I’ve been taking a look at lithium-ion super capacitors as an alternative to EDLC’s. The claim is that they have a much superior “specific energy” capability. Wikipedia quotes ‘specific energy’ as 11-14 Wh/kG, but then contradicts itself with 20 Wh/kG:
“The packaged energy density of an LIC is approximately 20 Wh/kg, roughly four times higher than an EDLC ….. “
One particular Japanese manufacturer claims 37 Wh/kG for their Li-ion supercap.
Meanwhile the manufacturers of EDLC’s give the ‘energy density’ of their products as around 4-6 Wh/kG.
Let’s see the numbers:
1) A 100F/3volt EDLC supercap.
Energy stored @ 3.0v = 0.5 X 100F X 3* = 450 Joules.
Typical weight of component = 22 g.
1 Joule = 2.78 x 10-4 Wh.
Hence energy density is 450/22 = 20.45 J/g. = 20.45 X 2.78 X 10 -4 X 10 +3 = 5.685 Wh/kG
Which agrees with that quoted by the manufacturers, depending on weight (which varies slightly with each manufacturer).
2) Now the lithium-ion hybrid supercap.
A 100F/3.8 volt Li-ion Supercap
The good news: At 3.8 v, these have a higher voltage rating than EDLC’s.
The bad news: They have a lower limit of 2.2 volts, below which de-intercalation takes place and is not recoverable. Therefore only 1.6 v is usable.
Energy stored = 0.5 X 100F X (3.8*2 – 2.2*) = 480 Joules.
Hardly any different from the EDLC type. Assuming the weights are similar – there’s nothing in it. Where is the “four times higher than an EDLC”? Am I missing something?
“The packaged energy density of an LIC is approximately 20 Wh/kg, roughly four times higher than an EDLC ….. “
One particular Japanese manufacturer claims 37 Wh/kG for their Li-ion supercap.
Meanwhile the manufacturers of EDLC’s give the ‘energy density’ of their products as around 4-6 Wh/kG.
Let’s see the numbers:
1) A 100F/3volt EDLC supercap.
Energy stored @ 3.0v = 0.5 X 100F X 3* = 450 Joules.
Typical weight of component = 22 g.
1 Joule = 2.78 x 10-4 Wh.
Hence energy density is 450/22 = 20.45 J/g. = 20.45 X 2.78 X 10 -4 X 10 +3 = 5.685 Wh/kG
Which agrees with that quoted by the manufacturers, depending on weight (which varies slightly with each manufacturer).
2) Now the lithium-ion hybrid supercap.
A 100F/3.8 volt Li-ion Supercap
The good news: At 3.8 v, these have a higher voltage rating than EDLC’s.
The bad news: They have a lower limit of 2.2 volts, below which de-intercalation takes place and is not recoverable. Therefore only 1.6 v is usable.
Energy stored = 0.5 X 100F X (3.8*2 – 2.2*) = 480 Joules.
Hardly any different from the EDLC type. Assuming the weights are similar – there’s nothing in it. Where is the “four times higher than an EDLC”? Am I missing something?