Electrolytes lithium cells

Fig. 1. Configuration for a soHd polymer electrolyte rechargeable lithium cell where the total thickness is 100 pm.

Lithium/carbon cells are typically made as coin cells. The lithium/carbon coin cell consists of several parts, including electrodes, separator, electrolyte and cell hardware. To construct a coin cell, we first must prepare each part separately. Successful cells will lead to meaningful results. The lithium/carbon coin cells used metallic lithium foil as the anode and a carbonaceous material as the cathode. The metallic lithium foil, with a thickness of 125 pm, was provided by Moli Energy (1990) Ltd.. Idie lithium foil is stored in a glove-box under an argon atmosphere to avoid oxidation. 

Another influence that electrolyte materials have on the cycle life of a practical lithium cell results from the evolution of gas as a result of solvent reduction by lithium. For example, EC and PC give rise to [53] evolution of ethylene and propylene gas, respectively. In a practical sealed-structure cell, the existence of gas causes irregular lithium deposition. This is because the gas acts as an electronic insulator and lithium is not deposited on an anode surface where gas has been absorbed. As a result, the lithium cycling efficiency is reduced and shunting occurs. 

The composition, structure, and formation process of the SEI on metallic lithium depend on the nature of the electrolyte. The variety of possible electrolyte components makes this topic very complex it is reviewed by Peled, Golodnitsky, and Penciner in Chapter III, Sec.6 of this handbook. The types and properties of liquid nonaqueous electrolytes, that are commonly used in lithium cells are reviewed by Barthel and Gores in Chapter III, Sec.7. 

The first electrolytes used for primary lithium cells [47, 48] were based on lith-... 

The electrolyte used in lithium cells, i.e., for aU hthium couples, must be completely anhydrous (< 20 ppm H2O) alkali metals in general are compatible with neutral salt solutions in aprotic solvents or neutral molten salts or solid ion-conductors. 

Kanehori K, Matsumoto K, Miyauchi K, Kudo T (1983) Thin film solid electrolyte and its application to secondary Lithium cell. Solid State Ionics 9-10 1445-1448 Py MA, Haering RR (1983) Structural destabilization induced by lithium intercalation in M0S2 and related compounds. Can J Phys 61 76-84... 

The electrolyte used in the lithium cell studies was typically 1,2M LiPF6 in ethylene carbonate (EC) propylene carbonate (PC) methyl ethyl carbonate (MEC) in a 3 3 4 mixture. The cells were cycled at room temperature using Maccor Series 4000 control unit in a galvanostatic mode under a constant current density of 0.1 to 1 mA/cm2. 

Figure 6. Voltage profiles of lithium cells with (a) uncoated MAG-10 graphite and (b) 11.7wt% Cu-graphite (MAG-10) electrodes in 30% PC blended electrolyte and at 50°C. 

The cycling improvement for the Cu-metallized graphite over the pristine graphite was also observed by K. Guo et al. [15] in their study of electroless Cu deposited on graphite cycled in a lithium cell with a 20% PC blend electrolyte. Also, they recorded a rate capability improvement in their Cu graphite material as well. At a current density of 1.4 mA/cm2, the cell achieved about 60% ( 200 mAh/g) of the charge capacity measured at 0.14 mA/cm2, compared to about 30% ( 100 mAh/g) for the non-treated pristine natural graphite cell [15]. 

Li2S204 being the SEI component at the Li anode and the solid discharge product at the carbon cathode. The Li—SOCI2 and Li—SO2 systems have excellent operational characteristics in a temperature range from —40 to 60 °C (SOCI2) or 80 °C (SO2). Typical applications are military, security, transponder, and car electronics. Primary lithium cells have also various medical uses. The lithium—silver—vanadium oxide system finds application in heart defibrillators. The lithium—iodine system with a lithium iodide solid electrolyte is the preferred pacemaker cell. 

A battery is a transducer that converts chemical energy into electrical energy and vice versa. It contains an anode, a cathode, and an electrolyte. The anode, in the case of a lithium battery, is the source of lithium ions. The cathode is the sink for the lithium ions and is chosen to optimize a number of parameters, discussed below. The electrolyte provides for the separation of ionic transport and electronic transport, and in a perfect battery the lithium ion transport number will be unity in the electrolyte. The cell potential is determined by the difference between the chemical potential of the lithium in the anode and cathode, AG = —EF. 

The available choice of lithium salts for electrolyte application is rather limited when compared to the wide spectrum of aprotic organic compounds that could make possible electrolyte solvents. This difference could be more clearly reflected in a comprehensive report summarizing nonaqueous electrolytes developed for rechargeable lithium cells, in which Dahn and co-workers described over 150 electrolyte solvent compositions that were formulated based on 27 basic solvents but only 5 lithium salts. ... 

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