Supercapacitors

Roland Gallay

State of the art and technology analysis,

EDLC, pseudo-capacitors and hybrid

devices

• Specific topics such as new materials, auxiliary systems, power electronics, control systems and interaction with other technologies are of utmost interest.

State of the art and technology analysis,

EDLC, pseudo-capacitors and hybrid

devices

• Which supercap technology offer the best compromise of economy, development level, reliability, etc.?

• EDLCs don’t suffer from destructive chemical reactions, unlike hybrid on 1 electrode or batteries on 2 electrodes.

• Hybrids cumulate the disadvantage of EDLC and battery because they incorporate an electrode of each technologies

• EDLC can be cycled millions of time

• EDLC support extremely high current

• Lifetime and reliability may be improved by reducing the cell gassing and increasing the system potential windows

• Investment cost may reduced by• increasing the potential windows to increase the cell voltage (today 3 V max, tomorrow 3.25 V)• Increasing the carbon accessible surface to increase capacitance

State of the art and technology analysis,

EDLC, pseudo-capacitors and hybrid

devices

• Electronic availability to couple supercap based systems to the network as a standalone solution or with other technologies (batteries, flywheels, etc.). Are they commercially available or they are ad hoc developments?

• BMS are available to balance the voltage on the cells connected in series• Texas Instrument TIDA-00258

• Power electronic companies produce DC/DC inverters

• Lot of applications with fuel cell stack, batteries and supercapacitors in parallel.

• SCAP manufacturers are delivering either single cells or modules

State of the art and technology analysis,

EDLC, pseudo-capacitors and hybrid

devices

• Are there environmental friendly materials that make the technology attractive from the point of view of disposal and recycling?

• EDLCs with long lifetime and 1’000’000 cycles need less maintenance and replacement, consequently less recycling.

• EDLC materials:• + Aluminum, carbon, polypropylene, cellulose, • + case Propylene carbonate (PC)• - case Acetonitrile (AN) is a particular topic. Japanese manufacturer don’t want to hear

about, even if there is no evidence of an actual regulation.

• Hybrid materials:• - Pb, H2SO4, (AN?), Ni• They follow basically the rule for the corresponding battery technology they use.

State of the art and technology analysis,

EDLC, pseudo-capacitors and hybrid

devices

• How the performance and health of supercaps are assessed?• Temperature measurement is a very good indicator for the state of health characterization.

Rs increases with time and is often the limiting factor for the supercapacitor.• Charging time may give a global information about the capacitance which is decreasing• Routine tests to assess the individual performance of each cell at the end of the production

process• Tightness test on each pieces• C, Rs and current leakage measurement on each pieces

• Type tests to assess the technology at the end of the development process• DC lifetime at different temperature and different voltage• Current cycling• Leakage current measurement• Environnemental and mecanical endurance test

• The supercap measurement

Scientific and technological challenges

• Development level and TRL of voltage and current balancing systems in supercaps banks?

• There are different technologies: R, diode, active

• There are already commercial available product for R + switch• Texas Instrument TIDA-00258

• The available circuit may be used to balance the cells with a very long time scale (small current capability). They will compensate for the cell selfdischarge value dispersion.

Scientific and technological challenges

• How to improve the per cell voltage? Which novel materials offer promising characteristics for their use in electrodes, electrolytes and separation membranes? Is there a way to control the manufacture process in order to guaranty voltage distribution?

• Improve electrolyte stability window• Optimize solvent salt conductivity• Optimize min and max temperature

• Improve carbon pores surface and purity

• The voltage distribution is controlled by the cell capacitance distribution (AC) and the cell selfdischarge distribution (DC). The latter is hard to obtain without a BMS.

• 1999: 2.3Vdc, 2004: 2.5 Vdc 2010: 2.7 Vdc 2015: 2.85Vdc 2017: (3 Vdc)

Scientific and technological challenges

• Which components represent the higher scientific and technological challenges to improve current technology? What are the limitations? (Processes, design, bank integration, useful life, others?)

• At the cell level • EDLC energy density and voltage are the main limitations. • Hybrid are basically limited by the chemical reactions

• for deep cycling (< 10’000)• High power (5-10 times less than EDLC)

• At the module level the cell balancing and the cooling are the challenge.

Scientific and technological challenges

• Maximum voltage levels (per cell, per stack, total capacitance?)

• EDLC: 0 to 3 Vdc (but could theoretically do -2.7 to +2.7 Vdc in the case of a perfect symmetric construction)• Voltage derating with T, exploitation time, balancing imprecision

• Hybrid: 2.2 to 3.8 Vdc

Scientific and technological challenges

• Cost expectations (dependency?)

• EDLC: price 0.01 – 0.005 USD/F depends on:• Power of the cell• Produced quantities• Key factors: carbon, electrolyte, purity, drying• Energy isn’t a good metric for supercap, but less resistance is difficult to

sell…

• Hybrid

World experiences of supercaps in

power system

• UPS: ABB standard product• voltage stabilizers: ABB Tosa (GVA)• frequency support:• wind generators pitch control: Enercon + others• high torque start of electric machines: car manufacturers for engine

crancking• intermittences smoothing: ABB Tosa (GVA), Solar, Wind

• etc.?