Device and Software to Measure Thermal Impedance of Electrochemical Systems
Different components within an electrochemical system (e.g., a battery) can generate heat due to inefficiencies in transport of the charges or exothermal reactions at different rates. For example, the joule heating of the connectors happens at a much shorter time period compared to the heat generated due to some of the reactions. By introducing current or voltage signals as input at the appropriate frequency and by carefully measuring the heat generated from the system (e.g., using a calorimeter) one can attribute the source of the heat generated to the specific phenomenon whose time constants match the time interval corresponding to the frequency of the input signal. By repeating the experiment over a suite of frequencies, one can then measure the amount of heat generated from the different individual or sets of processes.
Engineers at the National Renewable Energy Laboratory (NREL) have developed a device to measure quantitatively the heat generated due to the various phenomena happening within an electrochemical system. This is done using a careful design of experiments monitoring the voltage profile from the system under various load conditions. Related software captures the individual contributions of the various components including the kinetics and transport phenomena taking place within the battery to its thermal impedance using rigorous material, energy and charge balances.
The efficiency of reversible electrochemical reactions degrades over time and/or the number of cycles. For example, the usable duration for a battery decreases over several charge/discharge cycles. The device described above will help attribute the degradation in performance of the system to the individual components. For the battery example, the degradation of the electrolyte can be distinguished from the mechanical failure of the binder holding the electrode particles together based on the heat generation rates from the degraded electrolyte (with a lower ionic conductivity compared to a fresh cell) versus the decrease in the electronic conductivity across the electrodes (due to complacency in the binder properties). Another example is the change in the amount of heat generated due to the charge-transfer reaction between the fresh cell and an aged cell- indicating the drop in efficiency of the battery over time due to limitations in reversibility of the reaction. A highly sensitive calorimeter can be used to detect very small heat generated (a few microwatts) from the solid-state diffusion processes.
· Isolates the individual processes contributing to heat generation
· Improves accuracy of heat generation measurements
· Decreases cost of battery production
· Increases battery life
· Increases safety and reliability of battery components
· Distinguishes heat generated at the anode versus the cathode
· Works with coin-cells
Applications and Industries
· Battery calorimetry
· Lithium ion
· Energy storage
|Technology ID||Development Stage||Availability||Published||Last Updated|
|NREL ROI 13-66, SWR 13-15||Development||Available||03/22/2016||03/22/2016|