硫系电解液添加剂对镍钴锰酸锂//石墨锂离子电池性能的影响北大核心CSCD

本工作系统研究了6种添加剂[碳酸亚乙烯酯(VC)、亚硫酸乙烯酯(ES)、硫酸乙烯酯(DTD)、1,3-丙二醇环硫酸酯(PCS)、1,3-丙烷磺酸内酯(PS)、1,3-丙烯磺酸内酯(PST)]对镍钴锰酸锂(NCM111)//石墨体系锂离子电池电化学性能的影响,通过对比首次充放电效率、放电容量、倍率特性、低温放电能力、高温存储性能以及循环寿命等发现:VC在各方面性能比较均衡,碳碳双键(C=C)能够改善成膜特性,循环性能优异,可独立使用;ES在化成、循环和存储过程中因电解液持续分解而胀气,无法单独使用;硫酸酯添加剂(DTD和PCS)能够明显降低阻抗并提升低温性能,但高温性能稍差;磺酸内酯添加剂(PS和PST)对抑制高温胀气效果突出,含有双功能基团的PST循环性能及抑制电压衰减的能力优于PS,但低温阻抗较高。综合对比发现,单组分硫系添加剂在某些性能方面有自己的特色,但也存在显而易见的缺陷,无法独立使用。通过与VC进行等比例复配,硫系添加剂循环性能差的问题得以解决,而高首效、低内阻、大倍率和高温稳定性等特色功能得以保持,二元联用后的综合性能显著优于单组分添加剂,采用添加剂联用方式来改善电池综合性能是较佳选择。     

电化学阻抗谱识别不同化学体系退役动力锂离子电池北大核心CSCD

退役动力锂离子电池梯次利用可充分提高动力电池的经济性,然而目前动力电池标识信息混乱、电池荷电状态差异和工作电压重叠均导致无法直接或依据开路电压准确分辨磷酸铁锂动力电池与镍钴锰三元动力电池。为此,基于动力锂离子电池的结构和等效电路,建立了容量与动力电池界面电容、反应电阻、韦伯阻抗和液相电阻的对应关系,通过分析动力电池容量对电化学阻抗实部和虚部的影响探讨了利用阻抗法快速识别退役动力锂离子电池化学体系的可能性。结果表明电化学阻抗实部与虚部的比值与电池容量无关,据此可利用该比值随频率的变化差异快速识别不同化学体系的动力锂离子电池,从而避免依据充放电判断电池化学体系的低效率。此外,软包装磷酸铁锂和镍钴锰三元电池的测试结果也表明10 Ah、12.5 Ah和50 Ah的磷酸铁锂电池阻抗虚部与实部比值随交流信号频率的变化基本相同,但与镍钴锰三元电池明显不同,初步验证了该方法的有效性。     

双酸改性对低品位凹凸棒石吸附性能和白度的影响

以低品位凹凸棒石为原料,采用双酸活化法,对原料及酸改性样品进行了SEM、XRD、XRF、BET表征及分析,以其对大豆油的脱色率为性能评价,探讨了双酸改性对低品位凹凸棒石吸附性能和白度的影响规律。研究表明,低品位凹凸棒石的改性方法采用双酸活化法——先硫酸酸化再盐酸酸化,得到的样品对大豆油的脱色率为76.83%,达到国家标准值,白度也较高,为71.8%。低品位凹凸棒石原矿中含钙物质的杂质较多,硫酸改性后吸附性能没有得到明显提高,可能是由于微溶的硫酸钙残留在样品表面或孔隙中。此外,低品位凹凸棒石及酸改性样品对大豆油除了物理吸附外,还存在一定的化学吸附。     

氧化钴孕育剂的形成机理及精铸工艺的研究

为了提高动叶片的抗冷热疲劳和抗机械疲劳的性能，铸件表面需进行晶粒细化。通常是在熔模铸造表面涂料中加入一定量晶粒细化剂，靠金属液与面层涂料中的细化剂相互作用而使铸件表面晶粒细小。着重论述了氧化钴孕育剂的形成机制及氧化钴孕育剂的精铸工艺及金相分析。     

Structural and thermal stabilities of layered Li(Ni1/3Co1/3Mn1/3)O2 materials in 18650 high power batteries

The structural and thermal stabilities of the layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials under high rate cycling and abusive conditions are investigated using the commercial 18650 Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite high power batteries. The Li(Ni_1/3Co_1/3Mn_1/3)O₂ materials maintain their layered structure even when the power batteries are subjected to 200 cycles with 10 C discharge rate at temperatures of 25 and 50 °C, whereas their microstructure undergoes obvious distortion, which leads to the relatively poor cycling performance of power batteries at high charge/discharge rates and working temperature. Under abusive conditions, the increase in the battery temperature during overcharge is attributed to both the reactions of electrolyte solvents with overcharged graphite anode and Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode and the Joule heat that results from the great increase in the total resistance (R_cell) of batteries. The reactions of fully charged Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathodes and graphite anodes with electrolyte cannot be activated during short current test in the fully charged batteries. However, these reactions occur at around 140 °C in the fully charged batteries during oven test, which is much lower than the temperature of about 240 °C required for the reactions outside batteries.     

A modified Al2O3 coating process to enhance the electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2 and its comparison with traditional Al2O3 coating process

Al₂O₃-modified Li(Ni_1/3Co_1/3Mn_1/3)O₂ is synthesized by a modified Al₂O₃ coating process. The Al₂O₃ coating is carried out on an intermediate, (Ni_1/3Co_1/3Mn_1/3)(OH)₂, rather than on Li(Ni_1/3Co_1/3Mn_1/3)O₂. As a comparison, Al₂O₃-coated Li(Ni_1/3Co_1/3Mn_1/3)O₂ also is prepared by traditional Al₂O₃ coating process. The effects of Al₂O₃ coating and Al₂O₃ modification on structure and electrochemical performance are investigated and compared. Electrochemical tests indicate that cycle performance and rate capability of Li(Ni_1/3Co_1/3Mn_1/3)O₂ are enhanced by Al₂O₃ modification without capacity loss. Al₂O₃ coating can also enhance the cycle performance but cause evident capacity loss and decline of rate capability. The effect of Al₂O₃ coating and Al₂O₃ modification on kinetics of lithium-ion transfer reaction at the interface of electrode/electrolyte is investigated via electrochemical impedance spectra (EIS). The result support that the Al₂O₃ modification increase Li⁺ diffused coefficient and decrease the activation energy of Li⁺ transfer reaction but the traditional Al₂O₃ coating lead to depression of Li⁺ diffused coefficient and increase of activation energy.     

Mathematical Simulation of Lithium Bromide Solution Laminar Falling Film Evaporation in Vertical Tube

For utilization of the residual heat of flue gas to drive the absorption chillers,a lithium-bromide falling film in vertical tube type generator is presented.A mathematical model was developed to simulate the heat and mass coupled problem of laminar falling film evaporation in vertical tube.In the model,the factor of mass transfer was taken into account in heat transfer performance calculation.The temperature and concentration fields were calculated.Some tests were conducted for the factors such as Re numbe...     

发电厂循环水、真空等系统的技术改进

一些70年代建造的火电厂,由于长期运行,设备陈旧,运行维护工作量大,煤耗居高不下,直接影响了公司的经济效益,本文对本公司数年来的技改成果作了一些介绍。     

安全监测监控系统在高瓦斯矿井中的应用改进

随着煤矿安全问题日益凸显,安全监测监控系统在高瓦斯矿井中得到了广泛应用。主要针对安全监测监控系统在高瓦斯矿井中的应用改进进行了详细探讨,为煤矿安全生产起到重要指导作用。     

Effect of capacity matchup in the LiNi0.5Mn1.5O4/Li4Ti5O12 cells

The effect of the capacity matchup between cathode and anode in the LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ cell system on cycling property, choice of electrolyte, high voltage and overcharge tolerances was investigated by comparing the cells with Li₄Ti₅O₁₂ limiting capacity with the cells with LiNi_0.5Mn_1.5O₄ limiting capacity. The former exhibits better cycling performance and less limitation of electrolyte choice than the latter. Furthermore, the Li₄Ti₅O₁₂-limited cell exhibits better tolerance to high voltage and overcharge than the LiNi_0.5Mn_1.5O₄-limited cell, owing to taking advantage of the extra capacity of Li₄Ti₅O₁₂ below 1 V. It is thus recommended that the LiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂ cell whose capacity is limited by Li₄Ti₅O₁₂ anode should be used to extend the application of the state-of-the-art lithium-ion batteries.     

∏形锅炉转弯烟道内的烟气流场变化及其对对流管束传热影响的分析与烟道结构改进

∏形布置的水管锅炉,后部转弯烟道内的烟气偏流会带来对流受热面的传热和温度偏差。当偏差较大时,会影响锅炉的整体运行性能。以一台70 MW热水锅炉为例,为减小转弯烟道内受热面的传热和温度偏差,结合流场数值分析调整烟道形状和尺寸,以确定合理的结构改进方案。方案实施后,经运行监测,对流管束前后部的温度偏差由17℃降低到3℃,其他相关的运行参数也都接近于设计值,取得了预期效果。     

Investigation on the root cause of the decreased performances in the overcharged lithium iron phosphate battery

The overcharge of the lithium iron phosphate (LiFePO₄) batteries usually leads to the sharp capacity fading and safety issues, especially under low temperature environment. Thus, investigating their root cause originated from the electrode materials is critical for the safety performance optimization and market promotion of the LiFePO₄ batteries. In this work, the electrochemical/thermal behaviors of 18650 LiFePO₄ batteries are investigated after overcharge under room and low temperature of 25°C and ?20°C, respectively. The results demonstrate a decreased electrochemical performance and faster heating rate of the overcharged battery, particularly under harsh working environments such as high discharge rate and low temperature. Coupling with the analyses of the internal resistance, the crystal structure, and microstructure of the electrodes, the root cause is attributed to the damage of the crystal structure and microstructure, which reduce the electron/Li⁺ migrating capability and electrolyte diffusion/transfer efficiency.     

Comparison of the surface changes on cathode during long term storage testing of high energy density cylindrical lithium-ion cells

Nickel-based oxide cathode material taking out from lithium-ion cell after storage for 2 years at 45 °C is analyzed by electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM-EELS) and the result of STEM-EELS is compared with cobalt-based oxide cathode material which is treated as same manor as nickel-based oxide cathode material. The Ni-L_2,3 energy-loss near-edge structure (ELNES) spectra of nickel-based oxide cathode material show peak positions similar to original material before storage. This result indicates that nickel-based oxide material has no significant change in the surface structure. On the other hand, a remarkable shift to low energy is observed in the Co-L_2,3 ELNES spectra of the cobalt-based oxide cathode material after storage. The cycle test at 60 °C under the conditions of aggressive driving cycle (US06) mode for the nickel-based oxide cathode/graphite cell is also carried out. It is clear that cycle performance of the nickel-based oxide cathode/graphite cell is dependent on the depth of discharge (DOD).