Polypyrrole lithium battery electrodes

Many industrial and academic laboratories have investigated doped polymers as improved positive electrodes in rechargeable lithium batteries. A common example is the battery formed by a lithium anode, a liquid organic electrolyte (e.g. LiC104-PC solution) and a polypyrrole film... 

Fig. 9.16 Cyclic behaviour of lithium batteries using standard pPy(C104) polypyrrole electrodes and modified pPy(DS) electrodes.

The benefit of a hybrid phase for the intercalation-deintercalation of mobile species such as Li+ cations is well illustrated by the study of conductive polymers such as polyaniline or polypyrrole intercalated into a V2O5 framework as potential electrode materials in lithium batteries [34]. For PANI/V2O5, an oxidative post-treatment performed under an oxygen atmosphere allowed the authors to compare the conductivity attributed to the polymer, as in absence of reduced cations, there was no electronic hopping between ions, and the conductive state was due only to the... 

The electrosynthesis of polythiophene (PT) from thiophene must be performed under extremely anhydrous conditions, quite in contrast to polypyrrole [334]. Polymerization of 3-methylthiophene and bithiophene is much less sensitive to water. The advantage of PT is a higher theoretical capacity and a very positive potential (cf. Table 7). It is for these reasons that its application as a positive electrode in rechargeable lithium batteries [335-338] and in a metal-free PPy/PT cell [339] has been considered. Derivatives such as dithienothiophene [340] or rra/is-l,2-di(2-thienyl)ethylene [341] have also been polymerized, but the polymer materials suffer from low theoretical capacities [337]. 

The belief that lithium batteries may be the best way to power electric vehicles (EVs) has strongly stimulated interest in hthium. New battery configurations continue to be developed. Pyrrole is a suitable electrode material for rechargeable lithium batteries. In a flat cell, polypyrrole and Hthium films are sandwiched together. In a cylindrical cell the two films are wound concentrically. 

Polypyrrole (PPy) is another intensively studied conducting polymer used for energy storage applications. PPy has been synthesized from the polymerization of pyrrole by either electrochemical or chemical oxidation method [16, 19]. Since it is difficult to n-dope PPy, p-type PPy as positive electrode material is the common choice reported in lithium batteries. Typically, the specific energy of PPy falls in the range of 80-390 Wh kg with the open-circuit voltage of 3-4 V. One of ffie main drawbacks of PPy as cathode material is its relatively low theoretical capacity. 

Sodium dodecyl sulfate has been used to modify polypyrrole film electrodes. Electrodes synthesized in the presence of sodium dodecyl sulfate have improved redox processes which are faster and more reversible than those prepared without this surfactant. The electrochemical behavior of these electrodes was investigated by cyclic voltametry and frequence response analysis. The electrodes used in lithium/organic electrolyte batteries show improved performance [195]. 

Although the diffusion of the counterion is faster in polypyrrole than in polyacetylene, its value is still low enough to influence the rate of the electrochemical charge and discharge processes of lithium/polymer batteries. Indeed the current output of these batteries is generally confined to a few mA cm . Possibly, improvements in the electrode kinetics, and thus in the battery rates, may be obtained by the replacement of standard ... 

The majority of polymer electrodes cannot be doped to very high levels. For instance, polypyrrole may reach doping levels of the order of 33%. This inherent limitation combined with the fact that the operation of the lithium/polymer battery requires an excess of electrolyte (to ensure... 

A major goal of the research on conducting polymers has been the development of a rechargeable plastic battery. Cells based on polypyrrole and lithium electrodes have been developed in which the energy per unit mass and discharge characteristics are comparable to nickel-cadmium cells. Current interest appears to center around stable, processable polymers, such as polythiophene and its derivatives, and polyaniline. 

A battery cell where both the electrodes consist of dopable polymer is shown in Figure 5.23. The electrolyte in this case consists of Li+ClO 4 dissolved in an inert organic solvent, usually tetrahydro-furan or propylene carbonate. When two sheets of polyacetylene or PPP are separated by an insulating film of polycarbonate saturated in an electrolyte (lithium perchlorate), and completely encapsulated in a plastic casing, a plastic battery can be made. The two sheets of polyacetylene or PPP act as both anode and cathode for the battery. A schematic is shown in Figure 5.24. Although doped polyacetylene and polyaniline electrodes have been developed, polypyrrole-salt films are the most promising for practical appKcation. 

Polypyrrole cells using Li/LiC104 in PC as electrolyte have been proposed and extensively investigated [410-12]. Commercial application has been achieved two large companies have produced batteries based on litium/polypyrrole [413]. Recently a polypyrrole/Nafion composite was used in a lithium/poly(ethylenoxide) cell with improved characteristics over the simple polypyrrole electrode [414]. 

A polypyrrole battery has been developed and tested by BASF and VARTA Baterie AG. The positive electrode consisted of electrochemically synthesized polypyrrole doped with tetrafluoroborate. When PPy is used with a lithium counterelectrode at a cell voltage of 3.5 V, a thoretical energy density of 360 W h/kg is estimated for the PPy electrode, although in a practical cell the density is lower [428 30],... 

Ji L, Yao Y, Toprakci O, Lin Z, Liang Y, Shi Q, Medford AJ, Millns CR, Zhang X (2010) Fabrication of carbon nanofiber-driven electrodes from electrospun polyacrylonitiile/polypyrrole bicomponents for high-performance rechargeable lithium-ion batteries. J Power Sources 195(7) 2050-2056. doi 10.1016/j.jpowsour.2009.10.021... 

---