| The application of higher power and energy density devices, such as electric vehicle and hybrid electric vehicle, et al., enhances our requirements on the electrochemical performance of LIBs. As the core component of lithium battery, the electrode material play a critical role in the improving the performance of battery. Two major problems exist in the current stage of electrode development. The one is the largely unknown mechanism for the lithium storage, which leads to the great controversy on the lithium storage performance of the specific electrodes. The other is the poor electrical conductivity, weak Li adsorption strength, and the low capacity of the new-type electrodes, which should be strengthened and enhanced in future studies. In our thesis, three typical electrodes: b-Mn O2, MX2 heterostructures, and phosphorene nanoribbons were selected to investigate the lithium storage mechanism of electrodes, as well as the influence of the construction of the ribbon and double-layered heterostrctures on their electrochemical properties. The results presented here provide theoretical guidance for the designment and optimization of high performance Li-ion batteries.It is shown from experiments that different physicochemical properties, such as particle size, surface area, morphology, etc. can show hierarchical electrochemical properties in b-Mn O2. Thus, it is greatly urgent to unveil intrinsic mechanisms associated with storage and discharge of Li ions in b-Mn O2 electrode. The lithiation process of β-Mn O2 has systematically examined by first-principles calculations along with cluster expansion technique. The electrochemical voltages are from 3.47 to 2.77 e V, indicating the strong correlated effects of the β-Mn O2/Li Mn O2 system. The diffusion barrier of Li+ in the tunnel is 0.26 e V, which is comparable to other cathode materials. Besides, the mixed valence state of Mn3+ and Mn4+ during the lithiation process lead to the Jahn-Teller distortion in β-Mn O2 system. Our results indicate that β-Mn O2 has great potential as a cathode material for the high capacity Li-ion battery.To further expand the range of electrochemical properties achieved by MX2（M = Mo, W; X = S, Se） and phosphorene materials, it is desirable to enhance the capacity, Li binding strength, as well as the electrical conductivity of them by layer stacking or cutting to the nanoribbon/nanotube structure. As we first present DFT studies of the adsorption and diffusion properties of Li in MX2 heterostructures, it is shown that the heterostructure can significant enhance the electrical conductivity and Li binding strength of monolayer MX2. Interestingly, the lattice-mismatch of Mo S2/Mo Se2 heterostructure with diversified Li adsorption sites exhibit novel Li diffusion properties, which is highly beneficial for the rapid charge-discharge performance. Besides, by further investigated the adsorption and diffusion properties of lithium ions on the armchair and zigzag phosphorene nanoribbons. It is shown that both armchair and zigzag phosphoren nanoribbons have a significantly enhanced Li binding strength but without sacrificing the Li mobility due to the presence of unique edge states. However, the obvious depravation of the Li binding strength is found in AC-PNR, which is mainly due to its weak stiffness. Thus, it is highly expected to find ways to suppress the undesirable structural expansion, such as fixing the AC-PNR to other substrate materials. |
