Electrophoretic LiFePO4/ Graphene Composite for Li-Ion Battery Cathode Application

LiFePO₄ (LFP) is a most promising cathode material for lithium ion batteries (LIBs) due to its high theoretical capacity (170 mAh g-1), flat voltage plateau, long cycle life, abundant material supply, and excellent safety.  However, it suffers from low electronic conductivity, which results in sacrificed capacity and low rate performance of the cathode.  Finding efficient additives that enhances the electronic conductivity of LFP, while at the same time minimizing the content of both additives and binders, become a tempting goal as it would lead to high performance cathode with high packing density.  

In the present work, we demonstrate a binder free composite electrode of LiFePO₄/ graphene with ultrahigh LiFePO₄ mass ratio (91.5 wt% of LiFePO₄) using electrophoresis. No additional additive (other than graphene) is introduced.  Enhanced capacity and improved rate performance have been demonstrated in the electrophoretic composite cathode, when compared to either the conventional one or composite cathode formed by mechanically mixing LiFePO₄ and graphene. A number of key material/processing parameters have been investigated in a systematic manner in order to understand their effect on the final cathode electrochemical performance as well as identify the optimum composite cathode configuration. We also extend our discussion onto the beneficial effect of using three dimensional current collectors and the role of different ions employed during the electrophoresis process. The present methodology is simple and does not disturb the active material growth process. It can be generally applied to a variety of active material systems for both cathode and anode applications in Li-ion batteries. This work is supported by General Research Funding of the National Natural Science Foundation of China/ Research Grants Council Joint Research Scheme under project No. N_CUHK448/13.