1. Why Did Yoshino's Research on Conductive Plastic Lead to Batteries?
Yoshino’s research was not originally intended to create batteries. His starting point was polyacetylene, one type of conductive plastic (known as a conducting polymer) [2]. According to Asahi Kasei’s official page, in 1981, while exploring applications for polyacetylene, they found it difficult to use in solar cells. Consequently, they moved into research on rechargeable secondary batteries [4].
At that time, the battery industry faced a major problem. They were trying to develop new secondary batteries using metallic lithium on the negative side, but attempts to commercialize them kept failing. The industry was searching for new materials to replace metallic lithium [2].
Here is the answer to the main question of this article: The prototype battery made with polyacetylene did not meet the requirements. After that, by switching to a carbon material found in another laboratory within the same company, Asahi Kasei, they established the basic form of the lithium-ion battery in 1985 [2][4]. So, what was lacking in the polyacetylene battery?
2. Why Did Yoshino's First Prototype Battery Fail Even After Reaching Its Weight Goal?
In 1983, Yoshino made a prototype battery using lithium cobalt oxide on the positive side and polyacetylene on the negative side. The goal was to make the volume and weight one-third that of existing secondary batteries [2].
They achieved the weight goal but failed to meet the volume goal. The weight was about one-third that of a nickel-cadmium battery. However, the volume remained almost the same as the nickel-cadmium battery. The reason was that polyacetylene has a low true density (the density of the substance itself) [2]. Just like a block of Styrofoam is light but large, being light and being small are different things.
For portable devices like mobile phones and laptop computers, not only lightness but also small size is necessary. If the volume does not decrease, the requirements are not met.
At this point, Yoshino was stuck. Should he stick with polyacetylene or look for another material? Help came from an unexpected place.
3. How Did Another Asahi Kasei Laboratory's Carbon Fiber Help Solve the Problem?
The turning point was at Asahi Kasei’s fiber research institute. There, they had developed VGCF (vapor-grown carbon fiber). It was discovered that this material has a special crystal structure suitable for the negative electrode [2]. The answer was sitting outside the battery laboratory.
Thus, in 1985, the basic form of the lithium-ion battery was established, using lithium cobalt oxide on the positive side and a carbon material on the negative side. Asahi Kasei describes this as the completion of the world’s first basic structure [4]. A statement from the president of NEDO noted that finding a carbon material with a specific crystal structure led to practical use [5].
In the same year, they also performed safety tests by dropping iron balls onto handmade batteries. Reports say metallic lithium batteries caught fire, but the lithium-ion battery did not catch fire in the test. Yoshino has stated that he considered the lithium-ion battery to be born at the moment of this safety test [6].
Because VGCF is expensive, later batteries use it by mixing 1–2% into cheaper carbon materials [2]. Was Yoshino the only person who contributed?
4. How Did Yoshino, Goodenough, and a Third Winner Share the 2019 Nobel Prize in Chemistry?
On October 9, 2019, the Nobel Prize in Chemistry was announced for the development of lithium-ion batteries. The three winners were Yoshino Akira, John Goodenough from the United States, and Stanley Whittingham. Yoshino was born in 1948. At the time of the award, he was an honorary fellow at Asahi Kasei and a professor at Meijo University [1].
Let us look at how each contributed to the development. Whittingham proposed electrochemical intercalation (the reaction of inserting and removing lithium into materials) in 1975. Goodenough discovered lithium cobalt oxide for use on the positive side. Sources give different years for this development; NEDO states 1979, while other records indicate 1980, so it is best to say "around 1980." Yoshino completed the prototype in 1985 using a combination with carbon on the negative side [5][2].
This battery did not appear immediately. Sony commercialized it for the first time in the world in 1991. Since 1992, a joint venture between Asahi Kasei and Toshiba has produced them. Yoshino was involved in its establishment, but people like Sony’s Nishi Michio also contributed greatly to commercialization [4].
Sales increased rapidly around 1995. Yoshino says this battery supported the small, safe batteries needed for computers and mobile phones [7].
5. What Did Young Yoshino Read, and What Comes Next for Batteries?
Yoshino is from Suita City, Osaka Prefecture. He studied at Kyoto University and joined Asahi Kasei in 1972 [9]. His entry into chemistry began in elementary school. In interviews, he said he found Faraday’s "The Chemical History of a Candle" interesting after his homeroom teacher recommended it [3]. KADOKAWA also reports that reading this book, recommended by an elementary school teacher, was the origin of his interest [8].
Yoshino explains one reason for the award as its future potential to solve environmental and energy problems. He stated that after the IT revolution comes the Energy and Technology (ET) revolution. He predicted that the 2038 Nobel Prize in Chemistry would be awarded for contributions to solving environmental problems [6]. This is Yoshino’s personal prediction, not a confirmed fact.
Look around your home. Check if "Lithium-ion" is written on battery labels or manuals for smartphones and laptops. Count how many devices have it. Do not take batteries apart, crush them, or heat them. Only look at them.
Go to the library and find "The Chemical History of a Candle." You can peek into how chemistry began from the book Yoshino read when he was an elementary school student.