Lithium-sulfur batteries show fascinating potential for advanced energy storage systems due to their high specific capacity, low-cost, and environmental benignity. However, the shuttle effect and the uncontrollable deposition of lithium sulfide species result in poor cycling performance and low Coulombic efficiency. Despite the recent success in trapping soluble polysulfides via porous matrix and chemical binding, the important mechanism of such controllable deposition of sulfur species has not been well understood. Herein, we discovered that conductive Magnéli phase Ti4O7 is highly effective matrix to bind with sulfur species. Compared with the TiO2-S, the Ti4O7-S cathodes exhibit higher reversible capacity and improved cycling performance. It delivers high specific capacities at various C-rates (1342, 1044, and 623 mAh g(-1) at 0.02, 0.1, and 0.5 C, respectively) and remarkable capacity retention of 99% (100 cycles at 0.1 C). The superior properties of Ti4O7-S are attributed to the strong adsorption of sulfur species on the low-coordinated Ti sites of Ti4O7 as revealed by density functional theory calculations and confirmed through experimental characterizations. Our study demonstrates the importance of surface coordination environment for strongly influencing the S-species binding. These findings can be also applicable to numerous other metal oxide materials.

Two-dimensional transition metal carbide materials called MXenes show potential application for energy storage due to their remarkable electrical conductivity and low Li(+) diffusion barrier. However, the lower capacity of MXene anodes limits their further application in lithium-ion batteries. Herein, with inspiration from the unique metal ion uptake behavior of highly conductive Ti3C2 MXene, we overcome this impediment by fabricating Sn(4+) ion decorated Ti3C2 nanocomposites (PVP-Sn(IV)@Ti3C2) via a facile polyvinylpyrrolidone (PVP)-assisted liquid-phase immersion process. An amorphous Sn(IV) nanocomplex, about 6-7 nm in lateral size, has been homogeneously anchored on the surface of alk-Ti3C2 matrix by ion-exchange and electrostatic interactions. In addition, XRD and TEM results demonstrate the successful insertion of Sn(4+) into the interlamination of an alkalization-intercalated Ti3C2 (alk-Ti3C2) matrix. Due to the possible "pillar effect" of Sn between layers of alk-Ti3C2 and the synergistic effect between the alk-Ti3C2 matrix and Sn, the nanocomposites exhibit a superior reversible volumetric capacity of 1375 mAh cm(-3) (635 mAh g(-1)) at 216.5 mA cm(-3) (100 mA g(-1)), which is significantly higher than that of a graphite electrode (550 mAh cm(-3)), and show excellent cycling stability after 50 cycles. Even at a high current density of 6495 mA cm(-3) (3 A g(-1)), these nanocomposites retain a stable specific capacity of 504.5 mAh cm(-3) (233 mAh g(-1)). These results demonstrate that PVP-Sn(IV)@Ti3C2 nanocomposites offer fascinating potential for high-performance lithium-ion batteries.

Sodium (Na) metal is a promising alternative to lithium metal as an anode material for the next-generation energy storage systems due to its high theoretical capacity, low cost, and natural abundance. However, dendritic/mossy Na growth caused by uncontrollable plating/stripping results in serious safe concerns and rapid electrode degradation. This study presents Sn 2+ pillared Ti 3 C 2 MXene serving as a stable matrix for high-performance dendrite-free Na metal anode. The intercalated Sn 2+ between Ti 3 C 2 layers not only induces Na to nucleate and grow within Ti 3 C 2 interlayers, but also endows the Ti 3 C 2 with larger interlayer space to accommodate the deposited Na by taking advantage of the "pillar effect," contributing to uniform Na deposition. As a result, the pillar-structured MXene-based Na metal electrode could enable high current density (up to 10 mA cm −2 ) along with high areal capacity (up to 5 mAh cm −2 ) over long-term cycling (up to 500 cycles). The full cell using MXene-based Na metal anode exhibits superior electrochemical performance than that using host-less commercial Na. It is believed that the well-controlled MXene-based Na anode not only extends the application scope of MXene, but also provides guidance in designing high-performance Na metal batteries.

The application of solid polymer electrolytes (SPEs) is still inherently limited by the unstable lithium (Li)/electrolyte interface, despite the advantages of security, flexibility, and workability of SPEs. Herein, the Li/electrolyte interface is modified by introducing Li2S additive to harvest stable all‐solid‐state lithium metal batteries (LMBs). Cryo‐transmission electron microscopy (cryo‐TEM) results demonstrate a mosaic interface between poly(ethylene oxide) (PEO) electrolytes and Li metal anodes, in which abundant crystalline grains of Li, Li2O, LiOH, and Li2CO3 are randomly distributed. Besides, cryo‐TEM visualization, combined with molecular dynamics simulations, reveals that the introduction of Li2S accelerates the decomposition of N(CF3SO2)2− and consequently promotes the formation of abundant LiF nanocrystals in the Li/PEO interface. The generated LiF is further verified to inhibit the breakage of CO bonds in the polymer chains and prevents the continuous interface reaction between Li and PEO. Therefore, the all‐solid‐state LMBs with the LiF‐enriched interface exhibit improved cycling capability and stability in a cell configuration with an ultralong lifespan over 1800 h. This work is believed to open up a new avenue for rational design of high‐performance all‐solid‐state LMBs.

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