Study On Interface Modification Of Sodium Metal Anode Based On Electrolyte Optimization

Lithium-ion batteries have developed rapidly in the past decade,which used in electric vehicles,electronic products,aerospace and other fields.However,due to the increasing demand for lithium-ion batteries,the shortage of lithium resources is also becoming a serious problem.Sodium-ion batteries are considered to be one of the alternatives to lithium-ion batteries due to the similar working principles to lithium-ion batteries and the abundant sodium resources.At the same time,in pursuit of higher energy density,people use sodium metal anode instead of commercial hard carbon anode.However,the strong reduction of sodium metal will lead to the instability of the anode interface,and by optimizing the electrolyte system,improving the sodium metal anode/electrolyte interface can be a good solution to this problem.This paper proposes three ways to optimize the electrolyte system,which can stabilize the interface of sodium metal anode and improve the electrochemical performance of the sodium metal battery.The details are as follows:1.Antimony fluoride（Sb F₃）is used as electrolyte additive and added into the high-concentration electrolyte.The Sb³⁺in Sb F₃ can react with Na metal and form the Na-Sb alloy layer.This alloy layer formed on the surface of sodium metal anode exhibits superior mechanical strength,which can inhibit the growth of sodium dendrites,and realize the rapid transmission of Na⁺at the same time.The high-concentration electrolyte can increase the decomposition voltage of the solvent and form a Na F-rich solid electrolyte interface（SEI）on the surface of the anode.Through the synergy effect of high concentration electrolyte and Sb F₃ additive,the Na||Na₃V₂（PO₄）₃ cell delivers stable cycling nearly 1400 cycles with a capacity retention of 82.6%,which greatly improves the electrochemical performance of sodium metal battery.2.The 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether（TTE）is used as a diluent and added into the high-concentration electrolyte to form a localized high-concentration electrolyte（LHCE）.It doesn’t influence the original solvation structure of the high-concentration electrolyte,but it will enhance the conductivity and reduce the viscosity of the electrolyte.The performance of battery can be further improved by adding the Sb F₃.After the optimization of electrolyte,the Na||Na symmetric battery can cycle for more than 1200 hours at a current density of 0.5 m A/cm².3.The ultra-low concentration electrolyte is applied to the sodium metal battery,and the organic-dominated SEI formed on the surface of Na metal enables the battery to maintain good electrochemical performance under extreme temperature conditions.The silver trifluoromethanesulfonate（STFT）is used as a surface pretreatment reagent,the Na-Ag alloy layer formed on the surface of sodium metal can induce uniform deposition of Na⁺and inhibit the growth of dendrites.Through the synergy of low-concentration electrolyte and STFT,a wide-temperature,low-cost,high-performance sodium metal battery can be achieved.Based on this electrolyte design,the capacity retention of Na||Na₃V₂（PO₄）₃ battery is 92%after 1000 cycles.Under the high and low temperature conditions,the optimized electrolyte has better performance than traditional carbonate electrolyte with a higher capacity retention.