Because of its high resistivity and subsequent low electroactivity, sulfur is not normally considered a room-temperature battery cathode. An elemental sulfur cathode has been made with a measured capacity of over 900 ampere.hours per kilogram, more than 90 percent of the theoretical storage capacity of solid sulfur at room temperature, accessed by means of a lightweight, highly conductive, aqueous polysulfide interface through the electrocatalyzed reaction S + H(2)O + 2e(-) --> HS(-) + OH(-). This solid sulfur cathode was first used in a battery with an aluminum anode for an overall discharge reaction 2Al + 3S + 3OH(-) + 3H(2)O --> 2Al(OH)(3) + 3HS(-), giving a cell potential of 1.3 volts. The theoretical specific energy of the aluminum-sulfur battery (based on potassium salts) is 910 watt.hours per kilogram with an experimental specific energy of up to 220 watt.hours per kilogram.

Aluminum sulfur batteries based on concentrated polysulfide catholytes and an alkaline aluminum anode are introduced and investigated. The new battery is expressed by aluminum oxidation and aqueous sulfur reduction for an overall battery discharge consisting of 2AI + $42= + 2 OH-+ 4H20 --> 2AI(OH)3 + 4HS-Ec~, = 1.79VThe theoretical energy density of the AI/S battery (based on potassium salts) is 647 Wh/kg_ A first generation aluminum sulfur battery is demonstrated with an open-circuit voltage of 1.3 V, and energy densities based, respectively, on dry and total battery materials of 170 and 110 Wh/g.

Micron-sized Li4Ti5012 was prepared in a single-step solid-state reaction involving Ti02 and Li2CO3, and its electrochemical behavior was evaluated in Li and Li-ion cells containing a polyacrylonitrile (PAN)-based solid polymer electrolyte. The usefulness of Li4Ti5012 was demonstrated for three distinctive applications: (i) cathode of a 1.5 V rechargeable Li battery, (ii) auxiliary electrode for investigating the electrochemistry of Li insertion cathode materials, and (iii) anode of a Li-ion cell in conjunction with a high voltage cathode, e.g., cubic spinel LiMn2O4. The micron-sized Li4T15012 exhibited a capacity of 160 mAh/g at C/20-C/30 rates which is about 7% better than the capacity exhibited by this material prepared according to a previously published procedure. More importantly, the micron-sized oxide showed significantly better high rate capability, yielding 25-50% larger capacity at the 3C to 8C rates. Li/solid polymer electrolyte//Li4Ti5012 cells underwent extended, full-depth, charge/discharge cycling at 1C rates with virtually no capacity fade. The auxiliary electrode concept was demonstrated in Li(4+)Ti5012 (x -1.2)//solid polymer electrolyte//LiMn2O4 cells. At a 1C discharge rate, more than 150 cycles were demonstrated in these cells with a capacity fade rate of about 0.1% per cycle and an end utilization of -90 mAh/g for spinel LiMn2O4. Balanced Li4Ti5012//solid polymer electrolyte//LiMn2O4 cells of slightly cathodelimited configuration showed full-depth extended cycling capability at a utilization of -90 mAh/g f or LiMn2O4 at 1C rate and a capacity fade rate of about 0.08% per cycle. The capacity fade in the LiMn2O4-containing cells appears to come from this cathode. When fully packaged, specific energy of the Li//PAN electrolyte//Li4Ti5012 cell would be about 57 Wh/kg and that of the L14T15012//PAN electrolyte//LiMn2O4 cell is about 60 Wh/kg.

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Polyacrylonitrile (PAN)-based electrolytes with improved low temperature conductivity can be prepared using carefully selected plasticizer compositions from ternary solvent mixtures consisting of propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate (BC) or PC, EC, and 3-methyl-2-oxazolidinone (MEOX). All the electrolytes were prepared as freestanding films. A number of solid polymer electrolyte compositions potentially useful for ambient temperature applications were identified. The solid polymer electrolyte composition with 21.0 mole percent (m/o) PAN:37.8 m/o EC:22.9 m/e PC:12.3 m/o BC:6.0 m/o LiAsF6 exhibited conductivities of 1.12 x 10 _4 S cm -I at -40~ and 2.88 x 10 -3 S em i at 25~ Two other electrolytes contained MEOX; one with 21.0 m/o PAN:33.8 m/o EC:27.7 m/o PC:II.5 m/e MEOX:6.0 m/o LiAsF6 showed conductivities of 1.14 x 10 -4 S cm -I at --40 C and 2.98 x i0 3 S cm -I at 25~ and the other with 21.0 m/o PAN:I0.8 m/o EC:8.7 m/o PC:53.4 m/o MEOX:6.9 m/o LiAsF 6 had conductivities of 1.56 x 10 -~ S cm -~ at -40~ and 3.10x 10 -3 Sem -~ at 25~ Cyclic voltammetry of the electrolytes on Al indicated small oxidative currents of the order of 0.5 ~A/cm 2 at 4.2 V vs. Li+/Li. Pt, Ni, and carbon showed oxidative currents of the order of i, 30, and 60 ~A/cm ~, respectively, at the same potential. Alloy formation and plating were evident on A1 at 0.15 and -0.20 V, respectively. Platinum showed similar behavior with alloy formation at 0.45 V and Li plating at 0.05 V. Carbon showed an onset of Li intercalation around 1.5 V followed by Li plating at -0.1 V. Nickel showed a simple Li plating-stripping process at -0.05 and 0.15 V vs. Li+/Li, respectively. The rechargeability of the Li/solid polymer electrolyte/Li0.sMn204 cell showed short cycle life in electrolytes containing BC with cell failure caused by internal soft shorts on charge. In contrast, cells with MEOX-containing polymer electrolytes showed vastly improved cyclability. A typical cell retained more than 80% of the second cycle capacity through 140 cycles at O.l mA/cmL

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Parasitic reactions taking place at the carbon anode are primarily responsible for the capacity loss that occurs during the "formation cycles" of a carbon/LiMn2O4 Li-jon battery. The additional amount of cathode material required to supplement this irreversible capacity leads to a reduction in the specific energy of the battery. This can be overcome with the use of the overlithiated cathode material, Li1 Mn2O4, in which the excess Li, x, is used to compensate the irreversible apacity at the anode. This investigation highlights the usefulness of n-BuLi reduction to synthesize Li1Mn2O4 from LiMn2O4 and demonstrates the long-term rechargeability of these materials in Li cells. Reaction of cubic spinel LiMn2O4 with BuLi to form overlithiated cathode materials of the general formula Li1Mn2O4 (x = 0.1-1.0) was found to be quantitative under mild conditions at room temperature. The X-ray diffraction of each Li1Mn2O4 appeared to represent a nominal composition of a two-phase material consisting of LiMn2O4 and Li2Mn2O4 at a-x:x mole ratio, where x represents the number of moles of LiMn2O4 reacted with BuLi. Electrochemical characterization of Li1Mn2O4 indicated that the chemically introduced Li(x in Li1,Mn2O4) could be extracted nearly 100% in a voltage plateau around 3.0 V vs. Lit/Li. Furthermore, the rate capability and cycle life of these materials when cycled between 4.25 and 3.0 V were identical to those of the baseline LiMn2O4. In balanced carbon/LiMn2O4 full cells, the chemically inserted Li could be fully utilized to compensate for the irreversible capacity loss occurring in their formation cycles.

The Li-ion cell, Li,Ti5012//PAN electrolyte//LiMn,O,, appears to be a classic example of a battery with passivationfree electrodes. Its gross impedance characteristics remain steady during long-term cycling at high charge/discharge rates. The cell showed excellent rechargeability at >99.9% coulombic efficiency for nearly 250 full-depth cycles, at a 1C discharge rate and a C/5 charge rate. The capacity fade was low at approximately 0.12% per cycle at around 100 cycles and -0.05% at around 200 cycles. Excellent utilizations of the cathode and anode were observed with values of 100 mAh/g of LiMn20, and 140 mAh/g of Li,Ti,012 at 1C discharge rate, and 70 mAh/g of LiMn20, and 92 mAh/g of Li,Ti,012 at 7.5C discharge rate. Electrode utilizations were significantly better under pulse discharge conditions at the 8C-16C rates. The energy density of the cell, calculated with a cell voltage of 2.6 V and practically observed cathode and anode capacities at the C/10 discharge rate, is 60 Wh/kg. The weights of the electrodes, current collectors, and electrolyte are included in this value. It is suitable for applications where high power and very long cycle life are required.