One of the key challenges of aqueous supercapacitors is the relatively low voltage (0.8–2.0 V), which significantly limits the energy density and feasibility of practical applications of the device. ...Herein, this study reports a novel Ni–Mn–O solid‐solution cathode to widen the supercapacitor device voltage, which can potentially suppress the oxygen evolution reaction and thus be operated stably within a quite wide potential window of 0–1.4 V (vs saturated calomel electrode) after a simple but unique phase‐transformation electrochemical activation. The solid‐solution structure is designed with an ordered array architecture and in situ nanocarbon modification to promote the charge/mass transfer kinetics. By paring with commercial activated carbon anode, an ultrahigh voltage asymmetric supercapacitor in neutral aqueous LiCl electrolyte is assembled (2.4 V; among the highest for single‐cell supercapacitors). Moreover, by using a polyvinyl alcohol (PVA)–LiCl electrolyte, a 2.4 V hydrogel supercapacitor is further developed with an excellent Coulombic efficiency, good rate capability, and remarkable cycle life (>5000 cycles; 95.5% capacity retention). Only one cell can power the light‐emitting diode indicator brightly. The resulting maximum volumetric energy density is 4.72 mWh cm−3, which is much superior to previous thin‐film manganese‐oxide‐based supercapacitors and even battery–supercapacitor hybrid devices.
A very simple but unique phase‐transformation electrochemical activation strategy is developed to enable a solid‐solution Ni–Mn–O nanoprism array to suppress the oxygen evolution and exhibit ultrawide stable electrochemical window (0–1.4 V vs saturated calomel electrode). With such as an array as the cathode, a 2.4 V ultrahigh voltage aqueous supercapacitor is constructed, demonstrating high volumetric energy/power densities.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Air-stability is one of the most important considerations for the practical application of electrode materials in energy-harvesting/storage devices, ranging from solar cells to rechargeable ...batteries. The promising P2-layered sodium transition metal oxides (P2-Na
x
TmO
2
) often suffer from structural/chemical transformations when contacted with moist air. However, these elaborate transitions and the evaluation rules towards air-stable P2-Na
x
TmO
2
have not yet been clearly elucidated. Herein, taking P2-Na
0.67
MnO
2
and P2-Na
0.67
Ni
0.33
Mn
0.67
O
2
as key examples, we unveil the comprehensive structural/chemical degradation mechanisms of P2-Na
x
TmO
2
in different ambient atmospheres by using various microscopic/spectroscopic characterizations and first-principle calculations. The extent of bulk structural/chemical transformation of P2-Na
x
TmO
2
is determined by the amount of extracted Na
+
, which is mainly compensated by Na
+
/H
+
exchange. By expanding our study to a series of Mn-based oxides, we reveal that the air-stability of P2-Na
x
TmO
2
is highly related to their oxidation features in the first charge process and further propose a practical evaluating rule associated with redox couples for air-stable Na
x
TmO
2
cathodes.
Due to their high specific capacities beyond 250 mA h g
−1
, lithium-rich oxides have been considered as promising cathodes for the next generation power batteries, bridging the capacity gap between ...traditional layered-oxide based lithium-ion batteries and future lithium metal batteries such as lithium sulfur and lithium air batteries. However, the practical application of Li-rich oxides has been hindered by formidable challenges. To address these challenges, the understanding of their electrochemical behaviors becomes critical and is expected to offer effective guidance for both materials and cell development. This review aims to provide fundamental insights into the reaction mechanisms, electrochemical challenges and modification strategies of lithium-rich oxides. We first summarize the research history, the pristine structures, and the classification of lithium-rich oxides. Then we review the critical reaction mechanisms that are closely related to their electrochemical features and performances, such as lattice oxygen oxidation, oxygen vacancy formation, transition-metal migration, layered to spinel transitions, 'two-phase mechanism', and lattice evolution. These discussions are coupled with state-of-the-art characterization techniques. As a comparison, the anionic redox reactions of layered sodium transition metal oxides are also discussed. Finally, after a brief overview of the correlation among the aforementioned mechanisms, we provide perspectives on the rational design of lithium-rich oxides with high energy densities and long-term cycling stability.
This review summarizes the history and critical working mechanisms of Li-rich oxides with a special focus on anionic redox reactions.
Design and fabrication of electrochemical energy storage systems with both high energy and power densities as well as long cycling life is of great importance. As one of these systems, ...Battery‐supercapacitor hybrid device (BSH) is typically constructed with a high‐capacity battery‐type electrode and a high‐rate capacitive electrode, which has attracted enormous attention due to its potential applications in future electric vehicles, smart electric grids, and even miniaturized electronic/optoelectronic devices, etc. With proper design, BSH will provide unique advantages such as high performance, cheapness, safety, and environmental friendliness. This review first addresses the fundamental scientific principle, structure, and possible classification of BSHs, and then reviews the recent advances on various existing and emerging BSHs such as Li‐/Na‐ion BSHs, acidic/alkaline BSHs, BSH with redox electrolytes, and BSH with pseudocapacitive electrode, with the focus on materials and electrochemical performances. Furthermore, recent progresses in BSH devices with specific functionalities of flexibility and transparency, etc. will be highlighted. Finally, the future developing trends and directions as well as the challenges will also be discussed; especially, two conceptual BSHs with aqueous high voltage window and integrated 3D electrode/electrolyte architecture will be proposed.
The fundamental scientific principle, structure, and possible classification of battery‐supercapacitor hybrid devices (BSHs), outlining the recent advances on various existing and emerging BSHs, with the focus on materials and electrochemical performances, and finally providing the future developing trends and directions as well as the challenges are addressed in this review.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Layered transition metal oxides are the most important cathode materials for Li/Na/K ion batteries. Suppressing undesirable phase transformations during charge-discharge processes is a ...critical and fundamental challenge towards the rational design of high-performance layered oxide cathodes. Here we report a shale-like Na
x
MnO
2
(S-NMO) electrode that is derived from a simple but effective water-mediated strategy. This strategy expands the Na
+
layer spacings of P2-type Na
0.67
MnO
2
and transforms the particles into accordion-like morphology. Therefore, the S-NMO electrode exhibits improved Na
+
mobility and near-zero-strain property during charge-discharge processes, which leads to outstanding rate capability (100 mAh g
−1
at the operation time of 6 min) and cycling stability (>3000 cycles). In addition, the water-mediated strategy is feasible to other layered sodium oxides and the obtained S-NMO electrode has an excellent tolerance to humidity. This work demonstrates that engineering the spacings of alkali-metal layer is an effective strategy to stabilize the structure of layered transition metal oxides.
Energy storage with high energy density and low cost has been the subject of a decades-long pursuit. Sodium-ion batteries are well expected because they utilize abundant resources. However, the lack ...of competent cathodes with both large capacities and long cycle lives prevents the commercialization of sodium-ion batteries. Conventional cathodes with hexagonal-P2-type structures suffer from structural degradations when the sodium content falls below 33%, or when the integral anions participate in gas evolution reactions. Here, we show a "pillar-beam" structure for sodium-ion battery cathodes where a few inert potassium ions uphold the layer-structured framework, while the working sodium ions could diffuse freely. The thus-created unorthodox orthogonal-P2 K
Ni
Mn
O
cathode delivers a capacity of 194 mAh/g at 0.1 C, a rate capacity of 84% at 1 C, and an 86% capacity retention after 500 cycles at 1 C. The addition of the potassium ions boosts simultaneously the energy density and the cycle life.
A novel synergistic TiO2‐MoO3 (TO‐MO) core–shell nanowire array anode has been fabricated via a facile hydrothermal method followed by a subsequent controllable electrodeposition process. The ...nano‐MoO3 shell provides large specific capacity as well as good electrical conductivity for fast charge transfer, while the highly electrochemically stable TiO2 nanowire core (negligible volume change during Li insertion/desertion) remedies the cycling instability of MoO3 shell and its array further provides a 3D scaffold for large amount electrodeposition of MoO3. In combination of the unique electrochemical attributes of nanostructure arrays, the optimized TO‐MO hybrid anode (mass ratio: ca. 1:1) simultaneously exhibits high gravimetric capacity (ca. 670 mAh g−1; approaching the hybrid's theoretical value), excellent cyclability (>200 cycles) and good rate capability (up to 2000 mA g−1). The areal capacity is also as high as 3.986 mAh cm−2, comparable to that of typical commercial LIBs. Furthermore, the hybrid anode was assembled for the first time with commercial LiCoO2 cathode into a Li ion full cell, which shows outstanding performance with maximum power density of 1086 W kgtotal
−1 (based on the total mass of the TO‐MO and LiCoO2) and excellent energy density (285 Wh kgtotal
−1) that is higher than many previously reported metal oxide anode‐based Li full cells.
Synergistic TiO2‐MoO3 core–shell nanowire array anode is developed, showing high capacity (ca. 670 mAh g−1; 3.986 mAh cm−2), excellent cycleability (>200 times), and good rate performance. Ultrahigh energy density (285 Wh kgtotal −1) and power density (1086 W kgtotal −1) are further achieved for a full cell LIB device assembled using the TiO2‐MoO3 hybrid array as anode and commercial LiCoO2 film as cathode.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The search for high-energy batteries has promoted intense attention to anionic redox in layered transition metal oxides because of their ability of delivering much higher capacity than traditional ...cathodes. P2–Na0.67Ni0.33Mn0.67O2 electrode exhibits outstanding air-stability and high average potential. Very recently, the anionic redox in this promising sodium cathode has been evidenced by mapping of resonant inelastic X-ray scattering. However, the origin of this oxygen redox has not been recognized yet. Here, based on the combination of X-ray absorption spectroscopy and density functional theory (DFT) calculations, we demonstrate that with the remove of Na+, the Ni2+ oxidized to Ni3+ and followed by the oxidation of lattice oxygen. Our DFT calculation further confirms that the oxygen redox in Na0.67Ni0.33Mn0.67O2 is rooted from Ni–O anti-bonding (eg*) state rather than the non-bonding O2p band and result in the highly reversible oxygen redox reactions without O2 loss. Moreover, at very low sodium contents, it is highly possible that a charge redistribution process between the Ni and O ions occurs, which results in the inconsistent experimental observations in previous references.
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•Confirm the anionic redox reactions in P2–Na0.67Ni0.33Mn0.67O2 at low sodium contents via h-XAS and DFT calculations.•No oxygen loss is observed during the first charge process of P2–Na0.67Ni0.33Mn0.67O2.•Clarify the insights of anionic redox in P2–Na0.67Ni0.33Mn0.67O2.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Despite substantial research efforts in developing high-voltage sodium-ion batteries (SIBs) as high-energy-density alternatives to complement lithium-ion-based energy storage technologies, the ...lifetime of high-voltage SIBs is still associated with many fundamental scientific questions. In particular, the structure phase transition, oxygen loss, and cathode–electrolyte interphase (CEI) decay are intensely discussed in the field. Synchrotron X-ray and neutron scattering characterization techniques offer unique capabilities for investigating the complex structure and dynamics of high-voltage cathode behavior. In this review, to accelerate the development of stable high-voltage SIBs, we provide a comprehensive and thorough overview of the use of synchrotron X-ray and neutron scattering in studying SIB cathode materials with an emphasis on high-voltage layered transition metal oxide cathodes. We then discuss these characterizations in relation to polyanion-type cathodes, Prussian blue analogues, and organic cathode materials. Finally, future directions of these techniques in high-voltage SIB research are proposed, including CEI studies for polyanion-type cathodes and the extension of neutron scattering techniques, as well as the integration of morphology and phase characterizations.
As promising candidates for next-generation energy storage devices, aqueous rechargeable batteries are safer and cheaper than organic Li ion batteries. But due to the narrow voltage window of aqueous ...electrolytes, proper anode materials with low redox potential and high capacity are quite rare. In this work, bismuth electrode film was directly grown by a facile hydrothermal route and tested in LiOH, NaOH and KOH electrolytes. With low redox potential (reduction/oxidation potentials at
-0.85/-0.52 V
SCE, respectively) and high specific capacity (170 mAh·g
at current density of 0.5 A·g
in KOH electrolyte), Bi was demonstrated as a suitable anode material for aqueous batteries. Furthermore, by electrochemical impedance spectroscopy (EIS) analysis, we found that with smaller
and faster ion diffusion coefficient, Bi electrode film in KOH electrolyte exhibited better electrochemical performance than in LiOH and NaOH electrolytes.
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