vehicles, and grid energy storage systems, owing to their high energy density and long cycling lifetime. [1, 2] Unfortunately, the development of LIBs is approaching its bottleneck. Public safety concerns have arisen from frequently reported incidents such as electrolyte leakage, fire, and even explosion, [3] [4] [5] which has driven research interests for safer battery systems. To boost transport electrification, the ongoing demands of higher energy/power densities and safety require

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... e energy storage systems. [6] [7] [8] It was reported that an energy density augment of 40-50% can be achieved simply by replacing graphite with lithium metal, [9, 10] the latter is appealing for its extremely high specific capacity (3860 mAh g −1 ) and low redox potential (−3.04 V vs standard hydrogen electrode (SHE)). [11, 12] Apart from high flammability, high volatility, high toxicity, and a narrow operational temperature range, the conventional organic carbonatebased liquid electrolytes show incompatibility with highly reactive metallic lithium through furnishing the notorious dendritic lithium formation and further triggering cell short circuit. [4] Alternatively, solid-state batteries (SSBs) which enable the use of lithium metal as the negative electrode stand out for their inherent distinctive advantages, mainly no electrolyte leakage issues, reduced lithium dendrites growth, environmental friendliness, and wide operational temperature range. [13, 14] Furthermore, the implementation of solid NASICON-type Li 1+x Al x Ti 2−x (PO 4 ) 3 (LATP) solid electrolytes have developed as a promising candidate for solid-state lithium batteries. However, the brittle and stiff LATP suffers from poor physical contact with electrodes and chemical/electrochemical instability at electrode|electrolyte interfaces. Herein, a thin and flexible hybrid electrolyte comprised of LATP and poly(vinylidene fluoride-trifluorethylene) (PVDF-TrFE) incorporated with highly concentrated ionic liquid electrolyte (ILE) is prepared to resolve these prominent limitations. To further protect the LATP|Li interface, an ultrathin poly[2,3-bis(2,2,6,6-tetramethylpiperidine-N-oxycarbonyl)-norbornene] (PTNB) polymer is coated on Li, acting as an additional protective layer. Consequently, the lithium stripping-plating lifetime is prolonged from 128 to 792 h, with no dendritic lithium observed. The PTNB@Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 (PTNB@Li||NCM 811 ) cells achieve significantly improved rate capability and cycling stability, predominantly resulting from the drastically decreased interfacial resistances, prohibited dendritic lithium generation, mitigated cathode material phase evolution, and prevention of internal microcrack formation. The thinner interphases formed on NCM 811 and PTNB@Li electrodes also play a key role. The quasi-solid-state batteries allow for the fabrication of multi-layer bipolar cells with stable cycling. Even under some exertive circumstances, (limited lithium source, low temperature, e.g., 0 °C), the impressive electrochemical performance achieved highlights the importance of such quasi-solid-state lithium batteries as a viable solution for the next-generation high-performance lithium batteries.