Next level real-time characterisation of Li- and Na-ion batteries by automatic tuning/matching in situ NMR spectroscopy
My research in Cambridge (UK) was funded by
THE FRAMEWORK PROGRAMME FOR RESEARCH AND INNOVATION
Grant no. 65444 (ATMCinsituNMR)
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).
- 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.
- 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.
- 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.
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.
Overview of results and their exploitation and dissemination
Overall, we have established a huge range of new NMR equipment (ATMC in situ NMR, eATM ROBOT, PCC) to enable in situ NMR investigations with an outstanding flexibility. This is needed to balance the specific experimental conditions during the investigation of LIBs/NIBs.
ATMC in situ NMR on LFP, NFP, and NVPOF cathodes offered insights into sructural changes of these materials during cycling. Furthermore, in situ NMR on Na-metal anodes helped to monitor the formation of different Na-metal species, and to quantify the electrolyte consumption during the electrochemical experiment. In addition, ATMC in situ NMR in combination with other experimental techniques provided insights into the structure of hard carbon anodes in NIBs.
Exploitation and dissemination
The developments/findings have been published in 8 scientific articles and 3 publications from conference proceedings. Furthermore, the research outcomes were disseminated in 13 talks and 6 poster presentations at conferences. The hardware developments have been made accessible the world-wide community of researchers via an industry partner. In addition, we reached out to the public at large, in particular to school children, through (hands-on) experiments on batteries made out of lemons; we discussed energy storage at a "Scientific Lunch Break" talk in 2015 and the "Cambridge Science Festival" in 2016. Furthermore, the objectives of this research have been explained to the public in an interview (press release; print and online) with the "Cambridge News" as well as an "Instagram feature" in 2016.
Progress beyond the state of the art and impact
In situ investigations of energy storage materials are one of the major ways forward to satisfy the societal need for new, cheaper, and safer batteries. In the long run, such fundamental studies will be instrumental to keep pace with the increasing demand for storing energy generated from “green” sources. In situ NMR, which was at the heart of this project, is a highly suitable technique for these studies as it provides unique insights into the atomic-scale mechanisms under real-time working conditions of batteries. The new ATMC in situ NMR approach enabled highly sought-after investigations of batteries that had been impossible until the start of the project. The findings now provide a firm foundation for future studies and, ultimately, the application of new "beyond-Li" (such as NIBs) as a cheaper aletrnatives. The new hardware solutions are expected to have a significant impact in accelerating future developments of energy-storage materials.
J. M. Stratford, M. Mayo, P. K. Allan, O. Pecher, O. J. Borkiewicz, K. M. Wiaderek, C. J. Pickard, A. J. Morris, C. P. Grey. Investigating Sodium Storage Mechanisms in Tin Anodes: A Combined Pair Distribution Function Analysis, Density Functional Theory and Solid-State NMR Approach.Manuscript 2017, submitted.
O. Pecher, D. M. Halat, J. Lee, Z. Liu, K. J. Griffith, M. Braun, C. P. Grey. Enhanced efficiency of solid-state NMR investigations of energy materials via the external Automatic Tuning/Matching (eATM) robot. J. Magn. Reson. 2017, 275, 127-136.
O. Pecher, J. Carretero-González, K. J. Griffith, C. P. Grey. Materials’ Methods: NMR in Battery Research. Chem. Mater. 2017, 29, 213-242.
J. M. Stratford, P. K. Allan, O. Pecher, P. A. Chater, C. P. Grey. Mechanistic insights into sodium storage in hard carbon anodes using local structure probes. Chem. Comm. 2016, 52, 12430-12433.
O. Pecher, P. M. Bayley, H. Liu , Z. Liu, N. M. Trease, C. P. Grey. Automatic Tuning Matching Cycler (ATMC) in situ NMR spectroscopy as a novel approach for real-time investigations of Li- and Na-ion batteries. J. Magn. Reson. 2016, 265, 200-209.
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