Investigation of Gas Evolution and Safety of Materials for Lithium and Sodium-Ion Batteries

Abstract

The increased use of rechargeable batteries is one strategy in the fight against climate change, as a higher battery usage allows for the integration of more renewable energy sources. However, the development of batteries, particularly sodium-ion batteries, is still underway, with improvements to energy density and lifetime as the main research goals. Changes to the cell chemistry, the use of electrolyte additives, alloying negative electrode materials, and increasing the upper cut-off voltage to achieve higher cell capacity are all viable options to improve cell performance. This work explores electrolyte additives and Pb as a negative electrode material in sodium ion cells through on-line electrochemical mass spectrometry to investigate how these components impact the gases that are produced during battery operation. The electrolyte additives sodium difluorophosphate and 1,3,2-dioxathiolane 2,2-dioxide were studied in comparison to a control electrolyte through half cell tests and storage tests with notable differences in the gases evolved. Pb was compared to hard carbon and a blended electrode containing both materials to study the differences in carbonate and ether based electrolytes. Lastly, accelerating rate calorimetry was used to characterize the safety limits of a layered oxide positive electrode material for lithium-ion cells. Various upper cut-off voltages were used to probe the safety limitations of the material. Further investigation into the thermal response of the layered oxide positive electrode was completed using x-ray diffraction analysis. Overall, this work provides results for the gases produced from various cell chemistries in sodium-ion batteries, as well as the thermal responses seen in lithium-ion positive electrodes.