Accurate estimation of solid-phase diffusivity in natural graphite using a voltage relaxation technique

Natural Graphite (NG) is a widely used anode material in lithium-ion batteries (LIBs), prized for its high theoretical capacity, excellent electrical conductivity and cost-effectiveness. However, its performance is strongly influenced by lithium diffusion through its layered structure, influencing the charging rates, cycle life, and overall efficiency. Thus, accurate estimation of lithium diffusivity in NG is crucial for understanding and optimizing its performance. Traditional methods, like Galvanostatic intermittent titration technique (GITT), often provide inaccurate diffusivity estimates due to non-linear dependence of the open-circuit potential (OCP) on the state of charge (SOC), and assumptions that oversimplify the diffusion process. The recently introduced method, DELVRT (Diffusivity Estimation from Long-term Voltage Relaxation Technique), offers a promising alternative. By harnessing the subtle dynamics of voltage relaxation during rest periods, dominantly influenced by solid-phase diffusion, DELVRT provides a more accurate and robust diffusivity estimation. In this study, DELVRT is used to measure the diffusivity of Lithium in NG as a function of the SOC, under various conditions, providing consistent, reliable estimates, independent of the current history. This is important towards robust state estimations for electrochemical models of LIBs and for NG to unlock its full potential as an anode material, enabling more efficient and reliable LIBs. • Accurate and reliable Lithium diffusivity estimation in Graphite via DELVRT. • Independence from experimental conditions with DELVRT diffusivity measurements. • Validation through experimental data, capturing SOC-dependent diffusivity trends. • Improves electrochemical modelling for state estimation in lithium-ion batteries. • Contribution in enabling efficient and safer lithium-ion battery systems.