(487f) Tailoring Internal Pores for Mitigation of Volume Expansion in Silicon Graphene Hybrid Anodes for Lithium Ion Batteries

The current state of art Lithium ion batteries (LIB) are unable to satisfy the demands for electric vehicle (EV) applications due to their low energy density. To improve their energy density, silicon as anode material has been very promising due its extraordinary theoretical capacity. However, silicon undergoes huge volume expansion(~ 400%) during lithium-ion storage. This leads to the pulverization of the electrode structure over several cycles of lithiation and delithiation and consequently severe capacity decay. Thus, mitigation of this volume expansion has been a stumbling block for its commercialization. One approach to address this issue is to use silicon carbon-based composites and engineering void spaces for the effective accommodation of silicon volume expansion. The internal pores give breathing room for the silicon to expand, which maintains the structural integrity. Many scientists have researcher methods to mitigate the silicon volume expansion by engineering voids; however, there is a lack of direct correlation in terms of the size of pores created and the mitigation of volume expansion achieved. Additionally, the various approaches studied in the literature to create pore spaces invariably involve the use of expensive fabrication methods.

In our study we are using a two-step approach to form tailored internally porous silicon graphene hybrid anodes. In the first step, we form directly deposited silicon graphene hybrid anodes via air-controlled electrospray, and in the second step we use a mild heat treatment to thermally remove poly acrylic acid, which serves as our sacrificial template. This approach provides structural integrity and volume expansion accommodation. In order to prove our hypothesis of mitigation of silicon volume expansion via the creation of internal pores, we also study in-situ volume expansion via a dilatometer and compare the resulting mitigation of volume expansion for Si/Gr with pores and Si/Gr without pores. Our conclusions show the interplay of creation of pores and the mitigation of volume expansion over a number of charge/discharge cycles.