Investigation of the electrochemical performance of the graphite‒silicon composite in carbonate based solvents

Abstract

Nowadays, rechargeable Li-ion batteries represent almost all human activities. Therefore, the requirements of battery optimization for power density, energy density, and cycle life are becoming necessary. Based on negative commercial graphite, graphite‒silicon composite (G‒Si) material has become a potential anode for Li-ion batteries due to its high specific capacity and energy density. This paper presented the investigation the electrochemical performance of the G‒Si composite in the carbonate based solvents which consisted of 1 M LiPF6 dissolving in the solvent of EC‒DMC 1:1 (v/v), EC‒DEC 1:1 (v/v), or EC‒EMC 1:1 (v/v). The results showed that the G‒Si composite delivered a high capacity of 616.0 mAh/g with the highest capacity retention of 64.2% (50 cycles) at the current density of 40 mA/g in the EC‒EMC 1:1 (v/v) solvent. However, when the current density was doubled (80 mA/g), the capacity of G‒Si in EC‒DEC 1:1 (v/v) rapidly decreased, while the capacity of the EC‒EMC 1:1 (v/v) maintained the highest. The EIS showed that the Rsf and Rct values in the EC‒DEC 1:1 (v/v) based electrolyte gradually increased with cycles which appropriated to the GCPL results. Besides, the intercalation diffusion mechanism of Li+ into the G‒Si composite confirmed that this process could be divided into two main regions where the diffusion coefficients were the minimum and related to the plateaus in the discharge curves of G‒Si material. The diffusion coefficient of G‒Si was of 10-6‒10-12 cm2/s which was the smallest in the EC‒DEC 1:1 (v/v) system.