Preparation And Electrochemical Properties Of Sn-based Anode Materials For Li-ion Battery

Presently, Lithium-ion batteries have been widely used as power supplies forportable devices, electric vehicles and etc, because of various advantages of highwork voltage, large energy density, long cycle life and environmental safety, and soon. Carbon, as a coμmon coμmercial anode material, can not satisfy the demand ofa large capacity due to its low theoretical specific capacity (372mAh g^-1or818mAh mL^-1). Compared with the carbon material, Sn metal and its alloys own largertheoretical capacities, higher insertion voltages and higher safety, so, attract moreand more research foused on this area.In this paper, the Ag₅₂Sn₄₈alloy powders were prepared as a new anodematerial of the Li-ion cell through a mechanical alloying （MA） technique. Phasesand microstructural evolution of the powders during MA, charge/dischargeperformance of the alloy anode and microstructural change of the anode aftercharge/discharge cycles were studied. Furthermore, in order to slove twoweaknesses of the Ag-Sn alloy anode i.e., low cycle performance and high volumeeffect of the alloy anodes in the charge/discharge process, the author plans to addcarbon into the Sn-Ag alloy to fabricate Ag-Sn/Gr composite anode materials. Twomethods of adding Gr, including mechanical milling and organics high-temperaturedissociation, were employed to prepare the composite anode materials, andmicrostructures and cycle performances of the Ag-Sn/Gr composite anode materialswere also investigated.The milled Ag₅₂Sn₄₈alloy powders consist of two phases of Sn and Ag3Sn. Asincreasing the milling time, the Sn powders gradually turn to be an amorphous state,and the milled powders are finer and more spheroidic. After milled for65h, theaverage particle size of the powders is about6μm. The electrochemical test of thealloy anode shows that the Ag₅₂Sn₄₈alloy anode cell has the highest initial capacityup to800mAh g^-1and the best cycling performance with200mAh g^-1after10cycles, compared with other Ag₅₂Sn₄₈alloy powders milled for different time.The Sn-Ag/Gr composite powders were prepared with the65h milled Sn-Agalloy powders and the graphite powders, which are of a structure of a graphiteparticle core coated by fine Ag3Sn and Sn particles. Accordingly, the Sn-Ag/Gr composite powder anode cell displays an initial discharge capacity of1064mAh g^-1and250mAh g^-1after10cycles, which are pretty higher than those of the Ag-Snalloy powder anode. The graphite cores can considerably reduce the volume changeof the composite anode in the charge/discharge process, and hence remarkablyimprove the structural stability of the composite anode.Moreover, a high-temperature dissociation technique was also employed toprepare the Sn-Ag/Gr composite anode materials, using epoxy resin as a carbonsource. After coating the resin on the65h milled Sn-Ag powders andhigh-temperature dissociating, the alloy particle are covered with a carbon layer.The composite particle is spherical and even in size. The electrochemical test of thecomposite anode shows that the capacity and cycle property of the anode are notgood, but its capacity retain ratio is excellent. It is attributed to a hard carbon shellon the composite particle, which can relieve the volume expansion of the anode inthe charge/discharge process. Meanwhile, a SEI flim forms on the surface of thehard carbon shell in the first cycle, which has a higher stablility.