The primary mechanisms limiting lithium sulfur (Li-S) cell cycle life and thermal stability are discussed. Two major cycle life limiting mechanisms are identified: development of rough surface morphology on the metallic lithium anode with cycling; and depletion of lithium and electrolyte components through chemical reaction. The approach taken here to mitigate these problems, by employing physical protection, including multi-functional membrane assemblies and non-isotropic pressure is presented. Sulfur utilization of 92%, at C/5 discharge rates, increased cycle life and elimination of thermal runaway in 300 mAh Li-S cells was achieved.

Polyethylene exhaustively sulfurized with elemental sulfur shows paramagnetic (spin concentration 2.7--9.7" 1019 spg -1, g = 2.0041--2.0045, ~XH = 0.53--0.62 naT) and redox properties, which was demonstrated by both voltammetric and chemical methods (sodium reduction in liquid ammonia). The high concentration of unpaired electrons, the character of the electrochemical activity, and the chemical properties are in agreement with the presence in the polymers of polyconjugated ladder polythiophene and parquet polynaphthothienothiophene structures along with polyene-polysulfide blocks. The use of the polymers under consideration as an active cathode material in lithium batteries enables their repeated cycling with a specific charge capacitance of 150--340 mA h g-t.

We investigate the performance of organic electroluminescence devices employing a fluorinated diketone complex of europium (ETP) as the emitter material. The architecture of our devices isolates the emitter from the injecting contacts by sandwiching a thin layer of ETP between a hole-transporting diamine layer and an electron-transporting aluminum complex layer. The organic layers are deposited in high vacuum with rate-controlled sources onto glass substrates coated with indium–tin–oxide, and the cell is completed by evaporation of aluminum or calcium–aluminum cathodes. By varying the thickness of ETP layer in increments of 6 Å we demonstrate spatial confinement of the electroluminescence emission zone and optimal performance for an ETP thickness of 50 Å. Both the optical and electrical characteristics of these cells follow steep power-law relationships with voltage, which are indicative of trap-modified, space-charge-limited conduction. With aluminum cathodes we routinely achieve luminances up to 10 cd/m2 with direct current densities near 40 mA/cm2. The electroluminescence has a red–orange color and exhibits a narrow spectrum that is characteristic of trivalent europium ions.

No abstract

No abstract

No abstract

No abstract

No abstract