Research On[Py_1,4] FSI Ionic Liquid Electrolyte And Current Collector Modification In Lithium Metal Battery

Li metal is an ideal anode material for high energy density batteries due to its high theoretical capacity of 3860 mAh·g^-1,low reduction potential（-3.04 V vs H⁺/H₂）.However,Li metal is easy to form lithium dendrites and has a huge volume change during deposition,reducing the electrochemical performance of Li metal battery and increasing the potential safety hazard.This paper focuses on the problems of Li metal anode.The electrochemical properties of 1-butyl-1-methylpyrrolidinium bis-（fluoromethylsulfonyl）imide([Py_1,4]FSI)ionic liquid electrolyte with high safety were studied in lithium metal batteries.In situ AFM was used to study the interface structure between IL electrolyte and electrode with different Li⁺concentrations,and the effect of interface structure on the formation of solid electrolyte interface（SEI）film was investigated.Li Cl was introduced into SEI film with SO₂Cl₂ as IL electrolyte additive,which improved the stability and Li⁺diffusion rate of SEI film and promoted the uniform deposition of Li.A hierarchical porous nickel foam current collector with high specific surface area was constructed as the carrier of Li deposition,which reduced the local current density,avoided the formation of Li dendrite.Inorganic anions in IL can increase the content of inorganic components in SEI film.SEI film formed in IL electrolyte contains more inorganic components,such as Li F,Li₃N and Li₂O,which enhance the stability and ionic conductivity of SEI film.Li metal batteries show better electrochemical performances in IL electrolyte.Li//Li symmetric battery can cycle stably for 2000 h at the current density of 0.5 m A·cm^-2and the capacity of 1 m Ah·cm^-2.The capacity retention rate of Li//Li Fe PO₄ battery is84.6%after 200 cycles at 0.5 C rate.The interface structure between electrolyte and electrode has an important effect on SEI film formation.The interface structures between IL electrolytes with different Li⁺concentrations and electrode were studied by in-situ AFM.The result of research shows that both the solvation layer number in the interface structure and the forces needed to through the solvation layer decrease with the increase of Li⁺concentration,making[Li（FSI）₃]^2-ligand in the IL electrolyte with high Li⁺concentration is easier to reach the electrode surface and react electrochemically,which increases the initial potentials of lithium underpotential deposition and SEI film formation.Lithium halide has low Li⁺diffusion barrier and high Li⁺diffusion surface energy.The increase of lithium halide content in SEI film contributes to the uniform deposition of Li metal.[Py_1,4]FSI IL electrolytes with different additive contents([Py_1,4]FSI:SO₂Cl₂=1:0,100:1,80:1,60:1,40:1,volume ratio)were prepared using SO₂Cl₂ as an electrolyte additive.The SEI films formed on the surface of lithium metal anodes and the electrochemical properties of lithium metal batteries in different IL electrolytes were measured and characterized.XPS results show that Li Cl content in SEI film increases gradually with the increase of SO₂Cl₂,which is helpful to improve the stability and Li⁺diffusion rate of SEI film.When the content of SO₂Cl₂reaches 40:1,the electrochemical window of IL electrolyte decreases obviously,which reduces the electrochemical performance of lithium metal battery.In the electrolyte of E60:1,Li//Li Fe PO₄ battery exhibits good electrochemical performance,and the capacity retention rate is 89.9%after 200 cycles at 0.5 C rate.A hierarchical porous nickel foam（HPNF）current collector with high specific surface area was prepared by high temperature redox method,which can reduce the local current density and improve the nucleation uniformity of Li metal.The surface defects on the current collector are conducive to spontaneously form concave lithium structure,which can lead to uniform deposition of Li metal.The Li metal deposits on HPNF current collector are more uniform and compact,and there is no Li dendrite formation,which improves the electrochemical performances of Li metal batteries.In organic electrolyte,Li//Li@HPNF symmetric cell can cycle stably for 700 h at the current density of 1 m A·cm^-2 and the capacity of 1 m Ah·cm^-2.Li@HPNF//Li Fe PO₄battery has a capacity retention rate of 93.0%after 300 cycles at 1 C rate.In IL electrolyte,Li//Li@HPNF symmetric cell can cycle stably for 1000 h at the current density of 0.5 m A·cm^-2 and the capacity of 1 m Ah·cm^-2.Li@HPNF//Li Fe PO₄ battery has a capacity retention rate of 90.9%after 300 cycles at 0.5 C rate.