Construction And Electrochemical Performance Of SnO₂/Conductive Polymer Heterostructures Nanorod Arrays

With the growing demand for energy, solar energy, wind energy and otherrenewable energy sources have received unprecedented attention. At the same time,exploring new energy storage devices with excellent performance has also become ahot topic under today’s situation. Lithium batteries, with advantage of high capacity,long cycle life, fast charge and discharge rates, etc., become promising storagedevices in the field of electronic devices and electric vehicles. Electrode material, anextremely important part in lithium batteries, is also one of the key factors that mayrestrain the development of lithium batteries. Therefore, there are both practical valueand research significance for the design and construction of new electrode materials.Tin oxide, as a new kind of anode material for lithium batteries, has advantages ofhigh capacity, low cost and environmental friendly et al. which make it a promisingcandidate for future application.However, there are also some disadvantages that restrain the development of tinoxide as the anode material for lithium batteries: in the charge and discharge process,there is large volume expansion for tin dioxide. The large volume expansion not onlydestroys the integrity of the electrode material, but also seriously affects the cyclingproperties of the material. What’s more, solid electrolyte interphase (SEI) film may beformed and destroyed repeatedly due to the volume change of the material in chargeand discharge process, consuming a lot of lithium ions in the electrolyte and resultingin low coulombic efficiency. Further, the intrinsic low electronic conductivity andionic conductivity may seriously affect the rate performance of tin oxide. Therefore,the main task of this paper is to solve the problem of crush and expansion of tindioxide in charge and discharge process, to improve the electronic conductivity andionic conductivity, improving the cycle performance and rate capability.In this dissertation, SnO2/conductive polymer nanorod arrays have beensuccessfully constructed by hydrothermal method and subsequent electrochemicaldeposition method, to obtain better-performed electrode nanomaterials which havelong cycle life and high rate performance. Modern testing methods were performed to study the preparation, structure and properties of as-synthesized SnO2/conductivepolymer nanorod arrays. The main results are as follows:(1)Using as-prepared uniform SnO2nanorod arrays, we successfully constructedSnO2/PANI heterostructured nanorod arrays by electrochemical deposition method.The resulting samples were characterized by XRD, SEM, FTIR, etc.to analyze thestructure, phase analysis and to figure out the relationship between the parameters ofpreparation and morphology and explain its growth mechanism.(2)We test the electrochemical performance of SnO2/PANI heterostructured nanorodarrays，especially cycling performance and rate performance. Among two kinds ofheterostructured nanorod arrays, heterogeneous branched core-shell SnO2-PANInanorod arrays have exhibited better electrochemical performance. Theheterogeneous core-shell SnO2-PANI nanorod arrays exhibit a high reversiblecapacity of506mAh/g after100cycles, resulting in the capacity fading of0.579%per cycle between20to100cycles, much lower than that of nanosheet-assembledhierarchal SnO2-PANI nanorod arrays (1.150%) and bare SnO2nanorod arrays(1.151%). The enhanced electrochemical performance can be attributed to thebranched conductive PANI shells, which not only release the stress of volumeexpansion and maintain mechanical integrity during cycling, but also realize threedimensional transports for electrons.(3)SnO2/PPy co-axial structure and SnO2/PPy film were successfully constructed bythe time-constant deposition method respectively. Attributed to the high electricalconductivity and ion permeability, rate performance and cycle performance have beenimproved greatly. SEM, TEM, FTIR, EDS, etc. have been used to characterize thestructures, phase analysis, to analyze the relationship between the electrochemicalperformance and the morphology, and explain its modification mechanism.(4)We use the electrochemical measurements to test the property of the as-synthesizedmaterials. Compared with SnO2/PPy film and SnO2/PPy core-shell structure,SnO2/PPy film electrode was found to have greatly been improved on cycleperformance and rate capability. The SnO2/PPy film exhibits a high reversiblecapacity of683mAh/g after300cycles, resulting in the capacity fading of0.097%per cycle between20to100cycles, much lower than that of SnO2/PPy core-shellstructure (0.627%) and bare SnO2nanorod arrays (3.14%). T The excellent cycling performance can be attributed to PPy film layer, which can effectively release thestress of volume expansion. Besides, compared with the isolated electronic transportsof SnO2/PPy co-axial structure and one-dimensional electronic transports of SnO2nanorod arrays, SnO2/PPy co-axial structure is captured by PPy wholly, realizingcontinuous three dimensional electronic transports, thus improving the electricconductivity effectively.