Conductive Polymer Binder for High-Tap-Density Nanosilicon\nMaterial for Lithium-Ion Battery Negative Electrode Application

Abstract

High-tap-density\nsilicon nanomaterials are highly desirable as anodes for lithium ion\nbatteries, due to their small surface area and minimum first-cycle\nloss. However, this material poses formidable challenges to polymeric\nbinder design. Binders adhere on to the small surface area to sustain\nthe drastic volume changes during cycling; also the low porosities\nand small pore size resulting from this material are detrimental to\nlithium ion transport. This study introduces a new binder, poly­(1-pyrenemethyl\nmethacrylate-<i>co</i>-methacrylic acid) (PPyMAA), for a\nhigh-tap-density nanosilicon electrode cycled in a stable manner with\na first cycle efficiency of 82%a value that is further improved\nto 87% when combined with graphite material. Incorporating the MAA\nacid functionalities does not change the lowest unoccupied molecular\norbital (LUMO) features or lower the adhesion performance of the PPy\nhomopolymer. Our single-molecule force microscopy measurement of PPyMAA\nreveals similar adhesion strength between polymer binder and anode\nsurface when compared with conventional polymer such as homopolyacrylic\nacid (PAA), while being electronically conductive. The combined conductivity\nand adhesion afforded by the MAA and pyrene copolymer results in good\ncycling performance for the high-tap-density Si electrode.