Two New and Unique Energy Storage Solutions

Dean Sigler Batteries, Electric Aircraft Materials, Sustainable Aviation Leave a Comment

Lithium-ion and lithium-polymer batteries of various brands provide energy for Teslas, Leafs, and Bolts, but continue to disappoint by stalled energy density, power density, and safety concerns.  Two relative newcomers to the field might have answers to these concerns.  Unlike many other newcomers, production might be less than five years away.

Enovix Corp.

Ken Rentmeester, a good friend and retired chemical engineer, volunteers in the local TeenFlight program run by Dick VanGrunsven.  He shared his copy of the IEEE Spectrum containing an article about a new battery company that may have some answers to problems common to lithium batteries.

Stacked Deck: This cutaway view of an Enovix 3D Silicon lithium-ion rechargeable battery prototype has three stacked 1-millimeter-thick cells.

The company’s claims for their Enovix battery are impressive.  “Patented 3D cell architecture, a patented 100% silicon anode, photolithography, and wafer production increases energy density and eliminates thermal runaway.”

Thermal Runaway: The construction of a conventional Li-ion cell, adapted from magnetic-audio-recording tape production techniques, makes it susceptible to thermal runaway, which can result in catastrophic damage from explosions or fires.  llustration: Erik Vrielink

Making thermal runaway go away would make the Enovix battery a much desired energy source, especially for electric aircraft.  A recent fatal collision of a Tesla Model X with two other cars near Mountain View, California ignited a major battery fire, which after being extinguished at the scene, reignited repeatedly in the salvage yard to which the X was towed. Mountain View Fire Chief Juan Diaz told reporters that “During a thermal runaway event, temperatures can exceed over 900 degrees Fahrenheit.”’

“The battery reignited twice in the storage yard within a day of the accident and again six days later on March 29. Two weeks later, in an effort to avoid more fires, the NTSB and Tesla performed a battery draw down to fully de-energize it, Diaz wrote in [a] memo.”  This is not to denigrate Tesla’s battery technology, certainly among the finest in the world, but to show that current battery technology has some problems to resolve.

Enovix’s construction is unique, and makes thermal runaway highly unlikely.  Based on microelectromechanical systems (MEMS) fabricated in three dimensions with photolithography, the battery can be made using existing systems and techniques.  This should lower costs significantly.

Densely Packed: The 3D cell architecture orients and interlaces a cathode, 100 percent silicon anode, and ceramic separator in a thin (1 millimeter) flat plane, which significantly improves energy density and safety. Illustration: Jean-Luc Fortier

Material selection plays a part in how the battery works.  “Instead of graphite, we use silicon for the anode material. Silicon is attractive because it forms a Li22Si5 alloy. That very high ratio of lithium-to-silicon bonding allows silicon to store about 4,200 mAh/g, an extraordinary amount. But silicon’s increased absorption of lithium ions can cause it to swell by up to 400 percent.”

Enovix avoids problems with such swelling – something that has long been a deterrent to the use of silicon in batteries – with careful sizing and selection of cathode materials.  “Right now, we are using an NCA cathode, sized to match the capacity of the silicon anode. However, we can use any of the conventional Li-ion cathode materials, and that flexibility should allow us to meet the requirements of specific applications.”  The firm also makes the silicon porous, “So that expansion pushes its tiny internal cavities together rather than swelling the entire anode.”

On the basis of volume, Enovix claims its cells can pack 1.5 to 3 the energy of conventional lithium cells.  Considering the relative safety of the battery and its potential for low-cost mass production, this will be an attractive alternative for future development.

NAWA Technologies

Perhaps even more intriguing, NAWA Technologies makes their ultracapacitors in two flavors, NAWACAP Energy and NAWACAP Power.

The firm makes big claims for its NAWACAPs: “A new generation of high power and high energy density ultracapacitor (their bolding).”  The company predicts that “NAWACAP Energy will make it possible to store three to five times more energy than current ultracapacitors (15 Wh/kg today and expected to achieve 25 Wh/kg) while retaining the same power characteristics. (again, their bolding).”

Nanotubes comprise a great deal of NAWA’s ultracapacitor internal structure

NAWA says, “NAWACAP Power achieves power densities more than five times higher than existing ultracapacitors (100,000 W/Kg today and expected to achieve 500,000 W/kg).”

NAWA looks forward to developing hybrid ultracapacitor cells “With performance levels approaching those of lithium-ion batteries or even advanced lithium batteries that will surpass current lithium batteries in terms of fast charging and life cycle.”

Their nanotechnology is safe and recyclable, according to NAWA, because their ultracapacitors are made from carbon. “There is a significant difference in the way the batteries store electricity too. In a regular ultracapacitor, there is a purely electrostatic reaction, while with a lithium-ion battery there is a purely chemical reaction. NAWA Technologies’ combination of vertically aligned carbon nanotubes, a unique coating and a chemical electrolyte, allows its Ultra-Fast Carbon Batteries to sit between regular ultracapacitors and lithium-ion batteries, offering huge potential. That means higher-energy density and higher-power than regular ultracapacitors. They are also cleaner, safer, more reliable and kinder to the environment than current storage systems.”

NAWA’s website shows applications ranging from portable tools to large-scale grid energy storage, with the potential for large structures that also store energy.  This is of great interest for mobile applications.  One pdf shows potential for encapsulated ultracapacitors in various applications.    This link to the BBC shows even greater possibilities for everything from race cars to large industrial systems.

Although even ultracapacitors have lower energy density than conventional batteries, the concept of combining ultracapacitors with batteries, and then using them in a structural form, might lead to lightweight, energy-dense automotive or aircraft structures.  Certainly, the large surface area of wings, tails, fuselages and their internal components would allow using this energy storage in a way that would be lighter overall than a separate structure and energy storage system.  That such systems can provide over a million operational cycles would ensure a long life for the aircraft structure.

NAWA’s video of CEO Ulrick Grape presenting at Ecosummit London last November does show that the company is still looking for funding, a common plight among such firms.  It does remind us how dicey new developments are, however, and we might mellow our enthusiasm with a dose of economic reality.  New ideas always face this kind of resistance to progress, and we still hope for a good future for NAWA and Enovix.

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