Diagnosis of Electrochemical Impedance Spectroscopy in Lithium Ion Batteries

Corresponding author e-mail: [email protected]; [email protected][中文文摘]电化学阻抗谱(EIS)是研究电极/电解质界面发生的电化学过程的最有力工具之一,广泛应用于研究锂离子在锂离子电池嵌合物电极活性材料中的嵌入和脱出过程。本文从分析嵌合物电极的EIS谱特征入手,探讨了电化学阻抗谱中各时间常数的归属问题,重点讨论了与锂离子嵌脱过程相关的动力学参数,如电荷传递电阻、活性材料的电子电阻、扩散以及锂离子扩散迁移通过固体电解质相界面膜(SEI膜)的电阻等,对电极极化电位和温度的依赖关系。[英文文摘]Electrochemical impedance spectroscopy(EIS) is one of the most powerful tools to analyze electrochemical processes occurring at electrode/electrolyte interfaces,and has been widely used to analyze the insertion /desertion process of lithium ion in the intercalation electrode for lithium ion battery.In this paper,the ascription of each time constant of EIS spectra is discussed,based on analyzing the common EIS features of intercalation electrode.The kinetic parameters in the lithium ion insertion/desertion,desertion，dependent on temperature and electrode polarization，such as the charge transfer resistance，the electronic resistance of activated material，the resistance of SEI film that lithium ion transferring through，are also discussed based on the theoretical analysis.国家重点基础研究发展计划(973)项目(No.2009CB220102);中国矿业大学青年科技基金项目(No.ON080282)资

Effects of Temperature on the Intercalation-Deintercalation Process of Lithium Ion in the Spinel LiMn_2O_4

E-mail: [email protected], [email protected][中文文摘]运用电化学阻抗谱研究了商品化尖晶石LiMn2O4电极在1mol/L LiPF6-EC(碳酸乙烯酯):DEC(碳酸二乙酯)电解液中―10～30℃范围内的阻抗谱特征、固体电解质相界面(SEI)膜阻抗、电子电阻和电荷传递电阻等随温度的变化.研究结果表明,尖晶石LiMn2O4电极的阻抗谱特征与温度有关,随温度的升高,与活性材料电子电导率相关的半圆和与SEI膜相关的半圆会发生重叠而成为一个半圆.通过选取适当的等效电路拟合了实验所得的电化学阻抗谱数据,测得尖晶石LiMn2O4电极在1mol/LLiPF6-EC:DEC电解液中,锂离子迁移通过SEI膜的离子跳跃能垒平均值为15.49kJ/mol;电子电导率的热激活化能平均值为24.21kJ/mol;嵌入反应活化能平均值为53.07kJ/mol。[英文文摘]Variations of impedance spectra,electronic resistance,and the resistances of the solid electrolyte interphase(SEI) film,as well as the charge transfer reaction of commercially spinel LiMn2O4 electrode were investigated by electrochemical impedance spectroscopy(EIS) in 1 mol/L LiPF6-EC(ethylene carbonate):DEC(diethyl carbonate) electrolyte solutions with the temperature in the range of-10～30 ℃.It is found that,the common EIS features of spinel LiMn2O4 electrode are related to the temperature,the semicircles observed in the Nyquist diagram which related to the electronic conductivity of the material and the semicircles related to the SEI film become to overlap each other to form one semicircle at higher temperatures. The experimental EIS data was simulated by a suitable equivalent circuit that includes elements related to the electronic and ionic transport in addition to the charge transfer process. In 1 mol/L LiPF6-EC:DEC electrolyte solutions, the energy barriers for the ion jump relating to migration of lithium ions through the SEI film of the spinel LiMn2O4 electrode were determined to be 15.49 kJ/mol, the thermal active energy of the electronic conductivities to be 24.21 kJ/mol, and the intercalation-deintercalation reaction active energies to be 53.07 kJ/mol, respectively.国家重点基础研究和发展规划(No2009CB220102);中国矿业大学青年科技基金(NoON080282),中国矿业大学人才引进经费(NoZX280),中国矿业大学科技攀登计划(NoON090237)资助项

微米级甲烷化催化剂颗粒热质传递行为与反应机制的研究

甲烷化反应是煤制天然气工艺中重要的一环，但是其快速强放热的特性会对经济性生产构成威胁。为了解决这一问题，中国科学院过程工程研究所利用流化床反应器传热、传质效率高等优点，提出了&ldquo;输送床-固定床两段甲烷化工艺&rdquo;。其中输送床甲烷化工艺的一个优势是使用热容较高的催化剂颗粒作为主要的换热介质快速移除反应器内大量的反应热。催化剂表面产生的反应热，会同时向流体和催化剂颗粒传递，但二者之间的平衡机制尚不清楚，即当反应热形成瞬间，热量是更容易传递给催化剂颗粒还是产品气。所以本论文针对这一问题，通过实验与数学模型结合的方式，揭示了微米级催化剂颗粒上热质传递特性以及机制，主要研究内容如下：(1) 常压下毫米级单催化剂颗粒上甲烷化反应与温度变化动态特性研究。通过实验和二维动态单颗粒催化剂甲烷化反应数学模型，对 4-6 mm级催化剂颗粒上的反应和传热现象进行研究。实验结果与模拟结果吻合度高，证明了本论文所建立的数学模型有效。研究结果表明：1）催化剂颗粒内存在反应与扩散传递的竞争关系，当反应温度足够高，使得动力学速率足够快时，反应主要在催化剂颗粒表面区域进行，而当扩散速率较快时，主反应区域会向催化剂颗粒内部延伸。2）在系统稳态形成前的动态阶段，反应区域形成的反应热双向传递，即同时向催化剂颗粒和周围流体传递，使得催化剂颗粒的温度逐渐升高。3）颗粒内反应热的生成与传递之间的竞争平衡使稳态的温度分布为：直到颗粒内部具有甲烷化反应发生的位置（反应物能扩散进入的位置），温度由此向外逐渐降低，而由此向内温度几乎稳定在相同值，颗粒整体温度明显高于环境气体流温度，表明甲烷化反应明显升高了颗粒温度，使得催化剂颗粒表面区域形成的大量反应热向外传递进入流体相，而颗粒内部生成的较少反应热维持了由颗粒内部向表面逐渐降低的稳态温度分布。4）通过对毕渥数（Bip）的计算，确定了气-固相之间的热阻与催化剂颗粒内部的热阻的相对大小关系，表明气-固相之间热阻较大使反应热在初期动态阶段更多地被催化剂颗粒吸收，使催化剂颗粒温度升高。5）操作条件的变化，会对传热过程造成影响。增大催化剂颗粒的粒径会使气-固换热系数减小，而升高温度或增大气速则会使该值增大。(2) 输送床操作条件下微米级催化剂颗粒上的热质传递行为与反应机制。应用经实验验证的数学模型对输送床操作条件下微米级单催化剂颗粒上的热量传递、质量传递以及反应机制进行预测，结果表明：1）输送床反应器采用微米级催化剂颗粒，其热传递及反应效率高，送入床层的单个催化剂颗粒在0.1 s左右就能达到热平衡。2）由于催化颗粒微小，稳态下颗粒表面和内部的温度差极少，但仍然验证了温度由中心向表面逐渐降低的稳定分布特性，表明颗粒中心发生了甲烷化反应，是形成这种中心温度高的本质原因。3）稳态下催化剂颗粒内部的反应速率分布受两方面因素影响，一方面，催化剂颗粒的温度从表面向中心逐渐升高，使反应在中心位置具有最高的动力学速率；另一方面，反应物（合成气）向催化剂颗粒内部扩散的过程中存在阻力，导致反应物浓度在催化剂中心位置处较低，从而使得中心反应速率更低。二者相互协同竞争，在加压和较高气速反应条件下，催化剂颗粒内的传质速率快，颗粒内的甲烷化反应受动力学控制，导致反应速率由颗粒中心向表面逐步减低；反之，常压与低气速条件下，甲烷化反应受气体扩散控制，反应速率自催化剂表面向中心逐渐降低。;Methanation is an important unit in the coal-to-SNG (Synthetic natural gas) process. As a highly exothermic reaction, one of the major challenges for methanation technology is the efficient removal of the excessive reaction heat. Taking the full advantages of fluidized bed, mainly the high heat and mass transfer efficiency, a novel methanation process combined transport bed reactor with clean-up fixed bed reactor has been proposed by institute of Process Engineering, Chinese Academy of Science,. This process utilizes the catalyst particles rather than flowing gas as the main heat transfer medium. As methanation occurs over a catalyst particle, the generated reaction heat could transfer both inside of the catalyst itself and also the gas around the catalyst particles. However, there is deficient knowledge about how the balance between these two transfer pathways is achieved, i.e. whether the reaction heat generated will prefer transferring to particle center or directly to the surrounding gas. Aimed to solve these questions, the following research contents were covered in this thesis.(1) Dynamic characteristics of temperature for methanation over a single millimeter-scale catalyst particle under atmospheric pressure. Both experiments and 2D time dependent numerical simulations have been performed on catalyst particles with diameters ranging from 4-6 mm to investigate their reaction and heat transfer behavior under laboratory conditions. The experimental and calculated results fit well to each other verifying the applicability of the mathematical model. The results clarified that: 1) The competition between diffusion and reaction inside the catalyst particle. Under high operating temperature, the reactions mainly take place on the surface of the catalyst particle since the reaction rate is quick enough, on the contrary the reaction region would extend further inside the catalyst particle. 2) The bi-directional transfer behavior of the reaction heat. In the unsteady state, the generated reaction heat would transfer both outwards to the atmosphere and inwards to the inside of the catalyst particle, this effect increases the temperature inside the catalyst particle. 3) The competition between reaction heat generation and its transport. Both experimental and simulated results show that the temperature inside the catalyst particle decreased gradually from center to surface when the steady state is achieved. In particular, the location of reaction divided the temperature distribution profile into two parts, temperature inner than which remains nearly constant while temperature in the outer part decreases sharply. In steady state, the reaction heat generated in the near-surface region inside the catalyst particle would transfer more into the surrounding gas owing the intensive effect of convection, while that formed in the core region transfer less in this direction, thus leading the temperature distribution that the temperature decreased gradually from center to surface. 4) The influence of heat transfer resistance. Through the calculation of Biot number which serves as the criterion of the heat transfer resistances on the surface and at the inside of the body, it is suggested that interphase heat transfer resistance is relatively larger than its intra-phase counterpart so that the reaction heat tends to transfer more to the inside of catalyst itself. 5) The effects of operating conditions on heat transfer behaviors. Specifically, the gas-solid heat transfer coefficient would decrease when catalyst particle grows larger, and it would increase as the temperature or gas flowrate increases. 6) Heat transfer behavior when Biot number is slightly larger than 10. The external gas flow poses apparent influence on the temperature distribution on the catalyst particle.(2) The reaction mechanism and dynamic heat transfer over a single micrometer scale catalyst particle for transport bed nethanation. The heat and mass transfer behaviors as methanation occurs under the conditions in transport bed was predicted by the numerical simulations verified in the first part. The results revealed that: 1) The dynamic period over a single catalyst particle is short, on 100 &mu;m catalyst particle it takes only 0.1s to get through this period, and the temperature between gas and catalyst particle is quite little as well (0.02 K), this ensures the superiority of transport bed reactor which is rapid and isothermal. 2) The temperature profile still characterizes decreasing gradually from center to surface in spite of the little temperature difference between particle center and surface, suggesting that methanation reactions occur inside the catalyst particle. 3) The reaction distribution inside the catalyst particle is affected by two opposite factors. On one hand, as mentioned previously, the temperature increased from surface to center and it accelerates reaction at the center. On the other hand, however, the diffusion of reactant inside the catalyst particle would be hindered by the internal diffusion resistance thus resulting in lower reactant concentration in core area, which is unfavorable for reaction. Therefore, under conditions in which the reactants diffuse quick enough, methanation inside the particle is controlled by the kinetics, and the reaction rate would decrease from particle center to its surface. On the contrast, the reactions rate distribution would be reversely and the reaction is subject to mass transfer.&nbsp;</p

输送床甲烷化催化剂颗粒的热质传递行为与反应机制

采用数值模拟对输送床甲烷化的粒径100μm级单颗粒催化剂的反应与热传递行为进行了研究,揭示了反应热在单颗粒催化剂上的动态传递规律和典型条件下的反应控制机制。在输送床反应器中,热传递效率高,进入反应器的单个催化剂颗粒温度一般在0.1 s左右即可达到稳态。稳态的100μm级催化剂颗粒表面、中心、流体之间的温差很小,但催化剂颗粒的径向温度表现为由表面向中心逐渐升高的分布,证明了甲烷化反应热升高了催化剂颗粒温度,建立了温度升高的催化剂颗粒与反应气氛之间的热传递平衡。模拟甲烷化反应速率与组分气体在催化剂颗粒内的分布,揭示了在加压和较高气速反应条件下,反应物向催化剂颗粒的扩散加快,催化剂颗粒的局部甲烷化反应受动力学控制,反应速率由中心向表面逐步减低。反之,常压与低气速条件使得催化剂颗粒的甲烷化反应受气体扩散控制,反应速率自表面向中心逐渐降低

Parallel type light-duty robot joint variable-stiffness actuator

本发明属于机器人关节技术领域，特别涉及一种并联式轻型机器人关节变刚度执行器。包括动力输入部、动力输出部、刚度调节部及刚度变化执行部，其中动力输入部和动力输出部转动连接，刚度调节部设置于动力输入部上、且通过刚度变化执行部与动力输出部连接；当动力输出部受到不同载荷，动力输出部相对于动力输入部产生相对转动，使刚度变化执行部产生不同的工作状态，实现刚度的非线性变化；当动力输出部受到载荷一定时，通过刚度调节部调节刚度变化执行部的工作状态，使动力输入部和动力输出部的转动角度发生变化，实现刚度的主动调节。本发明体积更小，质量更轻，同时缩短了刚度调节时间

输送床甲烷化催化剂颗粒的热质传递行为与反应机制

采用数值模拟对输送床甲烷化的粒径100 μm级单颗粒催化剂的反应与热传递行为进行了研究,揭示了反应热在单颗粒催化剂上的动态传递规律和典型条件下的反应控制机制。在输送床反应器中,热传递效率高,进入反应器的单个催化剂颗粒温度一般在0.1 s左右即可达到稳态。稳态的100 μm级催化剂颗粒表面、中心、流体之间的温差很小,但催化剂颗粒的径向温度表现为由表面向中心逐渐升高的分布,证明了甲烷化反应热升高了催化剂颗粒温度,建立了温度升高的催化剂颗粒与反应气氛之间的热传递平衡。模拟甲烷化反应速率与组分气体在催化剂颗粒内的分布,揭示了在加压和较高气速反应条件下,反应物向催化剂颗粒的扩散加快,催化剂颗粒的局部甲烷化反应受动力学控制,反应速率由中心向表面逐步减低。反之,常压与低气速条件使得催化剂颗粒的甲烷化反应受气体扩散控制,反应速率自表面向中心逐渐降低

输送床甲烷化催化剂颗粒的热质传递行为与反应机制

采用数值模拟对输送床甲烷化的粒径100 μm级单颗粒催化剂的反应与热传递行为进行了研究,揭示了反应热在单颗粒催化剂上的动态传递规律和典型条件下的反应控制机制。在输送床反应器中,热传递效率高,进入反应器的单个催化剂颗粒温度一般在0.1 s左右即可达到稳态。稳态的100 μm级催化剂颗粒表面、中心、流体之间的温差很小,但催化剂颗粒的径向温度表现为由表面向中心逐渐升高的分布,证明了甲烷化反应热升高了催化剂颗粒温度,建立了温度升高的催化剂颗粒与反应气氛之间的热传递平衡。模拟甲烷化反应速率与组分气体在催化剂颗粒内的分布,揭示了在加压和较高气速反应条件下,反应物向催化剂颗粒的扩散加快,催化剂颗粒的局部甲烷化反应受动力学控制,反应速率由中心向表面逐步减低。反之,常压与低气速条件使得催化剂颗粒的甲烷化反应受气体扩散控制,反应速率自表面向中心逐渐降低

三尖瓣下移畸形合并房间隔缺损致儿童卒中1例报道 A Case of Childhood Stroke Caused by Ebstein’s Anomaly Combined with Atrial Septal Defect

儿童卒中是临床常见的危急症，是儿童致残和死亡的主要原因之一，病因复杂多样，其中心源性卒中不容忽视。三尖瓣下移畸形是一种少见的先天性心脏病，主要累及三尖瓣和右心室，少数可合并房间隔缺损或卵圆孔未闭引起矛盾栓塞，导致心源性卒中发生。本文报道1例由三尖瓣下移畸形合并房间隔缺损引起儿童卒中的病例，超声心动图技术有助于该类疾病的明确诊断、严重度评估以及其他异常的识别。 Abstract: Childhood stroke is a common critical disease, and is one of the main causes of disability and death in children. Its etiology is complex and diverse, meanwhile, cardiogenic stroke cannot be ignored. Ebstein’s anomaly is a rare congenital heart disease, mainly involving the tricuspid valve and the right ventricle, and a few patients may combine with atrial septal defect or patent foramen ovale, which leads cardiogenic stroke because of paradoxical embolism. This paper reported a case of childhood stroke caused by Ebstein’s anomaly combined with atrial septal defect. Echocardiography techniques can help to clarify the diagnosis, assess severity and identify other abnormalities

宝天曼典型森林植被碳库及其分配格局

森林类型和群落结构是影响森林植被碳库分配格局的重要因子。拟揭示宝天曼自然保护区栓皮栎林(幼龄)、鹅耳枥林、针叶林和针阔混交林植被碳库及其分配格局,明确森林类型和群落结构对研究区森林植被碳库及其分配格局的影响。采用样地调查法结合木本树种的异速生长方程的方法获得植被碳库,进而划分植物器官碳库以及群落径级。通过单因素方差分析和多重比较的方法,分析林型和群落结构对森林植被碳库及其分配格局的影响。结果表明:(1)栓皮栎林、鹅耳枥林、针叶林和针阔混交林4种林型的总植被碳库分别为54.86、102.22、116.91和132.16 t/hm~2。中龄林和幼龄林间的地上植被碳库、总植被碳库差异显著(P树枝>树根>树叶,栓皮栎林具有最大的根冠比。(2)栓皮栎林、鹅耳枥林和针叶林都以小树[胸径(DBH)鹅耳枥林>针叶林>针阔混交林的趋势,而大树(DBH为50～60 cm)的贡献率则表现为针阔混交林大于其他林型。栓皮栎林中小树对总植被碳库的贡献率为地下大于地上,针阔混交林中大树对植被碳库的贡献率为地上大于地下。建议森林管理应针对不同林型和林龄的特点采取相应的经营方案,以保持较高的植被碳库水平