Preparation And Electrochemical Properties Of Sn-Co Alloy Anode Composite For Lithium Ion Battery

Because of its high theoretical capacity (992mAh/g) and high density, tin has become ahighlighted topic in high capacity anode material for lithium ion battery. However, its structureis suffered from pulverization which is resulted from the large volume expansion during thecharge-discharge, leading to the deterioration of the cycle performance and thus losing itspractical value. Therefore, improving the cycle performance of Sn-based has become key scienceproblem.In this paper, the Sn-Co alloy composite was prepared by solid-state sintering method andball milling method, which is appropriate for industrial production. The structures andelectrochemical properities of nano Sn-Co alloy powder, graphite, Sn-Co/C and Sn-Co/Gcomposite were investigated systematically.In the Sn-Co alloy, the phase structure has significantly influence on the electrochemicalproperities. The CoSn2phase alloy with tetragonal crystal has high discharge capacity andcharge-discharge efficiency, the Co3Sn2phase alloy with orthorhombic crystal has high cycleperformance and the CoSn phase alloy with hexagonal crystal has appropriate discharge capacityand cycle performance. Besides, the refinement of particle size and grain size of Sn-Co alloyresults in the improvement of capacity and cycle performance.In the Sn-Co/C system, the novel Sn-Co-Zn/C composite prepared by adding the forthelement Zn into Sn-Co/C composite exhibis excellent electrochemical properities. The compositeeffect and the refinement of paticle size and grain size by adding C, the solid solution strengtheneffect and the multiphase compound effect of CoSn, CoSn2, Co3Sn2, Zn and Sn by adding Znimprove together the structure stabilities and electrochemical properities. The discharge capacityand charge-discharge efficiency of Sn-Co-Zn/C composite is440mAh/g and76.2%espectivelyand the capacity retention is88.6%after25cycles. So, the Sn-Co-Zn/C composite is appropriatefor application in lithium ion battery with high capacity.In the Sn-Co/G system, the artificial graphite is crushed and pickled firstly, and then makeSn-Co alloy into graphite by ball milling. The influence of surfactant, balling time and speed,alloy content on the structures and electrochemical properities of Sn-Co/G composite isinvestigated. Then, the integrate degree of Sn-Co alloy and graphite is improved by heattreatment. The discharge capacity and charge-discharge efficiency of Sn-Co/G composite after500℃heat treatment is362mAh/g and83.6%espectively and the capacity retention is92.8% after25cycles. Therefore, a technology approach to prepare the anode material for lithiumbattery with long cycle life has been found.In the Sn-Co/B system, the scope of nonmetal element which is compound with Sn-Co alloyextends to B element, the influence of B element on the structures and electrochemicalproperities of Sn-Co/B composite is investigated. The composite effect and the refinement ofpaticle size and grain size by adding B improve together the electrochemical properities ofcomposite. The discharge capacity and charge-discharge efficiency of Sn-Co/B composite is216mAh/g and51.1%espectively and the capacity retention is82.9%after25cycles. Howerer,more CoSn2phase forms by adding excessive B, which leads to the decreasing of cycleperformance.