NH4 + Pre-Intercalation and Mo Doping VS2 to Regulate Nanostructure and Electronic Properties for High Efficiency Sodium Storage.

Sodium-ion hybrid capacitors (SIHCs) have attracted much attention due to integrating the high energy density of battery and high out power of supercapacitors. However, rapid Na+ diffusion kinetics in cathode is counterbalanced with sluggish anode, hindering the further advancement and commercialization of SIHCs. Here, aiming at conversion-type metal sulfide anode, taking typical VS2 as an example, a comprehensive regulation of nanostructure and electronic properties through NH4 + pre-intercalation and Mo-doping VS2 (Mo-NVS2) is reported. It is demonstrated that NH4 + pre-intercalation can enlarge the interplanar spacing and Mo-doping can induce interlayer defects and sulfur vacancies that are favorable to construct new ion transport channels, thus resulting in significantly enhanced Na+ diffusion kinetics and pseudocapacitance. Density functional theory calculations further reveal that the introduction of NH4 + and Mo-doping enhances the electronic conductivity, lowers the diffusion energy barrier of Na+, and produces stronger d-p hybridization to promote conversion kinetics of Na+ intercalation intermediates. Consequently, Mo-NVS2 delivers a record-high reversible capacity of 453 mAh g-1 at 3 A g-1 and an ultra-stable cycle life of over 20 000 cycles. The assembled SIHCs achieve impressive energy density/power density of 98 Wh kg-1/11.84 kW kg-1, ultralong cycling life of over 15000 cycles, and very low self-discharge rate (0.84 mV h-1).

Ultrafast and Durable Sodium-Ion Storage of Pseudocapacitive VN@C Hybrid Nanorods from Metal-Organic Framework.

Vanadium nitride (VN) is a promising electrode material for sodium-ion storage due to its multivalent states and high electrical conductivity. However, its electrochemical performance has not been fully explored and the storage mechanism remains to be clarified up to date. Here, the possibility of VN/carbon hybrid nanorods synthesized from a metal-organic framework for ultrafast and durable sodium-ion storage is demonstrated. The VN/carbon electrode delivers a high specific capacity (352 mA h g-1), fast-charging capability (within 47.5 s), and ultralong cycling stability (10 000 cycles) for sodium-ion storage. In situ XRD characterization and density functional theory (DFT) calculations reveal that surface-redox reactions at vanadium sites are the dominant sodium-ion storage mechanism. An energy-power balanced hybrid capacitor device is verified by assembling the VN/carbon anode and active carbon cathode, and it shows a maximum energy density of 103 Wh kg-1 at a power density of 113 W kg-1.

2D heterostructural Mn2O3 quantum dots embedded N-doped carbon nanosheets with strongly stable interface enabling high-performance sodium-ion hybrid capacitors.

The ingenious architectural structural engineering is extensively identified as a cogent means for facilitating the electrochemical properties of conversion-type anode materials for sodium-ion storage. Herein, a delicate, scalable and controllable solvent-free strategy is proposed to synthesize ultrafine Mn2O3 quantum dots embedded into N-doped carbon to generate two-dimensional (2D) composites (MNC) with robust interfacial heterostructural interactions for high sodium ion storage and fast reaction kinetics, which averts the use of solvents and environmental pollution, greatly reduces time and production costs. The introduction of metallic Mn species simultaneously achieves the construction of ultrafine Mn2O3 quantum dots and strong interfacial heterostructural COMn bonds between metal species and 2D N-doped carbon matrix. The synergistic effect of the formation of oxide quantum dots, the combination of 2D N-doped carbon and the construction of robust interfacial interactions provides the stable electrode structure, fast reaction kinetics and high electrochemical storage capability of anode materials. Hence, MNC composites in SIBs convey remarkable reversible rate capability. Its superior capacity reaches 215 mAh g-1 for 50 cycles at 0.2 A g-1 and 155 mAh g-1 for 1000 cycles at a high current density of 5 A g-1, which shows good long-term stability. The assembled sodium-ion hybrid capacitors (SIHCs) device delivers outstanding energy density of 138 Wh kg-1 at a power density of 126 W kg-1 and 98% capacity retention after 2000 cycles at 2 A g-1, and tremendous capability for practical applications (69 LEDs can be easily lighted). This work not merely offers guidance for the rational interfacial engineering design of high-capacity Mn-based electrode materials in a feasible and scalable solvent-free tactics for Na+ storage, but also broadens the routes for projecting a better electrode material for other battery systems.

Kinetically well-matched porous framework dual carbon electrodes for high-performance sodium-ion hybrid capacitors.

Sodium-ion hybrid capacitors (SIHCs) have attracted extensive interest due to their applications in sodium-ion batteries and capacitors, which have been considered expectable candidates for large-scale energy storage systems. The crucial issues for achieving high-performance SIHCs are the reaction kinetics imbalances between the slow Faradic battery-type anodes and fast non-Faradaic capacitive cathodes. Herein, we propose a simple self-template strategy to prepare kinetically well-matched porous framework dual-carbon electrodes for high-performance SIHCs, which stem from the single precursor, sodium ascorbate. The porous framework carbon (PFC) is obtained by direct calcination of sodium ascorbate followed by a washing process. The sodium-ion half cells with PFC anodes exhibit high reversible capacity and fast electrochemical kinetics for sodium storage. Moreover, the as-obtained PFC can be further converted to porous framework activated carbon (PFAC) with rich porosity and a high specific surface area, which displays high capacitive properties. By using kinetically well-matched battery-type PFC anodes and capacitive PFAC cathodes, dual-carbon SIHCs are successfully assembled, which can work well in 0-4 V. The optimal PFC//PFAC SIHC exhibits high energy density (101.6 Wh kg-1 at 200 W kg-1), power density (20 kW kg-1 at 51.1 Wh kg-1), and cyclic performance (71.8 % capacitance attenuation over 10,000 cycles).

Coupling High Rate Capability and High Capacity in an Intercalation-Type Sodium-Ion Hybrid Capacitor Anode Material of Hydrated Vanadate via Interlayer-Cation Engineering.

Layered metal vanadates with intercalation pseudocapacitive behaviors show great promise for applications in sodium-ion hybrid capacitor anode materials due to their large interlayer distances, which benefit the fast Na+ solid-state diffusion. However, their charge storage capacity is significantly constrained by the limited available sites that allow the intercalation of Na+ ions. In this work, by engineering the interlayer cations, Ni0.12Zn0.2V2O5·1.07H2O is designed as a high-performance anode material in sodium-ion hybrid capacitors. The Ni/Zn codoping in the layered vanadate leads to the integration of high rate capability and high specific capacity. Specifically, the spacious interlayer spacing and the pillaring effects of Zn ions together lead to the high rate performance and decent cycling stability, while the redox reactions of the interlayer Ni ions efficiently upgrade the charge storage capacity of this layered material. Accordingly, this work offers a promising avenue to further optimizing the Na+ storage performance of layered vanadates via interlayer-cation engineering.

A Novel Hierarchical Structure of SnCu2Se4/d-Ti3C2Tx/NPC for a Lithium/Sodium Ion Battery and Hybrid Capacitor with Long-Term Cycling Stabilities.

To alleviate kinetics imbalance and capacity insufficiency simultaneously, a novel hierarchical structure (SnCu2Se4/d-Ti3C2Tx/NPC) composed of delaminated Ti3C2Tx, SnCu2Se4 nanoparticles, and N-doped porous carbon layers is designed as a battery-type anode for lithium/sodium ion hybrid capacitor (LIC/SIC). The combination of SnCu2Se4 nanoparticles with high specific capacity, d-Ti3C2Tx with accelerated ion diffusion path, and NPC with enhanced electronic conductivity makes the SnCu2Se4/d-Ti3C2Tx/NPC composite possess excellent cycling stabilities in half-cell lithium-ion and sodium-ion batteries (LIB and SIB), with capacities of 114 mAh g-1 after 6000 cycles at 10 A g-1 for LIB and 296 mAh g-1 after 900 cycles at 1.0 A g-1 for SIB. The rate performance is also outstanding, with recovered capacity of 738 mAh g-1 at 0.1 A g-1 after cycles at current densities up to 50 A g-1 for LIB. Subsequently, LIC and SIC based on the SnCu2Se4/d-Ti3C2Tx/NPC anode and activated carbon cathode exhibit high energy densities of 147.9 and 158.6 Wh kg-1 at a power density of 100 W kg-1, respectively. They also possess distinctive long lifespans with capacity retentions of 78 and 81% after 10,000 cycles at 1.0 A g-1, respectively, demonstrating the feasibility of SnCu2Se4/d-Ti3C2Tx/NPC toward energy devices requiring high energy density, power density, and long-term stability.

Recent Progress on Two-Dimensional Carbon Materials for Emerging Post-Lithium (Na+, K+, Zn2+) Hybrid Supercapacitors.

The hybrid ion capacitor (HIC) is a hybrid electrochemical energy storage device that combines the intercalation mechanism of a lithium-ion battery anode with the double-layer mechanism of the cathode. Thus, an HIC combines the high energy density of batteries and the high power density of supercapacitors, thus bridging the gap between batteries and supercapacitors. Two-dimensional (2D) carbon materials (graphite, graphene, carbon nanosheets) are promising candidates for hybrid capacitors owing to their unique physical and chemical properties, including their enormous specific surface areas, abundance of active sites (surface and functional groups), and large interlayer spacing. So far, there has been no review focusing on the 2D carbon-based materials for the emerging post-lithium hybrid capacitors. This concept review considers the role of 2D carbon in hybrid capacitors and the recent progress in the application of 2D carbon materials for post-Li (Na+, K+, Zn2+) hybrid capacitors. Moreover, their challenges and trends in their future development are discussed.

3D Printing of Porous Nitrogen-Doped Ti3C2 MXene Scaffolds for High-Performance Sodium-Ion Hybrid Capacitors.

3D printing technology has stimulated a burgeoning interest to fabricate customized architectures in a facile and scalable manner targeting wide ranged energy storage applications. Nevertheless, 3D-printed hybrid capacitor devices synergizing favorable energy/power density have not yet been explored thus far. Herein, we demonstrate a 3D-printed sodium-ion hybrid capacitor (SIC) based on nitrogen-doped MXene (N-Ti3C2Tx) anode and activated carbon cathode. N-Ti3C2Tx affording a well-defined porous structure and uniform nitrogen doping can be obtained via a sacrificial template method. Thus-formulated ink can be directly printed to form electrode architecture without the request of a conventional current collector. The 3D-printed SICs, with a large areal mass loading up to 15.2 mg cm-2, can harvest an areal energy/power density of 1.18 mWh cm-2/40.15 mW cm-2, outperforming the state-of-the-art 3D-printed energy storage devices. Furthermore, our SIC also achieves a gravimetric energy/power density of 101.6 Wh kg-1/3269 W kg-1. This work demonstrates that the 3D printing technology is versatile enough to construct emerging energy storage systems reconciling high energy and power density.