The invention of the lithium-ion battery

Readingtime 10 minutes

Electric cars, smartphones, laptops all contain lithium-ion batteries. Researchers such as John Goodenough, Stanley Whittingham, and Akira Yoshino created the necessary basis for energy storage – they have received the Nobel Prize for Chemistry for it just recently. But it took a long time from the first experiments of the Nobel Prize winners to commercial breakthrough.

TEXTBERND KALTWASSER

The early 1970s were a turbulent time. A proxy war between East and West was raging in Vietnam. German chancellor Willi Brandt was initiating his policy of détente. The Beatles split up, and the band ABBA was founded.

It was also an era of growing environmental awareness: Greenpeace was established, and politicians and experts gathered for the first time for a global conference on the environment. There was dire need for it, as industry and traffic were generating smog in metropolitan areas, while air pollution was considered the chief cause of dying forests.

Beginnings in the oil industry

These events also led to a shift in the business world, as automotive manufacturers and oil companies recognized that oil reserves were finite and began to change their policy. Thus, the U.S. oil company Exxon hired some of the leading energy scientists and gave them the freedom to research anything – except oil.

The group of scientists brought on board in 1972 included the chemist Stanley Whittingham, who - almost half a century later - would go on to receive the Nobel Prize in Chemistry as one of three battery researchers. The working conditions were ideal: “If you needed something for your research you asked for it, and it would be there in a week. Money was no issue,” Whittingham later recalled.

In his previous work at Stanford University, Whittingham had focused on solid materials with atom-sized spaces in which charged ions could attach, which in turn changed the material properties. At Exxon, the team around Whittingham initially concentrated on superconducting materials. “If you look at our publications [from that time], you will see a lot of basic science with no mention of batteries at all,” he now says.

PUBLICATION DATE

9 December 2019

Photo: Audrey Shtecinjo/stocksy.com

Whittingham develops the first lithium-ion battery

As the Exxon researchers began to investigate tantalum disulfides, they learned that they could control the temperature in which the layered material assumed superconducting properties by adding – or intercalating – different atoms or molecules between the layers. Potassium ions had the greatest effect. They created a very stable, especially energy-rich compound. The intercalating ions in the tantalum disulfide matrix released a few volts of power, which exceeded the performance of the batteries known at the time. This discovery suddenly put the focus on powerful energy storage.

After testing additional compounds, Whittingham ultimately chose lithium as the electron source for the anode of his battery. The alkali metal is extremely reactive and easily releases electrons to binding partners, but is less dangerous than potassium. He replaced the heavy tantalum disulfide at the cathode, the positive electrode, with lighter titanium disulfide.

This resulted in the first prototype of a lithium-ion battery: a rechargeable battery that could produce a little more than two volts. When Whittingham presented the new lithium battery at the corporate headquarters in New York, it was decided within 15 minutes to develop a commercially viable product.

Although other companies such as General Motors, Sohio, or the U.S. Argonne National Laboratory were researching lithium-based batteries at the same time, Whittingham's prototype was the only one to function at room temperature.

There were still a few problems to resolve. Thin whiskers of lithium grew at the lithium electrode in repeated charging cycles. When they reached the other electrode, battery short-circuits occurred, followed by what chemists politely describe as “thermal runaway": an explosion. In fact, the fire department had to put out so many fires in Whittingham's laboratory that it threatened to make him pay for the expensive special chemicals needed to extinguish lithium fires.

It never came to that. The researchers added aluminum to the metallic lithium electrode and replaced the electrolyte – the liquid between the two electrodes – to gradually resolve the problem. The first batteries were sold in 1976 to a Swiss clockmaker that wanted to use it in solar-powered clocks.

The end of the oil crisis in the early 1980s ultimately brought the era of Exxon’s battery research to a halt. Oil prices fell dramatically and moved the vision of electromobility far into the future. Exxon lost interest in Whittingham's work and licensed the technology to three different companies in three parts of the world.

Goodenough improves the cathode

The next development step was taken by the second prize winner, John Goodenough, born in 1922 in the Thuringian town of Jena, son of a US professor, who grew up near New Haven, Connecticut. In his youth, the American researcher could hardly imagine that he would go on to receive the Nobel Prize one day. “I couldn’t read very well. I’m still not a very good reader,” he recently said in an interview.

As a young man, Goodenough felt drawn to the world of mathematics and chose to study physics, enrolling at the age of 24, at the end of his WWII military service. “The [university] registration officer said to me, ‘Don’t you know that anybody who had done anything interesting in physics had done it by the time he was your age? And you want to begin?’” Goodenough did – and went on to become one of the best solid material physicists ever.

He worked at the Lincoln Laboratory of the Massachusetts Institute of Technology (MIT) for several decades, where he created the fundamental prerequisites for the development of computer memory. In the wake of oil crises, he became increasingly interested in energy research. In 1976, he transferred to the British Oxford University as a professor for inorganic chemistry to fully concentrate on the topic.

At this time, Goodenough was already familiar with Whittingham's battery. His specialized knowledge in material science told him that its cathode could have a higher potential if it was built using an oxide instead of titanium disulfide. Together with his team, he began to search for a suitable material. It had to produce high voltage with intercalating lithium ions, yet had to be stable enough not to collapse when the ions were removed. The researchers ultimately found what they were looking for in lithium cobalt oxide. The battery generated four volts instead of two - double the potential of Whittingham’s model. Goodenough first described the new concept in a technical journal in 1980. The U.S. scientist was the first to realize that batteries did not have to be manufactured in their charged state, as had been the practice previously. Instead, they could be charged after their assembly.

Yoshino builds the first commercially viable battery

While interest in alternative energy technology declined in the West in the early 1980s at the end of the oil crises, things were different in Asia, where emerging electronics companies had great hopes for powerful, lightweight batteries. They saw them as a crucial component to turn camcorders, mobile phones, and laptops into bestsellers.

Akira Yoshino, who worked as an engineer at the Japanese electronics company Asahi Kasei, recognized the new possibilities. “I just sort of sniffed out the direction that trends were moving,” the Nobel Prize winner later noted.

Yoshino was born in 1948 and grew up in Osaka, Japan's second largest city. His interest in chemistry dated back to a teacher in fourth grade, who introduced him to the book “The Chemical History of a Candle,” a collection of lectures by the British chemist Michael Faraday from the 19th century. Yoshino read the book and was excited: "Why do candles burn? Why are the flames yellow? What are the wicks for? I thought this seems kind of fun," he recalled at a press conference decades later.

After graduating from the University of Kyoto, Yoshino started researching a material called polyacetylene at Asahi Kasei. Although it is an organic substance, it conducts electricity. Yoshino was looking for a way to use polyacetylene as an anode in a battery, but was unable to find a suitable material for the cathode.

In 1983, he came across a technical article that discussed Goodenough's lithium cobalt oxide as a cathode material. Decades later, Yoshino recounted that the idea that would later lead to the development of lithium-ion batteries came to him during one of his free afternoons, after cleaning up his laboratory.

Instead of using polyacetylene, he built an anode on the basis of petroleum coke, a carbon byproduct of the oil industry. The special advantage of the material is based on its structure: Lithium ions can intercalate in petroleum coke without changing it. This last step established the basic structure of the world's first commercially viable lithium-ion battery. With one electrode made of petroleum coke and the other, of lithium cobalt oxide, the battery no longer contained any metallic lithium – a crucial safety gain. Sony launched the first batteries in 1991.

That event marked the end of the research work on lithium-ion batteries, for which Whittingham, Goodenough and Yoshino were recognized with the Nobel Prize in Chemistry in 2019. However, the development of the battery itself was by no means complete. To this day, the three Nobel Prize winners keep researching improvements, such as new electrode materials or design principles.

Photos: Bloomberg via Getty Images, AFP via Getty Images, Kyodo News via Getty Images

Are batteries safe?

The importance of further improvements to turn Nobel Prize-worthy research into commercially viable products became evident approximately 10 years ago. In the early 2010s, pictures of lithium-ion batteries in smartphones and tablets that had heated up to the point of bursting into flames circulated on social media. When a Tesla S burned out after an accident in October 2013, some US$3 billion of market capital were annihilated for the U.S. car manufacturer within a short time in a dramatic drop of the company’s stock price.

The topic had drawn global attention in January of the same year, when newly developed lithium-ion batteries, designed for Boeing 787 Dreamliner aircraft, caught fire in two airplanes within a few days of one another. The U.S. Federal Aviation Administration (FAA) followed up by demanding proof of safe battery operation. Authorities in other parts of the world followed suit, leading to a virtual global flying ban for Dreamliners. Boeing had to equip its planes with a new battery system before they were allowed to take off again in April.

“That was a critical moment for lithium-ion battery technology. It ran the risk of being rejected as unsafe by consumers,” says Guido Skudlarek, the head of Evonik’s special oxides business. The events caused major battery manufacturers to move further safety improvements to the top of their priority list worldwide.

This effort quickly led to the question of improving the separator, a thin, micro-porous film that electrically insulates the two electrodes from each other, but allows the ions to flow between the cathode and the anode. In lithium-ion batteries, separators typically are made of thermoplastic materials such as polyethylene and/or polypropylene. “These materials only have limited heat resistance and shrink under thermal influence,” Skudlarek explains. This can lead to short-circuits and thermal runaways of batteries when the electrodes come in direct contact.

Circuit of a lithium-ion battery whose cathode and separator are coated with AEROXIDE®

Contribution of additives

Ceramic coatings with fumed metal oxides such as AEROXIDE® prevent exactly those scenarios by improving the thermal and mechanical properties of the separator. In an event of a thermal runaway, at first the micro-pores in the polymeric membrane close and interrupt the flow of lithium ions. The AEROXIDE® coating prevents the shrinkage of the separator film and thus the direct short circuit of the battery. The energy storage system simply stops working and slowly cools down instead of spectacularly bursting into flames. There are also considerations to no longer coat the separator, but to introduce the metal oxide particles directly into the separator during the manufacturing process, so that they are later distributed homogenously throughout the interior of the separator . “Such a procedure would be especially resource-efficient because the coating process is eliminated,” says Skudlarek. At the same time, the battery design would be even thinner and take up less space – an important gain for mobile applications.

Optimizations have also involved the electrodes, not just the separator. By now, petroleum coke is no longer used at the anode and has been replaced with a mixture of graphite and silicon. Likewise, cathodes are no longer manufactured from pure cobalt oxide, but now consist of mixed oxides, which contain manganese and nickel in addition to cobalt. In the latest generation of such NMC(Nickel-Manganese-Cobalt) cathode active materials, the cobalt share in the cathode is just ten percent. “The trend is currently towards even higher nickel content to further increase the energy density. On the downside, that makes material less structurally stable and the surface even more reactive.” Skudlarek explains. AEROXIDE® additives from Evonik can also help in that case: When the NMC particles are coated with a thin layer of nano-structured aluminum oxide (Al2O3) and/or titanium dioxide (TiO2), this oxide layer partially reacts with the electrolyte to form a protective shell, a so-called defined solid electrolyte interface (SEI). Such an artificial layer protects the cathode material from decomposition while allowing Li-ions to pass. This keeps the battery at a higher capacity throughout its lifecycle.

Improvements in the area of electrolytes also offer greater safety. The most common solution currently in use involves liquid electrolytes, for example, lithium salts dissolved in aprotic solvents such as the toxic lithium hexafluorophosphate (LiPF6). Understandably, battery manufacturers are looking for ways to prevent electrolyte leakage in case of damaged battery cells. This can be achieved, for example, with a special surface-modified form of AEROXIDE®. The additive is applied to the separator as a ceramic coating as before. However, thanks to its special properties, it reacts with a component of the electrolyte solution. Based on cross-linking reaction with this substance, the reactive liquid turns into a gel-like electrolyte based on a polymer composite, further increasing the safety of the lithium-ion battery.

The technology for lithium-ion batteries has made huge advances since the first steps in the 1970s. It appears so advanced now that some professionals only see limited possibilities for further improvement. Nevertheless, it will be a few more years for the next generation of small, powerful storage devices such as solid-state batteries to emerge.

Lithium-ion batteries make a crucial contribution to the use of cleaner energy technologies and electromobility, helping to limit greenhouse gas emissions. As they have become mainstream, in the best sense of the word, they are found not only in submarines and satellites, but also in electric toothbrushes, pacemakers and home appliances. “In my opinion, that makes the well-deserved award of the Nobel Prize even more special,” says Evonik manager Skudlarek. “The prize in the past has frequently recognized basic principles with a hidden connection to products or processes, or referred to very specific developments that we occasionally encounter in our lives. This is very different.”

Illustration: KNSKB+

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