Vegetable Oil-Based Waterborne Polyurethane as Eco-Binders for Sulfur Cathodes in Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) suffer from well-known fast capacity losses despite their extremely high theoretical capacity and energy density. These losses are caused by dissolution of lithium polysulfide (LiPS) in ether-based electrolytes and have become the main bottleneck to widespread applications of LSBs. Therefore, there is a significant need for electrode materials that have a strong adsorption capacity for LiPS. Herein, a waterborne polyurethane (WPUN) containing sulfamic acid (NH₂ SO₃ H) polymer is designed and synthesized as an aqueous-based, ecofriendly binder by neutralizing sulfamic acid with a tung oil-based polyurethane prepolymer. UV-vis spectroscopy shows that the WPUN strongly immobilizes LiPS and thus is an effective inhibitor of the LiPS. Moreover, the WPUN binder has excellent adhesive and mechanical properties that improve the integrity of sulfur cathodes. The WPUN-based cathodes exhibit a significant improvement in their specific capacity and maintain a capacity of 617 mAh g^-1 after 200 cycles at 0.5C. Besides, the LSBs assembled with the WPUN-based cathodes show good rate performance from 0.2C (737 mAh g^-1 ) to 4C (586 mAh g^-1 ), which is significantly higher than that of LSBs assembled with a commercial polymer binder. The structural design of the presented binder provides a new perspective for obtaining high-performance LSBs.