AbstractNASICON‐type Li_1+xAl_xTi_2−x(PO₄)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_0.8Co_0.1Mn_0.1O₂ (PTNB@Li||NCM₈₁₁) 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 NCM₈₁₁ 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.