Meaning
Discharge cycles involve the return of ions to the cathode lattice structure following their movement through the electrolyte from the anode. Successful lithium reintercalation requires available vacant sites within the host material and a clear path for ion transport. This process converts chemical energy back into electrical current to power the external load.
Ion Transfer
Mobility of the lithium ions depends on the diffusion coefficient of the cathode material and the viscosity of the electrolyte. As the ions reach the surface of the electrode, they must overcome a desolvation barrier to enter the solid structure.
Voltage Recovery
Relaxing the battery after a high current pulse often shows a gradual rise in potential. This effect occurs during lithium reintercalation as the concentration of ions within the electrode particles equilibrates. If the ions cannot distribute themselves evenly, local areas of high stress develop and can lead to cracking of the cathode crystals.
Smooth insertion of the ions is essential for maintaining a stable voltage profile throughout the discharge. Efficient transport leads to higher usable energy because the cell can operate for longer before hitting the cut-off voltage.
Capacity Retention
Degradation of the host lattice over many cycles can block the entry points for the ions. When lithium reintercalation becomes difficult, the total amount of energy the battery can hold decreases over time.
