Lithium-Sulfur Capacitors.

Although many existing hybrid energy storage systems demonstrate promising electrochemical performances, imbalances between the energies and kinetics of the two electrodes must be resolved to allow their widespread commercialization. As such, the development of a new class of energy storage systems is a particular challenge, since future systems will require a single device to provide both a high gravimetric energy and a high power density. In this context, we herein report the design of novel lithium-sulfur capacitors. The resulting asymmetric systems exhibited energy densities of 23.9-236.4 Wh kg-1 and power densities of 72.2-4097.3 W kg-1, which are the highest reported values for an asymmetric system to date. This approach involved the use of a prelithiated anode and a hybrid cathode material exhibiting anion adsorption-desorption in addition to the electrochemical reduction and oxidation of sulfur at almost identical rates. This novel strategy yielded both high energy and power densities, and therefore establishes a new benchmark for hybrid systems.

Multi-functionalized herringbone carbon nanofiber for anodes of lithium ion batteries.

Herringbone carbon nanofibers (HCNFs) are prepared for use as anode materials in lithium-ion batteries (LIBs). HCNFs are prepared using a Ni-Fe catalyst and subsequently multi-functionalized with oxygen using the Hummers' method, and then with both oxygen and nitrogen-containing 2-ureido-4[1H]pyrimidinone (UHP) moieties, which endow the HCNFs with the ability to form quadruple hydrogen bonds (QHBs). The as-prepared HCNFs are, on average, 13 µm in length and 100 nm in diameter, with a highly graphitic structure. The oxidized HCNFs (Ox-HCNFs) obtained by Hummers' method are partially exfoliated, having double-bladed saw-like structures that extend in the direction of the graphite planes. QHBs are formed between the HCNFs after functionalization with the UHP moieties. The final surface-modified HCNFs (N-Ox-HCNFs) have more electrochemical sites, shorter Li+ diffusion lengths, and additional electron pathways compared with the as-prepared HCNF and Ox-HCNF. The introduction of oxygen- and nitrogen-containing functional groups improves the performance of LIBs: a high charge capacity of 763 mA h g-1 at 0.1 A g-1, excellent rate capability (a capacity of 402 mA h g-1 at 3 A g-1), and near 100% capacity retention after 300 cycles are reported.

Hierarchically structured activated carbon for ultracapacitors.

To resolve the pore-associated bottleneck problem observed in the electrode materials used for ultracapacitors, which inhibits the transport of the electrolyte ions, we designed hierarchically structured activated carbon (HAC) by synthesizing a mesoporous silica template/carbon composite and chemically activating it to simultaneously remove the silica template and increase the pore volume. The resulting HAC had a well-designed, unique porous structure, which allowed for large interfaces for efficient electric double-layer formation. Given the unique characteristics of the HAC, we believe that the developed synthesis strategy provides important insights into the design and fabrication of hierarchical carbon nanostructures. The HAC, which had a specific surface area of 1,957 m(2) g(-1), exhibited an extremely high specific capacitance of 157 F g(-1) (95 F cc(-1)), as well as a high rate capability. This indicated that it had superior energy storage capability and was thus suitable for use in advanced ultracapacitors.

Facile Synthesis of Nb2O5@Carbon Core-Shell Nanocrystals with Controlled Crystalline Structure for High-Power Anodes in Hybrid 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.

Synthesis and electrochemical properties of Li0.33MnO2 nanorods as positive electrode material for 3 V lithium batteries.

In this study, one-dimensional Li0.33MnO2 nanorods were synthesized by a solid state reaction using gamma-MnO2 as a precursor. Gamma-MnO2 was prepared under different reaction times by a redox process. The HR-TEM results showed that the diameter and length of the Li0.33MnO2 nanorods are 5-20 nm and about 200 nm, respectively. The Li0.33MnO2 nanorods delivered a discharge capacity of 157 mA h g(-1) at 1 C, and retained 97% of their initial capacity over 30 cycles. Good rate performance was also observed, with discharge capacities of 201 and 133 mA h g(-1) at 0.1 C and 2 C, respectively. The morphology of the nanorods could increase their electrochemical properties, resulting in higher capacity and rate performance.