Leyden Energy’s Li-imide electrolyte and the rise of start-stop vehicles

Battery start-up Leyden Energy plans to profit from the forecasted groundswell at the bottom of the electrification ladder: start-stop vehicles

The average person may see the trademarked Li-imide logo and rush to the nearest convenience store to try a tangy new soft drink. However, you, being a somewhat chemistry-savvy electric vehicle enthusiast, know that Li-imide’s likely association with lithium would make it neither delicious nor refreshing, unless of course you were a power-hungry battery for mobile electronics or EVs. 

Those are the areas that Leyden Energy has so far targeted for its patented lithium-ion-based chemistry, which utilizes a new electrolyte salt that the company developed using lithium-imide. Among other purported advantages, Li-imide’s greatest strength over legacy Li-ion is its thermal stability. 

Now, bolstered by a recent contract from the United States Advanced Battery Consortium (USABC), Leyden Energy looks to ramp up the commercialization of Li-imide for a less-publicized automotive sector: start-stop vehicles (SSVs). 

 

The company 

Born out of a patent purchased from Dupont in 2007, Fremont, California’s Leyden Energy developed that patent into its core technology, a heat-resistant, energy-dense and durable battery cell based on its Li-imide chemistry. It landed its first partnerships in the consumer electronics arena, securing deals in 2011 and 2012 with Dr. Battery, Powermat Technologies and Nvidia for tablet batteries, replacement batteries, and wirelessly chargeable batteries.  

Concurrently, Leyden was identifying a growth market in SSVs where its cells could provide an advantage over lead-acid and existing Li-ion batteries. That focus culminated this June in a $2.28 million contract from the USABC, a group comprised of Chrysler, Ford, and General Motors, to develop a 12 V start-stop battery system using Li-imide.

Mike Saft, Leyden’s Senior Director of Business Development, said that seven companies competed for the contract and he was proud that his small start-up won the first of only two contracts awarded. Of Leyden’s 55 employees, about 50 of them are scientists and engineers. “We focus on technology,” Saft said. “When Chrysler, Ford, and GM say, ‘we like your technology,’ it’s not only encouraging, but also a validation of the approach we’re taking.”

The DOE will co-fund the USABC contract, with a 50 percent cost-share by Leyden. So far, four venture capital firms have funded Leyden almost exclusively. In just the last two years, Leyden raised $30 million in Series B and C funding from these four investors: Lightspeed Venture Partners, New Enterprise Associates, Sigma Partners and Walden International. 

“We’re proud of the fact that our investors want to keep us going,” Saft said. “Batteries have been having a lot of negative press lately, and that reverberates. But our investors feel we have a good strategy and good technology; they stick with us. That’s verification as much as the USABC contract.”

 

Start-stop

In December 2011, Lux Research released a report on hybrids that included a vehicle electrification taxonomy beginning with non-electric internal combustion engines (ICE) and ending with fully electrified battery EVs. The most basic, first step to hybridizing an ICE vehicle is start-stop technology. An SSV does not idle; the ICE shuts off when the vehicle stops, and starts again seamlessly as the brake is released. While such a vehicle is stopped, the battery must power the lights, climate control, data and entertainment systems, etc. 

According to Leyden’s 2013 white paper (available on its website) basic start-stop technology alone can improve mileage by an estimated five percent, and that increases to 15 percent when “Mild hybrid” functions (including regenerative braking and part-time propulsion boost) are added. 

To help meet EU emissions standards, 40 percent of new cars sold in Europe already incorporate start-stop. In the US, however, current EPA tests don’t address the kind of urban traffic where start-stop affects mileage the most. With the EPA proposing new regulations to address that discrepancy, Lux Research forecasted a rosy outlook for SSVs in the US, where they could help reach the 54.5 mpg CAFE standards for 2025. Lux predicted 40 percent compound annual growth for US SSV sales, with 40 million SSVs projected to sell by 2017. 

That outlook meshes quite nicely with Leyden’s plans to have its commercialized Li-imide batteries in vehicles in about three years, in time for model years 2016 and 2017. Yet Leyden’s greatest leg-up for this market seems to be the shortcomings of lead-acid and existing Li-ion for start-stop applications, and the way that its Li-imide system addresses those problems. 

In the case of lead-acid batteries, the high-frequency charge and discharge cycles of start-stop conditions can wear out the battery in just a few months. Smaller, lighter-weight batteries are preferred. Existing Li-ion technology has filled the need so far, yet the heat generated by start-stop can also plague those cells. Most current Li-ion cells use LiPF6 electrolyte, which reacts with moisture left over from the manufacturing process to produce corrosive hydrofluoric acid, a process that accelerates at higher temperatures. 

 

Advantages of Li-imide

Leyden’s lithium-imide electrolyte doesn’t react with water, which grants it greater thermal stability. “It’s also safer because the salt doesn’t decompose at lower temperatures like the LiPF6 does,” Saft said. The company claims other big advantages as well, including a faster recharge rate for greater recovery from regenerative braking, and very long cycle life and calendar life. 

While Saft says the electrolyte is not tied to any specific Li-ion chemistry, Leyden has tailored its battery specifically for start-stop, which has different requirements than other vehicle energy storage applications. It utilizes an LTO/LMO (lithium titanate spinel oxide/lithium manganese oxide spinel) anode/cathode electrode. “There have been some historical problems with LTO/LMO,” Saft said, “and when we used Li-imide with them, we solved a lot of those problems. All of a sudden the LTO/LMO becomes really perfect for start-stop applications. It’s high power and has low-cost raw materials. Going to automakers, we need it to be low-cost. Titanium oxide is what they use in white paint, and LMO is the lowest-cost cathode material you can buy.”

LTO also contributes to a long life. “It’s called a zero strain material,” Saft said. “It doesn’t expand and contract like if you were using graphite. You’re not breaking up that structure every time you put in electrons.”

So far, Leyden’s safety tests indicate that the batteries can withstand nail penetration and overcharging, which has allowed them to simplify the battery management electronics. “Another advantage is that LTO/LMO can go down to zero volts,” Saft said. “With a lithium-ion discharge to zero volts, you’d kill the battery.” 

 

Challenges of production

While it’s all optimism from Leyden concerning the theoretical advantages of its Li-imide cells, the company doesn’t expect completely smooth sailing on its way to ramping up to commercial production. “We have scale-up challenges,” Saft said. “Right now we’re working with cells that are about 1 to 3 Ah, and we need to scale up to 7, 10, 20 Ah.”

For now, Leyden can produce its cells at its own pouch cell pilot manufacturing and safety/performance testing lab right at its headquarters in northern California. The facilities can build everything from the electrode slurries to the final packaging. 

Yet Leyden will remain primarily a technology developer with partners to do the manufacturing. Saft pointed to a couple of domestic companies it has allied with, to be announced in the coming year. “We’re trying to keep everything here in the States,” he said.

Besides its internal testing, Leyden’s goal is to send off cells to national labs within a year for integration with existing automotive systems and verification testing. “One of the advantages of our electrolyte is that it minimizes the need for thermal management,” Saft said. “We’ll have to verify that.”

Because every automaker likely will have its own physical and electrical solution for start-stop batteries, Leyden has another challenge of integrating with every possible combination. “Some auto makers are looking at a two-battery solution where you have a Li-ion battery which supports the auxiliary load, and maybe a lead-acid battery that does the start/stop,” Saft said. “In some architectures the lithium battery can do both. Also, this technology can fit into either a dual system with a 48 V and separate 12 V, or a single 48 V system, where you have one battery. Our battery has some flexibility to support all the OEMs’ different architectures for start/stop.”

 

This article originally appeared in Charged Issue 10 – OCT 2013