Ultracapacitors, or to be technically correct, electronic double layer capacitors, form a subset of the general category of electrochemical energy storage devices, in particular, that of electrochemical capacitors (ECs). This chapter introduces electrochemical energy storage devices including electrochemical couples or batteries.

The evolution of symmetric electrochemical capacitor (EC) specific energy has been incremental over the past 30 years, mainly because of the limits on cell potential by the available electrolytes and purity of activated carbon. Referring to Figure 3.1 it is evident that cell energy tracks closely to cell potential, which for organic electrolytes has trended from 2.3 to 2.7 V at present. This averages to 20 mV/year in cell potential and clearly revolutionary change in cell potential will not happen to this class of ultracapacitor other than what available materials can provide. It is anticipated that cell potential will increase to 2.85 V, perhaps 3.0 V or even 3.1 V at most, for high quality activated carbon. For example, Panasonic commercialized the power ultracapacitor in the mid-1980s rated 470 F, 2.3 V, and 3.9 mΩ, the increase in performance has been incremental with cell voltage increase to 2.5 V in 1999 and to 2.7 V by 2006. Power evolution, on the other hand, has been more dramatic and is projected to continue increasing with improvements in materials, manufacturing process, and cell potential gains. One projection is that specific power of ultracapacitors will reach 20 kW/kg by 2015.

The industrial application of energy storage is a very broad topical area that cannot be adequately treated in a short chapter. To convey the scope of such a diverse range of applications, this chapter focuses on just three representative industrial areas: (1) material handling trucks such as forklifts and front end loaders, (2) cranes and hoists such as the rubber tired gantry crane used for container loading and unloading in shipyards, and (3) earth moving equipment such as excavators and drag lines.

Ultracapacitors are now beginning to be applied in low-end hybrid electric vehicles for primarily idle-stop feature. In reality, an idle-stop system is not a true hybrid electric vehicle, rather a microhybrid, since it applies no electric torque to the vehicle-driven wheels. The PSA Peugeot Citroen system consists of a Valeo iStARS (integrated Starter-Alternator Reversible System) that provides engine stop-start function by way of the alternator belt. The iStARS delivers, on its own, a 15% fuel consumption reduction on the New European Driving Cycle (NEDC) when integrated into 1.4 and 1.6 L HDi diesels. The market appears to be approximately 1 million such units by 2012. This microhybrid represents two industry, a belt-driven system for a diesel and ultracapacitor for energy storage.

Possibly one of the most important innovations in electrically variable transmissions (EVTs) has been the introduction of the electric 2-mode by General Motors Allison for application in transit buses. This innovation went on to become the hybrid technology vehicle of choice in the General Motors-DaimlerChrysler BMW Hybrid Development Center collaboration during the era 2004-2008. A major advantage of the 2-mode is the uniform rating of the two electric machines needed to implement the electric variator function is shown in the chapter.

The chapter focuses on ultracapacitor abuse. But what exactly constitutes abuse conditions? The answer is one or a combination of the following factors: voltage, temperature, vibration, shock, extreme current, such as short circuit, and reverse polarity. Clinton Winchester of Naval Surface Warfare Center (NSWC) Caderock division, Maryland, presented results of ultracapacitor cell overvoltage and overtemperature abuse testing performed for the application of these cells in Navy equipment. This reference on abuse testing is an excellent introduction to the topic because it illustrates the response these cells have to abuse. The abuse testing presented was prefaced by proper preparation of the test cells, in this case Maxwell Technologies 3000 F ultracapacitors. First, the cell is wrapped with thermal tape and thermocouples are installed on center of cell and at terminal posts. Second, the cell is covered with insulation to obtain near adiabatic conditions, and lastly, the cell is connected to laboratory instrumentation. After this, the testing begins and electrical and thermal responses are measured and logged using data acquisition equipment.