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Effect of BOL storage temperature on SVO cell performance.

IP.com Disclosure Number: IPCOM000076749D
Publication Date: 2005-Feb-24
Document File: 6 page(s) / 52K

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Abstract

This invention relates to the effect of BOL storage temperature on SVO cell performance (specifically self-discharge rate, BOL voltage delay, and MOL pulse voltage).

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Title:  Effect of BOL storage temperature on SVO cell performance.

Date:  2/20/03

Inventors:  Hong Gan, Joseph Lehnes, Esther Takeuchi

Field of the invention:

This invention relates to the effect of BOL storage temperature on SVO cell performance (specifically self-discharge rate, BOL voltage delay, and MOL pulse voltage).

Description of the prior art:

Due to their intrinsic high power capability, Li/SVO cells have historically been used as a primary cell for such applications as implantable cardiac defibrillators.  Cell shelf-life and storage conditions are an important issue due to the potential effect that they may have on future cell performance.  Cell deliverable capacity can be reduced by storage as self-discharge can deplete the cell life. 

Another critical parameter for these types of cells is the loaded voltage as this is directly translated into the charge time in the device.  Often the batteries are tested prior to implant to make certain that they can provide adequate charge time.  However, if the cell has been stored for an extended period of time without pulsing, voltage delay can be observed resulting in a lowered pulse voltage exhibited by the cell.

It is also thought that the method that the cell is treated by at BOL can affect the cell’s performance throughout the cell life.

The current invention describes the effect that the temperature at which cells are stored at BOL has on cell performance.  Specifically, the lower storage temperatures improve cell performance by decreasing the rate of self-discharge experienced during storage, decreasing the magnitude of the voltage delay that is observed in the cells at BOL following storage, and decreasing the magnitude of the voltage delay that is observed in the cells at MOL.

Summary of the invention:

This invention relates to using cell storage temperature as a means of affecting cell electrochemical performance.  The storage temperatures used for each group described in examples 1-3 are provided in Table 1 below:

Table 1:  Storage Temperatures of Each Group

Group

BOL Storage Temperature

A

-10°C

B

10°C

C

25°C

D

37°C

E

50°C

Example 1:

Cells were stored at various temperatures at BOL for 6 months following the acceptance pulsing (a control group was also discharged without storage for comparison’s sake).  Following storage, the cells were discharged at 37°C via APT (Subjected to a pulse train consisting of four, 3.0 A pulses, 10 seconds in length, with a 15 second rest period between pulses.  This was repeated every 30 minutes until end of life).  5 cells were tested per group.  Figure 1 displays the background voltage profiles of a single cell from each group in an overlay.  The shift of the background voltage profiles in this figure with storage temperature is indicative of the higher self-discharge experienced by the cells stored at higher temperatures.  Table 2 summarizes the capacity delivered to a 2.7 V and 2.4 V cut-off.  This data indicates that at...