Trimming the Degrees of Freedom via a K+ Flux Rectifier for Safe and Long-Life Potassium-Ion Batteries

High degrees of freedom (DOF) for K+ movement in the electrolytes is desirable, because the resulting high ionic conductivity helps improve potassium-ion batteries, yet requiring support from highly free and flammable organic solvent molecules, seriously affecting battery safety. Here, we develop a K+ flux rectifier to trim K ion's DOF to 1 and improve electrochemical properties. Although the ionic conductivity is compromised in the K+ flux rectifier, the overall electrochemical performance of PIBs was improved. An oxidation stability improvement from 4.0 to 5.9 V was realized, and the formation of dendrites and the dissolution of organic cathodes were inhibited. Consequently, the K||K cells continuously cycled over 3,700 h; K||Cu cells operated stably over 800 cycles with the Coulombic efficiency exceeding 99%; and K||graphite cells exhibited high-capacity retention over 74.7% after 1,500 cycles. Moreover, the 3,4,9,10-perylenetetracarboxylic diimide organic cathodes operated for more than 2,100 cycles and reached year-scale-cycling time. We fabricated a 2.18 Ah pouch cell with no significant capacity fading observed after 100 cycles.

Automated summary

To improve the ionic conductivity and safety of potassium-ion batteries, researchers developed a K+ flux rectifier that limits the degree of freedom for K+ movement. The rectifier improved the electrochemical performance of the batteries, enhancing oxidation stability, inhibiting dendrite formation and organic cathode dissolution. The K||K cells cycled continuously for over 3,700 hours, K||Cu cells operated stably for 800 cycles with a Coulombic efficiency exceeding 99%, and K||graphite cells showed high capacity retention after 1,500 cycles. The organic cathodes operated for over 2,100 cycles and showed no significant capacity fading after 100 cycles in a pouch cell.