Lithium bis(trifluoromethanesulfonyl)imide, commonly known as LiTFSI, and its analogs are critical high-end electrolytes for lithium batteries and solar cells. However, the current commercialization of LiTFSI through thermal chemical synthesis relies on the use of NH₃ intermediates, involving multiple catalytic and purification processes, leading to substantial carbon emissions. Therefore, developing a method for the direct synthesis of LiTFSI from N₂ under mild conditions becomes particularly important. 

In a study published in Nature Catalysis, Prof. WANG Yaobing and his team from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences, proposed a cascade electrochemical synthesis strategy based on Li-N₂ batteries, and achieved efficient electrochemical synthesis of various nitrogen-containing compounds, including LiTFSI.

The specific strategy includes catalytically reducing N₂ to Li₃N during discharge, acylating Li₃N to form LiTFSI and the byproduct LiCl, and oxidizing LiCl during charging to complete the synthetic cycle.  

The researchers demonstrated the electrocatalytic reduction of N₂ to Li₃N through X-ray diffraction, low-temperature transmission electron microscopy combined with EDS spectra. They confirmed the feasibility of the S-N acylation reaction between Li₃N and CF₃SO₂Cl through nuclear magnetic resonance, mass spectrometry, and Fourier-transform infrared spectroscopy. Based on the color change of methyl orange from red to colorless during the charging process, the researchers proved that the byproduct LiCl was oxidized to Cl₂.  

The experimental results indicated that, under optimized conditions, the catalytic reduction efficiency from N₂ to Li₃N reached 53.2%, the conversion efficiency from N₂ to LiTFSI was 48.9%, and the energy efficiency of electrochemical synthesis of LiTFSI reached 3.0%.  

Moreover, the researchers utilized a flow cell device to achieve continuous electrochemical synthesis of LiTFSI, demonstrating the practical significance of this strategy in production.  

By expanding the substrate scope, the researchers provided a pathway for the direct electrochemical synthesis of analogs with different N-X bonds (X = S, C, etc.) and metal cations (Li⁺, Zn²⁺, etc.), proving the scalability of the strategy. 

This study presents a comprehensive electrochemical synthesis scheme for the practical production of nitrogen-containing chemicals, which offers a promising approach to synthesize high-end electrolytes with enhanced nitrogen atom efficiency. 

Schematic representation illustrating the cascade LiTFSI synthesis in a Li-N₂ battery (Image by Prof. WANG Yaobing’s group) 

Contact: 

Prof. WANG Yaobing 

Fujian Institute of Research on the Structure of Matter 

Chinese Academy of Sciences 

Email: wangyb@fjirsm.ac.cn