| With the information technology and the portable electronic equipment rapid development, second energy must have high specific energy. Lithium ion battery (LIB) is one of the important second energy. The graphite material that was used as anode of LIB mainly in present commercialized production has already approached its theoretical capacity limit of C6Li (372 mAh g-1). To meet with the rapid increasing demand on specific energy density of the LIB for diverse applications, the exploitation of new electrode materials with better performances has become the key subject in the development of the LIB. Extensive efforts have been paid to explore different types of materials to be employed as anode electrode in LIB, which are promising to exceed the capacity of carbon materials. Tin-based materials were widely studied among them as alternative anode material to carbon for LIB thanks to its much higher theoretical capacity than that of the carbon material. However, one of the most important problems in utilizing Sn-based intermetallic compound anodes is its poor cyclability due to mechanical fatigue caused by volume change during lithium insertion and extraction processes. To overcome this problem, some Sn-based intermetallic compounds with macroporous structure are presented. The main results are summarized as following.1. Monodisperse polystyrene (PS) spheres of 100 nm, 180 nm and 500 nm in diameter were synthesized by using an emulsion polymerization followed by a seed growth polymerization technique. The PS spheres were assembled onto a Ni-coated Cu sheet that was prepared by self-sedimentation in a slowly evaporating dispersion of PS spheres in ethanol. Using ethanol as disperse media can accelerate PS spheres sedimentation. Under the same self-sedimentated time, the bigger diameter of the PS spheres, the more order of the PS spheres template. Macroporous materials of Sn-based alloy were fabricated through PS template method and electrodeposition.2. The electrochemical properties of three different pore sizes macroporous Sn-Cu alloy electrodes was examined by galvanostatic cycling. The results demonstrated that the electrodes of macroporous Sn-Cu alloy with pore size respectively of 100 nm, 180 nm and 500 nm can deliver reversible capacity of 316.4, 332.0 and 253.0 mAh g-1 up to 70th cycles of charge/discharge. The cycle performance of the macroporous Sn-Cu alloy of 180 nm in pore size is better than that of the macroporous Sn-Cu alloy with 100 and 500-nm-diameter pores. The cycle performance of the macroporous Sn-Cu alloy with 500-nm-diameter pores is the worst. It can be attributed to that the pore wall of the macroporous Sn-Cu alloy with 500-nm-diameter pores is very thin, which is easily cracking and crumbling during lithium insertion/extraction. In comparison, for a Sn-Cu alloy anode without the macroporous structure, these macroporous Sn-Cu alloy have better cycle performance. It has revealed that the porous structure of the macroporous Sn-Cu alloy material is of importance to strengthen mechanically the electrode and to reduce significantly the effect of volume expansion during cycling by using SEM.3. In comparison the cycle performance of the macroporous Sn anode with 180-nm-diameter pores and the Sn anode without the macroporous structure, it is evident that the former demonstrates a better cycle performance than that of the latter. To some extent, the macroporous structure is of importance to strengthen mechanically the electrode and to reduce significantly the effect of volume expansion during cycling. However, the reversible capacity of the macroporous Sn anode was rapid decline after 36 cycles. It has observed that the macroporous structure was disappeared by using SEM.4. The texture of the macroporous Sn-Ni alloy electrode prepared by electrodeposition exhibits highly (110) preferred orientation. When used as an anode for a LIB, the macroporous Sn-Ni alloy electrode delivered a reversible capacity of 536.1mAh g-1 up to 75th cycles. Compared with the macroporous Sn electrode, the capacity and cycling performance of the macroporous Sn-Ni alloy electrode are significantly improved. It has revealed that the inactive element can buffer the large volume change and as a barrier against the aggregation of active material into large grains during Li-ion insertion and extraction processes. The SEM results revealed that the macroporous structure can buffer the volume expansion during cycling again.5. The results of galvanostatic cycling illustrated that the macroporous Sn-Co alloy film electrode can deliver a reversible capacity as high as 610 mAh g-1 up to 75th cycles. In comparison with the Sn-Co alloy film directly deposited on Ni coated Cu sheet substrate, the macroporous structure of the Sn-Co alloy electrode prepared by the present procedure has enhanced significantly the capacity and the cyclic performance. It has demonstrated that the macroporous structure has played an important role, in addition to the alloying effect, to overcome the effect of volume expansion during charge/discharge cycling of Sn-based alloy anodes. At the same time, the columbic efficiency of the macroporous Sn-Co alloy is more stably than that of the macroporous Sn-Ni alloy.6. The other active element Sb was introduced into the macroporous Sn electrode. The results of galvanostatic cycling illustrated that the macroporous Sn-Sb alloy electrode can delivere a reversible capacity as high as 400 mAh g-1 up to 40th cycles. Compared with the macroporous Sn electrode, the capacity and cycling performance of the macroporous Sn-Sb alloy electrode are improved. It is indicated that introduced an active element in the macroporous Sn electrode, which can also improved the cycle performance. However, compared to the macroporous Sn-Ni alloy and the macroporous Sn-Co alloy, the cycle performance of the macroporous Sn-Sb alloy is relatively poor. It may be attributed that the play of the buffer effect of the lithium-inserted active materials, due to volume expansion by itself, can be reduced.The innovation of this theme is based on: (1) Macroporous material of Sn-based intermetallic compounds were fabricated through PS colloidal crystal template method and electrodeposition; (2) The electrochemical properties of three different pore sizes macroporous Sn-Cu alloy electrodes was examined by galvanostatic cycling. It is revealed that the macroporous Sn-Cu alloy with 180-nm-diameter pores has the best cycle performance; (3) According to the results of the macroporous structure Sn-based intermetallic compounds, the mechanism of the macroporous structure has been presented. |
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