The Preparation And Structure Evolution Of Micro-Nano Dual-Scale Porous CuZnAl Memory Alloy Electrode

For the lithium-ion battery, Sn-based metallic anode materials draw more attentions due to their high theoretical capacity and good conductivity. However, there is a key problem which the capacity will be decayed quickly during charge-discharge cycling because of volume expansion. By combining the advantages of nanocrystallization, multi-phase composite and porous current collector structures, the preparation of porous CuZnAl shape memory alloy(SMA)/Sn composite electrode, in theory, can be used to solve the problem of capacity decaying, and improve the cycle performance at the same time. The purpose of this study is to prepare porous CuZnAl SMAs with dual-scale pores by dealloying method, and the pore morphology and microstructure were characterized by using XRD, SEM and TEM. The effect of processing parameters on the pore morphology and microstructure evolution were investigated systematically. Finally, a composite anode material was fabricated by loading Sn particle into porous CuZnAl SMA, and the electrochemical properties was determined. Some important conclusions can be concluded as follows:Firstly, for the Cu-34Zn-6Al pre-alloy with single β phase, 20% hydrochloric acid solution was chosen as the dealloying solution, it has been found that the optimized corrosion temperature is 50 oC, and the suitable dealloying time is 2-3 hours. Porous CuZnAl SMA with single β phase was successfully obtained, which the pores size is about 200-300 nm, moreover the nanopores are uniform distribution and inter-connected each other.Secondly, for the Cu-34Zn-6Al pre-alloy with β and γ dual-phase, 5% Hydrochloric acid ferric chloride solution was chosen as the dealloying solution. It had been found that porous CuZnAl alloy with dual-scale pores(micron scale of 1-2 m and nanometer scale of 5-50 nm) was fabricated by dealloying for 90 min at first step, moreover the micron pores inter-connected each other, and a composite Cu layer of amorphous and nanocrystalline of 5nm on the surface of these pore walls, the layer beneath Cu layer is the γ phase with grain size of about 5nm. After heat treatment at 850 oC for 3h, however the porous structure with dual-scale pores hasn’t been changed, the difference is that the γ phase is turned into the β phase, and there is a Cu layer of 50-200 nm thickness and 10 nm grain size on the surface of pore walls. Thus, porous CuZnAl SMA/Cu composite material with dual-scale pores was successfully obtained.Finally, the Sn/porous CuZnAl SMA composite electrode was fabricated by loading Sn by magnetron sputtering. From the results of electrochemical measurements, it has been found that the cyclic stability of Sn/porous CuZnAl SMA electrode is superior to that of Sn/copper foil electrode.