Relationship between Silicon Percentage in Graphite Anode to Achieve High-Energy-Density Lithium-Ion Batteries.

Abstract

High-weight-percentage silicon (Si) in graphite (Gr) anodes face commercialization hurdles due to fundamental and interrelated challenges. Nevertheless, using the existing manufacturing line, the optimized Si/Gr ratio is the most efficient and valuable way to fabricate high-energy-density lithium-ion batteries (LIBs). Still, literature has not thoroughly examined the Si/Gr ratio. This study addresses this critical gap by systematically evaluating Si content (5-20 wt %) in commercial graphite. The goal is to optimize the Si/Gr ratio for exceptional specific capacity while mitigating inherent Si limitations like cyclic stability and first-cycle irreversible capacity loss. This work employs a multidirectional approach, including in situ electrochemical impedance spectroscopy for interface analysis, rate capability assessment (up to 3 C-rate), Li diffusion coefficient measurement, and thorough cyclic stability evaluation. Increasing the silicon (Si) weight percent from 10% to 15% in the Si15Gr75 composite anode resulted in significant improvements in the first lithiation and delithiation capacities by approximately 16.8% and 16.0%, respectively. The Si15Gr75 cell delivered a high initial Coulombic efficiency of roughly 82.9%, nearly equivalent to a pure graphite anode. Furthermore, the Si15Gr75 Li cell exhibited excellent cyclic stability at a current rate of 0.5 C, retaining about 60% of its capacity after 215 cycles. Additionally, full-cell testing against a commercial NMC622 cathode showcases excellent performance across various current rates (0.1-0.5 C). This study paves the way for the development of high-energy-density LIBs by providing valuable insights into the optimization of Si/Gr composite anodes for commercial viability.