In situ construction of poly(acrylic acid)/conjugated organic framework binder with superior mechanical strength and ionic conductivity for Si-based anodes in Lithium-ion batteries

Poly(acrylic acid) (PAA) has been widely studied as a silicon (Si) negative electrode binder, however, its poor adhesion and insufficient ion conductivity have always constrained its practical application in lithium-ion batteries (LIBs). A multifunctional binder was created by the lithiophilic poly(hexaazatrinaphthalene) (PHATN) enhancing PAA via forming physical and chemical crosslinking network (PAA-PHATN), addressing the widespread challenges of active material detachment caused by the irreversible volume expansion and impedance increase caused by low ionic conductivity in Si anode. The -C=N- and -NH 2 groups in PHATN interacted with the carboxyl groups in PAA through hydrogen bonding and amide formation, respectively, resulting in exceptional tensile strength (>2.3 MPa), remarkable ductility (up to 490 % strain tolerance), and high Li + conductivity. When applied in silicon electrodes, PAA-PHATN binders effectively mitigate Si particle pulverization during lithiation, accelerate Li + diffusion (with a diffusion coefficient of D Li + ≈ 2.43 × 10 −9  cm 2  s −1 ), and promote the formation of an inorganic-rich solid-electrolyte interphase (SEI) dominated by LiF. Consequently, the PAA-PHATN-based silicon anode delivers outstanding stability (1587.6 mAh g −1 after 500 cycles at 0.5 A g −1 ) and rate capability (1074.1 mAh g −1 at 5 A g −1 ), outperforming conventional PAA binders. This work highlights an effective strategy of binder design in balancing mechanical strength, adhesion, ion conductivity, and SEI components for Si based anode.