Self-Discharge and Cycle Life

Secondary batteries are rechargeable. The rate of self-discharge is less critical in this case, because the battery can always be recharged before use. Cycle life, which is die 

4) According to tables of standard potentials, the open-circuit potential of this cell should be 3.58 V. Note, however, that standard potentials are given for aqueous solutions, whereas here the reaction occurs in the solid stale where the Gibbs energy of the reaction can be quite different 

5) Most of the cost is due to the extremely high reliability demanded in this kind of application. For other uses, such as memory back-up in computers, the same battery could be manufactured at a much lower cost 

---

The optimal temperature for the use of stationary batteries ranges from 20 to 30°C, although temperatures from -40 to 50°C can be tolerated. The effect of temperature on the capacity of stationary batteries at different discharge loads is shown in Fig. 23.41. High-temperature operation, however, increases self-discharge, reduces cycle life, and causes other adverse effects, as discussed in Sec. 23.8.1. 

The same configuration of the hybrid Pb02/MHj. secondary battery has been applied with gel electrolytes instead of aqueous electrolyte (cf. Sections 11.7 and 11.9.1) [56] to solve some issues on conventional batteries maintenance cost and acid stratification for the lead-acid battery, high self-discharge and short life cycles for high current discharge for nickel-metal hydride battery. In addition, gel electrolytes offer advantages such as leak proof, maintenance-free and corrosion-free. 

As with most hackup power systems, high reliability, availability, and calendar life are valued over the traditional battery attributes of long runtime and cycle life. These alternate attributes require extensive measurement and calculation capabilities in order to predict uptime and pending failures. Periodic self-imposed discharge measurement... 

From these data, the hydride cells contain approximately 30—50% more capacity than the Ni—Cd cells. The hydride cells exliibit somewhat lower high rate capabiUty and higher rates of self-discharge than nickel—cadmium cells. Life is reported to be 200—500 cycles. Though not yet in full production it has been estimated that these cells should be at a cost parity to nickel—cadmium cells on an energy basis. 

The specific energy stored and the specific power that can be delivered to the load are no doubt the crucial characteristics of a SC device along with others, such as its cycling life, self discharge current and efficiency. 

How much Conway appears to be out of touch with carbon (electrochemistry research is confirmed by his discussion of a 1972 paper by Thrower, presumably published in J Electroanal Chem anyone familiar with Peter Thrower s expertise—and that means any serious carbon researcher—knows that such a paper cannot (and does not ) exist. Finally, in the light of recent proposals regarding the edge chemistry of carbon surfaces [6], Conway s conclusion that [m]any porous or powder[ed] carbon materials have dangling surface bonds which are associated with free-radical behavior should also be viewed with caution (see Figure 5.4). Therefore, perhaps the most (and only ) reliable take-home message from this review is that much basic research of a substantive kind is required to relate the electrochemical behavior of various preparations more quantitatively to... (5) the surface chemistry of carbon preparations and their shelf-life stability, cycle life, and self-discharge characteristics. ... 

---