Studies on Li-ion cells with and without Li/Li ϩ reference electrodes confirm that the limiting factor for low-temperature performance is the carbon anode. The cycling behavior of MCMB ͑2528͒-LiCoO 2 cells were studied over the temperature range of Ϫ40°C to room temperature, and at all temperatures it is the polarization of the anode which limits performance. Even at modest ͑C/5͒ to low ͑C/10͒ rates of charge and discharge, deposition of metallic lithium at the anode for temperatures рϪ20°C causes permanent capacity loss. This loss is not attributed to electrolyte conductivities, which are relatively high over this temperature range, but rather to continual growth of the solid electrolyte interphase resulting from solvent/electrolyte reduction at freshly deposited metallic lithium. The studies also reveal that at low temperatures, lithium cannot be completely removed or inserted into the coexistence range of dilute stage 1 and stage 4. This may be a simple electrokinetic phenomenon or, more likely, the limiting solid-state diffusion of lithium in carbon.A number of recent papers have focused on the poor performance of Li-ion cells at low temperatures. 1-5 The poor performance of Li-ion cells at low temperatures has been attributed to poor solution transport properties ͑e.g., conductivities and transference of lithium ions 1,2,4 ͒, deposition of metallic lithium upon charge with subsequent growth of the solid electrolyte interphase ͑SEI͒, 3 and Li diffusivity into graphite. 5 In all likelihood, all these factors contribute to poor low-temperature performance with one exception; the conductivities of lithium salt solutions which, in reality, are high at low temperatures. For example, mixtures of various solvents such as alkyl and cyclic carbonates with low viscosity solvents such as esters or hydrocarbons have been designed with specific conductivities between 0.0003 and 0.001 S/cm at temperatures as low as Ϫ40°C.The studies reported in this paper were undertaken to expand on these concepts by employing a practical configuration of a Li-ion cell with and without a metallic Li reference electrode. ExperimentalAll cells used in this study are represented by 4 MCMB-2528 ͉ PVdF-based electrolyte ͉ LiCoO 2 ͓1͔Anode compositions were generally 80% MCMB, 4% Super P, and the remainder PVdF, and the typical thickness of this anode was 0.012 cm ͑4.7 mil͒ as discussed in Ref. 4. Cathode compositions were generally 80% LiCoO 2 ͑FMC͒, 7% Super P, and the remainder poly͑vinylidene difluoride͒ ͑PVdF͒, and the typical thickness of this cathode was 0.021 cm ͑8.3 mil͒. 4 All cells were anode limited, having a cathode/anode capacity ratio between 1.2 and 1.3. The PVdFbased electrolyte was prepared with Bellcore technology 6 with 1 mol dm Ϫ3 LiPF 6 in 1:3 wt % EC/EMC electrolyte. Sources and purity of materials and other cell details can be found in an earlier publication. 4 Cell 1 was used for studies on capacity retention during cycling at various temperatures. For more detailed studies, a metallic Li reference electrode was sandwic...

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Electrochemical kinetic studies are reported on the anodic oxidation of ammonia in aqueous potassium hydroxide solutions a t platinum black electrodes. A kinetic scheme of consecuti\~e reactions is proposed; Tafel slopes are deduced for various rate-determining mechanisms and compared with the experimental behavior. The reaction pathway is correlated with that iilvolved in the analogous catalyzed ammonia vapor decomposition. The exchange currents obtained, compared with those for hydrogen oxidation, render the system u~lfavorable for fuel cell applications.

A review is presented of the present state-of-the-art of Li-air cells and batteries. We examine the properties of this unique system in terms of the effects of solubilities of reactants and products in both nonaqueous (aprotic) and aqueous electrolyte solutions. Definite trends are observed, such as increasing cell-specific energy and capacity as both the oxygen solubility increases and viscosity decreases in organic solvents, but quantitative analyses are limited owing to the complex relations between solubility, solution viscosity, oxygen diffusion, and electrolytic conductivity. Adding to this complex relation is the dependence of the nature of the carbon-based air cathode (surface area and pore volume) upon practical specific capacities, which can be realized with Li-air cells that far exceed the specific energies and capacities of all present commercial metal-air and Li-ion cells and batteries.