Abstract
Lithium metal is a favorable anode material in all-solid Li-polymer batteries because of its high energy density. However, dendrite formation on lithium metal causes safety concerns. Here we obtain images of the Li-metal anode surface during cycling using in situ scanning electron microscopy. Constructing videos from the images enables us to monitor the failure mechanism of the battery. Our results show the formation of dendrites on the edge of the anode and isles of decomposed lithium bis(trifluoromethanesulfonyl)imide on the grain boundaries. Cycling at high rates results in the opening of the grain boundaries and depletion of lithium in the vicinity of the isles. We also observe changes in the surface morphology of the polymer close to the anode edge. Extrusion of lithium from these regions could be evidence of polymer reduction due to a local increase in temperature and thermal runaway assisting in dendrite formation.
Highlights
Lithium metal is a favorable anode material in all-solid Li-polymer batteries because of its high energy density
We investigate the failure mechanism of an allsolid Li-metal polymer battery following the evolution of a solid electrolyte interphase (SEI) using in situ scanning electron microscopy (SEM)
At the beginning of cycling, the polymer electrolyte-based battery was stabilized at 70 °C in order to have a total ionic conductivity of ~10−4 S/cm; after 2 days of cycling, the temperature was increased to 80 °C to further facilitate ionic conductivity and, the reactions at the interface
Summary
Lithium metal is a favorable anode material in all-solid Li-polymer batteries because of its high energy density. Our results show the formation of dendrites on the edge of the anode and isles of decomposed lithium bis(trifluoromethanesulfonyl)imide on the grain boundaries. Even though all-solid Li-metal polymer batteries are great replacements for batteries with liquid electrolytes, further investigation of higher charging rate cycling should be conducted, as this can cause the formation of dendrites that can perforate through this medium due to their carbide nature[10]. We investigate the failure mechanism of an allsolid Li-metal polymer battery following the evolution of a solid electrolyte interphase (SEI) using in situ scanning electron microscopy (SEM). This study shows formation of dendrites, opening of grain boundaries, and isles, and decomposition of the salt
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