Research on Interfacial Construction and Energy Storage Performance of Polymetallic Heterostructure Based on Zn-Ni 3d Orbital Modulation and DFT Study

In this study, ZnCo2O4 nanosheets and NiCo2O4 nanowires were successfully grown on nickel foam as anode materials for lithium-ion batteries by a low-temperature hydrothermal and immersion method. The nanosheets offered an enlarged electrically active surface area, and the nanowires provided support for the nanosheets, thereby forming a heterojunction interface. The ZnCo2O4/NiCo2O4 heterojunction demonstrated favorable electrochemical performance in electrochemical tests. In terms of its rated performance, the capacity of the composite electrode recovered to 1050 mAh g-1 when the current density ranged from 0.1 to 1 A g-1; its capacity was maintained even when the current density returned to 0.1 A g-1 after 60 cycles. The diffusion coefficient of lithium ions (DLi+) increased due to the reduction of the interfacial contact resistance under the interfacial electric field of the heterostructure, and they were continuously activated during repeated cycles. This further significantly enhanced the electrochemical activity of the electrode. The analysis results based on the density functional theory revealed the hybridization of the 3d orbitals of Ni and Zn and the augmented electronic state occupancy of the orbitals near the Fermi energy level. This process was accompanied by the migration of electrons, leading to a decrease in the band gap. Meanwhile, the Li+ diffusion barrier decreased, and the conductivity of the electrode materials was enhanced.

Enhanced Energy Storage Properties and DFT Investigation of a Zn-Co-Mo Heterojunction Rich in Oxygen Vacancies with Dual Electron Transport Pathways

Petal-like heterojunction materials ZnCo2O4/CoMoO4 with abundant oxygen vacancies are prepared on nickel foam (NF) using modified ionic hybrid thermal calcination technology. Nanoscale ion intermixing between Zn and Mo ions induces oxygen vacancies in the annealing process, thus creating additional electrochemical active sites and enhancing the electrical conductivity. The ZnCo2O4/CoMoO4 conductive network skeleton forms the primary transport pathway for electrons, while the internal electric field of the heterojunction serves as the secondary pathway. ZnCo2O4/CoMoO4 exhibits excellent rate performance and high capacity attributable to its unique double electron transport mode and the effect of oxygen vacancies. The initial discharge capacity at a current of 0.1 A g-1 is approximately 1774 mAh g-1, and the reversible capacity remains at 1100 mAh g-1 after 200 cycles. After a high current of 1 A g-1, the reversible capacity is observed to remain at approximately 1240 mAh g-1. The electronic structure, crystal structure, and work function of the heterojunction interface model are then analyzed by density functional theory (DFT). The analysis results indicate that the charge at the ZnCo2O4/CoMoO4 interface is unevenly distributed, which leads to an enhanced degree of electrochemical reaction. The presence of an internal electric field improves the transport efficiency of the carriers. Experimental and theoretical calculations demonstrate that the ZnCo2O4/CoMoO4 anode material designed in this work provides a reference for fabricating transition metal oxide-based lithium-ion batteries.

Facile synthesis of spongy NiCo2O4 powders for lithium-ion storage

Spongy NiCo₂O₄ powders were prepared by solution combustion synthesis (SCS) method for lithium ions storage. The effects of combustion parameters including fuel type (L-lysine, glycine, and urea) and fuel amount on the lithium storage performance of NiCo₂O₄ powders were analyzed by various characterization techniques. Single-phase NiCo₂O₄ powders with extremely porous microstructure showed a strong drop of initial specific capacity up to 350 mAhg^-1 which was recovered up to 666 mAhg^-1 following 100 charge/discharge cycles. However, the NiCo₂O₄ powders prepared by the urea and L-lysine fuels with the compacted microstructure showed the capacity loss without any recovery. The spongy NiCo₂O₄ powders showed an acceptable capability rate performance (404 mAhg^-1 @ 400 mAg^-1).

In Situ Growth of 2D Ultrathin NiCo2 O4 Nanosheet Arrays on Ni Foam for High Performance and Flexible Solid-State Supercapacitors

In order to further overcome the shortage of electrodes with additive/binder and modulate the structure of NiCo₂ O₄ for supercapacitors, ultrathin NiCo₂ O₄ nanosheet arrays have been in situ grown on Ni foam by optimizing hydrothermal reactions based on crystal growth dynamics. The structure of ultrathin NiCo₂ O₄ nanosheet arrays can expose more active sites, provide abundant diffusion channels and buffer the stress caused by phase transition during charge-discharge process of supercapacitors. The optimized hydrothermal reactions can provide more ordered crystal orientations by keeping nanosheets on Ni foam completely coming from in situ growth, which will decrease the inner resistance of ultrathin NiCo₂ O₄ nanosheets and improve the efficiency and kinetics of electrons transfer. By the virtue of such remarkable features, the electrochemical results confirm the rationality of structural modulation and crystal orientations optimization with a drastically enhanced specific capacitance of 2017.8 F g^-1 , admirable rate performance of 93.2% and outstanding stability retention of 90.9% after cycling 5000 times. More impressively, the assembled flexible solid-state asymmetric supercapacitor (ASC) shows superior energy density, power density, and high stability. The modification strategy in this paper may throw light on the rational design of new generation advanced electrode materials for high-performance flexible supercapacitors.

Electrochemical performance of Li+ insertion/extraction in Ni-substituted ZnCo2O4 as an emerging highly efficient anode material

With the industrial revolution in electronics, the demand for lithium-ion batteries, particularly those designed for electric vehicles and energy storage systems, has accelerated in recent years. This continuously increasing demand requires high-performance electrode materials, as commonly used graphite anodes show limited lithium intercalation. In this context, Ni-substituted ZnCo₂O₄ nanostructures, thanks to their high storage capacity, have potential for use as an anode material in lithium-ion batteries. Structural analysis concludes that the prepared materials show improved crystallinity with increasing Ni at the Zn-site in ZnCo₂O₄. The intermediate composition, Zn_0.5Ni_0.5Co₂O₄, of this series exhibits a specific capacity of 65 mA h g⁻¹ at an elevated current rate of 10 A g⁻¹. The lithium insertion/extraction mechanism is investigated via cyclic voltammetry, showing two redox peaks from ZnCo₂O₄ and a single redox peak from NiCo₂O₄. Additionally, the lithium diffusion coefficient in the prepared electrodes is computed to be 2.22 × 10⁻¹² cm² s⁻¹ for the intermediate composition, as obtained using cyclic voltammetry. Electrochemical impedance spectroscopy is used to observe the charge transport mechanism and the charge transfer resistance values of all the samples, which are calculated to be in the range of 235 to 306 Ω.

With the industrial revolution in electronics, the demand for lithium-ion batteries, particularly those designed for electric vehicles and energy storage systems, has accelerated in recent years.

Synthesis of Sea Urchin-Like NiCo2O4 via Charge-Driven Self-Assembly Strategy for High-Performance Lithium-Ion Batteries

In this study, hydrothermal synthesis of sea urchin-like NiCo₂O₄ was successfully demonstrated by a versatile charge-driven self-assembly strategy using positively charged poly(diallydimethylammonium chloride) (PDDA) molecules. Physical characterizations implied that sea urchin-like microspheres of ~ 2.5 μm in size were formed by self-assembly of numerous nanoneedles with a typical dimension of ~ 100 nm in diameter. Electrochemical performance study confirmed that sea urchin-like NiCo₂O₄ exhibited high reversible capacity of 663 mAh g^-1 after 100 cycles at current density of 100 mA g^-1. Rate capability indicated that average capacities of 1085, 1048, 926, 642, 261, and 86 mAh g^-1 could be achieved at 100, 200, 500, 1000, 2000, and 3000 mA g^-1, respectively. The excellent electrochemical performances were ascribed to the unique micro/nanostructure of sea urchin-like NiCo₂O₄, tailored by positively charged PDDA molecules. The proposed strategy has great potentials in the development of binary transition metal oxides with micro/nanostructures for electrochemical energy storage applications.

Hierarchical flower-like NiCo2O4@TiO2hetero-nanosheets as anodes for lithium ion batteries

Flower-like NiCo₂O₄consisting of nanosheets are synthesized by hydrothermal technique and subsequently surface-modified with a TiO₂ultrathin layer by a hydrolysis process at low temperature.

Designed Functional Systems for High-Performance Lithium-Ion Batteries Anode: From Solid to Hollow, and to Core-Shell NiCo2O4 Nanoparticles Encapsulated in Ultrathin Carbon Nanosheets

Binary metal oxides have been considered as ideal and promising anode materials, which can ameliorate and enhance the electrochemical performances of the single metal oxides, such as electronic conductivity, reversible capacity, and structural stability. In this research, we report a rational method to synthesize some novel sandwich-like NiCo2O4@C nanosheets arrays for the first time. The nanostructures exhibit the unique features of solid, hollow, and even core-shell NiCo2O4 nanoparticles encapsulated inside and a graphitized carbon layers coating outside. Compared to the previous reports, these composites demonstrate more excellent electrochemical performances, including superior rate capability and excellent cycling capacity. Therefore, the final conclusion would be given that these multifarious sandwich-like NiCo2O4@C composites could be highly qualified candidates for lithium-ion battery anodes in some special field, in which good capability and high capacity are urgently required.

Facile synthesis of a nickel vanadate/Ni composite and its electrochemical performance as an anode for lithium ion batteries

Ni₃V₂O₈/Ni composites are synthesized by a simple hydrothermal route, and show high-rate capability and outstanding long-life cycling stability as a new anode material for Li-ion batteries.

PSA modified 3 D flower-like NiCo2O4 nanorod clusters as anode materials for lithium ion batteries

3 D flower-like NiCo₂O₄ nanorod clusters as anode materials for lithium ion batteries exhibit excellent electrochemical performance.

Controllable growth of NiCo2O4 nanoarrays on carbon fiber cloth and its anodic performance for lithium-ion batteries

NiCo₂O₄/CFC anodes coated with different thicknesses of NiCo₂O₄ were fabricated to investigate the role of the CFC substrate.