> The experiment revealed that the cathode particles’ charging speeds did not depend on their size. Li and Min think that the most likely explanation for this unexpected behavior is that larger particles actually behave like a collection of smaller particles when they crack. Another possibility is that the lithium ions move very quickly in the grain boundaries—the tiny spaces between the nanoscale crystals comprising the cathode particle. Li thinks this is unlikely unless the battery’s electrolyte—the liquid medium in which the lithium ions move—penetrates these boundaries, forming cracks.