Automatic Tuning Matching Cycler (ATMC) in situ NMR spectroscopy as a novel approach for real-time investigations of Li- and Na-ion batteries

Abstract

We have developed and explored the use of a new Automatic Tuning Matching Cycler (ATMC) in situ NMR probe system to track the formation of intermediate phases and investigate electrolyte decomposition during electrochemical cycling of Li- and Na-ion batteries (LIBs and NIBs). The new approach addresses many of the issues arising during in situ NMR, e.g., significantly different shifts of the multi-component samples, changing sample conditions (such as the magnetic susceptibility and conductivity) during cycling, signal broadening due to paramagnetism as well as interferences between the NMR and external cycler circuit that might impair the experiments. We provide practical insight into how to conduct ATMC in situ NMR experiments and discuss applications of the methodology to LiFePO4 (LFP) and Na3V2(PO4)2F3 cathodes as well as Na metal anodes. Automatic frequency sweep (7)Li in situ NMR reveals significant changes of the strongly paramagnetic broadened LFP line shape in agreement with the structural changes due to delithiation. Additionally, (31)P in situ NMR shows a full separation of the electrolyte and cathode NMR signals and is a key feature for a deeper understanding of the processes occurring during charge/discharge on the local atomic scale of NMR. (31)P in situ NMR with "on-the-fly" re-calibrated, varying carrier frequencies on Na3V2(PO4)2F3 as a cathode in a NIB enabled the detection of different P signals within a huge frequency range of 4000 ppm. The experiments show a significant shift and changes in the number as well as intensities of (31)P signals during desodiation/sodiation of the cathode. The in situ experiments reveal changes of local P environments that in part have not been seen in ex situ NMR investigations. Furthermore, we applied ATMC (23)Na in situ NMR on symmetrical Na-Na cells during galvanostatic plating. An automatic adjustment of the NMR carrier frequency during the in situ experiment ensured on-resonance conditions for the Na metal and electrolyte peak, respectively. Thus, interleaved measurements with different optimal NMR set-ups for the metal and electrolyte, respectively, became possible. This allowed the formation of different Na metal species as well as a quantification of electrolyte consumption during the electrochemical experiment to be monitored. The new approach is likely to benefit a further understanding of Na-ion battery chemistries.

Unraveling the Reaction Mechanisms of SiO Anodes for Li-Ion Batteries by Combining in Situ 7Li and ex Situ 7Li/29Si Solid-State NMR Spectroscopy

“…7 Li NMR experiments. 36,37 Powder XRD Powder XRD patterns of a-SiO, d-SiO, and Li SiO 4 were acquired at 296(2) K on a Panalytical Empyrean diffractometer equipped with a Ni filter using Cu-K α radiation ( = 154.06 pm, 154.43 pm) in a Bragg-Brentano setup. Rietveld refinement was performed using the TOPAS Academic software package (version 4.1).…”

“…In addition, we use in situ (sometimes also referred to as operando to reflect data collection during battery cycling) 7 Li NMR spectroscopy to monitor the formation of Li x Si phases in real time. 36,37 We apply our analytical approach to investigate a-SiO, and a series of disproportionated SiO (d-SiO) phases, formed by heating a-SiO to 800 to 1100 C, in LIBs. We compare our results with those obtained from a crystalline Si (c-Si) anode, so as to investigate the influence of Si domain crystallinity and size on the formation of the different Li x Si phases.…”

In Situ Stripline Electrochemical NMR for Batteries

“…Moreover, the presence of the stripline does not compromise or hinder the performance of the battery itself: as the cathode and anode can overlap the stripline neck l (both the width and thickness of the stripline are very small), normal ion transport can be realized through the large open areas next to the stripline neck. Furthermore, as the active anode and cathode materials, which are deposited directly onto the respective current collectors, are pressed tightly against the central stripline ( vide infra ), the entire NMR‐sensitive region is filled with the electrolyte‐wetted battery materials, a much higher detector filling factor (a ratio between sample and NMR detection volumes) is achieved with the stripline detector (Figure ) than is achieved with current external in situ battery NMR configurations in which a rectangular flat Bellcore‐like plastic battery fills only a portion of the NMR‐sensitive region of the solenoidal coil . Consequently, this setup is ideal for measuring in situ battery NMR, as the higher detection sensitivity is expected to enable fast NMR data acquisition while the battery is cycled without disturbing the system during measurement.…”

Unravelling Local Atomic Order of the Anionic Sublattice in M(Al1−xGax)4 with M=Sr and Ba by Using NMR Spectroscopy and Quantum Mechanical Modelling

“…The hardening process of the glue powder suspension was performed outside or inside the magnetic field to achieve regular and aligned powder samples, respectively.T he NMR experiments were performed by using aB ruker Avance III spectrometer with am agnetic field of B 0 = 9.40 T. The corresponding 27 Al frequency is 104.269 MHz. Regular powder samples were measured by applying as eries of selective excitation experiments (frequency sweep) [17,30,61] with low power pulses of 50 and 25 msf or SrAl 4 and BaAl 4 ,r espectively.T he experiments were performed by using an eightfold cycle of pulse sequences with acycle delay of 0.25 s. [59,60] The static (no sample spinning) NMR experiments were performed with al ow-Q automatic tuning-matching goniometer (ATMG) probe system.…”