锂-氧气电池:正极催化剂的最新进展与挑战（英文）

非质子锂-氧气电池具有高理论能量密度,在过去几年里受到了广泛关注。然而,动力学缓慢的氧还原反应(ORR)/氧析出反应(OER)和放电产物Li₂O₂导电性差导致锂-氧气电池过电位大,放电容量有限,循环寿命短。开发有效的锂-氧气电池正极催化剂可以调控放电与充电过程中Li₂O₂的形成和可逆分解,减小放电/充电极化。尽管提升ORR/OER动力学的正极催化剂已经取得了一系列重要进展,但是对正极在放电和充电中Li₂O₂生成和分解过程的理解依然是不足的。这篇综述聚焦于锂-氧气电池正极催化剂的最新进展,总结了催化剂与Li₂O₂生成/分解的作用关系,本文首先指出了锂-氧气电池正极面临的科学问题,包括动力学缓慢的ORR/OER过程和导电性差的反应产物Li₂O₂钝化电极,并提出了锂-氧气电池正极设计准则。通过对最近报道的正极催化剂进行分类讨论,明晰调控催化剂活性位点策略,理解在正极反应过程中...     

高电压镍锰酸锂正极/电解液界面本征性质的研究

高电压正极材料的应用是提高锂离子电池能量密度的有效手段,然而高电压下正极/电解液界面稳定性成为决定锂离子电池在高电压工作条件下循环性能和安全性能的关键因素,因此高电压下正极/电解液界面具有重要的研究价值. 但是,目前报道的正极/电解液界面的研究中通常使用传统的极片制备方法,这需要引入导电剂和粘结剂,会对后期正极活性物质表面钝化膜的形貌和组分表征带来干扰,甚至造成固体电解质界面(SEI)膜存在的假象,难以获得正极材料与电解液之间界面的本征信息. 这里,我们采用溶胶凝胶旋涂法制备了不含导电剂和粘结剂的镍锰酸锂(LNMO)正极,以其为研究对象,通过扫描电镜(SEM)、原子力显微镜(AFM)和X射线光电子能谱(XPS)技术,结合电化学阻抗谱(EIS)研究了LNMO正极/电解液界面在充放电过程中的结构演变过程以及本征性质. 研究结果显示在充放电过程中,电解液中溶剂和电解质都会参与反应,其中LiPF₆的降解主要发生在高电压下,其降解产物在放电过程中又会被反应消耗掉. 它们的降解产物沉积到LNMO正极形成表面膜,该表面膜的主要成分随着电压的不同组分有所不同.     

苯甲醚及其溴取代物用作锂离子电池防过充添加剂的研究

选择苯甲醚、2-溴苯甲醚、3-溴苯甲醚作为锂离子电池有机电解液的防过充添加剂. 采用循环伏安测试、恒流充放电测试、电化学阻抗分析、扫描电镜分析等手段, 研究三种添加剂的防过充作用效果, 以及对LiNi_1/3Co_1/3Mn_1/3O₂ (NCM)正极性能的影响. 结果表明: 三种添加剂均具有合适的氧化电位和良好的氧化还原特性, 能够提高锂离子电池的防过充性能. 其中2-溴苯甲醚的防过充作用效果最优, 电池经0.1 C充电长达近50 h后才达到5 V截止电压, 且可承受过充的次数相对最多, 但该添加剂对NCM正极的循环性能影响较大; 苯甲醚的防过充效果仅次于2-溴苯甲醚, NCM正极在添加有苯甲醚的电解液中循环性能良好, 0.2 C充放电循环80次后容量仍能保持93.8%左右. 含上述三种添加剂的电池经过充后, 均会有一部分氧化还原产物吸附在NCM正极表面, 增加电池的整体阻抗, 其中含2-溴苯甲醚的电池表现最为明显.     

锂离子电池高电压电解液的研究现状

目前提高锂离子电池能量密度的途径主要有提高锂离子电池的工作电压和应用高工作电压的正极材料,因此,锂离子电池高电压电解液的研究和开发势在必行。本文概述了锂离子电池电解液和高电压电解液的特点,介绍了前线轨道理论中的HOMO和LUMO对电解液设计的指导意义。尤其是结合日本知名企业和科研机构在高电压电解液方面的研究成果,阐述了两种实现电解质高电压化的途径,即提高溶剂本身的耐氧化性和使用添加剂,总结了氟代酯、氟化醚、硼酸酯、砜类和耐氧化添加剂等用于高电压电解液中的关键物质类型,并讨论了目前高电压电解液研究开发所带来的启示。     

聚环氧乙烷聚合物电解质基高电压固态锂金属电池的研究进展

采用液态碳酸酯电解质的锂离子电池在遭遇极端工况时, 极易发生泄露、燃烧、甚至爆炸等重大安全事故. 相对比, 聚环氧乙烷(PEO)固态聚合物电解质可以显著提升锂电池的安全性, 并且其优异的可塑性使其可以被制成特定形状进而满足特殊领域的差异化需求; 更为重要的是: PEO固态聚合物电解质与锂金属负极兼容性好. 然而, PEO固态聚合物电解质电化学氧化窗口低, 难以匹配高电压正极材料(≥4 V), 极大限制了其在高电压、高能量密度固态聚合物锂金属电池中的进一步应用. 近期经过国内外科研工作者在PEO固态聚合物电解质结构设计、PEO端羟基改性、含硼锂盐引入、功能型粘结剂设计开发以及正极界面层构筑等方面所做出的不懈努力, PEO固态聚合物电解质基高电压固态锂金属电池取得了系列化重大科研进展. 基于此, 本综述主要从以下八个方面: (1)高电压正极片表面修饰超薄聚合物层、(2)高电压正极颗粒包覆、(3)对碳黑颗粒进行包覆、(4)使用富含羧基的粘结剂、(5)不对称固态聚合物电解质结构设计、(6)正极界面原位形成耐高电压界面层、(7)醚氧官能团(-OCH₃)封端PEO, 提升其本征耐高电压性能、(8)含硼锂盐做添加剂, 详细综述了采用PEO固态聚合物电解质构建的高电压固态锂金属电池所取得的最新研究进展以及相应的高电压固态锂金属电池界面稳定作用机制. 最后还对未来PEO固态聚合物电解质在高电压固态锂金属电池方面所存在的巨大挑战和发展趋势进行了详细展望和总结阐述.     

添加剂氟代乙烯碳酸酯对锂离子电池低温性能影响的机制研究

本文通过磷酸铁锂/碳电池研究了电解液添加剂氟代乙烯碳酸酯（FEC）对电池低温性能的影响. 电池充放电实验证明,FEC添加剂能够在负极表面形成良好的固体电解质界面层（SEI）. 电解液中添加5% FEC后,电池-40 ^oC低温放电容量保持率可以从31.7%提高至43.7%,还提高了电池放电电压平台. 交流阻抗测试表明,FEC的加入能够有效降低电池的界面传荷阻抗（R_ct）. 参比电极测试表明,其主要是降低了碳负极的低温极化.     

锂离子电池三元正极材料电解液添加剂的研究进展

三元层状氧化物{Li[Ni_xCo_yM_z]O₂（0 < x,y,z < 1,M＝Mn,缩写NMC;M＝Al,缩写NCA）}具有能量密度高、循环性能好、价格适中等优异的综合性能,是目前锂离子电池（LIBs）中最具应用前景的一类正极材料.随着纯电动汽车（EVs）及混合电动汽车（HEVs）的快速发展,人们对LIBs的能量密度、循环寿命以及安全性要求不断提高.然而,在传统电解液体系中,三元正极材料在高电压、高温下会发生剧烈的结构变化和界面副反应,给实际应用带来巨大挑战,尤其是高镍三元材料的循环寿命和安全性.其中,开发适配的电解液添加剂是提高锂离子电池电化学性能最经济有效的方法之一.从物质本征结构出发,综述了近5年来包括碳酸亚乙烯酯（VC）、氟代物、新型锂盐、含P、含B、含S、腈类等及其复合物作为电解液添加剂在NMC及NCA正极材料中的应用及作用机理,并进行总结与展望.     

非水系二次锂-氧电池正极

非水系二次锂-氧电池(NRLOB)在当前所研发的二次电池中理论能量密度最高,但存在循环性能差,充、放电电流密度低等显著问题;这些问题主要同其氧正极上的电化学反应相关,关键在于过氧化锂Li₂O₂可逆生成、分解反应能否在较高的速率下连续地进行。本文综述了近年来NRLOB正极电化学反应机理、正极碳材料、催化剂和电极结构、电解液分解导致电极副反应等方面的研究现状;归纳了今后需要进一步研究的主要问题。     

基于废旧锂电池回收制备LixMO (x=0.79, 0.30, 0.08; M=Ni/Co/Mn)材料作为锂-氧气电池正极催化剂的电化学性能研究

锂-氧气电池因其超高的理论比容量而受到科研界的广泛关注, 但其存在较为严重的充放电极化和较差的循环稳定性等问题, 从而极大地限制其商业化进程. 因此设计出有效的正极催化剂是解决锂-氧气电池面临的这些棘手问题的必要手段. 通过对不同充电状态的废旧锂电池正极进行回收制得三种不同锂含量的多元金属氧化物Li_xMO (x=0.79, 0.30, 0.08; M=Ni/Co/Mn), 并分别用作锂-氧气电池正极催化剂. 系统研究了Li_xMO材料中锂含量及晶体结构对其电化学性能的影响. 电化学测试结果表明, 与Li_0.79MO和Li_0.08MO催化剂相比, 基于Li_0.30MO为正极催化剂的锂-氧气电池在电流密度100 mA•g^–1和限定容量800 mAh•g^–1的条件下具有较高的放电比容量(14655.9 mAh•g^–1)、较低的充电电压(3.83 V)和较高的能量转换效率(72.2%). 而且该电池体系在充放电循环140圈后充电终止电压仍低于4.3 V. 最终认为制得的Li_0.30MO材料具有优异的催化性能归因于其稳定的层状-岩盐相复合结构以及结构中富含的氧化镍相和氧空位之间的协同作用. 这些优点能够促进放电产物的可逆形成与分解, 从而提高锂-氧气电池循环性能.     

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.     

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%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

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.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

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%).     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

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.