Charging/discharging currents

The value of Eff is affected by many experimental conditions other than the electrolyte and anode materials. The experimental conditions include such factors as the cell configuration, electrode orientation, electrode surface area, working electrode substrate, charge-discharge currents, charge quantity, and amount of electrolyte. 

Electrolyte = 2 mol Li 1 LiC104 -PC charge-discharge currents = 0.3 mA cm 2 cycling capacity... 

Activated carbons possess sufficient volumetric conductivity for electrolyte/collector current interchange. However, contact resistance between carbon particles in the electrode limits charge/discharge currents of the porous volumetric system and therefore EC s power capability. 

Figure 3. Dependence of the discharge capacity of the C1100+TRG electrodes on the charge-discharge current density.

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... 

FIGURE 8.37 Capacitance (open squares) and resistance (black squares) of a hybrid AC-Mn02 cell. Charge/ discharge current 40mA cm-2 between 0 and 2V. (From Brousse, T., et al., J. Power Sources, 173, 633, 2007. With permission.)... 

The studied BCAP0350 DLC has a D-cell battery shape factor which is defined in the standard with a 33 mm outside diameter and a 61.5mm length. The total external surface is about 80cm2. The production of losses inside the DLC is assumed to be uniform in the volume. In the case of a 30 A charge/discharge current the dissipated power is equal to 2.88 W. The measurements have been performed at room temperature 7 = 20°C which was constant during the experiment. The DLC is only cooled with a slowly moving airflow due to the natural convection. 

Figure 12 Cyclability capacitance vs. cycle number for EDLC using PMMA or PAN gel electrolyte (charge-discharge current 2 mA cm-2).

I = charging/discharging current t = charging/discharging time X = charges per repeating unit F = Faraday constant (26.8 Ah/mol) m = weighted mass of polymer M = molar mass of monomer unit. 

As explained before, the open-circuit potential of the battery depends on concentration, temperature, and transport limitations. The real voltage delivered by a battery in a closed circuit is affected by ohmic limitations (ohmic potential), concentration limitations (concentration overpotential), and surface limitations (surface overpotential). The close circuit potential of the cell is given by the open-circuit potential of the cell minus the drop in potential due to ohmic potential, concentration overpotential, and surface overpotential. The ohmic potential is due to the ohmic potential drop in the solution. It is mostly affected by the applied charge/discharge current of the battery. The concentration overpotential is associated with the concentration variations in the solution near the electrodes. It is strongly affected by transport properties such as electrolyte conductivity, transference number, and diffusion coefficients. Finally, the surface overpotential is due to the limited rates of the electrode reactions. 

Figure 11. Specific capacitance as a function of charge/discharge current density for MnC>2 nanowires solid squares), PEDOT nanowires hollow circles), M11O2 thin film hollow squares), and M11O2/PEDOT nanowires solid circles). Courtesy of Liu et al. Reprinted with permission from Liu and Lee. 220 Copyright 2008 American...

In this equation, I and U represent the constant charge-discharge current and the potential range corrected by ohmic drop, respectively. When constant current is used for charging and discharging processes, coulombic efficiency, 1], can be calculated as ... 

Results of charge/discharge current measurements on a liquid epoxy/polyamide resin sample in its glassy state... 

For the nonaqueous RFB systems, technical challenges still remain, including low energy efficiency, low charge-discharge current, high prices, and low active-species solubility in solvents. 

Figure 2.5 shows the evolution of the SOH of a lithium-ion device comprising two insertion materials (graphite for the negative electrode and mixed cobalt/nickel oxide for the positive electrode). Cycling was performed to a DOD of 75% for a C/5 charge/discharge current amplitude. 

This measurement method is partieularly advantageous with lithium technologies whose capacity depends very little on the charge/discharge current (see section 6.2.11.). For other technologies, we can apply coefficients on the basis of the amplitude and sign of the current. 

The nature of the carbon used as an electronic conductor may vary carbon black from different sources with particle size distributions (PSDs) of 30-40 nm and specific surface areas of 100-2,000 mVg (BET surface), activated carbons, carbon fibers or indeed carbon nanotubes (CNTs). The type of carbon, its morphology and its mode of dispersion or coating play a part in the resulting electrical properties of the electrode. For instance, carbon fibers or CNTs improve the electronic conductivity of thick electrodes, because their high shape factor enables them to form a good electronic percolation lattice.In the presence of CNTs, a capacity of 900 mAh/gs in the first cycle and 75% retention of capacity after 60 cycles (with a charge/discharge current density of 100 mA/g and 68% sulfur in the... 

The lifetime of a battery is strongly linked to the usage conditions. It depends on the number of cycles, the temperature, the state of charge, the charge/discharge current, etc. 

---