High Performance NiO and NiO/Graphene Composite Thin Film Electrode Via Electrostatic Spray Deposition for Lithium Ion Batteries

NiO has been widely studied due to its high theoretical capacity of 718 mAh g^-1 when it is used as anode material for LIBs. However, it shows poor cycling performance due to the low electrical conductivity and large volume change during charge/discharge. In the present research, NiO thin film electrode was synthesized by electrostatic spray deposition (ESD) technique and investigated as anodes for lithium ion batteries. 10% weight percent graphene nanoplates were added to form NiO/graphene nano-composite. We expect that additional graphene will provide a high conductive medium for electron transfer during the conversion reaction of NiO with lithium ions. In addition, the porous structure generated through ESD process will be benefical to buffering the volume expansion/constriction during the cycling.

The cycling of NiO electrode results show that it can deliver a reversible capacity of 708 mAh g^-1 under the current density of 0.5 A g^-1. The number is near the theoretical capacity of NiO which indicates the complete reaction of NiO with lithium ions. As the current density increases, the capacity gradually decreases to 80 at 5 A g^-1. For the NiO/graphene composite electrode, capacity decreased from 683 to 125 mAh g^-1 as the current density increased from 0.5 to 5 A g^-1. Comparing these two electrodes, it shows that additional graphene is not beneficial to the capacity testing under low current densities. Whereas, it has a positive synergistic effect towards the capacity testing under high current densities. It is probably because of two reasons: one is that graphene itself has lower theoretical capacity than NiO; another one is that the porous thin film structure can satisfy the kinetics requirement of the reactions under low current densities. In addition to rate capability tests, material characterization (such as SEM, XRD, FTIR) and additional electrochemical tests (cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc.) were performed to evaluate the performance of such electrodes. Detailed discussion will be provided during the meeting.