posted on 2017-07-10, 00:00authored byYuzhang Li, Yanbin Li, Yongming Sun, Benjamin Butz, Kai Yan, Ai Leen Koh, Jie Zhao, Allen Pei, Yi Cui
Lithium
(Li) metal is a high-capacity anode material (3860 mAh
g–1) that can enable high-energy batteries for electric
vehicles and grid-storage applications. However, Li metal is highly
reactive and repeatedly consumed when exposed to liquid electrolyte
(during battery operation) or the ambient environment (throughout
battery manufacturing). Studying these corrosion reactions on the
nanoscale is especially difficult due to the high chemical reactivity
of both Li metal and its surface corrosion films. Here, we directly
generate pure Li metal inside an environmental transmission electron
microscope (TEM), revealing the nanoscale passivation and corrosion
process of Li metal in oxygen (O2), nitrogen (N2), and water vapor (H2O). We find that while dry O2 and N2 (99.9999 vol %) form uniform passivation
layers on Li, trace water vapor (∼1 mol %) disrupts this passivation
and forms a porous film on Li metal that allows gas to penetrate and
continuously react with Li. To exploit the self-passivating behavior
of Li in dry conditions, we introduce a simple dry-N2 pretreatment
of Li metal to form a protective layer of Li nitride prior to battery
assembly. The fast ionic conductivity and stable interface of Li nitride
results in improved battery performance with dendrite-free cycling
and low voltage hysteresis. Our work reveals the detailed process
of Li metal passivation/corrosion and demonstrates how this mechanistic
insight can guide engineering solutions for Li metal batteries.