A polythiourea protective layer for stable lithium metal anodes

Uncontrolled Li dendrite growth and low Coulombic efficiency severely limit the practical applications of Li metal batteries (LMBs). Establishing a stable solid electrolyte interphase (SEI) on the surface of the Li metal anodes (LMAs) is considered to be an effective solution. Here, we report an organic-inorganic composite SEI at the molecular level that effectively reduces the consumption of electrolytes during SEI formation. The artificial SEI layer consists of Li salts and polythiourea. Upon cycling, inorganic components including LiF, Li2S and Li3N formed in situ, which enhanced the mechanical properties of the composite SEI and guaranteed facile ion transport. In addition, polythiourea itself carries abundant S atoms and polar groups, which can be closely bonded with LMAs to suppress the growth of Li dendrites. The polar groups can also guide a uniform Li+ flux and form a stable structure over a long period of time. The employment of an organic-inorganic SEI enables high efficiency Li deposition and stable cycling of Ni-rich Li||LiNi0.88Co0.09Mn0.03O2 (NCM88) cells. After 240 cycles, the capacity retention rate is 83.5%. This work provides another artificial SEI design with a promising building block.