New advanced electrode materials for lithium-ion battery

Abstract

This thesis includes five main studies/ first, in order to enhance the conductivity of LiTi₂0₄, a new doping strategy is used and LiTi₂0₄₋ₓCₓ ramsdellite is successfully fabricated. It is found that unit cell parameters a and b decline while c increases with more carbon inserted. The conductivity of LiTi₂0₄₋ₓCₓ increases with more carbon insertion. Material with more carbon shows better reversibility and lower electrochemical polarization observed from potentiostatic curve. The material has better retention rate and rate ability with more carbon substitute doped. LiTi₂0₃.₉₂₅C₀.₀₃₇₅ has 151 mAh∙g⁻¹ capacity under current density of 100 mAh∙g⁻¹ and capacity decreased by 5.57% after 100 cycles.

Second, in order to improve the capacity of LiTi₂0₄₋ₓCₓ, Ti₂0₄₋ₓCₓ is successfully fabricated through topotactic oxidation. It is found that the lattice parameters b and c decline while a keeps stable. With more carbon inserted, the retention ability increases. Ti0₁.₉₆₂₅C₀.₀₃₇₅ has the capacity 320 mAh∙g⁻¹ under 200 mAh∙g⁻¹ and capacity retention loss by 9.1% per 100 cycles due to the balance of high conductivity and disordered channel resistance.

Third, in order to study the process of lithium insertion, the structures and the atom sites of LiTi₂0₄₋ₓCₓ ( R ) are obtained through refinement of the neutron diffraction patterns. The unit cell parameters a and b increase while c keeps stable for more lithium, atoms insertion. The channels for lithium insertion become wider and more round with lithium arranged in a line when x rises in the range of 0<x<0.5. When the x increases to 1, the channels turn into ordered parallelogram.

Fourth, the lithium-contained spinelloid (a potential cathode material) is explored, but it is not found in this work. But spinels LI₁₋₀.₅ₓFe₂.₅ₓM₁₋ₓP₁₋ₓO₄ (M=Fe, Co, Ni, Mn) are found and phosphorous insertion makes the structure stable during cycling.

At last, to enhance the energy density, the 3D electrode is fabricated in in-situ growth by infiltration method. By powder infiltration, the load of activity material reaches over 60% of electrode mass. The morphology is porous and the particle size of the activity material is 20nm. The energy density based on LiCoO2 (250 WH∙g⁻¹) is much higher than that of the traditional (200 WH∙g⁻¹) 2D electrode reported.