Functionalization of separator with two-dimensional anionic nanosheets for interfacial regulation of lithium deposition in lithium metal batteries.

Lithium metal anodes suffer from dendrite growth, low coulombic efficiency, and safety concerns, limiting their practical application in rechargeable batteries. Herein, polypropylene (PP) separators are functionalized with ultrathin 2D anionic (H3Sb3P2O14) HSPO nanosheets to construct a negatively charged interfacial layer. The HSPO layer improves electrolyte affinity, increases the Li+ transference number from 0.5 to 0.8, and guides a more homogeneous Li+ flux toward the lithium metal surface. Density functional theory calculations indicate stronger interactions between HSPO and Li/electrolyte species than those on pristine PP, while finite-element simulations and in situ optical microscopy reveal a more uniform electric-field distribution and regulated lithium deposition process. As a result, Li||Cu cells show improved plating/stripping stability over 250 cycles, and the Li||Li symmetric cell achieves a sevenfold increase in lifespan. Notably, the interfacial regulation strategy enables exceptional full-cell durability, delivering 2000 cycles for Li||LiFePO4 at 1C and 12,000 cycles for Li||I2 at 5C. This work highlights charged two-dimensional nanosheets as interfacial modifiers for separator-mediated regulation of ion transport and lithium deposition.