Recently, hybrid supercapacitors (HSCs), which combine the use of battery and supercapacitor, have been extensively studied in order to satisfy increasing demands for large energy density and high power capability in energy-storage devices. For this purpose, the requirement for anode materials that provide enhanced charge storage sites (high capacity) and accommodate fast charge transport (high rate capability) has increased. Herein, therefore, a preparation of nanocomposite as anode material is presented and an advanced HSC using it is thoroughly analyzed. The HSC comprises a mesoporous Nb2O5/carbon (m-Nb2O5-C) nanocomposite anode synthesized by a simple one-pot method using a block copolymer assisted self-assembly and commercial activated carbon (MSP-20) cathode under organic electrolyte. The m-Nb2O5-C anode provides high specific capacity with outstanding rate performance and cyclability, mainly stemming from its enhanced pseudocapacitive behavior through introduction of a carbon-coated mesostructure within a voltage range from 3.0 to 1.1 V (vs Li/Li(+)). The HSC using the m-Nb2O5-C anode and MSP-20 cathode exhibits excellent energy and power densities (74 W h kg(-1) and 18,510 W kg(-1)), with advanced cycle life (capacity retention: ∼90% at 1000 mA g(-1) after 1000 cycles) within potential range from 1.0 to 3.5 V. In particular, we note that the highest power density (18,510 W kg(-1)) of HSC is achieved at 15 W h kg(-1), which is the highest level among similar HSC systems previously reported. With further study, the HSCs developed in this work could be a next-generation energy-storage device, bridging the performance gap between conventional batteries and supercapacitors.

Hybrid supercapacitors (battery-supercapacitor hybrid devices, HSCs) deliver high energy within seconds (excellent rate capability) with stable cyclability. One of the key limitations in developing high-performance HSCs is imbalance in power capability between the sluggish Faradaic lithium-intercalation anode and rapid non-Faradaic capacitive cathode. To solve this problem, we synthesize Nb2O5@carbon core-shell nanocyrstals (Nb2O5@C NCs) as high-power anode materials with controlled crystalline phases (orthorhombic (T) and pseudohexagonal (TT)) via a facile one-pot synthesis method based on a water-in-oil microemulsion system. The synthesis of ideal T-Nb2O5 for fast Li(+) diffusion is simply achieved by controlling the microemulsion parameter (e.g., pH control). The T-Nb2O5@C NCs shows a reversible specific capacity of ∼180 mA h g(-1) at 0.05 A g(-1) (1.1-3.0 V vs Li/Li(+)) with rapid rate capability compared to that of TT-Nb2O5@C and carbon shell-free Nb2O5 NCs, mainly due to synergistic effects of (i) the structural merit of T-Nb2O5 and (ii) the conductive carbon shell for high electron mobility. The highest energy (∼63 W h kg(-1)) and power (16 528 W kg(-1) achieved at ∼5 W h kg(-1)) densities within the voltage range of 1.0-3.5 V of the HSC using T-Nb2O5@C anode and MSP-20 cathode are remarkable.

Sodium‐ion hybrid supercapacitors (Na‐HSCs) have potential for mid‐ to large‐scale energy storage applications because of their high energy/power densities, long cycle life, and the low cost of sodium. However, one of the obstacles to developing Na‐HSCs is the imbalance of kinetics from different charge storage mechanisms between the sluggish faradaic anode and the rapid non‐faradaic capacitive cathode. Thus, to develop high‐power Na‐HSC anode materials, this paper presents the facile synthesis of nanocomposites comprising Nb2O5@Carbon core–shell nanoparticles (Nb2O5@C NPs) and reduced graphene oxide (rGO), and an analysis of their electrochemical performance with respect to various weight ratios of Nb2O5@C NPs to rGO (e.g., Nb2O5@C, Nb2O5@C/rGO‐70, ‐50, and ‐30). In a Na half‐cell configuration, the Nb2O5@C/rGO‐50 shows highly reversible capacity of ≈285 mA h g−1 at 0.025 A g−1 in the potential range of 0.01–3.0 V (vs Na/Na+). In addition, the Na‐HSC using the Nb2O5@C/rGO‐50 anode and activated carbon (MSP‐20) cathode delivers high energy/power densities (≈76 W h kg−1 and ≈20 800 W kg−1) with a stable cycle life in the potential range of 1.0–4.3 V. The energy and power densities of the Na‐HSC developed in this study are higher than those of similar Li‐ and Na‐HSCs previously reported.

A mesostructured spinel Li 4 Ti 5 O 12 (LTO)-carbon nanocomposite (denoted asMeso-LTO-C) with large ( > 15 nm) and uniform pores is simply synthesized via block copolymer self-assembly. Exceptionally high rate capability is then demonstrated for Li-ion battery (LIB) negative electrodes. Polyisoprene-blockpoly(ethylene oxide) (PI-b -PEO) with a sp 2 -hybridized carbon-containing hydrophobic block is employed as a structure-directing agent. Then the assembled composite material is crystallized at 700 °C enabling conversion to the spinel LTO structure without loss of structural integrity. Part of the PI is converted to a conductive carbon that coats the pores of the Meso-LTO-C. The in situ pyrolyzed carbon not only maintains the porous mesostructure as the LTO is crystallized, but also improves the electronic conductivity. A Meso-LTO-C/Li cell then cycles stably at 10 C-rate, corresponding to only 6 min for complete charge and discharge, with a reversible capacity of 115 mA h g − 1 with 90% capacity retention after 500 cycles. In sharp contrast, a Bulk-LTO/Li cell exhibits only 69 mA h g − 1 at 10 C-rate. Electrochemical impedance spectroscopy (EIS) with symmetric LTO/ LTO cells prepared from Bulk-LTO and Meso-LTO-C cycled in different potential ranges reveals the factors contributing to the vast difference between the ratecapabilities. The carbon-coated mesoporous structure enables highly improved electronic conductivity and signifi cantly reduced charge transfer resistance, and a much smaller overall resistance is observed compared to Bulk-LTO. Also, the solid electrolyte interphase (SEI)-free surface due to the limited voltage window ( > 1 V versus Li/Li + ) contributes to dramatically reduced resistance.

In order to achieve high-power and -energy anodes operating above 1.0 V (vs Li/Li + ), titanium-based materials have been investigated for a long time. However, theoretically low lithium charge capacities of titanium-anodes have required new types of high-capacity anode materials. As a candidate, TiNb 2 O 7 has attracted much attention due to the high theoretical capacity of 387.6 mA h g −1 . However, the high formation temperature of the TiNb 2 O 7 phase resulted in large-sized TiNb 2 O 7 crystals, thus resulting in poor rate capability. Herein, ordered mesoporous TiNb 2 O 7 (denoted as m-TNO) was synthesized by block copolymer assisted self-assembly, and the resulting binary metal oxide was applied as an anode in a lithium ion battery. The nanocrystals (∼15 nm) developed inside the confined pore walls and large pores (∼40 nm) of m-TNO resulted in a short diffusion length for lithium ions/electrons and fast penetration of electrolyte. As a stable anode, the m-TNO electrode exhibited a high capacity of 289 mA h g −1 (at 0.1 C) and an excellent rate performance of 162 mA h g −1 at 20 C and 116 mA h g −1 at 50 C (= 19.35 A g −1 ) within a potential range of 1.0−3.0 V (vs Li/Li + ), which clearly surpasses other Ti-and Nb-based anode materials (TiO 2 , Li 4 Ti 5 O 12 , Nb 2 O 5 , etc.) and previously reported TiNb 2 O 7 materials. The m-TNO and carbon coated m-TNO electrodes also demonstrated stable cycle performances of 48 and 81% retention during 2,000 cycles at 10 C rate, respectively.

We report mesoporous composite materials (m-GeO2, m-GeO2/C, and m-Ge-GeO2/C) with large pore size which are synthesized by a simple block copolymer directed self-assembly. m-Ge/GeO2/C shows greatly enhanced Coulombic efficiency, high reversible capacity (1631 mA h g(-1)), and stable cycle life compared with the other mesoporous and bulk GeO2 electrodes. m-Ge/GeO2/C exhibits one of the highest areal capacities (1.65 mA h cm(-2)) among previously reported Ge- and GeO2-based anodes. The superior electrochemical performance in m-Ge/GeO2/C arises from the highly improved kinetics of conversion reaction due to the synergistic effects of the mesoporous structures and the conductive carbon and metallic Ge.

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A general method to synthesize mesoporous metal oxide@N-doped macroporous graphene composite by heat-treatment of electrostatically co-assembled amine-functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N-doped macroporous graphene simultaneously is reported. Four mesoporous metal oxides (WO 3−x , Co 3 O 4 , Mn 2 O 3 , and Fe 3 O 4 ) are encapsulated in N-doped macroporous graphene. Used as an anode material for sodium-ion hybrid supercapacitors (Na-HSCs), mesoporous reduced tungsten oxide@N-doped macroporous graphene (m-WO 3−x @NM-rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m-WO 3−x @NM-rGO is based on Na + intercalation/de-intercalation. To the best of knowledge, this is the first report on Na + intercalation/de-intercalation properties of WO 3−x and its application to Na-HSCs.