Constructing NiS2/NiSe2 heteroboxes with phase boundaries for Sodium-Ion batteries

Tetrahedral Bonding Structure (Ni3 -Se) Induced by Lattice-Distortion of Ni to Achieve High Catalytic Activity in Na-Se Battery

Fabrication of transition-metal catalytic materials is regarded as a promising strategy for developing high-performance sodium-selenium (Na-Se) batteries. However, more systematic explorations are further demanded to find out how their bonding interactions and electronic structures can affect the Na storage process. This study finds that lattice-distorted nickel (Ni) structure can form different bonding structures with Na2 Se4 , providing high activity to catalyze the electrochemical reactions in Na-Se batteries. Using this Ni structure to prepare electrode (Se@NiSe2 /Ni/CTs) can realize rapid charge transfer and high cycle stability of the battery. The electrode exhibits high storage performance of Na+ ; i.e., 345 mAh g⁻1 at 1 C after 400 cycles, and 286.4 mAh g⁻1 at 10 C in rate performance test. Further results reveal the existence of a regulated electronic structure with upshifts of the d-band center in the distorted Ni structure. This regulation changes the interaction between Ni and Na2 Se4 to form a Ni3 -Se tetrahedral bonding structure. This bonding structure can provide higher adsorption energy of Ni to Na2 Se4 to facilitate the redox reaction of Na2 Se4 during the electrochemical process. This study can inspire the design of bonding structure with high performance in conversion-reaction-based batteries.

Homologous Heterostructured NiS/NiS2 @C Hollow Ultrathin Microspheres with Interfacial Electron Redistribution for High-Performance Sodium Storage

Nickel sulfides with high theoretical capacity are considered as promising anode materials for sodium-ion batteries (SIBs); however, their intrinsic poor electric conductivity, large volume change during charging/discharging, and easy sulfur dissolution result in inferior electrochemical performance for sodium storage. Herein, a hierarchical hollow microsphere is assembled from heterostructured NiS/NiS2 nanoparticles confined by in situ carbon layer (H-NiS/NiS2 @C) via regulating the sulfidation temperature of the precursor Ni-MOFs. The morphology of ultrathin hollow spherical shells and confinement of in situ carbon layer to active materials provide rich channels for ion/electron transfer and alleviate the effects of volume change and agglomeration of the material. Consequently, the as-prepared H-NiS/NiS2 @C exhibit superb electrochemical properties, satisfactory initial specific capacity of 953.0 mA h g-1 at 0.1 A g-1 , excellent rate capability of 509.9 mA h g-1 at 2 A g-1 , and superior longtime cycling life with 433.4 mA h g-1 after 4500 cycles at 10 A g-1 . Density functional theory calculation shows that heterogenous interfaces with electron redistribution lead to charge transfer from NiS to NiS2 , and thus favor interfacial electron transport and reduce ion-diffusion barrier. This work provides an innovative idea for the synthesis of homologous heterostructures for high-efficiency SIB electrode materials.

Breaking Barriers: Binder-Assisted NiS/NiS2 Heterostructure Anode with High Initial Coulombic Efficiency for Advanced Sodium-Ion Batteries

Developing sodium-ion batteries (SIBs) with high initial coulombic efficiency (ICE) and long-term cycling stability is crucial to meet energy storage device requirements. Designing anode materials that could exhibit high ICE is a promising strategy to realize enhanced energy density in SIBs. A trifunctional network binder substantially improves the electrochemical performance and ICE, providing excellent mechanical properties and strong adhesion strength. A rationally designed electrode material and binder can achieve high ICE, long cycling performance, and excellent specific capacity. Here, a NiS/NiS2 heterostructure as an anode material and a trifunctional network binder (SA-g-PAM) are designed for SIBs. Unprecedently, the anode comprising of an SA-g-PAM binder achieved the highest ICE of 90.7% and remarkable cycling stability for 19000 cycles at a current density of 10 A g-1 and maintained the specific capacity of 482.3 mAh g-1 even after 19000 cycles. This exciting work provides an alternate direction to the battery industry for developing high-performance electrode materials and binders with high ICE and excellent cycling stability for energy storage devices.

Yttrium trifluoride doped polyacrylonitrile based carbon nanofibers as separator coating layer for high performance lithium-metal batteries

In this study, the yttrium trifluoride-doped polyacrylonitrile(PAN) based carbon nanofibers (YF₃-PAN-CNFs) are successfully designed and prepared through the electro-blow spinning and carbonization strategies. And the YF₃-PAN-CNFs acted as main materials of functional layer for modifying separator of lithium metal batteries are systematically studied and analyzed. The prepared CNFs have long-range ordered structures and high conductivity, which can extremely improve the transport of lithium ions and electrons during charge-discharge processes. The lithiophilic YF₃ nanoparticles formed in the carbonization process can endow enough active sites to produce alloying reaction with Li, which makes the plating/stripping of Li more uniform. For the assembled Li||lithium iron phosphate (LiFePO₄) battery, it still maintains a high specific discharge capacity of 137.1 mAh g^-1 after 500 cycles at 0.5 C, which there is almost no specific discharge capacity degradation after long cycle. The modified separator for the Li||Li symmetric battery can effectively suppress the growth of lithium dendrites and improve cycle stability. Meanwhile, based on the strong chemical bonding between YF₃ and lithium polysulfide combining the effectively physical confinement of the YF₃-PAN-CNFs coating layer, the "shuttle effect" of lithium polysulfide also can be greatly suppressed. Thus the assembled Li||S battery using the separator has excellent electrochemical performance. Therefore, the YF₃-PAN-CNFs modified separator will have a promising application prospect in lithium metal batteries even other high performance secondary batteries.

A unique two-phase heterostructure with cubic NiSe2 and orthorhombic NiSe2 for enhanced lithium ion storage and electrocatalysis

Two-phase heterostructures have received tremendous attention in energy-related fields as high-performance electrode materials. However, heterogeneous interfaces are usually constructed by introducing foreign elements, which disturbs the investigation of the intrinsic effect of the two-phase heterostructure. Herein, unique heterostructures constructed with orthorhombic NiSe₂ and cubic NiSe₂ phases are developed, which are embedded in in situ formed porous carbon from metal-organic frameworks (MOFs) (O/C-NiSe₂@C). Precisely-controlled selenylation of MOFs is crucial for the formation of the O/C-NiSe₂ heterostructure. The heterogeneous interfaces with lattice dislocations and charge distribution are conducive to the high-speed transfer of electrons and ions during electrochemical processes, so as to improve the electrochemical reaction kinetics for lithium-ion storage and the hydrogen evolution reaction (HER). When used as the anode of lithium-ion batteries (LIBs), O/C-NiSe₂@C shows a superior electrochemical performance to the counterparts with only the cubic phase (C-NiSe₂@C), in view of the cycling performance (719.3 mA h g^-1 at 0.1 A g^-1 for 100 cycles; 456.3 mA h g^-1 at 1 A g^-1 for 1000 cycles) and rate capabilities (344.8 mA h g^-1 at 4 A g^-1). Furthermore, O/C-NiSe₂@C also exhibits better HER properties than C-NiSe₂@C, that is, much lower overpotentials of 154 mV and 205 mV in 0.5 M H₂SO₄ and 1 M KOH, respectively, at 10 mA cm^-2, a smaller Tafel slope as well as stable electrocatalytic activities for 2000 cycles/10 h. Preliminary observations indicate that the unique orthorhombic/cubic two-phase heterostructure could significantly improve the electrochemical performance of NiSe₂ without additional modifications such as doping, suggesting the O/C-NiSe₂ heterostructure as a promising bifunctional electrode for energy conversion and storage applications.

In-situ fabrication of active interfaces towards FeSe as advanced performance anode for sodium-ion batteries

Transition metal selenides have gained enormous interest as anodes for sodium ion batteries (SIBs). Nonetheless, their large volume expansion causing poor rate and inferior cycle stability during Na⁺ insertion/extraction process hinders their further applications in SIBs. Herein, a confined-regulated interfacial engineering strategy towards the synthesis of FeSe microparticles coated by ultrathin nitrogen-doped carbon (NC) is demonstrated (FeSe@NC). The strong interfacial interaction between FeSeand NC endows FeSe@NC with fast electron/Na⁺ transport kinetics and outstanding structural stability, delivering unexceptionable rate capability (364 mAh/gat 10 A/g) and preeminent cycling durability (capacity retention of 100 % at 1 A/g over 1000 cycles). Furthermore, variousex situcharacterization techniques and density functional theory (DFT) calculations have been applied to demonstrate the Na⁺ storage mechanism of FeSe@NC. The assembled Na₃V₂(PO₄)₂F₃@rGO//FeSe@NC full cell also displays a high capacity of 241 mAh/gat 1 A/g with the capacity retention of nearly 100 % over 2000 cycles, and delivers a supreme energy density of 135 Wh kg^-1 and a topmost power density of 495 W kg^-1, manifesting the latent applications of FeSe@NC in the fast charging SIBs.

Porous Microspheres Comprising CoSe2 Nanorods Coated with N-Doped Graphitic C and Polydopamine-Derived C as Anodes for Long-Lived Na-Ion Batteries

Metal-organic framework-templated nitrogen-doped graphitic carbon (NGC) and polydopamine-derived carbon (PDA-derived C)-double coated one-dimensional CoSe₂ nanorods supported highly porous three-dimensional microspheres are introduced as anodes for excellent Na-ion batteries, particularly with long-lived cycle under carbonate-based electrolyte system. The microspheres uniformly composed of ZIF-67 polyhedrons and polystyrene nanobeads (ϕ = 40 nm) are synthesized using the facile spray pyrolysis technique, followed by the selenization process (P-CoSe₂@NGC NR). Further, the PDA-derived C-coated microspheres are obtained using a solution-based coating approach and the subsequent carbonization process (P-CoSe₂@PDA-C NR). The rational synthesis approach benefited from the synergistic effects of dual carbon coating, resulting in a highly conductive and porous nanostructure that could facilitate rapid diffusion of charge species along with efficient electrolyte infiltration and effectively channelize the volume stress. Consequently, the prepared nanostructure exhibits extraordinary electrochemical performance, particularly the ultra-long cycle life stability. For instance, the advanced anode has a discharge capacity of 291 (1000th cycle, average capacity decay of 0.017%) and 142 mAh g^-1 (5000th cycle, average capacity decay of 0.011%) at a current density of 0.5 and 2.0 A g^-1, respectively.

Overcoming Ion Transport Barrier by Plasma Heterointerface Engineering: Epitaxial Titanium Carbonitride on Nitrogen-Doped TiO2 for High-Performance Sodium-Ion Batteries

Anatase TiO₂ is a promising anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) due to its high specific capacity, low cost, and excellent cycle stability. However, low electrical conductivity and poor Na⁺ ion transport in TiO₂ limit its practical applications. Here, substantially boosted Na⁺ ion transport and charge transfer kinetics are demonstrated by constructing a near-ideal non-rectifying titanium carbonitride/nitrogen-doped TiO₂ (TiC_x N_{1- x} /N-TiO₂ ) heterostructure. Owing to the fast plasma effects and metastable hybrid phases, the TiC_x N_{1- x} is epitaxially grown on TiO₂ . Energy band engineering at the interface induces high electron densities and a strong built-in electric field, which lowers the Na⁺ diffusion barrier by a factor of 1.7. As a result, the TiC_x N_{1- x} /N-TiO₂ electrode exhibits excellent electrochemical performance. The reversible specific capacities at rates of 0.1 and 10 C reach 312.3 and 173.7 mAh g^-1 , respectively. After 600 cycles of charge and discharge at 10 C, the capacity retention rate is 98.7%. This work discovers an effective non-equilibrium plasma-enabled process to construct heterointerfaces that can enhance Na⁺ ion transport and provides generic guidelines for the design of heterostructures for a broader range of energy storage, separation, and other devices that rely on controlled ionic transport.

General metal-organic framework-derived strategy to synthesize yolk-shell carbon-encapsulated nickelic spheres for sodium-ion batteries

Transition-metal compounds have attracted enormous attention as potential energy storage materials for their high theoretical capacity and energy density. However, the most present transition-metal compounds still suffer from severe capacity decay and limited rate capability due to the lack of robust architectures. Herein, a general metal-organic framework-derived route is reported to fabricate hierarchical carbon-encapsulated yolk-shell nickelic spheres as anode materials for sodium-ion batteries. The nickelic metal-organic framework (Ni-MOF) precursors can be in situ converted into hierarchical carbon-encapsulated Ni₂P (Ni₂P/C), NiS₂ (NiS₂/C) and NiSe₂ (NiSe₂/C) by phosphorization, sulfuration, and selenation reaction, respectively, and maintain their yolk-shell sphere-like morphology. The as-synthesized Ni₂P/C sample can deliver much lower polarization and discharge platform, smaller voltage gap, and faster kinetics in comparison with that of the other two counterparts, and thus achieve higher initial specific capacity (3222.1/1979.3 mAh g^-1) and reversible capacity of 765.4 mAh g^-1 after 110 cycles. This work should provide new insights into the phase and structure engineering of carbon-encapsulated transition-metal compound electrodes via MOFs template for advanced battery systems.