Ion-selectivity Of Electrode Materials For Alkali Metal-ion Batteries

Lithium-ion batteries have become a research hotspot in both academia and industry due to their advantages such as high energy density,long life-time,low comprehensive cost,etc.However,considering the limited reserves of Lithium and inconvenience of utilization,alternative battery systems including sodium ion batteries and potassium ion batteries have also received increasing attention.Above three kinds of alkali metal-ion batteries are the research object of this work.A series of Prussian blue materials are synthesized for studying ion-selective mechanism of available alkali-ion electrodes during the insertion/extraction process happened in mixed-ion electrolyte.It is found that K2FeFe?CN?6?K-FeHCF?,K₂FeCo?CN?₆?K-CoHCF?,K₂FeCu?CN?₆?K-CuHCF?all exhibit priority selection towards K⁺.Unfortunately,specific capacity of K-CoHCF testing in mixed-ion electrolyte is lower than that in a single-ion electrolyte,and thus is not suitable for hybrid aqueous batteries?HABs?.Though highest capacities of K-CuHCF has been obtained in mixed-ion electrolyte,but its cycle stability is quite poor owing to the high solubility of such materials.Hence K-FeHCF,which exhibits outstanding performance in the mixed-ion electrolyte,is the only one that suitable for HABs.Besides,aqueous metal-ion batteries have attracted considerable attention due to its safety,low costs,and environmental friendliness.Yet the poor-performance electrodes lead to a low feasibility of practical application.HABs fabricated using electrodes with selective cation channels could increase the electrode applicability and thus enlarge the application of rechargeable aqueous metal-ion batteries.Therefore,a high-voltage K–Na HAB based on K-FeHCF cathode and carbon coated NaTi2?PO4?3?NTP/C?anode is constructed on the basis of the above work.Due to the unique cation selectivity of both materials and ultrafast ion conduction of NTP/C,the hybrid battery delivers a high capacity of 160 mAh·g^-1 at a 0.5C rate.Considerable capacity retention of 94.3%is also obtained after 1000 cycles at even 60C rate.Meanwhile,high energy density of 69.6 Wh·kg^-1 based on the total mass of active electrode materials is obtained,which is comparable and even superior to that of the lead acid,Ni/Cd,and Ni/MH batteries.