Solvothermal Synthesis of Superfine Li1−xMn2O4−σ Powders

Superfine Li_1−xMn₂O_4−σ powders were successfully synthesized by the alcohol-thermal method using 0.01 mol of MnO₂, 0.01mol of LiOH·H₂O, and 0.06mol of NaOH as starting materials at 160-200°C. The products are characterized by XRD, TEM, ED, BET, and ICP. Results show that the Li_0.74Mn₂O_3.74 powder prepared at 200°C has an average size of 180 nm with BET surface areas of 16.44 m²/g. A possible formation mechanism is proposed. It was concluded that the alcohol acts not only as the solvent but also as the reducing agent in the synthesis of Li_1−xMn₂O_4−σ powders. The effects of reaction temperature and the contents of NaOH and LiOH on the formation of single phase Li_1−xMn₂O_4−σ were investigated.     

Thermochemistry of Li1+xMn2−xO4 (0?x?1/3) spinel

Lithium substituted Li_1+xMn_2−xO₄ spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na₂O·4MoO₃ at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn³⁺ to Mn⁴⁺ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn³⁺ to Mn⁴⁺ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.     

Synthesis of layered cathode material Li[CoxMn1−x]O2 from layered double hydroxides precursors

Cathode materials Li[Co_xMn_1−x]O₂ for lithium secondary batteries have been prepared by a new route—precursor method of layered double hydroxides (LDHs). In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with mass spectrometry (TG-MS) were used to monitor the structural transformation during the reaction of CoMn LDHs and LiOH·H₂O: firstly the layered structure of LDHs transformed to an intermediate phase with spinel structure; then the distortion of the structure occurred with the intercalation of Li⁺ into the lattice, resulting in the formation of layered Li[Co_xMn_1−x]O₂ with α-NaFeO₂ structure. Extended X-ray absorption fine structure (EXAFS) data showed that the Co-O bonding length and the coordination number of Co were close to those of Mn in Li[Co_xMn_1−x]O₂, which indicates that the local environments of the transitional metals are rather similar. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state of Co and Mn. The influences of Co/Mn ratio on both the structure and electrochemical property of Li[Co_xMn_1−x]O₂ have been investigated by XRD and electrochemical tests. It has been found that the products synthesized by the precursor method demonstrated a rather stable cycling behavior, with a reversible capacity of 122.5 mAh g⁻¹ for the layered material Li[Co_0.80Mn_0.20]O₂.     

用MnO_2离子筛吸附剂从溶液中提取锂(英文)

研究了MnO2离子筛的制备、表征及其提锂性能。通过控制低温水热合成反应条件制备了4种不同晶相的一维纳米MnO2,进一步用浸渍法制备了Li-Mn-O三元氧化物前驱体,并经酸处理后得到对Li+具有特殊选择性的离子筛。用XRD、吸附等温线、吸附动力学及pH滴定等手段对产物的晶相结构和Li+吸附性能进行了研究。结果表明,SMO-b和SMO-d离子筛的Li+平衡吸附量符合Freundlich吸附等温方程。反应物浓度对MnO2不同晶面的生长速率有不同的影响,但(NH4)2SO4对吸附容量并无提高。吸附速率方程符合一级动力学Lagergren方程。MnO2离子筛Li+的吸附量远远高于Na+。     

High-resolution X-ray diffraction, DIFFaX, NMR and first principles study of disorder in the Li2MnO3-Li[Ni1/2Mn1/2]O2 solid solution

X-ray diffraction patterns of Li[Li_(1−2x)/3Ni_xMn_2/3−x/3]O₂ show reflections between 20° and 35°, 2θ (CuKα) due to Li₂MnO₃-like ordering of the transition metal (Ni, Mn and Li) layers. The ordering is rarely perfect, resulting in characteristic broadening and changes in the intensities of these reflections. ⁶Li MAS NMR studies of Li₂MnO₃ show that the [Li_1/3Mn_2/3] layers are well ordered, the disorder arising from the stacking of the layers in the c-direction. DIFFaX was used to model the Li₂MnO₃ XRD data and extract the stacking fault frequency. The results show that even well-ordered cation layers may show only weak or no superstructure reflections, if there is no or little ordering in the c-direction.     

Origin of the irreversible plateau (4.5 V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 layered material

Layered LiNi_0.4Co_0.2Mn_0.4O₂, Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, Li[Li_1/3Mn_2/3]O₂ powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO₂. Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ can be considered to be the solid solution of LiNi_0.4Co_0.2Mn_0.4O₂ and Li[Li_1/3Mn_2/3]O₂. Detailed information from XRD, ex situ XPS measurement and electrochemical analysis of these three materials reveals the origin of the irreversible plateau (4.5 V) of Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of Li[Li_1/3Mn_2/3]O₂ component, which maybe extract Li⁺ from the transition layer in Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ through oxygen release. This step also activates Mn⁴⁺ of Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, it can be reversibly reduced/oxidized between Mn⁴⁺ and Mn³⁺ in the subsequent cycles.     

不同组分下富锂正极材料xLi_2MnO_3·(1-x)LiNi_(0.5)Mn_(0.5)O_2(x=0.1-0.8)的晶体结构与电化学性能

采用溶胶-凝胶法制备了一系列富锂锰基正极材料xLi2MnO3?(1-x)LiNi0.5Mn0.5O2(x=0.1-0.8),通过X射线衍射(XRD)仪,扫描电子显微镜(SEM)和电化学测试等检测手段表征了所得样品的晶体结构与电化学性能,研究了不同组分下富锂材料的结构与电化学性能.结果表明:Li2MnO3组分含量较高时,材料的首次放电容量较高,但循环稳定性较差;该组分含量较少时,所得样品中出现尖晶石杂相,且放电容量较低,但循环稳定性较好;综合来看,x=0.5时材料的电化学性能最优.x=0.4,0.6时材料也表现出了较好的电化学性能,值得关注.     

The Crystal Chemistry of Lithium in the Alluaudite Structure: A Study of the (Na1−xLix)CdIn2(PO4)3 Solid Solution (x=0 to 1)

Several compounds of the (Na_1−xLi_x)CdIn₂(PO₄)₃ solid solution were synthesized by a solid-state reaction in air, and pure alluaudite-like compounds were obtained for x=0.00, 0.25, and 0.50. X-ray Rietveld refinements indicate the occurrence of Cd²⁺ in the M(1) site, and of In³⁺ in the M(2) site of the alluaudite structure. This non-disordered cationic distribution is confirmed by the sharpness of the infrared absorption bands. The distribution of Na⁺ and Li⁺ on the A(1) and A(2)′ crystallographic sites cannot be accurately assessed by the Rietvled method, probably because the electronic densities involved in the Na⁺→Li⁺ substitution are very small. A comparison with the synthetic alluaudite-like compounds, (Na_1−xLi_x)MnFe₂(PO₄)₃, indicates the influence of the cations occupying the M(1) and M(2) sites on the coordination polyhedra morphologies of the A(1) and A(2)′ crystallographic sites.     

Composition and structure of acid leached LiMn2−yTiyO4 (0.2≤y≤1.5) spinels

Lithium manganese titanium spinels, LiMn_2−yTi_yO₄, (0.2≤y≤1.5) have been synthesized by solid-state reaction between TiO₂ (anatase), Li₂CO₃ and MnCO₃. Li⁺ was leached from the powdered reaction products by treatment in excess of 0.2 N HCl at 85 °C for 6 h, under reflux. The elemental composition of the acidic solution and solid residues of leaching has been determined by complexometric titration, atomic absorption spectroscopy and X-ray fluorescence analysis. Powder X-ray diffraction was used for structural characterization of the crystalline fraction of the solid residues. It has been found that the amount of Li⁺ leached from LiMn_2−yTi_yO₄ decreases monotonically with increasing y in the interval 0.2≤y≤1.0 and abruptly drops to negligibly small values for y>1.0. The content of Mn and Li in the liquid phase and of Mn and Ti in the solid (amorphous plus crystalline) residue, were related to the composition and cation distribution in the pristine compounds. A new formal chemical equation describing the process of leaching and a mechanism of the structural transformation undergone by the initial solids as a result of Li⁺ removal has been proposed.     

ZnAl2O4:Mn材料的制备及发光性能

以共沉淀法与煅烧法联用,成功制备了一系列ZnAl₂O₄:xMn样品。通过扫描电镜和X射线粉末衍射测试研究了样品的形貌和物相特征,结果表明尖晶石结构的ZnAl₂O₄中[AlO₆]的八面体位可以有效被Mn⁴⁺替代。通过荧光激发和发射光谱研究了样品的发光性能,发现Mn⁴⁺在ZnAl₂O₄体系中掺杂可以显示出明亮的红色发光(发射峰值位于680 nm处)。比较不同Mn⁴⁺浓度(Mn与Al的物质的量之比)掺杂样品的发光强度时发现,Mn⁴⁺最佳掺杂浓度为0.06%。通过德克斯特公式分析了发光强度与浓度关系,探究浓度猝灭机制,结果表明最邻近离子之间能量传递造成Mn⁴⁺浓度猝灭的发生。为了提高Mn⁴⁺的发光强度,选择了7种金属离子(Li⁺、Na⁺、K⁺、Ca²⁺、Sr²⁺、Sn²⁺和Ga³⁺)与Mn⁴⁺共掺杂进入ZnAl₂O₄基质中,其中效果较突出的为Li⁺和Ga³⁺,其共掺杂使Mn⁴⁺发光强度分别增强0.6倍和1倍。     

Cathodic materials for lithium-ion batteries based on spinels Li x Mn2−y Me y O4: Synthesis, phase composition, and structure of Li x Mn2−y Cr y O4 at x = 1.0−1.2 and y = 0−0.5

Extralithiated chromium-doped finely divided lithium-manganese spinels are synthesized as a result of a two-step solid-phase process with use made of the fusion-saturation method. The spinels are intended for application as cathodic materials in lithium-ion batteries. The phase composition and structural characteristics of samples of cathodic materials of the type Li _x Mn_2?y Cr _y O₄ are studied. The samples with x = 1.0?1.2 and y = 0?0.5 are characterized by phase purity and cubic syngony with parameter a = 0.817?0.823 nm and a disperseness equal to 1–2 nm. The maximum content of chromium and lithium in Li _x Mn_2?y Cr _y O₄ that does not lead to violation of cubic syngony is determined. Lithium excess in the cathodic material that does not exceed 0.2 formula units may be used for compensating the irreversible capacity. Replacing some manganese atoms by chromium may facilitate retention of the structures’s integrity in the course of cycling.     

Electrical properties and sulfur tolerance of La0.75Sr0.25Cr1−xMnxO3 under anodic conditions

Complex metal oxides with composition of La_0.75Sr_0.25Cr_1−xMn_xO₃(x=0.4,0.5,0.6) (LSCM) have been synthesized and examined as anode materials for solid oxide fuel cells (SOFCs). LSCM compositions show excellent tolerance to both reduction and oxidation but the crystal structure transforms from hexagonal in air to orthorhombic in H₂. The volume change associated with this phase transformation is only about 1%, thus having little effect on other properties. The total electrical conductivity increases with the content of Mn, whereas the resistance to sulfur poisoning increases with the content of Cr. Fuel cells using LSCM as the anode show very good performance when pure hydrogen is used as the fuel. However, they do not appear to be stable in fuels containing 10% of H₂S.     

溶胶-凝胶法合成Li1-xNaxMn2O4及其作为水系锂离子电池正极材料的电化学性能

用溶胶凝胶法合成了Na⁺离子掺杂的Li_1-xNa_xMn₂O₄(x=0,0.01,0.03,0.05)。X射线衍射图表明Na⁺取代Li⁺进入Li_1-xNa_x Mn₂O₄晶格中,扫描电镜图看出产物是粒径为100~300 nm的颗粒。恒流充放电测试结果表明,Li_0.97Na_0.03Mn₂O₄在2C倍率下循环100圈后放电容量保持率比未掺杂的LiMn₂O₄从51.2%提升到84.1%。循环伏安测试表明Na⁺离子掺杂降低了材料极化且增大了锂离子扩散系数。10C倍率下Li_0.97Na_0.03Mn₂O₄仍有79.0 mAh·g^-1的放电容量,高于未掺杂样品的52.1 mAh·g^-1。Na⁺离子掺杂可以稳定材料结构并提高锂离子扩散系数,从而提高LiMn₂O₄的电化学性能,是一种可行的改性方法。     

溶胶-凝胶法合成Li_(1-x)Na_xMn_2O_4及其作为水系锂离子电池正极材料的电化学性能

用溶胶凝胶法合成了Na+离子掺杂的Li_(1-x)Na_xMn_2O_4(x=0,0.01,0.03,0.05)。X射线衍射图表明Na+取代Li+进入Li_(1-x)Na_xMn_2O_4晶格中,扫描电镜图看出产物是粒径为100~300 nm的颗粒。恒流充放电测试结果表明,Li_(0.97)Na_(0.03)Mn_2O_4在2C倍率下循环100圈后放电容量保持率比未掺杂的LiMn_2O_4从51.2%提升到84.1%。循环伏安测试表明Na+离子掺杂降低了材料极化且增大了锂离子扩散系数。10C倍率下Li0.97Na0.03Mn2O4仍有79.0 m Ah·g-1的放电容量,高于未掺杂样品的52.1 m Ah·g~(-1)。Na+离子掺杂可以稳定材料结构并提高锂离子扩散系数,从而提高LiMn_2O_4的电化学性能,是一种可行的改性方法。     

Mn1-x(Li,Ti)xCo2O4尖晶石型复合氧化物的制备、表征与催化性能

用柠檬酸配位燃烧法合成了Mn_1-x(Li,Ti)_xCo₂O₄系列尖晶石型复合氧化物催化剂，使用FTIR和XRD方法对催化剂结构进行表征，通过程序升温氧化反应(TPO)技术对这些催化剂在模拟柴油机尾气条件下进行同时消除NO_x和柴油碳黑反应的活性评价。结果表明，掺杂Li或Ti后的Mn_1-x(Li,Ti)_xCo₂O₄系列催化剂仍然保持了完整的尖晶石型复合氧化物结构，这些催化剂对同时消除柴油机尾气中的碳黑颗粒和NO_x具有良好的催化性能，其中Li或Ti的掺杂量为x=0.05较佳，结合碳黑燃烧与NO_x还原总的催化效果，Mn_0.95Li_0.05Co₂O₄具有最好的催化活性。     

Synthesis and structural study of a new NASICON-type solid solution: Li1−xLax/3Zr2(PO4)3

A new complete solid solution of NASICON-type compounds between LiZr₂(PO₄)₃ and La_1/3Zr₂(PO₄)₃ was evidenced with the general formula Li_1−xLa_x/3Zr₂(PO₄)₃ (0?x?1). These phases were synthesized by a complex polymerizable method and structurally characterized from Rietveld treatment of their X-ray and neutron powder diffraction data. This solid solution results from the substitution mechanism Li⁺→1/3La³⁺+2/3□ leading to an increase of the vacancies number correlated to an increase of the La content. According to this substitution mechanism, the general formula can then be written Li_1−xLa_x/3□_2x/3Zr₂(PO₄)₃ (0?x?1) in order to underline the correlation between the La content and the vacancies rate. For all the compounds, the structure is clearly related to that of the NASICON family with three crystallographic domains evidenced. For 0?x?0.5, all the members adopt at high temperature the typical NASICON-type structure (s.g. R3¯c), while at lower temperature, their structure distorts to a triclinic form (s.g. C 1¯), as observed for LiZr₂(PO₄)₃ prepared above 1100 °C. Moreover, in this domain, the reversible transition is clearly soft and the transition temperature strongly depends of the x value. For 0.6?x?0.9, the compounds crystallize in a rhombohedral cell (s.g. R3¯), while for x=1, the phase La_1/3Zr₂(PO₄)₃ is obtained (s.g. P3¯, Z=6, a=8.7378(2) Å, c=23.2156(7) Å).This paper is devoted to the structure analysis of the series Li_1−xLa_x/3Zr₂(PO₄)₃ (0?x?1), from X-ray and neutron powder thermo diffraction and transmission electron microscopy (TEM) studies.     

Structural transformation and oxidation of Sr2MnO3.5+x determined by in-situ neutron powder diffraction

The oxidation of the n = 1 Ruddlesden-Popper phase, Sr₂MnO_3.5+x, where 0 ≤ x ≤ 0.5 has been investigated using a combination of in-situ diffraction techniques. In agreement with previous reports the room temperature structure of Sr₂MnO_3.5+x was determined to be monoclinic crystallising in space group P2₁/c. On heating in air the material undergoes rapid oxidation at a relatively modest temperature, ∼275 °C. The oxidation process is coincident with a significant change in the structure, with the material now adopting a tetragonal I4/mmm structure. In the oxygen deficient phase where x > 0 the Mn coordination is square pyramidal, with a sixth partially occupied oxygen position giving rise to octahedral coordination. Oxidation of Sr₂MnO_3.5+x results in the filling of the partially occupied O4 positions and a resulting increase in symmetry, with the Mn coordination now adopting solely a distorted octahedral environment.     

Mn environment in layered Li[Mg0.5−xNixMn0.5]O2 oxides monitored by EPR spectroscopy

X-band and high-frequency EPR spectroscopy were used for studying the manganese environment in layered Li[Mg_xNi_0.5−xMn_0.5]O₂, 0?x?0.5. Both layered LiMg_0.5Mn_0.5O₂ and monoclinic Li[Li_1/3Mn_2/3]O₂ oxides (containing Mn⁴⁺ ions only) were used as EPR standards. The EPR study was extended to the Ni-substituted analogues, where both Ni²⁺ and Mn⁴⁺ are paramagnetic. For LiMg_0.5−xNi_xMn_0.5O₂ and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂, an EPR response from Mn⁴⁺ ions only was detected, while the Ni²⁺ ions remained EPR silent in the frequency range of 9.23-285 GHz. For the diamagnetically diluted oxides, LiMg_0.25Ni_0.25Mn_0.5O₂ and Li[Li_0.10Ni_0.35Mn_0.55]O₂, two types of Mn⁴⁺ ions located in a mixed (Mn-Ni-Li)-environment and in a Ni-Mn environment, respectively, were registered by high-field experiments. In the X-band, comparative analysis of the EPR line width of Mn⁴⁺ ions permits to extract the composition of the first coordination sphere of Mn in layered LiMg_0.5−xNi_xMn_0.5O₂ (0?x?0.5) and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ (x>0.2). It was shown that a fraction of Mn⁴⁺ are in an environment resembling the ordered “α,β”-type arrangement in Li_1−δ1Ni_δ1[Li_{(1−2x)/3+δ1}Ni_2x/3−δ1)_α(Mn_(2−x)/3Ni_x/3)_β]O₂ (where and δ₁=0.06 were calculated), while the rest of Mn⁴⁺ are in the Ni,Mn-environment corresponding to the Li_1−δ2Ni_δ2[Ni_1−yMn_y]O₂ () composition with a statistical Ni,Mn distribution. For Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ with x?0.2, IR spectroscopy indicated that the ordered α,β-type arrangement is retained upon Ni introduction into monoclinic Li[Li_1/3Mn_2/3]O₂.     

球形PVC-MnO2离子筛的制备及锂吸附性能

本实验室前期所制备的Li4Mn5O12超细粉末在卤水体系中对Li+具有较大的吸附容量和良好的选择性。但由于超细粉体的流动性和渗透性差,无法直接应用于固定床,需对粉末吸附材料进行成型造粒,以便于实际应用。本论文采用聚氯乙烯为粘结剂,制备出粒径约为2.0~3.5 mm的球形PVC-Li4Mn5O12,经盐酸处理后得到球形PVC-MnO2离子筛。并通过扫描电镜(SEM)、X射线衍射仪(XRD)、静态和动态连续锂吸附实验研究了球形离子筛形貌和锂离子吸附性能。结果表明,球形离子筛对Li+的吸附容量高达5.28 mmol.g-1,在混合溶液中对Li+具有良好的选择性,这对于在盐湖卤水或海水提锂具有重要的实用意义。