A Lithium Metal Anode Surviving Battery Cycling Above 200 °C

Lithium (Li) metal electrode cannot endure elevated temperature (e.g., >200 °C) with the regular battery configuration due to its low melting point (180.5 °C) and high reactivity, which restricts its application in high‐temperature Li metal batteries for energy storage and causes safety concerns for regular ambient‐temperature Li metal batteries. Herein, this work reports a Li 5 B 4 /Li composite featuring a 3D Li 5 B 4 fibrillar framework filled with metallic Li, which maintains its initial structure at 325 °C in Ar atmosphere without leakage of the liquid Li. The capillary force caused by the porous structure of the Li 4 B 5 fibrillar framework, together with its lithiophilic surface, restricts the leakage of liquid metallic Li and enables good thermal tolerance of the Li 5 B 4 /Li composite. Thus, it can be facilely operated for rechargeable high‐temperature Li metal batteries. Li 5 B 4 /Li electrodes are coupled with a garnet‐type ceramic electrolyte (Li 6.5 La 3 Zr 0.5 Ta 1.5 O 12 ) to fabricate symmetric cells, which exhibit stable Li stripping/plating behaviors with low overpotential of ≈6 mV at 200 °C using a regular sandwich‐type cell configuration. This work affords new insights into realizing a stable Li metal anode for high‐temperature Li metal batteries with a simple battery configuration and high safety, which is different from traditional molten‐salt Li metal batteries using a pristine metallic Li anode.