Specific capacity

The term specific capacity (or related capacity) is used indiscriminately to speak of gravimetric capacity and volumetric capacity. The density of the materials is not the same for all secondary battery technologies or for all electrodes, so the two quantities are not really linked. Depending on the applications, it is the consideration of one or other of these two values which is meaningful. The ambiguity can be resolved by looking at the unit associated with the values quoted. This term can easily be avoided by using the term ad hoc. 

The notions of gravimetric capacity, volumetric capacity and specific capacity may apply to a single electrode, an element or indeed a whole battery pack. The gravimetric capacity of an electrode is an important point when choosing the components for a lithium secondary battery. 

Direct-current internal resistance and short-circuit current 

The term DC internal resistance is used to denote the sum of the real resistances (connections, electrodes, electrolyte, etc.) and the resistances due to the reaction sites. In the following sections (2.4.11 and 2.4.12), this value will be extended to the notion of AC impedance. 

Of course, in a battery, the internal resistance is proportional to the munber of elements (which must, of course, be identical) in series. 

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Most commercial lithium-ion cells maufactured today use graphitic carbons from region 1 of Fig. 2. These are of several forms, with mesocarbon microspheres and natural graphites being the most commonly used. The specific capacity of these carbons is near 350 mAh/g. 

Sony Energytec uses a disordered hard carbon of the type described in region 3 of Fig. 2. These carbons have been produced by a number of Japanese manufacturers including Kureha [41] and Mitsubishi Gas [40], Our recent work [44], and other work in the patent literature shows how such carbons can be produced from natural precursors like sugar and wood. This suggests that it should ultimately be possible to prepare such carbons very cheaply. The specific capacity of region-3 carbons which are in commercial production are around 500 mAh/g. 

Comparative calculations of specific capacities of different filters or their specific filter areas should be made as part of the evaluation. Such calculations may be performed on the basis of experimental data obtained without using basic filtration equations. In designing a new filtration unit after equipment selection, calculations should be made to determine the specific capacity or specific filtration area. Basic filtration equations may be used for this purpose, with preliminary experimental constants evaluated. These constants contain information on the specific cake resistance and the resistance of the filter medium. 

The low-concentration eluants used to separate the sample ions on the separator column allow a substantial number of samples (typically about 50) to be analysed before the suppressor column is completely exhausted. Clearly an important practical consideration is the need to minimise the frequency of regeneration of the suppressor column and, for this reason, the specific capacity of the column is made as large as possible by using resins of moderate to high cross-linking. Some instruments contain two suppressor columns in parallel,... 

Jervis used porous silica coated with chemisorbed polyacrylhydrazide for immobilization of adenosine monophosphate (AMP) [117]. After periodate oxidation of its ribose residue the ligand was coupled to the carrier and used for isolation of lactate dehydrogenase from rabbit muscle. The specific capacity was 2 mg of protein/g adsorbent with a ligand content of 10 pmol/g, whereas recovery of enzymatic activity after elution was 85%. Hipwell et al. [118] found that for effective binding of lactate dehydrogenases on AMP-o-aminoalkyl-Sepharose the spacer arm length required at least 4 methylene links. Apparently, a macromolecule of polyacrylhydrazide acts itself like an extended spacer arm and thus allow AMP to bind the enzyme. 

Main electrode features, which determine the energy density of an electrochemical storage cell, are the volumetric or specific capacity, i.e., the electric charge that electrodes can store per unit volume or weight, respectively, and the electrochemical potential they produce. Considering thermodynamic reasons, lithium, as being the most electropositive (-3.04 V vs. SHE) metal, is exceptional for use as... 

The main reaction product is carbon dioxide, but under certain conditions, other oxidation products are observed for short periods of time, such as formaldehyde, formic acid, and others. The oxidation of methanol to CO2 yields six electrons, so that the specific capacity of methanol is close to 0.84 Ah/g. 

The basic defect of film capacitors is tfieir low value of specific electrostatic capacity. Therefore, such capacitors are practically useful only in the pico- and nanofarad range. For this reason, valiant attempts have been made in recent years to increase the specific capacity of capacitors per unit of mass, volume, and plate (electrode) surface area. 

In recent years, many types of double-layer capacitors have been built with porous or extremely rough carbon electrodes. Activated carbon or materials produced by carbonization and partial activation of textile cloth can be used for these purposes. At carbon materials, the specific capacity is on the order of 10 J,F/cm of trae surface area in the region of ideal polarizability. Activated carbons have specific surface areas attaining thousands of mVg. The double-layer capacity can thus attain several tens of farads per gram of electrode material at the surfaces of such carbons. 

It follows from these data that the (theoretical) specific capacity of the active materials of such a double-layer capacitor may attain 100 F/g. This is many orders of magnitude above the values characterizing other capacitor types (film and electrolytic). For this reason such capacitors have also become known as super- or ultracapacitors. 

The supercapacitors described in the literature have an overall specific capacity of about 1 to 5 F/g (i.e., when allowing for the weight of the two electrodes, the leads, the electrolytes, and aU peripheral components). In them, electric energy can be accumulated with a density of 1 to 5 Wh/kg (which is one to two orders of mag-nimde less than in batteries). 

It was seen above that different types of electrochemical supercapacitors exhibit specific capacities many orders of magnitude higher than the film and electrolytic capacitors known before. It must be added at once, however, that the behavior of supercapacitors differs appreciably from that of ideal film capacitors. In contrast to... 

The figure illustration shows occurrence of clogging by plotting data from an observation well (OW) and compare that to the production well (PW). In this case the production well shows a decreased specific capacity while the observation well shows a steady level versus time. The only explanation is then that the resistance for water to enter the production well is increasing. The increased resistance will lower the drawdown inside the well, while the groundwater table outside the well is kept constant. This will increase the hydraulic gradient (the driving force) between the well and the aquifer and hence maintain a constant flow rate. 

LiCo02, one of the most widely used cathode materials in lithium rechargeable batteries because of its high specific capacity, has been prepared in the form of... 

Figure 1. Energy accumulated in a capacitor having specific capacity of 20 kF/kg as a function of voltage (E = Z2CU2).

It can be seen that an energy of ca. 150 kJ/kg, comparable to that accumulated in Pb02-Pb or Ni-Cd batteries, can be obtained at voltages of 4V. Somewhat lower energy (100 kJ/kg) is accumulated at a voltage of 3V. Consequently, the searched system carbon/electrolyte should be characterised by (i) specific capacity. > 160 F per gram of activated carbon and (ii) electrochemical stability window at the level of ca. >3V. 

Table 6. Specific capacities of an activated carbon (2000 m2/g) interface with 2mol/dnr solution of EMImPFf, in cyclic carbonates f12/...

Capacitors made of high-surface carbon with PVdF-co-HFP as a binder and filled with neat ionic liquids, without any molecular solvent, show high specific capacity, up to 180 F/g [13],... 

Table 7. Specific capacities of activated carbon interface with ionic liquids f 3]...

Anode EMF, V Specific capacity, Ah/g Specific energy, Wh/g Energy density, kWh/1... 

Lithium-Ion cell, graphite, specific capacity, irreversible capacity. 

The characteristics of a carbon material used as active reagent of the negative electrode (anode) of a Lithium-Ion cell considerably influence the power characteristics of the cell as a whole. Thus, the major parameters are the values of specific capacity per unit weight and volume, and also the... 

The raw material for the synthesis was methane. Powder of Nickel carbonyl (NC) or powder of nano-diamond (ND) was the catalyst. Attempts to synthesize pyro-carbon on copper powder were not successful. Powder with the composition 70%PC, 30%NC, and also the set of powders with various ratios of PC and ND were tested. Anodes made of the powder 70PC30NC showed satisfactory cycle behavior and had specific capacity 180 mAh/(g of powder) (260 mA-h/(g 0f carbon)) (Fig. 3a). The anodes made of powder xPCyND, irrespective of the components ratio, had specific capacity... 

The influence of the charge-discharge current density on the specific capacity properties of the electrodes is depicted in Fig. 3. One can conclude that even at a 0.2 mA/cm2 current density the potentialities of the material are not developed fully. Further increasing the cycling current density up to... 

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