Electrochemical in situ reaction cell for X-ray scattering, diffraction and spectroscopy

On-line monitoring of changes in materials undergoing chemical reactions is usually performed by using in situ reaction chambers. In the last two decades, countless X-ray in situ chambers have been designed for battery research applications. Since some of the battery electrode materials are very sensitive to corrosion in the ambient atmosphere, including in particular the alkaline metal-based systems such as lithium batteries, the sealing of the cells plays a very important role.

While many different cell designs have been successfully developed and tested for short-term experiments, only few have been reported that allow for experiments that extend over several days or even weeks. One research group has overcome many of the obstacles related to electrochemical in situ X-ray experiments by switching to energy-dispersive X-ray diffraction, that utilize rather high X-ray energies (Ronci et al., 2001); other groups depend on in situ cells that were manufactured in an industrial plant (Richard et al., 1997) and on a particular diffractometer type (Gérand et al., 1999). Another in situ cell (Koetschau et al., 1995) allowed for long-term experiments, but did not contain lithium metal counter electrodes. The McBreen group has performed in situ X-ray diffraction and absorption, but they measured the cathode of a high-rate industrial battery which could be studied in a short time (Balasubramanian et al., 2001).

Charging and discharging reactions in batteries are pronouncedly limited by diffusion and may take hours. Since the structure of electrodes may be dependent upon the number of charge and discharge cycles, experiments often take as long as weeks or months.

When exposed to the ambient atmosphere, the lithium reacts with the nitrogen in the air to form lithium nitride or, with the humidity to form lithium hydroxide. Some of the electrolytes used in batteries may also form aggressive reaction products; for instance, LiPF₆ forms hydrofluoric acid when in contact with the ambient humidity.

These corrosive reactions are common in batteries and must be minimized by using proper sealing. Regular battery test cells which are not used for in situ studies are usually very carefully designed to satisfy the strict sealing requirements and allow cycling experiments for several months.

In contrast, in situ cells need X-ray windows and thus are more prone to leakage. In some of them, leakage problems are overcome by extensive use of sealants, and those cells are often for one-time use only.

In this paper we present a convenient re-usable cell with beryllium X-ray windows and sealing rings. It allows charging and discharging of the battery for several days without noticeable traces of corrosion of the lithium metal.

The cell's design allows for it to be employed in the transmission mode at any hard X-ray source. In particular, the cell was tested at beamline 12-ID (Braun et al., 2001) at BESSRC-CAT, Advanced Photon Source, Argonne, IL, USA, and at beamlines 2-1 and 2-3 at Stanford Synchrotron Radiation Laboratory, Menlo Park, CA, USA.

To the best of our knowledge, this is the first time that a single in situ electrochemical cell has been used for X-ray techniques so different in nature such as X-ray diffraction, spectroscopy and anomalous small-angle scattering.