Optimizing interface concentration and electric fields for enhanced lithium deposition behavior in lithium metal anodes

Understanding dynamic fluctuations in complex multi-physics fields at an electrolyte/electrode interface is crucial for explaining the lithium deposition mechanism and developing efficient interface structures, but there are significant challenges. Here, we introduce an internal standard substance (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE)) to propose a quantitative in situ Raman spectroscopy method to disclose the variation of interfacial concentration field. It is proved that the formation of an anion depletion layer at the electrolyte/electrode interface during lithium deposition leads to the formation of a space charge layer (SCL) with local electric field, which can accelerate dendrite growth and is closely related to the withdrawal of anions from interface. Further, a high-anion-concentration interface (HACI) with immobilized anions is proposed. This HACI can effectively prevent anion depletion at the interface and enhance the interfacial Li+ transference number from 0.30 to 0.57, thus alleviating formation of SCL and facilitating uniform lithium deposition. Hence, a full cell with high-load NCM523 cathode (∼14 mg cm⁻²) and limited HACI@Li anode (∼50 μm) delivers excellent cycling over 200 cycles with a high discharge capacity retention of 77.6% (∼125.7 mA h g⁻¹). This offers critical insights for designing lithium battery systems from the perspective of multi-physics fields.