ISL OpenIR研究单元&专题: 盐湖资源与化学实验室

改性富锂锰基正极材料的设计、制备及构效关系研究

Thu, 02 Jun 2022 02:03:38 GMT

题名: 改性富锂锰基正极材料的设计、制备及构效关系研究作者: 董生德摘要:

锂离子电池已成为电动汽车、智能电网等大型储能领域的首选装置，更高的能量密度是其满足大规模应用的先决条件，而在锂离子电池中，能量密度很大程度上是由正极材料直接决定的。富锂锰基正极材料循环过程中超高的放电比容量使其受到广泛关注。研究表明，该材料如此高的放电比容量主要来源于电化学反应过程中材料晶格氧的不可逆氧化。然而，晶格氧的不可逆氧化在带来超高放电比容量的同时也造成了材料在循环过程中容量和电压的衰减，从而严重影响了富锂锰基正极材料的进一步应用。因此，本论文以富锂锰基正极材料作为研究对象，通过理论计算与实验相结合的方式，首先针对该材料结构基础与反应机制方面的问题，开展了对晶格氧氧化、氧空位形成、过渡金属还原、层状到尖晶石转变及两相反应的相关研究，其次针对起始库伦效率较低、电压降严重、容量和倍率性能差等问题开展了一系列理论设计、制备及改性方面的应用探索研究，具体工作包括以下几个方面：第一，首先通过溶剂热法合成 Ni-Co-Mn 基前驱体，以此来研究溶剂热合成过程中的各项反应条件。同时，基于优化条件下合成的富锂锰基正极材料，通过高角度环形暗场扫描透射电子显微镜（HAADF-STEM）分析验证了富锂锰基正极材料是一种两相复合结构，是由 R-3m 空间群的六方 LiMO2 和 C2/m 空间群的单斜 Li2MnO3 两种组分复合而成。其次，通过两相结构基础理论计算证明了富锂锰基正极材料倍率性能差和 Li2MnO3 组分的激活需要更高电压的直接原因。随后基于优化后的反应条件，利用溶剂热法合成了 Ni-Co 二元前驱体，并通过高温固相法合成了不同组分比例（Li2MnO3:LiMn1/3Co1/3Ni1/3O2）的富锂正极材料，对其进行相关特性评价，重点解释富锂锰基正极材料的相关反应机制。最后，基于第一性原理解释了晶格氧的氧化还原是导致富锂锰基正极材料中 Mn 和 Co 被还原从而造成电压衰减的根本原因。因此，通过电化学反应过程中控制氧的析出来调控局域结构是改善富锂锰基正极材料物化性能的重要途径，而晶格掺杂和表面包覆是实现这一途径的有效手段。改性富锂锰基正极材料的设计、制备及构效关系研究。第二，该部分设计并制备了 Nb 元素掺杂的富锂锰基正极材料，以此来探讨Nb 元素掺杂改善材料电化学性能的相关机制。首先利用密度泛函理论（DFT）计算证明了 Nb-O 键的结合能大于 Mn-O 键，同时通过对 Nb 元素掺杂与未掺杂材料的相关参数计算发现，Nb 元素掺杂之后的材料具有更小的锂离子迁移阻碍能和更大的氧空位形成焓，表明 Nb 元素掺杂改性加速了锂离子迁移，稳定了材料结构。基于这一理论指导，随后用高温固相法合成了原始和 Nb 元素掺杂的富锂锰基正极材料。采用各种测试手段分析了 Nb 元素掺杂对材料形貌、晶体结构、表面元素价态以及电化学性能的影响。研究表明：Nb 元素的掺杂使得材料电化学性能得到明显提升，特别是循环性能，即 300 次循环之后，2 mol%的 Nb 元素掺杂量下材料容量保持率可达 98.5%（0.2C），高于原始材料 86.68%（0.2C，300次循环）。第三，该部分设计并制备了混合包覆层（Al2O3 和 LiAlO2）改性的富锂锰基正极材料，以此来调控局域结构、探讨表面包覆改善材料物化性能的相关机理。首先通过理论计算证明了锂离子在 LiAlO2 包覆层中的迁移阻碍能要小于 Al2O3包覆层和原始正极材料中的阻碍能，同时相对于原始正极材料，LiAlO2 包覆层界面结构具有较低的氧空位形成能，这就使得 LiAlO2 界面改性可以加速锂离子的迁移，增加界面氧空位的形成，从而通过稳定界面结构中的 O 原子来减少氧的析出。此外，材料表面的 Al2O3 包覆层可以保护正极材料防止 HF 等副产物的腐蚀。基于这一理论指导，首先对富锂锰基正极材料在溶胶凝胶合成过程中的各项条件进行了探讨，其次利用异丙醇铝作为铝源的湿化学法对该材料进行改性，最终合成混合包覆层（Al2O3 和 LiAlO2）改性的富锂锰基正极材料。采用各种测试手段研究了改性前后富锂锰基正极材料的形貌、晶体结构及电子状态的变化。结果表明，混合包覆层改性提高了富锂锰基正极材料的电化学性能，即 0.1C 下混合包覆层改性后材料的起始放电比容量和首次库伦效率分别高达 272.7 mAh g-1和 88.55%，而原始正极材料分别只有 246.7 mAh g-1 和 75.5%；循环 300 次之后改性材料的容量保持率为 83.55%（0.5C），高于原始材料 53.96%（0.5C，300 次循环）。第四，针对晶格掺杂和表面包覆所具有的共同优势，该部分利用 Na3VO4 作为改性剂，发挥了其在富锂锰基正极材料中的三重改性效应。理论计算发现Na3VO4 作为富锂锰基正极材料的改性剂，可将 Na 元素掺杂到 Li 位，将 V 元素掺杂到过渡金属位，从而达到稳定材料结构，加速锂离子迁移的效果。此外，V元素在进入晶格的同时也会有部分在材料表面形成 Li3VO4 修饰物，这不仅可以减少正极材料表面残留锂化合物的生成，也可以作为锂离子导体进一步加速锂离子的迁移，并且保护正极材料防止 HF 等副产物的腐蚀。基于该三重改性效应原理，首先探讨了合成条件对材料物化性能的影响，其次利用适宜条件合成了原始和 Na3VO4 改性的富锂锰基正极材料。采用各种测试手段研究了改性前后材料形貌、晶体结构、元素价态以及电化学性能的变化。结果表明：Na3VO4 改性之后材料电化学性能得到明显改善，特别是 0.1C 下首次放电比容量和库伦效率最高分别可达 315.2 mAh g-1 和 89.37%，同等条件下原始材料分别只有 280.3 mAh g-1和 83.14%；针对其倍率性能，8C 下，Na3VO4 改性后材料的放电比容量为 145.2 mAh g-1，而原始材料只有 104.4 mAh g-1。综上所述，通过 Nb 元素掺杂、混合包覆层修饰、Na3VO4 改性这些方式可以发挥其各自的优点，起到协同效应同时解决多个问题，从而改善材料的电化学性能。此外，以上对富锂锰基正极材料在结构基础、反应机制和应用探索方面的研究，对指导其理论设计、优化改性与应用具有重要意义。

Effects of salinity and particle size on radium desorption from river sediments in the Qinghai-Tibet Plateau

Mon, 11 Apr 2022 02:45:53 GMT

题名: Effects of salinity and particle size on radium desorption from river sediments in the Qinghai-Tibet Plateau 作者: Su, Weigang; Ma, Yujun; Wang, Qiugui; Yan, Qiongxiong; Lu, Xiaohang; Ma, Zhe; Yi, Lei; Liu, Xiaobao; Chen, Fuhong; Han, Fengqing; Xu, Zhengfan 摘要: Natural radium isotopes have been widely used to study groundwater discharge in different systems. Therefore, it is of great significance to understand the desorption behavior of radium isotopes on sediments to trace waterland exchange processes. However, there is very limited studies observing the desorption Ra isotopes to lake water of the brine lake. Ra-224 desorption experiments with different salinities and particle sizes were carried out by collecting samples of brackish water from Qinghai Lake, brine from Dabuxun Lake and river sediments entering the lakes. The results show that the desorption activity of Ra-224 from the river sediments to lake water of Qinghai Lake is 0.2 dpm/g when the salinity is 10.07 parts per thousand. The maximum desorption activity of Ra-224 from river sediments to lake water of Dabuxun Lake is 0.195 dpm/g at a salinity of 40.81 parts per thousand. A salinity of 41.81 parts per thousand and particle size of 16.28 mu m are the threshold points affecting the desorption behavior of Ra. When the salinity is less than 40.81 parts per thousand, the desorption activity of Ra increases linearly with increasing salinity. When the salinity is greater than 40.81 parts per thousand, the desorption activity of Ra decreases nonlinearly with increasing salinity and tends toward a stable low value. When the particle size is larger than 16.28 mu m, the small particle size promotes desorption. The smaller the particle size is, the greater the desorption activity is. When the particle size is less than 16.28 mu m, the small particle size inhibits desorption. The smaller the particle size is, the smaller the desorption activity. The co-precipitation of Ra2+ with supersaturated Ca2+, SO42- and other ions may be the main reason for the threshold point of salinity and particle size in Ra desorption process in salt lake system.

Saline lakes on the Qinghai-Tibet Plateau harbor unique viral assemblages mediating microbial environmental adaption

Mon, 11 Apr 2022 02:45:52 GMT

题名: Saline lakes on the Qinghai-Tibet Plateau harbor unique viral assemblages mediating microbial environmental adaption 作者: Gu, Chengxian; Liang, Yantao; Li, Jiansen; Shao, Hongbing; Jiang, Yong; Zhou, Xinhao; Gao, Chen; Li, Xianrong; Zhang, Wenjing; Guo, Cui; He, Hui; Wang, Hualong; Sung, Yeong Yik; Mok, Wen Jye; Wong, Li Lian; Suttle, Curtis A.; McMinn, Andrew; Tian, Jiwei; Wang, Min 摘要: The highest plateau on Earth, Qinghai-Tibet Plateau, contains thousands of lakes with broad salinity and diverse and unique microbial communities. However, little is known about their co-occurring viruses. Herein, we identify 4,560 viral Operational Taxonomic Units (vOTUs) from six viromes of three saline lakes on Qinghai-Tibet Plateau, with less than 1% that could be classified. Most of the predicted vOTUs were associated with the dominant bacterial and archaeal phyla. Virus-encoded auxiliary metabolic genes suggest that viruses influence microbial metabolisms of carbon, nitrogen, sulfur, and lipid; the antibiotic resistance mediation; and their salinity adaption. The six viromes clustered together with the ice core viromes and bathypelagic ocean viromes and might represent a new viral habitat. This study has revealed the unique characteristics and potential ecological roles of DNA viromes in the lakes of the highest plateau and established a foundation for the recognition of the viral roles in plateau lake ecosystems.

Origin and Evolution of Saline Spring Water in North and Central Laos Based on Hydrochemistry and Stable Isotopes (delta D, delta O-18, delta B-11, and delta Cl-37)

Mon, 11 Apr 2022 02:45:51 GMT

题名: Origin and Evolution of Saline Spring Water in North and Central Laos Based on Hydrochemistry and Stable Isotopes (delta D, delta O-18, delta B-11, and delta Cl-37) 作者: Qin, Xiwei; Ma, Haizhou; Zhang, Xiying; Hu, Xiasong; Li, Guorong; Jiang, Ziwen; Cheng, Huaide; Han, Jibin; Li, Yongshou; Miao, Weiliang; Han, Wenhua; Yang, Sha; Song, Qian; Lei, Shang; Wang, Hongying 摘要: This paper discusses the origin and evolution of saline springs in north and central Laos, based on chemical and stable isotopes (delta D, delta O-18, delta B-11, and delta Cl-37). All the saline springs in this study are of the Na-Cl geochemical type. The geochemical and water isotope values suggest that the saline springs in this study are mainly derived from meteoric water and/or ice and snow melt from the surrounding mountains and that they also experienced strong evaporation and intense rock-water interactions. The ionic ratios, characteristic coefficients, ternary Ca-SO4-HCO3 phase diagrams, and saturation indices of minerals show that the dissolution of halite, sulfate, and carbonate rocks may be the solute sources for saline springs in this study, whereas the underground brines in the Thakhek potash mining area are geochemically influenced by the dissolution of carnallite and sylvite. The global geothermal delta B-11-Cl/B relationship and delta B-11 values (5.50 to 36.01 parts per thousand) of saline springs suggest a continental origin of B. This B is most likely derived from marine carbonate rocks and marine evaporates (gypsum and halite) of the late Cretaceous, which is similar to the saline springs of the Nangqen-Qamdo-Simao Salt Basin. The delta Cl-37 value (-0.12 to +0.79) and the Cl/Br ratio (4076 to 9853) show that dissolution of late cretaceous marine halite layers, atmospheric precipitation, and water-rock interactions between volcanic rocks, mudstones, and sandstone can restrict the delta Cl-37 values in saline springs. Results from silica geothermometry and multi-mineral equilibrium diagrams indicate that the reservoir temperatures for the saline springs range from 87-137 degrees C and experience deep circulation. Hydrochemical characteristic coefficients suggest that saline springs in the Muang Say basin may have leached sylvinite and carnallite and that the potash exploration prospect in this area is relatively good.

Speciation and correlation of boron and lithium in surficial sediments of the eastern and western Taijinar Salt Lake

Mon, 11 Apr 2022 02:45:50 GMT

题名: Speciation and correlation of boron and lithium in surficial sediments of the eastern and western Taijinar Salt Lake 作者: Li, Baolan; Wu, Jun; Li, Leiming 摘要: The eastern/western Taijinar Salt Lake in Qaidam Basin is rich in lithium and boron resources. Chemical speciation of boron and lithium is conducive to identify the migration way and enrichment of heavy metals which might cause certain effects on the environment of salt-lake area. A total of 28 surface sediment samples were collected from the Taijinar Salt Lake in June of 2020 to investigate the distribution, speciation and sources of boron and lithium in salt-lake sediments. The results showed that the average content of boron/lithium was low with value of 1.6/3.4 mu g kg(-1), while that of the other elements in sediments ranging from 0.035 mu g kg(-1) (Cd) to 48.20 mg kg(-1) (As) by following the order of As > Pb > Hg > Zn > Cr > Cd. Boron and lithium in sediments were mainly bound to Fe-Mn oxide and residual fractions with the average proportion of 29.87% and 35.36% for boron as well as 32.18% and 31.43% for lithium. Pb mainly existed in carbonate and residual fraction, while Zn mainly existed in the Fe-Mn oxide and residual bound with average value of 40.56% and 43.32%, respectively. Hg/Cr mainly existed in the residual with the average value of 58.68%/84.18%, while Cd mainly existed in the Fe-Mn oxide and residual fraction with an average proportion of 26.52% and 30.89%, respectively. As mainly existed in Fe-Mn oxide, residual, and organic fraction with an average proportion of 30.20%, 32.61% and 21.92%, respectively. Elements including Zn, Cr and Pb had a certain influence on the speciation of boron and lithium based on the correlation analysis. The enrichment of Cd, Cr and Pb might be mainly caused by anthropogenic sources. The findings of this study will provide some basic information on the important elements including lithium and boron in the salt-lake areas.

Functionalized graphene with Platelet-like magnesium hydroxide for enhancing fire safety, smoke suppression and toxicity reduction of Epoxy resin

Mon, 11 Apr 2022 02:45:48 GMT

题名: Functionalized graphene with Platelet-like magnesium hydroxide for enhancing fire safety, smoke suppression and toxicity reduction of Epoxy resin 作者: Guo, Fan; Zhang, Yuze; Cai, Liang; Li, Lijuan 摘要: With the rapid development of Graphene based hybrid materials, various of them were fabricated to improve the fire safety of EP. However, the effect of GO content in the hybrid material on flame retardancy of EP composites is rarely reported. In order to find the optimal ratio of GO/Mg(OH)2, platelet-like Mg(OH)2 functioned graphene (GPM) were synthesized with diverse content GO substance and then presented into EP resin for improving its fire retardancy. Various characterizations confirmed its composition, structure and morphology. The incorporation of GPM contains about 1% GO increased the tensile strength by 31.6% compared to that of untreated Mg (OH)2. The GPM contains about 5% GO exhibited the finest fire safety in various EP composites. The fireretardant assessments illustrated that the limiting oxygen index (LOI) of EP composite with 3 wt% GPM progressed to 27.8% compared with virgin EP (24.4%). In parallel, compared to virgin EP, the peak heat release rate, peak smoke production rate, total smoke production and peak CO production rate of EP/5GPM were diminished by 50.9%, 44.0 %, 25.5% and 53.1%, separately. The mechanism investigation revealed that the prominent flame retardancy and smoke suppression were attributed to the physical barrier of GO, the endothermic decomposition of Mg(OH)2, the barrier effect of MgO and synergistic effect between GO and Mg(OH)2 toward the optimized carbonization. In perspective, hierarchical platelet structure with synergistic effect offered an effective approach for the fire-safe polymer.

Corrosion behaviour of 316 stainless steel in NaCl-KCl-MgCl2 salt vapour at 700 degrees C

Mon, 11 Apr 2022 02:45:47 GMT

题名: Corrosion behaviour of 316 stainless steel in NaCl-KCl-MgCl2 salt vapour at 700 degrees C 作者: Liu, Qi; Xu, Hongxia; Yin, Huiqin; Li, Na; Wang, Wenrui; Li, Linfan; Tang, Zhongfeng; Qian, Yuan 摘要: The corrosion behaviour of 316 stainless steel in NaCl-KCl-MgCl2 salt vapour at 700 degrees C under static conditions was investigated in this experiment. Easy-to-peel oxide layers were formed on the surface, and their composition and structure changed as exposure continued. The initially formed oxide monolayer was gradually transformed into oxide multilayers, and the outermost layer changed from Cr-Fe oxide to Mg-Cr oxide. The evolution of surface oxide layers was due to the varying diffusion rates of elements in 316 stainless steel as well as to the differing reaction rate of MgCl2 in the salt vapour.

A study on the salt attack performance of magnesium oxychloride cement in different salt environments

Mon, 11 Apr 2022 02:45:46 GMT

题名: A study on the salt attack performance of magnesium oxychloride cement in different salt environments 作者: Huang, Qing; Zheng, Weixin; Xiao, Xueying; Dong, Jinmei; Wen, Jing; Chang, Chenggong 摘要: Anti-corrosion cement is urgently needed due to the rapid development of salt lake and marine engineering facilities, and ordinary Portland cement (OPC) concrete will undergo significant corrosion in salt environments. Due to its unique composition, magnesium oxychloride cement (MOC) has the potential to replace OPC in salt environments. In this work, the corrosion resistance of MOC in different salt environments was investigated. The results showed that the compressive strength and main hydration products in the MOC were stable in high salt environments. Moreover, the MOC exhibited excellent corrosion resistance in aging and raw brine solutions. In low salt environments, the compressive strength steadily decreased, and the main hydration products decomposed, indicating poor corrosion resistance in seawater and freshwater. In addition, the MOC mainly exhibited physical salt crystallization in high salt environments and chemical reactions in low salt environments.

The synergetic enhancement of piezo catalytic performance to remove tetracycline by K2Ti6O13_TiO2 composite

Mon, 11 Apr 2022 02:45:45 GMT

题名: The synergetic enhancement of piezo catalytic performance to remove tetracycline by K2Ti6O13_TiO2 composite 作者: Zhang, Shuo; Liu, Hangxi; Gao, Feixue; Fang, Ming; Zhang, Yifeng; Cai, Yawen; Li, Kexin; Kong, Mingguang; Tan, Xiaoli 摘要: Piezo catalysis has recently been considered an important technology in environmental treatment. In this study, a type II heterojunction of K2Ti6O13/TiO2 composite is successfully prepared by a hydrothermal method for the highly efficient piezo catalytic degradation of tetracycline. The factors influencing the piezo catalysis of tetracycline are systematically studied and discussed, including pH value, competition of anions/cations, ultrasonic power, ultrasonic frequency, and temperature, etc. Free radical sacrificial agents (EDTA-2Na, DMSO, AgNO3, and P-BQ, etc.) are utilized to better understand the degradation mechanism by piezo catalysis, and holes are found to play a dominant role in the catalytic process, and center dot O-2(-) comes the second. The combination of K2Ti6O13 and TiO2 constructs a type II heterojunction of the highly efficient separation of piezo electrons and holes, thus systematically increasing the piezo catalytic performance. This work provides a new idea to degrade organic pollution through piezo catalysis and the potential application of piezo catalysis in environmental treatment. (C) 2021 Elsevier B.V. All rights reserved.

Promoting effect and mechanism of several inorganic salts on hydration reaction of magnesium oxychloride cement at low temperature

Mon, 11 Apr 2022 02:45:45 GMT

题名: Promoting effect and mechanism of several inorganic salts on hydration reaction of magnesium oxychloride cement at low temperature 作者: Yan, Zhengbin; Yang, Pengwei; Huang, Jiaxin; Jia, Qian; Wen, Jing; Dong, Jinmei; Zheng, Weixin; Chang, Chenggong; Wang, Hongning; Chen, Ruoyu 摘要: In this work, the Magnesium oxychloride cement (MOC) added with five kinds of inorganic salts (CaCl2, Ca (NO3)2, KCl, LiCl, and NH4NO3) were prepared under the low temperature (5 degrees C), and the effects of inorganic salts on the hydration reaction and engineering properties were investigated. The results show that the addition of inorganic salt can significantly improve the hydration reaction rate, increase the content of the 5-phase, and shorten the curing time. Compared with pure MOC, the compressive strength of MOC added with CaCl2 increased by about 128% after 7 days of curing. Moreover, the existence of inorganic salts weakened the surface shielding layer [Mg(H2O)6]2+ of active MgO, thereby improving the zeta potential of active MgO and promoting the diffusion rate of Mg2+. Overall, these results could provide valuable information for studying the hydration reaction and engineering performance of MOC at low temperatures.