Key Engineering Materials Vol. 519

Abstract: The lithium ions transferring into cathode material are similar as nonequilibrium carrier in semiconductor while the cell discharges at constant current small enough. The inpouring Li-ions can be called nonequilibrium Li-ions. The electrochemical diffusion coefficient, named as D, can be worked out approximately in terms of the relationship between the concentration of nonequilibrium Li-ions and the relevant potential difference. The D was found 3.21×10-10cm²/s for LiFePO₄ doped with 10% acetylene black.

Abstract: As a positive electrode material for lithium-ion batteries, LiFePO₄ should be composited with carbonaceous materials due to its poor electrical conductivity. In this study, LiFePO₄/C (carbon) composite was synthesized with method of solution co-precipitation, in which glucose was used as a carbon source. The LiFePO₄ material was systematically optimized by X-ray diffraction, scanning electron microscopy. The crystalline structures, morphology and electrochemical performance of LiFePO₄ prepared by solution co-precipitation were compared with that obtained by solid-state reaction. It is found that LiFePO₄ is a pure phase with olivine structure, and exhibits a 3.4V discharge voltage plateau. In our experimental conditions, LiFePO₄/C including 10wt. % of residual carbon obtained by solution co-precipitation possess excellent electrochemical performance, whose first specific capacity was 131.4 mAh•g^-1 at 0.1C rate, the specific capacity was 128.3 mAh•g^-1 after 20 times cycling.

Abstract: Ta-doped Li3V2(PO4)3 cathode material coated by carbon was synthesized via a sol-gel method. Effects of Ta5+ doping on the physical structure and electrochemical performances of the Li3V2(PO4)3/C cathode materials were investigated. Compared with the undoped sample, the Ta-doped samples had no excess peaks but the larger particle size and the narrower distribution of the particle size, indicating that Ta5+ entered into the structure of (Li1-5xTax)3V2(PO4)3/C rather than forming any impurities. When x was up to 0.01, the best electrochemical properties of the Ta-doped cathode materials had been displayed at the charge and discharge rate of 0.1C with the voltage of 3.0～4.8V. The analysis of cyclic voltammetry revealed that the polarization of the Li3V2(PO4)3/C cathode materials could be effectively decreased by Ta5+ doping(x=0.01), mainly resulting from the better electronic conductivity.

Abstract: Li₃V₂(PO₄)₃/C with monoclinic structure were prepared respectively by V₂O₅ and low valence vanadium oxide V₂O₃ via solid state reaction. The structure, particle size and morphology of the powders were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed the pure phase Li₃V₂(PO₄)₃ with the highest performance can be synthesized at 750 degree by using V₂O₃ vanadium source. The capacity retention had nearly 100% after 40-cycles at 0.5 C. It has relative capacity retention and higher specific capacity, comparing with V₂O₅ vanadium source at the optimal synthesis temperature. The electrochemical impedance spectra (EIS) manifests the capacity degradation was mainly caused by the increased solution impedance and electrochemical impedance.

Abstract: The strain effect on the properties of Li₂MnO₃ cathode material is investigated by means of first principles method. The intercalation potential decreases with the strains at the extent of about 0.1V. The strain effect on the intercalation potential is anisotropic with the strain perpendicular to the host layer brings the largest decrease to the potential. Additionally, the tensile paralleling to the host layer can also open up the migrating pathway of lithium in the transition metal layer. The strain effect on the anomalously large charging capacity of Li₂MnO₃ stabilized LiMO₂ (M = Mn, Ni, Co, etc.) solid solution system is also evaluated from the two factors.

Abstract: The Mg-doped LiNi0.4Co0.2-xMn0.4MgxO2 cathode materials (x=0, 0.01, 0.02 and 0.03) were synthesized by a urea co-precipitation method. Its structure and electrochemical properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and electrochemical performance tests. XRD studies indicate that the Mg-doped LiNi0.4Co0.2Mn0.4O2 samples perform the same layered structure as the undoped LiNi0.4Co0.2Mn0.4O2. SEM images show that the particle size of Mg-doped LiNi0.4Co0.2Mn0.4O2 is smaller than the undoped LiNi0.4Co0.2Mn0.4O2 sample. Charge-discharge tests confirm that the rate capacity and cycling performance of LiNi0.4Co0.2-xMn0.4MgxO2 are improved by Mg-doped. The optimal doping content of Mg is x=0.02 in the LiNi0.4Co0.2-xMn0.4MgxO2 samples, which can achieve high initial charge-discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Mg-doping. The improved electrochemical performances of the Mg-doped LiNi0.4Co0.2Mn0.4O2 cathode materials are attributed to the addition of Mg2+ ion by stabilizing the layered structure.

Abstract: LiNi0.5Mn1.5O4 is a promising 5 V class anode material for high power applications, however, before applying in lithium-ion batteries, it is necessary to find more appropriate electrolyte systems to exert the perfect electrochemical performance of LiNi0.5Mn1.5O4. In this paper, the electrochemical performances of LiBOB-propylene carbonate (PC)/dimethyl carbonate (DMC) electrolyte are investigated. It shows high oxidation potentials (>5.5 V) and satisfactory conductivities, When used in LiNi0.5Mn1.5O4/Li cells, compared to the cell with the electrolyte system of LiPF6-ethylene carbonate (EC)/dimethyl carbonate (DMC) electrolyte, LiBOB-PC/DMC electrolyte exhibit several advantages, such as more stable cycle performance, higher discharge voltage plateau (>4.64 V), higher coulomb efficiency, and higher mean voltage (4.55 V).

Abstract: Lithium–oxygen coin cells without catalyst were assembled in argon atmosphere and tested in pure oxygen. Results showed that the first discharge performance of the batteries was strongly affected by the carbon loading, electrolyte amount and current density. At the carbon loading (0.4 mg/cm2), the electrolyte amount (160 μL/cell) and the current density (0.05 mA/cm2), a high capacity of 4586.5 mAh/g was obtained. The capacity decreased when the carbon loading or current density was increased. And the capacity would have a decrease when the amount of electrolyte was decreased. The highest capacity of 6010.2 mAh/g was obtained by optimizing the combination of carbon loading and electrolyte amount at current density of 0.01mA/cm2. However, the discharge capacity sharply decreased from the second cycle. It may be partly due to the fact that the pores of cathode surface were blocked by discharge products at the end of discharge.

Abstract: High pressure NiH2 battery is a kind of secondary power consists of a nickel electrode and the hydrogen electrode with the quality of high stability, long service life, overcharge and overdischarge resisting advantages, the United States, Russia and France have launched high pressure NiH2 batteries and has been widely used in satellite, space stations and other areas. Performance of strength, Ability of Antioxidation, Chemical Durability, Dimensional Stability and akali retaition ability were strictly required by NiH2 battery’s seporatosr, zirconia cloth seporator can satisfy the use requirement in many aspects. Physical and chemical properties of areo density, average thickness, alkaline retention ability, alkaline absorbing ratio and battery performance were tested in this paper.

Abstract: Theoretical study of the filling fraction limit (FFL) of the Fe-substituted Ba-filled skutterudite was carried out via first principle method calculations. The lattice constant of Ba_yFe_4xCo_4-4xSb₁₂ increases with the Ba filling fraction under fixed Fe content while it does not simply increases with Fe content under fixed Ba filling fraction. The FFL is determined by the competition between the formation of filled skutterudite phases and the corresponding secondary phases. The FFL of Ba in the Fe-substituted CoSb3 skutterudites increases monotonically from 37.5% with Fe content of 0 to 100% with Fe content of ~50%. The most stable composition of the Ba_yFe_4xCo_4-4xSb₁₂is expected to be Ba_yFe_2.8Co_1.2Sb₁₂.