Grain refining mechanisms: Initial levelling stage during nucleation for high-stability lithium anodes

Abstract

Lithium (Li) metal is considered as an ideal anode material for energy storage systems mainly due to its large theoretical capacity. However, uncontrolled lithium dendrite growth during Li plating and stripping results in low Coulombic efficiency, poor cycling performance, and potential risk concerns, significantly limiting the commercial application of Li metal anodes. Herein, hexafluoroacetylacetone (HFAA) is used as a novel electrolyte additive to regulate the even deposition of Li ions based on grain refining mechanism. Within the electrolyte, HFAA forms complexes with lithium ions to generate more nucleation sites during plating process, and thus facilitating smooth deposition on the lithium anode surface as grain refiner. As a result, greatly enhanced cycling stability is obtained both in the Li/Li symmetric cell and Li/LiNi0·5Co0·2Mn0·3O2 (Li/NCM) full cell using electrolyte containing HFAA. Especially, after introducing the co-additive of saccharin, prolonged cycle lifetime is observed, as which can act as levelling agent for pristine Li foil. The grain refining strategy advances research in developing efficient and practicable additives for metal Li batteries.