Conformal surface-nanocoating strategy to boost high-performance film cathodes for flexible zinc-ion batteries as an amphibious soft robot

To satisfy the increasing power demand for the rapid development of wearable and portable electronics, the design of quasi-solid-state aqueous zinc-ion batteries (QAZIBs) requires the advancement of flexible electrodes possessing excellent electrochemical performance and extraordinary mechanical strength. This purpose could be realized by utilizing electrospinning to obtain flexible film cathodes composed of layer-structured transition metal dichalcogenides@nitrogen-doped carbon nanofibers (TMD@N-CNFs), attributed to the synergetic effect between the nanostructured TMDs (for capacity) and interwoven 1D N-CNFs (for flexibility). However, their potentials are seriously impeded by the dissolution and structural instability of active materials during zinc-ion (de)intercalation process, leading to insufficient rate capability and much-shortened cycle life. Herein, to address this big challenge, we have demonstrated the approach of developing an ultrathin Al₂O₃ coating layer by atomic-layer-deposition (ALD) to greatly boost the electrochemical performance of vanadium diselenide nanosheets@N-CNFs (Al₂O₃@VSe₂ NSs@N-CNFs) film cathode in flexible QAZIBs. Moreover, the ALD-Al₂O₃ nanocoating provides desperately necessary mechanical robustness in the cross-2D nanosheet direction of VSe₂ standing on the N-CNFs surface, as confirmed by finite element simulation results. Consequently, the QAZIB delivers an outstanding stack energy density of ∼125 Wh kg⁻¹, an ultrahigh rate capability of 65.2% capacity retention after 200-fold increase in current density and an excellent cycling performance of 86.2% retention after 2500 cycles. Finally, we integrate the flexible QAZIB into a soft inchworm robot, which achieves reversible actuation both on land and in water and keeps good electrochemical stability, showing the prospective potentials of introducing energy storage devices for soft robotics with broad multifunctional applications.