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Battery Solutions for Energy Harvesting

By admin July 28, 2012

THINERGY MEC201

Rechargeable batteries ‒ known as “secondary” cells to differentiate them from “primary” or single-use cells ‒ are usually specified for this task. (For more details and explanation about storage battery performance metrics consult the Energy Harvesting TechZone article, Understanding Storage Battery Specifications for Energy Harvesting.)

Nickel-cadmium (NiCd) batteries have enjoyed the longest market run among secondary cells for portable electronics, resulting in a mature technology with low cost. For example, the latest NiCd batteries have very low internal resistance, rivaling that of standard alkaline batteries. Terminal voltage changes very slowly as the cell is discharged and NiCd cells do not deteriorate after long periods spent fully discharged. A common NiCd cell size is AA.

NiMH offers high discharge rate with low terminal voltage droop for relatively high depth of discharge. Energy density can be up to twice that of NiCd cells.

NiMH cells experience self-discharge rates similar to NiCd; some so-called hybrid cells incorporate a thicker electrode separator to reduce the effect.

Li-Po cells improve power output for a given weight compared to standard Li-ion cells. The electrolyte is solid state.

Solid-state EnerChip thin-film storage cells are also available as individual cells in standard IC packages. The rated capacity is 50 µAh at 2 C discharge rate. Figure 4: Cymbet 859-1009-1-ND 50-µAh 4.2-V thin-film cell.

Conventional batteries with a liquid electrolyte can freeze and even burst their battery cases. As the temperature reduces, internal cell resistance increases.

source : http://www.digikey.com/us/en/techzone/energy-harvesting/resources/articles/storage-battery-solutions.html