功能添加剂对锂离子电池的防过充电化学行为研究

研究了功能添加剂3-氯苯甲醚(3CA)和联苯(BP)联合使用在锂离子电池电解液中的防过充行为。通过采用微电极循环伏安法、动电位扫描分析、扫描电镜法和充放电法等手段研究表明：联苯和3-氯苯甲醚混合添加剂的聚合电位随3-氯苯甲醚含量的增加由4.7V前移至4.6V (vs. Li/Li+);电池在正常工作电压(2.75V~4.2V)下,添加剂不参与电池反应过程;当电压高于4.2V电池发生过充时,3-氯苯甲醚在电极表面首先发生氧化还原飞梭分流限压对电池进行过充保护;电压继续升高时,联苯在电极表面发生电聚合反应,生成的聚合膜表面光滑致密是电子的良导体能有效的阻止Li+的嵌入与脱出,并通过自放电使电池处于安全状态,防止电池过充发生爆炸。两种防过充机制共同作用,对电池实施多重护防,提高了电池的安全性能。     

4-溴苯甲醚用作锂离子电池过充保护添加剂的研究

通过在锂离子电池电解液中添加4-溴苯甲醚(4-Bromoanisole, 简称4BA)来提高锂离子电池的过充保护能力. 对电池分别进行了过充实验、循环伏安扫描、红外光谱分析、交流阻抗和容量特性测试, 实验结果表明, 在1 mol•L－1 LiPF6/EC＋DEC＋DMC(质量比1/1/1)中添加5% 的4BA(质量分数)时, 当外加电压为4.4 V(相对于Li/Li＋)时, 4BA开始发生电聚合反应且生成高分子聚合物膜, 使电池内阻增大而阻止电压的升高, 从而使电池处于比较安全的状态. 该体系正常充放电过程中, 添加5%的4BA对电池容量特性基本没有影响, 4BA 的防过充机理为阻断机理.     

过充保护添加剂1,2-二甲氧基-4-硝基苯和1,4-二甲氧基-2-硝基苯在锂离子电池中的应用

在锂离子电池电解液1 mol·L^-1 LiPF₆/(碳酸乙烯酯(EC)+碳酸二乙酯(DEC)+碳酸甲乙酯(EMC) (1:1:1,体积比))中分别添加1,2-二甲氧基-4-硝基苯(DMNB1)和1,4-二甲氧基-2-硝基苯(DMNB2)作为防过充添加剂.采用循环伏安(CV)、恒流充放电、过充测试、电化学阻抗谱(EIS)、扫描电子显微镜(SEM)等手段研究了DMNB1和DMNB2 的防过充效果, 以及添加剂与LiNi_1/3Co_1/3Mn_1/3O₂材料的相容性. 结果表明: DMNB1 和DMNB2 的氧化电位都在4.3 V (vs Li/Li⁺)以上, 且均能显著提高电池的过充保护性能. 100%过充和5 V截止电压过充测试表明, DMNB1 的防过充性能优于DMNB2. 采用基础电解液、添加0.1 mol·L^-1 DMNB1 和添加0.1 mol·L^-1DMNB2 电解液的LiNi_1/3Co_1/3Mn_1/3O₂/Li 电池, 0.2C 倍率下循环100 次, 容量保持率分别为98.4%、95.9%和68.1%. 证明硝基在添加剂苯环上的取代位置和其电化学性能之间有着密切联系.     

铈盐配合物对锂离子电池的抗过充性能

通过在锂离子电池的电解液中添加五硝酸根合铈(Ⅲ)酸四丁基铵的方法来提高电池的安全性,讨论了氧化还原添加剂的作用原理,并考察了作用效果.实验结果表明,五硝酸合铈(Ⅲ)配合物在锂离子电池电解液中的氧化电位在4.0 V左右,扩散系数为3.82×10-6cm2/s.L iFePO4/L i模拟电池的研究结果表明,当电池发生过充时五硝酸合铈(Ⅲ)配合物可以在电池的正极上氧化,并扩散到电池的负极上还原,通过在电池的正负极之间穿梭将电池的电压稳定在4.0 V.     

过充保护添加剂氰基功能化2, 5-二叔丁基对苯二酚的合成及其在锂离子电池中的应用

设计合成了单氰基功能化的2, 5-二叔丁基-1-（β-氰基乙氧基）-4-甲氧基苯（RS-MCN）和双氰基功能化的2, 5-二叔丁基-1, 4-（β-氰基乙氧基）苯（RS-DCN）,并用作氧化还原过充添加剂开展了其在锂离子电子中的应用研究。通过丙烯氰和2, 5-二叔丁基对苯二酚的迈克尔加成反应可高效合成RS-MCN和RS-DCN,氰乙基取代后的过充保护添加剂分子的可逆氧化还原电位分别为4.02、4.08 V（vs Li/Li⁺）;并且单氰基取代的RS-MCN在商业碳酸酯电解液1 mol·L^-1 LiPF6/EC+DEC+EMC（1：1：1,体积比）中的溶解度可高达0.3 mol·L^-1。RSMCN和RS-DCN对LiFePO₄/Li电池的过充保护性能和电极相容性也进行了深入的研究,实验结果表明：RSMCN具有更好的过充保护性能和电极相容性,其5 V截止电压过充保护时间可超过1200 h,100%过充保护大于90周循环;0.3 mol·L^-1 RS-MCN的添加能使100%过充的LiFePO₄/Li电池在2.5C倍率条件下正常循环,其放电比容量达153.5 mAh·g^-1。此外,RS-MCN的添加对LiFePO₄/Li电池在2.5-3.8 V条件下的循环性能有明显改善,添加有RS-MCN的电池在60周的循环后容量保持率高达94.4%,而商业电解液的电池在60周循环后的容量保持率降至84.3%。因此,氰基功能化RS-MCN是一类具有潜在应用前景的过充保护添加剂。     

高镍三元正极材料的表面包覆策略

锂离子电池(LIBs)因具有更高的重量/体积能量密度、 更长的使用寿命、 更低的自放电率等优点而逐渐被广泛应用. 相比于已经广泛使用的钴酸锂和磷酸铁锂等正极材料, 高镍三元正极材料Li[Ni_1-x-yCo_xMn_y]O₂(NCM)以其高电压和高容量等优点, 逐渐成为下一代高能锂离子电池的首选正极材料之一. 尽管高镍NCM正极材料具有上述优点, 但在进一步的实际应用前还需解决其循环稳定性、 倍率性能和安全性等问题, 这些问题主要源于NCM材料本身的晶体结构不稳定、 正极-电解液间界面副反应及高界面电阻等. 针对这些问题, 目前对高镍NCM正极电化学性能优化的大量研究都与电极-电解液界面有关, 如何通过改善界面稳定性、 增加离子在固液界面的迁移率、 抑制界面副反应、 提高正极材料的稳定性进而改善电池性能成为了关注焦点. 本文总结了目前对于其电化学性能衰减的机理解释, 分类概括了包括电化学惰性包覆锂、 残积物清除剂包覆和锂离子良导体包覆等对于高镍NCM正极材料的颗粒表面包覆策略, 简述了一些新兴的包覆策略, 并对高镍NCM正极材料的发展方向和前景提出了展望.     

阻燃剂对镍钴锰三元材料体系电化学性能的影响

测试了不同浓度的电解液阻燃添加剂对镍钴锰三元材料（LiNi_0.4Co_0.2Mn_0.4O₂）作为正极的锂离子电池电化学性能的影响. 实验结果表明,当阻燃剂浓度增加时,电池的放电容量下降,电化学反应电阻和锂离子扩散阻力都有所增加,但加入阻燃添加剂的锂离子电池,当充放电的电流相对比较小的时候,循环性能相比于不含阻燃剂的有所提高,循环稳定性得到了改善. 在0.5C倍率电流下,不含阻燃剂时容量保持率为89%,而当阻燃剂含量增至10%后保持率达到94.21%. 当充放电电流为1C时,未使用阻燃剂时容量保持率约为92.22%,当阻燃剂的浓度为10%时容量保持率为93.01%. 在2C倍率下,不含阻燃剂时容量保持率为87.92%. 阻燃剂浓度为10%时,容量保持率有所提升,达到92.16%. 与基础电解液相比,选用含有10%阻燃剂的电解液可使容量保持率提高5%左右,相比于其他浓度,包含10%阻燃剂的电池循环性能也最为稳定.     

锂离子电池正极界面修饰用电解液添加剂

提高电压是提高锂离子电池比能量的重要途径之一。例如,LiNi_0.5Mn_1.5O₄(4.7 V)、LiNiPO₄(5.1 V)和富锂锰基等电极材料在较高的充电截止电压下表现出较高的能量密度和较低的成本,具有很好的应用前景。另外,提高LiCoO₂和三元电池体系的充电截止电压是提升电池能量密度的简单有效措施。但是,当电池充电截止电压提高时,不仅会造成电解液在正极/电解液界面的氧化分解,还会加速正极中金属阳离子在电解液中的溶解,造成电池循环性能和安全性下降。采用不同的正极界面修饰用电解液添加剂,既可以有效钝化正极/电解液界面,抑制电解液的分解,还可以有效抑制正极结构的破坏。本文从添加剂的分子结构出发,介绍了磺酸酯、硼酸酯、磷酸酯、氟代碳酸酯、腈类、酸酐和锂盐等添加剂在正极界面的相关研究成果,并对不同添加剂的作用机理进行了详细的解释和归纳;另外,介绍了添加剂的联用技术在不同电池体系中的最新研究成果;最后,对新型正极界面修饰用电解液添加剂的开发进行了展望。     

铜-铈氧化还原液流电池性能

设计了一种新型Ce-Cu氧化-还原液流电池,研究了Ce³⁺/Ce⁴⁺和Cu⁰/Cu²⁺氧化还原电对的循环伏安特性,优化了电解液及电极材料,进而组装出液流电池,测试了电池的充放电性能。 结果表明,在45 mA恒电流充/放电条件下,电池放电平台电压约为1.0 V,库伦效率约100%,能量效率为75%以上,电池可稳定循环100次。     

3, 4-乙烯二氧噻吩单体用作锂离子电池安全性改善添加剂的研究

安全性是制约锂离子电池向电动汽车领域应用拓展的主要障碍. 本工作提出了一种能够有效改善锂离子电池安全性的电解液添加剂-3,4-乙烯二氧噻吩单体（EDOT）,研究了其在有机电解液中的电氧化聚合行为,以及对LiCoO₂电极高温热行为和电池安全性、电化学性能的影响. 循环伏安（CV）和透射电镜（TEM）表征结果表明,单体添加剂能够在电池充电过程发生电氧化聚合,在正极表面形成一层聚（3,4-乙烯二氧噻吩）（PEDOT）导电聚合物膜;差示扫描量热（DSC）分析结果显示,PEDOT隔离了电解液与正极表面的直接接触,减少了过热条件下电解液在正极表面的分解放热. 安全性测试结果表明,在电解液中仅添加0.1%的EDOT单体,即可将电池在150 ^oC高温热冲击下发生热失控的时间推迟13.8分钟. 电化学性能测试结果表明,聚合产物良好的电子导电性能有效改善正极的电子传导能力,在一定程度上提高电池的倍率性能和循环稳定性,而容量、低温性能等基本不受影响,展示出良好的应用前景.     

Molecular Modeling and Nuclear Overhauser Enhancement Spectroscopy (NOESY): Tools for Studying the Regioselective Bromination of 3-Bromoanisole

The use of molecular modeling for predicting chemical reactivity has been highly successful in the industrial and academic research communities. For this reason, increased emphasis has been placed on molecular modeling in the undergraduate curriculum. In the described experiment, the bromination of 3-bromoanisole, students are encouraged to use molecular modeling software as a tool for predicting chemical reactivity. Besides introducing students to molecular modeling, this experiment incorporates the use of nontraditional, less hazardous reagents and solvents for electrophilic aromatic bromination reactions. Lastly, nuclear Overhauser enhancement spectroscopy (NOESY) is introduced as a tool for structural elucidation. Although there are a number of aspects to this experiment, two 3-hour laboratory periods are sufficient because the results from semiempirical (AMI) geometry optimizations, which are complete in seconds, were almost identical to the higher order, more time-intensive ab initio (3-21G*) calculations. In addition, the experimental time was greatly shortened by the discovery that catalytic HCl(aq) reduces the reaction time from 5 hours to 18 minutes.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.