**4. Conclusions**

In summary, the supercapacitor electrode was prepared by the synthesis of graphene and perovskite material (LSMCO). XRD showed that it was well mixed without a secondary reaction. According to electrochemical analyses, for the G95 electrode, the specific capacitance ranges from 53 to 68 F/g, and the standard deviation is about 6. For the G70L25 electrode, the specific capacitance ranges from 49 to 55 F/g, and the standard deviation ranges from 1 to 2.5. The initial specific capacity of the G70L25 electrode of 49 to 55 F/g is about 10%–20% smaller than that of the G95 but has a small standard deviation. The cycling test showed that the specific capacitance of G70L25 was reduced (~5%) at all times, indicating that the cycling stability was improved compared to the unpredictable (both cases increasing or decreasing) results of G95. Therefore, the supercapacitor using LSMCO and graphene electrode is better for commercialization considering the repeatable performance and seems to be an excellent material for improving cycling stability in other electrochemical applications.

**Author Contributions:** Conceptualization, Y.-W.J. and J.S.; data curation, B.-M.K. and H.-Y.K.; investigation, B.-M.K. and H.-Y.K.; methodology, J.S.; supervision, Y.-W.J. and J.S.; validation, B.-M.K., H.-Y.K., Y.-W.J., and J.S.; visualization, B.-M.K. and H.-Y.K.; writing – original draft, B.-M.K.; writing – review and editing, Y.-W.J. and J.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (No. NRF-2018R1D1A1A02085324). This research was supported by the Mid-Career Researcher Program (No. NRF-2020R1A2C1007847) through the National Research Foundation of Korea, funded by the Korean government's Ministry of Education.

**Conflicts of Interest:** The authors declare no conflicts of interest.
