Study On The Low-Temperature Preparation And Electrochemical Performance Of Lithium Aluminum Titanium Phosphate

The rapid global consumption of fossil energy has caused serious environmental problems,prompting the development of new energy storage systems to reduce dependence on fossil fuels and alleviate ecological pressure.Lithium-ion batteries occupy an important position in the energy storage system market.However,the energy density of commercial lithium-ion batteries has reached its limit and the frequent safety incidents in recent years have posed serious challenges to the stable operation of energy storage systems.Therefore,the research and application of high safety energy storage battery systems are urgently needed.Solid-state lithium-metal batteries that use solidstate electrolytes instead of organic electrolytes are considered to be a safer battery system as they can solve problems such as poor antioxidation,high flammability,and poor compatibility with lithium-metal anodes.As a typical lithium-ion conductor,NASICON-type inorganic oxide Li1.3Al1.3Ti1.7(PO4)3 (LATP) has attracted much attention due to its wide electrochemical window,high ionic conductivity,and good air stability.However,the high grain boundary resistance and high synthesis temperature(> 950℃) limit the low-cost large-scale manufacturing of LATP electrolytes.At the same time,the high interface resistance and interface side reactions with the lithiummetal anode seriously hinder the practical application of LATP electrolytes in solidstate lithium-metal batteries.This thesis uses sintering aids to assist in the low-temperature preparation of highperformance lithium-ion conductor LATP,and LATP pellets prepared at 800℃ exhibit a high room temperature ionic conductivity of 5.2×10-4 S cm-1.At the same time,to both alleviate the issue of insufficient contact and prevent the occurrence of side reactions between LATP pellets and the lithium-metal anode,this thesis uses the in-situ encapsulation strategy to introduce two-dimensional silicate-containing gel layer,which promotes the fast and stable transport of lithium ions at the interface.The specific contents are as follows:1.Synthesis of lithium-ion conductor LATP electrolytes using sintering aids.The sintering aids phosphate and borate are introduced into the LATP electrolyte to prepare LATP ceramic pellets at a sintering temperature below 900℃.The sintering aids underwent phase transformation under the preparation conditions,which promotes the rearrangement of LATP grains and fills the gaps between the grains,making the prepared LATP ceramic pellets present high relative density.The optimal LATP ceramic electrolyte achieves a high ionic conductivity of 5.2×10-4 S cm-1 at a low sintering temperature of 800℃,with lower preparation cost and higher lithium transport performance compared with related sintering aid studies,promising practical applications for solid-state lithium metal batteries.2.Synthesis of two-dimensional silicate-containing gel layer based on in-situ encapsulation.The rigid and monodisperse ultrathin two-dimensional layered silicate(RUB-15) is introduced into the precursor solution of the gel electrolyte.After curing,a gel intermediate layer in close contact with both the LATP ceramic pellet and the lithium-metal anode is obtained.The surface of RUB-15 nanosheets have abundant polar functional groups (-OH),which can promote the dissociation of lithium salts and increase the room temperature ionic conductivity of the gel layer (1.46×10-3 S cm-1).The high rigidity and monodispersity of RUB-15 inhibit direct contact between the LATP pellet and the lithium metal anode,effectively preventing side reactions between the two.Therefore,the LATP-based lithium metal symmetrical battery with silicatecontaining gel layer achieve 450 h of cycling stability at a current density of 0.1 mA cm-2, and the LATP-based lithium metal full cell cycle 80 times at 0.2 C with a discharge specific capacity of 136.6 mAh g-1.This demonstrates that in-situ encapsulation of RUB-15 nanosheets can promote fast and stable lithium-ion transport at the interface,which may accelerate the practical application of LATP in high-energy density solidstate lithium metal batteries.