A branched hydrogen-bonded cross-linking fluorine-free waterborne binder for highly stable lithium-ion battery.

Binders are key components for maintaining the structural integrity of electrodes and improving electrochemical stability of lithium-ion batteries (LIBs). Currently, polyvinylidene fluoride (PVDF) serves as the main binder of LIBs, but suffer a number of drawbacks, including its high fluorine content, the use of organic toxic solvents (N-methylpyrrolidone, NMP) during processing, poor weak adhesion, low mechanical flexibility and non-recyclability. To address the shortcomings of PVDF binder, herein, a fluorine-free, waterborne binder acrylamide (AM) and itaconic (IA) acid grafted carboxylated chitosan (CS) copolymer (CMA), featuring a three-dimensional hydrogen-bonded cross-linking network, is proposed. Its richly branched hydrogen-bonded cross-linking structure increases the contact sites and improves the mechanical properties of the binder, slowing down the volume expansion and stress concentration of the particles, and improving the cycling stability of the battery. Therefore, when CMA is used as a binder for lithium iron phosphate (LFP) cathode, the capacity retention rate is as high as 96.55 % after 400 cycles at 0.5C. Even at higher active materials loading, the battery cycles well. When CMA is used as a binder for silicon (Si) anode, the capacity retention is 85.2 % after 100 cycles at 0.2C, urpassing the performance of PVDF binders tested. Furthermore, CMA exhibits pH-responsive recyclability, enabling efficient electrode component separation via acid treatment and advancing sustainable battery manufacturing, which offers a new perspective for recyclable, eco-friendly lithium-ion battery materials.