Design of functional binders for high-specific-energy lithium-ion batteries: from molecular structure to electrode properties

The binder adheres to each component of the electrode to maintain the structural integrity and plays an irreplaceable role in a battery despite its low content. Polyvinylidene difluoride (PVDF), as the dominant binder in commercial battery systems (for cathodes), has acceptably balanced properties between chemical/electrochemical stability and adhesive ability. However, in the pursuit of high-specific-energy batteries featuring high mass loading, high voltage, and large volume changes, the PVDF binder is unable to satisfy the versatile electrode demands and extreme operation conditions. Therefore, developing novel binders with task-specific functionality is of urgent need. Herein, we review the recently developed design strategies of functional binders from the insight of molecular design. The functions and failure mechanisms of the binders are elucidated first. Starting from the basic moiety (functional group) of the polymer molecule, how the constituents, molecular structure, and assembly into a supramolecule will affect the properties of the binders, and furthermore the performance of the electrodes, is discussed at length. Finally, we summarize and provide a future outlook on the opportunities and challenges of functional binders towards future high-specific-energy lithium-ion batteries.