Al2O3 coating on anode surface in lithium ion batteries: Impact on low temperature cycling and safety behavior

Commercial 18650-type lithium ion cells employing an Al2O3 coating on the anode surface as a safety feature are investigated regarding cycling behavior at low temperatures and related safety. Due to irreversible lithium metal deposition, the cells show a pronounced capacity fading, especially in the first cycles, leading to a shortened lifetime. The amount of reversibly strippable lithium metal decreases with every cycle. Post-mortem analysis of electrochemically aged anodes reveals a thick layer of lithium metal deposited beneath the coating. The Al2O3 coating on the electrode surface is mostly intact. The lithium metal deposition and dissolution mechanisms were determined combining electrochemical and post-mortem methods. Moreover, the cell response to mechanical and thermal abuse was determined in an open and adiabatic system, revealing a similar behavior of fresh and aged cells, thus, demonstrating no deterioration in the safety behavior despite the presence of a thick lithium metal layer on the anode surface.