Research progress of robust binders with superior mechanical properties for high-performance silicon-based lithium-ion batteries

Graphitic anode materials are commonly used in commercial lithium-ion batteries (LIBs), where the energy density potential has been fully exploited to about similar to 360 mA h g-1 (372 mA h g-1 for LiC6), and it is hard to make further significant improvement. Owing to their highest theoretical specific capacity (4200 mA h g-1 for Li4.4Si), abundant earth reserves and environment-friendly silicon anode materials have great potential to be installed in next-generation high-energy-density LIBs. However, the industrialization of silicon-based anodes is hampered by the considerable volume change (similar to 300-400%) upon the lithiation/de-lithiation process, which inevitably causes particles' pulverization, electrode cracking/swelling, and parasitic side reactions and leads to electric contact loss and eventual electrode destruction. Therefore, binders in silicon-based electrode systems adhere to active material particles and conducting additives, and tie up the matrix laminate and the current collector, which play a focal role in cell performances. Accordingly, the essential requirement of binders for Si-based anodes is briefly introduced; the binder's mechanical properties in terms of the tensile properties, adhesion strength of binders with Si particles and the peel strength of the electrode are emphasized. Moreover, the electronic conductivity and ionic conductivity of binders are proposed to improve the electrochemical performance of Si-based electrodes. Likewise, the mechanical degradation of the Si electrodes and their robust binder strategies will also be discussed. Finally, viable strategies are discussed to address the challenge of binders as the future development direction and application prospects. The mechanical properties of binders are emphasized: the intrinsic mechanical properties of binders and the adhesive strength of the binders with current collectors and active materials. The electronic and ionic conductivities of binders are introduced.