Lithium electrode, propylene carbonate

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

The structure and composition of the lithium surface layers in carbonate-based electrolytes have been studied extensively by many investigators [19-37], High reactivity of propylene carbonate (PC) to the bare lithium metal is expected, since its reduction on an ideal polarizable electrode takes place at much more positive potentials compared with THF and 2Me-THF [18]. Thevenin and Muller [29] found that the surface layer in LiC104/PC electrolyte is a mixture of solid Li2C03 and a... 

A point meriting attention is the voltage difference above. Doped polymers are rather electropositive (up to more than 4 V vs. a lithium electrode in the same solution), so much so that charging may have to be limited in order not to exceed the stability limits of the electrolyte (typically, propylene carbonate or acetonitrile as aprotic nonaqueous solvents). 

A second major event in the saga of polymer conductors was the discovery that the doping processes of polyacetylene could be promoted and driven electrochemically in a reversible fashion by polarising the polymer film electrode in a suitable electrochemical cell (MacDiarmid and Maxfield, 1987). Typically, a three-electrode cell, containing the (CH) film as the working electrode, a suitable electrolyte (e.g. a non-aqueous solution of lithium perchlorate in propylene carbonate, here abbreviated to LiC104-PC) and suitable counter (e.g. lithium metal) and reference (e.g. again Li) electrodes, can be used. 

Propylene Carbonate (PC) and Water. Data from both spectroscopic and thermodynamic studies for other solvent systems are sparse and some of it is of doubtful quality. For propylene carbonate, Salomon (40) has obtained emf data using lithium metal and thallium amalgam-thallous chloride or bromide electrodes. 

Solvents were initially selected primarily on the basis of the conductivity of their salt solutions, the classical example being propylene carbonate (PC). However, solutions based on PC on its own were soon found to cause poor cyclability of the lithium electrode, due to uncontrolled passivation phenomena. Solvent mixtures or blends were therefore developed and selection currently focuses on a combination of high dielectric solvents (e.g. ethylene carbonate, EC) with an alkyl carbonate (e.g. dimethy(carbonate, DMC), to stabilize the protective passivation film on the lithium electrode, and/or with a low viscosity solvent [e.g. 1,2-dimethoxyethane (DME) or methyl formate (MF)], to ensure adequate conductivity. 

There have been a number of attempts to produce commercial lithium rechargeable batteries. The V205 positive is currently used by the Matsushita Battery Industrial Co in Japan for the production of small capacity, coin-type cells. Fig. 7.24 shows a cross-section of one prototype. For the construction of the battery, V205 and carbon black are mixed together with a binder, moulded and vacuum-dried to form the positive electrode pellet. A solution of LiBF4 in a propylene carbonate-y-butyrolactone-1,2-dimethoxyethane mixture absorbed in a polypropylene separator is used as the electrolyte. 

Figure 6.19 Photocurrent as a function of time for a 10.0 mm thick nanocrystalline Ti02 electrode modified with [Ru(dcbpy)2(NCS)2], where the electrolyte is propylene carbonate containing 0.1 M KI with different concentrations of lithium trifluoromethanesulfonate (a) 0.1 M (b) 0.05 M (c) 0.025 M (d) 0 M. Reprinted with permission from A. Solbrand, A. Henningson, S. Sodergren, H. Lindstrom, A. Hagfeldt and S.-E. Lindquist, /. Phys. Chem., B, 103,1078 (1999). Copyright (1999) American Chemical Society...

Epelboin I, Froment M, Garreau M, Thevenin J, Warin D. Behavior of secondary lithium and aluminum-lithium electrodes in propylene carbonate. J Electrochem Soc 1980 127 2100-2104. 

Baranski AS, Fawcett WR. The formation of lithium-aluminum alloys at an aluminum electrode in propylene carbonate. J Electrochem Soc 1982 129 901-907. 

Geronov Y, Zlatilova P, Moshtev RV. The secondary lithium-aluminum electrode at room temperature I. Cycling in LiC104-propylene carbonate solutions. J Power Sources 1984 12 145-153. 

In a vessel for electrolysis three parallel nickel plates were installed. The inner nickel plate was the working electrode (anode), and the two outer nickel plates were counter electrodes (cathode). A 1.2 liter mixture consisting of fluorene (0.01 mol) and LiPFs (0.1 mol) dissolved in propylene carbonate were then added to the vessel. The three nickel plates were immersed in the mixture to a depth of 90 mm. Two lithium metal sheets were used as reference electrodes, with each sheet placed between the anode and the cathode. The electrolysis was carried out by a potential-sweep method for 4 hours under a potential width of 4.5 to 6.7 V with a sweep time of 50 mV/s. The inner... 

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