Lithium-ion migration

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 electrons follow the external circuit to the cathode and the lithium ions migrate across the electrolyte to reduce oxygen at the cathode. The oxygen is reduced in either a two or four electron process by the half-cell reaction as shown in Table 4.1. 

Nalsiyama, M., Kaneko, M., and Wakihara, M. (2012) First-principles study of lithium ion migration in lithium transition metal oxides with spinel structure. Phys. Chem. Chem. Phys.,... 

The high temperature polymorph has been extensively studied since the report in 1965 of exceptionally high ionic conductivity in this phase that reaches a maximum value of 3 S cm just below the melting temperature of 850 °C. Despite the simple structure implied by the crystallographic picture of both of these lithium sulfate structures the subtleties of local ion arrangements and the mechanism for lithium ion migration have been a subject of an occasionally fierce debate that lasted three decades. Even now, over 40 years after the initial report of fast ion conductivity in ot-Li2S04 there are features of the mechanism for ion transport that would still benefit from further illumination. 

Fils0 M0, Turner MJ, Gibbs GV, Adams S, Spackman MA, Iversen BB (2013) Visualizing Lithium-ion migration pathways in battery materials. Chemistry-A European Journal 19 15535-15544... 

When lithium ions become sufficiently mobile due to heating, they migrate from the anode to the cathode with the reactions shown in Fig. 5.24 and produce open circuit voltages of about 2.5 V under ideal conditions. In... 

Li" ion enters the adjacent, face-sharing site. It is clear that, in these materials, Li ions do not move by means of isolated, random hops in the LISICONS there is clear evidence for clustering of lithium ions and indeed, migration may involve a process of continual reorganisation of the clusters (Bruce and Abrahams, 1991). 

The lack of ionic mobility data causes a serious inconvenience when the ion conduction ability of an electrolyte is evaluated, because the measured conductivity is the result of the overall migration of both anions and cations, while for lithium batteries only the portion of the current that was carried by the lithium cation matters. This portion of the current from lithium ion movement, which determines the... 

This selective solvation of lithium ions by high-e solvent molecules would exclude the solvents of low-rj from the solvation sheath and leave the latter as free, noncoordinating solvent molecules. As a result, the media in which the solvated ions migrate are mainly composed of these free solvent molecules, which impart their low- to benefit the movement of the solvated ions. In this way, a synergistic participation from both high-e and low- solvents contributes to the optimization of ion conduction. 

The implication of such a picture of the solution structure on the microscopic level not only concerns ion transport but also further relates to the electrochemical stability of the electrolytes in lithium ion cells, because these solvent molecules in the solvation sheath, such as EC or PC, migrate with the ions to electrode surfaces and are probably more involved in the oxidative or reductive processes than the noncoordinating, low- solvent molecules, such as the linear carbonates. This could have a profound impact on the chemical nature of the electrolyte/electrode interfaces (section 6). 

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-... 

Diastereoselective [2,3]-sigmatropic rearrangement of lithium O-allyl-A-benzylhy-droxylamides (195) bearing a stereogenic center adjacent to the migration terminus was reported 3" 3 (equation 57). When the (E) and (Z)-iV-benzyl-0-(4-methoxy-4-phenylbut-2-enyl)hydroxylamines (194) rearrange, a chelation by the lithium ion occurs and the (Z)-(lR5, 2R5 )-l-phenyl-l-methoxy-3-iV-benzylaminobut-3-ene (196) is the major product... 

These materials are known as insertion or intercalation hosts. The overall electrochemical process of a lithium battery is illustrated schematically in Fig. 7.2. During discharge it involves the dissolution of lithium ions at the anode, their migration across the electrolyte and their insertion within the crystal structure of the host compound, while the compensating electrons travel in the external circuit to be injected into the electronic band structure of the same host. The charging process is the reverse and the cell reaction may be written as ... 

Fig. 9.7 Mechanism of lithium ion transport by vacancy motion in lithium iodide. Cell discharge is accompanied by the migration of lithium ion vacancies in the direction from cathode to anode. (By permission of John Wiley as Fig, 9,5)...

The electrolyte must be a pure ionic conductor, preferably with a high transport number for lithium ions, as an electronic conductivity of the electrolyte would create short-circuit ( leakage ) currents between the electrodes. Both electrodes must have a high electronic conductivity and a sufficient ionic conductivity for lithium. The metal current collectors foils (current collectors) are pure electron conductors that allow only electrons to migrate to the external electric leads to the consumer or charger unit. 

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