A Graphene-Coated Thermal Conductive Separator to Eliminate the Dendrite-Induced Local Hotspots for Stable Lithium Cycling

Practical lithium metal batteries (LMBs) are still far from market readiness, as a result of the severe Li degradation and safety issues caused by Li dendrites. Herein, by studying the thermodynamic behavior of lithium deposition, it is unveiled that the tip area of Li metal has an increasing heat generation rate as a function of the deposition time and overpotential. This triggers the emergence of the accumulated overpotential heat and local temperature “hotspots” due to poor local thermal diffusion, which exacerbates the undesirable irregular Li deposition and dendrite growth. To address this issue, a thermally conductive graphene-coated separator is constructed to eliminate these local hotspots. The graphene layer affords timely diffusion of local heat generated by irregular Li growth and incipient dendrite formation, achieving the stable and uniform lithium deposition to deter further degradation. As a result, the Li metal, suffering a drastic Coulombic efficiency (CE) decay to ≈60% using a conventional separator, can be recovered for continual cycling with a high CE of >95%. Notably, the corresponding Li||LiNi_0.8Mn_0.1Co_0.1O₂ cells present high capacity retention and recovery. This study highlights the thermodynamic factor of Li dendrite-induced local heat and its elimination to preclude Li anode deterioration, which provides insight into Li metal protection strategies for high performance LMBs.