Capacity lithium polymer batteries

The molecular orbital (MO) calculations within the PM3 method, using a MOP AC package, provided an explanation of the advantages of a new redox system, poly(l,4-phenylene-l,2,4-dithiazolium-3, 5 -yl) (PPDTA), as a cathode material for high-capacity lithium secondary batteries in comparison with three typical polymer conductors (poly-/>-phenylene, polypyrrole, and polythiophene). The MO calculation revealed that the S-S bond in the 1,2,4-dithiazo-lium moiety of PPDTA caused gap narrowing and a downshift of HOMO and LUMO levels, which is consistent with the electrochemical experiment (HOMO = highest occupied molecular orbital LUMO = lowest unoccupied molecular orbital) <2001MI2305>. 

Work at Harwell has concentrated on scaling up the lithium polymer battery technology for use in electric vehicle traction batteries. The project, supported by the Commission of the European Communities, has systematically scaled up the cell active area. The various cell sizes are shown in Figure 6.33. The larger cells were used to construct two 80 A h units which are shown in Figure 6.34. The results of the project have highlighted the need for capacity balance and excellent cell-to-cell reproducibility. 

Arie et al. [116] investigated the electrochemical characteristics of phosphorus-and boron-doped silicon thin-film (n-type and p-type silicon) anodes integrated with a solid polymer electrolyte in lithium-polymer batteries. The doped silicon electrodes showed enhanced discharge capacity and coulombic efficiency over the un-doped silicon electrode, and the phosphorus-doped, n-type silicon electrode showed the most stable cyclic performance after 40 cycles with a reversible specific capacity of about 2,500 mAh/g. The improved electrochemical performance of the doped silicon electrode was mainly due to enhancement of its electrical and lithium-ion conductivities and stable SEI layer formation on the surface of the electrode. In the case of the un-doped silicon electrode, an unstable surface layer formed on the electrode surface, and the interfacial impedance was relatively high, resulting in high electrode polarization and poor cycling performance. 

Lithium Polymer Battery The high theoretical capacity of lithium... 

Wilson AM, Zang G, Eguchi K, Xing W, Dahn JR. Pyrolysed silicon-containing polymers as high capacity anodes for lithium-ion batteries. J Power Sources 1997 68 195-200. 

Liu, G.,Xun, S., Vukmirovic, N., Song,X., Olalde-Velasco, R, Zheng, H., Battaglia, V.S., Wang, L.,Yang,W., 2011a. Polymers with tailored electronic structure for high capacity lithium battery electrodes. Adv. Mater. 23, 4679-4683. 

Recent demands of the market is for the mid- or large-sized lithium battery for the power-assisted bicycle, electronic bike, and hybrid vehicle. As the capacity of the battery increases, safety becomes very important. The gel polymer electrolyte contributes to keeping the battery safe even as the capacity of the lithium-ion battery increases. 

In this chapter, lithium secondary batteries using conductive polymers as positive electrodes are discussed with particular attention to the charge-discharge characteristics, discharge capacity, self-discharge, cycling life and so on. 

---