Prof. Dr. Helmut Ehrenberg
Karlsruher Institut für Technologie (KIT)
Institut für Angewandte Materialien - Energiespeichersysteme (IAM-ESS)
Titel: ‘In-operando’ Studies on Li-ion Batteries using Neutron and Synchrotron Radiation
Zusammenfassung: Electrochemical energy storage devices show a very pronounced interaction
between electrode materials and electrolyte. Therefore, fatigue and ageing of Li-ion batteries can
only be understood if the underlying changes in the materials are studied under real operation
conditions inside a fully working battery. This requires non-destructive probes which can penetrate
the housing, but nevertheless provide information about the details of the active materials inside the
complete device. High-energetic synchrotron and neutron radiation are ideal probes to reveal
structural changes of the anode and cathode materials of Li-ion batteries over many chargedischarge cycles. Both radiations are essentially complementary: synchrotron radiation allows much
fast data collection with a better time and spatial resolution and is more sensitive to heavier
elements, while neutrons are most sensitive to light elements (especially H, Li, C, and O), which play
the major role in light-weight energy storage. A combination of diffraction and tomography allows to
follow changes in the materials during cycling and with proceeding fatigue.
Selected examples are shown, mainly for commercial 18650-type Li-ion batteries [1]. Neutron
diffraction data allow a sophisticated analysis of the crystal structures and microstructures of the Liintercalated graphite anode and of the Li-extracted layered transition metal oxides, like LiCoO2 or
Li(Ni,Co,Mn)O2 (NCM). Rietveld refinement allows very reliable conclusions about the Li-distribution
in the crystalline materials and a correlation with the states of charge (SOC) and health (SOH) [2]. The
Li-occupation in the cathode material was compared in the charged and discharged state over 1000
cycles and reveals a reduced amount of exchanged "mobile" lithium within the fixed voltage window
in excellent agreement with the observed capacity loss. The ratio between LiC6 and LiC12 in the fully
charged state is also consistent with the observed degree of fatigue. Tomography gives an insight
into changes in the interior cell geometry and electrolyte distribution. These results are combined
with complementary post-mortem analysis and discussed in the light of fatigue and life time in
dependence on the conditions of operation.
[1] A. Senyshyn et al., J. Power Sources 203 (2012) 126– 129.
[2] O. Dolotko et al., J. Electrochem. Soc., in print.