How lithium shapes modern life

In

the summer after graduating from university, I worked for a research company studying rechargeable lithium batteries.

Our approach involved using lithium metal as one of the electrodes. The batteries worked fine but could be only recharged a few times. As the metallic lithium electrode was rebuilt during the charging phase, the structural integrity was lost. After ten or so recharging cycles, the battery wouldn’t work anymore.

This was an early part in the process of developing the technology. It is what research is all about - finding a result and trying to improve upon it. So my summer was spent trying to find a better electrolyte, solvent, or counter electrode – anything which would increase the life cycles for the batteries. We were trying to make a better battery.

During that summer, the head of research handed me and my co-workers a paper by Akira Yoshino on the use of intercalated lithium ions to form a rechargeable battery. It caused some consternation in the laboratory but really didn’t affect what we were doing as we weren’t equipped to follow up this line of research. Unfortunately.

I say “unfortunately” because this year’s Nobel Prize in Chemistry has been awarded to Akira Yoshino, M. Stanley Whittingham, and John B. Goodenough “for the development of lithium-ion batteries.” Their work in the 1970s and 80s facilitated the development of commercial lithium ion batteries in the early 1990s and eventually our modern connected world. Lithium ion batteries are found in smart phones, tablets, PCs, watches, and even in Dyson vacuum cleaners. They permeate our everyday lives.

Rechargeable batteries aren’t actually something new. The first rechargeable battery – the ubiquitous lead acid battery - was devised in the 1850s. They are still used for the starter motors in cars but they are very heavy and somewhat dangerous as the electrolyte is sulfuric acid.

In 1899, Waldemar Jungner described the first nickel-iron and nickel-cadmium batteries. These batteries were the precursor to the nickel-metal hydride batteries introduced in 1989 and used to power early cell phones.

However, lithium batteries offered two significant advantages over earlier rechargeable batteries. The first was weight. Lithium is the lightest metal we know. It is the third element on the periodic table and atom for atom it is roughly 30 times lighter than lead. Lithium ion batteries offered significant advantages in making devices portable.

The second advantage arises from the underlying mechanism for their operation. By intercalating the lithium ions into the layers of a solid support structure, the rebuilding problem disappears. This resulted in many more cycles with no loss in structural integrity.

That is, imagine you have to arrange a thousand blocks into a wall blindfolded. No matter how well you think you are performing the task, you will invariably have deviations and discrepancies in the positions of the blocks and you are likely to miss one or two along the way.

Now do the same thing again but instead of freely forming the wall, you have one thousand boxes into which you are to place a block. While it might be tiring work, your chances of getting a block correctly in each box are pretty high. Indeed, it would be very unlikely you would make a mistake. The latter is essentially what intercalation provides. Instead of forming a covalently or metallic bonded compound or sheet of metallic lithium, the lithium ions in the batteries fit into atomic sized boxes.

The original research showing lithium could be intercalated into metal chalcogenides – specifically titanium disulfide – was carried out by Walter Rudorff in 1965. This work inspired Whittingham to explore the electrochemical potential of the system and device a working rechargeable battery in 1976. It was cycled at a low charge/ discharge ratio for over 1,100 times without significant loss of reversibility but it did suffer from a flaw resulting from the growth of lithium whiskers.

A breakthrough in the technology came in 1980 as Goodenough and co-workers discovered cobalt oxide could be used instead of titanium disulfide increasing the potential from 2 to 4 volts. Further, they were able to switch from a lithium metal counter electrode to a lithium-vanadiumoxide electrode eliminating the generation of lithium whiskers.

Yoshino took the battery technology a step further by substituting heat-treated petroleum coke for the lithium-vanadiumoxide electrode reducing the weight and generating a longer lasting system. In effect, the lithium ion is simply transfer between the cobalt oxide and polymorphic graphite electrodes without disrupting the structure of either electrode. In theory, the batteries could be recycled indefinitely without breaking the electrodes down. Gone are the days when you had to run a rechargeable battery to zero before recharging.

The high voltage (up to 4.1 V) and energy density (up to 80 Wh/kg) mean lithium ion batteries are the ideal power source for driving our modern life and worthy of a Nobel Prize.