Lithium Iron Phosphate Cell Open Circuit Voltage Equilibrium Mapping
Lithium iron phosphate open circuit voltage equilibrium maps two-phase hysteresis using multi-hour relaxation testing for state of charge estimation
Phase Transformation Friction
Meaning
Energy dissipation occurs at the microscopic level during electrode material phase changes due to the resistance of phase boundaries moving through the crystalline structure. This resistance is termed phase transformation friction, and it acts as a thermal and electrical loss within the active particles. The phenomenon is especially prominent in materials that undergo first-order phase transitions, such as lithium iron phosphate.
Microstructural Process
As lithium ions are inserted, new phases nucleate and grow, pushing against the lattice of the host material. This movement requires overcoming an energy barrier associated with the mechanical strain at the phase boundary. The energy required to overcome this barrier is lost as heat, which increases the temperature of the cell during cycling.
Thermal Output
The heat generated by this structural resistance is distinct from ordinary Joule heating and cannot be calculated using simple internal resistance models. This additional thermal source becomes prominent during periods of continuous charging and discharging. Engineers must account for this behavior when designing thermal management systems for heavy-duty applications.
System Behavior
Voltage profiles show a flat plateau because the phase change happens at a constant chemical potential. This shift creates a voltage gap that directly reduces charging efficiency.