Construction Of Composite Interfaces And Heterostructures For Enhanced Charge Transfer Properties

The space charge layer was first applied to explain the conduction and energy band structure of semiconductors with two-phase interfaces,and later it was extended to understand the high conductivity at the interfaces in ion conductor systems.Based on the effect of potential difference at composite interface,space charge layer influences the mesoscale lithium ion conduction and micro energy band structure.The composite heterojunction and interfaces are constructed to regulate the charge transport,electrical and electrochemical properties,which will have great influence on macroscopic performance of thin-film batteries,solid-state batteries,and field electron emission devices.On one hand,the space charge layer of complex interface is to regulate the interfacial Li⁺conduction of cathode and composite electrolyte at mesoscopic scale.The radio frequency sputtering is used to fabricate Lithium Nickel Manganese Oxide/LiPON composite film.The space charge layer caused by the film heterojunction reduced the content of Mn³⁺,and Li⁺conduction is greatly enhanced by the difference of interface contact potential.The positive electrode capacity and rate performance were improved,and side reactions at cathode/electrolyte interface are suppressed.Furthermore,to improve the ionic conductivity of solid-state electrolyte,we developed a new type of composite electrolyte combined nanoscale garnet structure Li_6.4La₃Zr_1.4Ta_0.6O₁₂ with ionic liquid?IL?.Compared with the electrolyte of ionic liquid without lithium salt added,the lithium iron phosphate cathode capacity?144 mAh/g,at 0.2C?was greatly improved using the composite electrolyte.The additional ion conducting channels were caused by the interfacial space charge layer effect between garnet particles and IL.The double-layer mechanism was further analyzed and verified by qualitative solid-state nuclear magnetic resonance and quantitative Boltzmann distribution.This composite electrolyte with a fast lithium-ion conductive network provides Li-ions channels connecting with the space charge layers,and offers good contact between electrode and electrolyte to increase interfacial ionic conduction,which gives us a new direction for interface design.On the other hand,based on space charge layer,micro energy band structure adjustment of silicon-based nanoarrays are studied to understand the interface-enhanced electron transport.Then field electron emission is used as an application objective.Ag-catalyzed corrosion assisted by polystyrene sphere templates are used to prepare silicon nanowires?SiNWs?,then dry-oxidation is used to further control nanowires'dimensions.The SiNWs/metal silicide core-shell structure,3D spatial SiNWs/graphene arrays,and SiNWs/ZnO branched structure were fabricated.Their field electron emission performance with composition,morphology and energy band structure were further tested and studied.We established the relationship between work function,electron affinity,energy band bending,interface barrier and electron conduction efficiency at the heterojunction interface.It is improved that the contact interface is very important for electrons transporting from substrate to emitter tip,and field electron emission performance of silicon-based composite is effectively improved by the construction of ohmic contact at metal-semiconductor and p-n heterojunction.Furthermore,we used the unique nuclear detection technology—operando neutron depth profiling,complementary to microscopic studies,providing quantitative insight into the spatial distribution/density of Li during plating and stripping.The evolution of the Li metal density profile is shown to depend on the current density,electrolyte composition and cycling history,and allows to monitor the amount and distribution of inactive Li over cycling.Depending on the cycling strategy,solid electrolyte interface?SEI?formation is passivated and inactive Li can be reactivated,providing insights in the relation between the Li-metal/SEI formation and electrochemical conditions.A small amount of reversible Li uptake in Cu during plating and stripping is revealed,where the Cu grain boundaries appear responsible,providing a direction to prevent current collector degradation.The sensitivity of operando NDP towards Li offers possibility to gain more understanding on Li plating and stripping reactions,which is of significant importance for the design of future safe Li metal anodes.