I am very pleased to write up a blog post on the 2019 Nobel Prize in Chemistry, because it is well overdue. People have been saying that about recognition of the discovery of lithium-ion batteries for many years now, and like many others I’m just glad that the committee was able to recognize John Goodenough, who is now 97. He and his co-awardees, M. Stanley Whittingham of Binghamton and Akira Yoshino of Asahi Kasaie and Meijo Univ., changed the world with their discoveries in ways that every member of the general public can see immediately (which is definitely not always the case with science Nobel awards!)
Like almost all such discoveries, it’s a layered accomplishment with many players. All chemical batteries take advantage of the thermodynamics of chemical reactions; that’s where the energy is coming from. The key to lithium-ion batteries and their kin is the idea of an intercalation electrode, but first we’ll contrast that with a “classical” rechargeable battery (such as a lead-acid design, which was the first and is still the basis for a huge number of batteries in the world). Those work with solid electrodes at either end of an electrolyte solution. In the lead-acid case, you start with lead oxide at one side, lead metal at the other, and aqueous sulfuric acid in between, and in the fully discharged state you have two electrodes that are basically both lead sulfate, with mostly water in the electrolyte solution. You can hook the thing up to an external power source, though, and reverse that reaction, gradually regenerating lead and lead oxide electrodes and producing more sulfuric acid again along the way. If you balance the chemical equations out, the real driving force is the formation of water, from hydrogen cations on one side and oxygen anions on the other, and when you recharge the battery you’re doing water electrolysis to break it back down again. All the lead and sulfuric acid is just there to provide a robust chemical reaction framework for that to happen.
Earlier attempts to use lithium as a battery material relied on its cycling between lithium metal and the +1 cation, which is electrochemically attractive but practically. . .well, problematic. But it did introduce the idea of an cathode that relied on intercalation, the fitting of chemical species between layers of an atomic lattice structure in the solid state. Whittingham’s work with Exxon back in the 1970s realized this scheme (the first to do so) with an anode made of lithium and aluminum and a metal-sulfide cathode, titanium disulfide for the lithium ions to soak into. Well, lithium ions do indeed fit into TiS2, and you can make a battery that works, but the material is very moisture-sensitive and emits copious amounts of smelly and toxic hydrogen sulfide if that happens. Exxon tried to commercialize the design during the energy-crisis years of the late 1970s and early 1980s, but wasn’t successful. There was another problem: lithium metal itself is, as chemists well appreciate, a rather reactive substance, and having it pile up at one electrode of a working battery is inviting trouble. A big problem is that cycling through charging cycles tends to produce dendrite lithium metal structures on the anode, which can physically break through the layered battery structure and cause catastrophic short-circuits. Even later 1980s metallic lithium batteries would occasionally burst into roaring flames because of this and were obviously not a long-term solution.
Working with lithium ions the whole way is a better way to go. That plan sticks with the same sort of cathode of some kind of metal oxide or sulfide (although not titanium disulfide!) and and anode that can also intercalate lithium ions (now typically layered graphite, a refinement introduced by Rachid Yazami). You’re using intercalation at both ends, and it’s the thermodynamic difference between those two intercalated/nonintercalated states that provides the energy of the battery. There are, though, a long list of technical problems that had to be overcome to realize this idea. Those were dealt with by a tremendous amount of experimentation, because there are (still!) things that we don’t understand at the nanoscale of battery mechanisms. But the design has no lithium metal in it, no nasty things like cadmium or lead, can be cycled hundreds of times, doesn’t have to be deliberately discharged flat in order to keep working for the long term, and (similarly) has no “memory” effects from being charged before that state is reached. (That was a problem with some nickel-cadmium technology, although it’s a fairly complicated story in real-world use).
Goodenough came up with a practical lithium-cobalt-oxide material for the cathode during his years at Oxford (also investigated by Ned Godshall), but the first patent for such a battery was actually obtained by Sony in 1991. There are persistent stories of a Japanese postdoc in Goodenough’s research group transferring the idea back to Japan, and I am not equipped to speak on this issue (although there were indeed years of wrangling in the courts). But I will note this quote from Goodenough:
Professor Goodenough remembers Professor Bruce’s fellow student Clare Grey, who now has a competing group at Cambridge, as a rare undergraduate who could keep up with his lectures. “The crowd went down and down as we went on, and so she graciously put a bunch of teddy bears in the front row so I would have an audience”. The students that dropped out, he says, “probably became patent lawyers”
Yoshino developed the first commercial battery (1985) that used the carbon anode and Goodenough’s cathode material, and the design has undergone a huge number of refinements since then. The electrolyte material, the separator membrane between the electrodes, all sorts of additives to make the cycling more reliable and reproducible – I would hate to have the chronicle all the work that has gone into lithium-ion battery design. This is, of course, a very active field of research to this day, and the good news is that improved understanding at the nanoscale is slowly making us more aware of things that previously had to be worked out by brute-force experimentation coupled with a great deal of experience.
But the end result of all this work is running all the portable electronic devices in the world, and things like electric cars as well. And this despite the fact that they work at around 3.6 volts! If you can come up with a higher-voltage design that works as well, the world will be at your feet. But so far, there is no cathode material that simultaneously has high capacity, high voltage, and can undergo long-term cycling without gradually breaking down.