| Green energy technologies have been more and more important because of growing environmental pollution and energy crisis. Among them, lithium-ion batteries (LIBs) have been one important area of rechargeable batteries, ascribed to light-weight, high capacity, long cycle life, environmental benignity and no memory effect. On the other hand, the resources distribution and cost problems of LIBs would limit their development in the future. Benefiting from wide resources distribution in the world and low cost, sodium-ion batteries (NIBs) have attracted intense attention as one important alternative to LIBs. Graphite-based materials have been widely used in current commercial LIBs as anode materials due to excellent cycling stability. However, the low specific capacity of graphite (372 mA h g-1, LiC6) limited the energy density of LIBs. In addition, the low working potential of graphite in LIBs would lead to lithium deposition on the surface, forming lithium dendrites and resulting in safety problems. For NIBs, due to narrow interlayer spacing, graphite is not proper for sodium insertion. Therefore, much efforts have been devoted to research and development (R&D) of anode materials for LIBs & NIBs with high electrochemical performance. Among them, carbonaceous and alloy-type anode materials have gradually become next-generation anode materials for LIBs & NIBs with high electrochemical performance, due to higher specific capacity. The thesis focuses on the study of porous carbonaceous, germanium-based and phosphorus-based electrode materials, designing and fabricating several anode materials for LIBs & NIBs with high electrochemical performance.Chapter 1 gives a review of development, reaction mechanism and composition of LIBs & NIBs, focusing on summary of anode and cathode materials base on crystal structures and reaction types. Based on the summary, research background and strategies have been also provided.Chapter 2 gives a summary and a detailed description of raw materials, synthesization and characterization methods and equipment used in the experiment.Chapter 3 shows a strategy to prepare highly porous carbon nanofibers (HPCNFs) by combining electrospinning and activation with air as anode materials for LIBs. Through partial burning, the HPCNFs films displayed highly porous structure and excellent flexibility, which can be directly used as working electrodes for LIBs. It delivers a high reversible capacity as high as 1780 mAhg-1 after 40 cycles at 50 mAg-1 and ultralong cycle life (1550 mAhg-1 after 600 cycles at 500 mAg-1), and excellent rate performance.Chapter 4 shows a strategy to prepare porous carbon nanofibers (P-CNFs) by combining electrospinning and template-based methods as flexible anode materials for NIBs. Through the soft-template based methods, the P-CNFs also shows a variety of pores, providing numerous lithium-ion storage sites Benefiting from the porous structure, P-CNFs displays ultralong cycle life, delivering a high capacity of 140 mA h g-1 after 1000 cycles at a current density of 2 C.Chapter 5 provides a strategy to fabricate germanium-based anode materials by electrospinning, obtaining one flexible anode materials with germanium nanoparticles encapsulated in carbon nanofibers (Ge@CNFs) for LIBs. The prepared structure would accommodate the volume change of Ge nanoparticles during cycling, improving the cyclability with only 0.1% decay per cycle in capacity. In addition, the 3D interconnected CNFs would enhance electronic conductivity and rate capacity, realizing a high capacity of 300 mA h g-1 at a high current density of 25 C.Chapter 6 provides another strategy to prepare carbon coated germanium nanowires grown on the surface of carbon nanofibers (c-GeNWs-CNFs) by combining electrospinning and in situ CVD process and studies the effect of different dimension on the electrochemical performance of germanium-base materials. The hybrid Ge anode material showed excellent electrochemical performance with a high reversible capacity of 1520 mA h g-1 at a current density of 0.1 C and superior rate capacity of 480 mA h g"1 at a current density of 10 C.Chapter 7 provides a strategy to prepare red phosphorus (red P) based anode material with amorphous red P embedded in highly ordered mesoporous carbon (P@CMK-3) for LIBs & NIBs. The CMK-3 offers enough void space to accommodate the volume change of red P, finally improving the electrochemical performance of P@CMK-3. For LIBs, P@CMK-3 displays ultralong cycle life with a high capacities of 1500 mA h g-1 after 800 cycles at 1.2 C and another high capacity of 1000 mA h g"1 after 1000 cycles at 5 C. In addition, it delivers excellent sodium-ion storage performance. the highly ordered mesoporous structure of CMK-3 enhanced both electron and ions transfer, highly improving the rate capacity. Especially, P@CMK-3 has realized excellent capacity at current densities higher than 2 C. |
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