High-capacity Si-graphite composite electrodes with a self-formed porous structure by a partially neutralized polyacrylate for Li-ion batteries

NaOH-neutralized poly(acrylic acid) is examined as a binder for Si-based negative electrodes in rechargeable Li-ion batteries. To better understand the influence of polymer binder characteristics, the impact of neutralization degree (ND) of poly(acrylic acid) (PAH) on electrode performance of a Si-graphite composite is studied. The electrode performance of the Si-based composites is remarkably improved by appropriate neutralization of PAH because the NDs highly influence rheological properties of a slurry and thus the electrode morphology, such as porosity. It is found that 80% neutralized PAH provides the moderate porous structure inside the composite electrode with 10 wt% binder content because of a unique rheological property during the drying process after casting the slurry onto a current collector. The self-formed porous structure by the partially neutralized PAH is beneficial to buffer volume expansion caused by lithiation of Si. Therefore, an excellent capacity retention for a 100 cycle test with a high reversible capacity of approximately 1000 mA h g(-1) is achieved with the 80% neutralized PAH as a binder for Si-based composite electrodes.