How Graphite Particle Sizes Affect Fast Charging Performance of Ultra-Thin Layer Electrodes for Li- Ion Batteries

Abstract

Extreme fast charging (XFC, ≤15 min) of lithium-ion batteries is highly desirable to accelerate mass market adoption of electric vehicles.[1] However, great capacity fading, as well as safety issues due to the lithium plating, limit its implementation. In this study, we investigated the fast-charging capability of graphite materials with various particle sizes under different charging currents up to 6C. To eliminate Li+ ion gradients effects across the thickness of electrode[2], ultra-thin layer graphite electrodes were developed to investigate the “real" fast-charging capability of graphite at particle level by assessing its lithium plating limit. Observations derived from the electrochemical results as well as microscopy characterization revealed that smaller particles exhibited a superior fast-charging performance including better capacity reversibility, less polarization and less lithium plating. Moreover, smaller particles are observed to be able to handle higher C rate charging without Li plating, graphite electrodes with particle size of ~5μm can be safely charged to 80% SOC at 4C. While with particle size of ~15 μm, Li plating occurred on the graphite electrode at 2C. According to pseudo-2-dimensional (P2D) model, the superiority of the small particles might be due to the faster diffusion and intercalation through the particle because of their smaller size and faster rate kinetics due to their larger surface area. This work can help us to better understand the fast-charging behavior and provide the guidance to design the optimum electrode architecture for high-rate of lithium-ion batteries.Keywords: Ultra-thin electrode, Graphite Electrode, Particle Size, Fast Charging, Li-Ion Batteries[1] D. Howell et al., “Enabling Fast Charging: A Technology Gap Assessment,” 2017.[2] K. P. C. Yao, J. S. Okasinski, K. Kalaga, I. A. Shkrob, and D. P. Abraham, “Quantifying lithium concentration gradients in the graphite electrode of Li-ion cells using operando energy dispersive X-ray diffraction,” Energy Environ Sci, vol. 12, no. 2, pp. 656–665, Feb. 2019, doi: 10.1039/C8EE02373E.