Doubling Reversible Capacities in Epitaxial Li 4 Ti 5 O 12 Thin Film Anodes for Microbatteries
Daniel M. Cunha (University of Twente)
Theodoor A. Hendriks (University of Twente)
Alexandros Vasileiadis (TU Delft - RST/Storage of Electrochemical Energy)
Chris M. Vos (University of Twente)
Tomas Verhallen (TU Delft - RST/Storage of Electrochemical Energy)
Deepak P. Singh (University of Twente)
Marnix Wagemaker (TU Delft - RST/Storage of Electrochemical Energy)
Mark Huijben (University of Twente)
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Abstract
Despite the lower gravimetric capacity, Li
4
Ti
5
O
12
is an important alternative to graphite anodes, owing to its excellent high temperature stability, high rate capability, and negligible volume change. Although surfaces with lithium compositions exceeding Li
7
Ti
5
O
12
were observed previously during the first charge-discharge cycles, no stable reversible capacities were achieved during prolonged cycling. Here, structural engineering has been applied to enhance the electrochemical performance of epitaxial Li
4
Ti
5
O
12
thin films as compared to polycrystalline samples. Variation in the crystal orientation of the Li
4
Ti
5
O
12
thin films led to distinct differences in surface morphology with pyramidal, rooftop, or flat nanostructures for respectively (100), (110), and (111) orientations. High discharge capacities of 280-310 mAh·g
-1
were achieved due to significant surface contributions in lithium storage. The lithiation mechanism of bulk Li
4
Ti
5
O
12
thin films was analyzed by a phase-field model, which indicated the lithiation wave to be moving faster along the grain boundaries before moving inward to the bulk of the grains. The (100)-oriented Li
4
Ti
5
O
12
films exhibited the highest capacities, the best rate performance up to 30C, and good cyclability, demonstrating enhanced cycle life and doubling of reversible capacities in contrast to previous polycrystalline studies.
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