In-situ regulation of solid electrolyte interface formation by molecular designing of polymer binders for high-performance silicon/graphite anode

A new acrylic acid copolymer is prepared by free radical copolymerization with acrylic acid (AA) and hexafluoro butyl acrylate (HFA). The product is used as a polymer binder for Silicon/Graphite (Si/Gr) anode in a lithium-ion battery. The molecular structure of the copolymer and the electrochemical performance of binders are carefully investigated. The results show that the Si/Gr anode based on AA-HFA copolymers binders has good rate performance and excellent cycle stability after adjusting the amount of HFA. The initial charge/discharge capacity reachs about 771/914 mAh g−1 during the first charge-discharge cycle. Its Initial Coulomb Efficiencie (ICE) is higher than 84 %. The reversible specific capacity can be maintained to 504 mAh g−1 with in 350 cycles at 1 C, while it can reach 220 mAh g−1 at 5 C. The in-depth analysis further show that this kind of AA-HFA copolymer binder can effectively inhibit electrolyte decomposition since solid electrolyte interphases (SEI) can be constructed at a molecular level. This stable interphases can be attributed to the successful combination of the flexible molecular structure of AA-HFA copolymer with the rigid SEI layer formed between the active material and electrolyte. The success of this work provides a promising way to pursue lithium-ion batteries with long cycle life by molecular designing with polymer binders.