Joon-Ho Shin

PEO-Based Polymer Electrolytes with Ionic Liquids and Their Use in Lithium Metal-Polymer Electrolyte Batteries

The influence of adding the room-temperature ionic liquid (RTIL) N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 1 3 TFSI) to P(EO) 2 0 LiTFSI polymer electrolytes and the use of these electrolytes insolid-state Li/V 2 O 5 batteries has been investigated. P(EO) 2 0 LiTFSI + xPYR 1 3 TFSI polymer electrolytes with various PYR + 1 3 /Li + mole fractions (x = 0.66, 1.08, 1.73, 1.94, 2.15, and 3.24) were prepared. The addition of up to a 3.24 mole fraction of the RTIL to P(EO) 2 0 LiTFSI electrolytes, corresponding to a RTIL/PEO weight fraction of up to 1.5, resulted in freestanding and highly conductive electrolyte films reaching 10 - 3 S/cm at 40°C. The electrochemical stability of PYR 1 3 TFSI was significantly improved by the addition of LiTFSI. Li/V 2 O 5 cells using the polymer electrolyte with PYR 1 3 TFSI showed excellent reversible cyclability with a capacity fading of 0.04% per cycle over several hundreds cycles at 60°C. The incorporation of the RTIL into lithium metal-polymer electrolyte batteries has resulted in a promising improvement in performance at moderate to low temperatures.

An Elegant Fix for Polymer Electrolytes

The heart of modern electronics may be built from circuitry, but the lungs which breath life into such devices are batteries. Lithium batteries are increasingly dominating the consumer portable electronic and telecommunications markets and will power the implantable biomedical devices, hybrid electric vehicles and military/ national security communication and surveillance equipment of tomorrow. Current commercial batteries are based on ‘lithium-ion’ technology in which the anode consists of graphite or a similar material and the electrolyte is a liquid or polymer-gel containing molecular solvents/plasticizers. 1-3 Such batteries suffer a number of disadvantages relative to lithium-metal anode solid polymer electrolyte ~lithium-metal-polymer or LMP! batteries. 1-3 The use of graphite instead of lithium metal reduces the energy density while the liquid or gel electrolytes may leak or cause the battery to explode if volatilized. The molecular solvents used are typically not compatible with lithium metal. It is also difficult to easily adapt such batteries to the variable shapes and sizes desired for portable electronics.

Comparison of Solvent-Cast and Hot-Pressed P ( EO ) 20LiN ( SO 2 CF 2 CF 3 ) 2 Polymer Electrolytes Containing Nanosized SiO2

Solvent-cast and hot-pressed P(EO) 2 0 LiN(SO 2 CF 2 CF 3 ) 2 (LiBETI) polymer electrolytes containing ceramic fillers such as 7 nm SiO 2 and 2-4 μm γ-LiAlO 2 were prepared. The ionic conductivity and interfacial stability of these poly(ethylene oxide) electrolytes were investigated. The addition of ceramic fillers to solvent-cast and hot-pressed P(EO) 2 0 LiBETI polymer electrolytes did not result in any substantial improvement of ionic conductivity. However, solvent-cast SiO 2 -containing P(EO) 2 0 LiBETI polymer electrolytes showed a much higher interfacial resistance and Li stripping overvoltage than hot-pressed and filler-free solvent-cast electrolytes.

PEO ­ LiN ( SO 2 CF 2 CF 3 ) 2 Polymer Electrolytes V. Effect of Fillers on Ionic Transport Properties

Ionic transport properties, including ionic conductivity, lithium transference numbers, and diffusion coefficients, of poly(ethylene oxide) 20 LiN(SO 2 CF 2 CF 3 ) 2 [P(EO) 20 LiBETI] and P(EO) 20 LiBETI + x (x = 2, 5 and 10) wt % filler (7 nm SiO 2 , 12 nm SiO 2 , and γ-LiAlO 2 ) polymer electrolytes prepared by a solvent-free procedure developed at ENEA have been investigated using ac impedance, dc polarization, and cyclic voltammetry. Regardless of whether or not nanosize fumed SiO 2 particles were added, the ionic conductivity of all of the samples showed similar values and trends. Both the transference number and diffusion coefficient of lithium cations were decreased slightly by the addition of fumed SiO 2 particles. These results suggest that the presence of nanosize fumed SiO 2 particles in the P(EO) 20 LiBETI polymer electrolytes prepared under very dry conditions has little practical influence on the ionic transport properties.

Electrochemical Characteristics of Polyurethane-based Polymer Electrolyte for Lithium Sulfur Battery

Polyurethane was used as matrix for polymer electrolytes with liquid electrolyte consist of organic solvent as ethylene carbonate(EC), propylene carbonate(PC), and tetraethylene glycol dimethylether(TG) and 1M , which has high mechanical strength and porosity. Electrochemical properties fur polyurethane electrolytes with various liquid electrolytes were evaluated. The amount of immersed liquid electrolyte for TG with 1M was increased to about by weight, and initial discharge capacity and cycle performance was better than others. Ionic conductivity for TG/EC(v/v,1:1) and PC/EC(v/v, 1:1) with 1M was about