Improving the cyclic stability of lithium metal anodes is of particular importance for developing high-energydensity batteries. In this work, a remarkable finding shows that the control of lithium bis(fluorosulfonyl)imide (LiFSI) concentrations in electrolytes significantly alters the thickness and modulus of the related SEI layers, leading to varied cycling performances of Li metal anodes. In an electrolyte containing 2 M LiFSI, an SEI layer of ∼70 nm that is obviously thicker than those obtained in other concentrations is observed through in situ atomic force microscopy (AFM). In addition to the decomposition of FSI − anions that generates rigid lithium fluoride (LiF) as an SEI component, the modulus of this thick SEI layer with a high LiF content could be significantly strengthened to 10.7 GPa. Such a huge variation in SEI modulus, much higher than the threshold value of Li dendrite penetration, provides excellent performances of Li metal anodes with Coulombic efficiency higher than 99%. Our approach demonstrates that the FSI − anions with appropriate concentration can significantly alter the SEI quality, establishing a meaningful guideline for designing electrolyte formulation for stable lithium metal batteries.

Use of a protective coating on a lithium metal anode (LMA) is an effective approach to enhance its coulombic efficiency and cycling stability. Here, a facile approach to produce uniform silver nanoparticle‐decorated LMA for high‐performance Li metal batteries (LMBs) is reported. This effective treatment can lead to well‐controlled nucleation and the formation of a stable solid electrolyte interphase (SEI). Ag nanoparticles embedded in the surface of Li anodes induce uniform Li plating/stripping morphologies with reduced overpotential. More importantly, cross‐linked lithium fluoride‐rich interphase formed during Ag+ reduction enables a highly stable SEI layer. Based on the Ag‐LiF decorated anodes, LMBs with LiNi1/3Mn1/3Co1/3O2 cathode (≈1.8 mAh cm−2) can retain >80% capacity over 500 cycles. The similar approach can also be used to treat sodium metal anodes. Excellent stability (80% capacity retention in 10 000 cycles) is obtained for a Na||Na3V2(PO4)3 full cell using a Na‐Ag‐NaF/Na anode cycled in carbonate electrolyte. These results clearly indicate that synergetic control of the nucleation and SEI is an efficient approach to stabilize rechargeable metal batteries.

It is a significant challenge to design a dense high-sulfur-loaded cathode and meanwhile to acquire fast sulfur redox kinetics and suppress the heavy shuttling in the lean electrolyte, thus to acquire a high volumetric energy density without sacrificing gravimetric performance for realistic Li–S batteries (LSBs). Herein, we develop a cation-doping strategy to tailor the electronic structure and catalytic activity of MoSe2 that in situ hybridized with conductive Ti3C2T x MXene, thus obtaining a Co-MoSe2/MXene bifunctional catalyst as a high-efficient sulfur host. Combining a smart design of the dense sulfur structure, the as-fabricated highly dense S/Co-MoSe2/MXene monolith cathode (density: 1.88 g cm–3, conductivity: 230 S m–1) achieves a high reversible specific capacity of 1454 mAh g–1 and an ultrahigh volumetric energy density of 3659 Wh L–1 at a routine electrolyte and a high areal capacity of ∼8.0 mAh cm–2 under an extremely lean electrolyte of 3.5 μL mgs –1 at 0.1 C. Experimental and DFT theoretical results uncover that introducing Co element into the MoSe2 plane can form a shorter Co–Se bond, impel the Mo 3d band to approach the Fermi level, and provide strong interactions between polysulfides and Co-MoSe2, thereby enhancing its intrinsic electronic conductivity and catalytic activity for fast redox kinetics and uniform Li2S nucleation in a dense high-sulfur-loaded cathode. This deep work provides a good strategy for constructing high-volumetric-energy-density, high-areal-capacity LSBs with lean electrolytes.