Interphase stabilized electrospun SnO2 fibers as alloy anode via restricted cycling for Li-ion capacitors with high energy and wide temperature operation

Synergetic interface engineering and space-confined effect in CoSe2@Ti3C2Tx heterostructure for high power and long life sodium ion capacitors

The intriguing characteristics of two-dimensional (2D) heterostructures stem from their unique interfaces, which can improve ion storage capability and rate performance. However, there are still challenges in increasing the proportion of heterogeneous interfaces in materials and understanding the complex interaction mechanisms at these interfaces. Here, we have successfully synthesized confined CoSe2 within the interlayer space of Ti3C2Tx through a simple solvothermal method, resulting in the formation of a superlattice-like heterostructures of CoSe2@Ti3C2Tx. Both density functional theory (DFT) calculations and experimental results show that compared with CoSe2 and Ti3C2Tx, CoSe2@Ti3C2Tx can significantly improve adsorption of Na+ ions, while maintaining low volume expansion and high Na+ ions migration rate. The heterostructure formed by MXene and CoSe2 is a Schottky heterostructure, and its interfacial charge transfer induces a built-in electric field that promotes rapid ion transport. When CoSe2@Ti3C2Tx was used as an anode material, it exhibits a high specific capacity of up to 600.1 mAh/g and an excellent rate performance of 206.3 mAh/g at 20 A/g. By utilizing CoSe2@Ti3C2Tx as the anode and activated carbon (AC) as the cathode, the sodium-ion capacitor of CoSe2@Ti3C2Tx//AC exhibits excellent energy and power density (125.0 Wh kg-1 and 22.5 kW kg-1 at 300.0 W kg-1 and 37.5 Wh kg-1, respectively), as well as a long service life (86.3 % capacity retention over 15,300 cycles at 5 A/g), demonstrating its potential for practical applications.

Three-Dimensional Flexible SnO2@Hard Carbon@MoS2@Soft Carbon Fiber Film Anode toward Ultrafast and Stable Sodium Storage

Developing flexible electrodes for the application in sodium-ion batteries (SIBs) has received great attention and has been still challenging due to their merits of additive-free, lightweight, and high energy density. In this work, a free-standing 3D flexible SIB anode with the composition of SnO2@hard carbon@MoS2@soft carbon is designed and successfully synthesized. This electrode combines the energy storage advantages and hybrid sodium storage mechanisms of each material, manifested in the enhanced flexibility, specific capacity, conductivity, rate, cycling performances, etc. Based on the synergistic effects, it exhibits much higher specific capacity than SnO2 carbon nanofibers, as well as more excellent cycling performance (250 mA h g-1 after 500 cycles at 1 A g-1) than MoS2 nanospheres (32 mA h g-1). In addition, relevant kinetic mechanisms are also expounded with the aid of theoretical calculation. This work provides a feasible and advantageous strategy for constructing high-performance and flexible energy storage electrodes based on hybrid mechanisms and synergistic effects.

Carbon-Coated Tin-Titanate derived SnO2/TiO2 nanowires as High-Performance anode for Lithium-Ion batteries

Tin dioxide (SnO2) is a promising alternative material to graphite anode, but the large volume change induced electrode pulverization issue has limited its application in lithium-ion batteries (LIBs). In contrast, titanium dioxide (TiO2) anode shows high structure stability upon lithium insertion/extraction, but with low specific capacity. To overcome their inherent disadvantages, combination of SnO2 with TiO2 and highly conductive carbon material is an effective way. Herein, we report a facile fabrication method of carbon-coated SnO2/TiO2 nanowires (SnO2/TiO2@C) using tin titanate nanowires as precursor, which are prepared by reacting SnCl2·2H2O with layered sodium titanate (Na2Ti3O7) nanowires in the aqueous solution though the ion exchange between Sn2+ and Na+. After annealing under argon atmosphere, the hydrothermally carbon-coated tin-titanate nanowires decompose, forming a unique hybrid structure, where ultrafine SnO2 nanoparticles are uniformly embedded within the TiO2 substrate with carbon coating. Consequently, the SnO2/TiO2@C nanowires demonstrate excellent lithium storage capacity with high pseudocapacitance contribution, excellent reversible capacity, and long-term cycling stability (673.7/510.5 mAh/g at 0.5/1.0 A/g after 250/800 cycles), owing to the unique hybrid structure, as the well-dispersion of ultra-small SnO2 within TiO2 nanowire substrate with simultaneous carbon coating efficiently suppresses the volume changes of SnO2, provides abundant reactive sites for lithium storage, and enhances the electrical conductivity with shortened ion transport distance.