Within one year, a lithium battery design can be qualified for device use through the application of accelerated discharge testing, calorimetry measurements, real time tests and other supplemental testing. Materials and corrosion testing verify that the battery components remain functional during expected battery life. By combining these various methods, a high reliability lithium battery can be manufactured for applications which require zero defect battery performance

Buchman, R. C.

Helgeson, W. D.

Istephanous, N. S.

English

NASA Technical Reports Server

DESIGN EVALUATION OF HIGH RELIABILITY LITHIUM BATTERIES 
Richard C. Buchman, 
William D. Helgeson 
and Naim S. Istephanous 
Energy Technology, Division of Medtronic, Inc. 
INTRODUCTION 
High reliability batteries are required not only for space 
applications but also for implantable medical devices as well. 
In this paper, I will be discussing the techniques used by 
Medtronic to evaluate high reliability lithium batteries for 
implantable applications. 
Medtronic, Inc., through its Energy Technology division, 
began manufacturing lithium batteries for implantable device 
applications in 1977 with the introduction of its lithium-iodine 
system. Manufacture of lithium-thionylchloride batteries for use 
in higher current drain applications such as implantable drug 
pumps and pain control devices began several years later. 
Because of these applications, the evaluation of each battery 
design is very important and it is performed with a high re- 
liability goal in mind. 
BACKGROUND 
Once a new battery design has been established and assembly 
procedures finalized through prototype test builds, the design 
must successfully complete a three stage evaluation program. The 
first stage, design qualification, involves a large battery build 
intended as the qualification set for the final battery design. 
Within the next year, production qualification tests begin on 
actual production batteries. Concurrent with these qualification 
programs, real time or long term discharge tests are also 
initiated. The data, along with the qualification program 
results, are then used to project battery longevity and generate 
reliability data for each battery design. By utilizing this 
evaluation sequence, a lithium battery can be verified as capable 
of meeting the high reliability requirements demanded in applica- 
tions such as space or implantable medical devices. 
TEST METHODS AND RESULTS 
The typical design qualification program consists of 
accelerated discharge tests, calorimetry measurements, environ- 
mental exposure, destructive analysis and materials compatibility 
https://ntrs.nasa.gov/search.jsp?R=19850023067 2020-03-20T17:23:53+00:00Z
and corrosion resistance testing. Accelerated discharge is per- 
formed at 37OC under various constant current conditions in large 
walk-in ovens with the batteries positioned in various orienta- 
tions. Figure l shows the voltage behavior of a lithium-iodine 
battery at current drains of 50-400uA as a function of delivered 
capacity. The data are then used to construct a mathematical 
model to project battery longevity at application rates. 
During the accelerated discharge tests, several cells from 
specific tests are periodically monitored for heat output on a 
Tronac model 315RA calorimeter. The heat output, corrected for 
polarization effects, for a lithium-iodine battery and a lithium- 
thionylchloride battery are shown in Figures 2 and 3 respec- 
tively. Assuming the heat output is self-discharge related, and 
after correcting for the entropic heat effect, the capacity loss 
can be determined and included in the longevity projection calcu- 
lations. 
Environmental exposure tests are performed on all battery 
designs to simulate worst case conditions the battery might 
experience during shipping and handling. These tests include 
subjecting batteries to various combinations of +60 and -40°C 
temperature extremes combined with mechanical shock and vibration 
testing, followed by electrical discharge. Abuse tests such as 
over-discharge, charge, short circuit and shock are also 
performed on the thionylchloride batteries to determine safety 
characteristics. Destructive analysis tests are completed to 
verify the batteries are constructed according to the design 
engineer's specifications. 
The compatibility of all battery components with the 
reactive electrode and electrolyte materials is best determined 
by accelerated and actual temperature exposures over the 
projected battery lifetime. At pre-determined time intervals, 
several batteries are removed from application rate discharge at 
60 and 37OC and the various components shown in Table 1 are 
examined for signs of corrosion and chemical degradation utiliz- 
ing scanning electron microscopy, Auger electron spectroscopy, 
X-ray spectroscopy and other metallurgical and chemical 
techniques. 
Of the indicated phenomena of interest, degradation of the 
glass in the feedthrough is important, particularly in liquid 
electrolyte systems. Figure 4 shows a scanning electron 
micrograph of a typical glass seal from a fresh battery, while 
Figure 5 shows a glass seal from a liquid electrolyte lithium 
battery from another manufacturer after approximately 3.6 years 
exposure. The exposed feedthrough shows extensive glass 
fragmentation across its entire surface. 
This phenomenon has led to premature battery failure in 
various liquid electrolyte systems. To test for this problem, 
several of my colleaques have recently developed a technique that 
examines glass degradation in a matter of weeks instead of years. 
This technique, detailed at the Fall ECS meeting in New Orleans, 
involves sputtering nickel onto glass slides, discharging them in 
the electrolyte of interest and monitoring the current during 
discharge. SEM/x-ray spectra techniques can then be used to 
characterize the reaction products. 
The last step in the design evaluation involves real time or 
long term discharge tests. The batteries required for these 
tests originate from the design qualification build and time 
samples of production battery builds. Figure 6 compares the real 
time discharge results for a lithium-iodine battery to the 
longevity projection. The real time data are tracking the 
projected curve very well, just as other lithium-iodine battery 
designs have tracked their projected curves during the past eight 
years of using this technique. We therefore believe battery 
lifetime can be reliably forecast after one year of testing 
instead of the five to ten years typically required to discharge 
the battery at the application rates. 
One method of examining the reliability of batteries at 
application rate is the calculation of the random failure rate. 
A summary of random failure rate data for three general lithium- 
iodine battery designs are indicated in Table 2. Nearly 4400 
Type A batteries on laboratory test have accumulated 230 million 
hours at a random failure rate of 0.0023%/month at a 90%. confi- 
dence level. With this low rate, this battery design is exhib- 
iting a reliability comparable to silicon transistors and diodes. 
Type B and C batteries are also accumulating significant device 
hours with similar low random failure rates. 
CONCLUSIONS 
Within one year, a lithium battery design can be qualified 
for device use through the application of accelerated discharge 
testing, calorimetry measurements, real time tests and other 
supplemental testing. Materials and corrosion testing verify 
that the battery components remain functional during expected 
battery life. By combining these various methods, a high 
reliability lithium battery can be manufactured for applications 
which require zero defect battery performance. 
Table 1. MATERIALS AND COMPONENTS PERFORMANCE ASSESSMENT 
COMPONENT PHENOMENA OF INTEREST 
METALLIC 
NON-METALLIC 
FEEDTHROUGH 
WELD JOINTS 
CORROSION - TYPE AND EXTENT (IF ANY) 
CHEMICAL STABILITY AND STRUCTURAL 
INTEGRITY, INSULATION PROPERTIES 
GLASS DEGRADATION 
SEAL HERMETICITY 
LOCALIZED CORROSION 
INTEGRITY 
PENETRATION AND FUSION 
Table 2. RANDOM FAILURE RATES FOR LITHIUM IODINE BATTERIES 
INITIAL MAX. DEVICE- RANDOM FAILURE 
BATTERY SAMPLE YEARS HOURS RATE (%/MO.) 
-- 
-- -- 
TYPE A 4350 8.9 230x1 O6 0.0023 * 
TYPE 6 1887 5.9 84x106 0.0034 
TYPE C 1355 5.4 37x106 0.0045 
SILICON TRANSISTORS 
SILICON DIODES 
*LOWEST RFR PRIOR 1 O NATURAL END-OF-LIFE. 



Figure 4. Glass Seal From Fresh Battery 
Figure 5. Glass Seal After Exposure to Liquid Electrolyte 
I ,REAL TIME 
0 I I I I I I I I I 1 
0.0. .25 .50 .75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 
DELIVERED CAPACITY (AH) 
Figure 6 - Realtime Discharge Resul t s  For a Lithium Iodine Battery.  


Design Evaluation of High Reliability Lithium Batteries

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