Microstructure and Electrochemical Properties of the Si-M(M : Cr, Ni) Anode for Lib According to the Si Amount

Abstract

To enhance the cyclic performance of silicon binary alloy used in LIB as anode material, we used active/inactive nanocomposite. Active/inactive composite method is one of the methods to suppress silicon’s volume expansion. In this method active-Si particles are embedded in Inactive-matrix. Our previous results obtained using this method showed that Cr-Si alloy had better cyclic performance and fine microstructure than Ni-Si alloy which had dendritic structure. In this work we compared cyclic performance and microstructures of these alloys depending on the amount of Silicon. We design each alloy’s capacity using phase diagram and lever rule (356, 600, 900, 1,200 mAh/g). Silicon-Chromium (Cr-Si) and Silicon-Nickel(Ni-Si) nanocomposites were prepared using a melt-spinning method. Through the melt-spinning method, we can make alloy sample which has fine microstructure (structure size, < 100nm). Powder samples(D50 : ~20㎛) were prepared by Paint Shaker. Electrodes were prepared using Ketjen black carbon and PAI binder which is suitable for silicon alloy anode because of its good adhesive strength. So, it is able to bear stress caused from silicon volume expansion. We used PSA, ex-situ SEM, XRD to characterize samples and Coin cell test for electrochemical characteristic. Ex-situ SEM showed that each microstructure of Cr-Si (active-Si size : ~10nm) and Ni-Si has different behavior as the amount of silicon increases. These alloys were confirmed to have Active-Si and Inactive-Matrix (CrSi2 ,NiSi2) phases by ex-situ XRD measurement. Any other phases weren’t detected except these phase. Electrochemical tests show such characteristic features as all Cr-Si alloy has good Coulombic efficiency of more than 98% after 1st cycle. However, we couldn’t control the Ni-Si alloy’s electrochemical characteristic by the amount of Si.