Battery Life

As very clear was shown in the recent years - the battery soft shorting and overheating problem cannot be identified at a time when battery was manufacturing. Only after prolonged cycling (usage) this phenomena may occur.

Market forces battery manufacturers to extend battery life, achieve higher energy densities and faster charging times. This will force engineers to design higher density electrode and use thinner and higher porosity separators. The fact is the energy densities are double what they were five years ago using the same materials.

The battery separator plays an important role by regulating cell kinetics, allowing ionic flow, preventing electronic contact between the two electrodes, and sometimes by acting as a safety device. Because the separator is pressed between the two electrodes and filled with electrolyte, it is in contact with all of the active cell components. By regulating electrolyte distribution, it limits ionic diffusion and recombination rates, and thereby significantly impacts cell capacity, cell power, and available energy. Consequently, much work has been carried out to determine optimal separator character- istics, such as porosity and tortuosity.1-3 Separator degradation has been often observed in certain types of batteries, and shown to be responsible for battery failure or power loss. [R Kostecki, L Norin, X Song, F McLarnon, Diagnostic Studies of Polyolefin Separators in High-Power Li-Ion Cells. Journal of The Electrochemical Society (2004) vol. 151 (4) pp. A522-A526]

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Thus, increased energy density (higher pressure on separator polymer film) and higher power (wide range of temperature inside of cell generated by applied current) and longer cycle life (> 10 years for automotive ...

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...m environments, due point -45). HTI measurements was performed in the Teflon fixture with stainless steel electrode (diameter - 12 mm) placed on the hot plate and connected with Solartron 1255B (Frequency Response Analyzer) (as above). Temperature range from 50 to 200 oC was controlled at average rate 10 oC / min. (the reason why so fast...) Li-ion cell performance (assembled with coated separator in 18650 and Al pouch cells) such as charge/discharge characteristics and cycle-ability were investigated with the Bitrode battery tester.

3. Results and Discussion

Ionic conductivity and MacMullin number data of the non-coated and coated separators are given in Table 2. As for reference Asahi (PE) and Degussa (PET/ceramic) are listed as well. Table 2 Separators ionic conductivity and MacMullin number (Nm) (electrolyte: 1M LiPF6 in EC:EMC; conductivity - 9.1 mS/cm)