Self-Healing Double-Cross-Linked Supramolecular Binders of a Polyacrylamide-Grafted Soy Protein Isolate for Li–S Batteries

With extremely high theoretical energy density, lithium–sulfur (Li–S) batteries have attracted abundant interest as a promising next-generation energy storage device. Polymer binders as an ingredient of cathodes are of great significance in pursuit of stabilized electrochemistry. Herein, we fabricate a self-healing, water-based, and double-cross-linked soy protein isolate (SPI)-polyacrylamide (PAM) binder for the sulfur cathode, which is facilely synthesized by copolymerization of methacrylated SPI and acrylamide. It was demonstrated that methacrylated SPI acted as a macro-cross-linker, combining with dynamic hydrogen bonding cross-linking from PAM, endowing the SPI-PAM polymer binder satisfactory bonding strength and excellent self-healing ability. Moreover, the SPI-PAM exhibits superior lithium polysulfide anchoring capability to impede the dissolution and diffusion of lithium polysulfides in an electrolyte. Li–S batteries with such a robust SPI-PAM binder can stabilize the charge and discharge for 400 cycles at a high rate of 6 C; the average specific capacity loss per cycle is only 0.0545%, and even at an ultrahigh current density of 20 C, the specific capacity still remains at 148.2 mA h g^–1. With a sulfur loading of 2.3 mg cm^–2, the SPI-PAM-based sulfur cathodes demonstrate remarkable cycling performances at 0.5 C for 200 cycles, and the capacity remains at 707.7 mA h g^–1. The kind of green binders from bioresources modified with PAM have a good application in high-energy density Li–S batteries.