Two-dimensional transition-metal carbide materials (termed MXene) have attracted huge attention in the field of electrochemical energy storage due to their excellent electrical conductivity, high volumetric capacity, etc. Herein, with inspiration from the interesting structure of pillared interlayered clays, we attempt to fabricate pillared TiC MXene (CTAB-Sn(IV)@TiC) via a facile liquid-phase cetyltrimethylammonium bromide (CTAB) prepillaring and Sn pillaring method. The interlayer spacing of TiC MXene can be controlled according to the size of the intercalated prepillaring agent (cationic surfactant) and can reach 2.708 nm with 177% increase compared with the original spacing of 0.977 nm, which is currently the maximum value according to our knowledge. Because of the pillar effect, the assembled LIC exhibits a superior energy density of 239.50 Wh kg based on the weight of CTAB-Sn(IV)@TiC even under higher power density of 10.8 kW kg. When CTAB-Sn(IV)@TiC anode couples with commercial AC cathode, LIC reveals higher energy density and power density compared with conventional MXene 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.

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