Efficient Laser-Induced Construction of Oxygen-Vacancy Abundant Nano-ZnCo2 O4 /Porous Reduced Graphene Oxide Hybrids toward Exceptional Capacitive Lithium Storage

Fabrication of Porous Reduced Graphene Oxide Encapsulated Cu(OH)2 Core-shell Structured Carbon Fiber-Based Electrodes for High-Performance Flexible Supercapacitors

To explore next-generation flexible supercapacitors, lightweight, superior conductivity, low cost, and excellent capacitance are the preconditions for practical use. However, subjected to unsatisfactory conductivity, limited surface areas, and poor porosity leading to long ion transport channels, carbon fiber (CF)-based flexible supercapacitors need to further boost the electrochemical properties. Hence, a porous reduced graphene oxide encapsulated Cu(OH)2 core-shell structured CF-based electrode was fabricated through a scalable approach. The inexpensive Cu(OH)2 nanoarrays were controllably grown in situ on a CF substrate, with residual Cu promoting conductivity. Porous graphene oxide (PrGO), which served as the shell, was realized by Ni nanoparticle etching, which not only provided more active sites for capacitance as well as shortened accessible pathways for the ion transport but also effectively alleviated the exfoliation of the internal active materials. Moreover, thanks to this distinctive core-shell architecture, the extra space between the outer PrGO layer and the internal ordered Cu(OH)2 nanoarrays provided increased space for capacitance storage. The assembled PrGO/Cu(OH)2/Cu@CF electrode exhibited an excellent areal capacitance, reaching up to 722 mF cm-2 at a current density of 0.5 mA cm-2, attributed to its superior structure and materials advantages. The resulting PrGO/Cu(OH)2/Cu@CF//AC//CF asymmetric flexible all-solid-state supercapacitor achieved a high energy density of 0.052 mWh cm-2 and exhibited long-term durability. This work proposes a low-cost and effective way to fabricate hierarchically structured electrodes for wearable CF-based supercapacitors.

A ternary oxygen-vacancy abundant ZnMn2O4/MnCO3/nitrogen-doped reduced graphene oxide hybrid towards superior-performance lithium storage

Transition metal oxides (TMOs) and metal carbonates exhibit high specific capacity, abundant reserves on Earth, and environmental friendliness as anode materials for lithium-ion batteries (LIBs). However, their poor electrical conductivity and serious volume expansion lead to rapid capacity decay. Herein, a stable and highly conductive composite of an oxygen-vacancy abundant nitrogen-doped reduced graphene oxide (NG) encapsulated ZnMn2O4/MnCO3 (ZnMn2O4/MnCO3/NG) hybrid is successfully fabricated, which can provide more spaces for rapid ion diffusion and corroborate fast electron transport. The ZnMn2O4/MnCO3/NG hybrid exhibits an incredible reversible capacity (916 mA h g-1 at 0.1 A g-1), preeminent cycling stability (800 mA h g-1 at 1 A g-1 after 300 cycles) and outstanding rate capability (459 mA h g-1 at 2 A g-1). The excellent lithium storage performance of ZnMn2O4/MnCO3/NG is attributed to the synergistic effect between ZnMn2O4 and MnCO3, the addition of nitrogen and oxygen defects, and the stable structures of NG, which relieve the volume expansion of the electrode material, improve the electronic conductivity and enhance structural stability and surface capacitive response. This work provides a new idea for constructing oxygen-vacancy abundant NG encapsulated bimetal oxides for energy storage of LIBs.

Vacancy designed 2D materials for electrodes in energy storage devices

Vacancies are ubiquitous in nature, usually playing an important role in determining how a material behaves, both physically and chemically. As a consequence, researchers have introduced oxygen, sulphur and other vacancies into bi-dimensional (2D) materials, with the aim of achieving high performance electrodes for electrochemical energy storage. In this article, we focused on the recent advances in vacancy engineering of 2D materials for energy storage applications (supercapacitors and secondary batteries). Vacancy defects can effectively modify the electronic characteristics of 2D materials, enhancing the charge-transfer processes/reactions. These atomic-scale defects can also serve as extra host sites for inserted protons or small cations, allowing easier ion diffusion during their operation as electrodes in supercapacitors and secondary batteries. From the viewpoint of materials science, this article summarises recent developments in the exploitation of vacancies (which are surface defects, for these materials), including various defect creation approaches and cutting-edge techniques for detection of vacancies. The crucial role of defects for improvement in the energy storage performance of 2D electrode materials in electrochemical devices has also been highlighted.

Recent Advances of ZnCo2 O4 -based Anode Materials for Li-ion Batteries

ZnCo₂ O₄ has been attracted wide research attention as a promising anode material for lithium-ion batteries (LIBs) in recent years based on its high theoretical specific capacity, low toxicity as well as stable chemical properties. However, the further large-scale application of pristine ZnCo₂ O₄ anode have been impeded because of its undesirable Li⁺ ion conductivity, low electronic conductivity, and finite stability of electrolytes at high potentials. Recently, optimizing the micro/nano structure, modification with carbonaceous materials, incorporation with metal oxides and constructing a binder-free structure on conductive substrate for ZnCo₂ O₄ -based materials have been verified as promising effective routes for solving the above problems. In this review, the recent advances in underlying reaction mechanisms, synthetic methods and strategies for improving the performance of ZnCo₂ O₄ anodes are comprehensively summarized. The factors affecting the electrochemical properties of ZnCo₂ O₄ -based materials are mainly discussed, and paths to promote the specific capacity and cyclic stability are proposed. Finally, several insights into the future developments, challenges, and prospects of ZnCo₂ O₄ -based anode materials of LIBs are proposed.

A 3D structure C/Si/ZnCo2O4/CC anode for flexible lithium-ion batteries with high capacity and fast charging ability

ZnCo₂O₄ has attracted extensive attention as a bimetallic transition metal oxide anode material for lithium-ion batteries (LIBs) with high capacity. However, there is still a long way to go to meet the increasing demand for commercial batteries due to their modest conductivity and unobtrusive cycling stability. The use of finely controlled nanostructures and combination with other anode materials are the two main ways to improve the battery performance of ZnCo₂O₄. Herein, ZnCo₂O₄ (ZCO) nanosheets were in situ grown on carbon cloth (CC) through a facile solution method. Si was coated onto the ZCO nanosheet arrays by the magnetron sputtering method (SCZO/CC) to acheive the capacity increase. A layer of C was further coated onto SZCO/CC to improve the electrical conductivity of the whole electrode and to protect the SZCO nanostructure. The obtained CSZCO/CC electrode exhibits a high reversible areal capacity of 1.16 mA h cm^-2 at 5 mA cm^-2 after 500 cycles. At an ultra-high current density of 10 mA cm^-2, the CSZCO/CC electrode can still present a capacity of 0.38 mA h cm^-2 and maintain a capacity retention of 88.4% for 2000 cycles. In situ Raman spectroscopy was used to study the relationship between the electrochemical performance and structure of the electrode materials. The carbon cloth was found to have contributed a nonnegligible part of the capacity of the electrode.

Construction of nickel ferrite nanoparticle-loaded on carboxymethyl cellulose-derived porous carbon for efficient pseudocapacitive energy storage

The preparation of biomass-derived carbon electrode materials with abundant active sites is suitable for development of energy-storage systems with high energy and power densities. Herein, a hybrid material consisting of highly-dispersed nickel ferrite nanoparticle on 3D hierarchical carboxymethyl cellulose-derived porous carbon (NiFe₂O₄/CPC) was prepared by simple annealing treatment. The synergistic effects of NiFe₂O₄ species with multiple oxidation states and 3D porous carbon with a large specific surface area offered abundant active centers, fast electron/ion transport, and robust structural stability, thereby showing the excellent performance of the electrochemical capacitor. The best performing sample (NiFe₂O₄/CPC-800) exhibited a superior capacitance of 2894F g^-1 at a current density of 0.5 A g^-1. Encouragingly, an asymmetric supercapacitor with NiFe₂O₄/CPC-800 as a positive electrode and activated carbon as a negative electrode delivered a high energy density of 135.2 W h kg^-1 along with an improved power density of 10.04 kW kg^-1. Meanwhile, the superior cycling stability of 90.2% over 10,000 cycles at 5 A g^-1 was achieved. Overall, the presented work offers a guideline for the design and preparation of advanced electrode materials for energy-storage systems.

Metal–organic framework-derived porous CoFe2O4/carbon composite nanofibers for high-rate lithium storage

Upon assembled into full cells, metal–organic frameworks derived porous CoFe2O4/carbon composite nanofibers achieved long-cycling and high-rate performance, and a series of LED bulbs can be lit to demonstrate its potential in real applications.

Vertically Aligned ZnCo2O4 Nanoplates on Ti3C2 for High-Efficiency Hybrid Supercapacitors

Electrode materials marking higher structural stability, and electrochemical activity remain the priority in improving the electrochemical performance of supercapacitors (SCs). Herein we report the designed synthesis of novel nanoplate-on-nanosheet architecture...

Stable Rooted Solid Electrolyte Interphase for Lithium-Ion Batteries

Metal oxide-based materials are attractive anode candidates for lithium-ion batteries (LIBs) because of their high theoretical capacity. However, these materials suffer from large volume expansion and poor stability of solid electrolyte interphase (SEI) during the charge-discharge process, casusing rapid capacity degradation. Herein, we report that Li₃PO₄-rooted and intact SEI in situ formed on the phosphate-modified SnO₂/CNFs during cycling. The phosphate anions in the anode, could serve as the root to form Li₃PO₄ by bonding with Li ions and participate in the formation of the SEI, thus firmly anchoring and stabilizing the SEI layer. The rooted Li₃PO₄ and enriched LiF in the SEI could synergistically enhance the Li-ion diffusion, significantly reduce the volume expansion, and lead to ultrastable cycling performance over 1100 charge-discharge cycles at 1 A g^-1. This work provides a new avenue for forming stable SEI rooted into the anode and inspires the development of interface engineering toward electrochemical energy storage.

High-performance ZnCo2O4 microsheets as an anode for lithium-ion batteries

Mesoporous ZnCo₂O₄ microsheets are successfully obtained by using a MOF as a precursor. Benefiting from the special structure with favorable electron-transfer and Li-ion diffusion properties, the sample calcined at 600 °C exhibits superior lithium storage capacity of 816.2 mA h g^-1 at 100 mA g^-1 after 100 cycles, which has great application potential.

Oxygen Vacancies Boosting Lithium-Ion Diffusion Kinetics of Lithium Germanate for High-Performance Lithium Storage

Oxygen vacancies play a positive role in optimizing the physical and chemical properties of metal oxides. In this work, we demonstrated oxygen vacancy-promoted enhancement of Li-ion diffusion kinetics in Li₂GeO₃ nanoparticle-encapsulated carbon nanofibers (denoted as Li₂GeO_3-x/C) and accordingly boosted lithium storage. The introduction of the oxygen vacancies in Li₂GeO_3-x/C can enhance electronic conductivity and evidently decrease activation energy of Li-ion transport, thus resulting in evidently accelerated Li-ion diffusion kinetics during the lithiation/delithiation process. Thus, the Li₂GeO_3-x/C nanofibers exhibit an exceptionally large discharge capacity of 1460.5 mA h g^-1 at 0.1 A g^-1, high initial Coulombic efficiency of 81.3%, and excellent rate capability. This facile and efficient strategy could provide a reference for injecting the oxygen vacancies into other metal oxides for high-performance anode materials.

Semi-transparent reduced graphene oxide photodetectors for ultra-low power operation

The emerged demand for high-performance systems promotes the development of two-dimensional (2D) graphene-based photodetectors. However, these graphene-based photodetectors are usually fabricated by an expensive photolithography and complicated transferred process. Here, a semi-transparent reduced graphene oxide (rGO) photodetector on a polyethylene terephthalate (PET) substrate with ultra-low power operation by simple processes is developed. The photodetector has achieved a transmittance about 60%, a superior responsivity of 375 mA/W and a high detectivity of 10¹² Jones at a bias of -1.5 V. Even the photodetector is worked at zero bias, the photodetector exhibits a superior on/off ratio of 12. Moreover, the photoresponse of such photodetector displays little reduction after hundred times bending, revealing that the photodetector is reliable and robust. The proposed fabrication strategy of the photodetector will be beneficial to the integration of semi-transparent and low-power wearable devices in the future.

Oxygen Vacancy Enhanced Two-Dimensional Lithium Titanate for Ultrafast and Long-Life Bifunctional Lithium Storage

Boosting sufficient Li⁺ ion mobility in Li₄Ti₅O₁₂ (LTO) is crucial for high-rate performance lithium storage. Here, an ultrafast charge storage oxygen vacancy two-dimensional (2D) LTO nanosheet was successfully fabricated through a one-pot hydrothermal method. The selectively doped Al³⁺ into octahedron Li⁺/Ti⁴⁺ 16d sites not only provide bulk oxygen vacancy and appropriate distorted TiO₆ octahedra to facilitate Li⁺ ions diffusion, but also serve as a "pillar" to stabilize the Ti-O framework. The oxygen vacancy lowers Li⁺ ion diffusion energy barrier. Moreover, the 2D structure provides open diffusion channels for fast Li⁺ ion transport. As a result, the sample shows excellent electrochemical performance for bifunctional lithium storage. As a lithium-ion battery anode, the capacity retention reaches 112.8 mA h g^-1 after 5000 cycles at 40 C with a fading rate of 0.288% per 100 cycles. Meanwhile, as a lithium-ion capacitor anode, it exhibits an excellent rate capacity of 120 mA h g^-1 after 5000 cycles at 500 C with nearly 100% Coulombic efficiency. The produced LTO shows much higher rate capacity and longer lifetime than the reported LTO. Density functional theory calculations also demonstrate that oxygen vacancy can facilitate Li⁺ ion diffusion kinetics. The relationship between oxygen vacancy content and Li⁺ ions diffusion energy barrier in LTO is quantified. This work pioneers a defect engineering strategy for synthesized high-performance electrode materials.

Template-free formation of one-dimensional mesoporous ZnMn2O4 tube-in-tube nanofibers towards lithium-ion batteries as anode materials

Mesoporous ZnMn2O4 tube-in-tube nanofibers are firstly synthesized via a template-free strategy as an anode material towards lithium-ion batteries, along with a tentative formation mechanism.

Synergistic Interface-Assisted Electrode-Electrolyte Coupling Toward Advanced Charge Storage

Owing to the limited charge storage capability of transitional metal oxides in aqueous electrolytes, the use of redox electrolytes (RE) represents a promising strategy to further increase the energy density of aqueous batteries or pseudocapacitors. The usual coupling of an electrode and an RE possesses weak electrode/RE interaction and weak adsorption of redox moieties on the electrode, resulting in a low capacity contribution and fast self-discharge. In this work, Fe(CN)₆ ^4- groups are grafted on the surface of Co₃ O₄ electrode via formation of CoN bonds, creating a synergistic interface between the electrode and the RE. With such an interface, the coupled Co₃ O₄ -RE system exhibits greatly enhanced charge storage from both Co₃ O₄ and RE, delivering a large reversible capacity of ≈1000 mC cm^-2 together with greatly reduced self-discharge. The significantly improved electrochemical activity of Co₃ O₄ can be attributed to the tuned work function via charge injection from Fe(CN)₆ ^4- , while the greatly enhanced adsorption of K₃ Fe(CN)₆ molecules is achieved by the interface induced dipole-dipole interaction on the liquid side. Furthermore, this enhanced electrode-electrolyte coupling is also applicable in the NiO-RE system, demonstrating that the synergistic interface design can be a general strategy to integrate electrode and electrolyte for high-performance energy storage devices.