High Temperature Compatible Conflat Cell with Adjustable Stack Pressure for In-Situ and Operando X-Ray Studies of Lithium-Ion Battery Materials

Abstract

Lithium-ion batteries have emerged as the dominant energy storage technology for electronic devices, vehicles, and grid-scale applications [1,2]. Further improvements of cell design, components, and materials depend heavily on reproducible characterization. The challenge is to replicate real-world battery operation conditions in laboratory measurements, which makes designing robust in-situ / operando cells a challenging task. Cell materials should be as close as possible to those used in production cells (e.g. steel, aluminum, copper, nickel) [3] and lithium should only react with the test electrode, not with the cell components or the test environment. In addition, a controlled but significant mechanical pressure (0.1 - 1 MPa) should be applied to the electrochemically active material, and in some cases, the cell must operate over a wide temperature range. While existing in-situ and operando electrochemical cell designs meet many of these criteria, no design meets all of them.We have developed a Сonflat in-situ cell for X-ray diffraction studies based on Conflat vacuum flanges and electrical feedthroughs. This cell design is based on readily available components and can provide an ultra-high vacuum compatible seal and controllable and commercially relevant stack pressure over a wide temperature range [4]. Cell sealing is accomplished using knife edges impinging on a copper gasket. Conflat cells have a potential to meet all of the criteria for a robust and reproducible in-situ / operando cell. The challenge lies in properly incorporating an X-ray transparent window for X-ray measurements. While Beryllium windows can be attached to the Conflat flange using metal bonding techniques, such bonding can be cost prohibitive for many laboratories (e.g. thousands of dollars per flange). In our design, we used a readily available steel reinforced epoxy to attach the Beryllium window to the Conflat flange, making it an inexpensive and high quality alternative even for long-term in-situ and operando measurements. In-situ and operando X-ray powder diffraction results from Graphite and Aluminum electrodes cycled at 30℃ and 120℃, respectively, are provided in Fig. 1. Diffraction patterns were combined and plotted as a logarithmic-scale colormap together with the measured cell potential in Fig. 1a) for Graphite and Fig.1b) for Aluminum electrodes [5]. For the C-Li system in Fig.1a), only the C-Li peaks of interest are shown in the ranges of 20°-30° and 75°-85° scattering angle. From the voltage profile in Fig.1a), four intercalation stages can be discerned, as has been extensively reported before, and are marked with dashed red lines. Al-Li phases can be well defined both from the voltage profile and the diffraction pattern. In Fig.1b), the solid vertical lines that do not change their intensity with time, at approximately 42°, 52° and 71° are the peaks from the Beryllium window. The rest of the peaks that change their intensity and position with time can be attributed to the various phases of the Al-Li system that have been reported in our previous ex-situ studies [6]. Phase formation is reversible for both Graphite and Aluminum electrodes and a pure Graphite and Aluminum metal could be recovered when the cell was completely charged again. In both in-situ experiments, the cell performed very well and high quality data was obtained. We will present and discuss the X-ray diffraction data and all of the phases of the C-Li and Al-Li systems in more detail as well as results from the rigorous testing of the cell to assess its superior sealing and longevity [5].[1] M. Li et al., Advanced Materials 30 (33) 1800561 (2018).[2] H. C. Hesse et al., Energies, 10 (12) 2107 (2017).[3] M. Zwicker et al., Journal of Advanced Joining Processes 1 100017 (2020).[4] M.D. Fleischauer et al., Journal of The Electrochemical Society, 166 (2) A398-A402 (2019).[5] O. Sendetskyi et al., Journal of Applied Crystallography, In preparation (2021).[6] M. Ghavidel et al., Journal of The Electrochemical Society, 166 (16) A4034-A4040 (2019).Figure 1. Voltage profiles and operando X-ray diffraction patterns plotted as a log-scale intensity colormap for a) Graphite electrode measured at 30℃ and b) freestanding Aluminum foil electrode measured at 120℃ [5]. Figure 1