Structural Design Of Oxide Lithium-ion Conductors For Solid-state Lithium Batteries And Lithium Purification

Oxide electrolytes are widely studied in the next generation of energy storage batteries-solid state lithium batteries due to their lithium-ion conductivity,high thermal stability,high mechanical strength,and high compactness.The oxide electrolyte in solid-state lithium batteries is expected to make it different from the current lithium-ion batteries that use liquid electrolytes,and can have both high energy density and high safety.Aiming at the high interface impedance and energy density bottlenecks of solid-state lithium batteries based on oxide electrolytes,this thesis focus on the design of oxide electrolytes.In terms of the negative electrode/electrolyte interface,a polymer electrolyte coating is induced to avoid electrolyte be reduced by Li-anode and reduce interfacial resistance.In terms of the positive electrode/electrolyte interface impedance,an electrolyte membrane with a vertical ordered microporous structure on one side and an ultra-thin dense layer on the other side was constructed to reduce positive electrode/electrolyte interface impedance.In terms of energy density,an ultra-thin self-supporting electrolyte film is prepared by a tape casting method to reduce the limitation from volume and weight of electrolyte film on the energy density of the battery.This paper also takes advantages of the characteristics of oxide electrolyte that can only conduct lithium ions,and extends it to the separation,purification and concentration of lithium in salt-lake brines to achieve low-cost and efficient separation to obtain high-purity lithium product.The specific work is as follows:1.Perovskite-type Li_3xLa_2/3-xTi O₃ membrane with an asymmetric structure of vertical aligned micropores was constructed by phase inversion method.The asymmetric structure has a layer of vertical aligned micropores structure and a dense layer.The dense surface of electrolyte is coated with a thin layer of polyethylene oxide(PEO)electrolyte to avoid to be reducted for Ti⁴⁺in the electrolyte from lithium-metal anode.The coating of PEO electrolyte also benefit to a stable lithium deposition/stripping.Compared with the flat Li_3xLa_2/3-xTi O₃membrane,this membrane with a three-dimensional vertical aligned microporous structure can provide effective lithium-ion transport between positive electrode and electrolyte,and the interface impedance between electrolyte and the positive electrode is significantly reduced from853?cm² to 133?cm².The all-solid-state lithium battery using this designed electrolyte exhibited an initial discharge specific capacity of 127 m Ah g^-1 under constant current density of 0.05 C.Its capacity retention is high up to 98%after 50 cycles of discharge and charge.Rate performance of this battery has also been significantly improved compare to the one with planar Li_3xLa_2/3-xTi O₃ electrolyte.2.Li_0.34La_0.56Ti O₃ thin film with a thickness of 25?m is realized by tape casting and special sintering process.The thickness of 25?m means lithium ion only need to pass through a few large crystal grains from one side to the other side of electrolyte,which is beneficial to take advantage of high bulk lithium-ion conductivity of Li_0.34La_0.56Ti O₃ electrolyte.The ionic conductivity of this Li_0.34La_0.56Ti O₃ electrolyte film has a significant improvement to 2.0×10^-5 S cm^-1 compare to the electrolyte membrane prepared by cold pressing.The Li_0.34La_0.56Ti O₃thin film show a superior flexural strength of 264 MPa for battery assembly.The all-solid-state lithium batteries using a Li_0.34La_0.56Ti O₃ thin film with a thickness of 41?m can achieve a charge/discharge specific capacity of 145 m Ah/g and a capacity retention of 82%after 50 cycles of charge/discharge.3.The Li_1.5Al_0.5Ge_1.5(PO₄)₃ electrolyte membrane is used in electrodialysis separation device as separation membrane,and the Li⁺concentration in anolyte can be reduced from 0.1mol L^-1 to 0.002 mol L^-1 under electric field.According to the transit dose of Li⁺,the coulombic efficiency of current for electrodialysis can reach 90%.Due to the high compactness of oxide electrolyte membrane,lithium ions are transported by carriers in the electrolyte lattice,so the obtained dialysate has high purity and unrestricted concentration.sole Li⁺ion can steady traverse oxide electrolyte,while Mg²⁺,Ba²⁺and other hetero ion will be blocked at the electrolyte interface and generate steric-hinerance effect.Meanwhile,the hetero ion in anolyte can corrode the interface of Li_1.5Al_0.5Ge_1.5(PO₄)₃ interface thus reduce the life of membrane.