High Performance Electrode Materials And All-Solid-State Thin Film Lithium Microbatteries

To develop high performance energy materials and apply them into practical devices,we comprehensively study the physical and chemical properties of electrodes and the influence on the electrochemical performance.First,we introduce the working principles of lithium batteries.Based on the periodic table of elements,we discuss the potential high performance electrodes without lithium,as well as the current transition metal oxide cathodes with lithium.Second,we discuss the mechanism and protection of interface in lithium batteries.Third,we review state-of-the-art solid-state electrolytes and all-solid-state thin film lithium batteries.Afterwards,we discuss the synthesis,characterization and tests,including the related equipments and theories.The magnetron sputtering,sol-gel and solvothermal methods are employed in this thesis to develop novel multielement electrodes.By constructing nanomaterials,optimizing structures and modifying interfaces,the lithiation performance of electrodes can be improved.Meanwhile,we combine various characterization techniques to study the materials,and utilize micro-fabrication process to assemble all-solid-state thin film lithium microbatteries.The novel electrodes can increase the energy density of present power sources,and the related strategies can serve as references for energy materials.The major results are as follows:Cu-Sn-S nanomaterials:The facile sol-gel and solvothermal methods are presented to synthesize Cu-Sn-S self-assembled nanomaterials,which can also be used to fabricate similar complex nanomaterials.Combining theoretical calculations and experimental results,it is demonstrated that the Cu-Sn-S nanotubes are composed of different phases in core and shell layers,respectively.According to the theories of material and geometry,the core-shell structure can release the volumetric expansion of electrodes.This work not only explain the mechanism for the high lithiation performance of Cu-Sn-S nanotubes,and determine the phase composition,but also the calculation results provide theoretical evidence to future research of Cu-Sn-S.Cu₂ZnSnS₄ thin film:The Cu₂ZnSnS₄ thin film is prepared by magnetron sputtering and delivers a high capacity of 540 μAh cm-2 μm-1 or 950 mAh g-1 even after 500 cycles.The thin thickness and highly reversible sulfides facilitate the high lithiation performance.Moreover,it is integrated into thin film lithium microbattery by micro-fabrication process.The microbattery with Cu₂ZnSnS₄ thin film as anode exhibits more remarkable discharge plateau,higher capacity and better cycling performance than the SnOx microbattery.This work indicates the advantage of thin film electrodes and how to bridge the relationship between half-cells and microbatteries.Coated three-dimensional Cu₂ZnSnS₄ electrode:Utilizing the three-dimensional substrate and solid-state electrolyte,the LiPON coated three-dimensional Cu₂ZnSnS₄ electrodes are fabricated by magnetron sputtering.Owing to the suppressed dissolution of materials,protected surface and released volumetric expansion,the capacity and cycling performance is increased.This work demonstrates that applying both structural modification and surface protection can significantly improve the lithiation performance of alloys,which can be used for other materials.The simple and efficient strategy can be feasible for realistic application and mass production.LiPON/SnO₂ coating film:The LiPON/SnO₂ composite film is deposited on Si substrate as a protective film by magnetron sputtering,and the porous morphology is in-situ generated.Combining capacity and voltage limitation,it is reasonable to state that the protective film can improve the capacity and cycling performance of Si substrate without the cost of coulombic efficiency.Meanwhile,the porosity and the formation mechanism are studied in details.The major factors for the improved performance are examined by various electrochemical tests.This work discusses the mechanism for enhancing the lithiation of coated Si wafer,and the proposed method of in-situ generating porous film can be applied to other materials or fields.Si-based composite films:Si/Sn composite films are deposited on Si substrate as anode materials for lithium batteries.The LiPON/CuxSnOy film with in-situ induced porosity can greatly increase the lithiation performance of Si wafer.The effects of Cu doping to the material properties and lithiation process are discussed,including the reaction mechanism.Meanwhile,utilizing the three-dimensional Si substrate with inverted pyramid array fabricated by micro-fabrication process,the Cux-SnOy anode is integrated into the three-dimensional microbatteries,exhibiting better performance than the two-dimensional microbatteries.