Pedal to the metal for EV battery technology

So far, electric vehicle sales have not exactly set the world on fire. In the U.S., Nissan has to date sold 173 of its Leaf EVs, while GM has sold 928 Volts. These puny sales figures recently led a wag at the Wall Street Journal to opine that EVs were selling about as well as second-hand syringes.

One culprit catching a lot of the blame for the punk sales figures is EV batteries. They are expensive, and industry watchers feel most consumers can't live with the kind of range they deliver.

Thankfully for the auto industry, better battery technology is on the way. Improved lithium-ion-based batteries are coming to electric vehicles, and it looks as though researchers are giving both lithium-phosphate and nickel-manganese-cobalt types a more serious look.

There are about 20 established cell/battery companies and a handful of startups with a hand in the electric vehicle business. None of them has put all its eggs into the automotive basket. There's a lot of promise in marine, medical, industrial, and wind-power applications, and some of these opportunities look more lucrative than truck fleets and passenger cars. Few market reports see hybrid and EVs driving the battery market out to 2020.

Today battery technology is largely about cost and safety issues. A “mild hybrid” requires 1 to 2 kW-h-worth of battery; a plug-in hybrid needs 5 to 15, and an EV demands 20 to 30. High-end batteries for HEVs and EVs are presently estimated in the range of $700 to $800 per kilowatt hour; battery makers figure to cut that to well below $500 within two years.

Fortunately, there's no apparent availability shortage of natural materials for batteries, in contrast to rare earth elements that go into super-efficient electric motor magnets. Still, a few elements such as cobalt occasionally cycle through substantial price fluctuations and battery raw materials are not particularly environmentally friendly.

Five roads

While phosphate-based batteries are gaining more attention, each of the five major lithium-ion technologies has a following. That's because all have their own advantages and tons of intellectual property and/or manufacturing capability behind them. Most of these technologies show some strength in non-vehicle applications as well, and one is highly touted for the smart grid.

Under the lithium-ion umbrella there are two families or chemistries: lithium cobalt oxides and a number of derivatives used in phones and laptops; and the phosphate family. Lithium-titanate is also available from a few suppliers.

The major battery parameters include specific energy, specific power, overall performance, life span (includes cycle life and shelf life), cost, and safety. Lithium-iron-phosphate is among the leading choices when it comes to overall capability with respect to three of the most important parameters in automobiles: cost, safety, and lifespan. On the negative side, it's not particularly highly rated when it comes to specific energy.

“Most battery companies distinguish themselves based on the cathode chemistry,” explains Andy Chu, A123 Systems VP of Marketing. A123 employs lithium nanophosphate technology. Suppliers typically use a carbon-based anode, with the electrochemical difference between cathode and anode materials providing a nominal potential of perhaps 3.2 to 3.3 V for phosphate, and a bit higher for oxides. Four A123 batteries in series match the voltage for the typical lead-acid battery.

Use of anode materials other than carbon (e.g., lithium-titanate, often characterized as an “anode-based” technology) may well result in a lower cell voltage. That implies the cell will store less energy — energy density is often cited as an issue with lithium-titanate. Thus the designer will need more cells for a given application.

“We use a cathode based on a form of iron phosphate called nanophosphate,” says Chu. “We are the only company that uses it. Ours contains nanoscale materials developed at M.I.T. So it doesn't take much time to fill up that particle with lithium or to take lithium out. So you can have a very high rate of charge.” In addition to the high surface area and high porosity, nanophosphates are considered a “low-reactivity” material, a plus for safety.

A123's first product was in power tools, for Black & Decker. That initial success started them on a search for a battery with similar traits for automobiles. “Over the last four or five years, lithium-ion has become practical to use for vehicle applications,” says Chu. “Fifteen years ago, GM's EV1 used a NiMH battery, but it didn't have the range. Li-ion's used now are better than other battery technologies, and better than in your cell phone and laptop. Those were designed for only a few years. The new generation has much longer life, and much higher power capability for transportation and the grid.”

Nickel manganese cobalt (NMC) chemistry is also under development at Dow Kokam, a company established in 2009 and owned by The Dow Chemical Co., TK Advanced Battery LLC, and Groupe Industriel Marcel Dassault (Dassault). Its prismatic lithium-ion battery cells use the classic lithium-ion-type architecture of an anode, a cathode and a polymer separator. Dow Kokam commercial VP Chuck Reardon says the company works with NMC because of its energy density, energy/power balance, long life and good safety factors. Dow Kokam has ten years of experience building large-format NMC and is now using that experience to optimize the battery chemistry, materials and design process. The company uses a patented Z-Fold cell design optimized to deliver energy with minimal loss or thermal build-up.

Battery safety and cell life are related. Safety is also a hot button thanks to early era lithium-ion batteries and their catastrophic performance with laptop computers. In response, many cell and battery makers are migrating to lithium-phosphate (considered the safest of the “cathode chemistry” batteries). Users are also coming to understand the benefits of cycling the battery within a reasonable “state of charge” window.

“The safety issue concerns what happens when you mistreat a battery,” says Mark Shoesmith, project manager for electric vehicle cells development at E-One Moli Energy. The company is working on different batteries that use cobalt, phosphate, spinel (lithium-manganese), and mixed metal (lithium-nickel-manganese-cobalt).

“The worst case comes with high temperature exposure and trying to recharge the battery too much,” says Shoesmith. “Discharging lithium-ion batteries is not a problem as such, aside from deep-discharging, which can affect cycle life. If you try to put too much back in during charging, though, they will disable themselves. Overall, if you limit the amount of state-of-charge (SOC), the cell/battery will last longer.” In that context, automakers design their vehicles to remove just a few percent of a battery's energy during normal operation, allowing the battery to cycle many thousands of times and last as long as the rest of the car.

“There are two distinctive differences between the two types of batteries,” says Bob Kanode, CEO of Valence Technology, one of the firms working exclusively on lithium phosphate batteries. “One is safety. It's easy to have a thermal event with laptops. It's extremely difficult to have a thermal event with phosphates. The chemistry just doesn't easily allow for it.

“The second advantage is lifetime. If you are deep-discharging a battery, phosphates have a much longer life than oxides,” says Kanode. Say you get 3,000-plus cycles when you're aggressively using a phosphate. Oxides would last only 500 to 750 cycles.”

Another advantage of phosphates shows up in retained energy capacity. “After six months with a laptop, you'll notice quite a bit of diminished run time, and even more loss after a year. Phosphates deliver not only a long cycle life, but also don't fade much at all,” he says. Modern lithium-based batteries found in electric vehicles are considered to have reached their end-of-life when their maximum output falls to 70 to 80% of full energy capacity. In that context, a new industry is developing around the “reduce, reuse, and recycle” concept of using these batteries for something other than powering vehicles.

In the case of Dow Kokam NMC batteries, a water-cooled thermal management system cools the battery pack. NMC packs also incorporate a battery management system employing multiple methods to limit the charge of voltage of any cell to stay below a specified voltage range.

Wither the cost?

A cell phone battery accounts for only a small percentage of that product's cost. But that's not the case with a battery in an EV. The cathode material is the most expensive component, reportedly amounting to about one-third the total cost of the battery. Then comes the electrolyte, separators, and the anode. In some cases the separator, although not expensive in itself, is said to be a much more critical component when it comes to manufacturing the battery.

It generally costs more to make the cell than it does to put those cells in a pack that can provide 120 to 800 V, depending on the application. “Materials account for two-thirds or more of the cost of the battery,” says Andy Chu. “Modern lithium-ion batteries are made using a fairly automated process to ensure consistency. Anytime a human touches something, there are variations. Companies that are competitive have highly automated processes.”

Quality control goes beyond the cost of materials and the various binders and additives required to attach the materials to metal foils. The manufacturing environment must be clean and dry. And the process has to be repeatable; if the electrode is not uniformly thick, or there's inconsistency in the way cells are made, the resulting battery pack won't last long.

Manufacturers with phosphate-based portfolios appear to be the most optimistic about cutting expenses and boosting automation. “We're driving cost down significantly,” said Bob Kanode. “We manufacture a patented lithium-iron-magnesium phosphate and a critical cathode material. We have cut costs of that in half with that process in the short time I've been here. To our knowledge, ours is the only one-step process in the world to make cathode materials.”

Things to come

New battery technologies generally take about a decade to develop; some of the work done over the past few years is about to pay off. “This will be a decade of phosphate dominance,” says Bob Kanode. “We have patented lithium-vanadium-phosphate, which will outperform everything in lithium hands down. You will see it come out in cell form later this year, and you'll see us do our first systems next year.”

One of the big advantages will be its cell voltage, in the range of 5 to 6 V. Vanadium supplies won't be a problem, either, says Kanode, noting that the element can actually be produced from potash, a byproduct of refining petroleum.

Overall, most other industry observers see better cells (versus batteries) becoming available shortly. But they expect the gains for such parameters as cell density to be modest. On the down side, some of those advantages could well be swamped out by realities of packing cells into working batteries. “Once the cell goes into the battery, the energy density goes down because you have to add cell balancing electronics and packaging,” explains Mark Shoesmith. “Typically, in large battery packs as required for EVs you need space for cooling. So the energy density you can put into a cell is not what it seems at the vehicle level.”

Improvements in energy density will depend on pack design and the style of the cell. Manufacturers, for instance, can pack fewer cylindrical cells in a given area than flat cells. The industry's de facto standard is 18 mm in diameter by 65 mm long.

Also look for more industry help for battery development and manufacturing activity in the U.S. One recent development: The U.S. Advanced Battery Consortium recently awarded more than $5M to five companies in Texas and Calif. to assess and further develop various cathode and flat-pack technologies for HEV, PHEV, and EV designs.

In that same regard, Dow Kokam says it has surpassed the goals outlined by the USABC for energy and power density with its current technology, and is working on technologies that improve charge and discharge rates, cycle life and safety. The company wants to improve discharge rate by 50%, charge rate by 150%, and cycle life by 400%.

The case for lithium-titanate

While not particularly widely applied or hailed for electric vehicles, lithium-titanate nevertheless has made several inroads in that arena. One is the arrangement between battery maker Altairnano (Reno, Nev.) and Phoenix Motorcars (Ontario, Calif.). “Lithium-titanate cells are used by a few companies, primarily for high-power, short duration applications,” says Andy Chu. “Lithium-titanate-oxide is similar to NiMH (as for power drills), but LTO has an issue with run-time requirements. It's not going to be widely used for EVs (at least in the short term), but it might be used for certain types of HEVs. Nickel metal hydride (NiMH) doesn't even have the same power capabilities as the current lithium-ion, so you're going to see more of the HEVs changing to lithium-ion. The Prius first used NiMH, and the first HEVs used NiMH, but we think most vehicles will be moving to lithium-ion.”

Beyond that, the power industry is beginning to see lithium-titanate as a good system for the smart grid that will store energy during periods of low demand. During periods of peak demand it can be used for short-duration, fast-charging applications. It also offers promise for “load leveling” of such alternative power sources as wind and solar that can't generate a constant output.

Short-duration sources such as lithium-titanate could come in handy as more households go with EVs. But some studies now suggest that even just a few EVs could well present more of a load than local utilities could handle, at least during times of peak demand. All in all, most industry observers see more than a decade's worth of work ahead to boost grid capacity and create the power management infrastructure needed for charging autos off the grid.

“You might consider batteries (for charging EVs), but you wouldn't likely use them on the grid for that purpose unless you were really in need of fast charging,” says Andy Chu. “They might be better suited to roadside battery banks, instead of gas stations, when you need to charge cars quickly. But batteries on the grid for charging cars? That's not what people are talking about right now.”

The five principal technologies for electric cars as viewed by researchers at the Boston Consulting Group .The analysis doesn't include lithium-ion batteries for consumer products which typically use lithium-cobalt-oxide technology.

The “killer app” for lithium-ion

Battery makers see diversification well beyond HEVs/EVs as the key for surviving in the large format-lithium-ion market. “We started work with fleets for two reasons,” said Valance Technology's Bob Kanode. “First, in 2004 fleets were ready to go and so were we with a product. And we thought we could validate our technology if we did well in fleets. We really wanted to position ourselves so we were flexible. The technology was proven, manufacturing was proven, and we could easily scale to meet demands wherever the thread of lithium would go.”

But basic lithium-ion started with consumer, medical, and industrial applications, and large-format lithium-based batteries seem to be following the same path. There is still a lot of uncertainty about application areas that is forcing battery makers to keep their options open. “We don't yet know what the standards for the new lithium battery business will be,” says Kanode. “We've now moved into the marine sector, and the standards for the marine versus the automotive battery will be quite different in areas such as shock, vibration, and moisture resistance.”

Most of the companies primarily known for making cells have varying degrees of capability when it comes to integrating those cells in a battery manufacturing operation. A third-party integrator is often called in to add power-control electronics. The business model for each company often diverges significantly at the point-of-sale and is also a function of the application. In applications on the power grid, for example, the battery maker may guarantee a certain level of maintenance and overall performance for a specified time. The situation on the automotive side will likely be different, with dealers handling various vehicle warranties.

In any case, the industry direction appears to be one of horizontal expansion. “It may not be wise to watch the EV to gauge when things will mature,” says Bob Kanode. “We see major expansions in fleets and marine. By the time cars get here, there will be lots of people collaborating who have never worked together before.”