physisorption/shallow Faradaic reaction on the electrode surfaces/interfaces, display higher power density and longer lifespan but relatively lower energy density. [4-8] As a consequence, one point worth noting is that neither single LIBs nor ECs could fully meet the increasingly harsh demands currently, if they were just applied alone. [6-8] Recently, lithium-ion capacitors (LICs), as a competitive device incorporating both merits of LIBs and ECs in one, emerge and become a research hotspot in the field of energy storage. [9-13] Nevertheless, the kinetics of the battery-type anode materials fundamentally originating from electrochemical intercalation of lithium ions are much slower than the capacitive cathodes relying mainly on fast surface ion adsorption and desorption. [14,15] It becomes a critical yet challenging issue for advanced LICs how to effectively conquer the innate imbalance in electrochemical dynamics of the involved electrodes. Commonly, the cathodes for LICs are mainly porous carbonaceous materials with electric double layer capacitances, such as activated carbon (AC) [16] and graphene, [17] and so on. With the aim to well match the advanced cathodes, the anode materials themselves are required to possess high rate characteristics. Since the fast pseudocapacitance properties of RuO 2 were investigated by Trasatti and Buzzanca, various pseudocapacitive materials such as TiO 2 , [18] Li 4 Ti 5 O 12 , [19] MnO 2 , [20] and Nb 2 O 5 [12] have been widely investigated in LICs. They are ideal candidates to bridge the huge gap between the diffusion-limited Li-insertion process and the surface-controlled physical adsorption/desorption. [11,21,22] Particularly, niobium pentoxides (Nb 2 O 5) stands out from others, benefiting from its high safety, large theoretical capacity (≈200 mAh g −1), and extremely small volume expansion rate (≈5%) over electrochemical lithiation/delithiation. [23,24] So far, the hybridization with hetero-phase carbon materials and/or nanodimensional strategies have been intensively developed to purposefully enhance electronic/ionic transport of the Nb 2 O 5 itself toward efficient charge storage. [10,16,17,25,26] Moreover, specific crystal structures of Nb 2 O 5 , i.e., pseudohexagonal (TT-phase) and orthorhombic (T-phase) phases, hold a great influence upon their electrochemical properties. [27-29] Compared to the TT-Nb 2 O 5 , T-Nb 2 O 5 Lithium-ion capacitors (LICs) have attracted enormous interest thanks to their competitive power/energy densities and long-duration lifespan. However, the sluggish insertion kinetics of battery-type anodes seriously limits comprehensive performance of LICs. It is therefore imperative yet significant to develop advanced anodes with high-rate Li + intercalation. Herein, first the in-plane assembled single-crystalline orthorhombic Nb 2 O 5 nanorods (T-Nb 2 O 5 NRs) are designed and constructed via efficient hydrothermal and subsequent annealing treatment by employing few-layered Nb 2 CT x nanosheets as a niobium-based precursor. The inherent formation...

power properties, respectively. [3][4][5] However, each of them when singly operating cannot simultaneously achieve both larger energy and power densities in one electrochemical device. The exploitation in new EESDs with super electrochemical performance in both energy and power aspects is therefore more meaningful to meet the hash requirements nowadays. [6][7][8][9][10] Li-ion capacitors (LICs), as an emerging asymmetric device, can fully combine the superiorities of LIBs and SCs, and theoretically possess large energy/power density and long cycle life in one cell. [11][12][13] Nevertheless, the most serious challenge now is the kinetic imbalance between the involved anode and cathode, owing to their distinct charge storage mechanisms. [14][15][16] Specifically, the anodes of the LICs always adopt the battery-type materials, while the cathode is based on electric double-layer type materials dominated by the physical ad-/de-sorption. [17][18][19][20] When assembled for the LICs, the tremendous gap in ion diffusion rate between the two electrodes will lead to the instability of devices. Thus, it becomes a critical yet challenging issue by improving the rate properties of the anode material for further development of advanced hybrid EESDs.Typically, the pseudo-capacitive materials like TiO 2 and Li 4 Ti 5 O 12 with fast ion (de)intercalation are considered as a bridge to equalize the dynamics difference between the anode and cathode. [21,22] While, to a large extent, the relatively low theoretical specific capacities (TiO 2 , ≈168 mAh g -1 ; Li 4 Ti 5 O 12 , ≈175 mAh g -1 ) restrict their practical applications towards LICs. [23] Subsequently, the pseudo-capacitive T-Nb 2 O 5 with two redox pairs (Nb 5+ /Nb 4+ and Nb 4+ /Nb 3+ ) possessing a theoretical capacity of ≈200 mAh g -1 was investigated intensively for LICs. [11][12][13][14]18,19,21,24] Even so, its inherently low electronic conductivity, like TiO 2 and Li 4 Ti 5 O 12 , is detrimental to the rate performance of cells. For this, the common method is to combine the T-Nb 2 O 5 with conductive carbon materials. [16,17,25,26] Besides this, the purposeful construction of bimetallic M-Nb-O (denoted as MNO, M═Ti, Cu, W, Ga, Pb, etc.) by introducing another new transition metal elements into the Nb 2 O 5 turns out to be a promising avenue to radically improve the conductivity of Recently, Li-ion capacitors (LICs) have drawn tremendous attention due to their high energy/power density along with long cycle life. Nevertheless, the slow kinetics and stability of the involved anodes as bottleneck barriers always result in the modest properties of devices. The exploration of advanced anodes with both high ionic and electronic conductivities as well as structural stability thus becomes more significant for practical applications of LICs. Herein, a single-crystal nano-subunits assembled hierarchical accordion-shape WNb 2 O 8 micro-/nano framework is first designed via a one-step scalable strategy with the multi-layered Nb 2 CT x as a precursor. The underlying solid solutio...

Lithium-ion capacitors (LICs), combining both merits of lithium-ion batteries and supercapacitors, possess high energy/power density and long-duration lifespan in one device. However, the dynamic imbalance between the positive and negative...

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To reduce the kinetic imbalance between the anode and cathode electrodes of metal-ion capacitors (MICs), researchers have conducted intensive explorations to develop new anode materials. Niobium-based oxides (NBOs) have been established as typical anodes for MICs. Unfortunately, conventional NBOs can hardly meet the future demands for high-power applications. The niobium-based mixed oxides (NBMOs) formed by doping niobium oxides with other elements (Ti, P, V, Cr, etc.) are drawing immense interest for advanced MICs as competitive anodes. Unlike the conventional layered Nb2O5, NBMOs exhibit diverse structures (Wadsley–Roth phase, tungsten bronze structure, ABO3 perovskite structure, etc.), which renders them appealing merits including enhanced specific capacities, higher electronic/ionic conductivities, etc., for MICs. Even so, there is still extensive room for progress to further improve their electrochemical kinetics. In this Review, we systematically summarize the doping species, crystal structures, charge-storage mechanism, synthesis strategies, and recent contributions/progress of diverse NBMOs for advanced MICs toward advancing the process of practical applications. Besides, the challenges and prospects in the booming field are proposed. The review will guide future purposeful design and controllable synthesis of high-performance anodes for next-generation MICs.