Na+替位掺杂对Li2MnSiO4的电子结构以及Li+迁移过程的影响

在锂二次电池中, 硅酸锰锂作为正极材料得到广泛研究, 但其固有的电子和离子电导率较低, 直接影响着电池的功率密度和充放电速率. 本文建立了不同浓度的Na⁺离子替位掺杂Li⁺离子形成的Li_1-xNa_xMnSiO₄(x=0, 0.125, 0.25, 0.5)结构, 采用第一性原理的方法, 研究了掺杂前后硅酸锰锂的电子结构以及Li⁺离子的跃迁势垒. 发现在Li⁺位替代掺杂Na⁺, 导带底的能级向低能方向发生移动, 降低了Li₂MnSiO₄ 材料的禁带宽度, 有利于提升材料的电子导电性能. 随着掺杂浓度的升高, 禁带宽度逐渐变窄. CI-NEB结果表明, 在Li₂MnSiO₄体系中具有两条有效的Li⁺离子迁移通道, 掺杂Na⁺以后扩大了Li⁺ 离子在[100]晶向上的迁移通道, Li⁺离子的跃迁势垒由0.64 eV降低为0.48, 0.52和0.55 eV. 掺杂浓度为 x=0.125时, 离子迁移效果最佳. 研究表明Na⁺掺杂有利于提高Li₂MnSiO₄材料的离子和电子电导率.     

锂离子电池正极材料Li2FeSiO4的电子结构与输运特性

采用基于密度泛函理论第一性原理方法, 研究了对称性为Pmn2₁的正交结构聚阴离子型硅酸盐Li₂FeSiO₄及其相关脱锂相LiFeSiO₄的电子结构, 并进一步采用玻尔兹曼理论对其输运性质进行计算. 电荷密度分析表明, 由于强Si–O共价键的存在使Li₂FeSiO₄晶体结构在嵌脱锂过程中始终保持稳定, 体积变化率只有2.7%. 能带结构与态密度计算结果表明, 费米能级附近的电子结构主要受Fe-d轨道中电子的影响, Li₂FeSiO₄ 的带隙宽度明显小于LiFeSiO₄, 说明前者的电子输运能力优于后者. 输运性质计算表明, 电导率在300–800 K时对温度的变化并不敏感, 同时也证明了Li₂FeSiO₄晶体的电导率大于LiFeSiO₄晶体, 与能带和态密度分析结论一致.     

LixFePO4(x=0.0, 0.75, 1.0)电子结构与弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理研究方法,计算了不同嵌锂态Li_xFePO₄(x=0,0.75,1.0)的电子结构. 对于橄榄石型Li_xFePO₄正极材料,虽然Fe3d电子在费米能级附近相互交错,但由于受晶体场作用的限制,并不能真正成为自由电子,Fe3d电子对体系的导电性没有很大贡献,而Fe—O键在低能成键区形成p-d杂化的局域态共价键对稳定合金骨架具有重要作用. 随着锂离子的脱 关键词： 锂离子电池 4')" href="#">LiFePO₄ 电子结构 弹性性质     

锰酸锂掺杂Fe和Co的性质的第一性原理计算

文章基于密度泛函理论的第一性原理计算,研究了LiMn₂O₄电池材料在掺杂Fe和Co离子时的电子结构和电化学性能.发现Fe\Co取代Mn³⁺在热力学上是会更加稳定,提升电化学性能.掺杂Fe后,LiMn₂O₄电池材料晶格参数减小(约0.3%);掺杂Co后,LiMn₂O₄电池材料晶格参数减小(约0.5%).这两种掺杂方式让与之相邻的Mn³⁺被氧化成Mn⁴⁺,从而降低了Jahn-Teller畸变情况产生可能性.对于掺Fe尖晶石型锰酸锂(Li₈Mn₁₅FeO₃₂),Mn环境中的Li离子会更容易被提取,第一次放电电压从原来的3.7 V增加至4.623 V;对于掺Co尖晶石型锰酸锂(Li₈Mn₁₅CoO₃₂),第一次放电电压从原来的3.7 V增加至4.101 V.研究为锂电池...     

石墨/Li（Ni1/3Co1/3Mn1/3）O2电池充放电过程中电极材料的XRD研究

利用XRD系统地研究了石墨/Li（Ni_1/3Co_1/3Mn_1/3）O₂ 18650型锂离子电池充放电过程中正负极活性材料的晶体结构和微结构的变化.已观测到,由于Li原子的脱嵌,使得LiMO₂点阵参数a缩小,c增大,微应变增大,衍射强度比I₁₀₄/I₁₀₁和I₀₁₂/I₁₀₁降低;此外,由于Li原子的嵌入,2H-石墨的点阵参数a和c,以及微应变ε和堆垛无序度P都增加.同时,讨论了活性材料Li（Ni_1/3Co_1/3Mn_1/3）O₂和石墨在电池充放电过程中的嵌脱锂的物理机理.在充电时,正极Li（Ni_1/3Co_1/3Mn_1/3）O₂中处于（000）位的Li原子优先脱离晶体点阵,继后才是位于（2/3 1/3 1/3）和（1/3 2/3 2/3）位的Li原子离开点阵.锂嵌入石墨,优先进入碳原子六方网格面间的间隙位置,当负极的堆垛无序度达到一定值后,3R相逐渐析出.当电池满充或过充时,在六方石墨中形成LiC₁₂和LiC₆相.放电时,与上述过程相反,但并非是完全可逆的. 关键词： 锂离子电池 微结构 X射线衍射 嵌脱锂物理机理     

Mg,Al掺杂对LiCoO2体系电子结构影响的第一原理研究

为了研究Mg, Al掺杂对锂二次电池正极材料LiCoO₂体系的电子结构的影响，进而揭示Mg掺杂的LiCoO₂具有高电导率的机理，对Li(Co, Al)O₂和Li(Co, Mg)O₂进行了基于密度泛函理论的第一原理研究. 通过对能带及态密度的分析，发现在Mg掺杂后价带出现电子态空穴，提高了电导，并且通过歧化效应（disproportionation）改变了Co-3d电子在各能级的分布，而Al掺杂则没有这些作用. O关键词： 2')" href="#">LiCoO₂ 电子结构 第一原理 电导     

金属元素替代对Li4BN3H10储氢材料释氢影响机理的第一性原理研究

应用基于密度泛函理论的赝势平面波第一性原理方法研究了金属元素替代对Li₄BN₃H₁₀ 释氢的影响机理.计算给出了结合能、电子态密度、密集数, 分析了结构的稳定性和原子间的成键情况.结果表明: 晶体的结合能与(LiM)₄BN₃H₁₀(M=Ni,Ti,Al,Mg)释氢性能没有直接的关联.带隙的宽窄和带隙中是否存在杂质能级是决定(LiM)< 关键词： LiBNH系储氢材料 第一性原理 元素替代 释氢机理     

MO2,M2O5和MO3氧化物对锂硼酸盐玻璃离子导电性的影响

本工作测量了45Li₂O·50B₂O₃·5M_mO_n(M=Al,Ti,Zr,P,V,Nb,Ta,Cr,Mo,W)玻璃的总电导率和电子电导率,以Raman光谱研究了玻璃结构,依据作为锂离子定域体的阴离子团的性质讨论了MO₂,M₂O₃和MO₃氧化物对玻璃离子导电性的影响。 关键词：     

Li3VO4-Li4SiO4-Li4GeO4赝三元系相图的研究

本文用差热分析法和高温、室温X射线衍射法对Li₃VO₄,Li₄SiO₄的相变过程,Li₃VO₄-Li₄SiO₄,Li₃O₄-Li-4GeO₄赝二元系相图以及Li₃VO₄-Li₄SiO₄-Li₄GeO₄赝三元系相图室温截面进行了研究。发现在Li₃VO₄-Li₄SiO₄,Li₃VO₄-Li₄GeO₄赝二元系中,由于Li₄SiO₄或Li₄GeO₄的加入而使Li₃VO₄的高温γ_II相稳定存在于室温,从而得到一种新的具有高电导率的锂离子导体。作者认为探寻使高温态稳定存在于室温的方法是探索新的离子导体研究中有效途径之一。 关键词：     

Mg和Zn掺杂CuAlS2电子结构的分析

从能带结构和态密度分析了黄铜矿CuAlS₂的电子结构.对比未掺杂CuAlS₂,从晶体结构、电子结构、电荷密度分布讨论了Mg和Zn替位Al掺杂对CuAlS₂的影响.结果表明:Mg和Zn掺杂CuAlS₂都导致晶格常数增大,Mg掺杂晶胞体积增大更多;掺杂在价带顶引入受主态,形成p型电导;Mg掺杂比Zn掺杂的受主能级电离能略小;而Zn掺杂CuAlS₂体系总能更低,晶格结构更稳定. 关键词： 2')" href="#">CuAlS₂ p型掺杂 电子结构 能带结构     

Material design of new lithium ionic conductor, thio-LISICON, in the Li2S–P2S5 system

A new lithium ionic conductor of the thio-LISICON (LIthium SuperIonic CONductor) family was found in the binary Li₂S–P₂S₅ system; the new solid solution with the composition range 0.0≤x≤0.27 in Li_3+5xP_1−xS₄ was synthesized at 700 °C and characterized by X-ray diffraction measurements. Its electrical and electrochemical properties were studied by ac impedance and cyclic voltammetry measurements, respectively. The solid solution member at x=0.065 in Li_3+5xP_1−xS₄ showed the highest conductivity value of 1.5×10⁻⁴ S cm⁻¹ at 27 °C with negligible electronic conductivity and the activation energy of 22 kJ mol⁻¹ which is characteristic of high ionic conduction state. The extra lithium ions in Li₃PS₄ created by partial substitution of P⁵⁺ for Li⁺ led to the large increase in ionic conductivity. In the solid solution range examined, the minimum conductivity was obtained for the compositions, Li₃PS₄ (x=0.0 in Li_3+5xP_1−xS₄) and Li₄P_0.8S₄ (x=0.2 in Li_3+5xP_1−xS₄); this conductivity behavior is similar to other thio-LISICON family with the general formula, Li_xM_1−yM_y′S₄ (M=Si, Ge, and M′=P, Al, Zn, Ga, Sb). Conduction mechanism and the material design concepts are discussed based on the conduction behavior and the structure considerations.     

A new family of magnetoelectric materials: A2M4O9(A = Ta, Nb; M = Mn, Co)

The existence of the magnetoelectric (ME) effect in the transition metal niobates and tantalates A₂M₄O₉(A = Ta, Nb; M = Mn, Co) has been confirmed by the observation of the electrically induced magnetic moment in these materials. Both parallel and prependicular ME susceptibilities were measured as a function of temperature in powder specimens. The transition temperatures were found to be 110 ±1 (Nb₂Mn₄O₉), 103 ±1 (Ta₂Mn₄O₉), 27.0 ±0.5 (Nb₂Co₄O₉), and 20.6 ±0.5°K (Ta₂Co₄O₉) from the ME measurements.     

Effect of Sn doping on the magnetic and transport properties of LaMnO3+δ

We report the influence of the Sn doping on the magnetotransport properties of the LaMnO_3+δ perovskite. Two series of samples with nominal LaSn_xMn_1−xO_3+δ (I series) and La_{(1−x)/(1+x)}Sn_xMn_1−xO_3+δ (II series) compositions (x=0, 0.025, 0.05 and 0.10) were prepared at T_s=750°C. The M(T) data under 0.01 and 0.5 T for the I series reveal a depressed magnetization as the Sn content increases suggesting the presence of magnetic clusters with a superparamagnetic behavior. Resistivity measurements indicate an insulator material for all Sn content independently of the applied magnetic field. On the contrary, for the II series the M(T) and M(H) data reveal FM behavior and an improvement of the magnetization as Sn increases. These samples show magnetoresistance. The magnetotransport properties are discussed in terms of the presence of A-site cation vacancies.     

钙钛矿锰氧化物(La1-xGdx)4/3Sr5/3Mn2O7 (x=0, 0.025) 磁性和输运性质研究

采用传统的高温固相烧结法制备了双层钙钛矿锰氧化物(La_1-xGd_x)_4/3Sr_5/3Mn₂ O₇ (x=0, 0.025)多晶样品. 通过X射线衍射仪研究发现样品为Sr₃Ti₂O₇型四方结构, 空间群为I4/mmm; 磁性测量表明, Gd³⁺掺杂后的样品(La_0.975Gd_0.025)_4/3Sr_5/3Mn₂O₇的三维磁有序转变温度(T_C1^3D)、磁化强度(M)均降低, 这是由于Gd³⁺的掺杂引起晶格的畸变, 从而使得晶格常数发生改变, 减弱了铁磁耦合而导致的; 通过电子自旋共振谱测量发现, 在T_C^3D<T<300 K温度范围内, 两样品在顺磁的基体上均有短程的铁磁团簇存在, 出现了相分离现象. 电性测量表明: 两样品分别在T_C1^3D (La_4/3Sr_5/3Mn₂O₇ 样品的三维磁有序转变温度, T_C0^3D)<T<300 K温度范围内均以三维变程跳跃的方式导电, 分析得出Gd³⁺的掺杂使得载流子局域长度的减小. 这表明载流子需要吸收更多的能量才能克服晶格的束缚进行跳跃, 因此(La_0.975Gd_0.025)_4/3Sr_5/3Mn₂ O₇ 样品的电阻较高.     

Magnetic phase transition in (Fe,Mn)65Ni35 alloys

Magnetization measurements on the Fe₆₀Mn₅Ni₃₅ and Fe₅₀Mn₁₅Ni₃₅ alloy samples were carried out in the temperature range 80T300 K and in magnetic fields up to 8 kOe. The Fe₆₀Mn₅Ni₃₅ was found to order ferromagnetically with a Curie temperature, T_c, above 300 K. From the temperature dependence of the spontaneous magnetization, M_s, it was concluded that the magnetic behavior of Fe₆₀Mn₅Ni₃₅ follows Wohlfarth theory of weak itinerant ferromagnet. The Fe₅₀Mn₁₅Ni₃₅ sample exhibits a magnetic phase transition from ferromagnetism to paramagnetism at T_c=242 K. The critical amplitudes and critical exponents (β, γ and δ) have been determined by using Arrott plots, Kouvel–Fisher method and scaling plots of the reduced magnetization and reduced magnetic field. The values of β, γ and δ are discussed and compared with the results obtained for various theoretical models and also with the experimentally determined values for related systems obtained by others.     

Electrons and holes in undoped Nd2CuO4

Nd₂CuO_4±δ is the non-superconducting prototype of the Re_2−xM_xCuO₄t−y family (Re=Pr, Nd, Sm and M=Ceor Th) of n-type oxide superconductors. Four-probe DC conductivity, EMF in P(O₂) gradient, and thermopower measurements have been used to characterise its electric transport and defect structure between 300 and 900°C and between 5×10⁻⁴ and 1 atm oxygen partial pressure.

The results show that Nd₂CuO_4±δ can be oxygen under-stoichiometric (with n-type conductivity), near-stoichiometric, and over-stoichiometric (with p-type conductivity) in different T, P(O₂) ranges.     

Phase segregation of LixMn2O4 (0.6<x<1) in non-equilibrium reduction processes

Chemical synthesis routes to Li_xMn₂O₄ (0.15≤x≤1) in non-equilibrium reduction processes were developed to carry out detailed structural analysis. Non-equilibrium Li_xMn₂O₄ (0.15≤x≤1) samples were prepared by chemical lithiation of λ-MnO₂ with LiI for 24 h; longer than 1 week was needed to reach true equilibrium at room temperature. The samples were characterized by X-ray diffraction analysis. The phase diagram was different from that in the equilibrium state; three cubic phases (phases A, B and C) were observed for Li_xMn₂O₄ (0.15≤x≤1). There were two regions of two-phase coexistence: the region of 0.25<x<0.55 (phase B+phase C) and 0.6<x<1.0 (phase A+phase B). In the compositional range of 0.6<x<1.0, the lattice constants of phases A and B change with the lithium composition, this indicates that it is a structural anomaly with a metastable two-phase character in non-equilibrium reduction processes.     

碳硼富勒烯衍生物C18B2M(M=Li,Ti, Fe)的储氢性能计算研究

本文使用密度泛函理论(density functional theory, DFT)中的广义梯度近似(generalized gradient approximation, GGA)研究了经碱金属原子Li、过渡金属原子Ti和Fe原子修饰的富勒烯C₁₈B₂M(M=Li, Ti, Fe)的储氢性能. 研究发现, C₁₈B₂由于B的替代掺杂, 比C₂₀对金属原子具有更高的结合能. 由平均吸附能分析可知: C₁₈B₂Li对H₂的吸附能力较弱, C₁₈B₂Fe对H₂的吸附能力过强, 而C₁₈B₂Ti对H₂的平均吸附能介于0.45-0.59 eV 之间, 介于物理吸附和化学吸附之间 (0.2-0.6 eV), 因此可以实现常温下的可逆储氢. C₁₈B₂M(M=Li, Ti, Fe)能够吸附的H₂数目最多分别为4, 6和4. 由储氢机理分析可知: C₁₈B₂Li主要通过碱金属离子激发的静电场来吸附H₂, 而C₁₈B₂Ti和C₁₈B₂Fe主要通过金属原子与H₂之间的Kubas作用来吸附H₂. 由于C₁₈B₂Ti既有较大的储氢数目, 又可以实现可逆储氢, 因此有望开发成新型纳米储氢材料.