Ab Initio Investigations Of Lithium Intercalations In Anode Materials For Lithium-ion Batteries

In comparison with the conventional secondary batteries, such as nick-metal hydride, nickel-cadmium or lead-acid, lithium-ion batteries (LIBs) have many outstanding features: high voltages, high energy densities (both volumetric and gravimetric energy densities), low self-discharge rate, no memory effect, wide temperature range of operation, excellent cycle life and safety characteristics. These outstanding properties make LIBs be the current rechargeable power source of choice for portable electrics devices and electric vehicles. In the development of LIBs the key step is to look for more suitable electrode materials, which should store enough lithium and have excellent reversibility of lithium intercalation/extraction in order to fulfill the cell performance of high voltage, high energy density and excellent cycle life. In commercial applications the graphite and other carbonaceous materials were widely used as negative electrode materials, however, these carbon-based anode materials have some self-blemish. To get better anode materials, a large number of alternative possibilities for anodes of LIBs have recently been studied and reported in the literatures. Especially, the intermetallic compounds have attracted special attentions in the research of anode materials for LIBs.First principles calculations have been successfully used to identify the cathode materials for lithium ion batteries. However, there are less theoretical studies on the anode materials. We therefore apply the model of theoretical studies on cathode to anode materials. We perform first-principles calculations to investigate the lithium intercalations in anode materials such as intermetallic compounds, in order to provide some theoretical guides for the experimental studies of anode materials.This thesis consists of two parts. In the first part we present the basic theories employed in this study and the first-principles methods used for the present calculations. We firstly introduce the density function theory (DFT), which includes major ideas of DFT, Hobenberg-Kohn theorem, Kohn-Sham equations, and the approximations for exchange andcorrelations (the local density approximation and the generalized gradient approximation). We then describe the details of computational methods used in our work, i.e. the ab initio pseudopotential methods with the plane wave and mixed basis expansion of wavefunctions. We also present the major characters of the Vienna ab initio Simulation Package (VASP): a total-energy plane wave code. In addition, the principles of lithium ion batteries and the characteristics of cathode and anode materials were also introduced. We also described the models of first-principles calculations on the electrode materials and presented the approximations and concepts used in these models.In the second part, the ab initio pseudopotential method has been employed to investigate the lithium intercalations in intermetallic compounds anode materials such as MSb (M = Al, Ga, and In), CuSn, MgSn and SnSb, the geometrical structures and electronic properties of Mg2n and Li2MgSn, and the electronic structures of CuS2, CuSe2 and CuTe2. In the fourth chapter, the lithium intercalations in AlSb, GaSb and InSb have been studied by using the mixed basis ab initio norm-conserving pseudopotential method. The formation energies, changes of volumes, electronic structures and charge densities of lithium intercalations in zinc blende-type antimonides Li,MSb (M = Al, Ga, and In) are presented. Our calculations show that during lithium insertions in MSb the lithium intercalation formation energies per lithium atom are all around 2.0 eV. The volume expansions of AlSb, GaSb and InSb due to lithium insertions are relatively large, which might imply that the limit of Li intercalation in antimonides should be small. In the fifth chapter, the pseudopotential methods with mixed-basis and plane waves have been employed to investigate the non-carbon-baring anode materials, such as CuSn with zinc-blende structure, Mg2Sn with anti-CaF2 structure and SnSb wi...