Learn about the rugged old NiCd and compare with NiMH and Li-ion
To compare older and newer battery systems, Cadex tested a large volume of nickel-cadmium, nickel-metal-hydride and lithium ion batteries used in portable for communication devices. Preparations included an initial charge, followed by a regime of full discharge/charge cycles at 1C. The tables show the capacity in percent, DC resistance measurement and self-discharge obtained from time to time by reading the capacity loss incurred during a 48-hour rest period. The tests were carried out on the Cadex 7000 Series battery analyzers.
In terms of life cycling, nickel-cadmium is the most enduring battery. Figure 1 illustrates the capacity, internal resistance and self-discharge of a 7.2V, 900mA pack with standard NiCd cells. Due to time constraints, the test was terminated after 2,300 cycles. The capacity remained steady; the internal resistance stayed low at 75mWand the self-discharge was stable. This battery receives a grade “A” rating for almost perfect performance.
Figure 1: Performance of standard NiCd (7.2V, 900mAh)
This battery receives an “A” rating for a stable capacity, low internal resistance and moderate self-discharge over many cycles.
Courtesy of Cadex
The ultra-high-capacity nickel-cadmium offers up to 60 percent higher specific energy compared to the standard version, however, this comes at the expense of reduced cycle life. In Figure 2 we observe a steady drop of capacity during 2,000 cycles, a slight increase in internal resistance and a rise in self-discharge after 1,000 cycles.
Figure 2: Performance of ultra-high-capacity NiCd (6V, 700mAh)
This battery offers higher specific energy than the standard version at the expense of reducedcycle life.
Courtesy of Cadex
Figure 3 examines NiMH, a battery that offers high specific energy but loses capacity after the 300-cycle mark. There is also a rapid increase in internal resistance after cycle count 700 and rise in self-discharge after 1000 cycles. The test was done on an older generation NiMH.
Figure 3: Performance of NiMH (6V, 950mAh).
This battery offers good performance at first but past 300 cycles, the capacity, internal resistance and self-discharge start to increase rapidly. Newer NiMH has better results.
Courtesy of Cadex
Figure 4 examines the capacity fade of a modern Li-ion Power Cell at a 2A, 10A 15A and 20A discharge. Stresses increase with higher load currents, and this also applies to rapid and ultra-fast charging. (See BU-401a: Ultra-fast charging of Li-ion.)
Li-ion manufacturers often do not specify the rise of internal resistance and self-discharge as a function of cycling. Advancements have been made with electrolyte additives to keep the resistance low through most of the battery life. The self-discharge of Li-ion is low and is in par with lead acid.
Figure 4: Cycle characteristics of IHR18650C by E-One Moli. (3.6V, 2,000mA). 18650 Power Cell was charged with 2A and discharged at 2, 10, 15 and 20A. The internal resistance and self-discharge are N/A.
Courtesy of E-One Moli Energy
Batteries tested in a laboratory tend to provide better results than in the field. Elements of stress in everyday use do not always transfer well into test laboratory. Aging plays a minimal role in a lab because the batteries are cycled over a period of a few months rather than the expected service life of several years. The temperature is often moderate and the batteries are charged under controlled charging condition and with approved chargers.
The load signature also plays a role, and the nickel-based batteries were discharged with a DC load. All batteries deliver a slightly lower cycle life if discharged with pulses. (See BU-501: Basics About Discharging.) If a battery must repeatedly be loaded to peak currents, it is advised to install a pack with higher Ah rating.
Last Updated 2015-08-24
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