Conversion Synthesis of Self-Standing Potassium Zinc Hexacyanoferrate Arrays as Cathodes for High-Voltage Flexible Aqueous Rechargeable Sodium-Ion Batteries.

Prussian blue analogs exhibit great promise for applications in aqueous rechargeable sodium-ion batteries (ARSIBs) due to their unique open framework and well-defined discharge voltage plateau. However, traditional coprecipitation methods cannot prepare self-standing electrodes to meet the needs of wearable energy storage devices. In this work, a water bath method is reported to grow microcube-like K2 Zn3 (Fe(CN)6 )2 ·9H2 O on carbon cloth (CC) using Zn nanosheet arrays as the zinc source and reducing agent, directly serving as a self-standing cathode. Benefiting from fast ion diffusion and high conductivity, the cathode delivers a high areal capacity of 0.76 mAh cm-2 at 0.5 mA cm-2 and excellent capacity retention of 57.9% as the current density increases to 20 mA cm-2 . By coupling with NaTi2 (PO4 )3 grown on CC as an anode, a quasi-solid-state flexible ARSIB with a high output voltage plateau of 1.6 V is successfully assembled, exhibiting a superior areal capacity of 0.56 mAh cm-2 and energy density of 0.92 mWh cm-2 . In particular, the device shows admirable mechanical flexibility, maintaining 90.3% of initial capacity after 3000 bending cycles. This work is anticipated to open a new avenue for the rational design of self-standing electrodes used in high-voltage flexible ARSIBs.