Rational design of functional binder systems for high-energy lithium-based rechargeable batteries

Binders, which maintain the structural integrity of electrodes, are critical components of lithium-based rechargeable batteries (LBRBs) that significantly affect battery performances, despite accounting for 2 to 5 wt% (up to 5 wt% but usually 2 wt%) of the entire electrode. Traditional polyvinylidene fluoride (PVDF) binders that interact with electrode components via weak van der Waals forces are effective in conventional LBRB systems (graphite/LiCoO2, etc.). However, its stable fluorinated structures limit the potential for further functionalization and inhibit strong interactions towards external substances. Consequently, they are unsuitable for next-generation battery systems with high energy density. There is thus a need for new functional binders with facile features compatible with novel electrode materials and chemistries. Here in this review we consider the strategies for rationally designing these functional binders. On the basis of fundamental understandings of the issues for high-energy electrode materials, we have summarized seven desired functions that binders should possess depending on the target electrodes where the binders will be applied. Then a variety of leading-edge functional binders are reviewed to show how their chemical structures realize these above functions and how the employment of these binders affects the cell's electrochemical performances. Finally the corresponding design strategies are therefore proposed, and future research opportunities as well as challenges relating to LBRB binders are outlined.