Lithium-ion technology

The contribution by Rouzaud et al. teaches to apply a modified version of high resolution Transmission Electron Microscopy (TEM) as an efficient technique of quantitative investigation of the mechanism of irreversible capacity loss in various carbon candidates for application in lithium-ion batteries. The authors introduce the Corridor model , which is interesting and is likely to stimulate active discussion within the lithium-ion battery community. Besides carbon fibers coated with polycarbon (a candidate anode material for lithium-ion technology), authors study carbon aerogels, a known material for supercapacitor application. Besides the capability to form an efficient double electric layer in these aerogels, authors... 

Since the inception of lithium ion technology, there have been several reviews summarizing the knowledge accumulated about this new technology from various perspectives, with the latest being in 2003. Because electrolytes interact closely with both cathode and anode materials during the operation, their effect on cell performance has been discussed in... 

Solid polymer and gel polymer electrolytes could be viewed as the special variation of the solution-type electrolyte. In the former, the solvents are polar macromolecules that dissolve salts, while, in the latter, only a small portion of high polymer is employed as the mechanical matrix, which is either soaked with or swollen by essentially the same liquid electrolytes. One exception exists molten salt (ionic liquid) electrolytes where no solvent is present and the dissociation of opposite ions is solely achieved by the thermal disintegration of the salt lattice (melting). Polymer electrolyte will be reviewed in section 8 ( Novel Electrolyte Systems ), although lithium ion technology based on gel polymer electrolytes has in fact entered the market and accounted for 4% of lithium ion cells manufactured in 2000. On the other hand, ionic liquid electrolytes will be omitted, due to both the limited literature concerning this topic and the fact that the application of ionic liquid electrolytes in lithium ion devices remains dubious. Since most of the ionic liquid systems are still in a supercooled state at ambient temperature, it is unlikely that the metastable liquid state could be maintained in an actual electrochemical device, wherein electrode materials would serve as effective nucleation sites for crystallization. 

The above merits made LiPFe the salt of choice when lithium ion technology leaped from concept into product. In 1990, it was used by Sony in the first generation lithium ion cell, and since then, its position in the lithium ion industry has remained unchallenged. Like EC as an indispensable solvent component, LiPFe has become the indispensable electrolyte solute for almost all lithium ion devices manufactured in the past decade. 

Typically, the liquidus lines of a binary system curve down and intersect with the solidus line at the eutectic point, where a liquid coexists with the solid phases of both components. In this sense, the mixture of two solvents should have an expanded liquid range with a lower melting temperature than that of either solvent individually. As Figure 4 shows, the most popular solvent combination used for lithium ion technology, LiPFe/EC/DMC, has liquidus lines below the mp of either EC or DMC, and the eutectic point lies at —7.6 °C with molar fractions of - 0.30 EC and "-"0.70 DMC. This composition corresponds to volume fractions of 0.24 EC and 0.76 DMC or weight fractions of 0.28 EC and 0.71 DMC. Due to the high mp of both EC (36 X) and DMC (4.6 X), this low-temperature limit is rather high and needs improvement if applications in cold environments are to be considered. 

Unfortunately, this approach for electrochemical stability determination has not been widely adopted. The few exceptions include the seminal electrolyte work by Guyomard and Tarascon. In the formulation of new electrolytes for lithium ion technology, the spinel composite electrode was used as the standard working surface in all of the voltammetric measurements. The oxidative decomposition limits of the new electrolytes thus determined are summarized in Table 7 along with a handful of stability data that were determined in a similar approach for other electrolyte systems. 

Temperature Limits. The two indispensable components of the present lithium ion electrolyte systems are LiPFe as salt and EC as solvent. Unfortunately, these two components also impart their sensitivity to extreme temperatures to the lithium ion technology, thus imposing temperature limits to the operation of lithium ion cells. In a somewhat oversimplified account, one can hold EC responsible... 

Unlike the anode-targeted additives discussed in the preceding part, the additives intended for cathode protection have a much longer history than lithium ion technology itself and were originally developed for rechargeable cells based on lithium metal anodes and various 3.0 V class cathode materials. 

Accompanying the commercialization of lithium ion technology, the emergence of 4.0 V class cathode materials based on spinel, LiCo02, and LiNi02 presents a more stringent requirement for the selection... 

Following its rapid rise to dominance in the consumer cell market intended for portable electronics, lithium ion technology was actively considered for special applications such as those in military and space missions. However, the poor performance of the state-of-the-art lithium ion cells at temperatures below —20 °C remained a major obstacle to enabling the normal operations in harsh environments that are frequently encountered in those missions. For example, according to a comprehensive... 

Compared with the efforts spent on the low-temperature performance, less attention has been paid to the applications of lithium ion technology at elevated temperatures, with perhaps storage stability as the only exception. Cycling tests at temperatures above 50 °C have been rarely reported in the literature, most likely owing to the chemical instability of LiPFe in the organic solvents at elevated temperature and the difficulty of replacing it with new lithium salts. 

Even after all the above issues, that is, mechanical strength, ion conductivity, and interfacial resistance, have been resolved, SPEs still have to face the crucial issue of surface chemistry on each electrode if the application is intended for lithium ion technology, and there is no reason to be optimistic about their prospects. 

The solid polymer electrolyte approach provides enhanced safety, but the poor ambient temperature conductivity excludes their use for battery applications. which require good ambient temperature performance. In contrast, the liquid lithium-ion technology provides better performance over a wider temperature range, but electrolyte leakage remains a constant risk. Midway between the solid polymer electrolyte and the liquid electrolyte is the hybrid polymer electrolyte concept leading to the so-called gel polymer lithium-ion batteries. Gel electrolyte is a two-component system, viz., a polymer matrix... 

The final choice of the positive to be used in practical lithium ion batteries depends on the specific requirements of a particular developer. The characteristics of the three most common lithium metal oxide electrodes currently exploited in lithium ion technology are summarized in Table 7.3. 

Table 7.4 Comparison of lithium ion technologies being developed by various companies... 

MW installations. Recently there are also major efforts and some initial success in implementation of rechargeable lithium-ion technology for stationary applications. From the view point of global energy utilization and consumption, the ultimate goal for stationary batteries is power-line load leveling. 

PVDF homopolymers and copolymers have gained success in the battery and fuel cell industry as binders for cathodes and anodes in lithium ion technology, and... 

OEM research around lithium ion technology is ongoing and many issues still need to be overcome. Lithium ion batteries have a life span that is age dependent,... 

Development of these batteries took place at around the same time frame as lithium ion technologies in the 1980s. The NiMH type battery was used in the General Motors EV1, as well as other plug-in vehicles. The Toyota RAV4 EV, Honda EV Plus, Ford Ranger EV, and Honda Insight all use NiMH batteries. The reactions for nickel-metal hydrides are... 

Lithium ion technology offers high-energy density with the added benefit of low mass. These characteristics make it ideal for automotive applications. This technology is the fastest growing battery system [29], Protection circuits are needed to limit voltages for safety reasons. 

Specific Requirements for the Conductive Additive in the Lithium Ion Technology... 

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