| In recent years,with the upgrading of portable electronic devices and the popularization of new energy vehicles,more requirements are put forward for the energy density of the main power source lithium-ion batteries.Limited by its low theoretical capacity,traditional graphite anode is destined to be eliminated.In contrast,conversion-type anodes and alloy-type anodes with higher specific capacities are of more research significance.Among them,molybdenum trioxide anodes and silicon anodes have attracted a lot of attention due to their extremely high theoretical capacities(the theoretical capacity of MoO3 is 1117 mAh g-1 and the theoretical capacity of Si is 4200 mAh g-1).However,the pratical application of these two materials are both hindered by the large volume expansion during cycling and the poor electrical conductivity.It is very important to find a universal modification method.This paper starts with two strategies:designing nanostructured molybdenum trioxide/carbon composite anode material and developing new silicon anode binder,aiming to obtain anode materials with high specific capacity and stable cycling performance.The main research contents are as follows:(1)MoO3-C composites are prepared by the pyrolysis of PMA-BNP intermediate,which is obtained through the reaction between organic boronate nanoparticles(BNP)and phosphomolybdic acid(PMA).The obtained composites possess hierarchical pomegranate-like nanostructure.The highly active nitrogen-doped carbon core can effectively enhance the conductivity of the composites,and the molybdenum trioxide particles embedded on it are the main source of capacity.The ultra-thin carbon layer ensures the structural stability of the composites.(2)Comparing the morphology and electrochemical performance of products obtained at different calcination temperatures,it is found that 650? is the optimal pyrolysis temperature.Lower temperature will lead to thicker carbon shell,which reduces the specific capacity of anodes.Higher temperature will lead to the sublimation of MoO3 and the destruction of ultra-thin carbon shell,resulting in the reduction of the structural stability.PB650,as the best product,exhibits excellent cycling stability and rate performance.At the current density of 0.1 A g-1,an extremely high capacity of 1380 mAh g-1 is obtained and a reversible capacity over 800 mAh g-1 is maintained for 100 cycles.Even at the high current density of 5 A g-1,a stable capacity of 400 mAh g-1 can be maintained for more than 1000 cycles.(3)A novel binder for micron silicon anode is prepared based on the covalent crosslinking between polydopamine(PDA)and polyacrylic acid(PAA),in which the PDA layer is pre-doped with Fe3+ through a hydrothermal process.160? is found as the optimal hydrothermal temperature by analyzing the the composition information of the materials obtained at different hydrothermal temperatures and the surface morphology of corresponding anodes after cycling.At this temperature,powerful metal-chelated bond is formed between Fe3+ and pyrrolic nitrogen in PDA,which enhances the mechanical strength of PDA layer and enables it with a better ability to limit the volume expansion of silicon anodes.As a result,the volume expansion of Si@Fe3+-PDA-160/PAA anode after 100 cycles is only 47.2%.In addition,the doping of Fe3+also enhances the electrochemical activity of silicon anodes,as the CV curves of anodes doped by Fe3+ possess stronger peak intensity and larger peak area.(4)Batteries with Si@Fe3+-PDA-160/PAA anodes exhibit stable capacity of 3000 mAh g-1 in the first 30 cycles,with a nearly 100%coulombic efficiency.The capacity retention is 80%after 100 cycles.A rather good rate performance is also achieved with high capacities of 2800,2100,1400 and 350 mAh g-1 at current densities of 0.2,0.5,1 and 5 C,respectively. |
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