Abstract: During the past four decades, Solid State Ionics (SSI) field has attracted numerous researchers and engineers to cultivate new technologies which plays important roles in the development of sustainable energy utilization and clean transportation tools. The commercialization of lithium ion battery, sodium sulfur battery, sodium chloride battery, solid oxygen sensors have illustrated the success of SSI’s theories and technologies. The discovery and successful applications of ionic or mixed conductive materials, such as LiCoO2 and LiFePO4 as active materials of lithium ion battery cathode, Na-β/β″-Al2O3 ceramics as solid electrolytes and separators for sodium based batteries, ZrO2 as electrolytes for SOFC and oxygen sensors, and the newly developed Li10GeP2S12[1] and Li7La3Zr2O12[2] as lithium ion conductor, laid a solid foundation for the development of SSI technologies.
　　Recently, rechargeable lithium metal anode based batteries have become hot research topics in the field of SSI due to their extremely high specific capacity suitable for future generation of power sources in portable electronic devices, electric vehicles and energy storage systems. Among all the Li anode based batteries, Li-S and Li-air battery systems are the two most attractive candidates because of the low cost and abundance of sulfur and air as cathode active materials, especially the characteristics of easy access of active O2 from the surrounding air for Li-air batteries.
　　Breakthroughs have been made recently with these batteries. SION Power’s Li-S cells reached the highest practical specific energy as high as 350 Wh/kg, with a pack of 576 cells engineering the QinetiQ Zephyr Unmanned Aerial Vehicle (UAV) more than 336 h (14 d) of continuous flight, significantly surpassing the previous official record[3]. Their energy densities are higher than 500 Wh/kg for more than 500 cycles[3] and commercialization in the near future[4] are expected. Many Chinese institutions successfully prepared soft package lithium sulfur batteries[5]. The highest specific capacity of sulfur electrode over 900 mAh/g at 2C rate was realized by the Shanghai Institute of Ceramics, Chinese Academy of Sciences. Important advances in Li-air batteries were also made by designing carbon free air electrode [6,7] and by the aid of LATP solid lithium electrolyte lately[8]. However, the development of the rechargeable high energy lithium metal batteries are still hindered by the high reactivity of lithium metal with liquid electrolytes and the occurrence of dendrite growth during charge and discharge cycles. Moreover, the cycling stability of the batteries are still far away from the standard of practical applications of electric vehicle and electronic devices. Owing to the intrinsic highly resistive feature of the cathode materials, sulfur and lithium containing resultants with oxygen, structural and compositional designs of the cathode, the protection of lithium metal anode, and the control of the electrode/electrolyte interface are urgent matter to develop practical rechargeable lithium batteries.
　　SSI has been tackling the vital technical problems of high performance devices with solid ionic and mixed conductors as their key materials, which has great potential contribution to future energy and environmental needs of our society.