Conductive polymer-based binders for Si anode electrodes in lithium ion batteries

Silicon has attracted great attention as an anode material for lithium ion batteries due to its extremely high theoretical gravimetric capacity (~4200 mAh g-1), relative low discharging potential (0.2 V versus Li/Li+), environmental friendliness, and natural abundance. However, Si-based anodes undergo a huge volume variation upon lithiation and delithiation (~400%) that lead to pulverization of active materials, loss of electrical contact, an unstable electrolyte interphase on the silicon surface and consequently, capacity fading. In this study, conductive composites consisting of poly(acrylic acid) (PAA) and polyaniline (PANI) with different ratios were synthesized via a scalable and simple method. The synthesized poly(acrylic acid)-Polyaniline composites were used as a dual functional binder in fabricating silicon-based electrodes of lithium-ion batteries. The electrode with PAA-PANI as binder exhibited a capacity of ~1500 mAh g-1 after 100 cycles at a high current density of 4000 mA g-1 with a capacity retention of 78%. The results showed an improved initial efficiency, capacity cycle stability, and rate capacity due to the high binding strength and ability to accommodate volume variation. The influence of the PAA:PANI ratio was also studied. The results show that silicon-based electrodes with a PAA:PANI ratio of 2:1 has the best performance giving a capacity of ~1640 mAh g-1 after 100 cycles at a current density of 4000 mA g-1 with a capacity retention of 82%. This improvement can be attributed to the well-balanced electrical and mechanical properties. Interestingly, adding additional conductive agents such as BP2000 and carbon nanofiber didn’t improve the performance of electrodes indicating the advantage of this type of binder.