Synergistic tuning of inner and outer Helmholtz layers for ultra-stable fast charging in lithium-ion batteries

The sluggish interfacial kinetics of graphite anodes restricts the fast-charging capability of lithium-ion batteries (LIBs), inducing severe lithium plating and electrolyte decomposition, which markedly accelerates battery degradation and raises safety concerns. To address this challenge, we design a novel fast-charging electrolyte via the incorporation of trace-level additives, enabling LIBs to achieve ultra-stable fast-charging performance—an outcome not previously reported. Specifically, practical Ah-level graphite‖NCM523 pouch cells assembled with this electrolyte retain 90.14% of their 0.1C capacity at 8C and maintain over 82% capacity retention across 6000 cycles. Furthermore, this work uncovers a new synergistic mechanism. The 1-ethyl-3-methylimidazolium cation generates a strong electric field in the inner Helmholtz layer (IHL) through π–π interactions, while simultaneously forming an anion-mediated bridging network in the outer Helmholtz layer (OHL). This synergistic tuning of the IHL and OHL significantly accelerates Li⁺ desolvation kinetics. Our work unveils a new mechanism between the Helmholtz layer and interfacial kinetics, offering transformative insights for extreme fast-charging LIBs.