Nanostructured
antimony is a highly promising alloying electrode material for both
Li-ion and Na-ion battery systems, possessing a large gravimetric
charge storage capacity (660 mAh g–1) combined with
extraordinary rate capability (cycling at a 20C rate results in only
a ∼15% decrease in capacity, relative to 1C). However, temperature
can strongly affect the performance of these antimony electrode materials,
and their temperature-dependent cycling remains largely unexplored.
Changes in temperature-dependent cycling characteristics can occur
via a variety of mechanisms, potentially resulting in either reversible
or irreversible loss of capacity at lower temperatures. Here, we utilize
temperature-dependent electrochemical impedance spectroscopy (EIS)
to investigate the source of performance changes in these Na-ion battery
electrode materials. We find that increased charge transfer resistance
is predominantly responsible for the observed 100 mAh g–1 capacity reduction (∼20%) upon changing the cycling temperature
from 50 to 5 °C, with the double layer capacitance remaining
largely unchanged, negligible resistive and capacitive contributions
from charge transfer or ion mobility through the solid–electrolyte
interphase (SEI) layer, and slight changes in the Na-ion solid-state
diffusion rate in the antimony nanocrystals. As such, the observed
decrease in capacity at low temperature is almost entirely caused
by increased charge transfer resistance due to less facile Na-ion
transport across the SEI-layer–electrode interface.
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