Continuous Co-precipitation Method Research Articles

Application of precursor with ultra-small particle size and uniform particle distribution for ultra-high nickel single-crystal cathode materials by coprecipitation method

Ultra-high nickel single-crystal cathode materials have become the most promising for lithium-ion batteries. However, the preparation of ultra-high nickel single-crystal precursors by a continuous coprecipitation method has the disadvantages of large particle size, wide distribution, poor morphology. The extent of the inhomogeneous reactions can be more severe in single-crystal cathodes with larger particle size. Herein, the coprecipitation method with a solid concentrator was adopted, and citrate sodium was used as a complexing agent to improve the physical properties of precursors and electrochemical performance of single-crystal cathode materials. By analyzing the morphology and agglomeration mechanism of the precursor nucleuses under different pH values, it was found that hexagonal nanosheets grew along the 101 direction, and the primary particles showed thicker at pH of 11.4. The hexagonal nanosheets grew along the 001 direction, and the primary particles showed finer at pH of 12.2. The morphology and particle size uniformity of the secondary particles formed by agglomeration at these two pH values showed poor. However, hexagonal nanosheets grew synergistically along the 001 and 101 directions at pH of 11.8, so the primary particles with uniform particle size gradually agglomerated, and then the secondary particles with ultra-small particle size and uniform distribution obtained. Compared to materials prepared by the traditional continuous coprecipitation method, the precursor displays a smaller particle size(D50 = 1.8 µm), higher sphericity, uniformity and denser internal structure. In order to evaluate the performance of Ni0.94Co0.04Mn0.02(OH)2 with ultra-small particle size, the sintering conditions of LiNi0.94Co0.04Mn0.02O2 need to be explored. It was found that the LiNi0.94Co0.04Mn0.02O2 cathode material prepared at 790 °C exhibited higher discharge capacity, cycle and rate performance, compared to materials prepared at 760 °C and 820 °C. We further utilized TEM, EPMA, and XPS to test the internal structure and valence state of LiNi0.94Co0.04Mn0.02O2 cathode material. The results show that the LiNi0.94Co0.04Mn0.02O2 calcined at 790 °C has a good single crystal structure. The LiNi0.94Co0.04Mn0.02O2 cathode materials inherited the structure and particle size of Ni0.94Co0.04Mn0.02(OH)2 precursors, and displayed discharge capacity of 194.7 mAh/g and capacity retention rate of 89.8 % after 100 cycles at 1 C. The microstructure and phase transition of the as-prepared cathode material are well-maintained after long-term cycling, without obvious inter-crystalline micro-crack. The results indicate that its electrochemical performance is better than that of cathode materials with precursors prepared by a continuous coprecipitation method. This work provides new insights for the preparation of small-particle-size precursor and single-crystal cathode materials.

Coprecipitation preparation of copper -cobalt based catalysts for higher alcohol production

A series of K modified coppercobalt based catalysts were prepared using step by step continuous coprecipitation method, and the catalytic performance of the catalysts was investigated. The experimental results showed that the catalyst exhibited the best activity, CO conversion, the yield of C₂+OH in liquid products and the mass fraction of C₂+OH was 65.74%,0.062 g·(mL·h)-I and 18.95%, respectively, under the condition as follows: mass ratio of cobalt to copper 1:1, K₂CO₃ loading mass fraction 1%, pH=7.2 and reaction temperature 310 ℃.

Enhanced Direct Dimethyl Ether Synthesis from CO2-Rich Syngas with Cu/ZnO/ZrO2 Catalysts Prepared by Continuous Co-Precipitation

The manufacturing of technical catalysts generally involves a sequence of different process steps, of which co-precipitation is one of the most important. In this study, we investigate how continuous co-precipitation influences the properties of Cu/ZnO/ZrO2 (CZZ) catalysts and their application in the direct synthesis of dimethyl ether (DME) from CO2/CO/H2 feeds. We compare material characteristics investigated by means of XRF, XRD, N2 physisorption, H2-TPR, N2O-RFC, TEM and EDXS as well as the catalytic properties to those of CZZ catalysts prepared by a semi-batch co-precipitation method. Ultra-fast mixing in continuous co-precipitation results in high BET and copper surface areas as well as in improved metal dispersion. DME synthesis performed in combination with a ferrierite-type co-catalyst shows correspondingly improved productivity for CZZ catalysts prepared by the continuous co-precipitation method, using CO2-rich as well as CO-rich syngas feeds. Our continuous co-precipitation approach allows for improved material homogeneity due to faster and more homogeneous solid formation. The so-called “chemical memory” stamped during initial co-precipitation is kept through all process steps and is reflected in the final catalytic properties. Furthermore, our continuous co-precipitation approach may be easily scaled-up to industrial production rates by numbering-up. Hence, we believe that our approach represents a promising contribution to improve catalysts for direct DME synthesis.

Effect of concentration in the equilibrium and kinetics of adsorption of acetylsalicylic acid on ZnAl layered double hydroxide

• Acetylsalicylic acid adsorption onto ZnAl layered double hydroxide was studied. • The structure of ZnAl was partially reconstructed during kinetics study. • Drug adsorption isotherm was better fitted by Sips model. • Thermodynamic evaluation revealed that the process is exothermic and spontaneous. • The thermal treatment after adsorption allowing reuse for up to 6 cycles. In this work, the adsorption of pharmaceutical acetylsalicylic acid onto calcined ZnAl-layered double hydroxide was studied. The adsorbent solid was synthesized by the continuous coprecipitation method and characterized by the X-ray diffraction (XRD) and FTIR techniques. Adsorption batch experiments were carried out aiming to obtain the best adsorbent solid concentration, to determine the equilibrium time and the best isotherm model. The behavior of the adsorbent after the kinetics tests through XRD and FTIR and the adsorbent regeneration by thermal treatment were evaluated. The results showed that a 90% removal of acetylsalicylic acid was achieved using a solid concentration of 3 g L −1 and 45 min residence time. Adsorption kinetics is driven by two processes: the adsorption on the external surface and by reconstruction phenomenon of LDH structure “memory effect”. XRD patterns and FTIR shows that the ZnAl-C was reconstructed by acetylsalicylic acid after the adsorption. Adsorption equilibrium was studied in different temperatures as 15, 25, and 35 °C, where it revealed that Sips equation was more suitable to describe the isotherms behavior. The thermal regeneration provided the restructuring of the solid from the hydrotalcite phase to the mixed oxide, allowing its reuse up to 6 cycles. The results indicate that the process presents significant potential for the removal of acetylsalicylic acid.

Effect of Iron Precursor on Catalytic Performance of Precipitated Iron Catalyst for Fischer–Tropsch Synthesis Reaction

In this study, we synthesized three precipitated iron catalysts using continuous co-precipitation method with three different iron precursors: ferric nitrate Fe(NO3)3, ferrous sulfate FeSO4, ferrous oxalate FeC2O4. The catalysts were characterized with XRD, SEM, XPS, N2 sorption and H2-TPR, respectively. The results indicated that the phases of catalysts using ferrous salts as iron precursor were composed of Fe2O3 and Fe3O4. Especially, the catalyst sample prepared by ferrous oxalate (Fe–C) exhibited the largest crystallite size, the highest crystallinity (99.78%), and the easiest reducibility. Fischer–Tropsch synthesis reaction was carried out to study the catalytic performance of three precipitated iron catalysts. In comparison with the other two catalysts, Fe–C has showed ability of the highest catalytic activity, the best stability and the highest selectivity of C5+ hydrocarbons. All the results lead us to draw a conclusion that the properties of iron precursors can notably affect morphology, phase structure, reduction behaviors and catalytic performances of the catalyst.

Hydrogen production by glycerol steam reforming over Ni based catalysts prepared by different methods

Ni supported and co-precipitated catalysts promoted by Mg were evaluated for hydrogen production by the glycerol steam reforming. The samples were prepared by incipient wetness impregnation of alumina and by the continuous co-precipitation method. The catalysts were characterized by XRD, SBET, TPR, NH3-TPD, TPO and SEM/TEM. The catalytic tests were performed in the range from 500 to 650 °C in a fixed bed tubular reactor. The gaseous products were analyzed online by gas chromatography. It was found that the partial substitution of Ni by Mg improves the dispersion of Ni, decreases the acidity of the catalysts and increases the resistance to sintering of Ni. The unreduced catalysts presented higher selectivity for H2 than the previously reduced catalysts. The catalyst unreduced impregnated with 20% Ni showed the highest selectivity in the production of hydrogen (55%), at the temperature of 650 °C. Unreduced samples prepared by co-precipitation presented smaller Ni0 crystallite size after the reaction. The catalyst reduction step is unnecessary for this reaction.

Adsorbents derived from hydrotalcites for the removal of diclofenac in wastewater

Emerging compounds have received increasing attention because of their potential environmental hazards. The drug diclofenac has acute toxicity and has been detected in surface water and wastewater. Conventional treatment processes are not able to totally remove this compound. Adsorption has been widely used to remove pollutants and standing out as an unspecific and versatile operation. In this context, the present study investigated the application of mixed oxides of Mg, Ni, or Zn with Al, derived from hydrotalcite-type compounds, as adsorbents in the removal of sodium diclofenac from synthetic aqueous solutions. The solids were synthesized by the continuous coprecipitation method and characterized by the SBET, XRD, TGA, FTIR, and SEM techniques. The influence of adsorbent dosage and contact time parameters were evaluated. Adsorbent regeneration by thermal treatment was also evaluated. The results showed that sodium diclofenac highest removal rates were found applying the best experimental conditions: residence time and adsorbent dosage of 30 min and 2 g L−1 for C-Zn with maximum adsorption removal of 76.5%. The thermal treatment after the adsorption confirmed the regeneration of the solids, allowing reuse in the adsorption for up to 8 cycles. The application of mixed oxides as sorbent solids was technically feasible for the removal of diclofenac sodium in wastewater treatment.

Controlled synthesis of nickel-rich layered oxide cathodes with preferentially exposed {010} active facets for high rate and long cycling stable lithium-ion batteries

Controlling hierarchical structure assembled by nanoplates with exposed {010} active planes is essential to optimize the electrochemical performance of nickel-rich layered oxide cathode materials. In this work, nickel-rich layered oxide cathodes with various degrees of packing and surface area of exposed {010} facets were synthesized via a simple continuous co-precipitation method and a stepwise calcination process. The effects of structure and morphology on the Li+ transport kinetics of LiNi0.58Co0.25Mn0.17O2 were systematically evaluated by physical and electrochemical characterizations. The results show that the enhanced growth of {010} active facets, namely, the lateral plane of the primary nanoplates can facilitate the Li+ intercalation/deintercalation and thus improve the rate capability. Meanwhile, the compact micro-sized secondary particle guarantees the structural stability of the Ni-rich cathodes. The LiNi0.58Co0.25Mn0.17O2 material with optimized structure manifests high discharge capacities (185 mAh g−1 at 0.1 C), outstanding high-rate capability (106 mAh g−1 at 50 C) and excellent long cycle life (capacity retention of 78% after 500 cycles at 5 C).

Effects of Nb substitution on structure and electrochemical properties of LiNi0.7Mn0.3O2 cathode materials

Nb-doped cathode materials with the formula Li(Ni0.7Mn0.3)1−xNbxO2 (x = 0, 0.01, 0.02, 0.03, 0.04) have been prepared successfully by calcining the mixtures of LiOH·H2O, Nb2O5, and Ni0.7Mn0.3(OH)2 precursor formed through a simple continuous co-precipitation method. The effects of Nb substitution on the crystal structure and electrochemical properties of LiNi0.7Mn0.3O2 were studied systematically by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and various electrochemical measurements. The results show that the lattice parameters of the Nb substitution LiNi0.7Mn0.3O2 samples are slightly larger than that of pure LiNi0.7Mn0.3O2, and the basic α-NaFeO2 layered structure does not change with the Nb doping. What’s more, better morphology, lower resistance, and good cycle stability were obtained after Nb substitution. In addition, CV test exhibits that Nb doping results in lower electrode polarization and XPS results indicate that the valence of Mn kept constant but the component of Ni3+ decreased after doping. All the results indicate that Nb doping in LiNi0.7Mn0.3O2 is a promising method to improve the properties of Ni-rich lithium-ion batteries positive-electrode materials.

Facile synthesis and electrochemical properties of spherical LiNi0.85−xCo0.15AlxO2 with sodium aluminate via co-precipitation

Spherical nickel rich layer cathode materials (LiNi0.85−xCo0.15AlxO2 (x=0.02, 0.05 and 0.10), NCA) with excellent electrochemical performance for high energy densities lithium-ion batteries are successfully synthesized by a continuous co-precipitation method. An elaborate design of Al solution with sodium aluminate is successfully adopted, which can efficiently prevent rapid precipitation of Al(OH)3 and obtain the precipitated precursors. The thermodynamic model is established in the Ni—Co—Al—NH3—H2O system and investigation of precipitation mechanism is carried out systematically, and the results demonstrate that the spherical LiNi0.85−xCo0.15AlxO2 can be obtained through this route. Charge and discharge tests show that LiNi0.85−xCo0.15AlxO2 synthesized has a high initial discharge specific capacity of 208mAh/g at 0.1C and a good capacity retention of 90.2% after 200 cycles at 0.5C between 2.5 and 4.3V. It is expected that performance of NCA electrodes for advancing lithium-ion batteries could be improved with the new process proposed in this study.

Synthesis and electrochemical properties of LiNi0.8CoxMn0.2-xO2 positive-electrode material for lithium-ion batteries

Spherical Ni-rich LiNi0.8CoxMn0.2-xO2 (x=0, 0.05, 0.1, 0.15) positive-electrode materials were synthesized by calcining the mixtures of LiOH·H2O and Ni0.8CoxMn0.2-x(OH)2 precursor formed from a simple continuous co-precipitation method. The influences of Co content on the microstructures and electrochemical properties of LiNi0.8CoxMn0.2-xO2 positive-electrode materials were investigated through X-Ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope and electrochemical tests. The results showed that the intensity ratio of I(003)/I(104) for positive-electrode material became higher with increasing Co content, implying the layered structure became better. The electrochemical tests confirmed LiNi0.8Co0.15Mn0.05O2 (x=0.15) exhibited the best discharge capacity of 180.8mAhg−1 after 100 cycles between 2.75 and 4.3V at 0.2C, with an excellent capacity retention of 97.31% and an high capacity of 165.2mAhg−1 at 5C. Importantly no obvious structure and morphology change was observed for LiNi0.8Mn0.05Co0.15O2 before and after cycling processes. The improved cycling stability and rate capability maybe resulted from low Li/Ni cation mixing, high electric conductivity and good structure stability.

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

Synthesis of Ni0.8Co0.15Al0.05(OH)2 (NCA) with a more environmentally friendly chelating agent, 5-sulfosalicylic acid, by a continuous co-precipitation method.

Study on the synthesis–microstructure-performance relationship of layered Li-excess nickel–manganese oxide as a Li-ion battery cathode prepared by high-temperature calcination

Spherical composite oxide Li1.5Ni0.25Mn0.75O2.5 (or 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2) powder as a Li-ion battery cathode has been synthesized by high-temperature calcination of a mixture containing Li2CO3 and (Ni0.25Mn0.75)CO3, which is synthesized by a continuous co-precipitation method. The evolution in the microstructure of the oxide during calcination is studied mainly by transmission X-ray microscopy (TXM), complemented by X-ray diffraction and thermogravimetry, and it can be divided into three major stages. The first stage takes place below 400 °C, and is characterized by the decomposition of the transition metal carbonates to form amorphous oxides, leading to the formation of internal cracks due to extensive densification. The second stage occurs between 400 and 800 °C, and involves complete Li1.5Ni0.25Mn0.75O2.5 formation and the development of a unique radially-distributed pore structure. The third stage takes place above 800 °C and during prolonged heating at 900 °C, and is characterized by grain growth and change into a randomly distributed tortuous pore structure. TXM 3D-elemental analysis gives statistical evidence showing heterogeneity in the distributions of Ni and Mn, which causes capacity loss and might be a common problem encountered in the two-step precipitation–calcination process. The electrochemical performance of the resulting Li1.5Ni0.25Mn0.75O2.5 powder exhibits complex dependence on the microstructure. The radially distributed pore pattern and small grain size produced by moderate heating favor the rate performance of the composite oxide cathode by reducing charge-transfer resistance and enhancing apparent Li ion solid-state diffusivity. A large grain size resulting from prolonged heating, on the other hand, reduces the formation of the spinel MnO2 domain upon de-lithiation of the Li2MnO3 component of the composite oxide.

Synthesis of High-Density Nickel Cobalt Aluminum Hydroxide by Continuous Coprecipitation Method

Spherical nickel cobalt aluminum hydroxide (Ni(0.80)Co(0.15)Al(0.05)-hydroxide, NCA) was prepared by a continuous coprecipitation method. A new design of the Al solution and the feeding method was applied, which enabled to prevent rapid precipitation of Al(OH)(3) and to obtain spherical NCA with large enough particle size and high density. The active material (LiNi(0.80)Co(0.15)Al(0.05)O(2) or LNCA) prepared from it showed higher tap-density than that made from NCA prepared by general processes, and homogeneity of Al-distribution was also improved. It is expected that the electrode density of lithium ion batteries adopting LNCA could be improved with the new process proposed in this study.

Synthesis of [Zn–Al–CO 3] layered double hydroxides by a coprecipitation method under steady-state conditions

A continuous co-precipitation method under steady-state conditions has been investigated for the preparation of nanometer-size layered double hydroxide (LDH) particles using Zn 2Al(OH) 6(CO 3) 0.5·2H 2O as a prototype. The objective was to shorten the preparation time by working without an aging step, using a short and controlled residence time in order to maintain a constant supersaturation level in the reactor and constant particle properties in the exit stream over time. The effects of varying the operating conditions on the structural and textural properties of the LDHs have been studied, including total cation concentration, solvent, residence time, pH and intercalation anion. The products have been characterized using ICP, XRD, FTIR, BET, SEM and TEM. The LDHs prepared by the continuous coprecipitation method have a poorer crystallinity and lower crystallite sizes than those synthesized by the conventional batch method. The results have shown that increasing either cation concentration or the fraction of monoethylene glycol (MEG) in MEG/H 2O mixtures up to 80% (v/v) affect salt solubility and supersaturation, which gives rise to smaller crystallites, larger surface areas and more amorphous compounds. This increase is however limited by the precipitation of zinc and aluminum hydroxides occurring around a total cation concentration of 3.0×10 −1 M in pure water and 3.0×10 −2 M in H 2O/EtOH mixtures. Crystallite size increases with residence time, suggesting a precipitation process controlled by growth. Finally, the continuous coprecipitation method under steady-state conditions has been shown to be a promising alternative to the traditional coprecipitation technique in either pure water or mixed H 2O/MEG solvents.