Dilation behaviors of graphite and silicon based electrodes during lithiation and delithiation

Abstract

Lithium-ion batteries have become indispensable system for electronic devices and electric vehicles and many research groups have contributed to the advanced performance of lithium-ion batteries for the purpose of meeting diverse requirements for various applications along with the rapid expansion of lithium-ion batteries market. For the reliability of the batteries for devices and vehicles, controlling the dimensional changes of the lithium-ion battery caused by lithium ion insertion into the electrode materials is one of the most important ways for stable operation. Volume change and repetition of dilation and contraction of material results in the mechanical stresses in the electrode, which causes mechanical degradation of the electrode in the cell. In this study, microstructure of the anode electrode and material was controlled to understand the dilation behaviors of the anode electrode. Microstructure of graphite electrode was controlled by calendering and type of graphite to investigate the effect of pores in electrode and orientation of particles on the dilation properties of the graphite electrodes. In-situ monitoring analysis revealed that the dilation and contraction behaviors of the graphite electrode are highly dependent on the microstructure of the graphite electrode, including the pore structure and the preferred orientation of graphite particles in the electrode. Microstructure of silicon-based material affected to dilation behaviors of the electrode. Si-Gr-C composites synthesized by pelletization showed different dilation behaviors with respect to their surface area in limited binder content condition. In-situ monitoring analysis investigated that the electrode incorporating large surface areal Si-Gr-C composite showed higher dimensional change during lithiation because of weakened material-binder adhesion. Microstructure of silicon based electrode was also controlled by providing pores in the electrode through hollow graphene particles which can also act as an electronic interconnector. Large pores in the silicon electrode by hollow graphene absorbed the swelling of silicon during lithiation through flattening the free voids surrounded by the graphene shell, leading improvement of electrode stability. Some of the deflated hollow graphene returned to their initial shape upon delithiation due to the mechanical flexibility of the graphene shell layer.