Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-s... more Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2−5 times higher than that of conventional intercalation materials (e.g., LiCoO 2 and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.
Nb 2 O 5 is a Li + intercalation metal oxide that is of current interest for lithium ion battery ... more Nb 2 O 5 is a Li + intercalation metal oxide that is of current interest for lithium ion battery electrodes. The electrophoretic deposition (ED) of Nb 2 O 5 thin-films from aqueous, NbO x colloidal solutions is reported here. For films ranging in thickness from 38 to 144 nm, the mass loading of Nb 2 O 5 on the electrode is correlated with the coulometry of ED using quartz crystal microbalance gravimetry. Crystalline, phase pure films of orthorhombic, T-Nb 2 O 5 , are obtained by postdeposition calcination. These films exhibit unusually high specific capacities for Li +-based energy storage as a consequence of ≈70% porosity. For example, a 60 nm thick film displays a specific capacity, C sp , of 420 mAh/g at 5 A/g and 220 mAh/g at 50 A/g, which can be compared with the theoretical Faradaic capacity of 202 mAh/g. T-Nb 2 O 5 films also have a specific energy density in the range from 770−486 Wh/kg, and a specific power density in the range from 9 to 90 kW/kg. These excellent energy storage metrics are attributed to augmentation of the Faradaic capacity by high double-layer capacities enabled by the mesoporous structure of these films. 37 of a few k B T, for Li + transport in this material, as measured 38 using nuclear magnetic resonance. 39 T-Nb 2 O 5 is most often synthesized by hydrothermal 40 methods, 1,2,4,13,14 and highly dispersed T-Nb 2 O 5 on carbon 41 has demonstrated specific capacities of up to 590 F/g. 14 Other 42 methods for preparing Nb 2 O 5 films include electrospinning 43 followed by thermal annealing, 16 spray pyrolysis, 17 sol−gel 44 processing methods, 9,10,18 electrospinning, 19 and reactive 45 sputtering. 11 46 Electrodeposition has hardly been attempted, in spite of the 47 fact that it is an attractive method for both electrochromics and 48 battery/capacitor materials because it promotes an electrically 49 intimate contact with an electrode that can also serve as a 50 current collector. The reason is that electrodeposition of 51 Nb 2 O 5 is difficult: the cathodic electrodeposition of niobium 52 oxides (NbO x) is complicated by the very negative reduction 53 potential for Nb 3+ (−1.1 V vs NHE) which makes disruptive
The oxygen, O2, in air interferes with the detection of H2 by palladium (Pd)-based H2 sensors, in... more The oxygen, O2, in air interferes with the detection of H2 by palladium (Pd)-based H2 sensors, including Pd nanowires (NWs), depressing the sensitivity and retarding the response/recovery speed in air-relative to N2 or Ar. Here, we describe the preparation of H2 sensors in which a nanofiltration layer consisting of a Zn metal-organic framework (MOF) is assembled onto Pd NWs. Polyhedron particles of Zn-based zeolite imidazole framework (ZIF-8) were synthesized on lithographically patterned Pd NWs, leading to the creation of ZIF-8/Pd NW bilayered H2 sensors. The ZIF-8 filter has many micropores (0.34 nm for gas diffusion) which allows for the predominant penetration of hydrogen molecules with a kinetic diameter of 0.289 nm, whereas relatively larger gas molecules including oxygen (0.345 nm) and nitrogen (0.364 nm) in air are effectively screened, resulting in superior hydrogen sensing properties. Very importantly, the Pd NWs filtered by ZIF-8 membrane (Pd NWs@ZIF-8) reduced the H2 response amplitude slightly (ΔR/R0 = 3.5% to 1% of H2 versus 5.9% for Pd NWs) and showed 20-fold faster recovery (7 s to 1% of H2) and response (10 s to 1% of H2) speed compared to that of pristine Pd NWs (164 s for response and 229 s for recovery to 1% of H2). These outstanding results, which are mainly attributed to the molecular sieving and acceleration effect of ZIF-8 covered on Pd NWs, rank highest in H2 sensing speed among room-temperature Pd-based H2 sensors.
A nitrobenzoxadiazole (NBD) anchored mesoporous silica-based system has been designed and develop... more A nitrobenzoxadiazole (NBD) anchored mesoporous silica-based system has been designed and developed for the selective detection of fluoride in aqueous medium.
The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO2 and its properties fo... more The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO2 and its properties for electrical energy storage are investigated-specifically for ultrathick δ-MnO2 layers in the micron scale. Planar arrays of gold@δ-MnO2, core@shell nanowires, were prepared by electrodeposition with and without the HMTA and their electrochemical properties were evaluated. HMTA alters the MnO2 in three ways: First, it creates a more open morphology for the MnO2 coating, characterized by "petals" with a thickness of 6 to 9 nm, rather than much thinner δ-MnO2 sheets seen in the absence of HMTA. Second, the electronic conductivity of the δ-MnO2 is increased by an order of magnitude. Third, δ-MnO2 prepared in HMTA shows a (001) interlayer spacing that is expanded by ≈30% possibly accelerating Li transport. The net effect of "HTMA doping" is to dramatically improve high rate performance, culminating in an increase in the specific capacity for the thickest MnO2 shells examined here by a factor of 15 at 100 mV/s.
Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-s... more Although Li-ion batteries have emerged as the battery of choice for electric vehicles and large-scale smart grids, significant research efforts are devoted to identifying materials that offer higher energy density, longer cycle life, lower cost, and/or improved safety compared to those of conventional Li-ion batteries based on intercalation electrodes. By moving beyond intercalation chemistry, gravimetric capacities that are 2−5 times higher than that of conventional intercalation materials (e.g., LiCoO 2 and graphite) can be achieved. The transition to higher-capacity electrode materials in commercial applications is complicated by several factors. This Review highlights the developments of electrode materials and characterization tools for rechargeable lithium-ion batteries, with a focus on the structural and electrochemical degradation mechanisms that plague these systems.
Nb 2 O 5 is a Li + intercalation metal oxide that is of current interest for lithium ion battery ... more Nb 2 O 5 is a Li + intercalation metal oxide that is of current interest for lithium ion battery electrodes. The electrophoretic deposition (ED) of Nb 2 O 5 thin-films from aqueous, NbO x colloidal solutions is reported here. For films ranging in thickness from 38 to 144 nm, the mass loading of Nb 2 O 5 on the electrode is correlated with the coulometry of ED using quartz crystal microbalance gravimetry. Crystalline, phase pure films of orthorhombic, T-Nb 2 O 5 , are obtained by postdeposition calcination. These films exhibit unusually high specific capacities for Li +-based energy storage as a consequence of ≈70% porosity. For example, a 60 nm thick film displays a specific capacity, C sp , of 420 mAh/g at 5 A/g and 220 mAh/g at 50 A/g, which can be compared with the theoretical Faradaic capacity of 202 mAh/g. T-Nb 2 O 5 films also have a specific energy density in the range from 770−486 Wh/kg, and a specific power density in the range from 9 to 90 kW/kg. These excellent energy storage metrics are attributed to augmentation of the Faradaic capacity by high double-layer capacities enabled by the mesoporous structure of these films. 37 of a few k B T, for Li + transport in this material, as measured 38 using nuclear magnetic resonance. 39 T-Nb 2 O 5 is most often synthesized by hydrothermal 40 methods, 1,2,4,13,14 and highly dispersed T-Nb 2 O 5 on carbon 41 has demonstrated specific capacities of up to 590 F/g. 14 Other 42 methods for preparing Nb 2 O 5 films include electrospinning 43 followed by thermal annealing, 16 spray pyrolysis, 17 sol−gel 44 processing methods, 9,10,18 electrospinning, 19 and reactive 45 sputtering. 11 46 Electrodeposition has hardly been attempted, in spite of the 47 fact that it is an attractive method for both electrochromics and 48 battery/capacitor materials because it promotes an electrically 49 intimate contact with an electrode that can also serve as a 50 current collector. The reason is that electrodeposition of 51 Nb 2 O 5 is difficult: the cathodic electrodeposition of niobium 52 oxides (NbO x) is complicated by the very negative reduction 53 potential for Nb 3+ (−1.1 V vs NHE) which makes disruptive
The oxygen, O2, in air interferes with the detection of H2 by palladium (Pd)-based H2 sensors, in... more The oxygen, O2, in air interferes with the detection of H2 by palladium (Pd)-based H2 sensors, including Pd nanowires (NWs), depressing the sensitivity and retarding the response/recovery speed in air-relative to N2 or Ar. Here, we describe the preparation of H2 sensors in which a nanofiltration layer consisting of a Zn metal-organic framework (MOF) is assembled onto Pd NWs. Polyhedron particles of Zn-based zeolite imidazole framework (ZIF-8) were synthesized on lithographically patterned Pd NWs, leading to the creation of ZIF-8/Pd NW bilayered H2 sensors. The ZIF-8 filter has many micropores (0.34 nm for gas diffusion) which allows for the predominant penetration of hydrogen molecules with a kinetic diameter of 0.289 nm, whereas relatively larger gas molecules including oxygen (0.345 nm) and nitrogen (0.364 nm) in air are effectively screened, resulting in superior hydrogen sensing properties. Very importantly, the Pd NWs filtered by ZIF-8 membrane (Pd NWs@ZIF-8) reduced the H2 response amplitude slightly (ΔR/R0 = 3.5% to 1% of H2 versus 5.9% for Pd NWs) and showed 20-fold faster recovery (7 s to 1% of H2) and response (10 s to 1% of H2) speed compared to that of pristine Pd NWs (164 s for response and 229 s for recovery to 1% of H2). These outstanding results, which are mainly attributed to the molecular sieving and acceleration effect of ZIF-8 covered on Pd NWs, rank highest in H2 sensing speed among room-temperature Pd-based H2 sensors.
A nitrobenzoxadiazole (NBD) anchored mesoporous silica-based system has been designed and develop... more A nitrobenzoxadiazole (NBD) anchored mesoporous silica-based system has been designed and developed for the selective detection of fluoride in aqueous medium.
The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO2 and its properties fo... more The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO2 and its properties for electrical energy storage are investigated-specifically for ultrathick δ-MnO2 layers in the micron scale. Planar arrays of gold@δ-MnO2, core@shell nanowires, were prepared by electrodeposition with and without the HMTA and their electrochemical properties were evaluated. HMTA alters the MnO2 in three ways: First, it creates a more open morphology for the MnO2 coating, characterized by "petals" with a thickness of 6 to 9 nm, rather than much thinner δ-MnO2 sheets seen in the absence of HMTA. Second, the electronic conductivity of the δ-MnO2 is increased by an order of magnitude. Third, δ-MnO2 prepared in HMTA shows a (001) interlayer spacing that is expanded by ≈30% possibly accelerating Li transport. The net effect of "HTMA doping" is to dramatically improve high rate performance, culminating in an increase in the specific capacity for the thickest MnO2 shells examined here by a factor of 15 at 100 mV/s.
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