News Source & Editor: School of Chemistry and Chemical Engineering

Recently, Prof. Cao Minhua's team with the School of Chemistry and Chemical Engineering of Beijing Institute of Technology has made important progress in research on silicon cathode of lithium ion batteries. The research results were published online in the journalACS Energy Letterswith the title "Transgenic Engineering on Silicon Surfaces Enables Robust Interface Chemistry" (DOI: 10.1021/acsenergylett.2c01202).

During the operation of secondary ion batteries, when the electrodes are operated at extreme potentials far from the thermodynamic stability limit of the electrolyte, the electrolyte decomposes and forms a solid electrolyte interface (SEI) on the cathode surface. The continuous accumulation of SEI is one of the important factors that degrade the battery performance. Therefore, it is of great scientific importance to find an effective and universal regulation strategy for sustaining stable SEI, which is also a great challenge. The interface chemistry between the electrode and electrolyte plays a crucial role in manipulating the SEI membrane properties. Modulating the inner Helmholtz plane (IHP) of active film-forming materials adsorbed on the electrode surface for preferential reduction can effectively regulate the chemical composition and structure of the initial SEI. However, some materials with relatively inert surfaces cannot establish strong interactions with the target film-forming species by themselves to achieve characteristic adsorption within the IHP. As a result, how to manipulate the adsorption characteristics of the electrode is crucial for the rapid construction of stable SEI.

The paper provides a new idea to address this challenge by using a silicon cathode with high theoretical capacity as the research target. According to theoretical calculation, the edge structure of MoSe2 has a stronger adsorption effect on fluoroethylene carbonate (FEC) compared to silicon, while FEC decomposes more easily on the MoSe2 surface. Based on this, the authors designed the Si@MoSe2 featuring core shell structure, wjere MoSe2 has an abundant edge structure. According to Infrared and Raman studies, FEC molecules in the electrolyte can preferentially reduce and decompose on the Si@MoSe2 surface during the first discharge, which facilitates the construction of FEC-derived SEI to stabilize the electrode surface. Electrochemical test confirmed that Si@MoSe2 exhibited higher Coulomb efficiency, better cycling stability and multiplicative performance, and faster ion transport kinetics. The authors further analyze the SEI composition, structure, and mechanical strength characteristics. Atomic force microscopy and transmission electron microscopy show that the SEI on Si@MoSe2 surfaces are thin, strong, and uniformly distributed. And again, X-ray photoelectron spectroscopy and NMR demonstrate that the SEI on Si@MoSe2 surfaces have more Poly(VC) and LiF components. This strategy successfully modulates the component and morphology and other SEI properties on the silicon cathode surface, which leads to the performance of high lithium storage.

Fig. 1 (a,b) Si@MoSe2 characterization; (c,d,e) Electrochemical properties of Si@MoSe2 and Si electrode; (f) Formation process of SEI on the surface of Si@MoSe2 electrode during the first discharge; (g-j) SEI characterization on the surface of Si@MoSe2 and Si electrode.

Paper link：https://pubs.acs.org/doi/10.1021/acsenergylett.2c01202.

Author profile:

Minhua Cao, Professor of School of Chemistry and Chemical Engineering, Beijing Institute of Technology, PhD supervisor, New Century Excellent Talents of the Ministry of Education, Humboldt Scholar. Minhua Cao is mainly engaged in the research on function-oriented design and electrochemical mechanism of energy storage and conversion materials. Minhua Cao has published more than 100 SCI papers in journals such asJ. Am. Chem. Soc.,Angew. Chem. Int. Ed.,ACS Energy Letters,ACS Nano,Nano Energy,Chem. Mater., andJ. Mater. Chem. A.