Batteries / Research

The next generation of battery materials

In October 2017, Dr Andrew J. Morris was appointed as Senior Birmingham Fellow in the School of Metallurgy and Materials at the University of Birmingham. Dr Morris specialises in using high-throughput computation to discover and categorise next-generation battery materials.

There is urgent need for new battery materials with superior performance to present technologies. Incremental improvements in manufacturing and processing cannot provide the increase in capacities, cycle rates and lifetimes currently demanded of them. From the small (battery-on-a-chip or sensor for the “Internet of Things”), medium (pervasive electric vehicles) to large scale (grid-level storage for renewable energy sources) next-generation batteries, a disruptive change is required.

Using an analogy of a hydroelectric plan can help illustrate how a lithium-ion battery (LIB) works. In the hydroelectric plant water releases gravitational energy into turbines as it flows down a hill: in the LIB, lithium-ions release chemical energy as they flow from anode to cathode through an electrolyte. One can “pump” lithium back “uphill” thereby re-charging the battery.

For next-generation battery technologies the hydro analogy breaks down as there are many more possible improvements to the LIB than can be performed on a hillside. To make the LIB safer, the flammable liquid electrolyte can be replaced by solid ionic conductors. Both electrodes can be replaced by new materials, with higher capacities or voltages. Lithium ions can be switched for sodium ions, which are cheaper and more naturally abundant. Alternatively, since magnesium is doubly ionisable (Mg++ compared to Li+), using magnesium as a charge carrier instead of lithium would double the effective capacity of the battery.

What stands in the way of realising next-generation battery technologies is new materials. “Trial and error” plays a large part in the materials discovery. From the initial idea, the material must be synthesised and categorised before it can be tested which is slow, difficult and expensive. To cover the vast design space and accelerate these new battery materials from concept to market, the only possible recourse is rational computational design. High-throughput computation accelerates this process by suggesting then screening new materials, allowing us to ask “what if?” without the time and expense of manufacturing and categorizing samples.

Dr Morris has collaborations with world-leading battery experimentalists Professor Clare Grey from Cambridge University and Professor Ram Seshadri from the University of California, Santa Barbara. Since the atoms in the electrodes exhibit very different chemical bonding, and re-arrange at the sub-nanoscale as the battery charges, fully quantum-mechanical models are required.  Dr Morris’s group uses the BlueBEAR high-performance computing resource at the University of Birmingham and the UK’s regional Tier-2 centres and national research supercomputer ARCHER to solve these quantum-mechanical models.

In 2014, he predicted new phases of lithium germanide [1] which went on to be experimentally verified [2]. This year while working alongside Professor Grey’s experimental team, his group used computational techniques to understand how an anode made out of tin for a sodium-ion battery behaves [3].

He is looking forward to working with the other members of the Birmingham Energy Institute and developing his battery research programme at the University of Birmingham.

Schematic of the experimental discharge profile of a sodium-tin anode, showing how the voltage across the battery changes as sodium is added to it.

Schematic of the experimental discharge profile of a sodium-tin anode, showing how the voltage across the battery changes as sodium is added to it. Computation allows us to predict the phases of sodium-tin that form as sodium is included. The Na¬15Sn4 phase carries over twice the charge of the standard lithium-ion battery anode. Sodium is about 100th of the cost to mine and refine than lithium.

More information can be found from Dr Morris’s website http://www.andrewjmorris.org

[1] A. J. Morris, C. P. Grey and C. J. Pickard, Phys. Rev. B 90 054111 (2014). (http://doi.org/10.1103/PhysRevB.90.054111)

[2] H.  Jung, P. K. Allan, Y.-Y. Hu, O. J. Borkiewicz, X.-L. Wang, W.-Q. Han, L.-S. Du, C. J. Pickard, P. J. Chupas, K. W. Chapman, A.  J. Morris, and C. P. Grey, Chem. Mater. 27, 1031 (2015). (http://doi.org/10.1021/cm504312x)

[3] J. M. Stratford, M. Mayo, P. K. Allan, O. Pecher, O. J. Borkiewicz, K. M. Wiaderek, K. W. Chapman, C. J. Pickard, A. J. Morris and C. P. Grey,  J. Am. Chem. Soc. 139 7273 (2017).(http://doi.org/10.1021/jacs.7b01398)

 

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