Neutrons As a Probe to Characterize in Situ/Operando Electrodes of Li Ion Batteries
Authors: Gilles Ralph , Zinth Veronika , Seidlmayer Stefan , Paul Neelima , von Lüders Christian , Hattendorff Johannes , Buchberger Irmgard , Hofmann Michael , Erhard Simon Vincent , Karge Lukas , Kudejova Petra , Schulz Michael , Gasteiger Hubert A. , Jossen Andreas 
Published: February 2020

Non-destructive studies to investigate Li-ion batteries in situ/operando are a challenge although they show much more details on the processes during charging/discharging and aging. Especially, the high sensitivity of neutrons to light elements as Li and easier distinction of neighbor elements in comparison to X-rays lead to a powerful tool in battery research. With neutron diffraction, changes in a commercial 18650-type NMC (LiNi1/3Mn1/3Co1/3O2)/graphite cylindrical cell can be followed nicely at the graphite anode during intercalation/de-intercalation in the charging/discharging process by phase detection starting from pure graphite via LiCx phases [1,2]. In addition, the influence of temperature, C-rate or any relaxation if holding at a certain state of charge can be described in detail [2]. For direct visualization of electrodes, neutron radiography or neutron tomography was applied to observe directly spatial inhomogeneities down to <100 mm of full battery cells. Particularly, the low absorption of neutrons in metals enables it to penetrate even larger cells, such as ZEBRA batteries, to follow the change e.q. liquid Na-level in the charging and discharging process [3,4]. Smaller effects at the NMC electrode, such as transition metal dissolution, and their deposition on the graphite anode will be presented on graphite/LiNi1/3Mn1/3Co1/3O2 (NMC) lithium pouch cells using the PGAA (prompte gamma activation analysis) technique [5]. This method exploits the irradiation of sample material with neutrons and the subsequent detection of prompt gamma rays emitted during de-excitation of the compound nuclei. The method determines elemental composition and concentration of sample materials down to the ppm range. Thus PGAA can detect even trace amounts of elements on electrodes. If compositional changes during charging/discharging occur in thin pouch cells, the transmission method of small-angle neutron scattering can be applied to describe the gradual particle lithiation with the measured total integrated intensity in graphite/LiNi1/3Mn1/3Co1/3O2cells [6]. In addition if present objects as particles on the nanoscale level (1-300 nm) can be characterized.
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