| Lithium batteries（LBs）are kinds of secondary batteries which use lithium metal,lithium alloy or graphite as anode and non-aqueous electrolytes.Nowadays,LBs are widely used in portable devices such as mobile phone,laptop tablet PC and electric vehicles due to its advantages like smaller size,high specific capacity,high energy density and environment-friendly.And most of the electrolytes used in LBs are organic solvent electrolytes,such as propylene carbonate（PC）,ethylene carbonate（EC）,dimethyl carbonate（DMC）because of their advantages of low price,high conductivity and low melting point.However,those electrolytes also have the disadvantage of flammability which can lead to safety accident of lithium-ion battery fire.Therefore,the development of new safer electrolytes is of great significance to improve the safety of LBs.In this thesis,we have prepared three new electrolytes and applied to Li/LiFePO4 batteries or Lithium-Sulfur batteries,respectively.The properties of the electrolytes,the performance of the batteries and its safety are studied systematically.1.Poly（ionic liquid）-based electrolyte and its application in Li/LiFePO4 batteryThe poly（ionic liquid）,PATA,was successfully synthesized by free radical polymerization,and a novel PIL-based electrolyte,MPIL,by mixing a PATA with additives of 10 wt%propylene carbonate（PC）and 0.1 M Li Cl O4was fabricated and successfully applied in Li/LiFePO4 battery.The MPIL electrolyte exhibits high ionic conductivity of 8.3×10-5 S/cm at 25℃ or 2.0×10-4 S cm-1 at 60℃ with a wide electrochemical potential window up to 5.61V at 25℃.We found that MPIL can keep stable during the process of battery charging and discharging,and can form stable and excellent SEI film at the Li-MPIL interface.The Li/LiFePO4 batteries with MPIL electrolyte achieve high capacity,outstanding cycling stability and rate capability at 25℃ and improved performance at high temperature up to 60℃.This shows that the MPIL can be used in a wide range of temperature,and can also be used in Li/LiFePO4 batteries under a high temperature environment with enhanced safety performance.（2）Zwitterionic ionic liquid-based electrolyte and its application in Li/LiFePO4 batteryZwitterionic ionic liquid,TLP,which has a high thermal decomposition temperature of178℃ and an ionic conductivity of 3.25 x 10-4 S/cm at 25℃,was synthesized through the quaternization reaction.Then we add 7 wt%ethylene carbonate（EC）to obtain electrolyte named TLPEC,which has a wide electrochemical window of 1.65-5.10 V and a high ionic conductivity of 1 x10-3 S/cm at 20℃.Then we applied TLPEC to Li/LiFePO4 battery and tested the charge-discharge performance at room temperature and high temperature.The battery has a high discharge specific capacity of 135.4 m Ah/g with a current density of 0.1 C at 25℃ and improved performance at 60℃ due to the more uniform SEI film at the Li-TLPEC interface.And we found that the TLPEC is nonflammable,so it can improve the safety of LIBs.（3）Zwitterionic ionic liquid-based electrolyte and its application in Lithium-Sulfur battery（LSB）A novel zwitterionic ionic liquid TLTFSI with a high ionic conductivity of 3.7 x 10-3 S/cm,a wide electrochemical potential window from 1.51 to 4.82 V and a high thermal decomposition temperature of 275℃ was synthesized by quaternization reaction.An optimal TLTFSI-based electrolyte T70D30 is obtained and used in LSB,which consisted of 1 wt%Li NO3,70 v%TLTFSI,and 30 v%DDL that contained 50 v%DOL,50 v%DME and 1.9 M Li TFSI.The T70D30 electrolyte is nonflammable and has a robust ionic conductivity of 4.1 x 10-3 S cm-1,a wide electrochemical potential window from 1.36 to 4.44 V.In consequence,the lithium-sulfur batteries with T70D30 electrolyte achieve better performance than those of LSBs with widely-used T0D100 electrolyte both at 25 and 60℃.And we found that the T70D30 electrolyte can suppress the shuttle effect happened in LSBs.These advantages prove T70D30 is a promising electrolyte for high performance and high-safety LSBs. |
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