Electrolytic construction of nanosphere-assembled protective layer toward stable lithium metal anode

The uncontrolled dendrite growth and electrolyte consumption in lithium metal batteries result from a heterogeneous and unstable solid electrolyte interphase (SEI). Here, a high-voltage forced electrolysis strategy is proposed to stabilize the lithium metal via electrodepositing a spherical protective layer. This peculiar SEI is composed of a nanosized Li sphere that is encased with adjustable composition, as proved by cryo-transmission electron microscopy and multiple surface-sensitive spectroscopies. Such a three-dimensional nanosphere-assembled protective layer has homogeneous components, mechanical strength, and rapid Li-ion conductivity, enabling it to alleviate the volume expansion and prevent dendrite growth during Li deposition. The symmetric cell can be stably operated for ultralong-term cycling time of 2000 and 800 h even at high current densities of 1 and 10 mA cm⁻², respectively. Using this interface permits stable cycling of full cells paired with LiFePO₄ and LiNi_0.8Co_0.1Mn_0.1O₂ cathodes with low negative/positive capacity ratio, high current density, and limited Li excess. This tactic also fosters a novel insight into interface design in the battery community and encourages the practical implementation of lithium metal batteries.