Mechanisms for Lithium Nucleation and Dendrite Growth in Selected Carbon Allotropes

Using information gained from parallel investigations on lithiated/over-lithiated graphite and hard carbon, we propose two different processes for lithium nucleation and dendrite growth in the carbon allotropes based on their different crystal structures. In the case of graphite, lithium nucleation and initial growth of lithium dendrites occur inhomogeneously on the graphite surfaces during the over-lithiation process, which exposes lithium nucleation to the electrolyte causing formation of a large amount of electrolyte degradation products (EDPs) and knob-like dendrites covered with a thick lithium electrolyte interphase (LEI). However, in the, case of hard carbon, lithium nucleation and initial growth occur inside the hard carbon nanopores, which limits side reactions, provides a higher capacity (similar to 550 mA h/g vs similar to 370 mA h/g for graphite), and generates dendrites with smooth clean surfaces during the over-lithiation process. These findings could profoundly influence the overall electrode design, the improvement of performance, and the inherent safety of carbon-based electrodes for lithium ion batteries.