| Nowadays,with the rapid development of industry and the rise of artificial intelligence,the structure of the word's energy system must be changed to cope with the depltion of fossil fuels and the intensification of greenhouse effect.As the potential alternative to traditional fossil fuels,renewable energy resources have become an inevitable trend for their large-scale application,such as solar energy,wind energy,tidal energy,hydro energy,etc.However,these generation energy are geographically unevenly distributed and intermittent,making them difficult to use directly without affecting the weather/climate.Therefore,it is necessary to develop effective energy storage technology to store the intermittent energy generated by these resources.Among the existing energy storage technologies,secondary alkali metal ion batteries,such as lithium ion batteries(LIBs),sodium ion batteries(SIBs)and potassium ion batteries(PIBs)have been widely studied and applied in recent years.One major key to wholly develop alkali metal ion batteries is that they have the advantage of large specific capacity,long cycle life,sustainable energy supply,low cost and environmental friendliness,etc.The key parameters to evaluate the comprehensive performance of batteries during practical application mainly include energy density,power density,cycle stability and rate performance,and these parameters are closely related to electrode materials.Although some anode materials with excellent electrochemical performance have been reported for alkali metal ion batteries,there are still some challenges to explore the anode materials with high capacity and long cycle life of LIBs,SIBs and PIBs,as well as the change of morphology and structure in the process of electrochemical energy storage.Therefore,in-depth study of the electrochemical reaction mechanism between electrode materials and alkali metal ion batteries can provied theoretical guidance and experimental basis for the design of high-performance alkali metal ion batteries.In this pater,we prepared several new electrode materials from the perspective of material design and preparation by means of nano-structuralization/morphology control,compositing,self-healing and defect chemistry.And the application performance and mechnism of the prepared nanomaterials in alkali metal ion battery system were systermatically discussed.Through the optimization of electrode materials or systems,the ion migration rate and electron transfer rate can be improved,then the process of electrochemical reaction kinetics is accelerated.As a result,the advanced LIBs/SIBs/PIBs energy storage system with high rate performance and long cycle life can be realized.The main research contents and results are as follows:(1)In order to solve the problem of poor cycle performance and rate performance caused by the pulverization of traditional alloying anode materials,the LMNPs/SAN@PAN/SAN nanofiber film was prepared by using the self-healing property of room-temperature liquid metal Ga-Sn alloy combined with coaxial electrospinning method.The LMNPs@CS core-shell nanofibers were obtained by calcination in Ar at high temperature.The formation mechanism of the LMNPs@CSs and the effects of electrospinning parameters(flow rate ratio of inner and outer layers,polymer concentration of inner and outer layers)on the morphology of the composite fibers were further studied.The lithium storage performance of LMNPs@CSs as a free-standing electrode for LIBs was studied.Compared with the pure LMNPs and hollow carbon fiber,the anode of LMNPs@CSs shows obvious advantages in electrochemical performance due to the good synergistic effect between LMNPs and hollow carbon shell layer as well as the self-healing ability of LMNPs.The constructured LIBs has excellent rate performance(the specific capacity is 603.9 m A h g-1 at 1000 m A g-1,499 m A h g-1 at 2000 m A g-1)and long cycle life(552 m A h g-1 at 1000 m A g-1 after 1500 cycles).(2)Design and fabrication of pomegranate-like bismuth@carbon nanospheres(PBCNSs)with excellent performance,and investigation of their applications as electrode materials for SIBs.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)showed that this PBCNSs had pomegranate-like structure,and the bismuth nanoparticles(Bi NPs)were uniformly dispersed on the carbon sphere substrate.High-resolution transmission electron microscopy(HR-TEM)and X-ray diffraction(XRD)showed that these ultrafine Bi NPs loaded on the carbon spheres had good crystallinity.In addition,we prepared the PBCNSs electrode and studied the electrochemical properties when used as the anode for SIBs.The composite has a hierarchical structure with ultra-small Bi NPs embedded within carbon spheres which not only efficientively buffer the volume change of Bi NPs during the sodiation/desodiation but also increase the contact area between electrolyte and electrode and can enhance the diffusion rate of the Na ions.As a result,the electrode has excellent rate performance and cycle stability in the SIBs,demonstrating a capacity of 400.3 m A h g-1 at a current density of 200 m A g-1 and 372.5 m A h g-1 at a high current density of 25 A g-1.Besides,PBCNSs exhibit an extremely long cycle life with the specific capatity of 340 m A h g-1 after16000 cycles at 20 A g-1.Even at a high loading mass(11.33 mg cm-2),the reversible capacity is as high as 327.2 m A h g-1 at 0.5 A g-1.These results indicate that the PBCNSs can significantly improve the rate performance and cycle life of SIBs.(3)In order to explore the effect of material defects on migration rate of potassium ion,bilayer-Bi12O17Cl2 nanosheets(BBNs)with abundant oxygen vacancies(OVs)were designed and constructed.BBNs nanomaterials were prepared by a simple one-step hrdrothermal method,and studied the effects of hydrothermal temperature on the crystal structure and potassium storage properties of Bi12O17Cl2.As an anode for PIBs,it provide a high rate performance(534.1 m A h g-1 at 0.5 A g-1 and 420 m A h g-1 at 10 A g-1).Moreover,the specific capacity can still reach 198 m A h g-1 after 1500 cycles at a current density of 10 A g-1.This excellent performacne is mainly due to the bilayer structure that can offer a large electrode-electrolyte contact interface and a short path for K+diffusion.In addition,we further discussed the storage mechanism and diffusion coefficient of K+through in-situ electrochemical analysis and GITT test. |
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