**4. Conclusions**

A unique, flexible, and self-healing ECHs were synthesized through introducing TOCNF-CNT@PANI nanohybrid with a "core-shell" structure into viscoelastic PVA hydrogel matrix. The nanohybrid built a 3D hierarchical framework in the hydrogel matrix, which not only improved the viscoelasticity but also enhanced the electrochemical performance of the ECHs. The ECH possessed a

high mechanical toughness (σ<sup>s</sup> <sup>≈</sup> 128 kPa cm<sup>3</sup> <sup>g</sup>−<sup>1</sup> and *<sup>E</sup>*<sup>e</sup> <sup>≈</sup> 61 kPa), excellent viscoelastic characteristics (*G* <sup>∞</sup> <sup>≈</sup> 18.2 kPa and *G*"max <sup>≈</sup> 7.6 kPa), and ideal electroconductivity (up to 15.3 S m−1). The specific capacitance of the TOCNF-CNT@PANI/PVA-2 hydrogel electrode was 226.8 F g−<sup>1</sup> at a current density of 0.4 A g<sup>−</sup>1. The ECHs exhibited fast self-healing character within 20 s at room temperature and superior flexile performance due to the reversible and dynamic borate-associated network. The symmetric solid-state supercapacitor was fabricated by the TOCNF-CNT@PANI/PVA-2 hydrogel electrodes and TOCNF/PVA electrolyte; the capacitance retention was 90% after 10 cutting/healing cycles; the capacitance retention was 85.0% and 82.3% after 1000 bending and twisting cycles, respectively. Consequently, the novel ECHs provided an alternative platform for personal wearable electronic devices.

**Author Contributions:** Conceptualization, J.H. and X.X.; methodology, J.H. and X.X.; validation, Y.L., Y.Y., J.H. and X.X.; formal analysis, J.H. and X.X.; investigation, Q.W.; resources, J.H. and X.X.; writing—original draft preparation, H.W. and S.K.B. and S.Z.; writing—review and editing, Y.L., Y.Y., J.H., X.X., Q.W. and H.X.; supervision, J.H. and X.X. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors are thankful for the financial support from National Natural Science Foundation of China (31770609), Natural Science Foundation of Jiangsu Province for Outstanding Young Scholars (BK20180090), Qing Lan Project of Jiangsu Province (2019), 333 Project Foundation of Jiangsu Province (BRA2018337), Priority Academic Program Development (PAPD), and Analysis and Test Center of Nanjing Forestry University.

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