| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 107 === Lithium-ion battery(LIB) plays an important role in the modern social energy chain. It is widely used in mobile phones, laptops, solar power plants, and even electric vehicles and other equipment. But these applications are mostly restricted by safety issues such as poor thermal stability, flammable reaction products, and leakage of electrolyte and internal short circuits for the use of liquid electrolytes in LIB. The use of solid electrolyte to replace liquid electrolyte preparation of all solid lithium-ion battery is expected to overcome the above shortcomings, which makes solid electrolyte an important research direction in the field of energy.
In the first part, our study focused on Li1.3Al0.3Ti1.7(PO4)3(LATP) with a NASICON structure. Al-doped LiTiOPO4 precursor powder was synthesized by a simple solvothermal method with heterovalent ion doping to partially replace Ti4+ by Al3+. According to the materials characterization, the optimal composition is Li1.3Al0.3Ti1.7(PO4)3.
In the first part, hydrothermal method was used to synthesize orthorhombic structure of LiTiOPO4 powder. The SEM elemental analysis shows that the distribution of Al element is fairly uniform. The second part discusses the different sintering processes involved in obtaining LATP which includes the pre-sintering temperature of the precursor powder and the sintering temperature of the LATP pellets. The structure was analyzed by XRD and Rietveld refinement, and the effects of sintering temperature on porosity, microstructure and electrical conductivity were discussed.
The Rietveld refinement results show that the synthesized Li1.3Al0.3Ti1.7(PO4)3 crystal is a trigonal structure with a R-3c(167) space group. Through the discussion of two-stage sintering, it is found that the good contact between the grains and the lower amorphous content of the second phase between the grain boundaries are the key in obtaining high lithium-ion conductivity. The experimental results show that the optimum pre-sintering temperature of the precursor powder is 900℃. Through the Rietveld refinement calculation, it can be seen that the precursor powder, Li1.3Al0.3Ti1.7(PO4)3 has the highest phase composition after sintering at 900℃. The optimal sintering temperature of LATP pellet is at 1100℃, which has the activation energy is 0.17 eV, and the highest density is 99.07%. Its grain conductivity, grain boundary conductivity and total lithium-ion conductivity are 6.57*10-4, 4.59*10-4, 2.70*10-4 S cm-1, respectively.
Lastly, LATP was applied to lithium-ion batteries, and LATPS/NCM solid-state batteries were successfully assembled. After charging and discharging at 0.1C for 80 cycles, the discharge capacity retention was 95.76%, indicating that the LATPS/NCM solid-state battery has good cyclic stability. Therefore, LATP is a potential candidate as a solid electrolyte for lithium-ion batteries.
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