2, Sandia National Laboratories, Livermore, California, United States
Solid-state electrolytes have been explored increasingly for use in Li+ batteries on account of their ability to address the safety issues, packaging constraints, and volumetric design concerns associated with liquid electrolytes. Until recently however, their low ionic conductivity limited the achievable power density. Along with poor conductivity, high interfacial resistances stemming from the processing conditions or material incompatibility have limited their use in commercial cells. Recently, ionogels, pseudo-solid-state electrolytes consisting of an ionic liquid electrolyte confined in a mesoporous inorganic matrix, have attracted interest because of their high ionic conductivity, stability, and solution processability. There have been few studies, however, of the electrode-ionogel interface. This presentation will review our work directed at understanding the interface for solution-processable ionogel electrolytes with various electrode materials.
Recent work has shown that processing the ionogel as a sol on certain positive electrodes led to interfacial barriers for Li+ intercalation/deintercalation. This detrimental effect has been attributed to several possible sources such as surface reduction by the sol’s catalyst or silica nucleated on the surface hindering electrolyte percolation. Using XPS, Raman spectroscopy, and electrochemical testing to probe the electrode-ionogel interface, the surface reactions were identified as being the source of the interfacial barriers. Our results indicate that the acidity of the sol led to breakdown of the solvent and organic acid, forming an organic surface layer which impedes Li+ transport. By adjusting the pH of the sol or by adding a surface coating, these interfacial reactions can be avoided, leading to stable cycling.