锂离子电池LiTi0.25Fe0.75SO4F正极材料的电子结构

采用密度泛函理论平面波赝势的方法,计算了LiFeSO₄F和LiTi_0.25Fe_0.75SO₄F正极材料的电子结构。计算结果表明：当锂嵌入材料后,S、O和F的原子布居变化较小,电子主要填充在过渡金属的3d轨道,导致过渡金属被还原,成为电化学反应的活性中心。在嵌锂态中,锂和氧（氟）之间形成了离子键,而过渡金属（Ti和Fe）与氧（氟）之间则形成了共价键,S-O键的共价性最强。态密度的计算结果则表明：Ti和Fe均保持高自旋排列结构;LiFeSO₄F的两个自旋通道的带隙分别为2.88和2.29 eV,其导电性很差;Ti掺杂使体系的带隙消失,显著地提高了正极材料的导电性;LiTi_0.25Fe_0.75SO₄F系统中Ti-O和Ti-F键均比纯相中的Fe-O和Fe-F键的共价性更强,因此Ti掺杂材料具有更好的结构稳定性。     

过渡元素掺杂Fe_3O_4(001)表面磁电性能的理论研究

采用基于密度泛函理论的第一性原理方法,计算Fe_3O_4,Fe_3O_4(001)表面以及过渡元素掺杂表面的电子结构和磁性。结果表明Fe_3O_4的半金属性主要来源于B位Fe离子,并且Fe的3d轨道发生强烈自旋极化;比较(001)表面不同终端A和B终端的表面能和电子结构,得出两种终端稳定性存在差异且A终端较稳定同时表现半金属性;由过渡元素V、Cr、Mn、Co、Cu和Zn取代Fe_3O_4(001)表面A终端A位Fe进行掺杂,形成的6种新表面结构都保持了半金属性。对比它们的表面能和磁矩,Mn掺杂的表面结构最稳定并且磁矩明显增大。     

钛掺杂对LiNi0.75Co0.25O2结构与性能的影响

应用溶胶-凝胶法合成LiNi(0.75-x)Co0.25TixO2(x=0,0.1,0.25)系列正极材料,其结构、形貌、粒度、电化学性能由TG、XRD、SEM和电池充放电测试表征研究表明,材料的电化学性能与钛掺杂量密切相关.在钴含量不变的情况下,随着Ti含量(x)的增加,材料由六方层状结构逐渐向立方结构转变,x=0.25时,出现了立方相与六方相共存.根据实验和理论计算结果简要讨论了钛掺杂对正极材料LiNi0.75Co0.25O2结构和电化学性能的影响.     

《化学通报》网络版(Chemistry Online)2004年第4期论文摘要

[w0 2 5 ]磷酸铁锂锂离子电池正极材料的研究进展Research Progress on Li Fe PO4Cathode Materials for L ithium- ion Batteries吕正中　周震涛 (华南理工大学材料科学与工程学院　广州　 5 10 6 41)从材料的制备、改性、粒径控制、结构与性能等几方面综述了近年来对橄榄石型磷酸铁锂 (Li Fe PO4)锂离子电池正极材料的研究进展。材料的粒度大小及其分布、离子和电子的传导能力以及其中 Fe( )的含量对产品的电化学性能影响很大。在制备时 ,采用惰性气氛、掺杂导电材料和控制晶粒生长制备纳米粉体是获得性能优良的Li Fe PO4的有效方…     

锂离子电池正极材料LiNi0.5Mn1.5O4金属掺杂的第一性原理研究

近来尖晶石相LiNi0.5Mn1.5O4被认为是一种有前景的二次锂离子电池正极材料.但是其相对较差的循环性能和倍率性能限制了LiNi0.5Mn1.5O4的大规模应用.金属掺杂被认为是一种提高其电化学性能的有效方法.然而,还急需深层次地理解掺杂对材料结构和电化学性质的影响.采用第一性原理方法,系统地研究了金属掺杂的LiM0.125Ni0.375Mn1.5O4(M为Cr,Fe和Co)电极体系的结构与电子性质.计算结果显示,少量的过渡金属M取代LiNi0.5Mn1.5O4晶格中的Ni,能够有效抑制材料在电化学脱嵌锂过程中的体积变化(从锂化相到脱锂相,体积变化率约为4%,而未掺杂的情况为4.7%),提高材料循环性能.体系态密度表明金属掺杂能够减小体系的带隙,进而提高材料的电子传导.另外,通过Li离子的扩散计算,我们发现与未掺杂的LiNi0.5Mn1.5O4相比,Co掺杂使得Li在材料中两条不同扩散路径的扩散能垒分别降低了约90 meV和140 meV,表明Co掺杂有利于Li在材料中的快速扩散.     

过渡金属硫化物改性锂硫电池正极材料

锂硫电池(LSBs)由于单质硫正极具有超高能量密度(2600 Wh/kg)和超高理论比容量(1675 mAh/g),且环境友好、成本低廉,被认为是最有前景的储能体系之一。然而,硫正极的绝缘性和严重体积膨胀以及多硫化物(LiPSs)的“穿梭效应”等问题导致活性物质利用率低、循环稳定性差及电化学反应动力不足,严重阻碍了LSBs的商业化发展。最新研究表明,过渡金属硫化物作为载体或添加剂能够显著改善LSBs正极材料的电化学性能。本文从等效/共正极作用、导电性增强作用、LiPSs吸附作用和电化学反应催化作用四个方面梳理了过渡金属硫化物在LSBs正极材料中的改性机理,并指出多元过渡金属硫化物复合﹑纳米结晶和量子化作为增加比表面积和活性位点的方法是过渡金属硫化物用于锂硫电池正极材料的重要发展方向,可大幅提升LSBs的电化学性能。     

高比容量锂离子电池正极材料LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)的制备及性能北大核心CSCD

以LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)为研究对象,通过共沉淀法制备了不同F物质的量分数(0%、1%、3%、5%)的LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)三元正极材料(NCM),通过对NCM材料的晶格结构、微观形貌、电化学性能进行分析,结果表明:F掺杂后提高了NCM材料的结晶度,降低了阳离子混乱程度,适量的F掺杂有助于减小NCM三元正极材料的尺寸和提高均匀性,F的掺杂还能够降低NCM三元正极材料的极化现象,初始放电比容量随着F的掺杂含量升高呈现出先升高后降低的趋势,循环性能随着F的掺杂得到了提高,F掺杂物质的量分数为3%的NCM三元正极材料初始放电比容量167.2 mA·h/g,容量保持率达到98.5%,阻抗较小,电化学性能最优。     

Mo/Fe3O4(111)表面对燃煤烟气汞吸附的密度泛函研究

利用CASTEP软件包采用密度泛函理论计算研究了过渡金属Mo掺杂Fe_3O_4(111)Fe_(tet)表面对Hg~0、HgCl和HgCl_2的吸附特征,分析了Mo掺杂前后Fe_3O_4(111)Fe_(tet)表面上不同汞物种的吸附形态。结果表明,Mo掺杂Fe_3O_4(111)Fe_(tet)表面对HgCl和HgCl_2为化学吸附,而对Hg~0的吸附为物理吸附;与纯净表面相比,HgCl在Mo原子掺杂表面上的吸附能提高了40%-66%。HgCl_2在纯净Fe_3O_4(111)Fe_(tet)表面形成"M"形结构;而掺杂Mo原子后,由于Cl原子与Mo原子之间更强的相互作用,使得HgCl_2发生了完全解离,两个Cl原子分别与Mo原子和Fe原子成键吸附在表面,Hg脱附。相关研究结果可为脱除燃煤烟气中的汞提供一定的理论指导。     

过渡金属原子X (X=Mn、Fe、Co)掺杂单层Janus WSSe的第一性原理研究

二维Janus WSSe作为一种新兴的过渡金属硫族化合物(TMDs)材料,由于其打破了面外镜像对称性,且具有内在垂直压电和强Rashba自旋轨道耦合效应等丰富的物理特性,在自旋电子器件中具有巨大的应用潜力。本文基于密度泛函理论的第一性原理平面波赝势方法计算了过渡金属原子X(X=Mn、Fe、Co)掺杂单层Janus WSSe的电子结构、磁性和光学性质。结果表明：在Chalcogen-rich(硫族元素为多数元素)条件下的掺杂比在W-rich(钨元素为多数元素)条件下的掺杂展现出更高的稳定性,且掺杂后所有体系均表现出磁性。值得一提的是,对该体系进行Mn掺杂后,自旋向上通道出现杂质能级,WSSe由原来的非磁性半导体转变成磁矩为1.043μ_B的铁磁性半金属。而Fe、Co的掺杂使得自旋向上通道和自旋向下通道均出现杂质能级,呈现出磁矩分别为1.584μ_B、2.739μ_B的金属性。此外,掺杂体系的静态介电常数都显著增加,极化程度增强,且介电函数虚部和光吸收峰都发生了红移,说明掺杂有利于对可见光的吸收。     

SO~(2-)_4掺杂对Nasicon型Li_3Fe_2(PO_4)_3正极材料电化学性能的影响

采用溶胶-凝胶法用SO~(2-)_4部分代替Li_3Fe_2(PO_4)_3中的PO~(3-)_4阴离子制得Li_(3-x)Fe_2(PO4)_(3-x)(SO_4)_x(x=0~0.90)正极材料,通过X射线衍射、充放电技术、循环伏安特性测试及电化学阻抗谱表征了掺杂材料的相组成及电化学性能.结果表明,SO~(2-)_4主要以固溶形式存在于Li_3Fe_2(PO_4)_3中,产物中还伴有少量Fe_2O_3第二相析出.SO~(2-)_4掺杂使Li_3Fe_2(PO_4)_3的放电容量呈抛物线形规律变化,并在掺杂浓度x=0.60时达到最佳值,该样品在0.5C倍率下的首次放电容量为111.59 mA·h/g,比未掺杂的样品提高了18.4%;60次循环充放电后的容量保持率为96%;将该样品的放电倍率由0.5C逐渐提高至5C,再降至0.5C,并在每个倍率下循环10次,材料的最终放电容量仍能达到首次放电容量的97%.导致这些变化的原因是SO~(2-)_4掺杂使材料的氧化还原性能增强,电池内阻减小,极化程度降低及Li~+扩散系数增大.     

The crystal structures of the lithium-inserted metal oxides Li0.5TiO2 anatase,LiTi2O4 spinel,and Li2Ti2O4

The crystal structures of three lithium titanates by neutron diffraction powder profile analysis were determined. The tetragonal anatase form of TiO₂ becomes orthorhombic on ambient-temperature lithium insertion to Li_0.5TiO₂ due to the formation of TiTi bonds. The lithium partially occupies the highly distorted octahedral interstices in the anatase framework in fivefold-coordination with oxygen. Cubic LiTi₂O₄ formed by heating Li_0.5TiO₂ anatase has a normal spinel structure with Li in the tetrahedral sites. In Li₂Ti₂O₄ formed by reacting LiTi₂O₄ spinel with n-BuLi at ambient temperature, the titanium remains in the spinel positions but the lithium is displaced, filling all the available octahedral sites.     

Synthesis and electrochemical properties of pure LiFeSO4F in the triplite structure

Recently in the Li-ion battery community there has been an intense amount of attention focusing on developing positive electrodes which operate on the Fe²⁺/Fe³⁺ redox potential given that the environmental and economic advantages of Fe-based compounds compared to other transition metals are tremendous. Here we report that we have succeeded in preparing for the first time LiFeSO₄F in the triplite structure which shows an open circuit voltage of 3.9 V versus Li with a reversible capacity of approximately 85 mA h g^{− 1}, still well below the theoretical value of 148 mA h g^{− 1} due to poor electrode kinetics. Nevertheless, we additionally found that the volume change on removal of Li is 0.6%. Once optimized, this triplite phase of LiFeSO₄F could stand as a promising contender to LiFePO₄.     

ChemInform Abstract: Evaluation of Tavorite‐Structured Cathode Materials for Lithium‐Ion Batteries Using High‐Throughput Computing.

Tavorite‐structured oxyphosphates, fluorophosphates, oxysulfates, and fluorosulfates are evaluated for use as cathode materials in lithium ion batteries and activation energies for lithium diffusion through LiVO(PO₄), LiV(PO₄)F, and LiFe(SO₄)F are calculated.     

快离子导体LiTi2(PO4)3在LiNi0.8Co0.1Mn0.1O2正极材料表面的原位反应包覆及其电化学性能

通过原位反应法,利用富镍层状金属氧化物LiNi_0.8Co_0.1Mn_0.1O₂（LNCM811）正极材料表面残余的氢氧化锂和碳酸锂,与C₈H₂₀O₄Ti和（NH₄）H₂PO₄反应,在LNCM811表面原位生成快离子导体LiTi₂（PO₄）₃（LTP）包覆层。这种原位反应的包覆方法有利于移除LNCM811表面有害的残留物氢氧化锂和碳酸锂。而且,获得的LTP均匀包覆层不仅可以有效地抑制LNCM811表面和电解液的直接接触及其副反应,还可以确保充放电循环过程中LNCM811正极材料的快速Li⁺传导。因此,在LTP包覆层的多重作用下,LTP包覆的LNCM811正极材料具有优异的循环稳定性和倍率性能：在0.2C时,首次放电比容量高达200.6 mAh·g^-1,200圈后的可逆容量依然有155.7 mAh·g^-1;在2C和5C的高电流密度下,200圈后的可逆容量仍然有126.4和111.9 mAh·g^-1。     

Sol–gel processing and electrochemical characterization of monoclinic Li3FeF6

To find new cathode materials for future applications in lithium-ion batteries, lithium transition metal fluorides represent an interesting class of materials. In principle the Li intercalation voltage can be increased by replacing oxygen in the cathode host structure with the more electronegative fluorine. A facile pyrolytic sol–gel process with trifluoroacetic acid as fluorine source was established to synthesize monoclinic Li₃FeF₆ using nontoxic chemicals. The acicular Li₃FeF₆ powder was characterized with X-ray diffraction and a detailed structure model was calculated by Rietveld analysis. For the preparation of cathode films to cycle versus lithium monoclinic Li₃FeF₆ was ball milled with carbon and binder down to nanoscale. After 100 cycles galvanostatic cycling (C/20) 47 % fully reversible capacity of the initial capacity (129 mAh/g) could be retained. To the best of our knowledge the results presented in this work include the first rate performance test for monoclinic Li₃FeF₆ up to 1 C maintaining a capacity of 71 mAh/g. The redox reaction involving Fe³⁺/Fe²⁺ during Li insertion/extraction was confirmed by post-mortem XPS and cyclic voltammetry.     

Sodium/lithium 3d transition metalates for chemisorption of gaseous pollutants: a review

Sodium/lithium transition metalates have found tremendous potential as cathode materials for Na/Li batteries. These metalates have acid-base and redox characteristics, which could be utilized for the chemisorption of gaseous pollutants. Their use was focused mainly on CO₂ gas chemisorption at elevated temperatures. In recent years, these materials have found interesting applications in the chemisorption of CO, NO, SO₂, and H₂S gases. Some of these alkali ceramics have shown tremendous potential for the wet-oxidative removal of acidic gases, even in ambient conditions. The review presents an up-to-date account of alkali ceramics of 3d transition metals for the chemisorption of toxic gases, including CO₂, CO, NO, SO₂, and H₂S. To the best of our knowledge, Na/Li 3d transition metalates have never been reviewed in the context of air decontamination, which needs to be presented to the readers for air purification applications.     

New ramsdellites LiTi2−yVyO4 (0≤y≤1): Synthesis, structure, magnetic properties and electrochemical performances as electrode materials for lithium batteries

The new ramsdellite series LiTi_2−yV_yO₄ (0≤y≤1) has been prepared by conventional solid state chemistry techniques and was characterized by X-ray powder diffraction and electron diffraction. To our knowledge, this is the first report on ramsdellites containing vanadium. The magnetic behaviour of these ramsdellites is strongly influenced by its vanadium content. In this sense, LiTi₂O₄ (y=0) exhibits metallic-like temperature independent paramagnetism, but d electrons tend to localize with increasing V content. LiTiVO₄, though also paramagnetic, follows then the Curie-Weiss law. The crossover from delocalized to localized electrons is observed between compositions y=0.6 and 0.8. For y≥0.8 the magnetic results evidence an isovalent substitution mechanism of trivalent Ti by V. The electrochemical lithium intercalation and deintercalation chemistry of LiTi_2−yV_yO₄ is grouped into two different operating voltage regions. Reversible lithium deintercalation of vanadium-substituted ramsdellite titanates LiTi_2−yV_yO₄ in the high voltage range 2-3 V vs. Li occurs in two main steps, one at about 2 V and the other at about 3 V. The 3 V process capacity increases with the vanadium content, while the 2 V capacity decreases at the same time. The vanadium to titanium substitution rate in LiTi₂O₄ was found to be beneficial to the specific energy in as much as a 50% increase (1 V) of the working voltage is observed. On the other hand, reversible lithium intercalation in vanadium-substituted ramsdellite titanates LiTi_2−yV_yO₄ in the low voltage range 1-2 V vs. Li occurs in one main single step, in which the capacity is not affected by the vanadium content, although vanadium-doping produces an improved capacity retention with an excellent cycling behaviour observed for y≤0.6.     

Electrode materials for aqueous rechargeable lithium batteries

In this review, we describe briefly the historical development of aqueous rechargeable lithium batteries, the advantages and challenges associated with the use of aqueous electrolytes in lithium rechargeable battery with an emphasis on the electrochemical performance of various electrode materials. The following materials have been studied as cathode materials: LiMn₂O₄, MnO₂, LiNiO₂, LiCoO₂, LiMnPO₄, LiFePO₄, and anatase TiO₂. Addition of certain additives like TiS₂, TiB₂, CeO₂, etc. is found to increase the performance of MnO₂ cathode. The following materials have been studied as anode materials: VO₂ (B), LiV₃O₈, LiV₂O₅, LiTi₂(PO4)₃, TiP₂O₃, and very recently conducting polymer, polypyrrole (PPy). The cell PPy/LiCoO₂, constructed using polypyrrole as anode delivers an average voltage of 0.86?V with a discharge capacity of 47.7?mA?h?g^?1. It retains the capacity for first 120 cycles. The cell, LiTi₂(PO₄)₃/1?M Li₂SO₄/LiMn₂O₄, delivers a capacity of 40?mA?h?g^?1 and specific energy of 60?mW?h?g^?1 with an output voltage of 1.5?V over 200 charge?Cdischarge cycles. An aqueous lithium cell constructed using MWCNTs/LiMn₂O₄ as cathode material is found to exhibit more than 1,000 cycles with good rate capability.     

掺F影响LiNi0.8Co0.1Mn0.1O2结构和性能的微观机制

以氟化锂为氟源,通过高温固相法合成了F掺杂的LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2。采用X射线衍射仪(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)和电化学测试等手段研究F影响LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2结构和性能的微观机制。结果表明:适量F掺杂可以提高正极材料的放电比容量,改善其倍率性、循环性和热稳定性。当F掺杂量(物质的量分数)为1.5%时,材料的综合电化学性能最优,初始放电比容量(0.2C)和50周循环容量保持率(1C)分别由原始的174.0 mAh·g~(-1)(78.7%)提高到178.6 mAh·g~(-1)(85.7%)。LiNi_(0.8)Co_(0.1)Mn_(0.1)O_2材料性能的改善可归因于F能够增强过渡金属层、锂层与氧层之间的结合力,提高材料的结构稳定性。此外,F掺杂还有利于降低电化学反应中的界面电阻和电荷转移阻抗。