Micro Reference Electrode Diagnostic Techniques for Detecting Sub-Zero Lithium Plating
Micro reference electrodes reveal sub-zero lithium plating by detecting negative graphite anode potentials relative to metallic lithium equilibrium in real time.
Reversible Lithium
Meaning
The quantity of available metal determines the maximum energy capacity of a rechargeable cell. This quantity represents the portion of the total lithium inventory that remains available for energy storage after accounting for losses to the interphase layers. Reversible lithium is the primary driver of the discharge capacity in a commercial cell.
Inventory Loss
Some ions become permanently trapped in the solid electrolyte interphase or through the formation of inactive metallic deposits. Maintaining a high level of reversible lithium is essential for ensuring that a vehicle meets its range requirements over several years. Degradation of the anode host can lead to a steady decline in the amount of metal that can be stored.
This consumption of ions represents the most common cause of capacity fade in modern systems.
Coulombic Efficiency
Measurements of the ratio between charge and discharge capacity indicate how much of the metal is being conserved. Since reversible lithium decreases with every cycle, the battery eventually reaches a point where it no longer holds a functional charge.
Capacity Retention
Systems with stable electrode structures protect the ions from being consumed by side reactions. A sudden drop in reversible lithium often signals a catastrophic failure of the separator or a massive degradation of the cathode.