Sodium-ion batteries operating at room temperature have emerged as a generation of energy storage devices to replace lithium-ion batteries; however, they are limited by a lack of anode materials with both an adequate lifespan and excellent rate capability. To address this issue, we developed Nb 2 CT x MXene-framework MoS 2 nanosheets coated with carbon (Nb 2 CT x @MoS 2 @C) and constructed a robust threedimensional cross-linked structure. In such a design, highly conductive Nb 2 CT x MXene nanosheets prevent the restacking of MoS 2 sheets and provide efficient channels for charge transfer and diffusion. Additionally, the hierarchical carbon coating has a certain level of volume elasticity and excellent electrical conductivity to guarantee the intercalation of sodium ions, facilitating both fast kinetics and long-term stability. As a result, the Nb 2 CT x @MoS 2 @C anode delivers an ultrahigh reversible capacity of 530 mA h g −1 at 0.1 A g −1 after 200 cycles and very long cycling stability with a capacity of 403 mA h g −1 and only 0.01% degradation per cycle for 2000 cycles at 1.0 A g −1 . Moreover, this anode has an outstanding capacity retention rate of approximately 88.4% from 0.1 to 1 A g −1 in regard to rate performance. Most importantly, the Nb 2 CT x @MoS 2 @C anode can realize a quick charge and discharge at current densities of 20 or even 40 A g −1 with capacities of 340 and 260 mAh g −1 , respectively, which will increase the number of practical applications for sodium-ion batteries. KEYWORDS: Nb 2 CT x @MoS 2 @C, Nb 2 CT x MXene, 3D network, sodium-ion batteries, high rate performance, high capacity

Lithium–sulfur (Li–S) batteries have been considered as one of the most promising energy storage systems owing to their high theoretical capacity and energy density. However, their commercial applications are obstructed by sluggish reaction kinetics and rapid capacity degradation mainly caused by polysulfide shuttling. Herein, the first attempt to utilize a highly conductive metal–organic framework (MOF) of Ni3(HITP)2 graphene analogue as the sulfur host material to trap and transform polysulfides for high‐performance Li–S batteries is made. Besides, the traditional conductive additive acetylene black is replaced by carbon nanotubes to construct matrix conduction networks for triggering the rate and cycling performance of the active cathode. As a result, the S@Ni3(HITP)2 with sulfur content of 65.5 wt% shows excellent sulfur utilization, rate performance, and cyclic durability. It delivers a high initial capacity of 1302.9 mAh g−1 and good capacity retention of 848.9 mAh g−1 after 100 cycles at 0.2 C. Highly reversible discharge capacities of 807.4 and 629.6 mAh g−1 are obtained at 0.5 and 1 C for 150 and 300 cycles, respectively. Such kinds of pristine MOFs with high conductivity and abundant polar sites reveal broad promising prospect for application in the field of high‐performance Li–S batteries.

Lithium-sulfur batteries are a promising high energy output solution for substitution of traditional lithium ion batteries. In recent times research in this field has stepped into the exploration of practical applications. However, their applications are impeded by cycling stability and short life-span mainly due to the notorious polysulfide shuttle effect. In this work, a multifunctional sulfur host fabricated by grafting highly conductive Co 3 Se 4 nanoparticles onto the surface of an N-doped 3D carbon matrix to inhibit the polysulfide shuttle and improve the sulfur utilization is proposed. By regulating the carbon matrix and the Co 3 Se 4 distribution, N-CN-750@Co 3 Se 4 -0.1 m with abundant polar sites is experimentally and theoretically shown to be a good LiPSs absorbent and a sulfur conversion accelerator. The S/N-CN-750@ Co 3 Se 4 -0.1 m cathode shows excellent sulfur utilization, rate performance, and cyclic durability. A prolonged cycling test of the as-fabricated S/N-CN-750@Co 3 Se 4 -0.1 m cathode is carried out at 0.2 C for more than 5 months which delivers a high initial capacity of 1150.3 mAh g −1 and retains 531.0 mAh g −1 after 800 cycles with an ultralow capacity reduction of 0.067% per cycle, maintaining Coulombic efficiency of more than 99.3%. The reaction details are characterized and analyzed by ex situ measurements. This work highly emphasizes the potential capabilities of transition-metal selenides in lithium-sulfur batteries.

As a typical family of two-dimensional (2D) materials, MXenes present physiochemical properties and potential for use in energy storage applications. However, MXenes suffer some of the inherent disadvantages of 2D materials, such as severe restacking during processing and service and low capacity of energy storage. Herein, a MXene@N-doped carbonaceous nanofiber structure is designed as the anode for high-performance sodium-and potassium-ion batteries through an in situ bioadsorption strategy; that is, Ti 3 C 2 T x nanosheets are assembled onto Aspergillus niger biofungal nanoribbons and converted into a 2D/1D heterostructure. This microorganism-derived 2D MXene-1D N-doped carbonaceous nanofiber structure with fully opened pores and transport channels delivers high reversible capacity and long-term stability to store both Na + (349.2 mAh g −1 at 0.1A g −1 for 1000 cycles) and K + (201.5 mAh g −1 at 1.0 A g −1 for 1000 cycles). Ion-diffusion kinetics analysis and density functional theory calculations reveal that this porous hybrid structure promotes the conduction and transport of Na and K ions and fully utilizes the inherent advantages of the 2D material. Therefore, this work expands the potential of MXene materials and provides a good strategy to address the challenges of 2D energy storage materials. KEYWORDS: biosorption, Ti 3 C 2 T x MXenes, porous hybrid fibers, sodium-ion batteries, potassium-ion batteries, density functional theory calculations