Pre-constructing a mortice-tenon joint based-layer to achieve an enhanced SEI on Li metal anode

Abstract

One of the determining factors for lithium anode is an ideal protective layer which has two basic requirements: one is its own strength, the other is a strong bond with the substrate. There are many studies on the former, but very few reports on the latter. Here, a design idea to pre-construct a based-layer where the mortice-tenon joint that will connect the subsequent electrochemically SEI have been set on Li anode surface was proposed. First, a tightly bonded base-layer was chemically formed via reaction between 2-(fluorosulfonyl)difluoroacetate (DFSA) and lithium metal. Then the trimethylsilyl 2-(fluorosulphonyl)difluoroacetate (TSFSA), which has the similar molecular structure and the same functional group with DFSA, was introduced to be acted as an SEI enhancer that can preferentially decompose over carbonate solvents under electrochemical conditions with the same components of the based-layer, which was thus strengthened to form an enhanced SEI (ESEI). The Li anode with ESEI achieved long-cycling stability (≥ 2100 h) and high average CE (99.2%) in carbonate electrolytes. Full cells with high cathode loading (20.5 mg cm-2) also achieved high cycling stability at low N/P ratios, demonstrating its great prospects for practical applications in high energy density Li-metal batteries.