| The constant enhancement of the energy density of lithium secondary batteries along with their wide application in electronic products,transportation,energy storage system for new energy resources will bring about great challenge for the battery safety.How to improve the energy density of the batteries and simultaneously ensure their high safety is an important problem that need to be seriously solved.Replacing conventional organic electrolytes with high-safety electrolytes is an effective way to improve the battery safety.In this thesis,several series of high-safety and high-performance solid-state electrolytes have been prepared through structural design and compositional optimization,and their structures,thermal and electrochemical properties as well as lithium secondary battery performance have been systematically studied.The main contents in this thesis are shown as follows:Two classes of ionogel electrolytes have been prepared.Firstly,the ordered mesoporous silica,SBA-15,was chosen as the matrix for the first time to prepare ionogel electrolytes with an ionic liquid and LiTFSI salt through a facile one-pot route.The as-prepared ionogel electrolytes maintain the ordered mesoporous structures of SBA-15,which can provide stable interconnected 3D channels for the transport of lithium ions.The ionogel electrolytes show high room-temperature ionic conductivity(2.65?10-4 S cm-1 at 25?),good thermal?370??and electrochemical stability?5.1V?vs.Li/Li+??and advantage to promote uniform Li electrodeposition.Galvanostatic cycling tests reveal that Li/LiFePO4 cells using the ionogel electrolytes can achieve stable discharge capacity of about 150 mAh g-1 at room temperature under 0.1 C rate,as well as exhibit satisfactory cycling performance and acceptable rate capability.Secondly,TiO2-based ionogel electrolytes consisting of TiO2 as the matrix and LiTFSI-IL as the ion conducting phase were prepared by a one-pot sol-gel processing.TEM photos indicate that the as-prepared ionogel electrolyte shows an interconnected network structure consisting of TiO2 nanoparticles,which could hold abundant LiTFSI-IL and provide continuous channels for the transport of lithium ions.Meanwhile,the electrolytes reveal liquid-like high ionic conductivity(7.10?10-4 S cm-1 at 25?),good electrochemical stability?4.6 V?vs.Li/Li+??and ability to promote uniform lithium electrodeposition.Specifically,the Li/LiFePO4 cells containing the electrolyte deliver a discharge capacity of about 150 mAh g-1 at 25? under 0.1C rate,and show satisfactory cycling performance.Also,the cells exhibit acceptable rate capability and low-temperature discharge ability.In order to improve the flexibility of the inorganic material-based ionogel electrolytes,polymeric ionic liquid was introduced to prepare a new class of high-performance polymeric ionic liquid-silica hybrid ionogel electrolytes by a nonaqueous sol-gel route,in which LiTFSI-ionic liquid as the ion conducting phase is immobilized with a hybrid polymeric ionic liquid and silica matrix.Properties of the as-prepared electrolytes could be tuned by varying their composition.It is found that the electrolytes reveal good room temperature ionic conductivity(5.83×10-4 S cm-1 at25?),excellent thermal stability?377-388??,high electrochemical stability?5.2 V?vs.Li/Li+??and potential to suppress Li dendrite formation.In particular,Li/LiFePO4cells with the as-obtained electrolytes at 0.2C rate can deliver a discharge capacity of about 150 mAh g-1 at 25?,with excellent capacity retention.Moreover,the desirable rate performance can be achieved.Succinonitrile?SN?,a representative molecular plastic crystal,was introduced into the polymeric ionic liquid-LiTFSI system to prepare a series of composite polymer electrolytes.The as-obtained electrolytes reveal amorphous structures,and show high room temperature ionic conductivity(5.74×10-4 S cm-1),exceptional electrochemical stability?5.3 V?vs.Li/Li+??,as well as good mechanical strength with a Young's modulus of 4.94 MPa.Li/LiFePO4 cells assembled with the electrolyte at0.1C rate can deliver a discharge capacity of about 150 mAh g-1 at 25?,with excellent capacity retention.Furthermore,such cells are able to achieve stable discharge capacities of 131.8 and 121.2 mAh g-1 at 0.5 C and 1.0 C rate,respectively.In order to prepare solid-state electrolytes for wide temperature range lithium secondary batteries,organic ionic plastic crystal P12FSI with high melting point?200??was synthesized,and introduced in polymeric ionic liquid-LiTFSI electrolytes as a solid plasticizer.Properties of as-prepared solid-state electrolytes could be tuned by varying their composition.The electrolytes show amorphous structures,and reveal attractive ionic conductivity at room temperature and high temperature(1.54×10-4 S cm-1 at 25?,and 1.26×10-3 S cm-1 at 80?),good electrochemical stability?4.8 V?vs.Li/Li+??,high thermal stability?250??and suitable mechanical properties.Li/LiFePO4 cells assembled with the electrolyte can deliver high discharge capacity and excellent cycle performance at wide temperature range?25?–80??,as well as desirable rate capability. |
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