Fundamental Science of Lithium and Sodium-ion Batteries

The world must eliminate the use of fossil fuels. Renewable energy sources such as solar and wind need to be deployed at increasing rates. Battery energy storage is required to buffer the variability of solar and wind. Electric vehicle production will increase about 10-fold by 2030. Lithium-ion batteries are the state-of-the-art power source for these applications but there is concern about sufficient resources to deploy Li-ion batteries at the required scale. Therefore, sodium-ion batteries are being developed around the world and in our laboratory. Increasing the lifetime of Li-ion and Na-ion batteries will delay recycling and reduce the need for production. This proposal aims to help increase battery lifetime though innovative basic science experiments. We will perfect and employ a device that can monitor the movement of electrolyte in Li-ion cells in response to electrode volume changes. Some electrolyte can be pushed out of the electrode stack by expanding electrode particles during the charge cycle. If the subsequent discharge is too rapid, electrolyte cannot re-infiltrate the electrode stack rapidly enough and this can lead ultimately to cell failure after many charge discharge cycles. Our device continually measures the moment of inertia of a cylindrical Li-ion or Na-ion cell during operation. The moment of inertia depends on the mass distribution within the cell which depends on the electrolyte distribution. In a single charge-discharge cycle we will detect when the electrolyte does not flow completely back into the electrode stack, thus determining quickly the limits of discharge current versus temperature to avoid this issue. We will also measure the rates of degradation of Li-ion and Na-ion cells at temperatures between 20 and 100oC using electrochemical and other methods. We hope to be able to extract the kinetics of various degradation mechanisms as a function of temperature. This kinetic information can then, hopefully, be used to predict lifetime of cells at ambient temperature based on experiments conducted at elevated temperature. The lifetime of Li-ion cells at ambient temperature is already on the order of decades for good cells. To improve the lifetime of such cells is possible, but it is very difficult at present to know what the improved lifetime will be. This predictive ability is essential for grid storage batteries which, ultimately, should last 50 or more years. We will use high resolution X-ray computed tomography to study electrode and electrode particle degradation modes, such as microcracking and delamination, during operation of Li-ion or Na-ion cells. This work will be conducted at the Canadian Light Source. This Discovery Grant will support the training of battery scientists and engineers urgently needed as the "electrification of everything" proceeds. Graduates of this laboratory are heavily recruited even one year before they finish their degree due to the quality of their training.