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To improve the energy density of quasi‐solid‐state polymer electrolyte (QPE)‐based supercapacitors, the design of zwitterion‐containing QPE (ZQPE) with a high dielectric constant (ɛs) is proposed. This enhancement would increase the capacitance of ZQPE‐based supercapacitors, given the direct proportionality between capacitance and dielectric constant. The optimized ZQPE exhibits a high ionic conductivity (2.2 × 10−3 S cm−1) and good mechanical robustness (4.1 × 104 Pa) at room temperature. The ZQPE shows a much higher static dielectric constant (ɛs = 69) than the zwitterion‐free QPE (ɛs = 48), as supported by density functional theory calculations and molecular dynamics simulations. The flexible all‐solid‐state supercapacitor, fabricated with ZQPE and activated carbon electrodes, exhibits excellent electrochemical performance. The incorporation of zwitterion to QPE results in an increase in specific capacitance from 178 to 225 F g−1 with a wide operating potential window (0–4 V). The ZQPE‐based supercapacitor also exhibits a large energy density of 142 Wh kg−1 at a power density of 464 W kg−1 and remarkable long‐term electrochemical and mechanical cycling stability, retaining 80% of its capacitance retention over 10 000 cycles and even under rolling deformation for 1500 cycles. This strategy offers new insights for developing QPE designs for high energy density all‐solid‐state supercapacitors. [ABSTRACT FROM AUTHOR]

Anode‐free all‐solid‐state batteries (AF‐ASSBs) have received significant attention as a next‐generation battery system due to their high energy density and safety. However, this system still faces challenges, such as poor Coulombic efficiency and short‐circuiting caused by Li dendrite growth. In this study, the AF‐ASSBs are demonstrated with reliable and robust electrochemical properties by employing Cu–Sn nanotube (NT) thin layer (~1 µm) on the Cu current collector for regulating Li electrodeposition. LixSn phases with high Li‐ion diffusivity in the lithiated Cu–Sn NT layer enable facile Li diffusion along with its one‐dimensional hollow geometry. The unique structure, in which Li electrodeposition takes place between the Cu–Sn NT layer and the current collector by the Coble creep mechanism, improves cell durability by preventing solid electrolyte (SE) decomposition and Li dendrite growth. Furthermore, the large surface area of the Cu–Sn NT layer ensures close contact with the SE layer, leading to a reduced lithiation overpotential compared to that of a flat Cu–Sn layer. The Cu–Sn NT layer also maintains its structural integrity owing to its high mechanical properties and porous nature, which could further alleviate the mechanical stress. The LiNi0.8Co0.1Mn0.1O2 (NCM)|SE|Cu–Sn NT@Cu cell with a practical capacity of 2.9 mAh cm−2 exhibits 83.8% cycle retention after 150 cycles and an average Coulombic efficiency of 99.85% at room temperature. It also demonstrates a critical current density 4.5 times higher compared to the NCM|SE|Cu cell. [ABSTRACT FROM AUTHOR]

Lithium is considered to be the ultimate anode material for high energy‐density rechargeable batteries. Recent emerging technologies of all solid‐state batteries based on sulfide‐based electrolytes raise hope for the practical use of lithium, as it is likely to suppress lithium dendrite growth. However, such devices suffer from undesirable side reactions and a degradation of electrochemical performance. In this work, nanostructured Li2Se epitaxially grown on Li metal by chemical vapor deposition are investigated as a protective layer. By adjusting reaction time and cooling rate, a morphology of as‐prepared Li2Se is controlled, resulting in nanoparticles, nanorods, or nanowalls with a dominant (220) plane parallel to the (110) plane of the Li metal substrate. Uniaxial pressing the layers under a pressure of 50 MPa for a cell preparation transforms more compact and denser. Dual compatibility of the Li2Se layers with strong chemical bonds to Li metal and uniform physical contact to a Li6PS5Csulfide electrolyte prevents undesirable side reactions and enables a homogeneous charge transfer at the interface upon cycling. As a result, a full cell coupled with a LiCoO2‐based cathode shows significantly enhanced electrochemical performance and demonstrates the practical use of Li anodes with Li2Se layers for all solid‐state battery applications. [ABSTRACT FROM AUTHOR]