Lithium plating (accumulation of metallic lithium) is a safety-critical phenomenon that occurs mainly during fast charging of lithium-ion batteries at cold temperatures. It is caused on the anode by the limited capability to absorb lithium ions at the desired rate. Reversible and irreversible plating can be accompanied by the formation of dendrites and lead to safety-critical short circuits. Irreversible plating additionally leads to a significant capacity loss due to the loss of cyclable lithium. To optimize battery lifetime and safety for all requirement profiles, it is central to detect the formation of metallic lithium and dendrites at an early stage.
For this purpose, charge/discharge cycle tests with different test conditions (variable temperature (-5°C -> 45°C) and C-Rate (C/10 -> 4C)) were performed on high power graphite/LCO based pouch cells (Cn=850mAh). In subsequent differential voltage analysis (DVA), electrical markers for indications of limiting lithium-ion uptake as well as lithium stripping were investigated.
First stripping indicators could be seen from 5°C|3C, while the limited lithium-ion uptake during charging becomes visible already at higher temperatures and lower C-rates.
The reversible stripped lithium and the irreversible capacity lost both show a nearly linear behavior with increasing C-rate at a given temperature for the used cell.
To confirm the electrical indicators/markers, selected aging points are examined using post-mortem analysis. Using post-mortem analysis in combination with other electrical measurements (EIS, HPPC, etc.), a physical-chemical model is to be parameterized to simulate the cell behavior and therefore improve the understanding of processes related to plating.
The knowledge thus gained could provide both rapid and accurate feedback on the impact of temperature and charge rate on the behavior of lithium plating. In addition, the further development of electrical tests could enable better safety testing of cells.