Evaluation on a water-based binder for the graphite anode of Li-ion batteries

We evaluate poly(acrylamide-co-diallyldimethylammonium chloride) (AMAC) as a water-based binder for the graphite anode of Li-ion batteries. It is shown that AMAC has a similar bonding ability as the conventional poly(vinylidene fluoride) (PVDF) binder, and that the graphite electrodes bonded by AMAC and PVDF have nearly the same cyclability. Advantages of AMAC binder include: (1) it assists in forming a more conductive solid electrolyte interface (SEI) on the surface of graphite and (2) organic liquid electrolyte exhibits better penetration on the AMAC-bonded electrode. Impedance analysis shows that formation of the SEI on the surface of graphite includes two stages. The first stage takes place above 0.15 V and the second stage between 0.15 and 0.04 V. The SEI formed in the first stage is relatively resistive, while that formed in the second stage is highly conductive. For the first stage, the presence of AMAC may enhance the conductivity of the SEI. We performed a storage test on the AMAC-bonded graphite by monitoring the change of open-circuit voltage (OCV) of fully lithiated Li/graphite cells and by comparing their capacity change before and after storage. We observed that OCV of the cell increased gradually, and that capacity loss during the storage recovered in the subsequent lithiation process. Therefore, the OCV increase could be considered a self-delithiation process, which does not consume permanently Li+ ions.