Designing Crystalline/Amorphous NVNPF/NCK Cathode Toward High‐Performance Fully‐Printed Flexible Aqueous Rechargeable Sodium‐Ion Batteries (ARSIBs)

The flexible ARSIBs have great potential in portable and wearable electronics due to their high cost-effectiveness, safety, and amazing flexibility. Nevertheless, achieving both outstanding flexibility and high energy density remains a challenge. Herein, a battery-supercapacitor composite material Na₃V_1.95Ni_0.05(PO₄)₂F₃/10%NC-KOH (NVNPF/NCK) with coexistence of crystalline and amorphous phases is fabricated by loading nitrogenous carbon (NC) onto Na₃V_1.95Ni_0.05(PO₄)₂F₃ (NVNPF) and etching with KOH. It demonstrates high specific capacity (187.26 mAh g^-1), ultrahigh energy density (262.16 Wh kg^-1), and excellent cycle performance (the capacity retention is 81% at 1 C after 500 cycles). The high performance is achieved by doping Ni²⁺ loading NC and etching with KOH, which generates vacancy defects, enhances structural stability, and accelerates ion-diffusion kinetics. Furthermore, the fully-printed ARSIBs (F-NTP//NVNPF/NCK) with high specific capacity (60.37 mAh g^-1), amazing energy density (72.44 Wh kg^-1), and excellent cycle performance, are fabricated using screen-printing technique based on the NVNPF/NCK cathode and NaTi_1.7Fe_0.3(PO₄)₃ (F-NTP) anode. To the best of the authors' knowledge, F-NTP//NVNPF/NCK is the highest-performing fully-printed flexible ARSIB to date. In particular, these batteries can achieve tunability in shape and size, integration, and high-throughput manufacturing. Thus, this work can offer greater possibilities for the development of high-performance flexible ARSIBs.