Interphase stabilized electrospun SnO2 fibers as alloy anode via restricted cycling for Li-ion capacitors with high energy and wide temperature operation.

The second-generation supercapacitor comprises the hybridized energy storage mechanism of Lithium-ion batteries and electrical double-layer capacitors, i.e, Lithium-ion capacitors (LICs). The electrospun SnO2 nanofibers are synthesized by a simple electrospinning technique and are directly used as anode material for LICs with activated carbon (AC) as a cathode. However, before the assembly, the battery-type electrode SnO2 is electrochemically pre-lithiated (LixSn + Li2O), and AC loading is balanced with respect to its half-cell performance. First, the SnO2 is tested in the half-cell assembly with a limited potential window of 0.005 to 1 V vs. Li to avoid the conversion reaction of Sn0 to SnOx. Also, the limited potential window allows only the reversible alloy/de-alloying process. Finally, the assembled LIC, AC/(LixSn + Li2O), displayed a maximum energy density of 185.88 Wh kg-1 with ultra-long cyclic durability of over 20,000 cycles. Further, the LIC is also exposed to various temperature conditions (-10, 0, 25, & 50 °C) to study the feasibility of using them in different environmental conditions.

Carbon Nanotube Scaffolds Entrapped in a Gel Matrix for Realizing the Improved Cycle Life of Zinc Bromine Redox Flow Batteries.

Herein, we have successfully demonstrated a nanofiller (such as multiwalled carbon nanotubes (MWCNT)) dispersed in a polymer matrix (such as polyacrylonitrile (PAN)) as an effective pore filling agent to a microporous Daramic membrane for inhibiting bromine diffusion in zinc bromine redox flow batteries. A simple protocol of the MWCNT/PAN-Daramic membrane renders a major benefit for inhibiting bromine diffusion relative to the conventional microporous membrane. As a result, the MWCNT/PAN composite Daramic membrane exhibits remarkable electrochemical performance in zinc bromine redox flow batteries at various current densities. More impressively, the MWCNT/PAN composite Daramic membrane shows a 90% Coulombic efficiency compared to the pristine Daramic membrane and the PAN composite Daramic membrane with only 68.53 and 71.20% efficiencies at 160 mA cm-2, respectively. Moreover, the MWCNT/PAN composite Daramic membrane displays an extraordinary long cycling performance with a >97% Coulombic efficiency, whereas the Daramic membrane withstands only 200 cycles due to severe water transport from the catholyte to the anolyte. The zinc bromine redox flow battery assembled with the MWCNT/PAN composite Daramic membrane significantly reduces the self-discharge rate and retains an open circuit voltage of 1.69 V for 13.40 h in comparison to the Daramic membrane (10.83 h) and the PAN composite membrane (11.13 h). Thus, the extraordinary flow cell performance and stability of the MWCNT/PAN composite Daramic membrane lead to the development of an alternative to the microporous Daramic membrane in zinc bromine redox flow batteries.

Two-Dimensional Polymer Synthesized via Solid-State Polymerization for High-Performance Supercapacitors.

Two-dimensional (2-D) polymer has properties that are attractive for energy storage applications because of its combination of heteroatoms, porosities and layered structure, which provides redox chemistry and ion diffusion routes through the 2-D planes and 1-D channels. Here, conjugated aromatic polymers (CAPs) were synthesized in quantitative yield via solid-state polymerization of phenazine-based precursor crystals. By choosing flat molecules (2-TBTBP and 3-TBQP) with different positions of bromine substituents on a phenazine-derived scaffold, C-C cross coupling was induced following thermal debromination. CAP-2 is polymerized from monomers that have been prepacked into layered structure (3-TBQP). It can be mechanically exfoliated into micrometer-sized ultrathin sheets that show sharp Raman peaks which reflect conformational ordering. CAP-2 has a dominant pore size of ∼0.8 nm; when applied as an asymmetric supercapacitor, it delivers a specific capacitance of 233 F g-1 at a current density of 1.0 A g-1, and shows outstanding cycle performance.

S-Doped TiSe2 Nanoplates/Fe3 O4 Nanoparticles Heterostructure.

2D Sulfur-doped TiSe2 /Fe3 O4 (named as S-TiSe2 /Fe3 O4 ) heterostructures are synthesized successfully based on a facile oil phase process. The Fe3 O4 nanoparticles, with an average size of 8 nm, grow uniformly on the surface of S-doped TiSe2 (named as S-TiSe2 ) nanoplates (300 nm in diameter and 15 nm in thickness). These heterostructures combine the advantages of both S-TiSe2 with good electrical conductivity and Fe3 O4 with high theoretical Li storage capacity. As demonstrated potential applications for energy storage, the S-TiSe2 /Fe3 O4 heterostructures possess high reversible capacities (707.4 mAh g-1 at 0.1 A g-1 during the 100th cycle), excellent cycling stability (432.3 mAh g-1 after 200 cycles at 5 A g-1 ), and good rate capability (e.g., 301.7 mAh g-1 at 20 A g-1 ) in lithium-ion batteries. As for sodium-ion batteries, the S-TiSe2 /Fe3 O4 heterostructures also maintain reversible capacities of 402.3 mAh g-1 at 0.1 A g-1 after 100 cycles, and a high rate capacity of 203.3 mAh g-1 at 4 A g-1 .

ß-Co(OH)2 Nanosheets: A Superior Pseudocapacitive Electrode for High-Energy Supercapacitors.

In this work, ß-Co(OH)2 nanosheets are explored as efficient pseudocapacitive materials for the fabrication of 1.6 V class high-energy supercapacitors in asymmetric fashion. The as-synthesized ß-Co(OH)2 nanosheets displayed an excellent electrochemical performance owing to their unique structure, morphology, and reversible reaction kinetics (fast faradic reaction) in both the three-electrode and asymmetric configuration (with activated carbon, AC). For example, in the three-electrode set-up, ß-Co(OH)2 exhibits a high specific capacitance of ∼675 F g-1 at a scan rate of 1 mV s-1 . In the asymmetric supercapacitor, the ß-Co(OH)2 ∥AC cell delivers a maximum energy density of 37.3 Wh kg-1 at a power density of 800 W kg-1 . Even at harsh conditions (8 kW kg-1 ), an energy density of 15.64 Wh kg-1 is registered for the ß-Co(OH)2 ∥AC assembly. Such an impressive performance of ß-Co(OH)2 nanosheets in the asymmetric configuration reveals the emergence of pseudocapacitive electrodes towards the fabrication of high-energy electrochemical charge storage systems.

Polymeric Nanomaterials Based on the Buckybowl Motif: Synthesis through Ring-Opening Metathesis Polymerization and Energy Storage Applications.

Ring-opening metathesis polymerization (ROMP) of buckybowl corannulene-based oxa-norbornadiene monomer is shown to give rise to polymeric nanomaterials with an average pore size of about 1.4 nm and a surface area of 49.2 m2/g. Application in supercapacitor devices show that the corannulene-based nanomaterials exhibit a specific capacitance of 134 F·g-1 (1.0 V voltage window) in a three-electrode cell configuration. Moreover, the electrode assembled from these materials in a symmetric configuration (1.6 V voltage window) exhibits long-term cyclability of 90% capacitance retention after undergoing 10000 cycles. This work demonstrates that ROMP is a valuable method in synthesizing nanostructured corannulene polymers, and that materials based on the nonplanar polycyclic aromatic motif represents an attractive active component for fabrication of devices targeted at electrochemical energy storage applications.

Photopolymerization of Diacetylene on Aligned Multiwall Carbon Nanotube Microfibers for High-Performance Energy Devices.

Linear two-dimensional materials have recently attracted an intense interest for supercapacitors because of their potential uses as electrodes in next-generation wearable electronics. However, enhancing the electrochemical properties of these materials without complicated structural modifications remains a challenge. Herein, we present the preparation of a hybrid electrode system via polydiacetylene (PDA) cloaking on the surface of aligned multiwall carbon nanotubes (MWCNTs) through self-assembly based in situ photopolymerization. This strategy eliminates the need for initiators and binders that hinder electrochemical performance in conventional conducting polymer based composite electrodes. As noncovalent PDA cloaking did not alter the chemical structure of MWCNTs, high inherent conductivity from sp2 hybridized carbon was preserved. The resulting hybrid microfiber (MWCNT@PDA) exhibited a significant increase in specific capacitance (1111 F g-1) when compared to bare MWCNTs (500 F g-1) and PDA (666.7 F g-1) in a voltage window of 0-1.2 V at a current density of 3 A g-1 in 0.5 M K2SO4 electrolyte. The specific capacitance was retained (ca. 95%) after 7000 charge/discharge cycles. The present results suggest that aligned MWCNTs cloaked with conjugated polymers could meet the demands for future flexible electronics.

Ultralong Durability of Porous α-Fe2O3 Nanofibers in Practical Li-Ion Configuration with LiMn2O4 Cathode.

Prelithiated, electrospun α-Fe2O3 nanofibers display an exceptional cycleability when it is paired with commercial LiMn2O4 cathode in full-cell assembly. The performance of such α-Fe2O3 nanofibers is mainly due to the presence of unique morphology with porous structure, appropriate mass balance, and working potential. Also, synthesis technique cannot be ruled out for the performance.

Palladium- and gold-nanoparticle-modified porous carbon as a high-power anode for lithium-ion batteries.

Electrode materials: Ultrahigh-power insertion-type anodes are developed by simply decorating Pd nanoparticles on commercially available porous carbon.