Preparation And Electrochemical Performance Of Electrodeposited Sn-Sb Anodes For Lithium Ion Batteries

Lithium-ion batteries as a new clean energy with high specific energy andexcellent cycle performance and long life is expected to play an important rolein the field of electric and hybrid electric vehicles. However, at present highrate ability and high reversible capacity of Lithium ion batteries are urgentlyneeded to improve because they are the large obatacles for the application ofLithium ion batteries in electric vehicles.It is important to develop high capacity anode materials to increase theenergy density of lithium-ion batteries as the anode materials is one of the keyfactors affect the performance of lithium-ion batteries. Sn-Sb alloy electrodehas emerged as attractive candidate to replace conventional carbonaceousnegative electrodes due to their superior capacity. However, the application ofthe new negative electrodes has been frustrated by poor capacity retentionduring discharge-charge cycling. Both Sn and Sb undergo large volumechange during the reaction with Li, uneven volume expansion leads to cracks,a loss of electrical contact and poor cycling performance. To tackle thisproblem, we have prepared Sn-Sb two-dimensional thin film materials by electrodeposition, firstly prepared Sn-Sb-Cu-O nano-alloy thin films by heattreatment Sn-Sb films on copper substrate in air atmosphere and firstlyprepared Sn-Sb nano-structured electrode materials by an anodic aluminumoxide template-assisted growth method,to buffer the volume change of Sn andSb as these materials have special structure. The morphology, structure,composition and surface chemical state of these materials were characterizedby XRD, EDS, SEM and XPS, respectively. The electrochemical reactionmechanism, charge/discharge capacity and cycle performance were analyzedby various electrochemical measurements. And on this basis, we investigatedthe effect of preparation conditions on the material properties andelectrochemical performance, and the correlations between material propertiesand electrochemical performance of the electrode. The main results are asfollows:(1) The results showed that Sn-Sb alloy thin-film materials prepared byelectro-co-deposition at different current density and deposition time havedifferent composition, structure, morphology and electrochemicalperformances. Although the electrochemical properties of the Sn-Sb filmelectrode apparently related to the electodeposition parameters, but it isessentially related to the relative content of the SnSb intermetallic phase inSn-Sb film, the higher content of the SnSb intermetallic phase, the more stableof the electrode structure and the grain boundary structure, and thus the betterelectrochemical properties of the Sn-Sb film electrode. The content of the SnSb intermetallic phase is relatively high in the Sn-Sb film electrodeprepared with a current density of5mA/cm2for30min and thus with a higherinitial dischare and reversible capacity of818.3mAh/g and776.1mAh/g,respectively. The initial Coulomb efficiency is94.8%. Totally, the Sn-Sb filmelectrode prepared by electro-co-deposition has high initial reversible capacityand coulombic efficiency. However, the film electrode showed rapidlycapacity decline due to the volume effect has not been effectively bufferedafter15cycles and the capacity fading rate is60.1%after20cycles. In order toimprove the capacity retention of the Sn-Sb film electrode, we annealed theSn-Sb deposits on the copper substrate, when heat treatment temperature ishigher than the melting point of the Sn-Sb deposits, Copper and Oxygenelements were pull in the active materials, then multiphase Sn-Sb-Cu-Ocomposite electrodes were obtained. The Sn-Sb-Cu-O electrode prepared at acurrent density of5mA/cm2for30min and then annealed at400℃for2hshowed the best electrochemical performance. The initial reversible capacity is600.3mAh/g, the initial Coulomb efficiency is63.8%and maintained at about99.5%after the second cycle, and the high reversible capacity of over600mAh/g with no decay over100cycles. But too high heat treatmenttemperature will lead to excessive Copper and Oxygen, which is not benefitfor the improvement of the electrochemical properties.(2) In order to obtain Sn-Sb thin film electrode with desired Sn: Sbatomic ratio, we prepared Sn-Sb film electrode by two-step electrodeposition. The results showed that the Sn: Sb atom ratio of the film electrode can becontrolled by controlling the electrodepositon time of Sn and Sb. The contentof Sn and Sb affects the electrochemical properties of the material. When theSn: Sb atomic ratio is about1:1, the Sn-Sb film electrode shows the bestelectrochemical properties with an initial reversible capacity of855.4mAh/gand the initial Coulomb efficiency is92.6%. However, two-stepelectrodepositon method does not help to improve the cycle stability of theelectrode as the Sn-Sb film material prepared by two-step electrodepositoncontains part of pure Sn and Sb. The Sn-Sb film electrode prepared bytwo-step electrodepositon showed a fast decay after eight cycles and thecapacity decayed from773.4mAh/g of the8th cycle to about244.3mAh/g ofthe20th cycle. The Sn-Sb film electrode annealed at400℃for2h was amulti-phase composite electrode, which contains SnSb, SnO2, Cu2Sb, Sb2O5,Cu6Sn5and CuO phases, the complex multi-phase helps alleviate the volumeeffect of the active materials and improve the cycle stability of the material. Inaddition, the Sn and Sb content of the material also affect the electrochemicalproperties of the electrode. When the electrode with a Sn:Sb atom ratio ofabout1:1, the annealed Sn-Sb film electrode showed an initial reversiblecapacity of about1108.6mAh/g, which still remained767.7mAh/g after30cycles, the initial Coulomb efficiency was about77.0%.(3) Sn-Sb deposits on Copper nanopillars current collector and Sn-Sbnanostructured (nanotubes and nanopillars) materials on Copper substrate prepared by an anodic aluminum oxide template-assisted growth method havea special nano-space structure. Nanostructured materials with large specificsurface area allow more of Li+embedded, but the large specific surface areamay also bring a large irreversible capacity loss due to the formation of SEIfilm. The gaps of the nanostructured electrodes can accommodate the volumeexpansion of the active materials, thereby improving the cycle stability of theelectrodes. It is noteworthy that the Sn-Sb alloy growth along the wall of theAAO template, along with the increase of the deposition time, firstly formedtubular material, followed by the formation of the solid columnar material.The Sn-Sb nanotube electrode prepared with a current density of5mA/cm2for60min showed the best electrochemical property with an initial reversiblecapacity of823.9mAh/g. The reversible capacity not only did not decay, butstill remained849.8mAh/g after30cycles.