| Lithium-ion battery is widely used due to its numerous advantages. However, deficiencies are still present in such commercialized battery. First of all, graphite is commonly used as negative materials and Li ions tend to precipitate on its surface to form lithium dendrites, which may penetrate the membrane leading to internal shortage and safety issue. Secondly, battery capacity is confined by the structure of graphite, resulting in failure to meet the increasing demands of device performance. Last but not least, quick charge technology, in the meantime, is one of the public earnest concerns. Therefore, in order to meet the demands for future use, the cycle performance and rate capability of lithium ion battery should be improved under the circumstance of not apparently changing the size of the battery.The perfection of negative materials can effectively extend the lifespan and improve the rate capability of the lithium ion battery. The methods to improve negative materials include, without limitation, reducing the size of materials, creating hierarchical nanoscale structure and combining multiple kinds of materials. The reduction of material sizes to nanoscale can diminish the transport path of Li ions, beneficial for rapid solid diffusion. Besides, hierarchical nanoscale structure, especially nanoarrays, may enlarge the contact area between electrodes and electrolyte. Furthermore, the hybridization of multiple kinds of materials will overcome the shortage of each single material, which enhances the integrated performance through the synergistic effect. On the other hand, the advantages in low cost, abundant reservation on earth, being environmentally friendly, low toxicity and theoretical high capacity, make metal oxides/sulfides applicable for massive production and show their potentials to replace commercial graphite. Additionally, the relatively high working potential of metal oxides/sulfides can effectively prohibit the formation of the lithium dendrites. TiO2, unrivaled amongst them, stands out because of its "zero-strain" characteristic which bestows excellent stability upon the electrodes. Moderate modification of TiO2 is envisaged to deliver sustainable yet decent capacity. So, this thesis deals with combining high-capacity metal oxide/sulfide with TiO2 nanosheet arrays used as stable substrates in order to realize the enhancement of both capacity and stability. The two perspectives following are mainly focused on:Firstly,we synthesized interconnected TiO2@NiO nanosheet array anode material by a facile method.To begin with,TiO2 nanosheet arrays were grown on the Ti substrate, which would be used as the backbone afterwards,and then combined with large-area NiO nanosheets of high capacity.The aforementioned structure showed good cycle performance through a series of electrochemical measurements.The enhanced performance is ascribed to effective utilization to the "zero-strain" nature of TiO2.The successful combination of the two materials showed better battery performance rather than single component.Additionally,it is discovered that different deposition amount of NiO had a significant impact on battery performance,which means stable and high capacity cycle performance cannot be accessible by neither insufficient nor excessive input of NiO.Appropriate proportion of NiO could reach the best result,and in terms of this experiment,the optimal condition for deposition was 10 minutes. secondly,TiO2@MoS2 nanosheet array negative material was fabricated through a two-step hydrothermal method.As mentioned ahead,TiO2 nanosheet arrays were applied as the backbone directly.To achieve optimal performance,we controlled the amount of MoS2 loaded on the backbone by varying the duration of the second hydrothermal reaction.Structural characterization and electrochemical measurements indicate that reaction duration of 22 hours was the most ideal sample and of the highest capacity with 457.0 mAh/g after 100 cycles.Thanks to the good stability of TiO2 and positive synergistic effect between the two types of materials,the design of TiO2@MoS2 demonstrated favorable cycle performance. |
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