Cyclability

Although cyclability varies under regular use with cell chemistry and design, the most common factors leading to failure are given next. 

Carbons for Electrochemical Energy Storage and Conversion Systems 

FIGURE 1.4 Plots for LaNi45Mn05 hydriding and dehydriding. (From Leardini, F., et al., J. Electrochem. Soc., 154, A507, 2007. With permission.) 

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The figure of merit (FOM) for lithium cycling efficiency [24] also is often used to evaluate the cyclability of a lithium cell. The FOM is defined as the number of cycles completed by one atom of lithium before it becomes electrochemically inactive. Equation (2) is derived from the above definition. 

Carbon dioxide has been proposed as an additive to improve the performance of lithium batteries [60]. Aurbach et al. [61] studied the film formed on lithium in electrolytes saturated with C02, and using in situ FTIR found that Li2C03 is a major surface species. This means that the formation of a stable Li2C03 film on the lithium surface may improve cyclability [62], Osaka and co-workers [63] also studied the dependence of the lithium efficiency on the plating substrate in LiC104-PC. The addition of C02 resulted in an increase in the efficiency when the substrate was Ni or Ti, but no effect was observed with Ag or Cu substrates. 

In addition, the batteries can be rechargeable, the cyclability attained with them being limited now by the properties of Zn (Mg) electrodes and a separator. 

Due to its high energy density (3,860 mAh/g) and low voltage, lithium is the most attractive metal of the periodic table for battery application. Unfortunately lithium metal, and most of its alloys cannot be used in rechargeable batteries because of their poor cyclability. Therefore, lithium intercalation compounds and reversible alloys are among today s materials of choice for subject application. The most common active materials for the negative electrodes in lithium-ion battery applications are carbonaceous materials. The ability of graphitized carbonaceous materials to... 

Accordingly, the moles of the monomeric unit are given by the ratio of the dilference between the number of Faradays used for the entire process, and the number of cyclable Faradays, F yc, over the number of electrons for the entire process (ne, , = 2 in the case of (9.16)) ... 

The CORE-SOFC Project was designed to improve the durability of planar SOFC systems to a level acceptable for commercial operation. The work focuses mainly on materials selection for interconnects, contact layers and protective coatings to minimise corrosion between metallic and ceramic parts to achieve reliable and thermally-cyclable SOFCs. In all work packages, cells and stacks will be analysed by advanced chemical and ceramographic methods. 

Fig. 7.6 Effect of electrolyte composition on lithium cyclability. after V.R. Koch et al. of EIC Corporation, (a) UCIO4-PC (b) LiAsF6-PC (c) LiAsFe--2Me-THF...

Recently, new types of organic positives, formed by a mixture of dimercaptan with polyaniline, have been reported. These composite materials appear to have an energy density higher than that of most inorganic intercalation oxides and good cyclability. However, use of these materials in practical rechargeable lithium batteries has still to be confirmed. 

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. 

Work has therefore been devoted by a number of developers to improving the cyclability of the lithium metal electrode. Since passivation of lithium is an unavoidable phenomenon, one approach has been directed to the promotion of uniform and smooth surface passivation layers, for example by selecting the most appropriate combination of solvents and electrolyte salts. An example is the inclusion of 2-methyltetrahydrofuran (2-Me-THF), since the presence of the methyl group slows down the reactivity towards the lithium metal. The selection of fluorine-based elec-... 

This technique ensures good interfacial contact between the layers which in turn leads to low internal resistance (and thus to high rate capability) and to long cycle life. A cyclability of up to 1500 cycles to a cut-off of 80% of initial capacity at the 1 C rate at room temperature, energy densities of the... 

Ultralife Batteries Inc. has recently announced the development of their Rechargeable Solid State System based on this technology. A schematic drawing of the cell is shown in Fig. 7.41. Single cells and battery packs are now in production. Energy densities in the ranges 100-125 Wh/kg and 200-300 Wh/dm3, as well as cyclability up to 1200 deep cycles, have been reported. Excellent characteristics are claimed. Cellular telephones, portable computers and camcorders appear to be the most suitable outlets for these PLI batteries. 

Zinc-air modules for EV application are under development at the Edison company in Italy and by the Electric Fuel Ltd in Israel. In this case, the battery recharge also includes a mechanical step, namely the removal and replacement of the spent zinc electrodes. The actual electrochemical recharging process is carried out in a remote station. The proposed application to passenger vehicles considers the construction of specific stations where the removal and replacement of the spent zinc electrode pack is carried out automatically (Fig. 9.19). Energy and power densities of the order of 200 Wh/kg and 100 W/kg, respectively, and long cyclability, which may provide the car with a 300 km range and a... 

Since black C has a highly aromatic structure with a low level of substitution with functional groups, it is highly recalcitrant and therefore contributes to the stable fraction of soil C. At the global scale, formation of black C rapidly transfers fast-cyclable C from the biosphere to much slower-cyclable forms that may persist in the soil for millennia. It therefore represents an effective pathway for C sequestration. 

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