Deintercalation reversible

Like polymeric electrodes, carbon can form a positive or negative electrode by virtue of doping the material with anions or cations. The ions intercalate into the stmcture of the carbon and can often be deintercalated reversibly. In addition, work on carbons for Uthium-ion type cells where essentiaUy metaUic lithium intercalates into graphitic carbons has been studied. Preliminary reports of Uthium intercalation in carbon [97,176] were... 

Using dilatometry in parallel with cyclic voltammetry (CV) measurements in lmolL 1 LiC104 EC-l,2-dimethoxy-ethane (DME), Besenhard et al. [87] found that over the voltage range of about 0.8-0.3 V (vs. Li/Li+), the HOPG crystal expands by up to 150 percent. Some of this expansion seems to be reversible, as up to 50 percent contraction due to partial deintercalation of solvated lithium cations was observed on the return step of the CV. It was concluded [87] that film formation occurs via chemical reduction of a solvated graphite intercalation compound (GIC) and that the permselective film (SEI) in fact penetrates into the bulk of the HOPG. It is important to repeat the tests conducted by Besenhard et al. [87] in other EC-based electrolytes in order to determine the severity of this phenomenon. 

Both carbon materials were tested for their initial electrochemical performance in the 2-electrode electrochemical cells with Li metal as a counter electrode. Our findings have shown that with both types of carbon materials, achieving near theoretical reversible capacity upon Li+ deintercalation was possible. Thus, in a typical half cell environment (a CR2016 type coin cell with graphite and Li metal electrodes, a 1M LiPF6,... 

This may lead to the irreversible changes in the material, caused by partial oxidation of graphite, loss of reversibility of the system along with the efficiency of reaction for intercalation-deintercalation (1). 

Ag VjOj is a vanadium bronze with a composition range of 0.3 < x < 1.0, the bronze with x = 0.29-0.41 has the / -phase structure and that with X = 0.67-0.89 the 5-phase one. The 5-phase shows good reversibility for silver intercalation and deintercalation. The typical charge-discharge curves at a constant current of 0.3 mA cm for cell [11.3] are shown in Fig. 11.3. No significant deterioration was observed for several hundred... 

The metastable spinel form of TiS2, which has cubic close-packing of the sulfide ions, was similarly formed by the deintercalation of copper from CuTi2S4. ° This cubic structure can also be reversibly intercalated with lithium, although the diffusion coefficient is not as high as in the layered form. 

According to Peled s model, the existence of an SEI constitutes the foundation on which lithium ion chemistry could operate reversibly. Therefore, an ideal SEI should meet the following requirements (1) electron transference number 4 = 0 (otherwise, electron tunneling would occur and enable continuous electrolyte decomposition), (2) high ion conductivity so that lithium ions can readily migrate to intercalate into or deintercalate from graphene layers, (3) uniform morphology and chemical composition for ho-... 

In situ Raman spectra studies performed on graphite anodes also seem to reveal a cointercalation occurrence that leads to exfoliation. Huang and Freeh used solutions of LiC104 in EC/EMC and EC/DME as electrolytes and monitored the E2g2 band at 1580 cm in the Raman spectra of the graphite that was cycled between 2.0 and 0.07 Reversible lithium intercalation and deintercalation was indicated by... 

In other words, the overall lithium ion intercalation in and deintercalation from a variety of LiM02 bulk materials included the inevitable step of lithium ion migration through a certain surface layer in a manner very similar to that of the reversible lithium ion... 

The electrochemical properties of the microma-chined electrode arrays have been determined for several of the electrode materials. In these half-cell experiments, the electrode array served as the working electrode and lithium as the counter and reference electrodes. The first experiments were carried out on carbon arrays composed of powders of Ketjen Black. Reversible intercalation and deintercalation of lithium were obtained, and reversible capacities in the range of 0.4—0.5 mA h cm were reported. 

More recently, lithium vanadium phosphates (LisV2-(P04)s and Li3FeV(P04)3, with open NASICON framework structures, have also been studied. Reversible electrochemical lithium deintercalation/re-intercalation at a higher potential (in comparison to the couples seen for the oxides) of between 3... 

As discussed in the next section, lithiated carbon electrodes are covered with surface films that influence and, in some cases, determine their electrochemical behavior (in terms of stability and reversibility). They are formed during the first intercalation process of the pristine materials, and their formation involves an irreversible consumption of charge that depends on the surface area of the carbons. This irreversible loss of capacity during the first intercalation/deintercalation cycle is common to all carbonaceous materials. However, several hard, disordered carbons exhibit additional irreversibility during the first cycle, in addition to that related to surface reactions with solution species and film formation. This additional irreversibility relates to consumption of lithium at sites of the disordered carbon, from which it cannot be electrochemically removed [346-351],... 

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