Yanbing Cao

Enhancing the Thermal and Upper Voltage Performance of Ni-Rich Cathode Material by a Homogeneous and Facile Coating Method: Spray-Drying Coating with Nano-Al2O3

The electrochemical performance of Ni-rich cathode material at high temperature (>50 °C) and upper voltage operation (>4.3 V) is a challenge for next-generation lithium-ion batteries (LIBs) because of the rapid capacity degradation over cycling. Here we report improved performance of LiNi0.8Co0.15Al0.05O2 materials via a LiAlO2 coating, which was prepared from a Ni0.80Co0.15Al0.05(OH)2 precursor by spray-drying coating with nano-Al2O3. Investigations by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy revealed that an Al2O3 layer is uniformly distributed on the precursor and a LiAlO2 layer on the as-prepared cathode material. Such a coating shell acts as a scavenger to protect the cathode material from attack by HF and serious side reactions, which remarkably enhances the cycle performance at 55 °C and upper operating voltage (4.4 and 4.5 V). In particular, the sample with a 2% Al2O3 coating shows capacity retentions of 90.40%, 85.14%, 87.85%, and 81.1% after 150 cycles at a rate of 1.0C at room temperature, 55 °C, 4.4 V, and 4.5 V, respectively, which are significantly higher than those of the pristine one. This is mainly due to the significant improvement of the structural stability led by the effective coating technique, which could be extended to other cathode materials to obtain LIBs with enhanced safety and excellent cycling stability.

Synthesis of LiNi0.8Co0.15Al0.05O2 with 5-sulfosalicylic acid as a chelating agent and its electrochemical properties

A spherical LiNi0.8Co0.15Al0.05O2 (LNCA) cathode material with excellent electrochemical performance for lithium-ion batteries is successfully synthesized with the precursor of Ni0.8Co0.15Al0.05(OH)2 (NCA) prepared by a continuous co-precipitation method. A more environmentally friendly chelating agent, 5-sulfosalicylic acid (SSA, H3L), stable as well as non-toxic, is adopted in our synthesis process for the first time instead of traditional NH3·H2O. The thermodynamics of the precipitation from the Ni(II)–Co(II)–Al(III)–SSA–H2O system at 298 K is systematically investigated through thermodynamics model analysis. The results demonstrate that the stoichiometric spherical Ni0.8Co0.15Al0.05(OH)2 precursor can be obtained at pH = 11–13, with the SSA concentration from 0.05 mol L−1 to 0.5 mol L−1. LiNi0.8Co0.15Al0.05O2 prepared from the precursor has an initial discharge specific capacity of 203.1 mA h g−1 at 0.1C and a capacity retention of 93.3% after 200 cycles when cycled at 1C between 3.0 and 4.3 V, as well as excellent rate capability. The electrochemical performances are superior to those prepared by using ammonia as the chelating agent. It is expected that the LiNi0.8Co0.15Al0.05O2 cathode material can be synthesized by a more environmentally friendly method.

Hierarchical LiMnPO4 assembled from nanosheets via a solvothermal method as a high performance cathode material

A series of LiMnPO4 nanoparticles with different morphologies have been successfully synthesized via a solvothermal method. The samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The results show that the morphology, particle size and crystal orientation are controllably synthesized by various precursor composite tailoring with various Li : Mn : P molar ratios. At 3 : 1 : 1, a Li+-containing precursor Li3PO4 is obtained while at 2 : 1 : 1, only a Mn2+-containing precursor involving Mn5(PO4)2[(PO3)OH]2·4H2O and MnHPO4·2.25H2O is detected. Especially, at 2.5 : 1 : 1, the precursor consists predominantly of a Mn2+-containing precursor with a minor amount of Li3PO4. From 2 : 1 : 1 to 3 : 1 : 1, the particle morphology evolves from sheet to spherical texture accompanied with the particle size reducing. In the presence of urea, highly uniform LiMnPO4 with a hierarchical micro-nanostructure is obtained, which is composed of nanosheets with a thickness of several tens of nanometers. Thus, these unique hierarchical nanoparticles with an open porous structure play an important role in the LiMnPO4 cathode material. At a concentration of 0.16 mol L−1 for urea, the hierarchical LiMnPO4/C sample assembled from nanosheets with the (010) facet exposed shows the best electrochemical performance, delivering higher reversible capacity of 150.4, 142.1, 138.5, 125.5, 118.6 mA h g−1 at 0.1, 0.2, 0.5, 1.0, 2.0C, respectively. Moreover, the composites show long cycle stability at high rate, displaying a capacity retention up to 92.4% with no apparent voltage fading after 600 cycles at 2.0C.

Novel synthesis of Mn3(PO4)2·3H2O nanoplate as a precursor to fabricate high performance LiMnPO4/C composite for lithium-ion batteries

Mn3(PO4)2·3H2O precursor was synthesized by a novel precipitation process using ethanol as initiator, and was lithiated to LiMnPO4/C composite via a combination of wet ball-milling and heat treatment. The as-synthesized precursor was plate-shaped with nanosize thickness. After heat treatment of the ball-milled mixture of Mn3(PO4)2·3H2O, NH4H2PO4, Li2CO3 and glucose, the well crystallized and highly pure LiMnPO4 with the particle size of about 100 nm and the carbon coating layer of 2 nm was obtained. The LiMnPO4/C composite fabricated at 650 °C delivers discharge capacities of 141.7 mA h g−1 at 0.05C, 119.9 mA h g−1 at 1C and 88.7 mA h g−1 at 5C. Meanwhile, it can retain 95.2% of the initial capacity after 100 cycles at 0.5C, revealing a quite good cycling stability. The method described in this work could be helpful in the development of LiMnPO4/C cathode materials for advanced lithium-ion batteries.

Synthesis of spherical CoAl2O4 pigment particles with high reflectivity by polymeric-aerosol pyrolysis

Abstract Spherical cobalt blue particles with good reflectivity characteristics were synthesized by spray pyrolysis. Two different spray solutions were prepared to investigate the differences in the morphology and the reflectivity properties of cobalt blue particles. One was an aqueous solution, and the other was a polycation solution that was obtained by chemically modifying the aqueous solution with NH4OH. The cobalt blue particles prepared with the aqueous solution had an irregular morphology after heat treatment at 1000°C for 2 h. On the contrary, spherical and dense particles were obtained from the polycation solution. The spherical and dense cobalt blue particles showed remarkable improvement in reflectivity compared with that of irregular morphology particles as well as the commercial.

Conductive Polymers Encapsulation To Enhance Electrochemical Performance of Ni-Rich Cathode Materials for Li-Ion Batteries

Ni-rich cathode materials have drawn lots of attention owing to its high discharge specific capacity and low cost. Nevertheless, there are still some inherent problems that desiderate to be settled, such as cycling stability and rate properties as well as thermal stability. In this article, the conductive polymers that integrate the excellent electronic conductivity of polyaniline (PANI) and the high ionic conductivity of poly(ethylene glycol) (PEG) are designed for the surface modification of LiNi0.8Co0.1Mn0.1O2 cathode materials. Besides, the PANI-PEG polymers with elasticity and flexibility play a significant role in alleviating the volume contraction or expansion of the host materials during cycling. A diversity of characterization methods including scanning electron microscopy, energy-dispersive X-ray spectrometer, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared have demonstrated that LiNi0.8Co0.1Mn0.1O2 cathode materials is covered with a homogeneous and thorough PANI-PEG polymers. As a result, the surface-modified LiNi0.8Co0.1Mn0.1O2 delivers high discharge specific capacity, excellent rate properties, and outstanding cycling performance.

Sodium Doping to Enhance Electrochemical Performance of Overlithiated Oxide Cathode Materials for Li-Ion Batteries via Li/Na Ion-Exchange Method

Overlithiated oxide cathode materials show high capacity but poor cycle stability and voltage attenuation. In this work, a concentration difference driven molten salt ion exchange strategy is used to replace a small quantity of lithium ions by sodium ions. With the entry of sodium ions, the interplanar spacing is increased and the structure is stabilized. The electrochemical properties of materials have been improved obviously. The powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, and transmission electron microscopy are used to detect the entry of sodium ions and structural changes. The modified materials display high discharge specific capacity, excellent cycling performance, and reduced voltage attenuation.

Effect of Synthesis Temperature on the Structural and Electrochemical Properties of a Full Concentration Gradient LiNi 0.7 Co 0.15 Mn 0.15 O 2 Cathode Material

Spherical Ni 0.7 Co 0.15 Mn 0.15 (OH) 2 precursor with a full concentration gradient (FCG) of Ni, Co and Mn elements was obtained via co-precipitation method. The precursor was evenly mixed with LiOH·H 2 O and then sintered at 750~900℃ for 12 h in oxygen to synthesize FCG-LiNi 0.7 Co 0.15 Mn 0.15 O 2 cathode material with the Ni rich in core and Mn rich in the outer layer. The diffusion of Ni, Co, and Mn under different calcination temperatures led to various elements homogeneity, and was analyzed by energy-dispersive X-ray spectroscopy (EDXS). Then, the electrochemical properties of samples were investigated by the charge-discharge test and electrochemical impedance spectroscopy (EIS) test. The results indicate that the cathode material sintered at 800℃ has an obvious concentration-gradient distribution with a shell of LiNi 0.52 Co 0.24 Mn 0.24 O 2 and exhibits the optimal electrochemical performance. Under the voltage range 2.8~4.3 V, it deliveres an initial discharge of 186.1 mAh·g -1 at a charge-discharge rate of 0.2C, and shows an excellent capacity retention of 90.1% after 200 cycles at a high rate of 2C.

The new technique on separation of Cr and Fe as well as Ni-Co-Mn impurity in leaching sulfate solution of ferrochrome alloy

AbstractThe oxalic acid was employed to precipitate the ferrum, nickel cobalt and manganese from the leaching sulfate solution of ferrochrome alloy. The amount of oxalic acid, reaction temperature and terminal pH of the chromium sulfate solution were investigated. The results show that the deposition efficiency of ferrum reaches 99% and loss rate of chromium is less than 1% when 120% theoretical quantity of oxalic acid is used under 30°C and terminal pH = 3. At the same time the deposition efficiencies of nickel, cobalt and manganese in the solution are 98.4, 92.2, 97.5%, respectively. The iron content of ferrous oxalate precipitated from the chromium sulfate solution reaches 30.5% with uniform particle size distribution which can be used as the raw material of lithium iron phosphate. The new technique can solve the problem of separating the high content iron from the chromium sulfate solution, and the elements in the ferrochrome can be used comprehensively. So the new technique has a good industrial application prospect.Highlights—Oxalic acid was employed to separate iron in chromium sulfate solution.—Nickel,cobalt and manganese in chromium sulfate solution were coprecipitated with the iron.—A comparative study on metal separation behaviors was carried out.—FeC2O4 was obtained from chromium sulfate solution, and the metals separation was sufficient.

Synthesis of Li 2 FeSiO 4 /C Composite as Cathode Materials for Lithium Ion Battery by Microwave Assisted Solid Reaction Method: Synthesis of Li 2 FeSiO 4 /C Composite as Cathode Materials for Lithium Ion Battery by Microwave Assisted Solid Reaction Method

以Na 2 SiO 3 ·9H 2 O和FeCl 2 ·4H 2 O为原料, 采用低热固相反应获得了分散均匀的β-FeOOH/SiO 2 前驱体; 再以Li 2 CO 3 为锂源、聚乙烯醇和超导电炭黑为复合碳源, 通过微波辅助固相法合成了Li 2 FeSiO 4 /C材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征. 650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li 2 FeSiO 4 /C材料; 在选用的微波合成体系下, 超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行, 而且提高了Li 2 FeSiO 4 的整体导电性能. 制备的复合正极材料在60 ℃下0.05 C 倍率首次放电容量为129.6 mAh/g, 0.5 C 倍率下为107.5 mAh/g, 0.5 C 下15次循环后保持为104.8 mAh/g, 具有较好的放电比容量和良好的循环稳定性能. 结果表明, 微波辅助固相合成工艺是制备Li 2 FeSiO 4 /C复合材料的一种很有前景的方法.以Na 2 SiO 3 ·9H 2 O和FeCl 2 ·4H 2 O为原料, 采用低热固相反应获得了分散均匀的β-FeOOH/SiO 2 前驱体; 再以Li 2 CO 3 为锂源、聚乙烯醇和超导电炭黑为复合碳源, 通过微波辅助固相法合成了Li 2 FeSiO 4 /C材料. 通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒电流充放电测试等方法对材料的结构、微观形貌及电化学性能进行表征. 650℃下微波处理12 min可获得结晶好、晶粒细小均匀的Li 2 FeSiO 4 /C材料; 在选用的微波合成体系下, 超导碳和聚乙烯醇热分解的无定形碳不仅利于合成反应的顺利进行, 而且提高了Li 2 FeSiO 4 的整体导电性能. 制备的复合正极材料在60 ℃下0.05 C 倍率首次放电容量为129.6 mAh/g, 0.5 C 倍率下为107.5 mAh/g, 0.5 C 下15次循环后保持为104.8 mAh/g, 具有较好的放电比容量和良好的循环稳定性能. 结果表明, 微波辅助固相合成工艺是制备Li 2 FeSiO 4 /C复合材料的一种很有前景的方法.