Characterization of crystalline and amorphous content in pharmaceutical solids by dielectric thermal analysis

Morphological and thermodynamic transitions in drugs as well as their amorphous and crystalline content in the solid state have been distinguished by thermal analytical techniques, which include dielectric analysis (DEA), differential scanning calorimetry (DSC), and macro-photomicrography. These techniques were used successfully to establish a structure versus property relationship with the United States Pharmacopeia standard set of active pharmaceutical ingredient (API) drugs. A distinguishing method is the DSC determination of the amorphous and crystalline content which is based on the fusion properties of the specific drug and its recrystallization. The DSC technique to determine the crystalline and amorphous content is based on a series of heat and cool cycles to evaluate the drugs ability to recrystallize. To enhance the amorphous portion, the API is heated above its melting temperature and cooled with liquid nitrogen to ?120 °C (153 K). Alternatively a sample is program heated and cooled by DSC at a rate of 10 °C min^?1. DEA measures the crystalline solid and amorphous liquid API electrical ionic conductivity. The DEA ionic conductivity is repeatable and differentiates the solid crystalline drug with a low conductivity level (10^?2 pS cm^?1) and a high conductivity level associated with the amorphous liquid (10⁶ pS cm^?1). The DSC sets the analytical transition temperature range from melting to recrystallization. However, analysis of the DEA ionic conductivity cycle establishes the quantitative amorphous and crystalline content in the solid state at frequencies of 0.10–1.00 Hz and to greater than 30 °C below the melting transition as the peak melting temperature. This describes the “activation energy method.” An Arrhenius plot, log ionic conductivity versus reciprocal temperature (K^?1), of the pre-melt DEA transition yields frequency dependent activation energy (E _a, J mol^?1) for the complex charging in the solid state. The amorphous content is inversely proportional to the E _a where the E _a for the crystalline form is higher and lower for the amorphous form with a standard deviation of ±2%. There was a good agreement between the DSC crystalline melting, recrystallization, and the solid state DEA conductivity method with relevant microscopic evaluation. An alternate technique to determine amorphous and crystalline content has been established for the drugs of interest based on an obvious amorphous and crystalline state identified by macro-photomicrography and compared to the conductivity variations. This second “empirical method” correlates well with the “activation energy” method.     

Titanium Trisulfide Monolayer: Theoretical Prediction of a New Direct‐Gap Semiconductor with High and Anisotropic Carrier Mobility

A new two‐dimensional (2D) layered material, namely, titanium trisulfide (TiS₃) monolayer, is predicted to possess novel electronic properties. Ab initio calculations show that the perfect TiS₃ monolayer is a direct‐gap semiconductor with a bandgap of 1.02 eV, close to that of bulk silicon, and with high carrier mobility. More remarkably, the in‐plane electron mobility of the 2D TiS₃ is highly anisotropic, amounting to about 10 000 cm² V^?1 s^?1 in the b direction, which is higher than that of the MoS₂ monolayer, whereas the hole mobility is about two orders of magnitude lower. Furthermore, TiS₃ possesses lower cleavage energy than graphite, suggesting easy exfoliation for TiS₃. Both dynamical and thermal stability of the TiS₃ monolayer is examined by phonon‐spectrum calculation and Born–Oppenheimer molecular dynamics simulation. The desired electronic properties render the TiS₃ monolayer a promising 2D atomic‐layer material for applications in future nanoelectronics.     

Zn–Co Sulfide Microflowers Anchored on Three-Dimensional Graphene: A High-Capacitance and Long-Cycle-Life Electrode for Asymmetric Supercapacitors

Zinc–cobalt double-metal sulfides (ZCS) as Faradic electrode materials with high energy density have great potential for supercapacitors, but their poor transfer efficiency for electrons and ions hinders their electrochemical response. Herein, ZnCo₂(CO₃)_1.5(OH)₃@ZCS microflower hybrid arrays consisting of thin nanolayer petals were anchored on three-dimensional graphene (ZnCo₂(CO₃)_1.5(OH)₃@ZCS/3DG) by a simple hydrothermal method and additional ion-exchange process. A ZnCo₂(CO₃)_1.5(OH)₃@ZCS/3DG electrode delivered high capacitance (2228 F g⁻¹ at 1 A g⁻¹) and long cycling life (85.7 % retention after 17 000 cycles), which are ascribed to the multicomponent structural design. The 3DG conductive substrate improves the electron-transfer dynamics of the electrode material. Meanwhile, the microflowers consisting of thin nanolayer petals could not only provide many active sites for ions to improve the capacitance, but also alleviate the volume expansion to ensure the structural stability. Furthermore, an all-solid-state asymmetric supercapacitor based on a ZnCo₂(CO₃)_1.5(OH)₃@ZCS/3DG electrode achieved a high energy density of 27 W h kg⁻¹ at 528.3 W kg⁻¹ and exhibits exceptional cyclic stability for 23 000 cycles. Its ability to light a blue LED for 9 min verified the feasibility of its application for energy storage devices.     

Further studies of a zinc-air cell employing a Zn-PCH (PVA chemical hydrogel) anode

The capacity utilization of zinc anode is usually very low in alkaline solution because of extreme dissolution and the passivation of zinc surface. This problem can be substantially overcome by using the composite electrode of Zn-PCH (PVA chemical hydrogel). In this work, PCH hydrogel film coated on the surface of the ZnO particles can reduce the solubility of the zinc and the concentration of the Zn(OH)₄^2?. The cell with the Zn-PCH electrode reached 150 cycles before its capacity fell below 90% of the initial capacity, while the standard cell failed after 150 cycles. Based on the scanning electron microscopy observation of the Zn-PCH electrode, it shows a distribution of big spherical particles to form a loose and porous structure rather than a dense and compact film, which can help zinc electrode to stay in a loose and porous structure. Such texture is definitely in favor of the diffusion of OH^? ions, facilitating the utilization of active material. Therefore, the Zn-PCH electrode can effectively improve the cycle performance of the secondary Zn-air battery.     

Comparative investigations of LiVPO4F/C and Li3V2(PO4)3/C synthesized in similar soft chemical route

Triclinic LiVPO₄F and monoclinic Li₃V₂(PO₄)₃ are synthesized through a soft chemical process with mechanical activation assist, followed by annealing. In this process, ascorbic acid is used as reducing agent as well as carbon source. The as-prepared samples are coated with amorphous carbon. XPS analysis results show the expected valency states of ions in LiVPO₄F and Li₃V₂(PO₄)₃. The electrochemical properties of the prepared LiVPO₄F/C and Li₃V₂(PO₄)₃/C cathodes are evaluated. The as-prepared LiVPO₄F/C cathode shows an initial discharge specific capacity of 140?±?3 mAh?g^?1 at 30 mA?g^?1 in the voltage range of 3.0~4.4 V, compared with that of 138?±?3 mAh?g^?1 possessed by Li₃V₂(PO₄)₃/C. Both samples exhibit good cycle performance at different current densities. The capacity delivered by LiVPO₄F remains 95.5 and 91.7 % of its initial discharge capacity after 50 cycles at 150 and 750 mA?g^?1, respectively, while 97.4 and 90.6 % for Li₃V₂(PO₄)₃/C. But the rate capability of LiVPO₄F/C is not so good compared with as-prepared Li₃V₂(PO₄)₃/C.     

Nanostructured lithium-free oxyanion cathode, Li x Co2(MoO4)3 [0≤ x <3] for 3 V class lithium batteries

A new nanostructured framework-type polyanion material, Li _x Co₂(MoO₄)₃ [0≤?x?<3], was studied as a positive electrode for use in 3-Volt class lithium-ion cells for the first time. The new material was synthesized in a lithium-free composition and examined its structure, morphology, and electrochemical characteristics. Co₂(MoO₄)₃ was found to crystallize in a monoclinic structure with lattice parameters: a?=?14.280(9) ?, b?=?3.382(8) ?, c?=?10.557(1) ?, and β?=?117.9728° (space group P2/m). The redox behavior of this new material was demonstrated in lithium-containing test cells. The material offered a discharge capacity of approximately 110 mAh g^?1 between 3.5 and 1.5 V during the first cycle and retained 50% capacity at the end of the 20th cycle. The poor capacity retention is obviously attributed to the poor electronic conductivity of Co₂(MoO₄)₃ owing to its open framework structure. To overcome the intrinsic low electronic conductivity of polyanion materials, we have adapted a nanocomposite approach by way of adding nanoporous carbon matrix (particle size approximately 10 nm) together with the conventional conductive additive (acetylene black) and demonstrated that the overall electronic conductivity could be improved significantly, yielding an initial discharge capacity of 121 mAh g^?1 using nanocomposite electrode in the potential range 3.5 V down to 2.0 V.     

镍锡析氢活性阴极的电化学制备及其在碱性溶液中的电催化机理

采用恒电流电沉积法在铜箔基底上获得镍锡合金镀层电极. 电子能谱(EDS)、X射线衍射(XRD)以及高分辨透射电镜(HRTEM)分析表明, 随着锡含量的增加, 镀层由镍晶胚与非晶镍锡构成的非晶态结构转变为Ni₃Sn₄与Ni₃Sn₂的混晶结构. 扫描电镜(SEM)分析发现, 非晶结构镍锡合金电极表面粒子分布均匀且粒径细小, Ni₃Sn₄与Ni₃Sn₂混晶结构的镍锡合金电极表面粗糙且断面呈分层自组装结构. 在25℃, 1 mol·L^-1 NaOH溶液中的稳态极化曲线表明非晶结构的镍锡合金电极具有良好的催化活性, 其析氢过电位仅为85 mV. 交流阻抗测试表明, 非晶以及混晶结构的镍锡合金在析氢电催化反应过程中由电化学吸附(Volmer)以及电化学脱附(Heyrovsky) 两个电荷转移过程控制, 且非晶结构电极相比于Ni₃Sn₄与Ni₃Sn₂混晶结构电极的高活性源于其活性氢具有更快的电化学吸附以及脱附速度.     

Effect of Al2O3 -coating on the electrochemical performances of Li3V2(PO4)3/C cathode material

The effect of Al₂O₃ -coating on Li₃V₂(PO₄)₃/C cathode material for lithium-ion batteries has been investigated. The crystalline structure and morphology of the synthesized powders have been characterized by XRD, SEM, and HRTEM, and their electrochemical performances are evaluated by CV, EIS, and galvanostatic charge/discharge tests. It is found that Al₂O₃ -coating modification stabilizes the structure of the cathode material, decreases the polarization of electrode and suppresses the rise of the surface film resistance. Electrochemical tests indicate that cycling performance and rate capability of Al₂O₃-coated Li₃V₂(PO₄)₃/C are enhanced, especially at high rates. The Al₂O₃-coated material delivers discharge capacity of 123.03 mAh g^?1 at 4 C rate, and the capacity retention of 94.15 % is obtained after 5 cycles. The results indicate that Al₂O₃ -coating should be an effective way to improve the comprehensive properties of the cathode materials for lithium-ion batteries.     

Microwave-assisted hydrothermal synthesis and electrochemical studies of α- and h-MoO<Subscript>3</Subscript>

Two modifications of molybdenum trioxide with orthorhombic (α-MoO₃) and hexagonal (h-MoO₃) crystal structure have been synthesized by a microwave-assisted hydrothermal method, facilitated by formic acid. Characterization by means of X-ray diffraction, scanning electron microscopy, specific surface analysis, and Fourier-transform infrared, Raman, and UV-Vis spectroscopy reveals phase-pure crystalline powder samples of hexagonal h-MoO₃ microrods and of α-MoO₃ nanobelt bundles, respectively. The electrochemical properties of the MoO₃ compounds, studied by cyclic voltammetry and galvanostatic cycling vs. Li/Li⁺, strongly depend on the structure and the applied potential range. In the range of 1.5–3.5 V, Li⁺-ions can be reversibly intercalated into the α-MoO₃ nanobelts. Utilizing the material in this way as intercalation cathode material yields an initial discharge capacity of 295 mA h g^?1 at 100 mA g^?1 and comparably moderate capacity fading of 25% between cycles 20 and 100. Extending the potential range to 0.01–3.0 V induces the conversion reaction to Mo, which for both modifications yields high initial capacities of around 1500 mA h g^?1 but is associated with much stronger capacity fading.     

Design of hierarchical and mesoporous FeF3/rGO hybrids as cathodes for superior lithium-ion batteries

Iron fluoride (FeF₃) is considered as a promising cathode material for Li-ion batteries (LIBs) due to its high theoretical capacity (712 mAh/g) with a 3e^? transfer. Herein, we have designed a strategy of hierarchical and mesoporous FeF₃/rGO hybrids for LIBs, where the hollow FeF₃ nanospheres are the main contributor to the specific capacity and the 2D rGO nanosheets are the matrix elevating the electronic conductivity and buffering the volume expansion. The unique FeF₃/rGO hybrid can be rationally synthesized by a non-aqueous in-situ precipitation method, offering the merits of large specific surface area with rich active sites, fast transport channels for lithium ions, effective alleviation of volume expansion during cycles, and accelerating the electrochemical reaction kinetics. The FeF₃/rGO hybrid electrode possesses a high initial discharge capacity of 553.9 mAh/g at a rate of 0.5 C with 378 mAh/g after 100 cycles, acceptable rate capability with 168 mAh/g at 2 C, and feasible high-temperature operation (320 mAh/g at 70 °C). The superior electrochemical behaviors presented here demonstrates that the FeF₃/rGO hybrid is a potential electrode for LIBs, which may open up a new vision to design high-efficiency energy-storage devices such as LIBs based on transition metal fluorides.     

Advanced all-solid-state lithium-selenium batteries enabled by selenium-nitrogen doped hierarchic meso-microporous carbon nanospheres composite cathode

Selenium, an element belonging to the same group in the periodic table as sulfur, has a high electronic conductivity(1 × 10^-5S/cm) and a high volumetric energy density(3253 mA h/cm³), which is a prospective cathode material for high-energy all-solid-state rechargeable batteries. However, its wide use is hindered by large volume expansion and low utilization rate. In this work, Se-infused nitrogen-doped hierarchical meso-microporous carbon composites(Se/NHPC) are prepared by...     

Amorphous MnO2 as Cathode Material for Sodium‐ion Batteries

Amorphous MnO₂ has been prepared from the reduction of KMnO₄ in ethanol media by a facile one‐step wet chemical route at room temperature. The electrochemical properties of amorphous MnO₂ as cathode material in sodium‐ion batteries (SIBs ) are studied by galvanostatic charge/discharge testing. And the structure and morphologies of amorphous MnO₂ are investigated by X‐ray diffraction (XRD ), scanning electron microscopy (SEM ), transmission electron microscopy (TEM ) and Raman spectra. The results reveal that as‐synthesized amorphous MnO₂ electrode material exhibits a spherical morphology with a diameter between 20 and 60 nm. The first specific discharge capacity of the amorphous MnO₂ electrode is 123.2 mAh •g⁻¹ and remains 136.8 mAh •g⁻¹ after 100 cycles at the current rate of 0.1 C. The specific discharge capacity of amorphous MnO₂ is maintained at 139.2, 120.4, 89, 68 and 47 mAh •g⁻¹ at the current rate of 0.1 C, 0.2 C, 0.5 C, 1 C and 2 C, respectively. The results indicate that amorphous MnO₂ has great potential as a promising cathode material for SIBs .     

Amorphous Selenium and Crystalline Selenium Nanorods Graphene Composites as Cathode Materials for All-Solid-State Lithium Selenium Batteries

Selenium (Se) is an element in the same main group as sulfur and is characterized by high electrical conductivity and large capacity (675 mAh g⁻¹). Herein, a novel ultra-high dispersion amorphous selenium graphene composite (a-Se/rGO) was synthesized and a selenium nanorods graphene composite (b-Se/rGO) was prepared by hydrothermal method as the cathode material for all solid-state lithium−selenium (Li−Se) batteries, hoping to improve the efficiency and utilization rate of active substances in all solid-state batteries. The all-solid-state batteries were assembled using a heated thawing electrolyte (2LiIHPN−LiI; HPN=3-hydroxypropionitrile). The utilization rate of a-Se/rGO was 103 % and the capacity was 697 mAh g⁻¹, which remained at 281 mAh g⁻¹ (41.6 % of the 675 mAh g⁻¹) after 30 cycles under 0.5 C. Notably, a-Se/rGO showed excellent performance concerning its utilization rate, with a capacity of up to 610 mAh g⁻¹ at 2 C, due to the high availability of amorphous Se and the special properties of the electrolytes. However, in the charge and discharge cycles, the second discharge capacity of a-Se/rGO was more significantly attenuated than that of the first discharge due to the formation of larger crystals of selenium during the charging process. The battery assembled using b-Se/rGO maintained a capacity of 270.58 mAh g⁻¹ after 30 cycles (the retention rate of discharge capacity was 66.13 % compared with that in the first cycle). Through TEM and other relevant tests, it is speculated that amorphous selenium is conducive to capacity release, which, however, is affected by the formation of crystalline selenium after the first charge process.     

Effect of vanadium doping on electrochemical performance of LiMnPO4 for lithium-ion batteries

A series of LiMn_1-x V _x PO₄ samples have been synthesized successfully via a conventional solid-state reaction method. The active materials are characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. The electrochemical performances of the samples are tested using cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge measurement techniques. It is confirmed that the samples are in single phase when the content of vanadium (x) is lower than 0.05. If that content is higher than 0.1, the samples are shown to contain an additional conductive phase of Li₃V₂(PO₄)₃. The vanadium doping significantly enhances the electrochemical properties of LiMnPO₄. It is underlined that the optimal ratio for a low-vanadium doping with the best electrochemical performance is 0.1 and this material exhibits a corresponding initial charge and discharge capacity of 98.9 and 98.1 mAh g^?1 at 0.1 C under 50 °C. The capacity retention is higher than 99 % after 30 cycles. The dramatic electrochemical improvement of the LiMnPO₄ samples is ascribed to the strengthened ability of lithium-ion diffusion and enhanced electronic conductivity for the V-doped samples.     

高振实密度圆饼状LiFePO4/C的制备及电化学性能

以乙二醇为溶剂,采用溶剂热法一步合成圆饼状LiFePO₄,然后以葡萄糖为碳源与合成的LiFePO₄前躯体高温烧结得到碳包覆的LiFePO₄/C复合材料,其振实密度高达1.3 g·cm^-3。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对LiFePO₄/C复合材料进行了物相和形貌表征,研究结果表明制备得到的LiFePO₄呈圆饼状,且生成的圆饼是由单晶LiFePO₄纳米片堆积而成。此外,LiFePO₄颗粒表面碳层包覆均匀。将制备的LiFePO₄/C用作锂离子电池正极材料,电化学性能测试表明其具有高的充放电比容量(在0.1C时放电,其初始放电比容量为157.7 mAh·g^-1)与良好的循环性能(500次循环后容量保持率为82.4%)。     

Paper-based all-solid-state flexible asymmetric micro-supercapacitors fabricated by a simple pencil drawing methodology

A simple and novel methodology was developed for manufacturing interdigitated asymmetric all-solid-state flexible micro-supercapacitors (MSCs) by a facile pencil drawing process followed by electrodepositing MnO₂ on one of the as-drawn graphite electrode as anode and the other as cathode.     

Morphology and performance of CoOOH films synthesized via electrochemical oxidation: substrate effects

In the present work, CoOOH films are synthesized from the electrochemical oxidation of α-Co(OH)₂ as precursor. The substrate influences on the material electrochemical properties are studied. The samples are structural and morphologically characterized using techniques of X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques are used for the electrochemical characterization. The films deposited on steel substrate grew in the vertical hexagonal platelet form. Meanwhile, films on Ti plate presented morphology in agglomerated sphere form. After electrochemical oxidation, the film initial morphology is maintained. The films deposited on steel plate have a structure which favors charge storage showing a high specific capacity value (110.92 mA h g^?1) and cyclic stability of 92% after 1000 cycles. Finally, the relaxation time constant value calculated was 5.6 s. This fact is making this material as a possible good candidate for application as electrode material or additive for other materials, in energy storage devices.     

Facile synthesis of single-crystalline Co<Subscript>3</Subscript>O<Subscript>4</Subscript> cubes as high-performance anode for lithium-ion batteries

Transition metal oxides have great potential as anode for lithium-ion batteries (LIBs), owing to their high theoretical capacity and low cost. However, the poor cycling stability and electron conductivity have limited the widely expected application of transition metal oxides. In this work, highly single-crystalline Co₃O₄ cubes with 400 nm in the average side length are successfully synthesized by a facile hydrothermal method. When used as anode for LIBs, the Co₃O₄ single-crystalline cubes exhibit highly stable and substantial discharge capacities of the amount to 877 mA h g^?1 at 200 mA g^?1 after 110 cycles with remarkable capacity retention of 98%, and 576 mA h g^?1 even at a high rate of 2000 mA g^?1. The scalability of the preparation method and the impressive results achieved here demonstrate the potential for the application to the future development of transition metal oxides anodes. These results suggest that the single-crystalline Co₃O₄ is a promising electrode material for the high-performance energy storage devices.     

Nano MgFe2O4 synthesized by sol–gel auto-combustion method as anode materials for lithium ion batteries

In this work, spinel structure MgFe₂O₄ nano-crystals were synthesized by sol–gel auto-combustion method. Morphology and structure of the synthesized MgFe₂O₄ material is characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). And its electrochemical properties were investigated at different active material ratio. Galvanostatic charge/discharge and cyclic voltammograms (CVs) measurements show that the electrode with a ratio of 40:40:20, which is the ratio of active material: super-P carbon (SP): polyvinylidene fluoride (PVDF), presents relatively superior performance with the initial discharge capacity of 1,123 mAh g^?1 and charge/discharge efficiency of 96.7 %. And after 50 cycles, it still maintains at 635 mAh g^?1, which is nearly double that of the other two electrodes with active material ratio of 60:25:15 and 80:15:5. Electrochemical impedance spectra testing shows that the charge transfer resistance (Rct) decreases along with the increasing amount of SP, which is benefit for reducing the polarization and improving the cycling stability of the electrode to a certain extent.     

Electrochemical performance of novel Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites as electrodes for energy storage devices

The novel Li₃V₂(PO₄)₃ glass-ceramic nanocomposites were synthesized and investigated as electrodes for energy storage devices. They were fabricated by heat treatment (HT) of 37.5Li₂O–25V₂O₅–37.5P₂O₅?mol% glass at 450 °C for different times in the air. XRD, SEM, and electrochemical methods were used to study the effect of HT time on the nanostructure and electrochemical performance for Li₃V₂(PO₄)₃ glass-ceramic nanocomposites electrodes. XRD patterns showed forming Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The crystalline sizes were found to be in the range of 32–56 nm. SEM morphologies exhibited non-uniform grains and changed with variation of HT time. The electrochemical performance of Li₃V₂(PO₄)₃ glass-ceramic nanocomposites was investigated by using galvanostatic charge/discharge methods, cyclic voltammetry, and electrochemical impedance spectroscopy in 1 M H₂SO₄ aqueous electrolyte. The glass-ceramic nanocomposites annealed for 4 h, which had a lower crystalline size, exhibited the best electrochemical performance with a specific capacity of 116.4 F g^?1 at 0.5 A g^?1. Small crystalline size supported the lithium ion mobility in the electrode by decreasing the ion diffusion pathway. Therefore, the Li₃V₂(PO₄)₃ glass-ceramic nanocomposites can be promising candidates for large-scale industrial applications in high-performance energy storage devices.