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Ultrathin all‐solid‐state electrolytes with an excellent Li+ transport behavior are highly desirable for developing high‐energy‐density solid‐state lithium metal batteries. However, how to balance the electrochemical performance and their mechanical properties remains a huge challenge. Herein, an ultrathin solid electrolyte membrane with a thickness of only 3 µm and a weight of 11.7 g m−2 is well constructed by integrating individual functionalized organic with inorganic modules. Impressively, the optimized hybrid electrolyte membrane shows a set of merits including a high room‐temperature ionic conductivity of 1.77 × 10−4 S cm−1, large Li+ transference number of 0.65, and strong mechanical strength (strength of 29 MPa, elongation of 95%), as well as negligible thermal shrink at 180 °C. The analysis results reveal that the lithium sulfonate‐functionalized mesoporous silica nanoparticles in the membrane play a crucial role in the selective transport of Li+ through anion trapping and cation exchange. The pouch full cell is further assembled with a high‐voltage NCM cathode and thin lithium anode, which exhibits excellent long‐term cycling stability, outstanding rate performance at room temperature, and high safety against abused conditions. The current work provides an innovative strategy for achieving lithium metal batteries with ultrathin all‐solid‐state electrolytes. [ABSTRACT FROM AUTHOR]

Layered oxides with ultrahigh nickel content are considered promising high energy cathode materials. However, their cycle stability is constrained by a series of heterogeneous structural transformations during the complex solid-state lithiation process. By in-depth investigation into the solid-state lithiation process of LiNi 0.92 Co 0.04 Mn 0.04 O 2 , it is found that the protruded parts on the surface of precursor particles tend to be surrounded by locally excessive LiOH, which promotes the formation of a rigid and dense R 3 - m ${{\rm { R}}\mathrel{\mathop{{\rm { 3}}}\limits^{{\rm -}}}{\rm { m}}}$ shell during the early stage of lithiation process. The shell will hinder the diffusion of lithium and topotactic lithiation within the particles, culminating in spatially heterogeneous intermediates that can impair the electrochemical properties of the cathode material. The spheroidization of the precursor can enhance uniformity in structural evolution during solid-phase lithiation. Ultrahigh nickel cathodes derived from spherical precursors demonstrate high initial discharge specific capacity (234.2 mAh g -1 , in the range of 2.7-4.3 V) and capacity retention (89.3 % after 200 cycles), significantly superior to the non-spherical samples. This study not only sheds light on the intricate relationship between precursor shape and structural transformation but also introduces a novel strategy for enhancing cathode performance through precursor spheroidization., (© 2024 Wiley-VCH GmbH.)