Zhongdong Peng

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.

Influence of Ti4+ doping on electrochemical properties of LiFePO4/C cathode material for lithium-ion batteries

To improve the performance of LiFePO4, single phase Li(subscript 1-4x)Ti(subscript x)FePO4/C(x=0,0.005, 0.010, 0.015) cathodes were synthesized by solid-state method. A certain content of glucose was used as carbon precursor and content of carbon in every final product was about 3.5%. The samples were characterized by X-ray diffraction(XRD), scanning electron microscopy observations(SEM), charge/discharge test, carbon analysis and electrochemical impedance spectroscopy(EIS). The results indicate that the prepared samples have ordered olivine structure and doping of the low concentration Ti(superscript 4+) does not affect the structure of the samples. The electrochemical capabilities evaluated by charge-discharge test show that the sample with 1% Ti(superscript 4+) (molar fraction) has good electrochemical performance delivering about an initial specific capacity of 146.7mA•h/g at 0.3C rate. Electrochemical impedance spectroscopy measurement results show that the charge transfer resistance of the sample could be decreased greatly by doping an appropriate amount Ti(superscript 4+).

Preparation and electrochemical performance of tantalum-doped lithium titanate as anode material for lithium-ion battery

Abstract The electrochemical performance of Ta-doped Li 4 Ti 5 O 12 in the form of Li 4 Ti 4.95 Ta 0.05 O 12 was characterized. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the structure and morphology of Li 4 Ti 4.95 Ta 0.05 O 12 . Ta-doping does not change the phase composition and particle morphology, while improves remarkably its cycling stability at high charge/discharge rate. Li 4 Ti 4.95 Ta 0.05 O 12 exhibits an excellent rate capability with a reversible capacity of 116.1 mA·h/g at 10 C and even 91.0 mA·h/g at 30 C . The substitution of Ta for Ti site can enhance the electronic conductivity of Li 4 Ti 5 O 12 via the generation of mixing Ti 4+ /Ti 3+ , which indicates that Li 4 Ti 4.95 Ta 0.05 O 12 is a promising candidate material for anodes in lithium-ion battery application.

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.

Synthesis and characterization of layered Li(Ni1/3Mn1/3Co1/3)O2 cathode materials by spray-drying method

Spherical Li(Ni(subscript 1/3)Mn(subscript 1/3)Co(subscript 1/3))O2 was prepared via the homogenous precursors produced by solution spray-drying method. The precursors were sintered at different temperatures between 600 and 1000℃ for 10h. The impacts of different sintering temperatures on the structure and electrochemical performances of Li(Ni(subscript 1/3)Mn(subscript 1/3)Co(subscript 1/3))O2 were compared by means of X-ray diffractometry(XRD), scanning electron microscopy(SEM), and charge/discharge test as cathode materials for lithium ion batteries. The experimental results show that the spherical morphology of the spray-dried powers maintains during the subsequent heat treatment and the specific capacity increases with rising sintering temperature. When the sintering temperature rises up to 900℃, Li(Ni(subscript 1/3)Mn(subscript 1/3)Co(subscript 1/3))O2 attains a reversible capacity of 153 mA•h/g between 3.00 and 4.35V at 0.2C rate with excellent cyclability.

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.

Preparation of high active Pt/C cathode electrocatalyst for direct methanol fuel cell by citrate-stabilized method

Platinum nanoparticles supported on carbons (Pt/C, 60%, mass fraction) electrocatalysts for direct methanol fuel cell (DMFC) were prepared by citrate-stabilized method with different reductants and carbon supports. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV). It is found that the size of Pt nanoparticles on carbon is controllable by citrate addition and reductant optimization, and the form of carbon support has a great influence on electrocatalytic activity of catalysts. The citrate-stabilized Pt nanoparticles supported on BP2000 carbon, which was reduced by formaldehyde, exhibit the best performance with about 2 nm in diameter and 66.46 m^2/g(Pt) in electrocatalytic active surface (EAS) area. Test on single DMFC with 60% (mass fraction) Pt/BP2000 as cathode electrocatalyst showed maximum power density at 78.8 mW/cm^2.

Preparation of potassium chromate by roasting of carbon ferrochrome

The oxidizing roasting process of carbon ferrochrome to prepare potassium chromate in the presence of potassium carbonate and air was investigated. The effects of reaction temperature, reaction time, mole ratio of potassium carbonate to carbon ferrochrome were studied, and thermodynamics and kinetics were also discussed. It was observed that the reaction temperature and reaction time had a significant influence on the roasting reaction of carbon ferrochrome. The reaction mechanism changed greatly as the temperature varied. A two-stage roasting process was favorable for the roasting reaction, and a chromium recovery rate of 97.06% was obtained through this two-stage roasting method. The chromium residue yielded from this method was only 1/3 of the product. Moreover, the component of Fe in the residue was as high as 55.04%. Therefore, it can be easily recovered to produce sponge iron, realizing complete detoxication and zero-emission of chromium residue.

Improving electrochemical performances of LiFePO4/C cathode material via a novel three-layer electrode

Abstract As an improvement on the conventional two-layer electrode (active material layer|current collector), a novel sandwich-like three-layer electrode (conductive layer|active material layer|current collector) for cathode material LiFePO 4 /C was introduced in order to improve its electrochemical performance. LiFePO 4 /C in the three-layer electrode exhibited superior rate capability in comparison with that in the two-layer electrode in accordance with charge-discharge examination. Cyclic voltammetry and electrochemical impedance spectroscopy indicated that Fe 3+ /Fe 2+ redox couple for LiFePO 4 in the three-layer electrode displayed faster kinetics, better reversibility and much lower charge transfer resistance than that in the two-layer electrode in electrochemical process. For three-layer electrode, the holes in the surface of active material layer were filled by smaller acetylene black grains, which formed electrical connections and provided more pathways to electron transport to/from LiFePO 4 /C particles exposed to the bulk electrolyte.