Thursday, September 15, 2011

Aquion Raises $30 Million for Sodium-Based Battery

Aquion Energy, Inc., a developer and manufacturer of batteries and energy storage systems, closed a $30 million round of venture financing. Foundation Capital led the round with participation from returning investor Kleiner Perkins Caufield & Byers as well as new investors Advanced Technology Ventures (ATV) and TriplePoint Capital.

Aquion Energy, Inc. is a Pittsburgh-based company that is designing and manufacturing a revolutionary type of battery based on the research of Carnegie Mellon University Professor Jay Whitacre, who has developed a novel, sodium-ion, aqueous electrolyte battery (Whitacre is now the chief technology officer at Aquion).

Whitacre's U.S. patent filing gives some background into why it's an attractive energy storage solution.

Small renewable energy harvesting and power generation technologies (such as solar arrays, wind turbines, micro sterling engines, and solid oxide fuel cells) are proliferating, and there is a commensurate strong need for intermediate size secondary (rechargeable) energy storage capability. Batteries for these stationary applications typically store between 1 and 50 kWh of energy (depending on the application) and have historically been based on the lead-acid (Pb-acid) chemistry. Banks of deep-cycle lead-acid cells are assembled at points of distributed power generation and are known to last 1 to 10 years depending on the typical duty cycle.

While these cells function well enough to support this application, there are a number of problems associated with their use, including: heavy use of environmentally unclean lead and acids (it is estimated that the Pb-acid technology is responsible for the release of over 100,000 tons of Pb into the environment each year in the US alone), significant degradation of performance if held at intermediate state of charge or routinely cycled to deep levels of discharge, a need for routine servicing to maintain performance, and the implementation of a requisite recycling program. There is a strong desire to replace the Pb-acid chemistry as used by the automotive industry. Unfortunately the economics of alternative battery chemistries has made this a very unappealing option to date.

Despite all of the recent advances in battery technologies, there are still no low-cost, clean alternates to the Pb-acid chemistry. This is due in large part to the fact that Pb-acid batteries are remarkably inexpensive compared to other chemistries (<$200/kWh), and there is currently a focus on developing higher-energy systems for transportation applications (which are inherently significantly more expensive than Pb-acid batteries).

The Aquion sodium battery works like this:

The charge/discharge processes of the battery is based the transfer of sodium (Na) cations between the active cathode electrode material and the anode electrode, with a Na cation containing electrolyte acting primarily as an ionic conductor between the two electrodes. That is, the cation concentration in the electrolyte stays relatively constant through a charge/discharge cycle. As the system is charged, cations in the electrolyte solution are adsorbed onto the surface of the anode material. At the same time, cations deintercalate from the active cathode material, thus keeping cation electrolyte concentration roughly constant through the charging process. Conversely, as the system is discharged, cations in the electrolyte solution intercalate into the active cathode material. At the same time, cations desorb from the surface of the anode material, thus keeping cation electrolyte concentration roughly constant through the discharge process.

The patent goes on to describe the unique approach that's embodied in the Aquion sodium battery:

The highly-purified solvent-based non-aqueous electrolytes that must be used in energy storage devices, such as batteries, supercapacitors, or hybrid-energy storage systems, is a source of expense. Highly purified solvent-based non-aqueous electrolytes are typically necessary in Li-based systems because Li-ion systems are designed to have a relatively high operating potential, typically between about 3.3 and 4.2 V. Such high operating potentials are problematic for aqueous systems because water is electrolyzed at -1.3 V, so non-aqueous (i.e., solvent-based) electrolytes that are stable to >4 V are needed. This results in several undesirable consequences. First, the conductivity of these solvent-based electrolytes is much lower than water-based electrolytes, so Li-ion batteries are either significantly rate limited, or must be fabricated in such a way that they have very thin porous electrodes. Usually the latter design is selected despite being a much more complicated design with high surface area current collectors, very thin roll-coated electrodes, and a large-area polymer separator. Much of the cost associated with state of the art Li-ion batteries is a result of this design paradigm. Second, the cost of handling and fabrication is elevated since a moisture-free environment must be maintained during battery assembly. Third, a controlled moisture-free fabrication environment is required, which also increases cost and complexity.

In contrast, embodiments of the present invention provide a secondary (rechargeable) energy storage system which uses a water-based (aqueous) electrolyte, such as a Na-based aqueous electrolyte. This allows for use of much thicker electrodes, much less expensive separator and current collector materials, and benign and more environmentally friendly materials for electrodes and electrolyte salts. Additionally, energy storage systems of embodiments of the present invention can be assembled in an open-air environment, resulting in a significantly lower cost of production.

Secondary (rechargeable) energy storage systems of embodiments of the present invention comprise an anode (i.e., negative) electrode, an anode side current collector, a cathode (i.e., positive) electrode, a cathode side current collector, a separator, and a Na-ion containing aqueous electrolyte. Any material capable of reversible intercalation/deintercalation of Na-ions may be used as an active cathode material. Any material capable of reversible adsorption/desorption of Na-ions and can function together with such an active cathode material and an appropriate electrolyte solution may be used as an anode material.

Aquion says that its unique technologies and products provide "compelling" results on key performance factors including cycle/calendar life, round trip efficiency, discharge abuse tolerance, capital costs, maintenance costs, and safety. In addition, Aquion batteries are inherently green and contain no hazardous materials, corrosive acids or noxious fumes.

“Energy storage applications, particularly at grid-scale, provide enormous market opportunities for companies with truly enabling solutions,” said Steve Vassallo of Foundation Capital. “We see Aquion’s novel energy storage technology as a game-changer in several key markets and are delighted to be part of their world-class team.”

“The Aquion team is committed to changing the way the world uses energy by delivering safe, reliable, and economical energy storage solutions,” said Scott Pearson, Aquion’s CEO. “We are very excited about our new investment partners and the assistance, both financial and operational, they can provide the company as we launch our first products and begin to scale the company globally”.

In the fall of 2011 Aquion will begin shipping its first pre-production energy storage systems to external testing facilities and selected strategic partners. In addition, Aquion is currently in the process of identifying and selecting an appropriate site for its first high volume factory in the United States. This manufacturing facility is expected to become operational in 2013 and create more than 500 jobs across a wide range of employment categories.

Coincident with this financing, Steve Vassallo of Foundation Capital and Bill Wiberg of ATV have joined the Aquion board of directors. Prior to this round, Aquion had been supported with funding from Kleiner Perkins Caufield & Byers and the U.S. Department of Energy.

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