Molecularly Engineered Li⁺ Microenvironment via Ester-Based Electrolytes for Plating-Free Fast-Charging Li-Ion Batteries

The demand for extremely fast-charging (XFC, ≤10-min) lithium-ion batteries (LIBs) is rapidly increasing to accelerate the widespread adoption of electric vehicles (EVs). However, achieving XFC remains a critical challenge, particularly in EV-relevant cell configurations that utilize thick electrodes and high energy densities. In such cells, conventional carbonate-based electrolytes suffer from sluggish Li + transport and unstable interfaces, leading to severe Li plating and rapid capacity decay. Overcoming this XFC bottleneck requires engineering the electrolyte system to enable both fast Li + transport and low-resistance interface formation. In this study, we report a molecularly engineered Li + microenvironment realized through a methyl acetate (MA)-based high-concentration electrolyte (HCE) formulated with a fluoroethylene carbonate (3MF). Compared to a dimethyl carbonate (DMC)-based HCE, the smaller and more polar MA molecules form compact solvation clusters and a softer solvation sheath, which acts as molecular lubricants, promoting Li + percolation through the electrolyte bulk phase. As a result, despite its high salt concentration, the 3MF electrolyte exhibits much higher ionic conductivity than conventional carbonate-based electrolytes. Furthermore, the high salt concentration induces an anion-rich Li + coordination environment, which efficiently facilitates the Li + desolvation process. Additionally, the anion/3MF co-derived SEI ensures low energy barriers for Li + migration across the SEI. This 3MF electrolyte enables outstanding XFC cycling performance in graphite||NMC622 cells, retaining 98.4% capacity after 500 cycles at 10 C (6-min charging) with moderate electrode loading (3.0 mAh cm –2 ), and further demonstrates stable long-term cycling at 6 C with high loading (6.0 mAh cm –2 ), representing one of the few demonstrations of high-energy Li-ion cells capable of enduring over 500 XFC cycles without degradation. These findings highlight the critical role of solvation-level molecular design in overcoming the conventional trade-offs between fast charging and energy density, offering a viable path toward practical, high-performance XFC Li-ion batteries.