Intercalates, lithium

Carbon materials which have the closest-packed hexagonal structures are used as the negative electrode for lithium-ion batteries carbon atoms on the (0 0 2) plane are linked by conjugated bonds, and these planes (graphite planes) are layered. The layer interdistance is more than 3.35 A and lithium ions can be intercalated and dein-tercalated. As the potential of carbon materials with intercalated lithium ions is low,... 

Figure 5. Structure of LiC6. (a) Left schematic drawing showing the AA layer stacking sequence and the aa interlayer ordering of the intercalated lithium. Right Simplified representation [21. (b) In-plane distribution of Li in LiC6. (c) In-plane distribution of Li in LiC,.

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. 

According to equation 2, the amounts of each phase should vary linearly with intercalated lithium intercalated beyond LiCi2. 

Another vanadium oxide that has received much attention is LiVaOs, which has a layer structure composed of octahedral and trigonal bipyramidal ribbons that can be swelled just like other layered compounds and can intercalate lithium. Here again, the method of preparation is important to its electrochemical characteristics. West et al. made a systematic study of the impact of synthesis technique on capacity and cycling and showed that amorphous material increased the capacity above 2 V from 3—4 lithium per mole of LiVsOs at low current drains, 6—200 fiAlcm. ... 

On the basis of the above observation, Dahn and co-workers proposed a thermal reaction scheme for the coupling of carbonaceous anodes and electrolytes. The initial peak, which was almost identical for all of the anode samples and independent of lithiation degrees, should arise from the decomposition of the SEI because the amount of SEI chemicals was only proportional to the surface area. This could have been due to the transformation of the metastable lithium alkyl carbonate into the stable Li2C03. After the depletion of the SEI, a second process between 150 and 190 °C was caused by the reduction of electrolyte components by the lithiated carbon to form a new SEI, and the autocatalyzed reaction proceeded until all of the intercalated lithium was consumed or the thickness of this new SEI was sufficient to suppress further reductions. The corresponding decrease in SHR created the dip in the least lithiated sample in Eigure 35. Above 200 °C (beyond the ARC test range as shown in Eigure 35), electrolyte decomposition occurred, which was also an exothermic process. 

In addition to structural information, Li MAS NMR Tz relaxation measurements and analysis of Li line shapes have been used to probe the dynamics of the lithium ions. Holland et al. identified two different species with different mobilities (interfacial Li (longer Tz, rapid dynamics) and intercalated lithium (shorter Tz, slower dynamics)) in the elec-trochemically lithiated V2O5 xerogel matrix. Li hopping frequencies were extracted from an analysis of the Li line widths and the appearance of a quadru-polar splitting as the temperature decreased in a related system. ... 

Flandrois et al. considered that the stoichiometric coefficient x in Li Q (describing the amount of electrochemically intercalated lithium atoms per six carbon atoms) should be a sum of the contributions of aa, ap, and PP spaces, with xpp = 1 for the ideal graphite ... 

Carbon and graphite are used in batteries as electrodes or as additives in order to enhance the electronic conductivity of the electrodes. As electrodes, graphites and disordered carbons reversibly insert lithium, and hence they may serve as the anode material in -> lithium batteries. Graphitic carbons intercalate lithium in a reversible multi-stage process up to LiC6 (a theoretical capacity of 372 mAh g-1) and are used as the main anode material in commercial rechargeable Li ion batteries. As additives, carbon and graphite can be found in most of... 

The high cost and toxicity of cobalt compounds has prompted a search for alternative materials that intercalate lithium ions. Examples of these are LiMn204 [iv], LiCoo.2Nio.8O2. LiNio.5Mni.504 [v], LiNio.5Mno.5O2 [vi], LiFeP04 [vii], Lix VO [viii], and LixMrVOz (M = Ca, Cu) [ix], etc. 

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