Synergistically Achieving Superior Sodium Storage of Metal Selenides by Constructing N-Doped Carbon Foams and Utilizing Cu-Driven Replacement Reaction

A Defective Disc-Like Cu1.96S Anode Material with the Efficient Cu Vacancies for High-Performance Sodium-Ion Storage

Due to their significant capacity and reliable reversibility, transition metal sulphides (TMSs) have received attention as potential anode materials for sodium-ion batteries (SIBs). Nonetheless, a prevalent challenge with TMSs lies in their significant volume expansion and sluggish kinetics, impeding their capacity for rapid and enduring Na+ storage. Herein, a Cu1.96S@NC nanodisc material enriched with copper vacancies is synthesised via a hydrothermal and annealing procedure. Density functional theory (DFT) calculations reveal that the incorporation of copper vacancies significantly boosts electrical conductivity by reducing the energy barrier for ion diffusion, thereby promoting efficient electron/ion transport. Moreover, the presence of copper vacancies creates ample active sites for the integration of sodium ions, streamlines charge transfer, boosts electronic conductivity, and, ultimately, significantly enhances the overall performance of SIBs. This novel anode material, Cu1.96S@NC, demonstrates a reversible capacity of 339 mAh g-1 after 2000 cycles at a rate of 5 A g-1. In addition, it maintains a noteworthy reversible capacity of 314 mAh g-1 with an exceptional capacity retention of 96% even after 2000 cycles at 20 A g-1. The results demonstrate that creating cationic vacancies is a highly effective strategy for engineering anode materials with high capacity and rapid reactivity.

Efficient Sodium Storage in Cu1.96S@NC Anode Achieved by Robust S─C Bonds and Current Collector Self-Induced Forming Cu2S Quantum Dots

Transition metal sulfides are investigation hotspots of anode material for sodium-ion batteries (SIBs) due to their structural diversity and high storage capacity. However, they are still plagued by inevitable volume expansion during sodiation/desodiation and an unclear energy storage mechanism. Herein, a one-step sulfidation-carbonization strategy is proposed for in situ confined growth of Cu1.96S nanoparticles in nitrogen-doped carbon (Cu1.96S@NC) using octahedral metal-organic framework (Cu-BTC) as a precursor and investigate the driving effect of Cu current collector on its sodium storage. The generation of S─C bonds in Cu1.96S@NC avoids the volume change and structural collapse of Cu1.96S nanoparticles during the cycling process and improves the adsorption and transport capacity of the material for Na+. More exciting, the Cu species in the Cu current collector are self-induced forming Cu2S quantum dots to enter the original anode material during the initial few charging and discharging cycles, which unique small-size effect and abundant edge-active sites enhance the energy storage capacity of Cu1.96S. Thus, the Cu1.96S@NC exhibits a superior first discharge capacity of 608.56 mAh g-1 at 0.2 A g-1 with an initial Coulomb efficiency (ICE) of 75.4%, as well as provides excellent rate performance and long cycle durability up to 2000 cycles.

Towards metal selenides: a promising anode for sodium-ion batteries

Metal selenides have garnered significant attention as promising anode materials for sodium-ion batteries, thanks to their high theoretical capacity, excellent conductivity, and natural abundance. However, their potential is hampered by disappointing capacity retention and unsatisfactory lifespan, primarily attributed to volume expansion and unwanted structural collapse resulting from the insertion and extraction of relatively large Na+ ions during the charge and discharge processes. This feature article provides a brief overview of our endeavors to address the challenges associated with metal selenide-based anode materials, aiming to achieve high-performance electrode materials for sodium-ion batteries. Our strategy encompasses nanostructure design, materials composite engineering, heteroatoms doping, and topography and interface engineering. Additionally, future research directions are also outlined.

Mesoporous Nickel Sulfide Microsphere Encapsulated in Nitrogen, Sulfur Dual-Doped Carbon with Large Subsurface Region for Enhanced Sodium Storage

Nickel sulfides are promising anode candidates in sodium ion batteries (SIBs) due to high capacity and abundant reserves. However, their applications are restricted by poor cycling stability and slow reaction kinetics. Thus, mesoporous nickel sulfide microsphere encapsulated in nitrogen, sulfur dual-doped carbon (MNS@NSC) is prepared. The packaged structure and carbon matrix restrain the volume variation together, the N, S dual-doping improves the electronic conductivity and offers extra active sites for sodium storage. Ex-situ X-ray diffraction  appeals copper collector adsorbs polysulfide to inhibit the polysulfide accumulation and enhance conductivity. Moreover, the large subsurface attributed to C-S-S-C bonding further boosts pseudocapacitive capacity, conducive to charge transfer. As a result, MNS@NSC delivers a high reversible capacity of 640.2 mAh g-1 after 100 cycles at 0.1 A g-1, an excellent rate capability (569.8 mAh g-1 at 5 A g-1), and a remained capacity of 513.8 mAh g-1 after undergoing 10000 circulations at 10 A g-1. The MNS@NSC|| Na3V2(PO4)3 full cell shows a cycling performance of specific capacity of 230.8 mAh g-1 after 100 cycles at 1 A g-1. This work puts forward a valid strategy of combing structural design and heteroatom doping to synthesize high-performance nickel sulfide materials in SIBs.