Update on JCESR’s progress toward 5-5-5 battery for EV and grid applications; convergent and divergent research strategies
In 2012, the US Department of Energy (DOE) awarded $120 million over five years to establish a new Batteries and Energy Storage Hub known as the Joint Center for Energy Storage Research (JCESR). (Earlier post.) JCESR combines the R&D capabilities of five DOE national laboratories, five universities, and four private firms in an effort to achieve revolutionary advances in battery performance, with electric cars and the electricity grid as the targets. The goal is a battery five times more powerful and five times cheaper within 5 years.
At the Bay Area Battery Summit held at Berkeley Lab this week, JCESR Director George Crabtree gave an update on the Center’s progress toward the 5-5-5 battery and discussed how the Center is refining its approach now that it is almost three years into the five-year mission. (The JCESR award, based on results, is renewable one time for another 5 years.)
|Battery Technology Readiness Levels introduced by JCESR to codify the stages of battery technology development from discovery through translation to commercial prototyping. Crabtree (2015) Click to enlarge.|
Crabtree started by noting that the energy density of Li-ion batteries has increased linearly by a factor of three since their introduction in the 1970s. The density can increase another 50-100%, he said. The question, he added, is whether or not that increased density—which will hit a limit—is sufficient to “conquer” the transportation and electricity generation markets.
That’s a question we ought to think about. When you think about silicon in the semiconductor industry, gallium arsenide is way better, but we still have a silicon semiconductor industry because it keeps getting better and better and better. I think the difference [with Li-ion] is that there is a limit. It’s a question of whether you think that limit is enough for the two industries to blossom.
Almost everything you’ve tried in Li-ion has failed, and it failed not because it was a bad idea, it failed because there are a lot of side reactions in a battery that take place, and those side reactions sometimes consume the active ingredient or the electrolyte and limit the lifetime. So for a variety of reasons that have nothing to do with the quality of the original idea, most things fail. And that means you have to have backup plans.
Lots of strategic pivots are needed and we learned this lesson for JCESR for the next generation. [We need] a balance of what we call convergent—this means what I’d like to have—and divergent—which means what are my backup plans for when that convergent idea fails—[research]. I want to be able to bring something else to the table.—George Crabtree
JCESR has been pursuing three energy storage concepts for beyond Li-ion batteries: multivalent intercalation, which involves replacing singly charge lithium ions with doubly or triply charged working ions; chemical transformation; and redox flow, in which energy is stored in liquid electrodes.
Multivalent intercalation. Li ions carry a single positive charge. Replacing that with ions having two or three positive charges could increase storage capacity by a factor of two or three.
JCESR researchers conducted a computer-driven screening of 1,800 candidate multivalent host structures—the largest such systematic survey yet undertaken. This identified the most promising ions as magnesium (“the current favorite,” according to Crabtree) and calcium. Both of these have a two-plus charge. (Mg2+ and Ca2+).
The team has demonstrated that the Mg2+ ion can be inserted into and released from manganese oxide spinel cathodes. They have also identified two new electrolytes, that, while not yet good enough, are much better, Crabtree said.
Chemical transformation. Although Li-O2 batteries fall into this category, JECSR’s analysis found that storing energy in lithium-oxygen chemical bonds is less feasible than previously thought due to the cost of energy density penalty of dealing with a high-purity gaseous oxygen electrode.
We eliminated Li-oxygen from JCESR because we saw other opportunities that looked easier to do.—George Crabtree
JCESR has switched emphasis to lithium-sulfur instead, with a focus on developing a viable Li metal anode and preventing the polysulfide intermediates that form in the cathode from migrating to the anode and discharging the batteries.
The efforts have also yielded a new electrolyte that suppresses dendrite growth over thousands of cycles. Modeling has indicated that high sulfur concentration compared to the volume of electrolyte is a promising route to achieve the performance and cost targets.
Redox flow. Redox flow batteries replace crystalline electrodes with energy-dense liquids that charge and discharge as they flow through the battery. This type of battery is well-suited for grid storage applications. JCESR has developed new separator concepts for these.
For each of these approaches, Crabtree said, JCESR has to find the materials, make components out of them, and then integrate the components into proof of concept prototypes.
It’s not at all a linear process. We have our favorites and our sub-favorites. We want to continue our divergent research—those are the backup plans—all the way to the end of the 5 years because we expect that half of these will fail—maybe more than half—and we want to have something in the background to move into first place if we need it.—George Crabtree
|JCESR’s new paradigm for battery research and development, integrating discovery science, battery design, research prototyping and manufacturing collaboration in a single highly interactive organization. Crabtree (2015) Click to enlarge.|
George Crabtree (2015) “The Joint Center for Energy Storage Research: A new paradigm for battery research and development” AIP Conference Proceedings 1652, 112 doi: 10.1063/1.4916174