Fabrication of free-standing NiCo2O4 nanoarrays via a facile modified hydrothermal synthesis method and their applications for lithium ion batteries and high-rate alkaline batteries
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The primary objectives of this project were to develop the anode and cathode materials for high-energy density cells for use in plug-in hybrid electric vehicles (PHEVs) and in electric vehicles (EV) that offer substantially enhanced performance over current batteries used in PHEVs and with reduced cost. This was accomplished by performing research on both the anode and cathode components to improve their volumetric (and gravimetric) capacity. On the anode side the goal of doubling the capacity of today's graphite based anodes was accomplished, using a tin-iron composite anode. This anode was found to have a coulombic efficiency greater than silicon allowing for more than 500 cycles. It shows the technical viability of alternative anodes. On the cathode side, two materials were investigated, both of which can react with two lithium ions. The intercalation cathode, LixVOPO4, where 0≤x≤2, was shown to be highly reversible over two voltage plateaus, one at around 3.8 volts and the other at 2.5 volts. The total capacity exceeded 300 Ah/kg at low rates. The SnFe//LixVOPO4 couple was effectively cycled in full cells; the lifetime was limited by side-reactions on the cathode, which limited the overal cell coulombic efficiency to 98-99%. The conversion cathode, CuF2, had an initial capacity of 500 Ah/kg, but that fell rapidly due to transport of cuprous ions through all electrolytes studied. Summarizing, a new alternative anode for graphitic carbon was found that shows the technicla feasibility of using metal-based hosts for advanced anodes.
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Current methods for extending the cycle life of volume-expanded anode materials for lithium-ion batteries mainly focus on development of nanosize three-dimensional structures and composite materials. We propose a novel anode material of GeO2–Sn30Co30C40 that is synthesized by high energy ball milling (SPEX). This material depends on the nanosized and composite concept, which combines the advantageous properties of Sn–Co–C (long cycle life) and GeO2 (high capacity). The composite anode shows a reversible capacity over 800 mAh/g with good capacity retention. Furthermore, the first-cycle Coulombic efficiency is 80%, much higher than the 34.6% obtained for pure GeO2. Pair distribution function measurements indicated the reversible reaction of GeO2 and SnO2, which is the key factor in the improved Coulombic efficiency. This reversibility can be explained by the catalytic role of Co3Ge2 phase, which facilities the conversion reactions of metal oxides and acts as an electronic conductive component for the composite anode.
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