Quantitative Analysis of the Coupled Mechanisms of Lithium Plating, SEI Growth, and Electrolyte Decomposition in Fast Charging Battery

Lithium ion battery (LIBs) degradation under fast-charging conditions limits its performance, yet systematic and quantitative studies of its mechanisms are still lacking. Here, we used dynamic electrochemical impedance spectroscopy (DEIS), mass spectrometry titration (MST), nuclear magnetic resonance (NMR), and gas chromatography–mass spectrometry (GC-MS) to reveal the degradation mechanisms in LiFePO4//graphite batteries at different charging rates. DEIS reveals three distinctive lithium plating processes: no lithium plating (1 and 2 C), lithium nucleation and growth (3 C), and lithium dendrite growth (4 to 6 C). In aged batteries, Li/LixC6 (x < 1), organic SEI components, and VC decomposition increase exponentially with increasing charging rate, while inorganic SEI increases slowly. Lithium dendrite growth (trigger mechanism) under fast charging conditions selectively induces VC decomposition and organic SEI formation (coupling mechanism) and results in lithium dendrite detachment forming "dead" lithium (accompanying mechanism), which together lead to rapid battery degradation at high charging rates.