Hybrid metal‐ion capacitors (MICs) (M stands for Li or Na) are designed to deliver high energy density, rapid energy delivery, and long lifespan. The devices are composed of a battery anode and a ...supercapacitor cathode, and thus become a tradeoff between batteries and supercapacitors. In the past two decades, tremendous efforts have been put into the search for suitable electrode materials to overcome the kinetic imbalance between the battery‐type anode and the capacitor‐type cathode. Recently, some transition‐metal compounds have been found to show pseudocapacitive characteristics in a nonaqueous electrolyte, which makes them interesting high‐rate candidates for hybrid MIC anodes. Here, the material design strategies in Li‐ion and Na‐ion capacitors are summarized, with a focus on pseudocapacitive oxide anodes (Nb2O5, MoO3, etc.), which provide a new opportunity to obtain a higher power density of the hybrid devices. The application of Mxene as an anode material of MICs is also discussed. A perspective to the future research of MICs toward practical applications is proposed to close.
Hybrid metal‐ion capacitors are found to deliver high energy density and rapid energy delivery. The material design strategies particularly in pseudocapacitive oxide anodes in Li‐ion and Na‐ion capacitors (LICs and NICs) are systematically discussed. A perspective on the challenges and opportunities of LIC and NIC devices is also presented.
Metal‐ion capacitors are being widely studied to reach a balance between power and energy output by combining the merits of conventional batteries and capacitors. The main challenge for Na‐ion ...capacitors is that the battery‐type anode usually has unsatisfactory power density and long‐term stability since most Na host materials have a poor kinetic and structural stability. Herein, asymmetric hollow bowl‐like carbon (HBC) materials are rationally designed and fabricated through an in situ hard‐template approach. The formation originates from a subtle control of capillary force and the mechanical strength of the carbon shell. The HBCs possess abundant mesopores, high volumes of accessible surface area as well as an open macropore network. As a 3D host, MoSe2 nanocrystals are anchored onto the HBC matrix by a solid‐phase reaction. The obtained MoSe2@HBC nanobowl electrode exhibits pseudocapacitive sodium storage with fast kinetics, improved capacity at high currents, and cycle stability, which is also supported by DFT calculations. Sodium ion capacitor full cells are fabricated using the two bowl‐like architectures (MoSe2@HBC as the anode and HBC as the cathode), which deliver high energy and power densities, long cycle life, and a comparably low self‐discharge rate. Moreover, application of the HBC in a zinc‐ion capacitor (ZIC) is also demonstrated.
Hollow bowl‐like carbons are synthesized by an in situ hard‐template strategy and its composite with MoSe2 achieves excellent cycle stability during ultrafast sodium storage. The assembled sodium‐ion capacitor based on these hollow carbon bowls exhibits high energy and power densities, a long lifespan, and a low self‐discharge rate.
A novel hybrid Li‐ion capacitor (LIC) with high energy and power densities is constructed by combining an electrochemical double layer capacitor type cathode (graphene hydrogels) with a Li‐ion ...battery type anode (TiO2 nanobelt arrays). The high power source is provided by the graphene hydrogel cathode, which has a 3D porous network structure and high electrical conductivity, and the counter anode is made of free‐standing TiO2 nanobelt arrays (NBA) grown directly on Ti foil without any ancillary materials. Such a subtle designed hybrid Li‐ion capacitor allows rapid electron and ion transport in the non‐aqueous electrolyte. Within a voltage range of 0.0−3.8 V, a high energy of 82 Wh kg−1 is achieved at a power density of 570 W kg−1. Even at an 8.4 s charge/discharge rate, an energy density as high as 21 Wh kg−1 can be retained. These results demonstrate that the TiO2 NBA//graphene hydrogel LIC exhibits higher energy density than supercapacitors and better power density than Li‐ion batteries, which makes it a promising electrochemical power source.
A hybrid Li‐ion capacitor is developed using a porous graphene hydrogel cathode, TiO2 nanobelt arrays as the anode, and LiPF6 electrolyte. The demonstrated high energy and power densities of such a hybrid device could bridge the gap between Li‐ion batteries and EDLC supercapacitors.
A facile and bottom-up approach has been presented to prepare 2D Ni-MOFs based on cyanide-bridged hybrid coordination polymers. After thermally induced sulfurization and selenization processes, ...Ni-MOFs were successfully converted into NiS and NiSe2 nanoplates with carbon coating due to the decomposition of its organic parts. When evaluated as anodes of Li-ion batteries (LIBs) and Na-ion batteries (NIBs), NiS and NiSe2 nanoplates show high specific capacities, excellent rate capabilities, and stable cycling stability. The NiS plates show good Li storage properties, while NiSe2 plates show good Na storage properties as anode materials. The study of the diffusivity of Li+ in NiS and Na+ in NiSe2 shows consistent results with their Li/Na storage properties. The 2D MOFs-derived NiS and NiSe2 nanoplates reported in this work explore a new approach for the large-scale synthesis of 2D metal sulfides or selenides with potential applications for advanced energy storage.
Phosphorene, monolayer or few‐layer black phosphorus (BP), has recently triggered strong scientific interest for lithium/sodium ion batteries (LIBs/SIBs) applications. However, there are still ...challenges regarding large‐scale fabrication, poor air stability. Herein, we report the high‐yield synthesis of phosphorene with good crystallinity and tunable size distributions via liquid‐phase exfoliation of bulk BP in formamide. Afterwards, a densely packed phosphorene–graphene composite (PG‐SPS, a packing density of 0.6 g cm−3) is prepared by a simple and easily up‐scalable spark plasma sintering (SPS) process. When working as anode materials of LIBs, PG‐SPS exhibit much improved first‐cycle Coloumbic efficiency (60.2%) compared to phosphorene (11.5%) and loosely stacked phosphorene–graphene composite (34.3%), high specific capacity (1306.7 mAh g−1) and volumetric capacity (256.4 mAh cm−3), good rate capabilities (e.g., 415.0 mAh g−1 at 10 A g−1) as well as outstanding long‐term cycling life (91.9% retention after 800 cycles at 10 A g−1). Importantly, excellent air stability of PG‐SPS over the 60 days observation in maintaining its high Li storage properties can be achieved. On the contrary, 95.2% of BP in PG sample was oxidized after only 10 days exposure to ambience, leading to severe degradation of electrochemical properties.
A densely packed phosphorene–graphene composite is prepared by a simple and easily upscalable spark plasma sintering process, which exhibits much improved 1st‐cycle Coulombic efficiency, high volumetric capacity, good rate capabilities as well as an outstanding cycling life, especially robust air stability in maintaining its high Li storage properties.
•The pre-sodiation methods of sodium-ion capacitors are systematically summarized.•Advantages and disadvantages of each pre-sodiation method are discussed.•A perspective to the future pre-sodiation ...of SICs is proposed.
Rechargeable sodium-based energy storage devices have attracted much attention in recent years due to high abundance and even global distribution of sodium resources. As a new member of the sodium-storage family, sodium-ion capacitors (SICs) are expected to supplement lithium-based energy storage devices because they combine advantages of both sodium-ion batteries and supercapacitors. However, the absence of a sodium source in electrode materials, the formation of a solid electrolyte interface (SEI) during the first cycle and the loss of sodium ions during long-term cycles will have a fatal impact on the performance of a typical SIC. It is currently recognized that the effective approach is to perform the pre-sodiation process. Although the research on pre-lithiation of lithium-ion capacitors (LICs) has been widely reported, the related research in SICs has not received sufficient attention. This work will systematically summarize the pre-sodiation methods of SICs, and further to give some in-depth insights to the future research of SICs towards practical applications.
Lithium-ion capacitors (LICs) are considered to be promising power sources due to their combination of high-rate capacitors and high-capacity batteries. However, development of a high-performance LIC ...is still restricted by the sluggish intercalation reaction and unsatisfied specific capacities in battery-type bulk anodes. To overcome these issues, herein, we utilize two-step atomic layer deposition (ALD) to realize a uniform coating of FeO x and TiO2 on CuO nanorods, which results in the formation of ternary CuO@FeO x @TiO2 composite. After further treatment in H2/Ar atmosphere, the as-derived Fe3O4 is encapsulated between conductive Cu nanorod and hollow TiO2 shell (denoted as Cu@Fe3O4@TiO2). Owing to the rational design, the binder-free Cu@Fe3O4@TiO2 electrode exhibits an ultrahigh Li-ion storage capacity (1585 mA h g–1 at 0.2 A g–1), superior rate capability, and excellent cycle performance (no decay after 1000 cycles), which could efficiently boost the energy-storage capability of LICs. By employing an anode of Cu@Fe3O4@TiO2 and a cathode of activated carbon, the as-constructed full LIC device provides high energy//powder densities (154.8 Wh kg–1 at 200 W kg–1; 66.2 Wh kg–1 at 30 kW kg–1). These superior results demonstrate that ALD-enabled architectures hold great promise for synthesizing high-capacity anodes for LICs.
In this paper, the influences of conductive carbons on the red phosphorus (P) composites in sodium-ion batteries are studied. Electrochemical testing results show that Ketjen Black makes the P ...composites present much better cycling performances. Electrochemical impedance spectra (EIS) results indicate that when Ketjen Black is used, the total resistance of the electrode can be decreased. Since Ketjen Black is a low-cost and commercially available material, our results suggest that Ketjen Black might be a promising conductor for the alloying anodes such as P in sodium-ion batteries.
This work reports the pulsed laser reactive deposition of the NiO thin film by ablating nickel targets in low-pressure O2 atmosphere at room temperature. The electrode exhibits a porous structure, ...which facilitates ion transport in the electrode/electrolyte. When applied as an electrode, the porous NiO film exhibits the high specific capacitance (835F g−1 at 1A g−1). Meanwhile, the film exhibits a superb rate capability. At a very high current density of 40A g−1 there is more than 59% retention in the capacitance relative to 1A g−1. Furthermore, the excellent cycling performance (94% capacitance retention after 1000 cycles) is achieved for the film electrode. These results demonstrate that pulsed laser deposition (PLD) is a very promising technique for making the film electrodes for applications in electrochemical energy storage.
► Laser ablated nickel atoms and ions react with O2 to form NiO thin film. ► The electrode exhibits a porous structure and demonstrates a respectable specific capacitance of 835F g−1. ► The NiO film structure exhibits a superb rate capability. ► The excellent cycling performance (without degradation after 1000 cycles) is achieved.
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