| Lithium ion batteries have been considered as one of the most competitive electrochemical energy storage technologies due to their high energy density and long lifetime.However,present lithium ion batteries suffer from multiple potential safety risks such as leakage,corrosion,combustion and explosion due to the use of flammable liquid organic electrolyte.With the development of power battery and smart power grid energy storage technology,stricter safety requirements need to be applied to lithium ion batteries.Besides improving the life length and capacity of lithium ion batteries,solving the safety issue completely is also an important breakthrough.Replacing conventional liquid organic electrolyte with stable inorganic solid electrolyte is an effective solution to the safety problems of lithium ion battery.NASICON?Na super ionic conductor?type structure solid electrolyte is a kind of important oxide solid electrolyte,which possess good ion conducting capability and chemical stability.Li1.5Al0.5Ge1.5?PO4?3?LAGP?glass-ceramics with NASICON type structure was chosen as research subject in this thesis.The experiment parameters were strictly adjusted and optimized during research process.The experiments were performed to improve the phase composition,grain conductivity and grain boundary conductivity.Different phosphorus sources,hetero valent doping and TiO2 addition were studied to reveal the relationship between the phase composition,microstructure and ionic conductivity,disclosing the possible modification mechanism of LAGP-based glass-ceramics.In addition,LAGP-based glass-ceramics solid-state batteries were prepared and tested.The research work and major conclusions are listed as follow:Four different phosphorus sources,i.e.,Al?PO3?3+H3PO4?P2O5?H3PO4 and NH4H2PO4,were applied to prepare LAGP glass-ceramics material,respectively.The effects of different phosphorus sources were observed and discussed.The results indicate that the kinetics and thermodynamics properties vary from different phosphorus sources,resulting in different crystallization temperature and optimum thermal treatment temperature ranges of LAGP glass-ceramics.Thus,phosphorus sources could affect the phase compositions,microstructure and ion conducting property of LAGP glass-ceramics,applying the proper phosphorus source could optimize the phase composition and increase ionic conductivity.Glass-ceramics sample using H3PO4 as phosphorus source possess NASICON-type structure,low crystallization temperature,dense microstructure and contain no impurity phase.When treated at 850°C,the room temperature ionic conductivity of the sample is5.21×10-44 S cm-1,and the activation energy is 0.34 eV.Silica substitution was employed in LAGP glass-ceramics,and LAGSP glass-ceramics sample with high grain conductivity was obtained.The effects of silica substitution on microstructure and ion conducting property of glass-ceramics samples were systematically studied.The results indicate that proper amount of silica substitution could lower the crystallization energy barrier,promote orderly growth of grain.Besides,Si4+could replace P5+and increase the concentration of lithium ions,which has positive effects on grain conductivity.The optimum heat treatment temperature is determined to be 850oC,and the ion conductivity of glass-ceramics samples prepared at this temperature is 5.61×10-44 S cm-1,while the activation energy is 0.34 eV.Based on Silica substitution,TiO2 was added into LAGSP glass-ceramics and LAGSP-TiO2 glass-ceramics with high grain boundary conductivity was obtained.The effects of TiO2 on microstructure and ion conducting property of glass-ceramics samples were systematically studied.Research results indicated that the addition of TiO2 could promote grain growth and increase the ratio of perfect contact on the surface area of grains.On the other hand,it also lead to the formation of GeO2impurity.Both two factors could affect the grain boundary conductivity.The addition of proper amount of TiO2 could effectively increase the grain boundary conductivity of the sample.The optimum sinter temperature is 900oC.The ionic conductivity of sample sintered at 900oC is 1.07×10-33 S cm-1,while the activation energy is 0.33 eV.The fabrication process of glass-ceramics plates and all solid state lithium battery were carefully designed and investigated.Dense LAGSP glass-ceramics plates were prepared and on which composite cathode were prepared and improved to acquire functional all solid state lithium battery prototype.Results suggest that dense glass-ceramics plates could be prepared by tape-casting method,and the highest room temperature conductivity could reach 3.20×10-44 S cm-1.Compact composite cathode was prepared on the surface of glass-ceramics electrolyte plates through screen printing,and the component and optimum component ratio were systematically investigated.The results indicated that solid state battery with electrode composed of LiCoO2 and fine LAGSP glass-ceramics electrolyte powder at a ratio of 7:3 could obtain the optimum cycle performance and capacity,while the interfacial resistance is the lowest among all samples.After 10 cycles,the specific capacity was approximately 100 mAh g-1and the cycling efficiency was nearly 100%.The test results indicate that solid state battery possesses excellent safety properties.Besides,the fabrication process could be applied in solid state whole-cells and solid state battery packs.However,the increase of interfacial resistance and capacity fading was observed in the solid state battery due to the changes of cathode volume during charge-discharge process,which could be further improved through enhance the stability of the structure of electrode. |
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