Research In Anode Electrode Materials For High Performance Sodium Ion Batteries

For the construction of the society of new energy, wide-scale application of sustainable energy is the most key technique concerning our welfare. To meet the goals, cost and environmental bebefits are the primary factor, yet energy density comes second. Currently, among the various available energy storage technologies, the Li-ion batteries, is one of the most popular energy storage battery. Recently, researchers are trying to search some alternative batteries due to the higher cost to obtain Li. Comparatively, based on the wide availability, environment-friendly, long cycle life and low cost, sodium-ion batteries (SIBs) is fit for large-scale storage. Therefore, it becomes popular for the research on new electrode of more capacities, longer life and fast charge-discharge of sodium-ion batteries.The study in the dissertation mainly concentrates on the synthesis of a series of carbon composite thin films (C/Sb) and porous hard carbon nanofibers as anode materials for SIBs. Meanwhile, the effects of porous nanostructure and carbon composite have been investigated in this thesis.In Chapter 1, a general introduction is given as following aspects:the advantages of sodium ion batteries compared with other rechargeable batteries; the working principle and research status of some regular anode and cathode electrode materials based on their strcture.As effective synthesis methods for thin films, electrostatic spray deposition (ESD) is widely applied in many research areas. In Chapter 2, we set forth the working principle and experimental apparatus and an introduction of other experimental equipments and methods used in the project of this thesis.In Chapter 3, the nickel foam-supported antimony (Sb) nanoparticles encapsulated in three dimension (3D) reticular carbon network (denoted as Sb@3D RCN) films are successfully fabricated by electrostatic spray deposition (ESD) technique. The Sb@3D RCN films are directly used as binder-free anodes for Na-ion batteries which exhibited outstanding rate capabilities and excellent long-life cyclability:at 0.2C the Sb@3D RCN film electrode delivers a reversible capacity of 630mAhg-1, approaching 96% of its theoretical capacity. Cycle stability tests conducted at a high rate of 3C exhibits a reversible capacity of 224 mAhg-1 after 900 cycles. The excellent performance is attributed to the unique Sb@3D RCN:unique reticular, porous, and core-shell structure design that combines a variety of advantages:shorten diffusion length of ion/electron in electroactive particles and easy penetration of electrolyte.In Chapter 4, we choose bacterial cellulose (BC) as template, a high water absorption material, designing and synthesis of N, O-dual doped hard carbon (denoted as NOC) nanofibers network. During the process, we control the specific surface area and pore structure by regulating the KOH amount. The novel material exhibits excellent reversible capacity and super long cycle life:a capacity of 545 mAhg-1 at 100 mAg-1 after 100 cycles and retaining a capacity of 240 mAhg-1 at 2 Ag-1 after 2000 cycles. Moreover, we explore the sodium storage principle of NOC:the high specific surface area contributes to sufficient interact between the electrolyte and electrode, shortening the diffusion path for Na-ion. In addition, the N, O-dual doping in carbon enhances the electrical conductivity and surface hydrophilicity of carbon-based electrodes.On Chapter 4 basis (Chapter 5), we prepared 3D B, N co-doped hard carbon nanofibers (BN-CNFs) that displays high reversible specific capacity (581 mAhg-1 at 0.1 Ag-1), excellent rate performance as well as superior cycling stability (277 mAhg-1 at 10 Ag-1 after 1000 cycles). The observed superb performance of BN-CNFs is attributed to the synergistic effects associated with the large special surface area,3D reticular structure, enlarged carbon layer spacing and the B, N co-doping induced defects.Finally (Chapter 6), a summary on the achievements and deficiency of this thesis is made in the last part of the dissertation. Some prospects and suggestions in improvement are also proposed.