Facile Ion-Exchange Strategy for Na+/K+ Hybrid-Ion Batteries with Superior Rate Capability and Cycling Performance

Potassium-ion batteries (KIBs) have recently attracted growing attention as next-generation energy storage devices; however, their development is hindered by the poor rate and cycling performance because of the sluggish K+ diffusion kinetics. In this work, we first design a Na+/K+ hybridization strategy by a facile ion-exchange using a 4A molecular sieve as both an ion exchanger and dehydrant to greatly enhance the electrochemical performances of the KIB. By adjusting the adding amount of the 4A molecular sieve, the Na+ content in the electrolyte can be controlled, and 25 wt % 4A molecular sieve addition is found to be the optimized condition with the best electrochemical performance. Consequently, we successfully construct a full-cell configuration Na+/K+ hybrid-ion battery (NKHIB) based on the Na+/K+ hybrid-ion electrolyte with Sn foil as the anode and graphite as the cathode, which achieves excellent electrochemical performances including superior rate capability with 74% capacity retention up to 30 C and long cycle life with negligible capacity decay over 500 cycles, among the best values of the reported KIBs. Ex situ characterizations demonstrate that the NaSn alloy starts to form before KSn formation on the Sn anode, and density functional theory calculations further reveal that the presodiation in the Sn structure provides a fast channel for the following K-ion diffusion, thus enhancing the ion-diffusion kinetics in the NKHIB. In addition, this hybridizing strategy also enables the battery to exhibit stable performance in a wide working temperature range from −20 to 55 °C, suggesting its potential application for high-performance and wide-temperature-range energy-storage devices.