Flexible supercapacitors (SCs) are an emergent and promising technology for next-generation energy storage devices. However, low energy densities hindered their practical applications. Two-dimensional (2D) nanosheets can exhibit excellent electrochemical charge storage properties due to their short ion-diffusion distance and rich electroactive sites with multiple valence states. Herein, we report the direct growth of mesoporous 2D zinc cobaltite nanosheets on a flexible carbon cloth substrate (Zn–Co–O@CC) with an average thickness of ∼45 nm by a facile hydrothermal method at low temperature. The Zn–Co–O@CC electrode displays a high capacitance of 1750, 1573.65 and 1434.37 F g⁻¹ at a current density of 1.5 A g⁻¹ in LiCl, NaCl and KCl neutral aqueous electrolytes, respectively, with excellent rate capabilities at high current densities and demonstrates good cycling stability (>94%) for up to 5000 cycles. Moreover, highly flexible asymmetric supercapacitor (ASC) devices have been fabricated using Zn–Co–O@CC as a positive electrode and bimetallic organic framework (MOF)-derived nanoporous carbon polyhedra (NPC@CC) as a negative electrode (Zn–Co–O@CC//NPC@CC). The as-fabricated ASC can operate at a large potential window of 0.0–2.0 V and shows outstanding energy storage performance by delivering an ultra-high energy density of 117.92 W h kg⁻¹ at a power density of 1490.4 W kg⁻¹ with a cycling stability of 94% after 5000 charge/discharge cycles. To the best of our knowledge, the achieved energy storage performance of the ASC device is very competitive and the highest among all binary metal oxides, carbonaceous materials, and MXene-based SCs and ASCs to date. The applied strategy to fabricate SCs is capable of enhancing both electrochemical activity and cycling stability, and can be readily applied to other metal oxide-based SCs.

With the growing energy demand for a low carbon economy, it is important to develop new materials that can enhance the effectiveness of energy storage and energy conversion systems. We report a kinetics-controlled reaction for the synthesis of bimetallic organic frameworks. Furthermore, uniform ZnCoS@CoS yolk–shell structures were fabricated via sulfidation and then converted to ZnCoS@Co₉S₈/N-doped carbon single-holed hollow core–shell structures by calcination under nitrogen. Such a core–shell structure effectively withstands the dramatic volume change and inhibits the aggregation of metal nanoparticles. Meanwhile, the N-doped porous carbon offers fast electron transport to achieve exceptionally high rate capability. As a result, single-holed hollow core–shell ZnCoS@Co₉S₈/N-doped carbon shows admirable electrochemical activity as an anode material in lithium ion batteries. Furthermore, this paper also discloses the synergistic effect of the chalcogenide phase and metal on the Li storage capability.