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Low Coulombic efficiency and significant capacity decay resulting from an unstable solid electrolyte interphase (SEI) and dendritic growth pose challenges to the practical application of lithium‐metal batteries. In this study, a highly efficient protection layer induced by octaphenylsilsesquioxane (OPS) with LiFSI salt is investigated. The OPS exhibits a strong adsorption energy with lithium, its multi‐site gradient adsorption ability enables the simultaneous capture of 8 Li+ and the uniform regulation of Li ion flux. Moreover, the mechanical strength and electronic insulation of the OPS layer induces Li deposition under the protection layer and effectively inhibits lithium dendrite growth. Such a protection layer contributes to the stable and dendrite‐free performance of a lithium‐metal battery employing LiNi0.8Co0.1Mn0.1O2 (NCM811) as a cathode and an ultrathin OPS‐protected lithium foil (20 µm) as the anode. A remarkable capacity retention of 91.4% is achieved after 300 cycles at 1C. The OPS‐protected Li anodes and NCM811 are also tested in combination with a Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte, showing extended cyclability up to 300 cycles with an average Coulombic efficiency of 99.58% and capacity retention of 85.7%. [ABSTRACT FROM AUTHOR]

The poorly flammable room‐temperature ionic liquid‐based electrolyte composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and N‐butyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (Pyr14FSI) with fluoroethylene carbonate (FEC) as an additive is investigated towards its compatibility with the LiNi0.88Co0.09Mn0.03O2 (NCM88) cathode and a high‐capacity Si/graphite (SiG) anode, revealing a remarkably stable performance in lithium‐ion cells. Interestingly, this dual‐anion electrolyte with FEC additive forms a stable electrode‐electrolyte interphase on both sides, which suppresses the morphological degradation of the electrode materials and continuous electrolyte decomposition. Consequently, lithium‐ion cells using such dual‐anion ionic liquid‐based electrolyte display significantly improved cycling stability compared to conventional carbonate ester‐based electrolyte, achieving a high specific energy of 385 Wh kg−1 (based on both cathode and anode active materials weight) with a capacity retention of 74 % after 200 cycles at 0.2 C, demonstrating the possibility to realize safe and high energy density LIBs. [ABSTRACT FROM AUTHOR]

FSI−‐based ionic liquids (ILs) are promising electrolyte candidates for long‐life and safe lithium metal batteries (LMBs). However, their practical application is hindered by sluggish Li+ transport at room temperature. Herein, it is shown that additions of bis(2,2,2‐trifluoroethyl) ether (BTFE) to LiFSI‐Pyr14FSI ILs can effectively mitigate this shortcoming, while maintaining ILs′ high compatibility with lithium metal. Raman spectroscopy and small‐angle X‐ray scattering indicate that the promoted Li+ transport in the optimized electrolyte, [LiFSI]3[Pyr14FSI]4[BTFE]4 (Li3Py4BT4), originates from the reduced solution viscosity and increased formation of Li+‐FSI− complexes, which are associated with the low viscosity and non‐coordinating character of BTFE. As a result, Li/LiFePO4 (LFP) cells using Li3Py4BT4 electrolyte reach 150 mAh g−1 at 1 C rate (1 mA cm−2) and a capacity retention of 94.6% after 400 cycles, revealing better characteristics with respect to the cells employing the LiFSI‐Pyr14FSI (operate only a few cycles) and commercial carbonate (80% retention after only 218 cycles) electrolytes. A wide operating temperature (from −10 to 40 °C) of the Li/Li3Py4BT4/LFP cells and a good compatibility of Li3Py4BT4 with LiNi0.5Mn0.3Co0.2O2 (NMC532) are demonstrated also. The insight into the enhanced Li+ transport and solid electrolyte interphase characteristics suggests valuable information to develop IL‐based electrolytes for LMBs. [ABSTRACT FROM AUTHOR]

NASICON-type electrolytes such as Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3 (LAGP) potentially enable high safety and high energy for solid-state batteries. However, the poor interfacial stability with lithium metal remains a main issue. To overcome this challenge, we proposed a bilayer solid electrolyte architecture implementing a novel ultrathin solid polymer electrolyte (SPE) film in combination with LAGP to improve the interface with lithium metal. The SPE film is composed of a bis(fluorosulfonyl)imide-based ionic liquid and polyethylene oxide, which shows a remarkable ionic conductivity of 1.25 × 10−3 S cm−1 at room temperature. The application of this thin interlayer leads to an outstanding interface stability, allowing >2000 h of continuous Li stripping/plating in symmetric Li|SPE/LAGP/SPE|Li cells without any increase in polarization or indication of a short circuit. As a result, this approach enables Li|SPE/LAGP|NCM811 cells with a discharge capacity of ∼200 mAh g−1 at 0.1C and stable cycling for >400 cycles at 0.2C with a capacity retention of 83%. Additionally, the cell shows an extremely high average Coulombic efficiency of 99.96% demonstrating that the approach enables to achieve high-energy and long-term stable solid-state lithium-metal batteries. [Display omitted] • High energy lithium metal batteries. • Hybrid electrolytes enabled solid-state batteries. • Artificial interphases in high energy batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-protected SEI layer formed in carbonate-based electrolyte with vinylethylene carbonate. • Additives effectively suppress the further decomposition of carbonate solvent. • Uniform Li plating/stripping and high CE are achieved with the additives. • The anode-free cell Cu|NMC811 obtained high initial CE and cycling performance. Lithium metal is considered as the ultimate negative electrode for future high-energy batteries because of its lowest electrode potential and very high theoretical capacity. However, its practical application is severely plagued by the hazardous lithium dendritic growth upon charge and low coulombic efficiency resulting from the inhomogeneous mass and charge transfers across the Li/electrolyte interface. Herein we report an economical and effective approach to step out of this dilemma, using self-protected Solid electrolyte interphase (SEI) in carbonate-based electrolyte with Vinylethylene carbonate (VEC) additive. VEC as a sacrificing material can prevent the Li salts and solvent decomposition, and further free radical reaction of VEC decomposition products in-situ form self-protected highly uniform and mechanical strength SEI layer on Li metal surface. The versatile effects of this unique SEI layer are demonstrated by the uniform lithium plating/stripping and very high Coulombic efficiency (up to 96% after 150 cycles at 1 mA cm−2 with 1 mAh cm−2). Lithium metal batteries, employing the self-protected Li metal negative electrode coupled with LiFePO 4 , exhibit excellent performance in both cycling stability and rate capability. Even the anode free cell Cu|NMC811, an impressive high initial coulombic efficiency of 92.5% and promising improvement of cycling performance are achieved. [ABSTRACT FROM AUTHOR]