Lithium insertion potentials

Beginning in the early 1980s [20, 21] metallic lithium was replaced by lithium insertion materials having a lower standard redox potential than the positive insertion electrode this resulted in a "Li-ion" or "rocking-chair" cell with both negative and positive electrodes capable of reversible lithium insertion (see recommended papers and review papers [7, 10, 22-28]). Various insertion materials have been proposed for the anode of rechargeable lithium batteries,... 

From a thermodynamic point of view, apart from charge density and specific charge, the redox potential of lithium insertion into/removal from the electrode materials has to be considered also. For instance, the redox potential of many Li alloys is between -0.3 and -1.0 V vs. Li/Li+, whereas it is only -0.1 V vs. 

Figure 2. Redox potentials for lithium insertion into/removal from several anode materials for lithium cells.

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. 

When carbon electrodes are used, Li may be inserted/intercalated reversibly into the carbon at potentials as high as 1 V versus Li/Li+ (after the formation of surface films). In the case of disordered carbons, insertion may occur at even higher potentials. In the case of graphite (as described in the next section), the onset for lithium intercalation is around 0.3 V versus (Li/Li+). With glassy carbon, there is no considerable lithium insertion, and hence this electrode behavior depends solely on the solvent and anion used and their cathodic stability [28],... 

Lithium insertion negative electrodes — (i) Some transition-metal oxides or chalcogenides insert Li ion reversibly at low redox potentials, for example, TiC>2, LL I iOy, M0S2, M0O2. (ii) Lithium alloys - in this case lithium ions, react with other elements polarized to low potentials to reversibly form Li alloys. The reaction usually proceeds reversibly according to the... 

As Figure 14 shows, the combination of two lithium insertion materials (characterized by two different potentials of the lithium insertion process) yields a cell—the so-called rocking chair battery , after Armand [105] and Scrosati et al. [106]—in which during discharge lithium ions are released from the anode and travel through the electrolyte toward the cathode without variation in the composition of the... 

A relatively high reversible capacity (372mAh/g, i.e., one lithium for six carbon atoms in standard conditions) at a potential close to metallic lithium and a moderate irreversible capacity can be obtained with graphite-based anodes. A higher degree of reversible lithium insertion than in graphite, but also an important irreversible capacity, is observed with various kinds of nanostructured carbons. Therefore, an intensive research effort is focused on the optimization of the anodic carbon materials, with the objectives to enhance the reversible capacity and to reduce as much as possible the irreversible capacity and hysteresis, which are often important drawbacks of these materials. The next section will discuss the correlations between the electrochemical performance of nanostructured carbons and their nanotexture/structure and surface functionality. Taking into account the key parameters that control the electrochemical properties, some optimizations proposed in literature will be presented. 

On the other hand, from the results of CTs, it is likely that the rate of the lithium insertion/desertion should be limited by the internal cell resistance during potential scanning as well, not by lithium diffusion in the electrode. In fact, it has been reported by a few authors " that the linear sweep/cyclic voltanunograms from the intercalation compounds were difficult to analyze under the diffusion control concept. In addition, the voltammetric results in a number of... 

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