The Investigation Of Transition Metal Oxides Anode Materials For Lithium Ion Batteries

With the rapid development of portable electronic devices and electric vehicles, the commercialized lithium-ion batteries(LIBs) materials can hardly meet increasing needs. Therefore, searching for the high capacity, stable cycling performance candidate materials is the key to the development of LIBs. Herein, we investigate the transition metal oxides which including Fe2O3, TiO2 as anode materials. By tuning the microstructure and morphology, compositing the electrode materials, the relationships between the micro/nanostructure and electrochemical performances have been studied. By investigating the lithiation process and its impact to the microstructure, the relationship between materials microstructure and electrochemistry performances can be well understood. The main contents and results are as follows:(1) Hollow α-Fe2O3 microcubes were fabricated by a facile and cost-effective hydrothermal method in ethanol-water co-solvent system. The as-synthesized microcubes have a uniform size with the edge lengths about 1.5 μm. Time and solvent dependent experiments were carried out to investigate the hollow α-Fe2O3 microcubes formation mechanism. Oriented dissolution mechanism in the ethanol-water co-solvent was proposed which plays a key role to the hollow microtubes. As an anode for lithium-ion batteries, these α-Fe2O3 microcubes exhibit stable capacity of 458 mAh g-1 at 0.1 A g-1 after 100 cycles. Compared with solid one, hollow α-Fe2O3 shows enhanced rate performance. The remarkable electrochemical properties can be attributed to the unique hollow microstructure, which could remain structural stability, relieve stress and increase reaction areas.(2) Single crystalline structure α-Fe2O3 nano-rod was synthesized via a bacterial metabolic effect. Using this biological method in material processing means eco-friendly, mild reaction condition. The formation mechanism of single crystalline α-Fe2O3 nano-rod was studied by a series of detailed characterization. When using as an anode material in lithium-ion battery, α-Fe2O3 nano-rod shows a high performance of 614 mAh g-1 after 100 cycles. Detailed lithiation effect on α-Fe2O3 nano-rod morphology was intensely investigated. We found that as pulverization of α-Fe2O3 nano-rod companys with continuous cycling. While SEI layer network will generated and wrap around the α-Fe2O3 particles to stabilize the structure.(3) TiO2 composites with red phosphorus(RP) by using the high energy ball-milling and chemical deposition methods. Red phosphorus(RP) is an attractive anode material with an ultrahigh specific capacity of 2596 mAh g-1. However, its rapid capacity decay attribute to the volume expansion during the lithiation process presents a noteworthy technical challenge. Meanwhile, titanic oxide which is considered as a good candidate for its high safety and outstanding stability is restricted by the low capacity. Inspired by reinforced concrete structure, we fabricate RP built-in TiO2(A-TiO2) composite in consideration of achieving complementary effects. The study results that the nanosized A-Ti O2 particles completely wrap on the surface of RP, forming the reinforced concrete structure. A-TiO2 could act as concrete to prevent RP from escaping the electrode. While RP plays the role of “steel”, which could improve the electrochemical capacity of composite. As a result, RP/A-TiO2 composite demonstrates an enhanced cycling capacity of 369 mAh g-1 over 100 cycles as well as an acceptable rate capacity of 202 mAh g-1 at the current density of 1 A g-1. The as synthesized RP/A-TiO2 composite shows a great improvement compared with pure A-TiO2, which indicates the potential of “reinforced concrete structure” strategy for TiO2 modification.