Insights into the Effect of Heat Treatment and Carbon Coating on the Electrochemical Behaviors of SiO Anodes for Li-Ion Batteries

Significance 

Compared to graphite, silicon-based materials exhibit high specific capacity and long cycling life, making them promising candidates for increasing the energy densities of Li-ion batteries (LIBs). However, during lithiation, silicon’s high capacity is offset by its volume expansion resulting in the loss of contact between the Si particles and the electrodes. The formation of an unstable and thick solid-electrolyte interface due to the continuous reaction between the electrolyte and the Si deteriorates the transportation of Li+. These problems result in rapid capacity loss and low cycling efficiency, which require urgent solutions.

The compromised theoretical capacity, excellent cycling performance and relatively smaller volume expansion of SiO make it a suitable practical choice over Si alone for LIBs. While the irreversible reaction between the Li-ions and amorphous SiO2 matrix during the initial stages of the lithiation process can alleviate the volume change of the Si nanoclusters but also significantly contribute to the capacity loss. Thus, SiO anodes exhibit more rapid capacity failure than graphite anodes though slower than Si anodes. Other failure mechanisms include side reactions with electrolytes, volume changes induced electrical isolation effects and the intrinsic inferior electrical conductivity. Therefore, mitigating these failure mechanisms is crucial for commercializing SiO-based LIBs.

Several promising approaches, such as high-temperature carbon coating and structural design, have been developed to improve the electrical performance of SiO anode. These approaches involve heat treatment to calcinate SiO precursors. Unfortunately, the effects of heat treatments on SiO surface structure and composition, microstructure evolution and electrical properties of SiO anode remain unclear, partially due to its thermal instability. Additionally, the formation mechanism of the Si nanowires associated with heat treatment is not fully explored.

To address these issues, researchers at the University of North Dakota: Dr. Shuai Xu, Professor Xiaodong Hou, Mr. Yong Hou and Professor Michael Mann in collaboration with Dr. Dongniu Wang, Dr. Lucia Zuin and Dr. Jigang Zhou from Canadian Light Source Inc. presented a systematic study to shed light on these fundamental issues. Finally, a SiO structural model was developed to describe the relationship of “synthetic processes-microstructure electrochemical behaviors.” Their work is currently published in the journal, Advanced Energy Materials.

In their approach, the impact of carbon coating and heat treatment on the electrical behaviors, morphology, microstructure and chemical composition of SiO anodes used in LIBs was investigated using a series of microanalysis characterization techniques like X-ray Diffraction (XRD) and X-ray absorption near edge structure (XANES). The dynamic evolution of SiO and Si phases during the process was analyzed. Additionally, three different anodic particles, pristine SiO (P-SiO), D-SiO, and carbon-coated D-SiO ([email protected]) were analyzed and compared before and after cycling.

The research team showed that during heat treatment, the SiO structural transition from amorphous to disproportionated hierarchical structure hindered the lithiation processes. This was attributed to the severe electrode polarization caused by the formation of the Si nanowires (as-formed interior SiO2 matrix and dielectric exterior SiO2 shell), as evidenced by the TEM and SEM images. Subsequently, the as-formed dielectric SiO2 phases caused severe overpotential, resulting in deteriorated cycling life and capacity loss. The carbon coating on SiO was effective in restricting the growth of the SiO2 shell, thereby leading to better charge transfer and improved electrochemical performance. Thus, higher initial Coulombic efficiency of 79.3% and enhanced cyclability of 84.2% after 200 cycles were reported.

In summary, the study presented a systematic investigation of the structural evolution and composition of amorphous SiO under carbon coating and heat treatments and the resulting electrochemical behaviors. The findings resolved some important long-standing problems and issues regarding SiO. In a statement to Advances in Engineering, Professor Xiaodong Hou explained that the study provided would contribute to future design of high-performance SiO-based anode materials for commercializing SiO-based LIBs.

About the author

Dr. Xiaodong Hou, Research Associate Professor, is a material chemist at University of North Dakota (UND) with over 15 years of experience synthesizing and characterizing advanced functional materials. He holds a Ph.D. degree in polymer chemistry and physics from Shanghai Jiao Tong University in 2009 and worked at UND chemistry department as a postdoc from 2009-2013. He has over 40 peer-reviewed publications in the field of chemistry materials and holds five patents. His recent research interests focus on developing coal-derived carbon materials for advanced battery applications. Dr. Hou is the technical group manager – Battery technologies at UND, managing multiple U.S. Department of Energy funded projects directly related to developing advanced battery materials.

Reference

Xu, S., Hou, X., Wang, D., Zuin, L., Zhou, J., Hou, Y., & Mann, M. (2022). Insights into the Effect of Heat Treatment and Carbon Coating on the Electrochemical Behaviors of SiO Anodes for Li‐Ion BatteriesAdvanced Energy Materials, 12(18), 2200127.

Go To Advanced Energy Materials

Check Also

Topologically Induced Heterogeneity in Gradient Copolymer Brush Particle Materials - Advances in Engineering

Topologically Induced Heterogeneity in Gradient Copolymer Brush Particle Materials