, 5Kmin−1 and 10Kmin−1) depict an initial dominance of thermodynamic driving force superseded by kinetic forces in subsequent phase evolution. A certain interface velocity maximum is exhibited during phase formation, where the magnitude decreases progressively from 5.5 × 10−7ms−1 to 3.9 × 10−7ms−1 to 2.1 × 10−7ms−1 with a decrease of the cooling rates.