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A novel positive-temperature-coefficient (PTC) electrode was prepared by coating a thin layer of epoxy-carbon PTC material in between the electroactive LiCoO2 layer and the electrode substrate and used for self-actuating thermal cut-off of Li-ion batteries when the batteries are overheated. Experimental results from cyclic voltammetry, impedance spectrometry and charge–discharge measurements demonstrate that the PTC electrode exhibits normal electrochemical behaviors at ambient temperature, but shows an enormous increase in the resistance at the temperature range of 100–130 °C. This PTC behavior of the electrode provides a current-limiting effect, acting as a reversible thermal shutdown switch for rechargeable lithium batteries. [Copyright &y& Elsevier]

A novel Ba–Fe–Si/C composite was prepared by mechanical ball milling and lithium insertion reactions on the composite electrode were investigated by cyclic voltammetry, charge–discharge measurements, XRD and XPS spectroscopy. It is demonstrated that the composite electrode not only possesses sufficiently high reversible capacity of ca. 420 mA h/g, but also exhibits strong capacity retention with indiscernible capacity decay during charge–discharge cycling. The improved cycling ability of the composite is suggested from a cooperative action by inactive FeSi2 and BaSi2 matrix and outer graphite shell, which both buffer the volumetric changes of the active Si phase and provide a good connection for electronic and ionic conduction during lithium insertion and extraction processes. [Copyright &y& Elsevier]

Abstract: Polytriphenylamine (PTPAn) was chemically synthesized and tested as a cathode material for high-rate storage and delivery of electrochemical energy. It is found that the polymer has not only superior high power capability but also high energy density at prolonged cycling. At a moderate rate of 0.5C, PTPAn gives a high average discharge voltage of 3.8V and quite a high capacity of 103mAhg−1, which is very close to the theoretical capacity (109mAhg−1) as expected from one electron transfer per triphenylamine monomer. Even cycled at a very high rate of 20C, the polymer can still deliver a capacity of 90mAhg−1 at 1000th cycle with a nearly 100% coulombic efficiency. The excellent electrochemical performances of PTPAn are explained from the structural specificity of the polymer where the radical redox centers are stabilized and protected by conductive polymeric backbone, making the radical redox and charge-transporting processes kinetically facile for high-rate charge and discharge. [Copyright &y& Elsevier]

Abstract: Dimethyl methyl phosphonate (DMMP) was selected and tested as a non-flammable solvent for primary and secondary lithium batteries, because of its non-flammability, good solvency of lithium salts and appropriate liquidus properties. Experimental results demonstrated that DMMP can solvate considerable amount of commonly used lithium salts to form non-flammable and Li+-conducting electrolyte, which has very wide electrochemical window (>5V vs. Li) and excellent electrochemical compatibility with metallic lithium anode and oxide cathodes. Primary Li–MnO2 cells using DMMP-based electrolyte showed almost the same discharge performances as those using organic carbonate electrolytes, and also, Li–LiMn2O4 cells using DMMP electrolyte exhibited greatly improved cycleability and dischargeability, suggesting a feasible application of this new electrolyte for constructing high performance and non-flammable lithium batteries. [Copyright &y& Elsevier]

Abstract: An electroactive polytriphenylamine (PTPAn) was synthesized and used as separator material for providing a self-activating overcharge protection of rechargeable lithium batteries. The experimental results from the Li–LiFePO4 cells demonstrated that the electroactive separator could transform from an electronically isolating state to a conductive state at overcharge, producing an resistive internal short circuit to maintain the cell''s voltage at the safety value of ∼3.75V. In addition, the electroactive PTPAn separator works reversibly and has no negative influences on the normal charge–discharge behaviors of the Li–LiFePO4 cells. [Copyright &y& Elsevier]

Abstract: The ionic conductivities of EC-based multi-component electrolytes in various solvent compositions were measured over a wide temperature range of +40 to -40°C, and the factors affecting the low temperature conductivities of the electrolytes were discussed. It is revealed from the experimental results that the co-solvents with high dielectric constant and low viscosity can improve the ionic conductivity at room temperature, whereas, only the co-solvents which possess low melting points can effectively expand the operating temperature range of the electrolyte. The Li-ion batteries using the optimized electrolyte of 1M LiPF6/EC–DMC–EMC (8.3:25:66.7) show the capacity retentions about 90.3% of their nominal capacities when discharged to 2.0V at -40°C at 0.1C, demonstrating excellent low temperature performances. [Copyright &y& Elsevier]