Synergy Of Metallic Bismuth And Ether-based Electrolytes For Sodium Storage Performance Enhancement

Sodium-ion batteries（SIBs）have attracted much attention due to the abundance of sodium resources,low cost,safety,and so on.Electrode materials and electrolytes play important roles in SIBs.The battery performance is governed by electrode materials and electrolytes.However,large volume change occurs during sodiation/desodiation due to the larger radius of Na⁺,leading to a rapid fading of electrochemical performance.Moreover,the sluggish kinetics yields poor rate capability of SIBs.To address these issues,a synergy of electrode material and electrolyte was studied to promote cycling stability and rate performance of anode material for SIBs and the full battery.The main content and results are concluded as follows:The commercial bulk bismuth（Bi）is directly used as the anode material for SIBs,and the metallic sodium is used as the Na source.The electrochemical performance is investigated in different electrolytes.Scanning electron microscope（SEM）tests on Bi anode after different electrochemical cycles revealed that a 3D porous network was gradually formed,favored by its synergy with the ether-based electrolyte.It delivers very stable electrochemical performance.Ex-situ X-ray diffraction（XRD）was carried out to study the phase transition of Bi in a discharge-chargeprocess,and it wasfoundto exhibit tworeversible alloying/dealloying reaction processes.The initial coulombic efficiency reach as94.8%,and the reversible capacity is about 387 mAh·g^-11 at 400 mA·g^-11 with a capacity retention of 94.4%after 2000 cycles.The capacity is high up to 356.0mAh·g^-11 when the current density is increased to 2000 mA·g^-1,which indicates the excellent rate capability and cycling stability of Bi in ether-based electrolytes.Furthermore,a sodium-ion full battery based on the Bi anode,Na₃V₂（PO₄）₃mixed with multiwalled carbon nanotubes（NVP@CNTs）as cathode and NaPF₆-G2electrolyte was studied.The electrochemical measurement shows that both Bi and NVP@CNTs have good rate capability and cycling stability using the NaPF₆-G2electrolyte.A capacity of about 250 mAh·g^-1（based on the mass of Bi）was achieved by optimizing the ratio of the mass of anode and cathode.This sodium-ion full battery has a high energy density(154.5 Wh·kg^-1),and the power density reach as 927 W·kg^-1（based on the total mass of anode and cathode）.The capacity retention of the Bi//NVP@CNTs full battery is 97.7%after 200 cycles,which indicates the high power density and excellent cycling stability of the full battery.