Flexible nanostructured potassium-ion batteries

We describe a flexible and freestanding potassium-ion battery consisted of a bilayer-copper phosphide/copper nanowires (CuP2/Cu NWs) anode and perylene-3,4,9,10-tetracarboxylic dianhydride/carbon nanotubes (PTCDA@CNTs) cathode with superior rate capability and cyclability to simultaneously achieve fast K+-insertion/releasing and long shelf life on flexible-based electrodes. The extraordinary rate performance of anode and cathode deliver remarkable capacities of 90 mA h g-1 at 12,000 mA g-1 and 113 mA h g-1 at 5250 mA g-1, respectively. Furthermore, coin-typed full cell exhibits superior charging capacities of 117.3 mAh g-1 at 12,000 mA g-1 and the good retention (80% after 842 cycles at 400 mA g-1). The energy density in the high-power density region, especially the specific energy density under high power density (>104 Wkg- 1) displayed the better rate-capability retention compared with that of reported literatures of full cells (based on the total mass of anode and cathode). Considering the flexibility and stability, the pouch batteries examined by a bending test maintained ultra-stable open circuit voltage after 5000 cycles with a bending radius of 1.2 cm. Expectedly, the state-of-art nano-engineering design and excellent performance demonstrate the direction and opportunities to further improve the energy density and safety under ultrahigh reaction rates of the wearable potassium-ion batteries.