Effect Of Electrolyte Additives On The Electrochemical Performance Of Lithium Metal Batteries

Lithium metal has a higher theoretical specific capacity(3860 mAh g^-1),the lowest electrochemical potential（-3.040 V vs.SHE）and a lower density(0.534 g cm^-3),which is regarded as a new generation of negative electrode materials for lithium batteries.However,lithium dendrites generated during the cycling of lithium metal batteries can cause short-circuit failure or even uncontrollable explosions.Therefore,it is necessary to find a method to suppress lithium dendrites and improve the security of batteries.Nowadays,additives are the most effective and convenient method to inhibit lithium dendrites.In this paper,1-fluoropyridine tetrafluoroborate（1-FB）is used as a bifunctional additive to improve the interface properties between electrolyte and electrode.On the one hand,the boron atom in 1-FB can couple with the anion in the lithium salt,thereby promoting the dissociation of the lithium salt and increasing the Li⁺transference number.Since 1-FB has a high reduction decomposition potential,it can preferentially decompose to form a LiF-rich SEI layer on the electrode surface,which can increase the diffusion rate of lithium ions and improve the SEI stability.On the other hand,1-FB can alleviate the dissolution of the transition metal in the positive electrode material and inhibit the decomposition of the electrolyte,thereby maintaining the interface stability of positive electrode.After adding 0.5 wt%1-FB,the reversibility and stability of lithium metal batteries have been significantly improved.The Li||Li symmetrical batteries can increase the cycle life to more than 800 h at a current density of 1 mA cm^-2 and also have a stable interface impedance.The Li|||LiFePO₄ batteries can maintain a discharge specific capacity of 97.7 mAh g^-1 after 500 cycles at 5 C and have the capacity retention rate about 92.1%.In addition,it can be found that the deposition morphology of lithium becomes smoother after adding 1-FB through SEM and XPS characterization.This kind of bifunctional additive that can act on the positive and negative electrodes is expected to become the research focuses of subsequent study.