Quantifying Solid Interphase Formation Kinetics in Commercial Lithium Cells
High precision coulometry and differential voltage analysis isolate solid interphase formation kinetics and active lithium consumption in lithium cells.
Isothermal Calorimetry
Meaning
Thermal analysis identifies heat generation or absorption by maintaining a specimen at a constant temperature throughout a physical or chemical transition. Isothermal calorimetry detects minute energy fluctuations by measuring the electrical power required to maintain thermal equilibrium between a sample and a reference sink. This procedure produces a precise record of kinetic reaction rates and total energy release during battery charge, discharge, or storage cycles.
Measurement Principle
Sensitivity depends on the ability to quantify heat flow against a baseline within an isolated chamber. Isothermal calorimetry relies on Peltier elements that pump heat in or out of the sample vessel to compensate for internal chemical activity. Each milliwatt of power applied to the cooling or heating modules provides an exact equivalent of the thermal energy being produced or consumed by the electrolyte or electrode materials.
Testing Procedure
Sample preparation involves placing an active cell or material component inside a regulated block that mimics specific environmental conditions. Isothermal calorimetry operates by monitoring the baseline heat output until the system reaches a stable state before initiating an electrical load or thermal stress. Data acquisition systems record the power compensation needed to counteract any deviation from the set point, resulting in a continuous plot of heat flow versus time.
Safety Application
Thermal stability limits define the upper boundaries for cell operation under abusive conditions like internal shorts or runaway reactions. Isothermal calorimetry quantifies the exact temperature at which exothermic decomposition starts, providing data for the design of battery management systems and fire mitigation strategies. Engineers use this information to determine whether the chemical cooling capacity of a pack matches the heat production of the cells under standard use.