Rapid growing demands on electric-power based automotive transportation, grid applications and electronic devices require development of sustainable rechargeable batteries. This also arises from an urgent need to decrease CO2 emissions and to implement renewable energies into society. Unfortunately, improvements to battery materials has been slow and discovery of new materials with improved properties even slower. The reason for this is there are multiple interconnected processes that occur between multiple components during battery operation. Being able to “see” inside a battery while it is operating can uncover a wealth of information that would not be possible using post-mortem studies. One approach to tracking the changes non-destructively is in operando neutron diffraction.
With neutrons, larger commercial cells, such as the lithium battery inside your phone, can be investigated without modification due to the highly penetrating nature of neutrons. Further, due to the stronger interaction between neutrons and lithium atoms, the position of lithium and its effect on the electrode crystal structure can be monitored in real-time. However, while commercial cells can be used “as-is”, newly discovered materials require bespoke cell designs constructed of materials that do not interfere with the data obtained. Further, the custom cell must exhibit ideal electrochemical performance. Balancing these aspects is no easy feat as it can require months of optimization for every new material investigated. Multiple cells have been designed with the aim of simplifying construction, boosting electrochemical performance and the quality of the obtained diffraction pattern. These range from a cylindrical cell design, a smaller coin cell which uses equipment readily available in most battery labs and finally a more recent prismatic cell with neutron transparent windows. All cell designs take inspiration from commercial lithium ion batteries.
In operando neutron diffraction of new battery materials is being undertaken by Dr William Brant at the Department of Chemistry in the Ångström Laboratory at Uppsala University in collaboration with research groups at the ISIS Neutron Spallation Source and Oxford University in the UK. As the method becomes more accessible, further collaborations are building with research groups, such as from Karlsruhe Institute of Technology, exploring new materials which would benefit from neutron diffraction.
We are constantly looking to improve the cell designs that are available by taking what we and other research groups have learned in the past and adapting to new materials. In addition, my research group is expanding into other in operando and in situ techniques, such as in operando X-ray diffraction and in situ X-ray tomography, to form a comprehensive suite of methods and analysis tools to understand the dynamic changes that take place over multiple length scales in energy storage devices.