In Situ Growth of Iron Sulfide on Fast Charge Transfer V₂C‐MXene for Superior Sodium Storage Anodes

Abstract

and low cost. Although the "rockingchair" energy storage principle similar to lithium-ion batteries has driven the development of anode materials for SIBs to a certain extent, the larger ionic radius of Na + with high redox potential, 1.02 Å and −2.71 V versus NHE, tends to cause the poor electrochemical performance of SIBs. [3,4] Therefore, the search for suitable anode materials of sodium storage systems is urgently needed.Lately, conversion-reactive materials, such as metal oxides/sulfide, have attracted much attention due to their high theoretical capacity, among which sulfide exhibits better sodium storage properties as a SIB anode material due to its higher electronic conductivity, better structure maintenance and smaller potential negative drift. [5] As the most common metal, iron sulfide has been investigated for sodium storage capabilities and it shows high reversible capacities proving its feasibility as a high-performance SIB anode material. [6][7][8][9] Additionally, abundant resources, environmental compatibility, and low toxicity also make iron sulfide be more suitable for SIB application prospects as compared to other metal sulfides. Iron sulfide has various stoichiometries according to the different Fe valence states. In particular, pyrrhotite (Fe 7 S 8 ) with mixed-valence states has the characteristic of the intrinsic zero bandgap, which makes it as a promising high-rate anode material. [10] After Due to the upstream pressure of lithium resources, low-cost sodium-ion batteries (SIBs) have become the most potential candidates for energy storage systems in the new era. However, anode materials of SIBs have always been a major problem in their development. To address this, V 2 C/Fe 7 S 8 @C composites with hierarchical structures prepared via an in situ synthesis method are proposed here. The 2D V 2 C-MXene as the growth substrate for Fe 7 S 8 greatly improves the rate capability of SIBs, and the carbon layer on the surface provides a guarantee for charge-discharge stability. Unexpectedly, the V 2 C/Fe 7 S 8 @C anode achieves satisfactory sodium storage capacity and exceptional rate performance (389.7 mAh g −1 at 5 A g −1 ). The sodium storage mechanism and origin of composites are thoroughly studied via ex situ characterization techniques and first-principles calculations. Furthermore, the constructed sodium-ion capacitor assembled with N-doped porous carbon delivers excellent energy density (135 Wh kg −1 ) and power density (11 kW kg −1 ), showing certain practical value. This work provides an advanced system of sodium storage anode materials and broadens the possibility of MXene-based materials in the energy storage.

Multielectron Conversion: Peculiar Transition Metal Sulfides with Mixed Vulcanized States toward High‐Capacity Metal‐Ion Storage

“…[ 78b ] In the V 2 C/Fe 7 S 8 @C composites with hierarchical structures, the 2D V 2 CMXene as the growth substrate for Fe 7 S 8 greatly improves the rate capability of SIBs, and the carbon layer on the surface provides a guarantee for charge–discharge stability. [ 160 ]…”

“…[78b] In the V 2 C/Fe 7 S 8 @C composites with hierarchical structures, the 2D V 2 C-MXene as the growth substrate for Fe 7 S 8 greatly improves the rate capability of SIBs, and the carbon layer on the surface provides a guarantee for charge-discharge stability. [160] Various 3D carbonaceous materials have been utilized to construct the self-supported TMS-mV electrode, where the network structures with numerous voids contribute to exposing more reaction sites, providing more ionic/electronic channels, and accommodating volume expansion, resulting in additional shortened routes and fast mobility for 3D e − and M n+ transport. Meanwhile, they usually exhibit high energy density, high mechanical stability, and good flexibility.…”

Spatially Confined Fe7S8 Nanoparticles Anchored on a Porous Nitrogen-Doped Carbon Nanosheet Skeleton for High-Rate and Durable Sodium Storage

“…Additionally, Cao et al synthesized a layer of ultrathin amorphous TiO 2 on a MOF-derived Fe 7 S 8 /C composite, which achieved a capacity of 423.3 mAh g –1 after 200 cycles with an enhanced initial Coulombic efficiency (ICE) of 72% . More recently, Yan et al developed an in situ hydrothermal method for the synthesis of Fe 7 S 8 particles on highly conductive two-dimensional (2D) V 2 C-Mxene nanosheets and exhibited an elevated rate capability of 389.7 mAh g –1 at 5 A g –1 ascribing to the establishment of Na + diffusion channels and adsorption of polysulfides through the introduction of V 2 C-Mxene . Although great advances have been made in the past few years, many of these reported methods are complicated and time-consuming.…”

Constructing a VS4–V2CTx heterojunction interface to realize an ultra-long lifetime and high rate capability in sodium-ion batteries

“…Combined with other high specific capacity anodes, such as alloy, metal oxides, metal sulfides/selenides, etc., can enhance the electrical con-ductivity of electrode materials, as well as suppress the volume expansion of electrodes, 39 by inhibiting the side reactions between the electrolytes of electrode materials, 40 and accelerating ion transport. 41,42 Vanadium-based MXenes (V 2 CT x ) are another member of the MXene family which has the P/63mmc space group and hexagonal crystal structure. As a member of the MXene family, V 2 CT x also exhibits metallic properties so that it has a band gap of around 0 eV.…”