Demonstration of Mixed Metal Oxide Cathode Materials in Prismatic Li-ion Cells
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batteries. Further, applications such as computers or radios frequently require high rate pulse discharge capability. Lithium-ion (Li-ion) batteries which use a LiCoO 2 [1] cathode material have demonstrated exceptional performance in cost insensitive applications but their applicability has been limited by their high cost, especially when NiCd alternatives may be considered. Recently developed cathode materials, such as LiNij.xCoO 2[2], address the need for a low cost Li-ion technology by offering comparable performance at potentially reduced cost. Commercially available LiNij-xCoxO 2 materials have been demonstrated both in flat-plate prismatic Li-ion cells with carbon based anodes and laboratory coin cells with lithium metal anodes. The prismatic cell design is attractive as it takes full advantage of the available space in rectilinear battery boxes and provides good rate capability. The technology demonstrated in this paper utilized a rigid plastic cell case which enhanced the specific energy of the cell while providing the reliability and safety of a rigid cell case. Lightweight cells of this type are attractive for satellite applications as the high energy efficiency reduces solar cell and radiator requirements thus lowering satellite weight.
397 Mat. Res. Soc. Symp. Proc. Vol. 496 01998 Materials Research Society
Experiment 3Ah Prismatic Cells Prototype Flat plate prismatic cells were fabricated using a commercial LiNilxCoO 2 cathode material coated onto Aluminum foil and a graphitic anode material coated onto copper foil. Acetylene black and graphite were added to the cathode material to enhance its conductivity. The cell contained 21 electrodes separated by a microporous polypropylene film and was filled with an electrolyte of IM LiPF6 in EC:DMC 1:1. A sealed polypropylene cell case was utilized and exposure to moisture minimized. The cell was designed to be cathode limited to prevent over-reduction of the anode material. Coin cells with Li metal anodes were used to evaluate the LiNiI 5xCoO 2 material Coin Cells without effects from the carbon anode material used in the prismatic cell. The electrolyte was a IM solution of LiPF 6 in a 1:1 mixture of ethylene carbonate and dimethylcarbonate. Results and Discussion Cells were charged at 0.55 mA/cm 2 (C/5) at 25°C and discharged at Rate Capability various rates up to 3mA/cm (1.1 C). A plot of the discharge capacity versus current density is presented in Figure 1, a plot of the mean cell voltage versus current density is presented in Figure 2. At current densities between 0.5 and 3 mA/cm2 the cell demonstrated little loss in discharge capacity with increasing rate. At 3mA/cm 2, the discharge capacity was 95% of that observed at 0.5 mA/cm 2. Similarly, as shown in Figure 2, the cell did not become polarized over the regime investigated. At 0.5 mA/cm 2, the mean cell voltage during discharge was 3.64V. At the highest rate investigated the mean cell voltage during discharge was 3.55V demonstrating the rate capability of the system. Rate Capabilty 4Ah Prismatic
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