Synthesis And Electrochemical Properties Study Of High Performance Tin-based Film Anode For Lithium-ion Battery

Secondary rechargeable batteries are playing an important role in the clean energy conversion and storage.With the progress of science and technology,energy transfer and storage device is endowed with a higher mission.Developing new advanced anode with higher energy density,long life,cheap,low cost and higher safety is one of the most importance for both the large-scale and miniaturized lithium ion batteries?LIB?.Sn-based alloys have been widely researched as alternative anode for LIB due to their high theoretical capacity and moderate operation potential.However,their cycle performance should be further improved to cater to the actual application requirements.Multiphase and multiscale structures have been demonstrated to be benefit to the capacity and cycle-ability of Sn-Cu anodes.This thesis not only addresses the preparation and characterizations of various Sn-Cu anodes with multi-scaled multiphase structures,but also analyzes the influences of microstructure on the cycle performance and their mechanisms.The focus on Sn-Cu anodes is also aiming at development of a new generation of LIB.The main contents are listed as follows:Firstly,three-dimensional Sn/Cu₆Sn₅/Cu anodes prepared by vacuum thermal evaporation are discussed.Because of three-dimensional and polycrystalline phase unique construction,the wave-like Cu6Sn5 layer not only plays a dual role of buffering and binding for active substances,but also activates the Sn element of the effective components and exists synergy effect between Sn-Cu element of the anodes.The Sn/Cu6Sn5/Cu anode has excellent electrochemical performance.After 250 cycles,capacity retention ratio of the anode is85.7%with specific capacity of 720 mA h g^-1 under the current density of 200 mA g^-1.It also exhibits excellent cycle performance under high current density of 6000mA g^-1.After 500 cycles,capacity retention of the anode is 320 mA h g^-1 specific capacity.Secondly,the main factors of electro-deposition are optimized in order to study the relation with the electrochemical properties and the anode structure.We determine complex system of electro-deposited liquid that the mole ratio of K₄P₂O₇·3H₂O:triethanolamine is 7:3.We determine the current of electro-deposition that it is multi-level voltage current.The initial transient high voltage is very important to activate electro-deposited liquid and negative electrode plate,infiltrate into the substrate,merge the layer and the substrate,and control the sediment content.We determine the material formulation of additives to control close packing particle size of the anode and stabilize the Sn-Cu alloy composition.Thirdly,the Sn-Cu alloy anodes prepared by electro-deposition are researched.The specific capacity and cyclic stable relationship of anode is discussed,and the lithium storage mechanism model is determined.It has been found that bonding strength of Sn-Cu anodes between electro-deposited layer and the substrate has obvious influence on their cycle performance.The Sn-Cu anode has excellent electrochemical performance.After 400 cycles,capacity retention ratio of the anode is 89.9%with 728.3 mA h g^-1 specific capacity under the current density of 200 mA g^-1.Through the analysis of the electrochemical properties and SEM photos of repeated cycles of anode,we discussed the lithium storage"?"phenomenon of Sn-Cu anode,and built the activation-synergy mechanism between the copper and tin element of lithium storage mechanism model.Fourthly,the conductive polymer Sn-Cu flexible anodes and no current collector Sn-Cu alloy anodes prepared by electro-deposition are researched.We research the no current collector Sn-Cu alloy anode that has the advantages of the simple craft,controllability of component,large-scale production.The no current collector Sn-Cu alloy anode offers a new research idea for the preparation of the ally anode.This anode has close packing structure and excellent electrochemical performance.After 450 cycles,capacity retention ratio of the anode is 61.4%with 505.6 mA h g^-1 specific capacity under the current density of 200 mA g^-1.The anode also has excellent cycle performance under high current density of 6000 mA g^-1.After700 cycles,capacity retention ratio is 61.1%with 326.3 mA h g^-1 specific capacity.The no current collector Sn-Cu alloy anode abandons traditional anode construction that creates a new research direction in the field of alloy anode.Finally,a novel integrated electrode structure was designed and synthesized by direct electrodepositing of Sn-Cu alloy anode materials on the Celgard 2400 separator?Cel-CS electrode?.The integrated structure of the Cel-CS electrode not only greatly simplifies the battery fabrication process and increases the energy density of the whole electrode,but also buffers the mechanical stress caused by volume expansion of Sn-Cu alloy active material;thus,effectively preventing active material falling off from the substrate and improving the cycle stability of the electrode.The Cel-CS electrode exhibits excellent cycle performance and superior rate performance.A capacity of 728 mA h g^-1 can be achieved after 250 cycles at the current density of 200 mA g^-1.Even cycled at a current density of 5000 mA g^-1 for 700cycles,the Cel-CS electrode maintained a specific capacity of 938 mA h g^-1,which illustrates the potential application prospects of the Cel-CS electrode in microelectronic devices and systems.In summary,to alleviate the effect of volume expansion and pulverization of the electrode during the electrochemical cycles,and to improve cycling stability,rate capability,high current performance of the electrode,we synthesized several high-performance Sn-Cu alloy anode.Moreover,by changing the factors including deposition method,deposition substrate and deposition technological conditions,we studyed the lithium storage"?"phenomenon of Sn-Cu anode and built an activation-synergy mechanism model between Sn and Cu elements.In addition,the no current collector Sn-Cu alloy anode was firstly designed and prepared in our experiment so that a new direction of the electrode manufacture was created.Our work not only provided the reference for the structure-performance relationship of the anode,but also provided the experimental and theoretical basis for improving the performance of Sn-based anode.