5 ms·

I haven't seen any mention of the efficiency. Does anyone have any numbers comparing a regular battery to a graphene supercapacitor?

lutusp 14y ago
They won't know until they process this first step into a working device with conductors and all the essential elements of a real storage device. But in principle, a capacitor is a much better storage device than a battery -- no chemical conversions, no limit to charge-discharge cycles, many similar advantages.
- meaty 14y ago
  They aren't magic. They have a relatively high self-discharge (or leakage depending on how you measure it) compared to say Li-ion/NiMh cells which means basically they piss capacity away slowly. Don't expect your wonderful supercap car to actually be charged if you leave it sitting there for a few hours.
  - lutusp 14y ago
    > They have a relatively high self-discharge (or leakage depending on how you measure it) compared to say Li-ion/NiMh cells which means basically they piss capacity away slowly. Your claim is premature -- they haven't chosen an insulator yet. The graphene sheets are the conducting surfaces, not the insulating layer. Your claims are about the properties of the insulating layer between graphene sheets, which hasn't been selected yet. It looks like this: Graphene (+) --------------------------------- Insulator ------------------------------------ Graphene (-) ---------------------------------
    - meaty 14y ago
      Charge leaks through the conductors as well into the connecting circuits, through the packaging and the adhesives. No insulator doesn't leak.
      - lutusp 14y ago
        Your remark applies to any storage device, including batteries. So it's not an issue that sets supercapacitors apart.
        meaty 14y ago
        That is correct and is my point.
        lutusp 14y ago
        >> Your remark applies to any storage device, including batteries. So it's not an issue that sets supercapacitors apart. > That is correct and is my point. No, your point was that supercapacitors discharge faster than batteries because of leakage. But that's not true -- it depends on which insulating material is selected, and that hasn't been decided yet. Here is what you said: "They aren't magic. They have a relatively high self-discharge (or leakage depending on how you measure it) compared to say Li-ion/NiMh cells which means basically they piss capacity away slowly." It's false. So I said so. Any questions?
    - ableal 14y ago
      Nanoscale is fun. A measly voltage of 1 Volt across a gap of 100 nm means there's an electric field of 10 MV/m. It's kind of hard to keep electrically charged particles, such as electrons, from moving under that kind of stimulus. If memory serves, in air the disruptive voltage is 30kV/cm (or 3 MV/m) - above that one gets those sparkly electric arcs that melt metal, intentionally or not. (Other than that, air is an insulator.)
tehwalrus 14y ago
hmm, I was going to jump in with "Capacitors are never more than 50% efficient, because physics" but it seems only if you charge from nothing at a constant current: http://www.scribd.com/doc/79500452/ANALOG-SEEKrets-DC-to-Daylight#page=574 http://www.scribd.com/doc/79500452/ANALOG-SEEKrets-DC-to-Day... (filed under "today I learned")
- Dylan16807 14y ago
  You didn't know you could connect a capacitor to an inductor and let it bounce away until resistance slowly drained the power? And it's not constant current that would hurt you, it's constant voltage. Because the extra voltage bleeds away into the resistance of your components. If you had ideal components without resistance or inductance it would be impossible to actually apply a pure voltage source to a capacitor.

lutusp 14y ago

They won't know until they process this first step into a working device with conductors and all the essential elements of a real storage device. But in principle, a capacitor is a much better storage device than a battery -- no chemical conversions, no limit to charge-discharge cycles, many similar advantages.

meaty 14y ago
They aren't magic. They have a relatively high self-discharge (or leakage depending on how you measure it) compared to say Li-ion/NiMh cells which means basically they piss capacity away slowly. Don't expect your wonderful supercap car to actually be charged if you leave it sitting there for a few hours.
- lutusp 14y ago
  > They have a relatively high self-discharge (or leakage depending on how you measure it) compared to say Li-ion/NiMh cells which means basically they piss capacity away slowly. Your claim is premature -- they haven't chosen an insulator yet. The graphene sheets are the conducting surfaces, not the insulating layer. Your claims are about the properties of the insulating layer between graphene sheets, which hasn't been selected yet. It looks like this: Graphene (+) --------------------------------- Insulator ------------------------------------ Graphene (-) ---------------------------------
  - meaty 14y ago
    Charge leaks through the conductors as well into the connecting circuits, through the packaging and the adhesives. No insulator doesn't leak.
    - lutusp 14y ago
      Your remark applies to any storage device, including batteries. So it's not an issue that sets supercapacitors apart.
      - meaty 14y ago
        That is correct and is my point.
        lutusp 14y ago
        >> Your remark applies to any storage device, including batteries. So it's not an issue that sets supercapacitors apart. > That is correct and is my point. No, your point was that supercapacitors discharge faster than batteries because of leakage. But that's not true -- it depends on which insulating material is selected, and that hasn't been decided yet. Here is what you said: "They aren't magic. They have a relatively high self-discharge (or leakage depending on how you measure it) compared to say Li-ion/NiMh cells which means basically they piss capacity away slowly." It's false. So I said so. Any questions?
  - ableal 14y ago
    Nanoscale is fun. A measly voltage of 1 Volt across a gap of 100 nm means there's an electric field of 10 MV/m. It's kind of hard to keep electrically charged particles, such as electrons, from moving under that kind of stimulus. If memory serves, in air the disruptive voltage is 30kV/cm (or 3 MV/m) - above that one gets those sparkly electric arcs that melt metal, intentionally or not. (Other than that, air is an insulator.)

tehwalrus 14y ago

hmm, I was going to jump in with "Capacitors are never more than 50% efficient, because physics" but it seems only if you charge from nothing at a constant current: http://www.scribd.com/doc/79500452/ANALOG-SEEKrets-DC-to-Daylight#page=574 http://www.scribd.com/doc/79500452/ANALOG-SEEKrets-DC-to-Day... (filed under "today I learned")

Dylan16807 14y ago
You didn't know you could connect a capacitor to an inductor and let it bounce away until resistance slowly drained the power? And it's not constant current that would hurt you, it's constant voltage. Because the extra voltage bleeds away into the resistance of your components. If you had ideal components without resistance or inductance it would be impossible to actually apply a pure voltage source to a capacitor.