Cycle life test, separators

Table 7.11. Summary of cycle-life tests with hybrid separators [27]. ...

The life expectancy of a starter battery, according to DIN 43 5 39-02, is not affected by the separator. Experience has shown that all batteries with modern standard separators in cycle life tests not only last the required 5 weeks of cycling, but mostly 10 weeks or more. The cause of failure is typically positive grid corrosion - in good agreement with practice [49]. This fact supports this standard, which is supposed to reflect reality, but on an accelerated time scale. 

These segments can be tested separately or in a combined manner. All stages of development from conception to maturity and the detection of acute and delayed effects of exposure through one complete life cycle should be examined. The standard species are rodents, rats as the preferred rodent species for all study types and, the rabbit as the second nonrodent species for the embryo-toxicity studies. In some rare cases mice or monkeys are used too, if special conditions - usually kinetic data - justify such species. 

In the case of multi-ply packs some plies (particularly the foil) can be perforated but, as other plies may be continuous, leakage will not be detected by a vacuum test. However, this perforation may be sufficient to affect product life. This type of leakage may have to be detected by visual means (microscope) or by careful separation of the plies by suitable solvents. The other alternative is to subject the pack to a cycling climatic test, i.e. 15°C 50% RH and 37°C 90% RH with 12 h cycles. 

In battery cycle tests to a regular 72% DoD, the initial discharge capacities of the SWP-7 cells were 10% lower than for the AGM cell. This difference was attributed to the lower porosity of the SWP-7 separator and the attendant lower acid volume. Cells with SWP-7 separators achieved 300 cycles, but the AGM cell failed after 150 cycles (failure point 80% of initial capacity). It should be mentioned that whereas the SWP-7 cells were built with an assembly pressure of 48-58 kPa, the AGM cell used only 22 kPa and this may have contributed to its shorter cycle-life. 

There is some controversy as to the safety benefit of ceramic layers. Baba et al. [30] coated a PE separator with a Ti02/PVdF layer and made 2.4 Ah 18650-size lithium-ion cells. They found httle safety benefit in a hotbox test, but did see an improvement in cycle life. 

However it has to be conceded that after battery life cycle tests at such temperatures polyethylene separators also reach their limits, although this fact does not yet reflect in failure-mode studies [49], even in locations with extreme ambient temperatures. The tendency towards using ever-thinner backwebs cannot be continued, however, without seeking protective measures. Suitable provisions have to be made espc-... 

Several series of tests were carried out to optimize the amounts of sample and reagent, and the reaction time and temperature. Completeness of reaction was confirmed by GPC analyses. To shorten the analysis cycle time and increase the useful life of the FID, back-flushing of high-boilers was implemented. The fluorosilanes can be substantially separated by gas chromatography using two wide-bore Rtx-200 capillary columns df= 1 mm, / = 60 m, di = 0.53 mm) connected in series at 45°C isothermal. 

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