Lithium metal anodes hold great promise for enabling high-energy density devices compared with the commercialized graphite electrode. However, huge pressure changes during cycling will lead to the pulverization of the 2D lithium anode, thus deteriorating the battery life due to its poor mechanical strength. Herein we report a 3D lithium−boron (LiB) fibrous framework with great compressive strength through electrochemical delithiation. The LiB alloy fibers with a 3D stable structure play the role of an expansion-tolerant substrate, which could effectively hold the Li metal and reduce the internal pressure changes, showing only a 53.7% pressure change compared with the 2D Li/Cuanode-based pouch cell. A quasi-ionic-liquid-based polymer electrolyte layer is introduced by a scalable tape-casting method, generating a LiF-rich layer inside the 3D Li anode through the reaction between the polymer electrolyte and the internal free Li, which can guide the uniform nucleation and growth of Li metal. As a result, the asymmetric Li−Li cell can sustain 5 mAh cm −2 Li plating/ stripping for 1000 h. A 2.1 Ah pouch cell coupling to a LiF-rich interface-protected 3D Li/LiB anode and a Ni-rich cathode of 30 mg cm −2 exhibits an ultrahigh energy density of 403 Wh kg −1 and a stable cycle life of 100 cycles.

Lithium metal is being hailed as the holy grail of next‐generation high‐energy‐density all‐solid‐state batteries. However, the poor interfacial compatibility between Li and solid electrolyte and formation of lithium dendrite strongly impedes its practical application. Herein, a facile surface modification strategy is proposed to reconstruct the Li/Li10GeP2S12 interface in order to address these problems. Beneficial from amorphous Li3PO4 by radio frequency magnetron sputtering on Li, parasitic side reactions between Li and Li10GeP2S12 is strongly suppressed, resulting in a stable cycling performance in symmetric Li/Li cell with a low polarization voltage (about ±180 mV) up to 1000 hours. Moreover, the Li/Li10GeP2S12/LiCoO2 cell displays a reversible discharge capacity of 104.5 mA h/g at 0.1 C after 50 cycles. It indicates that Li3PO4 layer is not only favorable to improve interfacial stability between Li/Li10GeP2S12 but also advantageous to homogenize Li deposition.