The development of high-performance Li-air batteries (LABs) is an important quest for effectively utilizing high-energy density electric systems. One possible way to achieve this goal is by ...introducing novel bifunctional electrocatalysts at the battery cathode, enhancing the cycle life and the discharge capacity of the LABs by facilitating fast oxygen reaction kinetics. Understanding bifunctional catalysts' function and evolution is essential to developing a better-functioning LAB. In this review, we discuss the fundamentals, mechanisms, and key concepts related to LAB technology. We then provide critical discussions on recent advances in bifunctional catalysts used in LAB cathodes through material characterization, electrochemical analysis, battery performance, in-situ and ex-situ discharge product analysis, DFT calculations, and theoretical concepts to provide the most up-to-date, thorough, and broader discussion on the subject. These include the general and modified catalysts of carbon nanostructures, noble metals, transition metal oxides, nitrides, sulfides, and phosphides. Furthermore, special attention is given to techniques designed to enhance the catalytic activity of LABs through the modulation of electronic structures. Various facet engineering and eg electron engineering approaches are explored, including heteroatom doping, alloying, hybridization, stoichiometric optimization, and selective facet growth. Finally, we suggest potential prospective pathways for future research.
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•State-of-the-art electrocatalysts for Li-air batteries are comprehensively reviewed.•Preparation and characteristics of bifunctional electrocatalysts are discussed.•Electrocatalysts discussed include carbon nanostructures, noble metals and metal oxides.•Transition metal oxides, nitrides, sulfides and phosphides are thoroughly covered.•Current status of such catalysts and future possible developments are suggested.
This article presents 2D mica nanoplatelets as a novel additive to produce a stable engine lubricant. The planar structure and excellent mechanical properties of 2D mica contribute significantly to ...the improvements in tribological performance when evaluated under pure sliding and rolling/sliding contact configurations. The wear rate is reduced by 72 %, and the coefficient of friction (COF) decreases by 28 % when 2D mica is added to engine oil under pure sliding conditions. No tribological improvement was observed under rolling/sliding conditions. Our results also showed that nanosheet loading plays a significant role in nanolubricant performance, where 0.2 wt% is the optimum. These findings demonstrate superior performance to other 2D material nanoadditives and indicate the potential for commercial applications of 2D mica-based nanolubricants.
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•Mica-based nanolubricants demonstrated higher stability than other 2D materials.•Friction was reduced by 28 % by adding 0.2 wt% mica to the engine oil.•Wear was reduced by 72 % for 0.2 wt% mica/engine oil nanolubricant.•The tribofilm formed by the nanolubricants explains the large reduction in wear.•Mica-based nanolubricants did not reduce friction under rolling/sliding conditions.
•Reductive electrochemical exfoliation produced ∼90% graphene flakes <10 layers.•Restacking of graphene flakes occurs when the material is allowed to dry out.•Restacking of graphenic material to ...graphite had no impact on Li insertion.
Two potential pathways for Li+ diffusion occur within graphitic carbon with typically in-plane diffusion dominating (∼10−7cm2s−1) over diffusion along the crystallite grain boundaries (∼10−11cm2s−1). Reducing the flake thickness of microcrystalline graphite powders via electrochemical exfoliation offers a method to overcome the latter, sluggish grain boundary Li+ diffusion, thereby increasing the overall rate capability of the graphite negative electrode in a the Li-ion battery. Six micron particulate graphite was electrochemically exfoliated to give flakes of which ∼90% had a thickness of <10 graphene layers. This exfoliated material was then prepared as an ink and allowed to dry prior to forming a battery electrode. Analysis of the electrode and dried exfoliated powder using powder X-ray diffraction, scanning electron microscopy and Brunauer–Emmett–Teller isotherm analysis show that the material has, apart from a significant reduction of the rhombohedral fraction from 41% to 14%, near-identical properties to that of original starting graphite powder. Thus, once the exfoliated powder has been dried from the exfoliation process, as anticipated, major restacking of the multi-layer graphene flakes had occurred. Likewise there was no significant improvement in using the exfoliated material at high rates of delithiation and lower specific capacity, when tested within a half cell vs. lithium metal. In situ Raman analysis showed that the exfoliated material displayed similar spectral features to the pristine sample during lithiation, as did multi point measurements on differently disordered areas shown from the varying ID/IG-band intensity ratios, indicating that local surface disorder does not influence the course of lithium insertion. The re-aggregation of graphenic material is widely recognised, but seldom evaluated. This work shows the importance of keeping graphenic material dispersed at all stages of production.
So far, various graphite-Nickel Oxide (NiO) composites have been investigated as anodes for Li-ion batteries. However, developing an ideal composite that overcomes NiO's electrical conductivity ...limitations remains a significant challenge. The current study presents an in-situ one-step hydrothermal technique for integrating NiO into a 3D peony-like graphitic nanostructure (NiO-GNF), resulting in unique thin nanosheet arrays with porous, conductive channels. Notably, the composites endowed controlled aggregation and restacking of NiO, buffered electrode stress and improved electrical conductivity due to the expanded nature of graphite. In addition, the enlarged interlayer spacing of expanded graphite facilitated an improved Li-ion insertion. Overall, in comparison to pure NiO anodes, the NiO-GNF composite achieved an impressive electrochemical improvement exhibiting a highly reversible discharge capacity of 678.2 mAh/g after 370 cycles at a current density of 0.5 A g−1, corresponding to a capacity retention of 60.7 %. The composite also demonstrated a capacity of 752 mAh/g at a high current density of 1.2 A g−1.
•Graphitic nanostructures decorated with NiO nanoparticles have been obtained through co-exfoliation and functionalisation.•The synergy between NiO and the conductive carbon platform significantly improved the anode performance in Li-ion batteries.•Graphitic nanostructures minimize volume change during charge and discharge processes, thus enhancing the cyclic life.
Binary metal oxides exhibit a compelling combination of features that make them highly attractive electrode materials for supercapacitors. Herein, a facile hydrothermal method is employed for the ...preparation of defect-rich hierarchical nanostructured NiCo2O4 with various morphologies, including urchin-like nanostructure, nanoflowers, and 2D nanosheets; and their electrochemical performances as electrodes for hybrid supercapacitor are studies. Notably, the supercapacitor based on the urchin-like nanostructure with high oxygen vacancies delivers a high gravimetric energy density of 45.2 Wh/kg at the power density of 750 W/kg, maintaining remarkable cycling stability. The electrode exhibits specific capacitance of 423.9 and 292.0 F/g at the current density of 1.5 and 7.5 A/g, respectively, with high capacitive retention of ≈ 94 % after 1500 cycles. Crystalline defects identified in nanostructured NiCo2O4 are suggested to significantly contribute to the high ionic/electrical conductivity and the electrochemical stability of the electrodes.
•Various NiCo2O4 Nanostructures have been prepared and tested for hydride supercapacitor application.•The role of the crystal defects in enhancing the electrochemical performance was investigated•Urchin-like nanostructure showed excellent performance as electrodes for hybrid supercapacitors.
One-dimensional nanotubes constructed from interconnected Li sub(1.2)Mn sub(0.54)Ni sub(0.13)Co sub(0.13) O sub(2) secondary particles of diameters measuring ca. 40 nm, were synthesized by a one-pot ...electrospinning method. Novel electrodes were constructed from (a) nanoparticles only, and (b) hollow nanofibres, and employed as cathodes in Li-ion batteries. The nanotube cathode exhibited impressive specific charge capacity, good cycling stability, and excellent rate capability. A discharge capacity of 140 mAh g super(-1) with capacity retention of 89% at 3 C was achieved after 300 cycles. The significant improvement of electrochemical performance is attributed to the high surface area of the nanotubes, well-guided charge transfer kinetics with short ionic diffusion pathways, and large effective contact area with the electrolyte during the cycling process.
Utilising the solid-state synthesis method is an easy and effective way to recycle spent lithium-ion batteries. However, verifying its direct repair effects on completely exhausting cathode materials ...is necessary. In this work, the optimal conditions for direct repair of completely failed cathode materials by solid-state synthesis are explored. The discharge capacity of spent LiCoO
cathode material is recovered from 21.7 mAh g
to 138.9 mAh g
under the optimal regeneration conditions of 850 °C and n(Li)/n(Co) ratio of 1:1. The regenerated materials show excellent electrochemical performance, even greater than the commercial LiCoO
. In addition, based on the whole closed-loop recycling process, the economic and environmental effects of various recycling techniques and raw materials used in the battery production process are assessed, confirming the superior economic and environmental feasibility of direct regeneration method.
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