lithium-ion batteries

Science and the scientist

Didier Queloz and Michel Mayor won the 2019 Nobel Prize for physics for discovering a famous exoplanet (51 Pegasi b) in 1995. Their claim was first verified by a top astronomer at the time named Geoff Marcy. He was later found guilty of having harassed many of his students between 2001 and 2010.

Azeen Ghorayshi of Buzzfeed News published an excellent thread detailing how Marcy’s star as an astronomer rose at a time coinciding with many of his transgressions. As Ghorayshi observes, “Marcy’s place in the science—in a buzzy field, and [with lots of money]—became part of the power used against them.” It wasn’t that Marcy would harass a woman and the woman would continue to be an astronomer; she would often leave the profession entirely.

This should make us wonder: if not for Marcy and numerous other researcher-teachers like him, what would all those strong, wonderful women (who finally outed him) have accomplished? The answer is likely lots. So the celebration of the work of men like Marcy doesn’t only concern whether a ‘morally innocent’ body of knowledge is ‘tainted’ by their actions as people but in fact strikes that moral neutrality down in two ways: the work gave Marcy power in the academic structure, and Marcy used that power to harass and drive women out of academia.

Ultimately what Marcy achieved and who Marcy is aren’t separate. The science and the scientist are inseparable – just different labels for the same entity at two points on a continuum, the same continuum that Richard Feynman lived on and which Jeffrey Epstein enabled.

John B. Goodenough, who won the 2019 chemistry Nobel Prize yesterday for his part in inventing the lithium-ion battery, has said scientists’ inventions are morally neutral. They’re not, but saying so spares one the responsibility of confronting the consequences of its use. Lithium-ion batteries may not seem to have many consequences of this sort because their use has become so prevalent, abstracted through many layers of industrialisation, but what if one of the laureates had harassed a colleague who could have contributed?

This is why Marcy’s work as an astronomer is also morally debilitated.

The ‘could’ve, should’ve, would’ve’ of R&D

ISRO’s Moon rover, which will move around the lunar surface come September (if all goes well), will live and and die in a span of 14 days because that’s how long the lithium-ion cells it’s equipped with can survive the -160º C-nights at the Moon’s south pole, among other reasons. This here illustrates an easily understood connection between fundamental research and its apparent uselessness on the one hand and applied science and its apparent superiority on the other.

Neither position is entirely and absolutely correct, of course, but this hierarchy of priorities is very real, at least in India, because it closely parallels the practices of the populist politics that privileges short-term gains over benefits in the longer run.

In this scenario, it may not seem worthwhile to fund a solid-state physicist who has, based on detailed physicochemical analyses, fashioned for example a new carbon-based material that can store lithium ions in its atomic lattice and has better thermal characteristics than graphite. It may seem even less worthwhile to fund researchers probing the seemingly obscure electronic properties of materials like graphene and silicene, writing papers steeped in abstract math and unable to propose a single viable application for the near-future.

But give it twenty years and a measure of success in the otherwise-unpredictable translational research part of the R&D pipeline, and suddenly, you’re holding the batteries that’re supposed to be installed on a Moon rover and need to determine how many instruments you can pack on there to ensure the whole ensemble is powered for the whole time they’ll need to conduct each of their tests. Just as suddenly, you’re also thinking about what else you could’ve installed on the little machine so it could’ve lived longer, and what else it could’ve potentially discovered in this bonus time.

Maybe you’re just happy, knowing how things have been for research in the country in the last two decades and based on the spaceflight organisation’s goals (a part of which the government has a say in), that the batteries can even last for two weeks. Maybe you’re just sad because you think it could’ve been better. But one way or another, it’s an inescapably tangible reminder that investments in research determine what you’re going to get to take out of the technology in the future. Put differently: it’s ridiculous to expect to know which water molecules are going to end up in which plant, but unless you water the soil, the plants are going to start wilting.

Chandrayaan 2 itself may be lined up to be a great success but who knows, there could come along a future mission where a groundbreaking instrument developed by an inspired student at a state university has to be left out of an interplanetary satellite because we didn’t have access to the right low-density, high-strength materials. Or where a bunch of Indians are on a decade-long interstellar voyage and the captain realises crew morale is dangerously low because the government couldn’t give two whits about social psychology.

Better batteries from rice husk

Research in lithium-ion batteries (LIB) is booming because the industries that use it widely are growing in number and expanding in scale. There’s been a steady march toward increasing the charge-capacity of LIBs, and apart from uniquely innovative solutions, the prevalent tendency has been toward replacing graphite anodes with nanoparticulate or nanoporous silicon ones, increasing charge capacity by 400,000%. Manufacturing either isn’t especially difficult, but researchers from South Korea have found that nanoporous silicon dioxide exists naturally in rice husk. Treated properly, they were able to extract nanoporous silicon and use it as anodes in a high-performance LIB (CE 99.7% after 500 cycles). Here are more details.

A battery of power

Lithium ion batteries have found increasing usage in recent times, finding use in everything from portable electronics to heavy transportation. While they have their own set of problems, they’re not unsolvable. And when they are solved, they’ll also have to find other reasons to persist in a market whose demands are soaring.

The simplest upgrade that can be mounted on it is to increase its charge capacity. It will then last longer per application, reducing the frequency of replacement. During charging, electrical energy from a chemical reaction is stored in a material, inside the battery. So, the battery’s charge capacity is this material’s charge capacity.

At the moment, the material is graphite. It is widely available and easy to handle. Replacing it without disrupting how a battery is made or in what conditions it has to be stored will be helpful. Thus, a material as ‘easy’ as graphite would be the ideal substitute. Like silicon.

Silicon v. graphite

Studies have shown that silicon has 400 times the charge capacity of graphite. It is abundantly available, very resilient to heat, and is easy to produce, store and dispose. However, there’s a big problem. “The lithium-silicon system has a much higher capacity than Li-graphite, but shows a strong volume change during charging and discharging,” said Dr. Thomas Fassler, Chair of Inorganic Chemistry, Technical University of Munich.

When charging, an external voltage is provided that overpowers the battery’s internal voltage, forcing lithium ions to migrate from the positive to the negative electrode, where they’re stored in the material in question. When discharging, the ions move out of the negative electrode and into the positive, generating a current that a connected appliance draws.

If the storage material at the negative electrode is made of silicon, lithium ions entering the silicon atomic lattice stretch the lattice, making it taut. With further charging, its volume could change, fracturing then breaking the lattice. At the same time, silicon’s abundance and ubiquity are enticing attributes for materials scientists.

Two recent studies, from June 4 and June 6, propose workarounds to this problem. The earlier one was from researchers in Stanford University, Yi Cui and Zhenan Bao, assisted by scientists from Tsinghua University, Beijing, and the University of Texas, Austin. Use silicon, they say, but bolster its ability to withstand expansion while charging.

The hydrogel bolster

“Our team has used silicon-hydrogel composites to replace carbon to increase charge storage capacity by many times,” said Dr. Yi Cui. He is the David Filo and Jerry Yang Faculty Scholar, Department of Materials Science and Engineering.

Using a process called in situ synthesis polymerization, they gave silicon nanoparticles a uniform coating of a hydrogel, which is a network of polyaniline polymer chains dispersed in water. This substance is porous and flexible yet strong. When lithium ions enter the silicon lattice, it expands into space created by the hydrogel pores while being held in place.

Cui and Bao also found that the network of polymer chains formed a pathway through which the lithium ions could be transported. At the same time, because the hydrogel contains water, with which lithium is highly reactive, the battery could be ignited if not handled properly.

For such a significant problem, the scientists found a very simple solution. “We baked the water off before sealing the battery,” Bao said.

Hard to make, hard to break

The second study, from June 6, was published in the Angewandte Chemie International Edition. Instead of the elegant and industrially reproducible hydrogel solution, Dr. Fassler, who led the study, synthesized a new, sophisticated material called lithium borosilicide. He’s calling it ‘tum’ after his university.

Tum is a unique material. It is as hard as diamond. Unlike the allotrope, however, the arrangement of molecules in the tum lattice forms channels, like tubes, throughout the crystal. This facilitates an increased storage of lithium ions as well as assists in their transportation.

About the choice of boron to go with silicon, Fassler said, “Intuition and extended experimental experience is necessary to find out the proper ratio of starting materials as well as the correct parameters.” To test their out-of-the-box solution, Fassler, and his student Michael Zeilinger, went to Arizona State University and used their high-pressure chemistry lab to apply 100,000 atmospheres of pressure and 900 degrees Celsius to synthesize tum.

They found that it was stable to air and moisture, and could withstand up to 800 degrees Celsius. However, they still don’t know what the charge capacity of this new compound is. “We will build a so-called electrochemical half-cell and test it versus elemental lithium,” Fassler said.

The synthesis mechanism is no doubt inhibiting. Such high pressures and temperatures required to produce industrially commensurate quantities of tum will clearly be incompatible with the ubiquity that lithium-ion batteries enjoy. Fassler is hopeful, though. “In case the electrochemical performance turns out good, chemists will look for other, cheaper, synthetic approaches,” he said.

Rethinking the battery

Another solution to increasing the performance of lithium-ion batteries was proposed at Oak Ridge National Laboratory (ORNL), Tennessee, in the first week of June.

Led by Chengdu Lian, the team reinvented the internal structure of the battery and replaced the liquid electrolyte with a solid, sulphur-based one. This eliminated the risk of flammability and increased the charge capacity of the setup by almost 100 times, but necessitated elevated temperatures to enhance the ionic conductivity of the materials.

Commenting on the ORNL solution, Yi Cui said, “Recently, high ionic conductivity of solid electrolytes was discovered, it looks promising down the road. However, the high inter-facial resistance at the solid-solid interface still needs to be addressed. Also, the new electrode materials have very large deadweight.” He added that the cyclic performance was good – at 300 charge-discharge cycles – but not outstanding.

A battery of power

As the Stanford team continues testing its hydrogel solution, and awaits commercial deployment, the Munich team will verify tum’s electrochemical capability, and the ORNL team will try to up its battery’s performance. These solutions are important for American because, in many other countries, the battery industry is a critical part of the economy. As The Economist is quick to detail, Japan, South Korea and China are great examples.

Knowing that rechargeable and portable sources of power will play a critical role in the then-emerging electronics industry, Japan invested big in lithium-ion batteries in the 1990s. Soon, South Korea and China followed suit. America, on the other hand, kept away because manufacturing these batteries provided low return on investment at a time when it only wanted its economy to grow. Now, it’s playing catch up.

All because it didn’t see coming how lithium-ion batteries would become sources of power – electrochemical and economic.

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This post, as written by me, first appeared in The Copernican science blog on June 19, 2013.