High-density Energy Storage: Better Batteries through Simulation
|The figure shows the different ways lithium (Li) might diffuse between sites in the structure. The calculations revealed that the rate-limiting step for Li diffusion in this case becomes Li migrating from the Li2 site to Li3 site, because Li can easily go between Li3 sites using the path labeled as the ‘inside’ mechanism. This figure was generated by Charles Moore using data from calculations run at TACC.|
Most of our world is concerned with the organic chemistry of sustaining our lives. But most of the Earth — in fact most of the universe — is made up of inorganic materials formed by geological or cosmological processes. Despite their variety, all inorganic materials are composed of a not-so-terribly-large number of inorganic compounds: 50,000 to 200,000 depending on how you count. People have been studying these materials for millennia, but less than one percent of these have had their properties explored.
Gerbrand Ceder, professor of materials science and engineering at the Massachusetts Institute of Technology (MIT), aims to change that. You don’t want to calculate the elastic quotient of 50,000 materials in your head, but it’s not impossible for the world’s most powerful supercomputers, Ceder says. He estimates that the Ranger supercomputer at the Texas Advanced Computing Center could calculate a given property for all known compounds in 80 hours, and Ranger is just one of a pantheon of powerful systems in the U.S.
A new day is dawning in materials science, an interdisciplinary field that investigates the relationship between the structure of materials at atomic or molecular scales and their bulk properties. Thanks to the enormous advanced computing resources funded by the Department of Energy (DOE) and the National Science Foundation (NSF), discoveries are now only a simulation away.
Ceder and his research team’s computer-based investigations into new forms of lithium ion interfaces recently led to the discovery of a novel high-density cathode material with improved characteristics, as well as insights into the pathways by which lithium and other elements cycle through batteries. The findings were reported in the Journal of The Electrochemical Society in March 2012.
“The nice thing about computations is that they tell you what may be possible,” Ceder said. “Having it available really helps you organize your work and thinking.”
Ceder hopes this incredible rate of discovery and rapid prototyping will lead to swift advances in the areas that matter most to people, among them sustainable energy production. Breakthroughs in energy density are required if the nation is to achieve large-scale acceptability of electric cars. To stabilize the country’s electric power grid using batteries would require materials that can run for decades — a far cry from today’s technologies.
In their paper, Ceder and his team describe the creation of Li9M3(P2O7)3(PO4)2 or lithium pyrophosphate — a new material that never existed before — by means of artificial intelligence calculations performed on local clusters at MIT. The algorithm alters existing materials to produce new structures that are stable and display new and improved attributes.
“I’ve been in this field for 20 years, and I never would have dreamed of this material,” Ceder said. “But the computer came up with it all of its own.”
They then turned to the Ranger supercomputer at TACC, a system supported by the National Science Foundation, to perform diffusion calculations for the new material. The simulations on Ranger led the scientists to understand why the material worked better than its less-complex relatives, and how it can be improved further.
The researchers then synthesized and tested the material in the lab. It produced excellent energy density (the amount of power stored in a given system per unit volume), matching the simulations.
“The TACC resources helped us to evaluate lithium diffusivity in our predicted (and subsequently experimentally-realized) Li9V3(P2O7)3(PO4)2 material for use as battery cathodes,” said Anubhav Jain, co-author of the paper and discoverer of the new compound.
“These calculations clarified that lithium diffusion in this material probably does not occur down 1D channels, as it might first appear from visual inspection. Rather, almost all diffusion is expected to be 2D within lithium layers. Future efforts to improve diffusion in this material might focus on tuning layer spacing as was previously realized for layered metal oxides,” he said.
In the past, it took an average of 18 years from the discovery of a new material to its commercialization, “an excruciating amount of time,” Ceder said. Rapid computational search and exploration has changed all that. In the last 18 months, the start-up company Ceder co-founded, Pellion Technologies, has patented more insertion cathodes for experimental magnesium batteries than have been invented for lithium ion batteries in the last 25 years.
Ceder is attempting to bring these tools and results to the public. As one of the leads on the DOE-funded Materials Project, he uses high-throughput methods to predict properties that are important to industry for all known materials.
“Nobody wants to make a scientific career filling in missing data, but it is enormously useful as people go and design materials,” Ceder said. “It’s often this basic information that they need.”
The road from a predicted material to a breakthrough product is still long and winding, but Ceder is absolutely ebullient about the prospect of facing these challenges.
“It’s so exciting that we can actually design materials in a computer and go and make them,” Ceder said. “For a lot of fields of engineering, that seems so obvious: you can design a building and build it. But in materials science, that has almost never been done. We’re entering an era of designer materials. I set up my career with that goal, and we really are in that era now.”