|Other Abstract||Solid state electrolyte is one of key components for all solid state lithium ion batteries, which greatly determines the power density, cycle stability, safety performance, high and low temperature performance and the life of batteries. Herein, to improve the electrochemical performance and stability of solid state electrolyte, the preparation process for electrolyte materials and electrolytes was optimized. Moreover, the optimum process was identified. Meantime, in order to reduce the polarization resistance of intermediate temperature solid oxide fuel cell, the intrinsic properties and microstructure of cathode materials were optimized, and thus the cathode performance was improved.
The main conclusions of this paper can be sumarried as follows:
1. The Li1.3Al0.3Ti1.7(PO4)3 (LATP) electrolyte materials with NASICON structure were prepared via a modified Pechini synthesis method. By optimizing the preparation process parameters, such as dispersant, calcination temperature for electrolyte powders, sintering temperature and period for electrolyte pellets, the high performance LATP electrolyte was obtained with the highest electrical conductivity of 6.0 x 10-4 S/cm at 303 K, which is comparable to those reported in references. The excellent electrochemical performance is due to the high densification of electrolyte with the relative density of 95.76%. Additionally, the electrolyte has a negligible electronic conductivity, whose value is only 1.2 x 10-8 S/cm.
2. In order to inhibit the reaction between LATP electrolyte and Li anode, a Li1.3Al0.3Ge1.7(PO4)3 (LAGP) barrier layer was constructed on the surface of LATP electrolyte substrate to form a LATP/LAGP double-layer electrolyte via a simple and inexpensive dry-pressing technique. A dense and smooth solid state electrolyte with dense structure can be obtained using the LAGP starting materials sintered at 650 °C, which is due to the good sintering match between LAGP layer and LATP substrate. The electrolyte exhibited excellent electrochemical performances and stability. Its electrical conductivity at room temperature is 3.4 x 10-4 S/cm, and the value of electronic conductivity is 9.6 x 10-9 S/cm. When the electrolyte was placed in the air for a long time or contacted with Li metal, its electrochemical properties were not attenuated. The assembled LiFePO4 (LFP) battery showed the first charge and discharge capacities of 142 mAh/g and 130.6 mAh/g. After 3 cycles, the capacities was increased to 145.3 and 141.4 mAh/g.
3. A series of perovskite-type La0.3Sr0.7T1-xCoxO3 (LSCT, x=0.1-0.8) cathode materials for solid oxide fuel cells were synthesized via a convenient modified sol-gel method. By optimizing the content of Co dopant, high perforamce cathode materials were obtained. The LSCT cathode with “x= 0.8” has the best electrochemical performance, achieving the polarization resistances of 1.12, 0.40 and 0.15 Ω cm2 at 550, 600 and 650 °C, and the activation energy of the LSCT cathode was 1.435 eV, which was attributed to the enhancement of the molecular oxygen dissocation and charge transfer process in the cathode.|