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Enhancing the low-potential capacity of anode materials is significant in boosting the operating voltage of full-cells and constructing high energy-density energy storage devices. Graphitic carbons exhibit outstanding low-potential potassium storage performance, but show a low K+ diffusion kinetics. Herein, in situ defect engineering in graphitic nanocarbon is achieved by an atomic self-activation strategy to boost the accessible low-voltage insertion. Graphitic carbon layers grow on nanoscale-nickel to form the graphitic nanosphere with short-range ordered microcrystalline due to nickel graphitization catalyst. Meanwhile, the widely distributed K+ in the precursor induces the activation of surrounding carbon atoms to in situ generate carbon vacancies as channels. The graphite microcrystals with defect channels realize reversible K+ intercalation at low-potential and accessible ion diffusion kinetics, contributing to high reversible capacity (209 mAh g-1 at 0.05 A g-1 under 0.8 V) and rate capacity (103.2 mAh g-1 at 1 A g-1). The full-cell with Prussian blue cathode and graphitic nanocarbon anode maintains an obvious working platform at ca. 3.0 V. This work provides a strategy for the in situ design of carbon anode materials and gives insights into the potassium storage mechanism at low-potential for high-performance full-cells.
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Lithium-ion capacitors (LICs) are emerging as one of the most advanced hybrid energy storage devices, however, their development is limited by the imbalance of the dynamics and capacity between the anode and cathode electrodes. Herein, anthracite was proposed as the raw material to prepare coal-based, nitrogen-doped porous carbon materials (CNPCs), together with being employed as a cathode and anode used for dual-carbon lithium-ion capacitors (DC-LICs). The prepared CNPCs exhibited a folded carbon nanosheet structure and the pores could be well regulated by changing the additional amount of g-C3N4, showing a high conductivity, abundant heteroatoms, and a large specific surface area. As expected, the optimized CNPCs (CTK-1.0) delivered a superior lithium storage capacity, which exhibited a high specific capacity of 750 mAh g-1 and maintained an excellent capacity retention rate of 97% after 800 cycles. Furthermore, DC-LICs (CTK-1.0//CTK-1.0) were assembled using the CTK-1.0 as both cathode and anode electrodes to match well in terms of internal kinetics and capacity simultaneously, which displayed a maximum energy density of 137.6 Wh kg-1 and a protracted lifetime of 3000 cycles. This work demonstrates the great potential of coal-based carbon materials for electrochemical energy storage devices and also provides a new way for the high value-added utilization of coal materials.
RESUMEN
Graphite anode has great potential toward potassium ion storage for abundant reserves, yet it suffers from the large volume expansion and slow diffusion rate. Herein, the low-cost biochemical fulvic acid-derived amorphous carbon (BFAC) is employed to modify the natural microcrystalline graphite (BFAC@MG) by a simple mixed carbonization strategy. The BFAC smooths the split layer and folds on the surface of microcrystalline graphite and builds the heteroatom-doped composite structure, which effectively alleviates the volume expansion caused by K+ electrochemical de-intercalation processes, together with improving electrochemical reaction kinetics. As expected, the optimized BFAC@MG-0.5 exhibits superior potassium-ion storage performance, which delivers a high reversible capacity (623.8 mAh g-1), excellent rate performance (147.8 mAh g-1 at 2 A g-1), and remarkable cycling stability (100.8 mAh g-1 after 1200 cycles). As a practical device application, the potassium-ion capacitors are assembled using the BFAC@MG-0.5 anode and commercial activated carbon cathode, which exhibits a maximum energy density of 126.48 Wh kg-1 and superior cycle stability. Significantly, this work demonstrates the potential of microcrystalline graphite as the host anode material for potassium-ion storage.
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The solvation structure of Li+ in chemical prelithiation reagent plays a key role in improving the low initial Coulombic efficiency (ICE) and poor cycle performance of silicon-based materials. Nevertheless, the chemical prelithiation agent is difficult to dope active Li+ in silicon-based anodes because of their low working voltage and sluggish Li+ diffusion rate. By selecting the lithium-arene complex reagent with 4-methylbiphenyl as an anion ligand and 2-methyltetrahydrofuran as a solvent, the as-prepared micro-sized SiO/C anode can achieve an ICE of nearly 100%. Interestingly, the best prelithium efficiency does not correspond to the lowest redox half-potential (E1/2), and the prelithiation efficiency is determined by the specific influencing factors (E1/2, Li+ concentration, desolvation energy, and ion diffusion path). In addition, molecular dynamics simulations demonstrate that the ideal prelithiation efficiency can be achieved by choosing appropriate anion ligand and solvent to regulate the solvation structure of Li+. Furthermore, the positive effect of prelithiation on cycle performance has been verified by using an in-situ electrochemical dilatometry and solid electrolyte interphase film characterizations.
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The high energy/power lithium-ion battery using LiNi0.5Co0.2Mn0.3O2 (NCM523 HEP LIB) has an excellent trade-off between specific capacity, cost, and stable thermal characteristics. However, it still brings a massive challenge for power improvement under low temperatures. Deeply understanding the electrode interface reaction mechanism is crucial to solving this problem. This work studies the impedance spectrum characteristics of commercial symmetric batteries under different states of charge (SOCs) and temperatures. The changing tendencies of the Li+ diffusion resistance Rion and charge transfer resistance Rct with temperature and SOC are explored. Moreover, one quantitative parameter, § ≡ Rct/Rion, is introduced to identify the boundary conditions of the rate control step inside the porous electrode. This work points out the direction to design and improve performance for commercial HEP LIB with common temperature and charging range of users.
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With the associated advantages of low costs and abundant resources, sodium-ion capacitors (SICs) present a suitable means for large-scale energy storage. However, their practical application is still significantly limited by the sluggish electrochemical reaction kinetics of battery-type anodes. Herein, the nitrogen-doped carbon-encapsulated Fe7Se8 nanorods (Fe7Se8@NC) with a core-shell structure were prepared via an in-situ self-polymerization and carbonization-selenization approach, which improves ion transport and maintains the structural stability of the nanorods. The designed Fe7Se8@NC nanorods exhibit desirable rate capability with a capacity of 290.7 mAh/g at 10 A/g and long-term cyclability with 84.6 % retention over 6000 cycles at 5 A/g. Moreover, research has shown that the diffusion dynamics of Na+ is improved in ether-based electrolytes and that the irreversible reactions at low voltages can be inhibited by a high discharge cut-off voltage. Furthermore, we demonstrated the specific sodium storage mechanism and excellent electrochemical reversibility of the Fe7Se8@NC electrode through in-situ and ex-situ characterization techniques. As expected, the assembled SICs with the Fe7Se8@NC anode and active carbon cathode deliver prominent energy/power densities and an ultra-long cycle life over 5000 cycles, shedding new light on the design of transition metal dichalcogenides as anode materials for advanced energy storage systems.
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Potassium Prussian Blue (KPB) have been investigated as promising cathode materials for potassium-ion batteries. However, numerous structure defects and side reactions at electrode/electrolyte interface will deteriorate the electrochemical properties. Herein, dual stabilization strategy of structure of KPB particles and cathode/electrolyte interface is reported to enhance the capacity and electrochemical stability. The structure of KPB is stabilized through inhibiting nucleation and growth by addition of ethylenediaminetetraacetic acid dipotassium salt during co-precipitation, which can enlarge the particle size. Meanwhile, stabilizing the cathode/electrolyte interface via changing potassium hexafluorophosphate to potassium bis (fluorosulfonyl) imide (KFSI) electrolyte can further reduce side reactions to boost the coulombic efficiency of KPB cathode. Benefiting from dual engineering in structure of KPB and cathode/electrolyte interface, the half-cell in KFSI electrolyte possesses two discharge potential plateaus at 3.4 and 4.0 V with reversible capacity of 92.7 mAh g-1 at 0.03 A g-1. To demonstrate its practical use, KPB//graphite full-cell device is successfully constructed, exhibiting the capacity up to 102.4 mAh g-1 at 0.1 A g-1, high-rate (40.4 mAh g-1 at 1.5 A g-1) and superior cyclic stability (88% capacity retention from cycle 25 to 400 at 1 A g-1). This work provides a synergetic engineering strategy to realize the powerful application of high-performance potassium-ion full-cell devices in energy storage.
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Silicon combines the advantages of high theoretical specific capacity, low potential and natural abundance, which exhibits great promise as an anode for lithium-ion batteries. However, the main challenges associated with Si anode are continuous volume expansion upon cycling and intrinsic low electronic conductivity, leading to sluggish reaction kinetics and rapid capacity fading. Herein we propose a novel in-situ self-catalytic strategy for the growth of highly graphitic carbon to encapsulate Si nanoparticles by chemical vapor deposition, where the magnesiothermic reduction byproducts are used as templates and catalysts for the formation of three-dimensional (3D) conductive network architecture. Benefiting from the improved electronic conductivity and significant suppression of volume expansion, the as-synthesized Si carbon composites exhibit excellent lithium storage capabilities in terms of high specific capacity (2126 mAh g-1 at 0.1 A g-1), remarkable rate capability (750 mAh g-1 at 5 A g-1), and good cycling stability over 450 cycles. Furthermore, the as-fabricated full cell (Si//Ni-rich LiNi0.815Co0.185-xAlxO2) shows high energy density of 395.1 Wh kg-1 and long-term stable cyclability. Significantly, this work demonstrates the effectiveness of in-situ self-catalysis reaction by using magnesiothermic reduction byproducts catalytically derived carbon matrix to encapsulate alloy-type anode material in giving rise to the overall energy storage performance.
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Manganese dioxide (MnO2) promises for high-performance asymmetric suprecapacitors, owing to its high theoretical capacity, abundant source, and low cost. However, insufficient practically-achievable capacity and relatively narrow voltage window in alkaline electrolyte are blocking high energy density of MnO2-based supercapacitors, where strategies for activating its capacitive performance and widening voltage window are the top priorities to solve the bottleneck problems. Herein, both the fiber-in-tube (NCCM-FiT) and particle-in-tube (NCCM-PiT) nanostructures coulping active NiCoOx nanoparticles and conductive carbon with MnO2 tubes have been purposely fabricated, using the electrospun nickel cobalt oxides/carbon nanofibers (NCO/CNFs) as the self-template agents for enhanced energy density of MnO2-based supercapacitors. These hierarchical hollow nanotubes with gradient pores and unique compositions yield excellent capacitive properties, in terms of a competitive capacity (431.7 F g-1 or 431.7 C g-1, 0.5 A g-1), which is 2.7 times that of the MnO2 nanotubes-based electrodes. A maximum energy density of 46.4 Wh kg-1 is obtained at the power density of 400 W kg-1 for the asymmetric device assembled with the NCCM-PiT-based positive electrode and the electrospun CNFs-based negative electrode. The remarkable energy density demonstrated by these hierarchical hollow nanotubes exemplifies a novel and effective design in electrode materials for the asymmetric supercapacitors (ASCs) with superior performance.
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As a new type of capacitor-battery hybrid energy storage device, metal-ion capacitors have attracted widespread attention because of their high-power density while ensuring energy density and long lifespan. Potassium-ion capacitors (KICs) featuring the merits of abundant potassium resources, lower standard electrode potential, and low cost have been considered as potential alternatives to lithium-/sodium-ion capacitors. However, KICs still face issues including unsatisfactory reaction kinetics, low energy density, and poor lifetime owing to the large radius of the potassium ion. In this Review, the importance of emerging potassium-ion capacitor is addressed. The Review offers a brief discussion of the fundamental working principle of KICs, along with an overview of recent advances and achievements of a variety of electrode materials for dual carbon and non-dual carbon KICs. Furthermore, electrolyte chemistry, binders as well as electrode/electrolyte interface, are summarized. Finally, existing challenges and perspectives on further development of KICs are also presented.
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Electrospun carbon nanofibers (CNFs), with one-dimensional (1D) morphology, tunable size, mechanical flexibility, and functionalities by themselves and those that can be added onto them, have witnessed the intensive development and extensive applications in energy storage and conversion, such as supercapacitors, batteries, and fuel cells. However, conventional solid CNFs often suffer from a rather poor electrical conductivity and low specific surface area, compared with the graphene and carbon nanotube counterparts. A well-engineered porous structure in CNFs increases their surface areas and reactivity, but there is a delicate balance between the level and type of pores and mechanical robustness. In addition, CNFs by themselves often show unsatisfactory electrochemical performance in energy storage and conversion, where, to endow them with high and durable activity, one effective approach is to dope CNFs with certain heteroatoms. Up to now, various activation strategies have been proposed and some of them have demonstrated great success in addressing these key issues. In this review, we focus on the recent advances in the issue-oriented schemes for activating the electrospun CNFs in terms of enhancing the conductivity, modulating pore configuration, doping with heteroatoms, and reinforcing mechanical strength, in close reference to their applications in supercapacitors. The basic scientific principles involved in these activation processes and their effectiveness in boosting the electrochemical performance of CNFs are examined. Finally, some of the on-going challenges and future perspectives in engineering CNFs for better performance are highlighted.
RESUMEN
Lithium-ion capacitors (LICs) are regarded as the most potential devices in the energy storage systems. Unfortunately, the mismatched in the intrinsic kinetics and specific capacities between anode and cathode lead to a depressed electrochemical performance. Thus, designing an advanced electrode material that combines high performance with low-cost is one of the main challenges for LICs, especially in a sustainable anode material until now. Here, a high-energy LIC has been successfully developed using the defect-rich and N-doped hard carbon (DNC) as anode, which is prepared through the carbonization process of the low-cost biowaste sepia without additional template or catalyst. The DNC shows nanospherical structure with a diameter of about 100 nm. Owing to the two-pronged strategy of N-doping and defect engineering, it delivers a high specific capacity (580.3 mAh g-1 at 0.05 A g-1), excellent rate capability, and long cycle stability (1000 cycles). The electrochemical kinetic analysis and density functional theory (DFT) calculations have confirmed its prominent pseudocapacitive behaviors and excellent Li+ storage capability. As expected, the as-fabricated LIC delivers a remarkable energy density (101.7 Wh kg-1), an outstanding rate capability (56.3 Wh kg-1 at 12.5 kW kg-1), and a superior cycle lifespan (3000 cycles), demonstrating the tremendous potential for the next-generation energy storage systems.
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Sodium-ion capacitors (SICs), designed to attain high energy density, rapid energy delivery, and long lifespan, have attracted much attention because of their comparable performance to lithium-ion capacitors (LICs), alongside abundant sodium resources. Conventional SIC design is based on battery-like anodes and capacitive cathodes, in which the battery-like anode materials involve various reactions, such as insertion, alloying, and conversion reactions, and the capacitive cathode materials usually depend on activated carbon (AC). However, researchers have attempted to construct SICs based on battery-like cathodes and capacitive anodes or a combination of both in recent years. In this Minireview, charge storage mechanisms and material design strategies for SICs are summarized, with a focus on the battery-like anode materials from both inorganic and organic sources. Additionally, the challenges in the fabrication of SICs and future research directions are discussed.
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Among the various morphologies of carbon-based materials, hollow carbon nanostructures are of particular interest for energy storage. They have been widely investigated as electrode materials in different types of rechargeable batteries, owing to their high surface areas in association with the high surface-to-volume ratios, controllable pores and pore size distribution, high electrical conductivity, and excellent chemical and mechanical stability, which are beneficial for providing active sites, accelerating electrons/ions transfer, interacting with electrolytes, and giving rise to high specific capacity, rate capability, cycling ability, and overall electrochemical performance. In this overview, we look into the ongoing progresses that are being made with the nanohollow carbon materials, including nanospheres, nanopolyhedrons, and nanofibers, in relation to their applications in the main types of rechargeable batteries. The design and synthesis strategies for them and their electrochemical performance in rechargeable batteries, including lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, and lithium-sulfur batteries are comprehensively reviewed and discussed, together with the challenges being faced and perspectives for them.
RESUMEN
Interface design between current collector and electroactive materials plays a key role in the electrochemical process for lithium-ion batteries. Here, a thin graphene film has been successfully synthesized on the surface of Cu current collector by a large-scale low-pressure chemical vapor deposition (LPCVD) process. The modified Cu foil was used as a current collector to support spinel Li4Ti5O12 anode directly. Electrochemical test results demonstrated that graphene coating Cu foil could effectively improve overall Li storage performance of Li4Ti5O12 anode. Especially under high current rate (e.g., 10 C), the Li4Ti5O12 electrode using modified current collector maintained a favorable capacity, which is 32% higher than that electrode using bare current collector. In addition, cycling performance has been improved using the new type current collector. The enhanced performance can be attributed to the reduced internal resistance and improved charge transfer kinetics of graphene film by increasing electron collection and decreasing lithium ion interfacial diffusion. Furthermore, the graphene film adhered on the Cu foil surface could act as an effective protective film to avoid oxidization, which can effectively improve chemical stability of Cu current collector.