Effect of different conductive carbons on degradation mechanism of flake-shaped silicon anodes: Analysis using dynamic relaxation time distribution method

Abstract

The conductive agent is a bridge between the collector and the active material as well as the active material itself, and is an integral part of the silicon-based anode in lithium-ion batteries due to the low intrinsic conductivity of silicon. In previous studies, spherical silicon (dots) has been combined with 0-dimensional (dots), 1-dimensional (lines), and 2-dimensional (surfaces) conductive agents, and it has been found that the contact between the active material and the conductive agent is the key to the electrochemical performance. Flake-shaped silicon has different structural characteristics from spherical silicon, and it tends to be face-to-face stacked, which greatly limits its original performance, so the selection of suitable conductive agent or compounding method is crucial for the performance enhancement of flake-shaped silicon anode. In this experiment, three typical conductive agents with different dimensions, Super P, carbon nanotubes and graphene, were mixed with flake-shaped silicon respectively, and the different morphologies of the conductive agents bonded with flake-shaped silicon in different forms, which are reflected in the structural parameters such as tortuosity, pore size distribution, specific surface area and porosity of the electrode. We disassembled and subdivided the different impedances in the EIS data using the DRT method to explore the changes of different electrochemical processes in the cell cycling degradation, and analysed the effects of the above structural parameters on the cycling changes of R_s, R_sei, R_ct, and D_Li⁺.