Research On Preparation And Application Of New Type Sodium Metal Alloy/Sodium Composite Anode

Rechargeable sodium-based battery systems,including Na-ion batteries,Na-S batteries,Na-air batteries,and all-solid-state batteries,have attracted much attention due to their high energy density,resource abundance,and low cost.However,metallic sodium is active.Particularly,the evolution of the metal morphology on the negative electrode surface during cycling may affect safety performance of batteries and limit their capacities.The uncontrolled dendrite growth seriously restricts the application of sodium metal batteries.For the application of sodium metal batteries,one challenge is the irregular deposition and dendrite growth during cycling process.Herein,we report that spontaneous alloying reactions can occur by mechanical mixing and pressing processes of sodium metal and semi-metal bismuth powder,which can regulate the deposition of sodium ions.The improvement of the surface tension and affinity to sodium ions of metal anode can inhibit the dendrite growth.The alloy anode can be used not only in carbonates based electrolyte but also in flame-retardant electrolyte.(1)The semi-metal Bi powder and sodium metal were mechanically mixed,and the Na-Bi alloy composition formed spontaneously.With alloy electrodes,Na-Bi|Na-Bi cell shows a lower overpotential at the same current density.The addition of Bi element increases the affinity of the electrode interface to sodium ions and regulate the deposition of sodium ions.Compared to sodium metal electrode,the Na-Bi alloy electrode shows better ductility and higher hardness,and the thickness is reduced by 50%.On the contrary,the Na_0.67Ni_0.33Mg_0.1Mn_0.67O₂(NNMM)|Na-Bi cell shows a higher cycle performance and rate capability.And the symmetric battery with the flame-retardant electrolyte was assembled.The Na-Bi|Na-Bi cell shows lower overpotential and good cycle performance,which proves the applicability of the alloy electrode.(2)The Na-Sb alloy was prepared by the same method.Sb powder andsodium metal were mixed through mechanical mixing,and the alloy Na-Sb composition were formed spontaneously.During charge/discharge process,the Na-Sb alloy components appear on the surface of the electrode,and the affinity of electrode to sodium ions is improved.The addition of Sb powder not only improves the electrochemical performance of the electrode,but also improves the physical properties of the electrode.The overpotential in the symmetric battery kept at a low level,which is about 20 m V at 0.5 m A cm^-2.With the as-prepared gel electrolyte as the separator,the Na-Sb|PFR|Na-Sb symmetric battery maintains stable for more than 600 h.And the Na₃V₂(PO₄)₃(NVP)|gel electrolyte|Na-Sb battery maintains a high capacity retention and a low hysteresis voltage.It proves that the alloy anode has a better working voltage platform and a more superior rate capability.These results indicate the potential application of alloy electrodes in high-power and long-life sodium metal batteries.