Safety lithiated carbons

Sony dubbed the new cell, lithium-ion, as only lithium-ions and not lithium metal are involved in the electrode reactions. The lithiated carbon had a voltage of about 0.05 V vs. lithium metal and avoided the safety issues of mossy and dendritic lithium metal deposits. The lithium-ion rechargeable battery system has replaced the heavier, bulkier, Ni-Cd and Ni-MH cells in most applications,... 

There is another type of rechargeable lithium battery, however, which uses a lithiated carbon or other intercalation material for the negative electrode in place of lithium. The absence of metallic lithium in these lithium-ion batteries minimizes these safety concerns. This type of battery is covered in Chap. 35. 

Lithium ion can be intercalated, more or less, into most kinds of carbon, and the resulting lithiated carbons show extremely negative electrochemical potentials close to that of the metallic lithium electrode. The reversible intercalation/deintercalation reactions overcome the problem of dendrite formation of lithium and provide dramatic improvements in safety and cycleability. The carbon anodes are combined with non-aqueous electrolyte solutions and lithium-transition metal oxides such as LiCoOg as cathodes to fabricate 4 V-class LIBs. Only lithium ion moves back and forth between the cathode and the anode upon charging and discharging, which give rise to a potential difference of about 4 V between the two electrodes. The name, "lithium-ion" batteries came from this simple mechanism. 

If a complete cell is charged to, e.g., 4.1 V, then the potential Z carbon of the fully lithiated negative electrode will be about 0.1 V vs. Li/Li+. Therefore, the potential Eoxiie of the fully charged positive electrode in this example will be 4.2 V vs. Li/Li+. Needless to say that this trivial relationship must be remembered when data for half cells (vs. metallic lithium) are compared to the data for complete cells. An important consequence of this trivial relationship is the potential excursion of the counterelectrode in the case of an anomalous behavior of the carbon electrode (and vice versa). Imagine that, in the previous example the potential of the carbon would shift to 0.3 V vs. Li/Li+ due to a malfunction of the carbon electrode. If the end-of-charge voltage of the complete cell would be the same, namely 4.1V, then the potential of the positive electrode would be 4.4 V vs. Li/Li+. In such a case, the safety of the entire cell could be compromised. 

LIBs use the Li" ion intercalation materials for both the cathode and anode, between which the Li" ions are shuttled across the electrolyte absorbed in the separator. Figure 2 depicts the potential and specific capacity of typical cathode and anode materials suitable for the LIBs [2]. In order to assemble the battery in discharged state, the cathode materials are lithiated transition metal oxides and the anode materials are carbons or compounds capable of intercalating Li" ions or alloying with metallic Li. Research focuses have been on the increase of the battery energy/ power density, reduction of material cost, and the improvement of battery safety, which are outlined below. 

Several MOFs have also been used in innovative ways to form Li-ion battery anodes that store Li+ either via the intercalation or via the conversion-reaction mechanism. The group of Tarascon reported an initial specific capacity of 300 mAh g for a LiLterephthalate MOF in 1M LiPFg carbonate electrolytes. Perhaps even more important, the reaction between the lithiated Li -terephthalate MOF and electrolyte was three times less exothermic than that for LiCg, thereby affording a distinct safety improvement. Next, a Li -pyridinedicarboxylate MOF showed reversible Li extraction/insertion with a specific capacity of 160 mAh g at a rate of C/5. A first... 

Voltage profiles of the carbon-oxygen electrode (upper part) and the lithiated-silicon-carbon electrode (lower part) in lithium cells. (Reprinted with permission from J. Hassoun et al. A metal-free, lithium-ion oxygen battery A step forward to safety in lithium-air batteries, Nano Lett. 12,2012, 5775-5779. Copyright 2012. American Chemical Society.)... 

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