Efficient microwave hydrothermal synthesis of nanocrystalline orthorhombic LiMnO2 cathodes for lithium batteries

Rod-like orthorhombic LiMnO₂ nanocrystals were successfully synthesized using temperature-controlled microwave hydrothermal route (TCMH) in a short time (30 min) at a temperature as low as 160 °C. o-LiMnO₂ obtained by two different methods was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemistry test. SEM revealed that the product obtained in case of TCMH was rod-like with a diameter of 40 nm, while the nanoparticles with 200 nm diameter were obtained by traditional hydrothermal route (TH). The dramatic formation of o-LiMnO₂ in the microwave hydrothermal field influenced the morphology and crystal structure of the final products. The formation and preferred growth orientation mechanism of o-LiMnO₂ in the microwave irradiation process was discussed. Electrochemistry performance exhibited that the as-synthesized o-LiMnO₂ nanorods reached the maximum discharge capacity of 194.2 mAh g⁻¹ at 0.1 C rate after several cycles between 2.2 and 4.4 V vs. Li⁺/Li at room temperature, which was higher than the electrochemical performance of o-LiMnO₂ obtained by TH. The experimental results showed that the TCMH method provided an effective way for preparing o-LiMnO₂ cathode material in lithium-ion batteries.     

Hydrothermal synthesis and electrochemical behavior of orthorhombic LiMnO2

The most highlighted point of this work to emphasize is that it is the first trial to use Mn₃O₄ oxide as a precursor to synthesize orthorhombic LiMnO₂ by the hydrothermal method. A well-ordered orthorhombic LiMnO₂ phase was formed by the hydrothermal treatment of Mn₃O₄ with excess LiOH aqueous solution at 170 °C. According to TEM observation, the as-synthesized powder was single crystalline particle oxide. Comparing with other orthorhombic LiMnO₂ prepared by low temperature synthetic route and by high temperature calcination, the orthorhombic LiMnO₂ prepared by the hydrothermal route showed enhanced battery performance as a lithium battery cathode material. We believe that the new hydrothermal synthesis is expected as an excellent alternative of powder preparation method of high capacity cathode material to be used for Li-ion secondary battery.     

Synthesis and electrochemical characterization of orthorhombic LiMnO2 material

Well-defined orthorhombic LiMnO₂ was synthesized using LiOH and γ-MnOOH starting materials at 1000 °C in an argon flow by quenching process. X-ray diffraction (XRD) revealed that the compound showed an orthorhombic phase of a space group with Pmnm (a=2.806 Å, b=5.750 Å, and c=4.593 Å). The prepared compound was composed of particles of about 5-15 μm diameter with a bar-shape and small spherical one of about 1-2 μm. It showed very small initial discharge capacity of about 34 mA h g⁻¹ in the (3+4) V region at room temperature. However, after 12 h grinding, the LiMnO₂ delivered 201 mA h g⁻¹ in the first cycle and still delivered 200 mA h g⁻¹ after 50 cycles at room temperature. We found that the initial discharge capacity of LiMnO₂ agreed well with its specific surface area by Brunauer, Emmett and Teller (BET) analysis. Especially, the grinding treatment played an important role to activate the lithium insertion-extraction into the LiMnO₂ layer in the 3 V region.     

Hydrothermal synthesis of orthorhombic LiMnO2 nano-particles

Orthorhombic LiMnO₂ nano-particles were successfully prepared under mild hydrothermal conditions from KMnO₄ and MnCl₂ sources. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the LiMnO₂ particles. The influence of the molar ratio of Li/Mn and of the holding temperature was studied. The synthesized nano-particles were found to be highly crystallized with a diameter of 50-100 nm.     

Tailoring high-surface-area nanocrystalline TiO2 polymorphs for high-power Li ion battery electrodes

The crystallization and morphology of brookite and anatase titania (TiO₂) were controlled using the urea-mediated hydrolysis/precipitation route in the presence of the Ti³⁺ ions. Without the strong complexing agents and the non-hydrothermal conditions, simple alterations to the urea concentration led to the synthesis from brookite nanorods to anatase nanoflowers at a low temperature below 100 °C, whereas the BET specific surface area evolved from 102 to 268 m² g⁻¹, respectively. A possible formation mechanism was also proposed for these TiO₂ nanostructures. The excellent reversible capacity and rate capability were achieved for the anatase nanoflowers because of the small crystallite size and significantly large surface area.     

水热法制备正交结构层状LiMnO2正极材料的研究进展

层状LiMnO2正极材料的理论容量几乎为尖晶石型锰酸锂（LiMn2O4）的2倍,研究和应用前景广阔.作者较详细的介绍了近年来国内外有关水热法制备层状LiMnO2正极材料的研究工作,评述了由不同锰源制备层状LiMnO2正极材料所存在的优缺点,对今后水热法制备层状LiMnO2正极材料的研究及发展前景进行了展望.     

Cathodic performance of VOPO4 with various crystal phases for Li ion rechargeable battery

Cathodic performance of six different VOPO₄ phases for Li ion rechargeable battery was investigated. It was found that VOPO₄ exhibits a high flat discharge potential of 3.7 V for Li ion electrochemical intercalation and de-intercalation excepting for β- and ε-types. On the other hand, slightly higher flat discharge potential of 3.9 and 3.8 V was observed for β- and ε-types. Capacity for Li intercalation is strongly related with the crystal structure of VOPO₄. In particular, δ-phase exhibits the largest reversible capacity of ca. 130 mAh/g among the examined VOPO₄. High capacity for Li intercalation in δ-phase VOPO₄ hardly decreased over 30 times of charge and discharge cycles. Although the reversible capacity decreased with increasing the current density for charge and discharge, large capacity of 80 mAh/g was still sustained at 0.4 mA/cm² for δ-type VOPO₄.     

A hydrothermal reaction to synthesize CuFeS2 nanorods

A hydrothermal reaction route has been developed to prepare chalcopyrite phase CuFeS₂ nanorods at 200–250°C. X-ray powder diffraction and transmission electron microscopy results reveal that the CuFeS₂ synthesized displays nanorods with diameters of 20–40 nm and lengths of up to several micrometers. Elemental analysis gives the atomic ratio of Cu:Fe:S of 1:1.04:2.11. The ⁵⁷Fe Mössbauer spectrum exhibits a six-peak hyperfine magnetic spectrum and a like-splitted line non-magnetic peak. The factors influencing the formation of the CuFeS₂ nanorods were discussed.     

A study of lithium insertion into MnO2 containing TiS2 additive a battery material in aqueous LiOH solution

The electrochemical behavior and surface characterization of manganese dioxide (MnO₂) containing titanium disulphide (TiS₂) as a cathode in aqueous lithium hydroxide (LiOH) electrolyte battery have been investigated. The electrode reaction of MnO₂ in this electrolyte is shown to be lithium insertion rather than the usual protonation. MnO₂ shows acceptable rechargeability as the battery cathode. The influence of TiS₂ (1, 3 and 5 wt%) additive on the performance of MnO₂ as a cathode has been determined. The products formed on reduction of the cathode material have been characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), fourier transform infrared spectroscopy (IR) and transmission electron microscopy (TEM). It is found that the presence of TiS₂ to ≤3 wt% improves the discharge capacity of MnO₂. However, increasing the additive content above this amount causes a decrease in its discharge capacity.     

Hydrothermal synthesis of Li(Ni1/3Co1/3Mn1/3)O2 for lithium rechargeable batteries

Ultrafine powders of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials for lithium-ion secondary batteries were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/(Ni + Co + Mn) was studied. The products were investigated by XRD, TEM and EDS. The final products were found to be well crystallized Li(Ni_1/3Co_1/3Mn_1/3)O₂ with an average particle size of about 10 nm.     

Hydrothermal synthesis of LiNi0.9Co0.1O2 cathode materials

Ultrafine powders of LiNi_0.9Co_0.1O₂ were prepared under mild hydrothermal conditions. The product was characterized by XRD, TEM and EDS tests, which indicated that the obtained products were pure and well-crystallized LiNi_0.9Co_0.1O₂. The ICP-AES results indicated the products were lithium-deficient compounds. The addition of KOH hardly effected the crystallinity of the product but gave larger crystals.     

Synthesis and physical characteristics of ZnAl2O4 nanocrystalline and ZnAl2O4/Eu core-shell structure via hydrothermal route

Nanocrystalline zinc aluminate (ZnAl₂O₄) particles with a spinel structure were prepared by hydrolyzing a mixture of aluminum chloride hexahydrate and zinc chloride in deionized water. It was found that pH value and reaction temperature play critical roles in the formation of nano-sized ZnAl₂O₄. Depending on pH values in the precursor solution, ZnAl layered double hydroxide (ZnAl-LDH), ZnO, boehmite or gibbsite could be formed. At pH 7 and T>120 °C, the nanocrystalline ZnAl₂O₄ particles with average particle size of ∼5 nm are easily synthesized through ZnAl layered double hydroxide (ZnAl-LDH). After surface treatment with R-OH by using the cationic surfactant CTAB, the ZnAl₂O₄/Eu core-shell structure can be developed. The ZnAl₂O₄/Eu core-shell structure can show both emissions from ⁵D₀ to ⁷F₂ sensitivity energy level and ⁵D₂ to ⁷F₀ depth energy level.     

Electrochemical properties of TiP2O7 and LiTi2(PO4)3 as anode material for lithium ion battery with aqueous solution electrolyte

Some polyanionic compounds, e.g. TiP₂O₇ and LiTi₂(PO₄)₃ with 3D framework structure were proposed to be used as anodes of lithium ion battery with aqueous electrolyte. The cyclic voltammetry properties TiP₂O₇ and LiTi₂(PO₄)₃ suggested that Li-ion de/intercalation reaction can occur without serious hydrogen evolution in 5 M LiNO₃ aqueous solution. The TiP₂O₇ and LiTi₂(PO₄)₃ give capacities of about 80 mAh/g between potentials of −0.50 V and 0 V (versus SHE) and 90 mAh/g between −0.65 V and −0.10 V (versus SHE), respectively. A test cell consisting of TiP₂O₇/5 M LiNO₃/LiMn₂O₄ delivers approximately 42 mAh/g (weight of cathode and anode) at average voltage of 1.40 V, and LiTi₂(PO₄)₃/5 M LiNO₃/LiMn₂O₄ delivers approximately 45 mAh/g at average voltage of 1.50 V. Both as-assembled cells suffered from short cycle life. The capacity fading may be related to deterioration of anode material.     

The effect of Al(OH)3 coating on the Li[Li0.2Ni0.2Mn0.6]O2 cathode material for lithium secondary battery

Layered Li[Li_0.2Ni_0.2Mn_0.6]O₂ powder was modified by coating its surface with amorphous Al(OH)₃. Energy dispersive spectroscopy (EDS) showed that nano-sized Al(OH)₃ powders were homogeneously dispersed in the parent Li[Li_0.2Ni_0.2Mn_0.6]O₂ powders. Al(OH)₃ coated Li[Li_0.2Ni_0.2Mn_0.6]O₂ exhibited an greater retention capacity at higher rates compared to uncoated Li[Li_0.2Ni_0.2Mn_0.6]O₂. The low area specific impedance (ASI) value of the Al(OH)₃ is the major factor for its higher rate performance. The 1.4 wt.% Al(OH)₃ coated sample had an impedance of 41 Ω cm² while uncoated Li[Li_0.2Ni_0.2Mn_0.6]O₂ had a 57 Ω cm² at 30-80% state of charge. Electrochemical impedance spectroscopy (EIS) also showed that the Al(OH)₃ coated sample had a lower charge transfer resistance (R_ct) than the uncoated sample. Differential scanning calorimetry (DSC) analysis showed that Al(OH)₃ coating improved the thermal stability. Al(OH)₃ coating increased the onset temperature of thermal decomposition and reduced the amount of heat for the exothermic peak.     

A study on electrochemical characteristics of LiCoO2/LiNi1/3Mn1/3Co1/3O2 mixed cathode for Li secondary battery

In this study, the LiCoO₂/LiNi_1/3Mn_1/3Co_1/3O₂ mixed cathode electrodes were prepared and their electrochemical performances were measured in a high cut-off voltage. As the contents of LiNi_1/3Mn_1/3Co_1/3O₂ in the mixed cathode increases, the reversible specific capacity and cycleability of the electrode enhanced, but the rate capability deteriorated. On the contrary, the rate capability of the cathode enhanced but the reversible specific capacity and cycleability deteriorated, according to increasing the contents of LiCoO₂ in the mixed cathode. The cell of LiCoO₂/LiNi_1/3Mn_1/3Co_1/3O₂ (50:50, wt.%) mixed cathode delivers a discharge capacity of ca. 168 mAh/g at a 0.2 C rate. The capacity of the cell decreased with the current rate and a useful capacity of ca. 152 mAh/g was obtained at a 2.0 C rate. However, the cell shows very stable cycleability: the discharge capacity of the cell after 20th charge/discharge cycling maintains ca. 163 mAh/g.     

Preparation and characterization of V2O3 micro-crystals via a one-step hydrothermal process

Phase pure V₂O₃ micro-crystals with a hexagonal dipyramid morphology were fabricated for the first time via a facile one-step hydrothermal method. The crystals were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). A hexagonal dipyramid structure of V₂O₃ enclosed by well-grown {012} facets was obtained by hydrothermally reducing VO(acac)₂ precursor with N₂H₄·H₂O at 220 °C for 48 h. The results indicated that V₂O₃ can be well crystallized up to micron size with distinguished facets by only one step hydrothermal treatment. The formation mechanism and morphology evolution for V₂O₃ micro-crystals were discussed. Based on our experiments, the V₂O₃ nuclei formed and grew by a phase transformation through a dissolution–recrystallization process of VOOH, and the formation of the hexagonal dipyramids was ascribed to the specific adsorption of Hacac to the {012} facets restraining the growth in the directions normal to the {012} facets. The present work provides a facile method for preparing phase pure V₂O₃ micro-crystals with hexagonal dipyramid morphology, which can be used as a new powder material for ceramic fabrication.     

基于WO3-MoO3和TiO2/CdS复合电极的光电致变色器件

电致变色广泛应用于智能窗领域,但电致变色材料仍需外部电源驱动,将太阳能电池与电致变色材料结合起来的光电致变色器件可实现无需外部供电的智能变色调控。性能优异的变色阴极和光阳极是当下光电致变色器件的研究热点。通过水热法制备WO₃-MoO₃薄膜,研究其电致变色性能;通过水热法结合连续离子层沉积法制备TiO₂/CdS复合薄膜,研究其光电转换性能。最后将WO₃-MoO₃薄膜和TiO₂/CdS复合薄膜分别作为光电致变色器件的变色阴极、光阳极构建WO₃/MoO₃-TiO₂/CdS光电致变色器件。WO₃/MoO₃-TiO₂/CdS光电致变色器件具有较大的光学调制范围(630nm处为41.99%)、更高的着色效率(35.787%),将其作为智能窗应用在现代建筑、通行工具等领域具有重要应用价值。     

X-ray photoelectron spectroscopy and electrochemical behaviour of 4 V cathode, Li(Ni1/2Mn1/2)O2

Layered Li(Ni_1/2Mn_1/2)O₂ was prepared by the solution and mixed hydroxide methods, characterised by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and studied by cyclic voltammetry (CV) and charge discharge cycling in CC and CCCV modes at room temperature (r.t.) and at 50 °C. The XPS studies show about 8% of Ni³⁺ and Mn³⁺ ions are present in Li(Ni²⁺_1/2Mn_1/2⁴⁺)O₂ due to valency-degeneracy. The compound prepared at 950 °C, 12 h, solution method gives a second cycle discharge capacity of 150 mA h g⁻¹ (2.5-4.4 V) at a specific current of 30 mA g⁻¹ and retains 137 mA h g⁻¹ at the end of 40 cycles. CV shows that the redox process at 3.7-4.0 V corresponds to Ni²⁺↔Ni⁴⁺ and clear indication of Mn^3+/4+ couple was noted at 4.2-4.5 V. The observed capacity-fading (2.5-4.4 V) is shown to be contributed by the polarisation at the end of charging. The cathodic capacity is stable up to 40 cycles in the voltage window, 2.5-4.2 V both at room temperature and 50 °C.     

A comparison of preparation method on the electrochemical performance of cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2 for lithium ion battery

Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ as a cathode material for Li-ion battery has been successfully prepared by co-precipitation (CP), sol–gel (SG) and sucrose combustion (SC) methods. The prepared materials were characterized by XRD, SEM, BET and electrochemical measurements. The XRD result shows that the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ materials prepared by different methods all form a pure phase with good crystallinity. SEM images and BET data present that the SC-material exhibited the smallest particle size (ca. 0.1 μm) and the highest surface area (7.4635 m² g⁻¹). The tap density of SC-material is lower than that of CP- and SG-materials. The result of rate performance tests indicates that the SC-material showed the best rate capability with the highest discharge capacity of 178 mAh g⁻¹ at 5.0 C, followed by SG-material and then CP-material. However, the cycling stability of SC-material tested at 0.1 and 0.5 C is relatively poor as compared to that of SG-material and CP-material. The result of EIS measurements reveals that large surface area and small particle size of the SC-electrode result in more SEI layer formation because of the increased side reactions with the electrolyte during cycling, which deteriorates the electrode/electrolyte interface and thus leads to the faster capacity fading of the SC-material.     

Antimonides (FeSb2, CrSb2) with orthorhombic structure and their nanocomposites for rechargeable Li-ion batteries

Intermetallic FeSb₂ and CrSb₂ and their nanocomposites (FeSb₂/C and Sb/Cr₃C₂/C) were prepared using solid-state routes, such as heat-treatment and high-energy mechanical milling, in order to enhance the electrochemical properties of Sb. These electrodes were tested as anode materials for rechargeable Li-ion batteries. The reaction mechanism of intermetallic FeSb₂ and CrSb₂ was investigated using ex situ X-ray diffraction and high resolution transmission electron microscopy. The FeSb₂/C and Sb/Cr₃C₂/C nanocomposite electrodes exhibited greatly enhanced electrochemical behaviors compared to the FeSb₂ and CrSb₂ electrodes. Additionally, the Sb/Cr₃C₂/C nanocomposite electrode showed a better electrochemical performance than the FeSb₂/C nanocomposite electrode.