Lithium (Li) Ion Batteries (LIBs) are currently among the most desirable solutions for energy storage, but their prices will be driven up by increasing demand and geographically constrained reserves in the future. A potential alternative is given by Sodium (Na) Ion Batteries (NIBs) batteries due to high abundance, therefore low cost, and sodium’s highly suitable redox potential. This paradigm shift must be underpinned by fundamental scientific research: the chemical reactions are diverse and far from completely understood. Furthermore, comparative studies on LIBs vs. NIBs are needed to understand and optimise both materials. A deepened understanding of these chemistries will have a significant impact on battery research, engineering, and industry, leading to higher performance, cheaper, and safer batteries. This project focused on developing and applying new tools to study and develop LIBs and NIBs. In particular, it represents a milestone in the development of so-called “in situ” nuclear magnetic resonance (NMR) spectroscopy, i.e. investigations of the batteries while they are functioning. This offers the unique possibility of non-invasive real-time studies. Such experiments are very challenging because the batteries consist of many different components (typically, solid cathodes and anodes and a liquid electrolyte). The different components often lead to NMR signals at different chemical shifts, and it is challenging to either detect all relevant signals or to distinguish signals that overlap significantly. Furthermore, interferences between the NMR and external battery cycler circuit have impaired previous experimental attempts. Hence, to extend the field of battery materials studies using NMR, a new hardware system was developed in this project: a so-called automatic tuning/matching cycler (ATMC) in situ NMR probe with an entirely new design for the battery attachment inside the NMR probe (avoiding interference with the external cycler).
OBJECTIVES: (a) Overcome experimental challenges of in situ NMR on LIB/NIBs, by designing a new NMR probe system and a highly shielded in situ cell attachment setup. (b) Perform ATMC in situ NMR on lithium iron phosphate (LFP) cathodes as well as their Na-ion based “counterpart”, sodium iron phosphate (NFP). Comparing the underlying chemistries based on the in situ NMR experiment should facilitate the development of cheaper NIBs as an accessible alternative to LIBs in the near future. (c) Apply the ATMC in situ NMR hardware to other (so-called) “beyond-Li” battery materials, including tin and Na-metal anodes for NIBs, as well as hard carbon electrodes. In addition, the new approach should be enhanced to study promising (but highly complex) sodium vanadium phosphate fluoride (NVPOF) cathodes for NIBs.
CONCLUSIONS: The design and application of the new hardware has been a great success and pushed forward the current state-of-the-art in real-time studies of LIBs/NIBs materials. Our ATMC in situ NMR system overcame all hardware issues that impaired such in situ investigations before. In addition, a new in situ cell design, the plastic cell capsule (PCC), has been developed, making a variety of battery materials amenable for in situ NMR. The approach was applied to numerous battery materials as detailed below. Furthermore, based on some parts of this new ATMC in situ NMR equipment, an additional hardware device was designed: the external automatic tuning/matching (eATM) ROBOT, which we subsequently applied in numerous NMR investigations of energy storage materials. This eATM ROBOT helped to increase the measurement efficiency and, by automating several experimental steps, significantly accelerated this aspect of battery research. The ATMC in situ NMR approach, in conjunction with the PCC, has been applied to the above-mentioned electrode materials. These investigations afforded deep insights into structure-property-relationships of these materials, which helped to understand their electrochemical performance.
