Electrochemical properties of cathode materials LiNi1−y Co y O2 synthesized using various starting materials

LiNi_1−y Co _y O₂ samples were synthesized at 800 °C and 850 °C, by the solid-state reaction method, using the starting materials LiOH·H₂O, Li₂CO₃, NiO, NiCO₃, Co₃O₄ and CoCO₃. The LiNi_1−y Co _y O₂ synthesized using Li₂CO₃, NiO and Co₃O₄ exhibited the α-NaFeO₂ structure of the rhombohedral system (space group ). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of the Co ion is smaller than that of the Ni ion. The increase in c/a shows that a two-dimensional structure develops better as the Co content increases. The LiNi_0.7Co_0.3O₂ synthesized at 800 °C using LiOH · H₂O, NiO and Co₃O₄ exhibited a larger first discharge capacity of 162 mAh g⁻¹ than the other samples. The cycling performances of the samples with the first discharge capacity larger than 150 mAh g⁻¹ were investigated. LiNi_0.9Co_0.1O₂ synthesized at 850 °C using Li₂CO₃, NiO and Co₃O₄ showed excellent cycling performance. Samples with larger first discharge capacity will have a greater tendency for lattice destruction due to expansion and contraction during intercalation and deintercalation, than samples with smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.     

钴掺杂对Li1.2Mn0.6Ni0.2O2电化学性能的影响

利用共沉淀法制备了锂离子电池正极材料Li1.2Mn0.6Ni0.2O2和Li1.2Mn0.588Ni0.196Co0.016O2,并利用XRD、SEM和充放电测试对其晶体结构、形貌和电化学性能进行了表征.XRD结果表明:掺杂钴材料后,材料的层状结构保持完整,阳离子混排程度降低.电化学性能测试结果表明:掺钴材料的首次充放电效率和倍率放电性能明显优于Li1.2Mn0.6Ni0.2O2,且表现出较优的循环性能,其1、2、5C放电比容量分别为230.3、215.6、155.6 mA·h/g,1 C下循环50次的容量保持率为90.9％.     

Improving the electrochemical performance of Ni-rich cathode materials using a fast ion conductor coating of Li2O–B2O3–LiBr

The high-Ni layered metal oxide, LiNi_0.8Co_0.1Mn_0.1O₂ (LNCM811), has received widespread attention in the energy field because of its high specific capacity, but its large-scale applications are hindered due to severe capacity fading. Herein, a uniform and thin Li₂O–B₂O₃–LiBr-glass (LBBrO-glass) coating was deposited on LNCM811 by a liquid-phase coating and thermal treatment method. The experimental results suggested that the LBBrO-glass coating acted as a protective layer that inhibited transition metal dissolution and side reactions, which helped improve the electrochemical properties of LNCM811. Remarkably, after 200 cycles, the 2 wt% coating (LBBrO@LNCM-2) delivered a superior capacity retention of 88.9%, while only 71.8% was obtained for the pristine material (LNCM811). The discharge capacity of LBBrO@LNCM-2 was 163.5 mAh g^?1 at 5C, while it was only 139 mAh g^?1 for the pristine material.     

Improved electrochemical properties of vanadium substituted Na0·67Fe0·5Mn0·5O2 cathode material for sodium-ion batteries

Layered transition metal oxide Na_0·67Fe_0·5Mn_0·5O₂ is considered as a promising cathode material of sodium-ion batteries because of its naturally elemental abundance and high energy density. However, low rate capability and poor structural reversibility of Na_0·67Fe_0·5Mn_0·5O₂ greatly hinder its large scale application. In this study, V-substituted Na_0·67Fe_0·5Mn_0·5O₂ cathode material with improved electrochemical performance is successfully synthesized via a sol-gel method. The effects of V-substitution on chemical composition, crystal structure and morphology of Na_0·67Fe_0·5Mn_0·5O₂ are studied in detail. Furthermore, modification mechanisms on the improved electrochemical performance by V-substitution are investigated. The results demonstrate that the rate capability and cycle stability of Na_0·67Fe_0·5Mn_0·5O₂ cathode material is significantly elevated by V-substitution. And the enhanced electrochemical properties are mainly attributed to the improved Na⁺ diffusion rate and structural reversibility. This study suggests that introducing V ions into the lattice of Na_0·67Fe_0·5Mn_0·5O₂ crystals is a favorable strategy to improve its electrochemical properties.     

铝掺杂富锂锰基正极材料Li1.2Ni0.2Mn0.6O2的研究

针对无钴锰基富锂材料Li_1.2Ni_0.2Mn_0.6O₂固有的循环稳定性差、循环电压衰减严重等问题,研究了铝掺杂结合固相煅烧法对该材料在微观形貌及结构、电化学性能等方面的影响。研究结果显示,铝掺杂不仅能促使该材料的表层形貌更加致密,而且可以为该材料带来更稳定的晶体结构,这有利于该材料在长充放电循环中抵抗因结构降级带来的一系列不利因素,最终致使其电化学性能更加优异。此外,当铝掺杂量为1%（物质的量分数）时该材料在高倍率下的放电比容量、循环稳定性、电压保持率等均达到最优效果,在2.0~4.8 V电压区间内0.1C倍率下首圈放电比容量高达248.8 mA·h/g,200圈循环充放电后其放电比容量保持率由未掺杂时的57.9%提升至77.6%,循环电压保持率也由84.2%提升至85.6%。以上结果充分显示了1%铝掺杂对锰基富锂材料Li_1.2Ni_0.2Mn_0.6O₂具有优异的改良效果。     

Low temperature synthesis of LiCr0·3Co0·7O2 intercalation compounds using citrate,oxalate, succinate,and glycinate precursors

Abstract

The synthesis of Cr substituted lithium cobaltate LiCr_0·3Co_0·7O₂ using four different low temperature methods is presented. These wet chemical routes involve the mixing of either acetates or nitrates of Co and Cr with a chelating agent in aqueous solution, namely citric acid for the sol-gel method, oxalic acid for the coprecipitation method, succinic acid for the pyrolysis method, or the complexing agent glycine for the combustion method. The synthesised products were characterised by T G-DTA, XRD, SEM, and FTIR. Structural analysis revealed the R 3^-m space group for the solid solution. The electrochemical behaviour of LiCr_0·3Co_0·7O₂ was evaluated in a lithium cell.     

Electroless deposition of Ni–B, Co–B and Ni–Co–B alloys using dimethylamineborane as a reducing agent

Fundamental aspects of electroless Ni–B, Co–B and Ni–Co–B alloys have been systematically examined. The composition, crystal structure and deposition rate of the alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid), bath pH and Ni2+/Co2+ ratio. Changes in the deposition rate and metallurgical features of the alloys induced by the change in plating parameters are discussed, based on electrochemical polarization data and the formation enthalpy of the nickel and cobalt borides.     

Sol-gel synthesis of MnxGa1−xFe2O4 nanoparticles as candidates for hyperthermia treatment

Sol-gel synthesis of novel Mn_xGa_1−xFe₂O₄ (x=0–1) magnetic nanoparticles (MNP's) was studied. An inverse spinel crystalline structure was identified for all samples. Magnetization saturation values (Ms) were in the range of 21.4–42.6 emu/g, while coercive field (Hc) was less than 27.4 Oe in all cases. Selected compositions of Mn_xGa_1−xFe₂O₄ (x=0.6, 0.8) showed nanoparticles with near-spherical morphology and average size of 15 nm. Magnetic induction curves indicate that a suspension concentration of MNP's equal or higher than 4.5 mg/mL was sufficient to reach the temperature required for hyperthermia treatment (>43 °C) in less than 10 min. The incorporation of Mn ions into the crystalline structure led to an increase of the magnetic response of the MNP's when an alternate magnetic field was applied, requiring a shorter time of exposition and a low dose of MNP's, which make these nanoparticles potential candidates for magnetic hyperthermia.     

Synthesized K2O·11Al2O3 as sagger matrix for the preparation of Li-ion battery cathode materials at high temperatures

Refractory materials such as mullite, andalusite, forsterite, and cordierite are generally used to prepare saggers for the calcination of Li-ion battery Li(Ni_xCo_yMn_z)O₂ (LNCM) cathode material. However, these compounds are prone to be attacked by the LNCM materials, thereby leading to short life spans and contamination of the Li-ion battery cathode materials. To improve the corrosion resistance of refractory sagger materials, the most clear cut-way is enhancing the corrosion resistance of matrix using a new refractory component. Potassium aluminate (K₂O·11Al₂O₃, KA₁₁) with an excellent corrosion resistance against alkaline oxide was synthesized via solid-state method using potassium carbonate (K₂CO₃) and industrial alumina powder (Al₂O₃). Interactions between KA₁₁ and LNCM cathode materials at 800°C–1100°C were characterized by refractory-LNCM precursor laboratory-scale tests to understand the corrosion behavior of KA₁₁. The microstructure and phase composition of synthesized KA₁₁ and the calcined KA₁₁-LNCM mixture cylinders were analyzed with SEM and XRD. The observations reveal that KA₁₁ shows a better corrosion resistance to LNCM materials compared with mullite, cordierite, and forsterite. The addition of synthesized KA₁₁ also favors the thermal shock resistances of mullite-based sagger materials.     

Preparation of LiNi0·6Co0·2Mn0·2O2 by PVP modified liquid-phase assisted solid-phase method and its electrochemical energy storage performance

During the preparation process of LiNi_0·6Co_0·2Mn_0·2O₂ (NCM622) material via solid-phase method, the obtained NCM622 particle size is often inconsistent due to the inhomogeneous phase mixing, which makes the NCM622 material have low specific capacity and poor rate performance, and thus restrict the application of solid-phase method. In order to solve this problem and make full use of the advantages of solid-phase method, liquid-phase assisted mixing is used to replace the traditional mechanical mixing. At the same time, polyvinylpyrrolidone (PVP) is introduced to control the crystal morphology and particle size, thus a NCM622 material with excellent electrochemical energy storage performance has been prepared by the PVP modified liquid-phase assisted solid-state method in this paper. X-ray diffraction, scanning electron microscopy and Raman spectroscopy are used to characterize the morphology structure of the obtained materials. Their electrochemical energy storage performance is tested by program-controlled battery tester and electrochemical workstation after being assembled into button cells. The research results show that with the introduction of PVP, the particle size of the obtained material becomes smaller, the particle size distribution is more uniform, and the degree of cation mixing is further reduced. When the PVP adding amount is up to 1.6 wt %, the obtained material shows the best electrochemical performance: its first discharge specific capacity and coulomb efficiency are 183.19 mAh.g⁻¹ and 88 % (0.1C), respectively. The capacity retention rate is 96.5 % after 100 cycles at 1C (half-cell system and laboratory conditions), which is comparable or better than those by other preparation methods, showing a good application prospect.     

The effects of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide–based electrolyte on the electrochemical performance of high capacity cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2

The effects of ionic liquid (IL) N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py₁₄TFSI) based electrolyte on the electrochemical performance of cathode material Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ have been investigated. The results of thermogravimetric analysis (TGA), flammability and differential scanning calorimetry (DSC) tests indicate that Py₁₄TFSI addition enhances thermal stability of the electrolyte and reduces the safety concern of Li-ion battery. Electrochemical measurements demonstrate that the cathode material shows good electrochemical performance in Py₁₄TFSI-added electrolyte. The cathode material is able to deliver high initial discharge capacity of 250 mAh g^?1 in electrolyte with Py₁₄TFSI content up to 80% at 0.1 C. In addition, the cathode material delivers less initial irreversible capacity loss and higher initial coulombic efficiency in electrolyte with higher Py₁₄TFSI content. However, increasing Py₁₄TFSI content in the electrolyte affects rate capability of the cathode material distinctively. With 60% Py₁₄TFSI-added electrolyte, Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ shows better cycling stability with a capacity retention of 84.4% after 150 cycles at 1.0 C than that in IL free electrolyte. The superior cycling performance of the cathode material cycled in Py₁₄TFSI-added electrolyte is mainly ascribed to the formation of stable electrode/electrolyte interfaces, based on the results of scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS) and electrochemical impedance spectroscopy (EIS) investigations.     

Self-assembly synthesis of dumbbell-like MnPO4·H2O hierarchical particle and its application in LiMnPO4/C cathode materials

The large-scale and efficient synthesis of MnPO₄·H₂O is an urgent problem to be solved. In this paper, self-assembled dumbbell-shaped MnPO₄·H₂O particles were successfully synthesized just using KMnO₄ and commercial concentrated H₃PO₄, and then employed as the precursor to prepare LiMnPO₄/C composites. The XRD, SEM, TEM, and electrochemical performance tests were used to investigate MnPO₄·H₂O and the corresponding LiMnPO₄/C. The formation mechanism of MnPO₄·H₂O was discussed. The results showed that temperature and water content have a significant effect on the yield, purity, and morphology of MnPO₄·H₂O. The synthesized LiMnPO₄/C with reduced carbon content at 650 °C delivered a discharge capacity of 109.3 mA h g^-1 at 1 C and 104.3 mA h g^-1 at 2 C. This green and efficient synthesis method of MnPO₄·H₂O provides a new idea for the large-scale preparation of LiMnPO₄/C cathode materials.     

层状结构Li[Ni,Co,Mn]O2正极材料制备与改性研究进展

介绍了层状结构的Li[Ni,Co,Mn]O2作为锂离子电池正极材料具有良好发展潜力,制备过程与条件对Li[Ni,Co,Mn]O2的结构、性能与生产成本有重要的影响,表面修饰与改性是进一步提高其性能和稳定性的重要途径。归纳了Li[Ni,Co,Mn]O2正极材料的各种制备方法,并对各种改性方法进行比较。分析了层状结构Li[Ni,Co,Mn]O2正极材料存在的问题和今后的研究重点。     

Ni0.4Co x Cd0.6 − x Fe2O4 ferrites as prepared by autocombustion synthesis

Ni_0.4Co _x Cd_0.6?x Fe₂O₄ ferrites (x = 0.0, 0.2, 0.4, and 0.6) were prepared by autocombustion synthesis and characterized by XRD, SEM, and other physical methods. XRD reveals the formation of spinel structure without any impurity phase. With increasing x, the lattice parameter was found to decrease from 8.60 to 8.37 Å. The FTIR spectra show the presence of tetrahedral site (at 571.12 cm^?1) and octahedral site (at 407.07 cm^?1). SEM images indicated the formation of agglomerated grains with a size of about 4.3 μm. The resistivity of the ferrites was found to decrease from 24.53 to 10.02 × 10⁸ Ω cm while the drift mobility to increase from 2.30 to 4.41 × 10⁸ cm² V^?1 s^?1 with increasing x.     

Dielectric behaviour and magnetoelectric effect in Ni0·25Co0·75Fe2O4-Ba0·8Pb0·2TiO3 ceramic composites

Abstract

Dielectric and magnetoelectric properties are reported in magnetoelectric (ME) composites containing lead doped barium titanate as the electrical component and a mixed Ni-Co ferrite as the magnetic component. Changes were observed in dielectric properties as well as in the ME effect as the molar ratio of the components was varied. A maximum value of ME conversion factor of 0·42 mV cm ^{- 1} Oe ^{- 1} (52·78 VA ^{- 1}) was observed in the composite containing 15 mol-% ferrite. Larger ME effects were observed in composites with higher contents of ferroelectric phase. This conclusion differs from earlier theoretical studies which predict a large ME interaction in composites with a 1:1 molar ratio of participating phases. Apart from the technological importance of the ME effect, some anomalies in magnetic phase transition induced by electric fields are also of scientific interest. The variation in dielectric properties with temperature resulted in two maxima, corresponding to the ferroelectric and ferrimagnetic Curie temperatures. This behaviour is unlike anything previously observed in other ME composites.     

含铝化合物表面包覆对富锂材料(Li1.2[Mn0.54Co0.13Nio.13]O2)性能的影响

采用3种含铝化合物(AlPO4、A12O3和AlF3)对富锂锰基材料Li1.2[Mn0.54 Co0.13 Ni0.13]O2进行表面包覆改性,研究了表面包覆对富锂锰基材料的首圈库伦效率和循环性能的影响.结果 表明,与原始的Li1.2[Mn0.54 Co0.13 Ni0.13]O2的库伦效率(71.0％)相比,经过Al...     

Microstructure and magnetic properties of Ni0·75Zn0·25Fe2O4 ferrite prepared using an electric current-assisted sintering method

Using a Ni_0·75Zn_0·25Fe₂O₄ nanopowder synthesized by means of a hydrothermal method as a raw material, polycrystalline nickel zinc (NiZn) ferrite ceramics composed of sub-micron grains were successfully prepared via an electric current-assisted sintering method. Temperatures ranging from 800 °C to 950 °C and a dwell time of 20 min were employed. The phase composition and microstructure of the samples were characterized via X-ray diffraction and scanning electron microscopy, respectively. Moreover, the magnetic properties of the samples were investigated using a vibrating sample magnetometer and a ferromagnetic resonance system. The results revealed that each sintered sample was mainly composed of a spinel phase. With increasing sintering temperature, the specific saturation magnetization increased from 71.85 emu/g to 74.58 emu/g, owing mainly to the increase in the relative density and the average grain size of the NiZn ferrites. The coercivity and ferromagnetic resonance linewidth of the ferrite ceramics decreased monotonically with increasing sintering temperature, owing mainly to the magnetostriction coefficient, saturation magnetization, and porosity of the sintered ferrites.     

Adjusting electrochemical properties of PrBaCo2O6–δ as SOFC cathode by controllable Ca3Co4O9 additions

Composite electrode materials were successfully obtained by mixing of PrBaCo₂O_6–δ (PBCO) and Ca₃Co₄O_9±δ (CCO) oxides. No interactions between the components under long term sintering and SOFC's operating conditions were evidenced by means of x-ray diffraction analysis. Increase of CCO content is shown to contribute to the perceptible decline in thermal expansion coefficients in the background of a negligible decrease in electrical conductivity of ceramics. The obtained powdered composites are shown to possess a developed microstructure and an excellent adhesion with Ce_0.8Sm_0.2O_1.9 dense support. Low values of polarization resistances equal 0.28 and 0.69 Ω∙cm² at 873 K were achieved for compositions with 70% and 50% of the PBCO phase, respectively. The distribution relaxation times (DRT) method was implemented to reveal the rate-limiting steps of the electrochemical reaction. The applying of CCO as TEC lowering admixture to PBCO instead ceria-based oxides was demonstrated to be more effective approach.