Failed cells

The aimual production value of small, sealed nickel—cadmium cells is over 1.2 biUion. However, environmental considerations relating to cadmium are necessitating changes in the fabrication techniques, as well as recovery of failed cells. Battery system designers are switching to nickel —metal hydride (MH) cells for some appHcations, typically in "AA"-si2e cells, to increase capacity in the same volume and avoid the use of cadmium. 

The battery is maintenance-free and the battery housing is completely sealed by welding. In the case of the failure of one cell in a cell string, the failed cell shorts itself, which means the battery can be operated further even cell failures occur. The reason for this behavior is that in the case of cell failures the ceramic breaks and the sodium reacts with NaAlCl4 forming of a sponge of A1, which builds up in the cell between the cell case and the positive current collector. Freeze/thaw cycles have no adverse effect on the cells, and batteries will not fail by cooling down. 

Markov chains theory provides a powerful tool for modeling several important processes in electrochemistry and electrochemical engineering, including electrode kinetics, anodic deposit formation and deposit dissolution processes, electrolyzer and electrochemical reactors performance and even reliability of warning devices and repair of failed cells. The way this can be done using the elegant Markov chains theory is described in lucid manner by Professor Thomas Fahidy in a concise chapter which gives to the reader only the absolutely necessary mathematics and is rich in practical examples. 

Batteries can operate with many failed cells because such cells have a... 

Modeling Electrochemical Phenomena via Markov Chains and Processes gives an introduction to Markov Theory, then discusses applications to electrochemistry, including modeling electrode surface processes, electrolyzers, the repair of failed cells, analysis of switching-circuit operations, and other electrochemical systems... 

Subculture of suspension cells Subculture of adherent cells Rejection of failed cell cultures... 

Other defense mechanisms are also available. Cells have effective transport systems which pump out foreign chemicals. Our cells are very good at repairing chemically damaged DNA (deoxyribonucleic acid see Chapter 9 for a more detailed discussion of DNA) and even this event is not fatal. Only when the capacity for the cell to repair itself is overwhelmed does disease result. Again, dose is the determining factor. Finally, if all else fails, cells that become carcinogenic often induce an immune response to themselves and are eliminated by this route. When these mechanisms have been exhausted, or, in the case of extreme age, when they have become worn out, disease occurs. 

Here, i corresponds to the number of failed cells. The time required to reach k failed cells is now given by the time to reach state k when starting in state 0. This is known as a phase-type distribution (Neuts, 1981), but the inter-repair time distribution in this particular case is also known as a hypoexponential distribution ... 

In this paper we proposed a model for partial repair (or imperfect maintenance) based on the superposition of renewal processes. We showed how this model may he used to determine an approximate (asymptotic) proh-ahihty distribution of the time between repairs. Failed cells or components are not repaired until a predefined fraction of the total number has failed. 

The self-assembling system consists of 128 identical cells. Provided the self-repair code is still working, the system can tolerate 127 cell failures at any one time because each failed cell can copy the operating code from the one remaining cell. 

Bit map graphics Used to examine patterns of failing cells, characterize the... 

This is a key parameter, both because of the inconvenience of changing failed cells and because the overall economics of electric vehicle operation depend critically upon the maintenance costs being less than those of internal combustion engined vehicles. A battery life of at least three years is looked for. Also included under reliability are factors such as the incidence of cell failure eind the ability to cool the battery to room temperature and reheat without problems resulting from thermal expansion effects. 

The principle of tertiary containment was adopted to provide additional protection in the event of cell failure or accident damage. The carton of 44 cells is regarded, in this design, as a disposable unit which would be discarded in the event of cell failure. This design simplifies the detection of failed cells and the electrical wiring within the battery box. 

Small cracks in the ceramic electrolyte can be closed by formed salt and Al. When crack is larger, formed Al short-circuits between positive and negative electrode. This cell loses voltages, but still the whole system can be operated as long as failed cell was within 5-10 % of the total cells. The battery controller detects this and adjusts all operative parameters. In this meaning, ZEBRA battery is failure tolerant to some extent. 

Total Parallel Connection. If the total parallel option (Fig. AO.l ib) is used, then the resistance of each failed cell must be high to prevent discharge of the remaining cells in parallel. Because this condition hardly ever exists in practice, a device must be placed in series with each cell, which causes the cell to go to an open-circuit condition on cell failure. Such a device must have a very low electrical resistance prior to triggering. To date no success has been achieved with the development of such a device. 

---