Application of Small Angle Neutron Scattering for In Situ Measurements of Li-Ion Batteries

Small-angle scattering is a commonly used to gain informations about the nanostructure of the investigated materials (i.e. size, volume and shape of particles). Also, neutrons are a powerful tool for in-situ investigations because of their high material penetration depths. Therefore SANS is well suited for studying any changes of these parameters inside closed battery cells under operation. Up to now only a few publications exist dealing with the SANS method for batteries and battery materials. This is mainly caused by the fact that only new developed batteries provide a reasonable thickness for transmission measurements necessary for the applied method.

In 2012 Bridges et al. used a Li||Graphite coin cell for an in-situ SANS experiment, observing the growth of the anodic SEI-layer [1], while for example Nagao et al. used the method to investigate the Li-intercalation mechanism in carbon host materials [2].

However, one major drawback in these experiments is that only cells with Li-metal as counter electrode were used.

In our approach we assemble experimental cells consisting of the same anode and cathode materials as used in commercial cells and perform in-situ SANS experiment during charging/discharging. The cells are assembled as pouch bag or coffee bag cells.

We report on our measurements with the SANS-1 instrument at Heinz Maier-Leibnitz Zentrum (MLZ), Garching. In-situ small-angle neutron scattering data of NMC||Separator||Graphite cells was collected during a complete charging and discharging cycle. In addition single battery components were measured separately to distinguish the various component signals. The in-situ data shows a variation of the integrated total scattering intensity in dependence of the state of charge. The quite noticeable step in the curve can be associated with the volume changes of the cathode or anode materials caused by the Li-intercalation process. Combining the different data sets a feasible interpretation of the charging/discharging process will be presented.

Our future aim is to further develop the in-situ small-angle neutron scattering technique to be able to monitor aging and electrode deterioration processes without the need to open the cells.

[1] Bridges, C. A., X.-G. Sun, J. Zhao, M. P. Paranthaman and S. Dai. "In Situ Observation of Solid Electrolyte Interphase Formation in Ordered Mesoporous Hard Carbon by Small-Angle Neutron Scattering." The Journal of Physical Chemistry C, 2012, 116(14), 7701-7711.

[2] Nagao, M., C. Pitteloud, T. Kamiyama, T. Otomo, K. Itoh, T. Fukunaga, K. Tatsumi and R. Kanno. "Structure Characterization and Lithiation Mechanism of Nongraphitized Carbon for Lithium Secondary Batteries." Journal of The Electrochemical Society, 2006, 153(5), A914-A919.