X-ray photoelectron spectroscopy (XPS) and surface characterisation techniques have contributed a wealth of information to battery research. Batteries and power storage devices are complex structures where the electronic properties and heterogeneous interfaces between components are critical in the operation of the device.
In-situ and in-operando characterisation
X-ray photoelectron spectroscopy (XPS) is ideally suited to provide information relating to interfacial material properties critical to performance of modern batteries. Information derived from the technique can give insights into chemical composition, elemental or chemical distribution of species, defect sites or functional groups. Importantly, recent development of accessories for the AXIS spectrometers allow studies of these materials to be extended to in-situ and in-operando characterisation of model devices. Accessories are also available to enble air-sensitive samples to be transported from a glove box to the spectrometer without being exposed to ambient conditions, or within a glove box directly interfaced to the spectrometer.
Although Li-ion batteries are widely used, significant research continues to be applied to these high energy-density batteries. Limitations such as dendritic Li growth and insulating secondary electrolyte interphase (SEI) layer formation are being addressed by XPS and complementary surface analysis. Studies are also being extended to reduce limitations such as device stability and charging rates.
Lateral and depth distribution
Spatially resolved surface analysis is easily achieved using XPS imaging available as standard with AXIS spectrometers. Images of surface chemistry can be acquired with spatial resolution of a few microns over several millimetres.
Additionally, depth distribution of elemental and chemical states can be determined by combining Argon ion sputter depth profile cycles with XPS. AXIS spectrometers can be configured with a monatomic Ar+ ion source or an advanced Arn+ gas cluster ion source (Minibeam 6) GCIS. The GCIS has proved important in the correct determination of Li concentration through solid electrolyte materials. Use of a conventional monatomic Ar+ ion source has been demonstrated to induce Li+ ion migration through the electrolyte material towards the electrolyte/electrode interface. This is as a consequence of implanted Ar+ ions repelling the small, mobile Li+ ions. This repulsive bulk migration accounts for erroneous determination of Li concentration in monatomic Ar+ depth profiles and the increase in Li concentration at the interface with the electrode.
This brief introduction highlights the value of AXIS spectrometers for battery materials research and development. Examples of the capabilities of these instruments can be found in these applications notes.