Electrolytes are one of the four fundamental components of either batteries or ultracapacitors (the anode, the cathode, the separator and the electrolyte). Electrolytes are primary contributors to the performance, safety, and operating temperature range of energy storage devices. Compared to existing organic electrolytes, ionic liquids offer the potential for increased operating temperature, increased cycle life, improved safety, and increased energy density. All of these improvements ultimately translate to lower total cost of ownership for the batteries and ultracapacitors, either because the battery or ultracapacitor is physically smaller and requires less raw materials, lasts longer, or reduces the size and complexity of the cooling system.
Boulder Ionics’ ionic liquids and ionic liquid Iolyte™ electrolytes may be used in a variety of applications and market segments, including:
Boulder Ionics’ Iolyte-U series electrolytes are optimized for use in ultracapacitors for:
- stop-start micro-hybrid vehicles
- hybrid commercial, mass transit, and consumer vehicles
- wind-turbine blade pitch control systems
- industrial applications replacing lead-acid batteries
- a range of other applications
Ultracapacitors, also known as supercapacitors and electrochemical double layer capacitors (EDLCs), store energy in a nanometers-thick layer of charge in the electrolyte next to a high-surface-area electrode. Ultracapacitors share many characteristics with batteries but can be charged and discharged much faster, with the ability to fully charge and discharge in times less than one minute. They also tend to have much longer cycle lifetime, with some units capable of hundreds of thousands or even millions of cycles. This makes ultracapacitors ideal for applications which require short bursts of very high power. An industrial example is blade pitch drives in large wind turbines. These motors adjust the tilt of the blades as the wind changes. The small angle adjustments require tremendous power for a few seconds at a time, and these adjustments can occur every minute or two, racking up millions of cycles over the life of the turbine. Batteries would fail in under a month in this application; ultracapacitors can last tens of years. In automobiles, an ultracapacitor the size of a flashlight can start the car engine; slightly larger ones can absorb ten kilowatts of regenerative braking power and deliver this back to the vehicle battery at a rate the battery can handle.
In an ultracapacitor, the energy depends on the square of the operating voltage; the wide voltage window of ionic liquids could raise the operating voltage by almost 50%, more than doubling the energy in the device. In addition, many ionic liquid electrolytes are non-flammable, while acetonitrile, the electrolyte in many current units, has a flash point of only 2 °C. By greatly increasing the energy stored, improving safety, and allowing operation at higher temperatures, ionic liquids could rapidly expand the number of applications for ultracapacitors.
Use of ionic liquid electrolytes as additives in lithium-ion batteries provides several unique advantages, which cannot be obtained in conventional organic or aqueous electrolytes. As additives, Boulder Ionics’ ionic liquid electrolytes may improve the electrochemical stability window of the electrolyte and may improve the SEI layer. As the primary component in the electrolyte, Boulder Ionic’s products may reduce flammability, increase the electrochemical window and increase operating temperature range. The characteristics are particularly appealing for use in lithium-ion batteries. Boulder Ionics’ products also offer the potential for higher cell voltage which leads directly to higher energy density.
Boulder Ionics’ Iolyte™ electrolytes and ionic liquids can be used in next generation metal-air batteries.
Beyond lithium-ion batteries lie a host of advanced battery technology just emerging from research laboratories. Among the most attractive is the field of metal-air batteries, which could offer significantly higher energy density than today’s lithium-ion batteries. By replacing the solid cathode with oxygen from the air and ion-absorbing anodes with pure zinc, sodium or lithium metal anodes, the battery could potentially shed two-thirds of its weight. Almost all of the metal-air batteries are extremely sensitive to moisture; many operate at high voltage, and all present fire hazards. It is unlikely that these promising chemistries will ever reach the marketplace without a highly hydrophobic, low vapor pressure and non-flammable electrolyte—just the properties offered by ionic liquids. In an industry that is only advancing energy density at roughly 7%/year, ionic liquid electrolytes offer the immediate promise for 20% increases in energy density, and long-term increases of 2–10X.
Boulder Ionics’ ionic liquids can be used in a variety of other commercial and R&D settings, including use in:
- fuel cells
- dye-sensitized solar cells
- petroleum refining desulfurization
- university laboratory settings for scientific testing