Synthesis of Single‐Crystalline Spinel LiMn2O4 Nanorods for Lithium‐Ion Batteries with High Rate Capability and Long Cycle Life

The long‐standing challenge associated with capacity fading of spinel LiMn₂O₄ cathode material for lithium‐ion batteries is investigated. Single‐crystalline spinel LiMn₂O₄ nanorods were successfully synthesized by a template‐engaged method. Porous Mn₃O₄ nanorods were used as self‐sacrificial templates, into which LiOH was infiltrated by a vacuum‐assisted impregnation route. When used as cathode materials for lithium‐ion batteries, the spinel LiMn₂O₄ nanorods exhibited superior long cycle life owing to the one‐dimensional nanorod structure, single‐crystallinity, and Li‐rich effect. LiMn₂O₄ nanorods retained 95.6 % of the initial capacity after 1000 cycles at 3C rate. In particular, the nanorod morphology of the spinel LiMn₂O₄ was well‐preserved after a long‐term cycling, suggesting the ultrahigh structural stability of the single crystalline spinel LiMn₂O₄ nanorods. This result shows the promising applications of single‐crystalline spinel LiMn₂O₄ nanorods as cathode materials for lithium‐ion batteries with high rate capability and long cycle life.     

Biomimetic Synthesis of Metal Ion‐Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt‐Doped LiMn2O4 with Improved Electrochemical Properties through a Cobalt‐Doped MnCO3 Precursor

We have synthesized spinel type cobalt‐doped LiMn₂O₄ (LiMn_2?yCo_yO₄, 0≤y≤0.367), a cathode material for a lithium‐ion battery, with hierarchical sponge structures via the cobalt‐doped MnCO₃ (Mn_1‐xCo_xCO₃, 0≤x≤0.204) formed in an agar gel matrix. Biomimetic crystal growth in the gel matrix facilitates the generation of both an homogeneous solid solution and the hierarchical structures under ambient condition. The controlled composition and the hierarchical structure of the cobalt‐doped MnCO₃ precursor played an important role in the formation of the cobalt‐doped LiMn₂O₄. The charge–discharge reversible stability of the resultant LiMn_1.947Co_0.053O₄ was improved to ca. 12 % loss of the discharge capacity after 100 cycles, while pure LiMn₂O₄ showed 24 % loss of the discharge capacity after 100 cycles. The parallel control of the hierarchical structure and the composition in the precursor material through a biomimetic approach, promises the development of functional materials under mild conditions.     

Thermodynamic Stability of Transition‐Metal‐Substituted LiMn2−xMxO4 (M=Cr,Fe, Co,and Ni) Spinels

The formation enthalpies from binary oxides of LiMn₂O₄, LiMn_2?xCr_xO₄ (x=0.25, 0.5, 0.75 and 1), LiMn_2?xFe_xO₄ (x=0.25 and 0.5), LiMn_2?xCo_xO₄ (x=0.25, 0.5, and 0.75) and LiMn_1.75Ni_0.25O₄ at 25 °C were measured by high temperature oxide melt solution calorimetry and were found to be strongly exothermic. Increasing the Cr, Co, and Ni content leads to more thermodynamically stable spinels, but increasing the Fe content does not significantly affect the stability. The formation enthalpies from oxides of the fully substituted spinels, LiMnMO₄ (M=Cr, Fe and Co), become more exothermic (implying increasing stability) with decreasing ionic radius of the metal and lattice parameters of the spinel. The trend in enthalpy versus metal content is roughly linear, suggesting a close‐to‐zero heat of mixing in LiMn₂O₄—LiMnMO₄ solid solutions. These data confirm that transition‐metal doping is beneficial for stabilizing these potential cathode materials for lithium‐ion batteries.     

Electrochemical performance of rare-earth doped LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel cathode materials for Li-ion rechargeable battery

Spinel powders of LiMn_2−x RE _x O₄ (RE = La, Ce, Nd, Sm; 0 ≤ x ≤ 0.1) have been synthesized by solid-phase reaction. The structure and electrochemical properties of these electrode materials were characterized by X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge–discharge experiment. The part substitution of rare-earth element RE for Mn in LiMn₂O₄ decreases the lattice parameter, resulting in the improvement of structural stability, and decreases the charge transfer resistance during the electrochemical process of LiMn₂O₄. As a result, the cycle ability, 55 °C high-temperature and high-rate performances of LiMn_2−x RE _x O₄ electrode materials are significantly improved with increasing RE addition, compared to the pristine LiMn₂O₄.     

Enhanced Intrinsic Catalytic Activity of λ‐MnO2 by Electrochemical Tuning and Oxygen Vacancy Generation

Chemically prepared λ‐MnO₂ has not been intensively studied as a material for metal–air batteries, fuel cells, or supercapacitors because of their relatively poor electrochemical properties compared to α‐ and δ‐MnO₂. Herein, through the electrochemical removal of lithium from LiMn₂O₄, highly crystalline λ‐MnO₂ was prepared as an efficient electrocatalyst for the oxygen reduction reaction (ORR). The ORR activity of the material was further improved by introducing oxygen vacancies (OVs) that could be achieved by increasing the calcination temperature during LiMn₂O₄ synthesis; a concentration of oxygen vacancies in LiMn₂O₄ could be characterized by its voltage profile as the cathode in a lithiun–metal half‐cell. λ‐MnO_2?z prepared with the highest OV exhibited the highest diffusion‐limited ORR current (5.5 mA cm^?2) among a series of λ‐MnO_2?z electrocatalysts. Furthermore, the number of transferred electrons (n) involved in the ORR was >3.8, indicating a dominant quasi‐4‐electron pathway. Interestingly, the catalytic performances of the samples were not a function of their surface areas, and instead depended on the concentration of OVs, indicating enhancement in the intrinsic catalytic activity of λ‐MnO₂ by the generation of OVs. This study demonstrates that differences in the electrochemical behavior of λ‐MnO₂ depend on the preparation method and provides a mechanism for a unique catalytic behavior of cubic λ‐MnO₂.     

Kinetics of Li-ion transfer reaction at LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>, LiCoO<Subscript>2</Subscript>, and LiFePO<Subscript>4</Subscript> cathodes

Kinetics of LiFePO₄, LiMn₂O₄, and LiCoO₂ cathodes operating in 1 M LIPF₆ solution in a mixture of ethylene carbonate and dimethyl carbonate was deduced from impedance spectra taken at different temperatures. The most striking difference of electrochemical impedance spectroscopy (EIS) curves is the impedance magnitude: tens of ohms in the case of LiFePO₄, hundreds of ohms for LiMn₂O₄, and thousands of ohms for LiCoO₂. Charge transfer resistances (R _ct) for lithiation/delitiation processes estimated from the deconvolution procedure were 6.0 Ω (LiFePO₄), 55.4 Ω (LiCoO₂), and 88.5 Ω (LiMn₂O₄), respectively. Exchange current density for all the three tested cathodes was found to be comparable (0.55–1·10^?2 mAcm^?2, T = 298 K). Corresponding activation energies for the charge transfer process, \( {E}_{ct}^{\#} \), differed considerably: 66.3, 48.9, and 17.0 kJmol^?1 for LiMn₂O₄, LiCoO₂, and LiFePO₄, respectively. Consequently, temperature variation may have a substantial influence on exchange current densities (j _o) in the case of LiMn₂O₄ and LiCoO₂ cathodes.     

Advanced High‐Voltage Aqueous Lithium‐Ion Battery Enabled by “Water‐in‐Bisalt” Electrolyte

A new super‐concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra‐high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO₂ as the anode material, and a 2.5 V aqueous Li‐ion cell based on LiMn₂O₄ and carbon‐coated TiO₂ delivered the unprecedented energy density of 100 Wh kg^?1 for rechargeable aqueous Li‐ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the “water‐in‐salt” electrolyte further pushed the energy densities of aqueous Li‐ion cells closer to those of the state‐of‐the‐art Li‐ion batteries.     

A Self‐Healing Aqueous Lithium‐Ion Battery

Flexible lithium‐ion batteries are critical for the next‐generation electronics. However, during the practical application, they may break under deformations such as twisting and cutting, causing their failure to work or even serious safety problems. A new family of all‐solid‐state and flexible aqueous lithium ion batteries that can self‐heal after breaking has been created by designing aligned carbon nanotube sheets loaded with LiMn₂O₄ and LiTi₂(PO₄)₃ nanoparticles on a self‐healing polymer substrate as electrodes, and a new kind of lithium sulfate/sodium carboxymethylcellulose serves as both gel electrolyte and separator. The specific capacity, rate capability, and cycling performance can be well maintained after repeated cutting and self‐healing. These self‐healing batteries are demonstrated to be promising for wearable devices.     

The effect of nanolayer AlF<Subscript>3</Subscript> coating on LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cycle life in high temperature for lithium secondary batteries

The surface of the spinel LiMn₂O₄ was coated with AlF₃ by a chemical process to improve its electrochemical performance at high temperatures. The morphology and structure of the original and AlF₃-coated LiMn₂O₄ samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. It was found that the surfaces of the original LiMn₂O₄ samples were covered with a nanolayer AlF₃ after the treatment. The charge/discharge of the materials were carried at 220 mA/g in the range of 3.0 and 4.4 V at 55°C. While the original LiMn₂O₄ showed 17.8% capacity loss in 50 cycles at 55°C, the AlF₃-coated LiMn₂O₄ (118.1 mA h/g) showed only 3.4% loss of the initial capacity (122.3 mA h/g) at 55°C. It is obvious that the improvement in cycling performance of the coated-LiMn₂O₄ electrode at 55°C is attributed to the presence of AlF₃ on the surface of LiMn₂O₄. Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 817–819. The article is published in the original     

Deep‐Eutectic‐Solvent‐Based Self‐Healing Polymer Electrolyte for Safe and Long‐Life Lithium‐Metal Batteries

The deployment of high‐energy‐density lithium‐metal batteries has been greatly impeded by Li dendrite growth and safety concerns originating from flammable liquid electrolytes. Herein, we report a stable quasi‐solid‐state Li metal battery with a deep eutectic solvent (DES)‐based self‐healing polymer (DSP) electrolyte. This electrolyte was fabricated in a facile manner by in situ copolymerization of 2‐(3‐(6‐methyl‐4‐oxo‐1,4‐dihydropyrimidin‐2‐yl)ureido)ethyl methacrylate (UPyMA) and pentaerythritol tetraacrylate (PETEA) monomers in a DES‐based electrolyte containing fluoroethylene carbonate (FEC) as an additive. The well‐designed DSP electrolyte simultaneously possesses non‐flammability, high ionic conductivity and electrochemical stability, and dendrite‐free Li plating. When applied in Li metal batteries with a LiMn₂O₄ cathode, the DSP electrolyte effectively suppressed manganese dissolution from the cathode and enabled high‐capacity and a long lifespan at room and elevated temperatures.     

Facile synthesis of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> microsheets with porous micro-nanostructure as high-rate cathode materials for Li-ion batteries

Porous LiMn₂O₄ microsheets with micro-nanostructure have been successfully prepared through a simple carbon gel-combustion process with a microporous membrane as hard template. The crystal structure, morphology, chemical composition, and surface analysis of the as-obtained LiMn₂O₄ microsheets are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscope (XPS). It can be found that the as-prepared LiMn₂O₄ sample presents the two-dimensional (2-D) sheet structure with porous structure comprised with nano-scaled particles. As cathode materials for lithium-ion batteries, the obtained LiMn₂O₄ microsheets show superior rate capacities and cycling performance at various charge/discharge rates. The LiMn₂O₄ microsheets exhibit a higher charge and discharge capacity of 137.0 and 134.7 mAh g^?1 in the first cycle at 0.5 C, and it remains 127.6 mAh g^?1 after 50 cycles, which accounts for 94.7% discharge capacity retention. Even at 10 C rate, the electrode also delivers the discharge capacity of 91.0 mAh g^?1 after 300 cycles (93.5% capacity retention). The superior electrochemical properties of the LiMn₂O₄ microsheets could be attributed to the unique microsheets with porous micro-nanostructure, more active sites of the Li-ions insertion/deinsertion for the higher contact area between the LiMn₂O₄ nano-scaled particles and the electrolyte, and better kinetic properties, suggesting the applications of the sample in high-power lithium-ion batteries.     

2‐Azido‐2‐deoxycellulose: Synthesis and 1,3‐Dipolar Cycloaddition

Chitosan ( 1 ) was prepared by basic hydrolysis of chitin of an average molecular weight of 70000 Da, ¹H‐NMR spectra indicating almost complete deacetylation. N‐Phthaloylation of 1 yielded the known N‐phthaloylchitosan ( 2 ), which was tritylated to provide 3a and methoxytritylated to 3b . Dephthaloylation of 3a with NH₂NH₂?H₂O gave the 6‐O‐tritylated chitosan 4a . Similarly, 3b gave the 6‐O‐methoxytritylated 4b . CuSO₄‐Catalyzed diazo transfer to 4a yielded 95% of the azide 5a , and uncatalyzed diazo transfer to 4b gave 82% of azide 5b . Further treatment of 5a with CuSO₄ produced 2‐azido‐2‐deoxycellulose ( 7 ). Demethoxytritylation of 5b in HCOOH gave 2‐azido‐2‐deoxy‐3,6‐di‐O‐formylcellulose ( 6 ), which was deformylated to 7 . The 1,3‐dipolar cycloaddition of 7 to a range of phenyl‐, (phenyl)alkyl‐, and alkyl‐monosubstituted alkynes in DMSO in the presence of CuI gave the 1,2,3‐triazoles 8 – 15 in high yields.     

Comparison of different soft chemical routes synthesis of submicro-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and their influence on its electrochemical properties

A comparative study of submicro-crystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as hydrothermal and sol–gel methods is made. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, cyclic voltammogram, charge–discharge test, and electrochemical impedance spectroscopy (EIS). The results show that the electrochemical performances of spinel LiMn₂O₄ depend strongly upon the synthesis method. The LiMn₂O₄ powder prepared by hydrothermal route has higher specific capacity and better cycling performance than the one synthesized from sol–gel method. The former has the max discharge capacity of 114.36 and 99.78 mAh g⁻¹ at the 100th cycle, while the latter has the max discharge capacity of 98.67 and 60.25 mAh g⁻¹ at the 100th cycle. The selected equivalent circuit can fit well the EIS results of synthesized LiMn₂O₄. For spinel LiMn₂O₄ from sol–gel method and hydrothermal route in the first charge process R _SEI remain almost invariable, R _e and R _ct first decreasing and then increasing with the increase of polarization potential.     

尖晶石LiMn2O4的改性研究

由于资源丰富、价格便宜、易制备、对环境无污染、可回收利用等优点,尖晶石型LiMn2O4成为锂离子二次电池中最有希望的正极材料[1~3]。然而,在高电压充、放电条件下,由于电极中锰的溶解和Jahn鄄Teller效应的发生,会造成LiMn2O4容量迅速衰减[4~6]。为了改善LiMn2O4的电化学性能,研究者主要通过优化合成条件及合成方法来控制产品的粒径分布与形貌,以利于锂离子的脱、嵌[7,8];用掺杂的方法以稳定其结构,抑制Jahn鄄Teller效应的发生[9,10];用表面修饰的方式来减少活性物质与电解液的直接接触从而降低Mn的溶解[11,12]。掺杂方面,Co3 不仅有…     

Three‐dimensional networks in 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate

The two title proton‐transfer compounds, 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate, C₄H₇N₂⁺·C₇H₅O₆S⁻, (I), and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate, 2C₄H₇N₂⁺·C₇H₅O₆S²⁻, (II), are each organized into a three‐dimensional network by a combination of X—H...O (X = O, N or C) hydrogen bonds, and π–π and C—H...π interactions.     

Morphology‐Tuned Synthesis of NiCo2O4‐Coated 3D Graphene Architectures Used as Binder‐Free Electrodes for Lithium‐Ion Batteries

Nanostructured NiCo₂O₄ is directly grown on the surface of three‐dimensional graphene‐coated nickel foam (3D‐GNF) by a facile electrodeposition technique and subsequent annealing. The resulting NiCo₂O₄ possesses a distinct flower or sheet morphology, tuned by potential or current variation electrodeposition, which are used as binder‐free lithium‐ion battery anodes for the first time. Both samples exhibit high lithium storage capacity, profiting from the unique binder‐free electrode structures. The flower‐type NiCo₂O₄ demonstrates high reversible discharge capacity (1459 mAh g^?1 at 200 mA g^?1) and excellent cyclability with around 71 % retention of the reversible capacity after 60 cycles, which are superior to the sheet‐type NiCo₂O₄. Such superb performance can be attributed to high volume utilization efficiency with unique morphological character, a well‐preserved connection between the active materials and the current collector, a short lithium‐ion diffusion path, and fast electrolyte transfer in the binder‐free NiCo₂O₄‐coated 3D graphene structure. The simple preparation process and easily controllable morphology make the binder‐free NiCo₂O₄/3D‐GNF hybrid a potential material for commercial applications.     

Size‐Mediated Recurring Spinel Sub‐nanodomains in Li‐ and Mn‐Rich Layered Cathode Materials

Li‐ and Mn‐rich layered oxides are among the most promising cathode materials for Li‐ion batteries with high theoretical energy density. Its practical application is, however, hampered by the capacity and voltage fade after long cycling. Herein, a finite difference method for near‐edge structure (FDMNES) code was combined with in situ X‐ray absorption spectroscopy (XAS) and transmission electron microscopy/electron energy loss spectroscopy (TEM/EELS) to investigate the evolution of transition metals (TMs) in fresh and heavily cycled electrodes. Theoretical modeling reveals a recurring partially reversible LiMn₂O₄‐like sub‐nanodomain formation/dissolution process during each charge/discharge, which accumulates gradually and accounts for the Mn phase transition. From the modeling of spectra and maps of the valence state over large regions of the cathodes, it was found that the phase change is size‐dependent. After prolonged cycling, the TMs displayed different levels of inactivity.     

Quecksilber(II)‐chlorid‐ und ‐iodid‐Komplexe von Dithia‐ und Tetrathiakronenethern

Mercury(II) Chloride and Iodide Complexes of Dithia‐ and Tetrathiacrown Ethers The complexes [(HgCl₂)₂((ch)₂30S₄O₆)] ( 1 ), [HgCl₂(mn21S₂O₅)] ( 2 ), [HgCl₂(ch18S₂O₄)] ( 3 ) and [HgI(meb12S₂O₂)]₂[Hg₂I₆] ( 4 ) have been synthesized, characterized and their crystal structures were determined. In [(HgCl₂)₂((ch)₂30S₄O₆)] two HgCl₂ units are discretely bonded within the ligand cavity of the 30‐membered dichinoxaline‐tetrathia‐30‐crown‐10 ((ch)₂30S₄O₆) forming a binuclear complex. HgCl₂ forms 1 : 1 “in‐cavity” complexes with the 21‐membered maleonitrile‐dithia‐21‐crown‐7 (mn21S₂O₅) ligand and the 18‐membered chinoxaline‐dithia‐18‐crown‐6 (ch18S₂O₄) ligand, respectively. The 12‐membered 4‐methyl‐benzo‐dithia‐12‐crown‐4 (meb12S₂O₂) ligand gave with two equivalents HgI₂ the compound [HgI(meb12S₂O₂)]₂[Hg₂I₆]. In the cation [HgI(meb12S₂O₂)]⁺ meb12S₂O₂ forms with the cation HgI⁺ a half‐sandwich complex.     

Synthesis of high-energy-density LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode through surficial Nb doping for lithium-ion batteries

LiMn₂O₄ is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn₂O₄ is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn₂O₄ composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb⁵⁺ enrich in the surficial layer of the particles to form a LiMn_2-xNb_xO₄ phase. This kind of doping can increase the specific discharge capacity of LiMn₂O₄ materials. Contrast with the pristine LiMn₂O₄, the discharge capacity of LiMn_1.99Nb_0.01O₄-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g^?1 and the compacted density from 2.81 to 3.10 g cm^?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.

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Enhancing the Electrochemical Performance of the LiMn2O4 Hollow Microsphere Cathode with a LiNi0.5Mn1.5O4 Coated Layer

Spinel cathode materials consisting of LiMn₂O₄@LiNi_0.5Mn_1.5O₄ hollow microspheres have been synthesized by a facile solution‐phase coating and subsequent solid‐phase lithiation route in an atmosphere of air. When used as the cathode of lithium‐ion batteries, the double‐shell LiMn₂O₄@LiNi_0.5Mn_1.5O₄ hollow microspheres thus obtained show a high specific capacity of 120 mA h g^?1 at 1 C rate, and excellent rate capability (90 mAhg^?1 at 10 C) over the range of 3.5–5 V versus Li/Li⁺ with a retention of 95 % over 500 cycles.