Revealing the Fading Mechanism of Long-Term Cycling Performance of Graphite/Silicon Composite Anode for Lithium-Ion Batteries
Authors: Choi Yoon Jeong , Yu Seung-Ho 
Published: December 2024

Lithium-ion batteries (LIBs) have been employed across a diverse range of applications, spanning from small portable devices to large electric vehicles and stationary energy storage systems. With the growing market for electric devices, the demand for rechargeable batteries with higher energy densities than conventional LIBs has increased.
Graphite (Gr), of which theoretical capacity is 372 mAh g-1, is utilized as anode material in current LIBs because of its cycle stability, low price, and high conductivity. Despite these advantages, the graphite anode has used its maximum utilization, which has reached its theoretical capacity. Therefore, silicon (Si), of which theoretical capacity is 3579 mAh g-1, has emerged to achieve more higher energy density than that of Gr. Silicon anode, however, undergoes extremely large volume expansion during alloying/dealloying process, leading to pulverization, loss of electrical contact, and excessive solid electrolyte interface (SEI) layer formation. Eventually, this large volume expansion reduces cell life. Despite intensive effort for Si-dominant electrodes, a real application of this strategy to battery industry is unsure. In this regard, gradual replacement of Gr to Si is adaptable in practical perspective.
For the practical use of graphite/Si electrodes, the research on the long-term cycling performance of wide temperature range is highly important. However, most research has mainly focused on charge/discharge mechanisms in short cycles or conducted experiments with half cells, which do not represent the actual commercial battery systems. Therefore, research on the aging mechanism of composite anode under conditions similar to real operating environments is needed.
To reveal the aging mechanism of composite anode, full cell configuration with high mass loading electrodes was used for the electrochemical performance test. Under wide temperature range, different cycling performance were observed. The cell reassembly experiment is conducted to figure out which electrodes is mainly contributed to the capacity loss of full cell during cycling. From this experiment, the anode degraded more rapidly. Through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), we observed changes in the morphology of the electrodes with varying cycle numbers and temperatures. The composite anode is degraded during cycling, and notably, a peculiar structure of SEI was observed. Additionally, secondary-ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS) is conducted to analyze the SEI structure, which determines the cycle life of batteries. The deeper understanding of the mechanism of long-term cycling performance will provide as primary key for the commercialization of composite anode design.
Figure 1. a Scheme of the capacity loss of anode and cathode harvested from full coin cell after long-term cycling performance. b Voltage profiles of lithium half cell with aged anode and pristine electrode. c Voltage profiles of lithium half cell with aged cathode and pristine electrode.

Figure 1