Gradient Solid Electrolyte Interphase and Lithium ion Solvation Regulated by Bisfluoroacetamide for Stable Lithium Metal Batteries.

The structure and components of solid electrolyte interphase (SEI) are extremely important to influence the performance of full cells, which is determined by the formulation of electrolyte used. However, it is still challenging to control the formation of high-quality SEI from structure to components. Herein, we designed bisfluoroacetamide (BFA) as the electrolyte additive for the construction of a gradient solid electrolyte interphase (SEI) structure that consists of a lithophilic surface with C-F bonds to uniformly capture Li ions and a LiF-rich bottom layer to guide the rapid transportation of Li ions, endowing the homogeneous deposition of Li ions. Moreover, the BFA molecule changes the Li + solvation structure by reducing free solvents in electrolyte to improve the antioxidant properties of electrolyte and prevent the extensive degradation of electrolyte on the cathode surface, which can make sure superior cathode electrolyte interphase (CEI) with high-content LiF. In addition, the Li||LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) full cells show excellent cycling stability (a high capacity of 149 mA h g -1 after 200 cycles at 0.5 mA cm -2 ) and good rate capability (a capacity of 117 mA h g -1 at a high current density of 5 mA cm -2 ) when NCM622 was used as the cathode. This work demonstrates that the design of electrolyte additives is powerful to construct the structure and components of high-quality SEI and CEI through theoretical calculations.