Experimental study on the mechanical and electrochemical properties of aqueous emulsifiable diphenylmethane diisocyanate-modified silicon-carbon composite electrodes

Aqueous emulsifiable diphenylmethane diisocyanate (EMDI) can form strong chemical bonds with aqueous adhesives due to the large number of isocyanate (-NCO) groups, which can enhance the mechanical performance of the adhesives. Currently, sodium carboxymethyl cellulose (CMC)-styrene butadiene rubber (SBR) emulsion aqueous bonding agents are widely used in the preparation of anode materials for lithium-ion batteries (LIBs). In this study, EMDI was added to a porous silicon-carbon composite electrode prepared from CMC-SBR, and the evolution of the mechanical properties of the electrode with the EMDI content was first investigated via quasi-static uniaxial tensile and interfacial strength tests. Subsequently, the effect of the EMDI content on the electrochemical properties of the electrodes was analysed by electrochemical impedance spectroscopy (EIS) and constant-current (CC) charge/discharge performance tests. Finally, material characterisation of the electrodes was carried out by Fourier transform infrared (FTIR) spectroscopy and specific surface area (Brunauer-Emmett-Teller (BET)) analysis. The results show that the addition of EMDI with a mass ratio of 10-20% to the CMC-SBR binder can enhance the mechanical performance of the active layer and the interfacial performance between the active layer and the current collector of the silicon-carbon composite electrode; simultaneously, EMDI can significantly reduce the electrochemical impedance of the electrode material and improve the capacity retention of the electrode. This study provides a new solution for modifying silicon-carbon composite electrodes and promotes the development of high-performance silicon-carbon electrodes. Aqueous emulsifiable diphenylmethane diisocyanate (EMDI) can form strong chemical bonds with aqueous adhesives due to the large number of isocyanate (-NCO) groups, which can enhance the mechanical performance of the adhesives.