| Our country pay close attention to the development of materials and key technology for LIBs, and it is included the National Middle&Long-term Science and Technology Development Plan (2006-2020). Meanwhile, the high-speed development of EV, HEV and large power equipment represent a high standards of LIBs in capacity. Anode material is one of key materials producing an effect on capacity of LIBs. Tin based anode tin provides much higher theoretical capacity (993mAh/g) than graphite (372mAh/g), and behaves a slightly higher discharge voltage (0-400mV) than metallic lithium which could reduce safety concerns during cycling, however, pure tin presents a limited cycle life due to pulverization and delamination from copper foil current collector caused by volume expansion and contraction associated with the lithiation and delithiation. There are many ways to improve the cycle performance of tin based anode. One of the effective method is using carbon-based composites. And the approaches of carbon nanotubes (CNTs) composite tin based anode are increasing in these years. Integration material can reduce the redundant links section of traditional electrode materials(conductive agent and binder), and increase the utilization ratio for space and material. There for, it is widespread used in tin based anode.The present paper is aimed at solving the problems in commercialization of tin based anode, drawing on structure for integration material of active material and current collector, using electrodeposition and annealing, prepare different structured anode, and study the microstructure and lithium storage properties. The present paper obtain innovative research achievement as follows:(1) In order to improve the cycle performance of Sn-Cu alloy anode, we prepare integration Cu6Sn5alloy anode by annealing under specific temperature based on alternant Sn/Cu multilayer structure. We have prepared Sn/Cu multilayer structure with specific thickness by electrodeposition, and annealed it under specific temperature for different time. Then, we have studied the influence of parameters such as temperature to microstructure and cycle properties of as prepared electrode. The results shows that the alloy composition is different as the activity of atomics are different. The electrode of multilayer structure annealed under200℃for30mins has the best electrochemical property. And it has higher capacity and cycle stability, the capacity is26.9%higher then the traditional electrode. The reason for the higher properties are that the main phase content of electrode is Cu6Sn5, and it has small grain size with changed little after annealing.(2) In order to relieve the pulverization of tin anode during the process of charging and discharging, we have prepared integration Sn-CNTs anode based on CNTs with high strength and high electrical conductivity. We have prepared Sn-CNTs anode by electrodepostion and studied the influence of technological parameter and CNTs diameter on cycle performance.The results show that the content of CNTs changed with the Current density, the CNTs with a diameter of10～20nm shows the best cycle performance. The reason for higher properties of this anode is the content CNTs is the highest and the internal resistance is low.(3) In order to enhance binder strength between the current collector and the active material, and further more to relieve the pulverization of Sn-Cu alloy anode during charging and discharging process, we have designed a Sn/Cu-CNTs layer electrode structure based on Sn-CNTs composite electrode and Cu-CNTs composite coating. This structure can enhance the electrical connection between active material (tin-copper alloy) and collector (copper). We firstly electrode Cu-CNTs composite film on copper foil, then, specific thickness of Sn layer is electrodeposited on it. And finally, Sn-Cu-CNTs integration anode is obtained by annealing. We studied the influence of current density on surface topography of Cu-CNTs layer, content of CNTs, and the influence of annealing temperature on cycle properties. The results show that the electrode annealed under200℃for6h has the best cycle performance. The reason is that it has smaller grain size and the Cu-CNTs layer enhanced the adhesive strength between active material and current collector.(4) In order to enhance the content of carbon nanotubes in the active material and improve the cycling performance of tin-based alloy, we have designed Sn-CNTs/Cu-CNTs composite electrode which combining Sn-CNTs active material with connection layer of Cu-CNTs. We have prepared this composite electrode with composite electrodeposition. Firstly, Cu-CNTs composite coating is electrodeposited with copper as the base material. Then we electrodeposite Sn-CNTs composite coating on Cu-CNTs composite coating to prepared Sn-CNTs/Cu-CNTs composite electrode materials, and then, we have studied the effect of heat treatment time on the electrode cycle performance. The results show that:the cycle performance of the electrode by200℃,6h heat treatment is the best. The capacity of the electrode can still reach584.4mAh/g after100charge-discharge cycle in the1C rate; And its rate performance is very well, its capacity can be attained434.6mAh/g in the20C rate charge and discharge. Electrode cycle performance is optimal for the following reasons:Because of a large number of CNTs is distributed electrode active material in electrode active material, resistance is relatively small and ion conductivity is very well; Pore structure in the electrode can provide a buffer space for the volume change of tin-copper alloy in the process of insertion and extraction of lithium; Electrodes structure is mainly Cu6Sn5, content of Sn and Cu3Sn is relatively low.In this article, we have greatly improved the cycle performance of tin based alloy anode materials through designing of different types structure of the integration tin-based alloy anode materials with low cost. Due to the integration material design of the electrode, it can reduce the redundant connection components, and increase the utilization ratio for space of whole battery. This result has laid a solid foundation for the commercial application of tin based alloy anode material. |
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