锂离子电池正极材料Li_(1.2)Mn_(0.54-x)Ni_(0.13)Co_(0.13)Zr_xO_2的制备及电化学性能

为了改善富锂锰基正极材料Li1.2Mn0.54Ni0.13Co0.13O2的循环性能,采用燃烧法合成了正极材料Li1.2Mn0.54-xNi0.13Co0.13ZrxO2(x=0.00,0.01,0.02,0.03,0.06).通过X射线衍射(XRD)和扫描电镜(SEM)对其结构与形貌进行了表征,利用恒电流充放电测试,循环伏安(CV)及电化学交流阻抗谱(EIS)技术对其电化学性能进行测试.结果表明,Li1.2Mn0.54-xNi0.13Co0.13ZrxO2(x=0.00,0.01,0.02,0.03,0.06)正极材料均具有α-NaFeO2型层状结构;在室温,2.0-4.8 V电压范围,以0.1C和1.0C(充放电电流以1.0C=180 mA·g-1计算)倍率充放电进行测试,样品Li1.2Mn0.52Ni0.13Co0.13Zr0.02O2的首次放电比容量分别为280.3和206.4 mAh·g-1.其中,在1.0C倍率下,100次循环后容量保持率由原来的73.2%提高到88.9%;以5.0C倍率充放电进行测试,经50次循环后,掺杂正极材料的放电比容量为76.5 mAh·g-1,而未掺杂材料仅有15.0 mAh·g-1.在50、25和-10°C,2.0C倍率条件下,掺杂正极材料的电化学性能均得到有效改善,其中,在-10°C经过50次循环后正极材料Li1.2Mn0.52Ni0.13Co0.13Zr0.02O2比未掺杂的正极材料相比,其放电比容量提高了61.1%.     

Zn~(2+)掺杂富锂层状正极材料Li_(1.13)Ni_(0.3-x)Mn_(0.57)Zn_xO_2的合成与电化学性质

将通过共沉淀法制备的M(OH)2(M=Mn,Ni)前驱体与Zn O和Li2CO3混合,合成了不同Zn2+掺杂量的Li1.13Ni0.3-xMn0.57ZnxO2材料.X射线衍射结果表明,Zn2+掺杂提升了材料的层状属性,降低了Li+/Ni2+混排程度.在2.0~4.8 V电压范围内,Zn2+掺杂材料表现出更高的可逆比容量,并具有良好的倍率性能和循环稳定性.示差扫描量热测试结果显示,Zn2+掺杂材料的热安全性能明显优于未掺杂材料.在所合成的材料中,Li1.13Ni0.29Mn0.57Zn0.01O2(Zn2+掺杂量x=0.01)具有最高的放电容量、最好的倍率性能和循环稳定性及极佳的热安全性能.     

LiBOB对Li_(1.15)Ni_(0.68)Mn_(1.32)O_4电极电化学行为的影响

采用恒电流充放电技术研究了锂离子电池电解液添加剂双草酸硼酸锂(Li BOB)对Li1.15Ni0.68Mn1.32O4电极电化学性能的影响,用X射线衍射(XRD)、衰减全反射傅里叶变换红外光谱(FTIR-ATR)、电感耦合等离子体发射光谱(ICP)、扫描电子显微镜(SEM)和电化学阻抗谱(EIS)分析了Li BOB对Li1.15Ni0.68Mn1.32O4电极性能的影响.结果显示,Li BOB作为电解液添加剂能显著改善Li1.15Ni0.68Mn1.32O4电极的循环性能,原因是Li BOB在充放电过程中会在Li1.15Ni0.68Mn1.32O4电极表面发生分解,分解产物在电极表面沉积形成固体电解质界面(SEI)膜,SEI膜能够有效抑制Li1.15Ni0.68Mn1.32O4电极材料中Mn的溶解,确保其晶体结构的稳定性,从而提高Li1.15Ni0.68Mn1.32O4电极的循环性能.     

具有良好高温循环性能的Li(Li0.15N0.21Fe0.21Mn0.45)O2阴极材料的合成与性能表征

利用高温固相法制备了具有层状结构的Li(Li0.15Ni0.21Fe0.21Mn0.45)O2阴极材料,通过ICP-AEs测定了各金属含量,XRD研究表明该材料在充放电过程中发生了结构变化.进一步的电化学表征说明材料在结构转变后具有突出的高温循环性能(55℃),以300mA/g(2C)的电流密度循环428周后,仍然能够保持80%的初始放电容量.     

层状LiNi0.5Mn0.5O2正极材料的优化合成及电化学性能

采用沉淀法首先得到了Ni0.5Mn0.5(OH)2沉淀物,以其为原料与LiOH反应制备了LiNi0.5Mn0.5O2正极材料。采用XRD、SEM、充放电测试等研究了其结构与电化学性能,同时研究了Li过量时对材料电化学性能和结构的影响。SEM分析表明,Ni0.5Mn0.5(OH)2与LiNi0.5Mn0.5O2产物均为微小晶粒团聚成的颗粒。LiNi0.5Mn0.5O2材料在2.5~4.4V电位区间内,首次放电容量为130mAh/g,0.2C倍率下,50次循环后的容量保持率为87.8%。锂过量有助于形成良好的层状结构材料,并能显著提高材料的比容量和循环性能,Li1.1Ni0.5Mn0.5O2的首次放电容量为149mAh/g,0.2C倍率下,50次循环后的容量保持率为92.6%。     

锂离子正极材料Li(Ni_(1/3)Co_(1/3)Mn_(1/3))_(1-x)Al_xO_2的制备及电化学性能

以化学法合成Li(Ni1/3Co1/3Mn1/3)1-xAlxO2系列正极材料(0≤x≤0.1);用X射线衍射仪、扫描电子显微镜和充放电仪研究系列产物的晶体微观结构、表面形貌以及电化学性能,研究不同Al含量参杂对材料性能的影响。结果表明,合成的材料均属于六方晶系,R3m空间群,保持α-NaFeO2层状结构相;Li(Ni1/3Co1/3Mn1/3)0.95Al0.05O2的首次放电容量166.30 mA·h/g,在2.5~4.5 V区间60次循环后比容量衰竭率为4.43%。通过对比Li(Ni1/3Co1/3Mn1/3)0.95Al0.05O2和Li(Ni1/3Co1/3Mn1/3)O2的电极阻抗,分析它们的电化学循环机理,可知掺杂Al后的正极材料适合大倍率放电。     

锂离子电池正极材料Li[Li_(0.167)Mn_(0.583)Ni_(0.25)]O_2的合成与性能研究

应用低热固相法制备镍锰复合正极材料Li[Li0.167Mn0.583Ni0.25]O2.XRD、FESEM和恒电流充放电测试表明,该材料结晶良好,可标定为α-NaFeO2型结构(空间群R3-m),颗粒粒径约为60~100 nm,粒度均匀细小.在2.5~4.4 V之间以0.5 C(100 mA/g)做充放电循环时,可逆比容量在120 mAh/g以上,循环性能非常稳定.如将截止电压升高到4.6 V,则比容量大大提高,最高可达234 mAh/g.上述充放电测试都出现了比容量随循环次数上升的现象.主要原因可归结为材料中Mn(Ⅳ)向Mn(Ⅲ)的转变,但在不同的电压范围内导致该转变的起因并不相同.     

Ag/C包覆对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响

运用共沉淀和元素化学沉积相结合的方法,制备出了具有Ag/C包覆层的层状富锂固溶体材料Li [Li0.2Mn0.54Ni0.13Co0.13]O2.通过X射线衍射(XRD)、场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)、恒流充放电、循环伏安(CV),电化学阻抗谱(EIS)和X射线能量散射谱(EDS)方法,研究了Ag/C包覆层对Li[Li0.2Mn0.54Ni03Co013]O2电化学性能的影响.结果表明,Ag/C包覆层的厚度约为25 nm,Ag/C包覆在保持了固溶体材料α-NaFeO2六方层状晶体结构的前提下,显著地改善了Li[Li0.0Mn054Ni0.13Co013]O2的电化学性能.在2.0-4.8 V (vs Li/Li+)的电压范围内,首次放电(0.05C)容量由242.6 mAh·g-1提高到272.4 mAh·g-1,库仑效率由67.6％升高到77.4％;在0.2C倍率下,30次循环后,Ag/C包覆的电极材料容量为222.6 mAh·g-1,比未包覆电极材料的容量高出14.45％;包覆后的电极材料在1C下的容量仍为0.05C下的81.3％.循环伏安及电化学交流阻抗谱研究表明,Ag/C包覆层抑制了材料在充放电过程中氧的损失,有效降低了Li[Li02Mn0.54Ni0.13Co013]O2颗粒的界面膜电阻与电化学反应电阻.     

Ag/C包覆对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响

运用共沉淀和元素化学沉积相结合的方法,制备出了具有Ag/C包覆层的层状富锂固溶体材料Li[Li0.2Mn0.54Ni0.13Co0.13]O2.通过X射线衍射(XRD)、场发射扫描电子显微镜(SEM)、透射电子显微镜(TEM)、恒流充放电、循环伏安(CV),电化学阻抗谱(EIS)和X射线能量散射谱(EDS)方法,研究了Ag/C包覆层对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响.结果表明,Ag/C包覆层的厚度约为25 nm,Ag/C包覆在保持了固溶体材料α-NaFeO2六方层状晶体结构的前提下,显著地改善了Li[Li0.2Mn0.54Ni0.13Co0.13]O2的电化学性能.在2.0-4.8 V(vs Li/Li+)的电压范围内,首次放电(0.05C)容量由242.6 mAh·g-1提高到272.4 mAh·g-1,库仑效率由67.6%升高到77.4%;在0.2C倍率下,30次循环后,Ag/C包覆的电极材料容量为222.6 mAh·g-1,比未包覆电极材料的容量高出14.45%;包覆后的电极材料在1C下的容量仍为0.05C下的81.3%.循环伏安及电化学交流阻抗谱研究表明,Ag/C包覆层抑制了材料在充放电过程中氧的损失,有效降低了Li[Li0.2Mn0.54Ni0.13Co0.13]O2颗粒的界面膜电阻与电化学反应电阻.     

掺Ga对锂离子电池正极材料LiCo0.3-xGaxNi0.7O2的影响

采用溶胶-凝胶法在0≤x≤0.5的范围内合成了LiCo0.3-xGaxNi0.7O2的单相.对样品进行了XRD、粒度、比表面积和充放电循环测试.随着掺Ga量的增加,LiCo0.3-xGaxNi0.7O2的放电容量增加.其中LiCo0.25Ga0.05Ni0.7O2在2.8～4.3V和0.2C时的首次放电容量为177.5mA·h/g,经25次充放电循环后无容量衰减.LiCo0.25Ga0.05Ni0.7O2的放电容量随着放电倍率的增大而减小,随着充放电域压上限的增加而增大.但是材料的放电容量在高放电倍率下放电后仍可以完全恢复,且其循环性能与放电域压上限无关.此外,LiCo0.25Ga0.05Ni0.7O2在充放电循环中结构稳定,无相变发生.     

OH(3) (-) and O(2)H(5) (-) double Rydberg anions: predictions and comparisons with NH(4) (-) and N(2)H(7) (-)

A low barrier in the reaction pathway between the double Rydberg isomer of OH(3) (-) and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral NH(4) (-). Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state's electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the OH(3) (-) DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on O(2)H(5) (-) species. Three O(2)H(5) (-) minima with H(-)(H(2)O)(2), hydrogen-bridged, and DRA-molecule structures resemble previously discovered N(2)H(7) (-) species and have well separated VEDEs that may be observable in anion photoelectron spectra.     

Mixed ligand titanium(IV) complexes. Chlorobis(dithiocarbamato)bis(methylsalicylato)titanium(IV) andbis(dithiocarbamato)bis(methylsalicylato)titanium(IV)

Summary Dichlorobis(methylsalicylato)titanium(IV) reacts with potassium or amine salts of dialkyl or diaryl dithiocarbamates in 11 and 12 molar ratios in anhydrous benzene (room temperature) or in boiling CH₂Cl₂ to yield mixed ligand complexes: (AcOC₆H₄O)₂ Ti(S₂CNR₂)Cl (1) and (AcOC₆H₄O)₂ Ti(S₂CNR₂)₂ (2), R=Et, n-Pr, n-Bu, cyclo-C₄H₈ and cyclo-C₅H₁₀. These compounds are moisture sensitive and highly soluble in polar solvents. Molecular weight measurement in conjunction with i.r.,¹H and¹³C n.m.r. spectral studies suggest coordination number 7 and 8 around titanium(IV) in (1) and (2) respectively.     

Syntheses and structures of the infinite chain compounds Cs(4)Ti(3)Se(13), Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14)

The alkali metal/group 4 metal/polychalcogenides Cs(4)Ti(3)Se(13), Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14) have been synthesized by means of the reactive flux method at 823 or 873 K. Cs(4)Ti(3)Se(13) crystallizes in a new structure type in space group C(2)(2)-P2(1) with eight formula units in a monoclinic cell at T = 153 K of dimensions a = 10.2524(6) A, b = 32.468(2) A, c = 14.6747(8) A, beta = 100.008(1) degrees. Cs(4)Ti(3)Se(13) is composed of four independent one-dimensional [Ti(3)Se(13)(4-)] chains separated by Cs(+) cations. These chains adopt hexagonal closest packing along the [100] direction. The [Ti(3)Se(13)(4-)] chains are built from the face- and edge-sharing of pentagonal pyramids and pentagonal bipyramids. Formal oxidation states cannot be assigned in Cs(4)Ti(3)Se(13). The compounds Rb(4)Ti(3)S(14), Cs(4)Ti(3)S(14), Rb(4)Hf(3)S(14), Rb(4)Zr(3)Se(14), Cs(4)Zr(3)Se(14), and Cs(4)Hf(3)Se(14) crystallize in the K(4)Ti(3)S(14) structure type with four formula units in space group C(2)(h)()(6)-C2/c of the monoclinic system at T = 153 K in cells of dimensions a = 21.085(1) A, b = 8.1169(5) A, c = 13.1992(8) A, beta = 112.835(1) degrees for Rb(4)Ti(3)S(14);a = 21.329(3) A, b = 8.415(1) A, c = 13.678(2) A, beta = 113.801(2) degrees for Cs(4)Ti(3)S(14); a = 21.643(2) A, b = 8.1848(8) A, c = 13.331(1) A, beta = 111.762(2) degrees for Rb(4)Hf(3)S(14); a = 22.605(7) A, b = 8.552(3) A, c = 13.880(4) A, beta = 110.919(9) degrees for Rb(4)Zr(3)Se(14); a = 22.826(5) A, b = 8.841(2) A, c = 14.278(3) A, beta = 111.456(4) degrees for Cs(4)Zr(3)Se(14); and a = 22.758(5) A, b = 8.844(2) A, c = 14.276(3) A, beta = 111.88(3) degrees for Cs(4)Hf(3)Se(14). These A(4)M(3)Q(14) compounds (A = alkali metal; M = group 4 metal; Q = chalcogen) contain hexagonally closest-packed [M(3)Q(14)(4-)] chains that run in the [101] direction and are separated by A(+) cations. Each [M(3)Q(14)(4-)] chain is built from a [M(3)Q(14)] unit that consists of two MQ(7) pentagonal bipyramids or one distorted MQ(8) bicapped octahedron bonded together by edge- or face-sharing. Each [M(3)Q(14)] unit contains six Q(2)(2-) dimers, with Q-Q distances in the normal single-bond range 2.0616(9)-2.095(2) A for S-S and 2.367(1)-2.391(2) A for Se-Se. The A(4)M(3)Q(14) compounds can be formulated as (A(+))(4)(M(4+))(3)(Q(2)(2-))(6)(Q(2-))(2).     

Bis(trifluoroacetyl) peroxide, CF(3)C(O)OOC(O)CF(3)

Pure, highly explosive CF(3)C(O)OOC(O)CF(3) is prepared for the first time by low-temperature reaction between CF(3)C(O)Cl and Na(2)O(2). At room temperature CF(3)C(O)OOC(O)CF(3) is stable for days in the liquid or gaseous state. The melting point is -37.5 degrees C, and the boiling point is extrapolated to 44 degrees C from the vapor pressure curve log p = -1875/T + 8.92 (p/mbar, T/K). Above room temperature the first-order unimolecular decay into C(2)F(6) + CO(2) occurs with an activation energy of 129 kJ mol(-1). CF(3)C(O)OOC(O)CF(3) is a clean source for CF(3) radicals as demonstrated by matrix-isolation experiments. The pure compound is characterized by NMR, vibrational, and UV spectroscopy. The geometric structure is determined by gas electron diffraction and quantum chemical calculations (HF, B3PW91, B3LYP, and MP2 with 6-31G basis sets). The molecule possesses syn-syn conformation (both C=O bonds synperiplanar to the O-O bond) with O-O = 1.426(10) A and dihedral angle phi(C-O-O-C) = 86.5(32) degrees. The density functional calculations reproduce the experimental structure very well.