Ab initio Investigations of Lithium Intercalations in Anode Materials for Lithium-ion Batteries

锂离子电池与传统的二次电池相比保持了电压高、能量密度大、重量轻，又具有安全性能好、自放电小等优点，使之在便携电子设备以及电动汽车等方面有广阔的应用前景。开发锂离子电池的关键之一就是寻找合适的电极材料，使电池具有足够高的储锂量和很好的锂脱嵌可逆性，以保证电池的高电压、大容量和长循环寿命的要求。在应用中，大多以石墨和各种碳材料作为负极材料，但是碳负极材料存在一些自身的缺点。为了寻找性能更高的负极材料，许多新型的锂离子负极材料特别是金属间化合物在近来的锂离子电池研究中引起了相当的重视。 尽管近年来采用第一性原理对锂离子电极材料的理论研究取得了一些成功，但是大多集中于正极材料，对锂离子电池负极材料的...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 o...学位：理学博士院系专业：物理与机电工程学院物理学系_凝聚态物理学号：B200124001

Effects of Na-substitution on structural and electronic properties of Li2CoSiO4 cathode material

Na-substituted dilithium orthosilicate Li2CoSiO4 was investigated by performing density functional theory calculations within the GGA+U framework. The effects of Na-substitution on the electronic structures and structural properties of Li2CoSiO4 were presented. The results show that the Na-substitution on Li sites in Li2CoSiO4 induces a lowering of the conduction bands and a narrowing of the band gap, which could be helpful for enhancing the electronic conductivity. On the other hand, the Na-substitution on the Li ions in Li2CoSiO4 leads to the expansion of interlayer space of the adjacent corrugated layers. This lattice expansion effect would benefit the Li ion diffusion.National Basic Research Program of China [2007CB209702]; National Natural Science Foundation of China [10774124, 20473068

Interplay between gadolinium dopants and oxygen vacancies in HfO 2: A density functional theory plus Hubbard U investigation

The influence of gadolinium (Gd) doping on the oxygen vacancy (V O) in monoclinic HfO2 have been studied by the first-principles calculations within the spin-polarized generalized gradient approximation plus Hubbard U approach. It is found that the Gd dopant and V O show strong attractive interaction, resulting in a cooperative effect that the substitution of Gd for Hf (GdHf) would increase the probability of oxygen vacancies generation and vice versa. The GdHf is more energetically favorable to be next to the vacancy site of a three-coordinated oxygen (O3), forming a complex defect GdHf + V O. A single GdHf acts a hole donor and passivates the defect states of VO. Our results suggest that the decrease of the VO-related defect states observed in the photoluminescence spectra of Gd-HfO2 is because Gd doping passivates the defect states of V O, rather than caused by decrease of VO concentration. Our findings would clarify the debate about the influence of Gd doping on the oxygen vacancies in HfO2. ? 2014 AIP Publishing LLC

Interplay between gadolinium dopants and oxygen vacancies in HfO2: A density functional theory plus Hubbard U investigation

The influence of gadolinium (Gd) doping on the oxygen vacancy (V-O) in monoclinic HfO2 have been studied by the first-principles calculations within the spin-polarized generalized gradient approximation plus Hubbard U approach. It is found that the Gd dopant and V-O show strong attractive interaction, resulting in a cooperative effect that the substitution of Gd for Hf (Gd-Hf) would increase the probability of oxygen vacancies generation and vice versa. The Gd-Hf is more energetically favorable to be next to the vacancy site of a three-coordinated oxygen (O3), forming a complex defect Gd-Hf + V-O. A single Gd-Hf acts a hole donor and passivates the defect states of V-O. Our results suggest that the decrease of the V-O-related defect states observed in the photoluminescence spectra of Gd-HfO2 is because Gd doping passivates the defect states of V-O, rather than caused by decrease of V-O concentration. Our findings would clarify the debate about the influence of Gd doping on the oxygen vacancies in HfO2. (C) 2014 AIP Publishing LLC

Interaction and electronic structures of oxygen divacancy in HfO2

Project on Graduate Students' Education and Innovation of Jiangsu Province [CXZZ12_0388]We have studied the interaction between two neutral oxygen vacancies and the electronic structures of oxygen divacancy in the monoclinic phase of HfO2 by performing the first-principles calculations. It is found that the vacancyvacancy interaction depends not only on the distance but also on the coordination of the removed oxygen atoms. The oxygen divacancy is formed energetically by the removal of two fourfold coordinated oxygen atoms (O4) with a distance of about 2.73 angstrom. The interaction between two O4 vacancies is attractive, indicating that the O4 vacancies tend to form stable cluster in HfO2. The oxygen divacancy induces two in-gap defect levels, which correspond to a bonding state and an anti-bonding one. These results would provide insightful information to understand the formation of conductive filaments in HfO2-based resistive random access memory devices

Elastic anisotropy and phonon focusing in NiAl: Atomic study

Natural Science Foundation of the Education Department of Henan Province of China [2009B590001]; Henan Science and Technology Agency of China [092102210314, 132102210207]; State Key Laboratory of Superhard Materials (Jilin University) [201107]; National Natural Science Foundation of China [11104127]We have investigated the anisotropy and phonon focusing of NiAl using ultrasoft pseudopotentials within the generalized gradient approximation correction in the frame of density functional theory. Theoretical calculation of the three dimensional slowness surfaces gives insights into the mixing of longitudinal and transverse modes and shows the origin of the phonon caustics. The phonon focusing due to the elastically anisotropy, and the phonon phase and group velocities are explained. In general, the propagation of elastic waves in crystals is strongly affected by the elastic anisotropy of the lattice. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved

First-principles calculation of the vacancy formation energies in LiAl

【中文文摘】LiAl是一种非常典型和有重要用途的金属间化合物 .采用平面波展开和第一原理赝势法 ,计算了LiAl化合物中Li空位和Al空位的形成能和空位周围的原子弛豫 ,讨论了空位形成时电荷密度的重新分布、相应的电子态密度以及能带结构等性质 【英文文摘】The LiAl is a typical intermetallic compound which has many important applications. We have employed the first principles pseudopotentials and the plane wave energy band method to calculate the vacancy formation energies of Li and Al vacancies in LiAl intermetallic compound as well as the atomic relaxations around the vacancies. The charge redistribution around the vacancies, electronic density of states and their band structures are also discussed.国家自然科学基金 (批准号 :10 1740 5 8)资助的课

The phase stability and elastic properties of MgZn2 and Mg 4Zn7 in Mg-Zn alloys

To understand the precipitates in Mg-Zn alloys, we perform first-principles calculations to investigate the stability and elastic properties of Laves MgZn2 and monoclinic Mg4Zn7. We find that the relative stability of MgZn2 and Mg4Zn7 is dependent on their compositions, implying that either one or both of the phases can exist within β1′ precipitates. The elastic moduli indicate that the strain resistance of MgZn2 and Mg4Zn7 is much greater than that of Mg. ? 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

First-Principles Study of Lithium Adsorption and Diffusion on Graphene with Point Defects

National Natural Science Foundation of China [20973175, 20803080]; 973 Program [2010CB933501]To understand the effect of point defects on the Li adsorption on graphene, we have studied the adsorption and diffusion of lithium on graphene with divacancy and Stone-Wales defect using the first-principles calculations. Our results show that in the presence of divacancy Li adatom energetically prefers the hollow site above the center of an octagonal ring rather than the top sites of carbon atoms next to vacancy site. In the case of Stone-Wales defect, Li atom is energetically favorable to be adsorbed on the top site of carbon atom in a pentagonal ring shared with two hexagonal rings, and such adsorption results in a bucking of graphene sheet. For divacancy and Stone-Wales defects in graphene, their interactions with a Li adatom are attractive, suggesting that the presence of point defects would enhance the Li adsorption on graphene. The difference charge density and the Bader charge analysis both show that there is a significant charge transfer from Li adatom to it nearest neighbor carbon atoms

Ab Initio Calculation of the Formation Energies of Lithium Insertion in Mg_2Sn

【中文文摘】Mg2Sn是近来很受重视的锂电池负极材料.使用基于混合基表示的第一原理赝势法,计算了Mg2Sn的各种锂嵌入情况时的形成能以及相应的电子结构.讨论了锂嵌入时的体积变化、能带结构、电子态密度以及电荷分布等性质.计算表明,锂嵌入到主体材料的间隙位置时平均每个锂原子的形成能都大致在2.2eV. 【英文文摘】Mg2Sn has attracted a great attention in recent investigations as an anode material for lithium batteries. An ab initio method with mixedbasis and normconserving nonlocal pseudopotentials has been used to investigate the formation energies and electronic properties of lithium insertion in Mg2Sn. The changes of volume, band structures, electronic density of states and charge density distributions for lithium intercalation in Mg2Sn are discussed. The formation energy of Li insertion in Mg2Sn is found to be about 2. 2 eV per lithium.国家自然科学基金(10174058)资