Preparation And Modification Study On High Lithium Ion Conductivity Solid State Electrolyte

Due to its light weight, high energy density, high power density and long serving time, lithium ion battery is one of the most competitive electrochemical energy storage technologies. Besides improving lithium secondary battery’s cycle life and capacity, solving safety issue completely is also an important matter. Replacing conventional liquid organic electrolyte with inorganic solid electrolyte is an effective measure to solve the safety problems of rechargeable battery. Solid electrolyte with NASICON (Na super ionic conductor) structure is a kind of important oxide solid electrolyte which could be stably used in air. LAGP (Li1.sAl0.5Ge1.5(PO4)3) is a kind of typical solid electrolyte with NASICON structure.The ion conductivity of LAGP glass ceramics could reach over10-4S/cm, which is of great application potential. Traditional preparation method of glass ceramics is prepare parent glass, then crystallize the bulk glass. However, samples prepared with this method usually crack and deform during crystallization, besides, their shapes are limited by their moulds, so it is not convenient for large scale fabrication. In the present dissertation, we grinded the parent glass into powder, pressed it into pellets, then used ceramics sinter process to achieve crystallization in order to prepare LAGP glass ceramics material, which avoid problems such as crack and deformation, and can be applied conveniently when sinter into different desired shapes. Compared with LAGP ceramics electrolyte, glass ceramics electrolyte possesses higher density and less grain boundaries, thus has higher ion conductivity.In the process of preparing glass ceramics material, lithium loss is detected due to vaporization, which could affect sample’s microstructure and performance. In this dissertation, excess amount of lithium source is added in the ingredients and the effects of excess amount of lithium source are investigated. By controlling crystallization temperature and time, we have successfully prepared LAGP glass ceramics with high ion conductivity. The research conclusions are listed below:1. Results indicate that AIPO4and GeO2phase were detected in LAGP ceramics, its grains do not have good contact with each other and obvious pores were observed, too high sinter temperature would lead to main phase decompose and low density. Its ion conductivity is comparatively lower, at about10-5S/cm.2. Crystallization temperature and crystallization time have impact on sample’s microstructure and performance. As crystallization temperature rises, grain size increases, the pore rate lowers and grains gain good contact with each other, both grain conductivity and grain boundary conductivity increase. But when crystallization temperature is too high, impurity phase like GeO2、A1PO4appears and density lowers. Crystallization time shows similar effects on samples, while its effect is less obvious than crystallization temperature. Results indicate the optimum temperature is between850℃and950℃, the optimum time is about6h.3. The excess lithium source could compensate lithium loss during preparation, act as nucleating agent and increase density. As the amount rises, lithium ion concentration rises and density increases. But when lithium source is too much, lithium ions would block the conducting paths and result in lowering ion conductivity. Results indicate the optimum composition is LAGP-0.025LO. when crystallized at900℃, its ion conductivity reaches3.06×10-4S/cm.