High Adhesive Polyimide Binder for Silicon Anodes of Lithium Ion Batteries

Silicon has been extensively studied as an anode material in lithium-ion batteries due to its extremely high theoretical specific capacity of 3578 mAh/g (assuming Li 15 Si 4 as intermediate product). However, silicon undergoes huge volume variations during repeated discharge and charge, leading to poor electrode mechanical integrity, continual electrolyte decomposition and fast capacity decay. Developing high strength binders in silicon anodes have been considered as an efficient pathway to alleviate various capacity decay pathways. Currently, lithiated poly acrylic acid (LiPAA) is mostly used as the binder for silicon electrodes due to its strong binding capability and (electro)chemical compatibility with Si and electrolyte. However, cracks at the electrode level can still be observed for the cycled electrodes, which suggests that a stronger binder is required to mitigate volume expansion of Si electrode and hold the particles together. Herein we study the polyimide (PI) materials as the binders for Si anode in an attempt to achieve stable cycling performance. With PI binder, the silicon electrode exhibits a higher tensile strength than that of conventional PAA binder. The strong adhesion of the PI binder suppresses the structural collapse of the Si negative electrode during lithiation/delithiation, enabling high capacity retention and stable cycle life. However, the PI crosslinking process requires high temperature and inert atmosphere, which is a challenge for its practical application. In this work, we explore various PI crosslinking conditions and their effects on electrochemical performance. This work offers us an alternative binder material with high tensile strength for the Si electrode. Acknowledgement We gratefully acknowledge the support from the U.S. Department of Energy's Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is operated for DOE office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.