Intercalation Induced Stress Effects of the Core-Shell Anode Materials for Lithium Ion Battery

Rechargeable lithium-ion batteries are widely used as electric power for portable electronics and electric vehicle due to its excellent characteristics such as high voltage, and high energy density.

Silicon is a promising anode material for high performance lithium ion batteries, as it has very high theoretical reversible specific capacity (3579 mAh/g for Li₁₅Si₄) at room temperature. However, implementation of silicon-based materials has some challenges. Active particle pulverization caused by the large volume expansion leads to the loss of electrical contacts at the electrode. It is recognized as one of the major capacity fade with repeated charges–discharge cycling. Various experimental studies have been attempted to overcome this mechanical degradation using fabrication of nano-sized structures, porous materials and core-shell structures.

Especially, core–shell structure exhibits improved physical and chemical properties : suppressing large volume expansion resulting in inner core fracture, preventing the inner core from forming excessive SEI and enhanced electrical conductivity.

Experimental results have already provided a core-shell structure capability for LIBs. However, the analysis of core-shell structure using model simulation is not well explored to support experimental results.

Therefore, we propose a model of the intercalation-induced stresses for core-shell particles with various morphologies and deal with stress effects on Lithium ion diffusion in active particles. The radial compressive stress at the core-shell interface mitigates the crack growth of active core materials and this radial stress eventually enhances the cycling performance of LIBs. However, this compressive stress influences on the lithium ion diffusion and affects the electrochemical behavior over their single-component counterpart. So, we suggest the desirable range of shell thickness and allowable shapes of core-shell structure.

ACKNOWLEDGEMENT

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MEST) (No. 2012R1A3A2048841) and by the Industrial Strategic technology development program (10041589) funded by the Ministry of Knowledge Economy (MKE, Korea)