Data Sheet

AN1012 Battery technology
Doc ID 6395 Rev 4 7/33
2 Battery technology
STMicroelectronics uses both the BR1225 and the BR1632 lithium button cell batteries.
These have charge capacities of 48 mAh and 120 mAh, respectively. Their constituents
have non-toxic and non-corrosive characteristics, and are chemically and thermally stable
before, during, and after discharge. This makes these cells particularly attractive for use in
electrical components.
They contain a solid carbon cathode that is pressed into a tablet of predetermined weight
and height. The anode consists of high-purity lithium metal. The electrolyte is based on an
organic solvent instead of the corrosive alkaline or acidic solution found in most
conventional batteries. This greatly reduces the likelihood of internally-induced cell leakage,
and reduces the ill effects in cases of externally-induced cell leakage. The cell is then crimp-
sealed with a polypropylene grommet.
ST has conducted extensive tests on these cells, at temperatures up to 85 °C. Destructive
analysis was conducted (post-stress), in order to measure such factors as weight loss and
remaining charge capacity. The analysis determined that the cells were drying out, and that
the weight loss was due to electrolyte evaporation. Models were developed to predict the
nominal rate of electrolyte loss, and how this would be reduced by adding a second level of
encapsulation. This proprietary secondary seal encapsulation, adopted by ST, has been
found to provide up to a two-fold reduction of the electrolyte loss rate.
Both cells produce a nominal 2.9 V output with a flat discharge curve until the end of their
effective lives, and thus confirms that both are suitable for providing battery backup to low
leakage CMOS SRAMs (see Figure 3).
Figure 3. (A) BR1225 discharge rate and (B) BR1632 discharge rate
AI02519
0
1.0
1.5
2.0
2.5
3.0
3.5
Voltage (V)
LOAD CHARACTERISTICS Temp: 20°C
1000 2000 3000 4000 5000 6000
Duration (Hrs.)
(B)
15kΩ 30kΩ 50kΩ 100kΩ
0
1.0
1.5
2.0
2.5
3.0
3.5
Voltage (V)
LOAD CHARACTERISTICS Temp: 20°C
200 400 600 1200 1600 1800
Duration (Hrs.)
(A)
100kΩ
800 1000 1400 2000
15kΩ 30kΩ