All over the world, the research done on designing the novel methods for inventing flexible electrochemical energy storage devices is becoming of more interest each day while the development of new ...technology in fields such as public wearable, consuming portable electronics, and electronic skin proceeds. Taking their large power density, cyclic stability, and outstanding mechanical integrity completeness into account, flexible supercapacitors are being used as energy storage devices at a wide interval. In the past few years, researchers have devoted considerable energy to promoting different kinds of transition metal oxides (TMOs) to employ in supercapacitors. Their choice can be found in unique TMOs characteristics such as ideal capacitive performance, low cost, and environment friendly. Their charge storage mechanisms obey from pseudocapacitance behavior. In the present document, we aim to provide a brief collection of the latest outcomes about several electrode materials of flexible supercapacitors based on TMOs and present this review by categories. The most popular routes to produce TMOs-based electrode materials, and the typical fabrication techniques for flexible devices, are thoroughly discussed. To add, since there is a tight connection between the morphology of the electrode materials and the electrochemical performance, the evaluation of the electrode component effect on the mechanical flexibility of the fabricated devices is a necessity. Not far ago for making accurate predictions about the upcoming trends towards the comprehension of an ultimate-performance, TMOs-based flexible supercapacitors, a history of the throughout electrochemical nobles and current evolution of the reported devices has been reported.
•Different types of TMOs applied for flexible supercapacitors are studied.•Fabrication of TMOs-based electrode for flexible device, are thoroughly discussed.•The challenges and landscape of TMO-based flexible supercapacitors are highlighted.•Recent advances of TMOs -based flexible supercapacitors are reviewed.
•A specific capacity of 1419 F/g was obtained for ZnFe2O4-rGO.•ZnFe2O4-rGO showed great capacitance retention of 93% after 5000 CV cycles.•ZnFe2O4-rGO electrode exhibited better supercapacitor ...performance than the ZnFe2O4 electrode.
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Binary transition metal oxides (BTMOs) are active materials, which have the potential for supercapacitor materials due to their high theoretical capacity. Herein, a BTMO based on zinc and iron was experimentally investigated in both the bare and hybrid forms, i.e. as ZnFe2O4 nanorods and ZnFe2O4 nanorods on reduced graphene oxide (rGO). After the synthesis, the products were investigated by different analytical techniques. The performance of the nano-engineered products as supercapacitor electrode materials were probed by electrochemical analysis. The electrochemical results obtained from the cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy showed the huge potential of the prepared electrodes for supercapacitor applications. The specific capacitance of ZnFe2O4-rGO was estimated as 1419 F/g with cyclic stability of 93% after 5000 successive voltammetry cycles at the scan rate of 10 mV/s. The electrochemical tests confirmed that the addition of rGO, owing to its large surface area and high electrical conductivity, improved the discharge time and cyclic stability besides increasing the specific conductance of the electrodes. The enhanced capacitance of the ZnFe2O4-rGO electrode recommends that the ion diffusion rate and the active redox site have been increased for capacitive behavior. Therefore, this composite can be a good candidate for energy storage.
There is a growing interest in the application of supercapacitors in energy storage systems due to their high specific power, fast charge/discharge rates and long cycle stability. Researchers have ...focused recently on developing nanomaterials to enhance their capacitive performance of supercapacitors. Particularly, the utilisation of fibres as templates has led to theoretical and practical advantages owing to their enlarged specific surface area, which allows fast electrolyte-ion diffusion. In addition, the inclusion of redox-active components, such as transition metal oxides (TMOs) and conducting polymers (CPs), into the fibres is believed to play an important role in improving the electrochemical behaviour of the fibre-based materials. Nevertheless, supercapacitors containing TMO- and CP-based fibres commonly suffer from inferior ion-transport kinetics and poor electronic conductivity, which can affect the rate capability and cycling stability of the electrodes. Therefore, the development of TMO/CP-based fibres has gained widespread attention because they synergistically combine the advantages of both materials, enabling revolutionary applications in the electrochemical field. This review describes and highlights recent progress in the development of TMO-, CP- and TMO/CP-based fibres regarding their design approach, configurations and electrochemical properties for supercapacitor applications, at the same time providing new opportunities for future energy storage technologies.
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•The classification and charge storage mechanism of supercapacitor are explained.•Different types of nanofibres and their relationship with supercapacitor performance are discussed.•Recent advances of transition-metal-oxide- and conducting polymer-based fibres are reviewed.•The challenges and outlook of transition metal oxide/conducting polymer–based fibres in supercapacitors are highlighted.
Mixed transition‐metal oxides (MTMOs), including stannates, ferrites, cobaltates, and nickelates, have attracted increased attention in the application of high performance lithium‐ion batteries. ...Compared with traditional metal oxides, MTMOs exhibit enormous potential as electrode materials in lithium‐ion batteries originating from higher reversible capacity, better structural stability, and high electronic conductivity. Recent advancements in the rational design of novel MTMO micro/nanostructures for lithium‐ion battery anodes are summarized and their energy storage mechanism is compared to transition‐metal oxide anodes. In particular, the significant effects of the MTMO morphology, micro/nanostructure, and crystallinity on battery performance are highlighted. Furthermore, the future trends and prospects, as well as potential problems, are presented to further develop advanced MTMO anodes for more promising and large‐scale commercial applications of lithium‐ion batteries.
Mixed transition‐metal oxides (MTMOs), including stannates, ferrites, cobaltates, and nickelates, have attracted increasing attention in the application of high performance lithium‐ion batteries. The rational design, energy storage mechanism and the future trends and prospects of novel MTMOs are discussed in detail. It is believed that MTMOs with higher reversible capacity, better structural stability, and high electronic conductivity are some of the most promising candidates for anodes for lithium ion batteries.
Sodium‐ion batteries (SIBs) are attracting increasing attention and considered to be a low‐cost complement or an alternative to lithium‐ion batteries (LIBs), especially for large‐scale energy ...storage. Their application, however, is limited because of the lack of suitable host materials to reversibly intercalate Na+ ions. Layered transition metal oxides (NaxMO2, M = Fe, Mn, Ni, Co, Cr, Ti, V, and their combinations) appear to be promising cathode candidates for SIBs due to their simple structure, ease of synthesis, high operating potential, and feasibility for commercial production. In the present work, the structural evolution, electrochemical performance, and recent progress of NaxMO2 as cathode materials for SIBs are reviewed and summarized. Moreover, the existing drawbacks are discussed and several strategies are proposed to help alleviate these issues. In addition, the exploration of full cells based on NaxMO2 cathodes and future perspectives are discussed to provide guidance for the future commercialization of such systems.
Layered transition metal oxides have attracted increasing interests as cathode materials for sodium‐ion batteries. Recent progresses of NaxMO2 cathodes, including the existing drawbacks and relative alleviation strategies, are reviewed and summarized. The exploration of full cells based on NaxMO2 cathodes and future perspectives are also discussed to provide guidance for the future commercialization of such systems.
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One method of increasing the energy density of Li-ion batteries is to access reversible Li intercalation in conventional layered transition metal oxide cathode materials at high ...potentials (4.3–5 V vs. Li/Li+), and thus allow more electrochemical capacity per volume of active material. This comes at the cost of increased interfacial reactivity and often results in capacity fade over many cycles. Tracing gas evolution during electrochemical lithium extraction and insertion provides a useful strategy to understand this high voltage reactivity. In this study, we examine outgassing during Li extraction in well-known layered oxides (LiCoO2, LCO; LiNiO2, LNO; and Li2MnO3, LMO). We highlight key differences in the outgassing of each material. Whereas negligible O2 release is found in LCO and LNO, even with voltage holds at 5 V vs. Li/Li+, O2 release is found to account for a large portion of the electrochemical capacity and persists over many cycles in LMO. CO2 outgassing is observed to varying extents, following the trend of LMO ≈ LNO > LCO, and is due to a combination of residual solid carbonate oxidation and electrolyte degradation. Taken together, these results show the importance of quantitative analysis in understanding the role of transition metal composition on the chemistry of conventional Li-ion battery materials.
O3-type transition metal oxides as the cathodes for Na-ion batteries have attracted extensive attention owing to their high theoretical specific capacity and ease of synthesis. This work indicates ...enhanced electrochemical reversibility and improved air stability via a rational Zn2+ doping for O3-NaNi0.5Mn0.5O2. It exhibits a discharge capacity of 113 mAh g−1 at 0.5 C, excellent capacity retention of 80% after 150 cycles, and the capability to release a capacity of 82 mAh g−1 at 5 C in the voltage range of 2–4 V. The doped cathode undergoes a phase transition of O3-O3/O′3-P3-P′3-O''3 with a small volume change of approximately 2.00% in the voltage range of 2–4 V, and a subsequent slight structural change in the high voltage range of 4–4.2 V, which well demonstrates the enhanced cyclic stability. The assembled full cell confirms the feasibility of applying O3-type NaNi0.47Zn0.03Mn0.5O2 cathode for Na-ion batteries. Thus, the work suggests an efficient strategy to better release the potential of high-energy cathode for Na-ion batteries.
•O3-NaNi0.47Zn0.03Mn0.5O2 material with excellent electrochemical reversibility is obtained by doping with zinc cations.•NaNi0.47Zn0.03Mn0.5O2 cathode shows an excellent capacity retention of 80% within 150 cycles at 0.5 C at 2–4 V.•After the introduction of Zn2+, the phase change above 4 V was suppressed.•When exposed to air, NNZMO sample still showed significantly better electrochemical performance than NNMO.
The incorporation of atomic scale defects, such as cation vacancies, in electrode materials is considered an effective strategy to improve their electrochemical energy storage performance. In fact, ...cation vacancies can effectively modulate the electronic properties of host materials, thus promoting charge transfer and redox reaction kinetics. Such defects can also serve as extra host sites for inserted proton or alkali cations, facilitating the ion diffusion upon electrochemical cycling. Altogether, these features may contribute to improved electrochemical performance. In this review, the latest progress in cation vacancies‐based electrochemical energy storage materials, covering the synthetic approaches to incorporate cation vacancies and the advanced techniques to characterize such vacancies and identify their fundamental role, are provided from the chemical and materials point of view. The key challenges and future opportunities for cation vacancies‐based electrochemical energy storage materials are also discussed, particularly focusing on cation‐deficient transition metal oxides (TMOs), but also including newly emerging materials such as transition metal carbides (MXenes).
This review summarizes the synthetic approaches to incorporate cation vacancies for metal oxides/carbides, the advanced techniques to characterize such vacancies, and the investigations of their fundamental roles in enhancing electrochemical performance. Discussions of the remaining key challenges for the design of high‐performance cationdeficient metal oxides/carbides alongside an analysis of future opportunities.
In the search for high‐energy cathode materials for Na‐ion batteries (NIBs), Fe‐doped layered transition metal oxides have been recently proposed as promising systems that can ensure improved ...reversible capacity at high working voltage. Exploiting the anionic redox chemistry in this class of materials represents a great advance for the energy storage community, but uncontrolled oxidation process can lead to the formation of unbound molecular oxygen, with detrimental effects on overall capacity and stability upon cycling. The higher TM–O covalency provided by Fe doping seems to prevent oxygen loss and ensure full capacity recovery. Understanding anionic processes and the underlying mechanism with atomistic details can reinforce the experimental efforts and help to outline rational design strategies for novel high‐performing NIB cathodes. To this end, we present a state‐of‐the‐art first‐principles study on the P2‐type NaxTMO2 (TM = Fe, Ni, and Mn—NFNMO) oxide. We compare structural and electronic features of stoichiometric (NaxFe0.125Ni0.125Mn0.75O2) and Mn‐deficient (NaxFe0.125Ni0.125Mn0.68O2) NFNMO to identify and discuss the contribution of each element sublattice on charge compensation processes. Although Mn deficiency is predicted to increase the cathode working voltage, we find the charge compensation being mostly exerted by the Ni and Fe sublattices. Oxygen redox is unfold via the formation of superoxide species at low Na loads with a preferential breaking of more labile Ni–O bonds and binding to Fe atoms. Our calculations predict no release of molecular O2 upon desodiation, thus highlighting the key role of Fe dopant that provides a good TM–O bond strength, preventing oxygen loss while still enabling anionic redox reactions at high voltages with extra reversible capacity.
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