LiMn2O4 electrode prepared by gold–titanium codeposition with improved cyclability

An LiMn₂O₄ electrode was prepared based on mixed-metals (gold–titanium) codeposition method. By this method, titanium oxide is also incorporated into the electroactive film formed on substrate electrode. Formation of titanium oxide on the spinel surface avoids dissolution of Mn from the spinel at elevated temperatures. TiO₂can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the LiMn₂O₄ spinel can be improved by the surface modification with TiO₂. This action improves cyclability for lithium battery performance and reduces capacity fades of LiMn₂O₄ at elevated temperatures.     

Cycle characterizations of LiMxMn2−xO4 (M=Co, Ni) materials for lithium secondary battery at wide voltage region

LiM_xMn_2−xO₄ (M=Co, Ni) materials have been synthesized by a melt-impregnation method using γ-MnOOH as the manganese source. Highly crystallized LiM_xMn_2−xO₄ compounds were synthesized at a calcination temperature of 800°C for 24 h in air. All compounds show a single phase except for LiNi_0.5Mn_1.5O₄ based on the X-ray diffraction (XRD) diagram. With the increase of the doping content from 0.1 to 0.5, the capacity of doping materials decreases mainly in the 4 V region.

Although LiM_0.5Mn_1.5O₄ (M=Co, Ni) compound shows a small capacity in the (3+4) V region compared with parent LiMn₂O₄, it is a very effective material in reducing capacity loss in the 3 V region that is caused by the Jahn–Teller distortion. The doping of Co and Ni ions in the LiMn₂O₄ cathode material promotes the stability of this structure and provides an excellent cyclability.     

Electrochemical characteristics and cycle performance of LiMn2O4/a-Si microbattery

A LiMn₂O₄ thin film and an amorphous Si (a-Si) thin film were prepared by radio-frequency (rf) magnetron sputtering. Each thin film was electrochemically evaluated by cyclic voltammetry (CV) and galvanostatic cycling. The rate of capacity fade on cycling was monitored as a function of the voltage window and current density. This was compared with the cycle performance of cathode and anode using two kinds of electrolyte, 1 M LiPF₆ in EC/DMC and PC, for 100 cycles. It was found that the discharge capacity of optimized LiMn₂O₄/a-Si full-cell reached 24 μAh/(cm²-μm) in the first cycle, and a reversible capacity of about 16 μAh/(cm² μm) was still maintained after 100 cycles. In a voltage window of 3.0–4.2 V, LiMn₂O₄/a-Si full-cell exhibits relatively stable cycle performance compared to a voltage window of 2.75–4.2 V.     

Synthesis of LiNi0.8Co0.2O2 cathode material through sintering in an air environment and electrochemical properties characterization

制备锂离子电池正极材料LiNi_0.8Co_0.2O₂通常需要在纯氧气气氛下进行烧结.本工作以硫酸镍,硫酸钴和氢氧化钠为原料,采用并流共沉淀法制备了高密度Ni_0.8Co_0.2(OH)₂前驱体,再采用高温固相反应法在空气中烧结制备了锂离子电池LiNi_0.8Co_0.2O₂正极材料.采用X射线衍射(XRD),扫描电镜(SEM),恒流充放电测试(ECT),循环伏安(CV)与比表面积(BET)测试等方法对目标样品进行了表征,详细考察了烧结条件对材料结构,微观形貌及电化学性能的影响.结果表明,锂/(钴+镍)摩尔比为1.13∶1时,在管式炉中和空气气氛下于第一段烧结温度700 ℃保温9 h,于第二段烧结温度750 ℃保温12 h,合成的材料比表面积适中(0.78 m²/g),具有规则的六边形α-NaFeO₂层状结构,晶粒分布均匀,电化学性能最优.在0.5 C充放电倍率下和2.7~4.3 V电压范围内,其首次放电比容量达到153.0 mA·h/g,循环20次后放电比容量仍为150.7 mA·h/g,容量保持率达到98.5%,显示了优异的循环稳定性能,可用做高能量密度动力电池正极材料.     

Electrochemical and structural characteristics of metal oxide-coated lithium manganese oxide (spinel type): Part I. In the range of 2.5–4.2 V

The electrochemical and structural characteristics of the metal oxide-coated spinel were investigated in the range of 2.5–4.2 V. Metal oxide coating on commercial spinel powder (LiMn_2−xM_xO₄, M=Zr, Nikki, Japan) was carried out using the sol–gel method. Al₂O₃/(PtO_x or CuO_x)-coated spinel exhibited improved cyclability compared to bare spinel. Impedance analysis results indicated that electrochemical resistance value was not consistent with cycle performance. The improved cycle performance of metal oxide-coated spinel may be due to formation of a new Li₂Mn₄O₉, Li₂MnO₃ phase, which is expected to have stability to phase transition (Jahn–Teller distortion).     

Enhancing the elevated temperature performance of Li/LiMn2O4 cells by reducing LiMn2O4 surface area

Lithium-rich spinels were obtained with the same structure but different surface area by two different synthesis routes, namely the “once-annealed” and the “twice-annealed” methods. The elevated temperature performance of Li/Li_1+xMn₂O₄ cell is significantly improved using a spinel cathode with a small surface area: the cell at 50°C lost 5% of the initial capacity over the first 100 cycles based on a spinel cathode with the small surface area of 1.2 m²/g compared to 8% based on a large one of 6.2 m²/g. Also the mechanism responsible for the reaction of LiMn₂O₄ with LiOH to form lithium-rich spinel has been investigated.     

Electrochemical characteristics of metal oxide-coated lithium manganese oxide (spinel type): Part II. In the range of 3.0–4.4 V

Metal oxide-coated spinel was investigated with respect to electrochemical characteristics. Metal oxide coating on commercial spinel powder (LiMn_2−xM_xO₄, M=Zr, Nikki, Japan) was carried out using the sol–gel method. Al₂O₃/CuO_x-coated spinel exhibited stable cycle performance in the range from 3.0 to 4.4 V, and it had lower charge transfer resistance and higher double layer capacitance than bare spinel in later cycles. In the SEM image of the powder after the cell test, bare spinel showed abnormal surfaces formed by decomposition of the electrolyte, while Al₂O₃/CuO_x-coated spinel displayed a normal surface covered with a surface film. Therefore, it is expected that an Al₂O₃/CuO_x layer coated on the spinel powder can function as a protective film, which supresses the reaction between electrolyte and active material.     

Electrochemical performance of Nd0.6Sr0.4Co0.5Fe0.5O3−δ–Ag composite cathodes in intermediate temperature solid oxide fuel cells

The electrochemical performances of Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes have been investigated in intermediate temperature solid oxide fuel cells. The Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag cathodes prepared by ball milling followed by firing at 920 °C show the maximum performance (power density: 0.15 W cm⁻² at 800 °C) at 3 wt.% Ag. On the other hand, the Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ–Ag composite cathodes with 0.1 mg cm⁻² (0.5 wt.%) Ag that were prepared by an impregnation of Ag into Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ followed by firing at 700 °C (but the electrolyte–Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ assembly was prepared first by firing at 1100 °C) exhibit much better performance (power density: 0.27 W cm⁻² at 800 °C) than the composite cathodes prepared by ball milling, despite a much smaller amount of Ag due to a better dispersion and an enhanced adhesion. AC impedance analysis indicates that the Ag catalysts dispersed in the porous Nd_0.6Sr_0.4Co_0.5Fe_0.5O_3−δ cathode reduce the ohmic and the polarization resistances due to an increased electronic conductivity and enhanced electrocatalytic activity.     

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

The preparation of LiCo_yMn_xNi_1−x−yO₂ from LiOH·H₂O, Ni(OH)₂ and γ-MnOOH in air was studied in detail. Single-phase LiCo_yMn_xNi_1−x−yO₂ (0y0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1z1.11 for y=0.2) and the Co doping level (0.05y0.2) do not significantly affect the discharge capacity of Li_zCo_yMn_0.2Ni_0.8−yO₂. The doping of Co into LiMn_0.2Ni_0.8O₂ accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn_0.2Ni_0.8O₂ is determined to be 4, the formation of a solid solution between LiCo_yNi_1−yO₂ and Li₂MnO₃ is confirmed.     

Preparation of conductive fire retardant and its application in Li-ion battery

锂离子电池内短路是诱发电池热失控的主要原因,适当的安全性添加剂可以阻止电池热失控的发生。本文通过界面聚合法在聚乙烯蜡表面生成适量的导电聚苯胺,制备了一种具有良好导电性能的PTC材料（PANI-PEW）,并对PANI-PEW的微观形貌、电导率以及添加至LiFePO₄正极中的电化学性能进行了对比分析。测试结果表明,PANI-PEW在常温下的电导率为1.08×10^-3 S/m,在90~120℃时,其电阻值急剧增大。在0.5 C和1 C倍率下,PANI-PEW的加入对LiFePO₄电池的阻抗和循环性能影响较小,而经过120℃热处理后的含15%（质量分数） PANI-PEW的极片,其电池的阻抗大幅增加且首次放电比容量只有35.3 mA·h/g,在第12次循环后,放电比容量接近于0。以上结果表明,PANI-PEW是一种性能优异的PTC材料且能在120℃时阻止电池热失控的发生。     

Capacity fading with oxygen loss for manganese spinels upon cycling at elevated temperatures

The nominal LiMn₂O₄ and Li-doped spinels with different oxygen stoichiometry were prepared and investigated for capacity fading upon cycling at elevated temperatures. The discharge plateau at 3.2 V originating from oxygen defects in manganese spinels is observed to grow very quickly to nearly a maximum scale in initial 15 cycles at 60 °C. Meanwhile, the majority of capacity fading is lost. Therefore, the quick capacity fading in the initial stage is associated with the increase of oxygen deficiencies or oxygen loss upon cycling. It is proposed that the oxygen loss is originated from the decomposition of instable spinel phases that containing little Li cations on the 8a sites ([□₁]_8a[Mn_2−x]_16d[O_4−δ□_δ]_32e, etc.), which are formed upon charging to the upper voltage limit. This phenomenon is much severe for nominal LiMn₂O₄ spinels with oxygen deficiencies. After partial substitution of Mn with Li, part of the Li cations on the 8a sites will be retained upon charging to the upper voltage limit. Thereafter, the cycling performance can be improved for the stabilized spinel phases formed upon charging.     

Calculation of temperature rise in lithium polymer batteries of Sandia conceptual designs during USABC Dynamic Stress Test

Based on reported galvanostatic charge and discharge data of a Li/P(EO)₈LiClO₄/TiS₂ cell, heat generation rates within a battery during the USABC Dynamic Stress Test (DST) were calculated and compared with those during the Simplified Federal Urban Driving Schedule (SFUDS) dynamic power profile. Also, calculations of temperature rise in the C/Polymer electrolyte/LiMn₂O₄ batteries of Sandia conceptual designs for a Ford van and GM Impact, during a DST/Fast Charge/DST/Full Charge cycle were conducted with a three-dimensional thermal model.     

Preparation,electrochemical performance and phase transition of high voltage LiNi0.5Mn1.5O4 cathode material

尖晶石LiNi_0.5Mn_1.5O₄因其可在4.7 V高电位下工作并有良好的循环特性,已成为最具潜力的高能量密度锂离子电池正极材料。本文首先采用喷雾干燥辅助烧结法制备了LiNi_0.5Mn_1.5O₄正极材料,考察了热处理条件对材料结构与性能的影响。用XRD、SEM和FT-IR等技术对所制备的LiNi_0.5Mn_1.5O₄材料的结构和表面形貌进行表征,利用原位XRD技术研究了LiNi_0.5Mn_1.5O₄正极材料在充放电过程中结构相变规律。结果表明,所制备的LiNi_0.5Mn_1.5O₄材料均具有Fd-3m空间群的立方相尖晶石型结构,并具有优异的电化学性能,其0.1 C时首次放电容量为132 mA·h/g,首轮库仑效率93.48%,高倍率下该材料的电化学性能优越。原位XRD测量结果分析表明,尖晶石型LiNi_0.5Mn_1.5O₄材料在充电过程中存在4个显著的相变过程,在嵌脱锂过程中,从四面体相向立方相结构相变过程是可逆的。     

Ni-Co双金属催化剂上沼气重整制氢宏观动力学

用传统湿式浸渍法制备La2O3掺杂的商业γ-Al2O3负载的沼气重整催化剂Ni-Co/La2O3-γ-Al2O3,通过对NiCo双金属催化剂上沼气重整制氢在常压下的宏观动力学分析,得出该催化剂上CH4与CO2消耗、H2与CO生成时的表观反应速率方程.通过改变进料中CH4与CO2的分压,求出各物质的反应分级数,确定总反应...     

铁酸铜尖晶石催化甲醛氧化的性能研究

通过溶胶-凝胶-自蔓延燃烧法制备了系列Cu_xFe_3-xO₄尖晶石催化剂。采用XRD和XPS表征方法对催化剂晶相结构及表面元素价态进行了分析,考察了Cu_xFe_3-xO₄催化甲醛的氧化效率。采用密度泛函理论探究了甲醛吸附在CuFe₂O₄表面的最稳定构型和吸附机理。结果表明,Cu_xFe_3-xO₄催化剂主要由Cu-Fe尖晶石相和部分CuO、Fe₂O₃相组成。Cu_0.5Fe_2.5O₄催化甲醛氧化效率最佳,在温度高于250℃时氧化效率达到90%以上。甲醛在CuFe₂O₄(100)表面的吸附属于化学吸附,吸附能为 -107.15 kJ/mol。     

Electrochemical thermal stability of the LiFePO4/LiNi0.8Co0.15Al0.05O2 blend cathode material for lithium ion batteries

为了改善LiNi_0.8Co_0.15Al_0.05O₂正极材料的电化学热稳定性能,加入LiFePO₄共混制成了LiFePO₄/LiNi_0.8Co_0.15Al_0.05O₂锂离子电池用混合正极材料。使用X射线衍射（XRD）和扫描电子显微镜（SEM）表征了结构和形貌,测试了电化学性能。结果显示,简单球磨的混合LiFePO₄/LiNi_0.8Co_0.15Al_0.05O₂正极材料中,纳米LiFePO₄粒子包覆在LiNi_0.8Co_0.15Al_0.05O₂粒子表面提高了混合正极材料在充放电过程中的电化学稳定性和结构稳定性。LiFePO₄/LiNi_0.8Co_0.15Al_0.05O₂混合正极材料在50 ℃下循环100周容量保持率为82.0%,明显地优于单一LiNi_0.8Co_0.15Al_0.05O₂材料的72.9%。     

Preparation of LiNi0.80Co0.15Al0.05O2 cathode material via Li-rich method

本文采用共沉淀法制备球形Ni_0.80Co_0.15Al_0.05(OH)_2.05前驱体,经预氧化后,采用富锂配比在氧气和空气气氛下烧结合成LiNi_0.80Co_0.15Al_0.05O₂正极材料.用X射线衍射,扫描电镜和恒电流充放电测试等方法对该材料的结构,形貌及电化学性能进行表征.结果表明:当锂配比为1.15时,氧气和空气中烧结合成的LiNi_0.80Co_0.15Al_0.05O₂正极材料的形貌,结构和电化学性能相当.富锂配比方法可在空气气氛下制备出电化学性能优异的LiNi_0.80Co_0.15Al_0.05O₂正极材料.0.1 C放电克比容量在200 mA·h/g以上,首次效率在87%左右;1 C放电克比容量在168 mA·h/g以上;800周循环容量保持率在80%以上.     

Lithium ion cell safety

The safety characteristics of recent commercial lithium ion cells are examined in relation to their use for cellular phones. These are prismatic cells with an aluminum cell housing (can) and a 500–600 mA h capacity. They have one of two types of 4-V class cathodes, lithium cobalt oxide (LiCoO₂) or lithium manganese oxide (LiMn₂O₄). This report provides results of the safety tests that we performed on lithium ion cells and outlines our views regarding their safety.     

Rb掺杂Li4Ti5O12作为锂离子电池负极材料的合成及电化学性能

合成了不同Rb掺杂量的钛酸锂（Li_4-xRb_xTi₅O₁₂; x = 0.010, 0.015, 0.020）作为锂离子电池的负极材料。测试结果显示,Rb离子掺杂有效增强了钛酸锂的电子电导率。相同的测试条件下,相比于未掺杂样品和高Rb含量掺杂样品（x = 0.015, 0.020）,适量的Rb掺杂钛酸锂（Li_3.99Rb_0.01Ti₅O₁₂; x = 0.010）表现出最优的电化学性能。Li_3.99Rb_0.01Ti₅O₁₂材料表现出161.2 mA∙h/g的初始容量,且在1 C下经过1000次循环后容量保持率可达90.9%。此外,全电池Li_3.99Rb_0.01Ti₅O₁₂ // LiFePO₄在0.5 C条件下首次放电容量为144 mA∙h/g,经过150次循环后,容量保持率为78.8%。     

MW-assisted synthesis of LiFePO4 for high power applications

LiFePO₄/C was prepared by solid-state reaction from Li₃PO₄, Fe₃(PO₄)₂·8H₂O, carbon and glucose in a few minutes in a scientific MW (microwave) oven with temperature and power control. The material was characterized by X-ray diffraction, scanning electron microscopy and by TGA analysis to evaluate carbon content. The electrochemical characterization as positive electrode in EC (ethylene carbonate)–DMC (dimethylcarbonate) 1 M LiPF₆ was performed by galvanostatic charge–discharge cycles at C/10 to evaluate specific capacity and by sequences of 10 s discharge–charge pulses, at different high C-rates (5–45C) to evaluate pulse-specific power in simulate operative conditions for full-HEV application. The maximum pulse-specific power and, particularly, pulse efficiency values are quite high and make MW synthesis a very promising route for mass production of LiFePO₄/C for full-HEV batteries at low energy costs.