Nasicon solid electrolytes and reactivity with water solution for development of next generation Na ion batteries

Abstract

Fossil fuels have been consumed for the energy sources due to its high energy density. However, the environmental destruction issues caused by the use of fossil fuels have been raised. Accordingly, most of countries, including South Korea, are regulating the use of fossil fuels, and conducting research on renewable and eco- friendly resources. Because these types of resources, such as solar power and wind power, are difficult to obtain at the desired time or location, research on batteries that can store these resources has been conducted. As the battery markets continues to grow, Li-ion batteries(LIB) are widely commercialized in the battery market due to its high energy density. However, the price of lithium resources continues to increase due to the low lithium reserves on earth, and uneven distribution of resources and the increasing demand for batteries. Sodium-ion Batteries(SIB) using sodium resources with large reserves and low price is expected to solve the rapidly increasing demand for the batteries. However, the general SIBs using liquid electrolytes have lower theoretical energy density compared to LIBs. To overcome the energy density limitations of SIBs, it is researched to improve the theoretical energy density applying the use of metal anode or solid electrolytes. In chapter 1, the general explanations about lithium ion batteries were introduced. The basic principles of LIBs and the disadvantages of the present LIBs with liquid electrolytes. In chapter 2, the solid-state battery was introduced. The necessity of solid electrolytes, and several types of solid electrolytes for next-generation battery were studied. In chapter 3, research on the increasing total ionic conductivity of Nasicon (Na3Zr2Si2PO12) solid electrolytes was studied. Nasicon solid electrolyte has high ionic conductivity among other Na ion conducting solid electrolytes, but it is still lower than liquid electrolytes. By adjusting the chemical composition of Nasicon solid electrolyte, the ionic conductivity was increased. Also, by adding SnO2 to Nasicon solid electrolyte, the ionic conductivity and reactivity with Na metal of Nasicon-SnO2 composite was studied. In chapter 4, the reactivity of Nasicon solid electrolyte with water solution was studied. Due to the low energy density of cathode materials for SIBs, the solid-state Na ion battery using water solution or air as cathode materials which can continuously supply during cell operation were studied. The reactivity of Nasicon with water was studied to find the mechanisms of side reaction between Nasicon and water. Then, the research on the suppress the side reaction by several cations in water solution was studied.