Ultralight lithiophilic three-dimensional lithium host for stable high-energy-density anode-free lithium metal batteries

Anode-free Li metal batteries (AF–LMBs) can exhibit substantially higher energy densities than that of Li-ion batteries (LIBs) and conventional LMBs; however, irreversible Li losses during Li plating/stripping, high density and low mechanical strength of state-of-the-art anode current collectors significantly undermine the energy benefits of AF configuration. Herein, we report Au-decorated insulating polyimide (PI@Au) nanofibers used as three-dimensional (3D) hosts promoting dendrite-free Li deposition. Their lithiophilic surfaces with low Li nucleation energy barrier and insulating 3D network with low local current density can synergistically regulate the uniform Li nucleation/growth following an "on fiber – in plane – on top" plating behavior. The superb Li reversibility ensures robust cycling stability of an NCM811||PI@Au AF–LMB cell with a high areal capacity of 6.4 mAh cm−2 (mass loading of 32.0 mg cm−2) for 100 cycles and high capacity retention of 86.0%. Owing to the ultrathin (10 μm) and ultralight (0.54 mg cm−2) characteristics of PI@Au nanofibers, unprecedented energy densities of 475 Wh kg−1 and 1199 Wh L−1 were achieved at the practical cell level, exceeding those of LIBs (263 Wh kg−1 and 634 Wh L−1) and LMBs (414 Wh kg−1 and 994 Wh L−1), respectively. The combination of a 3D insulating scaffold with lithiophilic decoration represents an effective strategy for designing AF–LMBs with ultrahigh energy densities.