| Current commercial lithium-ion batteries use highly volatile and flammable organic electrolytes,which leads to safety issues such as combustion and explosion.At the same time,the development of new energy vehicles,grid peak shaving,and large-scale energy storage have put forward new requirements for new battery technologies.There is an increasing demand for developing energy storage devices with higher energy density,greater safety,and longer cycle life.Solid-state electrolytes have high chemical stability,a wider electrochemical window,and non-flammability,which not only addresses the safety issues caused by organic electrolytes but also enables the matching of high-voltage cathode materials to increase energy density.Therefore,solid-state lithium batteries will significantly enhance energy density and safety.NASICON-type Li1.5Al0.5Ge1.5（PO4）3（LAGP）inorganic solid electrolyte is one of the most promising solid electrolytes due to its extremely high chemical stability in air,good room-temperature ionic conductivity of about 10-4S cm-1,and a wide electrochemical window of up to 6 V.This paper focused on LAGP inorganic solid electrolyte and employed high-temperature solid-state method for material preparation.The effects of sintering process and ion doping on the performance of LAGP electrolyte were investigated.Additionally,the cycling performance of the assembled solid-state battery was tested.The main research contents and conclusions are summarized as follows:（1）The LAGP solid electrolyte was prepared using high-temperature solid-state method,and the effects of sintering temperature and holding time on the structure,morphology,density,and electrochemical performance of LAGP solid electrolyte were systematically investigated using XRD,SEM,EIS and other testing methods.The results showed that the ionic conductivity and density of LAGP increased first and then decreased with increasing sintering temperature and holding time.The LAGP sample sintered at 800℃for 4 h exhibited the best performance,with uniform grain size,high crystallinity,a relative density of 90.60%,room-temperature ionic conductivity of1.13×10-4S cm-1,and activation energy of 0.339 eV.（2）Based on the optimal sintering process,the effects of samarium（Sm）rare earth element doping with large ionic radius and low electronegativity on the LAGP solid electrolyte were systematically studied.Sm doping in the LAGP electrolyte increases the density,enhances ionic conductivity,and reduces the activation energy.XRD measurements showed that the crystal structure of the Li1.5Al0.5-xSmxGe1.5（PO4）3electrolyte after doping still belonged to the NASICON structure of Li Ge2（PO4）3.XPS testing indicated that Sm existed in the LAGP electrolyte in the form of Sm3+.When the doping amount was 0.025 mol,the contact between grains was the tightest,the relative density was the highest at 93.61%,and the room-temperature ionic conductivity was2.95×10-4S cm-1,which was 2.6 times that of the undoped LAGP electrolyte,and the activation energy was 0.278 eV.（3）Using Li1.5Al0.475Sm0.025Ge1.5（PO4）3with a Sm doping amount of 0.025 mol as the solid electrolyte,a solid-state lithium battery and a symmetrical lithium battery were assembled with lithium iron phosphate（LFP）as the cathode and lithium（Li）as the anode to study the electrochemical performance of the batteries.The assembled Li/Li1.5Al0.475Sm0.025Ge1.5（PO4）3/Li symmetrical battery can cycle stably for 600 h at current densities of 0.025 mA cm-2,0.05 mA cm-2,and 0.075 mA cm-2.The LFP/Li1.5Al0.475Sm0.025Ge1.5（PO4）3/Li solid-state lithium battery,at a current density of0.1 C,achieved a discharge specific capacity of 153.6 mAh g-1in the first cycle,with a coulombic efficiency of 95.47%.After 40 cycles,the discharge specific capacity was120.4 mAh g-1,and the capacity retention rate was 78.4%. |
