Lithium batteries chemical reactions

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

It has been known for some time that lithium can be intercalated between the carbon layers in graphite by chemical reaction at a high temperature. Mori et al. (1989) have reported that lithium can be electrochemically intercalated into carbon formed by thermal decomposition to form LiCg. Sony has used the carbon from the thermal decomposition of polymers such as furfuryl alcohol resin. In Fig. 11.23, the discharge curve for a cylindrical cell with the dimensions (f) 20 mm x 50 mm is shown, where the current is 0.2 A. The energy density for a cutoff voltage of 3.7 V is 219 W h 1 which is about two times higher than that of Ni-Cd cells. The capacity loss with cycle number is only 30% after 1200 cycles. This is not a lithium battery in the spirit of those described in Section 11.2. 

Both batteries and fuei cells utilize controlled chemical reactions in which the desired process occurs electrochemically and all other reactions including corrosion are hopefully absent or severely kinetically suppressed. This desired selectivity demands careful selection of the chemical components including their morphology and structure. Nanosize is not necessarily good, and in present commercial lithium batteries, particle sizes are intentionally large. All batteries and fuel cells contain an electropositive electrode (the anode or fuel) and an electronegative electrode (the cathode or oxidant) between which resides the electrolyte. To ensure that the anode and cathode do not contact each other and short out the cell, a separator is placed between the two electrodes. Most of these critical components are discussed in this thematic issue. 

As discussed above, LiPF6 and LiBF4 decompose to form HF in nonaqueous electrolyte solution. In addition, HF is often used as a fluorinated agent or a reaction medium when fluorine compounds are prepared. A trace of HF possibly remains in the salts and dissolved in nonaqueous electrolyte solution. Usually, HF was a typical undesirable species for battery system, but its function was not understood well before. Recently, a lot of reports have been published to discuss several chemical reactions of HF with the components contained in rechargeable lithium batteries. A very interesting behavior has been observed on lithium metal. 

What makes the sodium-sulfur cell possible is a remarkable property of a compound called beta-alumina, which has the composition NaAlnOiy. Beta-alumina allows sodium ions to migrate through its structure very easily, but it blocks the passage of polysulfide ions. Therefore, it can function as a semipermeable medium like the membranes used in osmosis (see Section 11.5). Such an ion-conducting solid electrolyte is essential to prevent direct chemical reaction between sulfur and sodium. The lithium-sulfur battery operates on similar principles, and other solid electrolytes such as calcium fluoride, which permits ionic transport of fluoride ion, may find use in cells based on those elements. 

O mile," says the photographer, as she pushes a button. The camera shutter opens and an /electric current from a small lithium battery sparks across a gap in the flash unit. This spark ionizes xenon gas, creating a bright flash of light. The energy from the chemical reaction in the lithium battery has been successfully put to use. 

There is no hazardous waste generated when lithium batteries are recycled at Toxco Inc. There is no municipal sewer system in the processing area and air emissions are collected via a direct-capture-system over each of the reaction areas. These fumes are processed through three air filters coimected in series the first is a wet bed fume scrubber which removes particulate material, the second is a traveling bed filter to further remove particulate material, and the third treats the emissions chemically. Each year Toxco is required to hire an outside environmental audit firm to test the emissions for conformance with their permit. The 1999 results are presented in Table 1. As one can see the emissions are quite minor in comparison to the allowable limits. 

The basic chemical reactions for these lithium sulfur dioxide battery packs are shown below. (Samuel C. Levy while at the Sandia National Laboratories under a grant from the U. S. Department of Energy developed this analysis). 

Batteries exposed to certain abusive conditions may experience thermal runaway - a series of coupled exothermic chemical reactions involving metallic lithium, lithium dithionite and possibly sulfur, resulting in the formation of sulfides. At the elevated temperatures resulting from these reactions, these products may further react with the carbon in the cathode to form carbon dioxide (CO2) and carbon disulfide (CS2). Carbon... 

These batteries are designed to be reehaiged and used multiple times. That is, they ean have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition. Thus these are also called rechargeable batteries. Cells of this type include nickel-cadmimn (NiCd), nickel-zinc (NiZn), and lithium-ion (Li-ion) cells. 

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