Full Cell Voltage Boundary Calibration to Prevent Crystalline Lithium Silicide Nucleation
Upper full cell voltage cutoff calibration limits local anode lithiation potential above 50 mV vs Li/Li+ to prevent crystalline silicon phase breakdown.
Binder Degradation
Meaning
Electrochemical and mechanical breakdown of the polymeric matrix holding electrode active materials and conductive agents together defines the process. Ongoing binder degradation leads to the isolation of particles from the current collector. The failure mode typically occurs due to chemical oxidation or mechanical stress during volume changes.
Adhesion Loss
Deterioration of the bond between the coating and the foil substrate represents a primary failure mode. When binder degradation occurs, the active material layer can delaminate or crack. Physical disconnection reduces the available surface area for ion transport and increases internal resistance.
Chemical Stability
Exposure to acidic byproducts or high potentials triggers the decomposition of the polymer chains. Most binder degradation involves the scission of long molecules into shorter fragments that no longer provide structural support. Polyvinylidene fluoride can react with trace moisture to form hydrofluoric acid which further accelerates the damage.
The process is most aggressive at the interface where the voltage is highest.
Capacity Impact
Reduction in the energy storage capability of the cell follows the loss of conductive pathways. Because binder degradation is often irreversible, it is a permanent contributor to the aging of the battery pack. Maintaining a stable operating temperature and voltage window helps slow the rate of decay.