Co9S8/NiCo2S4 core-shell array structure cathode hybridized with PPy/MnO2 core-shell structure anode for high-performance flexible quasi-solid-state alkaline aqueous batteries

The development of high-performance electrode materials for alkaline aqueous batteries (AAB) is important for the utilization of energy. Herein, we report a facile method for Co9S8 nanorods/NiCo2S4 nanosheets with core-shell structure growing directly on carbon cloth (CC). The unique structure allows for outstanding electrochemical performance when used as a cathode material, such as high specific capacity (314.7 mAh g−1), high cycling stability (88.5% after 5000 cycles) and excellent rate performance (90% at 10 A g−1). Further density functional theory (DFT) calculations reveal that the formation of a contact potential difference after NiCo2S4 coating on Co9S8 surface leads to raising the Fermi level by about 0.6 eV, which results in enhanced electronic activity and improved electrochemical properties. Subsequently, PPy/MnO2/CC anode with a core-shell structure is prepared by a simple two-step electro-deposition process and exhibits excellent capacity performance (234.4 mAh g−1). Impressively, the capacity of PPy can be increased by an order of magnitude by electro-deposition of MnO2, which solves the problem of low capacity of PPy as an anode material in alkaline electrolytes. The alkaline aqueous battery CS/NCS-6//PPy/MnO2-400 shows energy density of 74.71 Wh kg−1 at 800 W kg−1. Further assembled into a quasi-solid-state flexible battery, it can provide energy density of 0.1458 mWh cm−2 at 2.4 mW cm−2, and the devices can be used to drive a toy car for 0.32 m, run a small fan for 20 s and light up an LED for more than 3 min, which has potential applications in energy storage systems.