| In order to pursuit the green and sustainable development,“lucid waters and lush mountains are invaluable assets”,the study and application of new energy will be an irreversible trend.As the emerging energy source,solar cells,lithium-ion batteries,fuel cells and microbial batteries will have great potential in the fileds of energy storage,waste utilization,and environmental protection,which will make people's ordinary life become more convenient.As a typical representative of new green energy sources,lithium-ion batteries will become one of the most promising industrial pillars in the 21st century.The common graphite material in commercial lithium-ion batteries,has only theoretical capacity of 372 mAh g-1,which cannot meet the requirements of high capacity.Howerver,silicon-based and stannum-based materials have a much higher storage capacity than carbon materials.But such materials are accompanied by a huge volume change during charge and discharge processes.In the meantime,the active materials are easily pulverized and detached,resulting in rapid decline of capacity and short cycle life.Therefore,the anode materials with high specific capacity,high energy density,high stability,high output power and low cost,are still a research hotspot in lithium ion batteries.As an emerging lithium ion battery anode material,organic polymer materials have many advantages,such as low cost,high theoretical capacity,controllable structure and environmental friendliness,etc.Polyimide,as a typical conjugated carbonyl material,has received much attentions.In this paper,polyimide was used as binder to alleviate the volume expansion of silicon anode.Also polyimide was used as negative electrode for lithium ion battery.The specific work of this paper mainly includes the following two parts:?1?The flexible polyimide was used as the binder of silicon anode materials.The porous silicon/carbon nanotube composites were prepared by?-cyclodextrin pyrolysis method to alleviate the volume expansion of the silicon material during charge and discharge processes.It was proved by FT-IR,XRD and SEM that the porous silicon anode material with PI as binder was successfully prepared.And the influence of binder content on the electrochemical performance of silicon anode was discussed.The coin cell was assembled and the electrochemical performance was tested.The PI-Si-20%composite electrode with such a porous structural design delivered better electrochemical performance,with better coulombic efficiency?74.62%at first cycle?,and excellent specific capacity(1285.42 mAh g-1;after 100cycles of 200 mA g-1).Moreover,it also shows superior rate capability(574.35 mAh g-1 at current densities of 800 mA g-1).So,polyimide could alleviate volume expansion of silicon materials.?2?PI-rGO nanocomposites were prepared by in situ polymerization,chemical imidization and high temperature reduction.TEM and SEM have shown that the surface of graphene sheet layer structure was uniformly wrapped with a layer of polyimide polymer,which proved that the graphene monolayer structure has been completely embedded in the polyimide polymer.The PI-rGO composites reduced at different temperatures were assembled into coin battery to test their cycle performance with the current density was 100 mA g-1.Through the tests of charge-discharge process,the first coulombic efficiency of these composites were all maintained above 70%,which proved that the first utilization of electrodes were excellent.Among them,The PI-rGO composite prepared at the reduction temperature of 500°C showed the best cycle performance,with a specific capacity of 514.9 mAh g-1 and a retention capacity of 82.63%after 100 cycles.And it also presented an excellent rate performance(226.5 mAh g-1 at 2 A g-1). |
PDF Full Text Request