Innate Voids of Halloysite Enabling High-Volumetric Density Anodes for Silicon/Graphite Composites

Abstract

Silicon (Si) has been considered as a prospective anode material in lithium-ion batteries (LIBs) due to its exceptional high capacity and energy density than the commercialized carbon-based materials. However, volume expansion (~380%) caused by alloying chemistry of silicon affects the deterioration of electrodes and battery performance. To minimize these drawbacks, the fabrication of Si/graphite composite electrodes has emerged as a promising anode since graphite anodes possess less volume expansion (~10%) with a porous structure that contributes to the accommodation of the electrode level for Si expansion. It is well known that the specific capacity and cyclability would conflict in the composite anode as increasing silicon contents. With this interpretation, previous studies reported that the theoretical limit of Si contents in the composites was approximately calculated as 15% with a numerical optimization considering electrode porosity, expansion of active materials, and so on.

Considering aforementioned issues, we propose a novel method to enhance the energy density of the composite electrode by increasing the portion of Si by use of halloysite containing native voids in the structure, resulting in less volume expansion. As the production cost should be considered for practical application, we selected silicon nanotubes (SiNT) that derived from natural halloysite clay which is widely distributed in the earth crust. With facile and cost-effective synthesis process, the synthesized SiNT has less volume expansion (~200%). From the careful investigation via in-situ transmission electron microscopy, we found the optimal composition of SiNT in the silicon/graphite composites to overcome the limited volumetric density of the anodes. The physical and chemical properties, and battery performances will be discussed in detail in this presentation.