Posted by : Vanya Smythe in Lithium Iron Phosphate (LiFePo4), Nickel Cadmium (NiCd) 8 years ago
A comparison of Lithium Iron Phosphate (LiFePO4) with Nickel Cadmium (NiCd) batteries
- LiFePO4 batteries are very stable and safe, emit no flammable or toxic gasses, and contain no toxic or hazardous materials.
- LiFePO4 safe technology will not catch fire or explode with overcharging - they do not produce any flammable gasses under any circumstances
- LiFePO4 have almost twice the energy density than NiCad
- LiFePO4 weigh about one third to half of the weight of a NiCad battery of equivalent power
- 1000 to 5000 discharge cycles compared with the cycles from NiCad cells.
- LiFePO4 have relatively low self-discharge; less than half that of NiCad. Left uncharged, LiFePO4 cells can retain their charge for up to ten years.
- Higher cell voltage of LiFePO4 (3.6V) means fewer cells and associated connections and electronics are needed for high voltage batteries. One LiFePO4 cell can replace three NiCad or NiMH cells, which have a cell voltage of only 1.2 V. (110V NiCad = 87 to 91 links, LiFePO4 will have 33 or 34 links)
- LiFePO4 contain no liquid electrolyte which means they are immune from leaking. NiCad contain liquid potassium hydroxide which, if leaked, is extremely corrosive and so toxic it is fatal if ingested.
- NiCad cells contain cadmium which is a known carcinogen
- In higher discharge rate applications LiFePO4 can produce double the usable capacity of similarly rated NiCad batteries.
- Flat voltage discharge curve means maximum power available until fully discharged (no "voltage sag" as with NiCad batteries)
- LiFePO4 cells can deliver a very high discharge rate, 10C continuous, 20C pulse discharge
- LiFePO4 accept much higher charge rates - up to 3C = much faster recharging possibilities
- Unlike NiCad batteries, LiFePO4 can be left in a deep discharged state for extended periods without causing permanent reduction of battery capacity.
- LiFePO4 do not suffer from "thermal runaway"
- Can be used safely in high ambient temperatures, up to 65 oC without significant performance degradation. NiCad can only operate reliably at up to 35 to 40oC.
- LiFePO4 are 100% maintenance-free for the life of the battery. NiCad must be maintained (electrolyte checked and topped up) at least once every year, some NiCad manufacturers recommend maintenance once every six months.
- LiFePO4 can be operated in any orientation, including inverted
- LiFePO4 do not contain any toxic heavy metals such as lead, cadmium, nor any corrosive acids or alkalis.
- LiFePO4 batteries are the most environmentally friendly battery chemistry available today.
Phosphate based technology possesses superior thermal and chemical stability which provides better safety characteristics than those of lithium-ion technology made with other cathode materials. Lithium phosphate cells are incombustible in the event of mishandling during charge or discharge, they are more stable under overcharge or short circuit conditions and they can withstand high temperatures without decomposing. When abuse does occur, the phosphate based cathode material will not burn and is not prone to thermal runaway. Phosphate chemistry also offers a longer cycle life.
Recent developments have produced a range of new environmentally friendly cathode active materials based on lithinated transition metal phosphates for lithium-ion applications.
Doping with transition metals changes the nature of the active materials and enables the internal impedance of the cell to be reduced.
The operating performance of the cell can also be "tuned" by changing the identity of the transition metal. This allows the voltage as well as the specific capacity of these active materials to be regulated. Cell voltages in the range 2.1 to 5 Volts are possible.
Phosphates significantly reduce the drawbacks of the cobalt chemistry, particularly the cost, safety and environmental characteristics. Once more the trade off is a reduction of 14% in energy density, but higher energy variants are being explored.
Due to the superior safety characteristics of phosphate cells, batteries may be designed using larger cells and potentially with a reduced reliance upon additional safety devices.Share on Twitter Share on Facebook