There is an increasing demand for batteries with improved safety, higher energy density as well as high specific power for practical applications in portable electronics market and electric vehicle  industry. However, the energy density of conventional Li-ion batteries will soon reach their limit and they are also suffering from thermal runaway which is related to the flammable nature of liquid electrolyte used. The traditional Li-ion batteries provide sometimes insufficient energy density due to a relatively low specific capacity of graphite anodes (372 mA h g–1). Lithium metal, with ultra-high theoretical specific capacity (3860 mAh g–1) and the lowest reduction potential (-3.04 V vs standard hydrogen electrode), has been supposed to the promising candidate of anode to improve energy density in lithium metal batteries. Replacing liquid electrolytes with solid-state electrolytes, that are fabricating solid-state batteries, shows a great promise to address these issues. So far, there is still a large gap of available power density in solid-state batteries by a comparison of practical industry standard. This is because an internal short-circuit of battery will be invariably triggered when the operating current density of solid-state batteries is over a critical value. The failure mechanism at micro level is the growth of Li filaments and its penetration of solid electrolyte to connect cathode and anode inside battery. The academic community is intensely arguing where the Li filament is formed and how the soft Li can impale a rigid ceramic solid electrolyte. 

Solid-state electrolytes with high mechanical strength have been regarded as a promising approach to suppress the growth of Li metal filaments and ensure safety issues in solid-state Li metal batteries. Among many solid-state electrolytes, the NASICON based solid electrolytes like Li1+xGexTi2-x(PO4)3 (LAGP) and Li1+xAlxTi2-x(PO4)3 (LATP) possess good electrochemical stability and a wide electrochemical window thus providing a great potential for future industrialization. However, the pore formation and the presence of residual phases result often in a decrease of the Li-ion conductivity. The second phases, resulted from incomplete reactions and over-heating of solid electrolyte ceramic powder, appear upon the process of synthesis or sintering and seriously affect the quality of solid electrolyte powder. It worth noting that low relative density of solid-state electrolyte ceramics stems from improper sintering conditions and it affects electrolyte performance drastically. Additionally, microstructure features affect final key parameters, such as ionic conductivity, relative density and mechanical properties, thus making a significant impact on the cycling performance of solid electrolyte batteries. The work was aimed to create new effective energy sources based on new generation of lithium solid-state batteries with improved performance characteristics, in which a ceramic solid electrolyte is used.