Li-Ion system

The Li-Ion system was developed to eliminate problems of lithium metal deposition. On charge, lithium metal electrodes deposit moss-like or dendrite-like metallic lithium on the surface of the metal anode. Once such metallic lithium is deposited, the battery is vulnerable to internal shorting, which may cause dangerous thermal run away. The use of carbonaceous material as the anode active material can completely prevent such dangerous phenomenon. Carbon materials can intercalate lithium into their structure (up to LiCe). The intercalation reaction is very reversible and the intercalated carbons have a potential about 50mV from the lithium metal potential. As a result, no lithium metal is found in the Li-Ion cell. The electrochemical reactions at the surface insert the lithium atoms formed at the electrode surface directly into the carbon anode matrix (Li insertion). There is no lithium metal, only lithium ions in the cell (this is the reason why Li-Ion batteries are named). Therefore, carbonaceous material is the key material for Li-Ion batteries. Carbonaceous anode materials are the key to their ever-increasing capacity. No other proposed anode material has proven to perform as well. The carbon materials have demonstrated lower initial irreversible capacities, higher cycle-ability and faster mobility of Li in the solid phase. 

The Li batteries have recently received much attention from automobile industries thanks to their characteristics of light weight and good specific power however, the lower costs of Ni-MH batteries, together with their demonstrated durability and reliability performance, could retard the application of Li ion systems [33]. 

BAR 12] Darwiche A, MARINO C., SOUGRATI M.T., et al, Better cycling performances of bulk Sb in Na-ion batteries compared to Li-ion systems an unexpected electrochemical mechanism . Journal of American Chemical Society, vol. 134, pp. 20805-20811, 2012. 

Lithium secondary batteries can be classified into three types a liquid-type battery using liquid electrolytes, a gel-type battery using gel electrolytes mixed with polymer and liquid, and a solid-type battery using polymer electrolytes. The types of separators used in different types of secondary lithium batteries are shown in Table 20.1. The liquid Li-Ion cell uses microporous polyolefin separators while the gel polymer Li-Ion cells either use polyvinylidene difluoiide (PVdF) separator (e.g., PLION cells) or PVdF-coated microporous polyolefin separators. The PLION cells use PVdF loaded with silica and a plasticizer as the separator. The microporous structure is formed by removing the plasticizer and then filling with liquid electrolyte. They also are characterized as plasticized electrolyte. In solid polymer Li-Ion cells, the soM electrolyte acts as both electrolyte and separator. This chapter focuses only on the conventional liquid Li-Ion systems. 

James Hunter of Eveready Battery Co. was the first to patent spinel cathode material. The application of material to Li-ion system has been developed by J. M. Tarascon [59] and extensively studied by M. Thackeray [60]. Generally, lithium spinel oxides suitable for the cathode are limited to those with a normal spinel in which the lithium ions occupy the tetrahedral (8a) sites and the transition-metal ions reside at the octahedral (16d) sites. Currently, spinel is the center of much interest as the cathode material for large format lithium-ion cell for hybrid electric vehicle applications where high power, safety, and low cost are the strongly required features. 

Advanced quality control measures play a critical role keeping a check on PPB level safety issue. Moreover, new safety evaluation methods like abuse tolerance tests for cycled Li-ion cells would provide a clear insight in understanding the influence of high-surface Li deposits toward cell safety, and further increase the confidence level toward implementing Li-ion systems for several advanced applications like EDV and ESS. 

Because of the consciousness for environment and the economic situation for fuels, electric vehicles (EV) have become reconsidered. Higher energy density over 500 Wh kg is required for widespread of EV. Energy density of Li-ion battery system with rocking-chair mechanism is limited up to c.a. 250 Wh kg Theoretically Li-air, Li-S, and Zn-air can only be the candidates for this kind of high-energy battery overcoming the limitation of Li-ion system. So, Li-S system has been revived. 

Due to an energy ranging from 110 to 160 Wh/kg at the cell level, the LiFeP04/ graphite redox system cannot be considered as an alternative to the conventional Li-ion systems for high-energy applications. 

Taking in account the very large variety of Li-ion systems and technologies, it is difficult to give today an exhaustive and quantitative picture of aU the aging reactions likely to occur in any battery design. The aim of this document is to discuss some basic mechanisms, illustrated from chosen examples and data, which should help in the definition of propriate procedures to predict battery Ufe. 

Mechanical modiflcation of the composite electrode structure due to volume changes during cycling, leading to active particles deconnection from the conductive network. In Li-ion systems, this effect is limited, because the volume change of insertion material is quite small. 

In general, the cycle life is expected to increase when the DOD of cycling is smaller, because the mechanical stresses induced by the eventual molar volume change as a function of state of charge are reduced. In fact, because of the use of insertion electrodes, there are only small volume changes in the Li-ion systems, which minimizes this effect. 

This Li excess of about 15 % of nominal capacity remaining in the carbon at the end of a normal discharge condition shows interesting behavior in this Li-ion system concerning calendar or cycle hfe. This "free" lithium can be corroded with time or cycling before having any impact on practical cell capacity, thus extending the cell s useful life. 

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