Doping Effects Of Trivalent Transition Metal Oxide On The LLZO Solid Electrolyte Via High Throughput Experimentation

Lithium-ion batteries are considered as efficient energy storage units and widely applied in major fields of human society,such as new energy vehicles and portable electronic devices.Liquid electrolyte is commonly adopted as a medium for the transmission of lithium ions between anode and cathode in the traditional lithium-ion batteries,giving rise to potential safety risks,such as liquid leakage,inflammability,and explosion.Substituting the liquid electrolyte with the solid electrolyte is generally considered as a promising route to mitigate the safety issues.In a wide variety of inorganic solid electrolyte materials,the inorganic solid electrolyte based on garnet lithium lanthanum zirconium oxide(Li₇La₃Zr₂O₁₂,LLZO)receives numerous attentions from the research society thanks to its promising thermal stability,high ionic conductivity,and wide electrochemical window.However,the cubic LLZO exhibiting good ionic conductivity is unstable at room temperature.Metal cation doping is an effective way to stabilize the cubic phase of LLZO at room temperature and improve the ionic conductivity.Nevertheless,the traditional doping experiment requires"one component at a time".Due to the wide range of the element variety and doping components,it is inefficient to meet the rapid development needs of LLZO solid electrolyte materials.Recently,the high-throughput experiment is being developed to accelerate material researches.Its nature is to simultaneously prepare multiple samples with different compositions and properties in one run,based on the samples,it is possible to obtain a large amount of material data through rapid characterizations.The high-throughput techniques thus greatly improve experimental efficiency.Preparations and characterizations are two cores for high-throughput experiments.For the former,the hinge is to mix multiple elements systematically,following with sufficient diffusions according to kinetics and thermodynamics process,in order to form crystal or amorphous structures.The latter rapidly obtains the data from the prepared high-throughput combinatorial material sample library based on modern characterization methods.The combination of both factors together determines the systematicness and efficiency of high-throughput experiments.In this work,LLZO solid electrolyte materials doped with positive trivalent transition metal oxides are studied based on the high-throughput experimental method.The main research contents and innovation points are sketched as follows.1.A feasible preparation process of LLZO-In₂O₃ high-throughput combinatorial material sample library is developed based on the magnetron sputtering method.For the controllable distribution of sample components in the high throughput sample library,the major technical difficulty is the large area uniform deposition of thin films.To address this issue,the physical field of magnetron sputtering cathode is modeled and simulated.According to the simulation results,the effective deposition area is optimized,resulting in the high uniformity of the film.Thus,the demand will be satisfied for preparing the high-throughput combinatorial material sample library.For the vacuum deposition process of LLZO material,the poor lithium and the nonuniform multilayer film diffusion are two major issues required to be solved.Therefore,based on the premise of the correct stoichiometric ratio,Li₂CO₃ thin film layer is adopted as the supplementary lithium source.The thickness of each layer is controlled below 10 nm for the lamination structure.After the annealing process with low temperature diffusion,the uniform diffusion between multi-layer films of the LLZO-In₂O₃ high-throughput combinatorial material sample library is realized.2.The effects of different crystallization heat treatment temperatures on the crystallization and electrical properties of In₂O₃ doped LLZO high-throughput sample are studied.The XRD,SEM,and AC impedance spectra show that all the samples annealed at 600℃,700℃,and 800℃,respectively exhibit the c-LLZO phase.As the annealing temperature increases,the defects in the film increased with the growing of the grains,resulting in a decrease of ionic conductivity.In addition,after annealing at 800℃,the comparison between the In₂O₃-doped and the undoped samples indicates that In³⁺doping enlarges the lattice constant of cubic LLZO and reduce the charge repulsion between adjacent Li⁺,giving rise to a stabilized cubic phase structure.3.The LLZO-In₂O₃ high-throughput combinatorial material sample library is prepared based on the developed high-throughput synthesis process.The influence on the ionic conductivity from the dopant content of In₂O₃ is studied and discussed.The results show that along with the increase of the dopant content,the ionic conductivity increases at first and then decreases.Appropriate amount of doping can enlarge the lattice constant and reduce the Li⁺transmission barrier.Excessive doping will render the lattice distortion,along with an increase of the resistance at grain boundary,leading to a negative effect of the ion conductivity.In summary,the optimal dopant content is in the range of 8¹0 at.%,among which the sample with the dopant content of 8 at.%exhibits the highest ion conductivity of 1.1×10^-4 Scm^-1.