| With the environmental pollution and energy crisis,the development of new energy was boosted.Correspondingly designing and developing environmentally friendly,efficient,and stable energy storage and conversion devices have already been the urgent global demand The supercapacitor possesses many properties such as high-power density,long service life,high capacitance,main tain-free,no memory effect,and high security,et al.,making it one of the important energy storage devices.The supercapacitors can be classified into the liquid-state,quasi-solid-state,and all-solid-state categories based on the electrolyte used.Because of their excellent properties such as high safety,high mechanical strength,broad working temperature range,and easy assembly,the all-solid-state supercapacitors hold the critical importance in micro-electronic devices,wearable,military,and astronautic application fields.As the key component in an all-solid-state supercapacitor,the properties of the solid electrolyte are critical to the whole device.Due to the high bulk conductivity and chemical stability,Li3xLa2/3-xTiO3(LLT)perovskite ceramic is paid much attention as a promising solid electrolyte candidate,however,rare research was focused on its applications in the all-solid-state supercapacitors up to now.In this thesis,through improving the ionic conductivity of LLT,the performances of LLT as a solid electrolyte for supercapacitor were investigated.The main research results are listed as follows.(1)Li0.33La0.56TiO3 was synthesized at different calcination temperatures by using solid-state reaction approach and prepared as all-solid-state supercapacitors.The influences of calcination temperature on the microstructure,morphology,ionic conductivity,and the energy storage property of the as-prepared products were investigated.Results indicate that Li0.33La0.56TiO3 calcined at higher temperatures exhibited better performance,e.g.,the samples calcined at 1200℃ possess the highest bulk conductivity and grain boundary conductivity,which is 9.6×10-4 S/cm and 2.32×10-5 S/cm,respectively.Based on the capacitance property via a cyclic voltammogram measurement,the Li0.33La0.56TiO3 based all-solid-state supercapacitor mainly exhibit electric double-layer energy storage characteristics within a potential range of 3 V.A faradaic pseudo-capacitive behavior was observed when increasing the working potential to 4 V.(2)A series of Sr2+ions doped Li0.33SrxLa0.56-2/3xTiO3(LSLT)solid electrolytes were synthesized via a solid-state reaction approach,and their applications as an all-solid-state supercapacitor were investigated in detail.Results show that the doped element is distributed homogeneously in the LSLT bulk without impurities generated.A highest ionic conductivity was obtained for the LSLT when the doping amount was 0.25mol%,with bulk conductivity and grain boundary conductivity of 1.17×10-3 S/cm and 3.15×10-5 S/cm,respectively Substituting La3+ with Sr2+ can expand the bottleneck size for Li+transportation,because of the larger ionic radius of Sr2+.The bond strength of Li-O can also be changed after the introduction of the dopants,thus the ionic conductivity is enhanced.Moreover,the carrier concentration is a key factor to affect the ionic conductivity.The LSLT ceramics exhibit superior electric double-layer capacitive behaviors,while their capacitance is correlated with the ionic conductivity.The 0.25mol%Sr2+ doped LSLT ceramics exhibit a capacitance of 0.48 mF·g-1 within a potential range of 2 V under 10 mV/s.(3)A series of Li3xLa2/3-xTiO3(3x=0.33～0.42)are synthesized using a solid-state reaction approach,while a second ball milling and powder purification process are employed The obtained LLT ceramics are applied in the all-solid-state supercapacitor,while the working mechanism,capacitance affecting factors are investigated.Results show that all-solid-state supercapacitor has a working mechanism different from liquid supercapacitors because the electrode/electrolyte interface in the former can hardly form a close electric double-layer structure.As a result,the applied electric field cannot be balanced to create a shielding at the interface,which leads to the formation of the residual electric field.Under the residual electric field,the polarization capacitance can be formed between the electrode and the solid electrolyte as well as the internal electrolyte,leading to the decrease of the capacitance for all-solid-state supercapacitor.The capacitance of all-solid-state supercapacitor has a close relationship with the ionic mobility of ceramic electrolyte and can be easily influenced by the ambient temperature,the higher the ionic conductivity and the working temperature,the larger the capacitance(4)A series of Li0.33La0.56Ti1-xSnO3(x=0～5mol%,LLTS)solid electrolyte were synthesized using a solid-state reaction method,while second ball milling and cold isostatic pressing processes were employed.Results indicate that with a doping amount of 0.1 mol%of Sn4+,the as-prepared LLTS exhibit the highest ionic conductivity,while the bulk conductivity and grain boundary conductivity are 1.03×10-3 S/cm and 1.85×10-4 S/cm,respectively.It shows that when the doping ions are with a bigger radius,such as Sn4+compared with Ti4+ in the B site of the ceramic,positive effects like expanded bottleneck size,the inclination extent of the octahedra,and strengthened atomic bonds will occur,thus changing the Li+ ionic mobility and ionic conductivity.Under a constant Li-ions and vacancy concentration,the expanded bottleneck size effect and easy inclination of the octahedra dominate with a low doping amount of Sn4+ ions,thus the ionic mobility and the ionic conductivity increase.However,as more ST4+ions are doped,Li-O bond strength is increased,leading to a decreased ionic mobility as well as the ionic conductivity.The LLTS based all-solid-state supercapacitor exhibit an excellent electric double-layer capacitive behavior within a 2.5 V potential range.The 0.1mol%Sn4+ doped sample can release a capacitance of 2.42 mF/cm3 within 2.5 V,under 100 mV/s. |
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