Overcharge current

The cathode materials employed for the early lithium-based systems were 3.0 V class oxides or sulfides thus, the redox potential for the additive should be located in the neighborhood of 3.2—3.5 V. Accordingly, the first generation redox additive proposed by Abraham et al. was based on the iodine/ iodide couple, which could be oxidatively activated at the cathode surface at 3.20 V and then reduced at the lithium surface. " " " 2° For most of the ether-based solvents such as THF or DME that were used at the time, the oxidation potential of iodide or triiodide occurred below that of their major decompositions, while the high diffusion coefficients of both iodine and iodide in these electrolyte systems ( 3 x 10 cm s ) offered rapid kinetics to shuttle the overcharge current. Similarly, bromides were also proposed.Flowever, this class of halide-based additives were deemed impractical due to the volatility and reactivity of their oxidized forms (halogen). 

The second method uses a real accumulator the battery container shall be equipped with a battery made up of cells of the number, type and capacity it is intended to contain in service. An overcharging current shall be passed through the battery to produce hydrogen at a constant flow corresponding to the number, size, type of construction and capacity of the cells in the battery. The overcharging current is determined by... 

Fig. 9.14. Relative distribution of overcharge current as a function of VRLA saturation level between H2 evolution/H20 decomposition/grid corrosion and the oxygen cycle throughout cycle-life.

The catalyst efficiency is measured by the ratio of the volume of restored (recombined) water in the plug vs. the volume of the decomposed water. Watanabe and Yonezu have determined the gas recombination efficiency of some catalyst materials as a function of the overcharge current [5]. Figure 14.2 shows the obtained results. 

When the internal oxygen cycle is established, almost all the overcharging current is consumed by the internal oxygen cycle (center bar in the graph). The bar on the right corresponds to a vented battery. Internal resistance assumed as 0.8 mQ per 100 Ah of nominal... 

The overcharging current should be as low as possible to minimize hydrogen evolution and corrosion and thus water loss. 

The overcharge current must not exceed the maximum oxygen transport rate, so that all the oxygen that has been generated at the positive electrode reaches the negative electrode fast enough to be reduced. 

Note A quantity of 3 Ah that flows into the cell as an overcharging current decomposes approximately 1 cm of water from the electrolyte ... 

It should be stressed that the manufacturer s recommendations should be strictly adhered to in charging any battery. Excessive overcharge, current which is too high or too low, or the use of an inappropriate charging algorithm may result in reduced performance, reduced cycle life and potential safety hazards. Use only a charger specifically designed for the nickel-zinc battery. 

Oval cells are available at a rated capacity at the 1 h rate of 4 Ah at 25"C. Their continuous overcharge rate is 400 mA maximum and 200 mA minimum, and their internal resistance is 5pf2. These cells are available either as a standard cell for normal charge rates (model G04.0) or as a Goldtop cell for normal charge rates (model GO4.0ST). The rectangular cell VO-4 (model GR4.0) has a rated capacity of 4Ah at 25°C at the I h rate, maximum and minimum overcharge currents of 400 and 200 mA respectively, and an internal resistance of 4 p... 

Overcharge current The charging current flowing to the battery after all the active material has been converted into a dischargeable state. 

Standby charge A low overcharge current rate, of the order of 0.01-0.03C, applied continuously to a vented-cell batteiy to maintain its capacity in a ready-to-discharge state. Often called trickle charging-... 

Thermal runaway A condition whereby a battery on constant-potential charge at elevated temperature will destroy itself througli internal heat generation, which is caused by high overcharge currents. in constant-potential charging. 

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