Using graphene nanosheets as a conductive additive to enhance the rate performance of spinel LiMn2O4 cathode material

Graphene nanosheets (GNs) were directly used as a type of novel but powerful planar conductive additive in spinel LiMn2O4 (LMO)-based electrodes, to improve the low electronic conductivity of LMO. It was found that the specific capacity and cycling performance of LMO were obviously enhanced when GNs co-existed with acetylene black (AB), a conventional carbon-based conductive agent, at an appropriate weight ratio in the LMO-based electrode (GNs and AB were 5 wt% and 10 wt% of the total weight, respectively). The unusual phenomenon was attributed to the following two reasons: (i) the planar GNs could bridge LMO particles more effectively via a "plane-to-point" conducting mode; (ii) AB particles might serve as the fillings in the electrode and connect the isolated LMO particles to GNs through a "filling effect", thereby constructing a novel and more effective conducting network. In this way, the synergy effect between the "plane-to-point" conducting mode (due to GNs) and the "filling" mode (due to AB) significantly decreased the charge-transfer resistance of the LMO-based electrode. With the much faster charge-transfer process, the rate performance of LMO was greatly enhanced. In contrast, when GNs were in excess, the effective conducting network was weakened by the agglomeration of GNs and the absence of AB, so the conductivity and the rate performance of LMO were not improved and even decreased.