Al掺杂的锂离子电池层状正极材料Li(Li0.17Ni0.17Al0.04Fe0.13Mn0.49)O2结构稳定性及氧离子氧化的理论研究

锂离子电池(LIB)正极材料比容量及结构稳定性的提高是提升电池整体性能的重要因素. 本工作选取层状无钴正极材料Li(Li_0.17Ni_0.17Al_0.04Fe_0.13Mn_0.49)O₂ (LNAFMO)为研究对象, 使用GGA (generalized gradient approximation)+U (Hubbard U value)方法研究了体系在充电时几何和电子结构变化、氧释放焓、脱锂形成能和脱锂电压. 研究结果表明, 充电时LNAFMO体系首先Ni氧化, 然后Fe氧化, 最后O氧化. 与未掺杂Al的Li(Li_0.17Ni_0.17Fe_0.17Mn_0.49)O₂ (LNFMO)体系不同的是, 除具有线性Li-O-Li和Fe-O-Li构型的氧离子更容易给出电子外, 具有线性Al-O-Li构型的氧离子也参与电荷补偿, 并且氧离子具有很强的活性, 这将避免参与氧化的氧离子过分集中, 有利于结构的稳定; Al的掺杂能进一步抑制氧的释放, 这将提升体系的结构稳定性和电池循环性能. 该研究为设计一种低经济成本、循环性良好、高能量密度的锂离子电池正极材料奠定了坚实的理论依据.     

高容量正极材料0.08LiCo0.75Al0.25O2-0.92LiNiO2的合成与电化学性能研究

在恒定pH值下将层状钴铝双羟基复合金属氧化物(CoAl-LDH)均匀包覆在球状Ni(OH)2表面,与LiOH.H2O混合均匀后,经高温煅烧制得钴铝酸锂包覆镍酸锂0.08LiCo0.75Al0.25O2-0.92LiNiO2正极材料.电化学测试表明,0.08LiCo0.75Al0.25O2-0.92LiNiO2正极比容量高,具有良好的倍率性能和循环寿命,其0.1C放电比容量为211 mAh·g-1,0.5C放电比容量为195.6 mAh·g-1,3C放电比容量为161 mAh·g-1,0.5C 30周期循环后容量保持率为93.2%,明显优于LiNiO2和钴酸锂包覆镍酸锂0.08LiCoO2-0.92LiNiO2正极.     

阴离子硫氧化还原与Li_(1-x)NiO_(2-y)S_y的结构稳定性:第一性原理研究（英文）

高镍层状氧化物是电动汽车高能量密度锂离子电池正极材料的首选。本文通过第一性原理计算模拟了Li_(1-x)NiO_(2-y)S_y材料的脱锂过程。通过GGA+U计算分析了体系费米能级处的电子结构,充电过程中的氧化还原机制和热稳定性。在Li_(1-x)NiO_(2-y)S_y脱锂过程中,首次发现硫参与电荷补偿,抑制过渡金属的迁移,降低晶格扭曲幅度和提高体系中氧的稳定性。这种基于硫阴离子氧化还原对锂离子电池阴极材料电化学行为的调制有助于设计高稳定性的高镍正极材料。     

Li1+δNi1-xCoxO2-yFy的合成与电化学性能研究

采用固相反应法在空气气氛下合成了同时掺杂Co阳离子和F阴离子的镍系正极材料Li_1+δNi_1-xCo_xO_2-yF_y(0≤δ≤0.2, 0≤x≤0.5, 0≤y≤0.1),考察了不同来源的镍源为原料对目标材料性能的影响,并采用XRD, SEM, TEM, BET,激光粒度分布,电化学性能测试等手段对该材料进行了表征.结果表明,在正极材料LiNiO₂中同时掺杂Co阳离子和F阴离子后合成的Li_1+δNi_1-xCo_xO_2-yF_y镍系正极材料具有完整的层状结构、均一的表面形貌、较好的粒径分布和良好的电化学性能.在20～25℃,充放电电流为0.15～0.25 mA,截止电压为4.25～2.70 V,充放电速率为0.2～0.5 C,电流密度为0.2～0.5 mA/cm²条件下,LiNi_0.8Co_0.2O_1.95F_0.05的首次充放电容量分别达到165.70 mAh/g和146.10 mAh/g,而且循环稳定性能良好,在恒流充放电循环50次后,其可逆放电容量大于140 mAh/g.这主要归因于具有较高电负性的F阴离子的掺入改善了正极材料的结够稳定性和Co与F离子的协同作用.该正极材料初步显示了实际应用的可能性.     

锂离子电池正极材料LiMn2O4的低热固相合成与性能表征

锂离子电池具有比能量高、环境污染小等优点,广泛应用于手提电话、便携式电脑、摄像机等设备中。其正极材料的研究是锂离子电池的研究重点。层状结构的LiCoO2、LiNiO2和尖晶石结构的LiMn2O4是仅有的三种能在3.5V以上电位可嵌入Li的正极材料[1~3]。目前市售的锂离子电池主要采用LiCoO2作正极材料,但由于Co资源缺乏和价格相对昂贵,而锰资源丰富,价格低廉且无毒,对环境友好,因此世界各国都在大力进行以LiMn2O4为正极材料的锂离子电池的实用化研究。LiMn2O4传统的制备方法是高温固相反应合成法[4~7],但由于Mn的变价多,与Li形成贫Li或…     

锂离子电池正极材料LiMnPO4的电子结构

采用基于密度泛函理论的第一性原理计算方法,计算了锂离子电池LiMnPO4正极材料的电子结构。计算结果表明:当Li+嵌入体系后,O和P的原子布居变化较小,电子向金属原子的转移明显得到加强。Li+和O2-有弱相互作用,当Li+离子脱出以后,氧原子所得到的电子数减小,导致布居减小。锂是以离子形式存在的于LiMnPO4正极材料中。在LiMnPO4和MnPO4体系中,Mn原子具有磁性,其磁矩分别为4.78μB和3.84μB,其余原子磁性近似为0。氧为负离子,带负电荷,而P和Mn则为正离子。O2p与P3s、P3p轨道发生有效重叠,并形成共价键,Mn3d和O2p之间能够有效地发生重叠并形成共价键。在放电过程中有电子从外电路进入正极,大部分电子所带电荷分布在Mn原子上。     

客体预嵌策略提升水系锌离子电池正极材料电化学性能

随着人们对电子通讯器件、新能源汽车以及电网级储能技术的需求日益增长,开发安全、高效且兼具环保、低成本等优点的二次电池显得至关重要。近年来,水系锌离子电池因其高安全性、高容量、低成本以及环境友好等优点受到了广泛关注。在与锌负极相匹配的众多正极材料中,具有多电子转移特性的钒基和锰基材料表现出了广阔的应用前景。然而这些正极材料在电池循环过程通常面临着结构坍塌、组分溶解、衍生副反应、反应动力学缓慢等问题,严重制约了其商业化进程。近年来,大量研究表明,客体离子或分子预嵌正极宿主结构可以有效缓解上述问题,提升水系锌离子电池正极材料的电化学性能。本文综述了客体预嵌策略应用于水系锌离子电池钒、锰基正极材料的研究进展,对该策略所解决的问题以及其局限性进行了讨论和总结,并对未来水系锌离子电池钒基和锰基正极材料的研究发展方向进行了展望。     

采用第一原理方法研究Al3+掺杂LiMn2O4的电子结构

为了从理论方面研究掺杂Al3 对锂离子电池正极材料LiMn2O4结构及电化学性能的影响,对LiMn2O4中掺杂Al3 的电子结构进行了基于密度泛函理论的第一原理研究,得到了相应的晶格常数、费米能、能带图、态密度图及分态密度图.结果表明,掺杂Al3 后,晶格常数变小,材料结构更加稳定,循环性能更好,有效地抑制了Mn3 发生的Jahn-Teller畸变,掺入Al3 的缺点是使材料的电导率降低.     

镁-过渡金属复合物正极材料

高能量密度、大容量、高工作电压、低成本、环境友好的二次电池是未来储能电池技术的发展方向。高比能的镁离子电池（MIBs）是以镁或镁合金为负极的二次电池,是一种重要的有望用于电动汽车的新型绿色储能电池。镁离子电池发展缓慢的主要问题是镁离子在正极材料中扩散速度慢。因此,本文综述了五类晶体结构的镁-过渡金属复合物类型（包括一维隧道结构、二维层状结构、三维尖晶石结构、三维NASICON结构、三维橄榄石结构）、制备方法、电化学性能等,还阐述了镁离子在固体中扩散行为及提高扩散速度的措施,最后展望了镁离子电池正极材料镁-过渡金属复合物的重要研究方向。寻找高电压（大于3 V）、高比能量、高可逆性的正极材料和与其匹配的电解液是实现镁离子电池第三次突破的关键。我们希望本文有利于更深入地了解镁离子电池正极材料,促进镁离子电池的发展。     

高镍三元正极材料的表面包覆策略

锂离子电池(LIBs)因具有更高的重量/体积能量密度、 更长的使用寿命、 更低的自放电率等优点而逐渐被广泛应用. 相比于已经广泛使用的钴酸锂和磷酸铁锂等正极材料, 高镍三元正极材料Li[Ni_1-x-yCo_xMn_y]O₂(NCM)以其高电压和高容量等优点, 逐渐成为下一代高能锂离子电池的首选正极材料之一. 尽管高镍NCM正极材料具有上述优点, 但在进一步的实际应用前还需解决其循环稳定性、 倍率性能和安全性等问题, 这些问题主要源于NCM材料本身的晶体结构不稳定、 正极-电解液间界面副反应及高界面电阻等. 针对这些问题, 目前对高镍NCM正极电化学性能优化的大量研究都与电极-电解液界面有关, 如何通过改善界面稳定性、 增加离子在固液界面的迁移率、 抑制界面副反应、 提高正极材料的稳定性进而改善电池性能成为了关注焦点. 本文总结了目前对于其电化学性能衰减的机理解释, 分类概括了包括电化学惰性包覆锂、 残积物清除剂包覆和锂离子良导体包覆等对于高镍NCM正极材料的颗粒表面包覆策略, 简述了一些新兴的包覆策略, 并对高镍NCM正极材料的发展方向和前景提出了展望.     

Electronic structure of lithium nickel oxides by electron energy loss spectroscopy

The electronic structures of NiO, LiNiO2, and NiO2 are studied by the electron energy loss spectroscopy at Ni L(2,3), Ni M(2,3), and O K edges. The Ni L(2,3) edge spectra suggest that the formal charge of nickel is +2 in NiO, +3 with a low-spin state in LiNiO2, and +4 with a low-spin state in NiO2. This is well confirmed by first-principles calculations. The Ni M(2,3) edge spectra show similar chemical shifts to those of the Ni L(2,3) edge. Superposition of the Li K edge spectrum, however, hinders further analysis. Although the formal charge of oxygen is -2 in all the three phases, the O K edge spectra indicate a more remarkable difference in the electronic structure of the oxygen in NiO2 than that in either NiO or LiNiO2. The spectra suggest that lithium extraction from LiNiO2 reinforces the covalent bonding between the oxygen and nickel atoms and causes a notable reduction in electron density at the oxygen atoms.     

Studies on Synthesis and Electrochemical Performance of Li1+δNi1-xCoxO2-yFy Cathode Materials for Lithium-ion Rechargeable Batteries

It is a technological problem of LiNiO2 cathode material for lithium-ion secondary batteries because of the difficult preparation and hard purification, instable performance, remarkable capacity fading at initial discharge, worse thermal stability and safety of Ni-series cathode materials,and it is also the key factor of hindering LiNiO2 cathode material from practical applications.Recently, by doping some metal cations such as Co, Mn, Mg, Al, Cr and so on[1-5] into LiNiO2, the preparation difficulty and the purification hardness can be obviously improved, and the initial irreversible discharge capacity can be reduced, and the ratio of the initial discharge to charge capacity can be enhanced. But the cyclic stability, thermal stability and safety of LiNiO2 are not enough to satisfy the demand of commercial use.At present, the synthesis of LiNiO2 cathode material must be sintered under oxygen atmosphere in most cases, and the improved effect of fluoride doping on the electrochemical properties of LiNiO2 has seldom been reported in the literatures.In this paper, the cobalt cation and fluorine anion co-doping cathode materials Li1+δNi1-xCoxO2-yFy( 0≤δ≤0.2, 0≤x≤0.5, 0≤y≤0.1 ) were synthesized by solid state reaction method at 650℃ ～750℃ under air atmosphere, and characterized by XRD、 SEM、 TEM、 BET、 laser particle-size distribution measurement and electrochemical performance testing, the effect of different nickel sources on the properties of as-synthesized cathode materials was investigated. The results demonstrated that the cobalt and fluorine ions co-doping cathode materials Li1+δNi1-xCoxO2-yFy have complete layered structure, uniform surface morphology and better particle-size distribution as well as excellent electrochemical performances. At 20～25℃, 0.15～0.25mA charge and discharge current,4.25～2.70V cut-off voltage, 0.2～0.5C charge and discharge rate and 0.2～0.5 mA/cm2 current density,LiNi0.8Co0.2O1.95F0.05 cathode material has higher initial charge and discharge capacity and better cyclic properties which can be mainly attributed to the doping of the higher electronegativity fluorine which improves the structural stability and the synergistic reaction of cobalt and fluorine ions co-doping on the cathode materials. Under the above conditions, the initial charge and discharge capacity of LiNi0.8Co0.2O1.95F0.05 is 165.70mAh/g and 146.10mAh/g, respectively. After 50 cycles, it has more than 140mAh/g of discharge capacity and displays preliminary application possibility in the future.     

Coupled ion/electron hopping in Li(x)NiO2: a 7Li NMR study

Deintercalated "Li(x)NiO2" materials (x = 0.25, 0.33, 0.50, 0.58, and 0.65) were obtained using the electrochemical route from the Li0.985Ni1.015O2 and Li0.993Ni1.007O2 compounds. Refinements of X-ray diffraction data using the Rietveld method show a good agreement with the phase diagram of the Li(x)NiO2 system studied earlier in this laboratory. Electronic conductivity measurements show a thermally activated electron-hopping process for the deintercalated Li0.5NiO2 phase. In the Li(x)NiO2 materials investigated (x = 0.25, 0.33, 0.50, and 0.58), 7Li NMR shows mobility effects leading to an exchanged signal at room temperature. A clear tendency for Li to be surrounded mainly by Ni3+ ions with the 180 degree configuration is observed, particularly, for strongly deintercalated materials with smaller Li+ and Ni3+ contents, even upon heating, when this mobility becomes very fast in the NMR time scale. This suggests that Li/vacancy hopping does occur on the NMR time scale but that Ni3+/Ni4+ hopping does not occur independently. The position of Li seems to govern the oxidation state of the Ni around it at any time; the electrons follow the Li ions to satisfy local electroneutrality and minimal energy configuration. The observed NMR shifts are compatible with the Li/vacancy and Ni3+/Ni4+ ordering patterns calculated by Arroyo y de Dompablo et al. for x = 0.25 and x = 0.50, but not for x = 0.33 and x = 0.58.     

Nitridoborates of the lanthanides: synthesis,structure principles,and properties of a new class of compounds

Investigations of the nitridoborates of lanthanides (Ln) have progressed significantly during the last few years. New compounds have been synthesized and characterized and are presented here together with some of their properties. Currently two distinct methods serve for the preparation of nitridoborate compounds; either hexagonal boron nitride undergoes a fragmentation through the reaction with LnN, or dinitridoborate ions are converted into other nitridoborate ions. Lanthanide nitridoborates contain molecular anions such as [BN]n-, [BN2]3-, [B2N4]8-, [B3N6]9-, and [BN3]6- which may occur in combinations with other nitridoborates or with additional nitride ions. In crystal structures of lanthanide nitridoborates these anions are arranged in layers and are surrounded by metal atoms in a characteristic fashion. Terminal N atoms are capped by metal atoms forming a square-pyramid, and B atoms prefer a trigonal-prismatic environment of metal atoms. Nitridoborates form saltlike as well as metal-rich compounds and have the potential to show a lot of what are considered to be important solid-state properties, thus they have a good chance to establish their position within the group of relevant materials.     

锂离子二次电池正极材料镍酸锂的量子化学研究

利用周期性体系的Hartree-Fock方法计算了以LiC6／LiNiO2锂离子二次电池的平均电压，结果与实验值相差 15％。计算表明，NiO2中嵌入一个Li原子变成LiNiO2后，负电荷主要从Li转移到O上，转移到Ni上的负电荷仅约20％，讨论了其对Jahn-Tell效应的影响。以Li0.5NiO2作为嵌锂中间物的代表，研究了锂离子的可能迁移路径。通过对NiO2和LiNiO2的电子态密度的计算，研究了NiO2在嵌锂过程中的能带变化及其对电极的电化学性质的影响。     

LiAl_yNi_(1-y)O_2作为锂离子电池正极材料的研究

本文采用固相反应法合成了一系列不同 y值的LiAlyNi1- yO2 材料 ,通过对其电化学性能的研究发现 ,在适当的烧结条件下 ,LixAl0 .2 5 Ni0 .75 O2 作为二次锂离子电池的正极材料 ,其耐过充性和循环性能都有明显改善 .当Li含量大于 1时 ,在高电位范围充放 (3- 4 .8V) 30次循环后仍保持着首次放电容量的 95 % ,而LiNiO2 在此电压范围内经 2 0次循环后却只有首次放电容量的 5 6 % .通过循环伏安实验表明 :性能改善的主要原因可能是由于充电过程中 ,Al3+ 的掺杂阻止了LixAl0 .2 5Ni0 .75 O2 随Li+ 离子过量脱出而发生晶型转变 .     

Mono-, di-, and oligonuclear complexes of Cu(II) ions and p-hydroquinone ligands: syntheses, electrochemical properties, and magnetic behavior

Four highly soluble square-planar Cu(II) and Ni(II) complexes of siloxy-salens (2SiCu, 2SiNi) and hydroxy-salens (2Cu, 2Ni) have been synthesized. An X-ray crystal structure analysis was performed on 2SiCu, 2SiNi, and 2Ni. The compounds have been investigated by cyclic voltammetry, UV-vis-NIR spectroelectrochemistry, and EPR spectroscopy. According to these results, the monooxidized species [2SiCu]+ and [2SiNi]+ are to be classified as Robin-Day class II and III systems, respectively. Magnetic measurements on the dinuclear (PMDTA)Cu(II) complex 1Cu2 x (PF6)2 with deprotonated 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)-benzene (1) linker revealed antiferromagnetic coupling between the two Cu(II) ions thereby resulting in an isolated dimer compound. Coordination polymers [1Cu]n(H2O)(2n) of Cu(II) ions and bridging p-hydroquinone linkers were obtained from CuSO4 x 5 H2O and 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)benzene. X-ray crystallography revealed linear chains running along the crystallographic a-direction and stacked along the b-axis. Within these chains, the Cu(II) ions are coordinated by two pyrazolyl nitrogen atoms and two p-hydroquinone oxygen atoms in a square-planar fashion.     

草酸桥联双核Ni(Ⅱ)配合物的合成、光谱和结构

合成并表征了两个含有不同阴离子的双核镍(Ⅱ)配合物{[(tacn)Ni(H~2O)]~2(μ-C~2O~4)}I~2·2H~2O(1)和{[(tacn)Ni(H~2O)]~2(μ-C~2O~4)}(ClO~4)~2·2H~2O(2)(tacn=1,4,7-三氮杂环壬烷)。晶体结构分析表明这两个配合物中,两个Ni离子通过草酸根桥联,每个Ni离子还与一个大环配体tacn上的三个氮原子和一个水分子配位形成变形八面体结构。结晶水和配位水之间通过氢键相连。在紫外-可见区测定了配合物的固体反射谱和溶液吸收谱。     

REMGa3Ge and RE3Ni3Ga8Ge3 (M = Ni, Co; RE = rare-earth element): new intermetallics synthesized in liquid gallium. X-ray, electron, and neutron structure determination and magnetism

New quaternary intermetallic phases REMGa(3)Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE(3)Ni(3)Ga(8)Ge(3) (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa(3)Ge, a = 4.1748(10) A, c = 23.710(8) A, V = 413.24(2) A(3), I4/mmm, Z = 4; Gd(3)Ni(3)Ga(8)Ge(3), a = 4.1809(18) A, c = 17.035(11) A, V = 297.8(3) A(3), P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa(3)Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa(4)Ge(2)] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE(3+) free ions.