Polyethyleneimine/Polyacrylamide Composite as Cross-linkable Aqueous Binder for Si/C Anodes of Lithium-ion Batteries

High-capacity Si/C anodes face the huge volume change during Li insertion/extraction process, which consequently leads to the pulverization of the silicon and eventually capacity fading and poor cycle life of lithium-ion batteries. To tackle this issue, new binder materials is extensively explored to improve the cycle life by effectively alleviating the huge volume change, and thus improving the cycling life. In this work, a new cross-linkable aqueous composite binder based on branched polyethyleneimine and polyacrylamide (BPEI-PAM) for Si/C anodes is reported. TGA, DSC, FTIR measurements are performed to characterize the crosslinking reaction of BPEI and PAM and their thermal properties. The electrochemical performances of the Si anodes with BPEI-PAM new binder are investigated and compared with the conventional aqueous binder of carboxymethyl cellulose/styrene butadiene rubber (CMC/SBR). By using the optimized BPEI-PAM binder (1:6 in molar ratio), the Si/C electrode exhibits the higher peel strength of 0.82 N/cm as compared with 0.32 N/cm for CMC/SBR. Even at a high loading of 3.0 mg/cm(2), the Si/C electrode with BPEI-PAM can still maintain 81.3% capacity retention after 200 cycles, better than 76.1% for the electrode with CMC/SBR. This improved electrochemical performances can be attributed to the higher adhesion property of BPEI-PAM binder after crosslinking during the process of Si/C electrodes.