Artificial interphase layers for lithium metal anode

Abstract

Lithium (Li) metal is considered as the most promising anode material for high-energy-density batteries owing to its ultra-high theoretical capacity (3860 mAh·g−1) and the lowest negative electrochemical potential (−3.040 V versus standard hydrogen electrode). However, the unstable solid electrolyte interphase (SEI) layers, uncontrollable dendrite growth, and huge volume changes during the plating/stripping processes significantly limit the practical applications of Li metal anodes. Since the unstable SEI layers can promote the nucleation and growth of Li dendrites, they play a crucial role in the decay process of Li metal anodes. The fracture and regeneration of SEI layers continuously consume electrolytes and Li metal anodes during plating/ stripping processes, and the accumulation of SEI layers can increase the interface impedance. Therefore, building artificial interphase layers is one of the most effective strategies to construct a stable SEI, reduce dendrite growth, accommodate large volume changes, and thus obtain excellent cycling performance. In this review, artificial interphase layers have been summarized into three parts based on the conductive properties of interphase, including artificial SEI layers (electronically insulating while ionically conducting), mixed ionic and electronic conductor interphase layers, and nanostructured interphase passivation layers (both ionically and electronically insulating). Artificial SEI layers with high ionic conductivity and low electronic conductivity can be classified into inorganic, organic, and organic/inorganic complex SEI according to the composition of artificial SEI layers. The artificial inorganic SEI layers with a high Young’s modulus can suppress the dendrite growth. The artificial organic SEI layers with flexible features can accommodate large interface fluctuations and improve the interphase wettability. The artificial organic/inorganic complex SEI layers with a rigid-flexible structure can restrain dendrite growth and buffer volume change. The mixed ionic and electronic conductor layers possess high ionic conductivity and high Young’s modulus, which are beneficial for enhancing the interphase stability and reducing dendrite growth. The artificial alloy mixed conductor layers can improve the Li diffusion coefficient and reduce Li nucleation overpotential, guiding uniform Li plating/stripping. Furthermore, the artificial mixed conductor layers comprising inorganic and organic matter have commendable flexibility and excellent interface compatibility, thereby enhancing the interphase stability and reducing dendrite growth. The nanostructured interphase passivation layers with high chemical stability can deliver Li ion through a confined electrolyte in a uniform porous structure, thereby achieving homogeneous Li plating/stripping. In addition, the structure-effective relationship of artificial interphase layers has been analyzed, and methods for improving the performance of artificial interphase layers, such as physical and chemical stability, ion transportation, interface strength and flexibility, and interfacial compatibility, have been discussed in this review. Finally, we present the main challenge and perspectives of artificial interphase layers.