Atomic Sulfur Covalently Engineered Interlayers of Ti₃C₂ MXene for Ultra‐Fast Sodium‐Ion Storage by Enhanced Pseudocapacitance

Abstract

2D MXenes have been widely applied in the field of electrochemical energy storage owning to their high electrical conductivity and large redox‐active surface area. However, electrodes made from multilayered MXene with small interlayer spacing exhibit sluggish kinetics with low capacity for sodium‐ion storage. Herein, Ti3C2 MXene with expanded and engineered interlayer spacing for excellent storage capability is demonstrated. After cetyltrimethylammonium bromide pretreatment, S atoms are successfully intercalated into the interlayer of Ti3C2 to form a desirable interlayer‐expanded structure via TiS bonding, while pristine Ti3C2 is hardly to be intercalated. When the annealing temperature is 450 °C, the S atoms intercalated Ti3C2 (CT‐S@Ti3C2‐450) electrode delivers the improved Na‐ion capacity of 550 mAh g−1 at 0.1 A g−1 (≈120 mAh g−1 at 15 A g−1, the best MXene‐based Na+‐storage rate performance reported so far), and excellent cycling stability over 5000 cycles at 10 A g−1 by enhanced pseudocapacitance. The enhanced sodium‐ion storage capability has also been verified by theoretical calculations and kinetic analysis. Coupling the CT‐S@Ti3C2‐450 anode with commercial AC cathode, the assembled Na+ capacitor delivers high energy density (263.2 Wh kg−1) under high power density (8240 W kg−1), and outstanding cycling performance.

2 D MXene‐based Energy Storage Materials: Interfacial Structure Design and Functionalization

“…As anode of sodium‐ion capacitors (SICs), the Na‐Ti 3 C 2 electrode delivers a high energy density of 80.2 Wh kg −1 and high power density (6172 W kg −1 ). Additionally, S atoms were successfully intercalated into the Ti 3 C 2 interlayer to form a desirable interlayer‐expanded structure through Ti−S bonding by a facile procedure consisting of CTAB pretreatment, thermal diffusion with elemental S, and subsequent annealing process . The intercalated S atoms can interact with the interfacial Ti atoms to form a Ti−S bond at the interfaces of Ti 3 C 2 MXene.…”

“…Additionally,Sa toms were successfully intercalated into the Ti 3 C 2 interlayer to form ad esirable interlayer-expanded structure through TiÀSb onding by af acile procedurec onsisting of CTAB pretreatment, thermald iffusion with elemental S, and subsequenta nnealing process. [87] The intercalated Sa toms can interact with the interfacial Ti atoms to form aT i ÀSb ond at the interfaces of Ti 3 C 2 MXene. As ar esult, SICs coupling aS atom-intercalatedT i 3 C 2 (CT-S@Ti 3 C 2 -450) anode with ac ommercial active carbon (AC) cathode show ah igh energyd ensity and excellent cycling stability.…”

TiO2 Nanoparticles In Situ Formed on Ti3C2 Nanosheets by a One‐Step Ethanol‐Thermal Method for Enhanced Reversible Lithium‐Ion Storage

“…Furthermore, one notes that compared to the previous reports with disappearance of the (002) peak for Ti 3 C 2 due to oxidation, the two‐dimensional structure integrity of T−Ti 3 C 2 nanosheets is well maintained by our method, indicating the superiority of the ethanol‐thermal method to avoid the oxidation effect. In the meantime, it is worth noting that the (002) peak of T−Ti 3 C 2 in TiO 2 /T−Ti 3 C 2 shifts to a higher angle, i. e., from ∼6° to 6.5° (see Figure S1 in the supporting information) maybe due to the decomposition of TMA + ions during the ethanol thermal treatment at 200 °C, leading to escaping of TMA + from the interlayer of T−Ti 3 C 2 and thus resulting in the reduction of the layer spacing …”

Battery‐Type Electrode Materials for Sodium‐Ion Capacitors

“…With activated carbon as cathode, the fabricated NIC showed high energy and power densities (39 Wh kg −1 and 1140 W kg −1 ) and good cycling stability (84.2 % capacity retention after 4000 cycles). By a method of using cetyltrimethylammonium bromide (CTAB) pretreatment, thermal diffusion with elemental S, and followed annealing process, as shown in Figure , S atoms could be successfully intercalated into the interlayer of Ti 3 C 2 . The as‐obtained hybrid CT‐S@Ti 3 C 2 ‐450//AC NIC delivers a high energy density of 263.2 Wh kg −1 at a high power density of 8240 W kg −1 , and outstanding cycling performance with 73.3 % capacity retention after 10 000 cycles.…”