Specific energy

About: Specific energy is a research topic. Over the lifetime, 2282 publications have been published within this topic receiving 50908 citations. The topic is also known as: energy density & massic energy.

Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage

Abstract: Carbon-based supercapacitors can provide high electrical power, but they do not have sufficient energy density to directly compete with batteries. We found that a nitrogen-doped ordered mesoporous few-layer carbon has a capacitance of 855 farads per gram in aqueous electrolytes and can be bipolarly charged or discharged at a fast, carbon-like speed. The improvement mostly stems from robust redox reactions at nitrogen-associated defects that transform inert graphene-like layered carbon into an electrochemically active substance without affecting its electric conductivity. These bipolar aqueous-electrolyte electrochemical cells offer power densities and lifetimes similar to those of carbon-based supercapacitors and can store a specific energy of 41 watt-hours per kilogram (19.5 watt-hours per liter).

Highly conductive paper for energy-storage devices

Abstract: Paper, invented more than 2,000 years ago and widely used today in our everyday lives, is explored in this study as a platform for energy-storage devices by integration with 1D nanomaterials. Here, we show that commercially available paper can be made highly conductive with a sheet resistance as low as 1 ohm per square (Ω/sq) by using simple solution processes to achieve conformal coating of single-walled carbon nanotube (CNT) and silver nanowire films. Compared with plastics, paper substrates can dramatically improve film adhesion, greatly simplify the coating process, and significantly lower the cost. Supercapacitors based on CNT-conductive paper show excellent performance. When only CNT mass is considered, a specific capacitance of 200 F/g, a specific energy of 30–47 Watt-hour/kilogram (Wh/kg), a specific power of 200,000 W/kg, and a stable cycling life over 40,000 cycles are achieved. These values are much better than those of devices on other flat substrates, such as plastics. Even in a case in which the weight of all of the dead components is considered, a specific energy of 7.5 Wh/kg is achieved. In addition, this conductive paper can be used as an excellent lightweight current collector in lithium-ion batteries to replace the existing metallic counterparts. This work suggests that our conductive paper can be a highly scalable and low-cost solution for high-performance energy storage devices.

Reducing Carbon in LiFePO4 / C Composite Electrodes to Maximize Specific Energy, Volumetric Energy, and Tap Density

Abstract: Efforts were made to synthesize LiFePO 4 /C composites showing good rale capability and high energy density while attempting to minimize the amount of carbon in the composite. First, three carbon-coated samples, one coated with carbon after the synthesis of pure LiFePO 4 , one synthesized with sugar added before the heating steps, and one synthesized with sugar added before heating and subsequently coated with carbon, were studied. The resulting carbon contents for these samples arc 2.7, 3.5, and 6.2 wt %, respectively. Electrochemical tests showed that the latter two samples had comparable rate capabilities to the LiFePO 4 /C composite (15 wt % carbon) recently reported by Huang et al. We believe the synthesis of LiFePO 4 with sugar added before heating is the best method because it gives particles having uniform small size that are covered by carbon. Further studies of samples made by this method show that a very small percentage of carbon, even less than 1 wt %, causes a significant increase in rate capability, hut unfortunately, a dramatic decrease in tap density. To make LiFePO 4 /C composites having good rate capability, high energy density, and high tap density, the carbon content and method for coating carbon onto the LiFePO 4 particles must he given careful attention. However, based on the studies reported here, we are not certain that all desired parameters can he simultaneously achieved, and this may limit the usefulness of LiFePO 4 in some practical applications.

The concept of specific energy in rock drilling

Abstract: The fundamental problem in rock working is the breakage of fragments out of the face of a solid wall of rock. Mechanically this can be done only by forcing a tool into the rock surface, after the manner of an ‘indenter’ such as is commonly used for testing surface hardness. Since the process breaks rather than cuts solid rock into small fragments of assorted sizes it can be regarded as essentially one of crushing. As in crushing processes generally, energy/volume relationships are therefore of interest. ‘Specific energy’, defined as the energy required to excavate unit volume of rock, is a useful parameter in this context and may also be taken as an index of the mechanical efficiency of a rock-working process. In drilling data from a number of sources its minimum value appears to be very roughly correlated with the crushing strength of the medium drilled in, for rotary, percussive-rotary and roller-bit drilling. The implications of this are discussed.

Graphene Scroll-Coated α-MnO2 Nanowires as High-Performance Cathode Materials for Aqueous Zn-Ion Battery.

Abstract: The development of manganese dioxide as the cathode for aqueous Zn-ion battery (ZIB) is limited by the rapid capacity fading and material dissolution. Here, a highly reversible aqueous ZIB using graphene scroll-coated α-MnO2 as the cathode is proposed. The graphene scroll is uniformly coated on the MnO2 nanowire with an average width of 5 nm, which increases the electrical conductivity of the MnO2 nanowire and relieves the dissolution of the cathode material during cycling. An energy density of 406.6 Wh kg-1 (382.2 mA h g-1 ) at 0.3 A g-1 can be reached, which is the highest specific energy value among all the cathode materials for aqueous Zn-ion battery so far, and good long-term cycling stability with 94% capacity retention after 3000 cycles at 3 A g-1 are achieved. Meanwhile, a two-step intercalation mechanism that Zn ions first insert into the layers and then the tunnels of MnO2 framework is proved by in situ X-ray diffraction, galvanostatic intermittent titration technique, and X-ray photoelectron spectroscopy characterizations. The graphene scroll-coated metallic oxide strategy can also bring intensive interests for other energy storage systems.