Journal
ADVANCED ENERGY MATERIALS
Volume 5, Issue 15, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201500599
Keywords
germanium anodes; lithium-ion batteries; operando X-ray characterization; X-ray absorption spectroscopy; X-ray diffraction
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Funding
- U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences [DE-AC02-76SF00515]
- Energy Research Institute @ NTU
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Operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li15Ge4 (c-Li15Ge4) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of approximate to 1800 mAh g(-1) can be attained up to 100 cycles at a slow C-rate of C/21 when there is complete conversion of Ge anode into c-Li15Ge4. When the C-rate is increased to approximate to C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of approximate to 1000 mAh g(-1) is achieved with poorer electrochemical reversibility. An increase in C-rate to C/5 and higher reduces the capacity (approximate to 500 mAh g(-1)) due to an impeded transformation from amorphous LixGe to c-Li15Ge4, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C-rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high-capacity anodes.
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