Relative-High Concentration Electrolytes for High-Rate Cycling of Li-Metal Batteries Guided by Diffusion NMR and EPR Imaging

Lithium metal batteries face significant challenges in achieving stable high-rate cycling due to uncontrolled Li dendrite growth and poor interfacial stability. This study proposes a localized relative-high concentration electrolyte to enable high-rate operation without sacrificing ionic transport. By comparing three localized high-concentration electrolytes (3M|1M denoting 3M LiFSI in DME and 1 M LiFSI in DME&TTE, 5M|2M and 8M|3M) with diffusion NMR, we demonstrate that the 5M|2M system achieves an optimal balance between Li + diffusivity and anion-derived solvation structure, facilitating a robust inorganic-rich SEI. Employing electron paramagnetic resonance imaging (EPRI) with ultrahigh spatial resolution, we visualize the uniform Li deposition and minimal dead Li formation in the 5M|2M electrolyte due to balanced LiF content and F–S content in SEI. This work provides new insights into electrolyte engineering for fast-charging lithium metal batteries, highlighting the critical role of concentration-mediated SEI formation in stabilizing Li anode interfaces under high-rate conditions.