Extreme-fast-charging of energy-dense lithium metal batteries enabled by controlled grafting of ionic polymers

Lithium (Li)-metal batteries (LMBs) integrating ultrahigh energy outputs with extreme-fast-charging (XFC) are critical for forthcoming applications. However, the hostless nature of the metallic Li anode exacerbates interfacial polarization and dendrite formation, which underpins the undesirable trade-off between energy density and charging rate in batteries. Here, we design a molecularly defined interphase that is chemically tethered to the current collector. Such nanometer-thin and single-ion-conducting solid polymer interphase (SPI), different from the repetitively changing solid electrolyte interphase (SEI), offers constant control to accelerate charge transfer and foster uniform Li nucleation and dense plating, thus delivering ultrahigh energy density >300 Wh kg⁻¹ at 10 C with a thick cathode and lean electrolytes. The innovative interphase engineering strategy is projected to pave the way for versatile fast-charging technologies via manipulating interfacial kinetics of ions.