Imagine arriving at a chili competition and hearing the crowd whisper, "Have you heard ... more than half the contestants didn't use chili powder this year. They used something different and the judges are wild about it."

Well, a similar whisper is now traveling through the electric vehicle battery community.

A couple weeks ago, a Colorado company,Porous Power Technologies, LLC was named to the 2010 GoingGreen Silicon Valley 100 list. Some are saying Porous Power's SYMMETRIX battery separator is the industry's new chili powder, with the potential to become a standard ingredient in EV batteries worldwide.

According to the company, batteries using the SYMMETRIX separator technology will charge up to 50% faster and last, on average, 20-25% longer than cells made with conventional separators. Additionally, the technology will enable manufacturers to assemble EV cells about 50 times faster than they are able to do today, and deliver superior performance in the cold and hot weather extremes that can kill other batteries.

EV Batteries 101
To explain the unfolding drama, let's begin with a brief explanation of battery separators. EV batteries are made up of cells.Each cell has a negative and positive plate (electrodes), with a separator in between that keeps the plates (anode and cathode) from touching each other. If the plates touch, a cell can fail, or worse, it can catch fire.

Batteries also have electrolyte, a chemical compound that conducts the electric current. The battery separator holds the electrolyte. In the case of liquid electrolyte, the separator acts similarly to a sponge holding water.

Historically, battery makers have chosen separators based on their durability during cell production and not based on their performance in the finished battery. But experts are discovering that the separator is the rate-limiting component in many lithium-ion cells. It can dramatically influence how freely the current flows through a battery, which in turn affects charging speed, battery temperature, safety, the amount of power available from the battery and how long the battery will last.

Scientists have been experimenting with various materials for all four parts—anode, cathode, electrolyte and separator—in a race to create the perfect EV battery at a price consumers will accept. Porous Power's SYMMETRIX separators appear to be a key to solving several EV battery challenges, including the prickly cost issue. As such, a number of major auto manufacturers and their battery suppliers are now testing it in their battery recipes.

All Wound Up
Today, nearly all lithium-ion batteries are made via a winding process. Manufacturers take a long strip of anode, a long strip of cathode and two long strips of separator, and then wind them together into a jelly roll. Even batteries in flat cases generally have a wound construction inside - the manufacturer simply has flattened the roll into an oblong shape to fit the case.

The wound construction has a number of drawbacks:

• Batteries generate heat during their normal operation. Even if you surround the battery with fans or other cooling devices, it is very hard to get the heat out of the center of a wound cell. This heat negatively affects a battery's performance and shortens its life.
• The separator must be strong enough to tolerate the high-speed winding process without tearing. The methods used to strengthen a separator result in more constricted ion flow, meaning less power and more waste heat (which saps the battery's life).
• Winding creates curved edges, meaning wasted space in the corners of a rectangular container. You literally are putting a round peg in a square hole. EV batteries are large to begin with and manufacturers want to make them smaller. One obvious solution is to get rid of this wasted space.
• Imagine trying to squash a section of garden hose into a perfectly flat shape. You would end up with a skinny figure-eight, pinched in the middle and wider at the ends. This same shape occurs when pinching a wound cell into a rectangular container. There will be inconsistent compression across the battery, which reduces its cycle life and power output.
• Lastly, if you fold a piece of poster board, you will notice the color flakes off at the fold, leaving a white crease. Something similar happens when bending an electrode. When a battery is in use, the electrodes expand and contract. After many charge/discharge cycles, the material tends to flake off in areas where it is bent or creased, shortening the battery's life.

For cell phones and other small applications, these drawbacks are not a big deal. For high-power applications like electric vehicles, however, the bigger battery size magnifies the impact of each drawback. Taking a cell phone battery design and simply making it larger is not a viable long-term solution for electric vehicles.

Ream vs. Roll
Scientists favor a new type of cell construction - the flat-stacked battery - which is more like a ream of paper instead of a roll of paper. In this design, instead of using continuous rolls of anode, cathode and separator material, scientists take discrete pieces and stack them into a completed cell.

The end product fits precisely into a case, with no wasted space. You get consistent, uniform pressure between the electrodes and separator. It is easier to get the electrolyte distributed more thoroughly and uniformly throughout the cell. As the cell expands and contracts through each charge/discharge cycle, the electrodes are more likely to stay intact instead of flaking. And flat cells, with their large surface area, act like cooling fins. These improvements help the battery deliver more power and last longer and are a key to widespread adoption of electric vehicles.

To date, however, flat-stacked batteries have been difficult and unacceptably expensive to produce. An electrode is like a piece of foil but thinner than what you use in the kitchen. The separator is even thinner yet and can behave like the kitchen plastic wrap you use to cover bowls, sticking to itself or wrinkling. In a cell, the electrodes and separator must be aligned very precisely, which is exceedingly difficult and time-consuming with these thin materials.

The machines currently used to create flat-stacked batteries are robotic pick and stack devices. They use optical alignment technology to precisely place each individual component on to a stack. No matter how big or small the cell is, the stacker adds one layer at a time, at an average rate just under one second per layer. A typical EV battery may have 200 layers or more (50 electrode pairs and 100 layers of separator). Building just one at this rate takes nearly 200 seconds, or over three minutes. In comparison, the same size wound cells may take 30 seconds or less to make. This is why manufacturers have stayed with the winding process, despite its drawbacks. Until now, there has not been a quick, cost-effective way to manufacture the highest-performance cell designs.

The reason automakers are so enthusiastic about SYMMETRIX is that Porous Power has introduced an entirely new manufacturing paradigm that makes flat- stacked cells more practical to produce. Known as the Matrix Assembly System™(or MAS™ production), this production process enables manufacturers to create 20 or more cell assemblies at a time, instead of one at a time, paving the way for lower-cost EV batteries.

A key part of the process involves sticking SYMMETRIX directly on to the electrodes, either by thermally laminating it or directly coating it on in liquid form. Because it stays put, it is much easier and faster to align the cell components.

Icing on the Proverbial Cake
Several major auto manufacturers and their battery companies are currently evaluating SYMMETRIX, according to Porous Power's CEO Tim Feaver, who could not divulge names due to nondisclosure agreements. I asked him what aspects of SYMMETRIX seemed to be drawing the most attention from manufacturers and he unequivocally said, "Our solution cast process."

He explains, Separator material conventionally has been sold in rolls that come from a small number of manufacturers. We, too, sell rolls for companies that are making wound cells. We also, though, are licensing our separator technology to qualified companies so they can make separators in house using our patent-pending SYMMETRIX formulation and processes.

This enables manufacturers to make as much separator as they need, when they need it, instead of being reliant on the availability of separator film from outside suppliers (and experiencing the associated supply-and-demand cost fluctuations that can occur). Manufacturers also can introduce additional ingredients and cast them into their separator films. For example, one company is experimenting with integrating various ceramic and similar components into their SYMMETRIX separators to improve temperature control and safety characteristics.

Each manufacturer can experiment with additives in-house and create a unique separator that sets them apart from their competition, using SYMMETRIX as a foundation,” says Feaver. Manufacturers like the idea of having this high level of control over this vital battery component.

Porous Power is currently seeking $5 to $10 million in investment capital, either through conventional venture sources or strategic partners, primarily to add staff to meet the burgeoning interest in the solution cast process and MAS production technique.

The company's website includes some helpful animations to illustrate how separators work, as well as technical papers describing SYMMETRIX. For more information, you can reach the company at support@porouspower.com.

Leigh Steere writes for Porous Power Technologies and several other companies. She constantly scans the horizon for game-changing technology and ideas. On Twitter at http://twitter.com/IncisiveLS.