Theme Lecture | Thursday, 22 June 2017 | 12:00 – 12:30 hrs

Materially Better Electrochemical Energy Storage

Abstract:

Energy storage is one of the grand challenges of our time. The lithium battery, since its inception in the early 1990s, has transformed technologies such as the mobile phone, laptop computer and tablets. It is the technology of choice for the electrification of transport, and has an important role to play in storing renewable electricity on the grid. However, for all these applications new generations of lithium batteries are required that store more energy, can be recharged more rapidly, are safer and all at lower cost. Achieving these technological advances is in large measure a materials challenge. New multifunctional materials, or advances in existing materials, are required.

In the presentation, I shall consider advances in materials for the negative and positive electrodes, as well as the electrolyte. Currently the negative electrode in lithium-ion batteries is graphite. There is much effort in transitioning from graphite to silicon-based materials, LixSi. Although these offer substantial increases in energy storage this advantage comes with many problems, which will be discussed. Currently, lithium batteries use liquid electrolytes, such as LiPF₆ dissolved in mixtures of organic carbonates. Moving to solid electrolytes, and therefore all solid-state batteries, would transform safety, but many problems will have to be tackled. Two main options are the oxide garnets, e.g. Li_(7-x)La₃Zr_(2-x)Ta_(x)O₁₂ with x = 0.5 or 0.6,  and the sulphides, e.g. Li₇P₃S₁₁. The challenges will be discussed including a possible strategy for enabling the desired combination of high conductivity and suitable mechanical properties to act as an electrolyte (separator) in a lithium battery. Finally, consideration will be given to one possible route by which the energy stored in the positive electrode could be increased. The positive electrode in lithium ion batteries is usually a lithium intercalation compound based on a transition metal oxide, such as LiCoO₂. These compounds store electrons on the transition metal ions only. If reversible redox reactions could also be achieved involving the oxide ion, then the capacity to store charge (electrons) would be increased. Work on such compounds will be discussed.