Overcharge processes

The overcharge process is fundamentally different in VRLA batteries as compared with flooded products, and this is reflected in lifetimes and failure 

At a critical saturation level of 88 to 84% (the point will vary with design), the strength of the oxygen cycle increases dramatically. Correspondingly, the amount of 

Beyond the considerations above in the region of thermal danger , there are several other important points that can be gleaned from Fig. 9.14, as follows. 

---

From the above, it can be seen that most of the degradation factors in ESs are related to the electrolyte. Hahn et al. [91] used online mass spectrometry (differential eleetrochemical mass spectrometry, DEMS) to analyze the gas products evolved in an EDLC with AC electrodes in 1 M TEABF4/PC during the charging/ overcharging process. CO2 (m/z = 44), propene (m/z = 41), and H2(m/z = 2) were... 

In an S-Ni-Cd batter, there is recombination of the oxygen generated at the positive electrode during the overcharge process. 

Belov D, Yang M-H (2008) Investigation of the kinetic mechanism in overcharge process for Li-ion battery. Solid State Ionics 179(27-32) 1816-1821... 

No side effects during the reduction process to avoid its consumption during the overcharge process. 

Voltage-time curves of Li//liFeP04 cells during normal charge/discharge and overcharge processes (a) with 5 wt.% NPM and (b) without NPM. (Adapted from Wang, B. et al., Electrochem Commun. 10 727-730,2008.)... 

Overcharge Reactions. Water electrolysis during overcharge is an irreversible process. Oxygen forms at the positive electrode ... 

When these half-reactions are summed, there is no net reaction. Thus the material balance of the cell is not altered by overcharge. At open circuit, equation 19 at the negative electrode is the sum of a two-step process, represented by equation 15 and... 

Oxygen evolution occurs on nickel oxide electrodes throughout charge, on overcharge, and on standby. It is the anodic process in the self-discharge reaction of the positive electrode in nickel-cadmium cells. Early work in the field has been reviewed [9], No significant new work has been reported in recent years. 

Abuse tests can also be run in the laboratory if time is available. In these experiments reagents are purposely overcharged and undercharged to determine processing fate should errors be made. Experiments may also be carried out to determine the fate of similar excursions in pH, temperature, and other parameters. With suitable in-process monitoring, many of these modifications can be carried out during one or two experiments. 

Complete any appropriate abuse tests (overcharge/undercharge, pH, and temperature excursions) determined after laboratory process description was issued. Order additional materials as contingency if called for by IPC. 

Nickel batteries use P-Ni(OH)2 as electrode material. This material converts to P-NiOOH during the charging process and this rearranges to y-NiOOH when it is overcharged. This last process is accompanied by a significant expansion, because of the difference in density between P-NiOOH and y-NiOOH, which may result in poor electric contact between the current collector and P-Ni(OH)2/p-NiOOH, with concomitant decrease in the discharge capacity of the battery. Among others, layered double hydroxides of Ni and other metals, often termed stabilized a-Ni(()H), or doped Ni(0H)2, have been tested as electrode materials (Bernard et al., 1996). The effect of the interlayer anions on the electrochemical performance of layered double hydroxide electrode materials has been recently studied by Lei et al. (2008) (see Chapter 6). 

For analysing slow processes it is sufficient to consider the last reaction (29) describing the capture of a mobile ion by the overcharged complex. The equilibrium constant is given by... 

---