Application Research Of LiAlCl₄·3SO₂ Electrolyte In Lithium-ion Battery And Lithium Metal Battery

Lithium-ion batteries have the advantages of high specific energy and long cycle life,and are used in many products.However,the flammable and explosive organic electrolyte causes lithium-ion batteries with serious safety problems.Moreover,the graphite anode of the lithium-ion batteries does not to meet the requirements of high energy density,making the secondary lithium metal anode with negative potential and high specific capacity become a research hotspot.However,lithium dendrites are easily formed on the surface of the secondary lithium metal anode,resulting in a short circuit of the battery.At this time,if the battery system uses an organic electrolyte,it is more likely to cause battery combustion and explosion.In order to take into account the safety and high specific energy of the battery system at the same time,it is necessary to research and develop an electrolyte system that is non-combustible and compatible with the cathode material of the lithium-ion batteries and the secondary lithium metal anode.This thesis mainly studies the application of a non-flammable inorganic non-aqueous electrolyte LiAlCl4·3SO2 in lithium-ion batteries and secondary lithium metal batteries.The preparation of LiAlCl4·3SO2 electrolyte was explored.The study indicated that LiCl is the key factor affecting the synthesis of LiAlCl4·3SO2 electrolyte.Vacuum drying LiCl at 130℃ for 48 h is an advantageous condition for the synthesis of LiAlCl4·3SO2 electrolyte.The physical and chemical properties test of the LiAlCl4·3SO2 electrolyte showed that the electrolyte had non-combustible properties,which can improve the safety of the battery system;and had high ionic conductivity and lithium ion transference numbers,which were 37.51 mS·cm-1 and 0.42 at room temperature(20℃),respectively.However,the electrochemical window of LiAlCl4·3SO2 electrolyte is narrow,and oxidative decomposition of LiAlCl4·3SO2 electrolyte begins to occur above 4.0 V(vs.Li+/Li).Considering the electrochemical window characteristics of LiAlCl4·3SO2 electrolyte,the electrochemical performance of LiFePO4 and Li4Ti5O12 in LiAlCl4·3SO2 electrolyte were studied.At room temperature,compared with organic electrolytes,LiFePO4 and Li4Ti5O12 had higher specific capacity and rate performance in LiAlCl4·3SO2 electrolyte,and obtained good cycle performance.Under low temperature conditions(0℃),compared with organic electrolytes,LiFePO4 obtained more excellent rate performance and cycle performance in LiAlCl4·3SO2 electrolyte.The stability of secondary lithium metal anodes in LiAlCl4·3SO2 electrolyte and organic electrolyte was compared to analyze the working mechanism of the stability improvement of lithium metal electrode in LiAlCl4·3SO2 electrolyte.The charge and discharge test results of Li|Cu batteries and Li|Li symmetric batteries showed that,compared with organic electrolyte,lithium metal anode had better electrochemical stability in LiAlCl4·3SO2 electrolyte at room temperature and low temperature.The results of the electrochemical impedance spectroscopy test indicated that the lithium metal anode had lower Ohmic impedance,solid electrolyte interface film(SEI film)impedance and charge transfer impedance in LiAlCl4·3SO2 electrolyte.Scanning electron microscope test results showed that in LiAlCl4·3SO2 electrolyte,the lithium metal anode had a relatively smooth and compact surface.The experimental results showed that at room temperature and low temperature,lithium metal anodes had better interface stability in LiAlCl4·3SO2electrolyte than in organic electrolyte.The secondary lithium metal anode obtained better stability in LiAlCl4·3SO2 electrolyte,due to the high lithium ion transference numbers and high lithium salt concentration of LiAlCl4·3SO2 electrolyte.X-ray photoelectron spectroscopy test data showed that in LiAlCl4·3SO2 electrolyte,the main components of the SEI film on the surface of the lithium metal anode included LiCl,Li2SO4 and Li2S.A simple and effective solution(adding LiF in LiAlCl4·3SO2)was provied to improve the stability of lithium metal electrode in LiAlCl4·3SO2.The effects of LiF additive on the basic physical and chemical properties of LiAlCl4·3SO2 electrolyte and the stability of lithium metal anode in LiAlCl4·3SO2 electrolyte were studied.LiF additive possessed a wide electrochemical window and the ability to adjust the surface tension.In addition,LiF improved the stability of the electrolyte in humid air.Therefore,in this thesis,the addition of 0.3 wt%LiF improved the ion conductivity and lithium ion transference numbers of LiAlCl4·3SO2 electrolyte,broaden the electrochemical window of LiAlCl4·3SO2 electrolyte,and reduced the energy barrier of lithium ion migration through SEI film.Therefore,the lithium metal anode obtained optimal electrochemical stability in LiAlCl4·3SO2 electrolyte containing 0.3 wt%LiF additive.The results of the electrochemical impedance spectroscopy test indicated that the addition of 0.3 wt%LiF in LiAlCl4·3SO2 electrolyte allowed the lithium metal anode to have a lower SEI film impedance and charge transfer impedance.The scanning electron microscope test results showed that the addition of 0.3 wt%LiF made the lithium metal anode in LiAlCl4·3SO2 electrolyte with a relatively smooth and compact surface.Therefore,the addition of 0.3 wt%LiF makes the lithium metal anode had better interface stability in LiAlCl4·3SO2 electrolyte.The Arrhenius formula was used to simulate the process of lithium ion migration through the SEI film.The results showed that the mechanism of the LiF additive function was to stabilize the lithium ion electrodeposition by reducing the energy barrier of lithium ion migration through the SEI film.The addition of 0.3 wt%LiF improved the electrochemical performance of Li-SO2 batteries.