*2.2. Preparation of Electrodes (G95 and G70L25)*

To evaluate the electrochemical properties of the graphene nanoplatelets/LSMCO composites, electrodes were fabricated as follows: 5 wt% of polyvinylidene fluoride (PVDF, MTI corporation, California, CA, USA) was mixed with enough dimethyl sulfoxide (DMSO, Sigma-Aldrich, St. Louis, MO, USA) to dissolve the powder. Graphene nanoplatelets (GN, Alfa Aesar, Haverhill, MA, USA) used in the experiment have a specific surface area of 500 m2/g, and a particle diameter of smaller than 2 microns and a typical particle size of a few nanometers, depending on the surface area. For the G70L25 electrode, the graphene nanoplatelets and perovskite were mixed to a 70%:25% weight ratio for 30 min. For the G95 electrode, 95 wt% graphene nanoplatelets were used. Mixed active material was applied on a carbon paper substrate and baked in an oven at 150 ◦C for 15 min. The two-dimensional size of the electrode was 10 mm × 10 mm. The mass of active material in the working electrode was 1.0–2.0 mg.
