Mixed Ionic–Electronic Conducting Li4Ti5O12 as Anode Material for Lithium Ion Batteries with Enhanced Rate Capability – Impact of Oxygen Non-Stoichiometry and Aliovalent Mg2+-Doping Studied by Electron Paramagnetic Resonance
, Josef Granwehr
, Hans Kungl
, and Rüdiger-A. Eichel
1 Forschungszentrum Jülich, Institut für Energie und Klimaforschung (IEK-9: Grundlagen der Elektrochemie), D-52425 Jülich, Germany
2 Forschungszentrum Jülich, Institut für Energie und Klimaforschung (IEK-9: Grundlagen der Elektrochemie), D-52425 Jülich, Germany
3 RWTH Aachen University, Institut für Physikalische Chemie, Aachen, Germany
4 Jülich-Aachen Research Alliance, section JARA-Energy
Spinel-type Li4Ti5O12 is an attractive anode material for lithium-ion battery applications owing to its high specific energy and almost vanishing mechanical strain upon Li-(de)intercalation. The impact of oxygen non-stoichiometry and aliovalent Mg-doping on the defect chemistry of Li4Ti5O12 has been characterized by quantitative electron paramagnetic resonance (EPR) spectroscopy. The results obtained demonstrate that the Mg2+-ions are amphoterically incorporated at the here studied concentrations on both lithium (MgLi•) and titanium (Mg′′Ti) sites. Mg2+-doping thus simultaneously results in the formation of donor (MgLi•) and acceptor (Mg′′Ti) centers. Furthermore, upon both oxygen deficiency and Mg2+-doping, the concentration of `polaronic'-type Ti3+-states is increased, accounting for the enhanced electronic conductivity.
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