More Hope Than Hype: PolyPlus Pushes Toward Lithium-Sulfur

It’s often said the “future is electric” but despite what Elon Musk may tweet, others less outspoken but just as informed don’t think lithium-ion can fully get us there, so advanced battery companies such as PolyPlus are working hard to deliver said future on time.

Actually, Tesla has conceded new technologies will eventually be required, and PolyPlus CEO and CTO Steven J. Visco said his Berkeley based company is working on perceptibly needed rechargeable lithium-sulfur and lithium-air chemistries.

“What’s happened over the past couple of years is the growing realization that lithium-ion chemistry will not take EVs to a mass adoption vehicle,” said Visco in a one-hour interview on Wednesday. “It’s just too expensive and they’re too heavy.”

The PhD chemist should know, having personally overseen 57 U.S. patents and more than 200 international patents. He co-founded the now-27-employee company in 1991 that spun out from the Lawrence Berkeley National Laboratory, and to date it has resisted venture capital funding.

While PolyPlus is pushing the edge of what’s possible, it more modestly avoids tendencies seen by some in the battery development field – who are perhaps trying to keep paying investors interested – to verge toward over-promising and under-delivering eye-popping energy density projections on the horizon.

And, unlike A123 Systems that came and went with a splash of vanishing capital, PolyPlus is a comparatively lean machine albeit with over 140 patents for its efforts.

A PolyPlus rechargeable battery.

A PolyPlus rechargeable battery.

It eschews VC money at this point as those folks like to exit their positions with profits in hand too soon for the time frame advanced battery research needs, and besides that, PolyPlus is doing alright with federal money garnered by showing itself a worthwhile bet.

Visco readily says there’s plenty of “hype” co-mingled with genuine hope in the battery development field, and he opened the interview accompanied by Business Development Manager, Tommy Conry, PhD, talking about a “BS meter.”

We’re not sure what that means, maybe BS stands for battery space?

In any event, electric vehicles promise to become part of a home-grown trillion dollar industry, and battery industry revenues have been predicted by industry executives to surpass those for the semiconductor industry by 2020.

Recognized for achievements leading toward this scenario, PolyPlus has developed ties with industry leaders, memoranda of understanding with major automakers, and supply deals now and pending with the U.S. military.

They’re keeping tabs on its progress as it races ahead in an industry not unlike others in that it’s fraught with drama – and populated with winners, losers, showmen. And then you have the quiet guys in lab coats like those at PolyPlus who might do just as much to change the world as the most charismatic twitterers.

But that’s where the comparison to the semiconductor industry ends.

No Moores Law For Batteries

Before going further, allow us to disabuse anyone who still repeats the tired spin that just because computer chips evolved with rapid and predictable progress, battery technology must likewise follow simply because people now will it so.

This reality check is shared by Visco, Altairnano VP and intellectual property acquisitions guy, Jay Akhave, and even Microsoft’s Bill Gates has made similar comments as have others who can contemplate the challenges that lie ahead.

Materials science is not subject to the same rules as information technology, says Visco, and integrated circuits are about “moving electrons,” whereas batteries are about “moving atoms.”

Of course anything could happen – and Tesla, BMW, General Motors, Nissan and others are getting started with what they have now – but those working to take us “beyond lithium ion” say it will happen at its own pace.

But, they say, it will happen.

Li-S is Next

The electric “future” is threatened to be taken over by fuel cells, and lithium-air batteries loom as another “holy grail” Visco says, but those pushing for better energy storage are wagering lithium-sulfur will be first to replace li-ion. This we’ve also seen lately with developments by the Oak Ridge National Lab, the ongoing JCESR project, and Oxis.

Without contradiction to his aversion to over-promising and under-delivering, Visco says as far as he knows, PolyPlus is the farthest ahead toward bringing to market Li-S with significant energy density improvement over li-ion.

Twenty two years ago, PolyPlus started with an ”environmentally friendly and cost-effective lithium/organosulfur battery.” It has also commercially licensed a non-aqueous electrolyte based LI-S chemistry to Sion – one of the other key players in this industry, and a military contractor – but then PolyPlus shelved Li-S for several years.

PolyPlus aqueous Li-S cell.

PolyPlus aqueous Li-S cell.

In the past two years PolyPlus has come full circle with Li-S development after being prodded into it by some un-named major battery companies which persistently asked if PolyPlus would kindly pick up where it left off.

At first Visco and crew did not think it was possible, he said. They had stopped working on Li-S after being stumped by the second of two technical hurdles: one dilemma is what’s commonly called the “polysulfide shuttle,” and the other is a problem with sulfur solubility in test cells’ electrolyte.

The first problem PolyPlus had actually solved, but the solubility conundrum had proved tough enough it call it quits.

Visco said at the behest of the well-heeled corporate suitors, the small team at PolyPlus sat back and rethought what could be done.

Since shelving Li-S they had continued development with a proprietary protected lithium electrode (PLE) which uses a ceramic membrane that passes lithium ions, but utterly isolates chemically reactive materials.

The PLE had allowed PolyPlus to develop energy dense “primary” or non-rechargeable lithium-seawater batteries for the military, deep sea exploration, off-shore drilling uses, and more.

What they realized with Li-S was they had never used water-based electrolytes, but the PLE would now allow them to try.

“It’s a little bit of a crazy idea for a number of reasons,” Visco said of introducing a water-based electrolyte, “and we all kind of said ‘yeah that probably isn’t going to work,’ but then we started thinking more deeply about it.”

So, Visco said, they gave it a stab, and were soon pleasantly surprised.

The PLE which had been instrumental in solving the “polysulfide shuttle” – essentially a chemical short circuit that takes place in a cell when polysulfides diffuse between the electrodes – turned out to be the fix for the solubility issue too.

PolyPlus protected lithium electrode (PLE).

PolyPlus protected lithium electrode (PLE).

The water-based electrolyte proved superior to previous non-aqueous electrolytes that had given very poor cycle life. This was a deal breaker for EVs or any other application which needs to recharge over and over for years.

Conry described the problems as involving “sulfur salts with very limited solubility that are both ionically and electronically insulating.” As these salts precipitate from the positive electrode the cycle life of the battery degrades rapidly.

In layman’s speak: Every attempt with non-aqueous electrolytes had ended in a prematurely worn out Li-S battery.

PolyPlus’ aqueous electrolyte increases the solubility about 3,000 times, improving the accessible capacity of the cell. It has since allowed in excess of 100 cycles, and the promise for more is projected with further refinement.

“We’re the only company in the world right now that can build a water-based lithium-sulfur cell,” said Visco, “I mean, we’re it. And we think we can take it to market, but were not ready yet.”

With the light nonetheless evident at the end of the tunnel, PolyPlus also wanted to teach itself volume manufacturing.

In June 2012 PolyPlus accepted a $9 million grant from the U.S. Energy Department’s Innovative Manufacturing Initiative to develop a custom assembly line.

Then it approached a variety of vendors and settled on a major Japanese supplier to construct from scratch the unique assembly line needed to start pilot production of its PLE intended to be used with Li-S when is ready.

In January this year, the Japanese supplier delivered the first prototype PLE membranes. Within this time, PolyPlus had also contracted with Ohara of Japan to make the ceramic membrane vital to the PLE, and after that it allied with Owens Corning which is also capable forming the ceramic membrane, and as a bonus, it is U.S. based.

By March, PolyPlus was satisfied it knew what would be needed to scale up to mass production.

And it plans to scale up, when it’s sure it’s ready.

ARPA-E Funding

Having gotten so far as to have manufactured the PLE and with a potentially viable Li-S formula in the making, in February 2013 PolyPlus accepted $4.5 million to further develop Li-S to commercial viability under the high-risk/high-potential reward federal ARPA-E program.

“We’re very excited about this,” Visco said of Li-S development to date, “its moving quickly, and we’re actually ahead of schedule on the ARPA-E program. So, all indications are that we’re on the right track to getting a commercial lithium-sulfur product out into the market place.”

The gist of the deal is, at the end of the three-year ARPA-E program, PolyPlus has agreed to deliver an aqueous Li-S prototype with 400 Wh/kg and 650 Wh/L to an external evaluator for testing and Visco said they could exceed this goal.

“Based on lab tests and projections, we think we can get to market with probably 500 Wh/kg, maybe 700 Wh/liter.

Protected lithium electrode (PLE).

Protected lithium electrode (PLE).

This would “match li-ion on a volume basis but with half the weight,” he said.

The result could be lighter weight, less-expensive EVs. Their batteries may be still pretty bulky depending on what range a manufacturer wants to accomplish, but the possibility for a more cost-effective 300-mile or longer range EV will be there.

These Li-S cells would also allow a full discharge instead of only 80 percent as is the case with li-ion, and the safety factor with Li-S goes up in a big way too.

Fire safety remains a major concern with even the most benign li-ion chemistries.

The energy to travel 200-300 miles is a lot to be sitting on, Conry observed, and minimizing risk is in everyone’s best interest.

Realistic Expectations

Visco said he doubts anyone will have Li-S in a car inside of five years and possibly several years longer unless a lot more money than is presently being spent were dumped on the problem, and then only maybe.

Also note that 500 Wh/kg is about three times the energy density of the average commercially available li-ion, less than one-fifth of the theoretical capacity for Li-S of 2,700 Wh/kg, and actually, it’s not that better than the best li-ion.

Envia Systems has said it has 400 Wh/kg li-ion cells – the theoretical peak – but an inquiry to the company yielded no response, and it’s questionable what it can actually produce, though we’ve heard rumors.

Lithium-Air prototype.

Lithium-Air prototype.

So you have theory and what is believed can actually be done, and at this stage reality does not come close to theory.

Speaking of which, Oxis has said it will be the first to commercialize Li-S pouch cells with about 200 Wh/kg, but PolyPlus is waiting until 2016 or so to deliver 2- to 2.5-times this.

In order not to trip the hype meter, the proper thing to do is submit to third party verification where they weigh a battery and measure its energy. No fudge factor can come out of this level of scrutiny.

Lithium-Seawater prototype.

Lithium-Seawater prototype.

To date, PolyPlus has delivered disposable li-air battery prototypes to the the U.S. Army which tested them to have upwards of 800 Wh/kg, and PolyPlus has demonstrated disposable lithium seawater batteries with 1,300 Wh/kg.

This is about as potent as anyone can lay claim to despite theoretical limits being much higher, thus the need for secrecy as gains are costly and not guaranteed.

Visco said it’s a lot easier to make a single-use battery, and we asked whether he could divulge specific milestones PolyPlus has set for its ARPA-E program for rechargeable Li-S, but he candidly resisted that request.

“No are you kidding? Those are highly proprietary. Believe me I’d be an idiot to do that,” he said with a laugh. “The last thing I want is Samsung and Sony and Sanyo and China, Inc. to know what our technical milestones are. Believe me it would not serve the American public well.”