Cost-effective interfacial high-concentration electrolyte for stable lithium metal batteries.

High-concentration electrolytes are promising candidates for high-energy-density lithium metal batteries, yet their practical application is hindered by sluggish ionic transfer and high costs. Here, we show an interfacial high-concentration electrolyte that overcomes these limitations by localizing 5 M LiTFSI electrolyte at the Li anode surface, while maintaining a 1 M electrolyte in the bulk. This approach is facilitated by a bi-continuous phase-separated polymer layer that provides physical confinement and leverages hydrogen-bonding and ion-dipole interactions to prevent salt diffusion from the interfacial layer into the bulk electrolyte. This design preserves the high ionic conductivity of the bulk electrolyte while ensuring sufficient Li+ for rapid interfacial charge transfer. It also cuts lithium salt usage and associated costs by up to 70%, while retaining the benefits of high-concentration electrolytes, including the formation of a LiF-rich solid-electrolyte interphase. As a result, a 6.8 Ah Li | |NCM811 pouch cell delivers a specific energy of 506 Wh kg-1 at 0.1 C and maintains stable cycling over 200 cycles with 75.8% capacity retention at 0.5 C. This work demonstrates an effective electrolyte design that offers a cost-effective and sustainable pathway for high-energy-density lithium metal batteries.