Akira Yoshino by hamptonhalls

INTERVIEW: AKIRA YOSHINO

Meet the father of the lithium ion battery Batteries International met Akira Yoshino the founding figure behind the creation and commercialization of the lithium battery. The tale of its development is testimony to the ingenuity and persistence of its inventor.

There are probably a handful of people that one can truly say have shaped the way our planet is organized. Think Thomas Edison, Logie Baird, Alexander Graham Bell. Less well known are two unsung heroes of the modern world — Akira Yoshino and John Goodenough. Both were the key figures in the creation of the lithium battery. Without either man the modern world of the mobile phone, the laptop and, coming soon, a new generation of electric vehicles running on our roads, would not exist. Yoshino’s story began in January 1948, in Osaka, Japan where his early interest in electrochemistry was sparked by a teacher who gave him Michael Faraday’s The Chemical History of a Candle to read. In an odd kind of way two of his future passions in life were fuelled by the book — a compilation of Faraday’s lectures given to children in the 1840s — an intense interest in science and a passion for history. Talk to Yoshino now — as Energy Storage Journal did in February in Dusseldorf — and he will happily relate how the history of

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progress throws up lessons for the future, particularly in the recent adoption of technology. Making the connection between how technology advanced in the 1950s and 1960s, he says, gives us an understanding of how it will advance in the future. After graduating with a master’s degree from Kyoto University in April 1972 he joined the chemical giant Asahi Kasei — a corporation where he was to happily spend his entire career with. And even now, aged 71, he is an honorary fellow with the chemical giant and pleased to represent the corporation. He joined Asahi Kasei at a pivotal moment in the life of the specialist chemical and electrochemical markets. The onset of the oil crisis in 1973 meant that the issue of energy — its use, value and importance as a resource — had become one of the most debated areas of that decade’s science and politics. Meanwhile too the age of the Walkman was just around the corner. Leading electronics firms were already in a race to develop ever smaller and more powerful gadgets.

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“From my studies of R&D in the past we can get a glimpse of the future. If you look at, for example, what happened in the 1950s and early 1960s you can see that advances in technology took at least 10 to 15 years before they changed society”

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INTERVIEW: AKIRA YOSHINO

The way was finally open to mass adoption of a battery technology that would change the world completely. Portable electronics would be transformed forever, the world of telecoms was to be revolutionized and, with the rise and rise of hand-held cell phones, the internet — still hardly born in the early 1990s — would dominate the planet. After graduating with a master’s degree from Kyoto University in April 1972 — here pictured three months later — he joined the chemical giant Asahi Kasei — a corporation where he was to happily spend his entire career with.

By 1983 Yoshino had created the first test-tube cell — pictured here — the lithium ion battery had come of age.

Assembly of LIB prototypes June 1986

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In 1981 Yoshino became the lead researcher looking at how a relatively obscure compound, polyacetylene, could be put to practical purposes. Polyacetylene is a highly interesting organic polymer in that it is capable of conducting electricity when doping (adding impurities into the raw material) making the compound sometimes dubbed as a plastic metal. In the early 1970s they discovered that the polymer was superconductive at low temperatures. Yoshino was particularly fascinated by the possibility that the chemical could be used as the negative electrode for a new type of rechargeable battery that he envisaged using lithium as the source of the ion exchange. Lithium was a good start to work from. It is the metal with the lowest density and greatest electrochemical potential and energy-to-weight ratio. The low atomic weight and small size of its ions also speeds its diffusion, made it an ideal material for batteries. The first experiments on lithium as a potential battery source were made in 1912 by US physical chemist Gilbert Lewis but there was nothing commercially available until the early 1970s with the appearance of lithium-manganese dioxide, lithium iron disulfide and lithium thionyl-chloride cells. A specialist lithium iodine primary battery had been used in heart pacemakers since the 1960s. But these were all primary batteries — once discharged, their use was over. Yoshino was on the look-out for the means to formulate a secondary battery. And a secondary battery that could be cycled — charged and discharged — hundreds if not thousands of times. Primary batteries were expensive and he was aware that the power needs of some of the electronic equipment coming to market — the first Camcorder appeared in 1982 — would only be feasible if batteries could be charged and discharged. Yoshino was also aware that some research had already been done in the field.

Stanley Whittingham, for example, had demonstrated the reversible intercalation mechanism in the 1970s — intercalation being the insertion of an ion into layered solids such as graphite. A commercial version of sorts with a titanium disulfide cathode and a lithium aluminium anode had been produced by Exxon. But there were very many things wrong with the battery. While charging, lithium tends to precipitate on the negative electrode in the form of dendrites, which go on to cause shortcircuiting and the failure of the battery and the possibility of fire. Moreover, the high chemical reactivity of metallic lithium resulted in poor battery characteristics, including inadequate cycle durability due to side reactions, and what appeared to be an insurmountable problem the inherent risk of a thermal runaway reaction. The batteries weren’t cheap either. But it was when Yoshino came across the research that John Goodenough, then a American professor at Oxford University, had been doing that he had his own ‘Eureka’ moment. In 1979 Goodenough had identified that lithium cobalt oxide could be the positive electrode material of choice. Shortly afterwards Rachid Yazami, a Moroccan researcher working at the French Centre for Scientific Research, showed that graphite could work as a negative electrode — although there were many failings of this in practice. “The combination of lithium cobalt oxide with polyacetylene instead of graphite on the negative electrode showed an exciting way forward,” says Yoshino. “We at last had the building blocks to make a working cell that had commercial possibilities.” He modestly would say much later: “I consider the lithium ion battery to be the fruit of collective wisdom.” Collective wisdom aside, there was a host of difficulties that lay ahead for Yoshino, including the choice of electrolyte, separator, current collector and the development of a winding mechanism to create greater surface area.

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By 1983 Yoshino had created the first test-tube cell. The lithium ion battery had come of age. But if the first step had been taken the route ahead was a tricky one. Although this first cell was functional, the low real density of polyacetylene posed limitations on its capacity, and the chemical stability of polyacetylene was limited. Yoshino thus searched for a new carbonaceous material to use as a negative electrode. The organic electrolyte used at the time was propylene carbonate which was unsuitable for working with graphite — it decomposed during charging when graphite was used, and furthermore the use of solid electrolyte resulted in electrical resistance which was too high to en-

able practical charging and discharging. So Yoshino studied the suitability of other carbonaceous materials at the negative electrode. He finally hit on one crystalline structure that provided greater capacity without causing decomposition of the propylene carbonate electrolyte. The secondary battery which he successfully made — by hand — in the laboratory based on this new combination of component materials enabled stable charging and discharging, over many cycles for a long period. The result of this all was filing two patents — JP198923 in May 1985 and its US counterpart US4668595A filed the following May. But it was more than just filing a pat-

ent. The next task was how to commercialize the intellectual property. To take the experience of the laboratory and put it on the manufacturing line. Those outside the battery industry would be surprised to hear that it took seven years for the first commercial product to appear. For those inside the business, this was a process whose speed verged on the astonishing. “To take anything from the lab work bench to the production line takes something like 10 years, sometimes much longer,” says one battery veteran. “To introduce a new battery chemistry as a mainstream product with everything from the safety and performance guarantees was incredible,”

Without the lithium battery the modern world of the mobile phone, the laptop and, coming soon, a new generation of electric vehicles running on our roads, would not exist.

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INTERVIEW: AKIRA YOSHINO To take anything from the lab work bench to the production line takes something like 10 years, sometimes much longer. To introduce a new battery chemistry as a mainstream product in just seven with everything from the safety and performance guarantees was incredible Indeed Yoshino’s task was far from simple — there were basic electrochemical design problems that needed to be resolved before anyone could conceive of working out the process to put it on to a manufacturing line. Broadly speaking, everything had to be worked out from first principles. “Finding the right current collector was a long process as we had to work our way through a whole variety of metal combinations and thicknesses,” Yoshino recalls. “I eventually found that aluminum was the best current collector for the positive electrode and copper foil for the negative. The thickness of each was around 10µm.” Yoshino’s decision of aluminum was one of the most important aspects of this stage of work. Previously, only precious metals such as

gold and platinum were considered able to withstand a high voltage of 4V or more. However, Yoshino found that aluminum foil was suitable for use as positive electrode current collector material because a passivation layer — effectively a protective layer — forms on the aluminum surface. And the process of actually making the electrodes required new technology to be developed. The voltage barrier of an aqueous — ie water based — electrolyte of around 1.2V had to be overcome by using a non-aqueous electrolyte. But that raised problems due to its lower electro-conductivity and a lower current density was needed to prevent heat being generated. To get around this Yoshino increased the surface area by devising flat-sheet thin-film

INTERVIEW: AKIRA YOSHINO electrodes wound into a coil shape. “Basically we used the concept of winding used in making condensers and for that we needed a large machine that could do this and several visits to various manufacturers, It took us about two years to refine this part of the process,” says Yoshino, “to create a prototype.” The choice of separator was another issue that had to be resolved. Here, Yoshino had a stroke of luck. “At that time I was based in our R&D laboratory in Kawasaki and by a stroke of good fortune in the next building to ours they were working on new polyethylene separator material. “It was incredibly handy just to walk outside the offices to see how well they were doing. Safety, of course, was a prime concern — it was always on our mind,” he says. “What we developed in fact was a microporous polyethylene membrane 20 to 30 mm thick for use as a separator.” This acted like a fuse when an electric plug blows. Excessive heat causes the material to melt and the porosity of the membrane closes effectively stopping the current and acting as a brake to thermal runaway. Yoshino also devised what would

“I get great pleasure from being around young researchers, helping them where I can. love their enthusiasm and drive.”

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probably best be described as ‘peripheral technology’ which was instrumental to the development of a practical lithium ion battery. This included safety device mechanisms, protective circuit technology, and techniques for charging and discharging. One key example is a positive temperature coefficient device which is sensitive to both electric current and temperature. Incorporation of this in the battery resulted in greatly improved safety, particularly against overcharging. Yoshino worked on a variety of design prototypes and in 1986, a US company was contracted to make a number of semi-commercial prototype cells. These were then subjected to abuse testing — mistreating the cells in the worst of expected conditions — to see how they would perform in real life and exceptional circumstances. The results proved positive. They had the required level of safety to be used by the general public and this cleared the way to the battery’s commercialization. Asahi Kasei working with Toshiba released their first mass-manufactured lithium cells in 1992. The two firms were a few months behind Sony which had already been racing to develop lithium cells to match its But most importantly, the way was finally open to mass adoption of a battery technology that would change the world completely. Portable electronics would be transformed forever, the world of telecoms was to be revolutionized and, with the rise and rise of hand-held cell phones, the internet — still hardly born in the early 1990s — would dominate the planet. Since then Yoshino has witnessed an extraordinary boom in technology. “We little realized just how completely lithium batteries would change the world of electronics,” he says. “The step change of raising the voltage of the cell from nickel cadmium batteries’ 1.2V to 4.2V in lithium ion opened the bar to so much. “The first market we aimed to use them was for video cameras. We expected sales of around a million batteries a month. But looking back the market we entered them grew explosively. And perhaps nobody at the time in the early 1990s realized how comprehensive and extensive that would become.” The figures speak for themselves. Although lithium batteries now come in different chemistries, in 2018 some 148 gigawatt hours of batteries were sold.

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YOSHINO WINS JAPAN PRIZE For the last 20 years Yoshino has been feted for his achievements — talk is that John Goodenough and Yoshino have been nominated on many occasions for the Nobel Prize — but perhaps the most prestigious award he has received is the Japan Prize. The Japan Prize was established in 1982 by the Japanese government and Konosuke Matsushita, founder of what is now Panasonic. It is awarded annually to scientists not just for their original ideas, but also for serving “the cause of peace and prosperity for mankind”. In addition to the prize money — the award comes with a gift of ¥50 million (around $420,00) — Yoshino was given the rare honour of sitting next to His Imperial Majesty the Emperor Akihito during the ceremony.

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INTERVIEW: AKIRA YOSHINO Yoshino’s vision of the future is an optimistic one though he sees the energy disparity between the have’s of the first world and the have not’s of the developing world continuing. “That said eventually this energy revolution will sweep over everyone,” he says. “From my studies of R&D in the past we can get a glimpse of the future,” he says. “If you look at, for example, what happened in the 1950s and early 1960s you can see that advances in technology took at least 10 to 15 years before they changed society. “The move to electric vehicles is now firmly established though there’s still a long way to go. The next area of change is likely to happen with intelligent robotics which will affect everything we do from automated driving to devices around the home to working on the move.” In terms of future battery chemistries he reckons that there are still huge gains to be made and in a variety of chemistries. He is particularly interested in solid state lithium batteries which he says shows great promise. “In 2011 we saw that this was achievable, the question now is how to take it further,” he says. Yoshino maintains contact with fellow lithium pioneer John Goodenough — now in his late 90s but still working — and in particular the advances he has made in solid state batteries. Yoshino, aged 71 this January, is still active and leads a full life. He is a professor at the Graduate School of Science and Technology for Meijo University, a visiting professor at the Research and Education Center for Advanced Energy Materials, Devices and Systems at Kyushu University, president of the Lithium Ion Battery Technology and Evaluation Center as well as an honorary fellow of Asahi Kasei representing the firm internationally. So what interests him now? “I get great pleasure from being around young researchers, helping them where I can,” he says. “I love their enthusiasm and drive.” In a recent interview he said: “Young people tend to believe there is nothing left to explore in the field of natural science, because everything has been discovered and explained. But the reality is just the reverse. “Out of the whole discipline of the natural sciences, we’ve only just scratched the surface.”

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BASIC CELL AND ELECTRODE STRUCTURE OF THE LITHIUM CELL Here is the basic cell and electrode structure of the lithium cell as originally devised by Yoshino and which continues to be commercially applied in present-day batteries. A multilayer electrode assembly (electrode coil), is prepared by winding sheets of positive and negative electrode with separator membrane in between, is inserted into a battery can. This is then infused with non-aqueous electrolyte comprising LiPF6 (lithium hexaflourophosphate) or LiBF4 dissolved in a mixture of carbonate compounds, and sealed. Both the positive and negative electrodes are structured with electrode material coated on both sides of a current collector. The current collectors conduct electricity from the active electrode materials to tabs connected to the electrode terminals. Aluminum foil is used for the positive electrode current collector and copper foil is used for the negative electrode current collector, the thickness of each being around 10mm.

These essential constituent technologies impart the LIB with the following characteristics. • High electromotive force of 4V or more enabled through the use of LiCoO2 as positive electrode material and aluminum foil as positive electrode current collector. • High current discharge enabled with large-area thin-film electrodes using metal foil as current collector with electrode material coated on both sides. • Achievement of efficient, high-speed electrode production. • High-density packaging with the coil-shaped, multilayer thin-film electrode assembly emplaced in a battery can. • Significantly heightened battery safety with a polyethylene microporous membrane having a certain thermal characteristics used as separator. Source: Asahi Kasei