| Pollution of the environment and lack of oil resources are two of the momentous troubles Which are hindering the progress of human technological,and the conversion and use of clean energy is an effective way to address these issues.Reveal lithium-ion batteries 's talent,such as high energy density and power density,they emerge from many different energy storage technologies and have attracted concern over the whole creation in the past several decades.Since their successful commercialization in the 1990 s,rechargeable lithium-ion batteries have dominated the market for portable electronics,driving the rapid development of mobile end devices such as laptops,tablet PCs,Cellular Phone,digital cameras,etc.products.In recent years,they have become a candidate technology for large power systems such as electric vehicles and smart grids.However,existing lithium-ion battery commodities are still a long way from meeting the required conditions,and conventional lithium-ion batteries are mainly faced with problems such as low energy density,high cost and poor safety performance.Therefore,the development of electrode materials with high energy density per unit volume,abundant resources for easy processing and synthesis,and high efficiency and stability has become the primary goal of researchers.Several types of materials currently under study have inherent problems that are more or less difficult to solve: carbon materials have a low theoretical capacity(372 m Ah/g);silicon materials have a volume expansion rate of up to 400% during the charging and discharging process,which can easily cause negative electrode failure and is not conducive to cycle life;transition metal oxides react slowly in the fully charged and discharged state,which is not conducive to fast reaction kinetics.Therefore,the search for new anode materials with high energy density,good structural stability,high ion transport efficiency,clean and efficient,good safety and low cost is an inevitable trend.Organic anode materials show their advantages as a new type of anode material,where carbonyl compounds undergo enolization during the charging and discharging process to provide active sites for embedded lithium.It is a potential candidate for next-generation high-performance lithium-ion electrode anode materials.Therefore,the present work takes polyimide as a starting point to investigate its self-assembly behaviour from three perspectives,including synthesis conditions,chemical structure and stencil assembly,and to investigate its impact on lithium-ion battery materials.(1)A series of PI products were prepared by adjusting different process parameters in the solvent heat process,i.e.solvent heat time,PAA concentration and degree of pre-cyclisation.Combined with the results of FTIR,XRD and TGA tests,it was found that the PI products obtained by changing the process conditions showed little change in terms of chemical structure,crystallinity and thermal stability.However,it can be clearly observed from the SEM graphs that the PI products obtained by prolonging the thermal imidiation time showed a tendency of more complete nanoparticle structure and larger particle size in terms of microscopic morphology;the PI products obtained by decreasing the PAA concentration had a looser structure and smaller size;the higher the degree of chemical cyclization,the more imperfect the PI structure and smaller the size,and the specific surface area and pore volume of PI products with different morphology also differed greatly.The higher the degree of chemical cyclization,the more imperfect the PI structure and the smaller the size.This difference in microscopic morphology also has an impact on the electrochemical properties.For example,PI-4.4 g/m L with a high specific surface area of 92.9m2/g has a mass specific capacity of nearly 800 mAh/g after 100 cycles,while PI-original with a lower specific surface area of 78.4 m2/g has a mass specific capacity of nearly 1000 m Ah/g after100 cycles.(2)A series of PI products with different chemical structures were obtained by changing the reaction monomer under the same process conditions,all of which had excellent thermal stability;the introduction of alkyl chains into the chemical structure resulted in softer molecular chains,which were not as well ordered as the rigid structure and therefore had poorer crystallisation properties.PI-1,PI-2 and PI-5 all exhibit round spherical nanoflowers;PI-3 and PI-6 consist of bent nanosheets stacked in a "bow" shape with a tight centre and loose sides;PI-4 is somewhere between a "bow" and a "bow" shape.PI-4 is an intermediate state between the "bow" and spherical nanoflowers.The "bow" shape of PI-3 and PI-6 was found to be more conducive to achieving the theoretical capacity of 1398.6 m Ah/g and 1610.9 m Ah/g after 100 cycles at 0.1 A/g,which is 1473.4 m Ah/g and 1871.3 m Ah/g respectively.(3)GO@PI composites were prepared by in situ polymerization using GO as a template,and GO@PI composites with different GO mass fractions were obtained by adjusting the amount of GO added to the system.The resulting GO@PI and r GO@PI composites were used as active materials for the preparation of lithium anodes and the electrochemical properties were compared with those of pure PI electrodes.It was determined by SEM that the GO@PI composites were obtained by growing PI nanosheets as building blocks on GO,and that the PI nanosheets would preferentially grow vertically on the GO surface until the GO surface was full of PI nanosheets before additional PI nanosheets self-assembled into spherical nanoflowers.The morphology of the15% r GO@PI composites obtained after the thermal reduction of 15% GO was also not significantly altered.The specific charge capacities of the PI,15 % GO@PI and 15 % r GO@PI electrodes after 100 cycles at 0.1 A/g were 969.4 m Ah/g,1127.1 m Ah/g and 1128.8 m Ah/g,respectively,compared to 1202.4 m Ah/g,1206.2 m Ah/g and 1215.2 m Ah/g for the first cycle.The capacity retention rates of 80.6 %,93.4 % and 92.9 % demonstrate that the introduction of GO has significantly improved the cycling performance of the composite electrodes. |
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