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Abstract: The influence of cathode thickness on the electrochemical performance of an organic radical battery (ORB) with the radical polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) as the cathode active material is presented. The ORB consists of lithium metal anode and PTMA cathode with an active material content of 40 wt.%. An increase in cathode thickness results in a decrease in specific capacity and discharge voltage of the cell and an increase in electrode/electrolyte interfacial resistance. The best performance is achieved with a thin cathode of 17 μm that shows nearly 100% utilization of the active material (∼111 mAh/g) at current densities up to 1.0 mA/cm2. The cell exhibits excellent high-rate capability and cycle characteristics with a stable impedance behavior and an intact cathode structure on cycling. The results demonstrate that high performance can be achieved from the non-conductive PTMA cathode with higher active material content by using a thin and properly prepared cathode consisting of a uniform, nanometer range coating of the polymer layer on the conductive carbon particles. [Copyright &y& Elsevier]

Abstract: A new class of polymer electrolytes (PEs) based on an electrospun polymer membrane incorporating a room-temperature ionic liquid (RTIL) has been prepared and evaluated for suitability in lithium cells. The electrospun poly(vinylidene fluoride-co-hexafluoropropylene) P(VdF-HFP) membrane is activated with a 0.5M solution of LiTFSI in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) or a 0.5M solution of LiBF4 in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4). The resulting PEs have an ionic conductivity of 2.3×10−3 Scm−1 at 25°C and anodic stability at >4.5V versus Li+/Li, making them suitable for practical applications in lithium cells. A Li/LiFePO4 cell with a PE based on BMITFSI delivers high discharge capacities when evaluated at 25°C at the 0.1C rate (149mAhg−1) and the 0.5C rate (132mAhg−1). A very stable cycle performance is also exhibited at these low current densities. The properties decrease at the higher, 1C rate, when operated at 25°C. Nevertheless, improved properties are obtained at a moderately elevated temperature of operation, i.e. 40°C. This is attributed to enhanced conductivity of the electrolyte and faster reaction kinetics at higher temperatures. At 40°C, a reversible capacity of 140mAhg−1 is obtained at the 1C rate. [Copyright &y& Elsevier]

Abstract: The effect of incorporating a room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI), in the polymer electrolyte (PE) based on poly(ethylene oxide)-(lithium bis(trifluoromethanesulfonyl) imide) [PEO-LiTFSI] was investigated. BMITFSI content was varied between 20 and 80 parts by weight (pbw) in 100 pbw of PEO-LiTFSI and the influence on ionic conductivity, electrochemical stability and interfacial properties on lithium electrode was studied. A remarkable increase in ionic conductivity was achieved with BMITFSI addition, the effect being most pronounced at lower temperatures. Compared to PEO-LiTFSI, the PEs containing BMITFSI exhibited well-defined redox peaks corresponding to stripping and deposition of lithium. The PEs containing BMITFSI exhibited good electrochemical stability and significantly low interfacial resistance with the lithium electrode. Good discharge performance with 82% active material utilization and stable cycling property was achieved when the PE containing 60 pbw of BMITFSI was evaluated in Li/LiFePO4 cells at 40 °C. [Copyright &y& Elsevier]