Flash cycling; side reactions; lithium plating; SEI degradation; extreme fast charging; battery safety. 1. Introduction The demand for electric vehicles (EVs) and portable electronics capable of “flash” charging (<15 minutes) has pushed battery operating currents beyond 10C (6-minute full charge). While flash cycling enables convenience, it exacerbates side S —a collective term for parasitic and damaging processes occurring on the electrode’s side surfaces (edges, pores, and current collector interfaces) and at the solid-electrolyte interphase (SEI).

Author: [Your Name/Institution] Date: April 14, 2026 Journal: Journal of Power Sources Rapid Communications (hypothetical) Abstract Flash cycling—charging or discharging a battery in minutes or seconds—induces unique “side S” phenomena, where ‘S’ denotes secondary surface reactions, stress gradients, and spatial inhomogeneities at the electrode-electrolyte interface. This paper systematically analyzes the side effects of extreme rate cycling on anode materials (graphite, silicon, LTO). We identify three primary side-S mechanisms: (1) lithium plating under high overpotential, (2) localized thermal runaway due to Joule heating, and (3) mechanical fracturing of the solid-electrolyte interphase (SEI). Experimental data from symmetric coin cells cycled at 10C–50C rates show that side S leads to a 40–70% capacity loss within 200 cycles. Mitigation via electrolyte additives (FEC, VC) and porous electrode grading improves cycle life by 3×. We conclude that flash cycling side S is the dominant failure vector for extreme fast charging (XFC) batteries.